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SM – Seismology

EGU24-9250 | Orals | MAL30-SM | Beno Gutenberg Medal Lecture

Seismic images of the continental lithosphere 

Jaroslava Plomerová

Seismic waves propagating through the Earth sample its structure, carry information about its fabrics and physical characteristics and record its present-day state and evolution. In the past, several velocity discontinuities within the radial Earth, which separate its fundamental regions, were retrieved. The lower mantle-core boundary was named as Gutenberg discontinuity in recognition of the Gutenberg’s discovery of the Earth’s core in 1913. This discontinuity relates to the abrupt decrease in P-velocity and diminishing of S-waves in the liquid core. In present-day terminology, the Gutenberg discontinuity is associated with the bottom of the D’’ layer. An area of low velocities in the Earth’s upper mantle denoted as G-discontinuity, has related to Gutenberg’s name until now. The low velocity zone exists just below the oceanic lithosphere, and its characteristics are often used globally in studies of lithosphere thickness in the view of modern plate tectonics. Gutenberg’s Seismicity of the Earth (1941) became a major influence in later scientists’ efforts to describe the theory of plate tectonics. The accuracy and validity of the Earth models depend on data quality and coverage, i.e., earthquake foci - seismic station ray distribution within the Earth volume studied. Small-sized to large-scale international passive seismic experiments, operated during several recent decades, recorded an unprecedented huge amount of high-quality data, which along with new techniques and computational facilities represent a big step forward in our knowledge of the Earth’s structure. However, many questions still remain unanswered and require further research. Current close international cooperation among seismologists involved in the experiments follow the spirit of Beno Gutenberg’s action as a driving force behind the acceptance of seismology as an international science of earthquake detection and the Earth studies.

We present models of the European lithosphere derived from the propagation of body waves, shear-wave splitting and radial and azimuthal anisotropy of surface waves, including ambient noise. Data for individual studies has been collected from international seismological databases (ISC, EIDA) and from several passive experiments we have organized or participated in. Initial isotropic models are upgraded into anisotropic ones, following the fundamental condition that seismic anisotropy is a 3D phenomenon and thus it has to be evaluated in 3D to get more realistic images of the Earth. We invert/interpret jointly anisotropic parameters of independent observables (directional variations of P-wave travel times, shear-wave splitting parameters) which leads to 3D self-consistent anisotropic models of the continental lithosphere with tilted symmetry axes and characteristic domain-like structure. The individual domains at size from several tenths to several hundreds of kilometers are often sharply bounded and of different thicknesses. We interpret the often sharply bounded domains with systematically oriented dipping fabrics in the continental mantle lithosphere by successive subductions of ancient oceanic plates and their accretions enlarging primordial continent cores. Consequent continental break-ups and assemblages of wandering micro-plates preserve fossil anisotropic fabrics and create patchwork structures of the present-day continents. Supporting arguments for such model exist in petrological and geochemical studies (Babuska and Plomerova, 2020).

How to cite: Plomerová, J.: Seismic images of the continental lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9250, https://doi.org/10.5194/egusphere-egu24-9250, 2024.

EGU24-14636 | Orals | MAL30-SM | SM Division Outstanding ECS Award Lecture

Uncovering the tectonic secrets of the Atlantic with broadband ocean-bottom seismology 

Stephen P. Hicks

80% of earthquakes occur underwater, so ocean-bottom seismometers (OBS) are crucial for improving our understanding of earthquake source mechanics along unexplored offshore faults, and fillling key gaps in our images of the deeper solid Earth. Even for ocean islands and island arcs, land stations alone struggle to image underlying structures. Broadband OBSs have been through many design iterations, but many OBS deployments now yield high data recovery rates (>90%). 

Even though my first OBS deployment experience left me feeling seasick, I have since continued to seismically explore the oceans, taking part in several OBS projects. In this talk, I will focus on my recent results from experiments across the Atlantic Ocean. Compared to the faster-spreading and subducting Pacific lithosphere, the less well-studied Atlantic offers a key endmember for refining our knowledge of global tectonics and associated hazards.

In the Lesser Antilles subduction zone, subducting Atlantic lithosphere is heterogeneously hydrated. Local earthquakes recorded by OBSs (VoiLA experiment), allowed me to image seismic attenuation to map fluid and melt pathways through the slab and mantle wedge, showing how slab fluids precondition melt generation and volcanism in arc settings. In the mid-Atlantic, long transform faults can host large M~7 earthquakes in ultra-wide (20-30 km thick) fault zones, allowing a uniquely macro-scale view of how damage zones control seismogenesis. In 2017, OBSs (PI-LAB experiment) recorded a nearby Mw 7.1 earthquake on the Romanche transform fault, triggering detailed teleseismic analysis that show back-propagating rupture fronts, which have since been seen during the 2023 M7.8 Türkiye earthquake. More recently, I analysed a seismic swarm and dyke intrusion in the Azores, which lies on a diffuse transtensional plate boundary. Here, a temporary OBS network (UPFLOW project) installed around the uniquely narrow island of São Jorge yields high-resolution seismicity locations that shed light on magma inflow and drainage along pre-existing faults.

Overall, OBS experiments yield fascinating results, but these results come from vast team efforts, particularly from ship crews and OBS technicians, that often go uncredited. We need to work harder to ensure the long-term sustainability of data from these expensive, often publicly-funded projects, with OBS-specific data preprocessing complications a partial barrier to this.

How to cite: Hicks, S. P.: Uncovering the tectonic secrets of the Atlantic with broadband ocean-bottom seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14636, https://doi.org/10.5194/egusphere-egu24-14636, 2024.

SM1 – General Seismology

EGU24-169 | Posters on site | SM1.1

Dealing with uncertainties related to ground motion prediction models for Georgia, Caucasus Region. 

Nato Jorjiashvili, Ia Shengelia, Tea Godoladze, Irakli Gunia, and Dimitri Akubardia

Georgia is situated in the Caucasus region, which is one of the most seismically active regions in the Alpine-Himalayan collision belt. Analysis of the historical and instrumental seismology of this region shows that it is still of moderate seismicity. The seismicity of the area reflects the general tectonics of the region.

Recently, number of seismic stations and earthquake records in Georgia significantly increased. Thus, we can run more detailed studies regarding ground motion prediction. 

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. In this study ground motion prediction equations are obtained by classical, statistical way, regression analysis. Also, new data and new features such as local soil conditions, fault types, etc. were considered for analysis. In the study models are obtained for PGA (horizontal and vertical), 5%-damped pseudo-absolute-acceleration spectra (SA) are described for periods between 0.01 s and 10 s (for both vertical and horizontal components).

Next stage was to assess the standard deviation and its minimization. Fuzzy Analysis gives a possibility of making optimal decision when available data is insufficient and cannot represent real situation. In our case it is quite difficult to explain all physical processes related to earthquakes. However, it is very important to consider all processes during the hazard assessment. Also, during GMPE assessment it is very difficult to consider site effect very precisely because available data is still insufficient. In this case usage of Fuzzy Analysis is the best solution. We constructed membership functions based on shear wave velocity measurements for each site class. Site classifications were done according to Eurocode8. At the end a significant reduction of uncertainties (~30-40%) was observed.

How to cite: Jorjiashvili, N., Shengelia, I., Godoladze, T., Gunia, I., and Akubardia, D.: Dealing with uncertainties related to ground motion prediction models for Georgia, Caucasus Region., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-169, https://doi.org/10.5194/egusphere-egu24-169, 2024.

For decades, the seismological community has debated the scaling relationships of earthquake sources. The debate centers around whether the scaled energy (ER/M0) remains uniform across all magnitudes, indicating self-similarity, or if there is an increase in scaled energy with seismic moment, M0. To contribute to this discussion, we analyzed coda derived source displacement spectra of 303 local earthquakes that occurred in and around the segments of the North Anatolian Fault Zone (NAFZ) within the Sea of Marmara. Our database includes digital waveform recordings of the events that were occurred between 2018 and 2020 (2.5≤ ML ≤5.7 within a radius of 200 km) and were recorded at 49 seismic stations operated by the Kandilli Observatory and Earthquake Research Institute (KOERI) in the study area. We employed a joint inversion technique to optimize source-, path-, and site-specific factors simultaneously. This was achieved by comparing the observed coda envelope with its physically derived representative synthetic coda envelope based on Radiative Transfer Theory. Our inversion process, conducted across various frequency bands, enabled us to make reliable coda-based seismic moment (M0) and moment magnitude estimates (Mw-coda) consistent with local catalogue magnitudes. The variation of the scaled energy (ER/M0) calculated from the total seismic radiated energy (ER) using coda-derived source displacement spectra for each event tends to increase with seismic moment across most magnitude ranges. This indicates that the crustal earthquakes with Mw-coda 2.5 and Mw-coda 5.7 in this laterally heterogeneous region are likely to follow non-self-similarity. Our findings imply different rupture dynamics working for large earthquakes than small ones and relatively more efficient seismic energy radiation for larger earthquakes along the northwestern part of the NAFZ.

How to cite: Özkan, B., Eken, T., Gaebler, P., and Taymaz, T.: Implications for Non-Self Similar Energy and Moment Scaling of Small-to-Moderate Earthquakes Along the NAFZ: Source Displacement Spectra Derived from Coda Waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-749, https://doi.org/10.5194/egusphere-egu24-749, 2024.

EGU24-1310 | Orals | SM1.1

The seismic source parameters of the South Hangay Fault System in Central Mongolia 

Mungunsuren Dashdondog, Odonbaatar Chimed, Anne Meltzer, and Ankhtsetsteg Dorjsuren

The purpose of the study is to describe a geodynamic process in the study area using its focal mechanism and stress field inversion to characterize precise events along the study area, the rupture zones of the South Hangay Fault System (SHFS). This fault system was activated by four earthquakes which are occurred along the Bayanbulag fault (2012/10/03, Mw=4.7) and Bayankhongor fault (2013/01/05, Mw=4.2, & Mw=4.2; 2013/11/25, Mw=3.9). These earthquakes are the strongest in the fault zone.

From the Mongolian National Data Center's database, it has chosen 2228 occurrences (0.1ML5.4) from the Handay Experiments, which used 72 broadband seismometers to cover Hangay Dome. Using HypoDD with a double-difference technique, its seismic station density provides us with precise hypocenter location along the fault system. Among these events, 47 focal mechanism solutions were determined using the first-motion polarity of the P wave from the experimental seismic networks of Mongolia. Then, we classified the determined focal mechanism parameters. According to classification, three main cluster zones are related to the Bayanbulag (BB), Bayankhongor North (BHN), and Bayankhonor South (BHS) fault zones along the rupture area of the South Hangay Fault System. 

Furthermore, we determined the stress fields, stress regime, and the horizontal maximum (SHmax), and minimum (Shmin) stress orientations for all three zones.  

We concluded that the whole SHFS is a left-lateral strike-slip fault with normal and reverse components, NE-SW shortening, and corresponding NW-SE extension. Its compression orientation in the NE-SW direction is the same as the azimuth direction of the India-Asia collision.

We hope that this stress inversion results can be a useful tool for geodynamic and seismotectonic analysis of this part of Mongolia and it will give a better understanding of different stress regimes.

How to cite: Dashdondog, M., Chimed, O., Meltzer, A., and Dorjsuren, A.: The seismic source parameters of the South Hangay Fault System in Central Mongolia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1310, https://doi.org/10.5194/egusphere-egu24-1310, 2024.

EGU24-1533 | ECS | Orals | SM1.1

Earthquake source characterization in stable continental regions: Application to the Armorican Massif, France 

Marion Alloncle, Antoine Mocquet, and Mickaël Bonnin

The seismic moment M0, the associated moment magnitude Mw, and the corner frequency fc are essential parameters for earthquake studies and seismic risk management. In the context of stable continental regions (SCRs), remote from active plate boundaries, the assessment of these parameters is made difficult by the low energy release associated with each earthquake and the low density of seismological networks.

In the north west of France, the Armorican Massif and its surroundings are part of a SCR, where the densification of the seismological network, completed in 2019, now allows for a reassessment of the regional seismicity. Though characterized by very small strain rates, the region currently displays a high rate of low-to-moderate earthquakes (up to a few Mw lower or equal to 4.0 – 5.0). For such small earthquakes, these assessments are particularly sensitive to the signal-to-noise ratio, to the seismic structure of the region, to its attenuation properties, and to the azimuthal distribution of the regional network with respect to the focal mechanisms.

We attempt to determine the M0, and the fc, of 106 earthquakes, detected in northwestern France between 2015 and 2023, with local magnitudes ML ranging from 2.0 to 5.3, using spectral methods. We obtained a linear relationship between ML and Mw for Mw ranging from 1.5 to 5.0. Our analysis also highlighted the importance of the frequency dependence of attenuation on the assessment of the fc. This study will show the relation between M0 and fc in the region.

How to cite: Alloncle, M., Mocquet, A., and Bonnin, M.: Earthquake source characterization in stable continental regions: Application to the Armorican Massif, France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1533, https://doi.org/10.5194/egusphere-egu24-1533, 2024.

EGU24-1985 | Orals | SM1.1

ProbShakemap: a Python toolbox for urgent earthquake source uncertainty quantification 

Angela Stallone, Jacopo Selva, Louise Cordrie, Licia Faenza, and Alberto Michelini

Seismic urgent computing aims at assessing the potential impact of earthquakes through rapid simulation-based ground-shaking forecasts. However, uncertainty quantification remains a significant challenge in this domain.

While current practice accounts for the uncertainty arising from Ground Motion Models (GMMs), it neglects the uncertainty about the source model, which is only known approximately in the first minutes after an earthquake. Addressing this issue involves propagating earthquake source uncertainty from a multi-scenarios ensemble that captures source variability to ground motion predictions. In principle, this could be accomplished with 3D modelling of seismic wave propagation for multiple earthquake sources. However, full ensemble simulation is unfeasible under emergency conditions with strict time constraints.

Here we present ProbShakemap, a Python toolbox which generates multi-scenario ensembles and delivers ensemble-based forecasts for urgent source uncertainty quantification. It implements GMMs to efficiently propagate source uncertainty from the ensemble of scenarios to ground motion predictions at a set of points, while also accounting for model uncertainty (by accommodating multiple GMMs, if available) along with their intrinsic uncertainty. Notably, ProbShakemap does not rely on any recorded data, and only requires the following event-specific information: latitude, longitude, magnitude and time. ProbShakemap incorporates functionalities from two open-source toolboxes routinely implemented in seismic hazard and risk analyses: the USGS ShakeMap software and the OpenQuake-engine.

We quantitatively test ProbShakemap against past earthquakes, illustrating its capability to rapidly quantify earthquake source uncertainty.

How to cite: Stallone, A., Selva, J., Cordrie, L., Faenza, L., and Michelini, A.: ProbShakemap: a Python toolbox for urgent earthquake source uncertainty quantification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1985, https://doi.org/10.5194/egusphere-egu24-1985, 2024.

EGU24-2254 | Posters on site | SM1.1

Qc, Qp, Qs, Qi, and Qsc attenuation parameters in the southern part of Georgia 

Ia Shengelia, Nato Jorjiashvili, Tea Godoladze, and Albert Buzaladze

Georgia is located in the Caucasus between The black and the Caspian seas and is surrounded by the Greater and Lesser Caucasus. Among the seismic areas of Georgia, the volcanic upland of Javakheti situated in the south of Georgia is notable for its high level of seismicity where three large earthquakes with M6 occurred in the last century. The main goal of the study is to investigate the attenuation properties of the lithosphere in the region using a hundred and twenty local earthquakes in 2008-2020  recorded at five seismic stations equipped with broadband Guralp CMG40T and Trillium 40  seismometers. Earthquake magnitudes varied from 1.5 to 4.1; epicentral distances and depth were smaller than 60 km and 19 km, respectively. The quality factors of coda waves Qcand direct P, S waves Qp,and Qs have been estimated using the single back-scattering model and the extended coda normalization methods, respectively. Wennerberg’s approach has been used to estimate intrinsic Qi and scattering Qs attenuation parameters. The Q values were fitted to a  power-law, of form Q(f)= Q0 (f)n, where Q0 is the quality factor at 1Hz and n is the frequency relation parameter, which depends on the heterogeneity of the medium. The obtained values of Qc, Qp, Qs, Qi, andQsc show the frequency-dependent character in the frequency range of 1.5-24 Hz and are expressed as:

Qc = (47.6±3.8)(1.034±0.048)Qp = (17.4±2.3)𝑓(1.100±0.033), Qs = (28.8±3.3)𝑓(1.048±0.039)

Qi = (62 ± 4) f (0.969±0.052),  Qsc = (177 ± 6) f (0.932±0.051)

The calculated attenuation parameters characterize the entire earth's crust under the Javakheti plateau and the surrounding area. The observed Qc and Qi values are almost identical at different central frequencies and both of them are less than Qsc. This means that the effect of intrinsic attenuation is dominated by scattering attenuation. Comparison of our results for similar lapse times to those obtained in other tectonic and seismic active regions show that the Q values and their frequency-dependent relationships are in an interval of values of tectonically active and highly heterogeneous regions. The results obtained will be useful for source parameter estimation, ground motion prediction, and hazard assessment of the study regions.

How to cite: Shengelia, I., Jorjiashvili, N., Godoladze, T., and Buzaladze, A.: Qc, Qp, Qs, Qi, and Qsc attenuation parameters in the southern part of Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2254, https://doi.org/10.5194/egusphere-egu24-2254, 2024.

Through the utilization of P-Alert network data from Taiwan, this study endeavors to estimate earthquake magnitude (Mcaa) using the cumulative absolute absement (CAA) methodology across varying window lengths after the arrival of P-wave. It is differentiated that even the proximity of the nearest 12 stations to the epicenter results in robust magnitude estimations. Notably, the standard deviation between the estimated Mcaa and the moment magnitude (Mw) using 12 stations decreases with the increase in window length and is found minimum for 5s window length. For 3s window the variation between Mcaa and Mw is found ±0.385, whereas, for 5s window it is ±0.313. Consequently, the estimation of Mcaa remains reliable. The magnitude Mpd is alternatively deduced from Pd, utilizing the closest 12 stations situated near the epicenter. The standard deviation of the order of ±0.412 is observed between the estimated Mpd and Mw for 3s window, whereas for 5s window it is ±0.281. A difference is observed using Mpdand Mcaafor comparison with Mw. The standard deviation error decreases for Mcaaand Mpd with increase in window length. While Mpd performs better under a 5s window scenario, it tends to underestimate the magnitude of an earthquake with a magnitude of Mw 7.0. On the other hand, CAA surpasses Pd in magnitude estimation, though with a slightly higher standard deviation compared to Mcaa. As a result, Mcaa is considered a more reliable magnitude indicator.

How to cite: Wu, Y.-M.: Cumulative absolute absement for magnitude determination in earthquake early warning system using low-cost sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2969, https://doi.org/10.5194/egusphere-egu24-2969, 2024.

EGU24-3321 | ECS | Posters on site | SM1.1

Imaging of Crust and Lithospheric Mantle of the Incipient Okavango Rift Zone: Implications on the Rifting Mechanism 

Tuo Wang, Ling Chen, Stephen S. Gao, Kelly H. Liu, Youqiang Yu, Zhichao Yu, and Xu Wang

The Holocene Okavango Rift Zone (ORZ) marks the southern terminus of the Western Branch of the East African Rift System. Detailed knowledge of the crustal and lithospheric mantle structure of the ORZ is essential to decipher the rifting mechanism and nature of the lithosphere of this incipient continental rift. A 3-D shear wave velocity model from the surface to 160-km depth is constructed by jointly inverting the Rayleigh wave phase velocity dispersion and receiver function data through a non-linear Bayesian Monte-Carlo algorism. The crustal thickness estimates from our new velocity model generally agree with previous receiver function investigations of the region. The crust beneath the ORZ is thinned compared with the cratonic regions to both sides of the rift, suggesting a certain degree of continental stretching. Our velocity model also reveals two low velocity anomalies in the crust and upper mantle beneath the incipient rift, respectively. The shallow low velocity anomaly is mainly confined in the upper and middle crust, and the deeper low velocity anomaly extends from the Moho to at least 160 km depth, with a high-velocity lower crust (~4.0 km/s) in between. Although the two low velocity anomalies are probably both caused by rift-related decompression melting, the structural feature imaged suggests that they are generated separately and individually. Based on our observations, we propose that thermal upwelling and decompression partial melting in the upper mantle of the ORZ have a limited contribution to the stretching and thinning of the crust during the initiation of the continental rifting. The crustal rifting could be induced by an intra-plate relative motion between the South African block and the rest of the African continent along a pre-existing weak zone.

How to cite: Wang, T., Chen, L., Gao, S. S., Liu, K. H., Yu, Y., Yu, Z., and Wang, X.: Imaging of Crust and Lithospheric Mantle of the Incipient Okavango Rift Zone: Implications on the Rifting Mechanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3321, https://doi.org/10.5194/egusphere-egu24-3321, 2024.

EGU24-4004 | ECS | Orals | SM1.1

Full-waveform tomography for the lithospheric structure of southern Tibetan Plateau 

Qiwen Zhu, Nobuaki Fuji, and Li Zhao

The collision of the Indian and Eurasian plates has resulted in high-altitude Tibetan Plateau with active seismicity. In this study, we apply the seismic box tomography to the southern Tibetan Plateau, aiming to obtain a self-consistent and high-resolution (10−20 km) model of the crust and upper mantle beneath the region, including density as well as bulk and shear moduli without a priori constraints, which provides us with crucial constraints on the compositional and thermal structures of a highly deformed lithosphere in southern Tibetan Plateau.

In order to obtain the seismic tomographic model, we perform full-waveform inversion of teleseismic (30°−90°) surface- and body-wave waveforms recorded by the Hi-CLIMB network, a densely distributed (5−10 km station spacing) N-S oriented linear seismic array deployed during 2002 and 2005. In our iterative hierarchical inversion workflow, we calculate the sensitivity kernels based on the adjoint method and the model is updated by the L-BFGS algorithm. Data covariance matrices are introduced to control the data quality and objective weighting functions for different seismic events. We will present our preliminary results of the on-going study with comparison to existing models.

How to cite: Zhu, Q., Fuji, N., and Zhao, L.: Full-waveform tomography for the lithospheric structure of southern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4004, https://doi.org/10.5194/egusphere-egu24-4004, 2024.

EGU24-4895 | Orals | SM1.1

Dynamic responses of a building derived from microtremor and seismic signals 

Ruey-Juin Rau, Cheng-Feng Wu, Ying-Chi Chen, Hung-Yu Wu, and Chin-Jen Lin

We used the liquid-based R2 rotational seismometer in addition to several arrays of translation velocity seismometers on a 12-floor building in the National Cheng Kung University campus to evaluate the dynamic responses of the structure. During the observation period in August-October 2023, we encountered a moderate M 5.6 earthquake sequence 61 km north of the campus and one moderate typhoon passing through this 49-m-long and 12-m-wide building. By examining these data, we investigate the natural frequency and the rotation behavior of the long-strip-shaped building. Both the time-frequency and Fast Fourier Transform analyses of the microtremor and earthquake data show two dominant frequencies of ~1.2 Hz and 1.8 Hz occurred in the horizontal directions. The translation velocity and rotation rate are more significant in the transverse, short-axis direction and at the location away from the elevator of the building. The translation velocity array and rotational seismometer show rotations around the horizontal and vertical axes during the M 5.6 earthquake. The results of two natural frequencies and the corresponding rotational motions are most likely related to the asymmetric design of the building, which resulted in the non-rigid behavior of the structure. These findings may provide insights into improvements that could enhance the building’s resilience to seismic or typhoon events.

How to cite: Rau, R.-J., Wu, C.-F., Chen, Y.-C., Wu, H.-Y., and Lin, C.-J.: Dynamic responses of a building derived from microtremor and seismic signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4895, https://doi.org/10.5194/egusphere-egu24-4895, 2024.

In the continuation of the work carried out over the period 1962-2009 as part of the SI-Hex project, work is on going to revise the seismic catalog of mainland France from 2010 to 2018. This time period is characterized by both an upgrade of short-period stations with broadband stations and a major deployment of new broadband stations as part of the Résif-Epos research infrastructure (now called Epos-France), significantly increasing the amount of detected and processed events.

This catalog will benefit from our advances in the use of new artificial intelligence tools, such as PhaseNet, a deep learning automatic picking method, as well as in the development of a deep learning method for discrimination between earthquakes, quarry blasts and explosions.

This catalog will be built from those of the national observation service BCSF-Renass, CEA/LDG and regional seismological observatories (Isterre, OCA, OMP). The earthquake picks from these catalogs will be supplemented by those automatically obtained by deep learning on all the waveforms from the Epos-France (formerly Résif-Epos) stations daily used by BCSF-Renass (as part of its mission to monitor seismicity in mainland France) including stations from neighboring countries (GB, LU, BE, DE, CH, IT, ES), as well as those from temporary network stations (AlpArray, CifAlps2). 

The process workflow includes several steps. The first one consists in a clustering of picks close in time to reduce the amount of picks to process; duplicated picks are removed and priority is given to the manual ones. The second step is the association of seismic phases to create events, by combining the HDBSCAN algorithm - to merge picks close in time and space - with the PyOcto one - to discard picks that did not follow typical travel-time curves. The third step consists in event location using NonLinLoc algorithm with several regional models chosen based on the prior location obtained from PyOcto. At the last step, a moment magnitude Mw is computed (when possible) from waveform spectral fitting using a modified version of SourceSpec. To compute robust magnitudes in particular for low magnitude events, we include magnitude station corrections computed from statistics on magnitude differences between event and stations. Finally, events information (ie. origins, magnitudes) coming from the various catalogs are integrated into the multi-origin catalog according to the QuakeML standard, with the preferred location being the new one computed on the third step.

This catalog currently under revision will represent an update of seismicity in France over the period 2010-2018. Preliminary results show that it will incorporate a significantly increased number of low-magnitude events, detected thanks to the inclusion of picks from artificial intelligence tools. Event labeling is consolidated using our deep learning discrimination algorithm, and a Mw magnitude is calculated for each event using waveforms.

How to cite: Grunberg, M. and Lambotte, S.: A new workflow for revising the seismicity catalog for mainland France, covering the period 2010-2018, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5100, https://doi.org/10.5194/egusphere-egu24-5100, 2024.

EGU24-5890 | Posters on site | SM1.1

On the temporal variations of near-surface seismic structure of Taiwan and its geological inferences 

Hui-Chu Chen, Yuancheng Gung, Hsin-Yu Lee, and Li-Wei Chen

We report on the temporal variations of the near-surface (< 500 m) seismic structure (Vp, Vs, and Vs anisotropy) of Taiwan using the empirical Green’s functions of body waves between vertical station pairs at 60 borehole sites. In our previous work, the obtained near-surface anisotropy are categorized into stress-aligned anisotropy (SAA) and orogeny parallel anisotropy (OPA). Since all the major geological units of Taiwan are well sampled by borehole arrays, and drilling data for 52 sites are available, we were able to find that OPA is typically stronger than SAA, SAA strength is generally higher in sedimentary rocks, igneous rocks, and gravel sediments compared to fine-grained sediments, and OPA is more pronounced in foliated metamorphic rocks than in dipping sedimentary strata. In this study, we aim to address the following specific questions with the obtained results: (1) How do the temporal variations of near-surface seismic properties in different geological units of Taiwan correlate with seismic activity or nearby earthquake events? (2) Are there distinct patterns in the temporal variations of anisotropy strength based on the specific geological composition? (3) Do sites characterized by OPA exhibit different temporal variations in response to seismic activity compared to sites dominated by SAA?

How to cite: Chen, H.-C., Gung, Y., Lee, H.-Y., and Chen, L.-W.: On the temporal variations of near-surface seismic structure of Taiwan and its geological inferences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5890, https://doi.org/10.5194/egusphere-egu24-5890, 2024.

EGU24-7189 | ECS | Posters on site | SM1.1

Observation of intraplate repeating earthquakes within the fault zone of the 2008 ML 3.6 earthquake 

Seula Jung, Dong-Hoon Sheen, Chang-Soo Cho, and Kwangsu Kim

The repeating earthquake (RE) ruptures a single fault patch repeatedly and generates highly similar waveforms. The RE is often observed in the area of subduction zones (Uchida and Matsuzawa, 2013; Yu et al., 2013; Uchida, 2019). However, even in the intraplate region, the RE has been found in the ruptured fault zones (Li et al., 2007; Li et al., 2011; Bisrat et al., 2012). We searched for REs around the epicenter of the 2008 ML 3.6 Gyerong earthquake that occurred in Mount Gyeryong, the Korean Peninsula, located in a stable intraplate region. In the study area, 48 earthquakes (ML 0.4–3.6) were reported during 2002–2022, while we found 50 earthquakes during 2018–2022 using a template matching. We located the events based on the Hypoellipse (Lahr, 1999), and also refined the hypocenters using the double difference method (hypoDD; Waldhauser and Ellsworth, 2000) to obtain the high-resolution fault geometry. It is found that the epicenters exhibit a linear alignment of the fault striking along WNW-ESE consistent with one of the strikes of the ML 3.6 event which has a strike-slip focal mechanism with a strike of 108° or 198°, a dip of 83° or 88°, and a rake of -2° or -173°, which indicates that the ML 3.6 earthquake occurred with a left-lateral fault slip. We estimated the rupture directivity of the ML 3.6 event from the apparent source time functions obtained by the empirical Green’s function approach. A vast number of microearthquakes including aftershocks of the ML 3.6 event occurred in the rupture direction (i.e. the east-southeast of the epicenter of the ML 3.6 event). We identified REs based on the waveform similarity (cross-correlation coefficient > 0.95) and their locations (co-location) to distinguish them from neighboring earthquakes. We found that the REs occurred within the rupture radius of the ML 3.6 event. Upon categorizing these REs according to their family duration, we identified three swarm-type families that occurred in 2007, 2009, and 2010, along with a continuous-type family spanning from 2011 to 2019. These observations demonstrate the close relationship between the REs and the ML 3.6, specifically highlighting the fault’s rupture and healing process.

How to cite: Jung, S., Sheen, D.-H., Cho, C.-S., and Kim, K.: Observation of intraplate repeating earthquakes within the fault zone of the 2008 ML 3.6 earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7189, https://doi.org/10.5194/egusphere-egu24-7189, 2024.

EGU24-7660 | Orals | SM1.1

Source analysis of the 2022 Nord Stream and 2023 Balticconnector underwater explosions 

Andreas Steinberg, Nicolai Gestermann, Lars Ceranna, Gernot Hartmann, Björn Lund, Eric Dunham, Patrick Hupe, Peter Voss, Tine Larsen, Trine Dahl-Jensen, Andreas Köhler, Johannes Schweitzer, Christoph Pilger, Thomas Plenefisch, Klaus Stammler, Stefanie Donner, Peter Gaebler, and Christian Wiedle

On 26 September 2022 two seismic events near the Danish island of Bornholm in the Baltic Sea were detected. The first event with a magnitude Mw 2.3 occurred at 00:03 UTC 40 km east-southeast of Bornholm. The determined location and the origin time of the event are consistent with data of the pressure decrease on one of the Nord Stream 2 pipelines. Another sequence of events occurred 17 hours later at 17:03 UTC around 60 km north-east of Bornholm with a maximum magnitude of Mw 2.7. It consists of three closely successive, but separable, single events. Using relative localisation methods and the gas pressure inside the pipeline recorded at the landing site in Germany, we can assign the epicentres of the three events to the locations of the leaks in the pipelines of Nord Stream 1 and 2.

Based on comparable events in the region, which include both tectonic earthquakes and explosions, the explosive character of the investigated Nord Stream events can be verified. Infrasound signals associated with the destruction of the Nord Stream pipelines were recorded at two stations (I26DE in the Bavarian Forest and IKUDE near Kühlungsborn) in Germany. Particularly after the event sequence at 17:03 UTC, distinctive signals were registered whose characteristics indicate an explosive event with subsequent gas leakage at the surface.

Our modelling of the sources shows that the measured seismic signals can sufficiently be explained by the instantaneous gas release. Synthetic seismograms for such a source and a subsurface model adapted for the study area show high consistency with the measured signals. Based on the released energy and the characteristics of the recorded waveforms, we conclude that the impulsive gas release from the burst gas pipes constitutes the dominant part of the signal source. The model places an upper limit of approximately 50 kg TNT equivalent on the yield of the chemical explosive component of the events, but we note that smaller yields may also be consistent with the data.

We also carried out an analysis of the seismic signals of the event on the Balticconnector pipeline between Finland and Estonia on 8 October 2023 and found that again the instantaneous gas release can sufficiently explain the observed data. This supports a possible mechanical cause of the damage.

 

How to cite: Steinberg, A., Gestermann, N., Ceranna, L., Hartmann, G., Lund, B., Dunham, E., Hupe, P., Voss, P., Larsen, T., Dahl-Jensen, T., Köhler, A., Schweitzer, J., Pilger, C., Plenefisch, T., Stammler, K., Donner, S., Gaebler, P., and Wiedle, C.: Source analysis of the 2022 Nord Stream and 2023 Balticconnector underwater explosions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7660, https://doi.org/10.5194/egusphere-egu24-7660, 2024.

EGU24-8482 | ECS | Orals | SM1.1

Tracking a Vibroseis Truck and Investigating the Wavefield using 6 Rotational Sensors in Fürstenfeldbruck, Germany  

Gizem Izgi, Eva P.S. Eibl, Frank Krüger, and Felix Bernauer

Six-degree-of-freedom (6-DoF) measurements, which combine rotational sensors and seismometers, provide a comprehensive dataset that allows seismologists to determine the back azimuth of a potentially moving source from a single-point measurement. Our investigation focused on tracking the movement of a vibroseis truck operating from 20 November 2019, 11:00 UTC, to 21 November 2019, 14:00 UTC. Using 480 sweep signals, each lasting 15 seconds and covering a wide frequency range from 7 to 120 Hz, we measured at 160 different locations. Back azimuths for each sweep were derived from the 6-DoF data, and root mean squares were calculated for each component. This procedure was repeated for five additional rotational sensors of the same type.
During the first day, the north component of all sensors recorded larger amplitude signals than the East and Vertical, indicating the dominance of SV (shear-vertical) wave energy. Subsequently, we observed gradually increasing amplitudes on the east component, which was consistent with the direction of the moving vibroseis truck. Although the dominant wave type recorded was SV, and the method of comparing horizontal rotation rates was used to calculate the back azimuth, we observed a relatively decreasing accuracy of direction estimates as the truck moved away from the sensors due to increased scattering. To fully understand the reason for this, we investigated the specific fingerprint of each wave type in the wave field. Our results suggest that direction estimates should be made using only the portion of the wavefield containing SV-type waves when using this method, and then the moving source should be tracked accordingly. This approach provides insight into the trajectory of the truck and improves our understanding of the seismic signals generated during the experiment.

How to cite: Izgi, G., Eibl, E. P. S., Krüger, F., and Bernauer, F.: Tracking a Vibroseis Truck and Investigating the Wavefield using 6 Rotational Sensors in Fürstenfeldbruck, Germany , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8482, https://doi.org/10.5194/egusphere-egu24-8482, 2024.

EGU24-8735 | Orals | SM1.1 | Highlight

Near-real time detection of conflict-related explosions or suspicious events using seismological data  

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

Apart from classical earthquake monitoring, seismological data can also be used to detect explosions in near-real-time on both regional and global scales. We demonstrate how seismic and infrasound data can provide more comprehensive and objective information about conflict-related explosions or suspicious events that might be the result of targeted attacks. We can identify the underwater explosions at the Nord Stream pipeline infrastructure in the Baltic Sea in September 2022. Cross-correlation analysis allowed us to identify sub-events several seconds apart which can be associate with specific locations along the pipelines. Furthermore, we detect a signal at the Finish seismic array in October 2023 which may be associated with the damage along the Balticconnector. The other example is from Ukraine, where we present the ability to automatically identify and locate ground explosions related to the Russia-Ukraine conflict with data from the Malin array (AKASG). Between February and November 2022, we observe more than 1,200 explosions from the Kyiv, Zhytomyr, and Chernihiv provinces. Both seismic and infrasound detections can be used to verify and improve accurate reporting of military attacks and help to provide an unprecedented view of an active conflict zone. 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, airstrikes, or the destruction of the Kakhovka dam NE of Cherson.

How to cite: Goertz-Allmann, B., Dando, B. D. E., Koehler, A., Brissaud, Q., Schweitzer, J., and Kværna, T.: Near-real time detection of conflict-related explosions or suspicious events using seismological data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8735, https://doi.org/10.5194/egusphere-egu24-8735, 2024.

EGU24-9479 | Orals | SM1.1

Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France 

Mickaël Bonnin, Marion Alloncle, Maxime Bes de Berc, Éric Beucler, Damien Fligiel, Marc Grunberg, Céline Hourcade, Clément Perrin, Olivier Sèbe, Jérôme Vergne, and Dimitri Zigone

On June 16, 2023 at 16h38 UTC, a moderate earthquake of magnitude MW=4.9 stroke western France south of Niort city, near the small village of La Laigne (Charente Maritime). The shaking has been widely felt in the whole NW France and macroseismic intensity (EMS98) of VII was reached at the epicenter. Such an event is relatively rare in continental France and represents the second largest event in the western France in the last century. The epicentral region is located at the northern termination of the Aquitaine basin where 300 m of Mesozoic sediments covers the variscan basement. The focal mechanism obtained from waveform inversion corresponds to a pure dextral strike-slip motion or a pure senestrial strike-slip motion along a EW or NS striking fault plane, respectively.

The fault that ruptured on June 16 is not known. To gain insight on its characteristics, teams of Nantes (Osuna and LPG), of Strasbourg (EOST and ITES) and of the CEA deployed between June 17 and June 22, 2023 for approximately one month, a network of 3-components stations composed of 12 MEMS accelerometers, 104 five hertz geophones and 5 broadband velocimeters in a 40 by 30 km region around the epicenter, with a station inter-distance of approximately 4 km.

We present is this study the first results derived from this unique experiment. In particular, we show that the aftershock sequence (more than 600 events recorded) highlights a planar rupture zone of about 5.4 km2, trending NS and strongly dipping to the East (75°), located between 2 and 5 km depth. Site effect analysis allows us to better understand large ground motion distributions over the area and their link with macroseismic intensities. The installed array also allows us to infer a preliminary 3D VS model of the region. We show the extent to which a dense temporary network is mandatory for studying the fine structure of the fault plane in a region where previous knowledge of active geological structures is limited.

How to cite: Bonnin, M., Alloncle, M., Bes de Berc, M., Beucler, É., Fligiel, D., Grunberg, M., Hourcade, C., Perrin, C., Sèbe, O., Vergne, J., and Zigone, D.: Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9479, https://doi.org/10.5194/egusphere-egu24-9479, 2024.

EGU24-9598 | ECS | Orals | SM1.1 | Highlight

Seismic Precursor for the October 7th Terrorist Attack? 

Asaf Inbal

Seismic waves excited by human activity frequently mask signals due to tectonic processes, and are therefore discarded as nuisance.  Seismic noise-field analysis is, however, a powerful tool for characterizing anthropogenic activities. Here, I apply this analysis to examine seismic precursors to the October 7 Hamas attack on Israel. The precursory activity in Gaza included massive mobilization which took place in the hours leading to the attack, and was  documented on multiple media outlets. Favourable conditions, which arise due to a temporary lack of anthropogenic activity in Israel, allow remote seismic stations to record signals due to Gaza vehicle traffic. I use these seismograms in order to identify anomalous ground-motions, associate them with pre-attack mobilization, and precisely determine their location. By applying array analysis to three seismic stations located tens-of-kilometers from the Gaza strip, I was able to obtain valuable information on the Hamas attack plans. This suggests that embedding seismic noise-field analysis into decision-making protocols could enhance preparedness, thus providing an opportunity to blunt terrorist attacks and reduce the number of casualties.

How to cite: Inbal, A.: Seismic Precursor for the October 7th Terrorist Attack?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9598, https://doi.org/10.5194/egusphere-egu24-9598, 2024.

EGU24-11960 | ECS | Orals | SM1.1

Reassessment of the historical earthquake of 23 February 1887 in Liguria (north-western Mediterranean) on the basis of magnetogram recordings 

Gabriele Tarchini, Daniele Spallarossa, Stefano Parolai, Denis Sandron, and Angela Saraò

In the early morning of 23 February 1887, the ‘Ligurian earthquake’, a devastating seismic event currently estimated at MW 6.3-7.2, shook the towns of the Italian and French Riviera. It is the most devastating earthquake known in this region: it is thought to have claimed at least six hundred lives, displaced twenty thousand people, and destroyed many historic buildings and houses. As a result of the event, a tsunami with a maximum run-up of two meters near Imperia (Italy) also occurred and the record of the tide gauge in the port of Genoa (Italy) has long been considered the only existing record of the event.

However, we found that the 1887 earthquake was also recorded by historical magnetometers in the UK and France. These instruments were used to measure variations in geomagnetic field strength, but were also able to record seismic waves, which were essentially a simple ‘disturbance’. Almost uninterrupted records of this type of variometric data are held by the British Geological Survey (BGS). Traces recorded at Greenwich, Kew, and Falmouth magnetic observatories, which clearly show waveforms related to the event, were used. The Bureau Central de Magnetisme Terrestre (BCMT) also keeps magnetograms: in particular, we used the recordings of the instrument at Le Parc de Saint-Maur (Saint-Maur-des-Fossés, Paris).

The waveforms were digitized and processed according to the theory of Eleman (1966), which describes the response of a classical declinometer and/or a horizontal force instrument to harmonic ground displacement, and according to the work of Krüger et al. (2018).

The location of the epicenter and the magnitude of this historical earthquake are difficult to characterize with high accuracy, and the focal mechanism of the fault responsible for the event remains controversial to this day. We present the preliminary results of our research, which is focused on the revaluation of the Ligurian earthquake in terms of magnitude and focal mechanism. This would lead for the first time to a definition of magnitude on an instrumental basis for this important seismic event, whose macroseismic intensity is usually assessed based on studies conducted immediately after the event to determine the damage it had caused.

How to cite: Tarchini, G., Spallarossa, D., Parolai, S., Sandron, D., and Saraò, A.: Reassessment of the historical earthquake of 23 February 1887 in Liguria (north-western Mediterranean) on the basis of magnetogram recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11960, https://doi.org/10.5194/egusphere-egu24-11960, 2024.

EGU24-12248 | Posters on site | SM1.1

Seismic Data Compression and Telemetry Bandwidth Considerations for Earthquake Early Warning 

Michael Laporte, Michael Perlin, Marian Jusko, and David Easton

Earthquake early warning systems depend on the prompt, reliable arrival of seismic data at network data centers. Network operators invest significant resources into the design, installation and operation of real-time acquisition systems to ensure maximum data completeness and minimum data latency, to allow EEW processing modules to detect events and issue warnings as quickly as possible.

These mission-critical acquisition systems must perform before, during and after earthquakes, as main shocks are frequently preceded by foreshocks and followed by aftershocks, which are often just as dangerous. As such, a key consideration in the design of these systems is the impact that large earthquakes may have. Seismic data is generally encoded using Steim compression, which is a first difference algorithm. During large events the differences between samples grow, requiring more bits to record and, thus, increasing the data volume. This results in a surge in the throughput required during large events. System designers and network operators must be fully aware of this effect and plan for it accordingly.

This study expands on existing work to further characterize the impact of large events on seismic data compression and the corresponding spikes in throughput which must be supported by real-time acquisition systems. The study will examine the relationship between compression and various factors, including station magnitude, hypocentral distance, sample encoding technique, packet size, sample rate and system sensitivity.

How to cite: Laporte, M., Perlin, M., Jusko, M., and Easton, D.: Seismic Data Compression and Telemetry Bandwidth Considerations for Earthquake Early Warning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12248, https://doi.org/10.5194/egusphere-egu24-12248, 2024.

EGU24-12588 | Posters on site | SM1.1

Preliminary estimation of attenuation properties in the High Agri Valley (Southern Apennines, Italy) by the coda attenuation method 

Vincenzo Serlenga, Salvatore Lucente, Salvatore de Lorenzo, Edoardo Del Pezzo, Marilena Filippucci, Teresa Ninivaggi, Tony Alfredo Stabile, and Andrea Tallarico

High Agri Valley is an intermontane basin of the axial portion of Southern Apennines (Southern Italy), characterized by a very strong seismogenic potential. Indeed, a  Mw=7.0  earthquake occurred in 1857. Currently, the seismic networks managed by ENI Oil Company and INGV, installed in the area, continuously record a low-magnitude natural seismicity. Furthermore, two anthropogenic earthquake clusters are documented in two distinct sectors of the valley, located NE and SW of the artificial Pertusillo lake, respectively. The first cluster is related to the fluid-induced microseismic swarms caused by the injection, through the Costa Molina 2 well, of the wastewater produced by the exploitation of the Val d’Agri oilfield. The second cluster is due to a protracted reservoir induced seismicity (RIS) affected by the combined effects of the water table oscillations of the Pertusillo lake, the regional tectonics and likely the poroelastic/elastic stress due to aquifers in the carbonate rocks.

In this study we investigated the attenuation properties of the High Agri Valley crust by the estimation of the S-coda waves Qc-1, as it is widely recognized the role of fluids on this parameter. We selected a dataset of about 1800 events acquired from 2001 to 2015 by the two above mentioned seismic networks, with local magnitude (ML) ranging from 0 to 3.3. We estimated the attenuation of the target area by means of a linear regression analysis of the amplitude decay curves of the envelopes of the seismograms; these were filtered in the frequency ranges centered on 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16 Hz. The Qc estimates were performed by using different time windows for the envelope fitting, starting from the time T1 to the time TL (the lapse time). In detail, we adopted, as T1, 1.0*Ts, 1.5*Ts and 2.0*Ts (being Ts the S wave arrival time), and as TL 10s, 15s, 20s, 25s and 30 s from the event origin time. Only the components for which the condition T1<TL<T2 was fulfilled were considered for the linear regression, being T2 the end-time of the coda envelope; the latter was automatedly found by a proper methodology implemented in this study.

The obtained results show the increase of Qc as a function of f at all the considered TL. Compared with other tectonic regions worldwide, in the High Agri valley the Qc(f) is very low: the Q0, that is the Qc at 1 Hz, ranges between 8 and 57. At greater frequencies, the highest estimated Qc value is lower than 400. These evidences could be interpreted as the effect of fluids in the investigated crust, thus providing a further hint on their possible role in the seismicity of the area. A complete characterization of seismic attenuation of the High Agri Valley will require further investigations, that is the separation of scattering and intrinsic contributions in the total attenuation and a 3D imaging: indeed, the latter could highlight possible overlapping between spatial attenuation anomalies and seismicity distribution in the investigated area.

How to cite: Serlenga, V., Lucente, S., de Lorenzo, S., Del Pezzo, E., Filippucci, M., Ninivaggi, T., Stabile, T. A., and Tallarico, A.: Preliminary estimation of attenuation properties in the High Agri Valley (Southern Apennines, Italy) by the coda attenuation method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12588, https://doi.org/10.5194/egusphere-egu24-12588, 2024.

EGU24-12990 | Orals | SM1.1

Seismic Network Station Infrastructure as the Basis for Multi-Disciplinary Geophysical Stations 

Michael Perlin, Neil Trerice, Ted Somerville, and Marian Jusko

Geophysical monitoring requires the highest level of performance and reliability from purpose-built and tightly integrated instrumentation and infrastructure. Parallel and separate efforts between different scientific disciplines seen in the past came at the expense of duplicated infrastructure, telemetry and power subsystems, and even land use permits. This duplication increases costs, ultimately limiting station counts and reducing “the reach” of monitoring networks. Recent ambitions to combine multi-disciplinary geophysical applications into streamlined deployments led to initiatives such as the European Plate Observing System (EPOS) and the recent amalgamation of the SAGE and GAGE programs in the United States.

Modern seismic dataloggers, such as the Nanometrics Centaur, support a wide range of seismo-acoustic sensor interfaces and sensor types while maintaining ultra-low power consumption, precise timing, and reliable data transport with automatic back-fill features over flexible telemetry mediums. These properties transformed the Centaur’s capabilities to act as a highly versatile foundation in multi-disciplinary geophysical station deployments. 

Despite initially being designed as a high-performance data recorder for seismic applications, Centaur’s applicability has evolved to include data collection for the infrasonic, geodetic, magnetic, and meteorological domains. This triggered the development and addition of purpose-built features to support multi-disciplinary use cases with the same proven performance and reliability of a Centaur seismic station.

Both existing and planned capabilities that enable reliable and efficient multi-disciplinary science are discussed.

How to cite: Perlin, M., Trerice, N., Somerville, T., and Jusko, M.: Seismic Network Station Infrastructure as the Basis for Multi-Disciplinary Geophysical Stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12990, https://doi.org/10.5194/egusphere-egu24-12990, 2024.

Size distribution of earthquakes, characterized by the power law decay (b-value), sometime displays the major earthquakes before their occurrence. The b-value reflect state of stress and proximity of fault failure condition according to previous studies. However, the causes are difficult to separate each other. This study proposes an additional indicator reflecting the proximity. Seismic moment release in a volume by small earthquake indicates inelastic strain. The efficiency of inelastic strain on stress loaded medium exhibits proximity to strength of the medium based on Mohr diagram and Coulomb failure condition. Thus, we adopt the efficiency as the indicator. We examine b-value and the efficiency variation in pre- and post- seismic activity of the 2016 Kumamoto earthquake sequence. Weighted b-value distribution by the efficiency captured the initiation point of the Kumamoto earthquake. The result suggests utilizing both b-value and the efficiency contribute to improving earthquake alerts and disaster mitigation.

How to cite: Matsumoto, S.: Inelastic strain efficiency of small earthquakes as an indicator for proximity of the 2016 Kumamoto earthquake (M7.3), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13440, https://doi.org/10.5194/egusphere-egu24-13440, 2024.

Seismicity records during the 1990’s reveals that large inland earthquakes tend to concentrate near several active volcanoes in the central part of northeastern (NE) Japan (Hasegawa & Yamamoto, 1994 Tectonophysics). The inland seismicity around active volcanoes could be related to localized zones of high strain contraction detected by the GNSS measurements in 1997–2001 (Miura et al., 2004 JGR). Several studies speculated that the localized strain contraction is caused by inelastic deformation of weak lithosphere beneath the active volcanoes (Hasegawa et al., 2004 J. Seismol. Soc.). Such weak lithosphere (i.e., low-viscosity zone or LVZ) is inferred from high heat-flow observations (Tanaka et al., 2004 EPS), lithospheric strength simulation (Shibazaki et al., 2016 GRL; Muto, 2011 Tectonophysics) and seismic-velocity tomography (Hasegawa et al., 2005 JGR). However, because of complex interplay between elastic and inelastic processes during steady-state (i.e., interseismic) crustal deformation, the physical mechanism related to inelastic deformation is still poorly understood.

When the Mw9.0 2011 Tohoku-oki earthquake occurred, strong surface deformations were observed locally near the active volcanoes (Takada & Fukushima, 2013 Nat. Geosci.) and continued for several years after the mainshock (Muto et al., 2016 GRL). Past studies (e.g., Sun et al., 2014 Nature) advocated that the earthquake-related inelastic processes such as viscoelastic mantle relaxation dominates the crustal deformations in the postseismic period. In the present study, we identified localized strain contractions near the active volcanoes by extracting the short-wavelength strain rate (Meneses-Gutierrez & Sagiya, 2016 EPSL) from the GNSS observations during 2012–2014. We explained these localized strain contraction by building three-dimensional rheological models of small-scale LVZs beneath five active volcanoes of NE Japan. We simulated the volumetric deformation of viscoelastic LVZs using power-law Burgers rheology, which previously succeeded to explain the large-scale postseismic deformation of the 2011 Tohoku-oki earthquake (Agata et al., 2019 Nat. Commun.; Muto et al., 2019 Sci. Adv.; Dhar et al., 2022 GJI). The power-law Burgers rheology represents the bi-phasic nature of rock deformations (rapid transient with subsequent steady state) and power-law dependency of strain rate to evolving stress (proxy of dominating dislocation creep in high-stress mantle condition) (Muto et al., 2019 Sci. Adv. and references therein).

We found that the localized strain contraction near the active volcanoes can be explained by small-scale LVZs which have narrow tops of 10–20 km and wide roots of 60–100 km width. Our results conclude the minimum depths of the tops and roots of LVZs are 15 km and 40 km, respectively. The geometries of the LVZs vary (e.g., upright conic or inclined shape) from volcano to volcano. The effective viscosities of the LVZs are in the order of 1017 Pa·s immediately after the earthquake and increases to the order of 1018 Pa·s over the 3 years of postseismic deformation. Our results agree with the results of several past studies (Ohzono et al., 2012 EPS; Hu et al., 2014 EPS; Muto et al., 2016 GRL) who investigated the lithospheric rheology near Mt. Naruko using the postseismic surface displacements of the 2011 Tohoku-oki and 2008 Iwate-Nairiku earthquakes.

How to cite: Dhar, S., Takada, Y., and Muto, J.: Rheology of weak lithosphere beneath active volcanoes of NE Japan: Insights from postseismic deformation of 2011 Tohoku-oki earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13903, https://doi.org/10.5194/egusphere-egu24-13903, 2024.

A large crustal earthquake (Mw=7.5) struck the Noto Peninsula, central Japan, at 16:10 (JST = UT + 9 hours) on New Year's Day, 2024. The main-shock rupture extended ~150 km in length, which covered the source regions of intense swarm activity in the northeastern tip of the peninsula [Amezawa et al., 2023] as well as the previous large crustal earthquakes such as the 2007 (Mw=6.7) and 2023 (Mw=6.3) events. The aftershock distribution of the 2024 event provides fundamental information for understanding the rapture process of the main shock and seismotectonics in the Noto peninsula. Therefore, we relocated the earthquake hypocenters that occurred immediately after the 2024 event by considering the three-dimensional velocity structure [Matsubara et al., 2022]. In the relocation, we applied the method proposed by Shiina and Kano [2022] to the arrival time data on the earthquake catalog compiled by the Japan Meteorological Agency. The applied method utilized the Markov Chain Monte Carlo technique, allowing us to evaluate uncertainty in hypocenter locations. Thus, we can discuss the distributions of the crustal earthquakes in and around the source area of the 2024 event, taking account of the spatial variations in uncertainty in the hypocenters. For example, some aftershocks occurred offshore, indicating that estimation accuracy in that area may get worse due to limited station coverage compared with the inland area. As the result of the relocation considering the three-dimensional structure, the depth of these offshore events was shifted about 5 km shallower. These hypocenters suggested that the aftershocks of the 2024 event occurred mainly between the ground surface and the depth of 15 km.

How to cite: Shiina, T., Horikawa, H., and Imanishi, K.: Relocations of earthquake hypocenters in and around the source area of the 2024 Mw 7.5 Noto Peninsula earthquake, Japan, by Bayesian inference, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14903, https://doi.org/10.5194/egusphere-egu24-14903, 2024.

EGU24-15253 | ECS | Posters on site | SM1.1

Repeating events detection in northeastern Taiwan using a broadband seismometer array 

Chin-Shang Ku, Bor-Shouh Huang, and Cheng-Horng Lin

In this study, we document unusual and recurring events that transpired within one hour on November 17, 2021. These incidents were identified through a seismometer array deployed in the Yilan area and Turtle Island, northeastern Taiwan. Preceding this series of events, a shallow submarine volcano near Turtle Island emitted sulfur smoke from October 28, 2021, lasting until November 22, 2021. This eruption was marked by a significant release of white sulfur smoke from the sea near Turtle Island. It reached a height exceeding 3 meters and extended over 100 meters into the air, making it the most substantial eruption of the year. At first, we proposed that the giant bubble could be generated during the submarine eruption and expanded through the water and into the atmosphere; the collapse of this bubble was considered a potential source of the recurring events. However, a grid-search method utilizing the arrival times of seismic stations indicates that the source location is close to the seacoast of Yilan, still dozens of kilometers away from Turtle Island. Upon further analysis of the seismic waveforms, it was observed that the propagation velocity is close to the speed of sound and only detected by surface stations, not by shallow-hole stations. This suggests that the source likely produced signals that couple well with the atmosphere rather than the solid Earth. The waveforms exhibit high consistency between different events at the same station, indicating that the sources occurred at the exact location several times within one hour. The possibility of an aircraft-induced shock wave was considered but needs more investigation. Trustworthy sources and their mechanisms remain to be clarified, and additional data, such as infrasound and pressure data, will be essential for a more comprehensive understanding shortly.

How to cite: Ku, C.-S., Huang, B.-S., and Lin, C.-H.: Repeating events detection in northeastern Taiwan using a broadband seismometer array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15253, https://doi.org/10.5194/egusphere-egu24-15253, 2024.

When in 1997 we started to compute Regional CMT for seismic events in the Euro-Mediterranean region, we could not expect to create a Catalog that can well describe the seismicity, the seismotectonics of this really active region with such complex characteristics. The RCMT Catalog includes more than 3200 seismic moment tensors for earthquakes with a magnitude starting from 4.5, but for the Italian region also down to M 4.0, for the time span 1997 to 2023. All RCMTs are available on the web, on dedicated pages, with the possibility to select the preferred dataset choosing intervals for time, geography, magnitude, depth and quality factors (http://rcmt2.bo.ingv.it/searchRCMT.html). In the first years the RCMT computation was based only on the modelling of intermediate-period surface waves. After 2002, it has been possible to invert also for body waves, an improvement that for the RCMT computation has been important for events with M greater than 5.0. The homogeneity of the dataset given by the continuous use of the same algorithm is an added value that has been underlined by several comparisons with other regional catalogs. The lower magnitude threshold applied in the Euro-Mediterranean region produces a dataset three times more numerous with respect to what is available with the Global CMT data only. In 1997 RCMTs were the only seismic moment tensors available for earthquakes with M lower than 5.0 in the Euro-Mediterranean region. Later, several regional and local focal mechanisms have been computed, with different methods and for different sub-regions. At present, on average three or more regional solutions appear on the web after a M4.5 earthquake hits the Mediterranean. However, RCMT Catalog is the one with the longer time interval covered by homogeneous data. Today, the Catalog is continuously updated with a few months of delay between definitive and quick solutions, that are however available on the RCMT web pages up to the time the revised solution is ready.

How to cite: Pondrelli, S.: The European Mediterranean RCMT Catalog: more than 25 years of activity and data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15437, https://doi.org/10.5194/egusphere-egu24-15437, 2024.

EGU24-15494 | Orals | SM1.1

Geology and geomorphology of the Jan 1st 2024 Mw 7.6 Noto Peninsula Earthquake: observations and context. 

Luca C. Malatesta, Shigeru Sueoka, Kyoko S. Kataoka, Tetsuya Komatsu, Sumiko Tsukamoto, Lucile Bruhat, and Jean-Arthur Olive

On January 1st 2024, a Mw 7.6 earthquake shook the Noto Peninsula on the Sea of Japan coast of Central Japan causing over 202 casualties and >100 missing (at the time of submission). The quake follows a period of intensifying seismic activity starting in 2020. The Mw 6.3 Oku-Noto earthquake of May 5 2023 was the previous largest event of the sequence. The Jan. 1 2024 Noto Peninsula earthquake significantly impacted the Peninsula. A large number of landslides and rockfalls dissected the road network. Liquefaction damaged infrastructure up to 150 km away from the epicenter. Meter-scale coseismic uplift modified the northern shoreline with displacement of the coastline by up to 200 m seaward discernible on SAR and aerial image data. At the time of abstract submission (Jan. 10 2024) we only have limited preliminary observations. It appears that the Noto Earthquake ruptured the same or adjacent fault to the May 5 2023 Mw 6.5 earthquake and was in the vicinity of the March 25 2007 Mw 6.9 Noto earthquake. Coseismic displacement measured geodetically shows uplift of up to +3–4 m (SAR) in the northwest of the peninsula (Wajima-shi), and +1.06 m (GPS) in the main town of Wajima-shi. The uplift magnitude decreases gradually to the SE. The uplift is near zero (SAR) or -0.3 m (GPS) on Noto Island (Nanao-shi) 30 km to the south of the town of Wajima. Surface deformation goes back to near zero (GPS) a further 20 km to the south.

The coseismic deformation pattern broadly reflects the deformation recorded in the Noto landscape. Long-term moderate rock uplift in the north gives way to a complex history of long-term slow uplift around Noto Island that likely includes sustained episodes of subsidence, highlighted by its sinuous “drowned” coastline. Along the western shore (Shika-machi), marine terraces presumed to be 120 ka (last Interglacial) show a gradient in elevation also decreasing to the south. In the north, the newly emerged platform does not have a higher marine terrace counterpart. This may reflect the relationship between high wave power and moderate rock uplift resulting in the long-term retreat of the coastline and erosion of any terrace. The Noto Peninsula also holds widespread evidence of drainage reorganization that would reflect varying boundary conditions, in particular rock uplift, in deeper time beyond 100’s ka. The similarities between recent landscape morphology and coseismic displacement suggest that the Jan. 1 2024 rupture fits a recent pattern of crustal strain in Noto Peninsula (at least up to 100 ka). Earlier deformation pattern (>100’s ka) likely happened along different faults and/or at different rates as reflected by the transient drainage network.

By conference time, we will present field observations collected after the rescue and emergency work is completed.

How to cite: Malatesta, L. C., Sueoka, S., Kataoka, K. S., Komatsu, T., Tsukamoto, S., Bruhat, L., and Olive, J.-A.: Geology and geomorphology of the Jan 1st 2024 Mw 7.6 Noto Peninsula Earthquake: observations and context., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15494, https://doi.org/10.5194/egusphere-egu24-15494, 2024.

EGU24-15942 | Orals | SM1.1

Insights into the 36 Years of Seismic Activity at Vulcano Island, Italy, preceding the Volcanic Unrest in 2021 

Susanna Falsaperla, Giovanni Barreca, Ornella Cocina, and Salvatore Spampinato

Numerous episodes of volcanic unrest have taken place at Vulcano island (Italy) since its last Vulcanian eruption occurred 133 years ago. Decades-long seismic monitoring has documented some of them. We have collected and examined all available seismic data recorded since 1985, most of which were in analog format and/or dispersed in old repositories. We were able to compile catalogs where three different types of seismic events are considered according to their location and magnitude: events in the Fossa Crater, in the Lipari-Vulcano complex, and earthquakes with M>2.5. The primary goal of this data collection was to identify the main features of seismic activity on and around the island in the 36 years preceding the last volcano unrest, which began in mid-September 2021 with a high occurrence frequency of Very Long Period (VLP) events. Our review of the past seismic activity allows us to contextualize the newly recorded anomalous variations. Furthermore, we sought the connection with the structural framework of the region.

The duration of the episodes of volcanic unrest in 1985 and 1988 was relatively short (lasting just a few months) when compared to the recent one, which ended in December 2023. The source of the seismic events during those past unrests was mainly close to the reference station (now IVCR) with hypocenters mostly beneath the island at shallow crustal depths (up to 5 km below sea level). Their magnitude remained low (<2.5) during both the episodes (i.e., 1985, and 1988).

Overall, the seismicity recorded in and around the island has reached a maximum value of M4.6 both in the 36 years preceding and during the 2021 unrest. Some preliminary insights can be drawn by comparing the seismicity occurred during past and recent unrest episodes: i) the peculiarly long duration of the most recent unrest, and ii) the importance of broadband equipment, which documented the substantial contribution of VLP seismicity during the 2021-2023 episode.

How to cite: Falsaperla, S., Barreca, G., Cocina, O., and Spampinato, S.: Insights into the 36 Years of Seismic Activity at Vulcano Island, Italy, preceding the Volcanic Unrest in 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15942, https://doi.org/10.5194/egusphere-egu24-15942, 2024.

EGU24-17485 | ECS | Orals | SM1.1

Frequency-dependent delay time analysis for Bhutan Himalaya 

Sayan Bala, Abhisek Dutta, and Chandrani Singh

In this study, we have evaluated the scattering nature of the crust beneath the Bhutan Himalaya, located in the eastern part of the Himalayan arc. We have analysed high-quality waveforms of 566 events having magnitude (ML) below 6, recorded by broadband stations of the GANSSER network operated by the Swiss Seismological Service at ETH Zurich from Jan, 2013 to Nov, 2014. We have investigated the peak delay time (tpd), defined as the time interval between the initial S-wave appearance and the peak amplitude of its envelope, for the frequency ranges of 4–8, 6–12, 8–16 and 12–24 Hz. Initially, we have analysed frequency-dependent nature of tpd at 9 stations (BHE01, BHE09, BHE13, BHN02, BHN06, BHN11, BHW01, BHW10 and BHW16). The observed values of Bfreq, which indicates the frequency dependence of the peak delay time, show mostly low positive values up to 0.3. It shows that tpd is independent of frequency which may be associated with the relative proportions of large as well as small scale heterogeneities present in the mediumAt BHE09, Bfreq exhibits a negative value, which might be attributed to the limited sampling of high-frequency signals that capture small portions of the subsurface along their paths. The crust beneath BHE09 experiences reduced scattering, probably due to the absence of a strongly attenuating body in the subsurface. Furthermore, we aim to extend this study for all the stations and to compare the frequency-dependent nature of T5%-75% (time interval between 5% and 75% of the total integrated power value) and the tpd for the study region.

How to cite: Bala, S., Dutta, A., and Singh, C.: Frequency-dependent delay time analysis for Bhutan Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17485, https://doi.org/10.5194/egusphere-egu24-17485, 2024.

The North Anatolian Fault Zone in Turkey spans 1400 km, passing through densely populated areas, including Düzce, which experienced the destructive Mw 7.2 event in 1999 that caused more than 700 lives. On 23 November 2022, for the first time in over 20 years, a moderate Mw 6.1 earthquake struck the city and surrounding area. Despite its moderate magnitude, the event caused unexpectedly severe damage to numerous buildings, as reported by local institutions (Disaster and Emergency Management Presidency; AFAD). Recognizing the potential impact of near-field effects such as ground motion pulses and directivity effects, which are known to increase damage in the vicinity of the fault, we investigate these phenomena using the AFAD-Turkish Accelerometric Database. Our analysis delves into the spatial distribution of ground motion intensities, revealing higher peak ground velocities in certain azimuthal ranges than predicted by existing ground motion models. Surprisingly, our findings challenge outcomes derived from previous studies, suggesting that impulsive ground motions associated with directivity effects mainly occur on the fault-normal component of large-magnitude events. In contrast, our examination of near-fault recordings indicates a concentration of velocity pulses, primarily on the fault-parallel component, and thus questions the widely established understandings of earlier studies.

How to cite: Türker, E., Yen, M.-H., Pilz, M., and Cotton, F.: Importance of Pulse-Like Ground Motions and Directivity Effects in Moderate Earthquakes based on the 23 November 2022, Mw 6.1 Gölyaka-Düzce Earthquake (Turkey)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17715, https://doi.org/10.5194/egusphere-egu24-17715, 2024.

EGU24-18530 | Posters on site | SM1.1

Recalibration of the intensity prediction equation in Italy using the Macroseismic Dataset DBMI15 V2.0 

Barbara Lolli, Paolo Gasperini, and Gianfranco Vannucci

We re-compute the coefficients of the intensity prediction equation (IPE) in Italy using the data of the DBMI15 V2.0 intensity database and the instrumental and combined (instrumental plus macroseismic) magnitudes reported by the CPTI15 V2.0 catalog. We follow the same procedure described in a previous article, consisting of a first step in which the attenuation of intensity I with respect to the distance D from macroseismic hypocenter is referred to the expected intensity at the epicenter IEand a second step in which IEis related to the instrumental magnitude Mi, the combined magnitude Mc, the epicentral intensity I0 and the maximum intensity Imax, using error-in-variable (EIV) regression methods. 

The main methodological difference with respect to the original article concerns the estimation of the uncertainty of IEto be used for EIV regressions, which is empirically derived from the standard deviation of regression between IE and Miand also used for the regressions of IEwith Mc, I0 and Imax. 

In summary, the new IPE determined from DBMI15 V2.0 is

                                        𝐼=𝐼𝐸−0.0081(𝐷−ℎ)−1.072[ln(𝐷)−ln(ℎ)]

 where 𝐷=√(𝑅2+ℎ2), h=4.49 km and IEcan be calculated from the intensity data distribution of the earthquake. If the intensity data distribution is not available, IEcan be calculated from the following relationships

                                        𝐼𝐸=−2.578+1.867𝑀𝑤

                                                      IE=I0

                                       

How to cite: Lolli, B., Gasperini, P., and Vannucci, G.: Recalibration of the intensity prediction equation in Italy using the Macroseismic Dataset DBMI15 V2.0, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18530, https://doi.org/10.5194/egusphere-egu24-18530, 2024.

EGU24-18752 | ECS | Posters on site | SM1.1

The new earthquake catalog of the Gargano (Southern Italy) OTRIONS seismic network. 

Andrea Pio Ferreri, Annalisa Romeo, Rossella Giannuzzi, Gianpaolo Cecere, Salvatore de Lorenzo, Luigi Falco, Marilena Filippucci, Maddalena Michele, Giulio Selvaggi, and Andrea Tallarico

The OTRIONS seismic network (University of Bari Aldo Moro, 2013, FDSN code OT) is a local network installed in the Apulia region (Southern Italy) with the aim of monitoring the seismicity of the Gargano area (Northern Apulia) and the Salento area (Southern Apulia). OT network is managed by the University of Bari Aldo Moro (UniBa) and by the National Institute of Geophysics and Volcanology (INGV). It started to operate in 2013 and in 2019 the recording stations migrated to EIDA (all details can be found in Filippucci et al., 2021a). In 2021 a first database was collected, with the event detection achieved both manually and automatically with SeisComP3 (Helmholtz-Centre Potsdam), and was released (Filippucci et al., 2021a; Filippucci et al., 2021b).

Now, after ten years of operations, we focus on the microseismicity of the Gargano area with the aim of collecting a new seismic database for the period from April 2013 to December 2022, by using a recently acquired software, CASP (Complete Automatic Seismic Processor), for the automatic detection, picking and location of seismic events (Scafidi et al., 2019). The CASP software is installed on a remote server implemented by RECAS-Bari, the computational infrastructure of INFN and UniBa.

Through an appropriate parameter setting, we adapted CASP and NonLinLoc (Lomax et al., 2000) to the Gargano area and to the seismic stations available, both OT and INGV. We used the 1D velocity model of Gargano (de Lorenzo et al., 2017).

The recorded seismic events were organized in two catalogs: the first one is the automatic catalog, obtained from the automatic locations of CASP; the second one is the manual catalog, obtained through a manual revision of P and S waves arrival times. To evaluate the reliability of CASP, a comparison between the automatic and manual catalog was performed.

From a comparison of the manual catalog with the already released catalog of the Gargano seismicity (Filippucci et al., 2021b), the number of events detected by CASP increased a lot. Furthermore, the results show that the choice of the CASP parameters allows us to lower the minimum magnitude threshold of the recorded microseismicity in the Gargano area. Preliminary analysis of the earthquakes foci shows that the seismicity pattern retrace, substancially, the same discussed in the work of Miccolis et al., 2021.

How to cite: Ferreri, A. P., Romeo, A., Giannuzzi, R., Cecere, G., de Lorenzo, S., Falco, L., Filippucci, M., Michele, M., Selvaggi, G., and Tallarico, A.: The new earthquake catalog of the Gargano (Southern Italy) OTRIONS seismic network., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18752, https://doi.org/10.5194/egusphere-egu24-18752, 2024.

EGU24-20056 | ECS | Orals | SM1.1

Deep Scanning of the Bhutan Eastern Himalaya Seismic Dataset for Local Earthquakes 

Zamir Khurshid, Hamzeh Mohammadigheymasi, Dawei Gao, Jianxin Liu, and S. Mostafa Mousavi

Seismic networks monitor seismic activities across the globe, recording distinctive events within specific geographical and temporal frames. Whether old or new, each seismic record preserves valuable information, with its extraction relying mainly on the sophistication of the method. This study presents the implementation of an advanced earthquake detection workflow on a relatively old dataset, the Bhutan Pilot Experiment. This temporary five-station seismic network in Eastern Himalaya comprised a set of Broadband sensors deployed for 14 months from January 2002 to March 2003. However, outdated methodologies have limited the analysis of the recorded data, resulting in the reporting of only 175 local microearthquakes in this area. In this study, we reprocess the data using the recently introduced deep-scan Integrated Pair-Input deep learning and Migration Location workflow [1] to detect and locate local earthquakes. The IPIML employs the well-known Earthquake Transformer (EqT) model as its core function for initial phase picking, followed by a pair-input Siamese EQTransformer (S-EqT) to further mitigate the false negative rate using a pair-wise model. The S-EqT step demonstrated an approximately 40% increase in average detected phases compared to the standard EqT model. The detected phases are associated using the Rapid Earthquake Association and Location (REAL) method through grid searching, providing a preliminary list of detected events. This list encompasses 2458 detected events, several times larger than the previously reported catalog for this dataset. These events primarily cluster in central and eastern Bhutan, particularly along the Golpara lineament, a recognized strike-slip fault. The subsequent phase of this study involves precisely locating these events through the implementation of the Migration Location (MIL) method.

References
[1] H. Mohammadigheymasi et al., "IPIML: A Deep-Scan Earthquake Detection and Location Workflow Integrating Pair-Input Deep Learning Model and Migration Location Method," in IEEE Transactions on Geoscience and Remote Sensing, vol. 61, pp. 1-9, 2023, Art no. 5914109, doi: 10.1109/TGRS.2023.3293914.

How to cite: Khurshid, Z., Mohammadigheymasi, H., Gao, D., Liu, J., and Mousavi, S. M.: Deep Scanning of the Bhutan Eastern Himalaya Seismic Dataset for Local Earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20056, https://doi.org/10.5194/egusphere-egu24-20056, 2024.

EGU24-20889 | Posters on site | SM1.1

Local to moment earthquake magnitude conversion in mainland France and implications for seismic hazard assessment 

Pierre Arroucau, Clara Duverger, Paola Traversa, Guillaume Daniel, Jessie Mayor, and Gilles Mazet-Roux

Modern ground motion prediction equations used in probabilistic seismic hazard assessment studies are now almost exclusively expressed as a function of moment magnitude MW. Yet, earthquake catalogues produced by seismic observatories often provide local magnitude ML only. It is for instance the case for the Laboratoire de Détection Géophysique (LDG) catalogue recently published by Duverger et al. (2021) for mainland France. A conversion relationship was proposed by Cara et al. (2015) from ML (LDG) to MW. It appears however that this relationship does not result in a good fit when compared to recently compiled MW values for France and neighboring areas (Laurendeau et al., 2020). In this work, we propose a new conversion relationship based on the inversion of ML-MW couples for events present in both the LDG catalogue and the compilation of Laurendeau et al. (2021). In order to avoid the choice of an arbitrary number of segments to model the MW=f(ML) relationship, the inverse problem is solved in a Bayesian framework by means of the reversible jump Markov chain Monte Carlo (rj-McMC) algorithm (Green, 1995; Bodin et al., 2012). The number of segments, as well as their respective slopes and intercepts, are jointly invert for. As moment magnitude uncertainty is not known, it is also considered as an unknown, while the ML uncertainties provided in the LDG catalogue are fully accounted for by random sampling during the McMC process. We observe a geographical dependence of the differences between the available MW values and those obtained from calculation so a location-dependent term is also modeled. This allows to account for the regional attenuation variations that can affect ML estimates. The new conversion law is then applied to the full LDG catalogue and its impact on seismic hazard assessment is explored.

How to cite: Arroucau, P., Duverger, C., Traversa, P., Daniel, G., Mayor, J., and Mazet-Roux, G.: Local to moment earthquake magnitude conversion in mainland France and implications for seismic hazard assessment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20889, https://doi.org/10.5194/egusphere-egu24-20889, 2024.

EGU24-22522 | Orals | SM1.3

Foreshock sequence prior to the 2024 M7.6 Noto-Hanto earthquake, Japan 

Aitaro Kato and Takuya Nishimura

A destructive M7.6 earthquake occurred on January 1st, 2024, at shallow depths along the northern coast of Noto Peninsula on the back-arc side of Central Japan. The earthquake rupture started from an area where an intensive seismic swarm has lasted for more than 3 years (from December 2020). The seismic swarm consisted of numerous small planar faults dipping toward the southeast. In May 2023, an M6.5 event, that was the largest event before the M7.6 rupture, emanated from the swarm area toward shallow depths, resulting in the subsequent increase in the seismicity in the swarm area (Kato 2024 GRL). Then, the seismicity had gradually decayed to a level before the 2023 M6.5 event. Here we have explored the seismic and geodetic data to revel the nucleation process of the M7.6 event. Approximately two weeks before the M7.6 event, seismic activity exhibited a weak localization around the point of rupture initiation. After that, a foreshock sequence commenced roughly one hour before the occurrence of the M7.6 event, concentrated in proximity to the epicenter (within a 1-kilometer epicentral distance). The tightly clustered foreshock sequence consisted of around 20 events, including an M5.5 event 4 minutes prior and an M3 class event 1 second before the onset of M7.6 event. The M7.6 rupture nucleated from the deep side of one of planar clusters that were dominantly dipping toward the southeast direction. The growth process of the rupture in the M7.6 event is characterized by a complicated nature.

How to cite: Kato, A. and Nishimura, T.: Foreshock sequence prior to the 2024 M7.6 Noto-Hanto earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22522, https://doi.org/10.5194/egusphere-egu24-22522, 2024.

EGU24-22523 | Orals | SM1.3 | Highlight

The Impact of the 2024 Noto Peninsula Earthquake Tsunami 

Shunichi Koshimura, Bruno Adriano, Ayumu Mizutani, Erick Mas, Yusaku Ohta, Shohei Nagata, Yuriko Takeda, Ruben Vescovo, Sesa Wiguna, Takashi Abe, and Takayuki Suzuki

The tsunami generated by the Mw7.6 earthquake of Noto Peninsula, Japan left widespread impact. We analyzed multi-modal information and data to elucidate its impact.

We modeled the tsunami propagation and inundation with multiple tsunami source models based on GNSS-based crustal movement and tsunami waveform data to understand its propagation and inundation characteristics. The model results are verified by using post-tsunami field survey data. Preliminary tsunami modeling results implied that severe tsunami impacts were around Noto Peninsula (Shika to Nanao). Through the visualization of tsunami propagation model, we found that the remarkable tsunami refraction around the continental shelf of Noto Peninsula were responsible for high tsunamis in Suzu City. This distinctive sea bottom topography also affected the directivity of tsunami energy toward the Japan sea coasts, especially Joetsu city, Nigata Prefecture. Tsunami in Toyama bay had long duration of oscillation caused by multiple-reflection. The leading (negative) tsunami wave could not be explained by fault rupture and this implied the possibility of submarine landslides.

The post-tsunami field survey teams at Suzu City preliminarily found tsunami run-ups of 3 m or higher with flow depths of 2.5m or higher. Inside the tsunami inundation zone around Noto Peninsula, we found at least 648 houses out of 3398 were destroyed by both the strong ground motion and tsunami.

The cellphone-based population data (Mobile Spatial Statistics) were used to analyze the exposed population in the aftermath of the event. The hourly population estimates with 500m spatial resolution in the coastal communities implied how people reacted and were affected. Approximately 2500 population increase were found in the areas above 10 m after the major tsunami warning was issued.

How to cite: Koshimura, S., Adriano, B., Mizutani, A., Mas, E., Ohta, Y., Nagata, S., Takeda, Y., Vescovo, R., Wiguna, S., Abe, T., and Suzuki, T.: The Impact of the 2024 Noto Peninsula Earthquake Tsunami, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22523, https://doi.org/10.5194/egusphere-egu24-22523, 2024.

This presentation will report preliminary results of multifaceted analyses for the geomorphological aspects of the Mw 7.5 earthquake struck northern tip of the Noto Peninsula, Japan, at 16:10JST on January 1, 2024. The earthquake caused significant uplift of the northern coastal areas of the peninsula, accompanying a tsunami observed widely in the surrounding coastline, along with extensive tectonic deformations observed inland. Spatial extent of the crustal movements accords generally with the relief structures and distribution of marine terraces in the Noto Peninsula, implying the long-term tectonic forcing on the landscape evolution in this region. Numerous coseismic landslides occurred in steep mountainous terrains, which yield vast volume of sediment from hillslopes into fluvial channels. Inventory mapping revealed the localized distribution of the landslides, regulated most probably by geologic and topographic conditions. Areal density of the landslides can be explained by coupled factors of lithological susceptibility of the hillslopes to the seismic shaking and amplification of ground motion at the hilltops.

How to cite: Matsushi, Y.: Geomorphological consequences of the 2024 Noto Peninsula Earthquake: tectonic deformations, coseismic landslides, and their implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22535, https://doi.org/10.5194/egusphere-egu24-22535, 2024.

Since November 30, 2020, an intense earthquake swarm with over 22,000 M≥1 earthquakes and transient deformation have been continuously observed in the Noto Peninsula, central Japan, which is a non-volcanic/geothermal area far from major plate boundaries. During the earthquake sequence, Mw6.2 and Mw7.5 earthquakes occurred on May 5, 2023, and January 1, 2024, respectively. We report the transient and coseismic deformation related to the earthquake sequence by a combined analysis of multiple Global Navigation Satellite System (GNSS) observation networks, including one operated by a private sector company (SoftBank Corp.), relocated earthquake hypocenters, and tectonic settings. The start of the transient deformation coincides with a burst-type activity of small earthquakes in late 2020. A total displacement pattern in the first two years shows horizontal inflation and uplift of up to ~60 mm around the source of the earthquake swarm. The overall deformation rate gradually decreased with time except for the coseismic displacement of the Mw 6.2 earthquake and its postseismic displacement. On January 1, 2024, the coseismic horizontal and vertical displacements reached ~2 m at several GNSS sites. The pattern of the postseismic displacement for the first three weeks is similar to that of the coseismic displacement, though spatial decay of the postseismic displacement from the epicentral area is much gentler than that of the coseismic displacement. Viscoelastic relaxation of the mantle and/or lower crust is probably an important factor in explaining the observed deformation. In order to explain the transient deformation before the Mw6.2 and Mw7.5 earthquakes, we assumed a southeast-dipping fault plane based on the observed seismicity and regional tectonics and estimated the distribution of both reverse-slip and tensile components on the fault plane. In the first three months, a significant tensile component with a small slip component was estimated around a depth of ~15 km. The estimated volumetric increase is ~1.4 x 107 m3. Over the next 15 months, the observed deformation was well reproduced by shear-tensile sources, which represent an aseismic reverse-type slip and the opening of the southeast-dipping fault zone at a depth of 14–16 km. These slips and openings of the fault are estimated mainly at the down-dip extension of the intense earthquakes. We suggest that the upwelling fluid spread at a depth of ~16 km through an existing shallow-dipping permeable fault zone and then diffused into the fault zone, triggering a long-lasting sub-meter aseismic slip below the seismogenic depth. The aseismic slip further triggered intense earthquake swarms including the Mw6.2 and Mw7.5 earthquakes at the updip.

Acknowledgments: We are grateful to SoftBank Corp., ALES Corp., and GSI for providing us with GNSS data.

How to cite: Nishimura, T., Hiramatsu, Y., and Ohta, Y.: Deformation of the 2020-2024 Noto Peninsula earthquake sequence revealed by combined analysis of multiple GNSS observation networks in central Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22539, https://doi.org/10.5194/egusphere-egu24-22539, 2024.

