Content:
Presentation type:
SM – Seismology

SM1 – General Seismology

EGU23-1264 | ECS | Orals | SM1.1

Identification of a hidden fault associated with the Mw 5.6 (November 21, 2022) Cianjur Earthquake, West Java, Indonesia 

Pepen Supendi, Tom Winder, Nicholas Rawlinson, Conor Bacon, Daryono Daryono, Andrean Simanjuntak, Kadek Hendrawan Palgunadi, Hasbi Ash Shiddiqi, Andri Kurniawan, Priyobudi Priyobudi, Sri Widiyantoro, Andri Dian Nugraha, Suko Prayitno Adi, and Dwikorita Karnawati

A destructive earthquake (Mw 5.6) struck Cianjur, West Java, Indonesia, on 21 November 2022, resulting in at least 321 deaths, damage to 47,000 buildings, and economic losses of up to 7.7 trillion Indonesian Rupiahs (∼US $546 million). The causative fault that generated this earthquake was not previously recognised, therefore making further analysis crucial for assessing future seismic hazard in the region. In this study, we undertake automated event detection and location using QuakeMigrate from 10 days before to 23 days after the mainshock, prior to relocation using a double-difference method. We also determine the source mechanism for selected aftershocks from waveform inversion. Our result show that the mainshock was preceded by three clear foreshocks, and intriguingly the aftershocks appear to reveal the presence of a conjugate fault pair trending northwest-southeast with a length of ~8 km and southwest-northeast with a length of ~5 km.

How to cite: Supendi, P., Winder, T., Rawlinson, N., Bacon, C., Daryono, D., Simanjuntak, A., Palgunadi, K. H., Shiddiqi, H. A., Kurniawan, A., Priyobudi, P., Widiyantoro, S., Nugraha, A. D., Adi, S. P., and Karnawati, D.: Identification of a hidden fault associated with the Mw 5.6 (November 21, 2022) Cianjur Earthquake, West Java, Indonesia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1264, https://doi.org/10.5194/egusphere-egu23-1264, 2023.

We consider approximately 23,000 microearthquakes occurred between 2005 and 2016 in central Italy to investigate the crustal strength before and after the three largest earthquakes of the 2016 seismic sequence (i.e., the Mw 6.2, 24 August 2016 Amatrice, the Mw 6.1, 26 October 2016 Visso, and the Mw 6.5, 30 October 2016 Norcia earthquakes). We monitor the spatio-temporal deviations of the observed radiated energy, ES, with respect to theoretical values, ESt, derived from a scaling model between ES and M0 calibrated for background seismicity in central Italy. These deviations, defined here as Energy Index (EI), allow us to identify the onset of the activation phase one week before the mainshock. We show that foreshocks are characterized by a progressive increase in slip per unit stress, in agreement with the diffusion of highly pressurized fluids before the LAquila earthquake proposed by previous studies. Our results suggest that the largest events occur where EI is highest, in agreement with the existing link between EI and the mean loading stress.

Furthermore, our results show a progressive evolution of the dynamic properties of microearthquakes in the years following the Mw 6.1, 2009 LAquila earthquake, and the existence of high EI patches close to the Amatrice earthquake hypocenter. We show the existence of a crustal volume with high EI even before the Mw 6.5 Norcia earthquake. Our results agree with the previously suggested hypothesis that the Norcia earthquake nucleated at the boundary of a large patch, highly stressed by the two previous mainshocks of the sequence. We highlight the mainshocks interaction both in terms of EI and of the mean loading shear stress associated to microearthquakes occurring within the crustal volumes comprising the mainshock hypocenters. Our study shows that the dynamic characteristics of microearthquakes can be seen as beacons of stress change in the crust, and, thus, be exploited to monitor the seismic hazard of a region and help to intercept the preparation phase of large earthquakes.

How to cite: Picozzi, M., Spallarossa, D., Bindi, D., Iaccarino, A. G., and Rivalta, E.: Temporal and spatial evolution of radiated energy to seismic moment scaling during the preparatory phase of the Mw 6.1, 2009 L’Aquila earthquake (Italy) and the 2016 Central Italy Seismic Sequence., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1449, https://doi.org/10.5194/egusphere-egu23-1449, 2023.

EGU23-1534 | Orals | SM1.1

The 2021-2022 seismic sequence in southern Alboran Sea 

Lucia Lozano, Juan Vicente Cantavella, Elisa Buforn, Carolina López-Sánchez, Resurección Antón, Jaime Barco, María Victoria Manzanedo, Roberto Cabieces, and Maurizio Mattesini

The Alboran Sea is a complex tectonic region in the westernmost Mediterranean Sea, dominated by the present-day NW-SE convergence between Eurasia and Nubia plates. This compression regime accomodates long strike-slip active fault systems, together with several inverse structures, crossing the Alboran crust in a NE-SW trending shear deformation belt which mainly controlls the shallow seismicity in the area. In fact, the southern sector of the Alboran domain has experienced two large earthquakes in the last two decades, the Mw 6.3 2004 Alhoceima and the Mw 6.4 2016 Alboran events. Since mid-april 2021, and over the following 20 months, tens of moderate-magnitude shallow earthquakes (4≤Mw≤5.3, h<20 km) have been registered in this area, to the northwest of Melilla, between the 2016 main shock and the African coast. The two largest events, a Mw 5.1 on August 28, 2021 and a Mw 5.3 on May 20, 2022, were widely felt in Melilla city (maximum EMS-98 intensities of IV and IV-V, respectively) and along the southern Spanish and the Moroccan coasts. These moderate seismicity occurs together with thousands of low-magnitude events (M<3) in a swarm-type distribution, in contrast to previous seismic sequences in 2004 and 2016 which showed a more typical foreshock-mainshock-aftershock pattern. An accurate hypocentral location of this seismicity is a key point to better image the seismicity distribution and rupture area and, hence, to improve our knowledge of the active tectonics of this region, contributing to improve seismic and tsunami hazard assessments. In this study we perfom a high-precision relocation of a selected good-quality subset of moderate-magnitude earthquakes of the 2021-2022 seismic sequence and we compare them to a similar set of relocated earthquakes of the 2004 and 2016 series, using all the available seismic data. We apply a non-linear probabilistic location algorithm jointly with a 3-D velocity model for the Alboran-Betic-Rif system, to account for differences in wave propagation in the laterally heterogeneous crust. This approach is a powerful tool to improve the hypocentral parametres.

How to cite: Lozano, L., Cantavella, J. V., Buforn, E., López-Sánchez, C., Antón, R., Barco, J., Manzanedo, M. V., Cabieces, R., and Mattesini, M.: The 2021-2022 seismic sequence in southern Alboran Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1534, https://doi.org/10.5194/egusphere-egu23-1534, 2023.

EGU23-2507 | Posters on site | SM1.1

Fault strength dependency of natural earthquake-size distribution based on the precise focal mechanism data 

Satoshi Matsumoto, Yoshihisa Iio, Shinichi Sakai, and Aitaro Kato

“b-value”, which degree of power law decay in the earthquake-size distribution, is known showing spatial and temporal variation based on observational studies. Especially, the temporal variation sometime have detected before a large earthquake occurrence, showing that it can be an indicator for the occurrence and may help earthquake hazard mitigation. The b-value changes due to tectonic stress regime. In addition, laboratory experiments have revealed acoustic emission size distribution depends on differential stress magnitude and criticality of failure condition. However, it is unclear in natural earthquake activity that which factor controls b-value condition. In this study, we show b-value change of small earthquake sequences in normalized shear and normal stress.

We carried out dense seismic observation composed by over 1000 stations deployed in hypocentral area (with diameter about 35 km) of the 2000 Western Tottori Earthquake (M7.3). About one year observation enabled us to obtain hypocenters and focal mechanisms about 5000 small earthquakes. Relative stress tensor have been inverted by the focal mechanism data in spatial bins and relative shear and normal stress for individual earthquake also estimated.  We investigated b-value change in relative shear and normal stress condition of small earthquake dataset. The b-value dependency on relative shear stress were detected, showing that the b-value decrease with increasing shear stress. In addition, the b-value takes minimum value at normal stress at critical point where line following Coulomb Failure condition with friction coefficient of 0.6 touches the unit Mohr circle. This suggests that the b-value become small in case of fault plane in optimal direction.

How to cite: Matsumoto, S., Iio, Y., Sakai, S., and Kato, A.: Fault strength dependency of natural earthquake-size distribution based on the precise focal mechanism data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2507, https://doi.org/10.5194/egusphere-egu23-2507, 2023.

EGU23-2598 | Orals | SM1.1

Very Long-Period Seismic Signals and Collapse Events at the Kilauea Summit Crater in 2018 

Lingling Ye, Thorne Lay, Hiroo Kanamori, Emily Brodsky, Takao Ohminato, Mie Ichihara, Kazuya Yamakawa, Hiroshi Tsuruoka, and Kenji Satake

The 2018 Kilauea eruption and East Rift Zone dike intrusion have been accompanied by more than 60 earthquakes with magnitude 4.7 – 5.3 near the summit. Corresponding long-period moment tensor solutions (constrained to have no isotropic component) have nearly vertical P-axes with moderate to large non-double-couple components (~20%-80%). The predominantly normal faulting is consistent with summit deflation as magma drains to the rift zone. Ground velocities recorded by local broadband seismic stations (<5 km) along the edge of the crater show distinct behavior between mid-May events and subsequent events. From May 16 to 26, twelve M5 events with large eruptive plumes below the SE edge of Halema'uma'u crater generated very long-period (VLP) seismic pulses with durations of about 20-40 s at all azimuths, suggesting distinct static outward displacements. This group can be represented by either isotropic or CLVD source. Almost all VLP pulses ended with sharp arrivals that are likely from small collapses. Similar VLP signals had been observed during the 2000 Miyake-jima eruption (Kikuchi et al., 2001; Kumagai et al., 2001). After May 28, M5 events were located below both north and south edges of the crater and generated broadband ground motions at the same stations; with large amplitude fracture-generated high-frequency signals (often clipped). Seismicity at the summit was low during the VLP events but increased to have 20-40 events per hour before later M5 events followed by several hours of reduced activity. After May 28, seismicity has been quasi-periodic, with intervals from ~2 to ~1 day. Comparison with solid earth tides and volume strain variations suggests that they are not direct driving factors, because the time interval between collapse events varied significantly. We consider a model with two stages, stage 1 (from May 16 to 26) with inflation transients that causes VLP events with large ash/gas explosion, and stage 2 (after May 28) dominated by collapse with extensive shallow fracturing and weaker gas explosions. The rapid expansion of the VLP events may be due to water flashing to steam, or partial collapse into the magma causing abrupt inflation. We investigate these VLP events comprehensively with local broadband seismic data, infrasound signals, GPS and tilt signals in this study, along with comparisons with published studies for the 2018 Kilauea sequences. 

How to cite: Ye, L., Lay, T., Kanamori, H., Brodsky, E., Ohminato, T., Ichihara, M., Yamakawa, K., Tsuruoka, H., and Satake, K.: Very Long-Period Seismic Signals and Collapse Events at the Kilauea Summit Crater in 2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2598, https://doi.org/10.5194/egusphere-egu23-2598, 2023.

EGU23-4587 | Orals | SM1.1

Ambient Noise Tomography of the Lipari Volcanic Island (Southern Italy) from a Dense Nodal Array 

Marco Calò, Francesca Di Luccio, Patricia Persaud, Guido Ventura, and Mimmo Palano

We applied ambient noise tomography to continuous data recorded by a dense seismic array deployed on the volcanic island of Lipari in the southern Tyrrhenian Sea. Since most of Lipari’s seismicity occurs offshore and is not evenly distributed, this technique allowed us to obtain the first high-resolution images beneath the island down to ~2.5 km depth. Results show a complex seismic structure related to the various ages and compositions of the volcanic products characteristic of the different regions of the island. High shear wave velocities are found in western Lipari where active hydrothermal vents and N-S faults are mapped. Low wave speeds are revealed beneath southern and north-eastern Lipari, where more recent volcanic activity developed along N-S dike-like structures that are aligned with rhyolitic vents. We suggest these dikes likely represent the probable pathways of future volcanic eruptions.

 

Work funded by the Istituto Nazionale di Geofisica e Vulcanologia, sezione di Roma 1 and the Department of Geology and Geophysics of Louisiana State University and partially supported by the “Pianeta Dinamico” all, 2023-2025 CAVEAT Project. M.C. was supported by UNAM PASPA – DGAPA. 

How to cite: Calò, M., Di Luccio, F., Persaud, P., Ventura, G., and Palano, M.: Ambient Noise Tomography of the Lipari Volcanic Island (Southern Italy) from a Dense Nodal Array, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4587, https://doi.org/10.5194/egusphere-egu23-4587, 2023.

EGU23-4855 | ECS | Posters on site | SM1.1

A Study on the Identification of Explosions, Collapses and Earthquakes using KMA Seismic and Infrasound Networks 

Kyungmin Min, Mikyung Choi, Seolhan You, Yeongjae Choi, Gyeongdon Chai, and Suncheon Park

The Korea Meteorological Administration(KMA) uses seismic and infrasound networks data identifying  explosion, collapse, and earthquakes.
We identify events using various methods . First, Vp/Vs spectral amplitude ratio in the frequency domain is calculated by applying Fast Fourier Transform (FFT) and Power Spectrum Density (PSD) analysis methods. The Vp/Vs ratio more than 50% is distinguished as an explosion.
Second, Explosion, collapse, and earthquakes are distinguished by (using) the body wave method (Walter et al., 2018). The Pn/Lg, Lg/Lg ratios are used for studying the DPRK 6th test, collapse and induced earthquakes at Chuncheon, Sokcho, and Seohwa KMA seismic networks.
Finally, the KMA operates five infrasound networks for  monitoring DPRK nuclear test and Mt. Baekdu volcano in addition to the seismic networks.
Infrasound analysis calculates the apparent speed and azimuth of the infrasound source by applying Progressive Multi-Channel Correlation(PMCC)  algorithm.
The calculated azimuth and apparent velocity are  important factors in determining that the seismic and infrasound signals occurred at the same point during an explosion.

How to cite: Min, K., Choi, M., You, S., Choi, Y., Chai, G., and Park, S.: A Study on the Identification of Explosions, Collapses and Earthquakes using KMA Seismic and Infrasound Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4855, https://doi.org/10.5194/egusphere-egu23-4855, 2023.

The NEOM multi-billion-dollar project on the eastern coast of the Gulf of Aqaba will bring underground infrastructures, new cities, and tourist destinations. This project will dramatically increase the seismic risk associated with active faults in the Gulf of Aqaba and the northern Red Sea. The Gulf of Aqaba, located between northern Saudi Arabia and the Sinai peninsula and formed by the transtension at the southern termination of the Dead Sea Transform, is a 180-km-long fault system that can generate earthquakes of magnitude at least 7.3 (as occurred in 1995). South of the gulf, the fault system connects to the Red Sea rift, where an earthquake of magnitude larger than 5 occurred in 2020. To investigate the regional tectonics and to better understand the associated seismic hazard, we have run a temporary network of 12 broadband seismic stations in the area since 2019.

In this contribution, we present a new local magnitude scale calibrated by using more than 10,000 half-peak-to-peak amplitudes, automatically measured and Wood-Anderson-corrected, from earthquakes recorded by our network from May 2019 to February 2021. We used the amplitudes from the two horizontal components of each station to constrain the constants of the distance-dependent correction term of the local magnitude formula (n, related to the geometrical spreading, and k, related to the attenuation), magnitudes, and station corrections.

We used a least-square regression scheme in two steps to ensure the convergence of the solution and independence of the results from the initial values. In the first step, we only inverted for n, k, and magnitudes. In the second step, we also inverted for station corrections and we used the magnitudes obtained in the first step as initial values for the second step. Conversely to most previous studies, we did not introduce any constraints on the station corrections. We run several regressions in a grid search approach to tackle the trade-off between n and k and find the best solution.

We found that the estimated station corrections, because of the lack of constraints on them, are strongly correlated with the rock properties and topographic attributes. We also compared the frequency-magnitude distributions obtained with our best solution, including the station corrections (case A), the Hutton and Boore (1967) formula (case B), and Hutton and Boore formula with our station corrections (case C). We found that magnitudes for A are lower than for B and C. However, differences in statistical parameters, such as b-values, between A and C are neglectable.

Our work provides NEOM with a reliable and locally calibrated earthquake magnitude scale. This new magnitude scale can also be applied in surrounding regions with similar geological features (e.g., Egypt, Jordan, and Israel). Moreover, this work highlights that estimations of station corrections are critical, and at least, as important as a locally calibrated magnitude scale.

 

 

How to cite: Mai, P. M., Parisi, L., and Jónsson, S.: The importance of station corrections for local earthquake magnitudes: the example from the seismicity in NEOM (Gulf of Aqaba and northern Red Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4905, https://doi.org/10.5194/egusphere-egu23-4905, 2023.

EGU23-5367 | Orals | SM1.1

Advances in the knowledge of seismogenetic structures in the eastern edge of the Pyerenees 

Mario Ruiz, Jordi Diaz, Ariadna Canari, Maria Ortuño, and Jaume Vergés

Although the seismic activity at the eastern Pyrenees is nowadays moderate and sparse, with events usually not exceeding magnitudes 4.5, this area has been affected in the past by the most destructive event occurred in the Pyrenees, reaching an intensity of IX, whose seismogenic structure is not well  understood and still under debate. In order to progress in the knowledge of these structures, we present here the results derived from a 14 months-long broad-band seismic deployment focused on the Cerdanya Basin, but encompassing the eastern termination of the Pyrenees. The dense station coverage has allowed us to obtain accurate hypocentral locations, as well as up to 23 focal mechanisms from local low-magnitude earthquakes. In addition to a relatively sparce seismicity, several clusters of seismic events located in well-defined, small areas and depth ranges have been identified. The results show a few low-magnitude seismic events located in the southern limit of the Cerdanya Basin that could be related to oblique secondary faults within the footwall of the Têt Fault, the major tectonic structure in the area. Our data shows also that the Capcir Fault has associated seismicity, with some of the events located out of the fault plane, perhaps on secondary fault branches. To the east, a cluster of low-magnitude events is detected in the epicentral area of two relatively large earthquakes occurred recently, probably indicating the development of the preparatory phase. Further west, the Maladeta Massif has a sustained seismic activity, although its origin does not seem to be related to the most relevant structure in the area, the North Maladeta Fault. Regarding focal mechanisms, most of them show normal fault solutions with nodal planes NW-SE oriented, which are in agreement with the extensional regime perpendicular to the axis of the chain derived from the seismic and geodesic data.

 

How to cite: Ruiz, M., Diaz, J., Canari, A., Ortuño, M., and Vergés, J.: Advances in the knowledge of seismogenetic structures in the eastern edge of the Pyerenees, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5367, https://doi.org/10.5194/egusphere-egu23-5367, 2023.

CCS (Carbon Capture and Storage) is becoming an increasingly important technology to reduce global greenhouse gas emissions. The Norwegian part of the North Sea is an ideal place to conduct such projects as much of the infrastructure and experience is already in place due to current oil and gas operations. For safe CO2 storage an improved understanding of the natural background seismicity in the North Sea is still required. Currently, earthquakes in the region are monitored using onshore stations deployed on mainland Norway, resulting in low azimuthal sensor coverage and poorly constrained earthquake locations. However, permanent reservoir monitoring systems (PRMs), which are deployed offshore to surveil oil and gas fields, have the potential to reduce these station gaps and thus improve earthquake locations.

In this study we test the potential of incorporating offshore sensors at the Grane oil field for earthquake locations and detection utilizing array processing techniques. The advantage of array processing is that it can enhance seismic signals, decrease the detection threshold, and put additional constraints on direction and apparent velocities. Out of the 3400 sensors deployed at the Grane field, we have access to two subsets of data: i) Continuous data from 10 sensors spread along the boundaries of the field and, ii) segments of data from 30 sensors optimized for the purpose of array processing. Since the distances between the 10 sensors are large (6 km), traditional array processing methods are not applicable, and we therefore test and develop a new method for incoherent array processing using the kurtosis characteristic function. The kurtosis function is applied to the seismic signal prior to FK-analysis to make the signal more coherent.  The method showed great potential and worked for the majority of earthquakes analyzed in this study. The 30 sensor array was superior to the 10 sensor array and could potentially decrease the detection threshold of seismic events if continuous data are available. We conclude that the Grane sensors could be implemented as a part of a system for passive seismic monitoring in the North Sea. We recommend using the 30-sensors for this purpose. However, as we only have access to continuous data from 10 sensors, we found that these sensors are an appropriate replacement when the 30 sensors are not accessible. 

How to cite: Jerkins, A., Köhler, A., and Oye, V.: On the potential of offshore sensors and array processing for improving seismic event detection and locations in the North Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5528, https://doi.org/10.5194/egusphere-egu23-5528, 2023.

EGU23-5751 | ECS | Posters on site | SM1.1

CFM: a Convolutional network for First Motion polarity classification of earthquake waveforms. 

Giovanni Messuti, Silvia Scarpetta, Ortensia Amoroso, Ferdinando Napolitano, and Paolo Capuano

The knowledge of the crustal stress field is essential in the evaluation of the seismic hazard of an area.To this aim, it is necessary to derive reliable focal mechanisms mainly when small earthquakes have to be included in the computation. The first motion focal mechanism solution techniques are still widely used in modern softwares. The determination of P-wave polarities with manual procedures can lead to human errors and it is time-consuming. Automatic procedures can avoid these drawbacks. Polarity identification is not a classification task easily expressed in terms of mathematical procedures, in fact classical automatic procedures can lead to worse results than those obtained by human operators. For this reason, the use of machine learning approaches results necessary to accomplish this task.With low computational costs, real-time analysis capabilities, no need for complicated pre-processing procedures, and truly competitive results, properly designed convolutional networks can be the answer to various problems, including those related to seismology. 

In our work, we present the Convolutional First Motion (CFM) network, a Deep Convolutional Neural Network (DCNN) used to classify seismic traces based on first motion polarities of P-waves. We used waveforms contained in two datasets. We prepared the first dataset selecting approximatively 150˙000 waveforms contained in the Italian seismic catalogue INSTANCE, specifically designed for the application of machine learning techniques. To this end we devised an analysis procedure using Principal Component Analysis and Self-Organising Maps, through which a clustering process individuated groups of suitable traces. A second dataset, not specifically designed for machine learning techniques, is prepared manually picking approximatively 4˙000 waveforms of earthquakes occurred between 2010 and 2014 at Mt. Pollino area in Italy, avoiding possible overlapping of waveforms between the two datasets. The network, trained on ~130˙000 time windows centred on P-wave arrival times of waveforms in the INSTANCE catalogue, achieved accuracies of 95.7% and 98.9% on two test sets: the Mt. Pollino dataset and part of the INSTANCE catalogue. Further testing showed that if we give the network waveforms with uncertain arrival times, it acquires robustness to this type of noise, still showing high-level of performance.

We infer that the CFM network would be suitable in succession to automatic techniques that derive P-wave arrival times, for example techniques in which deep learning is used, in order to cover the entire data processing phase with machine learning. Given the incredible ability of DCNNs to model and process large volumes of data and their remarkable performance, it is reasonable to assume that deep learning will soon become the norm even in the context of first-motion polarity determination. 

This work was partially supported by the PRIN-2017 MATISSE project (no. 20177EPPN2), funded by the Ministry of Education and Research.

How to cite: Messuti, G., Scarpetta, S., Amoroso, O., Napolitano, F., and Capuano, P.: CFM: a Convolutional network for First Motion polarity classification of earthquake waveforms., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5751, https://doi.org/10.5194/egusphere-egu23-5751, 2023.

EGU23-5787 | ECS | Orals | SM1.1

Imaging of seismic sources by surface-wave time-reversal: long-period earthquakes 

Apsara Sharma Dhakal, Lapo Boschi, and Simone Cesca

The study of long-period events in a volcanic setting is of fundamental importance to better understand the physics of volcanic plumbing systems. We locate such events using a source-imaging method developed by our team, and successfully applied, e.g., to the great Sumatra earthquake (Dhakal et al. 2022). Our approach combines seismic time reversal with a surface-wave ray tracing algorithm based on generalized spherical-harmonic parameterization of surface-wave phase velocity, and accounting for azimuthal anisotropy. We present a new application, to recordings of a suite of Mayotte events that Cesca et al. (2020) have already studied and interpreted in terms of the drainage of a magma reservoir.

We first conduct synthetic tests to quantify the resolving power of our method, given the available data coverage for the events of interest. We then use low-frequency Rayleigh wave signals recorded by different stations, reverse them in time and back propagate them through a surface-wave phase-velocity model. The time-reversed wave field has a prominent maximum at the spatial location(s) and time(s) where and when the recorded signal had been generated. From the time- and space-distribution of such maximum, we can make inferences on the nature of the source. Results so obtained are compared with those determined by Cesca et al. (2020) via moment tensor inversion and found to be in good agreement. We infer that our methodology is applicable to volcanic settings, possibly providing new insights into the nature of long-period seismic sources related to volcanic activity. The precise location of such events can provide better constraints on the depth interpretations and the extent of the seismic source.

How to cite: Sharma Dhakal, A., Boschi, L., and Cesca, S.: Imaging of seismic sources by surface-wave time-reversal: long-period earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5787, https://doi.org/10.5194/egusphere-egu23-5787, 2023.

EGU23-5874 | Orals | SM1.1

Geodetic evidence that earthquakes start with precursory slip 

Quentin Bletery and Jean-Mathieu Nocquet

The existence of a potentially observable precursory phase of slip on the fault before large earthquakes has been debated for decades. Though observations preceding a handful of large events have been proposed as possible indicators of precursory slip, these observations do not directly precede the earthquakes, are not seen before most events and are commonly observed without being followed by earthquakes. Here we present a global analysis of geodetic measurements prior to large earthquakes, based on high-rate time series recorded before 78 large (Magnitude ≥ 7) seismic events. Our analysis highlights a 2 hour-long exponential signal consistent with acceleration of precursory slip on the fault. Our observation indicates that precursory phases of slip exist and that future improvements in measurement precision could allow to monitor them, making earthquake prediction potentially achievable.

How to cite: Bletery, Q. and Nocquet, J.-M.: Geodetic evidence that earthquakes start with precursory slip, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5874, https://doi.org/10.5194/egusphere-egu23-5874, 2023.

EGU23-7745 | ECS | Posters on site | SM1.1

How to discriminate between area-source models for probabilistic seismic hazard assessment in a more objective manner? 

Clara Duverger, Merlin Keller, and Gloria Senfaute

We propose a methodology to assist in the selection or definition of weights for components of seismic hazard models, which are combinations of seismic source models and ground motion models, in the context of probabilistic seismic hazard assessment (PSHA). The methodology uses Bayes's theory by optimally exploiting available observations that are the seismic catalogues and accelerometric databases. When compared to the current method of calculation, the proposed approach, simple to implement, allows a more exhaustive use of the data and discriminates between inputs without expert judgements to weigh branches of the PSHA logic tree.

We implement the proposed methodology in a Python package called Phebus to process the seismic source models (the first of the two main ingredients of the seismic hazard model) as a first step. The main purpose of this package is to estimate earthquake recurrence parameters and confidence intervals using a full Bayesian approach, and perform a Bayesian model averaging (BMA) amongst multiple seismic source models. More particularly, we focused our study on area-source models, which consist of subdivisions of a particular region of interest into zones that are assumed homogeneous in terms of seismic activity rate, and that are systematically used in PSHA calculations for low-to-moderate seismic regions. We conducted sensitivity analyses on the selection performances and the adjustments performances of recurrence parameters for simplistic toy models against a synthetic model-generated seismicity catalogue. We also illustrate the application of Phebus to the metropolitan France, a low-strain region, where at least four national, competitive and published area-source models are used by engineers and researchers for seismic hazard evaluation.

How to cite: Duverger, C., Keller, M., and Senfaute, G.: How to discriminate between area-source models for probabilistic seismic hazard assessment in a more objective manner?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7745, https://doi.org/10.5194/egusphere-egu23-7745, 2023.

EGU23-9148 | ECS | Orals | SM1.1

EuVeM2022: a new European GNSS velocity model 

Rebekka Steffen, Holger Steffen, Ambrus Kenyeres, Tobias Nilsson, and Martin Lidberg

The European continent is divided into several tectonic plates and velocity variations appear along plate boundaries. However, velocity changes inside a tectonic plate can also occur due to local effects or other geodynamic processes, which is of interest for researchers trying to understand intraplate deformations in the horizontal and vertical directions. These changes can be observed by a dense network of GNSS (Global Navigation Satellite System) stations or more recently by the usage of InSAR (Interferometric Synthetic Aperture Radar). However, a dense GNSS network cannot be maintained over large areas due to, e.g., high costs and topographical obstacles, thus a regional velocity model to study intraplate deformation has to be obtained via an interpolation of scattered GNSS station velocities. The obtained velocity models can be used to estimate strain rates, which can be compared to existing seismic hazard models. In addition, in areas with a limited amount of seismic information, strain rates obtained from GNSS velocity models can provide a useful input for seismic hazard models.

The increased availability of GNSS station velocities in Europe via the EUREF Permanent Network Densification (EPND) project (https://epnd.sgo-penc.hu) allows to obtain a complete picture of the horizontal and vertical deformation in Europe via an interpolation. Here, we apply a new interpolation technique to a velocity field solution from EPND. The homogenized and quality-checked velocity field is interpolated via a least-square collocation including the knowledge of existing plate boundaries to avoid a smoothing of nearby velocities on different tectonic plates. We also apply a moving variance approach to avoid effects of non-stationarity, which arise due to the variable station densities. The new 3D GNSS velocity model EuVeM2022 is used to estimate the strain rates and a comparison to seismic risk maps shows a clear correlation. However, in some areas increased shear strain rates as well as anomalies in the velocity model are visible where peak ground acceleration is not increased for example in Serbia.

How to cite: Steffen, R., Steffen, H., Kenyeres, A., Nilsson, T., and Lidberg, M.: EuVeM2022: a new European GNSS velocity model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9148, https://doi.org/10.5194/egusphere-egu23-9148, 2023.

EGU23-9184 | Posters on site | SM1.1

Volcanism and tearing in the Tyrrhenian subduction system: the CAVEAT project 

Laura Scognamiglio, Mimmo Palano, Francesca Di Luccio, Giuseppe Pezzo, Sofia De Gregorio, and Filippo Greco and the CAVEAT Team

In retreating subduction zones the proposed lithosphere tearing processes at slab edges are typically related to segmentation of subducting plate. A direct response to lithosphere tearing is the channeling of new asthenospheric mantle that can initiate magmatism. Tearing mechanisms have also been proposed for the Calabrian Arc, where slab migration led to the formation of the southeastern Tyrrhenian basin and was progressively accommodated by inherited and newly formed vertical tear faults whose oldest (~2 Ma) and youngest (~0.8 Ma) tectonic expressions in the upper plate are the Sisifo-Alicudi and the Aeolian-Tindari-Letojanni fault systems, respectively. The Western and Central-Southern Aeolian Islands nested along these structures as highlighted by a large number of geological and geophysical studies in the last decades. CAVEAT aims to apply a multidisciplinary approach to study in detail the local lithospheric structure, the pattern of crustal deformation and the geochemical signature of the Central-Southern Aeolian Islands. The acquisition of new data will provide a broad overview of the ongoing geodynamics of the southern Tyrrhenian region and will allow us to properly study the interplay of present-day tectonics and volcanic deformation and the related role and nature of the fluids and the hydrothermal activity.

How to cite: Scognamiglio, L., Palano, M., Di Luccio, F., Pezzo, G., De Gregorio, S., and Greco, F. and the CAVEAT Team: Volcanism and tearing in the Tyrrhenian subduction system: the CAVEAT project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9184, https://doi.org/10.5194/egusphere-egu23-9184, 2023.

EGU23-9201 | Posters on site | SM1.1

Benchmarking Automated Rayleigh-Wave Arrival Angle Measurements for USArray Seismograms 

Gabi Laske, William Frazer, and Adrian Doran

Surface wave arrival angles are an important secondary set of observables to constrain Earth's 3-dimensional structure. These data have also been used to refine information on the alignments of horizontal seismometer components with the geographic coordinate system. In the past, particle motion has been inspected and analyzed on single 3-component seismograms, one at a time. But the advent of large, dense seismic networks has made this approach tedious and impractical. Automated toolboxes are now routinely used for datasets where station operators cannot determine the orientation of a seismometer upon deployment, such as conventional free-fall ocean bottom seismometers. 

In a previous paper, we demonstrated that our automated Python-based toolbox DLOPy compares favorably with traditional approaches to determine instrument orientations. But an open question has been whether the technique also provides  individual high-quality measurements for an internally consistent dataset to be used for structural imaging. For this feasibility study, we compared long-period Rayleigh-wave arrival angles at frequencies between 10 and 25 mHz for 10 earthquakes during the first half of 2009  that were recorded at the USArray Transportable Array (TA), a component of the EarthScope program. After vigorous data vetting, we obtained a high-quality dataset that compares favorably with an arrival angle database compiled using our traditional interactive screen approach, particularly at frequencies 20 mHz and above. 

On the other hand, the presence of strong Love waves may hamper the automated measurement process as currently implemented. 
While the proper choice of the start time of the analysis window may depend on a particular geographic location of a seismic network, our observations for USArray data suggest that a slightly later start time than is currently used may yield more high-quality Rayleigh wave measurements.

How to cite: Laske, G., Frazer, W., and Doran, A.: Benchmarking Automated Rayleigh-Wave Arrival Angle Measurements for USArray Seismograms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9201, https://doi.org/10.5194/egusphere-egu23-9201, 2023.

EGU23-9245 | Posters on site | SM1.1

Insights into the fluid migration dynamics of Tajogaite eruption, La Palma 

Joana Carvalho, Graça Silveira, Virgílio Bento, Martin Schimmel, and Resurrección Antón

Volcanic eruptions are, generally, characterized by several recordable signals that can occur before, during and/or after the eruption. Such signals may reflect temporal changes in the seismic structure that can be associated with alterations in the seismic activity, fluid migration or outgassing, useful to track the volcano evolution through its eruptive phases.

Cumbre Vieja ridge, in La Palma, is the most active volcanic field in the Canaries. The last eruption occurred at the Tajogaite cone, lasting from 19 September to 13 December 2021. It is considered one of the best-monitored volcanic crises in the Canary Islands, thus allowing us to study the eruption from different scientific perspectives.

Ambient seismic noise interferometry has been widely applied to monitor temporal velocity changes, especially at volcanoes before the eruption. However, the causes of these velocity changes are not always fully understood. In this study we use a dataset of three years (2020 to 2022) recorded in two stations operating in La Palma to identify and characterize different physical processes before and after the eruption. For this purpose, we computed phase auto- and cross-correlations and stacked them through the time-frequency phase-weighted stack to create hourly cross-correlation functions.

Seismic velocity changes cause phase shifts in the auto- and cross-correlation functions waveforms. The phase shifts can be measured through the waveform similarity, which consists in comparing each correlation function with a reference correlation function trace, in a defined window. The reference trace corresponds to a calm period, in this case, the period before the eruption. We also compared the waveform similarity results with the ground deformation inferred from GPS.

Tajogaite eruption provides an opportunity to study the behaviour within the volcanic structure prior to the eruption and its recovery after the eruption and to improve our knowledge of the magmatic fluid migration. This recent and well-documented eruption may serve as a proxy for future eruptions.

This work is a contribution to project RESTLESS (PTDC/CTAGEF/6674/2020) and it was also supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020-IDL.

How to cite: Carvalho, J., Silveira, G., Bento, V., Schimmel, M., and Antón, R.: Insights into the fluid migration dynamics of Tajogaite eruption, La Palma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9245, https://doi.org/10.5194/egusphere-egu23-9245, 2023.

EGU23-9358 | Posters virtual | SM1.1

Certain problems related to earthquakes’ catalogs 

Vahan Davtyan, Armen Kazarian, and Haik Kazarian

The quality of the earthquakes’ catalogs plays the most important role in the study of seismicity, of active faults, in seismic hazard and risk assessment, etc. The quality of the catalog is evaluated by the absence of duplicate records or explosions in itself. For example, in catalogs of historical earthquakes, often the same earthquake, described by different historical sources, appears as two different earthquakes. The situation is much more complicated in instrumental catalogs, where often tremors of the surface of the earth's crust related to human vitality appear as natural earthquakes.

The study of the instrumental earthquakes’ catalogs using daily histograms and remote sensing methods made it possible to identify a large number of events that, in our opinion, are not natural earthquakes. In particular, the catalog of The International Seismological Center (ISC), on the territory of Northern Kazakhstan and South-East Russia, contains more than 10,000 events that are most likely explosions, and not earthquakes. Likewise, the catalog of the National Survey for Seismic Protection of Armenia (NSSP) in the region of the Armenia-Georgia border contains more than 1,000 events that are also explosions. Similar events were recorded in Spain, Egypt, Turkey, Syria.

The used methodology for the detection of false earthquakes is recommended for cleaning the instrumental catalogs of seismic events.

How to cite: Davtyan, V., Kazarian, A., and Kazarian, H.: Certain problems related to earthquakes’ catalogs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9358, https://doi.org/10.5194/egusphere-egu23-9358, 2023.

EGU23-9542 | Posters on site | SM1.1

A new earthquake catalogue for seismic hazard assessment in metropolitan France and neighboring countries 

Pierre Arroucau, Stéphane Drouet, Guillaume Daniel, Paola Traversa, and Kévin Manchuel

In this work, we present a new earthquake catalogue for metropolitan France (i.e. the part of France located in Europe), which can be used to derive parameters of interest for seismic hazard modeling in that region. The catalogue is built from the amalgamation of existing catalogues for France but also neighboring countries, for both historical (here, ante-1965) and instrumental times. It covers a period ranging from 250 to 2020. Magnitudes are homogenized as moment magnitudes (Mw) using adequate conversion laws when needed. Uncertainties on location and magnitude are also provided so they can be used to realistically quantify epistemic uncertainties in hazard models. This catalogue somehow represents an updated version of the catalogue used in Drouet et al. (2020), augmented from recently published information. It extends from -8.1°E to 11.°E in longitude and from 38°N to 51°N in order to encompass the three area source models that were used in that study. The core of this catalogue is FCAT-17 (Manchuel et al., 2018), completed using the most recent ESHM2020 catalogue, FCAT-17 being given priority on the French territory plus a 20 km buffer beyond its borders and exclusive economic zone. Then, national catalogues for neighboring countries (Portugal, Spain, United Kingdom, Ireland, Belgium, Netherlands, Luxembourg, Germany, Austria, Switzerland, Italy) are also incorporated and are given full priority over their territory. The final model contains more than 45,000 events with magnitudes as low as Mw=2.0. Such low magnitudes were considered in order to provide as much constraint as possible to recurrence models, despite the fact low magnitude events are -per se- of little interest for seismic hazard models.

How to cite: Arroucau, P., Drouet, S., Daniel, G., Traversa, P., and Manchuel, K.: A new earthquake catalogue for seismic hazard assessment in metropolitan France and neighboring countries, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9542, https://doi.org/10.5194/egusphere-egu23-9542, 2023.

EGU23-9964 | ECS | Posters on site | SM1.1

Global High-Resolution mid-Mantle Imaging with Multiple-Taper SS-Precursor Estimates 

William Frazer and Jeffrey Park

SS precursor imaging has long been used to detect sharp interfaces within Earth’s mid-Mantle. The topography of the 410- and 660-km discontinuities, the major interfaces in the mantle transition zone (MTZ), can provide valuable insight into the temperature of and material flow within the mantle. Additionally, negative velocity gradients and possible partial melt surrounding the MTZ in some regions provide evidence for a hydrogen-enriched mid-mantle, a feature that may have implications for global water circulation and long-term (~100 Ma) ocean-mass regulation. Here, we apply a novel SS-precursor deconvolution technique based on multiple-taper correlation (MTC). Typical SS-precursor techniques require tightly bandpassed signals (e.g., 0.02-0.1 Hz), limiting both vertical and horizontal resolution. Higher-frequency content allows for the detection of finer structure in and around the MTZ. MTC-based SS-precursor estimates can increase the frequency cutoff to above 0.5 Hz, thereby increasing vertical resolution to under 10 km. We conduct this analysis on a global data set of over 300,000 SS waveforms recorded on the permanent GSN, GEOSCOPE, and GEOFON networks as well as the temporary EarthScope TA and AlpArray. Such a large dataset provides unprecedented bounce-point density, particularly in the North Pacific Ocean. Preliminary results suggest a global average depth of ~409 km and ~665 km for the 410- and 660-km discontinuities respectively. In this work we used time-delays calculated for the 1-D ak135 velocity model. In general, we find moderate agreement with previous low-frequency SS precursor analysis. Additionally, we identify a sharp feature above the MTZ, north of the Hawaiian Islands, that was interpreted previously from an asymmetry in sidelobe amplitudes, suggesting a low-velocity zone with a sharp interface (<10-km thickness), rather than a thick wavespeed gradient. Further results will include corrections for 3-D structure with various mantle tomography models and focus on potential impacts to the solid-Earth water cycle.

How to cite: Frazer, W. and Park, J.: Global High-Resolution mid-Mantle Imaging with Multiple-Taper SS-Precursor Estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9964, https://doi.org/10.5194/egusphere-egu23-9964, 2023.

EGU23-10456 | ECS | Orals | SM1.1

Seismogenic Thickness of the Andean Crust 

Martin Riedel, Andrés Tassara, Catalina Cabello, Denisse Leal, and Mauro Castillo

The thickness of the seismogenic crust (Ts) controls the location and magnitude of crustal earthquakes. Its upper limit is generally found near the surface and correlates to crustal seismicity onset depth (SOD) while its base correlates to the brittle-ductile transition in the crust and the seismicity cutoff depth (SCD) (Chiarabba & De Gori, 2016; Wu et al., 2017 and Zuza & Cao, 2020). Thus, it is a proxy of the brittle crust thickness and limits how deep earthquake ruptures may propagate, influencing their magnitude. Furthermore, crust with a thin Ts is inherently weaker and may concentrate more earthquakes (Burov, 2010 and Zuza & Cao, 2020). Given these factors, knowledge of Ts can help constrain future earthquake’s locations and magnitudes, aiding in seismic hazard assessment and mitigation.

Previous authors have used seismic data to calculate Ts in Italy, California and Taiwan considering the depth distribution of earthquakes (eg., Chiarabba & De Gori; 2016, Wu et al., 2017 and Zuza & Cao, 2020). However, the Chilean case presents a special and complex scenario. Here, the Nazca plate subducts below the South American plate producing an abundance of subduction earthquakes. Comparatively, crustal seismicity is sparse which presents a challenge. Adding to the complexity of the problem, the geometry of subduction as well as crustal thickness change considerably in latitude and longitude.

In this work, we present the first attempt at a Ts map of Chile. Following the methodologies of Chiarabba & De Gori, 2016; Wu et al., 2017 and Zuza & Cao, 2020 we divided the study area (ie. the Chilean margin between 15º and 45ºS) into a grid of square cells superposed by 2/3 of their width and calculated the depth distribution of earthquakes in each cell. As no consensus on which depth percentile to use for SOD and SCD exists, we calculated the percentiles 1, 5 and 10 for SOD and 90, 95 and 99 for SCD. Ts was then calculated as the difference between SCD and SOD. We compared the different outcomes.

Furthermore, we test a new methodology, relaying on cells of variable radius. Here, cell size changes according to earthquake density. We believe this approach is optimal for heterogenous catalogues, such as is the case in Chile.

Our results indicate that Ts in Chile varies latitudinally and longitudinally. Longitudinally it is generally thin at or close to the subduction trench, becomes thicker towards the east, reaching a maximum thickness below the central valley and then becomes thinner once again towards the volcanic arc. Latitudinally, it varies with crustal thickness as well as with subduction geometry (ie. it is thicker above the flat slab region).

How to cite: Riedel, M., Tassara, A., Cabello, C., Leal, D., and Castillo, M.: Seismogenic Thickness of the Andean Crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10456, https://doi.org/10.5194/egusphere-egu23-10456, 2023.

EGU23-10540 | Orals | SM1.1

Thermomechanic control on crustal seismicity along the Andean margin 

Andres Tassara, Martin Riedel, Javiera Rioseco, and Iñigo Echeverria

Temperature controls the maximum depth of seismicity because it governs the transition between seismogenic brittle deformation at shallow levels to thermally-activated ductile creep at higher depths. We investigate this relationship for the Andean margin of western South America, an archetype of subduction-related active margins that host the largest megathrust earthquakes ever recorded and dense upper plate seismicity associated to crustal faults. We develop our own analytical formulation of the thermal state of the upper plate based on a 1D conductive geotherm with crustal heat production and known temperature at the base of the plate. To the east of the intersection of the subducted slab with the continental lithosphere-asthenosphere boundary (LAB), temperature at the LAB depth is prescribed by an asthenospheric adiabat. To the west of this intersection, temperature along the megathrust is calculated with the analytical expression of England (2018) that depends on the age and subduction velocity of the slab, megathrust friction, thermal conductivity and upper plate heat production. Because the shape of the megathrust and continental LAB for the study region are well constrained with geophysical data (Tassara and Echaurren, 2012), we can extrapolate the 1D approach to 3D and cover the entire margin between the trench and the eastern foreland. We select a preferred set of involved parameters (the preferred thermal model) by fitting a new compilation of surface heat flow measurements. Our results are then compared with the depth of earthquakes recorded along the study region by the catalogue of the Chilean Seismological National Center. For crustal earthquakes (located above the Moho depth), we computed the seismicity cutoff depth (SCD) at each location on a grid as the depth where 90% of the events have hypocentral depths shallower than SCD (for details see Riedel et al. in this meeting). As expected, the spatial distribution of SCD is positively correlated with temperature, although the actual average temperature for a given SCD can be different for different geological regions. This is explained by the dependency of the brittle-ductile transition (BDT) on rock type throughout creep properties of different lithologies, a concept that we use to infer the main rock type implied by the SCD-Temperature relation at each location. Thus, we convert the SCD map and thermal structure in a geological map of the middle-lower crust, which seems to be correlated with the geological structure and geophysical images of the Andean crust.

How to cite: Tassara, A., Riedel, M., Rioseco, J., and Echeverria, I.: Thermomechanic control on crustal seismicity along the Andean margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10540, https://doi.org/10.5194/egusphere-egu23-10540, 2023.

EGU23-11359 | ECS | Posters on site | SM1.1

Deployment of dense nodal network during unrest: investigation of the Vulcano-Lipari System (Italy) with Local Earthquake Tomography 

Célia Barat, Geneviève Savard, Francisco Muñoz, Douglas Stumpp, Salvatore Alparone, Tullio Ricci, Andrea Ursino, Mimmo Palano, Maria-Paz Reyes Hardy, Lucia Pruiti, Thomas Planes, Federica Sparacino, Costanza Bonadonna, Joël Ruch, Luca Caricchi, and Matteo Lupi

The Vulcano-Lipari System is a volcanic complex located in the central sector of the Aeolian Archipelago in southern Italy. The edifice is affected by complex tectonics and develops upon the trans-extension of the Aeolian-Tindari-Letojanni Fault System. This fault is proposed to control magmatism and acts as a preferential pathway for upwelling of magmatic and supercritical fluids. Over the last three decades, Vulcano Island underwent several volcanic crises and since September 2021 it has been showing signs of increasing activity and volcanic unrest. Temperature, degassing, seismic activity, and deformation rapidly increased causing temporal evacuation of the inhabitants of the most affected regions. During the unrest in October 2021, we deployed 196 3C geophones all around Vulcano and south of Lipari to record the seismic signals for a full month, as part of the VulcaNODES project. The resulting seismic catalog confidently contains more than 7000 volcano-seismic and volcano-tectonic events with an average local magnitude of -0.32. This catalog is used to produce an unprecedented travel-time time-lapse tomography of the unrest. Seismic tomography is a powerful tool for observing structures at depth beneath volcanic systems, using seismic waves generated by earthquakes. Such a dense network combined with the exceptional seismic signal recorded will provide tomographic time series of the plumbing system every 1-3 days for a month. The still ongoing VulcaNODES project aims at observing fluids evolution along the volcano’s tectonic structures on a daily basis, providing new insights on processes usually difficult to record on short timeframes, and shedding light on the plumbing system on a high resolution.

How to cite: Barat, C., Savard, G., Muñoz, F., Stumpp, D., Alparone, S., Ricci, T., Ursino, A., Palano, M., Reyes Hardy, M.-P., Pruiti, L., Planes, T., Sparacino, F., Bonadonna, C., Ruch, J., Caricchi, L., and Lupi, M.: Deployment of dense nodal network during unrest: investigation of the Vulcano-Lipari System (Italy) with Local Earthquake Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11359, https://doi.org/10.5194/egusphere-egu23-11359, 2023.

EGU23-11450 | ECS | Posters on site | SM1.1

Efficacy of automatic detection and classification methods for volcano seismicity 

Yen Joe Tan, Zilin Song, and Yiyuan Zhong

At volcanic islands, seismometers are the main tool for monitoring various active processes including seismicity that could forewarn impending eruptions. However, the sparse seismic networks, high background noise levels, large diversity of seismic signals, and high event rates during unrest episodes make automatic detection and classification of volcano seismicity a difficult challenge. In this paper, we use the Alaska Volcano Observatory’s catalogue of ~120,000 long-period (LP) and volcano-tectonic (VT) earthquakes at 34 volcanoes from 1989-2018 to evaluate the efficacy of automatic detection and classification methods. For each event, we calculate the frequency index (FI) based on the ratio of mean spectral amplitudes in the higher and lower frequency bands of the recorded waveforms. Using the local minima in the FI distribution at each volcano as the classification boundary, we find that our labels generally agree with the catalogue’s manual labels. The classification boundaries separating LP and VT earthquakes are also relatively consistent (FI = -1) between volcanoes. Therefore, the FI method is an effective method for automatic classification of volcano seismicity. We then evaluate the performance of two machine-learning-based models (PhaseNet and EQTransformer) and the cross-correlation-based template-matching method for automatic detection. While the template-matching method is computationally more expensive, we find that most of the catalogue events can be detected by using another event as a template, with relatively low false positive rates. In comparison, both machine-learning-based models’ performances are worse than previously reported results and deteriorate systematically with decreasing FI index values. The bias might have resulted from the models having been trained using earthquake catalogues from non-volcanic regions that lack LP events. Therefore, these models should be retrained with a dataset of volcano seismicity before being applied for automatic earthquake detection at volcanic regions.  

How to cite: Tan, Y. J., Song, Z., and Zhong, Y.: Efficacy of automatic detection and classification methods for volcano seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11450, https://doi.org/10.5194/egusphere-egu23-11450, 2023.

EGU23-11829 | Orals | SM1.1

Real-time monitoring of the Russia-Ukraine conflict using seismic and infrasound array data 

Ben D.E. Dando, Bettina P. Goertz-Allmann, Quentin Brissaud, Andreas Köhler, Johannes Schweitzer, and Tormod Kværna

Since the invasion of Ukraine in February 2022, daily media reports have shown the shocking effects of fighting and the inevitable devastation associated with war. However, getting a comprehensive and unbiased overview of the ongoing military attacks remains a challenge. The availability of geophysical data that can identify individual attacks provides much needed objectivity to this problem. The pressure waves generated by an explosion travel through the atmosphere and subsurface as sound and seismic waves, and their signature can be recorded by arrays of seismometers for ground motion or microbarometers for sound propagation. In this work, we demonstrate the first known case of using seismological data to detect conflict-related explosions in near-real-time. Using the Ukrainian primary station of the International Monitoring System (IMS), the Malin array (AKASG), we automatically locate explosions around the Kyiv and Zhytomyr provinces. We show how our resulting catalogue of explosions correlates with key events in the Ukraine conflict and how these data can be used to both verify and improve accurate reporting of military attacks. We analyze events with a variety of seismo-acoustic signatures and significant differences in explosive yield. These can be associated with various types of military attacks, including artillery shelling, cruise missile attacks and airstrikes. This work opens-up the possibility for future conflict monitoring using geophysical data.

How to cite: Dando, B. D. E., Goertz-Allmann, B. P., Brissaud, Q., Köhler, A., Schweitzer, J., and Kværna, T.: Real-time monitoring of the Russia-Ukraine conflict using seismic and infrasound array data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11829, https://doi.org/10.5194/egusphere-egu23-11829, 2023.

EGU23-11857 | Posters on site | SM1.1

Increased seismicity at the beginning of 20th century in the Czech Republic and adjacent areas 

Lucia Fojtíková, Jiří Málek, Ivan Prachař, Renata Lukešová, Róbert Kysel, Jiří Vackář, Jan Valenta, and Barbora Lachová

The Czech Republic is situated in an intraplate region with low seismicity. The seismic hazard is relatively low but not negligible. A new map of the seismic hazard of the Czech Republic computed using a probabilistic approach is being compiled and will be released in the second half of 2023. As a part of this project new catalogues of earthquakes, both historical (based on macroseismic observations) and instrumental (based on seismograms) were compiled. These include earthquakes on the territory of the Czech Republic and neighboring areas of Slovakia, Austria, Germany and Poland.
       When analyzing these new enhanced catalogues, we recognized a period of increased seismicity at the beginning of the 20th century. The annual seismicity rate in this time interval for earthquakes with a magnitude 4 and greater is several times higher than at present. One possible explanation is the inconsistent magnitude determination between the beginning of the 20th century and the present time. Therefore, we re-examine historical seismograms at the beginning of the 20th century and verify their magnitudes. We also compared macroseismic observations of historical earthquakes with modern ones having almost the same magnitude.
       We found out that the increased seismicity at the beginning of 20th century is real. During this period, relatively large earthquakes were observed in various source zones in the investigated region. Such earthquakes have not occurred since 1920-1930 to the present. 

How to cite: Fojtíková, L., Málek, J., Prachař, I., Lukešová, R., Kysel, R., Vackář, J., Valenta, J., and Lachová, B.: Increased seismicity at the beginning of 20th century in the Czech Republic and adjacent areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11857, https://doi.org/10.5194/egusphere-egu23-11857, 2023.

EGU23-12078 | ECS | Posters on site | SM1.1

Recent improvements in seismic monitoring of the Maltese archipelago: A case study from the 2020 seismic swarm. 

Cristina Caricato, Pauline Galea, Paola Baccheschi, Elisa Tinti, Fabio Villani, Matthew Agius, and Sebastiano D'Amico

The Maltese archipelago lies in the centre of the Sicily Channel (Central Mediterranean), a crustal domain subject to extension since the Miocene and characterised by the presence of several active graben systems in the Plio-Quaternary. This region is affected by diffuse seismicity, in the form of isolated swarms interspersed with long pauses of quiescence and events of modest magnitude, in general not exceeding 4.0. The key features of seismicity are poorly constrained by unfavourable geographical conditions and the scarcity of seismic stations in the area between southern Sicily and Tunisia. Until a few years ago, the only Maltese station operating (WDD of the MedNet network) was the only source of information to characterise local Maltese seismicity. On the other hand, the localisations of major events (M > 4) made by the other monitoring agencies (e.g. Istituto nazionale di Geofisica e Vulcanologia - INGV) are based on traveltime readings from seismograms recorded at great distances from Malta (> 100 km) and are therefore affected by considerable formal errors. Moreover, the only published catalogue of offshore seismicity around the Maltese islands (Seismic Monitoring and Research Group, University of Malta) is based on single station location at WDD up to 2014. This is characterised by considerable uncertainties in hypocentral parameters, in particular a lack of depth information. In consequence, therefore, it is very difficult to obtain information on the geometry and kinematics of active tectonic structures, both offshore and possibly on.

In recent years, there has been a considerable increase in the number of seismic stations on the Maltese archipelago: there are currently eight active stations, that make up the Malta Seismic Network (MSN). The study we present is an example of the application of 3-D localisation techniques of Maltese seismicity, which benefits from the recent implementation of the local seismic network. In particular, we focus on the swarm occurring offshore in the period September-October 2020, and characterised by an unusual number of events (> 100), including a main event (M > 4.0) that was strongly felt over the archipelago. We have handpicked P- and S-wave traveltimes for all the events using recordings from the MSN and a selected number of Italian stations according to quality criteria, and inverted them using the Hypoellipse code. The precise earthquake localisations allow us to obtain details of the structures activated during the swarm, together with a more detailed insight into the time evolution of the sequence. Accompanying these analyses, we calculated the moment tensor solutions for some of the largest events (M > 3) and performed a spectral analysis to distinguish the waveform characteristics of events occurring at shallow depths (< 10 km) from those nucleating in the mid-crust (> 15 km depth), as a function of different wavepaths through the crust. The prospect is that in the future it will be possible to better constrain the seismotectonics of the Maltese archipelago and have a more accurate picture of the seismogenic potential of active faults in this sector of the Mediterranean.

 

How to cite: Caricato, C., Galea, P., Baccheschi, P., Tinti, E., Villani, F., Agius, M., and D'Amico, S.: Recent improvements in seismic monitoring of the Maltese archipelago: A case study from the 2020 seismic swarm., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12078, https://doi.org/10.5194/egusphere-egu23-12078, 2023.

EGU23-12243 | ECS | Posters on site | SM1.1

Revisiting the 1978 ML 5.2 Mt.Sokri earthquake, Korea 

Doyoung Kim, Kwang-Hee Kim, Yu Jin Sohn, and Young-Cheol Lee

The ML 5.2 earthquake occurred in Mt.Sokri (September 16, 1978), the center of South Korea. It was the fourth largest earthquake in South Korea since the modern seismic observation began. The Korea Meteorological Administration (KMA), the United States Geological Survey (USGS), and the International Seismological Centre (ISC) announced the location of the hypocenter respectively, but they were different. In this study, we analyzed the subsurface fault structure using current micro-earthquakes. We have used data collected by temporary seismic stations installed in the Mt.Sokri area by Pusan National University since May 2019 and the permanent seismic stations installed by KMA since 1978. KMA reported 188 earthquakes from 2007 to 2021 in the study area. We detected additional 280 micro-earthquakes using STA/LTA and template matching methods. The initial result of earthquake locations using HYPOELLIPSE was scattered across the study area. To obtain reliable locations, we relocated earthquakes using HypoDD. As a result, 468 earthquakes were relocated, about twice as many as those reported by KMA. We recognized earthquakes have occurred along WNW-ESE subsurface faults at the depth of 14 to 18km. We determined the focal mechanisms of 15 earthquakes with magnitudes greater than 2. The location of the Mt.Sokri earthquake was reviewed by comparing these results with the locations announced by the three institutions. Joint analysis of the focal mechanisms, distribution of earthquakes, and geological setting, the WNW-ESE plane was interpreted as the major fault plane. Apparently, the micro-seismicity locations in this study better correlated with the epicenter announced by USGS. However, it is difficult to confidently specify the location of the 1978 earthquake only to the current earthquakes.

How to cite: Kim, D., Kim, K.-H., Sohn, Y. J., and Lee, Y.-C.: Revisiting the 1978 ML 5.2 Mt.Sokri earthquake, Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12243, https://doi.org/10.5194/egusphere-egu23-12243, 2023.

EGU23-12460 | Posters on site | SM1.1

Seismic tomography investigation at the Lipari-Vulcano complex (South Italy) provides new insights on the active degassing system 

Cristina Totaro, Marco Aloisi, Carmelo Ferlito, Barbara Orecchio, Debora Presti, and Silvia Scolaro

Seismic tomography represents a very powerful and effective tool to look at depths beneath volcanic systems thus helping to better understand their behavior. In particular, a key parameter useful to discriminate the presence of gas, fluids and melts is represented by the P-wave and S-wave velocity ratio. In the present study, we collected ~ 4400 crustal earthquakes that occurred in the last thirty years and we used the LOcal TOmography Software LOTOS to estimate the first 3D overall model of Vp, Vs and Vp/Vs for the Lipari–Vulcano complex belonging to the Aeolian islands system (southern Tyrrhenian sea). The investigated area has been characterized both in old and recent times by fumaroles, hydrothermal activity and active degassing. In particular, in the past decades several episodes of anomalous increases of fumarole temperature and strong degassing have interested the Vulcano Island, the latter of which started in September 2021.

The results of the tomographic investigation indicate the presence of two main anomalies of low Vp and low Vp/Vs, clearly depicted up to ~ 8 km depths, and related to gas-rich materials beneath the central-northern sector of Vulcano and the western off-shore of Lipari, respectively.

The anomaly beneath Vulcano is located in close correspondence with La Fossa caldera area and with the sector where fumaroles, hydrothermal activity and active degassing are widely documented. Moreover, beneath the western Lipari off-shore a new, previously undetected, volume of strong gas-concentration has been identified. Even if these two anomalies show almost the same intensity, no evidence of degassing activity is available for the latter one because of its location at sea depths where the relevant water column pressure may inhibit the observation of possible degassing processes.

The obtained results furnished a picture of the spatial distribution of gas-filled volumes feeding the main degassing activity of the Lipari-Vulcano complex and allowed to highlight the main role played by volcanic gas in the whole system, thus furnishing invaluable constraints for improved modelling of the volcanic system and of its possible evolution.

How to cite: Totaro, C., Aloisi, M., Ferlito, C., Orecchio, B., Presti, D., and Scolaro, S.: Seismic tomography investigation at the Lipari-Vulcano complex (South Italy) provides new insights on the active degassing system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12460, https://doi.org/10.5194/egusphere-egu23-12460, 2023.

EGU23-12988 | ECS | Orals | SM1.1

At which temperatures do crustal earthquakes nucleate? Northwestern South America as a case study 

Ángela María Gómez García, Álvaro González, Mauro Cacace, Magdalena Scheck-Wenderoth, and Gaspar Monsalve

Most crustal earthquakes occur between two depths: an upper boundary marked by the onset of seismicity and a lower one defined by the seismicity cut-off. The depth difference between them is the crustal seismogenic thickness (CST). As these boundaries are diffuse, they are usually determined from thresholds (percentiles) of the statistical distribution of earthquake hypocentral depths. This spatial earthquake distribution can be used as a proxy for the rheological conditions of the hosting rock, because earthquake generation is controlled by the mechanical rock properties, and in-situ temperature, pressure and strain rates.

Laboratory friction experiments with representative rocks and major rock-forming minerals indicate that earthquakes are expected to nucleate at <350±50°C in crustal rocks, and <700±100°C in ultramafic rocks typical of the mantle. However, the small spatial and temporal scales of these experiments hinder up-scaling their results to the geological conditions found in Nature.

In this contribution, we propose a solution for such upscaling: we use a 3D lithospheric-scale model of northwestern South America to compute the corresponding temperature field, and calculate the hypocentral temperatures of crustal earthquakes recorded in the region. The model is constrained by the integration of available geophysical data and 3D gravity modelling. For each layer, lithology-constrained thermal parameters (conductivity and radiogenic heat production) are assigned, either using direct samples when available, or from representative values. We use an S-wave tomography to set the temperature at 75 km depth as the lower boundary condition, and the measured average temperature at the Earth’s surface as the upper one. Furthermore, we use available measurements of heat flow and downhole temperatures to calibrate the model.

According to our results, most crustal earthquakes nucleated at <350°C, in agreement with laboratory experiments. The relatively few outliers are likely due to uncertainties in the Moho depths and/or in the earthquake hypocentral location. Also, they may be due to the presence of ultramafic rocks (which allow larger nucleation temperatures for seismicity) within the allochthonous crustal terranes accreted to this complex margin.

We map the depths of the upper and lower boundaries of the seismogenic crust using a spatial sampling procedure, defining them as the 10th and 90th percentiles of the hypocentral depths (D10 and D90, respectively). We find that D10, D90 and the resulting CST have significant spatial variations. Some of these correlate with crustal-scale faults which apparently separate crustal domains with different seismogenic behaviors.

Moreover, we point out that the two largest earthquakes recorded in the region (Ms = 7.3 and Ms = 6.8, of the Murindó sequence in 1992) nucleated at the lower boundary of the seismogenic crust, highlighting the importance of considering this lower boundary into account when characterizing seismogenic sources for hazard assessments.

Our approach could effectively bridge the scale gap between the laboratory rock friction experiments and Nature, as it enables to integrate the full geological complexity, including a realistic present-day lithospheric structure, the three-dimensional heat flow in the lithosphere, and the mantle temperatures imprint into the crustal thermal configuration.

How to cite: Gómez García, Á. M., González, Á., Cacace, M., Scheck-Wenderoth, M., and Monsalve, G.: At which temperatures do crustal earthquakes nucleate? Northwestern South America as a case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12988, https://doi.org/10.5194/egusphere-egu23-12988, 2023.

EGU23-13526 | Posters on site | SM1.1

The Miragoâne seismic clusters in southern Haiti triggered by the Mw 7.2 Nippes earthquake of August 14, 2021 

Sylvert Paul, Tony Monfret, Françoise Courboulex, Bertrand Delouis, Anne Deschamps, Roby Douilly, David Ambrois, Steeve Julien Symithe, Sadrac St Fleur, Eric Calais, and Jérôme Chèze

On August 2021, 14th, a Mw 7.2 earthquake struck Haiti’s southern peninsula, eleven years after the devastating Mw 7 January 12, 2010 earthquake that occurred near Port au Prince. This large event, called the Nippes earthquake, has been recorded locally by the citizen network composed of low-cost raspberry shake stations. A precise analysis of the mainshock rupture from geodetic and seismic data revealed both left lateral strike slip and trust motion.

Few days after the mainshock, a temporary network consisting of 12 broadband stations was deployed in the vicinity of the epicentral zone in order to better record the aftershock sequence. Data from August 20 to December 31, 2021, were used to determine a suitable 1D velocity model of the zone and relocate about 2500 aftershocks that highlight the activation of several structures.

In this study, we focus our analysis on the region of Miragoâne situated between the ruptures of the 2021 and the 2010 earthquakes.  Before the Nippes earthquake, only a few events were detected there. Then, the Nippes earthquake triggered a burst of seismicity that lasted two months and stopped on November 2, 2021 and resumed in January 14 until March 10, 2022 with the occurrence on January 24th of two earthquakes in less than an hour of magnitude 5.3 and 5.1 respectively. We use the new 1D velocity model and the NonLinLoc using Source-Specific Station Term Corrections method (NLL-SSST) to relocate this seismic sequence. We find that the two larger earthquakes of magnitude slightly greater than 5 are closely located and confirm their reverse faulting mechanism using the waveform inversion method FMNEAR. The relocated seismicity is distributed from the surface to 20 km deep between the coast and the Enriquillo left-lateral strike-slip fault and along a plane which dips southward at ~50°, in agreement with the reverse faulting mechanism of the two larger magnitude > 5 earthquakes.

How to cite: Paul, S., Monfret, T., Courboulex, F., Delouis, B., Deschamps, A., Douilly, R., Ambrois, D., Symithe, S. J., St Fleur, S., Calais, E., and Chèze, J.: The Miragoâne seismic clusters in southern Haiti triggered by the Mw 7.2 Nippes earthquake of August 14, 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13526, https://doi.org/10.5194/egusphere-egu23-13526, 2023.

EGU23-13651 | ECS | Orals | SM1.1

Blast Vibration Prediction 

Bernd Trabi and Florian Bleibinhaus

Predicting the peak ground velocity (PGV) of blast vibrations is important for blast mining in order to set the right amount of charge weights so that they do not exceed certain thresholds. One problem is the large dispersion in the observed PGV due to unknown complexity of seismic waves spread. Classical prediction methods most often use one of several empirical formulas. One very common method is the Scaled Distance (SD) approach, which has the fewest parameters to calibrate, is widely used and works for a single sensor. In this study, we use a dataset of 55 mining production blasts recorded by 81 seismic sensors to compare the performance of the different methods. The large array allows us to apply multi-sensor inversion, which gives more information about the physical meaning of various parameters. Our results show that classical SD methods are less suitable, at least on the site we reviewed, as the data contradicts the previous link between the radial amplitude decay constant b and the load weight exponent c. For the last we find a value of 0.5, which we express as an expression of the physical relationship between the charge, energy and amplitude, suggesting that it may be a global value independent of the specific site.

How to cite: Trabi, B. and Bleibinhaus, F.: Blast Vibration Prediction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13651, https://doi.org/10.5194/egusphere-egu23-13651, 2023.

EGU23-13752 | Posters on site | SM1.1

Factors influencing the long-term interseismic behavior of the Main Marmara Fault, NW Turkey 

Naiara Fernandez, Mauro Cacace, Magdalena Scheck-Wenderoth, and Oliver Heidbach

The North Anatolian Fault (NAF) is a right-lateral continental transform fault that extends from eastern Anatolia to the northern Aegean in the eastern Mediterranean. It is characterized by strong and frequent seismic activity, posing a high seismic hazard level to the region. The Main Marmara Fault (MMF), the northern branch of the NAF along the Marmara Sea (NW Turkey), has produced several major earthquakes (M7+) in the past with a recurrence rate of about 250 years. At present, there is a 150 km seismic gap along the MMF that has not ruptured since 1766. The MMF seismic gap shows distinct variability in its along-strike interseismic strain-accumulation with locked and creeping segments, but it is unclear which are the controlling parameter of this observation. Thus, the interseismic evolution of the MMF, especially its frictional state and its inter-to-pre-seismic behavior, is still a matter of debate. It has been proposed that the observed along-strike variation in strain localization around the MMF might be linked to a heterogeneous off-fault crustal and sedimentary rheological configuration.

Here, we use a forward numerical approach with visco-elastic rheology to investigate the space and time scales of the long-term seismic behavior of the Main Marmara Fault and its main controlling factors. The MMF is modelled following a Coulomb frictional constitutive law. The spatially variable rock properties are derived from a lithospheric-scale 3D structural model of the region around the MMF. This model has been generated with a data-driven approach in a previous stage of the work. The forward model is used to test the effect of varying boundary conditions (i.e. kinematic) and fault strength properties (i.e. coefficient of friction). Our modelling approach highlights the first order role of crustal rheology and fault-strength in the long-term behavior of the MMF (spatial distribution and recurrence of seismic events), as well as their potential to explain the along fault locking degree variability.

How to cite: Fernandez, N., Cacace, M., Scheck-Wenderoth, M., and Heidbach, O.: Factors influencing the long-term interseismic behavior of the Main Marmara Fault, NW Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13752, https://doi.org/10.5194/egusphere-egu23-13752, 2023.

EGU23-14189 | Posters on site | SM1.1

Seismicity and crustal structure of the Terceira Island, Azores 

João Fontiela, Nuno Afonso Dias, Graça Silveira, Mário Moreira, and Luís Matias

We present the analysis of the local and regional seismicity recorded in 2019-2021 by a temporary seismic network installed on Terceira Island. This new seismic dataset allow us to study the induced seismicity caused by fluid extraction in a geothermal powerplant and to image the subsurface seismic structure with local earthquake tomography. 

From the distribution of the seismicity, it is possible to highlight two regions with a high number of events amongst other areas. The first one, located in the central part of the island, is associated with the volcanoes of Pico Alto and Guilherme Moniz, with  low magnitude earthquakes, and hypocentre's depths less than 10 km. The geothermal power plant is located in the transition between these two volcanic systems. We identify a cluster of earthquakes in the neighbourhood of the geothermal power plant at depths ranging from 1 to 3 km, consistent with the induction by the powerplant operation. The second seismicity region is located on the island's western sector, at the Santa Bárbara volcanic system. There, the seismicity pattern is more complex, mainly by the occurrence of both tectonic and seismo-volcanic earthquakes.  

Local earthquake tomography allows imaging of the crust from the surface to the upper-middle crust, up to 8 km depth. The Santa Bárbara and Pico Alto volcanoes are characterized by low Vp and high Vp/Vs anomalies, stronger in the first and typically related to active volcanoes. In the transition between the two volcanoes, we observe shallow strong Vp and very low Vp/Vs anomalies typical of geothermal fields. On the other hand, the Guilherme Moniz volcano exhibits high Vp anomaly and normal Vp/Vs values.

The eastern sector of the Terceira is characterized by low seismicity and, consequently, low tomographic resolution. 

This work is a contribution to projects GEMMA (PTDC/CTA-GEO/2083/2021) and RESTLESS (PTDC/CTA-GEF/6674/2020), and it was also supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020-IDL, UIDB/04683/2020 - ICT and UIDP/04683/2020 - ICT

How to cite: Fontiela, J., Afonso Dias, N., Silveira, G., Moreira, M., and Matias, L.: Seismicity and crustal structure of the Terceira Island, Azores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14189, https://doi.org/10.5194/egusphere-egu23-14189, 2023.

EGU23-14218 | ECS | Orals | SM1.1

New Insights on the seismic unrest of La Palma 2021 eruption through a purely automatic analysis 

Eduardo Andrés Díaz-Suárez, Itahiza Dominguez Cerdeña, Carmen Del Fresno, Antonio Villaseñor, and Sergio Sainz-Maza Aparicio

We have analyzed the seismic series that preceded La Palma 2021 eruption using a purely automatic methodology based on Deep Learning. A new catalog has been retrieved, firstly 5797 absolute locations were obtained using NLLoc algorithm and considering a 3D velocity model of the island. At a further stage, these results were improved computing relative locations with HypoDD code. Our final catalog has doubled the number of events of the original manual catalog of the Instituto Geográfico Nacional. We observe new detailed features of the seismicity migration throughout the crust. We can clearly differentiate two phases within the sequence: the first one from September 11th to 16th and the second one from September 16th until the eruption onset. This differentiation can be described in terms of independent seismic parameters: inter-event time dispersion coefficient, b-value spatio-temporal distribution, hypocentral migration, magnitude distribution). Our results are in agreement with previous geodetic studies. Finally, we have developed a conceptual model describing the magmatic unrest and how the magma made its way to the surface prior to this eruption. 

How to cite: Díaz-Suárez, E. A., Dominguez Cerdeña, I., Del Fresno, C., Villaseñor, A., and Sainz-Maza Aparicio, S.: New Insights on the seismic unrest of La Palma 2021 eruption through a purely automatic analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14218, https://doi.org/10.5194/egusphere-egu23-14218, 2023.

EGU23-14699 | ECS | Posters on site | SM1.1

Utilization of crowdsourced macroseismic observations to distinguish damaging from harmless earthquakes globally within minutes of an event 

Henning Lilienkamp, Rémy Bossu, Fabrice Cotton, Francesco Finazzi, Matthieu Landès, and Graeme Weatherill

Rapid assessment of an earthquake’s impact on the affected society is a crucial step in the early phase of disaster management, determining the further organization of civil protection measures. In this study, we demonstrate that felt-reports containing macroseismic observations, collected via the LastQuake service of the European Mediterranean Seismological Center, can be utilized to rapidly estimate the probability of a felt earthquake to be “damaging” rather than “harmless” on a global scale. In our fully data-driven, transparent, and reproducible approach, we first map the reported observations to macroseismic intensities according to the EMS-98 macroseismic scale. Subsequently, we compare the distribution of felt-reports to documented earthquake impact in terms of economic losses, number of fatalities, and number of damaged or destroyed buildings. Using the distribution of felt-reports as predictive parameters and an impact measure as the target parameter, we infer a probabilistic model utilizing Bayes’ theorem and Kernel Density Estimation, that provides the probability of an earthquake to be “damaging”. For 22% of felt events in 2021, a sufficient number of felt-reports to run the model is collected within 10 minutes after the earthquake. While a clean separation of “damaging” and “harmless” events remains a challenging task, correct and unambiguous assessment of a large portion of “harmless” events in our dataset is identified as a key strength of our approach. We consider our method an inexpensive addition to the pool of earthquake impact assessment tools, that can be utilized instantly in all populated areas on the planet. Being fully independent of seismic data, the suggested framework poses an affordable option to potentially improve disaster management in regions that lack expensive seismic instrumentation today and in the near future.

How to cite: Lilienkamp, H., Bossu, R., Cotton, F., Finazzi, F., Landès, M., and Weatherill, G.: Utilization of crowdsourced macroseismic observations to distinguish damaging from harmless earthquakes globally within minutes of an event, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14699, https://doi.org/10.5194/egusphere-egu23-14699, 2023.

EGU23-14763 | Posters on site | SM1.1

Enhancement of Seismic Phase Identification using Polarization Filtering and Array Analysis 

On Ki Angel Ling, Simon Stähler, David Sollberger, and Domenico Giardini

Single-station polarization analysis allows us to extract wave parameters, such as inclination, azimuth, and ellipticity angle, directly from a recorded seismic signal theoretically. In reality, however, seismic data are not purely polarized in the finite analysis window due to varying noise levels, complex wavefield interactions, and calibration errors. Hence, this would potentially influence the observation window of phases of interest. In order to minimize these systematic errors, the involvement of arrays and array processing techniques can further increase the signal-to-noise ratio of coherent signals in a wavefield, which allows us to identify different seismic phases, especially the weaker phases that are usually difficult to observe in a single waveform, even after filtering for a desired wave type. In this study, we present a new approach that combines polarization analysis and filtering in the time-frequency domain using the S-transform with conventional array analysis such as beamforming to enhance seismic signals and distinguish different phases based on their expected slownesses and backazimuth. We apply this approach on AlpArray data and demonstrate wavefield separation in vespagrams using various polarization filters. We also discuss the benefits of our approach especially on small amplitude inner core phases (e.g., PKIKPPKIKP) and their applications for advancing seismological study of Earth’s inner core.

How to cite: Ling, O. K. A., Stähler, S., Sollberger, D., and Giardini, D.: Enhancement of Seismic Phase Identification using Polarization Filtering and Array Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14763, https://doi.org/10.5194/egusphere-egu23-14763, 2023.

EGU23-16905 | Orals | SM1.1

Study of modern regional and local anomal variations of seismicity in the Tavro-Caucasian region 

Jon Karapetyan, Eduard Geodakyan, Roza Karapetyan, Lilya Hovhannisyan, and Gurgen Matevosyan

The real-time monitoring of the seismicity of the territory of the Taurus-Caucasus region shows that at present, since 2021, geodynamic processes of significant intensity have been taking place in the earth's crust of the Taurus-Caucasus region, which can form anomalous areas of increased seismotectonic deformations on separate segments of seismically active faults. The article studies the activation of weak seismicity in the study area during the period of instrumental observations from 2021 to the present.  The structure of the set of sources of weak earthquakes in five-dimensional space (hypocenter, time, energy) is considered.  Based on the methods of statistical analysis of instrumental data, clusters of earthquake sources interconnected in space and time with magnitudes M≥3.0 (Figure 1).

Figure 1.

A detailed analysis shows that almost all types of anomalous manifestations of seismicity (swarms, earthquake doublets, pseudo-gaps, etc.) are observed in the same period in the Taurus-Caucasus region.  It was revealed that during the same period, the earthquake epicenters in real time line up mainly along trajectories that have a quasi-perpendicular direction with respect to the main seismically active faults of the Caucasus strike.  In the same period, in the Tavrokavkaz region, there is an alternation of seismotectonic stress variations in tense series of earthquakes in the magnitude range M=3.0-5.4 by sequential occurrence in the region of Eastern Turkey, Northern Armenia, Iran, Azerbaijan and the Greater Caucasus. The results obtained indicate that in the Taurus-Caucasus region there are regional and local significant changes in the stress-strain state of the earth's crust that are complex in their manifestation, which must be taken into account in a detailed study of seismic geodynamic processes in the Taurus-Caucasus region in order to identify possible zones of occurrence of strong earthquakes and medium-term earthquake forecast. This work was funded by the Science Committee of the Republic of Armenia, as part of the research project (No. ACH-01/22, 21SCG-1E021).

How to cite: Karapetyan, J., Geodakyan, E., Karapetyan, R., Hovhannisyan, L., and Matevosyan, G.: Study of modern regional and local anomal variations of seismicity in the Tavro-Caucasian region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16905, https://doi.org/10.5194/egusphere-egu23-16905, 2023.

On May 22, 2021, a MS7.4 earthquake occurred in Madoi County, Guoluo Prefecture, Qinghai Province. The epicenter was located at 98.34°E and 34.59°N (Officially determined by China Earthquake Networks Center). The earthquake occurred inside the Bayan Har block with a focal depth of 17 kilometers. The regional stress adjustment after a major earthquake directly causes the surrounding faults to undergo Coulomb stress changes, which affects the rate of seismic activity, off-fault aftershocks, and probability changes of occurrence of impending earthquakes. This paper uses the fault slip model to calculate Coulomb stress changes of main faults in Madoi area of Qinghai. Using the Dieterich earthquake occurrence rate model, a formula for the occurrence probability of an earthquake exceeding a certain magnitude under the Coulomb stress disturbance is obtained. We calculate the probability changes of MS≥7.0 and MS≥6.0 earthquake occurrence of the surrounding 8 faults (segments) which caused by the Coulomb stress increase. Affected by the Qinghai Madoi MS7.4 earthquake, the probability of the 8 faults earthquake occurrence has increased to varying degrees. For the Gander South Margin fault, Madoi-Gander fault and Tibet Dagou- Changmahe fault, the probability of earthquakes occurrence has increased rapidly in a short period of time (within about 10 years) after the main shock and it has stabilized later. There is a potential for destructive earthquakes, especially for earthquakes with MS≥6.0. For the Dari fault, since the increase in Coulomb stress has little effect, it is unlikely to occur MS≥7.0 or MS≥6.0 in the short term. However, as time goes by, the possibility of potentially destructive earthquakes occurring decades later cannot be ruled out. Particular attention to the possibility of earthquakes with MS≥6.0 should be paid to. The East Kunlun fault, especially the Maqin-Maqu section, is still a possible section for strong earthquakes in the future. This section still needs to focus on and prevent earthquakes with MS≥6.0 and even MS≥7.0. An earthquake with MS≥6.0 occurred on the Yushu-Ganzi fault, especially the risk of an earthquake with MS≥7.0 is not high, while the Ulan-Ula Lake-Yushu South fault has a potential risk of destructive earthquakes. It is necessary to strengthen prevention for earthquakes with MS≥6.0.

How to cite: Liu, B.: Effect of Qinghai Madoi MS7.4 earthquake on Coulomb stress and earthquake probability increment of adjacent faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17388, https://doi.org/10.5194/egusphere-egu23-17388, 2023.

EGU23-17567 | Orals | SM1.1

Repeating crustal and intermediate-depth earthquakes from the Vrancea seismic region. 

Natalia Poiata, Bogdan Grecu, Dragos Tataru, and Felix Borleanu

Vrancea seismic zone is the most important seismically active region in Romania, representing the main source of seismic hazard in the area and neighbouring countries. The largest significant earthquakes of the past century, M 7.7 and 7.4 in 1940 and 1977, caused major and widespread destruction. The intermediate-depth earthquakes from Vrancea have a particular space distribution, being constrained to a compact volume (60-180 km in depth and 20x50 km areal extent) and falling into the category of, so called, “seismic nests”, with a peculiar and not well understood seismogenic mechanisms.

We present first results of the repeating events identification for both the crustal and intermediate-depth activity from the Vrancea seismic region, obtained by multi-channel waveform-similarity (cross-correlation - cc) analysis for earthquakes extracted from the ROMPLUS catalogue. The analysed events cover the time-period of about 2.5 years (August 2016 – December 2018) and contains 1229 earthquakes with magnitude of 2.5 – 5.9. Of these events 630 correspond to crustal and 599 – to the intermediate-depth earthquakes. Our analysis identifies 37 families of similar events (cc > 0.7) with the largest one composed of 30 events. We observe that most of the repeating events families are located in the deeper portion of the Vrancea intermediate-depth seismic volume, at the depth greater than 100 km. The identified most active family corresponds to the average depth of 140 km. Most of the intermediate-depth families are characterized by the activity that is persistent in time over the analysed time-period. For the crustal seismicity, we identified over 35 similar event families, most of which corresponding to the short-lived activations of the local (fault) structures.

In the presentation, we will discuss how these results, in relation to the structural composition and tectonic regime of the region, can help to better understand the depth-dependent activity of the Vrancea seismic zone and whether there exists a potential correlation between the crustal and intermediate-depth seismicity.

How to cite: Poiata, N., Grecu, B., Tataru, D., and Borleanu, F.: Repeating crustal and intermediate-depth earthquakes from the Vrancea seismic region., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17567, https://doi.org/10.5194/egusphere-egu23-17567, 2023.

EGU23-1524 | Orals | SM1.2

Insights from the spatial variability of (multiple) uncertainties: Earth-ice interactions for East Antarctica  

Anya Reading, Tobias Stål, Ross Turner, Felicity McCormack, Ian Kelly, Jacqueline Halpin, and Niam Askey-Doran

Uncertainty, as applied to geophysical and multivariate initiatives to constrain aspects of Earth-ice interactions for East Antarctica, provides a number of approaches to appraise and interrogate research results.  We discuss a number of use cases: 1) making use of multiple uncertainty metrics; 2) making comparisons between spatially variable maps of inferred properties such as geothermal heat flow; 3) extrapolating crustal structure given the likelihood of tectonic boundaries; and 4) providing research results for interdisciplinary studies in forms that facilitate ensemble approaches.

 

It proves extremely useful to assess a research finding, such as a mapped geophysical property, through multiple uncertainty metrics (e.g., standard deviation, information entropy, data count).  However, a thoughtful appraisal of multiple metrics could be misleading, i.e., potentially not useful in isolation, in a case where there are significant unquantified uncertainties.  Uncertainties supplied with the mapped geophysical properties can potentially be extended to capture this broader range, but that range in turn could become less helpful as the fine detail in the quantified uncertainty will be lost.

 

In the case of a property such as geothermal heat flow, indirectly determined for East Antarctica, insights can be drawn by subtracting a forward model map from an empirically determined result (e.g. Aq1) to yield the non-steady state components excluded in the forward model.  In such investigations, including the maximum and minimum possible difference between maps is essential to understand which non-steady state anomalies are real, and which could be artifacts attributable to (quantified) uncertainty.

 

In further use cases, we show how the few available seismic measurements that constrain the crust and upper mantle structure of East Antarctica can be placed in context, given the likelihood of major tectonic boundaries beneath the ice, and link this to published constraints on the seismic structure (and hence, rheology) of the deeper lithosphere.  In terms of how the solid Earth interacts with the ice sheet above, the impact of fine scale-length variations in spatial uncertainty may be investigated in relation to, for example, ice sheet modelling. For a large region and relatively unexplored region such as East Antarctica, uncertainty yields many and varied insights. 

How to cite: Reading, A., Stål, T., Turner, R., McCormack, F., Kelly, I., Halpin, J., and Askey-Doran, N.: Insights from the spatial variability of (multiple) uncertainties: Earth-ice interactions for East Antarctica , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1524, https://doi.org/10.5194/egusphere-egu23-1524, 2023.

EGU23-2190 | ECS | Posters on site | SM1.2

Locating earthquake hypocenter using first arrivals and depth phase in 3D model at local and regional distances 

Tianjue Li, Jing Chen, and Ping Tong

Precise determination of earthquake hypocenter (longitude, latitude and depth) and its origin time is of fundamental importance for not only understanding the seismogenic process but also revealing the Earth’s interior structure. Instrumental coverage plays the first-order role in determining earthquake locations. For earthquakes that occurred in the continental interior, it is favorable to have seismic stations with full azimuthal coverage; nonetheless, precise determination of earthquake depth is often challenging due to its tradeoff with earthquake origin time. The situation is even worse for earthquakes that occurred in offshore regions, e.g., Pacific ring of fire, because regional seismic stations are mostly installed on the continent. To deal with those challenges aforementioned, we propose to constrain the earthquake hypocenter by jointly using first arrivals (P and S waves) and depth phase traveltimes. The theoretical travelling times of these phases are precisely and efficiently calculated in 3D velocity model through solving the Eikonal equation. Once the earthquake hypocenter is well constrained, we further improve the accuracy of the origin time. We tested and verified the proposed earthquake location strategy in the Ridgecrest area (southern California), which serves as an end member of continental setting, and central Chile, which serves as another end member of offshore setting. The station coverage is complete in the Ridgecrest area. We have identified and picked first arrivals and sPL phases at local distances. On the contrary, seismic stations are only installed on the continent in central Chile. We have identified and picked first arrivals and sPn phases at regional distances. Determined earthquakes have comparable location accuracy as the regional catalog in the horizontal plane, while the depth uncertainty has been reduced greatly. Our study shows that incorporating depth phases into the earthquake location algorithm together with first arrivals can greatly increase earthquake location accuracy, especially earthquake depth, which will lay the solid foundation for wide-scope topics in earth science studies.

How to cite: Li, T., Chen, J., and Tong, P.: Locating earthquake hypocenter using first arrivals and depth phase in 3D model at local and regional distances, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2190, https://doi.org/10.5194/egusphere-egu23-2190, 2023.

EGU23-2930 | Orals | SM1.2

Defining spatial uncertainty in main field magnetic models 

Ciaran Beggan and William Brown

Models of the Earth’s main magnetic field, such as the International Geomagnetic Reference Field (IGRF), are described by spherical harmonic (Gauss) coefficients to degree and order 13, which allows the continuous evaluation of the field at any location and time on or above the surface. They are created from satellite and ground-based magnetometer data and describe the large-scale variation (spatial scale of 3000 km) of the magnetic field in space and time under quiet conditions.

In its technical form, the model is a spectral representation and thus its formal uncertainty (as a wavelength) is of limited advantage to the spatial value expected by the average user.  To address this, we estimated the large-scale time-invariant spatial uncertainty of the IGRF based on the globally averaged misfit of the model to ground-based measurements at repeat stations and observatories between 1980 and 2021. As an example, we find the 68.3% confidence interval is 87 nT in the North (X) component, 73 nT in the East (Y) component and 114 nT in vertical (Z) component. These values represent an uncertainty of around 1 part in 500 for the total component which, for the (average) compass user is well below instrumental detectability.

For advanced users, in applications such as directional drilling, higher resolution models (<30 km) are required and the associated uncertainties are thus further divided into random and global as well as correlated and uncorrelated parts. However, the distribution of errors is Laplacian not Gaussian and communicating the subtleties of long-tailed distributions to end-users is often a difficult task. We describe the different types of uncertainties for magnetic field models and how these are used (or not) in industrial applications.

How to cite: Beggan, C. and Brown, W.: Defining spatial uncertainty in main field magnetic models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2930, https://doi.org/10.5194/egusphere-egu23-2930, 2023.

EGU23-4074 | Posters on site | SM1.2

Using information entropy to optimise and communicate certainty of continental scale tectonic models 

Tobias Stål, Anya M. Reading, Matthew J. Cracknell, Jörg Ebbing, Jacqueline A. Halpin, Ian D. Kelly, Emma J. MacKie, Mohamed Sobh, Ross J. Turner, and Joanne M. Whittaker

Antarctic subglacial properties impact geothermal heat, subglacial sedimentation, and glacial isostatic adjustment; critical parameters for predicting the ice sheet's response to warming oceans. However, the tectonic architecture of the Antarctic interior is unresolved, with results dependent on datasets or extrapolation used. Most existing deterministic suggestions are derived from qualitative observations and often presented as robust results; however, they hide possible alternative interpretations.

 

Using information entropy as a measure of certainty, we present a robust tectonic segmentation model generated from similarity analysis of multiple geophysical and geological datasets. The use of information entropy provides us with an unbiased and transparent metric to communicate the ambiguities from the uncertainties of qualitative classifications. Information theory also allows us to test and optimise the methods and data to evaluate how choices impact the distribution of alternative output maps. We further discuss how this metric can quantify the predictive power of parameters as a function of regions with different tectonic settings.

How to cite: Stål, T., Reading, A. M., Cracknell, M. J., Ebbing, J., Halpin, J. A., Kelly, I. D., MacKie, E. J., Sobh, M., Turner, R. J., and Whittaker, J. M.: Using information entropy to optimise and communicate certainty of continental scale tectonic models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4074, https://doi.org/10.5194/egusphere-egu23-4074, 2023.

Uncertainties of geological structural geometry constructed based on seismic reflections can stem from data acquisition, processing, analysis, or interpretation. Uncertainties arising from structural interpretations and subsequent estimates of geological slip have been particularly less quantified and discussed. To illustrate the implications of interpretation uncertainties for seismic potential and structural evolution, I use an example of a shear fault-bend fold in the central Himalaya. I apply a simple solution from the kinematic model of shear fault-bend folding to resolve the geological input slip of given structure and then compare the result with a previous study to show how differences in structural interpretations could impact dependent conclusions. The findings show that only a little variance in interpretations owing to subjectivity or an unclear seismic image could yield geological slip rates differing by up to about 10 mm/yr, resulting in significantly different scenarios of seismic potential. To reduce unavoidable subjectivity, this study also suggests that the epistemic uncertainty in raw data should be included in interpretations and conclusions.

How to cite: Hu, W.-L.: How do differences in interpreting seismic images affect estimates of geological slip rates?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4591, https://doi.org/10.5194/egusphere-egu23-4591, 2023.

EGU23-5116 | Posters on site | SM1.2

Realistic uncertainties for Surface Wave dispersion curves and their influences on 1D S-wave profiles 

Nicola Piana Agostinetti and Raffaele Bonadio

Surface wave (SW) dispersion curves are widely used to retrieve 1D S-wave profiles of the Earth at different depth-scale, from local to global models. However, such models are generally constructed with a number of assumptions which could bias the final results. One of the most critical issue is the assumption of a diagonal error covariance matrix as representative of the data uncertainties. Such first-order approximation is obviously wrong for any SW practitioner, given the smoothness of dispersion curves, and could lead to overestimate the information content of the dispersion curves themselves.

In this study, we compute realistic errors (i.e. represented by a non-diagonal error covariance matrix) for Surface Wave dispersion curves, computed from earthquakes data. Given the huge amount of data available worldwide, realistic errors can be easily estimated using empirical formulations (i.e. repeated measurements of the same quantity). Such approach leads to the computation of a full-rank empirical covariance matrix which can be used as input in standard Likelihood computation (e.g. to drive a Markov chain Monte Carlo, McMC, sampling of a Posterior Probability Distribution, PPD, in case of a Bayesian workflow).

We apply our approach to field measurements recorded along one decade in the British Islands. We first compute the empirical error covariance matrices for 12 two-stations dispersion curves, under different assumptions, and, then, we invert the curves using a standard trans-dimensional McMC algorithm, to find relevant 1D S-wave profiles for each curve. We perform both an inversion considering the full-rank error covariance matrix, and one inversion using a diagonal version of the same matrix. We compare the retrieved profiles with published results. Our main finding is that 1D profiles obtained using a full-rank error covariance matrix are often similar to profiles obtained with a diagonal matrix and published profiles obtained with different approaches. However, relevant differences occur in a number of cases, which leads to potentially question some details in 1D models. Given the extreme easiness of computing the full-rank error covariance matrix, we strongly suggest to include realistic error computation in SW studies.

How to cite: Piana Agostinetti, N. and Bonadio, R.: Realistic uncertainties for Surface Wave dispersion curves and their influences on 1D S-wave profiles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5116, https://doi.org/10.5194/egusphere-egu23-5116, 2023.

EGU23-5661 | ECS | Posters on site | SM1.2

3-D joint inversion of surface wave and receiver functions based on the Markov chain Monte Carlo 

Kuan-Yu Ke, Frederik Tilmann, Trond Ryberg, and Stefan Mroczek

Geophysical inverse problems (seismic tomography) are often significantly underdetermined meaning that a large range of parameter values can explain the observed data well within data uncertainties. Markov chain Monte Carlo (McMC) algorithms based on Voronoi cell parameterizations have been used for quantifying uncertainty in seismic tomography for a number of years. Since surface waves constrain absolute shear velocities and receiver functions (RFs) image discontinuities beneath receiver locations, joint inversion of both data types based on McMC become a popular method to reveal the structure near Earth's surface with uncertainty estimates.

 

Joint inversion is usually performed in two steps: first invert for 2-D surface wave phase (or group) velocity maps and then invert 1-D surface wave and RFs jointly to construct a 3-D spatial velocity structure. However, in doing so, the valuable information of lateral spatial variations in velocity maps and dipping discontinuities in RFs may not be preserved and lead to biased 3-D velocity structure estimation. Hence, the lateral neighbors in the final 3-D model typically preserve little of the 2-D lateral spatial correlation information in the phase and group velocity maps.

 

A one-step 3-D direct inversion based on the reversible jump McMC and 3-D Voronoi tessellation is proposed to improve the above issues by inverting for 3-D spatial structure directly from frequency-dependent traveltime measurements and RFs. We take into account the dipping interfaces according to the Voronoi parameterisation, meaning that back azimuth and incidence angle of individual RFs must be taken into account. We present synthetic tests demonstrating the method. Individual inversion of surface wave measurements and RFs show the limitation of inverting the two data sets separately as expected: surface waves are poor at constraining discontinuities while RFs are poor at constraining absolute velocities. The joint solution gives a better estimate of subsurface properties and associated uncertainties. Compared to two-step inversion which may produce bias propagating between two steps and lose valuable lateral structure variations, the direct 3-D direct inversion not only produces more intuitively reasonable results but also provides more interpretable uncertainties.

How to cite: Ke, K.-Y., Tilmann, F., Ryberg, T., and Mroczek, S.: 3-D joint inversion of surface wave and receiver functions based on the Markov chain Monte Carlo, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5661, https://doi.org/10.5194/egusphere-egu23-5661, 2023.

EGU23-8679 | Posters on site | SM1.2

Is Hamiltonian Monte Carlo (HMC) really worth it? An alternative exploration of hyper-parameter tuning in a time-lapse seismic scenario 

Alison Malcolm, Maria Kotsi, Gregory Ely, and Jean Virieux

Determining if uncertainty quantification is worth it or not is closely related to how that uncertainty is computed and the associated computational cost. For seismic imaging, it is typically done using Markov chain Monte Carlo algorithms (McMC). Solving an inverse problem using McMC means exploring and characterizing the ensemble of all plausible models through more or less point-wise random walk in the data misfit landscape. This is typically done using Bayes’ theorem via the computation of a posterior probability density function. Even though this can sound naively simple, it can come with a significant computational burden given the dimension of the problem to be solved and the expense of the forward solver. This is because as the number of dimensions grow, there are exponentially more possible guesses the algorithm can make, while only a few of these models will be accepted as plausible. More advanced uncertainty quantification methods such as Hamiltonian Monte Carlo (HMC) could be beneficial because they can handle higher dimensions because efficient sampling of the model space through pseudo-mechanical trajectories in the data misfit landscape is expected. In order for an HMC algorithm to efficiently sample the model space of interest and provide meaningful uncertainty estimates, three hyper-parameters need to be tuned for trajectory design: the Leapfrog steps L, the Leapfrog stepsize ε, and the Mass Matrix M. There has been already work showing how one can choose L and ε; however designing the appropriate M is far more challenging. We consider a time-lapse seismic scenario and use a local acoustic solver for fast forward solutions. We then use Singular value decomposition, in the vicinity of the true model, to transform our time-lapse optimal model to a system of normal coordinates and use only a few of the eigenvalues and eigenvectors of the Hessian as oscillators. By doing so, we can efficiently understand the impact of the initial conditions and the choice of M and gain insight on how to design M in the standard system. This gives us an intuitive way to understand the mass matrix, allowing us to determine whether gains from the HMC algorithm are worth the cost of determining the parameters.

How to cite: Malcolm, A., Kotsi, M., Ely, G., and Virieux, J.: Is Hamiltonian Monte Carlo (HMC) really worth it? An alternative exploration of hyper-parameter tuning in a time-lapse seismic scenario, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8679, https://doi.org/10.5194/egusphere-egu23-8679, 2023.

EGU23-8767 | ECS | Posters on site | SM1.2

Can Normalizing Flows make Uncertainty Quantification Practical for Time-Lapse Seismic Monitoring 

Changxiao Sun, Alison Malcolm, and Rajiv Kumar

Due to the nonlinearity of inversion as well as the noise in the data, seismic inversion results certainly have uncertainties. Whether quantifying these uncertainties is useful depends at least in part on the computational cost of computing them.  Bayesian techniques dominate uncertainty quantification for seismic inversion.  The goal of these methods is to estimate the probability distribution of the model parameters given the observed data. The Markov Chain Monte Carlo algorithm is widely employed for approximating the posterior distribution. However, generating the posterior samples by combining the prior and the likelihood is intractable for large problems and challenging for smaller problems. We apply a machine learning method called normalizing flows, which consists of a series of invertible and differentiable transformations, as an alternative to the sampling-based methods. In our work, the normalizing flows method is combined with full waveform inversion(FWI) using a numerically exact local solver to quantify the uncertainty of time-lapse changes. We integrate uncertainty quantification(UQ) and FWI by estimating UQ on the images generated by FWI making it computationally practical. In this way, a reasonable posterior probability distribution is directly predicted and produced by transforming from a normal distribution, measuring the amount and spread of variation in FWI images by sample mean and standard deviation. In our numerical results, the method for calculating the posterior distribution of the model is verified to be practical and advantageous in terms of effectiveness.

How to cite: Sun, C., Malcolm, A., and Kumar, R.: Can Normalizing Flows make Uncertainty Quantification Practical for Time-Lapse Seismic Monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8767, https://doi.org/10.5194/egusphere-egu23-8767, 2023.

EGU23-10003 | ECS | Orals | SM1.2

Variational Experimental Design Methods for Geophysical Applications  

Dominik Strutz and Andrew Curtis

The design of geophysical surveys or experiments (henceforth, the experimental design) significantly influences the uncertainty in scientific results that can be inferred from recorded data. Typical aspects of experimental designs that can be varied are locations of sensors, sensor types, and the modelling or data processing methods to be applied to recorded data. To tighten constraints on the solution to any inverse or inference problem, and thus to rule out as many false possibilities as possible, the design should be optimised such that it is practically achievable within cost and logistical constraints, and such that it maximises expected post-experimental information about the solution. 

Bayesian experimental design refers to a class of methods that use uncertainty estimation methods to quantify the expected gain in information about target parameters provided by an experiment, and to optimise the design of the experiment to maximise that gain. Information gain quantifies the decrease in uncertainty caused by observing data. Expected information gain is an estimate of the gain in information that will be offered by any particular design post-experiment. Bayesian experimental design methods vary the design so as to maximise the expected information gain, subject to practical constraints. 

We introduce variational experimental design methods that are novel to geophysics, and discuss their benefits and limitations in the context of geophysical applications. The family of variational methods relies on functional approximations of probability distributions, and in some cases, of the model-data relationships. They can be used to design experiments that best resolve either all model parameters, or the answer to a specific question about the system studied. Their potential advantage over some other design methods is that finding the functional approximations used by variational methods tends to rely more on optimisation theory than the more common stochastic uncertainty analysis used to approximate Bayesian uncertainties. This allows the wealth of understanding of optimisation methods to be applied to the full Bayesian design problem. 

Variational design methods are demonstrated by optimising the design of an experiment consisting of seismometer locations on the Earth’s surface, so as to best estimate seismic source parameters given arrival time data obtained at seismometers. By designing separate experiments to constrain the hypocentres and epicentres of events, we show that optimal designs may change substantially depending on which questions about the subsurface we wish the experiment to help us to answer. 

By accounting for differing expected uncertainties in travel time picks depending on the picking method used, we demonstrate that the data processing method can be optimised as part of the design process, provided that expected uncertainties are available from each method.

How to cite: Strutz, D. and Curtis, A.: Variational Experimental Design Methods for Geophysical Applications , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10003, https://doi.org/10.5194/egusphere-egu23-10003, 2023.

EGU23-11807 | Orals | SM1.2

Why probabilistic models are often true, but can be either useful or useless. 

Thomas Mejer Hansen and Rasmus Bødker Madsen

“All models are wrong but some are useful” (most often credited to George Cox) is a commonly used aphorism, probably because it resonates with some truth to many. We argue though, that it would be more correct to say “All deterministic models are wrong but some are useful “. Here, a deterministic model refers to any single, and in some quantitative way ‘optimal’ model, typically the results of minimizing some objective function. A deterministic model may be useful to use as a base for making decisions, but, it may also lead to disastrous results. The real disturbing issue with deterministic models is that we do not know whether it is useful for a specific application, because of a lack of uncertainties.

On the other hand, a probabilistic model, that is described by a probability density, or perhaps by many realizations of a probability density, can represent in principle arbitrarily complex uncertainty. In the simplest case where the probabilistic model is represented by a maximum entropy uncorrelated uniform distribution, one can say that “The simplest probabilistic model is true but not very useful.“.  It is true in the sense that the real Earth model is represented by the probabilistic model, i.e. it is a possible realization from the probabilistic model, but not very useful, as little to no information about the Earth can be inferred.

In an ideal case, a probabilistic model can be set up from a variety of different sources, such that it is both informative (low entropy), and consistent with an actual subsurface model in which case we can say “An informative probabilistic model can be true and also very useful.“. Any uncertainty in the probabilistic model can then be propagated to any other related uncertainty assessment using simple Monte Carlo methods. In such a case clearly, uncertainty is useful.

In practice though, when a probabilistic Earth model has been constructed from different sources (such as structural geology, well logs, and geophysical data) then one will often find that the uncertainty of each source of information will be underestimated, such that the combined model will describe too little uncertainty. This can lead to potentially worse decision-making than when using a deterministic model (that one knows is not correct), as one may take a decision related to a low probability of a risky scenario that may simply be related to the underestimation and/or bias of the uncertainty.

We will show examples of constructing both deterministic and probabilistic Earth models, based on a variety of geo-based information. We hope to convince the audience, that a probabilistic model can be designed such that it is consistent with the actual subsurface, and at the same time provides an optimal base for decision-makers and risk analysis.

In the end, we argue that: Uncertainty is not only useful but essential, to any decision-making, but also that it is of utmost importance that the underlying information is quantified in an unbiased way. If not, a probabilistic model may simply provide a complex base in which to take wrong decisions.

How to cite: Hansen, T. M. and Madsen, R. B.: Why probabilistic models are often true, but can be either useful or useless., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11807, https://doi.org/10.5194/egusphere-egu23-11807, 2023.

This work discusses the use of full waveform inversion (FWI) with fully nonlinear estimates of uncertainty, to monitor changes in the Earth’s subsurface due to dynamic processes. Typically, FWI is used to produce high resolution 2D and 3D static subsurface images by exploiting information in full acoustic, seismic or electromagnetic waveforms, and has been applied at global, regional and industrial spatial scales. To avoid the over-interpretation of poorly constrained parts of resulting subsurface images or models, it is necessary to know their uncertainty – the range of possible subsurface models that are consistent with recorded data and other pertinent constraints. Almost all estimates of uncertainty on the results of FWI approximate the model-data relationships by linearisation to make the calculation computationally efficient; unfortunately this throws those uncertainty estimates into question, since their raison d’etre is to account for possible model and data variations which are themselves related nonlinearly.

In a related abstract and associated manuscript we use variational inference to achieve the first Bayesian uncertainty analysis for 3D FWI that is fully nonlinear (i.e., involves no linearisation of model-data relationships: https://arxiv.org/abs/2210.03613 ). Variational inference refers to a class of methods that optimize an approximation to the probability distribution that describes post-inversion parameter uncertainties.

Here we extend those methods to perform nonlinear uncertainty analysis for 4D (time-varying 3D) FWI monitoring of the subsurface. Specifically we apply stochastic Stein variational gradient descent (sSVGD) to seismic data generated synthetically for two 3D seismic surveys acquired over a changing 3D subsurface structure based on the 3D overthrust model (Aminzadeh et al., 1997: SEG/EAGE 3-D Modeling Series No. 1). Iterated linearised inversion of each data set fails to image changes (~1%) in the wave speed of the medium, both when each inversion begins independently from the same (good) reference model, or when the best-fit model from inversion of the first survey’s data was used as reference model for the second inversion. Nonlinear inversion of each data set from the same prior distribution also fails to detect these ~1% changes. However, the changes can be imaged and their uncertainty estimated if variational methods applied to invert data from the second survey are initiated from their final state in the inversion of the first survey data. In addition, the methods then converge far more rapidly, compared to running each inversion independently.

We conclude that the probability distributions describing 3D seismic velocity uncertainty are sufficiently complex that the computations of 3D parameter uncertainty for each survey independently have not converged sufficiently to detect small 4D changes. However, the change in these probability distributions between surveys must be sufficiently small that the final solution found from the first survey could evolve robustly into the second survey solution, such that changes are resolved above the uncertainty using variational methods. Nevertheless, this change must be sufficiently complex that linearised methods can not evolve smoothly from one solution to the next, explaining why linearised methods fail, and highlighting why the estimation of nonlinear uncertainties is so important for imaging and monitoring applications.

 

How to cite: Curtis, A. and Zhang, X.: On Monitoring Changes in the Earth’s Subsurface using 4D Bayesian Variational Full Waveform Inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14914, https://doi.org/10.5194/egusphere-egu23-14914, 2023.

Determining the thermochemical structure of the mantle is crucial for understanding its evolution and dynamics. Temperature variations have long been known as important driving forces of mantle convection; however compositional differences can also influence dynamics. Additionally, compositional differences can act as indicators left behind by processes operating in the past. Both aspects have played a role in the ongoing discussions on the Large Low Shear Wave Velocity Provinces (LLSVP), the proposed Bridgmanite Enriched Ancient Mantle Structures (BEAMS) and the fate of subducted oceanic crust.

A prerequisite for determining compositional differences in terms of major oxides with geophysical techniques is a joint determination of several geophysical properties. A single geophysical property (density, velocity) could almost always be explained by temperature or composition variations alone – except in pathological edge cases. The geophysical signature of composition lies in the pointwise relation between properties. This pointwise relation can be distorted by spectral filtering or inversion smoothing and damping.

In this contribution, I parametrize the mantle as a collection of discrete spatial anomalies in terms of seismic velocity and density. Surface wave phase speed and satellite gravity data are used to constrain the anomalies. A transdimensional Monte Carlo Markov Chain method is used to generate ensembles of solutions that try to balance model complexity and data fit. An important aspect of this setup is that the two data sets used are complementary: While satellite gravity data are available (nearly) globally with homogeneous quality, coverage of phase speed data depends on the spatial distribution of seismic stations and large earthquakes. Conversely, the gravity field lacks true depth sensitivity, which surface wave data can provide by combining several frequencies.

I will present synthetic investigations that aim at determining how accuracy and coverage affect the simultaneous recoverability of seismic velocity and density.

How to cite: Szwillus, W.: Sensitivity of surface wave and gravity data to velocity and density structure in the mantle – insights from transdimensional inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15486, https://doi.org/10.5194/egusphere-egu23-15486, 2023.

EGU23-15776 | Orals | SM1.2

Assessing and reducing stratigraphic uncertainty in the subsurface: where are we standing? 

Guillaume Caumon, Julien Herrero, Thomas Bodin, and Paul Baville

Sedimentary strata are essential archives of the past conditions of the earth, and host significant natural resources in the subsurface. However, inferring the features of strata at depth (e.g., geometry, connectivity, physical or geological properties), remains a challenge prone to many uncertainties. Classically, the layers and their geometry are first interpreted from boreholes, geological outcrops and geophysical images, then layer properties can be addressed with geostatistical techniques and inverse methods. Theoretical models considering horizon depth uncertainty have been proposed decades ago, and geostatistical simulation can sample petrophysical uncertainties, but these approaches leave the number of layers fixed and are rely on conformable layering assumptions which are seldom met. We review some recent developments in well correlation in the frame of relative chronostratigraphy, which addresses the problem of locating potential gaps in the stratigraphic record. We also present some first results of the integration of the number of layers in inverse problems using a reversible jump Monte Carlo method. These two elements open interesting perspectives to jointly address topological, geometrical and petrophysical uncertainties at multiple scales in sedimentary basins. Although such uncertainties can have significant impact on quantitative geological and geophysical model forecasts, many computational challenges still lie ahead to appropriately sample uncertainties. Harnessing these challenges should open the way to finding, on a case-by-case basis, the suitable level of detail between detailed stratigraphic architectures and effective medium representations.

How to cite: Caumon, G., Herrero, J., Bodin, T., and Baville, P.: Assessing and reducing stratigraphic uncertainty in the subsurface: where are we standing?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15776, https://doi.org/10.5194/egusphere-egu23-15776, 2023.

EGU23-17147 | Orals | SM1.2

Addressing uncertainty in models for improved decision making 

Daniel Straub, Wolfgang Betz, Mara Ruf, Amelie Hoffmann, Daniel Koutas, and Iason Papaioannou

In science and engineering, models are used for making predictions. These predictions are associated with uncertainties, mainly due to limitations in the models and data availability. While these uncertainties might be reduced with further analysis and data collection, that is often not an option because of constrained resources. Whenever the resulting predictions serve as a basis for decision making, it is important to appraise the uncertainty, so that decision makers can understand how much weight to give to the predictions. In addition, performing uncertainty and sensitivity analysis at intermediate stages of a study can help to better focus the model building process on those elements that contribute most to the uncertainty. Decision sensitivity metrics, which are based on the concept of value of information, enable to identify which uncertainties most affect the conclusions drawn from the model outcomes. We have found that such decision sensitivity metrics can be a powerful tool to understand and communicate an acceptable level of uncertainty associated with model predictions.

In this contribution, we will discuss the general principles of decision-oriented sensitivity measures for dealing with uncertainty and will demonstrate them on two real-life cases: (1) the use of geological models for the choice of the nuclear waste deposit site in Switzerland, and (2) the use of flood risk models for decisions on flood protection along the Danube river.

 

How to cite: Straub, D., Betz, W., Ruf, M., Hoffmann, A., Koutas, D., and Papaioannou, I.: Addressing uncertainty in models for improved decision making, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17147, https://doi.org/10.5194/egusphere-egu23-17147, 2023.

EGU23-17474 | Posters on site | SM1.2

Inconsistency and violation of causality in Bayesian inversion paradigms 

Klaus Mosegaard

Probabilistic formulations of inverse problems are most often based on Bayes Rule, which is considered a powerful tool for integration of data information and prior information about potential solutions. However, since its introduction it has become apparent that the Bayesian inference paradigm presents a number of difficulties, especially in the phase where the problem is mathematically formulated.

 

Perhaps the most notable difficulty arises because Bayes Theorem is usually formulated as a relation between probability densities on continuous manifolds. This creates an acute crisis because of a problem described by the French mathematician Joseph Bertrand (1889), and later investigated by Kolmogorov and Borel. According to Kolmogorov's (1933/1956) investigations, conditioning of a probability density is underdetermined: In different parameterizations (reference frames), conditional probability densities express different probability distributions. Surprisingly, this problem is persistently neglected in the scientific literature, not least in applications of Bayesian inversion. We will explore this problem and show that it is a serious threat to the objectivity and quality of Bayesian computations including Bayesian inversion, computation of Bayes Factors, and trans-dimensional inversion.

 

Another difficulty in Bayesian Inference methods derives from the fact that data uncertainties, and prior information on the unknown parameters, are often unknown or poorly known. Because they are required in the calculations, statisticians have invented

hierarchical methods to compute parameters (known as hyper-parameters) controlling these uncertainties. However, since both the data uncertainties and the prior information on the unknowns are supposed to be known 'a priori', but are calculated 'a posteriori', this creates another crisis, namely a violation of causality. We will take a close look at the consequences of this mixing of 'prior' and 'posterior', and show how it potentially jeopardizes the validity of Bayesian computations.

 

How to cite: Mosegaard, K.: Inconsistency and violation of causality in Bayesian inversion paradigms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17474, https://doi.org/10.5194/egusphere-egu23-17474, 2023.

EGU23-17483 | Orals | SM1.2

Quantifying Uncertainty for Complex Systems 

Lucy Bailey, Mike Poole, Oliver Hall, and Lucia Gray

The ability to quantify uncertainty effectively in complex systems is not only useful, but essential in order to make good decisions or predictions based on incomplete knowledge.  Conversely, failure to quantify uncertainty, and a reliance on making assumptions, prevents a proper understanding of the uncertain system, and leads to poor decision-making. 

In our work to implement a geological disposal facility (GDF) for higher-activity radioactive waste, we need to be very confident in our demonstration of safety of the facility over geological timescales (hundreds of thousands of years). There are inevitably large uncertainties about the evolution of a system over such timescales.  We have developed a strategy for managing and quantifying uncertainty which we believe is more generally applicable to complex systems with large uncertainties.  At the centre of the strategy are three concepts: a top-down, iterative approach to building a model of the ‘total system’; a probabilistic Bayesian mathematical treatment of uncertainty; and a carefully designed methodology for quantifying uncertainty in model parameters by expert judgement that mitigates cognitive biases which usually lead to over-confidence.

Our total system model is a probabilistic model built using a top-down approach. It is run many times as a Monte-Carlo simulation, where in each realisation, parameter values are sampled from a probability density function representing the uncertainty. It is built with the performance measures of interest in mind, starting as simply as possible, then iteratively adding detail for those parts of the model where previous iterations have shown the performance measures to be most sensitive.  It sits well with a similar iterative approach to data gathering, the aim being developing understanding of what parts of the total system really matter. 

In our experience, to be both a tractable and effective strategy, it is essential that the level of detail and complexity in any quantitative analysis, is commensurate with the amount of uncertainty.  There needs to be a recognition that initial consideration of the system in too great a level of detail is futile when the uncertainty is large.  It is through iterative learning, understanding the sensitivities to the total system and refining our analysis and data gathering in areas of significance, that we can handle even complex uncertainty and develop a sound basis for confidence in decision making.

We are now looking to explore new techniques to iterative learning that involve maximising the information that can be gained, even from initially sparse datasets, to aid in confident decision-making.

 

How to cite: Bailey, L., Poole, M., Hall, O., and Gray, L.: Quantifying Uncertainty for Complex Systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17483, https://doi.org/10.5194/egusphere-egu23-17483, 2023.

EGU23-96 | ECS | Orals | TS3.10

Subduction, uplift and serpentinite in Cyprus: insights from seismicity 

Thomas Merry, Ian Bastow, David Green, Stuart Nippress, Charlie Peach, Rebecca Bell, Sylvana Pilidou, Iordanis Dimitriadis, and Freddie Ugo

Cyprus sits at the plate boundary between Anatolia in the north and Africa in the south, at a transition from oceanic subduction in the west to continental strike-slip and collision tectonics in the east. The nature of the plate boundary at Cyprus has been historically controversial and poorly understood, in part due to a lack of constraints on local seismicity. Ongoing subduction of either oceanic or continental African lithosphere is argued, with some invoking subduction of the Eratosthenes Seamount, a continental fragment to the south of Cyprus rising 2km above the sea floor, as a driver of uplift in Cyprus. At the centre and highest point of the Troodos ophiolite, which dominates the island, is the Mt Olympus mantle sequence, an outcrop of heavily serpentinised peridotite that is associated with a localised gravity low and proposed to be the top of a rising serpentinite diapir. Geophysical constraints to test these hypotheses at depth are lacking. 

 

We analyse data from a two-year deployment of five broadband seismometers along with the existing permanent network to create a new earthquake catalogue for Cyprus. We use our catalogue to constrain the first formalised 1-D velocity model for the island, improving earthquake locations. Earthquake hypocentres clearly delineate a northward-dipping African slab beneath Cyprus at 20-60 km depth. The most seismically active part of the island is at 15-20 km depth beneath the southern edge of the ophiolite, approximately the expected depth to the plate interface; thrust faulting focal mechanisms here are consistent with ongoing subduction. Hypocentral depths suggest a topography of the slab top, with the shallowest depths in the centre of the island, coincident with the greatest uplift in the overlying plate, supporting hypotheses of uplift driven by subduction of the Eratosthenes Seamount. A lack of seismicity in a 20km-wide zone at this ‘peak’ coincides with the outcropping Mt Olympus mantle sequence, and may be associated with the deep root of the proposed serpentinite diapir. 

How to cite: Merry, T., Bastow, I., Green, D., Nippress, S., Peach, C., Bell, R., Pilidou, S., Dimitriadis, I., and Ugo, F.: Subduction, uplift and serpentinite in Cyprus: insights from seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-96, https://doi.org/10.5194/egusphere-egu23-96, 2023.

EGU23-3431 | ECS | Posters on site | TS3.10

Investigation the performance of ensemble clustering techniques in latest GPS velocity field of Turkey 

Batuhan Kilic, Seda Özarpacı, and Yalçın Yılmaz

The primary active strike-slip faults in Turkey are the North and East Anatolian Faults (NAF and EAF), as well as the Ölüdeniz Fault. These transform boundaries are the result of various tectonic regimes, including the collapse of the oceanic lithosphere in the Hellenic and Cyprus arcs, continental collisions in the Zagros/Caucasus and Black Sea; Anatolia's related continental escape and expansion in western Turkey; and the Nubian, Arabian, and Eurasian plate interactions, which are Turkey's main tectonic domains. Block modeling may be useful for establishing slip rates for major faults or calculating block movements in order to better understand these regimes and deformations. Previous to block modeling, clustering analysis may be used to identify Global Positioning System (GPS) velocities in the absence of prior data.

Clustering analysis, as an unsupervised learning, is an essential technique to discover the natural groupings of a set of multivariate data. Its aim is to explore the underlying structure of a data set based on certain criteria, specific characteristics in the data, and different ways of comparing data. There have been many studies conducted in the last ten years that determine and investigate cluster/block boundaries without any a priori information by considering the similarity of GPS-derived velocities. With the rapid progress of clustering technology, various partitioning, hierarchical, and distribution-based techniques such as k-means, k-medoids, Balanced Iterative Reducing and Clustering using Hierarchies (BIRCH), Gaussian Mixture Model (GMM), and Hierarchical Agglomerative Clustering (HAC) have been utilized to find appropriate solutions that are acceptable and to determine boundaries before block modeling in geodetic studies.

Although clustering techniques are diverse and span in clustering GPS velocities, there are several common problems associated with clustering, including the inability of a single clustering algorithm to accurately determine the underlying structure of all data sets and the lack of consensus on a universal standard for selecting any clustering algorithm for a specific problem. To overcome this problem, ensemble clustering (consensus clustering) techniques that can employ from gathering the strengths of many individual clustering algorithms has been introduced (Kılıç and Özarpacı, 2022). Therefore, the objective of this study is to explore the performance of ensemble clustering techniques for clustering GPS-derived horizontal velocities. In the direction of this research, we used newly published horizontal velocities inferred from a combination of a dense network of long term GNSS observations in Turkey (Kurt et al., 2022). After that, we tested the number of clusters that best represents the data set using the GAP statistic algorithm, and we clustered GPS velocities using five different clustering techniques, including BIRCH, k-means, mini batch k-means, HAC, and spectral clustering. Then, we investigated the performance of three ensemble clustering techniques such as Cluster-based Similarity Partitioning Algorithm (CSPA), Hybrid Bipartite Graph Formulation (HBGF), and Meta-CLustering Algorithm (MCLA) by combining the strengths of five individual clustering algorithms. The outcome of this study revealed that the MCLA ensemble clustering algorithm can be utilized to determine cluster/block boundaries for this region and give enhanced results compared to single clustering techniques.

Keywords: Clustering analysis, GPS velocities, Ensemble clustering

 

How to cite: Kilic, B., Özarpacı, S., and Yılmaz, Y.: Investigation the performance of ensemble clustering techniques in latest GPS velocity field of Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3431, https://doi.org/10.5194/egusphere-egu23-3431, 2023.

EGU23-4723 | ECS | Orals | TS3.10

New 3D models for the subducted lithosphere of the Eastern Mediterranean Basin 

Sonia Yeung, Marnie Forster, Hielke Jelsma, Adam Simmons, Wim Spakman, and Gordon Lister

We present a new regional three-dimensional (3D) slab reconstruction of the Eastern Mediterranean Basin utilising the UU-P07 global tomography model and two earthquake data packages (GCMT and ISC) to produce 3D slab models to a depth of 2900 km. The model data are permissive of the presence of a south-eastward-propagating horizontal tear in the Aegean slab beneath the Rhodope Massif in the Balkanides extending towards the Thermaic Gulf. Alternatively: i) the local pattern of reduced amplitudes at ~ 200km depth could also reflect a different type of lithosphere; and/ or ii) tearing might have been preceded by down-dip stretching, resulting in abrupt thinning of the lithosphere in the extended zone.

Further to the southeast, beneath the Peloponnese and Crete, the model data support the existence of multiple subduction-transform (or STEP) faults. The subduction–transforms have since themselves begun to founder, and to roll back towards the southeast.  Even further east, beneath Cyprus, the model data appears to support the existence of yet another STEP fault, linking the slab to the east flank of the Arabia indenter.  

The 3D geometry of the subducted slabs demonstrates ‘lithological steps’ that formed as the lithosphere tore and bent while descending. Previous 3D reconstructions of the region’s deep lithospheric geometry confirmed the presence of fragmented segments but details on: i) the vertical extent of the descended slabs; and ii) the correlation between surface deformation structure and geometry at depth had yet to be established. In order to allow such a correlation, the 3D model was floated [or returned to the planet surface] utilizing a wire mesh with a Delaunay tessellation, using the program Pplates. This enabled area-balancing and therefore a more accurate approximation to the areal extent of the slabs prior to their subduction. The floated slab(s) can be incorporated in a 2D+time tectonic reconstruction to provide additional constraints not available using surface geology. The inferred tears correlate with surface structures such as the Strabo and Pliny trenches between the Hellenic Arc (Aegean Trench) and the Cyprian Trench near the Cyprus Arc, as well as with the seaward extent of the East Anatolian Fault separating the Cyprus Arc and the Arabian indenter. Such correlations between surface and deep lithospheric structures have four-dimensional (4D) implications for episodic closure of the West Tethys suture from its Mesozoic onset, through the tectonically active Tertiary to the present-day.

How to cite: Yeung, S., Forster, M., Jelsma, H., Simmons, A., Spakman, W., and Lister, G.: New 3D models for the subducted lithosphere of the Eastern Mediterranean Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4723, https://doi.org/10.5194/egusphere-egu23-4723, 2023.

EGU23-5380 | ECS | Posters on site | TS3.10

Strike-slip faulting in the western prolongation of the North Anatolian Fault: the Lichades – Oreoi Channel – Skiathos Basin lineament 

Fabien Caroir, Frank Chanier, Dimitris Sakellariou, Fabien Paquet, Julien bailleul, Louise Watremez, Virginie Gaullier, and Agnes Maillard

          The North Anatolian Fault (NAF) is one of the major active structures in the Eastern Mediterranean. Its right-lateral strike-slip fault initiated in eastern Turkey 13 Ma ago. The NAF westward propagation during Neogene and Quaternary times delineates the plate boundary between Eurasia and Anatolia-Aegean. The western termination of NAF is currently located in the North Aegean Trough (NAT) where NAF displays a NE-SW direction. In the NAT, the NAF termination is located near to the Sporades Islands. In the western prolongation of this termination, there is a wide domain characterised by distributed deformation. This major extensional area is mainly constituted by the Corinth rift and the North Evia domain, our study area. The whole zone experience a relative high seismicity with strike-slip focal mechanisms, especially right-lateral displacements along NE-SW-striking faults, which are mainly located between the North Evia domain and the Southern Thessaly.

          Our study is mostly based on new very-high-resolution seismic reflection profiles (Sparker) acquired during the WATER surveys (Western Aegean Tectonic Evolution and Reactivations) in July-August 2017 and 2021, onboard the R/V “Téthys II”. We also analysed several seismicity catalogues in order to connect the recent structures from seismic lines to active tectonics over the region. The interpretations from these datasets emphasize the evolution of the deformation of the North Evia domain, in particular, along the NE-SW striking lineament “Lichades Area – Oreoi Channel – Skiathos Basin” (L-O-S).

          The deformation in the Lichades Area is dominated by numerous active normal faults striking W-E or WNW-ESE and showing metric-scale offsets (up to 5 m.) within the Holocene sequence. One of the largest sub-active to active fault is striking NE-SW, parallel to the Oreoi Channel, and thus strongly oblique to the main rift deformation. The Oreoi Channel is a marine straight linking the Lichades Area and the Skiathos Basin. The seismic profiles highlight normal faults of different ages with a NE-SW direction. In the south-east, the Oreoi Channel is delineated by the Oreoi Fault, a mainly onshore normal fault which is dipping towards north-west. The Skiathos Basin is a newly discovered structure from our seismic dataset that is separated from the Skopelos Basin by a NE-SW striking acoustic ridge. The Skiathos Basin presents two main depocenters individualized by areas of rising acoustic basement. Some normal faults, oriented NE-SW and W-E, have been identified in the basin. Finally, many earthquakes focal mechanisms located in the Skiathos Basin and the Oreoi Channel indicate strike-slip faulting, with a right-lateral motion along the NE-SW direction.

          This detailed structural analysis together with the synthesis of seismic activity allow to propose a tectonic map with new insights on the recent deformation of the key-area “L-O-S” in the south-western prolongation of NAF. The Skiathos basin development shows indications of transtensive deformation. The Oreoi Channel is controlled by NE-SW-striking faults with a right-lateral component and the Lichades Area displays several fault with oblique direction and pure extension. We propose that the L-O-S tectonic system prolongs the NAF system and may progressively evolve as the future plate boundary.

How to cite: Caroir, F., Chanier, F., Sakellariou, D., Paquet, F., bailleul, J., Watremez, L., Gaullier, V., and Maillard, A.: Strike-slip faulting in the western prolongation of the North Anatolian Fault: the Lichades – Oreoi Channel – Skiathos Basin lineament, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5380, https://doi.org/10.5194/egusphere-egu23-5380, 2023.

Understanding the crustal structure of the Anatolian Plate has important implications for its formation and evolution, including the extent to which its high elevation is maintained isostatically. However, the numerous teleseismic receiver function studies from which Anatolian Moho depths have been obtained return results that differ by <21km at some seismograph stations. Thus, we determine Moho depth and bulk crustal Vp/Vs ratio (K) at 582 broadband seismograph stations across Anatolia, including ~100 for which H-K results have not been reported previously. We use a modified H-K stacking method in which a final solution is selected from a suite of up to 1000 repeat H-K measurements, each calculated using randomly-selected receiver functions and H-K input parameters, with the result quality assessed by ten quality control criteria. By refining Moho depth constraints, including identifying 182 stations, analysed previously, where H-K stacking yields unreliable results (particularly in Eastern Anatolia and the rapidly-uplifting Taurides), our new crustal model (ANATOLIA-HK21) provides fresh insight into Anatolian crustal structure and topography. Changes in Moho depth within the Anatolian Plate occur on a shorter length-scale than has sometimes previously been assumed. For example, crustal thickness decreases abruptly from >40km in the northern Kirsehir block to <32km beneath the Central Anatolian Volcanic Province and Tuz Golu basin. Moho depth increases from 30-35km on the Arabian Plate to 35-40km across the East Anatolian Fault into Anatolia, in support of structural geological observations that Arabia-Anatolia crustal shortening was accommodated primarily on the Anatolian, not Arabian, Plate. However, there are no consistent changes in Moho depth across the North Anatolian Fault, whose development along the Intra-Pontide and Izmir-Ankara-Erzincan suture zones was more likely the result of contrasts in mantle lithospheric, not crustal, structure. While the crust thins from ~45km below the uplifted Eastern Anatolian Plateau to ~25km below lower-lying western Anatolia, Moho depth is generally correlated poorly with elevation. Residual topography calculations confirm the requirement for a mantle contribution to Anatolian Plateau uplift, with localised asthenospheric upwellings in response to slab break-off and/or lithospheric dripping/delamination example candidate driving mechanisms.

How to cite: Ogden, C. and Bastow, I.: The Crustal Structure of the Anatolian Plate: Evidence from Modified H-K Stacking of Teleseismic Receiver Functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5855, https://doi.org/10.5194/egusphere-egu23-5855, 2023.

EGU23-6274 | Posters virtual | TS3.10

InSAR constraints on coseismic and postseismic deformation of the 2021 Ganaveh earthquake along the Zagros Foredeep fault 

Zahra Mousavi, Mahin Jafari, Mahtab Aflaki, Andrea Walpersdorf, and Khalil Motaghi

The moderate magnitude (Mw 5.8) Ganaveh earthquake, as a compressive event. occurred on 2021 April 18 in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran. We process Sentinel-1 SAR images in ascending and descending geometries to investigate the coseismic deformation and its source parameters. The resultant displacement maps indicate a maximum of 17 cm of surface displacement in the satellite line of sight direction with no evidence of surface rupture. The NW-oriented elliptical fringes in coseismic ascending and descending displacement maps are in agreement with the strike of the major Zagros structures. The InSAR displacement map is inverted to evaluate the earthquake source parameters and the inversion results reveal a low-angle NE-dipping fault plane characterized by a maximum dip slip of 95 cm at ~6 km depth and a slight sinistral slip component (2.9 cm). Inversion of 39 earthquake focal mechanism (from 1968 to 2021), including the Ganaveh mainshock and its five larger aftershocks indicate a regional compressional stress regime and applying this stress on the retrieved Ganaveh fault plane leads to a minor sinistral movement confirming the geodetic results. InSAR coseismic displacement and relocated mainshock and aftershocks situate on the hanging wall of the Zagros Foredeep fault. This underlines the ZFF as the causative fault of the Ganaveh earthquake. The occurrence of Ganaveh moderate magnitude earthquake on the Zagros Foredeep fault highlights its role as the western structural boundary for recurrent Mb>5 events in the Dezful embayment.

To examine the possibility of postseismic deformation after such a moderate magnitude earthquake in Zagros, we processed and created the interferograms using the Sentinel-1 SAR images based on the SBAS timeseries analysis approach after the mainshock until the end of 2021. The time series analysis of the constructed interferograms indicates a maximum of 7 cm of postseismic deformation with a similar strike and shape as the coseismic displacement. The short-term postseismic displacement of the Ganaveh earthquake is released seismically by aftershocks. The agreement between the cumulative displacement, cumulative number of aftershocks, and their related moment release through time and the similar pattern and direction of postseismic and coseismic deformation suggest that an afterslip mechanism can be the causative mechanism of the Ganaveh postseismic motion. We estimate a maximum of 30 cm slip at a depth of ~5 km along the coseismic causative fault plane by inverting the postseismic cumulative deformation map.

How to cite: Mousavi, Z., Jafari, M., Aflaki, M., Walpersdorf, A., and Motaghi, K.: InSAR constraints on coseismic and postseismic deformation of the 2021 Ganaveh earthquake along the Zagros Foredeep fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6274, https://doi.org/10.5194/egusphere-egu23-6274, 2023.

EGU23-6612 | ECS | Posters virtual | TS3.10

Seven years of postseismic deformation following Mw 7.7 2013 Saravan intra-slab earthquake from InSAR time series 

Meysam Amiri, Andrea Walpersdorf, Erwan Pathier, and Zahra Mousavi

The 2013 April 16 Mw 7.7 Saravan earthquake, an intra-slab earthquake with a normal faulting mechanism, occurred in the Makran subduction zone, where the Arabian oceanic lithosphere subducts northward under Iran and Pakistan. To examine the postseismic displacement of the Saravan earthquake, we processed one ascending (A13) and one descending track (D122) from 2014 to 2022. We construct 1000 and 504 interferograms for ascending and descending tracks, respectively. We remove the topographic and flatten-earth phase contributions using the 30 m Shuttle Radar Topography Mission Digital Elevation Model and precise orbital parameters. We correct the turbulent component of the tropospheric delay using atmospheric parameters of the global atmospheric model ERA-Interim provided by the European Center for Medium‐range Weather Forecast. Then, we filter the generated interferograms using Goldstein’s filter and unwrapped them with a branch-cut algorithm. Once all interferograms are corrected and unwrapped, we employ an SBAS time-series analysis based on the phase evolution through time for each pixel, to retrieve the mean velocity map and displacement through time. The mean velocity map in the LOS direction indicates a sharp signal close to the Saravan earthquake suggesting that the observed signal belongs to the postseismic phase of this event. The postseismic spatial profile derived from high-quality time series analysis of Sentinel 1-A images has the opposite pattern of displacement with respect to the coseismic profile derived from Radarsat-2 interferograms. Due to the 50-80 km depth of the earthquake, observing such a deformation approximately seven years after the earthquake is interesting and consequently, we decided to study it in detail.

Large earthquakes are usually followed by transient surface deformation which reflects the rheology of the lithosphere and sub-lithospheric mantle following three mechanisms: afterslip, viscoelastic relaxation, and poroelastic rebound. In this study, we investigate the responsible mechanism of Saravan 2013 postseismic deformation through the before mentioned mechanisms. Due to the opposite sense of deformation during co and postseismic periods, we first try to assess the viscoelastic relaxation mechanism using the PSGRN/PSCMP code. We calculate the time-dependent green functions of a given layered viscoelastic-gravitational half-space for our dislocation sources at different depths using the PSGRN code. Then, we use the result as a database for PSCMP, which discretizes the earthquake's extended rupture area into several discrete point dislocations and calculates the co- and post-seismic deformation by linear superposition. For the viscoelastic mechanism modeling, it is important to consider a proper layering and velocity structure of the earth. We use the velocity structure of the GOSH seismic station implemented by the Institute for Advanced Studies in Basic Sciences to define Green’s functions. Finally, we use the distributed fault slip resulting from coseismic linear modeling as a source for viscoelastic relaxation and modeled the surface displacement for different periods after the earthquake. In the next step, we will compare the observed postseismic deformation using InSAR analysis and modeled displacement to examine whether the viscoelastic rules the postseismic movement. ‌Besides, exploring other mechanisms like afterslip and poroelastic rebound is required to fully assess the possible mechanisms.

How to cite: Amiri, M., Walpersdorf, A., Pathier, E., and Mousavi, Z.: Seven years of postseismic deformation following Mw 7.7 2013 Saravan intra-slab earthquake from InSAR time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6612, https://doi.org/10.5194/egusphere-egu23-6612, 2023.

EGU23-7674 | Posters on site | TS3.10

Geometry and kinematics of the active structures along the Latakia Ridge (Cyprus Arc) 

Michelle Vattovaz, Nicolò Bertone, Claudia Bertoni, Lorenzo Bonini, Angelo Camerlenghi, Anna Del Ben, and Richard Walker
 

The eastern Mediterranean has been the locus of catastrophic earthquakes and related tsunamis (e.g., the 365 Crete and 1222 Cyprus earthquakes). The primary sources of these seismic events are structures related to the subduction of the Nubian Plate along the Hellenic and Cyprus arcs.  A detailed identification and description of the potential tsunamigenic sources are required as part of an assessment of earthquake and tsunami hazards. Here we focus on the Cyprus Arc region, in which the oceanic crust is still subducting beneath the Anatolian Plate in the west, whereas in the eastern sector, the oceanic crust has been completely subducted, and the lower plate consists of thinned continental crust. The rates of shortening are higher in the western sector than in the east. During recent decades, new data from extensive hydrocarbon exploration have allowed us to image structures that deform the seafloor and influence the shape of the recent basins in the eastern sector. The Latakia Ridge is the most prominent tectonic structure in the area. The present-day architecture of this ridge is the result of Meso-Cenozoic convergence followed by a transpressive phase related to the northward migration of the Arabian Plate. Therefore, the present geometry of the tectonic structure results from a complex interplay between reverse and strike-slip faults. Our reinterpretation of previously published seismic reflection profiles crossing the Latakia Ridge allows us to reconstruct the geometry of the main active faults and suggests their recent kinematics. Our findings could be crucial for the reassessment of seismic and tsunami hazards in the eastern sector of the Cyprus Arc. 

How to cite: Vattovaz, M., Bertone, N., Bertoni, C., Bonini, L., Camerlenghi, A., Del Ben, A., and Walker, R.: Geometry and kinematics of the active structures along the Latakia Ridge (Cyprus Arc), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7674, https://doi.org/10.5194/egusphere-egu23-7674, 2023.

EGU23-8525 | ECS | Orals | TS3.10

Geodetic evidence for compressional interseismic deformation onshore Paliki Peninsula, Cephalonia, Greece 

Varvara Tsironi, Athanassios Ganas, Sotiris Valkaniotis, Vassiliki Kouskouna, Ioannis Kassaras, Efthimios Sokos, and Ioannis Koukouvelas

We present new geodetic (InSAR) data (ground velocities) combined with GNSS data over the Paliki Peninsula, western Cephalonia, Greece. Paliki Peninsula suffers from strong, frequent earthquakes due to its proximity to the Cephalonia Transform Fault (CTF). The CTF, a 140 km long, east-dipping dextral strike-slip fault, accommodates the relative motion between the Apulian (Africa) and Aegean (Eurasia) lithospheric plates. The most recent earthquakes of Paliki include two events during early 2014 (Ganas et al. 2015); which occurred on 26 January 2014 13:55 UTC (Mw=6.0) and 3 February 2014 03:08 UTC (Mw=5.9), respectively. Long-term monitoring of active faults through InSAR has been successfully applied in many studies so far, not only towards identifying locked or creeping sections, but also to monitor the spatial and temporal patterns of deformation of the surrounding rocks. The processing of InSAR time series analysis was held by the LiCSBAS, an open-source package. To perform an estimate of the velocity of a surface pixel through time based upon a series of displacement data, we apply an SB (small baseline) inversion on the network of interferograms, in particular we applied the N-SBAS method. Then, we transformed the ground velocities of InSAR into Eurasia-fixed reference frame using the available GNSS station velocities. The time series analysis covers the period 2016-2022. The InSAR results demonstrate that active faults onshore Paliki are oriented approximately N-S and slip with rates between 2-5 mm/yr in line-of-sight (LOS) direction. The InSAR results also show that the horizontal component of movement is dominant, therefore supporting initial evidence of the existence of right-lateral strike slip faulting onshore the peninsula. The velocity pattern of the NW part of the peninsula also reveals a possible post-seismic motion along the ruptured plane of the 3 February 2014 earthquake. In addition, the time series analysis has identified other possible active structures (both strike-slip and thrust) onshore the Paliki peninsula and across the gulf of Argostoli that are confirmed by field geological data. The coastal town of Lixouri undergoes uplift (a few mm/yr) as it observed with positive LOS values in both satellite imaging geometries. Through the East-West velocity cross-sections, we determine several velocity discontinuities (block boundaries?) which are possibly bounded by active faults and/or crustal flexure. Overall, our results indicate a complex deformation pattern onshore the Paliki peninsula.

How to cite: Tsironi, V., Ganas, A., Valkaniotis, S., Kouskouna, V., Kassaras, I., Sokos, E., and Koukouvelas, I.: Geodetic evidence for compressional interseismic deformation onshore Paliki Peninsula, Cephalonia, Greece, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8525, https://doi.org/10.5194/egusphere-egu23-8525, 2023.

Plate boundary deformation zones represent a challenge in terms of understanding their underlying geodynamic drivers. Active deformation is well constrained by GNSS observations in the SW Balkans, Greece and W Turkey, and is characterized by variable extension and strike slip in an overall context of slow convergence of the Nubia plate relative to stable Eurasia. Diverse, and all potentially viable, forces and models have been proposed as the cause of the observed surface deformation, e.g., asthenospheric flow, horizontal gravitational stresses (HGSs) from lateral variations in gravitational potential energy, and rollback of regional slab fragments. We use Bayesian inference to constrain the relative contribution of the proposed driving and resistive regional forces.

 

Our models are spherical 2D finite element models representing vertical lithospheric averages. In addition to regional plate boundaries, the models include well-constrained fault zones like north and south branches of the North Anatolian Fault, Gulf of Corinth and faults bounding the Menderes Massif. Boundary conditions represent geodynamic processes: (1) far-field relative plate motions; (2) resistive fault tractions; (3) HGSs mainly from lateral variations in topography and Moho topology; (4) slab pull and trench suction at subduction zones; and (5) active asthenospheric convection. The magnitude of each of these is a parameter in a Bayesian analysis of ~100,000 models and horizontal GNSS velocities. The search yields a probability distribution of all parameter values including model error, allowing us to determine mean/median parameter values, robustly estimate parameter uncertainties, and identify tradeoffs (i.e., parameter covariances).

 

The average viscosity of the overriding plate is well resolved 4x10^22 Pa.s, which is higher than published models without faults. Westward velocities of Anatolia and significant trench suction forces from the Hellenic slab, including along the Pliny-Strabo STEP Fault, are required to reproduce the observations. Slab pull and convective tractions have a small imprint on the observed deformation of the overriding plate. HGSs are less important for fitting the regional pattern of velocities. Resistive tractions on most plate boundaries and faults are low.

How to cite: Govers, R., Herman, M. W., van de Wiel, L., and Nijholt, N.: Probabilistic Assessment of the Causes of Active Deformation in Greece, western Anatolia, and the Balkans Using Spherical Finite Element Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8603, https://doi.org/10.5194/egusphere-egu23-8603, 2023.

EGU23-8915 | Orals | TS3.10 | Highlight

Aseismic slip behavior along the central section of the North Anatolian Fault: insights from geodetic observations. 

Jorge Jara, Romain Jolivet, Alpay Ozdemir, Ugur Dogan, Ziyadin Çakir, and Semih Ergintav

Recent observations suggest seismogenic faults release elastic energy through a wide variety of slip modes covering a spectrum from sudden rapid earthquakes to slow aseismic slip. Aseismic slip releases energy very slowly without radiating seismic waves and plays an important role in the initiation, propagation, and arrest of large earthquakes. Aseismic slip is thought to be influenced by the presence/migration of fluids, stress interactions through fault geometrical complexities, and/or fault material heterogeneities. Descriptions of occurrences of aseismic slip at the surface and depth are hence required to feed into models and eventually characterize the factors controlling the occurrence of slow, aseismic versus rapid, seismic fault slip.

We focus on the central segment of the North Anatolian Fault, which has been creeping since at least the 1950s. This region was struck by the Mw 7.3 Bolu/Gerede earthquake in 1944, and since then, no earthquake of magnitude greater than 6 has been recorded. During the 1960s, aseismic slip was discovered as a wall built across the fault in 1957 was being slowly offset. Geodetic studies (InSAR, GNSS, and creepmeters) focused on capturing and analyzing aseismic slip around the village of Ismetpasa. Creepmeter measurements during the 1980s and 2010s, along with InSAR time series analysis, suggest that aseismic slip occurs episodically rather than persistently.

We use Sentinel-1 time series and GNSS data to provide a spatio-temporal description of the kinematics of fault slip. We show that aseismic slip observed at the surface is coincident with a shallow locking depth and that slow slip events with a return period of 2.5 years are restricted to a specific section of the fault. We contrast such results with GNSS time series analysis of a local network, confirming our findings. In addition, we discuss the potential rheological implications of our results, proposing a simple alternative model to explain the local occurrence of shallow aseismic slip at this location.

How to cite: Jara, J., Jolivet, R., Ozdemir, A., Dogan, U., Çakir, Z., and Ergintav, S.: Aseismic slip behavior along the central section of the North Anatolian Fault: insights from geodetic observations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8915, https://doi.org/10.5194/egusphere-egu23-8915, 2023.

EGU23-9062 | Posters on site | TS3.10

Source Model of the 2022 Mw6.0 Gölyaka, Düzce (Western Turkey) Earthquake 

Ali Ozgun Konca, Sezim Ezgi Guvercin, and Figen Eskikoy

On November 23, 2022 an Mw6.0 earthquake struck northwest Turkey. The location of this earthquake is along the boundary of the northeast striking Karadere and east striking Düzce segments of the North Anatolian Fault. Remarkably the area had already ruptured twice during the 1999 Mw7.4 Izmit and Mw7.1 Düzce earthquakes. In this study we analyzed the seismicity, aftershocks and the co-seismic rupture of the 2022 earthquake. Relocated aftershocks reveal a north dipping rupture plane consistent with the previously known fault segments. We modeled the co-seismic slip using InSAR data from Sentinel-1 satellite and near-source seismic waveforms. The kinematic model shows an up-dip bilateral rupture with majority of the slip to the west of the hypocenter.  While the slip is primarily right-lateral there is significant normal component. The fact that the rupture occurred at the junction of two segments, its depth extent and oblique rake angle implies that the 2012 earthquake ruptured along a geometrical complexity that sustained a remanent slip deficit after the 1999 earthquakes.

How to cite: Konca, A. O., Guvercin, S. E., and Eskikoy, F.: Source Model of the 2022 Mw6.0 Gölyaka, Düzce (Western Turkey) Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9062, https://doi.org/10.5194/egusphere-egu23-9062, 2023.

EGU23-9268 | ECS | Orals | TS3.10

The sprawl of the External Hellenides: from post-Alpine collapse to present-day kinematics 

Simon Bufféral, Pierre Briole, Nicolas Chamot-Rooke, and Manuel Pubellier

During the Neogene, the Aegean domain underwent intense deformation, leading to a thinning by a factor of two or more of the Alpine orogenic prism. Today, tectonic velocity gradients are still among the fastest in Europe due to the Anatolian extrusion induced by the Arabian indentation and by the Hellenic slab retreat. The present-day deformation essentially localizes in the subduction backstop. With respect to the central Aegean, which is almost stable today, this still-thick buttress has remained at a much earlier and brittle deformation stage. This is particularly the case in the ~east–west-extending External Hellenides (Southern Greece), shaped by a series of major NNW–SSE-oriented normal faults.

  • How has the crustal deformation been accommodated by the various fault systems present in the Peloponnese since the Paleogene?
  • Which of those fault systems are still active today?
  • To what extent can boundary forces such as the Hellenic slab pull be sufficient to explain this extension?

Thanks to a significant increase in the GNSS network density in the Peloponnese, we present an updated local strain field. The resulting strain confirms the ~east–west sprawl of the External Hellenides, with extension also, to a lesser extent, in the other directions. Through identifying low-angle detachments by field and satellite morpho-structural analysis, we show that this spreading has been occurring since the Pliocene, mostly by reusing décollement layers of the Alpine nappes as extensional structures. We suggest that the main high-angle normal faults existing in the Peloponnese correspond to a localization of the extension in the weakest azimuth dictated by the Alpine backbone. We propose that this surface sprawl results not only from the Hellenic slab retreat but also from the exhumation of the deep Peloponnesian stacked units, and the subsequent crustal gravity collapse.

How to cite: Bufféral, S., Briole, P., Chamot-Rooke, N., and Pubellier, M.: The sprawl of the External Hellenides: from post-Alpine collapse to present-day kinematics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9268, https://doi.org/10.5194/egusphere-egu23-9268, 2023.

EGU23-9851 | ECS | Posters on site | TS3.10

Preliminary Results from Comprehensive Seismic and Geodetic Observations Around the Caucasus Region 

Sezim Ezgi Güvercin, Mironov Alexey Pavlovich, Seda Özarpacı, Hayrullah Karabulut, Vadim Milyukov, Semih Ergintav, Cengiz Zabcı, Ali Özgün Konca, Uğur Dogan, Ruslan Dyagilev, Steblov Grigory Mikhailovich, and Eda Yıldıran

The active deformation and shortening in the Caucasus region are predominantly driven by the collision of Arabian and Eurasian plates where significant differences in the surface uplift, large basins, variations on the plate motion rates along the convergence are observed. To the west of the region the lack of sub-crustal seismic activity, low velocity anomalies in tomographic images and the decreased rate of shortening imply that western Caucasus has different kinematics compared to its east. Previous studies suggested that either slab detachment or lithospheric delamination is responsible for the complex deformation beneath the Caucasus. Large uncertainties due to sparse and non-uniform data coverage for local and regional tomography studies, diffuse seismicity, significant crustal thickness variations and strain field lead to poor understanding on the formation and active deformation of this fold and thrust belt. In this study, we aim to obtain a joint database collected from Turkey and Russia between 2007 and 2020. A waveform data base is created from 37 stations in Russia and more than 60 stations in Turkey. An improved seismicity catalog is built including relocated earthquakes with more than 100 stations. The crustal thickness map of the study region is updated by receiver function analysis using stations both from Turkey and Russia covering the Greater Caucasus. A high resolution Pn tomographic model is computed to determine velocity perturbations in uppermost mantle. The data from GNSS (Global Navigation Satellite System) stations both in Turkey and Russia are processed together for the first time and used to map the updated strain field. The new strain field is correlated with the crustal stress orientations from earthquake source mechanisms. New block models are determined for the Caucasus region in order to better estimate the block boundaries and related slip rates. By the improved azimuthal coverage of the seismic and geodetic stations the uncertainties of vertical and horizontal earthquake locations and the velocity field are reduced, thus; a reliable source for the geometry and kinematics of the faults in the Caucasus region is obtained. With the improved seismological and geodetic observations, reliable inferences on the seismic hazard and earthquake potential is expected for the region.

 

 

How to cite: Güvercin, S. E., Pavlovich, M. A., Özarpacı, S., Karabulut, H., Milyukov, V., Ergintav, S., Zabcı, C., Konca, A. Ö., Dogan, U., Dyagilev, R., Mikhailovich, S. G., and Yıldıran, E.: Preliminary Results from Comprehensive Seismic and Geodetic Observations Around the Caucasus Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9851, https://doi.org/10.5194/egusphere-egu23-9851, 2023.

EGU23-9911 | ECS | Posters virtual | TS3.10

Shallow deformation of the Mw 4.9 Khonj earthquake (6 January 2017) in the Zagros Simply Folded Belt, Iran 

Aram Fathian, Cristiano Tolomei, Dan H. Shugar, Stefano Salvi, and Klaus Reicherter

On 6 January 2017, an Mw 4.9 earthquake occurred c. 40 km northeast of the city of Khonj, in the Simply Folded Belt (SFB) of the Zagros, southwestern Iran. Using the JAXA ALOS-2 PALSAR as well as the Copernicus Sentinel-1 SAR images, we applied two-pass Interferometric Synthetic Aperture Radar (InSAR) to acquire the corresponding surface deformation of the Khonj earthquake. The fault plane solutions confirm the thrust mechanism for the earthquake that has a shallow depth of 5 km resulting in a subtle, permanent surface deformation visible through InSAR displacement maps. Concentric fringes on the interferograms in both ascending and descending geometries indicate the rupture has not reached the surface; nonetheless, they indicate shallow seismic deformation within the Zagros SFB. The Khonj earthquake is one of the smallest events with a discernible InSAR deformation field of c. 5–10 cm in the satellite line-of-sight (LOS). The epicenter of the earthquake is located in a plain between the northwestern and southeastern hinges of the Qul Qul and Nahreh anticlines. The source modeling from the InSAR data quantifies an NW-SE-striking fault either dipping to the northeast or the southwest. This shallow event is aligned with a zone in which the only documented surface ruptures in the Zagros—i.e., the Furg and Qir-Karzin earthquakes—are located.

How to cite: Fathian, A., Tolomei, C., H. Shugar, D., Salvi, S., and Reicherter, K.: Shallow deformation of the Mw 4.9 Khonj earthquake (6 January 2017) in the Zagros Simply Folded Belt, Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9911, https://doi.org/10.5194/egusphere-egu23-9911, 2023.

EGU23-10222 | Posters on site | TS3.10

Broadband seismological analyses in the Eastern Mediterranean: implications for late-stage subduction, plateau uplift and the development of the North Anatolian Fault 

Ian Bastow, Christopher Ogden, Thomas Merry, Rita Kounoudis, Rebecca Bell, Saskia Goes, and Pengzhe Zhou

The eastern Mediterranean hosts extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this region using broadband seismology: mantle tomographic imaging (Kounoudis et al., 2020), SKS splitting analysis of seismic anisotropy (Merry et al., 2021), and receiver function study of crustal structure (Ogden & Bastow, 2021). Anisotropy and crustal structure are more spatially variable than recognised previously, but variations correspond well with tomographically-imaged mantle structure. Moho depth correlates poorly with elevation, suggesting crustal thickness variations alone do not explain Anatolian topography: a mantle contribution, particularly in central and eastern Anatolia, is needed too. Lithospheric anisotropy beneath the North Anatolian Fault reveals a mantle shear zone deforming coherently with the surface, while backazimuthal variations in splitting parameters indicate fault-related lithospheric deformation. Anisotropic fast directions are either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone.

How to cite: Bastow, I., Ogden, C., Merry, T., Kounoudis, R., Bell, R., Goes, S., and Zhou, P.: Broadband seismological analyses in the Eastern Mediterranean: implications for late-stage subduction, plateau uplift and the development of the North Anatolian Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10222, https://doi.org/10.5194/egusphere-egu23-10222, 2023.

EGU23-10733 | ECS | Orals | TS3.10

Asymptomatic lithospheric drip driving subsidence of Konya Basin, Central Anatolia 

Julia Andersen, Ebru Şengül Uluocak, Oguz Göğüş, Russell Pysklywec, and Tasca Santimano

Geological and geophysical observations show instances of surface subsidence, uplift, shortening, and missing mantle lithosphere inferred as manifestations of the large-scale removal of the lower lithosphere. This process—specifically by viscous instability or lithospheric “drips” —is thought to be responsible for the removal or thinning of the lithosphere in plate hinterland settings such as: Anatolia, Tibet, Colorado Plateau and the Andes. In this study, we conduct a series of scaled, 3D analogue/laboratory experiments of modeled lithospheric instability with quantitative analyses using the high-resolution Particle Image Velocimetry (PIV) and digital photogrammetry techniques. Experimental outcomes reveal that a lithospheric drip may be either ‘symptomatic’ or ‘asymptomatic’ depending on the magnitude and style of recorded surface strain. Notably, this is controlled by the degree of coupling between the downwelling lithosphere and the overlying upper mantle lithosphere. A symptomatic drip will produce subsidence followed by uplift and thickening/shortening creating distinct ‘wrinkle-like’ structures in the upper crust. However, the ‘symptoms’ of an asymptomatic drip are subdued as it only yields subsidence or uplift, with no evidence of shortening in the upper crust. Here, we combine analogue modelling results with geological and geophysical data to demonstrate that the Konya Basin in Central Anatolia (Turkey) is one such example of an asymptomatic drip. Global Navigation Satellite System (GNSS) measurements reveal elevated vertical subsidence rates (up to 50 mm/yr) but no well-documented crustal strain or structural features such as fold-and-thrust belts. This work demonstrates that different types of lithospheric drips may exist since the Archean, and there may be instances where the mantle lithosphere is dripping with no distinct manifestations of such a process in the upper crust.

How to cite: Andersen, J., Şengül Uluocak, E., Göğüş, O., Pysklywec, R., and Santimano, T.: Asymptomatic lithospheric drip driving subsidence of Konya Basin, Central Anatolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10733, https://doi.org/10.5194/egusphere-egu23-10733, 2023.

EGU23-11399 | Orals | TS3.10 | Highlight

Geometry and kinematics of active normal faulting on Crete; implications for Hellenic subduction slab retreat 

Andy Nicol, Vasiliki Mouslopoulou, John Begg, Vasso Saltogianni, and Onno Oncken

The eastern Mediterranean island of Crete is located on the overriding plate of the Hellenic subduction thrust which is curved and changes strike from ~170° to ~50° in a west to east direction. Crete is located in the zone of maximum curvature of the subduction thrust. Basin and range topography together with prominent limestone scarps indicate that Quaternary deformation at the ground surface on Crete is dominated by normal faults with slip rates of up to ~1 mm/yr. These active faults comprise two primary sets that strike N-NNE (0-30°) and E-ESE (90-120°), with the more easterly faults dominating in southern Crete. Each fault set is characterised by dip slip and together they accommodate coeval W-WNW and N-NNE crustal extension. The E-ESE normal faults are approximately parallel to the strike of the subducting North African plate and form part of a regional fault system that swings in strike in sympathy with depth contours on the top of the concave northwards plate. By contrast, N-NNE normal faults are sub-parallel to the line of maximum curvature on the subduction thrust. These geometric relationships support the view that normal faulting on Crete formed, at least partly, in response to Cenozoic slab retreat (e.g., Jolivet et al., 2013), which continued into the Quaternary. In this model contemporaneous multi-directional crustal extension on Crete is driven by geologically simultaneous westward and southward retreat of the slab.

 Jolivet, L., Faccenna, C., Huet, B., Labrousse, L., Le Pourhiet, L., Lacombe, O., et al. (2013). Aegean tectonics: Strain localisation, slab tearing and trenchretreat. Tectonophysics, 597–598, 1–33. https://doi.org/10.1016/j.tecto.2012.06.011

How to cite: Nicol, A., Mouslopoulou, V., Begg, J., Saltogianni, V., and Oncken, O.: Geometry and kinematics of active normal faulting on Crete; implications for Hellenic subduction slab retreat, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11399, https://doi.org/10.5194/egusphere-egu23-11399, 2023.

EGU23-11592 | ECS | Posters on site | TS3.10

High-resolution N-S deformation of active normal faults in SW Turkey derived from Sentinel-1 InSAR time series 

Manuel-L. Diercks, Ekbal Hussain, Zoë K. Mildon, and Sarah J. Boulton

Active tectonics in south-western Turkey is dominated by rapid N-S extension at a rate of 22 mm/a (e.g. Aktug et al., 2009), which is mostly accommodated by several large E-W trending, graben-forming normal fault zones. Seismic activity of these fault zones appears to vary both spatially and temporally (e.g. Leptokaropoulos et al., 2013). Generally, Synthetic Aperture Radar interferometry (InSAR) is a useful technique to assess the recent deformation of fault zones and locate potentially creeping segments. However, as Sentinel-1 satellites orbit the Earth on approximately N-S directed tracks, line-of-sight (LOS) velocities are relatively insensitive to N-S deformation and therefore it can be a challenge to resolve deformation in this direction. With its rapid N-S extension, the SW-Anatolian graben system is a suitable study area to develop an approach to derive a tectonic N-S deformation signal from Sentinel-1 InSAR.

We compute InSAR LOS velocities from Sentinel-1 data for all ascending and descending frames covering the study area. A least-squares inversion is used to decompose the LOS velocities into north, east and up components. To reduce the number of unknowns, we constrain the E-W component with interpolated GNSS velocities, so we effectively only invert for N-S and up components. Mathematically, the inversion requires at least two time series products to be solved, but given the low sensitivity of InSAR to N-S deformation, we use three Sentinel-1 scenes, with at least one from ascending and descending tracks to increase the accuracy. As a result, this approach is limited to regions where either two ascending or two descending tracks are overlapping, which fortunately covers most of the large grabens in Western Turkey. Using our new technique, we compute a smooth velocity field for all three components of motion (N-S, E-W and up-down) on a N-S swath crossing all major E-W-trending normal fault systems in the region, at a pixel resolution of about 100x100 m. With some improvements to come, we are able to calculate swath profiles displaying surface deformation across all fault zones. Our approach resolves both the broad scale velocity field and localised deformation differences across individual fault zones.

Compared to GNSS velocities, InSAR has a much higher resolution, allowing us to infer localised information on surface deformation in the vicinity of major fault zones instead of just quantifying a broad, regional trend. This can be used to assess individual fault zones, quantify changes in N-S surface deformation across faults and compare these results with recorded seismicity to reveal detailed insights into the active deformation of the largest fault zones in the region. Once the technique is established, we aim to expand the studied region. This study shows that overlapping tracks of Sentinel-1 data are a valuable resource, enabling detailed analysis of fault zones that are otherwise hard to assess by InSAR data from N-S orbiting satellite systems.

References:

Aktug et al. (2009). Journal of Geophysical Research, 114(B10), B10404. https://doi.org/10.1029/2008JB006000

Leptokaropoulos et al. (2013) Bulletin of the Seismological Society of America, 103(5), 2739–2751. https://doi.org/10.1785/0120120174

How to cite: Diercks, M.-L., Hussain, E., Mildon, Z. K., and Boulton, S. J.: High-resolution N-S deformation of active normal faults in SW Turkey derived from Sentinel-1 InSAR time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11592, https://doi.org/10.5194/egusphere-egu23-11592, 2023.

EGU23-12210 | Orals | TS3.10

Active extensional tectonics along the Mirabello Gulf – Ierapetra Basin depression (Eastern Crete, Greece) 

Konstantinos Soukis, Stelios Lozios, Emmanuel Vasilakis, Varvara Antoniou, and Sofia Laskari

The present-day geotectonic regime of Crete Island is mainly controlled by the processes occurring along the seismically active Hellenic subduction zone, e.g., the fast convergence between Africa - Eurasian plates (at a rate of 36 mm/yr) and the simultaneous SSW-ward retreat of the subducting slab. The result is a large south-facing orogenic wedge extending from the southern coast of Crete up to the Hellenic subduction trench to the South. Contractional structures (thrusts, folds, and duplexes) have formed in the deeper parts of the wedge and caused the thickening of the crust. This has led to substantial regional uplift and extension of the upper part of the wedge. Hence, two significant arc-parallel and arc-normal sets of active normal faults crosscut the Cretan mainland, affecting the entire alpine nappe pile. These faults have created a characteristic basin and range topography expressed through impressive E-ESE and N-NNE horst and graben structures bounded by fault zones with segments ranging from 5 to more than 20 km.

 

Detailed fault mapping of the Mirabello Gulf – Ierapetra Basin depression revealed a dominant NNE-SSW fault system, occupying the central and northern part, and a subordinate E-W to ESE-WNW system, observed mainly along the southern coastal zone. In the ESE margin, the deformation is localized mainly along the 30 km long NNE-SSW Kavousi – Ieraptera fault zone. On the other hand, in the WNW margin, the deformation is distributed in a larger population of relatively minor faults, organizing in more complex second-order horst and graben structures. In the southern part of the Ierapetra Basin, the E-W to ESE-WSW faults are significantly less and concern 2-3 specific zones. Specific morphological structures such as the remarkable range high, the deep V-shaped gorges, the large scree thickness, and the prominent post-glacial fault scarps produced along the basin margins indicate the intensive activity of these faults during the Quaternary. The NNE-SSW fault system seems to be younger and more active, given that i) intersects the E-W or ESE-WNW faults of the southern part, ii) produces significant fault scarps and polished fault surfaces in the cemented scree along the fault zone, and iii) kinematically is compatible with the recent and present-day focal mechanisms (e.g., the 2021 Arkalochori earthquakes). In conclusion, the Ierapetra Basin has formed and developed through an overall E-W extension parallel to the present-day geometry of the arc.

How to cite: Soukis, K., Lozios, S., Vasilakis, E., Antoniou, V., and Laskari, S.: Active extensional tectonics along the Mirabello Gulf – Ierapetra Basin depression (Eastern Crete, Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12210, https://doi.org/10.5194/egusphere-egu23-12210, 2023.

EGU23-12258 | ECS | Orals | TS3.10

A new and uniformly processed GNSS-velocity field for Turkey 

Ali Değer Özbakır, Ali Ihsan Kurt, Ayhan Cingöz, Semih Ergintav, Uğur Doğan, and Seda Özarpacı

The Anatolia–Aegean domain represents a broad plate boundary zone, with the deformation accommodated by major faults bounding quasi-low deforming units. The main characteristics of the Anatolia-Aegean deformation were identified using a GNSS-derived velocity field. Recent advancements in GNSS measurements and networks have improved the spatial resolution of the Anatolia-Aegean deformation field, however, for a better understanding of the deformation, interstation distances that are smaller than fault-locking depth and consistent data processing using a single reference system are needed. Our goal is to address this gap and produce a uniform velocity solution.

In this study, we processed the time series of 836 stations, of which 178 are published for the first time with sub-millimeter accuracy. With a period of up to 28 years, we present the most accurate velocity field with increased spatial and temporal resolution and homogeneity. We used the improved coverage of the velocity field to calculate strain accumulation on the North and East Anatolian Faults.  Modeled slip rates vary between 20 and 26 mm/yr and 9.7 and 11 mm/yr for the North and East Anatolian faults, respectively. Further analysis of the data can help better understand the kinematics of continental deformation in general, and test outstanding hypotheses about the kinematics and dynamics of the Anatolia - Aegean domain in particular.

How to cite: Özbakır, A. D., Kurt, A. I., Cingöz, A., Ergintav, S., Doğan, U., and Özarpacı, S.: A new and uniformly processed GNSS-velocity field for Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12258, https://doi.org/10.5194/egusphere-egu23-12258, 2023.

EGU23-12408 | Posters on site | TS3.10

Evaluating the seismic activity of the Adriatic Sea region 

Orecchio Barbara, Debora Presti, Silvia Scolaro, and Cristina Totaro

The seismic activity occurred in the last decades in the Adriatic Sea region has been investigated by means of new hypocenter locations, waveform inversion focal mechanisms and seismogenic stress fields. After a preliminary evaluation of seismic distribution, the Bayloc non-linear probabilistic algorithm has been used to compute hypocenter locations for the most relevant seismic sequences and to carefully evaluate location quality and seismolineaments reliability. We also provided an updated database of waveform inversion focal mechanisms integrating data available from official catalogs with original solutions we properly estimated by applying the waveform inversion method Cut And Paste. This database has been used to compute seismogenic stress fields through different inversion algorithms. The seismic activity, mainly concentrated in the Central Adriatic region, indicates high fragmentation and different patterns of deformation. In particular, our results highlighted the presence of two NW-SE oriented, adjacent volumes: (i) the northeastern one, characterized by pure compressive domain with NNE-trending axis of maximum compression, and mainly W-to-NW oriented seismic sources; (ii) the southwestern one, characterized by a transpressive domain with NW-trending axis of maximum compression, where thrust faulting preferentially occurs on ENE-to-NE oriented planes and strike-slip faulting on E-W ones. We jointly evaluated seismic findings of the present study and kinematic models proposed in the literature for the Central Adriatic region. The present analysis, furnishing new seismological results provide additional constraints useful for better understanding and modeling the seismotectonic processes occurring in the Adriatic Sea region.

How to cite: Barbara, O., Presti, D., Scolaro, S., and Totaro, C.: Evaluating the seismic activity of the Adriatic Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12408, https://doi.org/10.5194/egusphere-egu23-12408, 2023.

EGU23-12937 | Posters on site | TS3.10 | Highlight

The North Anatolian Fault: an example to regularity of ‘irregular’ seismic behaviour of continental strike-slip faults 

Cengiz Zabcı, Erhan Altunel, and H. Serdar Akyüz

In the complex puzzling of the lithospheric plates, the transform boundaries and related strike-slip faults are under focus of earth scientists for more than a hundred years not only for their important role in the lithospheric-scale deformation, but also for being sources of destructive earthquakes. Particularly, spatial and temporal seismic behaviour of these faults has been a subject of great curiosity for several decades with a special emphasis on the relationship between their geometry and earthquake recurrence. The North Anatolian Shear Zone (NASZ) is one of these tectonic structures, which makes the northern boundary of the Anatolian Scholle connecting the Hellenic Subduction in the west and the Arabia-Eurasia Collision in the east. This dextral system has a remarkable seismic history, especially in the 20th century, when the westward migrating earthquake sequence generated surface ruptures of about 1100 km with addition of ~140 km from two out of sequence events, 1912 Mürefte and 1949 Elmalı earthquakes, leaving unbroken only Marmara in the west and Yedisu in the east along its most prominent structure, the North Anatolian Fault (NAF).

In this study, we aim to review palaeoseismic studies of more than three decades that provide invaluable information on the earthquake history all along the NAF with an attempt to understand which fault pieces have been involved in any of these palaeoevents. Thus, we decided to use their geometric properties, with an assumption that certain geometric discontinuities play an important role as end-points of an earthquake rupture. Palaeoseismological studies are grouped together according to the NAF’s geometric segments, on which they are located. In this classification, we excluded the ones with incomplete dating records or providing indirect evidence (i.e., cores). Then, we used a Bayesian approach to calculate the probability distributions of each palaeoevent, but applied it not to the individual sites but to the tectonostratigraphic data of merged trenches along the same fault segments. Our analyses suggest an ‘irregular’ seismic behaviour of the NAF although there are still gaps in data especially for the central parts. Large geometric complexities (e.g., Niksar step-over, Çınarcık Basin) significantly control the heterogenous stress conditions, but the ‘irregular’ behaviour is not only restricted to the segments close to these structures, but observed almost along the entire fault. In spite of the compiled 118 trench sites with more than 275 trenches, there is still necessity of further studies in order to increase the spatial and temporal resolution of palaeoseismic data along the NAF, especially for its central segments.

How to cite: Zabcı, C., Altunel, E., and Akyüz, H. S.: The North Anatolian Fault: an example to regularity of ‘irregular’ seismic behaviour of continental strike-slip faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12937, https://doi.org/10.5194/egusphere-egu23-12937, 2023.

EGU23-13568 | ECS | Posters on site | TS3.10

Coseismic and Early Postseismic of 23 November 2022 Mw = 5.9 Düzce Earthquake with InSAR and GNSS Measurements 

İlay Farımaz, Uğur Doğan, Semih Ergintav, Ziyadin Çakır, Cengiz Zabcı, Seda Özarpacı, Alpay Özdemir, Efe Turan Ayruk, Figen Eskiköy, Alpay Belgen, and Rahşan Çakmak

The North Anatolian Fault (NAF) was broken over the last century by a series of Mw > 7 earthquakes, most of which migrated westward, starting from the 1939 Erzincan Earthquake and ending with the 1999 Izmit and Düzce Earthquakes.  For 23 years the area remained silent for destructive earthquakes but also produced relatively small seismic activities until November 23, 2022 Düzce Earthquake, Mw 5.9.

In this study, we aim to investigate the source mechanism for the 23rd November 2022 Düzce Earthquake and associate it to the ruptures of 1999 Izmit and Düzce Earthquakes. For this purpose, in the same day that the earthquake occurred, our team established 8 new continuous GNSS sites covering the area to monitor the postseismic deformation and surveyed the historical sites to estimate coseismic field. Additionally, a stack of interferograms has been interpreted from Sentinel-1 data to densify the deformation fields.

Based on our first order analysis, the earthquake occurred at the overlap of the rupture zones of 1999 Izmit and Düzce Earthquakes (west of Eftani Lake on Düzce segment). Our GNSS and InSAR monitoring showed that the coseismic deformation is around <6 cm in the near field and ~33% of the InSAR coseismic deformation field is related with postseismic deformations.  

 

Keywords: Düzce earthquake, Coseismic and early postseismic deformation, InSAR, GNSS

How to cite: Farımaz, İ., Doğan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özarpacı, S., Özdemir, A., Ayruk, E. T., Eskiköy, F., Belgen, A., and Çakmak, R.: Coseismic and Early Postseismic of 23 November 2022 Mw = 5.9 Düzce Earthquake with InSAR and GNSS Measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13568, https://doi.org/10.5194/egusphere-egu23-13568, 2023.

EGU23-13724 | ECS | Posters on site | TS3.10

Kinematics of North Anatolian Fault Under the Constrain of New GNSS Velocity Field 

Efe T. Ayruk, Seda Özarpacı, Alpay Özdemir, İlay Farımaz, Volkan Özbey, Semih Ergintav, and Uğur Doğan

North Anatolian Fault (NAF) is one of the most important transform faults over in World. NAF produced an important earthquake sequence Mw ≥ 7 in the 20th century, that migrates westward between 1939 and 1999. The earthquake sequence has broke the great part of the NAF which is approximately 1000 km. Due to this seismic activity of NAF, it is important to keep strain accumulation up to date and use the recent data. Many precious works have been studied to clarify the kinematics of NAF using the data that collected with geodetic methods (terrestrial and space geodetic).

In this study, we compiled published GNSS data and analyzed it to understand the present strain accumulation of NAF, with TDEFNODE block modelling code using a simple block geometry. The study area extends between Sapanca Lake at the west (Sakarya) to Yedisu at the east (Bingöl) and it stretches out in the north-south direction from the north coast of Blacksea to 130 kilometers south.

The 90% of GNSS velocity field have RMS values less than 2 mm and the accuracy of estimated slip rates is increased. Additionally, with the dense station distributions in the near field, spatial resolution improved, dramatically.

According to the first order results, fault slip rates are estimated as 20.5 mm/yr at the east and 21.6 mm/yr at the west. Locking depth is also estimated as 15 km at the east while the middle and the west part of the study area has shallower locking depth values.

In the presentation, we will demonstrate the power of our new GNSS velocity field and discuss its contribution to the understanding of the NAF kinematics in detail.

keywords: North Anatolian Fault, Block Modelling, Velocity Field

How to cite: Ayruk, E. T., Özarpacı, S., Özdemir, A., Farımaz, İ., Özbey, V., Ergintav, S., and Doğan, U.: Kinematics of North Anatolian Fault Under the Constrain of New GNSS Velocity Field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13724, https://doi.org/10.5194/egusphere-egu23-13724, 2023.

EGU23-13785 | Posters on site | TS3.10

Recent kinematics of Crete, observed by InSAR, reveal complex, curved-forearc deformation and aquifers changes 

Sabrina Metzger, Md Aftab Uddin, Vasiliki Mouslopoulou, John Begg, Andy Nicol, Vasso Saltogianni, and Onno Oncken

Located on the overriding plate of the Hellenic subduction margin, the 250 km-long island of Crete offers a unique opportunity to study curved-forearc deformation. The African-Eurasian plate-convergence of ~40 mm/yr (~80 %) is primarily accommodated aseismically, but intense seismicity is recorded at the plate-interface and a reverse splay faults along the Hellenic trough; frequent M6+ earthquakes and (at least one) tsunami-genic event, causing up to 10 m of paleoshoreline uplift in western Crete, are reported. Global Navigation Satellite System (GNSS) data revealed N-S shortening of ~2 mm/yr within western Crete due to pure plate convergence. Further east, the curved subduction trench accommodates increased oblique slip, causing E-W extension of ~2 mm/yr in eastern Crete.

Recently, the European Ground Motion Service published dense InSAR surface deformation data in East and Up direction of whole Europe. The InSAR time-series comprise positioning samples every six days, respectively, every ~50 m, and, in Crete, exhibit long-wavelength deformation signals caused by deep-rooted, tectonic sources that are overlaid by (often seasonally-modulated) signals originating in shallow aquifers. We analyze these time-series in space and time and validate the results using available GNSS rates, a seismic catalog and an active fault data base. Preliminary results suggest a slight eastward tilt of Crete, which is not confirmed by published GNSS rates, and has to be investigated further. Spatially-confined uplift of up to ~5 mm/yr are observed at the karstic Omalos plateau, and up to ~30 mm/yr subsidence in the Messara basin, both probably related to groundwater replenishment/abstraction. Relative eastward motion increases towards eastern Crete, particularly in the fault zones embracing Mirabello bay and east of it, thus confirming the aforementioned E-W extension, and towards the southern coast.

How to cite: Metzger, S., Uddin, M. A., Mouslopoulou, V., Begg, J., Nicol, A., Saltogianni, V., and Oncken, O.: Recent kinematics of Crete, observed by InSAR, reveal complex, curved-forearc deformation and aquifers changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13785, https://doi.org/10.5194/egusphere-egu23-13785, 2023.

EGU23-14310 | ECS | Posters on site | TS3.10

Influence of fault rocks’ mineralogy on fault behaviour: implications from the Palu-Hazar Lake section of the East Anatolian Fault (Elazığ, Türkiye) 

İrem Çakır, Cengiz Zabcı, Mehmet Köküm, Hatice Ünal Ercan, Havva Neslihan Kıray, Müge Yazıcı, Mehran Basmenji, Özlem Yağcı, N. Beste Şahinoğlu, Uğur Doğan, and Semih Ergintav

The multi-disciplinary studies yield a more complicated picture on seismic cycles, especially with the increasing evidence on creeping, slow slip events, tremors and repeating earthquakes. Recent observations support triggering of large earthquakes even by small or slow earthquakes and creeping of different portions of the fault. The Palu-Hazar Lake section of the East Anatolian Fault (EAF) is an example place of such kind of behaviour, where the 24 January Mw 6.8 Sivrice Earthquake was nucleated along the neighbouring segments. This sinistral strike-slip fault forms the eastern boundary of the Anatolian Scholle between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş) in the southwest within the complex tectonic frame of the Eastern Mediterranean.

In this study, we aim to correlate any potential influence of bedrock lithology on this creeping section of the EAF. First, we revised the active fault and geological maps by using the multi spectral satellite images (e.g., Landsat 8 OLI) and high-resolution digital surface models (~0.65 m ground pixel resolution). Then, we determined potential exposures along the EAF and made systematic sampling both from cohesive and incohesive fault rock exposures within our study region. Collected samples are prepared for X-ray diffraction (XRD) measurements, especially for the determination of the fault clay types. Fault rock samples from ophiolitic (mafic and ultramafic) rocks and accretionary complexes (shale, sandstone, volcanics, ophiolite fragments) are mostly made of vermiculite and include minor amounts of smectite and chlorite according to our XRD measurements. Although the low shear strength of vermiculate may trigger aseismic slip at shallow depths with change in pore water pressure, it is possible that there may be no correlation between bedrock lithology and creeping, considering the poorly known seismic history of the EAF.

This study is supported by TÜBİTAK Project no. 118Y435.

Keywords: earthquake, East Anatolian Fault, creep, fault rocks

How to cite: Çakır, İ., Zabcı, C., Köküm, M., Ünal Ercan, H., Kıray, H. N., Yazıcı, M., Basmenji, M., Yağcı, Ö., Şahinoğlu, N. B., Doğan, U., and Ergintav, S.: Influence of fault rocks’ mineralogy on fault behaviour: implications from the Palu-Hazar Lake section of the East Anatolian Fault (Elazığ, Türkiye), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14310, https://doi.org/10.5194/egusphere-egu23-14310, 2023.

EGU23-14343 | Orals | TS3.10

Paleoseismicity of Northern Cyprus, implications from coastal geomorphology and geochronology 

Cengiz Yildirim, Daniel Melnick, Okan Tüysüz, Cevza Damla Altınbaş, Julius Jara-Munoz, Konstantinos Tsanakas, Orkan Özcan, and Manfred Strecker

The Cyprus Arc is one of the major sources of earthquakes in the Eastern Mediterranean Region. There is limited large-magnitude earthquake activity during the instrumental period. Still, archeoseismological data imply the occurrence of large-magnitude earthquakes that hit the island and gave rise to casualties and destructions. Nevertheless, these data are insufficient to give information about the source of the earthquakes. In this study, we focussed on coastal geomorphology to unravel paleoseismic activity, at least generated by near offshore faults, that released sufficient seismic energy to deform the shoreline in Holocene.

We mapped coseismically uplifted abrasion platforms, tidal notches, fish tanks and a surface rupture implying active near offshore faults in Holocene. The elevation of paleo shorelines varies between 0.4 m to 3 m above sea level, indicating multiple occurrences of paleo earthquakes. Our radiocarbon 14C ages from biological markers (algal rims, etc) indicate that the coseismic uplift of the shoreline starts from 4,5 ka to 1.2 ka BP.

The ages of the paleoearthquakes display non-uniform spatial distribution and show migration of paleoearthquakes from west to east, especially along the island's northern coast. This study is supported by Istanbul Technical University Research Fund (Project No: 37548) and Alexander von Humboldt Foundation, Germany.

How to cite: Yildirim, C., Melnick, D., Tüysüz, O., Altınbaş, C. D., Jara-Munoz, J., Tsanakas, K., Özcan, O., and Strecker, M.: Paleoseismicity of Northern Cyprus, implications from coastal geomorphology and geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14343, https://doi.org/10.5194/egusphere-egu23-14343, 2023.

EGU23-15463 | ECS | Orals | TS3.10

Structure and evolution of the Dead Sea Transform 

Jakub Fedorik and Abdulkader M. Afifi

The Dead Sea Transform (DST) extends from the Red Sea to the East Anatolian Fault, displaying various structural styles along its ~1100 km length. In this study, we combine previous work with new mapping of fault patterns and displacements, geochronological data, and analogue and numerical modeling to provide new insights on the temporal evolution of the DST.

In the southern DST, we mapped a 30 km wide distributed shear belt along the eastern margin of the Gulf of Aqaba (GOA), consisting of a distributed shear faulting, similarly to the western belt in Sinai. Total left lateral offset across the eastern distributed shear belt is ~ 15 km, with offset across individual faults ranging from a few meters up to 5.7 kilometers. Ar-Ar dating of sheared basalt dikes and U-Pb dating of calcite cements in faults indicate that the distributed shear system was activate between 22-16 Ma, overlapping with the rifting of the proto Red Sea and Gulf of Suez. This distributed shear is observed along the GOA and the deformed area narrowed along the Arava Valley. Distributed shearing marks the initial stage of continental break-up along the DST, which was abandoned by faulting concentration within the GOA and propagation of the DST towards the north.

The structural analysis of bathymetry data from the GOA and fault mapping along the entire DST highlight various structural styles: rotational transtension within the GOA, narrowing to simple strike-slip faulting of the Wadi Araba and Jordan Valley, and pull-apart basins along the Dead Sea, Sea of Galilee and Hula Basin. These structures are linked at depth to the principal displacement zone, nowadays-active plate boundary. Our analogue model produces similar structural styles and with the seismicity data it confirms that deformed area narrowed in the more recent stage of deformation. We also present an approach based on the boundary element method at the regional scale to test the structural interpretation of a complex transpressional mountain range of Lebanon Restraining Bend. These results are validated by structural evidences and highlight that various structural styles lead to formation of Mt. Lebanon, Anti-Lebanon and Palmyrides structures.

This review study of the DST emphasizes the role of structural styles, inherited structures and relative movement between tectonic plates in the transform continental break-up evolution.

How to cite: Fedorik, J. and Afifi, A. M.: Structure and evolution of the Dead Sea Transform, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15463, https://doi.org/10.5194/egusphere-egu23-15463, 2023.

EGU23-16089 | ECS | Orals | TS3.10

Monitoring spatio-temporal evolution of aseismic slip along the Ismetpasa segment between 2016-2023 with GNSS measurements 

Alpay Özdemir, Uğur Doğan, Jorge Jara, Semih Ergintav, Romain Jolivet, and Ziyadin Çakır

Aseismic slip (creep) is critical above the onset, propagation, and time of occurrence of large earthquakes on active faults. Also elastic strain in the crust between large earthquakes is controlled by the aseismic slip along the active faults. Key characteristics of aseismic slip behavior is that it is typically very slow and gradual, with the faults moving only a few millimeters or centimeters per year. This type of movement is often difficult to detect and measure, and may not be immediately apparent to observers.

Although it has been determined that the İsmetpaşa segment of the North Anatolian Fault has been slipped aseismically since 1970, without producing an earthquake, there is no reliable and detailed information about the spatial and temporal changes of this movement. After it was first recognized by Ambraseys in 1970, the creep movement is monitored by the researchers with terrestrial and campaign type GNSS measurements in the 6-point geodetic network established in Hamamlı. InSAR observations has made it possible to derive maps of ground velocities over the past 20 years that indicate aseismic slip is present along a ~100 km portion of the fault. Additionally, the aseismic slip rate changes spatially along the strike, peaking at 15–24 km to the east of Ismetpasa. Furthermore, InSAR time series and creepmeter measurements shows that aseismic slip in the Ismetpasa region behaves episodically rather than continuously, with stationary periods alternated with transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault, which has important implications for hazard along the seismogenic zone.

To answer these questions, it is necessary to expand terrestrial observation capacity along the creeping segment and to conduct a detailed examination of the change in creep accelerations by associating it with seismological activity. We established ISMENET -Ismetpasa Continuous GNSS Network- in July 2016 to monitor spatial and temporal variations in the aseismic slip rate and to detect slow slip events along the fault. ISMENET stations are located approximately 120 kilometers along strike. Stations are located within 200m to 10 km of the fault to investigate the shallow, fine spatiotemporal behavior of aseismic slip. In addition to this network, 19 GNSS stations belonging to the TUSAGA-Aktif network located in the vicinity of the İsmetpaşa segment have been added to this network. To reduce the influence of non-tectonic noises, we analyze the GNSS time series to extract the signature of creep movement using Multivariate Singular Spectrum Analysis (M-SSA). Initial estimations shows that creep rates change along the fault between 6-8 mm/yr at a 4-5 km depth 10 km east side of the Ismetpaşa town. On the western edge of the Ismetpaşa segment between Bayramören and Ilgaz towns creep rate decreases ~3-4 mm/yr.

In this study, we examine the results of the temporal and spatial variation of the aseismic slip between 2016-2023 from the GNSS stations located in the immediate vicinity of the İsmetpaşa segment.

Ismetpasa, Aseismic slip, GNSS, M-SSA, NAFZ

How to cite: Özdemir, A., Doğan, U., Jara, J., Ergintav, S., Jolivet, R., and Çakır, Z.: Monitoring spatio-temporal evolution of aseismic slip along the Ismetpasa segment between 2016-2023 with GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16089, https://doi.org/10.5194/egusphere-egu23-16089, 2023.

EGU23-17079 | Orals | TS3.10 | Highlight

Sequential development of shear zones in a Metamorphic Core Complex: cause and consequences in the Menderes Massif (Western Turkey) 

Vincent Roche, Laurent Jolivet, Stéphane Scaillet, Johann Tuduri, Vincent Bouchot, Laurent Guillou-Frottier, and Erdin Bozkurt

During the Cenozoic, the Menderes Massif (western Turkey) records several tectonic and thermal events from subduction to collision, then back-arc extension. But the detailed timing of the succession of different P-T regimes and deformation until today remains debated. To address this, we targeted the main shear zones, providing for the first time a full picture of the 40Ar/39Ar system across the massif. This approach is combined with Tmax, and P-T estimates tied to kinematic-structural data. Extensive sampling along the large top-S Selimiye shear zone allows constraining the deformation at least between 44 and 33 Ma. This shear zone acted as a thrust and was active under HT-MP (530 - 590 °C and 8.5 - 10 kbar). Conversely, the top-S South Menderes Detachment System is associated with a younging of 40Ar/39Ar ages related to exhumation and strain localization during the Late Oligo-Miocene in the Central Menderes Massif. The Bozdağ top-S shear zone then allowed the exhumation of the Bayındır nappe at ~ 21 Ma from high-temperature metamorphic conditions (590 °C). Based on these new elements, we propose for the first time a detailed scenario of the Menderes Massif evolution from the Late Cretaceous to the Present. We finally discuss why the Menderes Massif belongs currently to the regions with the highest geothermal potential in the world. We propose that geothermal activity here is not of magmatic origin but rather associated with active extensional tectonics (detachments) related to the Aegean slab dynamics (i.e., slab retreat and tearing).

How to cite: Roche, V., Jolivet, L., Scaillet, S., Tuduri, J., Bouchot, V., Guillou-Frottier, L., and Bozkurt, E.: Sequential development of shear zones in a Metamorphic Core Complex: cause and consequences in the Menderes Massif (Western Turkey), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17079, https://doi.org/10.5194/egusphere-egu23-17079, 2023.

EGU23-66 | ECS | Posters virtual | GD9.1

The time and geodynamics for the final large-scale lateral accretion of the southern Central Asian Orogenic Belt 

Hai Zhou, Guochun Zhao, Yigui Han, Donghai Zhang, and Xianzhi Pei

During Carboniferous time, tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt (CAOB), although its origin remains unclear. Our work presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia. These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons, probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north, indicative of a continental arc nature. In addition, they have a main zircon U-Pb age of ca. 370–330 Ma, positive Hf and Nd isotopes, and mafic-intermediate arc affinity, similar to the coeval arc magmatism. Moreover, the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time (ca. 350–370 Ma; Visean and Bashkirian stages) earlier than that in the southern area (mainly ca. 350–315 Ma; Serpukhovian and Bashkirian stages). Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean (PAO) during Carboniferous and Triassic times, we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback. Thus, the juvenile arc volcanism of Mongolia, together with other areas (e.g., Junggar) in the southern CAOB, represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO. This research was financially supported NSFC Project (42102260, 41890831, 42072267, and 41972229), Hong Kong RGC GRF (17307918), and HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100).

How to cite: Zhou, H., Zhao, G., Han, Y., Zhang, D., and Pei, X.: The time and geodynamics for the final large-scale lateral accretion of the southern Central Asian Orogenic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-66, https://doi.org/10.5194/egusphere-egu23-66, 2023.

EGU23-343 | ECS | Posters on site | GD9.1

Seismicity and active tectonics:  New insights from Sikkim Himalaya 

Mita Uthaman, Chandrani Singh, Arun Singh, Abhisek Dutta, Arun Kumar Dubey, and Gaurav Kumar

The Himalayas, which formed as a result of the impactful collision of the Indian plate with Eurasian plate, is a tectonically complex and seismically active region. It has been a hotspot for many great earthquakes in the past. The continued collision coupled with the complex structural features has led to the persistent seismic activity of the region. The progressive collision led to the formation of distinct tectonic units bounded by thrust faults. The northeastern state of Sikkim in India, which is sandwiched between Nepal and Bhutan in the Himalayas, has been prone to frequent great earthquakes. The deployment of a dense seismic network consisting of 27 broadband seismometers, across Sikkim Himalayas and the northern part of West Bengal, since April 2019 has enabled us to monitor the seismic activity in the study region.

Here, we present a study which aims at understanding the seismotectonic activity of the study region using local earthquakes (epicentral distance < 200km) recorded by the network between April 2019 and September 2022. The progressively improved relocation of local earthquakes recorded in the study region shows a diffuse cloud of micro-seismicity concentrated along a diagonal region extending from north of Assam in the southeast to south of Tibet in the northwest. From south to north we have observed clusters of earthquakes with a gradual increase in their hypocentral depths.

The upper-crustal earthquakes (~0-25km) are located near the down-dip end of the locked part of the Main Himalayan Thrust (MHT), along which India underplates Tibet. We also observe prominent lower crustal earthquakes at depths greater than 30 km. These earthquakes are possibly originating at the junctions of different blocks in an imbricated crust in response to active shortening. We also observe a mid-crustal seismicity pattern following the DCFZ (Dhubri-Chungthang Fault Zone), supporting observations from earlier studies. Striking variations are observed in the faulting mechanisms and orientation of stress axes along the north-south and east-west profiles, and also with depth. We plan to further investigate if these variations imply the presence of possible segmentation, its depth, extent, surface expression and determine its relation to the geodynamics of the region. Integrating the results obtained from the various studies and interpreting them will help in delineating the seismotectonic activity of the study region. Quality data recorded by the dense network will further complement in enhancing the resolution of the results obtained.

How to cite: Uthaman, M., Singh, C., Singh, A., Dutta, A., Kumar Dubey, A., and Kumar, G.: Seismicity and active tectonics:  New insights from Sikkim Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-343, https://doi.org/10.5194/egusphere-egu23-343, 2023.

EGU23-349 | ECS | Orals | GD9.1

Cretaceous magmatism from the Sava-Vardar Zone of the Balkans 

Kristijan Sokol, Dejan Prelević, and Ana Radivojević

Кеy words: Upper Cretaceous magmatism, Sava Vardar Zone, Adria, basalts

The complex geodynamic evolution of the northernmost Neotethys is the subject of a long-living controversy. The most perplexing issues are related to the waning stage(s) of the Tethyan ocean(s) in the Balkans and the timing of the Europe-Adria collision. Some authors consider this collision to have occurred in the Late Jurassic, whereas others envisage that have happened at the end of the Cretaceous along the Sava-Vardar Zone. The second model assumes this zone contains a relic suture between Africa- and Europe-derived units.

Late Cretaceous magmatism along the Sava-Vardar Zone includes several centers of small-volume transitional to alkaline Na-basalt (with subordinate rhyolitic rocks) and rare ultrapotassic lavas. This volcanism occurs in both Europe- and Africa- derived units of the collisional zone. The geochemical and isotope compositions of the Late Cretaceous lavas suggest that they are not a part of dismembered ophiolite sequences, but represent intracontinental magmas derived from variably enriched mantle sources. The transitional to alkaline Na-basaltic lavas show a clear “within plate” geochemical signature with typical mantle-like 87Sr/86Sri, 143Nd/144Ndi and 206Pb/204Pbi ratios with relatively high HFSE/LILE ratios, and without orogenic geochemical signatures such as high LILE/HFSE ratios, positive Pb and negative Ti–Nb–Ta anomalies, whereas the ultrapotassic lavas are lamprophyres demonstrating enriched 87Sr/86Sri, 143Nd/144Ndi and 206Pb/204Pbi ratios, LILE enrichment, and orogenic geochemical signatures. A broad range of MREE/HREE ratios in these locations suggests polybaric mantle melting.

Our working melting model is that the mafic melts were generated as a continuum with low-degree melting in the asthenospheric mantle within the garnet stability field and high-degree melting of the freshly metasomatized lithospheric mantle in the spinel stability field. The ultimate trigger of the mantle melting along the Sava-Vardar Zone should be localized extension during transtensional tectonics, in a system of pull-apart basins (Köpping et al., 2019).

Acknowledgments: This research was financed by the Science Fund of the Republic of Serbia through project RECON TETHYS (7744807).

Köopping, J., Peternell, M., Prelevi_c, D., Rutte, D., 2019. Cretaceous tectonic evolution of the Sava-Klepa Massif, Republic of North Macedonia e results from calcite twin based automated paleostress analysis. Tectonophysics 758. https://doi.org/10.1016/j.tecto.2019.03.010.

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How to cite: Sokol, K., Prelević, D., and Radivojević, A.: Cretaceous magmatism from the Sava-Vardar Zone of the Balkans, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-349, https://doi.org/10.5194/egusphere-egu23-349, 2023.

The majestic Himalayan-Tibetan mountains raised due to doubling of the continental crust during the India-Asia collision, which is commonly assumed to occur by under-thrusting of the Indian crust directly below the Asian crust. However, this model implies rheologically weak subducting and upper plate lithospheres and, thus, a collision system that is unable to support a high plateau and whose deformation style is inconsistent with the gross structural and metamorphic architecture of the Himalayan-Tibetan system. Numerical models show that collision between relatively stiffer plates generates strain and metamorphic structures as well as elevations more similar to those observed, but crustal doubling occurs by stacking the subducting crust underneath the rigid upper plate mantle lithosphere. A marked mantellic signature in fluids outflowing the suture zone, the geochemistry of south Tibetan mantle xenoliths, and long wavelength buckling of the Tibetan lithosphere further support the presence of intra-crustal mantle between the Indian and Asian continental crusts. Reconciling the available geophysical evidence with this new model of crustal doubling in the Himalayan-Tibetan range will entail profound implications for our understanding of mountain building during continental subduction and collision.

How to cite: Sternai, P.: Intra-crustal mantle underneath the Himalayan-Tibetan range, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1665, https://doi.org/10.5194/egusphere-egu23-1665, 2023.

EGU23-2259 | Posters on site | GD9.1

Frequency dependent attenuation and relative site response of western Tibet 

Chandrani Singh, Ashwani Kant Tiwari, Eric Sandvol, Shirish Bose, Namrata Jaiswal, Niptika Jana, and Arun Kumar Gupta

We have formulated frequency dependent Lg and Pg attenuation tomographic models to investigate the
crustal Q values and its tectonic implications beneath western Tibet. The frequency dependent
behaviour of both Lg and Pg are studied for the frequency bands of 0.2-0.6, 0.6-1.0 and 1.0-1.4 Hz at
central frequencies of 0.4, 0.8, and 1.2 Hz, respectively, implementing both Two-Station Method
(TSM) and Reverse Two-Station Method (RTSM). The amplitudes of both the waves are fundamentally
sensitive to the crustal structures and are controlled by both scattering and intrinsic attenuation. The
frequency dependent characteristics of QLg and QPg are consistent in nature for the region. Moderate to
high Q values evident in the Lhasa terrane could supplement the trace of underthrusting Indian
lithosphere beneath the region. The average Q values for both Lg and Pg increase with increasing
frequency. The frequency dependent parameter η shows quite high values, for both the waves using
TSM and RTSM, which may indicate strong heterogeneities present in the crust. Subsequently, relative
site responses at each station are studied using RTSM for the central frequencies of 0.4, 0.8, and 1.2
Hz. Weak to negative site responses are mostly dominant in western Tibet. Relative site responses are
found to vary with frequency which could be associated with the sampling depth. We found no
correlation of site responses with the elevation.

How to cite: Singh, C., Tiwari, A. K., Sandvol, E., Bose, S., Jaiswal, N., Jana, N., and Gupta, A. K.: Frequency dependent attenuation and relative site response of western Tibet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2259, https://doi.org/10.5194/egusphere-egu23-2259, 2023.

EGU23-2463 | Posters on site | GD9.1

Seismic constraints on the nature and geometry of the downwelling Indian crust beneath Sikkim Himalaya 

Arun Singh, Gaurav Kumar, Chandrani Singh, M. Ravi Kumar, Mita Uthaman, Dipankar Saikia, and Arun Kumar Dubey

  The exact role of subducting Indian continental crust in the formation of Himalaya-Tibet collision zone remains enigmatic. The mass budget estimates describing shortening across the orogen is partly derived from the observations made from seismic imaging of deep earth. Here using data from 38 broadband seismic stations covering Sikkim Himalaya, we produce high resolution seismic images in order to fill the crucial gaps in our understanding of the formation of Himalayan collision zone. We have used 11,594 high quality receiver functions using earthquakes of magnitude >5.5 in the distance range of 30-100°. Our data demonstrates a highly imbricated and heterogeneous crust beneath Sikkim Himalaya. The Main Himalayan thrust responsible for large scale earthquakes in the Himalayan collision zone is not so vivid in the migrated images, but is observed intermittently. The main cluster of earthquakes at shallower depths linked to the Main Himalayan thrust is marked by low amplitude arrivals. Overall trend suggests a gently dipping Moho attaining crustal depths of ∼60 km beneath Higher Himalaya compared to ∼40 km in the Himalayan foredeep. Moho as we see in this segment of Himalaya is with possible offsets and overlapping segments. Imbrication is well reported in the Himalayan orogenic wedge forming upper crust, we also observe this in the lower crust indicating lithospheric imbrication in response to collision. Interestingly, the lower crustal clusters of earthquakes fall at the juncture of offsets in the Moho. The offset positions at lower crustal depths seem more prone to earthquakes in response to active shortening. Seismic images reveal differences in amplitude of receiver functions and presence of conversions at deeper depths in the lithospheric mantle across Dhubri-Chungthang Fault Zone, possibly related to the segmentation of Himalaya.  

How to cite: Singh, A., Kumar, G., Singh, C., Kumar, M. R., Uthaman, M., Saikia, D., and Dubey, A. K.: Seismic constraints on the nature and geometry of the downwelling Indian crust beneath Sikkim Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2463, https://doi.org/10.5194/egusphere-egu23-2463, 2023.

EGU23-2521 | Orals | GD9.1

Early Indosinian magmatism in the West Qinling orogen and its tectonic implication 

Meng Wang, Xianzhi Pei, Zuochen Li, Ruibao Li, Lei Pei, Youxin Chen, Chengjun Liu, and Shaowei Zhao

The West Qinling Orogen (WQO), which is bounded by the Qilian Orogenic Belt, Qaidam Block and the Songpan-Ganzi Block, is the western extension of the Qinling Orogenic Belt, and experienced complex tectonic evolution processes, involving the opening, subduction and closure history of the Proto- and Paleo-Tethys Oceans. The WQO features widespread Indosinian magmatic rocks, which are crucial to constrain the tectonic evolution of the WQO. The Indosinian magmatic rocks were formed mainly in two stages, 250 to 240 Ma and 225 to 210 Ma. The Early Indosinian magmatic rocks (250 to 240 Ma) are mainly distributed in the west and middle northern WQO. In comparison, the Late Indosinian magmatic rocks are mainly exposed in the eastern WQO, but also in the western WQO and the Bikou terrane. Controversy has existed for a long time on the petrogenesis and tectonic setting of the Early Indosinian magmatic rocks. We selected four respective plutons, including the Heimahe pluton, the Ren’ai pluton, the Daerzang pluton and the Ganjiagongma pluton. Detailed field investigation, petrology, LA-ICP-MS zircon U-Pb dating, zircon Lu-Hf isotope analyses, whole rock geochemistry and Sr-Nd isotope analyses, and mineral EPMA analyses were conducted for the studied plutons. The studied plutons were emplaced between 246 to 241 Ma according to zircon U-Pb dating results. Based on detailed studies on petrology, geochronology and geochemistry, we emphasis the significance of magma mixing in the petrogenesis of the Early Indosinian granitic rocks. The high Mg# signature of the Early Indosinian granitic rocks were generated by magma mixing between mafic and felsic magmas, but not result of direct fractional crystallization of mafic rocks. The granitic rocks with high Sr/Y values in the WQO, represented by the Ganjiagongma pluton, were not derived from thickened continental crust. No evident continental thickening occurred in the WQO during the Early Indosinian. Combining with regional geological evidence, we propose an alternative tectonic model to explain the evolution history of the WQO during the early Mesozoic. The A’nimaque-Mianlue ocean subducted northward with low angle, then the subducted slab rolled back during the Late Permian to Middle Triassic, and the ocean closured in the Late Triassic. This model can explain the spatial and temporal distribution characteristics of the magmatic rocks and sedimentary rocks, as well as Late Triassic uplift and deformation event in the WQO.

How to cite: Wang, M., Pei, X., Li, Z., Li, R., Pei, L., Chen, Y., Liu, C., and Zhao, S.: Early Indosinian magmatism in the West Qinling orogen and its tectonic implication, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2521, https://doi.org/10.5194/egusphere-egu23-2521, 2023.

EGU23-2622 | Orals | GD9.1

Synced deformation of the Talesh-Alborz-Kopet Dagh belt and formation of the Iranian Plateau 

Yang Chu, Bo Wan, Ling Chen, Wei Lin, Morteza Talebian, Xiaofeng Liang, and Liang Zhao

Plate convergence has continued for over 25 Myr after the Arabia initially collided with the Eurasia, causing vast intracontinental deformation within the Central Iran Block at the southern margin of the Eurasia. During the same period, the Iranian Plateau grew as tectonic stress from continental collision propagated northwards, accompanied by strong deformation, crustal shortening and rapid rock exhumation, but the process of the plateau formation remains less discussed. From west to east, the Talesh-Alborz-Kopet Dagh (TAK) situates at the northern front of the Iranian Plateau and suffers intense folding and thrusting that creates the highest mountain range in Iran, so its tectonic evolution history carries important clues for the building of the current plateau.

To better constrain the spatial and temporal patterns of deformation and exhumation, we carried out comprehensive structural analysis and new geochronology-thermochronology dating for the TAK. As a first order feature of the collision zone, the TAK records an immediate response to the initial collision. Oligocene deformation is well documented but unevenly exhumed different segments of the belt along-strike. The Talesh and westernmost Alborz preserves late Neoproterozoic basement rocks (~570 Ma) and old, Mesozoic zircon U-Th/He ages (150-90 Ma), acting as a relatively rigid part resistant to Oligocene deformation. In contrast, the main part of Alborz was remarkedly shortened by folds and thrusts and exhumed rapidly, while the Kopet Dagh shows a simply folded belt dominated by box folds in deca-kilometer scale. All the TAK experienced enhanced exhumation since 20 Ma, peaked at the Late Miocene, suggesting the deformation was synced around 7 Ma when the internal tectonic organization along the belt and within the Central Iran Block had been much reduced. This Late Miocene switch reflects a reorganization of Arabia-Eurasia plate convergence. The causes could include that elevation increased to a level at which the Iranian Plateau was built and resisted further thickening, or internal heterogeneity was decreased and the whole region began to evolve as a single tectonic unit, causing deformation to be accommodated in other regions. The growth model of Iranian Plateau can also enlighten us on how Tibetan Plateau developed and expanded at its early stage.

How to cite: Chu, Y., Wan, B., Chen, L., Lin, W., Talebian, M., Liang, X., and Zhao, L.: Synced deformation of the Talesh-Alborz-Kopet Dagh belt and formation of the Iranian Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2622, https://doi.org/10.5194/egusphere-egu23-2622, 2023.

EGU23-3799 | Orals | GD9.1

NW Iran under pressure: Cristallization and metamorphic ages of the Shanderman eclogites. 

Daniel Pastor-Galán, Tatsuki Tsujimori, Alicia López-Carmona, and Keewook Yi

The Tethyan oceans are the internal sotry-tellers of the amalgamation, tenure and break up of Pangea. All tethyan oceans have been mostly consumend and only remnants of them occur now along the margins of the Atlantic, Mediterranean, Black and Caspian seas, as well as in the Alpine-Himalayan and adjacent orogens. The Rheic (~500 to ~300 ma, some-times Ran or Proto-Tethys) closed during the amalgamation of Pangea and the Neo-Tethys (~270 to ~20 ma) is the main witness of its break-up. The Paleotethys is the ocean that shared an internal position during most of Pangea’s tenure. There is no consensus about its origin, some suggest that opened during the latest stages of Pangea’s amalgamation (Devonian-Carboniferous) whereas others considert it a remnant of the mostly subducted Rheic ocean after Gondwana-Laurussia collision.

We have studied the Shanderman eclogites (NW Iran) and put them into their context within other HP rocks in the area because they a potential candidate to represent the Paleotethys ocean. They are metamorphosed oceanic rocks (protolith oceanic tholeiitic basalt with MORB composition). Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation.

In this contribution we will show the new petrological, geochemical and geochronological results from this eclogites to shed light on the evolution of the tethyan oceans during the Paleozoic. The protolithic oceanic crust of Shanderman crystallized ~350 Ma, metamorphic age suggest that this piece of ocean subducted soon after forming, representing, perhaps, a subduction initiation or a ride-subduction event. We also found a metasomatic event at ~280 ma. Considering its relation with other HP rocks in Iran, we interpret that the Shanderman ophiolites are not a fragment of the Paleotethys but a fragment of the Rheic (Ran/Prototethys) ocean.

How to cite: Pastor-Galán, D., Tsujimori, T., López-Carmona, A., and Yi, K.: NW Iran under pressure: Cristallization and metamorphic ages of the Shanderman eclogites., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3799, https://doi.org/10.5194/egusphere-egu23-3799, 2023.

EGU23-3845 | Posters on site | GD9.1

Orogenic Gold Mineralization and its Relationship to Tectonic Evolution of the Kalamaili Area, East Junggar, Northwest China 

Xuexiang Gu, Yongmei Zhang, Zhanlin Ge, Weizhi Chen, and Liqiang Feng

There are many lode gold deposits and occurrences in the Kalamaili area of the East Junggar, Northwestern China. The deposits are confined to a narrow zone between the regional NW- to NWW-trending Kalamaili and Qingshui-Sujiquan shear zones and are structurally controlled by secondary, high-angle faults of the regional shear zones. The orebodies occur in the Middle Devonian and Lower Carboniferous strata that are largely composed of zeolite to lower greenschist facies clastic sedimentary and pyroclastic rocks. Gold mineralization occurs as auriferous quartz-sulfide±tourmaline veins/veinlets and disseminated ores in the immediate altered wall rocks. The ore mineralogy is relatively simple and dominated by quartz with minor to trace amounts of sulfides (pyrite and arsenopyrite, typically <5% in volume), sericite, calcite, and gold. The hydrothermal alteration halos are characterized by a proximal, 0.5–5 m wide zone composed mainly of quartz-sericite (-tourmaline)-sulfide (-gold) and a distal, several to tens of meters wide zone with a calcite-chlorite-epidote assemblage. Hydrothermal processes essentially involve a pre-ore stage of barren quartz, a main-ore stage of quartz-sulfide-gold (±tourmaline), and a post-ore stage of barren quartz-calcite (±sericite).

Fluid inclusion microthermometry, stable isotopes, and hydrothermal zircon U-Pb dating were combined to constrain the nature and source of ore fluids, the timing of mineralization, and the mechanism of gold precipitation. The ore-forming fluid of the main-ore stage is uniformly characterized by a medium to high homogenization temperature (mostly 240° to 330℃), low salinity (typically <6 wt % NaCl equiv), reduced, and CO2-rich-H2O-NaCl±CH4 fluid. The hydrogen and oxygen isotope data (δ18OH2O=+8.4 to +17.3‰, δDH2O=–99 to –62‰) indicate a metamorphic origin for the mineralizing fluid. The majority of δ34S values of the sulfides range between 0 and +10‰ with a mean of +2‰ (n=62), indicative of a largely sedimentary rock reservoir of sulfur in the ore-forming fluids. LA-ICP-MS U-Pb isotope dating of the hydrothermal zircons from auriferous quartz veins yielded a weighted mean 206Pb/238U age of ~313 Ma.

Combined geological and geochemical evidence indicates that the transition from compressional to transcurrent deformation during the late- to post-orogeny in the late Carboniferous played a vital role for the gold-bearing fluid flow along regional shear zones and subsequent channeling into the second- and third-order faults. On a deposit scale, fault-valve behavior during seismic fault activity is a key mechanism that caused episodic changes in fluid pressure and the resultant phase separation of ore fluids and precipitation of gold. Sulfidation of wall rocks due to fluid-rock interaction is another important mechanism for the gold precipitation. Later since the Permian, the N-S compression resulted in uplift and exhumation of the East Junggar terrane and deformation of the orebodies. Target gold exploration in this region is suggested to focus on the northeast side of the Kalamaili fault zone, where there exist suitable faults that connect with the first-order fault zones at depth and lead to focused fluid flux into depositional sites at shallower levels.

How to cite: Gu, X., Zhang, Y., Ge, Z., Chen, W., and Feng, L.: Orogenic Gold Mineralization and its Relationship to Tectonic Evolution of the Kalamaili Area, East Junggar, Northwest China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3845, https://doi.org/10.5194/egusphere-egu23-3845, 2023.

Epithermal base and precious veins are typically structurally controlled, and structures are fundamental to fluid flow and mineralization in hydrothermal deposits. In recent mineral explorations in east Kerman, especially in the northeast of the Shahr-e Babak area, it was found that structures play a key role in the mineralization of epithermal gold deposits. Shahr-e Babak epithermal gold deposit is located at 30°27'54.80'' N, 54°31'47'' E in the southeast of the Sanandaj Sirjan Zone, east of Kerman. The lithological outcrops of the Shahr-e Babak deposit area consist of Cretaceous felsic to mafic intrusive and extrusive rocks, Eocene micrite limestone and sandstone intruded by hornblende diorite, granodiorite, and microgranite stocks and dykes. Gold mineralization with an average grade of 1.5 g/t, is associated with anomalous Ag, Mo, Pb, and Sb and is usually concentrated in jasperoids with argillic and silicification alteration halos which are < 120 m in length and average about 10 m in width within east-west trending structures.  

The Shahr-e Babak deposit area is located in a restraining bend of the Shahr-e Babak fault. There is a strike-slip duplex and E-W trending fault lens with an approximate 5×7 kilometers area related to the young movements of the Shahr-e Babak fault. For these reasons, the rocks in the deposit area have been ruptured and crushed which are not associated with extensive hydrothermal alterations. According to measurements, faults can be divided into three main groups. The first group is the main faults with 80–90-degree trending, the second group consists of faults with 100–120-degree trending and the last category is minor faults with NE-SW and NW-SE trending. A combination of field observations, measurements of faults and fractures, and drill core logging indicates that gold-bearing jasperoids are formed along strike-slip faults with a 100–120-degree trend in lens-shaped fault zones that change in thickness with depth. 

The recent discovery of the Shahr-e Babak epithermal gold deposit, located on a restraining bend of the Shahr-e Babak fault, highlights the exploration potential for epithermal gold mineralization in East Kerman. In addition, undiscoverable epithermal gold deposits may be hidden below the regionally extensive Quaternary cover.

How to cite: Shafiee, S., Niroomand, S., and Soleymani, M.: Identifying the Role of Structures in the Mineralization of Shahr-e Babak Epithermal Gold Deposit: Implications for Epithermal Gold Exploration in East Kerman, Southeastern Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3961, https://doi.org/10.5194/egusphere-egu23-3961, 2023.

High-pressure and ultrahigh-pressure minerals tend to be preserved in mafic and ultramafic metamorphic rocks, such as eclogites and garnet amphibolites, rather than felsic rocks. Generally, the garnet amphibolites preserve particular porphyroblastic and corona textures that provide important information of geological processes. Therefore, identification of garnet amphibolite might hint that subduction or collision processes were likely to have occurred.

The Yili Block is one microcontinent in southwest of Central Asian Orogenic Belt, with Precambrain basement rocks exposed in the northern and southern margin. The Middle to Late Ordovician arc-type magmatic rocks were identified in the northern margin of the Yili Block with a subduction-related calc-alkaline affinity infer that the southward subduction of the Junggar Ocran beneath the Yili Block, but the record of coeval metamorphism is rarely reported. The Toksai garnet amphibolites idientified from the Wenquan Group in the northern margin of Yili Block records a clockwise P-T-t path. Its near isothermal depressive retrogressive metamorphism was typical characteristic of the Western Alps P-T path, recording the process of subduction and collision. The protolith belongs to tholeiite, with high TiO2 and low K2O+Na2O contents (3.10~3.89 wt.%, 0.76~2.01 wt.% respectively), enrichment of large ionic lithophile elements and depletion of high field strength elements, and enrichment of rare earth elements, showing the geochemical characteristics of tholeiite in intra-continental rift setting (Th/Ta=1.70~2.76, Ta/Hf=0.23~0.37). The geochemical characteristics reveal that the magmatic rocks derived from an OIB-like mantle source. The garnet amphibolites also has low contents of MgO (4.82~6.40 wt.%), Cr (70.8~224 ppm), Ni (9.68~65.7 ppm) and low values of Mg# (34.0~41.3), Nb/U (14.3~36.3), Nb/Ta (9.70~16.2), indicating that their protolith are not primitive magma, were formed by separate crystallization of different mineral phases with a small amount of crustal contamination. The zircon U-Pb dating results suggest that the garnet amphibolites protolith was formed in the middle to late Neoproterozoic, and the metamorphic age is end of Late Ordovician (450~440 Ma). The zircon and monazite from surrounding rocks also record the coeval tectonic thermal event. Consequently, it is inferred that the protolith of the garnet amphibolites may have formed in an intraplate rifting setting as a result of the breakup of Rodinia, and indicating that the Yili Block maybe a continental fragment separated from the Tarim Block during the middle to late Neoproterozoic. In the Middle to Late Ordovician, the Wenquan Group as a part of Aktau-Wenquan contineantal domain was involved in the continental–arc collision and continuing accretion in north of the Yili/Kazakhstan Block with the southward subduction of the Junggar–Balkhash oceanic lithosphere, and experience high amphibolite facies metamorphism in the end of Ordovician.

How to cite: Chen, Y., Wang, M., and Pei, X.: Chronology, geochemistry, metamorphic evolution and its tectonic implications of the Toksai garnet amphibolites in the northern margin of Yili Block, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4041, https://doi.org/10.5194/egusphere-egu23-4041, 2023.

EGU23-4091 | ECS | Orals | GD9.1

Late Mesozoic continental arc in East China Sea: Constraints from detrital zircons 

Yuling Deng and Changhai Xu

The Late Mesozoic subduction of Izanagi beneath East Asia formed large-scale intraplate magmatism in SE China and subduction mélanges from SW Japan to eastern Taiwan (Müller et al., 2016; Wang et al., 2008; Wakita and Metcalfe, 2005), but the accompanying arc remains uncertain. The East China Sea (ECS) is settled between the intraplate and trench, in which previous studies have found some arc indications (Xu et al., 2017). ECS domains share a unified basement with, or are regarded as an exotic microcontinent of Cathaysia block, which is still up for debate.

Discerning delta facies and litharenite types of sediment samples support a typical proximal environment of Lishui-Jiaojiang sag, SW ECS. As its provenances, nearby Zhemin and Yandang swells provide Late Mesozoic voluminous felsic suites with minor metabasite materials. We conducted LA-ICP-MS U-Pb zircon dating and trace element analyses of proximal sandstones in the SW ECS to track a Jurassic to Cretaceous magmatic arc, which advantages over the use of a few drilled igneous rocks. Newly acquired data reveal an evolved magmatic arc in SW ECS from Jurassic to Cretaceous (200–86 Ma), which developed predominantly in episodes of 150–124 Ma and 124–102 Ma. Arc magmatism exhibits characteristics of low-T and continental zircon types, yielding high Th/U, U/Yb, Sc/Yb, and Th/Nb ratios and low Nb/Yb and Nb/Hf ratios. Trace elements U and Th in arc zircons indicate a decline in subduction fluids addition due to slab rollback and a rise in lower crustal addition owing to fluid-fluxed crustal melting from Jurassic to Cretaceous.

The swells of Yushan, Zhemin, Haijiao, and Hupijiao outline a Late Mesozoic magmatic arc in the West ECS. This magmatic arc, in conjunction with the SE China intraplate, and subduction mélanges, spatially forms a Late Mesozoic trench-arc-intraplate architecture in response to the Izanagi subduction beneath East Asia. Its identified tectonic scenarios mainly include slab strike-slip subduction (200–170 Ma), slab stagnation and intraplate foundering (170–150 Ma), slab rollback and removal of the thickened arc root (150–102 Ma), and trench retreat with arc migration (102–86 Ma). Detrital zircon data suggest that the West ECS and Cathaysia block share a unified basement that formed at ca. 2.44 Ga and ca. 1.85 Ga, which was reworked at ca. 780 Ma, ca. 442 Ma, and ca. 240 Ma. The West ECS magmatic arc evolved on this Cathaysia-type basement.

Keywords: magmatic arc; detrital zircon; Late Mesozoic; Izanagi subduction

 

 

Müller, R.D., et al., 2016. Ocean basin evolution and global-scale plate reorganization events since Pangea breakup. Annual Review of Earth and Planetary Sciences, 44(1), 107138.

Wakita, K., and Metcalfe, I., 2005. Ocean plate stratigraphy in East and Southeast Asia. Journal of Asian Earth Sciences, 24(6), 679–702.

Wang, Y.J., et al., 2008. Sr-Nd-Pb isotopic constraints on multiple mantle domains for Mesozoic mafic rocks beneath the South China Block hinterland. Lithos, 106(3–4), 297–308.

Xu, C.H., et al., 2017. Tracing an Early Jurassic magmatic arc from South to East China Seas. Tectonics, 36, 466–492.

How to cite: Deng, Y. and Xu, C.: Late Mesozoic continental arc in East China Sea: Constraints from detrital zircons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4091, https://doi.org/10.5194/egusphere-egu23-4091, 2023.

EGU23-4201 | ECS | Orals | GD9.1

Reassessment of the Phanerozoic net crustal growth: U–Pb and Hf zircon data for the Central Asian Orogenic Belt 

Ariuntsetseg Ganbat, Tatsuki Tsujimori, Daniel Pastor-Galán, and Alexander Webb

The Central Asian Orogenic Belt (CAOB) consists of several continental blocks, was assembled during the Phanerozoic, and preserves large volumes of Phanerozoic granitoids with juvenile Nd and Hf isotope characteristics, and thus regarded as the largest site of Phanerozoic continental growth on Earth. Nonetheless, it remains disputed whether the significant crustal additions occurred during the Phanerozoic. We compiled available zircon U–Pb geochronological and Hf-in-zircon isotopic data for granitoids from the orogenic segments of CAOB. Using this data, we estimated the percentage of juvenile versus evolved crustal portions in different Phanerozoic time slices of the CAOB.     

The areal distribution of Hf isotopic information shows a younging trend in the Hf model age and radiogenic Hf values from northeast to southwest. For many orogenic segments of the CAOB, the range of hafnium isotope signatures for the granitoids shifted towards more radiogenic compositions over time. We interpret these findings to indicate that the lower crust and lithospheric mantle beneath the CAOB continental blocks were largely removed during continuous oceanic subduction and replaced by juvenile crust. Melts of this crust display the radiogenic hafnium signature. The juvenile versus evolved crustal portion estimations in different time slices show that the crustal growth has taken place in a steady-state mode, and the rate of the radiogenic crustal generation is close to overall global averaged rates of crust generation. It follows that Phanerozoic net crustal growth in accretionary orogens, as exemplified by the CAOB, may have been overestimated as it has been compensated by crustal destruction.

How to cite: Ganbat, A., Tsujimori, T., Pastor-Galán, D., and Webb, A.: Reassessment of the Phanerozoic net crustal growth: U–Pb and Hf zircon data for the Central Asian Orogenic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4201, https://doi.org/10.5194/egusphere-egu23-4201, 2023.

EGU23-4461 | Posters on site | GD9.1

Thermochronologic constraints on exhumation associated with the Main Pamir Thrust 

Edward Sobel, Jonas Kley, Johannes Rembe, Rasmus Thiede, Johannes Glodny, Lennart Grimm, Maximilian Rometsch, Asil Newigy, Nowrad Ali, Wafaa Altyeb, and Daniela Espinoza Tapia

The Pamir orogen forms the northwest prolongation of the Tibetan plateau. The most important surficial structure bounding the northern and northwestern margin is the Main Pamir Thrust (MPT); however, despite the importance of the structure, surprisingly little is known about the displacement history of the fault. Together with the younger, foreland-oriented Pamir Frontal thrust system (PFT), displacement estimates range from 50 to over 300 km. The larger estimates are based on the estimated Cenozoic northward indentation of the Pamir with respect to Tibet as well as the length of the intracontinental Pamir seismic zone. However, recent work suggests that some of the indentation predates the Cenozoic or is related to an original Paleozoic embayed paleogeography and other studies have suggested that the seismic zone is not related to intracontinental subduction. Shortening estimates in the hanging walls of the MPT and PFT suggest more modest amounts: between 30 and 75 km in the north, with higher values for SE-NW shortening in the Tadjik depression.

Constraining the onset of deformation has proven challenging. Most publications suggest a late Oligo-early Miocene onset age. Cenozoic stratigraphic sequences are unfossiliferous and poorly dated. We have attempted to resolve this question by collecting samples for thermochronologic analysis from many locations along the arcuate margin. In general, zircon (U-Th-Sm)/He (ZHe) samples yield ages between ~60 and 17 Ma. Many are likely to be partially reset. Ages are slightly older in the east, which could reflect an overall westward increase in exhumation. The relatively small amount of exhumation in the north supports our structural interpretation that the MPT there has a low dip angle and might not have produced pronounced topography. Apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) are often much younger; often between <15 and 10 Ma in the MPT hanging wall and < 10 Ma in the footwall. These younger ages may reflect the activation of a second pulse of exhumation linked to motion along the PFT. We are modeling these data sets using QTQt to try to better constrain the exhumation history of the fault system. In turn, these should help constrain shortening estimates.

How to cite: Sobel, E., Kley, J., Rembe, J., Thiede, R., Glodny, J., Grimm, L., Rometsch, M., Newigy, A., Ali, N., Altyeb, W., and Espinoza Tapia, D.: Thermochronologic constraints on exhumation associated with the Main Pamir Thrust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4461, https://doi.org/10.5194/egusphere-egu23-4461, 2023.

The active deformation field between northern Tibet and central Mongolia is dominated by diffuse sinistral transpressional reactivation of the southern Altaids Phanerozoic terrane collage.   The angular relationship between NE-directed SHmax and pre-existing basement trends is the dominant control on Quaternary fault kinematics.  Along Tibet’s northern margin, the Altyn Tagh system is widening northwards by transpressional duplexing.  The Nanjieshan and Sanweishan comprise sinistral oblique-slip thrust ridges within a regional asymmetric flower structure centered on the Altyn Tagh Fault.  In the southern Beishan, interconnected lensoidal domains of transpressional and transtensional faulting are subtly indicated by Quaternary fault scarps, low-relief rejuvenated landscapes and alluvial sedimentation.  The SE Beishan and western Hexi Corridor region contain numerous Late Quaternary fault systems including the Heishan-Jinta'Nanshan sinistral strike-slip corridor and the Helishan-Longshoushan fault array that connects eastwards with the transtensional grabens of the Yabrai and Langshan in the eastern Alxa Block.  Further north, the Paleozoic terrane collage of the Gobi Corridor was repeatedly reactivated during the Permo-Triassic, Jurassic, Cretaceous and Neogene.  Late Cenozoic reactivation was likely facilitated by thermal weakening of the crust due to Jurassic-Miocene volcanism, and diffuse Cretaceous rifting and crustal thinning.  Although terrane boundaries and other faults are reactivated in many areas, thrust and oblique-slip reactivation of WNW striking shallowly dipping sedimentary bedding and metamorphic fabrics is equally important.  Conversely, modern E-W trending strike-slip faults in the Gobi Altai typically crosscut older basement trends. In the Altai and Gobi Altai, the Late Cenozoic fault array has created a transpressional  basin and range physiographic province.  Coalescence of separate ranges into topographically continuous mountain belts in the Altai, Gobi Altai and easternmost Tien Shan is an important mechanism of transpressional mountain building not predicted by classical plate tectonic models.  Throughout the vast deforming region north of Tibet, tectonic loading is shared amongst a diffuse fault network challenging assumptions about earthquake recurrence intervals and seismic hazard forecasting.

How to cite: Cunningham, D., Yang, H., and Zhang, J.: Late Cenozoic Crustal Reactivation of the North Tibetan Foreland, Western Hexi Corridor, Beishan, and Gobi Corridor: Implications for Intraplate Fault Networks, Mountain Building Processes and Earthquake Hazards in Slowly Deforming Regions of Central Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4597, https://doi.org/10.5194/egusphere-egu23-4597, 2023.

EGU23-4737 | ECS | Posters on site | GD9.1

Geophysical evidence of large-scale silica-rich fluid flow above the continental subduction interface 

Yuantong Mao, Liang Zhao, Marco Malusà, Stefano Solarino, Silvia Pondrelli, Baolu Sun, Coralie Aubert, Simone Salimbeni, Elena Eva, and Stéphane Guillot

Continental subduction zones are crucial tectonic settings where subducted slabs exchange crustal materials with the mantle, and geochemical changes occur with the participation of fluids at increasing temperatures and pressures. The occurrence of pervasive networks of quartz veins in exhumed sections of the Alpine subduction wedge provides evidence for major silica-rich fluid circulation in the shallowest levels of the subduction zone. However, the occurrence of silica-rich fluids at greater depths above the subduction interface remains speculative.

Rocks involved in the subduction zone experience variable temperature and pressure conditions and show a wide range of densities and seismic velocities that are not necessarily correlated. An integrated analysis of seismic velocities, Vp/Vs ratios and rock densities may provide a viable tool to detect compositional variations in the Earth’s interiors and infer the impact of large-scale fluid flows on the intrinsic physical properties of subducted rocks. We tackle this issue from a geophysical perspective, by applying H-κ stacking, receiver function analysis, and waveform and gravity modelling. We found a belt of high Vp/Vs ratios >1.9 in the rear part of the Alpine subduction wedge, consistent with a partly serpentinized upper-plate mantle, and a belt of unusually low Vp/Vs ratios <1.7 in the frontal part of the subduction wedge that we interpret as the effect of a pervasive network of silica-rich veins above the subduction interface. Laboratory experiment shows that Vp/Vs ratios are generally higher for serpentinite (2.0-2.2), and much lower for quartz (1.46-1.48).

Our results suggest a dominant role of silica-rich fluids in the subduction wedge. These silica-rich fluids rose within the subduction wedge until the change in ambient conditions precipitated the formation of a widespread network of quartz veins, as observed in the field. And this pervasive quartz-vein network changes the physical properties of the subduction-wedge rocks, implying a major impact on rheology favoring crustal deformation during continental subduction.

How to cite: Mao, Y., Zhao, L., Malusà, M., Solarino, S., Pondrelli, S., Sun, B., Aubert, C., Salimbeni, S., Eva, E., and Guillot, S.: Geophysical evidence of large-scale silica-rich fluid flow above the continental subduction interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4737, https://doi.org/10.5194/egusphere-egu23-4737, 2023.

EGU23-5179 | Posters on site | GD9.1

New constraints on the geological evolution of the SE corner of the Arabian Plate (NE Oman) 

Wilfried Bauer, Joachim Jacobs, Ivan Callegari, Andreas Scharf, and Frank Mattern

The Saih Hatat Dome is a tectonic window in northeastern Oman with a NW-SE extension of <95 km and an E-W extension of <50 km, rimmed by the allochthonous Samail Ophiolite and the underlain nappes composed of sedimentary rocks from the Neo-Tethyan Hawasina Basin. Rocks within the window were affected by an upper Cretaceous high- to ultra-high pressure/low-temperature eclogite- and blueschist-facies metamorphism.

Stratigraphically, the Saih Hatat Dome contains a several kilometer thick basal (“Autochthonous A”) sequence from what is believed Cryogenian Hatat schists to the Ediacaran Hiyam dolostone, unconformably overlain by 3400 m Cambro-Ordovician siliciclastics. This basal sequence is separated by a so-called ‘Hercynian’ unconformity from Permian to Jurassic overall shelf carbonates (“Autochthonous B”). In the eastern part of the window, intense Cretaceous deformation and metamorphism makes it difficult to identify this stratigraphic subdivision.

New U-Pb zircon LA-ICP-MS data from a quartzdiorite dyke, intruding the basal part of the Hatat schists gave a crystallization age of 845 +2/-4 Ma. Thus, the basal part of the Hatat schists is Tonian in age and older than the Cryogenian/Ediacaran strata of the nearby Jebel Akhdar Dome and Huqf area, 40 km to the west and 300 km to the south, respectively.

Two blueschist-facies tuffites from eastern Saih Hatat contain concordant detrital zircons, ranging in age between c. 530 and 2872 Ma with age clusters around 750 to 850 Ma and 1010 to 1164 Ma. The latter ages are not known from a source on the Arabian Plate and might be derived from an Indian source.

Based on the new results, we suggest a subdivision of the Saih Hatat stratigraphy with a Tonian accretionary wedge (Hatat schist) which might be coeval with igneous intrusion from the Ja’alab area, an Ediacaran carbonate platform, and a Cambrian sedimentary basin, unconformably overlain by upper Cambrian/Ordovician quartzites.

How to cite: Bauer, W., Jacobs, J., Callegari, I., Scharf, A., and Mattern, F.: New constraints on the geological evolution of the SE corner of the Arabian Plate (NE Oman), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5179, https://doi.org/10.5194/egusphere-egu23-5179, 2023.

EGU23-5946 | ECS | Posters virtual | GD9.1

Slab geometry and a diffuse plate boundary beneath Sumatra: constrained using a new receiver function analysis method 

Mingye Feng, Ling Chen, Shengji Wei, Xin Wang, Xu Wang, and Zimu Wu

Geometry and structure of the subducting plate boundary are key to understanding geodynamic processes of subduction and related geological phenomena. Located between the obliquely converging Indo-Australian and Sunda plates, the Sumatran subduction zone is featured by a strongly deformed slab coupling with the overlying plate, and complicated slab-mantle interactions, leading to frequent occurrence of great megathrust earthquakes (e.g., 2004 Mw9.2 and 2005 Mw8.7 events) and extremely intensive magmatism (e.g., Toba supervolcano). Previous seismic studies reveal a rugged slab surface with seamounts, and slab folding and tearing beneath Sumatra, both of which govern the features of earthquake rupture and magma generation associated with fluid release and mantle wedge hydration. However, the details of the slab geometry (e.g., along-strike variation of dip direction and dip angle) and the “slab dehydration-mantle hydration” process across the subducting plate boundary remain poorly known, due to limited data coverage and resolution of these studies.

To better reveal the geometry of the slab and the feature of “slab dehydration-mantle hydration” during the oblique subduction, in this study, we develop a Dip Direction Searching (DDS) method to constrain the dipping structure of slab and the nature of the slab upper boundary. In this method, we estimate dip directions of velocity discontinuities by grid search based on the back azimuthal variation of radial receiver functions (RFs). DDS is a single-station-based method thus applicable in the areas with sparse seismic instruments. Synthetic tests demonstrate that the DDS method has higher resolution (with uncertainty of several degrees) in dip direction estimation than traditional RF analysis approaches and is applicable to the cases with strong white noise contamination, incomplete/uneven back azimuthal coverage, <5%-10% crustal and mantle anisotropy, and their compound effects. The method also provides constraints on the thickness and depths of dipping layers.

Applying the DDS method, we find a dipping Low Velocity Layer (LVL) commonly beneath the forearc areas and constrain its depths, thickness, and dip directions. The depth and dip direction estimates are highly consistent with the Slab2 model, indicating that the LVL is at the subducting plate boundary. We interpret the lower boundary of the LVL as the subducting oceanic Moho, which is less deformed so its dip direction can represent the dip direction of the whole slab. The slab dip direction gradually increases from 47±5.3˚ in southern Sumatra to 70±10.7˚ in northern Sumatra, indicating an along-strike bending of slab, which is possibly related to the oblique subduction. We find that the dip directions at the upper and lower boundaries of the LVL differ up to 23˚ beneath central Sumatra, indicating the two boundaries are locally unparallel. The thickness of the LVL is estimated to be 10-14 km, larger than those of regular oceanic crusts (~7 km). These observations imply that the LVL is composed by not only the oceanic crust but also a low-velocity serpentinized mantle layer at the top. Therefore, the upper boundary of the LVL represents the serpentinization front, indicating a diffuse plate boundary.

How to cite: Feng, M., Chen, L., Wei, S., Wang, X., Wang, X., and Wu, Z.: Slab geometry and a diffuse plate boundary beneath Sumatra: constrained using a new receiver function analysis method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5946, https://doi.org/10.5194/egusphere-egu23-5946, 2023.

Abstract:

The development of faults governs the kinematics of continental deformation. The Songliao Basin, located at the central part of late Mesozoic lithospheric thinning province in East Asian region, experienced intense rifting during Early Cretaceous epoch and formed an intricate syn-rift fault system. However, the geometric and kinematic relationships inherent in the fault system have not yet been satisfactorily explained, hampering the understanding of basin formation and related marginal plate tectonic processes. Here, theories for polymodal faulting were applied to evaluate the faulting evolution of the Songliao Basin, based on which a quantitively deformation reconstruction was developed. Our reconstruction shows that the basin formation during the syn-rifting period was subdivided into three main stages: late Valanginian–Barremian(133-118.2Ma) initiation of extension, Aptian(118.2-113.9M) extension climax, and Albian(113.9-100.5Ma) extension wanning and initiation of post-extensional subsidence. The deformation of the Songliao Basin is spatially heterogeneous. Faulting analyses revealed a three-dimensional strain filed with a dominating horizontal ESE-WNW extension, a minor horizontal near N-S extension, and a large vertical shortening in the Northern Songliao Basin (NSL). The 3-D non-plane strain with non-zero intermediated extension(ε2) magnitude controlled the synchronous displacement of a NNE–SSW-striking fault set and a NNW–SSE-striking fault set in orthorhombic pattern to create the characteristic rhomboidal fault geometry. Whereas, the Southern Songliao Basin (SSL) deformed under a 2-D plane strain filed with a horizontal ESE-WNW extension and vertical shortening. The plane strain condition is interpreted as a special case with no intermediated strain(ε2), and produces a pair of near N-S-striking fault sets in conjugate symmetry. Our results illustrate that this particular three-dimensional deformation result in the intricate fault system in the Songliao Basin and that the fault geometry is controlled by the ratios of the principal strains, especially the relative magnitude of the intermediate strain. We argue that the three-dimensional strain field in the NSL reflected the trench retreat in the Paleo-Pacific subduction zone and the gravitational collapse of the thickened lithosphere, and that the extension of the SSL is merely the consequence of the trench retreat.

Keywords:

Songliao Basin, three-dimensional strain, orthorhombic fault, syn-rift deformation, quantitative reconstruction

How to cite: xing, H.: Late Mesozoic rift evolution and deformation reconstruction of the Songliao Basin, northeastern China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6117, https://doi.org/10.5194/egusphere-egu23-6117, 2023.

The stratigraphy of the southern half of Afghanistan has been studied and the timing of first order events have been established in some detail. By contrast, the structural evolution has not been treated with the same discernment. We here report the existence of a marginal fold and thrust belt within the Logar Syncline (western Afghanistan) that was detached along a décollement surface at the base of the Cambrian, mainly between Zargaran dolomites and polymictic conglomerates filling the underlying depressions. The basement consists of Pan-African magmatic and metamorphic rocks including volcanic tuffs making up the Loy Khwar Series. Some of this material has been worked into the conglomerates of the Loy Khwar. The overlying sedimentary package reaches from the Cambrian to the Permian and has been deformed into concentric folds. Nowhere do these folds expose the underlying Pan-African basement which crops out in the extreme SW, in a kind of root zone wherein the décollement separating the sedimentary package from the basement seems to root. Having a décollement within dolomites seems unexpected due to their presumed strength but a similar case has been reported from the Keystone Thrust of the Sevier Belt in Nevada. This phenomenon seems to be more widespread than previously thought.

How to cite: Lom, N. and Şengör, A. M. C.: The discovery of a Palaeozoic décollement in SW Afghanistan: orogenic events along the Tethyan edge of Gondwana-Land, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6614, https://doi.org/10.5194/egusphere-egu23-6614, 2023.

EGU23-7091 | ECS | Orals | GD9.1

Cenozoic Southwestern Tian Shan: Timing of Mountain Building, Intra-montane Basin Inversion, and Relation to Lithospheric Mantle Indentation 

Florian Trilsch, Sanaa Reuter, Ratschbacher Lothar, Shadi Ansari Jafari, Raymond Jonckheere, Birk Härtel, Christoph Glotzbach, and Bastian Wauschkuhn

Cenozoic reactivation of the Paleozoic thick-skinned fold-thrust belt of the southwestern Tian Shan has—as the Afghan-Tajik Basin inversion—been interpreted to reflect Indian mantle-lithosphere indentation underneath the Pamir. New low-temperature thermochronologic data, i.e. apatite fission-track (AFT), apatite (AHe), and zircon (ZHe) (U-Th)/He ages, reveal the exhumation history of the SW-Tajik Tian Shan along two N-S-transects. We date the reactivation and explore its temporal and spatial variations. Three domains emerged. In the Central Domain (Zeravshan-Gissar and Vashan), AFT data—aided by Raman-spectroscopic chemical-composition discrimination of detrital apatite samples and vitrinite-reflectance temperature estimates—record a ~10-13 Ma onset of shortening and >4 km exhumation. The Northern Domain, where the N-Zeravshan Fault constitutes a major Cenozoic structural divide reactivating the Paleozoic Zirabulak Suture, exhumed from <4 km, but apatite AHe ages outline a similar reactivation history as in the Central Domain. The synchronous structural reactivation implies rapid shortening propagation from the Pamir indenter across the Afghan-Tajik fold-thrust belt into and across the Tian Shan. In the Southern Domain (Gissar Batholith), ~7‒9 Ma AFT and ~4 Ma AHe ages suggest a southward shortening propagation from the northern Domains and anew thrust generation. In the hanging wall of major thrusts, ~3‒7 Ma-old AFT ages record significant and persistent exhumation but ZHe data limit it to <6 km. Most of the Southern and Central Domains cooled monotonously but temperature-time models indicate northward-decreasing reheating by syn-orogenic deposition, consistent with stratigraphic data.

How to cite: Trilsch, F., Reuter, S., Lothar, R., Ansari Jafari, S., Jonckheere, R., Härtel, B., Glotzbach, C., and Wauschkuhn, B.: Cenozoic Southwestern Tian Shan: Timing of Mountain Building, Intra-montane Basin Inversion, and Relation to Lithospheric Mantle Indentation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7091, https://doi.org/10.5194/egusphere-egu23-7091, 2023.

EGU23-7378 | ECS | Posters on site | GD9.1

Towards understanding the crustal response of slab tearing and detachment: inferences from the Dinarides-Hellenides transition 

Nikola Randjelovic, Liviu Matenco, Maja Maleš, Nemanja Krstekanic, Uros Stojadinovic, Branislav Trivić, and Marinko Toljić

Convergence zones are often characterized by numerous subduction- to collision-related dynamics in many orogenic areas worldwide. Processes such as continental indentation, extrusion and slab roll-back can occur simultaneously along orogens as a consequence of different rates of convergence. Such along-strike variability accross the orogen can lead to migration of deformation from partly detached slab to the still active oceanic or continental subduction. These conditions create slab tearing often followed by rotation, rapid roll-back of the attached slab and/or exhumation of previously buried crust in the upper plate above the already detached slab. The main mechanism that explains transition from slabs with contrasting kinematics to the crustal level strain partitioning is still not fully understood.

One very good example of strain partitioning associated with indentation, slab-detachment and slab-tearing is the junction between the Dinarides and Hellenides in southeastern Europe. Following the Jurassic – Eocene closure of the Neotethys Ocean and subsequent Adria – Europe collision, the Dinarides - Hellenides orogen has recorded a significant extensional deformation. This extension was driven by the Oligocene – early Miocene slab detachment of the Dinarides slab, while the Hellenides segment continued its evolution until the present day.

We have performed a field kinematic and structural study in the less understood area of Montenegro near Dinarides - Hellenides transition to determine the influence of Oligocene – early Miocene deformation on Dinarides composite nappes. The results imply that Oligocene – early Miocene slab detachment followed by slab tearing was accommodated in crustal domain by bi-directional extension associated with the exhumation of mid-crustal levels in the footwall of both orogen-parallel and orogen-perpendicular faults, reactivation of inherited Cretaceous-Paleogene nappe contacts and formation of extensional klippen.

How to cite: Randjelovic, N., Matenco, L., Maleš, M., Krstekanic, N., Stojadinovic, U., Trivić, B., and Toljić, M.: Towards understanding the crustal response of slab tearing and detachment: inferences from the Dinarides-Hellenides transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7378, https://doi.org/10.5194/egusphere-egu23-7378, 2023.

EGU23-7625 | Orals | GD9.1

Sinking-slab triggered formation of the giant Ordos basin in central China 

Neng Wan, Shaofeng Liu, and Zhang Bo

The giant Late Triassic Ordos basin, developed along northern Tethyan margin where prolonged terrane amalgamation and accretion occurred, is characterized by rapid subsidence rate along its southwestern margin, but slow and uniform subsidence rate within its interior. Its formation mechanism still remains poorly understood. Here, we use flexural simulation and 4D-geodynamic modeling to explore the potential role of basin adjacent mountain belts and deep mantle processes towards basin subsidence, respectively. Flexural backstripping of stratigraphic record spanning from 245-201 Ma, along two SW-NE trending well sections perpendicular to the southwestern margin of Ordos basin clearly demonstrates that there were long wavelength anomalous subsidence components, here termed residual subsidence, in addition to those induced by thrust loads and sediment loads. From 245-201 Ma, residual subsidence increases from 0 m to ca. 500 m and gradually decreases from southwest towards northeast. Our results indicate that basin adjacent thrust loads could act as the dominant driver for subsidence of foredeep but have limited control towards basin interior. Other mechanism is required to explain the basin-wide anomalous residual subsidence. Long-wavelength nature of residual subsidence and its general agreement, regarding both the magnitude and trend, with dynamic topography predicted by an independently designed geodynamic model suggest that the anomalous subsidence component might be of dynamic origin. We attribute this excess residual subsidence as dynamic subsidence induced by the sinking slab beneath North China plate during and after the oblique closure of Mianlue ocean between North China plate and South China plate. We argue that the Ordos basin is triggered by subduction related mantle processes while modulated by flexural loading along its margin. Our findings may also shed light on formation mechanisms of other giant basins with similar settings in East Asia.

How to cite: Wan, N., Liu, S., and Bo, Z.: Sinking-slab triggered formation of the giant Ordos basin in central China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7625, https://doi.org/10.5194/egusphere-egu23-7625, 2023.

Since Late Palaeozoic, the North China Block (NCB) experienced a unique tectonic process in which sequential plate subduction and collision took place around this once stable and rigid craton. Due to this multi-direction convergent setting and its small size, the NCB was characterized with intensive intracontinental deformation and associated depositional processes and magmatism during Mesozoic. However, conflicting debates on the timing and kinematics of the intracontinental deformations are still open to the geologist community and hamper the understanding of the driving forces. Our works focus on the syn-tectonic depositions, including syn-tectonic conglomerates and growth strata, in Mesozoic sedimentary basins in the Yanshan belt of northern NCB, and the high-precision zircon U-Pb geochronological data. Previously reported stratigraphic levels of regional unconformities and isotopic ages of igneous rocks in the Yanshan belt were also compiled in this study. Our results suggest that during Middle Triassic-earliest Jurassic (ca. 240-195 Ma), the northern NCB was dominated by nearly N-S compressional regime, leading to formation of large-scale E-W-trending thrust faults and basement-cored buckles. A significant magmatic lull was also witnessed within this period (ca. 210-195 Ma). This N-S crustal shortening was believed to be related with collision between the NCB and the Songliao-Nenjiang terrane along the Solonker suture. During Middle Jurassic-Early Cretaceous (ca. 172-135 Ma), the Yanshan belt underwent strong NW-SE contraction and gave rise to NE-SW-striking thrust faults, asymmetric folds, and reactivation of previous E-W thrust faults with prominent dextral component. Both deformation, deposition, and magmatism showed a westward younging trend in the Yanshan belt during Early Jurassic-Early Cretaceous (ca. 180-140 Ma), indicating their westward migration. However, magmatism turned to migrate toward east after that. All these lines of evidences could be integrated in a tectonic model with westward flat-slab subduction of the Paleo-Pacific/Izanagi plate beneath the East Asian continent. Early Jurassic witnessed an imported and profound transition from closure of the paleo-Asian Ocean to the subduction of the Paleo-Pacific Ocean plate.

How to cite: Lin, C. and Liu, S.: Mesozoic intracontinental deformations of the northern North China Block in a multi-direction convergent setting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7701, https://doi.org/10.5194/egusphere-egu23-7701, 2023.

EGU23-7851 | ECS | Orals | GD9.1

Devonian Andean-type orogeny in the southern Dunhuang block (NW China): Petro-structural, geochronological and metamorphic P−T constraints 

Jérémie Soldner, Yingde Jiang, Pavla Štípská, Karel Schulmann, Chao Yuan, Zongying Huang, and Robert Anczkiewicz

The Dunhuang block in NW China preserves Archean to Paleoproterozoic basement rocks that are exposed alongside Paleozoic magmatic and metamorphic rocks. Although both subduction-accretion and collisional processes have been proposed for the formation of Paleozoic metamorphic rocks, links between their metamorphic ages, P−T evolution and deformational history remains ambiguous. Here we present zircon and in-situ monazite U−Pb geochronology linked to P−T modelling of metapelites from the Hongliuxia belt in the southern Dunhuang block. Oriented inclusion trails in garnet from metapelites reveal rare relics of an S1 fabric. The earliest continuous metamorphic fabric is an originally steep N-S striking foliation S2. This fabric was further reworked by upright folds F3 associated with development of an ubiquitous steep, mainly south-dipping, E-W striking axial planar foliation S3. The Bt−Ms−St−Pl−Qz−Tur−Ilm assemblage forming inclusions in garnet is assigned as the D1-M1a event whereas the foliation S1b in metapelites is associated with Grt–Ky–St–Bt–Ms–Pl–Qz–Rt assemblage. The Grt−Ky−St aligned parallel to the S2 matrix in low-strain domains are considered as remnants of a dismembered M1 assemblage, while the S2 foliation is characterized by the Grt–Sil–Bt–Pl–Qz–Rt–Liq in high-strain domains. The S3 foliation is associated with the Grt–Sil–Bt–Ms–Pl–Qz–Kfs–Chl–Ilm assemblage. Altogether, metapelites record similar clockwise P–T evolution an early prograde (M1a) stage starting at 4.5–5 kbar and 500–550°C, metamorphic peak (M1b) stage at ~8 kbar and 700–725°C, decompressional heating to ~6 kbar and ~750°C (M2) and a retrograde stage to 4.5–5.5 kbar and 500–550°C (M3). Zircon U−Pb geochronological investigations suggest that metapelites from the basement record metamorphic ages of 1847 ± 11 Ma and 404 ± 15 Ma.  In-situ U–Pb dating of monazite combined to monazite trace-element composition analysis further suggest that the rock burial most likely started at c. 410 Ma, peak-P conditions M1b were reached at 400–395 Ma, M2 heating occurred at c. 390 Ma and M3 retrogression occurred between c. 384 and 353 Ma. The D1-M1 burial event reflects either underthrusting of the basement below the supra-subduction active margin system or propagation of the deformation front to the south of the Dunhuang block. The D2-M2 event is a consequence of thermal relaxation following crustal thickening, possibly accompanied by convective lithospheric thinning, whereas D3-M3 reflects exhumation during shortening of the system. Combined with the available regional data, it is suggested that the Devonian multi-stage tectono-metamorphic evolution described in the study area corresponds to a polyphase Andean-type deformation of the active margin of the Dunhuang block. Such a process can be regarded as a response to a progressive relocation of the Dunhuang block alongside with the Tarim-North China Collage in the Devonian.

 

Funding: This research is part of the project No. 2021/43/P/ST10/02996 co-funded by the National Science Centre and the European Union Framework Program for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie grant agreement No. 945339, as well as the President’s International Fellowship Initiative for Postdoctoral Researchers of the Chinese Academy of Sciences, grant No. 2021PC0013.

How to cite: Soldner, J., Jiang, Y., Štípská, P., Schulmann, K., Yuan, C., Huang, Z., and Anczkiewicz, R.: Devonian Andean-type orogeny in the southern Dunhuang block (NW China): Petro-structural, geochronological and metamorphic P−T constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7851, https://doi.org/10.5194/egusphere-egu23-7851, 2023.

EGU23-8253 | ECS | Posters on site | GD9.1

Seismic imaging of the lithospheric structures in the Iranian Makran subduction zone 

Zimu Wu, Ling Chen, Haiqiang Lan, Morteza Talebian, Xu Wang, Yifan Gao, Jianyong Zhang, Yinshuang Ai, Mingming Jiang, and Yingjie Yang

The Makran subduction zone (MSZ) is located in between the Zagros mountain belt to the west and Himalayan orogen to the east, forming a transition from oceanic subduction to continental collision on both sides along the Tethyan orogenic belt. The Arabian oceanic plate, a narrow remnant of the Neotethys ocean, is subducting northward beneath the Eurasian plate in Makran. Such a unique tectonic setting makes the MSZ an ideal place to investigate the geodynamic processes in response to subduction-collision transition. Since most of the Neotethys has already dived into the deep mantle and the associated geological records are not always well preserved due to the strong collision, the MSZ also provides a special opportunity to explore the evolution history of the Neotethys in a more direct way.

To better understand the deep dynamics of the subduction-collision transition and evolution of the Neotethys, we investigated the lithospheric structure, especially the depth variation of the lithosphere-asthenosphere boundary (LAB), across the Iranian MSZ by S-wave receiver function (SRF) imaging. The teleseismic data used were acquired from 67 broadband stations that were operational from March 2017 to September 2018 in southeastern Iran. This temporary array constitutes the third phase of seismic observations under the “China-Iran Geological and Geophysical Survey in the Iranian Plateau” project.

Our SRF migration images show clear structural variations of both the upper and lower plates in the MSZ. In the upper plate in the southeastern Iranian plateau, we image a thin lithosphere (70-90 km) with monotonic decrease in LAB depth from the plateau interior to the arc region. This arc-ward thinning is probably caused by the focused thermal and chemical erosion at the LAB by arc magmatism. The LAB of the subducting slab is imaged at ~110-90 km depth near the coast but with an unexpected ~20-km deepening along the trench-parallel direction. Assuming a 25-km-thick accretionary wedge (deduced from active-source data), the observed ~85-65-km-thick slab is consistent with the thermal predictions for a mature oceanic lithosphere. However, the trench-parallel LAB step can hardly be explained by the age difference of the Neotethys but may be a result of the Cretaceous plate-mantle plume interaction. The plume-modified slab could be characterized by low density and high viscosity, and thus play an important role in forming low-angle (<10°) subduction beneath the present-day Makran fore-arc region. Our results also suggest that the thin overriding lithosphere is a persistent feature in both the MSZ and the neighboring continental collision/subduction zone, which favors the idea that the vertical-axis rotation and possible convective thinning dominate the evolution of central-east Iranian microblocks during the late Cenozoic. In addition, we detect an east-dipping structure at 70-90 km depth beneath the Zagros-Makran border, perhaps indicating a relatively sharp contact relationship between the oceanic and continental portions of the Arabian plate. These new observations imply a much more complex tectonic evolution than previously envisaged in the MSZ and adjacent subduction-collision transitional area, which deserves future studies to understand the continuous process from Neotethys subduction to continental collision.

 

How to cite: Wu, Z., Chen, L., Lan, H., Talebian, M., Wang, X., Gao, Y., Zhang, J., Ai, Y., Jiang, M., and Yang, Y.: Seismic imaging of the lithospheric structures in the Iranian Makran subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8253, https://doi.org/10.5194/egusphere-egu23-8253, 2023.

EGU23-8755 | ECS | Posters virtual | GD9.1

Crustal Deformation of Biga Peninsula and Structural Controls on Porphyry Cu-Au and Epitermal Au Mineralization in Kirazlı Gold Deposit (Türkiye) 

Mehmet Çam, İlkay Kuşcu, Nuretdin Kaymakcı, and Mehtap Karcı

Kirazlı porphyry Cu-Au and epitermal Au mineralization is located in Biga peninsula where the region hosts numerious porphyry- and epithermal- style Au mineralizations within the Tethyan orogenic belt. Crustal deformation in the region is resulted by Cretaceous collusion during the closure of northern branch of Neotethys Ocean, related subduction, post-collusion, Cenozoic extension and following dextral strike-slip deformation regime which is emerged during the westward migration of Anatolian plate. The study includes regional fault mapping, slip data collection from regonal and district scale faults for paleostress analysis, oriented surface sampling of vein hosted deformational zones and micro-structural thin section examinations of oriented samples. Paleostress findings and fault orientations indicates two seperate character of deformations as nearly E-W trending extensional fault systems and subsequent NE-SW striking, steeply dipping dextral strike-slip faults with accompanying NNW-SSE trending left-lateral strike slip and ENE-WSW trending dextral strike-slip and oblique-slip faults. Later tectonic phase related with N-E Dextral strike-slip faults establishes the main deformational trend with accompanying district scale  R (synthetic) ENE-WSW trending dextral and NNW-SSE trending R' (antithetic) sinistral strike-slip faults. Slip data related to  E-W and ENE-WSW faults indicate that these faults are subjected to both N-S trending extensional and NE-SW trending dextral strike-slip tectonic regime. The petrographic and textural studies of oriented thin sections resulted in identification of two predominant vein directions as ENE-WSW and NNW-SSE of porphyry mineralization within the project area. ENE-WSW trending syntaxial, streched-blocky quartz bearing veins indicates multiple N-S extension and crack-seal events and postdated by NNW-SSE trending quartz veins. Also the veins with same orientation which were observed during field studies share similar orientations.

This study presents the early results off Ph.D. thesis "Crustal Extension and its Relationship to Porphyry Cu-Au and Epithermal Au Mineralization in the Kirazlı Gold Deposit (Çan, Çanakkale, Türkiye)" and supported by Alamos Gold Inc..

How to cite: Çam, M., Kuşcu, İ., Kaymakcı, N., and Karcı, M.: Crustal Deformation of Biga Peninsula and Structural Controls on Porphyry Cu-Au and Epitermal Au Mineralization in Kirazlı Gold Deposit (Türkiye), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8755, https://doi.org/10.5194/egusphere-egu23-8755, 2023.

EGU23-9971 | Orals | GD9.1 | Highlight

The Pacific basal mantle structure could be older than the African one 

Nicolas Flament, Omer Bodur, Simon Williams, Andrew Merdith, Dietmar Muller, John Cannon, Michael Tetley, Xianzhi Cao, and Sabin Zahirovic

Plate tectonics shapes Earth’s surface and is linked to motions within its deep interior. Cold oceanic lithosphere sinks into the mantle, and hot mantle plumes rise from the deep Earth, leading to volcanism. Volcanic eruptions over the past 320 million years have been linked to two large structures at the base of the mantle presently under Africa and the Pacific Ocean. This has led to the hypothesis that these basal mantle structures could have been stationary over geological time, in contrast to observations and models suggesting that tectonic plates, subduction zones, and mantle plumes have been mobile and that basal mantle structures are presently deforming. Here we reconstruct mantle flow from one billion years ago to the present day to show that the history of volcanism is statistically as consistent with mobile basal mantle structures as with fixed ones. In our reconstructions, cold lithosphere sank deep into the African hemisphere between 740 and 500 million years ago, and from 400 million years ago the structure beneath Africa progressively assembled, pushed by peri-Gondwana slabs, to become a coherent structure as recently as 60 million years ago. In contrast, the structure beneath the Pacific Ocean was established between 400 and 200 million years ago. These results confirm the link between basal mantle structures and surface volcanism, and they suggest that basal mantle structures are mobile, and aggregate and disperse over time, similarly to continents at Earth’s surface. This implies that the present-day shape and location of basal mantle structures may not be a suitable reference frame for the motion of tectonic plates.

How to cite: Flament, N., Bodur, O., Williams, S., Merdith, A., Muller, D., Cannon, J., Tetley, M., Cao, X., and Zahirovic, S.: The Pacific basal mantle structure could be older than the African one, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9971, https://doi.org/10.5194/egusphere-egu23-9971, 2023.

The plate tectonic history of the Pacific Ocean and its predecessor ocean, Panthalassa, are challenging regions on Earth to reconstruct during the Mesozoic-Cenozoic eras. More than 95% of Pacific-Panthalassa crust has been subducted into the Earth’s interior since the Jurassic, and this has created extensive (>9000 km length) plate reconstruction gaps between the Pacific and Eurasia/Laurasia. Here we build four contrasted NW Pacific-Panthalassa global plate reconstructions and assimilate their velocity fields into the global geodynamic models using the code TERRA: Andean-style subduction along East Asia following the corrected ‘R’ Matthews et al. (2016); and, three models that include intra-oceanic subduction within Pacific-Panthalassa with increasing tectonic complexity.   We compare our predicted present mantle structure, synthetic geoid and dynamic topography to Earth observations. P-wave tomographic filtering of predicted mantle structures allows for more explicit comparisons to global tomography.

All three plate reconstructions that include NW Pacific-Panthalassa intra-oceanic subduction fit better to the observed long-wavelength geoid and residual topography.  Correlations between modeled and imaged mantle structure do not systematically favor any single model, and this is attributed to limited tomographic resolution within the central Pacific mantle relative to variability in our modeled mantle structures.  Taken together, our results robustly show the likelihood of intra-oceanic subduction within NW Pacific-Panthalassa.  This presents a challenge to popular plate models of Andean-style subduction along East Asia, which are deeply-embedded into most published plate tectonic, geodynamic and geologic studies.  Our geodynamic models predict significant (>2000 km from Mesozoic to present) southeastwards lateral slab advections within the lower mantle that would confound ‘vertical slab sinking’-style restorations of ancient subduction zones.  Plate reconstructions that can better incorporate intra-oceanic subduction within Pacific-Panthalassa may improve our knowledge of past global CO2, mantle flow, and dynamic topography histories.

How to cite: Wu, J., Lin, Y.-A., and Colli, L.: NW Pacific-Panthalassa intra-oceanic subduction during Mesozoic-Cenozoic times from mantle convection and geoid models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10007, https://doi.org/10.5194/egusphere-egu23-10007, 2023.

EGU23-10233 | ECS | Orals | GD9.1 | Highlight

Strong variability in the thermal structure of Tibetan Lithosphere 

Bing Xia, Irina Artemieva, Hans Thybo, and Simon Klemperer

We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on the new thermal-isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady-state lithosphere thermal regime, and assumes that deviations from crustal Airy-type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200-240 km) with a predicted surface heat flow of 40-50 mW/m2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a ‘North Tibet anomaly’ with thin (<80 km) lithosphere and high surface heat flow (>80-100 mW/m2). We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120-160 km and a surface heat flow of 45-60 mW/m2, with patchy anomalies in eastern Tibet. While different uplift mechanisms for Tibet predict different lithospheric thermal regimes, our results in terms of a highly variable thermal structure beneath Tibet suggest that topographic uplift is caused by an interplay of several mechanisms.

How to cite: Xia, B., Artemieva, I., Thybo, H., and Klemperer, S.: Strong variability in the thermal structure of Tibetan Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10233, https://doi.org/10.5194/egusphere-egu23-10233, 2023.

A range of interpretations of regional geology have led to diverging models describing the elusive predecessor marginal basin to the South China Sea, with significant implications for interpreting regional extrusion tectonics and volcanic episodes. Interpretations contrast between the presence or absence of the Proto South China Sea, while models arguing for a Proto South China Sea also diverge in the geodynamic origin of the marginal sea as either 1) a trapped piece of Cretaceous-age proto Pacific (namely, Izanagi) crust, or 2) sourced from back-arc opening along the east Asian margin.

I will provide a comparison of proposed models for the Proto South China Sea, and I will argue that the existence of a Proto South China Sea, including in the region north of Borneo, is a necessity for reconciling multiple and independent geological and geophysical constraints. First, a back-arc basin along east Asia in the Late Cretaceous helps explain tectonic subsidence curves, the presence of Late Cretaceous ophiolites on Mindoro, and also the abandonment of Andean-style arc volcanism on the South China continental margin. Second, regional basin histories and even the tectonic structure of Luzon Island and northwest Borneo suggest continental or arc fragments from east Asia were accreted in both settings. And finally, the ~50 to 20 Ma subduction-related volcanic history on Borneo, the presence of mapped sutures, evidence of subducted slabs in seismic tomography, requires significant south-dipping subduction of a Proto South China Sea. However, interpretations of a number of features, including the Billiton Depression, the Bentong-Raub Suture, and the West Baram Line on Borneo, and the origin of the Natuna Islands granites continue to provoke continued divergence in models for the region.

I will present an updated plate tectonic reconstruction in GPlates that incorporates recent spatial and temporal constraints, such as the west-east division of Luzon island (South China and Pacific affinity, respectively), and the timing of Proto South China Sea back-arc opening, closure, and accretion events. To test the new model, I show that the model conforms to plate kinematic constraints (such as reasonable convergence rates, and associated arc volcanism). In addition, I present new forward models of mantle flow in CitcomS, and compare the predictions to high-resolution P-wave tomography models (e.g. MIT-P08, UU-P07).

Although more geochronological and geochemical constraints are needed to establish the nature and age of the sutures on northwest Borneo, a clearer tectonic model for this area is essential in guiding mineral exploration – as established models have proposed there has been no subduction in this region since ~100 Ma. The new model presented here argues that subduction ceased much more recently, likely by ~20-15 Ma, coinciding with the arrival of the Dangerous Grounds block in the northern Borneo Trough, choking subduction, triggering the Sabah Orogeny, the eruption of Sintang-area adakites (related to slab break-off), and the abandonment of seafloor spreading in the South China Sea at ~15 Ma. Reconciling these interpretations will improve our understanding of paleogeography, basin evolution, sedimentary provenance, and regional geodynamics.

How to cite: Zahirovic, S.: The geological, tectonic, and geodynamic fingerprint of the elusive Proto South China Sea back-arc basin in northern Borneo, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10720, https://doi.org/10.5194/egusphere-egu23-10720, 2023.

EGU23-10968 | ECS | Orals | GD9.1

Sedimentary Basins of Kazakhstan and Occurrence of Copper and Uranium: A Geological Overview and Tectonic Analysis 

Azam Soltani Dehnavi, Reimar Seltmann, and Fereshteh Shabani

 

Several sedimentary basins (out of 15 basins) in Kazakhstan are characterized by the association of sandstone-type uranium and sedimentary-hosted copper mineralization with oil, gas or coal fields. In central Kazakhstan, the Chu-Sarysu basin (along with Syr-Darya basin), both hosting a multicolored clay–gravel–sandstone sequence, are famous for roll-front type uranium deposits. The Chu-Sarysu basin is also the host of the world-class historical giant deposit of Dzhezkazgan (22 million metric tons) sandstone-hosted copper (by-product of rhenium) as well as smaller deposits of Zhaman-Aibat and the Zhilandy group. The Teniz depression, located in the northern Chu-Sarysu basin, is also prospective for the occurrence of sedimentary copper. Both basins share lithological and structural peculiarities significant to mineralization. The Teniz and Chu-Sarysu basins originated during the development of the Altaid Orogen (Wilhelm, et al., 2012). The Chu-Sarysu and Teniz basins are characterized by a continental-marine-continental depositional cycle from Devonian to Permian. The base of basins includes Early to Middle Devonian intermediate volcanic and volcanoclastic rocks grading upward into Late Devonian red beds (Box et al., 2012; Cossette et al., 2014). The Early Carboniferous is marked by the deposition of lagoonal to marginal-marine salt-bearing strata, which is overlain by Late Carboniferous to Permian alluvial-lacustrine red beds, and a shale-limestone sequence. Both Chu-Sarysu and Teniz basins endured the folding of rocks in the Permian, generating dome-and-basin forms. Both basins are marked by parallel strike-slip lineaments likely related to Permian Kazakhstan oroclinal bending, resulting in a back-arc/rift-graben development. The localization of most of the Cu deposits at the Chu-Sarysu basin is adjacent to the intersection of F2 anticlines (N-NW-trending) with the syn-depositional folding F1 anticlines (E-NE-trending) within the zones of sandstone bleaching. The F1 anticlines locally trapped petroleum fluid deposits. These structures are the pathway of the flow of dense ore brines across the petroleum-bearing anticlines, resulting in ore sulfide deposition via two fluids mixed. Satellite images display the same structural pattern in the Teniz basin, which can assist to narrow down the prospecting regions for copper occurrences. Since the sedimentary-hosted copper systems are complicated in terms of the mineralization events, the comparison of the two basins enables to generate valuable information related to depositional patterns and to guide exploration. Also, non-genetic special relationship between uranium and copper can be postulated.

 

References

Box, S. E., Syusyura, B., Seltmann, R., Creaser, R. A., Dolgopolova, A., & Zientek, M. L., 2012, Dzhezkazgan and associated sandstone copper deposits of the Chu-Sarysu Basin, Central Kazakhstan. Econ. Geol. Sp. Publ, 16, p. 303-328.

 

Cossette, P.M., Bookstrom, A.A., Hayes, T.S., Robinson, G.R., Jr., Wallis, J.C., and Zientek, M.L., 2014, Sandstone copper assessment of the Teniz Basin, Kazakhstan: U.S. Geological Survey Scientific Investigations Report 2010–5090–R, 42 p.

 

Wilhem, Caroline, Windley, B.F., and Stampfli, G.M., 2012, The Altaids of Central Asia—A tectonic and evolutionary innovative review: Earth-Science Reviews, v. 113, p. 303– 341.

How to cite: Soltani Dehnavi, A., Seltmann, R., and Shabani, F.: Sedimentary Basins of Kazakhstan and Occurrence of Copper and Uranium: A Geological Overview and Tectonic Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10968, https://doi.org/10.5194/egusphere-egu23-10968, 2023.

EGU23-11327 | ECS | Orals | GD9.1

Paleoelevation Reconstruction of Subduction Zones in Eastern Pacific Continental Margins Quantitatively with Igneous Geochemistry 

Bingxi Liu, Simon Williams, Guochun Zhao, Shan Yu, and Dongchuan Jian

Reconstructing past episodes of mountain building from the geological rock record is one of the main challenges for unravelling the ancient physical geography of Earth’s surface. Mountains and mountain ranges, often situated at convergent plate margins, play a pivotal role in many fields of the Earth, climate, and biological sciences. Established methods for quantifying past elevations traditionally relied on sedimentary rocks, but in recent years, alternative approaches have emerged on the basis that geochemical signatures of magmatic rocks formed in convergent settings correlate with crustal thickness or elevation. These correlations allow for empirical relations of igneous whole-rock ratios such as La/Yb and Sr/Y with Moho depth for modern convergent settings, which can then be used to estimate ancient crustal thickness or paleoelevation. Since a relatively large number of igneous samples are available for pre-Cenozoic times compared to other paleoelevation proxies, these methods have the potential to allow quantitative mapping of past topographic change for times where existing maps are largely based on a qualitative approach.

Here, we investigate the application of paleoelevation estimates derived from geochemistry using the Pacific margin of South America as a case study. We investigate their consistency with independent indicators of past elevations such as stratigraphy, stable isotopes, fossils etc. for Cenozoic samples along the Andean margin. For older times, we compare the estimated paleoelevations with other aspects of the geological record, as well as equivalent values from global paleogeography models widely used in climate modelling studies, to evaluate the extent to which these models are consistent with the igneous geochemical proxies. We derive paleoelevation estimates according to different data filtering schemes, showing that a major consequence of the choice of geochemistry filter is the number of data points left after the filtering. We find that the igneous geochemical proxies yield elevations broadly consistent with traditional results for the Cenozoic, though our results do not resolve some of the rapid uplifts recorded by other proxies. In deeper time, we show that igneous geochemistry quantifies changes in elevation related to documented phases of crustal thickening and thinning, and is thus likely to allow improvements to existing maps of paleotopography. 

How to cite: Liu, B., Williams, S., Zhao, G., Yu, S., and Jian, D.: Paleoelevation Reconstruction of Subduction Zones in Eastern Pacific Continental Margins Quantitatively with Igneous Geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11327, https://doi.org/10.5194/egusphere-egu23-11327, 2023.

EGU23-12290 | Orals | GD9.1

Lithium pegmatites of the Kalba-Narym Belt, East Kazakhstan: Geological overview 

Gleb Smirnov, Reimar Seltmann, and Azam Soltani Dehnavi

The Kalba-Narym Belt is part of the Central Asian Orogenic Belt (CAOB) and formed due to the
continental collision between Kazakhstan and Siberian plates in the Late Paleozoic. Several
plutons comprising the Kalba-Narym granitic batholith are considered post-orogenic. The
commonly accepted theory claims that these intrusive bodies might have been formed due to
the far-spreading influence of the Tarim mantle plume (Khromykh et al., 2019). However, the
volcanic facies, that are normally associated with plume-related activities are present only
sporadically in the Kalba-Narym area, which may imply that the heat source is plume-unrelated
and instead linked to mafic underplating and uplift processes of the crust. Amongst the variable
intrusive rocks formed in this region, highly-fractionated pegmatites are particularly important
but nevertheless remain poorly understood with origin controversially discussed. The
mineralized pegmatites are associated with Phase 1 granites of the Kalba complex, with a
40Ar/ 39Ar age of 297 to 290 Ma (Kotler et al., 2021). The formation of pegmatites, driven either
by the differentiation of granitic melts or by anatectic melting processes, was likely
supplemented by the inputs of volatiles and rare metals with fluids. The rocks of the best-
known pegmatite occurrences located near Asubulak village, such as Yubileynoye and Krasny
Kordon deposits, can be categorized as LCT pegmatites, including three main zones based on
mineralogical and geochemical assemblages of a) microcline-albite with pollucite and petalite
(Ta, Cs, Be, Sn), b) microcline-albite with spodumene (Ta, Nb, Cs, Li, Be, Sn), and c) spodumene-
albite (Li, Ta, Nb, Sn) (D'yachkov et al., 2021).
Apart from the mineralized pegmatites, there are known occurrences of barren pegmatites,
which creates an opportunity for comparison with the mineralized pegmatites specifically via
contrasting geochemical signatures. Aiming at a proper understanding of the pegmatite
genesis, mineralization mechanisms and geochemical approach on a bigger regional scale of the
Greater Altai may open up unique perspectives for the future exploration of the region.
Therefore, this presentation provides an overview and re-evaluation of the detailed geological
characteristics of the Kalba-Narym Belt, continuous into Chinese Altai, and the processes
involved in rare-metal pegmatite mineralization.

References:
D'yachkov, B. A., Bissatova, A. Y., Mizernaya, M. A., Zimanovskaya, N. A., Oitseva, T. A.,
Amralinova, B. B., Aitbayeva, S. S., Kuzmina, O. N., &amp; Orazbekova, G. B. (2021). Specific
Features of Geotectonic Development and Ore Potential in Southern Altai (Eastern
Kazakhstan). Geology of Ore Deposits, 63(5), 383–408.
https://doi.org/10.1134/s1075701521050020


Khromykh, S. V., Oitseva, T. A., Kotler, P. D., D’yachkov, B. A., Smirnov, S. Z., Travin, A. V.,
Vladimirov, A. G., Sokolova, E. N., Kuzmina, O. N., Mizernaya, M. A., &amp; Agaliyeva, B. B.
(2020). Rare-metal Pegmatite Deposits of the Kalba Region, Eastern Kazakhstan: Age,
Composition and Petrogenetic Implications. Minerals, 10(11), 1017.
https://doi.org/10.3390/min10111017

Kotler, P., Khromykh, S., Kruk, N., Sun, M., Li, P., Khubanov, V., Semenova, D., &amp; Vladimirov, A.
(2021). Granitoids of the Kalba Batholith, Eastern Kazakhstan: U–PB Zircon Age,
Petrogenesis and Tectonic Implications. Lithos, 388-389, 106056.
https://doi.org/10.1016/j.lithos.2021.106056

How to cite: Smirnov, G., Seltmann, R., and Soltani Dehnavi, A.: Lithium pegmatites of the Kalba-Narym Belt, East Kazakhstan: Geological overview, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12290, https://doi.org/10.5194/egusphere-egu23-12290, 2023.

EGU23-12729 | ECS | Orals | GD9.1

Detection and (re)location of earthquakes using Jammu And Kashmir Seismological NETwork 

Sk Shamim, Ayon Ghosh, Supriyo Mitra, Keith Priestley, and Sunil Kumar Wanchoo

Broadband waveform data from the recently established Jammu And Kashmir Seismological NETwork (JAKSNET) has been used to detect and locate earthquakes in the Jammu and Kashmir (J&K) Himalaya. Continuous data recorded by the network between 2015 and 2018 has been used for the analysis. The Coalescence Microseismic Mapping (CMM) algorithm is used to detect and locate hundreds of earthquakes, not reported in regional and global catalogs. These earthquakes are then relocated using a probabilistic relocation method of NonLinLoc (NLL). This produced a subset of earthquakes within 200 km of the network and having spatial uncertainty of less than 10 km. Most of the earthquakes are located beneath the Lesser and Higher Himalaya, with depth less than 25 km. A few earthquakes have depths between 30-60 km and lie across the entire region. The shallow earthquakes occur within the Himalayan wedge and define the locked-to-creep transition (unlocking) zone on the Main Himalayan Thrust. These earthquakes occur in clusters in the Jammu-Kishtwar segment, immediately south of the Kishtwar window, beneath the Kashmir Valley and in the NW Syntaxis, surrounding the 2005 (Mw 7.6) Kashmir earthquake source zone. These events provide the first evidence of the MHT locked segment beneath J&K Himalaya. The deeper events are within the underthrusting Indian crust, which reveal that the entire Indian crust is seismogenic. Double-difference algorithm is being used to improve the relative location of the shallow events to study possible clustering of earthquakes in the MHT.  

How to cite: Shamim, S., Ghosh, A., Mitra, S., Priestley, K., and Wanchoo, S. K.: Detection and (re)location of earthquakes using Jammu And Kashmir Seismological NETwork, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12729, https://doi.org/10.5194/egusphere-egu23-12729, 2023.

EGU23-13519 | ECS | Posters on site | GD9.1

Effects of strain- vs. strain-rate-dependent faults weakening for continental corner collision: insight from 3D thermomechanical models 

Luuk van Agtmaal, Attila Balazs, Dave May, and Taras Gerya

Geological and geophysical observations have highlighted the multi-stage deformation history of the continental lithosphere. Such inherited heterogeneities, observed from microscopic to kilometre-scales, lead to important mechanical weakening for the subsequent development of orogens. This strain-weakening may be frictional (fault gauge, filled veins), ductile (banding, recrystallisation, etc) or caused by changes in grain-size, and largely determines the response of the lithosphere to stresses (Bercovici & Ricard, 2014). Representing the microstructural weakening mechanisms with the relatively low resolution of regional and global numerical modelling studies has been a longstanding challenge. Mechanisms are often grouped into an “effective” plastic strain weakening implementation, where the frictional strength decreases with increasing accumulated strain. Alternatively, materials can be modelled to weaken depending on the local strain-rate (Ruh et al., 2014), which is characteristic for e.g. coseismic frictional weakening of faults. Here we show key differences of strain- vs. strain-rate-dependent faults weakening in terms of orogenic strain propagation patterns in numerical models of a corner collision setting, based on the eastern corner of the India-Eurasia collision. The numerical model I3ELVIS (Gerya & Yuen, 2007) consists of a finite-difference, marker-in-cell method coupled to a diffusion-advection-based finite-difference surface process model, FDSPM (Munch et al., 2022). We highlight key differences between the results of a model with strain-rate-dependent weakening, and a model with conventional strain-dependent weakening based on accumulated strain. The former shows significantly sharper shear zones, as well as a higher number of thrust faults that are relatively evenly spaced, which is more realistic in natural collision zones. 

 

Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1), 83–105. https://doi.org/10.1016/j.pepi.2007.04.015

Bercovici, D., & Ricard, Y. (2014). Plate tectonics, damage and inheritance. Nature, 508(7497), 513–516. https://doi.org/10.1038/nature13072

Ruh, J. B., Gerya, T., & Burg, J.-P. (2014). 3D effects of strain vs. Velocity weakening on deformation patterns in accretionary wedges. Tectonophysics, 615–616, 122–141. https://doi.org/10.1016/j.tecto.2014.01.003

Munch, J., Ueda, K., Schnydrig, S., May, D. A., & Gerya, T. V. (2022). Contrasting influence of sediments vs surface processes on retreating subduction zones dynamics. Tectonophysics, 836, 229410. https://doi.org/10.1016/j.tecto.2022.229410

 

How to cite: van Agtmaal, L., Balazs, A., May, D., and Gerya, T.: Effects of strain- vs. strain-rate-dependent faults weakening for continental corner collision: insight from 3D thermomechanical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13519, https://doi.org/10.5194/egusphere-egu23-13519, 2023.

EGU23-13642 | ECS | Orals | GD9.1 | Highlight

The Dynamics of the India-Eurasia Collision: A Suite of Faulted Viscous Continuum Models Constrained by New High-Resolution Sentinel-1 InSAR and GNSS Velocities 

Jin Fang, Greg Houseman, Tim Wright, Lynn Evans, Tim Craig, John Elliott, and Andy Hooper

Block versus continuum description of lithospheric deformation in the India-Eurasia collision zone has been hotly debated over many decades. Here we apply the adapted two-dimensional (2-D) Thin Viscous Shell (TVS) approach explicitly accounting for displacement on major faults in Tibet (Altyn Tagh, Haiyuan, Kunlun, Xianshuihe, Sagaing, and Main Pamir Thrust Faults) and investigate the impact of lateral variations in depth-averaged lithospheric strength. We present a suite of dynamic models to explain the key observations from new high-resolution Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) as well as Global Navigation Satellite System (GNSS) velocities. Comparisons between calculated and observed velocity and strain rate fields indicate: (a) internal buoyancy forces from Gravitational Potential Energy (GPE) acting on a relatively weak region of high topography (~2,000 m) contribute to dilatation of high plateau and contraction on the margins; (b) a weak central Tibet (~1021 Pa s relative to far-field depth-averaged effective viscosity of 1022 to 1023 Pa s) yields the observed long-wavelength eastward velocity variation away from major faults; (c) slip resistance on faults produces strain localization and clockwise rotation around the Eastern Himalayan Syntaxis (EHS). We discuss the tectonic implications for rheology of the lithosphere, distribution of geodetic strain, and partitioning of active faulting and seismicity in light of our best-fit geodynamic solutions.

How to cite: Fang, J., Houseman, G., Wright, T., Evans, L., Craig, T., Elliott, J., and Hooper, A.: The Dynamics of the India-Eurasia Collision: A Suite of Faulted Viscous Continuum Models Constrained by New High-Resolution Sentinel-1 InSAR and GNSS Velocities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13642, https://doi.org/10.5194/egusphere-egu23-13642, 2023.

EGU23-14244 | ECS | Posters virtual | GD9.1

The birth of the Mesotethys ocean recorded in the Southern Pamir Triassic basalts  

Jovid Aminov, Denis Mikhailenko, Sharifjon Odinaev, Mohssen Moazzen, Guillaume Dupont-Nivet, Yunus Mamadjanov, Aleksandr Stepanov, Jovid Yogibekov, and Sohibnazar Ashuraliev

The Pamir orogen, the western extension of the Tibetan plateau, formed and uplifted due to Mesozoic terrane amalgamation and Cenozoic India-Asia collision. The Mesozoic history of the amalgamation of Gondwana-derived Cimmerian terranes to the southern margin of Eurasia that produced the crust of the Pamirs is poorly understood. The birth and demise of an oceanic basin that divided Central and Southern Pamir in the early Mesozoic is an example of a gap in the knowledge of Pamir orogen formation throughout the Mesozoic and Cenozoic eras. Termed Mesotethys, this ocean likely originated in the early Permian when the Cimmerian super-terrane broke from Gondwana's northern limit. Geochemistry of early Permian basalts suggests this rifting event was driven by a plume that generated a seamount or series of seamounts that accreted to the Central Pamir before the Mesotethys closed in the late Triassic. Vestiges of the Mesotethys are preserved in the Rushan - Pshart suture zone.   This zone comprises Permian and Triassic marine sedimentary strata and thick layers of volcanic rocks, including the late Triassic basalts. This volcano-sedimentary sequence is intruded by the late Triassic – early Jurassic granites that have subduction-related affinity marking the closure of the Mesotethys. The current work focuses on the geochemical markers of late Triassic volcanism to evaluate whether a plume-related magmatic activity was responsible for the creation of the Mesotethys Ocean.

Our preliminary geochemical results indicate that the SiO2 content of basalts is low, ranging from 36.5 to 47.7 wt.%, which classifies the rocks as mafic and ultramafic. The rocks' TiO2 concentration is exceptionally high, ranging from 1.9 to 4.4 wt.%, which is not typical of arc-related basalts and instead resembles oceanic island basalts. Concentration of Al2O3 (7.5-18.8 wt.%), Fe2O3 (8.3-16.3 wt.%), MgO (2.7 – 14.9 wt.%) and CaO (2.5 – 12.4 wt.%) likewise fluctuate in a large range. Alkalis also vary across a wide range (K2O: 0.2 – 3.1 wt.%; Na2O: 1.4 – 5.5 wt.%) and add up to values (1.7 – 7 wt.%) that define the majority of the examined samples (11) as alkali basalts, with three samples plotting below the sub-alkaline – alkaline dividing line. The rocks' relatively high P2O5 (0.2 to 0.6 wt.%) may further reflect their OIB affinity. Normalized to the primitive mantle, trace element patterns on spidergrams reveal a small enrichment of Large-Ion Lithophile Elements and depletion of High-Field Strength Elements. However, positive anomalies in Nb (14.3 – 29 ppm) and Ti rule out subduction as the cause of the rocks' formation. Moreover, high ratios of Nb/La (1.1–1.7) and La/Yb (6.9–15) also support the non-subductional origin of the basalts. Thus, our collected geochemical data reveal a striking similarity to the basalts of oceanic islands.

 

How to cite: Aminov, J., Mikhailenko, D., Odinaev, S., Moazzen, M., Dupont-Nivet, G., Mamadjanov, Y., Stepanov, A., Yogibekov, J., and Ashuraliev, S.: The birth of the Mesotethys ocean recorded in the Southern Pamir Triassic basalts , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14244, https://doi.org/10.5194/egusphere-egu23-14244, 2023.

EGU23-14296 | ECS | Orals | GD9.1

The devastating 2022 M6.2 Afghanistan earthquake: challenges, processes and implications 

Sofia-Katerina Kufner, Lidong Bie, Ya-Jian Gao, Mike Lindner, Hamidullah Waizy, Najibullah Kakar, and Andreas Rietbrock

On June 21th, a Mw6.2 earthquake struck the Afghan-Pakistan-border-region, an area dominated by partitioned deformation related to the India-Asia collision. Despite its moderate size, 1150 deaths were reported, making the event the deadliest earthquake of 2022 so far. We investigate the event’s rupture processes, aiming to understand what made it that fatal. Our InSAR-constrained slip model and regional moment-tensor inversion reveal a sinistral rupture with maximum slip of 1.8 m at 5 km depth on a N20°E striking, sub-vertical fault. Field observations confirm fault location and slip-sense. Based on our analysis and a global comparison, we suggest that not only external factors (e.g. time of the event and building stock) but also fault-specific factors made the event excessively destructive. Surface rupture was favored by the local rock anisotropy (foliation), coinciding with the fault strike. The distribution of Peak Ground Velocity was governed by the sub-vertical fault. The maximum slip was large compared to other events globally and might have resulted in peak-frequencies coinciding with the resonance-frequency of the local one-story buildings. More generally, our study demonstrates the devastating impact of moderate earthquakes, being small enough to be accommodated by many tectonic structures but large enough to cause significant damage.

How to cite: Kufner, S.-K., Bie, L., Gao, Y.-J., Lindner, M., Waizy, H., Kakar, N., and Rietbrock, A.: The devastating 2022 M6.2 Afghanistan earthquake: challenges, processes and implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14296, https://doi.org/10.5194/egusphere-egu23-14296, 2023.

EGU23-14406 | Posters on site | GD9.1

Kinematics of the Pamir orogeny on a lithospheric scale 

Jonas Kley, Edward R. Sobel, Thomas Voigt, Johannes Rembe, and Rasmus Thiede

The south-dipping Benioff zone beneath the Pamir mountains marks the youngest, active slab accommodating India-Asia convergence near the western edge of the Indian indenter (75° E). Seismic tomography suggests the existence of two older slabs farther south, both interpreted as Indian lithosphere detached and sinking: the Tethys slab, broken off around 46 Ma concomitant with early collision and the more northerly and shallower Indian slab, detached around 25 Ma at the longitude considered here (Replumaz et al. 2010). The total length of the three slabs is about 1300 km (Tethys 600 km, India 300 km, Pamir 400 km), substantially less than the distance of more than 2000 km that India has moved north since 46 Ma. This discrepancy implies that either the tomographic record of subduction is incomplete or that Indian mantle lithosphere has underthrust (thin?) Asian lithosphere, with the stacked lithospheres unresolvable by tomography. As a consequence, the rate of slab lengthening and the age of slab initiation in the Pamir are poorly constrained. The absence of asthenosphere between the Pamir slab of Asian provenance and supposedly Indian mantle lithosphere above it suggests that India´s leading edge is advancing at the same rate as rollback of the Pamir slab. This rate could be as high as full India-Asia convergence at ca. 35 mm/yr (Kufner et al. 2016) or as low as present-day Pamir-foreland convergence at 15 mm/yr, corresponding to ages of the 300-400 km long slab of 9-12 Ma or 20-27 Ma. The wide range of possible ages makes it difficult to tie slab initiation to specific geologic events during the Pamir orogeny. Other evidence suggests that the direction and rate of India-Asia convergence may be poor predictors of mantle lithospheric motion above the slab: The shortening direction in the Tajik foreland thrust belt is WNW, and foreland shortening decreases northeastward from a maximum of 150 km in the Tajik belt to 75 and 30 km in the Alai Valley and westernmost Tarim. Slab length follows a similar trend, with a steeply east-dipping Benioff zone in the west and a more gently south-dipping one in the north, traced by earthquakes to depths of 250 km and 150 km, respectively. Also, the longest, NE-striking segment of the slab is relatively straight in map view and parallel to the axis of thickest crust (Schneider et al. 2019). These observations are difficult to reconcile with northward convergence. Instead, they suggest overall northwestward convergence during the Pamir orogeny. We speculate that this could be due to westward deflection at depth of an Indian lithosphere promontory interacting with the NW-trending edge of thick Tarim lithosphere.

Kufner, S.-K., et al. (2016). Deep India meets deep Asia: Lithospheric indentation, delamination and break-off under Pamir and Hindu Kush (Central Asia). Earth and Planetary Science Letters 435: 171-184.

Replumaz, A., et al. (2010). Indian continental subduction and slab break-off during Tertiary collision. Terra Nova 22: 290-296.

Schneider, F. M., et al. (2019). The Crust in the Pamir: Insights from Receiver Functions. Journal of Geophysical Research: Solid Earth 124(8): 9313-9331.

How to cite: Kley, J., Sobel, E. R., Voigt, T., Rembe, J., and Thiede, R.: Kinematics of the Pamir orogeny on a lithospheric scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14406, https://doi.org/10.5194/egusphere-egu23-14406, 2023.

EGU23-14762 | ECS | Posters virtual | GD9.1

Understanding Magma Nature of Post-Collisional Alkaline Granites Around Uludag (NW, Turkiye): Implications for New Geodynamic Scenarios 

Huseyin Kocaturk, Mustafa Kumral, Ali Tugcan Unluer, Mustafa Kaya, Merve Sutcu, Zeynep Doner, Huseyin Sendir, and Amr Abdelnasser

Magmatic Suite around Uludag Massif contains some alkaline (A-type or highly fractionated felsic I-type) granites that developed in post-collisional plate tectonic conditions. Their genesis involved by Eocene calc-alkaline and Oligocene strongly peraluminous granite magmatism. Their emplacement is linked to strike-slip shear movements and/or extension that occur after the Neo-Tethys collisional events. These granites are spatially related to the Izmir-Ankara Suture Zone (IASZ). The majority of these alkaline granites are formed by middle or lower crustal anatexis, extracted melt restite of I-type granites. Previously non-melted mafic meta-tonalites are considered to represent their source rocks. The mechanism for the required high melting temperatures will be well explained by our new model. However, models based on partial delamination of the base of the lithosphere or asthenospheric upwelling due to steepening and breaking of the subducted Tethyan oceanic slab are still consistent. As is the case for many well-known post-collisional regimes, transpressional to transtensional and/or moderately extensional tectonism predominates throughout to region. Although crustal thickening does not appear evident as in the notable arcs and microcontinent collisions, uplifting of particular regions associated with post-collisional calc-alkaline granite emplacement is observable. Understanding the nature of post-collisional highly fractionated granites around Uludag will extend the view of how Western Anatolia was affected by Alpine Orogeny in the Tethyan Realm. The challenge is drawing the geochemistry line for the tectono-magmatic setting between post-collision to post-orogenic. Describing the nature of alkaline magmatism through late-stage orogeny to intra-plate setting may need to be more precise because of trace elements' overprinting. However, a holistic view of the magmatism and source rocks points out a synchronous crustal growth and crustal rework. Our new possible geodynamic scenario suggests crust–mantle decoupling combined with slab retreat results in thinning of the lithospheric mantle. The 75-80 km decoupling depth calculated from obducted blueschists of Tavsanlı Zone confirms the plate motions controlled thermal relaxation temperature is enough at the base of the lithosphere for the geotherm-induced magma generation for the Tavsanlı Zone.

How to cite: Kocaturk, H., Kumral, M., Unluer, A. T., Kaya, M., Sutcu, M., Doner, Z., Sendir, H., and Abdelnasser, A.: Understanding Magma Nature of Post-Collisional Alkaline Granites Around Uludag (NW, Turkiye): Implications for New Geodynamic Scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14762, https://doi.org/10.5194/egusphere-egu23-14762, 2023.

Gneiss dome records the deformation and tectonothermal evolution of orogenic belt and lithosphere, which provides a perfect window for studying of collisional orogenic process and tectonic evolution. The North Himalayan Gneiss Domes, trending East-West, as one of the important tectonic units of the Himalayan orogen, experienced deep materials uplifting and lateral flow. Based on the above observations, we suggest that the RBD experienced 4 periods of tectonothermal evolutions (D1-D4) and 2 stages of tectonic background transformations. (1) D1: Crustal thickening, regional metamorphism and anatexis occurred during plate collision in the Eocene (46.3-40.6 Ma). (2) D2: Partial melting of middle-lower crust result in the development of channel flow which reduced the rheology of the middle-lower crust and led to the onset of the STDS and crustal thinning in the early Miocene (26.1-21.0 Ma). Therefore, the tectonic background transformed from N-S compression to N-S extension (the first tectonic background transformation). (3) D3: The ongoing of the STDS contribute to the decompression melting, small-scale diapirism and accompanied magmatic emplacement. The activity of the NSTRs started at mid-Miocene (12.0-10.2 Ma), the tectonic background shifted from N-S extension to E-W extension (the second tectonic background transformation). (4) D4: +With NSTRs’ activity peaking in the late Miocene (8.7-7.6 Ma), further crustal thinning, decompression melting and leucogranite intrusion occurred under extensional condition, which result in the contact metamorphism, and established the final tectonic framework, geometry, and thermalstructure of the RBD. The tectonothermal evolution of the RBD supports the middle-lower crustal channel flow orogenic model.

Fluid inclusion and oxygen isotope data for quartz veins in the Ramba Dome in the North Himalayan Gneiss Domes show limited variations in individual quartz veins, but δ18Oquartz values vary from 12.07 to 18.16‰ (V-SMOW) among veins. The corresponding δ18Ofluid values range from 7.71 to 13.80‰, based on equilibrium temperatures obtained from fluid inclusions. From the footwall to the detachment zone, δ18Ofluid values exhibit a broadly decreasing trend and indicate that the STDS dominated the fluid flux pathway in the crust, with more contributions of meteoric water in the detachment zone. We further quantified the contribution of meteoric fluids to 8–27% using a binary end-member mixing model. These data imply that the fluids were predominantly metamorphic/ magmatic in origin, and were mixed with infiltrating, isotopically light, meteoric water during extensional detachment shearing of the STDS. Based on the above research, we propose that metamorphic dehydration of lower crust and atmospheric precipitation "stimulate" new activity of Himalayan mountain building.

How to cite: Bo, Z.: The multistage extensional structure and excitation mechanism of Himalayan orogeny, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15394, https://doi.org/10.5194/egusphere-egu23-15394, 2023.

EGU23-16615 | Orals | GD9.1

Crustal Structure of the Jammu and Kashmir Himalaya 

Supriyo Mitra, Swati Sharma, Debarchan Powali, Keith Priestley, and Sunil Wanchoo

We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya, to model the seismic velocity structures of the crust and uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across major Himalayan thrust systems and litho-tectonic units. We perform depth–Vp /Vs (H-K) stacking of P-RF, common conversion point (CCP) stacking along 2D profiles and joint inversion with surface wave dispersion data. H-K analysis reveals increasing average crustal thickness from the foreland (∼40 km) to the hinterland (∼65 km), with felsic- to-intermediate (Vp /Vs of 1.71–1.80) average crustal composition. In CCPs the Indian crust Moho is marked by a large positive impedance contrast boundary, and the Main Himalayan Thrust (MHT) by a negative phase, indicating a low velocity layer (LVL). The underthrust Indian crust (between the MHT and Moho) has an average thickness of ∼40 km and the Moho dips northward at ∼7–9◦ . Moho flexure (or possible off-set) are observed in across-arc profiles, beneath the Shiwalik Himalaya, Higher Himalaya and the Kishtwar window. The Moho is remarkably flat at ∼55 km beneath the Pir Panjal Ranges and the Kashmir Valley. North of the Kishtwar window (E) and Kashmir Valley (W) the Moho dips steeply underneath the Tethyan Himalaya/Zanskar Ranges from ∼55 km to ∼65 km. The MHT LVL is at a depth of ∼8 km beneath the Shiwalik Himalaya, and dips gradually northeast at ∼7–9◦ , to reach a depth of ∼25 km beneath the Higher Himalaya. The MHT is marked by a frontal ramp beneath the Kishtwar window (E) and north of the Kashmir Valley (W). The MKT, MBT and MCT are marked by LVLs which splay updip from the MHT. To study the 3D variation of the crustal structure, we grid the region into 0.1◦ square grids and jointly model the P-RFs within each grid with Rayleigh wave dispersion data, obtained from regional tomography. The 3D models obtained from this analysis provide variations in Vs and Moho depth. The Kashmir Valley and Zanskar Ranges are underlain by the highest average crustal Vs followed by the Pir-Panjal Ranges. These are also regions of the thickest crust. The Shiwalik Himalaya is underlain by the slowest average Vs , with lateral variations along the MKT, Reasi Thrust and the Kotli Thrust. These are also regions of thinnest crust (~40 km). A remarkable lower Vs region extends SW-NE from Jammu to the Kishtwar window, along the reentrants of the MHT, MBT and MCT. This marks a strong E-W lateral variation in crustal Vs , Moho depth and a possible lateral ramp on the MHT, also highlighted by small-to-moderate earthquake clusters.

How to cite: Mitra, S., Sharma, S., Powali, D., Priestley, K., and Wanchoo, S.: Crustal Structure of the Jammu and Kashmir Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16615, https://doi.org/10.5194/egusphere-egu23-16615, 2023.

EGU23-17000 | Posters virtual | GD9.1

Paleo-Tethyan ocean evolution in the East Kunlun Orogen, northern Tibetan plateau 

Ruibao Li, Xianzhi Pei, Zuochen Li, Lei Pei, Guochao Chen, Zhanqing Liu, Youxin Chen, Chengjun Liu, and Meng Wang

The East Kunlun Orogen on the northern margin of the Tethyan orogenic system records a history of Gondwana dispersal and Laurasian accretion. Based on a synthesis of sedimentary, structural, lithological, geochemical, and geochronological data from the East Kunlun Orogen and adjacent regions, we discusses the spreading and northward consumption of the Paleo-Tethys Ocean during Late Paleozoic-Early Mesozoic times. The main evolutionary stages are: (1) During Carboniferous to Middle Permian, the Paleo-Tethys Ocean (Buqingshan Ocean) was in an ocean spreading stage, as suggested by the occurrence of Carboniferous MORB-, and OIB-type oceanic units and Carboniferous to Middle Permian Passive continental margin deposits; (2) The Buqingshan Ocean subducted northward beneath the East Kunlun Terrane, leading to the development of a large continental magmatic arc (Burhan Budai arc) and forearc basin between ~270-240 Ma; (3) During the late Middle Triassic to early Late Triassic (ca. 240-230 Ma), the Qiangtang terrane collided with the East Kunlun-Qaidam terranes, leading to the final closure of the Buqingshan Ocean and occurrences of minor collision-type magmatism and potentially inception of the Bayan Har foreland basin; (4) Finally, the East Kunlun Orogen evolved into a postcollisional stage and produced major magmatic flare-ups and polymetallic mineral deposits between Late Triassic to Early Jurassic (ca. 230-200 Ma), which is possibly related to asthenospheric mantle upwelling induced by delamination of thickened continental lithosphere and partial melting of the lower crust. Accordingly, we propose that the Wilson cycle-like processes controlled the Late Paleozoic-Early Triassic tectonic evolution of East Kunlun, which provides significant implications for the evolution of Paleo-Tethys Ocean.

How to cite: Li, R., Pei, X., Li, Z., Pei, L., Chen, G., Liu, Z., Chen, Y., Liu, C., and Wang, M.: Paleo-Tethyan ocean evolution in the East Kunlun Orogen, northern Tibetan plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17000, https://doi.org/10.5194/egusphere-egu23-17000, 2023.

EGU23-17021 | ECS | Orals | GD9.1

Rheological heterogeneities control the non-progressive uplift of the young Iranian plateau 

Yifan Gao, Ling Chen, Jianfeng Yang, and Kun Wang

The Iranian plateau is at the early stage of plateau development and intracontinental deformation in response to the Arabia-Eurasia collision. Its compressive deformation is concentrated in the northern plateau but skips the central counterpart, challenging the common views envisaging the progressive uplift from the collisional front to the hinterland. Based on three-dimensional, crustal-scale numerical models, we present how the rheological heterogeneities common in continents control the deformation of the young Iranian plateau. The weak northern plateau ensures itself a preferential zone in accommodating continental collision. The N-S strike-slip faults within the non-rigid central plateau, formed along the boundaries between the tectonic units with rheological contrast, suppress the shortening of the central plateau while further accentuating the compressive deformation of the northern plateau. Our results suggest a non-progressive intracontinental deformation pattern where rheological boundaries and mechanically weak zones, not necessarily those close to collisional fronts, preferentially accommodate continental convergence.

How to cite: Gao, Y., Chen, L., Yang, J., and Wang, K.: Rheological heterogeneities control the non-progressive uplift of the young Iranian plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17021, https://doi.org/10.5194/egusphere-egu23-17021, 2023.

EGU23-17123 | Orals | GD9.1 | Highlight

The Nature of the Cimmerian Continent 

A.M. Celâl Şengör, Demir Altıner, Cengiz Zabcı, Gürsel Sunal, Nalan Lom, and Tayfun Öner

We have compiled local stratigraphic, structural, palaeobiogeographical and reliable isotopic age data from the remnants of the Cimmerian Continent from western Turkey to Malaysia with a view to understanding its nature and evolution. Our principal conclusions are the following:

1) The entire northwestern margin of Gondwana-Land was an extensional Pacific-type continental margin much like the present-day western Pacific during the Permo-Carboniferous characterised by typical Gondwana-Land biotas.

2) Beginning with the Permian, the Cimmerian Continent began to pull away from the northeastern margin of Gondwana-Land from Turkey in the west to Malaysia in the east, although in Thailand and Malaysia rifting may have started already during the earlierst Carboniferous.

3) Synchronously with this rifting, the Wašer/Rushan-Pshart/ Banggong Co-Nu Jiang ocean, herein called the Maera, began opening in the Permian isolating the Lhasa/Victoria Land block from the rest of the Cimmerian Continent. In fact, the Himalayan sector of the Neo-Tethys may have opened slightly later than the Maeran ocean.

4) Central Iran consisted of two parts: the northest Iranian extensional area and the multi-block Central Iranian Continent consisting of the Yazd, Posht-e Badam, Tabas and the Lut blocks. These blocks were stacked against one another horizontally as a consequence of the Cimmeride collisions in the Pamirs and Afghanistan while Albors was rifted away from the Sanandaj-Sirjan zone, as the latter was also rifting away from Gondwana-Land, stretching northwestern Iran into its present-day triangular shape.

5) Significant arc magmatism characterised the entire Cimmerian continent from one end to the other during the Permian to the Liassic interval.

We thus maintain that the Cimmerian Continent was the site of supra-subduction extension throughout its history until it collided with Laurasia during the medial to late Jurassic. In some areas the collision may have been earlier. The Maeran ocean remained opened until the Aptian. The best analogue for the evolution of the Cimmerian Continent and its attendant small oceans is the present-day southwest Pacific arc/marginal basin systems from the Tonga-Kermadec system in the east as far west as Australia.

How to cite: Şengör, A. M. C., Altıner, D., Zabcı, C., Sunal, G., Lom, N., and Öner, T.: The Nature of the Cimmerian Continent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17123, https://doi.org/10.5194/egusphere-egu23-17123, 2023.

EGU23-17600 | ECS | Orals | SM1.6

Permanent Displacement Distribution From Strong Ground Motion Records of the 2023 Mw7.7 Earthquake. 

Emrecan Adanır and Gülüm Tanırcan

One of the most damaging earthquake effects occurring in the vicinity of the fault trace is fling step, also known as permanent displacement. However, due to the fact that the standard filtering techniques eliminate the low frequency portions of the motion, the permanent displacements are not seen on the displacement time histories derived from the accelerogram records. Thus, fling step is neglected in many engineering practices. To reveal the permanent displacements, special data processing schemes based on removal of the baseline shifts in separated time windows were proposed. In this study, the most recently proposed data processing scheme eBASCO (Schiappapietra et al., 2021) is improved and the effectiveness of the new scheme is tested by comparing the obtained displacements on the processed records with those derived from nearby GPS data for 25 records from worldwide earthquakes.

 Preliminary site screening efforts and geodetic observations demonstrated that the earthquake sequence of February 6, 2023 in Turkey caused remarkable permanent displacements, which might be one of the reasons for severe damage and collapse of the structures, especially those which have long fundamental periods such as pipelines, roadways and high-rise buildings. In this study, near fault records of the earthquake sequence are processed with the proposed scheme and the obtained permanent displacements are evaluated with those predicted by existing models.

How to cite: Adanır, E. and Tanırcan, G.: Permanent Displacement Distribution From Strong Ground Motion Records of the 2023 Mw7.7 Earthquake., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17600, https://doi.org/10.5194/egusphere-egu23-17600, 2023.

