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.