EGU24-22540 | Orals | SM1.3

Ground motions and geotechnical aspects of the Noto Peninsula earthquake, Japan 

Hiroyuki Goto, Ayaka Nakatsuji, Dongliang Huang, and Silvana Montoya-Noguera

The Noto Peninsula earthquake (MJ7.6, MW7.5) caused extensive damage to buildings and infrastructure in the Noto Peninsula located in the northern part of Ishikawa prefecture, Japan. The hypocenter was within the area of the earthquake swarm that started in 2020. However, the source fault bilaterally ruptured over a length of 150 km beyond this area. The main residential areas in Wajima, Suzu, and Anamizu are located almost above the western segment of the reverse fault. The geographical features of the Noto Peninsula pose significant challenges for aid and support, particularly due to embankment and soil failures that caused main road closure or limited access. This has led to increased traffic on the few accessible routes, further delaying the arrival of support. The situation has hindered the restoration of essential services such as water and sewage systems and has slowed down the process of demolishing buildings deemed dangerous.

Valuable strong motions were observed during this event. The maximum Peak Ground Acceleration (PGA) in the horizontal component reaching 2.78g was recorded at the K-NET ISK006 station, a location known for significant site amplification around 0.2s. This value aligns with the dominant period in the Spectral Acceleration (Sa), thus the extreme PGA was probably due to the enhanced short-period component in the shallow soil amplification. In addition, K-NET ISK002 and ISK005 recorded large PGVs of 1.31 m/s and 1.59 m/s, respectively, and observed the remarkable Sa with 1.3g and 2.2g at T=1.0s, respectively, which are similar to the damage-prone record in the 1995 Kobe earthquake (JR Takatori record).

In the main residential areas of Anamizu and Wajima, two seismic stations are operated. One is located on the stiff soil ground, and the other is located in zones where residential damage was most severe. In both Anamizu and Wajima, the records at the damage site were amplified in the periods of 1-4 s, suggesting that the residential damage is related to the site amplification. Since the spectral ratio of the weak motions shows the amplification at periods of less than 1s, the major reason for the amplification at periods of 1 to 4 seconds during the main event is due to the nonlinear response of the soil ground.

How to cite: Goto, H., Nakatsuji, A., Huang, D., and Montoya-Noguera, S.: Ground motions and geotechnical aspects of the Noto Peninsula earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22540, https://doi.org/10.5194/egusphere-egu24-22540, 2024.

EGU24-22541 | Orals | SM1.3

Extensive liquefaction and building damage on the Niigata Plain due to the 1 January 2024 Noto Peninsula Earthquake: Geomorphological and geological aspects and land-use in coastal and lowland areas 

Kyoko Kataoka, Atsushi Urabe, Ryoko Nishii, Takane Matsumoto, Hirofumi Niiya, Naoki Watanabe, Katsuhisa Kawashima, Shun Watabe, Yasuhiro Takashimizu, Norie Fujibayashi, and Yasuo Miyabuchi

The Niigata (Echigo) Plain facing the Sea of Japan is located downstream of two large rivers (the Shinano-gawa River and the Agano-gawa River), and has three sand dune ridges which formed along the coastal areas during the Holocene. Niigata city, with a population of ~770,000, lies in the lower catchment of the alluvial-coastal system. Despite the city being approximately 160 km away from the epicenter of the January 1st 2024 Mw 7.6 Noto Peninsula Earthquake, extensive damage to houses, buildings, and infrastructure occurred throughout Niigata city due to pervasive liquefaction (resulting from the earthquake) in the coastal and lowland areas.

Our field investigation focuses on the Nishi-ku (west ward) of the city, where much of the liquefaction-induced building damage (~ 700 houses at the time of submission of the abstract) is concentrated. Although our “ground truth” fieldwork is still ongoing, we have manually mapped the distribution of damaged houses/buildings, road deformation, sand boiling (sand volcanoes), cracks, slides, groundwater springs and other related phenomena onto map sheets, before then digitising these data using GIS.  The distribution of damage is concordant with geomorphology—such as the Holocene sand dunes (and associated landforms) and buried meander loop of the Shinano-gawa River—as well as with subsurface geology (e.g. the location of the water table). Some damage areas are coincident with artificially modified landforms.

Liquefaction conspicuously occurred on natural (i.e. not artificially modified) gentle slopes of the Holocene coastal sand dunes and interdune swale/lowland. In particular, ground was liquefied in the lower parts of the landward slope of the sand dune (formed ~1800­–900 years ago) which has a lateral extension of ~7 km at the elevation of ~0–3 m above sea level. Sandy subsurface geology and high groundwater level of the Holocene sand dune, together with the force of gravity on the slopes, were probable contributors to liquefaction.

Evidence for liquefaction —including damage to houses—was observed in modern residential areas developed above the buried meander loops of the Shinano-gawa River, which have been historically filled in artificially with sandy material. Damage was also noted in houses built upon an artificially buried pond. However, there was no liquefaction on the natural levee along the abandoned meander loops where relatively old settlements are present.

Similar liquefaction occurred in Niigata city on the sand dune slopes and associated lowlands at the time of the M 7.5 Niigata Earthquake in 1964; the epicenter was in the Sea of Japan, approximately 60 km from the city.  Despite the Noto Peninsula Earthquake occurring remotely from Niigata, the aftermath of the earthquake indicates that certain geomorphologic and geological factors, coupled with particular seismic conditions, can result in repeated liquefaction. 

The field observation is still ongoing after the earthquake. Therefore this abstract is based on tentative results and analysis of our investigation so far. Further information on liquefaction related to the geomorphology and subsurface geology in this area will be available by the time of the 2024 EGU General Assembly.

How to cite: Kataoka, K., Urabe, A., Nishii, R., Matsumoto, T., Niiya, H., Watanabe, N., Kawashima, K., Watabe, S., Takashimizu, Y., Fujibayashi, N., and Miyabuchi, Y.: Extensive liquefaction and building damage on the Niigata Plain due to the 1 January 2024 Noto Peninsula Earthquake: Geomorphological and geological aspects and land-use in coastal and lowland areas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22541, https://doi.org/10.5194/egusphere-egu24-22541, 2024.

EGU24-22563 | ECS | Orals | SM1.3

The 2024 Mw 7.5 Noto Earthquake, shallow rupture with a stagnant initiation in a fluid-rich immature fault zone 

Haipeng Luo, Zhangfeng Ma, Hongyu Zeng, and Shengji Wei

Seismic hazard evaluation at critical infrastructures, such as nuclear power plant, urges deeper understanding on the fundamental physics that govern the initiation, propagation and termination of damaging earthquakes. The 2024 moment magnitude (Mw) 7.5 Noto Peninsula earthquake produced great hazards and exhibited complex rupture process. We derive high-resolution 3D surface deformation of the event using dense space geodetic observations, which reveal two major deformation zones separated by ~40 km along the coast of the Peninsula. Two large (>10m) shallow slip asperities with over 10 MPa stress drop on the thrust faults explain excellently the geodetic observations. A calibrated back-projection using teleseismic array high-frequency data shows that the rupture was stagnant around the hypocentre for ~20s before it propagated bilaterally at the speed of 3.4 km/s and 2.8 km/s towards southwest and northeast, respectively. The slow start of the rupture coincides with the seismic swarm surged since 2020 due to lower crust fluid supply, suggesting low normal stress (high pore fluid pressure) at the bottom edge of the seismogenic zone slowed down the initial rupture. The first major asperity of the rupture was accompanied with intense high frequency seismic radiation, and such radiation is even stronger from the largest asperity located at the southern edge of the Peninsula where the Peak-Ground-Acceleration (PGA) exceeding 2.6G at a site that is less than 40km away from the nuclear power plant. Large stress accumulation together with rough fault geometry and/or friction are likely responsible for the exceedingly large high-frequency radiation, which is mostly responsible for devasting damages.

How to cite: Luo, H., Ma, Z., Zeng, H., and Wei, S.: The 2024 Mw 7.5 Noto Earthquake, shallow rupture with a stagnant initiation in a fluid-rich immature fault zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22563, https://doi.org/10.5194/egusphere-egu24-22563, 2024.

SM2 – Computational, Theoretical and Data-Intensive Seismology

EGU24-4424 | Posters on site | SM2.1

Improving Seismic Hazard Assessment in Southeast Spain through CyberShake: A Physics-Based Approach 

Natalia Zamora, Marisol Monterrubio, Otilio Rojas, Rut Blanco, Cedric Bhihe, and Josep de la Puente

The Eastern Betic Shear Zone (EBSZ) experiences slow seismic deformation that leads to relatively low seismicity rates. Due to this, historical records underscore the substantial impact that earthquakes have had on local communities. The dearth of comprehensive data on moderate to large seismic events in this area, limits the accurate generation of seismic hazard and risk maps, posing a significant challenge for seismic risk planning. A way to address these limitations is leveraging physics-based earthquake simulations in the Southeast Iberian Peninsula. These simulations first require integrating paleoseismic data, models of fault distribution –such as the Quaternary-Active Faults Database of Iberia, seismic source characterizations and historical seismic catalogs, to construct an Earthquake Rupture Forecast (ERF), where likelihood of each fault rupture is weighted by an occurrence probability. Our study focuses on developing physics-based rupture scenarios and shake maps using CyberShake. CyberShake is designed to perform physics-based probabilistic seismic hazard assessments (PB-PSHA) by simulating a vast set of synthetic ground-motion time histories from kinematic rupture scenarios on the ERF three-dimensional finite-fault array. Originally tailored for PB-PSHA studies in Southern California by the SCEC (Southern California Earthquake Center); this research represents the first CyberShake application for Southeast Spain. The resulting shake maps represent an alternative basis for updating regional probabilistic seismic hazard maps and also could support crucial decision-making processes following a local earthquake, offering valuable insights for effective response strategies.

How to cite: Zamora, N., Monterrubio, M., Rojas, O., Blanco, R., Bhihe, C., and de la Puente, J.: Improving Seismic Hazard Assessment in Southeast Spain through CyberShake: A Physics-Based Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4424, https://doi.org/10.5194/egusphere-egu24-4424, 2024.

The Central Italy area close to the town of Amatrice was hit by a seismic sequence that started with a Mw 6.2 mainshock and lasted more than 1 year, with the highest event being the Mw 6.5 earthquake in Norcia. Reliable prediction of ground motion is difficult due to the limited data available particularly in the near-source; for this reason, we need realistic simulations of near-source broadband ground motion for seismic hazard assessment. Such simulations should be accurate and computationally efficient. In this work, we performed physics-based simulations to investigate ground motion variability for the Amatrice and Norcia earthquakes. Using the Frequency-Wavenumber (FK) technique we generated broadband ground motion time histories up to 10 Hz for both earthquakes. We exploited accurate source rupture models and various sets of Green’s functions generated with 1D velocity models obtained by slightly modifying the 1D velocity model of the Central Apennine Area proposed by Hermann et al. (2011). First, we employed the Graves and Pitarka (2016) technique to generate kinematic rupture models. Then, FK Green's functions are computed using the propagator matrix method proposed by Zhu and Rivera (2002). Using the RotD50 SA goodness of fit (GoF) between the recorded and simulated ground motion, we conducted 1D velocity model sensitivity analysis. Overall, the simulated time histories match well the recorded ground motion. We found that the 1D velocity model of the Central Apennine Area, modified for the inclusion of thin near-surface sedimentary layers, performed better than the other 1D velocity models considered in the GOF analysis. Our ground motion simulations suggest that the FK-based simulation approach can effectively reproduce the recorded ground motion in the frequency range of 0-10 Hz. Consequently, this approach holds promise for the seismic hazard assessment in Central Italy, enabling significant computer time savings compared to more complex methodologies that involve 3D wave propagation modeling.

How to cite: Artale Harris, P., Pitarka, A., and Akinci, A.: Broadband Ground Motions Simulations for M≥6.0 Earthquakes in the 2016/2017 Central Italy Seismic Sequence through a 1D Frequency-Wavenumber Approach: a Velocity Models Sensitivity Analysis , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5129, https://doi.org/10.5194/egusphere-egu24-5129, 2024.

EGU24-5475 | ECS | Posters on site | SM2.1

Scattered wave and coda reliability in 3D elastic seismic simulation: new insights for the advancement of inversion studies. 

Mirko Bracale, Ludovic Margerin, Romain Brossier, and Michel Campillo

In this study we investigate the behavior of seismic waves in a high-scattering medium using numerical simulations of the full wavefied based on the Spectral Element Method solutions of the wave equation. The simulated 3D elastic medium was designed to have Laplacian correlated heterogeneity, creating a realistic representation of the complexities present in natural seismic environments. We conducted analyses on three distinct cases, each characterized by increasing levels of heterogeneity fluctuation, ranging from 10% to 25% standard deviation.
We checked the consistency between theoretical results and simulations with regard to the value of the mean free path, the asymptotic behavior at long times and the partitioning of energy between compressional and shear modes. Excellent agreements were obtained, indicating the reliability of the numerical models of coda waves used here.  Our analyses are made both at depth and at the free surface, allowing us to compare the behavior of seismic waves under varying conditions. Additionally, we validated our findings by conducting independent numerical simulations of wave energy densities that used Monte Carlo methods to solve the Radiative Transfer Equation, thus corroborating the robustness and accuracy of our results for long lapse times.
We show that under specific conditions, existing simulation codes can effectively replicate wave propagation in a highly scattered medium. This implies that a greater part of the waveform, namely the late envelops, could be employed in inversion processes, thus opening up new possibilities in the realm of inversion studies. Furthermore, we used these simulations to investigate the behavior of the wavefield and its gradient, exploring the information that can be extracted from their evolution over time to improve characterization of environmental heterogeneity.

How to cite: Bracale, M., Margerin, L., Brossier, R., and Campillo, M.: Scattered wave and coda reliability in 3D elastic seismic simulation: new insights for the advancement of inversion studies., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5475, https://doi.org/10.5194/egusphere-egu24-5475, 2024.

EGU24-6202 | ECS | Orals | SM2.1

The influence of gouge formation on seismicity and fault slip behavior.  

Miguel Castellano, Enrico Milanese, Camilla Cattania, and David Kammer

Through the progression of seismic activity, natural fault zones undergo a complex evolution characterized by the accumulation of damage and the formation of gouge within the fault core across multiple scales. Even though this is believed to be among the key factors affecting the evolution of fault seismicity over time, a deep understanding of the mechanisms at play is still missing. In this study, we explore the role of gouge production in the self-organization process of loaded rough faults, focusing on the evolving dynamics of earthquake nucleation, recurrence and moment partitioning during the seismic cycle. We model the stress and sliding dependence of gouge evolution by linearly coupling Archard's wear law with rate-and-state friction through the critical slip distance ( Dc ). Including this new formulation in 2D quasi-dynamic, elastic simulations of rough faults, we can reproduce the effects of spatially and temporally heterogeneous gouge evolution. Following the build-up of gouge over many cycles, we observe a progressive transition from cascade-driven to creep-dominated nucleation processes, marked by an increase of precursory slow slip and foreshock activity. A clear shift in the moment partitioning from faster to slower slip rates becomes evident as heterogeneity grows larger, followed by a reduction of the total cumulative moment released. Finally, the recurrence interval is observed to grow initially, then drop abruptly and become more unpredictable as the amplitude of Dc continues to rise. Incorporating a new formulation of gouge production in earthquake cycles simulations, this work sheds light on the role of gouge accumulation in the maturation process of natural faults, offering critical insights for seismic risk assessment and mitigation.

How to cite: Castellano, M., Milanese, E., Cattania, C., and Kammer, D.: The influence of gouge formation on seismicity and fault slip behavior. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6202, https://doi.org/10.5194/egusphere-egu24-6202, 2024.

In a three-dimensional Cartesian coordinate system, the deformation of the medium around a particle includes strain, translation, and rotation. Rotational motion is an important aspect of current seismological research. Seismologists have recognized the importance of rotational motion in dynamic response and damage of structures caused by certain earthquakes, through investigations into earthquake damage. In rapid earthquake intensity reports, it is essential to not only consider factors such as earthquake location, source depth, magnitude, and fault rupture model, but also to emphasize the analysis of the amplification effect of shallow media. We discuss the attenuation characteristics and difference between seismic translational and rotational components by medium viscoelasticity through two-dimensional numerical simulation, analyze the amplification effect of shallow viscoelastic low-velocity layer on ground motion by the reference site spectral ratio (RSSR), and discuss the difference of the amplification caused by different low-velocity layer factors. The results show that the seismic primary frequency decreases more with increasing viscoelasticity, and the energy of rotational component attenuates more significantly than that of translational component. The elastic low-velocity layer amplifies high-frequency signals of body waves greater than the viscoelastic low-velocity layer, especially in rotational component. When shallow low-velocity layers consist of multilayered sediments compared to a single sediment, the amplification of surface wave is stronger, particularly in rotation. We follow the research method used for seismic translation to discuss the amplification effect of shallow viscoelastic medium on seismic rotation, which is important for performance-based seismic design and earthquake damage analysis.

How to cite: Li, W., Zhang, Y., and Wang, Y.: Attenuation and amplification effects of seismic translational and rotational components in shallow media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7150, https://doi.org/10.5194/egusphere-egu24-7150, 2024.

We focus on the main rupture process of the Mw7.8 Februrary 6th 2023 01:17 UTC Pazarcık, Turkey, propagating to the south-west direction where more than ten acceleration stations recorded the ground motions within a distance of a few kilometers from the fault. On one hand, we estimate the frictional parameters directly from the waveforms of the acceleration records. Several stations are sufficiently close enough to characterize the cohesive zone length, and the estimated critical displacement (Dc) ranges from 90 cm to 150 cm. On the other hand, we carry out the dynamic rupture simulations along the constructed non-planar fault and also simulate the ground motions in the surrounding, using boundary integral equation and finite difference methods.  Upon the constructed standard model, we prepare different models of Dc distribution both along dip and strike. Our numerical simulations show that a longer Dc is necessary in the shallowest depth (2-3 km depth) than in the deep seismogenic zone. The observed ground motion pattern in terms of PGV (Peak Ground Velocity) shows a strong correlation with the estimated strike-variated Dc and the rupture process controlled by the fault geometry.

How to cite: Aochi, H. and Cruz-Atienza, V.: Characterization of shallow fault parameters from the near-field ground motion data and non-planar dynamic rupture simulations for the Mw7.8 February 6th Pazarcık, Turkey, earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7928, https://doi.org/10.5194/egusphere-egu24-7928, 2024.

EGU24-8160 | Orals | SM2.1

Inferred source models for Alpine Fault Earthquake Scenarios and influence on seismic hazard. 

Caroline Holden, John Townend, Calum Chamberlain, Emily Warren-Smith, Carmen Juarez-Garfias, Olivia Pita-Sllim, Kasper Van Wijk, and Marine Denolle

As part of the Southern Alps Long Skinny Array (SALSA) project, ~35+ seismometers have been deployed with 10–12 km spacing along a 450 km-long   section of the Alpine Fault. SALSA is focused on determining the ground motions likely to be produced by a future Alpine Fault earthquake. This project is addressing three principal objectives: (1) Determine the Alpine Fault’s subsurface geometry, present-day slip rates, and spatial variations in how tectonic stresses are currently accumulating on the fault, (2) Estimate the ground shaking that would be recorded at seismometers throughout central and southern New Zealand by localised slip at different points on the Alpine Fault, focusing on the synthesis of long-period Green's functions  representing accurate path effects between sources distributed along the fault and population centres throughout the South Island, and (3) Calculate the ground shaking hazard from geologically informed earthquake rupture scenarios. In this presentation we will address the influence of inferred Alpine Fault source models derived from empirical data as well as current knowledge of the fault geological and geophysical parameters on regional seismic hazard.

How to cite: Holden, C., Townend, J., Chamberlain, C., Warren-Smith, E., Juarez-Garfias, C., Pita-Sllim, O., Van Wijk, K., and Denolle, M.: Inferred source models for Alpine Fault Earthquake Scenarios and influence on seismic hazard., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8160, https://doi.org/10.5194/egusphere-egu24-8160, 2024.

Earthquakes that nucleate at depths shallower than a few km are very rare but pose high near-fault hazard despite moderate magnitudes. Some very shallow earthquakes have been associated with surface mass removal processes, both natural (e.g. glacier melting) and anthropogenic. A notable recent case is the November 11 2019 Mw 4.9 Le Teil, France earthquake. It called strong public attention because of its very shallow depth (slip shallower than 2 km), very strong ground motion (>1 g) affecting the near-fault population, and proximity to nuclear power plants. It has been proposed that this earthquake could have been triggered by mass removal from a large cement quarry located close to the epicenter. Indeed, the estimated Coulomb stress change induced by the quarry activity on the fault is of several 100 kPa. Here, we further evaluate the mechanical viability of the quarry-triggering hypothesis through 3D earthquake cycle simulations.

We consider a dipping fault governed by rate-and-state friction, with velocity-weakening steady-state behavior, and a realistic mass removal history constrained by analyses of aerial optical images across ~180 years of quarry activity. To account for uncertainties about the recurrence time of natural earthquakes on the fault and the timing of the previous natural event, we consider mass-removal loads starting at different times relative to the simulated natural earthquake cycle. Our simulations show that realistic mass removal rates can advance the failure time by thousands of years. Simulations with a constant mass-removal rate but same cumulative removed mass at 180 years produce a similar triggering timing. This indicates that the induced clock advance mostly depends on the cumulative load, rather than on its rate. The dependence on loading rate manifests through the following mechanism: the model with constant rate can trigger slow slip events instead of regular earthquakes, which postpones the next regular earthquake by a long time, whereas the model with realistic loading history (and higher load rates) always triggers regular earthquakes. The quarry's proximity to the fault and the frictional heterogeneity on the fault also play important roles. For example, clock advance is higher if the quarry location is closer to the edge of the velocity-weakening zone and lower in the middle. Also, the model with the classical rate-and-state model shows negligible impact if the quarry is at the top of a steady-state behavior zone and far away from the velocity weakening zone.

While these models confirm the possibility that mass removal can trigger shallow earthquakes on velocity-weakening faults, we will also report on additional simulations that examine whether such triggering can occur on a fault with velocity-strengthening behavior at shallow depth or it requires a more sophisticated fault rheology, such as friction with a transition from velocity-strengthening to velocity-weakening at increasing slip rate. These modeling efforts will be further constrained by ongoing laboratory experiments on representative materials of the fault that ruptured in the Le Teil earthquake.

How to cite: Sopaci, E. and Ampuero, J. P.: Triggering of very shallow earthquakes by surface mass removal processes - case study of the 2019 Mw4.9 Le Teil, France earthquake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9827, https://doi.org/10.5194/egusphere-egu24-9827, 2024.

The Mw 7.8 and Mw 7.5 doublets of the 2023 Turkey seismic sequence show strong velocity pulses that may have caused extensive damage to buildings and structures. We analyze the velocity pulses from the empirical data (both raw and processed) to understand the causes of these for these doublets. The analysis includes a comparison with the velocity pulses from the synthetic data of the Jia et al. (2023) dynamic rupture simulation available for the first Mw 7.8 event and an analysis of the variability of large instrumented earthquakes of the last 30 years. We characterize the properties of the ground motion pulses (e.g., period, velocity, and orientation) using the algorithm proposed by Shahi and Baker (2014). The identified pulses in the synthetic data show the main characteristics of the pulses (periods, PGV). However, the pulse properties in the synthetic data show less variability than the natural variability found in the empirical data, particularly a random behavior in the pulse orientation. The results then indicate that the pulse characteristics in the near-fault regions of large-magnitude earthquakes exhibit a significant variability and that this variability is similar to the one observed in past large earthquakes. This pronounced variability can be attributed to various factors, including directivity effects and site effects. This suggests that the full complexity of earthquake rupture processes and site configurations should be taken into account to be able to capture the high variability in pulse properties.

How to cite: Yen, M.-H., Türker, E., and Cotton, F.: An analysis of strong velocity pulses from the empirical data and dynamic rupture simulations of the 2023 Kahramanmaras earthquake doublets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9916, https://doi.org/10.5194/egusphere-egu24-9916, 2024.

EGU24-10403 | ECS | Orals | SM2.1

Thermal runaway as driving mechanism of deep earthquakes – Constraints from numerical modeling 

Arne Spang, Marcel Thielmann, and Daniel Kiss

Deep-focus earthquakes occur at depths of 300-700 km below the surface where brittle failure is unlikely due to the large lithostatic pressure. Instead, they require a ductile localization mechanism that can significantly reduce rock strength and create highly localized shear zones. The feedback loop of shear heating, temperature-dependent viscosity and localization is called thermal runaway and has been linked to deep-focus earthquakes.

We present one- and two-dimensional (1D and 2D) numerical, thermomechanical models that investigate the occurrence, nucleation and temporal evolution of thermal runaway in a simple shear setting. The models are characterized by a visco-elastic rheology where viscous creep is accommodated with a composite rheology of diffusion and dislocation creep as well as low-temperature plasticity. We utilize the pseudo-transient iterative method in combination with a viscosity regularization and adaptive time stepping to solve this nonlinear system of equations and avoid resolution dependencies.

Varying eight input parameters, we observe two distinct types of behavior. After elastic loading, models either release stress over hundreds to thousands of years, accompanied by low slip velocities and moderate temperature increase, or they release stress within seconds to minutes while slip velocity and temperature increase drastically – Thermal runaway occurs. With nondimensional scaling analysis, we unite the eight different input parameters into two nondimensional numbers that allow inferring the behavior. The ratio tr/td describes the competition between heat generation by viscous dissipation and heat loss due to thermal diffusion whereas the ratio Uel/Uth compares the elastic and thermal energy density before stress relaxation.

2D experiments show that thermal runaway allows highly localized ductile ruptures to nucleate at small heterogeneities and propagate like brittle fractures. The ruptures accelerate during propagation and reach the highest velocities when two tips link up. Rupture trajectories are usually parallel to the direction of background deformation but bend in the vicinity of other ruptures to allow for a link up. The results demonstrate that thermal runaway can create highly localized, propagating shear zones that reach slip velocities in line with slow earthquakes at upper mantle and transition zone conditions.

How to cite: Spang, A., Thielmann, M., and Kiss, D.: Thermal runaway as driving mechanism of deep earthquakes – Constraints from numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10403, https://doi.org/10.5194/egusphere-egu24-10403, 2024.

EGU24-10632 | ECS | Orals | SM2.1

A quantum computing concept for 1-D elastic wave simulation 

Malte Schade, Cyrill Bösch, Vaclav Hapla, and Andreas Fichtner

We present a quantum computing concept for 1-D elastic wave propagation in heterogeneous media with two components: a theoretical formulation and an implementation on a real quantum computer. The method rests on a finite-difference approximation, followed by a transformation of the discrete elastic wave equation to the Schrödinger equation, which can be simulated directly on a gate-based quantum computer. An implementation on an error-free quantum simulator verifies our approach and forms the basis of numerical experiments with small problems on an actual quantum computer. As the presented approach promises exponential speedup compared to classical numerical wave propagation methods, it has the potential to significantly push the limits of global full-waveform inversion, particularly maximum feasible frequencies, on future quantum computers.

How to cite: Schade, M., Bösch, C., Hapla, V., and Fichtner, A.: A quantum computing concept for 1-D elastic wave simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10632, https://doi.org/10.5194/egusphere-egu24-10632, 2024.

Natural faults exhibit complex geometry. In this study, we model cycles of earthquake ruptures on non-planar faults governed by a friction formulation that combines rate and state friction for low slip velocity and enhanced weakening friction in the form of flash heating for high slip velocity, both consistent with rock friction experiments. The numerical method allows non-matching meshes across the fault, continuously updates the fault geometry, and employs variable time steps with quasi-static and fully dynamic time integration schemes during slow and fast deformation stages, respectively. To prevent the development of large stresses on the fault, the model also accounts for fault wear and inelastic off-fault deformation. We investigate the effect of macro-scale roughness on the fault slip behavior and rupture dynamics in terms of event magnitude, stress drop, and rupture style and speed. We analyze the relationship between the fault geometry, stresses from the preceding earthquakes, and rupture characteristics.

The simulation results show a significant increase in event variability with roughness levels, with both small partial ruptures and ruptures significantly more intense than those on planar faults. The planar faults host a sequence of earthquakes that rupture the entire fault, exhibiting similar magnitudes and stress drops. The substantial reduction in friction enables the ruptures to propagate under a low background shear-to-normal stress ratio as self-healing slip pulses, with a sub-Rayleigh rupture speed. Faults with low roughness levels generally show a similar pattern. Prior to some events, the stress ratio along the fault slightly increases, leading to ruptures with secondary slip pulses and larger magnitudes. As roughness increases, stresses become more heterogeneous, resulting in a more complex sequence of ruptures, some of which arrest at restraining bends with a low stress ratio. However, stress accumulation and slip deficit during these partial ruptures result in high stress ratios on the unruptured fault segments. These are eventually released by large events of crack-like ruptures with supershear propagation speed and stress drops and slip significantly larger than a typical event on a planar fault. Therefore, while fault roughness can cause rupture arrest, consistent with previous studies, it can also substantially increase earthquake magnitudes. This factor should be accounted for in earthquake hazard assessments.

How to cite: Tal, Y.: Rupture Dynamics and Characteristics During Earthquake Cycles on Nonplanar Faults with Strongly Rate-Weakening Friction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11379, https://doi.org/10.5194/egusphere-egu24-11379, 2024.

EGU24-13834 | Orals | SM2.1

CyberShake simulation of strike-slip earthquakes on the Southwest Iceland transform zone 

Otilio Rojas, Farnaz Bayat, Marisol Monterrubio-Velasco, Claudia Abril, Scott Callaghan, Juan E. Rodríguez, Milad Kowsari, Benedikt Halldórsson, Kim Olsen, Alice-Agnes Gabriel, and Josep de la Puente

The Statewide Southern California Earthquake Center (SCEC) has designed and implemented CyberShake (CS), a high-performance computing (HPC) workflow to undertake Physics-Based Probabilistic Seismic Hazard Analysis (PB-PSHA) in California (CA). Here, we have ported CS from CA to the South Iceland Seismic Zone (SISZ) and the Reykjanes Peninsula Oblique Rift (RPOR), which experience sinistral transform motion and pose a very high earthquake risk to about 2/3 of the Iceland population. We consider a realization of the 3D SISZ-RPOR fault system, where fault areas are estimated from event magnitude through a scaling law (Mai & Beroza, 2017),  that fits maximum fault extents observed from slip inversions and surface mappings. The magnitude variability across the modeling region (~63.8°- 64.1°N, ~20°-23°W) is Mw 5-7. In this work, we employ CS to model ~2100 kinematic earthquake ruptures and quantify the resulting ground motion (GM) in terms of Pseudo Spectral Acceleration (PSA) intensity measures. An important computational milestone is the software development of an open-source in-house workflow manager at the Marenostrum Supercomputer that replaces the one used in CA by SCEC based on Pegasus and HTCondor. This new workflow manager handles input data (fault-plane geometries, rupture magnitudes, surface stations for GM recording and hazard studies), orchestrates the execution of CS components, and stores results (particle velocity seismograms and hazard curves). Among these components, the Graves-Pitarka (GP) kinematic rupture generator is used to produce finite-fault source descriptions characterized by a few large asperities. The other important component is the open-source fourth-order finite-difference staggered-grid AWP-ODC earthquake simulation code that allows for reciprocity and efficiently simulates rupture and seismic wave propagation in 3D heterogeneous Earth models. CS uses an adjoint computational procedure in which simulations of wave propagation are performed using a polarized delta source to compute the Strain Green Tensors (SGTs) at each fault point. The convolution of SGTs with GP ruptures yields particle-velocity seismograms at each station. SGT time histories are memory demanding, but the adjoint calculations are completely independent and therefore embarrassing parallel, making CS a highly efficient earthquake simulation tool. In this study, SGTs are constructed using a source frequency range of 0-1.0 Hz, generating ground motion synthetics resolved up to 0.5 Hz. CS rotation-invariant PSA values (3 and 5 sec periods) computed from our study show a good agreement with updated Bayesian ground motion prediction equations (Kowsari et al, 2022). This study is a first step towards a PB-PSHA in the SISZ-RPOR region and to routinely apply Cybershake outside of California.

REFERENCES:

Mai, M., & Beroza, G. Source scaling properties from finite-fault-rupture models. Bulletin of the Seismological Society of America, 90(3), 604-615, 2000.

Kowsari, M., Sonnemann, T., Halldorsson, B., Hrafnkelsson, B., Snæbjörnsson, J. &  Jonsson, S. Bayesian inference of empirical ground motion models to pseudo-spectral accelerations of South Iceland Seismic Zone earthquakes based on informative priors. Soil Dynamics and Earthquake Engineering, 132, 106075, 2020.

How to cite: Rojas, O., Bayat, F., Monterrubio-Velasco, M., Abril, C., Callaghan, S., Rodríguez, J. E., Kowsari, M., Halldórsson, B., Olsen, K., Gabriel, A.-A., and de la Puente, J.: CyberShake simulation of strike-slip earthquakes on the Southwest Iceland transform zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13834, https://doi.org/10.5194/egusphere-egu24-13834, 2024.

Friction plays a crucial role in rupture dynamics and yet its precise nature remains elusive. Consequently, a friction law must be assumed to model rupture. Commonly used constitutive laws for modeling friction include slip-weakening laws which are characterized by a drop from static to dynamic frictional strength. Within this framework, the prevailing understanding asserts that the frictional behaviour is solely controlled by the fracture energy - the area beneath the frictional strength versus the cumulated slip curve. In particular, it is claimed that the curve's shape itself has no influence on the system's response. Here we perform fully dynamic rupture simulations to challenge prevailing beliefs by demonstrating that the constitutive law shape exerts an intimate control over rupture profiles. For a consistent fracture energy but varying constitutive law shapes, the velocity profile is different: each abrupt slope transition leads to the localization of a distinct velocity peak. For example, in the case of a dual slip-weakening law featuring two different slopes, the rupture exhibits two distinct velocity peaks. This distinction significantly influences how a rupture responds to a stress barrier. These results are derived through two separate numerical schemes (spectral boundary integral and finite element methods) ensuring their independence from the computational approach employed.

How to cite: Ferry, R. and Molinari, J.-F.: Unveiling the influence of slip-weakening laws' shapes on rupture dynamics: beyond fracture energy in controlling rupture profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15557, https://doi.org/10.5194/egusphere-egu24-15557, 2024.

EGU24-16751 | ECS | Orals | SM2.1

Differences in breakdown work and fracture energy in slip weakening constitutive laws 

Chiara Cornelio, Shane Murphy, Elena Spagnuolo, Stefan Nielsen, and Massimo Cocco

Earthquakes are associated with the propagation of a dynamic rupture, which radiates elastic energy through seismic waves. The generation of seismic radiation is related to dynamic weakening of shear stress and stress drop. In modeling dynamic ruptures, shear stress evolution is commonly imposed through a constitutive law, such as the widely adopted slip weakening laws. According to these constitutive laws, shear stress evolves as a function of slip in each point of the rupturing fault, prescribing strength excess, stress drop and dynamic weakening.

Here, we compare two well-known slip weakening laws: namely, the classic Ida’s (1972) and the Ohnaka’s (1996) slip weakening laws. The former prescribes that fault stress increases from the initial stress to the peak stress with zero slip and then linearly decreases from the peak value to a residual value over a slip-distance Dc (dynamic weakening). The latter assumes that the initial stress hardening phase occurs over a non-negligible slip-distance Da and that shear stress decrease from the peak value is not linear. The Ohnaka’s law was validated with numerous laboratory experiments. The evolution of shear stress with slip allows the estimate of the breakdown work Wb, i.e. the excess of work above a minimum stress level with slip from 0 to Dc.

We collected data from high-velocity friction experiments to quantify yield, peak and residual stresses, Da and Dc distances for bare-rock samples of Carrara Marble and Gabbro deformed under various experimental conditions (room humidity, vacuum, pressurized fluids) and normal stress (from 5 to 40 MPa). The ratio Da/Dc is much lower for Carrara marble (0.015) than for Gabbro (0.12). We implemented the Ohnaka’s constitutive law in a 2D finite difference code for spontaneous dynamic ruptures characterized by a fault in a homogeneous elastic material.  We perform simulations using the two different slip weakening laws. We kept constant Dc, and we compared the results of the simulations in terms of rupture style, rupture velocity, breakdown work, and cohesive zone size. As expected both laws yield crack-like ruptures. Moreover, Ohnaka’s law in comparison to the linear slip weakening law produces:

  • rupture velocity ~2 % higher;
  • breakdown work (Wb) up to 60 % lower. Moreover, dividing the breakdown work into the energy dissipated between the yield stress and the peak stress over the slip-distance Da (Wba), we notice that Wba can reach up to the 30% of the total Wb in case of Gabbro (Da/Dc = 0.12).
  • a cohesive zone size (defined as the portion of the fault in which the slip velocity is higher than zero and the stress is higher than its residual value) up to 50% larger.

Therefore, Ohnaka’s law generates more energetic ruptures (i.e. faster rupture velocity and peak slip-rate) despite having a larger cohesive zone due to the lower breakdown energy dissipated during rupture propagation. We discuss our results in terms of the difference between breakdown highlighting the implications on dynamic rupture propagation and earthquake energy budget. We emphasize that common interpretations of energy dissipated during rupture propagation are model-dependent.

How to cite: Cornelio, C., Murphy, S., Spagnuolo, E., Nielsen, S., and Cocco, M.: Differences in breakdown work and fracture energy in slip weakening constitutive laws, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16751, https://doi.org/10.5194/egusphere-egu24-16751, 2024.

EGU24-18840 | Orals | SM2.1

Taiwan Non-Ergodic Ground Motion Prediction Equations for Spectral Accelerations and Instantaneous Powers 

Shu-Hsien Chao, Jyun-Yan Huang, Chiao-Chu Hsu, Che-Min Lin, Chih-Hsuan Sung, and Chun-Hsiang Kuo

Currently, available Taiwan ground motion prediction equations were developed based on ergodic assumption, which means that the same ground motion prediction equation is applicable to any ground motion scenarios occurred in Taiwan no matter what locations of earthquake sources are; what paths from sources to sites are, and what locations of sites are. However, several recent studies have shown that the regional differences of source, path and site effects of ground motion in Taiwan are significant. As a result, the prediction for some specific ground motion scenarios in Taiwan may be biased, and the aleatory uncertainty of the ground motion may be over-estimated by using current available Taiwan ground motion prediction equations. Based on it, the aim of this study is to develop new Taiwan ground motion prediction equations for spectral accelerations and instantaneous powers based on non-ergodic assumption which are depended on the source and site locations to consider the regional differences of source, path and site effects of ground motion in Taiwan by using available ground motion records, 3-D velocity models, and horizontal-to-vertical Fourier spectra ratios. A better ground motion prediction result with higher accuracy and lower uncertainty will be achieved based on the proposed non-ergodic Taiwan ground motion prediction equations in this study. Structural damage induced by a scenario-based earthquake can be estimated more precisely by using the proposed non-ergodic ground motion prediction models for spectral acceleration and instantaneous power at fundamental period simultaneously.

How to cite: Chao, S.-H., Huang, J.-Y., Hsu, C.-C., Lin, C.-M., Sung, C.-H., and Kuo, C.-H.: Taiwan Non-Ergodic Ground Motion Prediction Equations for Spectral Accelerations and Instantaneous Powers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18840, https://doi.org/10.5194/egusphere-egu24-18840, 2024.

EGU24-19294 | ECS | Orals | SM2.1

One-way linking of 3D long-term geodynamic models and short-term earthquake dynamic rupture models 

Anthony Jourdon, Nicolas Hayek, Dave May, and Alice-Agnes Gabriel

Tectonic deformation plays a crucial role in shaping the Earth's surface, with strain localization resulting in the formation of shear zones in depth and faults on the surface. These structures accommodate a significant portion of the displacement between tectonic plates. While long-term deformation can be approximated as continuous visco-plastic processes, earthquakes involve cycles of stress loading and unloading that trigger rapid and catastrophic elasto-plastic deformation. Earthquake dynamic rupture models offer valuable insights into studying and comprehending earthquakes. However, these models heavily rely on initial conditions that are often challenging to obtain solely from observations. Particularly, a mechanically self-consistent prestress state loading a fault prior a seismic event and 3D fault geometry, especially in depth, are commonly poorly constrained. Nonetheless, the prestress state and the fault geometry significantly impact earthquakes initiate, propagate, and arrest and the associate radiation of seismic waves and ground shaking.

To address the lack of information on stress and fault geometry, one promising approach is to use long-term geodynamic numerical simulations. In this study, we employ pTatin3D, a visco-plastic finite element software, to simulate the evolution of strike-slip deformation in 3D over geological time scales. To ensure a physically consistent long-term model, the fault geometry is not prescribed but solved for based on the lithospheric rheology and tectonic plate velocities. However, the geodynamics model describes faults as continuous volumetric fields of finite deformation and strain-rate, rendering them 3D objects, while earthquake dynamic rupture models typically represent faults as 2D interfaces.

In this study, we outline a new and versatile method to link 3D geodynamic simulations to rupture dynamics earthquake and seismic wave propagation modelling. We first extract 3D volumetric shear zones from the geodynamic model and automatically convert them into surface representations. Next, we generate meshes including these as faults for dynamic rupture models. Finally, we showcase 3D dynamic rupture models utilizing the stress states and faults self-consistently as derived from the long-term geodynamic model as initial conditions.

How to cite: Jourdon, A., Hayek, N., May, D., and Gabriel, A.-A.: One-way linking of 3D long-term geodynamic models and short-term earthquake dynamic rupture models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19294, https://doi.org/10.5194/egusphere-egu24-19294, 2024.

EGU24-19464 | ECS | Posters on site | SM2.1

A first look at the ground motion characteristics unveiled by accelerometric data: the case of Campi Flegrei area (Italy) 

Claudia Pandolfi, Donato Talone, Giusy Lavecchia, Giovanni Costa, Veronica Pazzi, Simone Francesco Fornasari, Luisa Filippi, Elisa Zambonelli, Alfredo Ammirati, Sebastiano Sirignano, Aybige Akinci, and Rita de Nardis

Campi Flegrei is a volcanic region in Southern Italy of great interest for volcanic risk due to the presence of a potentially dangerous caldera collapse structure in a very densely populated area. In historical times, the Campi Flegrei area experienced explosive eruptions (the most recent – the Monte Nuovo eruption, 1538 CE), and in recent times (from 1969 to 1972 and from 1982 to 1984) critical seismic activity and bradyseism crises. Since 2020 the increase of seismicity related with the acceleration of ground uplift is a matter of the scientific and civil protection debate, given the vulnerability of the urban settlements under the effect of the volcanic phenomena. The recent bradyseism crisis climaxed in September 2023, with a high number of seismic events per month (1000 events per month) and a maximum magnitude (Md) of 4.2— the strongest event recorded in the last forty years. In general, predicting attenuation law in volcanic areas poses a significant challenge due to the limited availability of strong motion records, the predominance of lower magnitude events, and the distinct characteristics of waveforms compared to tectonic earthquakes. Moreover, additional challenges arise from the potential anisotropic behavior of the area, which could lead to high seismic impact for specific directions of seismic wave propagation. This makes it difficult to establish predictive models for ground motion, hindering the development of reliable risk scenarios and the effective implementation of civil protection measures. Since September 2023, the Civil Protection Department started improving the station coverage of the accelerometric network (RAN, Rete Accelerometrica Nazionale) by installing 3 new seismic stations along coastal areas and around Pisciarelli locality. The accelerometric data, recorded from the 18th of September 2018 to the 4th of October 2023 by 12 accelerometric stations of the RAN, fill a gap of information and represent an important contribution in adding new constraints to ground motion characterization. Specifically, we analyzed 3771 three-component records whose 186 exhibit a magnitude exceeding 3.5. We derived the engineering interest parameters (e.g., Peak Ground Acceleration, PGA; Peak Ground Velocity, PGV; Housner Intensities, HI; Arias Intensities, AI; significant duration, Td; Spectral accelerations) and compared them with the available ground motion prediction equations defined in the tectonic and volcanic areas in Italy and abroad. For the two events >= 3.8 we perform a comprehensive analysis. Our results unveil a trend similar to that predicted in the ground motion prediction equations in the near field but with a steeper attenuation recorded beyond approximately 5 km of distance. Furthermore, a relevant result is the existence of elevated peaks in PGA (Peak Ground Acceleration) at considerable distances also for low magnitude values underscoring the potential existence of preferential directions in propagation. These findings are crucial for understanding the region's seismic impact and enhancing risk assessment and civil protection strategies in this densely populated volcanic area.

How to cite: Pandolfi, C., Talone, D., Lavecchia, G., Costa, G., Pazzi, V., Fornasari, S. F., Filippi, L., Zambonelli, E., Ammirati, A., Sirignano, S., Akinci, A., and de Nardis, R.: A first look at the ground motion characteristics unveiled by accelerometric data: the case of Campi Flegrei area (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19464, https://doi.org/10.5194/egusphere-egu24-19464, 2024.

Discrimination of underground explosions from naturally occurring earthquakes and other anthropogenic sources is one of the fundamental challenges of nuclear explosion monitoring. In an operational setting, the number of events that can be thoroughly investigated by analysts is limited by available resources. The capability to rapidly screen out events that can be robustly identified as not being explosions is, therefore, of great potential benefit. Nevertheless, possible mis-classification of explosions as earthquakes currently limits the use of screening methods for verification of test-ban treaties. Moment tensors provide a physics-based classification tool for the characterisation of different seismic sources and have enabled the advent of new techniques for discriminating between earthquakes and explosions. Following normalisation and projection of their six-degree vectors onto the hypersphere, existing screening approaches use spherically symmetric metrics to determine whether any new moment tensor may have been an explosion. Here, we show that populations of moment tensors for both earthquakes and explosions are anisotropically distributed on the hypersphere. Distributions possessing elliptical symmetry, such as the scaled von Mises-Fisher distribution, therefore provide a better description of these populations than the existing spherically symmetric models. We describe a method that uses these elliptical distributions in combination with a Bayesian classifier to achieve successful classification rates of 99% for explosions and 98% for earthquakes using existing catalogues of events from the western United States. Application of the method to the 2006–2017 nuclear tests in the Democratic People's Republic of Korea yields 100% identification rates. The approach provides a means to rapidly assess the likelihood of an event being an explosion and can be built into monitoring workflows that rely on simultaneously assessing multiple different discrimination metrics.

How to cite: Hoggard, M., Scealy, J., and Delbridge, B.: Improved classification of explosive moment tensors using elliptical distribution functions on the hypersphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2978, https://doi.org/10.5194/egusphere-egu24-2978, 2024.

EGU24-3453 | ECS | Posters on site | SM2.2

Identification of strong-velocity pulses in seismic ground motion signals 

Junhao Wang and Qingming Li

Seismic ground motions in the near-fault region produce strong pulses in the velocity-time history, resulting in severe damage to structures. To accurately and effectively monitor these ground motion signals with strong pulses, Shock-Waveform (SW) method is introduced to quantitatively extract the largest velocity pulse from a given ground motion. SW method is an energy-based and adaptive signal analysis method, which has proven capability of analyzing different physical and engineering signals initiated by sudden actions. It is suitable to identify pulse components in the signal with low error and high efficiency. Three variables are proposed to classify ground motions, which is combined with the Principal Component Analysis (PCA) for data dimensionality reduction and subsequent analysis. In addition, an optimum classification standard on pulse-like and non-pulse-like ground motion is established. To avoid the subjective judgement induced by manual selection, unsupervised machine learning classification method and Support Vector Machine (SVM) are used successively to find the decision boundary. In this study, about 100 pulse-like ground motions with large-velocity pulses are identified from approximately 1000 near-fault ground motion recorded in PEER Next Generation Attenuation-West2 database. It shows that most of the pulse-like ground motions are caused by the directivity effect. Based on the proposed classification approach, new models are developed to forecast the possibility of a single pulse, multi-pulses, and pulse period for a given earthquake event. 

How to cite: Wang, J. and Li, Q.: Identification of strong-velocity pulses in seismic ground motion signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3453, https://doi.org/10.5194/egusphere-egu24-3453, 2024.

EGU24-4186 | ECS | Orals | SM2.2 | Highlight

The frontiers of distributed acoustic sensing for seismological applications 

Ettore Biondi, Jiaxuan Li, Jessie Saunders, Allen Husker, and Zhongwen Zhan

Distributed acoustic sensing (DAS) is proving to be an effective technology for seismological applications. Its success is due to the ability to deploy DAS instrumentation on the existing ever-growing telecommunication fiber networks across the globe. However, the benefits of DAS are hindered by the sheer volume of data commonly recorded from single-instrument deployments, which can easily reach tens of TBs. Additionally, since DAS measures along fiber strain, new data analysis paradigms are necessary to exhaustively exploit all the information contained within these large datasets. 

We showcase successful applications of DAS experiments using existing fiber cables located in different scenarios, from volcanic systems to densely populated urban environments. To harness the information within these novel datasets, we combine machine-learning tools with efficient algorithms running on high-performance computing architectures. For example, we showcase how the arrival times obtained from PhaseNet-DAS can provide real-time earthquake detection and localization, allowing for the inclusion of DAS data within earthquake early warning systems. Moreover, we demonstrate the capability of integrating real-time streamed DAS channels within seismic network operations. Our processing paradigm is proving to be an effective ground for discoveries and for creating the next generation of seismic monitoring frameworks.

How to cite: Biondi, E., Li, J., Saunders, J., Husker, A., and Zhan, Z.: The frontiers of distributed acoustic sensing for seismological applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4186, https://doi.org/10.5194/egusphere-egu24-4186, 2024.

EGU24-4268 | Posters on site | SM2.2

Deep learning forecasting of induced earthquakes through the analysis of precursory signals 

Vincenzo Convertito, Fabio Giampaolo, Ortensia Amoroso, and Francesco Piccialli

The current limited knowledge about Earth system prevents deterministic earthquake prediction. This will probably continue for the foreseeable future. However, the improved capability of identifying reliable precursory phenomena can allow geoscientists to comprehend if the monitored system is evolving toward an unstable state. Among the premonitory phenomena preceding earthquakes, foreshocks represent the most promising candidate. Physically, two hand-member mechanisms have been proposed to interpret foreshocks. The first considers the failing of populations of small patches of fault that eventually but not necessarily become large earthquakes whereas the second assumes that foreshocks are a part of the nucleation process which ultimately leads to the mainshock. The prompt identification of foreshocks with respect to background seismicity is an issue and the task is worsened when dealing with low-magnitude earthquakes. However, the use of Artificial Intelligence (AI) can help real-time seismology to effectively discriminate precursory signals.

In the present study, we propose a deep learning method named PreD-Net (Precursor Detection Network) to address the precursory signal identification of induced earthquakes through the analysis of several statistical features. PreD-Net has been trained on data related to two induced seismicity areas, namely The Geysers, located in California, USA, and Hengill in Iceland. Notably, the network shows a suitable model generalization, providing considerable results on samples that were excluded from the training dataset of all the sites. The performed tests on related samples of induced relatively large events demonstrate the possibility of setting up a real-time warning strategy to be used to avoid adverse consequences during field operations.

This work is supported by project D.I.R.E.C.T.I.O.N.S. - Deep learning aIded foReshock deteCTIOn Of iNduced mainShocks, project code: P20229KB4F - - Next Generation EU (PRIN-PNRR 2022, CUP D53D23022800001)

How to cite: Convertito, V., Giampaolo, F., Amoroso, O., and Piccialli, F.: Deep learning forecasting of induced earthquakes through the analysis of precursory signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4268, https://doi.org/10.5194/egusphere-egu24-4268, 2024.

GEObit Instruments are proud to announce the market release of a new low-cost and low -latency seismic accelerograph, the GEO-T200, for earthquake monitoring, early waring applications, and structural monitoring. The device mainly consists of two sections, the triaxial sensor sensor and the digitizer. The architecture and the hardware is based on the GEObit GEOtiny platform.

The sensing elements are based in a re-designed previous generation GEObit force balance acceleration sensor unit [1], providing very high dynamic range 160+dB, and wide bandwidth, flat response DC to 260Hz. The acceleration range is user configurable and can be set between +/-4g to +/-0.5g but other ranges are also available upon request.

The digitizer is based on a 24bit ADC and provides high effective dynamic range 140dB, high sampling rate up to 4000sps, integrates seedlink server and the earthworm chain. The device is based on a locally running open-source components ported on ARM Linux board. It is able to apply local signal processing and trigger detection based on multiple schemes (amplitude, STA/LTA etc.) through open-source components ported from the Earthworm toolchain and transmit pick times over MQTT with ultra-low latency based signaling for trigger event distribution supporting multiple centralized or distributed schemes.

It Supports ethernet port and Wi-Fi. Also supports continuous data stream, triggered data stream (level, LTA/LTA, both) or both.

The device is housed into a small cylindrical enclosure, aluminum made, IP68 with dimensions 120mm diameter and 143mm height. Three leveling legs are provided along with a central bolt for proper mounting of the device. An bright OLED lcd screen reports the user about the instrument operation and state of health. The SOH stream is also transmitted in real time over TCP.

 

References:

[1]: Design, Modeling, and Evaluation of a Class-A Triaxial Force-Balance Accelerometer of Linear Based Geometry” N. Germenis, G. Dimitrakakis, E. Sokos, and P. Nikolakopoulos Seismol. Res. Lett. 93, 2138–2146, doi: 10.1785/0220210102

How to cite: Germenis, N.: A new low latency and low-cost force-balance accelerograph for earthquake and structural monitoring and for early waring applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5299, https://doi.org/10.5194/egusphere-egu24-5299, 2024.

GeoSphere Austria (GA, formerly ZAMG), the Italian National Institute of Oceanography and Applied Geophysics (OGS) and the Slovenian Environment Agency (ARSO) are the agencies dedicated to real-time seismological monitoring of Austria, north-eastern Italy and Slovenia, in cooperation with the respective civil protection authorities. In 2014, GA (then ZAMG), OGS and ARSO founded the “Central and Eastern Europe Earthquake Research Network” (CE3RN, http://www.ce3rn.eu/) to 1) formally establish the cross-border network, 2) define the rules of conduct for the management, improvement, extension and expansion of the network, 3) improve seismological research in the region and 4) support civil protection activities. As part of CE3RN, GA, OGS and ARSO have adoptd the “Antelope” software package for collecting, archiving, analysing and sharing seismological data.
In 2022, the international AdriaArray experiment was launched, following on from the previously successful AlpArray experiment. AdriaArray is a multinational effort to map the Adriatic plate and its active margins in the central Mediterranean with a dense regional array of seismic stations to understand the causes of active tectonics and volcanic fields in the region. GA, OGS and ARSO are actively involved in the AdriaArray experiment by providing data from their seismic monitoring networks and - in the case of OGS - also by installing and managing dedicated seismic stations. As part of the AdriaArray experiment, several additional seismic stations have been set up in Austria and north-eastern Italy. It is therefore to be expected that the additional seismic stations installed will improve the earthquake localization capabilities of GA, OGS and ARSO. This certainly applies to Austria and north-eastern Italy, but also to Slovenia, as a large part of its seismicity lies on the border with Italy.
The GOAT-CASE experiment aims to quantify the improvement in earthquake localization capability across the entire area. The underlying methodology is to locate earthquakes also using the additional seismic stations and to compare the results. The workload for the detections is distributed among the three partners, while the mapping is done centrally. An attempt will be made to use artificial intelligence to detect earthquakes and compare the results with the standard routines of the agencies.
The AdriaArray experiment is planned for a duration of 3 years starting around mid-2022. In this presentation we will illustrate the results of the first year of the experiment, from 01/07/2022 to 30/06/2023.

How to cite: Pesaresi, D., Horn, N., and Pahor, J.: GA-OGS-ARSO Transfrontier CE3RN AdriaArray Seismicity Experiment (GOAT-CASE): results of the first year of data collection and analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5459, https://doi.org/10.5194/egusphere-egu24-5459, 2024.

EGU24-5936 | ECS | Posters on site | SM2.2

A workflow for synthetic DAS data generation 

Giacomo Rapagnani, Sonja Gaviano, Davide Pecci, Giorgio Carelli, Gilberto Saccorotti, and Francesco Grigoli

Distributed Acoustic Sensing (DAS) is an emerging data acquisition technology that utilises an optical fiber to measure dynamic strain along its axis. Composed by an optical fiber and an interrogator unit (IU), the system emits laser pulses into the fiber and detects phase shifts in the backscattered light, converting them into strain or strain rate measurements. DAS is becoming popular in many seismological applications and, in particular, for logistically challenging environments such as offshore areas, boreholes, glaciers, and volcanic settings, where deploying conventional monitoring is challenging. Spatial and temporal sampling of DAS systems is much higher than traditional seismological instruments, offering a detailed picture of the recorded seismic wave field. This high spatial and temporal sampling of DAS systems results in massive data generation, especially over extended acquisition periods. For instance, a single day's data collected with a 1 km fiber, featuring inter-channel distances of approximately 1m and a temporal sampling rate of 0.5 ms, can easily reach 2 TB. This highlights the need for efficient data analysis procedures in Distributed Acoustic Sensing (DAS) with methods that are both computationally fast and capable of exploiting the extensive information embedded in such data. As DAS data acquisition experiments are still few in numbers, generating and using synthetic data becomes essential for evaluating performance across diverse DAS acquisition geometries and testing new data analysis techniques. Despite the constant growth of DAS systems, there is a lack of standard modelling and analysis tools that can be used within routine procedures. To address this issues, we formulated a versatile workflow designed to generate synthetic DAS data based on the convolutional model. A central component of this workflow is a travel-time calculator based on the solution of the Eikonal equation, accommodating various data acquisition geometries, including scenarios involving optical fibers deployed in deep boreholes—whether vertical or oblique. Synthetic DAS seismograms are subsequently generated by using the computed travel times, for both P and S phases, with the convolutional model. These seismograms contain several information, such as the radiation pattern of the source and the directivity of the fiber, with the possibility of selecting an arbitrary wavelet. While DAS synthetics computed using the convolutional model may be less realistic than those generated with methods like the reflectivity or the spectral element method, their computational speed is much higher. This efficiency becomes particularly crucial when dealing with the generation of extensive DAS synthetic datasets. The synthetic generation workflow can be used for 1) testing new seismic event detection and location methods for DAS data and 2) training machine learning models. Lastly, this work includes a comparative analysis of synthetics obtained through our workflow against those generated using the spectral element method, followed by an application with a waveform-based DAS event detector.

How to cite: Rapagnani, G., Gaviano, S., Pecci, D., Carelli, G., Saccorotti, G., and Grigoli, F.: A workflow for synthetic DAS data generation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5936, https://doi.org/10.5194/egusphere-egu24-5936, 2024.

EGU24-6310 | ECS | Orals | SM2.2

Accounting for shallow sedimentary layers for accurate earthquake localization using submarine Distributed Acoustic Sensing 

Alister Trabattoni, Marie Baillet, Martijn van den Ende, Clara Vernet, and Diane Rivet

Distributed Acoustic Sensing (DAS) technology facilitates the instrumentation of areas that are challenging to access with conventional instruments. In Chile, the presence of offshore submarine telecommunication cables offers a unique opportunity to instrument a major subduction zone close to the trench. Here we report an analysis of DAS data collected during a one–month campaign, sensing a commercial telecom cable connecting Concón to La Serena positioned several dozen kilometers off the coast.  

The earthquake recordings displayed P and S arrivals along with an additional Ps arrival, which is the result of the conversion of the P-wave at the bedrock/sediment interface. These three phase arrivals were identified and manually picked taking advantage of the spatial continuity of DAS measurements. To correctly account for the presence of the sediment layer in the localization procedure we introduced sedimentary corrections, which are a modification of the conventional station corrections. Instead of introducing an arbitrary constant time delay for each station and each phase, the corrections are derived from a physical first order modeling of the wave propagation in the sediments. The estimation of sedimentary parameters relies on: (i) the observed delay between the transmitted P-phase and the converted Ps-phase that give an indication of the sediment thickness; (ii) an inversion of the P- and S-wave speed in the sediments which is made possible thanks to the high sensor spatial density.   

We show that sedimentary corrections: (i) can represent most of the observed pick residual bias while only requiring the inversion of two global parameters (compared to station correction that requires three parameters per station); (ii) allow one to retrieve the sediment thickness and wave speed values that are consistent with common values for sediments; (iii) reduces the residuals of the earthquake hypocenter localization. The proposed correction method should improve the hypocenter estimation quality, facilitating the analysis of geological structures, and will contribute to a more detailed view of seismic activity in the studied area. 

How to cite: Trabattoni, A., Baillet, M., van den Ende, M., Vernet, C., and Rivet, D.: Accounting for shallow sedimentary layers for accurate earthquake localization using submarine Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6310, https://doi.org/10.5194/egusphere-egu24-6310, 2024.

EGU24-6552 | ECS | Posters on site | SM2.2

HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity 

Matteo Bagagli, Francesco Grigoli, and Davide Bacciu

Machine Learning (ML) applications in geoscience are growing exponentially, particularly in the field of seismology. ML has significantly impacted traditional seismological observatory tasks, such as phase picking and association, earthquake detection and location, and magnitude estimation. However, despite promising results, ML-based classical workflows still face challenges in analyzing microseismic data

Leveraging recent advances in Deep Learning (DL) methods, we present HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity. This tool utilizes an attention-based, spatiotemporal graph-neural network for seismic event detection and employs a waveform-stacking approach for event location, using output probability functions over a dense regular grid.

We applied HEIMDALL to a one-month dataset (December 2018) from the publicly available Hengill Geothermal Field in Iceland, collected during the COSEIMIQ project (active from December 2018 to August 2021). This dataset is ideal for testing seismic event detection and location algorithms due to its high seismicity rate (over 12,000 events in about two years) and the presence of burst sequences with very short interevent times (e.g., less than 5 seconds).

We assessed the methodology's performance by comparing our catalog with those obtained by two recent DL methods and one manually compiled by ISOR for the same period. The DL algorithms we considered are: (i) MALMI, a waveform-based location algorithm, and (ii) the recent GENIE graph-neural-network algorithm. For GENIE, we conducted a full repicking of continuous waveforms using the PhaseNet picking algorithm and subsequent retraining of its model to adapt it to the new seismic network.

Finally, we highlight the pros and cons of each method and discuss potential improvements for microseismic event detection and location, with a particular focus on induced seismicity monitoring operations at EGS sites.

How to cite: Bagagli, M., Grigoli, F., and Bacciu, D.: HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6552, https://doi.org/10.5194/egusphere-egu24-6552, 2024.

EGU24-7863 | ECS | Orals | SM2.2

The advantages of Standardization and Data Sharing: a swift compilation of a high-quality data set for seismological studies in the East Anatolian Fault Zone 

Leonardo Colavitti, Gabriele Tarchini, Daniele Spallarossa, Davide Scafidi, Matteo Picozzi, Antonio Giovanni Iaccarino, Dino Bindi, Patricia Martínez-Garzón, Fabrice Cotton, and Riccardo Zaccarelli

On 6 February 2023 at 01:17 UTC, the Mw 7.8 Pazarcık earthquake struck south-eastern Türkiye and Syria along the East Anatolian Fault Zone (EAFZ), in the province of Kahramanmaraş. The Mw 7.6 Elbistan earthquake occurred about 9 hours later, with an epicenter located about 95 km north-northeast of the Mw 7.8 quake. The combination of these two shocks produced a devastating effect with nearly 55,000 confirmed deaths and about 1.5 million people left homeless.

In this work, we describe the Complete Automatic Seismic Processor (CASP) procedure that has been implemented to develop a large and comprehensive data set consisting of about 63,000 events of magnitude greater than 2.0, that occurred in south-eastern Türkiye between January 2019 and June 2023. The starting catalogue contains about 3.8 million waveforms recorded by 262 velocimetric and accelerometric instruments (network codes KO, TK and TU). The earthquakes were located using the Non-Linear Location technique (NLLOC) with a regional 1-D velocity model, based on the precise picking of P- and S-wave arrivals provided by the RSNI-Picker2 implemented in CASP. After several quality controls, the final high quality catalogue contains 8,475 well-located earthquakes, with a significant difference in depth with respect to the AFAD catalogue.

We present the spatio-temporal distribution of earthquakes before and after the two mainshocks, as well as the distribution of strong-motion parameters, such as peak ground acceleration (PGA), peak ground velocity (PGV), and Fourier amplitude spectra (FAS). Furthermore, preliminary results on earthquake source parameters obtained by spectral decomposition applied separately to background and clustered seismicity are also discussed.

The compiled data set can serve as a basis for studying seismic sequences during seismic crises and identifying the preparatory phase of strong earthquakes in geologically active areas.

How to cite: Colavitti, L., Tarchini, G., Spallarossa, D., Scafidi, D., Picozzi, M., Iaccarino, A. G., Bindi, D., Martínez-Garzón, P., Cotton, F., and Zaccarelli, R.: The advantages of Standardization and Data Sharing: a swift compilation of a high-quality data set for seismological studies in the East Anatolian Fault Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7863, https://doi.org/10.5194/egusphere-egu24-7863, 2024.

EGU24-8614 | ECS | Orals | SM2.2

Recent Advances in Earthquake Monitoring in Madagascar 

Andriniaina Tahina Rakotoarisoa and Hoby N. T. Razafindrakoto

Earthquakes are acknowledged as a potent force of nature that can cause substantial harm to populations and result in widespread damage. Therefore, having a seismic public alerting system is crucial for swiftly broadcasting warnings to the public and relevant risk agencies in the event of an earthquake. The system will send instantaneous notifications to users, allowing them to quickly implement protective measures for risk agencies, as well as offer feedback on individuals’ situations during the earthquake. In this regard, this study aims to build a wrapper for near-real-time earthquake monitoring. Our development includes four steps: (1) improvement of earthquake detection using PhaseNet (Zhu & Beroza, 2018) with PhasePApy (Chen & Holland, 2016) and the Rapid Earthquake Association and Location (REAL, Zhang et al., 2019) for picks association, (2) earthquake location refinement using the HYPOINVERSE program (Klein, 2002), (3) event classification with the CNN classification method, and (4) rapid earthquake notification through email and a locally designed application called SeismicBox2 for smartphones that include earthquake information and USGS shakemap. We conduct testing and validation of the system using earthquake data from Madagascar (archive and near-realtime)

How to cite: Rakotoarisoa, A. T. and Razafindrakoto, H. N. T.: Recent Advances in Earthquake Monitoring in Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8614, https://doi.org/10.5194/egusphere-egu24-8614, 2024.

EGU24-9715 | ECS | Orals | SM2.2

Automatic detection and characterization of Very Long-period seismic events for volcanic monitoring applications. 

Sergio Gammaldi, Dario Delle Donne, Pasquale Cantiello, Antonella Bobbio, Walter De Cesare, Rosario Peluso, and Massimo Orazi

Real-time seismological applications are now crucial for the monitoring and surveillance of active volcanoes, as they are useful tools for the early detection of volcanic unrest. In open-vent active volcanoes,  Very Long Period (VLP) seismicity, typically associated with mild and persistent explosive activity, is of crucial importance for volcano monitoring, as its variations in occurrence rate and magnitude may prelude a phase of unrest.  Here we show a new method for the automatic real-time detection and characterization of  VLP seismicity at Stromboli active volcano (Italy).

The detection algorithm is based on the Three-Component Amplitude (TCA) obtained from waveform polarization and spectral analysis of the continuous recording, providing time of detection,  azimuth,  incidence,  amplitude, and frequency of the detected VLP events. The VLP amplitudes derived at all stations of the monitoring network, provided as peak-to-peak amplitudes and mean square amplitudes, are also used to perform an automatic localization of VLP source.

VLP detections and characterizations derived from our automatic detection algorithm are compared with detection derived from manual and automatic inspections of the seismic record and with VLP time histories from available published VLP datasets.

From this comparison, it turns out that the VLP detection time series produced by the automatic algorithm tracks fluctuations in the  VLP activity well,  as manually detected by the operators over a  ~20-year period, thus allowing us to include it into the real-time processing framework operating at Stromboli for volcano surveillance.

How to cite: Gammaldi, S., Delle Donne, D., Cantiello, P., Bobbio, A., De Cesare, W., Peluso, R., and Orazi, M.: Automatic detection and characterization of Very Long-period seismic events for volcanic monitoring applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9715, https://doi.org/10.5194/egusphere-egu24-9715, 2024.

EGU24-9764 | Orals | SM2.2

Creating an Inventory of Seismic Signals at Vulcano Island, Italy, using Unsupervised Learning Techniques 

Horst Langer, Susanna Falsaperla, Ferruccio Ferrari, and Salvatore Spampinato

The island of Vulcano gives its name to the so-called “Vulcanian eruptions”, an eruptive style with strong explosive characteristics and observed there for the first time. The last eruptive activity occurred between 1888 and 1890. Starting from mid-September 2021, an unrest, marked by relevant variations in geochemical and geophysical parameters, affected the island. Here, we analyze the seismic signals recorded from the onset of the unrest until December 2022. An increasing number of Very Long Period events was detected from September 2021 onwards, enhancing concerns linked to other measured anomalies, such as increasing CO2 emissions and fumarole temperatures. Numerous types of signals were generally recorded on the island, partly caused by various man-made sources, such as the close-by passage of ships, dropping anchors, etc. The large variety of the seismic signals made standard amplitude-based monitoring techniques, such as RSAM, questionable. We therefore focused on creating an inventory of the recorded signals exploiting unsupervised machine learning techniques, namely Self-Organizing Maps and Cluster Analysis. We were able to identify various classes of seismic events related to volcanic dynamics and to distinguish exogenous signals, such as anthropic noise. This allowed us to visualize the development of signal characteristics efficiently. This classification can help build an effective alert tool to automatically identify different types of seismic signals, useful for surveillance purposes. Furthermore, it is a preparative step for other studies, such as event location and source process modeling.

How to cite: Langer, H., Falsaperla, S., Ferrari, F., and Spampinato, S.: Creating an Inventory of Seismic Signals at Vulcano Island, Italy, using Unsupervised Learning Techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9764, https://doi.org/10.5194/egusphere-egu24-9764, 2024.

EGU24-10651 | ECS | Posters on site | SM2.2

Contribution of SeismoCitizen Raspberry Shake dense network in monitoring induced seismicity in northern Alsace (France) 

Mathieu Turlure, Marc Grunberg, Fabien Engels, Hélène Jund, Antoine Schlupp, and Jean Schmittbuhl

PrESENCE ANR project (2022-2025) focuses on seismic hazards induced by deep geothermal operations in northern Alsace, France, and their associated societal perception. Seismological observations are obtained using a large number of low cost internet-connected equipment (Raspberry Shake seismic station and associated open access data). The breakthrough strategy of the project relies on the deployment of the stations in residences or administrative buildings of non-seismologist volunteer citizens or authorities. The aim is to use those stations to densify the french permanent seismic network, and to improve the detection and location of seismic events, in particularly small ones. Our presentation will be focused on the Soultz-sous-Forêts and Rittershoffen areas (northern Alsace, France), which are sites of deep geothermal operations. 

 

The topology of the seismological network was determined by the location of permanent stations, from Epos-France permanent network (4) and public stations belonging to geothermal operators (2), the number of low-cost stations (35) to be deployed in the region, the location of deep geothermal power plants (Soultz and Rittershoffen) and the location of volunteer citizen hosts. Volunteer citizens were selected initially by word of mouth, then by a call for applications (through social networks, flyers, local newspapers). Twenty-one stations are currently (end of 2023) hosted in the area. About ten additional stations are planned to be deployed early 2024 in the area.

 

Based on our past experience in deploying similar networks in other contexts and regions (Mayotte, Vosges massif, Mulhouse, etc.), we have consolidated the installation of these stations to ensure reliable data acquisition and, in particular, to achieve better data completeness (acquisition directly at the station using the Seedlink protocol via a VPN, hardware watchdog). We use Ansible (an open source IT automation platform) to facilitate the deployment of Raspberry Shake stations configuration and management tasks, ensuring rapid and consistent production deployment.

 

The workflow for building the seismicity catalog benefits from our advances in the use of new artificial intelligence tools, such as PhaseNet, a deep learning automatic picking method, as well as in the development of a deep learning method for discrimination between earthquakes, quarry blasts and explosions. Our tests over the year 2023 show that even if the stations are installed in urban areas (and therefore in a noisy environment), the network is able to automatically detect and locate many small induced earthquakes, including around 250 with a high level of confidence, compared with the ten detected or so by the standard procedure of BCSF-Renass, the French National Observation Service.

How to cite: Turlure, M., Grunberg, M., Engels, F., Jund, H., Schlupp, A., and Schmittbuhl, J.: Contribution of SeismoCitizen Raspberry Shake dense network in monitoring induced seismicity in northern Alsace (France), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10651, https://doi.org/10.5194/egusphere-egu24-10651, 2024.

EGU24-10668 | ECS | Posters on site | SM2.2

A workflow for building an automatic earthquake catalog from near-real time DAS data recorded on offshore telecommunications cable in central Chile. 

Marie Baillet, Alister Trabattoni, Martijn van den Ende, Clara Vernet, and Diane Rivet

Distributed Acoustic Sensing (DAS) is of critical value for the offshore expansion of seismological networks. The work presented here is part of the 5-years ERC ABYSS project, which aims at building a permanent seafloor seismic observatory leveraging 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, constituting more than 37,500 virtual sensors sampled at 125 Hz. We develop a workflow to detect more than 3500 local, regional and teleseismic events with local magnitudes down to ML = 0.5, automatically processing over 72 TB of data. We show that applying those methods to DAS data combined with data from the national onland seismic network greatly increases the accuracy of the earthquake hypocenter localizations. As a first step, we perform automatic seismic phase arrival picking using PhaseNet pretrained on conventional seismological stations, followed by phase association with GaMMA. We then apply a correction of the phase picks to account for shallow sedimentary layers and invert for the event hypocenter with VELEST. Finally, we estimate a local magnitude based on peak ground displacements.  

The ABYSS project near-real time data collection started the 30th of September 2023 using three DAS units to sense two offshore telecommunications cables connecting the cities of Concón to La Serena and La Serena to Caldera. The DAS data covers over 500 km of cable, comprising 30,000 virtual sensors sampled at 62.5 Hz. These data are synchronized once a day with a storage server located in France, the volume of which is anticipated to reach an estimated 608 TB by the end of the project. By applying our workflow, tested and validated on the POST experiment, to our daily data, we are able to process data in near-real time to build a catalog that will span 5 years, and that will be used as a reference for subsequent studies within the framework of the ABYSS project. Furthermore, the size of our catalog, enriched with numerous offshore events is a significant improvement over the existing regional catalogs, which may aid future studies of the Chilean margin subduction zone seismicity. 

How to cite: Baillet, M., Trabattoni, A., van den Ende, M., Vernet, C., and Rivet, D.: A workflow for building an automatic earthquake catalog from near-real time DAS data recorded on offshore telecommunications cable in central Chile., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10668, https://doi.org/10.5194/egusphere-egu24-10668, 2024.

EGU24-10893 | ECS | Posters on site | SM2.2

Exploring the application of Characteristic Functions on DAS data and their influence in event detection performance. 

Sonja Gaviano, Giacomo Rapagnani, Davide Pecci, Juan Porras, Estelle Rebel, and Francesco Grigoli

Distributed Acoustic Sensing (DAS) has emerged as a powerful tool in seismological applications, transforming fiber-optic cables into dense arrays of geophones that can continuously sample seismic wavefields across several kilometers. DAS data acquisition presents a versatile approach, utilizing either ad hoc installations with specific cables or leveraging existing telecommunication optical fiber-network infrastructure. Its adaptability makes DAS particularly advantageous for seismic monitoring in logistically challenging environments like volcanoes or offshore areas, where traditional seismometers may face limitations.

 

Conventional seismological techniques struggle to effectively process DAS data due to its unique characteristics—typically, wavefields are sampled at 1 m spacing with frequencies exceeding 1 kHz. As a result, this technology provides a detailed mapping of the seismic wavefield across the length of the fiber, and it also generates a significant amount of data compared to the sparse seismometer installations. In order to efficiently analyze these data, we introduced HECTOR, a waveform-based detection method designed specifically for DAS data (Porras et al. 2024).

 

In this study, we investigate the capabilities of HECTOR following preprocessing of DAS data using various characteristic functions (CF). We explore non-negative functions, including Short Term Average to Long Term Average (STALTA), Energy, and Envelope, whose peculiarity is to preserve noise. Conversely, zero-mean characteristic functions such as Short Term Average to Long Term Average derivative (STALTA derivative), Kurtosis, and Kurtosis derivative enhance signals and mitigate noise. Our objective is to assess HECTOR's performance when analyzing preprocessed data compared to raw data.

 

To validate our findings, we initially test the detector on synthetic data. These simulations encompass diverse optical fiber geometries, source configurations, and locations. Subsequently, we apply the algorithm to real data collected in two distinct scenarios. The first scenario involves the FORGE experiment situated in Utah, US, which entails a borehole installation of 1 km optical fiber deployed above a geothermal reservoir characterized by induced seismic activity. The second scenario involves a 90 km horizontal optical fiber deployed in the Pyrenees region. The area is characterized by natural earthquake activity with magnitudes (2.01≥ML≥0.02), alongside anthropic events due to quarry blasts. 

Our evaluation focuses on quantifying the enhancement in HECTOR's performance following the application of CFs compared to analyzing raw data.

Through this comprehensive exploration, we aim to advance the understanding of DAS data processing, demonstrating the efficacy of HECTOR across diverse scenarios. 

We would like to thank TotalEnergies for sharing this data set with us as well as Febus Optic for providing the DAS interrogator used for the data acquisition.

 

References: 

A Semblance-based Microseismic Event Detector for DAS Data.

  • Porras, D. Pecci, G. Bocchini, S. Gaviano, M. De Solda, K. Tuinstra, F. Lanza, A. Tognarelli, E. Stucchi, F. Grigoli. Geophysical Journal International (GJI) 2024 (Accepted)

How to cite: Gaviano, S., Rapagnani, G., Pecci, D., Porras, J., Rebel, E., and Grigoli, F.: Exploring the application of Characteristic Functions on DAS data and their influence in event detection performance., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10893, https://doi.org/10.5194/egusphere-egu24-10893, 2024.

EGU24-12443 | ECS | Posters on site | SM2.2

Unveiling coupling properties of subduction zones with novel telesismic waveform approaches 

Francesco Rappisi, Tim Craig, and Sebastian Rost

Subduction zones are among the most active tectonic areas on the planet. Their primary characteristic is the enormous amount of stress accumulated at the interface between the subducting oceanic plate and the overriding plate. The release of this stress is accommodated by a wide range of behaviours, ranging from aseismic slip (slip at speeds too slow to radiate seismic energy), through the spectrum of slow slip and tremor, to seismic slip capable of generating major earthquakes. The main investigative tools for subduction zones to map out this range of behaviour, and to assess the coupling properties of the subduction interface, involve the direct observation of ground movements through geodesy (either terrestrial or satellite-based) or through local seismic surveillance using near-field instrumentation, all of which are logistically complex, and typically only feasible on land.

Utilizing the recent expansion of seismic arrays in continental regions, we propose an alternative approach for the study of subduction zones that bypasses the aforementioned limitations through the use of teleseismic waves—recorded at a distance between 30º and 90º from the epicenter—based on the identification of the presence (or absence) of highly reflective layers at the megathrust interface. Previous studies using local seismic data have observed the presence of highly reflective layers, characterized by strong impedance contrasts, located at the megathrust interface, capable of producing a reflection in the wavefield that results into the presence of precursors of depth phases. Since impedance contrasts in the solid Earth are linked to variations in the elastic properties of the medium, reflectivity offers a window into the rheology of the plate interface. Understanding the reasons behind such strong impedance contrasts, their potential variability over time and space, could pave the way for understanding why the degree of coupling of subduction interfaces varies, whether it is related to transient processes, or if it is stable over time.

Here, we present an automated waveform processing approach designed to detect such reflections in remote seismic data, and illustrate this with a test region from the Central America subduction zone.  We analyse waveforms produced by seismic events with magnitudes ranging from 4.5 to 5.5 occurring at different times and recorded by small aperture seismic arrays. Our observations in Central America prove to be an excellent tool for studying the coupling properties of the megathrust interface. This work represents a first attempt, with the ultimate goal of mapping subduction zones and their coupling properties, even in currently inaccessible submarine areas, allowing for a better understanding of the seismic risk that subduction zones represent.

How to cite: Rappisi, F., Craig, T., and Rost, S.: Unveiling coupling properties of subduction zones with novel telesismic waveform approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12443, https://doi.org/10.5194/egusphere-egu24-12443, 2024.

EGU24-13591 | ECS | Posters on site | SM2.2

Automatic determination of focal depth with the optimal period of Rayleigh wave amplitude spectra and uncertainty assessment in 3D velocity model 

Xiaohui He, Peizhen Zhang, Sidao Ni, Wenbo Wu, Risheng Chu, Yi Wang, and Kaiyue Zheng

Focal depth of earthquakes is essential for studies of seismogenic processes and seismic hazards. Surface waves are usually the strongest seismic phases at local and regional distances, and its excitation is sensitive to source depth. We observe that the optimal period (the period corresponding to the maximum amplitude) of Rayleigh waves at local distances shows an almost linear correlation with focal depth, based on which we propose a method for resolving the focal depth of local earthquakes. We propose an automated data processing workflow, and applications to earthquakes in diverse tectonic settings demonstrate that reliable focal depth with uncertainty of 1~2 km can be determined even with one or a few seismic stations. Then, we use the Longmenshan region as a case study to systematically assess the impact of the 3D velocity model on the results through forward simulation. A total of 191 events at depths ranging from 5 to 20 km are simulated. The standard deviation between the focal depths determined by this method and the input values is approximately 1.5 km, with 95% events having errors within 2 times the standard deviation. This indicates that the method exhibits good applicability even in regions with complex velocity structures, and highlights the applicability of the method in scenarios characterized by sparse network coverage or historical events.

How to cite: He, X., Zhang, P., Ni, S., Wu, W., Chu, R., Wang, Y., and Zheng, K.: Automatic determination of focal depth with the optimal period of Rayleigh wave amplitude spectra and uncertainty assessment in 3D velocity model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13591, https://doi.org/10.5194/egusphere-egu24-13591, 2024.

EGU24-15414 | ECS | Posters on site | SM2.2

Passive Assessment of Geophysical Instruments Performance using Electrical Network Frequency Analysis 

Mathijs Koymans, Elske de Zeeuw-van Dalfsen, Läslo Evers, and Jelle Assink

The electrical network frequency (ENF) of the alternating current operated on the power grid is a well-known source of noise in digital recordings. The noise (i.e., signal) is widespread and appears not just in close proximity to high-voltage power lines, but also in instruments simply connected to the mains powers grid. This omnipresent, anthropogenic signal is generally perceived as a nuisance in the processing of geophysical data. Research has therefore been mainly focused on its elimination from data, while its benefits have gone largely unexplored. It is shown that mHz fluctuations in the nominal ENF (50 - 60Hz) induced by variations in power usage can be accurately extracted from geophysical data. This information represents a persistent time-calibration signal that is coherent between instruments over national scales. Cross-correlation of reliable reference ENF data published by electrical grid operators with estimated ENF data from geophysical recordings allows timing errors to be resolved at the 1s level. Furthermore, it is shown that a polarization analysis of particle motion at the ENF may assist in the detection of instrument orientation anomalies at the surface. Furthermore, it is explored whether this method can be applied to determine orientations of geophones inside seismic boreholes.