EGU23-17601 | Orals | SM1.6

Evidence of Early Supershear Transition in the Mw 7.8 Kahramanmaraş Earthquake From Near-Field Records 

Ahmed Elbanna, Mohamed Abdelmeguid, and Ares Rosakis

The Mw7.8 Kahramanmaraş Earthquake was larger and more destructive than what had been expected for the tectonic setting in Southeastern Turkey. By using near-field records we provide evidence for early supershear transition on the splay fault that hosted the nucleation and early propagation of the first rupture that eventually transitioned into the East Anatolian fault. The two stations located furthest from the epicenter show a larger fault parallel particle velocity component relative to the fault normal particle velocity component; a unique signature of supershear ruptures that has been identified in theoretical and experimental models of intersonic rupture growth. The third station located closest to the epicenter, while mostly preserving the classical sub-Rayleigh characteristics, it also features a small supershear pulse clearly propagating ahead of the original sub-Rayleigh rupture. This record provides, for the first time ever, field observational evidence for the mechanism of intersonic transition. By using the two furthest stations we estimate the instantaneous supershear rupture propagation speed to be ~1.55 Cs and the sub-Rayleigh to supershear transition length to be around 19.45 km, very close to the location of the station nearest to the epicenter. This early supershear transition might have facilitated the continued propagation and triggering of slip on the nearby East Anatolian Fault leading to amplification of the hazard. The complex dynamics of the Kahramanmaraş earthquake warrants further studies.

How to cite: Elbanna, A., Abdelmeguid, M., and Rosakis, A.: Evidence of Early Supershear Transition in the Mw 7.8 Kahramanmaraş Earthquake From Near-Field Records, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17601, https://doi.org/10.5194/egusphere-egu23-17601, 2023.

EGU23-17602 | ECS | Orals | SM1.6

Preliminary Results of Dynamic Rupture Simulations of the Mw7.8 Kahramanmaras Earthquake 

Yasemin Korkusuz Öztürk, Nurcan Meral Özel, Jean-Paul Ampuero, and Elif Oral

It is essential to investigate how ruptures develop and propagate dynamically along the East Anatolian Fault (EAF) and what conditions explain the rupture propagation patterns observed for recent earthquakes. The northeast motion of the Arabian plate with respect to the Anatolian microplate and the African plate is accommodated along the left-lateral East Anatolian and Dead Sea faults.  The slip-rate along the northern Dead Sea Fault is about 4 mm/yr while the slip rate along the EAF increases from 5 mm/yr to ~12 mmm/yr towards the northeast where it connects to the North Anatolian Fault. The Mw7.8 Kahramanmaras earthquake on 6th of February 2023 initiated along a splay called the Narli fault and proceeded along the EAF bilaterally, rupturing a total of more than 300 km. The earthquake ruptured a significant portion of the EAF and a section of the Amanos Fault which connects to the Cyprus Arc offshore. One interesting point is that the rupture along the EAF was dynamically triggered by a splay which is at an acute angle of ~30°. This raises the question of how the slip distribution and rupture parameters were affected by the rupture initiation at a splay fault. Initial models indicate that the rupture propagated faster toward northeast and slower toward southwest, which might indicate that the directivity of the splay fault played an important role in the rupture dynamics of this earthquake. Remarkably, this complex event triggered another destructive earthquake with magnitude Mw7.6, west of the epicenter of the first mainshock, nine hours later. The second event caused a relatively short surface rupture (~80 km) with high stress drop. The analysis of 3D dynamic earthquake rupture simulations contributes to a comprehensive understanding of the effects of material properties and initial stresses on dynamic triggering and ground motion intensity. In this study we will show our preliminary results of the dynamic modeling of the Mw7.8 earthquake using the Finite Element community code Pylith. East and south Anatolia contain many faults which are capable of generating M>7.0 earthquakes in the near future. Therefore, understanding the dynamics of the Kahramanmaras earthquakes and stress transfer to neighboring faults is important in order to understand the potential for new destructive earthquakes in the surrounding area, and to generate scenarios of damage, shaking and PGA distributions.

How to cite: Korkusuz Öztürk, Y., Meral Özel, N., Ampuero, J.-P., and Oral, E.: Preliminary Results of Dynamic Rupture Simulations of the Mw7.8 Kahramanmaras Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17602, https://doi.org/10.5194/egusphere-egu23-17602, 2023.

EGU23-17603 | Posters on site | SM1.6

Geodetically and seismically informed rapid 3D dynamic rupture modeling of the Mw7.8 Kahramanmaraş earthquake 

Alice-Agnes Gabriel, Thomas Ulrich, Mathilde Marchandon, and James Biemiller

The destruction unfolding after the February 6, 2023 Turkey-Syria Earthquake sequence is devastating. First observations reveal complex earthquake dynamics challenging data-driven efforts. We present rapid, data-informed and physics-based 3D dynamic rupture simulations of the puzzling Mw7.8 Kahramanmaras earthquake providing a first-order mechanical explanation of this earthquake’s complexity and its implications for the Mw7.5 doublet event.

By incorporating detailed fault geometries constrained by satellite geodetic observations into 3D dynamic rupture simulations, we show how dynamic interactions between fault geometric complexity and the heterogeneous regional stress field generated the unique and unexpected rupture behaviors observed, including localized supershear, backwards rupture branching, and locally strong shaking.

Our supercomputing empowered simulations that tightly link earthquake physics with interdisciplinary observations can provide a direct understanding of the fault system mechanics, reconcile competing interpretations and serve as a constraint to understand the short- and long-term Eastern Anatolian Fault system interaction.

How to cite: Gabriel, A.-A., Ulrich, T., Marchandon, M., and Biemiller, J.: Geodetically and seismically informed rapid 3D dynamic rupture modeling of the Mw7.8 Kahramanmaraş earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17603, https://doi.org/10.5194/egusphere-egu23-17603, 2023.

EGU23-17604 | ECS | Posters on site | SM1.6

Delineation of Regional High Seismic Risk Zone for More Targeted Seismic Risk Mitigation 

Danhua Xin, Zhenguo Zhang, Bo Chen, and Friedemann Wenzel

Despite global efforts to reduce seismic risk, earthquake remains one of the most destructive natural disasters in the world, especially for seismic active zones when they are characterized by high densification of fixed assets and population. For a specific country or region, the most effective way to achieve earthquake resilience is preparedness prior to an earthquake. To mitigate potential seismic risk, it is important to understand where high seismic risk zone locates, since the budgetary resources available from the local government are always limited and they should be allocated to such zone with priority. This paper proposes a strategy to delineate regional high seismic risk zone by combing different seismic risk assessment results, aiming to make the seismic risk mitigation practice more targeted and operable. Our analyses show that while the delineated high seismic risk zone occupies only ~10% of the case study area, it accounts for ~90% of the total seismic risk in terms of economic loss. To achieve more targeted seismic risk mitigation, we recommend that such zone should be given top priority in seismic risk mitigation.

How to cite: Xin, D., Zhang, Z., Chen, B., and Wenzel, F.: Delineation of Regional High Seismic Risk Zone for More Targeted Seismic Risk Mitigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17604, https://doi.org/10.5194/egusphere-egu23-17604, 2023.

A devastating earthquake sequence occurred on February 6, 2023, within the East Anatolian fault system. Two main shocks, the Mw 7.7 Sofalaca-Şehitkamil-Gaziantep, and Mw 7.6 Ekinözü-Kahramanmaraş earthquakes occurred nine hours apart and affected 10 cities and more than an area of 100,000 km2 (PGA>0.08g). The earthquake-affected area mainly exhibits arid/semi-arid climatic conditions where approximately 15% of the landscape is characterized by steep topography (slope steepness>20°). Initial estimates of globally available predictive landslide models indicated extensive landslide distribution over the area.

We examined high-resolution satellite images and aerial photos to provide a better insight into this co-seismic landslide event and its possible post-seismic consequences. These observations are going to be validated and enriched by detailed field surveys. This research presents our preliminary findings as a result of these investigations. Our observations carried out in the first two weeks after the sequence showed that rock fall and lateral spreading are the dominant landslide types, and the overall landslide population could be less than expected. Therefore, the resultant co-seismic landslide event seems unexpected, given the intensity of ground shaking and landscape characteristics. Based on the preliminary investigations, lithology, topographic relief, and climatic conditions appear to be the main variables causing these below expectations for landslide distribution. We should stress that our historical records mostly lack landslide events in arid/semi-arid conditions, as we observed in this event. In this context, this event is going to be recorded as one of a few of its kind. Our observations also showed intense ground shaking and strongly deformed numbers of hillslopes, although most have not failed yet. In particular, heavy rain and snowmelt may result in a considerable number of failures on those hillslopes that are prone to cracking and deformation due to strong ground shaking. In this respect, this area needs to be monitored for a long time to understand the earthquake legacy effect and post-seismic hillslope response.

How to cite: Gorum, T. and Tanyas, H.: Less than expected? Landslides triggered by the 2023 Mw 7.7 and 7.6 Kahramanmaras (Türkiye) earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17606, https://doi.org/10.5194/egusphere-egu23-17606, 2023.

EGU23-17607 | ECS | Posters on site | SM1.6

Strong Ground Motion Simulations of the 2023 Turkey–Syria Earthquake Sequence Using CGFDM3D-EQR 

Tianhong Xu, Wenqiang Wang, and Zhenguo Zhang

On February 6th 2023, a large Mw 7.8 earthquake struck Turkey and Syria near the border area. Only 9 hours later, another Mw 7.5 earthquake occurred about 90 km northeast of the epicenter of the first earthquake. Up to now, the two earthquakes have killed at least 43,000 people and injured 120,000. Preliminary inversion results from USGS show that the geometric structure of the seismogenic fault is rather complex, and the rupture propagates through multiple sub-faults.

Massive casualties show the necessity and urgency of an earthquake rapid emergency response system, and ground motion simulation is a key component of this system. Empirical ground-motion prediction equations (GMPEs), which are widely used, can quickly provide the distribution of ground motion and seismic intensity. Unfortunately, the calculated seismic intensity is not accurate enough due to its incomplete consideration of the earthquake source and the complicated seismic wave propagation process(Paolucci et al., 2018; Infantino et al., 2020; Stupazzini et al., 2021). In contrast, the physics-based ground motion simulation method has more advantages. In this study, we employ the USGS's finite fault inversion results as kinematic source input to model the two earthquakes' strong ground motion using the CGFDM3D-EQR platform (Wang et al., 2022). The platform can quickly run an earthquake simulation while taking into account the three-dimensional complexity of topography, underground medium, and source, providing timely reliable distribution of ground motion and seismic intensity. Preliminary findings indicate that the first earthquake's maximum intensity is XI, the second earthquake's maximum intensity is X, which is consistent with the report issued by AFAD, and that the simulated intensity's spatial distribution range is also consistent. The simulation completely considers the effects of the source, geological environment, and topography, and the seismic intensity distribution exhibits complex non-uniform properties that are closer to the reality.

The rapid ground shaking simulations of the Turkey–Syria earthquake allows for the quick, accurate, and scientific assessment of earthquake damage. To reduce lives and financial losses, these results can serve as a scientific foundation and point of reference for the relevant authorities as they decide how best to respond in an earthquake and conduct out rescue operations.

 

 

 

 

References

Infantino M, Mazzieri I, Özcebe A G, et al. 3d physics-based numerical simulations of ground motion in istanbul from earthquakes along the marmara segment of the north anatolian fault[J]. Bulletin of the Seismological Society of America, 2020, 110(5): 2559-2576.

Paolucci r, Gatti F, Infantino M, et al. Broadband ground motions from 3d physics-based numerical simulations using artificial neural networksbroadband ground motions from 3d pbss using anns[J]. Bulletin of the Seismological Society of America, 2018, 108(3A): 1272-1286.

Stupazzini M, Infantino M, Allmann A, et al. Physics-based probabilistic seismic hazard and loss assessment in large urban areas: A simplified application to istanbul[J]. Earthquake Engineering & Structural Dynamics, 2021, 50(1):99-115.

Wang, W., Zhang, Z., Zhang, W., Yu, H., Liu, Q., Zhang, W., & Chen, X. (2022). CGFDM3D‐EQR: A Platform for Rapid Response to Earthquake Disasters in 3D Complex Media. Seismological Research Letters, 93 (4): 2320-2334.

How to cite: Xu, T., Wang, W., and Zhang, Z.: Strong Ground Motion Simulations of the 2023 Turkey–Syria Earthquake Sequence Using CGFDM3D-EQR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17607, https://doi.org/10.5194/egusphere-egu23-17607, 2023.

EGU23-17608 | Orals | SM1.6

Dynamic Triggering of Tremor and Earthquakes along the Dead Sea Transform by the 2023 Kahramanmaraş Earthquake Doublet 

Asaf Inbal, Itzhak Lior, Alon Ziv, and Ran Novitsky Nof

The Kahramanmaraş earthquake doublet, which struck south-eastern Turkey, imparted stress changes that dramatically affected neighboring regions: northern Israel, located about 600 km to the south of the epicenters, experienced roughly a hundred-fold increase in seismicity rates during the first week following the M>7 earthquakes. Here, we study seismic records along the Dead Sea Transform (DST) in order to identify, locate, and determine the characteristics of seismic sources triggered by seismic waves due to the M>7 earthquakes. We take advantage of a dense near-fault accelerometer network recently installed along the DST in Israel, and scan high- and low-pass filtered seismograms to look for body- and surface-wave triggering. We find that Love waves generated by the Mw7.5 earthquake triggered a small-magnitude earthquake in the northern Dead Sea lake area. Importantly, we find the first evidence of deep tectonic tremor along the DST, also triggered by the Mw7.5 Love waves. This tremor episode is composed of two 10 s bursts aligned with the strongest Love wave energy. Preliminary tremor envelope cross-correlation location results suggest it resides in the Jordan Valley, north of the Dead Sea lake, at 10 to 20 km depth, within the San Andreas Fault tremor depth range. Despite its larger magnitude, we do not find evidence for dynamic triggering due to the Mw7.8. The lack of dynamic triggering due to the Mw7.8, and the fact that waves from both earthquakes travel along similar paths to Israel, allow us to establish a threshold for dynamic earthquake triggering in the Dead Sea area.

How to cite: Inbal, A., Lior, I., Ziv, A., and Novitsky Nof, R.: Dynamic Triggering of Tremor and Earthquakes along the Dead Sea Transform by the 2023 Kahramanmaraş Earthquake Doublet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17608, https://doi.org/10.5194/egusphere-egu23-17608, 2023.

EGU23-17609 | Orals | SM1.6

Rupture processes of the 2023 Türkiye earthquake sequence: Main- and aftershocks 

Gesa Petersen, Pinar Büyükakpinar, Felipe Vera, Malte Metz, Joachim Saul, Simone Cesca, Torsten Dahm, and Frederik Tilmann

On February 6, 2023, southeastern Turkey was hit by two of the most devastating earthquakes in the instrumental period of the country, with Mw 7.7-7.8 and Mw 7.6, respectively. Both earthquakes caused massive damage and in total tens of thousands of casualties in Turkey and Syria. In this study, we analyze the rupture processes of main- and aftershocks by combining different seismic source characterization techniques using teleseismic, regional and local data. We perform finite source inversion and back projection-based analyses for the two main shocks and invert for probabilistic centroid moment tensor solutions of both main and aftershocks (M≥4). The first earthquake was bilateral and ruptured a seismic gap along the East Anatolian Fault Zone, with rupture first propagating to the north-east for ~200 km, and in a latter phase propagating to the SSW, probably coming to a halt only on a branch extending into the Mediterranean Sea. The total length of the rupture likely exceeds 500 km. The second event ruptured the EW oriented Sürgü-Misis Fault Zone to the NW of the first event. It shows a highly concentrated rupture near the epicenter, Rupture directivity analyses for M≥5.3 earthquakes provide additional insights into dynamic source aspects. Preliminary moment tensor solutions of numerous aftershocks indicate a remarkable variability of rupturing mechanisms, suggesting stress changes and the activation of multiple faults in the vicinity of the main ruptures. With our work, we aim to shed light onto multiple aspects of the complex rupture evolution and hope to provide new insights towards a better understanding of the devastating 2023 Türkiye earthquake sequence.

How to cite: Petersen, G., Büyükakpinar, P., Vera, F., Metz, M., Saul, J., Cesca, S., Dahm, T., and Tilmann, F.: Rupture processes of the 2023 Türkiye earthquake sequence: Main- and aftershocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17609, https://doi.org/10.5194/egusphere-egu23-17609, 2023.

EGU23-17610 | Orals | SM1.6

The 6 February 2023 Türkiye Earthquakes: Insights for the European Seismic Hazard and Risk Models 

Graeme Weatherill, Fabrice Cotton, Helen Crowley, Laurentiu Danciu, Karin Sesetyan, Eser Cakti, M. Abdullah Sandikkaya, Ozkan Kale, and Elif Türker and the Members of the 2020 European Seismic Hazard Model and 2020 European Seismic Risk Model Core Teams

The earthquakes that struck eastern Türkiye and Syria on 6 February 2023, first with a Mw 7.8 shock then followed only hours later by a second Mw 7.6 event, will have profound and long-lasting consequences for those living in this highly seismically active region. From the perspective of the European earthquake science and engineering communities, however, these events also force us to evaluate our models of seismic hazard and risk for the region, specifically the 2020 European Seismic Hazard Model (ESHM20, Danciu et al.. 2021) and European Seismic Risk Model (ESRM20, Crowley et al.. 2021), to identify potential shortcomings and focus on areas where improvement is needed. A single event such as this can neither validate nor invalidate probabilistic models, but as data emerge, we can compare these with components of our models and verify the extent to which the events themselves and their consequences are described.

We first verified that the ruptures associated to the two main earthquakes are present within the inventory of ruptures and associated probabilities within the source model (the earthquake rupture forecasts or ERFs) for the East Anatolian Fault (first event) and Sürgü-Cardak Fault (second event). These earthquakes are larger than those in the historical earthquake catalogue, but ruptures close in magnitude and dimension to those observed were present in the ESHM20 ERFs. Both magnitudes were between 0.2 – 0.4 Mw units lower than those defined for their respective faults on the different logic tree branches.

Preliminary ground motion observations allowed us to compare the observed shaking to that predicted by the ESHM20 ground motion model (GMM) and others in the literature. These were found to be consistent in their prediction of the expected shaking and its attenuation. The 6th February earthquakes do show that future models must address issues of time-dependence between earthquakes and allow for short-term clustering of large events on nearby ruptures. Recorded near-fault ground motions also suggest strong pulse-like behaviour, indicating the need for such phenomena to be better captured in the GMMs.

A complete assessment of the actual damage and consequences is not yet available from which we could compare the seismic risk model. We have run scenario risk calculations using the ESRSM20 site, exposure and vulnerability models for the two main earthquakes, along with other scenario ruptures on neighbouring faults. Expected fatalities were lower than those reported at the time of writing; however, many factors contribute to this. Further analysis is needed to understand the difference, but critical areas for future improvement to the risk models should include state-dependent fragility, modelling of further epistemic uncertainty in exposure and vulnerability, and inclusion of spatial- and temporal correlations in ground motions across a region. Future efforts by the seismic hazard and risk modelling community to address these issues considering the February 2023 earthquakes may have a lasting impact on risk mitigation, both in Türkiye and across Europe.

How to cite: Weatherill, G., Cotton, F., Crowley, H., Danciu, L., Sesetyan, K., Cakti, E., Sandikkaya, M. A., Kale, O., and Türker, E. and the Members of the 2020 European Seismic Hazard Model and 2020 European Seismic Risk Model Core Teams: The 6 February 2023 Türkiye Earthquakes: Insights for the European Seismic Hazard and Risk Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17610, https://doi.org/10.5194/egusphere-egu23-17610, 2023.

EGU23-17611 | ECS | Posters on site | SM1.6

Fault slip and fault-zone damage of the 6 February 2023 Kahramanmaraş earthquake duplet estimated from 3D displacement derivations of Sentinel-1 radar images 

Jihong Liu, Xing Li, Adriano Nobile, Yann Klinger, and Sigurjón Jónsson

We report on the surface displacements of the 6 February 2023 Kahramanmaraş earthquake duplet derived from pixel-offset tracking of Sentinel-1 radar images. From both ascending and descending orbit images, along-track (azimuth) and across-track (range) pixel offsets were derived, yielding four different offset images from which we inverted for three-dimensional surface displacements. The resulting horizontal surface displacements clearly show the left-lateral motion across the two main faults, with the vertical displacements small in comparison, confirming the almost pure strike-slip mechanism of both events. Comparison with GPS data indicates that an accuracy of ~10 cm can be achieved for the horizontal displacements. From the offset results, we mapped the main surface rupture of the first event along the East Anatolian Fault (EAF) for ~300 km and the surface rupture of the second mainshock for over 100 km, i.e., somewhat shorter than illuminated by the aftershocks. Using multiple profiles across the faults, of the fault-parallel displacements derived from the offset results, we find three slip maxima along the EAF, with the largest slip (6-7 m) found northeast of the epicenter, ~30 km east of the city of Kahramanmaraş. Another slip maximum (~4 m) is found further southwest, near Islahiye, with fault slip abruptly decreasing near Antakya at the southwestern end of the rupture. The maximum surface offset of the second fault is even larger than for the first rupture, or about 8 m, and it is found near the epicenter. In addition to localized deformation along the main rupture, across-fault profiles of both fault-parallel and fault-perpendicular displacement components also show deformation gradients that might be evidence for off-fault damage extending several km away from the surface ruptures. From the derived coseismic 3D displacements and GNSS observations, we inverted for spatially variable fault slip, revealing that most of the fault slip occurred above 15 km with maximum slip of both quakes reaching almost 10 m. The spatially variable slip model of the first mainshock has primarily three areas of high slip, like what is seen at the surface. Together the results have provided a quick and a complete overview of surface fault offsets and what faults were activated in the earthquake and will help assessing the influence these large earthquakes have had on other faults in the region.

How to cite: Liu, J., Li, X., Nobile, A., Klinger, Y., and Jónsson, S.: Fault slip and fault-zone damage of the 6 February 2023 Kahramanmaraş earthquake duplet estimated from 3D displacement derivations of Sentinel-1 radar images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17611, https://doi.org/10.5194/egusphere-egu23-17611, 2023.

EGU23-17612 | Posters on site | SM1.6

Mapping the ruptures of the Mw7.8 and Mw7.7 Turkey-Syria Earthquakes using optical offset tracking with Sentinel-2 images 

Floriane Provost, Jérôme Van der Woerd, Jean-Philippe Malet, Alessia Maggi, Yann Klinger, David Michéa, Elisabeth Pointal, and Fabrizio Pacini

Monday February 6, 2023, two large Mw7+ earthquakes struck Turkey and North-Syria. The first event occurred along the N60 striking East Anatolian Fault (EAF) and its prolongation towards the Dead Sea Fault, the N25 striking Karazu fault, with an epicenter 30 km south-east off the main rupture zone. The second event is located to the north of the first one, along the N100 Sürgü-Çartak fault. Focal mechanisms of both shocks exhibit a dominant left-lateral strike-slip component on sub-vertical faults. These ruptures and mechanisms are compatible with Anatolia westward extrusion between the North and East Anatolian faults in response to Arabia-Eurasia convergence. The complex geometry of the activated faults during this earthquake sequence sheds light on how strain is partitioned and distributed among the faults of this triple-junctions linking Nubia, Arabia and Anatolia.

The current constellation of Earth Observation satellites allowed for rapid acquisition of the whole impacted area shortly after the mainshocks. On February 9, 2023, the Copernicus Sentinel-2 satellite captured a set of optical images while the region was mostly cloud free. This dataset offers a complete coverage of the system of faults activated during these events at 10 m spatial resolution. Although this resolution is not sufficient to map surface ruptures directly from the images, image correlation (also known as offset tracking) techniques can be applied on these images to retrieve the distribution of the surface displacement. In the present work, we used the GDM-OPT-ETQ service of the ForM@Ter solid Earth data hub to measure (with the open source photogrammetry library MicMac) the co-seismic displacement between images of January 25, 2023 and February 9, 2023. The massive processing was performed on the Geohazards Exploitation Platform (GEP). The final products of the processing are East-West and North-South displacement maps covering an area of  300 km x 300 km at 10 m resolution and further 2D strain maps are also derived. Spatial offsets in the range of 3 to near 10 m are identified with large geographic variability along the faults. 

These maps significantly contribute to identify and map the ruptures of the Turkey-Syria earthquakes and determine the along fault displacement. The spatial distribution of the displacement will be discussed together with a first order cluster analysis of the seismic sequence using an aftershock catalogs. The combined datasets should allow us to better understand the complexity of the on-fault and off-fault deformation pattern.

How to cite: Provost, F., Van der Woerd, J., Malet, J.-P., Maggi, A., Klinger, Y., Michéa, D., Pointal, E., and Pacini, F.: Mapping the ruptures of the Mw7.8 and Mw7.7 Turkey-Syria Earthquakes using optical offset tracking with Sentinel-2 images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17612, https://doi.org/10.5194/egusphere-egu23-17612, 2023.

The double earthquakes of 6 February 2023 in central Turkey and their associated seismic activity show a composite cloud of thousands of epicenters that mimic the number 7 and extend from central Turkey to the east Mediterranean shoreline. The lower limb of this mighty “7” spreads along a trend that matches the onshore continuation of the Latakia ridge, which is one of the most prominent seafloor structures of the east Mediterranean region. This structure extends for about 200 km along the subduction zone of the Cyprus arc where compressional forces are dominant. We interpreted a major and active reverse fault system underneath the Latakia ridge using 3D seismic interpretation. The ridge’s reverse faults rupture the seafloor and display a relief up to 500 m in height. The fault system underneath this prominent seafloor rupture is capable of generating a high magnitude earthquake and can be considered a very plausible source of the 9 July 551 M 7.2 earthquake and its associated tsunami along the Levant coast. The magnitudes of the 6 February 2023 double earthquakes and the density and trend of their associated seismic activity highlight the importance of understanding the interconnection of the seismogenic structures in the east Mediterranean region, both onshore and offshore, with additional attention to those that are potentially tsunamigenic.

How to cite: Nemer, T., Faysal, R., and Sarieddine, K.: The double earthquakes of 6 February 2023 in central Turkey: a mighty “7” from continental strike-slip to subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17613, https://doi.org/10.5194/egusphere-egu23-17613, 2023.

Temporal seismic velocity changes have been reported to occur before, during and after major earthquakes. We applied seismic ambient noise interferometry to analyse transient velocity changes (dv/v) in the vicinity of the fault segment affected by the 6th of February East Anatolia earthquake sequence. The dataset consists of 5 months of continuous seismic records (from October 1st 2022 to February 15 2023)   recorded by three triaxial broadband stations deployed on the shoulders of the reactivated fault system. The open-access stations are operated by the Kandilli Observatory and Earthquake Research Institute of Turkey. Cross-correlation changes over time between station pairs reveal a large velocity co-seismic drop of about 2%   in the apparent velocity. We also examine the velocity variations in single-station cross-component analysis finding a co-seismic velocity variation of 1% more prominent on horizontal cross-components. These variations may be associated with changes in the effective stress of the upper crust and may be identified before and during the occurrence of important events. We are currently investigating precursory cross-correlations and auto-correlations of the signal in comparison to long-term seasonal trends. We show the importance of seismic interferometry as an additional method to monitor active fault systems.

How to cite: Muñoz-Burbano, F., Savard, G., and Lupi, M.: Temporal seismic Velocity variations prior and during the 7.8 and 7.5 MW earhquakes occurred in south-central Turkey implementing ambient noise interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17614, https://doi.org/10.5194/egusphere-egu23-17614, 2023.

EGU23-17616 | Posters on site | SM1.6

Surface Displacement and Source Parameters of the Mw 7.7 and Mw 7.6 Kahramanmaraş Earthquakes 

Haluk Özener, Çağkan Serhun Zoroğlu, Egehan Vardar, Emre Havazlı, Tülay Kaya Eken, and Mahyat Shafapour Tehrany

On February 6th, 2023, a devastating earthquake with a magnitude of Mw7.7 occurred in the Kahramanmaras region of Türkiye. The earthquake is caused by the rupture of a NE-SW oriented left lateral strike-slip Pazarcık fault segment located between the East Anatolian Fault (EAF) and Dead Sea Fault (DSF) fault systems. The aftershock sequence of the earthquake indicated that post-seismic deformation continued along the EAF and DSF toward the NE and SW. Just 9 hours later, another earthquake with a magnitude of Mw7.6 occurred along the EW-oriented left lateral Sürgü Fault, located approximately 100 km north of the first event. These two earthquakes released a significant amount of energy and affected ten provinces in southeastern Türkiye. The earthquake region is characterized by a complex tectonic structure actively deforming through a network of strike-slip, thrust, and normal faults formed by the convergence of the Arabian Plate to the Eurasian Plate and the westward movement of the Anatolian Plate. It is of utmost importance to understand the co-seismic and post-seismic surface deformation behavior to make reliable seismic hazard assessments.

To better understand the deformation patterns during and after the Kahramanmaraş earthquakes, we processed Interferometric Synthetic Aperture Radar (InSAR) data sets obtained before and after the earthquakes. We used both ascending and descending track SAR images of the ESA Sentinel-1 to detect the surface displacement. Then, we incorporated the post-seismic deformation patterns from the relocated aftershock events to the InSAR derived deformation field to gain insight into the source properties of the events. Our preliminary results revealed several meters of displacement across the faults.

How to cite: Özener, H., Zoroğlu, Ç. S., Vardar, E., Havazlı, E., Kaya Eken, T., and Shafapour Tehrany, M.: Surface Displacement and Source Parameters of the Mw 7.7 and Mw 7.6 Kahramanmaraş Earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17616, https://doi.org/10.5194/egusphere-egu23-17616, 2023.

EGU23-17617 | Posters on site | SM1.6

Multiple effects contributed to the intensive shaking recorded in the 6 February 2023 Kahramanmaraş (Türkiye) earthquake sequence 

Sigurjón Jónsson, Theodoros Aspiotis, Tariq Aquib, Eduardo Cano, David Castro-Cruz, Armando Espindola-Carmona, Bo Li, Xing Li, Jihong Liu, Rémi Matrau, Adriano Nobile, Kadek Palgunadi, Laura Parisi, Matthieu Ribot, Cahli Suhendi, Yuxiang Tang, Bora Yalcin, Ulaş Avşar, Yann Klinger, and P. Martin Mai

The Kahramanmaraş earthquake sequence caused strong shaking and extensive damage in central-south Türkiye and northwestern Syria, making them the deadliest earthquakes in the region for multiple centuries. The rupture of the first mainshock (M7.8) initiated just south of the East Anatolian Fault (EAF) and then ruptured bilaterally hundreds of km of the EAF, causing major stress changes in the region and triggering the second mainshock (M7.6) about 9 hours later. We mapped the surface ruptures of the two mainshocks using pixel-offset tracking of Sentinel-1 radar images and find them to be ~300 km and 100-150 km long. The distribution of aftershocks indicates that the fault ruptures may have been even longer at depth, or about ~350 km and ~170 km, respectively. The pixel-tracking results and finite-fault modeling of the spatially variable fault slip show up to 7 and 8 m of surface fault offsets at the two faults, respectively, and that fault slip was shallow in both events, mostly above 15 km. In addition, our back-projection analysis suggests the first mainshock ruptured from the hypocenter to the northeast towards the EAF (first ~15 sec), then continued along it to the northeast (until ~55 sec), and also to the southwest towards the Hatay province, later at high rupture speeds (until ~80 sec). Furthermore, strong motion recordings show PGA values up to 2g and are particularly severe in Hatay, where multiple stations show over 0.5g PGA values. Both events are characterized by abrupt rupture cessation, generating strong stopping phases that likely contributed to the observed high shaking levels. Together the results show that directivity effects, high rupture speed, strong stopping phases, and local site effects all contributed to the intensive shaking and damage in the Hatay province.

How to cite: Jónsson, S., Aspiotis, T., Aquib, T., Cano, E., Castro-Cruz, D., Espindola-Carmona, A., Li, B., Li, X., Liu, J., Matrau, R., Nobile, A., Palgunadi, K., Parisi, L., Ribot, M., Suhendi, C., Tang, Y., Yalcin, B., Avşar, U., Klinger, Y., and Mai, P. M.: Multiple effects contributed to the intensive shaking recorded in the 6 February 2023 Kahramanmaraş (Türkiye) earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17617, https://doi.org/10.5194/egusphere-egu23-17617, 2023.

EGU23-17618 | Posters on site | SM1.6

Global Distributed Fibre Optic Sensing recordings of the February 2023 Turkey earthquake sequence. 

Philippe Jousset, Andreas Wuestefeld, Charlotte Krawczyk, Alan Baird, Gilda Currenti, Martin Landrø, Andy Nowacki, Zack Spica, Sandra Ruiz Barajas, Fabian Lindner, Özgün A. Konca, Pascal Edme, Voon Hui Lai, Vladimir Treshchikov, Lena Urmantseva, Jan Peter Morten, Werner Lienhart, Bradley Paul Lipovsky, Martin Schoenball, and Kuo-Fong Ma and the “DAS-month” team (sample only!)

As part of a global distributed acoustic sensing (DAS) campaign, multiple DAS interrogators (from academia and industry) recorded simultaneously from 1st till 28th February 2023 in different regions of the globe. The objective is to define if and how a global monitoring system based on DAS could perform for teleseismic event record and analysis. Each participant uploaded triggered data window from earthquakes with magnitude larger than 5, as defined by global seismological networks, to a central storage location. Data was pre-processed following common filtering parameters (spatial and temporal sampling). Bottle-necks in data format, storage, and legal issues are identified and reviewed to pose the basis for a common DAS data archive strategy.

In this study, we present a selection of DAS records of the Turkey earthquake sequence, from borehole, surface, on-land, submarine telecommunication or dedicated cables all over the globe. They comprise a few kilometers long railroad track (Switzerland), an 0.8 km long deployed cable in the Limmat river, near Zürich (Switzerland), a 1 km deployed cable at Mt. Zugspitze in the Alps (Germany/Austria), a 21 km telecom cable in the forest around Potsdam (Germany), a 17 km telecom cable surface geothermal field (north Iceland), a 0.2 km borehole at Etna volcano (Italy), a telecom cable in the city of Istanbul (Turkey), a 25 km telecom cable in Melbourne (Australia), in the inner city line in Graz (Austria), in the city of Seattle, WA (USA), a submarine cable in the North Sea, a submarine cable connecting Ny Ålesund and Longyearbyen at Svalbard (Norway), a 0.8 km dedicated fibre in a quick clay area in Norway, amongst many others.

We show that signals from the two destructive earthquakes in Turkey were recorded all over the globe. We discuss the signal quality and their potential use to study teleseism signals. We analyze recorded strain amplitudes according to the different array geometries and the differing sensitivities to wave types (body, surface waves, possibly others) and deployment conditions. When available, comparison with other sensors located in the same place is performed. Finally, we analyze the influence of local geological conditions due to the passing large amplitudes waves.

With the increasing availability, reduced cost and improved simplicity of DAS systems and the wide spread existing fibre optic networks, we believe fibre-optic sensing will play an ever-increasing role in the global seismic monitoring.

How to cite: Jousset, P., Wuestefeld, A., Krawczyk, C., Baird, A., Currenti, G., Landrø, M., Nowacki, A., Spica, Z., Barajas, S. R., Lindner, F., Konca, Ö. A., Edme, P., Lai, V. H., Treshchikov, V., Urmantseva, L., Morten, J. P., Lienhart, W., Lipovsky, B. P., Schoenball, M., and Ma, K.-F. and the “DAS-month” team (sample only!): Global Distributed Fibre Optic Sensing recordings of the February 2023 Turkey earthquake sequence., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17618, https://doi.org/10.5194/egusphere-egu23-17618, 2023.

EGU23-17619 | Posters on site | SM1.6

Preliminary Seismic and Geodetic Observations of the Mw7.8 and Mw7.6 Earthquakes in Eastern Turkey 

Sezim Ezgi Güvercin, Ali Özgün Konca, Hayrullah Karabulut, Figen Eskiköy, James Hollingsworth, and Semih Ergintav

On 6 February 2023, Mw7.8 Kahramanmaraş earthquake sequence ruptured a section of ~300 km of the East Anatolian Fault (EAF). The rupture was initiated with a relatively small ~Mw7.0 event on the Narli Fault, a subparallel prolongation to the Amanos segment breaking ~50 km of its length to the north before reaching to the EAF, ~20s later. The Mw7.8 earthquake was followed by a Mw7.6 event rupturing E-W oriented Çardak Fault on the north of the EAF, ~9 hours later. The initial part of the rupture along the Narlı fault with Mw7.0 earthquake has significant normal component while the rest of the rupture is mostly left-lateral strike slip consistent with the EAF. The pixel correlation of satellite images shows that the rupture of the Mw7.8 event extends for 300 km along the EAF with a maximum slip of ~9 m near Kahramanmaraş Junction. Preliminary finite-fault models show that average rupture velocity toward north-east is faster (~ 3km/s) compared to the southwest (~2 km/s). The north-east extent of the rupture almost reached to the termination of the 2020, Mw6.8 Sivrice earthquake, while to the southwest, it extends to the east of the city of Antakya. The Mw7.6 earthquake has surface offset of ~10 m extending E-W for ~100 km between the EAF in the east and Savrun Fault in the west. The aftershock zone expanded over a wide region during the first few days, all over the eastern Anatolia. The seismic activities triggered on Malatya, Savrun and Göksun Faults are consistent with Coulomb stress increases. Earthquake focal mechanisms solutions are consistent with the kinematics of the ruptured faults with strike slip solutions. Normal fault solutions are observed at the terminations of the ruptures with Coulomb stress increases.  The normal fault is activated on the southern border of the Hatay Graben, with a continuation to the Cyprus Arc.  In this presentation we present the preliminary results of the seismicity, slip model including GNSS, seismic and InSAR data as well as the satellite obtained surface offsets.

How to cite: Güvercin, S. E., Konca, A. Ö., Karabulut, H., Eskiköy, F., Hollingsworth, J., and Ergintav, S.: Preliminary Seismic and Geodetic Observations of the Mw7.8 and Mw7.6 Earthquakes in Eastern Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17619, https://doi.org/10.5194/egusphere-egu23-17619, 2023.

EGU23-17620 | ECS | Posters on site | SM1.6

Strong ground motions due to directivity and site effects inflicted by the February 6 2023 earthquake doublet, along the East Anatolian Fault 

Theodoros Aspiotis, Tariq Anwar Aquib, David Castro-Cruz, Bo Li, Xing Li, Jihong Liu, Remi Matrau, Kadek Hendrawani Palgunadi, Laura Parisi, Cahli Suhendi, Yuxiang Tang, Yann Klinger, Sigurjon Jonsson, and Paul Martin Mai

Two powerful earthquakes (magnitudes 7.8 and 7.6) struck south-central Türkiye on February 6, 2023, causing significant damage across an extensive area of at least ten provinces in Türkiye as well as in multiple cities in northwestern Syria, making them one of the deadliest earthquakes in Türkiye for multiple centuries. The first mainshock started close to the well-known East Anatolian Fault (EAF) and then rupturing more than 300 km of that fault, whereas the second large earthquake occurred nine hours later around 90 km north of the first mainshock, on an east-west trending fault. In this study, we analysed recorded strong ground motions from the two events to better understand the factors contributing to the devastation caused by the earthquakes.

 

For this, we collected 250 and 200 strong ground motion records for the first and the second event, respectively, from the Disaster and Emergency Management Authority (AFAD) in Türkiye. Maximum peak ground accelerations (PGA) of 2g were observed at a distance of 31 km northeast of the first mainshock epicenter and 0.6g for the second event 65km west to its epicenter. In addition, we find particularly high amplitude ground motions in the Hatay province for the first event, which is consistent with the extent of damage reported in that region. High shaking levels in Antakya and other parts of Hatay can be explained by a combination of strong directivity and local site effects.

 

The results of our analysis imply that the PGA values derived from two local ground motion models (GMMs), adopted for the 2018 Turkish hazard map, are underestimated in comparison to observed strong motion recordings. In addition, we also compared observed peak and spectral ground motion characteristics with estimated seismic hazard values (10% probability to exceed in 50 years) in the East Anatolian Fault region (extracted from the 2018 Turkish seismic hazard map). Furthermore, we compare the recorded response spectra with the Turkish design code for several locations around the main faults.  The results show that the observations greatly exceed the hazard values and code guidelines in the Hatay province.

How to cite: Aspiotis, T., Aquib, T. A., Castro-Cruz, D., Li, B., Li, X., Liu, J., Matrau, R., Palgunadi, K. H., Parisi, L., Suhendi, C., Tang, Y., Klinger, Y., Jonsson, S., and Mai, P. M.: Strong ground motions due to directivity and site effects inflicted by the February 6 2023 earthquake doublet, along the East Anatolian Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17620, https://doi.org/10.5194/egusphere-egu23-17620, 2023.

EGU23-17621 | Posters on site | SM1.6

The Tsunami Warning triggered in the Mediterranean Sea by the 2023 February 6 Mw 7.8 Türkiye-Syria earthquake: from the present Decision Matrix (DM) to Probabilistic Tsunami Forecasting (PTF). 

Stefano Lorito, Jacopo Selva, Alessandro Amato, Andrey Babeyko, Basak Bayraktar, Fabrizio Bernardi, Marinos Charalampakis, Louise Cordrie, Nikos Kalligeris, Alessio Piatanesi, Fabrizio Romano, Antonio Scala, Roberto Tonini, Manuela Volpe, Musavver Didem Cambaz, and Doğan Kalafat

The 2023 February 6 Mw 7.8 earthquake was the first one of a doublet which shook Türkiye and Syria causing, as per the estimates at the time of writing of this abstract, more than 45,000 casualties.

The current standard operating procedures of the NEAMTWS (Tsunami Warning System in the North-Eastern Atlantic, the Mediterranean and connected seas, coordinated by UNESCO/IOC) for the initial tsunami warning message following an earthquake are based on a Decision Matrix (DM), whose input parameters are hypocentre and magnitude of the earthquake. Since the epicentre of this earthquake was located at a depth between 15-35 km at almost 100 km from the coast, both KOERI (Türkiye) and INGV (Italy) Tsunami Service Providers (TSPs) of the NEAMTWS issued a Tsunami Watch message (i.e., runup expected to exceed 1 m) for the whole Mediterranean Sea. NOA (Greece) did not issue any alert, because its initial location was more than 100 km from the coast.

In response to the tsunami warning, trains were stopped in different locations in Southern Italy for several hours, and evacuation of some coastal areas was enforced. However, only a relatively small tsunami was recorded by Turkish close-by tide-gauges in the Eastern Mediterranean, with a maximum recorded amplitude of less than 50 cm. Based on these measurements and on others showing little to no tsunami at increasing distances, the alert was then ended after 5 and 9 hours by INGV and KOERI, respectively, based on the available tide-gauge recordings and interaction with Civil Protection Officers.

This event has highlighted that NEAMTWS is an asset for the coastal communities. It can provide rapid alerts, which can save lives if the last-mile of the procedures is in place and the communities are “Tsunami Ready”, that is aware and prepared to respond with evacuations and other appropriate countermeasures. On the other hand, while it is reasonable – and dutiful based on current standard operation procedures – to issue a basin-wide, or at least a local alert, for an inland earthquake of unknown mechanism and of such a large magnitude, it is perhaps possible to improve the DM, which is totally heuristic and characterized by hard-thresholds, with consideration of numerical tsunami simulations and quantitative uncertainty treatment with more continuous variations. Moreover, there is no procedure currently in place to differentiate among locations where the expected time of arrival differs by many hours across the Mediterranean basin, nor a sufficient instrumental coverage that could make cancellation/ending faster due to a more solid observational basis.

We will discuss some of the scientific and operational aspects with the aim of identifying which lessons can be learned to improve the NEAMTWS efficiency. We will also compare the DM-based alerts with those that would be produced with the recently introduced Probabilistic Tsunami Forecasting (PTF, Selva et al., 2021, Nature Communications), presently in pre-operational testing at INGV.

How to cite: Lorito, S., Selva, J., Amato, A., Babeyko, A., Bayraktar, B., Bernardi, F., Charalampakis, M., Cordrie, L., Kalligeris, N., Piatanesi, A., Romano, F., Scala, A., Tonini, R., Volpe, M., Cambaz, M. D., and Kalafat, D.: The Tsunami Warning triggered in the Mediterranean Sea by the 2023 February 6 Mw 7.8 Türkiye-Syria earthquake: from the present Decision Matrix (DM) to Probabilistic Tsunami Forecasting (PTF)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17621, https://doi.org/10.5194/egusphere-egu23-17621, 2023.

EGU23-17624 | Orals | SM1.6

February 6, 2023, Mw 7.8 and 7.6 Kahramanmaraş (Turkiye) Earthquake Sequence: Insights from Co-seismic and Post-seismic Surface Deformation 

Seda Özarpacı, Alpay Özdemir, Efe Turan Ayruk, İlay Farımaz, Muhammed Turğut, Yusuf Yüksel, Figen Eskiköy, Uğur Doğan, Semih Ergintav, Cengiz Zabcı, Rahşan Çakmak, Mehmet Köküm, and Ziyadin Çakır

On 6 February 2023, 04:17 in local time, Mw 7.8 earthquake and nine hours later, 13:24 in local time, Mw 7.7 earthquake struck the same region resulting a massive destruction with loss of lives more than 41,000 in Türkiye and 4,000 Syria.  The earthquake took place on the East Anatolian Fault Zona (EAFZ) which is a plate boundary (~600 km) between the Anatolian and Arabian plates from Karlıova triple junction between Arabian, Anatolian and Eurasian plates to the Dead Sea Fault Zone (DSFZ) and parts of another triple junction at the south end between Adana block, Anatolian and Arabian plates at Kahramanmaraş. Secular plate velocities between Arabia and Anatolia range from 6 to 10 mm/yr and has resulted in destructive earthquakes in eastern Turkey as documented by historical records. The largest known earthquakes along the EAFZ occurred on November 29, 1114 (M > 7.8), March 28, 1513 (M > 7.4) and March 2, 1893 (M > 7.1).  The activity of these large devastating historical earthquakes contrasts with the low-level activity during the 20th century. The quiescence ended with the Mw 6.9 1971 Bingöl earthquake, which is followed about 50 year later by the Mw 6.9 January 24, 2020 Sivrice, Elazığ earthquake that ruptured only 45 km of the 95 km long Sivrice-Pütürge segment. With the latter event, seismicity accelerated along the rupture zone and activity moved towards to the SW.

Our aim is to monitor and estimate the co- and post- deformation field from geodetic measurements (InSAR and GNSS). While maximum co-seismic displacement at the ANTE GNSS station was 0.4 m in the first event (KMRS, Kahramanmaras), the biggest co-seismic displacement observed in the second event was 4.5 m in EKIZ (Ekinozu) station which is ~1.5 km away from the epicenter of the second earthquake. This co-seismic deformation field was estimated from open station of TUSAGA-Active GNNS Network. Following the earthquakes, we established three new continuous GNSS stations to monitor the postseismic deformation in Hatay province close to Türkoğlu segment of the East Anatolian Fault. Preliminary analysis indicates about 20 mm of postseismic deformation 10 days following the earthquakes. We have also conducted a GNSS campaign and occupied nearfield benchmarks. We will also monitor postseismic deformation using Sentinel and CosmoSkyMed SAR data field.

This work is supported by TUBITAK project number 121Y400 and 1002-C project “Mw 7.7 Pazarcik (Kahramanmaras) Earthquake Sequence”.

Keywords: 06.02.2023 Turkiye Earthquake Sequence, Kahramanmaras Earthquake, GNSS, InSAR, Coseismic and Postseismic Deformation

How to cite: Özarpacı, S., Özdemir, A., Ayruk, E. T., Farımaz, İ., Turğut, M., Yüksel, Y., Eskiköy, F., Doğan, U., Ergintav, S., Zabcı, C., Çakmak, R., Köküm, M., and Çakır, Z.: February 6, 2023, Mw 7.8 and 7.6 Kahramanmaraş (Turkiye) Earthquake Sequence: Insights from Co-seismic and Post-seismic Surface Deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17624, https://doi.org/10.5194/egusphere-egu23-17624, 2023.

EGU23-17626 | Posters on site | SM1.6

The contribution of Total Variometric Approachto the 2023 Türkiye earthquake sequences 

Michela Ravanelli, Federica Fuso, Elvira Astafyeva, and Mattia Crespi

The 2023 Türkiye earthquake sequences are among the most devastating events of recent years. The earthquake occurred on February 6th, 2023 and was characterized by several foreshocks starting from 1:17UT. The Mw 7.8 shock was the strongest and was caused by a shallow strike-slip faulting.
We applied the Total Variometric Approach (TVA) methodology to fully characterize the 2023 Turkey earthquake sequences from ground to the ionosphere [1].
The TVA technique simultaneously employs two variometric algorithms, VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) and VARION (Variometric Approach for Real-Time Ionosphere Observation), to retrieve earthquake ground shaking, co-seismic displacements and ionospheric Total Electron Content (TEC) variations in real-time. TVA was already successfully applied to the 2015 Mw 8.3 Illapel earthquake and tsunami.
In this case, we used IGS observations from 6 GNSS located in Turkey, Greece and Israeli and data from 60 GNSS receivers belonging to the Turkish network TUSAGA-Akitf [2].

Our first results show very strong ground shaking up to 10 cm/s in the East direction and up to 25 cm in the North direction. We notice great displacements especially in the horizontal plane (up to 30 cm). This is coherent with a strike-slip earthquake. Nonetheless, we also observe great displacements in the Up component (up to 1m). This could be the reason why we see this earthquake signature also in the ionosphere, although it is a strike-slip shock.
Indeed, preliminary ionospheric analyses reveal the signature of acoustic-gravity waves epicenter (AGWepi) especially for satellites G03, G04, G31 and E09.
A 30cm tsunami wave was also registered in Erdemil, along the Turkish coastline.

This study shows how the TVA can contribute to the complete understanding and rapid characterization of the seismic event, from ground to the atmosphere, and to manage and real-time earthquake hazard assessment.

[1] Ravanelli, M., Occhipinti, G., Savastano, G., Komjathy, A., Shume, E. B., & Crespi, M. (2021). GNSS total variometric approach: first demonstration of a tool for real-time tsunami genesis estimation. Scientific Reports, 11(1), 1-12.

[2] https://www.tusaga-aktif.gov.tr/

How to cite: Ravanelli, M., Fuso, F., Astafyeva, E., and Crespi, M.: The contribution of Total Variometric Approachto the 2023 Türkiye earthquake sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17626, https://doi.org/10.5194/egusphere-egu23-17626, 2023.

EGU23-17628 | Posters on site | SM1.6

Surface deformation retrieval of the February 2023 South-East Turkeyand Northern Syria Mw 7.8 and Mw 7.5 seismic events through Sentinel-1and SAOCOM-1 co-seismic SAR image analysis 

Francesco Casu, Fernando Monterroso, Yenni Lorena Belen Roa, Pasquale Striano, Simone Atzori, Manuela Bonano, Claudio De Luca, Marianna Franzese, Michele Manunta, Giovanni Onorato, Muhammad Yasir, Ivana Zinno, and Riccardo Lanari

On 6 February 2023 two Mw 7.8 and Mw 7.5 seismic events struck the South-East Turkey and Northern Syria regions, close to the cities of Gaziantep and Ekinözü, causing more than 50 thousands of fatalities and above 120 thousands of injured, with incalculable, widespread damage to the surrounding villages. Such earthquakes are related to the main geodynamic regime controlled by the triple junction between the Anatolian, Arabian and African Plates, and by the tectonic context associated with a shallow strike-slip faulting, including the East Anatolian Fault zone and the Dead Sea Transform. Immediately after the occurrence of these earthquakes, we started investigating the surface deformation field induced by the considered seismic events by applying the Differential SAR Interferometry (DInSAR) and the Pixel Offset (PO) techniques, within the framework of EPOS (European Plate Observing System), which is the European research infrastructure for the study of the solid Earth.

To this aim, we exploited several co-seismic SAR data pairs that have been collected by different satellite constellations. First of all, we exploited C-band (5.6 cm of wavelength) SAR data acquired by the Sentinel-1A sensor of the European Copernicus program from both ascending (Track 14) and descending (Track 94 and 21) orbits. Moreover, we benefited from the availability of a number of L-band (23 cm of wavelength) SAR images acquired by the twin satellites of the Argentine SAOCOM-1 constellation, programmed in collaboration with the Italian and Argentine Space Agencies.

The main focus of this work regards the joint exploitation of the Sentinel-1 and SAOCOM-1 SAR products to retrieve the 3D co-seismic deformation field. Further analysis is envisaged in order to model the co-seismic sources.

This work is supported by: the 2022-2024 IREA-CNR and Italian Civil Protection Department agreement, and by the H2020 EPOS-SP (GA 871121) and Geo-INQUIRE (GA 101058518) projects. The authors also acknowledge ASI for providing the SAOCOM data under the ASI-CONAE SAOCOM License to Use Agreement. Sentinel-1 data were provided through the European Copernicus program.

How to cite: Casu, F., Monterroso, F., Roa, Y. L. B., Striano, P., Atzori, S., Bonano, M., De Luca, C., Franzese, M., Manunta, M., Onorato, G., Yasir, M., Zinno, I., and Lanari, R.: Surface deformation retrieval of the February 2023 South-East Turkeyand Northern Syria Mw 7.8 and Mw 7.5 seismic events through Sentinel-1and SAOCOM-1 co-seismic SAR image analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17628, https://doi.org/10.5194/egusphere-egu23-17628, 2023.

EGU23-17632 | Posters on site | SM1.6

Direct Rupture Speed Estimation from "Rupture Phase" of the 2023 Turkey Mw 7.8 Earthquake 

Suli Yao and Hongfeng Yang

Rupture speed is a fundamental dynamic characteristic of earthquakes, which can be inferred by multiple approaches such as the back projection (BP) and kinematic fault slip inversion with near-field or far-field data as constraints. Here we propose a rapid estimate for rupture speed directly from the strong motion records along the southern segment of the Mw 7.8 Turkey earthquake on 6 Jan 2023. We collect data on 12 strong motion stations that are located within 3 km from the major fault trace. Due to the short distances to the fault, the ground motions on these stations can approximate a very local rupture phase, with the peak amplitudes of fault-parallel velocities corresponding to the rupture front passage. We pick peak velocities on three components and obtain an apparent propagation speed of ~ 3 km/s. To validate the correlation between the rupture speed and the apparent rupture-phase speed, we conduct 3-D dynamic rupture simulations for this Mw 7.8 event and compare the synthetic rupture front with the rupture phase. We find that the rupture speed is slightly higher than the rupture-phase speed with a difference of 5% - 10%. Based on our modeling results, we infer the actual rupture speed of ~3.2 km/s along the south segment in the Mw 7.8 Turkey earthquake. Different from those waveform-fitting methods that require certain assumptions on the earthquake source, such as the relation between the rupture front and the radiation process or the slip rate function, our approach provide a fast and robust rupture speed estimation that can be done in real time.

How to cite: Yao, S. and Yang, H.: Direct Rupture Speed Estimation from "Rupture Phase" of the 2023 Turkey Mw 7.8 Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17632, https://doi.org/10.5194/egusphere-egu23-17632, 2023.

EGU23-17634 | Posters on site | SM1.6

Sequence-specific updating of European ETAS model: Application to the 2023 Türkiye-Syria earthquake sequence 

Marta Han, Leila Mizrahi, Stefan Wiemer, and Irina Dallo

We analyse the spatio-temporal evolution of the aftershock sequence to the 2023 M7.8 Türkiye-Syria earthquake. Recently, we have calibrated a generic ETAS-based operational forecasting model for Europe, using the unified earthquake catalog developed within the European Seismic Hazard Model (ESHM20; Danciu et al., 2022) for data between 1990 and 2015. Focusing on the earthquake sequence that started in February 2023 in Türkiye, we analyse how our model would have forecasted the temporal and spatial evolution of the sequence. We observed that the productivity of the sequence is substantially higher than forecasted by our generic model. Similar observations have been made in earlier studies on other sequences, and strategies have been proposed to improve existing models based on sequence-specific data (e.g., Omi et al., 2015). Therefore, we conclude that sequence-specific updating is required to achieve an acceptable fit between model and observations.

Here, we investigate the best way to visualize the results of aftershock forecasting and operational earthquake forecasting, and propose a new strategy for sequence-specific updating of model parameters to accurately describe the productivity and the spatial aftershock distribution, while leveraging on the parameters obtained from larger amounts of data within the European model. Our approach strives to avoid biases in the description of the temporal decay due to relying on short-term data. This is done by keeping the parameters describing the temporal decay fixed to the values inverted with our baseline model and calibrating the remaining parameters, using data of the ongoing sequence. As an alternative way to better control productivity, we test model variants for which the a value is fixed to be equal to the GR law exponent b, as proposed by Hainzl et al. (2008). The variants with both fixed and calibrated temporal kernel and productivity are fitted to varying time periods of the Turkish sequence.

We assess the model’s consistency with observations by comparing the forecasts issued by the basic and modified models to the observed events. Preliminary results suggest that keeping the temporal kernel and the productivity parameter a fixed provides better forecasts than the baseline model, already when small amounts of data from the sequence are available. Having identified a promising strategy for sequence-specific model updating, we plan to test whether it is systematically successful by applying it to all earthquake sequences in Europe that occurred after the end of the baseline model training period in 2015. Moreover, we will develop prototypes of communication products that should support professional, societal stakeholders (e.g., decision makers, first responders) to take informed decisions, for example during rescue investigations. Thereby, we will follow evidence-based recommendations derived from the research efforts in the European Horizon-2020 project RISE (Freeman et al., 2023).

How to cite: Han, M., Mizrahi, L., Wiemer, S., and Dallo, I.: Sequence-specific updating of European ETAS model: Application to the 2023 Türkiye-Syria earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17634, https://doi.org/10.5194/egusphere-egu23-17634, 2023.

SM2 – Seismic Instrumentation and Infrastructure

EGU23-1069 | ECS | Orals | SM2.1

Seismic Anisotropy from 6C Observations 

Le Tang, Heiner Igel, and Jean-Paul Montagner

A new approach is proposed for measuring the local dispersion curves of surface waves in weakly anisotropic media using a single, multi-component station, which consists of translation and rotation or strain. We directly extract the local azimuth-dependent phase velocity of the Rayleigh wave from the 6C amplitude ratio using seismic arrays deployed in Southern California. The extracted dispersion curves match well with the theoretical 2φ azimuthal anisotropy term. And the estimated fast wave direction is also consistent well with results calculated from SKS and beamforming methods which demonstrates the feasibility of studying local seismic anisotropy directly from 6C amplitude observations.

How to cite: Tang, L., Igel, H., and Montagner, J.-P.: Seismic Anisotropy from 6C Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1069, https://doi.org/10.5194/egusphere-egu23-1069, 2023.

Distributed Acoustic Sensing (DAS) in geothermal wells is a particularly attractive technology to implement as part of routine seismic monitoring of geothermal plant operations. It brings a large network of sensors close to the monitoring target – the operated reservoir – increasing the sensitivity towards low magnitude events and allows the application of processing procedures inspired by large network or array processing. However, the technical management of the large flow of produced data and the suitability of the strain-rate acquisitions to monitor locally induced seismicity was yet to be fully assessed.

We present the results of a continuous 6-month monitoring period that aimed at testing an integrated system designed to manage the acquisition, the processing and the saving of DAS data collected from behind casing at the Schäftlarnstraße (SLS) geothermal project (Munich, Germany). The data management system links the existing on-site infrastructure to a cloud Internet-of-Things (IoT) platform integrated into the company’s IT infrastructure. The cloud platform has been designed to deliver both a secure storage environment for the DAS records and optimized computing resources for their continuous processing.

With a special focus on seismic risk mitigation, we investigate the potential of the monitoring concept to provide sensitive detection capabilities, despite operational conditions, while ensuring efficient data processing in order to strive for real-time monitoring. Further analysis of the records confirm additional logging capabilities of borehole DAS. We also evaluate the ability of DAS to provide reliable seismic source description, in particular in terms of location, moment magnitude, and stress drop.

Using two detected local seismic events, we demonstrate the relevance of the system for monitoring the SLS-site in an urban environment, while complementing advantageously the surface seismometer-based monitoring network.

How to cite: Azzola, J. and Gaucher, E.: Continuous seismic monitoring of a geothermal project using Distributed Acoustic Sensing (DAS): a case study in the German Molasse Basin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1292, https://doi.org/10.5194/egusphere-egu23-1292, 2023.

EGU23-2091 | Orals | SM2.1 | Highlight

Using DAS-fibres at ocean floor and lunar surface 

Martin Landrø

We have used two seabed fibre optic cables connecting Ny Ålesund and Longyearbyen at Svalbard, North of Norway, to track several whales for several weeks. Exploiting that we have access to two fibres we demonstrate that it is possible to track several whales in a fairly large region. It is possible to create sound records of whales that can be used for identification and discrimination between various species. The localization method has also been tested by using a small air gun to confirm the localization method used for whales. Examples of earthquake recordings, ship traffic monitoring and distant storms will be shown.

Based on the rapid and promising developments within DAS technology, there is a growing interest for using fibre optic cables at the moon. Some challenges and possibilities related to Lunar DAS applications will be discussed.

How to cite: Landrø, M.: Using DAS-fibres at ocean floor and lunar surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2091, https://doi.org/10.5194/egusphere-egu23-2091, 2023.

EGU23-2814 | Orals | SM2.1

Divergence-based estimation of Rayleigh wave dispersion curves 

Pascal Edme, David Sollberger, Tjeerd Kiers, Cedric Schmelzbach, Felix Bernauer, and Johan Robertsson

We present a novel seismic acquisition and processing technique to efficiently evaluate the local dispersion curves of Rayleigh waves for subsequent inversion of shear velocities and near-surface characterization.

The proposed approach consists of computing the ratio between the (time derivated) horizontal spectra H(f)=(∂tVx(f)2+∂tVy(f)2)1/2  and the pseudo-divergence spectra D(f), with D being the sum of the horizontal gradients of the horizontal components (i.e. D=∂xVx+∂yVy).

The processing method itself is comparable to the commonly used H/V approach, except that the H/D spectral ratio provides a direct estimate of the frequency-dependent phase velocities cR(f)  instead of the site frequency amplification(s). This is demonstrated using synthetic data.

We describe how the D component can be obtained in practice, i.e. by finite-differencing closely spaced horizontal phones or potentially using Distributed-Acoustic-Sensing (DAS) and fibre-optic deployed at the surface. Some limitations about wavelength dependency and impact of Love waves are discussed, as well as potential mitigation measures.

A field test on several hours of ambient noise data collected in Germany with multi-component geophones results in realistic values of Rayleigh wave velocities ranging from ~770 m/s at 10 Hz to ~500 m/ at 30 Hz. Thanks to the local and omni-directional nature of the estimation, the minimal number of required channels and the applicability to ambient noise, we believe that the proposed H/D method can be an attractive alternative to expensive array-based techniques.

How to cite: Edme, P., Sollberger, D., Kiers, T., Schmelzbach, C., Bernauer, F., and Robertsson, J.: Divergence-based estimation of Rayleigh wave dispersion curves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2814, https://doi.org/10.5194/egusphere-egu23-2814, 2023.

EGU23-3061 | Orals | SM2.1

Nano-strain resolution fiber-optic Fabry-Perot sensors based measuring systems 

Simon Pevec and Denis Donlagic

A work describes a deeply etched, long active length, high sensitivity short Fabry-Perot cavity nano-strain resolution sensor. The presented sensors exhibit high spectral sensitivity, low intrinsic temperature sensitivity which is for about 40 times lower than in case of FBG, small size and mounting comparable to conventional Fiber Bragg gratings. The sensor high potential is not only high sensitivity and low temperature intrinsic sensitivity, but also in short cavity length and its tunability, which can be simply accomplished in one production step. This brings versatility in interrogation with different general purpose and cost-efficient VIS-NIR widely available linear detector array-based spectrometers, while still providing strain sensing resolution within the range of few 10 nε. A strain resolution of 20 to 70 nε was demonstrated when using a cost-efficient VIS spectrometer. Furthermore, the sensor structure can be combined with multimode telecom lead-in fibers and low-cost broadband LEDs intended for automotive/lightning applications, which allow production of cost efficient solutions.

How to cite: Pevec, S. and Donlagic, D.: Nano-strain resolution fiber-optic Fabry-Perot sensors based measuring systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3061, https://doi.org/10.5194/egusphere-egu23-3061, 2023.

EGU23-3437 | ECS | Posters on site | SM2.1

Monitoring temperature at the ocean seafloor with fibre optic cables and DAS 

Julián Pelaez Quiñones, Anthony Sladen, Aurelien Ponte, Itzhak Lior, Jean-Paul Ampuero, Diane Rivet, Samuel Meulé, Frédéric Bouchette, Ivane Pairaud, and Paschal Coyle

Ocean water temperature measurements are fundamental to atmospheric and ocean sciences. Obtaining them, however, often comes along with major experimental and logistic challenges. Except for the uppermost ocean surface temperature, which can be measured from satellites, temperature data of the ocean is often poorly sampled or nonexistent, especially in deep-water regions.

Although Distributed Acoustic Sensing (DAS) technology has become popular because its high sensitivity to strains and mechanical vibrations, our work focuses on its usage on tens-of-kilometer-long underwater fibre-optic (FO) telecommunication cables to measure temperature anomalies at the seafloor at millikelvin (mK) sensitivity. This is possible because of the lack of dominant strain signals at frequencies less than about 1 mHz, as well as the poor coupling of the fibre with these signals while remaining highly sensitive to slow ambient temperature variations that locally affect its optical path length. DAS allows us to observe significant temperature anomalies at the continental shelf and slope of the Mediterranean sea, South of Toulon, France over periods of several days, with variability remaining relatively low at the deep ocean. By means of this approach, oceanic processes such as near-inertial internal waves and upwelling can be monitored at unprecedented detail.

Our observations are validated with oceanographic in-situ sensors and alternative Distributed Fibre Optic Sensing (DFOS) technologies established for temperature sensing. We outline key advantages of DAS thermometry over the aforementioned sensors in terms of spatial coverage, sensitivity, versatility and highest attainable frequency. At the current state of the art, DAS can only measure temperature anomalies as opposed to absolute temperature, a drawback that could be compensated via single temperature calibration measurements.

How to cite: Pelaez Quiñones, J., Sladen, A., Ponte, A., Lior, I., Ampuero, J.-P., Rivet, D., Meulé, S., Bouchette, F., Pairaud, I., and Coyle, P.: Monitoring temperature at the ocean seafloor with fibre optic cables and DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3437, https://doi.org/10.5194/egusphere-egu23-3437, 2023.

EGU23-3955 | ECS | Orals | SM2.1

Using Distributed Acoustic Sensing to Monitor and Investigate Eruptive Events at Stromboli Volcano, Italy 

Francesco Biagioli, Jean-Philippe Métaxian, Eléonore Stutzmann, Maurizio Ripepe, Alister Trabattoni, Pascal Bernard, Roberto Longo, Gianluca Diana, Lorenzo Innocenti, Yann Capdeville, Marie-Paul Bouin, and Giorgio Lacanna

Volcano seismology is essential for understanding, monitoring, and forecasting eruptive events. The use of distributed acoustic sensing (DAS) technology can be particularly useful for this purpose because of its high temporal and spatial resolution, which may help to overcome the challenges of deploying and maintaining seismic arrays on volcanoes.

Between 2020 and 2022, we installed 4 km of optical fibre on Stromboli volcano, Italy, whose persistent activity is well-suited for investigating the related dynamic strain rate. The cable was buried at a depth of 30 cm and the layout geometry was designed to provide wide coverage while being constrained by natural obstacles and topographical features. Seismometers were also installed along the fibre. DAS data were collected using a Febus A1-R interrogator, and the acquisition period increased from one week in 2020 to over four months in 2022. We recorded volcanic tremor, ordinary explosions (several per hour), two major explosions in 2021 and 2022, and the entire sequence of a pyroclastic flow in 2022. 

DAS and seismic data show good agreement in both time and frequency domains after converting strain rate to velocity and vice versa using different methodologies. Beamforming of DAS data shows a dominant signal in the 3-5 Hz frequency band coming from the active craters. We will also present preliminary results of major explosions and pyroclastic flow. This experiment demonstrates that DAS can be used for monitoring volcanic activity.

How to cite: Biagioli, F., Métaxian, J.-P., Stutzmann, E., Ripepe, M., Trabattoni, A., Bernard, P., Longo, R., Diana, G., Innocenti, L., Capdeville, Y., Bouin, M.-P., and Lacanna, G.: Using Distributed Acoustic Sensing to Monitor and Investigate Eruptive Events at Stromboli Volcano, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3955, https://doi.org/10.5194/egusphere-egu23-3955, 2023.

EGU23-4256 | ECS | Posters on site | SM2.1

Groundwater monitoring using fibre-optics and DAS: Application to the Lyon water catchment area. 

Destin Nziengui Bâ, Olivier Coutant, and Camille Jestin

Water resource management is a crucial socio-economic issue that requires developing high-resolution monitoring techniques, including non-invasive geophysical methods. Among them, passive seismic interferometry takes advantage of natural ambient seismic noise to recover the slight variations of the seismic wave velocity induced by changes in the groundwater level. In this study, we present the time and space monitoring of groundwater changes artificially generated by infiltration ponds at the exploitation field of Crépieux-Charmy (Lyon, France).  We deployed 3km of optical fibre and a dense array of fifty 3C geophones around infiltration basins. We recorded several cycles of filling-emptying with a DAS using a 2m spatial sampling (i.e., 1500 fibre sensors). The recorded signals are mainly associated with local anthropogenic noise (highways, trains, pumping, etc.). We could track seismic velocity variations with high temporal and spatial resolutions using ambient noise interferometry techniques. These variations are associated with the interaction between the water diffused from the basins and water table variations. This dynamic information helps understand and model water exchanges on the ground. The study confirms the possibility of groundwater monitoring using DAS records of ambient noise for seismic interferometry in a highly urbanized zone.

How to cite: Nziengui Bâ, D., Coutant, O., and Jestin, C.: Groundwater monitoring using fibre-optics and DAS: Application to the Lyon water catchment area., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4256, https://doi.org/10.5194/egusphere-egu23-4256, 2023.

EGU23-4769 | ECS | Orals | SM2.1

Arrival Picking for Distributed Acoustic Sensing seismic based on fractional lower order statistics 

Xiang Wang, Honghui Wang, Yuhang Wang, Shangkun Zeng, and Yiru Wang

In recent years, fiber-optic distributed acoustic sensing (DAS) has been gradually applied to seismology because of its long-distance and dense observation capability. It is a great challenge to effectively process the massive seismic data recorded by DAS. At present, the seismic data processing methods based on deep learning have achieved great success, especially in the tasks of seismic detection and arrival-time picking. However, due to the differences between DAS and geophone, such as sensing principles, spatial and temporal sampling rates, and noise intensity. The seismic arrival time picking model based on deep learning, which is trained by geophone seismic data with low spatial and temporal sampling rates and low noise intensity, severely degrades in performance on DAS seismic data with high spatial and temporal sampling rates and high noise intensity. In addition, a new seismic arrival time picking model is trained by fully supervised learning, which usually requires a large number of seismic data with accurate labels. However, the huge cost of manual picking and the lack of effective automatic picking models make it very difficult to build large-scale DAS seismic data sets with accurate labels. Therefore, it is very difficult to build an arrival time picking model based on fully supervised learning for DAS seismic data.

In this study, we propose a DAS seismic arrival time picking method based on fractional lower order statistics. Based on the difference of probability density function between noise and seismic signal, the proposed method uses alpha-stable distribution modeling noise (generally follow a Gaussian distribution) and seismic signal (generally follow a non-Gaussian distribution), and uses fractional lower order statistics under the assumption of alpha-stable distribution as the characteristic function to pick the arrival time.

Synthetic and actual DAS data tests show that the proposed method has better performance and robustness to random noise than other methods based on characteristic functions, such as STA/LTA, AR-AIC and kurtosis. Since the actual DAS seismic data has no ground truth of arrival time, we have further the performance of the proposed method on the geophone seismic data set. The proposed method provides better results on geophone seismic data and the data after up-sampling them to the typical time sampling rate of DAS.

How to cite: Wang, X., Wang, H., Wang, Y., Zeng, S., and Wang, Y.: Arrival Picking for Distributed Acoustic Sensing seismic based on fractional lower order statistics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4769, https://doi.org/10.5194/egusphere-egu23-4769, 2023.

EGU23-5455 | ECS | Posters on site | SM2.1

Active-source seismic experiments with DAS for monitoring reservoir rock in underground laboratories 

Katinka Tuinstra, Antonio Pio Rinaldi, Federica Lanza, Alba Zappone, Andreas Fichtner, and Stefan Wiemer

Underground laboratories have become indispensable in the understanding of physical processes during e.g., hydraulic stimulation and seismic monitoring of deep geothermal reservoirs or CO2 storage target reservoirs. They provide a test bench and constitute the bridge between small-scale laboratory studies and full-scale pilot sites. Here, we present results from multiple active source seismic campaigns in one of the Swiss underground laboratories: the Mont Terri Rock Laboratory. Here, DAS fibres are cemented behind the casing of multiple monitoring boreholes and active shots are taken with a P-wave sparker. This dense array of active seismic measurements enables us to obtain a baseline characterisation of the P-wave velocity of the rock before any activity (e.g., injection) takes place. During stimulations, dynamic measurements with an active sparker source are recorded, followed by a time-lapse monitoring approach where seismic measurements are collected through active seismic campaigns in set time intervals in the months after stimulations. In this way we can create high-resolution, four-dimensional monitoring and characterisations of the rock body and potential earthquakes during the full monitoring period. We show different configurations and measurements settings with their effect on the DAS recordings of active signals.

How to cite: Tuinstra, K., Rinaldi, A. P., Lanza, F., Zappone, A., Fichtner, A., and Wiemer, S.: Active-source seismic experiments with DAS for monitoring reservoir rock in underground laboratories, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5455, https://doi.org/10.5194/egusphere-egu23-5455, 2023.

EGU23-5701 | ECS | Posters on site | SM2.1

Investigating Vibroseis Sweeps using 6 Rotational Sensors in Fürstenfeldbruck, Germany 

Gizem Izgi, Eva Eibl, Frank Krüger, and Felix Bernauer

Rotational motions can be recorded directly or derived from translational motion recordings. Fairly new rotational sensors allow seismologists to directly record and investigate rotational motions. In order to further investigate and compare recently developed rotational sensors an experiment was made in Fürstenfeldbruck. Within this scope, a vibroseis truck was operated starting from 20 November 2019, 11:00 UTC until 21 November 2019, 14:00 UTC. We recorded 480 Sweep signals at 160 different locations. The truck was operating at 30%, 50%, and 70% relative to a peak force output of 276 kN exciting the ground vertically and each sweep lasted 15 seconds starting with 7 Hz increased up to 120 Hz. We derived back azimuths of each sweep from 6 rotational sensors and calculated root mean squares of each component. We observed that within the first day, the North component of all sensors recorded the largest ground motion energy SV type of energy is dominant. The sweep sources were distributed over two North–South profiles and two East–West profiles.  While the truck moved to the east and its location moved from west to south of the rotational sensors, the signals dominate more and more on the East component.. From our preliminary results, we state that although having different signal to noise ratios all rotational sensor calculated the direction of each sweep. Thus, we can follow the movements of vibroseis truck using all rotational sensors.

How to cite: Izgi, G., Eibl, E., Krüger, F., and Bernauer, F.: Investigating Vibroseis Sweeps using 6 Rotational Sensors in Fürstenfeldbruck, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5701, https://doi.org/10.5194/egusphere-egu23-5701, 2023.

EGU23-5955 | ECS | Orals | SM2.1

Two-dimensional phase unwrapping algorithm aided high-precision source positioning with DAS 

Jianhui Sun, Yuyao Wang, Jialei Zhang, Anchi Wan, Shibo Zhang, Zhenyu Ye, Fulie Liu, Gulan Zhang, and Zinan Wang

Seismic monitoring requires high temporal-spatial resolution and low deployment cost. Distributed acoustic sensing (DAS), as an emerging sensing technology for recording seismic data in recent years, can leverage communication cables for seismic monitoring, providing strong support for more intensive and real-time observation of geological activity. However, the traditional DAS phase unwrapping algorithms (PUAs) derived from Itoh requires the phase difference of adjacent pixels to be less than π, and thus make mistakes in the case of severe noise or large disturbance. In this paper, to the best of our knowledge, two-dimensional (2D) PUA is used to obtain seismograms in DAS for the first time. Satisfactory phase unwrapping is achieved by the 2D PUA method based on the transport of intensity equation (TIE), due to its robustness and noise immunity. Dynamic strain measurements in 80 m straight fiber-optic cable using homemade high-performance DAS, combined with TIE-based 2D PUA produce high-quality seismograms. Time Difference of Arrival (TDOA) Algorithm is applied based on the sensing signal of reliable channels in the seismograms, realizing the high-precision localization of the source. 2D PUAs apply to all phase-demodulation-based sensing techniques and are suitable for recovering spatially correlated objects such as seismic waves, thus having great potential in the field of seismic monitoring.

How to cite: Sun, J., Wang, Y., Zhang, J., Wan, A., Zhang, S., Ye, Z., Liu, F., Zhang, G., and Wang, Z.: Two-dimensional phase unwrapping algorithm aided high-precision source positioning with DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5955, https://doi.org/10.5194/egusphere-egu23-5955, 2023.

EGU23-6189 | ECS | Orals | SM2.1

Contribution of spatial features for classifying seismic events from Distributed Acoustic Sensing (DAS) data streams 

Camille Huynh, Clément Hibert, Camille Jestin, Jean-Philippe Malet, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) is an acoustic sensor instrument that turns a single optical fiber into a dense array of thousands of equally spaced seismometers. Geoscientists and companies have an interest in investing in DAS technologies for better understanding the Earth by observing natural and anthropogenic seismic events or assisting in large infrastructure monitoring with low installation and maintenance costs. However, this type of instrument generates a significantly larger amount of data than conventional seismometers, data that can be complex to store, exploit and interpret.

Several strategies for classifying seismic events from fiber-optics DAS data exist in the scientific literature. Conventional approaches rely on the use of features that describe the waveforms and frequency content of signals recorded individually at virtual stations along the fiber; they do not integrate the spatial density of information permitted by DAS. Several studies on dense seismological arrays have introduced similarity measures between the different time series data such as cross-correlations, dynamic time warping (DTW) or compression-based dissimilarity.

This study aims to quantify the contribution of spatial features for DAS data streams classification. We have chosen to explore spatial features related to both standard statistical measures (e.g., spatial mean, median, skewness, kurtosis), and advanced signal processing measures (e.g., auto-correlations, cross-correlations, DTW). This set of measures allows enriching a list of already used time series features which includes waveform, spectrum and spectrogram. A Random Forest (RF) classifier is then trained, and a Random Markov Field (RMF) algorithm is used after classification to account for redundant spatial and temporal information.

The evaluation of the spatial feature contribution is based on the output of the RF-RMF processing chain. Anthropogenically-triggered seismic data were acquired at the FEBUS Optics test bench. We consider five seismic sources: footsteps, impacts, excavators, compactor and fluid leaks. A class of noise is added as the RF-RMF algorithm is developed for processing DAS streams inherently affected by  noise.  Accurate  classification results can be obtained using only time features, and ongoing tests show a 2% increase in the correct classification rate with the use of both time and spatial features. The improvement allowed by the addition of spatial features is tangible but limited on our test dataset, but we think it should have a much greater impact on natural sources and we will discuss this perspective.

How to cite: Huynh, C., Hibert, C., Jestin, C., Malet, J.-P., and Lanticq, V.: Contribution of spatial features for classifying seismic events from Distributed Acoustic Sensing (DAS) data streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6189, https://doi.org/10.5194/egusphere-egu23-6189, 2023.

EGU23-6379 | Posters on site | SM2.1

Rotational ground motion recordings in the West Bohemia / Vogtland region for waveform inversion for seismic moment tensors 

Stefanie Donner, Johanna Lehr, Mathias Hoffmann, Frank Krüger, Sebastian Heimann, Rafel Abreu, and Stephanie Durand

In synthetic tests, rotational ground motion recordings proved to be beneficial for the wavefrom inversion for seismic moment tensors. In a next step, we want to verify these findings using real measurements. To do so, we installed two broadband rotational collocated to translational ground motion sensors in the West Bohemia / Vogtland area in summer 2022.

The area is characterised by regular seismic swarm activity, the last one occurring in December 2021. The seismic swarms are known to be connected with crustal flow of mantle fluids. However, the detailed mechanism of this connection is not well understood yet. Full seismic moment tensors, especially their non-double-couple part, will contribute to investigate the connection between swarm activity and fluid flow. So far, a lacking number of moment tensors and difficulties in the reliability of the non-double-couple part hampered the analysis in the study area. Including rotational ground motion recordings to waveform inversion will help to overcome these difficulties.

In seven months, we have recorded 120 events with magnitudes larger than M ≥ 0 in a distance of up to 35 km, thereof 35 around Nový Kostel, the center of the swarm activity. Considering that rotational sensors are about 2-4 times less sensitive than translational sensors (depending on the local phase velocity of the location) this is already a great success. Here, we show details of the sensor installations, first data analysis, and an estimate on the magnitude of completeness from rotational measurements.

How to cite: Donner, S., Lehr, J., Hoffmann, M., Krüger, F., Heimann, S., Abreu, R., and Durand, S.: Rotational ground motion recordings in the West Bohemia / Vogtland region for waveform inversion for seismic moment tensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6379, https://doi.org/10.5194/egusphere-egu23-6379, 2023.

EGU23-6422 | ECS | Posters on site | SM2.1

Effect of shallow heterogeneities on wavefield gradients measurements 

Mirko Bracale, Romain Brossier, Helle Pedersen, and Michel Campillo

In recent years, the use of rotational sensors and DAS has become a topic of increasing interest within the seismological community because of their increasing sensitivity and affordability. We analyze the sensitivity of wavefield gradients, in the form of normal strain and rotation, to localized shallow velocity changes in a homogeneous medium.
We performed several numerical simulations, using a suitably modified 3D-SEM code, to observe, in addition to wavefield itself, the normal strain and rotation as a direct output.
We analyzed two case studies in which a velocity anomaly is placed in a homogeneous medium. In the first case the velocity change between the anomaly and the surrounding medium is 10%, in the second case 70%. We analyzed the sensitivity of these new observables in terms of phase shift and amplitude change.
We observe a very local effect of the wavefield gradients, which show larger amplitude near the boundary between the medium and the anomaly, while away from it they behave like the displacement wavefield itself.

How to cite: Bracale, M., Brossier, R., Pedersen, H., and Campillo, M.: Effect of shallow heterogeneities on wavefield gradients measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6422, https://doi.org/10.5194/egusphere-egu23-6422, 2023.

EGU23-6915 | ECS | Posters on site | SM2.1

Modeling and analysis of Distributed Acoustic Sensing (DAS) data in Geothermal environments 

Davide Pecci, Juan Porras, Michele De Solda, Francesco Grigoli, Eusebio Stucchi, and Renato Iannelli

DAS technology is particularly suitable for microseismic monitoring application in geothermal environments. This instrumentation can resist to high temperatures (up to about 100°C or more) higher than the operational temperature of standard acquisition instruments (e.g., geophones), allowing the fiber to be located very close to the reservoir. For this reason, DAS is particularly useful for induced seismicity monitoring of Enhanced Geothermal System (EGS). Being of recent development, this acquisition technology still lacks appropriate modeling and analysis tools able to handle such a large amount of data without losing efficiency. Furthermore, open-access DAS datasets are still a rarity, if compared to other geophysical datasets (e.g., seismological data). Therefore, we aim to generate an open-access synthetic (but realistic) DAS dataset that may help the geophysical community to develop “ad hoc” data analysis methods suitable for this kind of data. In the presented work we make use of the spectral element modeling software 'Salvus', developed by Mondaic, which also allows the simulation of DAS data. In particular, it outputs a strain measurement between all points defined as receivers in the simulation. Using the repositories of DAS data collected at the geothermal test site Frontier Observatory for Research in Geothermal Energy (FORGE) located in Utah (USA), we tried to simulate realistic DAS acquisition conditions of seismic events related to low-magnitude natural seismic activity from the nearby Mineral Mountains and microseismic events related to hydraulic stimulation operations for the generation of an EGS.

In order to obtain realistic synthetic data, we first analyze the spectral properties of real noise waveforms by using the Power Spectral Density (PSD) Analysis. Starting from observed PSDs we model the synthetic noise waveforms using a stochastic approach. Then we add it to the synthetic event traces and compare them with the observed ones. We finally test a semblance-based event detector on a 1-hour continuous waveforms of synthetic data to evaluate the performance of the detector in different operational conditions (e.g., different noise levels and inter-event times).

How to cite: Pecci, D., Porras, J., De Solda, M., Grigoli, F., Stucchi, E., and Iannelli, R.: Modeling and analysis of Distributed Acoustic Sensing (DAS) data in Geothermal environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6915, https://doi.org/10.5194/egusphere-egu23-6915, 2023.

EGU23-6998 | ECS | Orals | SM2.1

Exploiting Terrestrial Meshed Optical Data Networks as Environmental Sensing Smart Grids 

Emanuele Virgillito, Stefano Straullu, Rudi Bratovich, Fransisco M. Rodriguez, Hasan Awad, Andrea Castoldi, Roberto Proietti, Andrea D'Amico, Francesco Aquilino, Rosanna Pastorelli, and Vittorio Curri

Optical networks for data transmission have become a pervasive infrastructure in the last years in order to cope with the increasing bandwidth request, thus there is a huge potential to be employed as a wide fiber optic sensing network. In the terrestrial scenario such networks are usually arranged on meshed topologies densely covering large areas of hundreths or thousands of kilometers. On the network's nodes, dedicated hardware is used to routed the data traffic between the connections' endpoints. Such nodes are interconnected by optical fiber links of hundreds of kilometers long, repeated every tenths of kilometers using optical amplifiers.

To fulfill the modern traffic requirements, optical networks are evolving towards multi-service autonomous, flexible, software defined entities based on a centralized intelligence orchestrating the networking functions and communicating with the network elements using standardized interfaces. This trend opens the perspective of using the optical network for evironmental sensing, such as earthquake detection or anthropic activities monitoring. 

Indeed, distributed acoustic sensing (DAS) systems based on Rayleigh scattering have demonstrated that optical fibers are excellent sensors of mechanical stress. However, such systems are expensive and pose some limitations on the maximum reach, so they cannot be deployed extensively. In this context, re-using the already deployed optical data infrastructure to support and integrate dedicated system sensing may be highly beneficial. In this work, we propose an optical data network architecture exposing sensing functionalities with minimum or no additional hardware simply by exploiting the pervasiveness of the telecommunication infrastructure and getting data from the physical quantities already monitored for data transmission purposes. Such architecture on a typical terrestrial optical data network is outlined in figure.

Modern coherent transceivers based on digital signal processing already track the evolution of the transmitted optical signal phase and polarization to recover the transmitted data at the receiver side. As those quantities are strongly affected by external strain, they already contain environmental information. Furthermore, some polarization-based processing can be implemented on cheaper non-coherent transceivers available at each amplifier site as data-service channel, providing several sensing sources.

In addition, further optical devices such as add-drop multiplexer or optical amplifiers typically have several other sensors already embedded (power monitors, temperature sensors) or they can be equipped with some others which can provide environmental data from other physical quantities.

The set of all such environmental data streams produced by the network elements constitutes the streaming telemetry fed to a network controller. A post-process agent may be implemented by exploiting the computational power available in typical network elements to perform local data analysis and reduce the amount of data sent to the sensing controller. By cross-processing the data coming from the network elements, a sensing controller is able to detect and localize events making the network act as a smart grid by continuously monitoring large areas and providing early warning signals.

To support our proposal, in this work we show the results of an experimental activity aimed at detecting and localizing anthropic activities in the city of Turin using a deployed fiber ring.

 

How to cite: Virgillito, E., Straullu, S., Bratovich, R., M. Rodriguez, F., Awad, H., Castoldi, A., Proietti, R., D'Amico, A., Aquilino, F., Pastorelli, R., and Curri, V.: Exploiting Terrestrial Meshed Optical Data Networks as Environmental Sensing Smart Grids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6998, https://doi.org/10.5194/egusphere-egu23-6998, 2023.

EGU23-7309 | ECS | Orals | SM2.1

Effects of cable geometry and specific noise sources on DAS monitoring potential 

Emanuele Bozzi, Nicola Piana Agostinetti, Alan F. Baird, Carlos Becerril, Biondo Biondi, Andreas Fichtner, Sara Klaasen, Nate Lindsey, Takeshi Nishimura, Patrick Paitz, Junzhu Shen, Arantza Ugalde, Fabian Walter, Siyuan Yuan, Tieyuan Zhu, and Gilberto Saccorotti

The Distributed Acoustic Sensing (DAS) method re-purposes fiber optic cables into a very-dense array of strain/strain-rate sensors, capable of detecting different types of seismic events. However, DAS data are characterized by lower SNRs compared with standard seismic sensors, mainly because of a) strong directivity effects, 2) ground coupling inhomogeneities, and 3) site effects. Hence, beyond the array geometry, specific noise sources may reduce the potential of DAS for seismic monitoring. Previous research has already shown successful case-studies for event detection/location. Nevertheless, a coherent test on the performances of various arrays of different sizes and geometries is still lacking.

In this study, an extensive DAS database is organized for such a goal, including 15 DAS arrays that recorded at least one seismic event (located at a range of distances from the arrays). P wave arrival times are exploited to estimate the epicentral parameters with a Markov Chain Monte Carlo method. Then, to analyze the effects of cable geometry and potential sources of noise/ambiguity on the location uncertainties, a series of synthetic tests are performed, where synthetic traveltimes are modified as follows: a) adding noise with equal variance to all the DAS channels (SYNTH-01), b) adding noise characterized by an increasing variance with the distance from the event (SYNTH-02), c) simulating the mis-pick between P and S phases (SYNTH-03) and d) adding noise with a variance influenced by cable coupling inhomogeneities (SYNTH-04). Results show that the epicentral locations with automatic P wave arrival times have different degrees of uncertainty, given the geometrical relation between the event and the DAS arrays. This behavior is confirmed by the SYNTH-01 test, indicating that specific geometries provide a lower constraint on event location. Moreover, SYNTH-04 shows that simulating cable coupling inhomogeneities primarily reproduces the observed location uncertainties. Finally, some cases are not explained by any of the synthetic tests, stressing the possible presence of more complex noise sources contaminating the signals.

How to cite: Bozzi, E., Piana Agostinetti, N., F. Baird, A., Becerril, C., Biondi, B., Fichtner, A., Klaasen, S., Lindsey, N., Nishimura, T., Paitz, P., Shen, J., Ugalde, A., Walter, F., Yuan, S., Zhu, T., and Saccorotti, G.: Effects of cable geometry and specific noise sources on DAS monitoring potential, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7309, https://doi.org/10.5194/egusphere-egu23-7309, 2023.

EGU23-7563 | ECS | Posters on site | SM2.1

TwistPy: An open-source Python toolbox for wavefield inertial sensing techniques 

David Sollberger, Sebastian Heimann, Felix Bernauer, Eva P. S. Eibl, Stefanie Donner, Céline Hadziioannou, Heiner Igel, Shihao Yuan, and Joachim Wassermann

In the past decade, significant progress has been made in the acquisition and processing of seismic wavefield gradient data (e.g., recordings of ground strain and rotation). When combined with conventional multicomponent seismic data, wavefield gradients enable the estimation of local wavefield properties (e.g., the local wave speed, the propagation direction, and the wave type) and the reconstruction of spatially under-sampled seismic wavefields. However, the seismological community has yet to embrace wavefield gradient data as a new observable.

We present TwistPy (Toolbox for Wavefield Inertial Sensing Techniques), an open-source software package for seismic data processing written in Python. It includes routines for single-station polarization analysis and filtering, as well as array processing tools. A special focus lies on innovative techniques to process spatial wavefield gradient data and, in particular, rotational seismic data obtained from dedicated rotational seismometers or small-aperture arrays of three-component sensors. Routines currently included in the package comprise polarization analysis and filtering in both the time domain and the time-frequency domain (for three-component and six-component data), dynamic tilt corrections, and beamforming (Bartlett, Capon, and MUSIC beamformers).  

With TwistPy, we attempt to lower the barrier of entry for the seismological community to use state-of-the art multicomponent and wavefield gradient analysis techniques by providing a user-friendly software interface.

Extensive documentation of the software and examples in the form of Jupyter notebooks can be found at https://twistpy.org.

How to cite: Sollberger, D., Heimann, S., Bernauer, F., Eibl, E. P. S., Donner, S., Hadziioannou, C., Igel, H., Yuan, S., and Wassermann, J.: TwistPy: An open-source Python toolbox for wavefield inertial sensing techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7563, https://doi.org/10.5194/egusphere-egu23-7563, 2023.

EGU23-8327 | Posters on site | SM2.1

Fibre-optic dynamic strain borehole sensing at Etna volcano 

Philippe Jousset, Gilda Currenti, Rosalba Napoli, Mario Pulvirenti, Daniele Pelligrino, Christian Cunow, Graziano Larocca, Alessandro Bonaccorso, Giuseppe Leto, and Charlotte Krawczyk

Volcano monitoring has been experiencing significant improvements in recent years, yet eruption forecasting and scenarios have still lack of understanding, due to the poor observations in low amplitude events and hindered by surface external noise of similar amplitudes. Volcanic events have been shown to be accurately recorded with fiber optic techniques at the surface. In this study, we present preliminary results of fibre optic cable deployed in a new 200 m deep borehole on the southern flank of Etna at about 6 km away from the summit crater. This borehole has been designed primarily for the future deployment of a new strain sensor type. We benefited from the drilling of this new borehole to deploy a single-mode fibre optic cable. We connected an interrogator and recorded dynamic strain rate during several periods: first, in 2020 for several days during the completion of the borehole and the final stage of the drilling; second, in 2021 for several weeks during an active volcanic period; and in December 2022 during a quiet activity period of several months. We present a selection of records of noise while drilling, local volcano-tectonic earthquakes and volcanic events and tremor that occurred during those periods. These examples show the benefit of deploying a fibre in a borehole far from the active area and demonstrate the great variety of signals fibre optic can record is such configuration.

How to cite: Jousset, P., Currenti, G., Napoli, R., Pulvirenti, M., Pelligrino, D., Cunow, C., Larocca, G., Bonaccorso, A., Leto, G., and Krawczyk, C.: Fibre-optic dynamic strain borehole sensing at Etna volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8327, https://doi.org/10.5194/egusphere-egu23-8327, 2023.

EGU23-8569 | Posters on site | SM2.1

Monitoring a commercially operating submarine telecom cable network in the Guadeloupe archipelago (Lesser Antilles) using Brillouin Optical Time Domain Reflectometry (BOTDR) 

Marc-Andre Gutscher, Lionel Quetel, Giuseppe Cappelli, Jean-Gabriel Quillin, Christophe Nativelle, Jean-Frederic Lebrun, and Melody Philippon

Submarine telecom cables criss-cross the oceans, connecting islands to continents and providing internet, financial and media services to consumers all around the world. Laser reflectometry as well as other optical techniques can potentially transform the optical fibers in these cables into sensors which can detect vibrations and ground motion from earthquakes, ocean waves, currents as well as permanent deformation of the seafloor. The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study movements at the seafloor.

 

Within the framework of the FOCUS project, and in collaboration with the “Conseil Regional” of Guadeloupe, in 2022 we began long-term monitoring of a network of submarine telecom cables that link the islands of the Guadeloupe archipelago. These cables connect the larger island of Basse Terre and Grande Terre to the smaller southern islands of Les Saintes, Marie Galante and La Desirade, with segment lengths ranging from 30 to 70 km. This network was deployed recently (in 2019) and is the property of the Conseil Regional of Guadeloupe, operated with the assistance of Orange. All cables contain twelve fiber pairs, of which three pairs are in use by mobile phone operators and thus unused fibers were available for this scientific monitoring project. In June 2022, we established BOTDR baselines on 8 optical fiber segments, in several cases in both directions. In December 2022, we repeated the measurements of the same fiber segments, allowing us to detect any strain along the cable over this period.

 

Here, we report that using the BOTDR technique, we detect significant strain signals  (50 micro-strain and more) in several locations along the cable network. These signals, which can be positive (elongation) or negative (shortening) occur typically in areas of steep seafloor slopes or in submarine valleys/canyons. Our tentative interpretation is that stretching and shortening of the cable (representing about 1 cm over a few hundred meters) is occurring, most likely due to sea-bottom currents. These currents may be related to the late summer/early autumn hurricane season, with the passage of tropical storm Fiona in Sept. 2022 dropping heavy rains, causing torrential floods and debris flows in some of the larger rivers with possible impacts further offshore. A longer time-series and more detailed analysis are necessary to test this preliminary hypothesis.

How to cite: Gutscher, M.-A., Quetel, L., Cappelli, G., Quillin, J.-G., Nativelle, C., Lebrun, J.-F., and Philippon, M.: Monitoring a commercially operating submarine telecom cable network in the Guadeloupe archipelago (Lesser Antilles) using Brillouin Optical Time Domain Reflectometry (BOTDR), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8569, https://doi.org/10.5194/egusphere-egu23-8569, 2023.

EGU23-8851 | ECS | Orals | SM2.1

Using Rotational Motions to understand material damage in Civil Engineering structure 

Anjali Dhabu, Felix Bernauer, Chun-Man Liao, Celine Hadziioannou, Heiner Igel, and Ernst Niederleithinger

The increasing evidence of rotational motions due to earthquakes is now motivating civil engineers to investigate the effects of rotational ground motions on structures. With the advancement in instrumentation techniques, rotational sensors have been developed in the past few years, which can measure three components of rotational waves in addition to the translational waves. Conventionally, buildings are designed to withstand horizontal and vertical translational ground motions to minimize the damage to human life and financial losses during an earthquake. Damage to the structure is identified at two levels; (i) structural and (ii) material. The structural damage in reinforced concrete buildings is visible in the form of cracks and spalling concrete, which reduces the overall load-carrying capacity of the building. The damage at the material level is not visible to the human eye. This damage can be identified using coda wave interferometry techniques. In this method, a high cross-correlation between the coda of two waves passing a point on different days of experiment indicates a negligible change in the shear wave velocity of the material. In comparison, a lower cross-correlation signifies considerable change in the material properties.    

In order to understand how rotational motions affect reinforced concrete structures and how these can be simulated, the present work makes a novel attempt to use the newly developed rotation measuring sensors, BlueSeis 3A and IMU50, to understand the damage in a model concrete bridge structure (BLEIB). We employ advanced sensors in addition to conventional broadband and ultrasonic sensors on the 24m long two-span continuous reinforced concrete bridge equipped with various non-destructive sensing techniques and subjected to a variable pre-tension force of up to 450kN and various static loads. As an initial analysis, we first identify the bridge's first three fundamental frequencies and mode shapes from both recorded translational and rotational data. The analysis shows that the same fundamental frequencies are obtained from the recorded translational and rotational data. However, we expect to see a difference in the mode shapes. Theoretically, rotations are maximum at the bridge support and minimum at the centre of the bridge span. This behaviour is the reverse of what we observe from translational motions, where maximum translations are observed at the centre of the span while minimum at the supports. As the study plans to simulate rotational motions for reinforced concrete structures, a finite element model of the prototype bridge is also developed, and the fundamental frequencies and mode shapes of the model are validated with those obtained from the recorded data. This work shall be extended to applying coda wave interferometry to the rotational data recorded on the bridge to understanding the change observed in material properties when the bridge is subjected to active and passive forces.

How to cite: Dhabu, A., Bernauer, F., Liao, C.-M., Hadziioannou, C., Igel, H., and Niederleithinger, E.: Using Rotational Motions to understand material damage in Civil Engineering structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8851, https://doi.org/10.5194/egusphere-egu23-8851, 2023.

EGU23-9089 | ECS | Orals | SM2.1

Detecting seismo-volcanic events based on inter-channel coherency of a DAS cable 

Julius Grimm, Piero Poli, and Philippe Jousset

Distributed Acoustic Sensing (DAS) has been successfully employed to monitor volcanic seismicity and to infer volcanic subsurface structures. Here, we analyse data recorded in September 2018 at Mount Etna by the 9N seismic network. The multi-instrument network includes a 1.3 km long fibre-optic cable that was buried 2-2.5 km away from the main craters. Additionally, 15 geophones were installed along the trajectory of the DAS cable, allowing for a comparison of strain-rate and ground velocity data.
During the acquisition period, tiny seismic events, likely caused by fluid movement and degassing, are visible with inter-event times in the range of 1 min. Volcanic explosions and volcano-tectonic earthquakes also occur frequently. We detect events over all frequency ranges by calculating the coherence matrix for very short time windows (stacking 15 windows of 5 seconds length). An eigendecomposition of the coherence matrices allows to extract the first eigenvectors, corresponding to the dominant source in the time window. The principal eigenvectors can be clustered to find groups of events with similar source properties. We also use the principal eigenvector of already known events as a matched filter to scan the whole dataset. The results of the DAS cable are compared to the observations of the geophone array. While largely obtaining similar findings, the DAS cable seems to better capture high-frequency features of certain events. We also explore the effects of stacking and downsampling of the DAS data prior to detection, which influences both resolution and computational efficiency of the algorithm.

How to cite: Grimm, J., Poli, P., and Jousset, P.: Detecting seismo-volcanic events based on inter-channel coherency of a DAS cable, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9089, https://doi.org/10.5194/egusphere-egu23-9089, 2023.

EGU23-9312 | Orals | SM2.1

Six-component wave type fingerprinting and filtering 

David Sollberger, Nicholas Bradley, Pascal Edme, and Johan O. A. Robertsson

We present a technique to automatically classify the wave type of seismic phases that are recorded on a single six-component recording station (measuring both three components of translational and rotational ground motion) at the earth's surface. We make use of the fact that each wave type leaves a unique 'fingerprint' in the six-component motion of the sensor. This fingerprint can be extracted by performing an eigenanalysis of the data covariance matrix, similar to conventional three-component polarization analysis. To assign a wave type to the fingerprint extracted from the data, we compare it to analytically derived six-component polarization models that are valid for pure-state plane wave arrivals. For efficient classification, we make use of the supervised machine learning method of support vector machines that is trained using data-independent, analytically-derived six-component polarization models. This enables the rapid classification of seismic phases in a fully automated fashion, even for large data volumes, such as encountered in land-seismic exploration or ambient noise seismology. Once the wave-type is known, additional wave parameters (velocity, directionality, and ellipticity) can be directly extracted from the six-component polarization states without the need to resort to expensive optimization algorithms.

We illustrate the benefits of our approach on various real and synthetic data examples for applications such as automated phase picking, aliased ground-roll suppression in land-seismic exploration, and the rapid close-to real time extraction of surface wave dispersion curves from single-station recordings of ambient noise. Additionally, we argue that an initial step of wave type classification is necessary in order to successfully apply the common technique of extracting phase velocities from combined measurements of rotational and translational motion.

How to cite: Sollberger, D., Bradley, N., Edme, P., and Robertsson, J. O. A.: Six-component wave type fingerprinting and filtering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9312, https://doi.org/10.5194/egusphere-egu23-9312, 2023.

EGU23-9314 | ECS | Orals | SM2.1

Using Distributed Fiber-optic Sensing for Tracking Caprock Fault Activation Processes 

Verónica Rodríguez Tribaldos, Chet Hopp, Florian Soom, Yves Guglielmi, Paul Cook, Tanner Shadoan, Jonathan Ajo-Franklin, Michelle Robertson, Todd Wood, and Jens Birkholzer

Identifying and monitoring the reactivation of faults and opening of fractures affecting low permeability, sealing formations in natural underground storage complexes such as Carbon Capture and Storage projects and Nuclear Waste repositories is essential to ensure storage integrity and containment. Although passive seismic monitoring can be effective for detecting induced failure, stress accumulation and fault reactivation can occur aseismically in clay-rich formations, preventing early failure to be recognized. Here, we investigate the potential of applying strain monitoring with fiber-optics sensing technologies to assess in-situ changing stress conditions at high spatial and temporal resolution.

We present results of fiber-optic sensing monitoring during the FS-B experiment, a controlled activation of a fault zone affecting the Opalinus Clay Formation in the Mont Terri underground Laboratory (Switzerland). Six constant flowrate water injections induced the hydraulic opening of the fault. A hydraulic connection between the injector and a monitoring borehole occurred, developing a flow path sub-parallel to the fault strike. A 2 km long fiber-optic cable looped through 10 monitoring boreholes surrounding and crossing the fault zone was used for distributed acoustic and strain sensing (DAS and DSS) before, during and after injection. Continuous low-frequency (< 1 Hz) DAS data reveals mechanical strain associated with fault reactivation. Increasing extensional strain is recorded near the point of injection and near the newly formed hydraulic flow path, reaching a value of ~150 μɛ. Post-activation residual strain of ~60 μɛ suggests irreversible fault zone deformation. Smaller strain changes are recorded above and below the high pressure flow path, suggesting a mechanically disturbed zone larger than the leakage zone. Low-frequency DAS data are consistent with co-located DSS strain data, local, 3D displacement measurements of fault movements and P-wave velocity anomalies derived from Continuous Active Source Seismic Monitoring (CASSM). Our results are promising and demonstrate the potential of fiber-optic sensing as a powerful tool for monitoring spatio-temporal evolution of fault reactivation processes and leakage in clay formations induced by fluid pressurization.

How to cite: Rodríguez Tribaldos, V., Hopp, C., Soom, F., Guglielmi, Y., Cook, P., Shadoan, T., Ajo-Franklin, J., Robertson, M., Wood, T., and Birkholzer, J.: Using Distributed Fiber-optic Sensing for Tracking Caprock Fault Activation Processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9314, https://doi.org/10.5194/egusphere-egu23-9314, 2023.

EGU23-9629 | ECS | Posters on site | SM2.1

Monitoring material properties of civil engineering structures with 6C point measurements 

Felix Bernauer, Shihao Yuan, Joachim Wassermann, Heiner Igel, Celine Hadziioannou, Frederic Guattari, Chun-Man Liao, Ernst Niederleitinger, and Eva P. S. Eibl

Observing motion within a building in six degrees of freedom (three components of translational motion plus three components of rotational motion) opens completely new approaches to structural health monitoring. Inspired by inertial navigation, we can monitor the absolute motion of a building or parts of it without the need for an external reference. Rotational motion sensors can directly measure harmful torsional modes of a building, which has always been challenging and prone to errors when using translation sensors only. Currently, we are developing methodologies including rotational motion observations for monitoring of material parameters in order to locate and characterize structural damage. Within the framework of the GIOTTO project (funded by the German Federal Ministry for Education and Research, BMBF) we explore these approaches.

Here, we introduce a newly developed 6C sensor network for structural health monitoring. It consists of 14 inertial measurement units (IMU50 from exail, former iXblue, France) that were adapted to the needs of seismology and structural health monitoring. We performed experiments at the BLEIB test structure of the Bundesanstalt für Materialforschung und -prüfung (BAM), a 24 m long concrete beam serving as a large scale bridge model. We present results on detecting changes in material properties (seismic wave speed) of the beam with varying pre-stress and load, as derived from a novel approach by comparing amplitudes of translational to rotational motions at a single measurement point. We compare our findings to results obtained with coda wave interferometry using rotational as well as translational motions.

How to cite: Bernauer, F., Yuan, S., Wassermann, J., Igel, H., Hadziioannou, C., Guattari, F., Liao, C.-M., Niederleitinger, E., and Eibl, E. P. S.: Monitoring material properties of civil engineering structures with 6C point measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9629, https://doi.org/10.5194/egusphere-egu23-9629, 2023.

EGU23-9641 | Posters on site | SM2.1

Loops of slack in dark fiber and their effect on interferometric analysis of ambient noise – symptoms, consequences and remedies 

Christopher Wollin, Leila Ehsaninezhad, Johannes Hart, Martin Lipus, and Charlotte Krawczyk

Seismic microzonation and ambient noise tomography via Distributed Acoustic Sensing (DAS) may contribute to the seismic hazard assessment and the exploration or monitoring of utilizable and utilised subsurface volumes at favorable costs. However, numerous technical aspects remain under investigation to further maturate this innovative seismological approach – particularly when applied to dark telecommunication fibers. For instance unknown coupling of the fiber to the ground or presence of loops of slack fiber may disturb the regular measuring of the stringed virtual sensors.

 

In this study, we investigate how loops of slack fiber affect the results of passive ambient tomography, a particularly appealing exploration approach due to its low footprint. We present results obtained with DAS recordings on purposefully installed as well as dark telecommunication optic fiber. Sledgehammer blows were recorded on an optic fiber laid out in an urban heating tunnel before and after introducing several loops of slack. The loops coiled up fractions and multiples of the utilized gauge length and were spaced in sufficient distance to independently analyze the surrounding wavefield. Discontinuous wavefronts can be observed once the coiled fiber exceeds the gauge length. Similar observations were made on the virtual shot gathers calculated along a 4.5 km long segment of dark fiber along a major road in the city of Berlin, Germany. We show how the loops of slack affect the further processing with respect to ambient noise tomography. On average, the removal of virtual sensors identified to be located in coiled fiber reduces the shear-wave velocities in the resulting model.

 

We conclude that the careful removal of virtual sensors within loops of slack is a mandatory processing step towards ambient noise tomography with linear DAS arrays. However, the calculation of virtual shot gathers can help to reveal the affected fiber segments.

How to cite: Wollin, C., Ehsaninezhad, L., Hart, J., Lipus, M., and Krawczyk, C.: Loops of slack in dark fiber and their effect on interferometric analysis of ambient noise – symptoms, consequences and remedies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9641, https://doi.org/10.5194/egusphere-egu23-9641, 2023.

EGU23-10767 | ECS | Posters on site | SM2.1

Exploring multiscale nonlinear NDTs for damage detection in concrete structures 

Marco Dominguez-Bureos, Celine Hadziioannou, Niklas Epple, Camila Sanchez Trujillo, and Ernst Niederleithinger

It has been shown that non-destructive tests (NDTs) based on nonlinear wave propagation are more sensitive to detecting very small damages in concrete structures than linear techniques. With the aim of exploring the nonlinear effects in civil structures as a damage indicator, we perform a 1-day multiscale vibration monitoring of a test bridge equipped with a pretension system.

We used the pretension system to subject the specimen to eight compression states in its longitudinal direction (400kN at the highest, and 280kN at the lowest). At every compression state, we struck the structure in the vertical direction three times at two locations on the bridge with an impulse source. Throughout the whole experiment, we recorded seismic ambient noise at different frequency bands with a 14-IMU50-sensor array to measure the acceleration and rotation rate, a 14-geophone array with a 4.5 Hz natural frequency, a DAS system, and 4 pairs of ultrasound transducers; the internal temperature of the concrete was also recorded.

At the structural scale (from 1 to 40 Hz) we were able to observe different responses of the structure to pre-tension changes, depending on where the measurement took place in relation to the vertical support pillars by estimating relative velocity changes using the Coda Wave Interferometry stretching processing technique.

At the material scale (ultrasound regime) we can observe temperature-dependent slow dynamics features related to changes in the seismic velocity of the concrete as a consequence of vertical strikes, and its recovery process that returns its physical properties to a steady state after the action of the impulse source.

With this work, we work towards the development of new NDTs that are increasingly sensitive to small cracks and imperfections using conventional and non-conventional seismic instruments to measure linear and nonlinear wave propagation.

How to cite: Dominguez-Bureos, M., Hadziioannou, C., Epple, N., Sanchez Trujillo, C., and Niederleithinger, E.: Exploring multiscale nonlinear NDTs for damage detection in concrete structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10767, https://doi.org/10.5194/egusphere-egu23-10767, 2023.

EGU23-11782 | ECS | Posters on site | SM2.1

A workflow to generate DAS based earthquake catalog, applied to an offshore telecommunication cable in central Chile 

Marie Baillet, Alister Trabattoni, Martijn Van Den Ende, Clara Vernet, and Diane Rivet

Fiber-optic Distributed Acoustic Sensing (DAS) is of critical value for the expansion of seismological networks, particularly in regions that are hard to instrument. The work presented here is part of the 5-year ERC ABYSS project, which aims at building a permanent seafloor observatory to increase our ability to capture low magnitude seismic signals from the subduction fault zone in the DAS data recorded by offshore telecommunication cables along the central coast of Chile.

In preparation for this project, a first experiment named POST was conducted from October to December 2021 on a submarine fiber-optic cable connecting the city of Concón to La Serena. DAS data were recorded continuously for 38 days over a distance of 150 km from Concón, constituting more than 36700 virtual sensors sampling at 125 Hz. This experiment provided an opportunity to anticipate what will be recorded over the next 5 years of the project, and to allow us to develop routines that will be applied later for real-time data processing.

As a first step, we developed an automated routine for generating a preliminary earthquake catalog, comprising various conventional signal processing steps, including data denoising, change-point detection, and separating seismic events from transient instrumental noise making use of the two-dimensional character of the DAS data. Over a span of 38 days (worth 72 TB of data), our pipeline detected more than 900 local, regional, and teleseismic events with local magnitudes down to ML < 2 (based on the Centro Sismológico Nacional (CSN) public catalog). The size of our catalog, enriched with numerous off-shore events, is a significant improvement over the current CSN catalog, which may aid future studies into the Chilean margin subduction zone seismicity.

How to cite: Baillet, M., Trabattoni, A., Van Den Ende, M., Vernet, C., and Rivet, D.: A workflow to generate DAS based earthquake catalog, applied to an offshore telecommunication cable in central Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11782, https://doi.org/10.5194/egusphere-egu23-11782, 2023.

EGU23-11842 | Orals | SM2.1

Using path-integrated strain in Distributed Acoustic Sensing 

Alister Trabattoni, Francesco Biagioli, Claudio Strumia, Gaetano Festa, Martijn van den Ende, Diane Rivet, Anthony Sladen, Jean-Paul Ampuero, Jean-Philippe Metexian, and Éléonore Stutzmann

Distributed Acoustic Sensing (DAS) is becoming a well-established technology in seismology. For historical and practical reasons, DAS manufacturers usually provide instruments that natively record strain (rate) as the principal measurement. While at first glance strain recordings appear similar to particle motion (displacement, velocity, acceleration) waveforms, not all of the seismological tools developed over the past century (e.g., magnitude estimation, seismic beamforming, etc.) can be readily applied to strain data. Notably, the directional sensitivity of DAS differs from conventional particle motion sensors, and DAS experiences an increased sensitivity to slow waves, often composed of highly scattered waves that are challenging to analyze. To address these issues, several strategies have been already proposed to convert strain rate measurements to particle velocity.

Based on a previously proposed mathematical formalism, we stress some fundamental differences between path-integrated strain and conventional displacement measurements. DAS inherently records arc length variation of the cable which is a relative motion measurement along a curvilinear path. We show that if the geometry of the DAS deployment is adapted to the wavefield of interest, path-integrated strain can be used to closely approximate the displacement wavefield without the need of additional instruments. We validate this theoretical result using collocated seismometers, discuss the limitations of this approach, and show two benefits: enhancing direct P-wave arrivals and simplifying the magnitude estimation of seismic events. While using path integrated strain is in some aspects more challenging, it achieves flat (hence lower) noise levels both in frequency and wavenumber. It also provides better sensitivity to high velocity phases, and permits the direct application of conventional seismological tools that are less effective when applied to the original strain data.

How to cite: Trabattoni, A., Biagioli, F., Strumia, C., Festa, G., van den Ende, M., Rivet, D., Sladen, A., Ampuero, J.-P., Metexian, J.-P., and Stutzmann, É.: Using path-integrated strain in Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11842, https://doi.org/10.5194/egusphere-egu23-11842, 2023.

EGU23-12213 | ECS | Posters on site | SM2.1

Near-surface seismic characterisation of a railway embankment slope using fibre-optic distributed acoustic sensing 

Giuseppe Maggio, Andrew Trafford, and Shane Donohue

The behaviour of geological slopes during seasonal weather patterns represents one of the challenges for assessing the geotechnical state of health of the ageing infrastructures. In the presence of man-made soil infrastructure slopes, rainfall and prolonged dry periods can cause cycles of swelling and shrinking of the ground that could potentially compromise their structural integrity. Recent research has found that time-lapse velocity monitoring, has the potential to provide information on climate-related deterioration of geotechnical infrastructure. Variations of the ground conditions could manifest as changes in seismic velocity, detectable through the seasons and after extreme weather events.

In this work, we perform seismic imaging and velocity-monitoring of a critical railway embankment in the United Kingdom using fibre optic distributed sensing (DAS). The study area is a 6 m tall, and 350 m long embankment slope built more than 100 years ago in the outskirts of London (Surrey). The railway is currently utilised mostly by commuter trains. Since August 2022, a passive DAS dataset rich in train signals has been acquired. data acquisition will continue until July 2023. Furthermore, periodic active surveys have been conducted along the slope.

Firstly, to validate the seismic response of the fibre (i.e., maximum usable frequencies based on the gauge length), we calculate and compare surface wave dispersion curves derived from both DAS and geophones using passive ambient noise, train signals and active sledgehammer shots. As a result, we obtain consistent and comparable dispersion curves ranging from ~200 m/s at 10 Hz to ~140m/s at 40 Hz. 

Secondly, we invert, using global search algorithms, DAS-derived dispersion curves for 1D depth-velocity models to identify and clarify the trend of the near-surface (top 10 m) seismic structures. 

Thirdly, we apply seismic interferometry and moving window cross-spectral techniques to measure changes in seismic velocity at the embankment using the 6-month passive DAS data acquired so far. 

The ultimate goal of this project is to develop a geophysical tool diagnostic of geotechnical deterioration of critical infrastructures by linking together DAS-based seismic observations, temporal seismic velocity changes, weather data and laboratory-based soil sample tests.

How to cite: Maggio, G., Trafford, A., and Donohue, S.: Near-surface seismic characterisation of a railway embankment slope using fibre-optic distributed acoustic sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12213, https://doi.org/10.5194/egusphere-egu23-12213, 2023.

EGU23-12740 | ECS | Orals | SM2.1

Coherence-based Amplification of Rayleigh Waves from Urban Anthropogenic Noise recorded with Distributed Acoustic Sensing 

Leila Ehsaninezhad, Christopher Wollin, Benjamin Schwarz, and Charlotte Krawczyk

At a local scale, e.g. in urban settlements, seismic subsurface characterization requires implementing experiments at high spatial resolution. Distributed acoustic sensing (DAS) provides the opportunity of using pre-existing fiber optic cables as dense receiver arrays, thus potentially reducing the effort for active seismic surveying in urban areas. Due to their small footprint, passive experiments appear particularly appealing. However, extracting coherent signals in an urban environment, i.e. in the presence of anthropogenic activity in the receivers' vicinity, remains a challenge.

 

In this study, we present results from combining the well known technique of Multichannel Analysis of Surface Waves (MASW) with the coherency-based enhancement of wavefields. The investigation is based on a DAS dataset acquired along a major road in Berlin, Germany. We analyse a 4.5 km long straight subsegment of a dark fiber that was sampled at 8 m intervals with 1000 Hz over a period of 15 days. After temporal decimation and the interferometric analysis, clear causal and a-causal branches of Rayleigh-surface waves emerge in the virtual shot gathers.

 

In the further processing, we employ coherence-based enhancement of wavefields to amplify the Signal to Noise Ratio of the virtual shot gathers. Compared to the traditional workflow of ambient-noise tomography the modified one yields improved dispersion curves particularly in the low-frequency part of the signal. This leads to an increased investigation depth along with lower uncertainties in the inversion result. The final velocity model reaches depths down to 300 m. We show that the application of coherence-based enhancement of the virtual shot gathers in the MASW-workflow may significantly relax the necessity of collecting long baselines for passive tomography in urban environments.

How to cite: Ehsaninezhad, L., Wollin, C., Schwarz, B., and Krawczyk, C.: Coherence-based Amplification of Rayleigh Waves from Urban Anthropogenic Noise recorded with Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12740, https://doi.org/10.5194/egusphere-egu23-12740, 2023.

EGU23-13600 | Orals | SM2.1

Long-awaited and delayed Transportable Highest grade of Fiber Optic Gyroscope for Seismology 

Frédéric Guattari, Guillaume Lenogue, Kevin Gautier, Arnaud Frenois, and André Couderette

First announced at EGU2021, and said to be “released soon”, the 1C rotation seismometer which complements the blueSeis product line on the high performance segment, will be finally disclosed at EGU2023.

2019 and 2020 results have been shared about large mockup of giant Fiber-Optic Gyroscope from iXblue, having diameter as large as 1.2 meters, and the development road to reach an industrial product had been drawn. But several critical additional issues raised on the track.

Keeping in mind all the requirement of the instrument, the need for a transportable, and easily deployable instrument, the calibration capability, the possibility to push the performance pilling up the sensors, and the need for an optional orthogonal structure, we finally come to an instrumental solution with high versatility at expected performances.

The full development story will be shared, and the tests results of first production units of blueSeis-1C will be disclosed. Explanation about the various way to use it will be offered too.

Perspectives and applications using this long-awaited sensor will be presented, from ocean-bottom system tilt denoising to improved inversion of the seismic source.

How to cite: Guattari, F., Lenogue, G., Gautier, K., Frenois, A., and Couderette, A.: Long-awaited and delayed Transportable Highest grade of Fiber Optic Gyroscope for Seismology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13600, https://doi.org/10.5194/egusphere-egu23-13600, 2023.

EGU23-13803 | ECS | Orals | SM2.1

Magnitude Estimation and Ground Motion Prediction to Harness Fiber Optic Distributed Acoustic Sensing for Earthquake Early Warning 

Itzhak Lior, Diane Rivet, Jean-Paul Ampuero, Anthony Sladen, Sergio Barrientos, Rodrigo Sánchez-Olavarría, German Alberto Villarroel Opazo, and Jose Antonio Bustamante Prado

Earthquake Early Warning (EEW) systems provide seconds to tens of seconds of warning time before potentially-damaging ground motions are felt. For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismological stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work, we harness available optical fiber infrastructure for EEW using the novel approach of Distributed Acoustic Sensing (DAS). DAS strain measurements of earthquakes from different regions are converted to ground motions using a real-time slant-stack approach, magnitudes are estimated using a theoretical earthquake source model, and ground shaking intensities are predicted via ground motion prediction equations. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes.

How to cite: Lior, I., Rivet, D., Ampuero, J.-P., Sladen, A., Barrientos, S., Sánchez-Olavarría, R., Villarroel Opazo, G. A., and Bustamante Prado, J. A.: Magnitude Estimation and Ground Motion Prediction to Harness Fiber Optic Distributed Acoustic Sensing for Earthquake Early Warning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13803, https://doi.org/10.5194/egusphere-egu23-13803, 2023.

EGU23-14093 | Posters on site | SM2.1

Six-component records of local seismicity in the Long Valley Caldera, Californica, US 

Johana Brokesova and Jiri Malek

Long Valley Caldera in the eastern part of California is a depression 32 km long and 18 km width, which was formed during a supervolcano eruption 760 000 years ago.  Weak volcanic activity manifested by hot springs, CO2 emmanations and earthhquake swarms in the caldera and neighboring Mammoth Mountain volcanic complex has been continuing until present. The seismicity in the area is the subject of intensive study. In 2016 - 2017 the monitoring system was supplemented by small-aperture array consisting of three short-period Rotaphone-D seismographs. The instruments were deployed in vaults few hundred meters apart at depts from 3.2 to 2.2 m. They are new short-period seismographs measuring three translational and three rotational components. The array enabled new methods of microearthquakes investigation. The noise from surface sources (mainly traffic along nearby highway) can be suppressed significantly by non-linear summing of redundant translational data from each Rotaphone. This enabled detection of very weak microearthquakes in the vicinity of the array with good signal-to-noise ratio. The true azimuth and phase velocity along surface are determined by two methods:  the zero-crossing point beamforming and rotation-to-translation relations. Based on these quantities, location of microearthquakes was performed and it was compared to the locations from the USGS catalogue of local earthquakes.

The six-component records in the Long Valley Caldera are extremely complex. Strong phases between P- and S-wave onsets and namely within the S-wave group are visible in most seismograms. They probably originated as reflection and refraction waves at distinctive interfaces beneath the sediment filling of the caldera. Six-component records enabled analysis of individual wavetypes in the seismograms. The seismic array was reinstalled in the summer 2021 with new data-acquisition system with bigger dynamic range (32 bits A/D converter). We expect even more sensitive measurements from this new observation. 

How to cite: Brokesova, J. and Malek, J.: Six-component records of local seismicity in the Long Valley Caldera, Californica, US, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14093, https://doi.org/10.5194/egusphere-egu23-14093, 2023.

EGU23-14444 | ECS | Orals | SM2.1

Modelling of DAS cable and ground coupling response using Discrete Particle Schemes 

Nicolas Luca Celli, Christopher J. Bean, Gareth O'Brien, and Nima Nooshiri

Since its first applications in the past decade, the use of fiber optic cables as ground motion sensors has become a central topic for seismologists, with successful applications of Distributed Acoustic Sensing (DAS) in various key fields such as seismic monitoring, structural imaging and source characterisation.

The instrument response of DAS cables however is largely unknown. Instrument response is a combination of instrument design, local site effects and ground coupling, and for DAS, the latter ones are believed to have a strong, spatially variable, but yet largely unquantified effect. This limits the application of a large number of staple seismological techniques (e.g. earthquake magnitude estimation, waveform tomography) that can require accurate knowledge of a signal’s amplitude and frequency content.

Here we present a method for accurately simulating a DAS cable and its response. The scheme is based on molecular dynamic-like particle-based numerical modelling, allowing the investigation of the effect of varying DAS-ground coupling scenarios. At first, we compute the full strain field directly, for each pair of neighbouring particles in the model. We then define a virtual DAS cable, embedded within the model and formed by a single string of interconnected particles. This allows us to control all aspects of the cable-ground coupling and their properties at an effective granular level through changing the bond strengths and bond types (e.g. nonlinearity) for both the cable and the surrounding medium. Arbitrary cable geometries and heterogeneous materials can be accommodated at the desired scale of investigation.

We observe that at the meter scale, realistic DAS materials, cable-ground coupling and the presence of unconsolidated trench materials around it dramatically affect wave propagation, each change affecting the synthetic DAS record, with differences exceeding at times the magnitude of the recorded signal. These differences show that cable coupling and local site effects have to be considered both when designing a DAS deployment and analysing its data when either true or along-cable relative amplitudes are considered.

How to cite: Celli, N. L., Bean, C. J., O'Brien, G., and Nooshiri, N.: Modelling of DAS cable and ground coupling response using Discrete Particle Schemes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14444, https://doi.org/10.5194/egusphere-egu23-14444, 2023.

EGU23-15048 | ECS | Posters on site | SM2.1

On Seismic Wave Equation Gradiometric Inversion for Density 

Marthe Faber and Andrew Curtis

It is of interest for environmental and resource applications to better characterise dynamic processes and properties of the near-surface critical zone of the solid Earth. Seismic wavefield gradiometry refers to a class of imaging techniques that estimate properties of the subsurface by calculating temporal and spatial gradients of incoming wavefields using dense array measurements, usually recorded at the Earth’s surface. One such method called wave equation inversion (WEI) has been shown to require only a few minutes of ambient seismic noise recordings to produce phase velocity maps, and shows promise for rapid field deployment.

Previous applications of WEI are based on the assumption that the 2D scalar Helmholtz wave equation adequately describes the dynamics of recorded wavefields. This approximation is severe for seismic waves because the Helmholtz equation fails to describe elastic wave dynamics. Since ambient noise recordings contain all kinds of interfering elastic wave types, the accuracy of subsurface material property estimates is compromised.

To investigate the potential to enhance the information available from WEI, we test the method synthetically using more sophisticated wave equations that represent wave propagation in the subsurface more accurately. Starting from a 3D seismic array geometry which provides wavefield gradient information both at the surface and at depth, WEI can be formulated in terms of the full elastic wave equation. From there we track approximations in both wave physics and field acquisition geometries that deplete information about the medium, eventually arriving at the conventional 2D scalar wave equation. These experiments highlight approximations that most deteriorate the solution, allowing us to target future effort to remove them.

One approximation made in all previous WEI studies is to assume that density is constant across the local array. In reality, subsurface density varies both laterally and with depth, yet remains poorly constrained in seismic imaging problems. Accurate density estimates would provide important insight into subsurface properties. This prompts us to test wavefield sensitivities to subsurface density contrasts via WEI. Synthetic results for 3D acoustic media suggest that it is possible to estimate relative density structure with WEI by using a full acoustic formulation for wave propagation along the surface. We show that using a constant density assumption for the medium can be detrimental to subsurface images, whereas the full acoustic formulation of gradiometry improves our knowledge of material properties. It allows us to estimate density as an additional material parameter as well as to improve phase velocity estimates by incorporating approximations to the density structure. By expanding this methodology to the elastic case, we will discuss the feasibility of estimating density with gradiometric WEI in the solid Earth.

How to cite: Faber, M. and Curtis, A.: On Seismic Wave Equation Gradiometric Inversion for Density, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15048, https://doi.org/10.5194/egusphere-egu23-15048, 2023.

EGU23-15050 | Orals | SM2.1

Low-frequency seismic wave sensing using coherent optical fiber networks for metrology 

Paul-Eric Pottie, Mads Tonnes, Maxime Mazouth-Laurol, Hendrix Montlavan-Leyva, Etienne Cantin, Benjamin Pointard, Hector Alvarez-Martinez, Rodolphe Le Targat, Olivier Lopez, Christian Chardonnet, and Anne Amy-Klein

Optical fiber networks are being implemented in several countries aiming at dissemination of ultra-stable time and frequency references. This enables the comparison of optical clocks, which is a key part of the roadmap towards the future redefinition of the International System of Units (SI) second. Furthermore, this enables uses in chronometric geodesy, where the sensitivity of the optical clocks to the gravitation field enables measurements of height differences as low as 1 cm [1].
The frequency signals in the optical fibers are sensitive to acoustic vibrations which are present in the ground, which is the main source of noise to the disseminated signals.
In recent years, this has enabled studies in the use of optical fiber links for the detection of earthquakes [2]. In such an approach, the measurement is the integrated noise over the fiber path. This typically allows for one to several orders of magnitudes longer range as compare to DAS techniques, but with the loss of localization along the fiber. Such integrated approaches include measurements of the total polarization change of the light along the fiber [3], or the total phase change of a coherent ultra-stable laser signal, potentially including distributed sensing techniques in submarine fibers [2,4].

Here, we will present the first quantitative studies on the use of coherent optical fiber links for seismic detection. Using a the fiber network REFIMEVE in France (see Fig. 1), we present studies on the sensitivity of coherent optical fiber links to seismic events. We describe the dependence of the sensitivity to a number of parameters like incident angle, magnitude and distance, and compare the sensitivity of a fiber link with that of conventional seismometers. We show, for a first time to our knowledge, the detection of seismic waves by a coherent optical fiber network, and we study the prospects of using such a network for the localization of earthquakes. Lastly, we discuss the principles and results of a machine learning algorithm, which enables automatic detection of earthquakes in a coherent optical fiber link.

Bibliography:
1. M. Takamoto et al., Test of general relativity by a pair of transportable optical lattice clocks, Nat. Phot., 14 (7), 411–415. doi:30210.1038/s41566-020-0619-8
2. G. Marra et al. , Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458. doi: 10.1126/science.aat4458279
3. J.C. Castellanos et al. ,Optical polarization-based sensing and localization of submarine earthquakes. In Optical fiber communication conference (OFC) 2022, doi:26210.1364/OFC.2022.M1H.4
4. G. Marra et al., Optical interferometry–based array of seafloor environmental sensors using a transoceanic submarine cable. Science, doi: 10.1126/science.abo193

Figure 1 : Map of the French REFIMEVE fiber network, shown in red lines. Dotted lines indicates indicate the full scale of the planned network, and continuous red lines indicate links used in these studies. Blue lines indicates the linear approximations of the links. All seismometers of the RESIF network is shown by small green triangles, and seismometers used in theses studies are shown by larger, turquoise triangles.

How to cite: Pottie, P.-E., Tonnes, M., Mazouth-Laurol, M., Montlavan-Leyva, H., Cantin, E., Pointard, B., Alvarez-Martinez, H., Le Targat, R., Lopez, O., Chardonnet, C., and Amy-Klein, A.: Low-frequency seismic wave sensing using coherent optical fiber networks for metrology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15050, https://doi.org/10.5194/egusphere-egu23-15050, 2023.

EGU23-15062 | ECS | Posters on site | SM2.1

Observing and analysing seismicity with a permanet 6C station 

Andreas Brotzer, Heiner Igel, Felix Bernauer, Joachim Wassermann, Robert Mellors, and Frank Vernon

In September 2022, a three-component rotational rate sensor (blueSeis-3A) provided by IRIS has been deployed at the underground vault of the Piñon Flat Observatory (PFO) near San Diego in California. A three-component broadband seismometer (Trillium 240s) is co-located on the granite pier, creating a 6C station for permanent observations of local and regional seismicity and wavefield studies. The permanent record is streamed online via IRIS and freely available with all required metadata (station: BlueSeis at Pinon Flat = BSPF). Additionally, the site offers observations of strain by optical fiber and vacuum laser strainmeters at PFO, allowing to study 7 components of the seismic wavefield in a quiet area with regard to seismic noise, but high seismicity (e.g. San Andreas fault zone, San Jacinto fault zone). Such a setup enables advanced studies of the seismic wavefield. Dense, large-N nodal experiments, temporarily deployed around PFO could provide dense sampling of the seismic wavefield for comparison studies. The seismic array of borehole sensors at PFO is well designed to compute array derived rotations with enables a direct comparison with the rotational record and applied methods. Moreover, the array is employed to compare array analysis with 6C methods (e.g. backazimuth estimation, wavefield separation, source tracking, local subsurface velocity changes). We present characteristics on the 6C station and preliminary analysis results.

How to cite: Brotzer, A., Igel, H., Bernauer, F., Wassermann, J., Mellors, R., and Vernon, F.: Observing and analysing seismicity with a permanet 6C station, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15062, https://doi.org/10.5194/egusphere-egu23-15062, 2023.

EGU23-15265 | ECS | Orals | SM2.1

Towards exploiting the advantages of a Standard telecom multi-fibre cable for volcano monitoring: an example from Mt. Etna 

Sergio Diaz-Meza, Philippe Jousset, Gilda Currenti, Air David, Andy Clarke, Anna Stork, Athena Chalari, and Charlotte Krawzcyk

Distributed Dynamic Strain Sensing (DDSS), also known as Distributed Acoustic Sensing (DAS), is becoming a popular tool for volcano monitoring. The sensing method relies on sending coherent light pulses into an optical fibre and measuring the phase-shift of Rayleigh back-scattered light due to strain on the fibre. This provides distributed strain rate measurements at high temporal and spatial sampling rates. Standard telecom fibres have been conventionally used for this purpose, however engineered fibres are being developed to enhance the back-scattered light, providing up to 100 times improved sensitivity in contrast to the conventional standard fibre. Despite the technical advantages of engineered fibres, standard fibres already have extensive coverage around the Earth surface, and so there is an interest in using the existing telecommunication infrastructure. In this study we compare stack DDSS data from a fibre loops made of several fibres within the same optical fibre cable, with DDSS data measured on an engineered fibre. We analyse how stacking can improve the signal quality of the recorded DDSS data. In an area located 2.5 km NE from the craters of Mt. Etna, we spliced 9 standard fibres together from a 1.5 km long cable to create a single optical path and interrogated using an iDAS unit. At the same time, we interrogated with a Carina unit a 0.5 km engineered fibre installed parallel to the standard multi-fibre cable. Both fibres were interrogated in a common period of 5 days. We use a spatial cross-correlation function to find the channel equivalences between each fibre and then stack them to evaluate the changes in the DDSS data and compare with the engineered fibre data. Our results show that, despite engineered fibres have lower noise, a stack of 5 fibres can achieve a maximum noise reduction of 20% outside of the optical noise band, in comparison to the engineered fibre. We achieved this noise reduction for our specific configuration, and so we show how the stack improvement is dependent on the type of configuration in terms of fibres stacked and length of the fibres. Our findings motivate the exploitation of multi-fibre cables in existing infrastructures, so-called dark fibres, for monitoring volcano and applications to other environments.

How to cite: Diaz-Meza, S., Jousset, P., Currenti, G., David, A., Clarke, A., Stork, A., Chalari, A., and Krawzcyk, C.: Towards exploiting the advantages of a Standard telecom multi-fibre cable for volcano monitoring: an example from Mt. Etna, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15265, https://doi.org/10.5194/egusphere-egu23-15265, 2023.

EGU23-15291 | ECS | Orals | SM2.1

Supporting the completion process of boreholes using combined fiber-optic monitoring technologies 

Johannes Hart, Martin Peter Lipus, Christopher Wollin, and Charlotte Krawzcyk

Efficient, safe and sustainable utilization of geothermal reservoirs depends on reliable well completion and monitoring technologies. Conventional borehole measurement methods can only be used after the completion process and usually show snapshots of the borehole conditions at discrete points in time. Therefore, the successful borehole completion is a risky process and mainly relies on the experience of the driller. By using distributed fiber-optic sensing technologies, it is possible to monitor all along the cable with dense spatial sampling and continuous in real-time.

In this presentation, we give insights into our newest case study in Berlin. A 450 m deep exploration well for an Aquifer Thermal Energy Storage was completed. We installed a fiber optic sensor cable along the whole production tubing, that contained several single-mode and multi-mode fibers in loose tube and tight buffered configuration. This cable allows to simultaneously measure distributed temperature (DTS), distributed acoustics (DAS) and distributed strain (DSS/DTSS) for the entire completion process.

Particularly with a combined analysis and interpretation of the different fiber-optic technologies, conventionally untraceable processes can be visualized. We are able to show changes of subsurface flow paths due to blockages. Processes to be prevented, like caving or bridging can be detected and the proper rise of gravel or cement can be surveyed. Provided to the driller in real time, subsurface uncertainties can be significantly reduced.

Monitoring geothermal wells with a fiber-optic sensing infrastructure is not only a powerful tool to reduce risks during well completion, which can lead to compromised well integrity. The installed equipment and technology can also be used to assess the well integrity over the whole cycle of the well, to ensure a longest possible lifespan.

How to cite: Hart, J., Lipus, M. P., Wollin, C., and Krawzcyk, C.: Supporting the completion process of boreholes using combined fiber-optic monitoring technologies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15291, https://doi.org/10.5194/egusphere-egu23-15291, 2023.

EGU23-15325 | Posters on site | SM2.1

Observation of the microseismic peak from Distributed Acoustic Sensing (DAS) measurements at the LSBB underground Laboratory 

Olivier Sèbe, Camille Jestin, Amaury Vallage, Stéphane Gaffet, Daniel Boyer, Alain Cavaillou, Jean-Baptiste Decitre, Charly Lallemand, Vincent Lanticq, and Olivier Rousseau

Thanks to its ability to provide dense strain rate measurements along Optical Fiber (OF) cable, the Distributed Acoustic Sensing (DAS) technique spreads over different seismic and geophysical domains. They range from exploration geophysics (Mestayer et al. 2011, Daley et al. 2013), to underground structure imaging (e.g. Ajo-Franklin et al. 2019, Cheng et al. 2021) or seismic activity and background noise monitoring (Jousset et al 2018, Nayak et al. 2021). Beyond the advantage of its dense spatial sampling and given a better understanding of its instrument response (e.g. Lindsey et al. 2020), the detection performance of these new DAS measurements also depends on its ability to precisely characterize the amplitude and phase of the seismic background noise in different environments. According to recent offshore seismic noise studies (Ugalde et al. 2021, Lior et al. 2021, Guerin et al 2022), we propose a study based on DAS recordings of the seismic background noise in an on-land quiet environment.

In 2020, a temporary seismic experiment PREMISE (PREliminary MIga Seismic Experiment) was carried out on the site of the underground low noise Laboratory (LSBB, Laboratoire Souterrain Bas Bruit) at Rustrel, France, in order to study the 3D seismic wave field properties in a pretty well-known underground geological structure. During this experiment, we deployed several kilometers of different OF in the LSBB galleries in order to create a multidirectional DAS array with a total fiber length of 10.5km and several ground-coupling conditions. We reprocessed two hours of “raw” DAS data, recorded with a FEBUS A1-R instrument, with different acquisition parameters to find the best configuration for enhancing the DAS measurement Signal to Noise Ratio. The power spectral density (PSD) of these reprocessed strain time-series reveals a peak in the background noise frequency range [0.08-0.25Hz] for gauge lengths of 90m and 150m. Independently, an estimation of the local strain field has been derived by a geodetic analysis (Spudich et al 1995) of the records from the LSBB broadband seismometers antenna. The comparison of the DAS and seismometers array-derived strain PSD shows a very good agreement with the secondary microseism peak in terms of frequency band, amplitude, and the wave field polarization, especially for DAS strain records processed with gauge-length of several tens of meters.

How to cite: Sèbe, O., Jestin, C., Vallage, A., Gaffet, S., Boyer, D., Cavaillou, A., Decitre, J.-B., Lallemand, C., Lanticq, V., and Rousseau, O.: Observation of the microseismic peak from Distributed Acoustic Sensing (DAS) measurements at the LSBB underground Laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15325, https://doi.org/10.5194/egusphere-egu23-15325, 2023.

EGU23-15589 | Posters on site | SM2.1

Variations of the system properties of a high-rise building over 1 year using a single station 6C approach. 

Yara Rossi, Konstantinos Tatsis, Yves Reuland, John Clinton, Eleni Chatzi, and Markus Rothacher

We demonstrate that the dynamic response of an engineered structure, including modeshape identification, can be obtained from just a single measurement at one position - if rotation is recorded in combination with translation. Such a single-station approach can save significant time, effort and cost when compared with traditional structural characterization using horizontal arrays. In our contribution we will focus on the monitoring of a high-rise building by tracking its dynamic properties and their variations due to environmental (e.g. temperature) and operational (e.g. wind) conditions (EOCs) over a 1-year period. We present a real-case structural identification procedure on the Prime Tower in Zurich. This is a 36-story tower of 126 m height, with a poured-in-place-concrete core and floors and precast-concrete columns; this concrete core structure, surrounded by a triple-glazed facade, is the third highest building in Switzerland. 
The building has been continuously monitored, over a 1-year period, by an accelerometer (EpiSensor), a co-located rotational sensor (BlueSeis) and a weather station located near the building center on the roof. Roof and vertical seismic arrays were deployed for short periods. The motion on the tower roof includes significant rotation as well as translation, which can be precisely captured by the monitoring station. More than 20 structural modes, including the first 6 fundamental modes, where translations are coupled with rotations, are tracked between 0.3 – 14 Hz. We will also show the variation of natural frequencies due to seasonal but also more short-term effects, in an effort to understand the effect of environmental and operational variability on structural deformation and response. Additionally, an amplification of the modes, not only during strong winds, but also during a couple of Mw 4.0 - 4.4 earthquakes at regional distance has been observed and analysed. The frequency band between 0.3 and 10 Hz is of key interest for earthquake excitation, making an investigation thereof essential. The work closes with a summary of the main benefits and potential in adopting collocated rotation and acceleration sensing for geo-infrastructure monitoring purposes.

How to cite: Rossi, Y., Tatsis, K., Reuland, Y., Clinton, J., Chatzi, E., and Rothacher, M.: Variations of the system properties of a high-rise building over 1 year using a single station 6C approach., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15589, https://doi.org/10.5194/egusphere-egu23-15589, 2023.

EGU23-15841 | Orals | SM2.1

Monitoring of elastic properties using DAS and DTS in a controlled experiment during road construction 

CharLotte M. Krawczyk, Martin P. Lipus, Johannes Hart, Christopher Wollin, Christian Cunow, and Philippe Jousset

Maintenance of infrastructure is costly and difficult to implement systematically when it spreads over wide areas, such as road or pipeline networks. In the monitoring of road ways, conventional methods to control the road integrity rely on discrete measurements in space and time. There is a large demand for innovative technologies that are able to assess the structural integrity as a whole and in regular intervals or even continuously. Distributed fiber-optic sensing opens the opportunity to measure numerous physical quantities such as temperature and strain with high spatial and temporal resolution over tens of kilometers. In addition, it is easily deployable at reasonable cost.

In order to address the issue of asphalt aging due to exposure to heavy traffic loads, we installed a fiber-optic cable into a reworked road interval and recorded fiber-optic data in a controlled experiment with numerous test vehicles of different sizes and weights. The recorded data suggests that elastic properties of the asphalt can be retrieved from the bypassing traffic. Vehicles can be characterized by the number of axes and load on the asphalt composite. In the next phase, we will monitor the aging of the test field to deduce how varying matrial properties can be better identified for geotechnical and geoscience applications.

How to cite: Krawczyk, C. M., Lipus, M. P., Hart, J., Wollin, C., Cunow, C., and Jousset, P.: Monitoring of elastic properties using DAS and DTS in a controlled experiment during road construction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15841, https://doi.org/10.5194/egusphere-egu23-15841, 2023.

EGU23-16307 | Orals | SM2.1

Local earthquake recordings using Distributed Acoustic Sensing (DAS) at BFO 

Nasim Karamzadeh Toularoud, Ya-Jian Gao, Jérôme Azzola, Thomas Forbriger, Rudolf Widmer-Schnidrig, Emmanuel Gaucher, and Andreas Rietbrock

The application of distributed acoustic sensing (DAS) in seismology is rapidly expanding due to its ability to perform a large number of high-density measurements, i.e., distributed sensing, without using many point sensors, which is cost-effective. DAS application includes vertical seismic profiling, microseismic measurements, and hydraulic fracturing monitoring and mainly focuses on the event detection capability of  DAS data. 

Febus optics DAS interrogator (A1-R) is continuously running at German Black Forest Observatory (BFO) since May 2021, recording RAW data (selectively stored) or strain-rate data (continuously stored). Our study is in the experimental phase and focuses on testing basic concepts of DAS data, i.e., the effect of gauge-length on the amplitude of measurement and comparing the amplitude of DAS with other seismological sensors such as strain-meter array and a STS2 broadband sensor as well as synthetic simulations. Such comparison is performed using background noise characteristics (power spectral density) and examples of local and regional events that are detectable at the BFO site. 

In this study, we show examples of strain rate measurements related to local earthquakes recorded by horizontal fiber optic cables, employing two different DAS interrogators, cable types and coupling of the cables to the ground. We compared simultaneous recordings using Febus A1 DAS interrogator and OptoDAS by Febus optic and Alcatel Submarine Networks (ASN), respectively, and, concluded about the frequency and gauge-length dependent sensitivity of recordings in two cases. In addition, we compare the amplitude of DAS recordings, for example of local earthquakes, with the synthetic strain simulated  at lower frequency bands using the spectral-element method (Salvus) based on 3D media and analytic approach (Qseis) for 1D model. 

 

How to cite: Karamzadeh Toularoud, N., Gao, Y.-J., Azzola, J., Forbriger, T., Widmer-Schnidrig, R., Gaucher, E., and Rietbrock, A.: Local earthquake recordings using Distributed Acoustic Sensing (DAS) at BFO, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16307, https://doi.org/10.5194/egusphere-egu23-16307, 2023.

EGU23-16459 | ECS | Orals | SM2.1

Deep learning approach for detecting low frequency events on DAS data at Vulcano Island, Italy 

Martina Allegra, Gilda Currenti, Flavio Cannavò, Philippe Jousset, Michele Prestifilippo, Rosalba Napoli, Mariangela Sciotto, Giuseppe Di Grazia, Eugenio Privitera, Simone Palazzo, and Charlotte Krawczyk3

Since September 2021, signs of unrest at Vulcano Island have been noticed after four years of quiescence, along with CO2 degassing and the occurrence of long-period and very long-period events. With the intention of improving the monitoring activities, a submarine fiber optic telecommunications cable linking Vulcano Island to Sicily was interrogated from 15 January to 14 February 2022. Of particular interest has been the recording of 1488 events with wide range of waveforms made up of two main frequency bands (from 3 to 5 Hz and from 0.1 to 0.2 Hz).

With the aim of the automatic detection of seismic-volcanic events, different approaches were explored, particularly investigating whether the application of machine learning could provide the same performance as conventional techniques. Unlike many traditional algorithms, deep learning manages to guarantee a generalized approach by automatically and hierarchically extracting the relevant features from the raw data. Due to their spatio-temporal density, the data acquired by the DAS can be assimilated to a sequence of images; this property has been exploited by re-designing deep learning techniques for image processing, specifically employing Convolutional Neural Networks.

The results demonstrate that deep learning not only achives good performance but that it even outperforms classical algorithms. Despite providing a generalized approach, Convolutional Neural Networks have been shown to be more effective than traditional tecniques in expoiting the high spatial and temporal sampling of the acquired data. 

How to cite: Allegra, M., Currenti, G., Cannavò, F., Jousset, P., Prestifilippo, M., Napoli, R., Sciotto, M., Di Grazia, G., Privitera, E., Palazzo, S., and Krawczyk3, C.: Deep learning approach for detecting low frequency events on DAS data at Vulcano Island, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16459, https://doi.org/10.5194/egusphere-egu23-16459, 2023.

In this study we use distributed acoustic sensing (DAS) on a 41-km-long submarine optical fibre (OF) cable located offshore Toulon, France. We record both the amplitude and frequency of seafloor strains induced by ocean surface gravity waves, as well as secondary microseisms. Combining the analysis of the two types of waves, we identify and localize local sources of secondary microseisms that manifest as Scholte waves generated by the reflection of oceanic gravity waves on the coastline. During the experiment, these local sources represent the most energetic contribution to the seismic noise recorded along the OF and by an onshore broad-band station located near the DAS interrogator. As a result, the characteristics of this noise are closely related to local wave conditions. One major challenge in performing seismic imaging using ambient seismic noise correlations using DAS data is that we cannot solve for the true seismic velocity because the noise wave field is dominated by local sources. To address this, we measure the incident angle of the dominant local noise sources, correct the apparent velocity using the incident angle retrieve from beamforming analysis and generate a 2D model. We then quantify the errors that arise from picking the dispersion curves of the most energetic velocities without correcting from the incident angle. Our results show that there are significant differences in velocities, with differences reaching up to several hundred meters per second. This highlights the importance of correcting these velocities before generating a tomography. Finally we evaluate an alternative strategy for a linear DAS fiber that cannot be use to localized the dominant noise source. We measure the dispersion curve of the slowest Scholte waves recorded and compare it to the corrected dispersion curves of the dominant source. Although this strategy suffers from limitation, it minimizes the error in the velocity model.

How to cite: Guerin, G. and Rivet, D.: Using localized microseismic noise sources to perform high-resolution seismic Imaging of seafloor using Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16640, https://doi.org/10.5194/egusphere-egu23-16640, 2023.

EGU23-17585 | Orals | SM2.1 | Highlight

Why high spatial resolution matters: narrow fault zone, but big effects observed by Taiwan Milun-fault Drilling and All-inclusive Sensing (Taiwan MiDAS) project 

Kuo-Fong Ma, Li-Wei Kuo, Hsin-Hua Huang, Sebastian von Specht, Chin-Jen Lin, Jing-Shan Ku, Chen-Ray Lin, En-Shi Wu, Chien-Yin Wang, and Wen-Yen Chang

Understanding fault zone dynamics in multi-scale is important to embrace the complexity of the earthquake behavior and its natural system. However, the opportunity to map and observe the fault zone behavior at depth with high spatial resolution are rare as also the challenge itself on targeting and identifying the fault zone at depth. We placed a 3D cross-fault fiber array with a downhole loop from surface to depth of 700m for Hole-A (Hanging wall site, crossing fault at depth), after drilling and coring to a frequent slip fault, Milun fault in a plate boundary zone, which ruptured during the 6 February 2018 Mw6.4 Hualien earthquake, and resulted in severe damage to several tall buildings with tens of casualties and injuries. Then, the surface segment crosses the surface fault rupture zone using commercial fiber, and to another downhole loop of 500m fiber for Hole-B (Footwall site). The high spatial resolution from distributed acoustic sensing (DAS) allows us to characterize the fault zone feature together with the retrieved core and geophysical logs after drilling through this frequent slip zone. This 3D route includes the experiment of using commercial fiber to the future application of surface rupture zone identification for seismic hazard mitigation. The project successfully retrieved the fault core associated with Milun fault zone, which could be also seen in geophysical logs with low velocity and resistivity, and mapped using Optical Fiber Sensing technique of the downhole fiber. Within the Milun fault zone, while a 20m thick fault core with grey and black gouge was discovered, a distinct seismic feature associated with this 20m fault gouge was found by its amplification of the strain records from DAS. This amplification ratio is about 2.5-3 when compared to the channels at deeper depth related to a consolidated rock material.  This amplification factor was frequency and azimuth independently, as genuinely observed from all events (e.g. local, and teleseismic earthquakes) with similar amplification factor. Our study shows that the amplification from this 20m fault gouge zone is mainly from the nature of the heterogeneous medium in elastic constant while crossing the fault zone, especially the fault core. Similar feature at surface but with wider surface rupture zone (~ 200m) was found in DAS data as well although less evidence using commercial fiber, while could be validated from the densely deployed geophones crossing the surface rupture of the 2018 Hualien earthquake. Through the depth, a high-resolution asymmetric feature of this active fault was evidenced from the downhole optical fiber and cores. This fault zone behavior would be hardly seen or confirmed without continuous viewing of the wavefields to this high spatial resolution to meter scale. Although the narrow fault gouge, the nature of its amplification in strain due to its strong material contrast from fault gouge was intriguing, and requires intensive attention to consider the contribution of the fault zone heterogeneity in the medium. This might give hints on the understanding of the observation of earthquake dynamics triggering reported worldwide after the occurrence of a mega-earthquake.

How to cite: Ma, K.-F., Kuo, L.-W., Huang, H.-H., von Specht, S., Lin, C.-J., Ku, J.-S., Lin, C.-R., Wu, E.-S., Wang, C.-Y., and Chang, W.-Y.: Why high spatial resolution matters: narrow fault zone, but big effects observed by Taiwan Milun-fault Drilling and All-inclusive Sensing (Taiwan MiDAS) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17585, https://doi.org/10.5194/egusphere-egu23-17585, 2023.

EGU23-4581 | ECS | Orals | SM2.4

Understanding Broadband Ocean Bottom Seismometer Noise: Fresh Insights and Future Directions 

Helen Janiszewski, Zachary Eilon, Joshua Russell, Brennan Brunsvik, James Gaherty, Stephen Mosher, William Hawley, and Sloan Coats

The proliferation of broadband ocean bottom seismometer (BBOBS) deployments over the last two decades has generated key datasets from diverse marine environments, improving our understanding of tectonics and earthquake processes. In turn, the community of scientists using this data has expanded. This growth in BBOBS data collection is likely to persist with the arrival of new seismic seafloor technologies, and continued scientific interest in marine and amphibious targets. However, the noise inherent in OBS data poses a challenge that is markedly different from that of terrestrial data. As a step towards improved understanding of the sources of variability in this noise, we present a new compilation and analysis of BBOBS noise properties from 15 years of US-led seismic deployments. We find evidence for similarity of noise properties when grouped across a variety of parameters, with groupings by seismometer type and deployment water depth yielding the most significant and interpretable results. Instrument design, that is the entire deployed package, also plays an important role, although it strongly covaries with seismometer and water depth. We find that the presence of tilt noise is primarily dependent on the type of seismometer used (covariant with a particular subset of instrument design), that compliance noise follows anticipated relationships with water depth, and that shallow, oceanic shelf environments have systematically different microseism noise properties (which are, in turn, different from instruments deployed in shallow lake environments). We discuss implications for the viability of commonly used seismic analysis techniques, and future directions for improvements in the efficiency of analysis of BBOBS data.

How to cite: Janiszewski, H., Eilon, Z., Russell, J., Brunsvik, B., Gaherty, J., Mosher, S., Hawley, W., and Coats, S.: Understanding Broadband Ocean Bottom Seismometer Noise: Fresh Insights and Future Directions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4581, https://doi.org/10.5194/egusphere-egu23-4581, 2023.

EGU23-5724 | ECS | Orals | SM2.4

Reverse Time Migration of offshore wide-angleseismic data: an efficient method to image deep crustal structures 

Susana Gonçalves, Philippe Schnürle, Marina Rabineau, Alexandra Afilhado, and Maryline Moulin

We image the Moho discontinuity and deeper crustal layers by applying the Reverse Time Migration (RTM) method to wide-angle seismic (WAS) data that were acquired along two different profiles in the NW and SE offshore Brazil. The application of this method is quite uncommon to ocean bottom seismometers (OBS) data due to the OBS wide spacing deployment and low folds. Also, we applied the method to each OBS without making any assumptions on the type of propagation generated inside the model. The long offset of the refractions obtained, allows us to image deeper crustal layers.

Being able to obtain an image of these deeper layer is useful when MCS streamer data are not available or, even when they are, do not image the same depths.

We analyze the effectiveness of the RTM method when applied to the reflectivity of the WAS data. We can image the structures by cross-correlating the forward and backward wavefields given by the acoustic seismic equation. This allows us to use each interface crossed by a ray as a source but also as a receiver.

The velocity models used to perform RTM were previously obtained by applying a procedure of two-dimensional forward ray-tracing followed by a damped least-squares travel time inversion.

The results obtained have an unexpected large contribution from the wavefield traveling as refractions within the earth. We obtain strong and continuous refractors for depths that correspond to the basement and the Moho discontinuity. As we move inland, the refractors that correspond to the Moho discontinuity disappear due to the move of this discontinuity to deeper depths. 

The obtained results are promising for a wide range of applications at a crustal scale seismic exploration, with wide-angle seismic data.

Funding: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL

How to cite: Gonçalves, S., Schnürle, P., Rabineau, M., Afilhado, A., and Moulin, M.: Reverse Time Migration of offshore wide-angleseismic data: an efficient method to image deep crustal structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5724, https://doi.org/10.5194/egusphere-egu23-5724, 2023.

EGU23-5838 | Posters on site | SM2.4

Seismic noise characteristics of PNU OBS network in 2021-2022 

Yu Jin Sohn, Kwang-Hee Kim, Su Young Kang, Doyoung Kim, and Young-Cheol Lee

Pusan National University deployed sixteen ocean bottom seismometers (OBSs) in the eastern offshore of the southern Korean peninsula. The primary purpose of the OBS network is monitoring earthquakes in the eastern offshore to investigate potential fault systems in the offshore region which was formidable using limited apertures by land-based observations. A seismic network's performance highly depends on each site's background noise level. We analyze the nature of the ambient noise and site response for ocean bottom seismometers (OBSs) deployed in the 2021-2022 period. The power spectral densities (PSDs) of the OBSs exhibited dis-similar features from those of land-based stations; most temporary broadband seismic stations on land showed relatively lower background noise levels. In the meanwhile, OBSs showed higher background noise levels. We report the nature of ambient noise at various channels, water depths, spatial locations, temporal variations, extreme weather conditions, and their potential causes. In general, horizontal components are noisier than vertical components. For longer periods, horizontal components are larger by ~45 dB. The probability density functions (PDFs) of OBSs show that the noise level is within the range of McNamara’s model (2004) for higher frequencies (3.5~50 Hz) although they are still high. When examining long periods (> 20 s), the noise level is higher than what would be given by McNamara’s model. Although we do not observe diurnal or weekly variations in OBS, as expected, we observe varying degrees of seasonal variations in OBSs. Apparently, water depth is the most important factor in deciding noise levels and their seasonal variations. At shallow-depth OBSs, we observe a strong correlation between noise levels and wave heights estimated by the Korea Meteorological Administration (KMA). The ambient noise is down to -130 dB for the band from 5 to 15 Hz, which provides the best signal-to-noise ratio for local microearthquakes. We also present the horizontal-to-vertical spectral ratio (HVSR) of the ambient noise recorded by OBSs. They present significant amplifications at lower frequencies, which indicates large amplification by combined effects due to lower density and lower wave velocity at shallow sediments, and greater depths to major impedance contrast. We confirm that modeling HVSR of noise data recorded by a three-component OBS offers a fast and inexpensive method for site investigation in deep water with the potential of in situ seafloor sediment characterization.

How to cite: Sohn, Y. J., Kim, K.-H., Kang, S. Y., Kim, D., and Lee, Y.-C.: Seismic noise characteristics of PNU OBS network in 2021-2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5838, https://doi.org/10.5194/egusphere-egu23-5838, 2023.

EGU23-5928 | ECS | Posters on site | SM2.4

Seasonal changes on tidal-induced noise on long-term OBS deployment 

Afonso Loureiro, Carlos Corela, Maria Tsekhmistrenko, Miguel Miranda, and Ana Ferreira and the UPFLOW Team

Currently, Ocean Bottom Seismometers (OBS) have sensors comparable to those used on land stations. However, they are exposed to very different conditions that degrade the recordings. One major issue is being directly exposed to global and tidal oceanic currents that, depending on the water velocity flowing around the instrument, can excite parts of the frame or produce drag and lift effects due to vortex shedding. Any of these conditions is detrimental for signal integrity, either from variations of the instrument-to-ground coupling or by introducing unwanted energy that is unrelated with the seismic events the experiment is aimed at.

The UPFLOW project is aimed at understanding mid-plate, deep upward flow that cannot be explained by plate tectonics, but is critical for continental growth, for returning volatiles to the atmosphere and for producing Earth’s largest melting events. For this reason, 50 OBS of different types were deployed for a year in the North Atlantic Ocean, including several prototypes aimed at reducing the tidal-induced noise generated by water flowing around the instrument's frame.

In this work, we show the seasonal variation of the tidal-induced noise on different instrument types across the Madeira and Seine abyssal plains of the North Atlantic Ocean during neap and spring tides between July 2021 and July 2022. In some instances, where harmonics are detected, individual frame components of the OBS can be identified as a major contributor, paving way to finding mitigation solutions on future deployments.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020.

How to cite: Loureiro, A., Corela, C., Tsekhmistrenko, M., Miranda, M., and Ferreira, A. and the UPFLOW Team: Seasonal changes on tidal-induced noise on long-term OBS deployment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5928, https://doi.org/10.5194/egusphere-egu23-5928, 2023.

EGU23-6910 | Posters on site | SM2.4

Novel Autonomous and Cabled OBS Solutions for Offshore Seismic Research 

Will Reis, James Lindsey, Dan Whealing, and Neil Watkiss

Seismologists have historically focused on land-based seismic research, due to the logistical and financial challenges presented by offshore installations. Guralp has developed technology which allows the seismology community monitor offshore seismicity with greater ease, improving global seismic data resolution. This is due to systems such as the Aquarius autonomous ocean bottom seismometer (OBS) and world-leading engineering advancements in Science Monitoring and Reliable Telecommunications (SMART) cables.

Autonomous free-fall OBS units allow users flexibility in deployment and ability to redeploy a number of times in different locations. The Guralp Aquarius functions at any angle without using a gimbal system, and can wirelessly transmit SOH and seismic data to the surface via an integrated acoustic modem. These features allow researchers to monitor and transmit data without offshore cabling, thereby reducing logistical challenges whilst maintaining some degree of real-time data transmission. Optional surface communications can be permanent (buoy-mounted), semi-permanent (wave-glider) or on demand (ship-of-opportunity or dedicated voyage).

Alternatively, cabled solutions give users access to high-resolution data in real-time via a physical link to an onshore data centre. As an example, the Guralp Orcus provides a complete underwater seismic station with observatory grade seismometer and strong-motion accelerometer in a single package. The slimline Guralp Maris also provides a more versatile solution, making use of the same omnidirectional sensor as the Aquarius and can be installed either on the seabed or in a narrow-diameter subsea borehole.

SMART cables show great potential for increasing the number of cabled ocean observatory deployments in the future with substantially reduced deployment costs to the research institute. Combining several applications into a single system, including seismic monitoring and telecommunications, large scale monitoring networks can be created cost effectively by combining efforts from several industries. Guralp is deploying a demonstration SMART Cable system to monitor volcanic and seismic activity offshore in the Ionian Sea in collaboration with Instituto Nazionale Di Geofisica e Vulcanologia (INGV). This will be the first practical demonstration of this technology and there are plans for additional projects in the future.

How to cite: Reis, W., Lindsey, J., Whealing, D., and Watkiss, N.: Novel Autonomous and Cabled OBS Solutions for Offshore Seismic Research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6910, https://doi.org/10.5194/egusphere-egu23-6910, 2023.

EGU23-8108 | ECS | Posters on site | SM2.4

UPLFOW ocean bottom seismometers data: preliminary performance report 

Maria Tsekhmistrenko, Roberto Diaz, Katrina Harris, Frederik Tilmann, Frank Krüger, Ana Ferreira, and Miguel Miranda and the UPFLOW Team

We present preliminary results from the UPFLOW (Upward mantle flow from novel seismic observations; https://upflow-eu.github.io/) project and associated large-scale amphibian experiment. The UPFLOW project, funded by the European Research Council (2021-2026), led a passive seismology large-scale experiment in the Azores-Madeira-Canary region starting in July 2021 and ending in September 2022. 

We recovered 49 (out of 50) OBSs deployed in a ~1,000×2,000 km2 area and with an average station spacing of ~150-200 km. Most instruments have three-component wideband seismic sensors (Trillium compact OBS version with a corner period of 120 s) and broadband hydrophones (type HTI-01 and HTI-04-PCA/ULF) with a corner period of typically 100 seconds. Three different designs of OBS frames were used LOBSTER, NAMMU and DUNE. We achieved data recovery rates of ~90-100% in 37 stations and ~50% in 6 stations, with only 7 stations being faulty, highly problematic or lost. 

We present various illustrative examples of seismic waveforms, spectrograms and data quality analysis from the recovered OBS data. Systematic probability power spectra density (PPSD) plots for all stations and over the whole deployment show a marked improvement in the quality of the long-period data (T>~30s) compared to previous experiments. 

We analyse the data performance as a function of the three models of OBS, recorder and seismometer types. Additionally, we present initial results from: (i) noise correlation analysis to quantify the clock skew during the deployment; (ii) estimation of horizontal component rotation angles from teleseismic data (body and surface waves); and, (iii) tilt and compliance analysis. 

Finally, we present an initial set of ~6000 multi-frequency body-wave travel time measurements generated with the UPFLOW OBS data and show a glimpse of preliminary body wave tomographic models built with this new dataset.

How to cite: Tsekhmistrenko, M., Diaz, R., Harris, K., Tilmann, F., Krüger, F., Ferreira, A., and Miranda, M. and the UPFLOW Team: UPLFOW ocean bottom seismometers data: preliminary performance report, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8108, https://doi.org/10.5194/egusphere-egu23-8108, 2023.

EGU23-8267 | Orals | SM2.4

MERMAID Tales: Travel-Times, Waveform Modeling, Infrasonic Spectral Densities, and Volcanic Eruptions 

Frederik J. Simons, Sirawich Pipatprathanporn, Joel D. Simon, and Jessica C. E. Irving

Since the launch of the first third-generation MERMAID in 2018, sixty-seven autonomous freely-drifting mid-column hydrophones have been afloat in the Pacific Ocean,  the South China Sea, and the Mediterranean. Over fifty-five instruments remain alive and well, and are continuing to report short, triggered, waveform segments of acoustic pressure variations, with six instruments directly reporting acoustic spectral densities. A new model equipped with a conductivity-temperature-depth (CTD) sensor is due for deployment (four new units). Over these last few years, many thousands of teleseismic arrival-times have been reported, and associated with global earthquake catalogs, so that their travel-time residuals with respect to global reference models can be determined in view of making tomographic models, especially of the area around French Polynesia, the original launch focus of the EarthScope-Oceans (ESO) fleet. The data stream has been flowing into the EarthScope (IRIS) data management center (DMC), and reporting short segments around first-arriving phases and the calculation of travel-times have become routine applications.

We briefly review those successes, but we focus on the latest data types (spectral densities computed in-situ rather than time-domain seismograms transmitted via satellite), on the codesign of MERMAID as an acoustic float with an environmental CTD sensor, on the latest modeling efforts at matching waveforms with synthetically computed pressure seismograms, and on the rich set of continuous records that were requested from MERMAID's one-year buffer in the hours and days immediately following the Hunga Tonga Hunga Ha'apai eruption, recorded by over twenty instruments over a wide epicentral distance and backazimuthal range.

Waveform modeling was not a design goal for MERMAID, but we discuss an innovative approach to circumvent the computational burden involved in matching the global earth ocean-bottom response to teleseismic earthquakes (computed using an axisymmetric spectral-element code) to the local oceanic mid-column pressure response, including the effects of bathymetry (computed using a local two-dimensional spectral-element modeling step). We applied our method, which is based on precomputed Green's functions via the publicly available code Instaseis and on a custom data base of ocean-floor-to-water-column response functions computed using SPECFEM-2D, to a set of over one thousand waveforms, after dynamically selecting the optimal bandwidth based on adaptive signal-to-noise considerations to steer clear of the noise generated by the ocean wave heave. The correlation between synthetics and observations is as high as 0.98, with a median of 0.72, and very coherent across the array, allowing for the determination of cross-correlation travel times and opening up MERMAID seismograms to conduct full-waveform tomography of Earth's mantle.

Similarly, volcanic monitoring was not a design goal for MERMAID, but in recovering, on-demand, the many hours of continuous records of the Hunga Tonga Hunga-Ha`apai eruption, we have obtained a unique data set from which are piecing together a detailed picture of the eruption sequence. We discuss signal correlations and disparities within and across the South Pacific Plume Imaging and Modeling (SPPIM) array, and address, in particular, path-dependent effects due to "bathymetric occlusion", the influence of seafloor topography on the coherent propagation of hydroacoustic energy over large distance ranges.

How to cite: Simons, F. J., Pipatprathanporn, S., Simon, J. D., and Irving, J. C. E.: MERMAID Tales: Travel-Times, Waveform Modeling, Infrasonic Spectral Densities, and Volcanic Eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8267, https://doi.org/10.5194/egusphere-egu23-8267, 2023.

EGU23-8862 | ECS | Orals | SM2.4

Observability of Seafloor Deformation in OBP Records: an A-0-A Experiment in the Context of the Mayotte Volcanic Crisis, Using Ocean Models 

Yann-Treden Tranchant, Valérie Ballu, Denis Dausse, and Laurent Testut

Ocean bottom pressure (OBP) records are an important source of information for monitoring seafloor motion due to tectonic and magmatic processes, such as earthquakes and volcanic eruptions, at a centimeter-level precision. Although centimeter-level resolution is commonly accessible with high-resolution sensors;  monitoring seafloor deformation of a few centimeters through time with OBPs is challenging due to the instrumental drift and the existence of oceanic variations at different timescales.

In the context of the Mayotte volcanic crisis, which occurred in the western Indian Ocean in 2018 and was characterized by a series of more than 10,000 small-magnitude earthquakes and a subsidence of tens of centimeters (Peltier et al., 2022), three RBR Ambient-Zero-Ambient (A0A) drift-controlled pressure gauges were consecutively deployed in 2020, 2021 and 2022 for seafloor vertical deformation monitoring. The A0A system allows the in-situ estimation of the instrumental drift  by periodic venting from ocean pressures to a reference atmospheric pressure (Wilcock et al., 2021). Since no significant vertical ground displacements are recorded by ground GNSS stations since 2020, the overall objective of this study is to assess the calibration method of these innovative pressure gauges, reduce the oceanic “noise” in corrected OBP records and thus discuss our ability to observe any seafloor deformation in the Mayotte region.

To do so, we investigated the use of numerical models, including available global ocean circulation reanalyses (OGCMs) and barotropic simulations, in order to better understand the relative influence of each processes evolving at different timescales, to reduce the oceanic “noise” in drift-corrected OBP records and thus improve our ability to derive accurate estimates of seafloor motion in the Mayotte region. In addition, we exploited temperature and salinity collected by repetitive glider transects to validate OGCMs in the region and quantify the contribution of unresolved fine-scale processes, such as sub-mesoscale eddies, to OBP records. 

Our results provide valuable insights into the feasibility of using numerical modeling for improving the accuracy of OBP-based monitoring in the context of the Mayotte seismic crisis as well as for other seafloor deformation monitoring. It also has important implications for future A0A deployments and in the perspective of the planned MARMOR seafloor cabled observatory.

References 

Peltier, Aline, et al. "Ground deformation monitoring of the eruption offshore Mayotte." Comptes Rendus. Géoscience 354.S2 (2022): 1-23.

Wilcock, W. S., Manalang, D. A., Fredrickson, E. K., Harrington, M. J., Cram, G., Tilley, J., ... & Paros, J. M. (2021). A thirty-month seafloor test of the A-0-A method for calibrating pressure gauges. Frontiers in Earth Science, 8, 600671.

How to cite: Tranchant, Y.-T., Ballu, V., Dausse, D., and Testut, L.: Observability of Seafloor Deformation in OBP Records: an A-0-A Experiment in the Context of the Mayotte Volcanic Crisis, Using Ocean Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8862, https://doi.org/10.5194/egusphere-egu23-8862, 2023.

EGU23-9886 | Orals | SM2.4

Microseismicity of the Macquarie Ridge Complex 

Nicholas Rawlinson, Tom Winder, Hrvoje Tkalcic, Joann Stock, and Mike Coffin

The Macquarie Ridge Complex (situated on the Australian – Pacific plate boundary, in the southwest Pacific Ocean) constitutes a unique geological site, being the only location on Earth where ‘normal’ oceanic crust protrudes above sea level within the ocean basin in which it formed. This raises fundamental questions, including what facilitates the obduction of oceanic crust in this locality (crucial for fully understanding the context around much-studied ophiolite complexes such as the Samail, Oman), and the conditions which led to the largest strike-slip earthquake of the 20th Century (Mw 8.2; May 23 1989).

To begin to answer these questions, an array of broadband ocean-bottom and land seismometers was deployed on and around Macquarie Island between October 2020 and February 2022. In this presentation, we summarise the data that were collected – and challenges faced – and show a preliminary catalogue of microseismicity for the duration of the deployment, generated using QuakeMigrate software. QuakeMigrate uses a waveform-based approach to earthquake detection and location, with advantages including improved performance in the presence of heterogeneous noise sources, during intense seismic swarms with small inter-event times, and in automating the processing of large quantities of continuous seismic data. Sophisticated time-domain algorithms allow us to maintain an appropriate detection threshold despite strongly varying noise levels (in the world’s stormiest ocean), varying numbers of operational stations, and in the presence of significant clipping issues on the ocean-bottom instruments’ horizontal channels.

We search for temporal variations in earthquake rates, and compute relative relocations (using GrowClust software) to produce high-resolution images of the faults on which the seismicity occurs. These results are interpreted in the context of the location of the most recent large earthquakes on this segment of the plate boundary, and together with complementary geophysical parameters including geodetic measurements and submarine and subaerial fault mapping.

How to cite: Rawlinson, N., Winder, T., Tkalcic, H., Stock, J., and Coffin, M.: Microseismicity of the Macquarie Ridge Complex, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9886, https://doi.org/10.5194/egusphere-egu23-9886, 2023.

Deep upward mantle flow is key to bring volatiles to the atmosphere and to produce Earth’s largest melting events extending through hundreds of thousands of kilometres, which coincide with major extinctions and changes in the geodynamo. Without knowing upward flow, we cannot understand global mantle flow and directly link the Earth’s interior with the surface. Yet, while downward flow (at subductions zones) is well constrained by seismology, plume-like mantle upwellings that connect the deepest mantle to the surface are poorly understood. The goal of the UPFLOW project (https://upflow-eu.github.io/) is to develop new high-resolution seismic imaging approaches along with new data collection, and to use them to constrain upward flow in unprecedented detail. We conducted a large amphibian experiment in the Azores-Madeira-Canary Islands region, which is a unique natural laboratory with multiple upwellings that are poorly understood in general. UPFLOW deployed 50 and recovered 49 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area in the Azores-Madeira-Canary Islands region starting in July 2021 for ~13 months, with an average station spacing of ~150-200 km. These data will be combined with land data from over 30 seismic stations in nearby islands. The seismic deployment and recovery involved institutions from five different countries: Portugal (IPMA, IDL, Univ. of Lisbon, ISEL), Ireland (DIAS), UK (UCL), Spain (ROA) and Germany (Potsdam University, GFZ, GEOMAR, AWI). In addition to its scientific component, the experiment also had a substantial science outreach component, with participation from children from primary schools in the UK, Germany, Portugal, Spain and Ireland, facilitated by UCL’s GeoBus project. We discuss some of the activities conducted, such as the children’s naming of the OBSs, their drawings on how they imagined the OBSs, their stories on what may have happened to the OBSs during the experiment and zoom sessions including live calls to the ship. Names chosen included Neptune, Triton, Jelly, Caesar and Thor. The deployment (28 days offshore) and recovery (35 days offshore) of the OBS instruments was carried out during two dedicated expeditions with IPMA’s research vessel NI Mário Ruivo with the strong support of its skilled and highly motivated crew. 32 OBSs were loaned from the DEPAS international pool of instruments maintained by the Alfred Wegener Institute (Bremerhaven), Germany, while other institutions borrowed additional instruments (7 from DIAS, 4 from IDL, 3 from ROA, 4 from GEOMAR). Most of the instruments have three-component wideband seismic sensors and hydrophones, but three different designs of OBS frames were used. Initial data analysis shows high-quality data, notably a substantial decrease in noise levels in the vertical component long-period data (T>~30s). We show illustrative recordings of teleseismic events, a local seismic swarm, and long-period seismic signals as well as of non-seismic signals such as whales vocalisations and ships’ noise. We discuss the lessons learned from our international collaborative expedition, as well as possible future directions. 

How to cite: Ferreira, A. M. and Miranda, M. and the UPFLOW team: The UPFLOW experiment: peeking from the sea floor to the deep mantle with a ~1,500 km aperture array of 49 ocean bottom seismometers in the mid-Atlantic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10019, https://doi.org/10.5194/egusphere-egu23-10019, 2023.

EGU23-10225 | Orals | SM2.4

Outcome and lessons from the Southern Mariana Ocean Bottom Seismic Experiments 

Hongfeng Yang, Gaohua Zhu, Han Chen, and Aqeel Abbas

The Challenger Deep in the Southern Mariana subduction zone has attracted enormous attention of scientific investigators and explorers during recent decades. Since late 2016, near-field active and passive source seismic experiments has been carried out in the region by deploying Ocean Bottom Seismographs (OBS) in various terms. Both active and passive source tomographic images clearly indicate a well hydrous incoming plate, which is consistent with the observed pervasive normal faults in the out-rise region. Numerous earthquakes have been detected from the OBS recordings, and their locations delineate the subducting plate as well as deep out-rise faults, showing significant along-trench variations. Earthquake clusters are also found beneath the southwestern Mariana Rift and diminish sharply in the north. In addition to the scientific findings, we have discovered unexpected problems with the OBS data, particularly on the timing accuracies that are crucial on seismic records. To fix the various timing problems, we develop a framework of integrating travel times of teleseismic earthquakes and ambient noise cross correlations in different time segments. Such a framework could be applied on other OBS dataset suffering from irregular timing problems.

How to cite: Yang, H., Zhu, G., Chen, H., and Abbas, A.: Outcome and lessons from the Southern Mariana Ocean Bottom Seismic Experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10225, https://doi.org/10.5194/egusphere-egu23-10225, 2023.

EGU23-10662 | ECS | Posters virtual | SM2.4

Probabilistic ambient noise imaging of the Macquarie Ridge Complex using ocean-bottom and land-based seismometers 

Thanh-Son Pham, Hrvoje Tkalcic, Xiaolong Ma, Robert Pickle, Jack Muir, Kenneth Duru, Tom Winder, Nicholas Rawlinson, Caroline Eakin, Millard Coffin, and Joann Stock and the Macquarie Ridge 3D Team

The Macquarie Ridge Complex, located at the boundary between Indo-Australian and Pacific plates in the southwest Pacific Ocean, hosts the largest sub-marine earthquakes in the 20th century, not associated with ongoing subduction. We deployed 27 ocean-bottom seismometers, of which 15 have been recovered successfully, to understand the origin of the sub-marine earthquakes and their potential earthquake and tsunami hazards to Australia and New Zealand. Additionally, we deployed five land-based seismometers on Macquarie Island.

We explore state-of-the-art processing methods to analyze the new seismic dataset from the retrieved seismic stations. One of the goals is to image the tectonic settings beneath the MRC. Here, we present a first-order tomographic model and its relevant uncertainty estimate of the region constructed from ambient noise surface waves using a probabilistic inversion framework. The tomographic image will be complemented with receiver-based imaging results such as those from P-wave coda autocorrelations and receiver functions to confirm the existence of possible geometries. The results are expected to supply a fresh understanding of the tectonic settings under the MRC and unpuzzle the origin of the significant underwater earthquakes in the 20th century.

How to cite: Pham, T.-S., Tkalcic, H., Ma, X., Pickle, R., Muir, J., Duru, K., Winder, T., Rawlinson, N., Eakin, C., Coffin, M., and Stock, J. and the Macquarie Ridge 3D Team: Probabilistic ambient noise imaging of the Macquarie Ridge Complex using ocean-bottom and land-based seismometers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10662, https://doi.org/10.5194/egusphere-egu23-10662, 2023.

At the Mariana Trench, the Pacific plate with increasing age to the east is subducting beneath Philippine Sea plate. This subduction zone includes a volcanic arc, back-arc spreading center and many serpentinite seamounts. The Central Mariana Trench is investigated by using seismic data from 32 OBSs and 20 stations deployed in islands. Cross-correlating ambient noise records between station pairs yields fundamental-mode Rayleigh- and Love-wave dispersion curves at periods from 3 s to 35 s and at periods from 3 s to 20 s, respectively and used a 3D reference model consisting of Crust1.0 and ak135 to obtain more accurate inversion results. In particular, we also estimate group velocities between asynchronous station pairs by using permanent stations on great circle as virtual sources. By jointly inverting Rayleigh- and Love-wave dispersion curves, we calculate an S-wave isotropic and radially anisotropic velocity model, which has resolutions down to 70 km depth for isotropic S-wave velocity model and down to 40 km depth for anisotropic model. Low velocity anomalies are imaged due to the serpentinization and volcanic arc and high velocity anomalies are caused by the stagnation of fore-arc material. On the other hand, negative radial anisotropy are observed dominantly down to 15 km depth, which may be caused by vertical dykes responsible for many seamounts in this region.

How to cite: Kim, T., Chang, S.-J., and Witek, M.: S-wave isotropic and radially anisotropic velocity structure around the Mariana Trench inferred from ambient noise tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10745, https://doi.org/10.5194/egusphere-egu23-10745, 2023.

EGU23-10875 | ECS | Posters virtual | SM2.4

Crustal Structure of the Macquarie Ridge Complex Constrained by the Ambient Noise and Earthquake Autocorrelograms 

Xiaolong Ma, Hrvoje Tkalčić, Caroline Eakin, Nicholas Rawlinson, Thanh-Son Pham, Tom Winder, Robert Pickle, Millard Coffin, and Joann Stock and the Macquarie Ridge 3D Team

The Macquarie Ridge Complex (MRC) constitutes the boundary between the Indo-Australian and Pacific plates in the southwest Pacific Ocean. It accommodates the world’s most potent sub-marine earthquakes that are not associated with ongoing subduction. To better understand the nature of MRC and its associated earthquakes, we aim to explore the crustal structures using recordings from island-based stations and ocean bottom seismometers (OBS). In particular, these OBSs, which are deployed in the surroundings of Macquarie Island from October 2020 to November 2021, enable us to image the refined oceanic structures beneath the study area. In this study, we obtain the body-wave reflections by computing phase coherence autocorrelations of both ambient noise and earthquake data. Our preliminary reflection profiles by both methods reveal coherent reflected P waves that may be related to Moho and additional structures within the crust and upper mantle.

How to cite: Ma, X., Tkalčić, H., Eakin, C., Rawlinson, N., Pham, T.-S., Winder, T., Pickle, R., Coffin, M., and Stock, J. and the Macquarie Ridge 3D Team: Crustal Structure of the Macquarie Ridge Complex Constrained by the Ambient Noise and Earthquake Autocorrelograms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10875, https://doi.org/10.5194/egusphere-egu23-10875, 2023.

EGU23-11314 | Posters on site | SM2.4

S-wave isotropic and radially anisotropic velocity structure in the Western Pacific inferred from partitioned waveform inversion 

Ji-hoon Park, Sung-joon Chang, Michael Witek, Sang-Mook Lee, YoungHee Kim, Hisashi Utada, Hajime Shiobara, Takehi Isse, Nozomu Takeuchi, and Hiroko Sugioka

In the Western Pacific, there are unique geologic/tectonic features such as oldest oceanic crust in the Pacific, seamount chains derived from the Caroline hotspot, the Ontong-Java plateau which is the largest large igneous province, and complex plate boundaries between major and microplates. Investigation of isotropic and anisotropic velocity structure for this region is essential to our understanding of those unique features aforementioned. We estimate an S-wave isotropic and radially anisotropic velocity model beneath the Western Pacific by applying partitioned waveform inversion to three-component seismograms collected from the Incorporated Research Institutions for Seismology Data Managing Center, the Oldest-1 Array deployed in 2018-2019 by a joint Korean-Japan research team, and the Ocean Hemisphere network Project (OJP, NM, and SSP networks). We nonlinearly invert three-component waveforms from 17,038 raypaths (Mw > 5.5) with a 3-D reference model consisting of Crust1.0 and AK135 and resulting constraints are used for iterative least-squares inversion to build an S-velocity model. Our isotropic Vs model shows low-Vs anomalies at ~40 km depth beneath the Ontong-Java Plateau indicating a thick crust, at ~200 km depth beneath the Woodlark spreading center and Caroline seamount chain and at ~600 km depth beneath the center of the Eauripik rise. High-Vs anomalies are observed beneath the center of the Ontong-Java Plateau at 40-150 km depth and at ~50 km depth beneath the West Philippine basin, the Parece-Vela basin, and the Caroline basin. Overall positive radial anisotropy anomalies are observed in the Western Pacific, but the contrast of anisotropy was found in the Pacific plate, Philippine Sea plate, and Caroline plate at ~50 km depth. Negative radial anisotropy anomalies found in the Perace-Vela basin at ~30 km depth, and strong positive anisotropy anomalies are observed at the northern boundary of the Ontong-Java Plateau and beneath the Sorol trough and Caroline seamount chain.

How to cite: Park, J., Chang, S., Witek, M., Lee, S.-M., Kim, Y., Utada, H., Shiobara, H., Isse, T., Takeuchi, N., and Sugioka, H.: S-wave isotropic and radially anisotropic velocity structure in the Western Pacific inferred from partitioned waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11314, https://doi.org/10.5194/egusphere-egu23-11314, 2023.

EGU23-11372 | Posters on site | SM2.4

The first network of Ocean Bottom Seismometers in the Red Sea to investigate the Zabargad Fracture Zone 

Laura Parisi, Nico Augustin, P. Martin Mai, and Sigurjón Jónsson

The Red Sea (RS) is an ideal natural laboratory to study the transition from continental rifting to seafloor spreading because it is one of the youngest rift basins on Earth. The RS is an ultra-slow spreading rift with an opening rate that decreases from 15 mm/yr in the south, at the Nubian-Arabian-Danakil triple junction, to 7 mm/yr in the north where it connects to the Dead Sea transform fault. While the southern RS has a well-developed seafloor spreading ridge with an axis parallel to the rift bounding faults, images of the northern RS seafloor provide limited information because of thick evaporite layers covering the main tectonic features. Nevertheless, the northern rift axis is geometrically different as it is more oblique to the bounding faults than in the south. Furthermore, the transition between the southern and northern RS is sharp with a ~100 km rift axis offset, named Zabargad Fracture Zone (ZFZ). However, the current knowledge of the seismic activity, transform fault configuration, and the crustal and upper mantle structure of the ZFZ area is too limited to assess the seismic hazard associated with this rift offset and understand the role of the ZFZ in the RS development.

To fill this gap, we deployed the first broadband seismic network in the Red Sea, within the ZFZ, from November 2021 to November 2022. This network included 12 Lobster OBSs from the DEPAS pool (equipped with Güralp CMG-40T-OBS sensors), 2 additional Trillium Compact sensors deployed directly on the seafloor mounted on minimalist frames through a collaboration with the company Fugro, as well as 2 Trillium Compact Horizon and 2 posthole sensors deployed on islands and inland in Saudi Arabia, respectively.

The overall data recovery rate is above 90%. Also, our preliminary data analysis confirms some of the known issues of the Lobster OBSs and their sensors (strong self-noise at periods >10 s of the Güralp sensors and high-frequency harmonic noise due to head-buoy cable strumming). Furthermore, we conducted a systematic comparison of the noise recorded by different station configurations. We find that while Lobster OBSs with a head-buoy cable set free to strum generate strong noise at about 10 Hz and its overtones, Lobster OBSs with tight cable still display harmonic noise from 10 to 40 Hz that increases during bad weather conditions, probably due to resonance of other OBS elements. The Fugro OBSs, despite their minimalist deployment setup, show noise at 40 Hz that also resonates in bad weather. All the OBSs also display a peak of noise between 0.5 and 5 Hz (separated from the secondary microseismic peak). While such a noise peak is not recorded by the inland stations, it is well exhibited by the two island stations suggesting that this is due to locally ocean-generated seismic waves, but not by the OBS frames. At periods >10 s, the Fugro OBSs perform as well as the island and inland stations. In fact, waveforms of teleseismic earthquakes recorded by the Fugro OBSs and island and inland stations have comparable signal-to-noise ratios.

How to cite: Parisi, L., Augustin, N., Mai, P. M., and Jónsson, S.: The first network of Ocean Bottom Seismometers in the Red Sea to investigate the Zabargad Fracture Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11372, https://doi.org/10.5194/egusphere-egu23-11372, 2023.

EGU23-11602 | ECS | Orals | SM2.4

Integrated Seismic Program (ISP): A New Python GUI‐Based Software for Earthquake Seismology and Seismic Signal Processing 

Roberto Cabieces, Andres Olivar-Castaño, Thiago C. Junqueira, Jesús Relinque, Jiří Vackár, Cristina Palacios, and Katrina Harris

Integrated Seismic Program (ISP) is a graphical user interface designed to facilitate and provide a user‐friendly framework for performing diverse common and advanced tasks in seismological research. ISP is composed of six main modules for earthquake location, time–frequency analysis and advanced signal processing, implementation of array techniques, seismic moment tensor inversion, receiver function computation and and a new module for ambient noise tomography.

Recently the Ambient Noise Tomography module has been upgraded with a tool specifically designed to synchronize Ocean Bottom Seismometers (OBSs) and to denoise the OBSs seismogram of the vertical component from tilt and compliance noise. The new tool has extensively been tested with data from UPFLOW project (https://upflow-eu.github.io).

In addition, several support tools are available, allowing the user to create an event database, download data from International Federation of Digital Seismograph Networks services, inspect the background noise, and compute synthetic seismograms.

ISP is written in Python3, supported by several open‐source and/or publicly available tools. Its modular design allows for new features to be added in a collaborative development environment.

How to cite: Cabieces, R., Olivar-Castaño, A., C. Junqueira, T., Relinque, J., Vackár, J., Palacios, C., and Harris, K.: Integrated Seismic Program (ISP): A New Python GUI‐Based Software for Earthquake Seismology and Seismic Signal Processing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11602, https://doi.org/10.5194/egusphere-egu23-11602, 2023.

EGU23-12825 | Orals | SM2.4

PickBlue: Seismic phase picking for ocean bottom seismometers with deep learning 

Thomas Bornstein, Dietrich Lange, Jannes Münchmeyer, Jack Woollam, Andreas Rietbrock, Grace Barcheck, Ingo Grevemeyer, and Frederik Tilmann

Detecting phase arrivals and pinpointing the arrival times of seismic phases in seismograms is crucial for many seismological analysis workflows. For land station data machine learning methods have already found widespread adoption. However, deep learning approaches are not yet commonly applied to ocean bottom data due to a lack of appropriate training data and models. Here, we compiled a large and labeled ocean bottom seismometer dataset from 15 deployments in different tectonic settings, comprising ∼90,000 P and ∼63,000 S manual picks from 13,190 events and 355 stations. We adapted two popular deep learning networks, EQTransformer and PhaseNet, to include hydrophone recordings, either in isolation or in combination with the three seismometer components, and trained them with the waveforms in the new database. The performance is enhanced by employing transfer learning, where initial weights are derived from models trained with land earthquake data. Our final model, PickBlue, significantly outperforms neural networks trained with land stations and models trained without hydrophone data. The model achieves a mean absolute deviation (MAD) of 0.06 s for P waves and 0.10 s for S waves. We integrate our dataset and trained models into SeisBench to enable an easy and direct application in future deployments.

How to cite: Bornstein, T., Lange, D., Münchmeyer, J., Woollam, J., Rietbrock, A., Barcheck, G., Grevemeyer, I., and Tilmann, F.: PickBlue: Seismic phase picking for ocean bottom seismometers with deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12825, https://doi.org/10.5194/egusphere-egu23-12825, 2023.

EGU23-14181 | ECS | Posters on site | SM2.4

Enhancing FAIRness for OBS data within the eFAIRs project 

Laura Hillmann, Susanne Hemmleb, Angelo Strollo, Javier Quinteros, Andres Heinloo, Christian Haberland, Martin Haxter, Mechita Schmidt-Aursch, Louis Ulmer, Anke Dannowski, Heidrun Kopp, and Wayne Crawford

Data from Ocean Bottom Seismometer (OBS) deployments nowadays are routinely integrated in federated seismological data centers, but often without following standardized procedures as recommended by the OBS community. This makes it difficult to locate and exploit these data mainly due to the restrictions imposed by the standard metadata format (stationXML) and the services.

In the context of the Helmholtz Metadata Collaboration (HMC), supported by OBS experts, we selected AWI and GEOMAR datasets to be archived at the GEOFON data center with standardized procedures according to the FDSN straw man proposal of W. Crawford for OBS data and metadata using also the OBSinfo tools developed at IPGP. In addition, a special emphasis was put on enhancing FAIRness for the selected datasets, for example identifiers of individual instruments were included, which are linked to instrument databases. Keywords were also added to make the data more easily findable and interoperable. From these experiences we formulated guidelines for OBS data management, which should help researchers to archive their OBS data consistently throughout EIDA data centers.

How to cite: Hillmann, L., Hemmleb, S., Strollo, A., Quinteros, J., Heinloo, A., Haberland, C., Haxter, M., Schmidt-Aursch, M., Ulmer, L., Dannowski, A., Kopp, H., and Crawford, W.: Enhancing FAIRness for OBS data within the eFAIRs project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14181, https://doi.org/10.5194/egusphere-egu23-14181, 2023.

EGU23-15012 | ECS | Orals | SM2.4

Determining clock errors of ocean-bottom seismometers: an ambient-noise based method designed for large-scale ocean bottom deployments 

David Naranjo, Laura Parisi, Sigurjón Jónsson, Philippe Jousset, Dieter Werthmüller, and Cornelis Weemstra

The timing of the recordings of ocean-bottom seismometers (OBSs) is critical for accurate earthquake location and Earth model studies. GNSS signals, however, cannot reach OBSs deployed at the ocean bottom. This prevents their clocks from being synchronized with a known reference time. To overcome this, we developed OCloC, a Python package that uses time-lapse cross-correlations of ambient seismic noise to synchronize the recordings of large-scale OBS deployments. By simultaneously quantifying deviations from symmetry of a set of lapse cross-correlations, OCloC recovers the incurred clock errors by means of a least-squares inversion. In fact, because non-uniform noise illumination patterns also break the symmetry of (lapse) cross-correlations, we introduce a distance-based weighted least-squares inversion. This mitigates the adverse effect of the noise illumination on the recovered clock errors. Using noise recordings from the IMAGE project in Reykjanes, Iceland, we demonstrate that OCloC significantly reduces the time and effort needed to detect and correct timing errors in large-scale OBS deployments. In addition, our methodology allows one to evaluate potential timing errors at the time of OBS deployment. These might be caused by incorrect initial synchronization, or by rapidly changing temperature conditions while the OBS is sunk to the sea bottom. Our work advances the use of OBSs for earthquake studies and other applications.

How to cite: Naranjo, D., Parisi, L., Jónsson, S., Jousset, P., Werthmüller, D., and Weemstra, C.: Determining clock errors of ocean-bottom seismometers: an ambient-noise based method designed for large-scale ocean bottom deployments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15012, https://doi.org/10.5194/egusphere-egu23-15012, 2023.

EGU23-15911 | ECS | Posters on site | SM2.4

Determining the shear velocity structure of the oceanic crust from measurements of seafloor compliance 

Mohammad-Amin Aminian, Eléonore Stutzmann, Jean-Paul Montagner, and Wayne Crawford

The ocean covers two-thirds of the Earth's surface, making it difficult to study the structure of the Earth in these areas.  The ocean, however, provides a pressure signal that can be used to study the oceanic crust, by measuring the seafloor deformation under this pressure signal.  We use continuous signals of seismic ground velocity combined with differential pressure at the sea floor recorded by ocean bottom stations (OBS).  By combining pressure and displacement data of the OBS, we can calculate the compliance function from the pressure signal of infra-gravity waves in the frequency band (0.003-0.03 Hz) . The displacement depends on the seismic properties of the earth's crustal layers, primarily its shear modulus.
The compliance function is very sensitive to the regions with a low shear velocity which makes it an excellent tool for investigating the earth crust for these regions.

To calculate the compliance function, the data must be preprocessed in several steps including glitch and earthquake removal, tilt correction, etc.
To remove earthquakes we used earthquake catalogs for large events and a recursive STA/LTA algorithm for local events. We use a comb
filter to remove hourly glitches  produced by the internal OBS system . 
Tilt noise is caused by deep ocean currents,  we minimize it on the vertical record by rotating the 3-component seismic data to an angle that minimize the variance of the vertical record, then by removing noise coherent with the horizontal components.

In this study, we used the French OBS of the Rhum-Rum experiment (Barruol and Sigloch, EOS, 2013) near La Reunion Island for 13 months in 2012, then calculated the compliance function. The crustal shear velocity structure below each station is then recovered by depth inversion of compliance.

How to cite: Aminian, M.-A., Stutzmann, E., Montagner, J.-P., and Crawford, W.: Determining the shear velocity structure of the oceanic crust from measurements of seafloor compliance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15911, https://doi.org/10.5194/egusphere-egu23-15911, 2023.

EGU23-1638 | ECS | Orals | SM2.5

A deep learning-based workflow for microseismic event detection 

Michele De solda, Francesco` Grigoli, Peidong Shi, Federica Lanza, and Stefan Wiemer

In the last few years, the number of dense seismic networks deployed around the world has grown exponentially and will continue to grow in the next years, producing larger and larger datasets. Among the different seismological applications where these massive datasets are usually collected microseismic monitoring operations are certainly the most relevant and are a perfect playground for data-intensive techniques. In these applications we generally deal with seismic sequences characterized by a large number of weak earthquakes overlapping each other or with short inter-event times; in these cases, pick-based detection and location methods may struggle to correctly assign picks to phases and events, and errors can lead to missed detections and/or reduced location resolution. Among the seismological data analysis methods recently developed, waveform-based approaches have gained popularity due to their ability to detect and locate earthquakes without the phase picking and association steps. These approaches exploit the information of the entire network to simultaneously detect and locate seismic events, producing coherence matrices whose maximum corresponds to the coordinates of the seismic event. These methods are particularly powerful at locating microseismic events strongly noise-contaminated, but despite their excellent performance as locators, waveform-based methods still show several disadvantages when used as detectors. Waveform-based earthquake detectors strongly depend on the threshold selected for a certain application. If it is too high, small events may be missed; if it is too low, false events might be detected. To solve this problem, deep learning techniques used for the classification of images can be used to remove the dependence on threshold levels during the detection process. When applied to continuous seismic data, waveform staking methods produce coherence matrices with clear patterns that can be used to distinguish true events from false ones (i.e. noise). The coherence matrices for a seismic event generally show a single and well-focused maximum while pure noise waveforms produce blurred images with low coherence values or many poorly focused maxima. Deep Learning algorithms are the perfect tool to classify these kinds of images and improve the detection capability of waveform-based techniques. The aim of this work is the development of a workflow that, through a Convolutional Neural Network (CNN), detects seismic events by classifying the coherence matrices. We aim to train the CNN by feeding them with synthetic coherence matrices. To generate realistic coherence matrices both for events and noise we use a stochastic modeling approach to generate synthetic noise records with the same spectral properties as the observed one. For each synthetic event or pure noise recording, we finally use waveform stacking to generate coherence matrices that will be used to train the CNN. One important feature of the workflow here exposed is that the training is performed entirely on synthetics without the need for large labeled data, often missing when new microseismic networks are deployed. To test the workflow we apply it to the recently released dataset collected in Iceland, within the COSEISMIQ project.

How to cite: De solda, M., Grigoli, F., Shi, P., Lanza, F., and Wiemer, S.: A deep learning-based workflow for microseismic event detection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1638, https://doi.org/10.5194/egusphere-egu23-1638, 2023.

Deployment of the mobile seismic network around Petrinja in the aftermath of the Petrinja earthquake

After the devastating Petrinja earthquake (ML 6.2) in December 2020, the Croatian Seismological Survey acquired 20 sets (seismographs and accelerographs ) to use as a mobile pool of seismic stations. From January 2021, the installation of more than 20 stations in the wider Petrinja area began. All stations were operational in less than two weeks. Initially, the mobile pool worked offline until a working data transmission solution was found, as DynDNS didn't work with the current cellular network operator. Finally, a VPN solution was applied by installing an OpenVPN server and creating a VPN network that was proven to work properly. Since April 2021, all stations have been online and transmitting data to the CSS headquarters, where the SeisComP3 machine is responsible for data acquisition and processing. After the Ljubinje earthquake in April 2022, some of the stations of the Petrinja mobile pool were relocated to the wider Dubrovnik area. Both sites use accelerographs and seismographs for earthquake detection purposes, with 100 Hz and 200 Hz sampling for seismographs and 200 Hz for accelerographs.The Petrinja Mobile Network is still active today as the aftershock sequence is still active in that area. Details of the equipment purchased, problems encountered and solutions found for data transmission, site selection procedures applied and results achieved are presented.

How to cite: Fiket, T.: Deployment of the mobile seismic network around Petrinja in the aftermath of the Petrinja ML 6.2 earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2142, https://doi.org/10.5194/egusphere-egu23-2142, 2023.

EGU23-2210 | Posters on site | SM2.5

Toward a renewed data processing of the Engineering Strong Motion (ESM) database 

Claudia Mascandola, Maria D'Amico, Emiliano Russo, Lucia Luzi, Giovanni Lanzano, Chiara Felicetta, Francesca Pacor, and Sara Sgobba

Strong-motion records and open access to strong-motion data repositories are fundamental to seismology, earthquake engineering and practice. The main archive to disseminate high quality processed waveforms for the European-Mediterranean region is the Engineering Strong-Motion Database (ESM, https://esm-db.eu). ESM is developed under the general coordination of the ORFEUS Strong-Motion Management Committee (Observatories and Research facilities for European Seismology; http://orfeus-eu.org/), with the aim to provide users daily access to updated strong-motion waveforms of earthquakes with magnitude greater than 4, mainly recorded in the Pan-European regions. ESM is fully compatible with the European Integrated Data Archive (EIDA; http://orfeus-eu.org/data/eida/) and disseminates waveforms and related metadata according to the Federation of Digital Seismograph Networks (FDSN, https://www.fdsn.org/networks/).

The strategy of ESM is to disseminate only manually processed data to ensure the highest quality. However, the rapid increase in the number of waveforms, due to the increment of seismic stations, leads to the need of automatic procedures for data processing and data quality control.

In this work, we present ESMpro, a modular Python software for a renewed processing framework of ESM. The ESM data processing  is improved with:

(1) automated data quality-check that speeds up the processing time through the rejection of poor-quality records;

(2)  advancement  of the automatic settings for waveform trimming and filtering;

(3) introduction of different algorithms for data processing (Paolucci et al., 2011; Schiappapietra et al., 2021);

(4) modular and flexible software structure that allows the addition of new algorithms and custom workflows.

The accuracy of the updated automatic processing is evaluated by comparison with the waveforms processed by expert analysts, used as benchmarks (Mascandola et al., 2022).

ESMpro is distributed in a stand-alone Beta version available on GitLab (D’Amico et al., 2022; https://shake.mi.ingv.it/esmpro/), following the Open Science principles to promote collaborations and contributions from the scientific community. In the next future, a renewed ESM web-processing frontend will be developed to include the ESMpro improvements, as well as new functionalities to process stand-alone data (i.e., not stored in the ESM database) and to allow different input seismic data formats.

How to cite: Mascandola, C., D'Amico, M., Russo, E., Luzi, L., Lanzano, G., Felicetta, C., Pacor, F., and Sgobba, S.: Toward a renewed data processing of the Engineering Strong Motion (ESM) database, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2210, https://doi.org/10.5194/egusphere-egu23-2210, 2023.

Building an earthquake early warning (EEW) network requires the installation of seismic instruments around the seismogenic zone. Using low-cost sensors to build a seismic network for EEW and to generate shakemaps is a cost-effective way in the field of seismology. The National Taiwan University (NTU) network employing 770 P-Alert low-cost sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years in Taiwan. This instrumentation is capable of recording the strong ground motions of up to ± 2g and is dense enough to record the near-field ground motion. The NTU system has shown its importance during various earthquakes that caused damage in Taiwan. Although the system is capable of acting as a regional as well as an on-site warning system, it is particularly useful for onsite warning. Using real-time seismic signals, each P-Alert device provided a 2–8 s warning time for the near-source earthquake regions situated in the blind zone of the Central Weather Bureau (CWB) regional EEW system, during the 2016 Mw6.4 Meinong and 2018 Mw6.4 Hualien earthquakes. The shakemaps plotted by the P-Alert dense network help to assess the damage pattern and act as key features in the risk mitigation process. These shakemaps are delivered to the intended users, including the disaster mitigation authorities, for possible relief purposes. Currently, the P-Alert network can provide peak ground acceleration (PGA), peak ground velocity (PGV), spectral acceleration (Sa) at different periods, and CWB intensity shakemaps. Using shakemaps it is found that PGV is a better indicator of damage detection than PGA. Encouraged by the performance of the P-Alert network, more instruments are installed in Asia-Pacific countries.

How to cite: Wu, Y.-M.: Development of an earthquake early warning and shakemaps system using low-cost sensors in Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2499, https://doi.org/10.5194/egusphere-egu23-2499, 2023.

EGU23-3032 | Posters on site | SM2.5

A Study on Earthquake Detection Performance of MEMS Sensors According to Seismic Observation Network Density 

Euna Park, Jae-Kwang Ahn, Eui-Hong Hwang, Hye-Won Lee, and Sun-Cheon Park

Earthquake early warning (EEW) is a technology that aims to reduce damage by notifying an alarm message before a large shaking due to an earthquake. The EEW currently adopted by most national or local governments is a network-based method. Network-based EEW produces seismic source information based on seismic wave detection from at least three observation stations, so the density of the observation network is a very important factor in shortening the warning time. However, a huge budget and space are required to construct a dense seismic observation network. In order to compensate for such limitations, all sensors capable of detecting vibration are being expanded and applied to seismometers. The Korea Meteorological Administration (KMA) signed an MOU with a private telecommunication service provider and installed about 6,700 MEMS sensors across the country. This is about 22 times more sensors than the existing KMA seismic observation network. In this study, the seismic detection performance of MEMS sensors and the KMA seismometers installed across the country was analyzed from the perspective of time. Since it is difficult to apply the existing seismic wave detection technology to the MEMS sensor as it is, an artificial intelligence-based seismic detection technology was applied. We compared the analysis results of the KMA observation network and the MEMS observation network in real-time for earthquakes of M 3.5 or greater. As a result of real-time detection, it was found that the high-density of observation network was more effective in detecting earthquakes than the performance of the sensor.

How to cite: Park, E., Ahn, J.-K., Hwang, E.-H., Lee, H.-W., and Park, S.-C.: A Study on Earthquake Detection Performance of MEMS Sensors According to Seismic Observation Network Density, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3032, https://doi.org/10.5194/egusphere-egu23-3032, 2023.

EGU23-3590 | Orals | SM2.5 | Highlight

Current situation and challenges for the Ukrainian seismic network 

Tetiana Amashukeli, Luca Malatesta, Liudmyla Farfuliak, Olexander Ganiev, and Kostiantyn Petrenko

In February 2022, the Ukrainian seismic network already faced multiple critical issues and its modernization was needed. The war exacerbated all existing issues and accelerated the need for a fundamental reorganization and modernization. In this presentation we will report on the network’s status and draft reconstruction plans. As of January 5th 2023, the Ukrainian seismic network has been damaged by the war as follows:

  • partial or complete destruction of facilities and infrastructure caused by power and internet outages;
  • inability to serve stations;
  • complete destruction of Zmiinyi Island (Snake Island) infrastructure where one seismograph was installed;
  • internal and external migration of people involved in the maintenance of stations;
  • delayed standardization of existing seismic stations.

While relatively quiescent, the Ukrainian territory needs an operational seismic network for safety and research purposes. Ukraine hosts a great number of industrial and agricultural facilities critical for the world’s food supply, as well as four nuclear power plants with 15 reactors are located. Seismicity in Ukraine is aligned along the Alpide seismic orogenic belt across the southern and western part of the territory. In addition, significant intraplate earthquakes are recorded in Central and Eastern Ukraine where heavy industries and iron ore mining are concentrated.

The Ukrainian seismic network is currently  divided into three autonomous branches that make up the seismic network of the Institute of Geophysics of the National Academy of Sciences of Ukraine (NAS): Carpathian, Crimean and Central. Unfortunately, these branches were not combined into one unified national network. The base station for observations in Central Ukraine is the IRIS KIEV seismic station (IU, Global Seismograph Network), which is operated by the Institute of Geophysics with support from the US Geological Survey Seismological Laboratory (Albuquerque).

The main goals of modernizing the network must focus on: access to seismological data; long-term data accessibility; calculation of seismic risk; geodynamic and seismic monitoring; surveillance of hazardous facilities. A modernized seismic network is not only a mean of surveillance, but also as a fundamental infrastructure for academic geophysical research in Ukraine.

The integration and data exchange in the European and international community require certificated, industry-standardized seismic instruments and up-to-date digital infrastructure. The seismic network of the Institute of Geophysics of the NAS is equipped with outdated and non-certificated seismic instruments that degrade instrumental data and hamper the exchange of observational materials and scientific analyses with the global community.

The first steps for the modernization of the Ukrainian seismic network started in 2019 with the initiation of a unified platform to process data. For this purpose, the industry-standard SeisComP seismic network software was adopted. In Nov. 2022, we purchased four low-cost Raspberry Shake Seismographs (RS3D) that will be tested in different setting across the territory of Ukraine. Deployment of budget seismometers is a stop-gap measure for both data collection and education in Ukraine.

How to cite: Amashukeli, T., Malatesta, L., Farfuliak, L., Ganiev, O., and Petrenko, K.: Current situation and challenges for the Ukrainian seismic network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3590, https://doi.org/10.5194/egusphere-egu23-3590, 2023.

EGU23-5304 | Orals | SM2.5

Providing unified data delivery statistics service from european seismological data centers 

Jonathan Schaeffer and Helle Pedersen and the EIDA staff

     Data delivery statistics is one of the classical key performance indicators for a large variety of usages : providing insight of data usage to founders, to seismological network managers, to data management centre operational teams.

EIDA is the European Integrated Data Infrastructure from the Orfeus project, federating 12 data management centres which distribute seismological data with the same standardized  methods, enabling users to seamlessly access data from seismological networks (more than 16000 stations) accross Europe.

Since the beginning of the project, various stakeholders have put interest in the data distribution statistics, but sharing the meaningfull indicators to build an unified view turned out to be very challenging. Nonetheless, since 2021, a complete unified statistics service is operational and provides meaningfull KPI over data distribution accross all EIDA nodes.

We will present the story of this project and the lessons learned from the different implementations, emphasising the identified caveats and the useful open source technologies which made the implementation possible.

How to cite: Schaeffer, J. and Pedersen, H. and the EIDA staff: Providing unified data delivery statistics service from european seismological data centers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5304, https://doi.org/10.5194/egusphere-egu23-5304, 2023.

EGU23-5389 | ECS | Posters on site | SM2.5

Seismological station placement in Vukovarsko-srijemska and Osječko-baranjska counties, Croatia: a GIS analysis of environmental noise effects for the CROSSNET project 

Antonio Brcković, Vedran Damjanović, Valentina Gašo, Stijepo Grljević, Marko Kapelj, Iva Kostanjšek, Viktorija Milec, Marko Pervan, Anamarija Tremljan, and Tomislav Fiket

The Republic of Croatia is a seismically highly active area and is currently insufficiently covered by seismological stations. Due to the shape of Croatia, a dense network of seismological stations is needed for more accurate determination of the magnitude and location of earthquakes. One of the main goals of the CROSSNET Project, which the Croatian Seismological Survey carries out, is to install 95 new seismological stations across the Republic of Croatia.

Selection of a site for a seismological station is a complex process that requires careful consideration of a range of factors to ensure that the station is at an optimal location for collecting accurate and reliable data on seismic activity. Field surveys will be required to verify methods used for spatial analysis. The location of the seismological station was chosen based on several factor maps, including natural and anthropogenic noise sources (such as roads, railways, energy infrastructure, industry, and surface waters), geology, and geomorphological criteria (such as slope and aspect).

This study aims to find the most appropriate locations for installing a network of seismological stations in Osječko-baranjska and Vukovarsko-srijemska counties in Croatia. It is necessary to set up seismological instruments at locations with reduced seismic noise conditions and favourable geological conditions to improve the quality of the data acquired.

Given the large scope of the project and the area it covers, an adequate approach is necessary to plan field investigations; therefore, the Suitability modeller in ESRI software ArcGIS Pro was used to evaluate locations for future field surveys. The suitability modelling identifies relevant criteria (factor maps), prepares criteria data, transforms values for each criterion to a standard suitability scale, weights criteria relative to one another according to their importance, combines the criteria into a suitability map, and finally locates the most suitable areas for field investigations.

This work has been fully supported by Next Generation EU and National Recovery and Resilience Plan under project C6.1. R4-I1.

How to cite: Brcković, A., Damjanović, V., Gašo, V., Grljević, S., Kapelj, M., Kostanjšek, I., Milec, V., Pervan, M., Tremljan, A., and Fiket, T.: Seismological station placement in Vukovarsko-srijemska and Osječko-baranjska counties, Croatia: a GIS analysis of environmental noise effects for the CROSSNET project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5389, https://doi.org/10.5194/egusphere-egu23-5389, 2023.

EGU23-5937 | Posters on site | SM2.5

ShakeMap-EU: an update on the shakemap service in Europe 

Alberto Michelini, Licia Faenza, Carlo Cauzzi, Valentino Lauciani, John Clinton, Philipp Kästli, Florian Haslinger, Stefan Wiemer, Nikolaos Melis, Nikolaos Theodoulidis, Maren Böse, Graeme Weatherill, Fabrice Cotton, and Domenico Giardini

We present the status of ShakeMap-EU, an initiative initially proposed in 2018 to: (i) provide an integrated archive of ShakeMaps at the European level built on EPOS Seismology (www.epos-eu.org/tcs/seismology) services & data products and modern community software; (ii) serve as a backup to authoritative ShakeMap implementations; (iii) deliver ShakeMaps for Euro-Mediterranean regions where no local capability is yet available. ShakeMap-EU products are accessible since mid-2020 at the web portal shakemapeu.ingv.it. Jointly governed by the institutions participating in the initiative, ShakeMap-EU is founded on voluntary institutional contributions and EC-funded projects. ShakeMap-EU has become a reliable European seismological service that can easily and consistently integrate authoritative models and workflows. The system is based on:  (a) the latest version of ShakeMap® (usgs.github.io/shakemap); (b) the earthquake information delivered by the EMSC (www.emsc-csem.org); (c) the earthquake shaking data distributed by ORFEUS (orfeus-eu.org/data/strong); (d) the ground motion models adopted within EFEHR (www.efehr.org) for mapping seismic hazard across Europe; (d) the official ShakeMap configurations of some of the most hazardous countries in Europe. Configuration of, and input to the system are managed via a GitHub repository that allows automatic / manual triggering and interaction by authorized users. ShakeMap-EU provides a collaboration framework and laboratory for seismological agencies to address the challenges posed by the heterogeneity of ground shaking mapping strategies across Europe and the need to promote homogenization and best practices in this domain. ShakeMap-EU is used in research projects as the test platform for novel international collaborative research: among recent examples are the ongoing enhancements towards an evolutionary hazard information system including real-time seismicity characterisation and information on earthquake-induced phenomena.

How to cite: Michelini, A., Faenza, L., Cauzzi, C., Lauciani, V., Clinton, J., Kästli, P., Haslinger, F., Wiemer, S., Melis, N., Theodoulidis, N., Böse, M., Weatherill, G., Cotton, F., and Giardini, D.: ShakeMap-EU: an update on the shakemap service in Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5937, https://doi.org/10.5194/egusphere-egu23-5937, 2023.

Shakemaps are important tools for characterizing and visualizing the geographic impact of seismic events. It is also a great support of communication and crisis management, especially in the early stage following an event. It is thus important to constrain at best the parameters controlling the calculation to have the most reliable shakemaps possible. 

Our study consists in optimizing the shakemaps in an application for moderate seismic activity in mainland France and French overseas territories. 

We studied the evolution from v3.5 to v4 of USGS ShakeMapTM and compared the associated shakemaps for past events. An in-depth study of the core calculations of the v4 was necessary to take advantage of their new approaches and optimize the parameters and configuration for the French territories. 

Our goal was not only to implement the ShakeMap v4 as the new automatic functional version on www.franceseisme.fr, the BCSF-Rénass website (Résif-Epos), but also to evaluate the prospects and limitations for computing high-resolution shakemaps. We analyzed the uncertainties of shakemaps between rapid shaking assessment based on preliminary data and the late reference shakemap based on complete validated datasets for recent damaging or largely felt events in France.

What can we improve today to reach high-resolution? What might be possible in a few years? Finally, what are the limits that we may never be able to overcome in the ShakeMapTM  program approach?

How to cite: Pellorce, L., Mendel, V., Schlupp, A., and Grunberg, M.: ShakeMapTM v4 study, analysis of rapid shaking assessment, optimization and evaluation of high-resolution prospects for mainland France and French overseas territories, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6302, https://doi.org/10.5194/egusphere-egu23-6302, 2023.

EGU23-6725 | Posters on site | SM2.5

The Minimus digitizer platform: a user-friendly ecosystem for efficient network management and seismic station configuration 

James Lindsey, Neil Watkiss, Will Reis, and Dan Whealing

The Guralp Minimus broadband digitizer has led the way with introducing a number of innovative features to broadband digitizers including easy network configuration, compact form-factor, extensive State of Health (SOH) monitoring and low latency digitization. Since its introduction, there have been major technological advances in processing chips resulting in the power consumption of seismic digitizers decreasing drastically in the last few years. The next iteration of Minimus, Minimus2, takes advantage of modern chip power consumption to reduce overall nominal power consumption by over 50% whilst maintaining high functionality. This significant decrease in power consumption will facilitate far more simplified field deployments for offline deployments.

The Minimus platform also provides a high level of functionality for online stations, including the industry unique option of sending State of Health (SOH) data via the SEEDlink protocol. This makes SOH monitoring far simpler for larger networks as SOH data be managed using similar methods as waveform data. This also allows for time-series analysis of SOH data to be able to proactively maintain stations and advance diagnose any issues before they result in any loss of data. The Minimus platform seamlessly interfaces the Discovery software to seamlessly integrate new stations into existing networks. The management of large numbers of real-time seismic stations is further enhanced with Guralp Data Centre (“GDC”) a cloud-based software package to build on the Discovery tool set.

The Minimus platform was built from the ground up to provide one of the lowest latency digitizers available with digitization latencies down to 40ms, making it well suited to Earthquake Early Warning applications. This is achieved with the use of causal decimation filters, high sample rates and Guralp’s proprietary GDI protocol. The Minimus platform is built as a modular digitizer platform that is available within a number of different packages to suit a range of applications, including as a standalone digitizer or built within Broadband seismometer and Force Balance Accelerometer systems. 

How to cite: Lindsey, J., Watkiss, N., Reis, W., and Whealing, D.: The Minimus digitizer platform: a user-friendly ecosystem for efficient network management and seismic station configuration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6725, https://doi.org/10.5194/egusphere-egu23-6725, 2023.

EGU23-6914 | Posters on site | SM2.5

The Swedish National Seismic Network - Infrastructure, Data Processing and Products 

Michael Roth, Björn Lund, Gunnar Eggertsson, Peter Schmidt, and Hossein Shomali

In recent years the Swedish National Seismic Network (SNSN) made an increased effort to modernize station and communication equipment, and thereby has significantly improved continuous real-time data availability and data quality.  Currently, the SNSN is operating 67 permanent broadband seismic stations evenly distributed in the South, along the Eastern shore and the North of Sweden. In addition, a temporay network of 13 stations was deployed in 2021 for a 3-year period to monitor small earthquakes associated with a linear cluster of events at the Western cost of the Gulf of Bothnia. SNSN transmits continuous real-time data to networks in the neighboring countries (Norway, Denmark, Finland, Germany) and in turn receives and processes data from about 120 stations abroad.

Compared to many other countries, Sweden has a relatively low seismicity. This makes it all the more important to focus on small seismic events in order to map crustal structures and processes and to provide a data basis for reasonable long-term seismic hazard assessments. Turning to small events means to deal with many events and most of them being man-made seismic events (blasts related to quarries, underground mines, road/tunnel constructions, etc). Within the last 22 years SNSN has recorded and analyzed about 170,000 seismic events out of which only 11,000 (~6.5%) were classified as natural events. Automatic event processing and event type classification are of the essence in order to cope with the amount of data and to decrease the workload of the analysts.

SNSN is running four different and independent automatic processing routines in parallel: SeisComp (SC), Earthworm (EW), MSIL and a migration stack algorithm (MS). The main purpose of SC and EW is to detect and locate events in realtime. Both systems are set up to be very sensitive in order to detect as small events as possible, which on the other side also increases the probability to generate spurious events. To counterbalance that we generate a common event catalogue (i.e. events that were located both by SC as well as EW) which turnes out to be very reliable. The common event bulletin captures events as small as about ML1 and contains almost all events ML > 1.5.  MSIL and MS are running in offline and delayed mode which allows the backfilling of potential data gaps, before processing. These systems are catching events down to about magnitude ML0. All events of the common bulletin and the MSIL bulletin are subject to an automatic Neural Network event typ classification into earthquakes, blasts and mining-induced events. In a final step all events classified as earthquakes, significant blasts (felt events or events of special interest) or events with unclear cassification are reviewed by SNSN analysts and are being made available on the SNSN web page. In the framework of EPOS-Sweden, SNSN will make available the waveform and metadata data of the permanent network via FDSN-services.

How to cite: Roth, M., Lund, B., Eggertsson, G., Schmidt, P., and Shomali, H.: The Swedish National Seismic Network - Infrastructure, Data Processing and Products, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6914, https://doi.org/10.5194/egusphere-egu23-6914, 2023.

EGU23-7144 | ECS | Orals | SM2.5

A Python tool to monitor noise characteristics in large seismic data bases 

Johanna Lehr and Klaus Stammler

Continuous monitoring of data quality is a major issue in seismology because the achievement of robust scientific results depends on the reliability of the underlying data resources. We present a Python package which provides means to perform a systematic analysis of noise data in the time and frequency domain. The tool is designed to process large amounts of channels and years of data. In a first step, average amplitude levels and power spectral densities are computed for large parts - preferably the whole available time range - of the data of a station. Depending on the size of the data set, this processing takes minutes to hours. Therefore, the results are stored in rapidly accessible HDF5-files. Subsequently, they are visualized using color-coded matrix displays (spectrograms) and interactive 3D-figures. The resulting figures give insight to characteristic noise patterns at the station and possible noise sources, like various forms of anthropogenic noise or wind generated noise. Furthermore, changes in noise levels or noise patterns are easily detectable. Such changes either indicate changes in the environmental conditions at the recording site or changes in the recording hardware improperly reflected by the station metadata, often signaling a problem with the metadata. Furthermore, the processed data can easily be restricted to selected times, e.g. to investigate the influence of day/night cycles or to obtain wind-speed dependent spectrograms. In this manner, a comprehensive picture of relevant characteristics at a station site may be acquired.

The package is build from established Python libraries like obspy, scipy and h5py. Matplotlib and plotly are used for data visualization. The core functionalities are accessible via command line interface while the underlying API allows for more customized workflows.

How to cite: Lehr, J. and Stammler, K.: A Python tool to monitor noise characteristics in large seismic data bases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7144, https://doi.org/10.5194/egusphere-egu23-7144, 2023.

EGU23-7852 | ECS | Posters on site | SM2.5

Data Quality and Availability Tests of public Seismometer Data in Europe 

Felix Eckel, Johannes Stampa, Máté Timkó, and Luděk Vecsey

The dense coverage of Europe with seismological stations offers a large variety of advanced seismological data processing options. With thousands of stations available a manual quality check of the data becomes more and more unfeasible. Moreover, with rising network traffic, increasing amounts of users, data requests and data size, errors are more likely to occur and the requested data will not always be available for various reasons. Identifying stations and networks that are more likely to be unavailable during data requests is also part of a data quality control. We show how randomized tests can be used to evaluate the data availability for the European stations and how very simple data processing routines calculating average noise levels at stations can be used to identify erroneous data or metadata.

How to cite: Eckel, F., Stampa, J., Timkó, M., and Vecsey, L.: Data Quality and Availability Tests of public Seismometer Data in Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7852, https://doi.org/10.5194/egusphere-egu23-7852, 2023.

EGU23-9051 | Posters on site | SM2.5

ORFEUS Data Services, Products and Actions to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region 

Carlo Cauzzi, Jarek Bieńkowski, Wayne Crawford, Susana Custódio, Sebastiano D'Amico, Christos Evangelidis, Christian Haberland, Florian Haslinger, Anastasia Kiratzi, Petr Kolínský, Giovanni Lanzano, Zafeiria Roumelioti, Karin Sigloch, Reinoud Sleeman, and Angelo Strollo

ORFEUS (Observatories and Research Facilities for European Seismology, orfeus-eu.org) is a non-profit foundation that coordinates and promotes seismology in the Euro-Mediterranean area and beyond, through harmonized collection, archival and distribution of seismic waveform data, metadata, alongside offering services and products managed at national level by more than 60 participating seismological Institutions. ORFEUS is one of the founding members of EPOS Seismology (www.epos-eu.org/tcs/seismology) and a fundamental partner of EC-funded projects. ORFEUS services are largely integrated in the EPOS Data Access Portal (www.ics-c.epos-eu.org). The key goals of ORFEUS (Bylaws, Article I.3: orfeus-eu.org/documents//ORFEUS_Bylaws_September_2022.pdf) are achieved through the development and maintenance of data services targeted to a broad community of seismological data users. ORFEUS comprises: (i) the European Integrated waveform Data Archive (EIDA; orfeus-eu.org/data/eida); (ii) the European Strong-Motion databases (orfeus-eu.org/data/strong); and iii) the recently established group representing the community of European mobile pools, including amphibian instrumentation (orfeus-eu.org/data/mobile). Products and services for computational seismology are also considered for integration in the ORFEUS domain. Currently, ORFEUS services  provide access to the waveforms acquired by ~18,000 stations in the Euro-Mediterranean region, including dense temporary experiments (e.g., AlpArray, AdriaArray), with strong emphasis on open, high-quality data. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services, clear policies and licenses, and acknowledging the crucial role played by data providers. Significant efforts are underway, by ORFEUS participating institutions,  to enhance the existing services to tackle the challenges posed by the Big Data Era, and to actively encourage interoperability and integration of multidisciplinary datasets in seismological and Earth Science workflows.  ORFEUS also implements Community services that include software and travel grants, webinars, workshops and editorial initiatives. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group, which comprises European Earth scientists with expertise on a broad range of disciplines. 

How to cite: Cauzzi, C., Bieńkowski, J., Crawford, W., Custódio, S., D'Amico, S., Evangelidis, C., Haberland, C., Haslinger, F., Kiratzi, A., Kolínský, P., Lanzano, G., Roumelioti, Z., Sigloch, K., Sleeman, R., and Strollo, A.: ORFEUS Data Services, Products and Actions to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9051, https://doi.org/10.5194/egusphere-egu23-9051, 2023.

EGU23-9171 * | Orals | SM2.5 | Highlight

GEOSCOPE: 40 years of global broadband seismic data 

Nicolas Leroy, Martin Vallée, Dimitri Zigone, Armelle Bernard, Jean-Yves Thoré, Constanza Pardo, Maxime Bes de Berc, Eléonore Stutzmann, Céleste Broucke, Frédérick Pesqueira, Alessia Maggi, Luis Rivera, Michel Le Cocq, and Olivier Sirol

The GEOSCOPE observatory provides more than 4 decades of high-quality continuous broadband data to the scientific community. Started in 1982 with a few stations, the network has grown over the years thanks to numerous international partnerships. The 33 operational GEOSCOPE stations are now installed in 18 countries, across all continents and on islands throughout the oceans, filling important gaps in the global Earth coverage (in Africa, Antarctica, Indian Ocean, Pacific Ocean islands and more). Most of the first installed stations are still running today allowing for long term observations and new sites are being prospected for future installations.

Over the years GEOSCOPE contributed to define today's global seismology standards through the FDSN (data format, data quality level, instrumentation requirements), being the french contribution to the international effort (with GSN, GEOFON and others) towards global seismic observations. The stations are equipped with the best quality seismometers (from the very first STS1 in the early 80's to the last STS-6A and Trilium T360 nowadays) and digitizers (Q330HR and Centaur), in order to record with a high fidelity the ground motions generated by all types of seismic sources. Furthermore, most of the stations are also equipped with accelerometers, pressure and temperature sensors allowing for a wider range of observable events such as the recent Hunga-Tonga eruption. All the data are sent in real-time to IPGP data center and are automatically transmitted to other data centers (IRIS-DMC and RESIF) and tsunami warning centers.

In 2022, a workshop has been organized to celebrate the 40th anniversary of GEOSCOPE and illustrate the main scientific achievements made possible by all the global networks. After a brief look at the history of the network and a feedback on the workshop, the recent evolutions of the observatory (new stations in Africa, new generation 360s sensors upgrades, IT infrastructure) and the perspectives (future stations) will be presented.

How to cite: Leroy, N., Vallée, M., Zigone, D., Bernard, A., Thoré, J.-Y., Pardo, C., Bes de Berc, M., Stutzmann, E., Broucke, C., Pesqueira, F., Maggi, A., Rivera, L., Le Cocq, M., and Sirol, O.: GEOSCOPE: 40 years of global broadband seismic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9171, https://doi.org/10.5194/egusphere-egu23-9171, 2023.

EGU23-9287 | ECS | Orals | SM2.5

High-latitude, high-altitude seismic stations on Mt. Erebus, Antarctica 

Avilash Cramer, Madeline Hunt, Kirsten Arnell, Alan Horton, Susan Stanford, Kent Anderson, and Bruce Beaudoin

Mt Erebus, the world’s southernmost active volcano, is only 30 miles from McMurdo Station (US) and Scott Base (NZ). Scientific instruments deployed on the volcano need to survive a range of environmental factors including high winds, extreme cold, lava bombs, and months of total darkness. Additionally, the reduced air pressure at high elevations affects the lift of the helicopters and the physiology of the engineers during installation.

We present a novel design for a network of environmentally hardened seismic stations intended specifically for the constraints of this polar volcano. The purpose of the network is to provide a baseline measurement of volcanic events and act as a fiducial array for future experiments. Stations are designed to function continuously over both summer and winter for years at a time. The station’s instrument package comprises a data logger recording broadband seismic and infrasound data, and a second data logger recording strong-motion seismic data.  The station design is modular and can be scaled for various experiment requirements and easily adapted for different instrument packages.

Station state-of-health will be monitored at the EarthScope Primary Instrument Center (EPIC, formerly IRIS PASSCAL) and low sample rate (20 sps) broadband data are transmitted by Iridium modems and captured in near-real time. Higher sample rate (100-200 sps) data are recorded locally and collected annually during the austral summer. All data will be available from the EarthScope Data Management Center (network codes 1G, 8E, and 2H).

A prototype was installed near McMurdo station in 2021/22 season and evaluated over the Antarctic winter. Based on this prototype, four stations recording data from nine instruments were installed around Mt Erebus in the 2022/23 season. An additional three stations of an older design that are recording data from five instruments were installed in previous seasons as part of an interim network. These stations will be upgraded to the new design in upcoming seasons.

Our talk will center on the following three components:

1) the electrical and mechanical design of this new station, including power electronics, satellite telemetry, insulation, and rigging;

2) the logistics of Antarctic volcanology, including site selection, geographical constraints, and US Antarctic Program helicopter operations;

3) recent results and future plans for maintaining and upgrading seismic networks on Mt. Erebus.

How to cite: Cramer, A., Hunt, M., Arnell, K., Horton, A., Stanford, S., Anderson, K., and Beaudoin, B.: High-latitude, high-altitude seismic stations on Mt. Erebus, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9287, https://doi.org/10.5194/egusphere-egu23-9287, 2023.

EGU23-10046 | Posters on site | SM2.5

Employing machine learning pickers for routine global earthquake monitoring with SeisComP: What are the benefits and how can we quantify the uncertainty of picks? 

Frederik Tilmann, Thomas Bornstein, Joachim Saul, Jannes Münchmeyer, and Moshe Beutel

Recent years have seen the development of several very powerful machine learning pickers for P and S waves. The recent development of the SeisBench platform (https://github.com/seisbench/seisbench) in combination with mixed regional teleseismic benchmark datasets published by the NEIC (USGS) and GEOFON (GFZ Potsdam) enabled the retraining of the most popular picker neural network models (PhaseNet and EQTransformer) optimised for global monitoring applications in the benchmark study of Münchmeyer et al (2021, J. Geophys. Res.).  

In this contribution we introduce a module scdlpicker, which connects SeisBench to SeisComP (https://www.seiscomp.de/)  through a client submodule, which listens to new event detections from the regular SeisComP automatic detection system and triggers repicking of those events with any picker implemented in SeisBench, using the improved picks to trigger a relocation. The machine learning picks are subsequently available within the SeisComP GUI in case further manual refinement or checking is desired. 
We demonstrate application of this system with the GEOFON global earthquake monitoring service (https://geofon.gfz-potsdam.de/eqexplorer), evaluating the benefits of using the machine learning picker with respect to the conventional workflow relying on traditional pickers with respect to timeliness of reporting earthquakes and reduction of manual work load, and improvement in the number of high quality picks available for each event. 
The quantification of the uncertainty of machine learning picks is important when weighing the contribution of different picks in many location algorithms, yet this information is not readily available from machine learning pickers. They do return, however, a characteristic function (nominally the confidence in the pick), whose properties might correlate with the uncertainty of the pick. We will show whether and how the picking uncertainty correlates with properties of the characteristic function. 

How to cite: Tilmann, F., Bornstein, T., Saul, J., Münchmeyer, J., and Beutel, M.: Employing machine learning pickers for routine global earthquake monitoring with SeisComP: What are the benefits and how can we quantify the uncertainty of picks?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10046, https://doi.org/10.5194/egusphere-egu23-10046, 2023.

EGU23-10584 | Orals | SM2.5

        WA array: the next state-wide passive seismic survey 

Ruth Murdie, Huaiyu Yuan, John Paul O'Donnell, Subhash Chandra, and Simon Johnson

The Government of Western Australia, through the Geological Survey of Western Australia, is funding a passive seismic acquisition  program, WA array, which has been designed to map Earth’s lithosphere at an optimal level of station spacing across the state of WA (over 2.5 million square kilometres).

The program, which started on 1 July 2022 will involve the deployment of an “array” of 165 seismometers arranged in a grid pattern spaced at 40 kilometre intervals, moving progressively across the state over a period of ten years. Instruments will be relocated on an annual basis across nine regional areas.

It is primarily designed to investigate the crustal and lithospheric mantle structure with the aim of identifying prospective regions for mineral exploration, especially in areas undercover. At the continental scale, the large lithospheric models will target the bulk lithospheric velocities and upper mantle discontinuities, which will provide direct information to better constrain tectonic deformation processes that operated through time. From the Archean nuclei to the Phanerozoic passive margins, WA is composed of many domains with a rich tectonic history; thus WA array will also provide an unprecedented opportunity to study lithospheric structure related to early Earth tectonics, Earth evolution and the Earth today.

The results of the program will step change in our understanding of Western Australia’s lithospheric architecture. This knowledge will provide a sound scientific basis for mineral and energy exploration, but also for evaluating crucial land use decisions over the coming decades, at a time when large areas of the State are expected to accommodate renewable energy projects.

In addition, the data will be used to evaluate the risks from seismic events, which would contribute to risk assessments for the placement industrial infrastructure such as pipelines and hydrogen generation and storage installations as well as building codes for housing and other buildings.

The first deployment of stations is now in the ground with 158 stations currently running. The first results and raw data will become available at the end of 2024. We will present and discuss the design of the array, initial modelling status and model updates, and related program applications.

How to cite: Murdie, R., Yuan, H., O'Donnell, J. P., Chandra, S., and Johnson, S.:         WA array: the next state-wide passive seismic survey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10584, https://doi.org/10.5194/egusphere-egu23-10584, 2023.

EGU23-12520 | Orals | SM2.5

Evolution of the Concordia seismological observatory station CCD (GEOSCOPE network): a new post-hole installation on Antarctica plateau 

Dimitri Zigone, Maxime Bes de Berc, Peter Danecek, Alain Steyer, Francesco Zanolin, Sophie Lambotte, Olivier Alemany, Philippe Possenti, Adriano Cavaliere, Stefano Marino, Jean-Yves Thore, Alessia Maggi, Armelle Bernard, Jean-Jacques Leveque, Luis Rivera, Martin Vallée, Nicolas Leroy, Eleonore Stutzmann, Frédéric Pesqueira, and Constanza Pardo

In the Southern Hemisphere, the prevalence of the oceans and the difficulty of access to land result in a lack of coverage of seismological station which is a strong limitation Our knowledge of the Earth’s structures and of large earthquakes sources. This is particularly critical inside the Antarctic continent where only two permanent seismological stations are currently available (QSPA and CCD). Among them, the seismological station CCD is a joint program between EOST (Strasbourg) and INGV (Roma) and is installed at the Concordia scientific base (75°S 123°E). This observatory, built in 2000 with state-of-the-art surface instrumentation installed in a vault made of snow-covered containers, meets the required quality criteria and has been part of the GEOSCOPE network since 2008. However, it has become necessary to replace this installation for safety reasons, recurring snow coverage issues and seismological performances. The existing seismic vault is deformed by the hydrostatic pressure of the snow. Its proximity to the base causes strong daytime noise (~30 dB) at high frequencies (>1 Hz); the unconsolidated layer of snow about 100m thick forms a waveguide that traps anthropogenic noise from the base. In addition, a coupling defect of the instruments in contact with the snow limits the performance at low frequencies (< 0.03 Hz) on the horizontal channels.

Eight years ago, we proposed to install a borehole seismometer at a depth of 120m to limit the waveguide effects. A new shelter on stilt and the borehole drilling were carried out in 2018/2019. The installation of all the instrumentation has been completed by our team in January 2020. The analyses of the data show that the high-frequency disturbances are very largely attenuated (-30 dB at 10 Hz) compared to the surface installation and that the horizontal channels have a lower noise level at low frequencies (-20 dB at 0.01Hz). In addition, data for all components are below the standard noise model for frequencies between 5 and 9Hz, which already makes this new station one of the quietest installations in the world for those frequencies. A few problems remain to be solved, such as atmospheric pressure-related perturbations for periods longer than 600s on the vertical component. We are currently implementing several patches to try to better insulate the borehole. Updates will be presented during the meeting. Despite this problem at long period, the new CCD borehole stations is a success with better-than-expected performances at all periods shorter than 500s. The data produced are now distributed in the world data centers as G.CCD.20.

How to cite: Zigone, D., Bes de Berc, M., Danecek, P., Steyer, A., Zanolin, F., Lambotte, S., Alemany, O., Possenti, P., Cavaliere, A., Marino, S., Thore, J.-Y., Maggi, A., Bernard, A., Leveque, J.-J., Rivera, L., Vallée, M., Leroy, N., Stutzmann, E., Pesqueira, F., and Pardo, C.: Evolution of the Concordia seismological observatory station CCD (GEOSCOPE network): a new post-hole installation on Antarctica plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12520, https://doi.org/10.5194/egusphere-egu23-12520, 2023.

EGU23-15147 | ECS | Posters on site | SM2.5

Enhancing remote monitoring of autonomous seismic stations 

Marcel Paffrath, Antje Schlömer, Markus Terpoorten, Sven Egdorf, Arne Schwab, and Wolfgang Friederich

As part of the “Deutsches Seismologisches Breitband Array” (DSEBRA), a mobile station array of 100 identical seismological broadband stations, the remote monitoring devices “PowBox” were developed by the Ludwig-Maximilians-Universität München.

The PowBoxes log and report the health status of the autonomously operating seismological stations, such as 12V/230V availability or battery temperature. With their various fail-safes the most common issues such as router and battery charger problems are fixed by automatic power resets and efforts and costs on unnecessary maintenance trips can be reduced.

More than 80 PowBoxes are now in operation for the first time with the deployment of the DSEBRA stations in South-East Europe as part of the AdriaArray project, a follow-up to the successful AlpArray project.

To ensure a good overview for the network operator, the modular Python software tool “survBot” was developed at the Ruhr-Universität Bochum. It analyses the different state-of-health channels of the PowBox and the Datalogger, displays them in a graphical user interface or as a html-webpage and informs about emerging problems via e-mail. It is openly available on github.

How to cite: Paffrath, M., Schlömer, A., Terpoorten, M., Egdorf, S., Schwab, A., and Friederich, W.: Enhancing remote monitoring of autonomous seismic stations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15147, https://doi.org/10.5194/egusphere-egu23-15147, 2023.

EGU23-15448 | Orals | SM2.5

Developments during 15 years of seismic monitoring in the Caribbean Netherlands 

Reinoud Sleeman, Elske de Zeeuw-van Dalfsen, and Andreas Krietemeyer

In the Caribbean Netherlands, on Saba, St. Eustatius and St. Maarten, the Royal Netherlands Meteorological Institute (KNMI) deploys the seismic network NA (Caribbean Netherlands Seismic Network) to monitor local tectonic earthquakes and volcanic seismicity. Saba and St. Eustatius are part of the Lesser Antilles volcanic arc and each host an active but quiescent volcano: Mt. Scenery on Saba and The Quill on St. Eustatius. The network comprises 11 broadband seismometers of which data are a) transmitted to KNMI by DSL, cellular connection and VSAT, b) processed in real-time at KNMI using SeisComP and a coincidence trigger, c) forwarded in real-time to the Pacific Tsunami Warning Center (PTWC) and d) openly available to research and monitoring communities through ORFEUS/EIDA and EPOS via standardized services. 

In the past six years we detected and located more than 350 earthquakes with magnitudes ranging from 0.4 to 6 within a 150 km radius from the center of the network. About 230 of these earthquakes were exclusively reported by KNMI as they were probably too small to be detected by, or too distant from, seismic networks operated by other agencies in the region. A previously unnoticed shallow (5-10 km depth) swarm of 22 tectonic earthquakes was detected and located through reanalysis of data from before 2017. This swarm took place in 2008, in the same area as the tectonic swarm of earthquakes in 1992, less than 15 km west of Saba, with magnitudes ranging between 2.3 and 4. One of the challenges for our network is building a reliable detection, identification and location system for volcanic earthquakes, which is hampered by the quiet state of both volcanoes. Another challenge is decreasing the hypocenter uncertainties, which are caused by the complex seismic velocity structure underneath the volcanoes, the large lateral velocity inhomogeneities in the subduction zone and the elongated set-up of the regional seismic networks.

How to cite: Sleeman, R., de Zeeuw-van Dalfsen, E., and Krietemeyer, A.: Developments during 15 years of seismic monitoring in the Caribbean Netherlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15448, https://doi.org/10.5194/egusphere-egu23-15448, 2023.

EGU23-16691 | Posters on site | SM2.5

Designing or Upgrading a Seismic Network To Meet Specific Performance Criteria Using Array Modeling, a Case Study 

Michael Laporte, Tim Parker, Valarie Hamilton, and Dan McNamara

More science, particularly related to hazard reduction and earthquake forecasting, is enabled via the availability of rich seismic datasets and event catalogs. Deployment of high performing monitoring networks, which produce high quality datasets, is an investment that enables ongoing and future science advancements.

One measure of network performance, magnitude of completeness (Mc), is determined by a number of factors including station density, network geometry, self-noise and passband of the system used, ambient noise environment and sensor installation method and depth.  Sensor installation techniques related to depth are of particular importance due to their impact on deployment cost and station performance. It is well established that deploying seismic sensors at greater depths reduces their exposure to cultural and environmental noise, improving seismic signal detection. When extended to overall network performance, this noise suppression results in improved (decreased) magnitude of completeness for the network. Using modeling tools, we assess the theoretical improvement in performance associated with an upgrade to borehole installations, increasing sensor depth, for a real world network in the Puget Sound area of Washington State.

The goals of monitoring networks and science are overlapping and dependent. Establishing measurable and achievable performance metrics for these supported networks helps the community understand the present distribution of performance and converge on recommendations for government agencies that will benefit both science and monitoring. For example, datasets from monitoring networks with reduced Mc are likely to inform and enable earthquake forecasting research with the potential to benefit hazard reduction for the general population.

How to cite: Laporte, M., Parker, T., Hamilton, V., and McNamara, D.: Designing or Upgrading a Seismic Network To Meet Specific Performance Criteria Using Array Modeling, a Case Study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16691, https://doi.org/10.5194/egusphere-egu23-16691, 2023.

Understanding, modeling and predicting the future of the Earth System in response to global change is a challenge for the Earth system scientific community, but a necessity to address pressing societal needs related to the UN Sustainable Development Goals and risk monitoring and prediction. These “wicked” environmental problems require the building of integrated modeling tools . The latter will only provide reliable response if they integrate all existing multi-disciplinary data sources. Open science and data sharing using the FAIR (Findable, Accessible, Interoperable, Reusable) principles provide the framework for such data sharing. However, when trying to put it into practice, we face a large fragmentation of the landscape, with different communities having developed their own data management systems, standards and tools.

When starting to work on the Theia/OZCAR Information System (IS) that aims to Facilitate the discovery, to make FAIR, in-situ data of continental surfaces collected by French research organizations and their foreign partners, we performed a “Tour de France” to understand the critical zone science users’ needs when searching for data. The common criterion that emerged was the variables names. We believe that this need is general to all disciplines involved in Earth System sciences and is all the more important when data is searched by scientists of other disciplines that are not familiar with the vocabularies of the other communities. This abstract aim is to share our experience in building the tools aiming at harmonizing and sharing variables names using FAIR principles.

In the Theia/OZCAR critical zone research community, long term observatories that produce the data have heterogeneous data description practices and variable names. They may be different for the same variable (i.e.: "soil moisture", "soil water content", "humidité des sols", etc.). Moreover, it is not possible to infer automatically or semi-automatically similarities between these variables names. In order to identify these similarities and implement data discovery functionalities on these dimensions in the IS, we built the Theia/OZCAR variable thesaurus. To enable technical interoperability of the thesaurus, it is published on the web using the SKOS vocabulary description standard. Other thesauri used in environmental sciences in Europe and worldwide have been identified and the definition of associative relationships with these vocabularies ensures the semantic interoperability of the Theia/OZCAR thesaurus. However, it is quite common that the variable names used for the search dimensions remain general (e.g. "soil moisture") and are not specific enough for the end user to interpret exactly what has been measured (e.g. "soil moisture at 10 cm depth measured by TDR probe"). Therefore, to improve data reuse and interoperability, the thesaurus now follows a recommendation of the Research Data Alliance and implements the I-ADOPT framework to describe the variables more precisely. Each variable is composed and described by relationships with atomic concepts whose definition is specified. The use of these atomic concepts enhances interoperability with other catalogues or services and contributes to the reuse of the data by other communities that those who collected them.

How to cite: Braud, I., Coussot, C., Chaffard, V., and Galle, S.: Theia/OZCAR Thesaurus: a terminology service to facilitate the discovery, interoperability and reuse of data from continental surfaces and critical zone science in interdisciplinary research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1099, https://doi.org/10.5194/egusphere-egu23-1099, 2023.

EGU23-1294 | Posters on site | GI2.3

A data integration system for ocean climate change research in the Northwest Pacific 

Sung Dae Kim, Hyuk Min Park, Young Shin Kwon, and Hyeon Gyeong Han

A data integration and processing system was established to provide long-time data and real-time data to the researcher who are interested in long-term variation of ocean data in the Northwest Pacific area. All available ocean data of 6 variables (ocean temperature, salinity, dissolved oxygen, ocean CO2, nutrients) in the NWP area (0°N - 65°N, 95°E - 175°E) are collected from the Korean domestic organizations (KIOST, NFIS, KHOA, KOEM), the international data systems (WOD, GTSPP, SeaDataNet, etc.), and the international observation networks (Argo, GOSHIP, GLODAP, etc.). Total number of data collected is over 5 millions and observation dates are from 1938 to 2022. After referring to several QC manuals and related papers, QC procedures and test criteria for 6 data items were determined and documented. Several Matlab programs complying with QC procedures were developed and used to check quality of all collected data. We excluded duplicated data from the data set and saved them in 0.25° grid data files. Long-term average over 40 years and standard deviation of data at each standard depths and grid point were calculated. All quality controlled data, qc flag, average, standard deviation of each ocean variables are saved in format of netCDF and provided to ocean climate researchers and numerical modelers. We also have 2 plans using the collected data from 2023 to 2025. The one is production of long-term grid data set focused on the NWP area, the other is developing a data service system providing observation data and reanalysis data together.

Acknowledgement : This research was supported by Korea Institute of Marine Science & Technology Promotion(KIMST) funded by the Ministry of Oceans and Fisheries(KIMST-20220033)

How to cite: Kim, S. D., Park, H. M., Kwon, Y. S., and Han, H. G.: A data integration system for ocean climate change research in the Northwest Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1294, https://doi.org/10.5194/egusphere-egu23-1294, 2023.

EGU23-1599 | Posters on site | GI2.3

Overview of the services provided to marine data producers by ODATIS, the French ocean data center 

Sabine Schmidt, Erwann Quimbert, Marine Vernet, Joël Sudre, Caroline Mercier, Dominique Obaton, Jean-François Piollé, Frédéric Merceur, Gérald Dibarboure, and Gilbert Maudire

The consequences of global change on the ocean are multiple such as increase in temperature and sea level, stronger storms, deoxygenation, impacts on ecosystems. But the detection of changes and impacts is still difficult because of the diversity and variability of marine environments. While there has been a clear increase in the number of marine and coastal observations, whether by in situ, laboratory or remote sensing measurements, each data is both costly to acquire and unique. The number and variety of data acquisition techniques require efficient methods of improving data availability via interoperable portals, which facilitate data sharing according to FAIR principles for producers and users. ODATIS, the ocean cluster of Data Terra, the French research infrastructure for Earth data, is the entry point to access all the French Ocean observation data (Ocean Data Information and Services ; www.odatis-ocean.fr/en/). The first challenge of ODATIS is to get data producers to share data. To that purpose, ODATIS offers several services to help them define Data Management Plan (DPM), implement the FAIR principles, make data more visible and accessible by being referenced in the ODATIS catalog, and better tracked and cited through a Digital Object Identifier (DOI). ODATIS also offers a service for publishing open scientific data on the sea, through SEANOE (www.seanoe.org) that provides a DOI that can be cited in scientific articles in a reliable and sustainable way. In parallel to the informatic development of the ocean cluster, further communication and training are needed to inform the research community of these new tools. Through technical workshops, Odatis offers data providers practical experience and support in implementing data access, visualization and processing services. Finally, ODATIS relies on scientific consortia in order to promote and develop innovative processing methods and products for remote, airborne, or in situ observations of the ocean and its interfaces (atmosphere, coastline, seafloor) with the other clusters of the RI Data Terra.

How to cite: Schmidt, S., Quimbert, E., Vernet, M., Sudre, J., Mercier, C., Obaton, D., Piollé, J.-F., Merceur, F., Dibarboure, G., and Maudire, G.: Overview of the services provided to marine data producers by ODATIS, the French ocean data center, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1599, https://doi.org/10.5194/egusphere-egu23-1599, 2023.

EGU23-5626 | Orals | GI2.3

An integration of digital twin technology, GIS and VR for the service of environmental sustainability 

Chen Wang, David Miller, Alessandro Gimona, Maria Nijnik, and Yang Jiang

A digital twin is a digital representation of real-world physical product, system, or process. Digital twins potentially offer a much richer capability to model and analyze real-world systems and improve environment sustainability.

In this work, an integrated 3D GIS and VR model for scenarios modeling and interactive data visualisation has been developed and implemented through the Digital Twin technology at the Glensaugh research farm. Spatial Multi-criteria Analysis has been applied to decide where to plant new woodlands, recognizing a range of land-use objectives while acknowledging concerns about possible conflicts with other uses of the land. The virtual contents (e.g., forest spatial datasets, monitored climate data, analyzed carbon stocks and natural capital asset index) have been embedded in the virtual landscape model which help raise public awareness of changes in rural areas.

The Digital twin prototype for Glensaugh Climate-Positive Farming was used at the STFC workshop 2021, GISRUK 2022, 2022 Royal Highland Show which provides an innovative framework to integrate spatial data modelling, analytical capabilities and immersive visualization.

Audience feedback suggested that the virtual environment was very effective in providing a more realistic impression of the different land-use and woodland expansion scenarios and environmental characteristics. This suggests considerable added value from using digital twin technology to better deal with complexity of data analysis, scenarios simulation and enable rapid interpretation of solutions.

Findings show this method has a potential impact on future woodland planning and enables rapid interpretation of forest and climate data which increases the effectiveness of their use and contribution to wider sustainable environment.

How to cite: Wang, C., Miller, D., Gimona, A., Nijnik, M., and Jiang, Y.: An integration of digital twin technology, GIS and VR for the service of environmental sustainability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5626, https://doi.org/10.5194/egusphere-egu23-5626, 2023.

EGU23-5866 | ECS | Posters on site | GI2.3

Mapping and Analysis of Anthrax Cases in Humans and Animals 

Tamar Chichinadze, Zaza Gulashvili, Nana Bolashvili, Lile Malania, and Nikoloz Suknidze

Anthrax is a rare but serious disease caused by gram-positive, stem-shaped bacteria Bacillus anthracis, which are toxin-producing, encapsulated, facultative anaerobic organisms. Anthrax is found naturally in the soil and mainly harms livestock and wildlife. It can cause serious illness in both humans and animals. Anthrax, an often fatal disease of animals, is spread to humans through contact with infected animals or their products. People get infected with anthrax when spores get into the body.

The study aims to monitor the anthill localization map of anthrax on geographical maps and identify geographical variables that are significantly associated with environmental risk factors for anthrax recurrence in Georgia (Caucasus), as specific diseases affect the geographical environment, soil, climate. etc.

We carefully analyzed a set of 1664 cases of anthrax in humans and 621 cases of anthrax in animals, up to 1430 locations in anthrax foci (animal burial sites, slaughterhouses, BP roads, construction, etc.) observed in Georgia. Literature and the National Center for Disease Control for over 70 years. We analyzed more than 30 geographical variables such as climate, topography, soil (soil type, chemical composition, acidity), landscape, etc., and created several digital thematic maps, and foci of ant distribution and detection. The identified variable will help you to monitor anthrax development foci.

How to cite: Chichinadze, T., Gulashvili, Z., Bolashvili, N., Malania, L., and Suknidze, N.: Mapping and Analysis of Anthrax Cases in Humans and Animals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5866, https://doi.org/10.5194/egusphere-egu23-5866, 2023.

EGU23-6357 | Posters on site | GI2.3

PANAME: a portal laboratory for city's environmental data 

Vincent Douet, Sophie Bouffiès-Cloché, Joanne Dumont, Martial Haeffelin, Jean-Charles Dupoont, Simone Kotthaus, Valéry Masson, Aude Lemonsu, Valerie Gros, Christopher Cantrell, Vincent Michoud, and Sébastien Payan

The urban is at the heart of many disciplinary projects covering very broad scientific areas. Acquired data or simulations are often accessible (when they are) via targeted thematic portals. However, the need for transdisciplinarity has been essential for several years to answer specific scientific questions or societal demands. For this, the crossing of human sciences data, health, air quality, land use, emissions inventories, biodiversity, etc., would allow new innovative studies in connection with the city.

PANAME (PAris region urbaN Atmospheric observations and models for Multidisciplinary rEsearch) developed by AERIS was designed as the first brick of a data portal that can promote the discovery, access, cross-referencing and representation of urban data from various sectors with air quality and urban heat islands as a starting point. The portal and future developments will be discussed in this presentation.

How to cite: Douet, V., Bouffiès-Cloché, S., Dumont, J., Haeffelin, M., Dupoont, J.-C., Kotthaus, S., Masson, V., Lemonsu, A., Gros, V., Cantrell, C., Michoud, V., and Payan, S.: PANAME: a portal laboratory for city's environmental data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6357, https://doi.org/10.5194/egusphere-egu23-6357, 2023.

EGU23-6873 | Posters on site | GI2.3

From local to global: Community services in interdisciplinary research data management  

Hela Mehrtens, Janine Berndt, Klaus Getzlaff, Andreas Lehmann, and Sören Lorenz

GEOMAR research covers a unique range of physical, chemical, biological and geological ocean processes. The department Digital Research Services develops and provides advice and tools to support scientific data workflows, including metadata description of expeditions, model experiments, lab experiments, and samples. Our focus lies on standardized internal data exchange in large interdisciplinary scientific projects and citable data and software publications in discipline specific repositories to meet the FAIR principles. GEOMAR aims at providing their services not only internally but as a collaborative RDM platform for marine projects as a community service. How to achieve this on the operational level is currently worked on jointly with other research institutions in community projects, e.g. within the DAM (German Alliance of Marine Research), the DataHUB, an initiative of several research centres within the Helmholtz research area Earth and Environment, and within the national research infrastructure NFDI4Earth, a network of more than 60 partners.  

Our latest use cases are the inclusion of the seismic data and numerical model simulations into the community portals to increase their visibility and reusability. We present the success stories and pitfalls of bringing a locally well established system in larger communities and address the challenges we are facing. 

How to cite: Mehrtens, H., Berndt, J., Getzlaff, K., Lehmann, A., and Lorenz, S.: From local to global: Community services in interdisciplinary research data management , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6873, https://doi.org/10.5194/egusphere-egu23-6873, 2023.

EGU23-7015 | ECS | Orals | GI2.3

Evaluation of five reanalysis products over France: implications for agro-climatic studies 

Mariam Er-rondi, Magali Troin, Sylvain Coly, Emmanuel Buisson, Laurent Serlet, and Nourddine Azzaoui

Agriculture is extremely vulnerable to climate change. Increase in air temperature alongside the more frequent extreme climate events are the main climate change’s negative impacts influencing the yields, safety, and quality of crops. One approach to assess the impacts of climate change on agriculture is the use of agro-climatic indicators (AgcIs). Agcls characterize plant-climate interactions and are practical and understandable for both farmers and decision makers.

Climate and climate change impact studies on crop require long samples of reliable past and future datasets describing both spatial and temporal variability. The lack of observed historical data with an appropriate temporal resolution (i.e., 30 years of continuous daily data) and a sufficient local precision (i.e., 1km) is a major concern. To overcome that, the reanalysis products (RPs) are often used as a potential reference data of observed climate in impact studies. However, RPs have some limitations as they contain some biases and uncertainties. In addition, the RPs’ evaluation is often conducted on climate indicators which raises questions about their suitability for agro-climatic indicators.

This work aims to evaluate the ability of five of the most used RPs to reproduce observed AgcIs for three specific crops (i.e., apple, corn, and vine) over France. The five RPs selected for this study are the SCOPE Climate, FYRE Climate, ERA5, ERA5 Land and the gridded dataset RFHR. They are compared to the SYNOP meteorological data provided by Météo-France, considered as a reference dataset from 1996 to 2021.

Our findings show a higher agreement between the five RPs and SYNOP for the temperature-based Agcls than the precipitation-based Agcls. RPs tend to overestimate the precipitation-based Agcls. We also note that, for each RP, the discrepancies between the AgcIs and the reference SYNOP dataset do not depend on the geographical location or the crop. This study emphasizes the need to quantify uncertainty in climate data in climate variability and climate change impact studies on agriculture.

How to cite: Er-rondi, M., Troin, M., Coly, S., Buisson, E., Serlet, L., and Azzaoui, N.: Evaluation of five reanalysis products over France: implications for agro-climatic studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7015, https://doi.org/10.5194/egusphere-egu23-7015, 2023.

We present a method for publishing high performance compute (HPC) code and results in a scalable, portable and ready-to-use interactive environment in order to enable sharing, collaborating, peer-reviewing and teaching. We show how we utilize cloud native elements such as kubernetes, containerization, automation and webshells to achieve this and demonstrate such an OpenScienceLab for the MAGE (Multiscale Atmosphere Geospace Environment) model, being developed by the recently selected NASA DRIVE Center for Geospace Storms.
We argue that a key factor in the successful design of such an environment is its (cyber)-security, as  these labs require non-trivial compute resources open to a vast audience. Benefits as well as implied costs of different hosting options are discussed, comparing public cloud, hybrid, private cloud and even large desktops.
We encourage HPC centers to test our method using our fully open source blueprints. We hope to thus unburden the research staff and scientists to follow FAIR principles and support open source goals without needing a deep knowledge of cloud computing.

How to cite: Roedig, C. and Sorathia, K.: Cloud native OpenScienceLabs for HPC : Easing the road to FAIR collaboration and OpenSource, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7703, https://doi.org/10.5194/egusphere-egu23-7703, 2023.

EGU23-8585 | Orals | GI2.3

Programmatic Update for NASA’s Commercial Smallsat Data Acquisition (CSDA) Program 

Aaron Kaulfus, Alfreda Hall, Manil Maskey, Will McCarty, and Frederick Policelli

Established in 2017 as a pilot project, the NASA Commercial Smallsat Data Acquisition (CSDA) Program evaluates and acquires commercial datasets that compliment NASA Earth Science research and application goals. The success of the pilot and recognition of the value commercial data provide to the scientific community led to establishment of a sustained program within NASA’s Earth Science Division (ESD) with objectives of providing continuous on-ramp of new commercial vendors to evaluate the potential to advance NASA’s Earth science research and application activities, enable sustained use of the purchased data by the scientific community, ensure long-term preservation of purchased data for scientific reproducibility, and coordinate with other U.S. Government agencies and international partners on the evaluation and use of commercial data. This presentation will focus on data made available for scientific use through the CSDA Program, especially those datasets added since the conclusion of the original pilot project, describe the process for end users to access of CSDA managed datasets, and provide a status overview of ongoing and upcoming vendor evaluation activities will be given. Recent scientific research results from CSDA subject matter experts utilizing commercial data will also be provided.

How to cite: Kaulfus, A., Hall, A., Maskey, M., McCarty, W., and Policelli, F.: Programmatic Update for NASA’s Commercial Smallsat Data Acquisition (CSDA) Program, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8585, https://doi.org/10.5194/egusphere-egu23-8585, 2023.

EGU23-12144 | Orals | GI2.3

FAIR & Open Material Samples: The IGSN ID 

Rorie Edmunds

Material samples are a vital output of the scientific endeavour. They underpin research in the Earth, Space, and Environmental Sciences, and are a necessary component of ensuring the transparency and reproducibility of such research. While there has been a lot of discussion in recent years about the openness and FAIRness of data, code, methods, and so on, material samples have been much less under the spotlight.

The lack of focus on material samples is in part due to them being unique as a research output, in the sense that they are inherently physical and thus they are mostly transported and managed by human beings rather than machines; it is rather more straightforward to archive and share both information about an output—and the output itself—for something that is already a digital object. However, it is for this reason that materials samples must be made more FAIR and treated as first-class citizens of Open Science. To do this, one needs to connect the physical and digital worlds. IGSN IDs enable these connections to be made.

The IGSN ID is a globally unique and persistent identifier (PID) specifically for labelling material samples themselves (i.e., they are for neither images nor data about a sample). Functionally a Digital Object Identifier (DOI) registered under DataCite services, the IGSN ID can be applied to all types of material samples coming from any discipline. Not only can IGSN IDs be used to identify individual material samples that currently exist in a repository, museum, or otherwise, but they can also be registered

  • At the aggregate level for sample collections.
  • For the sites from which the samples are taken.
  • For ephemeral samples.

Importantly, in all cases, when registering an IGSN IDs, one must supply metadata in the DataCite Metadata Schema, as well as create landing pages that supply additional, disciplinary, user-focussed information about the collection, site, or (sub)sample. Hence, by registering a PID for a physical object, it is given a permanently resolvable URI to a findable and accessible digital footprint, and through the provision of rich metadata, enables its interoperability and reusability. Sharing of associated data is also possible within the metadata, and one may even include the potential for relocation of a sample itself for reuse.

This presentation will briefly introduce the IGSN ID and the partnership between DataCite and the IGSN e.V. to transfer the IGSN PID infrastructure under DataCite DOI services. It will mainly highlight practical use cases of IGSN IDs, including what is needed to include them in the sample workflow. It will also talk about efforts to better support IGSN IDs and sample metadata within the DataCite Metadata Schema.

How to cite: Edmunds, R.: FAIR & Open Material Samples: The IGSN ID, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12144, https://doi.org/10.5194/egusphere-egu23-12144, 2023.

EGU23-12173 | Orals | GI2.3

ESPRESSO: Earth Science Problems for the Evaluation of Strategies, Solvers and Optimizers 

Andrew Valentine, Jiawen He, Juerg Hauser, and Malcolm Sambridge

Many Earth systems cannot be observed directly, or in isolation. Instead, we must infer their properties and characteristics from their signature in one or more datasets, using a variety of techniques (including those based on optimization, statistical methods, or machine learning). Development of these techniques is an area of focus for many geoscience researchers, and methodological advances can be instrumental in enhancing our understanding of the Earth.         

In our experience, progress is substantially hindered by the absence of infrastructure facilitating communication between sub-disciplines. Researchers tend to focus on one area of the earth sciences — such as seismology, hydrology or oceanography — with only slow percolation of ideas and innovations from one area to another. Indeed, silos often exist even within these subfields. Testing new ideas on new problems is challenging as it requires the acquisition of domain knowledge, an often difficult and time-consuming endeavour with uncertain returns. Key questions that arise include: What is a relevant field data set, and how has it been processed? Which simulation package is most appropriate to predict the data? What would a 'good' model look like and what should it be able to resolve? What is the current best practice?

To address this, we introduce the ESPRESSO project — a collection of Earth Science Problems for the Evaluation of Strategies, Solvers and Optimisers. It aims to provide  access to a suite of ‘test problems’, spanning a wide range of inference and inversion scenarios. Each test problem defines appropriate dataset(s) and simulation routines, accessible within a standardised Python interface. This will allow researchers to rapidly test new techniques across a spectrum of problems, share domain-specific inference problems and ultimately identify areas where there may be potential for fruitful collaboration and development. ESPRESSO is envisaged as an open, community-sourced project, and we invite contributions from across the geosciences.

How to cite: Valentine, A., He, J., Hauser, J., and Sambridge, M.: ESPRESSO: Earth Science Problems for the Evaluation of Strategies, Solvers and Optimizers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12173, https://doi.org/10.5194/egusphere-egu23-12173, 2023.

EGU23-12381 | ECS | Posters on site | GI2.3 | Highlight

An Exploratory Study on the Methodology for the Analysis of Urban Environmental Characteristics in Seoul City based on S-Dot Sensor Data 

Daehwan Kim, Kwanchul Kim, Dasom Lee, Jae-Hoon Yang, Seong-min Kim, and Jeong-Min Park

This paper identifies the aspects of living environment elements (PM2.5, PM10, Noise) throughout Seoul and the urban planning characteristics that affect them by utilizing the big data of the S-Dot sensor in Seoul, which has recently become a hot topic. In other words, it proposes a big data-based research methodology and research direction to confirm the relationship between urban characteristics and environmental sectors that directly affect citizens.  The temporal range is from 2020 to 2022, which is the available range of time series data for S-Dot sensors, and the spatial range is throughout Seoul by 500m*500m GRID. First of all, as part of analyzing specific living environment patterns, simple trends through EDA are identified, and cluster analysis is conducted based on the trends. After that, in order to derive specific urban planning characteristics of each cluster, basic statistical analysis such as ANOA and OLS, and MNL analysis were conducted to confirm more specific characteristics. As a result of this study, cluster patterns of PM2.5, PM10, noise and urban planning characteristics that affect them are identified, and there are areas with relatively high or low long-term living environment values compared to other regions. The results of this study are believed to be a reference for urban planning management measures for vulnerable areas of living environment, and it is expected to be an exploratory study that can provide directions to studies related to data in various fields related to environmental data in the future.

How to cite: Kim, D., Kim, K., Lee, D., Yang, J.-H., Kim, S., and Park, J.-M.: An Exploratory Study on the Methodology for the Analysis of Urban Environmental Characteristics in Seoul City based on S-Dot Sensor Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12381, https://doi.org/10.5194/egusphere-egu23-12381, 2023.

EGU23-13420 | ECS | Orals | GI2.3

Development of interoperable web applications for paleoclimate research 

Alessandro Morichetta, Anne-Marie Lézine, Aline Govin, and Vincent Douet

Studying how the Earth’s climate changed in the past requires a joint interdisciplinary effort of scientists from different scientific domains. Paleoclimatic records are increasingly obtained on multiple archives (e.g. marine and terrestrial sediments, ice cores, speleothems, corals) and they document past changes in various climatic variables of the different components of the climatic system (e.g. ocean, atmosphere, vegetation, ice). 

Most paleoclimatic records still rely on independent observations with no standard format describing their data or metadata, resulting in a progressive increase of variables and taxonomies. Therefore, despite the achievements of the last decades (e.g. NOAA, NEOTOMA and PANGAEA databases), the lack of a common language strongly limits the systematic reusability of paleoclimate data, for example for the construction of paleoclimatic data syntheses or the evaluation of climate model simulations.

The international project “Abrupt Change in Climate and Ecosystems: Data and e-infrastructure” (ACCEDE, funded by the Belmont Forum) aims at creating an ecosystem for paleoclimatic data in order to investigate the tipping points of past climatic changes. In this context, the recently formalized Linked PaleoData (LiPD) format is the core for the standardization of paleoclimate data and metadata, and it is acting as communication protocol between the different databases that compose the e-infrastructure.

Here we show two web-based solutions that are part of this effort and that take advantage of the LiPD ecosystem. The African Pollen Database, and the IPSL Paleoclimate Database, both hosted and developed by Institut Pierre-Simon Laplace, France, have the objectives (1) to give open access, while respecting the FAIR principles, to a variety of paleoclimate datasets - from pollen fossils to various tracers measured on marine sediments, ice cores or tree rings -, and (2) to combine and compare, using visualization tools, carefully selected and well dated paleoclimatic records from different disciplines to address specific research questions. 

The two databases are the result of data recovery from pre-existing and obsolete archives that followed a process of data (and metadata) consolidation, enrichment and formatting, in order to respect the LiPD specification and ensure the interoperability between them and the already existing databases. We designed harmonised web interfaces and REST APIs to explore and export existing datasets with the help of filtering tools. Datasets are published with DOI under an open license, allowing free access to the completeness of information. A LiPD upload form is embedded to the websites, in order to encourage both users and data stewards to propose, edit, add new records, and to bring the community into the use of LiPD format. We are currently working on finalizing visualization tools to evaluate aggregate data for research and education purposes.

With this effort we are developing a framework in which heterogeneous paleoclimatic records are fully interoperable, allowing scientists from the whole community to take advantage of the completeness of the available data, and to reuse them for very different research applications.

How to cite: Morichetta, A., Lézine, A.-M., Govin, A., and Douet, V.: Development of interoperable web applications for paleoclimate research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13420, https://doi.org/10.5194/egusphere-egu23-13420, 2023.

EGU23-13455 | Posters on site | GI2.3

The Transnational access and training in the Geo-INQUIRE EU-project, an opportunity for researchers to develop leading-edge science at selected facilities and test-beds across Europe 

Gaetano Festa, Shane Murphy, Mariusz Majdanski, Iris Christadler, Fabrice Cotton, Angelo Strollo, Marc Urvois, Volker Röhling, Stefano Lorito, Andrey Babeyko, Daniele Bailo, Jan Michalek, Otto Lange, Javier Quinteros, Mateus Prestes, and Stefanie Weege

The Geo-INQUIRE (Geosphere INfrastructure for QUestions into Integrated REsearch) project, supported by the Horizon Europe Programme, is aimed at enhancing services to make data and high-level products accessible to the broad Geoscience scientific community. Geo-INQUIRE’s goal is to encourage curiosity-driven studies into understanding the geosphere dynamics at the interface between the solid Earth, the oceans and the atmosphere using long data streams, high-performance computing and cutting-edge facilities.

In the framework of Geo-INQUIRE, Transnational Access (TA, both virtual and on-site) will be provided at six test beds across Europe: the Bedretto Laboratory, Switzerland; the Ella-Link Geolab, Portugal; the Liguria-Nice-Monaco submarine infrastructure, Italy/France; the Irpinia Near-Fault Observatory, Italy; the Eastern Sicily facility, Italy; and the Corinth Rift Laboratory, Greece. These test beds are state-of-the-art research infrastructures, covering the Earth’s surface, subsurface, and marine environments over different spatial scales, from small-scale experiments in laboratories to kilometric submarine fibre cables. The TA will revolve around answering scientific key-questions on the comprehension of fundamental processes associated with geohazards and georesources such as: the preparatory phases of earthquakes, the role of the fluids within the Earth crust, the fluid-solid interaction at the seabed, and the impact of geothermal exploitation. TA will be also offered for software and workflows belonging to the EPOS-ERIC and the ChEESE Centre of Excellence for Exascale in Solid Earth, to develop awarded user’s projects. These are grounded on simulation of seismic waves and rupture dynamics in complex media, tsunamis, subaerial and submarine landslides. HPC-based Probabilistic Tsunami, Seismic and Volcanic Hazard workflows are offered to assess hazard at high-resolution with extensive uncertainty exploration. Support and collaboration will be offered to the awardees to facilitate the access and usage of HPC resources for tackling geoscience problems. Geo-INQUIRE will grant TA to researchers to develop their own lab or numerical experiments with the aim of advancing scientific knowledge of Earth processes while fostering cross-disciplinary research across Europe. To be granted, researchers submit a proposal to the yearly TA calls that will be issued three times during the project life. Calls will be advertised at the Geo-INQUIRE web page https://www.geo-inquire.eu/ and through the existing community channels.

To encourage the cross-disciplinary research, Geo-INQUIRE will also organize a series of training and workshops, focused on data, data products and software delivered by research infrastructures, and useful for researchers. In addition, two summer schools will be organized, dedicated to cross-disciplinary interactions of solid earth and marine science.

The proposals, for both transnational access and training, will be evaluated by a panel that reviews the technical and scientific feasibility of the project, ensuring equal opportunities and diversity in terms of gender, geographical distribution and career stage. The first call is expected to be issued by the end of Summer 2023. The data and products generated during the TAs will be made available to the scientific community via the project’s strict adherence to FAIR principles.

How to cite: Festa, G., Murphy, S., Majdanski, M., Christadler, I., Cotton, F., Strollo, A., Urvois, M., Röhling, V., Lorito, S., Babeyko, A., Bailo, D., Michalek, J., Lange, O., Quinteros, J., Prestes, M., and Weege, S.: The Transnational access and training in the Geo-INQUIRE EU-project, an opportunity for researchers to develop leading-edge science at selected facilities and test-beds across Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13455, https://doi.org/10.5194/egusphere-egu23-13455, 2023.

EGU23-14423 | Posters on site | GI2.3

EPOS-GNSS DATA GATEWAY: a portal to European GNSS Data and Metadata 

Mathilde Vergnolle and Jean-Luc Menut

EPOS-GNSS is the Thematic Core Service dedicated to GNSS data and products for the European Plate Observing System.
EPOS-GNSS provides a service to explore and download validated and quality controlled data and metadata. This service is based on a network of 10 data nodes connected to a centralized portal, called "EPOS-GNSS Data Gateway". The service aims to follow the FAIR principles and continues to evolve to better meet them. It currently provides more than 4 millions of daily files in the RINEX standardized format for 1670 European GNSS stations and their associated metadata.
In addition to the integration into the multi-disciplinary EPOS data portal, the service proposes a direct access to the data and metadata for users with a need for more complex or more specific queries and filtering. A GUI (web client) and a specialized command line client are provided to facilitate the exploration and download of the data and metadata.
The presentation introduces the EPOS GNSS-Data Gateway (https://gnssdata-epos.oca.eu), its clients, and its use.

How to cite: Vergnolle, M. and Menut, J.-L.: EPOS-GNSS DATA GATEWAY: a portal to European GNSS Data and Metadata, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14423, https://doi.org/10.5194/egusphere-egu23-14423, 2023.

EGU23-14605 | Posters on site | GI2.3

Towards an interoperable digital ecosystem in Earth System Science research 

Wolfgang zu Castell, Jan Bumberger, Peter Braesicke, Stephan Frickenhaus, Ulrike Kleeberg, Ralf Kunkel, and Sören Lorenz

Earth System Science (ESS) relies on the availability of data from varying resources and ranging over different disciplines. Hence, data sources are rich and diverse, including observatories, satellites, measuring campaigns, model simulations, case studies, laboratory experiments as well as citizen science etc. At the same time, practices of professional research data management (RDM) are differing significantly among various disciplines. There are many well-known challenges in enabling a free flow of data in the sense of the FAIR criteria. Such are data quality assurance, unique digital identifiers, access to and integration of data repositories, just to mention a few. 

The Helmholtz DataHub Earth&Environment is addressing digitalization in ESS by developing a federated data infrastructure. Existing RDM practices at seven centers of the Helmholtz Association working together in a joint research program within the Research Field Earth and Environment (RF E&E) are harmonized and integrated in a comprehensive way. The vision is to establish a digital research ecosystem fostering digitalization in geosciences and environmental sciences. Hereby, issues of common metadata standards, digital object identifiers for samples, instruments and datasets, defined role models for data sharing certainly play a central role. The various data generating infrastructures are registered digitally in order to collect metadata as early as possible and enrich them along the flow of the research cycle.

Joint RDM bridging several institutions relies on professional practices of distributed software development. Apart from operating cross-center software development teams, the solutions rely on concepts of modular software design. For example, a generic framework has been developed to allow for quick development of tools for domain specific data exploration in a distributed manner. Other tools incorporate automated quality control in data streams. Software is being developed following guiding principles of open and reusable research software development.

A suite of views is being provided, allowing for varying user perspectives, monitoring data flows from sensor to archive, or publishing data in quality assured repositories. Furthermore, high-level data products are being provided for stakeholders and knowledge transfer (for examples see https://datahub.erde-und-umwelt.de). Furthermore, tools for integrated data analysis, e.g. using AI approaches for marine litter detection can be implemented on top of the existing software stack.

Of course, this initiative does not exist in isolation. It is part of a long-term strategy being embedded within national (e.g. NFDI) and international (e.g. EOSC, RDA) initiatives.

How to cite: zu Castell, W., Bumberger, J., Braesicke, P., Frickenhaus, S., Kleeberg, U., Kunkel, R., and Lorenz, S.: Towards an interoperable digital ecosystem in Earth System Science research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14605, https://doi.org/10.5194/egusphere-egu23-14605, 2023.

EGU23-15072 | Posters virtual | GI2.3

Automated Extraction of Bioclimatic Time Series from PDF Tables 

Sabino Maggi, Silvana Fuina, and Saverio Vicario

Since the development of the original specifications in the '90s the PDF document format has become the de-facto standard for the distribution and archival of documents in electronic form because of its ability to preserve the original layout of the documents, independently of the hardware, operating system and application software used to visualize them.

Unfortunately the PDF format does not contain explicit structural and semantic information, making it very difficult to extract structured information from them, in particular data presented in tabular form. 
The automatic extraction of tabular data is a difficult and challenging task because tables can have extremely different formats and layouts, and involves several complex steps, from the proper recognition and conversion of printed text into machine-encoded characters, to the identification of logically coherent table constructs (headers, columns, rows, spanning elements), and to the breaking down of the data constructs into elemental objects.

Several tools have been developed to support the extraction process. In this work we survey the most interesting tools for the automatic detection and extraction of tabular data, analyzing their respective advantages and limitations. A particular emphasis is given on programmable open source tools because of their flexibility and long-term availability, together with the possibility to easily tweak them to meet the peculiar needs of the problem at hand.

As a practical application, we also present a workflow based on a set of R and AWK scripts that can automatically extract daily temperature and precipitation data from the official PDF documents made available each year by Regione Puglia, in Italy. The lessons learned from the development of this workflow and the possibility to generalize the approach to different kinds of PDF documents are also discussed.

How to cite: Maggi, S., Fuina, S., and Vicario, S.: Automated Extraction of Bioclimatic Time Series from PDF Tables, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15072, https://doi.org/10.5194/egusphere-egu23-15072, 2023.

EGU23-15293 | ECS | Posters virtual | GI2.3 | Highlight

Environmental parameters as a critical factor in understanding mosquito population 

Anastasia Angelou, Sandra Gewehr, Spiros Mourelatos, and Ioannis Kioutsioukis

The transmission of West Nile Virus is known to be affected by multiple factors related to the behavior and interactions between reservoir (birds), vector (Culex-mosquitos), and hosts (humans). Environmental parameters can play a critical role in understanding WNV epidemiology. The aim of this research was to determine the association of various climatic factors with the Culex mosquito abundance in Greece during the period 2011-2022. Climate data were acquired from ERA5 (European Centre for Medium-Range Weather Forecasts), while Culex abundance data were obtained through the mosquito surveillance network of ECODEVELOPMENT S.A, who hold the biggest mosquito surveillance network in Greece. The research was conducted at the municipality level. Culex abundance depends in a nonlinear fashion from temperature (Figure 1). The spread of the measurements indicates however there are other factors that affect the abundance of mosquitoes.

Figure 1 Scatter plot of air temperature VS Culex abundance in a municipality (Delta) with relatively sizeable mosquito population.

Correlation heatmaps were used as a tool to visualize the correlation of vector abundance and average monthly temperature up to 2 months before at several municipalities in the Region of Central Macedonia. The correlations decrease with increasing the lag in temperature (Figure 2). Moreover, there are some municipalities in which the correlation coefficient is considerably greater than others. Those correlations cannot be explained without considering the mosquito breeding sites found in these municipalities. In these municipalities there is a presence of important water resources, such as rice paddies, drainage canals, wetland systems or a combination of all the above. When surface waters warm and the outside temperature rises, the mosquito life cycle is completed more quickly, resulting in more generations being produced in a shorter period of time.

Figure 2 Correlation heatmap of the correlation coefficient between the mosquito abundance (municipality scale) and the average monthly temperature up to 2 months before.

Scatterplots and correlation heatmaps calculated with the Culex abundance and total precipitation, relative humidity or wind speed did not reveal similar patterns. Ongoing analysis focuses in more factors, environmental and not, which affect the abundance of mosquitoes that transmit WNV.

Acknowledgments 
This research has been co‐financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH – CREATE – INNOVATE (project code: Τ2ΕΔΚ-02070). 

How to cite: Angelou, A., Gewehr, S., Mourelatos, S., and Kioutsioukis, I.: Environmental parameters as a critical factor in understanding mosquito population, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15293, https://doi.org/10.5194/egusphere-egu23-15293, 2023.

EGU23-15863 | Orals | GI2.3

Building an Open Source Infrastructure for Next Generation End User Climate Services 

Benedikt Gräler, Katharina Demmich, Johannes Schnell, Merel Vogel, Stefano Bagli, and Paolo Mazzoli

Climate Services (CS) are crucial in empowering citizens, stakeholders and decision-makers in defining resilient pathways to adapt to climate change and extreme weather events. Despite advances in scientific data and knowledge (e.g. Copernicus, GEOSS), current CS fail to achieve their full value proposition to end users. Challenges include incorporation of social and behavioral factors, local needs, knowledge and the customs of end users. In I-CISK, we put forward a co-design based requirement analysis to develop a Spatial Data Infrastructure and Platform that empowers a next generation of end user CS, which follow a social and behaviorally informed approach to co-producing services that meet climate information needs of the Living Labs of the European I-CISK project. Core to the project are climate extremes such as droughts, floods and heatwaves. The use-cases touch upon agriculture, forestry, tourism, energy, health, and the humanitarian sectors. We will present the summarized stakeholders' requirements regarding the new climate-service platform and their technical implications for the open source spatial infrastructure. The design also includes assessing, managing and presenting uncertainties that are an inherent component of climate models.

How to cite: Gräler, B., Demmich, K., Schnell, J., Vogel, M., Bagli, S., and Mazzoli, P.: Building an Open Source Infrastructure for Next Generation End User Climate Services, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15863, https://doi.org/10.5194/egusphere-egu23-15863, 2023.

EGU23-16416 | Posters virtual | GI2.3

The set up of the “UNO” project relational database for Stromboli volcano 

Simone Tarquini, Francesco Martinelli, Marina Bisson, Emanuela De Beni, Claudia Spinetti, and Gabriele Tarabusi

Active volcanoes are complex, poorly predictable systems that can pose a threat to humans and their infrastructures. As such, it is important to improve as much as possible the understanding of their behavior. The Stromboli volcano, in Italy, is one of the most active volcanoes in the world, and its almost persistent activity is documented since centuries. The persistent background activity is sometimes interrupted by much more energetic, dangerous episodes. The Istituto Nazionale di Geofisica e Vulcanologia (Italy) set up the interdisciplinary “UNO” project, aimed to understand when the Stromboli volcano is about to switch from the ordinary to the extraordinary activity. The UNO project includes an outstanding variety of research activities, such as sampling in the field, the modeling of Stromboli topography from ALS technique and satellite data, the 3D numerical simulations of ballistic trajectories, or the set up of an ultrasonic microphones system. Key to the success of the project is the collection of integrated high spatial and temporal resolution data and their joint analyses in a shared relational database. We present here the simplified logical model of such database, focusing on the identification of entities and their relationships.

How to cite: Tarquini, S., Martinelli, F., Bisson, M., De Beni, E., Spinetti, C., and Tarabusi, G.: The set up of the “UNO” project relational database for Stromboli volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16416, https://doi.org/10.5194/egusphere-egu23-16416, 2023.

EGU23-16605 | ECS | Orals | GI2.3

NASA’s Science Discovery Engine: An Interdisciplinary, Open Science Data and Information Discovery Service 

Kaylin Bugbee, Ashish Acharya, Carson Davis, Emily Foshee, Rahul Ramachandran, Xiang Li, and Muthukumaran Ramasubramanian

NASA’s Science Plan includes a strategy to advance discovery by leveraging cross-disciplinary opportunities between scientific disciplines. In addition, NASA is committed to building an inclusive, open science community over the next decade and is championing the new Open-Source Science Initiative (OSSI) to foster that community. The OSSI supports many activities to promote open science including the development of an empowering cyberinfrastructure to accelerate the time to actionable science. One component of the OSSI cyberinfrastructure is the Science Discovery Engine (SDE). The goal of the SDE is to enable the discovery of data, software and documentation across the five SMD divisions including Astrophysics, Biological and Physical Sciences, Earth Science, Heliophysics and Planetary Science. The SDE increases accessibility to NASA’s open science data and information and promotes interdisciplinary scientific discovery. In this presentation, we describe our work to develop the Science Discovery Engine in Sinequa, a Cognitive Search capability. We also share lessons learned about data governance, curation and information access.

How to cite: Bugbee, K., Acharya, A., Davis, C., Foshee, E., Ramachandran, R., Li, X., and Ramasubramanian, M.: NASA’s Science Discovery Engine: An Interdisciplinary, Open Science Data and Information Discovery Service, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16605, https://doi.org/10.5194/egusphere-egu23-16605, 2023.

As deep learning (DL) is gathering remarkable attention for its capacity to achieve accurate predictions in various fields, enormous applications of DL in geosciences also emerged. Most studies focus on the high accuracy of DL models by model selections and hyperparameter tuning. However, the interpretability of DL models, which can be loosely defined as comprehending what a model did, is also important but comparatively less discussed. To this end, we select thin section photomicrographs of five types of sedimentary rocks, including quartz arenite, feldspathic arenite, lithic arenite, dolomite, and oolitic packstone. The distinguishing features of these rocks are their characteristic framework grains. For example, the oolitic packstone contains rounded or oval ooids. A regular classification model using ResNet-50 is trained by these photomicrographs, which is assumed as accurate because its accuracy reaches 0.97. However, this regular DL model makes their classifications based on the cracks, cements, or even scale bars in the photomicrographs, and these features are incapable of distinguishing sedimentary rocks in real works. To rectify the models’ focus, we propose an attention-based dual network incorporating the microphotographs' global (the whole photomicrographs) and local features (the distinguishing framework grains). The proposed model has not only high accuracy (0.99) but also presents interpretable feature extractions. Our study indicates that high accuracy should not be the only metric of DL models, interpretability and models incorporating geological information require more attention.

How to cite: Zheng, D., Cao, Z., Hou, L., Ma, C., and Hou, M.: High accuracy doesn’t prove that a deep learning model is accurate: a case study from automatic rock classification of thin section photomicrographs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-244, https://doi.org/10.5194/egusphere-egu23-244, 2023.

EGU23-1183 | ECS | Orals | ITS1.5/GI1.5 | Highlight

Detection of anomalous NO2 emitting ships using AutoML on TROPOMI satellite data 

Solomiia Kurchaba, Jasper van Vliet, Fons J. Verbeek, and Cor J. Veenman

Starting from 2021 International Maritime Organization (IMO) introduced more demanding NOx emission restrictions for ships operating in waters of the North and Baltic Seas. All methods currently used for ship compliance monitoring are financially and time-demanding. Thus, it is important to prioritize the inspection of ships that have a high chance of being non-compliant. 

 

TROPOMI/S5P instrument for the first time allows a distinction of NO2 plumes from individual ships. Here, we present a method for the selection of potentially non-compliant ships using automated machine learning (AutoML) on TROPOMI/S5P satellite data. The study is based on the analysis of 20 months of data in the Mediterranean Sea region. To each ship, we assign a Region of Interest (RoI), where we expect the ship plume to be located. We then train a regression model to predict the amount of NO2 that is expected to be produced by a ship with specific properties operating in the given atmospheric conditions. We use a genetic algorithm-based AutoML for the automatic selection and configuration of a machine-learning pipeline that maximizes prediction accuracy. The difference between the predicted and actual amount of produced NO2 is a measure of inspection worthiness. We rank the analyzed ships accordingly. 

 

We cross-check the obtained ranks using a previously developed method for supervised ship plume segmentation.  We quantify the amount of NO2 produced by a given ship by summing up concentrations within the pixels identified as a “plume”. We rank the ships based on the difference between the obtained concentrations and the ship emission proxy.

 

Ships that are also ranked as highly deviating by the segmentation method need further attention. For example, by checking their data for other explanations. If no other explanations are found, these ships are advised to be the candidates for fuel inspection.

How to cite: Kurchaba, S., van Vliet, J., Verbeek, F. J., and Veenman, C. J.: Detection of anomalous NO2 emitting ships using AutoML on TROPOMI satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1183, https://doi.org/10.5194/egusphere-egu23-1183, 2023.

Compaction of agricultural soil negatively affects its hydraulic proprieties, leading to water erosion and other negative effects on the quality of the environment. This study focused on the effect of compaction on soil hydrodynamic properties under unsaturated and saturated conditions using the Hydraulic Property Analyzer (HYPROP) system. We studied the impact of five levels of compaction among loam sand soils collected in a potato crop field in northern Québec, Canada. Soil samples were collected, and the soil bulk densities of the artificially compacted samples were developed by increasing the bulk density by 0% (C0), 30% (C30), 40% (C40), 50% (C50), and 70% (C70). First, the saturated hydraulic conductivity of each column was measured using the constant-head method. Soil water retention curve (SWRC) dry-end data and unsaturated hydraulic conductivities were obtained via the implementation and evaluation of the HYPROP evaporation measurement system and WP4-T Dew Point PotentioMeter equipment (METER group, Munich, Germany). Second, the soil microporosity was imaged and quantified using the micro-CT-measured pore-size distribution to visualize and quantify soil pore structures. The imaged soil microporosity was related to the saturated hydraulic conductivity, air permeability, porosity and tortuosity measured of the same samples.  Our results supported the application of the Peters–Durner–Iden (PDI) variant of the bimodal unconstrained van Genuchten model (VGm-b-PDI) for complete SWRC estimation based on the root mean square error (RMSE). The unsaturated hydraulic conductivity matched the PDI variant of the unconstrained van-Genuchten model (VGm-PDI) well. Finally, the preliminary results indicated that soil compaction could strongly influence the hydraulic properties of soil in different ways. The saturated conductivity decreased with increasing soil compaction, and the unsaturated hydraulic conductivity changed very rapidly with the ratio of water to soil. Overall, the HYPROP methodology performed extremely well in terms of the hydraulic behavior of compacted soils.

How to cite: Mbarki, Y. and Gumiere, S. J.: Study of the effect of compaction on the hydrodynamic properties of a loamy sand soil for precision agriculture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1583, https://doi.org/10.5194/egusphere-egu23-1583, 2023.

EGU23-1902 | Posters on site | ITS1.5/GI1.5

TACTICIAN: AI-based applications knowledge extraction from ESA’s mission scientific publications 

Omiros Giannakis, Iason Demiros, Konstantinos Koutroumbas, Athanasios Rontogiannis, Vassilis Antonopoulos, Guido De Marchi, Christophe Arviset, George Balasis, Athanasios Daglis, George Vasalos, Zoe Boutsi, Jan Tauber, Marcos Lopez-Caniego, Mark Kidger, Arnaud Masson, and Philippe Escoubet

Scientific publications in space science contain valuable and extensive information regarding the links and relationships between the data interpreted by the authors and the associated observational elements (e.g., instruments or experiments names, observing times, etc.). In this reality of scientific information overload, researchers are often overwhelmed by an enormous and continuously growing number of articles to access in their daily activities. The exploration of recent advances concerning specific topics, methods and techniques, the review and evaluation of research proposals and in general any action that requires a cautious and comprehensive assessment of scientific literature has turned into an extremely complex and time-consuming task.

The availability of Natural Language Processing (NLP) tools able to extract information from scientific unstructured textual contents and to turn it into extremely organized and interconnected knowledge, is fundamental in the framework of the use of scientific information. Exploitation of the knowledge that exists in the scientific publications, necessitates state-of-the-art NLP. The semantic interpretation of the scientific texts can support the development of a varied set of applications such as information retrieval from the texts, linking to existing knowledge repositories, topic classification, semi-automatic assessment of publications and research proposals, tracking of scientific and technological advances, scientific intelligence-assisted reporting, review writing, and question answering.

The main objectives of TACTICIAN are to introduce Artificial Intelligence (AI) techniques to the textual analysis of the publications of all ESA Space Science missions, to monitor and evaluate the scientific productivity of the science missions, and to integrate the scientific publications’ metadata into the ESA Space Science Archive. Through TACTICIAN, we extract lexical, syntactic, and semantic information from the scientific publications by applying NLP and Machine Learning (ML) algorithms and techniques. Utilizing the wealth of publications, we have created valuable scientific language resources, such as labeled datasets and word embeddings, which were used to train Deep Learning models that assist us in most of the language understanding tasks. In the context of TACTICIAN, we have devised methodologies and developed algorithms that can assign scientific publications to the Mars Express, Herschel, and Cluster ESA science missions and identify selected named entities and observations in these scientific publications. We also introduced a new unsupervised ML technique, based on Nonnegative Matrix Factorization (NMF), for classifying the Planck mission scientific publications to categories according to the use of the Planck data products.

These methodologies can be applied to any other mission. The combination of NLP and ML constitutes a general basis, which has proved that it can assist in establishing links between the missions’ observations and the scientific publications and to classify them in categories, with high accuracy.

This work has received funding from the European Space Agency under the "ArTificiAl intelligenCe To lInk publiCations wIth observAtioNs (TACTICIAN)" activity under ESA Contract No 4000128429/19/ES/JD.

How to cite: Giannakis, O., Demiros, I., Koutroumbas, K., Rontogiannis, A., Antonopoulos, V., De Marchi, G., Arviset, C., Balasis, G., Daglis, A., Vasalos, G., Boutsi, Z., Tauber, J., Lopez-Caniego, M., Kidger, M., Masson, A., and Escoubet, P.: TACTICIAN: AI-based applications knowledge extraction from ESA’s mission scientific publications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1902, https://doi.org/10.5194/egusphere-egu23-1902, 2023.

EGU23-2388 | ECS | Orals | ITS1.5/GI1.5

Deep learning based identification of carbonate rock components in core images 

Harriet Dawson and Cédric John

Identification of constituent grains in carbonate rocks is primarily a qualitative skill requiring specialist experience. A carbonate sedimentologist must be able to distinguish between various grains of different ages, preserved in differing alteration stages, and cut in random orientations across core sections. Recent studies have demonstrated the effectiveness of machine learning in classifying lithofacies from thin section, core and seismic images, with faster analysis times and reduction of natural biases.  In this study, we explore the application and limitations of convolutional neural network (CNN) based object detection frameworks to identify and quantify multiple types of carbonate grains within close-up core images. Nearly 400 images of carbonate cores we compiled of high-resolution core images from three ODP and IODP expeditions. Over 9,000 individual carbonate components of 11 different classes were manually labelled from this dataset. Using transfer learning, we evaluate one-stage (YOLO v3) and two-stage (Faster R-CNN) detectors under different feature extractors (Darknet and Inception-ResNet-v2). Despite the current popularity of one-stage detectors, our results show Faster R-CNN with Inception-ResNet-v2 backbone provides the most robust performance, achieving nearly 0.8 mean average precision (mAP). Furthermore, we extend the approach by deploying the trained model to ODP Leg 194 Sites 1196 and 1190, developing a performance comparison with human interpretation. 

How to cite: Dawson, H. and John, C.: Deep learning based identification of carbonate rock components in core images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2388, https://doi.org/10.5194/egusphere-egu23-2388, 2023.

EGU23-3997 | ECS | Orals | ITS1.5/GI1.5

Artificial Intelligence Models for Detecting Spatiotemporal Crop Water Stress in schedule Irrigation: A review 

Elham Koohi, Silvio Jose Gumiere, and Hossein Bonakdari

Water used in agricultural crops can be managed by irrigation scheduling based on plant water stress thresholds. Automated irrigation scheduling limits crop physiological damage and yield reduction. Knowledge of crop water stress monitoring approaches can be effective in optimizing the use of agricultural water. Understanding the physiological mechanisms of crop responding and adapting to water deficit ensures sustainable agricultural management and food supply. This aim could be achieved by analyzing stomatal conductance, growth rate, leaf water potential, and stem water potential. Calculating thresholds of soil matric potential, and available water content improves the precision of irrigation management by preventing water limitations between irrigations. Crop monitoring and irrigation management make informed decisions using geospatial technologies, the internet of things, big data analysis, and artificial intelligence. Remote sensing (RS) could be applied whenever in situ data are not available. High-resolution crop mapping extracts information through index-based methods fed by the multitemporal and multi-sensor data used in detection and classification. Precision Agriculture (PA) means applying farm inputs at the right amount, at the right time, and in the right place. RS in PA captures images in different spatial, and spectral resolutions through in-field, satellites, aerial, and handheld or tractor-mounted such as unmanned aerial vehicles (UAVs) sensors. RS sensors receive the electromagnetic signals of plant responses in different spectral domains. Optical satellite data, including narrow-band multispectral remote sensing techniques and thermal imagery, is used for water stress detection. To process and analysis RS data, cloud storage and computing platforms simplify the complex mathematical of incorporating various datasets for irrigation scheduling. Machine learning (ML) algorithms construct models for the regression and classification of multivariate and non-linear crop mapping. The web-based software gathered from all different datasets makes a reliable product to reinforce farmers’ ability to make appropriate decisions in irrigating agricultural crops.

Keywords: Agricultural crops; Crop water stress detection; Irrigation scheduling; Precision agriculture; Remote Sensing.

How to cite: Koohi, E., Gumiere, S. J., and Bonakdari, H.: Artificial Intelligence Models for Detecting Spatiotemporal Crop Water Stress in schedule Irrigation: A review, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3997, https://doi.org/10.5194/egusphere-egu23-3997, 2023.

EGU23-6696 | ECS | Orals | ITS1.5/GI1.5 | Highlight

Satellite-based continental-scale inventory of European wetland types at 10m spatial resolution 

Gyula Mate Kovács, Stefan Oehmcke, Stéphanie Horion, Dimitri Gominski, Xiaoye Tong, and Rasmus Fensholt

Wetlands provide invaluable services for ecosystems and society and are a crucial instrument in our fight against climate change. Although Earth Observation satellites offer cost-effective and accurate information about wetland status at the continental scale; to date, there is no universally accepted, standardized, and regularly updated inventory of European wetlands <100m resolution. Moreover, previous satellite-based global land cover products seldom account for wetland diversity, which often impairs their mapping performances. Here, we mapped major wetland types (i.e., peatland, marshland, and coastal wetlands) across Europe for 2018, based on high resolution (10m) optical and radar time series satellite data as well as field-collected land cover information (LUCAS) using an ensemble model combining traditional machine learning and deep learning approaches. Our results show with high accuracy (>85%) that a substantial extent of European peatlands was previously classified as grassland and other land cover types. In addition, our map highlights cultivated areas (e.g., river floodplains) that can be potentially rewetted. Such accurate and consistent mapping of different wetland types at a continental scale offers a baseline for future wetland monitoring and trend assessment, supports the detailed reporting of European carbon budgets, and lays down the foundation towards a global wetland inventory.

How to cite: Kovács, G. M., Oehmcke, S., Horion, S., Gominski, D., Tong, X., and Fensholt, R.: Satellite-based continental-scale inventory of European wetland types at 10m spatial resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6696, https://doi.org/10.5194/egusphere-egu23-6696, 2023.

EGU23-8409 | ECS | Orals | ITS1.5/GI1.5

Evaluation of lagoon eutrophication potential under climate change conditions: A novel water quality machine learning and biogeochemical-based framework. 

Federica Zennaro, Elisa Furlan, Donata Melaku Canu, Leslie Aveytua Alcazar, Ginevra Rosati, Sinem Aslan, Cosimo Solidoro, and Andrea Critto

Lagoons are highly valued coastal environments providing unique ecosystem services. However, they are fragile and vulnerable to natural processes and anthropogenic activities. Concurrently, climate change pressures, are likely to lead to severe ecological impacts on lagoon ecosystems. Among these, direct effects are mainly through changes in temperature and associated physico-chemical alterations, whereas indirect ones, mediated through processes such as extreme weather events in the catchment, include the alteration of nutrient loading patterns among others that can, in turn, modify the trophic states leading to depletion or to eutrophication. This phenomenon can lead, under certain circumstances, to harmful algal blooms events, anoxia, and mortality of aquatic flora and fauna, or to the reduction of primary production, with cascading effects on the whole trophic web with dramatic consequences for aquaculture, fishery, and recreational activities. The complexity of eutrophication processes, characterized by compounding and interconnected pressures, highlights the importance of adequate sophisticated methods to estimate future ecological impacts on fragile lagoon environments. In this context, a novel framework combining Machine Learning (ML) and biogeochemical models is proposed, leveraging the potential offered by both approaches to unravel and modelling environmental systems featured by compounding pressures. Multi-Layer Perceptron (MLP) and Random Forest (RF) models are used (trained, validated, and tested) within the Venice Lagoon case study to assimilate historical heterogenous WQ data (i.e., water temperature, salinity, and dissolved oxygen) and spatio-temporal information (i.e., monitoring station location and month), and to predict changes in chlorophyll-a (Chl-a) conditions. Then, projections from the biogeochemical model SHYFEM-BFM for 2049, and 2099 timeframes under RCP 8.5 are integrated to evaluate Chl-a variations under future bio-geochemical conditions forced by climate change projections. Annual and seasonal Chl-a predictions were performed out by classes based on two classification modes established on the descriptive statistics computed on baseline data: i) binary classification of Chl-a values under and over the median value, ii) multi-class classification defined by Chl-a quartiles. Results from the case study showed as the RF successfully classifies Chl-a under the baseline scenario with an overall model accuracy of about 80% for the median classification mode, and 61% for the quartile classification mode. Overall, a decreasing trend for the lowest Chl-a values (below the first quartile, i.e. 0.85 µg/l) can be observed, with an opposite rising fashion for the highest Chl-a values (above the fourth quartile, i.e. 2.78 µg/l). On the seasonal level, summer remains the season with the highest Chl-a values in all scenarios, although in 2099 a strong increase in Chl-a is also expected during the spring one. The proposed novel framework represents a valuable approach to strengthen both eutrophication modelling and scenarios analysis, by placing artificial intelligence-based models alongside biogeochemical models.

How to cite: Zennaro, F., Furlan, E., Melaku Canu, D., Aveytua Alcazar, L., Rosati, G., Aslan, S., Solidoro, C., and Critto, A.: Evaluation of lagoon eutrophication potential under climate change conditions: A novel water quality machine learning and biogeochemical-based framework., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8409, https://doi.org/10.5194/egusphere-egu23-8409, 2023.

EGU23-8702 | ECS | Orals | ITS1.5/GI1.5 | Highlight

Evaluating the risk of cumulative impacts in the Mediterranean Sea using a Random Forest model 

Angelica Bianconi, Elisa Furlan, Christian Simeoni, Vuong Pham, Sebastiano Vascon, Andrea Critto, and Antonio Marcomini

Marine coastal ecosystems (MCEs) are of vital importance for human health and well-being. However, their ecological condition is increasingly threatened by multiple risks induced by the complex interplay between endogenic (e.g. coastal development, shipping traffic) and exogenic (e.g. changes in sea surface temperature, waves, sea level, etc.) pressures. Assessing cumulative impacts resulting from this dynamic interplay is a major challenge to achieve Sustainable Development Goals and biodiversity targets, as well as to drive ecosystem-based management in marine coastal areas. To this aim, a Machine Learning model (i.e. Random Forest - RF), integrating heterogenous data on multiple pressures and ecosystems’ health and biodiversity, was developed to support the evaluation of risk scenarios affecting seagrasses condition and their services capacity within the Mediterranean Sea. The RF model was trained, validated and tested by exploiting data collected from different open-source data platforms (e.g. Copernicus Services) for the baseline 2017. Moreover, based on the designed RF model, future scenario analysis was performed by integrating projections from climate numerical models for sea surface temperature and salinity under the 2050 and 2100 timeframes. Particularly, under the baseline scenario, the model performance achieved an overall accuracy of about 82%. Overall, the results of the analysis showed that the ecological condition and services capacity of seagrass meadows (i.e. spatial distribution, Shannon index, carbon sequestration) are mainly threatened by human-related pressures linked to coastal development (e.g. distance from main urban centres), as well as to changes in nutrient concentration and sea surface temperature. This result also emerged from the scenario analysis, highlighting a decrease in seagrass coverage and related services capacity, in both 2050 and 2100 timeframes. The developed model provides useful predictive insight on possible future ecosystem conditions in response to multiple pressures, supporting marine managers and planners towards more effective ecosystem-based adaptation and management measures in MCEs.

How to cite: Bianconi, A., Furlan, E., Simeoni, C., Pham, V., Vascon, S., Critto, A., and Marcomini, A.: Evaluating the risk of cumulative impacts in the Mediterranean Sea using a Random Forest model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8702, https://doi.org/10.5194/egusphere-egu23-8702, 2023.

EGU23-10681 | Orals | ITS1.5/GI1.5

EarthQA: A Question Answering Engine for Earth Observation Data Archives 

Dharmen Punjani, Eleni Tsalapati, and Manolis Koubarakis

The standard way for earth observation experts or users to retrieve images from image archives (e.g., ESA's Copernicus Open Access Hub) is to use a graphical user interface, where they can select the geographical area of the image they are interested in and additionally they can specify some other metadata, such as sensing period, satellite platform and cloud cover.

In this work, we are developing the question-answering engine EarthQA that takes as input a question expressed in natural language (English) that asks for satellite images satisfying certain criteria and returns links to such datasets, which can be then downloaded from the CREODIAS cloud platform. To answer user questions, EarthQA queries two interlinked knowledge graphs: a knowledge graph encoding metadata of satellite images from the CREODIAS cloud platform (the SPARQL endpoint of CREODIAS) and the well-known knowledge graph DBpedia. Hence, the questions can refer to image metadata (e.g., satellite platform, sensing period, cloud cover), but also to more generic entities appearing in DBpedia knowledge graph (e.g., lake, Greece). In this way, the users can ask questions like “Find all Sentinel-1 GRD images taken during October 2021 that show large lakes in Greece having an area greater than 100 square kilometers”.

EarthQA follows a template-based approach to translate natural language questions into formal queries (SPARQL). Initially, it decomposes the user question by generating its dependency parse tree and then automatically disambiguates the components appearing in the question to elements of the two knowledge graphs.  In particular, it automatically identifies the spatial or temporal entities (e.g., “Greece”, “October 2021”), concepts (e.g., “lake”), spatial or temporal relations (e.g., “in”, “during”), properties (e.g., “area”) and product types (e.g., “Sentinel-1 GRD”) and other metadata (e.g., “cloud cover below 10%”) mentioned in the question and maps them to the respective elements appearing in the two knowledge graphs (dbr:Greece, dbo:Lake, dbp:area, etc). After this, the SPARQL query is automatically generated.

How to cite: Punjani, D., Tsalapati, E., and Koubarakis, M.: EarthQA: A Question Answering Engine for Earth Observation Data Archives, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10681, https://doi.org/10.5194/egusphere-egu23-10681, 2023.

EGU23-11527 | ECS | Posters on site | ITS1.5/GI1.5

Global Layer——An integrated, fully online, cloud based platform 

Xingchen Yang, Yang Song, Zhenhan Wu, and Chaowei Wu

In the current stage of scientific research, it is necessary to break the barriers between traditional disciplines and promote the cross integration of various related disciplines. As one of the important carriers of research achievements of various disciplines, maps can be superimposed and integrated to more intuitively display the results of multidisciplinary integration, promote the integration of disciplines and discover new scientific problems. Traditional geological mapping is often based on different scales for single scale mapping, aiming at the mapping mode of paper printing results. It is difficult to read maps between different scales at the same time. To solve this problem,an integrated platform named Global Layer is being built under the support of Deep-time Digital Earth (DDE). Global Layer is embedded with several core databases such as Geological Map of the World at a scale 1/5M, Global Geothermal Database etc. These databases presented in form of electronic map which enables the results of different scales to be displayed and browsed through one-stop hierarchical promotion. In addition, Users can also upload data in four ways: local file, database connection, cloud file and arcgis data service, and data or maping results can be shared to Facebook, Twitter and other platforms in the form of links, widgets, etc. Construction of Global Layer could provide experience and foundation for integrating global databases related to geological map and constructing data platforms.

How to cite: Yang, X., Song, Y., Wu, Z., and Wu, C.: Global Layer——An integrated, fully online, cloud based platform, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11527, https://doi.org/10.5194/egusphere-egu23-11527, 2023.

EGU23-12373 | ECS | Posters on site | ITS1.5/GI1.5

Mapping streams and ditches using Aerial Laser Scanning 

Mariana Dos Santos Toledo Busarello, Anneli Ågren, and William Lidberg

Streams and ditches are seldom identified on current maps due to their small dimensions and sometimes intermittent nature. Estimates point out that only 9% of all ditches are currently mapped, and the underestimation of natural streams is a global issue. Ditches have been dug in European boreal forests and some parts of North America to drain wetlands and increase forest production, consequently boosting the availability of cultivable land and a national-scale landscape modification. Target 6.6 of the Agenda 2030 highlights the importance of protecting and restoring water-related ecosystems. Wetlands are a substantial part of this, having a high carbon storage capability, the property of mitigating floods, and purifying water. All things accounted for, the withdrawal of anthropogenic environment alterations can be on the horizon, even more because ditches are also strong emitters of methane and other greenhouse gases due to their anoxic water and sediment accumulation. However, streams and ditches that are missing from maps and databases are difficult to manage.

The main focus of this study was to develop a method to map channels combining deep learning and national Aerial Laser Scans (ALS). The performance of different topographical indices derived from the ALS data was evaluated, and two different Digital Elevation Model (DEM) resolutions were compared. Ditch channels and natural streams were manually digitized from ten regions across Sweden, summing up to 1923km of ditch channels and 248km of natural streams. The topographical indices used were: high-passing median filter, slope, sky-view factor and hillshade (with azimuths of 0°, 45°, 90° and 135°); while 0.5m and 1m were the DEM resolutions analysed. A U-net model was trained to segment images between ditches and stream channels: all pixels from each image were labelled in a way that those with the same class display similar attributes.

Results showed that ditches can be successfully mapped with this method and it can generally be applied anywhere since only local terrain indices are required. Additionally, when the natural streams are present in the dataset the model underperformed in predicting the location of ditches, while a higher resolution had the opposite effect. Streams were more challenging to map, and the model only indicated the channels, not whether or not they contained water. Further research will be required to combine hydrological modelling and deep learning.

How to cite: Dos Santos Toledo Busarello, M., Ågren, A., and Lidberg, W.: Mapping streams and ditches using Aerial Laser Scanning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12373, https://doi.org/10.5194/egusphere-egu23-12373, 2023.

EGU23-13099 | ECS | Posters virtual | ITS1.5/GI1.5

Mapping Swedish Soils with High-resolution DEM-derived Indices and Machine Learning 

Yiqi Lin, William Lidberg, Cecilia Karlsson, and Anneli Ågren

There is a soaring demand for up-to-date and spatially-explicit soil information to address various environmental challenges. One of the most basic pieces of information, essential for research and decision-making in multiple disciplines is soil classification. Conventional soil maps are often low in spatial resolution and lack the complexity to be practical for hands-on use. Digital Soil Mapping (DSM) has emerged as an efficient alternative for its reproducibility, updatablity, accuracy, and cost-effectiveness, as well as the ability to quantify uncertainties.

Despite DSM’s growing popularity and increasingly wider areas of application, soil information is still rare in forested areas and remote regions, and the integration with high-resolution data on a country scale remains limited. In Sweden, quaternary deposit maps created by the Geological Survey of Sweden (SGU) have been the main reference input for soil-related research and operation, though most parts of the country still warrant higher quality representation. This study utilizes machine learning to produce a high-resolution surficial deposits map with nationwide coverage, capable of supporting research and decision-making. More specifically, it: i) compares the performance of two tree-based ensemble machine learning models, Extreme Gradient Boosting and Random Forest, in predictive mapping of soils across the entire country of Sweden; ii) determines the best model for spatial prediction of soil classes and estimates the associated uncertainty of the inferred map; iii) discusses the advantages and limitations of this approach, and iv) outputs a map product of soil classes at 2-m resolution. Similar attempts around the globe have shown promising results, though at coarser resolutions and/or of smaller geographical extent. The main assumptions behind this study are: i) terrain indices derived from digital elevation model (DEM) are useful predictors of soil type, though different classification algorithms differ in their effectiveness; ii) machine learning can capture major soil classes that cover most of Sweden, but expert geological and pedological knowledge is required when identifying rare soil types.

To achieve this, approximately 850,000 labeled soil points extracted from the most accurate SGU maps will be combined with a stack of 12 LiDAR DEM-derived topographic and hydrological indices and 4 environmental datasets. Uncertainty estimates of the overall model and for each soil class will be presented. An independent dataset obtained from the Swedish National Forest Soil Inventory will be used to assess the accuracy of the machine learning model. The presentation will cover the method, data handling, and some promising preliminary results.

How to cite: Lin, Y., Lidberg, W., Karlsson, C., and Ågren, A.: Mapping Swedish Soils with High-resolution DEM-derived Indices and Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13099, https://doi.org/10.5194/egusphere-egu23-13099, 2023.

As human activities continue to expand and evolve, their impact on the planet is becoming more evident. These past years Murmuration has been studying one of the most recent and destructive trends that has taken off: mass tourism. In Malta, tourism has been on the rise since before the Covid-19 pandemic. Now that travel restrictions are beginning to lift, it's likely that this trend will go back to increasing in the coming years. While Malta’s economy is mostly based on tourism, it's essential that this activity does not alter the areas in which it takes place. To address these issues and ensure sustainable development, governments and organizations have developed a set of guidelines called Sustainable Development Goals (SDG). SDGs are a set of 17 goals adopted by the United Nations in 2015 to provide a framework to help countries pursue sustainable economic, social and environmental development. They include objectives for mitigating climate change, preventing water pollution and degradation of biodiversity, as well as providing economic benefits to local communities.

In order to help territories like the islands of Malta to cope with these environmental issues, Murmuration carries out studies on various ecological, human and economic indicators. Using the Sentinel satellites of the European Copernicus program for earth imagery data makes possible the collection of geolocated, hourly values on air quality indicators such as NO2, CO and other pollutants but also water quality and vegetation through the analysis of the vegetation health. Other data sources give access to land cover values at meter resolution, tourism infrastructures locations and many more human activity variables. This information is processed into understandable indicators, aggregated indexes which take international standards and SDGs in their design and usage. An example of these standards are the WHO air quality guidelines providing thresholds quantifying the impact on health of the air pollution in the area of interest. The last step is to gather all the data, maps and correlations computed and design understandable visualizations to make it usable by territory management instances, enabling efficient decision making and risk management. The goal here is to achieve a link between satellite imagery, internationally agreed political commitment  and ground level decision-making.

This meaningful aggregation comes in the shape of operational dashboards. A dashboard is an up-to-date, interactive, evolving online tool hosting temporal and geographical linked visualizations on various indicators. This kind of tool allows for a better understanding of the dynamic of a territory in terms of environmental state, human impact and ecological potential.

How to cite: Plantec, M. and Castel, F.: From satellite data and Sustainable Development Goals to interactive tools and better territorial decision making, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14519, https://doi.org/10.5194/egusphere-egu23-14519, 2023.

EGU23-15656 | Posters virtual | ITS1.5/GI1.5

Karst integration into groundwater recharge simulation in WaterGAP 

Wenhua Wan and Petra Döll

Karst aquifers cover a significant portion of the global water supply. However, a proper representation of groundwater recharge in karst areas is completely absent in the state-of-art global hydrological models. This study, based on the new version of the global hydrological model WaterGAP, (1) presented the first modeling of diffuse groundwater recharge (GWR) in all karst regions using the global map of karstifiable rocks; and (2) adjusted the current GWR algorithm with the up-to-date databases of slope and soil. A large number of ground-based recharge estimates on 818 half degree cells including 75 in karst areas were compared to model results. GWR in karst landscapes assuming equal to the runoff from soil leads to unbiased estimation. The majority of simulated mean annual recharge ranges from 0.6 mm/yr (10th percentile) to 326.9 mm/yr (90th) in nonkarst regions, and 7.5 mm/yr (10th) to 740.2 mm/yr (90th) in karst regions. The recharge rate ranges from 2% to 66% of precipitation according to ground-based estimates in karst regions, while the simulated GWR produces global recharge fractions between 4% (10th) to 68% (90th) in karst areas while that in nonkarst areas rarely exceeds 25%. Unlike the previous studies that claimed global hydrological models consistently underestimate recharge, we observed underestimation only in the very humid regions where recharge exceeds 300 mm/yr. These very high recharge estimates are likely to include preferential flow and adopt a finer spatial and temporal scale than the global model. In karst landscapes and arid regions, we demonstrate that WaterGAP incorporating karst algorithm gives a worthy performance.

 

How to cite: Wan, W. and Döll, P.: Karst integration into groundwater recharge simulation in WaterGAP, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15656, https://doi.org/10.5194/egusphere-egu23-15656, 2023.

EGU23-16252 | ECS | Posters on site | ITS1.5/GI1.5

GEOTEK: Extracting Marine Geological Data from Publications 

Muhammad Asif Suryani, Christian Beth, Klaus Wallmann, and Matthias Renz

In Marine Geology, scientists persistently perform extensive experiments to measure diverse features across the globe, hence to estimate environmental changes. For example, Mass Accumulation Rate (MAR) and Sedimentation Rate (SR) are measured by marine geologists at various oceanographic locations and are largely reported in research publications but have not been compiled in any central database. Furthermore, every MAR and SR observation normally carries i) exact locational information (Longitude and Latitude), ii) the method of measurement (stratigraphy, 210Pb), iii) a numerical value and units (2.4 g/m2/yr), iv) temporal feature (e.g. hundred years ago). The contextual information attached to MAR and SR observations is heterogeneous and manual approaches for information extraction from text are infeasible. It is also worth mentioning that MAR and SR are not denoted in standard international (SI) units.

We propose the comprehensive end-to-end framework GEOTEK (Geological Text to Knowledge) to extract targeted information from marine geology publications. The proposed framework comprises three modules. The first module carries a document relevance model alongside a PDF extractor, capable of filtering relevant sources using metadata, and the extraction module extracts text, tables, and metadata respectively. The second module mainly comprises of two information extractors, namely Geo-Quantities and Geo-Spacy, particularly trained on text from the Marine Geology domain. Geo-Quantities is capable of extracting relevant numerical information from the text and covers more than 100 unit variants for MAR and SR, while Geo-Spacy extracts a set of relevant named entities as well as locational entities, which are further processed to obtain respective geocode boundaries. The third module, the Heterogeneous Information Linking module (HIL), processes exact spatial information from tables and captions and forms links to the previously extracted measurements. Finally, the all-linked information is populated in an interactive map view.

How to cite: Suryani, M. A., Beth, C., Wallmann, K., and Renz, M.: GEOTEK: Extracting Marine Geological Data from Publications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16252, https://doi.org/10.5194/egusphere-egu23-16252, 2023.

EGU23-16813 | ECS | Posters on site | ITS1.5/GI1.5 | Highlight

The Use of Artificial Intelligence in ESA’s Climate Change Initiative 

Anna Jungbluth, Ed Pechorro, Clement Albergel, and Susanne Mecklenburg

Climate change is arguably the greatest environmental challenge facing humankind in the twenty-first century. The United Nations Framework Convention on Climate Change (UNFCCC) facilitates multilateral action to combat climate change and its impacts on humanity and ecosystems. To make decisions on climate change mitigation and adaptation, the UNFCCC requires systematic observations of the global climate system.

The objective of the ESA’s climate programme, currently delivered via the Climate Change Initiative (CCI), is to realise the full potential of the long-term, global-scale, satellite earth observation archive that ESA and its Member States have established over the last 35 years, as a significant and timely contribution to the climate data record required by the UNFCCC.

Since 2010, the programme has contributed to a rapidly expanding body of scientific knowledge on >22 Essential Climate Variables (ECVs), through the production of Climate Data Records (CDRs). Although varying across geophysical parameters, ESA CDRs follow community-driven data standards, facilitating inter- and cross-ECV research of the climate system.

In this work, we highlight the use of artificial intelligence (AI) in the context of the ESA CCI. AI has played a pivotal role in the production and analysis of these Climate Data Records. Eleven CCI projects - Greenhouse Gases (GHG), Aerosols, Clouds, Fire, Ocean Colour, Sea Level, Soil Moisture, High Resolution Landcover, Biomass, Permafrost, and Sea Surface Salinity - have applied AI in their data record production and research or have identified specific AI usage for their research roadmaps.

The use of AI in these CCI projects is varied, for example - GHG CCI algorithms using random forest machine learning techniques; Aerosol CCI algorithms to retrieve dust aerosol optical depth from thermal infrared spectra; Fire CCI algorithms to detect burned areas. Moreover, the ESA climate community has identified climate science gaps in context to ECVs with the potential for meaningful advancement through AI.

We specifically focus on showcasing the use of AI for data homogenization and super-resolution of ESA CCI datasets. For instance, both the land cover and fire CCI dataset were generated globally in low resolution, while high resolution data only exists for specific geographical regions. By adapting super-resolution algorithms to the specific science use cases, we can accelerate the generation of global, high-resolution datasets with the required temporal coverage to support long-term climate studies. 

How to cite: Jungbluth, A., Pechorro, E., Albergel, C., and Mecklenburg, S.: The Use of Artificial Intelligence in ESA’s Climate Change Initiative, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16813, https://doi.org/10.5194/egusphere-egu23-16813, 2023.

SM3 – Real-time and time dependent seismology

EGU23-124 | ECS | Posters on site | SM3.1

The impact of isolated noise sources on correlation wavefields 

Sven Schippkus, Roel Snieder, Mahsa Safarkhani, and Céline Hadziioannou

Seismic interferometry gives rise to a correlation wavefield that is closely related to the Green’s function under the condition of uniformly distributed noise sources. Asymmetric correlation wavefields result from the violation of this condition and are commonly observed in field data. In the presence of an additional isolated noise source a second contribution to the correlation wavefield is introduced that emerges from the isolated source location at negative lapse time. The two wavefield contributions interfere, resulting in biased surface wave dispersion measurements. Isolated noise sources that act continuously, such as machinery or ocean microseisms, further have significant impact on the coda of the correlation wavefield. The coda can be dominated by direct waves propagating from the isolated noise source, not by multiply scattered waves originating from the master station. This fundamentally challenges the current understanding of how velocity changes detected in the coda can be measured and interpreted.

How to cite: Schippkus, S., Snieder, R., Safarkhani, M., and Hadziioannou, C.: The impact of isolated noise sources on correlation wavefields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-124, https://doi.org/10.5194/egusphere-egu23-124, 2023.

EGU23-1171 | ECS | Posters on site | SM3.1

Estimation of amplitude noise reduction as a function of depth recorded by a deep vertical array (Northern Italy) 

Camilla Rossi, Francesco Grigoli, Paolo Gasperini, Stefano Gandolfi, Chiara Cocorullo, Timur Gukov, and Paolo Macini

To design an efficient seismic monitoring infrastructure, the characterization of the background seismic noise level of each potential seismic station installation site is one of the most important data-quality metrics used to evaluate the suitability of such sites to host the seismic network. The background seismic noise can be generated by different sources such as, ocean waves (microseisms), atmospheric turbolences (strong wind and storms), and anthropogenic activities. Such disturbances are characterized by specific frequency bands, time-occurrence (diurnal and seasonal variation), and site location (close to populated area or to the coasts). Reducing the effect of these noise sources is one of the main challenges to face for designing seismic monitoring networks and, more specifically, when selecting the hosting site of a seismic stations. A solution to attenuate the seismic noise effect is obtained by deploying seismic stations in boreholes. The noise level reduction with depth has been observed and studied by different authors, however a general law estimating the sufficient depth to gain is still missing. In this study, we analyse the continuous seismic noise level at S. Potito-Cotignola gas storage in the Po Valley (Northern Italy) recorded from January 2019 to December 2021 by a broadband (BB) seismic station at surface and a vertical array composed by 6-short period 3-components seismometers installed at depth ranging between 35 to 285 m in borehole. We aim to characterize the seismic noise by computing the amplitude noise reduction in terms of dB as a function of depth for different frequencies and the SNR by selecting three seismic events, with different epicentral distance and magnitude. Our results show that the noise level decreases with depth following a logarithmic empirical trend and the lowest magnitude event records the maximum SNR difference between the deepest sensor and the one at the surface. The estimated empirical relationships can be used to help the design microseismic monitoring networks in similar geological settings.

How to cite: Rossi, C., Grigoli, F., Gasperini, P., Gandolfi, S., Cocorullo, C., Gukov, T., and Macini, P.: Estimation of amplitude noise reduction as a function of depth recorded by a deep vertical array (Northern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1171, https://doi.org/10.5194/egusphere-egu23-1171, 2023.

EGU23-1284 | ECS | Posters on site | SM3.1

Wave field prediction for denoising of seismic measurements using an autoencoder network 

Jana Klinge, Dirk Gajewski, Celine Hadziioannou, and Jan Walda

The adoption of machine learning in different sectors demonstrates a huge potential of multiple techniques applicable to learn specific features of a dataset. We aim to make use of machine learning methods to predict the development of seismic wave fields between two seismic stations and use this information to remove random noise post-measurement, considering the phase and time information of the signal. Thereby, the initial approach follows the use of an autoencoder network in a self-supervised fashion. Aiming to reconstruct its input, the form of the autoencoder corresponds to the traditional U-Net structure but expands with residual blocks for increased network capacity. To refine results, we modify the interrelated training process of encoding and reconstruction and separate it into sequential phases. To make sure that the dataset includes multiple sources and thus provides various features, we use field data gathered at a seismic exploration site in an area containing several roads, wind turbines, oil pump jacks and railway traffic. Using the well-known autoencoder network structure and applying it in the context of transfer learning enables us to automatically learn a representation of the wave field and, more importantly, predict its spatial development based on different frequency bands. The gained knowledge can be used in future directions to exclude non-relevant parts of the data in the context of denoising and to compare results to currently used methods such as the Wiener optimum filters.

How to cite: Klinge, J., Gajewski, D., Hadziioannou, C., and Walda, J.: Wave field prediction for denoising of seismic measurements using an autoencoder network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1284, https://doi.org/10.5194/egusphere-egu23-1284, 2023.

Ambient seismic sources (e.g. ocean waves) generate ambient seismic waves, and thus in turn, one can use these waves to infer the source distribution and study the source properties. Many studies focus on the source distribution estimation result, but few discuss the uncertainty of the estimation result, even though the uncertainty is significant and should be taken into account in the interpretation. We propose to compute the uncertainty of the estimated source distribution using singular value decomposition. We focus on two commonly used estimation methods: matched field processing and full waveform inversion. We demonstrate the uncertainty of the two methods by assessing the associated point spread functions. We determine that the full-waveform inversion method possesses higher resolution than matched field processing given enough independent data.

How to cite: Mikesell, T. D. and Xu, Z.: Assessing the uncertainty of ambient-seismic-source-distribution estimation with matched field processing and full waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1932, https://doi.org/10.5194/egusphere-egu23-1932, 2023.

EGU23-3193 | ECS | Orals | SM3.1 | Highlight

Microseism and Medicane Apollo: a new approach to investigate the Mediterranean extreme weather events 

Alfio Marco Borzì, Vittorio Minio, Flavio Cannavò, Angelo Cavallaro, Sebastiano D'Amico, Raphael De Plaen, Adam Gauci, Thomas Lecocq, Gabriele Nardone, Arianna Orasi, Marco Picone, and Andrea Cannata

Microseism is the most continuous and ubiquitous seismic signal on the Earth and is caused by the interaction between the atmosphere, the hydrosphere and the Solid Earth. In literature, there are several studies that deal with the relationship between microseism and cyclonic activity considering in particular hurricanes, tropical cyclones and typhoons. However, the relationships between microseism and the small-scale tropical cyclones that occur in the Mediterranean Sea, called Medicanes, have never been analysed. For this reason, we considered the Medicane Apollo, which developed in the Ionian Sea and impacted the eastern part of Sicily during the period 25th October to 5th November 2021 causing heavy rainfall (> 400 mm/48h), strong wind gusts (104 km/h) and violent sea waves (significant wave height > 3.5 m). Furthermore, the heavy rainfall induced by the presence of Apollo, caused damage to infrastructure and agriculture forcing the Sicilian regional government to declare a state of emergency for 32 municipalities (in the provinces of Catania, Messina, Siracusa and Ragusa) that were mostly affected by the Medicane Apollo.

In this work, we analysed the microseism signal recorded by 78 seismic stations installed in South Italy, Malta and Greece coastline during the period under investigation. To obtain information about the significant wave heights, we consider the data obtained by hindcast maps and four wavemeters buoys. The spectral and amplitude analysis allowed us to obtain information about the space-time variations of the microseism amplitude and in addition, we were able both to differentiate the seismic stations that perceive Apollo (stations installed close to the Ionian Sea), the seismic stations that do not perceive the medicane (stations installed close to the Tyrrhenian sea) and the microseism bands influenced by the presence of the Medicane Apollo. Moreover, we tracked the position of the Apollo by using two different methods: i) grid search method based on the seismic amplitude decay using the 78 seismic stations first mentioned and ii) array technique by 15 seismic stations installed on Etna which may be considered an array thanks to their spatial distribution and geometry. We obtain a good match between the real positions of the Medicane Apollo derived from satellite images and the positions computed by the two analysis methods. This work shows that it is possible to extract information about the Mediterranean extreme meteo-marine events from microseism, a seismic signal that until not long ago was considered as noise, both for monitoring and research purposes.

How to cite: Borzì, A. M., Minio, V., Cannavò, F., Cavallaro, A., D'Amico, S., De Plaen, R., Gauci, A., Lecocq, T., Nardone, G., Orasi, A., Picone, M., and Cannata, A.: Microseism and Medicane Apollo: a new approach to investigate the Mediterranean extreme weather events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3193, https://doi.org/10.5194/egusphere-egu23-3193, 2023.

EGU23-4166 | ECS | Posters on site | SM3.1

Evaluating diffuse wavefield and its applications in seismic imaging 

Bo Yang, Haoran Meng, Ning Gu, Xin Liu, and Xiaofei Chen

The cross-correlation of ambient seismic noise data can be utilized to image subsurface geological structures from ambient noise fields at local, regional, and global scales by extracting Green's functions between seismograph pairs. Precise extraction of empirical Green's functions from the cross-correlations of noise records requires that the seismic wavefield be fully diffuse. This requires the coefficients of the eigenfunction expansion of the seismic records to satisfy the statistical characteristics derived by Weaver and Lobkis (2004) in the time domain. Due to the complexities of the Earth media and noise sources, it is not feasible to obtain accurate eigenfunctions with the corresponding coefficients and adopt these statistical characteristics to evaluate actual seismic data. To resolve this issue, we derive the equivalent expressions in the frequency domain with dimensionless evaluation criteria without requiring the eigenfunctions. The evaluation of random noise, wind-induced vibrations, car- and air-traffic-excited ground motions, earthquakes, and continuous ambient seismic noise records confirms the validity of our evaluation method. We further apply the method to the widely used preprocessing procedures of ambient noise imaging techniques by examining time-domain normalization and spectral whitening operations of earthquake waveforms, thus quantitatively demonstrating how these procedures down-weight the non-diffuse component and improve the degree of waveform diffuseness (as shown in Figure 1). As an application, we select the coda wave signals generated by road traffic and earthquakes that satisfy the diffuse wavefield characteristics and extract the higher-order surface wave dispersion curves from 20-100 s seismic recordings without performing preprocessing procedures. Compared with the traditional surface wave processing process, our method is highly efficient, does not require long recording time and preprocessing such as normalization and whitening, and can be widely used in evaluating diffuse wavefield, imaging subsurface velocity and attenuation structures, and monitoring the temporal changes with high temporal resolution.

How to cite: Yang, B., Meng, H., Gu, N., Liu, X., and Chen, X.: Evaluating diffuse wavefield and its applications in seismic imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4166, https://doi.org/10.5194/egusphere-egu23-4166, 2023.

EGU23-4258 | Posters on site | SM3.1

Characterization of ambient seismic noise sources for long term monitoring of a sea dike: preliminary results of the SEEWALL project. 

Maximilien Lehujeur, Amin Kahrizi, Odile Abraham, Loic Michel, Thomas Bardainne, Antoine Lescoat, Lila Vivin, Julien Blanchais, Christopher Boulay, Thibaud Devie, Sérgio Palma-Lopes, Olivier Durand, and Gautier Gugole

Protection against sea submersion is a key point for the management of coastal areas. Operators need tools to monitor the aging of the sea dikes in order to reduce the risk of catastrophic events such as the Xynthia storm that occurred in 2010 (west of France). Long-term monitoring of these structures can be done using the ambient seismic noise produced by a combination of natural sources (e.g. the impact of swell on the structure, water currents, the wind force on ground-anchored constructions, etc.) and/or nearby anthropogenic sources (e.g. road/pedestrian traffic, coastal activities, etc.).

Continuous ambient noise recordings can be used for monitoring structures by detecting small variations in seismic velocities related to localized degradations that cannot be detected visually. However, this monitoring technique requires sufficient energy in the proper frequency range for the intended application (typically at wavelengths of the order of the size of the structure or less). Additionally, the distribution of the sources must be relatively stable over time in order to interpret the velocity variations explicitly. The case of sea dikes is particularly challenging as the seismic noise is highly variable due various factors, like the water height variations during the tidal cycle, the variations in tidal intensity during the year, or the effects of the climatic conditions on the direction and intensity of the swell.

This study is conducted in the framework of the SEEWALL project, which aims to develop a system for monitoring sea dikes using ambient seismic sources. A dike located on the Noirmoutier Island (France) has been instrumented with permanent accelerometers along with several geophysical and meteorological probes which have been recording continuously for about one year. This contribution focuses on the identification of the essential properties of the ambient seismic noise recorded in this setting and seeks to evaluate how these properties affect our ability to measure temporal variations of the seismic waves velocity. In other words, our objective is to identify the noise sources that contribute most favorably to the approximated empirical Green’s functions and/or that are highly repeatable over time, in order to develop methods that can be applied to various dikes and to optimize the type and amount of seismic data required to monitor such structures.

How to cite: Lehujeur, M., Kahrizi, A., Abraham, O., Michel, L., Bardainne, T., Lescoat, A., Vivin, L., Blanchais, J., Boulay, C., Devie, T., Palma-Lopes, S., Durand, O., and Gugole, G.: Characterization of ambient seismic noise sources for long term monitoring of a sea dike: preliminary results of the SEEWALL project., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4258, https://doi.org/10.5194/egusphere-egu23-4258, 2023.

EGU23-5057 * | ECS | Orals | SM3.1 | Highlight

Why are some faults in the Alps active, and others not? Answers from stress-induced anisotropy of nonlinear elasticity 

Yongki Andita Aiman, Andrew Delorey, Yang Lu, and Götz Bokelmann

Major faults such as the Periadriatic Fault and the Giudicarie Fault have been active in the past, and they have even been central features of the larger-scale deformation in the Alps. It seems that these faults are not active anymore though and we investigate why this is so by inspecting the orientation of the regional stress field which loads the faults mechanically. The orientation of maximum horizontal compressive stress (SHmax) is commonly estimated from in-situ borehole breakouts and earthquake focal mechanisms. Borehole measurements are expensive, and therefore sparse, and earthquake measurements can only be made in regions with many well-characterized earthquakes. Here we derive the stress-field orientation using stress-induced anisotropy in nonlinear elasticity. In this method, we measure the strain derivative of velocity as a function of azimuth. We use a natural pump-probe approach which consists of measuring elastic wave speed using empirical Green’s functions (probe) at different points of the earth tidal strain cycle (pump). The approach is validated using a larger data set in the Northern Alpine Foreland region where the orientation of SHmax is known from borehole breakouts and drilling-induced fractures. The technique resolves NNW-SSW to N-S directed SHmax which is in good agreement with conventional methods and the recent crustal stress model. The technique is then applied to the Southern Alps to understand the contemporary stress pattern associated with the ongoing deformation due to the counterclockwise rotation of the Adriatic plate with respect to the European plate. Our results explain why the two major faults in Northeastern Italy, the Giudicarie Fault and the Periadriatic Line (Pustertal-Gailtal Fault) are currently inactive, while the currently acting stress field allows faults in Slovenia to deform actively. We have demonstrated that the pump-probe method has the potential to fill in the measurement gap left by conventional approaches, both in terms of regional coverage and depth. 

How to cite: Aiman, Y. A., Delorey, A., Lu, Y., and Bokelmann, G.: Why are some faults in the Alps active, and others not? Answers from stress-induced anisotropy of nonlinear elasticity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5057, https://doi.org/10.5194/egusphere-egu23-5057, 2023.

EGU23-5475 | ECS | Orals | SM3.1

The Main Himalayan Thrust beneath Nepal and Southern Tibet illuminated by seismic ambient noise and teleseismic P wave coda autocorrelation 

Hari Ram Thapa, Surya Pachhai, Abdelkrim Aoudia, Daniel Manu-Marfo, Keith Priestley, and Supriyo Mitra

Nepal is an actively deforming region due to its tectonic setting that hosts many destructive earthquakes including the most recent 2015 Gorkha earthquake of magnitude 7.8. To better understand the physics of earthquakes and their precise location as well as monitoring of seismicity and real-time seismic hazard in the region, a highly resolved 3-D structure of the crust is essential. This study presents a new 3-D shear S -wave velocity structure of the crust using group and phase velocity dispersions obtained from ambient noise tomography. This study further constrains the discontinuities beneath Himalaya Nepal using teleseismic compressional P-wave coda autocorrelation. Our results show significant variation in the crustal structure within the region and correlate well with known geological and tectonic features present there. The results from the P-wave coda autocorrelation identify major seismic discontinuities in the crust including the Main Himalayan Thrust (MHT). The MHT with two ramps correlates well with a low S-wave velocity layer obtained from the ambient noise tomography. The first ramp agrees with the duplex structure in the MHT beneath Lesser Himalaya while the second ramp connects flat low velocity beneath High Himalaya to a broad low-velocity zone beneath South Tibet. Moreover, the High Himalaya low-velocity layer is located where the GPS data show creeping north of the coseismic rupture of the 2015 Gorkha earthquake. The lateral variation of S-wave velocity on the MHT surface provides the details of lateral transitions that might have potentially controlled the rupture pattern of the 2015 Gorkha earthquake.

The geometry and extent of the High Himalaya low-velocity layer mimics the decollement coupling zone inferred from GPS data with widths of 50 to 70 km north of the nucleation of the 2015 Mw 7.8 Gorkha earthquake and 90 to 100 km north of the source of the Mw 8.4 1934 earthquake. The occurrence of millenary Mw>9.0 earthquakes in Central and Eastern Nepal would require either a wider coupling low velocity zone compared to the ones identified in this work or the involvement of southernmost Tibet low velocity decoupling zone so to store enough elastic energy.

How to cite: Thapa, H. R., Pachhai, S., Aoudia, A., Manu-Marfo, D., Priestley, K., and Mitra, S.: The Main Himalayan Thrust beneath Nepal and Southern Tibet illuminated by seismic ambient noise and teleseismic P wave coda autocorrelation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5475, https://doi.org/10.5194/egusphere-egu23-5475, 2023.

EGU23-5670 | ECS | Orals | SM3.1

A comprehensive beamforming toolbox to characterise surface and body waves in three-component ambient noise wavefields 

Katrin Löer, Claudia Finger, Ebitimi Obiri, and Heather Kennedy

We give an overview of a new toolbox for easy and fast beamforming analysis of three-component ambient seismic noise and discuss examples from different seismic arrays to solve different application challenges. From only a couple of hours of array recordings, the beamformer provides estimates of surface wave dispersion curves, surface wave azimuthal anisotropy, frequency-dependent wavefield composition including surface and body waves, and the direction of arrival for different wave types and frequencies. The beamformer can be used with three-component arrays from the lab to the field scale, provided ambient noise is available in the corresponding frequency range. Compared to standard (single-component) beamforming analysis, our approach integrates all three components recorded at every seismometer. Considering the phase shifts across the components, it identifies wave-specific particle motion and hence discriminates different wave types on account of their polarisation. The new implementation of the beamformer does not use the cross-spectral density matrix of the data explicitly (as done, for example, by the MUSIC algorithm and Capon beamformer), which reduces computation times significantly and makes it feasible to compute beam responses for a full day of data recorded on 100s of stations on a standard laptop PC. The toolbox will be available on github for both MATLAB and Python.

In an example from Los Humeros geothermal field (Mexico) we show Rayleigh wave azimuthal anisotropy as a function of frequency, corresponding to varying fast directions as a function of depth. A good agreement between the observed anisotropy and stress data from well logs as well as geological information indicates that fast directions correlate with the orientation of major faults and dykes. Anisotropy analysis thus provides a means to assess fault properties at depth, giving information about potential secondary permeability – a vital parameter in deep geothermal plays. Beamforming analysis of noise recordings in the Groningen area (Netherlands) reveals dominant prograde motion in both fundamental and 1st higher mode Rayleigh waves. This behaviour is indicative of a large impedance contrast between the very low shear-velocities in sedimentary basins and the underlying bedrock. The resolution of particle motion as a function of frequency allows us to observe the osculation frequency where fundamental and 1st higher mode Rayleigh waves approach each other and both modes change particle motion from prograde to retrograde and vice versa. The osculation frequency can be used to estimate the depth of the major impedance contrast, that is, the depth of the sedimentary basin. While body wave observations must be interpreted with care, considering the resolution capabilities of the array with respect to the expected (larger) wavelengths, the examples show that body waves contribute to the ambient noise wavefield with varying degree as a function of frequency, challenging the assumption of surface wave dominance common in ambient noise studies. Overall, we demonstrate that our beamforming toolbox provides direct information about structural features as well as fundamental a-priori information on wavefield composition and source characteristics, valuable for further ambient noise methods.

How to cite: Löer, K., Finger, C., Obiri, E., and Kennedy, H.: A comprehensive beamforming toolbox to characterise surface and body waves in three-component ambient noise wavefields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5670, https://doi.org/10.5194/egusphere-egu23-5670, 2023.

EGU23-5725 | ECS | Orals | SM3.1

Extraction of diving body waves from a dense network of seismometers at kilometric offsets: a case study from the Paris Basin 

Ali Riahi, Alexandre Kazantsev, Jean-Philippe Metaxian, Eleonore Stutzmann, Martin Schimmel, and Jean-Paul Montagner

We reconstruct the body and surface waves from the seismic ambient wave field, recorded by a dense seismic array deployment in the Paris Basin, France, with a final objective of performing a 3D seismic tomography by inversion of the retrieved P-phase arrivals. The array was installed in November 2010 and consists of around 100 stations. The stations were shifted to different locations every day, yielding around 580 recording locations with an interstation distance of about 400 m. Each station has continuously recorded around 3-4 days of the seismic ambient wavefield. We calculate the cross-coherency between each station couple in the frequency band of 1.0-4.5 Hz and estimate the empirical Green’s functions. We use the polarization properties of the cross-correlation tensors to separate the P- and Rayleigh wavefields. The results show the reconstruction of the fundamental and higher modes of Rayleigh and Love waves, as well as of diving P- waves. We observe the apparent group velocity of the fundamental and first higher mode of the Rayleigh wave around 0.5 and 1.5 km/s, respectively, and the apparent group velocity of around 0.8 km/s for the fundamental mode of the Love wave. The extraction of the P waves is challenging because of a high amplitude coherent artefact that can cause misinterpretation of the P- wave moveout. We propose a new approach to filter out the extracted P- wave in presence of this artifact and reconstruct the P-wave with a correct apparent velocity of around 2-3 km/s, validated against available active seismic data. This approach is based on template-matching and can be regarded as the most crucial step in P-wave retrieval from our dataset. Future steps will consist of using the extracted P-wave arrival time for a 3D tomography of the anticline structure located beneath the array.

How to cite: Riahi, A., Kazantsev, A., Metaxian, J.-P., Stutzmann, E., Schimmel, M., and Montagner, J.-P.: Extraction of diving body waves from a dense network of seismometers at kilometric offsets: a case study from the Paris Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5725, https://doi.org/10.5194/egusphere-egu23-5725, 2023.

EGU23-6237 | ECS | Orals | SM3.1

An improved attenuation tomography method based on ambient noise cross-correlation 

Hongrui Peng and Jiangtao Li

In the last decade, Empirical Green’s functions (EGFs) derived from ambient noise cross-correlation have been widely and successfully applied to measure seismic velocity and its temporal variation. However, it is still pending whether the amplitude of EGFs is reliable and whether it could be utilized in attenuation tomography. From our perspective, to develop a noise interferometry-based attenuation tomography method, it is necessary to overcome difficulties from two significant aspects. Firstly, in preprocessing, the relative amplitudes between different station pairs should be preserved, which precludes standard techniques, including one-bit/running-absolute-mean normalization and spectral whitening. Secondly, in addition to the intrinsic attenuation, amplitudes are also affected by other factors, such as noise source distribution, geometric spreading, instrument response, site effect, focusing and defocusing effect, etc. To obtain precise attenuation, it is necessary to separate all those factors carefully before or during inversion.

 

In this research, we develop a new workflow to perform attenuation tomography with ambient noise data. In preprocessing, we apply the asynchronous temporal flattening (ATF) normalization method (Zhou et al., 2020) to remove earthquake and abnormal signals in records while keeping relative amplitudes. Then we use the SNR and the symmetry of arrival times to select high-quality EGFs. Accounting focusing and defocusing effect of elastic heterogeneity, we predict it through finite-frequency theory (Zhou et al., 2004; Bao et al., 2016) and remove the effect from measured amplitudes. Finally, following the theory in (Weaver, 2013), we invert for attenuation, site effect, and wave field intensity of different incoming directions through a linear inversion. This workflow is feasible for both 1D and 2D arrays. It also delivers good results in the real data test of the Yellowstone national park region, with apparent high-attenuation anomaly beneath the Yellowstone Caldera.

 

References:

[1]L. Zhou, X. Song, and R. L. Weaver, ‘Retrieval of amplitude and attenuation from ambient seismic noise: synthetic data and practical considerations’, Geophysical Journal International, vol. 222, no. 1, pp. 544–559, Jul. 2020, doi: 10.1093/gji/ggaa194.

[2]Y. Zhou, F. A. Dahlen, and G. Nolet, ‘Three-dimensional sensitivity kernels for surface wave observables’, Geophysical Journal International, vol. 158, no. 1, pp. 142–168, Jul. 2004, doi: 10.1111/j.1365-246X.2004.02324.x.

[3]X. Bao, C. A. Dalton, and J. Ritsema, ‘Effects of elastic focusing on global models of Rayleigh wave attenuation’, Geophysical Journal International, vol. 207, no. 2, pp. 1062–1079, Nov. 2016, doi: 10.1093/gji/ggw322.

[4]R. L. Weaver, ‘On the retrieval of attenuation and site amplifications from ambient noise on linear arrays: further numerical simulations’, Geophysical Journal International, vol. 193, no. 3, pp. 1644–1657, Jun. 2013, doi: 10.1093/gji/ggt063.

How to cite: Peng, H. and Li, J.: An improved attenuation tomography method based on ambient noise cross-correlation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6237, https://doi.org/10.5194/egusphere-egu23-6237, 2023.

EGU23-6840 | ECS | Posters virtual | SM3.1 | Highlight

Ambient noise variation in the South Pole 

Gyanasmita Pradhan, Ramakrushna Reddy, and Paresh Nath Singha Roy

Ambient noises are generated due to the interaction of atmosphere with the solid Earth and the noises which occur within the time period of 2-20s are known as microseisms. As the noise generation mechanism is not very well understood in the extreme climatic condition of Antarctic continent, in this study we target to understand the microseism generation in the South Pole station situated in the Antarctic continent. We have carried out our analysis using continuous data from IRIS data management center. Our main focus is to characterize the source direction of noise and their seasonal amplitude variations. We have employed the frequency dependent polarization analysis through the Eigen decomposition of the 3×3 spectral covariance matrix.

 The source of the noise have been analyzed using the backazimuth and time period for all the three bands of microseism, SPDF (short period double frequency), LPDF (long period double frequency), and PM (primary microseism). We observed that the noise is mainly due to the strong winds of Southern Ocean and some amounts of noise are also from the Ross Sea. In southern hemisphere, winter starts from May and it ends in August and also the number of polarized signals is lower in the winter season, and it is comparatively higher in the summer season. Additionally, when we plot Power spectral density against time period we see the splitting of the double frequency microseism into SPDF and LPDF which is only observed in the summer months and not in the winter months (only one single peak is observed).  Because, in the winter month’s sea ice concentration is extremely high in the South Pole; therefore, there is no significant wind interaction with sea waves of the coastal part which generates the SPDF. In winter, the continent is completely frozen; however, the amplitude of noise is high due to the strong winds. In summer, the noise is generated due to the low pressure systems develops in Southern Ocean which leads to cyclones in the Ross Sea. Antarctic circumpolar current also plays a significant role in the generation of noise. Therefore, we can conclude that the source of noise is from the Southern Ocean and Ross Sea. Also, we noticed the seasonal variation in the splitting of the double frequency microseism due to variation in the sea ice concentration.

How to cite: Pradhan, G., Reddy, R., and Singha Roy, P. N.: Ambient noise variation in the South Pole, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6840, https://doi.org/10.5194/egusphere-egu23-6840, 2023.

EGU23-7003 | ECS | Posters on site | SM3.1

Array beamforming on ambient seismic noise correlations reveals repeating direct waves in the coda 

Mahsa Safarkhani, Sven Schippkus, and Céline Hadziioannou

Over the past two decades, the ambient seismic noise correlation method has revolutionized our ability to investigate the Earth's subsurface structure. Perfect reconstruction of the cross correlation wavefields towards Green's function demands some strong hypotheses about uncorrelated and spatially uniform seismic source distributions. In reality, violation of this assumption impacts the accuracy of the Green’s function estimate, which may bias applications in further studies. As this technique has become a standard method for subsurface imaging and monitoring, a methodology that identifies the effect of seismic source distributions plays an essential role in removing their contribution to achieve less-biased signals. Seismic array beamforming is commonly applied in estimating the direction of seismic waves crossing the array.

In this study, we use a new strategy based on beamforming of noise correlation signals. We consider several seismic stations surrounding the Gräfenberg array throughout Europe as virtual sources. We process two years of vertical component continuous noise recording from the Gräfenberg array in Germany and virtual sources in Poland, Italy, Portugal, France and Finland. Using the noise correlation-based beamforming method, we detect source directions for direct and coda waves for the primary (0.05-0.1 Hz) and secondary (0.1-0.4 Hz) microseism frequency bands. The source directions for the direct waves correspond to the converging and diverging part of the correlation wavefield. Throughout the coda, however, we detect the dominant noise source directions, i.e., surface waves generated by ocean microseisms in the Northern Atlantic during winter months and body waves from the Southern Pacific during summer months. This suggests that the coda of the correlation functions contains repeating direct waves from the dominant source regions, which may lead to incorrect estimates and interpretation of velocity variations if not accounted for. Knowledge of the ambient noise source origins and their spatiotemporal distribution is required to correctly interpret velocity variations.

How to cite: Safarkhani, M., Schippkus, S., and Hadziioannou, C.: Array beamforming on ambient seismic noise correlations reveals repeating direct waves in the coda, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7003, https://doi.org/10.5194/egusphere-egu23-7003, 2023.

EGU23-7289 | ECS | Orals | SM3.1 | Highlight

Seismic emissions from a passing train: turning ambient noise into a controlled source 

Théo Rebert, Thibaut Allemand, Thomas Bardainne, Caifang Cai, and Hervé Chauris

Train traffic is a powerful source of seismic vibrations. Recent studies have shown that trains illuminate geological structures both at the crustal and the geotechnical scale. Existing works have been able to reconstruct approximately the spectral characteristics of the wavefield emitted by a passing train. In this work, we show that we can recover information on the train itself with high accuracy by looking only at the seismic recordings.

We record passing trains with seismic accelerometers less than 2 meters away from the track. We can isolate the signal emitted by each wheel, and thus reconstruct the trajectory of the train. This trajectory reconstruction is performed using a non-linear waveform inversion algorithm involving the varying train speed, the spacing between the wheels and an apparent wavelet emitted when the wheel hits close to the seismic sensor. After low-pass filtering the data below 15 Hz for passenger trains passing at around 100 km/h, we obtain harmonious waveforms suitable for our inversion technique. Especially, we are able to pick each wheel from the raw trace, which allows for a robust initial model avoiding local minima trapping during the non-linear inversion. The estimated parameters are minimally influenced by seismic wave propagation speeds, because the closest sleeper dominates the signal in this frequency band.

These results suggest that train traffic is a repeatable seismic source that can be can be characterized with good accuracy.  By having a better information about the source process, it might be possible to extract more information from the noise recordings, and thus gain in resolution in the imaging of the near surface. Especially, we expect enhanced repeatability of Rayleigh velocities measurements which is important for subsurface monitoring. Further, this also allows for railway traffic monitoring as trains can be identified and their speed measured as they cross seismic arrays.

How to cite: Rebert, T., Allemand, T., Bardainne, T., Cai, C., and Chauris, H.: Seismic emissions from a passing train: turning ambient noise into a controlled source, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7289, https://doi.org/10.5194/egusphere-egu23-7289, 2023.

EGU23-7636 | ECS | Posters on site | SM3.1 | Highlight

Inferring deep soil moisture variations in Central Europe using seismic method 

Yang Lu, Qing-Yu Wang, and Götz Bokelmann

Soil moisture is a key metric to assess soil health. Water held in the shallow subsurface between soil particles enables various biogeochemical and hydrological processes indispensable to soil functions. Potential soil moisture deficit may raise the irrigation demands, which further exacerbates the stress on the water supply. The changes in soil moisture can impact climate, further amplifying the climatic anomalies and intensifying extreme weather events. Thus, understanding soil moisture and its dynamics over time are of broad scientifical interest and practical implications.

Despite the vital importance of soil moisture, it still lacks sufficient means to properly assess the parameter at a regional scale, which is an essential research dimension for addressing practical issues in the agricultural and environmental sectors.

Ambient noise seismology provides new possibilities to infer subsurface changes in a real-time, non-intrusive, and costless manner. In this study, we map the temporal variations in soil moisture for the great Alpine region and the Italy peninsular with ambient seismic noise. It is the first time that the seismic method has been applied to map water resources at a regional scale using an ordinary seismic network setup. The seismic method helps in bridging the resolution gap between current pointwise (e.g., tensio-, electrical- and neutron-meter) and global (e.g., satellite-based remote sensing) investigations, providing complementary information for both scientific research and public decision-making.

How to cite: Lu, Y., Wang, Q.-Y., and Bokelmann, G.: Inferring deep soil moisture variations in Central Europe using seismic method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7636, https://doi.org/10.5194/egusphere-egu23-7636, 2023.

EGU23-7992 | ECS | Posters on site | SM3.1

Influence of meteorology on the variations of crustal seismic velocity in Volcan de Colima, Mexico using Noise Interferometry 

Juan Ibarra Morales, Raphael S. M. De Plaen, Víctor Hugo Márquez Ramírez, Francisco Ramón Zúñiga Dávila-Madrid, and Raul Arámbula Mendoza

The temporal variation of seismic velocity gives us information about the crust’s stress state and the relative changes associated with magmatic, tectonic, and meteorologic activity. In the present study, we analyze the temporary seismic velocity changes under Volcan de Colima to identify its relationship with volcanic and non-volcanic sources, evaluate the seasonality of the variations and describe the impact that the meteorology has on the changes. The signals of seismic velocity variation used in this work were measured using the single-station cross-component correlation technique applied to traces registered at four stations in the period 2013 – 2017. The data was analyzed in two frequency bands: 0.1 – 1 and 1 – 2 Hz.

We validate the relationship between the velocity variations and three meteorological parameters, rain, temperature, and atmospheric pressure, using wavelet coherence analysis. After fitting a linear model, we identified the environmental factors with the most impact on the seismic velocity are: 1) the rainfall-induced pore pressure, correlated negatively with the seismic velocity and causing changes close to the order of -0.5%; 2) thermoelastic strains correlated positively with the seismic velocity and causing velocity variations between -0.5 and 0.5%. Atmospheric pressure has a smaller impact, mainly of the order of 10-3%.

How to cite: Ibarra Morales, J., De Plaen, R. S. M., Márquez Ramírez, V. H., Zúñiga Dávila-Madrid, F. R., and Arámbula Mendoza, R.: Influence of meteorology on the variations of crustal seismic velocity in Volcan de Colima, Mexico using Noise Interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7992, https://doi.org/10.5194/egusphere-egu23-7992, 2023.

EGU23-8432 | Posters on site | SM3.1

Crustal structure beneath the Western Himalayas from surface wave dispersion analysis 

Shubhasmita Biswal and Sushil Kumar

The Western Himalaya is one of the most complex and heterogeneous seismotectonic units of the Alpide-Himalaya seismic belt. The region has distinctive physiographic characteristics because of the way that they have changed and evolved over the course of time. The purpose of the present investigation is to understand the seismotectonic architecture beneath the study area which is seismically very active. Twenty broad-band seismic stations have been employed to record the surface wave data to study the crustal structure beneath the western Himalayas. We find phase and group velocities of Rayleigh waves for the region with periods between 4 and 30s. To obtain layered S wave velocity models, the dispersion curves are inverted. The crustal velocity structure beneath the region is found to vary significantly. The average estimated S-wave velocity is ~ 3.8 km/s down to 30 km depth. We also observed a low-velocity layer in the middle crust of the higher Himalayas section and the interpretation from the present analysis is consistent with available geological data.

 

How to cite: Biswal, S. and Kumar, S.: Crustal structure beneath the Western Himalayas from surface wave dispersion analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8432, https://doi.org/10.5194/egusphere-egu23-8432, 2023.

EGU23-8517 | Posters on site | SM3.1

On localising North Atlantic’s microseism sources using time reversal imaging 

Florian Le Pape, Christopher J. Bean, Athira Vijayan, and Mathias Fink

The ambient seismic noise is dominated by surface waves associated with ocean microseisms that are defined by a strong acoustic/seismic coupling at the seafloor. The understanding of microseism sources not only benefits seismic passive imaging and monitoring, but can also help track ocean storms using seismic signals recorded on land. Numerical simulations show that heterogeneous seafloor morphologies and structures can significantly affect the propagation of microseism’s surface waves and therefore the accuracy in locating their origin using traditional methods, such as array beamforming. Here, we aim to investigate how the use of time-reversal imaging can help overcome those limitations. The technique has mainly been developed for acoustics but has been applied successfully in seismology for earthquake localisation. Time-reversal imaging consists on back-propagating, through a realistic model, the signal measured at a network of receivers so that it eventually refocuses back at its origin. For this study, simulations are performed using the code SPECFEM3D and a regional 3D acoustic/elastic model of the Irish offshore, with seismic receivers homogeneously distributed along the coast of Ireland. First, methodologies and stations layout are tested with synthetic data generated from forward modelling using different source distributions. Processing approaches for the time-reversed simulation results are investigated in order to optimize the recovery of the original sources. Following those tests, real time windows of seismic noise “events” are then back-propagated into the model with the aim to map the microseism sources associated with local storms in the model area. The results are compared with microseism sources derived from global ocean wave models. Overall, the use of time-reversal imaging for microseism sources localisation looks promising. Although challenging due to the diffuse distribution of sources, there is good potential for developing further our understanding of microseism sources and monitor dominant microseism generation areas in the North Atlantic region with the implementation of a larger model.

How to cite: Le Pape, F., Bean, C. J., Vijayan, A., and Fink, M.: On localising North Atlantic’s microseism sources using time reversal imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8517, https://doi.org/10.5194/egusphere-egu23-8517, 2023.

EGU23-8654 | ECS | Orals | SM3.1 | Highlight

Autocorrelation infrasound interferometry for atmospheric sensing on Earth and Mars 

Hugo D. Ortiz and Robin S. Matoza

We develop a framework for retrieving time-varying atmospheric properties using a single infrasound sensor following an autocorrelation interferometry method. We compare relative velocity (effective sound speed) changes inferred from infrasound autocorrelations with independently measured air temperature and velocity variations. For the propagation geometry of the infrasound source (a waterfall) and receivers at El Reventador (Ecuador) we infer that effects from wind velocity can be assumed negligible and provide a mathematical model to derive temperatures from relative velocity changes. We further demonstrate that the autocorrelation method can be used to study the Martian atmosphere; specifically, we show that relative velocity changes derived from the pressure sensor on board the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport lander can track variations of the effective speed of sound. These results also suggest the presence of continuous background infrasound on Mars.

References:

  • Ortiz, H. D., Matoza, R. S., Johnson, J. B., Hernandez, S., Anzieta, J. C., and Ruiz, M. C. (2021). Autocorrelation infrasound interferometry. Journal of Geophysical Research: Solid Earth. https://doi.org/10.1029/2020JB020513
  • Ortiz, H. D., Matoza, R. S., and Tanimoto, T. (2022).  Autocorrelation infrasound interferometry on Mars. Geophysical Research Letters. https://doi.org/10.1029/2021GL096225

How to cite: Ortiz, H. D. and Matoza, R. S.: Autocorrelation infrasound interferometry for atmospheric sensing on Earth and Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8654, https://doi.org/10.5194/egusphere-egu23-8654, 2023.

EGU23-9477 | ECS | Orals | SM3.1

Turning standalone seismometers into strainmeters using tidal strain and ambient noise ‒ a feasibility study 

Jozef Müller, Tom Eulenfeld, and Ulrich Wegler

Solid Earth is subjected to nanostrain tidal deformations caused by gravitational attraction of the Moon and Sun. This causes periodic deformations of imperceptible fractures in the shallow rock that likely result into subtle variations of seismic velocities. It is possible to theoretically model the gravitational tidal deformations while the seismic velocities can be estimated, e.g., using ambient noise recordings processed with passive image interferometry. Combining these two pieces of information could allow for in-situ assessment of bedrock properties beneath seismic stations. In this study, we tried to accomplish this task using 18 standalone seismic stations (i.e., no array) from a network of the Integrated Plate Boundary Observatory Chile, complemented by several others in Europe and North America. The velocity changes were mostly estimated for frequencies of 1-4 and 4-7 Hz, using hourly Green's functions acquired after temporal stacking. Analysed coda lapse time windows of the Green's functions were 1-6, 5-10 and 8-13 seconds. Tide-related velocity changes were observed (mostly the M2 component). However, our results show that observability of such tide-related velocity variations seems to be strongly related to the station proximity to oceanic coastlines. This raises reasonable doubt about the required solid Earth tides origin of the observed tidal signals.

How to cite: Müller, J., Eulenfeld, T., and Wegler, U.: Turning standalone seismometers into strainmeters using tidal strain and ambient noise ‒ a feasibility study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9477, https://doi.org/10.5194/egusphere-egu23-9477, 2023.

EGU23-10372 | ECS | Posters on site | SM3.1

Exploring the feasibility of seismic monitoring using ambient noise coda Q: Experiments in the Aegean (Greece) 

Pratul Ranjan, Laurent Stehly, and Estelle Delouche

Ambient noise cross-correlations or auto-correlations provide near real-time information about subsurface properties. Changes in the Green’s function obtained from auto-correlations/cross-correlations inform us about velocity changes in the medium (dv/v). Numerous studies have found good correlation between dv/v and medium changes related to a large earthquake, volcanic activity, or even seasonal changes at shallow depths. Another seismic parameter which helps estimate such medium changes is the rate of decay of coda waves or the coda Quality factor (Qc). Low Qc estimates from earthquake data has been shown to represent cracks/fracture as well as fluid migration. Application of ambient noise data for Qc estimation are relatively recent (past 5 years), especially in the Alps and Japan, where good correlation was found with the regional geology. Qc measurements using ambient noise data can ensure continuous monitoring unlike those from earthquakes. In this work, we evaluate the feasibility of monitoring medium changes with Qc by using ambient noise data from Greece. We perform autocorrelation of noise data from the permanent network in Greece over a period of 2010-2021. Preliminary analysis shows a seasonal pattern in Qc at several stations when considering short period bands, which is likely related to seasonal changes at shallow depths due to precipitation. Stations with clear seasonal pattern in the dv/v are correlated with the seasonal pattern in Qc, which confirms that Qc perturbations indeed represent physical changes. Stations which show weak seasonality in dv/v have a seasonality pattern in Qc with a lag of similar number of days. These results suggest than Qc based monitoring has the potential to act as a supplementary data set to dv/v and may even provide more information about the nature of medium change based on whether Qc is related to scattering or intrinsic attenuation.

 

How to cite: Ranjan, P., Stehly, L., and Delouche, E.: Exploring the feasibility of seismic monitoring using ambient noise coda Q: Experiments in the Aegean (Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10372, https://doi.org/10.5194/egusphere-egu23-10372, 2023.

EGU23-10612 | ECS | Posters on site | SM3.1

Detecting seismic velocity change by noise-based direct surface wave 

Zhiqiang Liu

Recently, advances in the ambient noise analysis provide new ways to detect the velocity changes in the volcanic region by measuring the time delay of the daily cross-correlation functions (CCFs). Despite abundant studies on coda waves, studies examining the direct surface waves are relatively rare because of the influence of passive noise sources. However, direct surface waves have stronger energy and carry depth information, which can be obtained by the dispersion inversion. The direct surface waves' propagation direction along the great circle path is also beneficial for conducting tomography by finding a stable passive noise source, which is key to extracting depth-dependent velocity changes. Here, we used direct surface wave to detect velocity change caused by 2018 KIlauea volcano eruption and 2019 Ridgecrest earthquake. The results show that the noise-based direct surface wave is a powerful tool to study the change of earth medium caused by geological hazards, and can accurately obtain the information of the lateral position and depth position of the change.

 

How to cite: Liu, Z.: Detecting seismic velocity change by noise-based direct surface wave, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10612, https://doi.org/10.5194/egusphere-egu23-10612, 2023.

Surface wave dispersion curves derived from ambient noise recordings are frequently used to invert for subsurface velocity information. Rayleigh wave ellipticities and phase velocities are exploited, and sometimes jointly inverted, for the velocity structure beneath seismic arrays. Wavelengths of surface waves become large at low frequencies and are, thus, sensitive to great depths, but provide only very smooth velocity profiles. However, sudden velocity increases in the subsurface are of particular interest to delineate the extent of reservoirs, i.e., by sub-horizontal faults or detachments, or estimate the depth of sedimentary basins.

Here, we report a new approach to estimate sudden velocity increases in vertical velocity profiles using Rayleigh wave ellipticities and phase velocities. Using Kepler’s law of motion on elliptical orbits, we can theoretically delineate the frequency-dependent half-height and half-width of the energy ellipse described by Rayleigh waves.

In the presence of sudden velocity increases, fundamental and first higher mode Rayleigh waves have similar phase velocities at the so-called osculation frequency. This often leads to mode misidentification that biases inversion results. We show that this osculation frequency is close to the frequency where the Rayleigh ellipticity of the fundamental mode is one, i.e., motion is circular, and the ellipticity of the first higher mode has its maximum. At this frequency, our derived relation only requires the phase velocity of the first higher mode to estimate the half-height of the ellipse, which is a very good approximation of the depth of the sudden velocity increase.

To derive phase velocities and ellipticities of Rayleigh waves for synthetic three-component waveforms and real-world datasets from three sites (Weisweiler in Germany, FORGE in Utah, USA and Groningen, the Netherlands), we use three-component beamforming, which provides velocity and polarization parameters of recorded waves in short ambient noise time windows and thus can distinguish wave types and modes. From identified Rayleigh waves, we pick the phase velocity of the first higher mode at the osculation frequency directly in the beamformer plots and estimate the depth of sudden velocity increases using our new relation. No inversion scheme is needed for this approach.

This approach provides more accurate depth estimates of velocity jumps than other ambient noise methods. The depth sensitivity is only limited by the inter-station distances in the array configuration and the useable frequency range. The derived depths of sudden velocity increases can be used to constrain inversion schemes for more accurate velocity models or can be used directly to map structural changes in the subsurface.

How to cite: Finger, C. and Löer, K.: Depth of sudden velocity increases from multi-mode Rayleigh waves derived with three-component ambient noise beamforming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12396, https://doi.org/10.5194/egusphere-egu23-12396, 2023.

EGU23-13055 | ECS | Orals | SM3.1

Seasonal velocity variations in Greece associated with aquifers 

Estelle Delouche and Laurent Stehly

Velocity variations related to water movements in aquifers are relatively unknown, thus, we propose to study the temporal changes of velocity variations of several aquifers in Greece. To this end, the stretching method is applied to the early coda of the autocorrelation functions of 90 permanent stations. These results, complemented by GPS and precipitation studies, indicate that the record of seasonal variations on seismic velocities may originate from two mechanisms: 1) a natural mechanism associated with the filling of the aquifer by precipitation and 2) an anthropogenic mechanism related to groundwater pumping.

Between 1-3s of period, velocity variations can either vary as a function of water supply to the aquifer: increased water leads to a decrease in wave velocity; or record contraction/relaxation of the rocks beneath the aquifer that vary as a function of its recharge.

 

Thus, the investigation conducted in this study allows us to explain all the seasonal variations observed on the dv/vs in Greece between 1-3s of period.

 

 

How to cite: Delouche, E. and Stehly, L.: Seasonal velocity variations in Greece associated with aquifers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13055, https://doi.org/10.5194/egusphere-egu23-13055, 2023.

EGU23-13164 | ECS | Posters on site | SM3.1

Temporal changes in velocity and scattering properties in the Sichuan region, China 

Jinwu Li, Anne Obermann, Sin-mei Wu, Pilar Sánchez-Pastor, and Xiaodong Song

The 2008 M7.9 Wenchuan Earthquake is the most devastating event in the last two decades in China. Here, we analyze 8 years (2007–2014) of seismic records to track the normal background level of the media properties, as well as the transient changes associated with tectonic activities (e.g., earthquakes). Understanding the long-term background pattern contributes to identifying transient changes. Temporal velocity variations of the surface waves show clear seasonal fluctuations and a co-seismic velocity drop after the Wenchuan mainshock in the 2-10 s period band. A comparison with meteoric data allows us to conclude that the main mechanism of the seasonal variation is the loading due to precipitation. The seasonal velocity changes exhibit spatial characteristics, where the amplitudes of the seasonal velocity changes are larger in the Tibet Plateau and smaller in the Sichuan basin. The spatial pattern is consistent with that of the tectonic deformation. The deformation is strong in the Tibet Plateau, while the Sichuan basin is relatively stable. Furthermore, there is a higher density of cracks in the Tibet Plateau than that in the basin.

Moreover, we increased the time resolution of the noise cross-correlations to twenty days to investigate changes in media associated with the 2008 mainshock by analyzing 1.5 years of data from mid 2007 to 2008 for the surface wave at 2-10 s period band. Compared with the waveforms from seismically quiet time, we observe that the waveform similarity of surface waves decreased significantly about 10 days prior to the mainshock and persisted low until the end of September 2008. To exclude that our observation is related to a changing source pattern, we analyzed the seismic activity in the Sichuan region and the frequency spectrum of the ambient noise field in the corresponding time. Our results suggest that the decorrelation may indeed indicate a regional change in the scattering properties starting 10 days prior to the Wenchuan earthquake.

How to cite: Li, J., Obermann, A., Wu, S., Sánchez-Pastor, P., and Song, X.: Temporal changes in velocity and scattering properties in the Sichuan region, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13164, https://doi.org/10.5194/egusphere-egu23-13164, 2023.

EGU23-14308 | ECS | Orals | SM3.1

Seismic velocity changes in response to snow loading at Mount Ruapehu volcano, New Zealand, using passive seismic interferometry 

Alexander Yates, Corentin Caudron, Philippe Lesage, Aurélien Mordret, and Virginie Pinel

Passive seismic interferometry has become a popular technique for monitoring volcanoes over the past two decades. Despite this, volcanoes still represent challenging locations to apply the methodology due to the presence of volcano seismicity. Volcanic tremor, in particular, can significantly alter the character of cross-correlation functions. This leads to the possibility of mis-interpreting changes in phase or waveform shape as due to real subsurface processes.

Mount Ruapehu is one such volcano where volcanic tremor is regularly recorded above 1 Hz. Thus, a previous study applying passive interferometry at the volcano during its most recent eruptive period (2006–07) focused on lower frequencies to reduce the risk of contamination. In this work, we target the higher frequencies that include volcanic tremor (1–4 Hz) during approximately the same period (2005–2009), thus providing an opportunity to monitor changes at shallower depths within the volcanic system. To assess the suitability of the tremor as a repeatable seismic source, we first apply an unsupervised machine learning technique in the form of agglomerative hierarchical clustering of cross-correlation functions. Doing so allows us to form groups of data that share similar characteristics and, unlike commonly used similarity measures, does not require a defined reference period. Through this, we find that cross-correlation functions at higher frequencies are both relatively consistent in time and dominated by seasonal processes (with alternating summer and winter clusters clearly identified).

Applying the wavelet method to compute travel-time changes in the time-frequency domain reveals snow loading to be the most likely process influencing seismic velocities on the volcano. Amplitudes of +/- 0.5% are recorded at the seismic station closest to the summit, with peak velocites occurring at the same time as maximum snow thickness. In contrast, the seasonal trends recorded at seismic stations with minimal snow cover are of lower amplitude (+/- 0.1%), opposite in sign, and are best fit using a model based on fluid pressure changes in response to precipitation. No obvious short-term changes are detected prior to phreatic eruptions in 2006 and 2007. It is of interest, however, that both eruptions occur approximately one year apart following the initial decrease of velocities in response to snow unloading/melt, suggesting a causal relationship may exist.

How to cite: Yates, A., Caudron, C., Lesage, P., Mordret, A., and Pinel, V.: Seismic velocity changes in response to snow loading at Mount Ruapehu volcano, New Zealand, using passive seismic interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14308, https://doi.org/10.5194/egusphere-egu23-14308, 2023.

EGU23-14933 | ECS | Posters on site | SM3.1

Pocket beach management: the use of ambient noise to estimate beach sedimentary thickness 

Peter Iregbeyen, Sebastiano D'Amico, Luciano Galone, and Emanuele Colica

Pocket beaches, otherwise known as embayed beaches are beaches whose existence are traceable to human activity or natural occurrence. These beaches are found to be confined within the base of geological structures or artificially designed set up such as groin, hence, pocket beaches are always subject to various attacks via anthropogenic or natural forces. These attacks in many cases reflects in the thickness of the beach sediments and therefore determine the extent to which it can survive when hit by unfriendly environmental impact. Estimation of the sedimentary thickness of the beach is a vital tool in a successful geomorphological investigation geared towards the effective execution of coastal area management. This study aims to estimate the sedimentary thickness in several pocket beaches located in Malta using the passive seismic survey method of Horizontal-to-Vertical spectral ratio (H/V). This geophysical survey method employs seismic noise to estimate the depth or thickness of a sedimentary layer over a bedrock with higher shear wave velocity.  Although in recent years, this methodology has increased in popularity in geological investigations, however, there are few examples of the application of this approach to marine sandy beaches in the scientific literature, making this study a novel contribution to the field. The results of the study revealed clear H/V peaks on the beaches studied, with frequency variations corresponding to the expected sediment thickness variations. The latter was also computed by modelling of the H/V curves as well as the use of known data. The application of the H/V technique to the Maltese pocket beach system has demonstrated its effectiveness in providing valuable information for the effective use in the management of the coastal environments. This study has been supported by the SIPOBED project financed by the Malta Council of Science and Technology (MCST) - Space Reearch Funds

 

How to cite: Iregbeyen, P., D'Amico, S., Galone, L., and Colica, E.: Pocket beach management: the use of ambient noise to estimate beach sedimentary thickness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14933, https://doi.org/10.5194/egusphere-egu23-14933, 2023.

EGU23-15580 | ECS | Orals | SM3.1

Temperature-induced disturbances of the stress-strain equilibrium and their effects on seismic velocities 

Eldert Fokker, Elmer Ruigrok, and Jeannot Trampert

Subsurface temperature measurements are key to optimizing geothermal power plants and monitoring heat-storage systems. Previous studies showed that time-lapse variations in temperature can be correlated to variations in seismic velocity. Therefore, temperature monitoring through seismic velocity changes should be feasible. In this study, we provide a physical background for the correlation between temperature and seismic velocity changes. We model how temperature changes can disturb the equilibrium between stress and strain, and for specific boundary conditions, we can make a connection to changes in seismic velocity. Ultimately, we can construct a physics-based model of seismic velocity changes due to temperature variations.

How to cite: Fokker, E., Ruigrok, E., and Trampert, J.: Temperature-induced disturbances of the stress-strain equilibrium and their effects on seismic velocities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15580, https://doi.org/10.5194/egusphere-egu23-15580, 2023.

EGU23-16780 | ECS | Posters on site | SM3.1

Multimodal surface waves during energetic typhoons 

Xuping Feng and Xiaofei Chen

Ambient noise tomography is a revolutionary technique in past twenty years, and has many far-reaching applications from exploration, regional and continental to global scales. Recently, surface wave overtones have been efficiently extracted from ambient noise cross-correlations by the frequency-Bessel (F-J) transform method. The excitations of overtones from noise cross-correlations, however, have not be investigated well. Here we collect 16-day continuous seismic data recorded by a seismic array installed in Mongolia during two super typhoons in 2011. Utilizing the F-J transform, we extract daily multimodal dispersion curves with high signal-to-noise ratios from vertical-vertical (Z-Z) component cross-correlations and transverse-transverse (T-T) component cross-correlations. For both the fundamental mode and overtones, our results show that the cross-coefficients between the wind speeds and the Z-Z dispersion amplitudes over 0.1Hz are over 0.6 in typhoon track regions, which suggests that these two typhoons excite Rayleigh waves over 0.1Hz.  For T-T surface waves, however, typhoons only excite the fundament mode over 0.1Hz, and overtones do not relate to typhoons. Our results indicate that energetic typhoons can efficiently excite multimodal Rayleigh waves while Love waves during this period may not come from the microseisms excited by typhoons, which may help us to deepen our understanding of the coupling system among the atmosphere, oceans and the solid earth.

How to cite: Feng, X. and Chen, X.: Multimodal surface waves during energetic typhoons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16780, https://doi.org/10.5194/egusphere-egu23-16780, 2023.

EGU23-852 | ECS | Posters virtual | NH4.1

A suitable time-dependent conditional probability for Pacific strong earthquakes 

Cristiano Fidani

Statistical analyses of NOAA POES data have recently evidenced electron burst losses 1.5-3.5 h before strong earthquakes in the West Pacific and 55-59 h before strong earthquakes in East Pacific. The conditional probability of a strong seismic event after an ionospheric loss event was calculated depicting possible scenarios in both areas. It presented a geohazard risk reduction initiative that can gain valuable preparation time by adopting a probabilistic short-term warning a few hours prior, especially for tsunamis in those dangerous areas. As electron losses were detected in the same region both for West and East Pacific earthquakes, the probability of a strong event in the West Pacific would be first considered and vanish in less than 4 h. Then, after considering the seismic activity, a statistical evaluation of a disastrous event for the East Pacific coast is generated, so defining a time-dependent increase in conditional probability.

How to cite: Fidani, C.: A suitable time-dependent conditional probability for Pacific strong earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-852, https://doi.org/10.5194/egusphere-egu23-852, 2023.

EGU23-1592 | Posters virtual | NH4.1 | Highlight

Lower  Ionospheric  variation over Europe during the  tectonic activity in the area of Thessaly, Greece on March of 2021. 

Michael E. Contadakis, Demeter N. Arabelos, Pikridas Christos, Stylianos Bitharis, and Emmanuel Scordilis

This is one of a series of papers in which  we investigate the Lower ionospheric variation on the occasion of intense tectonic activity.In the present paper, we investigate the TEC variations during the intense seismic activity in Thessaly, on March 2021 over Europe. The Total Electron Content (TEC) data are been provided by the  Hermes GNSS Network managed by GNSS_QC, AUTH Greece, the HxGN/SmartNet-Greece of Metrica S.A, and the EUREF Network. These data were analysed using Discrete Fourier Analysis in order to investigate the TEC turbulence. The results of this investigation indicate that the High-Frequency limit fo of the ionospheric turbulence content, increases as aproaching the occurrence time of the earthquake, pointing to the earthquake epicenter, in accordane to our previous investigations. We conclude that the Lithosphere Atmosphere Ionosphere Coupling, LAIC, mechanism through acoustic or gravity waves could explain this phenomenology.

 

Keywords: Seismicity, Lower Ionosphere, Ionospheric Turbulence, Brownian Walk, Aegean area.

How to cite: Contadakis, M. E., Arabelos, D. N., Christos, P., Bitharis, S., and Scordilis, E.: Lower  Ionospheric  variation over Europe during the  tectonic activity in the area of Thessaly, Greece on March of 2021., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1592, https://doi.org/10.5194/egusphere-egu23-1592, 2023.

EGU23-2087 | Orals | NH4.1

Double resonance before earthquakes 

Chieh-Hung Chen, Kai Lin, Xuemin Zhang, and Yongxin Gao

An instrumental array was established in southwest China for Monitoring Vibrations and Perturbations in the Lithosphere, Atmosphere and Ionosphere (MVP-LAI).  We retrieved multiple-geophysical data from the array to investigate common characteristics in LAI before earthquakes.  Broadband seismometers are utilized to monitor ground vibrations in the lithosphere.  Barometers record changes in air pressure near the Earth’s surface.  Magnetometers monitor variations in the ionospheric currents ~100 km above the Earth’s surface.  Instead of GPSTEC (Global Positioning System Total Electron Content), electromagnetic signals transmitted from the BDS (BeiDou navigation system) geostationary satellites are received by ground-based GNSS (Global Navigation Satellite System) receivers to compute TEC data.  The BDSTEC from the geostationary satellites continuously monitor changes in TECs ~350 km in altitude right over the array.  We transferred these data into the frequency domain and found that ground vibrations, air pressure, the magnetic field, and BDSTEC data share the frequency ~5×10-3 Hz before major earthquakes.  Ground vibrations exhibit frequency characteristics of ~5×10-3 Hz due to resonance of nature frequencies before failure of materials (i.e., dislocations of faults, and earthquakes).  Ground vibrations with frequency of ~5×10-3 Hz persistently hit the bottom of the atmosphere that can trigger atmospheric resonance before earthquakes.  Double resonance (i.e., crustal and atmospheric resonance) provides the new way to reveal the seismo-anomalies of multiple geophysical parameters in LAI.  Double resonance would shed a light in earthquake prediction in practice once we face the major issue for efficiently retrieving resonance signals from multiple observation data. 

 

How to cite: Chen, C.-H., Lin, K., Zhang, X., and Gao, Y.: Double resonance before earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2087, https://doi.org/10.5194/egusphere-egu23-2087, 2023.

EGU23-2126 | Posters virtual | NH4.1

New features of the ELSEM-Net electromagnetic monitoring stations network and analysis of recent data associated with strong earthquakes. 

Dimitrios Z. Politis, Stelios M. Potirakis, Philopimin Malkotsis, Nikolaos Papadopoulos, Dionysios Dimakos, Michael Exarchos, Efstratios Liadopoulos, Yiannis F. Contoyiannis, Angelos Charitopoulos, Kyriakos Kontakos, Dimitrios Doukakis, Grigorios Koulouras, Nikolaos Melis, and Konstantinos Eftaxias

The ELSEM-Net (hELlenic Seismo-ElectroMagnetics Network, http://elsem-net.uniwa.gr) is a telemetric network of ground-based monitoring stations for the study of fracture-induced electromagnetic emissions. It comprises 11 telemetric stations, spanning all over Greece, and has continuously been operated for almost 30 years. In this paper we present the new, custom designed, instrumentation of the telemetric stations. Specifically, we present both the hardware and the firmware/software used, from antennae to data acquisition and data management. Finally, we present recent recordings prior to significant strong earthquakes (EQs) that have happened in Greece, as well as the obtained analysis results, using nonlinear time series analysis methods, indicating that the acquired signals embed important features associated with the impending EQ.

How to cite: Politis, D. Z., Potirakis, S. M., Malkotsis, P., Papadopoulos, N., Dimakos, D., Exarchos, M., Liadopoulos, E., Contoyiannis, Y. F., Charitopoulos, A., Kontakos, K., Doukakis, D., Koulouras, G., Melis, N., and Eftaxias, K.: New features of the ELSEM-Net electromagnetic monitoring stations network and analysis of recent data associated with strong earthquakes., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2126, https://doi.org/10.5194/egusphere-egu23-2126, 2023.

EGU23-2187 | ECS | Orals | NH4.1

Possible Lithosphere Atmosphere Ionosphere Coupling before 19 September 2021 La Palma volcano eruption 

Dedalo Marchetti, Hanshuo Zhang, Kaiguang Zhu, Zeren Zhima, Rui Yan, Xuhui Shen, Alessandro Piscini, Wenqi Chen, Yuqi Cheng, Xiaodan He, Ting Wang, Jiami Wen, Donghua Zhang, and Yiqun Zhang

On 19 September 2021, La Palma Volcano started a VEI 3 eruption. Here we will illustrate an investigation for at least six months before the eruption with the aim of searching possible lithosphere atmosphere and ionosphere couplings.

We identify and compare the anomalies from the seismic catalogue, the geomagnetic ground observatories, the atmospheric climatological datasets, TEC maps, CSES and Swarm satellites data with respect to the volcano location and the time cumulative trends of anomalies are analyzed.

We identify a temporal migration of the seismicity from one year before the eruption at a depth of 40 km possibly associated with magma migration, firstly to a deep chamber (20-13km depth) and in the last 10 days in a shallower magma chamber. CSES-01 detects an increase in electron density at the same time as vertical ground magnetic field anomalies, very likely due to the magma uprising. A final increase of carbon monoxide 1.5 months before the eruption with unusually high values of TEC suggests the degassing of magma before the eruption associated with shallow seismicity that preceded the eruption by ten days. We identify possible different coupling mechanisms, e.g., chain of mechanical, thermal, chemical and electromagnetic phenomena, or pure electromagnetic coupling). These different lithosphere-atmosphere-ionosphere coupling mechanisms can coexist.

Our results highlight the importance of integrating several observation platforms and datasets from the ground and space (earth observation satellites) to better understand the dynamics of the processes and associated natural hazards affecting our planet.

How to cite: Marchetti, D., Zhang, H., Zhu, K., Zhima, Z., Yan, R., Shen, X., Piscini, A., Chen, W., Cheng, Y., He, X., Wang, T., Wen, J., Zhang, D., and Zhang, Y.: Possible Lithosphere Atmosphere Ionosphere Coupling before 19 September 2021 La Palma volcano eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2187, https://doi.org/10.5194/egusphere-egu23-2187, 2023.

EGU23-3596 | ECS | Orals | NH4.1

Water chemical composition as indicator of geodynamic activity 

Armen Kazarian and Aik Kazarian

WATER’S GEOCHEMICAL COMPOSITION AS INDICATOR OF GEODYNAMIC ACTIVITY 

A.Kazarian, H. Kazarian IGN AN NAN

 

A detailed analysis of a long-term collection of hydro-geochemical data was carried out over a ten-year period. It revealed consistent iterations of signs of a process of earthquake preparation in this region. This preparation process has several distinct stages, which can be identified by noticeable changes in the geochemical composition of self-pouring well water. The earthquake preparation process is graphically visible and has a similar duration to the post-earthquake aftershock activity duration. The visualization of hydro-geochemical data from the pre- and post-earthquake periods for different (M> 6) earthquakes in this region shows a very similar pattern of behaviors and duration of behaviors for events of varying magnitudes and distances from the observation wells.

Changes in the main fluctuation trend of the geochemical data for helium (He) and a decrease in the standard deviation of the series for other main components appear as earthquake precursors (Na, K, HCO3, SO4, Cl, Ca, F). The detectable duration of a main shock's preparation process is approximately a year. The detailed examination of the data time series reveals a strong correlation between the overall geodynamic activity of the region and the hydrogeochemical composition of the observed wells.

The detailed analysis of earthquake activity in the region suggests a periodic nature of basic seismicity and its relationship with earthquake focal mechanisms. The obtained daily histograms for seismic activity in Armenia, Turkey, Greece, and Italy regions calculated by local time show cyclical activity patterns of 24 and 12 hours. This is consistent with variations in He and other important components in the well waters. The hypothesis and conclusion of this scientific research project are that in seismically active zones, the dynamics of hidden active tectonic processes can potentially be a priori diagnosed using this hydro-geochemical monitoring method.

How to cite: Kazarian, A. and Kazarian, A.: Water chemical composition as indicator of geodynamic activity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3596, https://doi.org/10.5194/egusphere-egu23-3596, 2023.

EGU23-3854 | Posters virtual | NH4.1

Comparison of the precursory effects in lithosphere, atmosphere and ionosphere of three large earthquakes with comparable magnitude: the cases of 2019 Kermadec Islands (NZ) and Ridgecrest (USA) earthquakes and 2021 Maduo (China) earthquake 

Angelo De Santis, Saioa A. Campuzano, Massimo Calcara, Gianfranco Cianchini, Serena D'Arcangelo, Mariagrazia De Caro, Domenico Di Mauro, Cristiano Fidani, Adriano Nardi, Martina Orlando, Loredana Perrone, Alessandro Piscini, Dario Sabbagh, and Maurizio Soldani

Three earthquakes of comparable magnitude and in different tectonic contexts occurred on 15 June 2019 (M7.2) in New Zealand (Kermadec Islands), on 6 July 2019 (M7.1) in California (Ridgecrest) and on 21 May 2021 (M7.3) in China (Maduo) (dates in UT). We applied a multiparameter - multilayer approach to lithospheric, atmospheric and ionospheric data, the latter taken from CSES  and Swarm satellites, before the mentioned large earthquakes to detect potential pre-earthquake anomalies. In all case studies, we note the following: a) similar precursor times of occurrences, confirming the Rikitake law for which the larger the earthquake magnitude the longer the anticipation time of the precursor and b) a clear acceleration of the possible precursory anomalies before each mainshock, as typical of critical systems approaching a critical state. We propose an interpretative model to take into account the chain of detected phenomena.

How to cite: De Santis, A., Campuzano, S. A., Calcara, M., Cianchini, G., D'Arcangelo, S., De Caro, M., Di Mauro, D., Fidani, C., Nardi, A., Orlando, M., Perrone, L., Piscini, A., Sabbagh, D., and Soldani, M.: Comparison of the precursory effects in lithosphere, atmosphere and ionosphere of three large earthquakes with comparable magnitude: the cases of 2019 Kermadec Islands (NZ) and Ridgecrest (USA) earthquakes and 2021 Maduo (China) earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3854, https://doi.org/10.5194/egusphere-egu23-3854, 2023.

EGU23-4399 | Orals | NH4.1 | Highlight

Transient effects in the atmosphere/ionosphere and their re-occurrence before large earthquakes. Case study for the 2022 “anniversary” events. 

Dimitar Ouzounov, Sergey Pulients, Jann-Yenq Liu, Katsumi Hattori, Menas Kafatos, and Patrick Taylor

We present a study on temporal and spatial characteristics of Thermal Radiation anomalies (TRA) and ionospheric total electron content (TEC) pre-earthquake abnormalities associated with the occurred in 2022 “anniversary” earthquakes. “Anniversary”  is a quake occurring on the same date and following the years after the main earthquake, plus or minus several days.

We studied eleven large earthquakes in four regions: i/Japan: M7.3 of 03.16.2022 and M9.0 of 03.11.2011 East Coast Honshu; ii/Mexico: M7.6 of 09.19.2022 Michoacan; M7.1 of 09.19.2017 Puebla and M8.0 of 09.19.1985 Mexico City;/iii Chile: M5.7 02.28.2022 Bio-Bio and M8.8 02.27.2010 Maule and /iv Taiwan: M6.9 of 09.18.2022 Taitung and M7.7 of 09.21.1999 Chi-Chil and M6.7 of 03.22.2022 Taitung and M6 of 03.27.2013 Nantou earthquake.

We analyzed for TRA and TEC anomalies concerning the earthquake preparation zone (EPZ). For EPZ estimates, we use Dobrovolsky et al. (1979), and Bowman et al. (1998) estimates where the EPZ radius scales exponentially with earthquake magnitude, especially from Mw ≥ 6.0 onwards, and gives an extended coverage at larger magnitudes to examine TRA and ionospheric TEC anomalies. The main goals of this study were: 1/to understand the seismotectonic conditions that preceded the earthquake re-occurrence in the same place and on the same day(s): 2/ to perform a validation study about pre-earthquake signal occurrences in the same atmospheric and solar-geophysical conditions and 3/ to understand the potential triggering mechanism. Our preliminary results show synergetic coordination between the appearance of pre-earthquake transients’ effects in the atmosphere and ionosphere (with a short time lag, from hours up to a few days). The spatial characteristics of pre-earthquake anomalies were associated with the large area but inside the preparation region estimated by Dobrovolsky-Bowman. The pre-earthquake nature of the signals in the atmosphere and ionosphere was revealed by simultaneous analysis of satellite, GPS/TEC, and Satellite Earth observations. The “anniversary” events are recognized with common pre-earthquake transient re-occurrence patterns in the atmosphere/ionosphere within EPZ, scaled to the extent of the earthquake magnitude.

How to cite: Ouzounov, D., Pulients, S., Liu, J.-Y., Hattori, K., Kafatos, M., and Taylor, P.: Transient effects in the atmosphere/ionosphere and their re-occurrence before large earthquakes. Case study for the 2022 “anniversary” events., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4399, https://doi.org/10.5194/egusphere-egu23-4399, 2023.

EGU23-5813 | Posters virtual | NH4.1

Mammal abundance varies with geochemical specialisation in the underlying rock formations. 

Rachel Grant, Alexander Shitov, and Andrey V. Karanin

There has been little research on how the composition of underlying rock formation affects animal species’ distribution and abundance. The subject is worthy of consideration as, for example,  it has been shown that ultrabasic and serpentine rocks in particular can give rise to plant biodiversity hotspots with a high level of endemism. Corresponding studies of fauna are lacking. We aim to test the hypothesis that rock type affects mammal abundance and biodiversity.

Here we present a comparative analysis of the abundance of mammals and its relationship with geological composition in the area of Gorny Altai, a mountainous region in Russia.

We used GIS approaches to map the influence of rock types on mammal abundance, while holding other factors such as soil type, relief, etc. constant. The study reveals significant correlations between underlying geology and variation in mammal distribution even when other factors such as soil type, climate and vegetation are held constant.

Intrusive rocks were found to have the greatest impact on variation in mammal distribution whereas sedimentary and metamorphic rocks have almost no effect. A characteristic feature of magmatic formations is their clear geochemical specialization, i.e. certain geochemical anomalies (Fe, Cu, Au, Hg, Ag, etc.) are confined to intrusions. We suggest that geophysical fields (magnetic and electric fields) and geochemical anomalies associated with intrusive rocks may have an impact on the distribution and species composition of mammals, as well as geodynamic processes such as fault activity. This finding has implications for further research into the phenomenon of animals’ anticipatory responses to earthquakes. 

How to cite: Grant, R., Shitov, A., and Karanin, A. V.: Mammal abundance varies with geochemical specialisation in the underlying rock formations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5813, https://doi.org/10.5194/egusphere-egu23-5813, 2023.

EGU23-8521 | Orals | NH4.1

Sub-ionospheric VLF/LF waveguide variations related to magnitude M>5 earthquakes in the eastern Mediterranean area 

Hans Eichelberger, Mohammed Y. Boudjada, Konrad Schwingenschuh, Bruno P. Besser, Daniel Wolbang, Maria Solovieva, Pier F. Biagi, Patrick Galopeau, Ghulam Jaffer, Özer Aydogar, Christoph Schirninger, Cosima Muck, Irmgard Jernej, and Werner Magnes

In this study we examine earthquakes with magnitude M>5 in the year 2022 where the epicenters are crossed by sub-ionospheric narrowband VLF/LF radio links. The study regions are Italy, Aegean area, and the Balkan Peninsula. Ideal suited for this task are paths from the transmitters TBB (26.70 kHz, Bafa, Turkey), ITS (45.90 kHz, Niscemi, Sicily, Italy), and ICV (20.27 kHz, Tavolara, Italy) to the seismo-electromagnetic receiver facility GRZ (Graz, Austria). The receiver is part of a wider network, this gives the opportunity to have multiple simultaneous crossings of an earthquake event.

We investigate electric field amplitude variations in the time span a few days around the main shock, in particular we apply the so-called night-time amplitude method. All electric field data sets have 1 sec temporal resolution. A crucial point is a certain threshold magnitude to obtain statistically significant results, but to firm up the results additional complementary investigations are necessary.

In summary, VLF/LF investigations of strong earthquakes show the complex interplay between the lithospheric events and electric field amplitude waveguide variations, multi-parametric observations in a network could be a tool to derive robust results.

How to cite: Eichelberger, H., Boudjada, M. Y., Schwingenschuh, K., Besser, B. P., Wolbang, D., Solovieva, M., Biagi, P. F., Galopeau, P., Jaffer, G., Aydogar, Ö., Schirninger, C., Muck, C., Jernej, I., and Magnes, W.: Sub-ionospheric VLF/LF waveguide variations related to magnitude M>5 earthquakes in the eastern Mediterranean area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8521, https://doi.org/10.5194/egusphere-egu23-8521, 2023.

EGU23-9395 | Orals | NH4.1

VLF transmitter signal variations as detected by Graz facility prior to Croatian earthquakes 

Mohammed Y. Boudjada, Pier F. Biagi, Hans U. Eichelberger, Konrad Schwingenschuh, Patrick H.M. Galopeau, Masashi Hayakawa, Maria Solovieva, Helmut Lammer, Wolfgang Voller, and Bruno Besser

We report on two earthquakes (EQs) that occurred in Croatia at a distance less than 200 km from the Austrian Graz facility (15.46°E, 47.03°N). Those EQs happened on March 22 and December 29, 2020, with magnitudes of Mw5.4 and Mw6.4, respectively. The epicenters were at geographical coordinates (16.02°E, 45.87°N; 16.21°E, 45.42°N) with focuses smaller than 10 km.  Austrian Graz facility leads to detect more than fifteen VLF and LF transmitter signals (Schwingenschuh et al., 2011, Biagi et al., 2019). Transmitter ray paths cross over the EQs epicenters in particular those localised in ICV and ITS (Italy) and TBB (Turkey). We emphasize in our study on the signal fluctuations before/after the sunrise- and sunset-times, or terminator times (TTs). Transmitter amplitude signals exhibit precursor anomalies that related to EQs disturbances occurring particularly at the falling off or the growth of the ionospheric D-layer. Ground-based stations (e.g. Rozhnoi et al., 2009) and satellite observations (e.g. Zhang et al., 2020) have reported such EQs ionospheric disturbances at several occasions.

 

References:

Biagi et al., The INFREP Network: Present Situation and Recent Results, Open J. Earth. Research, 8, 2019. Rozhnoi et al., Anomalies in VLF radio signals prior the Abruzzo earthquake (M=6.3) on 6 April, 2009, Natural Hazards and Earth System Science, 9, 2009. Schwingenschuh et al., The Graz seismo-electromagnetic VLF facility, Nat. Hazards Earth Syst. Sci., 11, 2011. Zhang et al., Multi-experiment observations of ionospheric disturbances as precursory effects of the Indonesian Ms6.9 earthquake on August 05 2018, Remote Sens. J., 12, 2020.

 

How to cite: Boudjada, M. Y., Biagi, P. F., Eichelberger, H. U., Schwingenschuh, K., Galopeau, P. H. M., Hayakawa, M., Solovieva, M., Lammer, H., Voller, W., and Besser, B.: VLF transmitter signal variations as detected by Graz facility prior to Croatian earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9395, https://doi.org/10.5194/egusphere-egu23-9395, 2023.

EGU23-10299 | ECS | Posters virtual | NH4.1

Connectivity of geoelectric network before strong earthquakes 

Hong-Jia Chen and Chien-Chih Chen

Earthquakes are reported to relate to rupture phenomena in complex self-organizing systems. Hence, the earthquake rupture is regarded as a critical point. The preparation process of an earthquake could be considered as the crustal system approaching this critical point. Complex dynamical systems can have critical tipping points at which a sudden shift to a contrasting dynamical regime may occur; in the meantime, the time series of the systems can behave much differently. Although it is extremely challenging to predict such critical points before they are reached, work in different scientific fields is now suggesting the existence of generic early-warning signals that may indicate a wide class of systems if a critical threshold is approaching. Those precursory signals include increasing correlations and variance, varying skewness, and so on. The critical transition of a system includes spatial criticality and temporal criticality. In this study, we attempt to research the spatial and temporal criticality of the crustal system by using the self-potential (SP) signals of the Taiwan Geoelectric Monitoring System (GEMS). The GEMS network consists of 20 SP stations with an interstation distance of 50 km. We calculate the correlations of the daily signals between any two stations, which formed an adjacency matrix. Then, we estimate the connectivity density based on the adjacency matrix and compare the daily connectivity density time series with ML ≥ 5 earthquakes. We would expect to find out high connectivity densities before a strong earthquake. This would mean that earthquake-related telluric currents flow out through the GEMS stations during the earthquake preparation process; hence, the SP signals of most stations would almost be connected. As a result, we might establish an earthquake forecasting technique using the SP data based on the concept of the critical-point theory.

How to cite: Chen, H.-J. and Chen, C.-C.: Connectivity of geoelectric network before strong earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10299, https://doi.org/10.5194/egusphere-egu23-10299, 2023.

The temporal sequences of magnitudes recorded in seismic active zones exhibit complex behavior which is associated with the wide diversity of scales of fractures sizes when an earthquake on the Earth’s crust occurs. Earthquakes can be considered to be nearly, or even critical phenomena exhibiting dynamic phase transitions, where a mainshock is the beginning of a new phase. Near the critical point is where phase transition (order-disorder) occurs, and scaling laws with long-range order correlations are produced, so that the complexity of seismicity allows earthquakes to be characterized by a more diverse and riche phenomenology. In the last years, the ideas linked to nonlinear time series analysis and complex network theory have been related. Among those ideas,  the visibility graph (VG) method has been applied to the study different complex phenomena. One of the characteristics of this method is its ability to capture dynamic properties, such as non-trivial correlations in nonstationary time series, without introducing elaborate algorithms such as detrending. Seismic processes have been of great interest and their complete understanding is still an open problem. In this work we use the VG method to study the temporal correlations in the seismic sequences monitored in three regions of the subduction zone belonging to the Cocos plate. Our analysis allows estimate persistence and the temporal correlations in the seismic activity monitored in Michoacan State, Mexican Flat Slab and Tehuantepec Isthmus, showing differences in all three.

How to cite: Ramírez-Rojas, A. and Flores-Márquez, E. L.: Correlations of the seismic activity monitored in three subduction zones belonging to Cocos plate by using the visibility graph method., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10458, https://doi.org/10.5194/egusphere-egu23-10458, 2023.

EGU23-10627 | ECS | Orals | NH4.1 | Highlight

Conductivity Anomalies before M > 6 Earthquakes in China during 2014 – 2019 

Zhiqiang Mao and Chieh-Hung Chen

The North-South Seismic Belt of China is one of the most active seismic areas on the Chinese continent.  More than ten strong earthquakes (Ms > 6) have occurred in this region since 2010.  However, Earthquake-related conductivity anomalies are rarely reported for those earthquakes.  In this study, 3-component geomagnetic data recorded at sixty geomagnetic stations are selected to compute the Parkinson vectors to monitor the changes of conductivity before and after the earthquakes.  Considering most fluxgate magnetometers have only been installed since 2014, we concentrate on six Ms > 6 earthquakes occurred during 2014–2019.  To mitigate artificial disturbances, low noise data during the 00:00 – 5:00 LT are utilized.  We compute the background distribution and monitoring distribution using the azimuth of the Parkinson vectors at each station within six years (2014 – 2019) and a 15-day moving window, respectively.  The background distribution is subtracted from the monitoring distributions to mitigate the influences of underlying inhomogeneous tectonic structures.  The obtained difference distributions binned by 10° within 400 km from each station are superimposed during 60 days before and after the earthquake to construct integrated maps.  To analyze the potential frequency characteristics, we compute the results from low to high frequency band.  The results show that for four earthquakes, the conductivity anomalies areas appear near the epicenter 10 to 20 days before earthquakes, while the rest two earthquakes have no anomaly.  The conductivity anomalies appear at all study frequency band from 0.0005 Hz to 0.1 Hz, and significantly at 0.001 – 0.005 Hz before earthquakes.  Meanwhile, we find that the lower frequency band corresponds to larger anomalies area.  These results suggest the change of underlying conductivity near the hypocenter is a possible phenomenon for strong earthquakes, and the frequency characteristics of the seismo-conductivity anomaly during the earthquake are helpful to understand the pre-earthquake anomalous phenomena.

How to cite: Mao, Z. and Chen, C.-H.: Conductivity Anomalies before M > 6 Earthquakes in China during 2014 – 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10627, https://doi.org/10.5194/egusphere-egu23-10627, 2023.

EGU23-13172 | Orals | NH4.1

ULF perturbations: modeling Earth-Atmosphere-Ionosphere coupling, signal processing using information entropy, determination of the electric and magnetic field components and “experiment-theory comparison“ 

Yuriy Rapoport, Volodymyr Reshetnyk, Asen Grytsai, Alex Liashchuk, Masashi Hayakawa, Volodymyr Grimalsky, Sergei Petrishchevskii, Andrzej Krankowski, Leszek Błaszkiewicz, Paweł Flisek, Angelo De Santis, and Carlo Scotto

We have used 2014–2017 data from the eight receiving stations of the Japan very low frequency (VLF) monitoring network. The nighttime data of the signals of the JJI transmitter on Kyushu Island, excited VLF electromagnetic waves (EMWs) in the Earth-Ionosphere waveguide (EIWG) had been processed. The wavelet transform with a preliminary detrending, to exclude influence of daily variations, has been applied. We have observed ultra-low frequency (ULF) modulation of VLF EMW spectra in the EIWG. We therefore concluded that modulating oscillations with periods of 4 minutes belong to the acoustic branch of acoustic-gravity waves (AGWs) in the Earth–Thermosphere waveguide; modulation of VLF with periods of 6–7 minutes corresponds to global evanescent/reactive Brunt–Väisälä AGW oscillations; the oscillations with periods 20–60 min and ~3 hours may characterize evanescent/reactive Lamb gravity wave mode of AGW [1]. The appearance of the combination frequency of VLF EMW and ULF AGW is likely due to the following effects: (1) the drag of charged plasma particles by ULF AGWs jointly with the background of VLF electron density disturbances and (2) the motion of charged plasma particles in the VLF EMW field jointly with the background of ULF changes in the plasma concentration caused by AGWs.

The theory [2,3] is extended to the excitation of ionospheric Schumann resonator (SR) [4] and ionospheric Alfvén resonator (IAR) in the ULF range. It is shown that IAR oscillations with a high quality factor (for geophysical resonators) (>10) can be excited in the SR range. The features of the excited ULF and VLF modes associated with the modification of the ionosphere as a result of the powerful eruption of the Hunga-Tonga volcano are under consideration [5,6].

A ULF model of perturbations in the atmosphere-ionosphere with a boundary transition from dynamic to static limit is developed and the preliminary results of the corresponding modelling will be presented. This ensures the "recovery" of magnetostatic disturbances "lost" in most of previous models of the atmospheric electrical circuit, important for understanding the mechanisms of seismo-ionospheric coupling, volcano-ionospheric coupling and influences of the other natural hazards on the ionosphere and ionospheric monitoring of the natural hazards.

[1] Rapoport et al. Sensors 22, 10.3390/s22218191, 2022; [2] Grimalsky et al. JEMAA 2012, 4, 192-198 ; [3] Yutsis V. et al. Atmosphere 2021, 12, 801 ; [4] Nickolaenko and Rabinovich Space Res. 1982, XX, 67-88 ; [5] Astafyeva et al. GRL, 2022 ; [6] D’Arcangelo et al., Rem. Sens., 14, 3649, 2022.

This research was partially funded by the National Science Centre, Poland, grant No. 970 2022/01/3/ST10/00072

How to cite: Rapoport, Y., Reshetnyk, V., Grytsai, A., Liashchuk, A., Hayakawa, M., Grimalsky, V., Petrishchevskii, S., Krankowski, A., Błaszkiewicz, L., Flisek, P., De Santis, A., and Scotto, C.: ULF perturbations: modeling Earth-Atmosphere-Ionosphere coupling, signal processing using information entropy, determination of the electric and magnetic field components and “experiment-theory comparison“, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13172, https://doi.org/10.5194/egusphere-egu23-13172, 2023.

EGU23-13588 | Posters on site | NH4.1 | Highlight

Improving RST-based analysis of long-term TIR satellite observations in relation with earthquake occurrence 

Valerio Tramutoli, Roberto Colonna, Carolina Filizzola, Nicola Genzano, Mariano Lisi, Nicola Pergola, and Valeria Satriano

In order to build and implement a multi-parametric system for a time‐Dependent Assessment of Seismic Hazard (t‐DASH) the preliminary assessment of the selected parameters is required. To this aim a long-term correlation analysis - among anomalous transients and earthquake occurrence – has to be performed to establish the corresponding forecast capability and particularly the expected false-positive rate. In fact, more than the missing rate (i.e. how many earthquakes occurs in absence of specific precursors) the reliability of the forecast is much more important when the continuity of the observations cannot be guaranteed. This is the case of satellite observations in the optical band  whose continuity can be prevented by the presence of meteorological clouds. Among the others candidate parameters anomalous transients in the Earth’s emitted Thermal Radiation observed from meteorological satellites in the Thermal InfaRed band (TIR) have been since long-term proposed in the framework of a multi-parametric t-DASH system. Results achieved by RST (Robust Satellite Technique) analyses of multi-annual (more than 10 years) time series of TIR satellite images in different continents and seismic regimes, allowed to identify (isolating them from all the others possible sources) those anomalies (in the spatial/temporal domain) possibly associated to the occurrence of major earthquakes. Main lesson learnt until now can be summarized as follows:

a) Thanks to a clear definition of (Significant Sequences of TIR Anomalies (SSTAs) and well-defined validation rules, for earthquakes with magnitude greater than 4 the false positive rate is around 25% (average value over Greece, Italy, Japan, Turkey) oscillating from 7% up to 40% strongly depending on the considered region;

b) Molchan error diagram analyses gave a clear indication that a non-casual correlation exist between RST-based SSTAs and earthquake occurrence time and location;

c) SSTAs are quite rare (sporadic) with quite limited (less than 0,05% of the total investigated) alerted space-time volumes;

d) The approach based on the application of the RETIRA index (Robust Estimator of TIR Anomalies) showed some limitation related to the contextual approach that, in order to take into account of possible large scale changes of the thermal background, consider not just the TIR signal itself but its excess respect to the background (large scale spatial average of the TIR signal) introducing, this way, a strong dependence on the presence and distribution of meteorolical cloud across the scene.

In order to overcome the d) issue an alternative possibility has been investigated which can locally filter-out the contributes of occasional warming (typically associated to meteorological fronts) without the need of analyzing the TIR signal at the large-scale. In this paper RST approach is implemented by introducing the RETIRSA (Robust Estimator of TIR Slope Anomalies) devoted to identify anomalous Nocturnal TIR  Gradients in relation with the preparation phases of earthquakes. The impact in reducing the overall false-positive rates will be particularly discussed in the case of recent earthquakes occurred in Italy, Japan and California. 

How to cite: Tramutoli, V., Colonna, R., Filizzola, C., Genzano, N., Lisi, M., Pergola, N., and Satriano, V.: Improving RST-based analysis of long-term TIR satellite observations in relation with earthquake occurrence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13588, https://doi.org/10.5194/egusphere-egu23-13588, 2023.

EGU23-14058 | Posters virtual | NH4.1

Improving the statistical correlations between low seismic events and CO2 variations subtracting the rain contribution 

Lisa Pierotti, Cristiano Fidani, Gianluca Facca, and Fabrizio Gherardi

A correlation between low seismic activity and CO2 measurements variations was observed at the Gallicano thermomineral spring, Tuscany, Italy, where an automatic monitoring multiparametric geochemical station is operative since 2003 (Pierotti et al., 2015). The above-mentioned correlation reported a time delay of about 2 days of small earthquakes with respect to CO2 anomalies. Starting from this correlation a conditional probability of earthquake occurrence given the CO2 anomaly detection was calculated, with a probability gain near 4 (Pierotti et al., 2022).  A statistical correlation was also calculated between rain events and CO2 anomalies which was observed for rain vents ahead CO2 anomalies of one days. This permitted to distinguish CO2 anomalies due to meteorological versus tectonic activities.  Following this distinction, and subtracting the rain contribution to the CO2 variations, a new correlation was observed between small earthquakes and CO2 anomalies which confirmed the past results whit a better performance. The new correlation peak is better defined and concentrated in the time lag of 2 days. The p-values of both earthquake and rain to CO2 correlations were calculated. The correspondent probability gain in an earthquake forecasting experiment, taking into account the rain events, increased from less than 4 to 4.5. 

     

 

Fidani, C. (2021). West Pacific Earthquake Forecasting Using NOAA Electron Bursts With Independent L-Shells and Ground-Based Magnetic Correlations. Front. Earth Sci. 9:673105.

Pierotti, L., Botti, F., D’Intinosante, V., Facca, G., Gherardi, F. (2015). Anomalous CO2 content in the Gallicano thermo-mineral spring (Serchio Valley, Italy) before the 21 June 2013, Alpi Apuane earthquake (M= 5.2). Physics and Chemistry of the Earth, Parts A/B/C, 85, 131-140.

Pierotti, L., Fidani C., Facca, G., Gherardi, F. (2022). Local earthquake conditional probability based on long term CO2 measurements. In 40st GNGTS National Conference, Trieste, 27 - 29 June 2022.

How to cite: Pierotti, L., Fidani, C., Facca, G., and Gherardi, F.: Improving the statistical correlations between low seismic events and CO2 variations subtracting the rain contribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14058, https://doi.org/10.5194/egusphere-egu23-14058, 2023.

EGU23-17023 | Orals | NH4.1 | Highlight

Ionospheric electric fields associated with seismo-ionospheric precursors and ionospheric storms observed by FORMOSAT-5/AIP 

Jann-Yenq Liu, Fu-Yuan Chang, Yuh-Ing Chen, and Chi-Kuang Chao

The mission of Advanced Ionospheric Probe (AIP) onboard FORMOSAT-5 (F5) satellite is to detect seismo-ionospheric precursors (SIPs) and observe ionospheric weathers.  F5/AIP plasma quantities in nighttime of 22:30 LT (local time) and the total electron content (TEC) of the global ionosphere map (GIM) are used to study SIPs of an M7.3 earthquake in the Iran-Iraq Border area on 12 November as well as two positive storms on 7 and 21-22 November 2017.  The TEC and the F5/AIP ion density/temperature anomalously increase over the epicenter area on 3-4 November (day 9-8 before the earthquake) and on the two storm days.  The anomalous TEC increase frequently appearing specifically in a small area near the epicenter day 9-8 before the earthquake indicates the SIP being observed, while those frequently occurring at worldwide high-latitudes are signatures of the two positive storms.  TEC increase anomalies most frequently appearing in the Iran-Iraq Border area on 21-22 November (day 10-9 before) is coincidently followed by an M6.1 earthquake on 1 December 2017, which again meets the temporal SIP characteristic.  The F5/AIP ion velocity uncovers that the SIPs of the two earthquakes are caused by eastward seismo-generated electric fields, and the two positive storms are due to the prompt penetration electric fields.

How to cite: Liu, J.-Y., Chang, F.-Y., Chen, Y.-I., and Chao, C.-K.: Ionospheric electric fields associated with seismo-ionospheric precursors and ionospheric storms observed by FORMOSAT-5/AIP, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17023, https://doi.org/10.5194/egusphere-egu23-17023, 2023.

EGU23-17053 | Posters virtual | NH4.1

Detection of correlated anomalous seismic and geomagnetic precursor signals before Vrancea moderate size earthquakes 

Iren Adelina Moldovan, Victorin Toader, Andrei Mihai, Felix Borleanu, Laura Petrescu, Anica Otilia Placinta, and Liviu Manea

Our study aims to detect anomalous seismic and geomagnetic precursor signals appearing before Vrancea, Romania medium sized earthquakes, that occurred in the last decade (2012-2022), using in the first step the visualization processing method, to identify the time lap between the two anomalies and the following earthquakes. During the study period, in Vrancea seismogenic zone there have been recorded 39 earthquakes with magnitude ML>=4.5, both at normal and intermediate depth. We have assumed that the zone of effective manifestation of the precursor deformations is a circle with the radius taken from the equation of Dobrovolsky, 1979, so the studies were done inside this zone. The Seismic data consists in seismic velocities vp and vs (vp/vs), computed from the arrivals of seismic waves at the NIEP stations situated in the earthquake preparation area. The calculations are done automatically by the Phenomenal platform https://ph.infp.ro/seismicity/data, using the corrected Romanian seismic bulletins. The seismic velocity is the geophysical property that has a key role in characterizing dynamic processes and the state of the stress around the faults, providing significant information regarding the change in tectonic regime. In the crust, velocities change before, during and after earthquakes through several mechanisms related to, for example, fault deformations, pore pressure, changes in stress state (pressure perturbation) and rebound processes.

The Geomagnetic data are obtained from Muntele Rosu (MLR) Seismological Observatory of NIEP, situated inside Vrancea seismogenic zone as primary station, and from Surlari (SUA) Geomagnetic Observatory of Intermagnet, as remote station, unaffected by medium size earthquake preparedness processes. Geomagnetic indices taken from GFZ (https://www.gfz-potsdam.de/kp-index) were used to separate the global magnetic variation from possible local seismo-electromagnetic anomalies, that might appear in a seismic area like Vrancea zone and to ensure that observed geomagnetic fluctuations are not caused by solar-terrestrial effect.

In this presentation we study the appearance of the changes of seismic propagation velocities (vp/vs) in time and the geomagnetic deviations from the normal trend before the occurrence of moderate size crustal and intermediate earthquakes from Vrancea zone, to emphasize the time span between the studied phenomena, in order to be able to find a statistical correlation between them.

Acknowledgements. This work was funded by: PN23 36 02 01/2023 SOL4RISC Nucleu Project, by MCD, Phenomenal Project PN-III-P2-2.1-PED-2019-1693, 480PED/2020 and AFROS Project PN-III-P4-ID-PCE-2020-1361, PCE/2021 supported by UEFISCDI

How to cite: Moldovan, I. A., Toader, V., Mihai, A., Borleanu, F., Petrescu, L., Placinta, A. O., and Manea, L.: Detection of correlated anomalous seismic and geomagnetic precursor signals before Vrancea moderate size earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17053, https://doi.org/10.5194/egusphere-egu23-17053, 2023.

EGU23-17076 | Posters on site | NH4.1 | Highlight

Development of Broadband Interferometer System for Pre-Earthquake Electromagnetic Radiation in LF Band :Design and Performance of Antenna Elements 

Katsumi Hattori, Yu-ichiro Ohta, Chie Yoshino, and Noriyuki Imazumi

Various preseismic electromagnetic variations have been reported so far. Oike et al. reported an increase in the number of electromagnetic pulses in the LF band for the 1995 Kobe Earthquake. However, there is a problem that the electromagnetic pulse due to lightning activity, which is a strong electromagnetic radiation source in the LF band, cannot be sufficiently distinguished from the electromagnetic pulse associated with earthquakes. At that time, it was difficult to observe waveforms with the observation equipment (especially digital measurement units), but with the development of today's ICT equipment and Internet technology, it is possible to realize an LF band broadband interferometer that can estimate the spatio-temporal sources of electromagnetic radiation. If it is an electromagnetic pulse due to lightning activity, the electromagnetic radiation source will move with the front or cloud, and if it is associated with an earthquake, the electromagnetic radiation source will be concentrated near the focal region. In this presentation, we will report the progress of the development of the LF band broadband interferometer, and the waveform analysis and pulse number variation of the nearby earthquake that occurred during the test of the interferometer element.

The developed system is a capacitive circular flat plate fast antenna, consisting of a 500 kHz low-pass filter, a 16bit AD converter, and a PC for data recording, and records 100 ms before and after the pulse waveform that exceeds the trigger level with 4 MHz sampling. The system is installed on the roof of the Faculty of Science Building No.5, Chiba University, and is conducting test observations.

First, we counted the total number of pulses recorded by the system, created an amplitude histogram, and targeted the top 15% of the pulses to investigate hourly fluctuations in the number of pulses. We calculated the average value m and standard deviation σ for the entire analysis period, and defined the anomaly in the number of pulses as m + 2σ. Next, using pulse waveforms and the mine location network blitzortung.org, waveforms (near and distant mines) caused by mine discharges were identified. In addition, we analyzed the earthquakes that occurred within 100 km of the epicenter distance and satisfied log(Es)>8 during the observation period, and investigated the relationship with the earthquakes. where Es=101.5M+4.8/r2 (M: magnitude, r: focal distance). As a result, 4 days before the M5.0 earthquake on November 27, 2018, an abnormal increase in the number of pulses greater than m+2σ was observed, unrelated to the anti-mine. Although similar pulse waveforms did not exceed the m+2σ threshold, they were also observed prior to four other log(Es) > 8 earthquakes during the observation period, and these pulses were associated with preseismic electromagnetic waves. Possible pulse due to radiation. On the other hand, it is also possible that the pulse waveform is caused by cloud discharge, and in order to discriminate between electromagnetic radiation caused by cloud discharge and earthquake precursor electromagnetic radiation, electromagnetic radiation position determination using an interferometer and comparison with satellite images and meteorological data are required. also found to be essential.

How to cite: Hattori, K., Ohta, Y., Yoshino, C., and Imazumi, N.: Development of Broadband Interferometer System for Pre-Earthquake Electromagnetic Radiation in LF Band :Design and Performance of Antenna Elements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17076, https://doi.org/10.5194/egusphere-egu23-17076, 2023.

SM4 – Deformation, Faulting, and Earthquake Processes (incl. seismotectonics, geodynamics, earthquake source physics)

EGU23-242 | ECS | Orals | SM4.1

Rupture-mode preferences of crustal earthquakes in Japan 

Ritsuya Shibata and Naofumi Aso

Fault rupture has various complexity in space and time. The temporal complexity could be expressed by the radiated energy enhancement factor (Ye et al., 2018), which is the ratio of the radiated energy to its theoretical minimum value. Regarding the spatial complexity, the rupture directivity has been well investigated from small scales (Boatwright 2007; Kane et al., 2013; Ross and Ben-Zion, 2016) to large scales (e.g. Ide and Takeo, 1997; Ruiz et al., 2016) by investigating the azimuthal dependency of dominant frequency or estimating the source process. While these studies focus on the spatiotemporal complexity of the entire fault rupture, the mesoscopic scale rupture complexity also exists through the rupture propagation, which is an important perspective of the rupture mechanics. Specifically, we can classify the rupture propagation into two endmembers: mode-II and -III ruptures. In this regard, we focused on the rupture propagations at the scale of subfault extracted from the waveform inversion.

In this study, we analyzed multiple M6-class inland earthquakes in Japan using waveform inversion with the radiation-corrected empirical Green’s functions (Shibata et al., 2022), which enable us to estimate slip distributions with slip directions by synthesizing the EGF waveforms for any focal mechanisms. Then, we introduced rupture-mode intensity to evaluate the rupture-mode preferences by comparing the rupture propagation direction with the slip direction for each earthquake. As a result, we confirmed that the rupture preferentially propagated parallel (mode II) or perpendicular (mode III) to the slip direction, which is expected from the fracture mechanics. In addition, the characteristic of rupture propagation at the early stage was similar to that during the entire rupture, implying that most rupture characteristics are determined at the early stage.

How to cite: Shibata, R. and Aso, N.: Rupture-mode preferences of crustal earthquakes in Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-242, https://doi.org/10.5194/egusphere-egu23-242, 2023.

Frictional sliding at bi-material interfaces (when contacting bodies possess different elastic properties) is important in context of earthquake dynamics. Dissimilarity in elastic materials across the interface give rises to complex rupture propagation phenomena and instabilities, compared to the case when the material is similar across the interface. This is due to the coupling between the normal stress and interfacial slip, which is absent in the homogenous case. In the literature, various numerical schemes have been proposed but still many aspects of bi-material ruptures are not well-understood such as the rupture mode, velocity selection and stability. The present work proposes a new numerical scheme to study frictional rupture at a bi-material interface governed by a rate- and state-dependent friction law. It uses a spectral form of the boundary integral equation method (BIEM) as derived in Ranjith (2015, 2022), to evaluate the field quantities at the interface. The BIEM approach computes elastodynamic convolution of traction over its temporal history at the interface only, without need to calculate in regions away from interface, making it numerically efficient, compared to other conventional approaches. In prior work, an alternative spectral form of BIEM was used by Breitenfeld and Geubelle (1998) for 2D in-plane elasticity and Morrissey and Geubelle (1997) for 2D antiplane elasticity. In their approach, time-convolution is performed of the displacement history at the interface. An advantage of Ranjith’s approach is that the convolution kernels for a bi-material interface can be expressed in closed form, whereas Breitenfeld and Geubelle (1998) had to obtain their convolution kernels numerically. Conversion between real space and spectral domain is done by the Fast Fourier Transform (FFT). Rupture propagation is studied for both in-plane and antiplane frictional sliding at a bi-material interface by coupling the BIEM with a rate- and state-dependent friction law. Such a friction law is known to be suitable for a bi-material interface because it gives rise to well-posed problems (Rice et al., 2001). In earlier studies, an alternative numerical scheme for rate- and state-dependent friction was proposed by Lapusta et al. (2001) to study earthquake sequences on a fault. The disadvantage of their approach is that convolution kernels need to be evaluated multiple times for higher order accuracy. In the present work, a simpler numerical scheme is proposed for bi-material interfaces following a rate- and state-dependent friction law which is computationally more efficient.

How to cite: Gupta, A. and Kunnath, R.: A numerical methodology for rupture propagation at bi-material interfaces with rate- and state-dependent friction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-379, https://doi.org/10.5194/egusphere-egu23-379, 2023.

EGU23-1165 | Posters on site | SM4.1

Contemporary publications in Europe on the Spanish earthquake of 1884  

Elisa Buforn, Agustín Udías, and Maurizio Mattesini

On 25th December 1884, a damaging earthquake shocked the Granada-Malaga (Spain) region, followed by a large number of aftershocks. This is the largest earthquake (Imax= IX-X, EMS-98, estimated magnitude 6.7) in southern Spain, with 750 persons killed and 1500 injured, and 4400 houses destroyed. After the occurrence of the main shock, a considerable number of reports on the damage caused by the catastrophic Andalusian earthquake were published mainly during the following year (1885) in several European journals, as well as in bulletins of scientific societies and books. A few of them were anonymous notes while others were signed by the most important geologists and seismologists from different European countries. Exceptional cases are the publications from the members of the three commissions (Spanish, French and Italian) that were specifically appointed to study this Andalusian earthquake, with the participation of prestigious seismologists, such as Macpherson, Mercalli, Taramelli, Fouqué, and Barrois. We present detailed information about the publications that appeared mainly during the following year (1885) of the occurrence of this earthquake. The prompt study of the Andalusian earthquake provided an opportunity for the scientific community at that time to present and disseminate new modern ideas about the nature of earthquakes and their relationship with the geodynamic processes and geology of the region abandoning the traditional explosive source.

How to cite: Buforn, E., Udías, A., and Mattesini, M.: Contemporary publications in Europe on the Spanish earthquake of 1884 , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1165, https://doi.org/10.5194/egusphere-egu23-1165, 2023.

EGU23-1344 | ECS | Posters virtual | SM4.1

Physics Informed Deep Learning for Modeling Coseismic Crustal Deformation 

Tomohisa Okazaki, Takeo Ito, Kazuro Hirahara, and Naonori Ueda

Crustal deformation, which can be modeled by dislocation models, provides critical insights into the evolution of earthquake processes and future earthquake potentials. In this presentation, we introduce our recent work on a novel physics-informed deep learning approach for modeling coseismic crustal deformation (Okazaki et al. 2022). Physics-informed neural networks were proposed to solve both the forward and inverse problems by incorporating partial differential equations into loss functions (Raissi et al. 2019). The use of neural networks enables to represent continuous displacement fields in arbitrary geometrical structures and mechanical properties of rocks without discretization. To accurately model the displacement discontinuity on a fault, which cannot be directly approximated by neural networks composed of continuous functions, the polar coordinate system is introduced. We illustrate the validity and usefulness of the proposed approach through forward modeling of antiplane dislocations, which are used to model strike-slip faults. This approach would have considerable potential for extension to high-dimensional, anelastic, nonlinear, and inverse problems in a straightforward way.

Reference

Okazaki T, Ito T, Hirahara K, Ueda N, Physics-informed deep learning approach for modeling crustal deformation. Nature Communications, 13, 7092 (2022). https://doi.org/10.1038/s41467-022-34922-1

How to cite: Okazaki, T., Ito, T., Hirahara, K., and Ueda, N.: Physics Informed Deep Learning for Modeling Coseismic Crustal Deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1344, https://doi.org/10.5194/egusphere-egu23-1344, 2023.

EGU23-1726 | ECS | Orals | SM4.1

Stochastic Source Modelling of the 2002 Denali Earthquake for Fault Displacement Hazard Assessment 

Parva Shoaeifar and Katsuichiro Goda

The Denali Fault earthquake was one of the largest strike-slip earthquakes with significant surface ruptures that occurred in 2002 in Alaska, United States. Probabilistic fault displacement hazard assessment (PFDHA) plays an important role in post-earthquake disaster management. This is because critical facilities and infrastructures in the vicinity of active faults are prone to major damage, leading to suspension of service due to fault displacement. Hence, in the present study, a PFDHA due to the Denali earthquake is conducted using a new methodology of stochastic source-based fault displacement hazard analysis. In this method, the surface rupture can be evaluated by applying Okada equations to simulated earthquake source models. The main differences between the methodology of the present study with conventional fault displacement assessment practices are to utilize the stochastic source models instead of the empirical predictive relationship of surface fault displacement and to calculate the distribution for surface fault displacement at a site of interest using the Okada equations. The new methodology is more versatile than the existing methods in several characteristics. First, it is applicable to all faulting mechanisms (e.g., strike-slip, normal, and reverse) by specifying different rake angles of the ruptured fault. Second, it has the ability to consider multi-segment fault rupture. Third, the calculation of three translational displacements by the Okada equations for a given location is available. Lastly, it provides physically consistent fault displacement modelling at two locations for a given earthquake scenario, allowing estimating of the differential fault displacement at two sites. Then the capability of the method is evaluated by applying it to the historical case of the 2002 Denali Fault earthquake. The satisfactory match of the modelled fault displacement and the observations, such as surface offset, Global Positioning System (GPS), and Interferometric Synthetic Aperture Radar (InSAR) data, is achieved based on calculating a performance metric. Therefore, more realistic ground deformation assessments can be carried out. Importantly, the obtained results significantly contribute to the hazard in earthquake-prone areas and reduce potential fatality and casualty risks as well as the post-earthquake damage repair costs of the built environment.

How to cite: Shoaeifar, P. and Goda, K.: Stochastic Source Modelling of the 2002 Denali Earthquake for Fault Displacement Hazard Assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1726, https://doi.org/10.5194/egusphere-egu23-1726, 2023.

Earthquake prediction relies on identification of distinctive patterns of precursory parameters that might precede a large earthquake. However, these patterns are typically not reliably observed in the field. Laboratory stick-slip experiments provide an analog of seismic cycle observed in nature in fully controlled conditions with the associated Acoustic Emission (AE) activity reproducing basic characteristics of seismicity preceding and following the large lab earthquake. Recent laboratory studies showed that the deployment of Machine Learning/Artificial Intelligence techniques has lead to new state of the art results in lab earthquake prediction on smooth faults while using simple statistical features derived from raw AE signals and AE-derived catalogs. However, not enough work has been done on explainability of earthquakes preparatory process on rough faults by leveraging deep learning techniques. In this work we attempt to mitigate this gap and analyze/grade a pool of  explainable seismo-mechanical features through the eyes of neural networks.

We used AE data from three laboratory stick-slip experiments performed in triaxial pressure vessel on Westerly Granite samples. Samples were first fractured at 75MPa confining pressure creating rough fault surfaces. The following stick-slip experiments were performed at constant displacement rate. The experimental procedure led to an extremely complex slip pattern composed of large and small slips of the whole surface, as well as the confined slips highlighted only with AE data and no externally measured slip. The AE catalog was used to extract temporal evolution of 16 seismo-mechanical and statistical features characterizing evolution of stress and damage in response to the axial stress change. The feature pool included clearly physically interpretable parameters such as AE rates, b-value, fractal dimension, AE localization, clustering and triggering properties, and features characterizing the variability of local stress field. 

We apply explainable AI techniques to identify what features are more important to forecast  axial stress and stress drop.  Our feature ranking and importance evaluation with the help of neural networks can serve as an indicator as to what research directions are more promising to take for further feature engineering efforts with an emphasis on explainability of earthquake phenomena.

How to cite: Caus, D., Grover, H., H. Goebel, T., Kwiatek, G., and Weigel, T.: Predicting fault stress level and stress drop using seismo-mechanical and statistical features derived from acoustic signals in laboratory stick-slip friction experiments and assesing feature importance via the derived models., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1967, https://doi.org/10.5194/egusphere-egu23-1967, 2023.

Predicting earthquakes has been a long-standing challenge. Recently, machine learning (ML) approaches have been employed to predict laboratory earthquakes using stick-slip dynamics data obtained from shear experiments. However, the data utilized are often acquired from only a few sensor points, thus insufficient in feature dimension and may limit the predictive power of ML. To address this issue, we adopt the combined finite-discrete element method (FDEM) to simulate a two-dimensional sheared granular fault system, from which abundant fault dynamics data (i.e., displacement and velocity) during stick-slip cycles are collected at 2203 “sensor” points densely placed in the numerical model. We then use the simulated data to train the LightGBM (Light Gradient Boosting Machine) models and predict the normalized gouge-plate shear stress (an indicator of stick-slips). Meanwhile, to optimize features, we build the importance ranking of input features and select those with top importance for prediction. We iteratively optimize and adjust the feature data, and finally reach a LightGBM model with an acceptable prediction accuracy (R2 = 0.91). The SHAP (SHapley Additive exPlanations) values of input features are also calculated to quantify their contributions to prediction. We show that when sufficient fault dynamics data are available, LightGBM, together with the SHAP value approach, is capable of accurately predicting the occurrence time and magnitude of laboratory earthquakes, and also has the potential to uncover the relationship between microscopic fault dynamics and macroscopic stick-slip behaviors. This work may shed light on natural earthquake prediction and open new possibilities to explore useful earthquake precursors using ML.

How to cite: Gao, K.: Predicting stick-slips in FDEM simulated sheared granular faults using machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2516, https://doi.org/10.5194/egusphere-egu23-2516, 2023.

EGU23-4934 | ECS | Orals | SM4.1

Slow rupture propagation and large stress drop during the 2020 Mw6.4 Petrinja earthquake 

Iva Lončar, Mathieu Causse, Martin Vallée, and Snježana Markušić

Seismological data from almost 100 broadband stations (70 < Δ < 420 km) from Croatia, Slovenia, Hungary, Italy, Austria, Bosnia and Hercegovina, Montenegro, and Slovakia have been used in the rupture analysis of the Petrinja (Croatia) MW6.4 earthquake, that occurred on the 29th of December 2020. Several foreshocks and aftershocks have been used as empirical Green’s function (EGF) to isolate source effects from propagation and local soil effects. First, P-wave mainshock seismograms are deconvolved from the EGF seismograms in the frequency domain to obtain the corner frequency (fc). Assuming Brune’s source model, the spectral analysis results in a large stress drop of 25 MPa. Second, using time-domain deconvolution of the Love wave time windows, apparent source time functions (ASTFs) have been computed and indicate an average source duration of 5 seconds. No significant directivity effects can be seen in both the fc values and source durations, whose weak variability suggests a bilateral rupture. Lastly, physical rupture parameters, such as rupture velocity, rupture dimensions, slip model and rise time, have been extracted from the ASTFs by two different techniques: (1) the Bayesian inversion method (Causse et al. 2017) and (2) the backprojection of the ASTFs on the isochrones (Király‐Proag et al. 2019). Both techniques indicate a slow rupture velocity (about 50% of the shear-wave velocity) and a rather short rupture length for an MW6.4 event (about 8 km), consistent with the obtained large seismological stress drop. Such features may be explained by the relatively complex and segmented fault system, typical of immature fault contexts.

 

References:

Causse, M., Cultrera, G., Moreau, L., Herrero, A., Schiappapietra, E. and Courboulex, F., 2017. Bayesian rupture imaging in a complex medium: The 29 May 2012 Emilia, Northern Italy, earthquake. Geophysical Research Letters44(15), pp.7783-7792.

Király‐Proag, E., Satriano, C., Bernard, P. and Wiemer, S., 2019. Rupture process of the M w 3.3 earthquake in the St. Gallen 2013 geothermal reservoir, Switzerland. Geophysical Research Letters46(14), pp.7990-7999.

How to cite: Lončar, I., Causse, M., Vallée, M., and Markušić, S.: Slow rupture propagation and large stress drop during the 2020 Mw6.4 Petrinja earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4934, https://doi.org/10.5194/egusphere-egu23-4934, 2023.

EGU23-5398 | ECS | Orals | SM4.1

Detecting the preparatory phase of induced earthquakes at The Geysers (California) using K-means clustering 

Antonio Giovanni Iaccarino and Matteo Picozzi

The generation of strong earthquakes is a long-debated problem in seismology, and its importance is increased by the possible implications for earthquake forecasting. It is hypothesized that the earthquake generation processes are anticipated by several phenomena occurring within a nucleation region. These phenomena, also defined as preparatory processes, load stress on the fault leading it to reach a critical state. In this paper, we investigate the seismicity preceding 19 moderate (Mw≥3.5) earthquakes at The Geysers, Northern California, aiming to verify the existence of a preparatory phase before their occurrence. We apply an unsupervised K-means clustering technique to analyze time-series of physics-related features extracted from catalog information and estimated for events occurred before the mainshocks. Specifically, we study the temporal evolution of the b-value from the Gutenberg-Richter (b), the magnitude of completeness (Mc), the fractal dimension (Dc), the inter-event time (dt), and the moment rate (Mr). Our analysis shows the existence of a common preparatory phase for 11 events, plus other 5 events for which we can guess a preparatory phase but with different characteristics of previous ones, indicating different possible activation behavior. The duration of the preparatory process ranges between about 16 hours and 4 days. We find that the retrieved preparatory process involves a decrease of b, Mc, and Dc, and an increase of Mr, as found by many authors. Finally, we show a clear correlation between events showing a preparation phase and the location of injection’s wells, suggesting an important role of fluids in the preparatory process.

How to cite: Iaccarino, A. G. and Picozzi, M.: Detecting the preparatory phase of induced earthquakes at The Geysers (California) using K-means clustering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5398, https://doi.org/10.5194/egusphere-egu23-5398, 2023.

EGU23-5810 | ECS | Orals | SM4.1

Using Deep Learning to understand variations in fault zone properties: distinguishing foreshocks from aftershocks 

Laura Laurenti, Gabriele Paoletti, Elisa Tinti, Fabio Galasso, Luca Franco, Cristiano Collettini, and Chris Marone

Fault zone properties can change significantly during the seismic cycle in response to stress changes, microcracking and wall rock damage. Lab experiments show consistent changes in elastic properties prior to and after lab earthquakes (EQ) and previous works show that machine learning/deep learning (ML/DL) techniques are successful for capturing such changes. Here, we apply DL techniques to assess whether similar changes occur during the seismic cycle of tectonic EQ. The main motivation is to generalize lab-based findings to tectonic faulting, to predict failure and identify precursors. The novelty is that we use EQ traces as probing signals to estimate the fault state.

We train DL model to distinguish foreshocks, aftershocks and time to failure of the Mw 6.5 2016 Norcia EQ in central Italy, October 30th 2016. We analyze a 25-second window of 3-component data around the P- and S-wave arrivals for events near the Norcia fault with M>0.5 and ±2 months before/after the Norcia mainshock. Normalized waveforms are used to train a Convolutional Neural Network (CNN). As a first task we divide events into two classes (foreshocks/aftershocks), and then refine the classification as a function of time-to-failure (TTF) for the mainshock. Our DL model perform very well for TTF classification into 2, 4, 8, or 9-classes for the 2 months before/after the mainshock. We explore a range of seismic ray paths near, through, and away from the Norcia mainshock fault zone. Model performance exceeds 90% for most stations. Waveform investigations show that wave amplitude is not the key factor; other waveform properties dictate model performance. Models derived from seismic spectra, rather than time-domain data, are equally good. We challenged the model in several ways to confirm the results. We found reduced performance in training the model with the wrong mainshock time and by omitting data immediately before/after the mainshock. Foreshock/aftershock identification is significantly degraded also by removing high frequencies (filtering seismic data above 25 Hz). We tested data from different years to understand seasonality at individual stations for the time period September to December and removed these effects. Comparing these seasonality effects defined from noise with our EQ results shows that foreshocks/aftershocks for the 2016 Norcia mainshock are well resolved. Training with data containing EQ offers a huge increase in classification performance over noise only, proving that EQ signals are the sole that enable assessing timing as a function of the fault status. To confirm our results and understand which stations are able to detect changes of fault properties we perform a further test cleaning the signals from the seasonality by confounding the DL with a shuffled noise (adversarial training).

We conclude that DL is able to recognize variations in the stress state and fracture during the seismic cycle. The model uses EQ-induced changes in seismic attenuation to distinguish foreshocks from aftershocks and time to failure. This is an important step in ongoing efforts to improve EQ prediction and precursor identification through the use of ML and DL.

How to cite: Laurenti, L., Paoletti, G., Tinti, E., Galasso, F., Franco, L., Collettini, C., and Marone, C.: Using Deep Learning to understand variations in fault zone properties: distinguishing foreshocks from aftershocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5810, https://doi.org/10.5194/egusphere-egu23-5810, 2023.

EGU23-6521 | ECS | Posters on site | SM4.1

A further explore the source features of the 2016 Mw 5.9 Menyuan earthquake by empirical Green's functions and dynamic simulations 

Duyuan Xu, Wenzheng Gong, Zhenguo Zhang, Houyun Yu, and Xiaofei Chen

A quantitative understanding of the factors that control earthquake rupture propagation is critical because it is helpful to estimate the eventual magnitude of an earthquake, which has significant implications for seismic hazard assessment. Previous studies suggest that the complex fault geometry and the heterogeneous material properties of the fault zone can slow and/or stop the rupture propagation. The 2016 Mw 5.9 Menyuan earthquake occurred near the Haiyuan fault system on the northeastern Tibetan plateau. Although some of the kinematic rupture properties of this earthquake have been known, the rupture process and some in-depth source properties remain to be understood. In this study, we first use the empirical Green's functions approach to reveal that the apparent source time functions (ASTFs) of this event display an approximately equal bell shape and have a total duration of about 3 s, which suggests that the rupture process of this earthquake is simple and exhibits no rupture directivity. Moreover, the spectra of ASTFs are very smooth and have no spectral holes. Then, we conduct two end-member spontaneous rupture models, namely the runaway rupture and the self-arresting rupture, to further explain the observed features of the ASTFs. We use the curved grid finite difference method (CG-FDM) to simulate the spontaneous rupture process with a linear slip-weakening friction law. Our results show that the synthetic data from the dynamic source fits well with the InSAR observations and strong ground motions, which indicates that the dynamic source captures the main features of this event. Significantly, the observed smooth spectra of ASTFs can be well explained by the self-arresting rupture process, which implies that this earthquake might be a self-arresting event. In other words, this earthquake may spontaneously stop before reaching the barriers. This finding suggests that some earthquake rupture processes may be deterministic by the initial stress state in which they nucleated. This work increases our understanding of what controls earthquake rupture propagation.

 

 

How to cite: Xu, D., Gong, W., Zhang, Z., Yu, H., and Chen, X.: A further explore the source features of the 2016 Mw 5.9 Menyuan earthquake by empirical Green's functions and dynamic simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6521, https://doi.org/10.5194/egusphere-egu23-6521, 2023.

EGU23-6666 | Orals | SM4.1

Revisiting the 2015 Mw=8.3 Illapel earthquake: Unveiling complex fault slip properties using Bayesian inversion. 

Zacharie Duputel, Emmanuel Caballero, Cédric Twardzik, Luis Rivera, Emilie Klein, Junle Jiang, Cunren Liang, Lijun Zhu, Romain Jolivet, Eric Fielding, and Mark Simons

The 2015 Mw=8.3 Illapel earthquake is one of the largest megathrust earthquakes that has been recorded along the Chilean subduction zone. Given its magnitude, different rupture scenarios have been obtained. Previous studies show different amounts of shallow slip with some results showing almost no slip at the trench and others showing significant slip at shallow depths, up to 14 meters. In this work, we revisit this event by assembling a comprehensive data set including continuous and survey GNSS measurements corrected for post-seismic and aftershock signals, ascending and descending InSAR images of the Sentinel-1A satellite, tsunami data along with high-rate GPS, and doubly integrated strong-motion waveforms. We follow a Bayesian approach using the AlTar algorithm, in which we aim to obtain the posterior PDF of the joint inversion problem. In addition, we explore a new approach to account for forward problem uncertainties using a second-order perturbation approach. 

Results show a rupture with two main slip regions, and with significant slip at shallow depth that correlates with outer-rise aftershocks. Furthermore, kinematic models indicate that the rupture is encircling two regions updip of the hypocenter that remain unbroken during the mainshock and its aftershocks. These encircling patterns have been previously suggested by back-projection results but have not been observed in finite-fault slip models. We propose that the encircled regions correspond to barriers that can potentially be related to secondary fracture zones in the Chilean subduction zone.

How to cite: Duputel, Z., Caballero, E., Twardzik, C., Rivera, L., Klein, E., Jiang, J., Liang, C., Zhu, L., Jolivet, R., Fielding, E., and Simons, M.: Revisiting the 2015 Mw=8.3 Illapel earthquake: Unveiling complex fault slip properties using Bayesian inversion., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6666, https://doi.org/10.5194/egusphere-egu23-6666, 2023.

EGU23-7112 | ECS | Orals | SM4.1

Deep Learning-based earthquake catalog and tomography reveal the rupture process of the 2022 Mw 6.9 Chihshang earthquake sequence 

Wei-Fang Sun, Sheng-Yan Pan, Chun-Ming Huang, Zhuo-Kang Guan, I-Chin Yen, and Hao Kuo-Chen

The Longitudinal Valley in eastern Taiwan, the arc-collision boundary between the Eurasian and Philippine Sea plates, is one the most seismic active areas in the world. On September 18, 2022, the Mw 6.9 Chihshang earthquake struck the south half of the valley and caused severe damage. Since November 2021, we have installed a five-station permanent broadband seismic array with station spacings of 10-20 km around the Chihshang area, and right after the Mw 6.5 foreshock occurred, we further installed a 46-station temporary dense array of nodal seismometers with station spacings of 2-5 km for 35 days. We use SeisBlue, a deep-learning platform/package, to extract the whole earthquake sequence including the Mw 6.5 foreshock, the Mw 6.9 main shock, and over 5,000 aftershocks from the broadband array, and to obtain over 40,000 aftershocks from the dense nodal array. With the high quality and quantity of P- and S-wave arrival times, we apply the finite difference travel time tomography, developed by Roecker et al. (2006). The improved resolution at the shallow part of the crust (at depth < 10 km) provides new constraints to get detailed (with grid spacing 1 km) and reliable Vp, Vs, and Vp/Vs velocity models at the local scale for the first time. Combined with the high-resolution velocity models and the much more complete seismicity, our results clearly depict not only the Central Range fault and the Longitudinal fault but also several local, shallow tectonic structures that have not been observed along the southern Longitudinal Valley.

How to cite: Sun, W.-F., Pan, S.-Y., Huang, C.-M., Guan, Z.-K., Yen, I.-C., and Kuo-Chen, H.: Deep Learning-based earthquake catalog and tomography reveal the rupture process of the 2022 Mw 6.9 Chihshang earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7112, https://doi.org/10.5194/egusphere-egu23-7112, 2023.

EGU23-7571 | ECS | Orals | SM4.1

Can deep learning help understand and characterize earthquakes? An example with deep learning optical satellite image correlation. 

Sophie Giffard-Roisin, Tristan Montagnon, Erwan Pathier, Mauro Dalla Mura, Mathilde Marchandon, and James Hollingsworth

Recent advances in machine learning are having a revolutionizing effect on our understanding of the Solid Earth, in particular in the automatic detection of geophysical events and objects (such as volcano movements in InSAR [Anantrasirichai et al. 2018], landslides in optical satellite imaging [Mohan et al. 2021], and earthquakes in seismic recordings [Zhu et al. 2019]). Yet, the understanding of geophysical phenomena requires us to be able to accurately characterize them: automatizing such tasks by machine learning is the new challenge for future years. One main difficulty resides in the availability of a high quality labeled database, that is a database with both input data (such as remote sensing acquisitions) together with their ground truth (what we are looking for). In this context, the problem of ground deformation estimation by sub-pixel optical satellite image registration (or correlation) is a good example.

Precise estimation of ground displacement at regional scales from optical satellite imagery is fundamental for the understanding of earthquake ruptures. Current methods make use of correlation techniques between two image acquisitions in order to retrieve a fractional pixel shift [Rosu et al. 2014, Leprince et al. 2007]. However, the precision and accuracy of image correlation can be limited by various problems, such as differences in local lighting conditions between acquisitions, seasonal changes in image reflectance, stereoscopic and resampling artifacts, which can all bias the displacement estimate, especially in the sub-pixel domain.

Image correlation is a valuable and unique source of information on the coseismic strain particularly in the near-field of earthquake ruptures, where InSAR can often decorrelate. However, the correlation process can be limited by the underlying assumption of a locally homogenous displacement within the correlation window (typically 3x3 to 32x32 pixels wide), leading to a bias when the correlation window crosses a fault discontinuity. Data-driven methods may provide a way to overcome these errors. Yet, no ground truth displacement field exists in real world datasets. From the generation of a realistic simulated database based on Landsat-8 satellite image pairs, with added simulated sub-pixel shifts, we developed a Convolutional Neural Network (CNN) able to retrieve sub-pixel displacements. In particular, we show how to specifically design discontinuities in the training set in order to reduce the near-field bias where the correlation window crosses the fault. Comparisions are made with state-of-the-art correlations methods both on synthetic (and realistic) data, and on real images from the Ridgequest area.
This preliminary study provides an example of how to use realistic synthetic data generation (combining real data with synthetic numerical approaches) for training a machine learning model able to estimate fault displacement fields. Such an approach could be applied to other characterization tasks, e.g. when realistic numerical simulation data is available, while sufficient ground truth data is not.

How to cite: Giffard-Roisin, S., Montagnon, T., Pathier, E., Dalla Mura, M., Marchandon, M., and Hollingsworth, J.: Can deep learning help understand and characterize earthquakes? An example with deep learning optical satellite image correlation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7571, https://doi.org/10.5194/egusphere-egu23-7571, 2023.

EGU23-7939 | ECS | Posters on site | SM4.1

Towards Bayesian Full-Waveform Source Inversion using Simulation-Based Inference 

Alex Saoulis, Ana Ferreira, Benjamin Joachimi, Alessio Spurio Mancini, and Davide Piras

Bayesian inference provides a pathway toward accurate predictions of source parameters (e.g., location and moment tensor), along with principled, well-calibrated uncertainty estimates. Unfortunately, standard Bayesian inference techniques can often require O(105) simulations per full waveform inversion, making the method infeasible when studying large numbers of events due to the high computational cost of seismological forward modelling. Machine Learning (ML) has emerged as a promising solution to this issue, with recent work demonstrating that ML-based emulators of the physics simulation can be used as rapid-executing surrogates of the forward model in the Bayesian inference workflow. It has been demonstrated that such models, in conjunction with an assumed likelihood model (e.g. Gaussian), can be used to efficiently perform Bayesian posterior inference over seismological source parameters.

 

This work explores an extension to the above method, often referred to as “likelihood-free” or “simulation-based” inference, which removes any assumptions about the likelihood model. This approach leverages a class of neural networks known as Neural Density Estimators (NDEs) to estimate the likelihood density directly given some representation of the observables. To simplify training of these NDEs, a compression technique that can reduce the observables (i.e., full seismograms) into a small set of parameters is required. This work investigates “classical” and ML-based compression techniques for creating a reduced dimension representation. It then demonstrates simulation-based inference on the problem of source location inversion applied to synthetic examples based on a recent seismic swarm on the São Jorge island in the Azores. Comparisons between the proposed approach and other inversion techniques are also presented.

How to cite: Saoulis, A., Ferreira, A., Joachimi, B., Spurio Mancini, A., and Piras, D.: Towards Bayesian Full-Waveform Source Inversion using Simulation-Based Inference, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7939, https://doi.org/10.5194/egusphere-egu23-7939, 2023.

EGU23-8901 | ECS | Orals | SM4.1

Stress Drop Segmentation in the Northern Chilean Subduction Zone: from Interface to Deep Seismicity. 

Jonas Folesky, Rens Hofman, and Jörn Kummerow

We produced a comprehensive stress drop catalog for northern Chile. To improve reliability, we applied a combination of two different stress drop estimation approaches. The result is a mapped stress drop distribution for more than 30,000 events covering the subduction zone from the trench to a depth of about 150 km. The stress drops were computed on the basis of a recently updated version of the IPOC seismic catalog, now spanning the years 2007 to 2021, using the spectral stacking technique as well as the spectral ratio technique.
The resulting distribution reveals a segmentation of median stress drop values for different seismogenic parts of the subduction zone: We find the lowest stress drops for interface events and slightly increased values for the two parallel bands of seismicity below, which lie inside the subducting plate. The upper plate events, show higher stress drops and the intermediate depth events bear the highest median stress drop. The variation of the median stress drops between classes is small: from 1.3 MPa for interface events to about 3.2 MPa for intermediate depth events. This being the values of the spectral ratio results. Using spectral ratios we find the exact same order of median stress drops between the classes with a range of 2.0 MPa to 5.8 MPa for interface and intermediate depth events, respectively. Interestingly, there is no stress drop increase with dept in the uppermost ~80 km, i.e. within each of the classes except for the intermediate depth events.
Additionally, we observe spatial stress drop variability, a noticeable increase with distance from the plate interface, and temporal variability connected with the two megathrust events in the study region, the Mw7.6 2007 Tocopilla event and the Mw 8.1 Iquique event. 

How to cite: Folesky, J., Hofman, R., and Kummerow, J.: Stress Drop Segmentation in the Northern Chilean Subduction Zone: from Interface to Deep Seismicity., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8901, https://doi.org/10.5194/egusphere-egu23-8901, 2023.

The 2019 Ridgecrest earthquake sequence is an exceptionally well-studied event, captured in nearly unprecedented geophysical detail. Three horizontal tensor borehole strainmeters (BSMs), ranging from ~2 to 30 kms near the trace of the rupture, offer a less-conventional and more sensitive measure of coseismic and postseismic deformation for the event. Historically, these instruments are noted as unreliable for measurements of coseismic strain because they are sensitive to small-scale, near-instrument heterogeneities, such as additional offsets triggered by dynamic strains or pore pressure effects. However, many studies compare the strains with pre-constrained forward models of slip. Our preliminary investigations show that we can better match the observed strains if we include BSM measurements in a joint inversion with GPS displacements for coseismic slip. Postseismically, the strainmeters record rapid, non-monotonic deformation that likewise does not match existing afterslip models with a single decay time. We present a new interpretation of co- and post-seismic deformation using BSM strains and GPS displacements at discrete time intervals marked by a change in sign or rate of strain accumulation. Our joint analysis resolves details of the co- and post-seismic slip history that remain otherwise hidden with more common satellite-based inversions from GPS and InSAR alone. 

How to cite: Hanagan, C. and Bennett, R.: Co- and post-seismic deformation resolved from joint inversion of GPS and borehole strainmeter measurements during the 2019 Ridgecrest earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9037, https://doi.org/10.5194/egusphere-egu23-9037, 2023.

EGU23-9150 | Orals | SM4.1

Free surface effects and rupture dynamics : insights from the 2019 Mw=8 northern Peru intraslab earthquake 

Martin Vallée, Yuqing Xie, Raphaël Grandin, Juan Carlos Villegas-Lanza, Jean-Mathieu Nocquet, Sandro Vaca, Lingsen Meng, Jean Paul Ampuero, Patricia Mothes, Paul Jarrin, Ciro Sierra Farfan, and Frédérique Rolandone

The 2019/05/26 Northern Peru earthquake (Mw=8) is a major intermediate-depth earthquake that occurred close to the eastern edge of the Nazca slab flat area. We analyze its rupture process using high-frequency back-projection and seismo-geodetic broadband inversion. Both imaging techniques provide a very consistent image of the peculiar space-time rupture process of this earthquake : its 60-second long rupture is characterized both by a main northward propagation (resulting in a rupture extent of almost 200km in this direction) and by a reactivation phase of the hypocentral area, particularly active 35s to 50s after origin time.

Given the depth of this earthquake (125-140km), the reactivation time window coincides with the arrival time of the surface-reflected elastic wavefield. Computed values of the dynamic Coulomb stresses associated with this wavefield are of the order of ten to several tens of kPa, in a range of values where dynamic triggering has already been observed. The reactivation phase of the Peru earthquake may thus originate from fault areas that were brought close to rupture by the initial rupture front before being triggered by stress increments provided by the reflected wavefield. Source time function complexity observed for other large intermediate-depth earthquakes further suggests that such a mechanism is not an isolated case. 

How to cite: Vallée, M., Xie, Y., Grandin, R., Villegas-Lanza, J. C., Nocquet, J.-M., Vaca, S., Meng, L., Ampuero, J. P., Mothes, P., Jarrin, P., Sierra Farfan, C., and Rolandone, F.: Free surface effects and rupture dynamics : insights from the 2019 Mw=8 northern Peru intraslab earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9150, https://doi.org/10.5194/egusphere-egu23-9150, 2023.

EGU23-12170 | Orals | SM4.1

Data-driven slow earthquake dynamics 

Gianmarco Mengaldo, Adriano Gualandi, and Chris Marone

Friction is a complex phenomenon. This can be seen, for example, in laboratory experiments where stick-slip motion of various kind (i.e., slow and fast instabilities) can be produced when adapting the normal stress applied to the system. Similarly, natural earthquakes also produce
complex stick-slip behaviour. A first challenge in the description of friction comes from the potentially high number of degrees of freedom (dofs) involved in the description of the dynamics of the sliding surfaces. Nonetheless, it was shown that friction can be described with a reduced number of dofs or variables of the dynamics. These may include the shear stress, the relative sliding slip rate, and one or more variables that describe the state of the contact of the sliding surfaces. We investigate the possibility to extract directly from the data the governing equations of friction starting from a simplified synthetic example. We further study the laboratory data with the Hankel Alternative View Of Koopman (HAVOK) theory, a method rooted in dynamical system theory that leverages data driven techniques and produces a Reduced Order Model (ROM) to reconstruct a shadow of the attractor of a system from observational data. We finally compare the results obtained for the laboratory experiments with Cascadia slow earthquakes.

How to cite: Mengaldo, G., Gualandi, A., and Marone, C.: Data-driven slow earthquake dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12170, https://doi.org/10.5194/egusphere-egu23-12170, 2023.

EGU23-12392 | ECS | Orals | SM4.1

Modeling dynamic ruptures on extended faults for microearthquakes induced by fluid injection 

Francesco Mosconi, Elisa Tinti, Emanuele Casarotti, Alice Gabriel, Ravil Dorozhinskii, Luca Dal Zilio, Antonio Pio Rinaldi, and Massimo Cocco

Understanding the dynamics of microearthquakes is a timely challenge to solve current paradoxes in earthquake mechanics, such as the stress drop and fracture energy scaling with seismic moment. Dynamic modeling of microearthquakes induced by fluid injection is also relevant for studying rupture propagation following a stimulated nucleation. We study the main features of unstable dynamic ruptures caused by fluid injection on a target preexisting fault (50m x 50m) generating a Mw=1 event. The selected fault is located in the Bedretto Underground Laboratory (Swiss Alps) at ≈1000m depth. We perform fully dynamic rupture simulations and model seismic wave propagation in 3D by adopting a linear slip-weakening law. We use the distributed multi-GPU implementation of SeisSol on the supercomputer Marconi100.

 Stress field and fault geometry are well constrained by in-situ observations, allowing us to minimize the a priori imposed parameters. We investigate the scaling relations of stress drop, slip-weakening distance (Dc) and fracture energy (Gc) focusing on their role in governing dynamics of rupture propagation and arrest for a target Mw=1 induced earthquake. We explore different homogenous conditions of frictional parameters, and we show that the spontaneous arrest of the rupture is possible in the modeled stress regime, by assuming a high ratio between stress excess and dynamic stress drop (the fault strength parameter S), characterizing the fault before the fluid pressure change. The rupture arrest of modeled induced earthquakes depends on the heterogeneity of dynamic parameters due to the spatially variable effective normal stress. Moreover, for a fault with high S values (not ready to slip), small variations of Dc (0.5÷1.2 mm) can drive the rupture from self-arrested to run-away. Studying dynamic interactions (stress transfer) among slipping points on the rupturing fault provides insight on the breakdown process zone and shear stress evolution at the crack tip leading to failure. The inferred spatial dimension of the cohesive zone in our models is nearly ~0.3-0.4m, with a maximum slip of ~0.6 cm. Finally, we compare stress drop and fracture energy estimated from synthetic waveforms with assumed dynamic parameters. Our results suggest that meso-scale processes near the crack-tip affect rupture dynamics of micro-earthquakes.

How to cite: Mosconi, F., Tinti, E., Casarotti, E., Gabriel, A., Dorozhinskii, R., Dal Zilio, L., Rinaldi, A. P., and Cocco, M.: Modeling dynamic ruptures on extended faults for microearthquakes induced by fluid injection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12392, https://doi.org/10.5194/egusphere-egu23-12392, 2023.

EGU23-12453 | ECS | Posters on site | SM4.1

The Petrinja earthquake series located and visualised using machine learning 

Dinko Sindija, Jean-Baptiste Ammirati, Marija Mustac Brcic, Josip Stipcevic, and Gyorgy Hetenyi

Earthquake detection and phase picking are crucial steps in the analysis of earthquakes. With the increasing number of seismic instruments available, large amounts of seismic data are generated, requiring the use of automatic algorithms to process earthquake series and to include events that would not be discovered with manual approaches.

The Petrinja earthquake series started with local magnitude ML5.0 earthquake on December 28, 2020, followed by ML6.4 earthquake one day later. In the two years of this earthquake series, human analysts picked a total of 16,000 earthquakes smaller than M2.0, 1528 with magnitudes M2.0-2.9, 156 with magnitudes M3.0-3.9, 17 with magnitudes M4.0-4.9, 2 with magnitudes M5.0-5.9 and one earthquake with magnitude greater than M6.0. While the seismic network at the onset of this sequence counted only a few instruments in the epicentral area, the rapid aftershock deployment of 5 stations in the near vicinity of the fault zone, and the further gradual yet still remarkable growth of the seismic network to more than 50 instruments, produced an extraordinary amount of data, which are perfectly suited for employing machine learning (ML) methods for seismic phase picking and earthquake detection.

In this study we present application of various ML methods to the Petrinja earthquake series. We also compare how the results change when we train a model using a subset of data from this earthquake series. Our results show that these machine learning methods are promising approaches for accurately detecting and picking phases in such earthquake series, and also delineate tectonic features responsible for generating them.

How to cite: Sindija, D., Ammirati, J.-B., Mustac Brcic, M., Stipcevic, J., and Hetenyi, G.: The Petrinja earthquake series located and visualised using machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12453, https://doi.org/10.5194/egusphere-egu23-12453, 2023.

EGU23-13506 | Posters on site | SM4.1

Fracture energy and breakdown work scaling with coseismic slip 

Elisa Tinti, Massimo Cocco, Stefano Aretusini, Chiara Cornelio, Stefan B. Nielsen, Elena Spagnuolo, Paul Selvadurai, and Giulio Di Toro

Geological observations reveal that earthquakes nucleate, propagate, and arrest in complex fault zones whose structural heterogeneity depends on the tectonic loading, geometry, lithology, rheology, presence of fluids, and strain localization processes. These fault zones can host a wide range of fault slip behaviors (e.g., creep, aseismic- and slow-slip events, afterslip, and earthquakes). This implies that the environment in which earthquakes occur is diverse, and that different physical and chemical processes can be involved during the coseismic dynamic rupture.

Earthquakes are generated by rupture propagation and slip within fault cores and dissipate the stored elastic and gravitational strain energy in fracture and frictional processes in the fault zone (from microscale - less than a millimeter - to macroscale - centimeters to kilometers) and in radiated seismic waves. Understanding this energy partitioning is fundamental in earthquake mechanics to describe dynamic fault weakening and causative rupture processes operating over different spatial and temporal scales.

The energy dissipated in earthquake rupture propagation is commonly called fracture energy (G) or breakdown work (Wb). Here we discuss these two parameters, and we review fracture energy estimates from seismological, modeling, geological, and experimental studies and show that fracture energy scales with fault slip and earthquake size. Our analysis confirms that seismological estimates of fracture energy and breakdown work are comparable and scale with seismic slip. The inferred scaling laws show modest deviations explained in terms of epistemic uncertainties. The original collection of fracture energy estimates from laboratory experiments confirms the scaling with slip over a slip range of more than 10 decades. Fracture energy associated with breaking of intact rocks is larger than for precut specimens and might suggest differences between the role of fracture and friction, or a different size of the rupture front zone. It is important to recall that fault products after deformation in the laboratory correspond to fault products observed in nature, and acoustic emissions recorded in the laboratory can be processed as seismic waves on a natural fault. We conclude that although material-dependent constant fracture energies are important at the microscale for fracturing grains of the fault zone, they are negligible with respect to the macroscale processes governing rupture propagation on natural faults.

In this study we discuss the scaling of fracture energy and breakdown work with slip, and we propose different interpretations relying on different processes characterizing complex fault zones. Our results suggest that, for earthquake ruptures in natural faults, the estimates of G and Wb are consistent with a macroscale description of the causative processes.

Reconciling observations and results from laboratory experiments and numerical modeling with geological observations can be done, provided that we accept the evidence that earthquakes can occur in a variety of geological settings and fault zone structures governed by different physical and chemical processes.

How to cite: Tinti, E., Cocco, M., Aretusini, S., Cornelio, C., Nielsen, S. B., Spagnuolo, E., Selvadurai, P., and Di Toro, G.: Fracture energy and breakdown work scaling with coseismic slip, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13506, https://doi.org/10.5194/egusphere-egu23-13506, 2023.

EGU23-13811 | ECS | Orals | SM4.1

DiffSD: Diffusion models for seismic denoising 

Daniele Trappolini, Laura Laurenti, Elisa Tinti, Fabio Galasso, Chris Marone, and Alberto Michelini

Seismic waves contain information about the earthquake (EQ) source and many forms of noise deriving from the seismometer, anthropogenic effects, background noise associated with ocean waves, and microseismic noise. Separating the noise from the EQ signal is a critical first step in EQ physics and seismic waveform analysis. However, this is difficult because optimal parameters for filtering noise typically vary with time and may strongly alter the shape of the waveform. A few recent works have employed Deep Learning (DL) model for seismic denoising, among which we have taken as a benchmark Deep Denoiser and SEDENOSS. These models turn the noisy trace into a  2D signal (spectrograms) within the model to denoise the traces, making the process pretty heavy. We propose a novel DL-powered seismic denoising algorithm based on Diffusion Models (DMs), keeping the signal in 1D. DMs are the latest trend in Machine Learning (ML), having revolutionized the application fields of audio and image processing for denoising (DiffWave), synthesis (Stable Diffusion), and sequence modeling (STARS). The training of DMs proceeds by polluting a signal with noise until the signal has completely vanished into noise, then reversing the process by iterative denoising, conditioned on the latent signal representation. This makes DMs the ideal tool for seismic traces cleaning, as the model naturally learns from seismic sequences by denoising, which aligns the ML training procedure and the final task objective. In a preliminary evaluation, we used the Stanford Earthquake Dataset (STEAD); our proposed Diffusion-based Seismic Denoiser (DiffSD) outperforms the state-of-the-art DL methods on the Signal Noise Ratio (SNR),  Scale-Invariant Source to Distortion Ratio (SI-SDR), and Source to Distortion Ratio (SDR) metrics. DiffSD also yields qualitatively pleasing EQ traces out of visual inspection in time and frequency. Finally, DiffSD proceeds from regenerating clean EQ signals from noise, which opens the way to data-driven EQ sequence generations, potentially instrumental to further study and dataset augmentations.

How to cite: Trappolini, D., Laurenti, L., Tinti, E., Galasso, F., Marone, C., and Michelini, A.: DiffSD: Diffusion models for seismic denoising, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13811, https://doi.org/10.5194/egusphere-egu23-13811, 2023.

EGU23-14611 | Posters on site | SM4.1

Inversion for Eigenvalues of Focal Region’s Elasticity Tensor from a Moment Tensor 

Çağrı Diner, Feyza Öztürk, and Mustafa Aktar

In this talk, a new geometric inversion method is proposed for obtaining the elastic parameters of an anisotropic focal region. More precisely, the eigenvalues of a vertical transversely isotropic (VTI) elasticity tensor of a focal region are obtained, up to a constant, for a given only one moment tensor, with an accuracy depending on the strength of anisotropy. The reason of using only one moment tensor is that although there occurs a lot of earthquakes in the same focal region, the orientation of the sources are similar. Hence one do not obtain independent equations from each earthquake, in order to use it in the inversion of elastic parameters of the focal region. Moreover, this method can be applied for real-time inversion once the moment tensor of an earthquake is evaluated.

The inversion method relies on the geometric fact that a moment tensor can be written as a linear combination of the eigenvectors of the anisotropic focal region's elasticity tensor. Then, in the inversion, we use the fact that each coefficient of this unique decomposition is proportional to the eigenvalues of the focal region's elasticity tensor. Two approximations are used in this inversion method; in particular for the potency and for the source orientations.

The strength of anisotropy of the focal region determines how accurate these approximations are and hence it also determines the resolutions of the inverted eigenvalues. Because of the anisotropy of the focal region, the errors in the inversion do depend on the orientations of the dip and rakes angles, but not the strike angle since the focal region is VTI. The accuracy of the inversion for the five parameters of VTI are shown on the steographic projection. The results are very promising along some orientations as shown in the figures. The last section of the talk deals with the inversion of eigenvalues, up to a constant, for a given set of moment tensors; not only one moment tensor. It turns out that the best fit corresponds to the average of inversion results obtained for different orientations of the sources.

How to cite: Diner, Ç., Öztürk, F., and Aktar, M.: Inversion for Eigenvalues of Focal Region’s Elasticity Tensor from a Moment Tensor, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14611, https://doi.org/10.5194/egusphere-egu23-14611, 2023.

EGU23-15105 | Posters on site | SM4.1

Seismological Oriented Machine lEarning (SOME) project 

Carlo Giunchi, Matteo Bagagli, Spina Cianetti, Sonja Gaviano, Dario Jozinović, Valentino Lauciani, Anthony Lomax, Alberto Michelini, Léonard Seydoux, Luisa Valoroso, and Christopher Zerafa

Recent developments of machine learning (ML) algorithms and software-platforms (e.g. Keras, TensorFlow, PyTorch) have opened new frontiers for Earth sciences. In seismology, these advances have affected different aspects of the earthquake physics studies, such as ground motion prediction, seismic phase detection and identification, and seismic big-data analysis.

Within the project Pianeta Dinamico (Working Earth) of Istituto Nazionale di Geofisica e Vulcanologia, funded by the Italian Ministry of University and Research, in 2021 we applied to an internal call with the aim of developing and using existing state-of-the-art machine learning techniques, and delivering useful benchmarking dataset for earthquake analysis. The project is named SOME (Seismological Oriented Machine lEarning).

This multidisciplinary project tackles different tasks that highlight the potential and possible pitfalls of ML applications:

  • Earthquake monitoring: testing and applying Convolutional Neural Network (CNN) and Graph Neural Network (GNN) architectures to predict the intensity measurements (IM) of medium-size seismic events (2.9 < M ≤ 5.1) recorded from a regional network.
  • Seismic waveforms characterization: development of an unsupervised framework for hierarchical clustering of continuous data based on a deep scattering network (scatseisnet). A first application is aimed to detect and classify seismic data from a mainly aseismic region in NE Sardinia (Sos Enattos mining site) to assess the anthropogenic and natural noise levels.
  • Development of a new picking algorithm: implementation of U-NET model architecture of PhaseNet algorithm by using characteristic functions derived from FilterPicker software. This newly developed software is called Domain Knowledge PhaseNet (DKPN).
  • Creation of 2 ML dataset for earthquake studies: 1) INSTANCE dataset, containing the seismicity recorded between January 2005 and January 2020 by the national seismic network of INGV (~1.2 million three-component waveform traces), 2) AQUILA-2009 dataset containing the aftershock sequence of the 2009 Mw6.1  L’Aquila earthquake collected by a dense array of the permanent and temporary network deployed after the mainshock (>63,704 events, nearly >1.2 million 3C three-component traces).

The INSTANCE and AQUILA-2009 dataset are already used as training sets for new picking algorithms, and will be employed for additional statistical analysis in the near future (e.g. hazard assessment, shakemaps) and transfer-learning approaches. The GNN for IM shows promising results for future developments for ground-shaking forecasting applications. The unsupervised learning clusterization algorithm clearly detects signals that differ from purely seismic ones, proving to be a great tool for seeking new patterns and features in time-series records. The DKPN algorithm achieves better results compared  to the original PhaseNet architecture, even if trained with a small dataset (<15.000 3C traces), and shows improved performance for cross-domain application.

Overall, the SOME project has produced many deliverables, some of which have already been released. We also aimed to provide reproducibility of ML experiments, creating Docker applications suitable for ML-picking algorithms (e.g. EQ-Transformer, PhaseNet, GPD) and contributing to the improvement of existing libraries, like SeisBench, for benchmarking purposes. Indeed, reproducibility is an additional yet paramount issue that must be addressed by the seismological community when dealing with ML applications.

How to cite: Giunchi, C., Bagagli, M., Cianetti, S., Gaviano, S., Jozinović, D., Lauciani, V., Lomax, A., Michelini, A., Seydoux, L., Valoroso, L., and Zerafa, C.: Seismological Oriented Machine lEarning (SOME) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15105, https://doi.org/10.5194/egusphere-egu23-15105, 2023.

EGU23-15437 | Orals | SM4.1

Physics-guided machine learning for laboratory earthquake prediction 

Parisa Shokouhi, Prabhav Borate, Jacques Riviere, Ankur Mali, and Dan Kifer

Recent laboratory studies of fault friction have shown that deep learning can accurately predict the magnitude and timing of stick-slip sliding events, the laboratory equivalent of earthquakes, from the preceding acoustic emissions (AE) events or time-lapse active-source ultrasonic signals. While there are observations that provide insight into the physics of these predictions, the underlying precursory mechanisms are not fully understood. Furthermore, these purely data-driven models require a large amount of training data and may not generalize well outside their training domain. Here, we present a physics-guided machine learning approach - by incorporating the relevant physics directly in the prediction model architecture - with the objectives of enhancing model predictions and generalizability as well as reducing the amount of required training data. We use data from well-controlled double-direct shear laboratory friction experiments on Westerly granite blocks exhibiting numerous regular and irregular stick-slip cycles. Simultaneously, AEs are recorded while the faults are also regularly probed by ultrasonic waves transmitted through the fault zone to monitor the evolution of the contact stiffness during shearing. Our physics-guided ML models take features extracted from AE time series or time-lapse active source ultrasonic signals and predict the shear stress history, which gives both the timing and size of the laboratory earthquakes. The models are constrained by friction laws as well as simplified physical laws governing ultrasonic transmission and AE generation. Our findings indicate that physics-guided ML models outperform purely data-driven models in important ways; they provide accurate predictions even with little training data and transfer learning is greatly enhanced when physics constraints are incorporated. These findings have important implications for earthquake predictions in the field, where training data are scarce.  

How to cite: Shokouhi, P., Borate, P., Riviere, J., Mali, A., and Kifer, D.: Physics-guided machine learning for laboratory earthquake prediction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15437, https://doi.org/10.5194/egusphere-egu23-15437, 2023.

EGU23-15640 | Posters on site | SM4.1

A neural network based approach to classify VLF signals as rock rupture precursors 

Alessandro Pignatelli, Adriano Nardi, and Elena Spagnuolo

Electromagnetic signals have been increasingly investigated in the last decade in association to natural earthquakes and laboratory rock fractures. Studies on this type of signals are hampered by  the lack of continuous recordings and, when data are available, the sampling rates (> kHz) is such to require an efficient and systematic processing of large data sets. Despite this limitation, previous studies performed under controlled conditions in the laboratory seem to suggest that electromagnetic signals exhibit characteristic patterns, called OIS - Ordered Impulsive Sequences, on a specific frequency band (the very low frequency, VLF) that correlate uniquely with the paroxistic rupture of rocks specimens under uniaxial tests. Importantly, these characteristic patterns were also detected in the atmosphere in association to moderate magnitude earthquakes occurring within a few days (up to 5) from their detection. The similarity of laboratory and atmospheric VLF offers a unique opportunity to study the relation between VLF and rock deformation on at least two different scales and to enlarge the dataset by combining laboratory and atmospheric data. Here, we deployed tools for a systematic monitoring of electromagnetic signals in the atmosphere and we show that the enlarged VLF dataset, which comprises both laboratory and natural electromagnetic signals, can be successfully processed using a neural network approach. Our neural network architecture was designed to deal with time series and is structured using a recurrent neural networks (RNN) and a Long Short Term memory (LSTM) as a state variable. After a careful data collection, signal sequences were classified as rock rupture precursors (“RUPTURE”) and some of them, including those composing the background noise, as no rupture precursors (“QUIET”). A deep BI-LSTM neural network with 1000 hidden units has been trained in order to fit the known classification and to implicitly acquire the most important features and cut offs to split the potential events to not events. Our main results are 1. laboratory and atmospheric OIS signals are similar and scalable; 2. the similarity is such that it can be successfully used to train a neural network for signal detection in the atmosphere; 3. the neural network is capable of detecting OIS from the huge data set which is made of all the atmospheric background; 4. the extracted signals are those which were typically recorded in association to earthquakes in a temporal window of a few days. The above results show that LSTM neural networks are effective “automatic detectors” for characteristic spectral patterns revealed in the VLF both in the laboratory and in atmospheric signals recorded in association with transient natural events involving fracturing of rock volumes (e.g. earthquakes). The above results suggest that the electromagnetic radiation in the very low frequency band is a promising and valuable signal to probe the deformation of the seismically active Earth crust.

How to cite: Pignatelli, A., Nardi, A., and Spagnuolo, E.: A neural network based approach to classify VLF signals as rock rupture precursors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15640, https://doi.org/10.5194/egusphere-egu23-15640, 2023.

Mechanical models of slip development on geological faults and basal slip development in landslide or ice-sheets generally consider interfacial strength to be frictional and deformation of the surrounding medium to be elastic. The frictional strength is usually considered as sliding rate- and state-dependent. Their combination, elastic deformation due to differential slip and rate-state frictional strength, leads to nonlinear partial differential equations (PDEs) that govern the spatio-temporal evolution of slip. Here, we investigate how (synthetic) data on fault slip rate and traction can find the system of PDEs that governs fault slip development during the aseismic rupture phase and the slip instability phase. We first prepare (synthetic) data sets by numerically solving the forward problem of slip rate and fault shear stress evolution during a seismic cycle. We now identify the physical variables, for example, slip rate or frictional state variable, and apply nonlinearity identification algorithms within different time durations. We show that the nonlinearity identification algorithms can find the terms of the PDE that governs the slip rate evolution during the aseismic rupture phase and subsequent instability phase.

In particular, we use nonlinear dynamics identification algorithms (e.g., SINDy, Brunton et al., 2016) where we solve a regression problem, Ax=y. Here, y is the time derivative of the variable of interest, for example, slip rate. A is a large matrix (library) with all possible candidate functions that may appear in the slip rate evolution PDE. The entries in x, to be solved for, are coefficients corresponding to each library function in matrix A. We update A according to the solutions so that A's column space can span the dynamics we seek to find. To find the suitable column space for A, we encourage sparse solutions for x, suggesting that only a few columns in matrix are dominant, leading to a parsimonious representation of the governing PDE. 

We show that the algorithm successfully recovers the PDE governing quasi-static fault slip and basal slip evolution. Additionally, we could also find the frictional parameter, for example, a/b, where a and b, respectively, are the magnitudes that control direct and evolution effects. Moreover, the algorithm can also determine whether the associated state variable evolves as aging- or slip-law types or their combination. Further, with the data set prepared from distinct initial conditions, we show that the nonlinear dynamics identification algorithm can also determine the problem parameters’ spatial distributions (heterogeneities) from fault slip rate and shear stress data. 

How to cite: Biswas, P. and Ray, S.: Finding governing PDEs of quasistatic fault slip and basal slip evolution from (synthetic) slip rate and shear traction data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16374, https://doi.org/10.5194/egusphere-egu23-16374, 2023.

EGU23-16782 | ECS | Orals | SM4.1

A Preliminary Green Function Database for Global 3-D Centroid Moment Tensor Inversions 

Lucas Sawade, Liang Ding, Daniel Peter, Hom Nath Gharti, Qinya Liu, Meredith Nettles, Göran Ekström, and Jeroen Tromp

Currently, the accuracy of synthetic seismograms used for Global CMT inversion, which are based on modern 3D Earth models, is limited by the validity of the path-average approximation for mode summation and surface-wave ray theory. Inaccurate computation of the ground motion’s amplitude and polarization as well as other effects that are not modeled may bias inverted earthquake parameters. Synthetic seismograms of higher accuracy will improve the determination of seismic sources in the CMT analysis, and remove concerns about this source of uncertainty. Strain tensors, and databases thereof, have recently been implemented for the spectral-element solver SPECFEM3D (Ding et al., 2020) based on the theory of previous work (Zhao et al., 2006) for regional inversion of seismograms for earthquake parameters. The main barriers to a global database of Green functions have been storage, I/O, and computation. But, compression tricks and smart selection of spectral elements, fast I/O data formats for high-performance computing, such as ADIOS, and wave-equation solution on GPUs, have dramatically decreased the cost of storage, I/O, and computation, respectively. Additionally, the global spectral-element grid matches the accuracy of a full forward calculation by virtue of Lagrange interpolation. Here, we present our first preliminary database of stored Green functions for 17 seismic stations of the global seismic networks to be used in future 3-D centroid moment tensor inversions. We demonstrate the fast retrieval and computation of seismograms from the database.

How to cite: Sawade, L., Ding, L., Peter, D., Gharti, H. N., Liu, Q., Nettles, M., Ekström, G., and Tromp, J.: A Preliminary Green Function Database for Global 3-D Centroid Moment Tensor Inversions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16782, https://doi.org/10.5194/egusphere-egu23-16782, 2023.

EGU23-896 | ECS | Posters on site | SM4.2

Spatiotemporal Variation in Low Frequency Earthquake Recurrence Along the San Andreas Fault 

Jessica Allen and Ting Wang

    Episodic tremor sequences comprised of overlapping low frequency earthquakes (LFEs) occur frequently along the San Andreas Fault. Accompanying slow slip activity has been detected from Global Navigation Satellite System (GNSS) data, confirming occurrence of the episodic tremor and slip (ETS) phenomenon here.        
    The characteristics of slow slip events (SSEs) impede comprehensive detection, making it challenging to study their occurrence patterns. We utilise extensive LFE data from a long running high resolution seismic network to gain insights into this more frequent and easily detectable aspect of the ETS process, with the aim to have a detailed understanding of the occurrence patterns and properties of LFEs. This will strengthen methods for the detection and modelling of SSEs.    
    Hidden Markov models were used to study the occurrence patterns of LFE events. Based on these models, LFE events along the San Andreas Fault can be classified into different states. Each state is a proxy for changes in the generating mechanisms that give rise to LFE events, with potential contributors including pore pressure and fault stress. We use the classification to illustrate a detailed picture of temporal changes in LFE activity - including the effects of events such as the 2004 Parkfield earthquake, and to highlight the diverse behaviours displayed across generating locations. 
    The evolution of LFE activity over space and time gives additional insights into how slow slip may propagate. We use clustering methods to reveal patterns in the migration of activity between spatially distinct generating locations, and identify locations with similar characteristics that are likely influenced by the same generating circumstances. 
    
    
    
 

How to cite: Allen, J. and Wang, T.: Spatiotemporal Variation in Low Frequency Earthquake Recurrence Along the San Andreas Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-896, https://doi.org/10.5194/egusphere-egu23-896, 2023.

EGU23-2181 | Posters on site | SM4.2

Estimation of broadband source time functions of seismic slow earthquakes 

Shunsuke Takemura, Kentaro Emoto, and Suguru Yabe

We propose a method for estimating broadband source time functions of seismic slow earthquakes, which can reproduce observed seismograms at both bands of very low frequency earthquake and tectonic tremor. In our method, we assume the broadband characteristics of seismic slow earthquakes (e.g., Ide et al., 2008; Masuda et al., 2020).

In our method, first, we estimated source time functions of very low frequency earthquakes using filtered seismograms at frequencies below 0.1 Hz via the simulated annealing method (e.g., Takemura et al., 2022ab). To achieve broadband source time function, we added random temporal fluctuations into obtained smooth source time function of very low frequency earthquakes. This approach is similar to previous studies for regular earthquakes (e.g., Koyama, 1985; Hisada, 2000). We assumed that fluctuations of source time function can be characterized by a von-Kármán autocorrelation function. A decay rate parameter of a von-Kármán autocorrelation function can model various decay rates at high-frequency ranges.

We confirmed the validity of our method using synthetic seismograms, which were made from Green’s function datasets using a 1D velocity model and the Brownian-walk source time function model (e.g., Ide, 2008; Ide & Maury, 2018). Our estimation well reproduced target seismograms of synthetic seismic slow earthquakes.

In our presentation, we will introduce our methodology and applications at shallow plate boundary in Nankai.

How to cite: Takemura, S., Emoto, K., and Yabe, S.: Estimation of broadband source time functions of seismic slow earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2181, https://doi.org/10.5194/egusphere-egu23-2181, 2023.

Slow slip and tremor (SST) has now been observed along many subduction margins worldwide, and the phenomenon is commonly linked to fluid and/or fluid pressure variations and migration. Crucial to understanding and modeling how fluids and seismicity might interact are estimates of porosity (Φ) and permeability (k) in and around the deforming subduction megathrust shear zone. Constraints on k from deeply buried metamorphic rocks are difficult to obtain, however. Experiments and some small-scale field observations indicate very low k for subduction-related lithologies, on the order of 10-18m2 or less. However, thus far no attempts have been made to quantify the large-scale (or transient) permeability of subduction shear zones at deep metamorphic conditions.

Here we use structural, microstructural and geochemical observations on an exhumed sliver of metamafic rocks, with thermal conditions comparable to the Cascadia subduction zone, to quantify the hydrological properties of the deep SST source region. The study locality (Megas Gialos, Syros Island, Greece) records structures consistent with ductile deformation during subduction, underplating, and subsequent partial exhumation under high pressure greenschist facies conditions within the subduction shear zone. 

The 100-m-length outcrop we studied consists of mafic greenschists with a strong ductile foliation and several generations of syn- to late-kinematic dilational faults and veins. Evidence for both along- and across-dip fluid flow is preserved in the form of metasomatic selvages parallel to the foliation, foliation-parallel quartz veins with foliation-perpendicular growth fibers, and dilational faults oriented at high angles to the foliation. The orientations and cross-cutting relationships between the foliation and multiple vein generations indicate the veins acted as transient fluid-flow conduits opened cyclically during background distributed viscous flow under extremely low differential stresses. In thin section, most of the veins exhibit crack-seal textures, consistent with episodic hydrofracturing. 

To estimate the porosity and 2D permeability tensor from outcrops, we mapped the youngest generation of veins using high resolution drone models, then used Matlab-based software FracPaq to calculate permeability. Our assumptions include a) the latest generation of veins were at some stages opened simultaneously or in close succession (consistent with evidence for very low differential stress magnitudes), and b) the characteristic opening aperture was assumed to be an average of measured crack-seal widths in thin section. This approach yields an estimate of Φ of ~0.8 to 8% and an anisotropic k of 6.0x10-15 to 1.4x10-14 m2 in the along-dip and across-dip orientations, respectively. These values are 3+ orders of magnitude greater than would be inferred for the background unfractured rock. They are broadly consistent with estimates of k from geophysical observations of tremor migration patterns, and with models of the permeability contrasts (background/transient) required for viscous compaction of fluid pressure to lead to unstable slip. The method we demonstrate can be applied to other outcrops with subduction contexts and can provide essential ‘ground-truthed’ data to test assumptions of fluid flow in the deep tremor source region.

How to cite: Muñoz-Montecinos, J. and Behr, W.: Quantifying paleo-permeability on the deep subduction interface from exhumed rocks: a case study from Syros Island, Greece, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2888, https://doi.org/10.5194/egusphere-egu23-2888, 2023.

EGU23-3294 | Posters on site | SM4.2 | Highlight

Characteristics of shallow tremor waveforms observed by distributed acoustic sensing using offshore fiber-optic cable at the Nankai Trough, southwest Japan 

Satoru Baba, Eiichiro Araki, Yojiro Yamamoto, Takane Hori, Gou Fujie, Yasuyuki Nakamura, Takashi Yokobiki, and Hiroyuki Matsumoto

Distributed acoustic sensing (DAS) measurement, which uses a fiber-optic cable as a strain sensor, allows us spatially high-density observation than seismometers; therefore, DAS has been widely used for seismic observations recently. We conduct DAS measurement with an offshore fiber-optic cable off the Cape Muroto, along the Nankai Trough in southwest Japan. This area is a typical area with adjacent occurrences of slow and megathrust earthquakes. As the relationship between slow and megathrust earthquakes is pointed out (e.g., Obara and Kato, 2016), monitoring of slow earthquakes with a high resolution is necessary to understand tectonic conditions in subduction zones. Although many studies have observed regular earthquakes by DAS measurement recently, there are few studies which observed slow earthquakes with DAS. We observed shallow tremors, a type of slow earthquake in a frequency range of 2–10 Hz, by DAS measurement.

We detected 28 shallow tremor signals off Cape Muroto by using DAS from January 30 to February 8, 2022. The signals of these tremors were also observed in broadband seismograms of the Dense Oceanfloor Network system for Earthquake and Tsunami (DONET) data. We manually picked the arrivals of the tremor signals in root-mean-square envelopes of DAS and DONET waveforms and located the tremor events at the point where the residual between synthetic and observed arrival times is the least by the grid search. Synthetic travel times were calculated based on a one-dimensional S-wave velocity structure model representing the area near the Nankai Trough (Nakano et al., 2013). The tremors were located mainly around 135.7ºE and 33.8ºN, which corresponds to a subducted seamount peak indicated by Nakamura et al. (2022).

The amplitude of tremor signals in the frequency range of 2–10 Hz observed in a DAS channel is 1–2 nstrain. Assuming a plane wave, the velocity waveforms can be calculated by multiplying the apparent velocity by the strain waveform (e.g., Daley et al., 2016). The apparent velocity of the tremor signal propagation was estimated to be ~4 km/s in DAS data; therefore, the amplitudes of the velocities were estimated to be 4000–8000 nm/s, which is similar to or one order larger than that in broadband seismometers of the nearest DONET stations. In detail, tremor signals in DAS data are composed of several phases with variable apparent velocities, and these phases are coherent within only 50–100 m. Generally, the duration of tremors observed in the DAS channels (40–60 s) is longer than that observed in velocity waveforms of DONET broadband seismometers (30–50 s). Comparing the waveforms of regular earthquakes in DAS and ocean bottom seismometers (OBSs) at the same location in December 2019, we found that the duration of the regular earthquakes in the DAS strain waveform is also longer than that in the OBS velocity waveform. The difference in waveform characteristics may be caused by that in the sensitivity of the incident angle between DAS and OBS.

How to cite: Baba, S., Araki, E., Yamamoto, Y., Hori, T., Fujie, G., Nakamura, Y., Yokobiki, T., and Matsumoto, H.: Characteristics of shallow tremor waveforms observed by distributed acoustic sensing using offshore fiber-optic cable at the Nankai Trough, southwest Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3294, https://doi.org/10.5194/egusphere-egu23-3294, 2023.

EGU23-3766 | ECS | Posters on site | SM4.2

Stress change and fault interaction of adjacent dip-slip, creeping faults in Taiwan 

Wei Peng and Kate Huihsuan Chen

Understanding the aseismic slip and its interplay with seismic slip is central to seismogenesis as it ultimately controls the space-time patterns of seismicity. The aseismic slip has mostly been documented on subduction zones, where the aseismic slip occurs close to the plate rate during the interseismic period and accelerates after/preceding a nearby mainshocks. In tectonically-active continental regions, the intensive efforts of mapping and characterizing aseismic slip have been made to strike-slip faults. Due to lack of recognized creep on dip-slip faults, the nature of fault creep and its role in large earthquake generation in dip-slip creeping fault remains unclear. Whether the spatial and temporal distribution of earthquakes?

The two segmented, ~150-km-long, creeping fault systems in Taiwan are characterized by fast deep slip rate (4-5 cm/yr), large damaging earthquakes, repeating earthquakes, and swarm activities. They provide a rare opportunity for studying the nature of fault creep in the dip-slip faults. As a boundary between the Philippine Sea plate and the Eurasian plate, the Longitudinal Valley on the eastern Taiwan is composed of two parallel structures with opposite dipping direction: the east-dipping Longitudinal Valley fault (LVF) to the east and the west-dipping Central Range fault (CRF) to the west, with the surface separation of shorter than 10 km. Since 1990, thirteen M6 earthquakes have occurred along the two faults. To understand the characteristics and mechanisms of earthquake interaction between the two adjacent active faults, three major works are conducted: (1) Identifying earthquakes that are responsible for the LVF and CRF activities based on relocated seismicity (2) Identifying earthquake clusters using a statistics-based algorithm (3) Quantifying the interaction between seismicity on two separate faults using the spatiotemporal distribution of earthquake clusters (3) computing the static stress change to verify the stress triggering relationship between the two adjacent faults.

Each of the two adjacent faults can be both divided into three segments. We found that only the southern segments exhibit strong interaction in earthquake clusters. On December 10, 2003, a M6.4 earthquake in the southern LVF likely triggered a M5.3 earthquake in southern CRF that occurred 8 days later, as promoted by 0.8 bar stress change. On April 1, 2006, a M6.2 earthquake in southern CRF on the other hand, is capable of triggering a M6.0 earthquake in the south segment of LVF two weeks later, imported by 0.6 bar stress change. Given that the southern segment of the LVF is characterized by the creep rate of 2-3 cm/yr on the surface and ~4 cm/yr at greater depth below 10 km, while the other segments reveal stronger fault coupling, we argue that the nature of fault creep may control the triggering potential in the adjacent fault. 

How to cite: Peng, W. and Chen, K. H.: Stress change and fault interaction of adjacent dip-slip, creeping faults in Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3766, https://doi.org/10.5194/egusphere-egu23-3766, 2023.

EGU23-3900 | Posters on site | SM4.2

Spontaneous Earthquake generation Experiments by Controlling Shear Stress in a Rotating Shear Apparatus 

Yohei Hamada, Takehiro Hirose, Wataru Tanikawa, and Takahiro Suzuki

Earthquake faults are stationary in a critical state where they either slip or not.

The fluid pressure fluctuation in the fault zone at this critical state is thought to be one of the factors that cause a variety of earthquakes that progress from slow to fast. This process of earthquake generation has been studied using the conventional "slip displacement - rate control" method, however, this does not reproduce the process of initiation and acceleration of slip as natural earthquake generation. In this study, we conducted experiments to induce spontaneous fault slip using a rotating friction apparatus that can control torque and fluid pressure rather than slip rate.

First, as a simple experiment, a sample (standard SiO2) whose frictional behavior was measured at low and constant velocity was used to continuously and gradually increase torque (0.3 N-m/s) under normal stress of 5 MPa. Slip started when the torque reached 200 N-m (corresponding to a shear stress of 4 MPa and a coefficient of friction of 0.8) and gradually accelerated to 170 microns/sec, at an acceleration of 20 micron/s/s. We also conducted an experiment in which the fluid pressure was increased in steps after the axial pressure and torque were applied at fixed values in advance, and similar acceleration behavior was obtained here as well. For both experiments, the termination velocity was 170 microns/sec and did not accelerate to the cm/sec order, which was set as the limit. These could have reproduced the onset of the slow earthquake, but it is also possible that the result may have been due to experimental problems that the torque was not controlled and decreased with the onset of the slip. The presentation will include this and other experimental results, as well as the interpretation of the torque-controlled experimental results and initiation of slow earthquake.

How to cite: Hamada, Y., Hirose, T., Tanikawa, W., and Suzuki, T.: Spontaneous Earthquake generation Experiments by Controlling Shear Stress in a Rotating Shear Apparatus, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3900, https://doi.org/10.5194/egusphere-egu23-3900, 2023.

EGU23-4600 | Posters on site | SM4.2 | Highlight

The role of afterslip in the stress interaction between repeating earthquakes and microseismicity in Parkfield 

Kate Huihsuan Chen, Kaj Johnson, Roland Burgmann, and Robert Nadeau

Earthquake can be triggered by small stress changes from local to distant earthquakes, seasonal forcing, and human activities. While the calculated magnitude and sign of stress change greatly varies with the assumption of source stress drop, receiver fault geometry, and consideration of aseismic slip, the near-field stress triggering can be easily misinterpreted. With a large number of repetitive occurrence times, small repeating earthquakes provides a unique opportunity to examine and model the extent to which fault interaction in the form of static stress changes and transient postseismic fault creep produces the observed aperiodicity in the occurrence of these events. Using the 655 repeating earthquakes (repeater) and M>1 4499 earthquakes during the period of 1984 – 2004 (before the M6 Parkfield event), the significant triggering between small earthquakes were previously documented as the increased rate of events producing(incurring) higher stress changes during the days preceding(following) a repeater. However, how to describe the stress in the vicinity of earthquakes has been a challenge especially that (1) the negative static shear stresses could be mistakenly resolved on the closely-located receiver and (2) the role of afterslip induced by very small earthquakes on the stress interactions could be largely underestimated. In this study, we propose the stress model that properly represents the relative three-dimensional location of the events and determine the instantaneous static stress fields associated with each event as well as the time-dependent contributions from afterslip. We hope to provide a better interpretation of the short-term triggering between the closely-spaced small earthquakes on the creeping strands of the SAF.

How to cite: Chen, K. H., Johnson, K., Burgmann, R., and Nadeau, R.: The role of afterslip in the stress interaction between repeating earthquakes and microseismicity in Parkfield, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4600, https://doi.org/10.5194/egusphere-egu23-4600, 2023.

EGU23-4667 | ECS | Orals | SM4.2 | Highlight

An ongoing triggered slow slip event after the 2006 Pingtung offshore earthquake in Hengchun Peninsula, Taiwan 

Shih-Han Hsiao, Kuo-En Ching, Wu-Lung Chang, Pei-Ching Tsai, Slawomir Giletycz, and Chien-Liang Chen

    An ongoing triggered slow slip event (SSE) on the inland Hengchun fault after the 2006 ML 7.0 Pingtung offshore earthquake in Taiwan is proposed in this study by analyzing the coordinate time series of 13 continuous GNSS stations, 37 campaign-mode GNSS stations and 3 precise leveling routes in Hengchun Peninsula from 2002 to 2022. Four surface velocity patterns have been determined based on these geodetic data: (1) the interseismic period from 2002 to the 2006 Pingtung offshore earthquake; (2) the 2nd period after the earthquake to April 2010; (3) the 3rd period from April 2010 to 2016; (4) the 4th period from 2016 till 2022. In general, a velocity discontinuity is discovered approximately located at 1-2 km east of the currently known Hengchun fault trace. Then we evaluate the slip deficit rate and slip rate distributions of the Hengchun fault through baseline inversion model and coseismic fault model, respectively. The modeling results shows that Hengchun fault is a reverse fault with a minor left-lateral component. Two asperities are shown in the southern and northern segments, respectively. Furthermore, the energy on the asperities has been gradually released from south to north after the 2006 earthquake, even though the postseismic deformation has faded. On the other hand, the geological investigation results also indicate that surface ruptures were generated on the Hengchun fault until 2017. Therefore, we infer that (1) the temporal pattern changes of surface velocity in Hengchun Peninsula are driven by the 2006 ML 7.0 Pingtung offshore earthquake; (2) the Hengchun fault ought to be relocated at 1-2 km to the east; (3) a SSE occurs on the Hengchun fault after the 2006 ML 7.0 Pingtung offshore earthquake. (4) the energy keeps releasing through the SSE after the earthquake and decrease the earthquake potential in Hengchun Peninsula.

How to cite: Hsiao, S.-H., Ching, K.-E., Chang, W.-L., Tsai, P.-C., Giletycz, S., and Chen, C.-L.: An ongoing triggered slow slip event after the 2006 Pingtung offshore earthquake in Hengchun Peninsula, Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4667, https://doi.org/10.5194/egusphere-egu23-4667, 2023.

A central goal of this work is to understand the extent to which fault friction vs. pore fluids and other factors is the cause of slow earthquakes and the spectrum of fault slip behaviors. Slow earthquakes and quasi-dynamic modes of fault slip such as tremor and LFEs have now been observed in essentially every tectonic setting, which suggests that the underlying mechanism(s) are generic rather than specific to a particular fault setting, rock type, or tectonic regime. Here, I discuss lab data that illuminate the mechanics of slow slip. I focus on frictional stick-slip failure events, the lab equivalent of earthquakes, that reproduce slow slip and the full range of slip behaviors observed on tectonic faults.  These studies document repetitive slip events and the complete lab seismic cycle for the full spectrum of slip behaviors from aseismic creep to slow slip and aperiodic elastodynamic failure. Working with data for repetitive slip events is critical for understanding the underlying mechanics. In the lab, we also document the rate of frictional weakening with slip kc = σn (b-a)/Dc  ––the so-called critical stiffness–– where σn is fault normal stress, (b-a) is the friction rate parameter and Dc is the critical slip distance. We measure kc for the same conditions of the slow slip events by altering the machine loading stiffness. These works assess directly frictional instability theory, which predicts the slip stability transition when the elastic stiffness of the fault zone k equals the frictional weakening rate kc. The lab work confirms friction theory in relation to the transition from stable to unstable slip but it also reveals additional complexity showing that kc varies with slip rate. Several works now document the velocity dependence of kc(V) and its role in dictating slow slip in the lab. These works show complex behavior near k/kc ≈ 1 including slow slip, aperiodic failure and chaotic motion. I discuss these results in the context of basic questions that remain regarding how slow ruptures can propagate quasi-dynamically, at speeds far below the Rayleigh wave speed, and how tectonic faults can host both slow slip and dynamic earthquake rupture.

How to cite: Marone, C.: Slow Earthquakes and the Spectrum of Fault Slip Modes: A View From the Lab, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5886, https://doi.org/10.5194/egusphere-egu23-5886, 2023.

EGU23-6369 | ECS | Posters on site | SM4.2

Detecting low-frequency earthquakes with deep learning 

Jannes Münchmeyer, Sophie Giffard-Roisin, Marielle Malfante, David Marsan, and Anne Socquet

Subduction megathrusts are the largest earthquakes occuring worldwide. Yet the generation of large subduction earthquakes is still poorly understood. Recent research revealed that aseismic deformation in the form of slow slip events (SSEs) might play a key rule in the build-up of these events. However, SSEs are hard to observe directly, due to there slow nature. One way to identify and study aseismic deformation is through co-occuring signals, for example, low-frequency earthquakes (LFEs). Yet these events are again difficult to observe due to their low signal-to-noise ratio and emergent onsets.

In this project, we build machine learning models to identify low-frequency earthquakes. These models are more flexible and transferable than the commonly employed template matching techniques for LFE detection. We focus on deep learning based models, building upon their excellent performance for the picking and detection of regular seismicity. To train and evaluate these models we have compiled a collection of LFE datasets from multiple world region in a format tailored for machine learning. We integrate our LFE detector into the SeisBench library to allow easy application of the model in future studies.

How to cite: Münchmeyer, J., Giffard-Roisin, S., Malfante, M., Marsan, D., and Socquet, A.: Detecting low-frequency earthquakes with deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6369, https://doi.org/10.5194/egusphere-egu23-6369, 2023.

EGU23-6821 | ECS | Orals | SM4.2

Hydroacoustic Monitoring of Earthquake Sequences on the Blanco Oceanic Transform Fault 

Hui Liu, Yen Joe Tan, and Robert Dziak

Understanding how earthquakes initiate lies at the heart of earthquake physics and analyzing foreshock sequences is one way to probe the initiation process of large earthquakes. A few oceanic transform fault (OTF) earthquakes have been observed to have more foreshocks compared to continental earthquakes. It has also been proposed that OTFs accommodate plate motion primarily by slow creep instead of rapid seismic slip, though with significant along-fault variability. These characteristics make OTFs unique laboratories for probing the physical processes underlying foreshocks and their relations with slow slip events. However, in the past, detailed studies at OTFs have been limited due to their distance from land-based seismic stations. Since 2015, small arrays of ocean-bottom seismometers and hydrophones have been permanently deployed on cabled seafloor observatories in the northeast Pacific Ocean, allowing for monitoring of seismicity on the Blanco Transform Fault (BTF) using the earthquake’s radiated hydroacoustic energy (T-phase). T-phases propagate through the SOFAR channel in the world’s oceans with little attenuation, allowing for the detection of low-magnitude earthquakes at large distances. In this study, we apply a suite of techniques to detect, associate, and locate foreshocks and aftershocks of large mainshocks occurring along the BTF since 2015. We define a mainshock as the largest event occurring within two weeks and a radius of 50 km. 19 Mw  5.0 mainshocks are selected from the GCMT catalogue. However, we are only able to analyze 12 mainshocks due to data availability issues. We use the STA/LTA algorithm to detect T-phase arrivals one week before and after each mainshock through the continuous waveforms recorded on both OBSs and hydrophones. For each detection, we then use the relative station arrival times compared to the mainshock to make sure we only retain events close to the mainshock, i.e., its foreshocks and aftershocks. We then employ the GLOBAL mode Non-Linear Location (NLLoc) program for event localization using a 3D ocean sound velocity model. Compared to the IRIS catalogue which only has a minimum detection level of magnitude 3, lower-magnitude T-phase events are successfully detected by our method. Using our T-phase catalogue, we quantify how the BTF sequences compare with earthquake sequences observed at continental transform faults and test the various proposed models to explain foreshock spatiotemporal behavior and the partitioning of seismic and slow slips along the BTF.

 

 

How to cite: Liu, H., Tan, Y. J., and Dziak, R.: Hydroacoustic Monitoring of Earthquake Sequences on the Blanco Oceanic Transform Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6821, https://doi.org/10.5194/egusphere-egu23-6821, 2023.

EGU23-7998 | ECS | Orals | SM4.2 | Highlight

How is geometrical complexity in fault zone recorded by geodesy and seismology? 

Michelle Almakari, Harsha S. Bhat, Navid Kheirdast, Carlos Villafuerte, and Marion Y. Thomas

Over the last decades, new observations of complex slip dynamics have emerged. We now observe a continuum of transients energy release happening on fault systems, such as slow slip events, LFEs and tremors. Present quasi-dynamic numerical models are capable of producing such complex slip events on fault planes by considering more realistic complex fault geometries. We aim in this study to bridge the gap between source modeling and observations by generating synthetic surface records. 

For this, we consider a fault system which consists of a main self-similar rough fault, surrounded by a dense network of off-fault fractures. We embed our 2D quasi-dynamic fault zone in a 3D elastic half-space and cover the free surface with a wide array of colocated broadband accelerometers and high rate GPS stations. Over multiple seismic cycles, we record broadband signals at 50 Hz and high rate GPS at 1 Hz. We aim to understand how the different sequences of complex behavior that we observe on the fault plane are recorded on the stations. What are the different contributions of the main fault and off-fault fractures to the radiated signals recorded on the stations? 

How to cite: Almakari, M., Bhat, H. S., Kheirdast, N., Villafuerte, C., and Thomas, M. Y.: How is geometrical complexity in fault zone recorded by geodesy and seismology?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7998, https://doi.org/10.5194/egusphere-egu23-7998, 2023.

EGU23-9067 | ECS | Posters on site | SM4.2

What makes low-frequency earthquakes low frequency? 

Qing-Yu Wang, William Frank, Rachel Abercrombie, Kazushige Obara, and Aitaro Kato

Low-frequency earthquakes are repetitive seismic events that occur downdip of the seismogenic megathrust where slow aseismic fault slip dominates the tectonic budget. These tiny events, distinct from regular earthquakes, have the potential to provide in-situ constraints on the fault rheology where slow slip occurs, but are hard to study due to their small signal amplitudes. We take advantage of the unique geometry of seismicity in the Nankai subduction zone, where low-frequency earthquake sandwich regular earthquakes, to study the source signature of low-frequency earthquakes and the local seismic structure. We isolate two 10 km-radius depth columns, one where low-frequency earthquakes periodically occur and one where they do not. Taking the collocated regular earthquakes below and above the subducting plate interface, we develop a three-step cluster-based approach to correct for local site effects, extract the accurate Empirical Attenuation functions, and apply them to the correction of Low-frequency earthquakes. The falloff of corrected displacement spectra inversely obeys the 𝝎-square hypothesis with a maximum possible corner frequency of fc at ~2 - 3Hz. The local 1-D vertical structure inverted from earthquake travel times suggests a distinct difference in the ratios of seismic attenuation and velocity. Assuming seismic waves go through similar paths within depth column, the local attenuation is insufficient to generate specific low-frequency spectral content that differs from fast earthquakes. Instead, our results support a relative contrast of Q over depth with a higher Q at shallow depth above the zone of low-frequency earthquakes. This high Q layer may serve as an impermeable layer and produce an environment with enhanced pore-fluid pressure and heterogeneous frictional characteristics different from the zone with regular earthquakes. This particular condition favors low-frequency earthquakes and generates distinct nucleation procedures or/and rupture processes of low-frequency earthquakes from regular earthquakes.

How to cite: Wang, Q.-Y., Frank, W., Abercrombie, R., Obara, K., and Kato, A.: What makes low-frequency earthquakes low frequency?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9067, https://doi.org/10.5194/egusphere-egu23-9067, 2023.

EGU23-15859 | ECS | Orals | SM4.2

The slip deficit rate, slow and fast earthquake at the Nankai subduction zone. 

Raymundo Omar Plata Martinez, Takeshi Iinuma, Fumiaki Tomita, Takuya Nishimura3, and Takane Hori

The Nankai subduction zone is considered as a region with a high seismic risk. Large earthquakes with magnitudes larger than 8 have occurred and will recur in the future. Additionally, several observations of slow earthquakes at the shallow and deep plate interface have continuously been being happening. Large and slow earthquakes originate from different types of frictional characteristics, mostly driven by an accumulation of interplate slip deficit. Here, we present results from geodetic observations to estimate the slip deficit rate at the Nankai subduction zone based on displacement rate data of the dense onshore GNSS array as well as that of the offshore GNSS-Acoustic stations during the period 2002 to 2016 (Nishimura et al. 2018). After removing co-seismic and post-seismic deformations due to earthquakes in other regions, we estimated the slip deficit rate at the plate interface by using a trans-dimensional reversible jump Markov chain Monte Carlo algorithm (Tomita et al. 2021). To obtain a smooth slip distribution without imposing smoothing constraints we used a Voronoi partitioning for slip parameters, in which the number of cells is automatically set during the inversion, based on the spatial resolution of data. In contrast to previous slip deficit inversions at the Nankai region, we included scaling weight factors for different types of data. The scaling factors were parameterized to be adjusted in the inversion procedure. Furthermore, we used elastic Green Functions estimated from a three-dimensional heterogeneous structure of the Nankai regions (Hori et al. 2021), instead of a homogeneous medium as previously done. We accomplished a new model of slip deficit rate for the Nankai subduction zone that complements previous models. Regions with high slip deficits agree with the rupture areas of historic large earthquakes. Lastly, the location of deep and shallow slow earthquakes agrees with estimated intermediate values of slip deficit. The slow earthquake region defines the transition between a locked and unlocked plate interface, while shallow slow earthquakes can also be generated by shallow heterogeneous patches or subsurface structures at the subducting plate.

How to cite: Plata Martinez, R. O., Iinuma, T., Tomita, F., Nishimura3, T., and Hori, T.: The slip deficit rate, slow and fast earthquake at the Nankai subduction zone., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15859, https://doi.org/10.5194/egusphere-egu23-15859, 2023.

EGU23-16838 | ECS | Orals | SM4.2

Detection and characterization of slow deformation from GNSS data by deep learning in the Cascadia subduction zone 

Giuseppe Costantino, Sophie Giffard-Roisin, Mauro Dalla Mura, Mathilde Radiguet, David Marsan, and Anne Socquet

The stress that accumulates on faults due to tectonic plate motion can be released seismically and aseismically. The seismic release of stress takes place during earthquakes at short time scales (seconds to minutes), and can be identified on seismic records. The aseismic part of this stress release occurs during Slow Slip Events (SSEs), that last from days to years and do not radiate energetic seismic waves. SSEs are monitored with dense Global Navigation Satellite System (GNSS) networks that record the deformation induced at the surface. A precise identification of slow slip events is key to better understand the mechanics of active faults and to better describe the role of aseismic slip in the seismic cycle. Yet, the characterization of SSEs of various sizes from existing GNSS networks is challenging, and extensive SSEs catalogs remains sparse and incomplete: for example, 64 events for SSEs in Cascadia (Michel et al., 2018), 24 long-term SSEs (Takagi et al., 2019) and 284 short-term SSEs (Okada et al., 2022) in Nankai, Japan. Traditional SSE characterization either focus on specific events, identified visually with high signal to noise ratio (e.g. Radiguet et al., 2016), use time series decomposition approaches such as ICAIM (independent Component analysis inversion method) (Michel et al., 2018; Radiguet et al., 2020), or, for small events, geodetic template matching (Okada et al., 2022; Rousset et al., 2017).

We focus on the Cascadia subduction zone, where a link between slow slip and bursts of tremors has been established (Rogers & Dragert, 2003). In this direction, tremor catalogues can be used to validate potential SSEs detections against the spatiotemporal distribution of tremors. Moreover, a catalogue of SSEs has been recently assessed by (Michel et al., 2019), providing additional benchmark to our analyses. We generate synthetic SSEs from synthetic dislocations (Okada, 1985) using the slab2 model (Hayes et al., 2018). Each SSE template, assumed as a sigmoidal-shaped transient, is further added to a window of noise obtained from real GNSS data (Costantino et al., in prep.).

We develop a deep learning-based method for the systematic detection and characterization of SSEs using a Convolutional Neural Network (CNN) in combination with a Graph Neural Network (GNN). We test our method both on synthetic and real position time series. Results on synthetic data are consistent and show a detection trade-off between the SSEs location, magnitude and the density of the GNSS network. Results on real GNSS positional time series show a good agreement with existing catalogues (cf. Michel et al., 2019). Moreover, new detections have been carried out, which correlate well with the temporal distribution of tremors, suggesting that those events could be new SSE detections, which will be further validated by assessing their spatial-temporal consistency through scaling laws output by the deep learning model.

How to cite: Costantino, G., Giffard-Roisin, S., Dalla Mura, M., Radiguet, M., Marsan, D., and Socquet, A.: Detection and characterization of slow deformation from GNSS data by deep learning in the Cascadia subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16838, https://doi.org/10.5194/egusphere-egu23-16838, 2023.

EGU23-16875 | ECS | Orals | SM4.2 | Highlight

The environment surrounding the subduction zone plate interface 

Michael Everett Mann, Geoffrey Abers, and Patrick Fulton

The interface between a subducting and overriding plate usually exhibits low seismic velocities within a thin (<6 km thick) layer. The hydrologic and petrologic conditions surrounding this layer control the behavior of the plate interface fault, which shows a wide range of rupture behavior from the megathrust through the down-dip transition to tremor and slow-slip. Many analyses of the properties of this plate interface low-velocity layer (LVL) use receiver functions (RFs), which sample sharp seismic velocity gradients and depend primarily on the time separation between RF phases from the top and bottom of the layer, to provide diagnostic estimates of thickness and Vp/Vs. Previous hypotheses for plate interface rupture behavior have invoked high pore-fluid pressure to explain inferences of apparently high Vp/Vs (exceeding 2.2) along the seismogenic zone and the adjacent down-dip slow-slip region determined from RF analyses. However, new higher-resolution analyses of scattered teleseismic P-wave coda that sample this region in two different subduction zones reveal Vp/Vs within the range of normal lithologies (1.6-2.0) and remove the observational requirement for a thick region of high pore-fluid pressure. These results agree with recent laboratory analyses of the properties of exhumed megathrust rocks. Instead, the mechanical properties of a thick damage zone surrounding the interface or entrained sediments explain both the scattered-wave observations and observed fault rupture behavior in the seismogenic zone and deeper. Pore pressure could play a role, but it may operate more locally or intermittently than conventionally thought. Additionally, from this analysis we find that the frequency content of the scattered phases generated at the delimiting boundaries of the LVL are limited and do not provide enough resolution to include direct (up-going P-to-S converted waves) conversions in LVL RF analyses without biasing the results to high values of Vp/Vs and thickness.

How to cite: Mann, M. E., Abers, G., and Fulton, P.: The environment surrounding the subduction zone plate interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16875, https://doi.org/10.5194/egusphere-egu23-16875, 2023.

EGU23-174 | ECS | Posters on site | TS3.7

A new velocity field for El Salvador derived from combined InSAR and GNSS data 

Juan Portela, Ian J. Hamling, Alejandra Staller, Marta Béjar-Pizarro, Douglas Hernández, Cecilia Polío López, and Manuel Díaz

The country of El Salvador lies on an active tectonic margin, where the Cocos plate is subducting under the Caribbean plate. A crustal fault system, the El Salvador Fault Zone (ESFZ), crosses the country from East to West through the Central American Volcanic Arc, accommodating more than 1 cm/yr of differential deformation between the Chortís block and the volcanic forearc sliver. 

Here we use GNSS and interferometric synthetic aperture radar (InSAR) data to measure interseismic ground deformation across ESFZ. We have processed and updated GNSS data in more than 110 continuous and episodic stations in the region. GNSS results have been useful for determining the broad pattern of the tectonic signal in the area. However, they are scarce and unable to characterise complex behaviour in the intra-fault basins.

SAR data acquired by the ALOS PALSAR L-band satellite (2006-2011), for both the ascending and descending tracks covering El Salvador, were used to form interferograms with a Small Baseline (SBAS) approach. The time series and average velocity were computed. The average coherence obtained for the area is overall good, and the results are coherent with the regional tectonics. 

How to cite: Portela, J., Hamling, I. J., Staller, A., Béjar-Pizarro, M., Hernández, D., Polío López, C., and Díaz, M.: A new velocity field for El Salvador derived from combined InSAR and GNSS data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-174, https://doi.org/10.5194/egusphere-egu23-174, 2023.

EGU23-552 | ECS | Posters on site | TS3.7

Long-term Earthquake Cycle along the eastern Altyn Tagh Fault, China 

Nicolás Pinzon Matapi, Yann Klinger, Xiwei Xu, Jing Liu, and Paul Tapponnier

Identifying earthquake recurrence times and slip distributions over the span of many seismic cycles is key to understand fault-rupture processes and to better assess the seismic hazard. In this study, we used three paleoseismological excavations along the Aksai segment of the Altyn Tagh Fault (ATF) to document preserved evidence of past earthquakes in the sedimentological record such as vertical offset, fault cracks, and folding. We integrated these findings with previous studies on the Annanba and Xorxoli segments in order to build a larger-scale rupture history of the ATF. We reported nine large paleo-earthquakes and three of these with ground rupture expression along the whole three segments (∼ 400 km). Based on a Bayesian approach we present 95-percentile range ages of 6149 – 5285 BC, 5296 – 4563 BC, 3026 – 2677, 2469 - 2254 BC, 2069 - 1964 BC, 1184 – 709 BC, 270 – 635 AD, 875 – 1325 AD and 1491 - 1741. Furthermore, we used high-resolution satellite imagery to measure horizontal offsets recorded in the morphology, which are associated with potential co-seismic deformation. We find that the mean recurrence time is 1171±425yr with a COV of ∼0.31 suggesting a quasi-periodic behavior with a characteristic slip motion based on the similar distribution of fault offsets. The last event seems to be strongly expressed in Xorxoli segment and also found along the Aksai segment, although we could not identify it along the Annanba bend. Whereas, the penultimate event and the two before this appear to well correlate across the Aksai, Annanba and Xorxoli segments. Thus, being strong candidates for the three largest and successive earthquakes along the ATF (roughly rupture longitude ≥ 350 km). Variations in the COVs along the eastern Altyn Tagh Fault accounts for the important control of local structural complexity and/or slip rate variations on the rupture behavior of major fault systems.

How to cite: Pinzon Matapi, N., Klinger, Y., Xu, X., Liu, J., and Tapponnier, P.: Long-term Earthquake Cycle along the eastern Altyn Tagh Fault, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-552, https://doi.org/10.5194/egusphere-egu23-552, 2023.

EGU23-1195 | Posters virtual | TS3.7

Irregular recurrence of surface-faulting paleoearthquakes along the Gowk fault, southeast Iran 

Mohammad Foroutan, Bertrand Meyer, Michel Sébrier, Andrew Murray, Mohammad-Ali Shokri, Shahryar Solaymani Azad, Hamid Nazari, Faezeh Azhandeh, Ailar Sajedi Far, and Mojtaba Bassiri

While long-averaged recurrence times of large earthquakes are documented on many slow-slipping fault zones in intracontinental settings, the variability of the return periods through multiple seismic cycles remains poorly known. Paleoseismic investigations across fault zones with the well-documented instrumental sequence of surface-breaking earthquakes are a way to tackle the problem. In this context, the Gowk fault, a 160-km-long dextral fault in central Iran, that experienced four surface-rupturing earthquakes with magnitudes ranging from Mw 5.8 to 7.0 during a 1981-1998 earthquake sequence offers a case study. The four earthquakes have ruptured a 90-km-stretch of the fault. The most recent one, the 14 March 1998 Fandoqa earthquake of Mw 6.6, produced a 23-km-long surface rupture along the northern part of the Gowk fault with a maximum right-lateral displacement of 3 m. With a Holocene slip-rate between 3.8-5.7 mm yr-1 and several recent seismic events testifying to its high level of seismicity, the Gowk fault is an appropriate target to conduct paleoseismic investigations and address the earthquake behavior of slow-slipping faults activated by a sequence of well-documented instrumental earthquakes. We excavated two neighboring trenches across the 1998 fault breaks and identified at least four Holocene event horizons that preceded the 1981-1998 earthquake sequence. The age of the faulted stratigraphic sequence is constrained by eighteen optically stimulated luminescence samples and one radiocarbon age on charcoal. The ages of the event horizons suggest an irregular seismic behavior of the Gowk fault characterized by significant variability in the return period of surface rupturing earthquakes.

How to cite: Foroutan, M., Meyer, B., Sébrier, M., Murray, A., Shokri, M.-A., Solaymani Azad, S., Nazari, H., Azhandeh, F., Sajedi Far, A., and Bassiri, M.: Irregular recurrence of surface-faulting paleoearthquakes along the Gowk fault, southeast Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1195, https://doi.org/10.5194/egusphere-egu23-1195, 2023.

EGU23-2262 | Orals | TS3.7

Deformation-dependent aftershocks in laboratory earthquakes sequences 

Axelle Amon, Ambroise Mathey, David Marsan, Jerome Weiss, and Jerome Crassous

We study an experimental model of a fault consisting in a stationary shear band in a compressed granular sample. To obtain those bands, we perform a biaxial compression of a granular sample constituted of glass beads during which we observe the spontaneous formation of shear planes along the Mohr-Coulomb directions in the sample. We study the post-failure regime during which all the deformation occurs along the stationary shear bands. Using an interferometric method of measurement of micro-deformations based on multiple scattering, we obtain full-field measurements of the local incremental deformation in the sample. The deformation measured are typically of $10^{-5}$ with a resolution of about 300 microns (3 bead diameters). Our technics gives access to the strain fluctuations inside the shear band and we show that the macroscopic mean deformation in the bands is the result of the accumulation of local, intermittent, shear events. The size distribution of those shear events follows the Gutenberg-Richter law. We observe clustering of those events following Omori's law and we apply a declustering method to reveal the causal structure underlying our sequences of events (Houdoux et al. 2021). 

In my talk, I will focus on recent experimental results regarding the dependence of the series statistics on the driving velocity. We have studied sequences of aftershocks for different compression velocities and we have shown that surprinsingly the aftershock sequences we observe are deformation-dependent and not time-dependent. We discuss such a deformation memory effect in the framework of an Olami-Feder-Christensen model.

Houdoux et al. Commun Earth Environ 2, 90 (2021)

How to cite: Amon, A., Mathey, A., Marsan, D., Weiss, J., and Crassous, J.: Deformation-dependent aftershocks in laboratory earthquakes sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2262, https://doi.org/10.5194/egusphere-egu23-2262, 2023.

EGU23-3813 | ECS | Orals | TS3.7

Automated workflow to compute earthquake chronologies on faults from paleoseismic datasets 

Octavi Gómez-Novell, Bruno Pace, and Francesco Visini

A major challenge in seismic hazard research is to quantify the frequency of large earthquakes along active faults, more so when the observational time windows of seismic catalogs are much shorter than the average fault recurrence intervals. In this respect, paleoseismology continues to prove to be an excellent tool to extend the seismic catalogs of faults into prehistorical times. The combination of the ever more advanced trenching surveys and accurate numerical dating techniques allows constraining the timing of paleoearthquakes and, for some datasets, approximating their recurrence models. Despite this, paleoseismic data carries along large uncertainties frequently related to dating technique limitations, poor stratigraphic preservation, and along-strike slip variability that hinder the identification of a complete paleoearthquake record. Subsequently, these issues, among others, challenge the constraint of reliable earthquake chronologies along faults and of the parameters defining their earthquake cycle.

We present an automatic workflow capable to compute and constrain earthquake chronologies along a fault based on the correlation of its available paleoseismic records, including multi-site and poorly constrained datasets. Our inherent premise is that the correlation of paleoseismic data from multiple along-fault locations can help to improve the time constraints and completeness of its paleoearthquake record. Given that paleoseismic records are, by definition, underpopulated, event correlation is not restricted to single occurrences. Instead, an event in a site might be simultaneously correlated with more than one in another if time compatible. Furthermore, to avoid subjectivity biases in event timing estimates and correlation, we exclusively rely on the trench numerical dates limiting each event horizon as the inputs. All earthquake chronologies are modelled probabilistically with a four-step algorithm as we detail. First, all earthquake times in each site are computed as probability density functions (PDFs) using the input numerical dates. The event PDFs from all sites are then integrated to derive a mean curve representing the overall event probabilities for the studied fault in the time span investigated. The probability peaks in this curve, which are assumed as indicative of the event timing at the fault scale, are automatically detected based on peak prominence analysis. A final PDF is then computed for each peak by multiplying all site event PDFs intersecting the peak position. The set of product PDFs constitutes the earthquake chronology of the fault, provided to the user in simple output files that can be externally used to calculate fault parameters for the seismic hazard assessment, and to visualize the modelling.

Preliminary tests on several paleoseismic datasets of the Central Apennines (Italy), the Eastern Betics (Spain), the Dead Sea Fault and the Wasatch Fault (US), have provided good outcomes. The approach significantly reduces the uncertainties in event timing of paleoearthquakes and provides an objective and reliable interpretation of the datasets, especially when these are complex or have wide uncertainties. By extension, the workflow has the potential to reduce the uncertainties in earthquake recurrence estimates and can give insight on the recurrence models that better describe the earthquake cycle in the studied faults.

How to cite: Gómez-Novell, O., Pace, B., and Visini, F.: Automated workflow to compute earthquake chronologies on faults from paleoseismic datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3813, https://doi.org/10.5194/egusphere-egu23-3813, 2023.

High-resolution geodetic measurements of the accumulated strains along active faults are important for faulting dynamics studies and seismic hazard evaluation. InSAR has been widely applied to measure the interseismic strain along active strike-slip faults. However, phase unwrapping errors, tropospheric delays, along with over-smooth effects in calculating the strain from velocity limit its capability of mapping the highly localized strain along faults. Phase-gradient stacking that sums up the wrapped phase differences of adjacent pixels has been successfully applied to reveal localized deformation across coseismic fractures and slow-moving landslides, yet lacks application to reveal interseismic strain along faults. Here, we conduct phase-gradient stacking on Sentinel-1 SAR interferograms, for the first time, to map the interseismic strain along the North Anatolian Fault with unprecedented resolution. We reveal several segments with extremely high strain rates attributed to shallow creep of the fault. By comparing with historical earthquake ruptures, we find that the creeps are either related to afterslip of recent earthquakes, or related to slip deficits of earthquakes occurred decades ago, challenging the opinion that the NAF has a uniform surface strain rate, particularly along its eastern portion. Our results show that the phase-gradient stacking can not only reduce the computation burden from phase unwrapping and tropospheric correction, but also achieve a much higher spatial resolution strain map than the traditional InSAR method. The proposed method can be applied to other large strikes-slip faults for distinguishing segments with surface creep and strong coupling and therefore better quantify the shallow strain budget and its associated hazards.

How to cite: Liu, Z. and Wang, T.: High-resolution Interseismic Strain Mapping from InSAR Phase-Gradient Stacking: Application to the North Anatolian Fault with Implications to the Non-uniform Strain Distribution Related to Historical Earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3915, https://doi.org/10.5194/egusphere-egu23-3915, 2023.

The propagation of the 2021 Mw7.4 Madoi earthquake rupture from the central Jiangcuo fault (JCF) onto the eastern portion exhibits the most complex geometry with a series of conjugate faults, bends, and stepovers. At the east ~50 km of the 2021 epicenter, the surface rupture along the Jiangcuo eastern branch (JCEB) deviating ~12° anticlockwise from the general strike provides a valuable chance for understanding the particularly complex surface ruptures propagation and the branching behavior of the poorly known JCEB. Using sub-metric orthophotos collected by UAV with a ground resolution of 6 cm, complemented by multiple field investigations, we implemented the surface rupture mapping and coseismic slip distribution of the JCEB in detail associated with this earthquake sequence. Our mapping illuminated the sporadic breaks of the tectonic region in the dune area immediately near the branching point and eastward propagated linear rupture trace. The measurements of the high-resolution coseismic slip along the JCEB show that the slip distribution reveals an approximate dogtail shape to the eastern termination with the maximum left-lateral strike-slip offset of 2.9 m. These data might support the perspective that the rupture propagated with a supershear velocity toward the east. Combined with the accrued displacements along the JCEB, these results indicate that the poorly known divergent branch could accumulate pre-2021 surface breaks as an immature fault and bifurcated in the Madoi quake due to the matched regional stress field. We found linear surface breaks along the NW-strike geologic faults indicating triggered coseismic slip on conjugate faults. In the meantime, the intersections with conjugate faults mark discontinuities in rupture geometry and surface slip on the main fault, suggesting strong fault interaction in the eastern tip zone of the Madoi rupture.

How to cite: Yao, W., Liu-Zeng, J., and Wang, Z.: Rupture Branching and Propagation at the Eastern End of the 2021 Mw 7.4 Madoi Earthquake, North Tibet Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4233, https://doi.org/10.5194/egusphere-egu23-4233, 2023.

EGU23-5124 | ECS | Orals | TS3.7

Quantifying the slip over various time scales on active normal faults in the Apennines (Italy):  the Liri fault from paleoearthquakes to long-term slip rate 

Magali Riesner, Lucilla Benedetti, Stéphane Baize, Stefano Pucci, Matthieu Ferry, Stéphanie Gautier, Régis Braucher, Jules Fleury, Hervé Jomard, Stéphane Mazzotti, and Fabio Villani

Long-term fault escarpments are built by the accumulation of individual earthquakes producing incremental surface displacements on the fault releasing crustal tectonic loading. Cumulative escarpment studies have revealed a spatial slip variability along active faults as well as a temporal variability with the alternation of phases of intense seismic activity over a short period of time followed by long periods of quiescence. Understanding this spatial and temporal slip variability on individual faults and over a complex fault system provide a better knowledge of co-seismic rupture extents, essential for estimating past earthquakes magnitude and for seismic hazard assessment.

Up to now, most studies have focused on a timeframe over few seismic cycles, making it difficult to apprehend the rupture barriers persistence and cumulative slip distribution.  Here, we aim at quantifying the slip variability over several timescales ranging from a few months to a few million years on the same fault.

Our study focusses on the ~50 km-long Liri fault, SW of the Fucino basin. The fault is located at the contact between Cretaceous limestone and patches of Quaternary deposits locally convering Mio-Pliocene flysch sediments. Detailed mapping of the fault trace on high-resolution Digital Elevation Model (DEM) from UAV-acquired images, Pleiades images and Lidar together with field observations revealed changes in the morphological expression of the fault north and south of an important wind gap located at Capistrello. To the north, the faut trace is ~16 km-long located on the eastern side of ~2km-wide limestone ridge, reaching ~1300m asl elevation. Two bends in the fault trace, made of ~5km long segments, can be observed with the fault strike varying between N115° and N140°. In this northern section, the fault scarp appears subtle and we did not observe Quaternary deposits on the hanging wall. In the 30 km-long section, south of Capistrello, the cumulative scarp composed of numerous splays is evidenced by a sharp trace, offsetting several morphological surfaces and associated Quaternary sediment packages. Three major bends are observed in this section of the fault, separating 10 to 30 km-long segments striking between N110° and N160°. An alluvial surface offset by ~14 m of cumulative displacement was dated at ~35kyr using 36Cl cosmogenic exposure dating suggesting a minimum slip rate of 0.4 mm/yr.  Other morphological markers that have accumulated displacement between ~10 and 70 m-high have also been sampled for 36Cl cosmogenic exposure dating. Moreover, we excavated two small trenches at the base of the fault scarp within the Quaternary deposits affected by the fault revealing 3 rupture-surfacing earthquakes over the last 2500 yr, the last one occurring after 1226 CE. 

We will present those results and will discuss how the displacement varies along the fault both in time and space.

How to cite: Riesner, M., Benedetti, L., Baize, S., Pucci, S., Ferry, M., Gautier, S., Braucher, R., Fleury, J., Jomard, H., Mazzotti, S., and Villani, F.: Quantifying the slip over various time scales on active normal faults in the Apennines (Italy):  the Liri fault from paleoearthquakes to long-term slip rate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5124, https://doi.org/10.5194/egusphere-egu23-5124, 2023.

Earthquakes on faults in the brittle upper crust cause sudden changes in pore fluid pressure as well as postseismic viscoelastic flow in the lower crust. Such transient processes change the velocity field in the crust and cause significant Coulomb stress changes on receiver faults in the vicinity of the source fault, which may trigger or delay next earthquakes. As previous studies focused on natural earthquakes and/or considered poroelastic and viscoelastic processes separately, the combined influence of poroelastic effects and viscoelastic relaxation on postseismic velocity and stress fields has not been systematically studied so far. In a previous study with 2D finite-element models, we showed that postseismic velocity fields contain signals from overlapping poroelastic and viscoelastic effects (Peikert et al., Tectonophysics, 2022). Here, we use 3D finite-element models with arrays of normal and thrust faults, respectively, to analyze the Coulomb stress changes resulting from the interaction between poroelastic effects and viscoelastic relaxation. In different experiments, we vary the permeability of the crust and the viscosity of the lower crust or lithospheric mantle, while keeping the other parameters constant. We also performed experiments with and without pore fluid flow and viscoelastic relaxation, to isolate the effects of fluid flow and viscoelastic relaxation from each other. Our results show that the coseismic (= static) Coulomb stress changes are immediately altered by the signal from poroelastic effects during the first month after the earthquake. In the first postseismic year, Coulomb stress changes arising from poroelastic effects are one order of magnitude stronger than Coulomb stress changes arising from viscoelastic relaxation. In models considering fluid flow, poroelastic effects dominate the stress field in the first two years. Viscoelastic relaxation already occurs in the early postseismic phase, but is overlapped by the strong signal from poroelastic effects and dominates the Coulomb stress change pattern from about the fifth postseismic year onward for several decades.  The Coulomb stress change patterns show a combined signal from poroelastic and viscoelastic effects already during the first postseismic year, if the viscosity is sufficiently low. For sufficiently low permeabilities, Coulomb stress changes induced by poroelastic effects overlap with the signals from viscoelastic relaxation and interseismic stress accumulation for decades. Finally, poroelastic and viscoelastic effects have a strong impact on the magnitudes and patterns of Coulomb stress changes and should therefore be considered together when analyzing Coulomb stress transfer between faults.

How to cite: Peikert, J., Hampel, A., and Bagge, M.: Relative Importance of Poroelastic Effects and Viscoelastic Relaxation for Co- and Postseismic Coulomb Stress Changes on Normal and Thrust faults: Insights from 3D Finite-Element Modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5555, https://doi.org/10.5194/egusphere-egu23-5555, 2023.

EGU23-5953 | ECS | Posters on site | TS3.7

Paleoseismic Investigation along the straight section of the central Altyn Tagh fault and its constrain on the rupture history 

Longfei Han, Jing Liu-Zeng, Guiming Hu, Yann Klinger, Wenxin Wang, Heng Wang, Jing Xu, Bo Zhang, Yunpeng Gao, Zijun Wang, Xianyang Zeng, and Xiaoli Liu

Paleoseismic records are essential for constraining the earthquake recurrence behavior of active faults and evaluating the rupture history. However, paleoseismic studies on the central Altyn Tagh fault (ATF) are still scarce, and previous studies indicate that this fault section with simple geometry is not periodic. In addition, paleoseismic data from two sites along central ATF reveal different amounts of paleoearthquakes and present discordant in time. Therefore, we conducted paleoseismic studies and documented six reliable paleoseismic events at the LaPeiQuan site along the straight section of the central ATF. The results indicate that the most recent event is a small earthquake with a tiny vertical offset. The data A.D. (1752–1880) yr (event A) is significantly later than the last event along the Xorkoli section. The penultimate event at the LaPeiQuan site is a large earthquake for the ages of this event B is A.D. (667–764) yr (event B), which is consistent with the Xorkoli site and Aksay double bend site, producing at least 140 km rupture. In addition, the large vertical offset measurement from the deformed sediment of event B also supports its large one. The ages of Event D are discordant with the adjacent paleoseismic sites. The ages of Event C, Event E and Event F are still in process. The reason earthquake histories are inconsistent may be that small-scale geometrical complexities can prevent earthquake rupture propagation.

How to cite: Han, L., Liu-Zeng, J., Hu, G., Klinger, Y., Wang, W., Wang, H., Xu, J., Zhang, B., Gao, Y., Wang, Z., Zeng, X., and Liu, X.: Paleoseismic Investigation along the straight section of the central Altyn Tagh fault and its constrain on the rupture history, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5953, https://doi.org/10.5194/egusphere-egu23-5953, 2023.

EGU23-6332 | ECS | Posters on site | TS3.7

Realistic interseismic strain rate uncertainties from inherently sparse GNSS-networks 

Taco Broerse, Mario D'Acquisto, Rob Govers, Celine Marsman, and Alireza Amiri-Simkooei

Before geodetically derived strain and rotation rates can be robustly compared to geological or seismological observations, we need reliable strain rate uncertainties. Various methods exist to compute strain rates from GNSS-derived interseismic velocities, but a realistic representation of interpolation uncertainties has remained a challenge. The main problem is that commonly used deterministic interpolation methods do not account for uncertainty resulting from the absence of information in between observation sites. We apply stochastic interpolation by means of ordinary kriging to propagate errors both from discontinuous data coverage as well as from observation uncertainties to our strain rate estimates. However, interseismic horizontal surface velocities in tectonically active regions are spatially highly non-stationary, with high spatial variability around active faults and lower velocity variability in tectonically more stable regions. This requires an extension of traditional ordinary kriging approaches. For interpolation uncertainties that reflect the local variability and spatial correlation of the observed surface velocities, we apply a novel method that incorporates the spatially variable statistics of the underlying data. We estimate realistic uncertainties and covariances of the interpolated velocity field. For regions with a high spatial velocity variability, we find a large increase in uncertainty with increasing distance from observation sites, while in areas with little spatial variability, we estimate a small increase in uncertainty with distance. Subsequently, we propagate interpolated velocity covariance to strain rate uncertainties, such that we can assess the statistical significance of the interpolated strain rate field. Applied to a number of actively deforming regions, including the Pacific coast of North America and Japan, we show to what degree we can robustly determine strain rates based on available GNSS-derived velocities. Realistic uncertainties assist the community to better discriminate continuous or localized deformation on active faults from the available geodetic data. 

 
 

How to cite: Broerse, T., D'Acquisto, M., Govers, R., Marsman, C., and Amiri-Simkooei, A.: Realistic interseismic strain rate uncertainties from inherently sparse GNSS-networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6332, https://doi.org/10.5194/egusphere-egu23-6332, 2023.

EGU23-6567 | ECS | Orals | TS3.7

Holocene deformation on a transform fault: Insights from paleoseismology on the Húsavík-Flatey Fault in North Iceland 

Rémi Matrau, Yann Klinger, Jonathan Harrington, Thorvaldur Thórdarson, Ármann Höskuldsson, Esther Gudmundsdöttir, Laura Parisi, Margherita Fittipaldi, Ulas Avsar, and Sigurjón Jónsson

Studies of Oceanic Transform Faults (OTFs) usually rely on geophysical data because of the OTF inaccessibility on the seafloor. The Húsavík-Flatey Fault (HFF) in northern Iceland is an OTF connecting the onshore rift in Iceland to an offshore rift segment of the Mid-Atlantic Ridge, accommodating 30% to 50% of the relative plate motion at this latitude between North America and Eurasia. The HFF is unique because its easternmost 25 km-long segment is exposed on land, allowing to study the long-term deformation of the fault. Two historical earthquakes of estimated magnitudes M6.5 - M7 have been reported on the eastern HFF in the last 270 years. However, almost no information exists from prior to the 18th century.

To study the Holocene deformation of the HFF and to build a catalogue of past earthquakes, we excavated 11 paleoseismology trenches at two locations, six on an alluvial fan and five in a pull-apart basin. We also excavated and tracked buried river channels to estimate long-term slip rates and to assess the coseismic displacement of single events. We used radiocarbon dating of birch wood samples together with major element compositions of volcanic ashes (tephras) to constrain the timing of events on the fault.

Trenches at both locations show clear evidence of deformation and surface rupturing events. From offset measurements of glacial morphologies and buried river channels, we calculate a Holocene slip rate of 4 - 6 mm/yr, slightly lower than the estimated present-day geodetic slip rate, suggesting that some of the deformation may be distributed. Based on upward terminations of cracks and faults, we identified eight events in the last ~6000 years, yielding fewer major earthquakes than expected from the 270-year record. We thus suggest that large earthquakes of magnitude ~M7 on the HFF, producing significant surface ruptures, are rare, with a return time of 500 to 600 years. We also propose that the short recurrence times often observed on OTFs may therefore not be representative of the full seismic cycle.

How to cite: Matrau, R., Klinger, Y., Harrington, J., Thórdarson, T., Höskuldsson, Á., Gudmundsdöttir, E., Parisi, L., Fittipaldi, M., Avsar, U., and Jónsson, S.: Holocene deformation on a transform fault: Insights from paleoseismology on the Húsavík-Flatey Fault in North Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6567, https://doi.org/10.5194/egusphere-egu23-6567, 2023.

EGU23-7209 | ECS | Orals | TS3.7

Impact of rupture complexity on seismic hazard: Case of the 2018 Mw7.5 Palu earthquake 

Liqing Jiao, Teng Wang, Guangcai Feng, Paul Tapponnier, Andrean V. H. Simanjuntak, and Chung-Han Chan

Rupture complexity results in difficulty in quantifying seismic hazards, such as the probability of an earthquake on multiple fault segments and spatial distribution of fault displacement on the surface. Here we tried to propose a dynamic model to fit the rupture behavior of the 2018 Mw7.5 Palu earthquake, which splays along several sub-fault plans on the surface. The Palu event was initiated on an unknown fault and propagated on a curved plane on the Palu-Koro and Matano faults. According to the Interferometric Synthetic Aperture Radar (InSAR) data, both principal (on-fault) and distributed (off-fault) faulting were identified and spatial displacement on the surface could be evaluated. To model the complex geometry of the coseismic rupture plane and corresponding deformation, we proposed a dynamic model through the Discrete Element Method (DEM). Our model demonstrated rupture along a planar fault at depth and several splay faulting with various deformations on the surface, corresponding to the observations. The simulations represented temporal rupture behavior that covers several earthquake cycles and the probability of superficial fault displacement, which shed light on subsequent seismic hazard assessment and probabilistic fault displacement hazard analysis, respectively.

How to cite: Jiao, L., Wang, T., Feng, G., Tapponnier, P., Simanjuntak, A. V. H., and Chan, C.-H.: Impact of rupture complexity on seismic hazard: Case of the 2018 Mw7.5 Palu earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7209, https://doi.org/10.5194/egusphere-egu23-7209, 2023.

EGU23-7301 | Posters on site | TS3.7

Is the Pampean flat-slab responsible for the differences in post-seismic motions between Maule and Illapel earthquakes? 

Emilie Klein, Hugo Boulze, Christophe Vigny, Luce Fleitout, and Jean-Didier Garaud

Ever since the Maule earthquake (Mw8.8, 2010), a quick vertical uplift is measured thanks to GNSS in the Andes, facing the rupture zone (~250 km to the trench). Models built for the Maule earthquake [Klein et al. 2016] have highlighted that a low-viscosity channel is required to explain the post-seismic uplift. This channel is located along the slab between 50 km and 130 km depth and has a viscosity of a few 1017 Pa.s - lower than in the asthenosphere, 1018 Pa.s. 

After the Illapel earthquake (Mw8.3, 2015), simple observations on GNSS time-series show that no uplift occurred in the Andes at an equivalent distance to the trench than in the case of the Maule earthquake. The subduction in the Illapel region is characterized by a flat-slab (called the Pampean flat-slab) in contrast with the normal-dipping subduction in the region of Maule.

Here, we investigate what is the impact of the Pampean flat-slab on the post-seismic deformations of the Illapel earthquake. In particular, we try to understand  whether the presence of the flat-slab inhibits the effect of the low-viscosity channel. For that purpose we compare GNSS vertical displacements with predictions in both regions of Maule and Illapel from a 3D spherical finite-element model that accounts for the slab geometry of the Chilean subduction zone.

How to cite: Klein, E., Boulze, H., Vigny, C., Fleitout, L., and Garaud, J.-D.: Is the Pampean flat-slab responsible for the differences in post-seismic motions between Maule and Illapel earthquakes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7301, https://doi.org/10.5194/egusphere-egu23-7301, 2023.

EGU23-7909 | Orals | TS3.7

The time-dependent stress changes within the seismic gap of the Eastern Marmara Sea (NW Türkiye) through multiple earthquake cycles since 715 AD. 

Murat utkucu, Hatice durmuş, Fatih uzunca, Süleyman nalbant, and Serap kIZILBUĞA

The M7.4 1999 İzmit earthquake apparently advanced the occurrence of possible future event or events along the segments of North Anatolian Fault Zone (NAFZ) beneath the Eastern Marmara Sea due to the positive stress load. This part of the NAFZ did not produce any large earthquake since the May 1766 earthquake, constituting a seismic gap close to the city of Istanbul. In the present study we constructed a Coulomb stress evolution model for the seismic gap that includes the effect of coseismic, time-dependent postseismic viscoelastic relaxation of the substrate beneath the elastic crust and secular stress loadings through the multiple earthquake cycles since 715 AD. The snapshots of stress changes before and after the large and destructive earthquakes of 740, 989, 1343, 1509, May 1766 and 1999 İzmit have been carefully examined. It has been estimated that the total stress changes before 989, 1343, 1509 and May 1766 earthquakes were in the range from 26 to131 bars. Present stress values at the eastern, middle and western sampling points on the faults within the gap are computed as 115, 131 and 85 bars respectively. Considering that the global mean of stress drops for continental strike-slip faults is about 35 bars, it is suggested that the earthquake hazard for the seismic gap critically high.

How to cite: utkucu, M., durmuş, H., uzunca, F., nalbant, S., and kIZILBUĞA, S.: The time-dependent stress changes within the seismic gap of the Eastern Marmara Sea (NW Türkiye) through multiple earthquake cycles since 715 AD., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7909, https://doi.org/10.5194/egusphere-egu23-7909, 2023.

EGU23-8011 | ECS | Orals | TS3.7

Crustal deformation of southwestern Tianshan orogenic belt based on InSAR and GPS observations 

Xiaohang Wang, Mahdi Motagh, and Caijun Xu

The Tianshan range, one of the most active mountain building belts in central Asia, has complex geological structures and frequent strong earthquakes since the Cenozoic. Due to lack of sufficient high-resolution geodetic survey measurments, little is known about detailed fault slip rates and seismic hazards related to main active faults in Tianshan. However, in recent years, the improvements in space-based geodetic technologies (Global Navigation Satellite System (GNSS) and interferometric synthetic aperture radar (InSAR)) with growing coverage and accuracy provide us an opportunity to image more subtle features in this area. In this study, we assesses inter-seismic deformation for the period 2014-2022 over the southwestern Tianshan based on ascending and descending Sentinel-1 SAR data.  Combined with GNSS data, we then constructed the 3D crustal deformation with high precision and high spatial resolution to study the active structures in southwestern Tianshan. The results indicate that: (1) The Tianshan orogenic belt (TSOB) has intense crustal deformation and the shortening rate is approximately 20 mm/yr. The Keping fold-thrust belt (KFB) is the most intensely deformed areas in TSOB, it’s convergence rate accounts for 1/3 of the entire southwestern Tianshan. (2) The South Tianshan fault (STF) and the Piqiang fault (PQF) have obvious left-lateral strike-slip components and the South Tianshan fault also has thrust characteristic. (3) The folds in both western and eastern KFB play an important role in accommodating regional strain, the shortening rate in KFB is accommodated by the thrust-anticlinal zone at the KFB front.

How to cite: Wang, X., Motagh, M., and Xu, C.: Crustal deformation of southwestern Tianshan orogenic belt based on InSAR and GPS observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8011, https://doi.org/10.5194/egusphere-egu23-8011, 2023.

Constraining the effective rheology of major faults is crucial to improve our understanding of the physics of plate boundary deformation. Laboratory studies have used analog experiments to propose rheological models based on viscoelasticity or friction that match laboratory-observed behavior under stress-controlled conditions. Such models have since been used to fit real-world observations of deformation near plate interfaces (both for co- and postseismic displacement timeseries), yielding a variety of estimates of key rheological parameters.
However, confidently differentiating between models using purely observations of a single earthquake (coseismic and postseismic deformation) is difficult — especially in the presence of coarse spatiotemporal sampling, inherent observational noise, and the simplifications of our forward models. In this study, we present a framework built on numerical probabilistic simulations aimed at using displacement timeseries across multiple earthquake cycles in a subduction zone, which successfully distinguishes between endmember constitutive models and recovers key rheological properties. Using synthetic Global Navigation Satellite System network datasets, we furthermore investigate the sensitivity of (hyper-)parameters to the recovery of the true underlying rheological models, and present progress made towards using real 3D observations of a megathrust.

How to cite: Köhne, T., Mallick, R., and Simons, M.: Description Of A Framework And Associated Sensitivity Analysis For Recovery Of Rheological Models And Their Key Parameters Using Multi-Cycle Fault Slip Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8837, https://doi.org/10.5194/egusphere-egu23-8837, 2023.

EGU23-9213 | Orals | TS3.7

An Adjoint-based Method for Inverting for Heterogeneous Material Properties and Fault Slip From Earthquake Surface Deformation Data 

Thorsten Becker, Simone Puel, Umberto Villa, Omar Ghattas, and Dunyu Liu

Analysis of geodetic and seismological data helps constrain earthquake dynamics and the physics of lithospheric deformation. Here, we discuss a new modeling approach based on an open-source finite-element framework to invert surface deformation data for constitutive laws and their parameters, such as the Poisson’s ratio or shear modulus in the crust and mantle wedge.

These inversions can be realized by using adjoint-based optimization methods which efficiently reduce the misfit between the calculated and observed displacements. To quantify the associated model uncertainties, we extend the inverse approach to a Bayesian inference problem. Since the data are usually informative only in a few directions in parameter space, we use a low-rank Laplace approximation of the posterior distribution to make the inverse problem computationally tractable. The mean and the posterior covariance are approximated by the solution of the inverse problem (MAP point) and the inverse of the Hessian of the negative log posterior evaluated at the MAP point, respectively. We show how smoothly varying parameter fields can be reconstructed satisfactorily from noisy data.

To improve the spatial resolution of the inverse solution we solve a Bayesian optimal experimental design problem to find the best station configuration by maximizing the expected information gain, defined as the Kullback-Leibler divergence between posterior and prior distributions. We show how and why the optimal network improves the material property inference more than evenly spaced stations. Based on our previous work on inverting for fault slip without Green’s function computations, we combine the two inversion schemes to jointly infer both model parameters, the coseismic slip, and material properties distribution. Lastly, we test this numerical forward/inverse framework with an application, the 2011 Tohoku-oki M9 earthquake. Both continuous land-based and six offshore acoustic GNSS stations located around the earthquake epicenter are inverted to jointly estimate the shear modulus and the fault slip during the megathrust event.

Our results demonstrates the potential of our computational framework and the general approach for inferring constitutive laws to evaluate sensitivity to parameters, and define strategies to improve our understanding of relevant parameters for earthquake dynamics. 

 

How to cite: Becker, T., Puel, S., Villa, U., Ghattas, O., and Liu, D.: An Adjoint-based Method for Inverting for Heterogeneous Material Properties and Fault Slip From Earthquake Surface Deformation Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9213, https://doi.org/10.5194/egusphere-egu23-9213, 2023.

EGU23-9752 | ECS | Posters on site | TS3.7

Interseismic deformation in the Tjörnes Fracture Zone, North Iceland from GNSS measurements 

Alejandra Barreto, Renier Viltres, Rémi Matrau, Benedikt G Ófeigsson, and Sigurjón Jónsson

The Tjörnes Fracture Zone poses significant seismic hazard to the town of Húsavík and other nearby coastal communities in North Iceland as it is capable of generating earthquakes of magnitude ~7. The 120 km long offset connects the offshore Kolbeinsey Ridge to the onshore Northern Volcanic Zone and accommodates approximately 18 mm/yr of transform motion between the North American and Eurasian plates. Most of the deformation is taken up by the two main structures of the fracture zone. The Grímsey Oblique Rift exhibits bookshelf faulting and consists of steeply dipping faults, arranged en-echelon and striking roughly N-S, bounding a series of left-stepping basins. The Húsavík-Flatey Fault is a ~100 km-long right-lateral strike-slip fault. It is mostly offshore, except for its easternmost ~25 km that comes onshore just north of Húsavík. To assess how the deformation is partitioned within the Tjörnes Fracture Zone and to calculate the rate of seismic moment accumulation on the Húsavík-Flatey Fault we use geodetic data from our North Iceland GNSS network. The network covers an area of roughly 200 km by 130 km in size and includes 21 continuous and 92 campaign-style GNSS stations. The continuous data now span up to ~21 years from 2001 to 2022. The first campaign measurements that focused on the HFF were carried out in 1995 and since then we have expanded the campaign-station network to the West towards Tröllaskagi and Skagafjörður and remeasured the network on several occasions. Data from the 2002, 2007, 2009, 2010, 2011, 2013, 2016, 2019, and 2022 campaigns are included in our study. In addition, several stations from the nationwide ISNET reference station network within our study area also included. The GNSS data is used to produce the most up to date velocity field from North Iceland. Relative to the North American plate, our results show a gradual increase of East velocities towards the Northeast across the two main transform structures that reach roughly 18 mm/yr on the Eurasian plate. At the northern tip of the Tjörnes peninsula, between the two transform structures, the velocities are roughly at half the total rate seen at the easternmost stations on the Eurasian plate. Limited deformation is found Southwest of the Húsavík-Flatey Fault in Tröllaskagi, within the so-called Dalvík zone, located on the North American plate.  These results are used to study the present day-kinematics of the Tjörnes Fracture Zone and to further improve the locking depth and slip-rate estimates of the main lineaments.

How to cite: Barreto, A., Viltres, R., Matrau, R., Ófeigsson, B. G., and Jónsson, S.: Interseismic deformation in the Tjörnes Fracture Zone, North Iceland from GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9752, https://doi.org/10.5194/egusphere-egu23-9752, 2023.

EGU23-10710 | ECS | Posters on site | TS3.7

The deep subduction earthquake machine: A synoptic view of the Chile Subduction Zone. 

Joaquín Julve, Marcos Moreno, Sylvain Barbot, Andrés Tassara, Rodolfo Araya, and Nicole Catalán

In the last 20 years, the Chile Subduction Zone (CSZ) has hosted two deep-located subduction events, the 2007 Mw 7.7 Tocopilla earthquake at the Mejillones Peninsula, and the 2016 Mw 7.6 Melinka earthquake at the south of the Chiloé Island. Interseismic seismicity at the Northern and Southern segments of the CSZ, show that in both cases, the ruptures initiated at the down-dip limit of the seismogenic zone. Locking degree models suggest that hypocenter location of this kind of megathrust earthquakes is spatially related with the transition from strongly to weakly locked areas. There are major differences in fault geometry, temperature-pressure regime, petrology at the plate interface and forearc structure between the North and South of the CSZ, raising the question about how such different tectonic settings allow a similar style of rupture. By constructing geologically and geophysically constrained dynamic numerical simulations, here we show that moderate-to-large deep nucleated earthquakes are controlled by petrology and pressure-temperature conditions at the plate interface, along with the structure of the forearc wedge. Our results explain the occurrence, recurrence times and coseismic upper crust deformation of both earthquakes, suggesting that blind ruptures are not only generated at specific conditions, but a suitable combination of the aforementioned parameters is needed. Since the Northern Chile subduction zone has no sediments at the megathrust, the frictional behavior is controlled by altered basalt at the seismogenic depth, and seismicity shows a strong temperature-dependence. Once altered basalt no longer behaves as a velocity weakening material, blueschist rocks allow slow-slip events to develop. The Southern Chile subduction zone is filled with Pliocene-to-present sediments feeding a quartz-dominated subduction channel that defines the seismogenic limit. Within this framework, basal accretion structures are overlapped with a fluid concentration zone at the Moho depth, where the Melinka earthquake initiated. These synoptic views of the CSZ manifest a strong interaction between fluid-rock and forearc structures, which explains the occurrence of blind ruptures at the subduction seismic cycle.

How to cite: Julve, J., Moreno, M., Barbot, S., Tassara, A., Araya, R., and Catalán, N.: The deep subduction earthquake machine: A synoptic view of the Chile Subduction Zone., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10710, https://doi.org/10.5194/egusphere-egu23-10710, 2023.

This study aims to forecast the magnitude of future strong (6.0≤M<7.0) and major (7.0≤M<8.0) earthquakes along the East Anatolian Fault Zone (EAFZ), a major fault zone of Turkey and an active plate boundary that lies between Arabian and Anatolian plates. We first investigated the segmentation of the EAFZ in this context after compiling the earlier research on its structural setting and historical earthquakes. In order to determine the distribution of slip deficit rates, we analyzed GPS slip rates to obtain back-slips. The current slip budgets on each fault segment are calculated using the resulting slip deficit estimates. To elaborate on whether b-values might be used to distinguish between locked and creeping fault segments, we also examined the distribution of b-values along the fault. As a result, we found a reverse correlation between slip deficit rates and b-values. According to our findings, the EAFZ has currently a slip deficit of 1.51 m. While there is a segment such as Hacılar with no slip deficit, there is enough slip deficit accumulation to generate three strong and three major earthquakes on the other fault segments. Presently, these fault segments have the potential to re-generate previous earthquakes, within the magnitude range of 6.8-7.4. The latest strong earthquake on January 24, 2020, the Elazığ earthquake (M 6.8) verified our magnitude forecasts for the Sivrice-Pütürge segment.

How to cite: Uçan, K. A. and Bulut, F.: Forecasting Earthquake Magnitudes along the East Anatolian Fault Zone using Fault Zone Segmentation, Historical Earthquakes, and GPS Slip Rates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11401, https://doi.org/10.5194/egusphere-egu23-11401, 2023.

EGU23-11616 | Orals | TS3.7

InSAR observations of syn-seismic slip on faults due to M~6 earthquakes 

Henriette Sudhaus, John Begg, Vasiliki Mouslopoulou, Julia Knüppel, and Tilman May

As well as slip on a primary fault plane, earthquakes can produce slip on neighbouring faults which are not directly linked to the main source. This slip is called syn-seismic. With modern space-borne observation techniques, we observe syn-seismic slip down to a few centimeters on active faults nearby the source. An excellent example is the mapped slip on secondary faults during the 2019 Ridgecrest earthquake sequence in California. The overall spatial pattern of syn-seismic slip with respect to the main fault suggest that these faults respond to local stress changes caused by the main shock.

Data that enable the detection of surface fault slip on such small scale are provided by optical and radar satellites which allow a very high precision with high spatial resolution. In particular, short revisit times of these satellite observations lead to high coherence between images matched in pixel-offset and radar interferometric techniques.

We present further examples of syn-seismic fault slip during ~M6 earthquakes from different regions, such as those recorded in Greece in 2021 (Tyrnavos and Arkalochori) and 2020 in Tibet (W Xizang and near Xegar). We use Sentinel-1 interferometric wide-swath SAR acquisitions, which we process on the highest spatial resolution and apply weak filtering only. Our examples have in common that their syn-seismic fault activation reveals slip of a few centimeters only, persistently along a section of the fault’s length. The slip directions commonly appear to follow the coseismic surface displacement gradients which, in some cases, results in reverse slip on long-term normal faults. The activated faults were either faults previously mapped or concealed faults which were identified due to InSAR.

It is difficult to estimate the depth of syn-seismic fault slip and therefore how much strain has been released due to localized stress changes. We are also uncertain of the extent to which this small slip release contributes to the long-term displacement and displacement rate on faults and whether its contribution should be included in dislocation fault slip models. Our compilation suggests that syn-seismic slip is rather common, despite the rarity of previous observations, and is now detectable only because of improved resolution provided by InSAR data.

How to cite: Sudhaus, H., Begg, J., Mouslopoulou, V., Knüppel, J., and May, T.: InSAR observations of syn-seismic slip on faults due to M~6 earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11616, https://doi.org/10.5194/egusphere-egu23-11616, 2023.

Using GPS measurements, historical earthquake records, and instrumental earthquake data, we investigated GPS slip rates along the rupture zone of the 1668 Great Anatolian Earthquake (M8.1). We found three complete and one incomplete earthquake cycles since 1254 compiling all available historical and paleo-earthquake records in the literature. These records verified that a ~750-kilometer section of the North Anatolian Fault Zone was ruptured in 1668.  To simultaneously estimate segment-based slip rates and locking depths, we combined all available GPS measurements and modeled them using an arctangent approach. Slip rates are used to estimate preliminary inter-seismic slip storages assuming fault segments are fully locked after a mainshock. Large residuals between preliminary slip estimates and co-seismic slips indicate that the fault segments do not store slip for some time after a major earthquake. The creeping and locked stages vary in time and space, as our investigation revealed. Our results show that the slip rates along the NAFZ systematically increase from east to west suggesting that the Aegean extensional regime is the main driving force for the westward movement of the Anatolian Plate. Additionally, the locking depths show an east-to-west decreasing pattern verifying east-to-west thinning of crustal thickness along the Anatolian Plate. The earthquakes over the past three complete cycles and the current incomplete cycle indicate that the failure of the NAFZ begins in the east and moves westward reflecting a decelerating pattern. The failure is typically completed within a time period of 239±3 years.

How to cite: Yıldırım, S. C., Bulut, F., and Garagon, A.: East to West Acceleration of the Slip Rates Along the North Anatolian Fault and Its Implıcations Regarding Plate Tectonics and Earthquake Cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11854, https://doi.org/10.5194/egusphere-egu23-11854, 2023.

EGU23-12158 | ECS | Orals | TS3.7

Modeling surface deformations during the seismic cycle along the Chilean subduction zone 

Hugo Boulze, Luce Fleitout, Emilie Klein, Christophe Vigny, and Jean-Didier Garaud

Thanks to space geodesy we know with a millimetric precision how the lithosphere deforms at each stage of the seismic cycle. In particular, during the post-seismic phase, it can deform over thousands of kilometers and for decades. These deformations are partly due to viscoelastic relaxation of the asthenosphere.

In a previous work, we have shown that at the temporal and spatial scale of the seismic cycle, the viscoelastic relaxation can be modeled by a linear creep law [Boulze et al. 2022]. Therefore, because of the linearity of the creep law, the superposition principle applies and the present day deformation is simply the sum of the post-seismic deformations induced by past earthquakes. Based on this result, the objective of our work is to determine what slip history is needed on the Chilean subduction interface to reproduce the current deformation of South America, which is well measured by GNSS.

To investigate this challenging problem, we first develop a 3D spherical finite-element model of the Chilean subduction zone. This model covers the entire South American continent and incorporates a slab with a geometry described by Slab2.0 model [Hayes et al. 2018]. Then, we compare different ways to model the seismic cycle using the backslip theory [Savage 1983]. Finally, by comparing GPS time-series with our seismic cycle model prediction, we discuss many ingredients of the model: e.g. the viscosity of the asthenosphere (Maxwell, Burgers), the impact of a flat slab and low viscosity zones, the magnitude and extent of historical earthquakes.

How to cite: Boulze, H., Fleitout, L., Klein, E., Vigny, C., and Garaud, J.-D.: Modeling surface deformations during the seismic cycle along the Chilean subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12158, https://doi.org/10.5194/egusphere-egu23-12158, 2023.

Measuring 36Cl cosmogenic nuclides on exposed bedrock fault scarps has now been used in several places in the Mediterranean to retrieve ages of the fault seismic history (e.g. Mechernich et al. 2022, Iezzi et al. 2021 and Cowie et al. 2017).

In Central Apennines, around the Fucino basin, at least 15 36Cl sampling sites were analyzed in previous studies to interpret the 36Cl data as seismic history or slip-rates. Several codes (e.g., Beck et al. 2018, Shlagenhauf et al. 2010) were used as a basis for solving 36Cl production equations to calculate the 36Cl concentration resulting from bedrock scarp exhumation history. Some codes included an MCMC routine to retrieve the seismic histories the closest to the dataset. The main differences between the various codes lie in: 1-the fault history prior to exhumation, 2-the parameters previous authors decided to inverse (as an example, mean density of the colluvium is inversed in Beck et al. 2018 but not in Tesson et al. 2019) and 3-the a priori distribution of those parameters (for instance, the time between two earthquakes follows an inverse gaussian distribution for Beck et al. 2018 but a uniform distribution for Tesson et al. 2019). I have compared the various codes and run them on the same dataset (one site at Campo Felice, one site at Roccapreturo and one site at Magnola) and found that retrieved seismic histories are similar, although the estimation of uncertainties differs.

Moreover, all previous cited codes run under Matlab or Fortran. Fortran codes have the advantage of fast computing time but could be cumbersomeI here propose a new code, adapted from Tesson et al. 2019, in the more accessible and widely used Python language. The inferred pre-exposure is also inversed and is a function of the height of the fault cumulative escarpment. The parameters considered are the number of events, ages of event, the associated slips, the long term slip rate, the quiescence and the pre-exposure and their optimal evaluation is done with a MCMC algorithm provided by Numpyro (Du Phan et al. 2019).

Using this new code, we have reanalyzed the 15 36Cl sites around the Fucino and, through a gaussian mixture algorithm, checked the hypothesis of common periods of activity throughout all the Fucino basin.

 

How to cite: Llinares, M., Benedetti, L., Gassier, G., and Viseur, S.: A new python code to invert 36Cl cosmogenic nuclide dataset on normal fault bedrock scarps: comparison with previous published codes and results on the accuracy of the retrieved seismic history of two normal fault systems in Central Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12874, https://doi.org/10.5194/egusphere-egu23-12874, 2023.

EGU23-13616 | ECS | Posters on site | TS3.7

Evolution of the Off-Fault Deformation during experimental strike-slip earthquakes 

Sarah Visage, Pauline Souloumiac, Nadaya Cubas, Bertrand Maillot, and Yann Klinger

Large continental strike-slip earthquakes produce spectacular surface deformations. However, ground displacements are only partially measured in comparison with the amount of slip inferred at depth. Relatively few estimates of the proportion of surface deformation accumulated on faults and deformation distributed regionally around faults are available. However, new technological advances such as state-of-the-art space imaging techniques now greatly improve the quality of surface rupture measurements. Their application has revealed that a significant amount of deformation is accommodated as diffuse deformation in an area of several hundred meters around the fault. This distribution is suggested to depend on the fault complexity. It is therefore essential to understand this distribution and its relation with fault segmentation to study the impact of fault complexities in a seismic context, we recently developed an innovative experimental prototype using some granular materials in layers similar to the earth's crust. They consist of a basal layer of rubber powder that stores elastic energy provided by the displacement of a basal plate sliding parallel to a second, fixed plate. The second layer is made of raw, twice broken rice that brings the stick-slip behaviour required for locking the slip between ruptures, and a third layer of sand with the frictional behaviour of cold shallow sediments at the surface. The surface sand layer allows following the evolution of the fault surface trace from the R-shears stage to the anastomosed fault zone composed of a succession of segments separated by zones of complexities. Using image correlation, we analyse the surface displacements. Since the rice layer causes a stick-slip behaviour, the analysis of the surface displacement is done on several seismic cycles: if the surface displacement is lower than the displacement imposed by the motor, it is an inter-seismic period, if the surface displacement is faster than the displacement imposed by the motor then it is a seismic event.

Once this catalog of events is established, the analysis of the gradient of the displacement Ux parallel to the basal enables us to quantify the deformation: localized (On-Fault Deformation) or distributed (Off-Fault Deformation).

At the R-shear stage, we measure [50~80] % of Off-Fault Deformation. Once the strike-slip fault is formed, the percentage of OFD drops between 20 to 30 %. These results are comparable to measurements made by experiments devoid of a stick-slip behaviours (with only of sand). Moreover, if we compare these values to the proportions of OFD estimated for natural earthquakes, we find the same distribution.

These experiments show that the more mature the fault, the more it will rupture seismically, in time as in space.

How to cite: Visage, S., Souloumiac, P., Cubas, N., Maillot, B., and Klinger, Y.: Evolution of the Off-Fault Deformation during experimental strike-slip earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13616, https://doi.org/10.5194/egusphere-egu23-13616, 2023.

EGU23-14568 | Posters on site | TS3.7

Active Tectonics in Southern Haiti and Surface Rupture of the 14 August 2021 Earthquake 

Newdeskarl Saint Fleur, Yann Klinger, Joseph Emmanuel Dessable, Germain Saint-Preux, Nathalie Feuillet, Dominique Boisson, Eric Calais, and Jean-Bernard de Chabalier

The 14 August 2021 earthquake occurred along the southern peninsula of Haiti only 11 years after the 12 January 2010 devastating earthquake. According to seismological and geodetic data, the events are both complex involving more than one fault. The 2021 rupture mainly portrayed reverse motion to the east near L’Asile town and left-lateral strike-slip motion to the west near Camp-Perrin town and Macaya mountain. A few days after the 2021 event, we conducted the first post-seismic field reconnaissance along the left-lateral Enriquillo-Plantain Garden Fault (EPGF) zone from L’Asile to Macaya mountain. We found numerous fresh cracks and landslides along that fault zone. The 111 cracks are mainly E-W-striking, some are oriented WNW-ESE, consistent with fault orientation in the area. In addition, the biggest cracks are mostly located to the west of the rupture zone, some of them may be potential fault surface rupture as revealed by seismological data. Furthermore, our observations along the northern coast of the southern peninsula revealed no significant coseismic coastal uplift as also suggested by InSAR data. Besides that field reconnaissance, we revisited the fault map around the epicentral area using high-resolution LiDAR data, Pléiades imagery and aerial photographs. We identified several left-lateral offsets of tens of meters corresponding to successive slips along the EPGF from L’Asile to Macaya mountain. In addition to the strike-slip deformation, we identified numerous geomorphic features related to long-term tectonic uplift to the north of the EPGF surface trace near the eastern part of the 2021 rupture. Those features are strikingly rare to the south. Such a pattern may indicate that the EPGF is north-dipping in the area. The 14 August 2021 rupture offers a new opportunity to constrain the kinematics and geometry of the EPGF system in southern Haiti.

How to cite: Saint Fleur, N., Klinger, Y., Dessable, J. E., Saint-Preux, G., Feuillet, N., Boisson, D., Calais, E., and de Chabalier, J.-B.: Active Tectonics in Southern Haiti and Surface Rupture of the 14 August 2021 Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14568, https://doi.org/10.5194/egusphere-egu23-14568, 2023.

Foreshocks are commonly observed before the happening of earthquakes in seismic catalogs. They provide critical precursors to reveal the process for the nucleation and rupture of earthquakes. Two mechanisms, pre-slip and cascade triggering, are thought to be the main physical process to explain the foreshock sequences and the mainshock. However, different from the regular micro-magnitude foreshock sequences (e.g. M1.0-3.0), some moderate-size (e.g. ~M6) foreshocks are also found before the mainshock (e.g. the M6.4 foreshock before the 2017 M7.1 Ridgecrest earthquake). How these moderate-size foreshocks affect the happen of mainshocks as well as their possible triggering mechanisms are still ambiguous and less studied.

In this study, fortunately, we obtain geodetic observations of moderate-size (M5.8 and M6.5) foreshocks for the 2020 M6.0 Turkey and 2022 M6.9 Taiwan earthquakes using Sentinel-1 Synthetic Aperture Radar (SAR) images. It is very rare for the geodetic observations of such foreshocks as they are very temporally close to the mainshocks within one day (i.e. ~10 hours and ~17 hours). We then invert for the fault geometries and slip distributions for these two earthquakes together with their moderate foreshocks constrained by these geodetic observations. Coulomb stresses on the fault planes of mainshocks produced by the moderate-size foreshocks are also calculated as well as the static stress drops of the mainshocks. Our study provides a unique opportunity to explore the possible triggering mechanism between moderate-size foreshocks and mainshocks as well as the conditions for the happening of earthquakes.

How to cite: Luo, H. and Wang, T.: Geodetic modeling of moderate-size foreshocks with mainshocks and the implication to earthquake trigger mechanisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15420, https://doi.org/10.5194/egusphere-egu23-15420, 2023.

EGU23-16199 | ECS | Orals | TS3.7

Assessing distribution and pattern of the earthquake-related deformation caused by large continental normal earthquakes using optical image correlation 

Lucia Andreuttiova, James Hollingsworth, Pieter Vermeesch, and Tom Mitchell

Earthquakes on normal faults in the continental setting are relatively uncommon. The scarcity of surface-rupturing events underpins an absence of surface displacement measurements. It is a common practice to use surface offset as a proxy to understand the fault structure at depth. Hence, the lack of comprehensive surface data impedes the subsurface reconstruction of seismogenic normal faults and prohibits the thorough assessment of earthquake hazards. To supplement the available surface displacement measurements and to make statistically significant inferences, we apply optical image correlation (OIC) methods to historical images from three large continental normal earthquakes in the western United States (1954 Dixie Valley (Mw 6.8) - Fairview Peak (Mw 7.1) earthquake sequence, the 1959 Mw 7.2 Hebgen Lake earthquake and the 1983 Mw 6.9 Borah Peak earthquake). The results of this study are displacement maps with three components of deformation from which we extract high-resolution 3-d measurements everywhere along the surface rupture. 

 

The high-resolution 3-d data are used to quantify the magnitude and direction of the earthquake-related offset, the percentage of off-fault damage as well as the width of the fault zone. These parameters represent the fault maturity, geometric complexity and subsurface structure of the fault. Our observations confirm behaviours previously observed along strike-slip faults (e.g. magnitude of off-fault deformation is proportional to the rupture complexity). In addition, a comparative assessment of the results from the three study areas demonstrates that features such as excess slip detected close to the fault scarp are not unique and can be found along multiple dip-slip faults. Consequently, this study documents the variation of the quantifiable parameters along the normal faults. It suggests that while some parameters are a universal reflection of the fault characteristics, others vary according to the geology or topography in the area and should not be accepted without further investigation.

How to cite: Andreuttiova, L., Hollingsworth, J., Vermeesch, P., and Mitchell, T.: Assessing distribution and pattern of the earthquake-related deformation caused by large continental normal earthquakes using optical image correlation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16199, https://doi.org/10.5194/egusphere-egu23-16199, 2023.

EGU23-16845 | ECS | Posters on site | TS3.7

Characterizing the transition from diffuse to localized deformation using optical image correlation: the 2021 Mw7.4 Maduo, Tibet, earthquake 

Solene L Antoine, Zhen Liu, Yann Klinger, Arthur Delorme, and Jing Liu-Zeng

The 2021 Mw7.4 Maduo earthquake generated a ~160 km-long fault rupture within the Eastern Tibetan plateau, at about 100-150 km to the south-west of the Eastern Kunlun fault. Fault slip measured on the field represents only 20% of the displacements from satellite Interferometric Synthetic Aperture Radar (InSAR) measurements, highlighting the primarily diffuse nature of the surface deformation for this earthquake. Most surface deformation associated with this event corresponds to diffuse shear, occurring over widths of a few hundreds of meters to a few kilometers, and sometimes associated with shearing and tensional cracks mapped in the field. In this study, we use sub-pixel correlation of Pleiades (0.5 m) and SPOT-6/7 (1.6 m) optical images to characterize the near-fault displacement patterns associated with the 2021 Maduo event. We also use other optical data to assess the impact of sensor resolution on the measurements. Our results cover three kilometers on both sides of the rupture area with a resolution of 0.5 m. These results show that, despite the large rupture gaps observed in the field, the shear deformation zone at the surface is continuous along the entire length of the 2021 rupture. Even though, we observe variations in the surface deformation patterns, with regions that present more localized deformation whereas others are primarily characterized by diffuse shear. Using the high-resolution displacement maps, we characterize the transitions from the localized to the diffuse shear along the rupture strike, and investigate the relations with the bulk rock properties, and coseismic slip distribution. We also determine the limit at which deformation starts to localize on fractures that are large enough to be visible in the field.

How to cite: Antoine, S. L., Liu, Z., Klinger, Y., Delorme, A., and Liu-Zeng, J.: Characterizing the transition from diffuse to localized deformation using optical image correlation: the 2021 Mw7.4 Maduo, Tibet, earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16845, https://doi.org/10.5194/egusphere-egu23-16845, 2023.

EGU23-17189 | ECS | Posters on site | TS3.7

Testing a novel cave-based proxy for palaeo-earthquake shaking on the Alpine Fault, Aotearoa/New Zealand. 

Jeffrey Lang, Joel Baker, Julie Rowland, Adam Hartland, Paul Williams, John Hellstrom, Jamie Howarth, Ingrid Ukstins, Travis Cross, and Christopher Wood

Speleoseismology aims to reconstruct palaeoseismic records by dating pre- and post-damage speleothem calcite. A common approach is to infer palaeo-earthquakes from evidence of coinciding damage features (e.g., rockfall and broken speleothems) at multiple locations, which can be challenging in regions of high tectonic strain where short recurrence intervals of large earthquakes require dating of an impractically large number of damage features. Alternative approaches concerned with dating successive growth changes in individual speleothems (e.g., axis changes and growth hiatuses) are better suited to high-seismicity settings, as closely spaced events are more readily resolved. However, the origins of these growth changes can be ambiguous.

This study tested a novel geochemical proxy for quantifying ground shaking that is amenable to high-resolution speleothem studies, and potentially more diagnostic of earthquake damage. We evaluated the hypothesis that past large earthquakes temporarily elevate Mg/Ca in cave drip waters via incongruent carbonate dissolution following host rock fracturing (ICDC), leading to corresponding Mg enrichments in speleothem calcite. To do this, we examined a well-dated Holocene stalagmite (GT1) from a cave near the Alpine Fault, which is Aotearoa/New Zealand’s longest (>500 km) active onshore fault and a major source of seismic hazard. The locality is 4 km from the Alpine Fault’s northern section, which typically ruptures every 414–470 yr in a major (MW >7) to great (MW >8) earthquake, resulting in shaking intensities of MMI >VIII at the study site (MMI: Modified Mercalli Intensity).

We present a record of Mg/Ca variability in GT1 since ~5 ka, obtained by laser ablation inductively coupled plasma mass spectrometry along the stalagmite growth axis, and constrained temporally by >40 U–Th ages. Preliminary data show high baseline Mg concentrations in GT1 that cannot be explained solely by other mechanisms of drip water Mg/Ca enrichment (i.e., prior calcite precipitation), suggesting an ongoing contribution of Mg to drip waters by ICDC. Anomalous Mg peaks are therefore interpreted as high-intensity shaking events that temporarily elevated drip water Mg/Ca above baseline values. Post-2.5 ka Mg peaks are generally more subtle (30–50% enrichment) than pre-2.5 ka peaks (40–100%). Magnesium peaks are also strongly associated with brown-stained laminae inferred to reflect soil-derived organics. We propose that the high-Mg/high-organics horizons represent large earthquakes that both fractured the host rock and enhanced the mobilisation of organics from overlying soil.

We compared the GT1 record with a proximal and independent 1.4-kyr record of well-dated seismically triggered lacustrine turbidites. Given the subtle nature of Mg peaks in this interval, we consider those associated with physical growth changes (i.e., growth onset/cessation and/or axis change) as more likely to represent earthquakes. Of nine Mg peaks identified, five are associated with major physical growth changes. Of the four largest (MMI >VIII) shaking events in the lake turbidite record, which correspond to northern Alpine Fault surface-rupturing earthquakes, three overlap in age with a GT1 Mg peak and physical growth change. Further, two of the three historic earthquakes that generated MMI ≥VII shaking at the study site also overlap in age with a Mg peak.

How to cite: Lang, J., Baker, J., Rowland, J., Hartland, A., Williams, P., Hellstrom, J., Howarth, J., Ukstins, I., Cross, T., and Wood, C.: Testing a novel cave-based proxy for palaeo-earthquake shaking on the Alpine Fault, Aotearoa/New Zealand., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17189, https://doi.org/10.5194/egusphere-egu23-17189, 2023.

EGU23-833 | ECS | Posters on site | TS3.9

Spatio-temporal monitoring of surface deformation of the North Anatolian Fault Zone in Düzce Region by InSAR technique 

Çağkan Serhun Zoroğlu, Tülay Kaya Eken, Emre Havazlı, and Haluk Özener

The North Anatolian Fault Zone (NAFZ), that represents a transform plate boundary between the Anatolian and Eurasian plates, generated several devastating earthquakes in the 20th century. The well-known seismic sequence along the NAFZ has begun with the 1939 M7.9 Erzincan Earthquake and followed a westward migrating pattern until the 1999 M>7 Izmit-Düzce ruptures. Although there have been extensive efforts on modeling co-seismic slip properties of the recent large events along the NAFZ, possible interplay of crustal properties with fault mechanics and inter-seismic loading parameters characterized by surface deformation behavior is less known. This study aims to determine the spatio-temporal behavior of long-term surface deformation along the Düzce Fault segment of the NAFZ. We examine the effect of physical properties of the crustal structure on the inter-seismic loading and surface creep parameters in this actively deforming area. For this purpose, we adopted the well-known InSAR timeseries method using publicly available Sentinel-1 data. Sentinel-1 observations covering our study area has a time span of 8 years between 2014 and 2022. We exploit geoelectrical properties and other available seismological observations/models of the crust to be evaluated with the velocity fields inferred from InSAR time series analysis. We further compare variations in the surface deformation prior to and after the most recent November 23rd, 2022, Mw6.0 Gölyaka-Düzce earthquake by using data obtained from the analysis of both ascending and descending InSAR datasets. Our preliminary results show the slip rate of ~25 mm/yr on the Duzce Fault.

This project is funded by the Bogazici University with the BAP Project No SUP-18161.

How to cite: Zoroğlu, Ç. S., Kaya Eken, T., Havazlı, E., and Özener, H.: Spatio-temporal monitoring of surface deformation of the North Anatolian Fault Zone in Düzce Region by InSAR technique, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-833, https://doi.org/10.5194/egusphere-egu23-833, 2023.

We used 70 campaign-mode, 12 continuous and 6 high-rate GNSS and InSAR data to examine the coseismic off-fault antithetic shear triggered by the 2016 Mw 6.4 Meinong oblique thrust earthquake at the Hsinhua fault area, ~30 km northwest of the epicenter. The GNSS and InSAR data were inverted to estimate the 3D coseismic displacement field at the Tainan frontal fold-thrust belt, where the deformation is mostly affected by the directivity along the rupture front direction of the Meinong earthquake. The coseismic deformation pattern shows dominantly synthetic shear along the rupture direction, on the contrary, a nearly N-S striking, 7-km-long and 5-km-wide area indicating antithetic motion appeared at northeast of the Tainan tableland and cross-cutting the ENE-WSW-striking Hsinhua fault at a high angle. The N-S striking structure at the Hsinhua fault area reveals coseismic horizontal displacements of 3.0-7.0 cm to the southeast and vertical displacements of 0.4 to 4.4 cm, and although in the opposite direction, the magnitude of horizontal displacements of the antithetic shear are comparable to those of the synthetic motion in the adjacent areas. We calculated the static Coulomb stress change on the possible west-dipping shallow structure at the Hsinhua area due to slip on the source fault of the 2016 Meinong earthquake. The calculated static stress change is about 0.05 bar, which is negligible and very unlikely to promote the structure or bedding to slip at 30-km away for such a moderate earthquake. We also processed 6 high-rate, two 50-Hz and four 1-Hz, GNSS data for the PPP displacement and SNIVEL GPS-derived velocities, in that two stations, one 50-Hz and one 1-Hz, are located inside the block with antithetic motion. The high-rate GNSS solutions indicate that the displacements occurred at the same time when the P and S waves arrived, and velocity pulses up to 90.0 cm/s appeared at all six stations. We suggest that, as evidenced by large velocity pulses resulted from the strong directivity effect, the dynamic stress change caused by the rupture of the 2016 Meinong earthquake triggered the structure 30-km away.

How to cite: Rau, R.-J., Lai, L.-C., and Ching, K.-E.: Coseismic off-fault antithetic shear deformation in southwestern Taiwan triggered by the 2016 Mw 6.4 Meinong earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1803, https://doi.org/10.5194/egusphere-egu23-1803, 2023.

EGU23-2188 | ECS | Posters on site | TS3.9

Seismic and aseismic slip on the Central Range fault associated with the 2013 Mw 6.3 Ruisui earthquake (Taiwan) 

Hsiao-Fan Lin, Alexandre Canitano, Yu-Fang Hsu, Adriano Gualandi, Ya-Ju Hsu, Hsin-Hua Huang, and Hsin-Ming Lee

The 2013 Ruisui earthquake is the first unequivocal evidence of the seismicity activity of the Central Range Fault (CRF) in the central Longitudinal Valley in Taiwan, and hence reveals the existence of aseismic slip on the CRF. The finite-fault coseismic model obtained from the Bayesian joint inversion of GNSS and strainmeter data suggests that the rupture area is mainly distributed on a 26 km × 22 km fault plane located at the depth of 3 to 19 km with a maximum slip of about 0.5 m. A variational Bayesian independent component analysis (vbICA) technique is applied to the detrended GNSS time series to extract postseismic deformations in the near-source region. Although the afterslip distribution was not able to be well inverted due to the lack of observation on the western side of the fault plane, using rate-and-state friction rheology to simulate the surface displacements generated by the stress-driven afterslip model, we infer for the first time the existence of a shallow velocity-strengthening region on the CRF, which is capable of hosting and sustaining aseismic transient deformations over months.

How to cite: Lin, H.-F., Canitano, A., Hsu, Y.-F., Gualandi, A., Hsu, Y.-J., Huang, H.-H., and Lee, H.-M.: Seismic and aseismic slip on the Central Range fault associated with the 2013 Mw 6.3 Ruisui earthquake (Taiwan), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2188, https://doi.org/10.5194/egusphere-egu23-2188, 2023.

EGU23-2484 | ECS | Posters on site | TS3.9

The Seismogenic Potential of the Southernmost Ryukyu Subduction Zone as Revealed by Historical Earthquakes and Slow Slip events 

Sean Kuanhsiang Chen, Yih-Min Wu, and Yu-Chang Chan

The southernmost Ryukyu subduction zone may have a geodetically inferred Mw 7.5 to 8.7 megathrust earthquake in a shallow locked region, the Ryukyu fault. Paleoseismological evidence of historical earthquakes available from the last 417 years indicates that only a 1920 Mw 7.7 earthquake occurred within this magnitude range, near the downdip end of the Ryukyu fault. As slow slip events downdip the locked seismogenic zone may trigger a large subduction earthquake, we investigate how the first observed slow slip events in 2005, 2009, and 2015 initiated downdip in the Ryukyu fault interface affect the occurrence of a megathrust. We establish possible megathrust earthquake cycles from Mw 7.5 to 8.7 on the Ryukyu fault using constraints from the magnitude-frequency relation based on local historical earthquakes. This analysis shows a b value of 1.2 for magnitudes greater than Mw 7.0, which is higher than the empirical 1.0 value. This indicates that the recurrence of an event up to Mw 8.7 is longer than previously thought if the megathrust events follow the observed magnitude-frequency relation. Then, we quantify the influence of slow slip events on the triggering of a potential megathrust earthquake by calculating the static stress increase. We find that stress perturbations caused by the three slow slip events are generally consistent with the values that have triggered the large interplate earthquakes in several subduction zones. However, a large earthquake has not yet been triggered on the Ryukyu fault after a sequence of slow slip events. If the 1920 Mw 7.7 earthquake is the last rupture of the Ryukyu fault, the earthquake cycle on the Ryukyu fault is very likely in an early stage. However, this is not true if the slow slip events occur toward the end of the earthquake cycle and there has been no megathrust earthquake at the fault interface in the last 417 years, as the 2011 Mw 9.0 Tohoku earthquake. Thus, higher potential for a megathrust earthquake may occur in the southernmost Ryukyu subduction zone.

How to cite: Chen, S. K., Wu, Y.-M., and Chan, Y.-C.: The Seismogenic Potential of the Southernmost Ryukyu Subduction Zone as Revealed by Historical Earthquakes and Slow Slip events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2484, https://doi.org/10.5194/egusphere-egu23-2484, 2023.

Since the relatively recent discovery of slow slip events (SSEs), the nature of the relationship between SSEs and ordinary earthquakes has become one of the most important questions in earthquake science.  Specifically, questions as to whether SSEs decrease or increase the likelihood of large-magnitude earthquakes, whether or how slow and fast earthquakes can occur on the same fault patch, and whether SSEs are potential earthquake precursors have important implications for earthquake hazards.

Here, laboratory friction experiments on simulated fault gouges are used to gain insight into the relationship between SSEs and ordinary earthquakes.  The experiments are conducted water-saturated, at room temperature and at low pressure (10 MPa effective normal stress) to simulate the shallow, near-surface portions of major fault zones.  A key feature of these experiments is employing driving velocities as low as 5 cm/yr (1.6 nm/s) to simulate natural far-field tectonic driving rates.  From a larger dataset which includes a wide range of simulated fault gouges, four gouge types exhibited consistent stick-slip and these are analyzed further.  These materials are pyrite, hematite, gypsum, and Carrara marble powders.

Preliminary results show that the pyrite and hematite gouges exhibit small stress drops and increases in sample sliding velocity, interpreted to be SSEs, prior to stick-slips.  The SSEs occur near the peak in friction before the large stick-slip stress drop, suggesting that they are precursors.  In hematite at 5 cm/yr, the precursory SSEs exhibit stress drops on the order of 10’s of kPa and peak slip velocities within an order of magnitude of the driving rate, whereas the stick-slips exhibit stress drops of about 1 MPa and peak slip velocities of up to ~1 mm/s.  The peak stress at which the SSEs occur is within 1% of the peak stress prior to the stick-slip events.  Gypsum and Carrara marble, however, did not exhibit SSEs prior to stick-slips.  The results suggest that both slow and fast slip can occur on the same fault patch under the same conditions, and indicate the possibility that SSEs can be used as earthquake precursors in some cases.  However, the lack of precursory SSEs in the gypsum and marble gouges suggests that precursory SSE behavior is not universal and requires further investigation.

How to cite: Ikari, M.: Slow slip events as stick-slip precursors in laboratory friction experiments on simulated fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2602, https://doi.org/10.5194/egusphere-egu23-2602, 2023.

EGU23-2745 | ECS | Posters on site | TS3.9

Largest aftershock nucleation driven by afterslip during the 2014 Iquique sequence 

Yuji Itoh, Anne Socquet, and Mathilde Radiguet

Megathrust faults are known to host both seismic and aseismic slip. Laboratory experiments and numerical simulations have demonstrated that seismic-aseismic interaction can be involved in the earthquake source process such as nucleation and termination. However, models of seismic-aseismic interaction regarding the source process are still controversial because their observational evidence is limited to the small number of events among instrumentally recorded earthquakes. This is likely due to the low signal-to-noise ratio of observations and/or short duration of the nucleation and termination processes. In this study, we newly report aseismic slip accompanying intriguing seismicity during the 2014 Iquique earthquake sequence by analysing seismicity and high-rate GPS crustal deformation data.

We document early postseismic deformation during the 3 days following the M 8.1 mainshock and demonstrate that afterslip started immediately after the mainshock and led 27 hours later to the M 7.6 largest aftershock which located ~120 km further south. The interevent afterslip peaks down-dip of the mainshock with decaying moderate aftershock rate, exhibiting typical postseismic megathrust response. A local peak of the afterslip is inferred between the mainshock and the largest aftershock epicentres. This local peak suggests that this area acted as an aseismic barrier to the southward mainshock rupture propagation so that the two big quakes did not occur simultaneously.

The geodetic moment everywhere decreased with time during the 27h interevent stage with different decaying rate. The decay was slower in the afterslip area between the two epicentres than the main down-dip peak. Interestingly, the seismicity rate and associated moment release in this area increased with time during the interevent 27 hours. We propose that the largest aftershock nucleation was driven by the afterslip. Contrary to predictions of some numerical simulation models, our result implies that aseismic slip during the nucleation process does not necessarily accelerate. Our new observational discovery illuminates the mechanical connection between sequential great earthquakes mediated by aseismic slip.

How to cite: Itoh, Y., Socquet, A., and Radiguet, M.: Largest aftershock nucleation driven by afterslip during the 2014 Iquique sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2745, https://doi.org/10.5194/egusphere-egu23-2745, 2023.

EGU23-4151 | ECS | Orals | TS3.9

Collective behavior of asperities before large stick-slip events 

Weiwei Shu, Olivier Lengliné, and Jean Schmittbuhl

The multi-scale roughness of a fault interface is responsible for multiple asperities that establish a complex and discrete set of real contacts. Since asperities control the initiation and evolution of the fault slip, it is important to explore the intrinsic relationships between the collective behavior of local asperities and the frictional stability of the global fault system. However, such a mechanism is still elusive due to the difficulty of imaging an exhaustive spatiotemporal variability of a fault interface at depth, and the limited computational efficiency of the numerical models with heterogeneity over a large time and space domain. Here we propose a novel analog experimental approach, which allows us to capture the temporal evolution of the slip of each asperity on a faulting interface. We link the collective behavior of asperities with the mechanical response of the whole fault interface. We find that many destabilizing events at the local asperity scale occurred in the frictional strengthening stage which is conventionally considered as the stable regime of a fault. We compute the interseismic coupling to evaluate the slipping behaviors of asperities during the fault strengthening stage. Based on a high-resolution topographical map of the fault surface, we evidence that the interseismic coupling is not only dependent on the normal load and the peak height of asperity but also can be affected by the interactions between asperities through the embedding soft matrix. Furthermore, we quantify the spatiotemporal interactions of asperities as slip episodes. The significant characteristics and scaling-laws observed in natural earthquakes, such as the magnitude-frequency distribution and the moment-duration scaling, are reproduced through the catalog of slip episodes to demonstrate the effective upscaling. We give geophysical implications for the physics and mechanics of natural faults and discuss some limitations of our experimental setup.

How to cite: Shu, W., Lengliné, O., and Schmittbuhl, J.: Collective behavior of asperities before large stick-slip events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4151, https://doi.org/10.5194/egusphere-egu23-4151, 2023.

Transient aseismic deformation is observed using dense geodetic measurements across the northern Jordan Valley Fault segment of the Dead Sea Fault. The fault was creeping until 2013 at a rate of 2.7±0.4 mm/yr. It stopped creeping between 2013 and 2018 and then started creeping again at a similar rate. These transitions between the creep and locked modes of deformation correlate well with the 2013 and 2018 seismic sequences that occurred near the tip of the northern Jordan Valley creeping segment. The creep caused the accumulation of Coulomb stresses near the fault tip, which promoted earthquake nucleation in this region. The 2013 seismic sequence was probably too small to release these stresses, and they were released during the 2018 seismic sequence, which allowed the fault to creep again. We suggest that seismic activity will continue to occur near the tip of this creeping segment.

How to cite: Hamiel, Y. and Piatibratova, O.: Interplay between seismic and aseismic deformation near the tip of a creeping segment: Insights from the northern Jordan Valley segment of the Dead Sea Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4225, https://doi.org/10.5194/egusphere-egu23-4225, 2023.

EGU23-4259 | Posters on site | TS3.9

A unified geodetic data-based earthquake catalog of Taiwan from 2006 to 2018 

Kuo-En Ching, Po-I Li, Wu-Lung Chang, Shih-Han Hsiao, Chien-Liang Chen, and Kwo-Hwa Chen

A unified geodetic data-based earthquake catalog may provide the asperity information to improve the seismic hazard assessment. Therefore, we propose a unified geodetic data-based earthquake catalog in Taiwan from 2006-2018 using the geodetic data from 333 campaign-mode GNSS stations and 19 precise leveling routes and the published continuous GNSS data to improve the spatial resolution and reliability of vertical component in coseismic displacement fields. The coordinate time series analysis was used to derive the coseismic displacements of each earthquake from the sGNSS and precise leveling data by using the least square method. This earthquake catalog involves 2006 ML 7.0 Pingtung offshore earthquake, 2010 ML 6.4 Jiashian earthquake, March 2013 ML 6.2 Nantou earthquake, June 2013 ML 6.5 Nantou earthquake, 2013 ML 6.4 Ruisui earthquake, 2016 ML 6.6 Meinong earthquake, and 2018 ML 6.2 Hualien earthquake. Then the coseismic source models of these events were evaluated by inverting the coseismic displacement fields. Based on this earthquake catalog, we provided high spatial resolution and precision in the vertical deformation and the resolution of the modeled fault dip angle is also improved. In addition, unknown coseismically reactivated anticlinal structures in SW Taiwan were discovered in this study, which may be associated with the active mud diapirs. Finally, because of abundant coseismic geodetic data adopted in this study, the spatial resolution of coseismic slip distribution is also increased in those earthquake events.

How to cite: Ching, K.-E., Li, P.-I., Chang, W.-L., Hsiao, S.-H., Chen, C.-L., and Chen, K.-H.: A unified geodetic data-based earthquake catalog of Taiwan from 2006 to 2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4259, https://doi.org/10.5194/egusphere-egu23-4259, 2023.

EGU23-4292 | ECS | Orals | TS3.9

Interactions between the dual-verging thrust faults in eastern Taiwan revealed by the 2022 Chihshang earthquake sequence and centennial historical seismicity 

Chi-Hsien Tang, Yunung Nina Lin, Hsin Tung, Yu Wang, Shiann-Jong Lee, Ya-Ju Hsu, J. Bruce H. Shyu, Yu-Ting Kuo, and Horng-Yue Chen

Nearby faults interact with each other through stress fluctuation incurred by seismic rupture, aseismic slip, and viscoelastic flow in the lithosphere. Understanding fault interactions and their temporal variation under different geometry are critical to regional seismic hazard and risk assessments. However, the complex interplay between adjacent faults is often unclear due to insufficient observations of large earthquakes with prolonged recurrence intervals. The 2022 Chihshang earthquake sequence in eastern Taiwan provides unprecedented insights into the interaction between two head-to-head thrust faults during and after a major earthquake. The Chihshang sequence was initiated by an Mw 6.5 foreshock on 17 September, followed by an Mw 7.0 mainshock 7 km to the north and 17 hours later. Based on the coseismic displacements constrained by field survey, optical satellite images, interferometric synthetic aperture radar (InSAR) data, and a dense network of Global Navigation Satellite System (GNSS) measurements, we map the major coseismic rupture on the east-verging Central Range fault (CRF), and the secondary induced slip on the west-verging Longitudinal Valley fault (LVF). The induced slip on the LVF accounts for 9-15% of the total moment release (Mw 7.1). Before the Chihshang earthquake sequence, the seismic hazard along the CRF was much overlooked due to the high seismic activity of the LVF. The 2022 Chihshang earthquake sequence demonstrates for the first time that the CRF is capable of generating earthquakes of Mw 7. The early afterslip primarily took place on the downdip extension of the CRF at great depth, indicating a contribution of ductile deformation there. Incorporating historical earthquake records over the past 120 years, we demonstrate that a rupture on the CRF or LVF reduces the stress level on the other, causing periods of seismic quiescence and an out-of-phase moment release pattern over time between the two faults. These results not only illuminate the fault geometry at the plate suture zone of eastern Taiwan, but also revise the conventional view of the nearby fault interaction. Integrating geometric complexity and fault slip history among adjacent faults in future modeling is essential for assessing realistic seismic hazards in similar structural settings.

How to cite: Tang, C.-H., Lin, Y. N., Tung, H., Wang, Y., Lee, S.-J., Hsu, Y.-J., Shyu, J. B. H., Kuo, Y.-T., and Chen, H.-Y.: Interactions between the dual-verging thrust faults in eastern Taiwan revealed by the 2022 Chihshang earthquake sequence and centennial historical seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4292, https://doi.org/10.5194/egusphere-egu23-4292, 2023.

EGU23-4704 | Orals | TS3.9

Creep and seismic rupture of a serpentinite-rich Sumatran fault segment 

Shengji Wei, Zheng-Yang Choong, Chenyu Li, Yukuan Chen, Muksin Umar, Karen Lythgoe, Arifullah Arifullah, and Andrean Simanjuntak

Earthquake is produced by shear dislocation of rocks across the fault, the frictional status and the area of locked/creeping patches on the fault thus govern the size and occurrence of damaging earthquakes. To better understand these fundamental earthquake physics issues, we deployed over 130 short period seismic nodal stations along the plate boundary type Sumatran fault in Aceh region to cover a segment that was reported to be creeping at various depths. We maintained the nodal array deployment from Jan 2020 to July 2021 by recharging the nodes every 35 days. A machine learning based earthquake detection algorithm was applied to the acquired dataset, which results in a high-resolution seismic catalog that has more than 8000 micro-seismic events. These events clearly delineate the subvertical creeping segment of the Sumatran fault and its Seulimeum branch to the northwest. The seismicity on the creeping segment is almost uniformly distributed from 3 to 12 km in depth, confirming the creeping nature of the fault segment as revealed by geodetic observations, but providing a much more accurate depth constraint. In contrast, the Seulimeum fault branch shows a much deeper seismicity at the depth range of 18 to 25 km, indicating the entire upper crust is fully locked. Sharp stepovers are observed along both strike (~10km) and strike-normal (~4km) directions between the seismicity on these fault segments. The creeping segment of the Sumatran fault, as defined by similar earthquake families, agrees well with the lenses of serpentinite, which has much smaller frictional coefficient that facilitates fault creep. Similar earthquake families show ~ km scale lineation along strike of the fault, where repeating earthquake pairs are identified. However, two shallow Mw6 earthquakes occurred on the creeping segment in the last 25 years. In particular, finite fault inversion of the 2013 Mw6.1 earthquake shows the rupture from 12 km to the surface. These observations suggest a partially creeping/locking or conditionally stable frictional status on the serpentinite-rich segment of the Sumatran fault, that should be considered in both single event and earthquake cycle simulations, as well as seismic hazard assessment.

How to cite: Wei, S., Choong, Z.-Y., Li, C., Chen, Y., Umar, M., Lythgoe, K., Arifullah, A., and Simanjuntak, A.: Creep and seismic rupture of a serpentinite-rich Sumatran fault segment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4704, https://doi.org/10.5194/egusphere-egu23-4704, 2023.

EGU23-5485 | ECS | Orals | TS3.9

Acoustic signatures of slow and fast earthquake: insights from laboratory experiments on simulated fault gouge 

Federico Pignalberi, Carolina Giorgetti, Elisa Tinti, Nathalie Casas, Chris Marone, Cristiano Collettini, and Marco Maria Scuderi

In the last decades, it has been observed that faults can slip both by slow aseismic creep and seismic events (i.e., earthquakes). Between these two slip modes, a wide variety of fault slip behavior can be observed, including low-frequency earthquakes, slow slip events and tremors. This wide variety of slip modes can radiate seismic energy at different frequencies whose content may be linked to the physical mechanisms at play. 

In the laboratory, it is possible to reproduce the entire spectrum of fault slip modes by modulating the loading stiffness of the apparatus depending on the critical fault rheologic stiffness (i.e. k/kc). This technique allows us to study, under controlled laboratory conditions, the acoustic signature of different fault slip modes to infer the physical mechanisms at their origin. To shed light on the nucleation mechanisms and seek for reliable precursors to failure of different slip modes, we performed friction experiments on powders that differ for granulometry and grain shape (i.e., glass beads with a grainsize < 150 µm; and quartz powders MinUSil with an average grain size of 10.5 µm),  to simulate fault gouge.  The experiments were conducted in a double direct shear configuration, instrumented with an array of piezoelectric sensors to record continuously Acoustic Emissions (AEs) at high recording rate (~10MHz). The experiments are performed at a constant displacement rate of 10 µm/s and using a spring to reduce the apparatus stiffness k, to match the critical fault rheological stiffness (kc). Following this procedure we  obtain slow slip events (i.e., k = kc) and fast events (i.e. k<kc). The continuous recording of the AE (a proxy for seismicity) during the seismic cycle shows an increase in the acoustic energy release while approaching failure, which is related to changes in fault physical properties associated with grain sliding/fracturing. This behavior is reflected in a systematic variation of the b-value approaching failure.

Through this work, we focus on the frequency content of AEs during the laboratory earthquakes to understand how different slip modes radiate acoustic energy. Indeed, we observe two orders of magnitude differences in frequencies associated with AEs in MinUSil and AEs in Glass Beads. The analysis of this frequency content can add important information on the deformation mechanism of fault gouge at the microscale and the size of the slip patch during laboratory earthquakes.

How to cite: Pignalberi, F., Giorgetti, C., Tinti, E., Casas, N., Marone, C., Collettini, C., and Scuderi, M. M.: Acoustic signatures of slow and fast earthquake: insights from laboratory experiments on simulated fault gouge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5485, https://doi.org/10.5194/egusphere-egu23-5485, 2023.

EGU23-6896 | ECS | Orals | TS3.9

Synchronous Slow Slip Event and Seismic Swarm in Central Ecuadorian forearc, 2013 

Alexander Wickham-Piotrowski, Yvonne Font, Marc Regnier, Quentin Bletery, Monica Segovia, Jean-Mathieu Nocquet, and Bertrand Delouis

In Ecuador, on some areas of the subduction interface, accumulated stress is released aseismically through slow slip events (SSE) synchronous to seismic swarms (S5). In the La Plata island region in the Central Ecuadorian forearc, recurrent and shallow S5 occur near a portion of the plate interface highly coupled by the subduction of a massive oceanic relief. This study shows a sequence of seismicity and SSE organization propitious to investigate the cause and effect relation-ship between both phenomena.

GPS data show that an SSE (Mw 6.3) initiated at the end of November 2012 and ruptured 2 shallow aseismic patches 25 km apart (~10 km along the vertical direction). The first patch (P1), located southeastward of the island on a moderately coupled portion of the plate interface at the leading edge of the subducting oceanic mount, has a rupture area of about 80 km2 and a maximum cumulated slip of 15 cm. Its slipping behavior is pulse-like for about a month and a half. Mid-January, the slip of the SSE suddenly accelerates. A day later, a second aseismic patch (P2), updip from P1, ruptured a highly coupled area of about 250 km2 with a maximum slip of 35 cm. This second rupture lasted 8 days and accounted for 80% of total aseismic moment. Both SSE patches stopped slipping by the end of January 2013.

The spatial-temporal distribution of 2,000 micro-earthquakes between November 2012 and February 2013 provides clues about the interface processes and highlights that faulting occurred on secondary faults during an S5. An outer rise seismic cluster with an ML 4.8 earthquake occurred on a bending fault of the Nazca Plate, 10 days before P1 started. The cluster is collinear with P1 with respect to the relative plate convergence direction, suggesting a possible causal relationship. Almost no seismicity affects the plate interface during the pulse-like development of P1 until mid-January. As the P1-SSE’s slip accelerates, an intense seismic swarm developed updip of P1 along a narrow NNE-SSW trending direction, organized in sub-vertically active structures within the subducting plate. The Coulomb stress variation computed from the cumulative slip of P1 as well as the velocity migration of the cluster (about 10 km/day) suggests that the intraplate swarm is triggered and developed at the P1-SSE’s rupture front. Synchronously to P2, seismicity developed at the Northern edge of the oceanic relief.