How to cite: Koymans, M., de Zeeuw-van Dalfsen, E., Evers, L., and Assink, J.: Passive Assessment of Geophysical Instruments Performance using Electrical Network Frequency Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15414, https://doi.org/10.5194/egusphere-egu24-15414, 2024.

EGU24-17429 | ECS | Orals | SM2.2

Relative methods of localization and their differences in results on the REYKJANET seismic network in Iceland 

Diana Konrádová, Jana Doubravová, Bohuslav Růžek, and Josef Horálek

Accurate earthquake localization is essential for advancing seismic processing and understanding geological structures. In this study, we explore the application of relative relocation methods—HypoDD (HD), GrowClust (GC), and Master Event (ME)—to refine event locations and analyze their implications beyond specific fault structure determination. While the primary focus is not exclusively on geological structures, the outcomes also serve broader purposes, contributing to critical aspects of seismic processing.
Our investigation employs a dataset from the REYKJANET seismic network located on the Reykjanes Peninsula in Iceland. The comparative assessment of these methods reveals significantly focused clusters in contrast to absolute event locations. Notably, individual event locations exhibit variations dependent on the chosen relocation method.
Furthermore, it is essential to note that Master Event (ME) is a program developed for event localization, offering the unique capability of sequential use. This feature proves valuable, especially in dynamic geological settings, such as the Reykjanes Peninsula in Iceland, where volcanic eruptions occur.
Additionally, we delve into the influence of control parameters for HD, GC, and ME on final location results, aiming to optimize these parameters while considering computational and memory demands. This research contributes to a comprehensive understanding of relative localization methods, emphasizing their broader applications and significance in seismic event analysis within the REYKJANET network.

How to cite: Konrádová, D., Doubravová, J., Růžek, B., and Horálek, J.: Relative methods of localization and their differences in results on the REYKJANET seismic network in Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17429, https://doi.org/10.5194/egusphere-egu24-17429, 2024.

Faults zones in the Earth’s crust alter permeability architecture relative to country rock and can function as fluid conduits. Documented cases of long-distance earthquake interactions suggest that pore-pressure gradients resulting from conduit flow can activate seismic slip where receiver faults might be sensitive to external forcing. When external stress forcing can be quantified, for example, in the form of ground motions that can be converted to stress, it provides an opportunity to measure the stress perturbation required to nucleate slip in cases where fault activation is triggered.  

 

In this study, we investigate the stress state of faults in the Lower Rhine Embayment (LRE), western Germany. We do so by quantifying the occurrence of remote dynamic triggering by transient stresses imparted by passing waves of distant mainshocks. The LRE hosts a system of normal faults with mean estimated slip rates of 0.1 mm/yr and moderate seismicity. We use the continuous Bensberg catalog starting in 1990 to estimate the statistical significance of seismicity rate changes surrounding teleseismic mainshocks identified as triggering candidates. We identify 21 teleseismic mainshocks with ML > 7 (1990 – 2015) and ML > 6 (2016 – present) that generate a theoretical peak-ground velocity (PGV) >0.02 cm/s within the study area. Two mainshocks associate with statistically significant seismicity-rate increases following the passing of their surface waves: the 1992 Roermond, and the 2021 M8.2 Chignik, Alaska earthquakes. Both mainshocks generated PGV values > 0.017 cm/s at 30s and have back-azimuths that are roughly parallel to the dominant strike of LRE faults. We observe a migrating sequence of earthquakes in the 10 days following the Roermond earthquake, where roughly half occur outside of the classical aftershock zone of ~2-3 fault lengths. We infer dynamic triggering to play a role in the generation of the migrating sequence, as migration outpaces diffusion time scales assuming realistic crustal diffusivity values of up to 3 m2/s. The July 2021 Alaska earthquake likely triggered a sequence of ~16 locatable earthquakes. The observed surface PGV values of the Alaska and Roermond earthquakes correspond to peak dynamic stress values of 1.4 kPa and < 30 kPa, respectively. Thus, stress values at the hypocentral depth of the triggered sequence of ~16 events inferred from 30s Rayleigh waves of the Alaska earthquake would correspond to 50-66% of the observed surface value.

 

Using remote dynamic triggering as a stress-meter to estimate stress thresholds that can potentially activate faults has important implications for earthquake physics, as well as for society. The LRE is being targeted for geothermal energy production. Prior work documents a series of 14 earthquakes of Mw > 5.0 since the 14th century, including the 1992 Mw 5.3 Roermond earthquake. Therefore, quantifying the triggerability of faults at a future energy production site prior to operation should be a key step in assessing the potential for fault reactivation.

How to cite: Roth, M. P. and Harrington, R. M.: Using remote dynamic earthquake triggering as a stress-meter of the Lower Rhine Embayment fault system in western Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20910, https://doi.org/10.5194/egusphere-egu24-20910, 2024.

EGU24-4154 | ECS | Posters on site | SM2.3

Clustering distributed acoustic sensing signals via curvelet transform and unsupervised deep learning 

Bolin Li, Sjoerd de Ridder, and Andy Nowacki

Distributed acoustic sensing (DAS), a technology that exhibits great potential for subsurface monitoring and imaging, has been regarded as a preeminent instrument for vibration measurements. In light of the tremendous amount of seismic data, numerous channels, and elevated noise levels, it becomes imperative to suggest an appropriate denoise procedure that is compatible with DAS data. In this regard, unsupervised deep learning with data clustering generally exhibits superior performance in facilitating the efficient analysis of sizable unlabeled data sets devoid of human bias. In addition, the clustering method is capable of detecting seismic waves, microseismic turbulence, and even unidentified new types of negligible seismic events, in contrast to a number of conventional denoising techniques. While current approaches reliant on f-k analysis remain valuable, they fail to fully exploit the information present in the wavefield due to their inability to identify the characteristic moveout observed in seismic data. In order to denoise DAS data more effectively, we investigate the capacity of the curvelet transform to extend existing deep scattering network methodologies. In this paper, we propose a novel clustering approach for the denoise processing of DAS data that utilises the Gaussian Mixture Model (GMM), curvelet transform, and unsupervised deep learning. 

The DAS data are initially subjected to the curvelet transform in order to derive the curvelet coefficients at various scales and orientations, which can be regarded as the first layer of extracted features. Following this, a deeper layer of features is obtained by applying the curvelet transform to the coefficients in the first layer. The aforementioned process continues in this manner until the depth of the layer satisfies the algorithm-determined expectation. By concatenating the curvelet coefficients from each layer, the original DAS data's features are generated. Afterwards, the signal is reduced to two dimensions using principal component analysis (PCA), which simplifies its interpretation by projecting the high-dimensional features onto two principal components, which facilitates the clustering of the features by GMM for achieving the final clustered results.

This methodology operates without the need for labels of DAS data and is highly appropriate for managing the substantial quantity and numerous channels of DAS. We used a variety of approaches, such as Bayesian information criteria and silhouette analysis, to determine the optimal number of clusters in GMM and evaluate the algorithm's clustering performance. We demonstrate the method on downhole data acquired during stimulation of the Utah FORGE enhanced geothermal system, and the results appear quite satisfactory, indicating that it can be utilised effectively to denoise DAS signals.

How to cite: Li, B., de Ridder, S., and Nowacki, A.: Clustering distributed acoustic sensing signals via curvelet transform and unsupervised deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4154, https://doi.org/10.5194/egusphere-egu24-4154, 2024.

EGU24-5031 | ECS | Posters on site | SM2.3

SeisPolar: Seismic Wave Polarity Module for the SeisBlue Deep Learning Seismology Platform 

I-Hsin Chang, Chun-Ming Huang, and Hao Kuo-Chen

Responding to challenges from increasing seismic data, our study leverages deep learning to enhance seismic data processing's automation and efficiency. Recognizing Taiwan's unique geological structure, we have developed deep learning models using data from dense seismic arrays since 2018. We have integrated the Transformer model with GAN training techniques for phase picking. Our latest system, SeisBlue, has evolved from phase picking and earthquake location to include magnitude and focal mechanism estimation, primarily using SeisPolar, a CNN model for P-wave polarity classification, crucial for focal mechanism analysis. Additionally, our redesign of the seismic monitoring process emphasizes data pipelines and integrates software engineering technologies, including hardware, system environment, database, data pipelines, model version control, task monitoring, data visualization, and Web UI interaction. The model shows high proficiency in identifying P-wave polarity and deciphering focal mechanisms, with an accuracy of 85%, and precision and recall rates for three categories [positive, negative, undecidable] at [87%, 77%, 53%] and [84%, 80%, 54%], respectively. It notably achieves about 70% Kagan angle under 40 degrees for focal mechanism analysis. This semi-automated workflow, from data processing to phase picking, earthquake location, magnitude determination, focal mechanism estimation and Web UI, significantly boosts seismic monitoring's efficiency and accuracy. It facilitates quicker and more meaningful engagement for researchers in subsequent studies, marking a notable advancement in seismic monitoring and deep learning application.

How to cite: Chang, I.-H., Huang, C.-M., and Kuo-Chen, H.: SeisPolar: Seismic Wave Polarity Module for the SeisBlue Deep Learning Seismology Platform, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5031, https://doi.org/10.5194/egusphere-egu24-5031, 2024.

EGU24-5044 | Posters on site | SM2.3

Event-based features: An improved feature extraction approach to enrich machine learning based labquake forecasting 

Sadegh Karimpouli, Grzegorz Kwiatek, Patricia Martínez-Garzón, Georg Dresen, and Marco Bohnhoff

Earthquake forecasting is a highly complex and challenging task in seismology ultimately aiming to save human lives and infrastructures. In recent years, Machine Learning (ML) methods have demonstrated progressive achievements in earthquake processing and even labquake forecasting. Developing a more general and accurate ML model for more complex and/or limited datasets is obtained by refining the ‘ML models’ and/or enriching the ‘input data’. In this study, we present an event-based approach to enrich the input data by extracting spatio-temporal seismo-mechanical features that are dependent on the origin time and location of each event. Accordingly, we define and analyze a variety of features such as: (a) immediate features, defined as the features which benefit from very short characteristics of the considered event in time and space, (b) time-space features, based on the subsets of acoustic emission (AE) catalog constrained by time and space distance from the considered event, and (c) family features, extracted from topological characteristics of the clustered (family) events extracted from clustering analysis in different time windows. We use AE catalogs recorded by tri-axial stick-slip experiments on rough fault samples to compute event-based features. Then, a random forest classifier is applied to forecast the occurrence of a large magnitude event (MAE>3.5) in the next time window. Results show that to obtain a more accurate forecasting model, one needs to separate background and clustered activities. Based on our results, the classification accuracy when the entire catalog data is used reaches 73.2%, however, it shows a remarkable improvement for separated background and clustered populations with an accuracy of 82.1% and 89.0%, respectively. Feature importance analysis reveals that not only AE-rate, seismic energy and b-value are important, but also family features developed from a topological tree decomposition play a crucial role for labquake forecasting.

How to cite: Karimpouli, S., Kwiatek, G., Martínez-Garzón, P., Dresen, G., and Bohnhoff, M.: Event-based features: An improved feature extraction approach to enrich machine learning based labquake forecasting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5044, https://doi.org/10.5194/egusphere-egu24-5044, 2024.

EGU24-5148 | ECS | Posters on site | SM2.3

Toward a Polarity Focal Mechanism Estimation via Deep Learning for small to moderate Italian earthquakes 

Flavia Tavani, Pietro Artale Harris, Laura Scognamiglio, and Men-Andrin Meier

One of the main tasks in seismology is the source characterization after an earthquake, in particular the estimate of the orientation of the fault on which an earthquake occurs and the direction of the slip. Currently, most seismological observatories compute moment tensor solutions for earthquakes above a certain magnitude threshold, but, for small to moderate earthquakes (i.e. aftershock sequences), or for large but close in time events, focal mechanism by first arrival polarities are often the only source information available (Sarao et al., 2021).

Focal mechanisms are important to better define the activated faults, to help in understanding the seismotectonic process, to improve the predicted ground shakings for early warning, the tsunami alert and the seismic hazard assessment. For these purposes, it becomes essential to produce and disseminate an estimate of the earthquake source parameters even for small events. Recently, machine learning techniques have gained significant attention and usage in various fields, including seismology where these algorithms have emerged as powerful tools in providing new insight into the earthquakes data analysis such as the prediction of the seismic wave's first arrivals polarities which can be used to compute focal mechanisms.

We present here a workflow developed to obtain earthquake focal mechanisms starting from the first p-wave polarities estimated through the method proposed by Ross et al (2018).

Our procedure consists of two stages: in the first stage, we use a combination of the available INGV web services (Bono et al., 2021) and the ObsPy functions to download the earthquake hypocentral location. We recover the waveforms recorded by the stations in the 0 -120 km distance range, and we create an input file with the appropriate information required for the prediction of the polarities for each waveform. We then use the convolutional neural network (CNN) proposed in Ross et al (2018) to obtain the polarities for each waveform, which can be UP, DOWN, or UNKNOWN. The second stage of the developed procedure aims to use the polarities that have been predicted to determine the focal mechanisms of the selected earthquakes. To do this, we use a modern Python implementation of HASH code (originally proposed in Fortran by Hardebeck et al. 2002, 2003) called SKASH (Skoumal et al. submitted). Finally, we present an application of this procedure to the September 2023, Marradi (Central Italy), seismic sequence that has been characterized by a magnitude Mw 4.9 mainshock followed by over 70 aftershocks in the magnitude range 2 - 3.4. Here, we focused on the estimation of the focal mechanism for events down to M 2.0. The application of the presented workflow permits to gain useful information about the kinematics of the earthquakes in the sequence, obtaining thus a more precise characterization of the activated structures.

How to cite: Tavani, F., Artale Harris, P., Scognamiglio, L., and Meier, M.-A.: Toward a Polarity Focal Mechanism Estimation via Deep Learning for small to moderate Italian earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5148, https://doi.org/10.5194/egusphere-egu24-5148, 2024.

Dynamic source inversion of earthquakes consists of inferring frictional parameters and initial stress on a fault consistent with co-seismic seismological and geodetic data and dynamic earthquake rupture models. In a Bayesian inversion approach, the nonlinear relationship between model parameters and data (e.g. seismograms) requires a computationally demanding Monte Carlo (MC) approach. As the computational cost of the MC method grows exponentially with the number of parameters, dynamic inversion of a large earthquake, involving hundreds to thousands parameters, shows problems with convergence and sampling. We introduce a novel multi-stage approach to dynamic inversions. We divide the earthquake rupture into several successive temporal (e.g. 0-10 s, 10-20 s, …) and spatial stages (e.g., 100 km, 200 km, …). As each stage requires only a limited number of independent model parameters, their inversion converges relatively fast. Stages are interdependent: earlier stage inversion results are a prior for a later stage inversion. Our main advancement is the use of Generative Adversarial Networks (GAN) to transfer the prior information between inversion stages, inspired by Patel and Oberai (2019). GAN are a class of machine learning algorithms originally used for generating images similar to the training dataset. Their unsupervised training is based on a contest between a generator that generates new samples and a critic that discriminates between training and generator’s images. The resulting generator should generate synthetic images/samples with noise in a low-dimensional latent space as an input. We train GANs on samples of dynamic parameters from an earlier stage of the inversion and use the GAN to suggest the dynamic parameters in a later stage of inversion. We show a proof of concept dynamic inversion of a synthetic benchmark, comparing performance of direct MC dynamic inversion with parallel tempering with our GAN approach. We efficiently handle large ruptures by adopting a 2.5D approximation that solves for source properties averaged across the rupture depth. The 2.5D modeling approach accounts for the 3D effect of the finite rupture depth while keeping the computational cost the same as in 2D dynamic rupture simulations. Additionally we show current results on the dynamic inversion of 2023 Mw 7.8 Kahramanmaraş, Turkey, earthquake.

How to cite: Premus, J. and Ampuero, J.-P.: Dynamic earthquake source inversion with GAN priors, with application to the 2023 Mw 7.8 Kahramanmaraş, Turkey earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6072, https://doi.org/10.5194/egusphere-egu24-6072, 2024.

EGU24-6371 | Posters on site | SM2.3

Detailed clustering of continuous seismic waveforms with deep scattering networks: a case study on the Ridgecrest earthquake sequence 

Reza Esfahani, Michel Campillo, Leonard Seydoux, Sarah Mouaoued, and Qing-Yu Wang

Clustering techniques facilitate the exploration of extensive seismogram datasets, uncovering a variety of distinct seismic signatures. This study employs deep scattering networks (Seydoux et al. 2020), a novel approach in deep convolutional neural networks using fixed wavelet filters, to analyze continuous multichannel seismic time-series data spanning four months before the 2019 Ridgecrest earthquake sequence in California. By extracting robust physical features known as scattering coefficients and disentangling them via independent component analysis, we cluster different seismic signals, including those from foreshock events and anthropogenic noises. We investigate the variability of intracluster (dispersion within each cluster) and examine how it correlates with waveform properties and feature space. The methodology allows us to measure this variability, either through distance to cluster centroids or 2D manifold mapping. Our findings reveal distinct patterns in the occurrence rate, daily frequency, and waveform characteristics of these clusters, providing new insights into the behavior of seismic events versus anthropogenic noises.

How to cite: Esfahani, R., Campillo, M., Seydoux, L., Mouaoued, S., and Wang, Q.-Y.: Detailed clustering of continuous seismic waveforms with deep scattering networks: a case study on the Ridgecrest earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6371, https://doi.org/10.5194/egusphere-egu24-6371, 2024.

As the amount of seismic data increasing drastically worldwide, there are ever-growing needs for high-performance automatic seismic data processing  methods and high-quality, standardized professional datasets. To address this issue, we recently updated the 'DiTing' dataset, one of the world's largest seismological AI datasets with ~2.7 million traces and corresponding labels,  with 1,089,920 three-component waveforms from 264,298 natural earthquakes in mainland China and adjacent areas, and 958,076 Pg, 780603 Sg, 152752 Pn, 25956 Sn earthquake phase arrival tags, in addition to 249,477 Pg, 41610 Pn first motion polarity tags from 2020 to 2023. We also collected 15375 non-natural earthquake waveforms in mainland China from 2009 to 2023 and a manually labeled noise dataset containing various typical noise signals from the China Seismological Network. With the support of the 'DiTing' dataset, we developed and trained several deep learning models referred as 'DiTingTools' for automatic seismic data processing. In the continuous waveform detection and evaluation of more than 1,000 stations over a year across China, 'DiTingTools' has achieved an average recall rate of 80% for event detection, mean square error ±0.2s for P phase picking, and ±0.4s for S, the average identification accuracy rate of Pg first motion polarity reached 86.7% (U) and 87.9% (D), and 75.1% (U) and 73.1% (D) for Pn first motion polarity, the average magnitude prediction error of a single station is mainly concentrated at ±0.5. The remarkable generalization capabilities of 'DiTingTools' were demonstrated through its application on the China Seismic Network. Specifically, 'DiTingPicker', a model within 'DiTingTools' designed for earthquake detection and phase picking, was employed to analyze the M 6.8  earthquake that struck Luding County, Sichuan Province, in 2022. This tool was instrumental in automatically processing data to examine the main shock and intricate fault structures of the aftershocks. The effectiveness of 'DiTingTools' in earthquake prevention and disaster reduction was further validated through these practical applications.

How to cite: Zhao, M., Xiao, Z., Zhang, B., Zhang, B., and Chen, S.: 'DiTing' and 'DiTingtools':a large multi-label dataset and algorithm set for intelligent seismic data processing established based on the China Seismological Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7119, https://doi.org/10.5194/egusphere-egu24-7119, 2024.

EGU24-7309 | Posters on site | SM2.3

Deep learning-based earthquake catalogs extracted from threebroadband/nodal seismic arrays with different apertures in Taiwan bySeisBlue 

Sheng-Yan Pan, Wei-Fang Sun, Chun-Ming Huang, and Hao Kuo-Chen

SeisBlue, a deep-learning-based earthquake monitoring system, is one of the solutions to deal with massive continuous waveform data and create earthquake catalogs. The SeisBlue workflow contains waveform data preprocessing, phase arrival detection by AI modules, phase associator, earthquake locating, earthquake catalog generation, and data visualization. The whole process can be done automatically and efficiently reduces the labor and time costs. In this study, SeisBlue is applied to three different regional seismic networks: the Formosa Array for the observation of magma chamber beneath the Tatun volcanic area, Taiwan (aperture ~80 km with 148 broadband stations and station spacing 5 km), the Chihshang seismic network (CSN) for monitoring micro-seismicity of Chihshang, Taiwan (aperture ~150 km with 14 broadband stations and station spacing 20 km), and the temporary dense nodal array for capturing the aftershock sequence of the 18 th Sep. 2022 Mw6.9 Chihshang earthquake, Taiwan (aperture ~70 km with 46 nodal stations and station spacing 3 km). The 2020 annual SeisBlue catalog of the Formosa Array contains 2,201 earthquakes, as background seismicity, compare to the 1,467 earthquakes listed in the standard catalog of the Central Weather Administration (CWA), Taiwan. The two-month SeisBlue catalog of the 2022 Mw6.9 Chihshang earthquake sequence, September to October, contains 14,276 earthquakes using the CSN dataset; however, the CWA standard catalog only lists 1,247 earthquakes during the same time period. By using waveform data of 18 th Sep. to 25 th Oct. 2022, SeisBlue detects 34,630 and 12,458 earthquakes extracted from the datasets of the dense nodal array and CSN, respectively. SeisBlue can effectively detects both background and aftershock seismicity and extracts small earthquakes via dense arrays.

Keywords: AI earthquake monitoring system, deep learning, AI earthquake catalog, SeisBlue, automatic waveform picking

How to cite: Pan, S.-Y., Sun, W.-F., Huang, C.-M., and Kuo-Chen, H.: Deep learning-based earthquake catalogs extracted from threebroadband/nodal seismic arrays with different apertures in Taiwan bySeisBlue, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7309, https://doi.org/10.5194/egusphere-egu24-7309, 2024.

EGU24-8233 | Posters on site | SM2.3

Double Acoustic Emission events detection using U-net Neural Network 

Petr Kolar, Matěj Petružálek, Jan Šílený, and Tomáš Lokajíček

In the past decade, the development of the Deep Neural Network formalism has emerged as a promising approach for addressing contemporary task in seismology, particularly in the effective and potentially automated processing of extensive datasets, such as seismograms. In this study, we introduce a 4D Neural Network (NN) based on the U-Net architecture, capable of simultaneously processing data from the entire seismic network. Our dataset comprises records/seismograms of Acoustic Emission (AE) events obtained during a laboratory loading experiment on a rock specimen. While AE event records share similarities with real seismograms, they exhibit simplifications in certain features.
To assess the capability of the proposed NN in handling complex data, including occurrences of multiple events observed during experiments, we generated double-event seismograms through the augmentation of unambiguous single-event seismograms. These augmented datasets were employed for training, validation, and testing of the NN. Despite the individual station detection rate being approximately 30%, the simultaneous processing of multiple stations significantly increased efficiency, achieving an overall detection rate of 97%.
In this work, we treat seismograms as "images," adopting an approach that proves to be fruitful. The simultaneous processing of seismograms, coupled with this image-based treatment, demonstrates high potential for reliable automatic interpretation of seismic data. This approach (possibly combined with other methodologies), holds promise for seismogram processing.

How to cite: Kolar, P., Petružálek, M., Šílený, J., and Lokajíček, T.: Double Acoustic Emission events detection using U-net Neural Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8233, https://doi.org/10.5194/egusphere-egu24-8233, 2024.

EGU24-8913 | ECS | Posters on site | SM2.3

Benchmarking seismic phase associators: Insights from synthetic scenarios 

Jorge Antonio Puente Huerta, Jannes Münchmeyer, Ian McBrearty, and Christian Sippl

In seismology, accurately associating seismic phases to their respective events is crucial for constructing reliable seismicity catalogs. This study presents a comprehensive benchmark analysis of five seismic phase associators, including machine learning based solutions, employing synthetic datasets tailored to replicate the seismicity characteristics of real seismic data in a crustal and a subduction zone scenario.

The synthetic datasets were generated using the NonLinLoc raytracer, using real station distributions and velocity models and simulating a large range of seismic events across different depths. In order to generate sets of picks with quality and diversity similar to a real-world dataset, some modifications such as adjustments to arrival times simulating picking errors, selective station exclusion, incorporation of false picks, were included. Such a controlled environment allowed for the assessment of associator performance under a range of different conditions.

As part of project MILESTONE, we compared the performance of five state-of-the-art seismic phase associators (PhaseLink, GaMMA, REAL, GENIE, and PyOcto) across multiple scenarios, including low-noise environments, high-noise background activity, out-of-network events, and complex aftershock sequences. Each associator's accuracy in identifying and associating true events amidst noise picks and its ability to handle overlapping sets of arrival times from different events were rigorously evaluated.

Additionally, we conducted a systematic comparison of the advantages and disadvantages of each associator, attempting a fair and unbiased evaluation. This included assessing their processing times, a critical factor in operational seismology. Our findings reveal significant differences in the precision and robustness of these associators.

This benchmark study not only underscores the importance of robust phase association in seismological research but also paves the way for future enhancements in seismic data processing techniques. The insights gained from this analysis are expected to significantly contribute to the ongoing efforts in seismic monitoring and hazard assessment, particularly in the realm of machine learning applications.

How to cite: Puente Huerta, J. A., Münchmeyer, J., McBrearty, I., and Sippl, C.: Benchmarking seismic phase associators: Insights from synthetic scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8913, https://doi.org/10.5194/egusphere-egu24-8913, 2024.

EGU24-8924 | Orals | SM2.3

Revealing and interpreting patterns from continuous seismic data with unsupervised learning 

Léonard Seydoux, René Steinmann, Sarah Mouaoued, Reza Esfahani, and Michel Campillo

Exploring large datasets of continuous seismic data is a challenging task. When targeting signals of interest with a good a priori knowledge on the signal's properties, it is possible to design a dedicated processing pipeline (earthquake detection, noise reduction, etc.). Many other sources can sign up in the data, with characteristics that differ from the targetted ones (changes in noise frequency, modulating signals, etc.). In this case, it is difficult to design a processing pipeline that will be robust to all the possible sources. In this work, we propose to use unsupervised learning to explore the data and reveal patterns in an interpretable way. We extract relevant features of continuous seismic data with a deep scattering network —a deep convolutional neural network with interpretable feature maps— and experiment various classical machine learning tools (clustering, dimensionality reduction, etc.) to reveal and interpret patterns in the data. We apply this method to various cases including to a decade of continuous data in the region of Guerrero, Mexico, and interpret the results in terms of seismicity and external datasets.

How to cite: Seydoux, L., Steinmann, R., Mouaoued, S., Esfahani, R., and Campillo, M.: Revealing and interpreting patterns from continuous seismic data with unsupervised learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8924, https://doi.org/10.5194/egusphere-egu24-8924, 2024.

EGU24-9120 | ECS | Posters on site | SM2.3

An up-to-date seismic catalogue of the 2020 Mw6.4 Petrinja (Croatia) earthquake sequence using machine learning 

Dinko Sindija, Marija Mustac Brcic, Gyorgy Hetenyi, and Josip Stipcevic

Identifying earthquakes and selecting their arrival phases are essential tasks in earthquake analysis. As more seismic instruments become available, they produce vast amounts of seismic data. This necessitates the implementation of automated algorithms for efficiently processing earthquake sequences and for recognising numerous events that might go unnoticed with manual methods.

In this study, we employed the EQTransformer, trained on the INSTANCE dataset, and utilised PyOcto for phase association, focusing specifically on the Petrinja earthquake series. This series is particularly interesting for its initial phase, which was marked by a limited number of seismometers in the epicentral area during the onset of the sequence in late December 2020. This limitation was subsequently addressed by the swift deployment of five additional stations near the fault zone in early January 2021, followed by a gradual expansion of the seismic network to over 50 instruments.

Our analysis covers the Petrinja earthquake series from its onset on December 28, 2020, up to present, offering a complete and up-to-date view of the seismic activity as the seismic activity is still higher than in the interseismic period. We compare our findings from the machine learning-generated catalogue with a detailed manual catalogue. Focusing on the first week of the series, when the seismic network was sparse and there was a high frequency of overlapping earthquakes, we achieved a recall of 80% and a precision of 81% for events with local magnitude greater than 1.0. In contrast, for the subsequent six months of processed data, a period still characterised by a high frequency of earthquakes but with the fully expanded network, our recall improved dramatically to 95% with over 20,000 detected events. This comparison allows us to demonstrate the challenges, evolution, and effectiveness of automatic seismic monitoring throughout the earthquake sequence.

How to cite: Sindija, D., Mustac Brcic, M., Hetenyi, G., and Stipcevic, J.: An up-to-date seismic catalogue of the 2020 Mw6.4 Petrinja (Croatia) earthquake sequence using machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9120, https://doi.org/10.5194/egusphere-egu24-9120, 2024.

The use of P-wave receiver function and surface wave dispersion data is crucial in exploring the structure of the Earth's crust and upper mantle. Typically, to address the ambiguity resulting from using a single type of dataset for inversion, these two types of seismic data, which have different sensitivities to shear wave velocity structure, are jointly inverted to achieve a detailed velocity structure. However, methods that rely on a linearized iterative joint inversion approach depend on the initial model selection, while non-linear joint inversion frameworks based on model parameter space search are computationally intensive. To address these challenges, this study suggests employing a deep learning strategy for the joint inversion of P-wave receiver function and surface wave dispersion data. Two distinct neural networks are developed to extract features from the P-wave receiver function and surface wave dispersion data, and different loss functions are tested to train the proposed neural network. The proposed method has been applied to actual seismic data from South China, and the results are comparable to those obtained by jointly inverting body wave first travel-time, P-wave receiver function, and surface wave dispersion data.

How to cite: Hu, J.: Joint inversion of P-wave receiver function and surface wave dispersion data based on deep learning. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9621, https://doi.org/10.5194/egusphere-egu24-9621, 2024.

Objectives and Scope:

Deep learning's efficacy in seismic interpretation, including denoising, horizon or fault detection, and lithology prediction, hinges on the quality of the training dataset. Acquiring high-quality seismic data is challenging due to confidentiality, and alternative approaches like using synthetic or augmented data often fail to adequately capture realistic wavefield variations, ambient noise, and complex multipathing effects such as multiples. We introduce an innovative seismic data augmentation method that incorporates realistic geostatistical features and synthetic multiples, enhancing the training and transferability of deep neural networks in multi seismic applications.

Methods and Procedures:

Our method comprises two primary steps: (1) Creating augmented impedance models from existing seismic images and well logs, and (2) Simulating seismic data from these models. The first step merges Image-Guided Interpolation (IGI, Hale et al., 2010) and Sequential Gaussian Simulation (SGS) to generate models that retain original structural features of the input seismic image and introduce random small-scale features aligned with the geostatistical properties of the input seismic data. The second step employs reflectivity forward modeling method (Kennett, 1984) to simulate both primary and multiple seismic data trace-by-trace. This approach, summing up infinite order internal multiples, effectively reproduces the full properties of reflection wavefields, which is a good approximation in areas without rapidly changing structures.

Results and Observations:

Our numerical tests validate the method's effectiveness. The IGI technique interpolates well log data into gridded velocity models, maintaining seismic horizons and smoothing fault features. The SGS method then generates stochastic velocity model implementations preserving the geostatistical distribution of the input seismic data. The resulting reflectivity forward modeling successfully distinguishes between multiples and primaries, facilitating the creation of nuanced training datasets and labels.

Further tests involve training two Transformer-based seismic fault detection neural networks: one with conventional data lacking multiples and another with our augmented data incorporating multiples. While both networks exhibit similar validation performance, their generalization capabilities differ markedly. The network trained with conventional data shows reduced accuracy and fault detection reliability on synthetic field data. In contrast, the network trained with our augmented data demonstrates better precision, accuracy, and recall on the same dataset.

Significance and Novelty:

Our approach generates augmented seismic data that retains the original seismic cubes' and well logs' geostatistical features and multiples, crucial for training deep learning models with high transferability for various seismological tasks. This method's novelty lies in its consideration of geostatistical characteristics, wavelet fluctuations, and multiples. The resulting data is more complex, varied, and realistic compared to conventional augmentation methods. Neural networks trained on this data exhibit enhanced transferability over those trained with traditional synthetic data incorporating only random noise. This advancement represents a significant leap in seismic data processing and interpretation, particularly for deep learning applications in geophysics.

How to cite: Zhou, T.: Seismic data augmentation with realistic geostatistical features and synthetic multiples for multi deep learning tasks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10219, https://doi.org/10.5194/egusphere-egu24-10219, 2024.

EGU24-12197 | Orals | SM2.3

Failures, successes and challenges of machine-learning-based engineering ground-motion models 

Fabrice Cotton, Reza Esfahani, and Henning Lilienkamp

The exponential growth of seismological data and machine learning methods offer new perspectives for analysing the factors controlling seismic ground motions and predicting earthquake shaking for earthquake engineering. However, the first models (e.g. Derras et al., 2012) using "simple" neural networks to predict seismic motions did not convince the earthquake engineering community, which continued to use more conventional models. We analyse the weaknesses (from the perspective of engineering seismology) of this first generation of ML-based ground motion models and explain why this first generation did not provide sufficient added value compared to conventional models.  Based on this experience, we propose two evolutions and new methods that have advantages over conventional methods and therefore have greater potential.  A first class of models (e.g. Lilienkamp et al., 2022), based on a U-net neural network, predicts spatial variations in seismic motions (e.g. site effects in three-dimensional basins) by considering seismic motions in map form. A second class of approaches) combines AI methods (conditional generative adversarial networks,  Esfahani et al., 2023) and hybrid databases (observations and simulations selected for their complementarity) to train simulation models capable of generating not only a few parameters (e.g. PGA) describing ground motions, but the full acceleration time histories. We will discuss the potential advantages of this new generation of ML-based methods compared to conventional methods, but also the challenges (and proposed solutions) to best combine simulations and observations, and to calibrate both the best estimate and the variability of future ground motions.

How to cite: Cotton, F., Esfahani, R., and Lilienkamp, H.: Failures, successes and challenges of machine-learning-based engineering ground-motion models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12197, https://doi.org/10.5194/egusphere-egu24-12197, 2024.

EGU24-12357 | ECS | Orals | SM2.3

Deep learning prediction of measured earthquake waveforms from synthetic data 

Alexander Bauer, Jan Walda, and Conny Hammer

Seismic waveforms of teleseismic earthquakes are highly complex since they are a superposition of numerous phases that correspond to different wave types and propagation paths. In addition, measured waveforms contain noise contributions from the surroundings of the measuring station. The regional distribution of seismological stations is often relatively sparse, in particular in regions with low seismic hazard such as Northern Germany. However, a detailed knowledge of the seismic wavefield generated by large earthquakes can be crucial for highly precise measurements or experiments that are carried out for instance in the field of particle physics, where seismic wavefields are considered noise. While synthetic waveforms for cataloged earthquakes can be computed for any point on the Earth’s surface, they are based on a highly simplified Earth model. As a first step towards the prediction of a dense seismic wavefield in a region with sparsely distributed stations, we propose to train a convolutional neural network (CNN) to predict measured waveforms of large earthquakes from their synthetic counterparts. For that purpose, we compute synthetic waveforms for numerous large earthquakes of the past years with the IRIS synthetics engine (Syngine) and use the corresponding actual measurements from stations in Northern Germany as labels. Subsequently, we test the performance of the trained neural network for events not part of the training data. The promising results suggest that the neural network is able to largely translate the synthetic waveforms to the more complex measured ones, indicating a means to overcome the lack of complexity of the Earth model underlying the synthetic waveform computation and paving the way for a large-scale prediction of the seismic wavefield generated by earthquakes.

 
 

 

 

How to cite: Bauer, A., Walda, J., and Hammer, C.: Deep learning prediction of measured earthquake waveforms from synthetic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12357, https://doi.org/10.5194/egusphere-egu24-12357, 2024.

EGU24-14134 | ECS | Posters on site | SM2.3

Recipe For Regular Machine Learning-based Earthquake Cataloging: A Systematic Examination in New Zealand, from Local to Regional Scale 

Wu-Yu Liao, En-Jui Lee, Elena Manea, Florent Aden, Bill Fry, Anna Kaiser, and Ruey-Juin Rau

Machine learning-based algorithms are emerging in mining earthquake occurrences from continuous recordings, replacing some routine processes by human experts, e.g., phase picking and phase association. In this study, we explore the combination of phase picker and phase associator with challenging application scenarios: the complex seismogenic structure, wide study area (15 degrees of both longitude and latitude and a depth of 600 km), hundreds of stations, and intensive seismicity during the 2016 Mw7.8 Kaikōura earthquake that correlates with at least seven faults. The deep learning-based phase pickers usually follow the prototype of PhaseNet, which maps the phase arrivals into truncated Gaussian functions with a customized model. Recent studies have shown poor generalizability of the advanced models on data out of the training distribution. In this study, we argue that appropriate data augmentation enables the RED-PAN model, trained on the Taiwanese data, to generalize well on New Zealand data even under intense seismicity. We applied RED-PAN on year-long continuous recordings over 439 stations of the GeoNet during 2016 and 2017. RED-PAN produces approximately three million P-S pairs over the New Zealand-wide network, enabling the exploration of the advanced phase associators' robustness on local and regional scales and under intense seismicity, e.g., back-projection, GaMMA, and PyOcto. Finally, we developed a six-stage automatic pipeline producing a high-quality earthquake catalog: phase picking, phase association, 3-D absolute location by NonLinLoc, magnitude estimation, weighted template matching, and 3-D relative location by GrowClust. 

How to cite: Liao, W.-Y., Lee, E.-J., Manea, E., Aden, F., Fry, B., Kaiser, A., and Rau, R.-J.: Recipe For Regular Machine Learning-based Earthquake Cataloging: A Systematic Examination in New Zealand, from Local to Regional Scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14134, https://doi.org/10.5194/egusphere-egu24-14134, 2024.

EGU24-14239 | ECS | Orals | SM2.3

Deep learning to predict time to failure of lab foreshocks and earthquakes from fault zone raw acoustic emissions 

Laura Laurenti, Christopher Johnson, Elisa Tinti, Fabio Galasso, Paul Johnson, and Chris Marone

Earthquake forecasting and prediction are going through achievements in short-term early warning systems, hazard assessment of natural and human-induced seismicity, and prediction of laboratory earthquakes.

In laboratory settings, frictional stick-slip events serve as an analog for the complete seismic cycle. These experiments have been pivotal in comprehending the initiation of failure and the dynamics of earthquake rupture. Additionally, lab earthquakes present optimal opportunities for the application of machine learning (ML) techniques, as they can be generated in long sequences and with variable seismic cycles under controlled conditions. Indeed, recent ML studies demonstrate the predictability of labquakes through acoustic emissions (AE). In particular, Time to Failure (TTF) (defined as the time remaining before the next main labquake and retrieved from recorded shear stress) has been predicted for the main lab-event considering simple AE features as the variance.

A step forward in the state of the art is the prediction of Time To Failure (TTF) by using raw AE waveforms. Here we use deep learning (DL) to predict not only the TTF of the mainshock with raw AE time series but also the TTF of all the labquakes, foreshocks or aftershocks, above a certain amplitude. This is a great finding for several reasons, mainly: 1) we can predict TTF by using traces that don’t contain EQ (but only noise); 2) we can improve our knowledge of seismic cycle predicting also TTF of foreshocks and aftershocks.

This work is promising and opens new opportunities for the study of natural earthquakes just by analyzing the continuous raw seismogram. In general laboratory data studies underscore the significance of subtle deformation signals and intricate patterns emanating from slipping and/or locked faults before major earthquakes. Insights gained from laboratory experiments, coupled with the exponential growth in seismic data recordings worldwide, are diving into a new era of earthquake comprehension.

How to cite: Laurenti, L., Johnson, C., Tinti, E., Galasso, F., Johnson, P., and Marone, C.: Deep learning to predict time to failure of lab foreshocks and earthquakes from fault zone raw acoustic emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14239, https://doi.org/10.5194/egusphere-egu24-14239, 2024.

EGU24-14438 | ECS | Posters on site | SM2.3

A deep learning-based earthquake simulator: from source and geology to surface wavefields 

Fanny Lehmann, Filippo Gatti, Michaël Bertin, and Didier Clouteau

Recent advances in scientific machine learning have led to major breakthroughs in predicting Partial Differential Equations’ solutions with deep learning. Neural operators, for instance, have been successfully applied to the elastic wave equation, which governs the propagation of seismic waves. They give rise to fast surrogate models of earthquake simulators that considerably reduce the computational costs of traditional numerical solvers.

We designed a Multiple-Input Fourier Neural Operator (MIFNO) and trained it on a database of 30,000 3D earthquake simulations. The inputs comprise a 3D heterogeneous geology and a point-wise source given by its position and its moment tensor coordinates. The outputs are velocity wavefields recorded at the surface of the propagation domain by a grid of virtual sensors. Once trained, the MIFNO predicts 6.4s of ground motion velocity on a domain of size 10km x 10km x 10km within a few milliseconds.

Our results show that the MIFNO can accurately predict surface wavefields for all earthquake sources and positions. Predictions are assessed in several frequency ranges to quantify the accuracy with respect to the well-known spectral bias (i.e. degradation of neural networks’ accuracy on small-scale features). Thanks to its efficiency, the MIFNO is also applied to a database of real geologies, allowing unprecedented uncertainty quantification analyses. This paves the way towards new seismic hazard assessment methods knowledgeable of geological and seismological uncertainties.

How to cite: Lehmann, F., Gatti, F., Bertin, M., and Clouteau, D.: A deep learning-based earthquake simulator: from source and geology to surface wavefields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14438, https://doi.org/10.5194/egusphere-egu24-14438, 2024.

EGU24-15571 | ECS | Orals | SM2.3

Self-Supervised Learning Strategies for Clustering Continuous Seismic Data 

Joachim Rimpot, Clément Hibert, Jean-Philippe Malet, Germain Forestier, and Jonathan Weber

Continuous seismological datasets offer insights for the understanding of the dynamics of many geological structures (such as landslides, ice glaciers, and volcanoes) in relation to various forcings (meteorological, climatic, tectonic, anthropic) factors. Recently, the emergence of dense seismic station networks has provided opportunities to document these phenomena, but also introduced challenges for seismologists due to the vast amount of data generated, requiring more sophisticated and automated data analysis  techniques. To tackle this challenge, supervised machine learning demonstrates promising performance; however, it necessitates the creation of training catalogs, a process that is both time-consuming and subject to biases, including pre-detection of events and subjectivity in labeling. To address these biases, manage large data volumes and discover hidden signals in the datasets, we introduce a Self-Supervised Learning (SSL) approach for the unsupervised clustering of continuous seismic data. The method uses siamese deep neural networks to learn from the initial data. The SSL model works by increasing the similarity between pairs of images corresponding to several representations (seismic traces, spectrograms) of the seismic data. The images are positioned in a 512-dimensional space where possible similar events are grouped together. We then identify groups of events using clustering algorithms, either centroid-based or density-based. 

The processing technique is applied to two dense arrays of continuous seismological datasets acquired at the Marie-sur-Tinée landslide and the Pas-de-Chauvet rock glacier, both located in the South French Alps. Both datasets include over a month of continuous data from more than 50 stations. The processing technique is then applied to the continuous data streams from either a single station or from the whole station network. The clustering products show a high number of distinct clusters that could potentially be considered as produced by different types of sources. This includes the anticipated main types of seismicity observed in these contexts: earthquakes, rockfalls, natural and anthropogenic noises as well as potentially yet unknown sources. Our SSL-based clustering approach streamlines the exploration of large datasets, allowing more time for detailed analysis of the mechanisms and processes active in these geological structures.

How to cite: Rimpot, J., Hibert, C., Malet, J.-P., Forestier, G., and Weber, J.: Self-Supervised Learning Strategies for Clustering Continuous Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15571, https://doi.org/10.5194/egusphere-egu24-15571, 2024.

EGU24-16930 | ECS | Orals | SM2.3

How to Limit the Epistemic Failure of Machine Learning Models? 

Alexandra Renouard, Peter Stafford, Saskia Goes, Alexander Whittaker, and Stephen Hicks

The intelligible understanding of natural phenomena such as earthquakes is one of the main epistemic aims of science. Its very aims are shaped by technological discoveries that can change the cognitive fabric of a research field. Artificial intelligence, of which machine learning (ML) is one of the fundamental pillars, is the cutting-edge technology that promises the greatest scientific breakthroughs. In particular, great hopes are placed in ML
models as a source of inspiration for the formulation of new concepts or ideas, thanks to their ability to represent data at different levels of abstraction inaccessible to humans alone.
However, the opacity of ML models is a major obstacle to their explanatory potential. Although efforts have recently been made to develop ML interpretability methods that condense the complexity of ML models into human-understandable descriptions of how they work and make decisions, their epistemic success remains highly controversial. Because they are based on approximations of ML models, these methods can generate misleading explanations that are overfitted to human intuition and give an illusory sense of scientific understanding.
In this study, we address the question of how to limit the epistemic failure of ML models. To answer it, we use the example of an ML model trained to provide insights into how to better forecast newly emerging earthquakes associated with the expansion of hydrocarbon production in the Delaware Basin, West Texas. Through this example, we show that by changing our conception of explanation models derived from interpretability methods,
i.e. idealised scientific models rather than simple rationalisations, we open up the possibility of revealing promising hypotheses that would otherwise have been ignored. Analysis of our interpreted ML model unveiled a meaningful linear relationship between stress perturbation distribution values derived from ML decision rules and earthquake probability, which could be further explored to forecast induced seismicity in the basin and beyond. This observation also helped to validate the ML model for a subsequent causal approach to the factors underlying earthquakes.

How to cite: Renouard, A., Stafford, P., Goes, S., Whittaker, A., and Hicks, S.: How to Limit the Epistemic Failure of Machine Learning Models?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16930, https://doi.org/10.5194/egusphere-egu24-16930, 2024.

EGU24-17061 | ECS | Posters on site | SM2.3

Further investigations in Deep Learning for earthquake physics: Analyzing the role of magnitude and location in model performance 

Gabriele Paoletti, Laura Laurenti, Elisa Tinti, Fabio Galasso, Cristiano Collettini, and Chris Marone

Fault zone properties can evolve significantly during the seismic cycle in response to stress changes, microcracking, and wall rock damage. Distinguishing subtle changes in seismic behavior prior to earthquakes, even in locations with dense seismic networks, is challenging. In our previous works, we applied Deep Learning (DL) techniques to assess alterations in elastic properties before and after large earthquakes. To do that, we used 10,000 seismic events that occurred in a volume around the October 30th 2016, Mw 6.5, Norcia earthquake (Italy), and trained a DL model to classify foreshocks, aftershocks, and time-to-failure (TTF), defined as the elapsed time from the mainshock. Our model exhibited outstanding accuracy, correctly identifying foreshocks and aftershocks with over 90% precision and achieving good results also in time-to-failure multi-class classification.

To build upon our initial findings and enhance our understanding, this follow-up investigation aims to thoroughly examine the model's performance across various parameters. First, we will investigate the influence of earthquake magnitude on our model, specifically assessing whether and to what extent the model's accuracy and reliability are maintained across varying minimum magnitude thresholds included in the catalog. This aspect is crucial to understand whether the model's predictive power remains consistent at different magnitudes of completeness. In terms of source location, our study will extend to evaluate the model's reliability by selectively excluding events from specific locations within the study area, and alternatively, by expanding the selection criteria. This approach allows us to discern the model's sensitivity to spatial variations and its ability to adapt to diverse seismic activity distributions. Furthermore, we’ll pay particular attention to the analysis of null-results. This involves meticulously analyzing cases where the model does not perform effectively, producing low-precision or inconclusive results. By carefully examining these scenarios, our goal is to further assess and confirm the high-performance results obtained from previous works.

Our results highlight the promising potential of DL techniques in capturing the details of earthquake preparatory processes, acknowledging that while complexities of machine learning models exist, ML models have the potential to open hidden avenues of future research.

How to cite: Paoletti, G., Laurenti, L., Tinti, E., Galasso, F., Collettini, C., and Marone, C.: Further investigations in Deep Learning for earthquake physics: Analyzing the role of magnitude and location in model performance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17061, https://doi.org/10.5194/egusphere-egu24-17061, 2024.

EGU24-18303 | Posters on site | SM2.3

Machine learning based rapid earthquake characterization using PEGS in Alaska 

Quentin Bletery, Kévin Juhel, Andrea Licciardi, and Martin Vallée

A signal, coined PEGS for Prompt Elasto-Gravity Signal, was recently identified on seismograms preceding the seismic waves generated by very large earthquakes, opening promising applications for earthquake and tsunami early warning. Nevertheless, this signal is about 1,000,000 times smaller than seismic waves, making its use in operational warning systems very challenging. A Deep Learning algorithm, called PEGSNet, was later designed to estimate, as fast as possible, the magnitude of an ongoing large earthquake from PEGS recorded in real time. PEGSNet was applied to Japan and Chile and proved capable of tracking the magnitude of the Mw 9.1 Tohoku-oki and Mw 8.8 Maule earthquakes within a few minutes from the events origin times. Here, we apply this algorithm to a very well instrumented region: Alaska. We find that, applied to such a dense seismic network, the performance of PEGSNet is drastically improved, with robust performances obtained for earthquakes with magnitudes down to 7.8. The gain in resolution also allows us to estimate the focal mechanism of the events in real time, providing all the information required for tsunami warning within less than 3 minutes.

How to cite: Bletery, Q., Juhel, K., Licciardi, A., and Vallée, M.: Machine learning based rapid earthquake characterization using PEGS in Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18303, https://doi.org/10.5194/egusphere-egu24-18303, 2024.

SM3 – Seismic Instrumentation and Infrastructure

EGU24-414 | ECS | Posters on site | SM3.1

Subsurface characterization using Distributed Acoustic Sensing (DAS) on an offshore fiber between Denmark and Norway 

Jonas Damsgård, Thomas Hansen, Peter Voss, Henrik Hansen, Simon Steffansen, Egon Nørmark, and Michael Fyhn

In April 2023 a seismic survey was carried out in southern Skagerrak using a towed-streamer and airgun setup. The aim of the survey was investigating the suitability of the Jammerbugt structure for CO2 storage. A fiber-optic cable is co-located with the Skagerrak 4 high-voltage interconnector cable between Denmark and Norway. The fiber was crossed multiple times by the surveying ship. Relative strain was measured along a 80 km section of the fiber using Distributed Acoustic Sensing (DAS) during the active seismic survey. 

Seismic arrivals from the airgun shots were clearly recorded by the fiber. The DAS data also contains a large number of other signals caused by passing ships and wave interactions. Shot-gathers were extracted from the DAS data using the timing and location of airgun shots. These were subsequently processed and compared with traditional shot-gathers recorded by the towed-streamer. The DAS data contains distinguishable direct, refracted and surface wave arrivals from the airgun shots. Reflection hyperbolas are also observed in the DAS data at larger receiver-offsets, but only when the source is close to the fiber.

The comparison indicates that DAS is able to at least partially record the same wavefield from an active source as that recorded by hydrophones. Consequently the DAS data can be used for imaging and subsurface characterization.

The utilized DAS interrogator unit is owned by the danish transmission system operator, Energinet, who provided the DAS data for this study. Data processing is carried out using MatLab and Promax.

How to cite: Damsgård, J., Hansen, T., Voss, P., Hansen, H., Steffansen, S., Nørmark, E., and Fyhn, M.: Subsurface characterization using Distributed Acoustic Sensing (DAS) on an offshore fiber between Denmark and Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-414, https://doi.org/10.5194/egusphere-egu24-414, 2024.

Ubiquitous acoustic gravity waves in the atmosphere lead to elastic deformations of the Earth’s surface via ambient barometric pressure variations at ground level. The induced ground deformations are composed of vertical and horizontal displacements as well as ground tilts or equivalently ground rotations around horizontal axes. To make inferences about background levels of rotational ground motions we exploit the fact that ground tilts are sensed by both suitably oriented gyroscopes, as well as horizontal component accelerometers through tilt coupled gravity.  Based on 20 years of data from the Global Seismic Network (GSN) we estimate coherence and admittance between ambient atmospheric pressure and horizontal acceleration from collocted sensors.

Since atmospheric acoustic gravity waves propagate too slowly to efficiently excite Rayleigh waves in the Earth, we attribute horizontal accelerations which are coherent with pressure to tilt coupled gravity. Based on this line of reasoning and by restricting the analysis to time windows with high coherence, we can estimate lower bounds of background tilt and background rotation rate for all GSN stations and for the GSN as a whole. We find that below 20mHz and in the least noisy time windows the  pressure induced background rotation rate is 30dB higher than similar estimates based on the assumption that the terrestrial noise floor for rotations around a horizontal axis is defined by Rayleigh wave motion.

A notable consequence of the above findings is that for frequencies below 20 mHz  atmospheric pressure induced ground tilts lead not only to the well established large difference between background noise levels for vertical and horizontal seismic accelerations, but also for rotations around vertical and horizontal axes.  We will present preliminary new rotational low noise models valid for frequencies below the band of the marine microseisms. The caveat for such models is that they are drived from inertial seismometers and not from gyroscopes. Data from the ROMY gyroscope are analyzed in a companion poster by Brotzer et al. in this same session SM3.3

How to cite: Widmer-Schnidrig, R. and Brotzer, A.: On the limit imposed by variable atmospheric pressure for the observation of small terrestrial rotations around horizontal axes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1797, https://doi.org/10.5194/egusphere-egu24-1797, 2024.

EGU24-2514 | Orals | SM3.1 | Highlight

Photonic Seismology: A New Decade of Distributed Acoustic Sensing in Geophysics from 2012 to 2022 

Feng Cheng, Ke Zhao, Longfeng Zhao, and Jonathan Ajo-Franklin

This work delivers an in-depth bibliometric analysis of Distributed Acoustic Sensing (DAS) research within the realm of geophysics, covering the period from 2012 to 2022 and drawing on data from the Web of Science. By employing bibliographic and structured network analysis methods, including the use of VOSviewer®, the study highlights the most influential scholars, leading institutions, and pivotal research contributions that have significantly shaped the field of DAS in geophysics. The research delves into key collaborative dynamics, unraveling them through co-authorship network analysis, and delves into thematic developments and trajectories via comprehensive co-citation and keyword co-occurrence network analyses. These analyses elucidate the most robust and prominent areas within DAS research. A critical insight gained from this study is the rise of 'Photonic Seismology' as an emerging interdisciplinary domain, exemplifying the fusion of photonic sensing techniques with seismic science. The paper also discuss certain limitations inherent in the study, and concludes with implications for future research.

How to cite: Cheng, F., Zhao, K., Zhao, L., and Ajo-Franklin, J.: Photonic Seismology: A New Decade of Distributed Acoustic Sensing in Geophysics from 2012 to 2022, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2514, https://doi.org/10.5194/egusphere-egu24-2514, 2024.

EGU24-2827 | Orals | SM3.1 | Highlight

Overview of distributed fibre-optic sensing in geophysical applications. 

Arthur Hartog

The technology of distributed fibre-optic sensors (DFOS) has developed over more than four decades, initially confined to temperature sensing, which remains a valuable tool. In the last 15 years, however, the addition of distributed vibration/acoustic sensing has vastly increased the use of DFOS in geophysical applications.

The combination of acoustic, temperature and static strain measurement has provided a deeper insight in the subterranean and subsea realms, ranging from hydrocarbon and geothermal energy production, earthquake monitoring to oceanography and glaciology. Spare or disused capacity on long-distance fibre-optic communications links has opened up many opportunities for sensing the environment, especially in oceanography. Techniques developed for oil and gas exploration and production have led to reliable methods for conveying optical fibres in the very hostile found in boreholes and this has extended the applications of DFOS to understanding tectonic movements and also to decarbonising the energy supply industry, e.g. in carbon sequestration and geothermal production.

The talk will provide a brief overview of the instrumentation used for DFOS and it will discuss some of the key applications in geophysics. It will also examine some of the untapped opportunities and how technological improvements might enable these to be realised.  

How to cite: Hartog, A.: Overview of distributed fibre-optic sensing in geophysical applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2827, https://doi.org/10.5194/egusphere-egu24-2827, 2024.

The reliable estimation of earthquake magnitude and stress drop are key in seismology. The novel technology of distributed acoustic sensing (DAS) holds great promise for source parameter inversion owing to the measurements' high spatial density. Here, I demonstrate the robustness of DAS for magnitude and stress drop estimation using the empirical Green's function deconvolution method. This method is applied to nine co-located earthquakes recorded in Israel following the 2023 Turkey earthquakes. Spectral ratios were stacked along the fiber, and fitted with a relative Boatwright source spectral model. Excellent fits were obtained even for similar sized earthquakes. Stable seismic moments and stress drops were calculated assuming the moment of one earthquake is known. DAS derived estimates were found to be more stable and reliable than those obtained using a dense accelerometer network. The results demonstrate the great potential of DAS for source studies.

How to cite: Lior, I.: Accurate Magnitude and Stress Drop Using the Spectral Ratios Method Applied to Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3214, https://doi.org/10.5194/egusphere-egu24-3214, 2024.

EGU24-3331 | ECS | Posters on site | SM3.1

Earthquake Coda Magnitude with Distributed Acoustic Sensing at Ridgecrest, California 

Peng Ye and Xin Wang

Distributed Acoustic Sensing (DAS) has emerged as a transformative technology in recent years, effectively converting optical fibers into dense seismic arrays. Numerous studies have demonstrated the widespread applications of DAS in seismology, including earthquake detection and subsurface structure imaging. In terms of earthquake source studies using DAS, the conventional approach for determining earthquake magnitudes primarily relies on maximum amplitude measurements. However, this approach faces limitations, such as unknown cable couplings and instrument responses, single-component sensing, complex source radiation patterns, and uncommon amplitude saturation behaviors. To overcome these challenges, we propose a novel method that calculates earthquake magnitudes based on coda waves using DAS. Utilizing a 10 km-long DAS array deployed in Ridgecrest, California, we derive coda wave energy decay to estimate source amplitude terms. Our findings reveal a strong linear correlation between these estimates and seismic magnitudes estimated using broadband seismic network. Furthermore, our study provides insights into the attenuation structure beneath the DAS array, aligning well with shallow velocity structures. This study not only advances our understanding of seismic source characterization using DAS, but also paves the way for more accurate earthquake magnitude estimation using DAS.

How to cite: Ye, P. and Wang, X.: Earthquake Coda Magnitude with Distributed Acoustic Sensing at Ridgecrest, California, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3331, https://doi.org/10.5194/egusphere-egu24-3331, 2024.

EGU24-3466 | ECS | Orals | SM3.1

Differential arrival times for source location with DAS arrays: tests on data selection and automatic weighting procedure 

Emanuele Bozzi, Nicola Piana Agostinetti, Gilberto Saccorotti, Andreas Fichtner, Lars Gebraad, Tjeerd Kiers, and Takeshi Nishimura

Distributed Acoustic Sensing (DAS) technology is currently used to monitor seismic activity, offering a unique spatially-dense representation of the along-the-cable strain wavefield. Traditional seismic networks typically rely on the timing of specific seismic phases to estimate source locations. In this context, DAS arrays may fail to provide accurate traveltimes because of spatially-heterogeneous waveforms. The motivations are (but not limited to) the directional sensitivity, the heterogeneous cable ground-coupling and the enhanced sensitivity to lateral variations in the medium elastic properties. The resulting fluctuations in signal-to-noise ratios of the dense DAS channels pose significant challenges in the automatic picking of body phases, e.g., P-wave Absolute Arrival Times (P-ARTs). Consequently, the complex distribution of the estimated traveltimes impacts the accuracy of event locations, especially if incorrect assumptions on error statistics (e.g., Normal distribution) are considered. In this study, we address this issue by exploiting the intrinsic DAS measurements' spatial density and testing selected P-wave Differential Arrival Times (P-DATs) for source location. We estimate P-DATs for all the possible DAS channel pairs by identifying the time delay corresponding to the peak of each cross-correlation function. Subsequently, we select P-DATs based on two criteria: interchannel distance and cross-correlation index value. This procedure is often employed to reduce the risk of mixing delay times from coherent and incoherent waveforms. As a first test, using a probabilistic inversion (Hamiltonian Monte Carlo method), we demonstrate how the selected P-DATs provide a better constraint on the event's azimuthal direction compared to P-ARTs. Then, as a second experiment, we move from a subjective selection of P-DATs. To do so, we test a fully-automated and data-driven covariance matrix weighting procedure, in a probabilistic inversion scheme. Specifically, we compute posterior probability distributions for both the physical parameters (event location) and hyperparameters related to data features (interchannel distance and cross-correlation index thresholds). In this scheme, the hyperparameters define each weight along the diagonal of the covariance matrix. These tests offer useful insights into the utilization of P-DATs for event location with DAS. Moreover, we provide an automatic approach to avoid subjective biases based on pre‐conceptions in the a-priori data selection.

How to cite: Bozzi, E., Piana Agostinetti, N., Saccorotti, G., Fichtner, A., Gebraad, L., Kiers, T., and Nishimura, T.: Differential arrival times for source location with DAS arrays: tests on data selection and automatic weighting procedure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3466, https://doi.org/10.5194/egusphere-egu24-3466, 2024.

EGU24-4418 | Orals | SM3.1

Smart Grid Optical Fiber Network for Earthquake Early Warnings 

Hasan Awad, Fehmida Usmani, Emanuele Virgillito, Rudi Bratovich, Stefano Straullu, Roberto Proietti, Rosanna Pastorelli, and Vittorio Curri

Optical fiber networks, commonly known for data communications, could be extended beyond their conventional use. In our research, we propose a groundbreaking method by leveraging these existing terrestrial optical networks as wide distributed array sensors for earthquakes early detection. This approach is centered around the use of light polarization changes within the fiber cable, analyzed through a robust machine learning model that provide early warning alerts upon Primary earthquake waves arrival that induce strain, and precede earthquake’s destructive Surface waves. Unlike previous methods such as Distributed Acoustic Sensing and Frequency Interferometric Techniques, our approach avoids the use of expensive and specialized hardware. We introduce a centralized smart grid system that exploits the network’s existing terrestrial infrastructure, yet ensure cost effective and high efficient network modeling for initiating emergency plans and earthquake countermeasures. Our initial studies started by conducting experimental tests on a deployed fiber ring in Turin, Italy, using commercial Intensity Modulated – Direct Detection transceivers and polarimeters as polarization sensing devices, yield in promising results. Additionally, we identified the Primary waves arrival for a real 4.9 magnitude earthquake struck in the Marradi region, central Italy, with a 98% accuracy rate. This achievement was the result of a python-based waveplate model empowered by machine learning algorithm.  

Basically, when an earthquake occurs, networks nodes communicates with a centralized optical network controller that detects alterations in the light’s state of polarization by leveraging a pre-trained machine learning model. Upon the model confirmation, the controller activates early warning system in accordance with a predetermined emergency response mechanism. Building up on these findings, our current objective is to explore the impact of earthquake depth on seismic wave characteristics and their influence on light’s polarization to further investigate the potential of this advanced smart grid methodology. We aim to analyze real ground motion waves generated by two distinct earthquakes with same magnitudes but different depths. This knowledge is crucial in refining our machine learning model, which in turn will refine model prediction capabilities. Our approach promises more efficient optical network, by transforming the network into long range seismic sensors.

How to cite: Awad, H., Usmani, F., Virgillito, E., Bratovich, R., Straullu, S., Proietti, R., Pastorelli, R., and Curri, V.: Smart Grid Optical Fiber Network for Earthquake Early Warnings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4418, https://doi.org/10.5194/egusphere-egu24-4418, 2024.

EGU24-5900 | ECS | Orals | SM3.1

Noise analysis of Distributed Acoustic Sensing (DAS) systems in borehole installations 

Davide Pecci, Simone Cesca, Giacomo Rapagnani, Sonja Gaviano, Gian Maria Bocchini, Giorgio Carelli, Eusebio Stucchi, Renato Iannelli, and Francesco Grigoli

In recent years, there has been an increasing interest in Distributed Acoustic Sensing (DAS) technology for microseismic monitoring, especially in operations involving borehole installations. Despite the widespread adoption of DAS systems in such contexts, many questions regarding the data quality of the recordings are still open. Is the DAS self-noise higher than traditional systems? How does the ambient noise recorded by a DAS system attenuate with the depth as observed with traditional geophones? It is known that various noise types, including optical, thermal, and mechanical noise coupled with the fiber, affect DAS data. Additionally, the noise frequency band often overlaps with the signal frequency band, making frequency filtering alone inadequate for denoising. Therefore, specialized noise reduction workflows, such as FK Filtering and SVD, are necessary. Mitigating the impact of noise on DAS data remains a primary challenge for the seismological and geophysical community. This study aims to examine and characterize the noise influencing DAS data collected in borehole installations, with a specific focus on the data recorded at the Frontier Observatory for Research in Geothermal Energy site in Utah, USA. We use Power Spectral Density analysis to assess depth-dependent noise reduction and its temporal variations. Furthermore, the depth dependence of the signal-to-noise ratio for various microseismic events is evaluated. Finally, a comparison is drawn with geophones data colocated with the fiber, offering a comprehensive exploration of the advantages and disadvantages of the two data acquisition technologies.

How to cite: Pecci, D., Cesca, S., Rapagnani, G., Gaviano, S., Bocchini, G. M., Carelli, G., Stucchi, E., Iannelli, R., and Grigoli, F.: Noise analysis of Distributed Acoustic Sensing (DAS) systems in borehole installations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5900, https://doi.org/10.5194/egusphere-egu24-5900, 2024.

EGU24-6263 | ECS | Orals | SM3.1

Full-waveform modelling of coupling and site effects for DAS cables 

Nicolas Luca Celli, Christopher J. Bean, and Gareth S. O'Brien

The use of optical fibre cables to sense ground motion is one of the most researched topics in seismology at present day. By using the technique of Distributed Acoustic Sensing (DAS), a single fibre can be turned into thousands of seismic sensors, providing unprecedented spatial resolution. The instrument response of optical fibre cables, however, is largely unknown and difficult to separate from source, path, and directivity effects on seismic records, preventing us from using the information from the full seismic waveform.

Here we present a full-waveform simulation scheme developed to model the DAS instrument response using a particle-based Elastic Lattice Model (ELM-DAS). The scheme allows us to simulate a virtual cable embedded in the medium and made of a string of connected particles. By measuring the strain along these particles, we are able to replicate the axial strain natively measured by DAS as well as the effects of irregular cable geometries. The scheme allows us to easily simulate complex properties of the material around the cable (e.g., unconsolidated sediments, nonlinear materials) as well as different degrees of cable-ground coupling, both of which are believed to be the key factors controlling the DAS instrument response.

By simulating DAS cables in 2D, 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. By expanding the scheme to 3D, we can accurately include the effects of realistic, complex–and at times sub-wavelength—cable geometries and how they influence DAS records. Our observations 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., and O'Brien, G. S.: Full-waveform modelling of coupling and site effects for DAS cables, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6263, https://doi.org/10.5194/egusphere-egu24-6263, 2024.

EGU24-6576 | ECS | Posters on site | SM3.1

Deep Learning Driven DAS Strain Conversion to Geophone Ground Motion 

Basem Al-Qadasi and Umair Bin Waheed

Distributed Acoustic Sensing (DAS) has become a revolutionary observational technology for different geophysical applications. DAS, known for its high spatial resolution, environmental resilience, and ease of deployment, which make it a potential replacement to the traditional physical sensors that have been used for decades in seismology. The primary distinction between DAS and conventional seismic sensors lies in the fact that DAS inherently captures strain (or strain rate), in contrast to seismic instruments which record translational ground motions. However, the problem of strain directional sensitivity poses challenges for its direct use in standard seismic analysis. Therefore, several physics-based methods have been proposed to convert DAS strain to ground motion response (displacement, velocity, or acceleration). Efficient conversion of strain to ground motion using physics-based methods relies on accurate estimation of phase velocity along the DAS cable which is unavailable in most cases. To overcome this problem, we introduce a novel deep learning (DL) approach to convert high-resolution Distributed Acoustic Sensing (DAS) strain measurements into ground motion (GM).  The DL model employs a Bidirectional Long Short-Term Memory (BiLSTM) network. The model is trained and evaluated utilizing data from the PoroTomo project at Brady Hot Springs Geothermal Natural Laboratory. This dataset includes earthquake waveforms recorded by collocated DAS channels and geophones. The model’s performance is evaluated using the Root Mean Squared Error (RMSE) metric. It demonstrated an average RMSE of 0.41 for training and 0.95 for testing, indicating the model's efficacy in transforming DAS strain to particle velocity. The comparison results of predicted and original geophone waveforms further validated the model's accuracy within the relevant frequency range. This study marks a significant advancement in adapting high-resolution DAS strain data for use with conventional seismic data analysis techniques, thereby expanding the capabilities of seismic monitoring and interpretation.

How to cite: Al-Qadasi, B. and Bin Waheed, U.: Deep Learning Driven DAS Strain Conversion to Geophone Ground Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6576, https://doi.org/10.5194/egusphere-egu24-6576, 2024.

EGU24-6610 | ECS | Orals | SM3.1

Towards back-projection earthquake rupture imaging with ocean bottom distributed acoustic sensing data  

Yuqing Xie, Jean-Paul Ampuero, Martijn van den Ende, Alister Trabattoni, Marie Baillet, and Diane Rivet

Distributed Acoustic Sensing (DAS) along seafloor fiber optic cables offers high-density and wide-aperture seismic data close to seismic sources, at a lower cost than conventional cabled ocean bottom seismic networks. It is thus a very promising approach to develop offshore monitoring systems for hazard mitigation and to obtain deeper insights into earthquake mechanics. We introduce a workflow for back-projection earthquake rupture imaging based on ocean bottom DAS data off the Chilean coast, taking full advantage of DAS data features to greatly refine the resolution and accuracy of source parameter estimation of local earthquakes. 

The workflow includes a number of steps that improve the back-projection performance. To reduce the negative effects of wave scattering on waveform coherence, we apply spatial integration to convert DAS strains into displacements. We refine travel time accuracy through shallow-sediment time corrections. We apply array processing on multiple overlapping cable segments (sub-arrays) to get the apparent slowness. The information from all sub-arrays is used jointly to locate the earthquakes using a 1D local velocity model.

Through systematic synthetic tests, utilizing the 120-km-long cable configuration off the coast of Chile, we identified a ‘high-precision, high-resolution source region”, which is also less sensitive to uncertainties of the velocity structure. This region extends to about 80 km laterally from the cable and reaches depths of up to 15 km, a range likely attributable to optimal signal focusing from various angles and that can be extended by increasing the cable length. We apply our method to data of roughly 50 local earthquakes with magnitudes from 1.5 to 3. We consistently obtain sharp back-projection images with high spatial accuracy, within 1 to 4 km, for earthquakes occurring within this defined region. Such precision is comparable to the location uncertainties of the seismic catalog.

The true strength of our approach is its potential for imaging the rupture process of larger earthquakes. We apply our method to the synthetic waveforms of a magnitude 7 earthquake constructed from multiple empirical Green's functions. We demonstrate that strong coda waves do not compromise the precise detection and location of subsequent sub-sources, if we apply a travel time calibration. The rupture speeds and locations of sub-sources are accurately recovered, even for concurrent multiple sources. We are currently improving the calibration of travel times to increase the location accuracy and resolution. These include waveform alignment with static calibration, 3D velocity model travel time tables, and slowness bias measurements and calibrations for each source-subarray pair. Collectively, these methods will increase the resolution and accuracy of our method, along with more sophisticated back-propagation methods for individual arrays. Our work holds promise for the development of earthquake and tsunami early warning, provided that we can effectively address the issue of amplitude saturation of DAS data.

How to cite: Xie, Y., Ampuero, J.-P., van den Ende, M., Trabattoni, A., Baillet, M., and Rivet, D.: Towards back-projection earthquake rupture imaging with ocean bottom distributed acoustic sensing data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6610, https://doi.org/10.5194/egusphere-egu24-6610, 2024.

EGU24-7603 | ECS | Posters on site | SM3.1 | Highlight

Advances in Avalanche Monitoring in Norway: Insights from Distributed Acoustic Sensing 

Antoine Turquet, Andreas Wuestefeld, Finn Kåre Nyhammer, Espen Nilsen, and Vetle Refsum

Snow avalanches pose significant risks in mountainous regions. Traditional detection methods often lack the precision and timely responsiveness crucial for effective risk management. This study introduces an innovative approach using Distributed Acoustic Sensing (DAS) to detect snow avalanches in Norway. The monitoring site is located along a road in Holmbuktura in northern Norway, close to Tromsø. The cable path is composed of two segments: In segment one (0 – 850 m) an existing telecommunication cable is used, while for segment two (850 - 1450 m) a new cable was installed. The pilot road was frequently impacted by avalanches. Over three winters, the system captured both avalanche occurrences and anthropogenic noises (e.g., vehicles, wind, sea waves, etc.). 

The area is monitored with an OptoDAS interrogator with a sampling frequency of 500Hz and 10m gauge length. A 5m channel spacing results in 270 virtual channels along the monitored road stretch. Our automatic detection process distinguishes is based on classical signal processing techniques. We can confidently detect avalanches that hit road level, and additionally determine snow deposit on the road. Furthermore vehicles are detected with exact location and speed, which is used to alert emergency units in case of trapped vehicles. In this project, the focus of the installation is to detect avalanches that hit the road and determine whether any vehicles were trapped under the avalanches. For the winter season of 2022-2023 eight avalanches hit the road. The DAS-based monitoring system managed to successfully detect and classify these avalanches.

Compared to conventional methods like radar, infrared, and camera-based systems DAS offers distinct advantages in avalanche monitoring. DAS excels in providing real-time, continuous monitoring with high sensitivity and precision over extensive areas, unaffected by visual obstructions and less impacted by adverse weather conditions. Its robustness and low maintenance needs stand out, particularly when compared to radar systems' high installation costs and limited area coverage, camera's susceptibility to weather/light conditions.

The application of DAS technology offers a promising avenue for real-time, accurate avalanche detection, potentially enhancing safety measures in high-risk areas. Furthermore, this concept, when fully operational, could detect the risk of collision between avalanches and vehicles and alert authorities in real-time, which would be crucial for time-sensitive rescue operations.

How to cite: Turquet, A., Wuestefeld, A., Nyhammer, F. K., Nilsen, E., and Refsum, V.: Advances in Avalanche Monitoring in Norway: Insights from Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7603, https://doi.org/10.5194/egusphere-egu24-7603, 2024.

EGU24-7791 | ECS | Orals | SM3.1

Enhancing 1D and 2D passive seismic imaging of urban ambient noise DAS recordings 

Leila Ehsaninezhad, Christopher Wollin, Verónica Rodríguez Tribaldos, Benjamin Schwarz, and Charlotte Krawczyk

Ambient noise tomography Derived from Distributed Acoustic Sensing (DAS) deployed on existing telecommunication networks provides an opportunity to image the urban subsurface at local to regional scales and high resolution effectively with a small footprint. This capability can contribute to the assessment of the urban subsurface's potential for sustainable and safe utilization in countless applications, such as geothermal development of an area. However, extracting coherent seismic signals from the DAS ambient wavefield in urban environments remains a challenge. One obstacle is the presence of complex noise sources in urban environments, which may not be homogeneously distributed. Consequently, long-duration recordings are required to calculate high-quality virtual shot gathers, which entails significant time and computational cost.

 

In this study, we present the analysis of 15 days of passive DAS data recorded on a pre-existing fiber optic cable (dark fibers) running along an 11~km long major road in urban Berlin (Germany). We identify anthropogenic activities, mainly traffic noise from vehicles and trains, as the dominant seismic source and use it for ambient noise interferometry. To retrieve Virtual Shot Gathers (VSGs), we apply interferometric analysis based on the cross-correlation approach. Before stacking, we designed a selection scheme to carefully identify high-quality VSGs, which optimizes the resultant stacked VSG . Moreover, we modify the conventional ambient noise interferometry workflow by incorporating a coherence-based enhancement approach designed for wavefield data recorded with large-N arrays. We then conduct Multichannel Analysis of Surface Waves (MASW) to retrieve 1D shear-wave velocity models of the subsurface along consecutive portions of the array and validate them against local lithologic models. Finally, a 2D velocity model of the subsurface is obtained by concatenation of individual 1D velocity models from overlapping array subsections. The expansion into 2D requires an automatic identification of high-quality VSGs based on unsupervised learning, such as clustering, to exclude transient incoherent noise in the process of selective stacking.

 

The clustering results reveal distinct groups of VSGs that exhibit similar patterns. These distinct groups provide valuable insights into the temporal variations in human activities and allow a better understanding and interpretation of the recorded DAS ambient noise data. We find that recordings obtained predominantly during rush hour are viable for further processing and improve the accuracy of dispersion measurements, in particular for traffic-induced noise data. Moreover, the resulting 1D velocity models correspond well with available lithographic information. The modified workflow yields improved dispersion spectra, particularly in the low-frequency band (< 1 Hz) of the signal. This improvement leads to an increased investigation depth along with lower uncertainties in the inversion result. Additionally, these enhanced results were achieved using significantly less data than required using conventional processing schemes, thus opening the opportunity for reduced acquisition times and efforts.

How to cite: Ehsaninezhad, L., Wollin, C., Rodríguez Tribaldos, V., Schwarz, B., and Krawczyk, C.: Enhancing 1D and 2D passive seismic imaging of urban ambient noise DAS recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7791, https://doi.org/10.5194/egusphere-egu24-7791, 2024.

EGU24-8486 | ECS | Posters on site | SM3.1

Exploring Unsupervised Clustering of Seismic Noise Sources in Urban DAS Data: A Methodology Guide 

Antonia Kiel, Céline Hadziioannou, and Conny Hammer

Seismic measurements record the superposition of many seismic sources, with anthropogenic ones dominating frequencies above 1 Hz. While the anthropogenic seismic vibrations in urban areas are too small to influence daily human life, measurements in high precision physics experiments, such as those carried out at the Deutsche Elektronen-Synchrotron (DESY) particle accelerators in Hamburg can be negatively influenced by these vibrations. To gain insight into the seismic wavefield at DESY, distributed acoustic sensing measurements were started in the WAVE initiative (www.wave-hamburg.eu). 

The goal of this study is to utilize unsupervised machine learning tools to detect and identify different anthropogenic seismic noise sources. Two different approaches were tested: the seismic measurements are clustered using a temporal average of one second on time-frequency representations and a deep embedded clustering technique. For the first method, the clustering methods fuzzy-c-means, Gaussian mixture model (GMM), hierarchical clustering and hierarchical density-based spatial clustering of applications with noise (HDBSCAN) were used. The clustering performance of all methods was compared using car signals on a short DAS fiber section as our ground truth data. Furthermore, the usage of spectrograms and continuous wavelet transforms was compared on the ground truth data set, with the continuous wavelet transform giving better results.

In a next step, the best-performing clustering methods GMM and HDBSCAN of the temporal average and deep embedded clustering were applied to the entire 12 km fiber to cluster seismic noise sources. Based on the results, the respective advantages and disadvantages of the different approaches were determined. The study was concluded with a "recipe'' on how to approach unseen DAS data based on scientific objectives and physical properties of interest, paving the way for an optimized DAS data analysis. 

How to cite: Kiel, A., Hadziioannou, C., and Hammer, C.: Exploring Unsupervised Clustering of Seismic Noise Sources in Urban DAS Data: A Methodology Guide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8486, https://doi.org/10.5194/egusphere-egu24-8486, 2024.

EGU24-9254 | Posters on site | SM3.1

Locating mine explosions in shallow waters from hydroacoustic waves using DAS 

Emil Fønss Jensen, Jonas F. Damsgård, Peter H. Voss, Thomas Funck, and Thomas Mejer Hansen

Of the roughly 50.000 mines that were deployed in Danish waters during the First and Second World Wars, the Royal Danish Navy estimates that 4.000 to 6.000 units remain unexploded. Naval mines are to this day regularly found by fishermen or during surveys related to offshore construction work and reported to the Royal Danish Navy who then undertakes their controlled detonation. Seismic and hydroacoustic signals from naval mine explosions have been recorded by distributed acoustic sensing (DAS) on subsea fiber optic cabling where the hydroacoustic waves are readily identified. We have developed a simple technique that uses inversion of the travel time of hydroacoustic signals to determine the location of explosions. The technique has also been tested on hydroacoustic waves from a marine air gun seismic survey that crosses a fiber cable in shallow water monitored by DAS. We present the inversion results in addition to the data processing and analysis.

How to cite: Jensen, E. F., Damsgård, J. F., Voss, P. H., Funck, T., and Hansen, T. M.: Locating mine explosions in shallow waters from hydroacoustic waves using DAS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9254, https://doi.org/10.5194/egusphere-egu24-9254, 2024.

EGU24-9611 | ECS | Orals | SM3.1

A new formulation for source parameters estimation from DAS native strain data. 

Claudio Strumia, Alister Trabattoni, Mariano Supino, Marie Baillet, Diane Rivet, and Gaetano Festa

Distributed Acoustic Sensing (DAS) is establishing as a promising technique in Seismology. This novel system turns a fibre optic cable into a continuous single component array with very dense spatial sampling. Simplicity of installation and availability of telecommunication cables (dark fibres) make the technique very advantageous for investigating harsh environments like seafloors, sensing up to hundreds of kilometres of fibre with fine spatial resolution. Given the high potential, the technology has been successfully tested in recent years for several earthquake monitoring tasks, such as location, subsurface characterization, focal mechanism determination, tomography, or source back projection. 
The transferability of standard seismological tools to DAS data is straightforward when working with time picking, while analysis of the amplitude content of the signal demands further research. This is the case of earthquake source characterization, where standard approaches require conversion of strain rate data into more classical kinematic quantities (i.e. acceleration or velocity). In this work we develop a new formulation that allows to estimate source parameters without the need for conversion. We start from the description of the far-field strain radiation emitted from a circular seismic rupture, showing that the time integral of the strain is related to the Source Time Function. Using this quantity, we develop the spectral modelling allowing for frequency domain inversion of DAS data for estimation of moment magnitude and corner frequency. The formulation accounts for the unique azimuthal sensitivity of the cable in the radiation pattern average, and explicitly shows DAS enhanced sensitivity to slow scattered waves propagating beneath the fibre.
We validated the proposed approach on two case-studies, for events in local magnitude range  0.4 - 4.3, comparing the results with estimates from standard seismic instruments. Earthquakes recorded on a 150km long cable offshore the coast of central Chile during a 1-month DAS survey exhibit scale invariant stress drops, with an average of Δσ=(0.8±0.6)MPa. Also, moment magnitude estimates agree with results from standard seismic instruments. The analysis of small magnitude events (ML<2.5) recorded on a 1km long fiber during a 5-month DAS survey in the Italian southern Appenines shows agreement of moment magnitude estimates when compared with local seismic network estimations. Nevertheless, site effects dominate the high frequency domain resulting in an apparent corner frequency around 5Hz and masking the actual event size. An appropriate modelling of site effects using a parametric EGF approach was thus adopted to estimate corner frequencies for the highest magnitude events in the catalogue. 
This study shows the possibility to work with raw DAS data to retrieve information about earthquake source and highlights the high potential of these systems in characterizing the seismic moment and the size of earthquakes in a wide magnitude range.

How to cite: Strumia, C., Trabattoni, A., Supino, M., Baillet, M., Rivet, D., and Festa, G.: A new formulation for source parameters estimation from DAS native strain data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9611, https://doi.org/10.5194/egusphere-egu24-9611, 2024.