The seismicity swarm witnesses the reactivation of oceanic bending faults within the Nazca plate. We hypothesize that this reactivation is likely responsible of a fluid release on the plate interface, that contributed to overpressuring the highly coupled area near P2, priory saturated with fluids, which ruptures aseismically afterwards. 

How to cite: Wickham-Piotrowski, A., Font, Y., Regnier, M., Bletery, Q., Segovia, M., Nocquet, J.-M., and Delouis, B.: Synchronous Slow Slip Event and Seismic Swarm in Central Ecuadorian forearc, 2013, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6896, https://doi.org/10.5194/egusphere-egu23-6896, 2023.

EGU23-7118 | Orals | TS3.9

Fault stability transition with slip and wear production: laboratory constraints 

Corentin Noël, Carolina Giorgetti, Marco M. Scuderi, Cristiano Collettini, and Chris Marone

Large earthquakes take place on mature faults with hundreds of meters to kilometres of cumulative slip. At shallow depths, the fault zone is generally composed of non-cohesive rock wear products, often referred to as gouge. Seismic and aseismic slip occur in this fault gouge and fracture/brecciation of the wall rock and damage zone can add to the fault gouge as part of the wear process. Gouge thickness generally increases linearly with the cumulative fault shear displacement and laboratory work shows that gouge tends to stabilize fault frictional stability. Previous works show that frictional stability of simulated fault gouge varies as a function of shear displacement. The stability evolution is interpreted as a consequence of the degree of shear localisation within the simulated fault gouge: the more the deformation is localized, the more the fault slip is unstable. This implies that for bare rock surfaces, unstable behaviour is expected as the deformations are forced to be localized at the interface between the two sheared surfaces.

On natural faults at large shear displacement (or for faults having a high gouge production rate), a competition must take place between 1) the localization of the deformation at rock-on-rock surfaces, 2) the delocalization of deformation due to gouge production and wall rock brecciation, 3) fault zone lithification and frictional healing and 4) shear localization within the gouge and wear material. The competition and interaction between these phenomena are modulated by cumulative fault slip, temperature and fluid chemistry. In turn, this competition may influence the frictional stability of faults with increasing shear displacement, and thus, their potential seismic activity.

To characterise the influence of shear displacement on fault stability, constant velocity and velocity step experiments were performed to large displacement. Two initially intact rocks were chosen as starting material: a high porosity Fontainebleau sandstone and a low porosity quartzite. These samples represent very different resistances to abrasion (i.e., wear production with slip) for the same initial mineral composition (< 95% quartz), which allows us to investigate wear and wear rate on fault stability. Additionally, simulated quartz gouge was tested for comparison. Mechanical data are analysed within the rate-and-state framework, and post-mortem microscopic analyses of the sample were performed. For initially bare surface experiments a threshold shear displacement is required to transition from stable to unstable sliding. Stick-slip events (laboratory earthquakes) evolve systematically as a function of fault zone shear displacement. The inversion of the rate-and-state parameters shows that shear displacement has a dominant influence on both (a-b) and Dc. For all the faults tested, (a-b) decreases with increasing shear displacement. For high wear rates and simulated gouge, Dc decreases with increasing shear displacement. However, for low wear rate faults, Dc is constant within the tested shear displacement. These results demonstrate that, under the tested boundary conditions, fault stability varies systematically with fault maturity and in particular that shear displacement and strain localization are the dominant parameters controlling fault slip stability.

How to cite: Noël, C., Giorgetti, C., Scuderi, M. M., Collettini, C., and Marone, C.: Fault stability transition with slip and wear production: laboratory constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7118, https://doi.org/10.5194/egusphere-egu23-7118, 2023.

Western Slovenia belongs to actively deforming north-eastern Adriatic region. Active tectonic deformations of the region are a response to the anti-clockwise rotation of Adria and still ongoing collision with Eurasia. Active deformations are generally accommodated by right-lateral strike-slip and thrust faulting at rates of 2–4 mm/yr.

Monitoring of active tectonics at the junction of seismically active NW External Dinarides and Southern Alps (Slovenia) through quantification of micro-displacements of faults began in 2004, with a TM 71 extensometer situated in Postojna cave (NW External Dinarides). At present there are 12 monitoring sites with TM 71 and 72 extensometers throughout Slovenia, 9 of the instruments are stationed in natural and artificial cave environments. Cave climates are considered to be stable and thus provide a reliable environment for micro-displacement monitoring, minimizing or nullifying the effect of fluctuating temperatures on the TM instrument. The instruments were preferably installed in major regional Dinaric fault zones (NW-SE direction). Where the latter wasn’t possible, suitable locations on their ancillary faults was chosen as an indirect substitute. All the monitored TM extensometer sites display tectonic displacements, that on average range from a few microns to several tens of microns in time scales from days to years. Postojna cave is one of the most intriguing micro-displacement monitoring sites. The site exhibited large tectonic transient signals that coincided with the local swarm-like earthquake activity in the years, 2009-2010 and 2014-2015. Monitoring site of Pološka cave in Julian Alps (Southern Alps) in addition to recording tectonic displacements, inadvertently records some displacements that are not tectonic in origin, but rather exhibits slope instability, likely deep-seated gravitational slope deformation. TM extensometer micro-displacement monitoring in Slovenia is still an ongoing project.

Of late, creepmeters were installed on major active western Dinaric regional faults, in 2022. In an effort to advance the understanding of characteristics and relationships between earthquake activity and potential fault creep. A fault creep monitoring campaign, with some instruments already installed, on two major active western Dinaric faults, Idrija and Raša fault, has begun and more are pending to be installed on the Dinaric fault system.

How to cite: Novak, U.: Monitoring active tectonics via fault micro-displacements in western Slovenia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7388, https://doi.org/10.5194/egusphere-egu23-7388, 2023.

The Xianshuihe Fault Zone (XSHF) is one of the most active strike-slip faults on the eastern Tibetan Plateau. Along the NW-striking, left-lateral XSHF, as many as 8 M >7 and 29 M >6.5 earthquakes have occurred since 1700 CE. The Kangding segment is a special part of the XSHF that has four active faults and can exhibit large earthquakes. From north to south, they are the Yalahe Fault, Selaha Fault, Mugecuo South Fault, and Zheduotang Fault. However, the activity and paleoearthquake sequence of branch faults in Kangding segment remain controversial. Our detailed research is focus on the Yalahe Fault and Zheduotang Fault in Kangding segment. We mapped accurate fault traces and deformed landforms based on detailed interpretations of high-resolution imagery and aerial photographs combined with field observations. Geological and geomorphological evidence was obtained for the Holocene activities. Paleoearthquake sequence was built based on the trench work. We discussed the recurrence characteristics and slip behavior.

The Yalahe Fault follows a quasiperiodic recurrence model and Zheduotang Fault displays uniform slip behavior. From the result of paleoearthquake, the Yalahe Fault, Selaha Fault, and Zheduotang Fault experienced cascading ruptures. Therefore, the branch faults in Kangding segment have ability to generate large earthquakes in the future.

How to cite: Ma, J., Zhou, B., and Wang, M.: Latest quaternary active faulting and paleoearthquakes on the Kangding segment of the Xianshuihe Fault Zone, Eastern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7491, https://doi.org/10.5194/egusphere-egu23-7491, 2023.

EGU23-7807 | ECS | Orals | TS3.9

3D Quasidynamic cycles accelerated using Hierarchical Matrices: Role of complex fault geometry 

Jinhui Cheng, Michelle Almakari, Carlo Peruzzo, Brice Lecampion, and Harsha Bhat

Fault systems have geometrically complex structures in nature, such as stepovers, branches, and roughness. Both geological and geophysical studies indicate that the fault geometry complexities can have a first order effect on spatio-temporally complex slip dynamics. However, a vast majority of models of slip dynamics are conducted on planar faults due to algorithmic limitations. We develop a 3D quasi-dynamic slip dynamics model with Hierarchical matrices to overcome this restriction. The calculation of elastic response due to slip is a matrix-vector multiplication, which can be accelerated by using hierarchical matrices and easily multi-threaded. The computational complexity is reduced from the order of O(N2) to O(NlogN). We cross-validate our code with the SCEC run SEAS benchmark/validation exercise. With this approach, we then explore the role of fundamental geometry complexities and realistic fault geometry on slip dynamics. We also plan to analyse synthetic signals and compare with seismological and geodetic observations.

How to cite: Cheng, J., Almakari, M., Peruzzo, C., Lecampion, B., and Bhat, H.: 3D Quasidynamic cycles accelerated using Hierarchical Matrices: Role of complex fault geometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7807, https://doi.org/10.5194/egusphere-egu23-7807, 2023.

EGU23-8512 | ECS | Orals | TS3.9

Quantifying stress fields to better understand shallow tectonics of the Hikurangi Subduction Margin, NZ 

Effat Behboudi, David McNamara, and Ivan Lokmer

Quantitative stress data is crucial to understanding the mechanical behaviour of faults and the variation of  interface slip behaviours at subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variations in subduction interface and fault slip behaviour, changing from shallow slow slip events (SSEs) and creep to interseismic locking and stress accumulation moving south. We quantify the shallow (<3km) HSM stress magnitudes and orientations and utilise this new data to determine tectonic variation along the HSM and discuss how this may relate to the large-scale observation in HSM subduction dynamics. For depths below ~650 mTVD results show σ3: Sv ratios of 0.92-1 along the entire HSM, and SHmax: Sv ratios of 0.95-1.81 in the central HSM, and 0.95-2.15 in the southern HSM. Such ratios infer that below ~650 mTVD a prevalent thrust to strike-slip (σ1=SHmax) faulting regime exists along the entire HSM. Our results also reveal a NE-SW (margin-parallel) SHmax orientation in the shallow central HSM, which rotates to a WNW- ESE/NW-SE (margin-perpendicular) SHmax orientation in the shallow southern HSM.

In the central HSM, we determine the  NE-SW orientation of SHmax= σ1, which is inconsistent with  NNE/NE striking reverse faults (inferring a NW-SE oriented SHmax= σ1) in the region. This suggests that the stress state evolved over time from a contractional to a strike/oblique-slip state. This temporal change in stress state in the central HSM is likely driven by development of clockwise rotation of the Hikurangi forearc and upper plate overpressures. A contemporary NW-SE oriented SHmax in the southern HSM, associated with NNE/NE striking faults, suggests the stress regime here remains contractional over time, and is less effected by forearc rotation. The variation in stress state along the HSM spatially correlates with reported along-strike variation in subduction interface slip behaviour. This spatial correlation suggests that contemporary stresses in the overriding plate above the subduction interface may reflect contemporary elastic strain accumulation processes related to subduction megathrust locking.

 

How to cite: Behboudi, E., McNamara, D., and Lokmer, I.: Quantifying stress fields to better understand shallow tectonics of the Hikurangi Subduction Margin, NZ, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8512, https://doi.org/10.5194/egusphere-egu23-8512, 2023.

EGU23-10525 | ECS | Posters on site | TS3.9

On the use of resolution test in calculating strain rate using GNSS velocity 

Zhengfeng Zhang, Huai Zhang, and Yaolin Shi

We proposed a method to simultaneously calculate the strain rate from GNSS (Global Navigation Satellite System) velocity data and present a set of inspection standards to assess the validity and resolution of this kind of method calculating strain rate using GNSS velocity in this study. We first explain the mathematical principle of the spherical spline method. And then, we introduce the spherical spline method to fit artificial GNSS velocity data of mainland China to illustrate inspection standards. In realization, we first calculate the artificial linear velocity value of the station with a rigid rotation model, then obtain the strain rate of the Chinese mainland by the spherical spline method. In this case, the theoretical rotational strain should be zero to illustrate the generality of the spherical coordinate method. Furthermore, we construct a spherical harmony model for the resolution test. By the test criteria, the spherical spline method can reproduce the velocity and strain rate field at quite a high level, suggesting that our method has high applicability and resolution in estimating strain rate. Finally, we used measured GNSS velocity data to calculate the strain rate field in mainland China using the spherical spline method. We also analyze the correlation between the seismic mechanism and the strain rate field of earthquakes since 1960 and consider the seismic rate of mainland China.

How to cite: Zhang, Z., Zhang, H., and Shi, Y.: On the use of resolution test in calculating strain rate using GNSS velocity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10525, https://doi.org/10.5194/egusphere-egu23-10525, 2023.

EGU23-10664 | ECS | Orals | TS3.9 | Highlight

Complex laboratory earthquake sequences show asperity interactions through creep fronts and illuminate the mechanics of delayed earthquake triggering 

Sara Beth Cebry, Chun-Yu Ke, Srisharan Shreedharan, Chris Marone, David Kammer, and Gregory McLaskey

Natural earthquakes occur in clusters or sequences that arise from complex triggering mechanisms, but direct measurement of the mechanisms responsible for complex temporal sequences and delayed triggering is rarely possible. A central question involved whether delayed triggering is due to slow slip and stress transfer or local weakening/fatigue processes such as stress corrosion. We investigate the origins of this complexity and its relationship to fault heterogeneity using a biaxial loading apparatus with an experimental fault that has two dominant seismic asperities. The fault is composed of a 5 mm layer of quartz powder, a velocity weakening material common to natural faults, sandwiched between 760 mm long polymer blocks that deform similar to the way 10 meters of rock would behave. Due to the higher local normal stress and the free surface boundary condition on the sample ends, the sample behaves like two asperities, one at each end, that can fail independently. As the quartz powder was continuously sheared, the friction properties changed, and we observed a transition from steady sliding to periodic repeating earthquakes that transitioned into aperiodic and complex sequences of fast and slow events. There is also reason to believe that friction properties evolved differently on the higher normal stress asperities and made them more unstable than the center part of the laboratory sample. Sequential ruptures on the two different asperities were linked via migrating slow slip which resembles creep fronts observed in numerical simulations and on tectonic faults. The propagation velocity of the creep fronts ranged from 0.1 to 10 m/s, which is broadly consistent with the velocity of slow slip fronts inferred from migrating tectonic tremor sources. Utilizing both local stress measurements and numerical simulations, we observe that the speed and strength of creep fronts are highly sensitive to fault stress levels left behind by previous earthquakes and may serve as on-fault stress meters.

How to cite: Cebry, S. B., Ke, C.-Y., Shreedharan, S., Marone, C., Kammer, D., and McLaskey, G.: Complex laboratory earthquake sequences show asperity interactions through creep fronts and illuminate the mechanics of delayed earthquake triggering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10664, https://doi.org/10.5194/egusphere-egu23-10664, 2023.

EGU23-11133 | Posters virtual | TS3.9

Seismotectonics of the northeast Indian region based on GPS velocities, stress and strain rate  field characterization 

Raj kumar, Sanjay Kumar Prajapati, Sanjit Kumar Pal, and Om Prakash Mishra

The North-Eastern (NE) area of India is bounded by the confluence of three major tectonic plates constituting two convergent plate boundaries that essentially govern the complex seismotectonic of this Himalayan region that renders it seismically most active.  The area studied in the present work is confined to the hyperactive zone contained in the grid 20o - 30o N latitude and 88o -100o E longitude.  We analyze five years of GPS data obtained from sixteen Global Positioning System (GPS) campaign mode stations and two permanent ones deployed in the NE region. These velocities are used in estimating dilatational and shear strain rates along with the principal axes of strains. The estimated dilatational strain rate ranges from -0.13 to 0.1 microstrain/yr. In general, the velocity and strain rate fields are consistent with ongoing India-Eurasia collision and Indo-Burma subduction processes. Superposed on this pattern, we find that the intense dilatational field corresponds to the vicinage of the region between the main boundary and central Himalayan thrusts (viz. MBT, MCT), and while it is moderate in some regions of Indo Burmese Arc (IBA). Three distinct regions with high compressive strain rate distribution are delineated along the thrust zones. Two of these regions corresponds to the regions where the Kopili fault and  Tista lineament transversely converge MCT and transgresses into the MBT/MCT in Sikkim Himalaya and Bhutan Himalaya respectively and other with northern syntax region,  posing a high seismic hazard. , Some pockets of moderate strain rate near to the intersection areas of Kopili, Dauki faults and IBA, positionally relate to the high seismic zones and are consistent well with the statistical seismology, seismic topography and potential field anomalies.  Our study focuses on velocity and strain rate distribution vis-à-vis seismicity and crustal heterogeneity in the region facilitating the estimation of earthquake hazard potential.

How to cite: kumar, R., Prajapati, S. K., Pal, S. K., and Mishra, O. P.: Seismotectonics of the northeast Indian region based on GPS velocities, stress and strain rate  field characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11133, https://doi.org/10.5194/egusphere-egu23-11133, 2023.

EGU23-12162 | ECS | Orals | TS3.9

Earthquake Cycle of the East Anatolian Fault Between Palu-Erkenek (Eastern Türkiye): Insights of Tectonic Geodesy 

Seda Özarpacı, Uğur Doğan, Semih Ergintav, Ziyadin Çakır, Cengiz Zabcı, Alpay Özdemir, Efe Turan Ayruk, İlay Farımaz, and Mehmet Köküm

The East Anatolian Fault (EAF) is one of the continental transform systems in the Eastern Mediterranean, with a length of about 420 km between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş). The 24 January 2020 Sivrice earthquake with Mw 6.8 once again demonstrated the seismic potential of this sinistral strike-slip fault.

The recent earthquakes and discoveries creeping along the Palu Segment (~100km far to the NE of epicenter of Mw6.8 earthquake) by geodesy- and seismology-based studies increase scientific attention. The spatio-temporal characteristics of the creep observed along the Palu Segment were investigated using nearfield GPS, InSAR, and creepmeter data. After Mw6.8 earthquake, we expanded our study area towards the Pütürge Segment in the south to determine the postseismic effects of the 24 January 2020 earthquake and the kinematics of the Pütürge Segment using multidisciplinary methods (GNSS, creepmeter, InSAR, seismology, paeloseismology) and to investigate the effects on the surrounding faults.

During the first year of the project work, a new GNSS network was established in the region and these networks will be regularly measured every six months. In addition, two permanent GNSS stations were installed. Additionally, using Sentinel-1 data sets, surface deformations mapped by PSINSAR analysis. Generally, post-earthquake effects continue and deformations moved to the SW part of unbroken part of Pütürge segment and based on the creepmeter data, surface deformations still continue at the epicenter locations, following the logarithmic afterslip responce.

This work is supported by TUBITAK project number 121Y400.

 

Keywords: East Anatolian Fault, Earthquake, GNSS, InSAR

How to cite: Özarpacı, S., Doğan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özdemir, A., Ayruk, E. T., Farımaz, İ., and Köküm, M.: Earthquake Cycle of the East Anatolian Fault Between Palu-Erkenek (Eastern Türkiye): Insights of Tectonic Geodesy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12162, https://doi.org/10.5194/egusphere-egu23-12162, 2023.

EGU23-13002 | Orals | TS3.9

Rupture dynamics driven by strain localisation within fault gouges 

Nicolas Brantut and Fabian Barras

During fast slip, fault strength may decrease due to weakening mechanisms linked to constitutive properties of the deformed material (e.g., flash heating, thermal pressurisation), but also due to structural effects driven by changes in strain distribution within the shear zone. Extensive theoretical work on thermally activated weakening mechanisms, such as thermal pressurisation of pore fluids, has shown that strain can spontaneously localise in very narrow zones during rapid shear, which promotes further macroscopic weakening of faults. Here, we develop a multiscale fault model which combines a detailed description of thermal pressurisation of fault gouges within large scale elastodynamic rupture simulations. We show that spontaneous strain localisation inside the fault gouge dramatically changes the dynamics of ruptures, and makes the faults more brittle, i.e., decreases the fracture energy and thus produces faster ruptures. We provide closed-form approximations for the resulting localised width and fracture energy as functions of rupture speed. Our work provides a link between structural observations and earthquake dynamics.

How to cite: Brantut, N. and Barras, F.: Rupture dynamics driven by strain localisation within fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13002, https://doi.org/10.5194/egusphere-egu23-13002, 2023.

EGU23-13207 | Orals | TS3.9 | Highlight

Improving active faults monitoring leveraging submarine telecom fiber optic cables : first results from central Chile 

Diane Rivet, Marie Baillet, Alister Trabattoni, Martijn van den Ende, Clara Vernet, Itzhak Lior, Sergio Barrientos, Anthony Sladen, and Jean-Paul Ampuero

Subduction zones host some of the greatest diversity in seismic and aseismic fault slip behaviors, such as recurrent slow slip, non-volcanic tremors and repeating earthquakes, that are large enough to be measurable at the surface. Our understanding of the mechanisms leading to fault rupture, especially the role of aseismic slip is limited by the sparsity of instrumentation near the nucleation zone, which is predominantly located offshore away from permanent onland seismic networks.

Fiber-optic Distributed Acoustic Sensing (DAS) offers a new opportunity for long-term seismic observation of off-shore active faults by turning existing fiber-optic seafloor telecom cables into dense arrays of seismic and acoustic sensors. We conducted a one-month long DAS experiment on the northern leg of the Concón landing site of the Prat cable belonging to the GTD company. The longitudinal strain rate was recorded every 4m over a 150km-long fiber section at a temporal sampling rate of 125 Hz, which enabled us to measure low magnitude earthquakes and to locate them precisely. The earthquake catalog generated from the DAS data comprises more than 900 seismic events, which greatly extends the existing regional catalog. A preliminary analysis indicates that several seismic sequences are clustered in time and space, which include numerous events that cannot be detected by the onland seismological network. The ABYSS project will deploy this new observation tool continuously over several years, which will offer a new opportunity to better characterize the distribution of the seismicity in time and space, and will provide new constraints to the models of fault behavior during the seismic cycle. Combined with other types of analysis, such as seismic wave velocity changes monitoring at depth, these data will also provide additional constraints on the aseismic deformation of the fault zone.

How to cite: Rivet, D., Baillet, M., Trabattoni, A., van den Ende, M., Vernet, C., Lior, I., Barrientos, S., Sladen, A., and Ampuero, J.-P.: Improving active faults monitoring leveraging submarine telecom fiber optic cables : first results from central Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13207, https://doi.org/10.5194/egusphere-egu23-13207, 2023.

EGU23-13761 | Posters on site | TS3.9

The early postseismic phase of Tohoku-Oki earthquake (2011) from kinematics solutions: implication for subduction interface dynamics 

Axel Periollat, Mathilde Radiguet, Jérôme Weiss, Cédric Twardzik, Nathalie Cotte, Lou Marill, and Anne Socquet

Earthquakes are usually followed by a postseismic phase where the stresses induced by the earthquakes are relaxed. It is a combination of different processes among which aseismic slip on the fault zone (called afterslip), viscoelastic deformation of the surrounding material, poroelastic relaxation and aftershocks. However, little work has been done at the transition from the co- to the postseismic phase, and the physical processes involved.

 

We study the 2011 Mw 9.0 Tohoku-Oki earthquake, one of the largest and most instrumented recent earthquakes, using GEONET GPS data. We focus on the few minutes to the first month following the mainshock, a period dominated by afterslip. 

Based on the method developed by Twardzik et al. (2019), we process 30-s kinematic position time series and we use it to characterize the fast displacements rates that typically occur during the early stages of the postseismic phase. We quantify precisely the co-seismic offset of the mainshock, without including early afterslip, and we also characterize the co-seismic offset of the Mw 7.9 Ibaraki-Oki aftershock, which occurred 30 minutes after the mainshock. We analyze the spatial distribution of the co-seismic offsets for both earthquakes. We also use signal induced by the postseismic phase over different time windows to investigate the spatio-temporal evolution of the postseismic slip. We determine the redistribution of stresses to estimate the regional influence of the mainshock and aftershock on postseismic slip.

 

From a detailed characterization of the first month of postseismic kinematic time series, we find that the best-fitting law is given by an Omori-like decay. The displacement rate is of the type v0/(t+c)p with spatial variation for the initial velocity v0 and for the time constant c. We find a consistent estimate of the p-value close to 0.7 over most of the studied area, apart from a small region close to the aftershock location where higher p values (p~1) are observed. This p value of 0.7 shows that the evolution of the Tohoku-Oki early afterslip is not logarithmic. We discuss about the implications of these observations in terms of subduction interface dynamics and rheology. We also discuss about the different time-scales involved in the relaxation, and how this model, established for the early postseismic phase over one month, performs over longer time scales (by comparison with daily time series lasting several years).

Twardzik Cedric, Mathilde Vergnolle, Anthony Sladen and Antonio Avallone (2019), doi.org/10.1038/s41598-019-39038-z 

Keywords: Early Postseismic, Afterslip, GPS, Kinematic, Omori Law

How to cite: Periollat, A., Radiguet, M., Weiss, J., Twardzik, C., Cotte, N., Marill, L., and Socquet, A.: The early postseismic phase of Tohoku-Oki earthquake (2011) from kinematics solutions: implication for subduction interface dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13761, https://doi.org/10.5194/egusphere-egu23-13761, 2023.

EGU23-14610 | ECS | Orals | TS3.9

Slip velocity and fault stability in serpentine-rich experimental faults 

Giacomo Pozzi, Cristiano Collettini, Marco Scuderi, Elisa Tinti, Telemaco Tesei, Cecilia Viti, Chris Marone, Alessia Amodio, and Massimo Cocco

Serpentinites are poly-mineralic rocks distributed almost ubiquitously in active tectonic regions worldwide. They are composed of rheologically weak (lizardite and crysotile) and strong (e.g., magnetite and pyroxene) phases. In particular, lizardite typically shows low friction coefficients and is supposed to localise deformation along weak shear zones characterized by aseismic behaviour. Major faults hosting serpentinite lithologies are characterised by seismic activity, tremors, and other slip modes. We advance the hypothesis that low strain domains, which are enriched in rheologically strong phases, can act as potential site of nucleation of unstable slip as the result of the velocity-dependent rheology of magnetite-rich serpentinites. Through an experimental and microstructural approach, we explore the different mechanisms whose interplay controls the complex behaviour of these lithologies.

For this study we collected natural samples of lizardite-magnetite rich serpentinites within the low strain domains of the Elba Island ophiolites (Italy). Rocks were characterised, powdered, and deformed in a set of shear experiments at four different normal stresses (25, 50, 75 and 100 MPa) in the biaxial apparatus BRAVA. The experiments consist of an initial phase of sliding at 10 μm/s, a slide-hold-slide test, and two series of velocity stepping (sliding velocity from 0.1 to 300 μm/s). Fundamental parameters to quantify the frictional properties of serpentinites are individuated in the (a-b) value, the critical slip distance Dc, and the critical stiffness kc, which is derived by their combination.

The material shows friction values of ~0.4 with velocity weakening behaviour and negative frictional healing. The module of the negative (a-b) parameter increases neatly with decreasing sliding velocity while Dc decreases, causing kc to rise. At low velocities (< 3 μm/s) sliding is unstable and the fault undergoes stick-slip behaviour. This is explained by the increase of the critical stiffness to values higher than the loading system stiffness. This systematic change of mechanical properties and fault slip behaviours with sliding velocity is interpreted to be the result of the time-dependent arrangement of grains in a heterogeneous experimental fault architecture.

Back-scattered SEM images of the principal slip zones of recovered samples support this hypothesis. Elasto-frictional behaviour is controlled by the build-up of a partial (granular) load-bearing framework of strong magnetite grains, while visco-frictional rheology is controlled by the (phyllosilicatic) anastomosing and foliated lizardite matrix. At low sliding velocities, the granular phase interacts creating force chains thus promoting frictional instabilities. At higher velocities, dilation promotes the activity of throughgoing weaker phyllosilicate planes thus favouring stable slip.

Our experiments shed light on the role of fault rock heterogeneity in nucleating dynamic slip in nature as well as in controlling the slip mode during earthquakes or slow-slip events in serpentinite terrains.

How to cite: Pozzi, G., Collettini, C., Scuderi, M., Tinti, E., Tesei, T., Viti, C., Marone, C., Amodio, A., and Cocco, M.: Slip velocity and fault stability in serpentine-rich experimental faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14610, https://doi.org/10.5194/egusphere-egu23-14610, 2023.

EGU23-15559 | Orals | TS3.9

Aseismic rupture on rate-weakening faults before slip instability 

Sohom Ray and Dmitry I. Garagash

The nucleation of earthquakes relies on an interfacial instability that facilitates the transition of a slow fault slip to a faster dynamic rupture. Here, we highlight the scenarios when (rate-weakening) interfaces exhibit a phase of slow aseismic rupture—before slip instability—that propagate large distances compared to the usual nucleation sizes. This aseismic rupture propagation results from rate-weakening interfaces' response to reach a state of steady sliding when forced to slip below steady-state frictional conditions. We numerically simulate the slip cycle—aseismic rupture, instability, and dynamic rupture—driven by prototype loading configurations:

  • Slip dislocation accrues at a constant rate at one end of a finite fault with the other end (a) at the free surface of an elastic half-space and (b) completely locked (buried) in an elastic full-space.
  • Imposed slip dislocation accruing at a constant rate on both ends of a finite fault
  • A localized distribution of shear traction that increases at a constant rate.

All the above loading conditions can permit a slow aseismic rupture along the fault when the fault is initially locked: a state of interfacial slip for which the frictional strength, at the current slip rate, is significantly less than the steady-state frictional strength at the same slip rate. The slow rupture occurs in all the above loading configurations when the fault is initially locked; the subsequent transition to instability, or not, shows a fault-size dependence for configurations 1a and 1b, even when the fault exceeds the usual nucleation sizes. The cut-off fault size that permits instability after aseismic rupture also depends on the friction parameters, the extent of initial contrast from steady-state sliding, and slip conditions towards which aseismic rupture progresses. The remaining loading configurations exhibit instability whenever the fault size exceeds the usual nucleation sizes. Further, we find that slow rupture’s transition to early-stage instability happens through an intermediate breathing (spatiotemporal oscillation) type evolution of slip rate.

How to cite: Ray, S. and Garagash, D. I.: Aseismic rupture on rate-weakening faults before slip instability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15559, https://doi.org/10.5194/egusphere-egu23-15559, 2023.

EGU23-16840 | ECS | Orals | TS3.9

Interplay between aseismic and seismic slip in an earthquake swarm in Western India 

Pathikrit Bhattacharya, Kattumadam Sreejith, Vineet Gahalaut, Adhaina Susan James, Subhasish Mukherjee, Ratna Bhagat, and Ritesh Agrawal

The Palghar Swarm in Western India is unique given its occurrence within the stable continental interior, its unusually long duration (having started in November 2018 it continues unabated), and extremely high seismicity rate (up to a few hundreds of earthquakes a day). Given the small spatial extent (around 100 km2) of the swarm and the dense seismic network deployed by Indian agencies to monitor it, the swarm offers a unique opportunity to understand the processes driving swarms within the stable interior of the Indian plate which, compared to continental interiors elsewhere in the world, is unusually seismically active. The swarm clusters along two lineaments not expressed on the earth surface. Our InSAR analysis, assuming the lineaments to be subsurface faults, reveals predominantly normal dip-slip motion along both faults during several time windows between March 2019 and January 2020. We find the geodetically inferred moment to be an order-of-magnitude larger than the cumulative seismic moment throughout this time window indicating the presence of substantial aseismic slip. The aseismically slipping patches on the two faults migrate spatially and seem well correlated with the migration of seismicity. We explore the interaction between aseismic slip and the swarm seismicity by calculating resolved Coulomb Stress changes due to migrating aseismic slip on each fault and at the hypocentres of earthquakes large enough for a reliable moment tensor to be inferred. Preliminary results suggest a complex relationship between aseismic and seismic slip and a possible involvement of fluids. These results raise the question whether aseismic slip is commonly associated with earthquake swarms within the Indian continental interior and if these might be associated with deep fluid sources within the Indian continental crust.

How to cite: Bhattacharya, P., Sreejith, K., Gahalaut, V., James, A. S., Mukherjee, S., Bhagat, R., and Agrawal, R.: Interplay between aseismic and seismic slip in an earthquake swarm in Western India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16840, https://doi.org/10.5194/egusphere-egu23-16840, 2023.

EGU23-1612 | Posters on site | GD5.1

Mesozoic structural characteristics and exploration potential of the offshore Indus Basin 

Lei Baohua, Gong Jianming, Liao Jing, Liang Jie, Chen Jianwen, and Li Sen

Due to the lack of drilling confirmation and the poor imaging quality of the early seismic data in deeper part, there was a great controversy on the understanding of the strata under the Cenozoic in the offshore Indus Basin: some scholars thought that the Deccan volcanic rocks were widely distributed; It is also believed to be Mesozoic sedimentary strata, but its stratigraphic framework, distribution and structural characteristics are not clear. This directly affects the evaluation of exploration potential in this area. Using the latest multi-channel seismic data, we have clearly identified Mesozoic sedimentary strata in the offshore Indus Basin. The offshore Indus basin is composed of the underlying Mesozoic rifting basin and the overlying Cenozoic passive continental margin sedimentary basin. It is a two-stage superimposed basin developed on the stretched and thinned crust of the Indian plate, drifting from the southern hemisphere to the present position together with the Indian continent. Through correlation of sea and land strata, it is found that the Mesozoic offshore Indus Basin is an offshore extension of the lower Indus Basin, and has similar stratigraphic distribution characteristics and structural characteristics to the lower Indus Basin. The correlation of seismic wave sets indicates that the Jurassic, Sembar Formation and Lower Goru Formation of Lower Cretaceous and the Upper Goru Formation of Upper Cretaceous were also deposited in the sea area. The Jurassic and Lower Cretaceous have the stratigraphic characteristics of eastern faulted and western overlapped, and the Upper Cretaceous has the characteristics of east-west double faulted. The basin rifting area expanded westward continuously during the Mesozoic. The Mesozoic strata were controlled by nearly N-S trending faults,the northern near-shore strata partially reformed by Cenozoic near E-W fault, and the western strata was influenced by the near N-S uplifting and strike-slip structure of Murray Ridge. The average thickness of Mesozoic strata is about 2000m, and the thickest can reach 12000m. The Mesozoic major depocenter is located in the southeast of the basin, the second one is in the northwest. The favorable structural types such as faulted nose, faulted anticline and anticline are mainly developed. These structures were mainly formed during the late Mesozoic compressive uplift period. Therefore, the Mesozoic in the Offshore Indus Basin has the material basis and structural geological conditions for the formation of oil and gas fields. If the favorable structure in Mesozoic can be configured with the depocenter, it will be conducive to hydrocarbon near-source charging. Like the Lower Indus Basin, the Mesozoic is also a favorable direction for petroleum exploration.

How to cite: Baohua, L., Jianming, G., Jing, L., Jie, L., Jianwen, C., and Sen, L.: Mesozoic structural characteristics and exploration potential of the offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1612, https://doi.org/10.5194/egusphere-egu23-1612, 2023.

EGU23-1937 | Posters on site | GD5.1

Fault Transportation and Hydrocarbon Accumulation in Offshore Indus Basin 

Gong Jianming, Liao Jing, Lei Baohua, Liang Jie, Chen Jianwen, and Li Sen

According to the geotectonic analysis and seismic data interpretation, the Offshore Indus Basin is the extension of the Lower Indus Basin in the sea area, with a double-layer structure of "lower fault and upper depression" similar to that of the Lower Indus Basin in the land area. That is, the Mesozoic is a fault basin and the Cenozoic is a depression basin. On the 2D seismic profile, the Mesozoic strata are characterized by many faults, large fault throw, steep dip angle and the development of transport system. There is a great difference between the shallow water area of the northern continental shelf and the deep water area of the southern part of the Cenozoic strata. In the northern part, there are more gravity slumping faults, larger fault throw, and more developed transport systems, while in the southern part, there are fewer faults, smaller fault throw, and less developed transport systems. By comparing and analyzing the small normal faults in the passive continental margin basin of Guyana, South America, and their reservoir forming models, it can be inferred that there may be many "invisible" normal faults with small fault throw, large density and steep dip angle developed in the Cenozoic slope break area of the offshore Indus Basin. In addition, in the strike slip area of Murray Ridge in the west of the basin, the Mesozoic and Cenozoic fault transport systems are developed. The results of sea land correlation and offshore drilling core analysis show that there may be three sets of widely distributed source rocks in the Offshore Indus Basin, which are Cretaceous, Paleo-Eocene and Lower Miocene mudstones. According to comprehensive analysis, the formation of oil and gas reservoirs in the Offshore Indus Basin is mainly controlled by Mesozoic large fault transportation, Mesozoic-Cenozoic fault relay transportation, Cenozoic collapse fault transportation and "hidden" fault transportation. The types of oil and gas pools may mainly include Mesozoic "self generated and self stored" or "side generated and side stored", Cenozoic "lower generated and upper stored" in the north and east of the basin, and "lower generated and upper stored" and "self generated and self stored" in the west of the basin.

How to cite: Jianming, G., Jing, L., Baohua, L., Jie, L., Jianwen, C., and Sen, L.: Fault Transportation and Hydrocarbon Accumulation in Offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1937, https://doi.org/10.5194/egusphere-egu23-1937, 2023.

EGU23-2710 | ECS | Orals | GD5.1

Deformable plate reconstructions of Atlantic Canada and its conjugates back to the Paleozoic 

Michael King, J. Kim Welford, and John Waldron

Atlantic Canada and its conjugate margins, the Irish, Iberian, and Moroccan margins, were subject to rifting and eventual breakup during the Mesozoic, following prior Appalachian Orogenesis from the early to mid-Paleozoic. The complexities of that older orogenesis, involving accretion and collision of Laurentian and peri-Gondwanan terranes during the closing of the Iapetus Ocean, contributed to the heterogeneous pre-rift template of the modern southern North Atlantic Ocean and the timing and extent of subsequent rift-related deformation.

In this work, we present newly-derived offshore and onshore present-day crustal thickness estimates of Atlantic Canada that are calculated using constrained 3-D gravity inversion and later reconstructed back to the onset of rifting and beyond, using GPlates and pyGPlates. In addition, deformable plate reconstructions are also used to reconstruct present-day magnetic anomalies, both onshore and offshore, back through time to track Appalachian orogenic trends beyond what can be deduced from geological field mapping alone. With the pre-rift template of the southern North Atlantic Ocean restored, we then attempt to extend these reconstructions further back in time to the Paleozoic to investigate strain localization within and between Appalachian terranes. Our results clearly reveal the fundamental influence of orogenic inheritance on subsequent rift events and the present-day variations in the crustal architecture that are observed along rifted margins. This study also provides the first quantitative assessment of Atlantic Canada’s crustal evolution from a compressive regime, to an extensional regime, to passive margin development.

How to cite: King, M., Welford, J. K., and Waldron, J.: Deformable plate reconstructions of Atlantic Canada and its conjugates back to the Paleozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2710, https://doi.org/10.5194/egusphere-egu23-2710, 2023.

EGU23-2721 | Orals | GD5.1

Unbending connects sea level to faulting at fast-spreading mid-ocean ridges 

Richard F. Katz and Peter Huybers

Topographic spectra of abyssal hills from fast-spreading mid-ocean ridges have concentrations of power at Milankovitch frequencies and, in particular, around 1/(41 ka) [1].  This frequency corresponds to variations in Earth’s obliquity and is prominent in many climate records, including Pleistocene sea-level variations. Sea-level variations are understood to induce variations in magma supply to the ridge axis [2]. How might these magma-supply variations pace the faulting that creates abyssal hills?  We hypothesise that magma-supply variations introduce a perturbation to elastic plate thickness that is correlated with crustal thickness [3]. Building on Roger Buck’s theory for plate unbending and faulting at fast-spreading ridges [4], we show how thickness perturbations lead to concentrations in bending stresses in thinner parts of the plate.  These concentrations can be significant relative to background unbending stresses and may therefore pace faulting, depending on their amplitude and wavelength.  Using perturbation analysis and numerical solutions of Euler-Bernoulli beam theory, we develop predictions for fault spacing as a function of spreading rate, amplitude of magma supply variations, and other physical parameters.

[1] Huybers, Peter, et al. "Influence of late Pleistocene sea-level variations on mid-ocean ridge spacing in faulting simulations and a global analysis of bathymetry." PNAS https://doi.org/10.1073/pnas.2204761119 

[2] Cerpa, Nestor G., David W. Rees Jones, and Richard F. Katz. "Consequences of glacial cycles for magmatism and carbon transport at mid-ocean ridges." EPSL https://doi.org/10.1016/j.epsl.2019.115845 

[3] Boulahanis, Bridgit, et al. "Do sea level variations influence mid-ocean ridge magma supply? A test using crustal thickness and bathymetry data from the East Pacific Rise." EPSL https://doi.org/10.1016/j.epsl.2020.116121 

[4] Buck, W. Roger. "Accretional curvature of lithosphere at magmatic spreading centers and the flexural support of axial highs." JGR https://doi.org/10.1029/2000JB900360 

How to cite: Katz, R. F. and Huybers, P.: Unbending connects sea level to faulting at fast-spreading mid-ocean ridges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2721, https://doi.org/10.5194/egusphere-egu23-2721, 2023.

The conceptual models of magma-poor rifted margins are greatly influenced by the continent-to-ocean transition structure of the archetypal magma-poor West Iberia Margin. Some previous works with West Iberia magnetic data have been used to constrain the structure and interpret the transition from the exhumed mantle domain to the oceanic crust formed at a spreading center. However, it is found that the resolution uncertainty of the geophysical data was generally overlooked, leading to over-detailed interpretations. In this work we use synthetic magnetic modelling to show that magnetic data acquired at sea-level cannot resolve sub-horizontal lithological layering in deep-water continental margins. Then, we present a new magnetic model guided by a refined velocity model of the wide-angle seismic IAM-9 profile in the Iberia Abyssal Plain. This new model supports that the J-anomaly is caused by a ~6 km thick oceanic crustal structure with locally increased magnetization compared to regular oceanic crust. This J-anomaly crust abuts the exhumed mantle across a nearly vertical boundary, and is the oldest accreted oceanic crust. These results support that mantle exhumation was abruptly terminated by the accretion of oceanic crust. Mantle melting creating oceanic crust was probably not driven by gradual lithospheric thinning and asthenospheric upwelling, but may be the result of seafloor spreading center propagation cutting across the lithosphere and creating the abrupt structure.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL. Support from FCT (PTDC/CTA-GEF/1666/2020), Spanish Ministry of Science and Innovation (CTM2015-71766-R, PID2019-109559RB-I00) and Spanish Research Agency (CEX2019-000928-S) is also acknowledged.

How to cite: Neres, M. and R. Ranero, C.: An appraisal using magnetic data of the Continent to Ocean Transition Structure West of Iberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3394, https://doi.org/10.5194/egusphere-egu23-3394, 2023.

The mid-ocean ridges of the Atlantic and Indian oceans remain essentially fixed with respect to a constellation of mantle plumes throughout Gondwana dispersal.  The Bouvet plume is central to the dispersal process.  A model for the complex early Bouvet (Africa-Antarctica-South America) triple junction provides a link between the relatively simple tectonic histories of the South Atlantic and Indian oceans.  The model is based on interpretation of ocean-floor topography and repeated, meticulous and iterative animation in ‘Atlas’ plate-modelling software.

East and West Gondwana started to separate at   ̴184 Ma (Toarcian) with a 2000-km-long dextral transtensional rift between Africa and Antarctica.  The earliest triple junction was initiated south of Africa as the Malvinas plateau started to move west along the Agulhas fault at   ̴165 Ma (Callovian).  Limpopia, a micro-fragment, at first remained attached to Antarctica while the Maurice Ewing Bank (MEB) retained its attachment to Africa.  New dynamism initiated rifting in the South Atlantic Ocean and between India and Antarctica-Australia early in the Cretaceous.  Complex reorganisation of micro-fragments near the Bouvet plume head led, by   ̴129 Ma (Hauterivian), to a triple junction configuration with the present outline of South America intact (including the MEB fixed off the Malvinas plateau) and with Limpopia, the continental core of the Mozambique Ridge (supplemented by copious Cretaceous volcanism) fixed to Africa.  This configuration was to prove long-lived.

It is interesting to speculate whether the large Morokweng meteorite impact in southern Africa (J/K boundary) could have triggered tectonic acceleration.

The model is illustrated in animation at https://www.reeves.nl/gondwana/aac-anim-1

How to cite: Reeves, C.: The Bouvet triple junction: a model of Gondwana fragmentation in Jurassic and Early Cretaceous times, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5784, https://doi.org/10.5194/egusphere-egu23-5784, 2023.

EGU23-6339 | ECS | Posters on site | GD5.1

Complex seafloor spreading Knipovich Ridge and its crustal structure: insights from aeromagnetic data 

Marie-Andrée Dumais, Laurent Gernigon, Odleiv Olesen, Ståle E. Johansen, and Anna Lim

The interest for the polar regions and complex continental margins and ocean has increased during the last few decades. New technologies allow to conduct research in this hostile environment, permitting to investigate the tectonic and geodynamic history of the North Atlantic and Arctic oceans. In particular, the crustal and lithospheric structure of the Fram Strait and the transition from the Knipovich Ridge to the Barents Sea shelf and Svalbard are still poorly understood. Several multi-geophysical investigations from various campaigns since the 90s along the Western Barents Sea margin and the Northeast Greenland margin resulted in limited and contradicting interpretations of the crust and upper mantle. In this work, we study the spreading of the Knipovich Ridge and the regional tectonic of the Fram Strait and the Svalbard Margin.

Our new KRAS-16 aeromagnetic data survey the complexity of the seafloor spreading history of the Fram Strait region. The high-resolution data identified the magnetic isochrons around the Knipovich Ridge and suggest the presence of several oceanic fracture zones and lineaments in the Fram Strait. The Knipovich ridge spreading initiated at C6 (20 Ma) and a ridge jump occurred at C5E. The oceanic crustal domain was consequently delineated. This new survey suggests that the continent-ocean boundary on the east Barents margin should be relocated up to 150 km farther west compared to previous studies. A 3-D magnetic inversion modelling identified zone with weak magnetization along the rift valley correlated with the absence of volcanic or bathymetric rise evidence. Combined with seismicity data available along the Knipovich Ridge, amagmatic and magmatic accretions show a segmentation of the seafloor spreading that correlates with the variation in magnetization along the rift valley. Furthermore, the new location of the continent-ocean boundary prompted to revise the existing 2-D seismic interpretations in terms of crustal interpretation and tectonic. This is tested further using joint 2-D gravity and magnetic field modelling and electromagnetic/magneto-telluric (CSEM/MT) data. A wide transition lithospheric domain likely comprising an exhumed lower crust or mantle is delineated from our interpretation. These results provide insights of the regional and structural nature of the Knipovich Ridge and its intricate development.

How to cite: Dumais, M.-A., Gernigon, L., Olesen, O., Johansen, S. E., and Lim, A.: Complex seafloor spreading Knipovich Ridge and its crustal structure: insights from aeromagnetic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6339, https://doi.org/10.5194/egusphere-egu23-6339, 2023.

EGU23-6881 | ECS | Posters on site | GD5.1

Continental breakup and slab pull driving force 

Tiphaine Larvet, laetitia le Pourhiet, Philippe Agard, and Manuel Pubellier

Although slab pull is recognized as the main driving force of tectonic plates, marginal basins formation is generally explained by slab roll back or mantle plume impingement. The link between the slab pull force and the continental breakup of the lower plate is still poorly investigated, maybe due to the scarcity of proven examples? The goal of this study is to identify the mechanical conditions for which the slab pull force can be transmitted to the continental lithosphere of the lower plate and generates a continental rifting and breakup. The first condition requires to transfer the slab pull force across the oceanic domain and generate tensional setting into the attached continental margin. Then the ocean needs to be free of any Mid-oceanic ridge, which means that the continental breakup of the lower plate can only happen after the subduction or the inactivation of the ridge. The other conditions cannot be assessed as easily, and therefore motivates our modelling.

We perform a set of 2D thermo-mechanical regional-scale simulations of ridge-free subduction with slab pull evolving self-consistently during the sinking of the slab. The aim is to understand how, when and where slab pull can lead to continental breakup. Two parametric studies are presented. One investigates the tectonic plates kinematic relatively to the upper mantle and another one focused on the strength of both the oceanic and the continental part of the lower plate. In the simulations, the continental rifting is driven by tensional forces internally generated by the subduction zone. Kinematic conditions are only prescribed to the boundaries of the simulation domains to simulate convergent setting and promote subduction. Our numerical simulations reveal that a significant increase of the slab pull induced by the crossing of the 410 km phase transition is responsible for the lower plate breakup. If the oceanic domain is weaker than the continental margin, the slab pull leads to the slab break-off. On the contrary, if the continental domain is weaker, we observe a continental breakup at around 500 km apart from the passive margin. If the lower plate moves compared to the asthenosphic mantle below it, the horizontal basal shear at the LAB prevents the localization of the deformation and leads to an aborted rift.

To synthetize in natural examples, we show that the slab pull can lead to continental breakup when the Mid-oceanic ridge is already subducted, the continental domain is weaker than the oceanic domain, and the horizontal displacement of the lower plate is the same as that of the astenospheric mantle underneath. In light of this new constrains, we discuss the plate reconstruction models proposed for (1) the Cimmerian blocks detachment from the Gondwana during the Permian and (2) the Oligocene South China Sea opening.

How to cite: Larvet, T., le Pourhiet, L., Agard, P., and Pubellier, M.: Continental breakup and slab pull driving force, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6881, https://doi.org/10.5194/egusphere-egu23-6881, 2023.

The Flemish Pass Basin is a Mesozoic basin offshore Newfoundland in Eastern Canada. This basin has proven petroleum systems, and formed via multiple rifting episodes as a part of the wider North Atlantic rift system during Pangaea’s disintegration. We utilise the Bay du Nord 3D seismic survey to derive 3D fault models, which include throws profile. The aim of this was to investigate fault nucleation and growth history, and how this may relate to previous interpretations of multi-stage rifting, plus the possible role of structural inheritance in controlling basin evolution.

Through our interpretation of the 3D volume, we identified three fault systems (1: NE-SW, 2: NW-SE & 3: NNE-SSW), plus one distinctive basin-bounding fault (trending E-W). The NE-SW basement-involved system typically comprises 12 – 17 km long faults dipping 10–25o, with throws of 250–1250 m. This fault system exhibits throws of 600–1250 m between the hanging wall and footwall of the interpreted Pre–Mesozoic cut–off horizon. We interpret this observation of large throw values to relate to the initiation of extension following the Pre-Mesozoic horizon, which likely coincides with the previously interpreted regional Late Triassic–Early Jurassic rift phase. Moreover, although lower throws (≤200 m) were recorded between the Base Upper Tithonian and Late Jurassic horizons, evidence of reactivation of this fault system is interpreted from the throw values, which range from 300–750 m between the Base Upper Tithonian and the Aptian horizons. We interpret this to result from further reactivation due to the previously interpreted 2nd regional rift phase in the Late Jurassic – Early Cretaceous. The NW-SE fault system constitutes 3 – 10 km long planar normal faults, with throws ranging from 50–300 m scattered between the Base Upper Tithonian and Late Cretaceous cut-off lines. We interpret that this fault set propagated downward and linked with pre-existing basement-involved faults, and that the nucleation of this fault set occurred during the 2nd rift phase. The NNE-SSW planar normal fault system is interpreted to be younger based on stratigraphic relationships and comprises 2–8 km long faults. This fault system was interpreted to correspond with the 3rd rift phase during the Cretaceous, and has throw values between the Base Upper Tithonian and the Base Cretaceous horizons ranging from 100–350 m. Finally, the distinct E-W striking basin-bounding normal fault revealed throws of 250–4000 m. This fault acts as a sub-basin confinement on the southern part of the 3D survey area, with throw variation distributed in the Pre-Mesozoic horizon from 1000–4000 m and between Base Upper Tithonian–Aptian Cretaceous horizons with values of 250-800 m.

Overall, our results demonstrate that: 1) in the Flemish Pass basin, there are three fault systems, and one distinctive basin-bounding fault, all of which display variable throw values corresponding to three rift phases (Late Triassic-Early Jurassic, Late Jurassic–Early Cretaceous, and Cretaceous) and 2) pre-existing structures influenced basin development by providing an initial seed for subsequent faulting and may have possibly formed a mechanical link aiding propagation.

How to cite: Guna, A. G. and Peace, A. L.: Geometries and kinematics of fault systems in the Flemish Pass Basin: Insights from the Bay du Nord 3D seismic survey, offshore Newfoundland, Eastern Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7509, https://doi.org/10.5194/egusphere-egu23-7509, 2023.

EGU23-8472 | ECS | Posters on site | GD5.1

A Pseudo-Gravity Magnetic Anomaly Transformation Map for the Central South Atlantic: Implications for Ocean Development after Breakup 

Michelle Graça, Nick Kusznir, and Natasha Stanton

We have processed the EMAG2v3 observed full field magnetic anomaly (Meyer et al., 2017) using the magnetic potential transformation to make a pseudo-gravity anomaly map for the South Atlantic between 15° S and 40° S. A pseudo-gravity transformation attempts to remove the dipolar complexity of a magnetic anomaly and produce the equivalent gravity anomaly assuming a constant ratio of magnetization to density contrast. We assume that magnetization is induced. Our South Atlantic study area encompasses the major bathymetric features of the Rio Grande Rise (RGR) and Walvis Ridge (WR), as well as the Brazilian and African rifted margins.

On the Brazilian continental margin, there are high positive pseudo-gravity anomalies on the São Paulo Plateau (SPP) in the Santos Basin, as well as on the Florianópolis Ridge (FR). The distal Campos Basin also shows high positive pseudo-gravity anomaly. The southern Pelotas Brazilian rifted margin shows negative pseudo-gravity anomaly becoming positive oceanward on the Torres High. In the oceanic domain the Rio Grande Rise (RGR) shows three units of high positive pseudogravity anomalies. Although the RGR presents high amplitude pseudo-gravity anomalies, they are not homogeneous. The Eastern RGR has the most intense and linear N-S anomaly, while its Central unit has a circular pseudo-gravity anomaly and is more constrained in area. The Western RGR has a lower amplitude pseudo-gravity anomaly. The C34 magnetic anomaly region, separating the Eastern and Central RGR, shows a negative pseudo-gravity anomaly. Negative pseudo-gravity anomalies indicate that the assumption of entirely induced magnetization used in the pseudo gravity transformation is invalid and that significant long wavelength remnant magnetization exists. This may indicate heterogeneity of the magnetized layer as well as the effects of magnetic field reversals.

On the African plate, very strong positive pseudo-gravity anomalies occur on the inner WR and the SW African continental margin. The positive pseudo-gravity anomalies of the WR and the beginning of the outer SW trending WR “tail” create a very strong continuous positive pseudo-gravity anomaly. Together with the South African rifted margin, it forms a strong positive anomaly with a “7” shape. Westwards of the C34 magnetic anomaly there are no significant large amplitude pseudo-gravity anomalies.

The map of the pseudo-gravity has been restored using the GPlates reconstruction software. At 110 Ma, the SPP is near the inner WR and both show high amplitude positive pseudo-gravity anomalies. At 110 Ma, the FR is close to the most distal portion of the inner WR, both showing positive pseudo-gravity anomalies. At 85 Ma, the Central RGR, the western extremity of the inner WR and the start of the WR “tail” show conjugate positive pseudo-gravity anomalies. After the C34 anomaly, seen as an intense negative pseudo-gravity anomaly, the Eastern RGR and its conjugate WR “tail” both show positive pseudo-gravity anomalies and separate at ~ 65 Ma. The pseudo-gravity anomaly map indicates that the RGR and WR comprise distinct units which are correlated across the ocean and which correspond to the multiple oceanic ridge jumps reported in Graça et al. (2019).

How to cite: Graça, M., Kusznir, N., and Stanton, N.: A Pseudo-Gravity Magnetic Anomaly Transformation Map for the Central South Atlantic: Implications for Ocean Development after Breakup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8472, https://doi.org/10.5194/egusphere-egu23-8472, 2023.

EGU23-8482 | Posters on site | GD5.1

Thermal inheritance in continental rifting. 

Laetitia Le Pourhiet, Thomas Francois, Anthony Jourdon, and Tiphaine Larvet

While a lot of literature exist modelling the effect of former tectonic structure faults, stacking of different lithologies with a dip or former lacolithes, little has been done in modelling the effect of heterogeneous thermal properties in the lithosphere and particularly in the crust and these contributions are old enough that some of their main results need to be reminded and extended using current modelling tools.  

I will first recall how much periodic variations in heat production rate in the crust may affect the temperature at the Moho and the thickness of the lithosphere using analytical solution, I will then use thermo-mechanical simulation to demonstrate how important are these effects in 2 and 3D at tectonic timescale especially while reactivating former post orogenic collapse structures such as metamorphic core complexes and migmatite domes. I will illustrate how the simulation might apply to the West European rift, the Menderes massif or the South China Sea.

I will finally show using 2D numerical simulations how much the repartition of heat production in the crust influences the long-term survival of mobile belts and can explain partly why the European lithosphere keeps large heat flow despites its thermos-tectonic age.

How to cite: Le Pourhiet, L., Francois, T., Jourdon, A., and Larvet, T.: Thermal inheritance in continental rifting., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8482, https://doi.org/10.5194/egusphere-egu23-8482, 2023.

EGU23-9465 | ECS | Orals | GD5.1

A revision of the Newfoundland Margin: new results from revisited legacy seismic datasets 

Laura Gómez de la Peña, César R. Ranero, Manel Prada, Valentí Sallares, and Donna Shillington

Models of continental margins evolution are largely based on incomplete information, much of it built on research that is now >20 years old. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with radically superior resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve.

We focused on the Newfoundland margin and applied bleeding-edge methodologies to a high-quality dataset acquired in 2000. The SCREECH data includes three primary transects with coincident multichannel seismic reflection data acquired on a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~10-20 km. This dataset was processed >15 years ago with now outdated methodologies. This re-processing in an HPC environment provided the high-resolution images that are needed to fulfill the characterization of this margin.

In particular, we performed the join inversion of multichannel and wide-angle seismic data, which radically improved the resolution of the velocity model and allow to perform a Pre-Stack Depth Migration of the multichannel data. The higher resolution of these images allows to characterize the different crustal domains of the margin in detail, as well as the tectonic structure.

Our results support a more complex structure than previously suggested, with crustal characteristics that change over short distances. In addition, reprocessing of the MCS data allowed to a better understanding of the crustal structure, as the Moho is imaged for the first time along the necking domain. Altogether, these results provide the high-resolution images needed to understand the formation and evolution of the Newfoundland margin.

Comparison of these results on the Newfoundland margin with the most novelty data on the West Iberian margin, acquired during the cruises FRAME (2018) and ATLANTIS (2022) (PI: C. Ranero, streamer data and coincident closely-spaced OBS data), provides a unique opportunity to further understand the evolution of the North Atlantic opening.

How to cite: Gómez de la Peña, L., R. Ranero, C., Prada, M., Sallares, V., and Shillington, D.: A revision of the Newfoundland Margin: new results from revisited legacy seismic datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9465, https://doi.org/10.5194/egusphere-egu23-9465, 2023.

EGU23-9908 | Orals | GD5.1

Quantification and Restoration of the Pre-Drift Extension Across the NE Atlantic Conjugate Margins During the Mid-Permian-Early Cenozoic Multi-Rifting Phases 

Mansour M. Abdelmalak, Sébastien Gac, Jan Inge Faleide, Grace E. Shephard, Filippos Tsikalas, Stéphane Polteau, Dmitry Zastrozhnov, and Trond H. Torsvik

The formation of the NE Atlantic conjugate margins is the result of multiple rifting phases spanning from the Late Paleozoic and culminating in the early Eocene when breakup was accompanied with intense magmatic activity. The pre-breakup configuration of the NE Atlantic continental margins is controlled by crustal extension, magmatism, and sub-lithospheric processes, all of which need to be quantified for the pre-breakup architecture to be restored. Key parameters that need to be extracted from the analysis of crustal structures and sediment record include stretching factors, timing of rifting phases, and nature of the deep crustal structures. The aim of this study is to quantify the pre-drift extension of the NE Atlantic conjugate margins using interpreted crustal structure and forward basin modeling. We use a set of eight 2D conjugate crustal transects and corresponding stratigraphic models, constrained from an integrated analysis of 2D and 3D seismic and well data. The geometry and thickness of the present-day crust is compared to a reference thickness which has experienced limited or no crustal extension since Permian time allowing the quantification of crustal stretching. Based on the eight conjugate crustal transects, the total pre-drift extension is estimated to range between 181 and 390 km with an average of 270–295 km. These estimates are supported by the results of forward basin modeling, which predict total extension between 173 and 325 km, averaging 264 km. The cumulative pre-drift extension estimates derived from basin modeling are in turn used to calculate the incremental crustal stretching factors at each of the three main rifting phases between the conjugate Greenland-Norwegian margins. The mid-Permian early Triassic rifting phase represents 32% of the total extension, while the equivalent values are 41% for the mid-Jurassic to mid-Cretaceous and 27% for the Late Cretaceous-Paleocene rifting phases. These values are used to establish and present at first, a full-fit palinspastic plate kinematic model for the NE Atlantic since the mid-Permian and will be the base for future work on more elaborated models in order to build accurate paleogeographic and tectonic maps.

How to cite: Abdelmalak, M. M., Gac, S., Faleide, J. I., Shephard, G. E., Tsikalas, F., Polteau, S., Zastrozhnov, D., and Torsvik, T. H.: Quantification and Restoration of the Pre-Drift Extension Across the NE Atlantic Conjugate Margins During the Mid-Permian-Early Cenozoic Multi-Rifting Phases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9908, https://doi.org/10.5194/egusphere-egu23-9908, 2023.

Earthquakes in the offshore Grand Banks region of Newfoundland pose a risk to lives and property in nearby coastal communities and to crucial commercial infrastructure and operations in offshore areas. The 1929 M7.2 Grand Banks earthquake, which was associated with a tsunamigenic landslide, devastated the coastal communities in southern Newfoundland and ruptured several trans-Atlantic telecommunications cables. Despite this event, we still know little about the structural setting and neotectonics of the area. In this study, we identified potentially active tectonic structures, and associated secondary deformation features, affecting the youngest strata and the seabed in this region through the interpretation of offshore two-dimensional (2D) seismic reflection profiles. Analysis of these profiles also allowed us to interpret the relationship of the younger, potentially seismogenic structures to inherited passive margin structures at depth. Our findings on the locations and geometries of potentially active faults can be utilized as a basis for seismic hazard inputs for the modelling of earthquake scenarios, which are useful for estimating the potential impacts of the rupture of faults/fault segments on certain populations and assets.

How to cite: Rimando, J., Alexander, P., Guna, A. G., and Goda, K.: Subsurface evidence for potentially seismogenic structures in the offshore Grand Banks region of Newfoundland, eastern Canada: present-day reactivation of inherited passive margin structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10392, https://doi.org/10.5194/egusphere-egu23-10392, 2023.

EGU23-11824 | Posters on site | GD5.1

Two decades of seismicity in the West Iberian Margin: current hypothesis and new ideas 

Gabriela Fernandez Viejo, Carlos Lopez-Fernandez, and Patricia Cadenas

The analysis of two decades (2003-2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin results in a picture of the clustered and moderate seismicity observed in this intraplate submarine area.

The study precise the trend of specific alignments, providing an accurate depiction of event distribution along two stripes 700 km long through the ocean floor in WNW-ESE direction. These alignments are parallel to the Africa-Eurasia plate boundary, but distinctly separated from its related seismicity ≈300 and ≈700 km respectively, enough distance to be considered as intraplate.

When trying to relate this seismicity to structural, and/or geophysical features, it doesn’t arise a conclusive picture. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in the proximity of undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable amount of events nucleating in the upper mantle. The focal mechanisms are predominantly strike-slip and a superposition of the event map with geophysical data shows a puzzling lack of affinity with any of them.

Considering these observations, different hypothesis are discussed to explain this relatively anomalous distribution of seismicity. Some of them previously advanced in the literature do not portray convincing arguments. Others are too unspecific. None of them are completely flawless, suggesting that maybe there is several factors at play. Despite being one of the most probed passive margins in the world, the present geodynamical state of the West Iberian Margin manifested in its modern seismicity, seems to remain unknown.

Interpreting these data within a global tectonic plate framework, together with the potential addition of sea bottom seismometers may give the key to understand this activity along one of the most archetypical margins of the Atlantic Ocean.

How to cite: Fernandez Viejo, G., Lopez-Fernandez, C., and Cadenas, P.: Two decades of seismicity in the West Iberian Margin: current hypothesis and new ideas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11824, https://doi.org/10.5194/egusphere-egu23-11824, 2023.

EGU23-12199 | ECS | Posters on site | GD5.1

Strike-slip influenced rift systems: the case study of the Moroccan Atlas system 

Athanasia Vasileiou, Mohamed Gouiza, Estelle Mortimer, and Richard Collier

The High Atlas is an aborted rift system along NW Africa that formed during the Mesozoic break-up of Pangaea and was inverted during the Alpine Orogeny. In contrast to the well-studied inversion, the Triassic-Jurassic rifting, synchronous to the Atlantic and the Tethyan opening, is still not fully understood. Orthogonal rifting is proposed to be active during the Triassic to early Early Jurassic, and was followed by an oblique extensional phase. The timing of this change in the kinematic of rifting is poorly constrained. Restoration of the Atlantic-Tethys triple junction suggests sinistral motion during the Middle Jurassic, which reactivated NE-SW trending Hercynian structures in a transtensional manner.

The Atlas system is a great field analogue to study and analyse extensional systems influenced by strike-slip tectonics since the well exposed syn-rift structures and sediments have been weakly affected by the contraction during the late Cenozoic Alpine inversion.

This work investigates the kinematic and geometry of the oblique rifting phase, the stress and strain variation lengthwise along the Atlas rift system, the relationship between the Triassic-Early Jurassic orthogonal rift structures, the Middle Jurassic strike-slip structures, and the potential synchronous volcanism occurring during the Middle Jurassic. This contribution highlights the fieldwork results of significant outcrops that we used to constrain the restoration of the rift system, evaluate extension and transtension, and produce a conceptual model of how strike-slip tectonics can influence the evolution of continental rifting.

How to cite: Vasileiou, A., Gouiza, M., Mortimer, E., and Collier, R.: Strike-slip influenced rift systems: the case study of the Moroccan Atlas system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12199, https://doi.org/10.5194/egusphere-egu23-12199, 2023.

EGU23-12301 | Posters on site | GD5.1

Onshore-offshore relationship and anatomy of a necking zone: insights from high-resolution aeromagnetic survey on the Finnmark Platform (Norwegian Barents Sea) 

Laurent Gernigon, Claudia Haase, Sofie Gradmann, Marie-Andrée Dumais, Trond Slagstad, Frode Ofstad, Aziz Nasuti, and Marco Bronner

We integrated high-resolution aeromagnetic data and 2D/3D seismic data from the Norwegian Southwestern Barents Sea. The main objective is to address the long-standing question on the role of pre-existing basement structures in controlling strain accommodation and extension in the Finnmark Platform and adjacent rift basins. The thorough qualitative analysis of the high-resolution magnetic data reveals fault geometries, regional kinematics, magmatism and inheritance of older Precambrian/Caledonian structures. Through the application of second order derivative filters and depth-to-magnetic-source modelling, the trends of the Caledonian metamorphic fabrics are identified and correlated with the structure of buried basement faults and shear zones also imaged at the same level of resolution on 2D/3D seismic data. The magnetic data reveal an unprecedented detail of the basement fabrics dominated by high-frequency NW-SE trending magnetic lineaments associated with the semi-regional Sørøya-Ingøya Shear Zone. The high-frequency magnetic lineaments are superimposed by lower frequency NNW-SSE trending magnetic lineaments that reflect the inheritance of older Precambrian structures. At the edge of the Tromsø Basin, the new magnetic data highlight sill intrusions also visible on seismic data. Fault geometries, regional kinematics, and spatial distribution of the magnetic sources suggest that old detachments and younger Mesozoic faults reactivated the basement fabrics found along the graben borders. Focusing of strain accommodation at the edge of the Hammerfest Basin is helped as well as modulated by the presence of back-thrusted Caledonian nappes interpreted on the Finnmark Platform. Offshore, surface ruptures associated with graben formation align with the dominant NNW-SSE trending magnetic lineaments defining steeper normal faults that are characterised by right-stepping segments along the southern flank of the Hammerfest Basin. Based on potential field models, we finally quantify the crustal architecture of the rift and platform system. At upper crustal level, we test the presence and significance of potential Palaeozoic basin preserved at the edge of the basement hinge-zones. Potential field modelling also highlights and quantifies several rift domains defined by moderate to extreme thinning of the crust (low-β stretched domain, necking, and high-β hyperextended regions). The development of the necking zone is clearly influenced by the existence of former first-order and multi-scale inherited basement features preserved in the Finnmark Platform.

How to cite: Gernigon, L., Haase, C., Gradmann, S., Dumais, M.-A., Slagstad, T., Ofstad, F., Nasuti, A., and Bronner, M.: Onshore-offshore relationship and anatomy of a necking zone: insights from high-resolution aeromagnetic survey on the Finnmark Platform (Norwegian Barents Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12301, https://doi.org/10.5194/egusphere-egu23-12301, 2023.

EGU23-12348 | ECS | Posters on site | GD5.1

Local seismicity in the obliquely spreading setting of Fram Strait constrained from ocean bottom seismometers: Implications for fluid flow and methane seepage 

Przemyslaw Domel, Vera Schlindwein, Andreia Plaza-Faverola, and Stefan Bünz

The Fram Strait opening is associated with a complex stress regime that results from the oblique relation between two ultra-slow spreading mid-ocean ridges, the Molloy ridge (MR) and the Knipovich Ridge (KR), offset by the Molloy Transform Fault (MTF). Gas-charged thick sedimentary deposits developed over both oceanic and continental crust. Sedimentary faulting reveals recent stress transfer into the sub-surface. However, the mechanisms by which stress accommodates across the west Svalbard margin and its effect on fluid flow and seepage dynamics remain poorly understood. An analysis of earthquake occurrence and focal mechanisms can shed light on the present state of tectonic forces in the area, their origin and potential influence on nearby faults. Conventional studies using land instrumentation provide incomplete seismological records even for such comparatively land proximal settings, due to still large distances to the nearest permanent observatories and a poor azimuthal coverage. We deployed 10 ocean bottom seismometers (OBS) for 11 months between 2020-2021 about 10 km north of the northern termination of KR to investigate patterns of stress transfer off the ridge and the influence on the sedimentary system. OBSs are spaced by about 10 km around an area characterized by fault-related seepage and sedimentary slumps visible on the bathymetry. Using partially automated routines we built a catalogue of local earthquakes and computed their epicenters and magnitudes. Earthquake locations roughly follow the plate boundaries and better focus seismicity along their bathymetric imprint versus the land observations. Along the MTF, we observe that the earthquakes are concentrated southwards on the North American plate and seismicity across the west-Svalbard margin is limited. A large number of earthquakes extend beyond the MTF and KR corner and concentrate at a bathymetric depression, adjacent to the recently revised continental-oceanic transition boundary. Focal mechanisms from past observations show a gradual change from strike-slip movement along the MTF to extensional faulting at the corner. The distribution of earthquakes correlates with highly faulted sedimentary overburden interpreted in high resolution seismic data, and with major structures in gravity and magnetic maps. This suggests an efficient stress release at the plate boundary and little to no transfer northward from the KR termination onto the Eurasian plate. We detected only a few events recorded along the Vestnesa contourite drift and on the continental shelf. These earthquakes may indicate reactivation of crustal faults under the weight of thick sedimentary deposits or other processes such as glacial isostacy. The inferred stress distribution in the region has implications for understanding fault-related gas transport and methane seepage at Arctic margins.

How to cite: Domel, P., Schlindwein, V., Plaza-Faverola, A., and Bünz, S.: Local seismicity in the obliquely spreading setting of Fram Strait constrained from ocean bottom seismometers: Implications for fluid flow and methane seepage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12348, https://doi.org/10.5194/egusphere-egu23-12348, 2023.

EGU23-13753 | ECS | Orals | GD5.1

The Central Afar region as an analogue for the development of oceanic plateaus? 

Valentin Rime, Anneleen Foubert, Joël Ruch, and Tesfaye Kidane

Oceanic plateaus are traditionally considered as oceanic crust thickened by magmatic processes. In the last decades, however, continental material significantly older than the surrounding oceanic crust has been recovered from drillings on oceanic plateaus (e.g. Rio Grande Rise, Mauritius and Mascarene Plateau, Elan Bank), leading to numerous questions about the origin of these structures.

The Central Afar region is part of the Afro-Arabian Rift System. It witnessed the eruption of the Ethiopian Flood Basalts approx. 30 My ago followed by rifting. Mapping, plate kinematic modelling and geophysical data show that, despite important extension, the area features relatively thick crust. This crust is characterized by important magmatic underplating, intrusions, and volcanic material with isolated continental fragments. Therefore, it might represent an analogue for the development of oceanic plateaus. Numerous rift jumps and magma-compensated thinning linked to the presence of the Afar hotspot can explain the structure of the Central Afar. Unlike Central Afar, the Danakil Depression in northern Afar shows more classical structures and will probably develop into a magma-rich margin. The Afar depression thus constitute a unique example of the early development of different types of passive margins and oceanic plateaus.

How to cite: Rime, V., Foubert, A., Ruch, J., and Kidane, T.: The Central Afar region as an analogue for the development of oceanic plateaus?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13753, https://doi.org/10.5194/egusphere-egu23-13753, 2023.

The Fram Strait (North-eastern Atlantic Ocean) developed along a narrow transform margin that separates the Arctic Basin in the north from the Atlantic Basins in the south. The transform margin developed from the Miocene to Present Day and provided the first oceanic gateway between the Arctic Basin and the Atlantic Basins, allowing the ventilation of a previously closed Arctic Basin and a dramatic shift in global ocean circulation. Existing tectonic models are over-simplified and do not account for new data acquired from 2017 onward. Understanding the tectonic complexity of the Fram Strait and reconciling the fine details in a globally robust plate model is critically important for global ocean circulation models but may also provide an important insight into the development of paleo-transform margins further back in time.  

Potential fields data provide a particularly useful screening tool, especially at high latitudes where sea-ice makes the acquisition of seismic and well data more difficult. Detailed analysis of the structural and crustal architecture of the Fram Strait was conducted using potential fields data for structural mapping, 2D gravity and magnetic models, and 3D inversions for depth-to-basement and depth-to-Moho; these all combine for a new, high-resolution, tectonic model for the region. The results reveal the geometries of ocean basins under transtension, where the ultra-slow and non-volcanic opening have no currently established thermal driver. The crust is low-density and formed by faulting, exhumation and serpentinization of deeper mantle layers.  This mode results from tectonically forced opening where transtension accommodates plate motion at established offset spreading ridges to the north in the Arctic Basin and to the south in the North-eastern Atlantic Ocean.  

Of particular importance is the arrangement of early fracture zones and the location of bathymetric ridges, which illustrate the segmented nature of early transform margins and variability of crustal type and evolution within individual segments. This variability has dramatically affected paleo-bathymetry and, therefore, has exerted significant control on ocean circulation and sediment transport.  

An incomparable advantage of globally available gravity and magnetic data is the ability to draw upon global analogues when investigating new or frontier areas. Analogues can be made between conjugate margins, but also between different systems around the planet. Younger, developing tectonic systems may provide important insights into the early evolution of more complicated areas, where poly-phase tectonic histories may have since matured or been subsequently overprinted. The Fram Strait model shares similarities with other examples of global transform margins, such as the Equatorial Atlantic. This provides an opportunity to re-examine the crustal architecture and structural relationships within other transform margin settings, using the Fram Strait as an analogue for early opening history.  

How to cite: Hill, C., Webb, P., and Masterton, S.: Challenging our understanding of the early evolutionary history of transform margins using a revised, high-resolution model of the Fram Strait, North-eastern Atlantic Ocean. , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15682, https://doi.org/10.5194/egusphere-egu23-15682, 2023.

EGU23-16556 | ECS | Posters on site | GD5.1

The Jurassic rifted margins and ocean basin, offshore Guyana-Suriname-Demerara and its link with Gulf of Mexico opening 

Júlia Gómez-Romeu, Nick Kusznir, Andy Alvey, and Emmanuel Masini

The Guyana-Suriname-Western Demerara (G-S-WD) continental margins are located at the junction of the Central Atlantic and proto-Caribbean oceanic basins as they developed in the Jurassic. The emplacement of the later Caribbean subduction partly destroyed the Jurassic record of the proto-Caribbean basin which implies that the Jurassic kinematics of this region are still debated. However, the G-S-WD margins escaped from subduction and preserve most of the Jurassic record. We investigate the architecture of the G-S-WD margins and the distribution of Jurassic oceanic crust. This allows us to determine the margins tectonic styles and gain insights into the Jurassic regional plate kinematics during the southward propagation of the Central Atlantic, the opening of the proto-Caribbean basin and its link with the development of the Gulf of Mexico (GoM).

We use 3D gravity inversion to map Moho depth, crustal basement thickness and continental lithosphere thinning factor. Input data for the gravity inversion is sediment thickness from seismic reflection grids, satellite free-air gravity data and digital bathymetry. From the resulting 3D Moho depth volume we produce margin crustal cross-sections to determine the structure and architecture of the G-S-WD margins. The Guyana segment shows a transform architecture, the Suriname segment a rift-transform architecture and the Western Demerara segment a magma-rich rifted margin with SDRs up to 20 km thick.

We also use crustal thickness mapping from gravity inversion together with regional magnetic anomaly superimposed satellite gravity anomaly data to determine the extent of Jurassic oceanic crust and delineate its boundary with Cretaceous Equatorial Atlantic oceanic crust. The boundary between Jurassic and Cretaceous oceanic crust is identified as running from the NW corner of the Demerara Plateau to Barbados. This boundary has the same orientation as the Guyana transform margin.

Plate reconstructions of crustal thickness from gravity inversion have been used to examine the relationship between the Jurassic opening of the Central Atlantic, the development and opening of the GoM and the formation of the Jurassic crust offshore G-S-WD.

A new plate reconstruction of the opening of the GoM based on transform fault small circles observed in satellite free-air gravity data shows that before the rotational opening of GoM at ~165 Ma, the early GoM and oceanic crust offshore G-S-WD formed a co-linear linked rift/sea-floor spreading system offset by a sinistral transform to the west of Florida.

How to cite: Gómez-Romeu, J., Kusznir, N., Alvey, A., and Masini, E.: The Jurassic rifted margins and ocean basin, offshore Guyana-Suriname-Demerara and its link with Gulf of Mexico opening, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16556, https://doi.org/10.5194/egusphere-egu23-16556, 2023.

EGU23-16613 | Posters on site | GD5.1

Iceland: mantle plume or microcontinent? A zircon study 

Alexander Peace, Jordan Phethean, Yang Li, and Gillian Foulger

In recent years, unexpected continental crust in areas presumed to be purely oceanic in nature has been discovered, indicated by the presence of Paleozoic zircons in rock samples. Notable examples include the Rio Grande Rise, Mauritius, and potentially also the Comoros islands, which have all previously been interpreted as mantle plume edifices. Iceland is also often interpreted as a hotspot of mantle plume origin, however the presence of a deep seated consistent thermal anomaly with depth has long been challenged, with implications for the wider regional geodynamic evolution.

Previous reports of Mesozoic and Paleozoic zircons from Iceland may allude to the presence of continental material at depth, although these are sometimes suggested to be the result of contamination. Nonetheless, geochemical evidence from erupted material at Öræfajökull may indicate a continental contribution to melts beneath SE Iceland, and the nearby Jan Mayen microcontinent readily demonstrates the ability of continental material to make its way to the ocean interior, coincident with hotspot volcanism. Furthermore, continental material in the NE Atlantic Ocean is perhaps more common than previously thought, with recent work suggesting that substantial components of the Greenland-Iceland-Faeroes region may be continental in nature.

Here, we test the hypothesis that the basaltic upper crust of Iceland is underlain by older continental crust. To do this, we have undertaken extensive, targeted sampling of Icelandic rocks and sediments using robust collection approaches to eliminate the possibility of contamination. Over a 3-week period in summer 2022, we collected samples from across the entirety of Iceland. We sampled both intrusive and extrusive rocks with a wide range of ages (both felsic and mafic, but with an emphasis on felsic rocks), as well as river sediments from above 250 m elevation (to avoid potential contamination from Greenland glacial debris). Zircons will be separated from these samples using contamination-safe approaches, and then U-Pb and Hf isotopic age analysis will be completed. The results from this preliminary study will be used to guide further sampling in summer 2023, allowing evaluation of the competing hypothesises for the origin of Iceland.

How to cite: Peace, A., Phethean, J., Li, Y., and Foulger, G.: Iceland: mantle plume or microcontinent? A zircon study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16613, https://doi.org/10.5194/egusphere-egu23-16613, 2023.

EGU23-431 | ECS | Posters on site | EMRP1.2

New insights into the rheology of a normal fault: the Mw6.1 2009 L’Aquila case study 

Rossella Fonzetti, Luisa Valoroso, Pasquale De Gori, and Claudio Chiarabba

The study of seismogenic faults is one of the most interesting topics in seismology.  Obtaining a more detailed image of the fault zone structure and of its properties (e.g., fluid content, permeability, lithology, rheology) is fundamental to understand how seismic ruptures originate, propagate and arrest and to study the triggering processes.  The 2009 Mw 6.1 L’Aquila seismic sequence is a perfect case study to reach this goal, thanks to the huge amount of multidisciplinary data available. 

In this study, we reprocess the high-precision large earthquake catalog available for the L’Aquila seismic sequence, focusing on the main (Paganica) seismogenic fault (about 20,000 earthquakes occurring between January-December 2009). We used cross-correlation and double-difference tomography methods to compute high-resolution (2.5 x 2.5 x 2 km grid spacing) Vp and Vp/Vs models along the fault plane. High-resolution Vp and Vp/Vs models give insights into the rheology of the Paganica fault, suggesting new ideas on earthquake generation, propagation and arrest.  

How to cite: Fonzetti, R., Valoroso, L., De Gori, P., and Chiarabba, C.: New insights into the rheology of a normal fault: the Mw6.1 2009 L’Aquila case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-431, https://doi.org/10.5194/egusphere-egu23-431, 2023.

EGU23-531 | ECS | Orals | EMRP1.2

Interplay between fluid flow and rock deformation in an exhumed hydrothermal fault-vein network 

Simone Masoch, Michele Fondriest, Rodrigo Gomila, Giorgio Pennacchioni, José Cembrano, and Giulio Di Toro

Faults can act as conduits for the migration of hydrothermal fluids in the crust, affecting its mechanical behaviour and possibly leading to earthquake swarm activity. To date, there are still few constraints from the geological record on how fault-vein networks develop through time in high fluid-flux tectonic settings. Here, we describe small displacement (<1.5 m) epidote-rich fault-vein networks cutting granitoids in the exhumed Bolfin Fault Zone (Atacama Fault System, Chile). The epidote-rich sheared veins show lineated slickensides with scattered orientations and occur at the intersections with subsidiary structures in the fault damage zone. FEG-SEM cathodoluminescence (CL) reveals that magmatic quartz close to the sheared epidote-rich veins is affected by (i) thin (< 10 µm) interlaced deformation lamellae and (ii) a network of CL-dark quartz epitaxial veinlets sharply crosscutting the lamellae. EBSD maps of the deformed quartz indicate minor lattice distortion associated with the lamellae and an orientation nearly orthogonal to the c-axis. These deformation features disappear moving away into the host rock. The epidote-rich sheared veins (i) include clasts of magmatic quartz with both the deformation lamellae and the healed veinlets and (ii) show cyclic events of extensional-to-hybrid veining and localized shearing. We propose that the microstructures preserved in the quartz next to the sheared veins (i.e. deformation lamellae and epitaxial veinlets) record the high-strain rate loading associated with dynamic crack propagation and rapid micro-fracture sealing. On the other hand, the cyclic dilation and shearing within the epidote-rich veins is interpreted as the expression of a highly connected fault-vein network dominated by pore pressure oscillations leading to seismic swarm activity.

How to cite: Masoch, S., Fondriest, M., Gomila, R., Pennacchioni, G., Cembrano, J., and Di Toro, G.: Interplay between fluid flow and rock deformation in an exhumed hydrothermal fault-vein network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-531, https://doi.org/10.5194/egusphere-egu23-531, 2023.

EGU23-1330 | ECS | Orals | EMRP1.2

Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events 

Tatiana Kartseva and Nikolai Shapiro

We propose an approach that is aimed to enrich the catalogs of acoustic emission events recorded in laboratory experiments with such parameters as seismic moment and corner frequency. Because of the difficulty of separation of direct waves in experiments performed on small samples, we use the coda waves that are composed of the reverberation of the acoustic field in the tested sample. After multiple reverberations, the resulting wavefield can be approximated as nearly homogeneously distributed over the sample and with signal amplitudes decaying exponentially in time (linearly in a logarithmic scale).

Within the framework of this model, the frequency-dependent coda amplitude at any moment of time is described as combination of a source spectra, of a decay rate combining internal attenuation with reverberation losses, and of a sensor response. One of the main difficulties with the laboratory experiments is that acoustic sensors are very difficult to calibrate and their absolute response function in most of cases remains unknown. With the simple reverberation model, the logarithms of coda amplitudes at different times and sensors and for multiple events are described by a system of linear equations that we solve in a least-square sense to find frequency-dependent coda-decay rates, relative signal spectra and sensor responses. In a next step, we compute spectral ratios between spectra of different events to eliminate the sensor responses and to estimate main source parameters such as corner frequencies and relative seismic moments.

We provide details of our data analyses technique and present time-dependent corner frequency vs relative moment diagrams for two experiments on granite of the Voronezh massif and Berea sandstone under pseudo-triaxial loading. The dependence close to the cubic that is frequently estimated for tectonic earthquakes observed on the first stages of both experiments when confining pressure steps applied to the intact rock and therefore to the pre-existing inhomogeneties. After applying axial load changes in stress-drop is being observed: with higher stress-drops prevailing in granite and lower stress-drops in sandstone. Also there is a significant difference in Gutenberg-Richter relation in these two experimental conditions observed.

How to cite: Kartseva, T. and Shapiro, N.: Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1330, https://doi.org/10.5194/egusphere-egu23-1330, 2023.

EGU23-2537 * | Posters on site | EMRP1.2 | Highlight

Fault rocks associated with the reservoir-triggered seismicity of the Koyna-Warna area (India) 

Giulio Di Toro, Alessio Chiesurin, Elena Spagnuolo, Rodrigo Gomila, and Sukanta Roy

In 1962, the Kyona Dam was completed in a rural area 250 km southeast of Mumbai (India), primarily for hydropower generation. Since then, the area, which was essentially devoid of natural seismicity, has been affected by a sequence of moderate to large magnitude earthquakes, including the one of December 11th, 1967 (ML6.3, 177 casualties), the largest human-induced earthquake so far. Major earthquakes (ML>4) are modulated by basin-filling and emptying operations, which follow the monsoon regime with peak rainfall between July and September. There are two peaks of seismicity: the first between August and September (“rapid-response”), corresponding to the rainy season, and the second in February (“delayed-response”) corresponding to the dry season. The ML>3 earthquakes have normal to strike-slip focal mechanisms, reactivate steeply-dipping faults/fractures, and are located between 3 and 10 km depth in the granitoid Indian basement (2.7-2.6 Ga) buried beneath the 0.5-2 km thick Deccan basaltic lava flows (68-60 Ma). The temperature at hypocentral depths is estimated to be between 80 and 200°C. Especially the delayed-response seismicity implies poro-elastic effects, also related to the percolation of water from the surface to hypocentral depths. To study the seismicity of the area, a large deep drilling project was completed by the Ministry of Earth Sciences (India) which includes nine wells down to 1.5 km depth and a pilot well down to 3 km depth. Here we describe the fault rocks (mylonites, cataclasites, breccia and faults/fractures filled by epidote, quartz, chlorite and calcite veins) collected in boreholes KBH1, KBH6 and KBH7.

Visual analysis of the cores plus mineralogical, microstructural and geochemical investigations (X-ray powder diffraction; scanning electron microscope equipped with Wavelength-Dispersive X-Ray Spectroscopy) allowed us to reconstruct the sequence of deformation events. Steeply-dipping faults/fractures filled by chlorite and calcite are the last deformation event as they cut through all other structural features. We recognized eight types of chlorites based on optical properties, crosscutting relations and chemical composition. The temperature of formation of the chlorite spans from 350°C (or HT-chlorite found in the shear zones cut by the Deccan basaltic dykes), to 200°C<T<250°C (or LT-chlorite filling fault/fractures cut by calcite veins, but with uncertain crosscutting relations with Deccan basaltic dykes), and 130°C<T<135°C (or Very-LT-chlorite filling fault/fractures, which are also cut by calcite veins, and cut the Deccan basaltic dykes). LT- and Very-LT-chlorite formation temperatures were estimated with the Bourdelle & Cathelineau (2015) chlorite geothermometer. The range of 130°C<T<250°C for chlorite formation, which can be extended to lower temperatures considering that these faults/fractures are cut by calcite veins, overlaps with the one (80°C<T<200°C) estimated at the hypocentral depths of the Koyna-Warna area. Moreover, these fault/fractures found in the boreholes are hosted in steeply-dipping fault/fractures (or sub-parallel to the structures illuminated by the hypocentral distributions), and are filled by minerals precipitated from percolating fluids (i.e., consistent with the evidence of delayed-response seismicity). We conclude that the faults/fractures currently reactivated by reservoir-triggered seismicity most likely correspond to those filled by calcite and LT- to Very-LT chlorites found in the deep boreholes.

How to cite: Di Toro, G., Chiesurin, A., Spagnuolo, E., Gomila, R., and Roy, S.: Fault rocks associated with the reservoir-triggered seismicity of the Koyna-Warna area (India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2537, https://doi.org/10.5194/egusphere-egu23-2537, 2023.

EGU23-2911 | Orals | EMRP1.2

Microstructural controls on seismicity distribution in simulated fault gouges 

Andre R. Niemeijer, Evangelos Korkolis, Tanmaya Mishra, Rens Elbertsen, Beunen Jop, and Ivan Pires de Vasconselos

In order to make seismic hazard estimates, it is necessary to assume some distribution of the number of earthquakes of a certain magnitude, i.e. a Gutenberg-Richter distribution. This is true for both natural seismicity as well as induced seismicity, but in both cases the number of historical earthquakes at the tail end of the distribution (i.e. the largest ones) is limited and often the maximum possible magnitude is unknown. In contrast, in a laboratory setting the maximum size of an unstable slip event (“stick-slip” or laboratory earthquake) is controlled by the size of the sample and the imposed stress. In our rotary shear apparatus, we can theoretically achieve unlimited fault displacement which allows us to produce earthquake-like distributions with thousands to tens of thousands event.

In this presentation, I will present results from experiments on simulated fault gouges which show unstable frictional behaviour at room temperature conditions. The results show that the event size distribution can change spontaneously, without any changes in the boundary conditions. Observations of fault gouge material after the experiment, suggest that wear of the granular material generates alternative surfaces for slip, which changes the macroscopic behaviour. Interestingly, the change in event size distribution is reversable, presumably because the fine-grained layers become disturbed with ongoing shear.

In an attempt to simulate the macroscopic behaviour, we have, for the first time, measured the rate-and-state frictional (RSF) properties on single grain contacts. Using these values in a numerical model for seismic slip (so-called “seismic cycle simulator”), we obtain maximum stress drops that are comparable to those obtained in the experiments, but with some differences. The differences are most likely due to the fact that the grains in our simulated fault are affected wear in previous slip events, which should change their RSF parameters. In addition, the normal stress at each individual grain contact is unknown in the experiment and could vary significantly from event to event.  This latter difference between model and experiment can be overcome by using a discrete element method with contact-scale RSF properties to simulate slip.

How to cite: Niemeijer, A. R., Korkolis, E., Mishra, T., Elbertsen, R., Jop, B., and Pires de Vasconselos, I.: Microstructural controls on seismicity distribution in simulated fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2911, https://doi.org/10.5194/egusphere-egu23-2911, 2023.

EGU23-3982 | ECS | Orals | EMRP1.2

Energy budget of quasi-dynamic earthquake cycle 

Navid Kheirdast, Michelle Almakari, Carlos Villafuerte, Marion Y. Thomas, and Harsha S. Bhat

The elastic medium that hosts several, multi-scale, faults could be regarded as an energy reservoir that is charged by the far field stress rate and discharged by friction dissipation during earthquake slips on the faults.  In this study, we carefully analyze the energy budget variations that occur throughout a synthetic, 2D plane-strain, earthquake cycle on a fault system comprising of a main fault surrounded by a hierarchy of off-fault slip planes/fractures. We evaluate the rate of kinetic energy variation, stress power across the continuum, far field power supply, and the dissipation due to the rate-and-state friction on the faults given a spectrum of slips ranging from slow-slip to rapid ruptures. We study how the medium's energy budget evolves after these components have been determined.  Additionally, we compute the dissipation rate for a variety of slip rates to determine the contributions of so-called slow-slip events, low-frequency earthquakes (LFEs), and tremors to this budget. We also evaluate the share of off-fault fractures to determine their energetic role during earthquake cycles.

How to cite: Kheirdast, N., Almakari, M., Villafuerte, C., Thomas, M. Y., and Bhat, H. S.: Energy budget of quasi-dynamic earthquake cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3982, https://doi.org/10.5194/egusphere-egu23-3982, 2023.

EGU23-5033 | Orals | EMRP1.2

Modelling seismicity based on fault geometry: maximum magnitudes and magnitude-frequency distributions. 

Vincent Roche, Mirko van der Baan, and John Walsh

Investigating clusters of events and geophysical screening often provides limited constraints on fault geometries. This imaging issue prevents the integration of realistic fault zone geometry into earthquake studies, which can affect our capacity to evaluate the role of pre-existing faults on seismicity. This study describes a modelling strategy accounting for realistic fault zone geometries. Our approach uses stochastic methods underpinned by quantitative fault zone parameterization, followed by an assessment of seismicity from simulations of rupture dynamics controlled by fault geometry. This method is used to investigate the role of fault maturity on seismicity for two case studies, including seismicity associated with the reactivation of a pre-existing fault network due to hydraulic fracturing in Harrison County, Ohio, from 2013 to 2015, as well as the natural seismicity associated with the Yushu-Ganzi left-lateral strike-slip fault system in central-eastern Tibet. In the Harrison County case, we analyze the effect of vertical variability in fault maturity and show how more mature faults in the deeper crystalline basement generate higher magnitude seismicity than shallow, immature faults in younger sedimentary rocks. In the Yushu-Ganzi case study, we show how lateral variability in structural maturity, arising from long-term fault propagation and strain rates, leads to different seismicity on individual fault segments. Our findings indicate that fault geometry determines seismic patterns, with rupture length controlled by fault zone geometry rather than fault lengths, and favour the adoption of a structural geological perspective for the integration of realistic fault geometry into seismicity prediction strategies.

How to cite: Roche, V., van der Baan, M., and Walsh, J.: Modelling seismicity based on fault geometry: maximum magnitudes and magnitude-frequency distributions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5033, https://doi.org/10.5194/egusphere-egu23-5033, 2023.

EGU23-6468 | ECS | Posters on site | EMRP1.2

Evidence for coseismic slip preserved in high-porosity sandstone at very shallow burial conditions (Crotone Basin, Italy) 

Mattia Pizzati, Nicolò Lieta, Anita Torabi, Luca Aldega, Fabrizio Storti, and Fabrizio Balsamo

The seismogenic zone is commonly defined as the portion of the Earth's upper crust where most earthquakes nucleate. According to seismological data, the seismogenic interval is typically located between 5 and 35 km depth. However, shallow seismicity, with earthquake hypocentral depths < 5 km, has been reported in several tectonic settings. Although less studied, such shallow seismic sources represent potential treats and deserve to be thoroughly investigated and included in seismic hazard evaluations.

For this purpose, we present the results of a multidisciplinary study focusing on faults affecting high-porosity fluvio-deltaic, sandstone-dominated deposits belonging to the Pliocene-Pleistocene succession of the Crotone Basin, South Italy. The studied fault zone is well exposed along the Vitravo Creek canyon, has a maximum displacement of ~50 m, and is characterized by an indurated, sharp master slip surface. The fault footwall displays an 8-10 m-wide deformation band-dominated damage zone with deformation bands occurring both as clusters and as single structures. The frequency of deformation bands increases towards the master slip surface. Approaching the master slip surface, a 1.5 m-thick mixing zone occurs, where strong tectonic mixing affected the sandstone strata with different grain size and thickness. The fault core consists of ~1 m-wide, calcite-cemented cataclastic volume and hosts a wealth of fault-parallel deformation bands and subsidiary slip surfaces. Due to its selective cementation, the fault core stems in strong positive relief compared to the host high-porosity sandstone. The hanging wall block is characterized by a dense network of thin deformation bands with diminishing frequency away from the fault surface. Along the master slip surface, at the top of the indurated fault core, a 1-2 cm-thick dark gouge layer is present. The gouge is persistent throughout all the fault exposure, and has been injected in the underlying, fractured cemented fault core. Microstructural analysis of the gouge reveals a strong cataclastic grain size reduction along thin (< 1 mm) slip zones alternated with portions showing lens-shaped (resembling S-C) fabric. XRD analysis of the < 2 µm grain-size fraction of the gouge layer displays short-ordered illite-smectite mixed layers which support deformation temperatures in the 100-120°C range. XRD analysis performed on clay fraction from the fault core, next to the dark gouge layer, indicates temperatures lower than 50-60°C, consistent with the expected shallow burial conditions. Following this, the anomalous temperature rise recorded within the dark gouge layer is suggested to be produced by frictional heating during coseismic deformation. We conclude that the microstructural observations, grain size, and XRD data provide a line of evidence supporting the occurrence of coseismic deformation affecting high-porosity granular materials at near surface conditions and could help in better evaluation and risk assessment of seismically active faults.

How to cite: Pizzati, M., Lieta, N., Torabi, A., Aldega, L., Storti, F., and Balsamo, F.: Evidence for coseismic slip preserved in high-porosity sandstone at very shallow burial conditions (Crotone Basin, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6468, https://doi.org/10.5194/egusphere-egu23-6468, 2023.

EGU23-6517 | Orals | EMRP1.2

On-fault damage evolution in laboratory earthquakes: a numerical perspective on fault complexity 

Guilhem Mollon, Jérôme Aubry, and Alexandre Schubnel

We propose a numerical model of laboratory earthquake cycle inspired by a set of experiments performed on a triaxial apparatus on sawcut Carrara marble samples. The model couples two representations of rock matter: rock is essentially represented as an elastic continuum, except in the vicinity of the sliding interface, where a discrete representation is employed. This allows to simulate in a single framework the storage and release of strain energy in the bulk of the sample and in the loading system, the damage of rock due to sliding, and the progressive production of a granular gouge layer in the interface. After independent calibration, we find that the tribosystem spontaneously evolves towards a stick-slip sliding regime, mimicking in a satisfactory way the behaviour observed in the lab. The model offers insights on complex phenomena which are out of reach in experiments. This includes the variability in space and time of the fields of stress and effective friction along the fault, the progressive thickening of the damaged region of rock around the interface, and the build-up of a granular layer of gouge accommodating shear. We present in detail several typical sliding events, we illustrate the fault heterogeneity, and we analyse quantitatively the damage rate in the numerical samples.

How to cite: Mollon, G., Aubry, J., and Schubnel, A.: On-fault damage evolution in laboratory earthquakes: a numerical perspective on fault complexity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6517, https://doi.org/10.5194/egusphere-egu23-6517, 2023.

EGU23-6974 | ECS | Orals | EMRP1.2

Depth dependence of coseismic off-fault damage 

Roxane Ferry, Marion Thomas, and Louise Jeandet

Faults are complex systems embedded in an evolving medium fractured by seismic ruptures. This off-fault damage zone is shown to be thermo-hydro-mechano-chemically coupled to the main fault plane by a growing number of studies. Yet, off-fault medium is still, for the most part modelled as a purely elastic -- hence passive -- medium. Using a micromechanical  model we investigate the depth variation of dynamically triggered off-fault damage and its counter-impact on earthquake slip dynamics. We show that if the damage zone becomes narrower with depth, it is also denser and thus, unlike what is commonly believed, remains an energy sink even at depth. The results are in agreement with the complementary model by Okubo et al., 2019. In contrast to study cited above, our model accounts for the dynamics changes of elastic moduli related to crack growth. This lead to the dynamic creation of low-velocity zone that can trapped seismic waves and further impact the earthquake dynamics, even at greater depth. We therefore claim that the intertwined dynamics between the main fault plane and its surrounding medium must be including along the all seismogenic.

How to cite: Ferry, R., Thomas, M., and Jeandet, L.: Depth dependence of coseismic off-fault damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6974, https://doi.org/10.5194/egusphere-egu23-6974, 2023.

EGU23-7142 | ECS | Orals | EMRP1.2

Investigating relationships between surface rupture and multiple source parameters of earthquakes 

Suli Yao, Hongfeng Yang, and Ziyue Tang

Surface rupture produced by earthquakes can pose great threat on near-surface infrastructures and elevate damages. Accessing the potential of surface rupture along faults is critical to mitigating such hazards. It is commonly suggested that earthquakes with Mw>6.5 will break the surface. However, there are events with much smaller magnitudes rupturing the ground. To understand the potential controlling mechanisms, we first collect source parameters for earthquakes with  and  surface-breaching events in seismically active regions including west China, North America, Europe, Taiwan, Japan, and Iran. For strike-slip and normal events, almost all earthquakes with magnitudes over 6.7 broke the surface. In contrast, buried and surface-breaching events co-exist with moderate magnitude (6.0-6.7). For reverse events, there is no clear magnitude boundary, as thrust buried events can be quite large due to the downdip size of the seismogenic zone. The relocated hypocenter depths for moderate-to-large events are concentrated at depth of 5 -20 km with no systematic difference between buried and surface-breaching ruptures. Differently, all  surface-breaching events occurred at very shallow depths (<5 km). We also conduct dynamic rupture simulations and propose two conceptual models to explain whether or not ruptures may break the surface. The first model represents a fault with a continuous but heterogeneous seismogenic zone (velocity-weakening) that can hold moderate-to-large earthquakes. In this case, ruptures need to overcome the shallow velocity-strengthening zone (VS) with certain energy sink to reach the surface. Therefore, a thinner shallow RS zone and a higher stress drop of the earthquake can promote surface rupture, consistent with our observations. However, ruptures nucleating from different locations on heterogeneous faults may lead to different surface rupture patterns and final magnitudes, shedding lights on the diverse behaviors among moderate earthquakes. The second model is for small surface-breaching earthquakes. Those events are supposed to occur on shallow isolated velocity-weakening patches, consistent with the fact that usually no large earthquakes have been reported on the same fault zones. Such asperities may be formed on bodies with high-strength materials, leading to energetic ruptures with intense stress release. Our study contributes to the understanding of the surface rupture behaviors references for assessing near-surface damage in future earthquakes.

 

How to cite: Yao, S., Yang, H., and Tang, Z.: Investigating relationships between surface rupture and multiple source parameters of earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7142, https://doi.org/10.5194/egusphere-egu23-7142, 2023.

EGU23-7167 | Posters on site | EMRP1.2

A deep catalogue of 56k focal mechanisms for the 2016 Amatrice, Italy earthquake sequence 

Men-Andrin Meier, Federica Lanza, and Patricia Martinez-Garzon

The 2016 Amatrice, Italy earthquake sequence occurred on a normal fault system in the Central Apennines, and contained over 1,300 M>=3 earthquakes. With ~140 permanent or temporary seismic stations directly above the seismic activity, the sequence has been exceptionally well recorded. Starting from a deep learning-based catalogue of earthquake hypocentres (~900,000 re-located events from ~15 million seismic phases; Tan et al., 2021), we use a convolutional neural network classifier to predict P-wave first motion polarities, from which we compile a deep catalogue of earthquake focal mechanisms. The catalogue consists of >56'000 focal mechanisms, about 8'000 of which have nodal plane uncertainties below 25 degrees.

In contrast to existing, conventional focal mechanism catalogues, the deep catalogue samples almost the entire study region, and almost the entire magnitude range (~M0-M5), although nodal plane uncertainties generally tend to increase with decreasing magnitude. We use the focal mechanism catalogue to study the kinematics of the Amatrice earthquake sequence, to test the hypothesis of a coseismic rotation of the static stress field by large and small events, and to analyse the complexity of the stress field before, during and after the earthquake sequence.

How to cite: Meier, M.-A., Lanza, F., and Martinez-Garzon, P.: A deep catalogue of 56k focal mechanisms for the 2016 Amatrice, Italy earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7167, https://doi.org/10.5194/egusphere-egu23-7167, 2023.

EGU23-7327 | Posters on site | EMRP1.2

The impact of fault surface 3D geometry on risking fault reactivation 

Janis Aleksans, Conrad Childs, and Martin Schöpfer

The reactivation of faults can occur when the effective stresses acting on them are perturbed. In some cases man-made changes in effective stress can result in fault reactivation that can have enormous impacts including loss of integrity of underground storage facilities. Current practical methods for making this assessment are generally based on shear stresses calculated over fault surfaces. Depending on the absolute or relative magnitudes of these resolved shear stresses, which depend primarily on the local orientation of the fault surface relative to the regional stress field, different faults or parts of faults are said to be closer or further from the Coulomb failure envelope and are therefore more likely to slip due to changes in effective stress. This proximity to failure/slip is referred to as the slip tendency or reactivation tendency.

Although the slip/reactivation tendency approach is firmly grounded in Coulomb theory and laboratory experiments, there may be issues applying it to the reactivation of irregular fault surfaces. A key assumption of the approach is that an area of a fault surface can be treated in isolation so that the slip tendency can be evaluated once its orientation and frictional properties are known. However, it is well established that fault surfaces are not planar but often have highly irregular geometries and fault rock distributions so that the likelihood that a particular part of a fault will reactivate must also depend, not only on the properties at that point but also on adjacent areas of the fault surface.

To investigate the significance of fault surface irregularity for the evaluation of fault slip/reactivation tendency, we conduct numerical modelling of fault reactivation resulting from an increase in pore pressure within a normal faulting stress regime. The modelling employs a form of the Discrete Element method that uses rigid blocks. This approach provides for both accurate representation of the geometry and frictional properties of the irregular slip surfaces and also failure in the surrounding wall-rock and is capable of modelling the variety of ways in which slip may initiate on, or adjacent to an irregular fault.

How to cite: Aleksans, J., Childs, C., and Schöpfer, M.: The impact of fault surface 3D geometry on risking fault reactivation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7327, https://doi.org/10.5194/egusphere-egu23-7327, 2023.

EGU23-7594 | ECS | Posters on site | EMRP1.2

Frictional behavior and rheology of bi-disperse quartz gouge mixtures 

Nathalie Casas, Carolina Giorgetti, Cristiano Collettini, and Marco Maria Scuderi

Earthquake nucleation has been understood as controlled by the frictional properties of fault zones. Mature fault zones host abrasive wear products, such as gouges, which result from the frictional sliding occurring in successive slip events. Shear localization in fault gouges is strongly dependent on, among others, fault mineralogical composition and grain size distribution, originating a wide variety of microstructural textures that may be related to different types of fault motion from aseismic creep, slow earthquakes to fast slip events. Additionally, within a fault, one can encounter different stages of maturity, ranging from an incipient and poorly-developed fault zone (i.e. discontinuous and thin gouge layer) to a mature fault zone that has experienced a lot of wear from previous sliding events (i.e. well-developed gouge layer). The localization of deformation within a mature gouge layer has been identified as possibly responsible for mechanical weakening and as an indicator of a change in stability within the fault.

To gain insights on the role of grain size distribution, and thus fault maturity, in slip behavior and fault rheology, we performed friction experiments on quartz fault gouge in a double direct shear configuration using a biaxial apparatus (BRAVA at INGV in Rome, Italy). The experiments were performed at a constant normal stress of 40 MPa and under 100% humidity.  We investigated different sliding velocities, from 10 µm/s to 1 mm/s, to assess time-dependent physical processes. Different bi-disperse mixtures of quartz were sheared to reproduce different initial grain size distributions within the fault (F110, average grain size  and Min-u-sil, average grain size ). Samples were carefully collected at the end of the experiments to prepare thin sections for microstructural analyses.

A first set of experiments was performed increasing the proportion between smaller and larger particles within a homogeneous blend. The friction evolves from a strain-hardening behavior for a sample with only F110 to a slip-weakening one for the one with only Min-u-sil. The difference in rheology is observable in the analyzed microstructures. Particularly, the two end members clearly show comminution and localization along boundary shear planes, whereas mixtures of the two sizes of particles only present a more diffused deformation. In the second set of experiments, we sheared gouges with a horizontal layering of the two grain sizes and observed different behaviors in terms of friction and rheology. These layered gouges present strain hardening behavior, with a strengthening part corresponding to the material of the layer in contact with the sliding block and a steady-state part with slightly higher friction than for the homogeneous mixtures.

These results give important information on the connection between grain size distribution, shear localization, and the resulting fault slip behavior. In this context, the proportion between small/large particles and their distribution and percentages within the fault plays an important role in controlling fault rheology. We also complete our knowledge by using Discrete Element Method, simulating gouge sliding with different grain scale properties (size, distribution, cementation…), and observing a detailed evolution of shear localizations.

How to cite: Casas, N., Giorgetti, C., Collettini, C., and Scuderi, M. M.: Frictional behavior and rheology of bi-disperse quartz gouge mixtures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7594, https://doi.org/10.5194/egusphere-egu23-7594, 2023.

EGU23-7849 | ECS | Orals | EMRP1.2

Dynamics and radiation of thrust earthquakes with coseismic off-fault damage 

Carlos Villafuerte, Kurama Okubo, Esteban Rougier, Raul Madariaga, and Harsha S. Bhat

Major earthquake ruptures occur predominantly in thrust faults producing devastating events and tsunamis such as the 2011 Mw 9.0 Tohoku earthquake, the 2004 Mw 9.2 Sumatra earthquake and the 1999 Mw 7.7 Chi-Chi earthquake. Understanding the mechanics of earthquakes in thrust faults and the effect of the free surface is thus crucial to explain their large shallow slip, their asymmetric ground motion and their damage patterns surrounding the fault and the free surface. In this work, we carry out 2D dynamic rupture simulations on thrust faults to accurately characterize a possible unclamping effect, its responsible physical mechanism, and to produce dynamically activated off-fault fracture networks. To conduct the simulations, we use the software tool based on the Combined Finite-Discrete Element Method (FDEM), HOSSedu, developed by Los Alamos National Laboratory. Our dynamic rupture models in an elastic medium confirm that unclamping occurs in thrust faults and increases significantly as the rupture reaches the free surface and for the fault models with lower dip-angles. We show that this is a consequence of the torque mechanism induced in the hanging wall, and the release of this torque when the rupture reaches the free surface produces a “flapping” in the toe of the wedge where the most significant unclamping (possibly leading to fault opening) is taking place. Our results indicate that the free surface produces a considerable reduction of the compressive normal stress when the rupture is propagating up-dip that facilitates the extension and the amount of slip close to the trench as observed for large thrust earthquakes.This significant normal stress change is reflected in the orientation of the principal stresses before and after the rupture, where under certain conditions, the greatest principal stress changes from subhorizontal to almost vertical leading to a post-rupture tensional stress state in the hanging wall that has been confirmed by observations of recent in-situ, seismological and geodetic studies. Finally, we investigate whether this dramatic normal stress reduction stands when we allow for the activation of coseismic off-fault damage and explore its role in the rupture dynamics, the near-field deformation and radiation patterns.

How to cite: Villafuerte, C., Okubo, K., Rougier, E., Madariaga, R., and Bhat, H. S.: Dynamics and radiation of thrust earthquakes with coseismic off-fault damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7849, https://doi.org/10.5194/egusphere-egu23-7849, 2023.

EGU23-7933 | Orals | EMRP1.2

Micromechanics of damage localisation and shear failure of a porous rock: sound and vision 

Alexis Cartwright-Taylor, Maria-Daphne Mangriotis, Ian G. Main, Ian B. Butler, Florian Fusseis, Martin Ling, Edward Andò, Andrew Curtis, Andrew F. Bell, Alyssa Crippen, Roberto E. Rizzo, Sina Marti, Derek D. V. Leung, and Oxana V. Magdysyuk

Catastrophic failure in brittle, porous materials initiates when structural damage, in the form of smaller-scale fractures, localises along an emergent failure plane or 'fault' in a transition from stable crack growth to dynamic rupture. Due to the extremely rapid nature of this critical transition, the precise micro-mechanisms involved are poorly understood and difficult to capture. However, these mechanisms are crucial drivers for devastating phenomena such as earthquakes, including induced seismicity, landslides and volcanic eruptions, as well as large-scale infrastructure collapse. Here we observe these micro-mechanisms directly by controlling the rate of micro-fracturing events to slow down the transition in a unique triaxial deformation experiment that combines acoustic monitoring with contemporaneous in-situ x-ray imaging of the microstructure. The results [1] provide the first integrated picture of how damage and associated micro-seismic events emerge and evolve together during localisation and failure and allow us to ground truth some previous inferences from mechanical and seismic monitoring alone. They also highlight where such inferences miss important kinematically-governed grain-scale mechanisms prior to and during shear failure.

The evolving damage imaged in the 3D x-ray volumes and local strain fields undergoes a breakdown sequence involving several stages: (i) self-organised exploration of candidate shear zones close to peak stress, (ii) spontaneous tensile failure of individual grains due to point loading and pore-emanating fractures within an emergent and localised shear zone, validating many inferences from acoustic emissions monitoring, (iii) formation of a proto-cataclasite due to grain rotation and fragmentation, highlighting both the control of grain size on failure and the relative importance of aseismic mechanisms such as crack rotation in accommodating bulk shear deformation. Dilation and shear strain remain strongly correlated both spatially and temporally throughout sample weakening, confirming the existence of a cohesive zone, but with crack damage distributed throughout the shear zone rather than concentrated solely in a breakdown zone at the propagating front of a pre-existing discontinuity.

Contrary to common assumption, we find seismic amplitude is not correlated with local imaged strain; large local strain often occurs with small acoustic emissions, and vice versa. The seismic strain partition coefficient is very low overall and locally highly variable. Local strain is therefore predominantly aseismic, explained in part by grain/crack rotation along the emergent shear zone. The shear fracture energy calculated from local dilation and shear strain on the fault is half of that inferred from the bulk deformation, with a smaller critical slip distance, indicating that less energy is required for local breakdown in the shear zone compared with models of uniform slip.

This improvement in process-based understanding holds out the prospect of reducing systematic errors in forecasting system-sized catastrophic failure in a variety of applications.

[1] Cartwright-Taylor et al. 2022, Nature Communications 13, 6169, https://doi.org/10.1038/s41467-022-33855-z

How to cite: Cartwright-Taylor, A., Mangriotis, M.-D., Main, I. G., Butler, I. B., Fusseis, F., Ling, M., Andò, E., Curtis, A., Bell, A. F., Crippen, A., Rizzo, R. E., Marti, S., Leung, D. D. V., and Magdysyuk, O. V.: Micromechanics of damage localisation and shear failure of a porous rock: sound and vision, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7933, https://doi.org/10.5194/egusphere-egu23-7933, 2023.

EGU23-8163 | ECS | Posters on site | EMRP1.2

Mechanical and microstructural characterization of spatially heterogenous simulated fault gouges, derived from the Groningen gas field stratigraphy 

Job Arts, André Niemeijer, Martyn Drury, Ernst Willingshofer, and Liviu Matenco

Gas production from the Groningen gas field in the northeast of the Netherlands causes compaction and induced seismicity within the reservoir and overlying/underlying lithologies. Recent earthquake localization studies show that seismicity dominantly occurs on complex normal fault systems that juxtapose lithologies of contrasting mechanical properties. However, little is known about the effects of along-fault heterogeneity on the frictional behaviour of these faults. This study aims at understanding how material mixing and clay-smearing in fault gouges affects the mechanical strength and stability of faults that juxtapose contrasting lithologies (e.g. clay-rich and quartz-rich) by performing friction experiments.

Velocity stepping tests are performed on homogeneously mixed and spatially segmented simulated fault gouges, within a rotary shear configuration. Experiments are performed under normal stresses ranging between 2.5 and 10 MPa and imposed velocities ranging between 10 and 1000 µm/s. The rotary shear configuration allows for the large shear-displacements (>145 mm in our experiments) required to study the effects of lithology mixing. Simulated gouges are saturated with DI-water and subsequently sheared under drained conditions. Because low-permeability clay-rich materials promote the build-up of local pressure transients, a specially designed piston with four installed pressure transducers is used to monitor fluid pressures in the vicinity of the simulated fault gouges.

The mechanical data on segmented gouges show an evolution in frictional strength, characterized by a phase of strong displacement-weakening followed by displacement-strengthening. The frictional stability strongly increases with shear-displacement, comprising a transition from velocity-weakening to velocity-strengthening. Microstructural analysis of the sheared gouges provides evidence for the development of clay-smears and strain-localization within localized shear bands, explaining the evolution in frictional stability and the initial phase of shear-weakening. However, the dilatation observed at large displacements suggests that the quartz-rich gouge is incorporated within the clay smear. This incorporation is confirmed by microstructural analysis of the clay smear and provides a mechanism responsible for the observed strengthening at large shear-displacements. Monitoring of local pore fluid pressures shows that segmented gouges are more susceptible to pressure transients, depending on the initial distribution of high porosity sandstone gouges and low permeability claystone gouges.

This study shows that the frictional strength and stability of spatially heterogeneous gouges highly depends on the amount of shear-displacement. The frictional strength is characterized by subsequent phases of displacement-weakening and strengthening, whereas the frictional stability only increases with shear-displacement. This eventually leads to relatively strong but also frictionally stable faults at large displacements. The results have important implications for modelling earthquake nucleation,  propagation, and arrest and apply to faults in geological settings that exhibit induced seismicity, like the Groningen gas field, but are also relevant for tectonically active faults located elsewhere.

How to cite: Arts, J., Niemeijer, A., Drury, M., Willingshofer, E., and Matenco, L.: Mechanical and microstructural characterization of spatially heterogenous simulated fault gouges, derived from the Groningen gas field stratigraphy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8163, https://doi.org/10.5194/egusphere-egu23-8163, 2023.

EGU23-8389 | Posters on site | EMRP1.2

Frictional melting and thermal pressurization during seismic slip controlled by drainage 

Wen-Jie Wu, Li-Wei Kuo, Chia-Wei Kuo, Wei-Hsin Wu, and Hwo‐Shuenn Sheu

frictional melting and thermal pressurization are commonly proposed to reduce dynamic shear resistance along a fault during earthquake propagation. The key factor on triggering either thermal pressurization or frictional melting may be the hydraulic properties of surrounding rock. Observations in Taiwan Chelungpu-fault drilling project (TCDP) Hole-A and Hole-B suggest that frictional melting and thermal pressurization occurred along the fault during the Mw 7.6 Chi-Chi earthquake, but the underlying process is still unclear. Here, we present the microstructural observation in experimental and natural fault gouge, the mechanical data at seismic rate and mineralogical characteristics. Results show that amorphous material only occurred at drained condition. Taken together, these results imply that the difference between Hole-A and Hole-B is attributed to the drainage.

How to cite: Wu, W.-J., Kuo, L.-W., Kuo, C.-W., Wu, W.-H., and Sheu, H.: Frictional melting and thermal pressurization during seismic slip controlled by drainage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8389, https://doi.org/10.5194/egusphere-egu23-8389, 2023.

EGU23-8634 | ECS | Orals | EMRP1.2

Laboratory Observations linking Fault Surface Characteristics to Preparatory Earthquake Processes and Fault Stability 

Sofia Michail, Paul Antony Selvadurai, Sara Beth Leach Cebry, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Markus Rast, Claudio Madonna, and Stefan Wiemer

Preparatory earthquake processes such as slow preparatory slip (preslip) are connected to variations in frictional strength linked to frictional instabilities and appear in various scales across the Earth’s crust. For dry and bare surfaces, the fault surface characteristics affect the contact conditions. These conditions are established through asperities, which are topographical heights where the normal stress concentrates, imposing variations in fault strength. The effect of surface conditions on preslip can be studied in the laboratory where fault surface characteristics can be identified. Developing a more refined understanding of features controlling preslip (e.g., roughness) will lead to more realistic models describing frictional stability. In this study, we performed a triaxial test at sequentially increasing confining pressure steps (P= 60, 80, 100 MPa) on a saw-cut sample of Carrara Marble in dry and unlubricated conditions. Two types of technologies were used to study this frictional response in space and time: (1) an array of acoustic emission sensors monitored localized precursory seismicity and (2) quasi-static deformation in the fault-parallel strain was monitored using distributed strain sensing (DSS) with fiber optics. The differential stress was also measured throughout and allowed us to study the onset of frictional weakening/strengthening. In the first confining pressure step (Pc = 60 MPa), a single stick-slip event was observed with an associated 43 MPa static stress drop. In the subsequent confining pressure steps of P= 80 and 100 MPa, even though the normal stress on the fault was increased, no stick-slip events were observed, and the fault smoothly transitioned to sliding with smaller magnitude stress drops of 3 and 4 MPa, respectively. That suggests that a change in the frictional nature of the interface was incurred during the first rupture at P= 60 MPa. The high-density DSS array displayed a significant heterogeneous distribution of fault-parallel strain in time and space and experienced sudden reorganization at various phases of the experiment. Due to the high spatial resolution, DSS allowed us to investigate local deviations from an elastic response attributed to inelastic processes. A larger amount of local strain accumulation was needed to produce a stick-slip instability. At higher normal stress on the pre-ruptured fault, this level of locking was not possible in the subsequent confining pressure steps. Dissipative inelastic deformation was attributed to local frictional weakening that resulted in non-uniform preslip. Furthermore, priori measurements of contact pressure heterogeneities were obtained using a pressure sensitive film. These results showed regions of lower normal stress along the fault that correlated with regions that incurred more anelastic response on the DSS array. Post-mortem contact pressure measurements showed clear changes in the normal stress distribution that correlated to visual damage and wear. We believe that this contributed to the fault's inability to lock as before and mitigate dynamic rupture. Our results provide more insight into potential mechanisms controlling preslip distribution leading to dynamic and quasi-static frictional weakening.

How to cite: Michail, S., Selvadurai, P. A., Cebry, S. B. L., Salazar Vásquez, A. F., Bianchi, P., Rast, M., Madonna, C., and Wiemer, S.: Laboratory Observations linking Fault Surface Characteristics to Preparatory Earthquake Processes and Fault Stability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8634, https://doi.org/10.5194/egusphere-egu23-8634, 2023.

EGU23-8778 | Orals | EMRP1.2

Dynamic damage in dry and wet rocks monitored by ultra-fast synchrotron imaging 

Francois Renard, Benoit Cordonnier, Mai-Linh Doan, Michele Fondriest, Bratislav Lukic, and Erina Prastyani

During earthquake propagation, a shock wave damages rocks at the rupture tip, creating numerous microfractures and altering the mechanical properties of fault zone rocks. This damage, which occurs dynamically at the millisecond time scale, controls rock strength during earthquake slip that occurs in the wake of rupture propagation. How the presence of water and the initial porosity of the rock control damage during high strain rate deformation remains an open question. We have performed a series of shock experiments using a split Hopkinson pressure bar apparatus installed at the European Synchrotron Radiation Facility. Using two ultra-fast cameras synchronized with the X-ray bunches of the synchrotron; we imaged deformation with microsecond time resolution on centimetre-scale core samples during shock wave damage. We deformed dry and water saturated low porosity Westerly granite and porous Berea sandstone samples. Several samples were surrounded by a thin aluminium jacket allowing recovering them after deformation and image them using X-ray microtomography with micrometre spatial resolution. Results confirm previous studies that have shown that rock pulverization occurs above a threshold strain rate produced by the shock wave. Water saturated samples are consistently weaker than dry samples as they pulverize under lower peak stress. Analyses of rock microstructure acquired using the ultrafast cameras and X-ray microtomography data shed light on the micro-mechanisms of damage production. Either the entire sample pulverized (Westerly granite) or a compaction of the sample occurred before shear zones were dynamically produced (Berea sandstone). These results demonstrate fundamental differences in dynamic damage production in crystalline and porous dry and wet rocks. Our data unravel mechanisms of gouge production before any significant slip has occurred on a fault, which control the shear strength during earthquake slip.

How to cite: Renard, F., Cordonnier, B., Doan, M.-L., Fondriest, M., Lukic, B., and Prastyani, E.: Dynamic damage in dry and wet rocks monitored by ultra-fast synchrotron imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8778, https://doi.org/10.5194/egusphere-egu23-8778, 2023.

EGU23-9600 | ECS | Posters on site | EMRP1.2

Fault-healing and tribochemical processes in granodiorite under hydrothermal conditions 

Rodrigo Gomila, Wei Feng, and Giulio Di Toro

Understanding the mechanical and geochemical processes of fault rock development is a key clue into the understanding of fault healing rates. Fault healing rate β – the change of the static friction coefficient (Δμ) with log time (β = μ0 + Δμ/log(1+thold /tcutoff)) – is a significant parameter in the seismic cycle, controlling the storage of the elastic strain energy in the fault wall rocks and allowing earthquakes to repeatedly occur in pre-existing faults.

Fault healing is investigated with slide-hold-slide (SHS) experiments aimed at reproducing the seismic cycle. However, most of these experiments have been conducted under room conditions, while natural earthquakes nucleate at temperatures T > 150°C and in presence of pressurized fluids. Under these conditions, fluid-rock interaction (reaction kinetics, pressure-solution transfer, sub-critical crack growth, etc.) may impact severely on β and on the magnitude of Δμ.

In this study, motivated by the evidence of intense fluid-rock interaction in exhumed seismogenic faults hosted in the continental crust (Gomila et al., 2021, G3), we performed SHS experiments in a rotary shear apparatus equipped with a dedicated hydrothermal vessel. The goal is to investigate (1) the tribochemical processes and healing behavior of gouge-bearing faults made of granodiorite and, (2) explore how the mechanical properties and healing rates evolve with fault maturity (e.g., fault displacement, duration of fluid-rock interaction).

For the simulated gouge samples (grain size < 75 µm), three set of experiment of SHS were conducted, the first with run-in duration of 500s, whereas the 2nd and 3rd with 5000s, and geochemically contrasted against a non-sheared sample. The fluid (deionized water) saturated gouges were kept under an effective normal stress (σneff) of 10 MPa, a fixed temperature T of 300°C and a constant pore fluid pressure Pf of 25 MPa, and they were slid for ca. 15 mm and 60 mm at a slip rate of 10 µm/s. Hold periods between slip events ranged from 3s to 10000s (1st and 2nd experiments) and from 3s to 300000s (3rd), to investigate the dependence of β and the underlying tribochemical processes with both cumulative slip and duration of the experiment.

Under these hydrothermal conditions, Δμ first increased with holding time (β value of ca. 2.0x10-2 , independently of run-in duration) and then decreased (β = -3.6x10-2, β = -3.0x10-2 and β = -2.6x10-2, for the 1st, 2nd and 3rd experiment, respectively). Bulk XRF analyses on sheared samples show an enrichment of TiO2, MgO and P2O5, while a loss of MnO and CaO oxides with respect to the non-sheared sample. Detailed SEM-EDS analyses show a main mineral loss of biotite and quartz within the main slip zone.

This suggest that under hydrothermal conditions, total shear displacement and duration of the fluid-rock interaction enhance mineral reactions that promote negative healing rates (β < 0) in faults during the seismic cycle. This would imply that during the life-span of an evolving fault, as it matures, it would be possible to (1) lower the fault yield strength due to and increasing fluid-rock interaction, henceforth (2) increase the recurrence but decrease the intensity of the seismic activity.

How to cite: Gomila, R., Feng, W., and Di Toro, G.: Fault-healing and tribochemical processes in granodiorite under hydrothermal conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9600, https://doi.org/10.5194/egusphere-egu23-9600, 2023.

EGU23-9616 | ECS | Orals | EMRP1.2

Healing of gabbro-built faults under hydrothermal conditions 

Wei Feng, Lu Yao, Rodrigo Gomila, Shengli Ma, and Giulio Di Toro

Fault frictional healing Δμ controls the storage of the elastic strain energy in the fault wall rocks and the re-occurrence of earthquakes in pre-existing faults. In the last 40 years, fault healing has been investigated with laboratory slide-hold-slide (SHS) experiments aimed at reproducing the seismic cycle. Experiments performed with different rocks types (e.g., granite, limestone, basalt) revealed that (1) Δμ increases with hold time th and, (2) the frictional healing rate βμ/log th >0. This increase in fault frictional strength with th is interpreted as due to the increase (1) in the real area of contact or (2) of chemical bond strength. However, most of these experiments were conducted under room conditions, whereas natural earthquakes generally nucleate at ambient temperatures T  >150℃ and in the presence of pressurized fluids. Under these ambient conditions, fluid-assisted and thermally-activated processes (pressure-solution transfer, stress corrosion, etc.) may impact on the magnitude of Δμ and on β.

In this study, SHS experiments were performed on gabbro-built gouges (grain size <88 mm) in a rotary shear machine equipped with a pressurized vessel to explore frictional healing under hydrothermal conditions. All experiments were conducted at a constant effective normal stress (σeff =50MPa), and temperature (T) ranging from 25 to 400 ℃  under dry or pore fluid (deionized H2O) pressure (Pf=30 MPa) conditions. In the SHS sequence, the imposed slip velocity was V=10 μm/s, and hold time th varied from 3 to 10000 s. For each experiment, two SHS sequences separated by a slip displacement interval of 40 mm were conducted.

Under dry conditions at all tested temperatures and under hydrothermal conditions but at T  <100℃, Δμ increases with th, consistent with previous experiments. Moreover, the Δμ and β values in the 2nd SHS sequence are slightly higher than those in the 1st sequence, possibly due to the smaller grain size at the larger displacement that promotes fault healing. By contrast, in the experiments performed under hydrothermal conditions but T >200℃, Δμ decreases and β switches to negative values (<0) when the hold is longer than a threshold hold time. In detail, at T=300℃: β= 0.0161±0.0017 for holds <300s and -0.0074±0.0043 for holds >300s, and at T=400℃: β= 0.0057±0.0020 for holds <100s and -0.0227±0.0042 for holds >100s.

The underlying mechanism responsible for the decrease in Δμ and the transition from β > 0 to β < 0 with the hold time, which could result in the transition from seismic to aseismic fault behavior in nature, is still poorly understood. However, high-resolution microstructural analyses conducted by scanning electron microscopy on experimental fault products rule out the formation of weak minerals (e.g., clays) in the gouge layer.  Consequently, the weakening of the fault is probably related to the decrease in bond strength at the asperity contacts.

The experimental data presented here suggest that fault healing of natural faults is controlled by the feedback of multiple physico-chemical processes associated with the slip history and type of fluid-rock interaction under hydrothermal conditions.

How to cite: Feng, W., Yao, L., Gomila, R., Ma, S., and Di Toro, G.: Healing of gabbro-built faults under hydrothermal conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9616, https://doi.org/10.5194/egusphere-egu23-9616, 2023.

EGU23-10016 | ECS | Orals | EMRP1.2

The role of loading path on fault reactivation: a laboratory perspective 

Carolina Giorgetti, Marie Violay, and Cristiano Collettini

Slip along pre-existing faults in the Earth’s crust occurs whenever the shear stress resolved on the fault plane overcomes fault frictional strength, potentially generating catastrophic earthquakes. The coupling between shear stress and normal stress during fault loading depends on 1) the orientation of the fault within the stress field and 2) the tectonic setting. In compressional settings, a load-strengthening path occurs because along thrust faults the increase in shear stress is coupled with an increase in effective normal stress. On the contrary, in extensional settings, the increase in shear stress is coupled with a decrease in effective normal stress, resulting in load-weakening paths for normal faults.

Analytical approaches to evaluate the potential for fault reactivation are generally based on the assumption that faults are ideal planes, characterized by zero thickness and constant friction, embedded in homogeneous isotropic elastic media. However, natural faults typically host thick fault cores and highly fractured damage zones, which can compact or dilate under different loading paths (i.e., different coupling between normal and shear stress). In addition, in most laboratory friction experiments, the fault is loaded under constant or increasing normal stress and at optimal orientation for reactivation. Here, we present laboratory experiments simulating reactivation of thick gouge-bearing faults that experienced different loading paths.

Our results show that the differential stress required for reactivation strongly differs from theoretical predictions, and unfavourably oriented faults appear systematically weaker, especially when a thick gouge layer is present. Before reactivation fault zone compacts in load-strengthening paths whereas dilation is observed in load-weakening path. Upon fault reactivation at comparable normal stress, load-strengthening promotes stable creep  whereas load-weakening results in accelerated slip. Our study highlights the importance of fault thickness and loading path in fault hydromechanical coupling and stability with significant implications for fluid circulation within fault zones and earthquake mechanics.

How to cite: Giorgetti, C., Violay, M., and Collettini, C.: The role of loading path on fault reactivation: a laboratory perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10016, https://doi.org/10.5194/egusphere-egu23-10016, 2023.

EGU23-10314 | ECS | Orals | EMRP1.2

Foreshocks preceding moderate earthquakes in Western Yunnan, China 

Gaohua Zhu and Hongfeng Yang

Although the physical mechanism of earthquake nucleation processes and the link with foreshocks are under debate, foreshocks are still considered as the most reliable earthquake precursors. Investigating the temporal and spatial evolution of foreshock sequences with high resolution and monitoring b-values in real time may shed light on these key issues. Many foreshock and aftershock sequences accompanying moderate mainshocks have been reported in the west of Yunnan Province, China, such as the 2016 Yunlong M 5.1 and 2021 Yangbi Ms 6.4 earthquake sequences. The recently improved coverage of seismic network in western Yunnan provides the opportunity to investigate how the foreshock sequence evolved and establish the temporal transient in b values. To find missing earthquakes and built more comprehensive earthquake catalogs, we carried out earthquake detection using the matched-filter detector. We used events in the standard catalog of China Earthquake Networks Center as templates to scan through continuous waveforms 3-6 months before and after the main shock. We then estimated the b-value and its temporal changes based on the newly developed catalogs. An obvious reduction in b-values before the major earthquake is observed in both the 2016 Yunlong and 2021 Yangbi sequences. We also found that the scattered spatial pattern of foreshocks exhibits a cascading manner and does not support the hypothesis of slow slip driving nucleation of mainshocks.

How to cite: Zhu, G. and Yang, H.: Foreshocks preceding moderate earthquakes in Western Yunnan, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10314, https://doi.org/10.5194/egusphere-egu23-10314, 2023.

The constitutive behavior of faults is central to many interconnected aspects of earthquake science, from fault dynamics to induced seismicity, to seismic hazards characterization. Yet, a friction law applicable to the range of temperatures found in the brittle crust and upper mantle is still missing. In particular, rocks often exhibit a transition from steady-state velocity-strengthening at room temperature to velocity-weakening in warmer conditions that is poorly understood. Here, we investigate the effect of competing healing mechanisms on the evolution of frictional resistance in a physical model of rate-, state-, and temperature-dependent friction. The yield strength for fault slip depends on the real area of contact, which is modulated by the competition between the growth and erosion of interfacial micro-asperities. Incorporating multiple healing mechanisms and rock-forming minerals with different thermodynamic properties allows a transition of the velocity- and temperature-dependence of friction at steady-state with varying temperatures. We explain the mechanical data for granite, pyroxene, amphibole, shale, and natural fault gouges with activation energies and stress power exponent for weakening of 10-50 kJ/mol and 55-150, respectively, compatible with subcritical crack growth and inter-granular flow in the active slip zone. Activation energies for the time-dependent healing process in the range 90-130 kJ/mol in dry conditions and 20-65 kJ/mol in wet conditions indicate the prominence of viscoelastic collapse of micro-asperities in the absence of water and of pressure-solution creep, crack healing, and cementation when assisted by pore fluids. 

How to cite: Barbot, S.: A rate-, state-, and temperature-dependent friction law with competing healing mechanisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10779, https://doi.org/10.5194/egusphere-egu23-10779, 2023.

EGU23-11776 | Orals | EMRP1.2

Dynamic weakening and rupture re-nucleation in rock gouge 

Vito Rubino, Ares Rosakis, and Nadia Lapusta

Many large and damaging earthquakes on mature faults in the Earth’s crust propagate along layers of rock gouge, the fine granular material produced by comminution during sliding. Characterizing gouge rheology is of paramount importance to improve our understanding of earthquake physics, as friction controls key processes of earthquakes, including nucleation, propagation and arrest and how damaging they can be.  In this work, we characterize friction evolution in rock gouge layers during the propagation of dynamic ruptures in a laboratory setting. The experimental setup features a hybrid configuration with a specimen made of an analog material and a rock gouge layer embedded along the interface. This configuration allows us to trigger dynamic ruptures due to the lower shear modulus of the analogue material while at the same time study the gouge frictional behavior during spontaneously evolving dynamic events. Ruptures are captured by the use of digital image correlation coupled with ultrahigh-speed photography. Our measurements reveal dramatic friction variations, with the gouge layer initially displaying strengthening behavior and inhibiting earthquake rupture propagation. However, the gouge layer later features dramatic frictional strength losses, and hosts rupture re-nucleation enabled by dynamic stressing and marked friction weakening at higher slip velocities. Our measurements of the weakening and strengthening behavior of friction in fine rock gouge illustrate the strong dependence of their rheology on slip velocity and related processes, including shear heating, localization/delocalization of shear, and dilation/compaction of the granular shear layer.

How to cite: Rubino, V., Rosakis, A., and Lapusta, N.: Dynamic weakening and rupture re-nucleation in rock gouge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11776, https://doi.org/10.5194/egusphere-egu23-11776, 2023.

EGU23-14284 | Posters on site | EMRP1.2

Frictional evolution of gouge-bearing faults during multiple seismic slip velocity pulses 

Chiara Cornelio, Stefano Aretusini, Elena Spagnuolo, Giulio Di Toro, and Massimo Cocco

Fault zones consist of one or more fault cores sandwiched by a damage zone surrounded by less deformed wall rocks. Most of the deformation is accommodated in the fault core through slip along one or more principal slipping zones. The thickness of fault cores (mm to m) and individual slipping zones (µm to dm) increases with fault slip displacement. In particular, small-displacement or immature faults have such thin slip zones that resemble bare rock surfaces. When exhumed from <5-6 km depth, slip zones are made by poorly cohesive fault gouges.

Several laboratory experimental configurations aim to reproduce the deformation processes activated during seismic slip episodes. In the laboratory, the slip zone is represented as the interaction volume of two bare rock surfaces (i.e., immature faults) or as a mm-thick gouge layer (i.e., more mature faults). Most studies have focused on the frictional behavior of gouge layers or bare rocks during single seismic events, and only a few on the mechanical and microstructural evolution of a gouge layer subjected to multiple events of seismic slip (e.g., Smith et al., 2015). Here, we present rotary-shear friction experiments that reproduce seismic slip on both gouge layers and bare rocks derived from calcite-rich marble. The aim of this study is to analyze the frictional evolution of a gouge layer undergoing multiple seismic slip pulses: four trapezoidal slip pulses at 1 m/s for 1 m of slip, with hold time of 120 s between each pulse. Moreover, we compare this evolution with one of bare rocks of the same material but slid only once at 1 m/s for a total slip higher than 1 m. Experiments were performed at normal stress of 10, 20, and 30 MPa under room humidity conditions.

Our experimental results show that despite the static and dynamic friction coefficients are higher in the gouge layer than in the bare rock experiments, the frictional work to achieve the dynamic friction decreases at each seismic slip pulse in the gouge experiments and is comparable with the bare rock one after the second pulse. High-resolution scanning electron microscope investigations of the sheared gouge layers show that in the first two slip pulses most of the frictional work is spent on (1) strain localization into newly-formed slip zones bounded by continuous ultra-smooth surfaces and, (2) grain size reduction, sintering and compaction (i.e., porosity reduction) within the bulk gouge layer. However, after the second pulse, the slip is localized in one or more well-developed slip zones bounded by ultra-smooth surfaces, that cut through the compacted gouge layer, and the mechanical behavior is similar to that of bare rocks.

Carbonate-bearing fault zones are common seismogenic sources in the Mediterranean area (e.g. 2009 L'Aquila Mw6.3 and 1981 Corinth M6.6 earthquakes). In a series of subsequent seismic slip events, it is shown that the evolution of a gouge layer in carbonate-bearing fault rocks tends to produce a similar mechanical behaviour of bare rocks although the volumetric distribution of strain is significantly different. Importantly, the energy spent by apparently different mechanical processes is eventually similar.

How to cite: Cornelio, C., Aretusini, S., Spagnuolo, E., Di Toro, G., and Cocco, M.: Frictional evolution of gouge-bearing faults during multiple seismic slip velocity pulses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14284, https://doi.org/10.5194/egusphere-egu23-14284, 2023.

In this paper, based on the model of thermal pressurization, we present a new way for the emergence of rate and state phenomenology (RSF, friction law) during the earthquake cycle. In the framework of fault mechanics, the common physical mechanism for the RSF phenomenology is slip and plastic deformation at the asperity contacts. We show that the fundamental physical mechanism of thermal pressurization together with viscosity inside the fault can also reproduce rate and state phenomenology.


More specifically, in our numerical analyses we model frictional weakening during large seismic slip due to thermal pressurization inside the fault. We introduce thermo-hydro-mechanical couplings to model thermal pressurization and a first order micromorphic Cosserat continuum, in order to avoid mesh dependence of the numerical results. Moreover, we introduce viscosity in the form of strain rate hardening. When we perform velocity stepping analyses, our numerical findings show that friction presents, initial peak over-strength and frictional oscillations around a residual value (see Figure). Our results, deriving from fundamental modeling assumptions, exhibit rate and state phenomenology, without the need to introduce the physical mechanism of slip at the asperity contacts.


Keywords: THM couplings; Viscosity; Cosserat continuum; Tribology; Earthquakes

How to cite: Stathas, A. and Stefanou, I.: Viscosity and thermal pressurization during large seismic slip lead to rateand state phenomenology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14607, https://doi.org/10.5194/egusphere-egu23-14607, 2023.

EGU23-15563 | ECS | Posters on site | EMRP1.2

A novel automated procedure for determining steady-state friction conditions in the context of rate- and state- friction analysis 

Piercarlo Giacomel, Daniel Faulkner, Valère Lambert, and Michael Allen

In the framework of empirically-derived rate- and state- friction (RSF) laws, friction constitutive parameters a, b, and Dc  (and further sets of state parameters) are obtained from inverse modelling of laboratory data on the assumption that steady-state conditions are reached following the velocity steps. This method also includes removing any slip-dependent linear trends in friction by linear regression when steady-state conditions are considered to be achieved. The choice of where linear detrending, thereby where to assume the attainment of steady-state friction conditions is therefore key for a correct retrieval of the modelled RSF parameters and their consequent use in modelling of earthquake nucleation. Nonetheless, to date this procedure is still user-dependent and as such, RSF outputs may differ ceteris paribus.

To better elucidate the detrimental consequences of an incorrect assumption of steady-state friction conditions in RSF analysis, in this study synthetic velocity steps were generated with superimposed random Gaussian noise, characterized by increasing characteristic slip distances in the second set of state variables, Dc2,from 0 to 500 µm. In each velocity step, steady-state conditions were assumed starting at progressively larger displacements with respect to the occurrence of the velocity jump. This means that the arbitrarily chosen “steady-state” may or may not correspond to the true steady-state conditions. To retrieve RSF parameters, a slip window of constant size (i.e., 100 µm) was applied from the selected “steady-state” point onwards to remove any linear trend in friction, implying that the remainder of the velocity step beyond the slip window is also at steady-state. During each RSF analysis, the slope calculated from linear regression within the 100 µm long slip window after the velocity steps is systematically compared with the slope computed from linear regression prior to the velocity steps.

Our results show that:

  • while a, b1 and Dc1 are essentially constant regardless of the choices of steady-state and equal to the true values used to generate the synthetic velocity steps, b2 and Dc2 may significantly differ if Dc2 is commensurate with the whole displacement window that contains the velocity step;
  • all modelled RSF parameters coincide with the true ones when the ratio of the slopes before and after the velocity steps approach unity; this observation can be regarded as a proxy for the achievement of the steady-state conditions and becomes increasingly relevant with larger Dc2.

Based on such evidence, we developed a routine that automates the above described work flow, providing a systematic and reproducible technique to determine steady-state friction and thus return the correct RSF parameters. Furthermore, this novel procedure determines the optimal minimum slip window size to remove slip-dependent linear trends in friction and alerts the user when steady-state is not reached within a given step length and hence when Dc2 and b2 cannot be properly determined with experimental data.

How to cite: Giacomel, P., Faulkner, D., Lambert, V., and Allen, M.: A novel automated procedure for determining steady-state friction conditions in the context of rate- and state- friction analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15563, https://doi.org/10.5194/egusphere-egu23-15563, 2023.

EGU23-16290 | Orals | EMRP1.2

Fault zone complexity naturally produces the full slip spectrum: Insights from numerical models 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In addition to regular earthquakes, observations of spatiotemporally complex slip events have multiplied over the last decades. These slip events range along different time scales: from creep , slow slip events to LFEs and tremors. At present, these events are generally interpreted by imposed frictional heterogeneities along the fault plane. However, fault systems are geometrically complex in nature over different scales. We aim in this work to investigate the role of “realistic” fault geometry on the dynamics of slip events. We consider a fault system in a 2D quasi-dynamic setting. The fault system consists of a main self-similar rough fault, surrounded by a dense network of off-fault fractures. All fractures are frictionally homogeneous (rate weakening) and can potentially undergo dynamic slip. We aim to understand how the deformation in the volume is accomodated by the off-fault damage zone and the main fault. What fraction of the “supplied” moment rate is hosted by the off-fault fractures during an earthquake cycle?

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: Fault zone complexity naturally produces the full slip spectrum: Insights from numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16290, https://doi.org/10.5194/egusphere-egu23-16290, 2023.

EGU23-16320 | Orals | EMRP1.2

How do earthquakes stop? Insights from a minimal model of frictional rupture 

Fabian Barras, Kjetil Thøgersen, Einat Aharonov, and François Renard

The question "what arrests an earthquake rupture?" sits at the heart of any potential prediction of earthquake magnitude. Here, we present a one-dimensional, thin-elastic-strip, minimal model, to illuminate the basic physical parameters that control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables, valid for both in-plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge-Knopoff model, with an added characteristic length scale, that corresponds to either the thickness of the damage zone for strike-slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and present closed-form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack- and pulse-like rupture propagation and arrest. Despite its simplicity, this minimal model is able to reproduce several salient features of natural earthquakes that are still debated (e.g. various arrest scenarios, stable pulse-like rupture, back-propagating front, asymmetric slip profiles).

How to cite: Barras, F., Thøgersen, K., Aharonov, E., and Renard, F.: How do earthquakes stop? Insights from a minimal model of frictional rupture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16320, https://doi.org/10.5194/egusphere-egu23-16320, 2023.

EGU23-16777 | ECS | Orals | EMRP1.2

The Stability Transition from Stable to Unstable Frictional Slip with Finite Pore Pressure 

Raphael Affinito, Derek Elsworth, and Chris Marone

Pore fluids are ubiquitous throughout the lithosphere and are commonly cited as a major factor producing slow slip and complex modes of tectonic faulting. Here, we investigate the role of pore pressure on slow slip and the frictional stability transition and find that the mode of fault slip is largely unaffected by pore pressure once we account for effective stress. Ambient temperature experiments are done on synthetic fault gouge composed of quartz powder with a median grain size of 10μm with an average permeability of  8E-17m2 – 6E-18m2 from shear strains 0 - 26. We conduct constant velocity experiments at 20MPa σn’, with Ppnratios of λ from 0.05 to 0.28. Under these conditions, dilatancy strengthening is minimal and we find that slip rate dependent changes in the critical rate of frictional weakening are sufficient to explain slow slip.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: The Stability Transition from Stable to Unstable Frictional Slip with Finite Pore Pressure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16777, https://doi.org/10.5194/egusphere-egu23-16777, 2023.

SM5 – Seismic Imaging Across Scales (from near-surface to global scale, incl. methodological developments)

EGU23-30 | ECS | Orals | SM5.1

SOLA Backus-Gilbert Rayleigh wave group velocity dispersion tomography of North-West of Iran using local-regional earthquakes and ambient seismic noise.  

Saman Amiri, Alessia Maggi, Mohammad Tatar, Dimitri Zigone, and Christophe Zaroli

Imaging seismic velocity of the Earth has been implemented widely for years. The majority of these studies are based on linear or non-linear methods that minimize the difference between seismic observations and predictions of these observations from simplified models of the Earth (tomographic models). Another family of methods, based on the work of Backus & Gilbert (1968), constrains Earth models by maximizing their resolution. A numerically tractable version of such linear local averaging methods, called SOLA, was recently been adapted to seismic tomography by Zaroli (2016). When correctly implemented, SOLA tends to reduce artifacts caused by uneven path coverage. It also provides information about model uncertainties and resolutions.

We are the first to have applied the SOLA Backus-Gilbert method to group velocity dispersion tomography of the Northwest Iranian plateau. We used Rayleigh wave dispersion curves obtained from vertical component seismograms of local and regional M ≥ 4.5 earthquakes that occurred from 2010 to 2021. We also used cross-correlations of ambient seismic noise from January 2013 to the end of December 2015. We allowed the resolution to vary with location and adapted the target resolution based on the local path density. We included data uncertainties based on the location uncertainties of the earthquakes and on the energy in the dispersion curves at each period. We selected the trade-off parameter between model resolution and model uncertainties using a standard L-curve.

We present group velocity maps at periods between 10 and 50 seconds as well as maps of model resolution lengths and uncertainties. We also present maps that mask regions where the anomalies are within the uncertainties to highlight the strongly anomalous regions. Our short-period maps reveal the relatively lower velocities in eastern Anatolia and western parts of NW Iran can be explained by partially melt zones in the crust, in accordance with the study of keshin (2003) who proposed extensive melting in the crust because of the interaction of hot asthenosphere with the Eastern Anatolian Accretionary Complex. Also, higher velocity anomalies along the Sanandaj-Srijan metamorphic zone (SSZ), can be related to the sedimentary and metamorphic Paleozoic-Cretaceous rocks. The low velocities observed along the Zagros fault thrust belt are also well correlated with high and shallow seismicity in this zone (Maggi et al 2000) which implies the presence of an upper crust tectonically very active.

Our long-period maps reveal high-velocity anomalies beneath the Alborz and low-velocity zone in SSZ. The low-velocity anomalies are mainly due to a thin lithosphere or the absence of a lithospheric mantle, while high velocities can be related to the presence of a stable continental mantle lid or an oceanic-like lithosphere.

Keywords: SOLA Backus-Gilbert, Group Velocity, Inverse theory, North-West of Iran, Tomography.

How to cite: Amiri, S., Maggi, A., Tatar, M., Zigone, D., and Zaroli, C.: SOLA Backus-Gilbert Rayleigh wave group velocity dispersion tomography of North-West of Iran using local-regional earthquakes and ambient seismic noise. , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-30, https://doi.org/10.5194/egusphere-egu23-30, 2023.

EGU23-1214 | Orals | SM5.1

Large Lithospheric Seismic Velocity Variations Across the Northern Canadian Cordillera Imaged by Ambient Noise Tomography 

Derek Schutt, Robert Porritt, Clément Estève, Pascal Audet, Jeremy Gosselin, Andrew Schaeffer, Richard Aster, Jeffrey Freymueller, and Joel Cubley

Global-scale seismic velocity models of the Northern Canadian Cordillera show high velocities to the east of the Cordilleran deformation front and low velocities to the west.    This velocity contrast is consistent with other geophysical observables, such as regional seismological studies, that indicate a weak and thin lithosphere to the west that transitions quickly to a strong and thick craton-like lithosphere at the deformation front.    We present new results using data collected by the Mackenzie Mountains EarthScope Project, which included an ~875 km-long line of 40 broadband seismographs across the Cordillera and into the craton extending from roughly Skagway, Alaska to Great Bear Lake, Northwest Territories.    The 3-year overlap of this deployment with other broadband seismic stations in the region, most notably the EarthScope Transportable Array and the Yukon Northwest Seismic Network, allows for detailed 3-D Rayleigh wave ambient noise imaging of the upper lithosphere.    Results show large velocity variations west of the deformation front.   Notably, we image a 5% Vs low that extends from the upper crust to the asthenospheric mantle.   This plume-like structure, and associated weakening, may be a primary cause for the ongoing uplift of the Mackenzie Mountains at their unusually eastward location.   We also image a low velocity feature in the lower crust extending to the west of the deformation front, which may facilitate eastward crustal translation along a large-scale (~800 km) decollement system driven by the Yakutat indentor consistent with the orogenic float hypothesis of Mazzotti and Hyndman (2002).    We also note strong lithosphere-scale lateral heterogeneity suggesting that 3-D effects are important in focusing deformation in the Mackenzie Mountain area.

How to cite: Schutt, D., Porritt, R., Estève, C., Audet, P., Gosselin, J., Schaeffer, A., Aster, R., Freymueller, J., and Cubley, J.: Large Lithospheric Seismic Velocity Variations Across the Northern Canadian Cordillera Imaged by Ambient Noise Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1214, https://doi.org/10.5194/egusphere-egu23-1214, 2023.

EGU23-1574 | ECS | Posters virtual | SM5.1

Lithospheric Imaging through Reverberant Layers: Sediments, Oceans, and Glaciers 

Ziqi Zhang and Tolulope Olugboji

The Earth, in large portions, is covered in oceans, sediments, and glaciers. High-resolution body wave imaging in such environments often suffers from severe reverberations, that is, repeating echoes of the incoming scattered wavefield trapped in the reverberant layer, making interpretation of lithospheric layering difficult. In this study, we propose a systematic data-driven approach, using autocorrelation and homomorphic analysis, to solve the twin problem of detection and elimination of reverberations without a priori knowledge of the elastic structure of the reverberant layers. We demonstrate, using synthetic experiments and data examples, that our approach can effectively identify the signature of reverberations even in cases where the recording seismic array is deployed in complex settings, for example, using data from (1) a land station sitting on Songliao basin, (2) an ocean bottom station in the fore-arc setting of the Alaska amphibious community seismic experiment (AACSE), and (3) a station deployed on ice-sediment strata in the glaciers of Antarctica. The elimination of the reverberation is implemented by a frequency domain filter whose parameters are automatically tuned using seismic data alone. On glaciers where the reverberating sediment layer is sandwiched between the lithosphere and an overlying ice layer, homomorphic analysis is preferable in detecting the signature of reverberation. We expect that our technique will see wide application for high-resolution body wave imaging across a wide variety of conditions.

How to cite: Zhang, Z. and Olugboji, T.: Lithospheric Imaging through Reverberant Layers: Sediments, Oceans, and Glaciers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1574, https://doi.org/10.5194/egusphere-egu23-1574, 2023.

EGU23-2387 | Posters on site | SM5.1

The SHIELD’21 deep seismic experiment, Ukraine 

Tomasz Janik, Vitaly Starostenko, Wojciech Czuba, Piotr Środa, Anna Murovskaya, Tamara Yegorova, Alexandra Verpakhovska, Katerina Kolomiyets, Dmytro Lysynchuk, Dariusz Wójcik, Victor Omelchenko, Tanya Amashukeli, Olga Legostaeva, Dmytro Gryn, and Serhii Chulkov

Carried out in 2021, the wide-angle reflection and refraction (WARR) SHIELD’21 profile crosses, from SW to NE, the main tectonic structures of Ukraine. It targeted the structure of the Earth’s crust and upper mantle of the southwestern margin of the East European Craton with overlying Neogene Carpathian Foredeep and Vendian-Paleozoic Volyn-Podolian Monocline, Archaean and Paleoproterozoic segments of Ukrainian Shield and Late Paleozoic Dnipro-Donetsk Basin. The ~650 km long SHIELD’21 profile is an extension of previously realized RomUkrSeis profile carried out in 2014 and running from the Apuseni Mountains to the southwestern Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile using TEXAN and DATA-CUBE short-period seismic stations provided high-quality seismic records. The field work was performed during the summer of 2021, included the deployment of autonomous seismic stations and drilling-explosive works. A total of 264 seismic receivers were involved, (160 DATA-CUBE and 104 TEXAN stations). The average spacing between observation points is about 2.65 km. The sampling interval for all stations was 0.01 s. Seismic energy was generated at 10 shot points (SP) with total charge in all wells 5775 kg. The distance between the SPs was about 50 km.

The main recorded seismic waves are the refractions of P- and S- waves in sediments, basement, crust and uppermost mantle, and reflections from crustal boundaries, Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times will allow to build a velocity model not only for P-, but also for S-waves and Vp/Vs ratio.

The main objective of the SHIELD’21 project is to get new seismic data that increase our knowledge on the lithosphere structure and geodynamics of the study region.

 

Starostenko, V., Janik, T., Mocanu, V., Stephenson, R., Yegorova, T., Amashukeli, T., Czuba, W., Środa, P., Murovskaya, A., Kolomiyets, K., Lysynchuk, D., Okoń, J., Dragut, A., Omelchenko, V., Legostaieva, O., Gryn, D., Mechie, J., & Tolkunov, A. (2020). RomUkrSeis: Seismic model of the crust and upper mantle across the Eastern Carpathians — From the Apuseni Mountains to the Ukrainian Shield. Tectonophysics, 794, 228620. https://doi.org/10.1016/j.tec to.2020.228620

How to cite: Janik, T., Starostenko, V., Czuba, W., Środa, P., Murovskaya, A., Yegorova, T., Verpakhovska, A., Kolomiyets, K., Lysynchuk, D., Wójcik, D., Omelchenko, V., Amashukeli, T., Legostaeva, O., Gryn, D., and Chulkov, S.: The SHIELD’21 deep seismic experiment, Ukraine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2387, https://doi.org/10.5194/egusphere-egu23-2387, 2023.

EGU23-3788 | ECS | Orals | SM5.1

3D Bayesian Variational Full-Waveform Inversion 

Xin Zhang, Angus Lomas, Muhong Zhou, York Zheng, and Andrew Curtis

Seismic full-waveform inversion (FWI) produces high resolution images of the subsurface by exploiting information in full acoustic, seismic or electromagnetic waveforms, and has been applied at global, regional and industrial spatial scales. FWI inverse problems are traditionally solved by using optimization, in which one seeks a best model by minimizing the misfit between observed waveforms and model-predicted waveforms. Due to the nonlinearity of the physical relationship between model parameters and waveforms, a good starting model is often required to produce a reasonable result. In addition, the optimization methods cannot produce accurate uncertainty estimates, which are required to better interpret final model estimates.

In principle, nonlinear Bayesian methods can be deployed to solve both issues. Monte Carlo sampling is one such class of algorithms which are computationally expensive, and all Markov chain Monte Carlo-based methods are difficult to parallelise fully. Variational inference provides a fully parallelisable alternative methodology. This is a class of methods that optimize an approximation to a probability distribution describing post-inversion parameter uncertainties. Both Monte Carlo and variational full waveform inversion have been applied previously to solve 2D Bayesian FWI problems, but neither of them have been applied in 3D.

In this study we apply three variational methods to a 3D FWI problem and analyse their performance. Specifically we apply automatic differential variational inference (ADVI), Stein variational gradient descent (SVGD) and stochastic SVGD (sSVGD), and compare their results and computational costs. These tests show that ADVI is the least computationally demanding method, but its results are systematically biased as uncertainty is underestimated. The method might therefore be used to provide relatively rapid but approximate insights into the Bayesian solution. SVGD demands the highest computational cost, yet produces equally biased results. Adding a randomized term in the SVGD dynamics produces sSVGD, a Markov chain Monte Carlo method based on variational principles. This provides the most accurate results, at intermediate computational cost. We conclude that 3D variational full-waveform inversion is practically applicable, at least in small problems, and can be used to image the Earth’s interior and to provide reasonable uncertainty estimates on those images.

How to cite: Zhang, X., Lomas, A., Zhou, M., Zheng, Y., and Curtis, A.: 3D Bayesian Variational Full-Waveform Inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3788, https://doi.org/10.5194/egusphere-egu23-3788, 2023.

EGU23-4213 | ECS | Posters on site | SM5.1

The potential of machine learning to solve the single step inversion problem in ambient noise tomography 

Joseph Fone and Nicholas Rawlinson

The two step inversion of ambient noise surface wave data is common practice due to its convenience and reliability of imaging structures that are consistent with other observations. It is performed by taking the inter station dispersion curves produced by cross-correlation of ambient noise and performing individual 2D travel time tomographic inversions to produce maps of phase and/or group velocity for Rayleigh and/or love waves and whichever frequencies and modes have been extracted from the ambient noise data. These maps are then sampled in discrete points to produce location based dispersion curves known as pseudo-dispersion curves. These pseudo-dispersion curves are then inverted for 1D velocity structure. The issue with this method is the many separate inversions that are performed are entirely separate from one another with no regularisation applied to the final 3D model only in the individual steps. This can lead to artefacts in the model, particularly in areas of low data coverage, as the pseudo-dispersion curves can have unphysical spikes and velocity changes and so often produce unrealistic 1D models. Post processing can partially remedy this, such as smoothing the final model, but it does not go all the way to solving the problem. Single step inversions are also possible. The forward problem involves taking the 3D model and sampling it in discrete locations and computing dispersion curves which can be converted into 2D maps of phase/group velocity etc. Then using some Eikonal solver the travel time between stations can be calculated. These calculated travel times are then used with the measured travel times extracted from ambient noise to perform an inversion. This obtains a 3D model directly from the observed dispersion curves with regularisation built into whichever inversion scheme being used. This is often much more computationally expensive than the two step as the forward problem is expensive and needs to be computed many times in a typical inversion scheme. In this preliminary study we investigate the potential of using neural networks to assist in the single step inversion process by training networks to perform the forward and inverse problems in single step tomography of interstation dispersion curves. This may result in significant speed ups in these processes or lead to different ways of approaching the one step process. To examine the potential of this we investigate possible efficient sampling algorithms to produce synthetic training data sets as well as network architectures that produce the most accurate mapping of model parameters to the data and vice versa.

How to cite: Fone, J. and Rawlinson, N.: The potential of machine learning to solve the single step inversion problem in ambient noise tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4213, https://doi.org/10.5194/egusphere-egu23-4213, 2023.

EGU23-4317 | ECS | Orals | SM5.1

Evidence for a higher porosity upper crust in the North Atlantic Ocean   

Lianjun Li, Jenny Collier, Tim Henstock, and Saskia Goes

The most common way to estimate the porosity of the mature oceanic crust, and hence its contribution to geochemical exchange, is from the inversion of active source seismic data. Previous studies have suggested that hydrothermal activity effectively ceases in crust older than 10 Ma. This is based on observations that the seismic velocity of the uppermost crust increases rapidly within 10 Ma but changes little beyond that. The velocity increase is widely explained by reduced porosity and permeability due to hydrothermal mineral precipitation and fracture closure due to sediment blanketing. However, a potential problem with conventional wide-angle Ocean Bottom Seismometer (OBS) modelling over mature oceanic crust is the imaging geometry, where the water wave obscures the onset of the crustal refractions for tomographic inversion needed to resolve the velocity of the upper hundred meters of the igneous crust.

 

To investigate the issue of imaging geometry and accurately extract the physical properties of the upper crust, we applied downward continuation on conventional OBS records across 65 Ma Atlantic Ocean crust. The method eliminates the effect of the thick water column by locating shots on a datum close to the seabed. This enables refractions from the uppermost 100-200 m of igneous crust to be viewed as first arrivals, and hence significantly improves the accuracy of the velocity inversion of the upper layers. Using travel time picks from downward continued and original OBS records, we applied tomographic inversion with three starting models taken from the latest compilation of crustal velocity-depth (VZ) models. The three models have a velocity variation of ±10% for the uppermost crust, representing a low, mean, and high bound for crustal VZ relations. By comparing the results, we show that with downward continued data the inverted velocity of the uppermost crust is less dependent on the starting model and converges to the same trend closer to the low bound of previous VZ relations. The average velocity of the uppermost crust inverted with downward continued data is ~0.3 km/s lower than that inverted with original data. These results would translate into a porosity of 14%, compared to 10% for the non-downward continued analysis. We also resolve stronger along-strike variation in the inverted velocity of the uppermost crust (4.2 km/s to 4.8 km/s) using downward continued data compared to original data, which may correspond to porosity as large as 18%, much higher than previously suggested porosity of 8 % for mature oceanic crust. This implies that open cracks may be still present and thick sediments may seal hydrologically but not close fractures that affect the seismic refraction data. Moreover, our results reconcile with the recent work in the South Atlantic performed with full-waveform inversion (FWI) on streamer data. Therefore, downward continuation, also FWI may need to be incorporated into the workflow of conventional wide-angle OBS modelling, especially for mature oceanic crust. This will improve the resolution and accuracy of the physical properties of the uppermost crust and may shed new light on its evolution and role in off-axis hydrothermal circulation and seawater chemistry.

How to cite: Li, L., Collier, J., Henstock, T., and Goes, S.: Evidence for a higher porosity upper crust in the North Atlantic Ocean  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4317, https://doi.org/10.5194/egusphere-egu23-4317, 2023.

EGU23-4387 | ECS | Posters on site | SM5.1

The impact of the 3D effect on the regional-scale velocity model building using 2D full-waveform inversion 

Andrzej Górszczyk, Romain Brossier, and Ludovic Métivier

Regional-scale active seismic surveys are the methods of choice to probe the lithosphere. One of the key parameters of these surveys is the spatial sampling of the investigated area. Dense sources and receivers sampling coupled with broadband frequency of signals translates to fine-scale probing of the subsurface from a broad range of perspectives. In practice, however,  acquisition design of academic deep crustal seismic surveys typically assumes a compromise between the experiment logistic and the key parameters of the acquisition geometry. This compromise often leads to 2D surveys realised with few tens of receivers deployed along the profiles that can be up to few hundred kilometers long. As a result the high costs of 3D surveys are mitigated at the price of the quality of the resulting data, that cannot be fully exploited by advanced processing techniques - such as waveform-based inversion methods. In particular, the 2D data acquisition and subsequent imaging pose the inconsistency between the 3D wavepath traveled during the survey and the 2D wavepath forced during the 2D processing. This is because geological heterogeneities cause changes of direction of wave propagation, which is indicated by the three-dimensional wave vector spanned at a given point of subsurface. If the 3D-effect is strong due to the complexity of the underlying structure, then the 2D assumption of wavefield propagation during processing cannot honor the field conditions and must lead to errors in the reconstructed velocity model or migrated image. 

Recent years have shown a massive development of waveform inversion and migration methods. In terms of regional-scale seismic imaging, there were few documented onshore and offshore case studies that attempted to process 2D archival academic data with full-waveform inversion (FWI) and extract structural information beyond the resolution-limit of the traveltime tomography. However, the limitations originating from the legacy acquisition make it difficult to fully exploit the potential of FWI. In this study we evaluate the ability of regional-scale velocity model-building technics to handle out-of-plane propagation and investigate how this effect manifests itself in the data. Through the insight of  wave propagation within complex subsurface models we underline the problem and make first attempts to the broader investigation of the optimization of 3D academic regional surveys. We extract various 3D target models from the synthetic model of a subduction zone and we use those models to generate seismic data along 2D OBS lines. Subsequently we use 2D FWI to evaluate how the out-of-plane propagation affects the results of 2D velocity model-building from the data generated along the 2D OBS lines but using 3D modelling and 3D target models. We compare those results with the scenario where the 2D FWI is applied to the data from the same 2D OBS lines but generated using 2D velocity models and 2D modelling. We perform polarization analysis to demonstrate how the 3D effect manifest itself in the OBS gathers. Finally we also run 3D FWI with different OBS acquisition settings to investigate their impact on the final model reconstruction.

How to cite: Górszczyk, A., Brossier, R., and Métivier, L.: The impact of the 3D effect on the regional-scale velocity model building using 2D full-waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4387, https://doi.org/10.5194/egusphere-egu23-4387, 2023.

EGU23-4416 | ECS | Orals | SM5.1

Imaging magma beneath the rift zones of Axial Seamount on the Juan de Fuca Ridge 

Michelle Lee, Suzanne Carbotte, and Adrien Arnulf

Axial Seamount is an active submarine volcano formed by the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg hot spot. The Axial Seamount volcanic system includes the central volcano marked by a caldera and bounding northern and southern rift zones. Prior studies of the last three eruptions at Axial (Jan. 1998, Apr. 2011, Apr. 2015) indicate lava flows and earthquake swarms extending from the summit caldera and into the rift zones. These eruptions are believed to have been sourced from the well-imaged large magma reservoir found beneath the summit caldera of Axial (Arnulf et al., 2014, Carbotte et al., 2020). However, areas beyond the summit caldera have not been explored for potential magma sources that could have contributed to these events.

In this study, we process and analyze multi-channel seismic (MCS) data acquired in 2002 from the Juan de Fuca Ridge to characterize the internal structure of the rift zones. The reflective profiles reveal small crustal magma bodies beneath and in the vicinity of lava flows in rift zones from the three prior eruptions. These magma bodies are less than 5km wide and are located at depths of ~1.5-5.2km beneath the seafloor. We also image wide magma bodies within the overlap regions between the rift zones and the neighboring Juan de Fuca segments. We image a 6.4km wide body under the eastern flank of the northern rift zone overlapping with the Coaxial segment and a 1km wide, ~400-500km thick magma body under the overlapping basin between the southern rift zone and Vance segment. Collectively the new observations from the MCS data reveals that, in addition to the main magma reservoir, there are also multiple small and discontinuous crustal magma bodies underlying the Axial segment. Through interpretations of the seismicity pattern and lava flow compositions, we believe that these magma bodies likely contribute the rift zone magmatism.  

How to cite: Lee, M., Carbotte, S., and Arnulf, A.: Imaging magma beneath the rift zones of Axial Seamount on the Juan de Fuca Ridge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4416, https://doi.org/10.5194/egusphere-egu23-4416, 2023.

EGU23-4819 | Posters on site | SM5.1

Imaging the Earth's Upper Mantle: Markov Chain Monte Carlo Joint Inversion of Geophysical Multi-observables 

Fatimah Abdulghafur, Steven Hansen, and Juan Carlos Afonso

Seismic data from several long-running broadband sensors around the globe will be used to investigate the statistical significance and geologic interpretation of negative velocity discontinuities in the upper-most mantle. Several previous studies have identified negative polarity arrivals in S-wave receiver function data which are variously interpreted as lithosphere-asthenosphere and/or mid-lithosphere boundaries.

One-dimensional joint-inversion is applied using the LitMod framework, which is a Bayesian statistical method driven by a Markov Chain Mote Carlo algorithm.

LitMod uses a thermodynamically consistent physical model of the mantle and thus provides important constraints for the interpretation of the receiver function results.

Joint inversions combine Rayleigh wave phase velocity measurements, both P and S-wave receiver functions, absolute elevation, and geoid height.

Particular attention is given to the calculation and inversion of S-wave receiver function data, which represents a new addition to the LitMod framework. 

How to cite: Abdulghafur, F., Hansen, S., and Afonso, J. C.: Imaging the Earth's Upper Mantle: Markov Chain Monte Carlo Joint Inversion of Geophysical Multi-observables, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4819, https://doi.org/10.5194/egusphere-egu23-4819, 2023.

Oil and gas industry is particularly interested in subsalt imaging because salt bodies often serve as seals for hydrocarbon reservoirs especially on the flanks and underneath the salt body. Classical imaging or full-wave inversion have encountered many difficulties in imaging such subsalt regions. The high velocity contrast between the salt body and its surroundings, the shape of the salt body, and the strong attenuation of waves propagating in the salt make accurate imaging difficult.

Imaging from surface seismic data has already been addressed. We propose to apply the full-wave inversion approach to borehole seismic data.  These data are supposed to provide more informative seismic signals (one-way, transmitted waves, scattered field near receivers, …) and should better constrain the salt flanks and bottom imaging. Unfortunately, this inverse problem is severely ill-posed due to the lack of data redundancy.  Introducing geological prior information through the parameterization of the salt geometry using the level set method partly overcomes this problem. This approach implicitly defines the salt/sediments interface through a smooth function. This hybrid  full-wave inverse problem combines the classical field gradient and the level set geometric gradient, allowing us to retrieve respectively the physical parameters and the salt body geometry.

The forward wave equation for a heterogeneous elastic domain is solved using the spectral element method. This method allows us to have a better representation of the salt/sediments interface, thus a more accurate modeling of the scattered wavefield due to interactions at the interface. Regarding the level set inversion, we define the implicit function in a parametric framework. We use compactly supported B-spline basis functions for their ability to represent a wide range of geometries compared to radial basis functions, for instance.

During the level set inversion process, when the salt/sediments interface evolves, updating the physical model parameters near the interface becomes an issue. We propose to perform a continuous deformation of the medium while conserving the mesh topology. The interface nodes are moved consistently with the implicit level set function. Furthermore, this approach  preserves a meshed representation of the interface through the inversion process allowing a more accurate seismic modeling. The mesh deformation is obtained by geostatistical kriging of node locations, constrained by the updated interface position.

In short, we propose a hybrid full-wave inversion method to estimate both material parameter fields and geometric parameters of the salt/sediments interface. The method is validated on several elastic models using synthetic seismic well data in a subsalt imaging context.

How to cite: Khazraj, K., Barnes, C., and Maillot, B.: Hybrid  full-wave inversion based on a B-spline level set mesh deformation method of borehole seismic data for a subsalt imaging context, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5219, https://doi.org/10.5194/egusphere-egu23-5219, 2023.

Abstract

We investigated the Moho depth and the velocity structure of the crust and upper mantle in northern Algeria. We used teleseismic P-wave receiver functions jointly inverted with Rayleigh wave dispersion curves obtained from local earthquakes. The events used are collected from the seismic broadband stations of the Algerian broadband seismic network. These stations are located in different geological settings including the Tell Atlas, High Plateaus, and the Saharan Atlas. The H–κ stacking method of receiver functions was applied to first obtain the crustal thickness and the Vp/Vs ratio. The inversion results show the variation in Moho depth in the different geological structures. The shallowest depths of the Moho (~20–30 km) are estimated along the Algerian continental margin and Tell Atlas. In the High Plateaus region, the Moho depths vary from 30–36 km, whereas the deepest Moho depths are found in the Saharan Atlas (36–44 km). The crust is divided in two layers in the whole study area. The upper crust, ~8 –14 km thick, presents an average shear velocity of ~3.0 km/s. The lower crust of about 12–30 km thick has an average shear-wave velocity that ranges between 3.4–3.8 km/s. The upper crust is thinner than the lower crust particularly in the Saharan Atlas. The upper mantle shear-wave velocity varies from 4.1 to 4.5 km/s maximum and is stable, generally, below ~60 km depth. We clearly observed two low-velocity zones particularly in the eastern part of the Tell Atlas and the High Plateaus. The obtained results are in accordance with the previous results found in the region, particularly those using land gravity and seismic data. As the first estimate of the Moho depth from earthquake data in northern Algeria, using the receiver function method, this study sheds new insights on the crustal structure and the Moho depth in this region of the world.

How to cite: Melouk, B., Yelles-Chaouche, A., Semmane, F., and Galiana-Merino, J. J.: Shear-wave velocity structure and Moho depth variation in northern Algeria from joint inversion of teleseismic P-wave receiver functions and Rayleigh wave dispersion from local earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5910, https://doi.org/10.5194/egusphere-egu23-5910, 2023.

EGU23-6305 | Orals | SM5.1

Adjoint-state traveltime tomography: A new modality of seismic imaging 

Ping Tong, Jing Chen, Masaru Nagaso, and Shijie Hao

We have witnessed a transit of seismic tomography from ray-based traveltime inversion to wave equation-based waveform inversion during the past two decades. As is widely known, full waveform inversion outperforms traveltime tomography in resolving velocity variations with dimensions comparable and smaller than the dominant wavelength. However, this may not be always true in real practice, mainly due to the presence of unknown data noise, the lack of accurate initial models for the iterative inversion process (including material properties and source mechanisms), and the high demand for computational resources. Further efforts are required to develop techniques for using full waveform contents in seismic imaging studies, especially for the use of high-frequency waveform data (>1 Hz on regional scales). We have attempted to use common-source double-difference traveltime data in wave equation-based adjoint tomography studies of subsurface structures beneath Northeast Japan and Alaska. Because of the high level of waveform similarity, reliable common-source double-difference traveltime data at neighboring seismic stations are measured via cross-correlation approach. Insightful results are obtained. However, it is still computationally prohibitive to model high-frequency data by solving 3-D wave equations, limiting the resolution of seismic images. We admit that there is still a long way to go for the possible wide application of high-frequency full waveform inversion.

Traveltime is the most reliable information that can be extracted from raw seismological recordings.  We have developed a new modality of seismic imaging, called adjoint-state traveltime tomography, to unleash the full potential of traveltime in imaging subsurface structures. To avoid potential failure of ray tracing in 3D complex media, isotropic eikonal equation and anisotropic eikonal equations are used to model seismic traveltime field in heterogenous and anisotropic media, and the associated inverse problems are solved by the efficient adjoint state method. No ray tracing is required for the novel adjoint-state traveltime tomography method. Importantly, the sensitivities of traveltime-related objective functions to material parameters can be accurately measured even in complex media. We view adjoint-state traveltime tomography as a new framework for seismic tomography, as it naturally implements various body wave and surface wave tomographic inversions in a very similar way. Good performances of the adjoint-state traveltime tomography method will be reported via various case studies in regions with typically different tectonic settings. It is worth noting that an accompanying software package, TomoATT, is under development.

How to cite: Tong, P., Chen, J., Nagaso, M., and Hao, S.: Adjoint-state traveltime tomography: A new modality of seismic imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6305, https://doi.org/10.5194/egusphere-egu23-6305, 2023.

EGU23-6435 | ECS | Orals | SM5.1

A dictionary-based approximation approach for seismic traveltime tomography 

Naomi Schneider, Volker Michel, Karin Sigloch, and Eoghan Totten

We attempt the reconstruction of the solid earth’s interior three-dimensional structure using seismic wave observations. The interior structure of the mantle deviates moderately from spherically symmetrical reference models and therefore seismological observables also vary moderately from spherically symmetrical predictions. Hence we consider here the linearized inverse problem of seismic traveltime tomography.

Usually, the solution is approximated in a fixed basis system: either global (e.g. polynomials) or local (e.g. finite elements) basis functions. Here we use a dictionary-based approximation approach, called the Learning Regularized Functional Matching Pursuit (LRFMP). A dictionary is an intentionally redundant set of diverse trial functions from which iteratively an approximation in a best basis is built. The next best basis element is chosen such that the Tikhonov functional is minimized.

The methods have been used for a variety of spherical as well as tomographic tasks from the geosciences as well as medical imaging. Here we apply them to seismic traveltime tomography for the first time. We discuss relevant developments and challenges in the process of tailoring the methods to the problem and show first promising results.

How to cite: Schneider, N., Michel, V., Sigloch, K., and Totten, E.: A dictionary-based approximation approach for seismic traveltime tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6435, https://doi.org/10.5194/egusphere-egu23-6435, 2023.

EGU23-6504 | ECS | Posters on site | SM5.1

Adjoint-state traveltime tomography in Central Java enhanced by a machine-learning-assisted catalog 

Yiming Bai, Mohamad Ramdhan, Shun Yang, Tianjue Li, Jing Chen, Masaru Nagaso, and Ping Tong

As one of the most populous regions, Central Java in Indonesia is prone to high seismic and volcanic hazards, mostly due to the progressive northward subduction of the Australian plate beneath the Sunda plate. Detailed velocity structure of the crust and uppermost mantle beneath Central Java is critical for an improved understanding of the subduction processes and the associated seismicity and volcanism. Despite several independent isotropic velocity models proposed for the region, crustal-scale anisotropic structure, which reflects past and ongoing deformation, has rarely been investigated. The reasons behind this include that 1) conventional ray tracing may fail in strongly anisotropic crust, especially in a heterogeneous forearc setting; and 2) reliable anisotropy tomography requires sufficient data coverage, while the existing seismic networks in Central Java are restricted.

In this study, we target on the crustal-scale P-wave azimuthally anisotropic structure beneath Central Java. The acquired seismic data were recorded by more than 200 seismic stations from multiple projects with different execution periods (from 6 months to > 2 years). To make full use of the open access data, machine learning phase picking and subsequent event association and location were applied to build a local earthquake catalog. The machine-learning-based workflow detects more than 1500 events, roughly double the amount by previous manual picking. Notably, the preliminary catalog includes a large number of earthquakes that were located in the offshore areas but were recorded by land stations to the north, resulting in huge back azimuthal gaps and potential bias in earthquake relocation. The current study attempts to involve depth phases, such as sPn and sPg, for more accurate earthquake locations and thus more reliable tomographic images. With the expanded and refined seismicity catalog, a ray-free adjoint-state traveltime tomography package called TomoATT will be used for the 3-D velocity heterogeneity and azimuthal anisotropy beneath Central Java.

How to cite: Bai, Y., Ramdhan, M., Yang, S., Li, T., Chen, J., Nagaso, M., and Tong, P.: Adjoint-state traveltime tomography in Central Java enhanced by a machine-learning-assisted catalog, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6504, https://doi.org/10.5194/egusphere-egu23-6504, 2023.

EGU23-6864 | ECS | Orals | SM5.1

Developing Joint Geophysical and Petrological Inversion to Determine Temperature and Image the Lithosphere and Asthenosphere: De-risking Ireland's Geothermal Potential (DIG) 

Emma Chambers, Yihe Xu, Raffaele Bonadio, Javier Fullea, Sergei Lebedev, Duygu Kiyan, Brian O'Reilly, Patrick Meere, Meysam Rezaeifar, Tao Ye, Aisling Scully, and Gaurav Tomar and the DIG Team

High-quality maps of the geothermal gradient and temperature are essential when assessing the geothermal potential of a region. However, determining geothermal potential is a challenge as direct measurements of in situ temperature are sparse and individual geophysical methods are sensitive to a range of parameters, not solely temperature. Here, we develop a novel approach to determine the geothermal gradient using a joint geophysical-petrological inversion which requires thermal property data, seismic and additional geophysical datasets. The seismic data provide new constraints on lithospheric boundaries which influence crustal geotherms. We utilise large seismic datasets and extract Rayleigh- and Love-wave phase velocity dispersion curves, measured for pairs of stations. The measurements were performed using two methods with complementary period ranges; cross-correlation of teleseismic earthquakes and waveform inversion, yielding measurements in a broad period range (4-500 s).

The joint analysis of Rayleigh and Love measurements constrains the isotropic-average shear-wave velocity, relatable to temperature and composition providing essential constraints on the thermal structure of a region's lithosphere. We demonstrate this by inverting the data using an integrated joint geophysical-petrological thermodynamically self-consistent approach (Fullea et al., GJI 2021), where seismic velocities, electrical conductivity, and density are dependent on mineralogy, temperature, composition, water content, and the presence of melt. The multi-parameter models produced by the integrated inversions fit the surface-wave and other data and reveal the temperatures and geothermal gradients within the crust and mantle which will be used for future geothermal exploration and utilisation.

We use Ireland as a case study (part of the De-risking Ireland's Geothermal Potential project - DIG) and find that our new methodology produces results comparable to past temperature and geophysical measures, and enhances resolution. Lithospheric and crustal thickness play a key control on the temperature gradient with areas of thinner lithosphere resulting in elevated geotherms. In some locations we observe geotherms elevated beyond expectations which result from high radiogenic heat production from granitic rocks. This new methodology provides a robust workflow for determining the geothermal potential in areas with limited direct measurements.

The DIG project is funded by the Sustainable Energy Authority of Ireland under the SEAI Research, Development & Demonstration Funding Programme 2019 (grant number 19/RDD/522) and by the Geological Survey of Ireland.

How to cite: Chambers, E., Xu, Y., Bonadio, R., Fullea, J., Lebedev, S., Kiyan, D., O'Reilly, B., Meere, P., Rezaeifar, M., Ye, T., Scully, A., and Tomar, G. and the DIG Team: Developing Joint Geophysical and Petrological Inversion to Determine Temperature and Image the Lithosphere and Asthenosphere: De-risking Ireland's Geothermal Potential (DIG), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6864, https://doi.org/10.5194/egusphere-egu23-6864, 2023.

EGU23-7031 | ECS | Posters virtual | SM5.1

Sn attenuation characteristics in the Bhutan Himalaya. 

Sukanta Sarkar, Chandrani Singh, Ashwani Kant Tiwari, M Ravi Kumar, Arun Kumar Dubey, Abhisek Dutta, Gaurav Kumar, and Arun Singh

Seismic attenuation structure of the uppermost mantle is investigated using Sn waves in Bhutan Himalaya. Sn phase is the uppermost mantle-refracted
phase, which travels with a velocity of 4.3 - 4.7 km/s. Visual inspection of all the seismograms are conducted to examine the efficient, inefficient and blocked paths in the region. The inefficient, and blocked S n phases are mainly observed from the western side of our study region. Sn attenuation is determined using the two-station Methodology (TSM ). We have generated 460 station pairs from 1539 seismograms with magnitude ≥ 4 within an epicentral distance of 200 - 1650 km recorded at 38 seismic stations. Furthermore, a 2D Sn Q model is produced to understand the upper mantle rheology of the area. The central part shows a low Q (≤100) value while high Q dominates in northern and western parts of Bhutan Himalaya. The overall results correlate well with the tectonic setting beneath the study region. A comparison study is also made with the adjacent Arunachal Himalaya for better understanding.

How to cite: Sarkar, S., Singh, C., Tiwari, A. K., Kumar, M. R., Dubey, A. K., Dutta, A., Kumar, G., and Singh, A.: Sn attenuation characteristics in the Bhutan Himalaya., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7031, https://doi.org/10.5194/egusphere-egu23-7031, 2023.

EGU23-7039 | ECS | Posters on site | SM5.1

Lateral variation of body wave attenuation in crust of Bhutan Himalaya 

Abhisek Dutta and Chandrani Singh

We have studied the spatial variation of body wave (P and S wave) attenuation properties in crust of Bhutan region using small magnitude (2-4 ML) earthquakes. We have used continuous waveform data of 385 local earthquakes recorded by the GANSSER network operated by Swiss Seismological Service at ETH Zurich. Initially, the attenuation quality factors (Qp, Qs) have been estimated using Extended Coda Normalization method for five different frequencies (1.5, 3,6,12,18 Hz) at each station, as well as for two zones (eastern and western Bhutan). Q0 (Q value at 1 Hz) values are found to vary between 21-102 and 43-191 for P wave and S wave respectively for the whole region. We observe Qp = (72 ± 6)f(0.94 ± 0.06) and Qs = (104 ± 6)f(1.03 ± 0.05) for the eastern Bhutan whereas for the western part, Qp = (28 ± 1)f(1.41 ± 0.03) and Qs = (90 ± 5)f(1.07 ± 0.05) are found. Overall, frequency dependent coefficient values indicate the strong frequency dependent nature of Bhutan Himalaya. The spatial maps of Q0 for both waves suggest P-wave attenuates faster in the crust of western Bhutan compared to the eastern part. Paro, located in eastern Bhutan, shows comparatively high attenuation for both P and S waves. Further, azimuthal variation of attenuation properties around each station has been evaluated. The observed results are in good agreement with the tectonic settings of the region. The estimated attenuation properties are well comparable with the tectonically active regions in the world.

How to cite: Dutta, A. and Singh, C.: Lateral variation of body wave attenuation in crust of Bhutan Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7039, https://doi.org/10.5194/egusphere-egu23-7039, 2023.

EGU23-7579 | ECS | Orals | SM5.1

Lithospheric control on the Paleogene uplift and volcanism in Ireland and Britain 

Raffaele Bonadio, Sergei Lebedev, and David Chew

Spectacular Paleogene uplift and volcanism in Ireland and Britain are thought to be associated with the Iceland Plume but their mechanisms are still unclear, considering, in particular, that the Iceland Hotspot was many hundred kilometres away from the volcanism. We obtain new insights into the mechanisms by combining new evidence from seismic tomography, petrological inversion of seismic data, and the geological data on uplift and volcanism. Optimal resolution tomography is a new approach, developed for surface wave tomography, that allows us to find the optimal resolving length at every point of a tomographic model grid. With this approach we evaluate the posterior model error at a point of the model grid empirically, estimating it by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure. We apply this method to the region of Ireland and Britain, using more than 11,000 interstation phase-velocity curves measured at station pairs recording simultaneously, to image the lithosphere and underlying mantle beneath the area. The use of cross-correlation of teleseismic earthquakes and waveform inversion produces measurements in a very broad period range, leads to an unprecedented data coverage of the region, and allows us to unveil exciting new insights into the structure and evolution of the area, from the crust to the deep asthenosphere at a unprecedented level of detail.

The composite, optimal resolution phase-velocity maps are inverted for a 3-D VS model, which reveals pronounced, previously unknown variations in the lithospheric thickness beneath the area. The model shows evidence of a robust, low-velocity anomaly beneath the Irish Sea and its surroundings that persists in the models from ~60 to at least 140 km depth, indicating an anomalously thin lithosphere and demonstrating that the assumption of a nearly constant lithospheric thickness across the area, previously adopted, is not valid. Phase velocity data at key locations are inverted using integrated geophysical-petrological inversion, to estimate the thermal structure of the lithosphere-asthenosphere system consistent with the seismic data, surface elevation, and heat-flow. The circum-Irish Sea area reveals a pronounced lithospheric thinning and matches the region of the Paleogene uplift previously suggested to be caused by a lateral branch of the Iceland mantle plume, which may have flowed into thin lithosphere areas surrounded by continental lithosphere during the evolution of the North Atlantic Ocean over the past 60 M.y. Our results show a striking correlation between lithospheric thickness and exhumation thermochronological measurements (as well as proposed underplating thickness, denudation, and the locations of the intraplate volcanism of the enigmatic North Atlantic Igneous Province) suggesting a significant lithospheric control on the volcanism of the area.

How to cite: Bonadio, R., Lebedev, S., and Chew, D.: Lithospheric control on the Paleogene uplift and volcanism in Ireland and Britain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7579, https://doi.org/10.5194/egusphere-egu23-7579, 2023.

EGU23-8214 * | ECS | Posters on site | SM5.1 | Highlight

Geophysical characterization of the Krafla volcanic area from seismic tomography and attenuation 

Maria Aurora Natale Castillo and Magdala Tesauro

Exploration and exploitation of natural resources, such as geothermal energy, require a proper understanding of the physical properties of the upper crust, where they are mostly allocated. Indeed, the transition from brittle to ductile deformation (BDT), occurring at these depths, marks a progressive change in crustal rheology and a reduction in the rock’s permeability. Therefore, the characterization of underground conditions is crucial for planning explorative studies in geothermal systems. It has been recently demonstrated that the analysis of the propagation of seismic waves provides information on physical rocks’ behavior and an alternative assessment of the BDT depth [1]. In particular, the decay of the amplitude of the seismic waves (i.e. seismic attenuation), which is usually described by a “quality factor” Q, depends on the seismic frequency, temperature, water content, and grain size of the rocks. Depending on the seismic scale, it could be used as an indicator of subsurface heterogeneities.    

In this study, we investigate the seismic velocity and attenuation sensitivity to the crustal heterogeneities in areas affected by young tectonics and hot thermal conditions. To this aim, we implement a Q seismic tomography in the volcanic system of Krafla. The volcanos of age 0.5–1.8 Myr extend over an area of 21 km by 17 km and are characterized by faults and fissures, which allow water to penetrate and circulate at shallow depths [2] easily. In these geothermal fields, the temperatures, in a range of 400-600 °C at a depth < 5 km [3], make the BDT depth close to the surface.

We apply the method that solves Qp perturbations, using a combination of a spectral decay technique to retrieve the attenuation operator (t*) and tomographic inversion [4]. The distribution of seismic wave velocities is obtained from a 3D tomographic inversion, using 1453 earthquakes detected from a local seismic network (2009-2012) [2]. Qp inversion is performed with the simul2014 algorithm [5], while a linearized technique solves a nonlinear problem that uses a damped least-squares inversion for model perturbations.

We obtain a map of Qp variations for the first 4 km, which we jointly interpret with the seismic wave velocities [2]. In this way, we can discriminate between anomalies related to temperatures and compositional heterogeneities. We also test the possibility to detect the BDT depth on the base of the reduction of the Qp, related to hot temperatures/melt conditions. The obtained results will contribute to understanding the dynamics of the tectonic features and help plan explorative studies of high enthalpy geothermal systems, adding constraints to the correlation between viscous rocks’ deformation and their seismic attenuation.

References

[1] Natale Castillo et al., 2022. Gloplacha 219, 103978, ISSN 0921-8181, https://doi.org/10.1016/j.gloplacha.2022.103978.

[2] Schuler et al., 2015. J. Geophys. Res. Solid Earth 120, 7156–7173, doi:10.1002/2015JB012350.

[3] Scott et al., 2015. Nature communications 6, 7837. 10.1038/ncomms8837. https://doi.org/10.1038/ncomms8837.

[4] Lanza et al., 2020. J. Volc. Geoth. Res. 393, 106804, ISSN 0377-0273. https://doi.org/10.1016/j.jvolgeores.2020.106804

[5] Evans et al., 1994. US Geological Survey Open File Report OFR 94- 431, p. 101. https://doi.org/10.3133/ofr94431

How to cite: Natale Castillo, M. A. and Tesauro, M.: Geophysical characterization of the Krafla volcanic area from seismic tomography and attenuation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8214, https://doi.org/10.5194/egusphere-egu23-8214, 2023.

Ocean Bottom Seismometers (OBS), in conjunction with an active source, have for a longtime been used to investigate the crust and upper mantle. Conventionally a number of Seismometers are deployed along a line with relatively large separation (several kilometers) between each instrument. A large air-gun array is then used to create a number of recordings with distance between the receiver and source varying from zero up to several hundred kilometers.

The data is usually analyzed with tomographic methods leading to a P-wave velocity model. Tomographic methods tend to produce velocity models with low resolution and lack of details. To increase resolution the Full Waveform Inversion (FWI) can be used. Velocity models estimated using FWI shows better resolution and are better constrained than tomographic models.

Our work sets out to develop a FWI workflow for a sparsely sampled OBS data. We demonstrate high resolution crustal-scale velocity model building workflow based FWI for a deep water and sparse (6km) sampled 300 km long wide-angle OBS data. We use an initial model traveltime tomography inversion. We apply waveform inversion to constrain crustal and upper mantle layers more confidently and with increased resolution compared to conventional traveltime tomography with layer-based parameterization. FWI allows to reduce significantly data-fit error (i.e. rms error) and explains better larger offsets of an observed data compared to traveltime tomography.

The workflow is developed and applied to data acquired in 2009 in the Japan Trench where the 130-150 Myrs old oceanic plate is subducting under Eurasia. Subduction zones plays an important role in Earth tectonics . Traveltme tomography inversion was used the 2009 Japan Trench dataset to construct velocity models and showed that P-wave velocities close to the trench axis, where the plate bends downward, are systematically lower than the P-wave velocities at larger seaward distances. This is interpreted as water penetration into the plate from the seafloor, causing serpentinization which decreases P-wave velocities. However, tomographic models does not reveal details of the velocity model, only smoothed averages. We hope that a velocity model generated by FWI has sufficiently increased resolution to reveal more details of the water penetration and geological setting along the Japan Trench.

 

How to cite: Arntsen, B., Khakhorov, U., and Weibull, W.: Crustal-scale Vp velocity model building for a sparse regional OBS survey using full-waveform inversion: a case study from Japan Trench, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8657, https://doi.org/10.5194/egusphere-egu23-8657, 2023.

A knowledge of Antarctica’s lithospheric properties is essential for understanding tectonic history and solid-earth influences on ice sheet dynamics. For example, the spatial variation of mantle temperature impacts both geothermal heat flow and mantle viscosity, which influence the ice sheet basal melt rate and glacial isostatic adjustment. Seismic tomography models can be used to constrain the mantle temperature. However, seismic velocity to temperature conversion is sensitive to variations in mantle composition, which are linked to changes in density that are also resolved in the gravity field.

Here we model Antarctica’s density distribution using a 3D finite element gravity inversion approach based on the esys-escript model in python. We derived a correction to an initial density distribution based on a seismic tomography model (ANT-20). From the resulting density distribution and the initial seismic velocity distribution we estimated mantle temperature and composition and calculated the lithosphere thickness, mantle viscosity, and geothermal heat flow. The result shows that East Antarctica has a dense, thick (>150 km) and cold lithosphere, whereas West Antarctica has a thin (<100 km) hot lithosphere. The new heat flow model suggests a higher heat flow estimation than previous continental scale estimations.

Our result highlights compositional heterogeneity within East Antarctica, with a highly depleted cratonic mantle in central East Antarctica. By considering compositional change, modelled mantle temperature increases up to 150 °C in depleted regions to accommodate lower density with fast seismic velocity. Higher modelled temperatures cause reduced lithospheric thickness up to 80 km compared with the initial model. In comparison to previous results in interior East Antarctica, a 5-10 mW/m2 higher heat flow is suggested by our model. In West Antarctica, large areas show heat flow of up to 110 mW/m2. Our result also suggests low mantle viscosity including Amundsen Sea Embayment, Marie Byrd Land and Antarctic Peninsula.

How to cite: Li, L., Aitken, A., Gross, L., and Codd, A.: Density, temperature and composition of Antarctica’s lithosphere and impact on geothermal heat flux and mantle viscosity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10364, https://doi.org/10.5194/egusphere-egu23-10364, 2023.

Adjoint-state traveltime tomography (ATT) is a new modality of traveltime tomography for determining subsurface velocity heterogeneity and seismic anisotropy. It formulates the tomographic inverse problem as an eikonal equation-constrained optimization problem solved by the ray-free adjoint-state method. Instead of using the ray-based methods, the theoretical traveltime is predicted by solving the anisotropic eikonal equation in spherical coordinates using the robust grid-based fast sweeping method. The influences of the seismic anisotropy and the Earth’s curvature are taken into account. Besides, the Fréchet derivatives of the objective function with respect to velocity and anisotropy are computed based on the adjoint field obtained by solving the adjoint equation without ray tracing. These two improvements ensure the accuracy of the forward modeling and avoid the potential failure of ray tracing techniques. Meanwhile, compared with wave-equation-based tomography methods, the computational cost of solving eikonal and adjoint equations is drastically cheaper. The usage of the reciprocity principle makes the computation cost nearly independent of the number of earthquakes, enabling the inversion involving massive earthquakes but with moderate computational cost. Due to these advantages, we develop the TomoATT package based on the ATT method, accommodating the tomographic problems on local, regional, and global scales. To be used on high performance computing systems, TomoATT implements a multilevel hybrid parallel algorithm, which utilizes MPI for inter-node parallelization and MPI Shared Memory for intra-node parallelization. The performance on single CPU is also improved using the Single Instruction Multiple Data (SIMD) instructions. This traveltime tomography package has been tested and verified in central California near Parkfield.

How to cite: Chen, J., Nagaso, M., and Tong, P.: TomoATT: A Software Package of Adjoint-State Traveltime Tomography for Imaging Subsurface Velocity Heterogeneity and Seismic Anisotropy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10556, https://doi.org/10.5194/egusphere-egu23-10556, 2023.

The Wave Gradiometry Method(WGM) has emerged as a powerful multipurpose tool to  extract strain and rotation tensor, identify phases, and most importantly to image the near surface or deep structure. The WGM measures the spatial gradients of the wavefield within a subarray to extract 4 major attributes: phase velocity, wave directionality, geometrical spreading and radiation pattern. These attributes can be further used to extract strain and rotation tensor (Langston and Liang CT, 2008; Sollberger et al. 2016) and structural information. An azimuth-dependent dispersion curve inversion (ADDCI, Liang et al. 2020) is applied together with the WGM method to extract both 3D shear wave velocity and 3D azimuthal anisotropy. Additionally, the geometrical spreading extracted by the WGM is used to find the attenuation of the materials. In this study, we review the theoretical foundation, technical development, major applications of the WGM and compare the WGM with other major array-based imaging method.

 Similar with the Ambient Noise tomography, the WGM is also boiled down to dispersion curve inversion. Even though it can be applied to arrays with a wide range of scales, here we concentrate on the applications to large scale arrays such as the USARRAY (average spacing of 70km), CHINARRAY (average spacing of 40km). It may also be applied to any other dense regional array, such as the ALPARRAY and others. The imaging depth is only limited by the corner frequency of the seismometer. We will compare our results with that from other techniques to highlight its advantage and disadvantages.

References:

Cao F H, Liang C T. 2022, 3D velocity and anisotropy of the southeastern Tibetan plateau extracted by joint inversion of wave gradiometry, ambient noise, and receiver function, Tectonophysics, https://doi.org/10.1016/j.tecto.2022.229690

Cao, F., Liang, C., Zhou, L., & Zhu, J. (2020). Seismic azimuthal anisotropy for the southeastern Tibetan Plateau extracted by Wave Gradiometry analysis. Journal of Geophysical Research: Solid Earth, 124, e2019JB018395.  https://doi.org/10.1029/2019JB018395

Liang, C., Liu, Z., Hua, Q., Wang, L., Jiang, N., & Wu, J. (2020). The 3D seismic azimuthal anisotropies and velocities in the eastern Tibetan Plateau extracted by an azimuth‐dependent dispersion curve inversion method. Tectonics, 39, e2019TC005747. https://doi.org/10.1029/2019TC005747 

Langston, C. A. (2007). Wave gradiometry in two dimensions. Bulletin of the Seismological Society of America, 97(2), 401–416. https://doi.org/10.1785/0120060138 

Porter R, Liu YY, and Holt WE (2016). Lithospheric Records of Orogeny within the Continental U.S.. Geophysical Research Letters, 43(1), 144–153. https://doi.org/10.1002/2015GL066950

Sollberger D Schmelzbach C, Manukyan E, Greenhalgh SA, Van Renterghem C and Robertsson JOA (2019). Accounting for receiver perturbations in seismic wavefield gradiometry. Geophysical Journal International, 218(3), 1748–1760. https://doi.org/10.1093/gji/ggz258.

How to cite: Liang, C., Cao, F., and Liu, Z.: A Review on the Wave Gradiometry Method and Applications to Image the 3D Shear Wave Velocity, Anisotropy and Attenuation of the Lithosphere and Asthenosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10671, https://doi.org/10.5194/egusphere-egu23-10671, 2023.

EGU23-11063 | ECS | Orals | SM5.1

Crustal and Uppermost Mantle Structure beneath the Indian Ocean Geoid Low using Surface Wave Tomography 

Silpa Sundaran, Bommoju Padma Rao, and Satish Maurya

The Indian Ocean Geoid Low (IOGL) is a significant negative geoid anomaly (-106 m), located south of the Indian subcontinent. Several studies have been carried out to investigate the causes responsible for IOGL, results indicate that its origin could be low velocity/density anomalies in the depth range of mid-to-upper mantle and/or high velocity/density anomalies in the depth range of lower mantle. However, a concrete model to explain the origin of IOGL and especially the effect of the shallow structure on IOGL is still enigmatic. In the present study, we investigate the high-resolution 3D shear velocity structure beneath the Indian Ocean region down to a depth of 300 km using surface wave tomography. For this analysis, collated extensive data from more than 700 broadband seismological stations of various data centres (IRIS: Incorporated Research Institutions for Seismology, FDSN: International Federation of Digital Seismograph Networks, IN: Indian Stations) to obtain a good azimuthal and spatial coverage. This dataset has been pre-processed and utilized to measure the fundamental mode of Rayleigh wave group velocities sampling the IOGL region. Further, visually checked the quality of the dispersion curves and considered only good-quality ones, which resulted in ~19,300 good-quality dispersion curves in a frequency range of 10-120 s and then applied the regionalization to extract the geographical distribution of local group velocities in different periods. Later, inverted the regionalized dispersion data using the trans-dimensional inversion approach. Regionalized shear wave velocity maps are in good agreement with surface tectonics such as low-velocity anomalies along the large-scale ridges and previous tomography studies. The western Indian Ocean shows very fast velocity anomalies at short-period (~20 s) and low-velocity anomalies in long periods (>100 s) which could be attributed to the magmatic underplating originating from the various hotspots and the presence of channelled flows asthenosphere towards eastward to spreading ridges. Further, the results rules-out that the contribution of the lithosphere could be negligible in explaining the IOGL as there are no low-velocity anomalies beneath the IOGL region. In addition, the obtained high-resolution regional surface wave tomography from this study enables the research community to obtain/measure the precise IOGL anomaly and understand the detailed tectonics and crustal/lithospheric deformation beneath the study region.

How to cite: Sundaran, S., Rao, B. P., and Maurya, S.: Crustal and Uppermost Mantle Structure beneath the Indian Ocean Geoid Low using Surface Wave Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11063, https://doi.org/10.5194/egusphere-egu23-11063, 2023.

EGU23-12551 | ECS | Posters on site | SM5.1

Rayleigh phase velocity maps for central Europe including the Eifel volcanic province 

Tatjana Weiler, Amr El-Sharkawy, and Thomas Meier

High-resolution Rayleigh phase velocity maps can help to improve our understanding of the 3-D vs anisotropic structure of the lithosphere of central Europe and its relationship to surface tectonics and volcanism.
Using seismic broad-band recordings for the time period from 1990 to 2020, 600,000 inter-station fundamental mode Rayleigh wave phase velocities have been automatically determined by performing strict quality checks. Only smooth and reliable phase velocity curves with path-wise averaging and a standard error of 0.5% were chosen. For periods between 8 s and 350 s azimuthally anisotropic phase velocity maps were calculated for Central Europe. The phase velocity maps at short periods of up to 30 seconds show an NW-SE fast propagation direction along the East European Craton. At periods longer than 60 s, the anisotropic fast propagation direction shows slight variations from NE-SW to ∼N-S. At 150 s map, a NE-SW fast direction is observed. This might indicate a layering of anisotropy. Along the Tornquist-Teisseyre Zone, the fast propagation direction at all periods is NW-SE, except along its northern part as it shows slight variations. This might be due to the sharp change from the Precambrian continental mantle lithosphere to the younger Phanerozoic Europe. At short periods, central Europe anisotropy is following the Variscan front which changes abruptly to SE-NW near the Elbe line, whereas at longer periods the fast direction follows the Rheic suture and Saxothuringian suture.
For the inversion of local azimuthally anisotropic phase velocity curves, we apply a newly elaborated stochastic inversion algorithm, the Particle Swarm Optimization algorithm (PSO). The result for extensive inversion and parameter tests of Rayleigh dispersion curves tests are shown. The lateral, as well as the vertical resolution of the resulting azimuthally anisotropic S-wave velocities and indications for layered anisotropy, are discussed.  

How to cite: Weiler, T., El-Sharkawy, A., and Meier, T.: Rayleigh phase velocity maps for central Europe including the Eifel volcanic province, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12551, https://doi.org/10.5194/egusphere-egu23-12551, 2023.

EGU23-12936 | Orals | SM5.1

Pushing the limits of the Marchenko method 

Kees Wapenaar and Joeri Brackenhoff

In recent years, the Marchenko method has proven to be a viable tool to create virtual seismic sources and receivers in the subsurface from reflection measurements at the surface. Applications range from suppressing internal multiples in seismic imaging to forecasting responses to induced seismic sources. One of the attractive aspects of the Marchenko method is that no detailed subsurface model is needed; a smooth background model suffices. All information needed to treat the internal multiples correctly comes from the reflection measurements at the surface. 

One of the underlying assumptions of the Marchenko method is that the seismic wave field can be decomposed into downgoing and upgoing waves at any position in the subsurface where one wants to create a virtual source or receiver. Although in many situations this implies no significant restrictions, it may hamper the imaging of steeply dipping flanks and it prevents the treatment of refracted and evanescent waves.

It can be shown that the Marchenko focusing function (the nucleus of the Marchenko method) can be expressed in terms of the so-called propagator matrix. The propagator matrix, which was introduced in geophysics in the nineteen-sixties for 1D systems and developed further in the nineteen-seventies for laterally varying 3D media, ‘propagates’ a wave field from one depth level to another. It does not rely on up-down decomposition and it accounts for propagating waves at all angles and for evanescent waves. By exploiting the link between the Marchenko focusing function and the propagator matrix, the applicability of the Marchenko method can be expanded. In the presentation we will review the underlying theory and discuss the potential application of the Marchenko method for refracted waves.

How to cite: Wapenaar, K. and Brackenhoff, J.: Pushing the limits of the Marchenko method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12936, https://doi.org/10.5194/egusphere-egu23-12936, 2023.

EGU23-13540 | ECS | Posters on site | SM5.1

Back and Through the Looking Glass - Space-time scattering of elastic waves 

Johannes Aichele, Jonas Müller, Zabreen Nissar, Dirk-Jan van Manen, and Marc Serra-Garcia
Due to causality wave scattering in time is simpler than scattering in space: In
contrast to multiple spatial boundaries, there are no infinite reflections between
temporal boundaries. Salem and Caloz, 2015 [1] showed that wave scatter-
ing can be simplified by constructing a time-space cross-mapping. We identify
the cross-mapped wavefields as the Focusing functions developed in data-driven
geophysical imaging. Experimentally, Bacot et al, 2016 [2] have shown that
time modulation of the medium properties of a capillary-gravity wave results in
time-refraction and time-reflection of the original wave. This experimental re-
sult should hold true for any system obeying Alembert’s equation. This should
in principle allow us to physically compute wavefields for the single-sided inverse
scattering problem through forward scattering experiments. We set up a sim-
ple comb-like discrete system for time-modulated 1D elastic wave propagation.
Elastic beams act as the masses and an electrostatic force as the springs of our
system. The effective coupling stiffness between the beams is modulated in time
through a variation of the electrostatic force. A Galerkin based wave propaga-
tion model shows that an experimental realization of hundreds of beams can be
achieved through micro-machining. Through time-modulations of the system’s
wavespeed a broadband excitation is refracted and reflected everywhere in space.
Time-scattering preserves the wave vector k, which implies that the frequency
ω is not conserved. To elucidate the dispersion relation at time boundaries,
we employ a correction method for spatial dispersion. Herefore, a correction
method for time-dispersion in finite difference simulations developed by Koene
et al 2018 [3] is mapped to the spatial dimension of our meta-material.
[1] Salem, Mohamed A., and Christophe Caloz. “Space-Time Cross-Mapping
and Application to Wave Scattering.” ArXiv:1504.02012 [Physics], April 7, 2015.
http://arxiv.org/abs/1504.02012. [2] Bacot, Vincent, Matthieu Labousse, An-
tonin Eddi, Mathias Fink, and Emmanuel Fort. “Time Reversal and Holography
with Spacetime Transformations.” Nature Physics 12, no. 10 (October 2016):
972–77. https://doi.org/10.1038/nphys3810. [3] Koene, Erik F M, Johan O A
1
 
 
Robertsson, Filippo Broggini, and Fredrik Andersson. “Eliminating Time Dis-
persion from Seismic Wave Modeling.” Geophysical Journal International 213,
no. 1 (April 1, 2018): 169–80. https://doi.org/10/gcz9wb.

How to cite: Aichele, J., Müller, J., Nissar, Z., van Manen, D.-J., and Serra-Garcia, M.: Back and Through the Looking Glass - Space-time scattering of elastic waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13540, https://doi.org/10.5194/egusphere-egu23-13540, 2023.

EGU23-14389 | ECS | Orals | SM5.1

Integrated geophysical-petrological inversion of surface wave and other data for the lithological structure of the Iberian crust 

Carlos Clemente-Gómez, Javier Fullea, and Mariano S. Arnaiz-Rodríguez

The Earth’s crust hosts most of the geo-resources of societal interests (e.g. minerals, geothermal energy etc.). Integrative approaches combining geophysical and petrological observations to study the mantle assuming thermodynamic equilibrium are relatively common nowadays. However, in contrast to the mantle, where thermodynamic equilibrium is prevalent, vast portions of the crust are thermodynamically metastable. This is because equilibration processes are essentially temperature activated and the temperature in the crust is usually too low to trigger them. Consequently, the mineralogical assemblage of crustal rocks is mostly decoupled from the in situ pressure and temperature conditions, reflecting instead the conditions present at the moment of rock formation. Here we present a new methodology for integrated geophysical-lithological multi-data modelling of the crust. Our primary constraining data are fundamental mode Rayleigh wave surface wave dispersion curves determined by interstation cross-correlation measurements and teleseisms, as well as surface elevation (isostasy) and heat flow. Additional prior information is provided by P-wave velocities coming from controlled source and body wave tomography data. The inversion is framed within an integrated geophysical-petrological setting where mantle seismic velocities and densities are computed thermodynamically as a function of the in situ temperature and compositional conditions. In the crust we invert for a three-layered crust defined by Vs, density and Vp/Vs ratios (or Poisson coefficients) linked according to statistical correlations from global petrophysical data sets. The new methodology is applied to the Iberian Peninsula and adjacent margins where we jointly invert for both the crustal and lithospheric mantle structure. Our results show that the Iberian upper-middle crust is characterized by a clear dichotomy between the high Vs and felsic lithologies (Vp/Vs<1.76) in the Iberian Massif, and the low Vs and mafic lithologies (Vp/Vs>1.81) in the Betic, Pyrenees and Cantabrian Alpine mountain chains. The pattern changes in the lower crust where we obtain felsic lithologies  in  the Central system, NE Betics and N Mediterranean margin, and mafic lithologies in the Ossa-Morena, South-Portuguese, Galician, and Asturian-Leones terranes in the Variscan Iberian Massif. Overall we find a good correlation with previous geophysical studies (receiver functions, controlled source seismics) and the petrology of the main magmatic episodes since the Neoproterozoic (575 Ma).

How to cite: Clemente-Gómez, C., Fullea, J., and Arnaiz-Rodríguez, M. S.: Integrated geophysical-petrological inversion of surface wave and other data for the lithological structure of the Iberian crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14389, https://doi.org/10.5194/egusphere-egu23-14389, 2023.

EGU23-15581 | Orals | SM5.1

Seismic tomography software tools at Barcelona Center for Subsurface Imaging 

Clara Estela Jimenez Tejero, Cesar R. Ranero, and Valenti Sallares

Seismic methods are one of the most powerful existing geophysical tools to extract information on the structure of the Earth’s subsurface. These techniques continue to be widely used to obtain images of the sediments and crust and to map the variations in physical properties. Particularly the P-wave velocity (Vp) distribution is the most commonly modelled property. 

The most widely applied seismic method to retrieve velocity models is seismic tomography, using either travel-time information as in travel-time tomography (TTT) or a more complete set of waveform attributes in full-waveform inversion (FWI). Whereas TTT is a robust, moderately non-linear technique providing coarse models, FWI is strongly non-linear and computationally demanding, but with the potential to provide higher resolution models. TTT and FWI are considered to be complementary, so that they are often combined and applied together. TTT is applied first to get a moderate-resolution model, which is then used as an initial model for FWI. In fact, the key to successfully apply FWI to seismic data, is the usage of a kinematically correct initial model, in which simulated and recorded waveforms are not cycle-skipped at the lowest frequency available. On this basis, it is crucial to extract the travel-time information of the refracted waves as accurate as possible. Particularly for marine multichannel reflection seismic (MCS) acquisition systems, where most refractions are masked by reflections and noise, data processing techniques like Downward Continuation (DC) allows to better retrieve refractions, and this is achieved by virtually redatuming streamer field data to the seafloor. 
 
We aim at showing the different user-friendly open source HPC software designed and built in the Barcelona Center for Subsurface Image (BCSI) to process seismic data from marine experiments, recorded by ocean bottom seismometers (OBS) and/or multichannel seismic (MCS) data recorded by towed streamers. The three tools, DC, TTT, and FWI, which can be used independently and/or combined together for a better performance, have the potential to produce high resolution models of the physical properties of the subsurface. While DC software is designed for 2D seismic data, the TTT tool also read 3D data, and allows the joint inversion of Vp, Vs and anisotropic properties for active and passive data, including earthquake relocation. At present, DC and TTT software tools are freely available and the last version updated at GitHub repositories and the FWI tool for 2D data is under development.

How to cite: Jimenez Tejero, C. E., R. Ranero, C., and Sallares, V.: Seismic tomography software tools at Barcelona Center for Subsurface Imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15581, https://doi.org/10.5194/egusphere-egu23-15581, 2023.

EGU23-15781 | ECS | Posters on site | SM5.1

Rayleigh and Love wave tomography from seismic noise of the North African and South Iberian Peninsula lithospheric structure and collision zone 

Alejandra Neri, Said Badrane, Beatriz Gaite, Antonio Villaseñor, Roberto Cabieces, César R. Ranero, and Arantza Ugalde

With more than 40 years of study, there are still uncertainties about the structure, evolution, and geodynamics of the North African and South Iberian Peninsula lithospheric structure and collision zone. Models of the lithosphere of the region coincide in some anomaly zones, such as the subduction slab under the Gibraltar arc. However, they show discrepancies in the distribution and polarity of the velocity anomalies in the onshore and offshore of most of North Africa.

To contribute to the study of the lithospheric structure and to unveil the tectonics in this controversial region, we constructed an ambient noise tomography (ANT) of Love and Rayleigh waves from temporary and permanent broadband stations located in the Iberian Peninsula, North Africa, and Atlantic islands (Madeira, Canarias, Balearic Islands). 

The methodology employed contemplates phase cross-correlation of 14 months of ambient noise records and the subsequent stacking of the cross-correlograms to obtain the Empirical Green's Function (EGF). To measure the dispersion characteristics of surface wave EGFs present in the ambient noise, we implemented the Frequency-Time Analysis (FTAN). And finally, the inversion of the dispersion measures to get the surface wave tomography.

The distribution of the almost 100 broadband stations in North Africa, Portugal, Spain, and the Atlantic islands, results in a broad path coverage in the North African and South Iberian Peninsula lithospheric structure and collision zone, complementing the previous Rayleigh wave velocity models. Furthermore, current studies in this region are Rayleigh-waves based, so the integration of Love waves in this ANT yields new information on the media velocity anisotropy.

How to cite: Neri, A., Badrane, S., Gaite, B., Villaseñor, A., Cabieces, R., Ranero, C. R., and Ugalde, A.: Rayleigh and Love wave tomography from seismic noise of the North African and South Iberian Peninsula lithospheric structure and collision zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15781, https://doi.org/10.5194/egusphere-egu23-15781, 2023.

EGU23-17461 | ECS | Posters on site | SM5.1

Ambient Noise and Earthquake Surface Wave Phase Velocity Tomography of the South American Lithosphere 

Lúcio Quadros de Souza, Amr El-Sharkawy, Marcelo Assumpção, and Thomas Meier

The development of new automated techniques to measure earthquake-based interstation phase velocities allows for more detailed imaging of the South American Lithosphere. We calculated Rayleigh-wave phase velocities using the earthquake records from 1022 broadband seismic stations (South America, Antarctica and the Caribbean) operated between 1990 and 2020. A total of 1.069.259 earthquakes were selected with the following criteria: (1) events aligned within 10° of the 2-station great circle path; (2) a linearly increasing minimum magnitude between 4 and 6 Mw as a function of the epicentral distance; (3) maximum magnitude of 8 Mw; and (4) epicentral distances between 2.5° and 30°.
We used surface wave fundamental mode dispersion curves calculated automatically using a new implementation of the 2-station cross-correlation method and a number of strict quality criteria, which include the selection of the phase velocity curves based on a 3D background model, curve smoothness and width of the considered frequency range. Following this process, we obtained 46.763 broad-band dispersion measurements between 4 and 315 s. Finally, the single-event dispersion curves were averaged for each interstation pair with associated error estimates and further quality control comparing results from both directions, evaluating smoothness and the standard deviation of the resulting dispersion curve.
The dispersion curves were simultaneously inverted for isotropic and anisotropic (2ψ and 4ψ) phase-velocity maps parameterized on a triangular grid with a knot spacing of 30 km.
The isotropic phase velocity maps at periods of 15 and 30 s indicate around 8% high-velocity perturbations in the regions of: (1) cratonic blocks of the South American platform (Brazilian Shield, São Francisco and Rio Apá cratons); and (2) the basement of the Pantanal basin (a 500 m thick sedimentary basin) possibly related to a high-velocity lower crust. For those periods, we also observed between -8 to -4% low-velocity perturbations associated with the Andean Mountain range root below the Altiplano Boliviano region (central Andes), the forelands of the Andes. The Paraná, Chaco and Parecis intracratonic basins also have lower velocities with relation to the neighboring cratonic areas.
At periods of 60 and 100 s, we observed around 4% high-velocity perturbation associated with the deep roots of the oldest region of the Amazonian craton (eastern area of the Brazilian Shield) and the São Francisco craton. Azimuthal anisotropy is laterally and vertically variable within the South American lithosphere. At longer periods, fast directions are pointing to asthenospheric flow guided by LAB topography, for example below the Pantanal basin (central-west Brazil).
For the next steps, we plan to jointly invert for a isotropic and anisotropic 3D model using earthquake and ambient noise dispersion curves with Rayleigh and Love waves.

How to cite: Quadros de Souza, L., El-Sharkawy, A., Assumpção, M., and Meier, T.: Ambient Noise and Earthquake Surface Wave Phase Velocity Tomography of the South American Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17461, https://doi.org/10.5194/egusphere-egu23-17461, 2023.

EGU23-28 | ECS | Posters virtual | SM5.2

The 2D resistivity measurement eror and its effect on the model accuracy 

Yonatan Garkebo Doyoro and Ping-Yu Chang

We examine the measurement noise of electrical resistivity tomography and assess its effect on the inverted results. The observed and numerically simulated resistivity datasets are analyzed regarding noise distributions. We evaluate and present the contact resistance, reciprocal and repeating errors, potential noise, artificial effect on 2D resistivity measurement, inversion misfit, and model accuracy. The result shows considerable measurement noise variation for dry and wet conditions. This study uses a 3% repeatability error cut-off, and about 3.2% of the dry season and 0.83% of the wet season datasets are above cut-off values.  The result also exhibits an inverse relationship between the precipitation and reciprocal error. The resistivity measurement in dry conditions generally indicates high contact resistance, repeatability error, and reciprocal errors, resulting in significant data discarding. We also reveal the misfit between observed and model-predicted resistivity data; a high discrepancy is exhibited for noisy data, leading to substantial model error. The depth of investigation (DOI) threshold depth decrease with increasing measurement noise. This study will give insight into measurement noise evaluation, allow cut-off value, assess data noise propagation and its effects on the data misfits and inverted models, and reduce model misinterpretation.

How to cite: Doyoro, Y. G. and Chang, P.-Y.: The 2D resistivity measurement eror and its effect on the model accuracy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-28, https://doi.org/10.5194/egusphere-egu23-28, 2023.

EGU23-313 | ECS | Orals | SM5.2

Identification of Point Diffractor body placed in dipping Vertically Transverse Isotropic medium using Reverse Time Migration 

Saurabh Sharma, Anand Joshi, Jyoti Singh, Mohit Pandey, Richa Rastogi, and Abhishek Srivastava

Numerical modelling has been proved as an incomparable tool to understand the structure of the earth and the processes beneath the earth’s surface. Finite difference method (FDM) plays a dominant role among various numerical methods for the purpose of seismic modelling and exploration. FDM provides a comprehensible solution to the partial difference equations defining the propagations of seismic wave. These partial differential equations consist of derivatives in time and space domain. FDM can be applied by defining the elastic wave-field and model parameters at every position on a discrete mesh. Reverse-time migration (RTM) is based on exploding reflector model and it is better than other migration techniques for the interpretation of various seismic models. The present work shows the forward modelling and reverse time migration of point diffractor body placed in dipping layer of vertically transverse isotropic (VTI) medium. A 12th order space and second order time differentiation RTM scheme have been used to interpret the location and extent of a point diffractor placed in dipping layer of VTI medium. The earth model under study is of the size 1400 m x 600 m. A dipping layer and a diffractor of size 18 m x 18 m has been placed in the VTI model. The FORTRAN code developed for FDM scheme of VTI model performs various requisite studies like stability criteria, numerical dispersion and the boundary conditions within the code. The output from the FDM code are the synthetic records at surface which after processing fed as an input in the FORTRAN code developed for RTM scheme. The position and extent of the diffractor placed in the dipping VTI medium layer has been detected properly using RTM scheme. Another FORTRAN code is developed in which forward and reverse wave propagation snapshots has been cross-correlated using various cross-correlation imaging conditions. A Laplace filter is then designed to efficiently resolve the position and extent of the diffractor in the dipping VTI medium layer.

How to cite: Sharma, S., Joshi, A., Singh, J., Pandey, M., Rastogi, R., and Srivastava, A.: Identification of Point Diffractor body placed in dipping Vertically Transverse Isotropic medium using Reverse Time Migration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-313, https://doi.org/10.5194/egusphere-egu23-313, 2023.

The Horizontal-to-Vertical Spectral Ratio (HVSR) method and Multi-Channel Analysis of Surface Waves (MASW) method are commonly used as a joint fit technique to retrieve the 1-D shear wave velocity. The Kumaon Himalaya consists of major thrusts like MFT, MBT, SAT, NAT and MCT, from South to North) and other tectonic features. These geological structures are observed in the form of lineaments on the surface. In the present study, 2-D section of shallow shear wave velocity structure has been estimated along the transect crossing South Almora Thrust (SAT) in the Kumaon Himalaya to study the variation of shear wave velocity across the thrust. In the present work, the ambient noise survey and Multi-Channel Analysis of Surface Wave (MASW) survey has been conducted along the road profile crossing the South Almora Thrust (SAT) at equally spaced stations of 3 Km. The 1-D shear wave velocity has been used to prepare the 2-D section of shear wave velocity. The lineaments in this division have been identified by the variation in the two dimensional shear wave velocity section prepared from the so obtained 1-D shear wave velocity in this profile. The study shows that there is a good correlation between variation of shear wave velocity in the region and major tectonic features of the area. The geological sections in this area has been compared with the obtained 2D structure which give a fair amount of idea about dip of SAT in this area.

How to cite: Pandey, M., Joshi, A., Sharma, S., and Singh, J.: Shear wave velocity variation across the South Almora Thrust, Kumaon Himalaya using Joint Inversion of Horizontal-to-Vertical Spectral Ratio (HVSR) and Dispersion curve, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-879, https://doi.org/10.5194/egusphere-egu23-879, 2023.

The Radio-Magnetotelluric (RMT) method is a geophysical near-surface imaging technique with a broad range of possible applications. In 2020, the GFZ Potsdam has acquired a newly developed horizontal magnetic dipole transmitter that allows the application of the RMT method even in regions with an insufficient coverage of radio transmitters which normally serve as source signal. First controlled-source RMT measurements were conducted at three different locations in Chile in 2020. Further measurements were recently conducted in Ireland.  As we are able to store the raw time series, we have full control over the subsequent data processing. The processing tools at GFZ include the modular processing suite EMERALD, which was originally designed for MT processing, but has recently been adapted to process RMT data. One main difference is that in RMT the transmitter data is considered as signal, while in natural source MT this would be regarded as electromagnetic noise that needs to be removed using automated robust statistical approaches. However, processing the entire time series in an automated manner has a large drawback: The different emitted frequencies are transmitted in a sweep implying that only a smaller fraction of the time series contains the required signal for a particular target frequency and leading to an unfavourable signal-to-noise ratio. Since it is technically impossible to have the same time base for the data logger and the transmitter with an accuracy of a few nanoseconds, an automated detection scheme is required to find time segments that contain the transmitter signal. Usually, several Gigabytes of raw time series are collected during field measurements, making manual editing and supervision of the time series virtually impossible. However, a careful selection of appropriate time segments is essential for the success of the data processing. To address the challenge, machine learning algorithms have a high potential to solve both problems. Initial experience was gained with a recurrent neural network approach in order to identify suitable time segments (Patzer & Weckmann, EMTF 2021 – conference contribution and personal communication). However, many questions remained open, e.g. if other machine learning algorithms can result in better performances, which machine learning algorithms are in principle suitable for the characteristics and properties of RMT time series and which parameters should be used as input variables (features) for the algorithms. A large number of machine learning algorithms exist, which can be divided into different groups according to their operating principle and their activity fields. We will test unsupervised methods, especially for clustering the data, to identify a set of suitable input variables. Subsequently, we will use these features to train supervised algorithms as logistic regression, support vector machine and different kinds of neural networks to find the best performing algorithm. We will mainly use the RMT data from Chile within the training process. Furthermore, we will test if the trained algorithm is applicable to other new data sets measured at different locations (e.g. Ireland) and/or with different equipment.

How to cite: Platz, A., Weckmann, U., and Patzer, C.: Smart data selection – Using machine learning for an automated controlled-source Radio-Magnetotelluric data processing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-917, https://doi.org/10.5194/egusphere-egu23-917, 2023.

EGU23-1953 | Orals | SM5.2

Sesimic Traveltime Tomography Using Deep Learning 

Jun Hyeon Jo and Wansoo Ha

Seismic inversion methods performed by a deep neural network trained in a supervised learning manner have shown successful inversion performance in synthetic data examples that target small areas. These deep-learning-based seismic inversions use time-domain wavefields as input data and subsurface velocity models as output data. Since the time-domain wavefields include both traveltimes and amplitudes of seismograms, the size of the input data is considerably large. Therefore, studies that apply deep-learning-based seismic inversions trained on large amounts of field-scale data have not yet been conducted. In this study, to apply the deep-learning-based seismic inversion technique to field-scale data, the velocity models are predicted using only traveltimes of seismic waves as the input data instead of the full time-domain wavefields. If the traveltime information is used as input data, the resolution of the inversion result is diminished, but the data size is significantly decreased, which can reduce GPU memory usage and speed up network training. We call this approach deep-learning traveltime tomography. The results obtained from this method can also be used as initial velocity models for full-waveform inversion. For network training, a large number of field-scale synthetic velocity models and corresponding first-arrival traveltimes with towed-streamer acquisition are created, and then the network is trained with the synthetic dataset. As a result of performing deep-learning traveltime tomography on an example of synthetic velocity models simulating the seafloor strata, inversion results similar to the labels were obtained. Therefore, it was confirmed that the deep-learning traveltime tomography method can immediately predict a field-scale velocity model, unlike the existing deep-learning-based seismic inversion.

How to cite: Jo, J. H. and Ha, W.: Sesimic Traveltime Tomography Using Deep Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1953, https://doi.org/10.5194/egusphere-egu23-1953, 2023.

EGU23-2183 | ECS | Posters on site | SM5.2

Seismic random noise attenuation in the Laplace domain using deep learning 

Wansoo Ha, Jun Hyeon Jo, and Lydie Uwibambe

We attenuated random noise in Laplace-domain seismic wavefields using a modified U-net. Laplace-domain wavefields can be obtained by Laplace-transforming time-domain wavefields. Due to the damping in the Laplace transform, small-amplitude noises near the first arrival signal can severely contaminate Laplace-domain wavefields. Therefore, time-domain denoising is not sufficient for seismic data processing in the Laplace domain. We trained a modified U-net in a supervised manner to generate clean wavefields from noisy wavefields. Since Laplace-domain wavefields show exponential decay with respect to offset, we used the logarithmic representation of the wavefields to train the network. Numerical examples show that the deep-learning approach can attenuate random noise better than denoising using singular value decomposition.

How to cite: Ha, W., Jo, J. H., and Uwibambe, L.: Seismic random noise attenuation in the Laplace domain using deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2183, https://doi.org/10.5194/egusphere-egu23-2183, 2023.

EGU23-2363 | ECS | Orals | SM5.2

Resolving capabilities of 3D electrode configurations for spectral induced polarization surveys 

Clemens Moser, Adrian Flores Orozco, and Andrew Binley

The induced polarization (IP) method is an extension of the electrical resistivity method that allows the measurement of both the electrical conductive and capacitive properties of the subsurface; it is one of the main methods applied in landfills to characterize the geometry and composition of waste as well as the migration of leachate. Commonly, landfill IP investigations are based on measurements along several 2D lines. Considering the complexity of landfills, we investigate here the resolving capabilities of 2D parallel electrode lines with inline measurements, and 3D electrode configurations (grid array with electrodes set in a quadratic mesh and circular array with electrodes set in four concentric circles) through a numerical study and field measurements. The field surveys were conducted on two landfills with different waste composition, with measurements in the frequency range between 1 and 240 Hz to solve the frequency-dependence of the electrical properties. The results of both the numerical study and the field data show a lack of sensitivity in the case of the 2D configuration leading to the creation of artefacts in the conductivity magnitude and phase imaging result. An underestimation of IP values is also seen for these arrays; such effects are particularly critical in the case of heterogeneously distributed IP anomalies, which are typical in landfills. In contrast, the tested 3D configurations are able to resolve the geometry of the electrical units correctly and anomalies are more sharply defined compared to the results obtained by 2D configurations. Furthermore, our results show that the grid array with crossline measurements and multiple dipole orientations provides better results than the circular array, which lacks in the resolution in the central area. Additional investigations of the frequency-dependence of the field data demonstrate that for the different study areas only 3D configurations provide smooth spectra of the conductivity magnitude and phase, which is essential for an accurate estimation of relaxation (e.g., Cole Cole) parameters.

How to cite: Moser, C., Flores Orozco, A., and Binley, A.: Resolving capabilities of 3D electrode configurations for spectral induced polarization surveys, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2363, https://doi.org/10.5194/egusphere-egu23-2363, 2023.

EGU23-2475 | Posters on site | SM5.2

Application of the signal processing to a short-offset seismic data in the Hupo basin, offshore Korea 

Woohyun Son, Byoung-Yeop Kim, and Dong‑Geun Yoo

In this study, seismic data were acquired using Tamhae2 R/V to identify the subsurface fault structures in the Hupo basin. The seismic data were generated by the air-gun source (30 cu. in.). The source distance is 12.5 m, and the receiver distance is 6.25 m. The number of channels is 32. The offset range of the seismic data is 50 to 250 m. The data processing for short-offset seismic data is mainly applied with simple processing techniques such as frequency filter, trace editing, and velocity analysis in consideration of cost efficiency. However, these simple data processing techniques cannot accurately image complex subsurface structures because it is difficult to remove severe noise and water-bottom (WB) multiples effectively. Therefore, in order to accurately identify the geological structures, it is necessary to apply high-resolution signal processing techniques that can remove severe random noise and WB multiples included in raw seismic data. Severe noise was removed by applying data processing techniques such as a low-cut filter, trace editing, swell noise attenuation, and random noise attenuation. In addition, predictive deconvolution, SRME, and Radon filter were applied to effectively attenuate WB multiples that cause difficulties in geological interpretation. Finally, pre-stack Kirchhoff time migration was applied to more accurately image the subsurface structures. From the data processing results, we confirmed that the high-resolution signal processing techniques applied in this study greatly improved the signal-to-noise ratio of seismic data and effectively eliminated WB multiples.

How to cite: Son, W., Kim, B.-Y., and Yoo, D.: Application of the signal processing to a short-offset seismic data in the Hupo basin, offshore Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2475, https://doi.org/10.5194/egusphere-egu23-2475, 2023.

EGU23-2585 | ECS | Orals | SM5.2

Integrated imaging of a landslide as a result of 4 years of observations  – A case study from Outhern Carpathians 

Artur Marciniak, Mariusz Majdański, Sebastian Kowalczyk, Justyna Cader, Adam Nawrot, Bartosz Owoc, Iwona Stan-Kłeczek, Andrzej Górszczyk, Wojciech Gajek, Szymon Oryński, and Rafał Czarny

The problem of landslides is one of the greatest challenges in geohazard research. Due to their unpredictability, and complicated genesis, their detailed and accurate observation is necessary. Despite many studies on the subject, a general scheme for their recognition has still not been developed. An additional, and important fact that has recently been observed is the impact of the current state of the climate, and the human response to it. 

In the presented research results, an example where anthropogenic factors can have a significant impact on the evolution of a creeping landslide is described. As a result of changes in precipitation over years, artificial snowmaking is necessary to extend and even maintain the ski season on ski slopes and results in the unique characteristics of those landslides. In this presentation we shows the results of 4 years of geophysical observations, integrating multiple methods from geophysical imaging and remote sensing to determine the characteristics of the landslide, its changes and potential danger. The methods used, such as passive seismological monitoring, seismic tomography, electrical resistivity tomography, reflection imaging, terrestrial laser scanning and electromagnetic slingram in a time-lapse scheme allowed us to obtain an image of a temporally and spatially variable structure with remarkable accuracy. Additionally, there were also made an AMT profile with deep recognition range. The results obtained and their joint interpretation can serve as a reference in the study of similar landslide cases, where anthropogenic and climatic factors can significantly impact the evolution of such phenomena.

This research was funded by the National Science Centre, Poland (NCN), grant number 2020/37/N/ST10/01486.

How to cite: Marciniak, A., Majdański, M., Kowalczyk, S., Cader, J., Nawrot, A., Owoc, B., Stan-Kłeczek, I., Górszczyk, A., Gajek, W., Oryński, S., and Czarny, R.: Integrated imaging of a landslide as a result of 4 years of observations  – A case study from Outhern Carpathians, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2585, https://doi.org/10.5194/egusphere-egu23-2585, 2023.

EGU23-3185 | ECS | Posters on site | SM5.2

Prospection of faults in the Southern Erftscholle with Refraction Seismics and Electrical Resistivity Tomography 

Nino Menzel, Norbert Klitzsch, Michael Altenbockum, Lisa Müller, and Florian Michael Wagner

As part of the Lower Rhein Embayment (LRE), the Southern Erft block is characterized by a complex tectonic setting that may influence hydrological and geological conditions on a local as well as regional level. The area presented in this study is located near Euskirchen in the south of North Rhine-Westphalia and traversed by several NW-SE-oriented fault structures. Past studies based on the lithological description of borehole cores and hydrological measurements stated that the present faults affect the local groundwater conditions throughout the targeted area. However, since the tectonic structures were located based on a sparse foundation of geological borehole data, the results include considerable uncertainties. Therefore, it was decided to re-evaluate and refine the assumed fault locations by conducting geophysical measurements.

Seismic Refraction Tomography (SRT) as well as Electrical Resistivity Tomography (ERT) was performed along seven measurement profiles with a length of up to 1.1 km. To allow a sufficient degree of model resolution, the electrode spacing was set to 5 m and halved for areas proximate to assumed fault locations. The geophone spacing was set to 2.5 m for all conducted seismic surveys. A large portion of data processing and inversion was performed with the open-source software package pyGIMLi (Rücker et al., 2017). In addition to compiling individual resistivity and velocity models for all deduced measurements, both ERT and SRT datasets were jointly inverted using the Structurally Coupled Cooperative Inversion (SCCI). This algorithm strengthens structural similarities between velocity and resistivity by adapting the individual regularizations after each model iteration.

This study emphasizes the benefit of multi-method geophysics to detect small-scale tectonic features. The surveys allowed to identify the fault locations throughout the area of interest, provided that the vertical displacements are large enough to be detected by the measurements. Previously assumed locations of the tectonic structures diverge from the new evidence based on ERT and SRT surveys. Especially in the western and eastern parts of the research area, differences between the survey results and formerly assumed locations are in the order of 100 m. Seismic and geoelectric measurements further indicate a fault structure in the southern part of the area, which remained undetected by past studies. The joint inversion provides minor improvements of the geophysical models, as most of the individually inverted datasets already provide results of good quality and resolution. Therefore, the effect of the SCCI algorithm is limited to underlining lithological and hydrological boundaries that are already present in the individually inverted ERT- and SRT-models.

 

References

Rücker, C., Günther, T., Wagner, F.M. (2017). pyGIMLi: An open-source library for modelling and inversion in geophysics, Computers and Geosciences, 109, 106-123, doi: 10.1016/j.cageo.2017.07.011.

How to cite: Menzel, N., Klitzsch, N., Altenbockum, M., Müller, L., and Wagner, F. M.: Prospection of faults in the Southern Erftscholle with Refraction Seismics and Electrical Resistivity Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3185, https://doi.org/10.5194/egusphere-egu23-3185, 2023.

EGU23-3223 | Orals | SM5.2

Joint inversion of Surface-wave Dispersions and Receiver Functions based on Deep Learning 

Feiyi Wang, Xiaodong Song, and Jiangtao Li

Joint inversion of surface-waves and receiver functions has been widely used to image Earth structures to reduce the ambiguity of inversion results. We propose a deep learning method (DL) based on multi-label Convolutional Neural Network (CNN) and Recurrent Neural Network (RNN) with a spatial attention module, named SrfNet, for deriving the Vs models from Rayleigh-wave phase and group velocity dispersions and receiver functions (RFs). We use a spline-based parameterization to generate velocity models instead of directly using the existing models from real data to build the training dataset, which improves the generalization of the method. Unlike the traditional methods, which usually set a fixed Vp/Vs ratio, our new method takes advantage of the powerful data mining ability of CNN to simultaneously constrain the Vp model. A loss function is specially designed that focuses on key features of the model space (such as the Moho and the surface sedimentary layer). Tests using synthetic data demonstrate that our proposed method is accurate and fast. Application to southeast of Tibet shows a consistent result and comparable misfits to observation data with the previous study, indicating the proposed method is reliable and robust.

How to cite: Wang, F., Song, X., and Li, J.: Joint inversion of Surface-wave Dispersions and Receiver Functions based on Deep Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3223, https://doi.org/10.5194/egusphere-egu23-3223, 2023.

Tunnel advance detection technology is an important method for determining the structure of a complex geological body in front of the tunnel face. Among the tunnel advance detection technologies, the seismic method is one of the most accurate methods with long detection distances. In seismic tunnel advance detection, the cylindrical configuration aggravates the complexity of the wave field in the tunnel space and significantly influences the accuracy of the detection results. Thus, it is crucial to simulate an accurate seismic full-wave field of the tunnel space and to understand the propagation and wave-field characteristics of individual seismic waves for seismic tunnel advance detection. Usually, in 3D Cartesian coordinates, the tunnel wall is approximated with a staircase boundary, but it is not sufficiently accurate in shape and generates numerical dispersion in the simulation, especially in the presence of surface waves. Therefore, we developed a variable staggered-grid finite-difference method in cylindrical coordinates to simulate the elastic full-wave field in a 3D tunnel space. Setting free-surface boundary conditions solves the propagation of surface waves on the tunnel wall and face. The free-surface boundary condition was validated by comparing the simulated seismic records with the finite element method. The interference of the instability and discontinuity of the pole axis in the seismic wave field simulation was eliminated using our method. Using this scheme, we simulated the elastic full-wave field of three geological bodies in front of the tunnel face, including the vertical interface, inclined interface, and karst cave. The results of the three models show that the excitation near the tunnel face is more conducive to the detection of geological bodies. Compared with the simulation results in Cartesian coordinates, the results in cylindrical coordinates show that numerical dispersion is negligible and conclude that a higher signal-to-noise ratio and more accurate seismic wave field can be simulated with cylindrical coordinates in the tunnel space. The new method can also be used as an accurate elastic wave propagator for reverse-time migration and full-waveform inversion under tunnel-observing geometries. Our simulation method provides theoretical and practical guidance for analyzing and interpreting seismic wave fields in tunnel advance detection.

How to cite: Zheng, Y., Cheng, F., and Liu, J.: Elastic full-wave field simulation in 3D tunnel space using a variable staggered-grid finite-difference method in cylindrical coordinates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3778, https://doi.org/10.5194/egusphere-egu23-3778, 2023.

EGU23-4987 | ECS | Orals | SM5.2

Ambient seismic noise processing to monitor sea dikes: the case of Noirmoutier, France 

Amin Kahrizi, Maximilien Lehujeur, Odile Abraham, Antoine Lescoat, Loic Michel, Thomas Bardainne, Lilas Vivin, Christopher Boulay, Julien Blanchais, Thibaud Devie, Sérgio Palma Lopes, Olivier Durand, and Gautier Gugole

The use of ambient noise for passive seismic imaging has evolved into a cutting-edge, low-cost, and environmentally acceptable method of exploring the subsurface. This technique dispenses with active seismic sources, alternatively uses ambient seismic noise. Theoretical investigations have approved that an estimate of the empirical Green’s function between receivers could be obtained from the cross-correlation of ambient noise and/or dispersed coda waves. This Green’s function is mostly made up of fundamental Rayleigh waves, propagating between two receivers as if they would be caused at one of them. The applications of ambient noise surface wave tomography, from engineering and urban developments to regional and continental scales, have led to the mapping of the area's velocity model, which chiefly corresponds to the structural/geological units.

Because of numerous devastating catastrophes in recent years, several countries have made flood protection a priority. However, sea-dikes are considered remarkably heterogeneous and may fail due to their construction and/or reinforcing structures; they are potentially subject to stress by sea waves during the tidal cycle and seasonal heat variations, resulting in the water infiltration. Internal abnormalities cannot be recognised in the early stages of erosion, although visual assessments may often be relied on. In this study, we outline a passive seismic survey that was carried out to investigate technical and methodological aspects of passive seismic methods along with their application in a sea dike monitoring perspective. 

The SEEWALL project is a collaborative project, seeking to create innovative methodology to monitor the temporal evolution of sea dikes and detect early deterioration. We deployed 160 permanent 3-component MEMS accelerometers spaced 2 meters apart on top of a dike on the island of Noirmoutier (France), which was exhibiting moderate water infiltrations at its base. Despite the inhomogeneous distribution of the ambient noise sources, exploitable empirical Green's functions can be retrieved mostly from the cross-correlation of vertical component data. We estimate the surface wave phase velocity dispersion curves  using a time-frequency analysis; strictly speaking, after preconditioning the data, the cross-correlation is carried out in the frequency domain by carefully windowing data, from which each  empirical Green's functions is derived; their cross-correlations are stacked linearly by hours. The arrival times of the causal and anti-causal parts are often not fully symmetrical, indicating the diversity of major noise sources. The phase velocities measured on both positive and negative lag-times, as a function of the frequency, are computed using the phase-shift method. Interpretation of the phase velocity dispersion curves is challenging due to the geometry of the dike at the scale of the intended wavelength (a few tens to hundreds meters). But the pattern of the dispersion data appears to be relatively stable over time. It is also consistent with the dispersion curves we have obtained using active seismic hammer-shots, performed along the structure. For monitoring, we suggest using F-K spectra to highlight the variety of energy density over time, in order to advance a deeper understanding of data analysis; this enables us to discover any changes that might not be otherwise obvious.

How to cite: Kahrizi, A., Lehujeur, M., Abraham, O., Lescoat, A., Michel, L., Bardainne, T., Vivin, L., Boulay, C., Blanchais, J., Devie, T., Palma Lopes, S., Durand, O., and Gugole, G.: Ambient seismic noise processing to monitor sea dikes: the case of Noirmoutier, France, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4987, https://doi.org/10.5194/egusphere-egu23-4987, 2023.

EGU23-5073 | Orals | SM5.2

Mapping sea cliff fracturation using passive seismic and self potential responses : case study of the Socoa flysh cliff (Basque Country, France) 

Jacques Deparis, Ianis Gaudot, Francois Bretaudeau, Jean-Michel Baltassat, and Christophe Garnier

EZPONDA is a FEDER funded project, which aims to study both the mechanichal and chemichal processes related to the erosion of the coastal area in the Basque country, France. In the Socoa flysh cliff, the presence of fractures roughly perpendicular to the shoreline control the nucleation and the growth of underground erosion cavities. The ‘Socoa Semaphore cavity’ is the most striking one, with a propagation of the void up to 30 m inland. Mapping sea cliff fracturation extent around this cavity is a critical aspect to anticipate possible future erosion processes.

Assuming the permeability of the fractured material is higher than the permeability of the nonfractured material, mapping water infiltration in the subsurface may be used as a proxy to map the fracturation extent. In this work, we propose to monitor the sea water infiltration during high tide using passive seismic listening and self potential electrical response to illuminate fractures in the surrounding of the ‘Socoa Semaphore cavity’.

72 vertical component autonomous 5 Hz seismic sensor were deployed at the surface over 5000 m2 with an average interstation distance of 10 m. Continuous records were collected between 19/09/2020 and 22/09/2020 (4 days) during a large tidal event to include 8 high tides with a coefficient higher than 100.  It should be noted that the first two days of measurements were carried out over the weekend. The self-potential signals were recorded at the ground surface using a set of 20 nonpolarizable Pb/Pbcl2 electrodes. Data were recording using a Campbell Scientific CR1000 datalogger, with multiplexer chips used to switch between the pole electrodes. Voltage were measured between the 19/09/2020 11am to 21/09/2020 16pm.

The seismic spectrograms show that between 5-20 Hz, anthropological activities such as trafic and harbour modulate the seismic energy for all sensors. In the 20-40 Hz frequency range, the sea height modulates the seismic energy for all sensors, with a seismic energy decreasing as a function to the distance to the coast.  For a large frequency range between 10-50 Hz, we observe that the relative change in median spectral amplitude during high tides with respect to the median amplitude during the full observation period exhibits highest value over a restricted area (400 m2) located east to the the ‘Socoa Semaphore cavity’, which extends far beyond the known void extent. We argue that this area with a singular geophysical signature may be related to the presence of fracturation. Self potential measurement shows a lower noise during the night (around 4 mV) compare to the day (about 10 mV). In addition the noise is higher on Monday (about 20 mV). Self potential measurement show periodic oscillations with a period of 6.4 hours approximately, corresponding to half the tidal cycle. Amplitude variations of self potential signal is more delicate to be interpreted and need further development. 

How to cite: Deparis, J., Gaudot, I., Bretaudeau, F., Baltassat, J.-M., and Garnier, C.: Mapping sea cliff fracturation using passive seismic and self potential responses : case study of the Socoa flysh cliff (Basque Country, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5073, https://doi.org/10.5194/egusphere-egu23-5073, 2023.

EGU23-5390 | Posters on site | SM5.2

Thickness estimation of CO2 transition layer using a deep learning 

Seonghyung Jang, Donghoon Lee, and Byoung-Yeop Kim

After CO2 injection into a reservoir, the behavior of CO2 depends on permeability, porosity, cap rock, reservoir fluids, CO2 characteristics, pressure gradient, and buoyancy effects. Therefore, the thickness of the reservoir is an essential parameter for CO2 monitoring. In the case of reservoir thickness prediction, it is practical to consider a geological reservoir as a transition zone in which the physical properties linearly change. In the transition zone, the seismic reflections in the stack section are the normal incident reflection coefficient with continuously changing velocity. Since this is composed of a function of the velocity ratio of the upper and lower layers, frequency, and transition zone thickness, the seismic signals apply to predict the thickness of the reservoir layer. In this study, we use the frequency characteristics with time-varying to estimate the thickness of the transition zone. First, we prepare the time-frequency spectrum with various thicknesses and then analyze it through deep learning to determine an optimum reservoir thickness. We use a convolution neural network (CNN) for predicting the transition zone thickness, which has two more hidden layers in the feature extractions. Unlike the fully connected layer, CNN is composed of a convolutional layer and a pooling layer and requires many data to prevent overfitting. Since CNN can efficiently process nonlinear data, it is applied to image classification and argumentation. For the numerical modeling experiment, we prepared a geological model in which the velocity of the shale layer (3000 m/s), cap rock, is greater than the lower sandstone layer (2200 m/s). We verify variation of phase and amplitude according to various transition zone thicknesses. For example, when the thickness is 10 m, it shows the phase changes at 65 Hz, and the amplitude decrease with increasing frequency. For the thickness of 50 m, the phase changes at the cut-off frequency of 13 Hz, and the amplitudes decrease until 25 Hz, increasing and decreasing repeatedly. We suggest that CNN is one of the methods to predict the thicknesses of CO2- injected reservoir using a time-frequency spectrum with various thicknesses.

How to cite: Jang, S., Lee, D., and Kim, B.-Y.: Thickness estimation of CO2 transition layer using a deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5390, https://doi.org/10.5194/egusphere-egu23-5390, 2023.

EGU23-6655 | Posters on site | SM5.2

Vs model for Oran city, obtained by joint-inversion of dispersion and HVSR curves 

ahmed saadi, Abdelouahab Issaadi, Fethi Semmane, Abdelkrim Yelles–Chaouche, Juan José Galiana-Merino, Khalissa Layadi, and Redouane Chimouni

Abstract

The city of Oran, which is located in the northwest of Algeria, in the Lower-Cheliff basin, has experienced several earthquakes in the past. Therefore, the characterization of its subsurface is crucial for a better assessment of the seismic hazard. Single-station ambient vibration measurements at 193 sites and array measurements at 15 sites have been analyzed with HVSR and F-K techniques, respectively, for the soil investigation.The HVSR curves showed a variation of the fundamental frequency peak between 0.3 and 7.4 Hz, increasing from east to west, and reaching a maximum amplitude of ~6. Rayleigh wave dispersion curves were obtained by F-K analysis. Joint-inversion of the dispersion and HVSR curves provided a shear wave velocity model and an estimate of the bedrock depth. The models showed 3 layers of sediments overlying the bedrock. The shear-wave velocity (Vs) of the softer sediments varies between 280 and 580 m/s, and at bedrock it varies between 1600 and 2500 m/s. The latter reached a maximum depth of 1050 m northeast of the city. In addition, these results were used to calculate the soil vulnerability factor (Kg), and the Vs30 in the entire area. Finally, a soil classification and a regression law between the fundamental frequency and the depth were proposed for the whole city.

How to cite: saadi, A., Issaadi, A., Semmane, F., Yelles–Chaouche, A., Galiana-Merino, J. J., Layadi, K., and Chimouni, R.: Vs model for Oran city, obtained by joint-inversion of dispersion and HVSR curves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6655, https://doi.org/10.5194/egusphere-egu23-6655, 2023.

EGU23-7067 | ECS | Orals | SM5.2

Structurally-constrained FD-EMI data inversion using a Minimum Gradient Support (MGS) regularization 

Tim Klose, Julien Guillemoteau, Giulio Vignoli, Philipp Koyan, Judith Walter, Andreas Herrmann, and Jens Tronicke

In geophysical data inversion, one way to decrease the non-uniqueness of the solutions is to incorporate structural constraints. Such structural constraints are typically derived from collocated geophysical data, which are more sensitive to subsurface structures and parameter contrasts than the to-be-inverted data. When using a smooth regularization operator, a straightforward approach is to reduce the local weight of the smoothness constraints in model regions where we expect an interface. However, when using such an inversion approach, the capability to reconstruct a sharp interface relies only on the structural a priori information; i.e., model areas where no structural a priori information is available are solely controlled by the standard smoothness constraints. Therefore, this approach is not optimal in practice, as the structural a priori information is often not complete.

In this study, we evaluate a structurally-constrained inversion approach based on the Minimum Gradient Support (MGS) regularization, which is capable to promote sharp interfaces also in areas where no structural a priori information is explicitly specified. We test and evaluate this regularization approach for the inversion of frequency-domain electromagnetic induction (FD-EMI) data, where we use a constant-offset 3D GPR data set to derive structural a priori information. Our field data set covers an area of about 120 m x 50 m and has been collected at a field site in Kremmen, Germany, to explore peat deposits. Our results demonstrate that the proposed structurally-constrained inversion approach helps in finding a reliable subsurface structures (e.g., peat thickness) as well as a reliable reconstruction of the subsurface electrical conductivity distribution within the peat formation (e.g., related to varying degrees of peat decomposition) and within the sandy substratum.

How to cite: Klose, T., Guillemoteau, J., Vignoli, G., Koyan, P., Walter, J., Herrmann, A., and Tronicke, J.: Structurally-constrained FD-EMI data inversion using a Minimum Gradient Support (MGS) regularization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7067, https://doi.org/10.5194/egusphere-egu23-7067, 2023.

EGU23-8048 | ECS | Posters on site | SM5.2

3D seismic tomography of the Harmaliére landslide (French Alps) by interferometry 

Giuseppe Provenzano, Stéphane Garambois, Jean Virieux, Romain Brossier, and Ludovic Métivier

Harmaliére, in southern France, is among the most active alpine landslides, posing a risk to the neighbouring settlements and infrastructures. A retrogressive slide in March 1981, that displaced a volume in the order of 100 m 3 , was followed in April 2016 by a landslide two order of magnitude larger, followed by minor reactivations in 2017 and 2018. Local bedrock paleo-topography and sedimentary structures within the glacio-lacustrine sediment layer are suspected to have a role in determining the dynamics of this slide, characterized by episodic large displacements as opposed to slow and continuous mass movements registered in neighbouring sites (e.g. Avignonet). However, current state of knowledge of the subsurface is limited to low-resolution volumes and local 1D layered S-wave profiles.

Within the RESOLVE project, in May-June 2021 a dense 3D array of 100 three-component geophones has been deployed to record continuously ambient seismic noise for a one-month period. This was complemented by the acquisition of an active dataset using 100 hammer-strike sources, with offsets ranging from 0 to 900 metres. The vertical component of the the active dataset has been used to obtain a 3D P-wave velocity model by first-arrival traveltime tomography. Particularly challenging field conditions, e.g. thick vegetation and surface water, along with the low-power of the hammer sources, required dedicated processing to enhance the signal-to-noise ratio and allow for confident first-arrival pickings.

Super-virtual interferometry (SVI) has been applied to improve the quality of offsets larger than 400 m, which contain head-waves key for the imaging of the sediment-bedrock interface. SVI enhances critically refracted arrivals by stacking the cross-correlations of traces pairs sharing a stationary-path in common-receiver gathers, and then convolving the resulting station-pair Green’s functions with the appropriate virtual sources in common-source gathers. An azimuth-varying approach has been developed to adapt SVI to the 3D problem, reducing the number of cross-correlations and mitigating artefacts resulting from non-stationary paths contributions. The dataset obtained by constrained automatic picking on the SVI dataset has been used for first-arrival traveltime tomography, yielding an improved-quality tomographic volume at depths larger than 50 m along with lower final data misfit, thanks to the greater number of reliable long-offsets picks compared to the pre-SVI dataset.

The P-wave velocities obtained within the sediment body, as well as the inferred bedrock topography, are sensible and appear to be consistent with independent geophysical data. In order to complete the elastic characterization of the site, a S-wave 3D model will be reconstructed from the empirical Green's functions obtained by interferometry on 1-month long noise recordings, opening the way towards a joint passive-active high-resolution 3D elastic remote characterization of the landslide volume, and thus an improved understanding of its controlling factors.

How to cite: Provenzano, G., Garambois, S., Virieux, J., Brossier, R., and Métivier, L.: 3D seismic tomography of the Harmaliére landslide (French Alps) by interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8048, https://doi.org/10.5194/egusphere-egu23-8048, 2023.

Gheith Alfakri Emmanouil Parastatidis1  Stella Pytharouli1

Abstract: Previous studies present evidence that microseismic monitoring could be a favourable potential technology for brownfield land site investigations, e.g. in the identification of buried objects in the shallow subsurface (< 3 m). More specifically, the presence of buried objects change the characteristics (amplitude and frequency) of a mechanical wave that propagates through a medium where this object lies. These changes have to-date only been observed at recordings from stations that are located directly above the buried object. To investigate whether a buried object can be ‘seen’ by more sensors located in the vicinity above the object, we carry out a series of numerical simulations. We examine the propagation of a sine wave emitted by a point source on the surface of a medium and study the frequency, amplitude and emitted energy from that sine wave and how these are affected by local changes in the mechanical properties of the model. For the duration of each simulation, we record the velocity history at a number of points on the free surface of the model. Numerical simulations are carried out in FLAC3D. First, we look on how the distance between the source and the monitoring points changes what we record. We examine two cases : In Case A, the monitoring stations and the buried object are at a distance less than 30 meters from the seismic wave source. In Case B, the monitoring stations and buried object are at a distance more than 30 meters from the seismic wave source. We apply spectral analysis to the resultant seismic velocity time histories as recorded at a number of monitoring stations at the free surface of the model. Our results for Case A show that an object can be detected at a monitoring station located directly above the object to a depth of 1-2 meters. Results for Case B show that an object can be detected at the monitoring station that is deployed directly above the object to a depth of up to 4-5 meters, and it can also be detected at neighbouring stations, at distances approximately equal to the depth of the object. In addition, we study factors having an impact on the amount of energy of the seismic wave emitted, i.e. depth of the object from the surface and its mechanical properties. Our analysis indicates that by increasing the depth of the object, the amount of reflected seismic energy decreases. The changes in the mechanical properties of the materials lead to a change in seismic wave propagation velocity and frequency. Results from our numerical simulations present evidence that microseismics can be used as a complementary, low-cost site investigation tool for applications where very shallow depths are of particular interest such as those at brownfield sites. This can have significant implications on the way site investigations on brownfield sites are carried out, with microseismics providing an alternative to sites where traditional non-intrusive methods such as GPR and/or resistivity tomography are limited due to ground properties.

 

How to cite: alfakri, G.: Microseismic monitoring of wave propagation through heterogeneous media: a tool for brownfield site investigation?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8304, https://doi.org/10.5194/egusphere-egu23-8304, 2023.

EGU23-8469 | ECS | Orals | SM5.2

Geophysical methods of soil fertility mapping for precision agriculture applications in semi-arid regions (Morocco) 

Fatima-Ezzahra Aallem, Anas Charbaoui, Laamrani Ahmed, Azzouz Kchikach, Mohammed Jaffal, and Younes Jnaoui

Experiments on a plot-scale of apparent electrical conductivity (ECa) and resistivity (ERT) variation with correlation of soil properties were studied for soil mapping at the experimental farm of Mohammed VI Polytechnic University of Benguerir (UM6P). The ElectroMagnetic Induction (EMI) technique was applied using a soil sensor EM38-MK2 which provides auxiliary ECa data sets with accuracy. The other method ERT was used to measure the electrical resistivity. The study was supported by soil sampling to ensure the reliability and potential of ECa measurements for soil mapping.  ECa readings in mS/ m ranged from 12 to 26 and 8 to 20 respectively in the vertical (ECa-V) and horizontal mod. ECa and ERT readings correlated best with soil properties such as texture (clay and sand), and upper soil chemical properties (OM, CEC, Ca2+, Fe2+and Mg2+). A modest correlation was found between ECa-V, clay and subsurface water content (r = 0.80), (r = 0.79). The linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the measured variability. The results of the study raised the hope that soil mapping by ECa measurement can fairly represent the spatial variation of soil properties such as texture, chemical fertility and organic matter content. The use of spatial variability in EC as a co-variate in statistical analysis could be a complementary tool in the evaluation of experimental results.

How to cite: Aallem, F.-E., Charbaoui, A., Ahmed, L., Kchikach, A., Jaffal, M., and Jnaoui, Y.: Geophysical methods of soil fertility mapping for precision agriculture applications in semi-arid regions (Morocco), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8469, https://doi.org/10.5194/egusphere-egu23-8469, 2023.

EGU23-8542 | Orals | SM5.2

A protocol for assessing the effectiveness of electrical resistivity imaging for agricultural dike investigation 

Peter Lelièvre, Elias Vandenberg, Heidi Hebb, Karl Butler, Xushan Lu, and Colin Farquharson

DC electrical resistivity surveying has shown much promise for investigating dikes and other earthen flood barriers. We are interested in the applicability of such data for aiding with maintenance and construction efforts in the Tantramar region of New Brunswick and Nova Scotia, Canada, where agricultural dikes form an important part of critical flood prevention infrastructure. Specifically, our goal is to develop efficient field survey and data processing protocols for detecting possible internal issues in the dikes ahead of further, more detailed geophysical surveying. The field survey protocol must be cost and time effective, given the large lengths of dikes that must be surveyed. The Tantramar dikes are expected to exhibit strong subsurface heterogeneity but accurately characterizing their internal structure may be challenging. Dikes have significant 3D geometry and traditional 2D DC surveying, and subsequent 2D inversion, fails to provide reliable and interpretable results. 3D surveying and inversion may be required but this represents significantly higher field costs. We performed a detailed synthetic inverse modelling study to help design our field surveying protocols. We used a representative model of a dike in the Tantramar region and we worked with the specifics of the surveying equipment available to us. We investigated and compared three possible data acquisition layouts proposed by other authors, we thoroughly compared the results of 2D versus 3D inversion on those layouts, and we performed a detailed investigation to assess best practices for 3D inversion mesh design. We are also incorporating joint interpretation with EM data, collected using mobile survey devices such as the Geonics EM31. Results from synthetic forward and inverse modelling are helping us develop future field data collection, processing and modelling protocols.

How to cite: Lelièvre, P., Vandenberg, E., Hebb, H., Butler, K., Lu, X., and Farquharson, C.: A protocol for assessing the effectiveness of electrical resistivity imaging for agricultural dike investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8542, https://doi.org/10.5194/egusphere-egu23-8542, 2023.

EGU23-8768 | Posters on site | SM5.2

Multidisciplinary approach to reconstruct the pathways of the CO2 nonvolcaning degassing in the thermal springs of Contursi and Oliveto Citra sector (southern Appennines, Italy) 

Maria Giulia Di Giuseppe, Sabatino Ciarcia, Claudio De Paola, Carmela Fabozzi, Roberto Isaia, Antonio Troiano, and Stefano Vitale

The southern Apennines are a fold-and-thrust belt characterized by the superpositions of different thrust sheets. The orogenic construction defined by thin- and thick-skinned tectonics occurred from the Paleocene to the early Pleistocene. In this orogen, evidence of nonvolcanic degassing is widely reported. The orogenic chain hosts the Mefite d'Ansanto (MdA) vent, the most significant nonvolcanic natural emission of low-temperature CO2 on Earth. Other degassing areas are located in the Sele River Valley, where several vents are aligned along major faults, including the thermal springs of Contursi and Oliveto Citra (COC).

Different investigations on these nonvolcanic emissive structures mark a close relation between degassing phenomena and tectonics, evidencing a likely dominant crustal gas origin for the COC vent. In any case, poor information is available about the characteristics of the CO2 reservoir (including the geometry and depth) and the fluid's rising pathways.

Different surveys have been performed, applying a multidisciplinary approach, including innovative methodologies, aiming to reconstruct the geometry of the shallow degassing pathways and investigate how the different geological and tectonic architecture influences the CO2 seeping and surficial degassing processes. The structures that convey and favour the upward gas migration, seeping and degassing have been imaged using geophysical and structural investigations.

Electrical Resistivity (ERT) and Induced Polarization (IP) tomographies, combined with Self-Potential (SP), Magnetic (Mag), and PH mapping have been performed in correspondence with the most degassing part of the COC area. The joint acquisition of such a multiparametric dataset ended in a better-constrained interpretation of the different detected anomalies. Furthermore, the obtained results allowed us to construct different geophysical maps and geological cross-sections of the investigated area and develop a model of the degassing vents area, highlighting the role of reconstructed lithological and structural settings in the shallow leaking processes.

How to cite: Di Giuseppe, M. G., Ciarcia, S., De Paola, C., Fabozzi, C., Isaia, R., Troiano, A., and Vitale, S.: Multidisciplinary approach to reconstruct the pathways of the CO2 nonvolcaning degassing in the thermal springs of Contursi and Oliveto Citra sector (southern Appennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8768, https://doi.org/10.5194/egusphere-egu23-8768, 2023.

EGU23-9713 | ECS | Orals | SM5.2

Deep learning diffraction separation for seismic and GPR data 

Alexander Bauer, Benjamin Schwarz, Jan Walda, and Dirk Gajewski

Within the last decade, the diffracted wavefield has gained increasing importance for the processing of both seismic and ground-penetrating radar (GPR) measurements. In both communities, the separation of the diffracted wavefield remains a notorious challenge that has been approached with different deterministic methods, ranging from poststack wavefront attributes to plane-wave destruction and coherent wavefield separation. While each of these deterministic methods has characteristic advantages and drawbacks, all of them require the adaptation of processing parameters for each application, particularly when crossing scales from seismic to GPR measurements. In this study, we propose to train a convolutional autoencoder to separate the reflected and diffracted wavefields in a generalized fashion. For this purpose, we have generated highly variable synthetic seismic data that contain reflections, diffractions and noise using an algorithm that allows to compute each component individually, resulting in an automatized generation of data and labels. In order to account for the complexity of field data, we complemented the synthetic data with a large set of reference seismic and GPR field data results from coherent wavefield separation, a deterministic method, in which the reflected wavefield is modeled and adaptively subtracted from the input data. With this dataset we trained a supervised convolutional autoencoder and applied the trained neural network to seismic and GPR field measurements that were not part of the training data. The results show that the trained autoencoder is able to generalize and successfully separate the reflected and diffracted wavefields even for complex field data, resulting in an on-the-fly diffraction separation that requires no choice of parameters and is likewise applicable to both seismic and GPR data.

 
 

 

 

How to cite: Bauer, A., Schwarz, B., Walda, J., and Gajewski, D.: Deep learning diffraction separation for seismic and GPR data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9713, https://doi.org/10.5194/egusphere-egu23-9713, 2023.

EGU23-11541 | Orals | SM5.2

Ambient noise shear-wave tomography for shallow landslide structural models retrieval from dense 3D seismological arrays. 

Myriam Lajaunie, Joachim Rimpot, Dimitri Zigone, Céleste Broucke, Jean-Philippe Malet, Elise Weiskopf, Clément Hibert, Joshua Ducasse, and Catherine Bertrand

The versatility, cost-efficiency and easy deployment of seismic sensor nodes facilitate geophysical monitoring in environments that were previously inaccessible for instrumentation, and among them landslides and unstable slopes, most of the time located in remote mountains. Using nodes allows for the setup of dense arrays with sensor inter-trace distances that become compatible with the geometries and dimensions of the geological structures to image. This becomes particularly true for landslides which have complex 3D architectures (hummocky bedrocks, layering, multi-dimensional fractures, diverse geotechnical material, deep and perched aquifers and water circulations) and are shallow processes with respect to the classical investigation depths and sensitivity of most geophysical survey techniques.

Here we develop a specific processing workflow to allow the computation of 3D shear-velocity models with Ambient-Noise-based tomography applied to dense arrays of seismic stations. The workflow is applied to a dataset acquired at the Viella shallow landslide (France) developed in altered schists and moraine deposits. We deployed 70 IGU-16HR-3C-5Hz SmartSolo sensors (EOST/PISE service) with inter station distances of 70 m for a period of 25 days.

The processing consists in several steps, all of them being tuned to the specific case of shallow depths of investigation. In areas where only few strong (ML>4) earthquakes are triggered, with a low azimuthal distribution, surface-waves velocity fields are complex to estimate with earthquakes. Ambient noise cross-correlation tomography has the advantage of using the ambient noise to model the surface waves velocities by retrieving the interstation Green’s functions. The main hypothesis for retrieving the Green’s functions is a homogeneous noise-source distribution, which is never achieved in a natural environment. Therefore, data filtering and daily stacking are crucial to reduce the effect of non-uniform noise distributions and lead to consistent velocity models. Due to the noisy environment of Viella (torrential flows, farming activity, anthropogenic noise), several procedures were implemented to optimize the processing (reduction of the coherent noises in the processed data, use of a pseudo-topography to estimate as accurately as possible the inter-station distances and travel times). We then computed the dispersion curve diagrams for the surface waves on which we applied a strict selection to only keep the consistent part of the surface waves dispersion curves. The selection parameters were optimized for the Rayleigh and Love waves. Then, we inverted the inter-station travel times to compute group velocities maps at several frequencies. Finally, we proceed to a Markov-Chain-Monte-Carlo inversion of each of the dispersion curves extracted from the group velocity maps. We finally obtained a 3D shear velocity model, which is further combined with geological and borehole information in order to document the 3D structure.

The objectives are to present the processing workflow developed specifically for shallow imaging and the retrieval of 3D heterogeneities; effects of the processing parameters will be discussed on the Viella dataset. The approach developed for Viella is generic and has been further applied to other geological processes (permafrost at the Chauvet rock glacier, Marie-sur-Tinée mudslide), and the models will be discussed.

How to cite: Lajaunie, M., Rimpot, J., Zigone, D., Broucke, C., Malet, J.-P., Weiskopf, E., Hibert, C., Ducasse, J., and Bertrand, C.: Ambient noise shear-wave tomography for shallow landslide structural models retrieval from dense 3D seismological arrays., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11541, https://doi.org/10.5194/egusphere-egu23-11541, 2023.

In (time-domain) Electromagnetic Induction (EMI) surveys, an image of the electrical conductivity of the subsurface is obtained non-invasively. An accurate interpretation of the data is computationally expensive as it requires a full (high fidelity) 3D simulation of the induced electric currents embedded within an iterative and ill-posed inverse problem. Therefore, this forward model is usually approximated with a 1D forward model (low fidelity model) which only considers horizontal layers and for which fast analytical forward models exist. Recent work [1] has shown that a multidimensional forward model can be relevant in time-domain Airborne EM inversion. To be more precise, we provided an appraisal tool for quasi/pseudo-2D inversion to indicate that fast forward 3D modelling for time-domain (Airborne) EM data is still worthwhile and, in fact, necessary, in some areas. Surrogate modelling and machine learning may replace 3D forward modelling on a mesh during a 3D inversion.

In this contribution, we first demonstrate the initial steps towards creating an efficient surrogate model for 3D modelling with only 5000 samples in the training dataset. Rather than predicting the high-fidelity or 3D data directly, we predict the relative error between the high and low fidelity data. The idea behind this approach is that predicting the difference with a relatively good low-fidelity model is easier and more robust than trying to find a surrogate for the full data set. The computation of low fidelity data via the 1D approximation is no longer a computational burden, yet it explains most of the variability in the observed data. The residual variability, originating from the non-1D nature of the subsurface, is predicted with a Gaussian process regression model. Combining the low-fidelity model with a trained correction term via Machine Learning saves significant computation times. We show encouraging results, currently limited to two layers, where the trained surrogate model proves to produce a significant ‘learning gain’ in 92,5% of the cases (see Figure 1), meaning that it can significantly reduce the residual multidimensional variability. The cases where the surrogate model makes the prediction of the high-fidelity data worse, occur at the limits of the training data space, indicating that those cases could be resolved by generating more training data in those areas.

Figure 1 – The learning gain on the test dataset by using the trained surrogate model

 

References

[1] Deleersnyder, W., Dudal, D., & Hermans, T. (2022). Novel Airborne EM Image Appraisal Tool for Imperfect Forward Modeling. Remote Sensing14(22), 5757. https://doi.org/10.3390/rs14225757

How to cite: Deleersnyder, W., Dudal, D., and Hermans, T.: Machine learning assisted fast forward 3D modelling for time-domain electromagnetic induction data – lessons from a simplified case, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12015, https://doi.org/10.5194/egusphere-egu23-12015, 2023.

EGU23-12063 | ECS | Posters on site | SM5.2

Geophysical quantification of porosity in the soda lakes of the Lake Neusiedl-Seewinkel Basin 

Nathalie Roser, Anna Hettegger, Teresa Müller, Matthias Steiner, Lukas Aigner, Arno Cimadom, and Adrian Flores Orozco

The Lake Neusiedl-Seewinkel Basin is home to a system of unique soda lakes, which harbor a variety of rare and endangered flora and fauna. The existence of these lakes is facilitated by a complex equilibrium between climate and surface-groundwater interactions, where capillary forces pull soda (NaHCO3) and clay from the shallow aquifer to the surface. The accumulation of clay develops an impermeable layer that acts as a hydraulic barrier near the surface allowing rain water to form the eponymous lakes. Assessing lateral and temporal variations in porosity, clay and salt content, in particular within this impermeable layer, is important to understand the surface-groundwater dynamics at site and address the impact of climate change and artificial drainage of groundwater on the lakes leading to their on-going degradation. We investigate here the applicability of seismic methods to quantify near surface variations in porosity, while information on clay content and salinity are resolved through electric methods. In particular, we conduct measurements with the multichannel analysis of surface waves (MASW), the P-wave seismic refraction tomography (SRT) and the induced polarization (IP) methods during dry (summer) and wet (winter) periods in three adjacent soda lakes: one considered active, one degrading, one degraded. Quantitative estimates of porosity and water saturation are inverted from MASW and P-wave SRT data sets based on the Biot-Gassmann fluid substitution theory and an extension of the Hertz-Mindlin contact theory accounting for capillary suction effects taking place in the vadose zone. The complementary IP measurements aid in the identification of the salt-bearing clay rich impermeable layer, associated with higher electrical conductivity values, to sustain the porosity estimation based on the seismic methods and gain information on the clay content and pore fluid salinity at each site. In August 2022, we installed a permanent IP monitoring profile within the active lake to observe temporal changes in electrical conductivity related to variations in soil moisture due to seasonal variations such as precipitation. Our results reveal different geophysical signatures in the three lakes corresponding to their presumed ecological state of degradation. In general, we observe higher P- and S-wave velocity values and lower Poisson’s ratio and electrical conductivity values for the degrading/degraded lake than in case of the intact lake. The impermeable layer of the intact lake is clearly distinguishable from MASW and IP images, whereas it is less well resolved and exhibits a higher porosity in the degraded lake. The joint inversion of SRT and MASW overall improves the subsurface characterization as it solves for shallow porosity variations within the impermeable layer, which were not detectable through the independent inversions, clearly revealing differences in porosity between the three sites.

How to cite: Roser, N., Hettegger, A., Müller, T., Steiner, M., Aigner, L., Cimadom, A., and Flores Orozco, A.: Geophysical quantification of porosity in the soda lakes of the Lake Neusiedl-Seewinkel Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12063, https://doi.org/10.5194/egusphere-egu23-12063, 2023.

EGU23-12280 | Posters on site | SM5.2

Sensitivity analysis on synthetic 3D Deep ERT data for the example of Plombières, Belgium 

Yannick Forth, Anne-Sophie Mreyen, Andreas Kemna, Joost Hase, Florian Wellman, Nils Chudalla, and Frédéric Nguyen

The E-TEST project (Einstein Telescope EMR Site & Technology) investigates the feasibility of constructing a large Laser Interferometer (Einstein Telescope) in the Euregio Rhine Meuse. The aim of this instrument is to detect gravitational waves. To reach a sufficient noise attenuation the telescope will be built deep underground (more than 200 meters depth). The infrastructure consists of multiple tunnels and caverns spanning several kilometers. As with any large-scale infrastructure, the geological model, especially the existence and orientation of faults, is of large importance for hydrogeophysical and geotechnical characterization. At such depths, few near-surface geophysical methods are able to provide information with enough details. The application of large 3D Deep ERT surveys helps understanding the local geological settings and to identify important geological features but suffers from ambiguous interpretation. However, such imaging requires measuring dipoles independent of the injection system (such as the Fullwaver System by IRIS Instruments) in contrast to conventional ERT Systems, and due to the large covered area, coarsely spaced. This results in a drastic decrease in resolution when compared to classical ERT measurements.

Here, we present a sensitivity analysis on a dataset based on the geologic setting in Plombières, Belgium to identify the impact of geology and survey setup on Deep 3D ERT surveys. The utilized geologic model was created with the Open-Source 3D structural geomodelling software GemPy and used as an input for forward modelling using the Open-Source modelling and inversion library pyGIMLi.

How to cite: Forth, Y., Mreyen, A.-S., Kemna, A., Hase, J., Wellman, F., Chudalla, N., and Nguyen, F.: Sensitivity analysis on synthetic 3D Deep ERT data for the example of Plombières, Belgium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12280, https://doi.org/10.5194/egusphere-egu23-12280, 2023.

EGU23-12499 | ECS | Orals | SM5.2

A new approach to quantify the reliability of Electrical Resistivity Tomography (ERT) images 

Maxime Gautier, Stéphanie Gautier, and Rodolphe Cattin

Anthropogenic and natural hazards assessments need a good knowledge of the structures. A classical approach based on geological observations or soil mechanics investigations is often insufficient to characterize both the structures and the nature of subsurface materials. For several decades, near-surface geophysical methods have been integrated into a multidisciplinary strategy to improve the characterization of small-scale features of the subsurface. Electrical Resistivity Tomography (ERT) is a standard approach among these methods. This technique has several advantages, including easy deployment in the field and sensitivity to lithology, fluid contents, or chemistry. With this method, it is possible to detect and characterize the geometry of sliding surfaces on landslides and actives faults. It is also possible to set a permanent survey and obtain time-lapse images to describe temporal changes of resistivity within the subsurface and investigate dynamic processes, such as groundwater flows or soil moisture variations.
The ERT method consists of recording apparent resistivity data and inverting them to map the resistivity distribution at depth and to capture possible time changes. Many softwares, such as  Res2DInv, R2, or PyGimli, are now available to carry out the inversion. However, the quality assessment of the obtained models remains an open and challenging question. Indeed,  the robustness of the ERT results depends on factors such as the acquisition geometry, data error,  the resistivity contrast in the subsurface, the inversion procedure, and its parametrization. 
To overcome these limitations and allow a more accurate interpretation of the ERT models, we propose a new approach for assessing the reliability of ERT images. We propose a new algorithm called PySAM (Python Sensitivity Approach iMprovement) based on the open-source library PyGimli. This new tool provides relative and absolute error assessment on resistivity images from any ERT inversion software. We first illustrate the relevance of this new tool from synthetic tests associated with a well-contrained resisvity model. Next, we revisit the ERT image of the Topographic Frontal Thrust (TFT), a major active fault located in South Central Bhutan, and discuss its geometry which is a crucial parameter to discuss strain accommodation, and improve the seismic hazard assessment in Nepal, Bhutan, and northern India, one of the most densely populated regions.

How to cite: Gautier, M., Gautier, S., and Cattin, R.: A new approach to quantify the reliability of Electrical Resistivity Tomography (ERT) images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12499, https://doi.org/10.5194/egusphere-egu23-12499, 2023.

EGU23-12582 | ECS | Posters on site | SM5.2

Geophysical and geological evidence of a previously undetected NW-trending fault crossing the historical centre of Messina (Sicily, south Italy) 

Silvia Scolaro, Paolo Pino, Antonino Torre, Sebastiano D'Amico, Giancarlo Neri, and Debora Presti

Extensive ambient noise measurements have been carried out in the historical centre of Messina (Sicily, South Italy) and the related HVSR results showed a clear variation of the fundamental peak frequency in the range between 0.4 Hz and 1.6 Hz. This frequency variation is detected across a NW-SE segment, and it can be imputed to a strong lateral heterogeneity of the sediment cover going from southwest to northeast of the study area. Moreover, we carried out a detailed geological field survey and analysis of land surface morphology based on topographic maps and DTM data that allowed us to detect the NW-trending fault, never documented in literature, crossing the historical centre of Messina. Geologic observations indicate clearly normal faulting and activity of this fault is documented at least until Middle Pleistocene, with likely prosecution during Upper Pleistocene.

The detected NW-trending fault is roughly perpendicular to the strike of the main structural system of the Straits of Messina framework to which the major earthquake of 1908 (M 7.1) is imputed. Therefore, deeper future investigations for appropriate framing into the local geodynamic context and for evaluation of its eventual prosecution in the offshore area are necessary.

In this preliminary study we identify structural discontinuities and faults which may represent new sources of hazard in a town exposed to very high seismic risk in Italy.

How to cite: Scolaro, S., Pino, P., Torre, A., D'Amico, S., Neri, G., and Presti, D.: Geophysical and geological evidence of a previously undetected NW-trending fault crossing the historical centre of Messina (Sicily, south Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12582, https://doi.org/10.5194/egusphere-egu23-12582, 2023.

EGU23-12610 | Posters on site | SM5.2

Stratigraphic characterization of the Heunghae Basin, Korea, using horizontal-to-vertical spectral ratio of microtremor records 

Ki Baek Kwon, Byeong Seok Ahn, Dabeen Heo, June Baek, Suhee Park, and Tae-Seob Kang

The Heunghae area of the Cenozoic Pohang Basin, located in the southeastern part of the Korean Peninsula, is a small-scale sub-basin covered with alluvium. The Jurassic granite is overlaid by the Cretaceous sedimentary and volcanic rocks, which form the basement of the basin composed of the Miocene non-marine and marine sediments. Therefore, the vertical distribution of strata in the Heunghae Basin can be summarized as a sequence of Quaternary alluvium, Tertiary and Cretaceous sedimentary layers, and Jurassic granite. Depending on each layer's formation time, a distinct difference in the physical properties of each layer may occur, which mechanically results in the contrast of acoustic impedance of elastic wave energy. The resonant frequency measured from the horizontal-to-vertical spectral ratio (HVSR) curve of microtremor records at a seismograph station is known to be an effective value for determining the depth to the basement with strong contrast in acoustic impedance. Based on the assumption that the boundaries formed by each layer in the Heunghae Basin have a distinct difference in acoustic impedance, we tried to estimate the resonant frequencies corresponding to each boundary from the HVSR. A total of 114 three-component geophones with a natural frequency of 5 Hz were evenly installed to obtain microtremor records over the Heunghae Basin. The distance between geophones is approximately 500 meters. The installation period is from September 24 to November 24, 2021, and the recording time varies from a minimum of 2 hours to a maximum of about 26 hours, depending on the measurement site. The recording was made at a sampling rate of 500 samples per second. The HVSR analysis used two-hour long recordings for all sites. One or more peaks can be identified in the HVSR curve of most sites. Since the resonant frequency that can be confirmed through the HVSR curve is related to the depth of the boundary between the layers where strong impedance contrast occurs under each geophone, the boundary at various depths can be determined from these frequencies of peaks. The range of resonant frequencies was found to be approximately 0.3 – 26 Hz. To compare the resonant frequency with the known geological information, the HVSR curve near the borehole site was compared with the geological logging information. In the case of some measurement sites, it was difficult to specify other peaks because one resonance frequency peak was dominant over the HVSR curve. Multiple resonant frequencies can be assumed to correspond to major layer interfaces. Due to the uncertainty of the velocity structure model, it was difficult to accurately determine the depth to the interface from these resonant frequencies. Nevertheless, the results show that the multiple resonant frequencies of the HVSR curve indicates the layer boundaries with a strong impedance contrast, and thus it can contribute to reveal the sequence stratigraphy of a basin with multiple episodes of deposits.

How to cite: Kwon, K. B., Ahn, B. S., Heo, D., Baek, J., Park, S., and Kang, T.-S.: Stratigraphic characterization of the Heunghae Basin, Korea, using horizontal-to-vertical spectral ratio of microtremor records, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12610, https://doi.org/10.5194/egusphere-egu23-12610, 2023.

EGU23-12845 | ECS | Orals | SM5.2

Exploring the potential of 3D diffraction imaging for GPR data 

Johanna Klahold, Benjamin Schwarz, Alexander Bauer, and James Irving

Diffraction imaging has become an established tool in exploration seismology thanks to its potential to provide high-resolution information that is complementary to that contained in the corresponding reflected wavefield. In ground-penetrating radar (GPR) research, data processing schemes often neglect the diffracted wavefield, focusing instead on higher-amplitude reflected arrivals. However, these data typically contain a rich diffraction background due to the structural complexity of the near surface environment. Whereas the application of diffraction imaging to 2D GPR data has already been demonstrated, the potential of diffraction imaging for 3D GPR data is still underexplored.

Building on recent studies, we adapt a coherence-based diffraction imaging workflow, originally designed for seismic data, to common-offset GPR data. The first step of the proposed scheme is the separation of diffracted arrivals from the often predominant reflections, i.e. the faint diffracted portion of the data is separated and made accessible for dedicated processing. To this end, we approximate the reflected wavefield in a fully data-driven fashion by means of a coherent stacking scheme, and we subtract it from the data. The remaining diffracted wavefield can then be further enhanced through a second local coherent stacking procedure. Ultimately, wavefield focusing of the diffraction-only data yields an image of the distribution of subsurface scatterers.

The above-described analysis is applied to a range of 3D GPR data sets in an exploratory fashion. The localization of diffracting structures in these data sets provides valuable additional information about small-scale subsurface heterogeneities that can complement standard reflection analyses.

How to cite: Klahold, J., Schwarz, B., Bauer, A., and Irving, J.: Exploring the potential of 3D diffraction imaging for GPR data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12845, https://doi.org/10.5194/egusphere-egu23-12845, 2023.

EGU23-13697 | ECS | Posters on site | SM5.2

P- and SH-wave reflection seismics of the reactivated intraplate Osning Thrust in northern Germany 

Sonja Halina Wadas and David Colin Tanner

Neotectonic movements can cause severe hazards and are scientifically and socially relevant, e.g. for seismic hazard assessment, and utilisation of the subsurface. In northern Germany, a presumed aseismic region, little is known about these processes and the associated structures, despite proven neotectonic activity, because many faults are hidden beneath sediments. To improve the knowledge of neotectonic activity, investigations of recently-active fault zones, like the Osning Lineament (OL) in North Rhine-Westphalia, are required.

To better understand the neotectonic evolution of the OL, we use near-surface geophysics, which have not been used at the OL so far. We used a combined approach using high-resolution 2D P- and SH-wave reflection seismics. P-wave seismic alone can often not properly image near-surface impressions of faults due to poor shallow resolution, but this gap can be closed using SH-wave reflection seismics, which offers very high resolution, even at shallow depth. Three P-wave profiles were measured with a hydraulically-driven vibrator vehicle (sweep frequency: 20 to 200 Hz) with a source point spacing of 10 m and plugged vertical geophones at 5 m intervals. Additionally, four SH-wave profiles were surveyed using an electro-dynamic micro-vibrator (sweep frequency: 20 to 160 Hz) with a source point spacing of 2 or 4 m and a landstreamer with horizontal geophones at 1 m intervals.

The seismic profiles show good results with respect to mapping the fault inventory. In the migrated depth sections of the P-wave profiles, several northward-dipping faults in the Cretaceous formations are recognizable, which are interpreted hitherto unknown extensions of the OL. The Quaternary, with a maximum thickness of 20 to 30 m, is only poorly imaged by the P-wave profiles, but there are nevertheless hints that the faults also extend into the Quaternary. The SH-wave profiles support this assumption, due to their higher resolution close to the surface, because of very-low wave velocities between 150 and 500 m/s. In the Quaternary sediments, further faulting and deformation features are recognizable, enabling a more comprehensive interpretation and understanding of the local fault geometry.

In the course of the project, we also carry out a full waveform inversion of the P- and S-wave data to improve the fault imaging. This will be accompanied by testing of different migration methods and seismic attribute analysis.

How to cite: Wadas, S. H. and Tanner, D. C.: P- and SH-wave reflection seismics of the reactivated intraplate Osning Thrust in northern Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13697, https://doi.org/10.5194/egusphere-egu23-13697, 2023.

EGU23-14363 | Posters virtual | SM5.2

A novel source-free frequency-domain full waveform inversion 

Qingjie Yang, Marcus Engsig, Meixia Geng, and Chaouki Kasmi

Full waveform inversion (FWI) is a challenging data-fitting procedure based on full wavefields to abstract quantitative information from seismograms. During the process, the wave propagation equation is solved for different sources and frequencies. Therefore, an efficient and effective wave propagation engine plays a critical role for FWI. The modelled data, theoretically, can be seen as the composites of Green’s function and source wavelet, convolution in the time domain, or multiplication in the frequency domain. So, the accurate source wavelet is essential for successfully applying full waveform inversion on a real dataset.  Yet, it remains a challenging task for data sets with sparse acquisition and noisy field datasets. In the traditional inversion procedure, the source signal can be estimated from observed seismograms as a part of FWI, which is time consuming and may result in inversion divergence. A source wavelet can also be extracted from the direct arrivals in the streamer dataset. However, the quality of the direct arrivals can be diminished by reflections and near-surface noise for land acquisition, vertical seismic profiling (VSP), and ocean bottom cable (OBC) datasets.

To avoid inaccurate source wavelet estimation, various source-independent methods are applied to FWI. Firstly, the deconvolution-based source-independent algorithm is proposed to mitigate the uncertainty of source wavelet estimation by normalizing the seismic data with a reference trace in the frequency domain. Then, the convolution-based source-independent algorithm is presented in the time domain to eliminate the source wavelet influence by convolving the observed data with a reference trace selected from a modelled wavefield, and the modelled data with a reference trace selected from an observed wavefield. To avoid an arbitrary or manual selection of the reference trace, we present a convolution-based source-free method implemented in the frequency domain. Thus, the convolution process becomes a multiplication in our source-free misfit function, achieving a significantly simpler implementation than in the time domain and requiring no artificial interposition.

How to cite: Yang, Q., Engsig, M., Geng, M., and Kasmi, C.: A novel source-free frequency-domain full waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14363, https://doi.org/10.5194/egusphere-egu23-14363, 2023.

EGU23-14984 | ECS | Posters virtual | SM5.2

Near-surface ambient-noise seismic tomography of Bucharest, Romania 

Alina Coman and Laura Petrescu

Bucharest is a densely populated urban region affected by strong earthquakes generated in the Vrancea seismogenic area. Studying and understanding its underground structure can help constrain seismic risk and improve estimates of seismic hazard and resilience. To obtain a 3D image of the near - surface structure beneath Bucharest, we analyse ambient noise records from 34 broadband seismic stations that operated throughout the city in 2004 ( the URS – URban Seismology network). We cross - correlate daily vertical component seismograms to obtain virtual Rayleigh waveforms and extract the phase velocity dispersion curves between pairs of stations using an automated Bessel - function analogue algorithm for periods between 2s and 10s. Dispersion curves are then combined in a fast marching seismic tomography (FMST) to estimate the lateral distribution of phase velocities at discrete periods. These are then jointly inverted with horizontal-to-vertical spectral ratios using Simulated Annealing methods under the assumption of a diffuse field to obtain shear wave velocity profiles with depth beneath each station. Preliminary results reveal seismic heterogeneities beneath Bucharest and offer fundamental constraints on the anomalous ground motion amplification and its relationship with complex geological structures from the uppermost crust.

How to cite: Coman, A. and Petrescu, L.: Near-surface ambient-noise seismic tomography of Bucharest, Romania, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14984, https://doi.org/10.5194/egusphere-egu23-14984, 2023.

EGU23-15261 | ECS | Posters on site | SM5.2

Adjoint-State Traveltime Tomography of Long Valley Caldera in California 

Chun Fei Chey, Tianjue Li, and Ping Tong

Long Valley Caldera is a depression located in eastern California, which is the Earth’s largest caldera. Geological structures beneath Long Valley Caldera are mapped by the novel adjoint-state traveltime tomography method. Adjoint-state traveltime tomography is an Eikonal equation-based seismic imaging method. It is computationally efficient as compared to wave equation-based adjoint tomography methods. Furthermore, the method avoids ray tracing in non-homogeneous media, which may fail using conventional ray tracing techniques. The data used in the method include P- and S-wave arrival times gathered from Northern California Earthquake Data Center (NCEDC). P-wave traveltimes are directly obtained from NCEDC, while high-quality S-wave arrivals are carefully picked on raw seismograms based on waveform similarity. With the abundant seismic traveltime data and adjoint-state traveltime tomography method, we can generate high-resolution P- and S-wave velocity models for the region of Long Valley Caldera. The relationship between velocity heterogeneity and seismic and magmatic activities will be investigated.   

How to cite: Chey, C. F., Li, T., and Tong, P.: Adjoint-State Traveltime Tomography of Long Valley Caldera in California, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15261, https://doi.org/10.5194/egusphere-egu23-15261, 2023.

EGU23-16673 | ECS | Posters on site | SM5.2

A Novel Transform For Extracting Dispersion Curve From Multiple Components of Ambient Noise Cross-correlation Function 

Gongheng Zhang, Xuping Feng, Xiaofei Chen, Qi Liu, and Lina Gao

Ambient noise tomography has been a widely used method for imaging the structure of the lithosphere. A key step in this method is extracting the dispersion curve from ambient noise cross-correlation. Based on the single force displacement formula of Generalized Reflection and Transmission method, we obtained the type of Bessel function in different components of the cross-correlation function. Borrowing the idea of the S transformation and replacing the exponential function in which with the corresponding Bessel function to different components of cross-correlation function, we define a new transformation, named SJ transformation, to extract Rayleigh wave dispersion curve from ZZ, ZR, RZ, RR component and Love wave dispersion curve from TT component. Using synthetic test, the extracted dispersion curve fits the theoretical dispersion curve well, which’s error rate < 1%, and in field data test, the extracted dispersion curve of the Rayleigh wave from different component matches each other well. Although the SJ spectrum of ZZ component may be distorted by noise, there may be no influence in other components, which provide the possibility to extract Rayleigh wave dispersion curve with a wider frequency band.

How to cite: Zhang, G., Feng, X., Chen, X., Liu, Q., and Gao, L.: A Novel Transform For Extracting Dispersion Curve From Multiple Components of Ambient Noise Cross-correlation Function, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16673, https://doi.org/10.5194/egusphere-egu23-16673, 2023.

EGU23-3885 | ECS | Orals | SM5.4

S-to-P receiver function analysis in the Alpine-Carpathian-Pannonian system 

Dániel Kalmár, Laura Petrescu, Josip Stipčević, Attila Balázs, and István János Kovács and the the AlpArray Working Group

We perform the first, detailed S-to-P receiver function analysis to determine the depth of the lithospheric thickness in the Eastern Alps, Carpathians, and the Pannonian Basin. The Pannonian Basin hosts deep sedimentary depocentres superimposed on a complex basement structure and it is surrounded by mountain belts. The geophysical data on which investigated the lithospheric thickness was derived in the whole Pannonian Basin, are more than 20 years old. The determination and compilation of a new dataset is timely. This work is the first uniform and comprehensive S receiver function study of the Alpine-Carpathian-Pannonian system. We present our detailed workflow from the data download via quality controls to the calculations and interpretations of the S receiver functions in this study.

We use data from the temporary seismic networks, the permanent stations of the Hungarian National Seismological network, as well as the permanent seismological stations in neighboring countries for the time range between 0.1.01.2002 and 31.01.2022. Owing to the dense station coverage we can achieve so far unprecedented resolution, altogether 389 seismological stations are used in this study. This enables us to provide new, hitherto unknown information about the lithospheric thickness of the region. We apply two different quality control procedures for the downloaded waveforms and the calculated S receiver functions. S receiver functions are determined by the iterative time domain deconvolution approach.

We apply 1D and 2D migration of the S receiver function. We compare our result maps with map from previous geophysical investigation. We show migrated Common Conversion Point cross-sections beneath the Pannonian Basin and Carpathians, and the Eastern Alps–Pannonian Basin transition zone. Furthermore, we would like to provide new information about lithospheric thickness in the eastern part of the investigated region (e.g., Apuseni Mountains, Eastern-, Southern-Carpathians, Moesian Platform and Transylvanian Plateau).

Furthermore, we jointly interpret the S receiver function results with the seismic tomography calculations of the P and S wave

How to cite: Kalmár, D., Petrescu, L., Stipčević, J., Balázs, A., and Kovács, I. J. and the the AlpArray Working Group: S-to-P receiver function analysis in the Alpine-Carpathian-Pannonian system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3885, https://doi.org/10.5194/egusphere-egu23-3885, 2023.

EGU23-3927 | Orals | SM5.4

Moho and sub-Moho structure in the larger Alpine area from S-to-P conversions 

Rainer Kind, Stefan Schmid, Felix Schneider, Thomas Meier, Xiaohui Yuan, Ben Heit, and Christian Schiffer

For the understanding of the fate of the lithosphere when continents are colliding, it is necessary to image the structures of the lithosphere. In the case of the Alps, the structure of the Moho is very well known. This is, however, not yet the case for the lower boundary of the lithosphere, the lithosphere-asthenosphere boundary (LAB). We are using S-to-P converted seismic waves to study the structures of the Moho and the LAB beneath the greater Alpine Area with data from the Alparray project and the European networks of permanent seismic stations. Besides a new European Moho map, we present more detailed information about negative velocity gradients (NVG) below the Moho which may be interpreted as LAB. We found the European mantle lithosphere is deepening from about 50°N below the Alps to the Apennines and Dinarides along the entire east-west extension of the Alps. This area has also an east dipping component towards the Pannonian Basin and the Bohemian Massif. In the East and West of this area the European mantle lithosphere is dipping towards the North. We also discuss possible source locations of the volcanoes of the European Cenozoic Rift System in the light of our data.

How to cite: Kind, R., Schmid, S., Schneider, F., Meier, T., Yuan, X., Heit, B., and Schiffer, C.: Moho and sub-Moho structure in the larger Alpine area from S-to-P conversions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3927, https://doi.org/10.5194/egusphere-egu23-3927, 2023.

EGU23-5577 | Orals | SM5.4

Where is the Eastern Alpine slab? 

Jaroslava Plomerova, Helena Zlebcikova, and AlpArray Working Group

First images of structure and dynamics of the Alpine orogeny came mostly from recordings of permanent observatories. Though density of permanent observatories has increased substantially since mid of the 20th century, yet it was not enough for detailed structural studies of the lithosphere-asthenosphere system in the complex Alpine-Mediterranean mountain belts. The tomographic images have changed especially during the last three decades, when several both small- and large-scale passive seismic experiments recorded huge amount of high-quality data at dense arrays, composed from both permanent and hundreds of temporarily installed stations. Thus the former monotonous eastward striking bend of the Alpine orogeny split into separated subductions with opposite polarity, one in the Western Alps and one in the Eastern Alps (Babuška et al., Tectonophysics 1990), later confirmed in more detailed tomography by Lippitsch et al. (2003), which included data from the TRANSALP experiment (TRANSALP Working Group, EOS 2001), the first research transect oriented on orogenic processes in the Eastern Alps. Data recorded during international AlpArray experiment, series of its complementary projects (e.g., EASI, SWATH-D, PACASE) as well as several other previous small-scale  experiments (e.g., ALPASS, BOHEMA, CIFALPS, CPB) allowed to unravel details of the Alpine structure and to search geodynamic models of the Alpine subductions. However, new questions arise with the new more precise images of the Alps. Following questions belong among them: 1) what is the origin of the E. Alpine subduction (Adriatic or European, or both); 2) if the E. Alpine slab is attached or detached, or, at which depth it resides; 3) how different methods, particularly crustal models incorporated into the body-wave tomography, disturb the real visualization of the E. Alpine slab. In this contribution we image the E. Alpine slab, evaluate effects of the crustal models on perturbations in the upper 100 km of the mantle and aim at answering the basic questions on the subduction beneath the Eastern Alps.

How to cite: Plomerova, J., Zlebcikova, H., and Working Group, A.: Where is the Eastern Alpine slab?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5577, https://doi.org/10.5194/egusphere-egu23-5577, 2023.

EGU23-5849 | Posters on site | SM5.4

Evolutionary 3D Vs crustal model for Central Apennines 

Irene Bianchi, Irene Menichelli, and Claudio Chiarabba

Detailed 3D elastic crustal models are of fundamental relevance to many applications in Geosciences, from geodynamic modelling, to simulation of seismic wave propagation and seismic engineering. However, most of the recent models suffer from two main drawbacks: (1) they are often obtained from interpolation of local 1D models; and (2) they cannot be easily updated, without recomputing the entire model (which, as a corollary, implies the availability of the complete data-set of raw seismic data). The first drawback leads to mainly oversmoothed models on the horizontal scale, where vertical boundaries are not considered either in the 1D models and in the interpolated 3D model. The second disadvantage implies that current models are generally "static" and their updates require a research effort which is often not paying back in terms of outputs.

In this study, we build the framework for an evolutionary elastic model of the Central Apennines. The starting data are represented by a huge data-set of local 1D S-wave velocity models (originally obtained from Receiver Function inversion). We invert such data-set following a Bayesian fusion approach, where the full posterior probability distribution (PPD) of the1D models is exploited to build the 3D elastic model (in absence of the full PPD information, estimators like mean posterior and standard deviation can also be used). The 3D distribution of elastic properties (i.e. a model) is represented by a 3D Voronoi tassellation of the study volume, where the number of 3D Voronoi cells and their positions are unknown. A Markov chain Monte Carlo (McMC) algorithm is used to sample the family of Voronoi models which "fit" the data adequately (here the "data" are the PPD of the 1D models). 

Our results are shown on a regular 5x5x5 km grid down to 100 km depth, and they are consistent with previous models in terms of difference in crustal structure between the Tyrrhenian and Adriatic side of the Apennines. The model shows which of the features are coherent between adjacent stations, and which areas are better resolved. Point of strength over previous models is the possibility of identifying  sub-vertical boundaries, that in a complex region of subduction and neo-formed crust are more likely than a horizontally layered structure. More complementary or additional data (in the form, e.g. of tomographic models or 1D models from dispersion curves) can be easily added to this model, to update it, as new data become available. In fact, new "data" can be either added to the full data-set or can be included modifying the PPD of the 3D Voronoi cells.

How to cite: Bianchi, I., Menichelli, I., and Chiarabba, C.: Evolutionary 3D Vs crustal model for Central Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5849, https://doi.org/10.5194/egusphere-egu23-5849, 2023.

EGU23-6047 | Orals | SM5.4

Kinematics of collisional processes in the Western and Central European Alps: Insights from a synthesis of geological data and new geophysical models 

Nicolas Bellahsen, Claudio Rosenberg, Ahmed Nouibat, Jean Baptiste Girault, Bastien Huet, Anne Paul, Loic Labrousse, Laurent Jolivet, Philippe Agard, Matthias Bernet, and Raphael pik

We provide new interpretations of the most recent geophysical models (Vs and Vp tomography mainly) coupled to geological surface information. We show that along-strike significant differences, but also first-order similarities in collision kinematics can be described from the Western to the Central Alps. Moreover, new, precise shortening estimates are obtained, giving some realistic convergence rates since 35 Ma.

In both the Western and Central Alps, after the subduction-collision transition (37-32 Ma), the orogen evolved to a doubly verging wedge with distributed shortening throughout the orogen during a first collision phase (~32-20 Ma) controlling the first mega-sequence of the molasse-type basin. From 20 Ma until recent times, the orogen was structured by localized west- or northwest-verging thrusts in the pro-side below the External Crystalline Massifs controlling the second mega-sequence of the molasse basin. This probably witnesses localization processes in the proximal European crust (i.e., below the Penninic Frontal Thrust) on a 10 Myr timescale. These structures (both distributed and localized ones) root in middle- to lower crustal low velocity (Vs) zones; the low seismic velocity being most probably controlled by fluid circulation, structural anisotropy, and/or metamorphic Alpine paragenesis (amphibolite facies). Balanced cross sections with realistic inherited Mesozoic structures allow locating the different paleogeographical domains at depth and then construction of the pre-collisional geometry.

In the Central Alps, the orogen forms a doubly verging wedge during both phases of collision with a strong amphibolite facies metamorphic imprint in the internal zone. There, the north-alpine foreland basin consists of a thick, large basin recording rather continuous sedimentation. At depth, the crustal root reaches a depth of around 50 km. Below the wedge, the subducting slab in the upper mantle is steep with no clear break-off, but possibly showing an area of attenuation.

In the Western Alps, doubly verging kinematics switch to west-verging kinematics between the two collisional phases and the overall collisional shortening is smaller than in the Central Alps; it is characterized by frontal accretion in the pro-side (while it corresponds to underplating/underthrusting in the Central Alps). As a consequence, the west alpine foreland basin is very segmented and composed of thin sub-basins. At depth, the crustal root is longer than in the Central Alps and underthrusted below the orogen down to at least 70 km. The slab in the upper mantle is moderately East-dipping with a probable break-off at around 120 km depth.

While similarities in terms of deformation localization in both parts of the orogen most likely reflect crustal rheology, the differences allow discussing the influence of both the inherited Mesozoic structure and the kinematics of Adria after the subduction phase.

How to cite: Bellahsen, N., Rosenberg, C., Nouibat, A., Girault, J. B., Huet, B., Paul, A., Labrousse, L., Jolivet, L., Agard, P., Bernet, M., and pik, R.: Kinematics of collisional processes in the Western and Central European Alps: Insights from a synthesis of geological data and new geophysical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6047, https://doi.org/10.5194/egusphere-egu23-6047, 2023.

EGU23-6250 | Orals | SM5.4

Ambient Noise Tomography Analysis in the Polish Sudetes: Preliminary results 

Somayeh Abdollahi, Piotr Sroda, Taghi Shirzad, and AniMaLS Working Group

During the last few years, the determination of the crust and upper mantle structures in southern Poland is the target of passive seismic experiments such as AniMaLS and PACASE. In this research, the area of Sudetes has been focused on that is located at the margin of the Bohemian Massif. This region represents the NE-most part of the Variscan internides between the Elbe Fault in SW and the Odra Fault in NE. The lithosphere of the region is a mosaic of several distinct units/terranes with complex tectonic history ranging from the upper Proterozoic to the Quaternary. 

To provide information about the crust and upper mantle structure beneath the Sudetes region, Ambient Noise Tomography Analysis has been used. As the input, continuous seismic data acquired during about 2 years (2017 to 2019)   have been used. The acquisition involved 41 broadband seismic stations — 23 temporary stations deployed in the area of Sudetes and Fore-Sudetic block in SW Poland, supplemented with the data from 12 permanent seismic stations, operating in this area in the Czech Republic, Germany, and Poland. Furthermore, data from 6 broadband seismic stations of the Alp Array Seismic Network have been used. 

Ambient seismic noise methods are now well-established and used in different period bands for different scales. To retrieve the surface wave dispersion curves from the vertical component of recorded noise for a given station pair, the cross-correlation in the frequency domain and stacking of noise records has been done. Then, the spectra from every combination of station pairs are cross-correlated by selecting the longest common time window available between the two stations and the average inter-station dispersion measurements with respect to the periods that have been retrieved. In the next step, the Multiple Filter Analysis technique was applied to analyze the waveforms and obtain the group velocity dispersion curves. In the final step, we are working on surface wave tomography and applying inversion for the shear (or compressional) velocities in the region. Based on the preliminary results, the depth resolution is between 5-50 km and the average shear velocity that is calculated so far is about 2.8 to 4.5 km/s at these depths. 

 Financial support 

This presentation is supported by the National Science Centre, Poland, according to the agreements UMO-2019/35/B/ST10/01628 and UMO-2016/23/B/ST10/03204. 

Acknowledgments 

"The AniMaLS Working Group comprises: Monika Bociarska, Wojciech Czuba, Marek Grad, Tomasz Janik, Kuan-Yu Ke, Weronika Materkowska, Marcin Polkowski and Monika Wilde-Piórko." 

 

How to cite: Abdollahi, S., Sroda, P., Shirzad, T., and Group, A. W.: Ambient Noise Tomography Analysis in the Polish Sudetes: Preliminary results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6250, https://doi.org/10.5194/egusphere-egu23-6250, 2023.

EGU23-6772 | ECS | Orals | SM5.4

Preliminary 3D isotropic full-waveform inversion model of the Alpine lithosphere from assimilation of AlpArray teleseismic body waves 

Stephen Beller, Najmieh Mohammadi, Vadim Monteiller, and Stéphane Operto

The Alps, which result from the convergence between the African and Eurasian plates, are an ideal natural laboratory to study the dynamics and evolution of continental orogens. This mountain range is indeed well documented both by geology and geophysics, which have notably allowed to highlight the different stages of continental subduction and collision during its formation. Nevertheless, large uncertainties remain about the 3D shape of structures and the internal composition of the Alps at crustal and upper mantle scales. This context motivated the European initiative AlpArray which deployed a dense array of more than 600 seismic sensors in the Alps and its periphery paving the way for the application of advanced seismic imaging techniques such as teleseismic waveform inversion (FWI). FWI is becoming a state-of-the-art method for lithospheric imaging as it allows the determination of various subsurface properties (seismic wavespeed, density, anisotropy or even attenuation) with high resolution and accuracy. In this study, we present the preliminary results of the LisAlps project which aimed at applying teleseismic FWI to the AlpArray  dataset to build isotropic and anisotropic high-resolution seismic models of the Alps from the surface down to the transition zone. Our preliminary application successfully built an isotropic (P and S seismic wave-speeds and density) model of the entire Alpine lithosphere from the assimilation of the first 60 s of the direct P waveforms of 18 teleseismic events within a period band ranging from 30 to 10 seconds. The resulting models recover large crustal structures of the Alpine range. In the crust, it recovers the surroundings sedimentary basins, crustal thickening in the internal part of the Alps as well as crustal thinning in the Ligurian sea and in the Ivrea zone. In the upper-mantle, where only the P wave-speed model is currently resolved, our model recovers large-scale mantle structures of the European and Apennines slabs.

How to cite: Beller, S., Mohammadi, N., Monteiller, V., and Operto, S.: Preliminary 3D isotropic full-waveform inversion model of the Alpine lithosphere from assimilation of AlpArray teleseismic body waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6772, https://doi.org/10.5194/egusphere-egu23-6772, 2023.

EGU23-7713 | Posters on site | SM5.4

New Interpretations of the Deep Structure of the Alps based on 3D Anisotropy 

Silvia Pondrelli, Judith M. Confal, and Paola Baccheschi

In a recent study, a large amount of splitting intensity measurements of the seismic anisotropy for the Central Mediterranean region has been made available, to retrieve an anisotropy tomography (see Baccheschi et al. and Confal et al. posters of session GD7.1). Here we focus on the images obtained for the Alpine region, that strongly benefit of AlpArray and Cifalps1 and 2 data. 
The 3-D distribution of seismic anisotropy, from 70 to 300 km of depth, has been compared with previous SKS shear wave splitting measurements and has been interpreted taking into account remnant and active pieces of slabs. Most of previously defined mantle flows are confirmed, as the asthenospheric toroidal flow around the tip of the slab beneath the Western Alps. Shallower anisotropy pattern show strong relation with main tectonic structures, from the Rhine Graben to the Western Alps arc and so on. However, the no uniqueness of available seismic velocity anomalies mapping keep some part of the interpretation open, as for instance the detectability of proper slab anisotropy. Out of the directional patterns, this splitting intensity tomography gives a map of anisotropy intensity and its variations with depth, with some strong heterogeneities corresponding to regions where previous seismic anisotropy studies described the presence of complex structure, as for the upper mantle beneath the Eastern Alps. All these new information, if integrated with the most recent studies for the Alpine region, may be a relevant support to innovative hypotheses on crust-to-mantle Alpine transition and structure.

How to cite: Pondrelli, S., Confal, J. M., and Baccheschi, P.: New Interpretations of the Deep Structure of the Alps based on 3D Anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7713, https://doi.org/10.5194/egusphere-egu23-7713, 2023.

EGU23-7881 | ECS | Posters on site | SM5.4 | Highlight

Geodynamic inversion to explain the present-day plate motion in the Alpine-Mediterranean area 

Christian Schuler and Boris Kaus

The Alpine-Mediterranean region is area of interest for many studies seeking to better understand the geological evolution as well as the present-day mantle and lithosphere structure. However, despite numerous studies, the geological structure of the upper mantle and the geometry of the different subduction zones remain matter of debate.

Here, we use 3D geodynamic models to investigate the impact of the structure and material properties of the upper mantle and lithosphere on the motion of the Alpine-Mediterranean area. The geodynamic simulations are performed by the finite-difference code LaMEM (Kaus et al. (2016)) and a visco-plastic rheology is used to explore the dynamic behaviour of the upper mantle. In particular, we use the recently developed Julia interface to LaMEM to start simulations and read back the results which simplifies postprocessing and comparing the results to observational constraints.

Specifically, we compare the models with recently compiled GPS velocity data (Serpelloni at al. (2022)). As a result of the geological history in the Mediterranean the density and viscosity structure of the upper mantle is rather complex and influenced by various subduction zones, such that geometry, viscosity and density structures are primary parameters of interest in this study.

First results suggest that the Calabria subduction and the Hellenic subduction explain the fastest horizontal velocities in the Mediterranean whereas the horizontal motion in the Alpine area cannot arise from an active subduction zone but rather from large density and viscosity differences caused by the remnants of older subduction zones.

 

Kaus B J P, Popov A A, Baumann T S, Pusok A E, Bauville A, Fernandez N, and Collignon M (2016): Forward and inverse modelling of lithospheric deformation on geological timescales. Proceedings of NIC Symposium.

Serpelloni E, Cavaliere A, Martelli L, Pintori F, Anderlini L, Borghi A, Randazzo D, Bruni S, Devoti R, Perfetti P and Cacciaguerra S (2022): Surface Velocities and Strain-Rates in the Euro-Mediterranean Region From Massive GPS Data Processing. Front. Earth Sci. 10:907897. doi: 10.3389/feart.2022.907897

How to cite: Schuler, C. and Kaus, B.: Geodynamic inversion to explain the present-day plate motion in the Alpine-Mediterranean area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7881, https://doi.org/10.5194/egusphere-egu23-7881, 2023.

EGU23-9451 | Posters on site | SM5.4

Imaging the upper crust in the eastern Pyrenees with ambient seismic noise 

Sergi Ventosa, Martin Schimmel, Jordi Díaz, and Mario Ruiz

We present here a 3D shear-velocity regional model of the eastern Pyrenees centered at the Cerdanya Basin using seismic ambient noise to image structure of the Iberian and Eurasian uppermost crust. In the context of the SANIMS project, we deployed a network of 24 broadband seismic stations that complement existing permanent stations from the CA, ES and FR networks and previous temporal deployments from the OROGEN project, and aside, a high-density short-period seismic network focused on the study the Cerdanya Basin. For the regional study, we use the broadband dataset to compute symmetric cross-correlations of the seismic noise using the wavelet phase cross-correlation and the time-scale phase weighted stack, then estimate the phase and group velocity of Rayleigh waves between 1.5 – 7 s and 1.5 – 5 s, respectively. Afterwards, we build a 3D S-wave velocity model from path-average velocities in two steps: regionalization and pointwise depth inversion. In the regionalization step, we build velocity maps from the dispersion curves measured using the fast marching method on the forward problem and a hybrid l1 – l2 norm criterion on the inversion to enforce robustness to outliers. In the depth inversion step, we apply transdimensional inference to explore for S-wave velocity profiles with an unknown number of layers of constant velocity and the noise variance of the Rayleigh phase and group velocity maps using a least-square misfit function. The best models show a top low-velocity layer 2 – 3 km thick followed by distinct velocity profiles to the North and to the South, corresponding to the expected differences between the Iberian and Eurasian plates. To the South we observe two layers with a boundary at 6 – 7 km depth and velocities of about 3.2 and 3.5 km/s respectively, while to the North velocities are generally lower, increase much less with depth and there is no clear boundary.

How to cite: Ventosa, S., Schimmel, M., Díaz, J., and Ruiz, M.: Imaging the upper crust in the eastern Pyrenees with ambient seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9451, https://doi.org/10.5194/egusphere-egu23-9451, 2023.

EGU23-9775 | ECS | Orals | SM5.4

A new 3D P-wave velocity model for the greater Alpine Region from 24 years of local earthquakes data. 

Matteo Bagagli, Edi Kissling, Tobias Diehl, and Irene Molinari

The European Alps and its surrounding mountain belts (e.g., the northern Apennines, the northwestern Dinarides, and the western Carpathians) forms a tectonically complex system, referred as the “greater Alpine region” (GAR). Although being extensively  investigated, the evolving dynamic tectonic system and microplates relation are still under debate.

From 2016-2019 the AlpArray project, with its seismic network of ~700 broadband sensors, created an unprecedented chance to uniformly investigate the recorded seismicity in the GAR. After the successful compilation of the AlpArray research seismicity catalog (AARSC, Bagagli et al., 2022) we took a major leap to repick the seismicity reported by the European-Mediterranean Seismological Centre (EMSC) from May 2007 to December 2015. We use the same approach as for the AARSC to repick and consistently relocate 1397 events. Eventually, we consistently and homogeneously re-calculated the local magnitudes on the vertical component only (MLv). This allows a better data selection for the inversion stages, avoiding the magnitude scales mixing reported in bulletins. In addition to these two dataset, we also use the already published dataset for the latest GAR tomography spanning the time-period from January 1996 to May 2007 (Diehl et al., 2009). These three combined dataset have an average picking error observations of 0.2 seconds and provide an unique opportunity to perform a local earthquake tomography (LET) in the GAR.

We select 2343 MLv >=2.5 well-locatable events (azimuthal gap <180 degree, number of P-observations > 7) for the calculation of a new Minimum 1D model for the GAR. For the inversion procedure, we select 2285 events for a total of 84664 rays. The 99% of the rays are shorter than 350 km. We use SIMULPS software to derive the 3D P-wave velocity model using a model parametrization of 20x20x10 km cells in the well-resolved area. 

The preliminary velocity model correctly delineates the GAR major tectonic features, and due to the dense ray coverage it provides excellent resolution of the shallow crustal heterogeneities. This model will help the seismological community push forward the understanding of the GAR geodynamics.

How to cite: Bagagli, M., Kissling, E., Diehl, T., and Molinari, I.: A new 3D P-wave velocity model for the greater Alpine Region from 24 years of local earthquakes data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9775, https://doi.org/10.5194/egusphere-egu23-9775, 2023.

EGU23-11633 | Orals | SM5.4

Towards a 3D crustal geomodel of the Western Alps in the French Geological Reference Platform (RGF) 

Anne Gaelle Bader, Philippe Calcagno, Nicolas Bellahsen, and Anne Paul

The French Geological Reference Platform (RGF) is a national programme for acquisition and management of geological data launched in the early 2010’s and coordinated by BRGM (https://rgf.brgm.fr). It involves the geosciences community to develop a new 3D knowledge of the underground to support innovative responses to a wide range of scientific first order questions as well as issues our society is facing. The RGF’s Alps and surrounding basins (Abp) worksite aims at a better understanding of the 3D structure of an emblematic mountain range and at addressing the impact of climate change and geological risk.

Within the RGF’s Abp, we proposed to build a 3D reference geomodel covering the area of the whole worksite ([41.5°N-48°N; 4°E-10°E]; ~350 000 km²) investigating the subsurface down to the Moho. This geomodel aims at federating the geoscientific community and intends to integrate existing data and information, e.g. geology, geophysics, relevant at that scale. It will be updated using the data acquired during the Abp worksite and serve to set up boundary information for local studies.

The geomodel is constructed in a collaborative approach where contributors discuss their data and knowledge and converge to a common interpretation of the investigated major geological boundaries that are the Moho (European lithosphere, Adriatic lithosphere, Ligurian backarc basin) and the boundaries of the subduction wedge.

We present here the state of progress of the geomodel based on the geological interpretive sections established at lithospheric scale by the RGF community (see Bellahsen at al., this session) and the integration of the available geophysical data and models (velocity models Vp and Vs, seismic reflection and refraction, gravimetry, etc.).

This work benefits from the French Geological Reference Platform - Alps and surrounding basins programme funding.

How to cite: Bader, A. G., Calcagno, P., Bellahsen, N., and Paul, A.: Towards a 3D crustal geomodel of the Western Alps in the French Geological Reference Platform (RGF), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11633, https://doi.org/10.5194/egusphere-egu23-11633, 2023.

EGU23-11792 | ECS | Posters virtual | SM5.4

Mapping the mantle transition zone beneath the Ibero-Maghrebian region with P-wave receiver functions 

Joan Antoni Parera-Portell, Flor de Lis Mancilla, and José Morales

Thermal and compositional anomalies are known to drive changes in the thickness of the mantle transition zone (MTZ), as they modify the P-T conditions under which phase transitions occur. Typically, the phase changes defining the upper and lower boundaries of the MTZ take place at 410 km and 660 km respectively, thus yielding a standard MTZ thickness of 250 km. These phase transitions have opposite Clapeyron slopes, so while a cold temperature anomaly makes the 410 discontinuity shallower and the 660 deeper, a hot anomaly has the contrary effect. In this ongoing study we use P-wave receiver functions to map the MTZ discontinuities below southern Iberia and northwestern Africa and identify anomalous regions that can be linked to regional structures in the mantle. In this area, convergence of the African and Eurasian plates led to the subduction of the ancient Tethys oceanic lithosphere, from which a remnant slab is stalled below the Gibraltar arc, introducing thermal and chemical heterogeneities that alter the MTZ.

Roughly 33000 receiver functions were obtained from 501 seismic stations, from both permanent and temporary deployments, including four seismic profiles with high density of stations (interstation distances from 2 to 10 km). We constructed a grid of N-S and W-E sections with a spacing of 0.25x0.25 degrees by depth-migrating and projecting the receiver functions with a phase-weighted common conversion point stacking method. An algorithm for the automatic detection of the MTZ discontinuities was then used, and the results allowed us to obtain preliminary 2D and 3D maps containing the depth, width and number of peaks of the pulses attributed to the 410 and 660 discontinuities. Overall, the MTZ reaches its maximum thickness under the Alboran basin (290 km), but the region with anomalous thickness extends well into southeastern Iberia. This feature is attributable to a cold temperature anomaly and matches the position where tomographic studies locate the stalled Tethys slab. Two small areas in the Gulf of Cadiz also stand out for displaying a MTZ thickness of 290 km, coinciding with a region where the 410 discontinuity splits in two pulses. On the contrary, the MTZ is generally thinner than usual towards the south and west of the Alboran basin, especially in sections of the Rif and the Strait of Gibraltar where it can reach 205 km. Our results show, though, that while changes in the 410 discontinuity can be correlated with the tectonic configuration of the region and known anomalies in the mantle such as the Tethys slab, the 660 displays a much more unpredictable pattern.

How to cite: Parera-Portell, J. A., Mancilla, F. D. L., and Morales, J.: Mapping the mantle transition zone beneath the Ibero-Maghrebian region with P-wave receiver functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11792, https://doi.org/10.5194/egusphere-egu23-11792, 2023.

EGU23-12284 | Posters on site | SM5.4

AdriaArray Seismic Network – status in April 2023 

Petr Kolínský, Thomas Meier, and the AdriaArray Seismology Group

With the advent of plate tectonics in the last century, our understanding of the geological evolution of the Earth system improved essentially. The internal deformation and evolution of tectonic plates remain however poorly understood. This holds in particular for the Central Mediterranean: The formerly much larger Adriatic plate is recently consumed in tectonically active belts spanning at its western margin from Sicily, over the Apennines to the Alps and at its eastern margin from the Hellenides, Dinarides towards the Alps. High seismicity along these belts indicates ongoing lithospheric deformation. It has been shown that data acquired by dense, regional networks like AlpArray provide crucial information on seismically active faults as well as on the structure and deformation of the lithosphere. The Adriatic Plate and in particular its eastern margin have however not been covered by a homogeneous seismic network yet.

Here we report on the status of AdriaArray – a seismic experiment to cover the Adriatic Plate and its actively deforming margins by a dense broad-band seismic network. Within the AdriaArray region, currently about 990 permanent broad-band stations are operated by more than 40 institutions. Data of 97% of these stations are currently available via EIDA. In addition to the existing stations, 414 temporary stations from 24 mobile pools are deployed in the region achieving a coverage with an average station distance of 50 – 55 km. The experiment is based on intense cooperation between local network operators, mobile pool operators, field teams, ORFEUS, and interested research groups. Altogether, more than 50 institutions are participating in the AdriaArray experiment. We will report on the time schedule, participating institutions, mobile station pools, maps of temporary station distribution with station coverage and main points of the agreed Memorandum of Collaboration. The AdriaArray experiment will lead to a significant improvement of our understanding of the geodynamic causes of plate deformation and associated geohazards.

How to cite: Kolínský, P., Meier, T., and Seismology Group, T. A.: AdriaArray Seismic Network – status in April 2023, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12284, https://doi.org/10.5194/egusphere-egu23-12284, 2023.

EGU23-12370 | Posters on site | SM5.4

Moho and LAB below the Western Alps from P and S Receiver Function analysis and joint inversion 

Caterina Montuori, Stephen Monna, Francesco Frugoni, Claudia Piromallo, Lev Vinnik, and AlpArray Working Group

We used the data from the dense, broadband AlpArray Seismic Network to derive a set of Receiver Function (RF) measurements on the Moho and Lithosphere-Asthenosphere Boundary (LAB) for a broad region encompassing the Western Alps and including the Ivrea Geophysical Body (IGB), a fragment of mantle emplaced in the lower continental crust. Our analysis fills an information gap since, in spite of numerous active and passive seismological investigations on the Alpine orogen, many of the observations focus on the Moho or the deeper part of the mantle, while reliable information on the LAB below the Alps is scarce. Moreover, our findings provide an additional contribution to resolving the debated topic of the existence of continuous or interrupted continental subduction below the Western Alps.

We derive seismic velocity profiles of the crust-uppermost mantle below each of the 50 analyzed stations down to about 250 km depth, through the joint inversion of P and S RFs. We constrain the lateral variations of the Moho and LAB topographies across the colliding plates, and quantify the errors related to our measurements. Our observations allow us to considerably expand the published data of the Moho depth and to add a unique set of new measurements of the LAB (Monna et al., 2022). 

Our results yield a comparable thickness (on average 90–100 km) of the Eurasia and Adria lithospheres, which are colliding below the IGB; Eurasia is not presently subducting below Adria with vertical continuity. These findings suggest that there is a gap between the superficial (continental) European lithosphere and the deep (oceanic) lithosphere, confirming the discontinuous structure imaged by some seismic tomography models.

the AlpArray Working Group: list on http://www.alparray.ethz.ch/home/

Monna, S., Montuori, C., Frugoni, F., Piromallo, C., Vinnik, L., & AlpArray Working Group (2022). Moho and LAB across the Western Alps (Europe) from P and S receiver function analysis. Journal of Geophysical Research: Solid Earth, 127, e2022JB025141. https://doi.org/10.1029/2022JB025141

How to cite: Montuori, C., Monna, S., Frugoni, F., Piromallo, C., Vinnik, L., and Working Group, A.: Moho and LAB below the Western Alps from P and S Receiver Function analysis and joint inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12370, https://doi.org/10.5194/egusphere-egu23-12370, 2023.

EGU23-12870 | ECS | Orals | SM5.4

AI based 1D and 3D P- and S-Wave Velocity Models for the Alpine Mountain Chain from Local Earthquake Data 

Benedikt Braszus, Andreas Rietbrock, Christian Haberland, and Trond Ryberg

The increase in seismic data availability as well as the improvement of automated picking algorithms allows us to reassess the seismicity and velocity structure in many regions around the globe with higher accuracy. Using the seismic recordings from a total of more than 1100 stations of the AlpArray Seismic Network and other permanent and temporary stations within the area we work towards a comprehensive 3D P- and S-wave crustal velocity model for the European Alpine region using Local Earthquake Tomography. Phase arrival times of local seismicity are determined by the widely used deep neural network PhaseNet.
We present first a P- & S-wave minimum 1D model of the Greater Alpine region computed with the established linearized inversion algorithm VELEST and compare it to our new 1D model using a bayesian Markov chain Monte Carlo (McMC) algorithm exploring a broader model space. Pg and Pn phase arrivals in the epicentral distance ranges from 0-130km and 300-600km, respectively, are included while picks within the triplication zone from 130-300km are not considered due to difficult phase identification. Both models match within the error margin of the McMC result, while the discrepancy is largest in the lower crust where the resolution decreases due to the chosen epicentral distance ranges. 
With our minimum 1D model as starting model we compute a 3D P-wave model using the SIMULPS code. As the remaining residual distributions of the 1D and 3D model show, the removal of outliers in the pick catalog is more accurate when based on the 3D residuals due to insufficient incorporation of velocity variations along epicentral distance and backazimuth in the 1D model. The most prominent first order structures of the 3D model are in agreement with previous local studies of the area and the model already can be used to consistently improve crustal correction terms on an orogenic scale for teleseimic tomographies and thus sharpen the seismic image of the upper mantle. Furthermore, it will allow to the associate the phases Pg, Pmp & Pn to picked onset times in the crustal triplication zone more accurately. Due to their ray paths these picks are of special importance to the resolution in the lower crust and will contribute significantly to the final 3D P- and S-wave model. Absolute velocities along the Moho interface are higher than in previous studies and therefore in better accordance with values expected from petrology.  

How to cite: Braszus, B., Rietbrock, A., Haberland, C., and Ryberg, T.: AI based 1D and 3D P- and S-Wave Velocity Models for the Alpine Mountain Chain from Local Earthquake Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12870, https://doi.org/10.5194/egusphere-egu23-12870, 2023.

EGU23-12921 | ECS | Posters on site | SM5.4

Spatial and Temporal Patterns in Eastern-Alpine Seismicity 

Rens Hofman, Jörn Kummerow, and Simone Cesca and the AlpArray Working Group

We exploit a new template matching based catalogue to study the spatial
and temporal patterns of seismicity in the Eastern and Southern Alps. Data
from the AlpArray Swath-D network from late 2017 to late 2019 were used to
enhance the resolution of the seismic catalogues provided by local
agencies. The template matching method was implemented using our own
GPU-accelerated algorithm to deal with the large data volume. All events
are relocated using waveform-based picking methods.

Based on this result, we study statistical characteristics of the extended
seismicity catalogue, which now has a magnitude of completeness of Mc=0.6
and contains about 7,500 seismic events. We analyse the main spatial and
temporal features of seismicity revealed by this novel dataset. Finally,
we analyse specific event clusters that originated from the template
matching method, and seek to link event interconnectivity to geometrical
properties of the clusters.

How to cite: Hofman, R., Kummerow, J., and Cesca, S. and the AlpArray Working Group: Spatial and Temporal Patterns in Eastern-Alpine Seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12921, https://doi.org/10.5194/egusphere-egu23-12921, 2023.

EGU23-13077 | ECS | Posters on site | SM5.4

Moho map and receiver functions database beneath the European Alps using data from recent large-scale passive experiments 

Konstantinos Michailos and the AlpArray Receiver Function working group

The Alpine orogen is a unique geological formation with a highly variable crustal structure. Despite numerous active and passive seismic investigations in the past, constraints on the crustal structure across the whole Alpine domain are still limited. To improve on this, we use waveform data from four past and ongoing large-scale passive experiments in the broader Alpine region: namely the AlpArray Seismic Network (AASN), which also includes many permanent stations in its footprint, the Eastern Alpine Seismic Investigation (EASI), the China-Italy-France Alps seismic transect (CIFALPS-1) and the Pannonian-Carpathian-Alpine Seismic Experiment (PACASE). This results in a composite seismic network of more than 700 broadband seismic stations, providing unprecedented data coverage.  

We apply a systematic processing workflow to these data and calculate Receiver Functions (RF). After applying strict quality control we obtained 107,633 high-quality RF traces, on average of 122 per station. Next, we developed codes to perform time-to-depth migration in a newly implemented 3D spherical coordinate system using a reference P and S wave velocity model. Finally, we compiled a new detailed Moho map by manually picking the depth of the discontinuity. Our Moho depth estimates generally support the results of previous studies in the region and vary from ca. 20 to ca. 55 km depth with the maximum values observed beneath the Alpine orogen. The RF dataset along with the codes and new Moho map are all open-access. 

The high quality and homogeneously calculated RF dataset, along with the new, coherently derived Moho depth map of the Alpine region, can provide helpful information for interdisciplinary imaging and modeling studies investigating the geodynamics of the European Alps orogen and its forelands (e.g., joint inversions with other geophysical and geological datasets). 

How to cite: Michailos, K. and the AlpArray Receiver Function working group: Moho map and receiver functions database beneath the European Alps using data from recent large-scale passive experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13077, https://doi.org/10.5194/egusphere-egu23-13077, 2023.

EGU23-13405 | ECS | Posters on site | SM5.4

The Berkovići (BA) 22 April 2022 earthquake sequence – seismological and seismotectonic analysis 

Iva Dasović, Davorka Herak, Marijan Herak, Helena Latečki, Marin Sečanj, Bruno Tomljenović, Snježana Cvijić-Amulić, Marija Mustać Brčić, Tena Belinić Topić, and Josip Stipčević

A strong earthquake, ML = 6.0 (MW = 5.7), occurred on 22 April 2022 at 21:07 UTC with an epicentre near Berkovići in Bosnia and Herzegovina, with focal depth of about 20 km. The earthquake was felt throughout Bosnia and Herzegovina, Montenegro, Croatia (especially Dalmatia), but also in Slovenia, Italy (especially the western coast of the Adriatic), Serbia, Albania and North Macedonia. The maximum intensity of the earthquake was rated as VII–VIII EMS in Berkovići and Ljubinje. A young woman in Stolac lost her life from a rock slide caused by the earthquake. In the wider epicentral area the earthquake caused a number of large or small rock falls, many chimneys were damaged, tiles fell from the roofs, plaster fell off, and there were also large cracks in the walls.

By 31 October 2022, the DuFAULT project researchers located 6220 aftershocks (39 with ML≥ 3.0), with as many as 900 located in the first 12 h of the series. The strongest aftershock, ML = 4.9, occurred on 24 April 2022 at 4:27 UTC with focus at a depth of about 25 km and the epicentre also close to Berkovići. The vast majority of earthquakes have their foci relatively deep for this area, at depths between 15 and 28 km. Most of the epicentres form a compact group slightly elongated parallel to the NW-SE Dinaric strike, however two smaller groups northwest and southeast of the main group stand out with extension perpendicular to the Dinaric strike with somewhat shallower foci. The analysis of the focal mechanism and the hypocentral spatial distribution suggest that the mainshock resulted from the NE-SW directed compression and occurred on a reverse fault, on a moderately NE-dipping plane. Interestingly though, this series is also characterized by earthquakes released by a tension along the NE-SW striking and approximately 45° dipping normal faults, documented in the smaller north-western group.

We will present spatio-temporal analysis of seismicity, resulting focal plane solutions and seismotectonic interpretation.

How to cite: Dasović, I., Herak, D., Herak, M., Latečki, H., Sečanj, M., Tomljenović, B., Cvijić-Amulić, S., Mustać Brčić, M., Belinić Topić, T., and Stipčević, J.: The Berkovići (BA) 22 April 2022 earthquake sequence – seismological and seismotectonic analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13405, https://doi.org/10.5194/egusphere-egu23-13405, 2023.

EGU23-13742 | ECS | Posters on site | SM5.4

3D high-resolution imaging of lithospheric VP, VS, and density structure in the Alps using full-waveform inversion of the teleseismic P waves 

Najmieh Mohammadi, Stephen Beller, Vadim Monteiller, and Stephane Operto

The convergence between the African and European plates has created the magnificent Alpine chain with a very complex geological structure. This natural laboratory helps researchers to decipher the geotectonic processes imposed on the region. One useful way to understand better the prevailing geodynamics system is to interpret high-resolution crustal and upper-mantle models developed by full wavefield tomographic methods simultaneously. The high density of broadband stations deployed during the AlpArray project allows us to apply Full Waveform Inversion (FWI) on the teleseismic earthquakes recorded in the Alpine region. FWI minimizes the misfit between the entire recorded and simulated seismograms to reconstruct multiparameter models of the Earth’s interior with a resolution close to the wavelength. We used 203 teleseismic earthquakes with 6.8MW7.4 and 8depth630 km recorded by 1232 stations including permanent seismological broadband stations and AlpArray temporary seismic network. To model the propagation of the teleseismic wavefields through the target area, we used a hybrid technique that couples a global wavefield computed by AxiSEM in axisymmetric Earth from the source to the boundaries of the study area to regional wavefield propagating through the lithospheric domain computed by SPECFEM3DCartesian. This target-oriented wavefield injection method mitigates the computational cost of the wavefield simulation at the global scale, hence making high-frequency wavefield simulations in the lithospheric target possible (up to the 1Hz period). We use the AK135 velocity model as the initial model and iteratively inverted the band-pass filtered data at 10-30 s periods using the limited-memory BFGS optimization algorithm to obtain a 3D high-resolution elastic VP, VS, and density model for the crust and upper mantle of the entire Alpine chain. Our results show that the main documented structures of the Alps have been recovered well in the crust and upper mantle and confirm that a reliable geotechnical interpretation in the Alps depends on the consideration of the geodynamical process on Apennine and Dinaric simultaneously.

How to cite: Mohammadi, N., Beller, S., Monteiller, V., and Operto, S.: 3D high-resolution imaging of lithospheric VP, VS, and density structure in the Alps using full-waveform inversion of the teleseismic P waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13742, https://doi.org/10.5194/egusphere-egu23-13742, 2023.

EGU23-14009 | Orals | SM5.4

Geophysical-petrological model for bidirectional mantle delamination of the Adria microplate beneath the Apennines and Dinarides orogenic systems 

Ivone Jimenez-Munt, Wentao Zhang, Montserrat Torné, Jaume Vergés, Estefanía Bravo-Gutierrez, Ana M Negredo, Eugenio Carminati, and Daniel Garcia-Castellanos

In this study we present a geophysical-geochemical integrated model of the thermochemical structure of the lithosphere and uppermost mantle of the Adria and Tisza microplates along two transects running from the Northern Apennines to the Pannonian Basin, and from the Southern Apennines to the Balkanides, respectively. The objectives are to image crustal thickness variations and characterize the different mantle domains. In addition, we evaluate the topographic response of opposed subductions and discuss their implications in the evolution of the region. Results show a more complex structure and slightly higher average crustal density of Adria compared to Tisza microplate. Below the Tyrrhenian Sea and Western Apennines, Moho is much shallower (< 25 km) than along the Eastern Apennines, where it can reach depths of 50-55 km. The LAB depth shows significant lateral variations, from the shallow LAB of the Tyrrhenian Sea and Western Apennines (< 80 km) to the thick LAB underneath the eastern Apennines and Adriatic Sea (150 and 125 km, respectively). Our results are consistent with the presence of two mantle wedges, resulting from the rollback of the Ligurian-Tethys and Vardar-NeoTethys oceanic slabs followed by continental mantle delamination of the eastern and western distal margins of Adria. These two opposed slabs beneath the Apennines and Dinarides are modelled as two thermal sublithospheric anomalies of -200°C. A Tecton garnet lherzolite (Tc_2 of Griffin et al., 2009) for the whole lithospheric mantle allows fitting geoid height and long-wavelength Bouguer anomalies. Most of the elevation along the profile is under thermal isostasy and departures can be explained by regional isostasy with an elastic thickness between 10 and 20 km.

This research has been funded by the GeoCAM Project (PGC2018-095154-B-I00) with the contribution of the China Scholarship Council.

How to cite: Jimenez-Munt, I., Zhang, W., Torné, M., Vergés, J., Bravo-Gutierrez, E., Negredo, A. M., Carminati, E., and Garcia-Castellanos, D.: Geophysical-petrological model for bidirectional mantle delamination of the Adria microplate beneath the Apennines and Dinarides orogenic systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14009, https://doi.org/10.5194/egusphere-egu23-14009, 2023.

EGU23-14741 | ECS | Posters on site | SM5.4

3D Crustal structure of the Basque-Cantabrian Zone (N Spain) through a nonlinear joint inversion of surface wave phase velocities, teleseismic receiver functions and Rayleigh wave ellipticity 

Andrés Olivar-Castaño, David Pedreira, Javier A. Pulgar, Marco Pilz, Alba Díaz-González, and Juan Manuel González-Cortina

The Basque-Cantabrian Zone (BCZ) is a large, inverted Mesozoic basin (the Basque-Cantabrian basin or BCB) forming part of the Pyrenean-Cantabrian mountain belt, in the north of Iberian Peninsula. The Mesozoic basin developed in one of the most subsident regions between the European plate and the Iberian sub-plate during the stage of crustal hyperextension linked to the rifting of the Central-North Atlantic and the opening of the Bay of Biscay. The high subsidence rate led to the accumulation of more than 15 km of sediments according to some estimates, and the significant crustal extension caused the exhumation of the mantle in the easternmost sector of the BCB. The Alpine orogeny caused the closure and inversion of the BCB and its incorporation to the Pyrenean-Cantabrian orogen. In this work, we studied the crustal structure of the BCZ resulting from this long and complex tectonic evolution using five years of continuous seismic recordings gathered by a local network of broadband stations, most of them deployed in the framework of projects SISCAN and MISTERIOS. A total of 66 locations were used (not all of them simultaneously), with an average spacing of ~30 km between stations. From this dataset, we extracted the multi-mode phase velocities of surface waves and the ellipticity of Rayleigh waves from cross-correlations of the seismic ambient noise. This allowed us to retrieve the shear-wave velocity structure of the crust, especially at shallow to intermediate depths. To better constrain the deeper crustal structure, we also extracted teleseismic P-wave receiver functions for all suitable events. Each dataset was carefully analyzed before performing a nonlinear, joint inversion using the simulated annealing technique. The result is a set of 1D shear-wave velocity models that represent a compromise between all three datasets. These 1D models were then used in a linear interpolation to build a 3D model of the BCZ. The main feature of the 3D model is a thickened crust of up to 50 km beneath the Cantabrian Mountains. A discontinuous, intracrustal level of high-velocities is identified in the northern part of the model, coherently with previous geological and geophysical observations, suggesting that the thick crustal root would be caused by the indentation of the Cantabrian Margin lower crust into the Iberian crust, as has been already proposed. This new 3D model fills a gap in the knowledge of the study area, whose seismic characterization was primarily based on active source studies, which often only provide estimates of the P-wave velocities along 2D profiles.

How to cite: Olivar-Castaño, A., Pedreira, D., Pulgar, J. A., Pilz, M., Díaz-González, A., and González-Cortina, J. M.: 3D Crustal structure of the Basque-Cantabrian Zone (N Spain) through a nonlinear joint inversion of surface wave phase velocities, teleseismic receiver functions and Rayleigh wave ellipticity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14741, https://doi.org/10.5194/egusphere-egu23-14741, 2023.

The collisional area between the ALCAPA microplate and East European Craton across the Carpathian Orogen, is one of the most intriguing geological areas in Europe.  Here, a variety of tectonic processes are occurring simultaneously, including extensional basins, oceanic subduction, post-collisional volcanism, and active crustal deformation due to the push of the Adria plate or the pull of the actively detaching Vrancea slab, creating it a distinctive tectonic setting.

To explore the lithospheric structure of this collision region, broadband stations operating in the Carpatho-Pannonian area between 2006and 2022 were transformed into virtual sources by cross-correlating simultaneous noise recordings at pairs of stations in the frequency domain and stacking the cross-correlations to obtain one inter-station cross-correlogram per pair (Empirical Green functions). Rayleigh and Love phase velocities, as well as Rayleigh wave attenuation coefficients, were measured and mapped at six discrete periods (5, 10, 15, 25, and 30s) using the latest multiscale seismic imaging algorithms. We used a least-squares inversion approach based on ray theory with adaptive parameterization to map the lateral variations in surface-wave velocity, whereas the attenuation structures were revealed by mapping the frequency-dependent Rayleigh-wave attenuation coefficient.

Our results reveal a strong correlation between geology and tomographic images, suggesting a highly heterogeneous crust. An inverse correlation trend between Rayleigh wave phase velocity and attenuation maps was obtained for all period ranges, revealing a contrast between high attenuation features from the Pannonian Basin, including intra-Carpathian areas, and stable platform regions placed in front of the Carpathians. The shallow crust shear velocity model shows low velocities beneath Neogene and Paleozoic sedimentary basins and volcanic regions and high velocities under collisional fronts. In the middle to lower crust (25–30 km), high shear velocities beneath the Pannonian basin are in agreement with the previous findings.

How to cite: Borleanu, F., Petrescu, L., Magrini, F., and De Siena, L.: Shear wave velocity and attenuation tomography acquired from seismic ambient noise data analysis in a complex collisional area at the edge of the East European Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15098, https://doi.org/10.5194/egusphere-egu23-15098, 2023.

Planetary magnetic field production mechanism may require consideration of fermi electrons. While avoiding the Boussinesq approximation and considering a presence of Fermi electrons in a planetary core, a new hypothesis how the planetary magnetic field may operate is proposed. The overall topology concerns both the core’s north hemisphere (NH) and south hemisphere (SH) that produce its own magnetic polarities due to a sense of the Earth’s rotation (Coriolis effect). Magnetism can be generated due to the electric current form the core’s fermi electrons that follow the more conducting spiraling plumes from the convection heat exchange. NH produces magnetic flux directed toward the north (reversed polarity) while SH produces magnetic flux directed to the south (normal polarity). When NH is more buoyant than SH, the overall dipolar reversed polarity is produced. When SH of the core is more buoyant, the overall normal magnetic polarity is produced. Overall planetary magnetic field is then generated from a core’s heat exchange competition between its NH and SH. For this hypothesis supports is found from the theoretical arguments, from the topology of finite element modeling, and from the evidence of a historical magnetic reversal record. Calculations considering the presence of Fermi electrons in the core allow for heat gradient generated magnetic flux estimate between 0.1 mT and 3 mT inside the liquid core. Finite element modeling topology of simulated magnetic dipoles near inner/outer core boundary (IOB) oriented only northward in NH and southward in SH supported that todays’ surface magnetic field observations are consistent with the outer core fields between 0.1 mT and 3 mT. Individual treatment of normal and reversed polarity durations supported that a predominance of magnetic polarity durations relates to the existing temperature models near the core/mantle boundary (CMB) that have a consistent effect on the heating exchange within the core.

How to cite: Kletetschka, G.: Origin of the Earth’s magnetic field from the Fermi electrons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2458, https://doi.org/10.5194/egusphere-egu23-2458, 2023.

Differential rotation of Earth’s inner core relative to the mantle above plays an important role in core dynamics and the core-mantle coupling. The rotation has been inferred from temporal changes of repeating seismic waves traversing the inner core. In our recent study1, we report remarkable observations that all the paths previously with significant temporal changes have now exhibited little changes over the recent decade. The consistent global pattern suggests strongly that the inner core rotates as a whole and the rotation has paused in the recent decade with a net torque of ~1016 Nm. Furthermore, the recent pattern seems associated with a gradual turning-back as a part of a long-period (about seven decades) oscillation with another turning point in the early 1970s. The multidecadal periodicity coincides with changes in several other geophysical observations, including the global mean temperature2, the global mean sea level rise3, and especially the length of day (LOD) and magnetic field variations4, pointing to a common resonating system of the Earth. Our observation provides important constraints to geodynamo models and the mantle-inner core gravitational coupling and offers key evidence for dynamic interactions between the Earth’s layers from the deepest interior to the surface.

References:

 

1. Yang, Y., & Song, X. (2023). Multidecadal variation of the Earth’s inner-core rotation. Nature Geoscience (in press). https://doi.org/10.1038/s41561-022-01112-z

2. Zotov, L., Bizouard, C., & Shum, C. K. (2016). A possible interrelation between Earth rotation and climatic variability at decadal time-scale. Geodesy and Geodynamics, 7(3), 216–222. https://doi.org/10.1016/j.geog.2016.05.005

3. Ding, H., Jin, T., Li, J., & Jiang, W. (2021). The contribution of a newly unraveled 64 years common oscillation on the estimate of present-day global mean sea level rise. Journal of Geophysical Research: Solid Earth, 126(8). https://doi.org/10.1029/2021JB022147

4. Roberts, P. H., Yu, Z. J., & Russell, C. T. (2007). On the 60-year signal from the core. Geophysical and Astrophysical Fluid Dynamics, 101(1), 11–35. https://doi.org/10.1080/03091920601083820

How to cite: Yang, Y. and Song, X.: Multidecadal variation of the inner core rotation and implications for global dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2826, https://doi.org/10.5194/egusphere-egu23-2826, 2023.

Core surface flow inversion using physics-informed neural networks

Jinfeng Li (1) and Yufeng Lin (1)

(1) Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen 518055, China.

Physics-informed neural networks (PINNs) have recently been widely used to solve PDEs or ODEs. An attractive feature of this method is that it can calculate the derivatives without truncation errors by the automatic differentiation method (Lu et al., 2021). Another advantage is that it can solve the inverse problem with slightly modified code for solving the forward problem (Raissi et al., 2020). In this study, we use the PINN to inverse the core surface flow from the geomagnetic observations. We start from the radial component of the induction equation under the frozen-flux approximation (Robert and Scott, 1965) and tangentially geostrophic flows assumption (Hills, 1979). Instead of using the large-scale approximation, which assumes the flows that generate the observed secular variation (SV) are large-scale, we model the flow field in the physic space and construct the unobserved magnetic field based on the power spectrum of numerical dynamo simulations. We examine the nonuniqueness of the inversion results by pre-setting the different initial parameters of the neural network. Our tests show that the uncertainty of large-scale flow field is small and the inversion scheme is robust.

We retrieve the core surface flow field between 2000 and 2020 using the core magnetic field model CHAOS-7 (Finlay et al., 2020). We then perform the dynamic mode decomposition method (DMD) (Schmid, 2010) of the retrieved core flow. This method decomposes the flow field and SV into several eigenmodes with time evolution. The consistency time evolution between the flow and the SV modes indicates the inversion algorithm is stable. Moreover, we calculate the secular acceleration (SA) of the magnetic field for each dynamic modes and find the mode with 8 years period can match the jerk events occurred in the equatorial region.

Reference

  • C. Finlay, C. Kloss, N. Olsen et al. 2020, The CHAOS-7 geomagnetic field model and observed changes in the South Atlantic Anomaly, Earth Planets Space, 72, 156.
  • G. Hills, 1979, Convection in the Earth’s Mantle Due to Viscous Shear at the Core-Mantle Interface and Due to Large-Scale Buoyancy. PhD Thesis, New Mexico State University, Las Cruces.
  • Lu, X. Meng, Z. Mao and G. E. Karniadakis, 2021, DeepXDE: A Deep Learning Library for Solving Differential Equations, SIAM Review, 63, pp. 208-228.
  • Raissi, A. Yazdani and G. E. Karniadakis, 2020, Hidden fluid mechanics: Learning velocity and pressure fields from flow visualizations, Science, 367, pp. 1026-1030.
  • H. Robert and S. Scott, 1965, On analysis of the secular variation. 1: A hydromagnetic constraint: Theory, Journal of Geomagnetism and Geoelectricity, 17, pp. 137-151.
  • J. Schmid, 2010, Dynamic mode decomposition of numerical and experimental data, J. Fluid Mech, 65, pp. 5-28.

How to cite: Li, J.: Core surface flow inversion using physics-informed neural networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3710, https://doi.org/10.5194/egusphere-egu23-3710, 2023.

EGU23-7723 | ECS | PICO | GD8.1

Did the dynamo cease during the Ediacaran Period prior to inner core nucleation? 

Tinghong Zhou, John Tarduno, Kenneth Kodama, Rory Cottrell, and Richard Bono

Models and paleointensity data continue to consistently point to the Ediacaran Period as the most likely time for the onset of inner core nucleation (ICN). The geodynamo models of Driscoll (2016) and Driscoll and Davies (2022) predict a weak field state, where core kinetic energy exceeds magnetic energy, prior to ICN. The paleomagnetic record of the Ediacaran Period shows a hyper-reversal frequency and unusually high secular variation. But the most telling characteristic of the Ediacaran magnetic field that suggests the dynamo approached the weak field state is its time-averaged ultralow paleointensity, more than 10 times weaker than today (Bono et al., 2019). The field subsequently regained strength in the early Cambrian (Zhou et al., 2022), consistent with Ediacaran ICN. Here, we investigate the possibility that the magnetic field may have ceased completely for some part of the Ediacaran Period. We report new field strength values from whole rocks that are less than 1-2 microTesla. These values are amongst the lowest terrestrial fields ever recorded, heightening the possibility of environmental effects due to the weakened magnetosphere that may have in turn influenced biotic evolution. But even these ultralow field values may overestimate the true ambient field strength because of subsequent thermal viscous magnetic overprints carried by nonideal magnetic carriers in whole rocks. We will discuss our efforts to use single crystal paleointensity methods to isolate ideal magnetic carriers to resolve this question.

How to cite: Zhou, T., Tarduno, J., Kodama, K., Cottrell, R., and Bono, R.: Did the dynamo cease during the Ediacaran Period prior to inner core nucleation?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7723, https://doi.org/10.5194/egusphere-egu23-7723, 2023.

EGU23-8209 | PICO | GD8.1

Low frequency eigenmodes of the Earth's fluid core 

Santiago Triana, Jeremy Rekier, Felix Gerick, and Veronique Dehant

Earth's rotation period varies over many time scales ranging from diurnal to several milennia, in addition to its secular increase due to tidal friction. These variations in the rotation period imply an exchange of angular momentum between the mantle and other fluid layers of the Earth, such as the atmosphere, oceans, and the fluid outer core. In order to disentangle the role of the outer core, a good understanding of its low frequency eigenmodes is necessary. We attempt to build a relatively simple model of the Earth's fluid core including gravitational, viscous, and magnetic coupling with the mantle and the solid inner core. Our goal is to assess whether observed length-of-day variations can be partially attributed to outer core eigenmodes, and if that is the case, to explore the implications related to the outer core-mantle and outer-inner core coupling mechanisms.

How to cite: Triana, S., Rekier, J., Gerick, F., and Dehant, V.: Low frequency eigenmodes of the Earth's fluid core, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8209, https://doi.org/10.5194/egusphere-egu23-8209, 2023.

The thermal conductivity values through Earth’s core and planetary cores have important implications for the thermal evolution and magnetism of these bodies. For the outer cores of small terrestrial planetary bodies, this study constrains the thermal conductivity of liquid Fe-8wt%S-4.5wt%Si at pressures 2-5 GPa. Thermal conductivity was estimated using the Wiedemann-Franz Law from electrical resistivity measurements of a small Fe alloy sample at high pressures and high temperatures in a 1000-ton cubic anvil press. The powder samples were prepared by mixing powders of three compositions: Fe, FeS, and Fe-9wt%Si. Electron microprobe analysis and micro X-ray diffraction verified the elemental composition and crystallographic structure of the sample material both before and after pressurization.

Resistivity-temperature plots of the Fe-8wt%S-4.5wt%Si data display trends common to Fe mixed with significant amounts of Si: a general rise in resistivity to a peak, a drop in resistivity through the melt, and a leveling of resistivity through the liquid state. Two reversals in slope occur between 800 K and 1000 K. At each integral pressure value between 2-5 GPa, an electrical resistivity in the range 300±100 μΩ·cm was found. Using the Sommerfeld value of the Lorenz number, thermal conductivities in the range 15±5 W/m/K were estimated. Comparative plots including resistivity data of Fe, Fe-4.5wt%Si, Fe-17wt%Si, and Fe-20wt%S are instructive to illuminate the relative effects of S and Si on the resistivity and thus the thermal conductivity and adiabatic heat flow of core mimetic Fe alloys. If the pressure at the top of the core is constrained using the assumptions of hydrostatic equilibrium and a bulk silicate mantle, then these thermal conductivity results may be applied to a number of known small terrestrial bodies, such as Io, in the case of a dominantly Fe-S-Si liquid outer core.

How to cite: Lenhart, E., Yong, W., and Secco, R.: Outer Core Heat Flux in Small Terrestrial Bodies from Electrical Resistivity Measurements of Liquid Fe-8S-4.5Si at High Pressure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10229, https://doi.org/10.5194/egusphere-egu23-10229, 2023.

Recent satellite missions provide accurate measurement of the time derivative of the Gaussian coefficients from which the secular variation spectrum can be calculated. The ratio of the magnetic energy spectrum to the secular variation spectrum gives a typical scale τ for the temporal variation of the geomagnetic field as a function of the spherical harmonics degrees l. There is much interest in the scaling of τ with l: τ ~ l β. Numerical simulations and the frozen flux hypothesis suggest the simple relation τ ~ l -1 while observational studies give a diverse range of value for β. A question here is whether the frozen flux hypothesis is applicable. It is plausible that magnetic diffusion can be neglected inside the outer core. However, the situation in a boundary layer under the core-mantle boundary (CMB) is less clear. A related question is whether τ observed at the Earth's surface is relevant to what is happening in the interior of the outer core as the form of the magnetic field above the CMB is constrained by the boundary conditions at the CMB. Here we use a numerical dynamo model to investigate these questions. We extend the definition of τ to the inside of the outer core. We find that in our simulations the exponent β undergoes a sharp transition just beneath the CMB, magnetic diffusion plays a role in the scaling of τ above the CMB and the frozen flux hypothesis is not applicable here.

How to cite: Tsang, Y.-K.: Scaling of the geomagnetic secular variation time scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10439, https://doi.org/10.5194/egusphere-egu23-10439, 2023.

EGU23-10448 | ECS | PICO | GD8.1

Turbulent Dissipation in the Boundary Layer of Precession Driven Flow in a Sphere 

Sheng-An Shih, Santiago Andrés Triana, and Véronique Dehant

The energy dissipation in the fluid flow near the boundary separating the core and the mantle (i.e. the CMB) of a planet or moon with a fluid interior is a crucial parameter to understand its rotational dynamics. This boundary layer is typically very small compared to the core radius, and can become turbulent under certain conditions, which presents a challenge for global scale simulations of the flow in the fluid core. Here we construct a local Cartesian model to study the boundary layer of a precessing planet or moon. The solutions we derive in the laminar regime, i.e. where the Reynolds number Re is small and the non-linear term is neglected, are consistent with previous studies. This gives us confidence to push the model further into the turbulent regime. We solve numerically the governing equations, i.e., the Navier-Stokes equation and the continuity equation for an incompressible fluid in a rotating frame. We observe that, when the flow is turbulent, the boundary layer dissipation is increased, compared to its laminar counterpart, as expected. Moreover, we found that the velocity profile agrees with the law of the wall, a theory developed to study turbulent flow near a solid boundary. Based on our numerical results, we further construct a turbulence model using similarity theory. Last but not least, due to chemical interaction on the planetary core-mantle boundary, small-scale topography or surface roughness might exist. To investigate this topographic effect, we impose a sinusoidal topography in our local model. Preliminary results show further increase of the dissipation. Our results may provide valuable insight into the boundary layer dissipation near the CMB for both the Earth and the moon.

How to cite: Shih, S.-A., Triana, S. A., and Dehant, V.: Turbulent Dissipation in the Boundary Layer of Precession Driven Flow in a Sphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10448, https://doi.org/10.5194/egusphere-egu23-10448, 2023.

Modern observations show that the fast fluctuations in geomagnetic acceleration and fluid core surface flow motions always occur at the equatorial regions, which may arise from the rapidly hydromagnetic waves atop the Earth’s core. But, the exact origins of these waves are still unclear, though the so-called eMAC waves may provide a potential mechanism. Given that the physical expressions of describing the physical properties (e.g., equatorial confinement and latitudinal distribution, damping rate, eigen-period) and the perturbed magnetic fields of the eMAC waves have not been given before, this work carefully revisits the currently eMAC wave theory and firstly gives the systematically analytical expressions for these physical properties. Importantly, the perturbation analysis indicates that the eMAC wave model can own the high accuracy (i.e., the relative errors are less than 5%) to describe the low-latitude waves with latitude below 25 degrees, which can cover the regions where the equatorial waves mainly locate. In summary, this work provides an important complement for the currently eMAC wave theory. The results of this work are significant to understand the physical mechanism responsible for the origins of the inferred equatorial waves, their physical properties and the dynamics of the Earth’s equatorial regions.

How to cite: Duan, P.: Analytical model of the equatorial Magnetic-Archimedes-Coriolis waves propagating at Earth’s core surface and the potential implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12751, https://doi.org/10.5194/egusphere-egu23-12751, 2023.

EGU23-15288 | ECS | PICO | GD8.1

The dipole–multipole transition in planetary dynamos 

Debarshi Majumder, Binod Sreenivasan, and Gaurav Maurya

We investigate the dipole–multipole field transition in rapidly rotating dynamos in the low-inertia regime relevant to planetary cores. Here, the Rossby number is small on the planetary core depth as well as on the length scale of core convection. Attention is focused on the dynamics of slow Magnetic-Archimedean-Coriolis (MAC), or magnetostrophic, waves generated in the energy-containing scales of the dynamo. The suppression of the slow MAC waves in a strongly driven dynamo is dynamically similar to the excitation of these waves in a moderately driven dynamo evolving from a small seed magnetic field. While the former regime causes polarity reversals, the latter regime produces the axial dipole field from a multipolar state. For either polarity transition, a Rayleigh number based on the mean wavenumber of the energy-containing scales bears the same linear relationship with the peak Elsasser number measured at the transition. This self-similarity can provide an estimate of the Rayleigh number that admits polarity reversals.

How to cite: Majumder, D., Sreenivasan, B., and Maurya, G.: The dipole–multipole transition in planetary dynamos, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15288, https://doi.org/10.5194/egusphere-egu23-15288, 2023.

EGU23-15588 | ECS | PICO | GD8.1

Constraints for Mercury’s Inner Core Size by Dynamo Modelling 

Patrick Kolhey, Daniel Heyner, Johannes Wicht, Thomas Gastine, and Ferdinand Plaschke

Mercury possesses an internally generated global magnetic field which significantly differs from Earth’s magnetic field in geometry and strength. While being much weaker (1% of Earth’s surface field strength), Mercury’s magnetic field is strongly aligned to the rotation axis and the magnetic equator is offset towards north. These characteristics of the field have been a challenging task for dynamo modelling. Current dynamo models for Mercury suggest that a stably stratified layer below the core-mantle boundary is necessary to explain the the weak, axisymmetric and offset dipole magnetic field. Although, having different geophysical measurements by NASA’s MESSENGER mission the inner core size of the planet is barely constrained. While interior models from geodetic measurements suggests an inner core sizes which can occupy half of the total core, dynamo models which generate a Mercury-like magnetic field have mostly a rather small inner core of around 400 km. In this study we performed dynamo simulations with a stably stratified layer below the core-mantle boundary which are able to reproduce Mercury’s magnetic field characteristics and we vary the inner core size in these models systematically. First results of the study reveal, that only dynamo models with a small inner core well below 750 km radius are capable of reproducing a Mercury-like magnetic field, while models with a larger inner cores cannot reproduce the offset magnetic equator.

How to cite: Kolhey, P., Heyner, D., Wicht, J., Gastine, T., and Plaschke, F.: Constraints for Mercury’s Inner Core Size by Dynamo Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15588, https://doi.org/10.5194/egusphere-egu23-15588, 2023.

EGU23-16047 | ECS | PICO | GD8.1

New constraints on shear properties of the Earth’s inner core from the global correlation wavefield 

Thuany Costa de Lima, Thanh-Son Pham, Xiaolong Ma, and Hrvoje Tkalčić

Seismological observations of J-phases, the seismic waves traversing the Earth’s inner core (IC) as shear waves, are critical to understanding the inner core shear properties. That, in turn, will shed light on the solidification process and the evolution of the inner core and our planet. Most body-wave detections of the J waves have been controversial due to their small amplitudes, which involve energy conversion from P- to S- and vice versa at the inner core boundary. Recent advances in understanding the nature of the late coda correlation offer a new way to sample the deep Earth, including the shear properties of the Earth’s inner core. The correlation-based features provide the sensitivity of the periods between 15 and 50 s, placing it between the body waves and normal mode data. Therefore, the observations of late coda correlation are vital in refining the shear properties of the IC, such as velocity, anisotropy, and attenuation.

This study employs several uninvestigated J-wave correlation features detected in the global coda-correlation wavefield building on the study of Tkalčić and Pham (2018) that determined the shear wave speed reduction of 2.5% relative to PREM. The correlation features observed in the coda-correlation wavefield arise from similar seismic phases in which one contains a shear-wave leg in the IC. Improved data selection process and knowledge acquired from recent theoretical and observational developments in understanding the anatomy of coda correlation wavefield enable significant improvements in the data quality. We benchmark the waveforms of observed correlation features using numerical modeling, confirm the observations of J waves and inner core solidity and update its shear properties’ values, including shear-wave speed and Poisson’s ratio.

How to cite: Costa de Lima, T., Pham, T.-S., Ma, X., and Tkalčić, H.: New constraints on shear properties of the Earth’s inner core from the global correlation wavefield, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16047, https://doi.org/10.5194/egusphere-egu23-16047, 2023.

EGU23-16247 | ECS | PICO | GD8.1

Precipitation of light elements from Earth’s liquid core: Can exsolution power the ancient geodynamo? 

Alfred Wilson, Monica Pozzo, Dario Alfè, Andrew Walker, Anne Pommier, Sam Greenwood, and Chris Davies

Earth’s core currently sustains a geodynamo through chemical convection in the liquid outer core. This power source originates from the growth of the solid inner core, where light elements are partitioned to the liquid at the lower most outer core. The inner core is expected to be ~1 Gyr old, meaning that for most of Earth history, the geodynamo required alternate power sources to produce a magnetic field. The paleomagnetic record shows that the field has been persistent for the last 3.5 Gyrs. Secular cooling is not capable of providing sufficient power for the geodynamo to remain active during this time if conductive heat transport is large. Recent experiments and calculations find that the thermal conductivity of the core is high, suggesting that the power available for geodynamo action would have been exhausted significantly before inner core growth began. Of the alternate power sources available to supplement secular cooling, precipitation of light elements is the most hopeful. We explore the solubility of silicon and other candidate light elements in iron-rich liquids of the core through ab initio calculations of partitioning. We apply these results to a thermodynamic model of partitioning, informed by experimental partitioning. When incorporated into thermal history models of the deep Earth, we find that the geodynamo can be sustained by silicon precipitation, provided that the oxygen concentration of the ancient core is less than 1.1 wt%. These results highlight the importance of the initial composition of the core and interaction between light elements on the available precipitative power in the core.

How to cite: Wilson, A., Pozzo, M., Alfè, D., Walker, A., Pommier, A., Greenwood, S., and Davies, C.: Precipitation of light elements from Earth’s liquid core: Can exsolution power the ancient geodynamo?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16247, https://doi.org/10.5194/egusphere-egu23-16247, 2023.

Surface waves contain critical information on seismic azimuthal anisotropy, which is directly related to underground geological dynamics. However, despite seismic azimuthal anisotropy, the topographic variation may also contribute to the azimuthal dependence of surface wave speed. To our knowledge, most surface wave traveltime tomography methods ignore the topographic variation in forward modeling. Furthermore, the theoretical propagation path is also calculated in isotropic media with flat surface. Undoubtably, inaccurate forward simulations could introduce artefacts to imaging results 

To address these problems, we develop a novel surface wave tomography method which tracks the surface wave propagation path in anisotropic media and incorporates the topographic variation. An elliptically anisotropic eikonal equation is used to describe the traveltime field of surface wave propagation, and sensitivity kernels with respect to shear wave velocity and azimuthal anisotropy are derived using the adjoint-state method. This new tomography method is tested and verified in Po Basin and adjacent regions, including the central Alps and northern Apennines.  

How to cite: Hao, S., Tong, P., and Chen, J.: Adjoint-State Surface Wave Tomography for Azimuthally Anisotropic Media: Eikonal Equation-Based Methods and Incorporation of Surface Topography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2522, https://doi.org/10.5194/egusphere-egu23-2522, 2023.

The singularity points are very important for elastic waves propagation in low-symmetry anisotropic media (Stovas et al., 2021a). Being converted into the group velocity domain, they result in internal refraction cone with anomalous amplitudes and very complicated polarization fields. In elastic orthorhombic (ORT) media, there is always one singularity point in the essential symmetry plane, (0,1,2) singularity points in remaining non-essential symmetry planes and (0,1) points in-between the symmetry planes (Stovas et al., 2021b).

I analyze the conditions for existence of a singularity point in-between the symmetry planes.

In order to do that I fix the diagonal elements of the stiffness coefficient matrix, cjj , j=1,6, and introduce new variables d12 = c12 +c66, d13 = c13 +c55 and d23 = c23 +c44. I also assume that the symmetry plane 2-3 is the essential one by introducing the inequality c55 < c44 < c66 . If c66 < c44 < c55, the 2-3 plane is still essential one but the properties of non-essential planes will interchange. In case of other inequalities for “S wave” stiffness coefficients, the corresponding properties of singularity points can be obtained by a cyclic rotation of stiffness coefficients and symmetry planes (Stovas et al., 2023).

For selected essential symmetry plane (2-3), I propose to fix two variables d12 and d13, and set the variable d23 as a free variable. By changing d23 only, I can define the trajectory of a singularity point in-between the symmetry planes. This trajectory is given by a continuous line connecting the symmetry planes. Then I define the traces of this trajectory on symmetry planes (maximum two points for each plane) by a specific value of the variable d23. These 6 values can be used for intervals of d23 where the singularity point in-between the symmetry planes exists. Analysis shows that there are 7 zones in (d12 , d13) plane with different intervals of d23, which guarantee the existence of singularity point in-between the symmetry planes. There are 3 intervals of d23 in one zone, two intervals in two zones and one interval in three zones. There is no singularity point in-between the symmetry planes for any d23 in remaining zone. These zones are separated by three straight lines that defined by d12 = d12(critical) , d13 = d13(critical)  and d13 = α d12, where α guarantees that trajectory of singularity point meets the essential symmetry plane.

 References

Stovas, A., Roganov, Yu., and V. Roganov, 2021a, Geometrical characteristics of P and S wave phase and group velocity surfaces in anisotropic media, Geophysical Prospecting, 68(1), 53-69.

Stovas, A., Roganov, Yu., and V. Roganov, 2021b, Wave characteristics in elliptical orthorhombic medium, Geophysics, 86(3), C89-C99.

Stovas, A., Roganov, Yu., and V. Roganov, 2023, On singularity points in elastic orthorhombic media, Geophysics, 88(1), C11-C32.

How to cite: Stovas, A.: On singularity point in-between the symmetry planes in elastic orthorhombic media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2613, https://doi.org/10.5194/egusphere-egu23-2613, 2023.

Talc and chloritoid are common metamorphic minerals observed in mafic-ultramafic rocks and/or high-pressure metapelitic rocks comprising subducting slabs. Crystallographic preferred orientations (CPOs) of elastically anisotropic minerals have been known to be important for interpreting seismic anisotropy observed in subduction zones. However, studies on the CPOs of talc and chloritoid have been very limited. In this study, CPOs of talc and chloritoid in garnet-chloritoid-talc schist samples from ultrahigh-pressure Makbal Complex (Tianshan, Kazakhstan-Kyrgyzstan) which has been regarded as a part of subducting slab were measured using SEM/EBSD technique. CPO-induced seismic properties of both talc and chloritoid were analyzed and compared. The results showed that both talc and chloritoid displayed strong CPOs characterized by the [001] axes aligned subnormal to the foliation (see also Lee et al., 2021). CPO-induced seismic properties of polycrystalline talc and chloritoid were calculated and they showed that both P-wave anisotropy (AVp = 5 – 72 %) and high S-wave anisotropy (AVs = 10 – 24 %) of talc and chloritoid were much higher than those of garnet (AVp = 0.4 %, AVs = 0.9 – 1.0 %). In addition, the AVp of polycrystalline talc was much higher than that of polycrystalline chloritoid. Analysis of S-wave delay time and fast-polarization direction based on the modelling study of subduction zone geometry showed that the CPOs of talc and chloritoid induced a long delay time of 0.3 – 0.5 s and trench-parallel polarization direction for high dip-angle subduction, which is consistent with the observation of strong trench-parallel seismic anisotropy in subduction zones. Our results suggest that the strong CPOs of talc and chloritoid would influence trench-parallel seismic anisotropy induced by subducting slab in subduction zones. Lee et al., 2021, Seismic anisotropy in subduction zones: evaluating the role of chloritoid, Frontiers in Earth Science, 9, 1-16.

How to cite: Lee, J. and Jung, H.: Crystallographic preferred orientations of talc and chloritoid and implications for seismic anisotropy in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3136, https://doi.org/10.5194/egusphere-egu23-3136, 2023.

EGU23-3947 | ECS | Orals | GD7.1

Slab-driven transport of ultra-low velocity material in the deep mantle 

Jonathan Wolf and Maureen D. Long

It has been suggested that the present-day locations of ultra-low velocity zones (ULVZs), which are thin features just above the core-mantle boundary (CMB), are influenced by mantle convection; however, apart from their preferential locations, there is little direct evidence for this connection. Observations of deep mantle anisotropy can be used to infer mantle dynamics but are not usually jointly analyzed with ULVZ structure. We newly detect and characterize a ULVZ beneath the Himalaya, located approximately at the edge between an (almost) isotropic and a large anisotropic region in the lowermost mantle. Using global wavefield simulations to model realistic mineral physics scenarios, we show that the seismic anisotropy is indicative of northeast-southwest flow directions. The southwestwards flow is likely induced by slab remnants at the CMB, and the ULVZ is located at the southwestern edge of the anisotropic province, which is indicative of slab-induced ULVZ displacement. 

How to cite: Wolf, J. and Long, M. D.: Slab-driven transport of ultra-low velocity material in the deep mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3947, https://doi.org/10.5194/egusphere-egu23-3947, 2023.

EGU23-4746 | ECS | Orals | GD7.1

Full-wave anisotropy tomography for the upper mantle of Northeast China using SKS splitting intensities 

Junliu Suwen, Yi Lin, Li Zhao, and Qi-Fu Chen

Northeast (NE) China is located in the eastern Central Asian Orogenic Belt, and has a complex deformation history. The evolution of NE China has been controlled by the (Paleo-)Pacific Plate since the late Mesozoic and was affected by the closure of the Paleo-Asian and Mongol–Okhotsk oceans. Meanwhile, large strike-slip faults and extensive intraplate volcanisms characterize active tectonics in NE China. Different mechanisms have been proposed to interpret the origin of the intraplate volcanism, such as interactions between the lithosphere and the big mantle wedge, and the subduction-induced upwelling within the gap of the stagnant Pacific slab.

Seismic anisotropy describes the directional dependence of the seismic velocities. In NE China, seismic anisotropy not only reveals the past and present deformations in the lithosphere but also helps us clarify the possible intraplate volcanism. In this study, we apply the full-wave multi-scale anisotropy tomography method to investigate the seismic anisotropy in NE China. We measure the splitting intensities of SKS waves, which can be linearly inverted for the 3D variation of anisotropy. We employ broadband seismograms recorded at ~450 regional seismic stations (including ~250 temporary stations deployed for 2 years) of unprecedented density from teleseismic events of magnitudes greater than 5.5 occurring in 2009-2018. We obtain a total of 4249 splitting intensity measurements, and perform the multi-scale inversion using sensitivity kernels computed by normal-mode summation. The resulting 3D anisotropic model of the upper mantle in NE China shows a dominant NW-SE fast axis, which highlights a strong correlation between the intraplate volcanoes and upper-mantle seismic anisotropy, and indicates that NE China is still mainly controlled by the Pacific Plate.

How to cite: Suwen, J., Lin, Y., Zhao, L., and Chen, Q.-F.: Full-wave anisotropy tomography for the upper mantle of Northeast China using SKS splitting intensities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4746, https://doi.org/10.5194/egusphere-egu23-4746, 2023.

EGU23-5235 | ECS | Orals | GD7.1

Azimuthal Anisotropy in the Eastern Alpine Crust from Ambient Noise Tomography 

Emanuel D. Kästle and the AlpArray Working Group

Making use of the dense AlpArray and SwathD networks in the eastern Alps, a large dataset of Rayleigh phase-velocity measurements is extracted. This dataset is the basis for a 3D azimuthally anisotropic shear-velocity model of the Alpine crust. A 2-step inversion approach is followed: First, phase-velocity maps are created which are inverted for the shear velocity structure at depth in a second step. In both steps, a Bayesian (rjMcMC) approach is used to find the posterior distribution of anisotropic models. The model uncertainties are propagated from the phase-velocity maps to the depth inversion to make sure that the data is not overfitted. The final model shows a 2 layer anisotropy in the Alpine crust, the upper crustal layer is mostly orogen parallel and follows the major fault structures. The lower crustal to uppermost mantle layer shows orogen-perpendicular fast axis in the Alps and an anisotropy following the curvature of the Alps in the northern foreland. The importance of microfabric such as microcracks and oriented mineral grains is difficult to estimate from the presented model on the effective regional-scale anisotropy. But the results suggest that the azimuthal anisotropy may be largely controlled by macro-scale structures. The transition from upper to lower crustal anistotropy takes place at approx. 20 km depth which is unlikely to be due to the brittle-ductile transition. But it could indicate that upper and lower crust are only weakly coupled underneath the Alps.

How to cite: Kästle, E. D. and the AlpArray Working Group: Azimuthal Anisotropy in the Eastern Alpine Crust from Ambient Noise Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5235, https://doi.org/10.5194/egusphere-egu23-5235, 2023.

EGU23-6183 | ECS | Orals | GD7.1

Novel Application of Receiver Function Analyses Dependent on Splitting Measurement: Crustal Anisotropy along the NAFZ 

Derya Keleş, Tuna Eken, Pan Wang, Zhouchuan Huang, and Tuncay Taymaz

Crustal scale deformation along the fault zone and dipping Moho structures can be constrained by azimuthal seismic anisotropy. Reliable knowledge of the geometry of fault and its vertical extent in the crust and uppermost mantle that often controls observed seismic anisotropy parameters is of great importance for proper seismic hazard assessments in active tectonic settings. The North Anatolian Fault Zone (NAFZ) extending from Karlıova Triple Junction in the east to the Aegean Sea in the west poses actively deforming areas. To elucidate the crustal anisotropy along the NAFZ we will apply a novel receiver function method that simultaneously measures the Moho orientation and average bulk crustal anisotropy. It employs an algorithm in which transverse polarization component minimization (TPCM) applied on the Pms (Moho converted phase) is being integrated into a joint objective method (JOF). The method is advantageous as it restrains the random and coherent noise in the data. Prior to raw data-based anisotropic parameter estimations, we performed synthetic tests mainly considering two hypothetic models devised to be analogous to the NAFZ case. Model-1 assumes S-anisotropy in the crust oriented along N45°E with 4% of strength with flat Moho. The Model 2 involves the same anisotropic properties but with 25° of dipping Moho. Our synthetic tests show that this new approach is able to exactly resolve true model parameters assumed for Model 1 resulting in a 0.987 per cent of model accuracy. The resultant 0.225 s of time delay corresponds to ~4% of anisotropic strength considering a crustal thickness with 30 km and 4.8 km/s average isotropic S-wave velocity for the medium. Our results obtained for Model-2 still tend to converge the true model parameters but show slight discrepancies, in particular, for anisotropic parameters resolved with 0.3 s of time delay and N40°E oriented fast wave azimuth. The test for Model-2 achieves 27.5° as the dipping angle of Moho which is fairly close to its true model parameter. We observe relatively low model accuracy with 0.710 per cent in the case of Model-2. At the further stage of this work, we will utilize digital waveforms of teleseismic earthquakes recorded at the KOERI and AFAD permanent seismic station networks along the NAFZ.   

How to cite: Keleş, D., Eken, T., Wang, P., Huang, Z., and Taymaz, T.: Novel Application of Receiver Function Analyses Dependent on Splitting Measurement: Crustal Anisotropy along the NAFZ, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6183, https://doi.org/10.5194/egusphere-egu23-6183, 2023.

EGU23-7321 | ECS | Posters on site | GD7.1

Testing the splitting intensity methodology to retrieve average, dipping, and depth dependent anisotropy from a complex subduction model 

Judith M. Confal, Paola Baccheschi, Silvia Pondrelli, Brandon P. VanderBeek, Foivos Karakostas, and Manuele Faccenda

Seismic anisotropy measurements provide a lot of information on the deformation and structure of the Earth’s interior, in particular of the upper mantle. Conventional methods of measurement of anisotropy have their limitations, especially regarding depth resolution. Splitting intensity (SI) is a seismic observable, related to the amount of energy on the transverse component waveform and, to a first order, it is linearly related to the elastic perturbations of the medium through the 3-D sensitivity kernels, that can be therefore inverted, allowing a high-resolution image of the upper-mantle anisotropy. Starting from synthetic SKS waveforms, we first derived high-quality SKS splitting intensity measurements; then we used the splitting intensity data as input into tomographic inversion. This approach enables high‐resolution tomographic images of horizontal upper‐mantle anisotropy through recovering vertical and lateral changes in anisotropy and represents a propaedeutic step to the real cases of subduction settings. Additionally, this approach was able to detect regions of strong dipping anisotropy by allowing a 360° periodic dependence of the splitting vector. Single and thick layers of dipping angles between 30 and 60° are clearly represented with a high dt2 value, while double layers or nearly vertical dips are more difficult to identify.

How to cite: Confal, J. M., Baccheschi, P., Pondrelli, S., VanderBeek, B. P., Karakostas, F., and Faccenda, M.: Testing the splitting intensity methodology to retrieve average, dipping, and depth dependent anisotropy from a complex subduction model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7321, https://doi.org/10.5194/egusphere-egu23-7321, 2023.

EGU23-7527 | ECS | Posters on site | GD7.1

The Memory of the Mantle: The Influence of a Time Varying Flow Field on Present Day Observations of Seismic Anisotropy 

James Ward, Andrew Walker, Andy Nowacki, James Panton, and Huw Davies

Seismic anisotropy in the lowermost mantle is thought to be caused by the non-random alignment of anisotropic crystals from texturing from the mantle flowfield. Therefore, seismic anisotropy observations are commonly interpreted in the context of mantle flow. It is unclear, however, how much of an influence the history of mantle convection has on lowermost mantle seismic anisotropy and whether the present-day flowfield is sufficient for interpretation.  

We investigate this by comparing the predicted anisotropy from an Earth-like mantle convection model, which includes plate motion histories from 600 Ma and a Rayleigh number of approximately 108. Therefore, these models should contain structures on similar length scales and in similar locations to the Earth. We create maps of anisotropy 50 km above the CMB using the present-day flowfield in one case and allowing the flowfield to change with time in another. For each point, we model the texture development of 500 post-perovskite crystals on their journey through the mantle to the location of interest. We then use single-crystal elastic constants to compute the full elastic tensor from the texture. To investigate what influences material properties have on the memory of mantle texture, we use three different deformation systems where we vary how easily texture can develop. 

We compare the two maps by taking the difference between radial anisotropy parameters ξ = VSH2/VSV2 and φ = VPV/VPH as this is what is often analysed from seismic tomography. We also present the difference in the final elastic tensors at each location because observations such as from shear wave splitting will be sensitive to more of the full elastic tensor. We find that no matter the deformation model, some regions show very different radial anisotropy strength (>10 % difference). Outside of these regions, there is little effect of a time-varying flowfield (<1 % difference) when assuming post-perovskite is easy to texture. If post-perovskite is hard to texture, the influence of mantle flowfield history has a greater effect on the final texture and therefore the anisotropy (>1 % difference). We find a similar pattern when comparing the full elastic tensors, though most regions do show some small differences. Comparing the most complex paths and quantifying the memory of the mantle shows varying results depending on the deformation models of post-perovskite and the flowfield sampled. Assuming an easy-to-deform material, the memory of the mantle was approximately 10 Ma along some paths. However, along other paths, the final texture is sensitive to flow it sampled at 125 Ma. These results show that, while a time-varying flowfield makes a significant difference along complex paths with difficult-to-texture minerals, a time-varying flowfield produces similar results to those when assuming the present-day flowfield. This work represents progress toward an understanding of the relationship between lower mantle seismic anisotropy and mantle convection.  

How to cite: Ward, J., Walker, A., Nowacki, A., Panton, J., and Davies, H.: The Memory of the Mantle: The Influence of a Time Varying Flow Field on Present Day Observations of Seismic Anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7527, https://doi.org/10.5194/egusphere-egu23-7527, 2023.

Despite the well known anisotropic structure of Earth’s upper mantle, the effect of seismic anisotropy on the construction of body wave shear velocity models remains largely ignored. Ignoring anisotropic heterogeneity can introduce significant model artefacts that may be misinterpreted as compositional and thermal heterogeneities. While effective anisotropic imaging strategies that improve model reconstruction have been developed for P-wave delay times, no such general framework exists for S-waves partly because, unlike P-waves, there is not a simple ray-based methodology for predicting S-wave travel-times through anisotropic media. Here, we apply a new methodology for the inversion of relative shear wave delay times and splitting intensity measurements for arbitrarily oriented hexagonally anisotropic model parameters using data collected across the western United States and Cascadia subduction system. We detail the data analysis procedure required for making measurements of shear wave observables suitable for anisotropic inversions (e.g. determination of incoming polarisation directions). We then present a preliminary anisotropic shear wave velocity model for Cascadia and compare the results to purely isotropic images. The imaged anisotropic heterogeneity is compared to the well-established patterns in shear wave splitting parameters observed in the study area.

How to cite: VanderBeek, B., Lo Bue, R., and Faccenda, M.: Imaging Upper Mantle Anisotropic Structure Using Teleseismic Shear Wave Delays and Splitting Intensity: Application to the Cascadia Subduction Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7790, https://doi.org/10.5194/egusphere-egu23-7790, 2023.

EGU23-8129 | Posters on site | GD7.1

High-resolution imaging of the deep structure of Italy through SKS anisotropy tomography 

Paola Baccheschi, Judith M. Confal, Silvia Pondrelli, Manuele Faccenda, Brandon P. VanderBeek, and Zhouchuan Huang

Seismic anisotropy is a fundamental key to gain knowledge of the mantle dynamics and structure. The image of seismic anisotropy over the upper mantle can be obtained with several methods, including surface waves and SKS splitting measurements. Taken together, these anisotropic measurements contribute to extensively catch anisotropy at different depths, yielding insights into the structure and dynamics of the crust and upper mantle. Nevertheless, mantle images resulting from surface waves result in poor lateral resolution, while the nearly vertically propagating SKS waves, when interpreted in a ray-based framework, results in little or no depth resolution, not allowing to easily image the distribution of the anisotropy through depth. Though the anisotropic seismic nature of the upper mantle is well established by a wealth of observational research, most of common teleseismic body-wave tomography studies neglect P- and S-wave anisotropy, thus producing artefacts in tomographic models in terms of amplitude and localization of heterogeneities. To overcome this problem different tomographic methods have been implemented to invert SKS splitting observations for anisotropic structures, most of which based on finite-frequency sensitivity kernels that relate elastic model perturbations to splitting observations. In this study we adopted the tomographic method relying on the inversion of the splitting intensity, a measure of the amount of energy on the transverse component of the waveform. Since is linearly related to the elastic perturbations of the medium through the 3-D sensitivity kernels, SI can therefore be easily inverted, providing the basis for a better interpretation of shear wave splitting measurements. In this study, we first compute the splitting intensity (SI) and splitting parameters using teleseismic shear-wave recorded at 824 available permanent and temporary stations in Italy and surrounding regions. Then, the dataset of SI has been used as an input for the tomographic inversion. The results obtained show changes of the anisotropic properties with depth, especially for the strength of anisotropy. A progressive depth-increase in anisotropy intensity has been recovered over Italy, affecting the bulge of the Alps and Apennines chain and the southern Tyrrhenian subduction system. On the contrary, weaker anisotropy characterizes the transition zone from the Apenninic to Alps domain beneath the Po plain and the Adriatic domain. The anisotropic tomography models obtained in this study allowed us to recover for the first time a new 3D-imaging of seismic anisotropy of Italy down to the deeper layers, allowing to better understand the dynamic of asthenospheric mantle flow and its relation with subducting plate, as well as the rheology of the continental lithosphere.

How to cite: Baccheschi, P., Confal, J. M., Pondrelli, S., Faccenda, M., VanderBeek, B. P., and Huang, Z.: High-resolution imaging of the deep structure of Italy through SKS anisotropy tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8129, https://doi.org/10.5194/egusphere-egu23-8129, 2023.

EGU23-8301 | ECS | Posters on site | GD7.1

Seismic anisotropy tomography: new insight into upper mantle structure and dynamics beneath the Mediterranean region 

Francesco Rappisi, Brandon Paul VanderBeek, and Manuele Faccenda

The Mediterranean region is an active plate margin characterized by the presence of both oceanic and continental lithosphere. Its tectonic history is marked by intense seismic and volcanic activity triggered by episodes of continental collision and slab rollback leading to the formation of mountain ranges and extensional basins. Our understanding of the structural heterogeneity and tectonic complexity of this region requires accurate imaging of the subsurface. Seismic anisotropy is a key parameter commonly used to study flow in the mantle and its relations with plate motions. In this study we present a three-dimensional anisotropic seismic tomography of the entire Mediterranean area performed using travel time from the new “Global Catalog of Calibrated Earthquake Locations” by Bergman et al. (2023). We present purely isotropic and anisotropic solutions. Compared to isotropic tomography, it is found that including the magnitude, azimuth, and, importantly, dip of seismic anisotropy in the inversions simplifies isotropic heterogeneity by reducing the magnitude of slow anomalies while yielding anisotropy patterns that are consistent with regional tectonics. The isotropic component of our preferred tomography model is dominated by numerous fast anomalies associated with retreating, stagnant, and detached slab segments. In contrast, relatively slower mantle structure is related to slab windows and the opening of back-arc basins. The anisotropic patterns reveal the deformation history of the area which has been characterized by intermittent phases of collision and tectonic relaxation. A diversity of dip angles is observed with near-horizontal and more steeply dipping fabrics found in different areas of the Entire Mediterranean, probably reflecting the entrainment effect of horizontal or vertical asthenospheric flows, respectively. We interpreted the high velocity zones of our best solution as subducting lithosphere and starting from this interpretation we built a 3D reconstruction of the main slabs found in the study region. To perform the tomography, we used the method proposed by Vanderbeek and Faccenda (2021) and already used by Rappisi et al. (2022) in a similar study on the Central Mediterranean area. This work returns the first anisotropic tomography of the entire Mediterranean and demonstrates the importance of seismic anisotropy to better constrain the upper mantle.

Bergman, E. A., Benz, H. M., Yeck, W. L., Karasözen, E., Engdahl, E. R., Ghods, A., ... & Earle, P. S. (2023). A Global Catalog of Calibrated Earthquake Locations. Seismological Society of America, 94(1), 485-495.

Rappisi, F., VanderBeek, B. P., Faccenda, M., Morelli, A., & Molinari, I. (2022). Slab Geometry and Upper Mantle Flow Patterns in the Central Mediterranean From 3D Anisotropic P‐Wave Tomography. Journal of Geophysical Research: Solid Earth, 127(5), e2021JB023488.

VanderBeek, B. P., & Faccenda, M. (2021). Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations. Geophysical Journal International, 225(3), 2097-2119.

How to cite: Rappisi, F., VanderBeek, B. P., and Faccenda, M.: Seismic anisotropy tomography: new insight into upper mantle structure and dynamics beneath the Mediterranean region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8301, https://doi.org/10.5194/egusphere-egu23-8301, 2023.

EGU23-8453 | Posters on site | GD7.1

Effects of large-scale layering and small-scale mineral fabric on the seismic anisotropy of Ivrea-type lower continental crust 

Zheng Luo, Othmar Müntener, György Hetényi, and Klaus Holliger

Most information on the P-wave seismic velocity of the lower continental is based on controlled-source wide-angle seismic experiments, for which the direction of wave propagation in the target region is largely horizontal. Following the common practice of interpreting such data in an isotropic framework, too high P-wave velocities would therefore be inferred in an anisotropic lower continental crust, for which the long axis of the anisotropy ellipsoid is roughly aligned with the horizontal direction. This, in turn, would result in a bias of the interpretation of the lower crustal bulk composition towards the mafic side and potentially also lead to incorrect estimations of crustal thickness. Anisotropy of this type can arise from the small-scale sub-horizontal alignment of anisotropic minerals and/or from large-scale sub-horizontal layering. To assess the likely importance of lower crustal anisotropy in general and the respective contributions of mineral fabric and layering in particular in Ivrea-type lower continental crust, we analyze a range of layered canonical models. The individual layers are parameterized based on published laboratory measurements of seismic velocities from pertinent rock samples. Our preliminary results indicate that anisotropy related to the mineralogical composition and fabric prevails over the corresponding effects of layering. For the considered canonical models, these effects are particularly prominent in the presence of metapelitic rocks, where a petrological interpretation of the inferred average horizontal P-wave velocity could indeed lead to a notable overestimation of the mafic component. Conversely, our initial results also indicate that in the absence of metapelitic rocks, the anisotropy-induced velocity bias may be sufficiently benign to allow for a reasonably reliable interpretation of the bulk composition of the lower continental crust based on the P-wave velocity inferred from wide-angle seismic data.

How to cite: Luo, Z., Müntener, O., Hetényi, G., and Holliger, K.: Effects of large-scale layering and small-scale mineral fabric on the seismic anisotropy of Ivrea-type lower continental crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8453, https://doi.org/10.5194/egusphere-egu23-8453, 2023.

EGU23-8563 | ECS | Posters on site | GD7.1

Joint Active and Passive P-wave Tomography reveals Mt. Etna's Seismic Anisotropy 

Rosalia Lo Bue, Manuele Faccenda, Ornella Cocina, Francesco Rappisi, and Brandon Paul Vanderbeek

 Characterized by persistent eruptive activity associated with a complex interaction between magma in its plumbing system and an articulated tectonic and geodynamic context, Mt. Etna (Sicily, Italy) is one of the most hazardous and monitored volcanoes in the world. Since the late 1990s, several seismic and tomographic experiments have been performed to obtain accurate images of the shallow-intermediate P-wave velocity structures of the volcano. Unfortunately, seismic tomography models, in particular those derived from body waves, typically relies on the approximation of seismic isotropy. This is a poor assumption considering that P-waves exhibit strong sensitivity to anisotropic fabrics and neglecting anisotropic heterogeneity can introduce significant velocity artefacts that may be misinterpreted as compositional and thermal heterogeneities (VanderBeek & Faccenda,2021; Lo Bue et al, 2022). Here, we discard the isotropic approximation and invert for P-wave isotropic (mean velocity) and anisotropic (magnitude of hexagonal anisotropy, azimuth and dip of the symmetry axis) parameters using the methodology proposed by VanderBeek & Faccenda (2021). We use active and passive seismic data collected by the TOMO-ETNA experiment (Ibanez et al. 2016a, b; Coltelli et al. 2016) between June and November 2014. We present 3D anisotropic P-wave tomography models of Etna volcano and compare them with purely isotropic images. Discriminating the anisotropic structures from the velocity artifacts allows to better recover the isotropic and anisotropic crustal structures and to improve our understanding on the major regional fault systems and on the processes that control magma and fluids ascent beneath the volcanic edifice.

 

Coltelli, M., Cavallaro, D., Firetto Carlino, M., Cocchi, L., Muccini, F., D'Aessandro, A., ... & Rapisarda, S. (2016). The marine activities performed within the TOMO-ETNA experiment. Annals of Geophysics.

Ibáñez, J. M., Prudencio, J., Díaz-Moreno, A., Patanè, D., Puglisi, G., Lühr, B. G., ... & Mazauric, V. (2016a). The TOMO-ETNA experiment: an imaging active campaign at Mt. Etna volcano. Context, main objectives, working-plans and involved research projects. Annals of Geophysics, 59(4), S0426-S0426.

Ibáñez, J. M., Díaz-Moreno, A., Prudencio, J., Patené, D., Zuccarello, L., Cocina, O., ... & Abramenkov, S. (2016b). TOMO-ETNA experiment at Etna volcano: activities on land. Annals of Geophysics, 59(4).

Lo Bue, R., Rappisi, F., Vanderbeek, B. P., & Faccenda, M. (2022). Tomographic Image Interpretation and Central-Western Mediterranean-Like Upper Mantle Dynamics From Coupled Seismological and Geodynamic Modeling Approach. Frontiers in Earth Science, 10, 884100.

VanderBeek, B. P., & Faccenda, M. (2021). Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations. Geophysical Journal International, 225(3), 2097-2119.

 

How to cite: Lo Bue, R., Faccenda, M., Cocina, O., Rappisi, F., and Vanderbeek, B. P.: Joint Active and Passive P-wave Tomography reveals Mt. Etna's Seismic Anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8563, https://doi.org/10.5194/egusphere-egu23-8563, 2023.

EGU23-9453 | ECS | Posters on site | GD7.1

Appraisal of D-Rex parameterization in simulating olivine crystallographic preferred orientation (CPO) evolution using microstructural properties 

Srivatsan Vedavyas, Menno Fraters, Magali Billen, and Yuval Boneh

Olivine is a major phase in the upper mantle and its crystallographic preferred orientation (CPO) carries strong implications for the interpretation of seismic anisotropy and geodynamic models of the upper mantle. The computational model D-Rex (Kaminski et al., 2004) is often used to depict the evolution of olivine CPO under various flow patterns. In its tracing of the crystallographic orientation of olivine and orthopyroxene aggregate D-Rex includes the process of dynamic recrystallization, a fundamental process associated with deformation under dislocation creep. Dynamic recrystallization and deformation mechanism are incorporated in D-Rex via different parameters - the efficiency of nucleation of new grains, grain boundary mobility, and the threshold value below which the grains deform by grain boundary sliding (GBS) (i.e., deformation does not result in rotation or recrystallization). These parameters were benchmarked with experiments to fit the overall CPO evolution. While D-Rex is set to predict the CPO, an appraisal of other pivotal microstructural properties like grain size, dislocation density, and recrystallization fraction has been neglected. Here, we use the implementation of D-Rex within ASPECT to model the shearing of grain to first trace the microstructural properties and further test how they are affected by the dynamic recrystallization parameters. We synthesize the results of tens of runs under a range of parameter space and strains. We observe that for grain size distribution, as the nucleation and threshold value for GBS increase the spread of grain sizes is relatively low while increasing mobility causes a large spread of grain size associated with a small group of grains that dominate the overall CPO. At low strains, the intermediate-sized grains are the major contributor to the CPO while with increasing strain, a smaller fraction of large grains dominate the CPO. Further, we find that the biggest grains keep growing bigger, while the smallest grains oscillate around the GBS threshold. Our analysis highlights the gap between the natural evolution of olivine microstructure and the microstructural properties evolution in D-Rex. The use and implications of different suggested parameters will be discussed. 

  Kaminski, É., Ribe, N. M., & Browaeys, J. T. (2004). D-Rex, a program for calculation of seismic anisotropy due to crystal lattice preferred orientation in the convective upper mantle. Geophysical Journal International, 158(2), 744–752. https://doi.org/10.1111/j.1365-246X.2004.02308.x

How to cite: Vedavyas, S., Fraters, M., Billen, M., and Boneh, Y.: Appraisal of D-Rex parameterization in simulating olivine crystallographic preferred orientation (CPO) evolution using microstructural properties, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9453, https://doi.org/10.5194/egusphere-egu23-9453, 2023.

EGU23-9927 | ECS | Orals | GD7.1

Reversible-Jump, Markov-Chain Monte Carlo seismic tomographic inversion for anisotropic structure in subduction zones 

Gianmarco Del Piccolo, Brandon VanderBeek, Manuele Faccenda, Andrea Morelli, and Joseph Byrnes

The implementation of stochastic methods in seismic tomography arises as a response to the limitations introduced by traditional non-linear optimization solvers. Since tomographic problems are generally ill-conditioned, additional constraints on the model are set in the misfit function, and the weight given to each minimization term has a level of arbitrariness; different solutions are obtained with different choices for the damping/smoothing factors. Non-linear optimization solvers are based on a perturbative approach which linearizes the forward modelling locally around a reference model, updated at each iteration until convergence. These methods need the evaluation of the derivatives of the predictions with respect to the parameters of the model, which is not always an easy task, and they generally do not provide the uncertainties associated with the solution model.
The Reversible-Jump Markov-Chain Monte Carlo is a stochastic method which performs a random walk in the model space sampling the posterior probability distribution associated with the model in the light of the observations. This method is a trans-dimensional Metropolis-Hastings where the number of parameters used to represent the continuous fields (as interpolation nodes) is treated as a parameter itself of the inversion, as the positions of the nodes. Using statistical estimators on the ensemble of models produced by the algorithm it is possible to extract a reference model, typically as an average of the ensemble. With this method no regularization is needed, and uncertainty can be estimated using the ensemble of models sampled. The limitations of non-linear optimization solvers are overcome at the cost of an increase in the computational time required.

The presented applications of this method involve seismic tomography in subduction zones, where the anisotropic component of the seismic velocity field is relevant, and the inversion of seismological data could provide an interesting insight into the dynamics of these regions. 

How to cite: Del Piccolo, G., VanderBeek, B., Faccenda, M., Morelli, A., and Byrnes, J.: Reversible-Jump, Markov-Chain Monte Carlo seismic tomographic inversion for anisotropic structure in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9927, https://doi.org/10.5194/egusphere-egu23-9927, 2023.

EGU23-10061 | ECS | Posters on site | GD7.1

Modelling of seismic anisotropy in the lowermost mantle with rheologically constrained geodynamic setup 

Poulami Roy and Bernhard Steinberger

Seismic anisotropy is an observation that is believed to yield information on the flow pattern in the mantle. There are many studies of anisotropy in the upper mantle; however, the lower mantle is still underexplored, due to problems in seismic imaging and complexities of modelling of flow laws of
different minerals. In this study, we modelled the radially anisotropic behavior of two different geodynamic setups, one is the rising of a mantle plume from the core-mantle boundary to the surface, and another is subduction of a slab reaching the lowermost mantle. We use ASPECT for modelling large scale mantle flow and ECOMAN to simulate the development of lattice preferred orientation of mantle fabric. We use the slip system of Bridgmanite following the previous experimental study by Mainprice et al. (2008). We then couple the results from ASPECT to ECOMAN for modelling the radial anisotropy and maximum shear wave splitting direction. We show that in the part of the lowermost mantle surrounding the plume horizontally polarized shear waves (Vsh ) are faster than the vertically polarized ones (Vsv ) while the inside of the plume tail shows opposite signature. However, Vsh becomes greater than Vsv when the plume flattens out at the surface. We also find that the maximum splitting direction is horizontal outside the base of the plume and it becomes vertical inside the plume tail and again becomes horizontal at the surface. This result corroborates previous seismic observations (Wolf et al., 2019) of the Iceland plume at the core-mantle boundary. Moreover, our result for the slab setup reveals that as the slab reaches the lowermost mantle, Vsh becomes higher than Vsv and maximum splitting is horizontal at the base of the slab.

 

References
Wolf, J., Creasy, N., Pisconti, A., Long, M.D., Thomas, C., 2019. An investigation of seismic anisotropy in the lowermost mantle beneath Iceland. Geophys. J. Int. 219, S152–S166.


Mainprice, D., Tommasi, A., Ferré, D., Carrez, P., Cordier, P., 2008. Predicted glide system and crystal preferred orientations of polycrystalline silicate Mg-
perovskite at high-pressure: implicaitons for the seismic anisotropy in the lower mantle. Earth Planet. Sci. Lett. 271, 135–144.

How to cite: Roy, P. and Steinberger, B.: Modelling of seismic anisotropy in the lowermost mantle with rheologically constrained geodynamic setup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10061, https://doi.org/10.5194/egusphere-egu23-10061, 2023.

EGU23-10460 | Orals | GD7.1

Detecting Anisotropy from Back-Azimuth Amplitude Dependence of Sp Converted Waves 

Jeffrey Park, Xiaoran Chen, and Vadim Levin

Many researchers have used S-to-P (Sp) converted waves to detect the Moho discontinuity, the lithosphere-asthenosphere boundary (LAB) and mid-lithospheric discontinuities (MLD). The anisotropy of Earth’s lithosphere is typically constrained with shear-wave birefringence.  Both theory and reflectivity computations, however, argue for a substantial influence of anisotropy on the initial amplitude of the Sp converted wave.  The effects of compressional anisotropy on initial Sp amplitudes are stronger than the effects of shear anisotropy for anisotropy with a tilted axis of symmetry, a geometry that is often neglected in birefringence interpretations.  This Sp behavior is not typically studied, but it has the potential to test the hypothesis that the seismic lithosphere-asthenosphere boundary (LAB) is caused by a transition in anisotropic layering at the base of Earth’s tectonic plates.

We develop and apply multiple-taper correlation estimates for Sp receiver functions, applicable to either SV or SH incoming polarization, or for a linear combination of SV and SH. In the context of incoming SV-polarized body waves, e.g., SKS phases, algorithms from multiple-taper Ps RFs can be borrowed to apply moveout corrections before the Fourier transform to target a particular interface depth in the crust or mantle.  With synthetic seismograms, we find that SH “receiver functions” can be computed from incoming SV waves, promising a diagnostic detecting SKS birefringence and to estimate an average splitting signal from a station. The SV and SH waveforms can be “unsplit” in the frequency domain by the estimated average birefringence to reconstruct the S waves that impinge the lithosphere from the deep mantle.  We will report analyses with data from permanent stations of the Global Seismographic Network and the USGS ANSS.

How to cite: Park, J., Chen, X., and Levin, V.: Detecting Anisotropy from Back-Azimuth Amplitude Dependence of Sp Converted Waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10460, https://doi.org/10.5194/egusphere-egu23-10460, 2023.

EGU23-10928 | ECS | Posters on site | GD7.1

Upper crustal anisotropy in the southeastern Korean Peninsula from shear wave splitting of local earthquakes 

June Baek, Tae-Seob Kang, Dabeen Heo, Jin-Han Ree, Kwang-Hee Kim, Junkee Rhie, and YoungHee Kim

Shear wave splitting (SWS) is a widely used technique to study the anisotropic properties of the Earth’s interior. The geological structure of the southeastern Korean Peninsula is represented as the Yangsan fault and Ulsan fault, which is controlled by the present-day compressional stress regime in the ENE-WSW direction. We analyzed shear wave splitting to understand the anisotropic features of the upper crust above the hypocentral depth in the southeastern Korean Peninsula using the local earthquake data from the Gyeongju Hi-density Broadband Seismic Network (GHBSN). The GHBSN is a dense array composed of 200 broadband stations, which covers an area of about 60×60 km2 in the southeastern Korean Peninsula. We used the MFAST program (Savage et al., 2010) to measure the SWS parameters of fast polarization and delay time from shear waves of local earthquakes from January 2019 to December 2020. In addition, the TESSA program (Johnson et al., 2011) was employed to inspect the spatial variation in the anisotropy of the study region. To obtain reliable measurements of SWS parameters, rigorous constraints including quality control of the original waveforms were applied, and then, cycle-skipped measurements were manually removed. In final, we obtained the SWS measurements of 4260 records. Because the seismicity in the region is concentrated at the epicentral region of the 2016 Gyeongju earthquake sequence and the hanging wall of the Ulsan fault, raypaths are limited to a narrow azimuthal range. Both the raw and spatially averaged fast-polarization directions are dominant to be parallel either to major faults (structural anisotropy) or to the ENE-WSW (stress-induced anisotropy). Also, some stations and regions show bi- or multi-modal rose diagram of the SWS, representing that there is more than one factor of anisotropy to induce the SWS. The delay time of the SWS showed the right-skewed distribution. Tomographic result of the SWS delay time shows that, relatively high anisotropy is observed at the epicentral region of the 2016 Gyeongju earthquake sequence and the hanging wall of the Ulsan fault. It implies that microcracks at these regions are better developed compared to the remaining regions.

How to cite: Baek, J., Kang, T.-S., Heo, D., Ree, J.-H., Kim, K.-H., Rhie, J., and Kim, Y.: Upper crustal anisotropy in the southeastern Korean Peninsula from shear wave splitting of local earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10928, https://doi.org/10.5194/egusphere-egu23-10928, 2023.

EGU23-11721 | ECS | Orals | GD7.1

Radially anisotropic shear-wave velocity structure of northern India, Himalaya and Tibet 

Monumoy Ghosh, Arijit Chakraborty, Siddharth Dey, Inashua Kharjana, Shubham Sharma, Sankar N. Bhattacharya, and Supriyo Mitra

3-component regional waveforms for ~14700 raypaths sampling India, Himalaya and Tibet, have been used for multi-taper polarization analysis of surface waves between periods of 10 and 120 s. Rayleigh (LR) and Love (LQ) wave energy arriving at the station within +/- 10 degree of the theoretical back azimuth have been used to compute 1D path average fundamental mode group velocity dispersion. Theoretical dispersion of fundamental and first two higher modes have been computed using each 1D path average velocity structure constructed from CRUST1.0 over IASP91 mantle model. These are compared with the observed dispersion dataset to identify and remove those periods with higher mode overlap with the observed fundamental mode picks. The shortlisted dispersion datasets consist of ~90% of the original dataset. To ascertain the lateral variation in the group velocity, the observed dispersion has been used to compute 2D tomography maps of LR and LQ group velocities at discrete periods between 10 and 120 s. From these maps, seven 2D profiles across northern India, Himalaya and Tibet have been extracted for modeling the radially anisotropic shear-wave velocity structure of the lithosphere. Haskell-Thompson (H-T) matrix method is used to calculate synthetic LQ dispersion. For the LR dispersion, the H-T method with reduced delta matrix has been used, considering Vph≠Vpv and Eta≠1. The inversion scheme uses genetic algorithms (GA) to search the model space parameterized using Vsh, Vph, Xi and thickness for 3 crustal layers and 2 mantle layers underlain by a mantle half-space. Synthetic tests have been performed using theoretical LR and LQ dispersion curves, computed from global models with 5% and 10% anisotropy, introduced in the mantle layers. The fit to the synthetic LR and LQ dispersion data and the model recovery using GA inversion is satisfactory for such tests. This inversion scheme is being applied to the observed LR and LQ dispersion data from the seven profiles and the results will be presented.

How to cite: Ghosh, M., Chakraborty, A., Dey, S., Kharjana, I., Sharma, S., Bhattacharya, S. N., and Mitra, S.: Radially anisotropic shear-wave velocity structure of northern India, Himalaya and Tibet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11721, https://doi.org/10.5194/egusphere-egu23-11721, 2023.

EGU23-12807 | ECS | Orals | GD7.1

Slab tear and rotation imaged with core-refracted shear wave anisotropy 

Laura Petrescu, Andrei Mihai, and Felix Borleanu

We investigate the complex flow field around the Vrancea slab in Romania, a steeply sinking seismogenic lithospheric block that experienced lateral tear-off and possible rotation. The Vrancea slab is located beneath the South-East Carpathians and generates frequent seismicity despite its remote location from active collisional boundaries. We analyse core-refracted shear wave (SKS) splitting recorded by permanent broadband seismic stations from the Romanian Seismic Network for periods up to 10 years, and compare our results with seismic tomography of the upper mantle. We identify several stations with large backazimuthal variations of SKS fast axis polarization and delay times both in the slab hinge zone, the back-arc and the circumslab region, indicating complex mantle deformation patterns. To investigate the effect of a two-level rotated slab we invert SKS waveforms using cross-convolutional misfit combined with a neighbourhood search algorithm to model two layers of anisotropy. In the shallow mantle, anisotropy aligns with the upper slab strike and reorients along the strike of the lower slab at depths below the hinge zone. In the backarc trench-perpendicular anisotropy switches to trench-parallel, due to the recent retreat and roll-back of the slab. Our results have important implications for understanding SKS interference from subducted slab fragments and provide evidence of the recent retreat, break-off and rotation of two Vrancea slab levels sinking into the upper mantle.

How to cite: Petrescu, L., Mihai, A., and Borleanu, F.: Slab tear and rotation imaged with core-refracted shear wave anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12807, https://doi.org/10.5194/egusphere-egu23-12807, 2023.

EGU23-13670 | Orals | GD7.1

Towards constraining mantle flow through imaging of radial anisotropy, with full uncertainty quantification 

William Sturgeon, Ana M.G. Ferreira, and Matthew Fox

The seismic imaging of radial anisotropy can be used as a proxy for the direction of mantle flow. Previous studies have imaged radial anisotropy throughout the mantle on a global scale and are starting to show some consistent features. However, the interpretation of existing models is hindered by the lack of uncertainties provided from the employed inversion method. To address this, we build a new global radially anisotropic model of the Earth’s upper mantle which consists of two main stages. Firstly, we build global Rayleigh and Love wave phase and group velocity maps using ~47 million measurements, including fundamental mode and up to 5th overtone measurements, and compute their associated uncertainties. Weights according to similar paths and data uncertainties are employed in the inversions. We construct a total of 310 2D maps, at periods between T16-375 s, expanded in spherical harmonics up to degree lmax=60 and observe many relevant small-scale structures, such as e.g. the curvature of the Tibetan plateau at T~40s (fundamental mode). As expected, uncertainties are higher in regions of poor data coverage (e.g., southern hemisphere and oceans). Then, we invert for 1D profiles of radial anisotropy using two Monte Carlo based inversion methods: the Neighbourhood Algorithm (NA) and the Reversible-Jump Markov Chain Monte Carlo algorithm (RJMCMC). The NA has been widely used for seismic inversion, as it efficiently explores the parameter space. However, the advantage of the RJMCMC is that in addition to constraining e.g. radial anisotropy, it can also constrain e.g. layer thickness. We compare the 1D profiles from both methods, and their associated uncertainties, which will lead to a new global 3D model of radial anisotropy.

How to cite: Sturgeon, W., Ferreira, A. M. G., and Fox, M.: Towards constraining mantle flow through imaging of radial anisotropy, with full uncertainty quantification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13670, https://doi.org/10.5194/egusphere-egu23-13670, 2023.

EGU23-15722 | ECS | Posters on site | GD7.1

Effect of olivine anisotropic viscosity in advancing and retreating subduction settings 

Yijun Wang, Agnes Kiraly, Clinton Conrad, Lars Hansen, and Menno Fraters

Lattice preferred orientation (LPO) of olivine crystals occurs due to deformation in the mantle. Different parts of the upper mantle can undergo a large variety of deformation paths. During simple processes, such as simple shearing below oceans due to the movement of tectonic plates, the LPO will reflect the direction of the movement of tectonic plates. On the other hand, in areas, such as around subduction zones, the mantle undergoes more complex deformation paths, resulting in a less easily predictable LPO. Seismic anisotropy has been used as a proxy for mantle flows and the LPO formed in the mantle. To interpret the seismic anisotropy observations more accurately, we need to understand how LPO forms in different regions of subduction.

LPO has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to viscous anisotropy, resulted from the summed effect of individual crystals that are deforming anisotropically. Anisotropic viscosity can affect deformation and in turn the resulting LPO. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV on LPO and the differences between the numerical methods that calculate them.

We choose three methods of olivine texture development to examine in this study. D-Rex is a polycrystal LPO model that is relatively balanced in computational efficiency and accuracy. From previous studies, D-Rex has been shown to produce faster texture development and stronger texture compared to other methods, including our second choice, the modified director method (MDM). The MDM parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. We also couple the MDM with a micromechanical model for olivine AV (which makes our third choice MDM+AV), to allow the anisotropic texture to modify the viscosity and in turn affect the formation of LPO.

Here we compare the LPO evolution under subduction settings with a slowly advancing trench and a retreating trench, with and without the effect of AV. Since the mantle flow pattern in subduction zones is not homogeneous, different particles experience a variety of deformation paths. We place 60 particles in each subduction model around the slab to track the deformation and resulting olivine texture. We compute olivine texture using the above-mentioned three different methods (D-Rex, MDM, MDM+AV). With the particles, we can identify characteristic textures developed in key regions such as the mantle wedge, sub-slab area, and lateral slab edge. We then run a statistical analysis on the texture parameter and anisotropic properties of the particles from both retreating and advancing subduction models, to study where anisotropic viscosity has the largest effect on the mantle flow. We expect AV to have a larger effect in a retreating slab setting since the mantle flows feeding material to the sub-slab region is more intensive.

How to cite: Wang, Y., Kiraly, A., Conrad, C., Hansen, L., and Fraters, M.: Effect of olivine anisotropic viscosity in advancing and retreating subduction settings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15722, https://doi.org/10.5194/egusphere-egu23-15722, 2023.

EGU23-15771 | Orals | GD7.1 | Highlight

Anistropy in the Earth's inner core 

Arwen Deuss, Hen Brett, and Jeroen Tromp

The Earth's inner core is one of the most strongly anisotropic regions of our planet. On average, the anisotropy appears to be aligned with the Earth's rotation axis with a larger wave velocity in the polar (North-South) direction than in the equatorial (East-West) direction. Over de last few decades, seismic studies of inner core anisotropy have revealed regional variations with ever increasing detail, suggesting that the top 60-80 km of the inner core is isotropic, the western hemisphere is more strongly anisotropic than the eastern hemisphere and that the anisotropy in the innermost inner core has an anomalous slow direction. Most previous studies assumed that the symmetry axis of the anisotropy is aligned with the rotation axis axis and then attributed regional variations to variations in the magnitude of the anisotropy. 

Here, we make a tomographic model of inner core anisotropy using seismic body waves observations using a different approach. We assume that the inner core is made of cylindrically symmetric anisotropy crystals that all have the same magnitude of anisotropy, and instead we allow the symmetry axis to vary. We find that our model fits the body wave data equally well as models in which the magnitude varies, with the advantage that our model requires fewer parameters. In our model, the anisotropy in the central part of the inner core is still mainly aligned with the rotation axis. In the upper part of the inner core we find two caps around South-East Asia and Central America with anisotropy aligned parallel to the inner core boundary.

Inner core anisotropy is most likely due to alignment of hcp iron crystal  formed either (i) during solidification at the inner core boundary or (ii) afterwards by deformation deeper in the inner core. Thus, our new model may be related to flow in the inner core or solidification processes at the inner core boundary and constrain geodynamic processes in the inner core. 

How to cite: Deuss, A., Brett, H., and Tromp, J.: Anistropy in the Earth's inner core, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15771, https://doi.org/10.5194/egusphere-egu23-15771, 2023.

EGU23-15777 | ECS | Orals | GD7.1

Signatures of the subduction/obduction processes in the lithosphere and asthenosphere beneath the Semail Ophiolites in Oman revealed by seismic anisotropy 

Abolfazl komeazi, Ayoub Kaviani, Georg Rümpker, Christian Weidle, and Thomas Meier

The obduction of the Semail Ophiolite onto the Arabian continental margin during the convergence of the Arabian and Eurasian plates has left a significant impact on the lithospheric structure beneath the Oman Mountains. However, there remains a degree of uncertainty concerning the extent to which the inherited structures (pre-existing features of the lithosphere) contribute to the obduction of ophiolites. To gain a deeper understanding of the impact of the obduction process on the mantle structure beneath northern Oman, we analyze seismic anisotropy beneath this region using splitting analysis of teleseismic shear wave data collected from a dense network of 40 seismic stations that have been operational for approximately 3 years since 2013. 

Based on azimuthal distribution of the shear wave splitting (SWS) parameters, φ and δt, we are able to divide the study area into two subregions. The stations located to the west of the Semail gap exhibit relatively azimuthally invariant SWS parameters suggesting a single anisotropic layer. On the other hand, at most of the stations located in the central and eastern regions we observe a 90-degree periodicity versus back-azimuth, indicative of a depth-dependent anisotropic medium. 

In the western part, the fast axes are aligned with the strike of the collision between the continental and oceanic plates, where the oceanic lithosphere is believed to be obducted over the continental lithosphere. We also invert the azimuthal variation of the SWS parameters from the central and eastern stations for two layers of anisotropy. The fast axes of the upper layer exhibit a predominantly NW-SE trend, in good agreement with the anisotropy directions of the one-layer models obtained in the western region. The fast axes of the lower layer display a NE-SW trend, possibly representative of the large-scale mantle flow resulting from the present-day plate motion. 

How to cite: komeazi, A., Kaviani, A., Rümpker, G., Weidle, C., and Meier, T.: Signatures of the subduction/obduction processes in the lithosphere and asthenosphere beneath the Semail Ophiolites in Oman revealed by seismic anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15777, https://doi.org/10.5194/egusphere-egu23-15777, 2023.

EGU23-16313 | ECS | Orals | GD7.1

Seismic Anisotropy in the Upper Mantle Beneath the Anatolian Plate and Surroundings Inferred from Shear wave Splitting Analyses 

Ceyhun Erman, Seda Yolsal-Çevikbilen, Tuna Eken, and Tuncay Taymaz

The eastern Mediterranean which is one of the most tectonically active collisional regions where Eurasian, African and Arabian plates converge, provides an excellent opportunity to investigate the evolution of various scales of deformation throughout the Earth. In such a region with highly complex and active tectonic structures, a detailed study of geodynamic processes and related mantle kinematics is required to better understand the development of complex structures at the surface. For example, the region of study, the Anatolian plate and surroundings host several complicated deformation regimes with two large transform faults (North and East Anatolian Faults; NAF and EAF, respectively), regions of extensional and compressional tectonics in the west and east of Anatolia. Seismic anisotropy provides a robust link between seismic observations and geodynamic processes which play a key role for controlling the past and/or present deformations in the mantle lithosphere and asthenosphere. In this study, we perform shear wave splitting analyses on teleseismic core-refracted S-waves (e.g. SKS and SKKS phases) recorded by ~600 broad-band seismic stations located in the region. We estimate seismic anisotropy parameters (e.g., fast polarization direction; FPD and delay time; DT) beneath each seismic station by employing conventional shear wave splitting (e.g., transverse energy minimization and eigenvalue) and splitting intensity approaches. Exploiting a large earthquake dataset, spanning through 2000-2022 with Mw ≥ 5.5 events, that covers a wide range of back-azimuths enables the reliable estimates of complex anisotropic models, such as two-layer and dipping anisotropy models. Our preliminary results largely indicate the NE-SW directed FPDs throughout the study area, except for SW Turkey (NW-SE) and central parts of Anatolia (E-W) that can be mainly explained by the lattice-preferred orientation (LPO) of olivine minerals in the upper mantle induced by the mantle flow related to the roll-back process of the Hellenic slab. Findings from our two-layer grid search algorithm indicated strong evidences for two-layer anisotropy models beneath the seismic stations in eastern Aegean and western Anatolia, in particular close to the western branches of NAF in the Aegean.

How to cite: Erman, C., Yolsal-Çevikbilen, S., Eken, T., and Taymaz, T.: Seismic Anisotropy in the Upper Mantle Beneath the Anatolian Plate and Surroundings Inferred from Shear wave Splitting Analyses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16313, https://doi.org/10.5194/egusphere-egu23-16313, 2023.

EGU23-1208 | ECS | Orals | TS2.1

Characteristics and evolution of strike-slip faults in a stable cratonic block 

Zhao Wang and Lei Huang

The deformation pattern in the interior of cratonic blocks has critical implications for regional structural evolution but still remains an unresolved question. The southwestern Ordos Basin is at the convergence of multiple blocks, leading to intense and complex tectonic stress at this location. However, how the interior of the Ordos block responds to the complex stress field around it is still elusive. This study analyzes the characteristics and evolutionary history of faults in the southwestern part of the inner Ordos Basin using 3D seismic data. Three dominant sets of faults trending NW, NEE, and N–S have developed in the study area. All three sets of faults have subvertical dip angles and straight fault traces and structures that are common in such fault zones, such as flower structures and en-echelon and horsetail arrangements (all indicating strike-slip movement) are present. Structural deformation varies from the center to the periphery of the Ordos block. All three sets of fault systems exhibit small displacements. The polarity of the strike-slip changed in different periods, reflecting the transformation of the stress field in the southwestern Ordos Basin. This illustrates that the formation of cratonic faults is controlled by the regional stress field, while the related strain pattern in the interior of the cratonic block is very different from the deformation around its periphery. These characteristics also demonstrate the special nature of cratonic fault deformation.

How to cite: Wang, Z. and Huang, L.: Characteristics and evolution of strike-slip faults in a stable cratonic block, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1208, https://doi.org/10.5194/egusphere-egu23-1208, 2023.

EGU23-2686 | ECS | Posters on site | TS2.1

Insights on the seismotectonic of Calabria-Lucania border region (Southern Italy): different tectonic styles at different depths 

Ada De Matteo, Paolo Capuano, and Mariarosaria Falanga

The Calabria-Lucania border region represents the transitional area between the Southern Apennines and the Northern sector of the Calabrian arc. Roughly the whole Apennine chain is struck by more or less intense earthquakes. While the northern and central parts of the chain are characterized by foreland contraction and hinterland extension, the Southern Apennine is characterized by a strike-slip kinematics in the eastern sector and by an extensional regime in the western sector. Strike-slip earthquakes have been observed also in the axial part of the Campania-Molise Apennines, rightly beneath the active extensional sector.

The Calabria-Lucania border region is considered a seismic gap in the Apennine chain; few paleo-earthquakes, with magnitude ranging from 5 to 7, have been recorded in the area. During 2010-2014 the region was affected by a low-moderate instrumental seismicity (known as Pollino seismic sequence): thousands of earthquakes occurred. Analysis of that seismicity revealed a shallow hypocentral distribution located into the first few km below the surface, and focal mechanisms of the strongest events of the sequence are consistent with upper crustal extensional deformation. While the shallow seismicity of Calabria-Lucania border region has been deeply studied after the 2010-2013 sequence, the sporadic deep seismicity needs a more detailed analysis.

As highlighted by previous studies, instrumental seismicity recorded from 2013 to 2015 reveals the presence of a sporadic deep (from 9 to more than 20 km) seismicity. The events located between 9 and 17 km deep have transcurrent to transpressional kinematics with NE-SW trending P axes; while deeper events show a strike-slip kinematics with NW-SE trending P axes.

We analyzed deep (> 10 km) seismicity recorded in the area from 2013 to nowadays. Starting from the picking of seismograms of more than 40 events (with M between 2.4 and 3.8), we analyzed the focal mechanisms of events computed using at least six good first motion observations. According to Ferranti et al., 2017, our results highlight the presence of a strike-slip/oblique kinematics at depths of more than 20 km. Between 10 and 20 km depth both dip-slip and strike-slip kinematics are present, with a predominance of the last ones, confirming the presence of a transition zone.  

Finally, we inverted the focal mechanisms dataset to infer about the stress field active in the region.

How to cite: De Matteo, A., Capuano, P., and Falanga, M.: Insights on the seismotectonic of Calabria-Lucania border region (Southern Italy): different tectonic styles at different depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2686, https://doi.org/10.5194/egusphere-egu23-2686, 2023.

The most common method of detecting subsurface structures on continental and marine surfaces is seismic imaging. Although technological advancements have been made, seismic analysis of carbonates remains challenging due to their strong petrophysical heterogeneity, which becomes more challenging when faults are incorporated. This work aims to produce unmigrated forward-seismic models to grasp the deformation behavior of carbonate-bearing fault systems and the related seismic response changes. The porous and faulted carbonates outcropping at the Majella Massif (central Italy) are here used as case study as an analogue of carbonate ramp reservoirs exploited worldwide. Field and laboratory petrophysical data of fault rocks collected at increasing distances from the fault planes show a damage zone/fault core architecture characterized by a decreasing porosity and an increase in shear modulus moving from host rocks towards fault planes. Starting from these observations, unmigrated stacked seismic models have been built simulating fault zones with both increased and decreased porosities with respect to the host rocks. Fault zones with lower porosity than the host rock show slight diffraction hyperbolas, while the diffractive component is pronounced in seismic images of fault rocks with higher porosity than the host rock. Such hyperbolas can be enhanced or weakened by modifying the dip angle of the fault plane or the width of the damage zone but a key role seems to be played by the decreased porosity. The existence of diffraction hyperbolas in unmigrated seismic models is then interpreted as evidence of a damage zone characterized by larger porosity compared to the host rock. Migrated stacked sections would not provide any evidence of increased porosity in the damage zone due to loss of information about the diffractive component resulting from the processing. Consequently, the absence of diffraction hyperbolas in actual unmigrated seismic images is suggested to be related to a decreased porosity in the fault zone. This can be related to cataclasis and solution/cementation of the damage zone rocks as observed in the study area, and related to confining stress acting at depth or fracture filling that counteracts the fracture-related increase in secondary porosity. On the other hand, diffraction hyperbolas in unmigrated seismic images can represent a clue of the presence of large-porosity fault zones.

How to cite: Tomassi, A., Trippetta, F., and de Franco, R.: Seismic signature of carbonate fault rocks changes with changing petrophysical properties: insights from unmigrated seismic forward modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3880, https://doi.org/10.5194/egusphere-egu23-3880, 2023.

EGU23-4803 | ECS | Posters on site | TS2.1

Offshore extension of the Ilan Fault in northeast Taiwan 

Chih-Chia Chang, Shu-Kun Hsu, Lien-Kai Lin, Ching-Hui Tsai, and Hsiao-Shan Lin

The Philippine Sea Plate (PSP) has subducted northwestward beneath the Eurasian Plate (EP) in the northeast Taiwan and has obliquely collided with the EP creating the mountain building. The offshore area of northeastern Taiwan is subject to post-collisional collapse and under extensional regime, forming a series of normal faults. The NE-SW trending Ilan Fault is situated between the Ilan Plain and the Hseushan Range. The Ilan Fault is also call North Ilan Structure (NIS). According to the Taiwan Earthquake Model published by TEC team in 2020, the probability for a Mw 6.9 earthquake happened in NIS in future fifty years is estimated about 13%. However, if the NIS extends to the offshore area, the risk will become greater. This study aims to understand the possible offshore extension of the Ilan Fault and analyze the structural activity. For that, we have collected 24-channel sparker reflection seismic profiles and sub-bottom profilers across the possible fault trace. Based on sparker seismic profiles and sub-bottom profiles, four major normal faults, Fa, Fb, Fc and Fd, trending NE are observed. Faults Fa and Fb are active and have outcropped to the seafloor. A negative flower structure is observed along Fault Fa, which indicates that the regional stress is under transtension. Furthermore, slope failures, slumps and sliding surfaces are found. Overlying on the Last Glacial Maximum (LGM) unconformity, sedimentary layers are tilted in the hanging wall of Fault Fb, indicating Fault Fb is a growth fault. On the other hand, Faults Fc and Fd dip to the NW and SE, respectively. They bound a graben trending NE and only ruptured to the LGM unconformity. It implies that Faults Fc and Fd are no more active.

How to cite: Chang, C.-C., Hsu, S.-K., Lin, L.-K., Tsai, C.-H., and Lin, H.-S.: Offshore extension of the Ilan Fault in northeast Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4803, https://doi.org/10.5194/egusphere-egu23-4803, 2023.

EGU23-4924 | ECS | Posters on site | TS2.1

Post-collisional Geological Structures off Gongliao District in Northern Taiwan 

Yi-Wen Lin, Shu-Kun Hsu, Ching-Hui Tsai, Yen-Yu Cho, and Lien-Kai Lin

The offshore area of northern Taiwan is subject to post-collisional collapse and under an extensional regime. Because of the change from a compressional environment to an extensional environment, a series of normal fault structures has occurred. The reverse faults in the Gongliao area of Taiwan, include the Longdong Fault, Wentzukeng Fault, Aodi Fault, and Fangjiao Faul, are distributed from inland to the coastline. However, their prolongations to the offshore area are unknown. In order to understand the possible fault extension to the offshore area and the possible fault activity, we conducted Sparker reflection seismic surveys in the offshore area of Gongliao. The Sparker seismic system is suitable for shallow water surveys and can provide high-resolution shallow structures. To understand the geological structures in our study area, sequence stratigraphy, seismic facies and faults identification are used to analyze our seismic profiles. According to the sequence stratigraphy, the transgressive surface, the last glacial maximum (LGM) unconformity, and last maximum flooding surface can be identified. In addition, the sand wave base surface, syn-rift unconformity and the acoustic basement are defined. We have identified 5 normal faults (i.e. Fa, Fb, Fc, Fd and Fe) in the prolongation of the onshore faults. All the identified faults cut through the basement and caused large offsets, forming half-graben basins. For the activity of these faults, the strata in the half-graben basin A formed by Fault a, is tilted, which was probably caused by the continuous growth of the fault. The strata in the half-graben basin B formed by Faults b and c, are inclined below the LGM unconformity, but the strata above the LGM unconformity are relatively flat. In contrast, only the sediments in the upper part of the half-graben basin B show the characteristics of sequence stratigraphy, which means the sediments deposit controlled by sea level change. In summary, we infer that the faults b and c were active before the LGM and relatively stable recently. Faults d and are covered by thick sediment layers, indicating early structures not active at all.

How to cite: Lin, Y.-W., Hsu, S.-K., Tsai, C.-H., Cho, Y.-Y., and Lin, L.-K.: Post-collisional Geological Structures off Gongliao District in Northern Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4924, https://doi.org/10.5194/egusphere-egu23-4924, 2023.

EGU23-5141 | Posters on site | TS2.1

The aftershock series of the 2016 Petermann Ranges earthquake in Central Australia 

Christian Sippl, Gregory Brenn, Sharmin Shamsalsadati, and Hrvoje Tkalčić

Although located far from any active plate boundaries, Central Australia features significant seismic activity, with a total of four M>6 events in the last four decades. The most recent such event was the May 25th, 2016 Petermann Ranges earthquake (Mw = 6.1), which occurred close to the border triangle between the Northern Territory, South Australia and Western Australia. The last tectonic reactivation of the region that hosted the earthquake occurred during the intraplate Petermann Orogeny that terminated about 540 Ma ago. It is commonly assumed that although recently inactive, this region still constitutes a lithospheric-scale zone of weakness, so that stresses imposed on the rigid Australian plate at its edges can localize and lead to seismicity here. Previous studies have shown that the Petermann earthquake occurred on a splay fault in the direct vicinity of the Woodroffe Thrust, one of the principal shear zones of the Petermann Orogeny. It occurred at a very shallow depth (<= 5 km) and had a thrust mechanism with a NW-SE oriented rupture plane. Due to its shallow depth, it created a surface rupture that was mapped over a length of about 20 km.

In the present study, we utilized a temporary deployment of 11 seismic stations that was installed in the aftermath of the Petermann earthquake to characterize its aftershock sequence. Since only a single permanent station was operating within a radius of 400 km around the rupture area before the deployments, we do not have much information about the earliest part (first two weeks) of the aftershock series.

We combine two different event catalogs, a handpicked one comprising 1231 events for the first 3.5 months of the aftershock sequence, and a semi-automatically derived one that contains a total of 4918 events. We derived an optimal 1D velocity model and station corrections from the handpicked catalog, and relocate all events with this model. In a second step, we apply a double-difference relocation to the entire dataset. Most of the relocated events occurred at depths between 2 and 4 km, and outline a tight NW-SE striking an NE-dipping plane that aligns well with the mapped trace of the surface rupture. As already indicated in previous studies, we also find scattered aftershock activity within the footwall of the fault.

We further applied a template-matching algorithm in order to further decrease the completeness magnitude of the catalog and to get the best possible estimate for event rate decay over time. Moreover, we present fault plane solutions for a few of the largest aftershocks.

How to cite: Sippl, C., Brenn, G., Shamsalsadati, S., and Tkalčić, H.: The aftershock series of the 2016 Petermann Ranges earthquake in Central Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5141, https://doi.org/10.5194/egusphere-egu23-5141, 2023.

The northern Tyrrhenian Sea separates the northern Apennines of the Tuscany coast (Italy) from the Corsica island (France). 

A comprehensive revision of a vast dataset of vintage public seismic reflection profiles was conducted, re-elaborating via dedicated vectorization codes to improve their resolution and interpretability. 

The bathymetry of this sector shows a very regular and almost flat geometry of the seafloor. Despite this, a close look at seismic profiles reveals an articulated topography of the pre-Neogenic deformed acoustic basement. This is organized in thrust-related structural highs and narrow, N-S and NNW-SSE trending basins, filled by sedimentary successions separated by unconformities.

Nowadays, the sedimentary sequences associated with the most recent evolution of the Tyrrhenian Sea completely sutured the previous morphology.

To date, we found strong evidence regarding the role of structural inheritance in shaping the current architecture of the shallow crust. We identified an intimate relationship between the thrust-related structural highs and the basins' position at the antiforms' forelimb and backlimb. Indeed, the Tuscan Shelf neogenic basins started to develop as intermontane fault-controlled basins along the flanks of the inherited antiforms.

We performed a structural analysis of the faults bounding the basins and a detailed seismic-stratigraphic analysis of the Neogenic succession deposited into such basins to reconstruct the Tyrrhenian Sea extension's initial phases and embed it into the broader evolution of the Mediterranean region.

The evolution of the sedimentary basins from the middle Miocene to the Pleistocene provides a more comprehensive and robust picture of the Tyrrhenian Sea. We were able to track the progressive activation and deactivation of high-angle normal faults controlling the basins deposition and the eastward migration of the extensional front. Such a setting influenced the asymmetrical or symmetrical evolution of the basins. Intriguingly, and partially in contrast with previous works, no evidence of low-angle normal fault was observed.

We also present the first reconstruction of a 3D geological model of the southern Tuscany offshore between Elba Island and Monte Argentario promontory (Italy). 

Such a model poses new questions on the crustal-scale mechanisms responsible for the extensional process, also establishing a unique starting point for fully unraveling the Tuscan Shelf and the Tyrrhenian Sea early stages of evolution.

How to cite: Buttinelli, M., Mazzarini, F., Musumeci, G., Maffucci, R., and Cavirani, I.: Tectonic-Sedimentary evolution of the Tuscan shelf (Italy): seismic-stratigraphic analysis of the Neogenic succession in the northern Tyrrhenian Sea between Elba Island and Monte Argentario promontory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5350, https://doi.org/10.5194/egusphere-egu23-5350, 2023.

Unveiling the geometry and kinematics of subsurface seismic faults is important for earthquake hazard assessment. Earthquake focal mechanisms can provide such fundamental aspects of faulting; however, they often require additional information to distinguish faults and auxiliary planes. We attempt to identify faults using a stress inversion technique, in which fault planes in individual focal mechanisms are selected based on the fault instability parameter. This stress inversion algorithm developed by Vavryčuk (2014) selects a higher instability nodal plane as the fault and finds 70-80% faults correctly to derive reliable stress results. Our tests using synthetic and simulated focal mechanism data with faults known beforehand show that faults are correctly identified especially when the instability of the selected fault plane is significantly higher than that of the auxiliary plane, which can be quantitatively expressed by the instability ratio of the fault plane to that of the auxiliary plane being higher than ~1.3. This constraint can improve further the ability to identify subsurface seismic faults. We apply this technique to the case of geothermal-induced earthquakes that occurred in Pohang, South Korea during 2016-2017. A total of 53 well-constrained and well-located focal mechanism data are inverted to derive a stress condition, during which faults are identified as higher instability nodal planes. These earthquakes occurred in spatially distinct portions of the region associated with water injection through two respective boreholes (PX-1 and PX-2). For the PX-2-related earthquakes, 70% of identified faults are well aligned in their locations and orientations with a large-scale fault, indicating that these earthquakes occurred on the patches of this fault. This fault is responsible for the 2017 Mw 5.5 main earthquake. Fault planes whose instability ratio is higher than ~1.3 are all consistent with this plane. There is more variation in identified fault orientations in PX-1 earthquakes. However, a few fault planes with high instability ratios are generally subparallel to one another. The locations and orientations of these high instability ratio planes are well aligned with a large-scale fault, which is different from, but subparallel to the PX-2 fault. This study demonstrates the possibility of identifying and imaging subsurface seismic faults only using faulting mechanics without other additional information.

How to cite: Chang, C.: Identifying seismic fault geometry from focal mechanisms based on fault instability ratio during a stress inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5622, https://doi.org/10.5194/egusphere-egu23-5622, 2023.

EGU23-5677 | ECS | Orals | TS2.1

The analysis of the Castelsaraceno microearthquake sequence (southern Italy) through a semi-automated template matching and machine-learning approach reveals an anti-apenninic fault 

Serena Panebianco, Vincenzo Serlenga, Claudio Satriano, Francesco Cavalcante, and Tony Alfredo Stabile

The accurate characterization of microearthquake sequences allows seismologists to shed light on the physical processes involved in earthquake nucleation, the deformation processes underlying rupture activation and propagation, and to image faults geometry at depth. The current methodologies used for this purpose first need the event detection and the phase-picking - usually manual-based - and earthquake locations, which require plenty of work even by expert analysts particularly in the case of microearthquake signals, commonly noise contaminated. Thus, improving standard procedures through semi-automatic or fully-automatic workflows would be an essential step forward towards the more efficient analysis of seismic sequences.

Here we show the results of a semi-automated template matching and machine-learning based workflow applied for the characterization of the foreshock-mainshock-aftershock microearthquake sequence occurred close to Castelsaraceno village (High Agri Valley, Southern Apennines, Italy) in August 2020. The analyses were performed on seismic data mainly recorded by a local seismic network belonging to the High Agri Valley geophysical Observatory (HAVO) deployed in the study area and located at a maximum epicentral distance of ~20 km from the seismicity cluster.

The application of the semi-automated single-station template matching technique to the continuous data-streams of the two nearest stations of the HAVO network (from 28th July to 12th October 2020) allowed us to detect more than twice the number of microearthquakes previously identified by standard manual detections. The phase-picking was automatically performed through a deep-learning algorithm (Phasenet) on the 202 ultimate detected microearthquakes. Finally, an automatic multi-step absolute and relative earthquake location procedure was carried out.

A total of 76 events were identified as belonging to the Castelsaraceno sequence, which occurred in a short time span (7-12 August) and in a limited range of depths (10 -12 km). Both the Ml 2.1 foreshock doublet and the Ml 2.9 mainshock occurred on 7 August ruptured the same seismogenic patch, thus suggesting the presence of a persistent asperity. The integrated analysis of the aftershocks distribution, the focal mechanism of the mainshock, and the geological framework of the study area, allowed revealing the seismogenic fault, not currently mapped in literature: a NE-SW striking (225°), high-angle (55°) fault with a left-lateral transtensional (rake -30°) kinematic. We also hypothesize that the seismic sequence occurred at depth in a brittle layer of the crystalline basement confined between two regions with more ductile rheology; futhermore, the estimated b-value (0.73±0.04) indicates the occurrence of the sequence in a relatively low-heterogeneity material and suggests the unimportant effect of pore-fluid pressure in driving its evolution. 

How to cite: Panebianco, S., Serlenga, V., Satriano, C., Cavalcante, F., and Stabile, T. A.: The analysis of the Castelsaraceno microearthquake sequence (southern Italy) through a semi-automated template matching and machine-learning approach reveals an anti-apenninic fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5677, https://doi.org/10.5194/egusphere-egu23-5677, 2023.

EGU23-5756 | ECS | Orals | TS2.1

Characterising faults in geothermal fields using surface waves: a numerical study 

Heather Kennedy, Katrin Löer, Amy Gilligan, and Claudia Finger

Subsurface characterisation of geothermal fields is important for the expansion of geothermal energy as a low-carbon resource. Faults and fractures provide secondary permeability, thus, their characteristics are crucial parameters in deep geothermal fields. Analysis of ambient seismic noise provides a relatively cheap and widely accessible method for constraining faults and fractures in geothermal settings.

 

Three-component (3C) beamforming is an array-based method that extracts the polarizations, azimuths, and phase velocities of coherent waves as a function of frequency from ambient seismic noise, offering a comprehensive understanding of the seismic wavefield. 3C beamforming can be used to determine surface wave velocities as a function of depth and the direction of propagation of waves. It is assumed that anisotropic velocities relate to the presence of faults, giving an indication of the maximum depth of the permeability essential for fluid circulation and heat flow throughout a geothermal field. Previous results suggests that some structures have a stronger effect on surface wave velocities than others. Numerical models are essential to study these relationships in more detail.

 

Here we present a numerical simulation of wave propagation through a model of the subsurface, with anisotropy depicted as faults. This is employed by a rotated staggered grid (RSG) finite-difference (FD) scheme. We model a homogeneous half-space with a fault-like structure (40 m width), changing fault parameters, such as depth, width, velocities and internal conditions of the fault (“fill”). We generate surface waves from a single source as well as multiple sources emulating an ambient noise wavefield.

 

We then use 3C beamforming on the synthetic data to characterise the modelled wavefield and observe the types of waves present. The polarisation and beam power of the synthetic data denote the composition of the synthetic wavefield and what percentage are retro- and prograde Rayleigh waves and Love waves. To investigate the strength of anisotropy introduced by a single fault we propagate surface waves across the fault in different directions, estimating velocities from array recordings using the beamformer. We are further able to assess the sensitivity of Rayleigh waves towards anisotropy at depth by considering Rayleigh waves at different frequencies sampling different depths.

How to cite: Kennedy, H., Löer, K., Gilligan, A., and Finger, C.: Characterising faults in geothermal fields using surface waves: a numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5756, https://doi.org/10.5194/egusphere-egu23-5756, 2023.

EGU23-7651 | ECS | Posters on site | TS2.1

3D scattering and absorption imaging of the Pollino seismic gap (Italy) 

Ferdinando Napolitano, Ortensia Amoroso, Luca De Siena, Simona Gabrielli, and Paolo Capuano

The Pollino area, one of the largest seismic gaps in Italy, has been struck between 2010 and 2014 by a long-lasting seismic sequence. More than 10,000 small-to-medium earthquakes followed a temporal evolution typical of a seismic swarm and, to a lesser extent, of  aftershocks following the two strongest events: a ML 4.3 on 28 May 2012 and a ML 5.0 on 25 October 2012. A delay of almost 4 months separated the two main events, with the first event occurring two years after the beginning of the swarm. A slow slip event began about three months before the strongest earthquake. High VP and high VP/VS values have been found in the swarm area, where clusters of events of similar waveforms have been identified in recent works. The distribution of seismicity has been driven by pore fluid pressure diffusion with relatively low diffusivity value.

The present work aims to provide the first 3D images of scattering and absorption of the Pollino area at different frequency bands, measured through peak delay mapping and coda-attenuation tomography, respectively. We collected 870 earthquakes from the 2010 - 2014 seismic sequence and surrounding area, characterized by ML > 1.7, already applied in a recent tomographic work. We used the manual P-wave pickings of the waveforms to compute the peak delay as the lag between the P-wave onset and the maximum of the envelope. Instead, the coda window has been fixed for the entire dataset at 30 seconds after the origin time of the earthquakes, lasting for 15 seconds. This late lapse time allows us to interpret Qc-1 as a marker of the absorption.

The preliminary results show a high scattering anomaly characterizing the seismogenic volume of the sequence and the newly identified faults surrounding the focal area. A strong scattering contrast has been identified south of the ML 5.0 plane. This contrast is likely related to the presence of a segment of the Pollino Fault that acts as a barrier for the Southern propagation of the sequence. High attenuation anomalies in areas already marked by high VP and high VP/VS confirm the role that fluids played in this complex sequence. These results, together with the recent outcomes, could give more insights about the seismic hazard of this complex area.

This work was supported by the PRIN-2017 MATISSE project (no. 20177EPPN2), funded by the Ministry of Education and Research.

How to cite: Napolitano, F., Amoroso, O., De Siena, L., Gabrielli, S., and Capuano, P.: 3D scattering and absorption imaging of the Pollino seismic gap (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7651, https://doi.org/10.5194/egusphere-egu23-7651, 2023.

EGU23-11176 | Orals | TS2.1 | Highlight

High-resolution 3-D geophysical imaging across a seismogenic fault: the TEst Site IRpinia fAult (TESIRA) project 

Pier Paolo Gennaro Bruno, Giuseppe Ferrara, Luigi Improta, Stefano Maraio, Vincenzo Di Fiore, David Iacopini, Mario Fusco, Michele Punzo, Valeria Paoletti, Giuseppe Cavuoto, and Paolo Marco De Martini

The scientific project TESIRA (TEst Site IRpinia fAult), funded in 2021 by the University of Naples “Federico II”, aims at acquiring multidisciplinary geophysical data above an active fault in an intramontane basin of the Southern Apennines and to achieve, through the integration of this multivariate dataset, an accurate 3D geophysical imaging of the shallow structure of the fault zone in order to understand the link between shallow faulting and petrophysical changes, which affect rock permeability and surface degassing. The target structure is the southern branch of the Irpinia Fault, one of the structures with highest seismogenic potential in the Mediterranean region, causing the 4th Italian earthquake of last century (1980, Ms=6.9, Pantosti & Valensise, 1990) and generating a modest surface throw at Pantano San Gregorio Magno (Salerno).

A microgravimetric survey and a 3D and 2D Electrical Resistivity measurements survey were acquired between September 2021 and January 2022. 3D seismic data were acquired in July 2022, using two overlapping arrays with a dense geophone distribution covering an area of about four hectares, with a detail of 2.5x2.5m. Moreover, four 2D seismic profiles intersect the 3D volume. An aeromagnetic survey, an extension of the gravimetric survey and a sampling of the CO2 surface degassing will be completed within this year. We will show the preliminary results of the individual surveys. Later, the different geophysical and geochemical measurements will be integrated using cooperative inversion and machine learning techniques.  We hope that this multidisciplinary approach will provide a more comprehensive understanding of the interaction between surface faulting and basin development in this key area of the Southern Apennines.

 

References

Pantosti, D.; Valensise, G.; [1990] Faulting Mechanism and Complexity of the November 23, 1980, Campania-Lucania Earthquake, Inferred From Surface Observations, JGR, 95, 319-341

How to cite: Bruno, P. P. G., Ferrara, G., Improta, L., Maraio, S., Di Fiore, V., Iacopini, D., Fusco, M., Punzo, M., Paoletti, V., Cavuoto, G., and De Martini, P. M.: High-resolution 3-D geophysical imaging across a seismogenic fault: the TEst Site IRpinia fAult (TESIRA) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11176, https://doi.org/10.5194/egusphere-egu23-11176, 2023.

EGU23-11539 | ECS | Posters on site | TS2.1 | Highlight

10 years of seismicity on the Reykjanes Peninsula, SW Iceland 

Jana Doubravová, Rögnvaldur Líndal Magnússon, Diana Konrádová, Josef Horálek, Tomáš Fischer, Thorbjörg Águstsdóttir, and Egill Árni Gudnasson

Reykjanes Peninsula (SW Iceland) is an extraordinary place from the geophysical perspective. Lying on the on-shore part of the Mid-Atlantic Ridge, interlaced by volcanic systems and hosting several high temperature geothermal areas, the seismic activity on the Peninsula is generally persistent on a microseismic level, but occasionally reaching up to ML~5-6. Throughout the years, many temporary seismic stations or small to medium size local seismic networks have been deployed there for various purposes, from geothermal prospection monitoring to short time passive seismic experiments. We analyzed 10 years of natural seismicity recorded by the semi-permanent local seismic network REYKJANET (in operation since 2013) together with several permanent stations of the SIL regional seismic network present in the area of interest, in total number of 22 stations covering an area of about 1200 km2. The timespan, 2013-2022, contains times of relative quiescence, several small tectonic earthquake swarms as well as very active periods of volcano-tectonic origin, with dyke intrusions and larger earthquakes of magnitudes up to ML- 5.4. We study the distribution of epicenters of the background seismicity as well as for the several seismically active periods with a consistent set of stations.

We compare several different automatically derived earthquake catalogues using different detection and location algorithms, and their common features such as the upper and lower limit of the epicenter occurrence, seismogenic faults, aseismic zones and void areas. The dataset contains dyke intrusions related events during the the 2021-2022 Fagradalsfjall volcano-tectonic event.

Depending on the exact quality criteria and method used, we deal with over 100,000 events with high quality stable locations imaging the subsurface beneath the Reykjanes Peninsula.

How to cite: Doubravová, J., Magnússon, R. L., Konrádová, D., Horálek, J., Fischer, T., Águstsdóttir, T., and Gudnasson, E. Á.: 10 years of seismicity on the Reykjanes Peninsula, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11539, https://doi.org/10.5194/egusphere-egu23-11539, 2023.

EGU23-13042 | Posters on site | TS2.1

High-resolution local earthquake tomography of seismogenic structures along the Rhone-Simplon fault zone (Swiss Alps) 

Tobias Diehl, Timothy Lee, Edi Kissling, and Stefan Wiemer

In this study, we explore the potential to image the seismic velocity structure of moderate-sized, upper-crustal seismogenic fault zones by means of local earthquake tomography (LET) methods. The study region, located in the transition zone between the Central and Western Alps, represents one of the most seismically active and hazardous areas within the Alpine Arc. Over the past 500 years, several damaging earthquakes with Mw up to 6.2 are documented in historical earthquake catalogs in the vicinity of the Rhone-Simplon Fault (RSF), the dominant tectonic feature of this region. In particular, two major seismogenic structures are imaged by instrumental seismicity on either side of the RSF. To the north, seismicity occurs in the approximately NE-SW striking, 30–40 km long Rawil Fault Zone (RFZ). To the south, diffuse seismicity occurs within the hanging wall of the Pennine Basal Thrust, forming the Penninic Fault Zone (PFZ).

Owing to the dense instrumentation and above-average seismic activity in the study region, the Pg and Sg travel-time data recorded since the year 2000 by the Swiss Seismological Service is of exceptionally high quality and allows for high-quality 3D LET images of the uppermost crust, potentially imaging the damage zones of seismogenic faults. Relative double-difference locations of a recent earthquake sequence within the RFZ, on the other hand, indicate that the width of this fault zone is only on the order of 1 km. Imaging such narrow fault zones with standard LET methods therefore requires model parametrizations with grid spacing of few kilometers and less. Such dense grid spacing, however, poses several challenges in terms of model resolution and the reliability of LET inversion results, especially in less well constrained parts of the model.

To minimize such effects, we therefore tested and applied two different LET inversion strategies to derive 3D Vp and Vs models. The first strategy follows the common approach to compute a minimum 1D model as initial model for the 3D LET. The second strategy uses a coarser 3D regional LET model as initial model for the high-resolution 3D inversion. Synthetic tests suggest that a minimum image resolution of 5x5x3 km can be achieved with the current data, covering a region of about 125x125 km between 0 and 10-15 km depth. The 3D Vp and Vs models derived with the two initial-model strategies are remarkably similar within well resolved parts of the model. This similarity indicates that the anomalies in these parts are well constrained by the data and the solution is stable with respect to differences in the two initial models. On the other hand, the results suggest that results derived with the 3D initial model are more reliable in regions of reduced resolution. Additional synthetic tests were performed to document the potential resolution for hypothetical damage-zone scenarios and to support the interpretation of the derived models presented in this study.

How to cite: Diehl, T., Lee, T., Kissling, E., and Wiemer, S.: High-resolution local earthquake tomography of seismogenic structures along the Rhone-Simplon fault zone (Swiss Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13042, https://doi.org/10.5194/egusphere-egu23-13042, 2023.

EGU23-13872 | Orals | TS2.1

New insights into vintage 3D reflection seismic data in hard-rock environment 

Felix Hlousek and Stefan Buske

The demand for reliable high-resolution reflection seismic exploration campaign in hard-rock environments increases continuously. The target of such surveys varies and covers e.g. mineral exploration, geothermal reservoir characterization or the exploration of potential nuclear waste deposit sites. Although the exploration targets are very different, the expectations on the seismic images and the challenges for data acquisition and processing are similar. The expected structures are often steeply dipping with varying strike directions and conflicting dip situations. Furthermore, the reflection seismic data often has to be acquired on land, possibly in populated areas, or in areas with severe accessibility restrictions. These limitations lead to irregular or sparse datasets in combination with sometimes low signal-to-noise ratio for the target reflections in the recorded data.

 

Therefore, robust imaging methods are needed to generate high resolution reflection seismic images for such kind of data. Focusing prestack depth migration methods have proven to deliver improved image quality compared to standard time- or depth migration approaches. We show the results of our focusing pre-stack depth migration techniques applied to a vintage 3D seismic data set (ISO89) acquired in 1989 around the German deep continental drill site (KTB). We show a comparison to other previously obtained seismic images for the same data set and how the image quality evolved over time.

How to cite: Hlousek, F. and Buske, S.: New insights into vintage 3D reflection seismic data in hard-rock environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13872, https://doi.org/10.5194/egusphere-egu23-13872, 2023.

EGU23-14033 | ECS | Orals | TS2.1 | Highlight

CARS - Catalog of Relative Seismic Locations of 1981-2018 Italian Seismicity 

Maddalena Michele, Raffaele Di Stefano, Lauro Chiaraluce, Diana Latorre, and Barbara Castello

The Istituto Nazionale di Geofisica e Vulcanologia (INGV) monitors the Italian peninsula seismicity by using the data recorded by the Italian National Seismic Network (RSN) together with the ones gathered by other permanent regional networks (PRN). Earthquakes are real-time located by the INGV surveillance system and manually revised by the Italian Seismic Bulletin (BSI) group analysts.

Starting from a catalog composed by homogeneous absolute locations (CLASS; Latorre et al., 2023), obtained by using a 3D regional-scale velocity model, we generated a catalog of relative seismic locations (CARS) of about 310,000 events occurred in Italy during 1981-2018.

We inverted absolute P- and S- waves arrival times derived from data collected by RSN plus PRN for the period 1981-2008 and only by RSN for 2009-2018 to apply the double-difference relocation algorithm (Waldhauser and Ellsworth, 2000).

For the second period, we combined the absolute travel times with relative ones obtained by waveforms cross-correlations analysis performed on pairs of similar events. The time domain cross‐correlation method proposed by Schaff et al., 2004 and Schaff & Waldhauser, 2005 was applied to seismograms of all pairs of events separated by 10 km or less and recorded at common stations. Seismograms were filtered in the 1–15 Hz frequency range using a four pole, zero phase band‐pass Butterworth filter. The correlation measurements were performed on 1.0 s long window for P- and S-waves. We collected a total of ~17 million P- and ~23 million S-wave delay times, retaining all measurements with correlation coefficients greater than 0.7.

1D velocity models characterising 18 different (geologically, seismically and tectonically homogeneous) Italian macroareas (after Pastori et al. B2-2019-2021, Wp1-task4) were used in the location procedure.

To cope with the memory limits (15,000 events with less than 200 readings) of the HypoDD code so to use it in a steady operational mode, we first subdivided the study region in the 18 macroareas related to the velocity models, then we additional discretize each in 100x100km2 cells, overlapped by the 80% in longitude and latitude. We repeatedly produced hypocentral locations of the same events that we merged by computing a final weighted mean location.

We present the double-difference catalog of Italian seismicity, allowing to depict alignments clearer with respect to the starting catalog (CLASS), to be related to seismogenic faults and/or to regional structures along the whole Italian peninsula.

How to cite: Michele, M., Di Stefano, R., Chiaraluce, L., Latorre, D., and Castello, B.: CARS - Catalog of Relative Seismic Locations of 1981-2018 Italian Seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14033, https://doi.org/10.5194/egusphere-egu23-14033, 2023.

EGU23-14206 | Posters on site | TS2.1

A local earthquake tomography model of the Fucino fault-controlled basin (central Apennines, Italy) obtained through a very dense temporary network 

Pasquale De Gori, Luigi Improta, Maurizio Vassallo, Fabrizio Cara, Gaetano De Luca, Alberto Frepoli, Samer Bagh, and Luisa Valoroso

The Fucino basin (central Italy) is the largest Plio-Quaternary tectonic depression of the Apennines extensional belt. The basin is bounded to the north and east by two main normal fault systems striking WSW-ENE and NW-SE, respectively. These fault systems controlled the syntectonic depositions of lacustrine and coarse clastic sequences that reach a total thickness of 1.5 km. The NW-SE fault system is the source of the Mw 7.0, 1915 central Italy earthquake and of previous M6-7 earthquakes recognized through paleoseismic trenching. On the other hand, current activity and seismogenic potential of the WSW-ENE structures are uncertain. The shallow architecture of both fault systems (< 2 km depth) is well defined by surface data and seismic reflection profiles, but the fault’s deep geometry is poorly known. Large uncertainties also regard the crustal structure underneath the basin at seismogenic depths (i.e.; 5-15 km depth) despite a close deep seismic reflection profile (i.e., CROP11 line). The instrumental seismicity occurring beneath the Fucino basin is scarce. On the contrary, an intense activity concentrated to the north (2009, Mw 6.3, L’Aquila sequence) and 25-30 km to the south, where both low-to-moderate sequences and diffuse swarm-like seismicity were recorded in recent years. In 2008-2009, a dense passive seismic survey was carried out in the Fucino area to investigate the basin seismic response and local site effects. The temporary network included 18 stations, with an average spacing of 2-3 km, operating in continuous mode with a sampling rate of 125 Hz and equipped with 5 second seismometers. In this study, we re-processed the data recorded by the Fucino temporary network, integrated by the permanent stations of the Italian seismic network and Abruzzo regional network installed on the surrounding ridges, to construct a new earthquake catalog and perform a local-scale passive tomographic survey. We used a standard (STA/LTA) algorithm to detect very local weak events in addition to those used in the previous site-effects study. P- and S-wave arrival times of the detected seismic events were hand picked and weighted according to a standard scheme. Seismograms for stations deployed in the Fucino basin show strong complexities especially for P-waves onsets that are often masked by background noise. We used the final dataset in terms of P- and S-waves arrival times as input for a Local Earthquake Tomography targeting the upper crustal velocity structure and active faults underneath the Fucino basin and surrounding ridges. The tomographic model, presented in terms of Vp and Vp/Vs, aimed at recovering the crustal heterogeneities with a spatial resolution finer with respect to previous tomographic surveys of central Apennines. The 3D distribution of Vp and Vp/Vs and of relocated events helped us to identify the velocity contrasts related to the main faults and to improve our knowledge on their geometry at depth.

How to cite: De Gori, P., Improta, L., Vassallo, M., Cara, F., De Luca, G., Frepoli, A., Bagh, S., and Valoroso, L.: A local earthquake tomography model of the Fucino fault-controlled basin (central Apennines, Italy) obtained through a very dense temporary network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14206, https://doi.org/10.5194/egusphere-egu23-14206, 2023.

EGU23-14260 | ECS | Posters on site | TS2.1

Comparison of relative locations methods and their accuracy for determining fault structures 

Diana Konrádová, Josef Horálek, and Jana Doubravová

Precise earthquake locations are a prerequisite for determining real fault structures. To improve the precision of the event location, a few relative locations methods are commonly used to refine event locations. Relative relocation methods reduce effects of an imperfect velocity model and errors due to arrival time measurement. We performed comparative tests of tree different relocation methods: HypoDD (HD), GrowClust (GC) and Master event (ME). We tested the efficiency and differences in the event locations using these three methods on dataset from REYKJANET seismic network operating in Iceland on Reykjanes Peninsula. All these methods provide substantially focused shapes of clusters compared to the absolute event locations but the locations of individual events differ evidently depending on the method used.

We also aimed at an effect of the control parameters of HD, GC and ME on final location results and their optimization as well as computational and memory demands.

How to cite: Konrádová, D., Horálek, J., and Doubravová, J.: Comparison of relative locations methods and their accuracy for determining fault structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14260, https://doi.org/10.5194/egusphere-egu23-14260, 2023.

EGU23-15556 | Orals | TS2.1 | Highlight

Rayleigh wave tomography in the north-eastern margin of the Tibetan Plateau by way of training physics-informed neural networks 

Sjoerd de Ridder, Yunpeng Chen, Sebastian Rost, Zhen Guo, and Yongshun Chen

Machine learning is rapidly becoming ubiquitous in the Earth Sciences promising to provide scalable algorithms for data-mining, interpretation, and model building. Initially heralded for its ability to exclude complicated physics from data analysis, recent innovations seek to merge machine learning  solutions with conventional physics-based methods in order to enhance their capability

We present a novel eikonal tomography approach for Rayleigh wave phase velocity and azimuthal anisotropy based on the elliptical-anisotropic eikonal equation, by formulating the tomography problem as the training of a physics informed neural network (PINN). The PINN eikonal tomography (pinnET) neural network utilizes deep neural networks as universal function approximators and extracts traveltimes and medium properties during the optimization process. Whereas classical eikonal tomography uses a generic non-physics-based interpolation and regularization step to reconstruct traveltime surfaces, optimizing the network parameters in pinnET means solving a physics constrained traveltime surface reconstruction inversion, tackling measurement noise and resolving the underlying velocities that govern the physics. The fast and slow velocity and the anisotropic direction information can be directly evaluated from the trained medium property networks. Checkerboard tests indicate that the input velocity model can be well recovered by using this approach and synthetic data.

We demonstrate this approach by applying it to multi-frequency surface wave data from ChinArray phase II sampling the north-eastern Tibetan plateau. We are able to use much less data to achieve similar subsurface images because of the benefit of including the physics constraint while reconstructing the traveltime surfaces. We are able to obtain excellent results using only 10 sources.  Comparing results from pinnET with conventional eikonal tomography, we find good agreement with distinct low velocity structures beneath the Songpang-Ganzi block, Qilian and Western Qinling Orogen. Large phase velocity uncertainties occur in a small part of the southeastern Ordos Block, the western Songpan-Ganzi Block and the eastern Sichuan basin, which correspond to the reduced data coverage dependent on the selection of the 10 sources. We also verify the accuracy and reliability of the pinnET by choosing only one station as virtual source, the retrieved velocities show relatively good resolution which is much better than in conventional eikonal tomography using similar sized datasets. The method is memory efficient because compressing the traveltimes as outputs to a NN is a concept akin to compressed sensing and offers advantages over traditional anisotropic eikonal tomography or neural network approaches.

How to cite: de Ridder, S., Chen, Y., Rost, S., Guo, Z., and Chen, Y.: Rayleigh wave tomography in the north-eastern margin of the Tibetan Plateau by way of training physics-informed neural networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15556, https://doi.org/10.5194/egusphere-egu23-15556, 2023.

EGU23-15881 | Posters on site | TS2.1

Accurate Earthquake Locations of the Adriatic Thrust Fault of the 2021 Seismic Sequence with sP Depth Phases. 

Raffaele Di Stefano, Maria Grazia Ciaccio, Paola Baccheschi, and Dapeng Zhao

We re-located 70 earthquakes belonging to the seismic sequence started on 2021 March 27th, with a mainshock of Mw 5.2 at 13:47 UTC, in the Central Adriatic region (Italy off-shore) by using the on-purpose designed code by Zhao et al. (2007, 2011), modeling the sP converted phases.

The mainshock of the 2021 seismic sequence occurred about 20 km north of the Palagruza island, 80 km from the Gargano promontory and about 40 km from the Croatian island of Lastovo. It was felt in many central-southern Italian regions, from Ancona to Foggia, and in Central Dalmatia. All the epicenters of this seismic sequence lie in the open sea, about 100km to the SE and about 50 km to the NW of the 2003 Jabuka seismic sequence, and the 1988 Palagruza seismic sequence, respectively.

Though the seismicity in the central Adriatic Sea has been recorded by improving seismic networks, especially in recent decades, the precise location of the Adriatic offshore earthquakes was hampered mainly by the large distance of the closest stations, and by the large gap in the distribution of seismic stations.

The possibility to model the sP depth phases enables us to estimate the epicentral parameters and focal depths of these offshore earthquakes more accurately, thanks to the peculiar ray-path that mimics the presence of a receiver approximately on top of the hypocenter. The refined earthquake locations allow us to make inferences on the structure responsible for the seismicity of the 2021 seismic sequence, a thrust fault NW-SE striking and ~35° NE-dipping, and on its seismotectonic context.

The use of depth-phase arrival times to constrain the off-network events' locations is of particular interest to Italy due to both the peculiar shape of the peninsula and the extreme scarcity of seafloor stations, whose cost and management are very expensive and complex.

We present the first attempt to apply this off-network location technique to the Italian offshore seismicity with the aim of improving the hazard estimation of these hard-to-monitor regions.

How to cite: Di Stefano, R., Ciaccio, M. G., Baccheschi, P., and Zhao, D.: Accurate Earthquake Locations of the Adriatic Thrust Fault of the 2021 Seismic Sequence with sP Depth Phases., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15881, https://doi.org/10.5194/egusphere-egu23-15881, 2023.

EGU23-218 | ECS | Orals | GD6.4 | Highlight

Oscillating tidal stress loading on the lithosphere 

Davide Zaccagnino and Carlo Doglioni

It is well known that oscillating stress sources play a relevant role in the stability of mechanical systems. The Earth is routinely subject to stress loading due to tides, hydrological cycles, atmospheric pressure variations and anthropical activities. However, the shallow part of our planet is far from being a simple system, so each component showcases a different response to perturbations depending on its physical properties. Macroscopically, the outer layers of the Earth form a two-tier system with respect to periodic stress changes: the brittle crust reacts forthwith to additional loads; conversely, the viscous lithosphere behaves as a low-pass filter. Such a dichotomy produces a wide range of different geodynamic, tectonic, and seismological processes. Seismicity becomes more and more sensitive to stress perturbations as strain accumulates so that earthquakes tend to occur, on average, during phases close to stress peak. We analyse the effect of solid and liquid tides in modulating seismicity during the seismic cycle in several regions of tectonic interest. Our study shows that the correlation between the amplitude of tidal CFS and seismic energy rate usually increases before large shocks, while it undergoes drops during foreshock activity and after the mainshock. A preseismic phase, featured by increasing correlation, is detected before large and intermediate (Mw > 4.5) shallow earthquakes in about 2/3 of cases. The duration of the anomaly T appears to be related to the seismic moment M of the future mainshock via the relationship T ∝ M^0.3 if the magnitude of the largest event is below 6.5. This power exponent, 1/3, is typical of seismic nucleation scaling of single seismic events; therefore, the increase of correlation between seismic rates and tidal stress on fault may be understood in the light of diffuse nucleation phases throughout the crust due to incoming large-scale destabilization. We also consider tremors and low-frequency earthquakes in the Cascadia region along the West coasts of British Columbia, Washington, Oregon and Northern California and the Nankai thrust in Japan. Their sensitivity to stress perturbations increases as the surrounding fault interface is seismically locked, showing an analogous response to fast seismic events. On the other hand, viscous layers of the lithosphere are almost unresponsive to high-frequency stress perturbations (e.g., at least up to annual periods); however, they can flow plastically under the action of long-lasting loading: it is the case of low-frequency Earth tides (e.g., lunar nodal 18.61-years-long cycle) which can be detected as millimetric modulations in relative plate velocities using single-station- and baseline- modes GNSS time series. On the light of thin ultralow viscosity zones spreading at the lithosphere-asthenosphere boundary and inside the asthenosphere, and of thermally active small-cell stratified convection in the super-adiabatic zones of the upper mantle, it is reasonable that such modulations may have geodynamic implications. This conclusion is also supported by several observations proving a worldwide asymmetry in global geodynamics such as the westerly oriented motions of plates which follow a mainstream with a 0.2-1.2°/Myr drift relative to the sub-asthenospheric mantle in the hotspot reference frame.

How to cite: Zaccagnino, D. and Doglioni, C.: Oscillating tidal stress loading on the lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-218, https://doi.org/10.5194/egusphere-egu23-218, 2023.

EGU23-526 | ECS | Orals | GD6.4

Investigation of Lithospheric Structure in NE India Based on Love Wave Data 

Nongmaithem Menaka Chanu, Naresh Kumar, Sagarika Mukhopadhyay, and Amit Kumar

We analyzed 228 earthquake data of 5≤Mw≤6.9 to estimate the Love wave group velocity tomographic image and investigate the lithosphere structure of NE-India. These events of 2001-2015 were recorded by 26 seismic stations of IMD, India, and IRIS. Multiple Filtering Technique is used to estimate fundamental mode Love wave group velocity dispersion curves between 4s and 70s for 846 paths. Then, we constructed Love wave group velocity maps at different periods from 6 s to 60 s through inversion over a 1°×1° grid indicating group velocity variations between ~2 km/s and 4.6 km/s in this part of the India-Eurasia and India-Burma collision zones. Tomographic maps at lower periods show good correlations with surface features. Group velocities at 6s to 16s are sensitive to the uppermost crust. They show high variation related to local geological features like sedimentary basins, basement rocks, Precambrian, and metamorphic rocks. Bengal-Basin and Indo-Burma Ranges have lower group velocities at periods ≤16s compared to those located at Shillong Plateau, Mikir Hills, and the Eastern Himalayan ranges. Low-velocity zone systematically shifts eastward towards the southern part of the Indo-Burma Range for periods from 16 to 38s. A prominent increase in group velocity from 38s is observed along a line trending in the NE direction through the Shillong Plateau, Mikir Hills, and Assam syntaxis. At periods >50s, low velocity is observed in the Tibetan plateau. Inversion of Love wave group velocity was carried out and a tomographic image of SH velocity variation was obtained for the study area. It shows a significant variation in the SH velocity for the crust and upper mantle region of the study area. Based on the estimated Love wave group velocity and SH velocity tomograms we came to the following conclusions. The sedimentary basins like the Bengal Basin, and Brahmaputra River Basin show up as low-velocity zones in both group and SH velocity tomograms. In the Bengal Basin, sedimentary layer thickness varies from 5km in the western part to 15km in the eastern part. Maximum thickness was observed in the SE part of the basin near the Indo-Burma Ranges. The Moho depth below the Bengal Basin varies between 28 km and 32km and 35km and 45km below NE India. The NE trending region showing high group and SH velocity values passing through the Shillong Plateau, Mikir Hills, and Assam syntaxis represent a zone where the Indian plate has buckled upward. This is caused by it being in a vice-like grip between the Eastern Himalayas towards its north and the Indo-Burma Ranges towards its east. The crust below the Tibet and Lasha block is much thicker (up to ~85 km) compared to other parts of the study area. A low-velocity zone is observed in the mid-to-lower crust beneath southern Tibet. This is caused by partial melting in this zone. Mostly the Love wave inversion result matches with previously observed Rayleigh wave inversion and discrepancies in some sections highlight the existence of radial anisotropy.

 

How to cite: Chanu, N. M., Kumar, N., Mukhopadhyay, S., and Kumar, A.: Investigation of Lithospheric Structure in NE India Based on Love Wave Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-526, https://doi.org/10.5194/egusphere-egu23-526, 2023.

The parallel linear landforms, frequent phenomena in many places on the Earth's crust surface, were systematically assessed in the area of central Europe (~3,000 km longitudinally, ~2,000 km latitudinally). In total, we estimated yet ~24,000 items. Several (>5) variously oriented large systems (networks) of such topographic features pervade fairly regularly the region.

Our study using the LiDAR or SRTM data (1) allowed to outline spatial distribution of the occurring lines, mostly by considering basic complex surface geometries or directional trends (including chaining of landforms of different types) instead of simple linear elements (valley sections, slopes, ridges) commonly applied during automatic extraction procedures. Primarily created in the Czech national conformal conic S-JTSK projection as straight features, the landforms are displayed as slightly bended curves in the WGS geographical coordinates. Usually, a general trend of some important regional fault system of Palaeozoic or Mesozoic origin served as primary direction at searching for analogous surface elements within the particular linear network in the surroundings. However, most of the linear landforms do not correspond to geological boundaries since the topographic features of all the distinguished directions are dispersed across many of regional geological units. But the elongated element clusters (zones) can accord with significant geological structures (basins, mountain ranges, or their margins) and some linear topographic features fairly correspond with current spatial limits of young sedimentary formations (covers).

(2) A plenty of other regional or local natural phenomena in the present-day landscape are closely associated with the linear landform systems. The regional features include general orientation and detailed shape of river and valley network sections (abundant deflections into the main directions), dense block segmentation of the topographic structure (separation of lower and higher surface levels) or location of concentrated surface erosion; all the main linear systems are followed by the same such expressions. Locally, smaller landforms like related saddles, cuestas, anomalously shaped meanders, river terrace risers, land slide or even cirque elements have evolved. Thus, the linear networks strongly influenced upper parts of the Earth's crust.

Besides aspects of the subject presented, a discussion on various development stages of linear landforms and related features in the deeper Earth's crust possibly including also some plate tectonics elements, as precursors of the focused surface expressions, is called for to provide proper explanation of the extensive phenomenon.

How to cite: Roštínský, P. and Nováková, E.: Regularly directed complex linear landforms in central Europe: a large-scale disperse or zone distribution, and indication of associated landscape phenomena, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2680, https://doi.org/10.5194/egusphere-egu23-2680, 2023.

EGU23-2901 | ECS | Orals | GD6.4

Implications of zircon Th/U for global continental crustal evolution and geodynamics 

Yujing Wu, Xianjun Fang, and Jianqing Ji

The continental crust is formed by the mantle’s successive crystallization differentiation and then aggregation, which is the result of the continuous energy acquisition and evolution of the mantle. This process has been objectively recorded in the growth of zircons which are widely present in the continental crust, owing to the close relationship between the zircon Th/U ratio and the crystallization temperature of zircons. As shown by theoretical calculations, phenomenon statistics, and/or crystallization simulations, higher zircon Th/U generally indicates higher zircon (re)crystallization temperature in metamorphic and magmatic systems. Here, we compiled ~600,000 zircon Th/U data from the global continental crust and obtained the time series of zircon Th/U ratios. The average level of the Th/U ratio in global zircons has a slow growth trend from old to new and fluctuates quasi-periodically around 0.5. There are two significant cycles of zircon Th/U ratios, ca. 600 and 120 Myr, which are associated with the supercontinent cycle and whole-mantle convection, respectively. It is inferred that the zircon Th/U periodicity is related to the periodic thermal state changes in the mantle, which might be regulated by tidal energy dissipation.

How to cite: Wu, Y., Fang, X., and Ji, J.: Implications of zircon Th/U for global continental crustal evolution and geodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2901, https://doi.org/10.5194/egusphere-egu23-2901, 2023.

We use P-wave receiver function (P-RF) analysis and joint inversion with Rayleigh wave group velocity dispersion data to model the shear-wave velocity (Vs) structure of sub-continental lithospheric mantle (SCLM) discontinuities beneath northeast (NE) India. The most prominent SCLM discontinuity is the Hales Discontinuity (H-D) observed beneath the Eastern Himalayan Foreland Basin (Brahmaputra Valley) and Shillong Plateau. The P-to-SV converted phase from the H-D (Phs) is a positive amplitude arrival at ∼10–12 s and has positive move out with increasing ray-parameter. From joint inversion, the H-D is modeled at a depth range of 90–106 km, with 9–12% Vs increase beneath the Brahmaputra Valley. Beneath the Shillong Plateau the H-D is at a depth range of 86–102 km, with 6–9% Vs increase. An intra-lithospheric discontinuity (ILD) has been identified in the Shillong Plateau station P-RFs, as a positive amplitude PILDs phase, arriving at 8–8.5 s. This is modeled at a depth range of 65–75 km with Vs increase of ∼7±4%. We construct 2D profiles of depth-migrated common conversion-point stack of P-RFs to distinguish the SCLM discontinuity arrivals from crustal phases. 3D spline-interpolated surface of the H-D has been constructed to visualize its lateral variations. We use xenolith data from the Dharwar Craton, which has similar geological age, petrology and seismic structure as the Shillong Plateau, to petrologically model the SCLM H-D and ILD Vs structure in NE-India. From the calculated Vs structure we conjecture that the H-D is a petrological boundary between mantle peridotite and kyanite-eclogite, with its origin as metamorphosed paleo-subducted oceanic-slab, similar to other global observations. We further speculate that the shallower ILD could be formed as a contact between frozen asthenosphere-derived metasomatic melts within the SCLM.

How to cite: Chaudhury, J. and Mitra, S.: Sub-Continental Lithospheric Mantle Discontinuities beneath the Eastern Himalayan Plate Boundary System, NE India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4829, https://doi.org/10.5194/egusphere-egu23-4829, 2023.

EGU23-5213 | Posters on site | GD6.4

Multiscale geophysical characterization of the continental crust of the Central Asian Orogenic Belt 

Alexandra Guy, Karel Schulmann, Christel Tiberi, and Jörg Ebbing

The Central Asian Orogenic Belt (CAOB) is a Paleozoic accretionary-collisional orogen located at the eastern Pangea in between the Siberian Craton to the north and the North China and Tarim cratons to the south. Several contradictory geodynamic models were proposed to explain the tectonic assemblage: oroclinal bending and strike-slip duplication of a giant intraoceanic arc or a progressive lateral accretion of linear continental and oceanic terranes towards the Siberian Craton. However, none is generally accepted. A multidisciplinary and multiscale approach integrating potential field analysis and modelling provides new insights into understanding the crustal structures beneath the CAOB.

First, we present a synthesis of the previous geophysical studies, which constitute the constraints for the modelling. Second, based on global gravity and magnetic anomaly grids, the large-scale statistical analysis of their lineaments reveals the distribution of the contrasting tectonic zones. Then, the topography of the Moho is determined by 3D forward modelling of the GOCE gravity gradients, which is then integrated into 2D and 3D crustal scale models of southern and central Mongolia. A geodynamic model is derived from the resulting crustal architectures. Thus, the combination of these methods allows us to: (1) unravel the existence and distribution of suspect terranes in accretionary systems; (2) correlate the contrasting tectonic zones with the gravity and magnetic signals and the thickness of the crust, thereby revealing the inheritance of Paleozoic and Mesozoic orogenic history; and (3) determine the significance and possible origin of the major anomalies, which are related to tectonic processes such as lower crustal relamination, presence of deep-seated fault zones and sutures, or delimitation of main tectonomagmatic domains. Finally, with the case study of Central Mongolia, we demonstrate the real benefit and the significant progress, which can be achieved by using potential field analysis combined with seismic receiver function and geological analyses.

How to cite: Guy, A., Schulmann, K., Tiberi, C., and Ebbing, J.: Multiscale geophysical characterization of the continental crust of the Central Asian Orogenic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5213, https://doi.org/10.5194/egusphere-egu23-5213, 2023.

EGU23-6029 | ECS | Posters virtual | GD6.4

Estimation of the Moho depth in the Bay of Bengal using gravity data and understanding of its tectonic implications 

Priyank Pathak, William Kumar Mohanty, and Prakash Kumar

At the beginning of the Cretaceous period, India and Antarctica started breaking apart. There were major changes to the seafloor in the Bay of Bengal (BOB) and geodynamic processes after this episode. Therefore, it is interesting to detailed understanding of the tectonics of the BOB. The BOB is surrounded by Bangladesh to the north, the Andaman-Sumatra arc to the east, and the eastern coast of India to the west. Bouguer gravity anomaly, elevation, and sediment thickness data are used in this study to determine the gravity Moho and Isostatic Moho topography of the BOB. The gravity effects of sediments are calculated by using the recent GlobSed model. Gravity Moho is derived from the inversion of sediments corrected gravity data using the Parker‐Oldenburg method. Generally, it is observed that the thin crust is associated with the BOB while the thicker crust is associated with two aseismic ridges: Ninetyeast and 85°E ridges, situated in the eastern and central parts of BOB, respectively. This suggests that these ridges may have formed due to the interaction of the plume-spreading centre. The thick depressed crust beneath the northernmost part of BOB, implies that it is due to a load of sediments, and abrupt ~12 km deepening of gravity Moho from eastern BOB (Sumatra trench) to Andaman Arc. The consequences of the difference between gravity and isostatic Moho for the isostatic state of the crust are examined in order to understand the geodynamics of the study area. The isostatic analysis of crust, which takes into account the difference between the two types of Moho, shows that all of the regions except for the north of Bengal fan, Ninetyeast ridge, and southern region of 85°E ridge are compensated. The Moho of the Andaman Arc and the north of Bengal fan, are overcompensated, which should be uplifted, while the Moho of the Sumatra trench, Ninetyeast ridge, and the southern region of 85°E ridge become depressed. In order to make isostatic compensation of the region, an additional upper mantle density variation between 47 to 62 kg/m3 has to be added. This implies an additional compensation mass is needed under the Ninetyeast ridge and the southern region of 85°E ridge is 47 kg/m3 and 56 kg/m3, respectively, for providing isostatic equilibrium.

How to cite: Pathak, P., Kumar Mohanty, W., and Kumar, P.: Estimation of the Moho depth in the Bay of Bengal using gravity data and understanding of its tectonic implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6029, https://doi.org/10.5194/egusphere-egu23-6029, 2023.

EGU23-6580 | ECS | Posters on site | GD6.4

Lithospheric evolution of eastern Arabia 

Lars Wiesenberg, Christian Weidle, Andreas Scharf, Philippe Agard, Amr El-Sharkawy, Frank Krüger, and Thomas Meier

The geology of eastern Arabia is dominated by a vast cover of mostly Phanerozoic sedimentary rocks and little was known about the architecture of the middle and lower crust. On the easternmost margin, obduction of the Semail Ophiolite during late Cretaceous times is the youngest first-order tectonic process that shapes the present-day geology across the Oman Mountains in northern Oman and the eastern United Arab Emirates. Within the obducted units, Neoproterozoic to Cretaceous autochthonous rocks of the Arabian shelf are exposed in two tectonic windows and provide a detailed view of the geodynamic evolution of the shallow Arabian continental crust during and after obduction. A new, unprecedented 3-D anisotropic shear-wave velocity (Vs) model reveals that - prior to obduction - the assembly of the eastern Arabian lithosphere in Neoproterozoic times and its modification during the Permian breakup of Pangea strongly control the present-day lithospheric architecture. Building upon previous geodynamic models that were restricted to the upper crust, reconstruction of the entire lithospheric evolution resolves some key unknowns in eastern Arabia’s geodynamics:

  • The NNE-striking Semail Gap Fault (SGF) is primarily an upper crustal feature but another NE-striking deep crustal boundary zone west of the Jabal Akhdar Dome segments the Arabian continental crust in two structurally different units.

  • While Permian Pangea rifting occurred on both eastern and northern margins of eastern Arabia, large-scale mafic intrusions occurred mostly east of the SGF. Eastward crustal thinning localizes at the eastern limit of obducted units, east of which the lower crust is strongly intruded and likely underplated.

  • Late Cretaceous exhumation and overthrusting at the end of ophiolite obduction is the likely cause for crustal thickening below today‘s topography of the Oman Mountains.

  • Lithospheric thickness is ~200-250 km in central Arabia but only ~100 km below the Oman Mountains. Thinning of the continental lithosphere is attributed to late Eocene times, which explains contemporaneous basanite intrusions into the continental crust and provides a plausible mechanism for observed crustal-scale extension and the broad, margin-wide emergence of the Oman Mountains. Thus, uplift of the mountain range might be unrelated to Arabia-Eurasia convergence.

How to cite: Wiesenberg, L., Weidle, C., Scharf, A., Agard, P., El-Sharkawy, A., Krüger, F., and Meier, T.: Lithospheric evolution of eastern Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6580, https://doi.org/10.5194/egusphere-egu23-6580, 2023.

EGU23-6733 | ECS | Orals | GD6.4

The Case of the Missing Diamonds: New global and regional thermo-compositional models of cratonic lithosphere 

Felix Davison, Sergei Lebedev, Yihe Xu, Javier Fullea, and Sally Gibson

Cratons are the ancient cores of continents, stable over billions of years. The thermochemical properties of their lithosphere are debated, with a number of open questions regarding their composition, the presence of volatiles and the degree of metasomatism.  Cratonic mantle lithosphere is thought to be dominated by depleted mantle peridotites, primarily harzburgites, which can provide chemical buoyancy and, therefore, long-term stability. Some recently proposed models, however, featured substantially metasomatised shallow mantle lithosphere, modified by the addition of volatiles (Eeken et al. 2018) or significant proportions of eclogite and diamond within the lithosphere (Garber et al. 2018). The broad range of the compositions proposed highlights the persisting uncertainty over what cratons are made of.

 

Arguments for cratonic lithosphere complexity often follow from difficulties in fitting seismic velocity profiles (taken from tomographic models beneath cratons) using peridotitic compositions. Some Rayleigh-wave inversions have also found difficulty fitting phase velocity dispersion curves without significant metasomatism, including models with up to 5wt% CO2.

 

Recently developed methods of petrological inversion can relate geophysical and geological observations directly to the thermochemical structure of the lithosphere and asthenosphere. Here, we invert Rayleigh and Love surface wave phase velocities, elevation and heat flow data for temperature and composition at depth (Fullea et al. 2021) beneath a selection of cratons around the world and a global craton average. We aimed to assemble the most accurate surface-wave dispersion data, with broad period ranges and small errors. The models fit the data within 0.1-0.2% of the phase-velocity values. This accuracy is important in order to extract the information on the radial structure of the lithosphere from the dispersion data.

 

Our models use a harzburgitic (depleted peridotite) composition with major oxide weight percentages taken from prior global modelling (Fullea et al. 2021) and produce very close fits for the Rayleigh and Love dispersion curves averaged over cratons globally, as well as the Rayleigh and Love dispersion data measured in several cratons around the world. The cratonic lithospheric thicknesses range from 180 km (Guyana) to almost 300 km (Congo). We demonstrate that these new models can also be produced by careful regularisation of purely seismic inversions of the same data.

 

Our results do not rule out extensive metasomatism in the cratonic uppermost mantle but suggest that it is likely to be a rare anomaly in particular locations, rather than a common occurrence. Ubiquitous presence of substantial quantities of eclogite and diamond in cratonic lithosphere is not required by the data.

 

References:

 

Eeken, T., et al., 2018. Seismic evidence for depth-dependent metasomatism in cratons. Earth Planet. Sci. Lett. 491, 148-159.

 

Fullea, J., Lebedev, S., Martinec, Z. et al., 2021. WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. Geophys. J. Int. 226, 146-191.

 

Garber, J.M., et al., 2018. Multidisciplinary constraints on the abundance of diamond and eclogite in the cratonic lithosphere. Geochem., Geophys., Geosyst. 19, 2062-2086. 

How to cite: Davison, F., Lebedev, S., Xu, Y., Fullea, J., and Gibson, S.: The Case of the Missing Diamonds: New global and regional thermo-compositional models of cratonic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6733, https://doi.org/10.5194/egusphere-egu23-6733, 2023.

EGU23-6967 | Posters on site | GD6.4 | Highlight

Continental and oceanic upper mantle thermochemical heterogeneity an density in the European – North Atlantic region. 

Alexey Shulgin and Irina Artemieva

We present a joint continental-oceanic upper mantle density model based on 3D tesseroid gravity modeling. On continent lithospheric mantle (LM) density shows no clear difference between the cratonic and Phanerozoic Europe, yet an ~300‐km‐wide zone of a high‐density LM along the Trans‐European Suture Zone may image a paleosubduction. Kimberlite provinces of the Baltica and Greenland cratons have a low‐density (3.32 g/cm3) mantle where all non‐diamondiferous kimberlites tend to a higher‐density (3.34 g/cm3) anomalies. LM density correlates with the depth of sedimentary basins implying that mantle densification plays an important role in basin subsidence. A very dense (3.40–3.45 g/cm3) mantle beneath the superdeep platform basins and the East Barents shelf requires the presence of 10–20% of eclogite, while the West Barents Basin has LM density of 3.35 g/cm3 similar to the Variscan massifs of western Europe. In the North Atlantics, south of the Charlie Gibbs fracture zone (CGFZ) mantle density follows half‐space cooling model with significant deviations at volcanic provinces. North of the CGFZ, the entire North Atlantics is anomalous. Strong low‐density LM anomalies (< −3%) beneath the Azores and north of the CGFZ correlate with geochemical anomalies and indicate the presence of continental fragments and heterogeneous melting sources. Thermal anomalies in the upper mantle averaged down to the transition zone are 100–150 °C at the Azores and can be detected seismically, while a <50 °C anomaly around Iceland is at the limit of seismic resolution. Presented results is a further development of the EUNA-rho model (doi:10.1029/2018JB017025)

How to cite: Shulgin, A. and Artemieva, I.: Continental and oceanic upper mantle thermochemical heterogeneity an density in the European – North Atlantic region., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6967, https://doi.org/10.5194/egusphere-egu23-6967, 2023.

EGU23-8306 | ECS | Orals | GD6.4

Crustal Features of Eastern Anatolia based on a Joint Grid Search Performed over Receiver Functions and P-wave Coda Autocorrelation 

Hazal Aygün, Tuna Eken, Derya Keleş, Tülay Kaya-Eken, Fabio Cammarano, Jonathan R. Delph, and Tuncay Taymaz

The complex tectonic structure of eastern Anatolia results from the superposition of subduction and collisional structures along a long-lived convergent margin between the Gondwanan (Arabian) and Eurasian plates. The geodynamic processes shaping the tectonic setting and uplifting history of the region still remain enigmatic despite the fact that the number of geophysical, geological, and petrographic-based models/interpretations in recent years has increased notably. Further issues, i.e., how the spatiotemporal patterns of seismic activity are controlled by pre-existing deformational zones in the lithosphere and/or modern convergent stresses, and how magmatism is related to the lithospheric variability along the margin, are unclear. Models of seismological features of the Earth’s interiors provide insights on isotropic heterogeneity that are of great importance for constraining the current physical and chemical conditions, as they likely control the localization of structures. For this purpose, the present study aims to constrain lateral variations of crustal thickness, Moho topography, and average seismic velocities (Vp, Vp/Vs) by leveraging information from both teleseismic scattered (receiver function) and reflected (autocorrelation) waves (H-k-Vp stacking). Incorporating teleseismic autocorrelation waveforms from the P-wave coda, we can better constrain average crustal P-wave velocities (Vp) by highlighting the amplitude term of the Moho-reflected Pmp phase. Our dataset consists of digital waveforms extracted from 512 teleseismic events (within the epicentral distance range from 30° to100° and with Mw>6) observed at 33 permanent broadband seismic stations operated under the KOERI network between 2013 and 2022 and will result in a new map of crustal architecture and its physical properties (crustal thickness, Vp, and Vp/Vs) below eastern Anatolia. Preliminary results indicate a thickening crust from south to north reaching down to depths of ~50 km. High Vp/Vs ratios mark volcanic provinces as well as fault damage areas presumably characterized by highly fractured rocks with high amounts of water content. Lateral variations of P-wave velocities along two continental fault zones (EAFZ and NAFZ) of the region imply that the degree of shear deformation and resultant seismic activity is well-correlated with density/seismic wave speed variations. Moho depth variations across the NAFZ further suggest a much narrow and localized distribution of deformation in the lower crust and upper mantle compared to the EAFZ. Further analysis of these results will lead to a better understanding of the controlling mechanisms behind seismicity and magmatism in the Eastern Anatolian Plateau.

How to cite: Aygün, H., Eken, T., Keleş, D., Kaya-Eken, T., Cammarano, F., Delph, J. R., and Taymaz, T.: Crustal Features of Eastern Anatolia based on a Joint Grid Search Performed over Receiver Functions and P-wave Coda Autocorrelation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8306, https://doi.org/10.5194/egusphere-egu23-8306, 2023.

EGU23-11855 | Posters on site | GD6.4

Crustal structure beneath the Nógrád-Gömör Volcanic Field from 3D density modelling 

Jaroslava Pánisová, Miroslav Bielik, Vladimír Bezák, and Dominika Godová

During the last 21 Ma, widespread and geo-chemically variable volcanism took place in the Pannonian Basin and surrounding areas. The Nógrád-Gömör Volcanic Field (NGVF) is the northernmost Neogene monogenetic alkali basalt volcanic field of the Carpathian–Pannonian region, where the magma transported numerous upper mantle xenoliths to the surface. Alkaline basalt volcanism in this area represents a typical intraplate association, which is a result of decompression melting at the interface of the mantle and asthenosphere. The deep structure of this area has long been of interest to the geologists, volcanologists, geophysicists and geochemists.

 

Long period MT data collected along a ~50 km long NNW-SSE profile helped to explain the electric conductivity behaviour of the lithospheric rocks and to indicate the LAB too (Patkó et al. 2021). A massive conductive wehrlitic cumulates were indicated at ~30-60 km depths which arose as a product of the mantle metasomatism. Wehrlite-bearing xenolith suites found in the central part of the NGVF supports this interpretation. We are aiming to understand the crustal architecture and interpret the rather complicated gravity field of the NGVF. Therefore, a robust 3D density model was constructed using the 3D potential field modelling tool IGMAS+.

 

Only the gridded gravity data were utilized in the modelling, as the amplitudes of multiple magnetic anomalies aligned in a belt formation indicates rather shallow sources related to basalt volcanism along the Hurbanovo-Diósjenő fault. To be able image the deeper structures we have constructed bigger starting 3D model containing all important geological interfaces, i.e. pre-Cenozoic basement, UC/LC boundary, Moho and LAB. Then all available geophysical and geological constraints (seismic, MT, faults positions, main tectonic units) were applied to produce a more detailed, structural model in the central part of the studied area.

 

The Hurbanovo-Diósjenő fault is confirmed to be a steep and deeply penetrating tectonic zone beneath the central part of the NGVF, separating the Trans-danubian Range and Bükk units from the Veporic and Gemeric units of the Inner Western Carpathians. Thanks to a higher density of wehrlite (3 350 kg/m3; Aulbach et al. 2020) we could identify the deep-seated geobody (located in a depth range of 30-55 km) through the gravity modelling. We assume that this mantle lithosphere geobody is closely related to alkaline basalt volcanism in the NGVF. It contributes with a smaller gravity effect of +5.7 mGal maximally to the overall positive gravity anomaly over the volcanic field. The observed Bouguer anomalies contain superimposed effects of the following upper crustal units too: Gemeric, South Veporic and crystalline basement probably of the Cadomian age.

 

Acknowledgement:

This work was supported by the projects Nos. APVV-16-0482, APVV-16-0146 and VEGA projects Nos. 2/0002/23 and 2/0047/20.

 

References:

Aulbach S. et al. 2020: Wehrlites from continental mantle monitor the passage and degassing of carbonated melts. Geochemical Perspective Letters 15, 30–34.

Patkó L. et al. 2021: Effect of metasomatism on the electrical resistivity of the lithospheric mante – An integrated research using magnetotelluric sounding and xenoliths beneath the Nógrád-Gömör Volcanic Field. Global and Planetary Change 197, 103389.

How to cite: Pánisová, J., Bielik, M., Bezák, V., and Godová, D.: Crustal structure beneath the Nógrád-Gömör Volcanic Field from 3D density modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11855, https://doi.org/10.5194/egusphere-egu23-11855, 2023.

EGU23-14376 | ECS | Posters on site | GD6.4

Imaging the South American Continental Interior with Waveform Tomography 

Bruna Chagas de Melo, Sergei Lebedev, Nicolas Celli, Janneke De Laat, and Marcelo Assumpção

The South American continent consists of an active mountain range on the west, formed by the subduction of the oceanic Nazca slab, and a large stable platform region, mainly composed of the Precambrian basement. Within South America, we find the cratons, blocks of differentiated continental lithosphere, characterized by their cold and buoyant behavior, and surrounding the cratons, mobile belts mostly from the Neoproterozoic form a complex collage network. The lithosphere and asthenosphere underlying a continent record most past tectonic events as much as control the different dynamic episodes of current deformation, magmatism, assembly, and large-scale rifting leading to break-up. However, our understanding of South America and how it has been affected by the underlying mantle processes is limited by the availability of both geophysical and geological data, hindered by the presence of thick sedimentary covers, dense forests, and large water masses.

Seismic tomography can resolve the 3D distribution of seismic-wave velocity, sensitive to temperature and composition in the crust and upper mantle. Until recently, seismic data sampling in South America was highly uneven, and high-resolution models were obtained mainly regionally. Here, we assembled all available seismic data including the data from the FAPESP “3-Basins Thematic Project.” The massive dataset includes data from the temporary deployments in South America that became available recently and is complemented by data from all over the globe.

We compute a new S-velocity tomographic model of the upper mantle of South America and surrounding oceans using the Automated Multimode Inversion of surface, S- and multiple S-waves. The increase in the data coverage of the model combined with the optimized tuning of the inversion parameters on the continent allows us to identify for the first time the fine details present in the lithospheric structure. We observe that regions of thinner lithosphere inside cratons correspond to areas where rifting has been proposed in previous tectonic cycles. Inside the boundaries of the Amazon craton, we image two cratonic blocks, separated by the Amazon basin. In this area, an aborted rift system preceded the formation of the Amazon basin in the Neoproterozoic, and rift reactivation occurred with the break-up of Pangea in the Mesozoic. Similarly, in the São Francisco Craton, we image a significantly thinner lithosphere in the Paramirim Aulacogen area, a Paleoproterozoic intracontinental rift system. We also image high-velocity lithospheric blocks under sedimentary basins. East of the Amazon craton, we image a high-velocity anomaly known as the Parnaíba block, and under the Paraná basin, a fragmented Paranapanema block. Finally, by imaging an accurate boundary of the cratonic units, we can analyze the distribution of magmatic events and large igneous provinces and how they correlate with our model’s seismic velocities at lithospheric and asthenospheric depths.

How to cite: Chagas de Melo, B., Lebedev, S., Celli, N., De Laat, J., and Assumpção, M.: Imaging the South American Continental Interior with Waveform Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14376, https://doi.org/10.5194/egusphere-egu23-14376, 2023.

The Beibu-Gulf Basin is one of the important petroleum-bearing basins in offshore South China Sea. Decades of exploration has found great petroleum resource potential in it, but the overall petroleum geological reserves level is not very high when it comes to specific structure unit. Traditional petroleum exploration was concentrated on the shallower sediment geological conditions, however some studies have shown that there is a close relationship between petroleum resources and deep earth structures, especially the Moho interface or the crust. In this abstract we calculated the depth of Moho interface in Beibu Gulf Basin by dual-interface fast inversion algorithm and the thickness of crust with satellite potential field data. It shows that the depth of Moho shallows from the land to sea area and reaches its highest value up to 46.5 km in the northwest land area, while there is an obviously uplift in the southwest Yinggehai Basin in which the depth only comes to 12.7 km, and ranges greatly from different sags in Beibu Gulf Basin. Based on these results, we researched the quantitative relationship between the distribution of petroleum-rich sags and the fluctuation deviation of Moho depth and its horizontal gradient, together with the stretch factor of crust. We also found that there is a strong correlation among the uplift zone of the Moho or the thinning area of crust (stretch factor>1.0) and the oil and gas sources or gathering places, which will produce a beneficial temperature, pressure, chemistry as well as structure condition for organic matter to form oil and gas. So this research will offer a perspective about the controlling mechanism of the differential distribution in petroleum-rich sags due to the deep earth structure, and help for the further selection of target areas in Beibu Gulf Basin.

How to cite: Wang, L., Wang, W., and Zhang, Y.: Study of the Moho interface and its controlling mechanism on petroleum-rich sag in Beibu Gulf Basin by satellite potential field data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14956, https://doi.org/10.5194/egusphere-egu23-14956, 2023.

EGU23-15239 | ECS | Orals | GD6.4

Crustal Structure across Central Scandinavia along the Silver-Road refraction profile 

Metin Kahraman, Hans Thybo, Irina Artemieva, Alexey Shulgin, Peter Hedin, and Rolf Mjelde

The western edge of the Baltic Shield is covered by the northeast – southwest oriented, 2500 m high mountain range, the Scandes at the northwestern Atlantic Ocean. This mountain range is located far from any active plate boundary and lack of sedimentary sequences precludes direct knowledge of the timing of uplift.

We present a crust and upper mantle scale velocity model, obtained along thea 600 km long Silver-Road seismic profile, which extends in a WNW to ESE direction in the northeastern Baltic Shield perpendicular to the coast between 8oE and 20oE. The profile has a 300 km long offshore section on the continental shelf and the deep ocean as well as a 300 km onshore section across Caledonian to Svecofennian units. The seismic data were acquired with 5 onshore explosive sources and offshore air gun shots from the vessel Hakon Mosby along the whole offshore profile. Data was acquired by 270 onshore stations at nominally 1.5 km distance and 16 ocean bottom seismometers on the shelf, slope and oceanic environment. The results of this study will provide new input to interpretation of the anomalous topography the Scandes and continental shelf in the northeast Baltic Shield.

We present results of ray tracing and gravity modeling along the profile. The vertical crustal structure in the upper, middle and lower crust are almost constant across the Caledonian and Svecofennian parts of the profile. The crust is 45 km thick along the whole onshore profile and abruptly thins to 25 km thickness in the continental shelf. Pn velocity is low ~7.6-7.8 km/s below the high topography areas with Caledonian nappes, whereas it is 8.4 km/s below the Svecofennian parts. Our gravity models, based on the seismic velocity structure, suggest a low density 3.20 g/cm3 for the low Pn zone below the high Caledonian topography in contrast to the very high density 3.48 g/cm3 below the Svecofennian parts with relatively low topography. We interpret these bodies as eclogitizised basaltic crustal material at different metamorphic grades. Isostatic calculation with a 60 km depth compensation depth predicts 2 km high topography which is ~1 km higher than observed. We therefore propose that the low-grade metamorphic unit below the high topography is underlain by a sequence with relatively high mantle density to 120 km depth.

How to cite: Kahraman, M., Thybo, H., Artemieva, I., Shulgin, A., Hedin, P., and Mjelde, R.: Crustal Structure across Central Scandinavia along the Silver-Road refraction profile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15239, https://doi.org/10.5194/egusphere-egu23-15239, 2023.

EGU23-15662 | ECS | Posters on site | GD6.4

Crustal Structures Across The Northern Scandinavia Along The SENJA OBS SURVEY Profile 

Rafet Ender Alemdar, Metin Kahraman, Alexey Shulgin, Rolf Mjelde, Irina Artemieva, and Hans Thybo

The Senja onshore-offshore seismic profile is located in the north-western part of Europe across the Norwegian coast into the North Atlantic ocean. A number of terranes and microcontinents collided to form this region from the Archean to the Paleoproterozoic. The Sveconorwegian (Grenvillian) and Caledonian orogenies significantly affected this region and created the major Caledonian mountain belt. Despite being far from any active plate boundaries, the Baltic Shield contains a mountain range called the Scandes that reaches heights of up to 2500 meters. This mountain range is oriented northeast-southwest and mainly correlates with the deformed Caledonian and Sveconorwegian part of the western North Atlantic coastal region.

We present a crustal scale seismic profile along the northwest-to-southeast-directed Senja OBS Survey Profile in northern Scandinavia between 12°E and 20°E. This profile extends offshore and onshore for a total of ~300 kilometres across the Norwegian shelf in the North Atlantic Ocean, the Senja Island and into mainland Norway. The seismic sources were airgun shots from the vessel Hakon Mosby along the offshore profile. The seismic data set was collected by 68 onshore stations located at 1.3 kilometer distance and 5 ocean bottom seismometers located on the shelf, slope, and within the oceanic environment. The results of this investigation will provide new data for interpretation of the cause of the unusual onshore topography and offshore bathymetry at the North Atlantic Ocean's edge. We present the results from ray tracing modelling of a seismic P-wave velocity section  along the profile.

 

How to cite: Alemdar, R. E., Kahraman, M., Shulgin, A., Mjelde, R., Artemieva, I., and Thybo, H.: Crustal Structures Across The Northern Scandinavia Along The SENJA OBS SURVEY Profile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15662, https://doi.org/10.5194/egusphere-egu23-15662, 2023.

EGU23-15669 | Orals | GD6.4

A study of the mantle flow field and lithospheric deformation beneath the Kuril-Kamchatka subduction zone using seismic anisotropy 

Ayoub Kaviani, Georg Rümpker, Christoph Sens‐Schönfelder, Abolfazl Komeazi Abolfazl Komeazi, and Nikolai Shapiro

We investigate the flow field and deformation in the mantle wedge and subslab mantle beneath the Kuril-Kamchatka subduction zone using seismological data from a recently deployed seismic network around the Klyuchevskoy Volcanic Group (KVG) complemented by data from previous temporary deployments and permanent stations to reach a total number of 145 seismic stations covering a region defined in the geographic coordinates 150°-167°E and 50°-61°N.

We perform splitting analysis of both local and core-refracted (SKS) shear waves to study mantle seismic anisotropy as a proxy for the pattern of the mantle flow field and deformation. Anisotropy in the mantle wedge is studied by shear splitting analysis (SWS) of waveform data from local mantle events that occurred along the subducting slab (Wadati-Benioff-Zone) and in the mantle wedge. Crustal anisotropy is also studied by SWS analysis of crustal events. The combined data set (SKS and local) allows us to discriminate the source of mantle anisotropy (sub-slab, mantle wedge, or crust). Shear-wave splitting measurements from the local shear waves give small delay times independent of the depth of the events suggesting that the mantle wedge is characterized by a weak anisotropic fabric. The fast directions of mantle wedge anisotropy are predominantly parallel to the strike of the slab indicating either a trench-parallel flow or B-type seismic anisotropy in the mantle wedge. The relatively small delay times from local shear waves suggest that SKS waves are less affected by potential anisotropy in the mantle wedge and that the results of the SKS-splitting analysis are mainly representative of the sub-slab anisotropy. Our SKS-splitting measurements indicate a trench-normal mantle flow beneath the eastern edge of the Kamchatka peninsula that converts to a more complex pattern beneath the KVG region. We argue that this pattern of fast polarization direction suggests the rotational mantle flow beneath the slab that may be related to the change in slab geometry at the junction between the Kuril-Kamchatka and Aleutian arcs. The observation of relatively strong sub-slab anisotropy against weak mantle-wedge anisotropy suggests that slab termination causes some disturbance in mantle flow; however, no significant component of an around-slab flow occurs in the mantle wedge.

How to cite: Kaviani, A., Rümpker, G., Sens‐Schönfelder, C., Abolfazl Komeazi, A. K., and Shapiro, N.: A study of the mantle flow field and lithospheric deformation beneath the Kuril-Kamchatka subduction zone using seismic anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15669, https://doi.org/10.5194/egusphere-egu23-15669, 2023.

EGU23-16052 | Orals | GD6.4

Analysis of shear-wave splitting to infer the seismic anisotropy of the lithosphere-asthenosphere system – inversion ambiguities, automatization, and machine-learning approaches 

Georg Rümpker, Ayoub Kaviani, Frederik Link, Miriam Reiss, Megha Chakraborty, Johannes Faber, Jonas Köhler, and Nishtha Srivastava

Seismic anisotropy provides a unique link between directly observable surface structures and the more elusive dynamic processes in the mantle below. The ability to infer the vertically- and laterally-varying anisotropic structures is of great significance for the geodynamic interpretation of surface-recorded waveform effects.

In the first part of this presentation, we assess the capabilities of different observables for the inversion XKS phases to uniquely resolve the anisotropic structure of the upper mantle. For this purpose, we perform full-waveform calculations for simple models of upper-mantle anisotropy. In addition to waveforms, we consider the effects on apparent splitting parameters and splitting intensity. The results show that, generally, it is not possible to fully constrain the anisotropic parameters of a given model, even if complete waveforms are considered. We also discuss advantages and disadvantages of using the different observables.

Recent technological advances have prompted implementations of large-scale seismic experiments producing huge amounts of seismic data. Standard processing procedures, thus, require automatization to facilitate fast and objective data processing. This also applies to the analysis of shear-wave splitting. A recent extension of the SplitRacer software code allows for an automatization of the analysis by choosing a time window based on spectral analyses and by categorization of results based on different splitting methods.

Finally, we will present new results from the application of Neural Networks to the analysis of shear-wave splitting. Our initial approach involves training based on synthetic data and deconvolution of the real waveforms. Current limitations and possibilities for extension will be discussed.

How to cite: Rümpker, G., Kaviani, A., Link, F., Reiss, M., Chakraborty, M., Faber, J., Köhler, J., and Srivastava, N.: Analysis of shear-wave splitting to infer the seismic anisotropy of the lithosphere-asthenosphere system – inversion ambiguities, automatization, and machine-learning approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16052, https://doi.org/10.5194/egusphere-egu23-16052, 2023.

EGU23-16446 | ECS | Posters on site | GD6.4

Observations of Regional Seismic Discontinuities in the Earth’s Upper Mantle from SS- and PP- precursors 

Lauren Waszek, Thuany Costa de Lima, Benoit Tauzin, Hrvoje Tkalčić, and Maxim Ballmer

The physical properties of regional seismic discontinuities in the upper mantle yield insights into lateral and radial thermochemical variations, with implications for our understanding of magmatism and convection in the mantle.The global distribution of the 300-km discontinuity (termed the “X” discontinuity) is relatively poorly resolved, as it is detected infrequently, likely due to its small impedance contrast. Reflectors observed near this depth are usually local and primarily detected beneath continent and subduction zones. Several mechanisms suggest that the X is associated with mineral transformations that occur in basalt-enriched material. Thus, imaging the X-discontinuity holds the key to mapping subducted oceanic crust remnants.

Another discontinuity, at around 520 km depth, is detected more frequently and sometimes observed to be split into two signals. Its existence is predicted by the wadsleyite to ringwoodite mineral phase transition. However, the variations in ambient thermochemistry, which influence its visibility, depth variation, reflectivity, and/or splitting, are not fully understood, necessitating further investigations. Improved constraints on the nature of the 520 will inform regarding thermal and compositional gradients within the mantle transition zone.

In this study, we use large global datasets of SS and PP precursors to obtain new maps of these discontinuities. Our observations indicate regionally weak yet clear signals at both depths, linked to variations in basalt fraction and potential temperature. We perform mineral physics modeling and investigate the characteristic temperature and composition associated with the signatures of these signals. These results provide insight into our understanding of the chemical segregation and plume stagnation in the upper mantle.

How to cite: Waszek, L., Costa de Lima, T., Tauzin, B., Tkalčić, H., and Ballmer, M.: Observations of Regional Seismic Discontinuities in the Earth’s Upper Mantle from SS- and PP- precursors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16446, https://doi.org/10.5194/egusphere-egu23-16446, 2023.

The Shangdan suture zone (SDZ) in the Qinling Orogenic Belt is a key to understanding the East Asia tectonic evolution. The SDZ gives information about convergent processes between the North China Block (NCB) and South China Block (SCB). In the Late Mesozoic, several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB, which was neglected in previous studies. These shear zones play an essential role in the tectonic evolution of the East Asia continents. This study focuses on the deformation and geochronology of Maanqiao shear zone (MSZ) distributed along the SDZ. The shear sense indicators and kinematic vorticity numbers (0.54–0.90) suggest MSZ have sinistral shear and simple shear deformation kinematics. The quartz’s dynamic recrystallization and c-axis fabric analysis revealed that the MSZ experienced deformation under green-schist facies conditions at ∼400–500 °C. The 40Ar/39Ar (muscovite-biotite) dating of samples provided a plateau age of 121~123 Ma. Together with previously published data, our results concluded that Qinling Orogen Belt was dominated by compressional tectonics during the late early Cretaceous. Moreover, we suggested that the Siberian Block move back to the South and Lhasa-Qiantang-Indochina Block to the North, which promoted intra-continental compressional tectonics.

How to cite: Sheir, F. and Li, W.: Structural Geology and Chronology of Maanqiao Shear Zone along the Shangdan Suture in Qinling Orogenic Belt: Implications for Late Mesozoic Intra-Continental Deformation of East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1587, https://doi.org/10.5194/egusphere-egu23-1587, 2023.

EGU23-3506 | Orals | GD4.4

Mississippian synorogenic sedimentation in the Variscan belt: Why are NW and SW Iberia flysch basins so different and yet so similar? 

Ícaro Dias da Silva, Manuel Francisco Pereira, and Emilio González Clavijo

Devonian-Carboniferous synorogenic sedimentation is described across the Variscan orogen, as well-preserved exposures in late orogenic structures between continental blocks. Variscan marine sedimentary sequences are described in both colliding continents: Gondwana representative of the southern subducting super-plate, and Laurussia considered as the overriding block. The Variscan synorogenic basin distribution on both sides of the alleged Rheic Ocean suture zone raised questions regarding the basin geodynamic classification and possible geographycal and temporal connections. The Devonian-Carboniferous turbiditic basins of the Variscan belt have been classified as foreland, forearc, or backarc, in line with their relative geographical position in the convergent plate boundary. However, the same Variscan basin may have different classifications depending on the proposed tectonic model and its current geographic position. The standard classification of the Variscan synorogenic basins fails due to a poor understanding of their relationship with the tectono-metamorphic and magmatic evolution of their basement, which means ambiguity and controversy in defining global tectonic models.

As a world-class natural laboratory, the Iberian Massif (Portugal and Spain), at the westernmost tip of the Variscan Belt, presents itself as a place to study orogenic processes, from depth (ductile deformation, metamorphism and plutonism) to shallow (synorogenic sedimentation and volcanism) crustal levels. Recent studies in NW and SW Iberia have revealed a regional-scale relationship between Mississippian turbiditic (flysch) basins and magmatic flare-ups. Although there are many similarities between the stratigraphy of NW and SW Iberia synorogenic basins and the tectono-metamorphic and magmatic evolution of their basements, there are still many unexplored features that must be envisaged to get a better understanding of the tectonic evolution of the Variscan belt. The Mississippian basins of NW and SW Iberia show the typical rhythmic sedimentation of turbiditic sequences that are locally disturbed by large olistostrome bodies bearing different-sized olistoliths derived from the previously deformed metamorphic basement. While NW Iberia Variscan flysch-type basins have been associated with the formation of an accretionary wedge, later incorporated at the base of an unrooted slice of allochthonous units, those from SW Iberia seem to reflect their original position, only locally detached at the base due to the relative motion of their basement. SW Iberia flysch basins are also contemporaneous with voluminous bimodal volcanism, more important but not confined to the base of the synorogenic sequences. The Mississippian volcanic rocks are one of the primary sources of Variscan flysch, as evidenced by the widespread occurrence of weakly deformed olistoliths of mafic and felsic volcanic rocks and the significant input of Mississippian zircon grains found in the flysch sequences, when compared with their NW Iberia correlatives. So, considering the geological information that is known and may be used for a preliminary comparative analysis of the Mississippian NW and SW Iberia flysch basins, the following doubt stands: Did they have a common spatial and temporal geodynamic evolution? If so, what is the geological meaning of this assumption?

This work was supported by the Grant PID2020-117332GB-C21funded by MCIN/AEI/10.13039/501100011033, by the FCT-Estímulo ao Emprego Científico (Norma Transitória), by the FCT grants FCT/UIDB/50019/2020-IDL and FCT/UIDB/04683/2020- ICT.

How to cite: Dias da Silva, Í., Pereira, M. F., and González Clavijo, E.: Mississippian synorogenic sedimentation in the Variscan belt: Why are NW and SW Iberia flysch basins so different and yet so similar?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3506, https://doi.org/10.5194/egusphere-egu23-3506, 2023.

EGU23-4175 | ECS | Posters on site | GD4.4

Arc splitting and back-arc spreading evolution: the control of hydration and melts 

Ana Gomes, Attila Balázs, and Taras Gerya

While there has been a lot of work focusing on improving our understanding of divergent and convergent plate boundaries, the complex nature of the back-arc region, where convergent margins transition into large-scale extension in the upper plate, is yet to be investigated fully. Indeed, why and how extensional basins open near the boundaries between convergent plates, followed by their tectonic inversion, have long been outstanding questions in plate tectonics.

Here we investigate a wide range of factors that influence the development of back-arc extension using 2D thermo-mechanical code I2VIS employing visco-plastic rheologies, hydration and dehydration processes, melting and surface processes. We systematically vary several parameters to determine their roles and respective importance, including a)  fluid and melt induced weakening, b) upper plate geothermal gradient and c) amount of sediment in the accretionary wedge. The fluid and melt induced weakening is implemented by using the Mohr–Coulomb yield criterion that limits the creep viscosity, altogether yielding an effective visco-plastic rheology, and controlled via the melt/fluid pore fluid pressure parameters, λfluid and λmelt. The upper plate geothermal gradient is controlled by the parameter TMoho . Finally, the amount of sediment in the accretionary wedge is changed through the parameter Sedlev, which controls the minimum y-coordinate sediments can occupy, throughout the model. The higher the Sedlev, the less the height of sediment that can accumulate in the accretionary wedge.

Our extensive series of high-resolution models led to the following conclusions:

  • a) a higher upper plate geothermal gradient predictably leads to a more ductile rheology, which then results in an initial wider rift, followed by enhanced melting and earlier arc splitting; 
  • b) higher erosion and sedimentation rates lead to increasing hydration of the mantle wedge and enhancing mantle melting, and decreasing the stress transfer from the lower to the upper plate; 
  • c) λfluid controls arc rifting to a greater extent, relative to λmelt, and for λfluid smaller than 0.2, arc rifting occurs. This means that the fluid induced weakening has to be high, in order to produce arc rifting.

These initial results suggest that the upper plate geotherm has the highest magnitude effects in modulating arc rifting, but fluid and melt induced weakening are also major controls in rift development, in the sense that they regulate whether it happens at all, or not. The height of the accretionary wedge works with the fluid weakening of the upper plate, facilitating arc rifting. 

How to cite: Gomes, A., Balázs, A., and Gerya, T.: Arc splitting and back-arc spreading evolution: the control of hydration and melts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4175, https://doi.org/10.5194/egusphere-egu23-4175, 2023.

EGU23-4323 | ECS | Posters on site | GD4.4

2D Geothermal model across the Peru-Chile trench and the Andean Cordillera above the Nazca Ridge subduction 

Sara Ciattoni, Matteo Basilici, Mazzoli Stefano, Megna Antonella, and Santini Stefano

The Nazca Ridge is a wide aseismic ridge subducting beneath the South American margin at latitude about 15°. The buoyancy of the thickened oceanic crust of the Nazca Ridge produces localized flat subduction influencing the geometry and the geological history of the whole area.  With the aim of analysing the spatio-temporal evolution of the deformation and uplift/subsidence history of the lithosphere above the Nazca Ridge flat slab, we have started from the study of the geothermal structure of the upper plate. We have built a crustal section with a length of 1000 km that reaches a depth of about 130 km. The section runs from the top of the Nazca Ridge in the west to the Amazonian Basin in the east, progressively crossing the Peru-Chile trench, the East Pisco Basin and the Andean Cordillera. Thereafter we have elaborated a 2D geothermal model based on the crustal section. We have considered the whole lithosphere composed of two main geological units: (i) crystalline basement, (ii) sedimentary cover (including the whole lithostratigraphic succession). For each unit we have assigned the following parameters: thickness, density, heat production and thermal conductivity. Moreover, we have also taken into account the friction coefficient, the convergence rate of the plates, the heat flux of the Moho, and the slip rate of the megathrust. Model parameters have been set up in order to obtain the best simulation of the heat flow contribution due to the large reverse fault responsible for the coastal seismic event of November 12, 1996, with epicentre on the section trace. Using these parameters and applying an analytical methodology we have calculated isotherms and geotherms. The resulting model may provide an important contribution on the investigation of the effects of the Nazca Ridge subduction and the associated flat slab geometry on the tectonic evolution of the area.

How to cite: Ciattoni, S., Basilici, M., Stefano, M., Antonella, M., and Stefano, S.: 2D Geothermal model across the Peru-Chile trench and the Andean Cordillera above the Nazca Ridge subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4323, https://doi.org/10.5194/egusphere-egu23-4323, 2023.

EGU23-4610 | ECS | Posters on site | GD4.4

Tectonostratigraphic evolution of the Hupo Basin in the western margin of the Ulleung back-arc basin, the East Sea 

Yongjoon Park, Nyeonkeon Kang, Boyeon Yi, Gwangsoo Lee, and Donggeun Yoo

The tectonostratigraphic evolution in the western margin of the Ulleung back-arc basin was reconstructed based on the seismic reflection data. According to our stratigraphic and structural analysis, the study area developed via four tectonostratigraphic stages, one extensional and two subsequent tectonic inversions. Together with the back-arc opening of the East Sea, most fault-controlled depocenters (e.g., half-grabens) were formed mainly in the western margin of the Ulleung Basin during the Early–early Late Miocene. This syn-extensional sedimentation occurred in non-marine to deep-marine environments analogous to typical rift-related linked depositional systems. During the early Late Miocene, the Ulleung back-arc basin had changed entirely into a compressive regime (NW–SE compression). Under the inversion tectonics, NNE–SSW and N–S trending extensional faults were mainly reactivated as reverse faults. The Hupo Basin was likely created by the regional flexural response to the crustal or thrust loading. As the formation of the Hupo Basin began, hemipelagic sedimentation accompanied by episodic gravity-controlled slope failures prevailed in the deep-water environment. Since the late Early Pliocene, the subsidence of the Hupo Basin was enhanced by the crustal shortening. The sedimentary condition became shallower gradually upward and coarse-grained terrigenous input into the Hupo Basin began, leading to deposition in shallow- to deep-marine environments. During the Quaternary, although the tectonic activity was subdued, the Hupo Fault was reactivated as a reverse fault, maintaining the uplift of the Hupo Bank and coeval flexural subsidence of the Hupo Basin. During this depositional period, shallow- to deep-marine deposition continued but a greater quantity of coarse-grained terrestrial sediments was transported into the Hupo Basin. The Quaternary depositional systems are likely the result of the interplay between tectonics and eustasy.

How to cite: Park, Y., Kang, N., Yi, B., Lee, G., and Yoo, D.: Tectonostratigraphic evolution of the Hupo Basin in the western margin of the Ulleung back-arc basin, the East Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4610, https://doi.org/10.5194/egusphere-egu23-4610, 2023.

EGU23-4690 | ECS | Posters on site | GD4.4

The formation and evolution of northeastern ends of the ECSSB, South Sea of Korea, and its significance for petroleum exploration 

Eul Roh, Yirang Jang, Areum Woo, and Sanghoon Kwon

 The South Sea of Korea has three offshore concession blocks, including a Joint Development Zone(JDZ) that is set up by the license agreement between Korea and Japan. The geological research of the offshore South Sea of Korea is insufficient to define the evolution history and its significance for petroleum accumulation. In this study, evolution of the Xihu Sag within the JDZ area at the South Sea of Korea is tackled based on re-interpretation of the seismic and well data, and are correlated tectonically with that of the ECSSB(East China Sea Shelf Basin). The ECSSB has been initially developed as a back-arc basin over the over-riding Paleo-Pacific plate, and experienced complex tectonic history by successive subduction of the tectonic plates including the Paleo-Pacific (Izanagi) Plate, the Pacific plate, and the Philippine plate since Late Cretaceous in age. The results indicate that the study area can be subdivided into three tectonic domains: Western Slope Belt, Central Uplift Belt, and East Slope Belt. The structural similarity with those of the ECSSB, although the details of structural characteristics are different in different localities, under regional influence of successive subductions of the same tectonic plates, resulting in the conclusion that the area can be assigned into the northeastern ends of the Xihu Sag of the northeastern ECSSB. This might be a common feature of oil–gas accumulation in the eastern ECSSB, and highlights the potential for petroleum exploration at the study area, although further studies on the play concept and complex petroleum system of the area are required.

How to cite: Roh, E., Jang, Y., Woo, A., and Kwon, S.: The formation and evolution of northeastern ends of the ECSSB, South Sea of Korea, and its significance for petroleum exploration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4690, https://doi.org/10.5194/egusphere-egu23-4690, 2023.

EGU23-4773 | Orals | GD4.4

A tale of two orogens- Taiwan and Mindoro 

Yuan-Hsi Lee, Lucas Mesalles, and Teresito Bacolcol

The Taiwan and Mindoro islands are located on the northern and southern ends of the Malina trench, and both orogens result from the deformation of the continental margin of the Eurasia plate. Comparing the exhumation histories of both orogens allow us to discuss the mechanism of mountain building of two orogens.
In Taiwan orogen, the timing of the mountain building starts from ca. 6-8 Ma, which can be identified using ZrnFT, Ar-Ar, and the timing of the developing foreland basin. 
For Mindoro island, we combine with ZrnFT, ApaFT, and ZrnHe to constrain the timing of the exhumation. It shows oldest ZrnFT ages are ca. 6-7 Ma. We further constrain that the latest stage of granite age in the rifted continental crust is ca. 13Ma indicating the collision should be later than this age. In addition, the ApaFT and ZrnHe ages for the granite are ca. 6Ma inferring a rapid cooling age which is consistent with regional ZrnFT dates. Those data imply the timing of mountain building of Mindoro orogen is ca. 6-7Ma which is similar to the Taiwan orogen.
Considering both orogens have similar timing of mountain building, we suggest that while the Philippine Sea changes the motion to NW trending at ca. 7-8Ma and Eurasia continental margin subducts to the Philippine Sea plate and Philippine Mobile belt, respectively, that results in both orogens deforming simultaneously.

How to cite: Lee, Y.-H., Mesalles, L., and Bacolcol, T.: A tale of two orogens- Taiwan and Mindoro, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4773, https://doi.org/10.5194/egusphere-egu23-4773, 2023.

EGU23-5077 | Orals | GD4.4 | Highlight

Back-arc basins: A global view from geophysical synthesis and analysis 

Irina M. Artemieva

This global study of 31 off-shore back-arc basins (BABs) identifies their principal characteristics based on a broad spectrum of geophysical and subduction-related parameters. My synthesis is used to identify trends in the evolution of BABs for improving our understanding of subduction systems in general. The analysis, based on the present plate configuration, demonstrates that geophysical characteristics and fate of the BABs are essentially controlled by the tectonic type of the overriding plate, which controls the lithosphere thermo-compositional structure and rheology. The type of the plate governs the length of the extensional zone in back-arc settings along the trench, the efficiency of lithosphere stretching, and the crustal structure, buoyancy and bathymetry of the BABs. Subduction dip angle apparently controls the location of the slab melting zone and the efficiency of slab roll-back with feedback links to other parameters. By the tectonic nature of the overriding plate (the downgoing plate is always oceanic) the back-arc basins are split into active BABs formed by ocean-ocean, arc-ocean, and continent-ocean convergence, and extinct back-arc basins. By geophysical characteristics, BABs formed on continental plates are subdivided into active BABs with and without seafloor spreading, and extinct BABs are subdivided into the Pacific BABs, possibly formed on oceanic plates, and the non-Pacific BABs with reworked continental or arc fragments. Six types of BABs are distinctly different. Extension of the overriding oceanic plate above a steeply dipping old oceanic plate, preferentially subducting nearly westwards, forms large deep back-arc basins with a thin oceanic- type crust. In contrast, BABs on the overriding continental or arc plates form at small opening rates and often by shallow subduction of younger oceanic plates with a random subduction orientation; these BABs have small sizes, shallow bathymetry, and hyperextended or transitional ~20 km thick arc- or continental-type crust typical of passive margins. The presence of a 2–5 km thick high-Vp lowermost crustal layer, characteristic of BABs in all settings, indicates the importance of magmatic underplating in the crustal growth. Conditions required for the initiation of a back-arc basin and transition from stretching to seafloor opening depend on the nature of the overriding plate. BABs formed on oceanic plates always evolve to seafloor spreading. BABs formed on continental or arc plates require long spreading duration with large (>8 cm/y) opening rates and a large crustal thinning factor of 2.8–5.0 to progress from crustal extension to seafloor spreading. On the present Earth such transition does not happen in the BABs formed behind a shallow subduction (<45o) of a young (<40 My) oceanic plate. The nature of the overriding plate also determines the fate of back-arc basins after termination of lithosphere extension: the extinct Pacific BABs with oceanic-type crust evolve towards deep old “normal” oceans, while the shallow non-Pacific BABs with low heat flow and thick crust are likely to preserve their continental or arc affinity. BABs do not follow the oceanic cooling plate model predictions. Distinctly different geophysical signatures for mid-ocean ridge spreading and for back-arc seafloor spreading are caused by principally different dynamics. https://doi.org/10.1016/j.earscirev.2022.104242

How to cite: Artemieva, I. M.: Back-arc basins: A global view from geophysical synthesis and analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5077, https://doi.org/10.5194/egusphere-egu23-5077, 2023.

EGU23-6572 | Posters virtual | GD4.4

Comparative analysis of U-Pb dating of zircons from Early Carboniferous volcanites and Middle Triassic alkaline granitoids of the Magnitogorsk zone (Southern Urals) 

Alexander Tevelev, Natalia Pravikova, Alexandra Borisenko, Petr Shestakov, Egor Koptev, Ivan Sobolev, Ekaterina Volodina, Alexey Kazansky, and Anastasia Novikova

Introduction. Determination of the age of igneous roc Comparative analysis of U-Pb dating of zircons from Early Carboniferous volcanites and Middle Triassic alkaline granitoids of the Magnitogorsk zone (Southern Urals)

ks by the U-Pb isotope method using zircons is currently one of the main dating methods. Here we present new isotopic data of zircons from alkaline granitoids of the Cheka massif and zircons from acidic volcanites of the lower Carboniferous of the Magnitogorsk zone (Southern Urals).

Materials and methods. The Middle Triassic isotopic age of the Cheka massif was determined by the Rb-Sr isochron method. Currently, we obtained new seven U-Pb dates based on zircons isolated from various phases of the massif. Early Carboniferous volcanites are represented by a contrast moderately alkaline series. Volcanites have been sampled at two points. The U-Pb dating was performed at the All-Russian Geological Research Institute using SHRIMP-II.

Results. At least two zircon populations of early Carboniferous isotopic age have been identified in acid volcanites. The first population is represented by full   crystals and their fragments 100-200 microns in size. They have a short-prismatic habit and a clear oscillatory zonation. This population is predominant in all samples. Zircons have a moderate content of U and Th. The population is homogeneous with average concordant age is 348.5 ± 3.1 Ma.

Zircons of the second population were found in all samples. They are small (about 50 microns), perfectly faceted crystals with an increased content of U and Th. Their isotopic ages (344 and 351 Ma) are entirely fit the age range of the first population. Thus, completely different in morphology and composition, zircons have the same isotopic age.

Two most representative samples of alkaline granitoids, provide zircons 150-250 microns in size. They are light in the cathodoluminescent image, with a clear fine oscillatory zonation and weakly expressed sectorial. The range of isotopic ages of these zircons in is 342.6–376.6 Ma, and their average concordant age is almost the same: 353.9±4.0 and 352.7±3.9 Ma.

Discussion. U-Pb dating of zircons from acidic volcanites confirmed their Tournaisian age. The morphology and composition of zircons turned out to be an important key to understanding the age of volcanites intruded by the alkaline granitoids.

Inherent zircons in alkaline granitoids may not be crystallized at all, since all zirconium should be concentrated in alkaline dark-colored minerals. In this case, only the inherited zircon will remain in the rock. In addition, the dissolution of inherited zircons can also occur in alkaline melts.

Early Carboniferous zircon grains in all samples of alkaline granitoids are similar to those from volcanites. They have a typically magmatic appearance and zonation and the concentration and ratio of uranium and thorium are also typical. At the same time, alkali-rich fluid-saturated magmatites are usually characterized by a Th/U ratio close to or significantly higher than 1. Uranium and thorium concentrations are usually very high. The described features most likely indicate the xenogenic nature of Early Carboniferous zircons in relation to granitoids.

Financial support. The research has been funded by RFBR (research project № 19-55-26009).

How to cite: Tevelev, A., Pravikova, N., Borisenko, A., Shestakov, P., Koptev, E., Sobolev, I., Volodina, E., Kazansky, A., and Novikova, A.: Comparative analysis of U-Pb dating of zircons from Early Carboniferous volcanites and Middle Triassic alkaline granitoids of the Magnitogorsk zone (Southern Urals), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6572, https://doi.org/10.5194/egusphere-egu23-6572, 2023.

EGU23-6778 | ECS | Posters on site | GD4.4

Arc and forearc rifting in the Tyrrhenian subduction system 

Marta Corradino, Attila Balazs, Claudio Faccenna, and Fabrizio Pepe

The evolution of backarc and forearc basins is usually treated separately, as the volcanic arc represents a clear barrier between them. We analyse their spatial and temporal relationships in the Tyrrhenian subduction system, using seismic profiles and numerical modelling. Our results highlight that the Marsili volcano, commonly interpreted as the spreading centre of the Marsili backarc basin, was instead a part of an old (Pliocene) volcanic arc associated with the development of the Vavilov backarc basin (4.3-4.1 to 2.6 Ma). The old volcanic arc was successively affected by arc rifting. This process caused the shift of the Marsili volcano eastwards and the formation of an oceanic backarc basin (~ 1.8 Ma) located between the Marsili volcano and the old remnant arc, which remained fixed. The eastern side of the Marsili basin, previously considered as the other half of the oceanic backarc basin, is instead a part of the forearc domain floored by serpentinised mantle. As slab rollback continued, volcanism migrated towards the trench and a new volcanic arc (Aeolian Island) formed at ~1 Ma in the forearc domain. The formation of the new volcanic arc represents the onset of the forearc-rifting that could lead to the opening of a new backarc basin between the old and young volcanic arc, resulting in the decrease of the initial forearc region extension.

The example of the Tyrrhenian Sea illustrates how the evolution of forearc and backarc domains is intimately interconnected. Fluids, released from the downgoing plates, control lithospheric hydration and mantle serpentinisation as well as asthenospheric mantle melting. Fluids and melts induce weakening of the volcanic arc region and drive the arc-rifting that led to the backarc basin formation. Later, the slab rollback causes the trench-ward migration of volcanism that led to the forearc- rifting under the control of fluids released from the downgoing plate.

How to cite: Corradino, M., Balazs, A., Faccenna, C., and Pepe, F.: Arc and forearc rifting in the Tyrrhenian subduction system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6778, https://doi.org/10.5194/egusphere-egu23-6778, 2023.

EGU23-7375 | ECS | Posters on site | GD4.4

Geological evolutionary model of the Costa Rica subduction margin 

Fabrizio Parente and Attilio Sulli

The Middle American Trench (MAT) is one of the most complex subduction margins all over the earth surface. Its geodynamical complexity is due to the interaction between five major lithospheric plates: North America, Caribbean, Cocos, Nazca and South America; between them is the Panama microplate.
We focused on the Costa Rica subduction margin, which is a portion of the MAT and it is characterized by some peculiarities with respect to the other portions of the MAT. Along the Costa Rica offshore the subduction of the Cocos Plate is currently developing towards NE, beneath both the Caribbean Plate and the Panama Microplate, with a rate that increases from NW (87 mm/yr), in correspondence of the Nicoya Peninsula, to SE (92-95 mm/yr), in correspondence of the Osa Peninsula.   
The Cocos Plate formed, together with the Nazca Plate, about 28 Ma from the Farallon Plate fragmentation in turn due to the formation of the East Pacific Rise (EPR). The subduction process is extremely seismogenetic and caused some earthquakes up to 7.8 Mw (1950): one of the most recent hits Nicoya on September 5th, 2012 (Mw 7.6). The migration of the Cocos Plate towards the Galapagos plume generated, about 14 Ma, the Cocos Ridge, a strip of oceanic ridge that is currently subducting beneath the southeastern margin of Costa Rica, in correspondence of the Osa Peninsula. The beginning of subduction, dated between 8 and 1 Ma, generated an isostatic rebound that gave rise to a general uplift generating the Cordillera de Talamanca, which emerged between 4.5 and 3 Ma and representing the extinct portion of the volcanic arc.    
The main aim of this study is to provide a reliable model about the evolution of the Costa Rica subduction margin, paying attention on the Cocos Ridge subduction and to understand how this affects the evolution of the margin. Through the seismostratigraphic interpretation of several multichannel seismic reflection profiles, together with morphobathymetric data, well data from ODP Leg 170, focal mechanisms and oceanic crust age variation chart along the MAT, as well as the Costa Rica geological map, produced by USGS, we recognized some evidence and mechanisms responsible for the uplift that affected the area (e.g. underthrusting process and strike-slip faults) and how this could be related to the subduction of the Cocos Ridge and of several seamounts recognized along the Costa Rica subduction margin. The Cocos Ridge subduction is also responsible for the magmatism recognized along the Nicoya Peninsula offshore, as well as of the variation of the slab geometry recognized through the realization of a 3D model of the Wadati-Benioff Plane.

How to cite: Parente, F. and Sulli, A.: Geological evolutionary model of the Costa Rica subduction margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7375, https://doi.org/10.5194/egusphere-egu23-7375, 2023.

EGU23-8131 | ECS | Orals | GD4.4

Role of variable plate kinematics history in the back-arc deformation regime along the western Pacific margin (Japan Sea) 

Eleonora Ficini, Marco Cuffaro, Taras Gerya, and Carlo Doglioni

Extension at back-arc basins generally occurs behind arc-trench systems and the mechanisms which act at its origin, as well as the deformation regime developed, are strongly related to the subduction of oceanic lithosphere. Here, we examine the Japan Sea back-arc basin evolution using numerical simulations along the western margin of the Pacific plate, where the subduction processes have been responsible for the deformation style during the last 57 Ma. We carried out 2D high-resolution thermo-mechanical numerical models of subduction dynamics in this area, increasing the simulation complexity integrating into the computations i) the kinematic variability of the Pacific plate over the geological past with respect to a fixed Eurasia, ii) a Low-Viscosity Zone within the asthenosphere, iii) a horizontal eastward mantle flow. Our results show a main kinematic control of the subduction trench position, which advances and retreats in time, providing stages of compression and extension in the Japan Sea back-arc basin. The obtained deformation regime is comparable with the tectonic evolution history occurred along the Eastern Eurasian margin and with analyses on paleo-volcanic front position and paleo-stress reconstructions in the Japan Sea area.

How to cite: Ficini, E., Cuffaro, M., Gerya, T., and Doglioni, C.: Role of variable plate kinematics history in the back-arc deformation regime along the western Pacific margin (Japan Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8131, https://doi.org/10.5194/egusphere-egu23-8131, 2023.

EGU23-8471 | Posters on site | GD4.4

Numerical modelling of opposing subduction in the Western Mediterranean 

Mireia Peral Millán, Manel Fernàndez, Jaume Vergés, Sergio Zlotnik, and Ivone Jiménez-Munt

The geodynamic evolution of the Western Mediterranean related to the closure of the Ligurian-Tethys ocean is not yet fully resolved. We present a new 3D numerical model of double subduction with opposite polarities fostered by the inherited segmentation of the Ligurian-Tethys margins and rifting system between Iberia and NW Africa. The model is constrained by plate kinematic reconstructions and assumes that both Alboran-Tethys and Algerian-Tethys plate segments are separated by a NW-SE transform zone enabling that subduction polarity changes from SE-dipping in the Alboran-Tethys segment to NW-dipping in the Algerian-Tethys segment. The model starts about late Eocene times at 36.5 Ma and the temporal evolution of the simulation is tied to the geological evolution by comparing the rates of convergence and trench retreat, and the onset and end of opening in the Alboran Basin. Curvature of the Alboran-Tethys slab is imposed by the pinning of its western edge when reaching the end of the transform zone in the adjacent west-Africa continental block. The progressive curvature of the trench explains the observed regional stress reorientation changing from N-S to NW-SE and to E-W in the central and western regions of the Alboran Basin. The increase of the retreat rates from the Alboran-Tethys to the Algerian-Tethys slabs is compatible with the west-to-east transition from continental-to-magmatic-to-oceanic crustal nature and with the massive and partially synchronous calc-alkaline and alkaline magmatism.

How to cite: Peral Millán, M., Fernàndez, M., Vergés, J., Zlotnik, S., and Jiménez-Munt, I.: Numerical modelling of opposing subduction in the Western Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8471, https://doi.org/10.5194/egusphere-egu23-8471, 2023.

The Black Sea Basin has been a focus of interest due to its economically promising hydrocarbon reserves and complex tectonic history. Several different theories were proposed to decipher its enigmatic basin formation and tectonic evolution processes.

One important characteristic of the Black Sea Basin that makes it unique is its isolation from the world oceans, and global sea level changes for long periods during the geological time. This provides a good realm to correlate tectonic episodes with rapid sedimentation patterns in its thick sedimentary section. With the aim of modelling this sequence of events, we reviewed and reinterpreted previously proposed scenarios. We focus on the back-arc rifting and subsequent tectonic inversion that led the surrounding mountain belts to form. By reinterpreting 24 long-offset 2D seismic lines acquired by GWL in 2011, we propose a new structural framework for the Black Sea Basin.

Our structural geology analyses show that in addition to basin-bounding normal faults and inversion tectonics, numerous flower structures occur in both the western and eastern Black Sea subbasins. These flower structures are typical indicators of strike-slip fault systems and in the Black sea Basin case, the orientation of these fault systems is roughly east-west. Our interpretations align with the hinge model that Stephenson and Schellart (Geological Society London Special Publications, 2010) proposed to explain the opening of the Black Sea Basin as one basin rather than the conventional interpretation of a two separate rifted basin configuration. The proposed tectonic framework sheds light on the geometry of the Black Sea Basin’s bounding faults, complex faulting and folding recognized in the sedimentary section, and complex ridge-depression geometry.

How to cite: Kaykun, A. and Pysklywec, R.: Existence and Distribution of Basin-Wide Strike Slip Fault Systems in an Asymmetrical Back Arc Rift System: The Black Sea Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9647, https://doi.org/10.5194/egusphere-egu23-9647, 2023.

EGU23-10333 | ECS | Orals | GD4.4

The history of Nepluyevka batholith: A glimpse into Laurussia-Kazakhstania interactions during the Early Carboniferous 

Egor Koptev, Alexey Kazansky, Alexander Tevelev, Natalia Pravikova, and Borisenko Alexandra

Introduction. The Early Carboniferous Nepluyevka polyphase granitic batholith is situated in the East Ural zone. Its emplacement happened during the Sudetian orogeny, which initially shaped the structure of the southwestern segment of the Ural-Mongolian fold belt. As such, the pluton is a repository of information on tectonic evolution and geodynamics of said orogen, which can be used to enhance our understanding of interactions between Laurussia and the microcontinent of Kazakhstania during the Early Carboniferous.

Methods and materials. We have investigated the existing data on the petrology, petrochemistry, isotope systems, and U-Pb geochronology of Nepluyevka batholith, and performed our own analysis of the trace element distribution of the constituting rocks using ICP-MS method. The mechanism of emplacement and its kinematic setting were investigated through an analysis of oriented fabrics and anisotropy of magnetic susceptibility (AMS) for each phase. Paleomagnetic methods were employed for establishing the position of pluton’s host terrain during its emplacement. A total of five specimen, characterizing all of the phases of the batholith, were chosen for petrochemical analyzes, and 186 oriented specimen from 16 sites were used for rock- and paleomagnetic studies.

Results. Combinations of 87Sr/86Sr (0,70491–0,70504) and εNd (-0,29-0,5) ratios for different phases indicate that both depleted mantle and crustal sources were involved in petrogenesis. Trace element distribution is characteristic of subduction settings. AMS parameters’ spatial distribution and observed fabric features show that the batholith was emplaced in a kinematic setting of sinistral transtension. Virtual geomagnetic poles (VGPs) obtained from ChRM components of remanent magnetization do not fall anywhere on the Carboniferous-Quaternary sections of apparent polar wander paths (AWP) for Eastern Europe or Siberia.

Discussion. Combined data on geological structure of the pluton, isotope systems, petrochemistry, and rock magnetic properties of rocks lead us to the conclusion that the batholith had developed as a part of a magmatic system associated with an oblique subduction setting. Paleotectonic reconstructions of pluton’s host terrane Visean location derived from our paleomagnetic data contradict the traditional models for the region. We suggest a model featuring rotation of the host terrane in a strike-slip displacement zone to deal with the contradiction. A paleotectonic reconstruction corrected for such a rotation puts the host terrane into the Visean paleo-position of Kazakhstanian microcontinent. This reconstruction agrees well with the the model proposed by Sengor, Natalin and Burtman in [Sengor et al., 1993], featuring a single subduction system (“Kipchak arc”) stretching from Laurussia to Siberia, which existed through much of the Paleozoic and controlled the crustal growth and development of what is now known as Ural-Mongolian fold belt.

Financial support. The research has been funded by RFBR and CNF as a part of the research project № 19-55-26009 with the use of materials of the "Geoportal" Center of the Lomonosov Moscow State University.

How to cite: Koptev, E., Kazansky, A., Tevelev, A., Pravikova, N., and Alexandra, B.: The history of Nepluyevka batholith: A glimpse into Laurussia-Kazakhstania interactions during the Early Carboniferous, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10333, https://doi.org/10.5194/egusphere-egu23-10333, 2023.

Melt production at subduction zones depends on numerous variables, including mineral composition, water content, age of the plate, dip angle of the plate subducting, rate of convergence, age of the slab, and forearc dimensions. To evaluate the importance of individual variables and their interaction with each other, we constructed 2D numerical models of subduction, tracking temperature, mantle flow, and melt production. This project examines differences in batch and fractional melting sensitivity to the changes of the different variables. Variables include modal clinopyroxene (cpx) and its exhaustion, mantle hydration, dip angle, convergence rate, and forearc depth. Models tracked total melt as parameters were altered. For this project, the dip angle of the slab varied from 45 to 60°, rate of the slab between 20 and 90 km/Myr, age of the plate between 20 and 90 Myr, forearc depth between 40-50 km, and hydration between 0.01 and 0.1 wt%. The slab age and initial modal cpx levels are held constant throughout all the trials at 60 Myr and 15%, respectively. With batch melting, melting peaks for models set with hydration content > 0.1%, a dip angle at 60°, the highest convergence rates, and the youngest ages. Melting decreases with greater ages and lower convergence rates. In both fractional and batch melting, increasing the hydration leads to an increase in melt production overall. For fractional melting with hydration less than 0.05wt%, the difference in amount of melt compared to batch melting is negligible. At greater initial hydration the difference becomes greater with less produced under fractional melting. Changes in forearc extent also affect total melt with longer forearcs resulting in less melt than shorter ones. Additionally, we explored the effects of permeability on the melt production. Most notably, a secondary region of melt begins to form for when permeability is about 0.02 or greater. The secondary region encompasses melting above the harzburgite solidus. While two melting regions were nearly always observed under batch melt conditions, typically only one region of melting was observed under fractional melt conditions. In both cases, hydration and the dip of subducting slab have the most effect on melt production, while the convergence rate and the depth of the forearc have a smaller effect on melt production.

How to cite: Burkett, F. and Conder, J.: Melt Production beneath subduction zones: Using numerical models to evaluate melt production under batch and fractional melt conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10992, https://doi.org/10.5194/egusphere-egu23-10992, 2023.

EGU23-12780 | Orals | GD4.4

Rapid large-amplitude vertical motions generated by subduction slab roll-back in back-arc basins (Valencia Trough, Western Mediterranean) 

Julie Tugend, Penggao Fang, Nick Kusznir, Geoffroy Mohn, and WeiWei Ding

The formation and evolution of back-arc basins is complex controlled by subduction dynamics, lithosphere delamination, magmatism, slab roll-back and extension. In such a complex geodynamic context, it is difficult to decipher the mechanisms which controls sedimentary basin subsidence history and distinguish the contribution of lithosphere tectonics from dynamic topography.

Here we focus on one of the main basins of the Western Mediterranean, the Valencia Trough, which formed in the Cenozoic in relation with the slab roll-back of the Tethyan oceanic lithosphere. More specifically, we investigate the subsidence and geodynamic context related to the formation of a regionally observed unconformity, which separates Mesozoic from latest Palaeogene to Neogene sediments, and here referred to as the Miocene Unconformity.

Using a dense grid of seismic reflection data, well data and 3D flexural backstripping, we show that the Miocene Unconformity subsided by more than 1.5 km from ~17 Ma to the present day at an average rate of 90 m/Myr in the SW Valencia Trough. The absence of Cenozoic extensional faults affecting the basement shown by seismic data indicates that this rapid subsidence is not caused by Cenozoic rifting. This subsidence cannot be explained by flexural loading related to the adjacent thin-skin Betic fold and thrust belt either, which only affects subsidence observed near the deformation front. Subduction dynamic subsidence generated by the positive mass anomaly of the subducting slab in the mantle is another mechanism that can control the subsidence evolution of back-arc basins. However, since the formation of the Miocene unconformity, the subduction has propagated westwards and southwards and has slowed or ceased under the Valencia Trough, which would have resulted in the progressive diminution of subduction dynamic subsidence, generating a relative uplift rather than subsidence.

We propose an alternative mechanism and interpret the 1.5 km subsidence of the Miocene Unconformity as the collapse of a back-arc transient uplift event. Erosion during the uplift, resulting in the formation of the unconformity, is estimated to exceed 4 km. This transient uplift was likely caused by heating of back-arc lithosphere and asthenosphere, combined with mantle dynamic uplift, both caused by segmentation of Tethyan subduction resulting in slab tear. Rapid subsidence subsequently resulted from the removal of mantle flow dynamic support from the Tethyan subduction slab roll-back and thermal equilibration.

Our observations and interpretation of rapid back-arc kilometre-scale uplift and collapse might have global applicability to explain some of the observed vertical motions and the subsidence evolution of other back-arc regions experiencing subduction segmentation and slab tear during subduction slab roll-back.

How to cite: Tugend, J., Fang, P., Kusznir, N., Mohn, G., and Ding, W.: Rapid large-amplitude vertical motions generated by subduction slab roll-back in back-arc basins (Valencia Trough, Western Mediterranean), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12780, https://doi.org/10.5194/egusphere-egu23-12780, 2023.

Introduction. This study examines the structural position and genesis of the Middle-Devonian Yarlykap jasper complex and associated manganese mineralization (Southern Urals).

Materials and methods. The studied sites are Gubaidullino and Mamilya potential manganese ore occurrences. They are located in the West Magnitogorsk paleovolcanic belt and are confined to the Middle Devonian sealing wax-red and grayish-yellowish jaspers and tuff sandstones of the Yarlykap formation. The Yarlykap formation is distributed as narrow extended bands and outliers stretching along the Irendyk mountain ridge, Southern Urals. The age of the Yarlykap formation is defined as the Eiffelian, which is proved by conodont finds.

Our complex study includes geochemical, geophysical (magnetic and electrical exploration) and structural (measurements of mesostructure elements).

Results. It was shown that the rock association at both sites of the Yarlykap formation underwent a single stage of deformation, while the jaspers experienced dislocations similar in type and intensity.

 Structurally, the group of Mamiliya ore occurrences is generally confined to a monocline complicated by folded-thrust mesostructures of the north-northeast strike and western vergence. It is assumed that the Yarlykap formation is limited from the east by the thrust of the western vergence.

The Gubaidullino ore occurrence is a synform complicated by a series of small folds.  Among them, there are both practically isoclinal structures and more open asymmetric folds of western vergence.

The structure of both sites can be clearly recognized according to the electrical survey data. At the Gubaidullino site, several submeridional elongated folded zones are obvious by the change of the pattern of apparent resistance. On the Mamiliya site, the isoanomals are stretched into a single submeridional zone.

Geochemical data indicates that the deficiency of light lanthanides and the Eu and Ce minima may serve as an indicator of deposits of metalliferous hydrotherms typical for volcanically active regions of the oceans.

 Discussion. Thus, a new model of formation of siliceous strata and associated manganese mineralization can be proposed. These sites represent areas of volcanic unloading of active areas of the ocean floor associated with hydrothermal vents. Most likely, the volcanoes were located to the east of the described ore occurrences, and now they are located under the allochthon composed of the Late Devonian tufopsamite strata. 

Differences in the structure of ore occurrences are probably related to differences in their position within the West-Irendyk thrust pack, which includes these fragments. Thus, the Gubaidullino site is confined to the frontal part of the thrust and the Mamiliya site is located in the rear part of this thrust, which results in its simpler structure.

Jasper formation occurred in a developed island arc environment with an intermittent chain of volcanic structures, and they were already deformed in the Late Paleozoic, during the Ural collision.

Financial support. The study was prepared with partial financial support of the RFBR, grant No. 19-55-26009.

How to cite: Borisenko, A., Gaintsev, I., and Tevelev, A.: Composition, structure and formation conditions of the Yarlykap complex of jasper of the West Magnitogorsk paleovolcanic belt (Southern Urals), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14180, https://doi.org/10.5194/egusphere-egu23-14180, 2023.

EGU23-14925 | ECS | Posters virtual | GD4.4

Sources of material drift into the Ural foredeep at the beginning of collision (Southern Urals) 

Ekaterina Volodina, Alexander Tevelev, Alexandra Borisenko, Egor Koptev, Petr Shestakov, Natalia Pravikova, and Anastasia Novikova

Introduction. This work is devoted to the study of the sources of   drift material during the formation of Late Paleozoic deposits of the southern part of the Pre-Ural trough. Sample for the study was taken in a quarry near the Urgala region, Bashkortostan area. The section is represented by conglomerates with a sand matrix. These deposits belong to Ural forland basin. The age of this conglomerate formation – Moscovian (Middle Carboniferous).

Materials and methods. The most reliable determination of sources is possible due to U-Pb zircon dating. We also analyzed some thin sections for detailed studying of sandstone composition.

Results and discussion. Zircon grains vary greatly in shape and size. In some grains, the core and edges are clearly visible; others are full of inclusions, cracks, and zones of metamict decay. The size of the crystals varies from 60 to 400 microns. Most of the ages obtained fall in the interval from the Ordovician to the Devonian, less on the Lower and Middle Riphean. Single grains are of Cambrian, Vendian and Late Riphean age. Early Proterozoic and Archean grains are absent in the sample.

The most difficult interval is from the Cambrian to the Devonian, it accounts for the majority of the ages (410-430 Ma). Within the studied territory, the volcanic rocks closest to the sampling site are located in Nyazepetrovsk and Bardym allochthons, as well as in the Tagil arc. In addition, Devonian granitoids are found within the Ufalei anticlinorium. The largest number of Precambrian dates falls on the Middle Riphean. The source of zircons during the middle Riphean could be the Mashak formation, whose age is 1350-1346 Ma, however, there are no grains with the age of the Mashak formation in the sample.

A relatively large number of grains have the early Riphean age of 1650-1500 Ma, which correlates perfectly with the age of the Ai formation. However, almost all Riphean formations, including the Ai formation, contain zircons with the peak at 2050 Ma (the age of migmatization in the Taratash block),but  the studied sample contains no zircons of 2050 million years age or older. This means that the Taratash block and the surrounding Riphean formations were not exposed at that time.

Also, the largest number of lithoclasts in the studied sandstones are represented by siliceous rocks. The similar rocks compose the Ordovician-Devonian section of the Mayaktau Allochthon, which is located closely to the sampling site. Also, the thickness Aziam  formation   increases towards Mayaktau Allochthon. In addition to the sources described above, there is jne more source – Asha series (Vendian), because there are quite a large number of Middle-Riphean dates in the sample, which are typical for the rocks of the Asha series.

Financial support. The research has been funded by RFBR and CNF as a part of the research project № 19-55-26009 Czechia_a

How to cite: Volodina, E., Tevelev, A., Borisenko, A., Koptev, E., Shestakov, P., Pravikova, N., and Novikova, A.: Sources of material drift into the Ural foredeep at the beginning of collision (Southern Urals), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14925, https://doi.org/10.5194/egusphere-egu23-14925, 2023.

EGU23-15948 | ECS | Posters on site | GD4.4

Records of continent-continent collisions in the Paleoproterozoic: exploring the effects of convergence obliquity and temperature on P-T-t paths 

Leevi Tuikka, Bérénice Cateland, David Whipp, and Miisa Häkkinen

In the Paleoproterozoic era (2.5-1.6 Ga ago), the mode of the plate tectonics was shifting from Archean plume-lid tectonics to modern tectonics, with colder and deeper subduction due to a decreasing mantle potential temperature. Hence, the geodynamic regime was different as well; subduction was more episodic and characterised by frequent slab breakoffs, while weaker lithosphere resulted in wider and lower-relief orogens. Metamorphic rocks also recorded a fingerprint of these conditions, generally lacking evidence of UHP metamorphism and indicating higher temperatures in the lithosphere.

However, studying Paleoproterozoic orogens is challenging, as metamorphic rocks at the present-day erosional level often represent the middle-to-lower crustal orogenic interior. We aim to overcome this issue using pressure-temperature-time (P-T-t) paths extracted from generic, geodynamic continent-continent collision models and comparing them to P-T-t paths reconstructed from metamorphic minerals. The models are loosely based on Paleoproterozoic Svecofennian orogen, which formed the majority of the bedrock in southern Finland. It is well studied by number of geological and geophysical means, but physics-based geodynamical models are still lacking.

The models were run using the 3D thermo-mechanical, finite-element geodynamic modeling code DOUAR (Braun et al., 2008), which uses the PETSc version of the direct matrix equation solver MUMPS and the landscape evolution model FastScape. The work explored the effects of various continental collision obliquity angles, temperature conditions, and crustal thicknesses in a set of 13 different models. The spatial dimensions of the models are 1000×1000×70 km and crustal thickness values of 35 km and 45 km were used. In the Svecofennian orogeny, continent-continent collision was an event between colder and hotter continental blocks, which is implemented in the models by including a temperature difference of 100ºC along the model base at 70 km depth. Along this boundary, heat production is varied laterally to explore three different temperature scenarios. The convergence obliquity angle is also varied between 0º, 30º and 60º, while the subduction dip angle is constant at 45º.

With the thinner 35 km crust, the models do not show much difference in the dynamics between the temperature scenarios, as the crust is too thin to develop wide orogens, and eventual partitioning of strain due to oblique collision. Similarly, the P-T-t paths represent only straightforward retrograde metamorphism, due to simple model dynamics and the lack of large-scale internal orogenic heating. Increasing the crustal thickness to 45 km significantly affects the orogenic development. The Paleoproterozoic temperature scenario with a 45 km crust creates both wide and lower-relief orogens, also producing clear strain partitioning for the 60º obliquity angle. This difference in dynamics further results in more variation in the recorded P-T-t paths, suggesting potential for their use to explore Paleoproterozoic orogen dynamics. Ongoing work is exploring which stable mineral assemblages these P-T-t paths would correspond in metamorphic rocks.

How to cite: Tuikka, L., Cateland, B., Whipp, D., and Häkkinen, M.: Records of continent-continent collisions in the Paleoproterozoic: exploring the effects of convergence obliquity and temperature on P-T-t paths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15948, https://doi.org/10.5194/egusphere-egu23-15948, 2023.

EGU23-675 | ECS | Posters on site | GM2.2

Can we monitor shallow groundwater using ambient seismic noise? 

Antonia Kiel, René Steinmann, Eric Larose, and Céline Hadziioannou

Nowadays, the majority of detailed information about groundwater is acquired by wells that provide limited insight in time and especially space. Therefore, it would be interesting to monitor groundwater by continuously measuring seismic velocity changes in the subsurface. The shallow soil is affected by environmental influences like temperature, rainfall or drought, which in turn changes the seismic velocity in the subsurface.

In this study, we use three-component seismometers, which are placed next to an in-situ measurement station of soil conditions (moisture and temperature at different depths) and a meteorological station in the city of Hamburg, Germany. We investigate the sensitivity of high-frequency (> 1 Hz) seismic waves with an anthropogenic origin to ground moisture changes in the uppermost layers of soil. To monitor velocity changes, Passive Image Interferometry is applied. Using the three-component data, we are able to retrieve Rayleigh and Love waves. Relative velocity changes are retrieved using the stretching method. A comparison of seasonal seismic velocity changes and environmental changes shows a positive correlation between velocity and temperature, as well as a negative correlation between velocity and groundwater content. Freezing events are exceptions, as they cause relative velocity increases twice as high as seasonal changes.

The aim of this work is to eliminate temperature effects to work towards inferring water content directly from seismic velocity changes. To eliminate the contribution of temperature, its relation to seismic velocity changes and water content is quantified using regression. Since the relative velocity change is influenced by both temperature and water content, a time period of stable water content is used to quantify the relation between velocity change and temperature. As a result, the residual relative velocity change reproduces the residual water content.

How to cite: Kiel, A., Steinmann, R., Larose, E., and Hadziioannou, C.: Can we monitor shallow groundwater using ambient seismic noise?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-675, https://doi.org/10.5194/egusphere-egu23-675, 2023.

EGU23-714 | ECS | Orals | GM2.2

Seismic imaging of the submarine Kolumbo Volcanic Chain reveals its volcano-tectonic evolution and link to Santorini 

Jonas Preine, Christian Hübscher, Jens Karstens, Gareth Crutchley, and Paraskevi Nomikou

Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo volcanic field is one of the most hazardous volcanic regions in the world and lies in an active continental rift zone. Northeast of Santorini lies the Kolumbo Volcanic Chain (KVC), which comprises more than 20 submarine volcanic cones, with the Kolumbo volcano representing the most prominent edifice of this chain. However, due to their inaccessibility, little is known about the spatio-temporal evolution and tectonic control of these submarine volcanoes and their link to the volcanic plumbing system of Santorini. We will present multichannel reflection seismic data that allow us to image the internal architecture of the KVC and study its link to Santorini. Using a seismostratigraphic framework, we are able to show the KVC evolved during two episodes, which initiated at approx. 1 Ma with the formation of mainly effusive volcanic edifices along a NE-SW trending zone. Most of the cones of the second episode represent submarine pumice cones that were formed by submarine explosive eruptions between 0.7 and 0.3 Ma and partly developed on top of volcanic edifices from the first episode. Our data show that two prominent normal faults underlie the KVC, indicating a direct link between tectonics and volcanism. In addition, we are able to reveal several buried volcanic centers and a distinct volcanic ridge connecting the KVC with Santorini, suggesting a connection between the two volcanic centers in the past. We argue that this connection was interrupted by a major tectonic event and, as a result, the two volcanic systems now have separate, largely independent plumbing systems despite their proximity.

How to cite: Preine, J., Hübscher, C., Karstens, J., Crutchley, G., and Nomikou, P.: Seismic imaging of the submarine Kolumbo Volcanic Chain reveals its volcano-tectonic evolution and link to Santorini, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-714, https://doi.org/10.5194/egusphere-egu23-714, 2023.

EGU23-900 | ECS | Posters on site | GM2.2

Optimising passive seismic investigations of the ice-bedrock interface zone for the great ice sheets 

Ian Kelly, Anya Reading, Tobias Staal, and Andrew Bassom

The need to better predict how the great ice sheets will respond to continued atmospheric and ocean warming is paramount. Ice deformation and mechanisms for ice sliding across the bedrock underneath are both key considerations. Constraints of this critical ice-bedrock interface zone, particularly over extensive inland areas of Antarctica and Greenland, remain a major hurdle in ice-sheet modeling and estimations of future sea level rise.

Passive seismology offers a logistically-efficient avenue for such investigations, with improvements in sensor technologies, autonomous power solutions and telemetry systems encouraging the deployment of temporary arrays for subglacial mapping and real-time monitoring. Previous experiments have demonstrated the potential of techniques such as receiver functions, horizontal-to-vertical spectral ratios (HVSR) and ambient noise interferometry for characterising the depth and nature of the ice-bedrock zone. This research looks to fully explore the sensitivity range of available passive seismic methods for the ice-bedrock interface, with a view towards optimising data collection and array geometries for future applications. In this contribution, we present an optimised workflow making use of HVSR analysis and the spatial autocorrelation (SPAC) technique using numerical simulations and field data collected from East Antarctica. The results from this study provide a benchmark to guide future deployments in the polar regions.

How to cite: Kelly, I., Reading, A., Staal, T., and Bassom, A.: Optimising passive seismic investigations of the ice-bedrock interface zone for the great ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-900, https://doi.org/10.5194/egusphere-egu23-900, 2023.

Karst is a landscape with distinctive hydrology and landforms that arise when the underlying rock is soluble. Locating the flowing conduits and pathways in karst is important in terms of water resource management, groundwater flooding, geotechnical and engineering projects. Understanding flow pathways is particularly important for road and railway construction, so as not to adversely affect hydrological networks, in particular those associated with Turloughs.

The aim of this study was to develop methods for directly detecting energetic groundwater flow in sub-surface conduits through passive seismic applications, by detecting the small ground vibrations (seismic microtremor) that flowing water in the sub-surface may generate. This is in contrast to the current ‘traditional’ approach of attempting to actively image the conduits using geophysical and other methods, in order to determine the geometry of flow paths. The imagery of conduits in karst is a very difficult problem and determining if they contain flowing structures is also a very significant challenge using traditional methods, which is the motivation for developing a new approach to the problem.

We undertook experiments at two sites on karst in Ireland; one gently-sloping shallow conduit and one relatively deep and complex-structured conduit. We chose these sites as the caves had previously been dived and we had access to the shapefiles of these caves to ground-truth our findings.

We observed that subterranean flow-related micro-tremor in karst appears as persistent frequency bands on the spectrograms that vary with time and seismic station location with respect to the conduit. This persistent frequency is different than the soil resonating frequency and relates to the subterranean water flow in the conduits. Application of an Amplitude Location Method (ALM)  clearly delineated the conduit as the source of the micro-tremor.

We also conducted an active Airgun experiment at the second site to locate the conduit by tracking a pressure wave, using two arrays of surface seismic stations, as it propagated into the conduit. This combination of detecting and locating seismic microtremor generated by water flow in the conduits and the use of seismic array analysis to track active Airgun source pressure waves propagating at depth in conduits offers a new tool kit for karst hydrology determination. In the next step, we will assess the applicability of Distributed Acoustic Sensing (DAS) using fiber optic cables as sensors for detecting sub-surface water flow, where we expect unrivaled spatial resolution of the flow-induced seismic wavefield. Such a study would be the first attempt to fill the current gap regarding an understanding of karst groundwater dynamics along the entire conduit pathway, at an exceptionally high spatial scale.

How to cite: Karbala Ali, H., Bean, C. J., and Chalari, A.: Detection and source location of the groundwater-induced seismic signal in karst using a combination of passive and active seismic approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1046, https://doi.org/10.5194/egusphere-egu23-1046, 2023.

EGU23-1601 | ECS | Orals | GM2.2

Groundwater Heights Prediction from Seismic Waves with Machine Learning 

Anthony Abi Nader, Julie Albaric, Marc Steinmann, Clément Hibert, Jean-Philippe Malet, Benjamin Pohl, and Christian Sue

Unlike surface water reservoirs, that can be easily quantified and monitored, underground conduits in karst systems are often inaccessible, hence challenging to monitor. Seismic noise analysis was proved to be a reliable tool to monitor ground water storage in a fractured rock aquifer (Lecocq et al. 2017). In underground karstic environments, seismic noise monitoring was able to detect hydrological cycles and monitor the groundwater-content variations (Almagro Vidal et al. 2021). The following approach relies on coupling passive seismic wavefield with hydrological data in a machine learning algorithm in order to monitor underground water heights. The studied site is the Fourbanne karst aquifer (Jura Mountains, Eastern France, Jurassic Karst observatory). The underground conduit is accessible through a drilled shaft and instrumented by two 3-component seismological stations, one located underground and the other one at the surface, and a water height probe. We applied a new approach based on the machine learning random forest (RF) algorithm and continuous seismic records (Hibert et al., 2017), to find characteristic signals to predict the underground river water height. The method consists on the computation on a sliding window of seismic signal features (waveform, spectral and spectrogram features) and using the corresponding water height at the same time window to train the algorithm, and then apply it on new data. The RF algorithm is capable of accurately detecting flooding periods and reproduce the groundwater heights with an efficiency exceeding 95% and 53% using the Nash-Sutcliffe criterion for the seismic stations located in the underground conduit and at the surface respectively. The obtained results are a first promising outcome for the remote study of water circulation in karst aquifers using seismic noise.

How to cite: Abi Nader, A., Albaric, J., Steinmann, M., Hibert, C., Malet, J.-P., Pohl, B., and Sue, C.: Groundwater Heights Prediction from Seismic Waves with Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1601, https://doi.org/10.5194/egusphere-egu23-1601, 2023.

EGU23-1677 | ECS | Posters virtual | GM2.2

Event Relations and Sources of Icequakes at the Grounding Line of Rutford Ice Stream, West Antarctica 

Ian Lee, Sridhar Anandakrishnan, Richard Alley, Alex Brisbourne, and Andrew Smith

Basal icequakes are generated as a glacier slides over its underlying bedrock, and the stick-slip motion of constant loading and unloading releases shear stresses that produce these very small magnitude (ML < 0) glacial microseisms. Detecting and locating nucleation of these fine-scale icequakes can provide highly useful insights into the deformation processes occurring at the bed and consequently the mechanisms governing glacier flow. We present icequake data derived from a seismic array installed at the grounding line of the Rutford Ice Stream in West Antarctica by Penn State University and the British Antarctic Survey during the 2018/19 austral summer. The region’s natural source seismicity was first processed using the earthquake detection and location software QuakeMigrate and the events were relatively relocated using HypoDD/GrowClust. We then clustered the events into sticky spot clusters using the unsupervised clustering algorithm DBSCAN, and finally from the clusters we selected “model” waveforms to perform template matching on the original seismic traces to create methodically comprehensive high-resolution icequake catalogs at the grounding line of Rutford. We present our methodology including the complete processing pipeline (supplemented by developed supporting open-source scripts) along with key tuning parameters, and describe how our catalogs were used to resolve glacier sliding patterns and key topographical features and characteristics of the bed like sticky spots. We additionally explore the effects of tidal modulation and Rutford ice flow motion on icequake occurrences. Our seismic traces primarily contain icequake signals that derive from stick-slip sliding, but also unique waveforms that might be derived from crevassing and teleseisms that we will also explore. Our results show that stick-slip basal icequakes and these resultant icequake catalogs are valuable data-rich resources that help improve our understanding of glacier flow dynamics and will be important toward improving glacier flow models used for constraining global mean sea level rise.

How to cite: Lee, I., Anandakrishnan, S., Alley, R., Brisbourne, A., and Smith, A.: Event Relations and Sources of Icequakes at the Grounding Line of Rutford Ice Stream, West Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1677, https://doi.org/10.5194/egusphere-egu23-1677, 2023.

EGU23-2707 | Orals | GM2.2

Thermo-Acousto-Elasticity (TAE) of natural rock cliffs: toward better understanding and monitoring damage and erosion process 

Eric Larose, Antoine Guillemot, Laurent Baillet, and Pierre Bottelin

Rainfalls and freeze-thaw cycles are well known to largely contribute to rock slopes erosion, including chemical processes (dissolution, alteration) together with mechanical action (stress change in fractures due to water freezing). The role of heat waves and thermal cycles is less studied in dry conditions. Here we present a thermo-acousto-elastic (TAE) model for rock volumes exposed to cyclic (daily to seasonal) thermal forcings, as an application of environmental seismology (1).

In our model, we assume that the rock temperature is constant at depth (a few meters in general), and that the free surface is exposed to heat fluxes (radiative and convective ones). In practice, these heat fluxes can be respectively derived from solar radiation normal to the rock surface and from the air temperature, both parameters are easily measured in the field. We then develop a numerical model based on a) thermal diffusion (heat propagation in the rock in 2D or 3D models, including complex geometries as cracks, rock columns…), b) thermal expansion relating temperature to strain, and c) acousto-elasticity relating the elastic parameters to the state of stress, (2). Such a model is run, for example, with COMSOL Multiphysics with a finite element scheme. We end up with a 2D or 3D numerical model of stress and deformation of the rock volume evolving over time ranging from sub-daily to yearly time scales.

As an application we test this model on various rock columns and observe that the developed model properly reproduces field observations, including daily and seasonal cycles: the natural resonance frequency of the rock column, a proxy for its rigidity, increases with increasing heat flux (3) and the rear crack closes up. As a result of fitting our numerical model to natural rock columns, we can evaluate the acousto-elastic constant that relates the rigidity to the state of stress, a parameter that is known to mainly depend on the state of damage of the material, opening the route for rockfall risk assessment, monitoring and early warning systems. Our model also allows to shed new light into fatigue and cyclic damage process of rock slopes and cliffs, a key to rock erosion.

 

References:

  • (1) Guillemot, L. Baillet, E. Larose, P. Bottelin : Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale : observations, modeling and insights to improve monitoring, Geoph. J. Int. 231, 894-906 (2022).
  • (2) Larose, E. & Hall, S.: Monitoring stress related velocity variation in concrete with a 2.10−5 relative resolution using diffuse ultrasound, J. acoust. Soc. Am., 125, 1853–1856 (2009).
  • (3) Bottelin, P., Levy, C., Baillet, L., Jongmans, D. & Gueguen, P.: Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps), Geophys. J. Int., 194, 849–858 (2013).

How to cite: Larose, E., Guillemot, A., Baillet, L., and Bottelin, P.: Thermo-Acousto-Elasticity (TAE) of natural rock cliffs: toward better understanding and monitoring damage and erosion process, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2707, https://doi.org/10.5194/egusphere-egu23-2707, 2023.

EGU23-3010 | Posters on site | GM2.2

Identification of bedrock depth and blind fault by HVSR analysis along two profiles in Pohang, South Korea considering optimal weather environment and seismometer burial depth 

Su Young Kang, Kwang-Hee Kim, Doyoung Kim, Byungmin Kim, Lanbo Liu, and Youngcheol Lee

Many deep faults do not reach the earth’s surface and thus are not recognized. Such faults are rarely mapped by standard surface geological mapping. This seriously hinders seismic risk mitigation efforts. In this study, we applied the horizontal-to-vertical spectral ratio (HVSR) method to identify blind faults invisible at the surface. Despite its simplicity and low-cost implementation, we noticed that HVSR results were unstable using data collected by exposed seismometers or under higher wind speeds. Therefore, three-component seismic sensors for ambient noise observations were buried at different depths to examine the effects of ground coupling, wind speeds, and precipitations. Results from a series of field tests under diverse conditions guided us to establish data selection criteria. The first required condition is that seismic sensors should be buried (>0.3 meters) to secure ground coupling and to avoid any direct exposure to wind or precipitations. The other is that data should be collected at low wind speeds (< 3 m/s). The requirements were applied to ambient noise data along two profiles traversing unnamed and inferred faults in Pohang, Korea. We initially estimated the resonance frequencies for each site, which varied from 0.41 to 2.52 Hz. They were then converted to bedrock depths using an empirical relationship between the resonance frequency and depth to bedrock observed at boreholes in the area. The estimated depths to bedrock along profiles ranged from 8.0 to -472.0 meters. The resulting depth profiles show significant lateral variations in the bedrock depth, including the one near the Gokgang fault at which the thickness to the major impedance contrasts decreased from 196 to 20 meters. Sudden variations were also observed at unexpected locations along the profile. We examined the details, especially for sites of apparent changes in bedrock depth, and compared their characteristics with other geophysical studies, including Vs30, MASW, Bouguer gravity anomaly, and adjacent stations correlation. Their results are all well correlated to each other and indicate rapid changes in bedrock depth. We attribute the rapid changes to vertical displacements by ancient faulting activity.

How to cite: Kang, S. Y., Kim, K.-H., Kim, D., Kim, B., Liu, L., and Lee, Y.: Identification of bedrock depth and blind fault by HVSR analysis along two profiles in Pohang, South Korea considering optimal weather environment and seismometer burial depth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3010, https://doi.org/10.5194/egusphere-egu23-3010, 2023.

EGU23-3593 | Posters on site | GM2.2

Meteo-Seismology: Harvesting the Seismic Signals of Weather Dynamics in the Critical Zone 

Michael Dietze, Christian Mohr, Violeta A. Tolorza, Benjamin Sotomayor, and Erwin Gonzalez

Weather conditions are an important driver of Earth surface dynamics, such as gravitational mass wasting, flood propagation, biological activity events and physical interactions within the critical zone. While there are dedicated sensors to capture meteorological parameters, these sensors are comparably expensive, have a small spatial footprint and often lack the temporal resolution needed to constrain high frequency meteorological dynamics. We introduce the concept of meteo-seismology, i.e. the measurement of first-order ground motion signatures of weather conditions by decisively installed seismic sensors. While meteorological manifestations are generally considered seismic noise and it may seem odd to use seismometers instead of weather stations, geophysical sensors circumvent or complement the above caveats and add further important data to a comprehensive picture of the rapidly changing state of the atmosphere and its interaction with the landscape we live in. Based on examples from prototype forested landscapes in Central Europe and Chilean Patagonia, we demonstrate how seismic stations can be used to infer properties of the pressure and wind field and its coupling to the biosphere, constrain rain intensity and drop properties, yield temperature proxies and their propagation into the ground, and survey ground moisture trends and discharge patterns. Understanding the seismic signatures of a meteorological origin also allows to, vice versa, better handle the contaminating side of these seismic sources in records, where high frequency signals are to be used for other than meteo-seismological studies. Our approach offers an alternative and complementary way to non-invasively monitor hydrometeorological energy and matter fluxes at high temporal and spatial resolution.

How to cite: Dietze, M., Mohr, C., Tolorza, V. A., Sotomayor, B., and Gonzalez, E.: Meteo-Seismology: Harvesting the Seismic Signals of Weather Dynamics in the Critical Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3593, https://doi.org/10.5194/egusphere-egu23-3593, 2023.

Large rockfalls often cause huge economic losses and casualties in densely populated mountain areas. Timely acquiring information on a large rockfall can help promptly assess the damage and residual risks and guide the emergency response. Recent works suggest that the seismic signals generated by large rockfalls can provide these key information, but most of them focused on exploring seismic signatures to understand rockfall dynamics, lacking a rapid disaster assessing scheme. Here, we establish a seismic signal-based assessment scheme and demonstrate its capability by taking a large event – the 5 April 2021 Hongya rockfall (Sichuan, China) – as a case study. This scheme consists of three components, which are rockfall identification, detection and location, and characterization. In the rockfall identification module, we show how a rockfall can be distinguished from an earthquake and a rockslide by analyzing its seismic signatures. In the detection and location module, we demonstrate how the kurtosis-based method can be used to rapidly detect the initiation of a rockfall and determine the seismic wave velocity accordingly, and how the arrival-time-based location method can be used to locate a rockfall event. In the rockfall characterization module, we show how rockfall volume can be estimated from the magnitude of radiated seismic energy and how to characterize the dynamic process of a rockfall by the signatures of seismogram, spectrum and recorded seismic energy. Our results show that the seismic signal-based scheme presented here is suitable to characterize large rockfalls and has certain potential for rapid and effective emergency management.

How to cite: Li, W., Wang, D., and Zhang, Z.: Large rockfall detection, location and characterization using broadband seismic records: A case study of Hongya rockfall, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3773, https://doi.org/10.5194/egusphere-egu23-3773, 2023.

EGU23-4500 | Orals | GM2.2

Ambient noise monitoring of the Bayou Corne sinkhole evolution 

Aurelien Mordret, Anais Lavoué, Benjamin Witten, Adam Baig, Sophie Beaupretre, Romeo Courbis, and Chloé Gradon

The collapse at depth of a cavern on the side of the Napoleonville salt dome, Assumption Parish, Louisiana, led to the formation of a large sinkhole at the surface. Besides surficial evidence from direct observations, the precise timeline of the evolution of the sinkhole is poorly known.  Here, we used two years of continuous ambient seismic vibrations recorded at 11 3-component seismic stations located around the Bayou Corne sinkhole to monitor the daily relative seismic velocity changes associated with the sinkhole activity. The sinkhole started to form in 2012 and had several phases of activity. The seismic network was installed in early 2013 and recorded the last major collapses before settling in 2014. Following standard seismic interferometry processing, we computed the full 9-component tensors of ambient vibrations cross-correlations between each pair of sensors. After a drastic quality check of the correlations, we rejected several components for which we did not have enough data or for which the data were corrupted in a way that was difficult to correct. We monitored the relative velocity variations (dv/v) during the studied period using the stretching method in the 0.9-3 Hz frequency band within the early coda of the correlations. We employed a reference-less inversion procedure to obtain a dv/v time series for each component and each pair of stations. The multi-component pairs curves are averaged to get the final time series. The results show significant velocity changes in early 2013 associated with the collapse phases of the sinkhole. The velocity recovers steadily after the second half of 2013 and all of 2014. Two seismically active periods generate smaller velocity drops. In agreement with the spatial extension of the sinkhole toward the southwest seen from the surface, the pairs of stations the most affected by large velocity drops are the ones located along the southwestern shore of the lake.
Our monitoring allows for refining the timeline of the events affecting the sinkhole and its overall activity with a daily temporal resolution. From the analysis of these two years of data, the sinkhole stabilized after intense activity in early 2013. The large velocity variations indicate a strong destructuring of the ground, with potential fracturing and water invasion.

How to cite: Mordret, A., Lavoué, A., Witten, B., Baig, A., Beaupretre, S., Courbis, R., and Gradon, C.: Ambient noise monitoring of the Bayou Corne sinkhole evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4500, https://doi.org/10.5194/egusphere-egu23-4500, 2023.

EGU23-5344 | Orals | GM2.2 | Highlight

Tracking storms in the Pyrenees using a dense seismic network 

Jordi Diaz, Mario Ruiz, Mireia Udina, Francesc Polls, Davis Martí, and Joan Bech

Data acquired by a dense seismic network deployed in the Cerdanya basin (Eastern Pyrenees) is used to track the temporal and spatial evolution of meteorological events such as rainfall episodes or thunderstorms. Comparing seismic and meteorological data, we show that for frequencies above 40 Hz, the dominant source of seismic noise is rainfall and hence the amplitude of the seismic data can be used as a proxy of rainfall. The interstation distance of 1.5 km provides an unprecedented spatial resolution of the evolution of rainfall episodes along the basin. Two specific episodes, one dominated by stratiform rain and the second one dominated by convective rain, are analyzed in detail, using high resolution disdrometer data from a meteorological site near one of the seismic instruments.

Seismic amplitude variations follow a similar evolution to radar reflectivity values, but in some stratiform precipitation cases, it differs from the radar-derived precipitation estimates in this region of abrupt topography where radar may suffer antenna beam blockage. Hence, we demonstrate the added value of seismic data to complement other sources of information such as rain-gauge or weather radar observations to describe the evolution of ground-level rainfall fields at high spatial and temporal resolution. The seismic power and the rainfall intensity have and exponential relationship and the periods with larger seismic power are coincident. The time periods with rain drops diameters exceeding 3.5 mm do not result in increased seismic amplitudes, suggesting that there is a threshold value from which seismic data are no longer proportional to the size of the drops.

Thunderstorms can be identified by the recording of the sonic waves generated by thunders. We show that single thunders can be recorded to distances of a few tens of kilometers. As the propagation of these acoustic waves is expected to be strongly affected by parameters as air humidity, temperature variations or wind, the seismic data could provide an excellent tool to investigate atmospheric properties variations during thunderstorms.

How to cite: Diaz, J., Ruiz, M., Udina, M., Polls, F., Martí, D., and Bech, J.: Tracking storms in the Pyrenees using a dense seismic network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5344, https://doi.org/10.5194/egusphere-egu23-5344, 2023.

EGU23-5610 | ECS | Orals | GM2.2

Evidence of sub-surface water flow dynamics within a karst conduit from ambient noise monitoring 

Axelle Pantiga, Vincent Allègre, Roland Lastennet, Nicolas Houillon, Sylvain Mateo, Fabien Naessens, and Alain Denis

Karst aquifers are characterized by their heterogeneity and complex underground geometry. A great part of the world relies on karst resources for drinkable water and understanding the functioning of karst systems is essential to assess their vulnerability and response to rainfall. Relevant continuous parameters to quantify the underground flow dynamics are still required for these studies as direct underground measurements are not possible. We used surface ambient noise measurements to estimate the seismic signature and amplitude associated with the water flow within an underground karst conduit. We combined geophysical measurements with hydro-chemical and hydrogeological data to build a multidisciplinary approach. The experimental site is the Glane spring, in Dordogne (France). The hydrogeological catchment of this Vauclusian-type spring is 75 km² and consists of upper Jurassic carbonate rocks. The Glane spring shows rapid and intense variations of discharge following rainfall events, ranging from 0.1 to 4 m3/s in 2021. Ambient noise has been continuously recorded since December 2021 using four seismic stations deployed upstream of the source and above the well-known karst terminal conduit. Hydro-chemical parameters and water level have been continuously monitored during a full hydrological cycle and a rain gauge was installed on site to monitor rainfall. During the first year of monitoring, we identified six flooding events. Each event was characterized by an increase in water flow associated with an increase in the seismic signal amplitude. We observed that the seismic amplitude standard level is higher during the high-water period than during the low water period suggesting a larger base water flow. We also observed hysteresis between the seismic power and hydro-chemical parameters. Correlations between the seismic recordings and hydrochemistry might suggest a change in water flow regime within the conduit prior to the flood. Seismic power variations associated with discharge variations are similar to what was already observed for sub-glacial melting flow. Other springs and swallow holes are currently instrumented to validate the approach in the field.

How to cite: Pantiga, A., Allègre, V., Lastennet, R., Houillon, N., Mateo, S., Naessens, F., and Denis, A.: Evidence of sub-surface water flow dynamics within a karst conduit from ambient noise monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5610, https://doi.org/10.5194/egusphere-egu23-5610, 2023.

EGU23-6049 | ECS | Posters on site | GM2.2

Towards quick clay monitoring in the city of Oslo, Norway with urban seismic noise 

Charlotte Bruland, Andreas Köhler, and Volker Oye

Historically, there is one larger quick clay landslide in Norway every year. Since 80 percent of those happen in known quick clay risk areas, it is important to monitor these sites continuously. Alna, a busy, urban area in Oslo, is an example of such a location where a quick clay slide could lead to substantial human and economical losses.

In this study we use ambient noise methods to monitor changes in the subsurface at Alna using a small array of three-component seismic sensors. To retrieve small velocity changes, we apply coda wave interferometry using 12 months of urban seismic noise (above 1 Hz).

We compare the observed day-to-day changes to air temperature, precipitation, and water levels in a nearby river, and observe environmental velocity fluctuations well correlated with air temperature and precipitation. In particular, freezing and thawing produces strong changes in seismic velocity (up to 4 percent). The surface wave-coda used here is sensitive to changes in shear wave velocity, which in turn can be used to detect changes of the sub-surface properties. Therefore, observed velocity variations at Alna could have potential for monitoring and early warning of quick clay instabilities.

How to cite: Bruland, C., Köhler, A., and Oye, V.: Towards quick clay monitoring in the city of Oslo, Norway with urban seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6049, https://doi.org/10.5194/egusphere-egu23-6049, 2023.

EGU23-6264 | Orals | GM2.2

Stalagmites' reactions to ground motion studied using modified Raspberry Shake and nodal sensors 

Aurélie Martin, Thomas Lecocq, Ari Lannoy, Yves Quinif, Thierry Camelbeeck, and Nathalie Fagel

Karstic zones are numerous on Earth and offer a particular field of study to evaluate the ground motion levels that occurred in the past in support of regional seismic hazard assessment. Indeed, some fine and slender candlestick stalagmites are intact and therefore indicate that a certain level of ground motion has not been exceeded since they exist. Many parameters must be considered in the behaviour of stalagmites to earthquakes such as their shape, their mechanical properties and their natural frequency. A good way to better understand and characterize the reaction of these stalagmites to earthquakes is to study their reaction to the current permanent ground motion. To do this, a study based on the measurement of ambient seismic noise is underway in the cave of Han-sur-Lesse (Ardenne, Belgium). The ambient seismic noise is measured both at the surface (above the limestone massif and in the nearest village), on the floor of the cave and on the stalagmites themselves. Different three-component seismic sensors are used in parallel: three SmartSolo IGU-16HR 3C and two Raspberry Shake 3D Personal Seismographs, one of which has been adapted to be easily attached to the stalagmites. This parallel configuration during two-week recording periods made it possible to determine the eigenfrequencies and the polarization of the associated movements of 16 stalagmites. In addition, daily and weekly variations in ambient noise and transient events are measured such as earthquakes, quarry explosions or flooding in the cave. The presence of sensors in different places over the same period also makes it possible to study the possible impact of the cave's local characteristics on these measurements.

How to cite: Martin, A., Lecocq, T., Lannoy, A., Quinif, Y., Camelbeeck, T., and Fagel, N.: Stalagmites' reactions to ground motion studied using modified Raspberry Shake and nodal sensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6264, https://doi.org/10.5194/egusphere-egu23-6264, 2023.

EGU23-6300 | Posters on site | GM2.2

Towards an unsupervised generic seismic detector for hazardous mass-movements: a data-driven approach 

Patrick Paitz, Małgorzata Chmiel, Lena Husmann, Michele Volpi, Francois Kamper, and Fabian Walter

Hazardous mass-movements pose a great danger to the population and critical infrastructure, especially in alpine areas. Monitoring and early-warning systems can potentially save many lives and improve the resilience of mountain communities to catastrophic events. Increasing coverage of seismic networks recording hazardous mass-movements opens up new warning perspectives as long as efficient algorithms screening the seismic data streams in real-time are available.

We propose to combine physical and statistical properties of seismic ground velocity recordings from geophones and seismometers as a foundation for an unsupervised workflow for mass movement detection. We evaluate the performance, consistency, and generalizability of unsupervised clustering algorithms like K-means and Bayesian Gaussian Mixture Models against supervised methods like the Random Forest classifier. Focusing on debris-flow records at the Illgraben torrent in Switzerland, we present a generic mass-movement detector with high accuracy and early-warning capability. We apply this detector to other datasets form other sites to investigate its transferability.

Since our results aim to enable mass-movement monitoring and early-warning worldwide, Open Research Data principles like Findability, Accessibility, Interoperability and Reusability (FAIR) are of high importance for this project. We discuss how using the Renku (renkulab.io) platform of the Swiss Data Science Center ensures FAIR data science principles in our investigation. This is a key step towards our ultimate goal to enable seismology-based early warning of mass-movements wherever it may be required.

How to cite: Paitz, P., Chmiel, M., Husmann, L., Volpi, M., Kamper, F., and Walter, F.: Towards an unsupervised generic seismic detector for hazardous mass-movements: a data-driven approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6300, https://doi.org/10.5194/egusphere-egu23-6300, 2023.

EGU23-6321 | ECS | Posters on site | GM2.2

Can we characterize groundwater reservoirs in central Europe from air-pressure-induced seismic velocity changes? 

Richard Kramer, Yang Lu, and Götz Bokelmann

In this study, we used coda wave interferometry to investigate four years of continuous data from AlpArray and other locations throughout Europe. We estimate the hourly Green’s function by cross-correlating ambient seismic noise recorded at pairs of stations. The results indicate short and long-term variations of the seismic velocities and show the feasibility of large-scale monitoring with ambient seismic noise at high temporal resolution. The relative seismic velocities (dv/v) show temporal variations on the order of 10-3 in a frequency band around 1 Hz. Spectra of the velocity time series contain strong daily and sub-daily behaviour, which are primarily caused by the coupling of atmospheric processes and solid Earth. The explanatory model focuses on depth variations of the groundwater table, linking atmospheric pressure (loading and unloading the Earth's surface) to variations in seismic velocity. This study aims to understand and explain differences in daily and sub-daily behaviour across Europe. This may contribute to the hydrological characterization of the near-subsurface in central Europe. 

How to cite: Kramer, R., Lu, Y., and Bokelmann, G.: Can we characterize groundwater reservoirs in central Europe from air-pressure-induced seismic velocity changes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6321, https://doi.org/10.5194/egusphere-egu23-6321, 2023.

EGU23-7136 | ECS | Orals | GM2.2

Towards a generic clustering approach for building seismic catalogues from dense sensor networks 

Joachim Rimpot, Clément Hibert, Jean-Philippe Malet, Germain Forestier, and Jonathan Weber

In the context of climate change, the occurrence of geohazards such as landslides or rockfalls might increase. Therefore, it is important to have the ability to characterise their (spatial and temporal) occurrences in order to implement protection measures for the potential impacted populations and infrastructures. Nowadays, several methods including Machine Learning algorithms are used to study landslides-triggered micro-seismicity and the associated seismic sources (eg. rockfalls and  slopequakes). Those innovative algorithms allow the automation of the processing chains used to build micro-seismicity catalogues, leading to the understanding of the landslide deformation pattern and internal structure. Unfortunately, each landslide context has its own seismic signature which requires the use of the most complete and handmade training samples to train a Machine Learning algorithm. This is highly time consuming because it involves an expert that needs to manually check every seismic signal recorded by the seismic network, which can be thousands per day.

The aim of this study is to develop semi-supervised and unsupervised clustering methods to characterise the micro-seismicity of landslides in near real time. Here, we present the preliminary results obtained for creating a landslide micro-seismicity catalogue from the analysis of a dense network of 50 seismic stations deployed temporarily at the Super-Sauze landslide (French Alps). First, we present the performance of supervised Random Forest and XGBoost trained models on the event signals. Then, an approach aimed at processing streams of raw seismic data based on 18s-length windows is explored. Finally, we discuss the clustering results and the transferability possibilities of the approach to other landslides and even environments (glaciers, volcanoes).

How to cite: Rimpot, J., Hibert, C., Malet, J.-P., Forestier, G., and Weber, J.: Towards a generic clustering approach for building seismic catalogues from dense sensor networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7136, https://doi.org/10.5194/egusphere-egu23-7136, 2023.

EGU23-7489 | ECS | Posters on site | GM2.2

Monitoring the cryoseismic activity of the Astrolabe glacier, Terre Adélie, Antarctica 

Tifenn Le Bris, Guilhem Barruol, Emmanuel Le Meur, Florent Gimbert, and Dimitri Zigone

In coastal Antarctica, outlet glaciers exhibit complex dynamics materialized by intense internal deformation, enhanced basal sliding and strong thermo-mechanical interactions with the ocean. Here we aim to use seismic observations to unravel these various processes and their link with glacier and ocean dynamics. As part of the SEIS-ADELICE project (2020-2024) supported by the French Polar Institute IPEV, in January 2022 we deployed four permanent and six temporary (1 month long) broadband seismic stations on and around the Astrolabe Glacier (Terre Adélie, East Antarctica), as well as four ocean-bottom seismometers at sea near the terminus of the floating tongue. In January 2023 we will be supplementing this setup by a temporary network of 50 seismic nodes above the grounding line of the glacier.

Preliminary detection and classification of seismic events reveals a wide variety of cryo-seismic signals. The most pervasive events correspond to icequakes, are located close to the surface, and exhibit clear tidal modulation. We interpret these events as being generated by the brittle fracturing of ice associated with crevasse opening. We also observe numerous short and similar repetitive events of much lower amplitude that are located at few restricted locations near the ice-bedrock interface. These events are likely produced by basal stick-slip over punctual bedrock asperities. Finally, we observe glacial tremors which could result from hydraulic sources at the ice-bedrock interface, although further analysis is required to confirm this hypothesis.

This preliminary work provides useful grounds for deeper analysis to be done in the future on source characteristics and their more quantitative links with glacier dynamics.

How to cite: Le Bris, T., Barruol, G., Le Meur, E., Gimbert, F., and Zigone, D.: Monitoring the cryoseismic activity of the Astrolabe glacier, Terre Adélie, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7489, https://doi.org/10.5194/egusphere-egu23-7489, 2023.

EGU23-7549 | ECS | Posters on site | GM2.2 | Highlight

Seabed seismometers reveal duration and structure of longest runout sediment flows on Earth 

Megan Baker, Peter Talling, Richard Burnett, Ed Pope, Sean Ruffell, Matthieu Cartigny, Michael Dietze, Morelia Urlaub, Michael Clare, Jeffrey Neasham, Ricardo Silva Jacinto, Pascal Kunath, and Christine Peirce

Seafloor sediment flows (turbidity currents) form some of the largest sediment accumulations on Earth, carry globally significant volumes of organic carbon, and can damage critical seafloor infrastructure. These fast and destructive events are notoriously challenging to measure in action, as they often damage any instruments anchored within the flow. We present the first direct evidence that turbidity currents generate seismic signals which can be remotely sensed (~1-3 km away), revealing the internal structure and remarkably prolonged duration of the longest runout sediment flows on Earth. Passive Ocean Bottom Seismograph (OBS) sensors, located on terraces of the Congo Canyon, offshore West Africa, recorded thirteen turbidity currents over an 8-month period. The occurrence and timing of these turbidity currents was confirmed by nearby moorings with acoustic Doppler current profilers.

Results show that turbidity currents travelling over ~1.5 m/s produce a seismic signal concentrated below 10 Hz with a sudden onset and more gentle decay. Comparison of the seismic signals with information on flow velocities from the acoustic Doppler current profilers demonstrates that the seismic signal is generated by the fast-moving front of the flow (frontal cell), which contains higher sediment concentrations compared to the slower-moving body. Long runout flows travelling >1000 km have a fast (3.7-7.6 m s-1) frontal cell, which can be 14 hours, and ~350 km long, with individual flows lasting >3 weeks. Flows travelling >1000 km eroded >1300 Mt of sediment in one year, yet had near-constant front speeds, contrary to past theory. The seismic dataset allows us to propose a fundamental new model for how turbidity currents self-sustain, where sediment fluxes into and from a dense frontal layer are near-balanced.

Seismic monitoring of turbidity currents provides a new method to record these hazardous submarine flows, safely, over large areas, continuously for years yet at sub-second temporal resolution. Monitoring these processes from land would considerably ease deployment efforts and costs. Thus, work is underway investigating if terrestrial seismic stations can record submarine seafloor processes in Bute Inlet, a fjord in western Canada where independent measurement of delta-lip failures and turbidity currents can be compared to a passive seismic dataset.

How to cite: Baker, M., Talling, P., Burnett, R., Pope, E., Ruffell, S., Cartigny, M., Dietze, M., Urlaub, M., Clare, M., Neasham, J., Silva Jacinto, R., Kunath, P., and Peirce, C.: Seabed seismometers reveal duration and structure of longest runout sediment flows on Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7549, https://doi.org/10.5194/egusphere-egu23-7549, 2023.

EGU23-7727 | Orals | GM2.2

Using Seismic Methods to Monitor Bedload Transport Along a Desert Environment Ephemeral Tributary 

Susan Bilek, J. Mitchell McLaughlin, Daniel Cadol, and Jonathan Laronne

Use of seismic monitoring and data analysis techniques in recent years have allowed for improved understanding of several shallow earth processes, such as glacial motion, subsurface water flow, and bedload transport. Early applications using seismic data collected at high energy alpine rivers suggest that seismic energy within certain frequency bands is linked to bedload discharge.  However, study of other river systems have been more limited, even though some of these systems, such as ephemeral streams in arid environments, transport large quantities of sediment during short-lived flash flood events.  Here we present seismic and hydrologic data collected in a unique sediment observatory within an ephemeral tributary to the Rio Grande River, in the desert southwest of the U.S., combining dense seismic observations with a variety of in-channel bedload and water monitoring measurements. We have seismic records for more than a dozen floods ranging in depth from a few centimeters to over one meter, encompassing bedload flux as high as 12 kg s-1 m-1, two orders of magnitude higher than in most perennial settings. Our efforts to date focus on identifying the noise sources within the seismic record, characterization of the seismic properties of the site, and determining the seismic frequency ranges best correlated with the automatically measured bedload flux. Within the 30-80 Hz frequency range, we find a linear relationship between seismic power and bedload flux. We hypothesize that variations in linear fit statistics between flood events are due to varying bedload grain size distributions and in-channel morphological changes.

How to cite: Bilek, S., McLaughlin, J. M., Cadol, D., and Laronne, J.: Using Seismic Methods to Monitor Bedload Transport Along a Desert Environment Ephemeral Tributary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7727, https://doi.org/10.5194/egusphere-egu23-7727, 2023.

EGU23-8127 | ECS | Posters on site | GM2.2

Benford's law in detecting rapid mass movements with seismic signals 

Qi Zhou, Hui Tang, Jens M. Turowski, Jean Braun, Michael Dietze, Fabian Walter, Ci-Jian Yang, Sophie Lagarde, and Ahmed Abdelwahab

Rapid mass movements are a major threat in populated landscapes, as they can cause significant loss of life and damage civil infrastructure. Previous work has shown that using environmental seismology methods to monitor such mass movements and establish monitoring systems offers advantages over existing approaches. The first important step in developing an early warning system for rapid mass movements based on seismic signals is automatically detecting events of interest. Though the approach, such as short-term average to long-term average ratio (STA/LTA) and machine learning model, was introduced to detect events (e.g., debris flow and rockfall), it is still challenging to calibrate input parameters and migrate existing methods to other catchments. Detection of debris flows, for instance, is similar to anomaly detection if we consider the seismic stations recording background signals as an overwhelming majority condition. 
Benford's law describes the probability distribution of the first non-zero digits in numerical datasets, which provides a functional, computationally cheap approach to anomaly detection, such as fraud detection in financial data or earthquake detection in seismic signals. In this study, seismic signals generated by rapid mass movements were collected to check the agreement of the distribution of the first digit with Benford's law. Subsequently, we develop a computationally efficient and non-site-specific model to detect events based on Benford's law using debris flows from the Illgraben, a Swiss torrent, as an example. Our results show that seismic signals generated by high-energy mass movements, such as debris flows, landslides, and lahars, follow Benford's law, while those generated by rockfall and background signals do not. Furthermore, our detector performance in picking debris-flow events is comparable to a published random forest and seismic network-based approach. Our method can be applied at other sites to detect debris-flow events without additional calibration and offers the potential for real-time warnings.

How to cite: Zhou, Q., Tang, H., Turowski, J. M., Braun, J., Dietze, M., Walter, F., Yang, C.-J., Lagarde, S., and Abdelwahab, A.: Benford's law in detecting rapid mass movements with seismic signals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8127, https://doi.org/10.5194/egusphere-egu23-8127, 2023.

EGU23-8986 | ECS | Posters on site | GM2.2

Monitoring of an Alpine landslide using dense seismic observations: combining Distributed Acoustic Sensing and 1000 autonomous seismic nodes 

Tjeerd Kiers, Cédric Schmelzbach, Pascal Edme, Patrick Paitz, Florian Amann, Hansruedi Maurer, and Johan Robertsson

Landslides are a major natural hazard that can cause significant loss of life and property damage around the world. As global temperatures rise and weather extremes become more frequent, we can expect an increase in the hazard emanating from landslides too. In order to better understand and mitigate landslide risks, a variety of strategies have been developed to characterize and monitor landslide activity. Many established approaches provide valuable information about surface displacement and surface properties, but are not suited to inspect the subsurface parts of a landslide body. In contrast, seismic imaging and monitoring methods allow us to study subsurface structures, properties, and internal processes that control landslide behaviour.

In our project, we develop novel seismic data acquisition and interpretation approaches to characterize and monitor one of the largest active unstable slopes in the Alps, the Cuolm da Vi landslide, with an unprecedented spatial resolution. We achieve this by combining an array of over 1’000 seismic nodes with fiber-optic based monitoring techniques such as Distributed Acoustic (DAS) and Strain Sensing (DSS).

The deep-seated Cuolm da Vi landslide is located near Sedrun (Central Switzerland) and consists of approximately 100-200 million m3 of unstable rock reaching displacement rates up to 10-20 cm/yr with clear seasonal cycles. In summer 2022, we buried over 6 kilometres of fiber-optic cable in this alpine environment covering the most active part of the landslide with multiple cable orientations. Additionally, we deployed a nodal array of 1046 accelerometers in a hexagonal grid covering around 1km2 with a nominal spacing of 28 meters. Seismic data were acquired with the nodes and the DAS system continuously for four weeks. This time period included the blasting of 163 dynamite shots for calibration and active-source imaging purposes. In 2023, we plan to conduct data acquisition for longer periods using primarily fibre-optic based techniques with a focus on the temporal evolution of the landslide dynamics.

Our first goal is to resolve the internal structure of the landslide based on the controlled-source data acquired in summer 2022 to construct, for example, a seismic velocity model. Based on the models derived from the active-source seismic data, we plan to exploit the continuous seismic recordings of ambient vibrations and potential seismic signals produced by the landslide activity to complement structural models and study the landslide dynamics. We will present our current results and discuss their implications for the next steps towards monitoring this landslide over time.

How to cite: Kiers, T., Schmelzbach, C., Edme, P., Paitz, P., Amann, F., Maurer, H., and Robertsson, J.: Monitoring of an Alpine landslide using dense seismic observations: combining Distributed Acoustic Sensing and 1000 autonomous seismic nodes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8986, https://doi.org/10.5194/egusphere-egu23-8986, 2023.

EGU23-11404 | ECS | Posters on site | GM2.2

Rapid shredding of the subglacial sediment export signal by proglacial forefields 

Davide Mancini, Michael Dietze, Tom Müller, Matthew Jenkin, Floreana Marie Miesen, Matteo Roncoroni, Andrew Nicholas, and Stuart Nicholas Lane

Alpine glaciers have been rapidly retreating and at increasing rates in recent decades due to climate warming. As a consequence, large amounts of suspended- and bed-load flux are being released to proglacial environments, such as proglacial forefields. These regions are among the most unstable geomorphic systems of the Earth because they rapidly respond to changing discharge and sediment conditions. Given this, it might be hypothesized that their intense morphodynamic activity, being a complex and non-linear process, could “shred” the sediment transport signal itself, and especially that related to subglacial sediment export.

To date, our knowledge on subglacial sediment export by subglacial streams is essentially dominated by suspended sediment dynamics recorded in front of shrinking glaciers because of the limitations in measuring bedload transport. The latter is usually monitored far downstream from glacier termini by permanent stations (e.g. water intakes, geophone systems) leaving major uncertainties in the absolute amounts and temporal patterns of transport in both glacial and proglacial environments, as well as the relative importance compared to suspended sediment in case of morphodynamic filtering. Thus, the aim of this project was to investigate the evolution of the both suspended- and bedload subglacial export signals within the proglacial forefield to quantify the extent and the timescale over which proglacial morphodynamics filter them.

This work focuses on a large Alpine glacial forefield, almost 2 km in length, that has formed since the early 1980s at the Glacier d’Otemma (southern-western Swiss Alps, Valais). Data were collected over two entire melt seasons (June-September 2020 and 2021) experiencing different climatic conditions, the first year warm and relatively dry and the second cold and relatively wet. Suspended transport was recorded using conventional turbidity-suspended sediment concentration relationship, bedload transport was monitored seismically, while the morphodynamic filtering was determined using signal post-processing techniques. At present, there are no studies combining continuous measurements of both suspended- and bed-loads in such environments.

Results show that the signal of subglacial bedload export, unlike suspended load export, is rapidly shredded by proglacial stream morphodynamics, which we show is due to a particle-size dependent autogenic sorting of sediment transport at both daily and seasonal time-scales. The result is that over very short distances, the signal of subglacial bedload sediment export is lost and replaced by a signal dominated by morphodynamic reworking of the proglacial braidplain. The suspended signal is less impeded but significant floodplain storage and release of suspended sediment was observed. These results question the reliability of current inferences of glacial erosion rates from sediment transport rates often measured some way downstream of glacier margins.

How to cite: Mancini, D., Dietze, M., Müller, T., Jenkin, M., Miesen, F. M., Roncoroni, M., Nicholas, A., and Lane, S. N.: Rapid shredding of the subglacial sediment export signal by proglacial forefields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11404, https://doi.org/10.5194/egusphere-egu23-11404, 2023.

EGU23-12107 | ECS | Orals | GM2.2

Seismic Monitoring of Permafrost Dynamics at Mt. Zugspitze (German/Austrian Alps) 

Fabian Lindner, Krystyna Smolinski, Riccardo Scandroglio, Andreas Fichtner, and Joachim Wassermann

As observed elsewhere on a global scale, mountain permafrost at the Zugspitze (German/Austrian Alps) is degrading in response to climate change, which affects the rock slope stability and thus the hazard potential. Recent studies suggest that passive seismology is a promising and emerging tool to monitor permafrost changes as the seismic velocity of rocks strongly decreases/increases upon thawing/freezing. Compared to other, more classical methods like borehole temperature logging or electrical resistivity tomography (ERT), seismology is less laborious and costly, non-invasive and allows continuous monitoring. At Mt. Zugspitze, we exploit these advantages using a permanent seismic station (installed in 2006) as well as three small seismic arrays and Distributed Acoustic Sensing (DAS; both available since summer/fall 2021), to infer permafrost dynamics with high spatio-temporal resolution. The seismic data show repeating diurnal noise generated by the operation of cable cars, which we leverage for cross-correlation analysis. Our results suggest that the dominant signal in the retrieved seismic velocity change time series is caused by the seasonal freeze-thaw cycles associated with permafrost bodies on the northern side of the mountain ridge. On the long-term, the time series show a gradual velocity decrease associated with permafrost degradation due to atmospheric warming and compare well with modeled velocity change time series using rock temperature data from a nearby borehole, which intersects the mountain ridge. We discuss differences in our seismic analysis results obtained from direct and coda waves as well as from single station to station pairs and DAS and interpret the results in the light of other measurements including ERT, rock temperature logging and meteorological parameters.