EGU24-9645 | ECS | Posters on site | SM3.1

Tremor analysis on dense network using Distributed Fiber Optic Sensing at La Palma 

Olivier Fontaine, Corentin Caudron, Thomas Lecocq, Luca D'Auria, and José Barrancos

The fast rise of Distributed Fiber Optic Sensing (DFOS, also known as DAS) technology in seismology has enabled to reach new horizons in volcano monitoring for example by its ability to attain hardly accessible environment and its high spatial and temporal resolution. Such advantages are extremely valuable for observatories located on islands where the ocean complicates the installation of traditional seismic networks and would require deploying ocean bottom seismometers.

In this research, we bring DFOS to a well-studied eruption that occurred in 2021 at La Palma (Canary Islands) by using a dark fiber, an unused telecom optic fiber, joining the islands together. The cable was interrogated using an HDAS (from Aragon Photonics) operated by INVOLCAN producing a 50 km-long array reaching outward from the island in the sea.

By using a combination of traditional seismic preprocessing and array detection methods such as CovSeisNet1, we recover low frequency signals across the entire fiber. These steps enable us to detect and locate episodes of tremor linked to the volcanic activity which we compare with complementary observables.

https://covseisnet.gricad-pages.univ-grenoble-alpes.fr/covseisnet/

How to cite: Fontaine, O., Caudron, C., Lecocq, T., D'Auria, L., and Barrancos, J.: Tremor analysis on dense network using Distributed Fiber Optic Sensing at La Palma, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9645, https://doi.org/10.5194/egusphere-egu24-9645, 2024.

EGU24-10033 | ECS | Posters on site | SM3.1

Constraining 6C-observed seismic anisotropy from seasonal ambient seismic noise 

Le Tang, Heiner Igel, and Jean-Paul Montagner

Our recent theory shows that the 6C ground motion (three-component translation and three-component rotation) of ambient seismic noise is capable of measuring the local seismic anisotropy using azimuth-dependent 6C-based cross-correlation functions. However, seasonal variations in ambient seismic noise result in large uncertainties in local velocity measurements due to inaccurate corrections in the azimuth of wave propagation. Here, we show that the time-dependent small azimuth variation of ambient seismic noise can be visualized using horizontal rotation-based cross-correlation functions, which can be applied to constrain the local seismic anisotropy of Rayleigh waves. We apply this approach to a small seismic array (deployed to retrieve the rotational motions of seismic ambient noise) of Pinon Flat Observatory in Southern California. The estimated anisotropy is compatible with results calculated based on azimuth-dependent 6C cross-correlation functions from multiple pairs of stations, demonstrating the applicability of the proposed method.

How to cite: Tang, L., Igel, H., and Montagner, J.-P.: Constraining 6C-observed seismic anisotropy from seasonal ambient seismic noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10033, https://doi.org/10.5194/egusphere-egu24-10033, 2024.

EGU24-10120 | Orals | SM3.1

An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy 

Simone Donadello, Cecilia Clivati, Aladino Govoni, Lucia Margheriti, Maurizio Vassallo, Daniele Brenda, Marianna Hovsepyan, Elio Bertacco, Roberto Concas, Filippo Levi, Alberto Mura, Andrè Herrero, Francesco Carpentieri, and Davide Calonico

Optical fiber sensing represents a promising technology for seismological monitoring, leveraging the widespread deployment of optical networks, and representing an important opportunity for the development of early warning systems. While so far Distributed Acoustic Sensing (DAS) has been widely employed in geosciences, this technology shows some limitations, like a restricted working range, requirement of dedicated fibers and criticalities in the management of big datasets. We focus on an alternative technique, coherent interferometry relying on ultrastable lasers, which is characterized by high sensitivity, long range, and full compatibility with the existing telecommunication infrastructure. The method allows detecting perturbations induced by seismic events through the measurement of the phase accumulated by an optical signal along the fiber path. The best performances are obtained employing narrow-linewidth lasers inherited from metrological applications due to their high coherence. While the technique was initially demonstrated on subsea cables, its application to on-land fibers poses new challenges. Indeed, the phase measurement integrates all the perturbations occurring along the fiber: this means that anthropic activities, such as vehicle traffic, represent important noise sources that must be taken into account. 

We present the details of an in-field implementation over a commercial fiber deployed in a highly seismic region in central Italy and connecting two populated towns. The experimental setup employs self-heterodyne interferometry detection, utilizing a continuous wave laser stabilized to an optical cavity through the Pound-Drever-Hall technique. The laser operates within a single channel of the Dense Wavelength Division Multiplexing (DWDM) grid, sharing the fiber with standard internet services. We show the results of continuous observations performed over a period of two years. We demonstrate the detection of about one hundred earthquakes, distinguishing them from typical noise sources such as acoustic interference and infrastructure oscillations. The results include the detection of both local and distant earthquakes, demonstrating the robustness of the technique. This allowed us to characterize for the first time the sensitivity curve of the technique, described by the probability of the event detection as a function of its magnitude and epicenter distance. We also show the correlation between the source magnitude and signal spectral analysis.

In conclusion, we present an operational fiber-based earthquake observatory, highlighting the compatibility of coherent interferometry with the existing telecommunication infrastructures and its effectiveness in seismic monitoring. The results are promising for the development of scalable sensing networks utilizing the extensive optical fiber infrastructure already in place, which can conveniently integrate in real-time the data acquired with the existing networks of classical seismological sensors.

How to cite: Donadello, S., Clivati, C., Govoni, A., Margheriti, L., Vassallo, M., Brenda, D., Hovsepyan, M., Bertacco, E., Concas, R., Levi, F., Mura, A., Herrero, A., Carpentieri, F., and Calonico, D.: An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10120, https://doi.org/10.5194/egusphere-egu24-10120, 2024.

EGU24-10604 | Posters on site | SM3.1

On DAS-recorded strain amplitude 

Thomas Forbriger, Nasim Karamzadeh, Jérôme Azzola, Rudolf Widmer-Schnidrig, Emmanuel Gaucher, and Andreas Rietbrock

The power of distributed acoustic sensing (DAS) lies in its ability to sample deformation signals along an optical fiber at hundreds of locations with one interrogator only. While the interrogator is calibrated to record ‘fiber strain’, the properties of the cable and its coupling to the rock control the ‘strain transfer rate’ and hence how much of ‘rock strain’ is represented in the recorded signal.

We use DAS recordings carried out with a Febus A1-R interrogator in an underground installation colocated with an array of strainmeters in order to measure the ‘strain transfer rate’ in situ. A tight-buffered cable and a standard loose-tube telecommunication cable (running in parallel) are used, where a section of both cables covered by sand and sandbags is compared to a section, where cables are just unreeled on the floor.

Signals from the Mw 7.7 and Mw 7.6 earthquakes that took place on the East Anatolian Fault on February 6th 2023 allow us a proper comparison of signals in the frequency-band between 50 mHz and 0.2 Hz. At lower frequencies the DAS signal-to-noise ratio is insufficient. At higher frequencies the invar-wire strainmeters show a parasitic response to vertical ground motion. For frequencies up to 1 Hz we use seismometer recordings to estimate strain for an incoming plane wave, based on the ray parameter and in this way extend the bandwidth of the comparison. The ray parameter varies along the recording but is sufficiently well known and can be validated against the strainmeter recording.

The ‘strain transfer rate’ is largely independent of frequency in the band from 0.05 Hz to 1 Hz and varies between 0.15 and 0.55 depending on cable and installation type. The sandbags show no obvious effect and the tight-buffered cable generally provides a larger ‘strain transfer rate’. The noise background for ‘rock strain’ in the investigated band is found at about an rms-amplitude of 0.1 nstrain in 1/6 decade for the tight-buffered cable. This allows a detection of the marine microseisms at times of high microseism amplitude.

How to cite: Forbriger, T., Karamzadeh, N., Azzola, J., Widmer-Schnidrig, R., Gaucher, E., and Rietbrock, A.: On DAS-recorded strain amplitude, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10604, https://doi.org/10.5194/egusphere-egu24-10604, 2024.

EGU24-10764 | Orals | SM3.1 | Highlight

SUBMERSE: Exploring the planet with live submarine telecommunications cables. 

Chris Atherton and the SUBMERSE Project

The integration of state-of-the-art fibre optic sensing technologies with telecommunication systems has not yet been achieved. There are many challenges which need to be overcome to allow for a pan-continental research instrument, all of which requires international collaboration. Such international collaborations would allow for the creation of novel applications and research into Earth science, such as cetology and abiotic and biotic marine interactions, oceanography, seismology, volcanology, and soundscape monitoring, to name but a few.

Over the past 5 years, research teams from National seismic and oceanographic infrastructures, together with National Research and Education Networks (NRENs), and partners from universities, research institutes and industry have pioneered sensing techniques to use submarine optical telecommunication fibres to monitor the Earth and its systems.

Fibre sensing technology and collaborations created by developing these techniques have now reached a level where a new paradigm shift can occur. This presentation will discuss the SUBMERSE project (SUBMarinE cables for ReSearch and Exploration), which is creating and delivering a pilot research instrument which could serve as a blueprint for continuous monitoring upon many more existing submarine fibre optic cables in the future.

The SUBMERSE project, which started in May 2023, is a Horizon Europe-funded, 36-month long initiative which is investigating the combined acquisition of SOP (State-of-Polarisation) and DAS (Distributed Acoustic Sensing) data from live telecom cables, with the aim to then make that data available to researchers globally and F.A.I.R. The project team, consisting of 24 organisations, uses existing fibre-optic infrastructure deployed across multiple national research infrastructures to create a pan-European research instrument.

Our presentation will discuss the latest field deployments of DAS and SOP technologies across 5 geographic locations on 3 cable systems, which are spread across the European continent and Atlantic Ocean. It will offer a first glimpse of the effects of running a DAS in the L-and C- Bands on a live DWDM telecoms system, in combination with SOP, in a submarine and terrestrial environment.

The aim of the SUBMERSE project is to disseminate the data following FAIR principles through established community data centres. The main challenges we have faced relate to ensuring compliance to security restrictions and handling huge data quantities generated by DAS.  The approaches to down sampling, frequency filtering, and potentially time-and-space-gating will also be presented.  We will discuss the approaches taken for acquiring, streaming from remote sites, data staging, pre-processing and raw file retention. We will also highlight the tools and approaches that we have adopted to develop best practices for running such a multi-national, distributed, sensing instrument which must take these elements into account.

Our work has shown that a pragmatic approach, with collaboration at heart, is needed to address these challenges. Without a strong commitment and collaboration between research communities and research infrastructure providers, the potential to lose valuable research data is high. This risk can be mitigated by focusing on datasets which are valuable to communities and ensuring the long-term availability of those data sets in a F.A.I.R manner.

How to cite: Atherton, C. and the SUBMERSE Project: SUBMERSE: Exploring the planet with live submarine telecommunications cables., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10764, https://doi.org/10.5194/egusphere-egu24-10764, 2024.

EGU24-10925 | Orals | SM3.1

Denoising DAS data in urban volcanic areas through a Deep Learning Approach 

Martina Allegra, Flavio Cannavo, Miriana Corsaro, Gilda Currenti, Philippe Jousset, Simone Palazzo, Michele Prestifilippo, and Concetto Spampinato

The notable benefits of Distributed Acoustic Sensing (DAS) technology—high coverage, high resolution, low cost—have led to its widespread application in the geophysical domain for high-quality data recording. Among possible applications, the ability to interrogate telecommunication cables has enabled the detection of a variety of seismic-volcanic events in poorly instrumented environments, such as densely populated urban areas.

Nevertheless, the sensing of commercial fiber optic cables has to deal with the presence of anthropogenic noise that frequently corrupts the seismic signal. Indeed, vibrations induced directly or indirectly by anthropogenic activities significantly reduce the signal-to-noise ratio by masking target events.

Taking advantage of the high spatiotemporal resolution of the DAS data, a deep learning approach has been adopted for noise removal. The architecture of the neural network together with the training strategy have enabled the extraction and preservation of salient information while neglecting anthropogenic noise.

The validation on real low-frequency seismic events recorded during the 2021 Vulcano Island unrest  has provided encouraging results, demonstrating the potential of the proposed approach as a pre-processing step to facilitate subsequent DAS signal analysis.

How to cite: Allegra, M., Cannavo, F., Corsaro, M., Currenti, G., Jousset, P., Palazzo, S., Prestifilippo, M., and Spampinato, C.: Denoising DAS data in urban volcanic areas through a Deep Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10925, https://doi.org/10.5194/egusphere-egu24-10925, 2024.

EGU24-11389 | ECS | Orals | SM3.1

Adjoint-Source Inversion of Microseismic Sources with DAS in Boreholes 

Katinka Tuinstra, Federica Lanza, Sebastian Noe, Andreas Fichtner, Antonio Pio Rinaldi, Pascal Edme, Martina Rosskopf, Anne Obermann, Marian Hertrich, Hansruedi Maurer, Domenico Giardini, and Stefan Wiemer and the Bedretto Team

Microseismic source processes can be closely monitored during hydraulic stimulations with optical fiber deployed behind borehole casing, using Distributed Acoustic Sensing (DAS). The Bedretto Underground Laboratory for the Geosciences and Geoenergies (BULGG) provides a test site at the scale of hundreds of meters (meso-scale), where multiple boreholes are instrumented with fibers around a stimulation well. This enables the characterization of source properties of induced seismicity thanks to the dense sampling of the wavefield close to the stimulated region.

In 2023 various stimulation activities in the BedrettoLab produced M<-1 events that were recorded on three fibers surrounding the stimulated region. The interrogated fibers are running through the stimulated seismicity zone, and surround the majority of the events. Some of these events are recorded with high coherency and signal-to-noise ratio, making them suitable for further source characterization, such as location and moment tensor inversion. These events were at the same time recorded with other co-located point sensors such as geophones and acoustic emission sensors, which enables comparison to other instruments.

In this work, we select and process a subset of events with clear DAS recordings, and invert for their location, source time and moment tensor components using an adjoint inversion method. This includes computing the full forward and adjoint wavefield and gradient using a spectral-element solver. Using the full waveforms to invert for these events greatly improves the resolution of the source estimates, allows for incorporation of the full velocity model, and only two simulations per iteration are required: a forward and adjoint simulation, and gradient computation. The receiver coverage of the focal spheres by the surrounding optical fibers is an excellent test bed for the method, and the simulated domain remains on the order of hundreds of meters, which means that the simulation can be pushed to high frequencies (>100 Hz). This study provides a step forward to monitoring microseismicity in hydraulic stimulations with fiber-optic measurements.

How to cite: Tuinstra, K., Lanza, F., Noe, S., Fichtner, A., Rinaldi, A. P., Edme, P., Rosskopf, M., Obermann, A., Hertrich, M., Maurer, H., Giardini, D., and Wiemer, S. and the Bedretto Team: Adjoint-Source Inversion of Microseismic Sources with DAS in Boreholes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11389, https://doi.org/10.5194/egusphere-egu24-11389, 2024.

EGU24-12344 | ECS | Posters on site | SM3.1

Groundwater monitoring in an alluvial aquifer with an underwater DAS cable recording urban seismic noise: Application to the Crépieux-Charmy Wellfield in France 

Destin Nziengui Bâ, Aurélien Mordret, Olivier Coutant, and Camille Jestin

Seismic interferometry applied to Distributed Acoustic Sensing (DAS) arrays is an increasingly common approach for subsurface investigations. In this study, we show that analysis of urban seismic noise acquired on a linear underwater DAS array can be used to track depth-dependent seismic velocity variations caused by groundwater level changes in an alluvial aquifer.

We apply our methodology to the Crépieux-Charmy wellfield, a strategic site for the water supply of the Lyon metropolitan area in France. We analyze 4 weeks of ambient noise recorded during a water infiltration experiment along a 200m DAS cable placed at the bottom of an infiltration basin.

Using ambient noise interferometry, we derived time-lapse phase velocity variations (dc(f)/c(f)) of Rayleigh waves and inverted them for depth-dependent shear wave velocity variations (dVs(z)/Vs(z)) in the first 50 m of the subsurface. The obtained seismic velocity changes appear to be associated with variations in water saturation and effective pore pressure for different compartments of the aquifer.

Our results suggest that DAS combined with noise-based passive monitoring provides a solution to track the dynamics of an alluvial aquifer and estimate hydrological parameters relevant for effective groundwater resource management.

How to cite: Nziengui Bâ, D., Mordret, A., Coutant, O., and Jestin, C.: Groundwater monitoring in an alluvial aquifer with an underwater DAS cable recording urban seismic noise: Application to the Crépieux-Charmy Wellfield in France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12344, https://doi.org/10.5194/egusphere-egu24-12344, 2024.

EGU24-12679 | Posters on site | SM3.1

On the influence of ambient atmospheric pressure on multi-component, direct observations of rotational ground motion 

Andreas Brotzer, Rudolf Widmer-Schnidrig, and Heiner Igel

A high-sensitive, large-scale ring laser gyroscope provides access to direct observations of local rotational ground motions. A tetrahedral configuration of ring laser gyroscopes, such as ROMY (ROtational Motions in seismologY), located in a Geophysical Observatory near Munich, Germany, enables to redundantly observe all three components of the rotation vector.
For seismic accelerations below 30 mHz, the separation of low noise background levels between vertical and horizontal component are well established and understood to result from local tilts driven by atmospheric pressure variations. The promise of multi-component rotational observations is that ideally they can be used to decontaminate a co-located horizontal component acceleration sensor from contributions of ground tilt. Moreover, knowing and understanding the background levels for vertical and horizontal rotational ground motions at long periods is essential as benchmarks for instrument development towards higher sensitivity.
We use several months of multi-component data of vertical and horizontal rotation rates by ROMY and a co-located atmospheric pressure sensor to derive the pressure compliance for both vertical and horizontal rotational motions. Focusing on frequencies below 20 mHz, we find that time windows with energetic weather patterns consistently lead to high coherence of atmospheric pressure and horizontal rotations, but only little coherence between the atmospheric pressure and vertical rotation.
We consider this as a first indication that atmospheric pressure induced ground tilts are detected by the ROMY horizontal components. Different effects of ambient atmospheric pressure changes on the optical gyroscope itself, such as cavity deformation, are discussed. A small aperture barometer array surrounding ROMY to detect lateral pressure gradients is currently being deployed to provide additional constraints on ground deformations from atmospheric pressure waves.

Here we focus on a detailed analysis of ROMY gyroscope data, while accelerometer data are analyzed in a companion poster by Widmer-Schnidrig et al. in this same session SM3.3.

How to cite: Brotzer, A., Widmer-Schnidrig, R., and Igel, H.: On the influence of ambient atmospheric pressure on multi-component, direct observations of rotational ground motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12679, https://doi.org/10.5194/egusphere-egu24-12679, 2024.

EGU24-13091 | Posters on site | SM3.1

 Long-term monitoring of seismic and volcanic activity using distributed fibre optic sensing: examples in Iceland (2015-2024) and Italy (2018-2024). 

Philippe Jousset, Gylfi Hersir, Gilda Currenti, Christopher Wollin, Sergio Díaz-Meza, Martina Allegra, Regina Maass, Michele Prestifilippo, Egill Gudnason, Rosalba Napoli, and Charlotte Krawczyk

Monitoring of seismic activity around volcanoes has been conventionally performed using data from continuous seismic and deformation networks, which give real-time information on the status of a volcano at any time. In case of a volcanic crisis, the number of earthquakes often increases with time and conventional networks are completed by deployment of additional sensors, which allow for a better hazard assessment, e.g., by lowering the detection threshold and improving earthquake locations. The deployment of such additional sensors is labour intensive and may be dangerous due to increased volcanic hazard.

Existing fibre optic telecommunication cables can be used with distributed dynamic strain sensing interrogators to density and complement the monitoring network. It has been demonstrated that the usage of fibre optic sensing allows for a rapid response and the acquisition of crucial data describing a developing crisis (e.g., at Vulcano, Italy). However, fibre optic interrogators are rarely deployed as permanent interrogating systems, despite the capability of such systems for long-term monitoring as demonstrated during a 7 months continuous recording on the Reykjanes Peninsula, Iceland, in 2020. Instead, interrogators are usually deployed for limited time periods when the activity occurs, ideally before new activity starts. For example, we connected an iDAS interrogator on the telecommunication 16-km long cable running between the Reykjanes and Svartsengi (“Blue Lagoon”) geothermal power plants in 2015 for an initial test of 10 days, in 2020 for 7 months (GFZ rapid response to the seismic crisis and precursory activity to the 2021 and 2022 eruptions of Fagradalsfjall volcano), and in November 2023 (recording still on 10.01.2024) as a GFZ rapid response before the 18 december 2023 eruption.

In this work, we investigate the possibility to use repetitive campaign-based measurements of dynamic strain sensing performed in the course of multiple years on the Reykjanes Peninsula (2015; 2020; 2023-2024) and at Etna volcano (2018; 2021; 2022; 2023-2024). Analysing earthquakes and ambient noise, we search for differences and similarities in the strain-rate response between the different and disjunct recording periods. We report preliminary results.

How to cite: Jousset, P., Hersir, G., Currenti, G., Wollin, C., Díaz-Meza, S., Allegra, M., Maass, R., Prestifilippo, M., Gudnason, E., Napoli, R., and Krawczyk, C.:  Long-term monitoring of seismic and volcanic activity using distributed fibre optic sensing: examples in Iceland (2015-2024) and Italy (2018-2024)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13091, https://doi.org/10.5194/egusphere-egu24-13091, 2024.

Distributed Acoustic Sensing (DAS) is a technology that enables continuous, realtime measurements along the entire length of a fiber optic cable. The low-frequency band of DAS can be used to analyze hydraulic fracture geometry and growth. In this study, the low-frequency strain waterfall plots with their corresponding pumping curves were analyzed to obtain information on fracture azimuth, propagation speed, number of fractures created in each stage, and re-stimulation of pre-existing fractures. We also use a simple geomechanical model, described in full detail in Ortega Perez and Van der Baan (Geophysics, 2024), to predict fracture growth rates while accounting for changes in treatment parameters. As expected, the hydraulic fractures principally propagate perpendicular to the treated well, that is, parallel to the direction of maximum horizontal stress. During many stages, multiple frac hits are visible indicating that multiple parallel fractures are created and/or re-opened. Secondary fractures deviate towards the heel of the well, likely due to the cumulative stress shadow caused by previous and current stages. The presence of heart-shaped tips reveals that some stress and/or material barrier is overcome by the hydraulic fracture. The lobes of the heart are best explained by the shear stresses at 45-degree angles from the fracture tip instead of the tensile stresses directly ahead of the tip. Antennas ahead of the fracture hits indicate the re-opening of pre-existing fractures. Tails in the waterfall plots provide information on the continued opening, closing, and interaction of the hydraulic fractures within the fracture domain and stage domain corridors. Analysis of the low-frequency DAS plots thus provides in-depth insights into the rock deformation and rock-fluid interaction processes occurring close to the observation well.

How to cite: van der Baan, M. and Ortega Perez, A.: Interpretation of low-frequency DAS data acquired during hydraulic fracturing treatments based on geomechanical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13428, https://doi.org/10.5194/egusphere-egu24-13428, 2024.

EGU24-13660 | Posters on site | SM3.1

Effect of ambient temperature fluctuation on DAS observation with a submarine cable 

Hiroyuki Matsumoto, Eiichiro Araki, and Takashi Yokobiki

Long-term Distributed Acoustic Sensing (DAS) using a submarine cable is being conducted in the Nankai Trough, Japan. The first long-term DAS observation shows that the apparent strain is observed along the relatively shallow water depth section (i.e., < water depth 1000 m) on the submarine cable, suggesting a periodic temperature fluctuation up to about 6 degrees Celsius associated with the ocean tide takes place in this region (Ide et al., 2021). However, it is difficult to discuss how the ambient temperature changes, or how the ambient temperature affects the submarine cabled DAS observation because of the lack of the in-situ observation. For this reason, we installed temperature sensors near the submarine cable by a Remotely Operation Vehicle (ROV). We did not discover the submarine cable at the seafloor, and therefore the detailed location of the temperature sensors, i.e., the accurate cable position could not be constraint so far. Simultaneous observations of the DAS and the long-term ambient temperature were conducted for a period from 16 August 2021 to 04 October 2021, i.e. about 50 days. A cross-correlation analysis between the DAS and the ambient temperature by dividing into the 5-day dataset has speculated the position of the temperature sensors to be 24.75 km of the submarine cable. Additionally, the strain coefficient of the optical fiber w.r.t. the temperature change has been determined to be 7 micro-strain per 1 degree Celsius, which is comparable to the previous experimental study (Zumberge et al., 2018). Finally, the temperature correction was performed, but the phase delay still remains, suggesting that the thermal measurement should be conducted beside the submarine cable.

How to cite: Matsumoto, H., Araki, E., and Yokobiki, T.: Effect of ambient temperature fluctuation on DAS observation with a submarine cable, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13660, https://doi.org/10.5194/egusphere-egu24-13660, 2024.

EGU24-14922 | Orals | SM3.1

Challenges of Rotational Ground Motion Measurements in the Local Distance Range 

Stefanie Donner, Johanna Lehr, Frank Krüger, Mathias Hoffmann, Manuel Hobiger, and Sebastian Heimann

Since almost two decades, there is a fast and steady progress in understanding the rotational part of the seismic wavefield and exploring possible applications. These achievements are based on studies using simulated data, array-derived measurements, and direct measurements of large (M > 5), teleseismic earthquakes by ringlasers. Since only a couple of years, direct measurements of smaller (M < 3) earthquakes in the local distance range are also feasible. This was made possible due to new instrumentation developments such as portable rotation sensors.

From experience with translational measurements, seismology has developed a relatively simple description of the seismic wavefield, as long as the observation is recorded in the source far-field, and site-effects at the point of observation can be neglected by choosing an appropriate frequency range for the analysis.

Within the NonDC-BoVo project two portable rotational sensors have been installed in the Vogtland/West-Bohemia earthquake swarm region with the goal to incorporate the rotational waveform data into the inversion for seismic moment tensors. Both sensors are located in an epicentral distance of ~10 km to the center of the swarm activity. So far, we have recorded 197 events with ML ≥ 1 and 6 events with ML ≥ 2.5.

Although we are positively surprised how well we can record rotational ground motion of earthquakes with even very small magnitudes, we encountered challenges in the details of the waveform recordings. At the sensor location in Landwüst (D) we recorded events down to ML ~ 0.5 with good signal-to-noise ratio in a frequency range of 5 to 25 Hz. At the second location in Skalna (CZ) the signal-to-noise ratio is worse and we recorded earthquakes only with ML ≥ 1.5. Relocating the sensor to Wernitzgrün (D), about 25 km to the North of Skalna, did not improve the quality of the waveform recordings. Technical issues with the sensor can be ruled out for both locations.

Here, we want to present details of the challenges with the rotational ground motion data from these small and local earthquake recordings. First analyses hint to a much stronger effect of local site conditions onto rotational than translational ground motion data. In addition, with the above-mentioned setting, we have to consider the complexities of the near-field part of the wavefield as well. With our contribution we aim to add another aspect to the understanding of the rotational wavefield.

How to cite: Donner, S., Lehr, J., Krüger, F., Hoffmann, M., Hobiger, M., and Heimann, S.: Challenges of Rotational Ground Motion Measurements in the Local Distance Range, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14922, https://doi.org/10.5194/egusphere-egu24-14922, 2024.

EGU24-15284 | ECS | Orals | SM3.1

Distributed Acoustic Sensing automated classifiers design via transfer learning for seismology 

Mathieu Donnadille, Antoine Turquet, Clément Hibert, and Cédric Richard

For a decade, Distributed Acoustic Sensing (DAS) has become an exciting new tool for research in geophysics. However, the vast amount of data produced by hundreds of virtual sensors presents a challenge, and the lack of labeled data hampers the training of new automated classifiers based on machine learning methods from scratch. Automatic classifiers are essential tools for labeling observations across large, complex, and continuous datasets. They are commonly used in seismology to classify all the geophysical events recorded by seismic stations with a high degree of accuracy. Transfer learning is a machine learning technique where a model trained on one task is repurposed on a second related task. This method is particularly beneficial as it allows for the reuse of pre-existing, labeled datasets, significantly reducing the need for new data collection and annotation. This approach is a promising way to create efficient DAS classifiers without requiring a lot of resources. We built three different classifiers: the first classifies events based on their location, distinguishing local earthquakes from distant events; the second differentiates anthropogenic events from natural ones, specifically quarry blasts from earthquakes; and the third is capable of identifying all three types of events - local earthquakes, distant events, and anthropogenic quarry blasts - simultaneously. We used random forest models to train our classifiers using a labeled dataset of 14345 seismometer signals from the NOA network made for seismological research and nuclear monitoring. We studied the transferability of those classifiers to DAS data from a new NORSAR facility called NORFOX. This infrastructure consists of 8 km of cables located in Norway with a sampling frequency of 100Hz. Its multidirectional cable configuration makes it ideal for seismological surveys. We built a small test dataset of 543 signals using 20 channels equally distributed along the array. Our approach succeeded in reaching F1 score thresholds above 76%. We also showed, by fine-tuning feature selection according to their correlations between the seismic and DAS domains, that these results can be improved. In this way, we were able to increase the scores of our models from 5.89% to 11.36%. Several transfer learning approaches were also explored and discussed. Those encouraging results highlight the potential of a transfer learning approach to build new DAS classifiers. By leveraging historical seismometer catalogs, this approach facilitates the creation of DAS classifiers, thereby saving substantial time and avoiding the need for creating specialized datasets exclusively for DAS. Several strategies for improving score thresholds for future classifiers based on these transfer learning methods can be derived.

How to cite: Donnadille, M., Turquet, A., Hibert, C., and Richard, C.: Distributed Acoustic Sensing automated classifiers design via transfer learning for seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15284, https://doi.org/10.5194/egusphere-egu24-15284, 2024.

EGU24-15616 | ECS | Orals | SM3.1

On the variation of ocean surface waves with wind speed and direction: A case study from offshore Svalbard, Norway 

Robin André Rørstadbotnen and Martin Landrø

Distributed Acoustic Sensing (DAS) has become increasingly popular due to its capacity of extremely high spatial and temporal strain sensing over long distances. Due to the long reach of the current fiber sensing technology, and that all the electronic components are placed on land, it holds great potential in marine applications. This presentation shows how DAS can be used to observe ocean surface waves inside Kongsfjord and in the open ocean West of Svalbard.

A well-known problem when monitoring ocean phenomena is the sensor undersampling in the world’s oceans. This problem limits observations of fundamental scientific questions, like the dynamics of the oceans (Sladen et al., 2019). Fiber optic sensing has already been used to observe numerous ocean phenomena, such as tides, OSGW (Ocean-Surface-Gravity-Wave), and internal waves (Lindsey et al., 2019, Ide et al, 2021, Williams et al., 2023).

A comprehensive DAS data set is being collected at the Centre for Geophysical Forecasting’s (CGF) research lab in Ny-Ålesund, Svalbard. Data has been collected continuously since June 2022 providing the possibility of investigating oceanographic signals over a long time period in different marine environments. In this presentation, we focus on how ocean surface wave signals are influenced by local wind conditions and how the signal changes characteristics as a function of wind speed and direction.

The results from analyzing this data will be presented, and it will be demonstrated how the local wind-induced waves interact with the background swell signal which hit West Svalbard from a South-West direction. The difference between the portion of the fiber located inside Kongsfjorden will be compared to the portions in open ocean. Additionally, the obtained results will be compared to previous studies from the area (e.g., Wojtysiak et al., 2018). Finally, we use the well-known dispersion relation for OSGW to compute the associated phase velocity along the whole stretch of the fiber cable.

How to cite: Rørstadbotnen, R. A. and Landrø, M.: On the variation of ocean surface waves with wind speed and direction: A case study from offshore Svalbard, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15616, https://doi.org/10.5194/egusphere-egu24-15616, 2024.

EGU24-16151 | ECS | Orals | SM3.1

Near Surface Imaging with Zig-Zag shaped DAS Arrays Based on Cross Correlation of Ambient Noise 

Peng Wu, Chen Gu, Yichen Zhong, Zhi Yuan, Zhuoyu Chen, and Borui Kang

Distributed Acoustic Sensing (DAS) has effectively transformed traditional telecommunication fiber-optic cables into highly efficient, dense seismic arrays. In this paper, we perform cross-correlation and stacking on the signals recorded by DAS fiber arrays in a Zig-Zag pattern, which increases the spatial coverage and improves the ability to detect and analyze various seismic waves modes. We observed that the resulting signals include both Rayleigh and Love waves. Additionally, the propagation characteristics of the wave field exhibit a Zig-Zag distribution pattern, consistent with the spatial distribution of the fibers. The challenge arises from the need to distinguish and accurately interpret the overlapping signals of Rayleigh and Love waves, which have different propagation characteristics. To address these challenges, we propose an inversion method specifically tailored for the near surface imaging with DAS array data when the fiber-optic cables are not laid in straight lines. We also conducted an on-site experiment using Zig-Zag shaped DAS arrays with known subsurface velocity model. This experiment was designed to record ambient noise signals over a week and analyze the propagation characteristics of both Rayleigh and Love waves within the surface waves captured by the DAS system. The inversion results obtained from the analysis of the recorded data showed a high degree of consistency with the ground truth subsurface structure of the test area. This demonstrates the effectiveness of the proposed method in overcoming the limitations of traditional dispersion curve-based inversion techniques, particularly in the context of non-linear fiber layouts. This research provides strong support for the practical application of dark fibers in near surface imaging, demonstrating the potential of dark fibers.

How to cite: Wu, P., Gu, C., Zhong, Y., Yuan, Z., Chen, Z., and Kang, B.: Near Surface Imaging with Zig-Zag shaped DAS Arrays Based on Cross Correlation of Ambient Noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16151, https://doi.org/10.5194/egusphere-egu24-16151, 2024.

EGU24-16375 | Orals | SM3.1

Sensing enabled submarine telecom networks for seismology 

Jan Petter Morten, Susann Wienecke, Ole Henrik Waagaard, Jan Kristoffer Brenne, and Erlend Rønnekleiv

Distributed acoustic sensing (DAS) on submarine fiber optic cables will contribute to resilient societies by significantly enhancing environment and hazard monitoring. Recent studies have emphasized applications to earthquake and tsunami early warning, volcanic eruptive events observation, and characterizing climate change effects. Widespread deployment of DAS instrumentation on the existing cable networks traversing the coastal zones and oceans can vastly expand data coverage with real-time capabilities at low cost. 


The use of DAS in existing long-haul telecommunication systems has so far been limited since most DAS interrogators rely on optical wavelengths that interfere with the existing telecom traffic. Recent developments in DAS technology enable co-existence of telecom traffic with the sensing application. Lab and field investigations have demonstrated that there is no detrimental effect from the interrogation on the transmission line performance when the DAS instrument is configured to operate at sufficiently separated wavelength channels. Thus, it is possible to utilize all existing cable networks for sensing applications in unison with continued telecom transmission without sacrificing any capacity in the link and maintaining high-quality DAS measurements.


This study describes a DAS deployment on a submarine cable system with live telecom traffic. The interrogation scheme facilitates consistent high sensing sensitivity exceeding 120 km range. The data quality and interrogator performance are quantified, and the localization and characterization for a representative set of environmental and anthropic signal sources is shown. We will describe real-time processing and detection implementations that transform such sensing enabled submarine telecom networks into measurement arrays suitable for seismic monitoring. Moreover, the technical solutions for DAS installation with existing terminal equipment and the practical aspects of data sharing will be described.

How to cite: Morten, J. P., Wienecke, S., Waagaard, O. H., Brenne, J. K., and Rønnekleiv, E.: Sensing enabled submarine telecom networks for seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16375, https://doi.org/10.5194/egusphere-egu24-16375, 2024.

EGU24-16414 | ECS | Orals | SM3.1

Distributed Fiber Optic Sensing and Artificial Intelligence: preliminary results on the Campi Flegrei caldera unrest 

Miriana Corsaro, Martina Allegra, Flavio Cannavò, Gilda Currenti, Gaetano Festa, Philippe Jousset, Daniele Pellegrino, Simone Palazzo, Michele Prestifilippo, Eugenio Privitera, Mario Pulvirenti, Patrizia Ricciolino, Concetto Spampinato, Francesco Scotto di Uccio, and Anna Tramelli

Since 2005 the Campi Flegrei caldera (Southern Italy) has been experiencing a long-term unrest characterized by a recent increase in seismicity and ground uplift rate. In August and September 2023, the unrest showed a sudden intensification in the number and maximum magnitude of earthquakes, culminated with the occurrence of a Md 4.2 event. In an effort to strengthen the monitoring activity, two Distributed Acoustic Sensing (DAS) devices were connected from October 2023 to telecommunication fiber optic cables in the densely populated Campi Flegrei area. The DAS interrogators are set up inside two TELECOM central offices in the city center of Naples and in Bagnoli. Dynamic strain rate data are continuously acquired with a gauge length of 10 m at an average spatial sampling of 4 and 5 m. In this framework, an automated real-time workflow has been implemented comprising both DAS data downsampling and transferring to INGV data processing center. 

From the beginning of the DAS acquisition (19 October 2023), more than 300 seismic events have been recorded by the INGV local seismic network, including a Md 3.0 earthquake occurred on 23rd November 2023. Unknown cable installation conditions, poor coupling of the fiber optic cable with the ground, intense traffic and anthropogenic activities make the DAS data highly noisy and, hence, pose challenges for the application of traditional seismic data processing algorithms. In this study, we propose and apply AI based algorithms to improve and fasten earthquake detection and seismic phase picking on the large data volume associated with the high number of DAS channels.  In particular, the compared algorithms cover recently published state-of-the-art deep learning networks. We show preliminary results that demonstrate the ability of the synergy between DAS and AI to contribute to the rapid response to volcanic crises.

How to cite: Corsaro, M., Allegra, M., Cannavò, F., Currenti, G., Festa, G., Jousset, P., Pellegrino, D., Palazzo, S., Prestifilippo, M., Privitera, E., Pulvirenti, M., Ricciolino, P., Spampinato, C., Scotto di Uccio, F., and Tramelli, A.: Distributed Fiber Optic Sensing and Artificial Intelligence: preliminary results on the Campi Flegrei caldera unrest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16414, https://doi.org/10.5194/egusphere-egu24-16414, 2024.

EGU24-17020 | ECS | Posters on site | SM3.1

Towards Fiber-optics-based, Next-generation Observational Platforms for Investigating the Urban Subsurface: the InDySE Project 

Verónica Rodríguez Tribaldos, Charlotte Krawczyk, Leila Ehsaninezhad, Patricia Martínez-Garzón, and Marco Bohnhoff

Urban sustainable development and improved resilience to geohazards requires an exhaustive understanding of the geological structure, physical properties and dynamics of the shallow subsurface underneath urbanized areas at the sub-kilometer scale. Yet, our current understanding of the urban subsurface is limited by our ability to image its structure and temporal variations at high resolution using classical geophysical approaches. Recently, the application of conventional ambient noise interferometry analysis to dynamic strain data recorded using Distributed Acoustic Sensing (DAS) deployed on unused telecommunication fiber-optic cables (dark fibers) has emerged as an attractive alternative for cost-efficient, regional scale (10’s of km) seismic imaging and monitoring at high spatial and temporal resolution. Still, its application to urban environments remains vastly underutilized. One of the most significant hurdles is the lack of adequate and efficient data exploration and processing tools to address and harness the unique challenges associated with DAS-based urban seismic noise recordings, which include the complexity of the noise field, unconventional array geometries and non-uniform coupling conditions, and increasingly massive data volumes.

The InDySE project (Interrogating the Dynamic Shallow Earth) aims at addressing these challenges to develop and validate the next-generation of subsurface imaging and monitoring platforms in urban areas based on the combination of existing fiber-optic networks and high-frequency infrastructure noise. The project comprises (1) developing high-performance computational tools, advanced processing workflows and machine learning approaches for efficient data exploration, selection and processing using existing datasets, (2) field experiments in target areas to retrieve high-resolution velocity models and monitor changes in seismic velocities, (3) integrating the resultant high-resolution seismic models with complementary datasets such as deformation maps derived from InSAR measurements. One of the selected study areas is the highly populated metropolitan area of Istanbul (Turkey), where understanding the structure, properties and dynamics of the shallow subsurface at high-resolution is critical for evaluating geohazard exposure. Among our objectives will be illuminating potential hidden faults underneath the city, obtaining high-resolution maps of geological materials and subsurface properties that can be translated into maps of local site response to large earthquakes, and tracking seismic velocity changes linked to hydrological dynamics that are known to be responsible for ground movements such as landsliding and subsidence. Ultimately, InDySE aims at developing efficient approaches for using dark fiber and ambient noise in urban subsurface investigations with implications in geohazard assessment.

How to cite: Rodríguez Tribaldos, V., Krawczyk, C., Ehsaninezhad, L., Martínez-Garzón, P., and Bohnhoff, M.: Towards Fiber-optics-based, Next-generation Observational Platforms for Investigating the Urban Subsurface: the InDySE Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17020, https://doi.org/10.5194/egusphere-egu24-17020, 2024.

EGU24-17284 | ECS | Orals | SM3.1

A complete feature set for classification of seismic sources with Distributed Acoustic Sensing (DAS) in the context of long-range monitoring 

Camille Huynh, Clément Hibert, Camille Jestin, Jean-Philippe Malet, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) exploits Rayleigh light backscattering to extract images of seismic wave propagation along a fiber optic in time and distance. The spatial distribution of virtual point sensors represents an opportunity to develop innovative methods for seismic event sources detection and identification. We develop in this study a method based on Machine Learning solutions for events classification.

This method relies on the development of features which translate the characteristics of the signals we observe into quantities that can be processed by machine learning algorithms to achieve the source classification. Three families of features investigating temporal and spatial characteristics and similarity of the signal are proposed, such as spatial and temporal analysis of the standard deviation, kurtosis or skewness of the signal or cross-correlation and dynamic time warping characterization and enables to quantify their individual contribution. Then we use a supervised machine learning model named XGBoost to perform classification based on these developed features. We tested this approach with a dataset recorded along a 91 km-long fiber optic deployed in the Pyrenees in France. The data acquisition has been achieved using a FEBUS A1-R DAS interrogator and with the support of TotalEnergies, from August 30 to September 20, 2022. During this period, 11 earthquakes and 6 quarry blasts have been recorded.

The trained model is validated using cross-validation techniques. Our Machine Learning processing chain successfully detect and classify 13 regional events from continuous background noise made by natural and anthropogenic activities. In particular, spatial features help to reduce the contribution of moving vehicles, whose presence is unavoidable along existing long-distance telecommunication fiber sections installed alongside roads.  In the continuity of this study, we investigate the potential of transfer learning from geophones deployed along the studied cable to DAS data or to another fiber optic cable installed in the same area.

How to cite: Huynh, C., Hibert, C., Jestin, C., Malet, J.-P., and Lanticq, V.: A complete feature set for classification of seismic sources with Distributed Acoustic Sensing (DAS) in the context of long-range monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17284, https://doi.org/10.5194/egusphere-egu24-17284, 2024.

EGU24-17595 | Orals | SM3.1

Analysis of DAS and slow strain measurements recorded during circulation tests at the FORGE geothermal underground laboratory 

Frantisek Stanek, Ismael Vera Rodriguez, Joseph Wolpert, David Podrasky, Anna Stork, Michal Chamarczuk, Matt Becker, and Jonathan Ajo-Franklin

FORGE (Frontier Observatory for Research in Geothermal Energy) is an underground field laboratory located in Utah, western United States, and sponsored by the US Department of Energy. The FORGE site is situated above a young, hot granitoid formation. The site has been used as a testbed for institutions interested in enhanced geothermal systems. As part of recent research work conducted at the site, a new deviated well was drilled adjacent to a previously stimulated well. Both wells were drilled into the granite volume. Circulation tests were performed over a period of approximately two days following completion of the second well. The circulation tests were monitored with two distributed optical sensing systems. One of the systems was recording in the new well and included measurements of distributed acoustics (DAS), temperature (DTS) and strain (DSS). The other system recorded from a preexisting well located about 500 m away and consisted of DAS measurements in a vertical cable.

Over the duration of the circulation tests, the two DAS systems detected on the order of 250 microseismic events in the close vicinity of the new well. A preliminary analysis of this group of events in terms of their hierarchical clustering allowed the selection of a small subset of them, which was used for the joint inversion of their absolute location and a layered velocity model for the site. The two-well DAS data of some of the events with absolute location was then used as a reference to estimate relative locations for the rest of the event’s catalogue. The estimated relative locations display a SW-NE alignment approximately perpendicular to the orientation of the new deviated well within the depth range of about 2300m to 2500m measured from the ground level. The location uncertainties more often show longer horizontal elongations suggesting a better depth constraint compared to the epicentral locations.

DTS data was analyzed in conjunction with slow strain data derived from the DAS data. Following the circulation tests, a ramp-like feature was observed beginning at approximate 1500m migrating upward throughout time in the slow strain data potentially indicating preferential fluid flow at this depth. Slow strain data is inextricably tied to temperature due to the thermal elongation of fiber, and as such, a thermal anomaly with similar characteristics is also observed at this depth. However, similar warming trends exist at various intervals throughout the well without the accompanied slow strain response indicating a truly anomalous interval that features unique DTS and slow strain response.

How to cite: Stanek, F., Vera Rodriguez, I., Wolpert, J., Podrasky, D., Stork, A., Chamarczuk, M., Becker, M., and Ajo-Franklin, J.: Analysis of DAS and slow strain measurements recorded during circulation tests at the FORGE geothermal underground laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17595, https://doi.org/10.5194/egusphere-egu24-17595, 2024.

EGU24-17644 | Orals | SM3.1

Understanding non-linear ground response with Distributed Dynamic Strain Sensing (DDSS) at Mt. Etna volcano, Sicily. 

Sergio Diaz-Meza, Philippe Jousset, Gilda Currenti, Lucile Costes, and Charlotte Krawczyk

Mt. Etna, the largest volcano in Europe, is known for its almost persistent activity and complex seismic wavefield, making it an attractive location for examining volcanic explosions and testing new instrumentation in seismology (e.g., rotational sensors, strain-meters, fiber optic sensing). In 2018, a study was conducted at the Pizzi Deneri (PDN) observatory, situated near Mt. Etna’s summit to understand new instrumentation responses to the local seismo-acoustic wavefield. During volcanic explosions the released energy is mainly partitioned into seismic waves traveling through the ground, and sound waves traveling through the atmosphere. To capture this phenomenon, a temporary multi-parameter network comprised of infrasound sensors, broad-band seismometers (BB) and a fiber optic cable buried within the local loosed granular medium (scoria layer). The fiber optic cable was connected to a Distributed Dynamic Strain Sensing (DDSS) interrogator.

At Etna, volcanic explosions were observed at co-located BB, infrasound and DDSS virtual sensors. A notable example(visible in both BB and DDSS data) is the successive occurrence of a 1-2 Hz seismic signal with a duration of ~4 seconds, followed by a ~2 Hz acoustic signal originating from the explosion, recorded at infrasound sensors. Unusually, simultaneous to the arrival of the acoustic signal observed at the infrasound sensors, DDSS and BB sensors record a signal with a frequency content of 15-20 Hz with a duration of ~2 seconds. We hypothesize that the 15-20 Hz signal is resulting from a non-linear ground response due to the air-to-ground coupling of the air pressure wave.

In order to better characterize this phenomenon, a second experiment was conducted in 2019 at PDN with a similar instrumentation as in 2018, but with a different spatial arragenment. During three months the infrasound sensors recorded each about 65000 volcanic explosions. In this work we analyze the respective ground responses of volcanic explosions observed in the DDSS records of the 2019 campaign. We observe similar phenomenon as in 2018 (non-linear ground response), nevertheless, not all explosion can trigger this response. We first characterize the explosion events from both infrasound and DDSS records, and then classify them using their waveform similarity. The preliminary results provide a broad characterization of the non-linear ground response phenomenon and an insight into the physical properties and processes that are necessary for a pressure wave to trigger a non-linear ground response. The outcomes of this work provide a better understanding of acoustic-to-ground energy coupling in volcanic environments and their potential to trigger other hazards.

How to cite: Diaz-Meza, S., Jousset, P., Currenti, G., Costes, L., and Krawczyk, C.: Understanding non-linear ground response with Distributed Dynamic Strain Sensing (DDSS) at Mt. Etna volcano, Sicily., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17644, https://doi.org/10.5194/egusphere-egu24-17644, 2024.

EGU24-17953 | Orals | SM3.1 | Highlight

Using Distributed Acoustic Sensing, Seismic and Infrasonic Observation to Track Pyroclastic Flows at Stromboli Volcano (Italy)  

Jean-Philippe Métaxian, Francesco Biagioli, Alister Trabattoni, Eléonore Stutzmann, Giorgio Lacanna, Gilda Risica, Pascal Bernard, Yann Capdeville, Anne Mangeney, Vadim Monteiller, Gianluca Diana, Lorenzo Innocenti, and Maurizio Ripepe

Pyroclastic flows are highly hazardous phenomena demanding precise detection, localization, and comprehensive characterization for effective volcanic risk management. During October and December 2022, the volcanic activity of Stromboli produced more than 60 pyroclastic flows. The flows propagated from the craters (~700 m a.s.l.) to the sea, resulting in tsunami waves ranging from centimetres to meters in height. These events coincided with an experiment involving distributed acoustic sensing (DAS) data acquisition with a dedicated 4-kilometer-long fibre-optic cable. A 3-component array consisting of 27 geophones and the multi-parameter monitoring network managed by the Laboratory of Experimental Geophysics (LGS) at the University of Florence were active simultaneously. We study two distinct pyroclastic flows of varying intensities. Using array processing techniques applied to DAS, seismic, and infrasonic measurements, we estimate back-azimuths that consistently track flows moving at velocities between 40 and 50 m/s from the craters to the shoreline. Validation of these measurements was accomplished through georeferenced images obtained by a visible camera, affirming their accuracy. These results demonstrate the effectiveness of the three datasets in monitoring pyroclastic flows and the need for multi-parametric observations for a better interpretation of volcanic phenomena.

How to cite: Métaxian, J.-P., Biagioli, F., Trabattoni, A., Stutzmann, E., Lacanna, G., Risica, G., Bernard, P., Capdeville, Y., Mangeney, A., Monteiller, V., Diana, G., Innocenti, L., and Ripepe, M.: Using Distributed Acoustic Sensing, Seismic and Infrasonic Observation to Track Pyroclastic Flows at Stromboli Volcano (Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17953, https://doi.org/10.5194/egusphere-egu24-17953, 2024.

EGU24-18170 | Posters on site | SM3.1

Near-source T-wave observations in the North Atlantic using Distributed Acoustic Sensing 

David Schlaphorst, Afonso Loureiro, Luis Matias, Susana Custódio, Carlos Corela, and Rui Caldeira

T phases are acoustic waves that propagate in the low velocity zone of the oceanic sound channel that acts as a waveguide, the SOFAR channel. They are generated by earthquakes through the conversion of seismic energy at the solid-liquid interface, but the exact processes involved are still under debate.

Due to their low attenuation and slow propagation velocity, these arrivals are especially useful for the detection and characterisation of small earthquakes in marine basins, as they can improve the location of the event while their waveforms can yield information on source rupture.

In October 2023, a Distributed Acoustic Sensing (DAS) interrogator was installed on the GeoLab dark fibre in the Atlantic, starting at the Praia Formosa CLS, in Madeira Island, Portugal. The instrumentation of this cable is part of a project by ARDITI and the Oceanic Observatory of Madeira where oceanographic data recorded by buoys and autonomous vessels are combined with DAS data to obtain a global view of the underwater environment of Madeira Island in all its physical, chemical and biological aspects, including the characterisation of regional seismicity. This initiative is also linked to the SUBMERSE project, as the Madeira cable is a pilot site to establish continuous DAS monitoring along many more submarine fibre-optic cables.

On October 27th, a near-source (<40 km) M2.9 earthquake was recorded by the DAS interrogator along the entire cable. The epicentre of the earthquake was east of the Desertas Islands, southeast of Madeira. Besides the P and S phases, very clear T phases are also visible. The recorded T waves have strain values larger than those of P and S waves. However, multiple T phases are identifiable, suggesting different points of conversion or even possible reflections.

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 (DOI: 10.54499/UIDB/50019/2020), UIDP/50019/2020 (DOI: 10.54499/UIDP/50019/2020) and LA/P/0068/2020 (DOI: 10.54499/LA/P/0068/2020), and by ERC project SUBMERSE, HORIZON-INFRA-2022-TECH-01-101095055.

How to cite: Schlaphorst, D., Loureiro, A., Matias, L., Custódio, S., Corela, C., and Caldeira, R.: Near-source T-wave observations in the North Atlantic using Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18170, https://doi.org/10.5194/egusphere-egu24-18170, 2024.

EGU24-18371 | ECS | Posters on site | SM3.1

Earthquake Early Warning Systems based on Fiber Optic Distributed Acoustic Sensing in the Sea of Marmara 

Zeynep Coşkun, Havva Gizem Özgür, Berkay Koç, Meryem Ece Dal, Erkan Özkan, Tayfun Erkorkmaz, Niyazi Bedri Pamukçu, Ramazan Can Şahin, Süleyman Tunç, Doğan Kalafat, Ali Pınar, Kadri Buldanlı, and Haluk Özener

The Istanbul Natural Gas Distribution Company (İGDAŞ) has recently embarked on utilizing existing Fiber-Optic (F/O) cables to enhance disaster prevention and mitigation efforts in Istanbul. We are exploring the potential of a novel technology called F/O Distributed Acoustic Sensing (DAS) for earthquake early warning systems. The strategic placement of the F/O cable, which crosses the North Anatolian Fault in the Marmara Sea, presents a unique opportunity for monitoring seismic activity. While seismic stations exist around the Marmara Sea, the absence of online operating Ocean Bottom Seismometer (OBS) stations makes the F/O cable the only sensor positioned across the fault lines expected to rupture during a major earthquake.

The monitored F/O cable, originally intended for telecommunications, spans 60 kilometers in the Sea of Marmara. Over the past 7 months starting in June 2023, more than 160 earthquakes ranging from magnitudes 1.0 to 7.5 have been recorded through the F/O cable. Notably, the F/O DAS system successfully captured significant distant events, notably the February 6, 2023, M7.8 and M7.5 earthquakes in Kahramanmaraş. This initiative highlights the critical stages, obstacles, and best practices associated with deploying this technology. It underscores the importance of precise cable layout, optimal sensor density, range optimization, and the conduction of shaking table tests.

Shaking table experiments were conducted to compare noise levels across various sampling rates. By subjecting a Force-Balanced Accelerometer (FBA) and F/O cable to simulated seismic activity resembling the 1999 Sakarya Earthquake (M6.9) with sine signals at frequencies of 0.25 Hz, 0.5 Hz, 1.5 Hz, 2 Hz, and 3 Hz, observations revealed that reducing the sample rate to 200 sps significantly lowered the interrogator's instrumental noise compared to 2000 sps. Hence, a lower sample rate proved advantageous in achieving a better Signal-to-Noise Ratio (SNR).

Through the analysis of acoustic signal variations along the F/O cable, the DAS systems can accurately pinpoint and characterize earthquake events, facilitating timely warnings. F/O DAS technology boasts distinct advantages in earthquake detection due to its capacity to capture a broad spectrum of seismic signals, ranging from low-frequency tectonic shifts to high-frequency ground vibrations. The effectiveness of F/O DAS measurements relies on proper coupling, ensuring the efficient transfer of acoustic signals to the optical fiber, thereby ensuring precise detection and interpretation of seismic activity.

How to cite: Coşkun, Z., Özgür, H. G., Koç, B., Dal, M. E., Özkan, E., Erkorkmaz, T., Pamukçu, N. B., Şahin, R. C., Tunç, S., Kalafat, D., Pınar, A., Buldanlı, K., and Özener, H.: Earthquake Early Warning Systems based on Fiber Optic Distributed Acoustic Sensing in the Sea of Marmara, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18371, https://doi.org/10.5194/egusphere-egu24-18371, 2024.

EGU24-19403 | ECS | Posters on site | SM3.1

Distributed Acoustic Sensing measurements in a box: a case-study for laboratory landslide test 

Micol Fumagalli, Nicola Piana Agostinetti, and Giovanni Battista Crosta

Distributed Acoustic Sensing (DAS) is a novel technology for monitoring seismic waves that shake fiber optic cables (FOC) buried in the ground, at unprecedented spatial resolution as low as 20 cm. Such technology can be in principle applied to laboratory experiments aimed to reproduce landslide phenomena. Here we present a preliminary study of DAS measurements in a 2m x 1m sand-box, where piles of sand act as landslide analogues. Our preliminary results demonstrate the capability of DAS recordings in locating seismic events occurring in the sand-box, related to the growth of the sand piles. This study opens to the possibility of using DAS technology to monitor large-scale (1-10m) laboratory analogue experiments aimed to reproduce geophysical and tectonic processes.

How to cite: Fumagalli, M., Piana Agostinetti, N., and Crosta, G. B.: Distributed Acoustic Sensing measurements in a box: a case-study for laboratory landslide test, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19403, https://doi.org/10.5194/egusphere-egu24-19403, 2024.

EGU24-19804 | ECS | Orals | SM3.1

A Fiber-Optic Approach for Cement Placement Monitoring of Deep Boreholes 

Johannes Hart, Berker Polat, Felix Schölderle, Toni Ledig, Martin P. Lipus, Christopher Wollin, Thomas Reinsch, and Charlotte Krawzcyk

Reliable well completion technologies are mandatory for the safe and sustainable use of subsurface reservoirs. Achieving subsurface well integrity requires displacing the entire drilling mud with homogenous cement. For this purpose, surface pump parameters (rate, density, pressure, and volume) are generally measured, yielding average values along the borehole. Here, distributed fiber-optic sensing offers new continuous monitoring options with dense spatial sampling within a borehole.

In the GFK-monitor project (https://gfk-monitor.de/en/), we investigated the primary cementation of an 874 m surface casing at a geothermal well in Munich, Germany. A 699 m long fiber optic cable, implemented by the Geothermie Allianz Bayern (GAB), was attached to the outside of the casing in the annulus between the casing and formation and cemented. This allowed for monitoring distributed dynamic strain rate (DDSS or DAS) throughout cement placement with a sampling rate of 1000 Hz and a spatial resolution of 1 m.

We analyzed the average vibration energy in the borehole by DDSS data using a root mean square approach in rolling windows for different frequency bands. Linear features with two different characteristics appear prominently in the frequency band between 0.2-0.3 Hz. One feature, which we named the “slow feature”, shows a varying slope resulting in velocities ranging from 2.5 to 6 m/s. In contrast, the accordingly called “fast feature” indicates a relatively constant velocity of around 6 m/s.

To better understand these features, a theoretical model was developed that simulates the rising velocity of fluids along the annulus. This model uses a cumulative approach and considers the cement pumping rate, borehole geometry, and timings from the daily reports. We assume, that the predicted minimum velocity is required to fill the whole breakout volume. This means that the faster the velocity the smaller the flow paths cross section.

A comparison of data and models reveals that the varying velocities of the "slow feature" correlate with velocities predicted by using the borehole geometry from the caliper log. The rather constant “fast feature” correlates instead with the predicted velocity of the model based on a uniform borehole geometry with the smallest possible radius, the drill diameter, which thus neglects all breakouts.

In summary, due to the nearly constant pumping rate during the monitoring campaign, we hypothesize that different rising velocities result from variations in the cross-sectional area of the flow path.  Based on our observations, the majority of the water spacer does not flush the borehole breakouts. With a good match to the minimum required velocity, these breakouts are filled by the first arriving cement. The following cement, with the same density, rises again on the fastest track. Thus, measuring the cement rising velocities with fiber optics and comparing them to the minimum required velocity from modeling might be a new tool to assess displacement efficiency in real-time.

How to cite: Hart, J., Polat, B., Schölderle, F., Ledig, T., Lipus, M. P., Wollin, C., Reinsch, T., and Krawzcyk, C.: A Fiber-Optic Approach for Cement Placement Monitoring of Deep Boreholes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19804, https://doi.org/10.5194/egusphere-egu24-19804, 2024.

EGU24-20360 | ECS | Posters on site | SM3.1

Towards a real-time railway monitoring system based on Distributed Acoustic Sensing and a Convolutional Neural Net 

Kevin Growe, Anna Tveit, Hefeng Dong, Susann Wienecke, Martin Landrø, and Joacim Jacobsen

Distributed Acoustic Sensing (DAS) enables cost-efficient retrieval of wavefield information alongside large linear infrastructure elements, such as pipelines, cables or railways. The massive datasets require automated approaches to detect and classify anomalies which can trigger further investigation through an operator, if necessary.

 

Within this work we exploit one week of DAS data from a fiber-optic cable co-located with a 50 km long railway line south of Trondheim, in the center of Norway. The data were acquired with a temporal sampling of 2 kHz and channel spacing of 4 m, resulting in 12500 channels. Treating the DAS time-space domain matrices like images we can make use of well-established techniques from the field of computer vision. We compute sliding RMS windows of 60 s and 1.5 km with 50 percent overlap and use them as input images for a Convolutional Neural Network. The network classifies events such as trains, cars, unknown events as well as different noise classes and artefacts. In order to thoroughly train the network, we labeled approximately 1000 RMS images per class and further applied a variety of data augmentation techniques to finally obtain about 5000 labeled images per class. Once trained, we can simply apply a forward pass through the network every 30 s for all the 1.5 km overlapping segments to obtain a live-classification of events along the entire railway line.

 

We present our workflow as well as initial results and discuss the potential of DAS for future railway monitoring and the challenges that we encounter. If successful, these methods can open up an opportunity to exploit a large amount of fibers co-located with railway lines enabling automatization of real-time railway monitoring.

Acknowledgements:

We acknowledge Bane NOR and Alcatel Submarine Networks for conducting the data acquisition for this project. This work is supported by the SFI Centre for Geophysical Forecasting under grant No. 309960.

How to cite: Growe, K., Tveit, A., Dong, H., Wienecke, S., Landrø, M., and Jacobsen, J.: Towards a real-time railway monitoring system based on Distributed Acoustic Sensing and a Convolutional Neural Net, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20360, https://doi.org/10.5194/egusphere-egu24-20360, 2024.

EGU24-1332 | Posters on site | SM3.2

Seismicity in the Bransfield Strait, Antarctica, using temporal Ocean Bottom Seismographs data 

Jinhoon Jung, Yongcheol Park, Won Sang Lee, and Seewon Park

The Bransfield Basin, located between the South Shetland Island and the Antarctic Peninsula in Western Antarctica, is formed by slab rollback of the South Shetland Trench and complementary extensional. The region also has large and small active volcanoes like the Orca volcano. Various earthquakes have occurred due to tectonic movement and volcanic activities. Since the Mw 4.9 earthquake struck at a depth of 10 km in the vicinity of South Shetland Islands on 29 August 2020 (USGS), moderate earthquakes have constantly been reported adjacent to Bransfield Basin like an earthquake swarm.The Extreme Geoscience Team (EGG) at the Korea Polar Research Institute (KOPRI) has been operating a seismic station at the King Sejong station. Other countries have been running their seismic stations in the South Shetland Islands, such as the Antarctic Seismographic Argentinean Italian Network (ASAIN) and Chilean seismic stations, to monitor local earthquakes associated with back-arc spreading and submarine volcanic activities in this area. However, these seismic stations are located on the islands, and the inter-station distance is over 50 km. To make up for the poor coverage of seismic stations, we installed 5 OBSs in the earthquake swarm area between 2020 and 2021.

Using cross-correlation with onland seismic data and OBSs data, we conducted the template matching analysis and detected 67,952 events from August 29, 2020, to December 31, 2021. We relocated 2,313 epicenters of the seismic events by manually picking the first arrival of the P-wave. We found that the earthquake swarm’s epicenters were mainly concentrated in the central basin of the Bransfield Strait.

We categorize the characteristics of the earthquake near Bransfield Basin. We will contribute to understanding the dynamics and evolution of subduction zones in Bransfield Basin.

 

How to cite: Jung, J., Park, Y., Lee, W. S., and Park, S.: Seismicity in the Bransfield Strait, Antarctica, using temporal Ocean Bottom Seismographs data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1332, https://doi.org/10.5194/egusphere-egu24-1332, 2024.

EGU24-2816 | ECS | Orals | SM3.2

SurfQuake (SQ): A new Python toolbox for the workflow process of seismic sources 

Roberto Cabieces, Thiago C. Junqueira, and Jesús Relinque

surfQuake is a new software designed to overcome the workflow process that involves the estimation of seismic source parameters. The complete set of toolboxes inside surfQuake allows the user the complete automation of seismic phases arrival times estimation and events association, event locations, magnitudes and attenuation, slowness vector, and moment tensor inversion.

The software is programmed in Python 3 and offers the users the possibility of three programming levels. From the core library, which allows the user to integrate the core of surfQuake into his own scripts, to the Command Line Interface, which gives the user access to an upper layer that simplifies the use of the core. Finally, surfQuake core is wrapped by a Graphical User Interface (GUI) and connected to a SQL Lite database to store all the results. The user has direct access to query the database tables to extract important information through the object Relational Mapper SqlAlchemy directly managed from the GUI.

The software has been fully tested with the earthquake cluster that occurred during the eruption of La Palma in 2021-22. The source parameters resulting from the eruption and the basic statistics associated with them are displayed using the database toolbox. Additionally, we offer a web tutorial with the documentation of surfQuake and a set of usage examples for the three programming levels.

How to cite: Cabieces, R., Junqueira, T. C., and Relinque, J.: SurfQuake (SQ): A new Python toolbox for the workflow process of seismic sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2816, https://doi.org/10.5194/egusphere-egu24-2816, 2024.

EGU24-4409 | Orals | SM3.2

Clock skew corrections of a large-aperture OBS array in the Atlantic Ocean reveal the need to include non-linear drift corrections 

Frank Krueger, Roberto Cabieces, Katrina Harris, Ana Ferreira, Maria Tshekmistrenko, Stephen Hicks, Wolfram Geissler, Katrin Hannemann, and Mechita Schmidt-Aursch

Accurate timing corrections for seismic data recorded by ocean bottom seismometers (OBS) are essential for a wide range of applications. The synchronization of internal OBS clocks with Global Positioning System (GPS) is only possible prior and subsequently to deployment in the seafloor. Thus, untracked, possibly nonlinear clock errors in seismic data may accumulate over the deployment period. The measurement of the clocks offset from GPS at retrieval, referred to as `skew’, can be used to correct the data solely under the assumption of a uniform rate of clock drift throughout the whole deployment. We estimate OBS clock drift curves for 40 OBSs of the large-scale UPFLOW amphibian array in the Madeira-Azores-Canaries region that lasted ~14 months in 2021-22. We use the relative shift of daily Empirical Green Functions obtained from seismic ambient noise recorded by all available data channels to track clock error. We find that 95% of our OBS clock drift observations have a substantial non-linear component, notably in the first months of the deployment. Overall, our estimated time-dependent clock drift curves accurately predict the final skew, with an average difference of ~160 ms to GPS skew values obtained at retrieval. We test our skew curves by using them to correct examples of recordings of teleseismic earthquakes and of local-regional seismicity. Uncertainty analysis of the skew curves gives a mean skew error of ~110 ms, indicating the suitability of the corrected data for future seismological studies such as for seismic tomography, seismicity analysis and moment tensor inversions. A dedicated open-source Graphical User Interface toolbox in Python 3 has been developed to facilitate OBS clock synchronization using seismic ambient noise.

How to cite: Krueger, F., Cabieces, R., Harris, K., Ferreira, A., Tshekmistrenko, M., Hicks, S., Geissler, W., Hannemann, K., and Schmidt-Aursch, M.: Clock skew corrections of a large-aperture OBS array in the Atlantic Ocean reveal the need to include non-linear drift corrections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4409, https://doi.org/10.5194/egusphere-egu24-4409, 2024.

EGU24-4486 | Orals | SM3.2

Pacific Array: international collaboration for large-scale array experiment in the Pacific basin 

Takehi Isse, Hitoshi Kawakatsu, Sang-Mook Lee, Bang-Yuan Kuo, and James B. Gaherty

             Constructing a seismic network in the oceans has been one of the most difficult challenges in seismology. Almost 70 % of the Earth's surface is covered by the ocean, so such a network is necessary for investigating the Earth's interior. Because the Pacific Ocean is the largest ocean basin, it was considered impractical to establish a large-scale dense seismic array.

              However, in 2014, Kawakatsu and colleagues proposed a new array concept (Kawakatsu et al., 2014). Deploying ~15+ BBOBS as an array unit for 1-2-year observation period, and repeating such observations in a leap-frog fashion for a decade or so, would enable us to cover a large portion of the Pacific Ocean. International collaboration was essential to successfully implement this strategy, and since 2015, the concept has been realized as "Pacific Array" via international collaboration between partners in Japan, U.S.A, EU, South Korea, Taiwan, and China.

              Since then, many array units have been funded, providing broadband data from across the Pacific. Oldest-1 (Japan-S. Korea), Oldest-2 (Japan-Taiwan), Young- and Old-ORCA, and OHANA (U.S.A) have all been completed; Galapagos and SaLOON (U.S. A.) are currently deployed; and HEB (Japan-Germany), GTJ, and EPIC (U. S. A.) will be deployed in the near future. Although each of these observations have their own scientific goals, they contribute to the larger international Pacific Array structure. We summarize recent progress of the Pacific Array and some of scientific result in each array.

How to cite: Isse, T., Kawakatsu, H., Lee, S.-M., Kuo, B.-Y., and Gaherty, J. B.: Pacific Array: international collaboration for large-scale array experiment in the Pacific basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4486, https://doi.org/10.5194/egusphere-egu24-4486, 2024.

EGU24-4563 | ECS | Posters on site | SM3.2

Seismic Activity in the Zabargad Fracture Zone (Red Sea): Insights from an Amphibious Seismic Network 

Hasbi Ash Shiddiqi, Laura Parisi, Eduardo V. Cano, P. Martin Mai, Nico Augustin, and Sigurjón Jónsson

The Zabargad Fracture Zone (ZFZ), located between 23.5o N – 26o N is the largest rift-axis offset in the Red Sea. The ZFZ is a fundamental tectonic element of ~100 km rift-axis offset that marks the transition between the northern and central Red Sea. Due to data scarcity, our understanding of the seismic activity and the potential presence of transform faults or non-transform offsets in the ZFZ area is limited. Local seismological datasets so far have been restricted to the onshore recordings, thus hampering the ability to study the ZFZ's role in the Red Sea’s tectonic evolution and to assess its potential seismic hazard associated with transform faults accommodating the rift-axis offset in the Red Sea.

To fill this data gap, we deployed 14 broadband Ocean Bottom Seismometers (OBS) and four land stations for 12 months within the ZFZ to collect continuous waveforms. The newly collected data span the period 11/2021 to 11/2022. First, we corrected recorded OBS-waveforms for clock drift using skew values measured at the time of the OBS recovery and time-shifts measured from ambient noise cross-correlations for stations whose skews could not be measured. Next, we applied a deep-learning-based algorithm to automatically detect earthquakes and pick P and S phases. We verified and, if necessary, manually corrected these phase picks; this approach identified more than 3500 local earthquakes.

To obtain reliable hypocentral locations, we inverted for an optimum crustal 1-D seismic velocity model of the ZFZ and station delays simultaneously. Using as reference a nearby land station installed on Precambrian bedrock, we obtained positive OBS station delays of up to 2 seconds. These delays correspond to late phase arrivals, most likely due to thick sedimentary and salt deposits. Our local magnitude (ML) calculations show that OBS-station ML values are up to 1.5 units larger than for the land stations. We find that station delays and ML deviations are correlated, highlighting the importance to account for the variability of shallow geological and bathymetric properties for accurate earthquake location and magnitude estimation.

Our seismicity analysis reveals two major distinct spatial clusters of earthquakes, in the southern (23.95 o N – 24.53 o N) and northern (24.68 o N – 25.43o N) parts of the ZFZ. Seismicity in the south higher seismicity rate and spatially concentrated than in the north. We also identified three seismic swarms in the south and one seismic swarm in the north lasted for one to three weeks each. Our preliminary analyses document the potential of this new dataset to address key questions on the seismotectonics and seismic activity of the ZFZ.

How to cite: Shiddiqi, H. A., Parisi, L., Cano, E. V., Mai, P. M., Augustin, N., and Jónsson, S.: Seismic Activity in the Zabargad Fracture Zone (Red Sea): Insights from an Amphibious Seismic Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4563, https://doi.org/10.5194/egusphere-egu24-4563, 2024.

EGU24-4888 | Posters on site | SM3.2

The Design of a Low-Angle Active Leveling Device for Short-Period Ocean Bottom Seismometer 

Chin-Heng Yang, Ching-Ren Lin, Yuancheng Gung, Feng-Sheng Lin, and Kun-Hui Chang

In this study, we focus on developing a low-angle active leveling device of geophone for Ocean Bottom Seismometers (OBS). The deployment of OBS in varied underwater environments poses a significant challenge due to unpredictable terrains, which often affect the positioning and orientation of these instruments. In such scenarios, the role of a leveling device becomes crucial, especially for self-floating OBS. Most of the leveling devices are designed with a 360° range, resulting in high costs and limited versality, our approach is informed by previous OBS positional data, suggesting that a limited corrective angle is adequate for underwater conditions. Our innovative leveling mechanism resembles a joystick in its transmission system, topped with a platform to enhance versatility. The control rod below the platform is controlled by two DC motors combined with worm gears, adjusting the rod along the X and Y axes with an approximate corrective angle of 30 degrees. For seismic sensing, our system utilizes one vertical and two horizontal geophones, housed in a custom sensor box to ensure the three axes are orthogonal to each other. This design simplifies the complexity of parts, combining off-the-shelf and custom components, offering a significant size and cost advantage. We have also tested its performance, with a focus on eliminating signal interference from resonance frequencies and assessing the system's stability. This includes a comparative analysis with older leveling mechanisms.

How to cite: Yang, C.-H., Lin, C.-R., Gung, Y., Lin, F.-S., and Chang, K.-H.: The Design of a Low-Angle Active Leveling Device for Short-Period Ocean Bottom Seismometer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4888, https://doi.org/10.5194/egusphere-egu24-4888, 2024.

EGU24-5502 | ECS | Posters on site | SM3.2

Empirical insights into ocean acoustic wave propagation and source localization using ocean-bottom seismometers 

Clara Gómez-García and Christopher J. Bean

Human activities in the marine environment coupled with the efficient propagation of acoustic waves, have significantly increased ocean noise levels. This rise poses a threat to marine biodiversity, especially impacting vocal-dependent marine mammals. Therefore, obtaining a more comprehensive understanding of the complex ocean soundscape, shaped by both natural and anthropogenic sources, is essential.

Ocean-bottom seismometer (OBS) datasets present an opportunity to explore the marine acoustic noise field. OBS hydrophones can be used to effectively study regional marine soundscapes. Additionally, the three-component OBS seismometers capture acoustic-to-seismic conversions from the water column, enabling the detection and localization of acoustic events.

Through the analysis of OBS hydrophone recordings from the NE Atlantic offshore Ireland, we develop a frequency-dependent empirical sound propagation model for the area. The model provides information on (1) the spectral amplitude decay of sound sources in the region and (2) the distance between OBSs and acoustic sources.

To construct the model, we consider ship noise from individual vessels recorded by OBSs at known distances from the source, using Automatic Identification System (AIS) ship-tracking data. As a ship moves away from its closest point of approach (CPA) to an OBS, the hydrophone records the evolution of the frequency-dependent ship's acoustic signal spectral amplitude with distance. This enables us to compute amplitude decay curves for narrow frequency bands from different vessel signals recorded at various OBSs. We apply a signal-to-noise ratio (SNR) quality control criterion and consider ships sailing along 'straight' paths at a constant speed (< 2 kn variation). After normalizing and scaling the CPAs of the different curves to a reference, we stack them for each frequency band and compute polynomial fits for the stacked amplitude decay curves. We analyse the number of vessel tracks needed to build a reliable empirical model. Numerical simulations are computed to further understand the acoustic propagation properties from our empirical model.

The goal is to investigate (1) how spectral amplitudes at different frequencies behave with distance from the sound sources, (2) the efficiency of frequency-dependent sound propagation in the ocean in regions with variable seafloor morphologies, and (3) the potential use of the empirical model to obtain distances to other sound sources with unknown locations, such as Baleen whales. To achieve this, we compute ratios of spectral amplitudes for pairs of different frequency bands using the fitted amplitude decay curves. We test the model's ability to locate other vessels with known AIS positions before using it to locate different sound sources with unknown positions. Locating a sound source employing the distance provided by the empirical model is valuable when OBSs are too far apart for 'traditional' multi-sensor methods. In such cases, the incoming direction of the sound source is determined by rotating the horizontal-component OBS seismic data to point to the source back-azimuth. Also, the amplitude decay information provided by the model has multiple applications in other areas where noise pollution may be a concern (e.g., marine infrastructure construction).

How to cite: Gómez-García, C. and Bean, C. J.: Empirical insights into ocean acoustic wave propagation and source localization using ocean-bottom seismometers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5502, https://doi.org/10.5194/egusphere-egu24-5502, 2024.

EGU24-6052 | ECS | Posters on site | SM3.2

Re-location and integration into the ISC Bulletin of earthquakes recorded by hydro-acoustic MERMAID instruments freely floating in the South Pacific Ocean 

Dalija Namjesnik, Karin Sigloch, Joel D. Simon, Tom Garth, James Harris, Dmitry Storchak, Frederik. J. Simons, Sébastien Bonnieux, Yong Yu, and Masayuki Obayashi

We present the analysis of more than 9000 hydro-acoustic earthquake records, recorded by a network of 50 instruments called Mobile Earthquake Recording in Marine Areas by Independent Divers (MERMAIDs), which are freely floating in the South Pacific Ocean. This network is part of the collaborative South Pacific Plume Imaging and Modeling (SPPIM) project. Our analysis focuses on evaluating how the MERMAID stations complement the conventional worldwide network of stations reporting to the ISC, comprising records of globally distributed seismic stations. In the context of routine earthquake (re)location, we evaluate the improvement of results of earthquake location estimates, particularly focusing on the Tonga-Kermadec subduction zone, where current distribution of seismic land stations is extremely sparse. MERMAIDs are often the closest “station” to earthquakes occurring in the Tonga subduction zone, and frequently fill significant station azimuthal gaps.

We matched the MERMAID records from June 2018 to December 2023 to more than 3000 earthquakes which are reported to the ISC by many international agencies worldwide, allowing us to construct the MERMAID catalogue, complimented with additional parametric data such as MERMAIDs locations, observed direct P-phase picks and travel time residuals with respect to ak135 model, as well as their corrections for bathymetry. These data were integrated into the existing ISC Bulletin, and relocated using the ISC hypocentre relocation algorithm ISCLoc. The results of this successful first integration of MERMAID data into ISC routines presents an important step towards routinely including MERMAID traveltime picks in ISC Bulletin.

How to cite: Namjesnik, D., Sigloch, K., Simon, J. D., Garth, T., Harris, J., Storchak, D., Simons, F. J., Bonnieux, S., Yu, Y., and Obayashi, M.: Re-location and integration into the ISC Bulletin of earthquakes recorded by hydro-acoustic MERMAID instruments freely floating in the South Pacific Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6052, https://doi.org/10.5194/egusphere-egu24-6052, 2024.

EGU24-6977 | Posters on site | SM3.2

Reprocessing of the ocean bottom seismic data of the TYDE experiment using modern techniques. 

Marco Calò, José Antonio Gamez Lindoro, Francesca Di Luccio, and Karina Bernal Manzanilla

During the TYrrhenian Deep-sea Experiment (TYDE) 14 Ocean Bottom stations were deployed in the period December 2000-May 2001 on the southern Tyrrhenian seafloor around the Aeolian islands All the stations were equipped with Hydrophones (OBH) and six of them with 3-component geophones (OBS). This experiment represented one of the first and most important passive ocean bottom data acquisition ever realized in southern Tyrrhenian and the records were mainly used to perform receiver functions, modeling of the seismic velocity field, and detect and locate seismicity.

In this work we present a reprocessing of these old data using modern techniques of analysis to improve the quality of the signals and extract more information of what has been already published.

We show the workflow used for cleaning the records together with Machine Learning approaches to improve the detection of small events and the application of methods that were not common at that time, such as the Ambient Noise analyses.

 

Work supported by the “Pianeta Dinamico” call, 2023–2025 CAVEAT

How to cite: Calò, M., Gamez Lindoro, J. A., Di Luccio, F., and Bernal Manzanilla, K.: Reprocessing of the ocean bottom seismic data of the TYDE experiment using modern techniques., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6977, https://doi.org/10.5194/egusphere-egu24-6977, 2024.

EGU24-8185 | Posters on site | SM3.2

HALIOS  an innovative and clever Broad Band OBS. 

Yann Hello, Charles Rebour, Karin Sigloch, Sebastien Bonnieux, and Olivier Philippe

A fruitful close collaboration between teams of researchers and engineers of Geoazur, a research laboratory specializing in seismic observation, and Osean, a dynamic company combining the talents of engineers in low-noise, low-power electronics specialized in underwater acoustics, gives this instrument a guarantee of robustness, reliability and innovation by capitalizing on all their knowledge in their respective fields. Halios has an autonomy of 18 months, dimensions of 1.1 x 1.1 x 1m and a total weight with ballast of 346 kg. Electrical power is supplied by lithium or alkaline batteries. Halios is made entirely from corrosion-resistant materials. The 4-panel, mortise-and-tenon structure naturally creates a well in which the seismometer is protected. This well is covered by two flaps that open when the OBS sinks into the water, and close when the OBS stops on the bottom. During descent, the seismometer is suspended in the well. Once the OBS is in place, the seismometer is released automatically or by an acoustic command to land on the ground without any mechanical contact with the structure. This type of coupling is ideal, and protects the sensor from underwater currents. Communication with the OBS is possible via Ethernet, Wi-fi or acoustics once in the water by non-specialists. An acoustic module makes it possible to retrieve a health report on demand, which groups together the essential parameters of the station, and to modify some of them once the OBS is in the water. Halios incorporates precise clock or a CSAC-type atomic clock, if time precision is required.The seismometer is a compact Nanometrics Trillium, integrated in a dedicated container which also houses an accelerometer. An hydrophone, a precision temperature sensor and an absolute pressure sensor complete the range of sensors integrated on Halios. An dedicated acoustic modem also enables partial data retrieval from the surface.To retrieve the OBS, an acoustic command activates a mechanical release which frees the ballast. Dynamic assistance from leaf springs accelerates the positive thrust provided by the OBS's high-density syntactic foam. This foam is injected into a PHD shell, which effectively protects the whole unit and, thanks to its compact shape, provides effective anti-shock protection. The ascent of the OBS into the water column can be monitored by the acoustic module.Once at the surface, the time difference between the OBS clock and the GPS datum is automatically calculated. The OBS sends its GPS coordinates to the ship by VHF to facilitate recovery. At night, an LED flashing light can also be used to pinpoint its position. Halios is equipped with an interface that enables it to be connected to a real-time cable network, making it a versatile OBS of the highest performance and innovation.

How to cite: Hello, Y., Rebour, C., Sigloch, K., Bonnieux, S., and Philippe, O.: HALIOS  an innovative and clever Broad Band OBS., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8185, https://doi.org/10.5194/egusphere-egu24-8185, 2024.