How to cite: Lindner, F., Smolinski, K., Scandroglio, R., Fichtner, A., and Wassermann, J.: Seismic Monitoring of Permafrost Dynamics at Mt. Zugspitze (German/Austrian Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12107, https://doi.org/10.5194/egusphere-egu23-12107, 2023.

EGU23-12128 | Posters on site | GM2.2

Probing temporal variation of suspended load to bedload ratio using seismic saltation model 

Chao Ting Meng, Wei An Chao, and Yu Shiu Chen

Monitoring temporal and spatial changes in sediment volume in the upstream reservoir is one of the important indicators for evaluating the reservoir project life, especially the information carried by bedload and suspended load. According to field condition, direct bedload monitoring is often difficult. Thus, bedload usually can be estimated by a specific proportion of suspended load depended on the flooding magnitude, which can cause a large uncertainty in estimates of total sediment load. In recent years, riverine micro-seismic signals have been applied to study bedload transport. Our study chose the Da-Pu Dam (location: 23.296500°N, 120.644611°E), located at the upstream of the Zeng-Wen Reservoir and the junction of the Zeng-Wen river and Cao-Lan river, which is the last check dam before entering the reservoir area. Its upstream catchment area is 30,312 hectares that comprise approximately 63% of the Zeng-Wen Reservoir catchment area (48,100 hectares). The length of the monitoring section of the Da Pu Dam is 1,100 meters, with an average width of 121 meters and an average slope of 0.36 degrees. With the available data composed of riverbed cross-section survey, sediment particle size distribution, fluvial measurements (water depth, surface flow velocity), orthoimagery, and suspended load measurement, our study applies seismic saltation model to estimate the bedload flux and compares the results with the measured suspended load. Results showed that there are different ratios between bedload and suspended load under similar hydrological condition during the plum rain season(May-June) and typhoon period(July-September). In a case of flooding event considering the flow stage from medium to high discharge, significant temporal changes in the ratio between bedload and suspended load can also be observed, which imply a complex transition process between the bedload and suspension particles. The temporal changes in sediment ratio obtained in this study can be applied to estimate the total volume of sediment load entering the reservoir. Our estimated results are consistent with the survey of sediment accumulation at the end of each year in the reservoir area.

How to cite: Meng, C. T., Chao, W. A., and Chen, Y. S.: Probing temporal variation of suspended load to bedload ratio using seismic saltation model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12128, https://doi.org/10.5194/egusphere-egu23-12128, 2023.

EGU23-12687 | ECS | Orals | GM2.2

Surprising seismological signals during the October 2015 Skaftá jökulhlaup 

Thoralf Dietrich, Eva P.S. Eibl, Eyjólfur Magnússon, Daniel Binder, Sebastian Heimann, and Sigrid Roessner

Understanding the spatiotemporal details in the occurrence of jökulhlaups, also referred to as glacier lake outburst floods (GLOFs), is important for improving early warning and forecasting future events. Jökulhlaups occur in many different glacier-related settings and differ in their characteristics depending on the natural conditions: From very rapid floods (minutes-hours) originating from moraine dammed lakes in steep valleys to gradual floods (days-weeks) from subglacial lakes such as the ones beneath Vatnajökull ice cap, in Iceland. Previous studies of the October 2015 Skaftá jökulhlaup suggested that several hours of early-warning is possible based on the generated seismic tremor. Here, for the first time, we looked into all three spatial components of GNSS and seismic array data, respectively. Previous studies have already analysed the seismic events (icequakes, tremor, other migrating transient events) in detail, yet only on the z component. We reprocessed all three components of the seismic array data using frequency-wavenumber -analysis (fk-analysis) and match field processing (MFP). Both techniques allow to locate distant signal sources, either by direction only (fk) or actual location (MFP). We specifically focused on the time period when the tremor source is moving with the flood front and found two unexplained seismic signals:

  • A second migrating signal is visible on the lowermost part of the flood path 6 hours later than the passing of the first flood front.

    We compared this with a GNSS observations on top of the subglacial flood path and a hydrometric station 25 km downstream from the glacier margin in the affected Skaftá-river.

    After aligning the time series by the arrival of the pressure wave, the timing of the second seismic signal fits well with a 10 cm uplift of the glacier at the GNSS station; but also with a change in the rate of water level rise at the hydrometric station.

    We discuss this in the context of either explaining GNSS, hydrometric and seismological data individually or giving a hypothetical process that explains all three together. That could be a second intraglacial water lense draining, after the emptying of the lake deformed the overlaying glacier and connected the two water bodies. However, radio echo sounding survey over the source area in spring 2015 did not indicate a significant intraglacal water lense above the subglacial lake. The GNSS data may be cleared as noise artifact and the hydrometric data explained by flow of water out of the river course of Skaftá and onto porous lava fields between Sveinstindur, where the discharge of Skaftá is measured, and the glacier. Yet: The seismic signal then is left unexplained and open for discussion.

  • Finally, 18 hours after the first pulse, we found a sudden deceleration in horizontal motion on the GNSS that coincided with a sudden increase in seismic signals originating at the glacier terminus. We discuss if what we see is actually the glacier stopping, after losing the flood lubrication.

 

How to cite: Dietrich, T., Eibl, E. P. S., Magnússon, E., Binder, D., Heimann, S., and Roessner, S.: Surprising seismological signals during the October 2015 Skaftá jökulhlaup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12687, https://doi.org/10.5194/egusphere-egu23-12687, 2023.

EGU23-13269 | ECS | Posters on site | GM2.2

Denoising Cryoseismological Distributed Acoustic Sensing Data Using a Deep Neural Network 

Johanna Zitt, Patrick Paitz, Fabian Walter, and Josefine Umlauft

One major challenge in Environmental Seismology is that signals of interest are often buried within the high noise level emitted by a multitude of environmental processes. Those signals potentially stay unnoticed and thus, might not be analyzed further.

Distributed acoustic sensing (DAS) is an emerging technology for measuring strain rate data by using common fiber-optic cables in combination with an interrogation unit. This technology enables researchers to acquire seismic monitoring data on poorly accessible terrain with great spatial and temporal resolution. We utilized a DAS unit in a cryospheric environment on a temperate glacier. The data collection took place in July 2020 on Rhonegletscher, Switzerland, where a 9 km long fiber-optic cable was installed, covering the entire glacier from its accumulation to its ablation zone. During one month 17 TB of data were acquired. Due to the highly active and dynamic cryospheric environment, our collected DAS data are characterized by a low signal to noise ratio compared to classical point sensors. Therefore, new techniques are required to denoise the data efficiently and to unmask the signals of interest. 

Here we propose an autoencoder, which is a deep neural network, as a denoising tool for the analysis of our cryospheric seismic data. An autoencoder can potentially separate the incoherent noise (such as wind or water flow) from the temporally and spatially coherent signals of interest (e.g., stick-slip event or crevasse formation). We test this approach on the continuous microseismic Rhonegletscher DAS records. To investigate the autoencoder’s general suitability and performance, three different types of training data are tested: purely synthetic data, original data from on-site seismometers, and original data from the DAS recordings themselves. Finally, suitability, performance as well as advantages and disadvantages of the different types of training data are discussed.

How to cite: Zitt, J., Paitz, P., Walter, F., and Umlauft, J.: Denoising Cryoseismological Distributed Acoustic Sensing Data Using a Deep Neural Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13269, https://doi.org/10.5194/egusphere-egu23-13269, 2023.

EGU23-13334 | Posters on site | GM2.2

Ambient H/V sensitivity to the dynamics of glaciers and ice sheets 

Janneke van Ginkel, Fabian Walter, Ana Nap, Mauro Häusler, and Martin Lüthi

Climate change is causing major shifts in the dynamics of the cryosphere, leading to sea-level rise, glacier break-off events, flooding, and landslides. Geological, thermodynamic and hydraulic processes at the base of an ice mass play a central role in ice flow dynamics, and understanding these is imperative for predicting ice body behavior in a changing climate. To this end, sustained ambient vibrations in glaciated environments can be used to monitor subglacial conditions over significant spatial extent with relatively low-cost acquisition.

In earthquake seismology, a well-established methodology to investigate subsurface properties is the horizontal-to-vertical spectral ratio (H/V) of ambient seismic ground unrest. In cryoseismology, the H/V approach is already used to invert for velocity profiles of ice or firn, to obtain bedrock topography and to identify the presence of basal sediments. To date, only a few hours of seismic vibration records are typically used. Yet in such short time records, biases may arise because of the dynamic character of the glacier. Seismic resonances within the soft ice layer and resulting H/V ratios are expected to vary with changes in subglacial hydraulic conditions.

We propose to leverage temporal variations in H/V spectra to investigate subglacial processes. As a case study, we first focus on the Glacier de la Plaine Morte (Switzerland), where a seismic array was deployed for four months in summer of 2016. During this time, an ice-marginal lake formed and suddenly drained through and under the glacier, making this seismic record ideal for our purposes. This drainage event is well recorded and strongly influences the H/V in terms of amplitude and resonance frequency. We next present ambient H/V measurements of the Sermeq Kujalleq in Kangia (also known as Jakobshavn Isbræ), one of Greenland’s largest outlet glaciers. Here, the H/V spectra show multiple resonances over time, whose origin we discuss in more detail. For both our study cases, separating variations in source and medium properties is pivotal. Tackling this challenge provides glaciologists with a valuable tool to investigate the poorly accessible subglacial environment, which holds the key to our understanding of ice flow and eustatic sea level rise.

How to cite: van Ginkel, J., Walter, F., Nap, A., Häusler, M., and Lüthi, M.: Ambient H/V sensitivity to the dynamics of glaciers and ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13334, https://doi.org/10.5194/egusphere-egu23-13334, 2023.

EGU23-13383 | ECS | Posters on site | GM2.2

Using a record of bedload transport from Leverett glacier in western Greenland to understand proglacial sediment transport processes from the ice sheet   

Marjolein Gevers, Davide Mancini, Stuart Lane, and Ian Delaney

Increased glacier melt leads to a change in sediment transport capacity below glaciers, which impacts the sediment transport within proglacial areas as well as downstream ecosystems and geomorphology. Previous work on Alpine glaciers shows that strong diurnal discharge variations lead to fluctuations in sediment transport capacity such that deposition and erosion can occur in the proglacial area over the course of the melt season. However, the exact processes controlling sediment transport at the outlet glaciers of ice sheet margins and in their proglacial areas remain uncertain. Data suggest that the diurnal discharge variations are substantially reduced and baseflow discharge is much greater, likely capable of maintaining significant sediment transport throughout the melt season. This difference in the hydrological regime as compared with Alpine glacial systems may drive different rates and variations in sediment transport and, ultimately, in proglacial braid plain morphodynamics.

We measure proglacial sediment transport at Leverett glacier, a land-terminating glacier located at the western margin of the Greenland Ice Sheet. As bedload transport is exceptionally difficult to measure in situ, two seismic stations were installed to evaluate bedload transport in the glacial meltwater stream in the summer of 2022. The first station is located close to the current glacier terminus, and the second one is about 2 km from the current glacier terminus. These two stations allow for the examination of the sediment transport processes within the proglacial area. By using a Fluvial Inversion Model the recorded seismic data is converted into bedload flux. The model is calibrated using active seismic surveys and statistical approaches to evaluate the physical parameters. Outputs of the Fluvial Inversion Model are validated with available water stage data.  The results provide insight as to whether the proglacial area is aggrading or eroding as sediment transport in the two locations at Leverett glacier evolves over the summer season. We discuss the relationship between bedload transport and level of the proglacial river, as well as the seasonal variations in proglacial sediment transport and deposition in Leverett glacier’s proglacial area.

How to cite: Gevers, M., Mancini, D., Lane, S., and Delaney, I.: Using a record of bedload transport from Leverett glacier in western Greenland to understand proglacial sediment transport processes from the ice sheet  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13383, https://doi.org/10.5194/egusphere-egu23-13383, 2023.

EGU23-16008 | ECS | Orals | GM2.2

Short-term fast ice dynamics derived from passive seismic data at a large Greenland outlet glacier 

Ana Nap, Fabian Walter, Adrien Wehrlé, Andrea Kneib-Walter, Guillaume Jouvet, and Martin P. Lüthi

Outlet glaciers and ice streams are the main channels through which ice sheets transport their mass towards the ocean. One of Greenland’s largest outlet glaciers Sermeq Kujalleq in Kangia (Jakobshavn Isbrae) has been broadly researched after experiencing a rapid retreat of the terminus and accompanying speedup to up to 40 m/day in the early 2000’s. However, such short-term ice dynamic variations remain poorly understood making numerical models difficult to constrain and predictions on future sea-level rise uncertain.

The short-term ice dynamics of Sermeq Kujalleq consists in transient states and can only be captured by in-situ measurements of high spatial and temporal resolution. Glacier seismology has proven to be a valuable tool to study these dynamics, it provides data with a high temporal resolution and can provide information on processes happening below the ice surface. Within the COEBELI project we combine passive glacier seismology with global navigation satellite system (GNSS) receivers, long-range drones, time-lapse cameras and terrestrial radar interferometry to capture processes such as calving and basal sliding at their respective timescales.

Here, we present results from a multi-array seismic deployment at Sermeq Kujalleq in Summer 2022. From May until September two arrays were deployed in the upstream part of the fast-flowing ice stream (>22 km from calving front) and one array on slower moving ice North of the main trunk. For a 3-week period in July, four more arrays were deployed on the fast-flowing ice stream closer to the calving front (<15 km). In the severely crevassed areas near the calving front (<15 km), the arrays consisted of custom-made autonomous seismic boxes whereas at more accessible upstream areas we installed borehole instruments. During the deployment we recorded multiple large calving events, glacier speedups and periodic multi-hour tremors accompanied by bursts of short-term high frequency (>50 Hz) icequakes. By studying these different signals, we are able to better constrain the processes and forces that control fluctuating ice-flow velocity and calving events.

How to cite: Nap, A., Walter, F., Wehrlé, A., Kneib-Walter, A., Jouvet, G., and Lüthi, M. P.: Short-term fast ice dynamics derived from passive seismic data at a large Greenland outlet glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16008, https://doi.org/10.5194/egusphere-egu23-16008, 2023.

High-melt areas of glaciers generate a rich spectrum of ambient seismicity. These signals do not only contain information about the source mechanisms (e.g. englacial fracturing, water flow, iceberg detachment, basal stick-slip motion) but also carry information about seismic wave propagation within the glacier ice and, therefore, the mechanical properties of the ice. In the summer of 2021 two seismic arrays were deployed in Southern Spitsbergen at the vicinity of Hansbreen’s terminus, one being placed directly on the glacial ice, yielding an 8-days long time series of glacial seismicity.

The direct and scattered wave fields from tens of thousands of icequake records (few thousands per day) were used to determine seismic velocities and monitor structural changes within the ice, while the analysis of the ambient noise was leveraged to constrain the ice thickness. The surface icequakes dominate the seismograms due to an abundance of englacial fracturing. Hence, Rayleigh waves and beam-based techniques were employed to characterise the patterns of microseismicity at the transform junction of two glaciers (Tuvbreen and Hansbreen). Several clusters of various-origin seismicity being active at certain times are identified with a majority of them located on stagnant, fast-melting Tuvabreen.

How to cite: Gajek, W.: Rayleigh wave is the coolest – resolving microseismicity of a tidewater glacier in Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16346, https://doi.org/10.5194/egusphere-egu23-16346, 2023.

Glaciers or ice-streams have many common points with tectonic faults. Glaciers can move by

stable or unstable slip or by creep within the glacier thickness. Like faults, glacier sliding can

produce “icequake” signals over a huge range of frequencies, rupture length and signal

duration, as well as tremor. But because glaciers are shallower, the sliding interface can be

accessed directly much more easily, by boreholes or cavities. And they move much faster than

tectonic faults, so that deformation is easier to estimate and icequake inter-event times are

much shorter than for earthquakes.

Here I present some observations of high- and low-frequencies repeaters of basal icequakes

in the Mont-Blanc areas. Both types of events occur as bursts lasting for a few days or weeks,

with quasi-regularly inter-events times of the order of a few minutes or hours, and progressive

changes in amplitude and inter-event times. High-frequency events (around 50 Hz) occur all

over the year, with no clear triggering mechanism, and are located on the lower-part of

glaciers, where ice is at the melting point temperature and the glacier mainly moves by stable

sliding. Low frequency events (around 5 Hz) are mainly located at higher elevations (mainly

above 3000 m asl), on steeper slopes, and have larger magnitudes (-2<m<0). They are mainly

observed during or shortly after snowfalls. At these elevations, glaciers are possibly coldbased,

or close to the melting-point temperature, so that they are stuck to their bed and

mainly deform by creep within the ice. We observe progressive changes in waveforms that

suggest slow and evolving rupture velocities. These low-frequency icequakes may be the

analog of low-frequency earthquakes, which also occur near the transition between stable and

unstable slip.

How to cite: helmstetter, A.: Clusters of low- and high-frequency repeating icequakes in the Mont-Blanc massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16571, https://doi.org/10.5194/egusphere-egu23-16571, 2023.

EGU23-434 | Posters on site | GD1.3

Neogene Mantle Dynamics of Western Mediterranean Region Constrained by Basalt Geochemistry and Residual Depth Anomalies 

Chia-Yu Tien, Nicky White, John Maclennan, Benedict Conway-Jones, and Megan Holdt

There is considerable interest in combining a range of geophysical, geochemical and geomorphic observations with a view to estimating the amplitude, wavelength and depth of mantle thermal anomalies on a global bases. Here, we wish to explore how forward and inverse modelling of major, trace and rare earth elements can be exploited to determine melt fraction as a function of depth for a mantle peridotitic source. Our focus is on an area that includes the Iberian Peninsula where previous work shows that long-wavelength topography is probably generated and maintained by sub-plate thermal anomalies which are manifest by negative shear-wave velocities. Geological and geomorphic studies suggest that this dynamic support is a Neogene phenomenon. 48 newly acquired Neogene basaltic samples from Spain were analyzed and combined with previously published datasets. Both major element thermobarometry and rare earth element inverse modelling are applied to estimate melt fraction as a function of depth. In this way, asthenospheric potential temperature and lithospheric thickness can be gauged. These estimates are compared with those obtained from calibrated shear-wave tomographic models. Our results show that potential temperatures and lithospheric thicknesses are 1250-1300 °C and 65-70 km, respectively. These values broadly agree with calibrated tomographic models which yield values of 1300-1350 °C and 45-70 km. We conclude that a region encompassing Iberia is dynamically supported by a combination of warm asthenosphere and thinned lithosphere. This conclusion broadly agrees with independently obtained residual depth anomalies which indicate that the Western Mediterranean region probably has moderately positive dynamic support.

How to cite: Tien, C.-Y., White, N., Maclennan, J., Conway-Jones, B., and Holdt, M.: Neogene Mantle Dynamics of Western Mediterranean Region Constrained by Basalt Geochemistry and Residual Depth Anomalies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-434, https://doi.org/10.5194/egusphere-egu23-434, 2023.

EGU23-650 | ECS | Posters on site | GD1.3

Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations 

Aisling Dunn, Nicky White, Robert Larter, Simon Stephenson, and Megan Holdt

Transient mantle processes generate and maintain topographic variations which cannot be accounted for by crustal isostatic effects.  Accurately constraining the importance of dynamic topography across Antarctica will yield valuable insights into spatial and temporal patterns of mantle convection that inform studies of key boundary conditions for ice sheet models, such as heat flux and palaeotopography. Global studies largely neglect Antarctica because of complications associated with ice cover. In contrast, regional studies tend to oversimplify the problem by exploiting gridded datasets that ignore crustal density variations. Residual elevations, calculated by isolating and removing isostatic contributions to observed topography, enable the amplitude and wavelength of dynamic support to be gauged. Here, the results of analysing legacy (i.e. refraction) and modern (i.e. wide-angle) seismic experiments, onshore receiver functions, as well as a regional shear-wave crustal tomographic model are presented. In this way, a comprehensive suite of spot measurements (n = 195) across West Antarctica are calculated which, in conjunction with a recently augmented database of residual depths in the surrounding Southern Ocean (n = 1106), permit spatial variations of residual topography to be quantified. Positive residual anomalies (1 - 2 km) from the Transantarctic Mountains, Marie Byrd Land and the Antarctic Peninsula are consistent with regions of slow shear-wave velocity anomalies within the upper mantle, positive free-air gravity anomalies, and Cenozoic intraplate basaltic volcanism, indicating that topographic support is attributable to mantle convective processes. Lithospheric thicknesses derived from inverse modelling of basaltic rare-earth element concentrations show that elevated topography coincides with thinned lithosphere, further attesting to the relationship between positive residual elevation and mantle convective upwelling. Steepened geothermal gradients associated with regions of plate thinning have significant implications for the delivery of heat flux to the base of the West Antarctic Ice Sheet.

How to cite: Dunn, A., White, N., Larter, R., Stephenson, S., and Holdt, M.: Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-650, https://doi.org/10.5194/egusphere-egu23-650, 2023.

EGU23-773 | ECS | Orals | GD1.3

The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks 

Fabian Christopher Dremel, Jörg Robl, Bjarne Friedrichs, and Christoph von Hagke

Remnants of the Variscan mountain belt can be found today throughout North America, North Africa, Europe, and Asia, which are typically characterized by hilly to mountainous topography. Since the topography of the Variscan orogen was already levelled in the Permian by post-orogenic erosion and thermal subsidence, processes independent of Variscan convergent tectonics must be responsible for the observed high topography. Central Europe encompasses several landscapes showing extensive post Variscan relief rejuvenation, including from west to east the Massif Central, the Vosges Mountains and Black Forest, and the Bohemian Massif. However, despite their spatial proximity, the underlying processes that led to uplift and relief rejuvenation could not be more different. For the Massif Central, mantle plume activity has been proposed, while continental rifting has been held responsible for uplift of the Black Forest and Vosges Mountains. Uplift of the Bohemian Massif has been attributed to the forebulge of the Alpine orogeny, or slab dynamics in the eastern Alps, respectively.

The aim of this study is to investigate the relationship between different uplift scenarios, relief formation and the response of the drainage system to spatial and temporal variations in uplift rates, focusing on the Massif Central, Black Forest and Vosges as well as the Bohemian Massif. The spatial and temporal succession of uplift rates as well as denudation rates in response to post orogenic uplift will be analysed based on an extensive compilation of low-temperature thermochronological data. Geomorphological analyses include the plan view and profile geometry of river networks, i.e., normalised steepness indices, across divide χ gradients and river orientation.

Although the underlying processes are different, relief rejuvenation is a striking feature in these mountain ranges. Low relief surfaces at higher elevations contrast with lower reaches, with deeply incised rivers and migrating knickpoints indicating temporal variations in uplift rates over the last millions of years. Furthermore, the organisation of river networks varies within the mountain ranges, highlighting the influence of underlying processes on the evolution of drainage networks. The Massif Central shows a radial, star-shaped drainage pattern with rivers steepening towards the centre of the plume related uplift. The Upper Rhine Graben is dominated by rift flank retreat governing drainage divide migration. This is expressed by short, steep rivers draining into the graben and long, low gradient rivers on the side facing away from the rift valley. The Bohemian Massif features a bowl-shaped topography, with tributaries of the Moldau (Vltava) draining north. However, the southern side of the Bohemian Massif drains into the Danube in short tributaries with steep lower reaches. These analyses in combination with thermochronometry pave towards constraining timing and spatial extent of the rejuvenation signal. Ultimately, this will allow for making inferences on the underlying driving mechanisms.

How to cite: Dremel, F. C., Robl, J., Friedrichs, B., and von Hagke, C.: The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-773, https://doi.org/10.5194/egusphere-egu23-773, 2023.

EGU23-788 | ECS | Posters on site | GD1.3

Observed Dynamic Topography and Cenozoic Magmatism of the Eastern Seaboard of Australia 

Philippa Slay, Nicky White, Megan Holdt, and Simon Stephenson

Topography and bathymetry on Earth is both isostatically and dynamically supported. The isostatic signal is dominantly controlled by variations in the thickness and density of crust and lithospheric mantle. Therefore the challenge is to identify the dynamic component of topographic support, which is caused by sub-plate density anomalies arising from convective mantle processes. Here, we exploit an observationally-led approach to determine residual (i.e., dynamic) topography across the Australian continent and its margins. Compilations of receiver function analyses, wide-angle/refraction seismic surveys and deep seismic reflection profiles are used to determine both crustal velocity structure and depth to Moho. A published compilation of laboratory measurements is used to convert crustal velocity into density. In this way, residual topography is carefully isolated and combined with existing offshore measurements. Australia’s isolation from plate boundaries combined with rapid northward translation suggest that long-wavelength dynamic topography is controlled primarily by the interaction of sub-plate convection and plate motion. Large-scale positive dynamic topography occurs along the eastern seaboard, which coincides with slow shear-wave velocity anomalies, positive long-wavelength gravity anomalies and Cenozoic basaltic magmatism. Geochemical modelling of both age-progressive and age-indepedent basalts suggests that the eastern seaboard is underlain by positive asthenospheric temperature anomalies and dramatically thinned lithosphere. These inferences are consistent with calibrated tomographic models, which show that the lithosphere is 60 km thick. In general, the pattern of continental dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia.

How to cite: Slay, P., White, N., Holdt, M., and Stephenson, S.: Observed Dynamic Topography and Cenozoic Magmatism of the Eastern Seaboard of Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-788, https://doi.org/10.5194/egusphere-egu23-788, 2023.

EGU23-843 | ECS | Posters on site | GD1.3

Global Analysis of lithosphere-asthenosphere dynamics using a revised plate cooling model 

Megan Holdt, Nicky White, and Fred Richards

A global understanding of the evolution of oceanic lithosphere yields key insights about lithosphere-asthenosphere interaction. An important starting point is that age-depth and heatflow measurements provide the fundamental constraints for progressive cooling of oceanic lithosphere. When jointly inverting these measurements to identify an optimal plate model, the robustness of the result is predicated upon their quality, number and global distribution. Here, we exploit a revised and extensively augmented database of accurate age-depth measurements (n = 10,874) and a published database of heatflow measurements (n = 3,753). These databases are jointly modelled using both analytical and numerical methodologies to obtain a plate model, which has an average asthenospheric temperature of 1325±50oC and a lithospheric thickness of 105±10 km. These recovered values agree with independent geochemical and seismic constraints of mantle potential temperature and lithospheric thickness. This revised plate cooling model is used to improve our understanding of lithosphere-asthenosphere interaction.  First, we use plate cooling to measure residual depth anomalies, which are a reliable proxy for mantle dynamic topography. Our results demonstrate that dynamic topography varies on wavelengths as short as 1000 km with amplitudes of ±1 km. Secondly, we combine plate cooling with the depth distribution of oceanic intraplate earthquakes to identify the isothermal surface above which brittle elastic behaviour occurs. Finally, we demonstrate that age-depth and heatflow measurements exhibit a sustained flattening from ~60 Ma, suggesting that resupply of heat from the asthenosphere is an essential component of the lithosphere-asthenosphere system. Our database of accurate residual depth measurements is used to explore links between mantle dynamics, asthenospheric temperature anomalies extracted from earthquake tomographic models, and basaltic melting. 

How to cite: Holdt, M., White, N., and Richards, F.: Global Analysis of lithosphere-asthenosphere dynamics using a revised plate cooling model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-843, https://doi.org/10.5194/egusphere-egu23-843, 2023.

EGU23-1257 | ECS | Orals | GD1.3

Separation of signal components in global gravity models 

Betty Heller-Kaikov, Roland Pail, and Martin Werner

Vertical movements of the Earth’s surface represent mass displacements, which cause a temporal gravity signal that can be measured by dedicated satellite gravity missions such as the GRACE or GRACE-FO missions. Especially observations of vertical movements that are caused by mantle dynamic processes would enable to constrain numerical mantle convection models using geodetic data sets, thereby improving our understanding about the physical behavior of the Earth’s interior.

Using satellite gravity data to observe the above-mentioned vertical movements poses two main challenges:

First, the small amplitudes of the geoid trend signals induced by mantle dynamic signals require data accuracies and record lengths that will only be met by future satellite gravity missions. Indeed, it is known from previous simulation studies that temporal gravity signals produced by mantle convection will be detectible in future double-pair satellite gravity missions such as the planned Mass Change and Geoscience International Constellation (MAGIC).

The second challenge to make use of gravity data sets for constraining geophysical mantle models is the extraction of the signal of interest from the total gravity signal. While temporal gravity data sets include the cumulative mass displacement signal, the problem of how to separate the superimposed signals produced by phenomena in the hydrosphere, cryosphere, atmosphere, oceans and solid Earth is still unsolved.

In this contribution, using the gravity signals given by the updated ESA Earth System Model, we address the task of signal separation in temporal gravity data and present two approaches for it. To this end, the knowledge of the spatial and temporal characteristics of the individual signal components is exploited by applying principal component analysis as well as a machine learning approach.

How to cite: Heller-Kaikov, B., Pail, R., and Werner, M.: Separation of signal components in global gravity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1257, https://doi.org/10.5194/egusphere-egu23-1257, 2023.

How the surface plates link to mantle slabs is fundamental for paleo-tectonic reconstructions and has implications on mantle dynamics. Assuming a simplified, vertical sinking slab, many tomography-based studies have vertically projected the surface features into the mantle, arguing for the tectonic explanations of mantle structures or vice versa. In contrast, geodynamic models continue to suggest that slabs can be laterally transported by a few hundred kilometers up to ~6000 km near the core-mantle boundary. The dynamics of mantle slabs remain controversial.

The Caribbean mantle has recently been suggested for vertical slab sinking. However, a vertically sinking slab at a near-stationary eastern Caribbean trench would require slab buckling in the mantle, because at least 1,200 km subduction needs to be accommodated within the upper 660 km mantle. Yet, mantle tomographies show expected (~100 km) slab thickness with limited slab thickening or buckling. With no need for a priori assumption on mantle dynamics, here, we used a slab-unfolding approach to restore and re-interpret the slab structures of the Lesser Antilles slab underneath the Caribbean. Our results show that the slab structure can be alternatively explained with limited intra-plate deformation if the slab was transported northwestward by ~900 km after subduction. Such lateral transportation in the mantle is possibly due to the physical connection with the North American plate, whose northwestward motion since the Eocene has been dragging the slab toward the same direction. We also provided our tectonic explanations on the edges and gaps of the slabs, supporting previous work that pre-existing weak zones and plate boundaries determine the fragmentation of the Lesser Antilles slab. The slab unfolding approach used in this study has the potential to be applied to other subduction zones, with no need for a priori assumption on mantle dynamics (i.e., vertical slab sinking) for future tomography-based analysis.

How to cite: Chen, Y.-W. and Wu, J.: Lesser Antilles slab reconstruction suggests significant northwestwards lateral slab transportation underneath the Caribbean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1352, https://doi.org/10.5194/egusphere-egu23-1352, 2023.

EGU23-1983 | ECS | Posters on site | GD1.3

Cenozoic history of North Atlantic surface motions: Implications for asthenosphere flow processes 

Zhirui Ray Wang, Giampiero Iaffaldano, and John Hopper

Mantle convection is a fundamental process that shapes Earth’s surface, as it provides driving and resisting forces for horizontal motions of tectonic plates, as well as for inducing non-isostatic vertical motion --- commonly termed “dynamic topography”. Growing geologic constraints of past plate motion variations and dynamic topography have led to better understanding of the history of mantle flow induced surface expression. Ultimately, the existence of a thin, mechanically weak asthenosphere allows geodynamicists to link such observables to mantle flow properties in the context of Couette/Poiseuille flow. Here we utilize publicly available geological and geophysical data sets to study Cenozoic plate kinematic changes and the spatial-temporal evolution of dynamic topography in the North Atlantic region. We employ quantitative, analytical Couette/Poiseuille flow models to link the inferred surface motion history to asthenosphere flow properties underneath. Our efforts aim at disentangling the role of asthenospheric channelized flow in influencing the Cenozoic surface expression of North Atlantic region.

How to cite: Wang, Z. R., Iaffaldano, G., and Hopper, J.: Cenozoic history of North Atlantic surface motions: Implications for asthenosphere flow processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1983, https://doi.org/10.5194/egusphere-egu23-1983, 2023.

EGU23-2575 | ECS | Orals | GD1.3

Pressure-driven upper-mantle flow in the Indo-Atlantic Realm since the Upper Jurassic inferred from continent-scale hiatus surfaces and oceanic spreading rate variations 

Berta Vilacís, Jorge N. Hayek, Ingo L. Stotz, Hans-Peter Bunge, Anke M. Friedrich, Sara Carena, and Stuart R. Clark

Mantle convection is a fundamental process responsible for shaping the tectonic evolution of the Earth. It is commonly perceived that mantle convection is difficult to constrain directly. However, it affects the horizontal and vertical motion of the lithosphere. The former is observed in the spreading rates, while the latter leaves various imprints in the geological record. In particular, the positive surface deflections driven by mantle convection create erosional/non-depositional environments, which induce gaps (hiatus) in the stratigraphic record (i.e., an absence or thinning of a sedimentary layer). Modern digital geological maps allow us to map long-wavelength no-/hiatus surfaces at continental scale systematically.

Here we compare our continent-scale hiatus mapping to plate motion variations in the Atlantic and Indo-Australian realms from the Upper Jurassic onward. In general, we find the datasets correlate except when plate boundary forces may play a significant role. There is a timescale on the order of a geologic series, ten to a few tens of millions of years (Myrs), between the occurrence of continent-scale hiatus and plate motion changes. This is consistent with the presence of a weak upper mantle. Furthermore, we find significant differences in the spatial extent of hiatus patterns across and between continents, which means they cannot simply be explained by eustatic variations but should be linked to variations in the upper-mantle flow.

Our results highlight the importance of geological datasets to map the temporal evolution of geodynamic processes in the deep Earth. Also, they imply that different timescales for convection and topography in convective support must be an integral component of time-dependent geodynamic Earth models. Studies of horizontal and vertical motion of the lithosphere to track past mantle flow would provide powerful constraints for adjoint-based geodynamic inverse models of past mantle convection.

How to cite: Vilacís, B., Hayek, J. N., Stotz, I. L., Bunge, H.-P., Friedrich, A. M., Carena, S., and Clark, S. R.: Pressure-driven upper-mantle flow in the Indo-Atlantic Realm since the Upper Jurassic inferred from continent-scale hiatus surfaces and oceanic spreading rate variations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2575, https://doi.org/10.5194/egusphere-egu23-2575, 2023.

It is generally accepted that East Asian mantle dynamics has been dominated by subduction and downwelling since Mesozoic times (e.g. Müller et al. (2016)). However, seemingly in contrast to this history, a variety of observations indicate a presence of anomalously hot asthenospheric material beneath East Asia during the late Cenozoic. First of all, tomographic models consistently reveal an extensive network of seismically slow anomalies at asthenospheric depths, which align spatially with a recent (< 30 Ma) phase of intraplate volcanism. The influence of this positively buoyant material at the surface is further highlighted by induced dynamic uplift, which is recorded in the geological record through an inter-regional sedimentary hiatus during the late Eocene—Oligocene. Residual topography studies additionally find swells of dynamic uplift throughout this region in the present day. Global mantle circulation models (MCMs) show that these observations can be reproduced in a subduction-dominated region by the spillover of anomalously hot asthenospheric material from the adjacent Pacific domain during ridge subduction events. In particular, the subduction of the Izanagi-Pacific ridge at ~55 Ma provides a large window through which Pacific asthenosphere could have flowed into East Asia. We test this hypothesis by comparing these MCMs to a variety of geological observations, including the distribution of sedimentary hiatus and intraplate volcanism during the late Cenozoic. We additionally compare the present-day distribution of hot material predicted by these models with the recently published full waveform inversion tomographic model of the region, Sinoscope 1.0, which highlights the distribution of seismically slow anomalies beneath the region. We find an encouraging match between asthenospheric flow predicted by these models and the observations considered, showing this to be a viable new hypothesis in explaining these observations. The mechanism of hot asthenospheric build-up during subduction and release during slab window opening may not be limited to East Asia, and could reconcile observations of intraplate volcanism and dynamic uplift in convergent regions more generally. 

How to cite: Brown, H., Ma, J., Colli, L., and Bunge, H.-P.: The influence of slab window asthenospheric flow on intraplate volcanism, dynamic uplift, and present-day mantle heterogeneity in East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3213, https://doi.org/10.5194/egusphere-egu23-3213, 2023.

Geological maps contain a large amount of information that can be used to constrain geodynamic models, but which has been often overlooked by the geodynamic community. Particularly significant are unconformable geologic contacts at continental scales: what is usually perceived as a lack of data (material eroded or not deposited) becomes instead part of the signal of dynamic topography.

We were able to use geological maps to constrain the dynamic processes in the mantle beneath Africa by understanding its Cenozoic elevation history, and by using it to distinguish between different uplift and subsidence scenarios. This was accomplished by mapping the spatio-temporal patterns of geological contacts at the series level using continental-scale geological maps, under the assumption that continental-scale unconformable contacts are proxies for vertical motions and for paleotopography. We also mapped the present-day elevation of marine sediments for each series.

We found that significant differences exist in interregional hiatus surfaces. For example, the total unconformable area at the base of the Miocene expands significantly compared to the base of the Oligocene, strongly suggesting that most of Africa underwent uplift in the Oligocene. In southern Africa there are no marine Oligocene or Pleistocene sediments, suggesting that this region reached a high in the Oligocene, subsided in the Miocene and Pliocene, and has been high again since late Pliocene to Pleistocene. More generally, to reproduce the pattern of marine sedimentation in Africa that we mapped, sea level increases between 300 and at least 500 m above present level would be required. These are well in excess of the maximum 150 m eustatic sea level rise that has been postulated by several authors for the Cenozoic. Our results therefore support a dynamic origin for the topography of Africa. Specifically, the time-scale of geologic series (at most a few tens of millions of years) is comparable to the spreading-rate variations in the south Atlantic, which have been linked to African elevation changes through pressure-driven upper mantle flow.

How to cite: Carena, S., Friedrich, A., and Bunge, H.-P.: Geological hiatus surfaces across Africa in the Cenozoic: implications for the timescales of convectively-maintained topography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3508, https://doi.org/10.5194/egusphere-egu23-3508, 2023.

It is well known that increasing pressure and temperature along upper-mantle geotherms combine to produce a zone of low seismic wave speeds. Beyond such behaviour arising from the anharmonicity of the crystal lattices of the constituent minerals, viscoelastic relaxation may result in further reduction of the wave speeds, along with appreciable attenuation of seismic waves. In order to better constrain such sub-solidus relaxation in olivine-dominated lithologies, we have recently prepared and tested in torsional forced oscillation several new specimens of synthetic polycrystalline olivine (Fo90 olivine buffered by ~5 wt% En90). These specimens were prepared by hot pressing sol-gel precursor powder encapsulated within metal foils (of Ni70Fe30 or Pt) at high temperature (1200-1350ºC) and pressure (300 MPa). Enclosure within Ni-Fe foil yields relatively reducing anhydrous conditions and average grains sizes d ≤ 5 μm. The more oxidising and hydrous conditions associated with Pt encapsulation are conducive to grain growth to at least 20 μm. Our forced-oscillation methods have been refined by replacement of the polycrystalline alumina control specimen with single-crystal sapphire, discontinuation of the use of Ni-Fe foils at the ends of the specimens in favour of direct contact with alumina torsion rods, and selective use of austenitic stainless steel as an alternative to the usual mild-steel material for the enclosing jacket. Such testing of fine-grained olivine polycrystals at periods of 1-1000 s and shear strain amplitudes < 10-5 has consistently revealed an essentially monotonically period- and temperature-dependent high-temperature background. The onset of high-temperature anelastic relaxation involves a superimposed dissipation peak of only modest amplitude plausibly attributed to elastically accommodated grain-boundary sliding. Grain-size sensitivity is incorporated into a Burgers type creep-function model fitted to the (G,Q-1) data for multiple specimens through power-law grain size dependencies of the key characteristic times. The Maxwell time τM, varying as d-mV, defines the transition from anelastic to viscous background behaviour, and τP ~ d-mA, the centre of the distribution of relaxation times for the dissipation peak. The data for the newly prepared pure synthetic specimens of 4-22 mm grain size, tested with the refined experimental methodology, require mV ~ 3 and mA < 1.5. These inferences are consistent with micromechanical models for grain-boundary sliding, but yield markedly stronger grain-size sensitivity than previously reported. However, mapping of the tested samples by electron back-scattered diffraction indicates that the density of geometrically necessary dislocations, responsible for lattice curvature, decreases systematically with increasing grain size, raising the possibility that any contribution from dislocation damping might enhance the apparent grain-size sensitivity. A preliminary extrapolation of the new model for grain-size sensitive viscoelastic relaxation in dry, melt-free dunite to upper-mantle conditions of grain size and pressure suggests shear modulus relaxation < 2% and dissipation Q-1 < 0.01 – thus unable to account for seismological observations of the mantle beneath young oceanic lithosphere and in subduction zones. Uncertainties in such extrapolation will be discussed, along with other factors that might enhance sub-solidus viscoelastic relaxation including the segregation of trace-element impurities to olivine grain boundaries, and the influence of oxygen and water fugacities. 

How to cite: Jackson, I., Qu, T., and Faul, U.: Seismic wave dispersion and attenuation within the asthenosphere: the role of sub-solidus viscoelastic relaxation revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4014, https://doi.org/10.5194/egusphere-egu23-4014, 2023.

EGU23-4053 | Orals | GD1.3 | Highlight

Influence of the Asthenosphere on Earth Dynamics and Evolution 

Mark Richards, Lawrence Cathles, Willy Fjeldskaar, Adrian Lenardic, Barbara Romanowicz, and Johnny Seales

The existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth, including the apparently early onset and persistence of plate tectonics, may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.

How to cite: Richards, M., Cathles, L., Fjeldskaar, W., Lenardic, A., Romanowicz, B., and Seales, J.: Influence of the Asthenosphere on Earth Dynamics and Evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4053, https://doi.org/10.5194/egusphere-egu23-4053, 2023.

EGU23-4232 | Orals | GD1.3

Geophysical modelling of vertical motion processes constrained by geodetic and geological observations (UPLIFT) 

Hans-Peter Bunge, Yi-Wei Chen, Anke Friedrich, and Roland Pail and the UPLIFT Team

Vertical motion of the Earth’s lithosphere (uplift) occurs on different spatial and temporal scales. Commonly assumed to be primarily related to plate tectonic mechanisms and isostatic adjustment, it has become clear that mantle related forcing and in particular mantle plumes are a significant contributor to uplift events in many regions of the world, making vertical motions a powerful probe into sublithospheric processes. Significant improvements of observational methods (e.g. satellite missions) and publicly-accessible databases (e.g. digital geological maps) make it now feasible to map vertical motions from geodetic to geologic time scales. This in turn provides invaluable constraints to inform key, yet uncertain, parameters (e.g. rheology) of geodynamic models. Such models also contribute powerful insight into complex landscape evolution processes at interregional to continental scales. Here we report on a new (starting date April 2022) Research Training Group (RTG) 2698, with 10 individual dissertation projects and a Post-doc project, funded by the German Research Foundation. An interdisciplinary approach of Geodynamics, Geodesy and Geology aims to answer questions related to how the interaction of exo- and endogenic forcing shapes a diverse array of earth processes from landscape evolution to the occurrence of earthquakes. The RTG uses a combined interpretation of interdisciplinary observations with different spatial and temporal sensitivity, in conjunction with physical models, to disentangle different uplift mechanisms, including the plume, plate and isostatic mode, based on their specific spatial and temporal patterns. We will give an overview on the key philosophy and main architecture of the RTG. Core components include an integrated geophysical process model, composed of an adjoint geodynamic model that accounts for seismic tomography and mineralogy, coupled with a landscape evolution model, with the lithosphere as a filter function, and targeted observations that include geodetic (geometric and gravimetry) data to reflect contemporary uplift processes combined with high precision, geological, magnetostratigraphic and geomorphologic data to reflect uplift processes and sedimentation rates on geological time scales. The modeling will be complemented by a thorough uncertainty analysis and an enhanced visualization of the key results.

How to cite: Bunge, H.-P., Chen, Y.-W., Friedrich, A., and Pail, R. and the UPLIFT Team: Geophysical modelling of vertical motion processes constrained by geodetic and geological observations (UPLIFT), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4232, https://doi.org/10.5194/egusphere-egu23-4232, 2023.

EGU23-4286 | ECS | Orals | GD1.3 | Highlight

Meteorological Tools for Assessing Mantle Flow-related Dynamic Topography Maps 

Ayodeji Taiwo, Hans-Peter Bunge, and George Craig

Construction of robust mantle flow trajectories plays an important role in understanding the parameters that govern mantle convection and relating them to geologic observables. In the past, the assessment of constructed trajectories focused majorly on metrics targeted at the mantle volume whilst neglecting the surface manifestations of mantle convection in the form of dynamic topography. However, an increasing amount of interest is being built around linking convection to surface effects, including dynamic topography. As such, it is vital to study ways in which mantle flow trajectories can be assessed via their dynamic topography predictions. Commonly used assessment and comparison metrics such as root-mean-square errors, suffer from the so-called double penalty problem --- a dynamic topography prediction that does not match a reference observation one-to-one is penalized twice: first as a miss and second as a false alarm. It is therefore attractive to investigate metrics that overcome this problem. Here, we introduce an object-based approach, first applied in meteorology, and show that this approach is not only amenable to studying dynamic topography, but that it also overcomes the double penalty problem whilst providing accurate model assessment.

How to cite: Taiwo, A., Bunge, H.-P., and Craig, G.: Meteorological Tools for Assessing Mantle Flow-related Dynamic Topography Maps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4286, https://doi.org/10.5194/egusphere-egu23-4286, 2023.

EGU23-4326 | ECS | Posters on site | GD1.3

TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing 

Eugenio D'Ascoli, Hamish Brown, Nils Kohl, Marcus Mohr, and Hans-Peter Bunge

Simulating the Earth’s mantle convection at full convective vigor on planetary scales is a fundamental challenge in Geodynamics even for state of the art high- performance computing (HPC) systems. Realistic Earth mantle convection simulations can contribute a decisive link between uncertain input parameters, such as rheology, and testable preconditions, such as dynamic topography. The vertical deflections predicted by such models may then be tested against the geological record. Considering realistic Earth-like Rayleigh numbers (∼ 108) a resolution of the thermal boundary layer on the order of ∼ 10 km is necessary considering the volume of the Earth’s mantle. Simulating Earth’s mantle convection at this level of accuracy requires solving sparse indefinite systems with more than a trillion degrees of freedom, computational feasible on exascale HPC systems. This can only be achieved by mantle convection codes providing high degrees of parallelism and scalability. Earlier approaches from applying a prototype framework using hierarchical hybrid grids (HHG) as solvers for such systems demonstrated the scalability of the underlying concept for future generations of exascale computing systems. In consideration of the TerraNeo project, here we report on the progress of utilizing the improved framework HyTeG (Hybrid Tetrahedral Grids) based on matrix-free multigrid solvers in combination with highly efficient parallelization and scalability. This will allow to solve systems with more than a trillion degrees of freedom on present and future generations of exascale computing systems. We also report on the advances in developing the scalable mantle convection code TerraNeo using the HyTeG framework to realise extreme-scale mantle convection simulations with a resolution on the order of ∼ 1 km.

How to cite: D'Ascoli, E., Brown, H., Kohl, N., Mohr, M., and Bunge, H.-P.: TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4326, https://doi.org/10.5194/egusphere-egu23-4326, 2023.

EGU23-5023 | ECS | Posters on site | GD1.3

A theory for mega-dyke propagation as driven by hotspot topography. 

Timothy Davis and Richard Katz

How can mega-dykes propagate hundreds of kilometres laterally through the crust? These blade-shaped dykes are enormous geological structures characterised by widths up to 100 metres. Ernst and Baragar (1992) showed that mega-dykes propagate away from a point at the centre of the dyke swarm. The magma for such dykes is believed to originate from a hotspot impinging on the base of the lithosphere, and this process typically precedes rifting events (Ernst, 2001; Srivastava et al., 2019). Current models do not adequately explain the mechanisms driving the propagation and termination of mega-dykes. We hypothesise that mega-dyke propagation is driven by the gradient in gravitational potential energy associated with the topography of a hotspot swell.

We present an analytical model linking the length of mega-dykes to the dimensions of a topographic swell above a hotspot. Our model accounts for various energy sources, including magma-source pressure and gravitational potential energy, and energy sinks such as viscous dissipation, elastic wall-rock deformation, and fracturing at the dyke tip. We define the ground surface deformation above a hotspot using an analytical model (Morgan, 1965) and demonstrate, in this context, that the dyke width scales with distance from the magma source. The final dyke length is computed by finding the point at which the sum of energy sources becomes less than the energy sinks. Furthermore, we explore the trade-offs between parameters controlling the swell size and the final length of a mega-dyke. We tentatively apply our findings to observed mega-dyke swarms and investigate the hot-spot sizes required to produce the observed lengths of these structures.

References

Ernst, R.E. and Baragar, W.R.A., 1992. Evidence from magnetic fabric for the flow pattern of magma in the Mackenzie giant radiating dyke swarm. Nature, 356(6369), pp.511-513. doi:10.1038/356511a0

Ernst, R.E., 2001. The use of mafic dike swarms in identifying and locating mantle plumes. Geological Society of America Special Papers, 352, p.247-265. doi:10.1130/0-8137-2352-3.247

Morgan, W.J., 1965. Gravity anomalies and convection currents: 1. A sphere and cylinder sinking beneath the surface of a viscous fluid. Journal of Geophysical Research, 70(24), pp.6175-6187. doi:10.1029/JZ070i024p06175

Srivastava, R.K., Ernst, R.E. and Peng, P. eds., 2019. Dyke swarms of the world: A modern perspective. Springer Geology. doi:10.1007/978-981-13-1666-1

How to cite: Davis, T. and Katz, R.: A theory for mega-dyke propagation as driven by hotspot topography., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5023, https://doi.org/10.5194/egusphere-egu23-5023, 2023.

EGU23-5621 | Orals | GD1.3

How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia 

Peter Japsen, Paul F. Green, Johan M. Bonow, James A. Chalmers, Ian R. Duddy, and Ilmo Kukkonen

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides limited documentation of the post-Caledonian history. But a more complete understanding can be obtained by also considering evidence of rocks that were formerly present but have since been removed (‘missing section’).

We report apatite fission-track data and associated thermal history constraints in 331 samples of Precambrian basement, Phanerozoic sediments and igneous rocks from outcrops and boreholes (up to 6 km depth) from Norway, Sweden and Finland, which define multiple episodes of cooling over the last billion years.

We are therefore able to establish a post-Caledonian history of Fennoscandia involving repeated episodes of kilometer-scale burial and exhumation with key episodes of exhumation beginning during late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene. The effects of these episodes are documented in the stratigraphic record and as prominent peneplains. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasizing the tectonic nature of the history.

Results from Finland record events also recognized in Norway and Sweden (though less pronounced) and are thus not consistent with long-term cratonic stability. We interpret the lack of preserved Phanerozoic sedimentary cover in Finland to be due to complete removal during multiple episodes of denudation. For example, our results show that about 2 km of Cambrian to Middle Triassic sediments covered the Sub-Cambrian Peneplain in southern Finland prior to the onset of Middle Triassic exhumation. In southern Scandinavia, Miocene exhumation led to formation of a peneplain which in Pliocene times was uplifted and dissected, producing the modern landscape, also by exhuming older peneplains from below their protective cover rocks.

The Carboniferous to Cretaceous exhumation episodes affected Fennoscandia as well as East Greenland, however, post-breakup episodes affected the conjugate margins of the NE Atlantic differently. Whereas Neogene uplift began in the early Miocene in Fennoscandia, it began in the late Miocene in Greenland. Pliocene uplift affected both margins at about the same time. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.

 

References

Bonow & Japsen, 2021, Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic. GEUS Bulletin.

Green et al., 2022a, Episodic kilometre-scale burial and exhumation and the importance of missing section. Earth-Science Reviews.

Green et al., 2022b, The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research.

Japsen & Chalmers, 2022, The Norwegian mountains: the result of multiple episodes of uplift and subsidence. Geology Today. https://doi.org/10.1111/gto.12377

Japsen et al., 2018, Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London.

Japsen et al., 2021, Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic. GEUS Bulletin.

Lidmar-Bergström et al., 2013, Stratigraphic landscape analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence. Global and Planetary Change.

How to cite: Japsen, P., Green, P. F., Bonow, J. M., Chalmers, J. A., Duddy, I. R., and Kukkonen, I.: How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5621, https://doi.org/10.5194/egusphere-egu23-5621, 2023.

EGU23-6676 | ECS | Orals | GD1.3

Ray-theoretical and finite-frequency seismic traveltime predictions for tomographic filtering of 3D mantle circulation models 

Roman Freissler, Bernhard S.A. Schuberth, and Christophe Zaroli

Linking geodynamic models to observations from seismology is essential for improving our understanding of the present-day thermodynamic state of the mantle. From the geodynamic perspective, 3D mantle circulation models (MCMs) yield physically relevant predictions of the global distribution of buoyancy forces, while complementing information is available from seismic data and tomography that can reveal the location and morphology of mantle heterogeneity. Investigating this powerful interplay in a fully synthetic framework has great potential. It allows us to make robust interpretations of mantle structure provided that quantitatively meaningful comparisons can be made. This especially relates to the magnitudes of heterogeneity that can not be effectively constrained by the individual modelling approaches.

Following this general concept, there are two possible links: 1) synthetic seismic data can be predicted from the MCM and statistically be compared against observed data. 2) the MCM gets modified by a tomographic operator (informing us about spatially variable seismic resolution and, if applicable, model uncertainty), and subsequently this filtered version gets compared against the corresponding tomographic image from real observations.

Here, we discuss these two strategies together based on observed data for S-wave cross-correlation traveltime residuals that have been applied to global seismic tomography. Taking the same set of source-receiver configurations, synthetic traveltime predictions are computed in a state-of-the-art MCM using ray theory (RT), paraxial finite-frequency kernels (FFK), as well as cross-correlation measurements on synthetic seismograms (SPECFEM). The latter requires computationally demanding 3D-wavefield simulations using SPECFEM3D_GLOBE for an earthquake catalog comprising over 4,200 teleseismic events.

These data sets can be used for tomographic filtering by application of the generalized inverse operator of the actual tomographic model. Filtered MCMs derived from the differently predicted data sets appear largely similar on a global scale with regards to the shape and amplitudes of imaged mantle heterogeneity. This is observed despite the lack of more accurate wave physics in RT or FFK and possible measurement errors for the SPECFEM data that, although being computed in a synthetic case, can not be completely ruled out. Stronger differences between filtered models appear in regions of higher image resolution where model uncertainty by propagated data errors can play a more prominent role.

We discuss the impact of the different filtering strategies by comparing filtered models to the original MCM and synthetic traveltime residuals to the underlying real observations. The results strongly highlight the need for incorporating both resolution and model uncertainty in combined tomographic-geodynamic studies.

How to cite: Freissler, R., Schuberth, B. S. A., and Zaroli, C.: Ray-theoretical and finite-frequency seismic traveltime predictions for tomographic filtering of 3D mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6676, https://doi.org/10.5194/egusphere-egu23-6676, 2023.

EGU23-7226 | ECS | Posters on site | GD1.3

The effect of asthenosphere’s rheology on mantle and surface tectonics : the role of composite rheology 

Maelis Arnould, Tobias Rolf, and Antonio Manjón-Cabeza Córdoba

Earth’s upper mantle rheology controls lithosphere-asthenosphere coupling and thus its surface tectonics. Although rock deformation experiments and seismic anisotropy measurements indicate that dislocation creep can occur in the Earth's uppermost mantle, the role of composite rheology (including both diffusion and dislocation creep) on global-scale mantle dynamics and surface tectonics remains largely unexplored.

Here, we investigate the influence of composite rheology on the planform of convection and on the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection with plate-like tectonics. We show that the consideration of composite rheology in the upper mantle leads to the self-generation of a discontinuous asthenosphere evolving fast, with a low-viscosity and a maximal thickness that depend on the rheological parameters for diffusion and dislocation creep. In mobile-lid models, the spatio-temporal evolution of the asthenosphere is mainly controlled by the location of slabs and plumes that generate regions of mantle deforming dominantly through dislocation creep. Moreover, the low upper-mantle viscosities caused by composite rheology produce substantial and contrasting effects on surface dynamics. For a strong lithosphere (high yield stress), the large lithosphere-asthenosphere viscosity contrasts promote stagnant-lid convection, while the increase of upper-mantle convective vigor enhances plate mobility for low lithospheric strength (small yield stress). We further show that composite rheology does not facilitate the onset of plate-like behavior at large lithospheric strength due to decoupling between the asthenosphere and the lithosphere.

How to cite: Arnould, M., Rolf, T., and Manjón-Cabeza Córdoba, A.: The effect of asthenosphere’s rheology on mantle and surface tectonics : the role of composite rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7226, https://doi.org/10.5194/egusphere-egu23-7226, 2023.

EGU23-8412 | Orals | GD1.3

Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence From Seismic Tomography And Integrated Geophysical-Petrological Thermochemical Modelling 

Amr El-Sharkawy, Thor H. Hansteen, Carlos Clemente-Gomez, Javier Fullea, Sergei Lebedev, and Thomas Meier

During the Cenozoic, the Circum-Mediterranean has experienced extensive and widespread igneous magmatism (i.e. intraplate, subduction-related and mixed-origin) that reflects the response of the upper mantle to the geodynamic evolution of this area. The exact origin of the volcanic activities and its relation to the underlying thin lithosphere especially in the continental regions have been long-lasting debated. We investigate the structure of the lithosphere and the sub-lithospheric mantle in the Circum-Mediterranean using regional high-resolution 3-D surface wave tomography and integrated geophysical-petrological thermochemical modelling of the temperature field and explore the relation to the occurrence intraplate and mixed-origin volcanic provinces (IMVPs).

We define 9 shallow asthenospheric volumes (SAVs) across the Circum-Mediterranean upper mantle that form an almost interconnected belt of reduced shear wave velocities starting from the western Mediterranean to the Middle East and surrounding the Calabrian, Adriatic, Alpine slabs, however only interrupted by the eastern Mediterranean thick oceanic lithosphere. The SAVs are characterized by pronounced variations in shear-wave velocity not only laterally but also vertically between 70 and 300 km depths. Results from integrated geophysical-petrological thermochemical modelling show that the low velocities of the SAVs correspond to areas of thinned lithosphere (i.e., 1300 ºC at about 60-80 km depth) and anomalously warm asthenosphere (down to 300 km approximately) with respect to the average ambient mantle geotherm. A remarkable correlation between these areas and locations of IMVPs is observed with a mean lateral distance of < 100 km separating any SAV to the neighboring IMVP. The maximum separating distances are in order of ~ 350 km indicating a dense network of volcanic provinces above the shallow SAVs.

The origin of the SAVs is related either to asthenospheric upwelling caused by slab rollback and decompressional melting during the formation of the back-arc basins (i.e., Agean-Anatolia, Pannonian, Moesian, Western Mediterranean) or to lithospheric thinning and rifting (Middle East and Rhone-Rheine areas). For the origin of the remaining SAVs (Adriatic, Central European, North Africa), other processes, i.e. thermal erosion feed by input from deep mantle sources, are suggested. According to the oldest ages of the IMVPs in the Circum-Mediterranean, the development of the SAVs started at least about ~ 60 - 70 Ma ago and accelerated in the Neogene.

How to cite: El-Sharkawy, A., Hansteen, T. H., Clemente-Gomez, C., Fullea, J., Lebedev, S., and Meier, T.: Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence From Seismic Tomography And Integrated Geophysical-Petrological Thermochemical Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8412, https://doi.org/10.5194/egusphere-egu23-8412, 2023.

EGU23-9490 | Orals | GD1.3

Coupling Models of Plate Motion History, Mantle Convection and the Geodynamo to explain long-term Geomagnetic Field Behavior 

Juliane Dannberg, Daniele Thallner, Rene Gassmoeller, Courtney Sprain, Frederick LaCombe, and Chloe Ritchie

Mantle convection and plate tectonics are crucial mechanisms for keeping conditions at the Earth’s surface in a suitable range for life. One important mantle process is the transport of heat out of the Earth’s outer core, which impacts the geodynamo that generates Earth’s magnetic field. This interaction makes it possible to use changes in the paleomagnetic record to infer the past dynamics of the Earth’s mantle and core.

We here couple a plate reconstruction, 3d global mantle convection models, and geodynamo simulations to quantify the largest possible influence of mantle heat transport on the magnetic field at the Earth’s surface. To constrain the core-mantle boundary heat flux, we set up compressible global mantle convection models using the geodynamic modeling software ASPECT, with material properties computed based on a mineral physics database. We prescribe the velocities at the surface using a plate reconstruction that describes plate motion history throughout the last 1 billion years, encompassing the complete cycle of supercontinent assembly and dispersal. This boundary condition imposes the location of subducted slabs in the model, which then sink down and interact with the thermal/thermochemical boundary later at the base of the mantle, affecting the amplitude and pattern of the heat flux out of the core and how it changes over time. Our models show that the distribution of hot and cold regions changes in terms of location, shape and number throughout the supercontinent cycle, depending on subduction location. Our results indicate that structures at the core-mantle boundary fluctuate and might have looked very differently throughout Earth’s history.

We then select endmember scenarios of core-mantle boundary heat flux patterns and amplitudes to apply them as boundary conditions to thermally driven numerical geodynamo simulations. To assess how well these simulations reproduce Earth’s long-term magnetic field behavior, we apply the Quality of Paleomagnetic Modeling criteria. This allows us to systematically explore the impact of the most extreme variations of CMB heat flux on the geodynamo and to determine if extreme anomalies in the paleomagnetic record, like the extreme weak field period in the Ediacaran, could be caused by mantle dynamics alone or if they require other mechanisms, such as the nucleation of the Earth’s inner core.

Our work shows how integrating multidisciplinary datasets into modeling studies improves our understanding of the mantle’s role in regulating the magnetic field throughout Earth's history, allowing us to re-evaluate the causes of variations in paleomagnetic data.

How to cite: Dannberg, J., Thallner, D., Gassmoeller, R., Sprain, C., LaCombe, F., and Ritchie, C.: Coupling Models of Plate Motion History, Mantle Convection and the Geodynamo to explain long-term Geomagnetic Field Behavior, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9490, https://doi.org/10.5194/egusphere-egu23-9490, 2023.

EGU23-9743 | ECS | Posters on site | GD1.3

Linking thermal and seismic mantle structure in the light of uncertain mineralogy and limited tomographic resolution 

Gabriel Robl, Bernhard Schuberth, Isabel Papanagnou, and Christine Thomas

Mantle convection is primarily driven by gravitational forces acting on thermally buoyant structures in Earth's interior. The associated vertical stresses generate phases of uplift and subsidence of the surface, leaving observable traces in the geologic record. Utilizing new data assimilation techniques, geodynamic inverse models of mantle flow can provide theoretical estimates of these surface processes, which can be tested against geologic observations. These so-called mantle flow retrodictions are emerging as powerful tools that have the potential to allow for tighter constraints on the inherent physical parameters.

To contain meaningful information, the inverse models require an estimate of the present-day buoyancy distribution within the mantle, which can be derived from seismic observations. By using thermodynamically self-consistent models of mantle mineralogy, it is possible to convert the seismic structure of global tomographic models to temperature. However, both seismic and mineralogical models are significantly affected by different sources of uncertainty and often require subjective modelling choices, which can lead to different estimated properties. In addition, due to the complexity of the mineralogical models, the relation between temperature and seismic velocities is highly nonlinear and not strictly bijective: In the presence of phase transitions, different temperatures can result in the same seismic velocity, further complicating the conversion between the two parameters.

 

Using a synthetic closed-loop experiment, we investigate the theoretical ability to estimate the present-day thermal state of Earth's mantle based on tomographic models. The temperature distribution from a 3-D mantle circulation model with earth-like convective vigour serves as a representation of the "true" temperature field, which we aim to recover after a set of processing steps. These steps include the “forward and inverse” mineralogical mapping between temperatures and seismic velocities, using a thermodynamic model for pyrolite composition, as well as applying a tomographic filter to mimic the limited resolution and uneven data coverage of the underlying tomographic model. Owing to imperfect knowledge of the parameters governing mineral anelasticity, we test the effects of changes to the anelastic correction applied in forward and inverse mineralogical mapping. The mismatch between the recovered and the initial temperature field carries a strong imprint of the tomographic filter. Additionally, we observe systematic errors in the recovered temperature field in the vicinity of phase transitions. Our results highlight that, given the current limits of tomographic models and the incomplete knowledge of mantle mineralogy, amplitudes and spatial scales of a temperature field obtained through global seismic models will deviate significantly from the true state. Strategies to recover the present-day buoyancy field must be carefully selected in order to minimize additional uncertainties.

How to cite: Robl, G., Schuberth, B., Papanagnou, I., and Thomas, C.: Linking thermal and seismic mantle structure in the light of uncertain mineralogy and limited tomographic resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9743, https://doi.org/10.5194/egusphere-egu23-9743, 2023.

EGU23-10217 | ECS | Posters on site | GD1.3

High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions 

Arushi Saxena, Juliane Dannberg, and Rene Gassmoeller

Plate tectonics can explain several geological and geophysical phenomena on Earth, and a number of mantle flow models have been developed to investigate the underlying plate tectonic forces. However, these models have come to contradictory conclusions on the balance between the resisting and driving forces. Additionally, they have used the same simplified model to represent the geometry of the plates, and therefore the impact of plate boundary geometry on surface deformation remains unknown.

To address these issues, we have developed high-resolution global instantaneous mantle convection models based on recent geophysical constraints with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different plate boundary configurations. We find a good fit to the observed GPS data for models with plate boundaries that are 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5×1017 and 5×1018 Pa s for all plate boundary configurations. We also find that the model with plate boundaries defined by the Global Earthquake Model (GEM, Pagani et al., 2018)—featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents—achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. These results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents.

Our models also quantify the contributions to the plate driving forces originating from heterogeneities in the upper mantle and the lower mantle, respectively, finding that the slab-pull in the top 300 km alone contributes ~70% of the total plate speeds. Noting the importance of slab pull as a major plate driving force, we further investigate the influence of subduction zone and slab geometry on surface plate motions and their fit to GPS data. Specifically, our models compare a simplified slab structure to a more detailed representation of slabs based on the Slab2 database (Hayes et al., 2018), and reaffirm that a realistic slab geometry is a crucial factor in the transmission of slab pull forces to the plate.

How to cite: Saxena, A., Dannberg, J., and Gassmoeller, R.: High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10217, https://doi.org/10.5194/egusphere-egu23-10217, 2023.

EGU23-10292 | ECS | Posters on site | GD1.3

Earth’s Wandering Rotation Axis as a Diagnostic for Global Mantle Convection Models 

Christopher M. Calvelage, Lorenzo Colli, Jonny Wu, and Yi-An Lin

Dynamic topography is the change in topography that arises from viscous flow within the Earth’s mantle. As such, dynamic topography is sensitive to past mantle flow states. Making predictions of dynamic topography through time often relies on complex mantle convection models. To better constrain mantle convection models, we compare their implied True Polar Wander (TPW) paths for a range of model parameters. TPW is the re-orientation of a planetary solid body with respect to its rotation axis and may be produced by large scale mass redistributions on the Earth’s surface or within the mantle that perturb the Earth’s moment of inertia.

Here we compare TPW histories estimated from two global plate tectonic reconstructions that were assimilated into the TERRA mantle convection code: (1) the widely-used Earthbyte global plate model (‘corrected R’ Matthews et al., 2016); and (2) TOMOPAC-22, a newly developed global plate tectonic model of the circum-Pacific using structurally-restored slabs from mantle seismic tomography (Wu et al., 2022). The time series of geodynamically-modeled mantle states are used to calculate synthetic TPW paths from perturbations in components of Earth’s moment of inertia from mass redistribution within the mantle; multiple (>10) viscosity-depth profiles were considered. We test these modeled TPW paths by comparing them against published paleomagnetic observations (Torsvik et al., 2012; Besse and Courtillot, 2002). Predicted TPW for plate Model 1 ranges widely (~90°) in azimuth from 120°W to 59°E with no consistent pattern across viscosity profiles. TPW rates reach maximums of 1.1°/Myr with excursions of ~25°. In contrast, predicted paths for Model 2 cluster within a smaller ~30° azimuthal range centered around ~29°E irrespective of the viscosity profile.  Predicted maximum rates were up to ~2°/Myr with excursions of up to 30°. Temporally, predicted paths for Model 2 drift toward northern Russia and then veer towards Greenland. Depending on the viscosity profile used some predicted TPW paths undergo stillstands from ~80 to ~30 Ma.  Ultimately, most model scenarios show longitudinal misfits up to 60° with observed paleomagnetic data; modeled TPW rates were within observed and theoretical ‘speed limits'. We discuss similarities and differences between our preliminary TPW history results and paleomagnetic observations, with a goal of developing an effective TPW test for constraining geodynamic parameters, plate tectonic reconstructions, and dynamic topography through time.

How to cite: Calvelage, C. M., Colli, L., Wu, J., and Lin, Y.-A.: Earth’s Wandering Rotation Axis as a Diagnostic for Global Mantle Convection Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10292, https://doi.org/10.5194/egusphere-egu23-10292, 2023.

EGU23-10376 | Posters on site | GD1.3

Daisy chain method applied to mapping the asthenosphere 

Lawrence Cathles, Willy Fjeldskaar, and Aleksey Amantov

The discovery of very rapid uplift rates under areas recently de-glaciated and the realization that such rapid uplift can stabilize ice sheets has generated interest in determining the properties of the asthenosphere.  The asthenosphere is also important to plate tectonics, and to the proper interpretation many important Earth observations.  The current approach to determining the properties of the asthenosphere is to calculate the observed rate of uplift in an area for a great many deglaciation and earth models, calculate the difference between the observed and calculated uplift rates and histories, and find the earth model (with error bars) that best matches the observations.  A faster, simpler, and in some ways better assessment method is to compute the isostatic adjustment response to a loading history consisting of linear segments.  This method determines the central response time from the dimensions of the load, the loading history, the lithosphere flexural rigidity (often not important), and the present rate of uplift.  The last can be easily measured today with GPS in INSAR.  Asthenosphere properties are indicated by the central response time so determined. The Daisy chain method will be described, evaluated against data and conventional modeling in northern Norway, and then applied to infer asthenosphere properties in a number recently-deglaciated continental localities.

How to cite: Cathles, L., Fjeldskaar, W., and Amantov, A.: Daisy chain method applied to mapping the asthenosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10376, https://doi.org/10.5194/egusphere-egu23-10376, 2023.

EGU23-11908 | ECS | Posters on site | GD1.3

Imaging 3-D electrical conductivity structure under US constrains lateral variations in the mantle water content 

Federico Daniel Munch and Alexander Grayver

Electrical conductivity variations provide unique constraints on chemistry, mineralogy, and physical structure of the crust and mantle. As a physical property, conductivity is highly sensitive to the presence of even small amounts of melt and water (i.e., hydrogen). Here, we present a new 3-D electrical conductivity model (MECMUS-2022) derived by inverting data from ~1300 USArray MT stations covering ∼80% of the contiguous United States on a quasi-regular 70-km grid. The use of a novel multi-scale imaging approach and locally refined meshes allows us to consistently incorporate a large range of spatial scales and image 3-D electrical conductivity distribution from the surface down to mantle transition zone. We find conductivity variations that correlate with known continental structures such as due to the active tectonic processes within the western United States (e.g., Yellowstone hotspot, Basin and Range extension, and subduction of the Juan de Fuca slab) as well as the presence of deep roots beneath cratons. We further interpret conductivity variations in terms of the upper mantle water content by coupling electrical conductivity with constrains on mantle thermo-chemical structure derived from the analysis of seismic data (in the form of P-to-s and S-to-p receiver functions). Further, we explore the links between electrical conductors and lithospheric controls on occurrence of critical mineral deposits.

How to cite: Munch, F. D. and Grayver, A.: Imaging 3-D electrical conductivity structure under US constrains lateral variations in the mantle water content, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11908, https://doi.org/10.5194/egusphere-egu23-11908, 2023.

EGU23-14852 | Orals | GD1.3 | Highlight

Whole Mantle Convection with Two Structures and Timescales of Flow 

Jason P. Morgan, Ya-Nan Shi, and Paola Vannucchi

Mantle convection has often been debated to be either a mode of ‘top-to-bottom’ whole mantle convection, or flow within separated geochemical ‘reservoirs’ such as a denser layer often proposed to be the origin of lower mantle LLSVPs. Here we propose a straightforward resolution in which plate tectonic downwelling is linked to a ~3000 km-broad N-S circumglobal ‘ring’ of higher-than-average seismic wavespeeds in the lower mantle that has been recognized since the first global models of non-radial seismic structure. In the high-viscosity lower mantle, subduction-linked downwelling occurs at speeds of <~1.3 mm/yr, which is the origin of the long-known ~1.7Ga ‘isochrons’ seen in both hotspot and mid-ocean ridge volcanism.  This ~3000 km-wide great-circle ring of slow downward flow is associated with two antipodal axial spokes of twice-as-fast but still very slow largescale upward flow in the ‘LLSVP’ regions. In addition to this background pattern of large-scale lower mantle circulation, upward counterflow to plate subduction preferentially takes material from a warmer D’’ thermal boundary layer at the core-mantle boundary through ~10-20 mantle plumes that feed a sublithospheric plume-fed asthenosphere. In the lower mantle, the relatively warmer and lower viscosity plumes preferentially rise through and are slowly attracted towards the LLSVP regions by the low-order mode of slow lower mantle flow, with plume-conduits further warming their surrounding LLSVP lower mantle.

In this contribution we review the seismological and geochemical observations that support this scenario of two interlocking modes of whole mantle convection with very slow flow in the lower mantle that is linked to and pierced by much faster flow in a D’’-plume-asthenosphere upward flow circuit. We then present 3-D thermomechanical models designed to elucidate under what conditions this mode of flow can arise from a highly variable viscosity mantle with both internal heating and significant heatflow across the core-mantle boundary. Finally we briefly touch on some further implications of this scenario for Earth’s radial mantle structure, supercontinent evolution, the geoid, and the geodynamo.

How to cite: Morgan, J. P., Shi, Y.-N., and Vannucchi, P.: Whole Mantle Convection with Two Structures and Timescales of Flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14852, https://doi.org/10.5194/egusphere-egu23-14852, 2023.

EGU23-15266 | ECS | Posters on site | GD1.3

Testing Dynamic Topographic Predictions of Mantle Convection Models Using Global Palaeobiological Datasets 

Conor O'Malley, Gareth Roberts, James Panton, Huw Davies, and Victoria Milanez Fernandes

Over geological timescales, aside from isostatic processes arising from crustal thickness variations, flow within the mantle has long been recognised to generate a significant component of Earth's topography, i.e. "dynamic topography". Therefore, geological and geophysical evidence of Earth's surface deflection can provide spatio-temporal evidence of deep Earth processes, if tectonic/crustal processes are accounted for. Mantle convection models can be used to calculate past and present dynamic topography in a number of ways, with the aim of matching surface observations to improve our understanding of mantle properties and flow characteristics. We analyse the global spatio-temporal patterns of dynamic topography predicted by a suite of models run using the TERRA code, which solves the Stokes and energy equations for mantle flow within a spherical shell. Both compressible/incompressible models are analysed, for a range of mantle viscosity structures. We calculate dynamic topography using two widely-used methods, focussing on the present-day where the pattern of dynamic topography is constrained in greatest detail. First, we examine dynamic topography using instantaneous surface stress calculated from full-resolution 3-D TERRA output. Secondly, model output is transformed into the spherical harmonic domain, and density anomalies at depth are propagated to surface stress variations, and therefore topographic deflections, using analytic sensitivity kernels i.e. the propagator matrix method. Each method makes subtly different assumptions about boundary conditions and mantle structure and properties. We demonstrate that uplift predictions calculated using each method can be compared with observational estimates derived from palaeobiological data, oceanic residual depth measurements, and continental gravity anomalies. We highlight key similarities and differences between dynamic topographic predictions from each method across a suite of mantle convection models, and identify correlation/misfit with observational constraints.

How to cite: O'Malley, C., Roberts, G., Panton, J., Davies, H., and Milanez Fernandes, V.: Testing Dynamic Topographic Predictions of Mantle Convection Models Using Global Palaeobiological Datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15266, https://doi.org/10.5194/egusphere-egu23-15266, 2023.

EGU23-15494 | ECS | Posters on site | GD1.3

Dynamic topography and satellite gravity data joint inversion using Reduced Order Models (DYGIRO) 

Olga Ortega-Gelabert, Javier Fullea, Mariano S. Arnaiz-Rodríguez, and Sergio Zlotnik

Geophysical observables, such as surface elevation, gravity field anomalies, seismic data, surface heat flow, etc, are essential pieces of information used to make inferences about the structure and dynamics of the Earth’s interior. Simultaneously fitting different observable datasets is crucial in order to obtain consistent models. Among geophysical data, gravity data from ESA’s GOCE satellite mission provides key information in properly constraining the Earth’s density distribution. WINTERC-G is a new global thermochemical model of the lithosphere and upper mantle (currently being extended into the transition zone and lower mantle) based on terrestrial and satellite gravity data (Fullea et al., 2021). The inversion procedure behind WINTERC-G has two main steps. In step 1, a 1D column-wise inversion of surface wave tomographic, surface elevation (isostasy) and heat flow data is performed. Then, in step 2, the output model from step 1 is used as prior information for the inversion of the gravity field data (filtered geoid anomalies and gravity gradients from GOCE at satellite height) to refine the 3D crustal density and upper mantle composition. The model predicts a residual, non-isostatic topography that can be considered as a proxy for dynamic topography.

However, within a rigorous framework, dynamic topography cannot be simply taken as a non- isostatic residual, but it should be explicitly computed (i.e. solving the Stokes equation for a given rheological and density distribution) and consistently integrated into the joint inversion of the gravity field and the terrestrial observation with feedback from both the static and dynamic parts. The goal of DYGIRO project is to add a third step into the global WINTERC-G inversion scheme that consistently integrates dynamic topography as an additional model constrain.

We present here the first steps of such integration at global scale. To do that, the dynamic topography is computed by solving the Stokes flow problem associated with the current WINTERC-G model down to the transition zone. The dynamic topography thus obtained is coupled with the static thermochemical model constrained by gravity and seismic data within an iterative scheme where the observed surface elevation coincides with the model’s isostatic plus dynamic elevation contributions. The high computational cost associated with the large- scale 3D flow computations will be alleviated by means of Reduced Order Models. Such models are based on the idea of creating surrogate models that approximate the solution at a much lower computational cost.

 

Fullea, J. Lebedev, S., Martinec, Z., Celli, N. L. (2021). WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data, Geophysical Journal International, 226(1), 146–191.

How to cite: Ortega-Gelabert, O., Fullea, J., Arnaiz-Rodríguez, M. S., and Zlotnik, S.: Dynamic topography and satellite gravity data joint inversion using Reduced Order Models (DYGIRO), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15494, https://doi.org/10.5194/egusphere-egu23-15494, 2023.

EGU23-15545 | ECS | Orals | GD1.3

Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction 

Björn H. Heyn, Grace E. Shephard, and Clinton P. Conrad

The interaction of mantle plumes with continental or cratonic lithosphere can result in (large-scale) volcanism and continental breakup, but these consequences seem to be limited to tectonic settings with pre-existing weak zones. In contrast, most parts of continental plume tracks, or their hypothesized tracks, show no extrusive magmatism. To reconcile this, our previous work has shown that even in the absence of melt, sustained plume-lithosphere interaction leads to lithospheric thinning, followed by elevated surface heat flux about 40-140 million years after the thermal anomaly in the mantle disappears. Therefore, melt-free continental plume tracks can be initially identified by a reduced lithosphere thickness, and later by an increased surface heat flux that temporally and spatially follows the thinned lithosphere.

Yet, even if melt is not erupted, variable amounts of melt may still be generated at the base of the lithosphere above the plume, and this melt can impact local dynamics. In order to assess the role of melt in plume-lithosphere interactions, we have developed a recent suite of numerical models of mantle convection that include melting/freezing and melt migration. Our results indicate a much stronger time-dependence of models with melt compared to models without melt. In particular, small-scale convection at the base of the lithosphere becomes more vigorous, which leads to patterns that feature more localized and larger amplitude lithospheric removal and stronger asymmetry across the plume track. The generation of melt in a thinned area has a self-enhancing effect; more melt thins the lithosphere faster, resulting in more melt generation. However, the effect of thinning for a moving plate is limited, both with respect to the affected area and the time during which this local thinning can be sustained. As a result, the surface heat flux pattern, which is a long-pass filtered image of the lithosphere thinning, does not change significantly compared to a case without melt. However, melt migration brings heat closer to the surface, which increases the amplitude of the heat flux anomaly, and reduces the delay time following lithosphere thinning. The amplification of local dynamics by melt migration is especially pronounced if the plume interacts with pre-existing topography of the lithosphere-asthenosphere boundary (LAB), e.g. steps in lithospheric thickness. Depending on the LAB topography, multiple events of melt generations and magmatic intrusion can be generated by a single plume over tens of millions of years . Such a scenario may explain the pulse-like prolonged activity of the High Arctic Large Igneous Province (HALIP; which erupted between 130-85 Ma) and potentially an early phase of an Iceland plume track under Greenland (pre-62 Ma).

How to cite: Heyn, B. H., Shephard, G. E., and Conrad, C. P.: Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15545, https://doi.org/10.5194/egusphere-egu23-15545, 2023.

EGU23-15705 | Orals | GD1.3

Analyzing geological maps at the continental scale 

Anke M Friedrich

Geological maps are essential products of geological work that display the results of generations of field geologists’ work. Most original geological maps are generated and utilized at local scales. At regional scales, geological maps have gained practical significance ever since William Smith’s 1815 geological map of England exemplified the robust nature of mapping and correlating strata beyond local scales. However, by comparison, geological maps compiled at continental scales appear to be of limited use outside of geological circles. They are often oversized, inhibiting their practical use, so they decorate our geoscience hallways and lecture halls with their beautiful colors and general esthetic appearance. Few outsiders can even read these maps. Their unique color-coding, the multiple non-diverging color schemes, and their complex legends further inhibit non-geologists from being able to recognize the enormous knowledge stored in these maps. I present an analysis of continent-scale geological maps by visualizing time not represented by the rock record (hiatus) and examining the dimensions of hiatal surfaces at interregional scales. The maps yield significant variability in sizes and space-time patterns of hiatal surfaces, a behavior expected in light of interregional-scale processes induced by both the plate and the plume mode of mantle convection. However, to rigorously test models of mantle convection, the temporal resolution of continent-scale maps must be increased to stages level, i.e., the temporal scale at which tectonic processes occur. In addition, synthesis of geological data on continent-scales requires the development and application of event-based stratigraphic-framework mapping.

How to cite: Friedrich, A. M.: Analyzing geological maps at the continental scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15705, https://doi.org/10.5194/egusphere-egu23-15705, 2023.

EGU23-16368 | ECS | Orals | GD1.3

Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates? 

Fred Richards, Sophie Coulson, Mark Hoggard, Jacqueline Austermann, Blake Dyer, and Jerry Mitrovica

Estimates of global mean sea level (GMSL) during past warm periods provide a key constraint on ice-sheet sensitivity to future climate change and inform projections of long-term sea-level rise. Measurements from the most recent periods of enhanced warmth are especially valuable since these intervals represent the closest climatic analogues to near-future conditions. Considerable focus has therefore been placed on reconstructing sea-level during the Mid-Pliocene Warm Period (MPWP; 3.3–3.0 Ma) and the Last Interglacial (~129–116 ka), periods characterised by mean temperatures 2­–3 °C and ~1 °C above preindustrial levels, respectively. Many GMSL estimates have been obtained from palaeoshoreline deposits since these geomorphic proxies provide a more direct and potentially more precise constraint on past sea-level than stable isotope records. However, estimates from different sites differ by several metres due to spatially variable vertical crustal motions caused by geodynamic processes, including glacial isostatic adjustment and dynamic topography.

To tackle this issue, we integrate a suite of Australian sea-level markers and geodynamic simulations into a probabilistic inverse framework to quantify and remove the effect of vertical crustal motions at a continental scale. We find that dynamic topography accounts for most of the observed MPWP sea-level marker deflection and is also significant for the LIG. After correcting for this process and glacial isostatic adjustment, we obtain a revised MPWP GMSL estimate of +16.0/10.4–21.5 m (50th/16th–84th percentiles). We also find that post-LIG dynamic topography may account for several metres of relative displacement across the Great Barrier Reef, potentially reconciling discrepant GMSL estimates from this region. Recalibration of sea-level projections with these revised estimates suggests a more stable Antarctic Ice Sheet under future warming scenarios and appears to rule out recent high-end forecasts.

How to cite: Richards, F., Coulson, S., Hoggard, M., Austermann, J., Dyer, B., and Mitrovica, J.: Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16368, https://doi.org/10.5194/egusphere-egu23-16368, 2023.

EGU23-16771 | Orals | GD1.3

Feedbacks between sea-floor spreading,trade winds and precipitation in the Southern Red Sea 

Kurt Stüwe, Jörg Robl, Syed Turab, Pietro Sternai, and Fin Stuart

Feedbacks between climatic and geological processes are highly controversial
and testing them is a key challenge in Earth sciences. The Great Escarpment of
the Arabian Red Sea margin has several features that make it a useful natural
laboratory for studying the effect of surface processes on deep Earth. These
include strong orographic rainfall, convex channel profiles versus concave
swath profiles on the west side of the divide, morphological disequilibrium in
fluvial channels, and systematic morphological changes from north to south
that relate to depth changes of the central Red Sea. Here we show that these
features are well interpreted with a cycle that initiated with the onset of
spreading in the Red Sea and involves feedbacks between orographic precipitation,
tectonic deformation, mid-ocean spreading and coastal magmatism.
It appears that the feedback is enhanced by the moist easterly trade
winds that initiated largely contemporaneously with sea floor spreading in the
Red Sea.

How to cite: Stüwe, K., Robl, J., Turab, S., Sternai, P., and Stuart, F.: Feedbacks between sea-floor spreading,trade winds and precipitation in the Southern Red Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16771, https://doi.org/10.5194/egusphere-egu23-16771, 2023.

EGU23-17312 | ECS | Posters on site | GD1.3

Using Earth’s free oscillations to assess mantle circulation models 

Anna Schneider, Bernhard Schuberth, Paula Koelemeijer, Federica Restelli, and Christophe Zaroli

For a thorough understanding of the impact of mantle convection on vertical motions of the lithosphere, computational modeling plays a crucial role. Mantle circulation can be modeled by solving the equations of motion of a fluid using Earth-like input parameters assimilating plate motions at the surface in discrete steps through time. Thus, a realistic Earth model relies on the robustness of the inserted information. However, apart from the general difficulty of inferring deep Earth’s properties, also the plate tectonic model introduces uncertainty. Especially the linking of relative plate motions to absolute position relies on controversial assumptions such as fixity of structures in the mantle (e.g., plumes or Large-Low-Shear-Velocity Provinces) or the association between subducted plates at depth and high velocity regions in tomographic images. The latter specifically are restricted by non-uniqueness and the need to regularize the inversions, distorting structures and damping heterogeneity amplitudes.

In order to infer secondary results from an MCM, it is thus important to validate the model against independent observations. Here, we employ Earth’s free oscillations that feature global sensitivity to 3-D structure for model assessment, complementing our earlier work using seismic body wave data. To this end, the temperature field of a published MCM is converted to seismic velocity with the help of a thermodynamic model of mantle mineralogy. An effective forward approach for the computation of normal mode data from synthetic Earth models is the calculation of splitting functions, describing the distortion of characteristic frequency peaks in the spectrum induced by even degree structural heterogeneity. A general problem is that the sensitivity of normal modes with depth often shows oscillatory behaviour preventing a straight forward relation of frequency shifts to structure in a certain depth range. This can be mitigated by combining kernels of several modes via a Backus-Gilbert approach to obtain focused sensitivity in pre-specified depth ranges of the mantle. For testing the significance of relevant model differences in splitting function data, geometrical alterations mimicking changes in the absolute reference frame and viscosity were applied to a pre-computed MCM. Current results indeed indicate that normal mode data are sensitive to such model changes within their respective uncertainty ranges.

How to cite: Schneider, A., Schuberth, B., Koelemeijer, P., Restelli, F., and Zaroli, C.: Using Earth’s free oscillations to assess mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17312, https://doi.org/10.5194/egusphere-egu23-17312, 2023.

EGU23-17452 | ECS | Orals | GD1.3

Retrodicting flow of the early Cenozoic mantle: perspectives from an adjoint modelling approach 

Siavash Ghelichkhan, Hans-Peter Bunge, and Jens Oeser

Convection in the mantle provides the primary forces that shape the long wavelength structure of the Earth's surface
through dynamic topography. These forces have long been known as the cause of key events in the Cenozoic era: the
termination of large-scale marine inundation in North America in the Palaeocene, the late Tertiary rise of Africa
relative to other continents and the long-wavelength tilting of Australia since the late Cretaceous. It is an
overarching goal in geodynamics to construct reliable models that can retrodict (make predictions about the past)
these key events correctly. This year marks the 20th anniversary since the introduction of adjoint modelling as a
powerful method to retrodict mantle flow. Using the adjoint method, various datasets are assimilated to optimize
dynamic earth models by deriving the necessary gradient information. Here we explore a suite of eight high-resolution
(about 670 million finite elements), compressible, global mantle flow retrodictions going back to 50 Ma. Our
retrodictions involve the dynamic effects from an upper mantle low-viscosity zone, assimilate a past plate-motion
model for the tangential surface velocity field, probe the influence of two different present-day mantle state
estimates derived from seismic tomography, and acknowledge the rheological uncertainties of dynamic Earth models
by taking in four different realizations for the radial mantle viscosity profile, two of which were published
previously. The retrodictions show for the first time that key Cenozoic events emerge jointly as part of global
Cenozoic mantle flow histories. We show that the retrodicted mantle flow histories are sensitive to the present-day
mantle state estimate and the rheological properties of the Earth model, meaning that this input information is
testable with inferences gleaned from the geological record. Retrodictions allow one to track material back in
time from any given sampling location, making them potentially useful, for example, to geochemical studies. Our
results call for improved estimates of non-isostatic vertical motion of the Earth’s surface — provided, for
instance, by basin analysis, seismic stratigraphy, landform studies, thermochronological data or the sedimentation
record — to constrain the recent mantle flow history and suggest that mantle flow retrodictions may yield synergies
across different Earth science disciplines.

How to cite: Ghelichkhan, S., Bunge, H.-P., and Oeser, J.: Retrodicting flow of the early Cenozoic mantle: perspectives from an adjoint modelling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17452, https://doi.org/10.5194/egusphere-egu23-17452, 2023.

SM6 – Crustal Fluids & Seismic Activity (incl. induced & triggered seismicity, volcano seismology

EGU23-1017 | ECS | Orals | SM6.1

Effects of rheological variations, erosion, and geotherm characteristics on tectonic setting and seismic activity in the Val d’Agri (Southern Italy) 

Alessio Lavecchia, Andrea Tallarico, Vincenzo Serlenga, Tony Alfredo Stabile, Giacomo Prosser, Marilena Filippucci, and Stuart Clark

Over the last decades, many studies highlighted the close relationship between thermal structure, surface processes, and tectonic forces in controlling the deformation of the lithosphere. The contribution of these key factors, however, is not constant in time and may result in a complex deformation history, as already observed in many regions around the globe. In this view, the rheology of the crust is pivotal to leading regional tectonic evolution.

Among the factors that may cause remarkable strength and rheological variations in the crust, the presence of fluid phases is undoubtedly one of the most prominent. The mechanisms of rock-fluid interaction are still a debated field of research. However, it has been suggested in many studies that a major effect of fluids is enhanced seismicity of regions where they are present.

In this framework, the Val d’Agri represents a perfect example of how crustal evolution can be influenced by several factors interacting with one another. In this region, we analyze the relationships between different mechanisms in the final structural setting of the region, with implications on the natural and induced seismicity. To this aim, we built up a numerical model that integrates the combined effects of rheological stratification of the crust, inherited zones of weakness, variations in the tectonic regime, surface erosion, and fluid presence. Our results show that variation in the strength of the evaporite layer between the carbonate platform and the basement has a profound impact on the tectonic style of the Val d’Agri. The uplifting and subsidence pattern in the region follows stages of slow vertical movements to stages of very fast uplifting and denudation, due to the activation of new tectonic structures where movement is enhanced. This reflects on pressure and temperature variations in time, that follow typical yo-yo patterns observed in several tectonically active regions. The present-day configuration of the VA is also influenced by the erosion rate. More in detail, a comparison between the observed structures in the area and our model’s results with varying erosion rates suggests that the VA has been subjected to medium to fast erosion during its evolutionary history. In addition, our model predicts the presence and orientation of faults where fluid percolation or injection at high pressure can generate clusters of microseismicity.

How to cite: Lavecchia, A., Tallarico, A., Serlenga, V., Stabile, T. A., Prosser, G., Filippucci, M., and Clark, S.: Effects of rheological variations, erosion, and geotherm characteristics on tectonic setting and seismic activity in the Val d’Agri (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1017, https://doi.org/10.5194/egusphere-egu23-1017, 2023.

EGU23-1018 | Posters on site | SM6.1

Role of crustal fluids and thermo-mechanical structure for lower crustal seismicity: the Gargano Promontory (southern Italy) 

Andrea Tallarico, Alessio Lavecchia, Marilena Filippucci, Giulio Selvaggi, Gianpaolo Cecere, and Sierd Cloetingh

Several regions around the globe are characterized by a seismically active lower crust, at depths where lithological, thermal and rheological conditions suggest stress release by ductile flow. The Gargano Promontory (GP, southern Italy) is an example where a recently installed seismic network has recorded an intense seismic activity at depths between 20 and 30 km, i.e. in the lower crust. We analyze a possible mechanism controlling the distribution of seismicity in the GP to identify the factors that make the lower crust seismically active. To this aim, we construct a thermo-rheological model of a layered continental crust, calibrated on the basis of geometrical, lithological and thermal constraints. The model takes into account a multiphase crustal lithology, the presence of fluids in the crystalline basement, lateral variations of geotherm and stress field.

The numerical simulations show that the presence of fluids is a key factor controlling the cluster of seismicity in the lower crust. Moreover, the presence of water in the upper crystalline basement and sedimentary cover provides a plausible explanation for upper crustal seismicity in a zone of very high heat flow SW of the GP. The distribution of the seismicity is probably affected by the composition of the crystalline basement, with mafic bodies injected into the crust during the Paleocene magmatic phase that affected the Mediterranean region. Our findings suggest that the presence of hydrous diapiric upwelling(s) in the upper mantle can feed a deep fluid circulation system, inducing lower crustal seismicity.

How to cite: Tallarico, A., Lavecchia, A., Filippucci, M., Selvaggi, G., Cecere, G., and Cloetingh, S.: Role of crustal fluids and thermo-mechanical structure for lower crustal seismicity: the Gargano Promontory (southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1018, https://doi.org/10.5194/egusphere-egu23-1018, 2023.

EGU23-1774 | ECS | Orals | SM6.1 | Highlight

Space-time monitoring of groundwaterfluctuations with passive seismicinterferometry 

Shujuan Mao, Albanne Lecointre, Robert D. van der Hilst, and Michel Campillo

Historic levels of drought, globally, call for sustainable freshwater management. Under pressing demand is a refined understanding of the structures and dynamics of groundwater systems. Here we present an unconventional, cost-effective approach to aquifer monitoring using seismograph arrays. Employing advanced seismic interferometry techniques, we calculate the space-time evolution of relative changes in seismic velocity, as a measure of hydrological properties. During 20002020 in basins near Los Angeles, seismic velocity variations match groundwater tables measured in wells and surface deformations inferred from satellite sensing, but the seismological approach adds temporal and depth resolutions for deep structures and processes. Maps of long-term seismic velocity changes reveal distinct patterns (decline or recovery) of groundwater storage in basins that are adjacent but adjudicated to water districts conducting different pumping practices. This pilot application bridges the gap between seismology and hydrology, and shows the promise of leveraging seismometers worldwide to provide 4D characterizations of groundwater and other near-surface systems.

How to cite: Mao, S., Lecointre, A., van der Hilst, R. D., and Campillo, M.: Space-time monitoring of groundwaterfluctuations with passive seismicinterferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1774, https://doi.org/10.5194/egusphere-egu23-1774, 2023.

EGU23-2043 | ECS | Orals | SM6.1

Hydrogeochemical characterization of the waters circulating in the seismically active area of the Pesaro-Urbino province (northern Marche, central Italy) 

Lorenzo Chemeri, Marco Taussi, Jacopo Cabassi, Francesco Capecchiacci, Franco Tassi, Alberto Renzulli, and Orlando Vaselli

The Province of Pesaro-Urbino (northern Marche, central Italy) represents one of most seismically active areas in Italy, since it is interested by the presence of two major composite seismogenic sources: i) the first one is located in the Umbria-Marche Apennines; ii) the second one is along the Adriatic coast from Cattolica to Ancona cities. This area has recently experienced an intense seismic activity, e.g., the 1781 “Cagli Earthquake” with a magnitude of 6.4 Mw, and the 1930 “Senigallia Earthquake” of 5.8 Mw. The last earthquake (5.5 Mw) occurred on November 9, 2022, with its epicenter located in the Adriatic Sea, 35 km away from the city of Pesaro. Since the geochemical knowledge of this area is limited, a large-scale sampling survey was carried out during spring and autumn 2022. A total of 87 samples were collected from different types of emergencies (i.e., cold springs, wells, mineral springs, sulfur springs and ditches) and various geological and tectonic-structural contexts. The study area is dominated by a complex sedimentary structure (e.g., limestones, clays and alluvial deposits) and by climatic and topographic conditions that may influence the chemical and isotopic composition of the investigated fluids. A detailed geochemical characterization is thus of paramount importance in order to define a geochemical background. The aim of this study was to (1) understand the possible interaction of deep-originated fluids and shallow aquifers and (2) evaluate the use of selected geochemical parameters as possible seismic tracers. The results showed the presence of five different geochemical facies: (i) calcium-bicarbonate waters with low TDS (<500 mg/L); (ii) calcium-bicarbonate waters with a strong enrichment in sulfate (up to 200 mg/L); (iii) waters with extreme sodium-carbonate composition and an alkaline pH (>8.8); (iv) calcium-sulfate waters; and (v) sodium-chloride waters. The water isotopic composition showed a clear meteoric origin for all the investigated samples. The composition of major dissolved gases showed two different compositional clusters: (a) N2-dominated gases with N2/Ar ratios similar to those of air and ASW (Air Saturated Water); (b) CO2- and CH4-rich gases pertaining to mineral and sulfur springs. The origin of Ca-HCO3 waters is almost exclusively related to the dissolution of carbonate minerals. On the contrary, Ca-HCO3(SO4) waters are probably originated by deep circulation pathways and interactions with the Upper Triassic Burano Formation, composed by anhydrite layers. The Ca-SO4 waters should be considered as the product of ongoing flows within Miocene gypsum formations, whilst Na-HCO3 waters as the consequence of long-lasting interactions between meteoric waters and silicate rocks (containing albite) in saturation/oversaturation conditions for carbonate-bearing minerals. Finally, the Na-Cl waters probably derive from mixing processes between meteoric and highly saline connate waters trapped into the foredeep clayey deposits. Therefore, the Ca-HCO3(SO4) and Ca-SO4 waters can be regarded as the most interesting fluids to be monitored for a geochemical network aimed at recognizing chemical and isotopic variations related to seismic activity. They are indeed showing a deeper hydrogeological pathway and appear to be less influenced by surface processes.

 

How to cite: Chemeri, L., Taussi, M., Cabassi, J., Capecchiacci, F., Tassi, F., Renzulli, A., and Vaselli, O.: Hydrogeochemical characterization of the waters circulating in the seismically active area of the Pesaro-Urbino province (northern Marche, central Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2043, https://doi.org/10.5194/egusphere-egu23-2043, 2023.

EGU23-2254 | ECS | Orals | SM6.1

Hydrogeologic processes drive deformations in the Matese massif (Southern Italian Apennines) 

Francesco Pintori, Federica Sparacino, and Federica Riguzzi

The Matese massif is an extensive outcrop of Apenninic Platform carbonate rocks located at the boundary between Central and Southern Apennines (Italy), extending ~74 km from NW to SE over an area of ~1600 km² and reaching a maximum height of 2050 m. Its geological history documents different phases of compressional and extensional tectonics which modeled the shape and size of faults within the massif. The present seismotectonic background belongs to the extensional style of the Central-Southern Apennine chain, with a series of NW-SE active extensional faults and occurrence of seismic activity, which reached intensities up to IX MCS.
The karst features of the Matese significantly affect the hydrology of the massif, where rainfall trends lead to large variations in the water reservoirs.
Recent papers report the presence of deformations induced by the elastic response of the loaded surface and the poroelastic properties of the ground. These two mechanisms are different: in the first the water load causes subsidence, in the second uplift. However, under anisotropic conditions, water pressure changes in poroelastic rocks can induce large horizontal deformations especially where highly fractured rocks may provide permeability for fluid flow. When the porosity is determined by systematic fractures, the medium is anisotropic and the surface deformation is mainly perpendicular to the fracture system. To study such processes, we analyzed the time series of 7 GNSS permanent stations located in the Matese area, and the seismicity, covering the 2005-2022 time interval. The GNSS time series of each station were detrended from a best-fitted linear model plus eventual steps due to instrumental changes, without modeling periodicities, obtaining three time series of residual displacements (N, E, Up) for each site. 
We also analyzed spring discharge and pluviometric data. The latter are used to compute the rainfall excess as the difference between the cumulated daily rainfall and the best-fitting straight line of the cumulated rainfall. Then, we applied an Independent Component Analysis to the GNSS data. This allowed us to extract from the time series, in a blind way, a signal very well correlated with hydrological data. This geodetic signal has a large horizontal amplitude and occurs perpendicular to the fracture orientations. This is also shown by the horizontal strain tensor estimated from the displacements associated with this signal, whose maximum extension axis reaches up 1µstrain perpendicular to the fault direction.
During wet periods, characterized by high rainfall excess and increasing values of spring discharge, we observe extensional deformation with stations moving “away” from the massif center; during dry periods a compressional deformation occurs, with stations coming back “toward” the massif. This suggests that the water stored within the massif is the driver of such geodetic signal: the larger the water pressure is, the larger the extensional deformation becomes; when the water level decreases, the water pressure is reduced and then compressional deformation occurs. 
Further studies should be done to understand if water circulation also indirectly affects the background seismicity. 

How to cite: Pintori, F., Sparacino, F., and Riguzzi, F.: Hydrogeologic processes drive deformations in the Matese massif (Southern Italian Apennines), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2254, https://doi.org/10.5194/egusphere-egu23-2254, 2023.

EGU23-4376 | Orals | SM6.1 | Highlight

Earthquakes and helium: evidences of the impulsive nature of earth degassing 

Antonio Caracausi

In seismic regions, fluids play active roles during the preparatory phases of large earthquakes and, through their chemical and isotopic signature, transport to the surface information about deep processes within the fault zones.

In this scenario, noble gases are useful to investigate earth degassing, and their isotopic ratios help to decipher the dynamics of natural processes such as volcanic eruptions and earthquakes. The lightest of noble gases is helium (He), and in natural fluids, it is present with two isotopes, 3He and 4He. The former being mainly primordial and stored in the mantle, the latter continuously produced by U and Th decay in the earth interior. In stable continental region the He flux is dominated by the radiogenic 4He that is produced into the crust (mantle He <1%).  In contrast, primordial 3He escape to the atmosphere in regions of active tectonic (from extensive to compressive).

Experimental studies highlighted that during rocks deformation micro-fracturation increases as an effect of dilation, and consequently, He is liberated from rocks and it escapes towards the pore fluids and successively to the atmosphere. Hence, it indicates a direct link between seismicity and the crustal 4He degassing. However, it is mandatory to know the volume of the rocks involved in earthquakes-induced rock-fracturation to quantify the amount of He released in seismic processes.

Fault zones are complex systems whose mechanical properties evolve over time. Field observations and experimental works allow to schematically simplify these zones into two main structural regions: (1) the fault core and (2) the damage zone. However, the lack of direct observations limits the knowledge of their architecture at depth. Thus, in order to understand the multi-scale, physical/chemical processes responsible for the faulting that earthquakes occur on, it is fundamental to consider phenomena that intersect different scientific research fields. Near Fault Observatories (NFOs) are grounded on multidisciplinary infrastructures, collecting near fault high resolution scientific data that allows generation of innovative observations (Chiaraluce et al., 2022).

Here, we analysed a 12-year earthquake catalogue (M<4) in the IRPINIA NFO (Italy), a region affected by high-magnitude disastrous earthquakes (i.e. M= 7.0 in 1857 and M= 6.9 in 1980).

The analysis of this earthquakes catalogue allows reconstructing year by year the volumes of both the fault core and the damage zone. We computed the 4He output from the two faults zone observing that the low-magnitude earthquakes (M < 4) efficiently contribute to variations of the crustal helium output into the atmosphere. Our results support the impulsive nature of He degassing in tectonically active continental regions (Caracausi et al., 2022). We recognized a quantitative relationship between crustal helium outputs and the volume of fault zones, and  we suggest that variations in helium flux may represent a gauge of changes in the stress field that are related to the nucleation of earthquakes.

 

References

Caracausi et al. (2022). doi:10.1038/s43247-022-00549-9.

Chiaraluce et al. (2022). doi:10.4401/ag-8778.

How to cite: Caracausi, A.: Earthquakes and helium: evidences of the impulsive nature of earth degassing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4376, https://doi.org/10.5194/egusphere-egu23-4376, 2023.

EGU23-5861 | ECS | Orals | SM6.1

The impact of tectonic structures on the 3D scattering imaging of the Central Italy Seismic Sequence 

Simona Gabrielli, Aybige Akinci, Luca De Siena, Edoardo Del Pezzo, Mauro Buttinelli, Francesco Maesano, and Roberta Maffucci

The Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) seismic sequence (hereafter AVN) struck the Central Apennines (Italy) in 6-7 months during 2016-2017, and it has been widely associated with fluid migration in the normal faults network. The analysis of attenuation parameters (e.g., scattering and absorption) gives information about material properties and the presence of fluids and fracturing. In this study, we investigate in a 3D mapping the scattering contribution to the total attenuation of the AVN seismic sequence (August 2016-January 2017), together with a pre-sequence dataset (March 2013-August 2016). We applied peak delay as a proxy of seismic scattering, to obtain further information on the fracturing processes in time and space. Previous 2D mapping of peak-delay time and coda attenuation tomography in the same study area indicated a substantial control on the scattering of seismic waves by structural (e.g., Monti Sibillini thrust) and lithological (e.g., Umbria- Marche and Lazio-Abruzzi geological domains) features.
Our 3D results show clear differences between the pre-sequence and the sequence, where we can identify an increase of scattering with time after the mainshocks. The substantial alterations in scattering are observed between 4 - 6 km depth, in the hanging wall of the Monti Sibillini thrust, which acts as a rheological barrier between high and low scattering zones. Peak delay variations detected a significant anomaly in the Triassic deposits layer, at the roots of the Acquasanta thrust, east of Monti Sibillini. Here, low scattering during the pre-sequence epoch is replaced by high scattering during the mainshocks. The low scattering along the Acquasanta thrust suggests an increment of pore pressure, associated with the presence of fluids in this geological formation. The subsequent release of those fluids may have caused the mainshocks of the seismic sequence, and a subsequent increase in fracturing, as observed by the high scattering anomaly. These results bring a new light on the importance to consider the thrusts systems in the tectonic framework of the Central Italy.

How to cite: Gabrielli, S., Akinci, A., De Siena, L., Del Pezzo, E., Buttinelli, M., Maesano, F., and Maffucci, R.: The impact of tectonic structures on the 3D scattering imaging of the Central Italy Seismic Sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5861, https://doi.org/10.5194/egusphere-egu23-5861, 2023.

EGU23-5872 | ECS | Posters on site | SM6.1

Study of interfacial seismoelectric signals in unsaturated pore media 

Ling Zeng, Hengxin Ren, Kaiyan Hu, Xuzhen Zheng, and Changcheng Li

The current theoretical study of the seismoelectric method is based on two sets of the governing equations, one is the electrokinetic coupling coefficient proposed by pride (1994) which is characterized by the zeta potential. The other is the electrokinetic coupling coefficient proposed by Revil & Linde (2006) which is based on the amount of excess charge in the pore volume. In this study, the Luco-Apsel-Chen generalized reflection and transmission method was used to solve the second set of seismoelectric governing equations and separate their interfacial response signals. The correctness of the algorithm is determined by comparing the consistency of the total interface signal with the superposition of the interface signals of each layer. The properties of the interface signals are investigated and it is found that different interface responses contribute differently to the overall signal and that the amplitude and phase of the interface signals are influenced by frequency and medium parameters.

How to cite: Zeng, L., Ren, H., Hu, K., Zheng, X., and Li, C.: Study of interfacial seismoelectric signals in unsaturated pore media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5872, https://doi.org/10.5194/egusphere-egu23-5872, 2023.

EGU23-6023 | ECS | Posters on site | SM6.1

Seismoelectric conversions due to a ground source in stratified porous media 

Xuzhen Zheng, Hengxin Ren, Changcheng Li, and Ling Zeng

The penetration and diffusion of fluids in fluid-saturated porous media can cause electromagnetic (EM) disturbances due to the electrokinetic effect. These mechanically induced EM waves, often known as the seismoelectric wave fields are sensitive to hydraulic parameters such as porosity and permeability. For in-situ seismoelectric field observations, the source and receivers are usually located at or near the ground surface. However, the current reflectivity-method-based seismoelectric modeling algorithms will suffer computational difficulties due to the slow convergence problem occurring when the source and receiver are located at close or the same depths. To overcome this problem, we extend the peak-trough averaging method to update the seismoelectric modeling algorithm based on the Luco-Apsel-Chen generalized reflection and transmission method. The updated seismoelectric algorithm is then applied to study the seismoelectric coupling phenomena. The results demonstrate that the electric signals recorded by a surface receiver are several milliseconds earlier than their causative seismic waves due to the evanescent seismoelectric conversion. This is capable to interpret similar phenomena reported in seismoelectric field observations over a long history. This time difference may have the potential to identify the location of the groundwater table. Therefore, the updated seismoelectric algorithm is a precise and efficient tool for forward modeling, which also benefits the interpretations of field seismoelectric observations.

How to cite: Zheng, X., Ren, H., Li, C., and Zeng, L.: Seismoelectric conversions due to a ground source in stratified porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6023, https://doi.org/10.5194/egusphere-egu23-6023, 2023.

EGU23-6668 | ECS | Orals | SM6.1

Strain sensitivity of seismic velocity variation induced by hydrological forcing of karst aquifers in the Apennines, Italy 

Stefania Tarantino, Piero Poli, Nicola D'Agostino, Gaetano Festa, Maurizio Vassallo, Gerardo Ventraffrida, and Aldo Zollo

Non-linear response of the elastic properties of the crust has been studied using the analysis of seismic velocity variations induced by various natural forcing agents (earthquakes, tides, volcanic processes, and others). Here we study 1) the variations of seismic velocities in response non-tectonic deformations associated to phases of groundwater recharge/discharge in large karstic aquifers in the Southern Apennines of Italy and discuss 2) the implications in terms of non-elastic behavior of the crust. Karst systems are complex aquifers common within the carbonate rocks of the Apennines. They store large amount of groundwater producing significant horizontal dilatational strains that modulate the secular, tectonic deformation (~3 mm/yr extension across the Apennines) and background seismicity (Silverii et al., 2019; D’Agostino et al., 2018) with seasonal and multi-seasonal signatures. The availability of accurate and temporally-long hydrological measurements (rainfall and karst spring discharge) in addition to dense seismic and geodetic networks provide the opportunity to assess the elastic response of the crust to strain forcing at various periods and the sensitivity of relative velocity variations to non-tectonic, hydrological strain variations. We performed velocity variation measurements on seismic noise autocorrelation signals recorded at seismic stations for different coda waves time lapse and compared them with strain measured by the GPS network. We observe that seismic velocities decrease during dilatation episodes (high hydraulic head) and increase during contraction (low hydraulic head). We find that the retrieved strain sensitivity of seismic velocity changes is of the order of ~103 and discuss such sensitivity with previous natural and laboratory results.

How to cite: Tarantino, S., Poli, P., D'Agostino, N., Festa, G., Vassallo, M., Ventraffrida, G., and Zollo, A.: Strain sensitivity of seismic velocity variation induced by hydrological forcing of karst aquifers in the Apennines, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6668, https://doi.org/10.5194/egusphere-egu23-6668, 2023.

This study investigates the perturbations of the surrounding stress field caused by the cascade effect of Xiluodu and Xiangjiaba reservoirs after impoundment and a three-dimensional pore-elastic coupling model of the impoundment of cascade reservoirs are established. The finite element method calculates the pore pressure field, elastic stress field, and variation of Coulomb stress on local faults. The results show that: 1) the spatial distribution of the earthquake cluster is obviously consistent with the area where the pore pressure increases; 2) The ΔCFS at the epicenters of the April 2014 Yongshan M_L5.1 earthquake and the August 2014 Yongshan M_L5.2 earthquake imparted by the reservoirs are: 0.67kPa and 10.87kPa, respectively, indicating that impoundment promotes these two earthquakes at different levels, and the latter is more significant; 3) The elastic stress field change imparted by the impoundment of Xiluodu reservoir has an impact on the Xiangjiaba Reservoir in the early stage. However, the earthquakes between two reservoirs are possibly triggered by the latter. The Xiangjiaba reservoir increases the pore pressure in its upstream part by 1.0 kPa; 4) the impoundment of the reservoirs increases the seismic risk of the southern section of the Yanfeng fault and the middle section of the Lianfeng fault, while the Manao fault is less affected.

How to cite: Yin, G., Zhang, H., and Shi, Y.: Cascade effects of triggered earthquakes of cascade dams: Taking Xiluodu and Xiangjiaba reservoirs as examples, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7137, https://doi.org/10.5194/egusphere-egu23-7137, 2023.

EGU23-7351 | ECS | Orals | SM6.1

Time-Domain Source Parameter Estimation of natural and man-induced micro earthquakes at The Geysers geothermal field 

Valeria Longobardi, Sahar Nazeri, Simona Colombelli, Raffaele Rea, Grazia De Landro, and Aldo Zollo

Water injection in geothermal areas is the preferential strategy to sustain the natural production of geothermal resources. In this context, monitoring microearthquakes is a fundamental tool to track changes in the reservoirs in terms of soil composition, response to injections, and resource exploitation in space and time. Therefore, the refined source characterization is crucial to better estimate the size, source mechanism, and rupture process of microearthquakes, as possibly related to industrial activities and to identify any potential variation of the background seismicity. Standard approaches for source parameters estimation are ordinarily based on the modelling of Fourier displacement spectra and its characteristic parameters, the low-frequency spectral level and corner frequency. Here we apply a time-domain innovative technique that uses the curves of P-wave amplitude vs time along the seismogram. The methodology allows estimating seismic moment, source radius, and static stress drop from the plateau level and the corner-time and of the average logarithm of P-wave displacement versus time with the assumption of a triangular moment rate function, uniform rupture speed, and constant/frequency-independent Q-factor. In the current paper, this time-domain methodology is implemented to a selected catalog of micro-earthquakes consists of 83 events with moment magnitude ranging between 1.0 and 1.5, occurred during 7 years (2007-2014) of fluid extraction/injection around Prati-9 and Prati-29 wells at The Geysers Geothermal field.

How to cite: Longobardi, V., Nazeri, S., Colombelli, S., Rea, R., De Landro, G., and Zollo, A.: Time-Domain Source Parameter Estimation of natural and man-induced micro earthquakes at The Geysers geothermal field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7351, https://doi.org/10.5194/egusphere-egu23-7351, 2023.

EGU23-7574 | Posters on site | SM6.1

Monitoring active fumaroles through electrical and magnetic survey: an application to the Pisciarelli fumarolic field (Campi Flegrei, Italy). 

Antonio Troiano, Claudio De Paola, Maria Giulia Di Giuseppe, Carmela Fabozzi, and Roberto Isaia

The hydrothermal area of Pisciarelli, together with the adjacent Solfatara volcano, currently represents the most active structure of the Campi Flegrei caldera in terms of degassing and seismic activity and recently manifesting significant morphological variations, including the opening of new fumarolic vents and mud emission episodes as well as changes in the geochemical characteristics of the gases/fluids. 
To define the structural setting of the Pisciarelli fumarolic field, Electrical Resistivity (ERT) and Time-Domain Induced Polarization (TDIP) tomographies, Self-Potential (SP), Temperature (T), PH and Magnetic (Mag) mapping have been recently realized. 
The geophysical tomographies furnished a 3D model of the area, which reconstructs the Pisciarelli subsurface in its area of maximum degassing, containing the main fumarole (“soffione”) and the mud pool. The comparison of the 3D model with SP, T, PH and Mag maps acquired in the area revealed the occurrence of zones characterized by intense and complex faulting and fracturing processes, affected by fluid circulation, as well as identifying sectors of the subsurface where gases accumulate as also evidenced at the surface by the presence of fumaroles and intense hydrothermal rocks alteration. In particular, the 3D model evidenced an upwelling channel in which fluids stored in a more profound reservoir rise toward the surface. Such a structure seems to be surmounted by a clay-cap formation that could govern the circulation of fluids and the abundance of gases/vapours emitted by the soffione.
The conceptual model proposed for the Pisciarelli fumarolic field suggests plausible mechanisms for explaining, at the same time, the soffione activity and the role played by the deeper origin fluid/gas in the shallow fluid circulation system. In addition, the advance in the understanding of the Pisciarelli fumarolic field setting could also improve the strategy for monitoring the unrest processes in the area and evaluating the associated hazards.

How to cite: Troiano, A., De Paola, C., Di Giuseppe, M. G., Fabozzi, C., and Isaia, R.: Monitoring active fumaroles through electrical and magnetic survey: an application to the Pisciarelli fumarolic field (Campi Flegrei, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7574, https://doi.org/10.5194/egusphere-egu23-7574, 2023.

EGU23-7667 | Orals | SM6.1 | Highlight

Seismic Imaging of the Nesjavellir geothermal field, SW-Iceland 

Ortensia Amoroso, Ferdinando Napolitano, Gylfi Páll Hersir, Þorbjörg Ágústsdóttir, Vincenzo Convertito, Raffaella De Matteis, Sveinborg Hlíf Gunnarsdóttir, Vala Hjörleifsdóttir, and Paolo Capuano

The harnessed Nesjavellir geothermal area is one of several geothermal fields on the flanks of the Hengill volcano, SW-Iceland. In this study, we present a detailed seismic imaging of the area through the mapping of the VP, VS and VP/VS ratio using seismic data recorded from 2016 to 2020 and compare them to a resistivity model from the same area and rock temperature measured in boreholes. To obtain reliable initial hypocenter locations and a reference seismic velocity, we solve the coupled hypocenter-velocity problem and obtain a reliable minimum 1D P-wave velocity model for the study area. First, we performed the relocation of all the events in the catalogue using the new 1D velocity model and the estimated  VP/VS value of 1.77. We chose the highest quality events based on the quality of the relocations and used them to perform the 3D tomographic inversion. We used an iterative linearized delay-time inversion to estimate both the 3D P- and S-wave velocity models and earthquake locations.

The results highlight that at depths less than 1 km the crust has a high VP/VS ratio (around 1.9) and low VP and VS values. Low resistivity at comparable depths in the same region has been explained as being due to the smectite clay cap. The observed low VP/VS ratio of 1.64 to 1.70 for depths between 1 and 3 km coincides with high resistivity values. The seismicity in this region, where temperatures often exceed 240°C, seems to be sparse and concentrated near the production wells. This seismicity has been explained as being caused by both production and tectonic activity.  At depths larger than 3 km significant high VP/VS ratio anomaly (>1.9) is observed and coincides spatially with a deep-seated conductive body that domes up at about 4.500 m b.sl. Elevated temperatures are observed above this structure in borehole temperature data. We propose that these signals reflect hot 600-900°C cooling intrusives, close to the brittle ductile transition - possibly the heat source(s) of the geothermal field above. These anomalies are at the same location as the last fissure eruption in Hengill almost 2,000 years ago. A deeper NNE-SSW trending seismic cluster at 3-6 km depth, likely outlining an active fault, is observed at the edge of this high VP/VS anomaly. The heat source of the Nesjavellir geothermal field is most likely connected to this most recent volcanism as reflected by the deep-seated low resistivity body and high VP/VS ratio, located beneath the deep fault that connects the flow path of the high temperature geothermal fluid, resulting in an actively producing reservoir.

The availability of a 3D model represents a starting point for 4D tomography study which will allow us to track changes in crustal properties over time and the estimation of fault mechanisms and kinematic source parameters.

This work has been partially supported by PRIN-2017 MATISSE project, No 20177EPPN2, funded by the Italian Ministry of Education and Research.

How to cite: Amoroso, O., Napolitano, F., Hersir, G. P., Ágústsdóttir, Þ., Convertito, V., De Matteis, R., Gunnarsdóttir, S. H., Hjörleifsdóttir, V., and Capuano, P.: Seismic Imaging of the Nesjavellir geothermal field, SW-Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7667, https://doi.org/10.5194/egusphere-egu23-7667, 2023.

EGU23-7724 | ECS | Orals | SM6.1

Earthquake source parameters in the Zagros region (Iran) from the time of evolutionary P-wave Displacement 

Sahar Nazeri, Fatemeh Abdi, Amir Ismail, Habib Rahimi, and Aldo Zollo

The rupture process of the recent moderate-to-large earthquakes in the longest seismic sector in Iran's plateau, the Zagros area, has been modeled using the strong motion data provided by the Iranian Building and Housing Research Center (BHRC). The selected dataset includes the largest and deadliest seismic event, the 2017 Mw 7.3, Sarpol-e Zahab earthquake. The earthquake source parameters (moment magnitude, source duration, rupture dimension, and average stress drop) are determined by implementing a parametric modeling technique in the time domain based on the time evolution of the P-wave displacement signals. The seismic source parameters are calculated from simulated trapezoidal and triangular moment-rate functions assuming the unilateral rectangle and circular crack models, respectively, where the rupture propagates at a constant velocity as a fraction (90%) of the average shear-wave velocity in the medium. The anelastic attenuation effect assuming the independent frequency-Q parameter ranging from 50 to 200 is accounted for by a post-processing procedure that retrieved the observed moment-rate triangular shape. Hence, the average stress drop with different varies between <Δ𝜎>=1.50 (1.14−1.95) and <Δ𝜎>=0.90 (0.71−1.14) MPa. Assuming a circular rupture model for Sarpol-e-Zahab, we estimate a moment magnitude of 7, rupture duration of 7 seconds, source radius of 16 km, and statistical stress drop of about 3.5 MPa. Alternatively, a unilateral rupture model calculates the fault length and width at 45 and 16 km, with a lower stress drop of 2 MPa.

How to cite: Nazeri, S., Abdi, F., Ismail, A., Rahimi, H., and Zollo, A.: Earthquake source parameters in the Zagros region (Iran) from the time of evolutionary P-wave Displacement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7724, https://doi.org/10.5194/egusphere-egu23-7724, 2023.

EGU23-8292 | Orals | SM6.1

The role of CO2 degassing in the seismogenic process of the Apennines, Italy 

Francesca Di Luccio and the The FURTHER Team

An accurate survey of old and new datasets allowed us to probe the nature and role of fluids in the seismogenic processes of the Apennines mountain range in Italy. Geodynamics, geophysical and geochemical observations highlight differences between the western and eastern domains of the Apennines, and the main characteristics of the transition zone, which spatially corresponds with the overlapping Tyrrhenian and Adriatic Mohos. Tomographic images exhibit a large hot asthenospheric mantle wedge that intrudes beneath the western side of the Apennines and disappears at the southern tip of the southern Apennines. This wedge modulates the thermal structure and rheology of the overlying crust as well as the melting of carbonate-rich sediments of the subducting Adriatic lithosphere. As a result, CO2-rich fluids of mantle-origin have been recognized in association with the occurrence of destructive seismic sequences in the Apennines. The stretched western domain of the Apennines is characterized by a broad pattern of emissions from CO2-rich fluids that vanishes beneath the axial belt of the chain, where fluids are instead trapped within crustal overpressurized reservoirs, favoring their involvement in the evolution of destructive seismic sequences in that region. In the Apennines, areas with high mantle He are associated with different degrees of metasomatism of the mantle wedge from north to south. Beneath the chain, the thickness and permeability of the crust control the formation of overpressurized fluid zones at depth and the seismicity is favored by extensional faults that act as high permeability pathways. This study strongly relies on the multidisciplinary analysis of different datasets (both existing and newly acquired) with the most advanced methodologies to stimulate the knowledge of the fluid-related mechanisms of earthquake preparation, nucleation and space-time evolution. Ongoing and future investigations will include the continuous and simultaneous geochemical and geophysical monitoring at the scale of the outcropping seismogenic faults to properly decipher the link between earthquake occurrence, surface rupture and fluid release.

How to cite: Di Luccio, F. and the The FURTHER Team: The role of CO2 degassing in the seismogenic process of the Apennines, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8292, https://doi.org/10.5194/egusphere-egu23-8292, 2023.

The Apennines mountain range develops all along Italy, presenting important variations in terms of both structural and tectonic environments, and seismogenic patterns as well. This is observed not only along the main NW-SE chain axis, but also by comparing multidisciplinary observations between the western Tyrrhenian and the eastern Adriatic domains (Di Luccio et al., 2022).

We focus on the southern Apennines, where the Adriatic plate subducts westward under the thinner Tyrrhenian plate and the highest seismic release is documented.

Recent studies showed that fluids play an important role in the seismic behavior of the area. The western domain is associated with heterogeneous and distributed patterns of CO2 gas emission at the surface; the latter ceasing in the east, where high-pressure fluids are trapped in crustal pockets and affect the seismogenic cycle (Chiodini et al., 2004; Improta et al., 2014; Di Luccio et al., 2022 and references therein).

We perform regional-scale P- and S-body waveform analysis and forward numerical modeling, for a selected catalog of crustal events recorded by the broadband seismic stations of the italian network, as well as of temporary passive seismic experiments. We focus on a SW-NE transect, which cross-cuts the southern portion of the Apennines chain, and along which the recorded waveforms exhibit important differences in terms of frequency content and pulse shape. Along the same transect, the waveforms from two events (2013 Mw5 Sannio-Matese and 2014 Mw4.5 Gargano earthquakes) show significant differences in the propagation towards the east and west, respectively.

Starting from two velocity models such as EPcrust (Molinari et al. 2011) and the adjoint tomographic model of Magnoni et al. (2022), we use the finite difference numerical modeling code nbpsv2d (Li et al. 2014) to produce synthetic waveforms to fit and explain the observations. By including information on the earthquake source mechanism and by improving the waveform fit in terms of both arrival time and body-wave coda, we provide new, preliminary information on the crustal structure of the southern Apennines, aimed at improving our understanding of the fluid-seismicity interaction in the area.

 

Research performed in the framework of FURTHER project (https://progetti.ingv.it/en/further).

 

References:

 

  • Chiodini G., Cardellini, C., Amato, A., Boschi, E., Caliro, S., Frondini, F., and Ventura, G. (2004). Carbon dioxide Earth degassing and seismogenesis in central and southern Italy. Geophys. Res. Lett., 31, L07615, doi:10.1029/2004GL019480.
  • Di Luccio et al., (2022). Geodynamics, geophysical and geochemical observations, and the role of CO2 degassing in the Apennines. Earth-Sci. Rev., https://doi.org/10.1016/j.earscirev.2022.104236
  • Improta L., P. De Gori, and C. Chiarabba (2014). New insights into crustal structure, Cenozoic magmatism, CO2 degassing, and seismogenesis in the southern Apennines and Irpinia region from local earthquake tomography, J. Geophys. Res. Solid Earth, 119, 8283–8311, doi:10.1002/ 2013JB010890.
  • Li, D., Helmberger, D., Clayton, R. W., & Sun, D. (2014). Global synthetic seismograms using a 2-D finite-difference method. Geophysical Journal International, 197(2),1166-1183.
  • Magnoni, F., Casarotti, E., Komatitsch, D., Di Stefano, R., Ciaccio, M. G., Tape, C., ... & Tromp, J. (2022). Adjoint tomography of the Italian lithosphere. Communications Earth & Environment3(1),1-12.
  • Molinari, I., & Morelli, A. (2011). EPcrust: a reference crustal model for the European Plate. Geophysical Journal International185(1), 352-364.

How to cite: Scarponi, M., Di Luccio, F., and Piromallo, C.: Waveform modeling of moderate earthquakes for the comprehension of the seismic structure and the fluid-seismicity interaction beneath the southern Apennines (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8375, https://doi.org/10.5194/egusphere-egu23-8375, 2023.

EGU23-8421 | ECS | Posters on site | SM6.1

Crustal fluid migration and gas-water-rock interaction processes in a seismic area: the case study of the Contursi hydrothermal system (Southern Appenines) 

Dario Buttitta, Giorgio Capasso, Michele Paternoster, Marino Domenico Barberio, Francesca Gori, Marco Petitta, Matteo Picozzi, and Antonio Caracausi

The geochemical characteristics of fluids that emerge at the Earth's surface are influenced by gas-rock-water interactions in the deep and shallow crustal layers, including mixing, outgassing of volatiles, and precipitation of minerals. The goal of the study was to understand the various interactions that influence the migration and behaviour of fluids within the Earth's crust and how they may change during the process of crustal fluid migration towards a hydrothermal system in the shallow crustal layers and within (Contursi basin, Italy). These processes can make it difficult to identify the source of deep gas by using the classical approach based on mixing processes of fluids and carbonate dissolution. Therefore, alternately the relationship between Total Dissolved Inorganic Carbon (TDIC) and the δ13CTDIC in groundwater from the Contursi hydrothermal system investigating the water-gas-rock interaction at the local scale through the detailed reconstructions of the geological framework at depth have been taken into consideration. We found that both the dissolved and free gas in the hydrothermal system probably originated from a deep CO2 endmember with a δ13CCO2 value ranging from +2.12‰ to +3.20‰ (PDB) depending on the presence of brine or freshwater in the local aquifers. However, we observed that this CO2 lost its pristine carbon isotopic signature during its storage in the deep dolomite-composed reservoirs (6-8 km), making it challenging to figure out its deep origin (decarbonation vs mantle/magmatic CO2). Our calculations also showed that the output of CO2, taking into account secondary processes (i.e. degassing CO2 and calcite precipitation) and interactions with water at different salt concentrations, could be at least 40% higher than estimates from the mixing-only approach, such that it is comparable with several active and quiescent worldwide volcanic systems. In order to interpret potential geochemical changes that may occur during future seismic events in sites like Contursi, which are earthquake-prone areas, it is necessary to implement models that can help us understand fluids origin and the processes that influence their chemical and isotopic signature.

How to cite: Buttitta, D., Capasso, G., Paternoster, M., Barberio, M. D., Gori, F., Petitta, M., Picozzi, M., and Caracausi, A.: Crustal fluid migration and gas-water-rock interaction processes in a seismic area: the case study of the Contursi hydrothermal system (Southern Appenines), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8421, https://doi.org/10.5194/egusphere-egu23-8421, 2023.

EGU23-8732 | Posters on site | SM6.1

Grande Comore and Mayotte gas-geochemistry and evidence of deep fluid migration during the 2018-2020 submarine eruption off Mayotte 

Marco Liuzzo, Andrea Di Muro, Andrea Luca Rizzo, Antonio Caracausi, Fausto Grassa, Guillaume Boudoire, Massimo Coltorti, and Bhavani Bénard

Located within the Mozambique Channel, the Comoros archipelago is situated within a complex geodynamic system of great interest owing to recent volcanic and seismic activity (2018-20), but where little gas geochemistry research has been conducted.

Focusing on Grande Comore and Petite Terre, a small islet off the northeast coast of Mayotte, our investigations set out to identify the gas-geochemistry characteristics of the islands, and explore any potential influence from the then ongoing unrest and/or volcanic activity.

Geochemical surveys included measurements of soil CO2 flux on both islands, and gas sampling from fumarolic areas at Karthala volcano (Grande Comore) and two bubbling areas at Petite Terre, with the aim of determining the chemical and isotopic characteristics of the main gases (CO2, CH4, He, Ne, Ar) and equilibrium temperatures of the hydrothermal system at Petite Terre.

δ13C values of soil CO2 emissions highlight evidence of a low magmatic contribution at Grande Comore, while a significantly higher contribution is evident at Petite Terre. 3He/4He data are consistent with average values of fluid inclusions for both Grande Comore and Petite Terre rocks, and are fixed at low value ranges (4.7≤Rc/Ra≤5.9 and 5.3≤Rc/Ra≤7.5 respectively). The gases detected at the two sites of Petite Terre primarily reflect the signature of deep gases in terms of geochemical tracers such as R/Ra and δ13C in CO2.  At one of the two emission sites at Petite Terre, namely the meromictic lake Dziani Dzaha, the gases are relatively more variable in relative proportion of CO2, CH4  and C isotopes; at this specific site, a significant influence from microbial activity is evidenced.

Our results allow us to infer that the general degassing characteristics between the two islands are similar. They also shed light on their reciprocal differences, which may either be attributable to local specifics within Petite Terre, or to different states of volcanic activity between Grande Comore and Petite Terre at the time of the surveys, the latter being a consequence of fluid migration to the mainland of Mayotte during the offshore submarine activity (2018-20).

The outcomes of this work provide a necessary step towards filling gaps in the knowledge of gas-geochemistry in Comoros, and contribute potential support for volcanic and environmental monitoring programmes.

How to cite: Liuzzo, M., Di Muro, A., Rizzo, A. L., Caracausi, A., Grassa, F., Boudoire, G., Coltorti, M., and Bénard, B.: Grande Comore and Mayotte gas-geochemistry and evidence of deep fluid migration during the 2018-2020 submarine eruption off Mayotte, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8732, https://doi.org/10.5194/egusphere-egu23-8732, 2023.

Reservoir-induced seismicity (RIS) related to water-level changes in artificial lakes is a well-documented phenomenon. The best known RIS example is the 6.3 Mw 1967 Koyna-Warna earthquake. However, it must be considered that small-to-moderate magnitude RIS occurs very often, both in relation to water load changes and poroelastic stress perturbation in pre-existing faults. Monitoring the temporal and spatial evolution of RIS is very important for assessing the mechanical state of faults, especially when artificial lakes are located in areas characterized by a high seismic hazard. Indeed, where the crust is affected by the presence of faults with a stress level close to failure, even static stress changes of a few tens of kPa associated with RIS might promote the worst-case scenario of large earthquakes.

Understanding of the physical processes that generate and characterize natural and induced earthquakes, including RIS, is often improved by studying the spatiotemporal evolution of the source parameters obtained through inversion of the seismic data, or by studying the mechanical properties of rocks through seismic velocities. Nevertheless, the source parameters for small magnitude earthquakes such as stress-drop and seismic energy are difficult to estimate, are model-dependent, and, above all, are affected by large uncertainties. Alternatively, the variability of RIS source processes can be investigated by studying the temporal and spatial variability of the ground motion intensity (δBe).

In this work, we investigate the spatiotemporal evolution of ground motion caused by RIS at the Pertusillo artificial lake in southern Italy. The area has a strong seismogenic potential, having been affected in the past by the 1857, Mw 7.0 Basilicata earthquake. We consider ∼1,000 microearthquakes that occurred from 2001 to 2018 and were recorded by a local network of nine seismic stations. The ground motion intensity associated with microseismicity allows us to identify two periods, each lasting approximately 2 years. They are characterized by a high rate of events but exhibit different source properties and spatial distributions. In the first period, the seismicity is spatially clustered close to the lake, on faults with different orientations and kinematics. In the second period, the seismicity is distributed along the Monti della Maddalena faults. Comparing the ground motion intensities of the two periods, we observe that events that occurred in the first period are associated with higher stress levels than others, in agreement with the b-values of the respective frequency-magnitude distributions. We compare the temporal evolution of the ground motion intensity with the rainfall and water levels measured at the artificial lake, as well as with the discharge of a ∼80 km distant spring, which is strictly controlled by climate trends. The results provide information about the regional processes acting on the southern Apennines. Our results show that the microseismicity is clearly associated with the Pertusillo artificial lake in the first period, whereas in the second period is a result of a combination of local effects due to water table oscillations of the lake itself, regional tectonics, and the poroelastic and elastic phenomena associated with carbonate rocks hosting aquifers.

How to cite: Stabile, T. A., Picozzi, M., and Serlenga, V.: Spatio-temporal evolution of ground motion intensity caused by reservoir-induced seismicity at the Pertusillo artificial lake (southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9324, https://doi.org/10.5194/egusphere-egu23-9324, 2023.

EGU23-9565 | Orals | SM6.1

Passive seismic and infrasonic monitoring at the Mefite d’Ansanto deep-CO2 degassing site (Southern Apennines, Italy). 

Luisa Valoroso, Spina Cianetti, Pasquale De Gori, Giovanni Diaferia, Carlo Giunchi, Luigi Improta, Davide Piccinini, Luciano Zuccarello, Rocco Cogliano, Antonio Fodarella, Felice Minichiello, Stefania Pucillo, and Francesca Di Luccio

The role of fluids in the preparatory phase of major earthquakes and in the evolution of aftershocks and swarms in space and time is well-documented. In particular, numerous studies evidence the primary role that mantle-derived fluids play in the generation of large upper crustal earthquakes in extensional domains, where crustal-scale faults act as preferential hydraulic pathways.  

We focus on the Mefite D'Ansanto degassing site, the largest low-temperature non-volcanic CO2 emission in the world, located at the northern tip of the Mw6.9 1980 Irpinia faults. The study area experienced strong historical earthquakes (1702, 1732 and 1930 M6+ earthquakes) but it is characterized by a relatively low background seismicity rate with respect to the nearby Sannio and Irpinia regions.    

To collect high-quality microseismicity data in this key sector of the southern Apennine extensional belt and investigate the relationship among seismicity, crustal fluids, and physical-hydraulic properties of the crust, we installed in July 2021 (up to May 2023) a temporary network composed of 10 stations equipped with short-period velocimeters (5 sec). The temporary network covers an area of approximately 30x30 km2 surrounding the Mefite d’Ansanto site and integrates with the numerous permanent stations of the INGV and ISNet networks located at the boundary of the survey area. 

Within the Mefite area, we also deployed a temporary seismo-acoustic dense array to study two CO2 vents. The seismo-acoustic array is composed of 5 infrasonic stations equipped with IST-2018 broadband microphones developed by The ISTerre (Université Savoie Mont Blanc, France), in addition to one seismo-acoustic station equipped with a co-located digital broadband seismometers (120s). The array is positioned approximately at the vertices of a star, with an aperture of about 50 meters. The deployment lasted for 1 week at the end of May 2022, allowing us to sample the emission site during “dry” weather conditions. 

We show first results of the analysis of seismicity recorded by the temporary network applying both standard (STA/LTA) detection algorithms or innovative enhanced techniques such as cross-correlation based template-matching algorithms and/or Deep-Learning-Phase-Recognition methods.

The activities are developed in the framework of the multidisciplinary project FURTHER (https://progetti.ingv.it/en/further).

How to cite: Valoroso, L., Cianetti, S., De Gori, P., Diaferia, G., Giunchi, C., Improta, L., Piccinini, D., Zuccarello, L., Cogliano, R., Fodarella, A., Minichiello, F., Pucillo, S., and Di Luccio, F.: Passive seismic and infrasonic monitoring at the Mefite d’Ansanto deep-CO2 degassing site (Southern Apennines, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9565, https://doi.org/10.5194/egusphere-egu23-9565, 2023.

EGU23-9822 | ECS | Posters on site | SM6.1

Monitoring pore-pressure from Vp/Vs ratio around the Costa Molina 2 wastewater disposal well in southern Italy 

Grazia De Landro, Tony Alfredo Stabile, Titouan Muzellec, Vincenzo Serlenga, and Aldo Zollo

Monitoring conditions of the medium embedding the reservoir is strictly required for the hazard assessment in exploited areas.

Fluid injection/extraction operations cause a pressure perturbation into the volume hosting the reservoir which, in turn, may trigger new failures and induce changes in the elastic properties of rocks. Therefore, technologies are needed to reconstruct pore-pressure evolution around injection wells.

To test how the conditions of the reservoir can be monitored noninvasively by using induced micro-seismicity, here we show a rock physics approach aimed to reconstruct the pore-pressure temporal evolution from the changes in Vp/Vs ratio.  

We applied this strategy to the volume affected by the wastewater disposal activity of the Costa Molina 2 injection well, located in the High Agri Valley (Southern Italy) and belongs to the Val d’Agri oilfield, the largest productive onshore oil field in West Europe that produces hydrocarbons (oil and gas) from a fractured carbonate reservoir. We analyzed an enhanced seismic catalogue of the induced micro-seismicity, occurred between 2016 and 2018, that consists of 196 located earthquakes in the magnitude range − 1.2 ≤ Ml ≤ 1.2. For the same period, both seismicity recordings and fluid-injection data are available.

For the evaluation of Vp/Vs ratio with the Wadati formula, the accurate measure of arrival time is critical, especially in case of micro-events. So, we first refined with high precision the first P- and S-wave arrival times by using waveform cross-correlation and hierarchical clustering and selected the events with a high DD location quality; then, we calculated the Vp/Vs ratio for each source-station couple and averaged the ratio values for all the events at the stations nearest to the well (INS1, INS2, INS3) to reconstruct the elastic properties temporal evolution in the source region around the well. 

We found that the Vp/Vs ratio temporal evolution well correlates with injection operational parameters (i.e. injected volumes and injection pressures). With a rock physics model, by using the Pride approach of the Biot theory, we reconstruct the pore-pressure temporal variation starting with the Vp/Vs as known parameters, thus demonstrating the value of seismic velocity monitoring as a tool to complement a monitoring system.

How to cite: De Landro, G., Stabile, T. A., Muzellec, T., Serlenga, V., and Zollo, A.: Monitoring pore-pressure from Vp/Vs ratio around the Costa Molina 2 wastewater disposal well in southern Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9822, https://doi.org/10.5194/egusphere-egu23-9822, 2023.

EGU23-11035 | ECS | Posters on site | SM6.1

Interdependent effects of injection volume and rate on fault slip behavior: A large-scale numerical study 

Riddhi Mandal and Semechah Lui

Various injection parameters have been shown to pose significant effects on human-induced seismicity due to a variety of activities such as wastewater injection, carbon storage and geothermal energy production. In this study, we used numerical modeling to investigate how different injection parameters, namely injected volume and injection rate, affect the behavior of faults in the context of fluid-induced seismicity. We tested a large model space (4500 simulations) and modeled injection cases with both spatially homogenous and heterogenous pore-pressure perturbations. Simulation results showed that the two parameters can have various impacts on fault behavior, and that in some cases their effects are interconnected. We discovered that aseismic slip plays a significant role in altering the timing of triggered earthquakes and has lasting impacts on future seismic activity. Moreover, we found that increasing the injection rate tends to increase the size of the triggered cluster of earthquakes, while increasing the injection volume increase the overall rate of earthquakes. We find that spatial heterogeneity has qualitatively similar effects as compared to spatially homogenous cases, with a few quantitative differences. Lastly, we also performed a case study of an injection scenario based on realistic values of pore-pressure diffusion and injection operations in Oklahoma, and we found that for an injection duration of one year, the pore pressure on the faults in the region does not go back to zero even after 70 years and can cause earthquakes years after the end of injection, perturbing the seismic cycles for ~200 years. Our work has potential important implications for safe operation of injection processes which can reduce the risk of seismic hazards.

How to cite: Mandal, R. and Lui, S.: Interdependent effects of injection volume and rate on fault slip behavior: A large-scale numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11035, https://doi.org/10.5194/egusphere-egu23-11035, 2023.

EGU23-11047 | Posters on site | SM6.1

Characteristics of microseismicity in the Kiskatinaw area, northeastern British Columbia, Canada 

Suhee Park, Dabeen Heo, Tae-Seob Kang, Junkee Rhie, Seongryong Kim, and Jan Dettmer

Since the early 2000s, lots of induced earthquakes have occurred due to fluid-injection during the development of unconventional resources at the Kiskatinaw Seismic Monitoring and Mitigation Area (KSMMA) located in northeastern British Columbia, Canada. The spatial-temporal distribution of microearthquakes induced by fluid-injection are important to understand the characteristics of crack and movement of fluid. Also, to mitigate earthquake disasters, it is essential to continuously monitor microearthquakes in fluid-injection areas. We used the seismic data recorded at the EON-ROSE seismic network, which is a dense seismic network consisting of 16 broadband seismic stations, and GSC-BCOGC seismic network to analyze the characteristics of microseismicity of the KSMMA in 2020. We detected the seismic signal (P- and S-wave) using the automatic seismic phase detection method, which is based on the short-term-average to long-term-average ratio (STA/LTA) and kurtosis. And then, we associated the seismic phase arrival data to combine to earthquakes from the automatic seismic phase association method using the temporal distribution of the detected signals and the spatial distribution of the seismic stations used. The hypocenter parameters of associated earthquakes were determined with the HYPOINVERSE location algorithm and the existing 1-D velocity model of KSMMA. The epicenter distributions of the detected earthquakes are concentrated in the area known as active fluid-injection, and the focal depths are also distributed at about 2 km. We analyzed the seismicity by dividing it with three periods based on COVID-19 lockdown and confirmed the low-seismicity of the lockdown period, which is consistent with the result of the independent study performed at the region.

How to cite: Park, S., Heo, D., Kang, T.-S., Rhie, J., Kim, S., and Dettmer, J.: Characteristics of microseismicity in the Kiskatinaw area, northeastern British Columbia, Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11047, https://doi.org/10.5194/egusphere-egu23-11047, 2023.

EGU23-11775 | ECS | Orals | SM6.1 | Highlight

Hydrogeologic and microseismic monitoring as a tool to evaluate fault criticality in karstic regions 

Léa Perrochet, Giona Preisig, and Benoît Valley

Natural groundwater level fluctuation in karstic networks resulting from significant recharge (precipitation and/or seasonal snowmelt) can potentially induce seismicity. Triggering is often considered to be the result of pore pressure diffusion front migrating from the surface to focal depth, assuming a homogeneous crust. Although this assumption can be acceptable in some cases (e.g. homogeneously fractured basement) it is hardly justified in known karstic area. Considering the specific features of karst and data of three case studies, we elaborate a conceptual model of rain-triggered seismicity in karstic regions by identifying potential triggering mechanisms and, using simplified analytical solutions, quantifying their impact on fault stability. Results of this analysis indicate that a direct hydrogeological connection between karstic conduits and the hypocenter can lead to pore pressure variation of the order of MPa, potentially initiating a rupture. To test the conceptual model, field investigations are carried out in the Jura Mountains, a well-known karstic area with low to moderate seismicity. Data acquisition consists in monitoring the natural microseismicity and the flowrate at karstic springs, used as a direct proxy for groundwater level fluctuations.Combining both data sets allows to identify events that are potentially rain-triggered and to acquire a quantitative knowledge on what pressure change, inferred from the hydraulic head increase, is affecting the fault’s stability, a valuable information when planning underground projects.

How to cite: Perrochet, L., Preisig, G., and Valley, B.: Hydrogeologic and microseismic monitoring as a tool to evaluate fault criticality in karstic regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11775, https://doi.org/10.5194/egusphere-egu23-11775, 2023.

EGU23-12491 | Orals | SM6.1 | Highlight

Adjoint Tomography of the Italian Lithosphere 

Federica Magnoni, Emanuele Casarotti, Dimitri Komatitsch, Raffaele Di Stefano, Maria Grazia Ciaccio, Carl Tape, Daniele Melini, Alberto Michelini, Antonio Piersanti, and Jeroen Tromp

The evolution and state of geological structure at Earth’s surface is best understood with an accurate characterization of the subsurface, where fluid distribution plays a key role. We present high-resolution seismic tomographic images of tectonic and geological features of the Italian lithosphere based on ground motion recordings and obtained through an iterative procedure. Enhanced accuracy is enabled by state-of-the-art three-dimensional wavefield simulations in combination with an adjoint-state method. The resulting tomographic model characterizes the subsurface structure in terms of compressional and shear wavespeed values at remarkable resolution, corresponding to a minimum period of ~10 s. As primary findings of our work, images of the lithospheric structure in Central Italy are consistent with recent studies on the distribution of fluids and gas (CO2) within the Italian subsurface, allowing us to infer the presence of deep melted material that induces shallow gas fluxes, or traps and deep storage of gas that can be correlated with seismicity. We illuminate Mt. Etna volcano and support the hypothesis of a deep reservoir (~30 km) feeding an intermediate-depth magma-filled intrusive body, which in turn is connected to a shallow chamber. We also investigate the intriguing features of the Adriatic plate offshore of the eastern Italian coast. Tomographic evidence reveals a structure of the plate made of two distinct microplates with different fabric and behavior, and separated by the Gargano deformation zone, indicating a complex lithosphere and tectonic evolution.

How to cite: Magnoni, F., Casarotti, E., Komatitsch, D., Di Stefano, R., Ciaccio, M. G., Tape, C., Melini, D., Michelini, A., Piersanti, A., and Tromp, J.: Adjoint Tomography of the Italian Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12491, https://doi.org/10.5194/egusphere-egu23-12491, 2023.

EGU23-12756 | ECS | Posters on site | SM6.1 | Highlight

Centroid full moment tensor analysis reveals fluid channels opened by induced seismicity at EGS, Helsinki region, southern Finland 

Annukka Rintamäki, Gregor Hillers, Sebastian Heimann, Torsten Dahm, and Annakaisa Korja

Understanding fluid injection induced seismicity is key to safe and successful operations of deep geothermal systems. Efficient geothermal energy extraction by an enhanced geothermal system (EGS) requires increased fluid flow between geothermal wells. The experimental 6-km-deep EGS in the Helsinki capital region, southern Finland is an intriguing natural laboratory in a cool Precambrian shield setting that yields excellent seismic data quality. We investigate the source processes of the earthquakes induced by weeks-long EGS stimulations in 2018 and 2020 via a probabilistic waveform fitting method. Detailed resolution of full moment tensor solutions and their opening components can reveal crucial information on earthquake nucleation and fluid flow patterns.

We present results of a centroid full moment tensor analysis for ~250 events from 2018 and 16 events from 2020 in the moment magnitude range 0.5–1.9. We use three-component data of ~30 stations within a 9-km radius of the well-head site. We fit P- and S-phases by modeling synthetic waveforms using Green’s functions with a 20 m grid spacing based on a homogeneous velocity model. We employ automatic high signal-to-noise ratio waveform selection and automatically determined channel-wise correction coefficients for time shifts and amplitude scaling to represent small scale crustal variations not reflected in the velocity model. With the application of both waveform selection and channel corrections, the uncertainty of the moment tensor decreases on average by ~60 % and the location uncertainty by ~85 %. This results in a catalog of well-resolved moment tensors and centroid locations.

The obtained high-quality solutions are dominated by reverse faulting mechanisms with variable compensated linear vector dipole (CLVD) contribution and non-significant isotropic component. The 3D event distribution reveals largest positive CLVD contribution in seismic sources close to the injection well, which indicates localized fracture opening under constant volume with a simultanous adjacent shear event. Farther from the well, seismic sources have pure double-couple mechanisms or even negative CLVD contribution which may be indicative of fracture lengthening or closing under constant volume at later stages of the stimulation.

Identifying clusters with respect to source type and location within the 3D event distribution supports the interpretation of physical source processes and reveals fluid flow channels, and zones of weakness. Events with positive CLVD component occurring close to fluid-filled fractures are potentially nucleated by direct contact with the injected fluid and the associated pore pressure change. Events with zero or negative CLVD component on the outer parts of the seismicity distribution may have been nucleated by poroelastic stress transfers without a direct hydraulic contact to the injected fluid. Our findings suggest that the full extent of injection induced seismicity may not be indicative of fluid flow and thus it should not be used to estimate the extent of an artificially created connected fracture network of a geothermal reservoir.

How to cite: Rintamäki, A., Hillers, G., Heimann, S., Dahm, T., and Korja, A.: Centroid full moment tensor analysis reveals fluid channels opened by induced seismicity at EGS, Helsinki region, southern Finland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12756, https://doi.org/10.5194/egusphere-egu23-12756, 2023.

EGU23-12806 | Posters on site | SM6.1

Seismological temporal patterns at Mefite d’Ansanto CO2 emission field. 

Simona Morabito, Lucia Nardone, Simona Petrosino, and Paola Cusano

Mefite d’Ansanto (Italy) is the largest non-volcanic CO2 emission field on the Earth. The isotopic signature of the CO2 testifies a deep origin of the gases emitted at this site, whose source is probably the mantle wedge beneath the Apennines along the Tyrrhenian side (Chiodini et al., 2010). Mefite is located between the Sannio and the Irpinia seismogenic regions, that are considered among the most active areas of the southern Apennines. The emission site falls at the northern tip of the Irpinia fault system that is associated with the destructive MS = 6.9, 1980 Irpinia earthquake. The gas leakage from this zone is linked to active faulting that characterized the area and determined large historical earthquakes

A temporary acquisition survey close to the Mefite emission field was carried out between 8 June and 28 September 2020 by using a seismic array, named Array MEfite (AME), composed of seven short-period stations. We have analyzed the characteristics of the recorded background seismic noise, e.g., spectral properties, energy temporal pattern (RMS) and polarization (Montalbetti et al., 1970), and estimated site effects (Nakamura, 1989; http://www.geopsy.org/). The seismological temporal patterns have been compared with the meteorological parameters, such as temperature and rainfall, to find possible relationships with exogenous factors. We found a well-defined spatial pattern for the spectral components above 5 Hz, which appear clearly linked to the emission field dynamics. On the other hand, the spectral components below 5 Hz result from the overlapping of multiple sources, of both exogenous, such as anthropogenic and meteorological factors, and endogenous nature. Application of the Independent Component Analysis (ICA) technique (Hyvärinen et al., 2001) contributed to discriminate between natural and anthropogenic sources.

 

References

Chiodini, G., D. Granieri, R. Avino, S. Caliro, A. Costa, C. Minopoli, and G. Vilardo (2010). Non‐volcanic CO2 Earth degassing: Case of Mefite d’Ansanto (southern Apennines), Italy, Geophys. Res. Lett. 37, L11303, doi: 10.1029/2010GL042858.

Hyvärinen, A., Karhunen, J. & Oja, E. (2001). Independent Component Analysis. Wiley, New York,

Montalbetti, J. R., Kanasevich, E. R. (1970): Enhancement of teleseismic body phase with a polarization filter. Geophys. J. Int. 21 (2), 119–129.

Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Railway Technical Research Institute, Quarterly Reports, 30 (1), 25-33.

How to cite: Morabito, S., Nardone, L., Petrosino, S., and Cusano, P.: Seismological temporal patterns at Mefite d’Ansanto CO2 emission field., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12806, https://doi.org/10.5194/egusphere-egu23-12806, 2023.

EGU23-13270 | ECS | Orals | SM6.1 | Highlight

Fluid migration in volcanic environment: thermo-poroelastic modelling of Solfatara crater. 

Andrea Barone, Gianluca Gola, Antonio Pepe, Pietro Tizzani, and Raffaele Castaldo

In volcanic environment, the fluids migration in the crust can affect the evolution of magmatic processes. Meteoric water can for instance infiltrate volcanic rocks developing shallow hydrothermal systems and descending meteoric water may encounter fluids rising up from deep magma feeding system. The accurate tracking of fluid storages and movements turn out to be crucial for the evaluation of the seismic and volcanic activity. Specifically, Campi Flegrei caldera is an example of fluids interaction of different nature, especially at Solfatara crater, where the complexity of this volcanic system is highlighted by diffuse degassing, high temperatures and bradyseism phenomenon.

The Solfatara crater was formed at about 4.2 ka and it consists of a sub-rectangular depression, whose geometry is controlled by N40-50W and N50E trending fault systems. Nowadays, degassing and fumarolic emissions occur at the Solfatara crater, together with a series of small uplift episodes and seismic swarms, particularly from 1984 to 2006 when the whole caldera subsided. Specifically, these earthquakes are likely to be associated with a buried cavity filled with a water-vapour mixture at poor gas-volume fractions.

In this scenario, we propose a 2D multi-physics study of Solfatara volcanic system via the integration of thermodynamic and poroelastic model results.

We start with the first model, for which we collect the available geological and geophysical information, such as the main faults, crustal parameters and the temperature distribution in the conductive regime. This information is merged into a multiphysics Finite Element Model by using COMSOL Multiphysics software: we simulate the crustal thermal regime beneath the Solfatara crater by performing a time-dependent convective thermal model in porous media. We also simulate the fluids circulation in accordance with the Darcy’s Law by considering the bi-phasic water properties (i.e., liquid and vapor states) as approximation to characterize the modelled fluid. Furthermore, the seepage of meteoric water through the high permeable volcanic rocks is also considered. At the end of the simulation, we observe the activation of a convective cell below the Solfatara crater, where the 250°C isotherm reaches ~500 m b.s.l.. The retrieved results is compared with the available data, as the resistivity model proposed by Siniscalchi et al. (2019) and the measured temperature at the CF23 well.

Within the same discretized numerical domain, we perform the second model by considering the previous fluid pore pressure modelled field; we detect the pressure source parameters better explaining the observed ground deformations of Campi Flegrei caldera. The analysed dataset consists of processed SAR images acquired by Sentinel-1A/B satellites constellation during the 2020 – 2022 time interval. We here compare the retrieved stress field within the caldera with the hypocenters distribution.

In conclusion, this study contributes to improve the knowledge about the role of fluids migration in the framework of the magmatic processes.

How to cite: Barone, A., Gola, G., Pepe, A., Tizzani, P., and Castaldo, R.: Fluid migration in volcanic environment: thermo-poroelastic modelling of Solfatara crater., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13270, https://doi.org/10.5194/egusphere-egu23-13270, 2023.

EGU23-14488 | ECS | Orals | SM6.1

Mapping of structures formed by hydraulic fracturing based on microseismic events location. 

Elzbieta Weglinska, Andrzej Lesniak, Andrzej Pasternacki, and Pawel Wandycz

Structures created by hydraulic fracturing can be identified using the location of induced microseismic events. Estimating the effectiveness of stimulation depends on fracture mapping. Event location errors make precise imaging of fractures in a scattered seismic cloud challenging. In order to increase the reliability of the determined structures on the basis of events with location error, we proposed a several-stage procedure. This procedure was demonstrated on microseismic events located during the fracturing of the Wysin-2H/2Hbis horizontal well, an exploration well for shale gas in northern Poland from June 9, 2016 to June 18, 2016. All located events were subjected to a collapsing that allows obtaining new locations of events that are equivalent to original locations in a statistical sense. The creation of such an equivalent point cloud allows us to see certain structures that may reflect, for example, fractures. To validate the results before and after collapsing method, all events were set against the probability of a given brittleness index map.  It is demonstrated that the collapsed events occurred in regions that were more rigid, while the locations of events prior to this procedure showed no relationship with the occurrence of areas with higher susceptibility to fracking. The unsupervised machine learning algorithm HDBSCAN was used on a collapsed cloud to automatically detect clusters of events. The directions of identified clusters agree with the direction of regional maximum horizontal stress.

How to cite: Weglinska, E., Lesniak, A., Pasternacki, A., and Wandycz, P.: Mapping of structures formed by hydraulic fracturing based on microseismic events location., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14488, https://doi.org/10.5194/egusphere-egu23-14488, 2023.

Earthquakes are typically followed by a series of aftershocks. Deeply trapped and internally generated high-pressure fluid diffuses along permeable paths and subsequently reactivates faults that drive thousands of seismic events. The thermal decomposition of CO2 in the carbonate regime in the central Apennines contributes significantly to seismogenesis and provides substantial quantities of internally derived high-pressure fluids. We develop a 3-dimensional model of non-linear diffusion with a source term that diffuses along faults and to the surroundings, triggering seismicity along the flow paths, and compare model results with the spatial and temporal observations from the 2009 L'Aquila (Mw 6.3) and the 2016 Amatrice-Visso-Norcia (Mw 6.5) earthquake sequences. The model mimics the generation of additional fluid by thermal decomposition and shows solid correlations in space by comparing the calculated fluid pressure field and the locations of over 50,000 well-constrained hypocenters.

In contrast, other earthquakes result in only a small number or even no aftershocks. These include the Peru earthquake (Sep. 25, 2013 -Mw 7.1), the Mexiko earthquake (Sep. 19, 2017 - Mw 7.1), and the Crete earthquake (Oct. 12, 2021). Additionally, great earthquakes in Pakistan (Jan. 18, 2011 - Mw 7.2) and Iran ( Apr. 16, 2013 -Mw 7.7) also spawned no aftershocks despite the high magnitudes. These phenomena can be linked to the dynamics of volcanic arcs.

How to cite: Gunatilake, T. and Miller, S. A.: Linking Aftershock-free significant earthquakes to the dynamics of volcanic arcs; and linking aftershock-rich significant earthquakes to devolitization., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15583, https://doi.org/10.5194/egusphere-egu23-15583, 2023.

EGU23-16074 | ECS | Orals | SM6.1

Exploring the characteristics of seismo-electromagnetic signals (SES) in both passive and active experiments 

Ivana Ventola, Gerardo Romano, Marianna Balasco, Michele de Girolamo, Salvatore de Lorenzo, Marilena Filippucci, Roselena Morga, Domenico Patella, Vincenzo Serlenga, Tony Alfredo Stabile, Andrea Tallarico, Simona Tripaldi, and Agata Siniscalchi

Seismo-electromagnetic signals are electromagnetic signals generated by the propagation of a seismic wave in a porous media containing fluids (Gao & Hu, 2010).These signals can potentially provide useful information on the poro-elastic media and the hosted fluids (Garambois & Dietrich, 2002).Thus, there has been a growing interest in the study of SES in recent years, due to their potential.

Researchers are focusing both on modelling and analysis of both passive and active experiments to investigate the characteristics of these signals (e.g. Honkura et al., 2000; Matsushima et al., 2002; Warden et al., 2013; Gao et al., 2016; Balasco et al., 2014; Dzieran et al., 2019).Passive experiments involve the observation and analysis of naturally occurring SES triggered by earthquakes, while active experiments involve the controlled generation of these signals using seismic source.

The aim of our work is to present the results deriving from the analysis of SES recorded with both approaches. As for the passive one, the data set consists of the time series recorded by two magnetotelluric stations in continuous monitoring, co-located with two seismic stations, in seismically active areas of Southern Italy (the Gargano promontory and the Agri valley).

As for the active one, the data set derives by an active seismic experiment carried out in the caldera of the Phlegrean Fields, the Italian super-volcano.

How to cite: Ventola, I., Romano, G., Balasco, M., de Girolamo, M., de Lorenzo, S., Filippucci, M., Morga, R., Patella, D., Serlenga, V., Stabile, T. A., Tallarico, A., Tripaldi, S., and Siniscalchi, A.: Exploring the characteristics of seismo-electromagnetic signals (SES) in both passive and active experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16074, https://doi.org/10.5194/egusphere-egu23-16074, 2023.

EGU23-16539 | ECS | Posters on site | SM6.1

Insights into shallow and deep fluid circulation of the Southern Apennines seismic belt (Italy) using borehole pore pressures 

Eleonora Vitagliano, Luigi Improta, Luca Pizzino, and Nicola D'Agostino

Pore pressures at depth are usually described in relation with hydrostatic pressures, implying an interconnection between pores and fractures from the earth's surface up to a certain depth. In some cases, pore pressures exceed hydrostatic values, and these overpressures can be interpreted as an equilibrium between geological pressurization mechanisms (e.g., under compaction, tectonics, hydrocarbon generation, dehydration reactions, various sources of fluids, etc.) and pressure dissipation processes, which mainly depend on rock properties (e.g., hydraulic diffusivity).

In actively deforming regions, other subsurface mechanisms may favor the generation of overpressure (e.g., parallel shortening of strata) and in addition, surface topography may drive meteoric groundwater to flow from positive reliefs to nearby lowlands, interacting with deeper fluids.

Within the framework of the PRIN FLUIDS project, the research presented here aims to study the pore pressures collected in 30 exploration wells of the Sannio and Irpinia regions (Southern Apennines thrust-and-fold belt, Italy), with the objective of clarifying if and how deep fluids (e.g., free gas phases such as CO2 and HCs, as well as saline paleo/formation waters with Na-Cl chemistry and high pCO2) interact with shallow waters and to investigate the relation between shallow and deep crustal fluid dynamics and seismogenesis. In the proposed study, pressures, normalized to a hydrostatic profile, have been first retrieved from borehole pressure data, and then projected on five geological transects, to recognize the spatial distribution of the pressure trends (i.e., hydrostatic, over-pressured and hydrostatic over-pressured zones) underneath the Apennines range (from the internal to the external thrust belt) and the Plio-Pleistocene Bradano foredeep. In addition to the structural features, we also used other information available from well profiles (i.e., litho-stratigraphy, geochemical data, thermal data and petrophysical parameters) and open sources (i.e., geothermal gradient and sedimentary facies distribution maps). This material was integrated with the distribution, at the surface, of deep-derived fluids (gas manifestations, thermal springs, CO2-rich groundwater) to calibrate the system. Moreover, the overall data enabled deepening the comprehension of the role of the pressurized layers in acting as possible vertical and lateral barriers to/for fluid migration, and estimating the possible origin and depths reached by the thermal circuits. Finally, with respect to the distribution of pore pressure zones, two other aspects related to the active deformation and fluid leakage were addressed: vertical stress magnitudes at depth and distribution pattern of low-magnitude background seismicity of the area. The analysis on these topics and the preliminary results will be shown at the end of the proposed workflow.

How to cite: Vitagliano, E., Improta, L., Pizzino, L., and D'Agostino, N.: Insights into shallow and deep fluid circulation of the Southern Apennines seismic belt (Italy) using borehole pore pressures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16539, https://doi.org/10.5194/egusphere-egu23-16539, 2023.

EGU23-17093 | Posters on site | SM6.1

Application of a time-domain method to estimate the attenuation quality factor from the Geysers geothermal field microearthquake records 

Aldo Zollo, Sahar Nazeri, Jin Zhen, and Grazia De Landro

To determine the crustal rock rheological properties and model wave propagation in an anelastic attenuating medium, it is necessary to determine the quality factor Q, which expresses the fraction of friction-dissipated energy to total seismic energy. Measuring time-broadening of the first P- and S-wave pulses, we propose a time-domain method to estimate the frequency-independent Q parameter of body waved from microearthquake records. We assume a uniform velocity, circular rupture model as represented by a triangular moment rate/displacement function, whose attenuated velocity pulse widths are analyzed in the near-source distance range. The attenuated velocity pulse width data allow the calculation of the source parameters, including rupture duration/radius and stress drop values, as well as the attenuation factor t* (travel distance/quality factor), used to determine the attenuation structure in the study area. It is noted that the constant coefficient of the pulse-width vs t* relationship, required for calculating the t* catalog, have been calibrated for a triangular displacement waveform through simulation analysis. An evaluation of the methodology was carried out on 126 micro-events with Mw ranging from 1 to 3 located around the PRATI-9 and PRATI-29 injection wells at the Geyser geothermal field, California. The analysis of the P- and S-waves indicates a Qp range of 55 to 100 and a Qs range of 89 to 189. To validate the the t* data, we have inverted them to obtain a 1D QP model that matches consistently with the profiles derived from existing tomographic QP models in the area.

How to cite: Zollo, A., Nazeri, S., Zhen, J., and De Landro, G.: Application of a time-domain method to estimate the attenuation quality factor from the Geysers geothermal field microearthquake records, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17093, https://doi.org/10.5194/egusphere-egu23-17093, 2023.

EGU23-2724 | ECS | PICO | SM6.2

Long-term evolution of the spectral content of continuous seismo-volcanic signals from a network-based analysis 

Emmanuel Caballero, Nikolai Shapiro, Cyril Journeau, Léonard Seydoux, Jean Soubestre, and Andrés Barajas

Volcanoes are multi-physics systems where different phenomena interact, such as magma transport, degassing, crystallization, and pressure-induced faulting. These interactions create a series of seismic signals, among which we have volcano-tectonic earthquakes, long-period events, and volcanic tremors. Thanks to these signals, there has been an improvement in the comprehension of volcanic systems. However, due to its complexity, there is still a debate regarding the observed seismic signals, i.e., their precise origin and characteristics. In the past, some techniques, such as spectral analysis and simple earthquake location were used. However, these techniques lack the resolution that we currently need. In this regard, network-based methods have been developed to determine the level of wavefield coherence and to classify different seismicity types from complex continuous signals.

In this work, we analyze eight years (from 2011 to 2020) of continuous seismic data of Piton de la Fournaise, la Réunion, France, using a network array including approximately 20 stations. We use a method based on the covariance matrix combining interstation single-component cross-correlations. From the continuous velocity records, we create temporal overlapping windows in which we estimate the covariance matrix in the frequency domain. We then evaluate its rank through the estimation of the width of its eigen-values distribution, in other terms, the number of independent seismic sources. This method allows us to quantitatively measure the presence of coherent sources recorded by the array and to characterize their frequency content.

The resulting distributions of the spectral width show that continuous signals are characterized by multiple narrow spectral peaks clearly observed in the co-eruptive tremors but also during periods without visible volcanic activity. To enhance these peaks, we re-normalize the distribution of spectral width in the frequency and time domains. As a result, we observe in the 1-3 Hz frequency band many spectral peaks that remain nearly constant during very long periods (weeks to months). At the same time, we observe a clear difference in the distribution of these frequencies between the co-eruptive and quiet periods and also some significant variations during long-standing eruptions. We suggest that variations of the spectral lines can be related to the properties of seismo-volcanic sources and eventually to the structural changes and, therefore, can be used in volcano monitoring.

How to cite: Caballero, E., Shapiro, N., Journeau, C., Seydoux, L., Soubestre, J., and Barajas, A.: Long-term evolution of the spectral content of continuous seismo-volcanic signals from a network-based analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2724, https://doi.org/10.5194/egusphere-egu23-2724, 2023.

EGU23-3374 | ECS | PICO | SM6.2

Evolution of shallow volcanic seismicity in the hydrothermal system of La Soufrière de Guadeloupe following the April 2018 Mlv 4.1 earthquake 

Laetitia Pantobe, Arnaud Burtin, Kristel Chanard, and Jean-Christophe Komorowski

La Soufrière volcano in Guadeloupe presents a seismo-volcanic (VT) activity associated with an active hydrothermal system. This microseismicity is principally shallow, produced by repeating earthquakes and triggered in swarms. Four recurrent families of VT repeaters are detected, including a main family accounting for more than 80% of the catalog since at least 2014.

By stacking seismic waveforms of repeaters and using a temporary dense seismic network, we build a MASTER event with a high Signal-to-Noise Ratio (SNR) and we better constrain the absolute location of the main MASTER event.

We report positive residuals between observed and predicted P-wave arrival times at nearly all stations, suggesting that the velocity model of the shallow part of the dome could be improved. We significantly lower these residuals by raising the P-wave velocity from 2 to 2.7 km/s and reducing the Vp/Vs ratio from 1.8 to 1.69, leading to an improved local velocity model.

We then locate each VT event relatively to is own MASTER hypocenter and image the hydrothermal seismic activity along a sub-vertical conduit, beneath the Tarissan crater acid lake found at the summit of Soufrière.

We also define a linear relationship between the peak amplitude of seismic events and their duration to obtain a pseudo local magnitude. The approach allows us to automatically and accurately estimate the magnitude of each event at the detection stage.

The April 2018 earthquake (MLv 4.1), the largest since the last phreatic eruption in 1976-77, occurred 2 km northwest of the summit and generated an increase in the number of events and seismic energy released. This event also resulted in the emergence of a secondary significant VT family during the summer 2018, located above the first one. We show that the increase of shallow microseismicity, following the April 2018, is likely explained by dynamic damage of the hostrock below the dome, thanks to the analysis of the associated distribution of Coulomb stress variation and relative velocity variations.

Finally, using a statistical approach, we detect periodicities in the number of events and the released seismic moment at La Soufrière. A dominant peak of seismic activity is observed in October-November and a second lower peak is detected in April.

How to cite: Pantobe, L., Burtin, A., Chanard, K., and Komorowski, J.-C.: Evolution of shallow volcanic seismicity in the hydrothermal system of La Soufrière de Guadeloupe following the April 2018 Mlv 4.1 earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3374, https://doi.org/10.5194/egusphere-egu23-3374, 2023.

The IMPROVE ITN project focuses its interdisciplinary approach on a better understanding of volcanic systems, partly with multiphysics imaging methods. One target of this project is Krafla, a volcano of the northern volcanic zone in Iceland, which erupted last during the Krafla fires in the 1970s and 80s. Also, in this period the national power company of Iceland (Landsvirkjun) built a geothermal powerplant inside the Krafla caldera, increasing the knowledge of the complex system through electro-magnetic and seismic imaging methods and seismological observations.
Nonetheless, the high-resolution imaging of the magmatic system still poses a challenge just as the origins of the seismicity remain poorly understood. To tackle these questions a multi-physics experiment has been carried out in June and July 2022.
The experiment included an active 3D ERT experiment to image the first kilometre of the geothermal system, the densification of the already existing MT measurements and the installation of a dense seismic array of 100 stations deployed for 1 month. In addition, Landsvirkjun provided continuous seismic data acquired from 12 broadband 3-C stations over the last 8 years.
With this dataset we aim to better understand temporal and spatial changes in stress, the anthropogenic influence on the system through the geothermal industrial activity and to image shallow magmatic pockets.
The broadband data of the 12 permanent seismic stations were used to analyse the seismicity with STA/LTA and Template Matching methods. The first P- and S-wave onsets were automatically picked and inverted using a joint hypocentre-velocity approach based on ray theory. It provides a new 3D P-wave velocity model and refined locations of the seismicity.
This updated earthquake catalogue, consisting of seismicity of the last 8 years, covers a deflation and an inflation period of Krafla, yielding the opportunity to better investigate the seismic properties in relation with geothermal industrial activity and long-term deformation of the volcano. The variability of the P-wave velocity will be compared to the available 3D resistivity models obtained from previous MT measurements.
In the future, the dense seismic array will be used for high resolution imaging at the geothermal upflow-systems and jointly interpreted with the ERT and MT data, while the 12 broadband recordings will be used for seismic noise monitoring purposes.

How to cite: Glück, E., Garambois, S., and Vandemeulebrouck, J.: First results of a multiphysics experiment at Krafla geothermal volcano: Seismicity pattern from joint hypocenter-3D travel-time tomography inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3550, https://doi.org/10.5194/egusphere-egu23-3550, 2023.

EGU23-3556 | ECS | PICO | SM6.2

An investigation of high frequency seismic tremor on Mt Etna 

Maurice Weber, Christopher Bean, Ivan Lokmer, Patrick Smith, Luciano Zuccarello, Silvio De Angelis, and Vittorio Minio

High frequency seismic data (> 10 Hz) on volcanoes have traditionally been less studied as precursory seismicity to volcanic eruptions is dominated by lower frequency signals. However, inspection of newly acquired data during a field campaign between July and September 2022 from individual high sampling rate seismic stations on Mt. Etna reveals the presence of high frequency (10-90Hz) signals, which are poorly understood. In an attempt to determine their location, mechanisms and wavefield properties, we deployed 104 nodal seismic sensors, mainly in 6 tuned circular array configurations consisting of several rings with increasing radius and number of nodes per ring around a central station. The nodes record at a sampling rate of 250Hz (125Hz Nyquist) and the frequency content of the recorded seismicity shows signals up to about 100 Hz. In addition to the high frequency nodes, we also deployed a profile consisting of 11 elements (infrasound, short period) as well as four broad band sensors.

A variety of signals were recorded, with coherent signals on different stations across the full spectral range. Thus far initial multi-array beamforming has been applied to the data, demonstrating a range of locations which varies depending on the frequency range looked at. Whilst sources near the summit region are most common (especially at frequencies below 5 Hz), there are also other locations from which tremor emanates, opening questions about their origin.  Comparisons with infrasound, gas and weather data are ongoing, in an effort to shed light on the sources of these unusual signals.

How to cite: Weber, M., Bean, C., Lokmer, I., Smith, P., Zuccarello, L., De Angelis, S., and Minio, V.: An investigation of high frequency seismic tremor on Mt Etna, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3556, https://doi.org/10.5194/egusphere-egu23-3556, 2023.

EGU23-6025 | ECS | PICO | SM6.2

Comparison of a rotational sensor and an array on Piton de la Fournaise volcano, La Réunion 

Nele I. K. Vesely, Eva P. S. Eibl, Valérie Ferrazzini, and Joachim Wassermann

Piton de la Fournaise is a shield volcano located on La Réunion island in the Indian Ocean and most recently tends to erupt once - twice annually. Besides volcanic tremor during eruptions and rockfall, long-period (LP) and volcano-tectonic (VT) earthquakes are dominating signals on the island.

In October 2022, a rotational sensor and an array of seven seismometers were installed within the Enclos Fouqué, the youngest caldera of volcano Piton de la Fournaise. We record volcano-seismic signals that were also detected by the seismic network of the Observatoire Volcanologique du Piton de la Fournaise (OVPF). Our aim is to test the performance of the rotational sensor and the conventional seismic array with respect to these events.

Local VT and rockfall events have been detected on all instruments and could be compared by calculations of backazimuth (BAZ) and signal-to-noise ratio (SNR). We derive the rotational rate using three array stations for array derived rotation (ADR). First results indicate an agreement between the BAZ obtained from the rotational sensor, the array and the location using the OVPF network for strong rockfall events. Summit VT and weak local earthquakes could furthermore be located by the array BAZ. Preliminary SNR results from all considered events indicate higher values for the array stations. Since the instruments could not be buried on site and the rotational sensor is likely affected by wind noise, it is assumed that comparison between the instruments will work best for strong and/ or close events.

How to cite: Vesely, N. I. K., Eibl, E. P. S., Ferrazzini, V., and Wassermann, J.: Comparison of a rotational sensor and an array on Piton de la Fournaise volcano, La Réunion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6025, https://doi.org/10.5194/egusphere-egu23-6025, 2023.

Microscopic dynamic processes associated with gas-liquid and fluid-solid interaction, as well as the magma/host-rock rheology and tectonic stress, determines the stability of magmatic/hydrothermal system underneath active volcanoes. Specifically, the overpressure in the system largely dictates the timing of upcoming eruptions, whereas the system volume controls the potential magnitude and impact of upcoming eruptions. While quantitative assessment of the system overpressure and volume provides invaluable insights into magma dynamics, eruption forecasting, and hazard mitigation, it is not trivial to constrain these fundamentals.

We devise a generic framework to estimate system overpressure and volume associated with repetitive volcano-seismic events such as VLP and LP.  Following the framework developed by Nishimura (1998), we derive the relationship between macroscopic seismic source parameters (i.e., seismic moment rate and single force), the acoustic properties of the fluid near the seismic source (i.e., sound speed and density), and system overpressure and volume. Macroscopic seismic source parameters can be obtained through waveform modeling and inversion. On the other hand, the acoustic properties of the fluid near the seismic source can be estimated by modeling the VLP/LP resonance peaks (i.e., resonance period and attenuation). Alternatively, the gas fraction obtained from the gas emission (rate) and magma output (rate), as well as local volcanic activities (e.g., hydrothermal or magmatic) could also help evaluate the fluid properties in the context of a variety of mixtures of gas, liquid and solid (e.g., Kumagai & Chouet, 2000).

As a proof of concept, we apply the newly developed framework in Aso volcano where repetitive VLP has been observed since 1930s. We show that the estimated overpressures associated with VLP during the 2014-2016 eruption cycle is on the order of ~1 MPa, generally consistent with the tensional rock strength. The size of pressurized system volume is on the order of ~106 m3, like the magmatic output in the same episode. In this report, after discussing the impact of various assumptions on the estimate of the system overpressure and volume, we will explore a global database to evaluate the system overpressure and volume and discuss relevant microscopic processes that are consistent with these findings. 

How to cite: Niu, J. and Song, T.-R. A.: Tracking magma plumbing system overpressure and volume through macroscopic seismic source parameters of repetitive volcanic-seismic events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6066, https://doi.org/10.5194/egusphere-egu23-6066, 2023.

EGU23-6804 | ECS | PICO | SM6.2

Increased complexity of seismic ground motion prior and during the 2014 Holuhraun eruption, Iceland 

Maria R.P. Sudibyo, Eva P.S. Eibl, Sebastian Hainzl, and Matthias Ohrnberger

The complexity of time series can be quantitatively measured using Permutation Entropy (PE). PE has recently been introduced as a potential tool in eruption forecasting by applying it to the seismic time series. Examples of successful applications are the eruptions at Strokkur Geyser, Iceland, the 1996 eruption of Gjálp, Iceland, and the eruptions of Shinmoedake volcano, Japan, in 2011, 2017, and 2018. While PE is able to show temporal changes prior to an eruption, these features are not always prominent. To improve this method, we calculate PE not only for the amplitudes of the seismic signals but also for the seismic instantaneous phases, called Phase Permutation Entropy (PPE). To understand the difference between PE and PPE, we performed synthetic tests by creating several synthetic waveforms using different numbers of sin wave superposition. We used more wave superposition with different frequencies to create complex waves containing broader frequency spectrum, while less superposition is used to create simpler waves containing narrower frequency spectrum. PE and PPE values are both low for simple waves and high for complex waves, but their absolute values differ, which might contain valuable information. The gap, dP = PE-PPE, is found to be smaller for complex waves compared to the more simple waves.  We then calculated PE and PPE for seismic data recorded from January 2014 to December 2015, which covered the eruption period of Holuhraun in Iceland. During the time of quiescence, both PE and PPE exhibit a long period variation which seems to be seasonal. Calculating dP weakens the long period noise and generates a more stable baseline.  We observe that the temporal variation of dP started to decrease below the baseline after 24 May 2014, indicating that the ground motion got more complex. An abrupt drop of dP to its lowest level was observed on 16 August 2014, when the dyke started to propagate from Bardarbunga to Holuhraun. While dP increases after the onset of eruption on 29 and 31August 2014, there is no prominent feature between the dyke propagation and the onset of the eruptions.  During the eruption period, dP stays lower than the background dP, indicating a higher ground motion complexity compared to the quiescence time. After January 2015, the gradual increase of dP back to the baseline level is clearly observed, showing the method’s potential to foresee the end of the eruption.

How to cite: Sudibyo, M. R. P., Eibl, E. P. S., Hainzl, S., and Ohrnberger, M.: Increased complexity of seismic ground motion prior and during the 2014 Holuhraun eruption, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6804, https://doi.org/10.5194/egusphere-egu23-6804, 2023.

EGU23-8298 | ECS | PICO | SM6.2

Models for the dynamic triggering of volcano seismicity at Sierra Negra, Galápagos Islands. 

Eleanor Dunn, Chris Bean, Andrew Bell, and Ivan Lokmer

Dynamic earthquake triggering is the process where local earthquakes are triggered by dynamic stress perturbations often from teleseismic earthquakes. Dynamic triggering from regional earthquakes can also trigger local volcanic seismicity. An understanding of dynamic triggering on volcanoes offers a window into volcano stress state and seismicity initiation, in general. Repeated episodes of dynamic triggering have been recorded at Sierra Negra, a large basaltic shield volcano on Isabela Island, Galápagos. Sierra Negra is a large elliptical summit caldera with a trap-door fault system and a 2km deep sill-like magma reservoir below the caldera. Sierra Negra erupted in June 2018, as part of a cycle of pre-eruption inflation, co-eruption deflation, and renewed post-eruption inflation. Dynamic earthquake triggering was observed at Sierra Negra following high magnitude teleseismic events that occurred from 2010-2018, with the number of dynamically triggered earthquakes increasing with increasing inflation of the magma reservoir. However, the locations and mechanisms of this dynamic triggering have not been determined. In this study, we aim to answer two questions: 1) is it possible to successfully interpret dynamic triggering on Sierra Negra and, 2) can dynamic triggering in Sierra Negra be used as a stress gauge? To interpret dynamic triggering, an STA/LTA detection algorithm has been designed which detects when a dynamically triggered event has happened. This provides insight into how regularly dynamic triggering occurs on Sierra Negra and how, if at all, it is related to teleseismic events. The detection algorithm has also been used to compare the dynamic triggering rate to the local seismic rate on Sierra Negra. We have also located where dynamic triggering occurs on Sierra Negra. To address question two; Peak Dynamic Strain (PDS) has been used as a threshold to detect when dynamic triggering occurs, PDS can be used to understand the stress state of Sierra Negra pre-, co- and post-2018 eruption. Looking forward we hope to understand the relationship between the location and timing of dynamic triggering, and its potential use in understanding volcano unrest state.

How to cite: Dunn, E., Bean, C., Bell, A., and Lokmer, I.: Models for the dynamic triggering of volcano seismicity at Sierra Negra, Galápagos Islands., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8298, https://doi.org/10.5194/egusphere-egu23-8298, 2023.

EGU23-8680 | ECS | PICO | SM6.2

Challenges in volcano magma chamber imaging: A numerical study 

Ka Lok Li, Christopher J. Bean, and Ólafur Gudmundsson

Volcanic eruption is a continuous threat to many places in the world. Despite recent advances in volcano monitoring techniques and developments in monitoring networks, eruption forecasting remains a challenging task, partly because an accurate description of the current state of a volcano is missing. Such a description requires knowledge about the time varying internal structures of the volcano. An ultimate goal is, therefore, to obtain snapshots of the volcano structures across multi scales. However, due to limitations in imaging techniques in highly heterogeneous volcanic environments, e.g., strong velocity gradient near surface and rich in small-scale scatterers throughout the volcano, only relatively large-scale structures are normally recovered. This is relevant to imaging all important magma chambers, which have often been illusive. Recent studies reveal that magma chambers can have large aspect ratio, i.e., a thin body that extends laterally more than a few times its thickness. This extreme geometry adds to the complexity of the imaging problem. In this research, we present a systematic study of how different factors affect the ability to recover a clear image of a magma body and their relative importance in the imaging problem. Classes of synthetic models with different weights of these factors are generated. The models are then used to generate synthetic seismograms using numerical simulations of full wavefield seismic wave propagation. The seismograms are used as the input to various image techniques for recovering images of the synthetic models. Our preliminary results show that even in a non-scattering environment, imaging a magma chamber can be challenging due to, e.g., weak velocity contrast between the magma body and the surrounding rock materials. The imaging problem is compounded by strong scattering. The aim of the work is to understand the limitations of current imaging and acquisition approaches, and to better understand what we can “expect to see”.

How to cite: Li, K. L., Bean, C. J., and Gudmundsson, Ó.: Challenges in volcano magma chamber imaging: A numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8680, https://doi.org/10.5194/egusphere-egu23-8680, 2023.

EGU23-9612 | ECS | PICO | SM6.2

Seismic imaging of shallow magma bodies at Krafla, Iceland. 

Regina Maaß, Christopher J. Bean, and Ka Lok Li

Imaging the subsurface geology at volcanoes is crucial for understanding their structure and dynamics. Knowledge about the existence of magma chambers, fault and fluid systems improves natural hazard assessment and geothermal energy exploitation. However, the highly heterogeneous subsurface at volcanoes complicates the identification of geologic layers and objects. A strongly scattered seismic wavefield is typically recorded that masks coherent energy reflected at interfaces of interest. In addition, small geologic features such as magma bodies are often smeared out by tomographic techniques. A well-known example that highlights this problem is Krafla, a volcano caldera in the north-east of Iceland. In 2009, a magma body was unexpectedly found at a depth of 2.1km during drilling for geothermal purposes. Even though Krafla is one of the best-studied volcanoes worldwide, the shallow magma body remained undetected. In the summer of 2022, we conducted a six weeks long field experiment at Krafla as part of the IMPROVE project. We deployed densely spaced short seismic profiles comprising 114 seismometers in a passive experiment. Our goal is to image the magma body at 2.1 km depth. At first, we carry out a comprehensive data characterization in order to better understand the seismic wavefield and the influence of source, propagation, and near-station effects. In a subsequent step we apply targeted imaging methods including local earthquakes and high-frequency industrial noise. Krafla provides an optimal setting to test and calibrate seismic imaging, because the location of the magma body is known (through drilling). By combining different methods, we seek to improve seismic imaging techniques in order to obtain a high-resolution image of the subsurface in complex media.

How to cite: Maaß, R., Bean, C. J., and Li, K. L.: Seismic imaging of shallow magma bodies at Krafla, Iceland., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9612, https://doi.org/10.5194/egusphere-egu23-9612, 2023.

EGU23-9796 | PICO | SM6.2

The eruption of the Hunga Tonga-Hunga Ha'apai volcano on 15 January 2022 as observed at seismic stations in Germany 

Thomas Plenefisch, Andreas Steinberg, Patrick Hupe, Christoph Pilger, Stefanie Donner, Peter Gaebler, Ole Ross, and Lars Ceranna

On 15 January 2022 at 04:15 UTC, an enormous explosive eruption of the Hunga Tonga-Hunga Haʻapai submarine volcano (short: Hunga) occurred in the Tonga-Kermadec volcanic area in the southern Pacific Ocean. It was one of the strongest volcanic eruption within the last 150 years. The eruption column reached a height of more than 50 kilometres causing heavy atmospheric turbulences. A strong Lamb and a tsunami wave were generated. Besides these phenomena also seismic waves could be observed on seismic stations all over the world.

Consequently, seismic body and surface waves of the Hunga main explosion could be clearly recorded at seismic stations in Germany. After about 19 minutes, the PKP phase was the first arriving body wave reaching the broadband stations of the German Regional Seismic Network and the Gräfenberg Array. Using the short-period WWSSN-SP filter it was possible to determine the onset times of relatively weak PKPbc phases at several stations. The onset times as well as slowness and azimuth determined by array methods allowed an unambiguous assignment to the Hunga event and an epicenter localization deviating approximately 1 to 1.5 degrees from the volcano.

While the PKP phase is only weakly visible in short periods it shows up clearly in the long-period range (SRO-LP filter). The onset times determined therein were still accurate enough to provide a localization similar to that obtained in the short-period range. Furthermore, at least one additional event is detected on the long-period seismograms about 4 minutes after the main event.

To assign a seismic magnitude to the Hunga event, we analyzed the surface wave trains. The Ms magnitudes vary between 5.8 and 6.3 within the individual stations of the GRSN, with a mean value of 6.0.

The Tonga-Kermadec subduction zone is characterized by strong earthquake activity. This allows us to compare the seismic recordings of the Hunga event with those of earthquakes from the same area with shallow focal depths and comparable magnitudes. It turns out that PKP phases of the Hunga eruption have significantly smaller amplitudes in the short-period range than for the compared earthquakes but similarly strong in the long-period range. We conclude that a long-period excitation is characteristic for the seismically relevant focal process of the Hunga event.

How to cite: Plenefisch, T., Steinberg, A., Hupe, P., Pilger, C., Donner, S., Gaebler, P., Ross, O., and Ceranna, L.: The eruption of the Hunga Tonga-Hunga Ha'apai volcano on 15 January 2022 as observed at seismic stations in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9796, https://doi.org/10.5194/egusphere-egu23-9796, 2023.

Swarms of earthquakes are often associated with eruptive processes, but many swarms occur near volcanoes that are not easily associated with eruptions, complicating their use in eruption forecasting.  In some cases, swarms may be caused by hydrothermal processes and can be considered as part of a volcano’s normal background seismic activity. Other swarms near volcanoes may be considered purely tectonic in origin, or some combination of tectonic, magmatic, and hydrothermal processes. Distinguishing driving processes for a volcanic swarm is often difficult using seismic data alone and yet seismic data may be the only monitoring stream available at many volcanoes.  Even when other monitoring data are available, seismic unrest often manifests itself first in the run-up process to an eruption.  Thus, tools that help distinguish whether a swarm is magmatic or not are desirable for observatories to improve forecasting efforts.

Determining when an eruption will follow a swarm is non-trivial, even if a swarm can be confidently linked to a magma intrusion.  Statistical comparison of an ongoing swarm to prior swarms at the volcano or at other volcanoes provides baseline probabilities for forecasting efforts and may reveal patterns in precursory activity in general. Swarms are often easy to visually identify in an earthquake catalog, but as no standard approach exists to consistently define and detect swarms across time and space, it is difficult to statistically compare them. At individual volcanoes, temporal changes in monitoring networks present challenges, while other factors, such as varying rates of background seismicity, complicate inter-volcano swarm comparisons.

To address some of these challenges, we have created a catalog of earthquake swarms covering 62 eruptions at 79 active volcanoes in the United States. The catalog balances consistency in methodology with the inherent variations between and among the volcanoes and their monitoring networks and is calibrated such that only concerning swarms, significantly above background levels, are retained.  We compute a suite of statistical attributes for each swarm and compare these attributes among various subgroups of swarms and volcanoes. Overall, we find that ~25% of the swarms in the catalog are associated with eruptions but only ~10% began prior to the eruption. In addition, though ~35% of eruptions are associated with swarms, only ~20% of eruptions have swarms that began prior to the eruption.  The eruptive and non-eruptive swarms show significant differences in evolution of moment release and event rate, but these differences vary depending on the types of volcanoes and eruptions considered. When tailored to the specifics of an ongoing swarm, analog swarm comparisons may help decipher driving process and likelihood of eruption.

 

 

 

 

How to cite: Pesicek, J. and Prejean, S.: A catalog of volcanic earthquake swarms in the United States: comparative analysis and use in eruption forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10114, https://doi.org/10.5194/egusphere-egu23-10114, 2023.

Inferring the seismic source mechanisms of small-to-medium-size earthquakes from the observed waveforms via inverse methods remains challenging. Firstly, a more generalized source representation is required to include a broader range of seismic sources. A seismic moment tensor (MT) is widely used to parameterize a seismic point source by assuming no net torque. However, there are well-documented seismic sources for which net torques are significant, and single force (SF) components are necessary to describe the physics of the problem, e.g., landslides and volcanic and glacier earthquakes. Secondly, the inter-parameter correlation, e.g., the tradeoffs between the MT’s isotropic and compensated-linear-vector-dipole components for shallow explosive events and the MT and SF components at all depths, can be significant. Therefore, there is imperative for advanced sampling algorithms to explore the parameter space thoroughly and effectively. Thirdly, a complete uncertainty treatment should consider theory error primarily due to the imperfection of Earth's structure (referred to as structural error) apart from data noise. To date, the uncertainty of the 1D Earth model (1D structural error) has been investigated and proven indispensable in source studies. A rigorous uncertainty estimate can improve the resolvability of source parameters, but its implementation has been challenging.

We propose a joint point-source MT and SF inversion within the hierarchical Bayesian framework to address the abovementioned set of challenges in treating the 2022 Hunga Tonga-Hunga Ha'apai event. MT and SF are combined to represent a broader range of sources in the waveform inversion. Our approach takes advantage of affine-invariant ensemble samplers to explore the parameter space thoroughly and effectively. Furthermore, we invert for station-specific time shifts to treat the structural errors along specific source-station paths (2D structural errors). After comprehensive synthetic experiments to demonstrate the feasibility of our approach, we focus on physics-based scenarios for the 2022 Hunga Tonga-Hunga Ha'apai volcanic earthquake. More specifically, we analyze the non-double-couple character and the role of SF in the source mechanism. Our approach provides further insights into this particular earthquake and a platform for future studies of seismic events in various geological environments.

How to cite: Tkalčić, H., Hu, J., and Pham, T. S.: The 2022 Hunga Tonga-Hunga Ha'apai Volcanic Earthquake’s Source Mechanism Revealed Through a Hierarchical Bayesian Treatment of Moment Tensor and Single-Force, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10288, https://doi.org/10.5194/egusphere-egu23-10288, 2023.

EGU23-11770 | PICO | SM6.2

Seismic monitoring of co-eruptive volcanic processes during the 2021 Fagradalsfjall Eruption, Iceland, using two small-aperture arrays 

Martin Möllhoff, Patrick Smith, David Craig, Chris J. Bean, Kristin S. Vogfjörd, Ka Lok Li, and Nima Nooshiri

The 2021 Fagradalsfjall eruption in the Reykjanes peninsula, Iceland, was marked by episodes with varying volcanic activity. Our study focuses on the period from eruption start on the 19th March 2021 until the 2nd May 2021. This phase was marked by relatively continuous lava flows and non-periodic lava fountaining observed at up to 12 different vents, increasing in intensity throughout the observation period. Seismic tremor emanating from co-eruptive processes like for example lava fountaining, collapse of crater walls and magma and lava migration is non-impulsive, often with emergent onsets and no defined phase arrivals. Thus it is difficult to locate the tremor sources with traditional network based methods. We show that using small aperture arrays it is possible to locate and monitor several tremor sources that were active simultaneously, providing good spatial resolution on the details of the eruptive fissure. We investigate how array processing of 3-component data can assist with the determination of different seismic wave types and lead to a better understanding of the underlying volcanic processes. We find that seismic arrays are well suited to monitor the location, type and strength of volcanic processes that are active simultaneously. This can have important implications for volcanic hazard monitoring, especially when visual monitoring with webcams is difficult for example due to remoteness or poor visibility.

How to cite: Möllhoff, M., Smith, P., Craig, D., Bean, C. J., Vogfjörd, K. S., Li, K. L., and Nooshiri, N.: Seismic monitoring of co-eruptive volcanic processes during the 2021 Fagradalsfjall Eruption, Iceland, using two small-aperture arrays, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11770, https://doi.org/10.5194/egusphere-egu23-11770, 2023.

EGU23-13351 | PICO | SM6.2

Relative earthquake location of low-energy volcanic seismicity at Campi Flegrei 

Stefania Danesi, Nicola Alessandro Pino, Stefano Carlino, and Christopher Kilburn

This work intends to contribute to the comprehension of the Campi Flegrei caldera (CFc) unrest, through the relative relocation of the diffuse seismicity recorded during the 1982-84 unrest and after its reactivation in 2005.

The CFc is one of the best monitored volcanic areas in the world, with a multi-parametric network of observing stations operating in the area. The shallow structure of the caldera, between 1 and 3 km, is a high-temperature hydrothermal system formed by a sequence of volcanoclastic, tuffs, lava, and marine deposits. The temperature gradient measured in deep boreholes, down to a depth of about 3 km, exceeds 150°C/km. A zone of pressurized gas and sill intrusion is possibly located at 3-4 km. A long-term magma reservoir is hypothesized in the deep structure (7-9 km), persistently supplying CO2 to the surface (observable for the continuity of gas emission to the fumaroles of Solfatara-Pisciarelli as well).

While the unrest of 1982-84 has been generally associated with magma injection, a mechanism of fluid pressurization and heating of the CFc hydrothermal system is thought to be the primary forcing of ground deformation and shallow seismicity of the ongoing unrest. However, the mechanisms that control the interaction between the rising of fluids from deeper volumes and the seismicity within and below the hydrothermal system are still debated.

In this work we use the arrival times of located seismic events to perform a double-difference relative relocation of earthquakes that occurred in the years 1982-84 and 2005-2022. Moreover, by using calibration laws for magnitude scales to infer the moment magnitude Mw from available catalogs of duration magnitude Md, we estimate the spatial distribution of the cumulative seismic energy released during the two considered time spans.

The final distributions of hypocenters and radiated seismic energy, and their spatio-temporal evolution, suggest constraints for the identification of preferential pathways of rising fluids and for the imaging of structural barriers. These results can be interpreted jointly in light of previous works and available tomographic models for the definition of possible scenarios of unrest evolution.

How to cite: Danesi, S., Pino, N. A., Carlino, S., and Kilburn, C.: Relative earthquake location of low-energy volcanic seismicity at Campi Flegrei, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13351, https://doi.org/10.5194/egusphere-egu23-13351, 2023.

EGU23-15014 | ECS | PICO | SM6.2

Investigation of Tremor Events Coinciding with Skaftár-Cauldrons Glacial Floods from 2015 to 2021 

Bethany Vanderhoof, Kristín Jónsdóttir, Bryndís Brandsdóttir, Ólafur Guðmundsson, Sylvain Nowe, Jean Soubestre, Corentin Caudron, Thomas Lecocq, Yesim Cubuk-Sabuncu, and Bergur Einarsson

The Skaftár cauldrons are a pair of depressions at the surface of the Vatnajökull glacier that signify subglacial lakes caused by geothermal heat sources at the underlying bedrock. These subglacial lakes continuously grow in volume and produce fast-rising jökulhlaups (glacial lake outburst floods) at the glacier outlet 35-40 km away. Seismic tremor events coincide with these large floods, but the exact source of this tremor is unknown. To investigate the origin and characteristics of these tremors, network covariance matrix spectral width, real-time seismic amplitude measurements (RSAM), and spectral analyses were conducted for eight jökulhlaups spanning the years 2015 to 2021, with joint interpretation alongside hydrological and GPS data. Seismic data was aquired by the Icelandic Meteorological Office's network. The several-day time period spanning the flood propagation and deepening of the ice cauldrons was dominated by small icequakes along the subglacial flood path and emergent low frequency, temporally regular earthquakes with repetitive waveforms. Once most of the water had drained from the cauldrons, strong tremor bursts with a duration on the order of 10s of minutes and a dominant frequency range between 0.5 and 3 Hz were recorded by seismic stations both on and off of the glacier. This tremor occurred during seven out of the eight floods examined, exhibiting fewer than 10 clear tremor bursts per flood over approximately a 24-hour period. Preliminary results show that the amplitude of the tremor bursts correlates to the magnitude of the flood, with the strongest tremor occurring in 2015, during the largest recent flood from the eastern cauldron. Due to the similarities shared between the shape of this tremor’s seismic envelope and that of the tremor during hydrothermal explosions, we interpret the tremor seen after the Skaftá cauldrons have drained as steam explosions facilitated by a drop in the overlying water pressure.

How to cite: Vanderhoof, B., Jónsdóttir, K., Brandsdóttir, B., Guðmundsson, Ó., Nowe, S., Soubestre, J., Caudron, C., Lecocq, T., Cubuk-Sabuncu, Y., and Einarsson, B.: Investigation of Tremor Events Coinciding with Skaftár-Cauldrons Glacial Floods from 2015 to 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15014, https://doi.org/10.5194/egusphere-egu23-15014, 2023.

Recent eruptive activity at Stromboli is mostly characterized by persistent, Strombolian explosive activity from summit craters. Occasionally, so-called major explosions occur, and more rarely paroxysms take place, such as on 3 July and 28 August 2019. We analyze monitoring data recorded between 2016 and 2022 to identify and characterize patterns in multi-parameter time series (considering in particular seismic, geochemical, meteorological, and sea-level gauges), with special interest in analyzing patterns observed before and during the occurrence of major explosions and/or paroxysmal eruptions. In practice, (i) we implement algorithms to automatically identify families of seismic events using waveform features; (ii) we analyze the effect of oceanic microtremor on continuous and discrete amplitude-based measurements; (iii) we study the temporal and size distribution of event occurrences, and use this information to assess likely trends in eruptive behavior. Moreover, (iv) we use noise cross-correlations and auto-correlations to compute seismic velocity variations of the shallow crust. 

Multi-parametric measurements provide interesting insights in the temporal evolution of the eruptive activity at Stromboli; for example, correlated changes in the pattern at which events occur in time, patterns in the distribution of extreme, large events, and evidence of a decrease in seismic velocity, seem to be phenomena occurring before paroxysmal eruptions. Detailed analyses of the produced time series, including also pattern recognition techniques, are required for better revealing likely patterns and for better understanding and interpretation of observations. 

How to cite: Garcia, A., Zaccarelli, L., and Sandri, L.: Analysis of eruptive activity at Stromboli volcano through a continuous monitoring of multi-parameter geophysical data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15097, https://doi.org/10.5194/egusphere-egu23-15097, 2023.

EGU23-15229 | ECS | PICO | SM6.2

Rotational sensor on Etna volcano: What can we learn about volcano-seismic events? 

Eva P. S. Eibl, Martina Rosskopf, Mariangela Sciotto, Giuseppe Di Grazia, Gilda Currenti, and Philippe Jousset

Rotational sensors have been deployed on several volcanoes worldwide including Kilauea, Stromboli, Etna and a few volcanoes in Iceland. Within this presentation we focus on our first experiment using a rotational sensor on Etna in Italy. We recorded the volcanic activity including degassing and vigorous strombolian activity in August to September 2019. We compare our results using a rotational sensor with a normal Trillium Compact seismometer and the seismic network maintained by the INGV. We detect LP events, VT events and volcanic tremor, study the wavefield and back azimuths of the events and derive phase velocities of the ground. Luckily, we were able to assess the quality of our results using the detailed earthquake catalogues and locations derived at the INGV. We can easily detect changes in the wavefield e. g. when strong strombolian activity kicks in and are looking forward to applications on other volcanoes where details of the volcanic activity or changes might go unnoticed if no rotational sensor is present.

How to cite: Eibl, E. P. S., Rosskopf, M., Sciotto, M., Di Grazia, G., Currenti, G., and Jousset, P.: Rotational sensor on Etna volcano: What can we learn about volcano-seismic events?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15229, https://doi.org/10.5194/egusphere-egu23-15229, 2023.

EGU23-15894 | PICO | SM6.2

Local stress field spatio-temporal variations at Campi Flegrei from crustal anisotropy measurements 

Lucia Zaccarelli, Dario Delle Donne, Claudio Martino, Paola Cusano, Danilo Galluzzo, Patrizia Ricciolino, Francesca Bianco, and Nicola Alessandro Pino

We compiled a database for the Campi Flegrei seismic events that occurred from 2011 to 2018 at all stations available (merging permanent and temporary networks). Then we computed the two observables of the crustal anisotropy: time delay between fast and slow S-wave’s arrivals, and polarization direction of the fast S-wave. These results provide useful information about the amount of crustal anisotropy and the main direction, respectively, with this latter representing a proxy for the local stress field. We could thus obtain a picture of their spatial and temporal distributions to be compared with other geophysical and geochemical observations. In particular we could identify common features, such as change points, to several time series. This helps us in building a more complete interpretation of the volcanic system changes that were occurring during the recent ongoing unrest phase, which started in 2005. 

How to cite: Zaccarelli, L., Delle Donne, D., Martino, C., Cusano, P., Galluzzo, D., Ricciolino, P., Bianco, F., and Pino, N. A.: Local stress field spatio-temporal variations at Campi Flegrei from crustal anisotropy measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15894, https://doi.org/10.5194/egusphere-egu23-15894, 2023.

EGU23-211 | ECS | Orals | SM6.3

One to many seismogenic sources: from single earthquakes to seismic sequences 

Davide Zaccagnino, Luciano Telesca, and Carlo Doglioni

One of the major challenges in seismology is the lack of a unified view of earthquake dynamics embracing all the spatial and temporal scales at which it takes place: while several models describe successfully how single seismic events develop and statistical laws have been set up to characterize the distribution of seismicity in magnitude, space and time, at least as a consequence of mainshocks, such dichotomic information is rarely put into communication to better understand how seismogenesis occurs. Although a comprehensive, cross-scale theory is intrinsically impossible because of the different levels of physical complexity involved in the seismological processes, it is possible to derive several well-known links, as well as interesting new ones, between coseismic properties and long-term statistical patterns. We introduce a simple model based on optimization criteria to explain such mathematical relationships. Given an initial energy perturbation localised on a fault segment, the interface breaks down if the perturbation increases its energy beyond the breakdown level. The slip occurs and the fracture spreads rapidly. Not only that (which is not enough to explain how the fault system will behave at large scales), since the fault zone is in an unstable and frustrated state, i.e., a configuration forced by tectonic stress: meanwhile the fracture propagates, the adjoining interfaces and volumes move towards a more stable energy level, amplifying energy release by a certain amount. Then, the latter can be interpreted as a measure of the triggering power of fracture and applied to connect local and collective dynamics. We focus on the role of tectonic setting and the differences between in-fault and off-fault seismicity. Our model can reproduce several features of seismicity, such as the dependence of the b-value of the Gutenberg-Richter law on the tectonic setting, the correlation between b- and p-value of the Omori-Utsu law, the fractal dimension of hypocentral time series, duration of seismic sequences and the efficiency of the seismogenic process. We utilise the same framework to analyse the composition of moment tensor solutions of global and regional shallow seismicity in terms of double-couple vs non-double-couple contributions. We find that thrust events are characterized by higher double-couples with respect to normal and strike-slip fault earthquakes. Our results are also coherent with the broadly studied stress dependence of the scaling exponent b-value of the Gutenberg-Richter law, which turns out to be anticorrelated to the double-couple contribution. Our work suggests that the structural and tectonic complexity of the seismogenic source marked by the roughness of faults and the width of the dislocation zones has a significant impact on coseismic dynamics, which should be considered in the routinely applied observational procedures to avoid systematic biases in the estimation of the parameters of the seismic source, e.g., the seismic moment.

How to cite: Zaccagnino, D., Telesca, L., and Doglioni, C.: One to many seismogenic sources: from single earthquakes to seismic sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-211, https://doi.org/10.5194/egusphere-egu23-211, 2023.

Earthquake swarms are bursts of relatively small to moderate earthquakes lasting from hours to months without a clear triggering mainshock. To shed new light on the physical processes driving the seismic swarm that occurred in 2013 along the Alto Tiberina low angle normal fault, we investigate the strain sensitivity to seismic velocity variations (dv/v). For that, we use continuous recordings of ambient noise recorded at 18 stations located in the vicinity of the Alto Tiberina fault for a period of four years. We then retrieve daily dv/v with a time lapse approach by applying the stretching technique. After decomposing our dv/v into tectonic and non-tectonic (thermoelastic and rain induced changes) components, we find a velocity drop (0.035%) coinciding with the seismic swarm. Our observations and the deduced strain sensitivity of roughly 1000 suggest that the triggering of the swarm is mainly caused by an aseismic slip enhanced by the presence of fluids at seismogenic depth (3 - 5 km) 

How to cite: Mikhael, N., Poli, P., and Garambois, S.: Non-linear seismic velocity variations observed during a seismic swarm in the Alto Tiberina low angle normal fault from ambient noise correlation measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-981, https://doi.org/10.5194/egusphere-egu23-981, 2023.

EGU23-1176 | Orals | SM6.3

Swarms of Microseismicity Beneath the Submarine Kolumbo Volcano Indicate Opening of Near‐Vertical Fractures Exploited by Ascending Melts 

Florian Schmid, Gesa Petersen, Emilie Hooft, Michele Paulatto, Kajetan Chrapkiewicz, Martin Hensch, and Torsten Dahm

The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyse the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocentres and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable.

How to cite: Schmid, F., Petersen, G., Hooft, E., Paulatto, M., Chrapkiewicz, K., Hensch, M., and Dahm, T.: Swarms of Microseismicity Beneath the Submarine Kolumbo Volcano Indicate Opening of Near‐Vertical Fractures Exploited by Ascending Melts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1176, https://doi.org/10.5194/egusphere-egu23-1176, 2023.

EGU23-1883 | ECS | Orals | SM6.3

40 years of seismic swarms in the the BR-CP transition zone in Central Utah 

Gesa Petersen, Katherine Whidden, and Kristine Pankow

Seismicity in Central Utah, USA, exhibits a remarkable diversity in swarm activity. Swarms in the study area may alter between high and low activity phases, show a comparably continuous moment release, or a rise and fall of magnitudes over time. While some swarms repeatedly occur in the same source area for several years, other large swarms occur in areas without any significant seismic activity. The diversity is attributed to the complex geo-tectonic transition zone between the Basin and Range province (BR) and the Colorado Plateau (CP) in Central Utah, which is manifested in tectonic forcing related to E-W extension, high heat flow, and hydrothermal processes. Based on the University of Utah Seismograph Stations' catalog, we analyzed forty years of seismic swarm activity within Central Utah, USA, regarding characteristic statistical features (e.g., duration, moment release over time, spatial variations). In-depth analyses of three seismic sequences, including event detections, relocations, MT inversions, waveform-based clustering, and repeater analysis, provide unique insights into the study area's complex and diverse faulting processes. This includes (1) swarm activity at a regional Basin and Range normal fault, (2) activation of a local fault deviating from the recent regional tectonic regime, and (3) the complex triggering of swarm activity by a mainshock. In a joint discussion of the single exemplary sequences and the characteristics of swarm activity, we aim to expand the discussion on swarm activity beyond the study area and shed light on its relation to geothermal and tectonic processes.

How to cite: Petersen, G., Whidden, K., and Pankow, K.: 40 years of seismic swarms in the the BR-CP transition zone in Central Utah, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1883, https://doi.org/10.5194/egusphere-egu23-1883, 2023.

Ample observations attest to the importance of pore pressure dynamics and fault-zone fluid flow in producing earthquake swarms, foreshocks, and aftershocks. However, poroelasticity effects incorporating the two-way coupling of solid and fluid phases where pore-pressure evolves due to e.g. slip, dilatancy, and compaction, are rarely considered in simulations of fault slip. Here we study how coupled dynamics of frictional slip, pore pressure, permeability and porosity evolution control the occurrence of precursory slow-slip and foreshocks leading to the mainshock. We model fully dynamic seismic cycles with a newly-developed Hydro-Mechanical Earthquake Cycles (H-MECs) code where uniform velocity-weakening rate-and-state friction and a constant and far-field loading rate are applied on a 2-D anti-plane fault model embedded in a poro-visco-elasto-plastic medium. We also include the effect of permeability barriers, represented by regions of low permeability and high pore-fluid pressure with wavelengths similar to the nucleation length. Despite the relatively simple model setup, a complex fault behavior arises from the numerical experiments, including small seismic events, complete ruptures, as well as aseismic slip transients. Our results indicate that permeability barriers – where pore-fluid pressure is high – lead to fault creep, whereas foreshocks and mainshocks unzip from locked asperities with relatively lower pore-fluid pressure. We find that the ratio between the size of locked asperity and the wavelength of permeability barriers controls both the nucleation and propagation of aseismic creep, slow-slip transients, cascade of foreshocks, and full seismic rupture. Further numerical experiments accounting for both permeability enhancement due to fault slip and permeability reduction due to healing and sealing show that, once the permeability seals break, fluid is injected and redistributed through the fault zone, which diffuses primarily on-fault, thus leading to the nucleation of a complete rupture. As a result, permeability evolution and pore-fluid pressure variations modulate the ratio of seismic to aseismic moment release of seismic swarms. Our results, compared to observations, demonstrate that pore-fluid pressure evolution and poroelastic effects on- and off-fault play a critical role in the dynamism of earthquake swarms, as they control the stability of faults and whether slip is seismic or aseismic.

How to cite: Ye, J. and Dal Zilio, L.: The role of poroelasticity and permeability barriers in governing the interplay between precursory slow slip and foreshocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2003, https://doi.org/10.5194/egusphere-egu23-2003, 2023.

EGU23-2298 | Posters on site | SM6.3

An atypical swarm at the North Mid-Atlantic ridge indicating spreading events 

Simone Cesca, Malte Metz, Pınar Büyükakpınar, and Torsten Dahm

A large seismic swarm affected the North Mid-Atlantic ridge between September and November 2022, with an outstanding seismicity rate and a cumulative moment equivalent to a magnitude Mw 6.3. We performed a detailed seismological analysis using regional, teleseismic and array data to reconstruct the spatiotemporal evolution of the seismicity. Combining template matching, relative location and full moment tensor inversion, we identify that most seismicity was located in a narrow band along the ridge, with typical normal faulting mechanisms. However, some of the latest and strongest events occurred up tp 25 km off the ridge axis, with thrust mechanisms that are atypical at mid-ocean ridges and inconsistent with the extensional tectonics. Seismicity also present a clear migration pattern, propagating over ~60 km from North to South, with the thrust mechanisms only occurring in the late phase of the swarm and only in the central-southern section. We hypothesize a magmatic intrusion as driver of the seismicity, with a vertical dyke first propagating southward, accompanied by normal faulting earthquakes, and then thickening, to produce a stress perturbation able to trigger thrust earthquakes on pre-existing structures on the side of the dike. The 2022 unrest provides evidence for sporadic spreading accompanied by large swarm episodes driven by magma intrusions at the mid-ocean ridge.

How to cite: Cesca, S., Metz, M., Büyükakpınar, P., and Dahm, T.: An atypical swarm at the North Mid-Atlantic ridge indicating spreading events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2298, https://doi.org/10.5194/egusphere-egu23-2298, 2023.

EGU23-2557 | ECS | Orals | SM6.3

Relative phase analysis for volcanic tremor detection and source location 

Andres Barajas and Nikolai Shapiro Shapiro

The analysis of highly coherent seismic signals produced during tremor episodes has been recently gained interest as a mean to study the structure of volcanic systems, and the underlying physical mechanism producing its activity. Volcanic tremor signals usually appear with a non-impulsive gradual onset and can last for long periods of time, ranging from hours to months, during which individual waves cannot be recognized. The lack of identifiable arrivals during tremor episodes and the long duration of the registered signals, renders ineffective classical methods based on the analysis of the travel times, making difficult the location of its sources. 

We present observations showing that during tremor episodes, the relative phase of inter-station cross-correlations is approximately constant, which is directly linked to the stability of the source position and mechanism. We propose a new method to identify the relative phase stability (and therefore, wavefield coherence) in recordings obtained from a seismic network, that can also be applied to recordings from a single pair of stations. Then, we use a new approach based on the relative phase measurements to find the position of the source of a tremor episode in 2015 at the Klyuchevskoy Volcanic Group.  In general, we show several of the advantages of extracting information from the relative phase as opposed from methods relying on the identification of arrival phases.

How to cite: Barajas, A. and Shapiro, N. S.: Relative phase analysis for volcanic tremor detection and source location, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2557, https://doi.org/10.5194/egusphere-egu23-2557, 2023.

EGU23-2618 | ECS | Orals | SM6.3

Propagation of a fluid-induced aseismic crack leads to earthquake swarm migration controlled by fluid volume 

Philippe Danré, Dmitry Garagash, Louis De Barros, Frédéric Cappa, and Jean-Paul Ampuero

Seismicity migration is one of the most remarkable features of earthquake swarms because of its ubiquity and the wide range of migration durations, velocities and shapes observed. The dynamic properties of swarms, like seismic moment or number of events, are often attributed to fluid circulation, directly or indirectly. However, classical models of fluid pressure diffusion aiming at explaining seismicity triggering and migration show some limitations.  An increasing body of evidence points at an important contribution of fluid-induced aseismic slip during swarms. Moreover, parameters like injection history and fault criticality are expected to intervene. In this work, we use a fracture mechanics framework to show that  earthquake migration can be explained as driven by the propagation of a fluid-induced aseismic slip transient on a rate-and-state fault. This theoretical model predicts a simple linear relation between the seismic migration distance and the square root of the injected fluid volume. This relation is validated by observations in two well-studied seismic sequences induced by injections for geothermal purposes (Basel and Soultz-sous-Forêts), in which the seismicity is mainly clustered around a single surface. In addition, the model helps constrain frictional, hydraulic and structural properties of the fault hosting aseismic slip, and can be reasonably generalized to all fluid-induced earthquake swarms, natural and anthropogenic.

How to cite: Danré, P., Garagash, D., De Barros, L., Cappa, F., and Ampuero, J.-P.: Propagation of a fluid-induced aseismic crack leads to earthquake swarm migration controlled by fluid volume, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2618, https://doi.org/10.5194/egusphere-egu23-2618, 2023.

EGU23-2833 | ECS | Posters on site | SM6.3

Microseismic triggering by small sinusoidal stress perturbations at the laboratory scale 

Martin Colledge, Jérôme Aubry, Kristel Chanard, François Pétrélis, Clara Duverger, Laurent Bollinger, and Alexandre Schubnel

Small transient stress perturbations are prone to trigger (micro)seismicity. In the Earth's crust, these stress perturbations can be caused by various sources such as the passage of seismic waves, tidal forcing, or hydrological seasonal loads. A better understanding of the dynamic of earthquake triggering by transient stress perturbations is essential to improve our understanding of earthquake physics and our consideration of seismic hazard.

Here, we study an experimental sandstone-gouge-filled fault system that undergoes creep with combined far field loading and periodic stress perturbations at crustal pressure conditions. This complex loading is analogous to the loading experienced by faults in the natural setting.

Microseismicity — in the form of acoustic emissions (AE) — strains, and stresses, are continuously recorded to study the response of the system as a function of loading rate, amplitude, and frequency of a periodic stress perturbation. 

The observed temporal distributions of the AEs disagree with the theoretical results of a Coulomb failure model considering both constant loading and oscillation-induced strain rates. This implies that the stress perturbations are of shorter period than the nucleation time of the AEs of the system. A susceptibility of the system’s AE response to confinement pressure amplitude is estimated, which highlights a linear relation between confinement pressure amplitude and the AE response amplitude, observations which are consistent with recent higher frequency experimental results on dynamic triggering.

The magnitude-frequency distribution of AEs is also computed. The Gutenberg-Richter b-value oscillates with the stress perturbations, the amplitude of the b-value oscillations increasing with the amplitude of the stress perturbations, as observed in natural catalogues with large stress oscillations. 

Our experiments may complement our understanding of the influence of low inertia stress phenomena on the distribution of seismicity, such as observations of dynamic triggering and seismicity modulation by solid earth tides or seasonal loading.

How to cite: Colledge, M., Aubry, J., Chanard, K., Pétrélis, F., Duverger, C., Bollinger, L., and Schubnel, A.: Microseismic triggering by small sinusoidal stress perturbations at the laboratory scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2833, https://doi.org/10.5194/egusphere-egu23-2833, 2023.

On 2nd October 2020, an unusual extreme rainfall event (600 mm) associated with the devastating “Alex storm” occurred in less than 24 hours in the Tinée valley, a low strain rate area (convergence rates of 0.3-0.9 mm/yr) of the Southern French Alps, located 20 kilometers from Nice city. This transitional zone between the Argentera Mercantour exhumed Alpine massif and the Nice/Castellane Arc, mainly filled with Cenozoic sediments covering inherited structures, has no clear active faults known and displays a low seismicity rate with only 60 events recorded between 2014 and October 2020 by the national RESIF-EPOS seismic network, with local magnitudes ranging from 0.6 to 2.6. However, in the days after the “Alex storm”, a sudden increase in the seismicity rate was observed, with 114 events detected by template matching (local magnitudes between -0.8 and 2.05). After a peak activity, reached on the 8th of October with more than 60 events detected, the seismic crisis ended around mid-December 2020. Here, we investigate how the intense rainfall can explain the seismic sequences and what are the triggering processes in such a low tectonically deformation area.
Basing our analysis on a precise relocation of the seismicity, using the double-difference relative method, three swarms successively activating from south to north, with focal depths around 5 kilometers have been revealed. The main swarm clearly presents a N160 alignment, which is quite consistent with the general orientation of the Southwestern Alps main faults. A geological field analysis has also shown the presence of major unmapped pluri-kilometers faults consistent with the seismicity location and orientation. Those faults may cross-cut the entire sedimentary layers, connecting more or less directly the ground surface to the deep basement with some highly-permeable channels for fluid flow. Moreover, this relocation analysis highlighted a bi-directional migration of the seismicity within the main swarm: northwestward with a velocity of 100 m/hr, compatible with aseismic slip-driven seismicity, and southeastward with a velocity of 4.5 m/hr, rather compatible with fluid diffusion-driven seismicity.
On top of that, preliminary numerical models, focusing on the analysis of Coulomb stress changes in response to the recorded rainfall rate, showed a correlation between the seismicity rate and the rainfall, which may indicate a rapid saturation of the shallow porous sedimentary layers with fluids after the storm. However, models of stress changes associated with increasing fluid pressure only or including the effect of poroelasticity are not sufficient to explain the temporal evolution of seismicity and its rates. The contribution of other driving processes is necessary and aseismic slip processes could be more relevant to explain the 3 main bursts of seismicity, the migration pattern and the few-days delay with the rainfall episode. Those rainfall-induced aseismic fault slip may have triggered local seismic ruptures along small seismogenic portions of unknown inherited structures. Thus, our study reveals that the Tinée valley area is a good example to study the complexity of aseismic triggering processes of seismicity in association with shallow rainfall-driven hydraulic perturbations in an intraplate region with a low-deformation background rate.

How to cite: Jacquemond, L., Cappa, F., Godano, M., and Larroque, C.: Locally triggered earthquake swarm in the low-deformation zone of Tinée Valley (Southwestern French Alps) following the extreme rainfall event associated with the 2020 Alex storm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3067, https://doi.org/10.5194/egusphere-egu23-3067, 2023.

EGU23-4073 | ECS | Posters on site | SM6.3

Application of Ocean Bottom Seismometer: Study of the 4 Aug 2021 southernmost Okinawa Trough M6.1 event. 

Shiou-Ya Wang, Shu-Kun Hsu, Min-Rui Wu, Chin-Wei Liang, and Yen-Yu Cho

The Southern Okinawa Trough (SOT) is a back-arc-basin and characterized by an active normal faulting system and magmatic activity. Most seismic activities beneath the Southern Okinawa Trough at shallow depths (<30 km) are located about 50 km east of Ilan Plain (122.15°E - 122.55°E).  The seismic rate has increased significantly after May 2021. An earthquake struck offshore area of Ilan Plain on 4 August (0804 earthquake). Its magnitude of 6.1 at 7.0 km made it one of the rare, extremely powerful quakes ever before in the study area. However, the cause and mechanism are still unclear and worthy of further investigation. Furthermore, the previous study shows that submarine landslides have occurred in the northern continental margin of SOT. The frequent earthquakes will raise the risk of slope failure and may generate a local tsunami causing damage around the northeast coast of Taiwan. In order to explore the generation of 0804 earthquake, we have deployed an Ocean Bottom Seismometer (OBS) network to capture the seismicity around the study area.  In total, 852 events have been relocated and most of them are located in the high positive magnetic anomaly zone. The distributions of the earthquake show an NW-SE trending direction and may be related to the magmatic activity.  

How to cite: Wang, S.-Y., Hsu, S.-K., Wu, M.-R., Liang, C.-W., and Cho, Y.-Y.: Application of Ocean Bottom Seismometer: Study of the 4 Aug 2021 southernmost Okinawa Trough M6.1 event., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4073, https://doi.org/10.5194/egusphere-egu23-4073, 2023.

EGU23-5145 | ECS | Orals | SM6.3

Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses 

Adnan Barkat, Yen Joe Tan, Guangyu Xu, Felix Waldhauser, Maya Tolstoy, and William S.D. Wilcock

Our understanding of dynamic earthquake triggering in submarine environments is limited due to the lack of offshore observations. Here, we analyze the triggering susceptibility of a magmatically robust, seismically active submarine volcano (Axial Seamount), located at the intersection of the Juan de Fuca ridge and the Cobb hotspot in the northeast Pacific Ocean. Axial Seamount hosts a cabled network of geodetic and seismic instruments since late 2014. Axial Seamount last erupted in April 2015 and has continued to inflate since. We utilize a high-resolution micro-seismicity catalog to evaluate the triggering response from July 2015 to July 2022 based on seismicity rate change estimates for potential triggering sources. We report statistically significant episodes of dynamic earthquake triggering for ~16% of cases, including instances of both instant (0 < 𝑡 < 2 ℎ𝑟) and delayed (2 < 𝑡 < 24 ℎ𝑟) increases in local earthquake rate following the arrival of teleseismic waves. Initial results do not show any obvious dependence of triggering strength on the amplitude of the peak ground velocity. To evaluate the possible influence of permeability change on dynamic earthquake triggering, we compute the phase lag between vent-fluid temperature and tidal loading for the 3-day periods before and after the arrival of teleseismic waves. We report permeability changes for both triggering and non-triggering cases. Our findings provide useful insights into the physical mechanisms controlling the dynamic earthquake triggering at submarine volcanic environments.

How to cite: Barkat, A., Tan, Y. J., Xu, G., Waldhauser, F., Tolstoy, M., and Wilcock, W. S. D.: Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5145, https://doi.org/10.5194/egusphere-egu23-5145, 2023.

EGU23-5772 | Posters on site | SM6.3

Different Tectonics, Same Approach:  Estimation of source parameters using the Coda Calibration Tool (CCT). 

Paola Morasca, Kevin Mayeda, Jorge I. Roman-Nieves, David R. Shelly, Katherine M. Whidden, Allison L. Bent, Charlie Peach, Stuart Nippress, David Green, William R. Walter, Justin Barno, and Dino Bindi

It is well known that the use of different methods (e.g., spectral fitting, empirical Green’s functions) for compiling catalogs of source parameters (e.g., seismic moment, stress drop) can results in significant inconsistencies (Baltay et al., 2022). In this study, we present the application of coda-wave source parameters estimation by the Coda Calibration Tool (CCT) to different tectonic settings for closer analysis of the regional variations.  CCT implements the empirical methodology outlined in Mayeda et al., (2003), which provides stable source spectra and source parameters even for events recorded by sparse local and regional seismic networks (e.g., Morasca et al., 2022). The main strength of the method is the use of narrowband coda waves measurements, which show low sensitivity to source and path heterogeneity. Additionally, we use independent ground-truth (GT) reference spectra for which apparent stresses are independently calculated through the coda spectral ratio (Mayeda et al., 2007), to break the path and site trade-off.  The use of GT spectra eliminates the need to assume source scaling for the region, reducing the impact of a-priori model assumptions on the interpretation of scaling laws of source parameters and their variability. The CCT is a freely available Java-based code (https://github.com/LLNL/coda-calibration-tool) that significantly reduces the coda calibration effort and provides calibration parameters for future use in the same region for routine processing.

Recently, several studies applied CCT in very different tectonic contexts, including (1) earthquakes in tectonically active regions (e.g., central Italy, Puerto Rico, southern California, Utah); (2) induced earthquakes in southern Kansas and northern Oklahoma; and (3) moderate-sized earthquakes in stable continental regions such as in Eastern Canada and the United Kingdom. There is excellent agreement between coda-derived Mw in all regions and available Mw from waveform modelling. In some cases, such as central Italy and Ridgecrest, the validation process also involved the comparison with estimates from different empirical techniques, such as spectral decomposition approaches applied to data sets sharing common events with CCT. Overall, there is a general consistency in the scaling laws obtained for different source parameters (e.g., seismic moment, corner frequency, radiated energy and apparent stress), with earthquakes in the UK and Canada having similar and higher apparent stresses than Utah, central Italy, Puerto Rico and southern California, while the induced regions are characterized by the lowest values. In conclusion, the application of a consistent methodological framework and the robustness demonstrated by the results of the seismic coda analysis allow comparison of source scaling relationships for different tectonic settings over a wide range of magnitudes.

How to cite: Morasca, P., Mayeda, K., Roman-Nieves, J. I., Shelly, D. R., Whidden, K. M., Bent, A. L., Peach, C., Nippress, S., Green, D., Walter, W. R., Barno, J., and Bindi, D.: Different Tectonics, Same Approach:  Estimation of source parameters using the Coda Calibration Tool (CCT)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5772, https://doi.org/10.5194/egusphere-egu23-5772, 2023.

EGU23-6541 | Posters on site | SM6.3

Earthquake swarm September/October 2022 on Disko Island, West Greenland 

Trine Dahl-Jensen, Peter H. Voss, and Tine B. Larsen

During 25 days in September and August 2022, the island of Disko in central west Greenland experienced a swarm of around 200 small earthquakes, ranging from ML 1.0 to ML 3.1. The majority of the earthquakes were concentrated on a small peninsula measuring 15 x 25 km. We have not received any felt reports, with  the closest inhabited area is approximately 20 km away. The island of Disko is part of the Palaeogene North Atlantic province. Swarms has been observed on and around Disko Island earlier, but not in the same place as the September/October 2022 swarm. In 2010, 27 earthquakes were detected in an area  around 20 km to the east [1], and in 2016 a swarm of over 250 earthquakes occurred following three mb 4.5+ earthquakes. These earthquakes occurred offshore and south of Disko Island, 60 km to the SSE [2]. The coverage with seismic stations is Greenland is sparse, with distances between stations in hundreds of km, but since 2019 three additional stations have been in operation in central west Greenland due to monitoring for landslide events, enabling better locations. The closest station to the swarm is GDH, at 60 km distance. The largest earthquakes in the swarm could be observed at a distance of more than 1600 km.

  • Larsen, T.B., et al., Earthquake swarms in Greenland. Geological Survey of Denmark and Greenland (GEUS) Bulletin, 2014. 31: p. 75-78.
  • Dahl-Jensen, T., P.H. Voss, and T.B. Larsen, [S01-4-01] Recent earthquakes at Disko Island, Greenland, with focal mechanisms in IAG-IASPEI Joint Scientific Assembly. 2017: Kobe, Japan.

How to cite: Dahl-Jensen, T., Voss, P. H., and Larsen, T. B.: Earthquake swarm September/October 2022 on Disko Island, West Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6541, https://doi.org/10.5194/egusphere-egu23-6541, 2023.

EGU23-6581 | ECS | Orals | SM6.3

Evidence of an aseismic slip event continuously driving the 2017 Valparaiso earthquake sequence 

Luc Moutote, Yuji Itoh, Olivier Lengliné, Zacharie Duputel, and Anne Socquet

Both laboratory experiments and friction theory predicts that earthquake ruptures do not begin abruptly but are preceded by an aseismic slip acceleration over a finite nucleation zone. Such a nucleation phase may also trigger precursory ruptures known as foreshocks. Therefore, the scalability of the nucleation phase and its detectability before actual earthquakes is an important question with direct implications for earthquake prediction and seismic hazard assessment. Both Slow Slip Events (SSEs) and seismicity rate increase have already been identified before a few large earthquakes and are often interpreted as evidence of their nucleation process. However, such observations still remain scarce and are associated with different characteristic lengths that raise doubt on the actual preparatory nature of these signals. Here, we further study the case of the 2017 Valparaiso Mw= 6.9 earthquake that was preceded both by an SSE and an intense seismicity suspected to reflect the nucleation phase. We further investigate seismic and aseismic interplay over the complete earthquake sequence, from foreshock up to post-mainshock times, to search for a possible connection with the mainshock occurrence. For that, we build a high-resolution catalog (Mc=2) of the region using cutting edge picking tools, reporting more than 100 000 events from 2015 to 2021 (compared with the ~8000 events reported by the Centro Sismológico Nacional over the same time-period). First, we search for anomalous seismicity rate increases in the vicinity of the mainshock compared to usual earthquake to earthquake triggering models. Using a modified Epidemic Type Aftershock Sequences model that accounts for short-term incompleteness (Hainzl 2021) and MISD declustering (Marsan and Lengliné 2008), we highlight a significant over-productive earthquake rate starting within the foreshock sequences and persisting continuously after the mainshock for several days. Then, thanks to repeating earthquakes, we show that the slow slip event is continuously decelerating from the foreshock sequences up to months after the mainshock. The estimated slip rate is lightly impacted by large magnitude occurrences and does not accelerate toward the mainshock or any large magnitude earthquake. The slip estimate from repeaters is also compared with original high-rate GPS observations during the complete 2017 sequence, further supporting the continuity of the slow slip from the foreshock up to post-mainshock times. The joint observation of an SSE and a transient background seismicity continuously from the foreshock up to post mainshock suggests a close connection between the SSE and the seismicity. Results suggest that the unusual seismic and aseismic activity observed do not reflect the nucleation phase accelerating to the mainshock dynamic rupture. The SSE would rather underlie the complete 2017 earthquake sequence, mediating a part of the seismicity, possibly by stress transfer. The resulting seismicity is then further enhanced with usual earthquake to earthquake triggering, building up the sequence. This suggests that high resolution analysis of seismic and aseismic processes over the complete earthquake sequence is needed to properly assess the significance of signals preceding mainshocks.

How to cite: Moutote, L., Itoh, Y., Lengliné, O., Duputel, Z., and Socquet, A.: Evidence of an aseismic slip event continuously driving the 2017 Valparaiso earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6581, https://doi.org/10.5194/egusphere-egu23-6581, 2023.

EGU23-9103 | Posters on site | SM6.3

Tectonic and volcano-tectonic seismicity below Tungurahua volcano (Ecuador) between 2013 and 2018 

Jean Battaglia, Monica Segovia, Silvana Hidalgo, and Edwin Villareal

Tungurahua (5023 m a.s.l.) is an andesitic stratovolcano located in Central Ecuador. The more recent eruptive cycle started in September 1999 and lasted until March 2016 with repeated phases of enhanced activity. Its activity included the occurrence of distinct eruptive phases separated by periods of quiescence, both lasting from few weeks to months. From October 2013 until March 2018, we operated at Tungurahua a temporary seismic network including up to 13 broadband stations. It complemented the permanent monitoring network operated by the Instituto Geofísico de la Escuela Politécnica Nacional (IG-EPN) and included stations up to 4275 m a.s.l. as well as stations on the remote Eastern flank.

Using IG-EPN catalogs and cross-correlation techniques, we identified several clusters of shallow and deep (volcano-)tectonic earthquakes. For these clusters, we manually picked a selection of larger events and used them to pick automatically other similar events. A visual inspection of the pickings was performed to confirm the absence of major biases. The comparison of P-phase times shows differences less than 0.1 s. Regarding S-phases, the cross correlation technique detected by far more S-phases per event, providing a general improvement in the location of events. Additionally we used seismic amplitudes and their decay as a function of distance to locate tremor and explosion quake sources during eruptive phases.

The seismicity below sea level defines 4 main clusters spread around the volcano between 2 and 10 km b.s.l.. The temporal evolution of these clusters displays a rather steady behavior for 3 of them and a swarm-type behavior for the fourth. Their relation with the eruptive phases is, however, unclear. Above sea level a single cluster of small volcano-tectonic events is observed about 2-3 km below the summit. This cluster displays a rather clear relationship with the eruptive phases and often preceded phases with strong explosive onsets. Most of tremor and explosion quake sources are found just above this cluster.

This study emphasizes the importance of dense, geographically well distributed networks, to identify seismic precursors and decipher volcanic plumbing systems.

How to cite: Battaglia, J., Segovia, M., Hidalgo, S., and Villareal, E.: Tectonic and volcano-tectonic seismicity below Tungurahua volcano (Ecuador) between 2013 and 2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9103, https://doi.org/10.5194/egusphere-egu23-9103, 2023.

EGU23-9466 | Orals | SM6.3

Co-seismic Deformation and Source Parameters of the Mw6.0 Düzce Earthquake by InSAR 

Tülay Kaya-Eken, Çağkan Serhun Zoroğlu, Emre Havazlı, and Haluk Özener

23 November, 2022 Mw 6.0 Düzce Earthquake occurred in the west of the North Anatolian Fault Zone (NAFZ) representing a nascent transform fault between the Eurasian Plate and Anatolian Plate. Well-documented seismic sequence along this fault zone started in the east with the 1939 M7.9 Erzincan Earthquake and migrated westward with M>7 earthquakes. Following 1999 Mw7.4 Izmit and Mw7.2 Düzce failures, the next major earthquake was expected to be on the branch of the NAFZ in the Sea of ​​Marmara. However, the 2022 Düzce Earthquake activated already broken Karadere segment during the 1999 Izmit earthquake but release the accumulated strain energy at the north-eastern end of this segment. In this study, we aimed to measure co-seismic surface deformation caused by the 2022 Düzce rupture and determine the source parameters by combining geodetic and geophysical measurements. The co-seismic deformation is analyzed by using Interferometric Synthetic Aperture Radar (InSAR) technique performed on the Sentinel-1 data. The pre- and post-earthquake ascending and descending SAR images were processed using the TopsApp module of the InSAR Scientific Computing Environment (ISCE) software to obtain interferograms of the co-seismic deformation. Our preliminary results show ~30 mm surface deformation. Our preliminary inversion, based on Okada elastic dislocation modeling, resulted in a fault geometry with ~267, 68 and -172 for strike, dip, and rake angles, respectively. This identifies a dominant right-lateral strike slip motion and is fairly compatible with both surface morphological properties of this segment as well as with initial seismology data-based mechanism solutions of various national/international monitoring centers (e.g. KOERI, GEOFON).

How to cite: Kaya-Eken, T., Zoroğlu, Ç. S., Havazlı, E., and Özener, H.: Co-seismic Deformation and Source Parameters of the Mw6.0 Düzce Earthquake by InSAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9466, https://doi.org/10.5194/egusphere-egu23-9466, 2023.

EGU23-9610 | Posters on site | SM6.3

Comparison of earthquake swarm detection methods: Case study at Mór Graben, Hungary 

Barbara Czecze, Dániel Kalmár, Márta Kiszely, Bálint Süle, and László Fodor

The seismicity of the Pannonian Basin can be described as moderate. The study area is located in the northern part of the Pannonian Basin, which is one of the most active area in terms of earthquakes.

We found that earthquake swarms occur in the Mór graben quite regularly. The Kövesligethy Radó Seismological Observatory deployed three temporary stations in the graben to monitor the local seismicity, and these stations operated for ca. 20 months. We can study the very small magnitude events because the detection capability is more sensitive from 2020.

After relocating the events with a multiple-event location algorithm, we compare three different real swarm detection methods based on the filtered three-component waveforms, to find the best one to collect a complete swarm event list in the Mór Graben.

Using the temporary and permanent stations of the Kövesligethy Radó Seismological Observatory and the GeoRisk Ltd. networks we can identify more than a hundred swarms with small magnitudes.

Our results show that the Mór Graben is still active, where some of the largest earthquakes occurred in Hungary in the past.

 

How to cite: Czecze, B., Kalmár, D., Kiszely, M., Süle, B., and Fodor, L.: Comparison of earthquake swarm detection methods: Case study at Mór Graben, Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9610, https://doi.org/10.5194/egusphere-egu23-9610, 2023.

EGU23-10099 | Orals | SM6.3

Apparent stress of moderate sized earthquakes in southern California 

Ralph Archuleta, Chen Ji, and Aaron Peyton

Using S-wave records at epicentral distances less than 60 km we determine the apparent stress for 62 Mw≥4.5 earthquakes in southern California since 2000. All earthquakes have reliable network moment tensor solutions. We compute seismic radiated energy with two methods: a time domain method by Kanamori et al. (2020) and a frequency domain method by Boatwright et al. (2002). The Kanamori approach (GR) is a modified Gutenberg-Richter in which attenuation and near surface effects are not considered. The Boatwright method uses path attenuation, near surface kappa0, and a station specific radiation pattern. With Boatwright we compute seismic energy 1) with an average radiation pattern (F0) and 2) with station specific radiation pattern (F1). The geometric means of apparent stress are 0.48, 0.40 and 0.57 MPa for GR, F0 and F1, respectively. Apparent stress is independent of seismic moment for these earthquakes. Converting apparent stress to Brune’s stress drop (Andrews, 1986), we find stress drops of 2.1, 1.7 and 2.5 MPa for GR, F0 and F1, respectively. From the perspective of seismic radiated energy, a Brune stress drop is nearly the same as that when using Madariaga (1976) and Kaneko and Shearer (2014) models (Ji, Archuleta and Wang, 2022). The standard deviation of stress drop (log10) is 0.35—almost the same for GR, F0 and F1. Cotton et al. (2013) show the standard deviation from stochastic vibration theory used in ground motion prediction equations is 0.15 for Mw>5.5 earthquakes. Seismic moment/corner frequency methods produce a standard deviation of 0.61, though the magnitude range is larger in some studies. Apparent stress (and consequently stress drop) shows a statistically significant depth dependence (~0.05 MPa/km).

How to cite: Archuleta, R., Ji, C., and Peyton, A.: Apparent stress of moderate sized earthquakes in southern California, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10099, https://doi.org/10.5194/egusphere-egu23-10099, 2023.

EGU23-10172 | Orals | SM6.3

Cascading Hazards in a Migrating Forearc-Arc System: Earthquake and Eruption Triggering in Nicaragua 

Machel Higgins, Peter C. La Femina, Armando J. Saballos, Samantha Ouertani, Karen M. Fischer, Halldór Geirsson, Wilfred Strauch, Glen Mattioli, and Rocco Malservisi

Strain partitioning in the Central American convergent margin between the subducting Cocos Plate and Caribbean Plate is accommodated along the Middle America Trench and faults in the forearc-arc regions. In Nicaragua northwest-directed (margin parallel) forearc motion occurs on northeast (margin normal) and northwest (margin parallel) trending faults within the arc. The proximity of active faults and magmatic systems has historically led to magma-tectonic interactions. We investigate the active tectonics of Nicaragua, including a triggered sequence of earthquakes and a volcanic eruption. We use GPS-derived co-seismic displacements and relocated earthquake aftershocks to study the April 10, 2014 (Mw 6.1), September 15, 2016 (Mw 5.7), and September 28, 2016 (Mw 5.5) as a triggered sequence of earthquakes on faults that accommodate forearc motion. Our analyses and modeling indicate that the April 10, 2014 earthquake ruptured a previously unmapped margin parallel right-lateral strike-slip fault in Lago de Managua (Xolotlan) and that the September 2016 earthquakes ruptured mapped arc-normal, left-lateral and oblique-slip faults. The April 10, 2014 earthquake promoted failure of the September 2016 earthquake faults by imparting static Coulomb failure stress changes of 0.02 MPa to 0.07 MPa. Additionally, the September 15, 2016, earthquake promoted failure (static Coulomb failure stress change of 0.08 MPa to 0.1 MPa) on a sub-parallel fault that ruptured five hours after the mainshock. The April 10, 2014 earthquake displaced the flank of Momotombo volcano ~6 cm coseismically and dilated (10s of µStrain) the shallow magma system of Momotombo Volcano, which led to magma injection, ascent, and eruption on December 1, 2015, after ~100 years of quiescence. In total, this sequence represents the potential for cascading hazards in a forearc-arc system, with earthquake and magmatic triggering over short spatial (10’s km) and temporal (yrs) scales.

How to cite: Higgins, M., La Femina, P. C., Saballos, A. J., Ouertani, S., Fischer, K. M., Geirsson, H., Strauch, W., Mattioli, G., and Malservisi, R.: Cascading Hazards in a Migrating Forearc-Arc System: Earthquake and Eruption Triggering in Nicaragua, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10172, https://doi.org/10.5194/egusphere-egu23-10172, 2023.

EGU23-12165 | ECS | Orals | SM6.3

Detection and characterization of seismic sequences in the normal fault system of the Irpinia region, Southern Italy 

Francesco Scotto di Uccio, Gaetano Festa, Maddalena Michele, Gregory C. Beroza, Lauro Chiaraluce, Matteo Picozzi, Antonio Scala, and Mariano Supino

Understanding mechanical processes occurring on faults and catching the preparation phase of large magnitude events require a detailed characterization of the microseismicity, which can be enhanced today using advanced techniques for earthquake detection. These techniques decrease the detection threshold of seismic networks and provide augmented catalogs, which enable improved statistical analysis associated with event occurrence and size. However, seismic events recorded at the level of the noise typically emerge only at a few stations, making earthquake characterization challenging. This issue is further complicated in areas where seismicity occurs deep in the crust, as happens in the normal fault system of the Irpinia region, Southern Italy, where earthquakes occur at depths between 8 and 15 km.

In this work we focus on the detection and characterization of seismic sequences occurring in the Irpinia region featuring low magnitude mainshocks (Ml∼3), using data from the Irpinia Near Fault Observatory.

Event detection for the sequences is performed through the integration of a machine learning based detector (EQTransformer, Mousavi et al., 2020) and a template matching technique (Chamberlain et al., 2018), with the former providing a wider set of templates for the similarity search. This strategy outperforms auto-similarity techniques based on fingerprints (FAST, Yoon et al., 2015) and template matching grounded in manual catalogs. On average, the final catalog of the analyzed sequences increases the manually revised network bulletin by a factor 7. We compared P- and S- arrival time estimates, grounded in the machine learning phase picking and cross-correlation for template matching, using manual identifications to assess the reliability of automatic picks; the mean residual between manual and automatic values is ~0 for both P- and S-waves, with a larger residuals standard deviation for the latter.
We apply a double-difference location technique using both catalog and cross-correlation differential travel times for locating the events, with the goal of resolving and highlighting fault structures where seismicity takes place. We finally track the spatio-temporal evolution of the seismicity, and apply a mechanical model based on static stress, to discriminate whether sequences in the area are mainly triggered by static stress change, dynamic stressing, or aseismic mechanisms such as fluid diffusion.

How to cite: Scotto di Uccio, F., Festa, G., Michele, M., Beroza, G. C., Chiaraluce, L., Picozzi, M., Scala, A., and Supino, M.: Detection and characterization of seismic sequences in the normal fault system of the Irpinia region, Southern Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12165, https://doi.org/10.5194/egusphere-egu23-12165, 2023.

EGU23-12252 | Orals | SM6.3

Fast migrating sequences within earthquake swarms 

Josef Vlcek, Tomas Fischer, and Sebastian Hainzl

The hypocenters of earthquake swarms and injection-induced seismicity usually show systematic migration, which is considered to be a manifestation of their triggering mechanism. In many cases, the overall growth of clusters is accompanied by short sequences of rapid migration events, the origin of which is still not sufficiently clarified. We review the possible triggering mechanisms of these migrating episodes and propose a graphical method for distinguishing internal and external triggering forces. We also analyze the theoretical relationship between the evolution of the cumulative seismic moment and the rupture area and propose two models, the crack model and the rupture front model, which can explain the spreading of hypocenters. We developed an automatic algorithm for detecting fast migration episodes in seismicity data and applied it to relocated catalogs of natural earthquake swarms in California, West Bohemia, and Iceland, and to injection-induced seismicity. Fast migration episodes have been shown to be relatively frequent during earthquake swarms (8-20% of cluster events) compared to fluid-induced seismicity (less than 5% of cluster events). Although the migration episodes were detected independently of time, they grew monotonically with time and square-root dependence of radius on time was found suitable for majority of sequences. The migration velocity of the episodes of the order of 1 m/s was found and it anticorrelated with their duration, which results in a similar final size of the clusters in the range of first kilometers. Comparison of seismic moment growth and activated fault area with the predictions of the proposed models shows that both the rupture front model and the crack model are able to explain the observed migration and that the front model is more consistent with the data. Relatively low estimated stress drops in the range of 100 Pa to 1 MPa suggest that aseismic processes are also responsible for cluster growth. Our results show that the fast migrating episodes can be driven by stress transfer between adjacent events with the support of aseismic slip or fluid flow due to dynamic pore creation.

How to cite: Vlcek, J., Fischer, T., and Hainzl, S.: Fast migrating sequences within earthquake swarms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12252, https://doi.org/10.5194/egusphere-egu23-12252, 2023.

EGU23-12362 | ECS | Posters on site | SM6.3

Persistent shallow microseismicity near a glacier in southwestern Switzerland (Arolla VS) revealed by enhanced earthquake catalogs 

Maria Mesimeri, Tobias Diehl, Marco Herwegh, John Clinton, and Stefan Wiemer

On October 05, 2021 an Mw4.0 earthquake struck 6 km south of the village of Arolla, near the tongue of the Arolla Glacier. Almost one year prior to this earthquake, an M3.5 event occurred on November 08, 2020 in the same location. Both earthquakes were followed by a few aftershocks that were detected and located by the Swiss Seismological Service (SED). The unusually shallow depth of 1-2 km of these earthquakes, indications for a mostly thrust-type mechanisms within a region characterized by a predominantly extensional stress regime, and unusual high CLVD (50-70%) components of SED’s routine moment tensor solutions raised questions regarding the triggering mechanism. To understand and explain the possible existence of shallow thrust earthquakes in the area, we perform a thorough seismotectonic analysis that is based on enhancing the existing earthquake catalog of the SED and complementary moment-tensor solutions computed by multiple algorithms. The original SED earthquake catalog contains 83 earthquakes that occur between January 01, 2020 and December 31, 2021 and locate ~5 km around the two mainshocks. Using a deep learning based algorithm (EQTransformer), we detect additionally 253 events, thus the new catalog contains 4 times more earthquakes than the original SED bulletin. Absolute locations for the additional earthquakes are obtained using the probabilistic NonLinLoc method in combination with a recently updated Vp and Vs crustal 3D velocity model. In addition, we compute local magnitudes (MLhc) using SED’s standard procedure, in order to compile a homogeneous catalog consistent with the SED bulletin. The enhanced catalog events are used as templates for a match filtering scheme, which increased the number of detections by at least one magnitude order. Last, we relocate the final catalog using the double difference method towards obtaining a high resolution enhanced earthquake catalog. Spatially, the main cluster shows an intense seismic activity, stretched in N-S direction that matches the strike of the fault planes derived from moment tensor inversion. An additional cluster, that is not present in the SED bulletin locations, is identified next to the area were the aftershock activity of the two main events locates. Furthermore, the enhanced catalog shows a smother temporal evolution with more background events than previously recorded. Overall, we explore the possibility of fluid driven microseismicity that might be related to the nearby glacier. With our study we emphasize the importance of enhanced earthquake catalogs using both machine learning pickers and template matching algorithms. These approaches lead to unravel prior unmapped structures and improve our understanding of the seismotectonic regime in the study area.

How to cite: Mesimeri, M., Diehl, T., Herwegh, M., Clinton, J., and Wiemer, S.: Persistent shallow microseismicity near a glacier in southwestern Switzerland (Arolla VS) revealed by enhanced earthquake catalogs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12362, https://doi.org/10.5194/egusphere-egu23-12362, 2023.

EGU23-12789 | Orals | SM6.3 | Highlight

Onset of a submarine eruption east of Mayotte, Comoros archipelago: the first ten months seismicity of the seismo-volcanic sequence (2018-2019) 

Jerome van der Woerd, Nicolas Mercury, Anne Lemoine, Cécile Doubre, Didier Bertil, Roser Hoste Colomer, and Jean Battaglia

Since 10 May 2018, an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over the period May 2018 – February 2019 are highly dependent on the small seismic network available. We therefore compare the locations of later events from a local ocean bottom seismometer network with locations estimated using a similarly small network. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified. They correspond to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor. We also observe progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir.

How to cite: van der Woerd, J., Mercury, N., Lemoine, A., Doubre, C., Bertil, D., Hoste Colomer, R., and Battaglia, J.: Onset of a submarine eruption east of Mayotte, Comoros archipelago: the first ten months seismicity of the seismo-volcanic sequence (2018-2019), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12789, https://doi.org/10.5194/egusphere-egu23-12789, 2023.

EGU23-13036 | ECS | Posters on site | SM6.3

Diffusion processes in minor normal faulting seismic sequences monitored by the Alto Tiberina Near Fault Observatory (Northern Apennines, Italy) 

Giulio Poggiali, Monica Sugan, Maddalena Michele, Samer Bagh, Raffaele Di Stefano, Alessandro Vuan, Emanuele Tondi, and Lauro Chiaraluce

The analysis of microseismicity has a fundamental role in understanding earthquakes, giving insights on the long- and short-term driving forces and processes preparing and generating the seismicity occurrence and its evolution in space and time.

Recent advances in detection and location algorithms, paired with dense seismic networks, and supported by higher computing capacity, allow dramatic increase in the quality and quantity of low magnitude earthquakes recorded resulting in high resolution earthquakes catalogs in terms of both location attributes and completeness.

Such catalogs enable us to analyze small magnitude (M<4) sequences having the advantage of a high frequency of occurrence, with unprecedented resolution in illuminating minor (few kilometers of extent) fault systems and seismicity patterns.

We present a detailed analysis of two seismic sequences occurred within an extensional sector of the Northern Apennines between 2010 and 2014: the Città di Castello and Pietralunga sequences (maximum magnitude ≤ 3.6). The area is within the Alto Tiberina Near Fault Observatory (TABOO-NFO), a multidisciplinary monitoring infrastructure dedicated to the investigation of the fault slip behavior of this very low angle normal fault.

The very high microseismic activity, the availability of a dense network and a complex tectonic setting involving shallow (H2O) and deep (CO2) fluids circulation, result in an ideal location to apply modern detection and analysis techniques to study microseismicity in detail.

We build the high-resolution catalog starting from the raw waveforms recorded by a seismic network composed of ~60 stations covering an area of 80x80km and applying a deep learning phase picker. The events are located with a probabilistic nonlinear algorithm and finally relocated with the double differences algorithm after undergoing a quality selection based on location parameters. The resulting catalog for these sequences counts 6 times the number of events documented in previously available standard catalogs.

The spatiotemporal distribution of events shows different characteristics, ranging from foreshock-mainshock-aftershock to more swarm-like patterns but almost all these patterns are compatible with pore-pressure diffusion (1 − 2m2s-1) processes and exhibiting along-strike migration. These are very similar behavior with respect to the ones observed during the larger extensional sequences occurred in the Apennines in recent years.

The case of fluid driven seismicity is coherent with the seismotectonic setting of the area showing large CO2 degassing phenomena and the presence of geologic formations prone to develop fluids overpressure. The comparison of the spatial distribution of events with a three-dimensional deterministic seismostratigraphic model based on different (non-seismic) geophysical data, highlights in fact a ubiquitous involvement of the Triassic Evaporites as hosting lithology, indicating a strong mechanical control and corroborating their seismogenic role.

How to cite: Poggiali, G., Sugan, M., Michele, M., Bagh, S., Di Stefano, R., Vuan, A., Tondi, E., and Chiaraluce, L.: Diffusion processes in minor normal faulting seismic sequences monitored by the Alto Tiberina Near Fault Observatory (Northern Apennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13036, https://doi.org/10.5194/egusphere-egu23-13036, 2023.

EGU23-14089 | Orals | SM6.3

Estimating the rupture directivity and source parameters of moderate to small earthquakes using the second seismic moment  

Arianna Cuius, Haoran Meng, Angela Saraò, and Giovanni Costa

Rupture processes of large earthquakes have been studied by seismic waveform analysis and directivity effects have also been observed in moderate and small earthquakes.

 

This effect leads to azimuthal and spectral variations in ground motion that can be used to estimate the fault plane orientation or a predominant rupture propagation direction in a particular region or during a seismic sequence. For moderate-to-strong events, directivity at low frequencies can result in potentially destructive pulses with large ground motions, while at high frequencies and for small-to-moderate events, the most pronounced effect is the shift in corner frequencies that results in high-frequency energy arriving in short time intervals.

 

It is therefore of the utmost importance to estimate the directivity effects in engineering applications and seismological studies of earthquake sources. While some methods appear to work well for high magnitude earthquakes, determining directivity and source parameters for small to moderate magnitude earthquakes remains a challenge.

 

One of the most common methods to estimate the directivity from moderate to small earthquakes relies on measuring the duration of the source pulse (the apparent source time function) at each location and then modeling it using a line source. Some approaches rely on the deconvolution of waveforms by an empirical Green’s function (eGf), to overcome the problems associated with the presence of path and site effects.

A promising approach for estimating the rupture directivity effect and associated source properties is based on the calculation of the second seismic moments. In this study we apply the method based on the calculation of the second seismic moments to estimate the rupture process and source parameters to study a Mw 4.7 earthquake that occurred in central Italy during the 2016 - 2017 seismic sequence recorded by the RAN (Rete Accelerometrica Nazionale) and RSN (Rete Sismica Nazionale) italian networks.

We first used synthetic apparent source time functions calculated from a geometric source model obtained from a real event to test the robustness of the method. Then, we applied the second-seismic moment method and the approach based on high-frequency S wave amplitude variations versus source azimuths analysis with an empirical Green's function deconvolution approach and compare the results.

 

How to cite: Cuius, A., Meng, H., Saraò, A., and Costa, G.: Estimating the rupture directivity and source parameters of moderate to small earthquakes using the second seismic moment , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14089, https://doi.org/10.5194/egusphere-egu23-14089, 2023.

EGU23-14154 | Posters on site | SM6.3

The activities of the EMERSITO INGV emergency task force following the Mw 5.5 Costa Marchigiana-Pesarese earthquake 

Daniela Famiani, Fabrizio Cara, Giovanna Cultrera, Giuseppe Di Giulio, Sara Lovati, Simone Marzorati, Francesca Pacor, Gaetano Riccio, and Maurizio Vassallo and the EMERSITO working group

EMERSITO is the INGV emergency task force (website available at http://emersitoweb.rm.ingv.it/) with skills and experience in seismic response studies and in seismic microzonation activities, and contributes to emergency interventions following significant seismic events (M>5.0 or lower if a noticeable level of damage is observed).

After the Mw 5.5 (ML 5.7) event of November 9, 2022 06:07:24 UTC (Italian time 07:07:24) localized in the Costa Marchigiana Pesarese area, EMERSITO acted immediately to collect multidisciplinary available information regarding the epicentral area and adjacent areas.

EMERSITO decided to focus the scientific intervention in the municipal area of Ancona which is the main city of the Marche region. This choice was driven by: a) the values of peak ground accelerations observed during the main shock in the city compared with other cities at the same or lower epicentral distance; b) the observed damage, fortunately minor, and evacuations reported by the technicians of Regione Marche and the Fire Brigade; c) the scientific interest in the evaluation of the local seismic response in the urban area that is characterized by strong lithological heterogeneities; d) the presence of an INGV office in Ancona which supported the activities of all the INGV emergency groups, including the EMERSITO working group. The intervention of EMERSITO concerned the installation of a temporary seismic network (registered as 6N; the code was released by FDSN, the Federation of Digital Seismograph Networks) consisting of 11 seismic stations equipped with both velocimetric and accelerometric sensors. A part of these stations (6) has been set up in real-time mode, while the remaining stations (5), have a local acquisition system, requiring periodic maintenance interventions for checking and downloading the data.

At the end of the experiment, after a quality check all continuous data will be transferred to the European Integrated Data Archive (EIDA) repository, with a Digital Object Identifier (DOI) and made public after a pre-established restriction period to allow both preliminary data analysis and a general publication about the intervention of the EMERSITO group.

Site selection for network 6N was planned on the basis of the geological map, damage survey and other information. It was preceded by field inspections in collaboration with the technicians of the Municipality of Ancona and Regione Marche and was supported by colleagues from the INGV headquarter in Ancona. Given the observed variability in the seismic response of the permanent stations, particular attention was paid to the identification of one or more reliable reference sites. The deployment of the network took place between 13 and 17 November.

In this work we present the seismic dataset composed of ambient vibrations and aftershock recordings acquired from the 6N network during the experiment. Preliminary data analysis suggests a variability of the site responses depending on the outcropping lithologies. We believe that the instrumental data acquired by EMERSITO task force, together with the microzonation study available for the municipality of Ancona can increase the knowledge on possible site effects that occurred in different areas of the city after the Mw 5.5 event of November 9, 2022.

How to cite: Famiani, D., Cara, F., Cultrera, G., Di Giulio, G., Lovati, S., Marzorati, S., Pacor, F., Riccio, G., and Vassallo, M. and the EMERSITO working group: The activities of the EMERSITO INGV emergency task force following the Mw 5.5 Costa Marchigiana-Pesarese earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14154, https://doi.org/10.5194/egusphere-egu23-14154, 2023.

EGU23-15577 | Orals | SM6.3

Using measured and modelled shear-wave velocity profiles for the assessement of site response in Groningen, the Netherlands 

Pauline Kruiver, Manos Pefkos, Xander Campman, Erik Meijles, and Jan van Elk

The site response input in the Groningen seismic hazard assessment is based on modelled shear-wave velocity (VS) profiles. Two sets of data were used to compare in situ (field) and model data of VS. The first set consists of data from several blocks of ~ 400 nodes. Inversion of passive seismic data from a coarse grid of ~ 6 km x 10 km resulted in VS profiles to a depth of 800 m and from a denser grid of ~ 1 km x 1 km more detail to a depth of 100 m. The field VS profiles were a combination these two depth ranges. The site response analysis based on either the field or model VS profiles showed on average similar amplification factors over periods relevant for seismic risk. The model VS profiles are therefore a good representation. The second set consists of VS data from MASW surveys on dwelling mounds. The local detailed field VS profiles reach a depth of 18 m. Site response analyses using the full model VS profiles or profiles with the top 18 m replaced by field VS showed that the amplification on dwelling mounds is underestimated significantly, on average by 7 to 28 %. Because of this, a frequency-dependent Penalty Factor has been derived. In the risk calculations, this Factor is to be applied to buildings on dwelling mounds to transform the estimated motions at the ground surface (based on model VS) into motions at the top of the dwelling mound.

How to cite: Kruiver, P., Pefkos, M., Campman, X., Meijles, E., and van Elk, J.: Using measured and modelled shear-wave velocity profiles for the assessement of site response in Groningen, the Netherlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15577, https://doi.org/10.5194/egusphere-egu23-15577, 2023.

EGU23-16208 | Orals | SM6.3

Stress transfer between volcanic dyke and seismic activity accompanying the 2021 and 2022 Fagradalsfjall eruptions, Iceland 

Tomáš Fischer, Josef Vlček, Pavla Hrubcová, Jana Doubravová, Þorbjörg Ágústsdóttir, and Egill Árni Guðnason

The 2021 Fagradalsfjall volcanic eruption in the Reykjanes Peninsula, Iceland, was preceded by an intensive earthquake swarm lasting one month. At the end of July 2022, a new intensive earthquake swarm occurred, which was followed on 3 August 2022 by a new effusive flow at the extension of the 2021 effusive fissure. We analyze seismic data of both swarms recorded by the Reykjanet local seismic network to trace the processes leading to the eruption to understand the relation between seismic activity and magma accumulation.

Precise relocations of the 2021 swarm show two hypocenter clusters in the depth range of 1-6 km. The WSW-ENE trending cluster of the 2021 and previous swarms show a stepover of ∼1 km offset, forming a pull-apart basin structure at the intersection with the dyke. This is the place where the 2021 eruption occurred, suggesting that magma erupted at the place of crustal weakening. The pre-eruption seismic activity in 2021 started with a M5.3 earthquake of 24 February 2021, which triggered the aftershocks on the oblique plate boundary and in the magmatic dyke area, in both cases in an area of elevated Coulomb stress. The co-existence of seismic and magmatic activity suggests that the past seismic activity weakened the crust in the eruption site area, where magma accumulated. The following M5.3 earthquake of 24 February 2021 also triggered the seismic swarm and likely perturbed the magma pocket which led to the six-months lasting eruption that started on 19 March.

The relocations of the July 2022 earthquake swarm show that only the northern part of the dyke-related swarm was activated compared to the 2021 swarm and both eruptions are located at the southern tip of the 2022 swarm. We compare the space-time and statistical characteristics of the 24 February 2021 aftershock sequence and of the 2021 and 2022 swarms to relate them to the different expected origin of these seismic activities.

How to cite: Fischer, T., Vlček, J., Hrubcová, P., Doubravová, J., Ágústsdóttir, Þ., and Guðnason, E. Á.: Stress transfer between volcanic dyke and seismic activity accompanying the 2021 and 2022 Fagradalsfjall eruptions, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16208, https://doi.org/10.5194/egusphere-egu23-16208, 2023.

EGU23-16210 | ECS | Posters on site | SM6.3

Modelling cascading ruptures on near-orthogonal strike-slip fault system: the 2019 Cotabato (the Philippines) earthquake sequence 

Yu Jiang, Shengji Wei, Judith Hubbard, Wan-Lin Hu, and Rino Salman

Earthquake sequences on near orthogonal strike-slip faults are not uncommon, as observed both in the subduction zone outer-rise region (e.g., the 2000 and 2012 Wharton basin earthquakes off-Sumatra, Robinson et al., 2001; Wei et al., 2013) and in the shallow continental crust (e.g., the 1987 Superstition Hills earthquakes, Hudnut et al., 1989; the 2019 Ridgecrest earthquakes, Shi and Wei, 2020). However, according to the Coulomb faulting theory (Anderson, 1951), strike-slip faults intersecting at an angle of around 90° (at 45° from the maximum principal stress) would require a near-zero friction coefficient, which is not consistent with the observed values 0.6~1 in nature, e.g., deep borehole stress measurements (Townend, 2006). Thus, the mechanisms controlling these cascading orthogonal ruptures remain poorly understood. The 2019 Cotabato earthquakes (the Philippines) provide a new opportunity to further explore the driving mechanism causing orthogonal strike-slip earthquakes, since abundant geodetic and seismic data sets are recorded in this sequence.

In this research, we focus on four Mw6.4+ events during the 2019 Cotabato earthquake sequence. Since the fault geometry is critical to analyze the potential stress triggering between earthquakes, careful processing and modelling of the data sets are required to provide a robust and reliable fault geometry. To better constrain the fault geometry, two types of observations were utilized, surface displacement data with a high spatial resolution and ground motion data with a high temporal resolution. (a) Geodetic modelling. We acquired eight ALOS-2 L-band SLC images, and generated ten interferograms monitoring the ground displacement, including seven ascending and three descending interferograms. To avoid the influence of phase unwrapping errors, we improved and applied an art-of-the-state Bayesian geodetic inversion approach (Jiang and González, 2020) by using the InSAR wrapped phase and allowing the estimation of multiple fault geometry simultaneously. (b) Seismic modelling. Seismic waveforms were collected from IRIS, including one regional station and over ten teleseismic stations. We performed Multiple Point Source inversions (Shi et al., 2018) to determine the subevents’ location and double-couple focal mechanism. Geodetic and seismic inversion results were cross-verified and updated to reconcile both datasets. Our results show that (1) in mid-October, the first Mw6.4 earthquake occurred on an NW-SE-striking fault at the depth range of 10-18 km; (2) the second Mw6.6 earthquake ruptured the shallow part of the same fault, followed by the third Mw6.5 earthquake two days later but rupturing a NE-SW-striking fault; (3) in mid-December, the most energetic Mw6.8 earthquake occurred on an NW-SE-striking fault, located at SE of the first two events. Coulomb stress analysis suggests that the friction coefficient on the NE-SW-striking fault has to be very low to allow the rupture on the near orthogonal faults. Our results indicate that the earthquake sequence is a cascading rupture that involved both weak and strong faults in which pore fluid pressure may have played a key role.

How to cite: Jiang, Y., Wei, S., Hubbard, J., Hu, W.-L., and Salman, R.: Modelling cascading ruptures on near-orthogonal strike-slip fault system: the 2019 Cotabato (the Philippines) earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16210, https://doi.org/10.5194/egusphere-egu23-16210, 2023.

EGU23-2742 | Orals | GMPV8.7 | Highlight

Years of deep magmatic upheaval preceding the 2021 eruption at Fagradalsfjall, Iceland 

Maren Kahl, Euan J.F. Mutch, John Maclennan, Dan Morgan, Fiona Couperthwaite, Enikő Bali, Thor Thordarson, Guðmundur H. Guðfinnsson, Richard Walshaw, Iris Buisman, Stephan Buhre, Quinten H. A. van der Meer, Alberto Caracciolo, Edward W. Marshall, Maja B. Rasmussen, Catherine R. Gallagher, William M. Moreland, Ármann Höskuldsson, and Robert A. Askew

Effective eruption forecasting and volcanic hazard management depend heavily on our ability to detect when a volcanic system switches from a state of unrest into a state of eruption. The 2021 eruption at Fagradalsfjall in SW Iceland, the first deep-sourced eruption on a mid-ocean ridge system monitored with modern instrumentation, presents an ideal opportunity to compare geophysical and petrological datasets to explore processes of deep magma mobilisation and eruption priming. Here we use diffusion chronometry to show that deep magmatic unrest in the roots of volcanic systems can precede apparent geophysical eruption precursors by a few years.  Early phases of magma accumulation and reorganisation in the near-Moho plumbing system, part of the priming for eruption, can occur in the absence of significant increases in shallow seismicity (<7 km depth) or rapid geodetic changes. In contrast, geophysical signals of unrest and crystal records of changing magmatic conditions both show significant increases in intensity in the months and days prior to eruption. This correlation may signal a rapid transition from a state of priming to full scale mobilisation in which magma begins to traverse the upper/ brittle crust. Our findings provide new insights into the dynamics of near-Moho magma storage and mobilisation. 

How to cite: Kahl, M., Mutch, E. J. F., Maclennan, J., Morgan, D., Couperthwaite, F., Bali, E., Thordarson, T., Guðfinnsson, G. H., Walshaw, R., Buisman, I., Buhre, S., van der Meer, Q. H. A., Caracciolo, A., Marshall, E. W., Rasmussen, M. B., Gallagher, C. R., Moreland, W. M., Höskuldsson, Á., and Askew, R. A.: Years of deep magmatic upheaval preceding the 2021 eruption at Fagradalsfjall, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2742, https://doi.org/10.5194/egusphere-egu23-2742, 2023.

EGU23-3542 | ECS | Orals | GMPV8.7

Crustal context of the Fagradalsfjall eruption: shear-wave velocity structure of the Reykjanes Peninsular from receiver function analysis 

Jennifer Jenkins, Tim Greenfield, Nicholas Rawlinson, Thorbjorg Agustdottir, Gylfi Páll Hersir, Egill Árni Gudnason, Josef Horálek, Anne Obermann, Torsten Dahm, and Claus Milkerei

Detailed investigation into local seismicity and geochemical analysis of erupted products from the 2021-22 Fagradalsfjall eruption has already provided new insights into the deep magma plumbing system beneath the Reykjanes Peninsular. Here we focus on producing a detailed regional-scale shear wave velocity model of the Reykjanes to provide wider scale crustal context for these results. Utilising seismic data from 105 stations operated by numerous groups on the peninsular from 2013 to present day, we use recordings of distant teleseismic earthquakes to observe P to s converted phases that provide insight into crustal structure through receiver function (RF) analysis. The total data set of nearly 3000 RFs is computed in several frequency bands. Small subsets of RFs from common backazimuths and epicentral distances displaying high waveform similarity are jointly inverted with surface wave dispersion measurements to produce approximately 300 individual velocity models across the area. These are migrated to depth within a 3D volume to define a single regional velocity model. Major interfaces such as the Moho and base of the upper crust are extracted to produce maps of peninsular wide variation. Computed velocity model inversion results are compared to  RF waveforms combined in multi-phase common conversion point stacks. We compare the velocity structure and interface depths extracted beneath Fagradalsfjall to magma depth estimates from geochemistry and potential structural changes hypothesised from local seismicity linked to the 2021-22 eruption.

How to cite: Jenkins, J., Greenfield, T., Rawlinson, N., Agustdottir, T., Hersir, G. P., Gudnason, E. Á., Horálek, J., Obermann, A., Dahm, T., and Milkerei, C.: Crustal context of the Fagradalsfjall eruption: shear-wave velocity structure of the Reykjanes Peninsular from receiver function analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3542, https://doi.org/10.5194/egusphere-egu23-3542, 2023.

EGU23-3678 | ECS | Posters on site | GMPV8.7 | Highlight

Eruption Parameters Measured In-flight during the 2022 Icelandic Meradalir Eruption 

Caroline Tisdale, Bruce Houghton, Jóna Sigurlína Pálmadóttir, and Thorvaldur Thordarson

The 2022 Icelandic eruption of Meradalir along the Reykjanes Peninsula, was captured via videography in exceptional detail over much of its 18-day duration. This eruption, like the 2021 Fagradalsfjall eruption, did not pose significant threat to human life or infrastructure. However, many lava-fountaining eruptions elsewhere of similar character (2018 Lower East Rift Zone, Hawaii & 2021 Cumbre Vieja, La Palma, Spain) have caused substantial destruction. Understanding eruption dynamics at these volcanoes is critical for fine-tuning of hazard and risk assessment. With the increasing use of high-speed/resolution cameras in field settings, we are able to quantify in-flight parameters such as particle size and particle exit velocities, rather than having to solely rely on deposit characteristics from samples collected once an eruption has ceased. This is an important development because ground samples can be rapidly buried or reworked and are subject to additional fragmentation during transport and when hitting the ground. The abundance of quantitative information we can obtain from this, coupled with qualitative observations, has allowed us to deepen our understanding of processes of weak explosive eruptions.

How to cite: Tisdale, C., Houghton, B., Sigurlína Pálmadóttir, J., and Thordarson, T.: Eruption Parameters Measured In-flight during the 2022 Icelandic Meradalir Eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3678, https://doi.org/10.5194/egusphere-egu23-3678, 2023.

EGU23-4209 | ECS | Orals | GMPV8.7

Multi-analytical characterization of a Reykjanes Peninsula (Iceland) basalt 

Daniel Stoicescu, Delia Dumitras, Octavian Duliu, Cristian Panaiotu, Gelu Costin, Inga Zinicovscaia, George Dinca, Cristian Necula, Ioana Porosnicu, and Otilia Culicov

To get more data concerning de geochemistry and volcanology of Reykjanes Peninsula (Iceland) lavas, more high-precision analytical methods such as Instrumental Neutron Activation Analysis (INAA), Electron Microprobe Analysis (EMPA), X-ray Fluorescence (XRF), X-ray Diffraction (XRD), ICP-MS, X-ray microtomography (XRMT) and magnetism, coupled with mineralogical investigations were used. INAA, EPMA, XRF and ICP-MS were used to determine both major and trace element mass fractions. In the case of major elements, despite some differences inherent utilization of different analytical techniques, all analysis suggested a tholeiitic composition. Several discriminating diagrams clearly emphasize the subalkaline and tholeiitic trend, while the tectonic discrimination diagram assigned a “continental affinity”, as well as the existence of a minor crustal contamination. At their turn, the distribution of incompatible trace elements, represented into several discriminating diagrams, in agreement with PetDB database on Reykjanes Peninsula, as well as Hawaii and St Helen volcanic rocks, confirming the previous hypothesis based on major elements distribution on the tholeiitic and evolved character of the Reykjanes Peninsula lava, with an affinity towards ocean island basalts with traces crustal contamination. The results of mineralogical as well as BSE images analysis evidenced an abundance of plagioclase (albite), pyroxene (augite and pigeonite), as well as Fe-Ti oxides, while minerals such as olivine and spinel were less present. XRMT images revealed the presence of a multitude of vesicles showing preferred orientations, most probable due to lava flow, as the XRMT images loaded into stacks and analyzed by appropriate image analyzing software suggested. This particular features could suggest the existence of an important amount of volatiles, which lowering lava viscosity make them visible among larger vesicles. Raman spectroscopy results concerning the phases of each mineral, compared with literature and RRUFFTM database confirmed previuous finding concerning the geochemistry of investigated Reykjaned Peninsula basalt sample. A magnetic analysis, performed by means of FORC diagrams as well as magnetic susceptibility dependence on temperature and the magnetic field, evidenced the presence of titanomagnetite as a main magnetic present in the sample.Therefore, all analyses suggested that the investigated basaltic lava present a tholeiitic composition, with an evolved continental affinity, but not related to rifting. The structural features suggests the presence of an important amount of volatiles existed prior the eruption.

How to cite: Stoicescu, D., Dumitras, D., Duliu, O., Panaiotu, C., Costin, G., Zinicovscaia, I., Dinca, G., Necula, C., Porosnicu, I., and Culicov, O.: Multi-analytical characterization of a Reykjanes Peninsula (Iceland) basalt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4209, https://doi.org/10.5194/egusphere-egu23-4209, 2023.

EGU23-5120 | ECS | Orals | GMPV8.7

Primary versus secondary degassing during basaltic eruptions 

Nicolas Levillayer and Olgeir Sigmarsson

Volcanic gases are a major concern, especially when eruptions take place in inhabited or touristic areas. Several studies have revealed that during basaltic eruptions, toxic metals such as Pb, Cd, As and Zn are efficiently outgassed, carried by the major gas species, mainly sulfur and halogens. However, part of the degassing occurs after the eruption, while the lava flow is solidifying, and the composition of this secondary gas is virtually unknown.

After the primary (syn-eruptive) degassing, the lava is depleted in sulfur, leading to relative enrichment in halogens in secondary (post-eruptive) gas emission. This change in major species concentration could impact the volatility of metals and thus the toxicity of the gas emitted.

To investigate this subject, we collected, using filter packs, gas samples of both the primary and the secondary gas phases of the Geldingadalir and Meradalir eruptions. The filters were then leached in diluted acid and the resulting solution analyzed for trace element composition.

Results show syn-eruptive gas samples with very homogeneous trace volatile element composition and distinct from all the post-eruptive gas. Conversely, the secondary gas is more diverse, with distinct composition in samples collected around the main Geldingadalir crater and those collected on the lava flow.

To compare our gas samples (having different air dilution factors), we normalized each element to Cu (well measured and moderately volatile). Overall, the lava flow post-eruptive gas appears enriched in Zn, Sb and Pb with respect to syn-eruptive (10-100 times higher normalized enrichment factor). These elements are known to form chloride species and could thus have an enhanced volatility due to higher Cl concentration in the secondary gas phase. The Sulfur-loving (chalcophile) element Te has, on the other hand, a 10 times lower normalized enrichment factor in the lava flow gas, which is consistent with a sulfur depletion.

It thus seems that volcanic gas emission changes radically between primary and secondary degassing. Increase volatility of some metals such as Lead or Zinc might lead to higher toxicity, with important hazard for the local population and environment.

How to cite: Levillayer, N. and Sigmarsson, O.: Primary versus secondary degassing during basaltic eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5120, https://doi.org/10.5194/egusphere-egu23-5120, 2023.

EGU23-6814 | Posters on site | GMPV8.7

Correlation of volcanic activity and S-wave attenuation anomalies in the Reykjanes Peninsula, Iceland 

Jiri Malek and Lucia Fojtikova and the NASPMON WP7

Increased attenuation of seismic S-waves propagating beneath a volcano is one of the most important seismic indicators of magma or partially melted rocks. We studied the attenuation in the Reykjanes peninsula, Southwest Iceland and its local anomalies in relation to the Fagradalsfjall eruption in March 2021.  

The Reykjanes Peninsula (situated on the rift between Eurasian and North American tectonic plates) is characterized by intensive volcanism that forms its unique geological structure and generates seismic swarm activity. Since 2013, it has been monitored by the REYKJANET network. Seismic activity intensified from December 2019 and lasted until the eruption of Fagradalsfjall volcano in March 2021. Seismicity during this period was distributed along the whole peninsula, not only in the vicinity of the eruption site. These data give us a unique opportunity to study the attenuation of seismic S-waves waves and their frequency dependence and to identify anomalies of attenuation.

The formula for mean attenuation is derived by estimating maximum seismic amplitudes as a function of earthquake magnitude accounting for hypocentral distance and station constants that reflect local conditions beneath the stations. It was derived for the vertical and horizontal components of S waves using the ground displacement, velocity and acceleration. Significant frequency dependence of attenuation was found with the attenuation coefficient proportional to the logarithm of the frequency. This explains different attenuation of the maximum amplitudes for stronger and weaker earthquakes, which have different prevailing frequencies. It was also found that the attenuation is not homogeneous in the entire area covered by REYKJANET (approximately 35 km x 15 km). The attenuation showed significant changes in time. Strong S-wave attenuation was detected for rays passing through the Krýsuvík volcanic system during the year 2020. This may indicate the presence of partially melted rocks at shallow depth. The attenuation beneath the eruption site at Fagradalsfjall was not anomalous during the year 2020; the anomalous values were only detected at the time of eruption.

 This study was supported by the NASPMON project.

How to cite: Malek, J. and Fojtikova, L. and the NASPMON WP7: Correlation of volcanic activity and S-wave attenuation anomalies in the Reykjanes Peninsula, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6814, https://doi.org/10.5194/egusphere-egu23-6814, 2023.

Fagradalsfjall eruption showed a remarkable pulsatory magma discharge activity in Jul-Aug 2021, with a characteristic timescale of ~36 hours (with cycles varying from 17 to 76 hours) and a duration of lava outflow from the crater of 10 to 70 hours. Active lava discharge coincides with the presence of both shallow and deep volcanic tremors that stops abruptly as soon as the active phase of the cycle finishes. The initial phase of each eruption cycle is characterized by some shifts of the tremor source between a depth of ~ 5 km and a shallow level, active degassing, and appearance of fresh lava at the top of the crater. Deep tremor source might be continuously active.

We propose that the pulsatory activity is caused by the dynamics of magma flow in a feeding dike. The model assumes purely elastic wall-rocks rheology and Newtonian temperature-dependent magma viscosity. Elastic displacement of host rocks is calculated by means of the analytical solution for an elliptic cavity subject to fluid overpressure. We assume that surrounding rocks temperature is linearly increasing with depth and the heat transfer from the magma following Newton’s law. The influx of the magma at the base of the dike is controlled by the dike overpressure. For reasonable values of governing parameters, the system shows pulsatory activity in accordance with the observed timescales. During low discharge rate magma viscosity in the upper part of the dike increases dramatically, magma flow stops, and the dike starts to inflate at depth storing large amounts of magma. As the pressure increases the flow of the fresh hot magma destroys the plug and discharge episode occurs. The dike deflates and the flow rate decreases leading to consequent cooling of the magma and blockage of the dike.

Parametric study reveals the influence of controlling parameters (magma influx rate, elastic modulus of rocks, heat exchange coefficient end others) on the period of discharge and the presence of pulsatory activity.

How to cite: Melnik, O., Soubestre, J., Shapiro, N., and Caudron, C.: Dynamics of pulsatory magma discharge at Fagradalsfjall volcano during Jul-Aug 2021: insights from observations, tremor locations and numerical models., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7505, https://doi.org/10.5194/egusphere-egu23-7505, 2023.

EGU23-8196 | ECS | Posters on site | GMPV8.7

Relatively relocated seismicity during the 2021 Fagradalsfjall dyke intrusion, Reykjanes Peninsula, Iceland: Detailed evolution of a lateral dyke, and comparison to Bárðarbunga-Holuhraun 

Esme Glastonbury-Southern, Tom Winder, Tim Greenfield, Thorbjörg Ágústsdóttir, Nick Rawlinson, Robert White, Bryndís Brandsdóttir, Tomas Fischer, Josef Horálek, Jana Doubravová, Conor Bacon, Egill Árni Gudnason, Gylfi Páll Hersir, Pavla Hrubcova, and Eva P. S. Eibl

The 2021 Fagradalsfjall eruption on Iceland’s Reykjanes Peninsula was preceded by more than 12 months of elevated seismic and inflationary activity, beginning around December 2019. On 24th February 2021, an exceptionally intense episode of seismicity covering the length of the Peninsula marked the initiation of a dyke intrusion, which continued to develop until the 19th of March 2021, when melt first erupted at the surface. During the intrusion, more than 80,000 microearthquakes marked the propagation of melt, first northeast towards Mt Keilir, then to the southwest, eventually forming a 10 km-long dyke. These events were recorded by a dense local seismic network and detected and located using QuakeMigrate[1].

We present relative relocations of the seismicity, and tightly constrained focal mechanisms for earthquakes from the dyke intrusion period. The high precision of the relative relocations reveals fine scale structure in the region, which is studied in relation to the orientation of fault planes rupturing in individual earthquakes, thus providing insight into the mechanism of dyke propagation and the controls on faulting in the region. We find that the strikes of the fault planes of individual earthquakes differ from the overall trend of dyke propagation across several propagating seismic swarms.

We compare our findings for the Fagradalsfjall seismicity to the 2014-2015 Bárðarbunga-Holuhraun intrusion and eruption seismicity [2], in the context of the contrasting tectonic settings, and markedly different precursory activity.

1: Tom Winder, Conor Bacon, Jonathan D. Smith, Thomas S. Hudson, Julian Drew, & Robert S. White. (2021). QuakeMigrate v1.0.0 (v1.0.0). Zenodo. https://doi.org/10.5281/zenodo.4442749

2: Woods, J., Winder, T., White, R. S., and Brandsdóttir, B., 2019. Evolution of a lateral dike intrusion revealed by relatively-relocated dike-induced earthquakes: The 2014–15 Bárðarbunga–Holuhraun rifting event, Iceland. https://doi.org/10.1016/j.epsl.2018.10.032

How to cite: Glastonbury-Southern, E., Winder, T., Greenfield, T., Ágústsdóttir, T., Rawlinson, N., White, R., Brandsdóttir, B., Fischer, T., Horálek, J., Doubravová, J., Bacon, C., Gudnason, E. Á., Hersir, G. P., Hrubcova, P., and Eibl, E. P. S.: Relatively relocated seismicity during the 2021 Fagradalsfjall dyke intrusion, Reykjanes Peninsula, Iceland: Detailed evolution of a lateral dyke, and comparison to Bárðarbunga-Holuhraun, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8196, https://doi.org/10.5194/egusphere-egu23-8196, 2023.

EGU23-9413 | ECS | Orals | GMPV8.7

Seismic Tremor Reveals Changes in Episode Duration throughout the 2021 Geldingadalir Eruption, Iceland 

Eva P. S. Eibl, Oliver Lamb, Thorvaldur Thordarson, Ármann Höskuldsson, Egill Á. Gudnason, Gylfi Páll Hersir, and Thorbjörg Ágústsdóttir

The Geldingadalir eruption on the Reykjanes peninsula, Iceland, lasted from 19 March to 18 September 2021. While it continuously effused lava in March and April, it transitioned to an episodic pattern from 2 May onwards. We based our analysis on seismometer data from stations NUPH and LHR located 5.5 and 2 km SE of the active vent, respectively.

From 2 May to 14 June the eruption featured minute-long episodes that were classified into 6 different periods based on the duration of the tremor, the repose time, and the seismic amplitude (Eibl et al. 2022, Bulletin of Volcanology).

Here we focus on the timespan from 14 June to 18 September and define another three periods with distinct patterns: (i) For most of June the tremor was continuous and transitioned on 6 July to a period with hour long effusion followed by minute-long episodic effusion, (ii) 19 July to 3 September which featured only hour-long lava effusion episodes, and (iii) from 11 September, a 2-day-long effusion was followed by several days of minute-long episodes.

We discuss these changes in the context of acoustic data, video camera data, geomorphological changes of the crater and the shallow subsurface. Overall, we find further indications for an evolving shallow magma compartment in July.

How to cite: Eibl, E. P. S., Lamb, O., Thordarson, T., Höskuldsson, Á., Gudnason, E. Á., Hersir, G. P., and Ágústsdóttir, T.: Seismic Tremor Reveals Changes in Episode Duration throughout the 2021 Geldingadalir Eruption, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9413, https://doi.org/10.5194/egusphere-egu23-9413, 2023.

EGU23-10209 | Posters on site | GMPV8.7

Volcanic degassing during the recent Fagradalsfjall and Merardalir eruptions, Iceland 

Samuel Scott, Melissa Pfeffer, Clive Oppenheimer, and Andri Stefánsson

The recent eruptions of Fagradalsfjall and Meradalir (Iceland) marks the first eruptive episode on the Reykjanes Peninsula in nearly 800 years. Open-path Fourier Transform Infrared (OP-FTIR) measurements of major and minor gas molecular species (including H2O, CO2, SO2, HCl, HF and CO) in the gas emissions have been performed on more than twenty occasions throughout the eruptions in 2021 and 2022. Generally, the gas emissions are water-rich (60-95 mol % H2O) and show CO2/SO2 molar ratios of ~4, consistent with magma generation at >15 km depth. Comparison of measured gas emissions with geochemical models of degassing of the Fagradalsfjall basaltic melt suggest that fractional degassing is necessary to explain the high-water contents of the fountaining gas at Fagradalsfjall, implying that a significant fraction of the CO2 that has exsolved from the magma is lost at depth prior to eruption. The measured vent gas emissions display enigmatic changes as a function of time, with lowest H2O/CO2 and H2O/SO2 ratios measured early in the eruption at Fagradalsfjall in 2021 and higher ratios during later stages and during the Meradalir eruption in 2022. The chemistry of the gas emissions is significantly affected by the style of degassing, with gas emitted by surface lava flows characterized by higher H2O/CO2 and H2O/SO2 and lower SO2/HCl and SO2/HF ratios compared to gas emitted at actively erupting vents. Moreover, the data record significant short-term temporal changes in chemistry on the timescales of minutes associated with intermittent fountaining and cooling/solidification of lava flows. This study highlights the utility of OP-FTIR techniques for tracing basaltic magma degassing in space and time. 

How to cite: Scott, S., Pfeffer, M., Oppenheimer, C., and Stefánsson, A.: Volcanic degassing during the recent Fagradalsfjall and Merardalir eruptions, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10209, https://doi.org/10.5194/egusphere-egu23-10209, 2023.

EGU23-10732 | ECS | Orals | GMPV8.7

Widespread fracture movements during the 2019–2021 volcano-tectonic unrest on the Reykjanes Peninsula from TerraSAR-X interferometry 

Cécile Ducrocq, Thóra Árnadóttir, Páll Einarsson, Sigurjón Jónsson, Vincent Drouin, Halldór Geirsson, and Ásta Rut Hjartardóttir

Fractures and tectonic structures have been related to dyke emplacements, eruption location or dynamics in several volcanic areas around the world. Mapping of active faults is therefore key for assessing the potential tectonic and volcanic hazard within a region. The 2021 eruption in the Fagradalsfjall volcanic area (Reykjanes Peninsula, SW Iceland) was preceded by two years of volcanic unrest, including four non-eruptive unrests in the Svartsengi and Krýsuvík volcanic areas and a dyke intrusion in the Fagradalsfjall volcanic segment. Nine earthquakes of magnitudes M 5–5.6 were recorded during this time period and were widely felt by the surrounding population. Using interferometric synthetic aperture radar (InSAR) applied to TerraSAR-X data collected over 2019–2021, we mapped fracture movements over the Reykjanes Peninsula. We identified ~1250 active structures across 54 interferograms during this time period, complementing previously mapped structures. Our study reveals extensive fracture movements across most of the Peninsula, extending from Reykjanes to NE Krýsuvík volcanic areas. We particularly highlight previously undetected structures beneath the town of Grindavík as well as a N45°E striking structure in the Fagradalsfjall volcanic area, active during summer-autumn 2020, prior to the 2021 dyke intrusion. We propose that this structure influenced the location of the longest lasting vent of the 2021 eruption. The observations presented in this study have important implications for improving our understanding of volcano-tectonic interactions and hazard assessments in Iceland and worldwide.

How to cite: Ducrocq, C., Árnadóttir, T., Einarsson, P., Jónsson, S., Drouin, V., Geirsson, H., and Hjartardóttir, Á. R.: Widespread fracture movements during the 2019–2021 volcano-tectonic unrest on the Reykjanes Peninsula from TerraSAR-X interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10732, https://doi.org/10.5194/egusphere-egu23-10732, 2023.

EGU23-13310 | ECS | Orals | GMPV8.7 | Highlight

Relative earthquake relocations and detailed evolution of failed and successful lateral dyke intrusions during the 2021-2022 Fagradalsfjall volcano-tectonic rifting event 

Thorbjörg Ágústsdóttir, Egill Árni Gudnason, Rögnvaldur Líndal Magnússon, Tomáš Fischer, Tom Winder, Eva P. S. Eibl, Esme Glastonbury-Southern, Gylfi Páll Hersir, Josef Horálek, Jana Doubravová, Josef Vlček, Pavla Hrubcová, Jiri Málek, Lucia Fojtíková, and Bryndís Brandsdóttir

The 6-month long fissure eruption that started in Geldingadalir valley within Mt. Fagradalsfjall, Reykjanes Peninsula, SW Iceland, on 19March 2021 was preceded by three weeks of intense seismic activity associated with a ~10 km long NE-SW oriented dyke intrusion, along the Fagradalsfjall volcanic system. This was the first eruption in over 800 years on the Peninsula. A multi-institutional seismic network, installed prior to the dyke intrusion, comprises 27, 3-component instruments (25 broadband and 2 short-period instruments) covering the whole Reykjanes Peninsula. Here we focus on the Fagradalsfjall area (~12x10 km) with 4 instruments located within a 2.5 km radius of the observed dyke seismicity. Accurate automatic earthquake locations using a new detection and location algorithm QuakeMigrate[1] obtain an order of magnitude higher number of earthquakes than conventional location methods. For high precision locations, events are cross-correlated and then relatively relocated using GrowClust[2]. Here we present detailed earthquake location results from 18 September 2021 to 30 September 2022. This period comprises i) the 2021 post-eruptive seismicity along the 10 km long 2021 dyke path; ii) an earthquake swarm about 5 km NE of the eruption site at 5-7 km depth in October; iii) a 5 day-long dyke intrusion in December 2021 that failed to breach the surface; iv) a 5-day-long dyke intrusion that breached the surface on 3 August 2022, and led to a 6 week-long fissure eruption in Meradalir, located about 0.5 km NE of the 2021 eruption site.

We find that the failed dyke in December 2021 and the 2022 dyke that successfully breached the surface share many of the same features. They both propagated at similar depths of 3-6 km, in the pathway of the initial 2021 dyke and both show some sparser seismicity closer to the surface. The time span of their propagation is almost identical; both are propagating for around 5 days, with similar lengths of about 6 km, which is considerably shorter than the 10 km long 3-week 2021 dyke propagation. They differ, however, in their location with respect to the 2021 eruption site. The failed 2021 dyke intrusion propagated mainly SW of the 2021 eruption site, whereas the successful 2022 dyke propagated NE of it. Interestingly, our results suggest that during the initial phases of the 2022 dyke intrusion, two dykelets propagate in opposite directions simultaneously.

How to cite: Ágústsdóttir, T., Gudnason, E. Á., Magnússon, R. L., Fischer, T., Winder, T., Eibl, E. P. S., Glastonbury-Southern, E., Hersir, G. P., Horálek, J., Doubravová, J., Vlček, J., Hrubcová, P., Málek, J., Fojtíková, L., and Brandsdóttir, B.: Relative earthquake relocations and detailed evolution of failed and successful lateral dyke intrusions during the 2021-2022 Fagradalsfjall volcano-tectonic rifting event, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13310, https://doi.org/10.5194/egusphere-egu23-13310, 2023.

The Reykjanes Peninsula in SW Iceland is a part of the Mid-Atlantic plate boundary. It forms its transtensional segment with several volcanic and faulting systems. We focus on the 2017 seismicity that occurred in the central part of Reykjanes at the place of Fagradalsfjall volcano prior to its eruption on March 19, 2021. We invert well-determined focal mechanisms of the 2017 seismicity and provide mapping of tectonic stress in space and time. Our results disclose heterogeneous stress field manifested by mix of shear, tensile and compressive fracturing.  Although the fracturing was diverse, directions of the principal stress axes were stable and consistent with the processes at the transtensional divergent plate boundary. The prominent stress direction was in the azimuth of 120°±8°, which represents the overall extension related to rifting in the Reykjanes Peninsula. The activity initiated on the transform fault segment with predominantly shear strike-slip events. The non-shear fractures occurred later being associated with normal dip-slips and corresponding to the opening of volcanic fissures trending in the azimuth of 30-35°, perpendicular to the extension. The dip-slips were mainly located above an aseismic dike detected in the centre of the 2017 swarm. This dike represents a zone of crustal weakening during a preparatory phase of future 2021 Fagradalsfjall volcanic eruption located at the same place. Moreover, we detected local variation of stress when the stress axes abruptly interchanged their directions in the individual stress domains. These stress changes are interpreted in a consequence of plate spreading and upcoming fluid flow during a preparatory phase of a rifting episode.

How to cite: Hrubcová, P. and Vavryčuk, V.: Tectonic stress changes related to plate spreading prior to the 2021 Fagradalsfjall eruption in SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13373, https://doi.org/10.5194/egusphere-egu23-13373, 2023.

EGU23-14037 | ECS | Posters virtual | GMPV8.7

Evolution of temporal seismic velocity changes and earthquake source mechanisms during the 2021 Fagradalsfall dyke intrusion 

Yesim Cubuk Sabuncu, Felix Rodríguez Cardozo, Halldór Geirsson, Kristín Jónsdóttir, Vala Hjörleifsdóttir, Thomas Lecocq, Corentin Caudron, and Aurelien Mordret

Late February 2021, the Reykjanes Peninsula in southwest Iceland experienced severe seismicity associated with the development of a 9 km long dyke. Eight earthquakes of magnitude M≥5  were registered in the vicinity of Fagradalsfjall from February 24 until the onset of the Fagradalsfjall eruption in mid-March, which lasted for six months. Here, we analyze the temporal variations in crustal seismic wave velocities and the source characteristics of earthquakes during the dyke formation phase (February-March 2021).

We apply ambient-noise seismic interferometry and compute seismic noise cross-correlations using the MSNoise software. Cross-wavelet analysis, a powerful technique that allows us to obtain frequency-dependence of velocity change, is used to investigate relative variations in seismic wave velocities (dv/v). Along with our wavelet-based dv/v results, we also present the stretching-based dv/v time-series that were calculated in real-time for volcano monitoring during the unrest. 

The Fagradalsfjall dyke intrusion induced temporal variations in seismic velocities and strong decorrelation that were picked up by the entire network across the peninsula. Beginning abruptly with the increased seismic activity, velocities at nearby seismic stations decreased by 1.5 percent. The amount of dv/v change was noticeably less than 1 percent at distant stations (15-30 km). 

The regional time-domain moment tensor inversion method (TDMT_INVC) was also applied to obtain earthquake mechanism solutions. Source parameters of 50 moderate-sized events with magnitudes Mw≥4.0 revealed predominantly normal and strike-slip faulting. We compare these to the deformation, dv/v and modeled Coulomb stress changes and present a joint interpretation.

We provide a summary of the complex spatial and temporal evolution of crustal seismic velocity changes in the weeks preceding the effusive eruption. The understanding of the pre-eruptive geophysical signatures of the Fagradalsfjall volcano will contribute to better predict future volcanic activity in the area.

How to cite: Cubuk Sabuncu, Y., Rodríguez Cardozo, F., Geirsson, H., Jónsdóttir, K., Hjörleifsdóttir, V., Lecocq, T., Caudron, C., and Mordret, A.: Evolution of temporal seismic velocity changes and earthquake source mechanisms during the 2021 Fagradalsfall dyke intrusion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14037, https://doi.org/10.5194/egusphere-egu23-14037, 2023.

EGU23-17131 | ECS | Posters on site | GMPV8.7

Cooling of the 2021 & 2022 Fagradalsfjall lavas: surface deformation and magnetic signatures 

Jóhanna Malen Skúladóttir, Elisa Johanna Piispa, Joaquin Munoz Cobo Belart, Halldór Geirsson, Vincent Drouin, and Kimberley Jean Hutchinson

Lavas are known to cool and contract following their emplacement, resulting in measurable subsidence at their surface. Magnetic surveying of the cooling lava can also provide insight into the causation of such subsidence, whether it be due to for example lava tunnel collapse and/or cooling of the lava. Repeated geodetic, photogrammetric, and magnetic measurements can be used to monitor the subsidence and can help determine the cooling rate of the lava. Here, we present initial results on subsidence and total magnetic field of the Fagradalsfjall lavas (Reykjanes Peninsula, Iceland), which were emplaced in March-September 2021 and August 2022. The post-emplacement deformation of the lavas is measured from comparison of Digital Elevation Models (DEMs) in 2x2 m derived from aerial photogrammetric surveys, in-situ Global Navigation Satellite System (GNSS) surveys of benchmarks in the lava flow, and Interferometric Synthetic Aperture Radar (InSAR). The DEM differences show subsidence of up to 7 m in the first year since the end of the 2021 eruption. Magnetic measurements were performed using drone surveys (MagArrow magnetometer suspended on DJI Matrice 600) and hiking profiles (GEM Systems GSM-19 Overhauser magnetometer). Our preliminary results show quite variable magnetization of the lavas. We suggest that the low magnetic anomalies are either associated with internal structures or show evidence of hot lava still above its Curie temperature and possibly even in liquid form and coincide roughly with the higher subsidence rates. During the August 2022 eruption, when the new lava was partly emplaced on top of the 2021 lava field, some of the older lava squeezed out from the western border of the 2021 flow, demonstrating that the 2021 lavas were still partly in liquid form. We expect the 2021-2022 lavas to continue to subside as the lava cools down and contracts, and plan further studies to provide insight into the cooling processes.

How to cite: Skúladóttir, J. M., Piispa, E. J., Belart, J. M. C., Geirsson, H., Drouin, V., and Hutchinson, K. J.: Cooling of the 2021 & 2022 Fagradalsfjall lavas: surface deformation and magnetic signatures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17131, https://doi.org/10.5194/egusphere-egu23-17131, 2023.

EGU23-40 | PICO | CR2.2

Investigating firn and ice anisotropy around the EastGRIP Camp, North East Greenland Ice Stream, from ambient noise surface waves 

Emma Pearce, Dimitri Zigone, Charlie Schoonman, Steven Franke, Olaf Eisen, and Joachim Rimpot

We use cross-correlations of ambient seismic noise data between pairs of 9 broadband three component seismometers to investigate variations in velocity structure and anisotropy in the vicinity of the EastGRIP camp along and across flow of the Northeast Greenland Ice Stream (NEGIS).

From the 9-component correlation tensors associated with all station pairs we derive dispersion curves of Rayleigh and Love wave group velocities between station pairs at frequencies from 1 to 25 Hz. The distributions of the Rayleigh and Love group velocities exhibit anisotropy variations for the along and across flow component. To better assess those variations, we invert the dispersions curves to shear wave velocities in the horizontal (Vsh) and vertical (Vsv) direction for the top 300 m of the NEGIS using a Markov Chain Monte Carlo approach.

The reconstructed 1-D shear velocity model revels radial anisotropy in the NEGIS. Along and across flow vertical shear wave velocities (Vsv) identify comparable velocity profiles for all depths. However, horizontal shear wave velocities (Vsh) are faster by approximately 250 m/s in the along flow direction below a depth of 100 m, i.e. below the firn-ice transition.

This type of anisotropy seems to arise from the alignment of a crystallographic preferred orientation, due to deformation associated with shear zones. The role of anisotropy as e.g. created by air bubbles in the firn and ice matrix, is yet unclear.

Faster Vsh velocities in the along flow direction support that the NEGIS has crystal orientation alignment normal to the plane of shear compression (i.e. ice crystals orientated across flow) within the upper 300 m of the ice stream and are in alignment with the results from other methods. We demonstrate that simple, short duration (2-3 weeks), passive seismic deployment and environmental noise-based analysis can be used to determine the anisotropy of the upper part of ice masses.

How to cite: Pearce, E., Zigone, D., Schoonman, C., Franke, S., Eisen, O., and Rimpot, J.: Investigating firn and ice anisotropy around the EastGRIP Camp, North East Greenland Ice Stream, from ambient noise surface waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-40, https://doi.org/10.5194/egusphere-egu23-40, 2023.

EGU23-92 | ECS | PICO | CR2.2

Improving identification of glacier bed materials using converted-wave seismics 

Ronan Agnew, Adam Booth, Alex Brisbourne, Roger Clark, and Andy Smith

When modelling ice sheet and glacier dynamics, a consideration of basal conditions is essential. Bed topography, hydrology and materials provide important controls on ice flow; however, the materials underlying large sections of the polar ice sheets are unknown. Seismic amplitude-versus-offset (AVO) analysis provides a means of inferring glacier bed properties, namely acoustic impedance and Poisson's ratio, by measuring bed reflectivity as a function of incidence angle.