EGU24-10807 | Posters on site | SM3.2

Pushing Boundaries with Ocean Bottom Seismometers (OBS) with a Pool-Ready System: Güralp Aquarius 

Aaron Clark, James Lindsey, Phil Hill, Connor Foster, Federica Restelli, Neil Watkiss, Ella Price, Mladen Nedimović, and Graeme Cairns

Cabled ocean bottom seismometer (OBS) solutions are financially and logistically challenging and autonomous OBS systems do not provide operators with seismic data until recovery. To address this issue Güralp has developed Aquarius, an ultra-low-power, free-fall OBS system, operational at any angle and with the ability to transmit seismic data in near-real-time from the seafloor without the use of cables.

The Güralp Aquarius incorporates seafloor-to-surface acoustic communication technology that allows state-of-health and noise performance interrogation during installation followed by retrieval of seismic data throughout the deployment period.

Omnidirectional broadband seismometer components allow the Aquarius to land and operate on steep slopes without requiring a gimbal mechanism that inherently introduces noise and failure modes. Raw data is recorded uncorrected for orientation to allow users to correct during post-processing.

These unique features allow the sensor to function on uneven seafloor as well as transmitting seismic data to the surface where the operator can use noise characteristics, location, and orientation data to determine if the landing site is suitable.

Intelligent battery design allows for typical 18-month deployments, with charging being possible alongside data transfer. This allows recharging, download and configuration simultaneously on the ship in between deployments.

Ease of configuration, deployment and recovery followed by simple data processing are all central themes to the Aquarius. The capital investment required to purchase OBS systems often means that the OBS instrument must be adaptable to a range of use-cases.

The Aquarius is in use in 6 different countries and is the unit of choice for the Canadian OBS pool, comprising 120 units for deployment around the globe. Aquarius units have been successfully deployed in the Mediterranean, North Atlantic as well as the North and South Pacific. Here, we focus on the mechanics of deployment and recovery for demonstrating to experienced and prospective principle investigators how this system simplifies and improves confidence in deployment.

How to cite: Clark, A., Lindsey, J., Hill, P., Foster, C., Restelli, F., Watkiss, N., Price, E., Nedimović, M., and Cairns, G.: Pushing Boundaries with Ocean Bottom Seismometers (OBS) with a Pool-Ready System: Güralp Aquarius, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10807, https://doi.org/10.5194/egusphere-egu24-10807, 2024.

EGU24-11062 | Orals | SM3.2

Successful Deployment of a 21km SMART Cable with Force-Feedback Seismometer and Accelerometers in the Mediterranean Sea 

Federica Restelli, John O'Neill, Bruce Nicholson, Neil Watkiss, Giuditta Marinaro, Francesco Simeone, Davide Embriaco, Ella Price, Connor Foster, and Aaron Clark

Autonomous Ocean Bottom Seismometer (OBS) deployments have often involved a degree of “drop-and-hope” due to the inherent lack of seismic data communication during installation as well as waiting extended periods before data collection. Cabled solutions provide real-time data during and immediately after deployment, sometimes with opportunity to adjust the instrument before it is left to operate remotely. However, cabled solutions are inherently financially and logistically challenging both in terms of seismic hardware and arguably more significantly, deployment hardware (ships, ROVs, cables etc.). The geographical reach of these experiments is also often limited to within a few hundred kilometres of the coast. These constraints often mean cabled OBS are beyond the scope of most scientific bodies.

Güralp Systems, in collaboration with INGV, has successfully manufactured and demonstrated a method of reducing financial and logistical constraints and extending geographical range by utilising force-feedback seismic instrumentation in cabled OBS systems. The recent successful deployment of the InSEA Wet Demo SMART (Science Monitoring And Reliable Telecommunications) cable displays a world first in how science can partner with industry to achieve this.

SMART cables are primarily telecommunication cables that secondarily serve as hosts for scientific monitoring equipment. Commercial viability for these systems relies on the cable being laid as if the science element did not exist, thereby minimising additional deployment costs and reducing barriers to cooperation with cable laying companies. GSL and INGV deployed 3 seismometer-accelerometer pairs housed inline repeaters along the 21km cable length using standard cable-laying techniques to show proof of concept.

This pioneering installation using telecommunication cables marks a significant step towards drastically improving local knowledge of inaccessible oceanic regions as well as global azimuthal coverage for teleseismic events, all in real time.

How to cite: Restelli, F., O'Neill, J., Nicholson, B., Watkiss, N., Marinaro, G., Simeone, F., Embriaco, D., Price, E., Foster, C., and Clark, A.: Successful Deployment of a 21km SMART Cable with Force-Feedback Seismometer and Accelerometers in the Mediterranean Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11062, https://doi.org/10.5194/egusphere-egu24-11062, 2024.

EGU24-11074 | ECS | Posters on site | SM3.2

Waveform tomography of the upper mantle beneath the North Atlantic region using regional seafloor and global data. 

Janneke I. de Laat, Sergei Lebedev, Raffaele Bonadio, Maria Thsekhmistrenko, and Nicolas L. Celli and the SEA-SEIS Team

The Iceland hotspot and its interaction with the Mid-Atlantic Ridge have strongly influenced the structure and evolution of the North Atlantic region. The Iceland hotspot has been linked to the presence of the underlying Iceland plume, rising from the deep mantle below Iceland. Due to the sparsity of the seismic data coverage in the North Atlantic Ocean, the structure and dynamics of the underlying plume, as well as its influence on the surrounding North Atlantic region, remain a topic of debate. As part of the project SEA-SEIS (Structure, Evolution And Seismicity of the Irish offshore), a network of ocean bottom seismometers was deployed across a large part of the North Atlantic Ocean—from Ireland and Britain to near Iceland—in September 2018. Over a period of 19 months, they recorded seismic data on the seafloor. 14 OBSs were retrieved in May 2020, of which 12 successfully recorded 19 months of seismic data. The data was thoroughly preprocessed, including the reduction of compliance and tilt noise on the vertical-component waveforms of teleseismic events. These waveforms were individually inverted for surface, S- and multiple S-waves using the Automated Multimode Inversion (AMI), extracting structural information on the lithosphere and underlying mantle.

Here, we combine this new seafloor seismic data with a massive global dataset of waveform fits for almost 1.5 million seismograms, with the coverage maximised in the hemisphere around the North Atlantic, and compute a new seismic waveform tomography model of the North Atlantic upper mantle: NA24. The tomography capitalises on the improved data coverage and reveals both the S-wave velocity and the azimuthal anisotropy structure below the Iceland hotspot, the adjacent mid-ocean ridge, and the entire North Atlantic region at a new level of detail. It shows low seismic velocities below Iceland and the adjacent Reykjanes Ridge and Kolbeinsey Ridge down to ~260 km depth, below which they merge into one low-velocity body located west of Iceland at around 330 km depth. Around 410 km depth, the low-velocity body is present below eastern Greenland where it remains throughout the transition zone. This observation implies that the Iceland plume is located below eastern Greenland in the transition zone, moving eastward as it rises in the upper mantle. In the shallow upper mantle, a strong ridge-parallel azimuthal anisotropy structure is revealed along the full length of the Reykjanes Ridge. This implies a strong channelled horizontal flow from the Iceland plume towards the south below the ridge axis, while any sign of a radial outward flow of the plume is absent.

How to cite: de Laat, J. I., Lebedev, S., Bonadio, R., Thsekhmistrenko, M., and Celli, N. L. and the SEA-SEIS Team: Waveform tomography of the upper mantle beneath the North Atlantic region using regional seafloor and global data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11074, https://doi.org/10.5194/egusphere-egu24-11074, 2024.

EGU24-11876 | ECS | Posters on site | SM3.2

Integrated Bayesian Approach for Station Location and Orientation in Marine Active-Source Seismic Shear Wave Studies 

Morgan Cryder, Robert Dunn, and Chong Xu

Since the introduction of the ocean bottom seismograph (OBS), it has played a pivotal role in the expansion of our comprehension of the Earth’s interior structure and dynamics. Typically deployed through free-fall from a ship, the position of the OBS on the seafloor and its orientation are initially unknown. When using airgun shots to locate and orient an instrument, a severe downside is the often-limited azimuthal distribution of shots around the OBS, possibly leading to large location and, subsequently, orientation errors. We introduce a novel and efficient method aimed at enhancing the accuracy of station locations in active-source seismic experiments. The approach uses airgun shots recorded as part of the experiment, and integrates both acoustic wave travel time information and waveform polarizations. The inverse problem of station location is formulated in terms of Bayesian inference. At each location of a search grid, the misfit of observed and theoretical water wave travel times and the clustering of polarization data are combined into one probabilistic formulation to map the relative likelihood of a station’s position and orientation. We demonstrate the practical utility of the method via application to the location and orientation of OBS deployed during a recent seismic experiment located across the Hawaiian Ridge. Thereafter, we will use the results to compute radial seismograms, extract the travel times of crustal and mantle S waves, and develop S-wave models of the oceanic lithosphere across the Hawaiian Ridge.

How to cite: Cryder, M., Dunn, R., and Xu, C.: Integrated Bayesian Approach for Station Location and Orientation in Marine Active-Source Seismic Shear Wave Studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11876, https://doi.org/10.5194/egusphere-egu24-11876, 2024.

EGU24-13081 | ECS | Posters virtual | SM3.2

How did the Largest Oceanic Plateau modify the Normal Oceanic Lithosphere? 

Ziqi Zhang and Tolulope Olugboji

The Ontong Java Plateau (OJP), formed around 120 Ma, represents a significant event in the Earth’s geologic history. It is the largest preserved Large Igneous Province (LIP) by volume on the Earth. The voluminous and rapid magmatism placed a thick 30-40 km crust on a normal oceanic lithosphere in submarine conditions. The lithosphere has since experienced low subsidence suggesting only modest thermal perturbation. Several hypotheses have been proposed to explain the unique emplacement history, including a hot mantle plume, meteorite impact, or passive mantle upwelling close to a fast-spreading ridge. In this study, we image the crust and upper mantle structure beneath the OJP using body waves and surface waves. A challenge of body wave imaging in submarine environments is the severe reverberations generated in the water column and seafloor sediments. Additionally, multiple reflections from shallow interfaces (e.g., Moho and intra-crustal layers) may interfere with deeper upper mantle phases, making interpretation ambiguous. In this work, we obtain high-resolution Ps-RFs at 17 OBS (ocean bottom seismometer) stations in the OJP region using a transdimensional hierarchical Bayesian deconvolution approach. We then take advantage of two recently developed techniques: (1) FADER (Fast Automated Detection and Elimination of Echoes and Reverberations), which uses autocorrelation and cepstral analysis to identify and remove water and sediment reverberations, and (2) CRISP-RF (Clean Receiver function Imaging with SParse Radon Filters), which uses sparse Radon transforms to eliminate multiples and incoherent noise. We anticipate applying our novel ideas to traditional seismic imaging will provide robust constraints on the discontinuities detected beneath the OJP, shedding new light on its lithospheric structure and origin.

How to cite: Zhang, Z. and Olugboji, T.: How did the Largest Oceanic Plateau modify the Normal Oceanic Lithosphere?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13081, https://doi.org/10.5194/egusphere-egu24-13081, 2024.

EGU24-14905 | Orals | SM3.2

Removing low frequency ocean bottom seismometer tilt noise using simple sensor reorientation 

Wayne Crawford, Gabi Laske, Nicholas Harmon, and Catherine Rychert

Ocean bottom seismometer data are strongly affected by noise from seafloor currents.  Techniques based on the transfer function between noise on the horizontal and vertical channels are commonly used to “clean” this noise from low-frequency (< 0.1 Hz) vertical channel data, but questions remain about the efficiency of this technique and its effect on seismological signals.  We present a method to “pre-clean” the vertical data through simple rotation of the seismometer to minimize the noise on the vertical channel.  The rotation is nearly identical to that indicated by the transfer function method, but has the advantage of losing no information.  Once this pre-cleaning is performed, transfer-function based cleaning can still be performed, generally resulting in lower noise levels than those obtained using the transfer function method alone and the remaining transfer function may provide information beyond that of the instrument’s mis-alignment with the gravitational field.  We will present examples from datasets around the world and discuss new information revealed.

How to cite: Crawford, W., Laske, G., Harmon, N., and Rychert, C.: Removing low frequency ocean bottom seismometer tilt noise using simple sensor reorientation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14905, https://doi.org/10.5194/egusphere-egu24-14905, 2024.

EGU24-16613 | ECS | Posters on site | SM3.2

Surface wave mantle anisotropy tomography of the Azores-Madeira-Canaries region using UPFLOW data: initial results 

Katrina Harris, Michael Witek, Ana M. G. Ferreira, Sung-Joon Chang, and Miguel Miranda

Upward mantle flow is key to understand global mantle geodynamics yet its imaging remains challenging due to potential associated low velocity contrasts and small lateral dimensions. In this study we use the UPFLOW ocean bottom seismometer (OBS) dataset to build images of radial anisotropy to constrain the patterns of mantle upwellings in the Azores-Madeira-Canary Islands region. We use the partitioned waveform inversion (PWI) method whereby non-linear waveform fitting of surface waves filtered between T~ 16 s and T~ 300 s is performed using a successive series of time-frequency windows in two stages. Firstly, the surface wave fundamental mode is extracted via phase match filtering and is used to obtain path average perturbations in shear radial anisotropy and isotropic shear wave velocity from a smoothed combination of the 1-D mantle model ak135 and the crustal model CRUST1.0. These perturbations establish a new initial model, which is subsequently used to estimate the path averaged radial anisotropy model that leads to the best fit between the observed trace and the synthetic waveform obtained by summing all overtones (up to n = 20). An iterative, regularized least squares inversion is used to invert for 3-D radially anisotropic mantle structure. Uncertainties are automatically quantified and used to interpret resolved seismic structures. Preliminary results are compared to previous tomographic models of the Atlantic region.

How to cite: Harris, K., Witek, M., Ferreira, A. M. G., Chang, S.-J., and Miranda, M.: Surface wave mantle anisotropy tomography of the Azores-Madeira-Canaries region using UPFLOW data: initial results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16613, https://doi.org/10.5194/egusphere-egu24-16613, 2024.

EGU24-19546 | Posters on site | SM3.2

Decoding Ocean Depths: Machine Learning Insights into Tidal Dynamics with UPFLOW’s OBS Data 

Carlos Corela, Alex Saoulis, Maria Tsekhmistrenko, Afonso Loureiro, Miguel Miranda, and Ana Ferreira

The iReverb project explores technical methodologies employed in the UPFLOW project, which addresses the challenges associated with tidal-induced noise on Ocean Bottom Seismometers (OBS) deployed in the North Atlantic Ocean. OBS sensors, unlike those on land stations, are exposed to oceanic currents, whose coupling with the instruments induces reverberations in the recordings. This project showcases a method for exploration of reverberations of tidally-modulated current-induced noise across different OBS types around the Azores, Madeira and Canaries region. The overarching objective is to present a comprehensive technical framework to enhance our understanding of Ocean Bottom Circulation (OBC), providing insights for calibrating current models. A central aspect of this project is the proposed utilisation of machine learning (ML) algorithms for automating the mapping of resonances and obtaining a proxy for OBC.

Here, we present the iReverb methodology, involving manual curation of a pixel-level annotated spectrogram dataset, after this, a ML classifier is trained to identify features in each spectrogram (known as supervised semantic segmentation). To begin with, 15-minute spectrograms between 1-20 Hz are manually annotated using an open-source labelling tool. A deep Convolutional Neural Network (CNN), consisting of a ResNet Encoder, a UNet decoder, and a pixel-wise classification head, is then trained to classify features in each spectrogram using supervised learning. We explore the various factors, such as architecture changes to the CNN, that contribute to improving the model performance for annotating key features. We also discuss insights into attempted alternatives to standard supervised learning (semi-supervised and synthetic labels).

Finally, we discuss the results and evaluate the effectiveness of the ML/DL approach in mapping resonances, demonstrating its potential in utilising resonances as signals for tracking ocean currents (and whales). 

This project was funded by the UPFLOW project (ERC grant 101001601). This work was partially funded by FCT I.P./MCTES through PIDDAC (UIDB/50019/2020, UIDP/50019/2020 and LA/P/0068/2020).

How to cite: Corela, C., Saoulis, A., Tsekhmistrenko, M., Loureiro, A., Miranda, M., and Ferreira, A.: Decoding Ocean Depths: Machine Learning Insights into Tidal Dynamics with UPFLOW’s OBS Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19546, https://doi.org/10.5194/egusphere-egu24-19546, 2024.

EGU24-21685 | Orals | SM3.2

Imaging of the West Indian Ocean Subsurface using Compliance from Ocean-Bottom Stations  

Mohammad-Amin Aminian, Eleonore Stutzmann, Wayne C Crawford, and Jean-Paul Montagner

This research focuses on deriving the compliance function from data collected by broadband ocean-bottom stations (OBS) during the RHUM- RUM experiment in the Indian Ocean. The primary objective is to determine the shear velocity structure beneath the ocean floor, a task essential for understanding the geological features of regions where data is sparse. The methodology revolves around analyzing the compliance function, a measure of the seafloor’s deformation in response to infra-gravity pressure signals at low frequencies (0.003 to 0.04 Hz). The compliance function, which represents the transfer function between vertical displacement and pressure, is greatly influenced by the shear velocity of the oceanic sub-structure beneath the station.

Our approach included several processing steps applied to the OBS data. These steps encompassed the removal of glitches, filtering out global and local seismic events, minimizing tilt effects, calibrating pressure gauges, and performing a linear search in the frequency and coherence domains to identify the optimal data window. The compliance function was computed using data recorded over 13 months in 2012 by the RHUM-RUM experiment’s broadband OBS near La Reunion Island, strategically placed at depths ranging from 3 to 5 km, predominantly over the central and southwest Indian Ridge.

Subsequently, we performed depth-velocity inversion of the compliance function using the Metropolis-Hastings algorithm and determined the oceanic crustal shear velocity structure up to a depth of 8 km.

This inversion process verified the compliance function’s stability and reliability throughout the observation period. Additionally, we developed specialized software, ’Compy’ designed to automate the processing steps required for this study, thereby enhancing efficiency and accuracy in seafloor compliance analysis. This research contributes significantly to our understanding of subsurface structures in marine environments, particularly in regions with limited data availability.

How to cite: Aminian, M.-A., Stutzmann, E., Crawford, W. C., and Montagner, J.-P.: Imaging of the West Indian Ocean Subsurface using Compliance from Ocean-Bottom Stations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21685, https://doi.org/10.5194/egusphere-egu24-21685, 2024.

EGU24-3477 | Posters on site | SM3.4

Status and Outlook of ORFEUS Data Services, Products and Activities to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region and Beyond 

Carlo Cauzzi, John Clinton, Wayne Crawford, Susana Custódio, Sebastiano D'Amico, Christos Evangelidis, Christian Haberland, Anastasia Kiratzi, Lucia Luzi, Petr Kolínský, Zafeiria Roumelioti, Jonathan Schaeffer, Karin Sigloch, Reinoud Sleeman, and Angelo Strollo

ORFEUS (Observatories and Research Facilities for European Seismology, http://orfeus-eu.org/) is a non-profit foundation that promotes seismology in the Euro-Mediterranean area and beyond through the collection, archival and distribution of seismic waveform data, metadata, and associated services and products. The data and services are collected or developed at national level by more than 60 contributing Institutions. They are further developed, integrated, standardised, homogenised and promoted through ORFEUS. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in managing digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and data management; (d) the promotion of open access to seismic waveform data, products and services for the broader solid Earth science community. These goals are achieved through the development and maintenance of data services targeted to a broad community of seismological data users, ranging from earth scientists to earthquake engineering practitioners. Three Service Management Committees (SMCs) are consolidated within ORFEUS, devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated waveform Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/); the European mobile instrument pools (https://orfeus-eu.org/data/mobile/). Products and services for computational seismologists are also considered for integration in the ORFEUS domain. ORFEUS services currently provide access to the waveforms acquired by ~ 24,000 stations, including dense temporary experiments (e.g. AdriaArray; https://orfeus.readthedocs.io/en/latest/adria_array_main.html), with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by the various ORFEUS institutions. Web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear policies and licenses, and acknowledging the crucial role played by data providers, who are part of the ORFEUS community. There are significant efforts by ORFEUS participating institutions to enhance the existing services to tackle the challenges posed by Big Data, with emphasis on data quality, improved user experience, and implementation of strategies (e.g. Cloud) for scalability, high-volume data access and archival. ORFEUS actively encourages interoperability and integration of multidisciplinary datasets in seismological and Earth Science workflows. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group (UAG), which comprises selected European Earth scientists with expertise on a broad range of disciplines. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal (https://www.ics-c.epos-eu.org/). ORFEUS is one of the founding Parties and a fundamental pillar of EPOS Thematic Core Service (TCS) for Seismology. ORFEUS and its community are actively involved in EC projects (http://www.orfeus-eu.org/organization/projects/), notably Geo-INQUIRE (https://www.geo-inquire.eu/) and DT-GEO (https://dtgeo.eu/) in 2024.

How to cite: Cauzzi, C., Clinton, J., Crawford, W., Custódio, S., D'Amico, S., Evangelidis, C., Haberland, C., Kiratzi, A., Luzi, L., Kolínský, P., Roumelioti, Z., Schaeffer, J., Sigloch, K., Sleeman, R., and Strollo, A.: Status and Outlook of ORFEUS Data Services, Products and Activities to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region and Beyond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3477, https://doi.org/10.5194/egusphere-egu24-3477, 2024.

EGU24-4414 | ECS | Posters on site | SM3.4

Initiation of the Seismic Network Expansion and Modernization in Ukraine 

Liudmyla Farfuliak, Tetiana Amashukeli, Andrea Chiang, Kevin Mackey, Oleksandr Haniiev, Bohdan Kuplovskyi, Kasey Aderhold, Daniel Burk, Vasyl Prokopyshyn, and Kostiantyn Petrenko

The seismic hazard department and department of the Carpathian region seismicity of the Subbotin Institute of Geophysics of the National Academy of Science of Ukraine, with the support and collaboration of the U.S. Department of Energy, Lawrence Livermore National Laboratory, Michigan State University, and the EarthScope Consortium had done first steps to expand the Ukrainian National Seismic Network (UT) through the installation of permanent broadband seismic stations in the territory of Ukraine.

The main goal of the Seismic Network Expansion and Modernization in Ukraine is to improve regional network coverage by making high-quality data from new stations openly available to the global scientific community in real time. It will strengthen national seismic monitoring and earthquake response capabilities in Ukraine by upgrading and expanding the national networks with high-quality broadband seismometers and strong motion sensors. It will emphasize data quality, real-time data exchange, and network sustainability through training in best practices on station site selection, installation, data management, and network operation.

To maximize the effectiveness of investigating existing and new seismic sites, multiple factors must be considered during the initial selection, preparation, and installation of new seismic stations. One critical component during the site selection process of any seismic network is an assessment of the seismic noise level at potential sites. The capacity of any seismic station to detect earthquakes and record high quality waveforms will be determined by the signal and noise characteristics of the site. Proper site selection is strongly related to the network's region and can be a critical issue. Besides the earth’s natural background noise, there are other noise sources to consider like those related to infrastructure close by (roads, traffic, mining activity, tenants, etc.). The goal of this work is to conduct noise surveys that can be quickly deployed in order to efficiently evaluate potential sites for the installation permanent seismic stations.

An initial noise survey was conducted at two sites: one at an existing site LUBU (near Liubeshka village, Lviv district) and one at a new site SUGL (near Mala Uhol`ka village, Zakarpattia district). We analyzed, and report the data in the form of both time-history examples and standardized Probability Density Function noise plots. Seismic spectral analysis based on the calculation of Power Spectral Density distribution using a Probability Density Function by McNamara approach.

How to cite: Farfuliak, L., Amashukeli, T., Chiang, A., Mackey, K., Haniiev, O., Kuplovskyi, B., Aderhold, K., Burk, D., Prokopyshyn, V., and Petrenko, K.: Initiation of the Seismic Network Expansion and Modernization in Ukraine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4414, https://doi.org/10.5194/egusphere-egu24-4414, 2024.

EGU24-7986 | ECS | Posters on site | SM3.4

SDQ (Seismic Data Quality): a Python project for seismo-accelerometric data quality check 

Fabio Varchetta, Marco Massa, Rodolfo Puglia, Peter Danececk, Sandro Rao, Alfonso Mandiello, and Davide Piccinini

In recent years, significant attention has been devoted both to seismic data processing and data quality procedures. At the Italian scale, EIDA Italia (https://eida.ingv.it/it/getdata) and ISMDq (http://ismd.mi.ingv.it/quality.php) represent the web portals currently available for checking seismic data quality. In this work, we introduce the SDQ (Seismic Data Quality) project, a new open-source Python-based tool, designed for the automatic data quality check of sismo-accelerometric stations considering both selected earthquakes and continuous data streams. Regarding earthquake data, the quality of individual waveforms is assessed by initially comparing – at first - the ground motion parameters derived from co-located accelerometers and velocimeters. SDQ operates by using a simple external input file including the INGV event-id and both station and network codes. Event information, station metadata, and waveforms are obtained from FDSN (https://www.fdsn.org) web services (https://www.fdsn.org/webservices/). Each single waveform is assigned to a quality class ranging from A (high quality) to D (data to be rejected) based on time- and frequency-dependent algorithms. Classification thresholds were empirically obtained by combining visual signal inspection and statistical analysis considering 15.000 waveforms recorded in Italy from 2012 to 2023 by IV (National Seismic Network, https://www.fdsn.org/networks/detail/IV/) and MN (MedNet network, https://www.fdsn.org/networks/detail/MN/) sismo-accelerometric stations. Concerning continuous data streams, mini-seed recording signals are analyzed at each selected station to set empirical thresholds considering several data metrics (i.e. frequency-dependent Root Mean Square, RMS, and Power Spectral Density, PSD) and data availability information (i.e. % gap and data availability, sum of gaps, maximum gap etc.) to build a station-quality archive. Users can select and build target time histories for each network, station, data stream and single ground motion component related to the selected input data included in a local mini-seed archive representing the starting point of the procedure. SDQ finally provides summary tables for both earthquake and continuous data, collecting all relevant parameters for each processed waveform and data stream, along with explanatory text files (log and warning files), allowing the user to better evaluate the results. Although SDQ is currently under development, now it is freely available and  downloadable at  https://gitlab.rm.ingv.it/EIDA/quality/sdq

How to cite: Varchetta, F., Massa, M., Puglia, R., Danececk, P., Rao, S., Mandiello, A., and Piccinini, D.: SDQ (Seismic Data Quality): a Python project for seismo-accelerometric data quality check, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7986, https://doi.org/10.5194/egusphere-egu24-7986, 2024.

EGU24-12258 | Posters on site | SM3.4

The automatic seismic event bulletin of the Swedish National Seismic Network 

Michael Roth, Gunnar Eggertsson, Peter Schmidt, Hossein Shomali, Behzad Oskooi, and Björn Lund

The Swedish National Seismic Network (SNSN) currently operates 67 permanent and 13 temporary broadband seismic stations. All stations transmit continuous realtime data to the data centre in Uppsala, and data streams of about 40 stations are automatically forwarded to subscribing institutes in the neighboring countries and to ORFEUS. In addition to the SNSN stations we receive realtime data from about 120 stations located in Norway, Finland, Denmark, Germany, Poland, the Baltic States, and Russia. 

SNSN processes the waveform data of this virtual network of about 200 stations using the SeisComp and Earthworm systems in parallel. Both systems are set up to be very sensitive in order to detect as small events as possible, which also increases the probability of generating spurious events. In order to screen out spurious events we generate a common bulletin which contains events that have been located by both systems independently. Our common bulletin is very reliable (no spurious events during the last 1.5 years), captures events down to about ML = 1 and contains almost all events with ML > 1.5 in Fennoscandia.

All events in the common bulletin are automatically classified by an artificial neural network as earthquakes, blasts or mining-induced events. The classifier has been developed in the framework of a PhD project, and was implemented into the SNSN processing queue during 2023 (Eggertsson et al, "Earthquake or Blast? Classification of Local-Distance Seismic Events in Sweden using Fully-Connected Neural Networks", accepted GJI 2024). It has been thoroughly tested, and, comparing the automatic classification with analyst-reviewed classification, we found a 97% match

Since December 2023, SNSN provides the automatic common bulletin as a simple webpage https://www.snsn.se/combullUTC/ - mainly for the general public and for quick reference. For the seismological community, SNSN has set up an automatic real-time forwarding of complete event parameters for all events with ML >= 2 to the European-Mediterranean Seismological Centre.

How to cite: Roth, M., Eggertsson, G., Schmidt, P., Shomali, H., Oskooi, B., and Lund, B.: The automatic seismic event bulletin of the Swedish National Seismic Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12258, https://doi.org/10.5194/egusphere-egu24-12258, 2024.

EGU24-12520 | Posters on site | SM3.4

Data quality of large dense seismic networks – lessons learnt from AlpArray and application to AdriaArray 

Petr Kolínský, Luděk Vecsey, Johannes Stampa, Felix Eckel, Tena Belinić Topić, the AlpArray Working Group, and the AdriaArray Seismology Group

Large dense seismic networks popping up around the world in the last two decades enable studying the wave propagation and structure of the Earth with unprecedented details. Hundreds of broadband seismic stations spaced by tens of kilometers produce large amounts of data, which is usually processed by automatic routines. The data is no longer supervised by seismologists on a detailed level of every record as thousands of hours of data are handled at once. Ensuring the quality of data and accompanying metadata is nowadays a discipline by and of itself. Besides the classical techniques, which investigate the properties of data at a single station, large dense seismic networks allow for a multi-station approach to review the quality of the data. The diagnostic tools of multi-station methods are based on the detection of outlying stations/records among many others. Properties of the wavefield of wavelengths longer than the station spacing vary smoothly and hence comparing the measurement at neighboring stations allows for identifying anomalous behaviors. These methods work under the assumption that most of the (meta-) data is correct, and therefore a small number of outliers can be detected. Thus, not only do large dense seismic networks contribute to research, which is their primary goal, but thanks to the design of these networks, data quality can also be tested more precisely than before. We review both types of techniques, showing examples of the AlpArray experiment (2015 - 2022), and discussing the development of the approaches over the years to what is nowadays applied to the AdriaArray Seismic Network. AdriaArray experiment started in 2022 and encompasses now around 1000 permanent as well as over 430 temporary broadband stations. We show how the availability and retrievability of the data are checked, how amplitude and phase information from the ambient and deterministic wavefields are used to assess the correctness of metadata and how we represent the results of these tests in maps and tables. The purpose of these tests is aimed in both directions: towards the users, so that they are aware of potential issues, as well as towards the station operators so that they can be notified and asked to fix the detected problems.

How to cite: Kolínský, P., Vecsey, L., Stampa, J., Eckel, F., Belinić Topić, T., Working Group, T. A., and Seismology Group, T. A.: Data quality of large dense seismic networks – lessons learnt from AlpArray and application to AdriaArray, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12520, https://doi.org/10.5194/egusphere-egu24-12520, 2024.

EGU24-12895 | Posters on site | SM3.4

MUDA: the dynamic geophysical and geocehmical multiparametric database 

Marco Massa, Elisa Ferrari, Andrea Rizzo, Sara Lovati, and Lucia Luzi

MUDA (geophysical and geochemical MUltiparametric DAtabase) is a new infrastructure of the National Institute of Geophysics and Volcanology (INGV, www.ingv.it) serving geophysical and geochemical multiparametric data, designed and developped in the framework of Dynamic Planet -Working Earth project (https://progetti.ingv.it/it/pian-din).

MUDA is a dynamic and relational database based on MySQL (https://www.mysql.com) with a web interface realised in php (https://www.php.net) using a responsive design technique. The multi-parametric data are stored and organised using a table-structure able of correlating different types of data that allow possible future integration with new type of data acquired through both real-time and off-line transmission vectors.

MUDA collects information from different types of sensors, such as seismometers, accelerometers, hydrogeochemical sensors, sensors for measuring the flux of carbon dioxide on the ground (CO2), sensors for detecting the concentration of Radon gas and weather stations with the aim of making possible correlations between seismic phenomena and variations in environmental parameters such as the level of groundwater as well as its temperature and electrical conductivity.

MUDA archives and publishes data of multiparametric stations belonging both to permanent (i.e. the National Seismic Network, RSN, https://www.fdsn.org/networks/detail/IV/) or temporary (e.g. PDnet, Massa et al., 2021, https://www.fdsn.org/networks/detail/ZO_2021/) INGV seismic networks, as well as data from a multi-parametric Salse di Nirano Reserve (MO) site in cooperation with the PD PROMUD 2023-2025 (Definition of a multidisciplinary monitoring PROtocol for MUD volcanoes) project and two additional multi-parametric sites installed in the inter-mountain basin of Norcia, as a part of the GEMME 2023-2025 project. Data from Radon stations belong to the INGV-IRON national network (Italian Radon Monitoring Network, https://www.ingv.it/en/monitoring-and-infrastructure/monitoring-networks/ingv-and-its-networks/iron).

MUDA daily publishes multi-parametric data updated to the previous day and offers the chence to view and download dynamic time series for all available data and for different periods, up to a maximum of 30 days. For longer periods, users can request data to muda@ingv.it.

MUDA is now published at http://muda.mi.ingv.it

How to cite: Massa, M., Ferrari, E., Rizzo, A., Lovati, S., and Luzi, L.: MUDA: the dynamic geophysical and geocehmical multiparametric database, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12895, https://doi.org/10.5194/egusphere-egu24-12895, 2024.

EGU24-13131 | Posters on site | SM3.4

Towards a community standard for DAS metadata: Latest advances within the Geo-INQUIRE project 

Javier Quinteros, Gilda Currenti, Michele Prestifilippo, John Clinton, Pascal Edme, Christopher Wollin, Diane Rivet, Shane Murphy, Jonathan Schaeffer, Helle Pedersen, and Angelo Strollo

In the last 5 years, the seismological community has experienced an impressive growth in the novel Distributed Acoustic Sensing (DAS) technique, in terms of both the number of experiments and the generated data volume. DAS experiments can generate data at a much finer resolution in space and time, than is seen with standard acquisition techniques. This creates challenges not only for data centres regarding the data management, but also for users that need to access and process this data. The current seismological standards for data and metadata formats, as well as community services specifications, are not capable of handling these datasets in an effective way - not unexpected considering that data volumes and ‘station’ numbers are orders of magnitude larger than typical broad-band experiments.

Within the context of the “Geosphere INfrastructures for QUestions into Integrated REsearch” project (Geo-INQUIRE, https://www.geo-inquire.eu/), we have defined a roadmap to advance towards community standards for some of these aspects. The main objective of improving the FAIRness of these datasets was separated in 3 steps. First, we defined how to archive downsampled versions of the datasets in standard community formats (i.e. miniseed and StationXML). Second, we wanted to support the definition (and foster the adoption) of a new metadata standard for DAS experiments based on the outcome of the DAS Research Coordination Network group (DAS-RCN), an initiative led by US researchers. And finally, we wanted to work on the definition of a data format capable of providing fast processing on the data centre side, as well as being able to provide the data to the user to be processed elsewhere.

We worked with 3 datasets from the Global DAS Month (February 2023), acquired by INGV, ETH and GFZ. These datasets had been published and made available in different non-standard formats. We used these experiments as test cases to later apply this workflow to the datasets generated by the Transnational Access Calls of this project at a variety of Research Infrastructures across Europe (e.g. at Etna, Bedretto, Ligurian, Madeira, Irpinia, and others).

Regarding the data volume and lack of standardisation, we have improved “dastools”, a software package developed at GFZ, to read DAS data in proprietary formats from different manufacturers and convert it to standard miniseed. Downsampling in time and space it provides a reduced version ready to be archived in seismological data centres.

Regarding metadata formats, we included in “dastools” the support for the DAS-RCN proposal, discussed and agreed within the community during the last 3 years. We can generate a first draft version of the metadata based on the information available in the raw data of the experiment. We also added a converter to StationXML (still beta) in order to support each step of the archival of a downsampled version of the DAS data.

We plan to work soon on the definition of a data format for this type of experiment as it is a key part of our project.

In parallel, we’ve just started the development of a Seedlink plugin (real-time transmission) to be deployed and tested at interrogators.

How to cite: Quinteros, J., Currenti, G., Prestifilippo, M., Clinton, J., Edme, P., Wollin, C., Rivet, D., Murphy, S., Schaeffer, J., Pedersen, H., and Strollo, A.: Towards a community standard for DAS metadata: Latest advances within the Geo-INQUIRE project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13131, https://doi.org/10.5194/egusphere-egu24-13131, 2024.

EGU24-13158 | Posters on site | SM3.4

The prospects of the Ukrainian seismic network:  Introducing a Low-Cost Seismic Network Initiative in Ukraine 

Tetiana Amashukeli, Luca Malatesta, Liudmyla Farfuliak, Oleksandr Haniiev, Bogdan Kuplovskyi, Vasyl Prokopyshyn, and Kostiantyn Petrenko

Seismic activity in Ukraine varies across regions with notable active zones in the Carpathians and Crimean-Black Sea segments. Southwest Ukraine is affected by the Vrancea seismic zone (Romania) and demands attention, alongside rare but potentially powerful seismic events in the stable Ukrainian shield. Mining and industrial activities also induce ground vibrations (Mw 2.5–4) in otherwise stable areas. Although major destructive earthquakes in Ukraine are infrequent, the cumulative impact of smaller seismic events can shape the geological and geophysical landscape of the region.

An effective seismic network is crucial for safety and research in Ukraine. Yet, the existing seismic network at the Institute of Geophysics of National Academy of Science of Ukraine faces numerous challenges, limiting its capacity to provide accurate seismic information. In addition, the Institute of Geophysics faces a demographic imbalance, with a critical shortage of younger scientists entering the field. This knowledge gap poses implications for the future of scientific research in Ukraine.

In response to these challenges, and considering the Russian invasion, we opted to distribute 28 budget Raspberry Shake Seismographs across schools and universities in Ukraine. Initially, these budget seismometers serve as a short-term solution for seismic data collection. Acknowledging the pros and cons of these stations in contrast to broadband sensors, it's noteworthy that their simplicity in installation, low cost, and near-real-time data transmission make them as a suitable option during the conflict in identifying and characterizing local and regional events.

This initiative also directly supports science teaching from middle to high school in Ukraine. Integrating seismometers into schools cultivates education based on real-time seismic records, familiarizing students with scientific data. The aim is to ignite students’ interest, nurturing a curiosity not only in seismology but also in science as a whole. This goal is accomplished not just through presentations and lessons but also through hands-on involvement, allowing students to take ownership by installing a seismometer and consistently monitoring its output. The analysis of time series seismic signals, regardless of their source – whether earthquakes or artificial noise – forms a fundamental component of any seismology-focused educational program. Currently, such initiatives are lacking in Ukrainian educational institutions.

Raspberry Shake 3D Seismographs have been installed at the Institute of Geophysics in Kyiv, Lviv Polytechnic National University, and Ivan Franko National University of Lviv. Two RS seismometers are at the Mykolaiv Water Hub to support the establishment of the Mykolaiv Innovation Lab in south Ukraine. In November 2023, educational materials for seismology at middle and high school levels in Ukraine were created with the assistance of the GFZ German Research Centre for Geosciences. This approach not only will help students develop practical skills but also provides a starting point for exploring numerical methods and coding at the university level.

How to cite: Amashukeli, T., Malatesta, L., Farfuliak, L., Haniiev, O., Kuplovskyi, B., Prokopyshyn, V., and Petrenko, K.: The prospects of the Ukrainian seismic network:  Introducing a Low-Cost Seismic Network Initiative in Ukraine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13158, https://doi.org/10.5194/egusphere-egu24-13158, 2024.

EGU24-14842 | ECS | Posters on site | SM3.4

Development of the new seismic network of the IGS, Armenia 

Gevorg Babayan, Elya Sahakyan, Hektor Babayan, Mikayel Gevorgyan, and Lilit Sargsyan

The Republic of Armenia and the neighboring areas are located in the central part of theArabia-Eurasia collision zone, which is characterized by active seismicity.Over the past decade, the Institute of Geological Sciences (IGS) of NAS RA has developed an advanced and dense seismic network.To develop the local seismic network, the Institute of Geological Sciences in collaboration with the National Taiwan University and Institute of Earth Sciences, Academia Sinica (Taiwan) established 11 seismic stations with broadband seismometers and 6 cGPS (continuous) stations. Data from the existing seismic stations were collected, archived and treated, and main earthquake parameters were determined; the conducted works included catalogue maintenance, recalculation of the main earthquake data, calculation of seismic tomography with the input of recalculated and updated data, and adjustment of the three-dimensional (3D) velocity model for the area of the RA.

Starting from 2017, the Institute of Geological Sciences has participated in two partner ISTC projects: A-2334 Project (Transect) “The Uplift and Seismic Structure of the Greater Caucasus” and KR-2452 Project (SNECCA) “Seismic Network Expansion in the Caucasus and Central Asia” with support from the U.S. Department of Energy.  In the framework of the indicated projects, 32 seismic stations with broadband seismometers were established along with 8 seismic borehole stations with fully broadband seismometers (Real Time) and 8 strong motion sensors. These two projects are implemented through the Seismic Targeted Initiative of the International Science and Technology Center and the Science and Technology Center in Ukraine.The records collected from the eight (8) already operational permanent seismic stations of the indicated network are in real-time mode sent to the International Seismology Center of the IRIS (Incorporated Research Institutions for Seismology). To download and archive the database of seismic stations, a new computer server was acquired under the project, and all required configurations were made to provide for its uninterrupted operation. Seiscomp software set is applied to produce automatic solutions for earthquakes recorded within the region. Adjustments and recalculations of the automatic earthquake solutions are implemented to produce the resulting main earthquake parameters with uncertainties reduced to the rate as low as possible. The collected data from all existing stations are widely used to determine and to re-estimate the main parameters of earthquake occurring in Armenia and in surrounding territories. These data are included in local bulletins and catalogues.For strong motions, the on-going research includes processing of design accelerograms, preparation and analysis of hazard response spectra (RS), selection of the actually recorded (real) acceleration time-history, and spectral matching of the time-history to the hazard response spectrum with application of Seismosoft (Earthquake Engineering Software Solutions, SeismoMatch, SeismoSignal, SeismoSelect, SeismoSpec) software set.All the results obtained from the data seismic stations mentioned above are used for the purposes of scientific research and are summarized in articles.

How to cite: Babayan, G., Sahakyan, E., Babayan, H., Gevorgyan, M., and Sargsyan, L.: Development of the new seismic network of the IGS, Armenia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14842, https://doi.org/10.5194/egusphere-egu24-14842, 2024.

EGU24-17386 | Posters on site | SM3.4

Güralp Data Centre Software for Easy Mass Data Acquisition and Station Metadata Monitoring 

Neil Watkiss, Philip Hill, Ella Price, Connor Foster, Aaron Clark, Federica Restelli, and James Lindsey

Güralp Data Centre (GDC) interface offers ‘one click’ tools to configure instruments to stream data to a central (typically cloud based) server where it is saved in miniSEED in configurable folder structures. This application is particularly important for operators dealing with large volumes of seismic waveform data from regional/national networks.

Additionally, the data can be transmitted to downstream processors such as Earthworm or SeisComP for more advanced seismic monitoring and data analysis. GDC has a simple interface to set up and monitor the operation of the network and is easy to implement into existing systems and networks with minimal configuration as industry standard protocols are employed throughout.

An integrated VPN/Tunnel circumvents Network Address Translations (NATs) present in internet modems and ADSL connections, providing the facility to remotely update digitizer firmware and upload configuration files to multiple units simultaneously.

Long term latency monitoring, network outages and bandwidth usage are captured and displayed in a number of applets that further simplify maintenance of large networks. The GDC dashboard allows network managers to view data integrity over time so that latency performance can be monitored.

Trigger events from instruments can be recorded and displayed on a map as part of a range of features dedicated to EEW implementations. This information is conveyed using the open Common Alert Protocol (CAP). The CAP messages are created by individual station or sub-network triggers and contain important parameters such the on-site recorded PGA, PGV and PGD, providing the lowest possible latency for network early warning.

How to cite: Watkiss, N., Hill, P., Price, E., Foster, C., Clark, A., Restelli, F., and Lindsey, J.: Güralp Data Centre Software for Easy Mass Data Acquisition and Station Metadata Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17386, https://doi.org/10.5194/egusphere-egu24-17386, 2024.

EGU24-17749 | ECS | Posters on site | SM3.4

The Italian multiparametric network for detection and monitoring of earthquake-related crustal fluids alterations 

Elisa Ferrari, Marco Massa, Andrea Luca Rizzo, Sara Lovati, and Federica Di Michele

Seismic signals coupling to physical (e.g., temperature, pH, Eh, electrical conductivity, flow rate) and geochemical changes in ground and spring waters as well as variations in soil flux regimes (e.g., CO2, CH4, radon) represent a valuable tool to better understand the interaction between tectonics and crustal fluids dynamics (e.g., Italiano et al., 2001, 2004; Wang and Manga, 2021; Chiodini et al., 2020; Gori and Barberio, 2022 and references therein). Pre-, co- and post-seismic modifications are markers of the local tectonic stress acting in the crust and are extremely site-specific due to the local geological and lithological features besides being simultaneously influenced by other environmental conditions (e.g., meteorological and climatic). Therefore, local continuous monitoring of all the involved parameters is needed to delineate crustal fluids response to seismicity site by site.
Multiparametric stations have been set up in Italy starting from the end of 2021, placed on the major seismogenic structures, and widely distributed among the Alps, Apennines and Pianura Padana. They are equipped with: (i) sensors installed in water wells measuring water level, temperature, and electrical conductivity; (ii) meteorological sensors measuring atmospheric pressure, temperature, rain, humidity, wind speed and direction; (iii) seismic sensors providing accelerometric and velocimetric datasets; (iv) radon sensors; (v) CO2 soil flux chamber. 
Data are transmitted in near real-time to an ad hoc developed dynamic relational database (MUDA-geophysical and geochemical MUltiparametric DAtabase) and displayed in a dedicated website (http://muda.mi.ingv.it). The built-in philosophy is to easily compare distinct parameters from the various sensors and possibly recognize cause-effect relationships among them. 
To our knowledge, our new multiparametric network is the first developed in Italy showing all these features.
A statistic approach is also applied to the time-series to investigate intra-annual and inter-annual trends and correlations among different parameters. Alternative methods (e.g., signal decomposition, spike detection) will be presented and discussed. 

References
-Chiodini G., Cardellini C., Di Luccio F., Selva J., Frondini F., Caliro S., Rosiello A., Beddini G., Ventura G., 2020: Correlation between tectonic CO2 Earth degassing and seismicity is revealed by a 10-year record in the Apennines, Italy. Science Advances, https://www.science.org/doi/10.1126/sciadv.abc2938
-Gori F., Barberio M.D., 2022: Hydrogeochemical changes before and during the 2019 Benevento seismic swarm in central-southern Italy. Journal of Hydrology, 604:127250
-Italiano F., Martinelli G., Nuccio P.M., 2001: Anomalies of mantle-derived helium during the 1997 – 1998 seismic swarm of Umbria-Marche, Italy. Geophysical Research Letters, 28(5):839-842
-Italiano F., Martinelli G., Rizzo A., 2004: Geochemical evidence of seismogenic-induced anomalies in the dissolved gases of thermal waters: A case study of Umbria (Central Apennines, Italy) both during and after the 1997–1998 seismic swarm. Geochemistry, Geophysics, Geosystems, 5:11, doi:10.1029/2004GC000720
-Wang C.-Y., Manga M., 2021: Water and Earthquakes. Lecture Notes in Earth System Sciences, Springer Cham, 387 pp., https://doi.org/10.1007/978-3-030-64308-9 

How to cite: Ferrari, E., Massa, M., Rizzo, A. L., Lovati, S., and Di Michele, F.: The Italian multiparametric network for detection and monitoring of earthquake-related crustal fluids alterations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17749, https://doi.org/10.5194/egusphere-egu24-17749, 2024.

EGU24-17890 | Posters on site | SM3.4

The mobile Finnish Seismic Instrument Pool 

Roméo Courbis, Gregor Hillers, Emilia Koivisto, Päivi Haapanala, Ilmo Kukkonen, Yinshuai Ding, Thomas Fordell, Suvi Heinonen, Niina Junno, Anssi Juntunen, Kari Komminaho, Elena Kozlovskaya, Jussi Leveinen, Kari Moisio, Jyri Näränen, Tahvo Oksanen, Pietari Skyttä, Eija Tanskanen, and Timo Tiira

We report on establishing the Finnish mobile seismic instrument pool that is owned and operated by seven Finnish academic and research institutions. The pool infrastructure is funded by the Research Council of Finland, through the FLEX-EPOS project and under the FIN-EPOS umbrella. It is financing the build-up stage and started in 2021 with an end in 2024. By then the seismic instrumentation is anticipated to include 46 Güralp broadband seismometers, 5 Güralp accelerometers, and 1197 and 70 Geospace and SmartSolo self-contained geophone units, respectively. It is making this probably the largest coherent mobile seismic instrument pool in Europe in the public sector. The pool supports domestic and international collaborative projects of temporary deployments to enhance data-driven subsurface and environmental applications. Those deployments are for active or passive experiments and can last a few days up to a few years. The acquisition of such pool is motivated and facilitated by the advent of efficient data storage and transmission and powerful computing systems; progress in the understanding of the seismic wavefield coupled with the development of new types of analysis techniques and algorithms; and the manufacturing of sensitive, affordable data-dense sensor systems. Despite these game-changing and promising developments, the access to many seismic sensors for large-N deployments is not pervasive. Even in developed countries, it is challenging for a single institution to acquire and maintain a sufficiently large mobile pool of instruments and ensure sustainable data production and distribution. Our report on the equipment, facilities, ownership, and governance structure, project management, and data systems is essential background information for the access to and utilization of the pool instruments, and the interaction with the support community. A discussion about best practices for establishing and maintaining a mobile pool infrastructure can benefit from our experience of building such an extensive public seismic infrastructure from the ground up, and it provides relevant information for communities considering similar research infrastructure projects. Among the many challenges and opportunities associated with establishing effective pool management and operations, we highlight the lack of a coherent community protocol to store, find, disseminate, and analyze the associated large datasets. The Finnish mobile seismic instrument pool actively engages with ORFEUS/EIDA and the Geo-INQUIRE project to contribute to developing community solutions for data discovery and accessibility.

How to cite: Courbis, R., Hillers, G., Koivisto, E., Haapanala, P., Kukkonen, I., Ding, Y., Fordell, T., Heinonen, S., Junno, N., Juntunen, A., Komminaho, K., Kozlovskaya, E., Leveinen, J., Moisio, K., Näränen, J., Oksanen, T., Skyttä, P., Tanskanen, E., and Tiira, T.: The mobile Finnish Seismic Instrument Pool, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17890, https://doi.org/10.5194/egusphere-egu24-17890, 2024.

EGU24-24 | Orals | NP4.1

The fractional Sinusoidal wavefront Model (fSwp) for time series displaying persistent stationary cycles 

Gael Kermarrec, Federico Maddanu, Anna Klos, and Tommaso Proietti

In the analysis of sub-annual climatological or geodetic time series such as tide gauges, precipitable water vapor, or GNSS vertical displacements time series but also temperatures or gases concentrations, seasonal cycles are often found to have a time-varying amplitude and phase.

These time series are usually modelled with a deterministic approach that includes trend, annual, and semi-annual periodic components having constant amplitude and phase-lag. This approach can potentially lead to inadequate interpretations, such as an overestimation of Global Navigation Satellite System (GNSS) station velocity, up to masking important geophysical phenomena that are related to the amplitude variability and are important for deriving trustworthy interpretation for climate change assessment.

We address that challenge by proposing a novel linear additive model called the fractional Sinusoidal Waveform process (fSWp), accounting for possible nonstationary cyclical long memory, a stochastic trend that can evolve over time and an additional serially correlated noise capturing the short-term variability. The model has a state space representation and makes use of the Kalman filter (KF). Suitable enhancements of the basic methodology enable handling data gaps, outliers, and offsets. We demonstrate our method using various climatological and geodetic time series to illustrate its potential to capture the time-varying stochastic seasonal signals.

How to cite: Kermarrec, G., Maddanu, F., Klos, A., and Proietti, T.: The fractional Sinusoidal wavefront Model (fSwp) for time series displaying persistent stationary cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-24, https://doi.org/10.5194/egusphere-egu24-24, 2024.

On some maps of the first military survey of the Habsburg Empire, the upper direction of the sections does not face the cartographic north, but makes an angle of about 15° with it. This may be due to the fact that the sections were subsequently rotated to the magnetic north of the time. Basically, neither their projection nor their projection origin is known yet.

In my research, I am dealing with maps of Inner Austria, the Principality of Transylvania and Galicia (nowadays Poland and Ukraine), and I am trying to determine their projection origin. For this purpose, it is assumed, based on the archival documentation of the survey, that these are Cassini projection maps. My hypothesis is that they are Graz, Cluj Napoca or Alba Julia and Lviv. I also consider the position of Vienna in each case, since it was the main centre of the survey.

The angle of rotation was taken in part from the gufm1 historical magnetic model back to 1590 for the assumed starting points and year of mapping. In addition, as a theoretical case, I calculated the rotation angle of the map sections using coordinate geometry. I then calculated the longitude of the projection starting point for each case using univariate minimization. Since the method is invariant to latitude, it can only be determined from archival data.

Based on these, the starting point for Inner Austria from the rotation of the map was Vienna, which is not excluded by the archival sources, and since the baseline through Graz also started from there, it is partly logical. The map rotation for Galicia and Transylvania also confirmed the starting point of the hypothesis.  Since both Alba Julia and Cluj Napoca lie at about the same longitude, the method cannot make a difference there; and the archival data did not provide enough evidence. In comparison, the magnetic declination rotations yielded differences of about 1°, which may be due to an error in the magnetic model.

On this basis, I have given the assumed projections of the three maps with projection starting points, and developed a method for determining the projection starting points of the other rotated grid maps. The results suggest that there is a very high probability that the section network was rotated in the magnetic north direction, and thus provide a way to refine the magnetic declination data at that time.

With this method I managed to give new indirekt magnetic declinations data from Central-East Europe, which can help to improve the historical magnetic field models. The main reason for this is that we don’t have any measurement from that region.

Furthermore the difference beetwen the angle of the section north and the declination data from gufm1 always 0.8-1°. Maybe there are systematical data error at that region.

Supported by the ÚNKP-23-6 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.

How to cite: Koszta, B. and Timár, G.: A possible cartographical data source for historical magnetic field improvement: The direction of the section north of the Habsburg first military survey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-582, https://doi.org/10.5194/egusphere-egu24-582, 2024.

EGU24-1988 | ECS | Posters on site | NP4.1

Predictive ability assessment of Bayesian Causal Reasoning (BCR) on runoff temporal series 

Santiago Zazo, José Luis Molina, Carmen Patino-Alonso, and Fernando Espejo

The alteration of traditional hydrological patterns due to global warming is leading to a modification of the hydrological cycle. This situation draws a complex scenario for the sustainable management of water resources. However, this issue offers a challenge for the development of innovative approaches that allow an in-depth capturing the logical temporal-dependence structure of these modifications to advance sustainable management of water resources, mainly through the reliable predictive models. In this context, Bayesian Causality (BC), addressed through Causal Reasoning (CR) and supported by a Bayesian Networks (BNs), called Bayesian Causal Reasoning (BCR) is a novel hydrological research area that can help identify those temporal interactions efficiently.

This contribution aims to assesses the BCR ability to discover the logical and non-trivial temporal-dependence structure of the hydrological series, as well as its predictability. For this, a BN that conceptually synthesizes the time series is defined, and where the conditional probability is propagated over the time throughout the BN through an innovative Dependence Mitigation Graph. This is done by coupling among an autoregressive parametric approach and causal model. The analytical ability of the BCR highlighted the logical temporal structure, latent in the time series, which defines the general behavior of the runoff. This logical structure allowed to quantify, through a dependence matrix which summarizes the strength of the temporal dependencies, the two temporal fractions that compose the runoff: one due to time (Temporally Conditioned Runoff) and one not (Temporally Non-conditioned Runoff). Based on this temporal conditionality, a predictive model is implemented for each temporal fraction, and its reliability is assessed from a double probabilistic and metrological perspective.

This methodological framework is applied to two Spanish unregulated sub-basins; Voltoya river belongs to Duero River Basin, and Mijares river, in the Jucar River Basin. Both cases with a clearly opposite temporal behavior, Voltoya independent and Mijares dependent, and with increasingly more problems associated with droughts.

The findings of this study may have important implications over the knowledge of temporal behavior of water resources of river basin and their adaptation. In addition, TCR and TNCR predictive models would allow advances in the optimal dimensioning of storage infrastructures (reservoirs), with relevant substantial economic/environmental savings. Also, a more sustainable management of river basins through more reliable control reservoirs’ operation is expected to be achieved. Finally, these results open new possibilities for developing predictive hydrological models within a BCR framework.

How to cite: Zazo, S., Molina, J. L., Patino-Alonso, C., and Espejo, F.: Predictive ability assessment of Bayesian Causal Reasoning (BCR) on runoff temporal series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1988, https://doi.org/10.5194/egusphere-egu24-1988, 2024.

EGU24-3857 | ECS | Posters on site | NP4.1 | Highlight

Spatial-Temporal Analysis of Forest Mortality 

Sara Alibakhshi

Climate-induced forest mortality poses an increasing threat worldwide, which calls for developing robust approaches to generate early warning signals of upcoming forest state change. This research explores the potential of satellite imagery, utilizing advanced spatio-temporal indicators and methodologies, to assess the state of forests preceding mortality events. Traditional approaches, such as techniques based on temporal analyses, are impacted by limitations related to window size selection and detrending methods, potentially leading to false alarms. To tackle these challenges, our study introduces two new approaches, namely the Spatial-Temporal Moran (STM) and Spatial-Temporal Geary (STG) approaches, both focusing on local spatial autocorrelation measures. These approaches can effectively address the shortcomings inherent in traditional methods. The research findings were assessed across three study sites within California national parks, and Kendall's tau was employed to quantify the significance of false and positive alarms. To facilitate the measurement of ecosystem state change, trend estimation, and identification of early warning signals, this study also provides "stew" R package. The implications of this research extend to various groups, such as ecologists, conservation practitioners, and policymakers, providing them with the means to address emerging environmental challenges in global forest ecosystems.

How to cite: Alibakhshi, S.: Spatial-Temporal Analysis of Forest Mortality, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3857, https://doi.org/10.5194/egusphere-egu24-3857, 2024.

Iram Parvez1, Massimiliano Cannata2, Giorgio Boni1, Rossella Bovolenta1 ,Eva Riccomagno3 , Bianca Federici1

1 Department of Civil, Chemical and Environmental Engineering (DICCA), Università degli Studi di Genova, Via Montallegro 1, 16145 Genoa, Italy (iram.parvez@edu.unige.it,bianca.federici@unige.it, giorgio.boni@unige.it, rossella.bovolenta@unige.it).

2 Institute of Earth Sciences (IST), Department for Environment Constructions and Design (DACD), University of Applied Sciences and Arts of Southern Switzerland (SUPSI), CH-6952 Canobbio, Switzerland(massimiliano.cannata@supsi.ch).

3 Department of Mathematics, Università degli Studi di Genova, Via Dodecaneso 35, 16146 Genova, Italy(riccomag@dima.unige.it).

The deployment of hydrometeorological sensors significantly contributes to generating real-time big data. The quality and reliability of large datasets pose considerable challenges, as flawed analyses and decision-making processes can result. This research aims to address the issue of anomaly detection in real-time data by exploring machine learning models. Time-series data is collected from IstSOS - Sensor Observation Service, an open-source software that stores, collects and disseminates sensor data. The methodology consists of Gated Recurrent Units based on recurrent neural networks, along with corresponding prediction intervals, applied both to individual sensors and collectively across all temperature sensors within the Ticino region of Switzerland. Additionally, non-parametric methods like Bootstrap and Mean absolute deviation are employed instead of standard prediction intervals to tackle the non-normality of the data. The results indicate that Gated Recurrent Units based on recurrent neural networks, coupled with non-parametric forecast intervals, perform well in identifying erroneous data points. The application of the model on multivariate time series-sensor data establishes a pattern or baseline of normal behavior for the area (Ticino). When a new sensor is installed in the same region, the recognized pattern is used as a reference to identify outliers in the data gathered from the new sensor.

How to cite: Parvez, I.: Exploring Machine Learning Models to Detect Outliers in HydroMet Sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4280, https://doi.org/10.5194/egusphere-egu24-4280, 2024.

EGU24-5268 | ECS | Orals | NP4.1

Unveiling Geological Patterns: Bayesian Exploration of Zircon-Derived Time Series Data 

Hang Qian, Meng Tian, and Nan Zhang

For its immunity to post-formation geological modifications, zircon is widely utilized as chronological time capsule and provides critical time series data potential to unravel key events in Earth’s geological history, such as supercontinent cycles. Fourier analysis, which assumes stationary periodicity, has been applied to zircon-derived time series data to find the cyclicity of supercontinents, and wavelet analysis, which assumes non-stationary periodicity, corroborates the results of Fourier Analysis in addition to detecting finer-scale signals. Nonetheless, both methods still prognostically assume periodicity in the zircon-derived time-domain data. To stay away from the periodicity assumption and extract more objective information from zircon data, we opt for a Bayesian approach and treat zircon preservation as a composite stochastic process where the number of preserved zircon grains per magmatic event obeys logarithmic series distribution and the number of magmatic events during a geological time interval obeys Poisson distribution. An analytical solution was found to allow us to efficiently invert for the number and distribution(s) of changepoints hidden in the globally compiled zircon data, as well as for the zircon preservation potential (encoded as a model parameter) between two neighboring changepoints. If the distributions of changepoints temporally overlap with those of known supercontinents, then our results serve as an independent, mathematically robust test of the cyclicity of supercontinents. Moreover, our statistical approach inherently provides a sensitivity parameter the tuning of which allows to probe changepoints at various temporal resolution. The constructed Bayesian framework is thus of significant potential to detect other types of trend swings in Earth’s history, such as shift of geodynamic regimes, moving beyond cyclicity detection which limits the application of conventional Fourier/Wavelet analysis.

How to cite: Qian, H., Tian, M., and Zhang, N.: Unveiling Geological Patterns: Bayesian Exploration of Zircon-Derived Time Series Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5268, https://doi.org/10.5194/egusphere-egu24-5268, 2024.

Semi-enclosed freshwater and brackish ecosystems, characterised by restricted water outflow and prolonged residence times, often accumulate nutrients, influencing their productivity and ecological dynamics. These ecosystems exhibit significant variations in bio-physical-chemical attributes, ecological importance, and susceptibility to human impacts. Untangling the complexities of their interactions remains challenging, necessitating a deeper understanding of effective management strategies adapted to their vulnerabilities. This research focuses on the bio-physical aspects, investigating the differential effects of spring and summer light on phytoplankton communities in semi-enclosed freshwater and brackish aquatic ecosystems.

Through extensive field sampling and comprehensive environmental parameter analysis, we explore how phytoplankton respond to varying light conditions in these distinct environments. Sampling campaigns were conducted at Müggelsee, a freshwater lake on Berlin's eastern edge, and Barther Bodden, a coastal lagoon northeast of Rostock on the German Baltic Sea coast, during the springs and summers of 2022 and 2023, respectively. Our analysis integrates environmental factors such as surface light intensity, diffuse attenuation coefficients, nutrient availability, water column dynamics, meteorological data, Chlorophyll-a concentration, and phytoplankton communities. Sampling encompassed multiple depths at continuous intervals lasting three days.

Preliminary findings underscore significant differences in seasonal light availability, with summer exhibiting extended periods of substantial light penetration. These variations seem to impact phytoplankton abundance and diversity uniquely in each ecosystem. While ongoing analyses are underway, early indications suggest distinct phytoplankton responses in terms of species composition and community structure, influenced by the changing light levels. In 2022 the clear water phase during spring indicated that bloom events have occurred under ice cover much earlier than spring, while in the summer there were weak and short-lived blooms of cyanobacteria. The relationship between nutrient availability and phytoplankton dynamics, however, remains uncertain according to our data.

This ongoing study contributes to understanding the role of light as a primary driver shaping phytoplankton community structures and dynamics in these environments.  Our research findings offer insights for refining predictive models, aiding in ecosystem-specific eutrophication management strategies, and supporting monitoring efforts of Harmful Algal Blooms.

How to cite: Kaharuddin, A. and Kaligatla, R.: Comparative Study of Spring and Summer Light Effects on Phytoplankton Communities in Semi-Enclosed Fresh- and Brackish Aquatic Ecosystems., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5733, https://doi.org/10.5194/egusphere-egu24-5733, 2024.

EGU24-6065 | ECS | Orals | NP4.1

Magnetospheric time history:  How much do we need for forecasting? 

Kendra R. Gilmore, Sarah N. Bentley, and Andy W. Smith

Forecasting the aurora and its location accurately is important to mitigate any potential harm to vital infrastructure like communications and electricity grid networks. Current auroral prediction models rely on our understanding of the interaction between the magnetosphere and the solar wind or geomagnetic indices. Both approaches do well in predicting but have limitations concerning forecasting (geomagnetic indices-based model) or because of the underlying assumptions driving the model (due to a simplification of the complex interaction). By applying machine learning algorithms to this problem, gaps in our understanding can be identified, investigated, and closed. Finding the important time scales for driving empirical models provides the necessary basis for our long-term goal of predicting the aurora using machine learning.

Periodicities of the Earth’s magnetic field have been extensively studied on a global scale or in regional case studies. Using a suite of different time series analysis techniques including frequency analysis and investigation of long-scale changes of the median/ mean, we examine the dominant periodicities of ground magnetic field measurements at selected locations. A selected number of stations from the SuperMAG network (Gjerloev, 2012), which is a global network of magnetometer stations across the world, are the focus of this investigation.

The periodicities retrieved from the different magnetic field components are compared to each other as well as to other locations. In the context of auroral predictions, an analysis of the dominating periodicities in the auroral boundary data derived from the IMAGE satellite (Chisham et al., 2022) provides a counterpart to the magnetic field periodicities.

Ultimately, we can constrain the length of time history sensible for forecasting.

How to cite: Gilmore, K. R., Bentley, S. N., and Smith, A. W.: Magnetospheric time history:  How much do we need for forecasting?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6065, https://doi.org/10.5194/egusphere-egu24-6065, 2024.

EGU24-6151 | Posters on site | NP4.1

Using information-theory metrics to detect regime changes in dynamical systems 

Javier Amezcua and Nachiketa Chakraborty

Dynamical systems can display a range of dynamical regimes (e.g. attraction to, fixed points, limit cycles, intermittency, chaotic behaviour) depending on the values of parameters in the system. In this work we demonstrate how non-parametric entropy estimation codes (in particular NPEET) based on the Kraskov method can be applied to find regime transitions in a 3D chaotic model (the Lorenz 1963 system) when varying the values of the parameters. These infromation-theory-based methods are simpler and cheaper to apply than more traditional metrics from dynamical systems (e.g. computation of Lyapunov exponents). The non-parametric nature of the method allows for handling long time series without a prohibitive computational burden. 

How to cite: Amezcua, J. and Chakraborty, N.: Using information-theory metrics to detect regime changes in dynamical systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6151, https://doi.org/10.5194/egusphere-egu24-6151, 2024.

EGU24-9367 | ECS | Orals | NP4.1

Fractal complexity evaluation of meteorological droughts over three Indian subdivisions using visibility Graphs 

Susan Mariam Rajesh, Muraleekrishnan Bahuleyan, Arathy Nair GR, and Adarsh Sankaran

Evaluation of scaling properties and fractal formalisms is one of the potential approaches for modelling complex series. Understanding the complexity and fractal characterization of drought index time series is essential for better preparedness against drought disasters. This study presents a novel visibility graph-based evaluation of fractal characterization of droughts of three meteorological subdivisions of India. In this method, the horizontal visibility graph (HVG) and Upside-down visibility graph (UDVG) are used for evaluating the network properties for different standardized precipitation index (SPI) series of 3, 6 and 12 month time scales representing short, medium and long term droughts. The relative magnitude of fractal estimates is controlled by the drought characteristics of wet-dry transitions. The estimates of degree distribution clearly deciphered the self-similar properties of droughts of all the subdivisions. For an insightful depiction of drought dynamics, the fractal exponents and spectrum are evaluated by the concurrent application of Sand Box Method (SBM) and Chhabra and Jenson Method (CJM). The analysis was performed for overall series along with the pre- and post-1976-77 Global climate shift scenarios. The complexity is more evident in short term drought series and UDVG formulations implied higher fractal exponents for different moment orders irrespective of drought type and locations considered in this study. Useful insights on the relationship between complex network and fractality are evolved from the study, which may help in improved drought forecasting. The visibility graph based fractality estimation evaluation is efficient in capturing drought and it has vast potential in the drought predictions in a changing environment.

Keywords:  Drought, Fractal, SPI, Visibility Graph

How to cite: Rajesh, S. M., Bahuleyan, M., Nair GR, A., and Sankaran, A.: Fractal complexity evaluation of meteorological droughts over three Indian subdivisions using visibility Graphs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9367, https://doi.org/10.5194/egusphere-egu24-9367, 2024.

EGU24-9537 | Posters on site | NP4.1

Wavelet-Induced Mode Extraction procedure: Application to climatic data 

Elise Faulx, Xavier Fettweis, Georges Mabille, and Samuel Nicolay

The Wavelet-Induced Mode Extraction procedure (WIME) [2] was developed drawing inspiration from Empirical Mode Decomposition. The concept involves decomposing the signal into modes, each presenting a characteristic frequency, using continuous wavelet transform. This method has yielded intriguing results in climatology [3,4]. However, the initial algorithm did not account for the potential existence of slight frequency fluctuations within a mode, which could impact the reconstruction of the original signal [4]. The new version (https://atoms.scilab.org/toolboxes/toolbox_WIME/0.1.0) now allows for the evolution of a mode in the space-frequency half-plane, thus considering the frequency evolution of a mode [2]. A natural application of this tool is in the analysis of Milankovitch cycles, where subtle changes have been observed throughout history. The method also refines the study of solar activity, highlighting the role of the "Solar Flip-Flop." Additionally, the examination of temperature time series confirms the existence of cycles around 2.5 years. It is now possible to attempt to correlate solar activity with this observed temperature cycle, as seen in speleothem records [1].

[1] Allan, M., Deliège, A., Verheyden, S., Nicolay S. and Fagel, N. Evidence for solar influence in a Holocene speleothem record, Quaternary Science Reviews, 2018.
[2] Deliège, A. and Nicolay, S., Extracting oscillating components from nonstationary time series: A wavelet-induced method, Physical Review. E, 2017.
[3] Nicolay, S., Mabille, G., Fettweis, X. and Erpicum, M., A statistical validation for the cycles found in air temperature data using a Morlet wavelet-based method, Nonlinear Processes in Geophysics, 2010.
[4] Nicolay, S., Mabille, G., Fettweis, X. and Erpicum, M., 30 and 43 months period cycles found in air temperature time series using the Morlet wavelet, Climate Dynamics, 2009.

How to cite: Faulx, E., Fettweis, X., Mabille, G., and Nicolay, S.: Wavelet-Induced Mode Extraction procedure: Application to climatic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9537, https://doi.org/10.5194/egusphere-egu24-9537, 2024.

EGU24-10258 | Orals | NP4.1

New concepts on quantifying event data 

Norbert Marwan and Tobias Braun

A wide range of geoprocesses manifest as observable events in a variety of contexts, including shifts in palaeoclimate regimes, evolutionary milestones, tectonic activities, and more. Many prominent research questions, such as synchronisation analysis or power spectrum estimation of discrete data, pose considerable challenges to linear tools. We present recent advances using a specific similarity measure for discrete data and the method of recurrence plots for different applications in the field of highly discrete event data. We illustrate their potential for palaeoclimate studies, particularly in detecting synchronisation between signals of discrete extreme events and continuous signals, estimating power spectra of spiky signals, and analysing data with irregular sampling.

How to cite: Marwan, N. and Braun, T.: New concepts on quantifying event data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10258, https://doi.org/10.5194/egusphere-egu24-10258, 2024.

EGU24-10415 | ECS | Orals | NP4.1

Application of Transfer Learning techniques in one day ahead PV production prediction 

Marek Lóderer, Michal Sandanus, Peter Pavlík, and Viera Rozinajová

Nowadays photovoltaic panels are becoming more affordable, efficient, and popular due to their low carbon footprint. PV panels can be installed in many places providing green energy to the local grid reducing energy cost and transmission losses. Since the PV production is highly dependent on the weather conditions, it is extremely important to estimate expected output in advance in order to maintain energy balance in the grid and provide enough time to schedule load distribution. The PV production output can be calculated by various statistical and machine learning prediction methods. In general, the more data available, the more precise predictions can be produced. This poses a problem for recently installed PV panels for which not enough data has been collected or the collected data are incomplete. 

A possible solution to the problem can be the application of an approach called Transfer Learning which has the inherent ability to effectively deal with missing or insufficient amounts of data. Basically, Transfer Learning is a machine learning approach which offers the capability of transferring knowledge acquired from the source domain (in our case a PV panel with a large amount of historical data) to different target domains (PV panels with very little collected historical data) to resolve related problems (provide reliable PV production predictions). 

In our study, we investigate the application, benefits and drawbacks of Transfer Learning for one day ahead PV production prediction. The model used in the study is based on complex neural network architecture, feature engineering and data selection. Moreover, we focus on the exploration of multiple approaches of adjusting weights in the target model retraining process which affect the minimum amount of training data required, final prediction accuracy and model’s overall robustness. Our models use historical meteorological forecasts from Deutscher Wetterdienst (DWD) and photovoltaic measurements from the project PVOutput which collects data from installed solar systems across the globe. Evaluation is performed on more than 100 installed PV panels in Central Europe.

How to cite: Lóderer, M., Sandanus, M., Pavlík, P., and Rozinajová, V.: Application of Transfer Learning techniques in one day ahead PV production prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10415, https://doi.org/10.5194/egusphere-egu24-10415, 2024.

EGU24-11897 | Posters on site | NP4.1

Results of joint processing of magnetic observatory data of international Intermagnet network in a unified coordinate system 

Beibit Zhumabayev, Ivan Vassilyev, Zhasulan Mendakulov, Inna Fedulina, and Vitaliy Kapytin

In each magnetic observatory, the magnetic field is registered in local Cartesian coordinate systems associated with the geographic coordinates of the locations of these observatories. To observe extraterrestrial magnetic field sources, such as the interplanetary magnetic field or magnetic clouds, a method of joint processing of data from magnetic observatories of the international Intermagnet network was implemented. In this method, the constant component is removed from the observation results of individual observatories, their measurement data is converted into the ecliptic coordinate system, and the results obtained from all observatories are averaged after the coordinate transformation.

The first data on joint processing of measurement results from the international network of Intermagnet magnetic observatories in the period before the onset of magnetic storms of various types, during these storms and after their end are presented. There is a significant improvement in the signal-to-noise ratio after combining the measurement results from all observatories, which makes it possible to isolate weaker external magnetic fields. A change in the shape of magnetic field variations is shown, which can provide new knowledge about the mechanism of development of magnetic storms.

How to cite: Zhumabayev, B., Vassilyev, I., Mendakulov, Z., Fedulina, I., and Kapytin, V.: Results of joint processing of magnetic observatory data of international Intermagnet network in a unified coordinate system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11897, https://doi.org/10.5194/egusphere-egu24-11897, 2024.

We introduce the CLEAN algorithm to identify narrowband Ultra Low Frequency (ULF) Pc5 plasma waves in Earth’s magnetosphere. The CLEAN method was first used for constructing 2D images in astronomical radio interferometry but has since been applied to a huge range of areas including adaptation for time series analysis. The algorithm performs a nonlinear deconvolution in the frequency domain (equivalent to a least-squares in the time domain) allowing for identification of multiple individual wave spectral peaks within the same power spectral density. The CLEAN method also produces real amplitudes instead of model fits to the peaks and retains phase information. We applied the method to GOES magnetometer data spanning 30 years to study the distribution of narrowband Pc5 ULF waves at geosynchronous orbit. We found close to 30,0000 wave events in each of the vector magnetic field components in field-aligned coordinates. We discuss wave occurrence and amplitudes distributed in local time and frequency. The distribution of the waves under different solar wind conditions are also presented. With some precautions, which are applicable to other event identification methods, the CLEAN technique can be utilized to detect wave events and its harmonics in the magnetosphere and beyond. We also discuss limitations of the method mainly the detection of unrealistic peaks due to aliasing and Gibbs phenomena.

How to cite: Inceoglu, F. and Loto'aniu, P.: Using the CLEAN Algorithm to Determine the Distribution of Ultra Low Frequency Waves at Geostationary Orbit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12928, https://doi.org/10.5194/egusphere-egu24-12928, 2024.

EGU24-12938 | Posters on site | NP4.1

Applying Multifractal Theory and Statistical Techniques for High Energy Volcanic Explosion Detection and Seismic Activity Monitoring in Volcanic Time Series 

Marisol Monterrubio-Velasco, Xavier Lana, Raúl Arámbula-Mendoza, and Ramón Zúñiga

Understanding volcanic activity through time series data analysis is crucial for uncovering the fundamental physical mechanisms governing this natural phenomenon.

In this study, we show the application of multifractal and fractal methodologies, along with statistical analysis, to investigate time series associated with volcanic activity. We aim to make use of these approaches to identify significant variations within the physical processes related to changes in volcanic activity. These methodologies offer the potential to identify pertinent changes preceding a high-energy explosion or a significant volcanic eruption.

In particular, we apply it to analyze two study cases. First, the evolution of the multifractal structure of volcanic emissions of low, moderate, and high energy explosions applied to Volcán de Colima (México years 2013-2015). The results contribute to obtaining quite evident signs of the immediacy of possible dangerous emissions of high energy, close to 8.0x10^8 J. Additionally, the evolution of the adapted Gutenberg-Richter seismic law to volcanic energy emissions contributes to confirm the results obtained using multifractal analysis. Secondly, we also studied the time series of the Gutenberg-Richter b-parameter of seismic activities associated with volcanic emissions in Iceland, Hawaii, and the Canary Islands, through the concept of Disparity (degree of irregularity), the fractal Hurst exponent, H, and several multifractal parameters. The results obtained should facilitate a better knowledge of the relationships between the activity of volcanic emissions and the corresponding related seismic activities.  

How to cite: Monterrubio-Velasco, M., Lana, X., Arámbula-Mendoza, R., and Zúñiga, R.: Applying Multifractal Theory and Statistical Techniques for High Energy Volcanic Explosion Detection and Seismic Activity Monitoring in Volcanic Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12938, https://doi.org/10.5194/egusphere-egu24-12938, 2024.

EGU24-13593 | ECS | Posters on site | NP4.1

Characterizing Uncertainty in Spatially Interpolated Time Series of Near-Surface Air Temperature 

Conor Doherty and Weile Wang

Spatially interpolated meteorological data products are widely used in the geosciences as well as disciplines like epidemiology, economics, and others. Recent work has examined methods for quantifying uncertainty in gridded estimates of near-surface air temperature that produce distributions rather than simply point estimates at each location. However, meteorological variables are correlated not only in space but in time, and sampling without accounting for temporal autocorrelation produces unrealistic time series and potentially underestimates cumulative errors. This work first examines how uncertainty in air temperature estimates varies in time, both seasonally and at shorter timescales. It then uses data-driven, spectral, and statistical methods to better characterize uncertainty in time series of estimated air temperature values. Methods for sampling that reproduce spatial and temporal autocorrelation are presented and evaluated. The results of this work are particularly relevant to domains like agricultural and ecology. Physical processes including evapotranspiration and primary production are sensitive to variables like near-surface air temperature, and errors in these important meteorological inputs accumulate in model outputs over time.

How to cite: Doherty, C. and Wang, W.: Characterizing Uncertainty in Spatially Interpolated Time Series of Near-Surface Air Temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13593, https://doi.org/10.5194/egusphere-egu24-13593, 2024.

EGU24-13879 | ECS | Posters on site | NP4.1

Understanding the role of vegetation responses to drought in regulating autumn senescence 

Eunhye Choi and Josh Gray

Vegetation phenology is the recurring of plant growth, including the cessation and resumption of growth, and plays a significant role in shaping terrestrial water, nutrient, and carbon cycles. Changes in temperature and precipitation have already induced phenological changes around the globe, and these trends are likely to continue or even accelerate. While warming has advanced spring arrival in many places, the effects on autumn phenology are less clear-cut, with evidence for earlier, delayed, or even unchanged end of the growing season (EOS). Meteorological droughts are intensifying in duration and frequency because of climate change. Droughts intricately impact changes in vegetation, contingent upon whether the ecosystem is limited by water or energy. These droughts have the potential to influence EOS changes. Despite this, the influence of drought on EOS remains largely unexplored. This study examined moisture’s role in controlling EOS by understanding the relationship between precipitation anomalies, vegetation’s sensitivity to precipitation (SPPT), and EOS. We also assess regional variations in responses to the impact of SPPT on EOS.

The study utilized multiple vegetation and water satellite products to examine the patterns of SPPT in drought and its impact on EOS across aridity gradients and vegetation types. By collectively evaluating diverse SPPTs from various satellite datasets, this work offers a comprehensive understanding and critical basis for assessing the impact of drought on EOS. We focused on the Northern Hemisphere from 2000 to 2020, employing robust statistical methods. This work found that, in many places, there was a stronger relationship between EOS and drought in areas with higher SPPT. Additionally, a non-linear negative relationship was identified between EOS and SPPT in drier regions, contracting with a non-linear positive relationship observed in wetter regions. These findings were consistent across a range of satellite-derived vegetation products. Our findings provide valuable insights into the effects of SPPT on EOS during drought, enhancing our understanding of vegetation responses to drought and its consequences on EOS and aiding in identifying drought-vulnerable areas.

How to cite: Choi, E. and Gray, J.: Understanding the role of vegetation responses to drought in regulating autumn senescence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13879, https://doi.org/10.5194/egusphere-egu24-13879, 2024.

EGU24-16981 | ECS | Orals | NP4.1

A machine-learning-based approach for predicting the geomagnetic secular variation 

Sho Sato and Hiroaki Toh

We present a machine-learning-based approach for predicting the geomagnetic main field changes, known as secular variation (SV), in a 5-year range for use for the 14th generation of International Geomagnetic Reference Field (IGRF-14). The training and test datasets of the machine learning (ML) models are geomagnetic field snapshots derived from magnetic observatory hourly means, and CHAMP and Swarm-A satellite data (MCM Model; Ropp et al., 2020). The geomagnetic field data are not used as-is in the original time series but were differenced twice before training. Because SV is strongly influenced by the geodynamo process occurring in the Earth's outer core, challenges still persist despite efforts to model and forecast the realistic nonlinear behaviors (such as the geomagnetic jerks) of the geodynamo through data assimilation. We compare three physics-uninformed ML models, namely, the Autoregressive (AR) model, Vector Autoregressive (VAR) model, and Recurrent Neural Network (RNN) model, to represent the short-term temporal evolution of the geomagnetic main field on the Earth’s surface. The quality of 5-year predictions is tested by the hindcast results for the learning window from 2004.50 to 2014.25. These tests show that the forecast performance of our ML model is comparable with that of candidate models of IGRF-13 in terms of data misfits after the release epoch (Year 2014.75). It is found that all three ML models give 5-year prediction errors of less than 100nT, among which the RNN model shows a slightly better accuracy. They also suggest that Overfitting to the training data used is an undesirable machine learning behavior that occurs when the RNN model gives accurate reproduction of training data but not for forecasting targets.