However, existing methods of applying AVO to glaciology only consider the compressional-wave component of the wavefield and solutions suffer from non-uniqueness. This can be addressed using multi-component seismic datasets, in which a strong converted-wave arrival (downgoing compressional-wave energy converted to shear-wave energy upon reflection at the glacier bed) is often present. We present a method of jointly inverting compressional (PP) and converted-wave (PS) seismic data to improve constraint of glacier bed properties.

Using synthetic data, we demonstrate that for typical survey geometries, joint inversion of PP- and PS-wave AVO data delivers better-constrained bed acoustic impedance and Poisson’s ratio estimates compared with PP-only inversion. Furthermore, joint inversion can produce comparably constrained results to PP inversion when using input data with a smaller range of incidence angles/offsets (0-30 degree incidence for joint inversion, versus 0-60 degrees for PP- only). This could simplify future field acquisitions on very thick ice, where obtaining data at large incidence angles is difficult.

Joint AVO inversion therefore has the potential to improve identification of glacier bed materials and simplify field acquisitions of glacial AVO data. We also present preliminary results from Korff Ice Rise, West Antarctica, where better constraints on bed conditions can help improve our knowledge of ice sheet history in the Weddell Sea sector. Routine measurements of this kind will help constrain ice-sheet model inputs and reduce uncertainty in predictions of sea-level rise.

How to cite: Agnew, R., Booth, A., Brisbourne, A., Clark, R., and Smith, A.: Improving identification of glacier bed materials using converted-wave seismics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-92, https://doi.org/10.5194/egusphere-egu23-92, 2023.

EGU23-93 | ECS | PICO | CR2.2

Efficient neural network-based detection of seismicity in fibre optic data from Store Glacier, West Greenland 

Andrew Pretorius, Adam Booth, Emma Smith, Andy Nowacki, Sjoerd de Ridder, Poul Christoffersen, and Bryn Hubbard

Seismic surveys are widely used to characterise the properties of glaciers, their basal material and conditions, and ice dynamics. The emerging technology of Distributed Acoustic Sensing (DAS) uses fibre optic cables as seismic sensors, allowing observations to be made at higher spatial resolution than possible using traditional geophone deployments. Passive DAS surveys generate large data volumes from which the rate of occurrence and failure mechanism of ice quakes can be constrained, but such large datasets are computationally expensive and time consuming to analyse. Machine learning tools can provide an effective means of automatically identifying seismic events within the data set, avoiding a bottleneck in the data analysis process.

Here, we present a novel approach to machine learning for a borehole-deployed DAS system on Store Glacier, West Greenland. Data were acquired in July 2019, as part of the RESPONDER project, using a Silixa iDAS interrogator and a BRUsens fibre optic cable installed in a 1043 m-deep borehole. The data set includes controlled-source vertical seismic profiles (VSPs) and a 3-day passive record of cryoseismicity.  To identify seismic events in this record, we used a convolutional neural network (CNN). A CNN is a deep learning algorithm and a powerful classification tool, widely applied to the analysis of images and time series data, i.e. to recognise seismic phases for long-range earthquake detection.

For the Store Glacier data set, a CNN was trained on hand-labelled, uniformly-sized time-windows of data, focusing initially on the high-signal-to-noise-ratio seismic arrivals in the VSPs. The trained CNN achieved an accuracy of 90% in recognising seismic energy in new windows. However, the computational time taken for training proved impractical. Training a CNN instead to identify events in the frequency-wavenumber (f-k) domain both reduced the size of each data sample by a factor of 340, yet still provided accurate classification. This decrease in input data volume yields a dramatic decrease in the time required for detection. The CNN required only 1.2 s, with an additional 5.6 s to implement the f-k transform, to process 30 s of data, compared with 129 s to process the same data in the time domain. This suggests that f-k approaches have potential for real-time DAS applications.

Continuing analysis will assess the temporal distribution of passively recorded seismicity over the 3 days of data. Beyond this current phase of work, estimated source locations and focal mechanisms of detected events could be used to provide information on basal conditions, internal deformation and crevasse formation. These new seismic observations will help further constrain the ice dynamics and hydrological properties of Store Glacier that have been observed in previous studies of the area.

The efficiency of training a CNN for event identification in the f-k domain allows detailed insight to be made into the origins and style of glacier seismicity, facilitating further development to passive DAS instrumentation and its applications.

How to cite: Pretorius, A., Booth, A., Smith, E., Nowacki, A., de Ridder, S., Christoffersen, P., and Hubbard, B.: Efficient neural network-based detection of seismicity in fibre optic data from Store Glacier, West Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-93, https://doi.org/10.5194/egusphere-egu23-93, 2023.

EGU23-952 | PICO | CR2.2

Variability of surface density at Dotson Ice Shelf, West Antarctica 

Clare Eayrs, Lucas Beem, Choon-Ki Lee, Won Sang Lee, Jiwoong Chung, Christopher Pierce, Jamey Stutz, and David Holland

The ice mass balance of Antarctica has been steadily and strongly decreasing over recent decades, with major ramifications for global sea levels. Satellite remote sensing offers global, daily coverage of ice mass changes, which is essential for understanding land ice changes and their effects on global climate. However, we need to correct for processes including firn densification, glacial isostatic adjustment, elastic compensation of the Earth’s surface, ocean tides, and inverse barometer effect. Of these corrections, understanding the changes to the firn layer constitutes one of the largest uncertainties in making estimates of the surface mass balance from space. Furthermore, the development of firn models that aid our understanding of firn densification processes is hampered by a lack of observations.

Radar sounder reflections contain information about the roughness and permittivity of the reflecting interface, allowing us to map the spatial variability of the ice surface characteristics. In 2022, a helicopter-mounted ice-penetrating radar system developed by the University of Texas Institute for Geophysics collected high-quality radar observations over the Dotson Ice Shelf, West Antarctica. These surveys obtained clearly defined surface and bed reflections. We derived near-surface density along these survey flight lines using the radar statistical reconnaissance method developed by Grima, 2014. We calibrated our estimates with contemporary observations, including ground penetrating radar, a shallow ice core, an Autonomous phase-sensitive Radio Echo-sounder (ApRES), and radar soundings of well-defined surfaces from a calibration flight.

How to cite: Eayrs, C., Beem, L., Lee, C.-K., Lee, W. S., Chung, J., Pierce, C., Stutz, J., and Holland, D.: Variability of surface density at Dotson Ice Shelf, West Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-952, https://doi.org/10.5194/egusphere-egu23-952, 2023.

EGU23-1137 | ECS | PICO | CR2.2

Hydraulic behaviour of a mountain permafrost subsoil revealed by an infiltration experiment and ERT time-lapse measurements 

Mirko Pavoni, Jacopo Boaga, Alberto Carrera, Giulia Zuecco, Luca Carturan, and Matteo Zumiani

Although rock glaciers represent a common periglacial landform in the alpine environment, and have a significant contribution to the hydrological regime of the related areas, their hydrodynamic is relatively less defined if compared to moraines, talus, and hillslope deposits. So far, the hydraulic behaviour of frozen layers that may be found inside rock glaciers has been investigated only with geochemical analysis of their spring water. These previous studies observed that the frozen layer acts as an aquiclude (or aquitard) and separates a supra-permafrost flow component, originating from snow-ice melting and rainwater, and a deeper aquifer at the bottom of the rock glacier systems.

In this work we verified, for the first time with a geophysical monitoring method, the low-permeability hydraulic behaviour associated to the frozen layer of mountain permafrost subsoils. In the inactive rock glacier of Sadole Valley (Southern Alps, Trento Province, Italy) we performed an infiltration experiment combined with 2D electrical resistivity tomography (ERT) measurements in time-lapse configuration. Considering the same ERT transect, a time zero dataset (t0) has been collected before the water injection, subsequently about 800 liters of salt water have been spilled (approximately in a point) on the surface of the rock glacier in the middle of the electrodes array, and 10 ERT datasets have been collected periodically in the following 24 hours. To highlight the variations of electrical resistivity in the frozen subsoil, related to the injected salt water flow, only the inverted resistivity model derived from t0 dataset has been represented in terms of absolute resistivities, while the other time steps results have been evaluated in terms of percentage changes of resistivity with respect to the t0 initial model.

Our results clearly agree with the assumption that a frozen layer acts as an aquiclude (or aquitard) in a mountain permafrost aquifer, since during the infiltration experiment the injected salt water was not able to infiltrate into the underlying permafrost layer. The positive outcome of this test, fronting impervious environment and logistic constraints, opens up interesting future scenarios regarding the application of this geophysical monitoring method for the hydraulic characterization of rock glaciers. The experiment, used in this work to evaluate the permeability of the frozen layer, could be adapted in future to evaluate (in a quantitative way) the hydraulic conductivity of the active layer in rock glacier aquifers.

How to cite: Pavoni, M., Boaga, J., Carrera, A., Zuecco, G., Carturan, L., and Zumiani, M.: Hydraulic behaviour of a mountain permafrost subsoil revealed by an infiltration experiment and ERT time-lapse measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1137, https://doi.org/10.5194/egusphere-egu23-1137, 2023.

EGU23-2250 | ECS | PICO | CR2.2

Ice slab thickening drives surface runoff expansion from the Greenland Ice Sheet’s percolation zone - and vice versa 

Nicolas Jullien, Andrew Tedstone, and Horst Machguth

On the Greenland Ice Sheet, the firn layer holds the potential to trap and refreeze surface meltwater within its pore space. Acting as a buffer, it prevents meltwater from leaving the ice sheet. However, several meter-thick ice slabs have developed in the firn during the last two decades, reducing subsurface permeability and inhibiting vertical meltwater percolation. Ice slabs are located above the long-term equilibrium line along the west, north and northeast coasts of the ice sheet. Through time, ice slabs have thickened while new ones have developed at higher elevations. Concomitantly, the area of the ice sheet drained by surface rivers has increased by 29% from 1985 to 2020. Nowadays, 5-10% of surface losses through meltwater runoff originates from these newly drained areas, which correspond strongly with where ice slabs are located.

Here, we demonstrate that the highest elevation which is drained by surface rivers – termed the maximum visible runoff limit – is controlled by the ice content in the subsurface firn. Using ice slab thickness derived from the accumulation radar and annual maximum visible limit retrievals from Landsat imagery from 2002 to 2018, we show that a sub-surface ice content threshold triggers the shift from a ‘firn deep percolation regime’ to a ‘firn runoff regime’. Although ice slabs act as an aquitard, vertical meltwater percolation can still take place where visible meltwater ponds at the surface. We show that once the firn runoff regime is underway, ice slabs are thicker in locations with active surface hydrology compared to locations where no meltwater is visible at the surface. Spatial heterogeneity in ice slab thickness is therefore predominantly controlled by surface hydrology features.

How to cite: Jullien, N., Tedstone, A., and Machguth, H.: Ice slab thickening drives surface runoff expansion from the Greenland Ice Sheet’s percolation zone - and vice versa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2250, https://doi.org/10.5194/egusphere-egu23-2250, 2023.

EGU23-2856 | ECS | PICO | CR2.2

New Representation of Synthetic Aperture Radar Images for Enhanced Ice-Sounding Interpretation 

Álvaro Arenas-Pingarrón, Hugh F.J. Corr, Paul V. Brennan, Carl Robinson, Tom A. Jordan, Alex Brisbourne, and Carlos Martín

The processing of Synthetic Aperture Radar (SAR) images is based on the coherent integration of Doppler frequencies. The associated Doppler spectrum is generated from the variation of the relative location between the radar and the scatterer. In geometries where the moving radar-platform follows a straight trajectory at constant velocity, the Doppler frequency depends on the angle of elevation from the radar to the scatterer, according to the electromagnetic (EM) propagation. In ice-sounding by airborne SAR, the EM path depends on the air-ice interface and the firn ice properties. For any of the scatterers under test, after integrating the received radar echoes from the multiple radar locations into a single pixel, the resulting amplitude image forgets which is the backscattering angle from each of the radar locations. However, this information is still within the Doppler spectrum of the image. We decompose the Doppler spectrum of the SAR image into three non-overlapping sub-bands; assign to each sub-band one of the primary colours red, green or blue, forming three sub-images; and finally merge the sub-images into a single one. Rather than a single full-beamwidth averaged amplitude value, the new composition now includes angular backscattering information, coded by one of the primary colours. Blue colour is assigned to scattering received from forwards, when the scatterer is ahead of the radar (positive Doppler frequencies); green approximately from the vertical (near zero-Doppler geometries); and red to scattering received from backwards (negative Doppler). Thus, heterogeneous scattering will be represented by one or two colours, whereas homogeneous scattering will be grey, with all the primary colours uniformly weighted. Features like internal layering, crevasses, SAR focussing quality and discrimination of multiple reflections from surface and bottom, can now be better interpreted. We present and discuss the results from the British Antarctic Survey (BAS) airborne radar PASIN2 for deep-ice sounding, in Recovery and Rutford ice streams, respectively in East and West Antarctica during seasons 2016/17 and 2019/20.

How to cite: Arenas-Pingarrón, Á., Corr, H. F. J., Brennan, P. V., Robinson, C., Jordan, T. A., Brisbourne, A., and Martín, C.: New Representation of Synthetic Aperture Radar Images for Enhanced Ice-Sounding Interpretation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2856, https://doi.org/10.5194/egusphere-egu23-2856, 2023.

In many regions of the Northern Hemisphere, permafrost is thawing due to climate change. In steep terrain, this permafrost degradation can affect slope stability. In one of Iceland's eastern fjords, Seyðisfjörður, nine major landslide cycles have occurred in the last century, originating from the lower parts (< 500 m a.s.l.) of the Strandartindur slopes, with the largest landslide event ever recorded in Iceland occurring in December 2020. Its triggering mechanism is being intensively studied and its development is being monitored. In addition to these instabilities, slow movements are also observed in the upper part (> 500 - 1010 m a.s.l.) of these slopes. In these upper areas, it is not known whether permafrost is present in the subsurface or what is causing it to creep downward. To further investigate the stability of these slopes, it is important to know and map the distribution and condition of possible permafrost layers. Therefore, electrical resistivity tomography (ERT) and ground penetrating radar (GPR) measurements were performed to study the presence and distribution of permafrost in the mountain, Strandartindur, above Seyðisfjörður. A combination of measurements is used as ERT responds primarily to the electrical resistivity of the subsurface, but this can depend strongly on other factors such as porosity, water content, etc., and GPR can help map the presence of different interfaces in the soil determined by their different physical properties, such as relative electrical permittivity, but also conductivity, which is the reciprocal of resistivity. Combining the two methods allows us to get a clearer picture of the subsurface. As a benchmark for ERT measurements in the field, a laboratory setup was performed with soil and rock samples at different temperatures and water saturations to study the behavior of frozen and non-frozen conditions in our geologic environment. With all of these measurements, we aim to answer the questions of whether permafrost is present in the selected area, what the distribution of permafrost is, whether we can use laboratory ERT to establish reference resistivity values, and if these methods are appropriate for this area.

How to cite: von der Esch, A., Piispa, E. J., and Sæmundsson, Þ.: Electrical Resistivity Tomography and Ground-Penetrating Radar Measurements for Permafrost Detection on a Mountain Slope at Strandartindur, Seyðisfjörður - East Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4135, https://doi.org/10.5194/egusphere-egu23-4135, 2023.

EGU23-4895 | ECS | PICO | CR2.2

Detecting permafrost freeze-thaw front propagation using time-laps ERT observations in a large column experiment 

Jelte de Bruin, Victor Bense, and Martine van der Ploeg

Cold regions are increasingly subjected to higher air temperatures, causing warming of permafrost and a deepening of the active layer. This activates hydrogeological groundwater flow and new groundwater pathways to emerge. Monitoring of the active layer depth occurs mainly with the use of temperature observations, but a more flexible and non-invasive method to study transient subsurface processes is with the use of Electrical Resistivity Tomography (ERT) observations. 

Automated time-laps ERT arrays are used to monitor the frozen ground evolution during various seasons, observing resistivity variations during freezing and thawing. Similarly, the leaching of meltwater into the ground under freezing/thawing conditions can be observed. Not only geophysical changes such as fluctuations in water content and water table, but also temperature variations affect the electrical resistivity field. In order to track the development of permafrost active-layer freeze-thaw fronts using ERT observations, it is thus essential that the effect of temperature on the resistivity is clearly defined at realistic scales representing field conditions. Our aim is to determine fluid resistivity at various stages during freezing and thawing and validate current temperature–resistivity relations for partly frozen soils.

This study used a soil column (0.4 m diameter, 1 m heigh) equipped with 96 stainless steel electrodes placed at 8 horizontal rings of 12 electrodes each at various heights around the circumference of the column alongside with temperature sensors. The column was fully insulated on the sides and top except for the bottom, creating a 1D heat transfer system. The soil column was filled with quartzite sand with a D50 of 350 (μm) and organic matter content of 5 (wgt %). The experimental setup was placed within a climate chamber where the column was frozen to -4 °C and thawed to 3 °C over a 3-month period. During the freezing and thawing phase, a full 3D resistivity image was collected using the ERT at a weekly interval. Initial results show that the setup is capable of simulating permafrost freezing and thawing dynamics and ongoing work focuses on the relation between the temperature and time lapse ERT resistivity observations.

How to cite: de Bruin, J., Bense, V., and van der Ploeg, M.: Detecting permafrost freeze-thaw front propagation using time-laps ERT observations in a large column experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4895, https://doi.org/10.5194/egusphere-egu23-4895, 2023.

EGU23-5545 | ECS | PICO | CR2.2

High resolution maps of the sub-ice platelet layer in Atka Bay from electromagnetic induction sounding 

Mara Neudert, Stefanie Arndt, Markus Schulze, Stefan Hendricks, and Christian Haas

We present maps of the sub-ice platelet layer (SIPL) thickness and ice volume fraction beneath the land-fast sea ice in Atka Bay adjacent to the Ekström Ice Shelf (southeastern Weddell Sea, Antarctica). The widespread SIPL beneath Antarctic fast ice is indicative of basal melt of nearby ice shelves, contributes to the sea ice mass balance and provides a unique ecological habitat. Where plumes of supercooled Ice Shelf Water (ISW) rise to the surface rapid formation of platelet ice can lead to the presence of a semi-consolidated SIPL beneath consolidated fast ice.

Here we present data from extensive electromagnetic (EM) induction surveying with the multi-frequency EM sounder GEM-2 between May and December, 2022. It includes monthly survey data along a fixed transect line across Atka Bay between May and October, as well as comprehensive mapping across the entire bay in November and December. The GEM-2 surveys were supplemented by drill hole thickness measurements, ice coring and CTD profiles. A new data processing and inversion scheme was successfully applied to over 1000 km of EM profiles with a horizontal resolution of one meter. We obtained layer thicknesses of the consolidated ice plus snow layer, the SIPL, and the respective layer conductivities. The latter were used to derive SIPL ice volume fraction and an indicator for flooding at the snow-ice interface. The robustness of the method was validated by drill hole transects and CTD profiles.

Our results support conclusions about the spatial variability of the ocean heat flux linked to outflow of ISW from beneath the ice shelf cavity. Temporally, we found that the end of SIPL growth and the onset of its thinning in summer can be linked to the disappearance of supercooled water in the upper water column.

How to cite: Neudert, M., Arndt, S., Schulze, M., Hendricks, S., and Haas, C.: High resolution maps of the sub-ice platelet layer in Atka Bay from electromagnetic induction sounding, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5545, https://doi.org/10.5194/egusphere-egu23-5545, 2023.

EGU23-5851 | PICO | CR2.2

Measuring snow and avalanche properties using acoustic and seismic distributed fiber optic sensing 

Alexander Prokop, Nicola P. Agostinetti, and Bernhard Graseman

Since 2012 we monitor avalanche activity using distributed acoustic and seismic fiber optic sensing at our avalanche test area at Lech am Arlberg, Austria. The method is based on an optical time domain reflectometer system that detects seismic vibrations and acoustic signals on a fiber optic cable that can have a length of up to 30 km in 80 cm resolution. While in the first years we focused on successfully developing an operational avalanche detection system that is able to tell in real time reliably when an avalanche was triggered and what the size of the avalanche is, we now present our investigations of the seismic signals to measure snow properties such as snow depth and avalanche properties such as flow behavior. Our test in winter 2022 recorded by blasting triggered avalanches and during data post processing we extracted seismic guided waves. We discuss methods for extracting information from guided waves for measuring snow depth, which was verified against spatial snow depth measurements from terrestrial laser scanning. Analyzing the seismic signals of avalanches with run-out distances ranging from a few metres to approximately 250 m allows us to differentiate between wet and snow avalanches, which is discussed in the context of avalanche dynamics.

How to cite: Prokop, A., Agostinetti, N. P., and Graseman, B.: Measuring snow and avalanche properties using acoustic and seismic distributed fiber optic sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5851, https://doi.org/10.5194/egusphere-egu23-5851, 2023.

EGU23-6935 | PICO | CR2.2

A new view of a 1970s radar dataset from Greenland 

Nanna Bjørnholt Karlsson, Dustin Schroeder, Louise S. Sørensen, Winnie Chu, Thomas Teisberg, Angelo Tarzano, Niels Skou, and Jørgen Dall

The short observational record is one of the main obstacles to improving the present understanding of the future of the Polar ice sheets. While the quantity and quality of observations presently are increasing observations from before the 1990s are scarce. Here, we present the first results from a newly digitized ice-penetrating radar dataset acquired over the Greenland Ice Sheet in the 1970s. The data consist of more than 170,000 km of radar flight lines. While the ice thickness information from the data has been digitized by previous studies, the data itself (notably the z-scopes) were until recently only available as 35-mm films, microfiche copies of the films, and enlarged positives: Formats that are not usable for digital analysis.

In 2019, the film rolls were scanned by a digital scanner and subsequently, a large effort has been directed at carrying out quality control of the data with the view of making them publicly available.  Here we present the first results from this digitization. The overall data quality is good, and we are able to retrieve valuable information on layer stratigraphy and ice-flow dynamics.

How to cite: Karlsson, N. B., Schroeder, D., Sørensen, L. S., Chu, W., Teisberg, T., Tarzano, A., Skou, N., and Dall, J.: A new view of a 1970s radar dataset from Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6935, https://doi.org/10.5194/egusphere-egu23-6935, 2023.

EGU23-7198 | PICO | CR2.2

Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations fromSouth Pole and EPICA Dome C ice cores 

Carlos Martin, Robert Mulvaney, Howard Conway, Michelle Koutnik, C. Max Stevens, Hugh Corr, Catherine Ritz, Keith Nicholls, Reinhard Drews, and M. Reza Ershadi

The climatic conditions over ice sheets at the time of snow deposition and compaction imprint distinctive crystallographic properties to the resulting ice. As it gets buried, its macroscopic structure evolves due to vertical compression but retains traces of the climatic imprint that generate distinctive mechanical, thermal and optical properties. Because climate alternates between glacial periods, that are colder and dustier, and interglacial periods, the ice sheets are composed from layers with alternating mechanical properties. Here we compare ice core dust content, crystal orientation fabrics and englacial vertical strain-rates, measured with a phase-sensitive radar (ApRES), at the South Pole and EPICA Dome C ice cores. In agreement with previous observations, we show that ice deposited during glacial periods develops stronger crystal orientation fabrics. In addition, we show that ice deposited during glacial periods is harder in vertical compression and horizontal extension, up to about three times, but softer in shear. These variations in mechanical properties are ignored in ice-flow models but they could be critical for the interpretation of ice core records. Also, we show that the changes in crystal orientation fabrics due to transitions from interglacial to glacial conditions can be detected by radar. This information can be used to constrain age-depth at future ice-core locations.

How to cite: Martin, C., Mulvaney, R., Conway, H., Koutnik, M., Stevens, C. M., Corr, H., Ritz, C., Nicholls, K., Drews, R., and Ershadi, M. R.: Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations fromSouth Pole and EPICA Dome C ice cores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7198, https://doi.org/10.5194/egusphere-egu23-7198, 2023.

EGU23-7695 | ECS | PICO | CR2.2

Spatial variation of ice crystal fabric and implications of anisotropic flow in the Northeast Greenland Ice Stream 

Tamara Gerber and Olaf Eisen and the NEGIS community

Anisotropic crystal fabrics in ice sheets develop as a consequence of deformation and hence record information of past ice flow. Simultaneously, the fabric affects the present-day bulk mechanical properties of glacier ice because the susceptibility of ice crystals to deformation is highly anisotropic. This is particularly relevant in dynamic areas such as fast-flowing glaciers and ice streams, where the formation of strong fabrics might play a critical role in facilitating ice flow. Anisotropy is ignored in most state-of-the-art ice sheet models, and while its importance has long been recognized, accounting for fabric evolution and its impact on the ice viscosity has only recently become feasible. Both the application of such models to ice streams and their verification through in-situ observations are still rare. We present an extensive dataset of fabric anisotropy derived from ground-based and air-borne radar data, covering approximately 24,000 km2 of the Northeast Greenland Ice Stream onset region. Our methods yield the horizontal anisotropy and are based on travel time anisotropy as well as birefringence-induced power modulation of radar signals. These methods complement each other and show good agreement. We compare the in-situ observations with the results obtained from a fabric-evolution model employed along flow line bundles in the ice stream onset to discuss the fabric in light of past flow history and its significance for the current flow mechanics of the ice stream.

 

How to cite: Gerber, T. and Eisen, O. and the NEGIS community: Spatial variation of ice crystal fabric and implications of anisotropic flow in the Northeast Greenland Ice Stream, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7695, https://doi.org/10.5194/egusphere-egu23-7695, 2023.

EGU23-8197 | ECS | PICO | CR2.2

Ice rise evolution derived from radar investigations at a promontory triple junction, Dronning Maud Land, East Antarctica 

M. Reza Ershadi, Reinhard Drews, Veronica Tsibulskaya, Sainan Sun, Clara Henry, Falk Oraschewski, Inka Koch, Carlos Martin, Jean-Louis Tison, Sarah Wauthy, Paul Bons, Olaf Eisen, and Frank Pattyn

Promontory ice rises are locally grounded features adjacent to ice shelves that are still connected to the ice sheet. Ice rises are an archive for the atmospheric and ice dynamic history of the respective outflow regions where the presence, absence, or migration of Raymond arches in radar stratigraphy represents a memory of the ice-rise evolution. However, ice rises and their inferred dynamic history are not yet used to constrain large-scale ice flow model spin-ups because matching the arch amplitudes includes many unknown parameters, e.g., those pertaining to ice rheology. In particular, anisotropic ice flow models predict gradients in ice fabric anisotropy on either side of an ice divide. However, this has thus far not been validated with observations.

 

The ground-based phase-sensitive Radio Echo Sounder (pRES) has previously been used to infer ice fabric types for various flow regimes using the co-polarized polarimetric coherence phase as a metric to extract information from the birefringent radar backscatter. Here, we apply this technique using quad-polarimetric radar data along a 5 km transect across a ridge near the triple junction of Hammarryggen Ice Rise at the Princess Ragnhild Coast. A comparison with ice core data collected at the dome shows that the magnitude of ice fabric anisotropy can reliably be reconstructed from the quad-polarimetric data. We use the combined dataset also to infer the spatial variation of ice fabric orientations in the vicinity of the triple junction. The observations are integrated with airborne radar profiles and strain rates based on the shallow ice approximation. We then discuss whether estimated anisotropy from radar polarimetry on ice rises, in general, can be another observational constraint to better ice rises as an archive of ice dynamics.

How to cite: Ershadi, M. R., Drews, R., Tsibulskaya, V., Sun, S., Henry, C., Oraschewski, F., Koch, I., Martin, C., Tison, J.-L., Wauthy, S., Bons, P., Eisen, O., and Pattyn, F.: Ice rise evolution derived from radar investigations at a promontory triple junction, Dronning Maud Land, East Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8197, https://doi.org/10.5194/egusphere-egu23-8197, 2023.

EGU23-9273 | ECS | PICO | CR2.2

Layer-optimized SAR processing with a mobile pRES to illuminate the internal layering of an alpine glacier 

Falk M. Oraschewski, Inka Koch, Mohammadreza Ershadi, Jonathan Hawkins, Olaf Eisen, and Reinhard Drews

The internal, isochronous layering of glaciers is shaped by accumulation and ice deformation. Information about these processes can be inferred from observing the layers using radar sounding. The reflectivity of the layers depends on density (permittivity) and acidity (conductivity) contrasts which tend to decrease with depth. At places like alpine glaciers where logistic limitations often only allow the deployment of lightweight and power-constrained ground-penetrating radar systems, it can therefore be challenging to illuminate the deeper radio-stratigraphy.

The phase-sensitive Radio Echo Sounder (pRES) is a lightweight frequency modulated continuous wave radar which allows the use of coherent Synthetic Aperture Radar (SAR) processing techniques to improve the signal-to-noise ratio of internal reflection horizons. Using a mobile pRES we collected a radar profile on an alpine glacier (Colle Gnifetti, Italy/Switzerland). Here, we demonstrate how to apply layer-optimized SAR techniques to make deep internal layers visible, which could not be seen by a conventional pulsed radar. We evaluate the requirements on spatial resolution and positioning accuracy during data acquisition, necessary for applying layer-optimized SAR processing, as they constrain the feasibility of the method. We further discuss implications on how density and acidity contribute to decreasing dielectric contrasts.

How to cite: Oraschewski, F. M., Koch, I., Ershadi, M., Hawkins, J., Eisen, O., and Drews, R.: Layer-optimized SAR processing with a mobile pRES to illuminate the internal layering of an alpine glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9273, https://doi.org/10.5194/egusphere-egu23-9273, 2023.

EGU23-9619 | ECS | PICO | CR2.2

High-density 3D and 4D GPR data acquisitions over alpine glaciers using a newly developed drone-based system. 

Bastien Ruols, Ludovic Baron, and James Irving

We have developed a drone-based GPR system at the University of Lausanne that allows for the safe and efficient acquisition of large, high-density, 3D and 4D datasets over alpine glaciers. The system is able to record approximately 4 line-km of high-quality GPR data per set of drone batteries in less than 30 minutes of operation which, combined with multiple sets of batteries and/or the possibility of charging at the field site, means that 3D datasets over a large area can be acquired with unprecedented efficiency. The latter performance is possible thanks to (i) a custom-made real-time-sampling GPR controller that has been specifically designed for glaciers studies, (ii) minimization of the total payload weight using custom-built antennas and carbon-fiber components, and (iii) development of an optimized survey methodology. Further, because the drone is equipped with real-time kinematic GPS positioning, survey paths can be repeated with great precision, which opens new opportunities in term of 4D data acquisitions.

In the summer of 2022, we acquired both 3D and 4D data over two Swiss glaciers. On the Otemma glacier, we surveyed a grid of 462 profiles representing a total length of 112 line-km of data in only four days. After 3D binning, the trace spacing intervals in the in-line and crossline directions were respectively 0.4 m and 1 m, making this arguably the largest 3D GPR dataset of such density ever recorded over ice. The interface between the ice and the bedrock, visible on all profiles, extends to 1000 ns which translates into a depth of approximately 80 m. In addition, internal englacial and subglacial 3D structures are clearly detectable.

In parallel, we visited the Rhône glacier on a monthly basis between June and September 2022. A collapse feature, identified by the presence of large circular crevasses, had formed and was evolving close to the snout of the glacier. This represented a great opportunity to test the 4D acquisition capabilities of our system. We collected four high-density 3D datasets on the same survey grid. The repeatability of the trajectories was excellent as the paths differ only by a few centimeters between occurrences. Clear variations in the internal structure of the glacier are visible which will be investigated in the upcoming months.

How to cite: Ruols, B., Baron, L., and Irving, J.: High-density 3D and 4D GPR data acquisitions over alpine glaciers using a newly developed drone-based system., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9619, https://doi.org/10.5194/egusphere-egu23-9619, 2023.

The Whillans Ice Stream (WIS) is a major outlet of the West Antarctic Ice Sheet. Significantly, the downstream portion of the WIS is presently decelerating, possibly stagnating by the end of this century. Additionally, this downstream region of WIS is unique in that it moves primarily by stick-slip motion. However, both the rate of deceleration as well as the percent of motion accommodated by stick-slip motion is spatially variable. Such spatial variability is potentially linked to associated variability in basal conditions. Active source seismic measurement are capable of providing high-resolution insights into basal conditions, however, they are time-consuming to collect, limiting the spatial extent over which they can be acquired. In this presentation, we will use passive seismic measurements collected at over 50 seismic stations to map sediment thickness and ice-bed conditions across the region. This will be done using the receiver function method which images the depth and physical properties of sediments by modeling the arrival times and amplitudes of seismic waves that interact with subglacial sedimentary structures. We will first map conditions at the ice-bed interface by using relatively high-frequency waveforms (> 2 Hz) as they are sensitive to the physical properties of the shallow (< 20m ) subglacial sediments layers. Across the entirety of the study region, we find that this uppermost layer of sediments is characterized by relatively high porosity sediments.  Second, we will utilize lower frequencies (< 2 Hz) to map the depth basement, finding that the entire region is underlain 100’s of meters of sediments (Gustafson et al., Science, 2022). We will use our maps of sediment properties and thickness to investigate potential mechanisms for the observed variability in deceleration and stick-slip behavior of the WIS.  

How to cite: Winberry, J. P.: Basal Conditions and Sedimentary Structure of the Whillans Ice Stream., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9621, https://doi.org/10.5194/egusphere-egu23-9621, 2023.

Englacial temperature and water content play critical roles in glacier dynamics, both within ice sheets and mountain glaciers. As radio wave attenuation is sensitive to both of these properties, radio-echo sounding (RES) serves as a useful tool for mapping out their distributions within glaciers. Ground-based bistatic surveys, in which multi-offset measurements are taken, provide a large diversity in bed incidence angles and travel-path lengths. Provided the anomaly of interest is sufficiently sampled, these measurements can be exploited to perform attenuation tomography, thereby recovering the distribution of englacial radio wave attenuation from which englacial temperature can be estimated. Extensive RES surveys have been carried out over Antarctica using airborne radar; however, due to the monostatic geometry, methods for estimation of englacial radio wave attenuation and basal roughness have relied primarily on nadir returns. These estimates are often derived from 2D spatial correlation of basal return power and ice thickness or by employing layer-tracking methods. These techniques are limited in that the former uses echoes from a large spatial footprint, preventing the detection of small-scale anomalies, while the latter assumes a known, spatially invariant reflectivity for tracked layers. However, by considering returns from off-nadir in airborne surveys, techniques from multi-offset surface surveys can be modified and extended to perform airborne attenuation tomography. While not reaching the range of path diversity achievable in surface-based surveys due to limitations imposed by total internal reflection at the ice-air interface, airborne off-nadir returns contain valuable information about subglacial and englacial conditions that is often ignored. Thus, we propose a method for estimating englacial attenuation and basal roughness using the drop in power from the peak to tail of hyperbolic scattering events in unfocussed radargrams associated with the rough bed surface. The travel-paths of the bed returns across a given hyperbolic event vary in both length and bed incidence angle. Thus, the drop in return power across a hyperbolic event gives insight into both the integrated attenuation along a travel-path, as well as the scattering function at the bed. Specular reflections from internal layers with varying dips similarly provide diversity in travel-path lengths, allowing the derivation of a relationship between path length and return power without the complications brought about by diffuse scattering at rough surfaces. Using the diverse path lengths and angles through the ice, a tomographic inversion to map the spatial distribution englacial attenuation anomalies can be implemented. This technique is applied to synthetic data, as well as data collected using the British Antarctic Survey’s Polarimetric-radar Airborne Science Instrument (PASIN), specifically to lines collected over the Eastern Shear Margin of Thwaites Glacier. This location was chosen as constraining bed conditions and identifying expected englacial thermal anomalies are critical to understanding the history and modelling the future of Thwaites.

How to cite: May, D., Schroeder, D., and Young, T. J.: Radar Attenuation Tomography for Mapping Englacial Temperature Distributions Using Off-Nadir Airborne Radio-Echo Sounding, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9833, https://doi.org/10.5194/egusphere-egu23-9833, 2023.

EGU23-10127 | ECS | PICO | CR2.2

Monitoring lake ice with acoustic sensors 

Christoph Wetter, Cédric Schmelzbach, and Simon C. Stähler

Monitoring of the thickness and elastic parameters of floating ice on lakes and the sea is of interest in understanding the climate change impact on Alpine and Arctic environments, assessing ice safety for recreational and engineering purposes, studying ice shelves as well as exploring possibilities for the future exploration of the icy crusts of ocean worlds in our solar system. A multitude of geophysical methods exist today to monitor sea and lake ice thickness as well as elastic parameters. Mostly, seismic and radar measurements are used. Both methods have in common that they come with significant logistical effort and expensive equipment. In this study, we present a novel low cost approach using acoustic sensors for ice monitoring.

We explored the possibility of using microphones deployed on frozen lakes in the Swiss Alps to monitor the lake ice-thickness using acoustic signals originating from frequently occurring ice quakes. Data were obtained during a three-month-long field campaign at Lake St. Moritz in Switzerland in winter 2021/2022. Three microphone stations were placed on the lake in addition to five conventional seismometers. These seismometers were used to compare the acoustic signals with the seismic ice quake recordings. Additionally, also active-source experiments were conducted using hammer strokes as source, which were used to constrain elastic parameters of the ice.

The acoustic recordings of ice quakes allowed us to exploit the unique characteristics of so-called air-coupled waves to determine time-dependent ice thickness curves of Lake St. Moritz for winter 2021/2022 using acoustic data only. Furthermore, the acoustic data allowed us to gain new insights into the ice/air coupling of seismic waves in ice. 

How to cite: Wetter, C., Schmelzbach, C., and Stähler, S. C.: Monitoring lake ice with acoustic sensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10127, https://doi.org/10.5194/egusphere-egu23-10127, 2023.

EGU23-11787 | ECS | PICO | CR2.2

Validating manual measurements of snow water equivalent against a reference standard 

Alexander Radlherr and Michael Winkler

The snowpack is a key component in several fields like climatology, hydrology, or natural hazards research and mitigation, not least in mountainous regions. One of the most considerable snowpack features is the snow water equivalent (SWE), representing the mass of water stored in the snowpack and – in another perspective – the weight straining objects the snow is settling on (snow load). In comparison to snow depth, measuring SWE is rather complex and prone to errors. Consecutive observations of SWE do not have a long tradition in many regions.

Despite various recent developments in measuring SWE by means of remote sensing or other noninvasive methods, e.g. with scales, GNSS reflectometry, signal attenuation and time delay techniques, cosmic-ray neutron sensing, etc. the standard measuring technique still are snow tubes or gauging cylinders, often in combination with digging pits. Tubing-technique is commonly used as reference for the validation of named modern methods, although studies addressing its accuracy, precision and repeatability are very rare.

This contribution provides results from comparing different types of SWE measurement tubes with reference standard oberservation. Several field tests were executed at different sites in the Austrian Alps covering a great variety of snow conditions (e.g. dry and wet), snow depths and SWEs. For the reference observation 3x4 m rectangular fields were dug snow-free and the respective snow masses have been weighted stepwise using ca. 50-liter-buckets. Due to the large total mass of snow of typically around two tons per rectangular, relative uncertainties are extremely small and the results highly accurate. Additionally, different snow tubes were compared to each other. The cylinder or tube designs vary a lot: from meters long metal coring tubes of typical inner diameters of ca. 4-7 cm (without the need of pits) or PVC cylinders with typical lengths of 0.5 to 1.5 m and diameters ranging from about 5-20 cm to small aluminum tubes holding a maximum of 0.5 liter of snow.  

Many statistical measures like variance and bias vary quite a lot primarily depending on the equipment used, but also on the different snow conditions. A synopsis on the suitability of the various methods depending on the questioning or objective of the observation is provided.

How to cite: Radlherr, A. and Winkler, M.: Validating manual measurements of snow water equivalent against a reference standard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11787, https://doi.org/10.5194/egusphere-egu23-11787, 2023.

EGU23-13127 | PICO | CR2.2

Snow depth sensitivity to mean temperature and elevation in the European Alps 

Matthew Switanek, Wolfgang Schöner, and Gernot Resch

Many of the gauged snow depth measurements in the European Alps began in the late 19th and early 20th centuries. We leverage this reasonably long period of record to investigate the historical sensitivity of snow depths as a function of precipitation, mean temperature, and elevation. By controlling for changes in precipitation, we can isolate the influence that different temperature changes have on snow depths at varying elevation bands. This simple, yet effective, approach to defining our historical sensitivity can provide a robust observational framework to evaluate the impact that a range of different future warming scenarios would have on snow depths across the Alps. As a result, adaptation and mitigation measures can be put in place for a variety of end users, such as ski tourism and water resource management. Furthermore, this provides an observational reference by which to evaluate the performance of climate model simulations.

How to cite: Switanek, M., Schöner, W., and Resch, G.: Snow depth sensitivity to mean temperature and elevation in the European Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13127, https://doi.org/10.5194/egusphere-egu23-13127, 2023.

EGU23-14390 | ECS | PICO | CR2.2

Long-time permafrost evolution in alpine bedrock: quantifying climate change effects with geoelectrical monitoring 

Riccardo Scandroglio, Maike Offer, and Michael Krautblatter

While climate change driven increase in air temperature has been correctly modeled in recent decades, the extent of its consequences is still uncertain. In high alpine environments, especially in steep rock walls, permafrost degradation reduces slope stability with critical consequences for people and infrastructures: to properly assess the risk, the rate of these changes must be monitored. In the last decades, electrical resistivity tomography (ERT) has been used in more than hundred studies to detect permafrost, but there are only limited long-term monitoring cases that mostly do not provide quantitative information. 

Here we compare ERT measurements from two alpine landforms with different altitude and lithology: Steintälli ridge (3160m asl, CH) and Mt. Zugspitze rock wall (2750 m asl, DE/AT). Standard procedures and permanently installed electrodes allow the collection of a unique dataset of consistent measurements since 2006. Supporting information like resistivity-temperature calibration from former studies, rock surface and borehole temperatures as well as active seismic refraction measurements enable an advanced quantitative interpretation of the results. 

Permafrost at both sites is close to disappearing and in both cases resistivity changes are evident and in good agreement with air temperature increase, although with different magnitudes according to the landform. The yearly 3D measurements of the Steintälli ridge show a sudden and conspicuous degradation (~40% of the volume in 15 years), while the monthly 2D monitoring of the north face of Mt. Zugspitze shows slow constant decrease in summer (~15% of the surface in 15 years) and a strong variation in winter in correlation with snow-height. 

For the first time we provide a quantification of alpine permafrost degradation rates in different landforms over 15 years. These datasets help to better understand the different characteristics of the thermal responses to the climate change induced stress on alpine permafrost environments.

How to cite: Scandroglio, R., Offer, M., and Krautblatter, M.: Long-time permafrost evolution in alpine bedrock: quantifying climate change effects with geoelectrical monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14390, https://doi.org/10.5194/egusphere-egu23-14390, 2023.

EGU23-16308 | ECS | PICO | CR2.2

Thwaites Glacier Eastern Shear Margin: Insights from two broadband seismic arrays 

Emma C. Smith, Marianne Karplus, Jake Walter, Nori Nakata, Adam D. Booth, Lucia Gonzalez, Andrew Pretorius, Ronan Agnew, Stephen Veitch, Eliza J. Dawson, Daniel May, Paul Summers, Tun Jan Young, Poul Christoffersen, and Slawek Tulaczyk

The stability of Thwaites Glacier, the second largest marine ice stream in West Antarctica, is a major source of uncertainty in future predictions of global sea level rise. Critical to understanding the stability of Thwaites Glacier, is understanding the dynamics of the shear margins, which provide important lateral resistance that counters basal weakening associated with ice flow acceleration and forcing at the grounding line. The eastern shear margin is of interest, as it is poorly topographically constrained, meaning it could migrate rapidly, causing further ice flow acceleration and drawing a larger volume of ice into the fast-flowing ice stream. 

We present initial insights from a 2-year-long seismic record, from two broadband seismic arrays each with 7 stations, deployed across the eastern shear margin of Thwaites Glacier. We have applied a variety of processing methods to these data to detect and locate icequakes from different origins and analyse them in the context of shear-margin dynamics. Preliminary results suggest there is basal seismicity concentrated near the ice-bed interface on the slow-moving side of the margin, as opposed to within the ice-stream itself. Some of the identified seismic events appear to exhibit clear shear-wave splitting, suggesting a strong anisotropy in the ice, which would be consistent with polarization observed in recently published radar studies from the field site. Further analysis of the split shear-waves will allow us to better constrain the region's ice-fabric, infer past shear-margin location, and assess the future stability of this ice rheology.  

With such a large quantity of data, manual event identification is unpractical, and hence we are employing machine-learning approaches to identify and locate icequakes of interest in these data. Our results and forthcoming results from upcoming active-seismic field seasons have important implications for better understanding the stability of glacier and ice stream shear margins. 

How to cite: Smith, E. C., Karplus, M., Walter, J., Nakata, N., Booth, A. D., Gonzalez, L., Pretorius, A., Agnew, R., Veitch, S., Dawson, E. J., May, D., Summers, P., Young, T. J., Christoffersen, P., and Tulaczyk, S.: Thwaites Glacier Eastern Shear Margin: Insights from two broadband seismic arrays, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16308, https://doi.org/10.5194/egusphere-egu23-16308, 2023.

EGU23-16342 | PICO | CR2.2

Intercomparison of quantification methods for snow microstructure during the SnowAPP experiment 

Anna Kontu, Leena Leppänen, Roberta Pirazzini, Henna-Reetta Hannula, Juha Lemmetyinen, Petri Räisänen, Amy McFarlane, Pedro Espin Lopez, Kati Anttila, Aleksi Rimali, Hanne Suokanerva, Jianwei Yang, Teruo Aoki, Masashi Niwano, Ghislain Picard, Ines Ollivier, Laurent Arnaud, Margaret Matzl, Ioanna Merkouriad, and Martin Schneebeli

Snow microstructure defines the physical, mechanical and electromagnetic properties of snow. Accurate information of snow structure is needed by many applications, including avalanche forecasting (Hirashima et al., 2008) and numerical weather prediction (de Rosnay et al., 2014). The interaction of electromagnetic waves with snow properties can be applied in satellite remote sensing to retrieve, for example, global information of snow mass (Pulliainen et al., 2020). Objective in-situ observations of snow microstructure are needed to validate and develop both physical models and satellite snow retrieval algorithms. Conventional measurements of snow grain size are unsatisfactory in this regard, as the parameter is difficult to measure objectively, and even its definition is ambiguous (Mätzler, 2002). Hence, recent efforts have focused on developing forward models of microwave interactions and snow specific surface area (SSA), which can be objectively measured in field and laboratory conditions using various methods. A recently proposed approach links SSA to microwave scattering properties through another physically defined parameter (Picard et al., 2022).

In the SnowAPP project, three field campaigns were carried out at the Finnish Meteorological Institute Arctic Research Centre in Sodankylä, with the goal of collecting data on snow microstructural properties and establishing the relation of microstructure to both optical reflectance and microwave emission and scattering from snow.  During the spring 2019 campaign, six different methods were used for measuring SSA; and several methods were used for measuring snow density, another important factor affecting especially the extinction of microwave energy. Furthermore, multi-frequency radiometry and a wide-band, high resolution spectrometer were used to measure microwave emission and reflectance. In this study, we compare objectively the SSA and density values obtained by the different methods in a round-robin exercise. The relation of measured snow microstructures to measured spectral properties of snow are discussed.

SnowAPP was funded by the Academy of Finland, with contributions from WSL Institute for Snow and Avalanche Research SLF, Centre Tecnològic de Telecomunicacions de Catalunya, Beijing Normal University, National Institute for Polar Research, Meteorological Research Institute (Japan), and Université Grenoble Alpes.

 

de Rosnay, P., Balsamo, G., Albergel, C., Muñoz-Sabater, J., & Isaksen, L. (2014). Initialisation of land surface variables for numerical weather prediction. Surveys in Geophysics, 35(3), 607–621. https://doi.org/10.1007/s10712-012-9207-x

Hirashima, H., Nishimura, K., Yamaguchi, S., Sato, A., & Lehning, M. (2008). Avalanche forecasting in a heavy snowfall area using the snowpack model. Cold Regions Science and Technology, 51(2–3), 191–203. https://doi.org/10.1016/j.coldregions.2007.05.013

Mätzler, C., 2002. Relation between grain-size and correlation length of snow. J. Glaciol., (48)162: 461-466.

Picard, G., Löwe, H., Domine, F., Arnaud, L., Larue, F., Favier, V., & Meur, E. le. (2022). The Microwave Snow Grain Size: A New Concept to Predict Satellite Observations Over Snow-Covered Regions. https://doi.org/10.1029/2021AV000630

Pulliainen, J., Luojus, K., Derksen, C., Mudryk, L., Lemmetyinen, J., Salminen, M., Ikonen, J., Takala, M., Cohen, J., Smolander, T., & Norberg, J. (2020). Patterns and trends of Northern Hemisphere snow mass from 1980 to 2018. Nature, 581(7808), 294–298. https://doi.org/10.1038/s41586-020-2258-0

 

How to cite: Kontu, A., Leppänen, L., Pirazzini, R., Hannula, H.-R., Lemmetyinen, J., Räisänen, P., McFarlane, A., Espin Lopez, P., Anttila, K., Rimali, A., Suokanerva, H., Yang, J., Aoki, T., Niwano, M., Picard, G., Ollivier, I., Arnaud, L., Matzl, M., Merkouriad, I., and Schneebeli, M.: Intercomparison of quantification methods for snow microstructure during the SnowAPP experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16342, https://doi.org/10.5194/egusphere-egu23-16342, 2023.

EGU23-16522 | ECS | PICO | CR2.2

Resolving ice content heterogeneity within permafrost peatlands using high-frequency induced polarisation. 

Madhuri Gopaldas Sugand, Andreas Hördt, and Andrew Binley

Permafrost peatlands are highly vulnerable ecosystems in a warming climate; their thaw greatly impacts carbon storage capacity and endangers existing landscape morphology. Due to their remoteness and, in some cases, protected status, it is difficult to characterise and monitor the subsurface using invasive methods. Geophysical investigations are useful in such cases allowing relatively rapid and extensive subsurface mapping. We focus here on the emerging high-frequency induced polarisation (HFIP) method, which can be effective in permafrost hydrology research as the geoelectrical properties of frozen water display a characteristic frequency-dependence between ranges of 100 Hz and 100 kHz.

HFIP field measurements were conducted using the Chameleon-II equipment (Radic Research) on two peat permafrost sites located in Abisko, Northern Sweden: Storflaket mire and Heliport mire. The sites have been subject to routine permafrost monitoring since 1978 and are known to have an upper peat layer underlain by a silt-rich subsoil. We present the results of 2D surveys measuring frequencies ranging from 1 Hz to 57 kHz, which capture a high-frequency phase shift peak. Field data are inverted for each measured frequency separately with ResIPy, using an appropriate data error quantification model. The spectral data analysis captures heterogeneity within the subsurface, i.e., layered medium, permafrost mire boundary and ice-rich versus ice-poor regions. Identification of spectrally distinct regions allows the application of an appropriate relaxation model. For this study, we apply a two-component mixture model for ice-content estimation. Our results extend the existing knowledge at this site by quantifying ice content in a 2D plane, thus improving the foundation for further modelling studies.

How to cite: Sugand, M. G., Hördt, A., and Binley, A.: Resolving ice content heterogeneity within permafrost peatlands using high-frequency induced polarisation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16522, https://doi.org/10.5194/egusphere-egu23-16522, 2023.

Shallowing of slabs during their descend into the upper ~200 km of the mantle, i.e. flat subduction, can be associated with extensive geochemical, structural, and dynamic modification of the continental lithosphere. Anomalously buoyant oceanic lithosphere, overthrusting, and interactions with cratonic keels have been suggested to explain flat slabs, but the dynamics of flat slab subduction remain to be fully understood. Here, we explore self-consistent flat-slab subduction using the finite element code ASPECT with adaptive mesh refinement and a free surface boundary condition. We focus on the role of the structure of the overriding continental plate including the role of keels. Results show that flat slabs arise when the subduction interface is weak and the overriding continental lithosphere is positively buoyant, leading to trench rollback. Substantiating previous work, we also observe that a strong continental keel further enhances flat slab formation. Our results also indicate that as the slab flattens, regions of pronounced subsidence and extension develop within the foreland region, on top of more typical, larges-scale subsidence recorded within the continental interior. Regional uplift and subsidence of the overriding plate are not only linked to flat slab emplacement and removal, but also affected by slab dynamics of the shallow upper mantle. Our work can contribute to a better understanding of continental deformation including sediment transport on continent-wide scales.

How to cite: Grima, A. G. and Becker, T.: Modeling the interactions between slab dynamics and continental overriding plate deformation during flat subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1322, https://doi.org/10.5194/egusphere-egu23-1322, 2023.

EGU23-1559 | Orals | GD4.2

Horizontal and vertical slab tearing as different stages of a self-sustaining process developing in a non-collisional setting with oblique subduction 

Alexander Koptev, Nevena Andrić-Tomašević, Giridas Maiti, Taras Gerya, and Todd Ehlers

Slab break-off is usually referred to as an early collisional process driven primarily by the slowing of the subduction rate as negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere that is attempting to subduct. In this context, slab tearing (or slab break-off propagation) is traditionally attributed to continental corner dynamics, when the subducting plate first detaches in the area of continental collision and then the slab window opens toward the adjacent segment of the convergence boundary, where ocean-continent subduction continues. Another important process, previously thought to be independent of slab break-off and horizontal slab tearing, is a fragmentation of the subducting slab along vertical planes perpendicular to the convergence direction. Previous numerical studies have linked this vertical slab tearing to pre-existing weakness within the subducting plate and/or abruptly changing convergence rates along the trench.

In our study, we use a 3D thermo-mechanical numerical approach to study slab tearing in a non-collisional geodynamic context. The effects of subduction obliquity angle, age of oceanic slab, and partitioning of boundary velocities have been investigated. We show, for the first time, that horizontal and vertical slab tearing are different stages of the same process, which can develop in a self-sustained manner in a non-collisional environment of oblique ocean-continent subduction. Even with an initially absolutely homogeneous oceanic plate and laterally unchanging and temporally constant boundary velocities, the obliquity of the active margin appears to be a sufficient factor to trigger complex system evolution, which includes the transition from horizontal to vertical slab tearing along with additional processes such as retreat and rotation of the trench, decoupling of the overriding and downgoing plates by upwelling asthenosphere in the mantle wedge (also termed “delamination”), initiation of new subduction, and formation of a transform fault.

Our results show striking similarities with several features – such as trench curvature, subduction zone segmentation, magmatic production, lithospheric stress/deformation fields, and associated topographic changes – observed in many subduction zones (e.g., Marianas, New Hebrides, Mexico, Calabrian).

How to cite: Koptev, A., Andrić-Tomašević, N., Maiti, G., Gerya, T., and Ehlers, T.: Horizontal and vertical slab tearing as different stages of a self-sustaining process developing in a non-collisional setting with oblique subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1559, https://doi.org/10.5194/egusphere-egu23-1559, 2023.

Subduction of oceanic lithosphere has been proposed as the main driving mechanism for plate tectonics for decades and it represents a key process for the geochemical cycles on Earth. However, the physical processes and melting that occur as the subduction zone began foundering and evolved to reach a mature stage is still debated. The Izu-Bonin-Mariana (IBM) intra-oceanic subduction zone, that represents the boundary between the Pacific Plate and the Philippine Sea, is an ideal natural laboratory to study subduction zone processes from their inception to their stabilization. The rock record produced in IBM reveals a rapid compositional variability in slab-fluid tracers as well as in mantle depletion-enrichment over a short timescale (within 1 to 5 Ma of subduction inception). Despite this geochemical evolution, it is still highly debated whether IBM initiated as a forced or spontaneous subduction zone, i.e. induced by or in the absence of horizontal forcing, respectively.

Here, we conducted 2D high-resolution petrological-thermomechanical subduction models that include spontaneous deformation, erosion, sedimentation and slab dehydration processes, as well as melting, assuming a visco-plastic rheology using the i2VIS code. We aimed to model the initiation and the early stage of IBM with ultra-low horizontal forcing and inception triggered by transform collapse. Our new numerical model proposes a viable scenario for the transition from juvenile to mature subduction zone. This evolution includes initiation by gravitational collapse of the slab and the development of a near-trench spreading, the gradual build-up of a return flow of asthenospheric mantle and the progressive maturation of the volcanic arc. Our numerical results of mantle depletion within the mantle wedge and the overall subduction history of IBM are compared further with seismological and geochemical evidences.

How to cite: Ritter, S., Balázs, A., Ribeiro, J., and Gerya, T.: Magmatic Fingerprints of Subduction Initiation and Mature Subduction of the Izu-Bonin-Mariana Subduction Zone: Numerical Modelling and Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2071, https://doi.org/10.5194/egusphere-egu23-2071, 2023.

EGU23-2103 | Orals | GD4.2

Scaling of Free Subduction on a Sphere 

Neil Ribe, Alexander Chamolly, Gianluca Gerardi, Stephanie Chaillat, and Zhong-hai Li

Because Earth's tectonic plates are doubly curved shells, their mechanical behavior during subduction can differ significantly from that of flat plates. We use the boundary-element method (BEM) to study free (gravity-driven) subduction in axisymmetric and 3-D geometry, with a focus on determining the dimensionless parameters that control the dynamics. The axisymmetric model comprises a shell with thickness h and viscosity η1 subducting in an isoviscous planet with radius R0 and viscosity η2. The angular radius of the trench is θt. Scaling analysis based on thin-shell theory reveals two key dimensionless parameters: a `flexural stiffness' St = (η12)(h/lb)3 that is also relevant for flat plates, and a new `dynamical sphericity number' ΣD = (lb/R0)cotθt that is unique to spherical geometry. Here lb is the `bending length', or the sum of the lengths of the slab and of the seaward flexural bulge. The definition of ΣD implies that the dynamical effect of sphericity is greater for small plates than for large ones; we call this the `sphericity paradox'. By contrast, the purely geometric effect of sphericity is opposite, i.e. greater for large plates than for small ones. The dynamical and geometrical effects together imply that sphericity significantly influences subduction at all length scales. We confirm the scaling analysis using BEM numerical solutions, which show that the influence of sphericity on the slab sinking speed (up to a few tens of percent) and on the hoop stress (up to a factor of 2-3) is largest for small plates such as the Juan de Fuca, Cocos and Philippine Sea plates. We next study a 3-D model comprising a plate bounded by a ridge and a semicircular trench subducting in a three-layer earth consisting of an upper mantle, a lower mantle and an inviscid core. We examine the linear stability of the shell to longitudinal perturbations corresponding to buckling, and determine a scaling law for the most unstable wavelength that we compare with the observed shapes of northern/western Pacific trenches. 

How to cite: Ribe, N., Chamolly, A., Gerardi, G., Chaillat, S., and Li, Z.: Scaling of Free Subduction on a Sphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2103, https://doi.org/10.5194/egusphere-egu23-2103, 2023.

EGU23-2573 | ECS | Posters on site | GD4.2

Numerical modelling of mantle exhumation in inverted rift systems 

Frank Zwaan, Sascha Brune, Anne Glerum, John Naliboff, and Dylan Vasey

The tectonic exhumation of mantle material is a well-known phenomenon and may occur during both rifting and subsequent (large-scale) basin inversion. However, the processes leading to the exhumation of dense and therefore negatively buoyant (sub-)lithospheric mantle material remain poorly understood. We therefore conducted a series of thermomechanical simulations using the geodynamics code ASPECT (coupled with FastScape for the inclusion of surface processes) testing the impact of various parameters on mantle exhumation in inverted rift systems.

We find that rift duration strongly impacts mantle exhumation, both during the rift phase, as well as during subsequent inversion. When only limited rifting is applied, the dense mantle material cannot reach the surface as the overlying crustal layers remain connected. Basin inversion then tends to create a symmetric pop-up structure by reactivating rift boundary faults, and the dense mantle material is forced down by the thickening of low-density crustal layers on top of it. Only after certain amount of extension, the crust is sufficiently thinned so that mantle material can be exhumed. This mantle material may then remain near the surface or be further exhumed during basin inversion. Such further mantle exhumation is favoured if asymmetric reactivation of the rift basin occurs, so that mantle material is thrust on top of the downgoing plate.

The establishment of such asymmetric orogenic systems allowing for efficient mantle exhumation is further promoted by having only short-lived tectonic quiescence between rifting and inversion, so that no thermal equilibration of the exhumed mantle domain can occur. As a result, the rift basin remains a weakness that is readily exploited during inversion. Longer periods of tectonic quiescence restore the strength of the lithosphere, so that delayed inversion generates more symmetric structures, with limited opportunities for mantle exhumation.

Within this tectonic context, erosion efficiency is another key factor. First, more efficient erosion during inversion removes crustal material so that the mantle can be exhumed (even in symmetric orogenic systems). Second, efficient erosion also leads to the development of asymmetric orogenic systems, thus doubly contributing to mantle exhumation. Somewhat similarly, high plate velocities during inversion introduce larger amounts of crustal material into the system, which erosion cannot remove in a timely manner, whereas slow plate velocities allow erosion more time to remove material. Hence, mantle exhumation is positively correlated to erosion efficiency, and is negatively correlated to plate velocities during inversion

Finally, serpentinization of mantle material can occur close to the Earth’s surface (i.e. in the uppermost kilometres) and strongly reduces the material’s density and brittle strength. Although our models so far only show a limited effect of serpentinization, the overall weakness of serpentinized mantle material at the rift basin floor seems to reduce localization of inversion-related deformation, thus generating more symmetric inversion systems with limited mantle exhumation.

How to cite: Zwaan, F., Brune, S., Glerum, A., Naliboff, J., and Vasey, D.: Numerical modelling of mantle exhumation in inverted rift systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2573, https://doi.org/10.5194/egusphere-egu23-2573, 2023.

The Mariana convergent margin provides the environment where a natural process brings materials from great depths directly to the surface. The Mariana forearc contains the only current active serpentine mud volcanism in a convergent margin setting. Here, serpentinite mud volcanoes are numerous, large (averaging 30 km diameter and 2 km high) and active. They are composed principally of unconsolidated flows of serpentine muds containing clasts of serpentinized mantle peridotite and several other lithologies, such as blueschist materials derived from the subducting slab.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench subduction zone along a south-to-north transect: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). These cores consist of serpentinite mud containing lithic clasts and minerals derived from the underlying forearc crust and mantle, as well as from the subducting Pacific Plate. Fluids upwell within these mud volcanoes at a rate that is in excess of the mud matrix. Such fluids originate from the downgoing plate but are highly altered, are reducing and have pH values in the range of 9 to 12.5.

For the purposes of this study ultramafic and mafic rock clasts from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed in order to reconstruct processes of fore-arc mantle alteration, fluid activity and fluid-rock interaction. Additionally, several samples from Asùt Tesoru Seamount consisting of cryptocrystalline serpentine mud with commonly occurring lithic clasts (>2 mm) in different amounts and size were investigated.

In general the mineral paragenesis of the serpentinized peridotite clasts, including mainly lizardite and chrysotile serpentine group minerals, along with brucite as well as andradite, and the apparent absence of high-temperature phases such as antigorite and anthophyllite, tentatively constrains an upper temperature limit of 200 – 300 °C. However, the presence of fine-grained matrix antigorite associated with lizardite suggests metamorphic temperature of at least 340 °C.

Hydrogarnet is a common secondary, hydrothermal mineral phase in the studied samples and it defines a serpentinization temperature of c. 230 °C. Garnet crystals with subhedral habitus and almost pure andraditic composition are found within a carbonate matrix. However, also Cr-rich garnets are common within the serpentinite clasts. They are subhedral to anhedral and contain chromite inclusions with similar composition to the unaltered chromites in the same sample. These textural observations suggest a secondary origin for the Cr-rich garnets as well, most probably related to hydrothermal fluids that infiltrated the ultramafic protolith. The formation of Cr-rich garnet after Cr-rich spinel is usually associated with hydrothermal or metasomatic reactions, although the precise mechanism of formation remains unclear. Generaly Cr-rich hydrogarnets in serpentinites crystallize below 400 °C, which is in line with the obtained metamorphic conditions and indicate an overall evolution of a hydrothermal fluid from c. 350 °C (antigorite in serpentinites) to c. 100 °C and below.

How to cite: Kurz, W., Miladinova, I., Krenn, K., and Hilmbauer-Hofmacher, T.: Fore-arc mantle alteration, fluid activity and fluid-rock interaction revealed from Serpentinite Mud Seamounts at the Mariana Convergent Margin System (IODP Expedition 366), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2657, https://doi.org/10.5194/egusphere-egu23-2657, 2023.

EGU23-2981 | Orals | GD4.2

Magmatic response to the subduction initiation of Early Cretaceous Nidar Ophiolite Complex, eastern Ladakh, NW Himalaya 

Takeshi Imayama, Akinori Sato, Dripta Dutta, Yasuaki Kaneda, Shota Watanabe, Takeshi Hasegawa, Masayo Minami, Yuki Wakasugi, Shigeyuki Wakaki, and Yi Keewook

Early Cretaceous Nidar Ophiolite Complex (NOC, eastern Ladakh) is associated with the north-dipping supra-subduction of the Neo-Tethyan Ocean along the Indus suture zone. The supra-subduction zone ophiolite formed in the forearc setting records the magmatic response to the subduction initiation, but the magmatic evolution in the NOC is poorly constrained. The low-Ti gabbros have low SiO2 in whole-rock composition and high Mg# in clinopyroxene. They also record highly depleted magma In contrast, dolerites and basalts have relatively higher SiO2 in whole-rock composition and lower Mg# in clinopyroxene, with flat REE patterns accompanied by fractional crystallization. Significant variation in Yb content relative to Tb/Yb ratio also supports fractional crystallization from gabbros to basalts. In Th/Yb-Nb/Yb diagram, all samples plot in the region from the MORB type to the island arc tholeiite. The Nd-Sr isotopes and high Ba/La ratio suggest that the NOC was originally derived from a single depleted mantle source similar to the MORB and was subsequently affected by hydrothermal alteration, resulting in greenschist- to lower amphibolite-facies overprint to form albite, actinolite, epidote and chlorite. Detrital zircon U-Pb ages from volcanic sediments associated with the NOC concentrated at ca. 136 Ma, representing the timing of the main magmatic phase in the NOC. Our data, combined with the geochronological and geochemical data in previous studies, suggest that the low-Ti, highly depleted magma in the NOC was firstly generated at extensional spreading in the upper plate during subduction initiation, and then changed to island arc tholeiite composition with the development of the subduction zone during Early Cretaceous.

How to cite: Imayama, T., Sato, A., Dutta, D., Kaneda, Y., Watanabe, S., Hasegawa, T., Minami, M., Wakasugi, Y., Wakaki, S., and Keewook, Y.: Magmatic response to the subduction initiation of Early Cretaceous Nidar Ophiolite Complex, eastern Ladakh, NW Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2981, https://doi.org/10.5194/egusphere-egu23-2981, 2023.

EGU23-3130 | ECS | Orals | GD4.2

Micro to Macroscale: the three-dimensional network characteristics of serpentinite dehydration veins 

Austin Arias, Andreas Beinlich, Lisa Eberhard, Marco Scambelluri, Timm John, Alissa Kotowski, and Oliver Plümper

On Earth, subduction zones facilitate the cycling of volatiles between the Earth’s surface and interior. Volatile cycling has significant effects on the long-term state of the Earth’s climate and tectono-magmatic events, including volcanism and earthquakes. A key stage in the volatile cycle is the devolatilization of the subducting oceanic lithosphere, in which volatiles can escape the previously hydrated rocks. However, it is not well known how efficiently volatiles are transported at this stage. To better understand how volatiles escape at these conditions, we have analyzed the dehydration-related vein networks of the Erro-Tobbio meta-serpentinites (ET-MS), Italy. The ET-MS display well preserved networks of metamorphic olivine veins. These veins are the result of the dehydration reaction of antigorite and brucite to produce H2O and olivine. However, due to the low permeability of serpentinite at depth, the dehydration reaction requires the formation of self-organizing vein networks to allow the produced fluid to escape [1]. Thus, the metamorphic olivine veins in ET-MS may be used as a proxy for fluid flow pathways. We took a multiscale approach to analyzing the network architectures. For microscale (~16 µm voxel size) and mesoscale (~200 µm voxel size) resolutions, X-ray tomography methods are sufficient to visualize the three-dimensional structure of the networks. However, for large scale observations these methods are inapplicable. To solve this, we apply a novel workflow to analyze outcrop scale (~10 m) network systems in three dimensions using only two-dimensional data. By training a generative adversarial network (GAN) with two-dimensional data conditioned by spatial orientation, we can generate statistically representative three-dimensional networks that mimic those of the ET-MS. These representations also display similar characteristics in their respective pore-network-models. With this method, it is possible to produce reasonable three-dimensional approximations of the ET-MS vein networks using only photogrammetry data of the outcrops. In turn, this allows us to extract metrics, such as permeability, that describe the volatile transport efficiency of the ET-MS, and further, how these characteristics change at a broad range of scales.  

[1] Plümper et al. (2017) Nature Geoscience 10(2), 150-156. 

How to cite: Arias, A., Beinlich, A., Eberhard, L., Scambelluri, M., John, T., Kotowski, A., and Plümper, O.: Micro to Macroscale: the three-dimensional network characteristics of serpentinite dehydration veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3130, https://doi.org/10.5194/egusphere-egu23-3130, 2023.

EGU23-4422 | Posters on site | GD4.2

From Subduction Initiation to Polarity Reversal: Zircon Age and Geochemical Constraints from Solomon Islands 

Rashmi Battan, Truong Tai Nguyen, Sun-Lin Chung, Tsuyoshi Komiya, Shigenori Maruyama, Andrew Tien-Shun Lin, Hao-Yang Lee, and Yoshiyuki Izuka

Intra-oceanic arc’s collision with an oceanic plateau plays a crucial role in the development of complex tectonic setting and induce subduction polarity reversal. Despite several studies and investigations, the origin and timing of subduction initiation in Solomon Island Arc (SIA) is still ambiguous. This study presents first robust zircon U-Pb ages and in-situ Hf isotope data from Choiseul, Santa Isabel (SI) and New Georgia Group (NGG), three major islands of SIA. Magmatic zircons and Hf isotope data from one gabbro sample, geochemically identical to N-MORB with Nb, Ta depletion in spidergram yielded 46 ± 1 Ma, which we decipher as the timing of Stage I magmatism by subduction of Pacific plate and subduction initiation in Choiseul. Six Choiseul andesites gave a mean age 206Pb/238U of 0.7 Ma, with εHf(t) values from +9 to +15 which represents the youngest crystallization age of Stage II magmatism with typical island arc-like signatures and a depleted mantle source. Detrital zircons from two sand sample yielded a population of mean age ranging from 0.3-0.7 Ma, 10 Ma and 48-46 Ma with εHf(t) values +9 to 15, +11 to +12 and +11 to +14 respectively and third sample has yielded a mean age 207Pb/206Pb 2.6 Ga and 500-1600 Ma with εHf(t) values -8 to +9, probably associated with Australian-type source indicating presence of a continental fragment beneath SIA. 

Similar ages of ca. 2.6 Ma have been obtained from inherited zircons from three gabbroic dyke sample from Santa Isabel with εHf(t) values +1 to +9 whereas one gabbroic dyke sample yields 110 ± 1 Ma, with εHf(t) values +14 to + 16 which we interpret as the basement age of SI.

U-Pb dating of zircons from mafic to felsic rocks along NGG, covered mostly by Quaternary eruptive lavas. The youngest age population indicate Late Pliocene-Pleistocene 206Pb/238U ages, 2.5-1.5 Ma, interpreted as  zircon crystallization ages of Stage II arc magmatism resulting from subduction of the Solomon Sea plate, as those of Choiseul Andesite. The first U-Pb age from ca. 36.8±0.5 Ma granite on Ghizo Island in New Georgia Group, revealing Late Eocene-aged magmatic zircon. This age represents the magmatic emplacement as the basement of plutonic rock from NGG that has not been reported before.

We conclude that, (i) The Solomon Islands has a Cretaceous basement preserved in SI. (ii) The timing of subduction initiation and Stage I N-MORB type tholeiitic magmatism in SIA is 46 Ma followed by episodic eruptions from the early Eocene to late Eocene. (iii) Oligocene (30-20 Ma) magmatic hiatus, probably the time of subduction polarity reversal from subduction of Pacific plate to subduction of Solomon Sea plate. (iv) Stage II island arc magmatism initiated at 20-18 Ma in NGG to youngest emplacement age of Pliocene to Pleistocene in Choiseul as well as in NGG. (v)Abundant Archean zircons are present in samples from all three islands, indicate presence of micro-continent beneath Islands of Solomon. We are still working on the whole rock isotopic analysis to better constrain the tectonic and magmatic evolution of SIA.

How to cite: Battan, R., Nguyen, T. T., Chung, S.-L., Komiya, T., Maruyama, S., Lin, A. T.-S., Lee, H.-Y., and Izuka, Y.: From Subduction Initiation to Polarity Reversal: Zircon Age and Geochemical Constraints from Solomon Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4422, https://doi.org/10.5194/egusphere-egu23-4422, 2023.

EGU23-4644 | ECS | Orals | GD4.2

Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture? 

Marie Genge, César Witt, Massimiliano Zattin, Delphine Bosch, Olivier Bruguier, and Stefano Mazzoli

Shifts in isotopic and trace element composition in magmatic zircon are commonly related to internal forcing independent of plate parameters (e.g., crustal thickness, delamination), or external factors that are governed by parameters of the down-going plate, particularly the slab dip. U-Pb geochronology, trace elements and Hf-O isotope analyses on detrital zircon from central Patagonia (45 °S – 48 °S) were used in this study as fingerprint for monitoring slab dip variations and related processes (e.g., arc migration, slab rollback) as well as upper-plate stress regime evolution. According to literature, main geodynamic events include: (i) two shallow slab episodes during late Triassic and late Early Cretaceous – early Paleogene times, the latter characterized by significant contraction; (ii) two phases of slab rollback during Jurassic – Early Cretaceous and late Paleogene, associated to a steep slab configuration, extensional processes and crustal thinning; (iii) a slab window episode during the Paleogene; and (iv) a Miocene contractional phase following an increase of plate convergence rates. Although slab dynamics seems structurally related with upper-plate architecture, it appears to exert little to null control on the magmatic arc reservoirs. Indeed, our results, integrated with published data from a larger area (40 °S – 52 °S), show long-lasting trends ( > 70 Ma) in the isotopic and trace elements record, that are mostly independent of these events. We thus consider that other processes, eventually coeval, controlled the enrichment of magmas and may overtake the influence of slab dip and upper-plate architecture on the isotopic and trace elements signature. These other processes include subduction erosion, ridge subduction, subduction of a younger slab, potential slab tearing, and/or change in convergence rates that affects mantle flow. 

How to cite: Genge, M., Witt, C., Zattin, M., Bosch, D., Bruguier, O., and Mazzoli, S.: Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4644, https://doi.org/10.5194/egusphere-egu23-4644, 2023.

EGU23-4710 | Orals | GD4.2

Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain 

Rhodri Davies, Fangqin Chen, Saskia Goes, and Lior Suchoy

It has long been recognised that the shape of subduction zones is influenced by Earth’s sphericity, but the effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics: most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. There are therefore many outstanding questions relating to the key controls on the dynamics of subduction. For example, do predictions from Cartesian subduction models hold true in a spherical geometry? When combined, how do subducting plate age and width influence the dynamics of subducting slabs, and associated trench shape? How do relic slabs in the mantle feedback on the dynamics of subduction? These questions are of great importance to understanding the evolution of Earth's subduction systems but remain under explored.

In this presentation, we will target these questions through a systematic geodynamic modelling effort, by examining simulations of multi-material free-subduction of a visco-plastic slab in a 3-D spherical shell domain. We will first highlight the limitation(s) of Cartesian models, due to two irreconcilable differences with the spherical domain: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, the impact of which cannot be captured in Cartesian domains, especially for subduction zones exceeding 2400 km in width. We will then demonstrate how slab age (approximated by co-varying thickness and density) and slab width affect the evolution of subducting slabs, using spherical subduction simulations, showing that: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; (ii) wider slabs can develop along-strike variations in trench curvature due to toroidal flow at slab edges, trending toward a `W'-shaped trench with increasing slab width, and (iii) the width effect is strongly modulated by slab age, as age controls the slab's tendency to retreat. Finally, we will show the diverse range of ways in which remnant slabs in the mantle impact on subduction dynamics and the evolution of subduction systems.

How to cite: Davies, R., Chen, F., Goes, S., and Suchoy, L.: Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4710, https://doi.org/10.5194/egusphere-egu23-4710, 2023.

EGU23-5078 | Posters virtual | GD4.2

Subduction of bathymetric irregularities along active margins: insights from numerical modeling 

Vlad Constantin Manea, Marina Manea, and Lucian Petrescu

Oceanic plates are far from homogeneous, and a large number of bathymetric discontinuities such as seamounts of different sizes are transported along by plate motion towards the mid ocean trenches and beyond. Seamounts currently colliding with plate margins show a major role in shaping the forearc morphology, and several studies even suggest that they might be related with seismicity. However, it is not clear what happens after seamounts are subducted, they can be accreted to the forearc, carried down into the subduction zone and recycled into the deep mantle, or a mix of the two scenarios. Using high-resolution two-dimensional thermomechanical numerical simulations, we investigate subduction processes of oceanic plates with a heterogeneous structure marked by a series of basaltic seamounts arranged in a chain like structure. We solve the 2D momentum, continuity and energy equations with the finite differences coupled with PIC (particle-in-cell) method. Our models also incorporate a depth-dependent, realistic non-Newtonian visco-elasto-plastic rheology, and plasticity is implemented using a yield criterion which limits the creep viscosity. Preliminary results show that initially seamounts preserve they structure when impacting with the trench. Their integrity is partially conserved until they subduct to a depth of about 25-30 km when they finally start to succumb to the great deformations and stresses along the slab interface. We observed that the lower part of the seamount continuously deforms and amalgamates along the slab interface. The upper part is detached and incorporated into the forearc structure. The subsequent seamounts that trail the first seamount, follow the same deformation pattern, and the top of them are maintained in the highly deformed forearc region. Our preliminary modeling results confirm that seamount subduction represent a key tectonic process that influences on a long-term time scale the structure and evolution of subduction zones.

How to cite: Manea, V. C., Manea, M., and Petrescu, L.: Subduction of bathymetric irregularities along active margins: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5078, https://doi.org/10.5194/egusphere-egu23-5078, 2023.

The subduction zone interface is a shear zone of varying thickness that defines the boundary between the subducting slab and overriding plate. The rheology of this shear zone controls several important aspects of subduction dynamics, but accurately estimating its rheology can be complex due to the wide range of subduction materials and their varying rheological properties. Of particular importance is the relative strengths of metasedimentary and metabasic rocks at various temperature and pressure conditions. To better understand these rheological contrasts in naturally deformed rocks, we are conducting field and microstructural work in the Eclogite Zone in the Tauern Window, Austria. The eclogite zone preserves intercalated metamafic (metabasalt and metagabbro) and metasedimentary (quartzite, garnet mica schist, marble and calc-schist) rocks that were subducted and exhumed to the surface as a single structural unit. Using high resolution drone imaging, 2D structural mapping, and 3D structural modeling, we have documented map-scale relationships between metamafic and metasedimentary rocks in the Eissee region near Matrei. Our mapping demonstrates that the mafic eclogites consistently define slabs, lenses and boudins of up to 2 km in along-strike length and 0.2 km in thickness, embedded within the metasedimentary units, all of which are relatively uniformly deformed to very high strain. This suggests that eclogitized metamafic rocks persisted as rheological heterogeneities within the subduction channel through both the subduction and exhumation paths. Additionally, we are using microstructural observations to document the deformation mechanisms of individual rock units and to understand the weakening mechanisms that allowed some of the eclogites to break down from boudins to strongly foliated layers intercalated with the metasediments. At the interface between select metasedimentary and eclogite units there is a marked rheological change in eclogite rheology, likely due to fluids leached from the metasedimentary rocks, resulting in strain localization and increased foliation development within eclogite layers from meter to micron length scales. Integration of our mapping, outcrop, and microstructural observations will provide insights into the length scales of rheological heterogeneity on the deep interface and large-scale geodynamics of subduction through influencing the bulk viscosity of the interface.

How to cite: Tokle, L., Behr, W., Braden, Z., and Cisneros, M.: Persistence of initial lithological heterogeneity to deep subduction conditions: Implications for the rheology of the subduction zone interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5162, https://doi.org/10.5194/egusphere-egu23-5162, 2023.

EGU23-5221 | ECS | Orals | GD4.2

The role of sediments on subduction dynamics and geometry: insights from numerical modeling 

Silvia Brizzi, Thorsten Becker, Claudio Faccenna, Whitney Behr, Iris van Zelst, Luca Dal Zilio, and Ylona van Dinther

It is widely recognized that sediments play a key role for subduction. For example, sediments subducted along the shallow seismogenic plate interface are thought to influence seismic coupling and the occurrence of megathrust earthquakes, as well as the morphologies of accretionary prisms. Due to their weakening and/or lubricating effect, subducted sediments are also thought to promote faster plate speeds. However, global observations are not clear-cut on the relationship between the amount of sediments and plate motion. Here, we use 2D thermomecanical models to investigate how incoming plate sediments can influence subduction dynamics and geometry. We find that thick sediments can promote slower subduction due to an increase of the shear stress along the plate interface as the accretionary wedge gets wider, and a decrease of slab pull as more buoyant material is subducted. Our results also show that the larger interface shear stress and slab buoyancy due to thick sediments increase the slab bending radius. This study offers a new perspective on the role of sediments on large-scale subduction dynamics, suggesting that sediment buoyancy and wedge geometry might also affect plate motion and geometry.

How to cite: Brizzi, S., Becker, T., Faccenna, C., Behr, W., van Zelst, I., Dal Zilio, L., and van Dinther, Y.: The role of sediments on subduction dynamics and geometry: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5221, https://doi.org/10.5194/egusphere-egu23-5221, 2023.

EGU23-5229 | ECS | Posters on site | GD4.2

Modeling fluid-driven seismic cycles in subduction zones 

Betti Hegyi, Luca Dal Zilio, Whitney Behr, and Taras Gerya

Various geological and geophysical observations from different subduction zones attest to the importance of pore pressure fluctuations and fluid flow in triggering regular earthquakes, slow slip events and tectonic tremors. We use the Hydro-Mechanical Earthquake Cycle (H-MEC) code to model fluid-driven earthquake cycles in a subduction megathrust environment. The code uses  a finite differences-marker in cell method, and couples solid rock deformation with fluid flow. The code solves the mass and momentum conservation equations for both solid and fluid phases, with the addition of gravity and temperature-dependent viscosity. The brittle/plastic deformation is resolved through a rate-dependent strength formulation and the development of slip instabilities is governed by compaction-induced pore fluid pressurization. With such code we can demonstrate how the fluid pressurization can lead to localisation of deformation with slip rates up to m/s in a fully compressible poro-visco-elasto-plastic media. The models can reproduce all slip modes observed in nature from regular earthquakes to transient slow slip phenomena to aseismic creep. Here we investigate various controls on dominant slip mode and their expected distributions and interactions along a subduction interface model setup. Our initial results show that the dominant slip mode depends on porosity, permeability, plastic dilatation and viscosity of the matrix. An increase in the porosity will lead to aseismic deformation in the form of slow slip events and creep. We also investigate the effects of inclusions (clasts) along the subduction channel, acting as stress heterogeneities, with physical properties different from the subduction channel. We attempt to understand the role of inclusions with different viscosities and permeabilities embedded in the matrix. With this numerical framework, we can better understand fluid-driven seismicity, and the effects of fluids on long-term geodynamic processes. Our study also contributes to better understand the role of fluid pressure cycling in seismic and aseismic deformation in subduction zone environments, as well as provides new insights in the role of stress heterogeneities within the frictional-viscous shear zone. 

How to cite: Hegyi, B., Dal Zilio, L., Behr, W., and Gerya, T.: Modeling fluid-driven seismic cycles in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5229, https://doi.org/10.5194/egusphere-egu23-5229, 2023.

EGU23-5747 | Orals | GD4.2

Subduction invasion polarity switch (SIPS):  A new mechanism of subduction initiation, with an application to the Scotia Sea region 

Wouter P. Schellart, Vincent Strak, Anouk Beniest, Joao C. Duarte, and Filipe M. Rosas

The initiation of subduction remains an enigmatic process and a variety of conceptual models has been proposed to explain such initiation. Conceptual models have been tested with geodynamic models and have been applied to various subduction settings around the globe. None of these tested models, however, are applicable to the Scotia subduction zone in the Southern Atlantic (also referred to as South Sandwich subduction zone), where subduction started in the Late Cretaceous/Early Cenozoic in a pristine ocean basin setting devoid of other subduction/collision zones. How this subduction zone initiated remains intensely debated, as exemplified by the variability of published plate tectonic reconstructions. We present new tectonic reconstructions of the Scotia region involving a relatively simple middle-Late Cretaceous plate boundary configuration that involves a new mechanism of subduction initiation, Subduction Invasion Polarity Switch (SIPS). SIPS involves a long-lived, wide and deep subduction zone (South American-Antarctic subduction zone) that imposes major horizontal trench-normal compressive deviatoric stresses on the overriding plate. The overriding plate consists of a narrow continental lithospheric (land) bridge at the trench (Cretaceous-Early Cenozoic Antarctica-South America land bridge) with oceanic lithosphere behind it (Weddell Sea-Atlantic Ocean). The stresses cause shortening and thrusting at the continent-ocean boundary in the backarc region of the overriding plate, forcing oceanic lithosphere under continental lithosphere, starting the subduction initiation process, and eventually leading to a new, self-sustaining, subduction zone (Scotia subduction zone) with an opposite polarity (dipping westward) compared to the long-lived subduction zone (dipping eastward). The model thus involves invasion of a new subduction zone into a pristine ocean basin (Atlantic Ocean), with the primary driver being a long-lived subduction zone in another ocean basin (Pacific Ocean). To test the physical viability of the SIPS model, we have conducted numerical geodynamic simulations of buoyancy-driven subduction. Numerical results demonstrate that the SIPS model is viable, with compressive stresses in the overriding plate resulting from strong trenchward basal drag induced by subduction-driven whole-mantle poloidal return flow and compression at the subduction zone plate boundary due to the high resistance of the subduction zone hinge of the long-lived subduction zone to retreat westward. Subduction initiation starts in the overriding plate after ~100 Myr of long-lived subduction, eventually resulting in the formation of a new, opposite-dipping, subduction zone. Notably, this new subduction zone develops at the continent-ocean boundary for models without and with a pre-imposed weak zone. Apart from the Scotia Sea region, the SIPS model might also be applicable to subduction initiation that has occurred elsewhere in the geological past (e.g. the New Caledonia, Lesser Antilles-Puerto Rico, Rocas Verdes and Arperos subduction zones), and that is presently in a very early stage of development in the Japan Sea.

How to cite: Schellart, W. P., Strak, V., Beniest, A., Duarte, J. C., and Rosas, F. M.: Subduction invasion polarity switch (SIPS):  A new mechanism of subduction initiation, with an application to the Scotia Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5747, https://doi.org/10.5194/egusphere-egu23-5747, 2023.

EGU23-6155 | Orals | GD4.2

Dynamics of multiple microcontinent accretion during oceanic subduction 

Zoltán Erdős, Susanne Buiter, and Joya Tetreault

Microcontinent accretion during oceanic subduction is one of the main contributors to continental crustal growth. Many of the continental mountain belts we find today were built from accretionary orogenesis, for example, the Cordillera of the west coast of the Americas, the European Alps, and the Australian Lachlan orogen. Continental growth can also be observed in modern accretionary orogens such as the Pacific accretionary belt, with the collision of the Philippine microplate, and the Taiwan-Luzon-Minduro Belt. In many of these systems, multiple bathymetric highs, such as microcontinental terranes, island arcs, or oceanic plateaus, are accreted before full oceanic closure, thus significantly altering the subduction zone before continental collision occurs.
The process of accretion implies a complex balance of multiple geodynamic forces that can result in either microcontinent subduction, microcontinent accretion, or subduction stalling (which could lead to the initiation of an altogether new subduction zone). The most important driving forces in this system are the slab-pull force arising from the negative buoyancy of the down-going slab and the far-field force which is the result of large-scale plate-motions external to the subduction zone. These forces are counteracted (among others) by friction along the subduction interface and the buoyancy of the downgoing microcontinent. The resulting net forces control the overall stress-field of the overriding plate as well as the state of stress and potential deformation of any further microcontinents embedded within the oceanic lithosphere that are not yet in the subduction zone. 
When multiple microcontinents are embedded in the subducting oceanic plate, the friction along the subduction interface and its temporal variations can take a crucial role. The accreting microcontinents have a first order effect on the length and the rheology of the subduction channel, thereby controlling the interface friction. The fate of the microcontinents (e.g. full or partial accretion, or subduction) also affects the overall buoyancy of the slab, altering the balance of forces through the slab-pull.
Using 2D thermo-mechanical experiments with the finite-element software SULEC-2D, we explore the roles of the structure and rheology of multiple accreting microcontinents (controlling their integrated strength) as well as the velocity of the subducting plate (controlling the far-field and the slab-pull force) to better understand how accretion of crustal units can modify the subduction zone and affect later continental collision. Our setup is comprised of a subducting oceanic basin surrounded by two continents. In this setup the oceanic plate is either “empty” or one or two microcontinents are embedded within it.
Our first results show that microcontinent accretion is promoted by the presence of a weak rheological detachment layer within the microcontinent. In turn, strong coupling of the microcontinental crust to its host-lithosphere promotes terrane subduction and may ultimately lead to the stalling of subduction. Moreover, the behavior of the microcontinents during accretion and subsequent continental collision has a first order effect on the structural style of the resulting orogen as the rheology of the microcontinents controls the degree of localization of deformation in the subduction channel.

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: Dynamics of multiple microcontinent accretion during oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6155, https://doi.org/10.5194/egusphere-egu23-6155, 2023.

EGU23-6363 | ECS | Posters on site | GD4.2

200 Ma of magmatism along the northern border of the West African Craton during Pan-African convergence 

Alex Bisch, Antoine Triantafyllou, Gweltaz Mahéo, Jamal El Kabouri, Olivier Bruguier, Delphine Bosch, Julien Berger, Jérôme Ganne, and Frédéric Christophoul

Convergence zones are marked by a variety of settings that may follow each other in modern-day tectonics, including compressive phases such as subduction, obduction, collision but also extensive ones such as back-arc opening or stress-relaxation during orogenesis. Hence, the protracted evolution leading to a super-continent block amalgamation may be difficult to decipher and so may be the forcings on external enveloppes such as volcanism or erosion caused by the different phases.

This question arises critically at the time of the Pan-African Orogenesis (1-0.5 Ga) assembling Gondwana, a time of supposedly dramatic and diachronical changes for external envelopes: glaciations of debated scales, deposition of various Banded Iron Formations, first (Ediacarian) fauna, replacement by Cambrian faunas. Our goal is to explore in detail the geodynamical succession leading to the amalgamation of blocks along the northern margin of the West African Craton (WAC), outcropping in the Central Anti-Atlas region, Morocco. This region is characterized by the occurrence of extended convergence-related magmatism, ophiolite emplacement and basins fillings (including BIF) during Cryogenian and Ediacaran periods.

Data obtained from compilation of cartographic work, whole-rock geochemistry and datation reveals a polyphased but still poorly constrained evolution through proxies of continentality (εNd) and of crustal thickness (Sr/Y ratio). We present new data spanning metamorphic petrology, basin stratigraphy, coupled datation and trace element analysis in detrital zircons in order to better understand the evolution of the geodynamic, magmatic and drainage systems. We propose a geodynamic scenario based on these data:

  • Development of an early oceanic arc (760-720 Ma) with juvenile magmatic signature (3<εNd(t)<7), its accretion on the WAC is followed by an episode of calc-alkaline magmatism (710-700 Ma).

  • Second arc development (700-670 Ma) only seen in detrital and inherited zircons, its accretion at 670 Ma is followed by late-orogenic magmatism (660-650 Ma) associated with decreasing crustal thickness (from 70 to 25 km).

  • Third arc development on the newly formed continent margin (640-600 Ma) until oceanic closure and collision. Intense late orogenic magmatism occurs (590-570 Ma), coeval with the decreasing crustal thickness (from 100 to 30 km).

  • A late phase of calc-alkaline is recorded (570-550 Ma) at constant and regular crustal thickness (25 km). A 550 Ma compressive event is recorded, very few calc-alkaline follows.

  • The onset of Cambrian with the development of a large passive margin capping the whole region. This change coincides with disappearance of ice-house climate evidence from the global sedimentological record.

How to cite: Bisch, A., Triantafyllou, A., Mahéo, G., El Kabouri, J., Bruguier, O., Bosch, D., Berger, J., Ganne, J., and Christophoul, F.: 200 Ma of magmatism along the northern border of the West African Craton during Pan-African convergence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6363, https://doi.org/10.5194/egusphere-egu23-6363, 2023.

EGU23-6505 | ECS | Posters on site | GD4.2

Global inversion and parametrization for building tomographic velocity models 

Umedzhon Kakhkhorov, Børge Arntsen, Wiktor Waldemar Weibull, and Espen Birger Raknes

Traveltime tomography is applied to investigate seismic structures of the Earth's subsurface. An accurate tomographic velocity model is important for a high-resolution waveform velocity building and its availability is one of the main components to mitigate the nonlinear inverse problem. We present a new methodology of obtaining velocity models for traveltime tomography studies. We found a way to get a highly accurate first-arrival traveltime tomography in combination with global optimization. The role of global optimization is twofold: to find initial solutions that are close to ‘truth’, and to guide tomographic inversion towards a geologically consistent model that explains the data. The main advantage of our workflow is a data-driven approach avoiding the use of a conventional layer-based parameterization and incorporation of manual interpretations into the velocity model. 

To date, a few geophysical studies have been focused on developing data-driven and a labour non-intensive regional tomographic velocity model building workflow. In our study, we present the tomographic velocity model building workflow as a combination of first-arrival traveltime tomography and global optimization. Global optimization allows to search for velocity parameters and depth to interfaces in the larger search area with a higher chance of convergence. After defining the geometry of main layers and general velocity trends, traveltime tomography with a bi-cubic B-spline model parameterization can be fitted to further update the velocity model. Our approach allows obtaining a highly accurate velocity model which can be used for seismic depth migration and as a starting model for a FWI seismic imaging. The workflow is developed and applied to synthetic and field regional seismic datasets. 

The developed methodology is applied for a shallow seismic engineering data and regional Ocean Bottom Seismic data. We identify four key components that lead to building an accurate tomographic velocity model: (i) understanding prominent horizons and possible velocity distribution of a layer within the study area. (ii) Performing ray penetration test to define offset ranges which carry the velocity information for the defined layers. (iii) Determining inversion schema to a perform global search for the velocity trends and major boundaries, and a local search to update lateral velocity variation. (iv) Iteratively update a set of defined layers (i.e., sediment, igneous crust and basement) in a top-down manner. 

How to cite: Kakhkhorov, U., Arntsen, B., Weibull, W. W., and Raknes, E. B.: Global inversion and parametrization for building tomographic velocity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6505, https://doi.org/10.5194/egusphere-egu23-6505, 2023.

Intermediate-depth earthquakes in many subduction zones occur in two distinct layers, forming an upper and a lower seismic zone separated vertically by an aseismic or weakly seismic region. This setting is widely known as Double Seismic Zone (DSZ). Notably, intermediate-depth seismicity in Northern Chile shows a pattern of intraslab seismicity which is distinct from the aforementioned conventional DSZ. Here, two parallel seismicity planes are present in the updip part of the slab, but at a depth of ∼80–90 km, there is a sharp transition to a highly seismogenic volume of 25–30 km thickness, which closes the gap between the two seismicity planes.

While such an observation is unique to Northern Chile, understanding the processes behind the formation of this feature should provide important constraints on the mineral processes that govern seismicity in DSZs as well as the role and involvement of fluids. As seismic velocities contain important information about mineralogy and fluid content, we aim at a high-resolution characterization of the seismic wavespeeds of the Northern Chile subduction zone, mainly focusing on the subducting Nazca slab. Data from the seismic stations of the permanent IPOC (Integrated Plate boundary Observatory Chile) deployment in the Northern Chile forearc form the backbone of the dataset, but are complemented by several temporary deployments that span shorter time sequences as well. We use the seismicity catalog of Sippl et al. (2018) that contains >100,000 earthquakes and 1,200,404 P- and 688,904 S-phase picks for the years 2007 to 2014, and limit our analysis to events that have more than 14 P-arrivals as well as more than 7 S-arrivals. Constraining the hypocentral depth range to 40-155 km and the longitude range to 68° W- 72°W, we perform local earthquake tomography using the FMTOMO algorithm (Rawlinson et. al., 2006) with a dataset of 10102 events comprising 163,359 P- and 113,036 S- phase picks.

We present first 3D models of P- and S-wavespeeds from the Northern Chile forearc between about 18.5° S and 24.5° S, as well as images of ray coverage, relocated seismicity and synthetic resolution tests. Tomography models for different choices of grid spacing and damping-smoothing parameters are compiled and compared in order to derive the optimal settings for the inversion.

 

The presented seismic velocity distribution will eventually be compared with theoretical wavespeeds that are forward calculated assuming different mineralogical compositions in order to narrow the range of possible reactions that may be occurring at depth.

 

How to cite: Hassan, N. and Sippl, C.: Looking deep into the subducting Nazca plate under the Northern Chile forearc with local earthquake tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6845, https://doi.org/10.5194/egusphere-egu23-6845, 2023.

EGU23-7182 | Orals | GD4.2

Upper-plate shortening and Andean-type mountain-building in the context of mantle-driven oceanic subduction 

Robin Lacassin, Tania Habel, Anne Replumaz, Benjamin Guillaume, Martine Simoes, Thomas Geffroy, and Jean-Jacques Kermarrec

To explore the conditions that lead to mountain-building in the case of an oceanic subduction, we conduct analog experiments (with silicon putty upper and lower plates, glucose syrup upper mantle) where subduction is driven by slab pull but also by an underlying mantle flow. Here, plate displacement is not imposed as in most models, but is controlled by the overall balance of forces in the system. We simulate three scenarios: no mantle flow (slab-pull driven subduction), mantle flow directed toward the subducting plate, and mantle flow directed toward the overriding plate. In the case of this latter scenario, we also test the influence of pre-existing rheological contrasts in the upper plate to best reproduce natural cases where inheritance is common. Our experiments show that when plate convergence is also driven by a background mantle flow, the continental plate deforms with significant trench-orthogonal shortening (up to 30% after 60 Myr), generally associated with thickening. We further identify that upper plate shortening and thickening is best promoted when the mantle flow is directed toward the fixed overriding continental plate. The strength of the upper plate is also a key factor controlling the amount and rates of accommodated shortening. Deformation rates increase linearly with decreasing bulk strength of the upper plate, and deformation is mostly localized where viscosity and strength are lower. When compared to the particular natural case of the Andes, our experiments provide key insights into the geodynamic conditions that lead to the building of this Cordilleran orogen since the Late Cretaceous - Early Cenozoic.

 

How to cite: Lacassin, R., Habel, T., Replumaz, A., Guillaume, B., Simoes, M., Geffroy, T., and Kermarrec, J.-J.: Upper-plate shortening and Andean-type mountain-building in the context of mantle-driven oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7182, https://doi.org/10.5194/egusphere-egu23-7182, 2023.

EGU23-7188 | ECS | Orals | GD4.2

How a subducting plateau impacts regional and global tectonics? 

Yang Liu, Nicolas Coltice, Laetitia Le Pourhiet, and Ziyin Wu

Plateau subduction is a common process at different plate convergent margins, and they often modify subduction and affect slab behaviour. However, fewer studies have been conducted in the intraoceanic subduction context, and the physical and rheological parameters involved imply a strong hypothesis on the initial conditions (thermal state, no flow in the mantle, no interaction with the tectonic network). Here, we use global three-dimensional spherical mantle convection models to investigate the potential impacts of a subducting plateau on subduction zones and plate reorganization from regional to global scales in a fully self-consistent plate-like tectonics system. Our models show that plateaus with different sizes (length, width and thickness) can locally slow down the trench retreat rate. A larger plateau prevents trench migration, eventually terminating the subduction. The buoyancy of plateaus is found to influence the shape of the trench. Low buoyancy plateaus do not deform the trench as they subduct while in models with buoyant plateaus, the trench advances landward in front of a plateau forming an arcuate shape in the map. This arcuate shape of the trench is further enhanced with decreasing buoyancy and increasing viscosity. If the oceanic plateau has a higher yield stress, it will always drive the formation of the arcuate trench before fully subducted, regardless of the buoyancy. The simulations suggest that any single plateau rheology variable (buoyancy, or yield stress) except the viscosity can influence trench migration behaviour on a regional scale. We will also explore how plateau subduction modifies the global tectonic evolution over 100 My.

How to cite: Liu, Y., Coltice, N., Le Pourhiet, L., and Wu, Z.: How a subducting plateau impacts regional and global tectonics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7188, https://doi.org/10.5194/egusphere-egu23-7188, 2023.

EGU23-7211 | Orals | GD4.2 | Highlight

How do subduction zones spread over Atlantic-type oceans? 

João C. Duarte, Nicolas Riel, Patricia Cadenas, Filipe M. Rosas, J. Kim Welford, and Boris Kaus

There is a long-standing mystery regarding how subduction zones enter internal Atlantic-type oceans to complete their Wilson cycle. While the process of subduction initiation is challenging to tackle, the Atlantic is a natural laboratory that allows understanding of some of the different stages of the process of invasion of new subduction zones. Three different subduction zones seem to be entering the Atlantic from different edges: the Caribbean Arc, the Scotia Arc and around the Iberia Peninsula. While the first two examples constitute fully developed subduction zones, it is unknown how they will propagate in the future. Will they spread intra-oceanically or will the subduction migrate along the Atlantic passive margins? Iberia is a good place to investigate the processes involved in the formation of new subduction zones. There have been places of aborted subduction (along the Cantabrian margin), places of incipient subduction (North, West and Southwest Iberia) and there is a subduction arc currently propagating into the Atlantic Ocean (the Gibraltar Arc). We will focus on this last case. Last year, we presented a numerical model that showed that the Gibraltar Arc may indeed further propagate into the Atlantic. This year, we present new models that investigate the factors controlling such propagation. We test different parameters such as the presence of weak zones in the adjacent margins and in the oceanic lithosphere (fracture zones) to obtain insights into the main factors controlling the first stages of propagation of new subduction zones in Atlantic-type oceans.

 

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL

How to cite: Duarte, J. C., Riel, N., Cadenas, P., Rosas, F. M., Welford, J. K., and Kaus, B.: How do subduction zones spread over Atlantic-type oceans?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7211, https://doi.org/10.5194/egusphere-egu23-7211, 2023.

EGU23-7314 | ECS | Orals | GD4.2

Trench retreat rates in narrow subduction zones controlled by overriding plate thickness 

Pedro J. Gea, Flor de Lis Mancilla, Ana M. Negredo, and Jeroen van Hunen

Subducting slabs are the main drivers of plate motion and flow in Earth’s mantle. Thus, much effort has been put into understanding the main factors controlling slab dynamics and subduction-induced mantle flow. Slab width (W) has been shown to have a major role in controlling the subduction dynamics and more specifically, the trench motion (e.g., Stegman et al., 2006; Schellart et al., 2007). Both numerical modelling experiments and retreat velocities observed in wide subduction zones show that the trench retreat velocity (VT) decreases as the slab is wider. However, observations on natural narrow subduction zones (W ≤ 1000 km, e.g. Calabria, Gibraltar, Scotia) do not show a direct relation between W and VT, thus indicating that other factors, still poorly understood, may play a more relevant role on trench retreat velocities. The aim of this work is to identify which are these factors that exert a dominant control. To accomplish this, we use self-consistent 3D numerical subduction models to systematically evaluate the effect of slab width, strength of coupling with the lateral plate and overriding plate thickness on trench motion. In contrast to what happens in moderate to wide subduction zones, our simulations show that slab width has little influence on trench retreat velocity for narrow subduction zones, which is a robust result for different viscous couplings at the lateral slab edge.  On the contrary, our results indicate that the major influence is exerted by the thickness of the overriding plate, with the trench retreat velocities decreasing noticeably as the plate thickness increases. These results are in agreement with retreat velocities observed in narrow subduction zones showing no direct relation with slab width, but an inverse dependence on overriding plate thickness.

 

References

Schellart, W. P., Freeman, J., Stegman, D. R., Moresi, L., and May, D. (2007). Evolution and diversity of subduction zones controlled by slab width, Nature, 446(7133), 308–311. doi:10.1038/nature05615

Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D. (2006). Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback, Geochemistry Geophysics Geosystems, 7(3), Q03012–. doi:10.1029/2005gc001056

How to cite: Gea, P. J., Mancilla, F. D. L., Negredo, A. M., and van Hunen, J.: Trench retreat rates in narrow subduction zones controlled by overriding plate thickness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7314, https://doi.org/10.5194/egusphere-egu23-7314, 2023.

EGU23-7467 | ECS | Posters on site | GD4.2

Combined natural and numerical-modeling constraints on subduction interface strength at deep metamorphic conditions 

Ana Lorena Abila, Whitney Behr, and Jonas Ruh

The integrated stress magnitude or bulk effective viscosity of subduction interface shear zones is a key component of both long- and short-term subduction dynamics. Current constraints on average subduction interface viscosity come from laboratory flow laws for subduction-related rock types and range from 1018 Pa.s (quartz-rich lithologies) to 1023 Pa.s (metabasaltic lithologies) for typical subduction strain rates and viscous subduction interface conditions (e.g. T between 400-900 °C). However, this viscosity range is based on end-member flow laws, which means it likely overestimates the true range in viscosity that is possible along the subduction interface. In nature, subduction shear zones are commonly a mixture of multiple rock types in various distributions (e.g. clast-matrix melanges); and furthermore, natural shear zones show a range in width from place to place, suggesting varying strain rates. Our goal in this study is to place more precise bounds on the global range of shear zone viscosity (or integrated shear stress) for natural subduction shear zones at deep subduction conditions. To do so, we curated a set of 9 geologic maps of eclogite facies shear zones from existing literature, focusing on those that a) show minimal retrogressive overprint, b) have defined shear zone widths, and c) have well-constrained PT conditions. These maps were digitized and implemented in a simple shear visco-elasto-plastic numerical model with constant strain rate (10-12 s-1) boundary conditions and experimentally constrained flow laws assigned to each rock type, including eclogite (eclogite mafic blocks), wet quartz (quartz-rich blocks, schists, gneisses), blueschist (blueschist mafic blocks), wet olivine (peridotites), antigorite (serpentinites), and aragonite (calcareous blocks). Numerical experiments  ran for a restricted amount of time steps to assure  steady-state stress/viscosity (<10 ky). Resulting integrated shear stresses and viscosities were then compared for the different example shear zones. Initial results indicate that natural shear zones should exhibit effective viscosities that vary by at least 1-2 orders of magnitude at a specific temperature, depending on the distribution of weak vs. strong blocks and the matrix rheology. Additional results and statistical analysis of all of the shear zones will be presented at the meeting. 

How to cite: Abila, A. L., Behr, W., and Ruh, J.: Combined natural and numerical-modeling constraints on subduction interface strength at deep metamorphic conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7467, https://doi.org/10.5194/egusphere-egu23-7467, 2023.

EGU23-8492 | Orals | GD4.2

Understanding the role of structural inheritance and flat slab geometry in Central Andes 

Michael Pons, Constanza Rodriguez Piceda, Stephan V. Sobolev, Magdalena Scheck-Wenderoth, and Manfred R. Strecker

The Sierras Pampeanas (29 - 35°S) located south of the Altiplano-Puna plateau above the Chilean subduction zone, consist of uplifted foreland basement blocks that are an expression of the eastward propagation of compresive deformation. Their presence is one of the most enigmatic features of the Andes. The formation of these ranges is considered an end member of the thick-skinned foreland deformation style, which involves the deformation of the sedimentary cover and the crystalline basement. At 33°S, the onset of compression occurs at 22Ma, and the change between thin and thick skinned deformation style at 16Ma. However, the mechanism responsible for this evolution remains controversial. Two main hypotheses have been proposed to explain this evolution. The first one atributes the change in foreland deformation style to the setting of the Pampean flat slab at 12 Ma, which is contemporanous to the southward migration and subduction of the Juan Fernandez hotspot ridge at 33S. Alternatively, it has been proposed that the reactivation of pre-existing structures inherited from pre-Neogen tectonic events could better explain the onset of deformation about 10 Ma before the arrival of the flat-slab. To resolve this controversial debate, we have developed a data-driven 3D geodynamic model using the FEM geodynamic code ASPECT. We incorporated the present-day geometrical and thermal configuration of the southern central Andes and the flat-slab from previous models. This approach allowed us to study the structural and thermomechanical factors responsible for the location of deformation in the Sierras Pampeanas (e.g., topography, temperature and composition, strength of the lithosphere and velocity of the plates).  Moreover,  we investigated the role of the geometry of the Nazca plate on the foreland deformation, and proposed a new mechanism ("flat slab conveyor)" that reconciles the timing of the main geological events (onset of shortening, change in tectonics style of deformation of the foreland, growth of the topography, cessation of volcanic activity, uplift of the basement, and propagation of the deformation). This work expands our understanding of how plates interact at convergent boundaries, in particular at the subduction zones, and how and where deformation is expressed at the surface of the the upper continental plate.

How to cite: Pons, M., Rodriguez Piceda, C., Sobolev, S. V., Scheck-Wenderoth, M., and Strecker, M. R.: Understanding the role of structural inheritance and flat slab geometry in Central Andes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8492, https://doi.org/10.5194/egusphere-egu23-8492, 2023.

EGU23-8670 | Posters on site | GD4.2 | Highlight

The role of subduction in the formation of Pangean oceanic large igneous provinces 

Philip Heron, Erkan Gün, Grace Shephard, Juliane Dannberg, Rene Gassmöller, Erin Martin, Aisha Sharif, Russell Pysklywec, R. Damian Nance, and J. Brendan Murphy

Large igneous provinces (LIPs) have been linked to both surface and deep mantle processes related to supercontinent formation. During the formation, tenure, and breakup of Pangea, the most recent supercontinent, there is a noted contemporaneous increase in the number of emplacement events of both continental and oceanic LIPs. There is currently no clear consensus on the origin of LIPs, but the most widely recognized hypothesis relates their formation to crustal emplacement of hot plume material originating in the deep mantle. The interaction of subducted slabs with the lowermost mantle thermal boundary and subsequent return-flow is a key control on plume generation. This mechanism has been explored for LIPs below the interior of a supercontinent (e.g., continental LIPs). However, a number of LIPs related to Pangea formed at the supercontinent’s exterior (e.g., Ontong Java Plateau in the Pacific Ocean), with no consensus on their formation mechanism. In this research, we consider the dynamics of global-scale supercontinent processes resultant from numerical models of mantle convection, and analyse whether circum-supercontinent subduction could generate both interior (continental) and exterior (oceanic) deep-mantle plumes. Our 2-D and 3-D numerical models show that subduction related to the supercontinent cycle can reproduce the location and timing of the Ontong Java Plateau, Caribbean LIP, and potentially the Shatsky Rise, when relating these LIPs to a deep mantle exterior plume. The findings here highlight the importance of taking into consideration mantle dynamics in every stage of the supercontinent cycle.

How to cite: Heron, P., Gün, E., Shephard, G., Dannberg, J., Gassmöller, R., Martin, E., Sharif, A., Pysklywec, R., Nance, R. D., and Murphy, J. B.: The role of subduction in the formation of Pangean oceanic large igneous provinces, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8670, https://doi.org/10.5194/egusphere-egu23-8670, 2023.

EGU23-8910 | ECS | Orals | GD4.2

Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models 

Erkan Gün, Russell Pysklywec, Philip Heron, Gültekin Topuz, and Oğuz Göğüş

The theory of plate tectonics acknowledges that drifting lithospheric plates are rigid and do not undergo substantial deformation except near or at plate boundaries. However, studies have shown that intra-plate deformation is a feature for continental lithosphere and can originate from different mechanisms such as lithospheric drips, delamination, and in-plane stresses. On the other hand, there is not well-known understanding of tectonic deformation within the interior of ocean plates. We compile data to show there is geological and geophysical evidence documenting that the drifting Pacific plate has been undergoing appreciable extensional deformation at the locations of its oceanic plateaux. Namely, the Ontong Java, Shatsky Rise, Hess Rise, and Manihiki plateaux show extensive evidence for normal faults, horst-graben structures, and extension related magmatic activity at a significant distance from plate boundaries. Furthermore, this deformation occurred after the initial emplacement of their associated large igneous provinces (LIPs) and before their arrival to subduction zones.

We present numerical geodynamic experiment results demonstrating that terranes embedded in ocean plates can undergo extensional deformation prior their accretion to the overriding plate due to slab-pull (e.g., a “subduction pulley”).  Our numerical models show that the subduction pulley is also a valid mechanism for the extensional deformation of the Pacific oceanic plateaux even at remote locations from the plate boundaries. For instance, tensional stress originated from down-going slabs can be transmitted through strong oceanic lithosphere over long distances (>1000 km) and deform the plate at its weak oceanic plateaux regions. The numerical experiments further demonstrate that high crustal thickness reduces the bulk strength of ocean lithosphere at the location of oceanic plateaux and makes them susceptible to slab-pull related extension—manifesting on the surface as intra-ocean plate deformation.

How to cite: Gün, E., Pysklywec, R., Heron, P., Topuz, G., and Göğüş, O.: Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8910, https://doi.org/10.5194/egusphere-egu23-8910, 2023.

Although positive buoyancy of young lithosphere near spreading centers does not favor spontaneous subduction, subduction initiation occurs easily near ridges due to their intrinsic rheological weakness when plate motion reverses from extension to compression. It has also been repeatedly proposed that inherited detachment faults may directly control the nucleation of new subduction zones near ridges subjected to forced compression. However, recent 3D numerical experiments suggested that direct inversion of a single detachment fault does not occur. Here we further investigate this controversy numerically by focusing on the influence of brittle-ductile damage on the dynamics of near-ridge subduction initiation. We self-consistently model the inversion of tectonic patterns formed during oceanic spreading using 3D high-resolution thermomechanical numerical models with strain weakening of faults and grain size evolution. Numerical results show that forced compression predominantly reactivates and rotates inherited extensional faults, shortening and thickening the weakest near-ridge region of the oceanic lithosphere, thereby producing ridge swellings. As a result, a new megathrust zone is developed, which accommodates further shortening and subduction initiation. Furthermore, brittle/plastic strain weakening has a key impact on the collapse of the thickened ridge and the onset of near-ridge subduction initiation. In contrast, grain size evolution of the mantle only slightly enhances the localization of shear zones at the brittle-ductile transition and thus plays a subordinate role. Compared to the geological record, our numerical results provide new helpful insights into possible physical controls and dynamics of natural near-ridge subduction initiation processes recorded by the Mirdita ophiolite of Albania.

How to cite: Liu, M. and Gerya, T.: Forced subduction initiation near spreading centers: effects of brittle-ductile damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9669, https://doi.org/10.5194/egusphere-egu23-9669, 2023.

EGU23-9814 | Orals | GD4.2

Molybdenum Isotope Systematics of the Kamchatka Subduction Zone System 

Matthias Willbold and Gerhard Wörner

Molybdenum (Mo) isotopes in magmatic rocks are a promising tool in high-temperature isotope geochemistry. In particular, basalts from subduction zones that are geochemically controlled by mass transfer through slab-fluid addition have systematically higher δ98Mo values (i.e. measured 98Mo/95Mo ratio in a sample relative to that in a standard) than the depleted mantle (δ98Mo = –0.21‰). In these rocks, the elevated δ98Mo values are linked to high Pb/Ce and high (238U/230Th) ratios and can be reconciled by the addition of isotopically heavy Mo via a slab fluid component1,2. So far, these systematics are best expressed in subduction zone basalts from the Mariana and Izu arc systems that also form coherent mixing trends between fluid-enriched mantle domains in δ98Mo versus 143Nd/144Nd and 176Hf/177Hf space1,2.

The Kamchatka arc system represents the northernmost expression of the W-Pacific convergent margin. Volcanic front lavas are dominated by slab-to-mantle mass transfer through fluid transport, whereas subduction of the Emperor seamount ridge gives rise to back-arc basalts with a geochemical and isotopic affinity to within-plate basaltic rocks3.

Here, we report δ98Mo data for 47 basalts from an E-W transect across the Kamchatka peninsula that have previously been analysed for their major, trace element, radiogenic and stable isotope data. The δ98Mo data extent the trend defined by samples from the Marianas and Izu arcs starting from moderately high δ98Mo and Pb/Ce values towards sub-depleted mantle δ98Mo and mantle-like Pb/Ce ratios that indicate the presence of a source component formed by partial melts of a rutile-bearing mafic crust4.

The common geochemical and isotopic trends formed by the combined Mariana – Izu – Kamchatka datasets suggest a surprisingly uniform Mo isotope composition of a subduction zone fluid endmember for more than 5000 km along-strike of the Circum-Pacific subduction zone system. Our data also confirm the presence of an enriched source component in the Kamchatka mantle wedge, possibly originating from the subducted Emperor seamount chain5.

1Freymuth, H., et al., EPSL 432, 176-186 (2015). 2Villalobos-Orchard, J., et al., GCA 288, 68-82 (2020). 3Churikova, T., et al. JPet 42, 1567-1593 (2001). 4Chen, S., et al., Nat. Comm. 10, 4773 (2019). 5Shu,Y., et al.,Nat. Comm. 13, 4467 (2022).

How to cite: Willbold, M. and Wörner, G.: Molybdenum Isotope Systematics of the Kamchatka Subduction Zone System, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9814, https://doi.org/10.5194/egusphere-egu23-9814, 2023.

EGU23-9902 | ECS | Orals | GD4.2

Origin of S-type granites in the forearc accretionary complex of the East Kunlun Orogenic Belt, northern Tibetan Plateau 

Xiang Ren, Yunpeng Dong, Dengfeng He, and Christoph Hauzenberger

A forearc environment is usually characterised by a relatively low geothermal gradient and hence little magmatic activity occurs. However, S-type granites were discovered within the forearc accretionary complex of the East Kunlun Orogenic Belt. The S-type granites intruded into an upper amphiolite facies partially migmatitic crystalline basement in form of dikes and sills at ca. 440 Ma which corresponds to the transition of the Proto-Tethyan to the Paleo-Tethyan realm in the northern Tibetan Plateau. The observed granites contain either garnet + biotite + muscovite or garnet + muscovite: (1) muscovite granite is strongly peraluminous with an aluminous saturation index (ASI) of more than 1.1 (ASI = molar [Al2O3/(Na2O+K2O+CaO]) and has high-K calc-alkaline characteristics, low Sr/Y (1.9–16.1) and LaN/YbN (1.85–13.2) ratios. (2) Two-mica granite is moderately peraluminous (ASI = 1.02–1.09), has high Ca and low K contents as well as high Sr/Y (16.8–67.7) and LaN/YbN(10.9–33.3) ratios. Other trace element contents and their ratios also show striking differences with high Sr (207–324 ppm) content and CaO/Na2O (0.47–0.96) ratio, and a low Rb/Sr (0.04–0.32) ratio for two-mica granite, but low Sr (63–126 ppm) content and CaO/Na2O (0.08–0.20) ratio, and a high Rb/Sr (0.56–2.53) ratio for muscovite granite. The observed differences are due to different protolith chemistries and melting mechanisms. Based on melting experiments of metasedimentary rocks (Patiño Douce and Harris, 1998), muscovite granite was most likely produced by dehydration melting of a metapelitic source and the two-mica granite by H2O-fluxed melting of a metagreywacke. Zircon Hf isotopes of the two S-type granites have εHf(440 Ma) values of -6.85 to +12.02 indicating the involvement of a mantle-derived magma which probably triggered the anatexis of supracrustal rocks deposited in a forarc regime. Coveal adakites with a younging westward trend as well as mafic rocks have been reported in this accretionary complex, which together with anatexis and metamorphism of accreted material support the occurrence of a slab window beneath the forearc accretionary complex of the East Kunlun Orogenic Belt during subduction of the Tethyan oceanic slab.

 

References

Patiño Douce, A.E., Harris, N., 1998. Experimental constraints on Himalayan anatexis. Journal of Petrology 39, 689–710.

How to cite: Ren, X., Dong, Y., He, D., and Hauzenberger, C.: Origin of S-type granites in the forearc accretionary complex of the East Kunlun Orogenic Belt, northern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9902, https://doi.org/10.5194/egusphere-egu23-9902, 2023.

EGU23-10756 | Orals | GD4.2

Time dependent slab temperatures, metamorphism, and mechanical properties: Insights from dynamic subduction models 

Adam Holt, Cailey Condit, Valeria Turino, Gabe Epstein, Ryan Stoner, and Victor Guevara

The thermal structure of subduction zones enacts a first-order control on many geological processes and properties, including the locus and degree of slab devolatilization, and the associated densities and strengths of subducting material. Modeling studies with fixed subduction geometries and plate velocities have been used to map out how various subduction parameters affect the pressure-temperature conditions of slabs and, in turn, the depths of major dehydration reactions. However, there is abundant geological evidence that slab properties, and the associated temperatures, evolve over few-Myr timescales. In this study, we use numerical subduction models to target this time dependence. Specifically, we focus on the styles and drivers of thermal transience and the imprint of this on subducting slab dehydration and slab strength.

Specifically, we have developed 2-D and 3-D subduction models that enable slab properties to evolve through time in a dynamically consistent fashion using the ASPECT finite element code1-3. We use these models to investigate: i) the extent to which slab thermal conditions – and the associated metamorphic reactions and slab strength – evolve throughout the lifetime of a subduction zone, ii) the effects of first-order subduction zone properties on this evolution, and iii) the degree to which three-dimensionality (i.e., the presence of a slab edge) impacts this evolution. Regardless of imposed basic subduction parameters (e.g., plate ages, crustal strengths), our model subduction zones exhibit highly time-dependent thermal evolutions. The slab top, for example, exhibits rapid cooling during initiation and slower cooling subsequently, with along-strike temperature variations of up to ~40°C in the 3-D models. This thermal transience has fundamental implications for the geophysical and geochemical evolution of subduction zones; it manifests in a strong time dependence of dehydration depths and magnitudes and, in turn, substantial variability in slab strength. 

 

1: Bangerth, W., Dannberg, J., Gassmoeller, R., & Heister, T. (2020). ASPECT v2.1.0, Zenodo. https://doi.org/10.5281/ZENODO.3924604

2: Heister, T., Dannberg, J., Gassmöller, R., & Bangerth, W. (2017). High accuracy mantle convection simulation through modern numerical methods - II: Realistic models and problems. Geophys. J. Int., 210(2), https://doi.org/10.1093/gji/ggx195

3: Holt, A. F., & Condit, C. B. (2021). Slab temperature evolution over the lifetime of a subduction zone. Geochem., Geophys., Geosys., 22, doi:10.1029/2020GC009476.

How to cite: Holt, A., Condit, C., Turino, V., Epstein, G., Stoner, R., and Guevara, V.: Time dependent slab temperatures, metamorphism, and mechanical properties: Insights from dynamic subduction models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10756, https://doi.org/10.5194/egusphere-egu23-10756, 2023.

EGU23-10847 | Posters on site | GD4.2 | Highlight

Reconstructing slab dip through deep time to explain pulses in kimberlite eruptions 

Ben Mather, Dietmar Müller, Christopher Alfonso, Maria Seton, and Nicky Wright

The recycling of oceanic lithosphere at subduction zones constitutes the largest driving force of plate tectonic motion. The angle at which subducting plates enter the mantle influences the magnitude of this force, the distribution of subduction-related earthquakes, intensity of volcanism, and mountain building. However, the factors that control subduction angle remain unresolved. We develop a novel formulation for calculating the subduction angle based on trench migration, convergence rate, slab thickness, and plate density which reproduces the present-day dynamics of global subduction zones. Applying this formulation to reconstructed subduction boundaries from the Jurassic to present day, we relate subduction angle combined with slab flux to pulses in kimberlite eruptions. High rates of subducting slab material trigger mantle return flow that stimulates fertile reservoirs in the mantle. These convective instabilities transport slab-influenced melt to the surface at a distance inbound from the trench corresponding to the subduction angle. Our deep-time slab dip formulation has numerous potential applications including modelling the deep carbon and water cycles, and an improved understanding of subduction-related mineral deposits.

How to cite: Mather, B., Müller, D., Alfonso, C., Seton, M., and Wright, N.: Reconstructing slab dip through deep time to explain pulses in kimberlite eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10847, https://doi.org/10.5194/egusphere-egu23-10847, 2023.

EGU23-10944 | ECS | Orals | GD4.2

Seismic Evidence of Slab Segmentation and Melt Focusing Atop the 410-km Discontinuity in NE Asia 

Jung-Hun Song, Seongryong Kim, and Junkee Rhie

The geometry of subducting slabs is largely controlled by mantle rheology and time evolving processes of surface plate boundaries. Imaging of a detailed slab distribution and its surrounding can provide information of physical, chemical, and dynamical properties of the upper mantle. Based on new high-resolution 3-D tomography of subducting Pacific slab in northeast Asia, we revealed a prominent gap within the stagnant portions of the slab showing an abrupt change in its lateral trends that follow the trace of plate junctions associated with plate reorganization at the western Pacific margin during the Cenozoic. Focused partial melting above the slab gap was inferred based on the spatial coincidence between the high Vp/Vs anomaly and the negative reflectivities above the 410-km discontinuity from local receiver function studies. The slab gap is possibly filled with low-velocity anomalies within the MTZ as evidenced by wavefield focusing of teleseismic body waves and absolute velocity imaging from previous studies. We explain the spatial coincidence between the low-velocity anomaly within the MTZ and the focused melt layer above the MTZ by the process of mantle dynamics related with secular variation of slab geometries by tearing. Isolated low-velocity anomalies within the MTZ imaged by seismic tomography without previous thermal disturbances (e.g., hot plume) are suggested to be the products of distinct MTZ compositions disturbed by former nearby slab subductions. Our results suggest a close dynamical relationship between the subducting slab and the MTZ, which promotes the formation of multi-scale chemically distinct domains in the deeper upper mantle.

How to cite: Song, J.-H., Kim, S., and Rhie, J.: Seismic Evidence of Slab Segmentation and Melt Focusing Atop the 410-km Discontinuity in NE Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10944, https://doi.org/10.5194/egusphere-egu23-10944, 2023.

EGU23-11018 | ECS | Posters on site | GD4.2

Magmatic arc compositions governed by climate change: A biogeodynamic perspective from the Eastern Equatorial Pacific 

Carlos Errázuriz-Henao, Arturo Gómez-Tuena, Mattia Parolari, and Marion Weber

Magmatic arcs modulate global climate over geological timescales through outgassing and rock weathering, but recognizing the fingerprints of climate change in arc magmas remains challenging. Based on a detailed reconstruction of oceanographic, atmospheric, and climatic processes since the middle Miocene, as well as an extensive geochemical database of Miocene and active arc-front magmas from the Trans-Mexican Volcanic Belt, Central American Volcanic Arc, and the North Andean Colombian Arc we developed a conceptual framework by which biogeochemical proxies in oceanic sediments can be tracked down to the composition of arc magmas. Using this framework, we show that the well-documented increases in biologically mediated authigenic Ba and U contents of seafloor sediments from the Eastern Equatorial Pacific (EEP) at the onset of the so-called “carbonate crash” (12–9 Ma) were triggered by an escalation in biological productivity and an augmented efficiency of respiratory carbon storage. We suggest that the temporal modification of the oceanic carbon cycle was regulated by the synchronous formation of three wind-powered seasonal upwellings systems —Tehuantepec, Papagayo, and Panama— that developed in the context of steepening meridional temperature gradients, intensified atmospheric circulation and global climate cooling since the Middle Miocene. Sediments deposited in the context of these newly established upwelling systems became anomalously enriched in authigenic U and Ba not only in comparison to older sediments, but also with respect to geographically adjacent areas of the EEP where vigorous upwellings are absent. These peculiar environmental conditions thus produce a heterogeneous ocean floor that upon subduction and eventual interaction with the mantle wedge creates arc volcanoes with compositional fluctuations that mimic those of the ocean sediments. These findings indicate that the oceanographic and biogeochemical effects of climate change can be engraved on the continental crust and mantle.

How to cite: Errázuriz-Henao, C., Gómez-Tuena, A., Parolari, M., and Weber, M.: Magmatic arc compositions governed by climate change: A biogeodynamic perspective from the Eastern Equatorial Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11018, https://doi.org/10.5194/egusphere-egu23-11018, 2023.

EGU23-11540 | ECS | Orals | GD4.2

Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles 

Stephen Hicks, Lidong Bie, Catherine Rychert, Nicholas Harmon, Saskia Goes, Andreas Rietbrock, Songqiao Wei, Jenny Collier, Timothy Henstock, Lloyd Lynch, Julie Prytulak, Colin Macpherson, David Schlaphorst, Jamie Wilkinson, Jonathan Blundy, George Cooper, Richard Davy, and John-Michael Kendall

Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ-1/Qµ-1 > 0.6) and VP/VS (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.

How to cite: Hicks, S., Bie, L., Rychert, C., Harmon, N., Goes, S., Rietbrock, A., Wei, S., Collier, J., Henstock, T., Lynch, L., Prytulak, J., Macpherson, C., Schlaphorst, D., Wilkinson, J., Blundy, J., Cooper, G., Davy, R., and Kendall, J.-M.: Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11540, https://doi.org/10.5194/egusphere-egu23-11540, 2023.

EGU23-11688 | ECS | Posters on site | GD4.2

Numerically modelling along-strike rheologic variations in 3D subduction zones 

Derek Neuharth, Whitney Behr, and Adam Holt

Because subduction zones can extend thousands of kilometers along-strike, many previous studies have used 2D subduction models which inherently assume homogeneity along-strike. However, in nature we see that subduction zones are often heterogeneous along-strike and can exhibit significant variations in the subducting plate age, thickness, and viscosity, trench location, as well as in the geometry of the overriding plate. While 2D models can test large system-wide changes to these parameters by assuming homogeneity along-strike, how variabilities in the geometry and rheology interact with each other in a three-dimensional setting is poorly understood.

To understand how along-strike variations affect an evolving subduction zone, we developed self-consistent 3D subduction models using the finite element code ASPECT. The models include a thermally-defined subducting plate and overriding plate, and a constant-viscosity crust/interface. We vary two primary parameters along-strike: 1) the viscosity of the interface shear zone and 2) the thickness of the overriding plate, which affects the interface shear zone length. We explore how varying each of these parameters affects the subduction, convergence, and trench rollback velocities, slab morphology, and the stress distribution and topography formation within the overriding plate.

We find that along-strike variations to the interface viscosity or overriding plate thickness has only minor effects on the slab morphology and convergence velocities, but largely affects the surface stress distribution. While variations in the overriding plate thickness or interface viscosity do not affect the convergence velocity along-strike, having a thicker overriding plate or stronger interface leads to a reduction in the system-wide convergence velocity. Despite the similar velocities along-strike, slab morphology changes along-strike, with lower dips seen in regions with a greater overriding plate thickness or weaker interface viscosity. Most importantly, along-strike changes to either parameter results in significant differences in the surface stress distribution. Higher stresses build within the side that has a thicker overriding plate or stronger interface. This increase in stresses results in greater topography, with a maximum variation along-strike of up to ~1.2 km.

How to cite: Neuharth, D., Behr, W., and Holt, A.: Numerically modelling along-strike rheologic variations in 3D subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11688, https://doi.org/10.5194/egusphere-egu23-11688, 2023.

EGU23-13467 | Orals | GD4.2

Processes related to the rift-to-collision transition in the eastern Betics as revealed by low-temperature thermochronology on magmatic, U-Pb dating and clumped isotopes on calcite-filled veins 

Frédéric Mouthereau, Marine Larrey, Louise Boschetti, Nicolas Beaudoin, Stéphanie Brichau, Nick Roberts, Damien Huyghe, Matthieu Daëron, Véronique Miegebielle, and Sylvain Calassou

The Alboran margin in the Betics formed as a result of backarc crustal thinning oblique to the direction of the slab retreat. The history of sediment infill, subsidence and faulting reveals extension at upper crustal levels operated from the Serravallian-early Tortonian to the late Tortonian (14-8 Ma) synchronously with Ca-K magmatism. Only recently, around 8 Ma, the retreating slab detached resulting in the onset of the tectonic inversion of the margin. Here we report new apatite (U-Th)/He thermochronological analyses from Cabo de Gata magmatic province, and new U-Pb dating, Oxygen (O) and carbon (C) stable isotopic analyses of calcite-filled veins from the Tabernas basin combined with fluid temperatures determined by clumped isotope D47 analyses. U-Pb ages from 8.56 ± 0.21 to 4.88 ± 0.45 Ma are remarkably synchronous with late alkaline Tortonian-Messinian magmatic events and post-Messinian uplift. Low-temperature thermochronology confirms that magmatic edifices cooled below sea-level at around 8-7 Ma, and then slowly exhumed onshore during shortening along the Carboneras fault and regional kinematic reorganisation associated with slab detachment. C and O isotopic compositions (-17.23‰ to -9.08‰ for O and -15.77‰ to -1.60‰ for C, in V-PDB) of calcite veins are close to carbonates endmember of the Alpujárride basement. The O and C isotopes trend highlights a burial where all δ18O and δ13C calcite have depleted values compared with host rocks indicating a higher temperature of calcite precipitation (estimated at 83.7°C) and an increasing organic matter degradation with depth. The concordance on ages suggests that deep processes including mantle delamination and hot mantle triggered CaCO3 fluid precipitation and uplift during the transition from extension to onset of tectonic inversion. The deep mantle processes related to the 8 Ma event impacted not only the uplift of the Alboran basin that caused the Messinian Salinity Crisis that is well recorded in the Betics, but also the recent uplift of Iberia and Western Europe.

How to cite: Mouthereau, F., Larrey, M., Boschetti, L., Beaudoin, N., Brichau, S., Roberts, N., Huyghe, D., Daëron, M., Miegebielle, V., and Calassou, S.: Processes related to the rift-to-collision transition in the eastern Betics as revealed by low-temperature thermochronology on magmatic, U-Pb dating and clumped isotopes on calcite-filled veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13467, https://doi.org/10.5194/egusphere-egu23-13467, 2023.

EGU23-13615 | ECS | Orals | GD4.2

Lithospheric Controls on the Distribution of Porphyry Copper Deposits 

Simon Stephenson, Mark Hoggard, Marcus Haynes, Karol Czarnota, and Krystian Czado

Lithospheric structure in subduction settings controls the distribution of thermal, compositional and rheological interfaces.  It therefore plays a key role in the generation, fractionation and transport of subduction-related melts that are a vital ingredient of the formation of porphyry copper deposits.  Renewed efforts to understand the linkage between lithospheric structure and the location, grade and endowment of porphyry copper deposits has raised the possibility of using crustal and lithospheric mantle structure as an exploration tool.  One example is a suggested relationship between the genesis of porphyry copper deposits – known to be associated with evolved, silica-rich magmas – and the thickness of the crust.  Here, using a new compilation of spot measurements, we explore the utility of crustal thickness as an exploration tool for porphyry copper deposits.

How to cite: Stephenson, S., Hoggard, M., Haynes, M., Czarnota, K., and Czado, K.: Lithospheric Controls on the Distribution of Porphyry Copper Deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13615, https://doi.org/10.5194/egusphere-egu23-13615, 2023.

EGU23-13902 | ECS | Posters on site | GD4.2

Multi-scale numerical modelling of subduction interface rheology 

Paraskevi Io Ioannidi and Wouter Pieter Schellart

The physical nature and the rheology of the subduction interface play an important role in the deformation of the overriding plate, the degree of locking of the subduction zone plate boundary, and the rate of subduction. Here, we employ the Finite Element Method (FEM) to determine the effect of matrix rheology on the bulk interface deformation. We use the open-source particle-in-cell FEM code Underworld (Moresi et al., 2007) to create synthetic 2D visco-plastic models of the subduction interface that deform by simple shear. The models comprise meter-scale blocks of continental affinity encompassed within a metasedimentary matrix. We investigate the effect of constant, Newtonian, and non-Newtonian matrix viscosities on the deformation and stress distribution in the models for large finite shear strains. We vary the percentage of block concentration from 10% to 65%, as well as the shear velocity while making sure the strain rates produced remain within the interseismic range, and we calculate strain localization and stresses within the models. Finally, we use the same viscosity formulations in large-scale 2D models of a subduction zone to investigate their influence on upper plate deformation and subduction rate during the interseismic stage. With this multi-scale analysis, we gain insight into how the same rheological law can affect deformation at different scales.

How to cite: Ioannidi, P. I. and Schellart, W. P.: Multi-scale numerical modelling of subduction interface rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13902, https://doi.org/10.5194/egusphere-egu23-13902, 2023.

EGU23-14047 | ECS | Posters on site | GD4.2

The growth of Turkish – Iranian Plateau and comparative models for understanding the deformation on the overriding plate during plateau formation 

Uğurcan Çetiner, Jeroen van Hunen, Oguz H. Gogus, Mark B. Allen, and Andrew P. Valentine

The Arabia-Eurasia collision, which started during Late Eocene (~35 Ma) or afterward across the Bitlis-Zagros suture, resulted in the formation of the Turkish – Iranian Plateau. Even though the average elevation throughout the plateau is around 2 km, the lithospheric structures between East Anatolian and the Iranian parts may be different. For instance, seismological studies suggest that East Anatolia is underlain by anomalously low-speed anomalies/hot asthenosphere whereas the Iranian part is associated with a rather thick (>200 km in some places) and strong lithosphere. Therefore, the area may be regarded as two distinct regions, namely, the East Anatolian Plateau and the Iranian Plateau. The growth of the plateau is mostly attributed to slab break-off combined with crustal shortening. Other processes often associated with the collision are lithospheric delamination and tectonic escape of microplates. These hypotheses suggested for the growth of the plateau are yet to fully explain the dualistic nature of the lithosphere in a region where elevations are roughly similar. In this work, by using 2D numerical experiments we aim to investigate the physical, geometric, and rheological parameters affecting the deformation of the plate during pre-, syn-, and post-collision. Our preliminary model results show an extension (up to ~70 km) on the terrane that is dragged behind the subducting plate, while the overriding plate undergoes shortening during the collision. The collision results in ~100 km of underthrusting in 50 Myrs which is in the range for the measured amounts of underthrusting across the plateau. We aim to expand the study by creating comparative model sets (i.e., models representing East Anatolia vs. models representing Iran) with a parameterization of varying lithospheric structures (e.g., different crust and mantle thicknesses), and strength profiles, which will help us to understand the kinematics and dynamics of such orogenic growth.

How to cite: Çetiner, U., van Hunen, J., Gogus, O. H., Allen, M. B., and Valentine, A. P.: The growth of Turkish – Iranian Plateau and comparative models for understanding the deformation on the overriding plate during plateau formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14047, https://doi.org/10.5194/egusphere-egu23-14047, 2023.

EGU23-14049 | Orals | GD4.2

A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress 

Lior Suchoy, Saskia Goes, Fangqin Chen, and D. Rhodri Davies

The subduction of positively buoyant features has been suggested to cause flat or shallow dipping slabs, the formation of cusps in trench geometry and periods of reduction or full cessation of arc magmatism. Additionally, recent earthquake data indicates that the subduction of the Hikurangi plateau near New Zealand causes a rotation of intraplate stresses. In this study, we present a series of multi-material 3-D simulations of free subduction to investigate how subduction of buoyant elongated features, or ridges, impact downgoing plate velocities, trench motions, slab morphology and intraplate stress regime. We examine how these parameters are affected by the age of the subducting plate and the relative buoyancy and position of the buoyant ridge. We find that buoyant ridges change slab sinking and trench retreat rates and locally rotate intraplate stresses. These, in turn, modify the evolution of slab morphology at depth and trench shape at the surface, as trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young and weak plates, the change in trench shape is more localised than on old and strong plates. We observe slab shallowing around the ridge only in young plates, while the stronger pull by the more negatively buoyant old plates causes slab steepening near the buoyant ridge. Buoyant ridges on old plates which are located near stagnating or advancing regions, typical in wide slabs, modify trench behaviour more strongly than ridges in other regions of the trench. Bending-related intraplate earthquakes are more likely in older plates where higher stress is accumulated and the rotation due to the buoyant ridge is more widespread than for younger plates. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.

How to cite: Suchoy, L., Goes, S., Chen, F., and Davies, D. R.: A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14049, https://doi.org/10.5194/egusphere-egu23-14049, 2023.

EGU23-14144 | ECS | Orals | GD4.2

Insights into slab detachment dynamics from 0D to 3D numerical experiments   

Andrea Piccolo, Marcel Thielmann, and Arne Spang

Slab detachment is a process that has been invoked to explain rapid uplift, deep seismicity and magmatic activity in several active orogens (e.g., Alps, Himalaya). The negative buoyancy force associated with a slab at depth and its progressive removal during detachment results in a reorganization of forces within the lithosphere and the detaching slab. However, it is not yet clear to which extent slab detachment is the primary cause of the different observations. Deciphering the impact of slab detachment on the observations mentioned above therefore requires a thorough understanding of the physical processes controlling deformation within and around the detaching slab. 

Here, we employ numerical models to investigate the nonlinear coupling between mantle flow and slab detachment. Due to the three-dimensional nature of slab detachment and the variety of involved processes, it is difficult to pinpoint the first order controls on the time scale of this process. As a first step, we therefore develop a simplified 0D necking model that describes the temporal evolution of the thickness of a detaching slab, additionally taking into account the effects of the nonlinear coupling between upper mantle and detaching slab. This allows us to derive a set of nondimensional numbers which ultimately control the slab detachment process.  

Based on these findings, we then use 2D and 3D numerical models to further determine higher dimensional geometrical effects on slab detachment. Results show that the predictions from the 0D experiments predict the 2D and 3D experiments sufficiently well if simple slab geometries are used. For more complex slab geometries, higher dimensional results deviate from the 0D predictions. Nevertheless, the combination of 0D and 2D/3D numerical models allows to efficiently determine first order controls on slab detachment and thus also on specific geological observations such as seismicity and surface response. 

How to cite: Piccolo, A., Thielmann, M., and Spang, A.: Insights into slab detachment dynamics from 0D to 3D numerical experiments  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14144, https://doi.org/10.5194/egusphere-egu23-14144, 2023.

Continental collision zones form at convergent plate boundaries after negatively buoyant oceanic lithosphere subducts entirely into the Earth's mantle, whereafter collision ensues, and colliding continents are sutured together. In models of free subduction, the volume of the preceding and adjacent negatively buoyant oceanic lithosphere controls the system's driving force and dynamics. To investigate the dynamics of long-term continental subduction, indentation and collisional boundary migration and associated slab dynamics we designed large-scale numerical models of subduction-and-collision including two sets of modelled depths: whole mantle (2880 km) and upper mantle + partial lower mantle (960 km) and varying the trench parallel length ratio (1.5 - 2) of the indenting continental lithosphere (~2300 km) and adjacent oceanic lithosphere. In this contribution, we present the contrasting evolution of continental subduction and indentation coupled with adjacent oceanic slab rollback focusing on the different slab dynamics observed by varying the depth of the mantle in the models. Intriguingly, the whole mantle models show sustained continental indentation and concurrent deep continental subduction to mid-low upper mantle depths resulting in deep slab tearing at the subducted continental margin and shallow slab tearing at the trench parallel boundaries of the continental plate. In addition, the models also show continental underthrusting beneath the overriding plate and underplating of the continent, coeval with indentation and adjacent oceanic slab rollback. Together, these results provide insights into the India-Eurasia collision zone where the prolonged northward indentation of India during the last 50 Myrs and the rollback of the Sunda slab appear linked.

How to cite: Laik, A., Schellart, W., and Strak, V.: Protracted continental subduction, indentation and collisional boundary migration coupled with adjacent oceanic slab-rollback and slab detachment in large-scale buoyancy-driven 3D whole-mantle scale numerical models of subduction-and-collision., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14232, https://doi.org/10.5194/egusphere-egu23-14232, 2023.

EGU23-15571 | Orals | GD4.2 | Highlight

Sharpening our community research on the initiation of subduction zones 

Fabio Crameri

Current research on how, when, and where subduction zones initiate (one of the key, long-lasting open questions in the Earth Sciences) spans a multitude of (if not all) Earth and Planetary Science disciplines, engages most geoscientists at least once during their career, occupies research vessels and supercomputers, remains a steady appearance in overarching science journals, and often is considered the holy grail of our field.

It is maybe not surprising that the study of subduction zone initiation (SZI) has therefore created a multitude of different research approaches and divided sub-disciplines applying specific methodologies and field-specific jargons and terms, of which neither is understood across sub-discipline boundaries any longer. To make it worse, a few leading SZI researchers have stopped acknowledging each other’s work, even scientifically.

Within all sub-disciplines that exploit the rock record, plate reconstructions, geophysical measurements like seismic tomography, and theoretical and numerical modelling, we have never learned more about the formation of subduction zones than in the past couple of years. As a community, however, we failed to bring the dispersed knowledge (and sources of information) to a common ground and progress: Numerous numerical models on passive margin SZI made some geoscientists believe that it is the most likely place for SZI to occur. Misleading terminology made others believe that SZI can occur "spontaneously" or that "fore-arc basalts" (FABs) are formed in fore-arcs.

With the community-based, community-driven, community-accessible Subduction-Zone Initiation (SZI) Database (www.SZIdatabase.org), we turn the helm towards a more unified, collaborative approach again. We provide the most extensive and detailed collection of current, trans-disciplinary SZI data (and from just this, a wealth of new insights), suggest a commonly-accessible SZI-related terminology, and offer a platform for community-wide, always-on discussion (see Crameri et al., 2020).

Everything is put in place to reunite, and not loose track of, all our individual efforts and advances, so we, as a community, can learn and understand more about this enigmatic, truly cross-disciplinary hallmark of our fascinating planet.

 

Crameri, F., V. Magni, M. Domeier, G.E. Shephard, K. Chotalia, G. Cooper, C. Eakin, A.G. Grima, D. Gürer, A. Király, E. Mulyukova, K. Peters, B. Robert, and M. Thielmann (2020), A transdisciplinary and community-driven database to unravel subduction zone initiation, Nature Communications, 11, 3750. doi:10.1038/s41467-020-17522-9

How to cite: Crameri, F.: Sharpening our community research on the initiation of subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15571, https://doi.org/10.5194/egusphere-egu23-15571, 2023.

SM7 – Seismic Hazard Assessment (earthquake forecasting, engineering seismology, seismic and/or multihazard probabilistic assessment)

EGU23-19 | ECS | Posters on site | SM7.2

Pattern identification of strong earthquakes in North American- Puerto Rico region through Correlation fractal dimension and Coulomb stress 

Haritha Chandriyan, Ramakrushna Reddy, Tejaswini Mangalagiri, and Paresh Nath Singha Roy

This study attempts to investigate the patterns of correlation fractal dimension (Dc) prior to the occurrence of strong earthquakes by implementing modified Grassberger and Procaccia (1983) algorithm.  The primary input for current research is earthquake epicentre locations. Through this method, dispersed and clustered seismicity can be distinguished by analysing spatiotemporal distribution of earthquake clusters. The low Dc values suggest dense clusters while high Dc values imply a scattered distribution of occurrences. In other words, low Dc represents a highly stressed region. Therefore, by monitoring the variations in Dc, we get valuable insights regarding spatiotemporal clustering of events as well as state of stress. To confirm the high stress brought on by dense clusters prior to the mainshock, we make use of the coulomb failure criterion to measure the Coulomb stress. For testing this hypothesis we have done analysis in southern California (SC), Baja California (BaC), and Puerto Rico Island (PRI).

Major plate movement between the North American plate and the Pacific plate is accommodated by the San Andreas Fault (SAF) and the remaining is by Eastern California Shear Zone (ECSZ). However, the ECSZ has experienced three strong earthquakes in the last thirty years. This indicates an anomalous pattern of seismicity developing in ECSZ. The recent rupture of 2019 Ridgecrest earthquake has caused stress perturbation along Garlock Fault (dormant fault, capable of producing M >7 earthquakes) throws light on the probable future event. We did fractal analysis on 30 years (1990-2020) of data considering 50 earthquakes per each window. Four strong earthquakes have chosen for studying; 2019 Ridgecrest (Mw7.1), 2010 El-Mayor Cucapah (Mw7.2), 1999 Hectormine (Mw7.1), and 1992 Landers (Mw7.3).In general, a relative decrease in Dc before each of the events is observed.

The commencement of 2019 Puerto Rico sequence trailed by the incidence of Mw6.4, 07 January 2020, earthquake highlights the importance of studying seismicity patterns in the PRI. Tectonic setting of the PRI is highly complex; characterized by dynamic seismicity. We have analysed ~32 years of seismicity data (M≥ 2.8). The fractal study of the Puerto Rico earthquake suggests a relative decline in Dc during 2019. It should be noted that the emergence of spatially closed clusters occurred at the same time in the southwestern PRI. When the static stress is calculated, the southwestern clusters indicate a highly stressed crust. This validates the relationship between the stress and low Dc observed prior to the occurrence of Mw6.4 January 2020 event.

Based on our study, it is possible to conclude that a significant drop in the Dc proceeds the mainshock. This pattern is explicit in the five major earthquakes in the study area. So we propose that our approach based on the patterns of correlation fractal dimension is a novel method to identify numerical precursors of strong earthquakes before the rupture.

How to cite: Chandriyan, H., Reddy, R., Mangalagiri, T., and Roy, P. N. S.: Pattern identification of strong earthquakes in North American- Puerto Rico region through Correlation fractal dimension and Coulomb stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-19, https://doi.org/10.5194/egusphere-egu23-19, 2023.

Two moderate-sized earthquakes occurred recently in Nepal on 8th November 2022 (Mw=6.1) and on 12th November 2022 (Mw=6.0). The location of these earthquakes falls at 384km and 329km respectively NW of the 25th April 2015 Gorkha earthquake. Both these earthquakes have been studied to understand the source rupture process employing Moment Tensor analysis by estimating the focal mechanism, and source parameters and relocating their hypocentral parameters using their regional waveforms recorded by the 18-stations broadband seismograph network deployed around Tehri dam in the Garhwal Himalaya Uttarakhand.

The epicentral distance of all the stations was less than 10◦. We employ the Moment Tensor Inversion approach to invert the broadband waveforms for the mechanism and depths and assume a one-dimensional velocity model developed for the adjacent Himalayan Region. Moment tensor solutions of the events were calculated along with the simultaneous calculation of the centroid position. Joint analysis of the hypocenter position, centroid position, and nodal planes produced clear outlines of Himalayan Fault lines. The epicenter of these earthquakes is located south of the MCT.

The obtained source mechanisms are consistent with those reported in the USGS centroid moment tensor (CMT) and NEIC solutions. We evaluated the performance of waveform inversion with just two broadband stations, and the result seems extremely reliable.

Inversion results indicate that the focal mechanism of the 8th Nov 2022 earthquake is a thrust fault type, and the obtained strike (283◦), dip (43◦), and rake (83◦) from the Present study are in accordance with CMT results of the USGS (strike (286◦), dip (58◦), and rake (97◦)) and NEIC (strike (285◦), dip (37◦), and rake (82◦)). The seismic moment is 1.583e+19 and the obtained DC% is 93% hence, the mechanism is considered to be Double-Couple. The identification of the source parameters is significant to the investigation of seismic hazards in this region.

How to cite: Mahto, P. and Gupta, S. C.: Source-Characterisation of two moderate-sized earthquakes in Nepal employing detailed Moment Tensor Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1428, https://doi.org/10.5194/egusphere-egu23-1428, 2023.

EGU23-1957 | Posters on site | SM7.2

Building Vulnerability Assessment using Artificial Intelligence forLandslide Susceptibility Zone in Champawat District, India 

Yaggesh Sharma, Arun Tyagi, Mukat Lal Sharma, Priyanka Sharma, and Ashish Aggarwal

The evaluation of the vulnerability of society aroused to landslide-related tragedy is an enlarged
topic. Few studies talk about this issue and limited research has been carried out on the
relationship between landslides and their potential impact on buildings and infrastructure.
Uttarakhand Province in India is a highly landslide-prone area in the Himalayan region. The
present study focused on assessing the building vulnerability for the landslide susceptibility zone
in the Champawat district of Uttarakhand state. The building footprint areas are identified by
using an image segmentation algorithm in artificial intelligence. Moreover, the landslide-prone
zone was identified based on the historical and recent information collected from various
authenticated sources and the field investigations made on the recent landslides whereas, more
than ten landslide causative parameters/landslide conditioning factors (LCF) have been used to
generate a susceptibility map. The frequency ratio method has been applied to carry out the
susceptibility zone in the entire study area. Most buildings are found in dangerous areas that are
highly correlated by using published and in-situ datasets.
Keywords: Landslide Susceptibility Zone, Artificial Intelligence, Vulnerability, Building Footprints

How to cite: Sharma, Y., Tyagi, A., Sharma, M. L., Sharma, P., and Aggarwal, A.: Building Vulnerability Assessment using Artificial Intelligence forLandslide Susceptibility Zone in Champawat District, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1957, https://doi.org/10.5194/egusphere-egu23-1957, 2023.

A critical part of planning and managing road infrastructures in mountainous regions is the
pragmatic assessment of the prevailing and credible landslides hazard. Such assessments assume
greater significance for the Himalayan region, where seismically induced landslides present a
greater threat than commonly recognized, and require a robust comprehension of two hazards:
earthquake and the landslides induced by the former. However, the traditional practice of
landslide hazard assessment often neglects seismic factor due to paucity of pertinent data, which
may further be ascribed to the rarity of an extreme event. In this context, an endeavor has been
made in this study to evaluate the seismically induced landslide hazard for a scenario earthquake
of 10% exceedance probability in 50 years for an important road corridor in the lower Indian
Himalayas using Fuzzy algorithms. Probabilistic Seismic Hazard Assessment (PSHA) has been
carried out for the study area to calculate the Peak Ground Acceleration (PGA) of the scenario
earthquake, which is then used as a landslide triggering factor. PGA is integrated with eight
different landslide controlling factors viz. lithology, slope angle, aspect, elevation profile,
distance form fault, distance from drainage, distance from road, and land-use-land-cover patterns
in a Geographical Information System (GIS). 232 numbers of landslides are mapped for the
study area using high resolution Google earth imagery platform. The Fuzzy Cosine Amplitude
method is used to define the degree of similarity (strength of correlation) between the observed
landslides (dependent variable) and the landslide causative factors (independent variable(s)).
Expectedly, the probability of landslide occurrence correlates (degree of similarity) to the PGA
in a linear pattern (goodness of fit = 0.9954). The result of the study is discussed in terms of a
seismically induced Landslide Hazard Zonation (LHZ) map for the study, which is generated
using three Fuzzy operators (AND, OR and GAMMA). The prepared LHZ map demarcates more
than 40% of the study area as the zones of high to very high landslide hazard under the scenario
earthquake, with a prediction accuracy of 80%. The study shows that probabilistically generated
PGA can be included as seismic parameter for a more comprehensive assessment of the landslide
hazard in seismically active regions.

Keywords: Fuzzy Cosine Amplitude, Probabilistic Seismic Hazard Assessment (PSHA), Peak
Ground Acceleration (PGA), Landslide Hazard Zonation (LHZ), the Himalayas

How to cite: Tyagi, A., Nath, R. R., and Chaurasia, S.: Application of Fuzzy Algorithm for Assessing Seismically Induced Landslide Hazard for an Important Road Corridor in the Lower Indian Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3041, https://doi.org/10.5194/egusphere-egu23-3041, 2023.

EGU23-3077 | ECS | Posters virtual | SM7.2

Probabilistic Seismic Hazard Assessment of Assam, North-East India with the Incorporation of Topography Based VS30 Values 

Mayuri Borah, Ramanand Dubey, and Josodhir Das

In this study, Probabilistic seismic hazard assessment (PSHA) is performed for Assam, North-East (NE) India. NE India being bounded by latitude 200-300 N and longitude 870-980 E, is considered as one of the most earthquake-prone areas in the world. As per seismic zoning map of India (IS 1893 (2016), Part 1), most of the states in NE region have been placed in seismic zone V, which has the highest zone factor in the country. Among the eight north-eastern states, Assam serves as the gateway to the other seven states. As this region lies on one of the most vigorous tectonic plates in the world, it has experienced several devastating earthquakes in the past. Considering the seismicity of this region, seismic hazard assessment plays a significant role to assess the seismic risk for the future. The NE India region is broadly divided into four seismogenic sources, and further sub-divided into nine seismogenic sources based on the tectonic features and seismicity characteristics. For the study of hazard assessment, a unified moment magnitude catalogue has been used, where the events are assembled from various databases (ISC, IMD, USGS-NEIC). The catalogue has been declustered and the seismicity parameters are calculated for each source zone. The hazard maps have been presented at the bedrock level, in terms of peak ground acceleration (PGA) and spectral acceleration (Sa) values. The PGA values vary in between 0.16-0.57 g, while the Sa values are obtained in the range of 0.12-0.77 g. Further, topography based VS30 values have been considered for all the source zones and hazard maps are prepared with the incorporation of the site-specific VS30 values. These hazard maps are expected to give insight to the local site-specific seismic hazard variation for the Assam region and would be useful for the preparedness of risk and disaster mitigation measures.

Keywords: PSHA, NE India, Assam, PGA, Hazard Map

How to cite: Borah, M., Dubey, R., and Das, J.: Probabilistic Seismic Hazard Assessment of Assam, North-East India with the Incorporation of Topography Based VS30 Values, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3077, https://doi.org/10.5194/egusphere-egu23-3077, 2023.

Time-averaged shear-wave velocity in the topmost 30 meters of soil (Vs30) is a broadly accepted tool employed for site characterization. Adoption of Vs30 in the development of region-specific ground motion prediction equations and seismic design provisions marked it as a global parameter for local-site effect studies. Challenges arise in tectonically complex regions where an evaluation of Vs30 requires great exertion including mobility of equipment and manpower. Over the period, where researchers are still engaged in studying the effects and limitations of Vs30 at a location of interest, during the years various proxies have arrived for Vs30 estimation. Also, the selection of proxy depends upon the existing prior information about the region and its relationship with measured Vs30 values. Data scarce region requires interpolation techniques to address extensive geographical area with limited attainable datasets. Various deterministic (Inverse distance weighing, spline, etc.)  and probabilistic (kriging formats) interpolation techniques are widely used for robust estimation. In this study, an attempt has been made for a reliable region-specific selection of interpolation techniques. 35 Vs30 measurements are used as primary data and the topographic-slope proxy-based Vs30 model by U.S. Geological Survey is used as secondary data. Quantitative assessment acknowledges the existence, and validity which provides an understanding of the merits and flaws of interpolation techniques. The applicability of IDW, kriging and Bayesian scheme for sturdy estimation of Vs30 with focus on Southern Bihar region is examined for seismic response studies providing paramount importance to hazard and risk mitigation.

Keywords: Vs30, Topographic-slope Proxy, IDW, Kriging, Bayesian Scheme.

How to cite: Srivastava, M. and Sharma, M. L.: Comparison of Deterministic and Probabilistic framework for Vs30 estimation in data scarce region: a case study for Southern Bihar, India., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4108, https://doi.org/10.5194/egusphere-egu23-4108, 2023.

The 9.12 Gyeongju earthquake(Sep. 12, 2016, Ml 5.8) and the Pohang earthquake(Nov. 15, 2017, Ml 5.4) have occurred in the Korean Penisula, resulting in emphasizing the stability of nuclear power plants. For safety evaluation, it is necessary to study the earthquake vulnerability caused by input ground motion. The input ground motion can be obtained from the earthquakes, and it is essential to acquire good quality and many samples input ground motion database for accurate evaluation. In this study, we tried to develop a platform that can automatically generate a ground motion database from past or real-time waveforms. To determine the detailed time window for data processing, deep learning-based earthquake detection, and phase-picking models were used. A voting method was conducted on these models to increase reliability in various environments. The platform produces a RotD50 5% damped pseudo-spectral acceleration, peak ground acceleration, and meta information related to site, hypocenter, and path. It also provides a web service to confirm generated data and meta information. The database generated by the platform could be used as input ground motion data to evaluate the safety of operating power plants and could be applied as fundamental data for the seismic design of planned nuclear power plants.

How to cite: Lee, J. K. and Seo, J.: A study on input ground motion processing platform for evaluating seismic fragilities using Deep Learning Phase Determination Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4709, https://doi.org/10.5194/egusphere-egu23-4709, 2023.

EGU23-4810 | ECS | Posters virtual | SM7.2 | Highlight

Lithospheric imaging beneath North India using surface wave tomography 

Deepak Kumar, Suresh Gaddale, Satish Maurya, and Subhash Chandra Gupta

We provide a shear wave velocity model of the Indo-Gangetic plain (IGP) that extends down to a depth of 100 km.  Using vertical component seismograms of 108 broadband (BB) stations (50 and 58) of IRIS-DMC and National Centre for Seismological (NCS) respectively, located in and around the Northern Indian plate. The group velocity dispersion of the Rayleigh wave has been picked along  ~3000 paths across the study region over a period range of 8 to 80s. To construct the 3D shear wave velocity structure, we employ a two-step surface wave tomography procedure. In the first step, regionalized dispersion maps are prepared for each period of correlation length of 60km, and subsequently, we employ the Markov chain Monte Carlo (McMC) trans-dimensional Bayesian inversion algorithm to obtain the shear wave velocity structure. In regionalized dispersion maps, at short periods (~8s) we see slow velocity in northern IGP and region reported thick basement (~6km) from previous studies. For moving towards increasing periods map indicate slow velocity anomalies in the Himalayan and Tibetan plateau region are associated with a thick crust (>50) in contrast to the typical crust (~40km) of IGP. The fast and slow velocities areas are identified which are associated with the Indian shield and thick crust in the Himalayas. Further, we inverted regionalized geographical locations to get shear wave velocity at each point to make a 3D lithospheric model. We have used 20 chains with 600k burn-in phase and 300k in the main phase for sampling the posterior distribution and from the final posterior distribution best 500k models with of 5% deviation has been selected after removing those model that has outlier chains with unrealistic models.

Keywords:  Surface waves, Bayesian inversion, Seismic tomography, Northwestern Himalayas.

How to cite: Kumar, D., Gaddale, S., Maurya, S., and Gupta, S. C.: Lithospheric imaging beneath North India using surface wave tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4810, https://doi.org/10.5194/egusphere-egu23-4810, 2023.

EGU23-5710 | ECS | Posters on site | SM7.2 | Highlight

Rapid source characterization of the Maule earthquake using Prompt Elasto-Gravity Signals 

Gabriela Arias, Quentin Bletery, Andrea Licciardi, Kevin Juhel, Jean-Paul Ampuero, and Bertrand Rouet-Leduc

The recently identified Prompt Elasto-Gravity Signals (PEGS), generated by large earthquakes, propagate at the speed of light and are sensitive to the earthquake magnitude and focal mechanism. These characteristics make PEGS potentially more accurate than P-wave based early warning algorithms (which produce saturated magnitude estimations) and faster than Global Navigation Satellite Systems (GNSS)-based systems. We use a deep learning model called PEGSNet, originally developed for application in Japan, to track the temporal evolution of the magnitude of the 2010 Mw 8.8 Maule earthquake. The model is a Convolutional Neural Network (CNN), trained on a database of synthetic PEGS -- simulated for an exhaustive set of possible earthquakes distributed along the Chilean subduction zone -- augmented with empirical noise. The approach is multi-station and leverages the information recorded on all the available stations to estimate as fast as possible the magnitude and location of an on-going earthquake. Our results indicate that PEGSNet could have estimated an  Mw > 8.7 earthquake after 100 seconds in the Maule case. Our synthetic tests using real data and noise recordings further support the instantaneous tracking of the source time function of the earthquake.

How to cite: Arias, G., Bletery, Q., Licciardi, A., Juhel, K., Ampuero, J.-P., and Rouet-Leduc, B.: Rapid source characterization of the Maule earthquake using Prompt Elasto-Gravity Signals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5710, https://doi.org/10.5194/egusphere-egu23-5710, 2023.

EGU23-6433 | Orals | SM7.2 | Highlight

Earthquake Early Warning with 3 seconds of records on a single station 

Pablo Lara, Quentin Bletery, Jean-Paul Ampuero, and Inza Adolfo

We introduce the Ensemble Earthquake Early Warning System (E3WS), a set of Machine Learning algorithms designed to detect, locate and estimate the magnitude of an earthquake using 3 seconds (or more) of P waves recorded by a single station. The system is made of 6 Ensemble Machine Learning algorithms trained on attributes computed from ground acceleration time series in the temporal, spectral and cepstral domains. The training set comprises datasets from Peru, Chile, Japan, and the STEAD global dataset. E3WS consists of three sequential stages: detection, P-phase picking and source characterization. The latter involves magnitude, epicentral distance, depth and back-azimuth estimation. E3WS achieves an overall success rate in the discrimination between earthquakes and noise of 99.9%. For P-phase picking, the Mean Absolute Error (MAE) is 0.14s. For source characterization, the MAEs for magnitude, distance, depth and back-azimuth are 0.34 magnitude units, 27 km, 15.7 km and 45.2°, respectively. By updating estimates every second, the approach gives time-dependent magnitude estimates that follow the earthquake source time function. E3WS gives faster estimates than present alert systems, providing additional valuable seconds for potential protective actions.

How to cite: Lara, P., Bletery, Q., Ampuero, J.-P., and Adolfo, I.: Earthquake Early Warning with 3 seconds of records on a single station, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6433, https://doi.org/10.5194/egusphere-egu23-6433, 2023.

EGU23-8376 | ECS | Orals | SM7.2

Understanding dynamics of ground movement based on seismic monitoring 

Deepak rawat and Mukat lal sharma

Given the unique geology, topography, and hydrology of the Himalayas, it is imperative that a long-term strategy be developed to reduce the destructive potential of landslides in the region. Monitoring and an early warning system for landslides are the best non-structural measures for preventing landslide disasters. The study's overarching objective is to highlight why it's crucial to keep an eye out for landslides and how seismic sensor arrays can be used to issue early warnings. The implications of large mass flows in the study area must be carefully considered for sustainable hydropower and other socio-economic development projects. Seismic data, satellite imagery data, Time-Frequency analysis (TFA), and videos and photos taken by eyewitnesses form the basis of our investigation.

First, we gather precise event data, and then we collect signals from the seismology observatory at the Indian Institute of Technology Roorkee for that time frame. The signals from the collection have been processed with signal processing methods like STA/LTA, Filtering, and TFA. One synthetic signal, two landslide events, and two local earthquakes were analyzed to better comprehend the dynamics and behavior of a natural distractive event.

Seismic records reveal that various types of events have distinctive dynamic properties. There are three distinct stages to a landslide event: (1) the detachment of slope-forming materials, (2) the debris flow, and (3) the flood flow. The P and S waves, the onset and end times, and the duration of an earthquake have all been determined. We have used synthetic signals to learn about TFA and have found the method that works best for interpreting seismic signals. We use the classification method developed by Provost et al. in 2017. Time-domain amplitude levels are a feature that can be easily extracted and classified, but they are also vulnerable to noise. Energy concentration in the time-frequency domain is one such method that, while requiring more complex operations, can lead to more trustworthy feature extraction and accurate classification. The absence of the distinct P- and S-wave arrival time, as is typical of earthquakes, is another feature of the seismic waveform that is indicative of a landslide. The results of the seismic record analysis also shed light on the breadth of monitoring for slope-moving disaster events in the North-West Himalayas.

How to cite: rawat, D. and sharma, M. L.: Understanding dynamics of ground movement based on seismic monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8376, https://doi.org/10.5194/egusphere-egu23-8376, 2023.

EGU23-9036 | ECS | Orals | SM7.2

Simulation of ground motions with high frequency components obtained from Fourier neural operators 

Tariq Anwar Aquib and Paul Martin Mai

Seismic hazards analysis relies on accurate knowledge of ground motions arising from potential earthquakes to assess the risk of damage to buildings and infrastructure. It is necessary to perform ground motion simulations because recorded strong-motion data from specific combinations of earthquake magnitudes, epicentral distances, and site conditions are still limited. Physics-based simulations provide reliable ground motion estimates, but their application in practice is limited to frequency ranges f < 1Hz, largely due to limited computational resources and lack of information regarding earthquake sources and medium. While hybrid ground-motion computations combining deterministic low frequency components with stochastic high frequency components are often used,  their stochastic high frequency components fail to correctly account for source and path effects and lead to inconsistent building responses.

The large database of ground motion records from Japan lends itself to develop machine learning approaches to estimate high frequency ground motions. Applying state-of-the-art machine learning techniques, like Fourier neural operators (FNOs) and Generative Adversarial Networks (GANs), we estimate seismograms at higher frequencies from their low frequency counterparts. In our approach, the time and frequency properties of ground motions are estimated using two different FNO models. In the time domain, a relationship is established between normalised low pass filtered and broadband waveforms. Frequency domain analysis involves the learning of high frequency spectrum from low frequency spectrum. Finally, the time and frequency properties are combined to produce broadband ground motions. Source, site, and path aspects are naturally incorporated into the training process.

We use ground motion data collected between 1996 and 2020 at 18 stations in the Ibaraki province of Japan to train our models and validate them on different events (Mw 4 to 7) around Japan. Using goodness of fit measures (GOFs), we show that the resulting ground motions match the recorded observations with good to acceptable GOF values for most of the predictions. To enhance our predictions, we include uncertainty estimation by utilizing a conditioned GAN approach. Lastly, to demonstrate the practicality of the approach, we compute high frequency components for a physics based simulated hypothetical Mw 5.0 earthquake in Japan.

How to cite: Aquib, T. A. and Mai, P. M.: Simulation of ground motions with high frequency components obtained from Fourier neural operators, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9036, https://doi.org/10.5194/egusphere-egu23-9036, 2023.

Recently, various attempts for earthquake detection and seismic observation using low-cost vibration sensors are being actively conducted, and among them, MEMS and Geophone are the most frequently attempted sensors. MEMS and Geophone sensors have different characteristics and strengths and weaknesses, and it is necessary to understand them to select a sensor suitable for the purpose. In this study, MEMS and Geophone sensors were compared and tested for P-wave detection for earthquake early warning and ground and structure earthquake motion observation. For this purpose, the two types of sensors were mounted together on one aluminum plate, vibration table tests were conducted, and earthquake detection results were compared through real-time earthquake detection over several months. Through this, only for the tested sensor models, we could conclude that Geophone is suitable for P-wave detection and pattern extraction for noise classification, and MEMS is suitable for strong vibration measurement.

How to cite: Seo, J. B.: Comparison of Characteristics of MEMS and Geophone Sensors for Earthquake Detection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10532, https://doi.org/10.5194/egusphere-egu23-10532, 2023.

EGU23-10932 | ECS | Posters virtual | SM7.2

Scenario Seismic Risk assessment of 1934 Bihar-Nepal Earthquake 

CLal lawmawma and Mukat Lal Sharma

This paper presents seismic risk assessment of Bihar considering a hypothetical earthquake event similar to 1934 Bihar-Nepal earthquake. Assessment of risk has been carried out for all districts of Bihar and risk is presented in terms of economic loss. The loss estimation is performed through the combination of seismic hazard, structural vulnerability, and exposure data. Regarding the seismic input, a non-linear probabilistic approach is used to estimate the hypocenters of 1934 Bihar-Nepal earthquake and other source parameters are taken from literature. Abrahamson and Silva (2014) ground motion prediction equation is used to generate the strong ground motion at the surface level. Building exposure data are based on national census survey of India 2011. The census data provides common building typologies for each district and their relative distribution. On the basis of wall material used for construction all the buildings are grouped into four class, and seismic vulnerability functions (Martin and Silva,2011) are assigned to each building class. For each districts, total number of buildings are aggregated at the location of the maximum ground motion.  The area per building class has been assumed and reconstruction costs per square metre for each districts have been assigned based on local expert input and values identified in the literature. Finally, the district level distribution of economic loss for this earthquake scenario is obtained using the OpenQuake-engine. From this study, the expected economic loss is highest in Madhubani district followed by Muzzafarpur, Dharbanga and Sitamarhi district. Un-reinforced masonry buildings type construction, most prevalent in the rural region would experience maximum loss. A repeat of 1934 Bihar-Nepal earthquake in present day would have devastating consequences, although this scenario addresses a hypothetical event, the seismic risk assessment constitute important tools for framing public policies toward land-use planning, building regulations, insurance, emergency preparedness and could eventually minimizes economic disruption caused by earthquake.

How to cite: lawmawma, C. and Sharma, M. L.: Scenario Seismic Risk assessment of 1934 Bihar-Nepal Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10932, https://doi.org/10.5194/egusphere-egu23-10932, 2023.

EGU23-11549 | ECS | Orals | SM7.2

Ground Motion Model For Data Sparse Regions: Machine Learning Approach 

Vemula Sreenath, Jahnabi Basu, and Raghukanth stg

Ground motion models (GMMs) to the recorded ground motion time histories are essential input to the hazard analysis. With recent vast array of strong motion instruments to seismically active regions such as Japan, California, and Mexico, large amounts resulted in abundant recorded data huge metadata. Several global and regional GMMs are developed with these strong motion datasets. However, many active regions (e.g., The Himalayas) are in dearth of recorded strong motion data and metadata to develop predictive models. Despite recent instrumentations by different networks to the Himalayan region, the problem of near-field strong-motion records resulting from sparse instrumentation is the key concern. Traditionally, stochastic models are used in developing GMMs, as developing empirical models with limited data is challenging. Additionally, GMMs developed to other data-rich regions with similar tectonics are used in the hazard estimations. Thus, developing predictive models to these data-poor regions is a key concern which needs to be addressed. In the current work, we address this problem from the data-driven approach such as neural network. Neural networks learn the functional form from the data during training making it suitable for our present problem. Magnitude, epicentre distance, hypocentre depth, and shear wave velocity flag are used as inputs to estimate both the horizontal and vertical response spectra. In this regard, we attempt several approaches in developing the GMM using shallow neural network. Initially we develop model with seven neurons in the hidden layer using the available regional Western Himalayan crustal data and as one expects the model scaled poorly at the near-field. The obtained mean squared error (MSE) mean absolute error (MAE), and coefficient of determination (R2) are 0.6858, 0.6504, and 0.7592, respectively. To address this lack of near-field data, we supplement our regional data with records from global near-field strong motion and in developing GMM. This model has seven neurons in the hidden layer and performed better than the previous model but still had scaling issues at the large magnitude near-field. Further, supplementing data from other regions would influence the predictions. The obtained MSE, MAE, and R2 of the combined database are 0.5690, 0.5830, and 0.8659, respectively. However, the MSE, MAE, and R2 of the Western Himalaya data are 0.8006, 0.7057, and 0.7216, respectively. Finally, we use transfer learning technique: we develop GMM to the global crustal data and global near-field data and use it as a base model to develop GMM with six neurons in the hidden layer using the Western Himalayan data. The obtained MSE, MAE, and R2 of the Western Himalayan database are 0.8688, 0.7282, and 0.6970, respectively. Despite large error compared to previous two models, this model could capture large magnitude near-field effects and distance scaling effects and performed better than the previous two models. We conclude that transfer learning could be used to regions with limited strong motion data in developing GMM.

How to cite: Sreenath, V., Basu, J., and stg, R.: Ground Motion Model For Data Sparse Regions: Machine Learning Approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11549, https://doi.org/10.5194/egusphere-egu23-11549, 2023.

EGU23-11563 | ECS | Posters virtual | SM7.2

Deterministic Seismic Hazard Assessment by revisiting 1991 Uttarkashi and 1999 Chamoli Earthquake for Uttarakhand, India 

Yaggesh Sharma, Mudit Srivastava, Priyanka Sharma, and Deepak Kumar

Deterministic Seismic Hazard Assessment is a quantitative site-specific evaluation of ground response for a particular region. Destructive effects caused due to occurrence of natural seismic hazards can be minimized by accounting mindful mitigation measures. One of the fundamental phases in risk assessment is the précised determination of the risk over a certain period. Considering the earthquake rupture model and a couple of defined region-specific ground motion models as input, earthquake scenarios to determine peak ground acceleration (PGA) and spectral periods (SA) are examined. In the present study, the Topographic slope as a proxy for shear wave velocity in upper soil of 30-meter (Vs30) estimation is assessed for rapid prediction and first-order studies. Further, two distinct major earthquake scenarios, the 1991 Uttarkashi and 1999 Chamoli earthquakes are revisited to estimate the distribution of PGA and SA at 0.2 sec and 1 sec for the area of interest. Thus, obtained results for Uttarakhand are presented in terms of Vs30, PGA, 0.2 sec, and 1-sec spectral values respectively.

Keywords: Deterministic seismic hazard, Vs30, 1991 Uttarkashi, 1999 Chamoli, scenario earthquakes, PGA, SA.

How to cite: Sharma, Y., Srivastava, M., Sharma, P., and Kumar, D.: Deterministic Seismic Hazard Assessment by revisiting 1991 Uttarkashi and 1999 Chamoli Earthquake for Uttarakhand, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11563, https://doi.org/10.5194/egusphere-egu23-11563, 2023.

EGU23-15028 | Orals | SM7.2 | Highlight

Temporal variation of Qc and its implications in medium characterization 

Subhash Chandra Gupta, Mukat Lal Sharma, Sanjay Kumar Jain, and Arup Sen

The heterogeneities in the medium play important role not only in earthquake genesis but also strong ground motion simulation due to its bearing on attenuation characteristics. Observational data is one of the prerequisites for such studies which are acquired through deployment of seismological networks in active seismic regions. The Himalaya is considered as one of the most seismically active region in the world. It is also source of many river valley projects, like Tehri dam and others. The Tehri dam with 260.5 meter height is highest dam in India, located in the Lesser Himalaya of the Garhwal Himalaya that lies in seismic zone IV as per the seismic zoning map of India. Besides this, a number of development activity such as road and railway infrastructures are in progress. Thus, there is need to understand the effect of physical state of media on propagation of seismic waves in the Himalayas. The medium/path characteristics of this  region has been measured by determining the seismic wave attenuation of high frequency waves of local earthquakes which is accomplished by estimating the quality factor of coda waves (Qc). In the present study, Qc, has been determined using local earthquakes recorded during last fourteen years from 2008 to 2021. The local earthquakes used in the study have been obtained through deployment of 12 to 18 stations local seismological network around Tehri dam reservoir. The results showed in the study that there is no significant change in Qc is observed in the region during this period after dam impoundment. These results found in agreement with the findings that no reservoir trigger seismicity is observed in the region associated with Tehri dam reservoir during last sixteen years.

How to cite: Gupta, S. C., Sharma, M. L., Jain, S. K., and Sen, A.: Temporal variation of Qc and its implications in medium characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15028, https://doi.org/10.5194/egusphere-egu23-15028, 2023.

EGU23-15719 | Orals | SM7.2

Development of an hybrid GMPE-less ShakeMap implementation for real-time ground shaking  maps reconstruction 

Simone Francesco Fornasari, Veronica Pazzi, and Giovanni Costa

Ground shaking maps are an essential tool for seismic monitoring and civil defence operations as they provide information about the area and amplitude of the ground motion relative to a seismic event.

Such maps are developed integrating spatially sparse data recorded by the stations, which also provide a constraint to the process, and theoretical values obtained from ground motion prediction equations (GMPEs), given the magnitude and location of the earthquake, also accounting for local site effects.

One of the problems arising during the development of a real-time implementation of these techniques is the lack of information in real-time needed to compute the GMPE.

One possible solution to the problem is to develop algorithms that can constrain the interpolation process using only the ground motion parameters recorded at the stations (Fornasari et al., 2022).

We propose a hybrid model combining the conditioned multivariate normal distribution (MVN; Worden et al., 2018) technique adopted by ShakeMap and a neural network replacing the GMPE.

The neural network provides a purely data-driven approximation of the GMPE results based only on the spatially sparse data from the stations, with possible correction for the site effects. 

The network is trained using a supervised approach with labelled data obtained from GMPEs used for the Italian territory. Moreover, by limiting the use of a neural network to a specific task we improve its explainability with respect to end-to-end models.

This approach is easily integrable into the existing workflow, combines the well-studied interpolation techniques and neural networks in a clearly explainable structure, and provides high-resolution estimates of the ground-shaking fields in real-time with potential relevance in the context of early warning.

 

References:

Simone Francesco Fornasari, Veronica Pazzi, Giovanni Costa; A Machine‐Learning Approach for the Reconstruction of Ground‐Shaking Fields in Real Time. Bulletin of the Seismological Society of America 2022; 112 (5): 2642–2652. doi: https://doi.org/10.1785/0120220034.

C. Bruce Worden, Eric M. Thompson, Jack W. Baker, Brendon A. Bradley, Nicolas Luco, David J. Wald; Spatial and Spectral Interpolation of Ground‐Motion Intensity Measure Observations. Bulletin of the Seismological Society of America 2018; 108 (2): 866–875. doi: https://doi.org/10.1785/0120170201

How to cite: Fornasari, S. F., Pazzi, V., and Costa, G.: Development of an hybrid GMPE-less ShakeMap implementation for real-time ground shaking  maps reconstruction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15719, https://doi.org/10.5194/egusphere-egu23-15719, 2023.

EGU23-16903 | Posters virtual | SM7.2

Evaluating Seismic Hazard based on Simulated Earthquake Strong Ground Motions in Himalaya 

Dinesh Kumar, Anjali Sharma, and Renu Yadav

The importance of site-specific earthquake strong ground motions for the proper evaluation of seismic hazard of a region has now been well recognized.  It is useful to generate site-specific ground motions required for the designing of earthquake resistant buildings in seismic active regions as required number of observed records are not available at all the sites of interest.  The simulated time histories enhance the sparse data base of observed accelerograms which is useful for improving seismological understanding of an earthquake process.  Most of the earthquakes in Indian region occur in Himalaya which is the result of collision of northward drifting Indian plate with Eurasian plate.  The seismic hazard is severe in the region of Himalaya.  The first step to mitigate the seismic hazard is to evaluate the same.

In the present study, the seismic hazard has been estimated in the regions of Himalaya using simulated strong ground motions from earthquakes.  A modified hybrid technique has been used for the simulation of earthquake strong ground motions. In this technique a composite source model (Zeng et al, 1994) has been combined with semi-empirical envelope technique (Midorikawa, 1993).  In the technique, the envelope function of target earthquake is computed by summation of envelope functions that are generated from small size earthquakes distributed randomly on the fault plane. In order to simulate the ground motions at surface level, the high frequency decay parameter and site amplification functions have been taken into account.

The strong ground motions have been simulated at large number of points distributed spatially in the region.  The scenario hazard maps in the form of spatial distribution of peak ground acceleration values have been presented due to a great earthquake (M 8.5) in Central Seismic Gap of Himalaya and a major earthquake (M 6.9) in NE Himalaya.  The scenario hazard maps prepared in the present study may be useful to the local administrators for the mitigation of the earthquake hazard in the region.  These maps give the idea about the possible scenario in case of similar size future earthquake occurs in the region. The maps presented here are useful to mitigate the seismic hazard from the region.

How to cite: Kumar, D., Sharma, A., and Yadav, R.: Evaluating Seismic Hazard based on Simulated Earthquake Strong Ground Motions in Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16903, https://doi.org/10.5194/egusphere-egu23-16903, 2023.

EGU23-346 | ECS | Orals | NH4.2

Seismic Risk Assessment of Natural Gas Networks considering Cascading Effects 

Chen-Yu Nieh and Szu-Yun Lin

Earthquake disasters may not only damage buildings but significantly influence the standard of living due to the impacts on critical infrastructure such as lifeline systems. This study focuses on the seismic risk and resilience of the natural gas network and the cascading effects. We analyze the risk of failure in the mid/low-pressure pipelines under a major earthquake scenario and evaluate the impacts on systemic service levels considering the secondary disasters of earthquakes. In this study, repair rate, R.R., is applied to evaluate the failure of natural gas pipeline. With the R.R. of pipelines and ground motion parameters, e.g., PGA and PGD, the failure probability of the pipeline can be derived by Poisson distribution. By overlay analysis with seismic parameters from Taiwan Earthquake Loss Estimation System (TELES) and the GIS data of the natural gas network, the number of damaged pipelines, the number of affected users, and the closure probability of valves can be estimated through Monte Carlo simulation. The service level and resilience of the system can be further assessed. In addition to the impacts on the natural gas system, the leaking gas can also cause a potential risk of worsening post-earthquake fire. On the other hand, the repairment of damaged pipelines may affect the surrounding traffic. These should be considered during the restoration process. This study proposes a risk assessment approach for the natural gas pipeline subjected to earthquakes considering not only the physical damage of the pipeline but the closure of valves, the risk of worsening post-earthquake fire, and the sequential influence on the traffic. The proposed framework was applied to the natural gas system in Tainan, Taiwan, as the case study. This study assesses the earthquake hazard risk of natural gas pipelines from the perspective of system functionality and community resilience. Decision-makers can plan appropriate disaster mitigation strategies based on the analysis results.

How to cite: Nieh, C.-Y. and Lin, S.-Y.: Seismic Risk Assessment of Natural Gas Networks considering Cascading Effects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-346, https://doi.org/10.5194/egusphere-egu23-346, 2023.

Seismic hazard assessment (SHA) and associated risks (SRs) require necessarily an adequate understanding of earthquake distribution in magnitude, space, and time at regional scale. The Neo-Deterministic Seismic Hazard Assessment (NDSHA) is the innovative multi-disciplinary scenario-physics-based approach for reliable evaluation of seismic hazard and risks, which have been developed to overcome evident shortcomings of the outdated and very often wrong Probabilistic Seismic Hazard Analysis (PSHA). The NDSHA applications in many countries worldwide (Panza et al., 2021) pass intensive testing by instrumental and historical evidence, as well as by realistic modelling of scenario earthquakes. NDSHA results confirm reliable and effective input for mitigating object-oriented SRs. We applied two agents of the NDSHA synergy, i.e. Unified Scaling Law for Earthquakes (USLE) and anisotropic propagation of seismic effect, to evaluate SRs for the railway infrastructure in the Lake Baikal region.

USLE states that the logarithm of expected annual number of earthquakes of magnitude M or larger in an area of linear dimension L follows within the magnitude range [M– , M+] the relationship log N(M, L) = A + B×(5 − M) + C×log L, where A, B and C are constants. Naturally, A and B are analogous to the a- and b-values of the classical Gutenberg-Richter relationship (G-RR), while C compliments to G-RR with an estimate of local fractal dimension of earthquake epicentres allowing for realistic rescaling seismic hazard to the size of exposure at risk. USLE implies that the maximum magnitude MX expected with p% chance in T years can be obtained from N(MX, L) = p%, then used for estimating ground shaking effect.

We used as essentials (i) macroseismic intensity scale that provides a robust estimate for realistic modelling of maximal potential ground shaking in assessment of regional seismic hazard and associated risks and (ii) anisotropic propagation of seismic effect that is evidently following, in most cases of large earthquakes, dominant direction of active faults nearby epicentre and apply these to the earthquake catalogue compiled at the Baikal Division of the Geophysical Survey, Federal Research Centre of the Russian Academy of Sciences (http://www.seis-bykl.ru/), Active Faults of Eurasia Database (http://neotec.ginras.ru/database.html) and data on railroads from the OpenStreetMap project (https://www.openstreetmap.org).

We present the SRs for railway lines, hubs and tunnels in the Lake Baikal region based on the maps of maximum macroseismic intensity expected in a period of 50 years with a probability of 10%, 5% and 1% (Nekrasova&Kossobokov, 2022) and different model vulnerability functions attributed to the exposed infrastructure elements of different kind.

The study is carried on in the framework of the Russian State Task of Scientific Research Works of IEPT RAS and IPE RAS.

 

References

Nekrasova A, Kossobokov V (2022) Seismic risk assessment for the infrastructure in the regions adjacent to the Russian Federation Baikal–Amur Mainline based on the Unified Scaling Law for Earthquakes. Natural Hazards, https://doi.org/10.1007/s11069-022-05750-9

Panza G, Kossobokov V, De Vivo B, Laor E (Eds) (2021) Earthquakes and Sustainable Infrastructure: neo-deterministic (NDSHA) approach guarantees prevention rather than cure. Elsevier, xxv, 672 p. https://doi.org/10.1016/C2020-0-00052-6

How to cite: Nekrasova, A., Kossobokov, V., and Podolskaia, E.: Seismic risk assessment of the Lake Baikal railway infrastructure based on Unified Scaling Law for Earthquakes and anisotropic seismic impact, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1710, https://doi.org/10.5194/egusphere-egu23-1710, 2023.

EGU23-1870 | Posters on site | NH4.2

Characterization of Earthquake Clustering in Contractional Regions, based on Nearest-Neighbor distances and Network Analysis 

Antonella Peresan, Mohammad Talebi, and Mehdi Zare

The features of earthquake clusters in two contactional domains, located in Northeastern Italy and North-Central Iran, have been investigated. The tectonic and seismicity of the two study areas, namely the Alps-Dinarides junction and the Alborz regions, are controlled by the convergence between the African and Arabian plates and the Eurasia plate. Both regions are characterized by a rather complex structural setting, mainly including reverse and strike-slip faulting systems, and by moderate to high seismic activity.

The nearest-neighbor approach has been used for the identification of the earthquake clusters in the space-time-energy domain. This approach permits for a data-driven identification of clusters so that, within multi-event clusters, the features of secondary and higher orders dependent events can be explored. The investigation of seismicity in Northeastern Italy is based on bulletins compiled at the National Institute of Oceanography and Applied Geophysics (OGS) in 1977-2018, while in North-Central Iran the dataset was extracted from the catalog compiled by the Iranian Seismological Center (IRSC) for the period 1996-2022. According to preliminary analysis of the used earthquake catalogs, two corresponding regions have been identified, where a satisfactory completeness level is assessed for events with magnitude greater than 2.0. Robust values of the scaling parameters, namely the b-value and the fractal dimension of epicenters, have also been computed and are used to calculate the nearest-neighbor distances and to identify the earthquake clusters.

The results obtained in the two regions confirm that the complexity of clusters structure depends on the tectonic, structural, and geophysical properties of the area. Moreover, the complexity measures, borrowed from network theory (i.e. the Centralization and Outdegree indexes), consistently capture the complexity of the identified clusters. Besides, in both investigated regions, the results allowed us identifying two macro-areas, which are characterized by different clustering features, namely: high complexity indexes,, which indicate simple (burst-like) structure of clusters, and low complexity indexes, corresponding to complex multi-level (swarm-like) structure of clusters. Specifically, we found that "swarm-like" (high complexity) sequences are prevalent along the thrust faulting Alpine and Central-West Alborz systems, whereas "burst-like" (low complexity) sequences prevail along the strike-slip Dinaric and Central-East Alborz domains.

How to cite: Peresan, A., Talebi, M., and Zare, M.: Characterization of Earthquake Clustering in Contractional Regions, based on Nearest-Neighbor distances and Network Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1870, https://doi.org/10.5194/egusphere-egu23-1870, 2023.

EGU23-1897 | Posters on site | NH4.2

Theoretical analysis of the productivity of seismic events 

Elisa Varini, George Molchan, and Antonella Peresan

We investigate earthquake clustering, a prominent feature of seismic catalogs, in terms of distribution of the number of triggered events as described by a branching process (Kagan and Knopoff, Phys. Earth Planet. Inter., 1976; Saichev et al., Pure Appl. Geophys., 2005, and references therein). According to recent literature (e.g. Shebalin et al., Geophys. J. Int., 2020, and references therein), the productivity of a magnitude m event is defined as the number of triggered events of magnitude above m-Δ, where Δ is a positive default value. For a magnitude m event, we distinguish between the number of its direct descendants and the total number of its descendants, denoted respectively by the random variables v and V, both depending on Δ. Empirical analysis often testifies in favor of the identity of the type of distribution of both quantities (v and V) associated with the main event, and hypothetically is exponential. The testing or substantiation of this hypothesis is important for modeling seismicity and presents a serious challenge for seismic statistics.

In the standard Epidemic Type Aftershock Sequence – ETAS – model (Ogata, Ann. Inst. Stat. Math., 1998), the distribution of v is Poissonian. Therefore we consider the general ETAS model adapted to any distribution of v and prove that the branching structure of the model excludes the possibility of having a common distribution type (for example, Poisson or exponential) for both v and V at once  (Molchan et al., Geophys. J. Int., 2022). The second theoretical result relates to the behaviour of the tails of the productivity distribution. We show that there is a fundamental difference in tail behavior of the V-distributions for general-type clusters and for clusters with a dominant initial magnitude:  the tail is heavy in the former case and light in the latter. The real data display similar behavior. Theoretical conclusions are also illustrated through the analysis of a synthetic earthquake catalog.

How to cite: Varini, E., Molchan, G., and Peresan, A.: Theoretical analysis of the productivity of seismic events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1897, https://doi.org/10.5194/egusphere-egu23-1897, 2023.

EGU23-5879 | ECS | Posters virtual | NH4.2

b- value mapping in Sikkim and adjoining Himalayas 

Maitreyi, Chandrani Singh, Arun Singh, Mita Uthaman, Abhisek Dutta, Gaurav Kumar, and Arun Kumar Dubey

The b-value in the frequency-magnitude relation is one of the fundamental seismological parameters to define an assemblage of earthquakes. This study focuses on the use of b-value as a precursor to know the chances of occurrence of major earthquake events in Sikkim and adjoining Himalayas. A catalogue containing 9192 earthquakes (M ≥ 0.30) recorded across Nepal, Sikkim and Bhutan Himalayas during 1980-2022 is considered for the present study. The study area has been divided into three blocks encompassing Nepal, Sikkim and Bhutan segments and the b-values are computed. The results show variations in b-value across these three blocks which might be associated with the differential stress pattern across the regions. Further, we map the spatial variation of frequency-magnitude distribution by dividing the entire region into 0.1⁰ x 0.1⁰ grids. The grids with less than 30 earthquake events are excluded to ensure the reliability of our results. The results suggest that the entire segment belongs to a high stressed region. The lowest b-values are mostly observed in Sikkim and western Nepal, reflecting the possible zones of future earthquakes.

How to cite: Maitreyi, , Singh, C., Singh, A., Uthaman, M., Dutta, A., Kumar, G., and Kumar Dubey, A.: b- value mapping in Sikkim and adjoining Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5879, https://doi.org/10.5194/egusphere-egu23-5879, 2023.

At present, seismic prediction technology is still not available. Scientific decision-making and rescue after an earthquake are the main means of mitigating the immediate consequences of earthquake disasters. If earthquake emergency response level, fatalities, and economic losses can be estimated rapidly and quantitatively, this estimation will provide timely, scientific guidance to government organizations and relevant institutions to make decisions on earthquake relief and resource allocation, thereby reducing potential losses and more conducive to the implementation of social activities such as post-disaster reconstruction and reinsurance. To achieve this goal, a rapid earthquake disaster loss estimation method is proposed herein, based on a combination of physical simulations and empirical statistics. The numerical approach was based on the three-dimensional curved grid finite difference method (CG-FDM), implemented for graphics processing unit (GPU) architecture, to rapidly simulate the entire physical propagation of the seismic wavefield from the source to the surface for a large-scale natural earthquake over a 3-D undulating terrain. Simulated seismic intensity data were used as input for the earthquake disaster loss estimation model to estimate the fatality, economic loss, and emergency response level. The estimation model was developed by regression analysis of the data on human loss, economic loss, intensity distribution, and population exposure from the composite damaging earthquake catalog. We used the 2021 Ms 6.4 Yangbi earthquake as a study case to provide estimated results. The number of fatalities estimated by the model was in the range of 0–10 (five expected fatalities). The most probable economic loss range was 1–10 billion RMB (the expected economic loss was 4.862 billion RMB). Therefore, Level IV earthquake emergency response plan should have been activated (the government actually overestimated the damage and activated a Level II emergency response plan). The local government finally reported three deaths and 3.32 billion RMB economic losses during this earthquake, which is consistent with the model predictions.

How to cite: Li, Y., Zhang, Z., Wang, W., and Xin, D.: Rapid Estimation of Earthquake Disaster Loss Based on Physical Simulation and Empirical Statistics—A Case Study of the 2021 Yangbi Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7690, https://doi.org/10.5194/egusphere-egu23-7690, 2023.

EGU23-10882 | Posters on site | NH4.2

Deconvolution of site effects in ground-motion using site response function derived from HVSR method 

Byeong Seok Ahn, Tae-Seob Kang, and Hyun Jae Yoo

Site effects caused by unconsolidated sediments laying on the bedrock amplify or attenuate ground motions propagated to the surface. Site effect is unique site-by-site, and thus, makes analyzing actual attenuation characteristics of ground motions difficult. In the southern Korean Peninsula, 17 seismic stations administered by KMA and KIGAM were equipped with a pair of accelerometers; one is installed at the surface, and the other at the borehole (namely SB station). We estimate the site response functions of the stations using ambient noise data. First, the horizontal-to-vertical spectral ratios (HVSR) of the stations were calculated. Then, calibration ratios to adjust the amplitude of HVSR to that of surface-to-borehole spectral ratio (SBSR) were estimated and applied to the amplitude of HVSR. These amplitude-corrected HVSRs are used as the site response function to correct linear site effects in ground motions. To deconvolve the site effect of ground motions, we designed linear zero-phase FIR filters based on the site response functions. Then we divided the spectral amplitudes of the ground motions by the frequency response of the FIR filter. For the SB stations, site response functions of ten stations were obtained, and ground-motion data of 39 events with ML > 2 were corrected using these site response functions. In the result, the peak ground motion (PGA) of corrected ground motions at the surface was reduced by 20-76% on average compared to raw ground motions. Comparing ground motions of the borehole and surface sensors, the corrected PGA of the surface was 1.8-4.9 times bigger than the raw PGA of the borehole. For the whole surface stations of 176, the site-response functions of 75 stations were estimated, and ground-motion data of 210 events with ML > 3 were corrected by their site-response functions. We found that surface ground motions are deamplified to the level of borehole ground motions through the site effect correction.

How to cite: Ahn, B. S., Kang, T.-S., and Yoo, H. J.: Deconvolution of site effects in ground-motion using site response function derived from HVSR method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10882, https://doi.org/10.5194/egusphere-egu23-10882, 2023.

EGU23-11178 | Orals | NH4.2

Time-dependent Seismic Hazard Parameters Evaluation with SHAPE MATLAB Package 

Konstantinos Leptokaropoulos

Seismic processes can be often time dependent at different time scales. Earthquake interactions (e.g., static and dynamic stress changes), anthropogenic activities (e.g., mining, fluid injection, hydrocarbon exploitation) fluid dynamics (e.g., in geothermal fields and volcanic areas) and periodic phenomena (e.g., earth and ocean tides) result to changes in frequency and magnitude distribution of earthquakes. These changes apply in a wide range of time scales from seconds to decades and their evaluation is vital, for seismic hazard assessment in the vicinity of urban and industrial areas. In addition, such estimates can be used in industrial sites to facilitate production optimization, and they also may offer better insights for the underlying physical mechanisms of seismogenesis (e.g., stress transfer, fluid migration pathways and pore pressure, chemical alteration and frictional properties in depth).

SHAPE (Seismic HAzard Parameters Evaluation), is an open source toolbox, based on MATLAB, developed within the SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe) Project, and is available for use by seismologists and other scientists and engineers in related fields. SHAPE probabilistically estimates the time-dependent, source components of seismic hazard, namely the magnitude distribution and the seismic activity rates, expressed jointly as changes in the exceedance probability of a given magnitude within a predefined period. Alternatively, the changes of the mean return period of a given magnitude is evaluated in moving time windows. Four different magnitude distribution models are included (unbounded and truncated Gutenberg-Richter law and non-parametric kernel). Interactive parameter selection and data filtering routines are also incorporated in the package.

The presentation will cover the capabilities of SHAPE and a demonstration of selected examples from published and ongoing case studies:

  • Mining induced seismicity at Rudna Mine, Poland.
  • Seismicity triggered by water reservoir impoundment in Song Trahn 2 artificial lake, Vietnam.
  • Tidal triggering of microseismicity recorded by an ocean bottom seismometer network in the equatorial mid-Atlantic ridge.

The SHAPE package is developed in two standalone versions (an interactive Graphical User Interface version and a function) as well an online version, integrated in the Thematic Core Service Anthropogenic Hazards (TCS-AH) of the European Plate Observing System (EPOS). The standalone versions can be downloaded for free from a public repository.

How to cite: Leptokaropoulos, K.: Time-dependent Seismic Hazard Parameters Evaluation with SHAPE MATLAB Package, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11178, https://doi.org/10.5194/egusphere-egu23-11178, 2023.

EGU23-12679 | Orals | NH4.2 | Highlight

Advancing exposure modelling from seismic risk to multi-hazard analysis in urban and metropolitan areas 

Massimiliano Pittore, Juan Camilo Gomez Zapata, Christian Geiß, Piero Campalani, and Kathrin Renner

Exposure modelling is a critical factor in the assessment of risk from natural hazards. Athough often its role has been overshadowed by other risk components (most notably, hazard), an efficient estimation of exposure is key to improve confidence in impact analysis and forecasting and ultimately support decision makers to improve risk mitigation activities. This is particularly relevant in urban and metropolitan areas, where the density and complexity of the interplay between population, socio-economical assets and infrastructure is likely to foster non-linear risk amplification, possibly due to cascading phenomena. 
In the last decade several innovative methodological approaches have been proposed, building upon statistical modelling, exploiting heterogeneous data from remote sensing, and integrating machine learning techniques in order to improve understanding, formal description and representation of exposure in a wide range of applications. These activities have been originally developed within the community of seismic risk, and later increasingly extended to other natural hazards, acknowledging the need for a more general and flexible approach to exposure modelling in the context of multi-hazard and multi-risk applications.
This is ever more important considering also the ongoing convergence of Disaster Risk Reduction (DRR) and Climate Change Adaptation (CCA) in the broader context of Comprehensive Risk Management (CRM).
In this contribute we aim at providing an overview of the most recent advances that the authors have proposed in the field, outline the current challenge and perspectives in the field of exposure modelling, and draw a tentative roadmap for the next future. 

How to cite: Pittore, M., Gomez Zapata, J. C., Geiß, C., Campalani, P., and Renner, K.: Advancing exposure modelling from seismic risk to multi-hazard analysis in urban and metropolitan areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12679, https://doi.org/10.5194/egusphere-egu23-12679, 2023.

EGU23-12982 | Orals | NH4.2 | Highlight

UCIS4EQ applied to the South Iceland region 

Marisol Monterrubio-Velasco, Marta Pienkowska, and Josep de la Puente

Urgent Computing (UC) refers to the use of High-Performance Computing (HPC) and High-Performance Data Analytics (HPDA) during or immediately after emergency situations. It typically combines complex edge-to-end workflows with capacity computing, where multiple model realizations are required (to account for input and model uncertainties) under strict time-to-solution constraints. Enabling urgent HPC for emergency scenarios, such as earthquakes, can prove valuable towards resilience and relief. The temporal horizon for UC typically ranges from minutes to a few hours.

A novel  HPC-based urgent seismic simulation workflow, the Urgent Computing Integrated Services for Earthquakes (UCIS4EQ),  focuses on short-time reports of the consequences of moderate to large earthquakes. UCIS4EQ automatically prepares and manages sets of physics-based deterministic simulations to rapidly obtain synthetic results. Based on pre-computed and on-the-fly simulations, UCIS4EQ delivers estimates of relevant ground motion parameters, such as peak ground velocity, peak ground acceleration, or shaking duration, with very high spatial resolution.  The physics-based engine includes pre-trained Machine Learning (ML) models fed with pre-computed simulation databases and r full 3D simulations on demand, providing results in minutes and hours, respectively.  The combined results, when well-calibrated, could complement GMPEs for rapid hazard assessment

To demonstrate the potential of UC in seismology, we show the capability of the UCIS4EQ workflow both for the ML predictions and for deterministic simulations in the South Iceland Seismic Zone (SISZ) and the Reykjanes Peninsula Oblique Rift (RPOR). The largest historic earthquakes in Iceland have occurred within these zones and have exceeded magnitude 7. The study region  (63.5°-64.5°N, 20°-22°W) is where the largely sinistral East-West transform motion across the tectonic margin is taken up by a complex array of near-vertical and parallel North-South oriented dextral transform faults in SISZ-RPOR. The high seismic activity in the area widely affects the capital Reykjavik, the most populous city in Iceland. 

This work has been supported by the ChEESE and eFlows4HPC projects.

How to cite: Monterrubio-Velasco, M., Pienkowska, M., and de la Puente, J.: UCIS4EQ applied to the South Iceland region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12982, https://doi.org/10.5194/egusphere-egu23-12982, 2023.

EGU23-13313 | ECS | Posters on site | NH4.2

PSHA for the Dominican Republic 

Kendra Johnson, Thomas Chartier, Marco Pagani, Yesica Perez, Vladimir Guzmán, Maria Betania Roque Quezada, and Catalina Yepes Estrada

The Dominican Republic, situated on eastern Hispaniola Island in the Caribbean, is subject to moderate to high seismic hazard mostly controlled by oblique convergence at the Caribbean/North American plate boundary. Offshore of the island, the North Hispaniola Trench (NHT) and Los Muertos Trough (LMT) subduction-like structures accommodate shortening, while crustal faults both onshore and offshore also take up some deformation. Historically, the Dominican Republic’s large cities, as well as those in Haiti (which shares Hispaniola) have been damaged by earthquakes, the worst of which required the population to relocate (e.g. the 1562 Santiago de los Caballeros earthquake).  Given the elevated hazard, the Dominican Republic was selected to engage in the Global Earthquake Model (GEM) Foundation coordinated USAID-funded “Training and Communication for Earthquake Risk Assessment” project, which aimed to improve earthquake risk assessment capacity in Latin American cities. This project and the collaborations that emerged were the basis for developing a seismic hazard model for the Dominican Republic.

The seismic hazard model is implemented in the OpenQuake Engine, and mostly uses GEM’s model-building tools and state-of-practice. Two main datasets were used for the seismic source characterization: a homogenized earthquake catalogue that benefited from local seismicity records contributed by the Servicio Geológico Nacional (SGN) and Universidad Autónoma de Santo Domingo (UASD), and an active faults database that combines GEM’s global database and one compiled by SGN during recent seismic hazard projects. Together, these datasets were used to constrain seismic source geometries and rates for active shallow crustal earthquakes, subduction interfaces and subduction-like thrusts, and intraslab earthquakes. Active shallow crustal sources were characterized as a combination of fault ruptures and off-fault (distributed) smoothed seismicity. Fault rupture geometries were pre-defined using the Seismic Hazard and Earthquake Rate In Fault Systems (SHERIFS) method, which allows multi-fault ruptures, incorporating epistemic uncertainty in the magnitude scaling relationship (and thus maximum magnitude), portion of earthquakes modelled on and off faults, and slip rates of two major fault systems. Additional uncertainty was considered in the assumptions used to smooth distributed seismicity rates. The NHT and LMT were also modelled using the SHERIFS method, while the other subduction sources were modelled using GEM’s more standard approaches (i.e. a single fault with complex geometry for the interface and pre-defined ruptures constrained to the intraslab volume). Two end-member magnitude frequency distributions were used for the Puerto Rico Trench interface: one assigning more moment to large magnitudes, and one obeying the Gutenberg-Richter relationship. For intraslab sources, epistemic uncertainty was captured in the assumptions for smoothing rupture probabilities according to past earthquakes. The ground motion characterization relied on residual analyses performed in past GEM projects, but replacing outdated GMPEs on subduction sources with more recent counterparts.

Hazard results generally reinforce former perceptions. In Santiago de los Caballeros, PGA reaches ~1g for 2% probability of exceedance in 50 years, controlled by the Septentrional Fault, while in the capital (Santo Domingo) PGA of ~0.5g is impacted by all tectonic region types, and includes contributions from moderate magnitude earthquakes (Mw 5-6).

How to cite: Johnson, K., Chartier, T., Pagani, M., Perez, Y., Guzmán, V., Betania Roque Quezada, M., and Yepes Estrada, C.: PSHA for the Dominican Republic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13313, https://doi.org/10.5194/egusphere-egu23-13313, 2023.

EGU23-15665 | ECS | Orals | NH4.2 | Highlight

PARATUS case-study Bucharest. A new seismic risk assessment model. 

Dragos Toma-Danila and Iuliana Armas

Bucharest can be considered Europe's most endangered capitals due to earthquakes. Intermediate-depth events occurring in the Vrancea Area, with magnitudes greater than 7, can significantly affect Bucharest. In the XXth century, the city experienced two major damaging earthquakes: in 1940 and 1977. But lessons were not fully learned. The number of vulnerable buildings is highly considerable: over 30% are built before 1963 (of which 22%, before 1941). The increased complexity of our society and new challenges among which climate change, pandemics and globalization are new problems to address. In this context, multi-hazard and multi-risk analyses are more than ever necessary.

If the 1977 earthquake generated numerous research with the aim of quantifying the vulnerability of the building stock and improving seismic design, social vulnerability to seismic risk was addressed only after 2000 by the Risk Research Center, University of Bucharest, based on a repeated spatial vulnerability assessment at city-level. Applying the additive approach of the multi-criteria and decision-making analysis in GIS, the spatial social vulnerability was identified by indicators of social and economic metrics, among which social capital and inequality, distance analysis, and on empirical taxonomies: gender, age, social status, ethnicity, type of housing, etc., based on 1992, 2002 and 2011 census data. Calibrating results using remote sensing and social surveys, helped identify vulnerable hotspots and the dynamic of social differences at city level.  

Superimposed on these detailed vulnerability maps for Bucharest based on computed vulnerability indices, a critical decision-making tool for safe access routes in the emergency intervention was developed supported by large sets of traffic and network data, time-dependent analysis, and seismic loss-estimations. This tool, called Network-Risk, uses a state-of-the-art network analysis methodology embedded in GIS, with the potential of integrating live traffic data.

All these topics will be continued in the recently started PARATUS European Project, where Bucharest is a case-study area. In our presentation, we talk about the new data and procedures that we consider for seismic risk assessment (among which new exposure data from a recent census or retrieved from remote sensing missions using deep learning, new data collecting procedures, vulnerability models and city-scale ShakeMap development) and which are the challenges – especially in the nowadays context.

How to cite: Toma-Danila, D. and Armas, I.: PARATUS case-study Bucharest. A new seismic risk assessment model., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15665, https://doi.org/10.5194/egusphere-egu23-15665, 2023.

EGU23-17432 | ECS | Posters on site | NH4.2

Constructing a 3D Smoothed Seismicity Model for the Seismic Hazard Assessment in the Adriatic Thrust Zone, Italy 

Aybige Akinci, Claudia Pandolfi, Matteo Taroni, Giusy Lavecchia, and Rita De Nardis

In any probabilistic seismic hazard analysis (PSHA), the computation of earthquake forecasting models is a fundamental step. A widely used approach is the smoothed seismicity, which uses seismic catalogs to produce earthquake forecasts in time, space, and magnitude. Early smoothed seismicity models, called fixed smoothing, used spatially uniform smoothing parameters such that the kernels were invariant to spatial variations in seismicity rate. However, recently developed adaptive smoothing methods spatially adapt the smoothing parameters according to the earthquake density. All these fixed or adaptive methods are mainly used in regions with complex seismic source characterization since they do not rely on geological, tectonic, or geodetic information, and they overcome the difficulties in characterizing and segmenting complex geological set-ups. Nevertheless, the standard smoothed seismicity approaches may not properly present the seismicity rates for complex seismotectonic areas.

In this study, we propose an innovative 3D approach for fixed and adaptive smoothed seismicity methods that can be advantageously exploited in all contexts with available well-constrained 3D fault models derived from high-quality seismic catalogs. This approach presents a 3D kernel in the algorithm to smooth the location of earthquakes on a spatial grid by considering the earthquake's depth and spatial coordinates. This allows the use of a three-dimensional grid built on a 3D fault model to represent the depth variations of the structure and also provide the rupture parameters. We tested our method with the Adriatic Basal Thrust (ABT) in eastern Central Italy, a regional active contractional structure with a well-constrained 3D fault model and a related high-quality location catalog.

The eastern Central Italy seismotectonic set-up is characterized by contractional active regional thrusts, such as ABT, representing the outermost and still active front of the Apennine fold-and-thrust belt and by coaxial extensional faults observable along the axis of the Apennine Chain. This complex framework shows different kinematic seismogenic sources overlapping at different depths and represents a perfect case study to test the 3D smoothed seismicity with fixed and adaptive methods. The 3D seismicity model was constructed for the ABT using a detailed catalog with completeness magnitude Mc ≥ 1.4 opportunely selected to identify ABT activity and declustered for the time-independent (Poisson) model.   We then applied the 3D kernel algorithm with the adaptive and fixed smoothed seismicity approaches to calculate the M ≥ 4.5 ABT earthquake rates. We also include a series of geological information regarding the depth, the fault strike, the dip angle, the seismogenic layers depth, and the rake of the slip direction that can be used for the seismic hazard analysis in the region. Finally, we presented the impact of the 3D smoothed seismicity model on PSHA in central Eastern Italy using OpenQuake software.

How to cite: Akinci, A., Pandolfi, C., Taroni, M., Lavecchia, G., and De Nardis, R.: Constructing a 3D Smoothed Seismicity Model for the Seismic Hazard Assessment in the Adriatic Thrust Zone, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17432, https://doi.org/10.5194/egusphere-egu23-17432, 2023.

This work investigates how the uncertainty in the soil parameters influences the frequency content of the earthquake accelerograms that are expected to occur at a specific site. To this end, the Clough-Penzien power-spectrum is parametrized using random variables to describe the stochastic soil parameters and an artificial set of accelerograms is generated using the Spectral-Representation method. Subsequently, the equations of motion of a single degree-of-freedom oscillator are solved numerically for each earthquake scenario and the response spectrum is extracted. By comparing the derived response spectrum with the one obtained from considering deterministic soil parameters, useful conclusions are drawn pertaining to structural design and analysis.

How to cite: Michailidis, A.: Uncertainty quantification of seismic structural response due to randomness in the soil properties, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17557, https://doi.org/10.5194/egusphere-egu23-17557, 2023.

A tsunami induced by a shallow offshore earthquake of magnitude Mw=6.7 occurred south of the island of Crete (Greece) on May 2nd, 2020. The initial tsunami alert message (TAMs) received by the Egyptian National Tsunami Warning Focal Point for Egypt (i.e. Egyptian National Research Institute of Astronomy and Geophysics-NRIAG) was issued by the Geodynamic Institute of the National Observatory of Athens (NOA-HLNTWC), and was based on preliminary, rather inaccurate hypocenter and magnitude estimates. About 36 minutes after the earthquake, a follow-up message with an increased tsunami warning level was issued; the updated warning was motivated by a significant revision of earthquake source parameters estimates. The later message, however, was issued without taking into account the available observations from sea-level data.

In this study we investigate the effectiveness and usefulness of the TAM messages received by NRIAG for the coastal areas of Egypt (including the issue time and the source parameters on which the messages are based), by cross-checking them against observed and modelled seismological and sea level data. Based on results from the critical review of the tsunami warning messages, disseminated by NOA-HLNTWC and other TSPs in the Eastern Mediterranean Sea and received by NRIAG (which is a TWFP for Egypt), a comprehensive revision of the tsunami early warning system tools and procedures seems urgently needed in the region. The active involvement of countries along the southern coast of the Mediterranean turns out to be crucial, as the analysis shows that tsunami warning can only be efficient with international cooperation on data (seismic and sea level) and procedures.

How to cite: Hassan, H. and Peresan, A.: Assessing Effectiveness of the Tsunami Alert Messages Issued by NEAMTWS-TSPs: a case study from May 2nd, 2020 South Crete Earthquake Tsunami alert for Egypt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17572, https://doi.org/10.5194/egusphere-egu23-17572, 2023.

EGU23-17573 | ECS | Posters on site | NH4.2

Spatial clustering of seismic events analysis using the Discrete Perfect Sets (DPS)algorithm: Pribaikalye 

Anastasiia Agaian and Anastasia Nekrasova

The study aims to get new insights in the evolving clustering of seismicity to be the preconditions for the further effective use of the improved SHA technique in earthquake-prone regions. Discrete Mathematical Analysis DMA (Gvishiani et al. 2008; Agayan et al. 2018) is a series of algorithms for analyzing discrete data, united by a common formal basis, which is fuzzy models of discrete analogs of the fundamental concepts of classical mathematical analysis: limits, continuity, smoothness, connectivity, monotonicity, extremum, etc. In this study, the use of DMA is associated with clustering: it has to select clusters of discrete observations according to a given criterion (classification of discrete observations belonging to one of the clusters) (Gordon, 1981). The results of application of the Discrete Perfect Sets DPS topological filtering algorithm to seismic events in the Baikal area are presented. For the purpose of our analysis, we consider the Baikal Division of the Geophysical Survey, Federal Research Center of the Russian Academy of Sciences, BDRGS (2020) catalogue data. Specifically the epicenters for magnitudes equal to or more than 2.6 (energy class K≥8.6, accepted in catalogue homepage) for the period 1989–2018 within 48–58°N and 99–122°E. The study was carried out as part of the Russian Federation State task of Scientific Research Works on "Seismic hazard assessment, development and testing of earthquake prediction methods"(No. 0143-2019-0006).

How to cite: Agaian, A. and Nekrasova, A.: Spatial clustering of seismic events analysis using the Discrete Perfect Sets (DPS)algorithm: Pribaikalye, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17573, https://doi.org/10.5194/egusphere-egu23-17573, 2023.

EGU23-189 | ECS | Posters on site | NH5.1

How are Singapore and the rest of Southeast Asia affected by tsunami from the Manila Trench? 

Elaine Tan, Linlin Li, Qiang Qiu, Constance Ting Chua, Masashi Watanabe, and Adam Switzer

The 2004 Indian Ocean, 2010 Chile and 2011 Tohoku-Oki tsunami events have demonstrated the destructiveness of tsunami to both near and far-field communities. Globally, many coastal cities have started to place more emphasis on preparing for these rare but potentially catastrophic events by developing probabilistic tsunami hazard assessments (PTHAs). Previous work in the region has identified the Manila Trench to be a potential tsunami source within the South China Sea. Here we model the wave propagations from heterogeneous fault slips, for magnitudes ranging from 7.4 to 8.4, along the southern segment of the Manila Trench, and develop hazard curves for 52 sites in equatorial Southeast Asia. Our results show that the hazard, based on wave heights and arrival times, is variable on both the regional and local scales. Amongst the Southeast Asian countries studied, the Philippines and Vietnam are identified to be most at risk, with high mean peak nearshore amplitudes and short wave travel times. The least impacted countries include Singapore, western Malaysia, Indonesia (excluding the Natuna Islands), Thailand and Cambodia. Although the hazard for Singapore appears to be low, tides and wave run-up are not accounted for in this regional study. To address this we re-model the worst-case scenario adjusting for the highest astronomical tides and bottom friction. Our preliminary results show that Singapore can experience maximum wave heights up to 0.15 m. The relatively low wave heights yield low maximum inundation distances and suggest that the tsunamigenic hazard in Singapore is low. Hazard from tsunami currents, however, remains undetermined at this stage.

How to cite: Tan, E., Li, L., Qiu, Q., Chua, C. T., Watanabe, M., and Switzer, A.: How are Singapore and the rest of Southeast Asia affected by tsunami from the Manila Trench?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-189, https://doi.org/10.5194/egusphere-egu23-189, 2023.

EGU23-506 | ECS | Orals | NH5.1

A meteotsunami in the north Indian Ocean triggered by Hunga Tonga volcanic eruption. 

Anup Nambiathody, Vijith Vijayakumaran, Rohith Balakrishnan, Sreeraj Puthiyadath, Linta Rose, Arjun Sabu, Sudeep Kumar B L, Krishnamohan Krishnapillai Sukumarapillai, Sunil Anakuzhikkal Sudarsanan, and Sunil Poikayil Sukumaran

The Hunga Tonga Volcano in the southwest Pacific islands of Tonga erupted in January 2022. The massive explosion resulted in the generation of Lamb waves that propagated globally with a speed of ~ 300m/s and generated a tsunami that has affected numerous Pacific countries. In this study, we use observations and a numerical model to show the impact of this volcanic eruption on the Indian coastline. The Lamb wave took roughly 10 to 11 hours to reach the Indian coast, as observed in atmospheric pressure at mean sea level. Further, the signatures of high-frequency sea-level perturbations were observed from coastal tide-gauge networks along the Indian coastline. Our analysis shows that sea-level oscillations with considerable amplitude (10-20 cm) were observed along the Indian coastline during this period. The predominant frequency and amplitude, and oscillation were different at different locations. Further, an asymmetry between east and west coast stations was observed in the nature of high-frequency oscillations forced by the Hunga Tonga volcanic eruption. Finally, a numerical model was utilised to demonstrate how topography contributes to the observed sea-level disturbances. The model simulations imply that bathymetry is crucial to the observed sea-level variability. Thus, a 12000 km away event has significantly impacted the sea level along the Indian coastline. This work paves the way for understanding the importance of high-frequency variabilities along the Indian coastline and discusses the necessity to enhance the capability of our early warning systems by incorporating these variabilities.

How to cite: Nambiathody, A., Vijayakumaran, V., Balakrishnan, R., Puthiyadath, S., Rose, L., Sabu, A., Kumar B L, S., Krishnapillai Sukumarapillai, K., Anakuzhikkal Sudarsanan, S., and Poikayil Sukumaran, S.: A meteotsunami in the north Indian Ocean triggered by Hunga Tonga volcanic eruption., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-506, https://doi.org/10.5194/egusphere-egu23-506, 2023.

EGU23-5215 | ECS | Posters on site | NH5.1

Analysis of tsunami signals from tide gauges and ocean-bottom pressure gauges through Iterative Filtering 

Cesare Angeli, Alberto Armigliato, Stefano Lorito, Fabrizio Romano, Martina Zanetti, and Filippo Zaniboni

Time-series from coastal tide gauges and ocean-bottom pressure gauges play a fundamental role in the study and monitoring of tsunami. A typical tsunami record is the result of the superposition with the tsunami itself of different physical phenomena, such as tides, and seismic waves that relatively close to the earthquake source may overlap with the tsunami. In the case of coastal gauges, nonlinear interactions with local bathymetric and coastal morphology features characterize the tsunami evolution. In this study, we apply the recently developed Iterative Filtering (IF) technique, specifically tailored to non-stationary and non-linear signals, to tsunami time-series. IF is a data-driven algorithm that decomposes signals into elementary oscillatory components, called Intrinsic Mode Functions (IMFs), each containing distinct frequency bands. This technique attempts to separate different physical phenomena present in the time-series into different IMF.

To complement the decomposition, a time-frequency analysis technique called IMFogram is used. The IMFogram relies on computing for each IMF the local frequency, computed based on the distribution of zero-crossings, and local amplitude, computed interpolating the absolute values of relative maxima. Despite their simplicity, these definitions produce a time-frequency representation that generalizes the traditional spectrogram. The output of the IMFogram algorithm, given in matrix form, can be used to pinpoint time and amplitude of special features of the signal both graphically and quantitatively.

The ability to separate the different components of a measured record into different IMFs and analyze their spectral properties is shown by applying the technique to available real-world data, for tsunami of different “intensity” and frequency content. The results are compared to other techniques, such as classical filtering techniques and the Empirical Mode Decomposition (EMD). It is shown that IF results, unlike classical linear filters, do not depend on experts’ choice and, unlike the EMD, are stable w.r.t. to noise. Special attention is given to recent events in the Mediterranean Sea, where robust analysis of each signal is needed to remedy the  absence of deep sea tsunami sensors, the sparsity of coastal tide gauges, and the morphological complexity. At last, the possibility of real-time application in early warning system is considered.

How to cite: Angeli, C., Armigliato, A., Lorito, S., Romano, F., Zanetti, M., and Zaniboni, F.: Analysis of tsunami signals from tide gauges and ocean-bottom pressure gauges through Iterative Filtering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5215, https://doi.org/10.5194/egusphere-egu23-5215, 2023.

The estimation of expected damage and losses from natural hazards requires that uncertainties in the modelling and knowledge of future events be quantified and taken into consideration. This is true not only in a fully probabilistic context but also in future scenario calculations, particularly when looking at two or more cascading hazards in which the link between them is not univocal. An offshore earthquake that triggers a tsunami would be one such case. Even if the moment magnitude and rupture size and location of the earthquake were fully defined, it is not possible to know a priori the slip distribution along the rupture and the subsequent co-seismic topographic displacements. Many feasible slip distributions can be associated with the same moment magnitude and dimensions of the rupture, and these lead to a distribution of subsequent topographic displacements and, with that, a diversity of tsunami outcomes. Exactly how much variety exists in the resulting tsunamis, in terms, for example, of maximum wave height or maximum flow velocity at points of interest, and, ultimately, damage to buildings and losses, is the question driving the present study, which is part of the “risk workflow for CAScading and COmpounding hazards in COastal urban areas” (CASCO) project. The ultimate objective is to understand the relevance of this uncertainty and whether it needs to be modelled in the whole damage/loss calculation chain.

To investigate this, 500 realisations of stochastically generated rupture slip have been produced for the 1908 Mw 7.1 Messina earthquake, whose rupture source is taken from the Italian Database of Individual Seismogenic Sources (DISS). The subsequent realisations of ground surface deformation (at the bottom of the sea and on land) were used as input to run realisations of the resulting tsunami in the Strait of Messina, eastern Sicily and western Calabria with the TsunAWI software. Maximum wave heights, maximum absolute velocities and maximum flux can vary significantly for selected observation points along the coast and within the Messina Strait. While a weak correlation has been identified between these tsunami outputs and inputs such as the maximum initial co-seismic vertical displacement, a stronger correlation has been observed with respect to the distance to the centroid of rupture slip. So far, results indicate that the uncertainty in the co-seismic slip along the rupture and the subsequent vertical displacements has a relevant impact on the resulting tsunami, suggesting that this source of uncertainty should not be entirely neglected in models. Using these tsunami outputs to estimate damage to buildings in the area allows us to understand the ultimate final impact on damage and loss calculations, and to develop and test strategies to reduce the resulting computational demand.

How to cite: Nievas, C. I., Androsov, A., and Weatherill, G.: Earthquake-Triggered Tsunamis: Impact of the Uncertainty in the Rupture Slip Distribution on the Resulting Tsunami Wave Heights and Flow Velocities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6291, https://doi.org/10.5194/egusphere-egu23-6291, 2023.

EGU23-6414 | Posters on site | NH5.1

Nonlinear processes in tsunami simulations for the Peruvian coast with a focus on Lima/Callao 

Alexey Androsov, Sven Harig, and Natalia Zamora

Numerical simulations of the tsunami inundation processes require a highly nonlinear scheme. The main inundation properties, such as the
flow depth and velocity depend critically on topographical imprints and bottom friction parameters. Here, we investigate the tsunami inundation in Lima and Callao resulting from the extensive 1746 (Mw 9.0) earthquake that ruptured along the Peruvian coast.

Two numerical tsunami codes have been used in this analysis based on shallow water equations. We determine the relative importance of different parts in these equations with a focus on nonlinear terms. Particular focus is put on the momentum advection, bottom friction, and volume conservation in different mesh (triangular meshes and nested grids). We determine the influence on large-scale quantities like inundation extent and volume, flow velocities, and small-scale fluctuations. In that respect, also sensitivities regarding the bottom friction parameters are investigated.

How to cite: Androsov, A., Harig, S., and Zamora, N.: Nonlinear processes in tsunami simulations for the Peruvian coast with a focus on Lima/Callao, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6414, https://doi.org/10.5194/egusphere-egu23-6414, 2023.

EGU23-6878 | Orals | NH5.1

Energy transfer optimum in subaerial landslide impulse waves 

AmirHossein Parvinashtiani, Stephane Abadie, Kamal El Omari, and Yves Le Guer

Subaerial landslides can generate impulsive waves which, in turn, may cause significant damages to the facilities and people on the surrounding coasts. In spite of the numerous studies related to this complex phenomenon in the last decades, there is still a lot to understand, especially physically speaking.

The present work aims at better understanding the energy transformation process from the slide initial potential energy to the final wave train energy. In particular, we would like to emphasize the existence of an optimum energy rate of transformation and investigate the reason for this existence.

To do so, we rely on a Navier-Stokes two or three phases model (OpenFoam) and perform numerical experiments, fixing a few parameters (slope, density, rheology) and studying the effect of the others. The physics of the phenomenon is highly complex, involving liquid phases interaction, transient wave formation, nonlinear wave processes, dispersion, wave breaking, etc. Such a numerical model, despite its inherent uncertainty, is anyway able to provide a rich information, which may be later completed with experimental results. In particular, the model gives access to all the flow variables which allows to characterize in depth the energy processes. The free surface signal analysis is also valuable for wave celerity, and hence generation zone extent and dispersion analysis.

In terms of research strategy, in order to restrict the complexity and allow a better understanding of the phenomenon, the idea is to start with a very simple rheology, the inviscid case, and progressively increase the numbers of rheological parameters (i.e., viscous flows, Bingham and finally Herschell Bulkley).

During the conference, we will first illustrate the existence of an optimum in the rate of energy transformation for the inviscid slide by progressively increasing the slide volume. We will try to relate this optimum with the physical processes at stake (liquid mass interaction, wave breaking types, dispersion, etc.). Next, we will show the influence of the slide rheology in the process of energy transfer and in particular how the energy optimum varies with respect to the rheological parameters.  

How to cite: Parvinashtiani, A., Abadie, S., El Omari, K., and Le Guer, Y.: Energy transfer optimum in subaerial landslide impulse waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6878, https://doi.org/10.5194/egusphere-egu23-6878, 2023.

EGU23-7313 | ECS | Orals | NH5.1

Wave generation due to the collapse of partially and fully submerged granular columns in large-scale laboratory experiments 

Erica Treflik-Body, Elisabeth Steel, Andy Take, and Ryan Mulligan

Under changing climate, coastal regions are increasingly vulnerable to a variety of hazards, including rapid subaerial and submarine landslides. These hazards can generate tsunamis and dense turbidity currents, which threaten both onshore and offshore infrastructure. Due to the complex geomechanics of failure, limited physical modelling has been conducted that encompasses both the triggering of granular landslides and subsequent waves associated with partially and fully submerged mass failures. Further, experimental modelling of submerged failures has primarily focused on the waves generated in the direction of failure (seaward) and not on the waves formed above and behind the failure (shoreward). To this effect, a series of large-scale granular collapse experiments were conducted by releasing 0.75 m and 0.5 m tall columns of 9.25 mm nominal diameter river stone into reservoir depths ranging from 0.20 m to 1.10 m to explore the wave generation and runup processes in both seaward and shoreward directions. The columns were released by a pneumatically-actuated vertically rising gate designed for the 2.10 m wide and 1.20 m high glass-walled flume. The gate lifts rapidly in 0.7 s, which enables the instantaneous loss of support of the source volumes and results in granular collapse. The wave amplitude is measured using wave capacitance gauges and the failure mechanics are captured with high speed cameras. Overall, the wave amplitudes measured in these highly instrumented large-scale physical models are in good agreement with empirical relationships developed in a previous study using smaller-scale models. The large-scale experimental results provide insight and opportunity to develop relationships between the initial column submergence depth and the magnitude of the shoreward propagating waves, which has previously not been explored. Connecting the amplitude of the waves with the tsunamigenic potential for partially to fully submerged granular materials will assist in understanding risk to offshore infrastructure and communities in coastal regions.

 

 

How to cite: Treflik-Body, E., Steel, E., Take, A., and Mulligan, R.: Wave generation due to the collapse of partially and fully submerged granular columns in large-scale laboratory experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7313, https://doi.org/10.5194/egusphere-egu23-7313, 2023.

In the framework of operational conditions, the real time coastal modeling in near field is challenging to obtain accurate and reliable tsunami warning products for flooding hazard. Maps of inundation and impacts for planning community response can be produced through coastal predictions with run-up computation by solving numerically high-resolution forecast models in real time, taking into account all local effects. However, these runs are too time consuming in near field and operational context. An alternative approach is based on early prediction tools of the coastal wave amplitude calculated from empirical laws or transfer functions derived from these laws. Such tools are suitable in near field context (almost ten times faster than the high-resolution runs), but all local effects are not well taken into account and the assessment of run-up is missing. The linear approximations of coastal tsunami heights are provided very quickly using the maximum wave heights from a computationally cheap regional forecast, with global and conservative estimates.

Within the French Tsunami Warning Center (CENALT), a forecasting tool based on a transfer function method is being implemented. This fast prediction technique is based upon a recently extended version of the usual Green's Law (Giles et al., 2022[1]), which introduces local amplification parameters with the aim of capturing the neglected localized effects. The method includes an automated approach which optimizes for these local amplification parameters by minimizing a cost function.

Local amplification parameters are calculated for the entire French Mediterranean coastline at 25 m resolution from a data set of 12 scenarios (high-resolution simulations). The forecasting results capabilities are analyzed, and shown for several coastal sites. The local tsunami wave heights modeled from the transfer function present a good agreement with the time-consuming high resolution models. The linear approximation is obtained within 1 min and provides globally estimates within a factor of two in amplitude. Although the resonance effects in harbors and bays are not reproduced and the horizontal inundation calculation needs to be studied further, this tool is well suited for an early first estimate of the coastal tsunami threat forecast.


[1] Giles, D., Gailler, A., & Dias, F. (2022). Automated Approaches for Capturing Localized Tsunami Response—Application to the French Coastlines. Journal of Geophysical Research: Oceans, 127(6), e2022JC018467.

How to cite: Gailler, A. and Hébert, H.: Fast coastal tsunami amplitude forecasting along the French Mediterranean shoreline based on a transfer function method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7359, https://doi.org/10.5194/egusphere-egu23-7359, 2023.

EGU23-7459 | ECS | Orals | NH5.1

Site specific emulators for tsunami run-up simulations 

Erlend Storrøsten, Steven Gibbons, and Finn Løvholt

Local Probabilistic Tsunami Hazard Analysis (PTHA) aims to quantify the probability distribution of inundation intensity parameters, such as maximum flow-depth, at a given location over a specified period of time. In a Monte Carlo framework such an analysis is dependent on the simulation of a large number of scenarios. A particularly expensive step, from a computational point of view, is the solving of the nonlinear shallow water equations associated with the tsunami run-up. This problem is even more pronounced in the context of Tsunami Early Warning and Probabilistic Tsunami Forecasting (PTF). A site specific (local) tsunami run-up emulator, trained on precalculated simulation results, enables rapid estimation of inundation maps allowing an assessment of a large number of scenarios with limited computational resources. While high dimensional input and output, dependence on topography and nonlinear dynamics has made the problem intractable for traditional statistical methods, the problem has recently been approached using new techniques developed within the field of Machine Learning. In this work we consider the problem of predicting onshore maximal flow-depth based on timeseries associated with simulated offshore gauge measurements. The site of study is the town of Catania in eastern Sicily. The dataset comprises more than 32,000 tsunami simulations for different earthquake sources in the Mediterranean Sea. Promising results have been obtained using only a small fraction of the total number of simulations as training data. The ML-based inundation predictions for locations close to the water's edge, which are flooded in many of the scenarios, show excellent correspondence with the numerical simulation results. Predicting inundation at locations further inland, which are flooded in only a small number of the simulations, is more challenging.

How to cite: Storrøsten, E., Gibbons, S., and Løvholt, F.: Site specific emulators for tsunami run-up simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7459, https://doi.org/10.5194/egusphere-egu23-7459, 2023.

EGU23-7763 | ECS | Orals | NH5.1

Deep learning approach for real-time tsunami impact forecasting in near field context – application to the French Mediterranean coastline 

Pierre Andraud, Audrey Gailler, Frédéric Dias, and Nicolas Vayatis

Tsunami warning systems currently focus on the first parameters of the earthquake, based on a 24-hour monitoring of earthquakes, seismic data processing (Magnitude, location), and tsunami risk modelling at basin scale.

The French Tsunami Warning Center (CENALT) runs actually two tsunami modelling tools where the water height at the coast is not calculated (i.e., Cassiopee based on a pre-computed database, and Calypso based on real time simulations at basin scale). A complete calculation up to the coastal impact all along the French Mediterranean or coastline is incompatible with real time near field or regional forecast, as nonlinear models require fine topo-bathymetric data nearshore and indeed a considerable computation time (> 45 min). Predicting coastal flooding in real time is then a major challenge in such context. To overcome these limitations, non conventional approches such as machine learning methods are being explored. Among the huge number of actual models, deep learning techniques are becoming increasingly popular. Severals studies have shown the interest of using MLPs (Multilayer perceptrons) and CNNs (Convolutional neural networks) to quickly transform a deep ocean simulation result into a coastal flooding model. Once trained on a specific output area with a large dataset, the networks are able to predict in seconds the tsunami inundation map from any earthquake scenario drawn from a seismic source database representative of the seismotectonic context of the region of interest.

A first study training neural networks to predict the maximum water height maps was performed on three specific French cities (Nice, Antibes and Cannes) to evaluate the capacity of the models to reproduce the ground truth. The objective here is to extend the method to predict, in addition to maximum wave heights and runups, maximum retreats and currents along the entire French Mediterranean coastline. The spatial resolution of the finer bathymetric grids is set to 25 meters. To be representative of reality, the training dataset is fed with seismic scenarios derived from the CENALT fault database and taking into account a stochastic slip distribution. The method provides promising early results.

How to cite: Andraud, P., Gailler, A., Dias, F., and Vayatis, N.: Deep learning approach for real-time tsunami impact forecasting in near field context – application to the French Mediterranean coastline, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7763, https://doi.org/10.5194/egusphere-egu23-7763, 2023.

EGU23-9530 | Orals | NH5.1

Comparison between the uncertainty in the tsunami forecast from slip models obtained from geophysical data inversion and by a Phase Variation Method 

Fabrizio Romano, Patricio Catalan, Stefano Lorito, Escalante Sanchez Cipriano, Simone Atzori, Thorne Lay, Roberto Tonini, Manuela Volpe, Alessio Piatanesi, Macias Sanchez Jorge, and Castro Diaz Manuel J

Subduction zones are the most seismically active regions in the world and hosted many great tsunamigenic earthquakes in the past, often with destructive coastal consequences. Hence, an accurate estimate of the tsunami forecast is crucial in Tsunami Early Warning Systems (TEWS) framework. However, the inherent uncertainties associated with the tsunami source estimation in real-time make tsunami forecasting challenging. 

In this study, we consider the South American subduction zone, where in the last 15 years occurred, three M8+ tsunamigenic earthquakes; in particular, we focus on the 2014 Mw 8.1 Iquique event.

Here, we evaluate the variability of the tsunami forecasting for the Chilean coast as resulting i) from the coseismic slip model obtained by geophysical data inversion and ii) from an expeditious method for the tsunami source estimation, based on an extension of the well-known spectral approach. 

In the former method, we estimate the slip distribution of the 2014 Iquique earthquake by jointly inverting tsunami (DARTs and tide-gauges) and GPS data; we adopt a 3D fault geometry and Green’s functions approach.

On the other hand, a set of stochastic slip models in the latter is generated through a Phase Variation Method (PVM), where realizations are obtained from both the wavenumber and phase spectra of the source.

In the analysis, we also evaluate how the different physics complexity included in the tsunami modelling (e.g. by including dispersion or not) can be mapped into the tsunami forecasting uncertainty. Finally, as an independent check, we compare the predicted deformation field from the slip models (inverted or by PVM) with the RADARSAT-2 InSAR data.

 

How to cite: Romano, F., Catalan, P., Lorito, S., Cipriano, E. S., Atzori, S., Lay, T., Tonini, R., Volpe, M., Piatanesi, A., Jorge, M. S., and Manuel J, C. D.: Comparison between the uncertainty in the tsunami forecast from slip models obtained from geophysical data inversion and by a Phase Variation Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9530, https://doi.org/10.5194/egusphere-egu23-9530, 2023.

EGU23-10851 | ECS | Posters on site | NH5.1

Sensitivity analysis of tsunami heights to shallow bathymetric resolution 

Raquel Felix, Judith Hubbard, and Adam Switzer

Both retrospective tsunami analyses and assessments of future tsunami hazards depend on accurate modeling of how tsunami waves generated offshore propagate through shallow waters near the coast. Accurate models of tsunami propagation in shallow water require high-resolution bathymetric maps, but these are often inaccessible because of the time and cost required to acquire them. In addition, tsunami models based on high resolution bathymetry have high computational processing requirements. Hence, it has been common to use globally available datasets with coarser resolutions, such as the GEBCO dataset, in modeling.

Here, we examine how variations in bathymetric resolution, from 5 m to ∼455 m (GEBCO), affect simulated coastal tsunamis. Our case study includes four study sites with available LiDAR bathymetry datasets (1 m resolution). At each site 30 sets of points were randomly extracted from the LiDAR bathymetry datasets and used to generate bathymetric grids with resolutions of 5, 10, 20, 30, 40, 50, 100, 200, and 300 m at each site. These were also compared to a bathymetry based purely on the GEBCO dataset for that region (∼455 m resolution), that we modified to match the coastlines of the other bathymetry models. Tsunami waves offshore were generated by setting up an instantaneous rupture sourced from a hypothetical fault model and we used the commonly used COMCOT software to model tsunami propagation towards the coast.

Using the model run with 5 m resolution bathymetry as a high resolution reference model, we observed that bathymetric grids with resolutions of 10 – 50 m can reproduce coastal wave heights reasonably well, with the maximum wave height overestimated by ≤5% or underestimated by ≤10%. For coarser bathymetric grids, however (≥100 m resolution), there is an increasing trend of underestimation. Wave heights are underestimated by at least 10% and with up to 30%, 40% and 60% underestimation for bathymetric resolutions of 100, 200, and 300 m, respectively. Notably, the commonly used GEBCO model underestimated coastal tsunami heights by as much as 70%. We also examined the impact on tsunami arrival time: and found that resolutions of 10 – 50 m exhibited a first wave arriving ∼10% earlier than expected, while coarser resolutions showed more variability, with the first wave arriving either ≤20% later or ≤10% earlier. For GEBCO-based models, the  arrival time estimate tends to be underestimated by 10 – 30% or overestimated by 20 – 50%. Our study demonstrates that using GEBCO bathymetry in numerical modeling of tsunami wave propagation in the coastal region likely leads to a significant underestimation of the wave height, with the wave also predicted to arrive too early. However, a reasonably accurate result can be achieved using a bathymetric resolution in the 10 m – 50 m range, and is achievable with reasonable computational efficiency. This study highlights the importance of shallow bathymetry in the numerical modeling of tsunami propagation.

How to cite: Felix, R., Hubbard, J., and Switzer, A.: Sensitivity analysis of tsunami heights to shallow bathymetric resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10851, https://doi.org/10.5194/egusphere-egu23-10851, 2023.

EGU23-11090 | Orals | NH5.1 | Highlight

Two major near-field tsunamis (2017 and 2022) on the coast of Mexico: Observations, spectral properties and numerical modelling 

Alexander B. Rabinovich, Oleg Zaytsev, Elizaveta Tsukanova, and Richard E. Thomson

Two prominent near-field tsunamis impacted the nearby coasts of Mexico. The first tsunami was   generated by a major (Mw 8.2) intraplate normal-fault earthquake on 8 September 2017 in the Gulf of Tehuantepec (Chiapas, Mexico). Tsunami waves from this event were measured by a large number of high-resolution coastal tide gauges located along the coasts of California, Mexico and Central America, by three open-ocean DART stations anchored offshore from the affected region and by several distant DARTs. The second tsunami was produced by a thrust fault Mw 7.6 earthquake on 19 September 2022 within the coastal zone of Michoacán, Mexico. The 2022 tsunami was recorded by six coastal tide gauges and a single offshore DART station. All seven instruments were located within 250 km of the source. No tsunami was detected at larger distances along the coasts of North and Central America, but the tsunami signal was detected at the Hawaii and Samoa islands. All available coastal and open-ocean data were used for comprehensive analyses of these two events. Maximum trough-to-crest wave heights for the 2017 tsunami were recorded at Puerto Chiapas (351 cm), Salina Cruz (209 cm), Acapulco (160 cm) and Huatulco (137 cm), while for the 2022 tsunami they were observed at Manzanillo (172 cm) and Zihuatanejo (102 cm). For both events, the “strengths” of the recorded tsunami waves were mostly determined by distance from the source rather than by the specific resonant characteristics of individual sites. Estimates of the frequency content (“colour”) of the two tsunami events revealed that the 2017 tsunami was mostly long-period (“reddish”), with 87% of the total tsunami energy at periods >35 min, while the 2022 tsunami was short-period (“bluish”) with 91% of energy at periods <35 min. A noteworthy feature of the 2022 event was the seismically generated 7 min period seiche observed at Puerto Vallarta that began immediately after the main earthquake shock and persisted for about one hour. Numerical modelling of the events closely reproduced the coastal and offshore tsunami records and demonstrated the markedly different character of the tsunami energy radiation patterns: the 2017 tsunami spread energy widely in a semicircular pattern emanating from the source whereas  the main beam of offshore energy radiating outward from the 2022 event was directed like a “searchlight” oriented normally to the mainland coast.

How to cite: Rabinovich, A. B., Zaytsev, O., Tsukanova, E., and Thomson, R. E.: Two major near-field tsunamis (2017 and 2022) on the coast of Mexico: Observations, spectral properties and numerical modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11090, https://doi.org/10.5194/egusphere-egu23-11090, 2023.

EGU23-11328 | ECS | Orals | NH5.1

A Conditional Probability based Tsunami Prediction for the Pacific Ring of Fire 

Nazeel Sabah and Daya Shanker

The Pacific Ring of Fire, stretching over 15 countries, is one of the earth's most Tsunami-prone regions. 80 Percent of the Tsunami Occurrences could be directly or indirectly associated with this region. This study deals with the development of Conditional Probability and Total Probability based approaches for estimating the probability of Tsunami Occurrence in the study area. This study suggests ten regions with a high probability of tsunami occurrence in the region. The prediction results are validated by computing the occurrence probabilities of the known tsunami events in the region. The study reveals that East Asian Countries like Japan, North and South Korea and Parts of China have a probability, more than 75 per cent, of experiencing a strong tsunami (Mw > 7.5) in the next three years from now. Also, certain South American countries like Peru, Chile and Ecuador, Southeast Asian Counties like Indonesia and South Pacific Countries like Papua New Guinea, Australia, and the Solomon Islands have a high probability of tsunami occurrence (90 Percent and above) in the next five years.  Based on this methodology, it has been possible to predict the Indonesian Tsunami of December 14th, 2021, with a probability of 83 Percent.

How to cite: Sabah, N. and Shanker, D.: A Conditional Probability based Tsunami Prediction for the Pacific Ring of Fire, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11328, https://doi.org/10.5194/egusphere-egu23-11328, 2023.

EGU23-11461 | Orals | NH5.1

Simulation of submarine landslides and generated tsunamis in Mayotte : comparison  of different models 

Pablo Poulain, Anne Le Friant, Anne Mangeney, Rodrigo Pedreros, Gilles Grandjean, Anne Lemoine, Enrique Fernandez-Nieto, Manuel Castro-Diaz, and Marc Peruzzetto

Since May 2018, Mayotte island has experienced an important seismic activity linked to the on-going sismo-volcanic crisis. Although variations in the number of earthquakes and in their distribution have been observed since the start of the eruption in early July 2018, a continuous seismicity persists. It could weaken the steep submarine slopes of Mayotte, as highlighted by the high-resolution bathymetry data collected during the MAYOBS cruise in May 2019. This could trigger submarine landslides with associated tsunamis.

To address the hazards associated with such events, we analyzed geomorphological data to define 8 scenarios of potential submarine landslides with volumes ranging from 11,25.106 to 800.106 m3. We simulated the resulting landslide dynamics as well as generated waves (Poulain et al. 2022). In order to estimate the uncertainty associated to the modeling approach, a hierarchy of different model approximations was tested, spanning hydrostatic, non-hydrostatic and multilayer approaches. A sensitivity analysis was also performed by varying the initial released mass, the rheological parameters describing the landslide, its interaction with the water column, the Manning friction coefficient as well as the resolution of the bathymetry description. The combination of all these elements provides an estimate of the uncertainty on simulation results. We show that, in the context of Mayotte, non-hydrostatic effects have the most prominent influence on simulated water elevation and waves velocity. Other key factors include the friction coefficient within the landslide and the resolution of the bathymetry. These results show that landslide-tsunami models should still be improved as well as the estimates of the parameters involved to reduce the related uncertainties on the water wave calculation (water elevation, velocity) that can exceed a factor two.

Poulain, P., et al. (2022). Numerical simulation of submarine landslides and generated tsunamis: application to the on-going Mayotte seismo-volcanic crisis. Comptes Rendus. Géoscience354(S2), 1-30.

 

How to cite: Poulain, P., Le Friant, A., Mangeney, A., Pedreros, R., Grandjean, G., Lemoine, A., Fernandez-Nieto, E., Castro-Diaz, M., and Peruzzetto, M.: Simulation of submarine landslides and generated tsunamis in Mayotte : comparison  of different models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11461, https://doi.org/10.5194/egusphere-egu23-11461, 2023.

EGU23-11778 | Orals | NH5.1 | Highlight

Triple jeopardy: The Tonga tsunami, a storm surge, and a meteotsunami simultaneously hit the US East Coast on 16-17 January 2022 

Jadranka Sepic, Alexander B. Rabinovich, Igor Medvedev, and Richard E. Thomson

The eruption of the Tonga–Hunga underwater volcano in the Central Pacific on 15 January 2022 generated pronounced atmospheric pressure waves that circumvented the globe several times during the next five days. Propagating with a sound speed of ~10 spherical degrees/hour, the pressure waves forced substantial tsunami waves in the Atlantic Ocean that impacted the East Coast of the United States. Almost simultaneously, on 16-17 January 2022, a deep midlatitude cyclone crossed the East Coast. The cyclone, which formed over the northern part of the Gulf of Mexico, began to rapidly intensify as it moved northward. When it reached 40° N, the system produced a pressure change of 36 hPa/24 hours, classifying the cyclone as a “bomb cyclone”. Strong high-frequency (period <4 h) atmospheric pressure disturbances accompanied the cyclone. Both the large-scale atmospheric low and the markedly enhanced pressure disturbance reached their full strengths during the early morning of 17 January 2022 in the proximity of Atlantic City. As a consequence, three hazardous events - storm surge caused by the midlatitude cyclone, a tsunami caused by the Tonga air pressure waves and a meteotsunami caused by the HF atmospheric pressure disturbance struck the US East Coast on 16-17 January 2022, producing cumulative devastating effects in the coastal zone. Severe coastal flooding affected the Atlantic City region, where sea level heights were increased by as much as 150 cm. This unique joint event is examined in detail and the properties of the atmospheric processes and associated sea level response are thoroughly analysed. The contributions from the various sea level components are assessed and their interaction evaluated.

How to cite: Sepic, J., Rabinovich, A. B., Medvedev, I., and Thomson, R. E.: Triple jeopardy: The Tonga tsunami, a storm surge, and a meteotsunami simultaneously hit the US East Coast on 16-17 January 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11778, https://doi.org/10.5194/egusphere-egu23-11778, 2023.

Tsunami urgent computing procedures quantify the potential hazard due to an earthquake right after its occurrence, that is within a few hours. The hazard is quantified by simulating the propagation of the tsunami waves in the sea, accounting for the uncertainty due to the scarce knowledge of the source parameters and wave modelling uncertainty.

In the context of the European project eflows4HPC, a workflow is currently in development for tsunamis hazard urgent computing, which consists of the following steps: 1) Retrieval of information about the tsunamigenic seismic event (magnitude, hypocentre and their uncertainties); 2) Definition of an ensemble of seismic sources; 3) Simulation of seismic/tsunamigenic waves propagation for each scenario in the ensemble; 4) Results aggregation to produce an estimate of seismic and tsunami hazard, which also incorporates a basic treatment of modelling uncertainty. The ensembles cover the uncertainty on source characteristics and may consequently be very large (generally 10,000 to 100,000 of scenarios; Selva et al., Nat. Comm.), requiring very high computational resources for the urgent computing context. It is thus necessary to reduce the size of these ensembles to limit the number of simulations and to converge faster towards stable results of hazard calculation.

We developed and tested several sampling procedures aiming to reduce the number of scenarios in the ensemble and, at the same time, to integrate the new incoming information as they become available (e.g. solutions for focal mechanisms, seismic or tsunami records). When applied to several past earthquakes and tsunamis (e.g., the 2003 Boumerdes and the 2017 Kos-Bodrum earthquakes), our novel sampling strategies yielded a reduction of 1 or 2 order of magnitudes of the ensemble size, allowing a drastic reduction of the computational effort. Also, the update of the ensemble based on the incoming of new data, which strongly reduce the uncertainty, yields to an update of the probabilistic forecasts without compromising its accuracy. This may result very important for mitigating the risk far from the seismic source, as well as improving the risk management by better informing decision making in a frame of urgency.

How to cite: Cordrie, L., Selva, J., Bernardi, F., and Tonini, R.: Using available and incoming data for reducing and updating seismic source ensembles for probabilistic tsunami forecasting (PTF) in early-warning and urgent computing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12363, https://doi.org/10.5194/egusphere-egu23-12363, 2023.

EGU23-12935 | ECS | Orals | NH5.1

Use of Neural Networks for Tsunami Maximum Height and Arrival Time Predictions 

Juan Francisco Rodríguez Gálvez, Jorge Macías Sáncez, Manuel Jesús Castro Díaz, Marc de la Asunción, and Carlos Sánchez-Linares

Operational Tsunami Early Warning Systems (TEWS) are crucial for mitigation and highly reducing the impact of tsunamis on coastal communities worldwide. In the North-East Atlantic, the Mediterranean, and connected Seas (NEAM) region, these systems have historically utilized Decision Matrices for this purpose. The very short time between tsunami generation and landfall in this region makes it extremely challenging to use real-time simulations to produce more precise alert levels and the only way to include a computational component in the alert was to use precomputed databases. Nevertheless, in recent years, computing times for a single scenario have been progressively reduced to a few minutes or even seconds depending on the computational resources available. In particular, the EDANYA group at the University of Málaga, Spain, has focused on this topic and developed the GPU code Tsunami-HySEA for Faster Than Real Time (FTRT) tsunami simulations. This code has been implemented and tested in TEWS of several countries (such as Spain, Italy, and Chile) and has undergone extensive testing, verification and validation.

In this study, we propose the use of neural networks (NN) to predict the maximum height and arrival time of tsunamis in the context of TEWS. The advantage of this approach is that the inference time required is negligible (less than one second) and that this can be done in a simple laptop. This allows to consider uncertain input information in the data and still providing the results in some seconds. As tsunamis are rare events, numerical simulations using the Tsunami-HySEA are used to train the NN model. This part of the workflow requires producing a large amount of simulations and large HPC computational resources must be used.

Machine learning (ML) techniques have gained widespread adoption and are being applied in all areas of research, including tsunami modeling. In this work, we employ Multi-Layer Perceptron (MLP) neural networks to forecast the maximum height and arrival time of tsunamis at specific locations along the Chipiona-Cádiz coast in Southwestern Spain. In the present work, initially several individual models are trained and we show that they provide accurate results. Then ensemble techniques, which combine multiple single models in order to reduce variance, are explored. The ensemble models often produce improved predictions.

The proposed methodology is tested for tsunamis generated by earthquakes on the Horseshoe fault. The goal is to develop a neural network (NN) model for predicting the maximum height and arrival time of such tsunamis at multiple coastal locations simultaneously. The results of our analysis show that deep learning is a promising approach for this task. The proposed NN models produce errors of less than 6 cm for the maximum wave height and less then 212 s for the arrival time for tsunamis generated on the Horseshoe fault in the Northeastern Atlantic.

How to cite: Rodríguez Gálvez, J. F., Macías Sáncez, J., Castro Díaz, M. J., de la Asunción, M., and Sánchez-Linares, C.: Use of Neural Networks for Tsunami Maximum Height and Arrival Time Predictions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12935, https://doi.org/10.5194/egusphere-egu23-12935, 2023.

EGU23-12944 | ECS | Orals | NH5.1

Estimation of the economic impact of tsunamis on the Spanish coasts 

Alex Gonzalez del Pino, Jorge Macías, Marta Fernández, Miguel Llorente, Carlos Sánchez-Linares, Julián García-Mayordomo, and Carlos Paredes

Tsunamis are low-probability phenomena with high-risk potential. Lack of field data emphasizes the need of using simulation software to model the potential devastating effects of a tsunami and use this information to develop safety, sustainable actions and social resilience for the future. These measures may include, among many others, spatial planning; designing of evacuation routes; or the allocation of economic resources through insurance or other instruments to mitigate tsunami impacts. Our work introduces a Monte Carlo-like method for simulating the potential impact of tsunamis on the Spanish coastlines, specifically in the provinces of Huelva and Cádiz for the Atlantic region, and Balearic Islands, Ceuta, Melilla and eastern Iberian coast for the Mediterranean region. The method introduces a pseudo-probabilistic seismic-triggered tsunami simulation approach, by considering a particular selection of active faults with associated probabilistic distributions for some of the source parameters, and a Sobol’s sequences-based sampling strategy to generate a synthetic seismic catalogue. All roughly 4000 crafted seismic events are simulated along the areas of interest in high-resolution grids (five meters pixel resolution) using a two-way nested mesh approach, retrieving maximum water height, maximum mass flow and maximum modulus of the velocity at each grid cell. These numerical simulations are computed in a GPU environment, harnessing resources allocated in several high-performance computing (HPC) centres. The numerical database of retrieved variables generated throughout this study offers an excellent foundation for evaluating various tsunami-related hazards and risks.

The final resulting product focuses on generating frequency distributions for the economic impacts for the Spanish insurance sector (Consorcio de Compensación de Seguros, CCS). The CCS is a public-private entity insuring most natural catastrophic events in Spain. A consistent spatially-distributed economic database regarding insurance building-related values has been constructed and aggregated in conjunction with the numerical tsunami simulations. The proposed procedure allows to associate an economic impact indicator to each source. Further statistical analysis of the economic impact estimators yields to varied conclusions such as an improved definition of worst-case scenario (effect-based rather than worst-triggered), most and least likely economic impact, highest hazardous fault sources overall and locally and many others.

How to cite: Gonzalez del Pino, A., Macías, J., Fernández, M., Llorente, M., Sánchez-Linares, C., García-Mayordomo, J., and Paredes, C.: Estimation of the economic impact of tsunamis on the Spanish coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12944, https://doi.org/10.5194/egusphere-egu23-12944, 2023.

EGU23-13511 | ECS | Orals | NH5.1

On the relation between seismic source dynamics, tsunami generation and propagation, and numerical modelling complexity in subduction zones 

Antonio Scala, Stefano Lorito, Fabrizio Romano, Alice Abbate, Gaetano Festa, Manuel J. Castro Diaz, Cipriano Escalante Sanchez, and Jorge Macias Sanchez

The features of the seismic ruptures, such as the duration of shallow earthquakes in subduction zones, may affect the tsunami generation and the inundation intensity. Numerical and experimental results have shown how the interaction between the shallow part of the fault and the seismic radiation trapped in the hanging wall, can lead to enhanced up-dip rupture propagation. This in turn may result in shallow slip amplification producing larger vertical displacement, and even transient ground motion that is larger than the final static displacement. On the other hand, tsunami modelling for hazard assessment and early warning is generally based on static sea-floor displacement obtained with an instantaneous elastic dislocation (without shallow slip amplification) on a simplified hydrostatic model for tsunami generation and propagation. Here, we aim to analyze the relative importance of these effects and the optimal modelling strategy for the tsunami generation. Using a Tohoku-like setting, we impose time dependent initial conditions as computed from 1-D dynamic rupture simulations, by varying the rupture extent and duration over a wide range of stress-drop, rigidity and average slip values (corresponding to earthquake magnitudes between 7.5 and 9, approximately). We performed 1-D numerical tsunami simulations using both the hydrostatic and the multi-layer non-hydrostatic versions of Tsunami-HySEA. We also account for different coastal morphologies, modelling the presence of shelf and/or fjords and variable slope bathymetry. We address, first, how the time-dependent sea-floor displacement characteristics effects may affect (enhancing or reducing) the tsunamigenic potential. To do this, we investigated the resulting tsunami features, in terms of maximum wave height above sea level (also seaward) and maximum run-up, in relation to the spatial and temporal characteristic scales of the transient sea floor displacement. We also compare the simulations with a time-dependent initial condition against those where a static sea-floor displacement is used. We show that the use of a static source systematically overestimates the tsunami effects on the mainland, with the more realistic tsunami reduced due to the seaward seismic rupture (up-dip) directivity, opposite to the direction of the tsunami propagation. Moreover, the slower the rupture, the larger the overestimation. Conversely, as the rupture slows down, the seismic rupture propagating in the same direction of the tsunami increases the tsunami amplitude toward the open ocean. Second, we wish to assess in which conditions and to what extent it is enough to use a shallow-water tsunami model and when, instead, a more complex tsunami modelling scheme is required. The hydrostatic simulations lead to overestimate the inundation, although less significantly with respect to the static/dynamic comparison. We finally investigate how the discrepancy between simplified and complex modelling is controlled by different trench, shelf, and coastal morphologies.

How to cite: Scala, A., Lorito, S., Romano, F., Abbate, A., Festa, G., Castro Diaz, M. J., Escalante Sanchez, C., and Macias Sanchez, J.: On the relation between seismic source dynamics, tsunami generation and propagation, and numerical modelling complexity in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13511, https://doi.org/10.5194/egusphere-egu23-13511, 2023.

EGU23-15864 | Orals | NH5.1 | Highlight

Tsunami Ready in Italy: towards the UNESCO recognition 

Alessandro Amato, Cecilia Valbonesi, Lorenzo Cugliari, Laura Graziani, and Fabrizio Romano

It is well known that an efficient end-to-end tsunami warning system must not only be fast and robust in delivering alert messages to the authorities, but also ensure that these messages reach the residents and the tourists, and that they are aware of the risk and of the right behavior in case of an alert. One of the most effective tools to reach this goal is through the Tsunami Ready programme, promoted by UNESCO IOC since 2015, and a key contribution to achieving the societal outcome ‘A Safe Ocean’ of the Ocean Decade. The NEAMTWS ICG has solicited Member States efforts towards Tsunami Ready since 2020.

Italy has started to join the Tsunami Ready initiative in 2020. The main steps undertaken in these two years include:

1) The identification of three pilot municipalities that decided enthusiastically to join the programme: Minturno (Lazio), Palmi (Calabria), Marzamemi/Pachino (Sicily) (September 2020)

2) The formal deliberations of the three Local Tsunami Ready Committees ((between December 2020 and April 2021)

3) The establishment of the Italian National Tsunami Ready Board - NTRB (May 4, 2021) and the acknowledgment by IOC Executive Secretary (May 18, 2021).

Since then, several achievements have been reached in all three municipalities, including updating the civil protection plans, improving the local alerting systems, organizing outreach and educational activities in schools and with citizens, also during the World Tsunami Awareness Day (WTAD). At the same time, some criticalities have emerged, due to financial and bureaucratic reasons, that have delayed a full accomplishment until now.

In this contribution, we report on the state of the art in the three municipalities, and discuss the achievements and the criticalities of the programme. We envisage that the first one or two formal candidatures will be advanced later this year to the NTRB.

Finally, we will discuss a proposal to extend the results of this pilot project to all the coastal municipalities in Italy, also based on the analysis of the liability aspects of such recognition in the Italian legal system.

How to cite: Amato, A., Valbonesi, C., Cugliari, L., Graziani, L., and Romano, F.: Tsunami Ready in Italy: towards the UNESCO recognition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15864, https://doi.org/10.5194/egusphere-egu23-15864, 2023.

EGU23-15923 | ECS | Posters on site | NH5.1

Longitudinal assessment of tsunami knowledge in an Italian school. 

Lorenzo Cugliari, Massimo Crescimbene, and Alessandro Amato

Italy is at tsunami risk, a phenomenon characterized by low frequency of occurrence that can cause widespread and destructive impact on coastlines.

The activities carried out by the INGV's Tsunami Alert Center (CAT-INGV), in concert with Italian Department of Civil Protection, include tsunami risk mitigation through: i) the study of tsunami risk perception, ii) the Tsunami Ready program, and iii) educational and dissemination activities with different methodologies.

In this work we analyze the effectiveness and durability of learning about knowledge and tsunami risk with Lazzaro Spallanzani Scientific High School students, in Tivoli (Rome province).

The assessment involved the administration of an online questionnaire composed of selected items from the tsunami risk perception survey carried out by CAT for the tsunami risk perception study (Cerase et al., 2019, Cugliari et al., 2022).

The survey sample consists of 90 students identified by age group (16-19 y.o.) and study address (high school scientific address).

The assessment was made administering the questionnaire in two stages, two months apart (March 2022 and May 2022) before and after a tsunami scientific lesson with the support of multimedia tools (photos, videos, animations and infographics).

A third survey is planned for March 2023, respecting the statistical-methodological survey criteria.

Data analysis shows an evident increase in tsunami risk knowledge. Student educational needs also emerge that can be used as leverage to structure targeted and effective interventions and increase young people's awareness of tsunami risk in other areas. There is also evidence that fieldwork, with the aid of multimedia and possibly interactive or assisted media, provides successful maintenance of attention and facilitates assimilation

How to cite: Cugliari, L., Crescimbene, M., and Amato, A.: Longitudinal assessment of tsunami knowledge in an Italian school., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15923, https://doi.org/10.5194/egusphere-egu23-15923, 2023.

EGU23-15937 | ECS | Orals | NH5.1

Simulation of the hydro-acoustic and gravity waves generated by a landslide 

Juliette Dubois, Sébastien Impériale, Anne Mangeney, and Jacques Sainte-Marie

In this work we propose a linear model describing the propagation of acoustic waves and gravity waves in the ocean. This model can be used for describing the propagation of a tsunami and the acoustic waves generated by an underwater earthquake or a landslide.

The acoustic-gravity waves are considered as first order perturbation of an equilibrium state for the ocean. The equilibrium state is as follow: there is no mean current and the pressure, temperature and density are vertically stratified. The model is obtained from a linearization around this equilibrium state of the compressible Euler equations. Unlike several other works on acoustic-gravity waves, the two types of waves are not decoupled during the linearization. The complete derivation of the model and the comparison with the other models of the literature are presented in [1].

As a first application we present the simulation of a simplified landslide. We aim at a better understanding of the acoustic wavefield generation process. The equations are discretized with the finite element method in space and a finite difference scheme in time. In-field data on the acoustic waves generated by a landslide are already available in the literature [2] and provide the relevant scales for the simulation.

[1] Juliette Dubois, J., Imperiale, S., Mangeney, A., Bouchut, F., Sainte-Marie J. (2022), Acoustic and gravity waves in the ocean: a new derivation of a linear model from the compressible Euler equation, Submitted.

[2] Caplan-Auerbach, J., Dziak, R. P., Bohnenstiehl, D. R., Chadwick, W. W., and Lau, T.- K. (2014), Hydroacoustic investigation of submarine landslides at West Mata volcano, Lau Basin, Geophys. Res. Lett., 41, 5927– 5934, doi:10.1002/2014GL060964.

How to cite: Dubois, J., Impériale, S., Mangeney, A., and Sainte-Marie, J.: Simulation of the hydro-acoustic and gravity waves generated by a landslide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15937, https://doi.org/10.5194/egusphere-egu23-15937, 2023.

We explored the capability of forecasting meteotsunamis using machine learning (ML) approaches. We selected meteotsunami events along the coast of Portugal where the atmospheric pressure jumps propagate from the south and southwest. Since this type of meteotsunamis is usually observed along the entire coast of Portugal (Kim & Omira, 2021; Kim et al., 2022), the southern tide gauges can act as a meteotsunami precursor for forecasting the northern coastal areas. For training and testing sets of ML, we started with the atmospheric pressure records (18 cases) which induced meteotsunamis, and then performed 1296 numerical simulation by varying the pressure inputs with different strength (jump magnitude), speed and direction. Then, the tidal gauge data from numerical simulations were used to apply neural networks (variational autoencoders and ARIMA) and to demonstrate the capability of meteotsunamis forecast based on one or more tide gauge observations. We observed that the ML models are capable of providing good predictions from short duration observations from the southern tide gauges. This work is supported by the project FAST—Development of new forecast skills for meteotsunamis on the Iberian shelf—ref. PTDC/CTAMET/32004/2017-funded by the Fundação para a Ciência e Tecnologia (FCT), Portugal.

 

References

Kim J, Omira R (2021) The 6–7 July 2010 meteotsunami along the coast of Portugal: insights from data analysis and numerical modelling. Nat Hazards 106:1397–1419. https://doi.org/10.1007/s11069-020-04335-8

Kim J, Omira R, Dutsch C (2022) Meteotsunamis along the Portugal coast from 2010 to 2019. 2nd World Conference of Meteotsunamis

Liu CM, Rim D, Baraldi R, LeVeque RJ (2021) Comparison of Machine Learning Approaches for Tsunami Forecasting from Sparse Observations. Pure Appl Geophys 178:5129–5153. https://doi.org/10.1007/s00024-021-02841-9

Omira R, Ramalho RS, Kim J, et al (2022) Global Tonga tsunami explained by a fast-moving atmospheric source. Nature 609:734–740. https://doi.org/10.1038/s41586-022-04926-4

How to cite: Kim, J. and Omira, R.: Machine Learning Approaches for Meteotsunami Forecasting on the Coast of Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16620, https://doi.org/10.5194/egusphere-egu23-16620, 2023.

EGU23-16705 | Orals | NH5.1

Significant tsunami hazards in Indonesia from landslide and volcanic sources 

Mohammad Heidarzadeh, Danny Hilmann Natawidjaja, Marina C. G. Frederik, Mudrik R. Daryono, Purna Putra, Adi Patria, Aditya Riadi Gusman, and Iyan E. Mulia

Tsunamis from landslide and volcanic sources have been responsible for significant destruction and fatalities worldwide as evidenced most recently during the January 2022 Tonga volcanic tsunami (Heidarzadeh et al., 2022: https://doi.org/10.1016/j.oceaneng.2022.112165). Indonesia is a hot spot for such tsunamis from landslide and volcanic sources as the region suffered from destructive events in the past, such as the 1883 tsunami following the Krakatau eruption which costed at least 36,000 lives. More recently the region was struck by the 2018 Anak Krakatau volcanic tsunami with approximately 450 deaths, and the 2018 Palu (Sulawesi) tsunami with more than 4,000 casualties. Therefore, it is vital to further study the generation potential and mechanisms of such tsunamis and to improve hazard knowledge base.

Here, we study three recent tsunamis in Indonesia, two of which occurred following an earthquake while the other one occurred following a volcanic eruption. All three have a landslide component in their sources: the June 2021 Seram Island tsunami (earthquake), the December 2018 Palu tsunami (earthquake), and the December 2018 Anak Krakatau tsunami (volcanic eruption).

A tsunami was observed on 16th June 2021 in Seram Island following an Mw 5.9 earthquake. The tsunami amplitude was approximately 50 cm at Tehoru tide gauge whereas two other stations showed amplitudes of less than 4 cm. Such a relatively large tsunami (50 cm) is unexpected from a normal-faulting Mw 5.9 earthquake. We hypothesize that that a secondary source (i.e., a landslide) was involved. We applied tsunami modelling and source analysis to examine this hypothesis. Tsunami simulations confirmed that that the earthquake could only have contributed to a few centimeters of the tsunami and thus cannot reproduce the 50 cm waves. However, we could reproduce the tsunami observations using a landslide source. For more information see here: https://doi.org/10.1785/0120210274.   

Regarding the September 2018 Palu tsunami, it is now commonly accepted that a submarine landslide should have most likely contributed to the tsunami generation in addition to the earthquake. However, the nature of the landslide whether submarine or subaerial, and the contribution of the two sources are not clear. We propose a novel dual landslide-earthquake source that explains most of the observation of the 2018 Palu event. Our dual model comprises the USGS earthquake model (length = 264 km, width = 37 km, slip = 0 – 8.5 m) combined with a submarine landslide with a length of 1.0 km, a width of 2.0 km, and a thickness of 80.0 m. For more information see here: https://doi.org/10.1080/21664250.2022.2122293.         

For the December 2018 Anak Krakatau tsunami, we present the results of our field surveys. We surveyed 29 locations and measured tsunami runups from 0.9 m to 5.2 m, tsunami heights from 1.4 to 6.3 m, and inundation distances from 18 to 212 m. For more information, see here: https://doi.org/10.1007/s00024-020-02587-w.

We also discuss future directions towards expanding our limited understanding of tsunamis from landslide and volcanic sources in Indonesia which are often unpredictable and deadly. This research is funded by The Royal Society (UK), grant number CHL/R1/180173.   

How to cite: Heidarzadeh, M., Hilmann Natawidjaja, D., Frederik, M. C. G., Daryono, M. R., Putra, P., Patria, A., Gusman, A. R., and Mulia, I. E.: Significant tsunami hazards in Indonesia from landslide and volcanic sources, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16705, https://doi.org/10.5194/egusphere-egu23-16705, 2023.

EGU23-17571 | ECS | Orals | NH5.1

Fault Based Tsunami Generation and Hazard Analysis: A Probabilistic Study for Aegean Coasts of Türkiye 

Gozde Guney Dogan, Ahmet Cevdet Yalciner, Arda Ozacar, Zeynep Gulerce, Duygu Tufekci-Enginar, Mehmet Lutfi Suzen, Onur Kanun, Onur Pekcan, and Semih Yucemen

The coasts of Türkiye are vulnerable to tsunami hazards due to the intensive use of coastal areas and the activity of faults in the surrounding seas. The Samos-İzmir earthquake occurred on October 30, 2020, followed by a tsunami that affected the Sığacık Bay revealed this fact once again, demonstrating the importance of accurately modeling the tsunami hazard across the country. Probabilistic Tsunami Hazard Assessment (PTHA) results for various coastal engineering parameters (i.e., tsunami wave height, tsunami inundation distance) constitute one of the essential inputs of performance-based tsunami risk analysis. The TSUMAPS-NEAM project that ended in 2018 was one of the studies following the probabilistic approach for the Northeast Atlantic, Mediterranean, and connected seas (Basili et al. 2021). The primary objective of this study which is constructed within the TUBITAK (Scientific and Technological Research Council of Turkey) funded 121M750 project, is to develop a comprehensive probabilistic tsunami hazard analysis framework in which the uncertainties regarding active faults that can generate tsunamis for our country's Aegean Sea coasts are addressed fully. For this purpose, a holistic seismotectonic database has been created by compiling catalogs of active faults that can generate tsunamis in the Aegean Sea and its surroundings, important fault parameters, earthquake and focal mechanism solutions from national and international sources. The compiled database is utilized to determine possible tsunami source scenarios and model the epistemic and aleatory uncertainties in these scenarios. In this regard, a complete probabilistic set of tsunami source scenarios that have not been included in previous studies is being developed, and the near-shore tsunami wave height estimations will be determined by performing high-resolution tsunami simulations for each scenario. Considering the lack of hazard-based tsunami assessment for the coasts of the Aegean Sea, the near-shore tsunami wave height hazard curves to be obtained as a result of the project are of great importance in determining the effects of possible tsunamis and assessing the tsunami risk.

Acknowledgement: This study is supported by TUBITAK 1001-Grant Project No: 121M750.

How to cite: Dogan, G. G., Yalciner, A. C., Ozacar, A., Gulerce, Z., Tufekci-Enginar, D., Lutfi Suzen, M., Kanun, O., Pekcan, O., and Yucemen, S.: Fault Based Tsunami Generation and Hazard Analysis: A Probabilistic Study for Aegean Coasts of Türkiye, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17571, https://doi.org/10.5194/egusphere-egu23-17571, 2023.

SM8 – Computational, Theoretical Seismology and Big Data

EGU23-945 | ECS | Orals | SM8.1

The Influence of Fluids on Earthquakes: Insights from Mechanical Modelling 

Valentin Marguin and Guy Simpson

The strength and sliding behavior of faults in the upper crust are largely controlled by friction and effective stress, which is itself modulated by the fluid pressure. However, while many studies have investigated the role of friction on the earthquake cycle, relatively little effort has gone into understanding the effects linked to dynamic changes in fluid pressure. Here, we explore coupled interactions between slow tectonic loading and fluid pressure generation during the interseismic period with rapid sliding and elastic stress transfer during earthquakes on a plane strain thrust fault in two dimensions. Our models incorporate rate- and state-dependent friction along with dramatic changes in the fault permeability during sliding. In these modes, earthquakes are nucleated where fluid pressures are locally high and then propagated as slip pulses onto stronger parts of the fault. For the model without overpressure, the ruptures are more crack-like. Our model produces a wide range of sliding velocities from rapid to slow earthquakes, which occur due to the presence of high pore pressures prior to rupture. The models also show evidence for aftershocks that are driven by fluid transfer along the fault plane after the mainshock. Overall, we find that the presence of relatively modest fluid overpressures tends to reduce coseismic slip, stress drop, maximum sliding velocity, rupture velocity, and the earthquake recurrence time relative to ruptures in a dry crust. This study shows that fluids can exert an important influence on earthquakes in the crust, which is mostly due to modulation of the effective stress and variations in permeability, and to a lesser extent to poroelastic coupling.

How to cite: Marguin, V. and Simpson, G.: The Influence of Fluids on Earthquakes: Insights from Mechanical Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-945, https://doi.org/10.5194/egusphere-egu23-945, 2023.

EGU23-1678 | ECS | Orals | SM8.1

A synthetic ambient-noise data set fortime-lapsed monitoring 

Sérgio Nunes, Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, and Nuno Garcia
Synthetic simulation of seismic wave propagation is a fundamental way to evaluate the accuracy and performance of signal processing methods developed for application to real seismic datasets. Various research papers have introduced state-of-the-art synthetic active and passive seismic datasets to implement this critical step. However, a versatile seismic data set for ambient noise is still missing in the literature. In this study, we conducted synthetic simulations by leveraging the noise simulation modules of SPECFEM3D Cartesian open-source codes. The simulation is carried out for the geometries of station pairs of the YB Cavola Broadband Dense Array temporary network installed in 2004 through the village of Cavola, northern Apennine, Italy. This is a dense array (8m separation one way and
10m the other way) installed on an active landslide through the village of Cavola, northern Apennines, Italy. By considering a fixed crustal velocity model reported for this region, a noise correlation seismogram is computed for each station pair by implementing three processing steps: 1) simulation for generating wavefields, 2) simulation for ensemble forward wavefields, and 3) simulation for ensemble adjoint wavefields and sensitivity kernels. The generated cross-correlation seismograms are post-processed, detrended, and decimated by a factor of 2 to obtain a dataset with a sampling rate of 0.01sec. Then the traces are rotated to the transverse-radial-vertical coordinate system making 3-component data for each station pair. To make the simulation more realistic, the data is contaminated by Gaussian noise (bandpass-filtered in the range of [0.02, 100] Hz) to give a Signal to Noise Ratio (SNR) of 10. The generated dataset provides one epoch of a synthetic time-lapsed ambient noise dataset as a reference for evaluating time-lapsed processing algorithms. This research contributes to the ALLAB project.
 
The authors would like to thank the support of the Instituto de Telecomunicaçõe. This work is funded by FCT/MCTES through national funds.

How to cite: Nunes, S., Mohammadigheymasi, H., Tavakolizadeh, N., and Garcia, N.: A synthetic ambient-noise data set fortime-lapsed monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1678, https://doi.org/10.5194/egusphere-egu23-1678, 2023.

EGU23-2497 | ECS | Posters virtual | SM8.1

Scalar wave equation modeling with dispersion relation based on finite difference method 

Vanga Mounika and Maheswar Ojha

The finite-difference method(FDM) is widely used in the numerical modeling of wave equations. Conventional FDM stencils for spatial derivatives are usually designed in the space domain, which creates difficulty in satisfying the dispersion relations exactly while solving the wave equations. We use an automated and optimized FDM using a genetic algorithm to optimally compute second-order spatial derivatives. In our method, the explicit finite-difference stencils are calculated using the genetic algorithm to minimize the dispersion (phase velocity) for all wavenumbers without using any specific window function. The amplitudes of the pseudo-spectral window are optimized by making the phase velocity close to the analytical solution at each wavenumber, where the stability is close to that of the conventional FDM. Although finite difference coefficients in this method depend on velocity, grid spacing and time step, less dispersive solutions can be achieved by computing suitable finite-difference coefficients for varying cases. We compare our results with the solutions of an existing pseudo-spectral method (with Kaiser window function), conventional FDM, joint time-space optimization method, and the least square method. The normalized phase velocity and the absolute error of our method show very promising results.

How to cite: Mounika, V. and Ojha, M.: Scalar wave equation modeling with dispersion relation based on finite difference method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2497, https://doi.org/10.5194/egusphere-egu23-2497, 2023.

A central problem in earthquake physics and fault mechanics is understanding the coupling of fluid and solid phases during fault slip. This coupling is mostly treated as a one-way coupled problem where the pore pressure is imposed as a perturbation in effective normal stress. However, more recent work indicates that the two-way coupling of a porous fluid-filled bulk and pressure changes in the shear zone significantly alters rupture properties. Further, a qualitative analysis of this problem in a poroelastic medium reveals that pore pressure inside an mm to micron thick frictional shear zone cannot be constant as slip dynamically evolves. This analysis calls into question the practice of imposing pore pressure as a perturbation to effective normal stress at an infinitesimal interface and raises fundamental questions regarding the interpretation of the effective stress principle. Here we explore two ways to couple shear zone processes on a mm-micron scale to the meter-kilometer scale bulk processes. Efficient coupling across these scales is achieved with a spectral boundary integral representation of a poroelastic bulk. Furthermore, the boundary integral representation reduces the dimension of the computational problem that needs to be discretized by one. In other words, it allows us to simulate 3D physics by only discretizing in 2D. We develop boundary integral solutions in 2D and 3D medium that are appropriate for modeling shear zone that can undergo pressure changes, expansion/contraction, and shear localization. First, we explore an efficient approach where shear zone properties are averaged and dimensionally reduced, thus with finite shear zone effects built into the boundary conditions of the bulk in 2D and 3D. Second, we show how a shear zone can be explicitly modeled, but the coupling to the surrounding bulk is done with a boundary integral representation. Thus, offering relatively efficient modeling of processes such as shear localization, dilatancy, thermal pressurization, and how such processes interact with the bulk. We suggest that such use of boundary integrals may be applied more generally to achieve two-way fluid-solid coupling at lower computation expense.

How to cite: Heimisson, E. R. and Wang, Y.: Linking fluid flow in a shear zone to the surrounding bulk with poroelastic boundary integral solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4283, https://doi.org/10.5194/egusphere-egu23-4283, 2023.

The instantaneous weakening of rocks during the passage of seismic waves has first been observed in laboratory experiments. The change of elastic rock moduli during and after the dynamic perturbations typically includes three phases – a gradual drop of moduli, a dynamically steady state and the recovery over a time scale that is larger than that of the perturbations. Such changes have been referred to as slow dynamics (Johnson and Sutin, 2005). With the development of the long-term continuous monitoring of the velocity field inside the Earth using methods such as ambient noise interferometry, coseismic rock weakening and post-seismic recovery of rock strength have also been recorded in the field over the past two decades. The question that we want to answer is: how relevant is the non-classical nonlinearity observed in the lab to the coseismic velocity drop in the field? To this end, we aim to adapt an analytical model that explains the lab observations and apply it to field observations using numerical simulations. Our first step is to identify the appropriate nonlinear model(s). Most of the proposed physical models that explain the phenomenon contain many parameters and are hard to constrain. Moreover, most of the existing physical models are restricted to 1D analysis and are difficult to generalize to 2D or 3D modeling.

 

We apply two models within the framework of the continuum damage mechanics: (i) the internal variable model (Berjamin et al., 2017) and (ii) the continuum damage model that accounts for parallel micro-cracks oriented perpendicular to the maximum tension or compression (Lyakhovsky et al., 1997). Both models can generalize to 2D and 3D. We formulate both models as nonlinear hyperbolic partial differential equations (PDEs) and solve them with the arbitrary high-order discontinuous Galerkin method using ExaHyPE (Reinarz et al., 2020) in 2D and 3D. We show that both models successfully reproduce the three phases during and after dynamic perturbations observed in the laboratory. We find that the continuum damage model can explain the amplitude- and frequency-dependent damage with a good match against the lab measurements. We also compare the simulation results using both models quantitatively with the observations in a 2D copropagating acousto-elastic testing (Feng et al., 2018). Our sensitivity analysis of the model parameters using the Markov chain Monte Carlo method quantitatively estimates the uncertainties and correlations among the parameters of both models. We believe our work paves the way towards a model of nonlinear rock deformation with slow dynamics that can be used in large scale 2D and 3D seismic wave propagation simulations for direct analysis of field observations, such as the Tohoku earthquake, 2011 (Brenguier et al., 2014).

How to cite: Niu, Z., Gabriel, A.-A., and Igel, H.: Numerical Simulation and Uncertainty Quantification of Models for Coseismic Damage and Healing of Rocks in 1D, 2D and 3D, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4450, https://doi.org/10.5194/egusphere-egu23-4450, 2023.

EGU23-4960 | ECS | Orals | SM8.1

An efficient poroelastic wave simulation based on discontinuous grid and nonuniform time step 

Heng Zhang, Hengxin Ren, Yao-Chong Sun, Mingbo Li, Tao Wang, and Changjiang Fang

The existence of slow P wave, in addition to fast P wave and S wave, makes it tricky for grid-based numerical simulation methods to conduct poroelastic wave modeling. The grid spacing has to be fine enough to capture the slow P wave since the velocity of slow P wave is much smaller than that of the other two waves. Dense space and time steps significantly increase the computation cost. In this study, we propose a poroelastic finite-difference simulation method that combines discontinuous curvilinear collocated-grid and non-uniform time step Runge-Kutta scheme. Only the space and time steps for the areas near interfaces, where the contribution of slow P wave is non-negligible, are refined in an effort to speed up the computation. The refined space step is determined by the velocity of slow P wave, while the coarse space step is determined by the velocity of shear wave. The coarse and refined time steps are set according to the non-uniform time step Runge-Kutta scheme, which is derived with Taylor expansion and avoids interpolation or extrapolation for communication between different time levels. This scheme helps maintain fourth-order accuracy in the whole domain. The accuracy and efficiency of the proposed method are verified by numerical tests. Compared with the conventional curvilinear collocated-grid finite-difference method that uses a uniform space grid as well as a uniform time step, the computation efficiency is improved significantly and the computation time can be saved by more than 80%.

How to cite: Zhang, H., Ren, H., Sun, Y.-C., Li, M., Wang, T., and Fang, C.: An efficient poroelastic wave simulation based on discontinuous grid and nonuniform time step, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4960, https://doi.org/10.5194/egusphere-egu23-4960, 2023.

EGU23-5365 | ECS | Posters on site | SM8.1

Ground motion simulation of the 2021 Mw 5.2 Central Adriatic earthquake 

Helena Latečki, Irene Molinari, and Josip Stipčević

In the last few decades, several series of earthquakes in the Central Adriatic Sea have been detected and analyzed, indicating the complexity of the tectonics within the Adriatic microplate. The most recent earthquake series suggests higher seismic potential than what was previously assumed and opens questions regarding present-day tectonic stress distribution within the Adria microplate in general. Therefore, studying seismic activity and identifying active faults is crucial when it comes to better understanding of the seismotectonics of this area, and consequently, improvement of the seismic hazard estimation. In this work we focus on the Mw 5.2 March 27, 2021 earthquake which occurred in the Central Adriatic Sea close to the island of Vis (Croatia). To evaluate the expected ground motion parameters of the event, we make use of physics-based waveform modelling. We simulate the earthquake using a newly defined 3D crustal model which honors surface topography, reflects main geological features and is embedded within the existing regional crustal model EPCrust. We compute broadband seismograms by making use of the hybrid approach where low-frequency and high-frequency parts are obtained separately and then combined into a single time series. We compare simulated waveforms against the recorded data and validate our results by assessing the goodness of fit for different ground-motion metrics. We then focus on simulating the waveforms using different descriptions of the source in order to investigate how its parametrization affects final results. This allows us to get a better understanding about the physical properties of the driving forces and mechanisms responsible for the seismicity in this region.

How to cite: Latečki, H., Molinari, I., and Stipčević, J.: Ground motion simulation of the 2021 Mw 5.2 Central Adriatic earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5365, https://doi.org/10.5194/egusphere-egu23-5365, 2023.

EGU23-5411 | Posters on site | SM8.1

How asperity size and neighboring segments can change the frictional response and fault slip behavior: insights from laboratory experiments and numerical models 

Fabio Corbi, Giacomo Mastella, Elisa Tinti, Matthias Rosenau, Laura Sandri, Silvio Pardo, and Francesca Funiciello

Accurate assessment of rate and state friction parameters is essential for producing realistic rupture scenarios and, in turn, for seismic hazard analysis. Those parameters can be directly measured in the laboratory, with experimental apparati that reproduce fault conditions in nature. Alternatively, indirect estimates (i.e., inversion) of rate and state parameters are based on postseismic slip evolution studies and numerical modeling. Both direct and indirect approaches require a series of assumptions that might bias the results.

Here we take advantage of a downscaled analog model reproducing experimentally megathrust earthquakes. The analog model shares many characteristics of real subduction zones, although being intentionally oversimplified with respect to nature. This allows reducing the number of potential sources of bias (e.g., fault geometry and asperity size). 

We perform five analog models with a single, rectangular asperity of different lengths embedded in a nearly velocity neutral matrix. We focus on two different physical conditions, namely the along-strike asperity length and the asperity to neighboring segments length ratio, and study systematically how they tune the model seismic behavior. Then, by coupling quasi-dynamic numerical models with the simulated annealing algorithm, we retrieve rate and state parameters that allow reproducing both the recurrence time, rupture duration and slip amplitude of the analog model, in ensemble. 

We identify a tradeoff between (a-b) of the asperity and (a-b) of neighboring creeping segments, with multiple combinations that allow mimicking the analog model behavior and variability. We also identify a negative correlation between (a-b) of the asperity and asperity size, with Dc remaining relatively constant within the investigated asperity size range. When estimating (a-b), poorly constrained properties of neighboring segments are responsible for uncertainties in the order of per mille. Roughly one order of magnitude larger uncertainties derive from asperity size. Those results provide a first order assessment of the variability that rate and state friction estimates retrieved for nature conditions might have when used as constraint to model fault slip behavior.

How to cite: Corbi, F., Mastella, G., Tinti, E., Rosenau, M., Sandri, L., Pardo, S., and Funiciello, F.: How asperity size and neighboring segments can change the frictional response and fault slip behavior: insights from laboratory experiments and numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5411, https://doi.org/10.5194/egusphere-egu23-5411, 2023.

EGU23-5539 | ECS | Posters virtual | SM8.1

Critical nucleation length for frictional slipping of an elastic layer over an elastic half-space 

Abhishek Painuly and Ranjith Kunnath

The interplay of geological forces and shear resistance of slipping surfaces leads to the expansion of earthquake ruptures, which nucleate in creeping zone patches. Once the dimension of the nucleating creeping zone exceeds a critical length, ruptures accelerate dynamically. The present work provides an analytic model to determine the critical nucleation length of a slip rupture. It is determined by performing a linear stability analysis of steady-state sliding of an elastic layer (having a finite height) over an elastic half-space in the quasi-static regime. Interfacial frictional behaviour is modelled using a rate- and state-dependent friction law with velocity weakening behaviour in the steady state, mimicking the experimental observations of interfacial friction. Results for critical nucleation length at the interface with similar and dissimilar materials across the interface are presented and the effect of layer height on the critical nucleation length is explored numerically.

How to cite: Painuly, A. and Kunnath, R.: Critical nucleation length for frictional slipping of an elastic layer over an elastic half-space, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5539, https://doi.org/10.5194/egusphere-egu23-5539, 2023.

EGU23-6056 | Posters on site | SM8.1

Seismic hazard assessment of the Lebanese Restraining Bend: A neo-deterministic approach 

Tony Nemer, Franco Vaccari, and Mustapha Meghraoui

The Lebanese Restraining Bend is an active bend along the Dead Sea Transform Fault in the eastern Mediterranean region where several destructive earthquakes happened throughout history. In this paper, we assess the gross features of seismic hazard of the Lebanese Restraining Bend by applying a neo-deterministic method that involves the generation of synthetic seismograms distributed on a regular grid over the study area. We use the regional seismicity, seismic source zones, focal mechanism solutions, and velocity structural models. We present maps of ground displacement, velocity, and acceleration. This is the first study that generates neo-deterministic seismic hazard maps for the Lebanese Restraining Bend using representative ground motion modelling. Our results show that displacement values of 15-30 cm and velocity values of 30-60 cm/s can be expected along most of Lebanon. In addition, 0.15-0.30 g acceleration values can dominate most of the Lebanese territory and surrounding areas. It is evident from these results that the study area in general and Lebanon in particular constitute a high seismic hazard area, which necessitates further attention from the authorities regarding the precaution measures needed to mitigate the effects of potential catastrophic seismic events; in addition, more detailed investigations are needed at local scale for specific sites of interest.

How to cite: Nemer, T., Vaccari, F., and Meghraoui, M.: Seismic hazard assessment of the Lebanese Restraining Bend: A neo-deterministic approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6056, https://doi.org/10.5194/egusphere-egu23-6056, 2023.

EGU23-6471 | ECS | Orals | SM8.1

SPHY3D: A hybrid seismic computational framework for box-tomography of spherical Earth 

Foivos Karakostas, Andrea Morelli, Irene Molinari, Brandon VanderBeek, and Manuele Faccenda

Computational seismology encountered a dramatic advance during the past decades with the development of SEM codes that use the simultaneous increase of the available computational power. Meanwhile, the use of teleseismic events for regional seismic tomography is suggested with the application of the box-tomography methodology (Masson and Romanowicz, 2017). In this work we use these advances in order to suggest a package for box-tomography, using AxiSEM for 1-D global wavefield simulations (Nissen-Meyer et al., 2014) and SPECFEM3D for 3-D regional seismic simulations (Komatitsch and Tromp, 1999). These codes have been previously used and validated for such hybrid simulations (Monteiller et al., 2021), however with the limitation on the dimensions of the examined region, where 3-D full waveform topography is applied, due to the Cartesian setting that does not honour the curvature of the Earth. Although recent advances solved this limitation for SPECFEM3D Global, by permitting the use of a small Earth chunk, the Cartesian description of the regional model allows computing the injection of the 1-D computed wavefield from the global model to the regional box. Therefore, we developed and present comparative results of a package that transforms the geometry of the Cartesian simulation in a "spherical Earth" setting and allows the performance of hybrid simulations for box tomography in regions larger than a couple of degrees. The code changes the shape of a Cartesian rectangular mesh into a curved one and through a series of interpolations adjusts the geometry of any given structure model, the topography of the surface and the interfaces, and the position of the receivers. The simulations are tested against real data, as we perform our computations on a dynamically interesting area, with the presence of a subduction slab in the central Mediterranean. We test the methodology on seismological inverse models for the local structure (Rappisi et al., 2021).

References:

Komatitsch, D. and Tromp, J., 1999. Introduction to the spectral element method for three-dimensional seismic wave propagation. Geophysical journal international, 139(3), pp.806-822.

Masson, Y. and Romanowicz, B., 2017. Box tomography: localized imaging of remote targets buried in an unknown medium, a step forward for understanding key structures in the deep Earth. Geophysical Journal International, 211(1), pp.141-163.

Monteiller, V., Beller, S., Plazolles, B. and Chevrot, S., 2021. On the validity of the planar wave approximation to compute synthetic seismograms of teleseismic body waves in a 3-D regional model. Geophysical Journal International, 224(3), pp.2060-2076.

Nissen-Meyer, T., van Driel, M., Stähler, S.C., Hosseini, K., Hempel, S., Auer, L., Colombi, A. and Fournier, A., 2014. AxiSEM: broadband 3-D seismic wavefields in axisymmetric media. Solid Earth, 5(1), pp.425-445.

Rappisi, F., VanderBeek, B.P., Faccenda, M., Morelli, A. and Molinari, I., 2022. Slab geometry and upper mantle flow patterns in the Central Mediterranean from 3D anisotropic P-wave tomography. Journal of Geophysical Research: Solid Earth, p.e2021JB023488.

How to cite: Karakostas, F., Morelli, A., Molinari, I., VanderBeek, B., and Faccenda, M.: SPHY3D: A hybrid seismic computational framework for box-tomography of spherical Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6471, https://doi.org/10.5194/egusphere-egu23-6471, 2023.

EGU23-6708 | ECS | Orals | SM8.1

On the importance of 3D stress state in 2D earthquake rupture simulations with off-fault deformation 

Marion Thomas, Louise Jeandet, and Harsha Bhat

During the last decades, many numerical models have been developed to explore the conditions for seismic and aseismic slip. Those models explore the behavior of frictional faults, embedded in either elastic or inelastic mediums, and submitted to a far field loading (seismic cycle models), or initial stresses (single dynamic rupture models). Those initial conditions impact both fault and off-fault dynamics. Because of the sparsity of direct measurements of fault stresses, modelers have to make assumptions about the initial conditions. To these days, Anderson theory is the only framework that can be used to link fault generation and reactivation to the three-dimensional stress field.  In this study, we focus on the initial stresses in 2D plane strain models developed to compute off-fault deformation. It has been demonstrated that initial conditions, in particular the angle between fault and the greatest compressive stress, is of crucial importance for the localization and intensity of off-fault inelastic deformation. However, because those models are performed on a 2D plane, the importance of the out-of-plane stress have never been investigated. We show that it can lead to set up a stress field that is not in agreement with Anderson theory (i.e., modelling a strike-slip fault in a three-dimensional stress field appropriate for reverse faulting). We investigate the influence of initial stresses by comparing equivalent models with “correct” and “incorrect” initial stress fields, keeping constant rupture-related parameters (stress drop, seismic ratio), angle between fault and greatest principal stress, and depth. We first use purely elastic models to study the influence of initial stresses on the assessment of two plastic criteria (Drucker-Prager and Coulomb stress change). We show that setting up the incorrect initial stress field can lead to underestimating the different yield criteria. The error is of the order of magnitude of the dynamic stress drop. Moreover, setting up the incorrect pre-stresses leads to errors in the estimation of potential off-fault failure modes. Then, we explore the influence of pre-stresses conditions on off-fault inelastic deformation. Using two different modelling strategies (a plastic deformation model and a micromechanics model computing dynamic damage), we show that setting up the incorrect stress field can lead to underestimate the size of the damage zone by a factor of 3 to 6 for the studied cases.  Moreover, because of the interactions between fault slip and off-fault deformation, we show that initial stress field influences the rupture propagation. Setting up the correct stress field can significantly slow the rupture, because of the more important quantity of damage induced.

How to cite: Thomas, M., Jeandet, L., and Bhat, H.: On the importance of 3D stress state in 2D earthquake rupture simulations with off-fault deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6708, https://doi.org/10.5194/egusphere-egu23-6708, 2023.

EGU23-7207 | Orals | SM8.1

Deciphering earthquake source observations to motivate questions for physics-based models of earthquake simulation 

Rebecca M. Harrington, Yajing Liu, Hongyu Yu, Alessandro Verdecchia, Kilian B. Kemna, Gian Maria Bocchini, Armin Dielforder, Marco P. Roth, James Kirkpatrick, Elizabeth S. Cochran, Hilary Chang, and Rachel E. Abercrombie

Earthquake stress drop values estimated from ground-motion spectra commonly vary by several orders of magnitude, particularly for small earthquakes (~M < 3). Stress-drop values have been found to vary with faulting style, faulting type (intraplate, interplate), depth, and to exhibit differences between natural and induced earthquakes. Nevertheless, distinguishing uncertainties from real trends across data sets is challenging, in part due to the variation in methodological approaches and observational constraints. However, the proliferation of high-quality, dense seismic data in recent years has shown that at least some of the variability in stress drop values almost certainly reflects diversity in fault strength and geological conditions. Coupling well-constrained observations to a variety of modeling approaches will help uncover what controls earthquake rupture processes, but deconvolving observational constraints from real variation in rupture behavior is key.

We present our stress drop estimates from data sets representing a wide range of fault loading conditions and geological environments, from interplate, intraslab and forearc subduction faults, to volcanic, intraplate, and human induced events. Stress-drop values range primarily between 1 – 100 MPa for events that meet the criteria for spectral-ratio analysis.  We present correlations of low relative stress drop values in areas of high seismic attenuation indicative of lower rock strength, and a slight correlation with depth that corresponds to modeled deviatoric stress values. We also show one notable subset of induced events near active injection wells that exhibit stress drop values of ~0.1 MPa and have distinctive low-frequency content. Their spatial distribution, waveform, and source spectral characteristics suggest either slower rupture, lower stress drop values, or a combination of both, and may represent part of the transition between aseismic and seismic slip. We show using a Large-n array that while stress drop values are roughly constant (within 2 orders of magnitude), estimates can vary by roughly 25% when station coverage is limited to 15 stations or less with a maximum azimuthal gap of 90°.  Our findings highlight the importance of using modeling approaches to explore relative influence of fault strength and methodological approaches in stress drop variation. In particular, models that incorporate both frictional and thermoelastic approaches may provide clues to the variability of conditions that can activate faults, both within stable sliding and seismic rupture conditions.

 
 
 
 

How to cite: Harrington, R. M., Liu, Y., Yu, H., Verdecchia, A., Kemna, K. B., Bocchini, G. M., Dielforder, A., Roth, M. P., Kirkpatrick, J., Cochran, E. S., Chang, H., and Abercrombie, R. E.: Deciphering earthquake source observations to motivate questions for physics-based models of earthquake simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7207, https://doi.org/10.5194/egusphere-egu23-7207, 2023.

EGU23-7795 | ECS | Posters on site | SM8.1

Testing sedimentary basin models for ground motion simulation: the case of the Fucino intramountain basin in the Apennines (Italy) 

Giulia Sgattoni, Irene Molinari, and Giuseppe Di Giulio

Sedimentary basins are of great interest for ground motion simulations, because of their power to amplify seismic motion and because urban areas are often built on sediment covers. Realistic and detailed 3D basin models have shown to significantly improve the physics-based ground motion modeling in terms of fit between recorded and synthetic seismograms. However, discerning between the uncertainties due to source, path or site effects is not simple.

A good proxy of the seismic response of small- to moderate-scale sedimentary basins is their resonance frequencies, often investigated by experimental measurement of the Horizontal to Vertical spectral ratio (H/V) computed on ambient seismic vibrations or earthquake records. Since these parameters strongly depend on the geometry and mechanical properties of the sediment fill, a wavefield numerical simulation in a realistic 3D media should ideally reproduce them. The comparison of resonance frequencies obtained from real and simulated waveforms can help in discerning inconsistencies in the 3D models, and may help in evaluating the goodness of the model and highlighting areas where it may be improved

We apply this approach in the Fucino intermountain sedimentary basin (Central Apennines, Italy) for which several stratigraphic models, exploration and geophysical data are available in the literature. We critically combine the stratigraphic models of the basin with regional crustal models available in the literature and build an appropriate 3D velocity model. We then perform 3D seismic wave propagation simulations using a spectral-element code; and we compare simulated and experimental seismograms and resonance frequencies for different basin models observing similarities and discrepancies.

How to cite: Sgattoni, G., Molinari, I., and Di Giulio, G.: Testing sedimentary basin models for ground motion simulation: the case of the Fucino intramountain basin in the Apennines (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7795, https://doi.org/10.5194/egusphere-egu23-7795, 2023.

EGU23-8199 | ECS | Posters on site | SM8.1

Grid-based Ray Theory Amplitude Calculation for Teleseismic Moment Tensor Sources 

Anne Mohr and Wolfgang Friederich

Direct numerical modeling of seismic wave propagation at high frequencies remains a computational challenge despite ever-increasing processing capabilities. Ray theory, which is based on a high-frequency solution of the seismic wave equation, provides an alternative to direct numerical modeling for sufficiently smooth velocity models. Here, we present a hybrid 1D-3D approach to model grids of seismic amplitudes of P-phases based on ray theory and dynamic ray tracing. They may serve to construct P-phase synthetic seismograms to be used in high-frequency teleseismic full waveform inversion or the interpretation of scattered and converted waves as done, for example, in receiver function analysis.

The modeling domain is split into two parts: 1D bulk earth and a box encompassing a regional study area for which a 3D model is used. 1D dynamic ray tracing and amplitude calculation for a moment tensor source is performed using ray paths calculated with Obspy TauP and the resulting transformation matrices and amplitudes are stored at the box boundaries. In the regional box ray paths from the box boundary to each grid point are calculated using the FM3D software by Rawlinson and Sambridge (2005) and de Kool, Rawlinson and Sambridge (2006). Subsequently, 3D dynamic ray tracing along all calculated rays is initialized from the box boundaries yielding amplitudes at each grid point.

The 1D method is tested by comparing amplitude ratios with those calculated using the software Gemini (Friederich and Dalkolmo 1995). The 3D method is tested using a 1D model and comparing amplitudes calculated using the hybrid 1D-3D method with amplitudes calculated using only the 1D method. Additionally, a 3D spherical velocity anomaly is inserted into a 1D background model to test the plausibility of the resulting amplitude grid for this model. The calculated amplitude grid clearly shows the expected focusing effects caused by the anomaly.

How to cite: Mohr, A. and Friederich, W.: Grid-based Ray Theory Amplitude Calculation for Teleseismic Moment Tensor Sources, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8199, https://doi.org/10.5194/egusphere-egu23-8199, 2023.

EGU23-8447 | ECS | Posters on site | SM8.1

The effects of 3D normal fault interactions in seismic cycles 

Constanza Rodriguez Piceda, Zoë Mildon, Martijn van den Ende, and Jean Paul Ampuero

Numerical earthquake simulators are valuable tools for investigating the causal dynamics between seismic events and improving our understanding of seismic sequences. This approach has been widely applied to single strike-slip faults, but physics-based simulations of earthquake cycles for normal fault(s) and networks are still limited. This is partly due to the focus on studying the California fault system and the computational cost of modelling dip-slip faults, which involve additional computations related to normal stress changes during the earthquake cycle. We aim to address this gap by focusing on the effect of normal fault interaction in the generation of complex seismic sequences. Using the open-source boundary-element method QDYN, we model two 3D normal faults incorporating rate-and-state friction and elastic interactions. We examine the impact of variable spatial offsets between the faults on different properties of the earthquake cycle, including slip, slip rate, magnitude distribution, and recurrence intervals within and between faults. By doing so, we aim to provide a physical explanation for the spatial and temporal variability observed in the geological record of natural normal fault networks, such as those found in the Central and Southern Apennines in Italy. Our results will shed light on the behaviour of normal fault networks and contribute to a more comprehensive understanding of earthquake cycles in these systems.  