How to cite: Sato, S. and Toh, H.: A machine-learning-based approach for predicting the geomagnetic secular variation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16981, https://doi.org/10.5194/egusphere-egu24-16981, 2024.

EGU24-17344 | Posters on site | NP4.1

Introducing a new statistical theory to quantify the Gaussianity of the continuous seismic signal 

Éric Beucler, Mickaël Bonnin, and Arthur Cuvier

The quality of the seismic signal recorded at permanent and temporary stations is sometimes degraded, either abruptly or over time. The most likely cause is a high level of humidity, leading to corrosion of the connectors but environmental changes can also alter recording conditions in various frequency ranges and not necessarily for all three components in the same way. Assuming that the continuous seismic signal can be described by a normal distribution, we present a new approach to quantify the seismogram quality and to point out any time sample that deviates from this Gaussian assumption. To this end the notion of background Gaussian signal (BGS) to statistically describe a set of samples that follows a normal distribution. The discrete function obtained by sorting the samples in ascending order of amplitudes is compared to a modified probit function to retrieve the elements composing the BGS, and its statistical properties, mostly the Gaussian standard deviation, which can then differ from the classical standard deviation. Hence the ratio of both standard deviations directly quantifies the dominant gaussianity of the continuous signal and any variation reflects a statistical modification of the signal quality. We present examples showing daily variations in this ratio for stations known to have been affected by humidity, resulting in signal degradation. The theory developed can be used to detect subtle variations in the Gaussianity of the signal, but also to point out any samples that don't match the Gaussianity assumption, which can then be used for other seismological purposes, such as coda determination.

How to cite: Beucler, É., Bonnin, M., and Cuvier, A.: Introducing a new statistical theory to quantify the Gaussianity of the continuous seismic signal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17344, https://doi.org/10.5194/egusphere-egu24-17344, 2024.

EGU24-17566 | ECS | Posters on site | NP4.1

Unveiling Climate-Induced Ocean Wave Activities Using Seismic Array Data in the North Sea Region 

Yichen Zhong, Chen Gu, Michael Fehler, German Prieto, Peng Wu, Zhi Yuan, Zhuoyu Chen, and Borui Kang

Climate events may induce abnormal ocean wave activities, that can be detected by seismic array on nearby coastlines. We collected long-term continuous array seismic data in the Groningen area and the coastal areas of the North Sea, conducted a comprehensive analysis to extract valuable climate information hidden within the ambient noise. Through long-term spectral analysis, we identified the frequency band ranging from approximately 0.2Hz, which appears to be associated with swell waves within the region, exhibiting a strong correlation with the significant wave height (SWH). Additionally, the wind waves with a frequency of approximately 0.4 Hz and gravity waves with periods exceeding 100 seconds were detected from the seismic ambient noise. We performed a correlation analysis between the ambient noise and various climatic indexes across different frequency bands. The results revealed a significant correlation between the North Atlantic Oscillation (NAO) Index and the ambient noise around 0.17Hz.

Subsequently, we extracted the annual variation curves of SWH frequency from ambient noise at each station around the North Sea and assembled them into a sparse spatial grid time series (SGTS). An empirical orthogonal function (EOF) analysis was conducted, and the Principal Component (PC) time series derived from the EOF analysis were subjected to a correlation analysis with the WAVEWATCH III (WW3) model simulation data, thereby confirming the wave patterns. Moreover, we conducted the spatial distribution study of SGTS. The spatial features revealed that the southern regions of the North Sea exhibit higher wind-wave energy components influenced by the Icelandic Low pressure system and topography, which explains the correlation between ambient noise in the region and the NAO index. Furthermore, spatial features disclosed a correlation between the first EOF mode of the North Sea ocean waves and the third mode of sea surface temperature anomalies. This research shows the potential of utilizing existing off-shore seismic monitoring systems to study global climate variation and physical oceanography.

How to cite: Zhong, Y., Gu, C., Fehler, M., Prieto, G., Wu, P., Yuan, Z., Chen, Z., and Kang, B.: Unveiling Climate-Induced Ocean Wave Activities Using Seismic Array Data in the North Sea Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17566, https://doi.org/10.5194/egusphere-egu24-17566, 2024.

EGU24-18061 | ECS | Orals | NP4.1

A new methodology for time-series reconstruction of global scale historical Earth observation data 

Davide Consoli, Leandro Parente, and Martijn Witjes

Several machine learning algorithms and analytical techniques do not allow gaps or non-values in input data. Unfortunately, earth observation (EO) datasets, such as satellite images, are gravely affected by cloud contamination and sensor artifacts that create gaps in the time series of collected images. This limits the usage of several powerful techniques for modeling and analysis. To overcome these limitations, several works in literature propose different imputation methods to reconstruct the gappy time series of images, providing complete time-space datasets and enabling their usage as input for many techniques.

However, among the time-series reconstruction methods available in literature, only a few of them are publicly available (open source code), applicable without any external source of data, and suitable for application to petabyte (PB) sized dataset like the full Landsat archive. The few methods that match all these characteristics are usually quite trivial (e.g. linear interpolation) and, as a consequence, they often show poor performance in reconstructing the images. 

For this reason, we propose a new methodology for time series reconstruction designed to match all these requirements. Like some other methods in literature, the new method, named seasonally weighted average generalization (SWAG), works purely on the time dimension, reconstructing the images working on each time series of each pixel separately. In particular, the method uses a weighted average of the samples available in the original time series to reconstruct the missing values. Enforcing the annual seasonality of each band as a prior, for the reconstruction of each missing sample in the time series a higher weight is given to images that are collected exactly on integer multiples of a year. To avoid propagation of land cover changes in future or past images, higher weights are given to more recent images. Finally, to have a method that respects causality, only images from the past of each sample in the time series are used.

To have computational performance suitable for PB sized datasets the method has been implemented in C++ using a sequence of fast convolution methods and Hadamard products and divisions. The method has been applied to a bimonthly aggregated version of the global GLAD Landsat ARD-2 collection from 1997 to 2022, producing a 400 terabyte output dataset. The produced dataset will be used to generate maps for several biophysical parameters, such as Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), normalized difference water index (NDWI) and bare soil fraction (BSF). The code is available as open source, and the result is fully reproducible.

References:

Potapov, Hansen, Kommareddy, Kommareddy, Turubanova, Pickens, ... & Ying  (2020). Landsat analysis ready data for global land cover and land cover change mapping. Remote Sensing, 12(3), 426.

Julien, & Sobrino (2019). Optimizing and comparing gap-filling techniques using simulated NDVI time series from remotely sensed global data. International Journal of Applied Earth Observation and Geoinformation, 76, 93-111.

Radeloff, Roy, Wulder, Anderson, Cook, Crawford, ... & Zhu (2024). Need and vision for global medium-resolution Landsat and Sentinel-2 data products. Remote Sensing of Environment, 300, 113918.

How to cite: Consoli, D., Parente, L., and Witjes, M.: A new methodology for time-series reconstruction of global scale historical Earth observation data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18061, https://doi.org/10.5194/egusphere-egu24-18061, 2024.

EGU24-18197 | ECS | Orals | NP4.1 | Highlight

The regularity of climate-related extreme events under global warming 

Karim Zantout, Katja Frieler, and Jacob Schewe and the ISIMIP team

Climate variability gives rise to many different kinds of extreme impact events, including heat waves, crop failures, or wildfires. The frequency and magnitude of such events are changing under global warming. However, it is less known to what extent such events occur with some regularity, and whether this regularity is also changing as a result of climate change. Here, we present a novel method to systematically study the time-autocorrelation of these extreme impact events, that is, whether they occur with a certain regularity. In studies of climate change impacts, different types of events are often studied in isolation, but in reality they interact. We use ensembles of global biophysical impact simulations from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) driven with climate models to assess current conditions and projections. The time series analysis is based on a discrete Fourier transformation that accounts for the stochastic fluctuations from the climate model. Our results show that some climate impacts, such as crop failure, indeed exhibit a dominant frequency of recurrence; and also, that these regularity patterns change over time due to anthropogenic climate forcing.

How to cite: Zantout, K., Frieler, K., and Schewe, J. and the ISIMIP team: The regularity of climate-related extreme events under global warming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18197, https://doi.org/10.5194/egusphere-egu24-18197, 2024.

EGU24-18210 | ECS | Posters on site | NP4.1

Long-term vegetation development in context of morphodynamic processes since mid-19th century 

Katharina Ramskogler, Moritz Altmann, Sebastian Mikolka-Flöry, and Erich Tasser

The availability of comprehensive aerial photography is limited to the mid-20th century, posing a challenge for quantitatively analyzing long-term surface changes in proglacial areas. This creates a gap of approximately 100 years, spanning the end of the Little Ice Age (LIA). Employing digital monoplotting and historical terrestrial images, our study reveals quantitative surface changes in a LIA lateral moraine section dating back to the second half of the 19th century, encompassing a total study period of 130 years (1890 to 2020). With the long-term analysis at the steep lateral moraines of Gepatschferner (Kauner Valley, Tyrol, Austria) we aimed to identify changes in vegetation development in context with morphodynamic processes and the changing climate.

In 1953, there was an expansion in the area covered by vegetation, notably encompassing scree communities, alpine grassland, and dwarf shrubs. However, the destabilization of the system after 1980, triggered by rising temperatures and the resulting thawing of permafrost, led to a decline in vegetation cover by 2020. Notably, our observations indicated that, in addition to morphodynamic processes, the overarching trends in temperature and precipitation exerted a substantial influence on vegetation development. Furthermore, areas with robust vegetation cover, once stabilised, were reactivated and subjected to erosion, possibly attributed to rising temperatures post-1980.

This study demonstrates the capability of historical terrestrial images to enhance the reconstruction of vegetation development in context with morphodynamics in high alpine environments within the context of climate change. However, it is important to note that long-term mapping of vegetation development through digital monoplotting has limitations, contingent on the accessibility and quality of historical terrestrial images, as well as the challenges posed by shadows in high alpine regions. Despite these limitations, this long-term approach offers fundamental data on vegetation development for future modelling efforts.

How to cite: Ramskogler, K., Altmann, M., Mikolka-Flöry, S., and Tasser, E.: Long-term vegetation development in context of morphodynamic processes since mid-19th century, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18210, https://doi.org/10.5194/egusphere-egu24-18210, 2024.

EGU24-19601 | ECS | Posters on site | NP4.1

Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform 

Palangio Paolo Giovanni and Santarelli Lucia

Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform

  • Palangio1, L. Santarelli 1

1Istituto Nazionale di Geofisica e Vulcanologia L’Aquila

3Istituto Nazionale di Geofisica e Vulcanologia Roma

 

Correspondence to:  lucia.santarelli@ingv.it

 

Abstract

In this paper we present an application of  the SSA Transform to the detection and reconstruction of  very weak geomagnetic signals hidden in noise. In the SSA Transform  multiple subspaces are used for representing and reconstructing   signals and noise.  This analysis allows us to reconstruct, in the time domain, the different harmonic components contained in the original signal by using  ortogonal functions. The objective is to identificate the dominant  subspaces that can be attributed to the  signals and the subspaces that can be attributed to the noise,  assuming that all these  subspaces are orthogonal to each other, which implies that the  signals and noise  are independent of one another. The subspace of the signals is mapped simultaneously on several spaces with a lower dimension, favoring the dimensions that best discriminate the patterns. Each subspace of the signal space is used to encode different subsets of functions having common characteristics, such as  the same periodicities. The subspaces  identification was performed by using singular value decomposition (SVD) techniques,  known as  SVD-based identification methods  classified in a subspace-oriented scheme.The  quasi-periodic variations of geomagnetic field  has been investigated in the range of scale which span from 22 years to 8.9 days such as the  Sun’s polarity reversal cycle (22 years), sun-spot cycle (11 years), equinoctial effect (6 months), synodic rotation of the Sun (27 days) and its harmonics. The strength of these signals vary from fractions of a nT to tens of nT. Phase and frequency variability of these cycles has been evaluated from the range of variations in the geomagnetic field recorded at middle latitude place (covering roughly 4.5 sunspot cycles). Magnetic data recorded at L'Aquila Geomagnetic observatory (geographic coordinates: 42° 23’ N, 13° 19’E, geomagnetic coordinates: 36.3° N,87°.2 E, L-shell=1.6) are used from 1960 to 2009.

 

 

How to cite: Paolo Giovanni, P. and Lucia, S.: Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19601, https://doi.org/10.5194/egusphere-egu24-19601, 2024.

EGU24-22262 | ECS | Posters on site | NP4.1

Temporal Interpolation of Sentinel-2 Multispectral Time Series in Context of Land Cover Classification with Machine Learning Algorithms 

Mate Simon, Mátyás Richter-Cserey, Vivien Pacskó, and Dániel Kristóf

Over the past decades, especially since 2014, large quantities of Earth Observation (EO) data became available in high spatial and temporal resolution, thanks to ever-developing constellations (e.g.: Sentinel, Landsat) and open data policy. However, in the case of optical images, affected by cloud coverage and the spatially changing overlap of relative satellite orbits, creating temporally generalized and dense time series by using only measured data is challenging, especially when studying larger areas.

Several papers investigate the question of spatio-temporal gap filling and show different interpolation methods to calculate missing values corresponding to the measurements. In the past years more products and technologies have been constructed and published in this field, for example Copernicus HR-VPP Seasonal Trajectories (ST) product.  These generalized data structures are essential to the comparative analysis of different time periods or areas and improve the reliability of data analyzing methods such as Fourier transform or correlation. Temporally harmonized input data is also necessary in order to improve the results of Machine Learning classification algorithms such as Random Forest or Convolutional Neural Networks (CNN). These are among the most efficient methods to separate land cover categories like arable lands, forests, grasslands and built-up areas, or crop types within the arable category.

This study analyzes the efficiency of different interpolation methods on Sentinel-2 multispectral time series in the context of land cover classification with Machine Learning. We compare several types of interpolation e.g. linear, cubic and cubic-spline and also examine and optimize more advanced methods like Inverse Distance Weighted (IDW) and Radial Basis Function (RBF). We quantify the accuracy of each method by calculating mean square error between measured and interpolated data points. The role of interpolation of the input dataset in Deep Learning (CNN) is investigated by comparing Overall, Kappa and categorical accuracies of land cover maps created from only measured and interpolated time series. First results show that interpolation has a relevant positive effect on accuracy statistics. This method is also essential in taking a step towards constructing robust pretrained Deep Learning models, transferable between different time intervals and agro-ecological regions.

The research has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the KDP-2021 funding scheme.

 

Keywords: time series analysis, Machine Learning, interpolation, Sentinel

How to cite: Simon, M., Richter-Cserey, M., Pacskó, V., and Kristóf, D.: Temporal Interpolation of Sentinel-2 Multispectral Time Series in Context of Land Cover Classification with Machine Learning Algorithms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22262, https://doi.org/10.5194/egusphere-egu24-22262, 2024.

SM4 – Earthquake Sources, Deformation and Faulting (incl. seismotectonics, geodynamics, earthquake source physics)

EGU24-2384 | ECS | Orals | EMRP1.6

Frictional slip sequences in homogeneous and bimaterial interfaces 

Songlin Shi, Meng Wang, Yonatan Poles, and Jay Fineberg

Earthquake-like ruptures disrupt the frictional interface between contacting bodies and initiate frictional motion (stick-slip). The interfacial slip (motion) immediately resulting from a rupture during each stick-slip event is usually much smaller than the total slip recorded during the duration of the event. Slip after the onset of friction is generally attributed to the continuous motion of global ‘dynamic friction’. Here, we demonstrate that numerous hitherto invisible secondary ruptures are initiated immediately after each initial rupture by directly measuring the contact area and slip at the frictional interface. Each secondary rupture generates incremental slip that, when not resolved, may appear as steady sliding of the interface. Each slip increment is linked, via fracture mechanics, to corresponding variations of contact area and local strain. Cumulative interfacial slip can only be described if the effects of these secondary ruptures are taken into account. These weaker slip sequences can also be observed in bimaterial interfaces and exhibit strong directional effects. In addition, the seismic moments we estimate based on slip sequences are consistent with the Gutenberg-Richter (G-R) law. These results have important implications for our fundamental understanding of frictional motion and the important role of aftershocks within natural faults in generating earthquake-mediated slip/afterslip.

How to cite: Shi, S., Wang, M., Poles, Y., and Fineberg, J.: Frictional slip sequences in homogeneous and bimaterial interfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2384, https://doi.org/10.5194/egusphere-egu24-2384, 2024.

EGU24-3912 | ECS | Orals | EMRP1.6

Back-Propagating Rupture: Nature, Excitation, and Applications 

Xiaotian Ding, Shiqing Xu, Eiichi Fukuyama, and Futoshi Yamashita

In recent years, an intriguing feature of back-propagating rupture (BPR) has been reported during some earthquakes (Ide et al., 2011; Houston et al., 2011; Hicks et al., 2020; Okuwaki et al., 2021; Vallée et al., 2023). The occurrence of BPR challenges the classical interpretation of rupture propagation as a “forward” problem, while remaining less understood by the earthquake science community. Here, using fracture mechanics, we first argue that BPR is nothing but an intrinsic component of rupture propagation; however, its observability is usually masked by the superposition effect of interfering waves behind the primary, forward-propagating rupture front. We then suggest that perturbation to an otherwise smooth rupture process can break the superposition effect and hence can make BPR observable. To test our idea, we report results of mode-II rupture propagation from both numerical simulations and laboratory observations. By introducing a variety of perturbations (lateral variation in bulk or interfacial properties along the fault, singular stress drop, coalescence of two rupture fronts, etc.) during rupture propagation, we show that prominent phases of BPR indeed can be successfully excited. We further classify BPR into two modes: higher-order rupture or interface wave, depending on whether the already-ruptured fault is quickly healed and whether additional stress drop can be produced. Lastly, we propose several application potentials for BPR, such as constraining the velocity structure of fault zones, probing the mechanical state of faults, and studying the stability of perturbed slip along a homogeneous or bimaterial interface. Our study refines the understanding of the nature and complexity of rupture process, and can help improve the assessment of earthquake hazards.

How to cite: Ding, X., Xu, S., Fukuyama, E., and Yamashita, F.: Back-Propagating Rupture: Nature, Excitation, and Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3912, https://doi.org/10.5194/egusphere-egu24-3912, 2024.

EGU24-5187 | Orals | EMRP1.6

The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes  

Fabio Corbi, Giacomo Mastella, Elisa Tinti, Adriano Gualandi, Laura Sandri, Matthias Rosenau, Silvio Pardo, and Francesca Funiciello

Modeling the seismic cycle requires multiple assumptions and parameters. Providing a quantitative assessment of the model behavior is pivotal for determining the degree of similarity between different scales and modeling strategies and for exploring dependencies with respect to selected parameters. Here we compare stick-slip ruptures nucleating spontaneously in scaled seismotectonic models (i.e., laboratory experiments capturing the first-order physics of the seismic cycle of subduction megathrusts) with slow earthquakes in nature. We rely on two non-dimensional parameters, namely the Ruina number (Ru) and system dimension (D) to quantify model behavior. Ru is proportional to the ratio of the asperity size to the critical nucleation size. Within the rate- and state friction framework, for velocity weakening asperities Ru controls the behavior of the system, which can be either periodic or not, and it can exhibit both slow and fast ruptures. D measures how complicated the system evolution is. D reveals how many variables are required to describe the seismic cycle because it tells us the minimum dimension needed to embed the observed dynamics. 

By coupling the Simulated Annealing algorithm and quasi-dynamic numerical simulations, we retrieve rate and state friction parameters characterizing single asperity models with different lateral extent of the velocity weakening patch. Similarly to slow earthquakes, we found optimal rate and state parameters indicative of low (< 4) Ru. We also found a direct proportionality between Ru and the lateral extent of the asperity. 

Next, we implement tools from non-linear time-series analysis and Extreme Value Theory to compute D from models of different sizes, materials, deformation rates and frictional configurations (single or twin asperities along strike). Our analysis supports the existence of a low dimensional attractor (D<5) describing the dynamics of scaled seismotectonic models. In particular, our models display D=3.0-4.2, which is remarkably similar to D=3.2 of slow earthquakes identified along the Cascadia subduction zone. Under the explored conditions, D appears more affected by the material behavior of the analog upper plate (i.e., gelatin vs. foam rubber) than by the lateral frictional segmentation of the megathrust.

Despite the different spatio-temporal scales, our results support a scenario where scaled seismotectonic models and slow earthquakes share similar dynamics.



How to cite: Corbi, F., Mastella, G., Tinti, E., Gualandi, A., Sandri, L., Rosenau, M., Pardo, S., and Funiciello, F.: The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5187, https://doi.org/10.5194/egusphere-egu24-5187, 2024.

EGU24-5767 | ECS | Posters on site | EMRP1.6

Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity  

Pierre Romanet, Marco Scuderi, Stéphanie Chaillat, Jean-Paul Ampuero, and Frédéric Cappa

Numerical modeling of Discrete Fracture Networks (DFNs) is commonly used to assess the behavior and properties of hydraulic diffusion and seismicity in the Earth’s crust within a network of fractures and faults, and to study the hydromechanical evolution of fractured reservoirs stimulated by hydraulic injection and production. The modelling of such fractures is typically carried out under a quasi-static approximation, and occasionally accounting for elasto-dynamics in single-rupture studies that assume a slip-weakening friction law. 

In this work, we develop a 2D DFN model to simulate fluid-induced seismicity that couples hydraulic diffusion and slip governed by rate-and-state friction on multiple interacting faults. The main goal of this numerical model is to establish a connection between laboratory derived friction parameters and field observations, enabling the inference of the long-term evolution of fractured reservoirs and crustal fault systems undergoing multiple earthquakes and (slow) slip events induced by fluid pressure perturbations.

In the model, the elastic interactions are computed with a boundary element method, accelerated by the hierarchical matrix method. We assessed the convergence of the method at fracture junctions and verified it does not create unphysical singularities. The use of rate-and-state friction makes it possible to model several seismic events over the injection duration.

The simulations will be later used to fit measurements of permeability and friction collected in laboratory experiments, in-situ observations of fault slip and opening from fluid injection experiments at decametric scale, and finally, induced seismicity at reservoir scale.

 

How to cite: Romanet, P., Scuderi, M., Chaillat, S., Ampuero, J.-P., and Cappa, F.: Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5767, https://doi.org/10.5194/egusphere-egu24-5767, 2024.

EGU24-6284 | ECS | Posters on site | EMRP1.6

Fault drainage state and frictional stability in response to shearing rate steps in natural gouge 

Raphael Affinito, Derek Elsworth, and Chris Marone

Elevated pore fluid pressures are frequently implicated in governing fault zone seismicity. While substantial evidence from geodetic and geological studies supports this notion, there is a notable scarcity of experimental observations of how fluid pressure influences fault stability during shear. Understanding the precise interplay between porosity, fault slip rate, and frictional stability is pivotal for assessing the significance of processes like dilational strengthening or thermal pressurization in the context of seismic hazards. Here, we prepare fault gouges from the Utah FORGE enhanced geothermal field injection well 16A at depths corresponding to seismic events (between 2050 – 2070m). Experiments were conducted inside a pressure vessel and loaded under a true-triaxial stress state, replicating in-situ stress conditions observed at the Utah FORGE site. The applied fault normal stress and during the experiments were held constant at 44MPa. Pore fluid pressure was varied between successive experiments (13, 20, and 27 MPa) to span a range of effective stresses to examine impacts on fault dilation/compaction and the successive frictional stability. Different fluid pressure boundary conditions: constant volume or pressure were applied to explore how changes in shearing rate influence gouge stability thought the fault drainage state. Our data indicate that the Utah FORGE samples are velocity-neutral and transition to velocity-weakening behavior at elevated pore pressure and shear strains >7. We find dilatancy coefficients e = ∆f/∆ln(v), where f is porosity and v is fault slip velocity, consistent with quartz-feldspathic-rich rocks ranging from 5–12^10-4, indicating a conditionally unstable regime. Furthermore, our results demonstrate that the boundary conditions for pore fluids influence frictional stability viachanges in effective normal stress. For example, when pore volume has zero flux, an expansion in the void volume during slip results in a decrease in pore pressure, transitioning the system towards frictional stability. Our results indicate that the connectivity of pore conduits may be more important than the imposed pore pressure conditions when considering the impact on fault stability. We suggest that the interplay between fault slip and fluid mobility within a fault is a delicate balance for predicting and managing seismic hazards.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: Fault drainage state and frictional stability in response to shearing rate steps in natural gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6284, https://doi.org/10.5194/egusphere-egu24-6284, 2024.

EGU24-7508 | Orals | EMRP1.6

A granular numerical model for the friction and wear of a lab-scale fault asperity 

Guilhem Mollon, Adriane Clerc, Amandine Ferrieux, Lionel Lafarge, and Aurelien Saulot

Seismic faults are often represented using two different and self-excluding conceptual models. In the first representation, seismic faults are seen as the interface between two surfaces of bare rock, with a roughness extending at all scales. These surfaces interact mechanically through a certain number of “asperities” which constitute the “real contact area”. When adopting this view, attention is paid on the statistics of the asperities population in the fault plane. Faults are thus considered as 2D objects, since their thickness is disregarded.

In the second representation, seismic faults are seen as mathematical planes separated by a certain thickness of granular gouge created by abrasive wear of the surfaces during previous slips. This view is analogous to the tribological “third body” theory, and is supported by field observations and experimental evidences of gouge creation in rotary shear and triaxial experiments. It is convenient to adopt this perspective when weakening phenomena within the gouge are to be spatially resolved in the direction orthogonal to the fault plane. Variations along this plane are then ignored, as well as fault roughness, and faults are mostly seen as 1D objects.

Unification of these two representations requires a better understanding of the interactions between geometrical asperities and a layer of gouge, and in particular of the phenomena that lead to the creation of the latter through the wear of the former. In this communication, we present a numerical model which aims at reproducing lab tests of millimetric single-asperity friction and wear. The model is essentially granular in order to represent the progressive degradation of the asperity along sliding, the separation of powdery matter, its successive ejection and reinjection by the contact (thanks to a periodicity in boundary conditions), and the build-up of a gouge layer. It also includes a coupling with continuum mechanics in order to maintain a meaningful stress field in the asperity beyond the region of degradable rock.

Numerical results show that: (i) the rate of wear of the asperity and the counterface are directly linked to the normal load applied to the contact; (ii) an established layer of gouge develops in the interface and controls the friction coefficient; (iii) a constant level of surface roughness is established after a sufficient sliding distance, both for the asperity and the counterface; (iv) an accurate control of the asperity boundary conditions is necessary in order to obtain repeatable friction and wear. These results are a first step towards a better understanding of the wear kinetics as a function of asperity geometry, load, and roughness, before the introduction of thermal aspects (including melting) in a future version of the model.

How to cite: Mollon, G., Clerc, A., Ferrieux, A., Lafarge, L., and Saulot, A.: A granular numerical model for the friction and wear of a lab-scale fault asperity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7508, https://doi.org/10.5194/egusphere-egu24-7508, 2024.

EGU24-7803 | ECS | Posters on site | EMRP1.6

Fluid driven seismic cycle modelling in subduction zones 

Betti Hegyi, Taras Gerya, Luca Dal Zilio, and Whitney Behr

The role of fluid flow in triggering earthquakes in subduction zones is a critical yet complex aspect in seismology. Despite extensive study through geological, geophysical observations, and laboratory experiments, fully understanding and modelling these processes within a coupled solid-fluid interaction framework remain challenging. This study employs a coupled seismo-hydro-mechanical code (i2elvisp) to simulate fluid-driven earthquake sequences in a simplified subduction megathrust environment. We incorporate non-uniform grid resolution, enhancing the resolution of seismic events within the subduction channel. The code integrates solid rock deformation with fluid dynamics, solving mass and momentum conservation equations for both phases, alongside gravity and temperature-dependent viscosity effects. Brittle/plastic deformation is modelled through a rate-dependent strength formulation, with slip instabilities governed by compaction-induced pore fluid pressurisation. Our approach demonstrates the significant impact of fluid pressurisation on deformation localization, achieving slip rates up to metres per second in a fully compressible poro-visco-elasto-plastic medium. By refining the vertical model resolution in the subduction channel to less than or equal to 200 metres, we ensure convergence in terms of event recurrence interval and slip velocity. The models successfully replicate various slip modes observed in nature, ranging from regular earthquakes (including partial and full ruptures) to transient slow slip phenomena and aseismic creep. This research focuses on the parameters influencing the dominant slip mode, their distributions, and interactions along a modelled subduction interface. Our findings indicate that the dominant slip mode and the earthquake sequences are significantly influenced by porosity, permeability, and temperature-dependent viscosity. We explore two distinct viscosity gradients in the subduction channel to represent subduction zones with differing thermal profiles. In 'hot' subduction models, the brittle-ductile transition commences at shallower depths than in 'cold' subduction cases, influencing the nucleation depth of seismic events. These viscosity variations markedly impact model evolution; regular earthquakes exhibit higher velocities and slip rates in 'hot' scenarios, which are also more conducive to hosting aseismic creep or slow slip events. In conclusion, our study elucidates the pivotal role of fluid pressure evolution in seismicity within subduction zones and provides deeper insights into earthquake source processes. Through comprehensive modelling and analysis, we enhance understanding of the complex dynamics governing fluid-induced seismic activity and contribute to the broader field of earthquake source processes. 

How to cite: Hegyi, B., Gerya, T., Dal Zilio, L., and Behr, W.: Fluid driven seismic cycle modelling in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7803, https://doi.org/10.5194/egusphere-egu24-7803, 2024.

EGU24-8381 | Posters on site | EMRP1.6

Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure 

Lei Zhang, Changrong He, and Sylvain Barbot

To investigate the frictional behavior of basalt under hydrothermal conditions, we apply sliding experiments using basalt gouge under the temperature of 100-600ºC, effective normal stress of 150MPa, and fluid pressure of 30MPa and 100MPa, respectively. Experiment results under 30MPa pore pressure show that basalt exhibits velocity-strengthening behavior at 100-200ºC and changes to velocity-weakening behavior at 400-600ºC; meanwhile, at 400ºC, velocity dependence of basalt evolves with slip from initial velocity weakening to velocity-strengthening. Results under 100MPa fluid pressure show a similar transition of velocity dependence at 300ºC; however, at higher temperatures of 400-600ºC, velocity strengthening behavior occurs, accompanied by strong slip weakening behavior at the slowest loading rate (0.04μm/s). During the velocity step, the experiment exhibits a rate-dependent creep without transient evolution with slip. Microstructure observation reveals significant differences between samples sheared under 30MPa and 100MPa fluid pressure. At higher fluid pressure and temperatures of 400-600ºC, the porosity of the basalt gouge layer is significantly reduced, and deformation is characterized by pervasive shear with no apparent localization. Such results suggest that the healing process/plastic deformation is activated at higher fluid pressure, leading to slip stability transition and slip-weakening of frictional strength.

How to cite: Zhang, L., He, C., and Barbot, S.: Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8381, https://doi.org/10.5194/egusphere-egu24-8381, 2024.

EGU24-8887 | ECS | Posters on site | EMRP1.6

High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge 

Jianhua Huang, Bo Zhang, Junjie Zou, Honglin He, Jiaxiang Dang, and Jinjiang Zhang

        Abundant cherts (nodules and bands) were discontinuously hosted by dolostones of the Mesoproterozoic group Strata (∼1.5 Ga) in the Shanxi graben system, North China, where earthquakes are common. Measurements of the shear strength and stability of granular quartz reveal that quartz is a typical tectosilicate which exhibits high frictional strength and velocity-weakening properties. Conversely, dolomite is usually frictionally weak but velocity strengthening. The two minerals also behave differently during coseismic slip. Due to the high temperature generated by frictional heating, the thermal decomposition of dolomite usually results in calcite, periclase nanoparticles and carbon dioxide. However, quartz melts by friction at high temperatures. In order to investigate the role of quartz in dolomite fault rock during the process of coseismic slip, high velocity shear experiments were conducted on the quartz-bearing dolomite fault gouge taken from Yuguang Basin South Margin Fault (YBSMF), northeast of the Shanxi graben system. Also, we carried out high velocity experiments with the synthetic quartz-dolomite gouge with different mass ratio. For a slip velocity ≥ 0.1 m/s and normal stresses from 1.0 to 1.5 MPa, the friction values of the gouge decrease exponentially from a peak value of more than 0.5 to a steady-state value from 0.1 to 0.4. This high-velocity weakening feature was observed in the synthetic quartz-dolomite gouge as well as in the YBSMF gouge. With the increase of quartz content, the slip weakening distance (Dw) increases from 4.27 to 13.24 m, and the steady-state friction coefficient increases from 0.2 to 0.4 at 1.0 MPa normal stress and 1.0 m/s slip velocity. The textures of the gouge are characterized by grain comminution, R shear planes and localized deformation zone in the friction weakening stage. The slip surfaces are characterized by mirror-like smooth surface and nanoparticle aggregates. The theoretical calculation results show that the temperature inside the gauge layer did not exceed 300 °C during the experiments. However, the microstructures present that the dolomite experienced thermal decomposition, indicating that the temperature at the asperity exceeds 550 ℃. We suggest that thermal decomposition together with flash heating may lead to the slip-weakening behavior of quartz-bearing dolomite gauge, and the addition of quartz will increase of the strength of the dolomite gouge.

How to cite: Huang, J., Zhang, B., Zou, J., He, H., Dang, J., and Zhang, J.: High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8887, https://doi.org/10.5194/egusphere-egu24-8887, 2024.

EGU24-9165 | ECS | Posters on site | EMRP1.6

Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland) 

Wei-Hsin Wu, Wei Feng, Rodrigo Gomila, Telemaco Tesei, Marie Violay, Anette K. Mortensen, and Giulio Di Toro

Fault’s frictional strength and particularly its ability to heal during the interseismic period (fault frictional healing Δμ) is critical to understand the seismic cycle, yet the understanding of temperature and phase-dependent healing characteristics of natural geothermal conditions remains limited. Here we examined the frictional healing of both simulated fresh and chlorite-altered basaltic gouge from Krafla geothermal field (Iceland) under realistic geothermal conditions of water temperature Tf = 100-400 ˚C and pressure Pf = 10-30 MPa (water in liquid, vapor and supercritical state) by performing Slide-Hold-Slide (SHS) experiments. All experiments were performed under a constant effective normal stress of 10 MPa and initiated with a 5-mm run-in slip at a loading point slip rate V of 10 mm/s before the SHS sequence. For each SHS sequence, shearing was held from 3 s to 10,000 s, separated by a slip interval of 1mm. Our mechanical results indicate that frictional healing, the difference between peak friction reached upon re-shear and the steady-state friction before the hold, increases with increasing logarithm of hold time in all experiments, as suggested by previous studies. Meanwhile, frictional healing rate (β = Δμ/log(1+ thold/tcutoff)), commonly regarded as the quantification of the rate of healing, increases with increasing temperature for both fresh and altered basalt. For fresh basalt, β increases from 0.007 at Tf = 100 ˚C to 0.060 at Tf = 300 ˚C (liquid) before dropping to 0.036 at Tf = 400 ˚C (vapor) and eventually increases to 0.096 at Tf = 400 ˚C (supercritical). For altered basalt, β  increases continuously from 0.003-0.007 at Tf = 100 ˚C to 0.013-0.022 at Tf = 300 ˚C and reaches its maximum value of β = 0.024-0.035 at Tf = 400 ˚C (vapor) and β = 0.030 at Tf = 400 ˚C (supercritical). Besides this temperature-dependent relationship, the dramatic decrease of β in fresh basalt to values similar to those of altered basalt when water changed from liquid to vapor state also suggests that the physical state of water can control the healing rate. Subsequent microanalytical analyses (XRPD, XRF, SEM-EDS) performed on the deformed gouges from altered basalts suggest an increase in hydrothermal alteration with increasing temperature, as shown by a depletion in K2O at Tf ≥ 300 ˚C. SEM-BSE images of fine platy matrices in shear bands formed at Tf = 400 ˚C point towards a dissolution of quartz, pyroxene and plagioclase. Therefore, we suggest that the healing rate of both fresh and altered basalt not only scales with the ambient temperature but is also affected by the physical state of water, particularly in the case of fresh basalt, potentially related to more intense fluid-rock interactions with increasing temperature.

Keywords: frictional healing, frictional healing rate, hydrothermal fluids, basaltic gouge, Krafla geothermal field

How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9165, https://doi.org/10.5194/egusphere-egu24-9165, 2024.

EGU24-9541 | Posters on site | EMRP1.6

Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures 

Marco Scuderi, Nathalie casas, Giuseppe Volpe, and Cristiano Collettini

Mineralogy, fabric, and frictional properties are fundamental aspects of natural and experimental faults that concur in controlling the fault strength and the fault slip behavior. Mineralogy controls the fabric evolution influencing the micro-mechanisms at play during fault deformation and needs an in-depth investigation to better understand and foresee the frictional response of experimental faults. Classically, this investigation has been conducted by relating the fault frictional behavior to the post-experimental microstructures. However, this “classical” approach provides a direct but static view of the fault deformation where the evolution of fabric with deformation can be only speculated.

To investigate in “real-time” the deformation micro-mechanisms at play during the experiments, the recording and analyses of Acoustic Emissions (AEs) produced by the deforming fault gouge can provide new insights.

In this study, we present a systematic study of microstructural, mineralogical, frictional, and AEs analysis coming from a suite of frictional experiments in a double direct shear configuration (biaxial apparatus, BRAVA2). We conducted experiments on gouges made of bi-disperse and layered mixtures of quartz and phyllosilicate. These experiments were performed at a constant normal stress of 52MPa and under 100% humidity. The friction evolves with the phyllosilicate content from µ ~ 0.6 for 100% quartz to µ ~ 0.4 for 100% phyllosilicates. At the end of the experiments samples were carefully collected and prepared for microstructural analysis. The fabric of the experimental samples show an evolution from localized to distributed and foliated fabric with increasing amount of phyllosilicate content.

We then integrate specific features of AEs, such as amplitude and AE rate, to unveil the micro-mechanisms at play during the experimental fault deformation. Our results show that the overall AE behavior is controlled by mineralogy. Deformation of quartz gouge produces the largest number of AEs whereas phyllosilicates are almost not producing AEs. Furthermore, the AE behavior of bi-disperse mixtures of quartz and phyllosilicates is strongly controlled by the amount of phyllosilicates. In fact, increasing the amount of phyllosilicate, the number, the rate, and the amplitude of AEs decrease. This behavior could be explained by the lubricant role of phyllosilicates which hinder the interaction between quartz grains favoring foliation sliding as main deformation mechanism and thus reducing the frictional strength. These results suggest that for bi-disperse mixtures the AEs reflect the frictional behavior of the mixture. Layered quartz-phyllosilicates mixtures show instead a non-trivial acoustic emission behavior which cannot be directly related to the measured frictional strength of the layered mixture: friction is controlled by the frictionally weaker mineral phase, whereas the AEs are probably dependent by the interplay between the stronger and weaker phase of the layered mixture.

Our results show that fault fabric together with mineralogy strongly control the micro-mechanisms at play during deformation and therefore the frictional response. Our findings support the use of the AE analysis as a new tool for the investigation of the micro-mechanisms at play during deformation, improving our interpretation of the mechanical behavior of fault gouges.

How to cite: Scuderi, M., casas, N., Volpe, G., and Collettini, C.: Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9541, https://doi.org/10.5194/egusphere-egu24-9541, 2024.

EGU24-9941 | ECS | Posters on site | EMRP1.6

Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge 

Michele De Solda, Michele Mauro, Federico Pignalberi, and Marco Scuderi

In the last decades, rock mechanics laboratory experiments have allowed framing earthquake physics as a frictional problem. When the accumulated stress on a fault exceeds the frictional forces holding it in place, a rapid acceleration occurs. This movement can be stable or unstable, involving phases of adhesion (stick) and rapid sliding (slip). In these terms, an earthquake results from the release of mechanical energy during one of these slip phases.

 

Modern friction theories propose that the frictional forces holding the fault in place are controlled by small asperities defining the real contact area (RCA). Therefore, understanding the mechanics of contacts on the fault and their evolution under stress and velocity changes can shed light on the microphysical processes underlying earthquakes.

 

In the laboratory, it is now possible to investigate the dynamics of experimental faults, predicting their instability behavior based on Rate and State Friction theory and its experimentally obtainable parameters (a-b, Dc). However, these parameters lack an explicit relationship with contact mechanics, necessitating additional measurements complementing the system's state information. One of the most widely used techniques for studying RCA during laboratory experiments involves investigating changes in acoustic transmissivity (velocity, amplitude) of generated and recorded ultrasonic waveforms (UW) passing through the sample during the deformation. At a given wavelength, analytical expressions for these quantities depend on the elastic properties and densities of the fault portion crossed by the wave. Simultaneous knowledge of stress conditions and elastic properties allows the formulation of constitutive laws for the evolution of contacts between fault asperities.

 

In double direct shear experiments (DDS) within biaxial apparatuses, the sample dimensions (gouge) impose stringent limits on the spatial and temporal resolution of the signal. These limits highlight the current sensor technology's deviation from the ideal behavior.

 

Here, we present a methodology and a waveform recording and synchronization protocol

implemented on the biaxial apparatus BRAVA2 in the Rock Mechanics and Earthquake Physics laboratory at Sapienza University of Rome. We focus on the types of sensors used and their specifications to provide accurate measurements of the deformation processes occurring within the gouge layers.

 

Several studies have conducted DDS experiments using UW, but they rarely take into account the characterization of the impulse signal, various reflections in the sample assembly, and conversion modes of the generated waveforms. These are all essential components to identify the interaction of the experimental system with the propagation of the ultrasonic waves, to exploit the received signal in its entirety.

We believe that a careful signal characterization is necessary to fully understand the physical processes during deformation within the sample and, consequently, to attempt upscaling to natural earthquakes.

How to cite: De Solda, M., Mauro, M., Pignalberi, F., and Scuderi, M.: Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9941, https://doi.org/10.5194/egusphere-egu24-9941, 2024.

EGU24-10564 | Posters on site | EMRP1.6

An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions 

Yu-Han Wang and Elías Rafn Heimisson

The interactions between fluids and fault structures play a pivotal role in understanding fault slip behavior. Over the years, various numerical methods have been developed to simulate these interactions. Volume-based methods, like the finite difference method (FDM), excel in their capacity to handle the intricacies of real-world fault structures, including material heterogeneity. On the other hand, the spectral boundary integral method (SBIM) is renowned for its computational efficiency. Recently, a hybrid approach has garnered significant attention, offering the benefits of both volume-based and SBI methods. This hybrid method allows for the consideration of fault structures' heterogeneity while maintaining computational efficiency. In this study, we introduce a novel hybrid method that bridges the SBIM and the FDM to model fluid migration in fault structures. Through rigorous model verification, we establish that our hybrid method can achieve a remarkable speedup of up to one thousand times compared to the FDM. Furthermore, we conducted two parametric studies to address open questions in fluid migration modeling within fault structures. First, we investigate the mobility contrast ratio between the host rock and the damage zone to determine the limits under which we can assume a zero-leak-off interface. Second, we explore the role of fault zone width in maintaining the validity of this zero-leak-off assumption. Building upon these foundational investigations, we demonstrate the possibility of extending the numerical framework to describe fault-fluid interactions considering poroelastic coupling.

How to cite: Wang, Y.-H. and Rafn Heimisson, E.: An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10564, https://doi.org/10.5194/egusphere-egu24-10564, 2024.

The slip behavior of crustal faults is known to be controlled by the mineralogic composition of the fault gouge. The exact properties determining the frictional behavior of geologic materials, including diverse remains an important question. Here, we use a geochemical approach considering the role of water-rock interactions. As a mechanism, we suspect that the mineral surface charge allows attractive and repulsive forces (Van Der Waals type), and that those forces may influence the static mechanical behavior of clays (cohesion, static friction).  On the other hand, we suspect that the water bound to the mineral surfaces may play a role during shearing.  To address these ideas, we measured the cation exchange capacity (CEC) of 10 different rock and mineral types, including non-clays and a range of phyllosilicate minerals, using CEC as a proxy for the mineral surface charge and the ability to bind water to the mineral surfaces.  For these materials, we conducted laboratory shearing experiments measuring the pre-shear cohesion, peak friction coefficient, residual friction coefficient, post-shear cohesion, and velocity-dependent friction parameters under 10 MPa effective normal stress.  
Our results show that low CEC materials (< 3 mEq/100g) tend to exhibit high friction, low cohesion, and show velocity-weakening frictional behavior. The phyllosilicate minerals exhibit larger CEC values up to 78 mEq/100g and correspondingly lower friction coefficients, higher cohesion, and velocity-strengthening frictional behavior. Zeolite exhibits a relatively high CEC value typical of phyllosilicates, but its strength and frictional characteristics are that of a non-clay with low CEC. This suggests that grain shape and contact asperity size may be more important for non-phyllosilicates. For phyllosilicates, we suggest that the systematic patterns in strength and frictional behavior as a function of CEC could be explained by water bound to the mineral surfaces, creating bridges of hydrogen or van der Waals bonds when the particles are in contact. Such bonding explains the large cohesion values for high-CEC materials under zero effective stress, whereas surface-bound water trapped between the particles under load explains low friction.  Beyond the results of this study, CEC appears to be a controlling factor for other properties such as permeability and even the amount of bound DNA in sediments.

 

How to cite: Ikari, M. and Conin, M.: Cation Exchange Capacity Quantifies the Link Between Mineral Surface Chemistry and Frictional-Mechanical Behavior of Simulated Fault Gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10969, https://doi.org/10.5194/egusphere-egu24-10969, 2024.

During natural and induced seismic activities, pore fluid pressure within fault zones and their surrounding rock may respond differently to stress variations, introducing additional complexities to seismic hazard assessment. While theoretical investigations have recognized the influence of such poroelastic heterogeneity on fault instability, incorporating phenomena like slip-induced dilation or compaction, the chosen poroelastic properties in these studies lack robust constraints from experimental measurements. Addressing this gap, our study focuses on quantifying the heterogeneity of poroelastic properties in the presence of a fresh fault, aiming to elucidate the coupling between poroelasticy and fault dilatancy during fault slip.

In our experimental investigation, we examined the evolving dynamics of pore pressure both on- and off-fault in initially intact Westerly granite samples. Applying confining stress of 100 MPa and a pore pressure of 60 MPa at two sample ends to replicate crustal settings, we induced a sliding fault plane through loading to failure under a constant strain rate. In the faulted samples, we measured the pore pressure response under sudden step loading in the direction of the maximum compression σ1. Each loading step of around 5 MPa was imposed incrementally increasing the differential stress from 5 MPa to approximately 80 MPa (frictional resistance) after achieving pore pressure equilibrium. Detailed measurements, including displacement, bulk deformation, differential stress, local pore pressure and acoustic emissions were recorded throughout these tests. A spring-slider model coupled with 1-D fluid diffusion was used to try to simulate experimental observations.

Our results indicate that both the shear zone and the bulk exhibit a diminishing Δp/Δσ1 with increasing differential stress. Measurements within the fault zone consistently yield positive values, surpassing those off the fault, with the discrepancy more pronounced at lower stress levels. In regions farther away from the shear zone, the off-fault response Δp/Δσ1 presents a smaller value compared to locations proximal to the fault zone and may even exhibit slight negativity. During fault slip, on-fault measurements exhibit an instantaneous increase upon step loading followed by a gradual decrease, as a result of the interplay between poroelasticity and fault dilatancy. These observations were effectively reproduced by the numerical model integrating the poroelastic measurements and rate-and-state fault friction with slip-dependent dilatancy. The implications of this investigation extend to an enriched understanding of the heterogeneity in poroelastic responses between fault zones and host rocks, serving as valuable benchmarks for informing future numerical simulations, particularly in the context of naturally formed fresh faults. 

How to cite: Liu, D. and Brantut, N.: Poroelastic heterogeneity in the presence of a fresh fault: experimental insights and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10998, https://doi.org/10.5194/egusphere-egu24-10998, 2024.

EGU24-11200 | Orals | EMRP1.6

Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front 

Francois Passelegue, Pierre Dublanchet, Nicolas Brantut, and Hervé Chauris

A growing amount of evidence indicate that aseismic transients driven by overpressure play an important role in the triggering of induced seismicity. Understanding the physical control on aseismic slip development is thus important for seismic hazard assessment. We conducted an investigation into the propagation dynamics of a fluid-driven slip front along a laboratory frictional interface composed of granite. The experiments were carried out under a confining pressure of 90 MPa, with an initial uniform fluid pressure of 10 MPa. Fault reactivation was initiated by injecting fluids through a borehole directly connected to the fault.

Our findings reveal that the peak fluid pressure at the borehole leading to reactivation exhibits an increase proportionate to the injection rate. Employing three fluid pressure sensors and eight strain gauges strategically positioned around the experimental faults, we performed an inversion analysis to image the spatial and temporal evolution of (i) hydraulic diffusivity and (ii) kinematic fault slip during each injection experiment. Our inversion methods integrated both deterministic and Bayesian procedures, facilitating the tracking of the fluid pressure front along the fault interface and the subsequent propagation of the slip front over time.

The migration pattern shares many similarities with natural slow slip events suspected to play a role in the development of natural and induced earthquake swarms or aftershock sequences.  We demonstrate that increasing the fluid injection rate induces a transition from a quasistatic propagation of the slip front correlated with the increase in fluid pressure to a dynamic scenario where the slip front outgrows the fluid pressure front, accelerating during its propagation. Furthermore, we establish that temporarily shutting off fluid pressure during injection induces the propagation of a pore-pressure back-front, which halts the propagation of the slip front, aligning with theoretical expectations.

How to cite: Passelegue, F., Dublanchet, P., Brantut, N., and Chauris, H.: Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11200, https://doi.org/10.5194/egusphere-egu24-11200, 2024.

EGU24-11407 | ECS | Posters on site | EMRP1.6

Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear 

Sofia Michail, Paul Antony Selvadurai, Markus Rast, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Claudio Madonna, and Stefan Wiemer

Faults in nature exhibit complex surface characteristics with patches of the fault (asperities) that may slip dynamically while other sections are more prone to creep (Beeler et al., 2011). Asperities forming in nature may be due to the geometric interactions between surfaces within a fault that contribute to complex stress states that are not well understood. Fault roughness is believed to play an important role in the control of the contact conditions established by asperities, directly affecting its potential to slip unstably. How the asperities are formed and how their seismogenic properties evolve due to wear is an important question with implications to slip budget and earthquake potential.

In this study, we performed a triaxial experiment at sequentially increasing confining pressures (Pc = 60, 80, 100 MPa) on a saw-cut sample of Carrara marble. We analysed the quasi-static frictional response that benefited from novel arrays of distributed strain sensors (DSS) obtained using fiber optics. This sensor offered unique insight into the axial strain with a spatial resolution of 2 mm. The frictional behaviour during the first confining pressure step exhibited a dynamic instability in the form of a stick-slip event (SS) that produced a measurable stress drop. In the subsequent confining pressure stages, where an increase in confining pressure translated to increased normal stress, the fault behaved in a stable manner and no dynamic instabilities were produced. This observation is inconsistent with frictional stability theory (e.g. Rubin and Ampuero, 2005) and required pre- and post-mortem campaigns into the surface characteristics and their evolution to explain this abnormal behaviour. Therefore, we employed experimental techniques (pressure sensitive film (PSF), optical and stylus profilometry) along with finite element (FE) model in ABAQUS to characterize the pressure and roughness.

The DSS array showed extensional axial strain closer to the edges of the fault, while only compression was expected in this triaxial loading test. The pre-experimental profilometry revealed an asperity located at the centre of the fault with a curvature ratio of h/L=0.1% inherited from the hand-lapping preparation, which dominated the initial contact conditions prior to the SS and explained the DSS observations. The DSS results were confirmed using a FE model which justified the effect of the fault geometry (h/L) on the strain response. After the SS, wear and smoothening of the central asperity was seen in roughness measurements. The profilometric measurements showed that gouge was deposed adjacent to the high normal stress asperity center (PSF) and were characterized by increased RMS roughness. These small amounts of gouge on the fault surface were sufficient to suppress the seismic response of the asperity. These findings show that the seismic potential of a carbonate (softer) asperity, may be highly influenced by the debris produced during wear. Its impact on earthquake nucleation could provide insight into large-scale earthquake preparation processes on carbonate faults in nature.

 

References:

  • Beeler, M., Lockner, D. L. and Hickman, S. H. (2001), Bull. Seis. Soc. Am., 91 (6): 1797–1804
  • Ampuero, J.-P. and Rubin, A. M. (2008), J. Geophys. Res., 113, B01302

How to cite: Michail, S., Selvadurai, P. A., Rast, M., Salazar Vásquez, A. F., Bianchi, P., Madonna, C., and Wiemer, S.: Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11407, https://doi.org/10.5194/egusphere-egu24-11407, 2024.

EGU24-11536 | Orals | EMRP1.6 | Highlight

Fault activation from up close 

Men-Andrin Meier, Domenico Giardini, Stefan Wiemer, Massimo Cocco, Florian Amann, Elena Spagnuolo, Paul Selvadurai, Elisa Tinti, Luca Dal Zilio, Alba Zappone, Giacomo Pozzi, Mohammadreza Jalali, and Valentin Gischig and the FEAR science team

Our understanding of earthquake rupture processes is generally limited by the resolution of available observations. In all but exceptional cases, earthquake observations are made at comparatively large distances from the rupture itself, which puts a limit on what spatial scales can be resolved. At the same time, it is clear that small scale processes may play a crucial, if not dominant, role for various seismogenic processes, including rupture nucleation, co-seismic weakening and stress re-distribution.

The Fault Activation and Earthquake Rupture ('FEAR') project aims at collecting and interpreting a multitude of earthquake-relevant observations from directly on and around the process zone of an induced earthquake. To this end, we attempt to activate a natural granitic fault zone in the BedrettoLab, at a depth of ~1km, after instrumenting the fault zone with a multi-domain and multi-scale monitoring system. The goal is to observe and study earthquake rupture phenomena in a natural setting, from unusually close distance.

In this talk, we outline the project status, the science goals, and the plans for the main experiments, which are scheduled for the years 2024 - 2026. Notable milestones we report on include

  • the identification and detailed characterisation of the target fault zone
  • the beginning of niche and tunnel excavations
  • laboratory experiments that characterise the frictional and mechanical behaviour of both gauge material and host rock of the target fault zone
  • development of numerical models for 2D and 3D dynamic rupture propagation
  • development of tailored monitoring methods for seismicity, strain, temperature, pressure, bio-geo-chemistry and other relevant observables
  • development of remote experiment control methods
  • test stimulations in a nearby rock volume of similar geology, with an already existing monitoring system, where we tested the influence of pre-conditioning injection protocols
  • similar test stimulations in the same volume where we aim at triggering a larger event (target Mw~0)
  • active seismic experiments in an underground salt mine, to calibrate the very- to ultra-high frequency (1k Hz - 500k Hz) acoustic emission sensors

Together, these and other efforts constitute the necessary ingredients we need for interpreting the near-source observations that we will collect during the fault activation experiments.

How to cite: Meier, M.-A., Giardini, D., Wiemer, S., Cocco, M., Amann, F., Spagnuolo, E., Selvadurai, P., Tinti, E., Dal Zilio, L., Zappone, A., Pozzi, G., Jalali, M., and Gischig, V. and the FEAR science team: Fault activation from up close, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11536, https://doi.org/10.5194/egusphere-egu24-11536, 2024.

EGU24-12986 | ECS | Posters on site | EMRP1.6

Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations 

Elvira Latypova, Fabio Corbi, Giacomo Mastella, Jonathan Bedford, and Francesca Funiciello

The short seismic record with respect to the return time of large subduction earthquakes and the spatial fragmentation of available geophysical data represent unfavourable conditions for robust hazard assessment. Over the last decade, data from scaled seismotectonic models have become useful in filling the observational gaps of seismic and geodetic networks. Such models allow reproducing hundreds of analogue seismic cycles in a few minutes of experimental time and with the advantage of known and controllable boundary conditions. 

Here we present experimental results from Foamquake – an established 3D seismotectonic model, which simulates megathrust subduction. Recent technical advances in experimental monitoring have allowed us to include into our research a high-frequency camera to record model surface deformation at 50 Hz and a network of 5 accelerometers (located on the model surface) that measure the three components of acceleration at 1 kHz. To analyse the camera data, we used particle image velocimetry (PIV) to derive surface displacements, such as in a dense, homogeneously distributed geodetic network spanning updip to scaled depths that are often offshore and, therefore, typically under-monitored in natural subduction zones.

We performed 33 experiments exploring 10 different geometrical configurations of asperities along the analog megathrust. In particular, we varied the number of asperities, their size, location, and extra normal load. We observed that the rupture pattern of analogue earthquakes predictably changes as the extra normal load varies and the distribution of asperity configurations becomes more complex. Depending on the number and size of the asperities and the size of the barrier between them, we noticed different ratios between full and partial ruptures with different recurrence time (Rt) intervals. In some experiments we detected cascades of ruptures. We used the coefficient of variation (CoV) of recurrence time to quantify analog earthquakes periodicity. Most of our models display quasi-periodic analog earthquakes recurrence with CoV<0.5, but multi-asperity experiments with variable-size and extra normal load lean toward random behaviour as testified by CoV~0.8.

Future investigations include the following steps – exploring this great volume of data using machine learning, looking for spatial and temporal relationships between accelerometer and PIV displacements, and tracking in detail the aseismic processes that may precede and follow earthquake rupture.

How to cite: Latypova, E., Corbi, F., Mastella, G., Bedford, J., and Funiciello, F.: Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12986, https://doi.org/10.5194/egusphere-egu24-12986, 2024.

EGU24-13117 | ECS | Posters on site | EMRP1.6

A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach 

Ludovico Manna, Giovanni Toscani, Matteo Maino, Leonardo Casini, and Marcin Dabrowski

The 2D, plane strain, Finite Element Method-based linear elastic model that I present aims to assess the differential stress response to variations in the geometric configuration of a system of multiple collinear elliptic cracks intercepting a body of rock undergoing elastic deformation. The assumption underlying this simulation is that a collection of thin voids in a continuum medium can replicate the features observed in a system consisting of rough fault profiles in partial contact subjected to shear. The linear elastic model is designed to reproduce the stress and displacement fields around a rough fault, with a specific focus on stress concentration around its contact asperities. The model also allows to record the principal stress field on the domain for a wide range of scales and geometric properties of the system of collinear cracks embedded in the deforming rock. Analyzing the dependence of differential stress on parameters describing the geometry of rough fractures allows for considerations on the primary factors influencing brittle failure. Additionally, the examination of principal stresses around the tips of the cracks helps evaluate the potential orientation of new fracture patterns that may emerge when the yield strength of the deforming material is locally exceeded. The magnitude and orientation of the principal stresses are also crucial for the understanding of fracture coalescence and frictional reactivation of shear cracks in an elastic rock, which in turn is one of the main factors that govern the seismic cycle of natural faults. Furthermore, a comparison of the results of the present model with recent wing crack models of brittle creep suggest that our code may also be useful to obtain estimates of the critical distance between cracks for their interaction to coalesce into larger fractures. The process is assumed to indefinitely continue at greater scales, which offers the chance to propose a model for fault formation and propagation.

How to cite: Manna, L., Toscani, G., Maino, M., Casini, L., and Dabrowski, M.: A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13117, https://doi.org/10.5194/egusphere-egu24-13117, 2024.

EGU24-13433 | Orals | EMRP1.6

The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading 

Michele Fondriest, Fabio Arzilli, Benoit Cordonnier, Michael Carroll, and Mai-Linh Doan

The propagation of earthquake fault ruptures in the crust involve the generation of unloading stress pulses sufficiently large to induce dynamic failure of water-saturated rocks under tensional stresses and hydrofracturing. Similar processes are also activated during underground rock mass excavation activities in mines and tunnels. The current knowledge about rock fracturing via dynamic unloading is mainly limited to empirical records and numerical simulations, while there is a general paucity of experimental studies, due to difficulties in reproducing large instantaneous decompressions on rock samples using standard triaxial rigs. Until now rapid decompression and fracturing of large rock samples in dry conditions was reported only by using an unconventional gas-confined vessel.

Here, we report rock-fracture results for newly conceived rock decompression experiments, completed through the innovative use of a “cold-seal pressure vessel” (CSPV) apparatus which is routinely employed in experimental petrology. We applied instantaneous large decompressions on water-saturated rock samples equilibrated at high confinement (up to 200 MPa) and temperatures (up to 540°C). The tested rock samples were fine-grained Westerly granite, coarse-grained tonalite and micritic limestone. During the decompressions the rock samples hydrofractured due to the confinement dropping faster than the pore pressure within the rock. Porosity measurements, SEM imaging and X-ray µCT acquired before and after the tests suggest that the magnitude of dynamic fracturing not only positively correlates with the pressure drops but it mostly increases when the decompression is associated to a phase change of the pore water (e.g. supercritical fluid to subcritical gas) . Water vaporization or degassing imply an instantaneous volume expansion (up to 70 times) which critically enhances dynamic fracture propagation along rock grain boundaries. The induced fractures span from mm-long transgranular cracks to microcracks with submicrometric aperture. Therefore, synchrotron light high-resolution microtomography (final pixel resolution of 0.3 µm) was employed to fully resolve and quantify the 3D fracture networks of these deformed rock samples. Such unique dataset allowed us to determine at different scales the fracture intensity, aperture and connectivity of the dynamically induced fracture networks and to assess the key contribution of pore-water physical state changes on the initial stages of dynamic fracturing in rocks at crustal conditions. Such results will contribute to close a current knowledge gap in rock mechanics.

How to cite: Fondriest, M., Arzilli, F., Cordonnier, B., Carroll, M., and Doan, M.-L.: The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13433, https://doi.org/10.5194/egusphere-egu24-13433, 2024.

Establishing a constitutive law for fault friction is a crucial objective of earthquake science. However, the complex frictional behavior of natural and synthetic gouges in laboratory experiments eludes explanations. Here, we present a constitutive framework that elucidates the slip-rate, state, temperature, and normal stress dependence of fault friction under the relevant sliding velocities and temperatures of the brittle lithosphere during seismic cycles. The competition between healing mechanisms explains the low-temperature stability transition from steady-state velocity-strengthening to velocity-weakening as a function of slip-rate and temperature. In addition, capturing the transition from cataclastic flow to semi-brittle creep accounts for the stabilization of fault slip at elevated temperatures. The brittle behavior is controlled by the real area of contact, which is a nonlinear function of normal stress, leading to an instantaneous decrease of the effective friction coefficient upon positive normal stress steps. The rate of healing also depends on normal stress, associated with an evolutionary response. If these two effects do not compensate exactly, steady-state friction follows a nonlinear dependence on normal stress. We calibrate the model using extensive laboratory data covering various relevant tectonic settings. The constitutive model consistently explains the evolving frictional response of fault gouge from room temperature to 600º for sliding velocities ranging from nanometers to millimeters per second, and normal stress from atmospheric pressure to gigapascals. The frictional response of faults can be uniquely determined by the in situ lithology and the prevailing hydrothermal conditions.

How to cite: Barbot, S.: Constitutive behavior of rocks during the seismic cycle in non-isothermal, non-isobaric conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14003, https://doi.org/10.5194/egusphere-egu24-14003, 2024.

EGU24-14504 | Posters on site | EMRP1.6

The role of poroelasticity in rupture dynamics across fault stepovers 

Luyuan Huang, Luca Dal Zilio, and Elías Rafn Heimisson

Understanding earthquake rupture propagation across fault stepovers is pivotal for assessing the seismic hazard, offering vital insights into dynamic rupture processes within intricate fault geometries. However, the role of poroelastic effects within strike-slip fault systems featuring stepovers remains unexplored in dynamic models simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Many existing models neglect poroelastic effects, and among those that consider them, a typical standard value of 0.8 is adopted for Skempton's coefficient B. Furthermore, a single dynamic rupture simulation is unable to address the frequency at which ruptures propagate through the stepover. Instead, these simulations only provide a binary status, indicating whether the ruptures jump or arrest. Thus, the investigation into how poroelasticity influences the likelihood of an earthquake jumping through a stepover emerges as a significant area of study. In response, we introduce a quasi-dynamic boundary element model that simulates 2D plane-strain earthquake sequences. This model incorporates undrained pore pressure responses affecting the fault's clamping and unclamping mechanisms and is governed by rate-and-state friction, with state evolution defined by the aging law. We first illustrate that dynamic rupture occurring in either left-lateral or right-lateral fault stepovers leads to a dynamic decrease (unclamping) or increase (clamping) in the effective normal stress. Dynamic variations of the effective normal stress depend on Skempton's coefficient. Consequently, higher Skempton's coefficients can promote rupture jumping across fault segments even for larger stepover distances. We then conduct a thorough parameter space study, evaluating the effects of Skempton's coefficient variations and stepover width on fault interactions within a fluid-filled porous environment. The likelihood of rupture jumping involves a trade-off between Skempton's coefficient and stepover width. We validate the numerical model by comparing it to an analytical solution that involves a plane strain shear dislocation on a leaky plane within a linear poroelastic, fluid-saturated solid. This validation demonstrates that a simple analytical solution, primarily dependent on fault dislocation and Skempton's coefficient, has the potential to effectively predict the pore pressure change. The critical jumping width for 50% chance of rupture jumping predicted by our model explains the threshold dimension of the fault step, above which ruptures do not propagate. This study highlights the significance of incorporating poroelastic effects on- and off-fault in understanding the dynamic variations of the effective normal stress, which could significantly alter the overall length of fault rupture.

How to cite: Huang, L., Dal Zilio, L., and Rafn Heimisson, E.: The role of poroelasticity in rupture dynamics across fault stepovers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14504, https://doi.org/10.5194/egusphere-egu24-14504, 2024.

EGU24-14566 | Posters on site | EMRP1.6

Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions 

Weifeng Qin, Lu Yao, Tongbin Shao, Wei Feng, Jianye Chen, and Shengli Ma

The frictional properties of faults are primarily controlled by their mineral composition, as well as ambient and deformation conditions, such as temperature, pore fluid, normal stress, and slip displacement. While many studies have been conducted to decipher how temperature and pore fluid may affect the frictional behavior of faults, less attention has been paid to the slip displacement effects, especially under hydrothermal conditions. By employing a rotary shear apparatus equipped with an externally-heated hydrothermal pressure vessel, we conducted large-displacement (up to 521 mm) friction experiments on chlorite under temperature (T) of 25 to 400℃ and pore water pressure (Pp) of 30MPa. The imposed effective normal stresses were 200 MPa and the slip rates ranged from 0.4 to 10 μm/s. The experiments unveiled significant slip strengthening in chlorite within the temperature range of 25 to 400 °C. Moreover, with increasing temperatures, there was an overall increasing trend in both the rate of slip strengthening and the ultimate frictional strength. For example, under T = 25 °C, the friction coefficients at displacements of 5, 90, and 521 mm were 0.33, 0.49, and 0.59, respectively, in contrast to 0.46, 0.79, and 0.88, respectively, at the same three displacements under T =400 °C. Under all the temperature and displacement conditions, chlorite exhibited velocity strengthening behavior without discernible temperature dependence, although the velocity-dependence parameter (a-b) increased with slip displacement. Microstructural analysis revealed that, the entire layer of the chlorite gouge experienced pervasive and intense shear deformation after slip of 521 mm, with extremely remarkable grain-size reduction. The thermogravimetrical and FTIR data of the deformed chlorite samples, together with the microstructural data, suggest that the dehydroxylation and the distortion of crystal structure of chlorite might occur during the friction experiments conducted at T ≥ 200 °C. Such changes may explain the more pronounced slip strengthening of chlorite with increasing temperatures towards 400 °C. This explanation can be further demonstrated by a comparative experiment conducted under varying temperatures (400°C for the first 100 mm of slip, followed by 25°C for the rest of 100 mm slip), wherein the friction coefficient at T = 25°C during the latter stage of slip remains as high as that at T = 400°C. These findings highlight the importance of slip displacement in controlling the frictional strength and its variations of chlorite-bearing faults at depths, and have profound implications for understanding the fault slip behaviors and earthquake mechanisms in subduction zones.

How to cite: Qin, W., Yao, L., Shao, T., Feng, W., Chen, J., and Ma, S.: Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14566, https://doi.org/10.5194/egusphere-egu24-14566, 2024.

EGU24-15205 | ECS | Posters on site | EMRP1.6

Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults 

Federica Paglialunga, Francois Passelegue, and Marie Violay

Many aspects of earthquake physics are still not completely understood given its intrinsically complex nature. Among the others, the nucleation process; when and where an earthquake will occur, as well as its magnitude. Seismology is a commonly used method for studying earthquakes, but it faces challenges in accessing precise information about the physical processes taking place on the fault plane.

Here, we show how laboratory seismology can directly shed light on fault plane dynamics. Our approach involves reproducing in the laboratory on a large biaxial apparatus with a fault length of 2.5 m generated by two analog (PMMA) samples brought into contact. The experimental setup allows to impose both a heterogeneous loading distribution through the use of independent pistons loading the fault in the normal direction and specific boundary conditions (i.e. by modifying stopper and puncher dimensions). The stress state is measured through strain gauges at high frequency (40 KHz) along 15 locations along the fault. The experiments provide insights into two crucial aspects of laboratory earthquakes: (i) the nucleation location of ruptures and (ii) the complexity of the seismic cycle.

Our findings reveal that the initial on-fault stress distribution plays a significant role in both aspects. We observe that ruptures consistently nucleate in locations where the stress ratio τ/σn is the highest. Notably, such values change among experiments, challenging the widespread notion that a friction coefficient solely governs the onset of instability. Furthermore, we demonstrate how the heterogeneity of the initial prestress distribution along the fault controls the complexity of the seismic cycle. In certain cases, the seismic cycle manifests as system-size events with complete ruptures occurring regularly in time, devoid of precursors. Conversely, other initial stress distributions generate more complex cycles, characterized by multiple precursors before a main rupture, predominantly occurring in zones of elevated τ/σn (referred to as 'friction asperity'). The complexity of the seismic cycle can be described in terms of the number of precursory events, inter-event time, and the size of finite ruptures.

This study, carried out in a long laboratory fault, highlights the complexities that emerge when heterogeneous, hence more realistic, stress conditions are applied, providing valuable insights into the physics of natural earthquakes.

How to cite: Paglialunga, F., Passelegue, F., and Violay, M.: Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15205, https://doi.org/10.5194/egusphere-egu24-15205, 2024.

EGU24-15273 | ECS | Orals | EMRP1.6

Impact of multiscale heterogeneities on the nucleation of earthquakes 

Mathias Lebihain, Thibault Roch, Marie Violay, and Jean-François Molinari

Earthquake nucleation is traditionally described using cascading or slow pre-slip models. In the latter, nucleation occurs as the sudden transition from quasi-static slip growth to dynamic rupture propagation. This typically occurs when a region of the fault of critical size Lc, often called nucleation length, is sliding. This transition is relatively well-understood in the context of homogeneous faults. Yet, faults exhibit multiple scales of heterogeneities that may emerge from local changes in lithologies or from its self-affine roughness. How these multiscale heterogeneities impact the overall fault stability is still an open question.

Combining the nucleation theory of [Uenishi and Rice, JGR, 2003] and concepts borrowed from statistical physics, we propose a theoretical framework to predict the influence of brittle/ductile asperities on the nucleation length Lc for simple linear slip-dependent friction laws. Model predictions are benchmarked on two-dimensional dynamic simulations of rupture nucleation along planar heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three (in)stability regimes: (i) a local regime, where fault stability is controlled by the local frictional properties, (ii) an extremal regime, where it is governed by the most brittle asperities, and (iii) a homogenized regime, in which the fault behaves at the macroscale as if it was homogeneous and the influence of small-scale asperities can be averaged.  

Using this model, we explore the overall stability of rough faults, featuring multiscale distributions of frictional properties. We also investigate the stability of velocity-neutral faults that features brittle asperities. Overall, our model provides a theoretical basis to discriminate which heterogeneity scales should be explicitly described in a comprehensive modelling of earthquake nucleation, and which scales can be averaged.

How to cite: Lebihain, M., Roch, T., Violay, M., and Molinari, J.-F.: Impact of multiscale heterogeneities on the nucleation of earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15273, https://doi.org/10.5194/egusphere-egu24-15273, 2024.

EGU24-18100 | ECS | Posters on site | EMRP1.6

Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods 

Nico Bigaroni, Julian Mecklenburgh, and Ernest Rutter

During interseismic periods a fault at depth can experience non-constant effective normal stress due to fluctuations in the pore-fluid pressure. Pore-pressure oscillations may influence the healing capability of the fault and ultimately affect its reactivation. Thus, studying the behaviour of faults during interseismic periods is a critical factor in understanding the seismicity. Triaxial tests were conducted using saw-cut (45o) samples of Pennant Sandstone to investigate the influence of pore-pressure oscillations during slide-hold-slide (SHS) tests (th = 900 – 7300s) on its frictional behaviour and fault reactivation. The cylindrical samples were hydrostatically compacted at 30 MPa and pore-pressurized with argon gas at 5, 10 and 18 MPa resulting in effective normal stress (σ’n) 25, 20 and 12 MPa, respectively. Then the saples were deformed at a constant shear displacement rate ≈ 4.5 μm/s. To overcome the displacement hardening tendency of the sample geometry, we servo-controlled the confining pressure so that the resolved normal stress on the sliding surface is kept constant. Experimental observations revealed a significant influence of pore-pressure oscillation on the frictional behaviour resulting in an increase in both frictional healing and creep relaxation. Moreover, this effect was enhanced as the effective normal stress was increased further. To understand better the underling mechanism(s) that influences these time-dependent processes we coupled the frictional results with permeability measured using the oscillating pore pressure method during the SHS tests. Finally, we tested how the pore-pressure oscillation affected the fault reactivation by conducting creep experiments at constant shear stress while the fault was brought to reactivation via progressive increase in fluid pressure. Our results demonstrated how non-constant effective normal stress history during interseismic periods deeply affects the fault behaviour, with important implications for natural and human-induced seismicity.

How to cite: Bigaroni, N., Mecklenburgh, J., and Rutter, E.: Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18100, https://doi.org/10.5194/egusphere-egu24-18100, 2024.

EGU24-19397 | Orals | EMRP1.6

The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model 

Fabian Barras, Einat Aharonov, and François Renard

Observations suggest that large earthquakes often propagate as self-healing slip pulses but the mechanical reason of this ubiquity remains debated. Pulse-like ruptures differ from the classical crack-like dynamics by the fact that the slipping portion of the fault is limited to the immediate vicinity of the propagating tip. In this work, we first propose a minimal model describing the dynamics of large earthquakes. In its simplest form, the model contains only two free parameters: a dimensionless stress parameter characterizing the initial state of stress along the fault and a ratio of elastic moduli. The model illuminates how self-healing slip pulses can be produced by the paucity of elastic strain energy that arises once the rupture dynamics interplays with the finite geometry of fault zones—even in the absence of additional mechanisms such as rate-dependent friction.

Next, we discuss the example of faults surrounded by a damage zone whose reduction in elastic wave velocity restricts the flow of strain energy to the rupture tip and promotes pulse-like rupture. Using the proposed model, we demonstrate how the contrast in wave velocities and the initial stress level in the fault zone mediate the propagation mode of the earthquake.

How to cite: Barras, F., Aharonov, E., and Renard, F.: The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19397, https://doi.org/10.5194/egusphere-egu24-19397, 2024.

EGU24-249 | ECS | Posters on site | TS1.11

Competitive methane bubble growth in aquatic muds 

Xiongjie Zhou and Regina Katsman

Methane (CH4) bubbles developed in shallow aquatic muds present a significant environmental risk. Macroscopic CH4 gas content in the muds is accommodated in discrete bubbles that grow from below the pore scale size to the maximum size defined by muddy sediment mechanical properties. The bubbles force out the water within the pores and distort the structure of the muddy sediment by moving the grains apart at their growth above the pore scale. However, the interaction between growing bubbles was not understood. This study uses a mechanical/reaction-transport numerical model to simulate the interaction of competitive CH4 bubbles paired with fracture-driven growth of varying initial sizes in aquatic muds. It reveals that mechanical and solute transport dynamics play a crucial role at different stages of bubble growth, particularly hindering the development of smaller bubble growth in competition. The stress from the larger bubble impacts the inner pressure and diffusive CH4 flux to the smaller bubble, slowing its initial growth (at t < 40 s). Additionally, the larger bubble later diverts CH4 from the smaller one, further inhibiting its growth expansion. This interaction may cause more horizontally oriented smaller bubbles and significant deformations in the larger bubble, especially as the distance between the bubble pair decreases. Such competitive bubble growth may explain the bubble size distributions observed in lab experiments and in situ, promoting CH4 retention in muddy sediments and the formation of gas domes, which are precursors to pockmarks that can cause abrupt gas releases to the water and potentially the atmosphere. The study provides a foundation for upscaling to different models of gassy muddy sediment acoustic characteristics and models of gas retention evolution, while maintaining single bubble growth metrics. It contributes to better evaluating and potentially reducing long-persisting uncertainties around CH4 emissions from shallow aquatic sediments.

How to cite: Zhou, X. and Katsman, R.: Competitive methane bubble growth in aquatic muds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-249, https://doi.org/10.5194/egusphere-egu24-249, 2024.

EGU24-392 | Orals | TS1.11

Dykes and their magma overpressure 

Tridib Kumar Mondal and Sirshendu Kumar Biswas

Dykes are essentially magma filled fractures within the earth’s crust often formed by the pressure imparted by the intruding magma. Magnitude of the magma overpressure has been traditionally determined utilizing elastic properties of the host rock and the complete dimension i.e., full length and maximum width of the fractures. Full exposures of dykes (from tip to tip) are rare, however, as most of the dyke bodies encountered in the field are subject to erosion or disruption along its length as a result of geological time, making estimation of aspect ratios challenging.

We propose a new method of estimating total length and maximum width of dykes from their partial outcrops featuring at least one exposed tip. Taking into account the fact that majority of dykes form as dominantly opening mode fractures with an elliptical shape of opening, the method involves solving the equation of this ellipse using every conceivable combination of a pair of ground points recorded on the dyke margin considering the visible tip as the origin. Validity of the method has been checked using published data obtained from incomplete dyke outcrops exposed in the caldera walls of Miyake-jima volcano in Japan. The calculated estimates are in line with the results acquired through a previous published method. The present method has been effectively utilized to calculate the aspect ratios of partially exposed mafic dykes emplaced within the younger granite of the Chitradurga Schist Belt in the western Dharwar craton of peninsular India. We discuss the ranges of their magma overpressure and depths of origin as well as the stress intensity factors associated with the host granite.

 

How to cite: Mondal, T. K. and Biswas, S. K.: Dykes and their magma overpressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-392, https://doi.org/10.5194/egusphere-egu24-392, 2024.

EGU24-782 | ECS | Posters on site | TS1.11

(Un)certainties in tectonic stylolite stress inversion 

Saskia Köhler and Daniel Koehn

Over the last two decades application of stylolite roughness inversion has become a common tool to reconstruct paleostress-fields, stress magnitudes and burial depth. While the orientation of the highest principal stress is free of any doubt, there are uncertainties coming along with tectonic stylolite inversion that require a differentiated debate. This includes data quality, rock physical parameters, timing of stylolite growth and burial depth.

We present results of statistical data analysis, showing that data quality depends on the number of samples as well as on the sample size. Thus, the dataset can be of very high quality and stable in outcrop scale. This is faced by field and microscopic observations and results of the stress inversion itself, that demonstrate that some common assumptions, i.e. that modelled paleodepth can be used for tectonic stylolite inversion, are not generally valid. We want to open the discussion towards the question of how we can refine such assumptions and parameters for our paleo stress models and better prediction of recent deformations.

 

How to cite: Köhler, S. and Koehn, D.: (Un)certainties in tectonic stylolite stress inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-782, https://doi.org/10.5194/egusphere-egu24-782, 2024.

Observations of crustal stress orientation from the regional inversion of earthquake focal mechanisms often conflict with those from borehole breakouts. In particular, stress orientations from focal mechanism inversion tend to show little heterogeneity on length scales of kms to 10s of km, while borehole stress measurements often exhibit substantial short-length-scale heterogeneity.  Some of the difference may be because the two methods sample different locations within the crust, possibly indicating local stress heterogeneity, either laterally or with depth. We attempt to reconcile these two types of stress measurements, and investigate the implications for crustal stress heterogeneity. We compiled SHmax estimates from previous studies for 57 near-vertical boreholes with measured breakout azimuths across the Los Angeles region. We identified subsets of earthquake focal mechanisms from established earthquake catalogs centered around each borehole with various criteria for maximum depth and maximum lateral distance from the borehole. Each subset was independently inverted for 3-D stress orientation, and the SHmax direction compared with the corresponding borehole breakout-derived estimate. We find good agreement when both methods sample the basement stress (breakouts are close to the sediment-basement interface), or when both methods sample the mid- basin stress (sufficient earthquakes are present within a sedimentary basin). Along sedimentary basin margins, in contrast, we find acceptable agreement only when focal mechanisms are limited to shallow and close earthquakes, implying short-length-scale heterogeneity of <20 km. While the region as a whole shows evidence of both lateral and vertical stress orientation heterogeneity, we find a more homogeneous stress state within basement rock, over length scales of 1–35 km. These results reconcile the apparently conflicting observations of short-length-scale heterogeneity observed in boreholes, which sample primarily the basins, with the relative homogeneity of stress inferred from focal mechanisms, which sample primarily the basement.

How to cite: Hardebeck, J. and Luttrell, K.: A Unified Model of Crustal Stress Heterogeneity from Borehole Breakouts and Earthquake Focal Mechanisms , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3672, https://doi.org/10.5194/egusphere-egu24-3672, 2024.

EGU24-3863 | ECS | Orals | TS1.11

Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction 

Jean-baptiste Jacob, Benoît Cordonnier, Jonathan Wright, and François Renard

Understanding the mechanisms controlling brittle rock failure at the grain to sub-grain scale is a fundamental challenge in geosciences. Recent advances in triaxial compression and dynamic shock experiments combined with dynamic X-ray microtomography provide unparalleled insights into the 3D strain field evolution within deforming rocks. However, these methods do not accurately predict the heterogeneous internal stress field prior to failure, which is crucial for predicting microfracture initiation and propagation, leading to macroscopic failure. In the past decade, efforts have focused on developing synchrotron X-ray diffraction techniques leveraging the high penetrative capacity of hard X-rays from the last generations of synchrotron light sources. These techniques offer spatially resolved information on crystal phase orientation and elastic strain within a 3D volume. The local orientation and elastic strain tensor is reconstructed grain-by-grain, with precision down to approximately 10-3 radian for orientation and 10-4 for strain. Stress is then calculated using Hooke's law for anisotropic materials and the elastic constants of the crystal phases. We employed 3D X-ray diffraction to investigate the internal stress field evolution in a rock core sample deformed under triaxial compression in the Hades apparatus. A 5mm-diameter core of Berea sandstone was subjected to axial step loading under constant radial stress of 10 MPa, reaching brittle failure at around 90 MPa differential stress. Elastic strain of individual quartz grains were measured at different load steps, and elastic stresses were calculated, providing maps of the internal strain and stress field in the sample. Results reveal progressive elastic shortening of quartz grains parallel to the compression axis and elongation in orthogonal directions due to the Poisson’s effect. Reorientation of principal stress components is also observed with increasing axial stress, which tend to align with the macroscopic stress field. Internal stresses distribution varies within a range of ca. 300 MPa, suggesting local stress amplifications occurred interpreted as force chains, potentially favoring crack nucleation. This experiment is among the first ones to characterize in-situ the stress distribution in a natural rock under compressive loading, and demonstrates the potential of synchrotron diffraction techniques for investigating strain and stress in geological materials.