How to cite: Rodriguez Piceda, C., Mildon, Z., van den Ende, M., and Ampuero, J. P.: The effects of 3D normal fault interactions in seismic cycles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8447, https://doi.org/10.5194/egusphere-egu23-8447, 2023.

EGU23-9857 | ECS | Posters on site | SM8.1

Propagation of SH waves in 2-D random media: from ballistic to diffusive behavior 

Malcon Celorio, Emmanuel Chaljub, Ludovic Margerin, and Laurent Stehly

Random inhomogeneities in the earth can highly influence the characteristics of propagating seismic waves. They exist at all scales and can become an important source of epistemic uncertainty in the ground motion estimation. Despite several works have evaluated these effects, few of them have verified the accuracy of their numerical solutions or controlled the propagation regime they were simulating. In this work we present a comprehensive study of SH wave propagation in 2D random media, which covers from ballistic to diffusive behaviors. In order to understand and identify the interaction of these regimes, we analyzed the coherent and incoherent components of the wavefield. The random media consist in correlated density and velocity fluctuations described by von Kármán autocorrelation function with a Hurst coefficient of 0.25 and a correlation length a=500 m. The Birch correlation coefficient which relates density to velocity fluctuations takes 4 possible values between 0.5 and 1, and the standard deviation of the perturbations is either 5% or 10%. Spectral element simulations of SH wave propagation excited by a plane wave are performed for normalized wavenumbers (ka) up to 5. By measuring the amplitude decay of the coherent wave we obtain the scattering attenuation, which is then compared with theoretical predictions from the mean field theory. Similarly, mean intensities from synthetic waveforms are also compared with those from radiative transfer theory. Both sets of comparisons show excellent agreement between numerical and theoretical predictions. Addionally, we perform statistical analyses on the fluctuations of the ballistic peak which exhibits a transition from log-normal to exponential distribution. These two types of distribution characterize the ballistic and diffusive behaviors, respectively, which means that after certain propagation distances the quasi-ballistic peak is composed mainly by multiply-diffused components. Such critical distance is of the order of the scattering mean free path and offers an alternative method to measure this parameter. Finally, we pay particular attention on the attenuation of the quasi-ballistic peak, which in the forward scattering regime appears to decay exponentially over a length scale known as the transport mean free path.

How to cite: Celorio, M., Chaljub, E., Margerin, L., and Stehly, L.: Propagation of SH waves in 2-D random media: from ballistic to diffusive behavior, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9857, https://doi.org/10.5194/egusphere-egu23-9857, 2023.

EGU23-10800 | ECS | Orals | SM8.1

The 1934 Bihar-Nepal Earthquake – Simulation of Broadband Ground Motions and Estimation of Site Amplification 

Jahnabi Basu, Sreejaya kp, and Raghukanth stg

The 1934 Bihar-Nepal earthquake, one of the most catastrophic events ever to occur in the Himalayas, inflicted extensive devastation with reported MMI of IX-VI in the Kathmandu valley and the Indo-Gangetic (IG) basin. The earthquake triggered significant ground liquefaction and landslides as it occurred in the proximity of densely populated river basins causing a huge economic loss and over 15700 fatalities. However, it is unfortunate that there are no ground motion data available for the event, as it remained unrecorded due to a lack of instrumentation. Therefore, simulating ground motions for the 1934 Bihar-Nepal earthquake would provide new insights into the influence of regional characteristics on Himalayan earthquakes. However, incorporating the Himalayan topography and the IG basin in the ground motion simulation is very challenging. In contrast, proper validation of modeling of ground motions is difficult due to the unavailability of recorded data. To circumvent these challenges, we simulated broadband ground motions for the 2015 Nepal earthquake, another significant catastrophe that occurred in the same seismo-tectonic region in the Himalayas which provides a well-recorded database. For the 2015 Nepal earthquake, a thorough comparison of the recorded and simulated ground motion spectra reveals that the simulated ground motions are consistent with the recorded data in terms of amplitude, strong motion duration, and spectral ordinates. Therefore, we considered the same medium characteristics to simulate broadband seismograms for the 1934 Bihar-Nepal earthquake by combining deterministically generated low-frequency (LF) and stochastically simulated high-frequency (HF) ground motions. The HF accelerograms are generated by considering incident and azimuthal angles obtained from rays of P and S waves traced from the finite fault slip model to the station, passing through the regional layered stratified velocity model, free surface factors and energy partition factors (Otarola and Ruiz, 2016). For deterministic simulation, a 3D computational model (Sreejaya et al., 2022) for the study region of approximately 9°×7° (between 80°–89°E longitude and 23°-30°N latitude), incorporated with basin geometry, material properties, and topography of the region is embedded with the finite fault rupture model of the event to generate LF ground motions. For the finite fault source model, five samples with various spatial variability of the slip on the rupture plane are simulated as a random field (Mai and Beroza, 2000; 2002) using the seismic moment and fault dimensions provided by Pettanati et al. (2017). Ultimately, the broadband (0.01–25 Hz) ground motions are obtained at 6461 hypothetically gridded stations with a 0.1°×0.1° spacing by combining the suitably filtered LF and HF ground motions in the frequency domain with the target frequency of 0.3 Hz with a bandwidth up to 0.05 Hz. A systematic comparison of estimated MMI values (Iyengar and Raghukanth, 2003) and the observed MMI values at 459 sites revealed that the PGA between 0.25-0.6g is significant within 200 km of the epicentral distance. Thus, the results can be used for addressing the ground failure and liquefaction caused due to the earthquake and also find applications in seismic hazard assessment of the cities in the basin.

How to cite: Basu, J., kp, S., and stg, R.: The 1934 Bihar-Nepal Earthquake – Simulation of Broadband Ground Motions and Estimation of Site Amplification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10800, https://doi.org/10.5194/egusphere-egu23-10800, 2023.

EGU23-10831 | ECS | Orals | SM8.1

Do the statistical properties of aftershocks change in fluid-induced settings? 

Omid Khajehdehi and Joern Davidsen

Fluid-induced earthquakes are an adverse effect of industrial operations like hydraulic fracturing (e.g., 4.7 Mw in Alberta, Canada), and enhanced geothermal systems (e.g., 5.5 Mw in Pohang, South Korea). Identifying all underlying physical processes contributing to fluid-induced seismicity presents an open challenge. Recent work reports signatures of event-event triggering or aftershocks --- common for tectonic settings --- within the context of fluid-induced seismicity. In particular, the statistical properties including the productivity relation and the Omori-Utsu relation appear to hold for fluid-induced seismicity as well. Here, we investigate the underlying potential cause of these field observations from a modelling perspective. By extending a novel conceptual model by integrating (non-)linear viscoelastic effects with a combination of fluid diffusion and invasion percolation associated with a point source, we are able to capture the essential characteristics of crustal rheology and stress interactions in a porous medium. We show that this gives rise to realistic aftershock behaviour with statistical properties indistinguishable from the case of seismicity resulting from tectonic loading. This is even true if the loading due to fluid injections occurs at time scales much faster than the tectonic loading. In our model framework, such tectonic loading can be mimicked by a spatially uniform drive replacing the point source of the fluid injection and its propagation to initiate slips and earthquakes. This indicates that the emergence of the Omori-Utsu relation is independent of how the system is loaded or driven and it is indeed only controlled by the viscoelasticity of the medium. Similarly, the scaling exponent of the productivity relation --- which quantifies how the number of aftershocks increases with the magnitude of the main shock --- is independent of how the system is driven. At the same time, the spatial footprint of fluid-induced events and its dependence on the permeability field are primarily unaltered by the presence of aftershocks. Finally, within our model framework, we systematically investigate the impact of varying fluid injection rates during the viscoelastic stress redistribution on the detection of aftershocks and event-event triggering sequences. When the injection rate is sufficiently high, the aftershock detection and recovery of the Omori-Utsu and productivity relations is only feasible when the internal stress redistribution is directly accessible. 

How to cite: Khajehdehi, O. and Davidsen, J.: Do the statistical properties of aftershocks change in fluid-induced settings?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10831, https://doi.org/10.5194/egusphere-egu23-10831, 2023.

Both numerical simulations and observational pieces of evidence suggest that the earthquake triggering mechanism depends non-linearly on time. The rate and state friction (RSF) demonstrate these dependencies with a changing weight of healing and weakening terms during its state's evolution. A clock advance due to a nearby rupture using the RSF models either agrees well with the Coulomb's static failure during the fault healing stage or becomes highly susceptible to velocity changes when the failure is imminent. Here we aim to formulate an analytical relation for earthquake triggering effects on nearby faults using transient signals. The dynamic mechanical weakening on the fault interface is quantified as a function of a transient oscillatory signal's peak ground velocity (PGV) and peak spectral frequency (PSF), elastic properties of the fault, and different state weakening terms. So far, the tested numerical simulations show a good agreement with our proposed analytical approach. As a case study, nearby seismic waveforms recorded during the M6.4 (04.07.2019) event that preceded the larger  M7.1 (06.07.2019) Ridgecrest earthquake are used to calculate mechanical weakening, which correlates well with the computed PGV values attenuating with distance. The results support that if inadequate instrumentation exists, those dynamic weakening effects can be approximated empirically using the source parameter of the triggering event as a function of distance and directivity. Derivation of this analytical relation with additional verifications from numerical simulations will contribute to simultaneously including dynamic and static effects. This may lead to a more realistic estimation of increased seismic risk on nearby faults after an earthquake.  

How to cite: Sopacı, E. and Özacar, A. A.: Transient signal-based quantification of earthquake triggering effects on nearby faults using rate and state friction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11198, https://doi.org/10.5194/egusphere-egu23-11198, 2023.

An M6.8 earthquake occurred in Luding, Sichuan province, China on September 5, 2022. Since towns and villages in the earthquake-stricken area are densely populated, the earthquake caused severe fatalities and economic losses. Rapid estimation of earthquake intensity and disaster losses is significantly important for post-earthquake emergency rescue, scientific anti-seismic deployment, and the reduction of casualties and financial losses. Therefore, we make a preliminary rapid estimation of the earthquake intensity and disaster losses in the aftermath of the Luding earthquake. The seismic intensity represents the distribution of earthquake disasters and the degree of ground damages and can be directly converted from the peak acceleration velocity (PGV) map. To obtain a reliable PGV distribution map of this earthquake, we combined the finite-fault model constrained by seismic observations, with the complex three-dimensional (3D) geological environment and topographical features to perform strong ground motion simulation. Then, we compared the consistency between the simulated ground motion waveforms and observations, indicating the plausibility and reliability of simulations. In addition, we transformed the PGV simulation results into intensity and obtained a physics-based map of the intensity distribution of the Luding earthquake. The maximum simulated intensity of this earthquake is IX, which is consistent with the maximum intensity determined from the post-earthquake field survey. Based on the simulated seismic intensity map of the Luding earthquake and the earthquake disaster loss estimation model, we rapidly estimated the death and economic losses caused by this earthquake. The estimation results show that the death toll caused by this earthquake is most probably in the range of 50-300, with a mathematic expectation of 89 The government should launch a Level II earthquake emergency response plan. The economic losses are likely to be in the range of 10-100 billion RMB, with a mathematical expectation of 23.205 billion RMB. Such seismic intensity simulations and rapid estimation of disaster losses are expected to provide a preliminary scientific reference for governments to carry out the targeted deployment of emergency rescue and post-disaster reconstruction.

How to cite: Wang, W. and Zhang, Z.: Rapid Estimation of Disaster Losses by Physics-based Simulation for the M6.8 Luding Earthquake on September 5, 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11250, https://doi.org/10.5194/egusphere-egu23-11250, 2023.

EGU23-11710 | Orals | SM8.1

Deterministic and Stochastic Chaos characterise Laboratory Earthquakes 

Adriano Gualandi, Davide Faranda, Chris Marone, Massimo Cocco, and Gianmarco Mengaldo

We analyze frictional motion for a laboratory fault as it passes through the stability transition from stable sliding to unstable motion. We study frictional stick-slip events, which are the lab equivalent of earthquakes, via dynamical system tools in order to retrieve information on the underlying dynamics and to assess whether there are dynamical changes associated with the transition from stable to unstable motion. We find that the lab seismic cycles exhibit characteristics of a low-dimensional system with average dimension similar to that of natural slow earthquakes (<5). We also investigate local properties of the attractor and find maximum instantaneous dimension >10, indicating that some regions of the phase space require a high number of degrees of freedom (dofs). Our analysis does not preclude deterministic chaos, but the lab seismic cycle is best explained by a random attractor based on rate- and state-dependent friction whose dynamics is stochastically perturbed. We find that minimal variations of 0.05% of the shear and normal stresses applied to the experimental fault influence the large-scale dynamics and the recurrence time of labquakes. While complicated motion including period doubling is observed near the stability transition, even in the fully unstable regime we do not observe truly periodic behavior. Friction's nonlinear nature amplifies small scale perturbations, reducing the predictability of the otherwise periodic macroscopic dynamics. As applied to tectonic faults, our results imply that even small stress field fluctuations (less or about 150 kPa) can induce coefficient of variations in earthquake repeat time of a few percent. Moreover, these perturbations can drive an otherwise fast-slipping fault, close to the critical stability condition, into a mixed behavior involving slow and fast ruptures.

How to cite: Gualandi, A., Faranda, D., Marone, C., Cocco, M., and Mengaldo, G.: Deterministic and Stochastic Chaos characterise Laboratory Earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11710, https://doi.org/10.5194/egusphere-egu23-11710, 2023.

EGU23-11827 | ECS | Posters on site | SM8.1

The role of frictional heterogeneities, stress-state and fluid flow on fault slip behavior during fluid pressure perturbations. 

Silvio Pardo, Elisa Tinti, Martijn van den Ende, Jean-Paul Ampuero, and Cristiano Collettini

In the last 15 years, activities for geo-energy production are associated to subsurface fluid injection in enhanced geothermal systems,  for enhanced oil recovery, for the disposal of wastewater or for carbon dioxide capture and storage. In several regions, M>3 earthquakes occurred following fluid injection, and some of these earthquakes have caused extensive damage, putting geo-energy production projects at risk of being discontinued. Evaluating the conditions under which fluid injection can induce earthquakes is therefore important to safeguard local infrastructures and to ensure continuity of geo-energy projects.  

To shed light on the effect of fluid injection on a fault located in the proximity of a reservoir, we implemented into the Q-DYN seismic cycle simulator the fluid diffusion equation (one-way coupling). We ran models of seismic cycles on a rate-and-state-dependent fault under a quasi-dynamic approximation, and we developed a systematic study to assess how fault frictional heterogeneities, the stress state of the fault upon injection, the timing of injection relative to the phase of the seismic cycle and factors controlling fluid flow, i.e. permeability, porosity, flow-rate, influence fault slip behavior and earthquake magnitude. 

Our results show that localized pore-pressure perturbations allow us to gain deeper physical insight into the propagation and arrest of earthquake ruptures and that changes in the fault physical properties can promote a spectrum of fault slip behavior and recorded magnitudes.

How to cite: Pardo, S., Tinti, E., van den Ende, M., Ampuero, J.-P., and Collettini, C.: The role of frictional heterogeneities, stress-state and fluid flow on fault slip behavior during fluid pressure perturbations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11827, https://doi.org/10.5194/egusphere-egu23-11827, 2023.

EGU23-11928 | ECS | Orals | SM8.1

Moment vs local magnitude scaling of small-to-moderate earthquakes from seismic moment estimation of 10 years (2009-2018) of Italian seismicity 

Mariano Supino, Lauro Chiaraluce, Raffaele Di Stefano, Barbara Castello, and Maddalena Michele

We computed moment (Mw) and local magnitude (ML) of about 250,000 earthquakes occurred in Italy from 2009 to 2018 and recorded at seismic stations of the Italian National Network managed by INGV.

For moment magnitude computation, we start from raw velocity waveforms and invert the displacement spectra of more than 2,000,000 S-waves manually picked. We use the probabilistic method of Supino et al. [2019] to estimate the a-posteriori joint probability density function of the source parameters: seismic moment M0, corner frequency fc and high-frequency decay γ. Mw is obtained from M0 using the Kanamori [1977] equation.

We start from the same waveforms to compute local magnitude using two designed on purpose codes, PyAmp and PyML [Di Stefano et al., 2023], and an attenuation law specific for the Italian region, Di Bona et al. [2016], obtaining ML values characterized by quality and homogeneity.

Both magnitude catalogs can be reproduced due to the availability in open databases of all the input and output parameters used for processing.

We observe a self-similar scaling between fc and M0 for Mw larger than ~2.0. For smaller magnitudes, S-wave spectra show an almost constant corner frequency (~10 Hz), which does not scale with the earthquake source (seismic moment). We interpret this as the constant cut-off frequency of the anelastic attenuation, which acts as a low-pass filter and produces an apparent corner frequency. The latter is lower than expected, and corresponds to an apparent larger source duration.

Because of the conservation of total displacement integral after a low-pass filtering, signals must exhibit a maximum amplitude lower than expected to “compensate” the apparent larger source duration. ML values are therefore expected to be underestimated while moment magnitudes, by definition, are not affected by this as they are proportional to the displacement integral.

Coherently, the comparison of our Mw and ML estimates shows the systematic underestimation of ML with respect to Mw for small magnitude events. The deviation from a 1:1 scaling relationship between ML and Mw overlaps the magnitude range where the constant apparent corner frequency arises in the M0-fc scaling (ML <~ 2).

Regarding the upcoming of a new generation of earthquake catalogs characterized by very low completeness magnitudes (MC << 2), our results suggest that a robust analysis of the statistical features of these catalogs (e.g., event size distribution) should consider the use of a precise magnitude estimate such as Mw instead of ML.

How to cite: Supino, M., Chiaraluce, L., Di Stefano, R., Castello, B., and Michele, M.: Moment vs local magnitude scaling of small-to-moderate earthquakes from seismic moment estimation of 10 years (2009-2018) of Italian seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11928, https://doi.org/10.5194/egusphere-egu23-11928, 2023.

Ground motion prediction equations (GMPE) are traditionally used in site specific seismic hazard analysis to obtain design response spectra. These equations are obtained by regression analysis on the available strong motion data in a given tectonic and geological region. Assuming ergodicity regional GMPE are routinely used in site-specific probabilistic seismic hazard analysis. Since these empirical equations are region specific, However the obtained seismic hazard curves are not specific to the site. Due to lack of data for all possible combinations of magnitude and distances, development of site-specific GMPE is not possible in the near future. The only way to develop a site-specific GMPE is through numerical models. Given a 3D velocity structure, topography and source information these models can simulate site-specific ground motion. Once calibrated with the recorded strong motion data, numerical models can be used to simulate ensemble of ground motions by including the uncertainty in the slip models. In regions lacking strong motion data, these models have an additional advantage compared to GMPE. In the present study, an broad band simulation model is developed for a typical site in peninsular India. Spectral finite element method (SPECFEM) is used to simulate the low frequency ground motion by incorporating the 3D velocity structure in the medium. The high frequency ground motion is simulated from the stochastic seismological model (Otarola and Ruiz, 2016). Statistical kinematic rupture model is used to represent the earthquake source (Dhanya and Raghukanth 2018). The rupture length, width and correlation lengths of the random field are estimated from magnitude. Assuming the phase as random, a total of 30 rupture models are simulated for each magnitude. An ensemble of ground motions is simulated at the site for various possible combination of faults and magnitudes in a region around 500 km from the site. The simulated low-frequency and high-frequency ground motions are combined in the frequency domain to obtained broad band ground motions (0-100 Hz). The mean and standard deviation of the response spectra are estimated from these simulated motions for all possible combinations of magnitudes and distances at the given site. Further, probabilistic seismic hazard analysis is carried out using the simulated data to obtain hazard curves for spectral accelerations at various natural periods. Uniform hazard response spectra (UHRS) for 475yr and 2475 yr is obtained from the hazard analysis. A comparison with traditional hazard analysis using region specific GMPE is also presented. It is observed GMPE based UHRS show a smooth trend compared with site-specific UHRS obtained from broad band models. The PGA values obtained from physics based model are slightly higher than that obtained from GMPE based PSHA.

How to cite: Stg, R.: Physics based ground motion model in seismic hazard assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12317, https://doi.org/10.5194/egusphere-egu23-12317, 2023.

EGU23-12897 | ECS | Posters on site | SM8.1

Resolving Hydro-Mechanical Earthquake Cycles with a GPU-based Accelerated Pseudo-Transient Solver 

You Wu, Luca Dal Zilio, Albert De Monserrat, and the Bedretto Team

Modeling earthquake source processes is a multi-physics and multi-scale endeavor that tightly links several disciplines, including seismology, numerical computing, continuum mechanics, materials science, and engineering. In particular, incorporating the full range of coupled mechanisms, including complex fault geometries, off-fault inelastic processes, realistic shear-layer response, and fluid effects, brings significant programming and computational challenges. Furthermore, the development of highly efficient, robust and scalable numerical algorithms lags behind the rapid increase in massive parallelism of modern hardware. To address this challenge, we present a physically motivated derivation of coupled solid-fluid interactions on faults using an innovative accelerated pseudo-transient (PT) iterative method. The general approach involves transforming a time-independent problem into an evolution problem, which allows us to utilize the benefits of the Method-of-Lines (MOL) approach with the accelerated PT method. Additionally, we provide an efficient numerical implementation of PT solvers on graphics processing units (GPUs) using the Julia programming language. Julia solves the “two-language problem”, where developers who write scientific software can achieve desired performance, without sacrificing productivity. As a result, this enables us to develop high-performance code for massively parallel hardware with modern GPU-accelerated supercomputers, without requiring architecture-specific code. We aim to unveil preliminary results on the application of PT solvers to fully compressible poro-visco-elasto-plastic media, wave-mediated fully dynamic effects, rate-and-state dependent friction, and an adaptive time stepping to resolve both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of dynamic rupture. Our work can contribute to a better understanding of the accelerated PT method and its potential for facilitating the implementation of various numerical models in the field of computational earthquake physics. 

How to cite: Wu, Y., Dal Zilio, L., De Monserrat, A., and Team, T. B.: Resolving Hydro-Mechanical Earthquake Cycles with a GPU-based Accelerated Pseudo-Transient Solver, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12897, https://doi.org/10.5194/egusphere-egu23-12897, 2023.

EGU23-13098 | ECS | Orals | SM8.1

Simulations of ground motion in the Tehran basin based on newly developed 3D velocity model 

Saeed Soltani, Cecile Cornou, Bertrand Guillier, and Ebrahim Haghshenas

Tehran urban area serves as the main hub for economic and social activities in Iran. The city is located on a sedimentary basin including faults and folds, and thus it is vulnerable to large site effects. Analysis of earthquakes recorded by a temporary seismological network has approved a large amplification of seismic ground motion (about 4 to 8) over a broad frequency range.

In order to better understand and predict the effects of the geometry and mechanical properties on surface ground motions, we developed a 3D shear-wave velocity model of Tehran by integrating extensive geophysical surveys including almost 600 single station measurements and 33 ambient vibrations arrays, with geotechnical and geological data. This 3D model shows that the bedrock depth varies between 100 and 900 meters with a general increasing depth from N-NE toward the S-SW. Also, there are two main velocity layers in the basin. A surface layer, which drops from 950 m/s to 600 m/s from NE to SW and a deeper layer with Vs up to 1300 m/s.

We then used the open-source spectral-element code, EfiSpec3D (DiMartin et al., 2011), to simulate ground motion by this new sedimentary basin model at the defined 50*50 kilometers tilted square simulation block up to the maximum target frequency of 2 Hz. The source time function is a 2-Hz lowpass filtered Dirac impulse injected from the defined z-plane at 5 km depth.

The results reveal a good correlation between real and simulated earthquake ground motion by the comparison between experimental and synthetic standard spectral ratios (SSR). The results also reproduced the experimental H/V frequency peaks over the basin relatively well and suggest that 3D geometry always should be considered for an accurate estimation of realistic basin response.

How to cite: Soltani, S., Cornou, C., Guillier, B., and Haghshenas, E.: Simulations of ground motion in the Tehran basin based on newly developed 3D velocity model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13098, https://doi.org/10.5194/egusphere-egu23-13098, 2023.

The model discretization by the grid points has a great influence on the accuracy of the finite-difference seismic waveform simulation. Discretizing the discontinuous velocity model by the medium parameters of local points will lead to artefacts diffraction from stair-step representation and the inaccuracy of the calculated waveforms due to the interface error. To accurately represent layered models and reduce the interface error of finite-difference calculation, many equivalent medium parametrization methods have been developed in recent years. Most of these methods are developed for the fourth-order staggered-grid scheme and may not be accurate enough for coarse grids when applying higher-order and optimized schemes.

In this work, we develop a tilted transversely isotropic equivalent medium parametrization method to suppress the interface error and the artefact diffraction caused by the staircase approximation under the application of coarse grids. We also present an efficient algorithm for implementing equivalent medium parameterization methods for complex layered models.

How to cite: Jiang, L. and Zhang, W.: A discrete representation and the implementation for the finite-difference seismic waveform simulation with coarse grid, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13217, https://doi.org/10.5194/egusphere-egu23-13217, 2023.

EGU23-13574 | ECS | Orals | SM8.1

Evidence of frequency-dependent directivity effects from non-ergodic ground motion modelling of Spectral Acceleration in Central Italy 

Leonardo Colavitti, Giovanni Lanzano, Sara Sgobba, Francesca Pacor, and František Gallovič

Rupture directivity and its potential frequency dependence is an open issue in the seismological community, especially for small-to-moderate earthquake. Directivity itself is the focusing of the radiated seismic wave energy due to the rupture propagation along the direction of the fault.

In this research, we calibrate a non-ergodic ground motion model for the ordinates of the 5% acceleration response spectra (computation interval 0.04-2 sec) and we analyse, earthquake by earthquake, the azimuthal dependence of the aleatory component, i.e. the residual terms corrected for systematic source, site and path contributions. The final aim is the calibration of a prediction model including directivity effects that can be used for engineering purposes such as seismic hazard assessment and shaking scenarios generation.

The study area is the Central Italy, which was affected by several seismic sequences in the last 20 years, occurred on normal fault systems. The dataset we used is composed by almost 300,000 seismic recordings of 456 earthquakes in the magnitude range from 3.4 to 6.5 within the time frame 2008-2018. We find that about one-third of the analysed events are directive, characterized by unilateral ruptures along the Apennine faults direction.

Directivity effects occur over a wide frequency band and can be described by spectral curves peaked in different frequency ranges according to the event magnitude: the stronger the earthquake, the lower the frequency at which these effects are visible. Vice versa, we find no correlation between the amplitude of such peaks and the events magnitude. When normalized to the peak, the directivity curves can be grouped into families characterized by similar amplification trends variable with frequency, with the exception of 16 events, which we classify as "super-directive", that differ markedly from the others generating broadband amplifications.

Preliminary results suggest that is possible to obtain similar shapes of directivity curves for defined frequency families and that they can consequently be modeled for non-ergodic ground motion model and predictive shaking scenarios.

How to cite: Colavitti, L., Lanzano, G., Sgobba, S., Pacor, F., and Gallovič, F.: Evidence of frequency-dependent directivity effects from non-ergodic ground motion modelling of Spectral Acceleration in Central Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13574, https://doi.org/10.5194/egusphere-egu23-13574, 2023.

EGU23-13815 | ECS | Posters on site | SM8.1

Numerical modeling of fault and rupture co-evolution using a damage-breakage rheology with granular rate-and-state friction 

Casper Pranger, Dave May, Ludovic Raess, Yehuda Ben-Zion, and Alice-Agnes Gabriel

A recently developed continuum formulation of rate and state friction (Pranger et al., 2022) treats fault friction as an internal flow process in a granular medium, instead of its conventional treatment as a sliding process on a surface between juxtaposed rocks. The spurious mesh dependency that is typically associated with strain softening rheologies is avoided by including a diffusion process with an associated diffusion length scale.

We show that this granular rate and state friction law can be understood as a flow involving the breakage component of the damage-breakage rheology (DBR) of Lyakhovsky and Ben Zion (2014a,b). Modeling the episodic transitions from local damage accumulation in the solid to the fluid-like granular flow phase during larger collective failure events, the DBR is both significantly broader in scope and better grounded in the thermodynamic theory of irreversible processes than the phenomenological rate and state friction law.

A promising next step is to consider the damage and breakage components simultaneously in coupled continuum models of fault and rupture co-evolution. Doing so at sufficient resolution requires highly performant algorithms and a specialized numerical treatment of the coupled non-linear partial differential equations, including a robust time integration scheme with adaptive step size control and a flexible implicit-explicit split. We aim to discuss our numerical methods and computing paradigms supported by proof-of-concept modeling results of interacting damage and breakage pulses in 2D.

References:
Pranger et al. (2022), Rate and state friction as a spatially regularized transient viscous flow law. Journal of Geophysical Research: Solid Earth, 127, e2021JB023511.
Lyakhovsky and Ben-Zion (2014a), Damage–breakage rheology model and solid-granular transition near brittle instability. Journal of the Mechanics and Physics of Solids, 64, 184-197.
Lyakhovsky and Ben-Zion (2014b), A Continuum Damage–Breakage Faulting Model and Solid-Granular Transitions. Pure and Applied Geophysics, 171, 3099–3123

How to cite: Pranger, C., May, D., Raess, L., Ben-Zion, Y., and Gabriel, A.-A.: Numerical modeling of fault and rupture co-evolution using a damage-breakage rheology with granular rate-and-state friction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13815, https://doi.org/10.5194/egusphere-egu23-13815, 2023.

EGU23-13982 | Posters virtual | SM8.1

Effect of 3D Topography on Physics-Based Earthquake Ground Motion characteristics. 

Vishal Vats, Lav Joshi, and Jay Prakash Narayan

This paper presents the effects of 3D conical topography on the pseudo-dynamically simulated ground motion characteristics. The simulation of pseudo-dynamic ground motion has been carried out using a fourth-order accurate staggered-grid time-domain 3D finite-difference method. In the case of numerical simulations, the radiation of seismic energy from the rupture plane as per Brune’s model as well as avoiding the coherency effects is a challenging job for the simulators. The randomization of slip, rise-time, and peak-time of the source time function and the rupture arrival time, as well as the incorporation of fault-roughness and damage zone, play important roles in seismic energy release from the rupture plane as well as in the reduction of currency effects on the high-frequency seismic radiations. Firstly, the ground motions have been simulated for a hypothetical strike-slip Mw 6.0 earthquake. The efficacy of the presented code has been validated with a good match of the computed average pseudo-spectral acceleration (PSA) using the simulated ground motion with that obtained using NGA-West2 GMPEs in the frequency range 0.1–5.0 Hz. The code has been able to correctly incorporate the rupture directivity effect. Further, the effect of 3D conical topography has been estimated with azimuthal coverage of receivers. The effect of the direction of the source on the topographic amplification has also been estimated. It has been observed that topography plays an important role in the amplification of earthquake ground motion. Also, the direction of the source plays an important role in estimating the pattern of topographic amplification.

How to cite: Vats, V., Joshi, L., and Narayan, J. P.: Effect of 3D Topography on Physics-Based Earthquake Ground Motion characteristics., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13982, https://doi.org/10.5194/egusphere-egu23-13982, 2023.

EGU23-14252 | ECS | Posters on site | SM8.1

Hamiltonian Monte Carlo Method and Symplectic Geometry 

Feyza Öztürk, Çağrı Diner, and Tevfik Mustafa Aktar

Hamiltonian Monte Carlo (HMC) method is an application of non-Euclidean geometry to inverse problems. It is a probabilistic sampling method with the basis of Hamiltonian dynamics. One of the main advantages of the HMC algorithm is to draw independent samples from the state space with a higher acceptance rate than other MCMC methods. In order to understand how a higher acceptance rate is achieved, I have studied HMC in the light of symplectic geometry. Hamiltonian dynamics is defined on the phase space (cotangent bundle), which has a natural symplectic structure, i.e. a differential two-form that is non-degenerate and closed.

Symplectic geometry lies at the very foundations of physics: Geometry is the method of abstracting the solutions of physical phenomena. Once the use of phase space in the solutions of mechanical systems (e.g. simple harmonic motion, or ray-tracing) is abstracted via geometry, then it can be used in other branches such as optimization problems (e.g. Hamiltonian Monte Carlo). I present two different applications of symplectic geometry: Ray-tracing and Hamiltonian Monte Carlo.

First, the Hamiltonian function is defined on the phase space, which corresponds to an invariant of the system (e.g. total energy for the HMC method and wavefront normal for ray-tracing problem), and then by using the non-degeneracy property, a vector field can be found in which Hamiltonian function is invariant along the integral curves of the field. The invariance of the Hamiltonian function results in a high acceptance rate, where we apply the accept-reject test to satisfy the detailed-balance property.

After describing the concept of phase space for both mechanical systems and optimization problems, I am going to show different applications of HMC, including 2-dimensional travel-time tomography on a synthetic complex velocity structure. 

How to cite: Öztürk, F., Diner, Ç., and Aktar, T. M.: Hamiltonian Monte Carlo Method and Symplectic Geometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14252, https://doi.org/10.5194/egusphere-egu23-14252, 2023.

EGU23-14727 | Orals | SM8.1

Fast Boundary Element Methods for fault mechanics and earthquake control 

Laura Bagur, Stéphanie Chaillat, Jean-François Semblat, Ioannis Stefanou, and Pierre Romanet

Earthquakes due to either natural or anthropogenic sources cause important human and material damage. In both cases, the presence of pore fluid influence the triggering of seismic instabilities. Preliminary results, done in the context of the European Research Council CoQuake’s project (www.coquake.eu), show that the earthquake instability could be avoided by active control of the fluid pressure [Stefanou, (2019)].
In this contribution, we propose to study the ability of Fast Boundary Element Methods (Fast BEMs) [Chaillat and Bonnet (2013)] to provide a multi-physic large-scale robust model required for modeling earthquake processes, pore-fluid-induced seismicity and their control.
The main challenges concern:

  •  the modelling of a realistic on-fault behaviour as well as hydro-mechanical couplings;
  • the extension of Fast Boundary Element methods to fault mechanic problems incorporating the effect of fluid injection of the on-fault behaviour;
  • the simulation of both small and large time scales corresponding to earthquakes and fluid diffusion respectively by using a single advance in time algorithm.

The main methods used for numerical modeling of earthquake ruptures at a planar interface between two elastic half-spaces are spectral BEMs as in [Lapusta and al. (2000)]. As a first step, we consider this method for a simple problem in crustal faulting. A rate-and-state friction law is considered and different adaptive time stepping algorithms inspired from the literature are tested to take into account both small and large time scales with the correct resolution in time. These solving methods are compared on different benchmarks and convergence studies are conducted on each of them.
Then, poroelastodynamic effects are considered. To this aim, a dimensional analysis of generic poroelastodynamic equations [Schanz (2009)] is performed. It allows determining which of the poroelastodynamics effects are predominant depending on the observation time of the fault. The obtained equations corroborate and justify simplified multiphysics models from the literature, for example [Heimisson and al. (2021)]. A first multi-physics test using Fast BEMs to solve a simplified crustal faulting problem with fluid injection is considered. The objective of this project is to provide a viable efficient tool to explore the advantages and limitations of novel strategies of earthquake control using fluid injection to drive the fault from an unstable state of high potential energy to a stable state of lower potential energy.

References:

S. Chaillat, M. Bonnet. Recent advances on the fast multipole accelerated boundary element method for 3D time-harmonic elastodynamics, Wave Motion, 1090-1104, 2013
E. R. Heimisson, J. Rudnicki, N. Lapusta. Dilatancy and Compaction of a Rate-and-State Fault in a Poroelastic Medium: Linearized Stability Analysis., Journal of Geophysical Research: Solid Earth, 126(8), 2021
N. Lapusta, J. Rice and al.. Elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate- and state-dependent friction, Journal of Geophysical Research: Solid Earth, 23765-23789, 2000.
M. Schanz. Poroelastodynamics: Linear Models, Analytical Solutions, and Numerical Methods., Applied Mechanics Reviews, 62(3)., 2009.
I. Stefanou. Controlling Anthropogenic and Natural Seismicity: Insights From Active Stabilization of the Spring‐Slider Model, Journal of Geophysical Research: Solid Earth, 8786-8802, 2019.

How to cite: Bagur, L., Chaillat, S., Semblat, J.-F., Stefanou, I., and Romanet, P.: Fast Boundary Element Methods for fault mechanics and earthquake control, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14727, https://doi.org/10.5194/egusphere-egu23-14727, 2023.

Large-scale and high-resolution earthquake simulations are very significant to earthquake hazard evaluation and exploration seismology. However, high-resolution earthquake simulations require large computing and storage resources, which increase the economic cost of computing. Compared with single-precision floating-point numbers (FP32), half-precision floating-point numbers (FP16) have faster calculation speed and lower storage requirements, which have been applied to computing platforms such as Nvidia GPUs, Sunway series supercomputers, and Ascend processors. However, the stored range of FP16 is very narrow, and numerical overflow or underflow may occur during the calculations. Therefore, in order to solve the wave equations stably, we introduce two scaling factors Cv and Cs, and rescale physical quantities to the range of the stored values of FP16. Thus, we derive new equations, which can be calculated with FP16. Based on half-precision floating-point arithmetic operations, we develop a multi-GPU earthquake simulation solver using the curved grid finite-difference method (CGFDM). Moreover, we perform several simulations and compare the seismograms with the standard CGFDM to verify the solver. Consequently, the calculation efficiency is remarkably improved, and the memory usage is reduced to 1/2.

How to cite: Wan, J., Wang, W., and Zhang, Z.: The optimization with half-precision floating-point numbers for 3-D seismic simulation based on the curved grid finite-difference method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15141, https://doi.org/10.5194/egusphere-egu23-15141, 2023.

EGU23-17013 | ECS | Posters on site | SM8.1

Physics-Based Ground Motion Simulations Using Kinematic and Dynamic Sources: A Case Study of the 2020 Mw 6.8 Elaziğ, Turkey Earthquake 

Zhongqiu He, Wenqiang Wang, Zhenguo Zhang, Zijia Wang, and Yuhao Gu

Physics-based 3D numerical simulations for earthquake rupture dynamics and ground motion simulations capable of incorporating complex non-planar fault systems, rough surface topography and the heterogeneous structure of the media are playing an increasingly role in the study of the earthquake physics and earthquake engineering. Recent advances in high-performance computing allow deterministic 3D regional-scale broadband ground motion simulations to resolve frequencies up to 10 Hz (e.g., Heinecke et al., 2014; Zhang et al., 2019; Rodgers et al., 2020; Pitarka et al., 2021). Such simulations commonly assume kinematic or dynamic rupture sources. However, systematic analysis of the effects of kinematic and dynamic rupture sources on simulations is lacking. In this work, we first resolve the kinematic rupture model of the 2020 Mw 6.8 Elaziğ, Turkey earthquake from near-field seismic and InSAR observations. We then conduct dynamic rupture scenarios that aim to reproduce the slip characteristics of the preferred kinematic model and to assess its mechanical viability. The curved grid finite-difference method (CG-FDM) is adopted to implement dynamic rupture simulations on complex non-planar fault (Zhang Z. et al., 2014; Zhang W. et al., 2020). The heterogeneous initial stresses are generate from the projection of regional tectonic stress field and the modification of static stress drop calculated from the kinematic model. Ground motion using physics-based numerical methods that consider 3D complexities in topography, medium and source is simulated on the CGFDM3D-EQR platform (Wang et al., 2022). Our result indicates that dynamic source with heterogeneity is an important factor for physics-based seismic hazard assessment.

 

References

Heinecke, A., Breuer, A., Rettenberger, S., Bader, M., Gabriel, A. A., Pelties, C., ... & Dubey, P. (2014, November). Petascale high order dynamic rupture earthquake simulations on heterogeneous supercomputers. In SC'14: Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (pp. 3-14). IEEE.

Pitarka, A., Akinci, A., De Gori, P., & Buttinelli, M. (2022). Deterministic 3D Ground‐Motion Simulations (0–5 Hz) and Surface Topography Effects of the 30 October 2016 M w 6.5 Norcia, Italy, Earthquake. Bulletin of the Seismological Society of America, 112(1), 262-286.

Rodgers, A. J., Pitarka, A., Pankajakshan, R., Sjögreen, B., & Petersson, N. A. (2020). Regional‐Scale 3D ground‐motion simulations of Mw 7 earthquakes on the Hayward fault, northern California resolving frequencies 0–10 Hz and including site‐response corrections. Bulletin of the Seismological Society of America, 110(6), 2862-2881.

Wang, W., Zhang, Z., Zhang, W., Yu, H., Liu, Q., Zhang, W., & Chen, X. (2022). CGFDM3D‐EQR: A Platform for Rapid Response to Earthquake Disasters in 3D Complex Media. Seismological Research Letters, 93 (4): 2320-2334.

Zhang, W., Zhang, Z., Fu, H., Li, Z., & Chen, X. (2019). Importance of spatial resolution in ground motion simulations with 3‐D basins: An example using the Tangshan earthquake. Geophysical Research Letters, 46(21), 11915-11924.

Zhang, W., Zhang, Z., Li, M., & Chen, X. (2020). GPU implementation of curved-grid finite-difference modelling for non-planar rupture dynamics. Geophysical Journal International, 222(3), 2121-2135.

Zhang, Z., Zhang, W., & Chen, X. (2014). Three-dimensional curved grid finite-difference modelling for non-planar rupture dynamics. Geophysical Journal International, 199(2), 860-879.

How to cite: He, Z., Wang, W., Zhang, Z., Wang, Z., and Gu, Y.: Physics-Based Ground Motion Simulations Using Kinematic and Dynamic Sources: A Case Study of the 2020 Mw 6.8 Elaziğ, Turkey Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17013, https://doi.org/10.5194/egusphere-egu23-17013, 2023.

EGU23-1035 | ECS | Orals | NH4.3

Is the stress relaxation relevant for long term forecasting? 

Giuseppe Petrillo, Jiancang Zhuang, and Eugenio Lippiello
The seismic gap hypothesis states that fault regions, where no large earthquake has recently occurred, are more prone than others to host the next large earthquake. This could allow an estmate of the occurrence probability of the next big shock on the basis of the time delay from the last earthquakes. Recent results, both numerical and instrumental, have shown that aftershock occurrence can provide important insights about the validty and range of applicability of the GAP hypothes. Here we discuss how to include the information of these new results in Self Exciting Point Process SEPP models, oiginally developed to describe only aftershock spatio-temporal patterns. In particular, using as testing laboratory a numerical model which reproduces all relevant statistical features of earthquake occurrence, we show as the introduction of stress release in SEPP models can improve long term earthquake prediction.

How to cite: Petrillo, G., Zhuang, J., and Lippiello, E.: Is the stress relaxation relevant for long term forecasting?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1035, https://doi.org/10.5194/egusphere-egu23-1035, 2023.

EGU23-1309 | ECS | Orals | NH4.3

Seismic Signal Denoising with Attention U-Net 

Deniz Ertuncay, Simone Francesco Fornasari, and Giovanni Costa

Seismic stations record superpositions of the seismic signals generated by all kinds of seismic sources. In earthquake seismology, seismic noise sources can be natural events such as wind or anthropogenic events such as cars. In this study, we developed a machine learning (ML) based algorithm to remove the noise from earthquake data. This is important since the information related with the features of the seismic event may be overlapped by the noise. The presence of noise in the recordings can affect the performance of the seismic network, lowering its sensibility and increasing the magnitude of completeness of the seismic catalogue. To train ML model, 10000 thousand earthquake records with relatively low signal to noise ratio (SNR) are selected and contaminated by 25 noise records that are magnified up to 50% of peak amplitude of the earthquake signal and frequency content of those signals are stored as three component traces. The architecture used consists of an Attention U-Net, i.e. an encoder-decoder model using an attention gate within the skip connections: the encoder maps samples from input space (the waveform STFTs) to a latent space while the decoder maps the latent space to the output space (the signal-noise mask). Skip connections are introduced to recover, from previous layers, fine details lost in the encoding-decoding process. Attention gates identify salient regions and prune inputs to preserve only the ones relevant to the specific task. The use of attention gates in skip connections allows to pass "fine-detailed" information to high levels of the decoder that the model itself considers useful to the waveform segmentation. Trained model is tested with a new set of data to understand its capabilities. It is found that trained model can significantly improve the SNR of noise signals with respect to standard filtering methods. Hence, it can be considered as a strong candidate for seismic data filtering method. 

How to cite: Ertuncay, D., Fornasari, S. F., and Costa, G.: Seismic Signal Denoising with Attention U-Net, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1309, https://doi.org/10.5194/egusphere-egu23-1309, 2023.

EGU23-4169 | Orals | NH4.3

Stochastic models for earthquake occurrence 

Eleftheria Papadimitriou

The complexity of seismogenesis requires the development of stochastic models, the application of which aims to improve our understanding on the seismic process and the associated underlying process. Semi Markov models are introduced for estimating the expected number of earthquake occurrences with the classification of the model states based on earthquake magnitudes. The instantaneous earthquake occurrence rate between the model states as well as the total earthquake occurrence rate can be calculated. Seismotectonic characteristic of the study area, incorporated in the model as important component of the model, increase the consistency between the model and the process of earthquake generation and support a classification that integrates magnitudes and style of faulting, thus being more effective for the seismic hazard assessment. For revealing the stress field underlying the earthquake generation, which is not accessible to direct observation, the hidden Markov models (HMMs) are engaged. The HMMs consider that the states correspond to levels of the stress field and its application aim to reveal these states. Different number of states may be examined, dependent upon the organization of observations, and the HMMs are capable to reveal the number of stress levels as well as the way in which these levels are associated with the occurrence of certain earthquakes. Even better results are obtained via the application of hidden semi–Markov models (HSMMs) considering that the stress field constitutes the hidden process and which, compared with HMMs, allow any arbitrary distribution for the sojourn times. The investigation of the interactions between adjacent areas is accomplished by means of the linked stress release model (LSRM), based upon the consideration that spatio–temporal stress changes and interactions between adjacent fault segments constitute the most important component in seismic hazard assessment, as they can alter the occurrence probability of strong earthquakes onto these segments. The LSRM comprises the gradual increase of the strain energy due to continuous tectonic loading and its sudden release during the earthquake occurrence. The modeling is based on the theory of stochastic point process, and it is determined by the conditional intensity function. In an attempt to identify the most appropriate parameterization that better fits the data and describes the earthquake generation process, a constrained “m–memory” point process is introduced, the Constrained–Memory Stress Release Model (CM–SRM) implying that only the m most recent arrival times are taken into account in the conditional intensity function, for some suitable mÎN, instead of the entire history of the process. The performance of the above mentioned models application are evaluated and compared in terms of information criteria and residual analysis.

How to cite: Papadimitriou, E.: Stochastic models for earthquake occurrence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4169, https://doi.org/10.5194/egusphere-egu23-4169, 2023.

EGU23-5729 | ECS | Posters on site | NH4.3

Forecasting strong aftershocks in the Italian territory: a National and Regional application for NESTOREv1.0 

Piero Brondi, Stefania Gentili, and Rita Di Giovambattista

In most of the recent intense earthquakes in Italy, a strong subsequent event (SSE) of comparable or higher magnitude was observed. Its effects, in combination with the strong mainshock, may lead to the collapse of already weakened buildings and to a further increase in damage or even in the number of fatalities, with serious consequences for society. Therefore, the forecasting of an SSE is of strategic importance to reduce the seismic risk during the occurrence of a seismic sequence. To this end, we have recently developed the machine learning-based multi-parameter algorithm NESTORE (Next STrOng Related Earthquake). The first MATLAB version (NESTOREv1.0) was applied to Italian seismicity to forecast clusters where the difference between the magnitude of the mainshock Mm and that of the strongest aftershock is less than or equal to 1. These clusters are called type A by the NESTOREv1.0 software, while the other cases are called type B. NESTOREv1.0 is based on nine seismicity features that measure the number of events with M > Mm-2, their spatial distribution, magnitude, and energy trend over time in increasing time intervals following the occurrence of the mainshock. The software identifies seismic clusters above a threshold for mainshock magnitude Mth, finds appropriate thresholds for features to distinguish A and B cases in a training database, and uses them to provide an estimate of the probability that a cluster is of type A in a test set. For the application of NESTOREv1.0 to Italy, we considered both a national and a regional approach. In the first case, we analysed the seismicity recorded by the INGV network from 1980 to 2021, while in the second case we used the seismic catalogue of the dense OGS network in northeastern Italy for the period 1977-2021. In the nationwide application of NESTOREv1.0, we observed an area between Tuscany and Emilia-Romagna with anomalously high seismic activity concentrated in bursts of short duration. Since this area is almost exclusively populated by type B and therefore not suitable for a specific training procedure, we excluded it from the following analyses. In the remaining national area, we trained NESTOREv1.0 with clusters in the time period 1980-2009 (24 clusters) and tested it in the period 2010-2021 (14 clusters). For the regional case, we considered a rectangular area in northeastern Italy, where we could lower Mth due to the higher local density of seismic stations of the OGS seismic network compared to the mean density of the national network. In this area, 13 clusters from 1977 to 2009 were used as training set, and the performance of NESTOREv1.0 was evaluated using 18 clusters from 2010 to 2021. For both approaches, we obtained good results in terms of the rate of correct forecasting of cluster typology. In the 12 hours following the mainshock, the rate is 86% for the nationwide analysis and 89% for the regional analysis, respectively, which supports the application of NESTOREv1.0 on the Italian territory.

Funded by a grant from the Italian Ministry of Foreign Affairs and International Cooperation

How to cite: Brondi, P., Gentili, S., and Di Giovambattista, R.: Forecasting strong aftershocks in the Italian territory: a National and Regional application for NESTOREv1.0, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5729, https://doi.org/10.5194/egusphere-egu23-5729, 2023.

EGU23-5738 | Posters on site | NH4.3

Forecasting Strong Subsequent Earthquakes in Greece Using NESTORE Machine Learning Algorithm 

Stefania Gentili, Eleni-Apostolia Anyfadi, Piero Brondi, and Filippos Vallianatos

It is widely known that large earthquakes are followed by aftershocks that can affect numerous facilities in a city and worsen the damage already suffered by vulnerable structures. In this study, we apply NESTORE machine learning algorithm to Greek seismicity to forecast the occurrence of a strong earthquake after a mainshock. The method is based on extracting features used for machine learning and analyzing them at increasing time intervals from the mainshock, to show the evolution of knowledge over time. The features describe the characteristics of seismicity during a cluster. NESTORE classifies clusters into two classes, type A or type B, depending on the magnitude of the strongest aftershock. To define a cluster, a window-based technique was applied, using Uhrhammer's (1986) law. We used the AUTH earthquake catalogue between 1995 and 2022 over a large area of Greece to analyze a sufficiently large number of clusters. The good overall performance of NESTORE in Greece evidenced the algorithm's ability to automatically adapt to the area under study. The best performance was obtained for a time interval of 6 hours after the main earthquake, which makes the method particularly attractive for application in the field of early warning, as it allows estimating the probability of a future hazardous earthquake occurring after a strong initial event.

 

Funded by a grant from the Italian Ministry of Foreign Affairs and International Cooperation and Co-funded by the Erasmus+ programme of the European Union (EU).

How to cite: Gentili, S., Anyfadi, E.-A., Brondi, P., and Vallianatos, F.: Forecasting Strong Subsequent Earthquakes in Greece Using NESTORE Machine Learning Algorithm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5738, https://doi.org/10.5194/egusphere-egu23-5738, 2023.

EGU23-5868 | ECS | Orals | NH4.3

Earthquake Magnitude Prediction Using a Machine Learning Model 

Neri Berman, Oleg Zlydenko, Oren Gilon, and Yohai Bar-Sinai

Standard approaches to earthquake forecasting - both statistics-based models, e.g. the epidemic type aftershock (ETAS), and physics-based models, e.g. models based on the Coulomb failure stress (CFS) criteria, estimate the probability of an earthquake occurring at a certain time and location. In both modeling approaches the time and location of an earthquake are commonly assumed to be distributed independently of their magnitude. That is, the magnitude of a given earthquake is taken to be the marginal magnitude distribution, the Gutenberg-Richter (GR) distribution, typically constant in time,or fitted to recent seismic history. Such model construction implies an assumption that the underlying process determining where and when an earthquake occurs is decoupled from the process that determines its magnitude.

In this work we address the question of magnitude independence directly. We build a machine learning model that predicts earthquake magnitudes based on their location, region history, and other geophysical properties. We use neural networks to encode these properties and output a  conditional magnitude probability distribution, maximizing on the log-likelihood of the model’s prediction. We discuss the model architecture, performance, and evaluate this model against the GR distribution.

How to cite: Berman, N., Zlydenko, O., Gilon, O., and Bar-Sinai, Y.: Earthquake Magnitude Prediction Using a Machine Learning Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5868, https://doi.org/10.5194/egusphere-egu23-5868, 2023.

EGU23-5934 | ECS | Orals | NH4.3

Can Seismicity Declustering be solved by Unsupervised Artificial Intelligence ? 

Antoine Septier, Alexandra Renouard, Jacques Déverchère, and Julie Perrot

Due to the complexity and high dimensionality of seismic catalogues, the dimensional reduction of raw seismic data and the feature selections needed to decluster these catalogues into crisis and non-crisis events remain a challenge. To address this problem, we propose a two-level analysis.

 

First, an unsupervised approach based on an artificial neural network called self-organising map (SOM) is applied. The SOM is a machine learning model that performs a non-linear mapping of large input spaces into a two-dimensional grid, which preserves the topological and metric relationships of the data. It therefore facilitates visualisation and interpretation of the results obtained. Then, agglomerative clustering is used to classify the different clusters obtained by the SOM method as containing background events, aftershocks and/or swarms. To estimate the classification uncertainty and confidence level of our declustering results, we developed a probabilistic function based on the feature representation learned by the SOM (spatiotemporal distances between events, magnitude variations and event density).

 

We tested the two-level analysis on synthetic data and applied it to real data: three seismic catalogues (Corithn Rift, Taiwan and Central Italy) that differ in area size, tectonic regime, magnitude of completeness, duration and detection methods. We show that our unsupervised machine learning approach can accurately distinguish between crisis and non-crisis events without the need for preliminary assumptions and that it is applicable to catalogues of various sizes in time and space without threshold selection.

How to cite: Septier, A., Renouard, A., Déverchère, J., and Perrot, J.: Can Seismicity Declustering be solved by Unsupervised Artificial Intelligence ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5934, https://doi.org/10.5194/egusphere-egu23-5934, 2023.

EGU23-6202 | ECS | Orals | NH4.3

Supervised Learning for Automatic Source Type Discrimination of Seismic Events in Sweden 

Gunnar Eggertsson, Björn Lund, Peter Schmidt, and Michael Roth

Distinguishing small earthquakes from man-made blasts at construction sites, in quarries and in mines is a non-trivial task during automatic event analysis and thus typically requires manual revision. We have developed station-specific classification models capable of both accurately assigning source type to seismic events in Sweden and filtering out spurious events from an automatic event catalogue. Our method divides all three components of the seismic records for each event into four non-overlapping time windows, corresponding to P-phase, P-coda, S-phase and S-coda, and computes the Root-Mean-Square (RMS) amplitude in each window. This process is repeated for a total of twenty narrow frequency bands. The resulting array of amplitudes is passed as inputs to fully connected Artificial Neural Network classifiers which attempt to filter out spurious events before distinguishing between natural earthquakes, industrial blasts and mining-induced events. The distinction includes e.g. distinguishing mining blasts from mining induced events, shallow earthquakes from blasts and differentiating between different types of mining induced events. The classifiers are trained on labelled seismic records dating from 2010 to 2021. They are already in use at the Swedish National Seismic Network where they serve as an aid to the routine manual analysis and as a tool for directly assigning preliminary source type to events in an automatic event catalogue. Initial results are promising and suggest that the method can accurately distinguish between different types of seismic events registered in Sweden and filter out the majority of spurious events.

How to cite: Eggertsson, G., Lund, B., Schmidt, P., and Roth, M.: Supervised Learning for Automatic Source Type Discrimination of Seismic Events in Sweden, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6202, https://doi.org/10.5194/egusphere-egu23-6202, 2023.

EGU23-6343 | ECS | Orals | NH4.3

New CNN based tool to discriminate anthropogenic from natural low magnitude seismic events 

Céline Hourcade, Mickaël Bonnin, and Éric Beucler

Over the past 15 years, the deployment of dense permanent seismic networks leads to a dramatic increase in the amount of data to process. The seismic coverage and the station quality pave the way toward a comprehensive catalogue of natural seismicity. This means to i) detect the lowest magnitudes as possible and ii) to discriminate natural from anthropogenic events. To achieve this discrimination, we present a new convolutional neural network (CNN) trained from 60 s long three component spectrograms between 1 and 50 Hz. This CNN is trained using a reliable database of labelled events located in Metropolitan France between January 2020 and June 2021. The application of our trained model on the detected events in Metropolitan France between June and November 2021 gives a high discrimination accuracy of 98.18%. To demonstrate the versatility of our approach, this trained model is applied to different catalogues: from a post-seismic campaign in NW France (48 events) and from University of Utah Seismograph Stations, Utah, USA, (396 events between January and March 2016). We reach an accuracy of 100.00% and 96.72%, respectively, for the discrimination between natural and anthropogenic events. Since each discrimination comes with a level of confidence, our approach can be seen as a decision making tool for the analysts. It also allows to build reliable seismic event catalogues and to reduce the number of mislabelled events in the databases.

How to cite: Hourcade, C., Bonnin, M., and Beucler, É.: New CNN based tool to discriminate anthropogenic from natural low magnitude seismic events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6343, https://doi.org/10.5194/egusphere-egu23-6343, 2023.

EGU23-6806 | Posters on site | NH4.3

Comparison of seismic phase association algorithms and their performance. 

Jorge Antonio Puente Huerta and Christian Sippl

Seismic phase association is a fundamental task for earthquake detection and location workflows, as it gathers individual seismic phases detected on multiple seismic stations and associates them to events.

Current phase picking algorithms are capable of generating large phase datasets, and together with new improved phase association algorithms, they can create larger and more complete earthquake catalogs when applied to dense seismic networks (permanent or temporary).

As part of project MILESTONE, which aims at the automatic creation of large microseismicity catalogs in subduction settings, the present study evaluates the performance of three different phase association algorithms, both by comparing their outputs with a handpicked benchmark dataset and by the retrieval of synthetic events.

For this purpose, we used seismic data from the IPOC (Integrated Plate boundary Observatory Chile) permanent deployment of broadband stations in Northern Chile.

We manually picked P and S phases of raw waveforms on randomly chosen days, with event rates in excess of 100-150 per day. All events that were visually recognizable were picked and located, leading to a dataset to be used as “ground truth”.

We do the phase picking with EQTransformer (Mousavi et al. 2020) and evaluate the performance of three seismic phase associators: 1) PhaseLink (Ross et al. 2019), a deep learning based approach trained on millions of synthetic sequences of P and S arrival times, 2) REAL (Zhang et al. 2020), that combines the advantages of pick-based and waveform-based methods, primarily through counting the number of P and S picks and secondarily from travel-time residuals, and 3) GaMMA (Zhu et al. 2021), an associator that treats the association problem as an unsupervised clustering problem in a probabilistic framework.

In the synthetic test we use NonLinLoc raytracer and add random noise, as well as false picks to simulate an automatic picker output.

In both experiments we evaluate the number of correctly associated and lost events, and the number of constituent picks per event.

How to cite: Puente Huerta, J. A. and Sippl, C.: Comparison of seismic phase association algorithms and their performance., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6806, https://doi.org/10.5194/egusphere-egu23-6806, 2023.

As the number of seismic stations and experiments greatly increases due to ever greater availability of instrumentation, automated data processing becomes more and more necessary and important. Machine Learning (ML)methods are becoming widespread in seismology, with programsthat identify signals and patterns or extract features that can eventually improve our understanding of ongoing physical processes.

We here focus on critically evaluating the performance of a popular machine-learning-based seismic event detection and arrival time picking program, EQ-Transformer, forseismic data from the IPOC deployment in Northern Chile, using handpicked benchmark datasets.By using the open-source framework SeisBench, we can test the effect of using different pre-trained models as well as modify critical parameters such as probability thresholds.

By performing this evaluation, we want to decide whether it is necessary to retrain EQTransformer with local data, or if its performance with one of the supplied pre-trained sets is sufficiently good for our purposes.

We prepared alarge handpicked benchmark dataset for Northern Chile, which we use to find the optimal configuration of EQTransformer. For this benchmark dataset, we select a total of 35 days distributed throughout the 15 years covered by the IPOC deployment. Our goal was to pick all of the many small events in the dataset, even when they are only visible at one or two stations, with high accuracy. We found around three hundred events per day, which highlights the very high seismic activity of the region. We then ran EQTransformer for the same days, using a wide range of parameter choices and pre-trained models.

We need to find if our data is similar to seisbench benchmark dataset or if we should use our data to calibrate the EQTransformer for picking in subduction zones.

We use our handpicked benchmark dataset to evaluate the detection rate (missed events, false detections) as well as the picking accuracy (residuals to handpicks) achieved with EQTransformerin the various tested configurations. We present results of choosing different event detection thresholds, showingtrue positive rate vs. false positive rate plots in order to find optimal thresholds, and evaluate the pick accuracy of obtained arrival time picks by comparing to the handpicked benchmark. This comparison of picking times (P & S) is visualized with residual histograms. Lastly,we also show examples for a visual comparison of picks fromEQTransformer with manual picks.

The present study is the first step towards the design of an automated workflow that comprises event detection and phase picking, phase association and event location and will be used to evaluate subduction zone microseismicity in different locations.

How to cite: Najafipour, N. and Sippl, C.: Optimizing the performance of EQTransformer by parameter tuning and comparison to handpicked benchmark datasets in a subduction setting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6844, https://doi.org/10.5194/egusphere-egu23-6844, 2023.

EGU23-6862 | ECS | Orals | NH4.3

How does a denoising autoencoder improve earthquake detection and the estimation of magnitude in seismic networks? 

Janis Heuel, Meggy Roßbach, and Wolfgang Friederich

Seismogram records always contain seismic noise from different sources. Previous studies have shown that denoising autoencoders can be used to suppress different types of disturbing noise at seismological stations, even when earthquake signal and noise share common frequency bands. A denoising autoencoder is a convolutional neural network that learns from a large training data set how to separate earthquake signal and noise. To train the denoising autoencoder, we used earthquake signals with high signal-to-noise ratio from the Stanford Earthquake Dataset and noise from single seismological stations. We used 160 seismological stations in Germany and surrounding countries and trained a denoising autoencoder model for each station. Afterwards, one year of continuous recorded data have been denoised.

EQTransformer, a deep-learning model for earthquake detection and phase picking, was then applied to the raw and denoised data of each station. Working with denoised data leads to a massive increase of earthquake detections. First results show that in dense seismic networks more than 100% additional earthquakes can be detected compared to events detected in the raw data set. Moreover, the localization accuracy is increased as more stations can be used.

However, like common filter techniques, denoising autoencoders decrease the waveform amplitude. Since earthquake magnitudes are often determined from these amplitudes, we expect a lower amplitude and thus a lower magnitude when using denoised data instead of raw data. So far, we did not find an empirical relation between the raw and denoised magnitude.

How to cite: Heuel, J., Roßbach, M., and Friederich, W.: How does a denoising autoencoder improve earthquake detection and the estimation of magnitude in seismic networks?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6862, https://doi.org/10.5194/egusphere-egu23-6862, 2023.

EGU23-7028 | ECS | Posters on site | NH4.3

Application of machine learning to hydro-acoustic seismic and magmaticevents detections 

Pierre-Yves Raumer, Sara Bazin, Dorian Cazau, Vaibhav Vijay Ingale, Aude Lavayssière, and Jean-Yves Royer

Hydrophones arrays have proven to be an efficient and affordable method to monitor underwater soundscape, in particular magmatic and tectonic events. Indeed, thanks to the sound fixing and ranging (SOFAR) channel in the ocean, acoustic waves undergo a very low attenuation over distance and thus propagate further than they would do across the solid Earth. The MAHY array, composed of four autonomous hydrophones, has been deployed off Mayotte Island since October 2020. It contributes to monitor the recent volcanic activity around the island, and enabled to detect short and energetic acoustic events sometimes reffered to as impulsive events. As for their cause, it has been proposed that these signals are generated by water-lava interactions on the seafloor. So far, these events have been searched by visually inspecting the data, which is a cumbersome and somewhat observer-dependent task. To face these issues, we have developped an automatic picking algorithm tailored for these impulsive events. After some initial signal processing, a supervised neural network model was trained to detect such signals, which can be later checked by a human operator. Taking advantage of the genericity of this detection framework, we applied it to other hydroacoustic data sets (OHASISBIO and IMS-CTBT) to explore the feasibility of detecting T-wave generated by submarine earthquakes. The next step will be to improve the model with unsupervised or semi-supervised feature learning, in order to improve our metrics and, in the end, facilitate the study of specific acoustic signals.

How to cite: Raumer, P.-Y., Bazin, S., Cazau, D., Ingale, V. V., Lavayssière, A., and Royer, J.-Y.: Application of machine learning to hydro-acoustic seismic and magmaticevents detections, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7028, https://doi.org/10.5194/egusphere-egu23-7028, 2023.

EGU23-9874 | Orals | NH4.3

Spatio-temporal localization of seismicity in relation to large earthquakes 

Ilya Zaliapin and Yehuda Ben-Zion

Progressive localization of deformation may signify a regional preparation process leading to large earthquakes [Ben-Zion & Zaliapin, GJI, 2020; Kato & Ben-Zion, Nat Rev Earth Environ. 2021]. The localization framework describes the evolution from distributed failures in a rock volume to localized system-size events. Ben-Zion & Zaliapin (2020) documented robust cycles of localization and de-localization of background earthquakes with M > 2 in Southern California that precede the M7 earthquakes within 2-4 years. This analysis has been done on regional scale, without posterior selection of the examined areas (e.g., around epicenters of large events). Similar results are observed before M7.8 earthquakes in Alaska using background seismicity with M > 4, and in laboratory acoustic emission experiments.

In this work we examine spatial characteristics of the localization process, identifying sub-regions that are responsible for the observed localization and delocalization. The analysis focuses on relative (with respect to other areas) changes in the background intensity. On sub decadal temporal scale, the observed relative seismic activity tends to concentrate on and switch between several subsets of the regional fault network. Within 2-10 years prior to a large event, there is relative activation in a large volume that not necessarily include the impending epicenter. This is followed by a prominent deactivation 2-3 years prior to a large event, reminiscent of the “Mogi donut”, potentially reflecting a transition to aseismic or small events. Some regions may experience multiple activation episodes before a large earthquake. The results emphasize the importance of examining small-magnitude events and joint analyses of seismic and geodetic data.

References:

  • Ben-Zion, Y. and I. Zaliapin (2020) Localization and coalescence of seismicity before large earthquakes. Geophysical Journal International, 223(1), 561-583. doi:10.1093/gji/ggaa315
  • Kato, A. and Y. Ben-Zion (2021) The generation of large earthquakes. Nat Rev Earth Environ 2, 26–39 https://doi.org/10.1038/s43017-020-00108-w

 

How to cite: Zaliapin, I. and Ben-Zion, Y.: Spatio-temporal localization of seismicity in relation to large earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9874, https://doi.org/10.5194/egusphere-egu23-9874, 2023.

EGU23-10395 | ECS | Orals | NH4.3

OBSPicker: A generalized transfer-learned OBS phase picker 

Alireza Niksejel and Miao Zhang

Offshore earthquakes recorded by Ocean Bottom Seismometers (OBS) are crucial to studying tectonic activities in the subduction zones and mid-ocean ridges. In recent years, the ever-advancing Machine Learning (ML)-based phase pickers have shown promise in land earthquake monitoring, but there are few available ML models to handle OBS data due mainly to the lack of labelled training sets and low signal-to-noise ratios. Though land ML-based phase pickers may roughly work for OBS data, they introduce a large number of false negatives and false positives, leading to numerous events being missing and fake.

In this study, we create a tectonically inclusive OBS training data set and develop a generalized deep-learning OBS phase picker - OBSPicker using the EQTransformer (EQT; Mousavi et al., 2019) and the transfer learning approach. To create an inclusive OBS training data set, we collect earthquake waveforms from routine catalogues recorded at 11 OBS networks worldwide with different tectonic settings and geographic locations. Earthquakes are recorded in local and regional distances with diverse magnitudes (ML 0.0-5.8), source depths (0-250 km), and epicentral distances (0-3 deg). To label their phase picks, we adopt a sequence of processing steps including 1) initial phase arrival detection and picking by EQT, 2) identifying and discarding samples with multiple (unwanted) events using STA/LTA method, and 3) refining phase picks using the Generalized Phase Detection method (GPD, Ross et al., 2018), resulting in ~38,000 well-labelled earthquake samples. In addition, we also collect ~150,000 OBS noise samples from the same OBS networks for training augmentation instead of using the commonly adopted Gaussian noises. Those OBS noise samples are used to simulate low-magnitude earthquakes under different marine environments. Initial results show that our transfer-learned OBS phase picker outperforms the EQTransformer base model in both accuracy and precision, especially in presence of higher levels of noise.

How to cite: Niksejel, A. and Zhang, M.: OBSPicker: A generalized transfer-learned OBS phase picker, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10395, https://doi.org/10.5194/egusphere-egu23-10395, 2023.

EGU23-11042 | ECS | Posters on site | NH4.3

Benchmarking Study of EQTransformer Autopicker for Seismic Phase Identification in Northern Chile 

Javad Kasravi and Jonas Folesky

One of the vital open questions in seismology is rapid, high quality phase identification and picking. Measurements of earthquake arrival time or phase picking are often done by expert judgment with many years of experience. Due to advances in technology and seismometer deployment, the amount of recorded data has increased dramatically in the previous decade, leading up to a point, where it has become almost impossible for humans to deal with this amount of data flow. Therefore, automatic picking algorithms are being used.  In recent years multiple machine learning algorithms have been introduced that bear the potential to combine both, high picking accuracy and the capability of processing large amounts of data. 
In this contribution, we demonstrate the performance of the EQTransformer autopicker, when applied to continuous seismic data from the Northern Chilean subduction zone. To test this deep neural network, we chose a random day and carefully hand picked the continuous data on 18 IPOC stations, selecting only combinations of picks which should lead to locatable events (e.g. with at least five picks). This results in the identification of  3040 P and 2310 S picks. We compare the results of two different training versions of EQTransformer with hand-picked data and with the IPOC seismicity catalog. As it turns out, the comparison is not straightforward, because the evaluation of the picks is highly complicated, given that the true number and type of phase arrivals is and remains unknown. However, the autopicker is able to detect most of the hand-picked phases and arrival times. It outperforms the IPOC catalog by a factor of about 10-15 and thusly it appears to be a valid alternative for advanced seismic catalog construction.

How to cite: Kasravi, J. and Folesky, J.: Benchmarking Study of EQTransformer Autopicker for Seismic Phase Identification in Northern Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11042, https://doi.org/10.5194/egusphere-egu23-11042, 2023.

EGU23-11052 | ECS | Posters on site | NH4.3

Preliminary earthquake catalog (2012–2021) of the southern Korean Peninsula by deep learning-based techniques 

Jongwon Han, Keun Joo Seo, Ah-Hyun Byun, Seongryong Kim, Dong-Hoon Sheen, and Donghun Lee

Earthquake monitoring has been stepped up due to high-density permanent networks in the southern Korean Peninsula, though its relatively low seismicity. With the dramatic increase of data volume, deep learning techniques can be effective ways to process them. In this study, we present a preliminary, but comprehensive earthquake catalog in the southern Korean Peninsula for research purposes by applying a series of deep learning-incorporated methods including for earthquake and phase detection, event discrimination, and focal mechanism determination. We first improved the EQTransformer by re-training it with hybrid local and STEAD datasets to perform earthquake and phase detection for 10-year-long data from 2012 to 2021. Then, the subsequent phase association was carried out using the algorithm based on a Bayesian gaussian mixture model. In the result, 66,855 events were identified and located from 691,077 phase detections. Among them, 27,429 natural earthquakes were separated with a novel CNN model trained using event waveforms and origin time constraints. The natural seismicity suggested various earthquake clusters that constrained by tectonic structures, such as the Okcheon belt and Gyeongsang basin, and showed significantly low rate of occurrence in the Gyeonggi massif. In addition, we developed a CNN model for the determination of focal mechanisms that identify the polarity of initial P-waves in input waveforms, and the application of it resulted in 2,345 reliable solutions. Strike-slip motions were dominant in the inland, while reverse faulting of coastal earthquakes, showing an average P-axis direction of N74E in both areas. Despite the massive volume of data, it took less than a week to perform all of the processes with more cataloged earthquakes than those in the previous one (9,218). The extended earthquake catalog accompanied by focal mechanisms underpins data-driven studies such as tomography, stress field estimation, earthquake hazards assessment, and burial fault mapping.

How to cite: Han, J., Seo, K. J., Byun, A.-H., Kim, S., Sheen, D.-H., and Lee, D.: Preliminary earthquake catalog (2012–2021) of the southern Korean Peninsula by deep learning-based techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11052, https://doi.org/10.5194/egusphere-egu23-11052, 2023.

Artificial Neural Networks (ANNs) are well known for their ability to find hidden patterns in data. This technique has also been widely used for predicting the time, location, and magnitude of future earthquakes. Using various data and neural networks, previous works claimed that their models are effective for predicting earthquakes. However, these scores provided by the evaluation metrics with poor reference models, which are non-professional in statistical seismology, are not robust. In this work, we first take the Nighttime Light Map (NLM) as the input of Long-short Term Memory (LSTM) networks to predict the earthquakes with M>=5.0 for the whole Chinese Mainland, and NLM records the lumens of nighttime artificial light, and it is retrieved from the nighttime satellite imagery. The NLM is not physically related to earthquakes; however, the scores provided by Receiver Operating Characteristics curve, Precision-Recall plot, and Molchan diagram with spatial invariant Poisson model indicated that NLM is effective for predicting earthquakes. These results reaffirmed that researchers should be cautious when using these evaluation metrics with poor reference models to evaluate earthquake prediction models. Moreover, the original loss functions of ANNs, such as Cross Entropy (CE), Balanced Cross Entropy (BCE), Focal Loss (FL), and Focal Loss alpha (FL-alpha), contain no knowledge about seismology. To differentiate the hard and easy examples of earthquake prediction models during the training steps of ANNs, the punishment of CE, BCE, FL, and FL-alpha for positive examples will be further weighted by P0 and the punishment for negative examples will be weighted by P1, where P1/P0 is the prior probability provided by the reference model that at least one or no earthquakes will occur for the given example and P1+P0=1. The reference models are supposed to be as close to the real spatial-temporal distribution of earthquakes as possible, and the spatial variable Poisson (SVP) model is the simplest version which is also friendly to data mining experts. In this work, we choose the SVP as the reference model to revise these previous loss functions and take the estimated cumulative earthquake energy in the time-space unit (1 degree*1 degree*10 days) as the input of the LSTM to predict the earthquakes with M>=5.0 in the whole Chinese Mainland, and we use the Molchan diagram (SVP) and Area Skill Score (ASS) to evaluate the performance of these models. Results show that the majority of models (134 out of 144) trained by original loss functions are ineffective for predicting earthquakes; however, the scores of models trained using the revised loss functions have been obviously improved, and 83 out of 144 models are proved to be better than SVP in predicting earthquakes. Our results indicate that designing a more complex structure for ANN and neuron is not the only way to improve the performance of ANNs for predicting earthquakes, and how combining the professional knowledge of data mining experts and seismologists deserves more attention for the future development of ANN-based earthquake prediction models.

How to cite: Zhang, Y. and Huang, Q.: Improved ANN-based earthquake prediction system with reference model engaged in the evaluation metrics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11684, https://doi.org/10.5194/egusphere-egu23-11684, 2023.

EGU23-11763 | Posters virtual | NH4.3

Cascading occurrence of moderate magnitude seismicity in the active fault system of Thiva (central Greece) 

Parthena Paradisopoulou, Eleni Karagianni, Ioanna Karagianni, Areti Panou, Odysseus Galanis, Dominikos Vamvakaris, Vasileios Karakostas, Despina Kementzetzidou, and Eleftheria Papadimitriou

Intense and continuous seismicity in the last two years (October 2020 – September 2022) that took place in a rather small area near the city of Thiva is investigated here. The activity started with an M4.6 earthquake (2 of December 2020) followed by its own aftershock sequence. The activity migrated slightly to the west, with a persistent swarm in July 2021-September 2022 (largest magnitudes M4.3, on 11 July 2021, M4.0 on 2 September 2021 and M4.3, on 10 April 2022). Aiming to constrain the geometry and kinematics of the activated fault segments along with the spatiotemporal evolution of the seismic activity, processing of the recording of the regional seismological network was accomplished that includes the determination of the focal coordinates using the HYPODD software. The above information will provide a better understanding of the seismic sequence and seismic hazard in the region so that there is better prevention and preparation against a future strong earthquake. Aiming to study in detail the properties of this seismicity manifestation, the recordings of the Hellenic Unified Seismological Network (HUSN) are used to accurately determine the seismic parameters of earthquakes with magnitudes M≥1.5. Phases (P, S phases) are gathered from the Geophysical Department of the Aristotle University of Thessaloniki and the Geodynamics Institute of National Observatory of Athens from October 2020 to September 20212. Then, the bulletins were merged, and an initial earthquake catalogue was compiled containing ~6000 events. Earthquake relocation was initially performed using HYPOINVERSE software and all the available manually picked P and S phases. An appropriate local velocity model and the VP/VS ratio were necessary to defined. The Wadati method was applied to the dataset and the resulting VP/VS ratio equals to 1.76. The one-dimensional velocity model used for this study is calculating by the VELEST software. Time corrections relative to the crustal model were calculated considering the mean residual for each station. For the relocation of the events the calculated time delays were taken into account. To improve the obtained locations, we relocate the earthquakes using the double difference inversion algorithm, hypoDD with differential times derived from phase-picked data.

Τo define the stress regime in the area, the moment tensors of earthquakes with ML ≥ 3.5 were estimated using the ISOLA and FPFIT software. The fault plane solutions from the largest earthquakes of the seismic sequence have been used for Coulomb stress changes calculation. The stress field is calculated according to the focal mechanism of the next large event, whose triggering is inspected, so it can be checked if foreshocks contributed to the occurrence of the largest earthquakes of the sequence and the possible sites for future strong earthquakes can be assessed as well.

How to cite: Paradisopoulou, P., Karagianni, E., Karagianni, I., Panou, A., Galanis, O., Vamvakaris, D., Karakostas, V., Kementzetzidou, D., and Papadimitriou, E.: Cascading occurrence of moderate magnitude seismicity in the active fault system of Thiva (central Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11763, https://doi.org/10.5194/egusphere-egu23-11763, 2023.

EGU23-11985 | ECS | Orals | NH4.3

Denoising InSight’s marsquake recordings with deep learning 

Nikolaj Dahmen, John Clinton, Men-Andrin Meier, Simon Stähler, Savas Ceylan, Constantinos Charalambous, Doyeon Kim, Alexander Stott, and Domenico Giardini

Marsquake recordings by NASA’s InSight seismometer often have low signal-to-noise ratios (SNR) owing to low marsquake amplitudes - only a handful of events are over M3.5 and epicentral distances are large, due to the single station being located in a seismically quiet region, and highly fluctuating atmospheric, spacecraft and instrumental noise signals.

We have previously shown [1] how deep convolutional neural networks (CNN) can be used for 1) event detection - thereby producing an event catalogue consistent with the manually curated catalogue by the Marsquake Service (MQS) [2], and further extending it from 1297 to 2079 seismic events - as well as for 2) separating event and noise signals in time-frequency domain. Due to the low number of events readily-available for network training, we trained the CNN on synthetic event data combined with recorded InSight noise.

Here, we construct a semi-synthetic data set (with real marsquake & noise data) to assess the denoising performance of the CNN w.r.t. to various evaluation metrics such as SNR, signal-distortion-ratio, cross-correlation, and peak amplitude of the recovered event waveforms, and compare modifications of the CNN architecture and the training data set.

For a large number of identified events [1,2] no distance estimates are available (or only with high uncertainty), and for all but a small subset the back azimuth is unclear, as the relatively high background noise often obscures this information in the waveforms. We explore how the denoised waveforms can support the phase picking and polarisation analysis of marsquakes, and with that their localisation, as well as their general characterisation.

 

References:

[1] Dahmen et al. (2022), doi: 10.1029/2022JE007503

[2] Ceylan et al. (2022), doi: 10.1016/j.pepi.2022.106943

How to cite: Dahmen, N., Clinton, J., Meier, M.-A., Stähler, S., Ceylan, S., Charalambous, C., Kim, D., Stott, A., and Giardini, D.: Denoising InSight’s marsquake recordings with deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11985, https://doi.org/10.5194/egusphere-egu23-11985, 2023.

EGU23-13113 | Orals | NH4.3

Detection of Deep Low-Frequency Tremors from Continuous Paper Records at a Station in Southwest Japan About 50 Years Ago Based on Convolutional Neural Network 

Hiromichi Nagao, Ryosuke Kaneko, Shin-ichi Ito, Hiroshi Tsuruoka, and Kazushige Obara

The establishment of the High Sensitivity Seismograph Network (Hi-net) in Japan has led to the discovery of deep low-frequency tremors. Since such tremors are considered to be associated with large earthquakes adjacent to tremors on the same subducting plate interface, it is important in seismology to investigate these tremors before establishing modern seismograph networks that record seismic data digitally. We propose a deep-learning method to detect evidence of tremors from seismogram images recorded on paper more than 50 years ago. In this study, we trained a convolutional neural network (CNN) based on the Residual Network (ResNet) with seismogram images converted from real seismic data recorded by Hi-net. The CNN trained by fine-tuning achieved an accuracy of 98.64% for determining whether an input image contains tremors. The Gradient-weighted Class Activation Mapping (Grad-CAM) heatmaps for visualizing model predictions indicated that the CNN successfully detects tremors without being affected by teleseisms. The trained CNN was applied to the past seismograms recorded from 1966 to 1977 at the Kumano observatory, in southwest Japan, operated by Earthquake Research Institute, The University of Tokyo. The CNN showed potential for detecting tremors from past seismogram images for broader applications, such as publishing a new tremor catalog, although further training using data including more variables such as the thickness of the pen would be required to develop a universally applicable model.

How to cite: Nagao, H., Kaneko, R., Ito, S., Tsuruoka, H., and Obara, K.: Detection of Deep Low-Frequency Tremors from Continuous Paper Records at a Station in Southwest Japan About 50 Years Ago Based on Convolutional Neural Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13113, https://doi.org/10.5194/egusphere-egu23-13113, 2023.

EGU23-13927 | Posters on site | NH4.3

SeisBlue: a deep-learning data processing platform for seismology 

Chun-Ming Huang, Li-Heng Chang, Hao Kuo-Chen, and YungYu Zhuang

Deep learning has greatly improved the efficiency of earthquake detection and phase picking tasks, as demonstrated by neural network models such as PhaseNet and EQTransformer. However, the code released by these authors is not production-ready software that can be easily integrated into our lab's workflow. To solve this problem, we developed "SeisBlue," a platform that brings all the necessary steps together in one place. It includes these major components: database client, data inspector, data converter, model trainer, model evaluator, and pick associator, and is designed to be modular and interchangeable to allow for easy experimentation with different combinations.

SeisBlue has been used in several major earthquake events in Taiwan, including the 918 Taitung earthquake (magnitude 6.9 Mw). In this event, we were able to capture over 1,200 events near real-time in just two days - a task that would have taken over a month to complete manually. The quickly-released earthquake catalog provided insight into the complex behavior of the blind fault.

How to cite: Huang, C.-M., Chang, L.-H., Kuo-Chen, H., and Zhuang, Y.: SeisBlue: a deep-learning data processing platform for seismology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13927, https://doi.org/10.5194/egusphere-egu23-13927, 2023.

EGU23-14001 | ECS | Orals | NH4.3

Towards an Operational Earthquake Forecasting Model for Europe 

Marta Han, Leila Mizrahi, and Stefan Wiemer

The go-to models for developing time-dependent earthquake forecasts are Epidemic-Type Aftershock Sequence (ETAS) models. They model earthquake occurrence as a spatio-temporal self-exciting point process, using basic empirical laws such as the Omori-Utsu law for the temporal evolution of aftershock rate, the Gutenberg-Richter law to describe the size distribution of earthquakes, the exponential productivity law and so on. The main focus and core strength of ETAS lie in modelling aftershock occurrence. An important aspect which holds great potential for improvement is the modelling of background seismicity.

In this study, we focus on the data sets and expert solicitations acquired for building the European Seismic Hazard Model (ESHM) 2020. Since these data sets cover a wide range of space and time, the properties of the earthquake catalogs (completeness magnitude, magnitude resolution, time and space resolution, b-value) vary by region and time period. We address these issues using the model accounting for the time-varying completeness magnitude (Mizrahi et al., 2021) and other adjustments, then develop an ETAS model that allows the background seismicity rate to vary with space and be covariate-dependent. The expectation-maximisation-based algorithm allows for these rates to be given as an input, in our case based on fault locations, estimated long-term seismicity rates and area sources, or estimated during inversion for expert-defined zonations. We test the models retrospectively for self-consistency and pseudo-prospectively to identify the ones that lead to the best operational forecasting model for Europe.

How to cite: Han, M., Mizrahi, L., and Wiemer, S.: Towards an Operational Earthquake Forecasting Model for Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14001, https://doi.org/10.5194/egusphere-egu23-14001, 2023.

EGU23-15180 | Orals | NH4.3

An automated earthquake detection algorithm by combining pair-input deep learning and migration location methods 

Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, Peidong Shi, Zhuowei Xiao, S. Mostafa Mousavi, and Rui Fernandes

Modern seismology can benefit from a rapid and reliable earthquake catalog preparation process. In recent years Deep Learning (DL)-based methods attracted seismologists’ attention to keep up with the constantly increasing seismic data for maximally processing and locating the recorded events. This study focuses on deploying an optimized workflow that integrates DL and waveform migration algorithms to achieve a comprehensive automated phase detection and earthquake location workflow. The goal is to deeply scan the seismic datasets for Pand S- phases, associate and locate the detected events, and improve the performance of DL algorithms in processing out-of-distribution and low signal-to-noise ratio data. The workflow consists of six steps, including the preparation of one-minute data segments by employing the framework of ObsPy, deep investigation of the recorded data for P- and S- phases by a low threshold EQTransformer (EQT), and a pair-input Siamese EQTransformer (S-EQT), phase association by Rapid Earthquake Association and Location (REAL) method, applying MIgration Location (MIL) to accurately locate the outputs of REAL, and calculating the local magnitude of the located earthquakes. Eighteen months of the Ghana Digital Seismic Network (GHDSN) dataset (2012-2014), is processed by this integrated and automatic workflow, and a catalog of 461 earthquakes is acquired. Although S-EQT and EQT, with the respective number of 758 and 423 earthquakes, show a figurative superiority in the number of detected events, they are scattered with inaccurate hypo-central depth. Conversely, the compiled catalog show high accordance with the previously interpreted seismogenic sources by Mohammadigheymasi et al. (2023), and a new seismogenic source is also delineated. This workflow significantly enhanced the seismic catalog compilation process and lowered the computational costs while increasing the accuracy of phase detection, association, and location processes. This work was supported by the European Union and the Instituto Dom Luiz(IDL) Project under Grant UIDB/50019/2020, and it uses computational resources provided by C4G (Collaboratory for Geosciences) (Ref. PINFRA/22151/2016). P. S. is supported by the DEEP project (http://deepgeothermal.org) funded through the ERANET CofundGEOTHERMICA (Project No. 200320-4001) from the European Commission. The DEEP project benefits from an exploration subsidy of the Swiss federal office of energy for the EGSgeothermal project in Haute-Sorne, canton of Jura (contract number MF-021-GEO-ERK), which is gratefully acknowledged.

How to cite: Mohammadigheymasi, H., Tavakolizadeh, N., Shi, P., Xiao, Z., Mousavi, S. M., and Fernandes, R.: An automated earthquake detection algorithm by combining pair-input deep learning and migration location methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15180, https://doi.org/10.5194/egusphere-egu23-15180, 2023.

EGU23-15321 | ECS | Orals | NH4.3

b-value variation through the seismic cycle: Revisiting Parkfield 

Aron Mirwald, Laura Gulia, and Stefan Wiemer

The Parkfield section of the San Andreas fault has a history of frequently occurring moderate (M~6) earthquakes with recurrence times ranging from 12 to 38 years. Since 1985, it has been extensively monitored as part of the experiment to predict the next moderate earthquake. Using the rich data resulting from the high-resolution monitoring, studies have revealed several interesting and consistent patterns of the frequency-magnitude distribution (FMD) of earthquakes, measured by the b-value of the Gutenberg-Richter law. The fault consists of patches of low b-values (b < 0.6) that correlate well with locked patches and with the areas that slipped in the 2004 M6 earthquake. High b-values (b > 1.3) were found to correlate with creeping section of the faults, and both observations support the hypothesis of an inverse relation between differential stress and b-values. Further, the b-value was found to increase during the aftershock periods of the 2004 earthquake, but so far, no gradual loading throughout the seismic cycle has been documented at Parkfield.

Here we revisit the b-values along the Parkfield section 19 years after the last M6 event, with the objectives to monitor and better understand the evolution of b-values in space and time as the segment approaches the next rupture. Our aim is first to benchmark and enhance approaches to map and monitor transients, to optimize uncertainty quantification, robustness, and resolving power of our statistical methods. This is best targeted by creating synthetics catalogues with known properties and then benchmarking different methods for spatial mapping and time-series analysis of b-values. We specifically investigate the recently introduced b-positive estimator and convert observed b-values and activity rates to earthquake probabilities. In a second step, we analyse the observed patterns in a context of gradual fault loading and repeated moderate events, to derive insights into the underlying physical processes. Finally, our aim to set up a ‘b-value’ observatory that will continuously monitor the space-time evolution of b-values and earthquake probabilities.

How to cite: Mirwald, A., Gulia, L., and Wiemer, S.: b-value variation through the seismic cycle: Revisiting Parkfield, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15321, https://doi.org/10.5194/egusphere-egu23-15321, 2023.

EGU23-16410 | ECS | Orals | NH4.3

Increasing the reliability of seismic classification: A comparison of strategies to deal with class size imbalanced datasets. 

Chantal van Dinther, Marielle Malfante, Pierre Gaillard, and Yoann Cano

Recent employment of large seismic arrays and distributed fibre optic sensing cables leads to an overwhelming amount of seismic data. As a consequence, the need for reliable automatic processing and analysis techniques increases. Therefore, the number of machine learning applications for detection and classification of seismic signal augments too.

A challenge however, is that seismic datasets are highly class imbalanced, i.e. certain seismic classes are dominant while others are underrepresented. Unfortunately, a skewed dataset may lead to biases in the model and thus to higher uncertainties in the model predictions. In the machine learning literature, several strategies are described to mitigate this problem. In presented work we explore and compare those approaches.

For our application, we use catalogues and seismic continuous recordings of the RD network in France [RESIF, 2018]. Using a simple 3-layered convolutional neural network (CNN) we aim to differentiate between six seismic classes, which are based on hand-picked catalogues. The training set we obtained is highly skewed with earthquakes as the majority class, containing 77% of the samples.  The remaining classes (quarry blasts, marine explosions, suspected induced events, noise and earthquakes with unquantifiable magnitude) represent 2.1 - 7.5% of the dataset.

We compare four strategies to deal with an imbalanced datasets for a multi-class classification problem. The first strategy is to resample the dataset (i.e. reduction of the majority class). Another approach is the adaptation of the loss function by weighting the classes when penalizing the loss (i.e. increasing the weight of the minority classes). Those class weights can be adjusted either w.r.t. the reciprocal of class frequency [inspired by King and Zeng, 2001] or w.r.t. the effective number of samples [Cui et al., 2019]. Lastly, we have explored the use of a focal loss function [Lin et al., 2020].

Using balanced accuracy as a metric while minimizing the loss, we found that in our case adjusting the class weights in the loss function according to the reciprocal of the class frequency provides the best results.

 

References:

- RESIF, 2018: https://doi.org/10.15778/RESIF.RD

- King, G., & Zeng, L. (2001). Logistic regression in rare events data. Political analysis9(2), 137-163.

- Lin et al. (2020), Focal Loss for Dense Object Detection, IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 42, NO. 2, FEBRUARY 2020

- Cui et al. (2019), Class-Balanced Loss Based on Effective Number of Samples, https://doi.org/10.48550/arXiv.1901.05555

How to cite: van Dinther, C., Malfante, M., Gaillard, P., and Cano, Y.: Increasing the reliability of seismic classification: A comparison of strategies to deal with class size imbalanced datasets., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16410, https://doi.org/10.5194/egusphere-egu23-16410, 2023.

EGU23-16438 | Orals | NH4.3

Earthquake Detection and Location in the Cameroon Temporary Network Data Using Deep Learning 

Luis Carvalho, Hamzeh Mohammadigheymasi, Paul Crocker, Nasrin Tavakolizadeh, Yahya Moradichaleshtori, and Rui Fernandes

A temporary seismic network consisting of 32 broadband seismic sensors was installed in Cameroon between March 2005 and December 2006 to study the seismic structure of the crust and upper mantle beneath the Cameroon Volcanic Line (CVL). This study aims to re-evaluate the seismicity in this period by processing this database and calculating an updated crustal velocity model for the region incorporating the acquired earthquake bulletin. 

The earthquake detection and location procedure applies hybrid deep learning (DL) and phase validation methods. We use an integrated workflow composed of Earthquake Transformer (EqT) and Siamese Earthquake Transformer (S-EqT) for initial earthquake detection and phase picking. Then, PickNet is used as a phase refinement step, and REAL for earthquake association and rough location. A set of thresholding parameters for earthquake detection and P- and S-picking equal to 0.2 and 0.07 are adjusted, respectively. By combining a set of 33282 P and 29251 S-picked phases associated with 743 earthquakes with 1.3 ≤ ML ≤ 4.6, we implement a joint inversion for estimating an updated 1D crustal velocity model. The obtained mode comprises thicknesses of 8, 12, 14, 20, and 30km, from the surface to a depth of 45km, with Vp = 6.1, 6.4, 6.6, 7.6, 8.25, and 8.5km/s, respectively. The newly detected events are primarily concentrated in three main clusters, 1) the east flank of Mount Cameroon, 2) an area between Mount Cameroon and Bioko Island, and 3) southern Bioko Island. The compiled catalog for this time interval is 1.7 times larger than the already reported catalog for this data set. Finally, we present a 3D time-lapsed animation of the detected earthquake sequences.

Acknowledgements: The authors would like to thank the support of the Instituto de Telecomunicações. This work is funded by FCT/MCTES through national funds and, when applicable co-funded EU funds under the project UIDB/50008/2020.

How to cite: Carvalho, L., Mohammadigheymasi, H., Crocker, P., Tavakolizadeh, N., Moradichaleshtori, Y., and Fernandes, R.: Earthquake Detection and Location in the Cameroon Temporary Network Data Using Deep Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16438, https://doi.org/10.5194/egusphere-egu23-16438, 2023.

EGU23-17092 | ECS | Orals | NH4.3

Frequency-size parameters as a function of dynamic range – the Gutenberg-Richter b-value for earthquakes 

Gina-Maria Geffers, Ian G. Main, and Mark Naylor

The Gutenberg-Richter b-value represents the relative proportion of small to large earthquakes in a scale-free population and is an important parameter used in earthquake hazard assessment. Discussion of the amount of data required to obtain a robust b-value has been extensive and is ongoing. To complement these analyses, we show the effect of the b-value with changes to the dynamic range – the difference between minimum magnitude (or magnitude of completeness) and maximum magnitude, which is inherently linked to the sample size, but not proportionately correlated. Additionally, we show that biases in high b-values are due to the bias in the mean magnitude of a catalogue, which asymptotically converges from below.

We derive and analytic expression for the bias that arises in the maximum likelihood estimate of b as a function of dynamic range r. Our theory predicts the observed evolution of the modal value of the mean magnitude in multiple random samples of synthetic catalogues at different r, including the bias to high b at low r and the observed trend to an asymptotic limit with no bias. In the case of a single sample in real catalogues, the situation is substantially more complicated due to the heterogeneity, magnitude uncertainty and lack of knowledge of the true b-value. We summarise that these results explain why the likelihood of large events and the associated hazard is often underestimated in small catalogues with low r, for example in some studies of volcanic and induced seismicity.

How to cite: Geffers, G.-M., Main, I. G., and Naylor, M.: Frequency-size parameters as a function of dynamic range – the Gutenberg-Richter b-value for earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17092, https://doi.org/10.5194/egusphere-egu23-17092, 2023.

EGU23-113 | ECS | PICO | TS8.2

Numerical modelling of intra-oceanic rifting: the rift-to-drift transition time frame 

Nuno Rodrigues, Filipe Rosas, João Duarte, Afonso Gomes, Jaime Almeida, and Nicolas Riel

Numerical modelling of rifting has been focused on cases involving extension and breakup of the continental lithosphere. However, the oceanic lithosphere has also been known to undergo rifting in specific geo-tectonic settings, as in the case of the Terceira ridge in the Azores triple junction (N-Atlantic). The rift-to-drift evolution of a segment of oceanic lithosphere potentially bears major implications for the Wilson cycle evolution of an oceanic basin, justifying the importance of carrying out the present numerical modelling study.

We used the Underworld geodynamic code to carry out 2D numerical models of oceanic rifting. To this extent, we systematically tested two main parameters which control the timing of the evolution from initial oceanic extension to breakup and drifting, namely: a) different total extension rates between 4 mm/yr and 160 mm/yr, and b) different oceanic plate ages ranging between 10 Myr and 90 Myr, which act as proxies for the lithospheric thickness.

Our results show that during oceanic rifting, the time required to achieve breakup of the extending oceanic lithosphere decreases logarithmically with an increasing extensional rate (i.e., the time needed to achieve breakup reaches a plateau). Our modelling also shows that lithospheric thickness plays a secondary, yet significant role in the type of oceanic rift that is formed (i.e., its structural configuration). This oceanic rift structure can comprise either a unique major graben or two main grabens, as preferable sites of extensional strain localization. Furthermore, when two main grabens develop, one of them often accommodates the bulk of the deformation, while the other wanes and eventually aborts. In this case, a more distributed pattern of extensional strain (comprising two main grabens) seemingly implies some delay in achieving full oceanic break-up, when compared with the single major graben scenario.

Acknowledgements: numerical modelling was financed by Projeto GEMMA - PTDC/CTA-GEO/2083/2021, Fundação para a Ciência e Tecnologia. This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL.

How to cite: Rodrigues, N., Rosas, F., Duarte, J., Gomes, A., Almeida, J., and Riel, N.: Numerical modelling of intra-oceanic rifting: the rift-to-drift transition time frame, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-113, https://doi.org/10.5194/egusphere-egu23-113, 2023.

EGU23-122 | PICO | TS8.2

Harmonic dynamic of the Earth (C) 

xianwu xin

Abstract.

In this paper, the physical simulation of the meridional movement of the crust is carried out by experiments; According to the geometry relationship between the peak point of the earth's crust and the earth's rotation under the action of tidal force, a mathematical model of the meridional movement of the crust is established. The velocity field of global continental drift is calculated using the meridional motion equation derived from the model, and is compared with the measured value of ITRF2000. It can be seen from the comparison between adjacent calculated values and measured values that the magnitude and direction of the two velocity vectors are basically the same. It follows that the meridional movement of the crust is a reciprocating harmonic movement. The continent and the ocean floor, under the action of the reciprocating harmonic dynamic process, float back and forth along the meridian. Due to the difference between forward and reverse resistance, there will be fixed displacement in one direction. So far, the series of papers on "Harmonic dynamic of the Earth (C)" have completed the kinematic analysis, driving force calculation, energy conversion calculation and verification of observation results of the earth harmonic dynamic process. Velocity field, driving force and energy consumption are the three basic indicators of mechanical power process. Many possibilities of geophysical evolution mechanism determine that the study of its main dynamic mechanism is inseparable from the detailed discussion of the three major indicators.

How to cite: xin, X.: Harmonic dynamic of the Earth (C), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-122, https://doi.org/10.5194/egusphere-egu23-122, 2023.

EGU23-380 | ECS | PICO | TS8.2

Stress-strain relationships at elongated calderas in extensional settings: what analogue models say 

Daniele Maestrelli, Pietro Facincani, Federico Sani, Marco Bonini, Domenico Montanari, Chiara Del Ventisette, and Giacomo Corti

Collapsed calderas are circular to elongated large depressions originating from the subsidence induced by depletion and/or migration of magma from a shallow or deep reservoir during eruptions. Despite being distributed in all tectonic settings, they are particularly important in extensional settings where are often associated with rifting processes, e.g., the East African Rift System. Therefore, their structural architecture can be strongly perturbed by extensional faults associated with regional extension or related to earlier stages of caldera formation. Calderas often bear an elongated shape in plain view, and have been considered valuable proxies for the regional stress (e.g., Nakamura, 1977) and regional strain (e.g. Casey et al., 2006). Moreover, other authors have related the elongated calderas to the influence of preexisting structures reactivated during extension (Acocella et al., 2003). We therefore aim to investigate the mechanical interactions between collapsed calderas and regional extension leading to elongated edifices. Analogue models of caldera collapse were performed by placing a circular magma chamber (simulated with poly-glycerine) placed below a sand-mixture package. We induced the collapse by draining out the analogue magma from the base, reproducing the classical fault architecture observed at many collapsed calderas (i.e., early inner outward-dipping reverse faults and late outer inward-dipping normal fault). Once completed, the collapsed depression was stretched such that normal faulting produced caldera elongation and segmentation. Finally, we compared the elongation and the structural pattern deriving from the interacting caldera-related and rift-related structures with natural examples from the East African Rift System. Our results suggest that different interacting factors may contribute to the development of elongated calderas, thereby questioning whether elongated calderas can be considered as a fully reliable proxy for the regional strain.

Acocella, V., Korme, T., Salvini, F., and Funiciello, R. (2003). Elliptic calderas in the Ethiopian Rift: control of pre-existing structures. J. Volcanol. Geotherm. Res., 119, 189–203.

Casey, M., Ebinger, C., Keir, D., Gloaguen, R., and Mohamed, F. (2006). Strain accommodation in transitional rifts: extension by magma intrusion and faulting in Ethiopian rift magmatic segments. Geol. Soc. Lond. Spec. Publ., 259(1), 143–163.

Nakamura, K., (1977). Volcanoes as possible indicators of tectonic stress orientation— principle and proposal. Journal of Volcanology and Geothermal Research 2, 1–16

How to cite: Maestrelli, D., Facincani, P., Sani, F., Bonini, M., Montanari, D., Del Ventisette, C., and Corti, G.: Stress-strain relationships at elongated calderas in extensional settings: what analogue models say, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-380, https://doi.org/10.5194/egusphere-egu23-380, 2023.

EGU23-432 | ECS | PICO | TS8.2

analogue modelling of multiple compressive phases deforming and extended margin 

oumaima badraoui, Chiara Del Ventisette, Daniele Maestrelli, Mohamed Najib Zaghloul, and Federico Sani

Earlier extended continental margins are frequently involved into late compressive deformation during mountain building (i.e. orogenesis). This process gives rise to positive inversion of previous extensional faults, but these structures may also play different roles during late compressive phases, interacting in various ways with inherited structures from older tectonic stages.

Moreover, different orientation of compression direction related to different phases affecting extended continental margins may give rise to complex structural settings whose evolution is often difficult to reconstruct. To address this problem, we performed an analogue model experimental series aiming at extending a continental margin and then imposing on the same margin differently oriented compressive phases. Models were quantitatively analyzed through particle image velocimetry (PIV) to highlight fault interaction, and by using Digital Elevation Models reconstructed with Structure from Motion (SfM) techniques. Our results show that well developed and favorably oriented normal fault systems drive the location of successive compressive structure, often through inversion processes, but they also condition the final geometrical setting without inversion. Moreover, an important role is also played by the orientation of the direction of compression (obliquity angle a varied from 0° to 90°), which gives rise to different structural patterns when is superimposed to extensional structures as a first compressive phase or is superimposed to already formed compressive structure as second compressive phase. The resultant complex structural patterns show differently oriented structures cutting each other even at high angles, a feature often seen in nature. Therefore, these experiments may be applied to a variety of natural cases, helping to decipher geological evolution of the analyzed areas basing on the geometrical relationships among structures.

How to cite: badraoui, O., Del Ventisette, C., Maestrelli, D., Zaghloul, M. N., and Sani, F.: analogue modelling of multiple compressive phases deforming and extended margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-432, https://doi.org/10.5194/egusphere-egu23-432, 2023.

EGU23-691 | ECS | PICO | TS8.2

Enhanced-gravity Analog Modelling of the Influence of Pre-existing Brittle Fabrics on Continental Rifting 

Yaoyao Zou, Giacomo Corti, Daniele Maestrelli, Chiara Del Ventisette, Liang Wang, and Chuanbo Shen

Along with other parameters (e.g., plate kinematics), the presence of pre-existing structures at all lithospheric scales has been proven to be of primary importance in controlling the evolution and characteristics of continental rifts. Indeed, observations from many natural examples show that even in conditions of orthogonal rifting (when extension should result in simple fault patterns dominated by normal faults orthogonal to the extension vector) the presence of inherited fabrics may result in complex arrangements of differently-oriented extension-related structures.

Here, we explored the influence of pre-existing fabrics on the evolution and pattern of rift-related structures by conducting a series of analogue models deformed in an enhanced gravity field produced by a centrifuge apparatus. The crustal models reproduced a brittle-ductile system and considered the presence of pre-existing discrete fabrics in the upper, brittle crust under conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction.

Modelling results show that pre-existing fabrics have a significant influence on the rift-related fault pattern. These fabrics cause curvature of extension-related faults, resulting in S-shaped faults and -in some cases- en-echelon arrangement of oblique fault segments. In addition, the presence of these heterogeneities influences the rift floor subsidence by inducing significant segmentation and development of isolated depocenters. These effects are more visible during initial rifting and less pronounced for more advanced rifting stages. Similarly, increased syn-rift sedimentation tends to decrease the impact of pre-existing structures. Model results show many significant similarities with the fault pattern in many rift basins worldwide, and these findings have important insights into the development of continental rift systems in nature.

 

How to cite: Zou, Y., Corti, G., Maestrelli, D., Del Ventisette, C., Wang, L., and Shen, C.: Enhanced-gravity Analog Modelling of the Influence of Pre-existing Brittle Fabrics on Continental Rifting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-691, https://doi.org/10.5194/egusphere-egu23-691, 2023.

EGU23-2782 | ECS | PICO | TS8.2

A systematic study of mantle drag effect on subduction dynamics and overriding plate deformation 

Thomas Geffroy, Guillaume Benjamin, Replumaz Anne, Simoes Martine, Lacassin Robin, Kermarrec Jean-Jacques, and Habel Tania

Plates and the convective mantle interact with each other over geological time scales, leading to mantle flow, plate motion, and deformation along plate boundaries.  At convergent boundaries undergoing subduction, the role played by mantle drag remains poorly understood despite its potential impact on subduction dynamics, and in turn on the deformation regime of the overriding plate. Previous studies were generally conducted in two dimensions, limiting their ability to faithfully reproduce processes taking place on Earth. Instead, in this study, we present 11 three-dimensional analog models of subduction at the scale of the upper mantle, including an overriding plate, and in which we control mantle drag at the base of the lower or upper plate by imposing a controlled unidirectional background mantle flow perpendicular to the trench. We systematically vary the velocity and the direction of the imposed horizontal mantle flow and quantify its impact on horizontal and vertical upper plate deformations, plate and subduction velocities, and the geometry of the slab. The geometry of the slab is only marginally affected by the velocity and direction of the mantle flow. In the absence of mantle flow, slab rolls back and deformation is accommodated by trench-orthogonal stretching in the upper plate. Instead, the addition of a background flow dragging the lower or upper plate toward the trench  systematically results either in the absence of upper plate deformation, or in trench-orthogonal shortening with strain rates that increase linearly with increasing mantle flow. We show that the upper plate strain rate is primarily controlled by the velocity of the free plate in the model, which itself results from the drag exerted by the mantle at the base of the plate. Coupling between mantle and plate is larger for models with flow directed toward the upper plate, resulting in strain rates that are about three times larger than for equivalent models with flow directed toward the lower plate. This systematic study provides a better understanding of the effect of mantle drag on plate displacements and deformation along subduction zones, leading to a better understanding of the ingredients required to form Andean-type mountain ranges.

How to cite: Geffroy, T., Benjamin, G., Anne, R., Martine, S., Robin, L., Jean-Jacques, K., and Tania, H.: A systematic study of mantle drag effect on subduction dynamics and overriding plate deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2782, https://doi.org/10.5194/egusphere-egu23-2782, 2023.

 Abstract

The Nanchuan region is located on the southeastern margin of the Sichuan Basin, South China. Silurian Wufeng-Longmaxi Formation, buried between 2000-4500m deep in this area, is an important shale gas-producing formation. Influenced by multi-phase tectonic action during Mesozoic- Cenozoic [1], the maximum compressive horizontal principal stress (σHmax) directions are complex and the orientation changes rapidly (55°-135°). Therefore, effectively predicting the maximum compressive horizontal principal stress (σHmax) is important for improving the shale gas production capacity and optimizing the fracturing scheme development.

In this paper, the SHELLS finite element stress field modeling [2] was introduced and used to understand the above problems. Based on the increased and improved resolution of its program, and faults topography, heat flow, petrophysical parameters, and boundary conditions in the shale gas target layer, the σHmax directions in the study area were modeled and calculated. The prediction results show that σHmax directions in the Nanchuan region vary multi-directionally (0-180°), and are consistent with 11 of the 13 drilled wells, with only two drilled wells having minor differences (Figure 1). 85% of the predicted wells are consistent with the measured wells, achieving significant geological results and laying the foundation for the effective development of shale gas production capacity and optimized fracturing schemes in the area.

Keywords: Stress field modeling, maximum compressive horizontal principal stress directions, shale gas, mid-deep, the Nanchuan region

Figure 1 σHmax directions in the Nanchuan region compared to actual drilling

References:

[1] Tang J G., Wang K M., Qin D C., Zhang Y., Feng T., 2021. Tectonic deformation and its constraints to shale gas accumulation in the Nanchuan area, southeastern Sichuan. Bulletin of Geological Science and Technology. 40(5), 11-21. ( in Chinese version).

[2] Bird, P., 1999. Thin-plate and thin-shell finite-element programs for forward dynamic modeling of plate deformation and faulting 1. Comput. Geosci. 25, 383–394.

How to cite: Yang, R., Yang, F., and Hu, P.: Prediction of the maximum compressive horizontal principal stress directions of medium to deep shale gas in the Nanchuan region, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4245, https://doi.org/10.5194/egusphere-egu23-4245, 2023.

Continental transform faults transition to a new plate boundary type when strike-slip, transpression or transtension are no longer the most efficient way to accommodate plate motion. In some instances, rather than the transform fault ‘transforming’ plate motion directly to its connecting plate boundary, the continental transform fault can become ‘misaligned’ with its connecting plate boundary. Where a plate boundary misalignment occurs, plate motion that was localised on the transform fault can become distributed over a broad, intervening transition zone between the two major plate boundary faults. In this study we use scaled analogue models to investigate the development of fault networks in regions of localised and distributed simple shear and the transition between the two. We use digital image correlation (DIC) to analyse the surface deformation of the analogue model experiment and present results as incremental shear strain maps of the surface of the analogue models.  The results are compared to natural examples of plate boundary transition zones (e.g., Alpine Fault, New Zealand; North Anatolian Fault, Turkey; San Andreas Fault, USA).  In our previous analogue model experiments, regions of localised and distributed simple shear have been generated in an analogue shear box using a four-way stretchable fabric to adjust the basal boundary conditions. These experiments were limited by the elasticity of the stretchable material, which cannot deform infinitely. Here we will present preliminary results from a new shear box apparatus that uses carbon fibre rods to adjust the basal boundary conditions. This new apparatus has been designed to minimise the boundary effects caused by the limitations of the four-way stretchable fabric in our previous experiments.

How to cite: Withers, M. and Cruden, A.: A new shear box apparatus for investigating distributed deformation at the termination of continental transform faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4555, https://doi.org/10.5194/egusphere-egu23-4555, 2023.

EGU23-6125 | PICO | TS8.2

The use of collaborative robots (cobots) in an analog modeling laboratory 

Lorenzo Bonini and Nicolò Bertone

During the last decades, analog models have taken extraordinary advantage of new technologies. High-resolution cameras, analytical methods to extract quantitative data from the experiments (e.g., Digital Image Correlation), and new analog materials are only a few examples of the new improvement. The ease of extraction of quantitative data means that the modeling results can be used to provide new views on natural processes. Reducing unwanted uncertainties is crucial to propose robust new theories. One of the main difficulties for analog modelers is reducing the uncertainties related to the initial setup arrangement. Most of these uncertainties are classically referred to the handmade processes, such as handling analog materials. In the Analog Modeling laboratory of the University of Trieste, we tested the use of a cobot (a cobot is a robot for direct physical interaction with a human user within a shared workspace) to simulate pre-existing faults in wet clay boxes. We present two different sets of experiments. The first set has been designed to evaluate the kinematic efficiency of Riedel shears. The second reproduces differently oriented inherited dip-slip faults in an experimental box reproducing extension. In both cases, we reproduced the same setup more than one time. The collaborative robot reduced the variability of the results, demonstrating the effectiveness of the use of cobots in analog modeling laboratories.

How to cite: Bonini, L. and Bertone, N.: The use of collaborative robots (cobots) in an analog modeling laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6125, https://doi.org/10.5194/egusphere-egu23-6125, 2023.

EGU23-6318 | ECS | PICO | TS8.2

The coupled evolution of forearc and back-arc basins: inferences from 2D and 3D numerical modelling 

Attila Balazs, Ana Gomes, Claudio Faccenna, and Taras Gerya

The subsidence history of forearc and back-arc basins reflects the relationship between subduction kinematics, mantle dynamics, magmatism, crustal tectonics, and surface processes. The distinct contributions of these processes to the topographic variations of active margins during subduction initiation, oceanic subduction, and collision are less understood.

We conducted a series of 2D and 3D thermo-mechanical numerical models with the codes 2DELVIS and 3DELVIS, based on staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations. Physical properties are transported by Lagrangian markers that move with the velocity field interpolated from the fix Eulerian grid. We discuss the influence of different subduction obliquity angles, the role of mantle flow variations and their connection with sediment transport and upper plate deformation. Furthermore, slab tearing and the gradual propagation of slab break-off is modelled during collision.

The models show the evolution of wedge-top and retro-forearc basins on the continental overriding plate, separated by a forearc high. They are affected by repeated compression and extension phases. Compression-induced subsidence is recorded in the syncline structure of the retro-forearc basin from the onset of subduction. The 2–4 km upper plate negative residual topography is produced by the gradually steepening slab, which drags down the upper plate. Trench retreat leads to slab unbending and decreasing slab dip angle that leads to upper plate trench-ward tilting. Back-arc basins are either formed along inherited weak zones at a large distance from the arc or are connected to the volcanic arc evolution leading to arc splitting. Backarc subsidence is primarily governed by crustal thinning that is controlled by slab roll-back and supported by the underlying mantle convection. High subduction and mantle convection velocities result in large wavelength negative dynamic topography. Collision and continental subduction are linked to the uplift of the forearc basins; however, the back-arc records ongoing extension during a soft collision. During the hard collision, both the forearc and back-arc basins are ultimately affected by the compression. Our modeling results are compared with the evolution of Mediterranean subduction zones.

How to cite: Balazs, A., Gomes, A., Faccenna, C., and Gerya, T.: The coupled evolution of forearc and back-arc basins: inferences from 2D and 3D numerical modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6318, https://doi.org/10.5194/egusphere-egu23-6318, 2023.

EGU23-6598 | ECS | PICO | TS8.2

Lithosphere-asthenosphere interaction as the source for intraplate deformation in the Gulf of Guinea 

Jaime Almeida, Nicolas Riel, Marta Neres, Hamzeh Mohammadigheymasi, Susana Custódio, and Stephanie Dumont

Despite extensive research, intraplate earthquakes and required intraplate deformation remain relatively unexplained. To explore this problematic, we tested the possibility that these could derive from the dynamic interaction between the lithosphere and the upper mantle. This was performed by conducting a thorough geophysical exploration of a region with both low plate velocities and clear asthenosphere dynamics, specifically the Gulf of Guinea (GOG) and adjacent Western Africa.

In this work, we developed 3D numerical geodynamic models of the asthenosphere-lithosphere interaction in the GOG, ran with the state-of-the-art LaMEM modelling code. To assess the contribution of individual intraplate deformation sources, we tested various initial/boundary conditions namely: (a) the spreading rate of the individual segments of Central Atlantic mid-ocean ridge, (b) the presence/absence of weak zones, such as the Romanche or Central-African shear zones, as well as (c) the stress contribution by an active mantle plume head with varying width. Seismicity data was utilized as a criterion to assess the validity of the modelled stress/strain localization sites.

Our results suggest that intraplate deformation within the GOG is mostly controlled by the spreading rate of the mid-ocean ridge, with different localization sites deriving from their relative proximity to the shear zones and plume head. This work aims to expand our knowledge of intraplate deformation mechanisms and to contribute towards improving seismic hazard assessment away from plate boundaries.

This work was supported by the European Union and the Instituto Dom Luiz (IDL) Project under Grant UIDB/50019/2020, and it uses computational resources provided by C4G (Collaboratory for Geosciences) (Ref. PINFRA/22151/2016). It was also partly supported by the Fundação para a Ciência e a Tecnologia (FCT) in the content of the Project SHAZAM “Sismicidade e Perigosidade da Margem Atlântica sub-Saariana,” with the reference PTDC/CTA/GEO/31475/2017; POCI-01-0145-FEDER-031475, co-financed by FEDER-COMPETE/POCI 2020.

How to cite: Almeida, J., Riel, N., Neres, M., Mohammadigheymasi, H., Custódio, S., and Dumont, S.: Lithosphere-asthenosphere interaction as the source for intraplate deformation in the Gulf of Guinea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6598, https://doi.org/10.5194/egusphere-egu23-6598, 2023.

EGU23-7077 | ECS | PICO | TS8.2

Laser-based seismic imaging of analogue models 

Jasper Smits, Fred Beekman, Ernst Willingshofer, and Ivan Vasconcelos

We present and demonstrate our new application of a geophysical seismic technique to acoustically characterise and image layers with different impedance contrast in analogue models. A high-powered pulsed laser in combination with a mirror galvanometer is used to generate a powerful acoustic shockwave at any point of the surface of the analogue model. Reflections, refractions, and diffractions of the acoustic source wave, induced by internal structures inside an analogue model, produce vibrations of the top surface of a model, which are measured by laser vibrometer.

Using our setup, we acquire seismic receiver gathers in less than a minute. Interpretation of the gathers allowed to identify the presence of internal reflecting and refracting material interfaces. In a series of test models, we determined the speed of both P-waves and surface waves in a multitude of brittle analogue materials. In uniform layered models we performed 1D inversion using the gathered waveform data. The results are validated by simulating the test experiments in a finite-difference solver. The novel method will be developed further, aiming to determine stress build-up in the material prior to fault formation or activity.

How to cite: Smits, J., Beekman, F., Willingshofer, E., and Vasconcelos, I.: Laser-based seismic imaging of analogue models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7077, https://doi.org/10.5194/egusphere-egu23-7077, 2023.

EGU23-7248 | PICO | TS8.2

Geodynamic modelling of continental subduction beneath oceanic lithosphere 

Filipe Rosas, Afonso Gomes, Nicolas Riel, Wouter Schellart, Joao Duarte, and Jaime Almeida

Subduction of an oceanic plate beneath either an oceanic, or a continental, overriding plate requires two main conditions to occur in a steady state: i) a high enough subduction rate (~5 cm/yr, Schellart in print); and ii) a weak (efficiently softened/lubricated) subduction channel (Gerya and Meilick, 2011). The first requirement prevents thermal diffusive re-equilibrium of the subducting slab within the asthenospheric ambient mantle, maintaining the slab cold and dense enough to provide the slab-pull subduction driving force. The second condition, is achieved with the contribution of a strong dehydration of the serpentinized oceanic plate, with resulting pervasive fluid circulation in the subduction channel significantly promoting its weakening, thus preventing strong coupling between the subducting and the overriding plate. Avoiding such a coupling has been shown to be key to maintain stable subduction, since it generally leads to a halt in the subduction process and to slab break-off (Duarte et al., 2015). Both these conditions are seemingly not favoured in a continental subduction scenario, since continental lithosphere is positively buoyant and much less, or not al all, serpentinized. Hence, the (geo)dynamics governing continental subduction is still not fully understood.

We thus carried out a set of geodynamic numerical modelling experiments to further understand the first order geodynamic constraints governing continental subduction in the specific scenario that considers the subduction of a continental plate beneath an oceanic one, i.e., upon the arrival of a continental plate at an intra-oceanic subduction zone. The 2D numerical experiments were conceived and constructed using the Underworld code (Moresi et al., 2007), to better understand the influence on continental subduction efficiency, as well as on related synthetic ophiolite obduction, of considering either a scenario of dominant trench retreat (roll-back) or trench advance (roll forward) subduction regime. Roll-back subduction was prescribed in our models by fixing the trailing edge of the overriding plate, whereas roll-forward subduction was favoured (allowed) by leaving it free to move. Our experiments ensure dynamic self consistency in all cases.  

Our preliminary results show that, although synthetic obduction is possible to achieve in both situations, the overall first order (geo)dynamic differences implied by the two different simulated regimes, bear important consequences on the timing, overall kinematic configuration and local stress/strain distribution of the considered continental subduction-exhumation cycle in each case.

Acknowledgments

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL

References

Duarte, J.C., Schellart, W.P., Cruden, A.R., 2015. How weak is the subduction zone interface? Geophysical Research Letters 42, 2664–2673. doi:10.1002/2014GL062876.

Gerya, T.V., Meilick, F., 2011. Geodynamic regimes of subduction under an active margin: effects of rheological weakening by fluids and melts. Journal of Metamorphic Geology 29, 7–31. doi:0.1111/j.1525-1314.2010.00904.x.

Moresi, L., Quenette, S., Lemiale, V., Mériaux, C., Appelbe, B., Muhlhaus, H.B., 2007. Computational approaches to studying non-linear dynamics of the crust and mantle. Physics of the Earth and Planetary Interiors 163, 69–82. doi:10.1016/j.pepi.2007.06.009.

Schellart, W.P., in print. Subduction zones: A short review, in Dynamics of Plate Tectonics and Mantle Convection, Editor: João Duarte, ISBN: 9780323857338.

How to cite: Rosas, F., Gomes, A., Riel, N., Schellart, W., Duarte, J., and Almeida, J.: Geodynamic modelling of continental subduction beneath oceanic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7248, https://doi.org/10.5194/egusphere-egu23-7248, 2023.

Flow perturbation can deflect the layering of the host rock around slip surfaces in shear zones resulting in the development of flanking structures. The details of flanking structure geometry can provide important clues about shear sense, flow kinematics, and finite strain, although not without ambiguities. The developing structures share similarities to fault-related folds that play an important role in sedimentary basins.

Mechanical anisotropy has been shown to have a major influence on both the slip rate and flow perturbation. Willis (1964) derived an analytical solution for an elliptical inclusion embedded in a homogeneous anisotropic elastic matrix subject to a uniform load in the far field. The solution can be reduced to the case of an incompressible viscous medium and an arbitrarily oriented inviscid slit (slip line). The reduced solution, which is exact for the initial state of homogeneous planar anisotropy, provides useful insights into the initial stages of deformation and it can be used to approximately study finite strain deformation of a power-law host. However, anisotropic fluids such as ductilely deforming foliated rocks keep a ‘memory’ of deformation due to their evolving microstructure, which affects the flow field. In this study, I will use different numerical modeling techniques to examine the impact of host layering on the perturbing flow and structure development around a slip surface in shear zone.

How to cite: Dabrowski, M.: Numerical modelling of flanking structures in layered viscous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7357, https://doi.org/10.5194/egusphere-egu23-7357, 2023.

EGU23-7370 | ECS | PICO | TS8.2

2D numerical modelling of Tethyan-type ophiolite emplacement: The role of overriding plate age, serpentinization, and OCT width. 

Afonso Gomes, Filipe Rosas, João Duarte, Nicolas Riel, Wouter Schellart, and Jaime Almeida

Ophiolites are exposed remnants of oceanic lithosphere that are emplaced onto a continental domain, and Tethyan-type ophiolites, specifically, are those that are emplaced within a continental passive margin. The emplacement process for this type of ophiolites occurs when a continental passive margin subducts, and subsequently exhumes, beneath an oceanic overriding plate (future ophiolite). It is the exhumation of the passive margin’s crust that triggers both the separation of the ophiolite from the remaining oceanic overriding plate (OP) and its ensuing emplacement within the continental domain.

Analogue and numerical models have demonstrated the feasibility of this process (Chemenda et al., 1996; Duretz et al., 2016; Porkoláb et al., 2021); however, its specific geodynamic constraints are still poorly understood. For example, the geological record appears to be heavily skewed towards the fast emplacement of very young lithosphere, but it is unclear whether it is possible to emplace older lithosphere via the same process. Here we use 2D numerical models to test the sensitivity of this process to three key parameters: a) overriding plate age (10-60Myr), b) width of ocean-continent transition (OCT, 0-500km), and c) existence/absence of a serpentinization layer in the OP. The models use temperature and strain-rate dependent visco-plastic rheologies, are driven by buoyancy forces (without imposed non-zero velocity conditions), and are run using the Underworld code (Moresi et al., 2003).

Preliminary results show that the continental subduction/exhumation cycle and the ophiolite emplacement process are highly sensitive to variations in initial model conditions. Nevertheless, the emplacement process is physically viable under a somewhat wide range of conditions, being optimized for a narrow OCT and adjacent continental margin subducting beneath a young and serpentinized OP. A 10 Myrs old OP leads to a fast continental subduction-exhumation cycle (15-20 Myrs), while a 60 Myrs old OP induces a slow (>30 Myrs) cycle, but still leads to ophiolite emplacement. A long and tapered margin (OCT, 500km) also promotes a slow (>30 Myrs) cycle, with only a thin melange of exhumed crust, which hinders the formation and emplacement of individual ophiolite klippen; the reverse is true for a very short OCT. The existence of a serpentinization layer greatly facilitates the emplacement of the ophiolite klippe.

Acknowledgments

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia I.P./MCTES through national funds (PIDDAC)–UIDB/50019/2020-IDL and through scholarship SFRH/BD/146726/2019.

References

Chemenda, A., Mattauer, M., Bokun, A. (1996). Continental subduction and a mechanism for exhumation of high-pressure metamorphic rocks: New modelling and field data from Oman. EPSL, 143, 173–182.

Duretz, T., Agard, P., Yamato, P., Ducassou, C., Burov, E., Gerya, T. (2016). Thermo-mechanical modeling of the obduction process based on the Oman Ophiolite case. GR, 32, 1–10.

Moresi, L., Dufour, F., Mühlhaus, H. B. (2003). A Lagrangian integration point finite element method for large deformation modeling of viscoelastic geomaterials. Journal Comp. Physics, 184, 476–497.

Porkoláb, K., Duretz, T., Yamato, P., Auzemery, A., Willingshofer, E. (2021). Extrusion of subducted crust explains the emplacement of far-travelled ophiolites. Nature Commun., 12, 1499.

How to cite: Gomes, A., Rosas, F., Duarte, J., Riel, N., Schellart, W., and Almeida, J.: 2D numerical modelling of Tethyan-type ophiolite emplacement: The role of overriding plate age, serpentinization, and OCT width., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7370, https://doi.org/10.5194/egusphere-egu23-7370, 2023.

EGU23-10149 | ECS | PICO | TS8.2

Not all basins are created equal: Lithospheric-scale analogue experiments of selective basin inversion 

Anindita Samsu, Weronika Gorczyk, Fatemeh Amirpoorsaeed, Timothy Schmid, Eleanor Morton, Peter Betts, and Alexander Cruden

The inversion of rift basins is commonly associated with the reactivation of normal, basin-bounding faults or shear zones. Analogue models have shown how the reverse reactivation of these pre-existing structures facilitates the uplift of a basin’s sedimentary infill. However, few of these models examine the viscous processes occurring beneath the brittle crust, which may or may not drive basin inversion. In our study, we use lithospheric-scale analogue experiments of orthogonal extension followed by shortening to simulate rifting followed by inversion and orogenesis. Here we explore how the flow behaviours of ductile layers underneath rift basins promote or suppress basin inversion.

In our experiments, we simulate rifting by extending a multi-layer, brittle-ductile lithosphere which floats on a fluid asthenosphere, creating a system of distributed basins. This extension is followed by shortening of the model, during which strain is accommodated by the reactivation of basin-bounding faults and folding or upwelling of the ductile layers. These experiments reveal that the rheology of the ductile lower crust and lithospheric mantle, modulated by the imposed bulk strain rate, determine: (1) how rift basins are distributed during extension and (2) whether all or only some of these basins are inverted during shortening. We interpret that this selective basin inversion is related to the superposition of crustal-scale and lithospheric-scale boudinage during the basin-forming extensional phase. Our findings demonstrate that lithospheric-scale analogue models can be a powerful tool for investigating the interaction between brittle and viscous deformation during basin inversion.

How to cite: Samsu, A., Gorczyk, W., Amirpoorsaeed, F., Schmid, T., Morton, E., Betts, P., and Cruden, A.: Not all basins are created equal: Lithospheric-scale analogue experiments of selective basin inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10149, https://doi.org/10.5194/egusphere-egu23-10149, 2023.

We present a new numerical method to simulate the structural patterns emerging from the long-term large-deformation tectonic flows in both two and three spatial dimensions.  The domains of different material properties are each represented by a level set function discretized on a Eulerian mesh with the discontinuous Galerkin method. The level sets are advected by a velocity field provided by a coupled Stokes flow solver. Our method accurately captures the material interface by the adaptive mesh refinement, reduces the computational expenses compared to the traditional particle-in-cell method and offers straightforward handling of geometric splitting and merging.  Under the unified finite element framework, our method promises the flexibility in the choice of mesh geometry as well as the potential for extending to complex rheology.  With passive tracers geat and around areas of interest, the finite strain of the flow field can be integrated through any time interval within the total simulation time.  The strain ellipsoids thus obtained offers the possibility for ground-truthing the simulated deformation patterns with the field structural analysis.  Our results demonstrate identical physical behaviour when compared with established structural geology and geodynamic benchmarks.

The style of the crustal dynamics on the Archean Earth has been subject to controversy on whether a vertical tectonic style in the form of Rayleigh-Taylor instability, induced by an inverted density profile, prevails in the early history of the Earth and if so, how the transition to the present-day plate tectonics, characterized by dominantly horizontal movement, is manifested in the rock record.  Equipped with our modelling scheme, we construct numerical models to simulate the lithological distributions and deformation patterns resulted from a synchronous operation of vertical tectonism and horizontal shearing. The latter can be viewed as a possible result of some far-field tectonic boundary condition (e.g. oblique convergence).  Many aspects of the simulation in terms of the map pattern, foliation/lineation trend and strain distribution compare favorably with the field observations in Neoarchean granitoid-greenstone terranes in the Superior Province as well as worldwide.  Therefore, it is concluded that the vertical and horizontal tectonism are not mutually exclusive tectonic regimes  The symbiosis of both tectonic processes is a viable mechanism for establishing the crustal architecture and the deformation pattern we see today in many Neoarchean terranes and might represent a transition from the former to the latter in the Neoarchean.

How to cite: Wu, Q. and Lin, S.: Modelling tectonic flow with discontinuous Galerkin level set method: Case studies and applications  for the Neoarchean crustal dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10353, https://doi.org/10.5194/egusphere-egu23-10353, 2023.

The structural style of inverted rift basins is controlled by the inherited structures and stratigraphic elements but also by the presence of salt layers or welded equivalents. Salt acts as a main detachment during extension and, depending on its thickness, different degrees of linkage develop between the basement and overburden. The presence and distribution of salt structures, the linkage between the basement and overburden, and the continuity of salt on these salt-bearing rifted basins have a strong impact on thick- to thin-skinned deformation during inversion. As the weakest rock of the basin infill, salt acts as a contractional detachment and buried diapirs rejuvenate during early inversion. With increasing shortening thick-skinned deformation folds and uplifts the basins while the diapirs are squeezed and welded by thin-skinned deformation.

Using an approach based on systematic analogue models, this work analyses how extensional basins develop above a pre-rift salt layer and how the inherited salt structures evolve during subsequent inversion. A first set of models only affected by extensional deformation was carried out examining how the variation of different parameters such as salt and overburden thicknesses impact the structural style of salt structures developed during thick-skinned extension. Afterwards, some of these models were repeated to understand how pre-existing extensional and salt structures condition the evolution during total inversion tectonics. The experimental apparatus consists of five metal fault blocks simulating a domino basement-fault system that rotate counter-clockwise during extension and clockwise during inversion. Deformation was transferred to the blocks by a motor worm-screw at a constant velocity of 4.6 mm/h until reaching 10 cm of total extension. During the inversion phase, the same velocity was applied until reach total inversion of the basins. A layered unit of sand capped by a uniform-thickness polymer layer and additional layers of sand simulated the pre-kinematic unit. While different sand layers were added during extension, no syn-inversion sedimentation was considered.

The results of this study show that the structural style during inversion is highly conditioned by the inherited extensional configuration but also by the salt thickness that condition the degree of coupling/decoupling of the pre- and syn-kinematic successions. The study also revealed that the thickness of the overburden has a minor impact during the inversion of the basins. Such is the case that in models with either thin or thick overburden succession, the extensional geometry might be preserved if the salt is thick independently of the overburden thickness. Contrary, models with a thin salt layer are characterized by a total inversion of the ramp-syncline basin that as an inversion anticline is developed, crestal collapse extensional faults minimize the developed structural relief. Finally, the analogue modelling allowed to understand how compression caused primary weld reactivation, diapir rejuvenation, salt thickening and/or thrust emplacement. The reactivation of some of these salt-related structures is extremely impacted by the salt thickness distribution that resulted from the extensional phase. Therefore, to characterize structural style and understand the evolution of the basin it is needed an understanding of the inherited salt-related structures.

How to cite: Ferrer, O., Carola, E., and McClay, K.: Experimental approach (analogue modelling) of thin- to thick-skinned inversion of extensional basins with pre-rift salt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11040, https://doi.org/10.5194/egusphere-egu23-11040, 2023.

EGU23-11554 | ECS | PICO | TS8.2

Numerical and Analogue Modelling of Salt-Bearing Rifted Margins 

Mahdi Bakhtbidar, Jonas B. Ruh, Pablo Santolaria Otín, Pablo Martinez Granado, and Oscar Gratacos Torra

Due to their high economic (natural resources) and scientific (e.g., global archive of climate changes) potential, rifted margins have been studied using different approaches including sequence stratigraphy, high-resolution mapping, structural analysis, or seismic imaging. Sandbox analogue modelers have also assessed rifted margins and tested the driving and controlling parameters that determine their structural styles and evolution. In this research, we present a series of physical analogue models aimed at testing the influence of downbuilding and dominant gliding instabilities on the evolution and configuration of salt-bearing rifted margins. Being aware of the limitations of this experimental technique we go a step further and use numerical modelling to implement parameters that are not easy to simulate using analogue modelling. Several numerical experiments have been defined to test the main governing mechanisms (differential loading vs dominant gliding) and different key parameters such as the rheology of salt and temperature.

Comparison of the two approaches yields valuable insights into the processes that control the evolution and structural styles of salt-bearing rifted margins as well as clarifies the limitations and complementarity between both techniques. Our models provide stratigraphic, structural and kinematic templates to better understand salt-bearing rifted margins worldwide.

How to cite: Bakhtbidar, M., B. Ruh, J., Santolaria Otín, P., Martinez Granado, P., and Gratacos Torra, O.: Numerical and Analogue Modelling of Salt-Bearing Rifted Margins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11554, https://doi.org/10.5194/egusphere-egu23-11554, 2023.

EGU23-13434 | ECS | PICO | TS8.2

The effects of inward and outward dipping craton margin geometry on upper crustal deformation: Insights from analogue modelling 

Fatemeh Amirpoorsaeed, Anindita Samsu, Peter Betts, Alexander Cruden, and Robin Armit

Craton margins undergo intense deformation influenced by the pre-existing crustal and lithospheric architecture, rheology, and far-field kinematics. The role of rheological contrasts and weak zones at the edge of the craton has been discussed, but it is unclear whether deformation in the upper crust is influenced by the geometry of the craton margin itself (i.e., whether the margin dips towards or away from the interior of the craton). Our analogue experiments are aimed at studying the influence of craton margin geometry on structures formed during rifting and inversion, as craton margins are prone to reworking and reactivation during superimposed tectonic events.

The experiments are designed based on the geometries of the eastern and southern margins of the North Australian Craton which has experienced multiple stages of extension and shortening. The inward vs. outward dipping craton margins in these areas were interpreted from crustal-scale seismic reflection data.  In our experiments, we see that strain and deformation style varies with proximity to the craton margin. During the extensional phase of both inward and outward dipping experiments, we observe that rifts are mainly formed by boudinage and necking in the lower crust. The inward dipping model prevents the propagation of a major normal fault at the margin, resulting in a number of smaller faults. Subsequent shortening of the inward dipping model results in modest basin inversion above the craton margin, suggesting that the majority of strain is accommodated by reactivation of normal faults away from the margin. In contrast, the outward dipping model shows the propagation of a single major normal fault along the craton margins, leading to significant thinning of the lower crust. A major rift is also being formed away from the craton margin in this model. Inversion of the outward dipping craton margin model shows more intense inversion at the margin compared to the inward dipping model, with lower strain and smaller reactivation of normal faults away from the margin. We can therefore conclude that the geometry of a craton margin exerts a first-order control on the deformation of the upper crust during rifting and subsequent inversion.

How to cite: Amirpoorsaeed, F., Samsu, A., Betts, P., Cruden, A., and Armit, R.: The effects of inward and outward dipping craton margin geometry on upper crustal deformation: Insights from analogue modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13434, https://doi.org/10.5194/egusphere-egu23-13434, 2023.

EGU23-14818 | PICO | TS8.2

Dyke propagation and dynamics during rift initiation 

Yuan Li, Adina Pusok, Timothy Davis, Dave May, and Richard Katz

Dykes are tensile fractures that rapidly transport magma from the hot, ductile asthenosphere across the cold, brittle upper lithosphere. They play an important role in tectonic extension settings by drastically reducing the force needed for rifting (Buck, 2004). Yet the balance of mechanisms that drive dyke propagation and how they promote rift initiation remain unclear. Here we investigate the physics of dyke propagation in a two-phase continuum model that can approximate both faults and dykes in an extensional tectonic setting.  

Dykes are fluid-filled fractures, typically modelled as discrete inclusions in an extended elastic continuum.  These models suggest that dyking is dominated by magma buoyancy and that its direction can be altered according to the competition between tectonic stress and the topographic load (Maccaferri et al., 2014). However, this method assumes a constant background stress field in the lithosphere during dyking. Therefore this method cannot capture the interaction between dykes and the long-term deformation of the lithosphere. To resolve this issue, dyking has been prescribed as a weak material in a continuum, one-phase rifting model in which dyking is included in the conservation of mass, momentum and/or energy (Liu and Buck, 2018). This method respects the scale separation between dyking and long-term dynamics, but still neglects the feedback of dyking on the stress field.

We present a geodynamic model that incorporates a novel poro-viscoelastic–viscoplastic rheological formulation with a hyperbolic yield surface for plasticity. With this model, both dyking and faulting can be simulated consistently (Li et al., in review). We validate our theory by comparing the stress field at the tip of the dyke with that from the linear elastic fracture mechanics theory. We then investigate dynamics of dyking in a geodynamic rifting model. We show that dyking assists rifting and its localisation. First, it reduces the yield strength in the brittle layer as the pore pressure balances the compressive stress; second, it promotes the development of near-surface normal faults localised in a relatively narrow rift region near the rift axis. We investigate the physics of dyke propagation with respect to the balance between buoyancy and tectonic forcing, and the effect of topography.

References

Buck, W .R., (2004). Consequences of asthenospheric variability on continental rifting. In Rheology and deformation of the lithosphere at continental margins, chapter 1, pages 1–30. Columbia University Press. doi: 10.7312/karn12738-002.

Maccaferri, F., Rivalta, E., Keir, D., and Acocella, V., (2014). Off-rift volcanism in rift zones determined by crustal unloading. Nature Geoscience 7, 297–300. doi: 10.1038/ngeo2110.

Liu, Z. and Buck, W. R., (2018). Magmatic controls on axial relief and faulting at mid-ocean ridges. Earth and Planetary Science Letters, 491:226–237. doi: 10.1016/j.epsl.2018.03.045.

Li, Y., Pusok, A., Davis, T., May, D., and Katz, R., Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, in review of Geophysical Journal International.

How to cite: Li, Y., Pusok, A., Davis, T., May, D., and Katz, R.: Dyke propagation and dynamics during rift initiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14818, https://doi.org/10.5194/egusphere-egu23-14818, 2023.

EGU23-1562 | ECS | Posters virtual | GI2.1

A new finite-difference stress modeling method governed by elastic wave equations 

Zhuo Fan, Fei Cheng, and Jiangping Liu

Numerical stress or strain modeling has been a focused subject in many fields, especially in assessing the stability of key engineering structures and better understanding in local or tectonic stress patters and seismicity. Here we proposed a new stress modeling method governed by elastic wave equations using finite-difference scheme. Based on the modeling scheme of wave propagation, the proposed method is able to solve both the dynamic stress evolution and the static stress state of equilibrium by introducing an artificial damping factor to the particle velocity. We validate the proposed method in three geophysical benchmarks: (a) a layered earth model under gravitational load, (b) a rock mass model under nonuniform loads on its exterior boundaries and (c) a fault zone with strain localization driven by regional tectonic loading that measured by GPS velocity field.  Because the governing equations of the proposed method are wave equations instead of equilibrium equations, we are able to use the perfectly matched layer as the artificial boundary conditions for models in unbounded domain, which will substantially improve the accuracy of them. Also, the proposed scheme maps the physical model on simple computational grids and therefore is more memory efficient for grid points’ positions not been stored. Besides, the efficient parallel computing of the finite-different method guarantees the proposed method’s advantage in computational speed. As a minor modification to wave modeling scheme, the proposed stress modeling method is not only accurate for geological models through different scales, but also physically reasonable and easy to implement for geophysicists.

How to cite: Fan, Z., Cheng, F., and Liu, J.: A new finite-difference stress modeling method governed by elastic wave equations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1562, https://doi.org/10.5194/egusphere-egu23-1562, 2023.

EGU23-2228 | ECS | Posters on site | GI2.1

Non-destructive geophysical damage analysis of medieval plaster in the cloister of the St. Petri Cathedral Schleswig (Germany) 

Yunus Esel, Ercan Erkul, Detlef Schulte-Kortnack, Christian Leonhardt, Julika Heller, and Thomas Meier

Buildings that have existed for centuries undergo structural changes over time due to variations in use. In addition, many structures are severely damaged for example by moisture intrusion. To determine the distribution of moisture in the structure, they are often examined pointwise by core sampling. In addition to invasive methods, non-destructive methods may be applied to obtain three-dimensional hints on the moisture distribution with structures of interest.            
The purpose of this paper is to show that non-destructive determination of moisture distribution is possible by using and combining geophysical measurement methods such as infrared thermography (IR), ultrasound (US) and ground penetrating radar (GPR). There are examples for the combination of these methods for non-destructive examination, but it is not yet commonly applied in the field of restoration and conservation of historic buildings.            
We present results of geophysical investigations of medieval wall paintings in the cloister of the cathedral in Schleswig (Federal State Schleswig-Holstein, Northern Germany) in the framework of a project funded by the German Federal Foundation for the Environment (Deutsche Bundesstiftung Umwelt - DBU). In the cloister, large-scale alterations of the medieval red-line paintings occurred due to gypsum deposits and a shellac coating. In order to quantify the material properties of a vault section (yoke) in the cloister during the restoration ultrasound surface wave measurements, passive and active thermography and ground penetrating radar measurements were carried out.
Repeating measurements at intervals of several months made it possible to evaluate the effectiveness of the test treatments by different solvents to remove the shellac as well as the gypsum deposits. In addition, our results from the passive thermography measurements show that in one section a defect in the horizontal barrier could be responsible for moisture ingress and associated damage. The radargrams recorded in this area confirm that a significant change in reflection amplitudes is present in the areas of increased moisture.

How to cite: Esel, Y., Erkul, E., Schulte-Kortnack, D., Leonhardt, C., Heller, J., and Meier, T.: Non-destructive geophysical damage analysis of medieval plaster in the cloister of the St. Petri Cathedral Schleswig (Germany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2228, https://doi.org/10.5194/egusphere-egu23-2228, 2023.

EGU23-2347 | ECS | Posters on site | GI2.1

Non-destructive testing methods and numerical development for enhancing airfield pavement management 

Konstantinos Gkyrtis, Christina Plati, and Andreas Loizos

Pavements are an essential component of airport facilities. Airport infrastructures serve to safely transport people and goods on a day-to-day basis. They promote economic development, both regionally and internationally, by also boosting tourist flows. In times of crisis, they can be used for societal emergencies, such as managing migration flows. Therefore, airports need pavements in good physical condition to ensure uninterrupted operations. However, interventions on airfield pavements are costly and labor intensive. Aspects of pavement structural performance related to bearing capacity and damage potential remain of paramount importance as the service life of a pavement extends beyond its design life. Therefore, structural condition evaluation is required to ensure the long-term bearing capacity of the pavement. 

The design and evaluation of flexible airfield pavements are generally based on the Multi-Layered Elastic Theory (MLET) in accordance with Federal Aviation Administration (FAA) principles. The most informative tool for structural evaluation is the Falling Weight Deflectometer (FWD), which senses pavement surfaces using geophones that record load-induced deflections at various locations. Additional geophysical inspection data using Ground Penetrating Radar (GRP) is processed to estimate the stratigraphy of the pavement. The integration of the above data provides an estimate of the pavement's performance and potential for damage. However, GRP is not always readily applicable.

In addition, the most important concern in pavement evaluation is the mechanical characterization of pavement materials. At the top of pavement structures, asphalt mixtures behave as a function of temperature and loading frequency. This viscoelastic behavior deviates from MLET and this issue needs further investigation. Therefore, this study integrates measured NDT data and sample data from cores taken in-situ. The pavement under study is an existing asphalt pavement of a runway at a regional airport in Southern Europe. A comparative evaluation of the strain state within the pavement body is performed both at critical locations and at the pavement surface, taking into account elastic and viscoelastic behaviors. Strains are an important input to models of long-term pavement performance, which has a critical influence on aircraft maneuverability. In turn, the significant discrepancies found highlight the need for more mechanistic considerations in predicting the damage and stress potential of airfield pavements so that maintenance and/or rehabilitation needs can be better managed and planned.

Overall, this study highlights the sensing capabilities of NDT data towards a structural health monitoring of airfield pavements. Ground-truth data from limited destructive testing enrich pavement evaluation processes and enhance conventional FAA evaluation procedures. The study proposes a numerical development for accurate field inspections and improved monitoring protocols for the benefit of airfield pavement management and rehabilitation planning. 

How to cite: Gkyrtis, K., Plati, C., and Loizos, A.: Non-destructive testing methods and numerical development for enhancing airfield pavement management, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2347, https://doi.org/10.5194/egusphere-egu23-2347, 2023.

The Laacher See Event- (LSE-) volcanism isochrone of 12.850 yrs BP (Bujatti-Narbeshuber, 1997), proxy for P/H boundary KISS (Bujatti-Narbeshuber, 1996), was improved from Gerzensee varves to 13.034 cal yrs BP (Van Raden, 2019).

    This LSE date now separates end Pleistocene, first, mainly oceanic-water KISS, from the second, Holocene-Younger Dryas Onset (YDO), continental-ice impact, as predicted by KISS-hypothesis, separating:„ a continental Koefels-comet ice-impact, from the mainly oceanic KISS, at the Pleistocene/Holocene boundary, associated with global warming, dendro C14 spikes, faunal mass extinction...“ (Bujatti-Narbeshuber, 1996; Max, 2022).

    Oceanic-water LSE-KISS (13.034 cal yrs BP, varves) of end Alleroed temperature maximum, separates by 157 yrs from continental-ice YDO-KISS (12.877 cal yrs BP, varve-date). A larger gap of 184 yrs results, taking C 14 dated YD-KISS (12.850 cal yrs BP), approaching 200 yrs of earlier varve-studies (Bujatti-Narbeshuber, 1997).

    LSE-KISS varve-date differs by 47 yrs from geo-magnetic Gothenberg Excursion Onset- (GEO-) isochrone of 13.081 cal yrs BP (Chen, 2020), suggesting geo-magnetic reversal, True Polar Wander (TPW) GEO-TPW-KISS from 2 Koefels-comet (Taurid-) fragments. This considers end-paleolithic Magdalenian Impact Sequelae Symbolisations (MISS).

    Questioning P/H isostatic-unloading volcanism (Zielinsky, 1996), LSE-KISS volcanism is from Mid Atlantic Ridge & Mid Atlantic Plateau (MAR&MAP) impact (Bujatti-Narbeshuber, 1997, 2022), as further corroborated by Greenland (NGRIP) ice-core sulfate monitoring: from LSE-KISS-volcanism (12.978 cal yrs) to YDO (12.867 cal yr BP), within 110 yrs, an unprecedented, bipolar-volcanic-eruption-quadruplet resulted (Lin, 2022).

    The first Taurid LSE-KISS (Varves-date: 13.034 cal yrs BP, GEO-date: 13.084 cal yrs BP.) into oceanic-water is evident from two 700 km Mid Atlantic Ridge & Plateau Lowering Events (MARPLES) releasing two separate Tsunamis (Bujatti-Narbeshuber, 2022): Resulting in submarine explosive-magmatism-silicates, seafloor-carbonates, volcanic-ash and sea-water in huge strato-meso-spheric overheated steam-plume moving eastward by eolian transport, descending in drowning rain-flood, largely contributing to Eurasian loess sediment layer (Muck, 1976).

    This is stratigraphically verified in e.g. relative stratigraphic positions in Netherland, Geldrop-Aalsterhut, with Younger Coversand I, bleached (!) (AMS 13.080- 12.915 cal yrs BP) underlying intercalated (!), charcoal rich (AMS 12.785-12.650 cal yrs BP) Usselo Horizon (Andronikov, 2016). It corresponds to US, Black Mats stratigraphy from second Taurid, continental-ice, YD-KISS (12.850 cal yrs BP, C14) plus Carolina Bays (CB) with: 1. Soft, white, loess sediment from first oceanic LSE-KISS. 2. YD-KISS proxies-stratum. 3. e.g. Carolina-Florida-coast-sand-disturbances, within 1.500 km radius of continental-ice YD-KISS ice-ejecta impact-curtain of 500.000 CB (LIDAR) 4. Black Mats after YD-KISS.

    After visiting Koefels-crater an “below continental-glacier-ice, circular geomagnetic-anomaly with paleoseismic Koefels-corridor of twelfe Holocene rockfalls”, Eugene Shoemaker (Vienna, May 5th 1997), when asked about Carolina Bays causation, is quoted: “Eugene spoke of a late Pleistocene origin of the Bays and as glaciological features while I preferred the paleoseismic interpretation. I interprete them as paleoseismic impact-seismic liquefaction features. They … are the first evidence for a late Pleistocene impact event. Dated by me …12.850 BP (1950) in calendar years”. (Bujatti-Narbeshuber, NHM letter to John Grant III, Sept. 22nd 1997).

    Both P/H-impacts break&make, Pleistocene criticality&Holocene damped flow, through 700 km geomorphological threshold (GLOVES) submersion & through (GTT) water, CO2 Greenhouse-gas-production, beyond glaciation threshold for hot climate prediction.

How to cite: Bujatti-Narbeshuber, M.: Pleistocene/Holocene (P/H) boundary oceanic Koefels-comet Impact Series Scenario (KISS) of 12.850 yr BP Global-warming Threshold Triad (GTT)-Part III, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2869, https://doi.org/10.5194/egusphere-egu23-2869, 2023.

To evaluate the feasibility of CO2 sequestration in offshore, South Korea, we studied numerical modelling with elastic velocity model. The CO2 storage candidate is a brine saturated aquifer formation overlain by basalt caprock in the Southern Continental Shelf of Korea. Basalt formation without joint and fracture can seal a storage volume preventing leakage of injected CO2. Result of preliminary two-dimensional seismic exploration estimated that storage potential would be from 42.07 to 143.79 Mt of CO2. The input model include P- and S-wave velocity and density of shallow sediment and vasalt layer. To simulate CO2 injection, we assumed an area of CO2 plume at the interval beneath the depth of basalt formation and artificially decreased P-, S-wave velocities, and density values. Synthesized seismic records are comparable with survey's gather as direct arrival and primary reflections. The ongoing work can be extended on a quantitative verification concerning serveral cased of varying velcoties and densities.

How to cite: Cheong, S., Kang, M., and Kim, K. J.: Numerical modelling of seismic field record with elastic velocity construction for CO2 sequestration in offshore, South Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2980, https://doi.org/10.5194/egusphere-egu23-2980, 2023.

EGU23-4861 | Orals | GI2.1

Decay diagnosis of tree trunks using 3D point cloud and reverse time migration of GPR data 

Zhijie Chen, Hai Liu, Meng Xu, Yunpeng Yue, and Bin Zhang

Health monitoring and disease mitigation of trees are essential to ensure the sustainability of wood industry, safety of ecosystems, and maintenance of climatic conditions. Several non-destructive testing methods have been applied to monitor and detect the decays inside the trunks. Among them, ground penetrating radar (GPR) has gained recognition due to its high efficiency and good resolution. However, due to the wide beam width of the antenna pattern and the complicated scattering caused by the trunk structure, the recorded GPR profile is far from the actual geometry of the tree trunk. Moreover, the irregular contour of the tree trunk makes traditional data processing algorithms difficult to be performed. Therefore, an efficient migration algorithm with high resolution, as well as a high accuracy survey-line positioning method for curved contour of the trunk should be developed.

In this paper, a combined approach is proposed to image the inner structures inside the irregular-shaped trunks. In the first step, the 3D contour of the targeted tree trunk is built up by a 3D point cloud technique via photographing around the trunk at various angles. Subsequently, the 2D irregular contour of the cross-section of trunk at the position of the GPR survey line is extracted by the Canny edge detection method to locate the accurate position of each GPR A-scans [1]. Thirdly, the raw GPR profile is pre-processed to suppress undesired noise and clutters. Then, an RTM algorithm based on the zero-time imaging condition is applied for image reconstruction using the extracted 2D contour [2]. Lastly, a denoising method based on the total variation (TV) regularization is applied for artifact suppression in the reconstructed images [3].

Numerical, laboratory and field experiments are carried out to validate the applicability of the proposed approach. Both numerical and laboratory experimental results show that the RTM can yield more accurate and higher resolution images of the inner structures of the tree cross section than the BP algorithm. The proposed approach is further applied to a diseased camphor tree, and an elliptical decay defect is found the in the migrated GPR image. The results are validated by a visual inspection after the tree trunk was sawed down.

Fig. 1 Field experiment. (a) Geometric reconstruction result using point cloud data, (b) migrated result by the RTM algorithm and (c) bottom view of the tree trunk after sawing down. The red and yellow ellipses indicate the cavity and the decay region in the trunk, respectively.

References:

[1] Canny, "A Computational Approach to edge detection," IEEE Transactions on Pattern Analysis and Machine Interllgent, vol. PAMI-8, no. 6, pp. 679-698, 1986, doi: 10.1109/TPAMI.1986.4767851.

[2] S. Chattopadhyay and G. A. McMechan, "Imaging conditions for prestack reverse-time migration," Geophysics, vol. 73, no. 3, pp. S81-S89, 2008, doi: 10.1190/1.2903822.

[3] L. I. Rudin, S. Osher, and E. Fatemi, "Nonlinear total variation based noise removal algorithms," Physica D, vol. 60, pp. 259-268, 1992, doi: 10.1016/0167-2789(92)90242-F.

How to cite: Chen, Z., Liu, H., Xu, M., Yue, Y., and Zhang, B.: Decay diagnosis of tree trunks using 3D point cloud and reverse time migration of GPR data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4861, https://doi.org/10.5194/egusphere-egu23-4861, 2023.

EGU23-6795 | ECS | Orals | GI2.1

Relaxing requirements for spatio-temporal data fusion 

Harkaitz Goyena, Unai Pérez-Goya, Manuel Montesino-San Martín, Ana F. Militino, Peter M. Atkinson, and M. Dolores Ugarte

Satellite sensors need to make a trade-off between revisit frequency and spatial resolution. This work presents a spatio-temporal image fusion method called Unpaired Spatio-Temporal Fusion of Image Patches (USTFIP). This method combines data from different multispectral sensors and creates images combining the best of each satellite in terms of frequency and resolution. It generates synthetic images and selects optimal information from cloud-contaminated images, to avoid the need of cloud-free matching pairs of satellite images. The removal of this restriction makes it easier to run our fusion algorithm even in the presence of clouds, which are frequent in time series of satellite images. The increasing demand of larger datasets makes necessary the use of computationally optimized methods. Therefore, this method is programmed to run in parallel reducing the run-time with regard to other methods. USTFIP is tested through an experimental scenario with similar procedures as Fit-FC, STARFM and FSDAF. Finally, USTFIP is the most robust, since its prediction accuracy deprecates at a much lower rate as classical requirements become progressively difficult to meet.

How to cite: Goyena, H., Pérez-Goya, U., Montesino-San Martín, M., F. Militino, A., Atkinson, P. M., and Ugarte, M. D.: Relaxing requirements for spatio-temporal data fusion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6795, https://doi.org/10.5194/egusphere-egu23-6795, 2023.

Continual monitoring of tree roots, which is essential when considering tree health and safety, is possible using a digital model. Non-destructive techniques, for instance, laser scanning, acoustics, and Ground Penetrating Radar (GPR) have been used in the past to study both the external and internal physical dimensions of objects and structures [1], including trees [2,3]. Recent studies have shown that GPR is effective in mapping the root system's network in street trees [3]. Light Detection and Ranging (LiDAR) technology has also been employed in infrastructure management to generate 3D data and to detect surface displacements with millimeter accuracy [4]. However, scanning such structures using current state-of-the-art technologies can be expensive and time consuming. Further, continual monitoring of tree roots requires multiple visits to tree sites and, oftentimes, repeated excavations of soil.

This work proposes a Virtual Reality (VR) system using smartphone-based LiDAR and GPR data to capture ground surface and subsurface information to monitor the location of tree roots. Both datasets can be visualized in 3D in a VR environment for future assessment. LiDAR technology has recently become available in smartphones (for instance, the Apple iPhone 12+) and can scan a surface, e.g., the base of a tree, and export the data to a 3D modelling and visualization application. Using GPR data, we combined subsurface information on the location of tree roots with the LiDAR scan to provide a holistic digital model of the physical site. The system can provide a relatively low-cost environmental modelling and assessment solution, which will allow researchers and environmental professionals to a) create digital 3D snapshots of a physical site for later assessment, b) track positional data on existing tree roots, and c) inform the decision-making process regarding locations for potential future excavations.

Acknowledgments: Sincere thanks to the following for their support: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust. The Authors would also like to thank Mr Dale Mortimer (representing the Ealing Council) and the Walpole Park for facilitating this research.

References

[1] Alani A. M. et al., Non-destructive assessment of a historic masonry arch bridge using ground penetrating radar and 3D laser scanner. IMEKO International Conference on Metrology for Archaeology and Cultural Heritage Lecce, Italy, October 23-25, 2017.

[2] Ježová, J., Mertens, L., Lambot, S., 2016. “Ground-penetrating radar for observing tree trunks and other cylindrical objects,” Construction and Building Materials (123), 214-225.

[3] Lantini, L., Alani, A. M., Giannakis, I., Benedetto, A. and Tosti, F., 2020. "Application of ground penetrating radar for mapping tree root system architecture and mass density of street trees," Advances in Transportation Studies (3), 51-62.

[4] Lee, J. et al., Long-term displacement measurement of bridges using a LiDAR system. Struct Control Health Monit. 2019; 26:e2428.

How to cite: Uzor, S., Lantini, L., and Tosti, F.: Low-cost assessment and visualization of tree roots using smartphone LiDAR, Ground-Penetrating Radar (GPR) data and virtual reality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6908, https://doi.org/10.5194/egusphere-egu23-6908, 2023.

EGU23-8384 | ECS | Orals | GI2.1

A Study on the Effect of Target Orientation on the GPR Detection of Tree Roots Using a Deep Learning Approach 

Livia Lantini, Federica Massimi, Saeed Sotoudeh, Dale Mortimer, Francesco Benedetto, and Fabio Tosti

Monitoring and protection of natural resources have grown increasingly important in recent years, since the effect of emerging illnesses has caused serious concerns among environmentalists and communities. In this regard, tree roots are one of the most crucial and fragile plant organs, as well as one of the most difficult to assess [1].

Within this context, ground penetrating radar (GPR) applications have shown to be precise and effective for investigating and mapping tree roots [2]. Furthermore, in order to overcome limitations arising from natural soil heterogeneity, a recent study has proven the feasibility of deep learning image-based detection and classification methods applied to the GPR investigation of tree roots [3].

The present research proposes an analysis of the effect of root orientation on the GPR detection of tree root systems. To this end, a dedicated survey methodology was developed for compilation of a database of isolated roots. A set of GPR data was collected with different incidence angles with respect to each investigated root. The GPR signal is then processed in both temporal and frequency domains to filter out existing noise-related information and obtain spectrograms (i.e. a visual representation of a signal's frequency spectrum relative to time). Subsequently, an image-based deep learning framework is implemented, and its performance in recognising outputs with different incidence angles is compared to traditional machine learning classifiers. The preliminary results of this research demonstrate the potential of the proposed approach and pave the way for the use of novel ways to enhance the interpretation of tree root systems.

 

Acknowledgements

The Authors would like to express their sincere thanks and gratitude to the following trusts, charities, organisations and individuals for their generosity in supporting this project: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust. The Authors would also like to thank the Ealing Council and the Walpole Park for facilitating this research.

 

References

[1] Innes, J. L., 1993. Forest health: its assessment and status. CAB International.

[2] Lantini, L., Tosti, F., Giannakis, I., Zou, L., Benedetto, A. and Alani, A. M., 2020. "An Enhanced Data Processing Framework for Mapping Tree Root Systems Using Ground Penetrating Radar," Remote Sensing 12(20), 3417.

[3] Lantini, L., Massimi, F., Tosti, F., Alani, A. M. and Benedetto, F. "A Deep Learning Approach for Tree Root Detection using GPR Spectrogram Imagery," 2022 45th International Conference on Telecommunications and Signal Processing (TSP), 2022, pp. 391-394.

How to cite: Lantini, L., Massimi, F., Sotoudeh, S., Mortimer, D., Benedetto, F., and Tosti, F.: A Study on the Effect of Target Orientation on the GPR Detection of Tree Roots Using a Deep Learning Approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8384, https://doi.org/10.5194/egusphere-egu23-8384, 2023.

EGU23-8667 | ECS | Posters on site | GI2.1

An Investigation into the Acquisition Parameters for GB-SAR Assessment of Bridge Structural Components 

Saeed Sotoudeh, Livia Lantini, Kevin Jagadissen Munisami, Amir M. Alani, and Fabio Tosti

Structural health monitoring (SHM) is a necessary measure to maintain bridge infrastructure safe. To this purpose, remote sensing has proven effective in acquiring data with high accuracy in relatively short time. Amongst the available methods, the ground-based synthetic aperture radar (GB-SAR) can detect sub-zero deflections up to 0.01 mm generated by moving vehicles or the environmental excitation of the bridges [1]. Interferometric radars are also capable of data collection regardless of weather, day, and night conditions (Alba et al., 2008). However, from the available literature - there is lack of studies and methods focusing on the actual capabilities of the GB-SAR to target specific structural elements and components of the bridge - which makes it difficult to associate the measured deflection with the actual bridge section. According to the antenna type, the footprint of the radar signal gets wider in distance which encompasses more elements and the presence of multiple targets in the same resolution cell adds uncertainty to the acquired data (Michel & Keller, 2021). To this effect, the purpose of the present research is to introduce a methodology for pinpointing targets using GB-SAR and aid the data interpretation. An experimental procedure is devised to control acquisition parameters and targets, and being able to analyse the returned outputs in a more clinical condition. The outcome of this research will add to the existing literature in terms of collecting data with enhanced precision and certainty.

 

Keywords

Structural Health Monitoring (SHM), GB-SAR, Remote Sensing, Interferometric Radar

 

Acknowledgements

This research was funded by the Vice-Chancellor’s PhD Scholarship at the University of West London.

 

References

[1] Benedettini, F., & Gentile, C. (2011). Operational modal testing and FE model tuning of a cable-stayed bridge. Engineering Structures, 33(6), 2063-2073.

[2] Alba, M., Bernardini, G., Giussani, A., Ricci, P. P., Roncoroni, F., Scaioni, M., Valgoi, P., & Zhang, K. (2008). Measurement of dam deformations by terrestrial interferometric techniques. Int.Arch.Photogramm.Remote Sens.Spat.Inf.Sci, 37(B1), 133-139.

[3] Michel, C., & Keller, S. (2021). Advancing ground-based radar processing for bridge infrastructure monitoring. Sensors, 21(6), 2172.

How to cite: Sotoudeh, S., Lantini, L., Munisami, K. J., Alani, A. M., and Tosti, F.: An Investigation into the Acquisition Parameters for GB-SAR Assessment of Bridge Structural Components, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8667, https://doi.org/10.5194/egusphere-egu23-8667, 2023.

EGU23-8762 | ECS | Orals | GI2.1

Joint Interpretation of Multi-Frequency Ground Penetrating Radar and Ultrasound Data for Mapping Cracks and Cavities in Tree Trunks 

Saeed Parnow, Livia Lantini, Stephen Uzor, Amir M. Alani, and Fabio Tosti

As the Earth's lungs, trees are a natural resource that provide, amongst others, food, lumber, and oxygen. Therefore, monitoring these wooden structures with non-destructive testing (NDT) techniques such as ground penetrating radar (GPR) and ultrasound can provide valuable information about inner flaws and decays, which is an essential step for tree conservation.  

In recent years, GPR and ultrasound have been used to delineate the interior architecture of tree trunks [1-3]. However, more research is required to improve results and consequently have a more reliable interpretation. Due to limitations in depth penetration and signal-to-noise ratio [4], these approaches have a limited capacity for resolving features. The use of gain functions and higher frequencies to compensate for wave attenuation may exaggerate events and reduce resolution, respectively.

In this context, an integration between GPR multi-frequency and ultrasound data can be used to address this issue. Data were collected on a tree trunk log at the Faringdon Centre for Non-Destructive Testing and Remote Sensing using two high-frequency GPR systems (2GHz and 4GHz central frequencies) and an ultrasound (supporting a wide range of transducers from 24 kHz up to 500 kHz) testing equipment. Internal features of interest in terms of extended perimetric air gaps at the bark-wood interface, natural cracks and small artificial cavities were investigated through electromagnetic and mechanical waves. After compilation of data, a joint interpretation strategy for data analysis is developed. The processed data were mapped against the cut sections of the tree for validity purposes.

Although study of stand tree trunks would be more challenging, the findings of this research may be applied for wood timbers and pave the way to future research for living tree trunks.

 

Acknowledgements

This research was funded by the Vice-Chancellor’s PhD Scholarship at the University of West London.

 

References

[1] Arciniegas, A., et al., Literature review of acoustic and ultrasonic tomography in standing trees. Trees, 2014. 28(6): p. 1559-1567. 

[2] Giannakis, I., et al., Health monitoring of tree trunks using ground penetrating radar. IEEE Transactions on Geoscience and Remote Sensing, 2019. 57(10): p. 8317-8326.

[3] Espinosa, L., et al., Ultrasound computed tomography on standing trees: accounting for wood anisotropy permits a more accurate detection of defects. Annals of Forest Science, 2020. 77(3): p. 1-13.

[4] Tosti, F., et al., The use of GPR and microwave tomography for the assessment of the internal structure of hollow trees. IEEE Transactions on Geoscience and Remote Sensing, 2021. 60: p. 1-14.

 

How to cite: Parnow, S., Lantini, L., Uzor, S., Alani, A. M., and Tosti, F.: Joint Interpretation of Multi-Frequency Ground Penetrating Radar and Ultrasound Data for Mapping Cracks and Cavities in Tree Trunks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8762, https://doi.org/10.5194/egusphere-egu23-8762, 2023.

EGU23-10874 | ECS | Orals | GI2.1

Ground subsidence risk mapping and assessment along Shanghai metro lines by PS-InSAR and LightGBM 

Long Chai, Xiongyao Xie, Biao Zhou, and Li Zeng

Ground subsidence is a typical geological hazard in urban areas. It endangers the safety of infrastructures, such as subways. In this study, the ground subsidence risk of Shanghai metro lines was mapped and assessed. Firstly, PS-InSAR was used for the ground subsidence survey, and subsidence intensity was divided into five classes according to subsidence velocity. 10 subsidence causal factors were collected and the frequency ratio method was applied to analyze the correlation between subsidence and its causal factors. Then LightGBM model was used to generate a ground subsidence susceptibility map. And receiver operating characteristic curve and area under the curve (AUC) were adopted to assess the model. And AUC is 0.904, which suggests the model's performance is excellent. Finally, a risk matrix was introduced to consider the intensity and susceptibility of ground subsidence. The risk of ground subsidence was mapped and classified into five levels: R1 (very low), R2 (low), R3 (medium), R4 (high), and R5 (very high). The results showed that the risk of subway ground subsidence exhibited a regional-related characteristic. Metro lines located in areas with higher ground subsidence risk levels also had higher ground subsidence risk levels. Meanwhile, the statistical results of subway ground subsidence risk levels showed that subway stations were safer than sections.

How to cite: Chai, L., Xie, X., Zhou, B., and Zeng, L.: Ground subsidence risk mapping and assessment along Shanghai metro lines by PS-InSAR and LightGBM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10874, https://doi.org/10.5194/egusphere-egu23-10874, 2023.

EGU23-12226 | ECS | Orals | GI2.1

Evaluation of Spectral Mixing Techniques for Geological Mixture in a Laboratory Setup: Insights on the nature of mixing 

Maitreya Mohan Sahoo, Kalimuthu Rajendran, Arun Pattathal Vijayakumar, Shibu K. Mathew, and Alok Porwal

Geological mixtures having endmembers mixed at a fine scale pose a challenge to estimating their fractional abundances. Light incident on these mixtures interacts both at multilayered and surface levels, resulting in volumetric and albedo scattering, respectively. Accounting for these effects necessitates a nonlinear spectral mixing model approach rather than conventional linear mixing. In this study, we evaluate the performances of linear and various nonlinear spectral mixing models for an intimately mixed geological mixture, i.e., a banded hematite quartzite (BHQ) sample. The BHQ sample with distinct endmembers of hematite and quartzite facilitated our study of the behavior of light on two-component nonlinear mixtures. In a laboratory-based experimental setup, we used a spectroradiometer of full spectral range in the visible and near-infrared regions (350 to 2500nm) to acquire a hyperspectral image of the BHQ sample. It was followed by the identification of nonlinearly mixed regions and inferring changes in their spectral features. The nonlinearity induced in these regions was attributed to two significant causes- (1) the fine scale of spectral mixing and (2) the spectroradiometer sensor’s limited ability to spatially distinguish between focused and neighboring points, thereby producing a point spread effect. We observed the effects of nonlinear spectral mixing for our sample by changing the sensor’s height from 1mm to 5mm, to simulate fine and coarse-resolution images, respectively. The spectral mixing was modeled using the existing mapped ground truth fractional abundances and library endmembers’ spectra by linear mixing and established nonlinear techniques of the generalized bilinear model (GBM), polynomial post-nonlinear model (PPNM), kernel-based support vector machines (k-SVMs). The evaluated performance metric of reconstruction error revealed the nonlinearity effect in image pixels through statistical tests and nonlinearity parameters used in these models. It was further observed that the associated nonlinearity increases from fine to coarse-resolution images. The minimum error of image reconstruction was observed for the polynomial post-nonlinear model, with a single nonlinearity parameter and an average reconstruction error (ARE) of 0.05. Our study provided insights into the nature of nonlinear mixing with endmember composition and particle sizes.

How to cite: Sahoo, M. M., Rajendran, K., Pattathal Vijayakumar, A., Mathew, S. K., and Porwal, A.: Evaluation of Spectral Mixing Techniques for Geological Mixture in a Laboratory Setup: Insights on the nature of mixing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12226, https://doi.org/10.5194/egusphere-egu23-12226, 2023.

EGU23-13163 | ECS | Orals | GI2.1

High-resolution grain-size analysis and non-destructive hyperspectral imaging of sediments from the Gaoping canyon levee to establish past typhoon and monsoon activities affecting Taiwan during the late Holocene 

Joffrey Bertaz, Kévin Jacq, Christophe Colin, Zhifei Liu, Maxime debret, Hongchao Zhao, and Andrew Tien-Shun Lin

Non-destructive and high-resolution hyperspectral analyses are widely used in planetary and environmental sciences and in mining exploration. In recent years, the scanning method was applied to lacustrine sediment cores in complement to XRF core scanning. However, this approach was rarely applied to marine sediments. The Gaoping canyon, located south of Taiwan island, is connected to the Gaoping River and is a very active canyon with large sediment transfer capacity. In particular, about 4 typhoon-driven hyperpycnal flows have been recorded by mooring systems in every recent year. Studying their frequency and intensity responding to past climate and environmental changes is a key to understand future tropical storm frequency and related climate variability. Core MD18-3574 was collected on the western levee of the Gaoping canyon and displays numerous fine laminations (millimetric to centimetric) recording the deposition of the gravity flows occurring in the canyon and on the slope. In this study, we combined non-destructive analyses such as XRF core scanning and hyperspectral imaging with high-resolution grain size and XRD bulk mineralogy analyses to understand the sedimentological and geochemical variations at the scale of the laminae. Core MD18-3574 sediments consist mainly of fine silt, presenting an alternance of fine-grained and coarse-grained laminations. The average mean grain size is 13.4 µm ranging from 9 to 20.5 µm. Thick coarser grained laminations are showing grain size distributions and asymmetric sorting of typical turbidite sequence. Grain size and bulk mineralogy display great visual and statistical correlation with XRF (Fe/Ca, Si/Al) and hyperspectral proxies (sediment darkness (Rmean), Clay_R2200). Principal component analyses (PCA) demonstrates that darker laminae are composed of coarser sediments with high Si/Al (quartz and feldspar-rich) and Clay_R2200 values and low Fe/Ca (calcite-rich) resulting from gravity flows.  Inversely, lighter laminae consist of finer sediments with low Si/Al (muscovite and illite-rich), Clay_R2200 and high Fe/Ca resulting from hemipelagic deposition. Thus, such interpretation was extended to the core scale to identify gravity flows deposits layers. Moderate intensity tropical storm frequency is decreasing since the last 4 ka in response to the sea surface temperature (SST) decrease and enhanced East Asian winter monsoon since the middle Holocene. Tropical storm intensity increased after 2 ka in La Niña like periods indicating that the surge of super-typhoons hitting Taiwan could be triggered by El Niño Southern Oscillation (ENSO) state and variability. We can then assess that tropical storm activity is controlled by SST, monsoon system and ENSO conditions. This study brings new insights in the prediction of the ongoing climate change impacts on storms activity in the western Pacific Ocean.

How to cite: Bertaz, J., Jacq, K., Colin, C., Liu, Z., debret, M., Zhao, H., and Lin, A. T.-S.: High-resolution grain-size analysis and non-destructive hyperspectral imaging of sediments from the Gaoping canyon levee to establish past typhoon and monsoon activities affecting Taiwan during the late Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13163, https://doi.org/10.5194/egusphere-egu23-13163, 2023.

EGU23-13329 | ECS | Orals | GI2.1

Combined use of NDT methods for steel rebar corrosion monitoring 

Giacomo Fornasari, Federica Zanotto, Andrea Balbo, Vincenzo Grassi, and Enzo Rizzo

This paper describes laboratory tests performed with an NDT geophysical methods: Ground Penetrating Radar (GPR), Self Potential (SP) and Direct Current (DC) methods in order to monitor the corrosion of a rebar embedded in concrete. Even if the GPR is a common geophysical method for reinforced concrete structures, the SP and DC techniques are not widely used. Rebar corrosion is one of the main causes of deterioration of engineering reinforced structures and this degradation phenomena reduces their service life and durability. Non-destructive testing and evaluation of the rebar corrosion is a major issue for predicting the service life of reinforced concrete structures.

Several new experiments were performed at Applied Geophysical laboratory of University of Ferrara, following the experiences coming from previous tests (Fornasari et al., 2022), where two reinforced concrete samples of about 50 cm x 30 cm were cast, with a central ribbed steel rebar of 10 mm diameter and 35 cm long, were partially immersed in a plastic box with salty and distilled water. In this experiment, we applied a new protocol, where an epoxy resin was used in order to focalize the corrosion only along the exposed part of the rebar. The steel rebar was partially painted with a waterproof resin in order to leave only the central part uncovered for a length of 8 cm. The same waterproof epoxy resin was applied on part of the concrete sample, in order to have a specific chlorides diffusion across a freeway zone of about 10cm x 8cm defined below the exposed rebar.

The experiments were carried out on two identically constructed reinforced concrete samples, exposed to distilled water (sample “A”) and the second, exposed to a salty water with chlorides (sample “B”). Both samples were partially immersed for only 1 cm form the lower surface. The sample B was immersed in a salty water plastic box with different NaCl concentrations. An initial NaCl concentration of 0.1 % was adopted for 7 days, then the concentration was increased to 1% and finally to 3.5% for further 7 days. The experiment was set up in two phases. In the first phase of this study, we monitored the "natural" corrosion occurred on sample "B" due to the diffusion of chlorides towards the steel rebar comparing the obtained data with those of sample "A" exposed to distilled water. In the second phase of the study, accelerated corrosion was applied to sample "B" in order to induce an increment of the corrosion phenomena. The accelerated corrosion was designed in order to reach different theoretical levels of mass weight loss in the steel rebar, which were of 2%, 5%, 10% and 20%. During the experiments, 2GHz C-Thrue GPR antenna, Multivoltmeter with non-polarized calomel referenced electrode for SP and ABEM Terrameter LS for resistivity data, were used to monitor the rebar corrosion monitoring. The collected data were used for an integration observation to detect the evolution of the corrosion phenomenon on the reinforcement steel rebar and to define a quantitative analysis of the phenomena.

 

How to cite: Fornasari, G., Zanotto, F., Balbo, A., Grassi, V., and Rizzo, E.: Combined use of NDT methods for steel rebar corrosion monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13329, https://doi.org/10.5194/egusphere-egu23-13329, 2023.

EGU23-13720 | ECS | Posters on site | GI2.1

A fully customizable data management system for Built Cultural Heritage surveys through NDT 

Irene Centauro, Teresa Salvatici, Sara Calandra, and Carlo Alberto Garzonio

A fully customizable data management system for Built Cultural Heritage surveys through NDT

The diagnosis of Built Cultural Heritage using non-invasive methods is useful to deepen the understanding of building characteristics, assessing the state of conservation of materials, and monitoring over time the effectiveness of restoration interventions.

Ultrasonic and sonic tests are Non-Destructive Techniques widely used to evaluate the consistency of historic masonry and stone elements and to identify on-site internal defects such as voids, detachments, fractures. These tests, in addition to being suitable for Cultural Heritage because they are non-invasive, provide a fundamental preliminary screening useful to better address further analysis.

Ultrasonic and Sonic velocity tests performed on monuments involve a lot of different information obtained from many surveys.  It is therefore important to optimize the amount of data collected both during documentation and diagnostic phase, making them easily accessible and meaningful for analysis and monitoring. In addition, investigations set-up should be following a standard methodology, repeatable over time, suitable for different types of artifacts, and prepared for comparison with other techniques.

An integrated data management system is then also useful to support the decision-making processes behind maintenance actions.

This work proposes the development of a complete management IT solution for the Ultrasonic and Sonic measurements of different types of masonry, and stone artifacts. The system consists of a browser-based collaboration and document management platform, a mobile/desktop application for data entry, and a data visualization and reporting tool. This set of tools enable the complete processing of data, from the on-site survey to their analysis and visualization.

The proposed methodology allows the standardization of the data entry workflow, and it is scalable, so it can be adapted to different types of masonry and artifacts. Moreover, this system provides real-time verification of data, optimizes survey and analysis times, and reduces errors. The platform can be integrated with machine learning models, useful to gain insight from data.

This solution, aimed to improve the approach to diagnostics of Cultural Heritage, has been successfully applied by the LAM Laboratory of the Department of Earth Sciences (University of Florence) on different case studies (e.g., ashlar, frescoed walls, plastered masonries, stone columns, coat-of-arms, etc.) belonging to many important monuments.

How to cite: Centauro, I., Salvatici, T., Calandra, S., and Garzonio, C. A.: A fully customizable data management system for Built Cultural Heritage surveys through NDT, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13720, https://doi.org/10.5194/egusphere-egu23-13720, 2023.

EGU23-13934 | Orals | GI2.1

Pavements Layered Media Characterizations using deep learning-based GPR full-wave inversion 

Li Zeng, Biao Zhou, Xiongyao Xie, and Sébastien Lambot

The possibility to estimate accurately the subsurface electric properties of the pavements from ground-penetrating radar (GPR) signals using inverse modeling is obstructed by the appropriateness of the forward model describing the GPR subsurface system. In this presentation, we improved the recently developed approach of Lambot et al. whose success relies on a stepped-frequency continuous-wave (SFCW) radar combined with an off-ground monostatic transverse electromagnetic horn antenna. The deep-learning based method were adopted to train an intelligent model including the waveform of the Green’s functions. The method was applied and validated in laboratory conditions on a tank filled with a two-layered sand subject to different water contents. Results showed agreement between the predictions of measured Green’s functions deep-learning model and the measured ones. Model inversions for the dielectric permittivity and heights of antenna further demonstrated for a comparison of presented method.

How to cite: Zeng, L., Zhou, B., Xie, X., and Lambot, S.: Pavements Layered Media Characterizations using deep learning-based GPR full-wave inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13934, https://doi.org/10.5194/egusphere-egu23-13934, 2023.

EGU23-14658 | Orals | GI2.1

Influence of tectonic deformation on the mechanical properties of calcareous rocks: drawbacks of the non-destructive techniques  

Elisa Mammoliti, Veronica Gironelli, Danica Jablonska, Stefano Mazzoli, Antonio Ferretti, Michele Morici, and Mirko Francioni

Discontinuity surfaces are well known to influence the mechanical behaviour of rocks under compression. Non-destructive techniques, such as ultrasonic pulse velocity and sclerometers, are increasingly used to estimate uniaxial compressive strength of rocks. In this study, several core samples derived from the doubling works of the railway network near Genga (Marche Region, Central Italy) were analysed in order to assess the influence of the structural geological context (proximity to folds, faults etc.) and tectonic deformation on rock strength. Tests were conducted in rock specimens through: i) conventional uniaxial compressive experiment, ii) non-destructive rebound-based methods such as Schmidt Hammer and Equotip  and iii) ultrasound. In this way, it was possible to make a critical analysis of the use of these techniques in the estimation of the uniaxial compressive strength (considering also information about discontinuity type, orientation and nature of the filling). Finally, a petrographic analysis using optical microscope has been undertaken as a support to the observations derived from the analysis at the sample scale. The results indicate that there are two main factors influencing the strength at the scale of the specimen. The first and most decisive factor is the presence of natural pre-existing fractures. The second is the tectonic deformation ratio: the greater the deformation is, the little the strength. Furthermore, through the combined use of uniaxial compressive experiment, non-destructive rebound-based methods and ultrasounds it was possible to highlights the advantages and limitations of each technique and define/propose new guidelines for their use. 

How to cite: Mammoliti, E., Gironelli, V., Jablonska, D., Mazzoli, S., Ferretti, A., Morici, M., and Francioni, M.: Influence of tectonic deformation on the mechanical properties of calcareous rocks: drawbacks of the non-destructive techniques , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14658, https://doi.org/10.5194/egusphere-egu23-14658, 2023.

EGU23-14846 | ECS | Orals | GI2.1

Combined NDT data for road management through BIM models 

Luca Bertolini, Fabrizio D'Amico, Antonio Napolitano, Jhon Romer Diezmos Manalo, and Luca Bianchini Ciampoli

One of the main priorities for road administrations and stakeholders is the management and monitoring of critical infrastructures, especially transportation infrastructures. In this context, Building Information Modeling (BIM) can be one of the more effective methodologies to be used to optimize the management process. In Italy, several laws and regulations have been issued, making the use of BIM procedures mandatory for the design of new infrastructures and emphasizing its role in the management of existing civil works [1, 2].

Monitoring operations of transportation infrastructures are generally conducted by on-site surveys. Non-Destructive Testing methods (i.e., GPR, LiDAR, Laser Profilometer, InSAR, etc.) have been used to perform these inspections as their outputs have been proven to be effective in determining the conditions of the infrastructure and its assets [3]. Moreover, BIM methodology could prove a valuable tool to manage the data provided by these surveys, as it consists in the creation of digital models capable of containing information related to the object that they are representing. These models can be used to store over time the different information obtained by the NDT surveys to carry out integrated analysis on the conditions of the infrastructure [4].

This study aims to analyze a potential BIM process capable of integrating different NDT surveys’ outputs, to generate an informative digital model of an infrastructure and its assets. The proposed methodology is then able to merge the data provided by the inspections, which is typically obtained by different operators and comes in different file formats, in a single BIM model. The main goal of the research is to provide a process to optimize the management procedures of transportation infrastructures, by creating digital models capable of reducing the problems typically associated with the monitoring and maintenance of these critical civil works. By merging different information in a single environment and relying on survey data that are commonly analyzed separately, an integrated analysis of the infrastructure can be carried out and data loss can be reduced.

The study was developed by relying on real data, obtained from on-site surveys carried out over Italian infrastructures. As different outputs have been collected, BIM models of different assets of the analyzed infrastructures were defined. Preliminary results have shown that the proposed methodology can be a viable tool for optimizing the management process of these critical civil works.

Acknowledgements

The research is supported by the Italian Ministry of Education, University and Research under the National Project “Extended resilience analysis of transport networks (EXTRA TN): Towards a simultaneously space, aerial and ground sensed infrastructure for risks prevention”, PRIN 2017. Prot. 20179BP4SM.

References

[1] MIT, 2018. Ministero delle Infrastrutture e dei Trasporti, D. Lgs 109/2018

[2] MIT, 2021. Ministero delle Infrastrutture e dei Trasporti, D.M. 312/2021

[3] D’Amico F. et al., 2020. Integration of InSAR and GPR Techniques for Monitoring Transition Areas in Railway Bridges. NDT&E Int

[4] D’Amico, F. et al., 2022. Integrating Non-Destructive Surveys into a Preliminary BIM-Oriented Digital Model for Possible Future Application in Road Pavements Management. Infrastructures 7, no. 1: 10

How to cite: Bertolini, L., D'Amico, F., Napolitano, A., Manalo, J. R. D., and Bianchini Ciampoli, L.: Combined NDT data for road management through BIM models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14846, https://doi.org/10.5194/egusphere-egu23-14846, 2023.

EGU23-14899 | ECS | Orals | GI2.1

Fusion of in-situ and spaceborne sensing for environmental monitoring 

Konstantinos Karyotis, Nikolaos Tsakiridis, and George Zalidis

Measuring soil reflectance in the field, rather than in a laboratory setting, can be very useful when it comes to numerous applications such as mapping the distribution of various soil properties, especially when prompt estimations are needed.  Recent advances in spectroscopy, and specifically in the development of low-cost Micro-Electro-Mechanical-Systems (MEMS) based spectrometers, pave the way for developing real-time applications in agriculture and environmental monitoring. Compared to high-end spectrometers, whose spectral range extends from Visible (VIS) and Near-InfraRed (NIR) to Shortwave InfraRed (SWIR), MEMS cover limited parts of the electromagnetic spectrum resulting in missing important information. In parallel, new space missions such as Planet Fusion are operationally ready and provide optical imagery (RGB and NIR) with high spatial (3m) and temporal (daily) resolution. To this end, we assessed the potential of augmenting the bands captured from a commercial MEMS sensor (Spectral Engines Nirone S2.2 @ 1750 – 2150 nm) by adjoining the Planet Fusion bands at the exact sampling date and location that in-situ scans originate.

Employing the above, a set of portable MEMS was used at a pilot area in Cyprus (Agia Varvara, Nicosia district) to develop a regional in-situ Soil Spectral Library (SSL). A set of 60 distinct locations were selected for capturing in situ spectral reflectance after the stratification of Planet Fusion pixels of the pilot area, while a physical soil sample was analyzed at the laboratory for the determination of Soil Organic Carbon (SOC) content. During the visit, topsoil moisture was also measured.

The resulting SSL, containing the in-situ spectra, SOC, and moisture content was further augmented by the 4 bands of Planet Fusion imagery acquired on the exact date of the field visit. At this stage, three Random Forest models for SOC content estimation were fitted using as explanatory variables initially only the MEMS data with moisture content, then Planet Fusion bands, and finally all three available inputs.

The results presented an observable decrease in RMSE of SOC content estimations when fusing in-situ with spaceborne data, highlighting the importance of the information contained at VIS-NIR when modeling SOC. On the other hand, the synergy of the two sensors is mutually beneficial; SOC absorption bands can also be found in the SWIR region and are hard to detect with remote sensing means since they fall within the strong water absorption region (around 1950 nm). MEMS-based systems operating at the SWIR part can support this process, and if combined with ancillary environmental measurements such as soil moisture, can provide a cost-effective solution for measuring SOC and other soil-related parameters. To loosen the necessity of laboratory analysis, it is necessary to establish protocols and guidelines for spectral data collection and management to ensure that the data collected is consistent and of high quality and develop representative SSLs that can be used to serve different modeling scenarios. 

How to cite: Karyotis, K., Tsakiridis, N., and Zalidis, G.: Fusion of in-situ and spaceborne sensing for environmental monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14899, https://doi.org/10.5194/egusphere-egu23-14899, 2023.

EGU23-14981 | ECS | Orals | GI2.1

Implementation of a Digital Twin integrating remote sensing information for network-level infrastructure monitoring 

Antonio Napolitano, Valerio Gagliardi, Luca Bertolini, Jhon Romer Diezmos Manalo, Alessandro Calvi, and Andrea Benedetto

Nowadays, there is an emerging demand from public authorities and managing bodies, to evaluate the overall health of infrastructures and identify the most critical transport assets. Considering the national-scale level, thousands of transport infrastructure are in critical conditions and require urgent maintenance actions. Currently, most of available Digital Twins (DT) allow to explore and visualize data including limited kind of information. This issue still limits the operative and practical use by infrastructure owners, that require fast solutions for managing several amount of data. Moreover, this idea is perfectly in line with European and national actions related to the development of a DT of the earth’s systems, including the “DestinE” programme of the European Commission by EUSPA and the European Space Agency (ESA). For this purpose, a dynamic DT model of a critical infrastructure is developed, using the available data about design information, historical maintenance operations and monitoring surveys based on satellite imageries.

In this context, this study presents an innovative concept of Digital Twin, which integrates all the details coming from NDTs surveys, on-site inspections and satellite-based information, to store, manage and visualize valuable information. This is made possible by analysing the main several gaps and limitations of existing platforms, providing a viable integrated solution developing an upgradable strategic analysis tool. To this purpose, remote sensing methods are identified as viable technologies for continuous monitoring operations. More specifically, data coming from satellites and the processing techniques, such as the Multi-Temporal SAR Interferometry approach, are strategic for the continuous monitoring of the displacements associated to transport infrastructures. An advantage of these techniques is the lighter data-processing required for the assessment of displacements and the detection of critical areas [1, 2].

The study introduces two main levels of innovation. The first one is associated to the integrated approach for transportation planning, integrating quantitative data from multi-sources, into the more traditional territorial analysis models. The second one is related to the technological engineering discipline, and it consists of the fusion of observation data from multi-source, with the last-generation dynamic data connected to the environment.

Acknowledgements

This research is supported by the Project “M.LAZIO”, accepted and funded by the Lazio Region, Italy.

References

[1] D'Amico, F. et al., “Implementation of an interoperable BIM platform integrating ground based and remote sensing information for network-level infrastructures monitoring”, Spie Remote Sensing 2022.

[2] Gagliardi, V. et al., “Bridge monitoring and assessment by high-resolution satellite remote sensing technologies”, Spie Future Sensing Technologies 2020.

How to cite: Napolitano, A., Gagliardi, V., Bertolini, L., Manalo, J. R. D., Calvi, A., and Benedetto, A.: Implementation of a Digital Twin integrating remote sensing information for network-level infrastructure monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14981, https://doi.org/10.5194/egusphere-egu23-14981, 2023.

EGU23-15542 | ECS | Orals | GI2.1

Novel perspectives in transport infrastructure management: Data-Fusion, integrated monitoring and augmented reality 

Valerio Gagliardi, Luca Bianchini Ciampoli, Fabrizio D'Amico, Alessandro Calvi, and Andrea Benedetto

Infrastructure networks are crucial elements to ensure the sustainability of the current development model in which the movement of people and goods is essential. On the other hand, transport assets are increasingly exposed to several issues, including climatic conditions changing, vulnerability and exposure to natural hazards such as hydraulic, geomorphological, landslides and seismic phenomena, which can affect the structural integrity causing damages and deteriorations. The context is made even more serious by the degradation of materials and the progressive ageing of infrastructure, often accelerated by environmental conditions and inadequate, or not always effective, maintenance actions. This requires the investigation of novel methods for the large-scale detection of network-scale linear infrastructures, and simultaneously, of detail to diagnose causes and determine the priorities for the most effective countermeasures.

The proposed solution is based on a Data-Fusion approach, merging data coming from multi-source and multi-scale data, to enhance the interpretation process in a holistic sense. The information comes from spaceborne Multi-temporal SAR Interferometry, complemented by more detailed aerial data, detected by UAVs and Ground Based Non-Destructive Testing Methods, including laser scanner surveys for resolution and digital integrability, high-resolution camera measurements assisted by artificial intelligence for the surface degradation and from prospecting data collected by Ground Penetrating Radar technology. All these data can be simultaneously analyzed into a comprehensive digital platform, providing a useful tool to support operators and public bodies to prioritize maintenance actions.

The digital platform can be investigated also using augmented reality tools, capable of generating and reproducing the Digital Twin of the inspected infrastructure into a real environment. This allows any monitoring evaluation through a diagnostic technique that integrates spatial, aerial, ground-based and geophysical surveys, allowing navigation within the infrastructure. Potential applications are numerous, ranging from mapping of wide areas affected by potential criticality to the definition of the main vulnerabilities related to the seismic and hydraulic risks, the analysis of land changes surrounding the assets following extreme natural events, and the reconstruction of historical deformative trends of roads, railways and bridges through the interpretation of SAR data.

Acknowledgments

This research is supported by the Italian Ministry of Education, University, and Research under the National Project “EXTRA TN”, PRIN2017, Prot. 20179BP4SM. In addition, this research is supported by the Project “MLAZIO” funded by Lazio Region (Italy).

How to cite: Gagliardi, V., Bianchini Ciampoli, L., D'Amico, F., Calvi, A., and Benedetto, A.: Novel perspectives in transport infrastructure management: Data-Fusion, integrated monitoring and augmented reality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15542, https://doi.org/10.5194/egusphere-egu23-15542, 2023.

EGU23-16471 | ECS | Orals | GI2.1

Hydrogen isotope fractionation between leaf wax compounds and source water in tropical angiosperms 

Amrita Saishree, Shreyas Managave, and Vijayananda Sarangi

The hydrogen isotope fractionation between leaf wax compounds and source water, the apparent fractionation (εapp), necessary for the reconstruction of hydrogen isotopic composition (δD) of precipitation, is mainly assessed through field and transect studies. The current εapp dataset, however, exhibit a bias toward mid-latitude regions of the Northern Hemisphere. Here we report the results of an outdoor experiment wherein four evergreen and three deciduous species were grown with water of known δD value (-1.8‰) in a tropical semi-arid monsoon region. This allowed us to estimate εapp more accurately and also quantify εapp variability within a species and among different species. Among-species εapp values varied by -119 ± 23‰ (for n-alkane of chain length n-C31) and -126 ± 27‰   (for n-alkanoic acid of chain length n-C30). The similarity of the among-species variability in εapp reported here and that observed in field and transect studies suggested the species-effect, rather than uncertainty in δD of source water, control the uncertainty in community-averaged εapp. The fractionation of  δD between n-C29 alkane and n-C30 alkanoic acid (ε29/30) and between n-C31 alkane and n-C32 alkanoic acid (ε31/32) were 7 ± 25‰ and 6 ± 15‰, respectively, suggesting minimal fractionation of hydrogen isotopes during decarboxylation. Further, as we did not observe a systematic difference between the εapp of deciduous and evergreen species; changes in the relative proportion of this vegetation in a community might not affect its εapp value.

How to cite: Saishree, A., Managave, S., and Sarangi, V.: Hydrogen isotope fractionation between leaf wax compounds and source water in tropical angiosperms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16471, https://doi.org/10.5194/egusphere-egu23-16471, 2023.

EGU23-16632 | ECS | Orals | GI2.1

Development of a flexible 2D DC Resistivity modelling technique for use in space domain 

Deepak Suryavanshi and Rahul Dehiya

Geoelectric non-destructive imaging and monitoring of the earth's subsurface requires robust and adaptable numerical methods to solve the governing differential equation. Most of the time, the DC data is acquired along a straight line. Hence, we solve the DC problem for the 2D case. But the source for the DC method exhibits a 3D nature. To account for the source's 3D nature, the 2D DC resistivity modeling is often carried out in the wavenumber domain. There have been studies that suggest ways for the selection of optimum wavenumbers and weights. But, this does not guarantee a universal choice of wavenumbers. The chosen wavenumbers and related weights strongly influence the precision of the resulting solution in the space domain. Many forward modeling studies demonstrate that selecting effective wavenumbers is challenging, especially for complicated models with topography, anisotropy, and significant resistivity differences. Moreover, forward modeling requires many wavenumbers as the models get more complex. 

This study focuses on developing a method that can completely omit wavenumbers for 2D DC resistivity modeling. The present work finds its motivation in a numerical experiment on a simple half-space model. Since the analytical response for such a model can be easily calculated, we match the analytical solution against the responses obtained from various wavenumbers and weights used in the literature. All the responses deviated from the analytical solution after a certain distance, and none of them were found to be accurate for large offsets. It was discovered after thorough testing of the numerical scheme that the wavenumbers selected for the forward modeling significantly impacted how practical the approach is for large offsets. 

To overcome this problem, a new boundary condition is derived and implemented in the existing numerical scheme. The numerical scheme chosen to perform the forward modeling is Mimetic Finite Difference Method (MFDM). We consider that the source is placed on the origin of the coordinate system. This removes the dependency of the source term, expressed in the Fourier domain, on the wavenumber. The solution obtained by solving the resulting equation will be an even function of the wavenumber and be real-valued. This ensures that the potential in the space domain for the 2D model will also be a real-valued even function with a symmetry about a plane perpendicular to the strike direction and passing through the origin. Because the first-order derivative of an even function at the plane of symmetry vanishes, mathematically, it can be expressed as a Neumann boundary condition at the considered plane. Therefore, we propose a scheme to solve the 2D resistivity problem in the space domain using the boundary condition mentioned here.

The developed algorithm is tested on isotropic and anisotropic two-layer models with large contrasts. It is found that the numerical solutions obtained using the modified boundary condition described above show considerable accuracy even for large offsets when compared with the analytical solution. On the other hand, the results obtained using available wavenumbers in the literature are also compared and are found to deviate considerably from the analytical solution at large offsets.

How to cite: Suryavanshi, D. and Dehiya, R.: Development of a flexible 2D DC Resistivity modelling technique for use in space domain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16632, https://doi.org/10.5194/egusphere-egu23-16632, 2023.

Approximately eight years ago, after a research activity that I started in the nineties on the application of GPR and, later, of NDTs to civil engineering, I realized that no technology can be considered as self standing. This is the consequence of the high complexity related to the civil engineering works and to the highly unpredictable impacts of ordinary processes and exceptional natural events. At the beginning of this century it was clear that a reliable and comprehensive monitoring of a phenomenon affecting bridges, tunnels, structures, or any civil engineering work is possible only by integrating data from different sources.

GPR was at that time a very promising technology, and many investigated in this field measuring e.g. pavement deformation, asphalt moisture, ballast degradation, also the mechanical properties of materials. The accurate outcomes represent a great step forward for the science in this sector, but the final results demonstrated to be partial, because the approach failed under a holistic perspective.

So, in the second decade of 2000, the need of a novel paradigm for investigation raised, in order not only to identify and quantify the problem, but also to diagnose its causes.

It was the stimulus to fuse data from different NDTs, under the assumption that information A and B give much more than A+B. It means that one information (A) can be explanatory of one or more characters contained in a second (B) that cannot be inferred by the knowledge of only one single standing information (B).

Based on this I decided, with very high level international colleagues, to establish a new session at EGU. It was the 2018. Today the sixth edition!

During these years a number ranging from 80 to 120 of researchers took part to each session. Also the number of countries involved is impressive, ranging for each session from 10 to 17. The institutions ranged from 36 to 50.

The number of contributions presented in the five editions is 141.

After 2018 we have seen several special issues of prominent journals were dedicated to data fusion. Recently, beyond the typical technologies as GPR, UT, ERT, a great attention was given to Lidar, Satellite and UAV.

Data fusion was also directed to other interesting and promising fields as archaeology, agriculture, urban planning, only to cite a few.

I would like to underline that this great interest started in Europe and in USA, but actually the geographical coverage is much wider and it includes at a same level also Asiatic and emerging countries.

There is now a new frontier that has to be. My vision is that this holistic approach can be used to develop an innovative immersive environment through the integration in augmented reality platforms on which a digital twin can be generated and dynamically upgraded through an adaptive interface, as well as using AI and machine learning paradigms.

How to cite: Benedetto, A.: Data fusion in civil engineering: personal experience, vision and historical considerations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16864, https://doi.org/10.5194/egusphere-egu23-16864, 2023.

Building Information Modeling is a software-based parametric design approach that allows a full interoperability between the various actors involved in a design or management process. Notwithstanding It has been specifically created for buildings projects, its use has been adapted to a wide range of applications, including transport infrastructure design and, more recently, cultural heritage. In regard to this field, it has been mainly applied to raise accuracy and effectiveness of restoring and stabilization activities for historical architectures.
The present study aims at demonstrating how the use of BIM may return remarkable outcomes in improving the current quality level of digital valorisation and virtual reconstructions of historical structures, especially when their rate of conservation is limited. Indeed, even though current digital reconstruction models are, usually, verified under an archaeological perspective, their structural consistency is never tested. This involves that many virtual reconstruction models are likely to represent structures that are historically accurate but that have no structural sense as, according to their geometric features and the construction materials/techniques, they would not stand their weight.
In this perspective, this study proposes a novel BIM-based methodology capable of both driving the archaeological reconstruction hypotheses and testing the reconstruction hypotheses on a structural basis. The model can be schematically represented by the following process:
1- Survey of the emerging: acquisition of data from superficial archaeological surveys (topographic data, laser scanner, aero photogrammetry, satellite images)
2- Survey of the hidden: acquisition of data from hypogeal surveys (georadar, electrical tomography, magnetometry);
3- Mechanical characterization: gathering of information concerning the materials of the find, proven in their mechanic qualities also through load stress tests;
4- Virtual reconstruction: proposal of a possible hypothesis of virtual reconstruction linked to structural and morphological features known to be present in the referred historical periods;
5- Structural test: engineering and structural confirmation of the forwarded hypothesis by means of finite element algorithms.
The proposed methodology was tested on the archaeological area of the Villa and Circus of Maxentius along the Ancient Appian Way in Rome; all the planned activities have been shared and authorized by the Sovrintendenza Capitolina ai Beni Culturali, within the context of the Project BIMHERIT, funded by Regione Lazio (DTC Lazio Call, Prot. 305-2020-35609).

How to cite: Santarelli, R. and Ten, A.: Integration of non-destructive surveys for BIM-based and structural-verified digital reconstruction of archaeological sites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17489, https://doi.org/10.5194/egusphere-egu23-17489, 2023.

EGU23-582 | ECS | Posters on site | ITS1.13/AS5.2

Modeling the Variability of Terrestrial Carbon Fluxes using Transformers 

Swarnalee Mazumder and Ayush Prasad

The terrestrial carbon cycle is one of the largest sources of uncertainty in climate projections. The terrestrial carbon sink which removes a quarter of anthropogenic CO2 emissions; is highly variable in time and space depending on climate. Previous studies have found that data-driven models such as random forest, artificial neural networks and long short-term memory networks can be used to accurately model Net Ecosystem Exchange (NEE) and Gross Primary Productivity (GPP) accurately, which are two important metrics to quantify the direction and magnitude of CO2 transfer between the land surface and the atmosphere. Recently, a new class of machine learning models called transformers have gained widespread attention in natural language processing tasks due to their ability to learn from large volumes of sequential data. In this work, we use Transformers to model NEE and GPP from 1996-2022 at 39 Flux stations in the ICOS Europe network using ERA5 reanalysis data. We can compare our results with traditional machine learning approaches to evaluate the generalisability and predictive performance of transformers for carbon flux modelling.

How to cite: Mazumder, S. and Prasad, A.: Modeling the Variability of Terrestrial Carbon Fluxes using Transformers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-582, https://doi.org/10.5194/egusphere-egu23-582, 2023.

EGU23-1825 | ECS | Orals | ITS1.13/AS5.2

Spatial representation learning for ensemble weather simulations using invariant variational autoencoders 

Jieyu Chen, Kevin Höhlein, and Sebastian Lerch

Weather forecasts today are typically issued in the form of ensemble simulations based on multiple runs of numerical weather prediction models with different perturbations in the initial states and the model physics. In light of the continuously increasing spatial resolutions of operational weather models, this results in large, high-dimensional datasets that nonetheless contain relevant spatial and temporal structure, as well as information about the predictive uncertainty. We propose invariant variational autoencoder (iVAE) models based on convolutional neural network architectures to learn low-dimensional representations of the spatial forecast fields. We specifically aim to account for the ensemble character of the input data and discuss methodological questions about the optimal design of suitable dimensionality reduction methods in this setting. Thereby, our iVAE models extend previous work where low-dimensional representations of single, deterministic forecast fields were learned and utilized for incorporating spatial information into localized ensemble post-processing methods based on neural networks [1], which were able to improve upon model utilizing location-specific inputs only [2]. By additionally incorporating the ensemble dimension and learning representation for probability distributions of spatial fields, we aim to enable a more flexible modeling of relevant predictive information contained in the full forecast ensemble. Additional potential applications include data compression and the generation of forecast ensembles of arbitrary size.

We illustrate our methodological developments based on a 10-year dataset of gridded ensemble forecasts from the European Centre for Medium-Range Weather Forecasts of several meteorological variables over Europe. Specifically, we investigate alternative model architectures and highlight the importance of tailoring the loss function to the specific problem at hand.

References:

[1] Lerch, S. & Polsterer, K.L. (2022). Convolutional autoencoders for spatially-informed ensemble post-processing. ICLR 2022 AI for Earth and Space Science Workshop, https://arxiv.org/abs/2204.05102.

[2] Rasp, S. & Lerch, S. (2018). Neural networks for post-processing ensemble weather forecasts. Monthly Weather Review, 146, 3885-3900.

How to cite: Chen, J., Höhlein, K., and Lerch, S.: Spatial representation learning for ensemble weather simulations using invariant variational autoencoders, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1825, https://doi.org/10.5194/egusphere-egu23-1825, 2023.

EGU23-3117 | Orals | ITS1.13/AS5.2

AtmoRep: Large Scale Representation Learning for Atmospheric Data 

Christian Lessig, Ilaria Luise, and Martin Schultz

The AtmoRep project asks if one can train one neural network that represents and describes all atmospheric dynamics. AtmoRep’s ambition is hence to demonstrate that the concept of large-scale representation learning, whose principle feasibility and potential was established by large language models such as GPT-3, is also applicable to scientific data and in particular to atmospheric dynamics. The project is enabled by the large amounts of atmospheric observations that have been made in the past as well as advances on neural network architectures and self-supervised learning that allow for effective training on petabytes of data. Eventually, we aim to train on all of the ERA5 reanalysis and, furthermore, fine tune on observational data such as satellite measurements to move beyond the limits of reanalyses.

We will present the theoretical formulation of AtmoRep as an approximate representation for the atmosphere as a stochastic dynamical system. We will also detail our transformer-based network architecture and the training protocol for self-supervised learning so that unlabelled data such as reanalyses, simulation outputs and observations can be employed for training and re-fining the network. Results will be presented for the performance of AtmoRep for downscaling, precipitation forecasting, the prediction of tropical convection initialization, and for model correction. Furthermore, we also demonstrate that AtmoRep has substantial zero-short skill, i.e., it is capable to perform well on tasks it was not trained for. Zero- and few-shot performance (or in context learning) is one of the hallmarks of large-scale representation learning and to our knowledge has never been demonstrated in the geosciences.

How to cite: Lessig, C., Luise, I., and Schultz, M.: AtmoRep: Large Scale Representation Learning for Atmospheric Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3117, https://doi.org/10.5194/egusphere-egu23-3117, 2023.

Numerical Earth system models (ESMs) are our primary tool for projecting future climate scenarios. Their simulation output is used by impact models that assess the effect of anthropogenic global warming, e.g., on flood events, vegetation changes or crop yields. Precipitation, an atmospheric variable with arguably one of the largest socio-economic impacts, involves various processes on a wide range of spatial-temporal scales. However, these cannot be completely resolved in ESMs due to the limited discretization of the numerical model. 
This can lead to biases in the ESM output that need to be corrected in a post-processing step prior to feeding ESM output into impact models, which are calibrated with observations [1]. While established post-processing methods successfully improve the modelled temporal statistics for each grid cell individually, unrealistic spatial features that require a larger spatial context are not addressed.
Here, we apply a cycle-consistent generative adversarial network (CycleGAN) [2] that is physically constrained to the precipitation output from Coupled Model Intercomparison Project phase 6 (CMIP6)  ESMs to correct both temporal distributions and spatial patterns. The CycleGAN can be naturally trained on daily ESM and reanalysis fields that are unpaired due to the deviating trajectories of the ESM and observation-based ground truth. 
We evaluate our method against a state-of-the-art bias adjustment framework (ISIMIP3BASD) [3] and find that it outperforms it in correcting spatial patterns and achieves comparable results on temporal distributions. We further discuss the representation of extreme events and suitable metrics for quantifying the realisticness of unpaired precipitation fields.

 [1] Cannon, A.J., et al. "Bias correction of GCM precipitation by quantile mapping: How well do methods preserve changes in quantiles and extremes?." Journal of Climate 28.17 (2015): 6938-6959.

[2] Zhu, J.-Y., et al. "Unpaired image-to-image translation using cycle-consistent adversarial networks." Proceedings of the IEEE international conference on computer vision. 2017.

[3] Lange, S. "Trend-preserving bias adjustment and statistical downscaling with ISIMIP3BASD (v1.0)." Geoscientific Model Development 12.7 (2019): 3055-3070.

How to cite: Hess, P., Lange, S., and Boers, N.: Improving global CMIP6 Earth system model precipitation output with generative adversarial networks for unpaired image-to-image translation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3128, https://doi.org/10.5194/egusphere-egu23-3128, 2023.

EGU23-3256 | Orals | ITS1.13/AS5.2

Emulating radiative transfer in a numerical weather prediction model 

Matthew Chantry, Peter Ukkonen, Robin Hogan, and Peter Dueben

Machine learning, and particularly neural networks, have been touted as a valuable accelerator for physical processes. By training on data generated from an existing algorithm a network may theoretically learn a more efficient representation and accelerate the computations via emulation. For many parameterized physical processes in weather and climate models this being actively pursued. Here, we examine the value of this approach for radiative transfer within the IFS, an operational numerical weather prediction model where both accuracy and speed are vital. By designing custom, physics-informed, neural networks we achieve outstanding offline accuracy for both longwave and shortwave processes. In coupled testing we find minimal changes to forecast scores at near operational resolutions. We carry out coupled inference on GPUs to maximise the speed benefits from the emulator approach.

How to cite: Chantry, M., Ukkonen, P., Hogan, R., and Dueben, P.: Emulating radiative transfer in a numerical weather prediction model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3256, https://doi.org/10.5194/egusphere-egu23-3256, 2023.

EGU23-3321 | ECS | Orals | ITS1.13/AS5.2

Using machine learning to improve dynamical predictions in a coupled model 

Zikang He, Julien Brajard, Yiguo Wang, Xidong Wang, and Zheqi Shen

Dynamical models used in climate prediction often have systematic errors that can bias the predictions. In this study, we utilized machine learning to address this issue. Machine learning was applied to learn the error corrected by data assimilation and thus build a data-driven model to emulate the dynamical model error. A hybrid model was constructed by combining the dynamical and data-driven models. We tested the hybrid model using synthetic observations generated by a simplified high-resolution coupled ocean-atmosphere model (MAOOAM, De Cruz et al., 2016) and compared its performance to that of a low-resolution version of the same model used as a standalone dynamical model.

To evaluate the forecast skill of the hybrid model, we produced ensemble predictions based on initial conditions determined through data assimilation. The results show that the hybrid model significantly improves the forecast skill for both atmospheric and oceanic variables compared to the dynamical model alone. To explore what affects short-term forecast skills and long-term forecast skills, we built two other hybrid models by correcting errors either only atmospheric or only oceanic variables. For short-term atmospheric forecasts, the results show that correcting only oceanic errors has no effect on atmosphere variables forecasts but correcting only atmospheric variables shows similar forecast skill to correcting both atmospheric and oceanic errors. For the long-term forecast of oceanic variables, correcting the oceanic error can improve the forecast skill, but correcting both atmospheric and oceanic errors can obtain the best forecast skill. The results indicate that for the long-term forecast of oceanic variables, bias correction of both oceanic and atmospheric components can have a significant effect.

How to cite: He, Z., Brajard, J., Wang, Y., Wang, X., and Shen, Z.: Using machine learning to improve dynamical predictions in a coupled model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3321, https://doi.org/10.5194/egusphere-egu23-3321, 2023.

EGU23-3340 | ECS | Orals | ITS1.13/AS5.2

An iterative data-driven emulator of an ocean general circulation model 

Rachel Furner, Peter Haynes, Dan(i) Jones, Dave Munday, Brooks Paige, and Emily Shuckburgh

Data-driven models are becoming increasingly competent at tasks fundamental to weather and climate prediction. Relative to machine learning (ML) based atmospheric models, which have shown promise in short-term forecasting, ML-based ocean forecasting remains somewhat unexplored. In this work, we present a data-driven emulator of an ocean GCM and show that performance over a single predictive step is skilful across all variables under consideration. Iterating such data-driven models poses additional challenges, with many models suffering from over-smoothing of fields or instabilities in the predictions. We compare a variety of methods for iterating our data-driven emulator and assess them by looking at how well they agree with the underlying GCM in the very short term and how realistic the fields remain for longer-term forecasts. Due to the chaotic nature of the system being forecast, we would not expect any model to agree with the GCM accurately over long time periods, but instead we expect fields to continue to exhibit physically realistic behaviour at ever increasing lead times. Specifically, we expect well-represented fields to remain stable whilst also maintaining the presence and sharpness of features seen in both reality and in GCM predictions, with reduced emphasis on accurately representing the location and timing of these features. This nuanced and temporally changing definition of what constitutes a ‘good’ forecast at increasing lead times generates questions over both (1) how one defines suitable metrics for assessing data-driven models, and perhaps more importantly, (2) identifying the most promising loss functions to use to optimise these models.

How to cite: Furner, R., Haynes, P., Jones, D., Munday, D., Paige, B., and Shuckburgh, E.: An iterative data-driven emulator of an ocean general circulation model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3340, https://doi.org/10.5194/egusphere-egu23-3340, 2023.

EGU23-4337 | Orals | ITS1.13/AS5.2 | Highlight

Towards a new surrogate model for predicting short-term NOx-O3 effects from aviation using Gaussian processes 

Pratik Rao, Richard Dwight, Deepali Singh, Jin Maruhashi, Irene Dedoussi, Volker Grewe, and Christine Frömming

While efforts have been made to curb CO2 emissions from aviation, the more uncertain non-CO2 effects that contribute about two-thirds to the warming in terms of radiative forcing (RF), still require attention. The most important non-CO2 effects include persistent line-shaped contrails, contrail-induced cirrus clouds and nitrogen oxide (NOx) emissions that alter the ozone (O3) and methane (CH4) concentrations, both of which are greenhouse gases, and the emission of water vapour (H2O). The climate impact of these non-CO2 effects depends on emission location and prevailing weather situation; thus, it can potentially be reduced by advantageous re-routing of flights using Climate Change Functions (CCFs), which are a measure for the climate effect of a locally confined aviation emission. CCFs are calculated using a modelling chain starting from the instantaneous RF (iRF) measured at the tropopause that results from aviation emissions. However, the iRF is a product of computationally intensive chemistry-climate model (EMAC) simulations and is currently restricted to a limited number of days and only to the North Atlantic Flight Corridor. This makes it impossible to run EMAC on an operational basis for global flight planning. A step in this direction lead to a surrogate model called algorithmic Climate Change Functions (aCCFs), derived by regressing CCFs (training data) against 2 or 3 local atmospheric variables at the time of emission (features) with simple regression techniques and are applicable only in parts of the Northern hemisphere. It was found that in the specific case of O3 aCCFs, which provide a reasonable first estimate for the short-term impact of aviation NOx on O3 warming using temperature and geopotential as features, can be vastly improved [1]. There is aleatoric uncertainty in the full-order model (EMAC), stemming from unknown sources (missing features) and randomness in the known features, which can introduce heteroscedasticity in the data. Deterministic surrogates (e.g. aCCFs) only predict point estimates of the conditional average, thereby providing an incomplete picture of the stochastic response. Thus, the goal of this research is to build a new surrogate model for iRF, which is achieved by :

1. Expanding the geographical coverage of iRF (training data) by running EMAC simulations in more regions (North & South America, Eurasia, Africa and Australasia) at multiple cruise flight altitudes,

2. Following an objective approach to selecting atmospheric variables (feature selection) and considering the importance of local as well as non-local effects,

3. Regressing the iRF against selected atmospheric variables using supervised machine learning techniques such as homoscedastic and heteroscedastic Gaussian process regression.

We present a new surrogate model that predicts iRF of aviation NOx-O3 effects on a regular basis with confidence levels, which not only improves our scientific understanding of NOx-O3 effects, but also increases the potential of global climate-optimised flight planning.

References

[1] Rao, P.; et al. Case Study for Testing the Validity of NOx-Ozone Algorithmic Climate Change Functions for Optimising Flight Trajectories. Aerospace 20229, 231. https://doi.org/10.3390/aerospace9050231

How to cite: Rao, P., Dwight, R., Singh, D., Maruhashi, J., Dedoussi, I., Grewe, V., and Frömming, C.: Towards a new surrogate model for predicting short-term NOx-O3 effects from aviation using Gaussian processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4337, https://doi.org/10.5194/egusphere-egu23-4337, 2023.

Time transfer functions describe the change of state variables over time in geoscientific numerical simulation models. The identification of these functions is an essential but challenging step in model building. While traditional methods rely on qualitative understanding or first order principles, the availability of large spatio-temporal data sets from direct measurements or extremely detailed physical-based system modelling has enabled the use of machine learning methods to discover the time transfer function directly from data. In this study we explore the feasibility of this data driven approach for numerical simulation of the co-evolution of soil, hydrology, vegetation, and grazing on landscape scale, at geological timescales. From empirical observation and hyper resolution (1 m, 1 week) modelling (Karssenberg et al, 2017) it has been shown that a hillslope system shows complex behaviour with two stable states, respectively high biomass on deep soils (healthy state) and low biomass on thin soils (degraded or desertic state). A catastrophic shift from healthy to degraded state occurs under changes of external forcing (climate, grazing pressure), with a transient between states that is rapid or slow depending on system characteristics. To identify and use the time transfer functions of this system at hillslope scale we follow four procedural steps. First, an extremely large data set of hillslope average soil and vegetation state is generated by a mechanistic hyper resolution (1 m, 1 week) system model, forcing it with different variations in grazing pressure over time. Secondly, a machine learning model predicting the rate of change in soil and vegetation as function of soil, vegetation, and grazing pressure, is trained on this data set. In the third step, we explore the ability of this trained machine learning model to predict the rate of system change (soil and vegetation) on untrained data. Finally, in the fourth step, we use the trained machine learning model as time transfer function in a forward numerical simulation of a hillslope to determine whether it is capable of representing the known complex behaviour of the system. Our findings are that the approach is in principle feasible. We compared the use of a deep neural network and a random forest. Both can achieve great fitting precision, although the latter performs much faster and requires less training data. Even though the machine learning based time transfer function shows differences in the rates of change in system state from those calculated using expert knowledge in Karssenberg et al. (2017), forward simulation appeared to be possible with system behaviour generally in line with that observed in the data from the hyper resolution model. Our findings indicate that discovery of time transfer functions from data is possible. Next steps need to involve the use observational data (e.g., from remote sensing) to test the approach using data from real-world systems.

 

Karssenberg, D., Bierkens, M.F.P., Rietkerk, M., Catastrophic Shifts in Semiarid Vegetation-Soil Systems May Unfold Rapidly or Slowly. The American Naturalist 2017. Vol. 190, pp. E145–E155.

How to cite: Pomarol Moya, O. and Karssenberg, D.: Machine learning for data driven discovery of time transfer functions in numerical modelling: simulating catastrophic shifts in vegetation-soil systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4454, https://doi.org/10.5194/egusphere-egu23-4454, 2023.

EGU23-4695 | Posters on site | ITS1.13/AS5.2

Development of PBL Parameterization Emulator using Neural Networks 

Jiyeon Jang, Tae-Jin Oh, Sojung An, Wooyeon Park, Inchae Na, and Junghan Kim

Physical parameterization is one of the major components of Numerical Weather Prediction system. In Korean Integrated Model (KIM), physical parameterizations account for about 30 % of the total computation time. There are many studies of developing neural network based emulators to replace and accelerate physics based parameterization. In this study, we develop a planetary boundary layer(PBL) emulator which is based on Shin-Hong (Hong et al., 2006, 2010; Shin and Hong, 2013, 2015) scheme that computes the parameterized effects of vertical turbulent eddy diffusion of momentum, water vapor, and sensible heat fluxes. We compare the emulator performance with Multi-Layer Perceptron (MLP) based architectures: simple MLP, MLP application version, and MLP-mixer(Tolstikhin et al., 2021). MLP application version divides data into several vertical groups for better approximation of each vertical group layers. MLP-mixer is MLP based architecture that performs well in computer vision without using convolution and self-attention. We evaluate the resulting MLP based emulator performance. MLP application version and MLP-mixer showed significant performance improvement over simple MLP.

How to cite: Jang, J., Oh, T.-J., An, S., Park, W., Na, I., and Kim, J.: Development of PBL Parameterization Emulator using Neural Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4695, https://doi.org/10.5194/egusphere-egu23-4695, 2023.

EGU23-4817 | ECS | Posters on site | ITS1.13/AS5.2

Algorithmic optimisation of key parameters of OpenIFS 

Lauri Tuppi, Madeleine Ekblom, Pirkka Ollinaho, and Heikki Järvinen

Numerical weather prediction models contain parameters that are inherently uncertain and cannot be determined exactly. Traditionally, the parameter tuning has been done manually, which can be an extremely labourious task. Tuning the entire model usually requires adjusting a relatively large amount of parameters. In case of manual tuning, the need to balance a number of requirements at the same time can lead the tuning process being a maze of subjective choices. It is, therefore, desirable to have reliable objective approaches for estimation of optimal values and uncertainties of these parameters. In this presentation we present how to optimise 20 key physical parameters having a strong impact on forecast quality. These parameters belong to the Stochastically Perturbed Parameters Scheme in the atmospheric model Open Integrated Forecasting System.

The results show that simultaneous optimisation of O(20) parameters is possible with O(100) algorithm steps using an ensemble of O(20) members, and that the optimised parameters lead to substantial enhancement of predictive skill. The enhanced predictive skill can be attributed to reduced biases in low-level winds and upper-tropospheric humidity in the optimised model. We find that the optimisation process is dependent on the starting values of the parameters that are optimised (starting from better suited values results in a better model). The results also show that the applicability of the tuned parameter values across different model resolutions is somewhat questionable since the model biases seem to be resolution-specific. Moreover, our optimisation algorithm tends to treat the parameter covariances poorly limiting its ability to converge to the global optimum.

How to cite: Tuppi, L., Ekblom, M., Ollinaho, P., and Järvinen, H.: Algorithmic optimisation of key parameters of OpenIFS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4817, https://doi.org/10.5194/egusphere-egu23-4817, 2023.

EGU23-5003 | ECS | Posters on site | ITS1.13/AS5.2

Towards machine-learning calibration of cloud parameters in the kilometre-resolution ICON atmosphere model 

Hannah Marie Eichholz, Jan Kretzschmar, Duncan Watson-Parris, Josefine Umlauft, and Johannes Quaas

In the preparation of the global kilometre-resolution coupled ICON climate model, it is necessary to calibrate cloud microphysical parameters. Here we explore the avenue towards optimally calibrating such parameters using machine learning. The emulator developed by Watson-Parris et al. (2021) is employed in combination with a perturbed-parameter ensemble of limited-area atmosphere-only ICON simulations for the North Atlantic ocean. In a first step, the autoconversion scaling parameter is calibrated, using satellite-retrieved top-of-atmosphere and bottom-of-atmosphere radiation fluxes. For this purpose, limited area simulations of the north atlantic are performed with ICON. In which different cloud microphysical parameters are changed, in order to evaluate possible influences on the output of radiation fluxes.

How to cite: Eichholz, H. M., Kretzschmar, J., Watson-Parris, D., Umlauft, J., and Quaas, J.: Towards machine-learning calibration of cloud parameters in the kilometre-resolution ICON atmosphere model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5003, https://doi.org/10.5194/egusphere-egu23-5003, 2023.

EGU23-5149 | ECS | Posters on site | ITS1.13/AS5.2

Machine Learning Parameterization for Super-droplet Cloud Microphysics Scheme 

Shivani Sharma and David Greenberg

Machine learning approaches have been widely used for improving the representation of subgrid scale parameterizations in Earth System Models. In our study we target the Cloud Microphysics parameterization, in particular the two-moment bulk scheme of the ICON (Icosahedral Non-hydrostatic) Model. 

 

Cloud microphysics parameterization schemes suffer from an accuracy/speed tradeoff. The simplest schemes, often heavy with assumptions (such as the bulk moment schemes) are most common in operational weather prediction models. Conversely, the more complex schemes with fewer assumptions –e.g. Lagrangian schemes such as the super-droplet method (SDM)– are computationally expensive and used only within research and development. SDM allows easy representation of complex scenarios with multiple hydrometeors and can also be used for simulating cloud-aerosol interactions. To bridge this gap and to make the use of more complex microphysical schemes feasible within operational models, we use a data-driven approach. 

 

Here we train a neural network to mimic the behavior of SDM simulations in a warm-rain scenario in a dimensionless control volume. The network behaves like a dynamical system that converts cloud droplets to rain droplets–represented as bulk moments–with only the current system state as the input. We use a multi-step training loss to stabilize the network over long integration periods, especially in cases with extremely low cloud water to start with. We find that the network is stable across various initial conditions and in many cases, emulates the SDM simulations better than the traditional bulk moment schemes. Our network also performs better than any previous ML-based attempts to learn from SDM. This opens the possibility of using the trained network as a proxy for imitating the computationally expensive SDM within operational weather prediction models with minimum computational overhead. 

How to cite: Sharma, S. and Greenberg, D.: Machine Learning Parameterization for Super-droplet Cloud Microphysics Scheme, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5149, https://doi.org/10.5194/egusphere-egu23-5149, 2023.

EGU23-5523 | ECS | Orals | ITS1.13/AS5.2

Using weak constrained neural networks to improve simulations in the gray zone 

Yvonne Ruckstuhl, Raphael Kriegmair, Stephan Rasp, and George Craig

Machine learning represents a potential method to cope with the gray zone problem of representing motions in dynamical systems on scales comparable to the model resolution. Here we explore the possibility of using a neural network to directly learn the error caused by unresolved scales. We use a modified shallow water model which includes highly nonlinear processes mimicking atmospheric convection. To create the training dataset, we run the model in a high- and a low-resolution setup and compare the difference after one low-resolution time step, starting from the same initial conditions, thereby obtaining an exact target. The neural network is able to learn a large portion of the difference when evaluated on single time step predictions on a validation dataset. When coupled to the low-resolution model, we find large forecast improvements up to 1 d on average. After this, the accumulated error due to the mass conservation violation of the neural network starts to dominate and deteriorates the forecast. This deterioration can effectively be delayed by adding a penalty term to the loss function used to train the ANN to conserve mass in a weak sense. This study reinforces the need to include physical constraints in neural network parameterizations.

How to cite: Ruckstuhl, Y., Kriegmair, R., Rasp, S., and Craig, G.: Using weak constrained neural networks to improve simulations in the gray zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5523, https://doi.org/10.5194/egusphere-egu23-5523, 2023.

EGU23-5766 | ECS | Orals | ITS1.13/AS5.2

Best Practices for Fortran-Python Bridges to Integrate Neural Networks in Earth System Models 

Caroline Arnold, Shivani Sharma, Tobias Weigel, and David Greenberg

In recent years, machine learning (ML) based parameterizations have become increasingly common in Earth System Models (ESM). Sub-grid scale physical processes that would be computationally too expensive, e.g., atmospheric chemistry and cloud microphysics, can be emulated by ML algorithms such as neural networks.

Neural networks are trained first on simulations of the sub-grid scale process that is to be emulated. They are then used in so-called inference mode to make predictions during the ESM run, replacing the original parameterization. Training usually requires GPUs, while inference may be done on CPU architectures.

At first, neural networks are evaluated offline, i.e., independently of the ESM on appropriate datasets. However, their performance can ultimately only be evaluated in an online setting, where the ML algorithm is coupled to the ESM, including nonlinear interactions.

We want to shorten the time spent in neural network development and offline testing and move quickly to online evaluation of ML components in our ESM of choice, ICON (Icosahedral Nonhydrostatic Weather and Climate Model). Since ICON is written in Fortran, and modern ML algorithms are developed in the Python ecosystem, this requires efficient bridges between the two programming languages. The Fortran-Python bridge must be flexible to allow for iterative development of the neural network. Changes to the ESM codebase should be as few as possible, and the runtime overhead should not limit development.

In our contribution we explore three strategies to call the neural network inference from within Fortran using (i) embedded Python code compiled in a dynamic library, (ii) pipes, and (iii) MPI using the ICON coupler YAC. We provide quantitative benchmarks for the proposed Fortran-Python bridges and assess their overall suitability in a qualitative way to derive best practices. The Fortran-Python bridge enables scientists and developers to evaluate ML components in an online setting, and can be extended to other parameterizations and ESMs.

How to cite: Arnold, C., Sharma, S., Weigel, T., and Greenberg, D.: Best Practices for Fortran-Python Bridges to Integrate Neural Networks in Earth System Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5766, https://doi.org/10.5194/egusphere-egu23-5766, 2023.

EGU23-6287 | Orals | ITS1.13/AS5.2

Approximation and Optimization of Atmospheric Simulations in High Spatio-Temporal Resolution with Neural Networks 

Elnaz Azmi, Jörg Meyer, Marcus Strobl, Michael Weimer, and Achim Streit

Accurate forecasts of the atmosphere demand large-scale simulations with high spatio-temporal resolution. Atmospheric chemistry modeling, for example, usually requires solving a system of hundreds of coupled ordinary partial differential equations. Due to the computational complexity, large high performance computing resources are required, which is a challenge as the spatio-temporal resolution increases. Machine learning methods and specially deep learning can offer an approximation of the simulations with some factor of speed-up while using less compute resources. The goal of this study is to investigate the feasibility, opportunities but also challenges and pitfalls of replacing the compute-intensive chemistry of a state-of-the-art atmospheric chemistry model with a trained neural network model to forecast the concentration of trace gases at each grid cell and to reduce the computational complexity of the simulation. In this work, we introduce a neural network model (ICONET) to forecast trace gas concentrations without executing the traditional compute-intensive atmospheric simulations. ICONET is equipped with a multifeature Long Short Term Memory (LSTM) model to forecast atmospheric chemicals iteratively in time. We generated the training and test dataset, our ground truth for ICONET, by execution of an atmospheric chemistry simulation in ICON-ART. Applying the ICONET trained model to forecast a test dataset results in a good fit of the forecast values compared to our ground truth dataset. We discuss appropriate metrics to evaluate the quality of models and present the quality of the ICONET forecasts with RMSE and KGE metrics. The variety in the nature of trace gases limits the model's learning and forecast skills according to the variable. In addition to the quality of the ICONET forecasts, we described the computational efficiency of ICONET as its run time speed-up in comparison to the run time of the ICON-ART simulation. The ICONET forecast showed a speed-up factor of 3.1 over the run time of the atmospheric chemistry simulation of ICON-ART, which is a significant achievement, especially when considering the importance of ensemble simulations.

How to cite: Azmi, E., Meyer, J., Strobl, M., Weimer, M., and Streit, A.: Approximation and Optimization of Atmospheric Simulations in High Spatio-Temporal Resolution with Neural Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6287, https://doi.org/10.5194/egusphere-egu23-6287, 2023.

EGU23-6836 | ECS | Posters on site | ITS1.13/AS5.2

Parameterising melt at the base of Antarctic ice shelves with a feedforward neural network 

Clara Burgard, Nicolas C. Jourdain, Pierre Mathiot, and Robin Smith

One of the largest sources of uncertainty when projecting the Antarctic contribution to sea-level rise is the ocean-induced melt at the base of Antarctic ice shelves. This is because resolving the ocean circulation and the ice-ocean interactions occurring in the cavity below the ice shelves is computationally expensive.

Instead, for large ensembles and long-term projections of the ice-sheet evolution, ice-sheet models currently rely on parameterisations to link the ocean temperature and salinity in front of ice shelves to the melt at their base. However, current physics-based parameterisations struggle to accurately simulate basal melt patterns.

As an alternative approach, we explore the potential use of a deep feedforward neural network as a basal melt parameterisation. To do so, we train a neural network to emulate basal melt rates simulated by highly-resolved circum-Antarctic ocean simulations. We explore the influence of different input variables and show that the neural network struggles to generalise to ice-shelf geometries unseen during training, while it generalises better on timesteps unseen during training. We also test the parameterisation on separate coupled ocean-ice simulations to assess the neural network’s performance on independent data.  

How to cite: Burgard, C., Jourdain, N. C., Mathiot, P., and Smith, R.: Parameterising melt at the base of Antarctic ice shelves with a feedforward neural network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6836, https://doi.org/10.5194/egusphere-egu23-6836, 2023.

EGU23-7281 | ECS | Posters on site | ITS1.13/AS5.2

Neural network surrogate models for multiple scattering: Application to OMPS LP simulations 

Michael Himes, Natalya Kramarova, Tong Zhu, Jungbin Mok, Matthew Bandel, Zachary Fasnacht, and Robert Loughman

Retrieving ozone from limb measurements necessitates the modeling of scattered light through the atmosphere.  However, accurately modeling multiple scattering (MS) during retrieval requires excessive computational resources; consequently, operational retrieval models employ approximations in lieu of the full MS calculation.  Here we consider an alternative MS approximation method, where we use radiative transfer (RT) simulations to train neural network models to predict the MS radiances.  We present our findings regarding the best-performing network hyperparameters, normalization schemes, and input/output data structures.  Using RT calculations based on measurements by the Ozone Mapping and Profiling Suite's Limb Profiler (OMPS/LP), we compare the accuracy of these neural-network models with both the full MS calculation as well as the current MS approximation methods utilized during OMPS/LP retrievals.

How to cite: Himes, M., Kramarova, N., Zhu, T., Mok, J., Bandel, M., Fasnacht, Z., and Loughman, R.: Neural network surrogate models for multiple scattering: Application to OMPS LP simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7281, https://doi.org/10.5194/egusphere-egu23-7281, 2023.

EGU23-7368 | ECS | Posters on site | ITS1.13/AS5.2

Comparison of Methods for Learning Differential Equations from Data 

Christof Schötz

Some results from the DEEB (Differential Equation Estimation Benchmark) are presented. In DEEB, we compare different machine learning approaches and statistical methods for estimating nonlinear dynamics from data. Such methods constitute an important building block for purely data-driven earth system models as well as hybrid models which combine physical knowledge with past observations.

Specifically, we examine approaches for solving the following problem: Given time-state-observations of a deterministic ordinary differential equation (ODE) with measurement noise in the state, predict the future evolution of the system. Of particular interest are systems with chaotic behavior - like Lorenz 63 - and nonparametric settings, in which the functional form of the ODE is completely unknown (in particular, not restricted to a polynomial of low order). To create a fair comparison of methods, a benchmark database was created which includes datasets of simulated observations from different dynamical systems with different complexity and varying noise levels. The list of methods we compare includes: echo state networks, Gaussian processes, Neural ODEs, SINDy, thin plate splines, and more.

Although some methods consistently perform better than others throughout different datasets, there seems to be no silver bullet.

How to cite: Schötz, C.: Comparison of Methods for Learning Differential Equations from Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7368, https://doi.org/10.5194/egusphere-egu23-7368, 2023.

EGU23-7391 | ECS | Posters on site | ITS1.13/AS5.2

Learning fluid dynamical statistics using stochastic neural networks 

Martin Brolly
Many practical problems in fluid dynamics demand an empirical approach, where statistics estimated from data inform understanding and modelling. In this context data-driven probabilistic modelling offers an elegant alternative to ad hoc estimation procedures. Probabilistic models are useful as emulators, but also offer an attractive means of estimating particular statistics of interest. In this paradigm one can rely on proper scoring rules for model comparison and validation, and invoke Bayesian statistics to obtain rigorous uncertainty quantification. Stochastic neural networks provide a particularly rich class of probabilistic models, which, when paired with modern optimisation algorithms and GPUs, can be remarkably efficient. We demonstrate this approach by learning the single particle transition density of ocean surface drifters from decades of Global Drifter Program observations using a Bayesian mixture density network. From this we derive maps of various displacement statistics and corresponding uncertainty maps. Our model also offers a means of simulating drifter trajectories as a discrete-time Markov process, which could be used to study the transport of plankton or plastic in the upper ocean.

How to cite: Brolly, M.: Learning fluid dynamical statistics using stochastic neural networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7391, https://doi.org/10.5194/egusphere-egu23-7391, 2023.

EGU23-7492 | Posters on site | ITS1.13/AS5.2

Machine Learning and Microseism as a Tool for Sea Wave Monitoring 

Flavio Cannavo', Vittorio Minio, Susanna Saitta, Salvatore Alparone, Alfio Marco Borzì, Andrea Cannata, Giuseppe Ciraolo, Danilo Contrafatto, Sebastiano D’Amico, Giuseppe Di Grazia, and Graziano Larocca

Monitoring the state of the sea is a fundamental task for economic activities in the coastal zone, such as transport, tourism and infrastructure design. In recent years, regular wave height monitoring for marine risk assessment and mitigation has become unavoidable as global warming impacts in more intense and frequent swells.
In particular, the Mediterranean Sea has been considered as one of the most responsive regions to global warming, which may promote the intensification of hazardous natural phenomena as strong winds, heavy precipitation and high sea waves. Because of the high density population along the Mediterranean coastlines, heavy swells could have major socio-economic consequences. To reduce the impacts of such scenarios, the development of more advanced monitoring systems of the sea state becomes necessary.
In the last decade, it has been demonstrated how seismometers can be used to measure sea conditions by exploiting the characteristics of a part of the seismic signal called microseism. Microseism is the continuous seismic signal recorded in the frequency band of 0.05 and 0.4 Hz that is likely generated by interactions of sea waves together and with seafloor or shorelines.
In this work, in the framework of i-WaveNET INTERREG project, we performed a regression analysis to develop a model capable of predicting the sea state in the Sicily Channel (Italy) using microseism, acquired by onshore instruments installed in Sicily and Malta. Considering the complexity of the relationship between spatial sea wave height data and seismic data measured at individual stations, we used supervised machine learning (ML) techniques to develop the prediction model. As input data we used the hourly Root Mean Squared (RMS) amplitude of the seismic signal recorded by 14 broadband stations, along the three components, and in different frequency bands, during 2018 - 2021. These stations, belonging to the permanent seismic networks managed by the National Institute of Geophysics and Volcanology INGV and the Department of Geosciences of the University of Malta, consist of three-component broadband seismometers that record at a sampling frequency of 100 Hz.
As for the target, the significant sea wave height data from Copernicus Marine Environment Monitoring Service (CMEMS) for the same period were used. Such data is the hindcast product of the Mediterranean Sea Waves forecasting system, with hourly temporal resolution and 1/24° spatial resolution. After a feature selection step, we compared three different kinds of ML algorithms for regression: K-Nearest-Neighbors (KNN), Random Forest (RF) and Light Gradient Boosting (LGB). The hyperparameters were tuned by using a grid-search algorithm, and the best models were selected by cross-validation.  Different metrics, such as MAE, R2 and RMSE, were considered to evaluate the generalization capabilities of the models and special attention was paid to evaluate the predictive ability of the models for extreme wave height values.
Results show model predictive capabilities good enough to develop a sea monitoring system to complement the systems currently in use.

How to cite: Cannavo', F., Minio, V., Saitta, S., Alparone, S., Borzì, A. M., Cannata, A., Ciraolo, G., Contrafatto, D., D’Amico, S., Di Grazia, G., and Larocca, G.: Machine Learning and Microseism as a Tool for Sea Wave Monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7492, https://doi.org/10.5194/egusphere-egu23-7492, 2023.

EGU23-7561 | ECS | Posters on site | ITS1.13/AS5.2

Deep Learning guided statistical downscaling of climate projections for use in hydrological impact modeling in Danish peatlands 

Thea Quistgaard, Peter L. Langen, Tanja Denager, Raphael Schneider, and Simon Stisen

A course of action to combat the emission of greenhouse gasses (GHG) in a Danish context is to re-wet previously drained peatlands and thereby return them to their natural hydrological state acting as GHG sinks. GHG emissions from peatlands are known to be closely coupled to the hydrological dynamics through the groundwater table depth (WTD). To understand the effect of a changing and variable climate on the spatio-temporal dynamics of hydrological processes and the associated uncertainties, we aim to produce a high-resolution local-scale climate projection ensemble from the global-scale CMIP6 projections.

With focus on hydrological impacts, uncertainties and possible extreme endmembers, this study aims to span the full ensemble of local-scale climate projections in the Danish geographical area corresponding to the CMIP6-ensemble of Global Climate Models (GCMs). Deep learning founded statistical downscaling methods are applied bridge the gap from GCMs to local-scale climate change and variability, which in turn will be used in field-scale hydrological modeling. The approach is developed to specifically accommodate the resolutions, event types and conditions relevant for assessing the impacts on peatland GHG emissions through their relationship with WTD dynamics by applying stacked conditional generative adversarial networks (CGANs) to best downscale precipitation, temperature, and evaporation. In the future, the approach is anticipated to be extended to directly assess the impacts of climate change and ensemble uncertainty on peatland hydrology variability and extremes.

How to cite: Quistgaard, T., Langen, P. L., Denager, T., Schneider, R., and Stisen, S.: Deep Learning guided statistical downscaling of climate projections for use in hydrological impact modeling in Danish peatlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7561, https://doi.org/10.5194/egusphere-egu23-7561, 2023.

EGU23-8288 | Orals | ITS1.13/AS5.2

Learning operational altimetry mapping from ocean models 

Quentin Febvre, Ronan Fablet, Julien Le Sommer, Clément Ubelmann, and Simon Benaïchouche

In oceanography, altimetry products are used to measure the height of the ocean surface, and ocean modeling is used to understand and predict the behavior of the ocean. There are two main types of gridded altimetry products: operational sea level products, such as DUACS, which are used for forecasting and reconstruction, and ocean model reanalyses, such as Glorys 12, which are used to forecast seasonal trends and assess physical characteristics. However, advances in ocean modeling do not always directly benefit operational forecast or reconstruction products.

In this study, we investigate the potential for deep learning methods, which have been successfully applied in simulated setups, to leverage ocean modeling efforts for improving operational altimetry products. Specifically, we ask under what conditions the knowledge learned from ocean simulations can be applied to real-world operational altimetry mapping. We consider the impact of simulation grid resolution, observation data reanalysis, and physical processes modeled on the performance of a deep learning model.

Our results show that the deep learning model outperforms current operational methods on a regional domain around the Gulfstream, with a 50km improvement in resolved scale. This improvement has the potential to enhance the accuracy of operational altimetry products, which are used for a range of important applications, such as climate monitoring and understanding mesoscale ocean dynamics.

How to cite: Febvre, Q., Fablet, R., Le Sommer, J., Ubelmann, C., and Benaïchouche, S.: Learning operational altimetry mapping from ocean models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8288, https://doi.org/10.5194/egusphere-egu23-8288, 2023.

EGU23-9285 | ECS | Orals | ITS1.13/AS5.2

Stabilized Neural Differential Equations for Hybrid Modeling with Conservation Laws 

Alistair White and Niklas Boers

Neural Differential Equations (NDEs) provide a powerful framework for hybrid modeling. Unfortunately, the flexibility of the neural network component of the model comes at the expense of potentially violating known physical invariants, such as conservation laws, during inference. This shortcoming is especially critical for applications requiring long simulations, such as climate modeling, where significant deviations from the physical invariants can develop over time. It is hoped that enforcing physical invariants will help address two of the main barriers to adoption for hybrid models in climate modeling: (1) long-term numerical stability, and (2) generalization to out-of-sample conditions unseen during training, such as climate change scenarios. We introduce Stabilized Neural Differential Equations, which augment an NDE model with compensating terms that ensure physical invariants remain approximately satisfied during numerical simulations. We apply Stabilized NDEs to the double pendulum and Hénon–Heiles systems, both of which are conservative, chaotic dynamical systems possessing a time-independent Hamiltonian. We evaluate Stabilized NDEs using both short-term and long-term prediction tasks, analogous to weather and climate prediction, respectively. Stabilized NDEs perform at least as well as unstabilized models at the “weather prediction” task, that is, predicting the exact near-term state of the system given initial conditions. On the other hand, Stabilized NDEs significantly outperform unstabilized models at the “climate prediction” task, that is, predicting long-term statistical properties of the system. In particular, Stabilized NDEs conserve energy during long simulations and consequently reproduce the long-term dynamics of the target system with far higher accuracy than non-energy conserving models. Stabilized NDEs also remain numerically stable for significantly longer than unstabilized models. As well as providing a new and lightweight method for combining physical invariants with NDEs, our results highlight the relevance of enforcing conservation laws for the long-term numerical stability and physical accuracy of hybrid models.

How to cite: White, A. and Boers, N.: Stabilized Neural Differential Equations for Hybrid Modeling with Conservation Laws, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9285, https://doi.org/10.5194/egusphere-egu23-9285, 2023.

EGU23-10135 | ECS | Orals | ITS1.13/AS5.2

Exploring physics-informed machine learning for accelerated simulation of permafrost processes 

Brian Groenke, Moritz Langer, Guillermo Gallego, and Julia Boike

Permafrost, i.e. ground material that remains perennially frozen, plays a key role in Arctic ecosystems. Monitoring the response of permafrost to rapid climate change remains difficult due to the sparse availability of long-term, high quality measurements of the subsurface. Numerical models are therefore an indispensable tool for understanding the evolution of Arctic permafrost. However, large scale simulation of the hydrothermal processes affecting permafrost is challenging due to the highly nonlinear effects of phase change in porous media. The resulting computational cost of such simulations is especially prohibitive for sensitivity analysis and parameter estimation tasks where a large number of simulations may be necessary for robust inference of quantities such as temperature, water fluxes, and soil properties. In this work, we explore the applicability of recently developed physics-informed machine learning (PIML) methods for accelerating numerical models of permafrost hydrothermal dynamics. We present a preliminary assessment of two possible applications of PIML in this context: (1) linearization of the nonlinear PDE system according to Koopman operator theory in order to reduce the computational burden of large scale simulations, and (2) efficient parameterization of the surface energy balance and snow dynamics on the subsurface hydrothermal regime. By combining the predictive power of machine learning with the underlying conservation laws, PIML can potentially enable researchers and practitioners interested in permafrost to explore complex process interactions at larger spatiotemporal scales.

How to cite: Groenke, B., Langer, M., Gallego, G., and Boike, J.: Exploring physics-informed machine learning for accelerated simulation of permafrost processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10135, https://doi.org/10.5194/egusphere-egu23-10135, 2023.

EGU23-10256 | ECS | Posters on site | ITS1.13/AS5.2

Foehn Wind Analysis using Unsupervised Deep Anomaly Detection 

Tobias Milz, Marte Hofsteenge, Marwan Katurji, and Varvara Vetrova

Foehn winds are accelerated, warm and dry winds that can have significant environmental impacts as they descend into the lee of a mountain range. For example, in the McMurdo Dry Valleys in Antarctica, foehn events can cause ice and glacial melt and destabilise ice shelves, which if lost, resulting in a rise in sea level. Consequently, there is a strong interest in a deeper understanding of foehn winds and their meteorological signatures. Most current automatic detection methods rely on rule-based methodologies that require static thresholds of meteorological parameters. However, the patterns of foehn winds are hard to define and differ between alpine valleys around the world. Consequently, data-driven solutions might help create more accurate detection and prediction methodologies. 

State-of-the-art machine learning approaches to this problem have shown promising results but follow a supervised learning paradigm. As such, these approaches require accurate labels, which for the most part, are being created by imprecise static rule-based algorithms. Consequently, the resulting machine-learning models are trained to recognise the same static definitions of the foehn wind signatures. 

In this paper, we introduce and compare the first unsupervised machine-learning approaches for detecting foehn wind events. We focus on data from the Mc Murdo Dry Valleys as an example, however, due to the unsupervised nature of these approaches, our solutions can recognise a more dynamic definition of foehn wind events and are therefore, independent of the location. The first approach is based on multivariate time-series clustering, while the second utilises a deep autoencoder-based anomaly detection method to identify foehn wind events. Our best model achieves an f1-score of 88%, matching or surpassing previous machine-learning methods while providing a more flexible and inclusive definition of foehn events. 

How to cite: Milz, T., Hofsteenge, M., Katurji, M., and Vetrova, V.: Foehn Wind Analysis using Unsupervised Deep Anomaly Detection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10256, https://doi.org/10.5194/egusphere-egu23-10256, 2023.

EGU23-10351 | ECS | Orals | ITS1.13/AS5.2

Deep learning of systematic sea ice model errors from data assimilation increments 

William Gregory, Mitchell Bushuk, Alistair Adcroft, and Yongfei Zhang

Data assimilation is often viewed as a framework for correcting short-term error growth in dynamical climate model forecasts. When viewed on the time scales of climate however, these short-term corrections, or analysis increments, closely mirror the systematic bias patterns of the dynamical model. In this work, we show that Convolutional Neural Networks (CNNs) can be used to learn a mapping from model state variables to analysis increments, thus promoting the feasibility of a data-driven model parameterization which predicts state-dependent model errors. We showcase this problem using an ice-ocean data assimilation system within the fully coupled Seamless system for Prediction and EArth system Research (SPEAR) model at the Geophysical Fluid Dynamics Laboratory (GFDL), which assimilates satellite observations of sea ice concentration. The CNN then takes inputs of data assimilation forecast states and tendencies, and makes predictions of the corresponding sea ice concentration increments. Specifically, the inputs are sea ice concentration, sea-surface temperature, ice velocities, ice thickness, net shortwave radiation, ice-surface skin temperature, and sea-surface salinity. We show that the CNN is able to make skilful predictions of the increments, particularly between December and February in both the Arctic and Antarctic, with average daily spatial pattern correlations of 0.72 and 0.79, respectively. Initial investigation of implementation of the CNN into the fully coupled SPEAR model shows that the CNN can reduce biases in retrospective seasonal sea ice forecasts by emulating a data assimilation system, further suggesting that systematic sea ice biases could be reduced in a free-running climate simulation.

How to cite: Gregory, W., Bushuk, M., Adcroft, A., and Zhang, Y.: Deep learning of systematic sea ice model errors from data assimilation increments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10351, https://doi.org/10.5194/egusphere-egu23-10351, 2023.

Current numerical weather prediction models contain significant systematic errors, due in part to indeterminate ground forcing (GF). This study considers an optimal virtual GF (GFo) derived by training observed and simulated datasets of 10-m wind speeds (WS10) for summer and winter. The GFo is added to an offline surface multilayer model (SMM) to revise predictions of WS10 in China by the Weather Research and Forecasting model (WRF). This revision is a data-based optimization under physical constraints. It reduces WS10 errors and offers wide applicability. The resulting model outperforms two purely physical forecasts (the original WRF forecast and the SMM with physical GF parameterized using urban, vegetation, and subgrid topography) and two purely data-based revisions (i.e., multilinear regression and multilayer perceptron). Compared with original WRF forecasting, using the GFo scheme reduces the Root Mean Square Error (RMSE) in WS10 across China by 25% in summer and 32% in winter. The frontal area index of GFo indicates that it includes both the effects of indeterminate GF and other possible complex physical processes associated with WS10.

How to cite: Feng, J.: Mitigate forecast error in surface wind speed using an offline single-column model with optimal ground forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10394, https://doi.org/10.5194/egusphere-egu23-10394, 2023.

EGU23-10726 | Posters virtual | ITS1.13/AS5.2

A hybrid VMD-WT-InceptionTime model for multi-horizon short-term air temperature forecasting in Alaska 

Jaakko Putkonen, M. Aymane Ahajjam, Timothy Pasch, and Robert Chance

The lack of ground level observation stations outside of settlements makes monitoring and forecasting local weather and permafrost challenging in the Arctic. Such predictive pieces of information are essential to help prepare for potentially hazardous weather conditions, especially during winter. In this study, we aim at enhancing predictive analytics in Alaska of permafrost and temperature by using a hybrid forecasting technique. In particular, we propose VMD-WT-InceptionTime model for short-term air temperature forecasting.

This proposed technique incorporates data preprocessing techniques and deep learning to enhance the accuracy of the next seven days air temperature forecasts. Initially, the Spearman correlation coefficient is utilized to examine the relationship between different inputs and the forecast target temperature. Following this, Variational Mode Decomposition (VMD) is used to decompose the most output-correlated input variables (i.e., temperature and relative humidity) to extract intrinsic and non-stationary time-frequency features from the original sequences. The Wavelet Transform (WT) is then employed to further extract intrinsic multi-resolution patterns from these decomposed input variables. Finally, a deep InceptionTime model is used for multi-step air temperature forecasting using these processed sequences. This forecasting technique was developed using an open dataset holding 20+ years of data from three locations in Alaska: North Slope, Alaska, Arctic National Wildlife Refuge, Alaska, and Diomede Island region, Bering Strait. Model performance has been rigorously evaluated of metrics including RMSE, MAPE and error.

Results highlight the effectiveness of the proposed hybrid model in providing more accurate short-term forecasts than several baselines (GBDT, SVR, ExtraTrees, RF, ARIMA, LSTM, GRU, and Transformer). More specifically, this technique reported RMSE and MAPE average increase rates amounting to 11.21% and 16.13% in North Slope, 30.01% and 34.97% in Arctic National Wildlife Refuge, and 16.39%, 23.46% in Diomede Island region. In addition, the proposed technique produces forecasts over all seven horizons with a maximum error of <1.5K, a minimum error of >-1.2K, and an average error lower than 0.18K for North Slope. For Arctic National Wildlife Refuge, a maximum error of <1K, a minimum error of >-0.9K, and an average of < 0.1K. While a maximum error of <0.9K, a minimum error of >-0.8K, and an average of <0.13K, for Diomede Island region. However, the worst performances achieved were errors of around 6K in the third horizon (i.e., 3rd day) for North Slope and the Arctic National Wildlife Refuge and the last horizon (i.e., 7th day) for the Diomede Islands region. Most of the worst performances of the proposed technique in all three locations can be attributed to having to produce forecasts of higher variations and wider temperature ranges than their averages.

Overall, this research highlights the potential of the decomposition techniques and deep learning to: 1) reveal and effectively learn the underlying cyclicity of air temperatures at varying resolutions that allows for accurate predictions without any knowledge of the governing physics, 2) produce accurate multi-step temperature forecasts in Arctic climates.

How to cite: Putkonen, J., Ahajjam, M. A., Pasch, T., and Chance, R.: A hybrid VMD-WT-InceptionTime model for multi-horizon short-term air temperature forecasting in Alaska, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10726, https://doi.org/10.5194/egusphere-egu23-10726, 2023.

EGU23-10810 | ECS | Orals | ITS1.13/AS5.2

Oceanfourcast: Emulating Ocean Models with Transformers for Adjoint-based Data Assimilation 

Suyash Bire, Björn Lütjens, Dava Newman, and Chris Hill

Adjoints have become a staple of the oceanic and atmospheric numerical modeling community over the past couple of decades as they are useful for tuning of dynamical models, sensitivity analyses, and data assimilation. One such application is generation of reanalysis datasets, which provide an optimal record of our past weather, climate, and ocean. For example, the state-of-the-art ocean-ice renanalysis dataset, ECCO, is created by optimally combining a numerical ocean model with heterogeneous observations through a technique called data assimilation. Data assimilation in ECCO minimizes the distance between model and observations by calculating adjoints, i.e., gradients of the loss w.r.t. simulation forcing fields (wind and surface heat fluxes). The forcing fields are iteratively updated and the model is rerun until the loss is minimized to ensure that the numerical model does not drastically deviate from the observations. Calculating adjoints, however, either requires  disproportionately high computational resources  or rewriting the dynamical model code to be autodifferentiable. 

Therefore, we ask if deep learning-based emulators can provide fast and accurate adjoints. Ocean data is smooth, high-dimensional, and has complex spatiotemporal correlations. Therefore, as an initial foray into ocean emulators, we leverage a combination of neural operators and transformers. Specifically, we have adapted the FourCastNet architecture, which has successfully emulated ERA5 weather data in seconds rather than hours, to emulate an idealized ocean simulation.

We generated a ground-truth dataset by simulating a double-gyre, an idealized representation of the North Atlantic Ocean, using MITgcm, a state-of-the-art dynamical model. The model was forced by zonal wind at the surface and relaxation to a meridional profile of temperature — warm/cold temperatures at low/high latitudes. This simulation produced turbulent western boundary currents embedded in the large-scale gyre circulation. We performed 4 additional simulations by modifying the magnitude of SST relaxation and wind forcing to introduce diversity in the dataset. From these simulations, we used 4 state variables (meridional and zonal surface velocities, pressure, and temperature) as well as the forcing fields (zonal wind velocity and relaxation SST profile) sampled in 10-day steps. The dataset was split into training, validation, and test datasets such that validation and test datasets were unseen during training. These datasets provide an ideal testbed for evaluating and comparing the performance of data-driven ocean emulators.

We used this data to train and evaluate Oceanfourcast. Our initial results in the following figure show that our model, Oceanfourcast, can successfully predict the streamfunction and pressure for a lead time of 1 month. 

We are currently working on generating adjoints from Oceanfourcast.  We expect the adjoint calculation to require significantly less compute time than that from a full-scale dynamical model like MITgcm.  Our work shows a promising path towards deep-learning augmented data assimilation and uncertainty quantification.

How to cite: Bire, S., Lütjens, B., Newman, D., and Hill, C.: Oceanfourcast: Emulating Ocean Models with Transformers for Adjoint-based Data Assimilation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10810, https://doi.org/10.5194/egusphere-egu23-10810, 2023.

EGU23-10904 | ECS | Posters on site | ITS1.13/AS5.2

On the choice of turbulence eddy fluxes to learn from in data-driven methods 

Feier Yan, Julian Mak, and Yan Wang

Recent works have demonstrated the viability of employing data-driven / machine learning 
methods for the purposes of learning more about ocean turbulence, with applications to turbulence parameterisations in ocean general circulation models. Focusing on mesoscale geostrophic turbulence in the ocean context, works thus far have mostly focused on the choice of algorithms and testing of trained up models. Here we focus instead on the choice of eddy flux data to learn from. We argue that, for mesoscale geostrophic turbulence, it might be beneficial from a theoretical as well as practical point of view to learn from eddy fluxes with dynamically inert rotational fluxes removed (ideally in a gauge invariant fashion), instead of the divergence of the eddy fluxes as has been considered thus far. Outlooks for physically constrained and interpretable machine learning will be given in light of the results. 

How to cite: Yan, F., Mak, J., and Wang, Y.: On the choice of turbulence eddy fluxes to learn from in data-driven methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10904, https://doi.org/10.5194/egusphere-egu23-10904, 2023.

EGU23-10959 | Orals | ITS1.13/AS5.2

Deep learning parameterization of small-scale vertical velocity variability for atmospheric models 

Donifan Barahona, Katherine Breen, and Heike Kalesse-Los

Small-scale fluctuations in vertical wind velocity, unresolved by climate and weather forecast models play a particularly important role in determining vapor and tracer fluxes, turbulence and cloud formation. Fluctuations in vertical wind velocity are challenging to represent since they depend on orography, large scale circulation features, convection and wind shear. Parameterizations developed using data retrieved at specific locations typically lack generalization and may introduce error when applied on a wide range of different conditions. Retrievals of vertical wind velocity are also difficult and subject to large uncertainty. This work develops a new data-driven, neural network representation of subgrid scale variability in vertical wind velocity. Using a novel deep learning technique, the new parameterization merges data from high-resolution global cloud resolving model simulations with high frequency Radar and Lidar retrievals.  Our method aims to reproduce observed statistics rather than fitting individual measurements. Hence it is resilient to experimental uncertainty and robust to generalization. The neural network parameterization can be driven by weather forecast and reanalysis products to make real time estimations. It is shown that the new parameterization generalizes well outside of the training data and reproduces much better the statistics of vertical wind velocity than purely data-driven models.

How to cite: Barahona, D., Breen, K., and Kalesse-Los, H.: Deep learning parameterization of small-scale vertical velocity variability for atmospheric models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10959, https://doi.org/10.5194/egusphere-egu23-10959, 2023.

EGU23-11293 | ECS | Posters on site | ITS1.13/AS5.2

National scale agricultural development dynamics under socio-political drivers in Saudi Arabia since 1990 

Ting Li, Oliver López Valencia, Kasper Johansen, and Matthew McCabe

Driven in large part by policy initiatives designed to increase food security and realized via the construction of thousands of center-pivot irrigation fields since the 1970s, agriculture development in Saudi Arabia has undergone tremendous changes. However, little is known about the accurate number, acreage, and the changing dynamics of the fields. To bridge the knowledge gap between the political drivers and in-field response, we leveraged a hybrid machine learning framework by implementing Density-Based Spatial Clustering of Applications with Noise, Convolutional Neural Networks, and Spectral Clustering in a stepwise manner to delineate the center-pivot fields on a national scale in Saudi Arabia using historical Landsat imagery since 1990. The framework achieved producer's and user's accuracies larger than  83.7% and 90.2%, respectively, when assessed against 28,000 manually delineated fields collected from different regions and periods. We explored multi-decadal dynamics of the agricultural development in Saudi Arabia by quantifying the number, acreage, and size distribution of center-pivot fields, along with the first and last detection year of the fields since 1990. The agricultural development in Saudi Arabia experienced four stages, including an initialization stage before 1990, a contraction stage from 1990 to 2010, an expansion stage from 2010 to 2016, and an ongoing contraction stage since 2016. Most of the fields predated 1990, representing over 8,800 km2 in that year, as a result of the policy initiatives to stimulate wheat production, promoting Saudi Arabia as the sixth largest exporter of wheat in the 1980s. A decreasing trend was observed from 1990 to 2010, with an average of 8,011 km2 of fields detected during those two decades, which was a response to the policy initiative implemented to phase-out wheat after 1990. As a consequence of planting fodder crops to promote the dairy industry, the number and extent of fields increased rapidly from 2010 to 2015 and reached its peak in 2016, with 33,961 fields representing 9,400 km2. Agricultural extent has seen a continuous decline since 2016 to a level lower than 1990 values in 2020. This decline has been related to sustainable policy initiatives implemented for the Saudi Vision 2030. There is some evidence of an uptick in 2021 — also observed in an ongoing analysis for 2022 — which might be in response to global influences, such as the COVID-19 pandemic and the more recent conflict in the Ukraine, which has disrupted the international supply of agricultural products. The results provide a historical account of agricultural activity throughout the Kingdom and provide a basis for informed decision-making on sustainable irrigation and agricultural practices, helping to better protect and manage the nation's threatened groundwater resources, and providing insights into the resilience and elasticity of the Saudi Arabian food system to global perturbations.

How to cite: Li, T., López Valencia, O., Johansen, K., and McCabe, M.: National scale agricultural development dynamics under socio-political drivers in Saudi Arabia since 1990, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11293, https://doi.org/10.5194/egusphere-egu23-11293, 2023.

EGU23-11687 | ECS | Orals | ITS1.13/AS5.2

Objectively Determining the Number of Similar Hydrographic Clusters with Unsupervised Machine Learning 

Carola Trahms, Yannick Wölker, and Arne Biastoch

Determining the number of existing water masses and defining their boundaries is subject to ongoing discussion in physical oceanography. Traditionally, water masses are defined manually by experts setting constraints based on experience and previous knowledge about the hydrographic properties describing them. In recent years, clustering, an unsupervised machine learning approach, has been introduced as a tool to determine clusters, i.e., volumes, with similar hydrographic properties without explicitly defining their hydrographic constraints. However, the exact number of clusters to be looked for is set manually by an expert up until now. 

We propose a method that determines a fitting number of clusters for hydrographic clusters in a data driven way. In a first step, the method averages the data in different-sized slices along the time or depth axis as the structure of the hydrographic space changes strongly either in time or depth. Then the method applies clustering algorithms on the averaged data and calculates off-the-shelf evaluation scores (Davies-Bouldin, Calinski-Harabasz, Silhouette Coefficient) for several predefined numbers of clusters. In the last step, the optimal number of clusters is determined by analyzing the cluster evaluation scores across different numbers of clusters for optima or relevant changes in trend. 

For validation we applied this method to the output for the subpolar North Atlantic between 1993 and 1997 of the high-resolution Atlantic Ocean model VIKING20X, in direct exchange with domain experts to discuss the resulting clusters. Due to the change from strong to weak deep convection in these years, the hydrographic properties vary strongly in the time and depth dimension, providing a specific challenge to our methodology. 

Our findings suggest that it is possible to identify an optimal number of clusters using the off-the-shelf cluster evaluation scores that catch the underlying structure of the hydrographic space. The optimal number of clusters identified by our data-driven method agrees with the optimal number of clusters found by expert interviews. These findings contribute to aiding and objectifying water mass definitions across multiple expert decisions, and demonstrate the benefit of introducing data science methods to analyses in physical oceanography.

How to cite: Trahms, C., Wölker, Y., and Biastoch, A.: Objectively Determining the Number of Similar Hydrographic Clusters with Unsupervised Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11687, https://doi.org/10.5194/egusphere-egu23-11687, 2023.

EGU23-11906 | ECS | Orals | ITS1.13/AS5.2

Untapping the potential of geostationary EO data to understand drought impacts with XAI 

Basil Kraft, Gregory Duveiller, Markus Reichstein, and Martin Jung

Ecosystems are affected by extreme climate conditions such as droughts worldwide but we still lack understanding of the involved dynamics. Which factors render an ecosystem more resilient, and on which temporal scales do weather patterns affect vegetation state and physiology? Traditional approaches to tackle such questions involve assumption-based land surface modeling or inversions. Machine learning (ML) methods can provide a complementary perspective on how ecosystems respond to climate in a more data-driven and assumption-free manner. However, ML depends heavily on data, and commonly used observations of vegetation at best contain one observation per day, but most products are provided at 16-daily to monthly temporal resolution. This masks important processes at sub-monthly time scales. In addition, ML models are inherently difficult to interpret, which still limits their applicability for process understanding.

In the present study, we combine modern deep learning models in the time domain with observations from the geostationary Meteosat Second Generation (MSG) satellite, centered over Africa. We model fractional vegetation cover (representing vegetation state) and land surface temperature (as a proxy for water stress) from MSG as a function of meteorology and static geofactors. MSG collects observations at sub-daily frequency, rendering it into an excellent tool to study short- to mid-term land surface processes. Furthermore, we use methods from explainable ML for post-hoc model interpretation to identify meteorological drivers of vegetation dynamics and their interaction with key geofactors.

From the analysis, we expect to gather novel insights into ecosystem response to droughts with high temporal fidelity. Drought response of vegetation can be highly diverse and complex especially in arid to semi-arid regions prevalent in Africa. Also, we assess the potential of explainable machine learning to discover new linkages and knowledge and discuss potential pitfalls of the approach. Explainable machine learning, combined with potent deep learning approaches and modern Earth observation products offers the opportunity to complement assumption-based modeling to predict and understand ecosystem response to extreme climate.

How to cite: Kraft, B., Duveiller, G., Reichstein, M., and Jung, M.: Untapping the potential of geostationary EO data to understand drought impacts with XAI, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11906, https://doi.org/10.5194/egusphere-egu23-11906, 2023.

EGU23-11958 | ECS | Posters on site | ITS1.13/AS5.2

Modelling Soil Temperature and Soil Moisture in Space, Depth, and Time with Machine Learning Techniques 

Maiken Baumberger, Linda Adorf, Bettina Haas, Nele Meyer, and Hanna Meyer

Soil temperature and soil moisture variations have large effects on ecological processes in the soil. To investigate and understand these processes, high-resolution data of soil temperature and soil moisture are required. Here, we present an approach to generate data of soil temperature and soil moisture continuously in space, depth, and time for a 400 km² study area in the Fichtel Mountains (Germany). As reference data, measurements with 1 m long soil probes were taken. To cover many different locations, the available 15 soil probes were shifted regularly in the course of one year. With this approach, around 250 different locations in forest sites, on meadows and on agricultural fields were captured under a variety of meteorological conditions. These measurements are combined with readily available meteorological data, satellite data and soil maps in a machine learning approach to learn the complex relations between these variables. We aim for a model which can predict the soil temperature and soil moisture continuously for our study area in the Fichtel Mountains, with a spatial resolution of 10 m x 10 m, down to 1 m depth with segments of 10 cm each and in an hourly resolution in time. Here, we present the results of our pilot study where we focus on the temperature and moisture change within the depth down to 1 m at one single location. To take temporal lags into account, we construct a Long Short-Term Memory network based on meteorological data as predictors to make temperature and moisture predictions in time and depth. The results indicate a high ability of the model to reproduce the time series of the single location and highlight the potential of the approach for the space-time-depth mapping of soil temperature and soil moisture.

How to cite: Baumberger, M., Adorf, L., Haas, B., Meyer, N., and Meyer, H.: Modelling Soil Temperature and Soil Moisture in Space, Depth, and Time with Machine Learning Techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11958, https://doi.org/10.5194/egusphere-egu23-11958, 2023.

EGU23-12218 | Posters on site | ITS1.13/AS5.2

Bias correction of aircraft temperature observations in the Korean Integrated Model based on a deep learning approach 

Hui-nae Kwon, Hyeon-ju Jeon, Jeon-ho Kang, In-hyuk Kwon, and Seon Ki Park

The aircraft-based observation is one of the important anchor data used in the numerical weather prediction (NWP) models. Nevertheless, the bias has been noted in the temperature observation through several previous studies. As the performance on the hybrid four-dimensional ensemble variational (hybrid-4DEnVar) data assimilation (DA) system of the Korean Integrated Model (KIM) ⸺ the operational model in the Korea Meteorological Administration (KMA) ⸺ has been advanced, the need for the aircraft temperature bias correction (BC) has been confirmed. Accordingly, as a preliminary study on the BC, the static BC method based on the linear regression was applied to the KIM Package for Observation Processing (KPOP) system. However, the results showed there were limitations of a spatial discontinuity and a dependency on the calculation period of BC coefficients.

In this study, we tried to develop the machine learning-based bias estimation model to overcome these limitations. The MultiLayer Perceptron (MLP) based learning was performed to consider the vertical, spatial and temporal characteristics of each observation by flight IDs and phases, and at the same time to consider the correlation among observation variables. As a result of removing the predicted bias from the bias estimation model, the mean of the background innovation (O-B) decreases from 0.2217 K to 0.0136 K in a given test period. Afterwards, in order to verify the analysis field impact for BC, the bias estimation model will be grafted onto the KPOP system and then several DA cycle experiments will be conducted in the KIM.

How to cite: Kwon, H., Jeon, H., Kang, J., Kwon, I., and Park, S. K.: Bias correction of aircraft temperature observations in the Korean Integrated Model based on a deep learning approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12218, https://doi.org/10.5194/egusphere-egu23-12218, 2023.

EGU23-12355 | ECS | Orals | ITS1.13/AS5.2

Comparison of NWP Models Used in Training Surrogate Wave Models 

Ajit Pillai, Ian Ashton, Jiaxin Chen, and Edward Steele

Machine learning is increasingly being applied to ocean wave modelling. Surrogate modelling has the potential to reduce or bypass the large computational requirements, creating a low computational-cost model that offers a high level of accuracy. One approach integrates in-situ measurements and historical model runs to achieve the spatial coverage of the model and the accuracy of the in-situ measurements. Once operational, such a system requires very little computational power, meaning that it could be deployed to a mobile phone, operational vessel, or autonomous vessel to give continuous data. As such, it makes a significant change to the availability of met-ocean data with potential to revolutionise data provision and use in marine and coastal settings.

This presentation explores the impact that an underlying physics-based model can have in such a machine learning driven framework; comparing training the system on a bespoke regional SWAN wave model developed for wave energy developments in the South West of the UK against training using the larger North-West European Shelf long term hindcast wave model run by the UK Met Office. The presentation discusses the differences in the underlying NWP models, and the impacts that these have on the surrogate wave models’ accuracy in both nowcasting and forecasting wave conditions at areas of interest for renewable energy developments. The results identify the importance in having a high quality, validated, NWP model for training such a system and the way in which the machine learning methods can propagate and exaggerate the underlying model uncertainties.

How to cite: Pillai, A., Ashton, I., Chen, J., and Steele, E.: Comparison of NWP Models Used in Training Surrogate Wave Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12355, https://doi.org/10.5194/egusphere-egu23-12355, 2023.

EGU23-12403 | ECS | Orals | ITS1.13/AS5.2

PseudoSpectralNet: A hybrid neural differential equation for atmosphere models 

Maximilian Gelbrecht and Niklas Boers

When predicting complex systems such as parts of the Earth system, one typically relies on differential equations which often can be incomplete, missing unknown influences or include errors through their discretization. To remedy those effects, we present PseudoSpectralNet (PSN): a hybrid model that incorporates both a knowledge-based part of an atmosphere model and a data-driven part, an artificial neural network (ANN). PSN is a neural differential equation (NDE): it defines the right-hand side of a differential equation, combining a physical model with ANNs and is able to train its parameters inside this NDE. Similar to the approach of many atmosphere models, part of the model is computed in the spherical harmonics domain, and other parts in the grid domain. The model consists of ANN layers in each domain, information about derivatives, and parameters such as the orography. We demonstrate the capabilities of PSN on the well-studied Marshall Molteni Quasigeostrophic Model.

How to cite: Gelbrecht, M. and Boers, N.: PseudoSpectralNet: A hybrid neural differential equation for atmosphere models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12403, https://doi.org/10.5194/egusphere-egu23-12403, 2023.

EGU23-12458 | ECS | Posters on site | ITS1.13/AS5.2

Training Deep Data Assimilation Networks on Sparse and Noisy Observations 

Vadim Zinchenko and David Greenberg

Data Assimilation (DA) is a challenging and expensive computational problem targetting hidden variables in high-dimensional spaces. 4DVar methods are widely used in weather forecasting to fit simulations to sparse observations by optimization over numerical model input. The complexity of this inverse problem and the sequential nature of common 4DVar approaches lead to long computation times with limited opportunity for parallelization. Here we propose using machine learning (ML) algorithms to replace the entire 4DVar optimization problem with a single forward pass through a neural network that maps from noisy and incomplete observations at multiple time points to a complete system state estimate at a single time point. We train the neural network using a loss function derived from the weak-constraint 4DVar objective, including terms incorporating errors in both model and data. In contrast to standard 4DVar approaches, our method amortizes the computational investment of training to avoid solving optimization problems for each assimilation window, and its non-sequential nature allows for easy parallelization along the time axis for both training and inference. In contrast to most previous ML-based data assimilation methods, our approach does not require access to complete, noise-free simulations for supervised learning or gradient-free approximations such as Ensemble Kalman filtering. To demonstrate the potential of our approach, we show a proof-of-concept on the chaotic Lorenz'96 system, using a novel "1.5D Unet" architecture combining 1D and 2D convolutions.

How to cite: Zinchenko, V. and Greenberg, D.: Training Deep Data Assimilation Networks on Sparse and Noisy Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12458, https://doi.org/10.5194/egusphere-egu23-12458, 2023.

EGU23-12566 | Posters on site | ITS1.13/AS5.2

Comparison of PM2.5 concentrations prediction model performance using Artificial Intelligence 

Kyung-Hui Wang, Chae-Yeon Lee, Ju-Yong Lee, Min-Woo Jung, Dong-Geon Kim, Seung-Hee Han, Dae-Ryun Choi, and Hui-young Yun

Since PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 µm) directly threatens public health, in order to take appropriate measures(prevention) in advance, the Korea Ministry of Environment(MOE) has been implementing PM10 forecast nationwide since February 2014. PM2.5 forecasts have been implemented nationwide since January 2015. The currently implemented PM forecast by the MOE subdivides the country into 19 regions, and forecasts the level of PM in 4 stages of “Good”, “Moderate”, “Unhealthy”, and “Very unhealthy”.

Currently PM air quality forecasting system operated by the MOE is based on a numerical forecast model along with a weather and emission model. Numerical forecasting model has fundamental limitations such as the uncertainty of input data such as emissions and meteorological data, and the numerical model itself. Recently, many studies on predicting PM using artificial intelligence such as DNN, RNN, LSTM, and CNN have been conducted to overcome the limitations of numerical models.

In this study, in order to improve the prediction performance of the numerical model, past observational data (air quality and meteorological data) and numerical forecasting model data (chemical transport model) are used as input data. The machine learning model consists of DNN and Seq2Seq, and predicts 3 days (D+0, D+1, D+2) using 6-hour and 1-hour average input data, respectively. The PM2.5 concentrations predicted by the machine learning model and the numerical model were compared with the PM2.5 measurements.

The machine learning models were trained for input data from 2015 to 2020, and their PM forecasting performance was tested for 2021. Compared to the numerical model, the machine learning model tended to increase ACC and be similar or lower to FAR and POD.

Time series trend was showed machine learning PM forecasting trend is more similar to PM measurements compared with numerical model. Especially, machine learning forecasting model can appropriately predict PM low and high concentrations that numerical model is used to overestimate.

Machine learning forecasting model with DNN and Seq2Seq can found improvement of PM forecasting performance compared with numerical forecasting model. However, the machine learning model has limitations that the model can not consider external inflow effects.

In order to overcome the drawback, the models should be updated and added some other machine learning module such as CNN with spatial features of PM concentrations.

 

Acknowledgements

This study was supported in part by the ‘Experts Training Graduate Program for Particulate Matter Management’ from the Ministry of Environment, Korea and by a grant from the National Institute of Environmental Research (NIER), funded by the Ministry of Environment (ME) of the Republic of Korea (NIER-2022-04-02-068).

 

How to cite: Wang, K.-H., Lee, C.-Y., Lee, J.-Y., Jung, M.-W., Kim, D.-G., Han, S.-H., Choi, D.-R., and Yun, H.: Comparison of PM2.5 concentrations prediction model performance using Artificial Intelligence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12566, https://doi.org/10.5194/egusphere-egu23-12566, 2023.

EGU23-13013 | ECS | Posters on site | ITS1.13/AS5.2

Using cGAN for cloud classification from RGB pictures 

Markus Rosenberger, Manfred Dorninger, and Martin Weißmann

Clouds of all kinds play a large role in many atmospheric processes including, e.g. radiation and moisture transport, and their type allows an insight into the dynamics going on in the atmosphere. Hence, the observation of clouds from Earth's surface has always been important to analyse the current weather and its evolution during the day. However, cloud observations by human observers are labour-intensive and hence also costy. In addition to this, cloud classifications done by human observers are always subjective to some extent. Finding an efficient method for automated observations would solve both problems. Although clouds have already been operationally observed using satellites for decades, observations from the surface shed a light on a different set of characteristics. Moreover, the WMO also defined their cloud classification standards according to visual cloud properties when observations are done at the Earth’s surface. Thus, in this work a utilization of machine learning methods to classify clouds from RGB pictures taken at the surface is proposed. Explicitly, a conditional Generative Adversarial Network (cGAN) is trained to discriminate between 30 different categories, 10 for each cloud level - low, medium and high; Besides showing robust results in different image classification problems, an additional advantage of using a GAN instead of a classical convolutional neural network is that its output can also artificially enhance the size of the training data set. This is especially useful if the number of available pictures is unevenly distributed among the different classes. Additional background observations like cloud cover and cloud base height can also be used to further improve the performance of the cGAN. Together with a cloud camera, a properly trained cGAN can observe and classify clouds with a high temporal resolution of the order of seconds, which can be used, e.g. for model verification or to efficiently monitor the current status of the weather as well as its short-time evolution. First results will also be presented.

How to cite: Rosenberger, M., Dorninger, M., and Weißmann, M.: Using cGAN for cloud classification from RGB pictures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13013, https://doi.org/10.5194/egusphere-egu23-13013, 2023.

EGU23-13143 | ECS | Posters on site | ITS1.13/AS5.2

Comparison of LSTM, GraphNN, and IrradPhyDNet based Approaches for High-resolution Solar Irradiance Nowcasting 

Petrina Papazek, Irene Schicker, and Pascal Gfähler

With fast parallel computing hardware, particularly GPUs, becoming more accessible in the geosciences the now efficiently running deep learning techniques are ready to handle larger amounts of recorded observation and satellite derived data and are able to learn complex structures across time-series. Thus, a suitable deep learning setup is able to generate highly-resolved weather forecasts in real-time and on demand. Forecasts of irradiance and radiation can be challenging in machine learning as they embrace a high degree of diurnal and seasonal variation.

Continuously extended PV/solar power production grows into one of our most important fossil-fuel free energy sources. Unlike the just recently emerging PV power observations, solar irradiance offers long time-series from automized weather station networks. Being directly linked to PV outputs, forecasting highly resolved solar irradiance from nowcasting to short-range plays a crucial role in decision support and managing PV.

In this study, we investigate the suitability of several deep learning techniques adopted and developed to a set of heterogeneous data sources on selected locations. We compare the forecast results to traditional – however computationally expensive - numerical weather prediction models (NWP) and rapid update cycle models. Relevant input features include 3D-fields from NWP models (e.g.: AROME), satellite data and products (e.g.: CAMS), radiation time series from remote sensing, and observation time time-series (site observations and close sites). The amount of time-series data can be extended by a synthetic data generator, a part of our deep learning framework. Our main models investigated includes a sequence-to-sequence LSTM (long-short-term-memory) model using a climatological background model or NWP for post-processing, a Graph NN model, and an analogs based deep learning method. Furthermore, a novel neural network model based on two other ideas, the IrradianceNet and the PhyDNet, was developed. IrradPhyDNet combines the skills of IrradianceNet and PhyDNet and showed improved performance in comparison to the original models.

Results obtained by the developed methods yield, in general, high forecast-skills. For selected case studies of extreme events (e.g. Saharan dust) all novel methods could outperform the traditional methods.  Different combinations of inputs and processing-steps are part of the analysis.

How to cite: Papazek, P., Schicker, I., and Gfähler, P.: Comparison of LSTM, GraphNN, and IrradPhyDNet based Approaches for High-resolution Solar Irradiance Nowcasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13143, https://doi.org/10.5194/egusphere-egu23-13143, 2023.

EGU23-13322 | ECS | Posters on site | ITS1.13/AS5.2

Nodal Ambient Noise Tomography and automatic picking of dispersion curves with convolutional neural network: case study at Vulcano-Lipari, Italy 

Douglas Stumpp, Elliot Amir Jiwani-Brown, Célia Barat, Matteo Lupi, Francisco Muñoz, Thomas Planes, and Geneviève Savard

The ambient noise tomography (ANT) method is widely adopted to reconstruct shear-wave velocity anomalies and to generate high-resolution images of the crust and upper-mantle. A critical step in this process is the extraction of surface-wave dispersion curves from cross-correlation functions of continuous ambient noise recordings, which is traditionally performed manually on the dispersion spectrograms through human-machine interfaces. Picking of dispersion curves is sometimes prone to bias due to human interpretation. Furthermore, it is a laborious and time-consuming task that needs to be resolved in an automatized manner, especially when dealing with dense seismic network of nodal geophones where the large amount of generated data severely hinders manual picking approaches. In the last decade, several studies successfully employed machine learning methods in Earth Sciences and across many seismological applications. Early studies have shown versatile and reliable solutions by treating dispersion curve extraction as a visual recognition problem. 

We review and adapt a specific machine learning approach, deep convolutional neural networks, for use on dispersion spectrograms generated with the usual frequency-time analysis (FTAN) processing on ambient noise cross-correlations. To train and calibrate the algorithm we use several available datasets acquired from previous experiments across different geological settings. The main dataset consists of records acquired with a dense local geophone network (150 short period stations sampling at 250 Hz) deployed for one month in October 2021. The dataset has been acquired during the volcanic unrest of the Vulcano-Lipari complex, Italy. The network also accounts for additional 17 permanent broadband stations (sampling at 100 Hz) maintained by the National Institute of Geophysics and Volcanology (INGV) in Italy. We evaluate the performance of the dispersion curves extraction algorithm. The automatically-picked dispersion curves will be used to construct a shear-wave velocity model of the Vulcano-Lipari magmatic plumbing system and the surrounding area of the Aeolian archipelago.

 

How to cite: Stumpp, D., Amir Jiwani-Brown, E., Barat, C., Lupi, M., Muñoz, F., Planes, T., and Savard, G.: Nodal Ambient Noise Tomography and automatic picking of dispersion curves with convolutional neural network: case study at Vulcano-Lipari, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13322, https://doi.org/10.5194/egusphere-egu23-13322, 2023.

EGU23-13367 | ECS | Posters on site | ITS1.13/AS5.2

Framework for creating daily semantic segmentation maps of classified eddies using SLA along-track altimetry data 

Eike Bolmer, Adili Abulaitijiang, Luciana Fenoglio-Marc, Jürgen Kusche, and Ribana Roscher

Mesoscale eddies are gyrating currents in the ocean and have horizontal scales from 10 km up to 100 km and above. They transport water mass, heat, and nutrients and therefore are of interest among others to marine biologists, oceanographers, and geodesists. Usually, gridded sea level anomaly maps, processed from several radar altimetry missions, are used to detect eddies. However, operational processors create multi-mission (processing level 4) SLA grid maps with an effective spatiotemporal resolution far lower than their grid spacing and temporal resolution. 

This drawback leads to erroneous eddy detection. We, therefore, investigate if the higher-resolution along-track data could be used instead to solve the problem of classifying the SLA observations into cyclonic, anticyclonic, or no eddies in a more accurate way than using processed SLA grid map products. With our framework, we aim to infer a daily two-dimensional segmentation map of classified eddies. Due to repeat cycles between 10 and 35 days and cross-track spacing of a few 10 km to a few 100 km, ocean eddies are clearly visible in altimeter observations but are typically covered only by a few ground tracks where the spatiotemporal context within the input data is highly variable each day. However conventional convolutional neural networks (CNNs) rely on data without varying gaps or jumps in time and space in order to use the intrinsic spatial or temporal context of the observations. Therefore, this is a challenge that needs to be addressed with a deep neural network that on the one hand utilizes the spatiotemporal context information within the modality of along-track data and on the other hand is able to output a two-dimensional segmentation map from data of varying sparsity. Our approach with our architecture Teddy is to use a transformer module to encode and process the spatiotemporal information along with the ground track's sea level anomaly data that produces a sparse feature map. This will then be fed into a sparsity invariant convolutional neural network in order to infer a two-dimensional segmentation map of classified eddies. Reference data that is used to train Teddy is produced by an open-source geometry-based approach (py-eddy-tracker [1]). 

The focus of this presentation is on how we implemented this approach in order to derive two-dimensional segmentation maps of classified eddies with our deep neural network architecture Teddy from along-track altimetry. We show results and limitations for the classification of eddies using only along-track SLA data from the multi-mission level 3 product of the Copernicus Marine Environment Monitoring Service (CMEMS) within the 2017 - 2019 period for the Gulf Stream region. We find that using our methodology, we can create two-dimensional maps of classified eddies from along-track data without using preprocessed SLA grid maps.

[1] Evan Mason, Ananda Pascual, and James C. McWilliams, “A new sea surface height–based code for oceanic mesoscale eddy tracking,” Journal of Atmospheric and Oceanic Technology, vol. 31, no. 5, pp. 1181–1188, 2014.

How to cite: Bolmer, E., Abulaitijiang, A., Fenoglio-Marc, L., Kusche, J., and Roscher, R.: Framework for creating daily semantic segmentation maps of classified eddies using SLA along-track altimetry data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13367, https://doi.org/10.5194/egusphere-egu23-13367, 2023.

EGU23-13771 | Orals | ITS1.13/AS5.2

Machine Learning Emulation of 3D Shortwave Radiative Transfer for Shallow Cumulus Cloud Fields 

Jui-Yuan Christine Chiu, Chen-Kuang Kevin Yang, Jake J. Gristey, Graham Feingold, and William I. Gustafson

Clouds play an important role in determining the Earth’s radiation budget. Despite their complex and three-dimensional (3D) structures, their interactions with radiation in models are often simplified to one-dimensional (1D), considering the time required to compute radiative transfer. Such a simplification ignores cloud Inhomogeneity and horizontal photon transport in radiative processes, which may be an acceptable approximation for low-resolution models, but can lead to significant errors and impact cloud evolution predictions in high-resolution simulations. Since model developments and operations are heading toward a higher resolution that is more susceptible to radiation errors, a fast and accurate 3D radiative transfer scheme becomes important and necessary. To address the need, we develop a machine-learning-based 3D radiative transfer emulator to provide surface radiation, shortwave fluxes at all layers, and heating rate profiles. The emulators are trained for highly heterogeneous shallow cumulus under different solar positions. We will discuss the performance of the emulators in accuracy and efficiency and discuss their potential applications.

How to cite: Chiu, J.-Y. C., Yang, C.-K. K., Gristey, J. J., Feingold, G., and Gustafson, W. I.: Machine Learning Emulation of 3D Shortwave Radiative Transfer for Shallow Cumulus Cloud Fields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13771, https://doi.org/10.5194/egusphere-egu23-13771, 2023.

EGU23-14051 | ECS | Posters on site | ITS1.13/AS5.2

Multi-modal data assimilation of sea surface currents from AIS data streams and satellite altimetry using 4DVARNet 

Simon Benaïchouche, Clément Le Goff, Brahim Boussidi, François Rousseau, and Ronan Fablet

Over the last decades, space oceanography missions, particularly altimeter missions, have greatly advanced our ability to observe sea surface dynamics. However, they still struggle to resolve spatial scales below ~ 100 km. On a global scale, sea surface current are derived from sea surface height by a geostrophical assumption. While future altimeter missions should improve the observation of sea surface height, the observation of sea surface current using altimetry techniques would remains indirect. In the other hands, recent works have considered the use of AIS (automated identification system) as a new mean to reconstruct sea surface current : AIS data streams provide an indirect observational models of total currents including ageostrophic phenomenas. In this work we consider the use of the supervised learning framework 4DVARNet, a supervised data driven approach that allow us to perform multi-modal experiments : We focus on an Observing System Simulation Experiment (OSSE) in a region of the Gulf-Stream and we show that the joint use of AIS and sea surface height (SSH) measurement could improve the reconstruction of sea surface current with respect to product derived solely from AIS or SSH observations in terms of physical and time scale resolved. 

How to cite: Benaïchouche, S., Le Goff, C., Boussidi, B., Rousseau, F., and Fablet, R.: Multi-modal data assimilation of sea surface currents from AIS data streams and satellite altimetry using 4DVARNet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14051, https://doi.org/10.5194/egusphere-egu23-14051, 2023.

EGU23-15183 | ECS | Orals | ITS1.13/AS5.2

Deep learning approximations of a CFD model for operational wind and turbulence forecasting 

Margrethe Kvale Loe and John Bjørnar Bremnes

The Norwegian Meteorological Institute has for many years applied a CFD model to downscale operational NWP forecasts to 100-200m spatial resolution for wind and turbulence forecasting for about 20 Norwegian airports. Due to high computational costs, however, the CFD model can only be run twice per day, each time producing a 12-hour forecast. An approximate approach requiring far less compute resources using deep learning has therefore been developed. In this, the relation between relevant NWP forecast variables at grids of 2.5 km spatial resolution and wind and turbulence from the CFD model has been approximated using neural networks with basic convolutional and dense layers. The deep learning models have been trained on approximately two year of the data separately for each airport. The results show that the models are to a large extent able to capture the characteristics of their corresponding CDF simulations, and the method is in due time intended to fully replace the current operational solution. 

How to cite: Loe, M. K. and Bremnes, J. B.: Deep learning approximations of a CFD model for operational wind and turbulence forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15183, https://doi.org/10.5194/egusphere-egu23-15183, 2023.

EGU23-15684 | ECS | Posters on site | ITS1.13/AS5.2

Semi-supervised feature-based learning for prediction of Mass Accumulation Rate of sediments 

Naveenkumar Parameswaran, Everardo Gonzalez, Ewa Bur­wicz-Ga­ler­ne, David Greenberg, Klaus Wallmann, and Malte Braack

Mass accumulation rates of sediments[g/cm2/yr] or sedimentation rates[cm/yr] on the seafloor are important to understand various benthic properties, like the rate of carbon sequestration in the seafloor and seafloor geomechanical stability. Several machine learning models, such as random forests, and k-Nearest Neighbours have been proposed for the prediction of geospatial data in marine geosciences, but face significant challenges such as the limited amount of labels for training purposes, skewed data distribution, a large number of features etc. Previous model predictions show deviation in the global sediment budget, a parameter used to determine a model's predicitve validity, revealing the lack of accurate representation of sedimentation rate by the state of the art models. 

Here we present a semi-supervised deep learning methodology to improve the prediction of sedimentation rates, making use of around 9x106  unlabelled data points. The semi-supervised neural network implementation has two parts: an unsupervised pretraining using an encoder-decoder network. The encoder with the optimized weights from the unsupervised training is then taken out and fitted with layers that lead to the target dimension. This network is then fine-tuned with 2782 labelled data points, which are observed sedimentation rates from peer-reviewed sources. The fine-tuned model then predicts the rate and quantity of sediment accumulating on the ocean floor, globally.

The developed semi-supervised neural network provide better predictions than supervised models trained only on labelled data. The predictions from the semi-supervised neural network are compared with that of the supervised neural network with and without dimensionality reduction(using Principle Component Analysis).

How to cite: Parameswaran, N., Gonzalez, E., Bur­wicz-Ga­ler­ne, E., Greenberg, D., Wallmann, K., and Braack, M.: Semi-supervised feature-based learning for prediction of Mass Accumulation Rate of sediments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15684, https://doi.org/10.5194/egusphere-egu23-15684, 2023.

EGU23-15756 | ECS | Posters on site | ITS1.13/AS5.2

Physiography improvements in numerical weather prediction digital twin engines 

Thomas Rieutord, Geoffrey Bessardon, and Emily Gleeson

The next generation of numerical weather prediction model (so-called digital twin engines) will reach hectometric scale, for which the existing physiography databases are insufficient. Our work leverages machine learning and open-access data to produce a more accurate and higher resolution physiography database. One component to improve is the land cover map. The reference data gathers multiple high-resolution thematic maps thanks to an agreement-based decision tree. The input data are taken from the Sentinel-2 satellite. Then, the land cover map generation is made with image segmentation. This work implements and compares several algorithms of different families to study their suitability to the land cover classification problem. The sensitivity to the data quality will also be studied. Compared to existing work, this work is innovative in the reference map construction (both leveraging existing maps and fit for end-user purpose) and the diversity of algorithms to produce our land cover map comparison.

How to cite: Rieutord, T., Bessardon, G., and Gleeson, E.: Physiography improvements in numerical weather prediction digital twin engines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15756, https://doi.org/10.5194/egusphere-egu23-15756, 2023.

EGU23-15892 | ECS | Posters on site | ITS1.13/AS5.2

Towards emulated Lagrangian particle dispersion model footprints for satellite observations 

Elena Fillola, Raul Santos-Rodriguez, and Matt Rigby

Lagrangian particle dispersion models (LPDMs) have been used extensively to calculate source-receptor relationships (“footprints”) for use in greenhouse gas (GHG) flux inversions. However, because a backward-running model simulation is required for each data point, LPDMs do not scale well to very large datasets, which makes them unsuitable for use in GHG inversions using high-resolution satellite instruments such as TROPOMI. In this work, we demonstrate how Machine Learning (ML) can be used to accelerate footprint production, by first presenting a proof-of-concept emulator for ground-based site observations, and then discussing work in progress to create an emulator suitable to satellite observations. In Fillola et al (2023), we presented a ML emulator for NAME, the Met Office’s LPDM, which outputs footprints for a small region around an observation point using purely meteorological variables as inputs. The footprint magnitude at each grid cell in the domain is modelled independently using gradient-boosted regression trees. The model is evaluated for seven sites, producing a footprint in 10ms, compared to around 10 minutes for the 3D simulator, and achieving R2 values between 0.6 and 0.8 for CH4 concentrations simulated at the sites when compared to the timeseries generated by NAME. Following on from this work, we demonstrate how this same emulator can be applied to satellite data to reproduce footprints immediately around any measurement point in the domain, evaluating this application with data for Brazil and North Africa and obtaining R2 values of around 0.5 for simulated CH4 concentrations. Furthermore, we propose new emulator architectures for LPDMs applied to satellite observations. These new architectures should tackle some of the weaknesses in the existing approach, for example, by propagating information more flexibly in space and time, potentially improving accuracy of the derived footprints and extending the prediction capabilities to bigger domains.

How to cite: Fillola, E., Santos-Rodriguez, R., and Rigby, M.: Towards emulated Lagrangian particle dispersion model footprints for satellite observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15892, https://doi.org/10.5194/egusphere-egu23-15892, 2023.

EGU23-15994 | ECS | Posters on site | ITS1.13/AS5.2

Uncertainty quantification in variational data assimilation with deep learning 

Nicolas Lafon, Philippe Naveau, and Ronan Fablet

The spatio-temporal reconstruction of a dynamical process from some observationaldata is at the core of a wide range of applications in geosciences. This is particularly true for weather forecasting, operational oceanography and climate studies. However, the re35 construction of a given dynamic and the prediction of future states must take into ac36 count the uncertainties that affect the system. Thus, the available observational measurements are only provided with a limited accuracy. Besides, the encoded physical equa38 tions that model the evolution of the system do not capture the full complexity of the real system. Finally, the numerical approximation generates a non-negligible error. For these reasons, it seems relevant to calculate a probability distribution of the state system rather than the most probable state. Using recent advances in machine learning techniques for inverse problems, we propose an algorithm that jointly learns a parametric distribution of the state, the dynamics governing the evolution of the parameters, and a solver. Experiments conducted on synthetic reference datasets, as well as on datasets describing environmental systems, validate our approach.

How to cite: Lafon, N., Naveau, P., and Fablet, R.: Uncertainty quantification in variational data assimilation with deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15994, https://doi.org/10.5194/egusphere-egu23-15994, 2023.

EGU23-16287 | ECS | Posters on site | ITS1.13/AS5.2

A machine learning emulator for forest carbon stocks and fluxes 

Carolina Natel de Moura, David Martin Belda, Peter Antoni, and Almut Arneth

Forests are a significant carbon sink of the total carbon dioxide (CO2) emitted by humans. Climate change is expected to impact forest systems, and their role in the terrestrial carbon cycle in several ways – for example, the fertilization effect of increased atmospheric CO2, and the lengthening of the growing season in northern temperate and boreal areas may increase forest productivity, while more frequent extreme climate events such as storms and windthrows or drought spells, as well as wildfires might reduce disturbances return period, hence increasing forest land loss and reduction of the carbon stored in the vegetation and soils. In addition, forest management in response to an increased demand for wood products and fuel can affect the carbon storage in ecosystems and wood products. State-of-the-art Dynamic Global Vegetation Models (DGVMs) simulate the forest responses to environmental and human processes, however running these models globally for many climate and management scenarios becomes challenging due to computational restraints. Integration of process-based models and machine learning methods through emulation allows us to speed up computationally expensive simulations. In this work, we explore the use of machine learning to surrogate the LPJ-GUESS DGVM. This emulator is spatially-aware to represent forests across the globe in a flexible spatial resolution, and consider past climate and forest management practices to account for legacy effects. The training data for the emulator is derived from dedicated runs of the DGVM sampled across four dimensions relevant to forest carbon and yield: atmospheric CO2 concentration, air Temperature, Precipitation, and forest Management (CTPM). The emulator can capture relevant forest responses to climate and management in a lightweight form, and will support the development of the coupled socio-economic/ecologic model of the land system, namely LandSyMM (landsymm.earth). Other relevant scientific applications include the analysis of optimal forestry protocols under climate change, and the forest potential in climate change mitigation.

 

How to cite: Natel de Moura, C., Belda, D. M., Antoni, P., and Arneth, A.: A machine learning emulator for forest carbon stocks and fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16287, https://doi.org/10.5194/egusphere-egu23-16287, 2023.

EGU23-16597 | Posters on site | ITS1.13/AS5.2 | Highlight

Global Decadal Sea Surface Height Forecast with Conformal Prediction 

Nils Lehmann, Jonathan Bamber, and Xiaoxiang Zhu

One of the many ways in which anthropogenic climate change impacts our planet is
rising sea levels. The rate of sea level rise (SLR) across the oceans is,
however, not uniform in space or time and is influenced by a complex interplay
of ocean dynamics, heat uptake, and surface forcing. As a consequence,
short-term (years to a decade) regional SLR patterns are difficult to model
using conventional deterministic approaches. For example, the latest climate
model projections (called CMIP6) show some agreement in the globally integrated
rate of SLR but poor agreement when it comes to spatially-resolved
patterns. However, such forecasts are valuable for adaptation planning in
coastal areas and for protecting low lying assets.
Rather than a deterministic modeling approach, here we explore the possibility
of exploiting the high quality satellite altimeter derived record of sea surface
height variations, which cover the global oceans outside of ice-infested waters
over a period of 30 years. Alongside this rich and unique satellite record,
several data-driven models have shown tremendous potential for various
applications in Earth System science. We explore several data-driven deep
learning approaches for sea surface height forecasts over multi-annual to
decadal time frames. A limitation of some machine learning approaches is the
lack of any kind of uncertainty quantification, which is problematic for
applications where actionable evidence is sought. As a consequence, we equip
our models with a rigorous measure of uncertainty, namely conformal prediction which
is a model and dataset agnostic method that provides calibrated predictive
uncertainty with proven coverage guarantees. Based on a 30-year satellite
altimetry record and auxiliary climate forcing data from reanalysis such as
ERA5, we demonstrate that our methodology is a viable and attractive alternative
for decadal sea surface height forecasts.

How to cite: Lehmann, N., Bamber, J., and Zhu, X.: Global Decadal Sea Surface Height Forecast with Conformal Prediction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16597, https://doi.org/10.5194/egusphere-egu23-16597, 2023.

EGU23-16936 | ECS | Orals | ITS1.13/AS5.2

Analysis of marine heat waves using machine learning 

Said Ouala, Bertrand Chapron, Fabrice Collard, Lucile Gaultier, and Ronan Fablet

Sea surface temperature (SST) is a critical parameter in the global climate system and plays a vital role in many marine processes, including ocean circulation, evaporation, and the exchange of heat and moisture between the ocean and atmosphere. As such, understanding the variability of SST is important for a range of applications, including weather and climate prediction, ocean circulation modeling, and marine resource management.

The dynamics of SST is the compound of multiple degrees of freedom that interact across a continuum of Spatio-temporal scales. A first-order approximation of such a system was initially introduced by Hasselmann. In his pioneering work, Hasselmann (1976) discussed the interest in using a two-scale stochastic model to represent the interactions between slow and fast variables of the global ocean, climate, and atmosphere system. In this paper, we examine the potential of machine learning techniques to derive relevant dynamical models of Sea Surface Temperature Anomaly (SSTA) data in the Mediterranean Sea. We focus on the seasonal modulation of the SSTA and aim to understand the factors that influence the temporal variability of SSTA extremes. Our analysis shows that the variability of the SSTA can indeed well be decomposed into slow and fast components. The dynamics of the slow variables are associated with the seasonal cycle, while the dynamics of the fast variables are linked to the SSTA response to rapid underlying processes such as the local wind variability. Based on these observations, we approximate the probability density function of the SSTA data using a stochastic differential equation parameterized by a neural network. In this model, the drift function represents the seasonal cycle and the diffusion function represents the envelope of the fast SSTA response.

 

How to cite: Ouala, S., Chapron, B., Collard, F., Gaultier, L., and Fablet, R.: Analysis of marine heat waves using machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16936, https://doi.org/10.5194/egusphere-egu23-16936, 2023.

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