How to cite: Jacob, J., Cordonnier, B., Wright, J., and Renard, F.: Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3863, https://doi.org/10.5194/egusphere-egu24-3863, 2024.

Abstract

The shale reservoir in the Lower Permian Fengcheng Formation of Mahu Sag, the Junggar Basin is prospective in hydrocarbon exploration and development. Due to the complex structures of the study area and the strong heterogeneity of shale reservoirs, the distribution of in-situ stress in the research area has always been poorly understood. Previous studies on in-situ stress are mostly limited to mechanical experiments, logging calculation and simple 2D numerical simulations. Nevertheless, this study combines multiple technical means to simulate the complex 3D in-situ stress in a more accurate and precise way. In this study, a detailed geological model was established by utilizing the method of ant tracking. Post-stack acoustic impedance, logging data and acoustic emission tests were used to jointly invert the accurate 3D geomechanical model. The orientation of the in-situ stress in the study area was determined by digesting the information from FMI (Formation MicroScanner Image) while the boundary condition was fixed by acoustic emission experiments. Finally, the in-situ stress distribution of the study area was clarified through finite element numerical simulation. As is shown by the simulation results, the in-situ stress modeling revealed that the complicated stress state, stress differences, and stress difference coefficients, all of which can provide valuable guidance for well deployment optimization and hydraulic fracturing in the study area, are closely related to burial depth, faults, and rock mechanics parameters. The stress regime in the research area is mainly reverse faulting type. However, as the burial depth increases, the stress regime will change accordingly, transforming from reverse faulting stress regime to strike-slip faulting stress regime. In the same time, the existence of faults will also affect the stress regime to a certain degree. In addition, most faults in the research area are stable and show little tendency of slippage, but there may be a higher risk of slippage in the deep strata. Therefore, it is advisable to avoid these areas as much as possible during geological exploration.

Keywords: 3D in-situ stress field, numerical simulation, shale reservoir, Mahu Sag

How to cite: Chen, P., Qiu, H., and Chen, X.: 3D numerical simulation of complex in-situ stress fields in shale reservoirs: A case study in the northwestern Junggar Basin of China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4458, https://doi.org/10.5194/egusphere-egu24-4458, 2024.

Knowledge of the present‐day stress field in the Earth's crust is key for understanding the mechanical behaviour of rocks and structures under tectonic forces. The study of stress fields therefore remains a pivotal area for understanding the mechanical behaviour of rocks, fluid flow at depth and in revealing mechanisms that cause tectonic plates to creep, fail, or rupture. stress patterns in the Earth's crust appear on different scales: first order (plate scale), second order (regional scale), and third order (local scale). The latter is mainly controlled by basin geometry, topography, local inclusions, density contrasts, and active faults and can mask regional and plate stress patterns.

In this contribution, a couple of examples of stress states at the local, regional and large scale are presented using borehole breakouts as main stress indicator for the current stress field orientation.

In order to understand the influence of stress field evolution at local scale, a case study in Hawai´i concerns the effects of the two large overlapping shield volcanoes on the stress field at depth. The analysis reveals that the two-competing gravitational loads primary control the orientation of the present-day stress field, which deviates significantly from the plate and regional tectonic stress field. Therefore, knowledge of local and shallow stress fields can have a significant impact on future borehole planning. From a more regional point of view, an example of current stress orientation in Sweden is presented. The main objectives are to constrain the orientation of horizontal stresses using borehole data, and to discuss implications for geothermal exploration. Thus, obtaining detailed and accurate data on the stress state is of paramount significance to optimise the design of underground installations in order to maximise fluid flow and minimise the risks of wellbore instability. Finally, a large-scale study in Italy investigates the stress field at plate scale to reveal whether the orientation of horizontal stresses may change with depth or laterally indicating stress perturbations and heterogeneities related to areas with complex geo-tectonic setting.

In conclusion, this contribution aims to illustrate and emphasise the relevance of determining the horizontal stress orientation at depth in order to improve the understanding of subsurface stress fields and their applications in different fields of geosciences and different geological settings.

How to cite: Pierdominici, S.: Reconstruction of the state of stress in the upper crust by borehole breakouts stress indicators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5744, https://doi.org/10.5194/egusphere-egu24-5744, 2024.

Transient stress perturbations caused by passing waves of distant earthquakes have been observed to activate fault slip. Observations of remotely triggered earthquakes at distances greater than ~2-3 mainshock fault lengths suggest that certain conditions promote fault activation, including large-amplitude shaking at periods below ~ 10 seconds within a geothermal setting and extensional and/or transtensional tectonics. Yet, it is still unclear if remote dynamic triggering is ubiquitous. An additional complication to determining the prevalence of triggering is that there are likely many small-magnitude earthquakes within sparsely instrumented regions that are uncataloged. Additionally, large mainshock signals can mask smaller local events that also are missing from the local catalogs. As a result, possible triggering mechanism(s) remain enigmatic. Bounding the necessary physical conditions for remote triggering, such as determining the upper or lower bounds of stress or strain amplitudes, the orientation of the seismic wave’s traversal with respect to the local stress field or fault geometry, or the geologic properties conducive to triggering can help provide clues about the physics of remote triggering. 

            The northern Chilean subduction margin provides an ideal setting to study remote dynamic triggering. Its dense instrumentation provides a long history of both seismic and aseismic deformation in both the subduction system and forearc faults, including the Atacama fault system. Our investigation combines a new, detailed regional earthquake catalog (2007-2021) from Sippl et al., (2023) and documented cases of triggered aseismic slip in the Atacama fault system (Victor et al., 2018). We use a twofold approach to determine the prevalence of earthquake triggering by candidate mainshocks that produce strains at our target location ranging from 1 to ~140 microstrain. The approach uses 1) a difference-of-means test of cataloged seismicity outside of the mainshock cluster (including foreshocks and aftershocks), and 2) a waveform-based approach to look for earthquake triggering at seismic stations located close to creepmeters that recorded triggered aseismic slip events.  We find a lack of evidence of persistent, statistically significant seismicity increases outside of the mainshock cluster associated with any of the candidate mainshocks.  Notably, there is an absence of significant seismicity changes outside of clustered foreshock or aftershock seismicity associated with the series of 11 M6.2-8.2 earthquakes that produced high-strain-rate events during the 2014 Iquique sequence. Seismic recordings of the 2011 M9.1 Japan earthquake at stations CX.PB01-CX.PB14 located near creep meter stations CAR3 and CH01 on the Mejillones peninsula near the Chomache fault reveal evidence of remote triggering. We observe local, uncataloged earthquakes that are only visible after applying a high pass filter that removes the mainshock signal that otherwise overprinted and swamped the local signals.  The uniformity of particle motions (circular or oblong) generated by local earthquakes on multiple stations (N=9) is lacking in most non-triggering mainshocks. This uniformity suggests that the orientation of transient stress perturbations imparted by the mainshock waveforms, in relation to the local fault orientations, may play a role in the triggering process. 

How to cite: Harrington, R. M., Kilb, D., Verdecchia, A., and Victor, P.: Putting faults into motion by remote dynamic triggering: local ground-motion orientations seem to eclipse strain in the northern Chilean subduction forearc crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6650, https://doi.org/10.5194/egusphere-egu24-6650, 2024.

EGU24-6837 | Posters on site | TS1.11

Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary  

Mojtaba Rajabi, Moritz Ziegler, Oliver Heidbach, and Malte Ziebarth

The complex interplay between the Pacific and Australian plates in New Zealand offers a unique opportunity to investigate the present-day stress field in a tectonically active area. This study examines the present-day stress pattern of New Zealand through the analysis and compilation of data from 289 boreholes, 4291 earthquake focal mechanism solutions, and 72 neotectonic geological structures. Utilizing the Moho depth of New Zealand, we developed both crustal and mantle stress maps. Stress data above the Moho depth is categorized as the crustal stress map, while data below the Moho is classified as the mantle stress map.

The crustal stress map reveals a consistent ESE-WNW orientation of the maximum horizontal stress (SHmax) across much of the South Island, presenting a high angle to the strike of major active strike-slip faults. In the North Island, the crustal SHmax pattern is variable, highlighting the predominant role of the Pacific Plate subduction beneath the Australian Plate along the Hikurangi Margin. Within the Hikurangi Subduction Zone, both the crustal and mantle SHmax orientations are variable. However, the Taupo Rift Zone exhibits completely different stress pattern in mantle and crust, highlighting the Moho as a strong decoupling horizon in this region.

An examination of neotectonic stress regimes, derived from the neotectonic fault database, in comparison with the present-day stress regime from our stress database across 28 tectonic domains in New Zealand indicates a correlation between observed faults, faulting styles, and the stress field. Nevertheless, discrepancies emerge in certain domains, where the acting stress field diverges from the one expected according to the observed faults, suggesting non-optimal fault orientations.

How to cite: Rajabi, M., Ziegler, M., Heidbach, O., and Ziebarth, M.: Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6837, https://doi.org/10.5194/egusphere-egu24-6837, 2024.

The Sichuan-Yunnan region of the SE and E margin of the Tibetan Plateau, situated at the transitional nexus between the seismically-active intensely-deformed Tibetan Plateau and the tectonically stable Yangzi block with comparatively low seismicity, has experienced substantial geological transformations during the Quaternary. Given the pronounced seismicity, there is an escalating imperative for an accurate and refined distribution of the stress field in the region. To unravel the contemporary stress state within major active blocks and along active faults in the study area, an elaborate computation of their tectonic stress field is undertaken by comprehensive updated earthquake focal mechanisms catalog. The tectonic stress field in Sichuan-Yunnan region exhibits obvious lateral variations, with the principal compressive stress direction demonstrating a notable correlation with the azimuth of the P axis. The directions of the stress field show a variation from north to south at ~ 28°N. The directions of the maximum and minimum principal compressive stress in the north show nearly E-W compression and N-S tension, respectively. Conversely, in the south, there is a discernible clockwise rotation trend from east to west. Localized normal faulting stress regimes are observed in the middle section of Xianshuihe fault and southwest side of Litang fault. The extensional environment of the former may be attributed to the tectonic activities such as block translation, clockwise rotation and vertical uplift, as well as the clockwise rotation of the Xianshuihe fault from NW-SW to NNW-SSE. The latter may be related to the extensional structures, rift basins and the normal fault movements in the crust formed by the detachment of the plates and delamination of the mountain roots at the end of Triassic. We also found that the tectonic stress field under the large faults, such as Longmenshan fault, Red River fault, Xiaojiang fault and Lijiang-Xiaojinhe fault, show segmented variation. The findings yield invaluable insights into the intricate dynamics of tectonic deformation along the SE margin of the Tibetan Plateau [supported by NSFC Projects 42330311, 42074065 & 41730212].

How to cite: Tian, J., Gao, Y., and Li, Y.: Present-day stress field in Sichuan-Yunnan region based on comprehensive updated earthquake focal mechanisms catalog, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7176, https://doi.org/10.5194/egusphere-egu24-7176, 2024.

EGU24-7664 | Orals | TS1.11

Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021 

Rostislav Melichar, Ivo Baroň, Matt Rowberry, Jan Jelének, Ľuboš Sokol, Maria del Puy Papí Isaba, Christiane Freudenthaler, Helmut Hausmann, Lukas Plan, Bernhard Grasemann, Josef Stemberk, Richard A. Schultz, and Roland Bürgmann

Short-term earthquake prediction remains one of the primary goals of seismotectonics. Here detailed observations of unusual fault kinematic behaviour and near-surface crustal stress variations are presented from before, during, and shortly after an earthquake series which culminated with two Mw 4.6 and 4.4 events near Breitenau, Vienna Basin, Austria, on 30 March 2021 and 19 April 2021, respectively. The oblique normal NNE-SSW trending Pitten Fault is exposed in Altaquelle Cave close to the southern margin of the Vienna Basin in the eastern Alps, which is known to have hosted several historical earthquakes of Mw = > 5. This cave has developed in Triassic marbles of the Central Alpine Permomesozoic. The observed branch of this active steeply dipping fault is associated with the seismogenic sinistral Vienna Basin Fault and the NE-SW trending Mur-Mürz Fault. To investigate the fault activity, TM71 moiré extensometers have been used to obtain precise three-dimensional records of fault kinematic behaviour at the micron scale while the recently developed SMB2018 protocol has been used to define the stress state associated with each fault reactivation event. The observations were then compared to the Copernicus European Ground Motion Service InSAR time series derived from Sentinel-1 data. From late 2018 to early 2021, the three-dimensional kinematic behaviour of the fault comprised a variety of different on-plane as well as out-of-plane hanging block displacements ranging in magnitude from 3 to 19 μm. Then, around the time of the earthquake series in 2021, four significant displacement events were recorded: (i) 0.186 mm along a vector of 186/-12° (i.e. upward) on 16 March; (ii) 0.615 mm along a vector of 177/-88° (upward) on 26 March; (iii) 0.066 mm along a vector of 013/26° (downward) on 30 March; and (iv) 0.022 mm along a vector of 308/54° (downward) on 11 May. The third of these events occurred on the same day as the largest earthquake. These events are all much larger than any other record of fault displacement recorded in the Eastern Alps since 2013. This contribution details this unusual fault displacement behaviour and compares the calculated stress states with both the focal solutions for each earthquake and InSAR maps of E-W and vertical ground motion. A comprehensive understanding of this important seismotectonic event helps to shed further light on potential earthquake precursory phenomena.

How to cite: Melichar, R., Baroň, I., Rowberry, M., Jelének, J., Sokol, Ľ., del Puy Papí Isaba, M., Freudenthaler, C., Hausmann, H., Plan, L., Grasemann, B., Stemberk, J., Schultz, R. A., and Bürgmann, R.: Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7664, https://doi.org/10.5194/egusphere-egu24-7664, 2024.

EGU24-9228 | Orals | TS1.11

Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust 

Luca Menegon, Giovanni Toffol, Hugo W. van Schrojenstein Lantman, David Wallis, Giorgio Pennacchioni, and Bjørn Jamtveit

Field studies established that seismicity in the lower crust is linked to brittle failure of dry, strong rocks. Failure of these strong rocks implies build-up of differential stresses to gigapascal (GPa) levels, but this requirement contrasts with current models of continental lithosphere deformation, which favour distributed flow of weak viscous lower crust. Although several mechanisms have been proposed to generate transiently high stresses, direct measurements are lacking. Recent advancements in microanalytical techniques (i.e., high-angular resolution electron backscatter diffraction, HR-EBSD) have proven successful at measuring the residual stress resulting from elastic strain retained in mineral grains.

We investigated with HR-EBSD the residual stresses in garnet and diopside from exhumed faults containing pseudotachylytes (quenched frictional melts produced during seismic slip). The samples come from Lofoten (Norway), Holsnøy (Bergen Arcs, Norway), and Musgrave Ranges (Central Australia). Pseudotachylytes from all three localities represent single earthquake events and formed at lower-crustal conditions (T = 500–720 °C, P = 0.5–1.0 GPa). Pseudotachylytes from Holsnøy show an asymmetric damage distribution, where host-rock garnet is pulverized nearby the fault on the side subjected to predominantly tensional stresses during rupture propagation, while garnet is intact on the other side. This asymmetry provides an opportunity to compare the residual stresses on both sides of the fault.

All samples preserve intragrain residual stress heterogeneities reaching 100s of MPa to GPa levels due to local high density of unrecovered lattice defects (dislocations). However, the timing of formation of lattice defects with respect to the seismic event differs. In samples from the Musgrave Ranges, the absence of any later deformation along with the sluggish mobility of dislocations in garnet at the ambient deformation conditions (500 °C, 0.5 GPa) allowed preservation of the high dislocation density produced during the earthquake rupture propagation, recording stress heterogeneities of as much as 6 GPa. In Holsnøy, residual stress heterogeneities of up to 1 GPa are only measured in pulverized grains and are also associated with unrelaxed dislocations generated during the earthquake rupture propagation. Intact garnet grains from the less damaged side of the fault show a limited range of intragrain stress heterogeneities, generally within 100 MPa, and a low density of dislocations. Residual stresses in diopside from Lofoten are only elevated (600 MPa) within 200 µm of the pseudotachylyte. Diopside recorded the progressive build-up of stress during interseismic loading, as suggested by the presence of coseismic cracks crosscutting lattice undulations that preserve the greatest stress heterogeneities. However, the ability of diopside to build up stress is limited, as stress is efficiently dissipated by the development of deformation twins.

In conclusion, great stress heterogeneities can be preserved in mineral grains that experienced the earthquake cycle in the lower crust. Different mineral phases can preserve stress heterogeneities to different extents, depending on the mobility of dislocations after their formation and on other relaxation mechanisms (e.g., twinning). Information on residual stress have important implications for the energy budget of an earthquake, the earthquake cycle deformation, and crustal rheology.

How to cite: Menegon, L., Toffol, G., van Schrojenstein Lantman, H. W., Wallis, D., Pennacchioni, G., and Jamtveit, B.: Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9228, https://doi.org/10.5194/egusphere-egu24-9228, 2024.

EGU24-9630 | ECS | Posters on site | TS1.11

Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye) 

Gian Maria Bocchini, Patricia Martínez-Garzón, Armin Dielforder, Luca Smeraglia, Rebecca M. Harrington, and Marco Bohnhoff

The Armutlu Peninsula in north western Türkiye, a horst zone in an active transtensional pull-apart basin, is bounded by two major sub-branches of the North Anatolian Fault zone and host high rates of seismicity in the northern part. The ~25-station SMARTnet surface seismic network was installed in 2019-2020 with the purpose of augmenting permanent seismic stations in the northern part of the Armutlu Peninsula and to help increase the detection of small-magnitude earthquakes. Here, we employ a waveform-based clustering method that integrates detailed information from the seismicity and focal mechanism distribution enabled by the added station coverage to investigate the geometry and kinematics of the seismically active structures. We start by using an enhanced earthquake catalog of >4,000 double-difference-relocated events and >150 focal mechanisms obtained using P-wave polarities and amplitudes in the time period between January 2019 and February 2020. We perform a formal inversion of the stress field orientation from focal mechanisms to investigate the regional deviatoric stress field and its relation with activated fault structures. The stress-field inversion uses input data that combines the enhanced focal-mechanism catalog from background seismic events together with published focal mechanisms of M≥2.5 events that occurred between 1999 and 2019. Stress inversion results show an extensional stress regime for the broader northern Armutlu Peninsula and a transtensional stress regime for a narrow region of ~80 km2, referred to as the Esenköy Seismic Zone (ESZ). Within the ESZ, the minimum principal stress (σ3) is approximately horizontal and NE-trending, while the maximum (σ1) and intermediate (σ2) principal stresses are close in magnitude and vary between near vertical and near horizontal. We observe clusters of normal and strike-slip faulting events identified in the ESZ through waveform-based clustering analysis that are optimally oriented with respect to the stress field we derive for the area. The minimum principal stress in the ESZ is rotated clockwise by ~10-15° with respect to the minimum principal stress inferred for the broader Armutlu Peninsula and eastern Sea of Marmara. Based on the Mohr-Coulomb failure criterion, we quantify the relative and absolute magnitudes of the principal stresses, determine the local crustal stress and strength conditions, and will present a discussion of the implications for regional tectonic forces.

How to cite: Bocchini, G. M., Martínez-Garzón, P., Dielforder, A., Smeraglia, L., Harrington, R. M., and Bohnhoff, M.: Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9630, https://doi.org/10.5194/egusphere-egu24-9630, 2024.

EGU24-10591 | ECS | Posters on site | TS1.11

Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes 

Thomas P. Ferrand, Jacques Précigout, David Sifré, Frédéric Savoie, Rémi Champallier, and Fabrice Gaillard

Electrical conductivity measurements on well-characterized materials in the laboratory allow accurate interpretations of electrical anomalies within the lithosphere and asthenosphere. But so far, most measurements have been performed statically, and hence, the effect of deformation and/or differential stress on electrical conductivity remains largely unknown. Here we report the first successful deformation experiments performed in a new-generation Griggs-type apparatus adapted for electrical conductivity measurements. The experiments were conducted on samples of Åheim dunites at a confining pressure of 1 GPa and temperatures of 500, 650 and 800°C. In silicate polycrystals, electrical charges are known to preferentially travel through grain boundaries, which act as high-diffusivity pathways. Our results show that stress and strain can significantly impact the electrical conductivity of peridotites by changing the thickness and the number of grain boundaries, respectively. At fixed P-T conditions, the electrical conductivity varies within an order of magnitude during deformation. This motivates to reappraise interpretations of electrical anomalies in mantle rocks, at least in tectonically active regions. The design presented in this study is fully stable at 1 GPa (≈ 30 km depth) and should be stable up to 2 GPa at least, and to average temperatures as high as 1000°C. Further developments should soon enable similar measurements at pressures up to 4 GPa (120 km depth). These experimental achievements open a new research field, which will help to understand electrical anomalies and strain localization processes in rocks under stress at depth, notably within the lower crust, the upper mantle, and subducting slabs.

How to cite: Ferrand, T. P., Précigout, J., Sifré, D., Savoie, F., Champallier, R., and Gaillard, F.: Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10591, https://doi.org/10.5194/egusphere-egu24-10591, 2024.

EGU24-10900 | Orals | TS1.11

The development of kinematic shear-stress free faults  

Daniel Koehn, Daniel Hafermaas, and Saskia Koehler

Faults are normally thought to present shear fractures that develop at an angle to the main principal stresses, so that they have shear stresses active parallel to the fault plane and thus move. Here we present two “fault” features that deviate from this principle, they develop not due to stress but during kinematic movement, they are both oriented parallel to two of the main principle stresses and as such have no shear stresses in their planes. On the large tectonic plate scale one of these features are the well known transform faults between mid ocean ridges. The ridges themselves are extensional features with the lowest principle stress perpendicular to the ridge. Transform faults are oriented perpendicular to the ridges and show movement only or mainly between the ridges where the plates move in opposite directions. These are faults that do not develop due to shear stress, they develop only because of differential movement and are therefore only or mainly kinematic. On the small scale a very similar feature is the side of a stylolite tooth. Stylolites are dissolution features, they are thus in a way the opposite to mid ocean ridges and have the largest principal stress oriented perpendicular to the stylolite plane. Due to differential movement and growth of the stylolite roughness they develop steep teeth where the sides of teeth become oriented perpendicular to the stylolite plane. These are also movement surfaces or “faults” that have no shear stress.

What does this mean for stress inversion analysis? At least stylolite teeth show a quite pronounced set of striations on their sides and slikolites are also often developed on fault planes, at least in limestone. How do we separate a purely kinematic from a stress-related fault? This discussion and the potential consequences for stress inversion studies is not new, but remains to be very important and should be debated.

How to cite: Koehn, D., Hafermaas, D., and Koehler, S.: The development of kinematic shear-stress free faults , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10900, https://doi.org/10.5194/egusphere-egu24-10900, 2024.

Understanding the stress conditions of active subduction zones has been a longstanding hurdle with critical implications for natural disasters considering stress/strain orientations and magnitudes can control shallow earthquakes and tsunamigenesis. The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines is an exhumed subduction channel with exposures of up to 9 km paleodepth, having reached up to 200°C. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twin data from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation.

During subduction, the maximum principal stress axis was oriented at a low angle to the subduction interface and the minimum principal stress axis oriented at a high angle, indicating N/NE directed compression. As subduction ceased and exhumation initiated, stress orientations inverted with the maximum principal stress axis becoming oriented at a high angle to the subduction interface and the minimum principal stress axis oriented at a low angle, indicating N/NE directed extension driven by primarily the weight of overburden material. These findings are consistent with theoretical orientations for both of these tectonic regimes and agree with previous studies interpreting subduction zone stress orientations. Calcite twin paleopiezometry and geothermometry suggests the rotation of principal stresses coincides with higher differential stresses during early exhumation. Based on the interpreted differential stresses and the reconstructed paleostress orientations, we model different possible explanations including contrasting mechanical strength between the contractional and extensional faults or changes in pore fluid pressure conditions between the two different tectonic regimes.

How to cite: Williams, S., French, M., and Rubin, C.: Determining the deformation temperatures and paleostress conditions of the Sestola-Vidiciatico Unit in the Northern Apennines, an exhumed shallow subduction zone, using calcite deformation twins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14306, https://doi.org/10.5194/egusphere-egu24-14306, 2024.

EGU24-15071 | Posters on site | TS1.11

Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines 

Silvia Mittempergher, Francesca Remitti, Telemaco Tesei, and Giancarlo Molli

During their activity, faults experience multiple seismic cycles, implying that faults recover strength between subsequent failures. Fault strengthening after failure (“fault healing”) occurs through processes having different space and time scales, including fault rock compaction, contact strengthening, contact area increase, fracture self-healing and precipitation of minerals in fractures (sealing). The efficiency of different processes varies depending on the geological setting, fault mechanics and availability and geochemistry of fluids. Here, we present preliminary data from a field-based study of the healing mechanisms of thrust faults inside the Sestola Vidiciatico Unit (SVU) in the Northern Apennines, a tectonic unit interpreted as the plate boundary shear zone between the Ligurian complex and the underthrusting Adria microplate during early-to-middle Miocene, active at temperatures up to 150°C.

The thrusts are sharp surfaces lined by calcite shear veins juxtaposing hectometer to kilometer-sized tectonic slices consisting of marls, shales, sandstones and mud-rich mass transport deposits. The marls and shales of the SVU bear a penetrative deformation pattern of fractures and incipient cleavage planes bounding oblate lithons, whose flattening planes define a foliation approximately parallel to the tectonic contacts. In the marls and shales adjacent to the main thrusts decimetric to metric-thick sheared domains may be observed showing an oblique foliation compatible with the sense of transport of the thrusts. Subvertical extensional calcite veins are common in the competent rock lithons. Multiple generations of normal faults lined by calcite shear veins crosscut the thrust faults, the oldest being rotated and deflected within the thrust-related shear zones. Calcite shear veins, in both thrusts and normal faults, display crack and seal domains and implosion breccias.

The lack of cataclastic rocks along faults indicates that the thrusts and normal faults were active at low differential stresses and high fluid pressures. Normal faults and subvertical extensional veins mutually crosscutting with thrusts are compatible with episodes of post-failure switching from reverse to normal fault stress regimes. Fault healing is dominated by calcite precipitation, which occurs both during fault slip (in crack and seal veins and implosion breccias), and after failure into subvertical extensional veins. Thrust compaction due to stress rotation is likely to be a factor promoting fault compaction and healing. Furter investigations will be conducted to constrain the origin of fluids involved in the vein cementation and the role of stress rotation in promoting different healing mechanisms.

How to cite: Mittempergher, S., Remitti, F., Tesei, T., and Molli, G.: Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15071, https://doi.org/10.5194/egusphere-egu24-15071, 2024.

EGU24-15970 | Posters on site | TS1.11

Paleostress inversion of fault slip data: what is the problem? 

Christophe Pascal

Paleostress inversion methods based on fault slip data (i.e. “fault slip inversion methods” or FSIMs) were formalised fifty years ago to become, shortly after, classical tools in structural geology and tectonics. The great popularity quickly gained by the methods was as remarkable as the enduring scepticism they prompted in the geological community. FSIMs belong to the rather narrow collection of methods, which allow for bridging traditional field observations and measurements (of fault planes and their respective slickenlines in the present case) to the stress tensor, a complex mathematical object. The latter statement highlights the originality of the approach and, perhaps, the roots of FSIM scepticism: stress are “observed” (or derived from observation of the nature) and not “measured” with the help of physical instrumentation, as it is traditionally done.

FSIMs are thus methods that involve mathematical processing of field data after adequate encoding of these. They rely primarily on the so-called “Wallace-Bott hypothesis”, which assumes parallelism between the measured fault stria and the computed maximum resolved shear stress, and on additional background conditions. The purpose of the present contribution is to discuss the limits of FSIMs in the light of their theoretical background and of realistic geological situations. The discussion will mostly focus on key-issues (e.g. is the stress restored by FSIMs in agreement with the formal definition of mechanical stress?) and will try to propose some future research tracks.

How to cite: Pascal, C.: Paleostress inversion of fault slip data: what is the problem?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15970, https://doi.org/10.5194/egusphere-egu24-15970, 2024.

EGU24-16586 | Posters on site | TS1.11

The recent crustal stress state of Germany - results of a new geomechanical–numerical model 

Steffen Ahlers, Karsten Reiter, Andreas Henk, Tobias Hergert, Luisa Röckel, Sophia Morawietz, Oliver Heidbach, Moritz Ziegler, Birgit Müller, and Victoria Kuznetsova

Knowledge of the recent crustal stress state is crucial for a better understanding of crust stability. However, the amount of available stress data in Germany is low. Therefore, a reliable and comprehensive prediction of the complete stress tensor is not possible with these only. However, 3D geomechanical-numerical models, which represent the geometry of the subsurface and its mechanical properties and are calibrated to stress data, allow a continuum-mechanics based prediction of the complete stress tensor and its lateral and vertical variability. A new geomechanical-numerical model of Germany provides new insights into the recent crustal stress field. In contrast to previous models, an improved geological model with a significantly higher stratigraphic resolution is used, a high vertical resolution of ~40 m allows a better mechanical representation of individual units and mechanical inhomogeneities and new data records are used for calibration.

The results provide a comprehensive prediction of the complete stress tensor for Germany and can be used for a wide range of scientific questions and applications. Examples are the prediction of the fracture potential, the slip tendency of faults or as boundary conditions for small-scale models usable for example for engineering applications.

How to cite: Ahlers, S., Reiter, K., Henk, A., Hergert, T., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., Müller, B., and Kuznetsova, V.: The recent crustal stress state of Germany - results of a new geomechanical–numerical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16586, https://doi.org/10.5194/egusphere-egu24-16586, 2024.

Seismicity studies on both fast- and slow-spreading ridge systems have found along-strike variations in mantle mechanical behavior on oceanic transform faults (OTFs), at pressure and temperature conditions above the long-term brittle-ductile transition of peridotites at ~700°C. Plate motion on some sections of the fault is accommodated by aseismic slip only (ductile deformation), whereas motion on other sections is by slip and deep swarms of microearthquakes (semi-brittle deformation) of mantle rocks (e.g., McGuire et al., 2012; Yu et al., 2021). To explore the mechanisms responsible for lateral variations in mantle mechanical behavior and the occurrence of this deep mantle microseismicity, we carried out an integrated study on peridotite mylonites dredged from two OTFs on the Southwest Indian Ridge that record deformation at 700-1000°C.

The samples show variable degrees of deformation, ranging from proto- to ultra-mylonitic textures. The most deformed zones of the mylonites are characterized by an increase in the proportion of fine grained (<10 micron) mylonitic shear bands compared to coarse grained (millimeter) porphyroclasts inherited from the protolith. These shear bands contain syn-deformation chlorine-rich amphibole indicating seawater-peridotite interaction during shear band formation.

Olivine and pyroxene porphyroclasts in protomylonites contain evidence for intense brittle deformation. The presence of subgrain walls, high aspect ratios, and internal misorientations crosscut by fractures imply that they deformed by low-temperature plasticity before brittle deformation. Fractures are sealed by the fine-grained shear bands present in the samples. In (ultra)mylonites, porphyroclasts also show evidence of fracturing after flowing through low-T plasticity. Fracturing was coeval with viscous flow of surrounding weak and hydrated mylonitic shear bands and triggered by hardening of larger grains due to dislocation accumulation. From existing flow laws, such brittle deformation of peridotite minerals necessitates high strain rate deformation, from 10-9 to 10-5s-1, similar to strain rates associated with slow slip events.

From these results we propose that swarms of microseismicity on OTFs are triggered by deformation of a heterogeneous mantle. Seismic rupture occurs in lenses of coarse-grained peridotites, possibly driven by aseismic creep of surrounding hydrated mylonitic shear zones. Importantly, observations also suggest plastic flow of brittle (seismic) patches before rupture.

How to cite: Cécile, P. and Jessica, W.: Origin of brittle deformation and microseismicity in the ‘ductile’ mantle on oceanic transform faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16752, https://doi.org/10.5194/egusphere-egu24-16752, 2024.

EGU24-16807 | ECS | Orals | TS1.11

First-order global stress patterns inferred from hierarchies of upper mantle flow models 

Jorge Nicolas Hayek Valencia, Ingo Leonardo Stotz, Hans-Peter Bunge, Sara Carena, and Sia Ghelichkhan

Understanding the intricate dynamics of mantle flow and their influence on lithospheric stress patterns is critical for assessing reservoir responses to potential CO2 or nuclear waste storage, as well as for hazard and risk assessment. Stress patterns play a first-order control in the mechanical response within inherited tectonic structures, with varying stress sources governing different spatiotemporal scales. Our understanding of the present-day mantle flow state has much improved over the past decades, reflected in models that are consistent with first-order features. The World Stress Map (WSM) project serves as a primary observational dataset to validate our understanding of Earth's dynamics through a global compilation of crustal stress indicators.

Here we study mantle flow models as a simplified superposition of Couette and Poiseuille flow types, which have been useful in explaining sub-continental scale deformation in the lithosphere. We aim to understand the role of mantle flow as a stress driver by generating stress fields from an analytical representation of upper mantle flow, derived from the superposition of steady-state flow models. Our approach allows us to build first-order expectations and conduct fast hypothesis testing for upper mantle flow states.

How to cite: Hayek Valencia, J. N., Stotz, I. L., Bunge, H.-P., Carena, S., and Ghelichkhan, S.: First-order global stress patterns inferred from hierarchies of upper mantle flow models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16807, https://doi.org/10.5194/egusphere-egu24-16807, 2024.

EGU24-16849 | ECS | Orals | TS1.11

Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust 

Alix Osinchuk, Brendan Dyck, Dave Wallis, and Alfredo Camacho

Strength-depth profiles for ductile portions of continental crust are derived from either extrapolation of flow laws from deformation experiments or paleopiezometric estimates in deformed and nominally hydrated plate margins. Lower continental crust in intracontinental settings, in contrast, is relatively dry and should be considerably stronger than the lower crust of hydrated plate margins. The relative strengths of dry quartz and feldspar are poorly constrained by experiments and paleopiezometric estimates from such rocks are sparse. As such, the strength of intracratonic lower crust is difficult to ascertain. Here, we use a recently calibrated subgrain-size piezometer to estimate paleostresses from feldspar and quartz deformed in relatively dry (<20 ppm H2O) lower continental crust of the Musgrave Ranges in central Australia. Neocrysts of plagioclase, K-feldspar, and quartz mantle partially recrystallized porphyroclasts, which is indicative of bulging and subgrain-rotation recrystallization. Using crystallographic preferred orientations and plotting misorientation axes of subgrain boundaries of each phase, we infer that dislocation creep involved the slip systems (010)[100] and (010)[001] for plagioclase, (010)[101] for K-feldspar, and (0001)<11-20> and {01-10}<0001> for quartz. Titanium in quartz and gradients in concentration of Ca and K in feldspars within neocrysts and along subgrain boundaries verify that subgrains in all three phases were formed at a temperature of ~650°C under dry, eclogite-facies conditions. Subgrain sizes of 10.6–18.1 µm in quartz, 11.5–16.9 µm in plagioclase, and 12.0–17.5 µm in K-feldspar correspond to differential paleostresses between 22–36 MPa and are consistent with a single mean paleostress of 28 MPa. Our results demonstrate that there is minimal stress partitioning between dry quartz, plagioclase and K-feldspar under typical crustal thermal gradients. Moreover, the differential stress accommodated by felsic rocks in the Davenport shear zone is lower than predicted by previous strength-depth profiles of lower cratonic crust.

How to cite: Osinchuk, A., Dyck, B., Wallis, D., and Camacho, A.: Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16849, https://doi.org/10.5194/egusphere-egu24-16849, 2024.

EGU24-16995 | ECS | Posters on site | TS1.11

Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India   

Subha Kundu, Uddipta Mohanta, and Sudheer Kumar Tiwari

Paleostress analysis is commonly used to understand the brittle exhumation process of deeper crustal rocks to the surface. In this research, we have assessed different stress fields and associated tectonic events in the southern part of Chotanagpur Gneissic Complex (CGC) using fault slip data. The southern CGC comprises two significant crustal-scale shear zones: South Purulia Shear Zone (SPSZ) and the North Purulia Shear Zone (NPSZ), along and across which our fault slip data has been collected. These shear zones exhibit high-grade (amphibolite to granulite) facies Proterozoic rocks consisting mainly of felsic gneisses and migmatites in which low-grade metapelite of North Singhbhum Mobile Belt (NSMB), calc-silicate and mafic granulites of CGC occur as enclaves.

 There has not been any previous study to determine the major stress orientations during brittle exhumation acting upon the Proterozoic rocks in the study area. Thus, our main aim in this study is to understand the variation in stress regime along and across these shear zones and also try to reconstruct the paleostress orientation to determine the history of brittle exhumation of the lower crustal rocks during major orogenic stages of the Proterozoic period. Almost 1000 homogeneous fault slip data have been analyzed using Win-Tensor software. The primary fault data within both shear zones exhibits an approximate E-W orientation, whereas other sets range from NW-SE to NE-SW. Reconstructing stress fields using the age, overprinting relationship and sense of fault movements show that during the Neoproterozoic period (1.0-0.95 Ga), the direction of the compressional stress regime was in N-S orientation. This indicates an oblique-slip movement (thrusting and sinistral strike-slip fault) of the northern CGC block with respect to the NSMB resulting in crustal thickening. The evidence of E-W striking, orogen-parallel normal faults was produced from an N-S directed extensional stress and is primarily responsible for brittle exhumation of these widely distributed granulite facies rocks especially the CGC gneisses in the Purulia region through crustal extension and thinning at 0.95–0.85 Ga.

How to cite: Kundu, S., Mohanta, U., and Tiwari, S. K.: Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16995, https://doi.org/10.5194/egusphere-egu24-16995, 2024.

EGU24-17092 | ECS | Posters on site | TS1.11

Record of high-stress deformation before and during an earthquake at intermediate-depth conditions 

Giovanni Toffol, Giorgio Pennacchioni, Marco Scambelluri, and Luiz Fernando Grafulha Morales

Exhumed pseudotachylytes (quenched coseismic frictional melts) and their wall-rocks represent a source of information to investigate earthquake mechanics at hypocentre depth. Pseudotachylytes produced at eclogite-facies conditions in subducted oceanic rocks are of particular interest as they open a window into the elusive mechanics of intermediate-depth earthquakes1.

Here we present observations from pseudotachylytes hosted in oceanic gabbros and peridotites from Moncuni (Lanzo Massif, W Alps). These pseudotachylytes record seismic faulting occurred at ca. 70 km of depth during subduction of oceanic lithosphere and have been explained as the result of brittle failure under high differential stress in dry rocks2,3.

We focus on the pervasive damage surrounding pseudotachylytes within olivine-bearing gabbros. Brittle deformation comprises aseismic (cataclasite bands and foliated cataclasites) and coseismic (pulverized domains with shattering in-situ) features associated with the pseudotachylyte veins. Fluid-absent conditions promoted preservation of the pristine brittle features, including pseudotachylyte glass, throughout the exhumation path.

Pseudotachylyte veins and the associated sharp micro-faults are commonly bound by cataclastic domains. Locally, these domains develop an S-C fabric with ultracataclasites along the shear planes. This fabric shows a progressive localization of strain toward the core pseudotachylyte that cut through the S-C fabric, with the cataclastic aggregates proximal to the pseudotachylyte frequently impregnated by melt. Wall-rock olivine grains show evidence of low-temperature plasticity (deformation lamellae and undulatory extinction) and microfracturing. Both deformation lamellae and microfractures are oriented perpendicular to olivine c-axis. These deformation microstructures are also shown by olivine clasts within the cataclasites bounding the pseudotachylytes suggesting a temporal sequence of (i) crystal plastic deformation and (ii) shattering and pulverization. The small olivine clasts in contact with the sharp margin of the pseudotachylyte show substructures a few hundred nanometres in size and are characterized by absence of Kikuchi diffraction patterns. The lack of diffraction bands is interpreted as evidence of extremely high density of dislocations leading to amorphization of the material.

We interpret the low temperature plasticity of olivine and the progressive evolution of the S-C fabric to represent the precursory stage of stress localization predating the abrupt propagation of the seismic rupture, whose instantaneous high stress pulse is recorded by the shattered olivine clasts.

 

[1] Toffol et al., Earth and Planetary Science Letters, 2020, 578: 117289

[2] Scambelluri et al., Nature Geoscience, 2017, 10.12: 960-966

[3] Pennacchioni et al., Earth and Planetary Science Letters, 2020, 548: 116490

How to cite: Toffol, G., Pennacchioni, G., Scambelluri, M., and Grafulha Morales, L. F.: Record of high-stress deformation before and during an earthquake at intermediate-depth conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17092, https://doi.org/10.5194/egusphere-egu24-17092, 2024.

EGU24-17191 | ECS | Orals | TS1.11

Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks  

Natalia Nevskaya, Alfons Berger, Holger Stünitz, Weijia Zhan, Oliver Plümper, Marcus Ohl, and Marco Herwegh

To comprehend the rheology of the Earth's crust and the relevant rock properties, one key approach is to deform rocks and minerals at elevated pressures and temperatures and then extrapolate the measured stress and strain rate values to natural conditions using constitutive equations. Laboratory experiments are mostly conducted on monomineralic rocks, with quartz being considered as the weakest constituent of the middle continental crust. However, field observations suggest that this is an oversimplification, and polymineralic fault rocks may be weaker than monomineralic quartz rocks. This study presents the first experiments on fine-grained, solid, natural rock samples, containing their natural homogeneities and inhomogeneities, demonstrating that granitoid rocks may be weaker than quartz at mid-crustal conditions. It also highlights the importance of pre-existing faults and polymineralic fine-grained zones for strain localisation and proposes values for extrapolation to natural conditions and their use in numerical models of the deformation of the granitoid crust.

Cylindrical granitoid ultramylonite samples, composed of qtz + ab + K-fsp + bt + ep, with grain sizes of 125-15 μm are deformed in a Grigg’s type apparatus at T=650°C, confining P=1.2 GPa, strain rates=10-3 to 10-5s-1, and 0.2 wt% H2O added. Mechanical data are combined with light microscope, SEM, TEM, and quantitative image analysis to connect microstructures with stress and strain evolution. We show that polymineralic granitoid rocks deform through other mechanisms than monomineralic quartz aggregates at pressure and temperature conditions characteristic for the middle crust: Ultra-fine grain size reduction down to <50nm is developed by nucleation and growth of new grains in a polymineralic mixture. Grain size remains small because of pinning processes. We therefore refer to the deformation mechanism as pinning-controlled dissolution-precipitation creep (P-DPC).

Furthermore, we establish a new constitutive equation for this P-DPC, based on an exponential diffusion creep flow law, to model our experiments and tackle the extrapolation to various natural conditions. This flow law is supported by the microstructural evidence for the deformation mechanisms. Extrapolations show that the shear zones of the granitoid middle crust may be magnitudes weaker than extrapolated so far, and deformation may occur at magnitudes faster rates. The brittle to viscous transition may be shifted to shallower levels. This may have implications for the seismogenic zone and/or stress fields below geothermal reservoirs. Most importantly, we show the necessity to take polymineralic rocks into consideration for various numerical model applications.

How to cite: Nevskaya, N., Berger, A., Stünitz, H., Zhan, W., Plümper, O., Ohl, M., and Herwegh, M.: Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17191, https://doi.org/10.5194/egusphere-egu24-17191, 2024.

EGU24-19186 | Orals | TS1.11

Could earthquakes cause rapid dehydration of serpentinite? 

Lucie Tajčmanová, Sebastian Cionoiu, and Dan Schuppenhauer

Dehydration reactions can influence the occurrence of earthquakes at a range of depths, highlighting the importance of understanding these reactions in the study of seismic activity. We have performed several pilot experiments that included the construction of a controllable fast pressure drop unit attached to the piston-cylinder apparatus. This setup makes it possible to simulate conditions that represent a fast pressure drop during an earthquake event. We focused on serpentinite dehydration because 1/ it plays an important link between the deep geodynamic processes occurring in subduction zones and the seismic and volcanic activity and 2/ the interplay between serpentinite dehydration and deformation during the earthquake cycle is not yet fully understood. To test the experimental setting, we first performed a series of static experiments under the conditions that are already in the olivine stability field. After the static experiments at high pressure (1.1 GPa), we performed the controlled fast pressure drop experiments to 0.3 GPa as well as the ramping experiments, in which a series of pressure build-ups and drops were performed maintaining the high temperatures (570 to 640 °C) to simulate the earthquake cycle. In these experiments, olivine was an order of magnitude more abundant than in the one-hour low-pressure static experiment. The pressure drop occurs in seconds. The ramping experiment lasted only 10 mins before cooling down. The results may challenge conventional wisdom about the timescales of mineral reactions under extreme conditions, such as during earthquakes.

How to cite: Tajčmanová, L., Cionoiu, S., and Schuppenhauer, D.: Could earthquakes cause rapid dehydration of serpentinite?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19186, https://doi.org/10.5194/egusphere-egu24-19186, 2024.

EGU24-19980 | ECS | Posters on site | TS1.11

Eurasian plate-scale stress model considering driving and resistive forces 

Renato Gutierrez Escobar and Rob Govers

Our goal is to constrain magnitudes and directions of forces that may explain present-day natural stresses within the Eurasian plate. Driving forces such as horizontal gravitational stresses (HGSs), mantle convective tractions including dynamic topography, and plate interaction tractions with bounding plates are considered. HGS resulting from lateral variations in gravitational potential energy are particularly relevant in the context of the Eurasian plate because there are no major slabs attached to it (i.e., no slab pull force). We illustrate that recently published models of lithospheric density including lateral variations in the lithosphere-asthenosphere boundary result in significantly different HGSs. Furthermore, we include observed major faults into a 2D spherical cap elastic model of the Eurasian plate. We present results of forward FEM calculations and compare them with observed stress directions from the world stress map. We propose different objective functions that determine the misfit of the modelled and observed stresses, fault slip directions, and magnitudes, the deviation of the net torque on the plate from zero, and the model representation error. Our analysis represents a first step towards a Bayesian inference workflow to constrain the dynamics of the Eurasian plate.

How to cite: Gutierrez Escobar, R. and Govers, R.: Eurasian plate-scale stress model considering driving and resistive forces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19980, https://doi.org/10.5194/egusphere-egu24-19980, 2024.

EGU24-20499 | Posters on site | TS1.11

Three-dimensional numerical modelling of drilling-induced tensile wall fractures 

Martin Schöpfer, Mario Habermüller, Nicola Levi, and Kurt Decker

Drilling-induced tensile fractures (DITFs) form due to stress concentrations around a wellbore and are in vertical wells typically parallel to the largest horizontal far-field stress and normal to the least horizontal far-field stress. The peak pressure in the wellbore exerted by the drilling mud that the wall rock can sustain is given by the so-called Hubbert-Willis (H-W) criterion, which predicts that wall rock failure takes place when the circumferential effective stress at the borehole wall reaches the tensile strength of the wall rock. However, even though the H-W criterion is a valuable fracture-initiation criterion, it cannot predict if and how an initiated fracture propagates. Linear elastic fracture mechanics (LEFM) can provide a solution to these questions under simple loading conditions, e.g. a vertical borehole in a rock mass that is under an Andersonian stress state. Predicting the initiation and propagation of DITFs in more complex settings, such as inclined boreholes or wellbores in mechanically layered sequences, however, necessitates three-dimensional numerical modelling.

Here we present results of three-dimensional numerical Rigid Body Spring Network (RBSN) lattice modelling. The model comprises so-called rigid blocks (tetrahedra in the present study), that interact with each other and can be bonded at their contacts; these bonds fail when the effective normal stress exceeds the bonds tensile strength, which corresponds to micro-fracture of the wall rock. Coalescence of these micro-cracks leads to the formation of macroscopic fractures. Wellbore failure is modelled by means of a hollow cylinder discretised by these bonded rigid blocks. The remote (tectonic) stress is applied to the hollow cylinder’s outer surface whilst the pressure exerted by the drilling mud is applied to its inner surface. Fractures connected to the wellbore receive the same internal pressure as the wellbore and quasi-static fracture propagation is achieved by gradually increasing the pressure on the borehole wall.

Validation of the numerical model under simple loading conditions illustrates that fracture lengths and associated aperture profiles as a function of wellbore pressure correspond well with LEFM predictions. Numerical models of moderately inclined boreholes exhibit stepping DITFs, where fracture stepping is most pronounced when the wellbore is inclined towards the least horizontal stress direction and no fracture stepping occurs when the wellbore is inclined towards the greatest horizontal stress direction. In mechanically layered sequences comprised of layers with different Young’s modulus, DITFs first nucleate in the stiff beds. Complex fracture geometries emerge in mechanically layered sequences, such as fracture stepping within individual beds or at layer boundaries. The detailed evolution of these more complex DITFs depends on several factors, such as the orientation of the remote principal stresses and layering relative to the wellbore axis. Our numerical modelling approach permits to systematically investigate the effects of these different factors on the geometry of DITFs and therefore offers a new tool that can assist in construing the mechanical genesis of fractures imaged in borehole logs and the current stress in the Earth’s crust.

How to cite: Schöpfer, M., Habermüller, M., Levi, N., and Decker, K.: Three-dimensional numerical modelling of drilling-induced tensile wall fractures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20499, https://doi.org/10.5194/egusphere-egu24-20499, 2024.

The 1D Geomechanical Models (1DGM) were done for four vertical boreholes in the Early Paleozoic shale sequences of the Baltic Basin in Poland. The models assumed an elastic rock behaviour with anisotropy in VTI symmetry. The far-field horizontal stresses were calculated as the sum of two components: the vertical stress derivative acting on the horizontally constrained rock column and the effect of elastic tectonic strains. Local stresses in the borehole wall were assumed to induce breakouts (BBs) and drilling-induced tensile fractures (DITFs). Hydraulic fracturing tests additionally validated the stress modelling results.

Micro-resistivity images from XRMI logging revealed irregular BBs, usually confined to individual layers, often non-symmetrical, and with a tendency to encompass the entire borehole wall. Despite their irregularity, statistical analysis of their orientation provides a good quality and stable stress orientation.

The initial modelling results, balancing the cumulative length of the modelled (BBM) and observed (BBO), revealed a systematic misfit between BBm and BBo locations. A detailed comparison between the BBm and BBo intervals concluded that the artificial degradation of Young's modulus and Poisson's ratio is caused by the perturbation of the velocity of the acoustic wave from the dipole acoustic tool passing through the intervals with irregular BBs. This makes it impossible to model the BBs in the places where they are present. To deal with this, the initial stress models were recalculated to the final models in which the BBm were avoided in intervals where there were no BBO.

The initial and final stress models differ significantly in terms of the tectonic strain values and the combined length of the BBm. Still, their stress profiles are similar due to the small contribution of tectonic strain to the far-field stresses. We concluded that irregular BBs developed due to small differential horizontal stresses, causing abrupt BB failure with rapidly growing angular width. The stress layering between lithostratigraphic units was obtained with a dominance of the normal faulting stress regime in the lower borehole sections and the reverse faulting present in the upper sections. The minor regional elastic tectonic strain value for the shale sequence was determined to be an order of magnitude lower than the strain in the crystalline basement, as determined from the satellite geodetic strain rate. We expect that this discrepancy could be explained by a higher rate of viscous relaxation in the shale sequence with > 60% of the clay mineral content. This suggests the need to implement the viscous relaxation into the 1DGM of sedimentary sequences.

How to cite: Jarosinski, M., Bobek, K., and Pachytel, R.: Geomechanical models of the shale sequence of the Baltic Basin (Poland): possible case of elastic properties degradation and viscous stress relaxation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20951, https://doi.org/10.5194/egusphere-egu24-20951, 2024.

EGU24-21427 | Orals | TS1.11

Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting 

Giulia Mingardi, Julien Gasc, Robert Farla, and Alexandre Schubnel

Numerous studies have illustrated that mineral transformations have the capability to induce faulting at elevated pressure and temperature (PT), circumstances in which ductile flow would typically dominate. This mechanism, commonly known as transformational faulting, emerges as a plausible explanation for the puzzling phenomenon of deep-focus earthquakes occurring at depths up to 700 km. Currently, the debate partly revolves around determining why certain phase transformations lead to faulting while others do not. To better understand this phenomenon, we can compare different transformations taking place in similar experimental conditions and see how they do or do not cause strain localization and faulting. In this regard, we conducted a series of five deformation experiments in the large volume press at the PB61 beamline at DESY synchrotron. Two of these experiments involved deforming germanium-olivine samples as they transformed into ringwoodite (the high-pressure phase). The other three experiments were carried out on quartzite (novaculite) samples while they were transforming to coesite. Throughout the experiments, we collected X-ray diffraction patterns and images concurrently with the collection of Acoustic Emissions (AEs).

The results indicate, in both quartz and olivine experiments, the growth of the high-pressure phase at various rates depending on PT conditions and equilibrium overstep. Specifically, we observed rapid olivine-ringwoodite kinetics at elevated PT, far from equilibrium, while slower kinetics were noted for the quartz-coesite transformation. Thousands of AEs were collected in each experiment, and their locations reconstructed using arrival times on the six transducers used. Interestingly, the spatial distribution of these AEs revealed that for some quartz-coesite experiments, AEs originated from fault planes that formed within the initially intact rock cores. Furthermore, an analysis of the AE catalogues, focusing on the magnitude-frequency distribution, revealed a wide range of b-values influenced by varying PT conditions and transformation kinetics. This observation underscores the different underlying mechanisms since the obtained b-values are high when transformation and strain are distributed and lower when strain is localized (i.e., when a fault plane develops).

Our study supports the major role of mineral transformations in inducing faulting under high PT. These findings will help better quantify the intricate relationships between mineral transformations and faulting and in turn contribute to a better understanding of the fundamental geological processes behind deep and intermediate earthquakes.

How to cite: Mingardi, G., Gasc, J., Farla, R., and Schubnel, A.: Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21427, https://doi.org/10.5194/egusphere-egu24-21427, 2024.

EGU24-428 | ECS | Orals | TS1.6

AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS 

Efe T. Ayruk, Muhammed Turğut, İlay Farımaz, Mehmet Köküm, Roger Bilham, and Uğur Doğan

The Mw 7.8 earthquake of 2023 ruptured the southern (main) branch of the East Anatolian Fault (EAF), followed by the Mw 7.6 earthquake on the northern (Çardak Fault) branch of the EAF nine hours later. In March, we installed ten carbon-rod extensometers across segments of the main and northern branches of the ruptured faults, where potential slip deficits were considered possible, to investigate if afterslip continues. It is important to measure afterslip to understand the behaviour of a fault, if any, resulting from stresses associated with local coseismic slip deficits.  Seven of these extensometers recorded less than a few millimetres of slip since March. In Göksun near the western end of the Çardak fault, we recorded more than a 25 mm of accelerating afterslip preceding local aftershocks of magnitude ≤Mw5.1.

The Mw 6.8 Elazığ-Sivrice earthquake of January 24, 2020, and the Mw 7.8 Kahramanmaraş earthquake of February 6, 2023, stopped in the Pütürge region, where it is named as Pütürge Gap. To understand why these two earthquakes terminated there, an array of five extensometers were ultimately deployed. One of the extensometers, which is 52 m long, shows that slip > 3.8 mm/yr continues at depth. Extensometers spaced 45 km apart recorded an eastward propagating subsurface creep event in September 2023. Four cGPS stations recording at 5 Hz were installed in an array to better investigate the subsurface evolution of aseismic slip on the Pütürge Fault in the village of Taşmış.

How to cite: Ayruk, E. T., Turğut, M., Farımaz, İ., Köküm, M., Bilham, R., and Doğan, U.: AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-428, https://doi.org/10.5194/egusphere-egu24-428, 2024.

EGU24-2299 | ECS | Posters on site | TS1.6

Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults 

Silvia Aldrighetti, Giulio Di Toro, and Giorgio Pennacchioni

Earthquakes are the result of propagation at ∽km s-1 of a rupture and associated slip at ∽m s-1 along a fault. The total energy involved in a seismic event is unknown, but qualitatively most of it is dissipated by rock fracturing and frictional heat. Seismic fracture energy G (J m-2) is the energy dissipated in the rupture propagation and can be estimated by the inversion of seismic waves. However, its physical significance remains elusive. G may include the contributions of both rock fracturing (energy to form new rock surfaces US, J m-2) and fault frictional heating (Q, J m-2) per unit fault area. Here we determine both US and Q in natural and experimental pseudotachylyte-bearing faults, following the approach used by Pittarello et al. (2008). In fact, in pseudotachylytes, or solidified frictional melts produced during seismic slip, (i) US is proportional to the surface of new fragments produced in both the slip zone and in the wall rocks, and (ii) Q is proportional to the volume of frictional melt.

The selected natural pseudotachylytes belong to the east-west-striking, dextral, strike-slip Gole Larghe Fault Zone (Adamello, Italian Alps). To estimate US we employed Electron Back-Scatter Electrons (EBSD), High Resolution Mid Angle Back-Scattered Electrons (HRMABSD) and Cathodoluminescence-Field Emission Scanning Electron Microscopy (CL-FESEM). In particular, CL-FESEM imaging reveals a microfracture network in the wall rocks that cannot be detected with the other techniques. In the pseudotachylyte-bearing fault, the microstructural analysis reveals (i) a high degree of fragmentation of the wall rock adjacent to the pseudotachylyte fault vein (formed along the slip surface), with clast size down to <90 nm in diameter, and (ii) a systematic difference in fracture density and orientation of the microfractures in the two opposite wall rock sides of the fault. In fact, in the northern wall rock the fracture density is low and the microfractures are oriented preferentially east-west, while in the southern wall rock the fracture density is high and oriented preferentially north-south. Instead, this asymmetric microfracture pattern is absent in the experimental pseudotachylytes produced by shearing pre-cut cylinders of tonalite (the rock that hosts natural pseudotachylytes) in the absence of a propagating seismic rupture. Thus, the formation of the asymmetric microfracture pattern is associated with the propagation of the seismic rupture and, therefore, can be used to estimate US.

In natural pseudotachylytes, fracture density decreases exponentially from the pseudotachylyte-wall rock contact towards the wall rock. The rock volumes with highest coseismic damage at the contact with the pseudotachylytes were assumed to represent the host-rock damage preceding frictional melting along the slip zone. Based on this assumption, US was estimated in the range 0.008-1.35 MJ m-2, while Q was estimated from the thickness of the pseudotachylyte vein to be ∽32 MJ m-2. In the case of the Gole Larghe Fault, numerical modelling of seismic rupture propagation yields fracture energies G in the range 8-67 MJ m-2 suggesting that US is a subordinate component of G and that most of the seismological fracture energy is heat.

How to cite: Aldrighetti, S., Di Toro, G., and Pennacchioni, G.: Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2299, https://doi.org/10.5194/egusphere-egu24-2299, 2024.

EGU24-3922 | ECS | Orals | TS1.6

Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence 

Fengjiang Ju, Haoran Meng, Xiaofei Chen, and Chunquan Yu

Advancing our understanding of earthquake nucleation process can shed lights on earthquake prediction, early warning, and hazard assessment. Foreshocks, which usually refer to smaller earthquakes that occur before an earthquake, exhibit good temporal and spatial correlations with the mainshock. Investigating the relationship between foreshocks and mainshocks can therefore provide valuable insights into earthquake nucleation mechanisms and contribute to the improvement of earthquake prediction and early warning capabilities.

A recent study on the 2019 Mw 7.1 Ridgecrest earthquake sequence suggests that immediate foreshocks often share similar waveforms to the P-waves of subsequent earthquakes, differing only in amplitude. This similarity is believed to arise from the fractal nature of fault fracture processes. Consequently, there might be many immediate foreshocks with similar waveforms hidden in ambient noise that have gone undetected. Two methods have been proved to be effective in detecting small events: the Matched Filter Technique (MFT) and the Source-Scanning Algorithm (SSA). The MFT relies on template events to detect small events by stacking cross-correlograms between the waveforms of the templates and potential events. The conventional MFT, however, requires that the small events be located in the vicinity of one of the template events and does not provide the accurate locations of detected events. On the other hand, SSA is a migration-based approach that involves stacking non-negative waveforms, envelopes, and their extended characteristic functions. However, due to their tendency to provide absolute locations, SSA are heavily influenced by the accuracy of the velocity model and struggle to accurately detect earthquakes that are obscured by noise.

In our study, we prioritize the accuracy of relative event locations when studying the relationship between foreshocks and mainshocks. To address this concern, we have developed an advanced method that combines the strengths of cross-correlation and beamforming analyses. This method allows us to detect and relatively locate small seismic events simultaneously using dense array data. For the 2021 Ms 6.4 Yangbi  aftershock sequence, we first compute the cross-correlograms of the contentious records with the P-waves/S-waves of the target earthquake, respectively. We then grid searches around the hypocenter using N-th root stacking to detect and locate the immediate foreshocks. Upon detecting numerous immediate foreshocks, we proceed to statistically quantify the earthquake nucleation process or investigate the nucleation mechanism.

How to cite: Ju, F., Meng, H., Chen, X., and Yu, C.: Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3922, https://doi.org/10.5194/egusphere-egu24-3922, 2024.

EGU24-4427 | Orals | TS1.6

Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults 

Kevin P. Furlong, Matthew W. Herman, and Kirsty A. McKenzie

A general correlation between maximum co-seismic fault slip and fault length has been well constrained by observations from numerous earthquakes occurring on many crustal faults. In spite of this global consistency, there are notable examples of co-seismic fault slip magnitudes that far exceed the expected maxima for the fault dimensions.  Two instances of extreme fault slip that occurred on short-to-moderate length upper-plate faults in subduction systems, where the megathrust lies at shallow depths are the 2016 Kaikoura (New Zealand) earthquake, and the 1855 Wairarapa (New Zealand) earthquake. In both cases, co-seismic fault slip was 5 to 10 times greater than expected from the rupture length - fault slip scaling relationships. The typical crustal fault model  is a fault with a brittle-to-ductile transition at depth; in this scenario, co-seismic slip is inhibited by viscous resistance from the deeper, ductile component of the fault.  In contrast, the tectonic characteristics of faults that experience extreme co-seismic slip, involve upper plate faults that truncate against the megathrust at seismogenic depths (i.e. are fully frictionally coupled over their entire depth extent). During a megathrust earthquake, the plate interface unlocks and upper-plate faults that extend to the ruptured plate interface transiently experience free-slip boundary conditions on both their upper (surface) and lower (megathrust) ends. As a result, such upper-plate faults can potentially experience full strain release (and therefore maximum slip), independent of their length. For appropriately oriented faults, this effect may be enhanced by co-seismic stress changes associated with the megathrust earthquake. 

Geologic evidence of large displacement (and/or displacement rate) upper-plate faults in other subduction systems indicates this process may commonly occur. One example is a set of upper-plate faults along the Cascadia margin (near Newport, Oregon), that have strike-slip geologic slip rates, averaged over 10s of thousands of years, exceeding tens of mm/yr and approaching local plate convergence rates. These upper-plate Cascadia faults are also located where the plate interface is sufficiently shallow and seismogenic, indicating that these high-slip, upper-plate faults are likely frictionally locked over their entire depth range. In spite of the high overall slip rates of these upper-plate faults, because they are locked along their entire depth extent between earthquakes,  they may be unrecognized by inter-seismic geodetic observations.

How to cite: Furlong, K. P., Herman, M. W., and McKenzie, K. A.: Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4427, https://doi.org/10.5194/egusphere-egu24-4427, 2024.

EGU24-4550 | Posters on site | TS1.6

Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations 

Yariv Hamiel and Roger Bilham

We use geodetic measurements to characterize aseismic deformation along the western boundary fault of the Dead Sea pull-apart basin, which is located at the southern part of the sinistral Dead Sea Fault. This research provides constraints on patterns and timescales of deformation and its dependence on regional tectonics and the rheology of the upper crust. We use creepmeter, GNSS, InSAR and airborne LiDAR observations and show transient aseismic slip on the western boundary fault of the Dead Sea basin. A biaxial creepmeter with a 30 s sampling interval was installed in early 2021 showing high extensional deformation (an average rate of ~8.6 mm/yr), which is consistent with the ~30 cm of subsidence recorded 2017-2019 differential LiDAR data. The data imply modulated slip on a 60° dipping normal fault with maximum slip rates of ~0.5 µm/hour starting in late August and varying close to zero in late April. We attribute these large movements to local tectonics, sediment compaction, thermo-elastic response and dissolution of subsurface salt responsible for the formation of sink-holes in the region. The creepmeter measurements also show some sinistral deformation with an average rate of ~2.1 mm/yr, comparable to the rate of 2.5±0.4 mm/yr that was observed for the Sedom Fault, the southernmost segment of the western boundary fault, using GNSS data. Several minor creep events were detected by the creepmeter. The 19 Feb 2022 creep event lasted more than an hour following heavy rain in this area with abrupt sinistral slip of ~2.5 mm preceding dilation and dip-slip by 20 minutes. Small Baseline Subset (SBAS) analysis of InSAR data reveals up to 7mm/yr of line-of-sight deformation across the western boundary fault, north of the creepmeter. It also reveals high subsidence rate (up to ~20 mm/yr) along the southern shores of the Dead Sea Lake that can be explained by high compaction rate of clay sediments and reduction of pore pressure along the lake shores. This high subsidence rate is also observed in our near shore GNSS stations. Our results indicate that deformation within the Dead Sea basin is not solely controlled by the active tectonics. The observed vertical deformation is apparently modulated by the response of sediments to seasonal variations of local conditions.

How to cite: Hamiel, Y. and Bilham, R.: Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4550, https://doi.org/10.5194/egusphere-egu24-4550, 2024.

EGU24-4561 | Orals | TS1.6

Boso seismicity swarm propagation driven by slow slip stress change 

Baptiste Rousset, Asaf Inbal, Roland Bürgmann, Naoki Uchida​​, Anne Socquet, Lou Marill, Takanori Matsuzawa, and Takeshi Kimura

The interactions between aseismic slip and seismicity is mostly studied during postseismic afterslip associated with the generation of aftershocks following large earthquakes. However because of the large stress perturbations produced by the coseismic rupture, it remains difficult to distinguish the contribution of the coseismic stress perturbation and the effects of stresses induced by the afterslip on the triggering of aftershocks. Studying seismicity triggered by slow slip events enables us to understand the direct effect of aseismic slip on the generation of the seismicity. While most subduction slow slip events are deep-seated, at the down-dip edge of seismogenic zones accompanied by tectonic tremors, some are also observed at shallower depths associated with seismic swarms. Among them are the well-studied Boso slow slip events located on the Sagami trough, between 10 and 20 km depth. Recorded every ~4 years since 1996, they are always accompanied by swarms of Mw 1 to 5 earthquakes on their northern and western flanks. Being located right beneath the Boso Peninsula coastline, the kinematics of these slow slip events is particularly well imaged by dense GNSS and tiltmeter networks. In this study, we model the time dependent aseismic slip of the 2018 Boso slow slip event, with the largest moment released of all Boso slow slip events, by inverting time step by time step the slip on the fault with joint GNSS and tiltmeter data. We do not impose arbitrary temporal smoothing in the inversion and find that the well constrained fault slip is first growing and then migrating southwestward with a migration speed of ~ 2 km/day. In order to model the interaction with the seismicity, we compute the Coulomb stress change due to the transient slip on receiver faults located in 9 cubes centered in the seismicity swarm and parallel to the subduction interface. From June 2nd to June 18th, the seismicity is migrating up-dip at a rate of 1 km/day. This migration period coincides with the peak slip rate and with Coulomb stress produced by the slow slip migrating updip together with the seismicity, indicating a causal relationship. Adopting a rate and state friction formalism to explain the nucleation of the seismicity, we finally investigate the ensemble of parameters, in particular the constitutive parameter that relates changes in stress to logarithmic changes of slip velocity, the effective normal stress and the tectonic stressing rates, that can explain the seismicity rate. 



How to cite: Rousset, B., Inbal, A., Bürgmann, R., Uchida​​, N., Socquet, A., Marill, L., Matsuzawa, T., and Kimura, T.: Boso seismicity swarm propagation driven by slow slip stress change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4561, https://doi.org/10.5194/egusphere-egu24-4561, 2024.

EGU24-5061 | ECS | Orals | TS1.6

Complex Frictional Behavior of Clay and Implications for Slow Slip  

Giuseppe Volpe, Cristiano Collettini, Jacopo Taddeucci, Chris Marone, and Giacomo Pozzi

The shallowest region of subduction megathrust accommodates deformation by a spectrum of seismic modes including continuous aseismic creep and peculiar seismic phenomena as slow slip events. However, the mechanisms behind these phenomena remain enigmatic because they are not explained by conventional frictional models. This because the shallowest regions of subduction zones are characterized by unconsolidated, clay-rich lithologies that, nominally, cannot nucleate seismic events due to their frictionally weak and rate-strengthening attributes. Here we present laboratory friction experiments showing that clay-rich experimental faults with bulk rate strengthening behavior and low healing rate can contemporaneously creep and nucleate slow slip events. These instabilities are self-healing, slow ruptures propagating within a thin shear zone and driven by structural and stress heterogeneities. We propose that the bulk rate-strengthening frictional behavior promotes the observed long-term aseismic creep whereas local frictional mechanism causes slow rupture nucleation and propagation. Our results illustrate the complex behavior of clay-rich lithologies, providing a new paradigm for the interpretation of the genesis of slow slip as well as significant implications for seismic hazard.

How to cite: Volpe, G., Collettini, C., Taddeucci, J., Marone, C., and Pozzi, G.: Complex Frictional Behavior of Clay and Implications for Slow Slip , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5061, https://doi.org/10.5194/egusphere-egu24-5061, 2024.

The acoustic emissions (AEs) produced during the shearing of granular materials reflect the accumulation and release of stress, offering valuable insights into the failure mechanisms of seismic faults and stick-slip-controlled landslides. While various characteristics such as amplitude, energy, counts, and frequency of AE signals generated by stick-slip have been studied, the stress changes corresponding to different frequency AEs at various stages of the stick-slip process remain unclear. This knowledge gap hinders our understanding of the precursory signals leading to stick-slip failure. In order to enhance our comprehension of the physical mechanisms underlying granular stick-slip, we conducted monitoring of both mechanical and AE signals using high-frequency (2 MHz) synchronous acquisition. This was done during the constant-speed shearing of packs containing uniform glass beads of different sizes under varying normal stresses. Our findings revealed an accelerated release rate of AE energy in tandem with sample volume dilatation. Additionally, the stress drop during stick-slip increased with higher normal stress and particle size. This study identified three distinct events during a single cycle of stick-slip: main slip, minor slip, and microslip. We analyzed the AE frequency spectra associated with each of these events. Main slip and minor slip correlated with stress drop, generating high-frequency AEs (approximately several hundred kHz). In contrast, microslip produced lower AE frequencies (around tens of kHz) and exhibited stress strengthening. These characteristics, overlooked in prior studies due to low-frequency acquisition, suggest that microslip is primarily a result of sliding on grain contacts, while main slip and minor slip arise from the breakage and reformation of force chains. The low-frequency AEs from microslip may serve as a crucial precursor to seismic faults and landslides, providing a deeper understanding of the granular stick-slip phenomenon.

How to cite: Gou, H. and Hu, W.: Detection of Stick-Slip Nucleation and Failure in Homogeneous Glass Beads Using Acoustic Emissions in Ring-Shear Experiments: Implications for Recognizing Acoustic Signals of Earthquake Foreshocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5252, https://doi.org/10.5194/egusphere-egu24-5252, 2024.

EGU24-5921 | ECS | Posters on site | TS1.6

Interaction of fault slip with fast fluid pressure transients in subduction zones 

Avinash Gupta, Nikolai M. Shapiro, Jean-Paul Ampuero, Gaspard Farge, and Claude Jaupart

This study investigates the dynamic interplay between fluids and fault slip transients in the portion of subduction zones subject to slow earthquakes. The permeable subduction interface in this region is believed to be saturated with fluids supplied by metamorphic dehydration reactions in the downgoing plate. Following Farge et al. (2021), we consider a model of a heterogeneous subduction channel filled with low-permeability plugs that behave as elementary fault-valves. Such a system is characterized by an intermittent fluid transport and rapid and localized pressure transients. Episodic rapid build-ups and releases of the fluid pressure affect the frictional strength on the fault and can result in transient slip accelerations. To study the possible effect of episodic fast fluid pressure variations on fault slip, we use numerical simulations in a 2D in-plane shear geometry. The fault is governed by rate-and-state friction, with velocity-strengthening steady-state properties, and is forced with time and spatially variable pore fluid pressure. In an initial set of tests, we show that periodic pore pressure oscillations can accelerate the fault slip akin to observed slow slip events. We then investigate how the fault slip responds to more complex and “realistic” pore pressure histories generated by the dynamic permeability model of Farge et al. (2021). Our results underscore the possible role of input fluid flux and permeability structure in determining the variations of fault slip and, in particular, in facilitating the slow slip events. 

How to cite: Gupta, A., Shapiro, N. M., Ampuero, J.-P., Farge, G., and Jaupart, C.: Interaction of fault slip with fast fluid pressure transients in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5921, https://doi.org/10.5194/egusphere-egu24-5921, 2024.

EGU24-7813 | Posters on site | TS1.6

The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia 

Manel Prada, Sara Martínez-Loriente, Jonas B. Ruh, and Valentí Sallarès

The present-day Eurasia-Africa plate convergence offshore SW Iberia gives rise to a diffuse plate boundary marked by deep lithospheric thrust and strike-slip faults. The Horseshoe Abyssal Plain Thrust (HAT) stands out as a key structure accommodating plate convergence, and it has been the site of deep (> 30 km depth) and large magnitude (Mw > 6) earthquakes. Additionally, the HAT has been proposed to be the source of the 1755 Lisbon earthquake (estimated Mw≥8.5), one of the most destructive earthquakes and tsunami in the history of Europe. The geometry of the fault and the physical properties of rocks surrounding it have been determined through tomographic models derived from controlled-source seismic data. Although large earthquakes along the HAT primarily occur at considerable depths within the peridotitic mantle (~40 km depth), the fault intersects a region of serpentinized mantle at shallower depths (10-20 km depth). In contrast to peridotite that undergoes seismic deformation, the frictional behaviour of serpentinized peridotite depends on factors such as pressure, water content, temperature, and slip velocity. Laboratory measurements indicate that serpentinite transitions from rate-strengthening behaviour at plate tectonic rates to rate-weakening at seismic slip rates. This dual nature suggests that large deep earthquakes, nucleated in pristine peridotite, could rupture seismically through the weaker serpentinized peridotite. While this mechanism has been proposed to explain the HAT's potential to generate large tsunamigenic earthquakes, it remains untested. In this study, we use dynamic rupture numerical simulations to investigate the role of serpentinized peridotite in the rupture process and the tsunamigenic potential of the HAT. In particular, we explore various frictional scenarios to determine the slip pattern necessary to account for the previously estimated tsunamigenic uplift associated with the 1755 Lisbon earthquake.

How to cite: Prada, M., Martínez-Loriente, S., B. Ruh, J., and Sallarès, V.: The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7813, https://doi.org/10.5194/egusphere-egu24-7813, 2024.

Topographic features such as seamounts can influence the buoyancy of the slab and the short- and long-timescale mechanical properties of the subduction interface. How seamounts in the trench interact with the upper plate accretionary wedge during subduction— their stress field, their potential for ‘decapitation’, and their ability to host large megathrust earthquakes— is not fully understood. We utilize exhumed rocks to investigate seamount–upper plate interactions at shallow subduction interface conditions. 

We focus on a 250-m-thick cross-section of deformed, weakly metamorphosed basalt, limestone, chert, argillite and greywacke exposed in the inboard part of the Chugach accretionary complex near Grewingk glacier, southern Alaska. Temperatures from Raman spectroscopy on graphite yield ~260°C, suggesting deformation and metamorphism down to ~15-20 km depth. Detrital zircon data from greywacke lenses within and outside the shear zone overlap within error suggesting emplacement over less than ~1 m.y. at ~167 Ma. 

Basalts in the shear zone are dismembered into ~3 slices up to 35 m thick, all of which contain limestone patches suggesting the basalt is derived from the seamount’s very top (limited decapitation). The basalt slices are bounded by high-strain melange-like shear zones up to 25 m thick, interpreted to represent décollements along which the seamount slices were underplated. These mélange belts exhibit a block-and-matrix texture with a macroscopically ductile argillite and chert matrix, and pervasively disaggregated and brittlely deformed greywacke and basalt lenses. Both the matrix and the blocks show several generations of dilational and shear veins, suggesting high fluid pressures and low differential stresses. Features suggesting deformation at fast (potentially seismic) strain rates include fluidized cataclasites, but these do not extend along strike for more than 0.25 m and do not occur within the larger (m-to-dm-scale) basalt lenses, suggesting that large-magnitude earthquakes were limited during seamount underplating. Instead, the observed mix of brittle and macroscopically ductile deformation at high fluid pressures is more consistent with a potential record of shallow tremor and slow slip.

Our findings support geophysical observations and numerical models that suggest relatively weak mechanical and seismic coupling between seamounts and the overriding plate, and are consistent with recent suggestions (e.g. for the Hikurangi margin) that sediment envelopes around subducting seamounts are conducive to slow slip and tremor.

How to cite: Behr, W., Akker, I. V., and Rast, M.: Deformation processes during seamount dismemberment and underplating along the shallow subduction interface: a case study from the Chugach Complex, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8244, https://doi.org/10.5194/egusphere-egu24-8244, 2024.

EGU24-8731 | ECS | Posters on site | TS1.6

Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet 

Xinze Li, Yongsheng Zhou, Lining Cheng, and Jianfeng Li

A large number of tourmaline fault mirrors are exposed in the north-south normal fault system in the southern part of the Tibetan Plateau. Microstructure analysis shows that the tourmaline fault mirror has the characteristics of co-seismic high speed friction sliding and high temperature plastic rheology. In order to reveal the mechanical process of friction-rheological strength and co-seismic slip of tourmaline fault, the frictional and rheological experiments were carried out on the gas-medium triaxial high temperature and high pressure experimental system using undeformed tourmaline in southern Tibet to determine the formation conditions of tourmaline fault mirror. The effective normal stress of frictional experiments is 100Mpa.The pore water pressure is 30MPa. The temperature is 25-500℃, and the shear slip rate is switched between 1μm·s-1, 0.2μm·s-1, 0.04μm·s-1. The experimental results show that stick-slip occurs at 200-350℃, and the speed weakens at 400℃ and 500℃. The rheological experiment temperature is 850-950℃. The pressure is 300MPa, and the strain rate is switched between 2*10-5s-1, 1*10-5s-1, 5*10-6s-1, 7.5*10-6s-1. The experimental results show that the natural tourmaline sample is mainly fractured flow under the experimental conditions. The strength of hot-pressed dry tourmaline sample decreases with increasing temperature. The rheological strength of water samples synthesized by hot pressing was significantly reduced.

How to cite: Li, X., Zhou, Y., Cheng, L., and Li, J.: Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8731, https://doi.org/10.5194/egusphere-egu24-8731, 2024.

EGU24-8767 | ECS | Posters on site | TS1.6

A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data 

Roxane Tissandier, Adriano Gualandi, Lauro Chiaraluce, Enrico Serpelloni, Mike Gottlieb, Catherine Hanagan, and Chris Marone

Low-angle normal faults (i.e. with a dip < 30°) were assumed to have a very low seismic potential (Sibson et al., 1985). However, several observations have shown that earthquakes and aseismic slip can occur along such faults. For instance, the Alto Tiberina Fault (ATF), a 60-km long normal fault with a 15° low angle dip located in the active sector of the Northern Apennines (Italy), is seismically active as well as is actively accommodating part of the Apennines extensional strain. However, the relative contribution of seismic and aseismic slip on it is still unclear. The central and northern Apennines experienced several seismic sequences in the recent decades and a Mw ∼ 4.6 aseismic event accompanied by a seismic swarm of similar or smaller size was also recorded in 2013-2014 along two synthetic and antithetic fault in the hanging-wall of the ATF (Gualandi et al., 2017). The interactions between such minor conjugate faults and the ATF compose a system undergoing complex behavior making the area an ideal candidate to improve our understanding of interactions between different slipping modes. We benefit from data of the Alto Tiberina Near Fault Observatory (TABOO-NFO; Chiaraluce et al., 2014) looking for aseismic events on the ATF and its surrounding faults. The dense network of GNSS, seismometers and borehole strainmeters provides a rarely attained high spatial (inter-distance < 10km) and temporal (from 2009 to nowadays) resolution framework enabling the study of the ATF fault system slip history. We search for transients with a semi-automatic detection tool of slow slip events based on kinematic inversions of strainmeters time series. We also test if these events interact with larger seismic events of the region. We present the strain time series processed with the EarthScope Strain Tools (EarthScope Consortium) and the preliminary signals detected with our tool. The fine analysis of the ATF would help better constraining the behavior of faults and more generally large events. 

How to cite: Tissandier, R., Gualandi, A., Chiaraluce, L., Serpelloni, E., Gottlieb, M., Hanagan, C., and Marone, C.: A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8767, https://doi.org/10.5194/egusphere-egu24-8767, 2024.

EGU24-9007 | Orals | TS1.6 | Highlight

A mechanical insight into the continuous chatter of a fault volume 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In recent decades, there has been a proliferation of observations related to spatiotemporally intricate slip events occurring in fault systems. These events encompass a spectrum of transient energy releases, ranging from slow slip events to low-frequency earthquakes (LFEs) and tremors, in addition to the more familiar creep and fast ruptures. The prevailing focus in recent research has been to interpret these events by considering variations in frictional behavior along the fault plane.

However, it is crucial to acknowledge the inherent geometric complexity of fault systems across multiple scales. Recent studies have illuminated the significance of incorporating a fault volume or damage zone surrounding the fault in the analysis of slip dynamics. In the context of this study, we endeavor to investigate the influence of "realistic" fault geometry on the dynamics of slip events. To achieve this, we approach the problem from three interrelated perspectives:

  • Forward Source Modeling: We employ forward source modeling techniques to simulate and understand the behavior of slip events.
  • Bridging Source Modeling and Observations: We establish a connection between our source modeling and observed data by generating synthetic surface records that can be compared to actual observations.
  • Energy Budget Analysis: We meticulously analyze the variations in the energy budget that occur throughout the earthquake cycles to gain insights into the mechanics of slip events.

Our primary objectives include deciphering how deformation within the volume is accommodated by both the off-fault damage zone and the primary fault. Specifically, we aim to determine the proportion of the supplied moment rate that is absorbed by off-fault fractures during an earthquake cycle. Additionally, we seek to unravel how the diverse sequences of complex behavior observed on the fault plane manifest in the signals recorded by seismic stations. This entails assessing the distinct contributions of the main fault and off-fault fractures to the radiated signals detected at the monitoring stations. Lastly, we delve into the evolution of the medium's energy budget throughout the earthquake cycles and evaluate the dissipative contribution of off-fault fractures to ascertain their energetic role in the context of earthquake cycles.

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: A mechanical insight into the continuous chatter of a fault volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9007, https://doi.org/10.5194/egusphere-egu24-9007, 2024.

EGU24-9169 | ECS | Posters on site | TS1.6

A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle 

Silvio Pardo, Elisa Tinti, Martijn Van den Ende, Jean-Paul Ampuero, and Cristiano Collettini

Fluid induced seismicity represents a significant issue for numerous activities related to geo-energy production. Enhanced geothermal systems, enhanced oil recovery, disposal of wastewater and carbon dioxide capture and storage are associated with subsurface fluid injection that can change the state of stress within the crust and can induce or trigger earthquakes. In several regions, M>3 earthquakes occurred following fluid injection, whereas in others seismicity has been accompanied by slow slip events. Although several mechanisms have been proposed to explain slow slip associated with fluid injection, the conditions leading to the observed spectrum of fault slip behavior still remain elusive. Here we used a quasi-dynamic boundary element method, the QDYN earthquake cycle simulator, to model the response of a fault governed by rate-and-state friction to fluid injection within a reservoir. We imposed low long-term loading rates to simulate a fault located in an area of slow active deformation, leading to natural earthquake cycles with very long recurrence times. We then imposed fluid pressure perturbations (one-way coupling) at different stages of the seismic cycle, to evaluate pore-pressure effects on the triggering of the next event. 

Our results show that for injection at high fluid pressure, earthquakes are in general immediately triggered (during injection or soon after) irrespective of the stage (early or late) of the seismic cycle, whereas at lower fluid pressure fast triggering is observed only when injecting in the late stages of the seismic cycle. Our models produce a spectrum of fault slip behavior, from regular to slow earthquakes. The latter are observed for specific fluid pressure, flow rate and injection time relative to the seismic cycle. The physics underlying this complex slip behavior remain to be explained, and further studies are required to define the injection conditions that favor the occurrence of slow slip instead of regular earthquakes.

How to cite: Pardo, S., Tinti, E., Van den Ende, M., Ampuero, J.-P., and Collettini, C.: A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9169, https://doi.org/10.5194/egusphere-egu24-9169, 2024.

EGU24-9437 | Orals | TS1.6

Creeping sections on continental strike slip faults as the signature of deep fluid upwelling 

Romain Jolivet, Dmitry Garagash, Dublanchet Pierre, and Jorge Jara

Aseismic slip has been recognized over the last 50 years as one of the modes of elastic stress accommodation by large tectonic faults. Long strike slip faults have been imaged with InSAR and scrutinized with GNSS networks and creepmeters, revealing the strikingly ubiquitous occurrence of aseismic slip globally. From the 600-km-long creeping section of the Chaman to the 70 km-long Ismetpasa creeping section along the North Anatolian Fault, geodetic imaging illustrates the rich behavior of such aseismic slip, from mm-scale transient episodes of slip to seemingly continuously sliding fault segments.

Most models explaining the occurrence of aseismic slip along continental faults rely entirely on an ad hoc parameterization of the frictional rheology of the fault. While the friction law governing slip along faults has been determined from laboratory experiments, the inference of the constitutive parameters of such friction law entirely derives from reproducing geodetic data in most cases. In particular, most creeping sections are interpreted as the signature of rate-strengthening material, diffusing stress through stable sliding. However, most rocks at seismogenic depths exhibit a rate-weakening behavior and some even show transient episodes of slip incompatible with purely strengthening properties. In addition, other mechanisms, including complex geometric configuration of faults or fluid circulation may offer the conditions for slow slip. Therefore, the direct inference of constitutive properties of a fault zone from kinematic observations may not be simple.

We propose here a model in which upwelling of fluids sourced in the upper mantle through a vertical fault zone leads to the conditions for slow slip, irrespective of the fault constitutive properties. We map aseismic slip along three different fault zones, including the North Anatolian Fault (Turkiye), the San Andreas Fault (USA) and the Leyte fault (Philippines) and find a systematic relationship between the effective locking depth and the occurrence of aseismic slip. Our model explains this modulation of locking depth along strike and the subsequent modulation of surface shear stressing rate with the along strike variation in the mantle fluid source. This model applied to fault segments with relatively high mantle fluid source leads to low effective normal stress, large nucleation size of a frictional instability, and predicts occurrences of shallow aseismic slip. We perform numerical modeling to show that the critical parameter is the flux of upwelling fluid through the fault zone, which increase leads to the widening of the near-surface region of aseismic slip and transition to full-fault aseismic slip at large enough flux. We finally discuss the potential sources of fluids explaining such behavior.

How to cite: Jolivet, R., Garagash, D., Pierre, D., and Jara, J.: Creeping sections on continental strike slip faults as the signature of deep fluid upwelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9437, https://doi.org/10.5194/egusphere-egu24-9437, 2024.

EGU24-9595 | Orals | TS1.6

Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments 

Corentin Noël, Pierre Dublanchet, and François Passelègue

Deformation within the upper crust is mainly accommodated through slip on fault systems. These systems can accommodate slip via different modes, going from aseismic creep (i.e., stable motion) to dynamic earthquake (i.e., unstable motion). Notably, a single fault is not confined to a specific slip mode, as recent geodetic observations have indicated that a single fault can exhibit both stable and unstable motions. The distinct slip behaviours have been attributed to fault spatial heterogeneity of the frictional properties, rheological transitions, or geometrical fault complexities.

To comprehensively characterize the impact of frictional heterogeneities, we deformed heterogeneous fault samples in a triaxial apparatus, at confining pressure ranging from 30 to 90 MPa. The fault planes, sawcut at a 30° angle from the sample axis, consisted of two materials: granite and marble. Experiments were conducted for both marble asperities embedded in granite and vice versa, alongside homogeneous fault samples of single lithology. The selection of granite and marble was based on their different mechanical and frictional characteristics, with granite exhibiting seismic behaviour, while marble demonstrated aseismic behaviour across the pressure range tested.

Our findings reveal that the stress drops of seismic events are dependent on fault composition, with faults containing higher granite content exhibiting larger seismic events. In addition, by coupling the inversion of the kinematic slip from strain-gauge measurements and the records of acoustic activity during experiments, we demonstrate that the nucleation and propagation of seismic events are significantly influenced by lithological heterogeneity on the fault plane. In the case of homogeneous faults, the seismic event nucleation is relatively straightforward, initiating in the highest stressed region and propagating uniformly. Conversely, heterogeneous faults display more intricate nucleation patterns, often featuring multiple nucleation regions converging into a major dynamic event. The dynamic event propagation is expedited when traversing granite areas and more restrained within the marble. Remarkably, our experiments demonstrate that heterogeneities are required in order to induce earthquake afterslip. These results emphasize the crucial role of fault heterogeneity in earthquake nucleation and propagation, highlighting that even minor lithological heterogeneities are sufficient to complicate laboratory earthquake dynamics.

How to cite: Noël, C., Dublanchet, P., and Passelègue, F.: Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9595, https://doi.org/10.5194/egusphere-egu24-9595, 2024.

EGU24-9961 | Orals | TS1.6 | Highlight

Do earthquakes start with precursory slow aseismic slip? 

Quentin Bletery and Jean-Mathieu Nocquet

The existence of an observable precursory phase of aseismic slip on the faults before large earthquakes has been debated for decades. We conducted a global search for short-term precursory slip in GPS data. We summed the displacements measured by 3026 high-rate (5-minutes sample) GPS time series—projected onto the displacements expected from precursory slip at the hypocenter—during 48 hours before 90 (moment magnitude ≥7) earthquakes. Our approach revealed a ≈2-hour-long exponential acceleration of slip before the ruptures, suggesting that large earthquakes do start with a precursory phase of slip acceleration. The results have since been questioned as being due to an unfortunate combination of common mode noise in GPS time series. We investigate this possibility along with complementary tests to quantify the likelihood of the proposed pre-slip and the common mode hypotheses.

How to cite: Bletery, Q. and Nocquet, J.-M.: Do earthquakes start with precursory slow aseismic slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9961, https://doi.org/10.5194/egusphere-egu24-9961, 2024.

EGU24-10783 | Orals | TS1.6

Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening. 

Einat Aharonov, Pritom Sarma, Renaud Toussaint, and Stanislav Parez

Many previous studies have explored the role of granular media in controlling friction of faults. A gap exists though in understanding the failure process and sliding of a fluid-saturated fault gouge. Here we use a coupled 2D DEM-fluid code to simulate fault-gouge as a layer of grains, sheared by a constant stress boundary. We explore and compare two scenarios: 1) a dry granular layer, in which shear stress on the top wall is incrementally increased, or 2) a fluid-saturated granular layer, into which fluid is injected, so that fluid pressure is incrementally increased. Once the applied stress/pressure is high enough, the layer fails and starts accelerating, until it reaches a steady-state sliding rate (determined by the layers’ velocity-strengthening friction). We next incrementally step-down the shear stress or fluid pressure. Consequently, the slip-rate is observed to slow down linearly with decreasing stress/pore-pressure, until the layer finally stops, at a stress/pressure lower than that required to initiate the failure. Both the dry and fluid-saturated granular systems exhibit two main behaviors: 1) velocity-strengthening friction, following the mu(I) rheology, 2) a hysteresis effect between friction and velocity, porosity and grain coordination numbers. The hysteresis and strain-rate dependence agree with previous experimental, numerical and theoretical results in dry granular media, yet our work suggests these behaviors extend to fluid-filled granular media. We theoretically predict the transient and steady-state observations for dry and fluid-saturated layers, using the mu(I) friction rheology with an added component of hysteresis. Importantly, we show that fluid-filled faults exhibit a process which is absent in dry systems: fluid-injected layers may exhibit failure delay, with some time passing between pressure rise and failure. We link this delay to pre-failure creeping dilative strain, interspersed by small dilative slip events. Our numerical and analytical results may explain: (i) field measurements of fault creep triggered by fluid pressure rise (e.g. via injection), (ii) fault motion which is triggered by fluid-injection but continues even after fluid pressure returns to its pre-injection level. (iii) observed delay prior to failure in fluid-injection experiments.

How to cite: Aharonov, E., Sarma, P., Toussaint, R., and Parez, S.: Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10783, https://doi.org/10.5194/egusphere-egu24-10783, 2024.

EGU24-10887 | Orals | TS1.6

Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks 

Paul Antony Selvadurai, Antonio Felipe Salazar Vasquez, Patrick Bianchi, Claudio Madonna, Leonid Germanovich, Alexander M. Puzrin, Carlo Rabaiotti, and Stefan Wiemer

A growing number of observations made using geodetic approaches have been able to detect large preparatory regions that experience accelerated deformation prior to and in close proximity to an earthquake’s hypocenter. An uptick in localized seismicity has also been observed in these regions and represents an opposite end-member of the spectra of deformation, in both space and time, from the opposite broad and slow process. If and how these preparatory observations are linked are not well understood. To study this, we conducted a triaxial experiment on a granitic rock sample instrumented with calibrated acoustic emission (AE) sensors and a distributed strain sensing (DSS) method using fibre optics. These two technologies were sensitive to seismic (100 kHz to 1 MHz) and aseismic (DC to 0.4 Hz) deformation at our sample scale and these were monitored as it was loaded and experienced brittle shear failure. DSS measurement allowed us to visualize the emergence of slow, heterogeneous strain fields that localized well before the failure of the sample. In the early stages of localized deformation, the regions exhibiting preferential damage were growing and doing so without producing seismicity. However, when approaching failure, these regions accommodating slow deformation began to accelerate and now produced clusters of seismicity. The cumulative seismic moment of the precursory seismicity was a fraction of the total anelastic deformation (< 0.1%) precluding the runaway dynamic failure. We also examined the clustering and frequency-magnitude distribution of the seismicity with respect to the localized strain field. In the later stages, moments prior to nucleation, the b-value begins to drop and becomes anti-correlated to the rapidly accelerating average volumetric strain rate measured using the DSS array. This observation better constrains the hypothesis that dilation of the relatively large preparation zone can host larger precursory earthquakes therein. These findings can help constrain models that better replicate the physics associated with the large spectrum of brittle deformation and will in turn help with our understanding of preparatory earthquake processes.

How to cite: Selvadurai, P. A., Salazar Vasquez, A. F., Bianchi, P., Madonna, C., Germanovich, L., Puzrin, A. M., Rabaiotti, C., and Wiemer, S.: Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10887, https://doi.org/10.5194/egusphere-egu24-10887, 2024.

Natural fault zone are complex objects. They not only consist of a fine-grained narrow fault core where the extensive shearing is observed, but it is also surrounded by pervasively fractured rocks, within an intricate 3-D geometry. If fault slip behavior is intrinsically linked to the properties of the fault core, the complex structure of fault zone systems impacts the rheological properties of the bulk, which influence the modes of deformation, and slip, as underlined by recent observations. Fault zone structure is therefore of key importance to understand the mechanics of faulting. Within the framework of a micromechanics based constitutive model that accounts for off-fault damage at high-strain rates, this numerical study aims to assess the interplay between earthquake ruptures along non-planar fault and the dynamically evolving off‐fault medium. We consider 2D inplane models, with a 1D self-similar fault having a root mean square (rms) height fluctuations of order 10-3 to 10-2 times the profile length. We explore the dynamic effect of fault-roughness on off-fault damage structure and on earthquake rupture dynamics. We observe a high‐frequency content in the radiated ground motion, consistent with strong motion records. It results from the combined effect of roughness-related accelerations and decelerations of fault rupture and slip rate oscillations due to the dynamic evolution of elastic moduli. These scenarios underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes, with a particular emphasis on seismic hazard assessment.

How to cite: Thomas, M. Y. and S. Bhat, H.: Combined Effect of Brittle Off-Fault Damage and Fault Roughness on Earthquake Rupture Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12095, https://doi.org/10.5194/egusphere-egu24-12095, 2024.

EGU24-12752 | Posters on site | TS1.6

Healing of fault surfaces: a field vs. experimental perspective 

Telemaco Tesei, Giancarlo Molli, Silvia Mittempergher, Giacomo Pozzi, and Francesca Remitti

“Fault healing” is the ability of fault rocks to recover strength after rupture, due to a combination of several physical processes that include cementation, compaction, asperity growth etc. Healing is fundamental in the earthquake physics because it allows for the repeated accumulation of energy along faults over multiple seismic cycles. Fault healing is commonly studied in the laboratory, through Slide-Hold-Slide (SHS) tests and cementation experiments. However, laboratory measurements and the microstructures of experimental fault rocks are difficult to compare with natural rocks, due to the difference in kinetics of physical mechanisms and the small spatio-temporal scale of experiments.

Here, we review the field and microstructural evidence of various processes of fault healing along a carbonatic fault surface, taking advantage of an outstanding case study: the Pietrasanta Normal Fault (NW Tuscany, Italy). In the field, the most common evidence of fault healing is the occurrence of cohesive fault rocks (cataclasites) and veins, but other fault surface properties may influence the re-strengthening of fault surfaces: e.g. adhesion phenomena (sidewall ripouts and fault surface patches) and geometrical complexity.

We compare these observations with frictional healing experiments carried out on carbonatic fault rocks, in which both fault gouges and cohesive slip surfaces were used. We propose that a fault surface composed by “patches” of cohesive fault rocks bounded by anastomosing slip zones are the result of complex cycles of gouge formation and healing, which modulate the interplay of adhesion and localization along the fault surface.

How to cite: Tesei, T., Molli, G., Mittempergher, S., Pozzi, G., and Remitti, F.: Healing of fault surfaces: a field vs. experimental perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12752, https://doi.org/10.5194/egusphere-egu24-12752, 2024.

In earthquake research, the discovery and ongoing investigation of interseismic transient processes has revealed that faults are non-steady between large earthquakes. These transients are typically identified in continuously operating tectonic GNSS stations, whereby an acceleration away from the average interseismic rates of displacement can be identified with a variety of time series analysis methods. However, the features of these transients can vary depending on the processing strategy employed to derive displacement time series from the raw GNSS observables.

In the processing strategy, the definition of the geodetic datum is necessary to determine global terrestrial reference frames (TRFs), providing an accurate and stable absolute reference of Earth's locations. It is essential for comprehending the dynamic changes in Earth's geometry driven by factors like tidal and non-tidal loading, plate tectonic seismic activity, and ongoing climate change. Therefore, just as geodesy aims for accuracy and stability in the TRF, the datum definition—i.e., the realization of the TRF-defining parameters origin, orientation, and scale—may emerge as a critical factor in processing GNSS networks for geodynamic purposes.

The purpose of this study is to assess up to what extent the transient velocities obtained from GNSS-derived displacement time series change under different regional and global datum definitions for the Cascadia subduction zone and Hikurangi margin; regions with very well-known catalog of interseismic transient tectonic events. In our study, we process data from Cascadia to produce network solutions both NNR (No-Net-Rotation) and NNR+NNT (No-Net-Translation) constraint for regional and global datum definition, respectively. We employed dual-frequency ionosphere-free linear combination observations from 125 GNSS stations for the time between 2015 and 2020. The same GNSS processing strategy is then followed for the Hikurangi subduction zone using a set of 72 stations from the GeoNet project as well as the same control stations used for Cascadia spanning from 2002 to 2010.

For the Cascadia displacement time series, we find variations in transient velocities under different datum definitions emphasizing the need for a comprehensive understanding of its impact on dynamic geophysical processes. Processing and analyses of the New Zealand data is ongoing and results will be presented, along with recommendations for both regions on how to reduce the occurrence of likely non-tectonic transients in the displacement time series. Ultimately, our results may have implications for improving the estimate of the slip budget at plate boundaries that is released aseismically.

How to cite: Garcia, C., Bedford, J., Männel, B., and Glaser, S.: Impact of datum definition on transient velocities from GNSS displacement time series in Networks mode: A Case Study of Cascadia Subduction Zone and Hikurangi margin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12979, https://doi.org/10.5194/egusphere-egu24-12979, 2024.

EGU24-13514 | ECS | Posters on site | TS1.6

Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction 

Lin Zhang, Jianye Chen, Bowen Yu, and Miao Zhang

It is believed that seismic failure conditions are sensitive to strain-softening behavior of nominal rock or fault gouge, and that precursors prior to a big earthquake (i.e., tectonic trains, water level changes, and Vp/Vs anomalies, etc) are provided by the acceleration of local slip. Previous studies of earthquake nucleation on laboratory faults show that the initiation of unstable fault slip is spatiotemporal dependent and consists of an interval of fault preslip (or creep) that localizes and accelerates to a dynamically propagating rupture. We pose that perturbation-type experiments can provide a natural condition to help analyze the potential mechanisms between instability events and the stress loading. In this study, we conducted three sets of double-direct shear experiments on a 300 mm long fault filled with gypsum-rich gouges, under normal stress of 10 MPa superimposed with perturbations of various amplitudes (i.e., 0-0.5 MPa) and a fixed frequency (0.1 Hz). The result showed that during each cycle of the stick slip behavior, the applied normal stress perturbations were redistributed along the fault zone as revealed by the along-fault strain measurement in the normal direction. As such, the fault can be divided into different zones characterized by varied coupling with respect to the applied perturbations. We found, coincidently, nucleation of the final instability, as revealed by the strain measurement in the shear direction, tended to occur at the boundary between the so-called strong and weak coupling zones (‘Transition Zone). Moreover, local normal stress near the nucleation zone also showed some weakening prior to the instability, which was similar to that seen in the local shear stress, and hereafter referred to as ‘normal failure’. Based on these observations, we proposed an empirical equation to fit the normal strain or stress data, giving the distribution of the coupling coefficient (c-value) and the anomaly (a-value) along the simulated fault. Finally, we applied the proposed equation to fit the water level data from 6 monitoring stations along the fault that hosted a nature earthquake (~ML 4). The fitting results predicted a Transition Zone, which was close to the hypocenter. In the end, we propose that this approach can be tested widely to natural observations of various precursory signals, especially those considered to be sensitive to fault-normal deformation (“dilatation” or “compaction”), such as water level, soil gas, and Vp/Vs anomalies. Hopefully, the results can shed some lights on the location of the earthquake nucleation zone. 

How to cite: Zhang, L., Chen, J., Yu, B., and Zhang, M.: Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13514, https://doi.org/10.5194/egusphere-egu24-13514, 2024.

EGU24-13838 | ECS | Posters on site | TS1.6

Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones 

Jun Xie, Xiaotian Ding, and Shiqing Xu

A rich spectrum of slip behaviors, spanning from aseismic creep (mm/yr) to seismic slip (m/s), has been observed in many subduction zones and some strike-slip faults. Slow earthquakes, intermediate between these two end-member modes, exhibit transitional slip behaviors in fault sections adjacent to the seismogenic zone. Focusing on subduction zones, it is shown that they experience deformation not only along discrete fault planes but also over distributed frictional-viscous shear zones, the latter of which are thought to be responsible for the observed diverse slip behaviors. Here we employ a frictional-viscous mélange model consisting of brittle blocks surrounded by a viscous matrix to investigate its influence on slip behaviors. By varying the mélange's rheological and frictional properties, we observe a diverse range of slip behaviors. We also reproduce the source scaling relations observed in natural faults, including the relation between seismic moment and duration and that between moment magnitude and stress drop. Additionally, we find a close link between the modeled shear zone deformation patterns and the various geological structures observed in natural fault zones. Our study demonstrates that the interaction between the frictional and viscous compositions of the mélange is responsible for the resulting slip behaviors and their transitions under different compositional ratios. These results provide useful clues for constraining the environmental and rheological conditions of different subduction zone sections from the observed slip behaviors.

How to cite: Xie, J., Ding, X., and Xu, S.: Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13838, https://doi.org/10.5194/egusphere-egu24-13838, 2024.

EGU24-15197 | ECS | Posters on site | TS1.6

Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea 

Sejin Jung, Ji-Hoon Kang, Youngwoo Kil, and Haemyeong Jung

The 5.5 magnitude (Mw) earthquake in Pohang, South Korea in 2017 was one of the largest triggered earthquakes at an enhanced geothermal system (EGS) site. Faults that ruptured in Pohang were not identified by preliminary geological investigations or geophysical surveys, and the subsequent study of the fault rocks at the Pohang EGS site was limited to depths of 3790–3816 m. In this study, we present new observations of fault rocks from drill cuttings retrieved from the Pohang EGS. The drill cuttings obtained from 3256 to 3911 m contained “mud balls,” which showed a clay matrix with foliation and a cataclastic texture, indicating a typical fault gouge or breccia. Furthermore, the mud ball samples retrieved from depths of 3256 m and 3260 m contained black fragments. Scanning and transmission electron microscopy revealed that the black fragments consisted of glass-like material, which is indicative of frictional melting during coseismic slip (Jung et al., 2023). The presence of these black fragments suggests that at least one seismic event had occurred at the Pohang EGS site prior to the hydraulic stimulation test.

Jung, S., J. -H. Kang, Y. Kil and H. Jung, 2023, Evidence of frictional melting in fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea. Tectonophysics, 862, 229964.

How to cite: Jung, S., Kang, J.-H., Kil, Y., and Jung, H.: Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15197, https://doi.org/10.5194/egusphere-egu24-15197, 2024.

EGU24-15878 | ECS | Orals | TS1.6

Fault orientation in earthquake seismic precursors: insights from the laboratory 

Carolina Giorgetti and Nicolas Brantut

Faults in the brittle crust lie at any orientation to the far-field stress. However, laboratory experiments designed to investigate earthquake physics commonly simulate favorably oriented faults, potentially overlooking the complexity of natural fault behavior. Here, we assess the role of stress field orientation in fault reactivation and earthquake precursors by conducting triaxial saw-cut experiments with laboratory faults oriented at different angles to the maximum principal stress, ranging from 30° to 70°. The samples were instrumented with strain gauges and piezo-electric sensors. Laboratory well-oriented faults describe a rather simple system in which the elastic energy is stored via the deformation of the surrounding host rock during the inter-seismic period and released via on-fault slip during the co-seismic phase with associated precursor acoustic activity. Consistent with previous laboratory data, an abrupt increase in the on-fault acoustic emission rate occurs shortly before the laboratory earthquake. A more complex picture emerges when deforming laboratory misoriented faults. Particularly, acoustic emissions and strain gauge data indicate that when the fault is misoriented, off-fault permanent deformation occurs well before fault reactivation. The stress state in the host rock surrounding the fault is indeed far beyond the one required for the onset of inelastic deformation. In this case, acoustic activity distributed in the rock volume during the pre-seismic phase is associated with permanent deformation in the critically stressed host rock and is not a direct precursor to the following laboratory earthquake. Unlike well-oriented faults, laboratory mis-oriented faults lack detectable seismic precursors. The laboratory-observed increase in acoustic activity prior to, but not precursor of, mis-oriented fault reactivation impacts our understanding of earthquake precursors in natural faults.

How to cite: Giorgetti, C. and Brantut, N.: Fault orientation in earthquake seismic precursors: insights from the laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15878, https://doi.org/10.5194/egusphere-egu24-15878, 2024.

EGU24-16581 | ECS | Posters on site | TS1.6

Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series 

Rens Elbertsen, Ivan Vasconcelos, and André Niemeijer

Laboratory stick-slip experiments are a simple analogue for the earthquake cycle. The acoustic emissions (AE) of these experiments have been shown to contain hidden patterns. Machine Learning (ML) can extract these patterns and information on the fault state can be inferred (e.g. shear stress and time to failure). Two different ML approaches have been used in the past: 1) ensemble tree models, which are relatively easy to evaluate why they made a certain prediction, but only look at a snapshot in time and 2) deep neural networks using Long Short-Term Memory (LSTM), which have the ability to find patterns in the temporal changes in the signal, but act more as a black-box model, so the final predictions are hard to evaluate. Here we introduce an additional step in the workflow that can be used to allow the ensemble tree models information about the temporal changes of the input features. Furthermore, it is able to quantify and visualize whether a pattern is repetitive or not. Like earlier studies we start by calculating (statistical) features using a rolling window on the AE. The features are not directly used as the input of the model, but are placed in a larger Hankel matrix, where the consecutive time windows are the rows of the matrix. Using Principal Component Analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) we create an embedded version of this array that holds temporal information of features calculated in the previous step. Visual inspection of these embeddings shows that some features map to very distinct patterns that are repetitive over the majority of the stick-slip cycles. The advantage of this method is that an inverse mapping is easily available, allowing for an interpretable embedding of the data.

How to cite: Elbertsen, R., Vasconcelos, I., and Niemeijer, A.: Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16581, https://doi.org/10.5194/egusphere-egu24-16581, 2024.

EGU24-18746 | ECS | Posters on site | TS1.6

Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed 

Navid Kheirdast, Harsha Bhat, Michelle Almakari, Carlos Villafuerte, and Marion Thomas

Seismic observations confirm that natural fault systems radiate waves across a continuum of frequency and amplitude. Within this spectrum, faulted systems exhibit a continuous range of slip rates, allowing them to irreversibly dissipate energy stored in rocks over a broad range of seismic moment. Despite advancements in observations and numerical modeling models, the question on how a given fault system can host such a wide range of ruptures, including slow ruptures, VLFEs, LFEs, and fast earthquakes needs a careful attention. Addressing this question requires a framework rooted in fracture mechanics, which explores the rate at which energy provided to a crack drives the rupture front forward and how this process radiates energy throughout the medium.

This work delves into the question of how frictional instability and mechanical interactions between faults and fractures, particularly concerning the geometrical distribution of off-fault damage, can generate observed rupture patterns in seismic catalogs. A model of a representative fault system is proposed, featuring a main fault embedded within a fractured zone where all fractures can slip independently. The length distribution of the off-fault fractures follows a power-law. The study then explores the fracture processes within the system, examining rupture speed from an energetic standpoint and exploring the impact of the damaged zone on the supply or reduction of energy to the process zone, ultimately influencing whether ruptures propagate rapidly or slowly.

The influence of this process is further examined by analyzing the amount of energy radiated away from the fault system. Moment-radiated energy and moment-fracture energy scaling relationships will be presented as mechanical quantities that both slow and fast earthquakes adhere to on a common curve. We will discuss radiation efficiency as a function of rupture speed to illustrate how a fault adjusts its rupture speed according to the energy provided to it and the amount of its breakdown work. The effect of damage on the process zone of the rupture will be discussed to examine how interactions between multiple fractures supply or detract energy to an active process zone, affecting its rupture speed and, consequently, the fast or slow advancement of the front.

How to cite: Kheirdast, N., Bhat, H., Almakari, M., Villafuerte, C., and Thomas, M.: Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18746, https://doi.org/10.5194/egusphere-egu24-18746, 2024.

EGU24-20753 | Posters on site | TS1.6

Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System 

David Essing, Kaan Cökerim, Gian Maria Bocchini, and Rebecca M. Harrington

The Hellenic Subduction System (HSS) in the eastern Mediterranean is the oldest active subduction margin on earth. It is a segmented boundary that hosts the continuum of faulting styles over a ~200km range in depth and can generate large earthquakes with high tsunamigenic potential.  The complexity of deformation styles and rates leave key aspects of the system poorly understood. For example, historical records of Mw<8 earthquakes fail to explain the current observed convergence rate (~35mm/year), and recent geodetic measurements suggest that the degree of locking within the system is heterogeneous. The density of geodetic measurements is increasing rapidly, nevertheless, the inherent time lag required to accumulate data that will enable identifying regions that undergo slower (than seismic) deformation transients will necessitate inferences from seismic signals. In this work, we aim to further close the observational gap between heterogeneous deformation styles and rates using the features of seismicity distributions to infer where deformation rates, and by inference, locking, vary most.   

To that scope, we will present new results of an enhanced earthquake catalog that we will use to explore the spatio-temporal distribution of seismicity features (e.g., b-value, effective stress drop, seismic-moment-release skewness) to infer variability in deformation rates and loading. Catalog enhancement exploits data from the temporary (EGELADOS) broadband seismometer network that operated between 2005 until 2007 combined with permanent stations leading to a station spacing of ~40 km and covering the entire southern Aegean Sea. We first use the combined network to detect earthquakes using machine learning approaches (EQTransformer, PhaseLink) for detection, phase picking and association. After performing initial locations using NonLinLoc combined with a 1D velocity model and quality control procedure, we enhance the number of small-magnitude detections using a multi-station template-matching approach. Next, we scan the enhanced high-resolution catalog for distinct spatial and temporal patterns of seismicity using unsupervised clustering. We then quantify the clustered seismicity using b-value, effective stress drop, and seismic-moment-release skewness (among other parameters). We will present our clustering results in the context of the variability in slip phenomena related to earthquake-earthquake interactions (e.g., static and dynamic triggering) as well as in the context of external forcing (e.g., aseismic triggering or fluid migration).  

The preliminary results that we will present will provide a basis for our more broad-scale study of interplay between seismic and aseismic deformation. In particular, where the latter is gradually becoming increasingly resolvable using GNSS data within the HSS, this work will provide a basis for links with geodetically observed deformation in the future.  

How to cite: Essing, D., Cökerim, K., Bocchini, G. M., and Harrington, R. M.: Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20753, https://doi.org/10.5194/egusphere-egu24-20753, 2024.

EGU24-20908 | ECS | Posters on site | TS1.6

Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction  

Giacomo Mastella, Federico Pignalberi, Carolina Giorgetti, and Marco Scuderi

Double direct shear experiments serve as established methods for delving into the physics of laboratory earthquakes. Using a biaxial shearing apparatus with dual fault configurations, these friction experiments simulate real Earth faults' behaviors during loading and failure. 

Despite the presence of distinct layers, double direct shear experiments are commonly perceived as a unified fault system, where the evolution of fault zone properties captured through passive or active seismic imaging can be correlated with the instantaneous stress state affecting both layers uniformly. To further explore the physics of seismic cycles generated in this setup, we perform friction experiments aiming to independently monitor the behavior of each fault layer. In our experiments, we use granular quartz (medium grain size 40 µm) to simulate fault gouge, amd we vary the normal load and shear velocity, allowing us to modify the apparatus's loading stiffness, which relies on the critical fault rheologic stiffness (kc). In the Rate-and-State framework, increasing the normal load results in an  increase of kc, pushing the system towards instability, occurring when k/kc <1, where k is the fault stiffness. Under 50 MPa of  normal loads and 10 µm/s of loading rate, these conditions result in highly non-cyclic seismic cycles marked by significantly variable stress drops and recurrence times. This situation offers an exceptional opportunity to investigate stress partitioning between the two layers and understand their interactions. Experiments are monitored using high-frequency calibrated piezoelectric sensors with a sampling rate of 6 MHz, placed on each of the two forcing blocks. Such a sampling rate allows us to clearly distinguish the time delay between the Acoustic Emissions (AEs) generated from microslip events in different layers. Phase arrivals are detected using retrained, Deep Learning-based algorithms. By associating these phase arrivals using the DBSCAN clustering algorithm, we classify events as occurring on a single gouge layer or on both layers. Subsequently, we analyze the catalog of AEs,, and single seismic waveforms, in terms of general characteristics and frequency content, to look for differences in the physical sources generating them. Unsupervised clustering may help identify classes of AEs linked to specific stages within seismic cycles. By potentially using established supervised Machine Learning technique, it would be possible to verify the relation between AEs variance for each layer and macroscopic apparatus features, like instantaneous friction or time to failure. All of these techniques reveal differences in acoustic energy released before failure for each layer, observations that can be associated to changes in fault physical properties, asperity scale processes and/or  grains sliding or fracturing. In conclusion, our findings demonstrate that double-direct shear experiments can emulate a system of interacting double faults. In such a context, the continuous monitoring of AEs can provide insights into the stress partitioning between the two layers, a process that may guide the nucleation of major slip events as well as the long term behavior of the system. Additionally, our analysis may be helpful to investigate processes like fault interactions, faults synchronization, static, and dynamic stress triggering.

How to cite: Mastella, G., Pignalberi, F., Giorgetti, C., and Scuderi, M.: Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20908, https://doi.org/10.5194/egusphere-egu24-20908, 2024.

EGU24-1239 | Posters on site | TS2.1

Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements 

Young-Gyun Kim, Jong Kuk Hong, Young Keun Jin, and Byung Dal So

The Amerasia Basin, one of two major basins that comprise the Arctic Ocean, is thought to have a more complex formation history than its counterpart, the Eurasian Basin. Because the harsh conditions for marine expeditions last the entire year, there is a lack of observational data for constraining the tectonic history of the Chukchi Basin. Thus, there are multiple existing hypotheses for its tectonic history, with contrasting formation ages ranging from Mesozoic to Cenozoic and crustal types ranging from hyper-extended continental crust to oceanic crust. Recently, during the 2018 and 2021 Arctic expeditions of the Korean ice-breaking research vessel Araon, we obtained the new marine heat flow data along the east-west and northeast-southwest transect lines from the abyssal plain to the continental slope/shelf of the basin. These data may play an important role in constraining the formation age of the basin, as the extending axis among the hypotheses is likely oriented from north-south. Assuming an oceanic crust, the formation age can be inferred to be Late Cretaceous. This information concerning the formation age enhances our understanding of the underestimated complex tectonic history of the Amerasia Basin, because such inferred timing aligns with the formation age of the adjacent Chukchi Borderland.

How to cite: Kim, Y.-G., Hong, J. K., Jin, Y. K., and So, B. D.: Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1239, https://doi.org/10.5194/egusphere-egu24-1239, 2024.

EGU24-1615 | ECS | Orals | TS2.1

Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece 

Costantino Zuccari, Francesco Mazzarini, Enrico Tavarnelli, Giulio Viola, Luca Aldega, Roelant Van der Lelij, and Giovanni Musumeci

Extensional detachments are commonly considered key structures in accommodating the exhumation of deeply buried or subducted crustal slivers, and in facilitating the syndeformation emplacement of plutons during the evolution of wide rift systems (i.e., Basin and Range type). In those settings, ductile shear zones and brittle faults may act for several million years to accommodate important vertical and horizontal displacements such that multiply reactivated and highly complex shear zones and faults may form. The analysis of these complexities, together with the possibility to constrain the age of strain and deformation localisation, is thus pivotal in reconstructing the onset and evolution of the processes that steer(ed) the crustal extension.

Aiming at better understanding these structural/chronological intricacies, we have studied the brittle Mykonos Detachment (MD), which is thought to have facilitated the emplacement of the Mykonos granite starting in the Middle Miocene (~14-9 Ma) and following the activation of the earlier (ductile) Livada Detachment (LD) that would have favoured the beginning of pluton cooling during the structuring of the Aegean rifting. The Mid. Miocene age of the MD is, however, only loosely constrained by the stratigraphic age of syn-tectonic siliciclastic deposits in the hanging wall of the fault. No absolute ages exist yet on the activation of the brittle MD or the ductile LD, and a detailed description of the internal architecture of the MD is still not available.

Aiming to fill this gap(s), we carried out a detailed study that couples a Brittle Structural Facies – based structural analysis with K-Ar dating on authigenic illite from fault gouge(s) that compose the MD fault core. Fault gouges normally rest on and are cut by the MD principal slip surface (PSS), which reasonably postdates the gouge formation and represents the effects of the latest fault activity. We have obtained a 7.1 ± 0.1 Ma K-Ar age from a fault gouge suggesting that the MD activation postdated the widely accepted ~14-9 Ma of the granite cooling, also considering that the PSS postdates the 7.1 Ma gouge, as indicated by field evidence. On this ground, together with published thermochronological data showing that the granite experienced a rapid cooling from ~14 to ~11 Ma before experiencing slow cooling until ~9 Ma, we can state that most of the granite exhumation cannot be ascribed to the MD, the activation of which postdates the late stage of the granite cooling.

These new geochronological data (which are soon to be implemented with new K-Ar dates) and the description of the architectural evolution of the MD fault zone, stress the role of the detachment during the unroofing of the Mykonos granite in the Aegean rifting context. In this perspective, the granite exhumed is mostly assisted by the ductile LD, which acted before the MD. The latter acted instead only at a later stage when it juxtaposed the Miocene siliciclastic against an already cooled and unroofed granite, which had reached a temperature of ~40°C about 2Ma before the latest Late Miocene activation of the MD, as shown by our preliminary age constraint.

How to cite: Zuccari, C., Mazzarini, F., Tavarnelli, E., Viola, G., Aldega, L., Van der Lelij, R., and Musumeci, G.: Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1615, https://doi.org/10.5194/egusphere-egu24-1615, 2024.

A new onshore-offshore 3-D constrained gravity inversion methodology that incorporates onshore topography and laterally variable inversion mesh depths is used to determine the crustal density distributions, Moho depths, and crustal thicknesses of Iberia, Morocco, and their respective rifted continental margins. The results largely show an excellent correspondence with crustal characteristics determined from sparsely distributed controlled-source and passive seismic experiments, while also allowing the layered density structure of the region to be explored and analyzed in terms of upper, middle, and lower crustal layers. These detailed regional views as a function of depth can improve characterization of crustal types (continental versus oceanic versus transitional), and the resulting interpretations can be directly compared against equivalently derived crustal characteristics for onshore-offshore Atlantic Canada, which encapsulates both Iberia’s and Morocco’s conjugate rifted margins. Collectively, the conjugate 3-D crustal-scale density models allow for the extraction of mega-transects across both sides of the southern North Atlantic, joined together back through geological time using kinematic plate reconstructions.

How to cite: Welford, J. K.: Crustal structure of onshore-offshore Iberia, Morocco, and their rifted continental margins, from constrained 3-D gravity inversion using variable mesh depths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3196, https://doi.org/10.5194/egusphere-egu24-3196, 2024.

EGU24-3979 | ECS | Posters on site | TS2.1

Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin 

Jie Chen, Sylvie Leroy, Louise Watremez, and Adam Robinson

Continental rifting is the Earth’s fundamental tectonic process that may result in a new plate boundary, i.e., mid-ocean ridges, with the accretion of new oceanic crust. At present, continental rifted margins are classified into two end-members based on the amount of magmatism that occurred during the rifting process: magma-rich and magma-poor. However, various factors influence the formation of these margins, such as the inheritance of segmentation, extension obliquity, syn-rift magmatism, and sedimentation. The Gulf of Aden represents a good example for understanding such spatial variations in the formation of rifted margins. It consists of an oblique rifting system, with young and segmented margins (34-17.6 Ma) and thin sediments. In addition, the Gulf of Aden exhibits magma-rich margins in the west, related to the Afar hotpot, and magma-poor margins in the east, with a possible zone of exhumed continental mantle.

In this study, we develop a 3-D P-wave velocity model across the north-eastern Gulf of Aden continental margin, using wide-angle seismic refraction data from a combined onshore-offshore survey with 35 ocean-bottom seismometers and 13 land seismometers. Approximately 187,000 P-wave first arrivals were picked and inverted in 3-D, with the modelling informed by constraints from previously published 2-D velocity models. Here, we present our preliminary tomographic results that illustrate the spatial variations in the crustal velocity structure of the continent, continent-to-ocean transition (COT), and oceanic domains, as well as the comparison between our 3-D and the published 2-D velocity structures of the north-eastern Gulf of Aden continental margin.

How to cite: Chen, J., Leroy, S., Watremez, L., and Robinson, A.: Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3979, https://doi.org/10.5194/egusphere-egu24-3979, 2024.

During the final stages of breakup at magma-poor rifted margins, mantle rocks are commonly exhumed and altered to serpentinite due to the ingress of ocean water. This mantle exhumation phase is followed by an increase in magmatism as new oceanic crust begins to form. However, the degree to which serpentinisation is focused at faults and whether the onset of magmatism is abrupt or gradual are both unclear. These processes are difficult to untangle with seismic data alone because the P wave velocities of mafic crustal rocks and partially serpentinised mantle rocks can be similar. However, serpentinised mantle rocks are generally more conductive, often by about an order of magnitude, than mafic crustal rocks, so controlled source electromagnetic (CSEM) and magnetotelluric (MT) techniques provide a promising route to resolve controversies around the structure of lithosphere formed during the onset of seafloor spreading.

To take advantage of the complementary information provided by seismic and electromagnetic data, in September 2023 we acquired a coincident and densely sampled wide-angle seismic, CSEM and MT datasets across the continent-ocean transition at Goban Spur, southwest of the UK. Our c. 200-km profile is coincident with a pre-existing high-quality seismic reflection profile. It extends from thinned continental crust, whose nature is confirmed by drilling, across a broad zone that is inferred on the basis of a previous wide-angle seismic experiment to be composed of exhumed and serpentinised mantle, and into oceanic crust, evidenced by the presence of the prominent seafloor-spreading magnetic anomaly A34. Along this profile, we deployed 49 seafloor instruments at c. 4-km spacing that were each capable of recording seismic, electric field and magnetometer data, plus an additional two instruments recording the inline electric field on 200-m dipoles. These instruments were on the seafloor for about two weeks. During this time we acquired two wide-angle seismic profiles: one using a 5200 cu. in. airgun array shot at 90-s intervals and a second using a 3900 cu. in. airgun array shot at 30-s intervals. We also acquired a frequency-domain  CSEM profile using a transmitter towed c. 100 m above the seabed that powered a 300-m electric dipole with a c. 100-A current at a fundamental frequency of 0.25 Hz. Preliminary data analysis showed that seismic signals were recorded to c. 90 km offset and CSEM signals to c. 8 km offset, while high-quality MT data were recorded at periods of 20-10000 s.

Thus we expect to recover coincident high-resolution images of the seismic velocity and resistivity structure of the upper few km of the basement, sufficient to image patterns of serpentinisation and mafic intrusion. We also expect to recover lower-resolution images of the resistivity to tens of km below the seabed and thus to distinguish continental mantle lithosphere from depleted oceanic lithosphere. We will present examples of the data acquired and the results of some preliminary analysis.    

How to cite: Minshull, T., Bayrakci, G., and Constable, S.: An integrated seismic, controlled source electromagnetic and magnetotelluric study of the continent-ocean transition southwest of the UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6227, https://doi.org/10.5194/egusphere-egu24-6227, 2024.

EGU24-6331 | ECS | Orals | TS2.1

How developing grabens dictate volcanism shifts in rifts 

Gaetano Ferrante, Eleonora Rivalta, and Francesco Maccaferri

Volcanism in continental rifts is generally observed to shift over time from the inside of the graben to its flanks and back. These patterns are commonly observed across rifts from different tectonic contexts, different abundance of melt, and regardless of the rifts' specific complexities, suggesting a common control. However, despite recent advances, the mechanisms governing the spatio-temporal evolution of rift magmatism are still poorly understood. Here we test the hypothesis that the spatio-temporal evolution of rift volcanism is controlled by the crustal stresses produced during the development of the rift basin. To do so, we couple a gravitational unloading model of crustal stresses with a boundary element dike propagation code to investigate the effect of a deepening graben on the evolution of magma trajectories in rifts. We find that the progressive deepening of a graben rotates the direction of the principal stresses in the crust, deflecting ascending dikes. This causes a relatively sudden shift of volcanism from the inside of the graben to its flanks during the early stages of rifting. The intensification of this stress pattern, caused by further deepening of the basin, promotes the formation of lower crustal sill-like intrusions. These horizontal bodies can stack under the rift, shallowing the depth at which dikes nucleate, eventually causing a late stage of in-rift axial volcanism, which can alternatively be induced by compensation of graben unloading by sediment infill. Our model reproduces the general patterns of volcanism in rifts and provides a framework to explain their commonalities and account for possible differences. Given the agreement between our model results and observations, we conclude that the evolution of the stresses generated by a developing rift basin can account alone for the major aspects of the spatio-temporal evolution of rift magmatism.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: How developing grabens dictate volcanism shifts in rifts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6331, https://doi.org/10.5194/egusphere-egu24-6331, 2024.

EGU24-6401 | ECS | Posters on site | TS2.1

Reactivation of inherited faults in rift basins: insight from analogue modeling 

Pauline Gayrin, Daniele Maestrelli, Giacomo Corti, Sascha Brune, and Chiara Del Ventisette

Continental rifts accommodate shallow extensional stresses both by brittle deformation (normal faulting) and volcanism (i.e. dykes and lava flows). Lava flows, together with clastic sedimentation reshape the topography of the rift floor, forming fresh new layers of rock that cover ancient faults. Therefore, the influence of the inherited buried faults on the development of the new faults and the processes of linkage at depth between them remain difficult to investigate. Here we use analogue brittle-ductile modeling with orthogonal extension to elucidate fault growth and reactivation modes, and then compare the results with data from natural rift systems.

In our models, deformation is produced above an elastic band placed between a fixed and a moving wall controlled by a stepper motor. A  layer of viscous material distributes the deformation within the model. On top of the viscous material we use a  layer of sand mixture to simulate the brittle properties of the upper crust. A first phase of extension develops an entire normal fault network, which is then carefully buried under a variable thickness of sand, simulating a cover of sedimentary or volcanic deposits. A second phase of extension allows us to study the mode of reactivation of the inherited faults.The progress of the deformation is tracked using top view images and digital elevation models interpolated from perspective images. At the very end of the model, cross sections cut at regular intervals show the faults at depth by overlaying coloured brittle layers. The high quality of the images allow us to map and analyze the network semi-automatically. We derive displacement/length profiles to characterize the style of fault growth and propagation mode.

Model results show the development of normal faults creating systems of fault-bounded basins, horst-graben structures and conjugated faults. The setup creates a gradient of deformation from the moving wall, where the faults nucleate first near the fixed wall. We thus observe the coexistence of faults of slightly different ages on the same model, as would occur in nature over time. The cross-section shows an upward propagation and the propagation of faults from depth to surface. The preliminary results indicate different styles of reactivation depending on the stage of fault development: reactivation according to a propagating fault mode where faults still have space at tips to develop and a constant-length fault mode where the network is already fully developed. In addition, we find that the surface overlying the inherited structures first bends, then fractures (without observable vertical displacement), and finally develops from the fracture into a proper fault before it finally propagates to connect laterally within the network. This latter growth mode is consistent with the process observed in Iceland by Braham et al. (2021). Understanding the processes of fault network inheritance holds broader applications to many areas where lava or sediments cover faults, layer after layer, such as magma rich rifts like the Eastern Africa Rift or Iceland.

How to cite: Gayrin, P., Maestrelli, D., Corti, G., Brune, S., and Del Ventisette, C.: Reactivation of inherited faults in rift basins: insight from analogue modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6401, https://doi.org/10.5194/egusphere-egu24-6401, 2024.

EGU24-6489 | Orals | TS2.1

Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs 

Laurent Jolivet, Laurent Arbaret, and Romain Augier

Rifting in back-arc basins is characterized by large extension rates, low-angle normal faults and metamorphic core complexes (MCC) displaying partially molten cores and granitic intrusions. The Aegean metamorphic core complexes (MCC) were exhumed underneath crustal-scale detachments accommodating large displacements of the order of 50-100 km and were intruded by Miocene syn-kinematic granites. A common finite geometry and kinematics of all these detachment/pluton systems is recognized with asymmetric intrusive bodies extracted from anatectic lower crust, whose internal structure is controlled by the large-scale dynamics, from the magmatic stage to mylonitization and final exhumation in brittle conditions. Detachments are organized in sets of structures working sequentially evolving from ductile to brittle, the successive branches of the detachment being progressively inactivated by emplacing plutonic batches. The Mykonos-Delos-Rheneia (MDR) MCC shows these interactions between lower crustal migmatites and different syn-kinematic plutons. Our new detailed map of Delos (1/5000) shows geometrical and kinematic relationships between the different magmatic venues during deformation. A strong internal orientation of granites is observed from the magmatic stage until the last ultramylonites below the upper detachments. The deepest magmatic batches are rich in high-grade rocks septae and mafic enclaves, also oriented parallel to regional stretching. Evidence for magma mixing and mingling further indicates interactions with mafic venues at the base of the crust from the mantle. Large high-grade rocks septae are intensely molten and the contact zone between host gneiss and plutons shows intense migmatitization with a foliation parallel to the granite magmatic foliation. Characteristic banded facies marking the contacts between the different intrusions result from high-temperature shearing at the magmatic stage. At all scales foliation and lineation in magmatic rocks and surrounding gneisses are parallel, suggesting a similar weak rheology. Delos shows the roots of these intrusions emplaced as a large-scale sheath-fold whose axis is parallel to the regional stretching direction. The quality of outcrops in Delos, Rheneia and Mykonos, as well as the links between magma emplacement and regional tectonics makes the MDR MCC a natural laboratory for studying the interactions between magmatic intrusions and crustal deformation in tectonically active and hot contexts. In such contexts magmatic and tectonic processes in the lower and middle crusts appear closely interconnected, working at a similar pace and interacting with mantle deformation and melting.

How to cite: Jolivet, L., Arbaret, L., and Augier, R.: Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6489, https://doi.org/10.5194/egusphere-egu24-6489, 2024.

EGU24-6912 | ECS | Orals | TS2.1

Upper mantle anisotropy under the strike-slip Dead Sea rift 

Huikai Xu, Youqiang Yu, and Jiaji Xi

Continental rifting is one of the fundamental tectonics of the Earth evolution while our current knowledge on the dynamic mechanism of the strike-slip ones are seriously limited. Here, a systematically shear-wave splitting investigation has been performed in the typical strike-slip Dead Sea rift to illuminate the upper mantle azimuthal anisotropic status across a transform boundary. Totally, 1855 well-defined anisotropic measurements are observed from 102 stations with dominantly N-S fast orientation, which is parallel to the rift strike but deviate from the absolute plate motion direction, mainly result from the plate-driven mantle flow deflected by the thick lithosphere of the eastern Arabian plate. Additionally, the significant fluctuation patterns of splitting times are identified on both the rift-parallel and rift-orthogonal profiles, among which the relatively large splitting times are generally concentrated at the rift zone and attributed to additional coupling lithospheric deformation from the shearing-oriented melt pockets. The consistent rift-parallel fast orientations, combined with the other geoscientific evidences, rule out the role of mantle plume or edge-driven convection in the rift development and further infer the Dead Sea rift to evolve in a passive mode.

How to cite: Xu, H., Yu, Y., and Xi, J.: Upper mantle anisotropy under the strike-slip Dead Sea rift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6912, https://doi.org/10.5194/egusphere-egu24-6912, 2024.

EGU24-7884 | ECS | Posters on site | TS2.1

A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand 

Malte Froemchen, Ken McCaffrey, Tom Phillips, Mark Allen, and Jeroen van Hunen

The evolution of continental rifts is influenced by the pre-rift rheology of the lithosphere and discrete lithospheric structures that segment the rift. The Great South Basin, offshore New Zealand, is a Cretaceous rift system that formed across heterogenous basement terranes which influence the rift architecture. Faults locally rotate or splay and segment along these terrane boundaries. While the impact of terrane boundaries on rift architecture is well understood, the temporal evolution of these rotated faults is poorly constrained. Here we use 3D reflection seismic data to investigate the timing and slip rate evolution of the rotated and segmented faults along two terrane boundaries. Our results show that these have a significant but variable impact on rift evolution and architecture: Faults in the Murihiku terrane show asymmetric throw-length profiles and are rotated along the terrane boundary to the Dun Mountain-Maitai terrane, as they detach into shallow crustal fabrics. Faults in the DMM terrane show less evidence of rotation and more symmetric throw-length profiles but are segmented along the DMM and Caples terrane boundary. The curving faults of the Murihiku terrane likely formed early on but remained as isolated segments only linking up during later stages of rifting when other faults became inactive. These results show the influence of the terrane boundaries was not only active early during initial segmentation but also during the linkage of curved fault segments in the later stages of rifting. These results may help understand the temporal evolution of lithospheric and crustal inheritance on rift evolution in other regions around the world like East Africa or North China.  

How to cite: Froemchen, M., McCaffrey, K., Phillips, T., Allen, M., and van Hunen, J.: A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7884, https://doi.org/10.5194/egusphere-egu24-7884, 2024.

Lithospheric extension leads to rift formation and may continue to the point of breakup, with oceanic ridge initiation and the formation of two conjugate rifted margins. In some settings, extension can cease, and the rift may be abandoned. These so-called failed rifts archive snapshots of early phases of deformation, with geometries that may help better constrain the parameters that can prevent a rift from reaching breakup, such as lithospheric rheology, thermal state, rift opening direction and rate, inheritance.

This contribution summarizes a study of the Norwegian Continental Shelf which includes the North Sea Rift and the Møre and Vøring rifted margins. We proceeded to the interpretation of a new dataset of deep penetrating seismic reflection profiles and worked at the regional scale, deliberately ignoring local particularities, to focus on the large-scale structural picture. The aim is to list architectural similarities and differences between the failed rift and the successful rifted margins.

The mapping shows that the North Sea structural geometries and basement seismic facies are very similar to the observations listed for the adjacent Møre and Vøring rifted margins. Various types of tectonic structures are observed, from thick anastomosing shear zones possibly evolving into core-complex geometries, to composite large-scale detachment faults and standard high-angle normal faults. These are categorized into five classes and interpreted as exemplifying the rift tectonic evolution through distinct generations of deformation structures that can activate, de-activate and re-activate. Based on these observations, rift failure dynamics are discussed, and it is proposed that the North Sea rift abandonment may not be related to pre-rift local conditions but rather to the ability to initiate specific tectonic structures such as distal breakaway complexes.

How to cite: Peron-Pinvidic, G.: Structural observations of the northern North Sea: insights into rift failure dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7915, https://doi.org/10.5194/egusphere-egu24-7915, 2024.

EGU24-8883 | Posters on site | TS2.1

Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe 

David Ulicny, Vladimír Cajz, Karel Mach, Lenka Špičáková, Matěj Machek, Stanislav Čech, Radomír Grygar, Jan Mrlina, and Filip Havlíček

The present-day surface morphology and fabric of the lithosphere of west-central Europe in the foreland of the Alpine orogen have been significantly affected by formation of a system of rifts and associated volcanic domains during the Oligocene and Neogene, known as the European Cenozoic Rift System (ECRIS). In order to better understand the geodynamic causes of formation of ECRIS and its volcanism, it is important to improve the knowledge of chronology of tectonic events in the entire ECRIS, and to test the validity of existing palaeostress interpretations. The Oligo-Miocene Eger Rift, so far the least-studied part of ECRIS, has the potential to bring new clues to some persisting controversies.

The axis of the Eger Rift roughly follows the trend of a major Variscan lithosphere-scale boundary, the Teplá-Barrandian/ Saxothuringian suture (TSS) formed during the collisional phases about 380-320 Ma. Following the Variscan collision, the lithosphere of the Bohemian Massif was affected by formation of a Late Paleozoic extensional basin system which in the western part of the Bohemian Massif largely follows the NE strike of the TSS. Another major structure in the basement underlying the Eger Rift is the WNW-striking Elbe Zone, with main periods of activity during the Paleozoic and Mesozoic through early Cenozoic.

We present a synthesis of presently available structural and stratigraphic data and a resulting first-order interpretation of tectonic evolution of central and eastern Eger Rift. The main data sources were borehole, outcrop, seismic reflection data, targeted field mapping, digital elevation models, and gravity data from both public and industry sources. Several stratigraphic levels (within the Neogene, Cretaceous, and top of Late Palaeozoic) were used as structural datums.

Analysis of fault populations in central and eastern Eger Rift shows that overall, the Late Paleozoic fracturation of the upper crust of the Bohemian Massif was key for localization of the main fault systems of the Eger Rift. This includes dextral shearing within the Elbe Zone that affected the basement structural grain responsible for segmentation of the Eger Rift during the Cenozoic. Changes between oblique and orthogonal extension modes are interpreted from the geometries and temporal relationships of key structures - both in time, likely due to a changing regional paleostress field, and in space, due to different orientations of basement structures between the rift segments.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Ulicny, D., Cajz, V., Mach, K., Špičáková, L., Machek, M., Čech, S., Grygar, R., Mrlina, J., and Havlíček, F.: Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8883, https://doi.org/10.5194/egusphere-egu24-8883, 2024.

Ocean closure and collisional orogeny frequently enrich the lithospheric mantle in incompatible chemical elements. The most intensive enrichment usually occurs during the subduction of continent-derived sediments and continental crust. Radioactive isotopes of uranium and thorium are part of the HFSE (high-field-strength elements) group of incompatible elements and, therefore, can be also characterized by increased concentration within the post-orogenic lithospheric mantle in comparison to the common lithospheric mantle. The anomalously high content of uranium and thorium within the post-orogenic mantle lithosphere is reflected by the composition of potassic and ultrapotassic magmas, which are sometimes extremely enriched in these radioactive elements. This enrichment is well documented by numerous studies and, therefore, cannot be ignored during the numerical modelling of rifting processes.

According to pure conductive thermal modelling, the anomalously increased content of radioactive elements within the post-orogenic lithospheric mantle causes a time-dependent rise in temperature, providing favourable conditions for intracontinental rifting more than 20-100 million years after the closure of the ocean. A time gap between the orogeny and highly increased temperature within the lithosphere is controlled by two major factors: (1) the amount of thorium and uranium and (2) the size of the anomalous lithospheric mantle. According to numerical thermo-mechanic modelling, the post-orogenic increase in temperature not only weakens the lithosphere but also causes thermal expansion of the lithosphere which can be sufficient to initiate the first stage of intracontinental rifting without involving regional extensional forces.

Therefore, we propose a new concept of intracontinental rift initiation as a result of time-dependent temperature increase and thermal expansion of the post-orogenic mantle lithosphere due to the decay of radioactive elements. The described rather simple mechanism of rift formation provides a significant advance in our understanding of both local rift processes and global tectonic cycles on our planet.

How to cite: Maystrenko, Y. and Slagstad, T.: Post-orogenic radiogenic initiation of intracontinental rifting within the lithospheric mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9325, https://doi.org/10.5194/egusphere-egu24-9325, 2024.

EGU24-9513 | Posters on site | TS2.1

Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia 

Michal Rajchl, Karel Mach, Filip Havlíček, David Uličný, and Matěj Machek

The present-day geological and morphological expression of the Cenozoic Eger Rift in central Europe is dominated by the faulted edge of the Krušné Hory (Erzgebirge) Mts., a plateau uplifted to c. 1 km above sea level following the mid-Miocene, resulting in partial deformation and erosion of parts of the Eger Rift sedimentary and volcanic infill. The main phase of the uplift is considered to have occurred in Plio-Quaternary times, but details of this process and its relation to the Eger Rift itself remain unclear.

The Oligo – Miocene Most Basin is the most extensive sedimentary basin preserved within the Eger Rift. The basin, bounded at the NW by the Krušné Hory uplift, is characterized by an economically important coal seam, up to 35 m thick. Previous research has shown that during the formation of the basinwide swamps in early Miocene the basin was hydrologically open, with at least one but probably more outlets draining its area toward the North and Northwest, across today’s Krušné Hory (Erzgebirge) Fault Zone (KHFZ). During the earliest Miocene times, most of the region of today’s Krušné Hory / Erzgebirge uplifted block was thus a generally low-relief area. Paleogeographic changes in the Most Basin suggest an increasing activity of its marginal faults, some of which were predecessors of the present-day KHFZ, still during the early to mid-Miocene. For understanding the formation of this major fault zone it is important to answer the question of the timing, magnitude and character of initial relief growth along the nw. edge of the Eger Rift.

The stratigraphic and structural record exposed recently at the KHFZ provides evidence of a small-scale relay ramp that formed between two overlapping normal faults of E-W general strike and breached later by a normal fault of NE strike. Debris-flows conglomerates were found interbedded with carbonaceous mudstones and lignite layers belonging to the early Miocene main coal seam, in the close vicinity of the lower bounding fault containing boulders from a tectonic breccia of the fault damage zone. This fact indicates the existence of a prominent fault scarp developed along the fault plane of the above fault and considered the source of coarse-grained clastics during the initial, coal-bearing, phase of the basin formation. The subsequent acceleration of the Most Basin subsidence that resulted in basin-wide expansion of the swamp environment, can be explained by linkage of the border faults accompanied by breaching and drowning of some relay ramps.

The studied sedimentary record provides evidence of faulted relief with an elevation of tens of metres that contributed to the supply of clastic material to the incipient rift during early Miocene time. The subsequent breakage and drowning of the relay ramp provide evidence for syn-sedimentary activity some of NE-SW segments of the KHFZ previously thought to be a manifestation of later, post-rift deformation.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S. We acknowledge support by the Severní energetická, a.s., and Ing. Petr Šulcek in conducting research in the Důl ČSA Mine.

How to cite: Rajchl, M., Mach, K., Havlíček, F., Uličný, D., and Machek, M.: Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9513, https://doi.org/10.5194/egusphere-egu24-9513, 2024.

EGU24-9770 | Posters on site | TS2.1

Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe 

Filip Havlíček, David Uličný, Ondřej Krýza, Matěj Machek, Michael Warsitzka, and Prokop Závada

Continental lithosphere undergoing the process of rifting has typically previously experienced a complex deformation history resulting in a highly heterogeneous mechanical structure. This structural inheritance can affect the developing continental rift across all scales, from rift localization and segmentation to individual fault geometries. Assessing the impact of such inherited structures on extensional basin geometries can be difficult, especially in the case of fossil rifts where uncertainties may arise about the orientation of regional stresses during extension. One such example is the Eger Rift which developed during the Oligocene to early Miocene as the easternmost branch of the European Cenozoic Rift System (ECRIS). Earlier interpretation proposed a two-phase extensional history for the rift.

We use a series of crustal-scale, brittle-viscous analogue models, based on the geometry of the central and eastern parts of the Eger Rift, to explore the development of a segmented rift in a multiphase setting with evolving extension direction. Our model crust rests on a basal velocity discontinuity (VD), a discrete boundary of a mobile base plate simulating a reactivated basement weakness localizing our model rift. The geometry of this weakness is a simplified representation of the geometry of older, mainly Upper Paleozoic basins, which are hypothesized to have greatly influenced the localization and geometry of principal fault systems and rift segments that they define. The VD thus consists of 3 segments oriented at various angles with respect to extension direction. The Model surface is imaged by stereoscopic cameras and analyzed by Particle Image Velocimetry (PIV) techniques to track surface deformation and topography evolution during the run.

Our results confirm that in a setting with an abrupt change in extension direction, the first extensional phase plays a key role in defining the final observed fault pattern with new second-phase faults generally being few in number and of limited length. This effect is enhanced above a segmented VD. If a larger portion of the VD is optimally oriented with respect to the first-phase extension, the final fault pattern is dominated by first-phase structures with the growth of second-phase faults being nearly inhibited. In a contrasting scenario, where most of the VD is initially oblique to extension direction, second-phase faults are more abundant, leading to a bimodal final fault pattern. By comparing our results with newly mapped fault populations in the Eger Rift we conclude that the proposed two-phase history for the rift is plausible with a major role of the initial phase of approximately N-S extension.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Havlíček, F., Uličný, D., Krýza, O., Machek, M., Warsitzka, M., and Závada, P.: Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9770, https://doi.org/10.5194/egusphere-egu24-9770, 2024.

EGU24-9947 | ECS | Orals | TS2.1

New results on the crustal configuration of the Newfoundland margin: Implications for rifting 

Laura Gómez de la Peña, César R. Ranero, Manel Prada, Donna Shillington, and Valentí Sallarès

Driven by discovery of contrasting structures of Continent to Ocean Transition (COT) discovered at rifted continental margins during the 90’s, several high-quality seismic datasets were acquired in these margins during the early 2000 to unravel the structure of unexplored regions. Despite the fact that some of these datasets are basically comparable to modern data in quality, the processing, imaging and modelling methodologies at the time of acquisition can be now refined and improved. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with enhanced 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 up-to-date methodologies to the high-quality SCREECH dataset (2000). These data include three primary transects with coincident multichannel seismic (MCS) reflection data acquired with a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~15 km. We reprocessed the streamer data and also performed the join inversion of streamer and wide-angle OBS/OBH seismic data, using reflections and refraction arrivals, which significantly improved the resolution of the velocity model. We performed a statistical uncertainty analysis of the resulting model, supporting the reliability of the observed features. In particular the new velocity model provides a detailed definition of the top of the basement where the largest abrupt velocity change occurs. The comparatively high-resolution velocity model obtained from the joint tomography allowed to properly perform a Pre-Stack Depth Migration of the MCS. The improved velocity model and seismic images permit to characterize the different crustal domains of the margin with less uncertainty that previous attempts, and relate them to the tectonic structure.

The different domains reveal previously undetected crustal characteristics that change over short distances. The reprocessing of the MCS data allowed to a better understanding of the crustal structure, as the Moho is imaged for the first time under the slope domain.

Comparison of these new results on the Newfoundland margin with the most modern data on the West Iberian margin, acquired during FRAME (2018) and ATLANTIS (2022) cruises provides a new view of the evolution of the North Atlantic opening.

How to cite: Gómez de la Peña, L., R. Ranero, C., Prada, M., Shillington, D., and Sallarès, V.: New results on the crustal configuration of the Newfoundland margin: Implications for rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9947, https://doi.org/10.5194/egusphere-egu24-9947, 2024.

EGU24-11403 | Posters on site | TS2.1

The story of double spreading centers formed during continental rifting in 2D 

Laetitia Le Pourhiet and Fan Zhou

It is common wisdom, based on many years of published simulations of continental rifting followed by spreading that in 2D when a mid-oceanic ridge form in a numerical simulation of continental rifting, extension stops and spreading take over the extension. This is generally due to the complete loss of strength of the mantle lithosphere that cannot transmit forces horizontally across the spreading zone anymore. Actually, in general even the onset of mantle lithosphere necking in a simulation can cause the end of the extension and for many years, I actually claimed very load in the past that two active necking system must be the signature of some obliquity causing 3D extensional conditions. However, recently, a whole series of 2D simulations produced systematically two spreading centers active at the same time. These results surprised me a lot. These simulations were very complex, including a lot of inheritance, the first easy conclusion could have been to say that inheritance causes multiple spreading… But we spent some time and effort to understand if this behavior was due to inheritance or something else. Simplifying our model set-up to the strict minimum, we found it was not inheritance, but a quite cold mantle temperature which permitted a larger shear coupling between the upper mantle dynamics and the mantle lithosphere.  A 50°C difference in mantle temperature radically change the results of the simulation and thanks to our failure, we have found the embryo of an alternative explanation to 3D interactions for the occurrence multiple active necking zones.

How to cite: Le Pourhiet, L. and Zhou, F.: The story of double spreading centers formed during continental rifting in 2D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11403, https://doi.org/10.5194/egusphere-egu24-11403, 2024.

EGU24-11494 | ECS | Posters on site | TS2.1

The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data 

Silvia Foiada, Marta Neres, Pedro Brito, Laura Gomez de la Peña, Irene Merino, and César Ranero

The FRAME geophysical cruise, conducted in 2018 onboard the Spanish R/V Sarmiento de Gamboa, acquired new multichannel seismic reflection (MCS) data on the SW Iberia and NW Moroccan margins. MCS data were acquired with a 6 km long solid-state digital streamer Sercel SENTINEL towed at 19 m water depth, and a 3920 c.i. source with two sub-arrays with 20 guns towed at 10 m depth. The system was designed to provide high penetration and map the entire crust and the upper mantle structure and retain enough resolution to image well the stratigraphy.

In this work we present a 220 km long seismic line acquired on the NW Moroccan margin, from the shallow continental shelf across the continental slope and extending across the deep abyssal plain of the Gulf of Cadiz. The NW Africa margin was selected because the region was the focus of several geophysical campaigns, and several DSDP drill sites that drilled into the synrift strata.  However, limited modern data has imaged the crustal-scale tectonic structure to unravel the late Triassic - early Jurassic rift history of the region.

We applied a seismic processing flow tailored to the attenuation of the multiple energy, signal designature and for the creation of a detailed macro-velocity model to image the lateral changes of the synrift tectonic structure and stratigraphy. The high-quality image of the structure of this rifted margin reveals a complex tectonic structure from the shelf to the deep-water basin where a deep basement containing salt bodies across the entire profile extension. These new results are of high importance for the understanding of the rifting and continent-ocean transition (COT) processes on the northern Central Atlantic and Neothetys domains, as well as for the subsequent compressive deformation processes in the Gulf of Cadiz related to the Africa-Eurasia plate collision.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds through the project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020).

How to cite: Foiada, S., Neres, M., Brito, P., Gomez de la Peña, L., Merino, I., and Ranero, C.: The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11494, https://doi.org/10.5194/egusphere-egu24-11494, 2024.

EGU24-11825 | ECS | Posters on site | TS2.1

Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin 

Mateus Rodrigues de Vargas, Geoffroy Mohn, Julie Tugend, Nick Kusznir, and Andrew Lin

The wide rifting mode that preceded the opening of the South China Sea (SCS) in the Cenozoic generated a set of Paleogene rift basins presently buried under thick post-rift sedimentary infill. Much of the tectonostratigraphic evolution of the South China Sea is now relatively well-constrained (e.g., Pearl River Mouth Basin). However, the SCS's northeasternmost part (i.e., the Tainan margin sensu lato), which might represent the oldest passive margin segment, remains to be integrated into the framework of the rifting and opening of the SCS.

This work aims to review and revisit the tectonostratigraphic evolution of the Tainan margin. To do so, an integrative approach has been used combining the analysis of seismic reflection and gravity data. We use 3D gravity inversion to determine the distribution of Moho depth and crustal thickness within this margin segment. The gravity inversion scheme incorporates a lithosphere thermal gravity anomaly correction, which is critically important because of the elevated geothermal gradient within the young oceanic lithosphere of the South China Sea and its continental margins. In the Tainan margin, results show contrasted crustal domains from the continental shelf, to the distal margin and oceanic domain.

Only limited crustal thinning is observed over the continental shelf where a succession of rift basins is documented (i.e., Taihsi, Nanjihtao, and Penghu basins) that are part of the Northern Rift System. In contrast, the distal Tainan margin shows greater crustal thinning to less than 10 km thick under an aborted breakup basin, thereby forming the Southern Rift System. To the south, this basin is separated from the unambiguous oceanic domain (6 to 8 km thick) by a comparatively thicker crustal block (~ 10 to 15 km thick). This crustal block forms the Southern High where numerous volcanic edifices and magmatic intrusions are observed or inferred.

Half-grabens of the Northern Rift System are controlled by counter-regional faults and filled by Paleocene to Eocene syn-rift sediments. For the distal domain, no well calibration is available. There, we identified several seismic units bounded by regional unconformities. Our results show relatively thin syn-rift sediments locally controlled by a low-angle normal fault system in the Southern Rift System. In contrast, thick post-rift sequences are observed except over the Southern High.

Based on our results, we propose a review of structural style and age correlations from the continental shelf to the distal domains of the Tainan margin. To illustrate along-strike variations of the crustal structure and stratigraphic style, we build an array of regional geological cross-sections that are further compared with existing observations in the adjacent Pearl River Mouth Basin.

How to cite: Rodrigues de Vargas, M., Mohn, G., Tugend, J., Kusznir, N., and Lin, A.: Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11825, https://doi.org/10.5194/egusphere-egu24-11825, 2024.

EGU24-11854 | Posters on site | TS2.1

Rifting style and continental breakup of Marginal Seas 

Geoffroy Mohn, Jean-Claude Ringenbach, Etienne Legeay, Julie Tugend, William Vetel, and François Sapin

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the processes related to their formation from rifting to seafloor spreading initiation remain debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup used to be derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of Atlantic margins.

Here, we describe and discuss the rifting style and the mode of continental breakup of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading.

In these three examples, continental extension is accommodated by a succession of hyper-extended basins controlled by low-angle normal faults that may form and be active at 30° (or less). These hyper-extended basins are filled by polyphase syn-rift sequences showing atypical geometries. These complex stratigraphic architectures result from the development of the low-angle normal faults interacting with antithetic faults, controlling the formation of extensional fishtails for example. The formation of such low-angle normal fault systems is enhanced by basement inheritance of the previous orogenic system.

Continental breakup and final extension are contemporaneous with an important magmatic activity emplaced in the distalmost part of these margins including volcanoes, dykes and sills. Continent-Ocean transitions (COTs) are characterized by a sharp juxtaposition of the continental crust against igneous oceanic crust suggesting that a rapid shift from rifting to spreading occurred. High extension rate prevents conductive cooling allowing the focusing of volcanic activity in sharp COTs, quickly evolving to magmatic accretion.

In conclusion, the rifting style and mode continental breakup are most likely associated with initial rheological conditions with hot geotherm combined with fast extensions rates likely directed by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones.

How to cite: Mohn, G., Ringenbach, J.-C., Legeay, E., Tugend, J., Vetel, W., and Sapin, F.: Rifting style and continental breakup of Marginal Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11854, https://doi.org/10.5194/egusphere-egu24-11854, 2024.

EGU24-11873 | Posters on site | TS2.1

Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications 

Julie Tugend, Geoffroy Mohn, Nick Kusznir, Sverre Planke, Christian Berndt, Ben Manton, Dmitrii Zastrozhnov, and John, M. Millet

The Mid-Norwegian volcanic rifted margin and its NE-Greenland conjugate formed in relation to continental breakup in the latest Palaeocene to earliest Eocene during the emplacement of the North Atlantic Igneous Province (NAIP). The development of the NAIP and opening of the North Atlantic occurred contemporaneous to the Paleocene Eocene Thermal Maximum (PETM) which corresponded to a rapid 5-6 °C global warming episode.

The cause of this rapid global warming, explored as part of IODP Expedition 396, is thought to relate to the thermogenic gases released to the atmosphere via thousands of hydrothermal vents. The thermogenic gases were produced by contact metamorphism of carbon-rich sediments during widespread sill emplacement from the NAIP. The potential of hydrothermally-released greenhouse gases to influence climate depends strongly on the water depth at which they get released. Unless it is released in a shallow marine environment most methane will be oxidized before it reaches the atmosphere.

Early results from IODP Expedition 396 have documented that at least one of the Mid-Norwegian hydrothermal vents was emplaced in shallow marine to potentially sub-aerial conditions. The aim of this contribution is to constrain further the paleo-water depth at which hydrothermal vents formed along the other parts of the mid-Norwegian volcanic rifted margin. This study focuses on an integrated workflow of quantitative geophysical and geodynamic analyses calibrated by new IODP drilling results and structural and stratigraphic observations. We use a 3D flexural-backstripping, decompaction and reverse thermal subsidence modelling to predict the palaeobathymetry and palaeostructure at keys stages of the syn- to post-breakup evolution that can be compared with palaeo-water depths estimated from biostratigraphic data.

Results provide new constraints on the paleobathymetry of hydrothermal vent complexes required to confirm whether the global warming recorded by the PETM was triggered by the magma-rich continental breakup leading to the opening of the northeast Atlantic Ocean. 

How to cite: Tugend, J., Mohn, G., Kusznir, N., Planke, S., Berndt, C., Manton, B., Zastrozhnov, D., and Millet, J. M.: Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11873, https://doi.org/10.5194/egusphere-egu24-11873, 2024.

EGU24-11877 | Orals | TS2.1

Along-strike magma-poor/magma-rich spreading transitions 

Michal Nemcok and Brian Frost

1D/2D data-based studies of active spreading centres brought the knowledge of extension ratedependent stretching-dominated v. buoyancy-dominated spreading. 3D reflection seismic data from the extinct centre of an initial oceanic corridor in the Caribbean allow us to see an along-strike transition between stretching- and buoyancy-dominated spreading where the spreading through detachment faulting is a precursor to the magma-assisted spreading. Studying progressively more evolved portions of the spreading centre, going from its end towards its centre, we see a progressively higher ascent of the asthenosphere, which heats the developing

core complex in the exhuming footwall of the initial stretching-dominated system. The asthenospheric ascent is associated with thermal weakening of the core complex, which eventually results in ductile deformation reaching the upper portion of the complex. Subsequently, the core complex is penetrated by the dyke located at the top of the asthenospheric body. The dyke, which subsequently evolves to a diapir-shaped body, reaches the sea floor

and establishes a magma-assisted steady-state seafloor spreading. These observations lead to a model explaining the initiation of the magma-assisted spreading in the initial oceanic corridor. Furthermore, they also improve our knowledge of multiple interacting mechanisms involved in the breakup of the last continental lithospheric layer, subsequent disorganized spreading and younger organized spreading.

How to cite: Nemcok, M. and Frost, B.: Along-strike magma-poor/magma-rich spreading transitions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11877, https://doi.org/10.5194/egusphere-egu24-11877, 2024.

EGU24-12130 | ECS | Posters on site | TS2.1

Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data 

Ibrahim Yusuf, Stephen M Jones, Tim Reston, Thomas Funck, Brian M O'Reilly, and John R Hopper

The Porcupine Basin, situated in the North Atlantic, serves as a unique natural laboratory for investigating the temporal evolution of magma-poor rifts. Notably, the basin exhibits a progressive increase in the total degree of stretching from north to south, offering a valuable opportunity to interpret its structure in terms of the temporal evolution of magma-poor rifted margins. This study, as part of the broader PORO-CLIM project, focuses on Profile 2 to construct a whole-crustal seismic velocity model and integrate it with existing data to unravel the complete rifting history of the Porcupine Basin.

In the northern region, Reston et al. (2004) identified a detachment fault, the P-reflector, indicating substantial rifting  [1]. Recent analyses by Prada et al. (2017) extended this understanding to the central basin, revealing progressive crustal thinning and mantle serpentinization [2]. However, the southern sector remains largely unexplored. This project aims to capitalise on newly acquired Ocean Bottom Seismometer (OBS) data from PORO-CLIM Profile 2 to image the deep crustal structure and complement this with basement mapping of the southern Porcupine Basin using industry 2D seismic data.

Seismic refraction data from 20 OBS along a 226 km transect form the basis for constructing a comprehensive crustal velocity model. Utilising the RAYINV modelling package, a layer-by-layer forward modelling approach is employed to correlate calculated and observed travel times. Concurrently, structural mapping using long-offset 2D seismic reflection data assists in delineating major faults and regions of mantle unroofing, contributing to the understanding of the Porcupine Basin's subsurface. Preliminary findings reveal extreme crustal thinning and asymmetry, highlighting north-to-south crustal thinning and the emergence of the P-reflector in the southern region of the Porcupine Basin.

[1] Reston, T.J., Gaw, V., Pennell, J., Klaeschen, D., Stubenrauch, A. and Walker, I. (2004). Extreme crustal thinning in the south Porcupine Basin and the nature of the Porcupine Median High: implications for the formation of non-volcanic rifted margins. Journal of the Geological Society, [online] 161, pp.783–798.

[2] Prada, M., Watremez, L., Chen, C., O’Reilly, B.M., Minshull, T.A., Reston, T.J., Shannon, P.M., Klaeschen, D., Wagner, G. and Gaw, V. (2017). Crustal strain dependent serpentinisation in the Porcupine Basin, offshore Ireland. Earth and Planetary Science Letters, [online] 474, pp.148–159.

How to cite: Yusuf, I., M Jones, S., Reston, T., Funck, T., M O'Reilly, B., and R Hopper, J.: Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12130, https://doi.org/10.5194/egusphere-egu24-12130, 2024.

EGU24-12991 | ECS | Orals | TS2.1

Tectonic structure and evolution of Brazilian Equatorial Margin  

Julia Fonseca, César Ranero, Paola Vannucchi, David Iacopini, and Helenice Vital

The Brazilian Equatorial Margin (BEM) is classically interpreted as a transform margin formed during the last phases of the Atlantic rifting of Gondwana. However, rift kinematics and subsequent continental break up has not been constrained.

We present a new model based on the interpretation of a 2D seismic grid acquired along the BEM. The datasets, provided by the Brazilian National Agency for Petroleum (ANP), expand for ~600 km of the margin and consist of approximately 10.000 km of crustal scale 2D seismic reflection profiles which have been calibrated with industry drillholes. The integration of crustal-scale tectonic structures and age and distribution of synrift sediment deposits allowed to determine the style and the timing of the different tectonic phases and to define the crustal thinning evolution of the entire rift system along the Potiguar and East Ceará Basins (NE Brazil).

Our findings indicate that: 1. rifting started ~140-136 My, 2. extension stopped earlier (late Aptian) in the shallow sector of the basin than in the deep-water (early Albian) domains. The shallow basin domains presents minor crustal thinning (~35 thick crust over ~100 km wide), whereas in the deep-water domains, about ~60 km wide, the crust is 4-8 km thick and it extended into the early Albian (116-110 My).

The distribution of deformation structures supports a model of rift evolution where: deformation is initially distributed while forming a shallow basin; it evolves by focusing the extension; finally, extension migrates toward the basin centre to form the deep-water domain. Constraints from seismic reflection data and drillholes help define an abrupt continent to ocean transition (COT), and breakup occurred during the early Albian. Basin sedimentation from its onset to the late Aptian is terrigenous, indicating an isolated environment disconnected from the Northern and Southern Atlantic oceans. Sedimentation changed during the late-most Aptian to the early Albian when marine facies deposited during a rapid ocean water infill of a previously endorheic basin.

The seismic images document that rifting across the margin is not dominated by transcurrent deformation, with strike-slip faulting limited to a relatively small sector, whereas most of the margin extended through normal faulting deformation during opening.

From the interpretation of the 2D seismic reflection grid it was possible to distinguish abrupt lateral changes in the architecture of the basement. These changes defined three distinct, first order segments along the margin named Southern, Central, and Northern segments. The different evolution of the three segments throughout the rifting process is defined by thickness map of the basement. The Northern segment is the only region that shows evidence of potential late synrift magmatism, likely formed during the COT emplacement, which defines second order segmentation. Our interpretation suggests a spatial correlation between first-order tectonic segmentation and second-order magmatic segmentation during the embryonic formation of the spreading center with the definition of fracture zone/transform faults. These findings suggest that most transform faults formed on the spreading centers may have originated from the pattern of continental segmentation during rifting.

How to cite: Fonseca, J., Ranero, C., Vannucchi, P., Iacopini, D., and Vital, H.: Tectonic structure and evolution of Brazilian Equatorial Margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12991, https://doi.org/10.5194/egusphere-egu24-12991, 2024.

EGU24-13269 | ECS | Posters on site | TS2.1

Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin 

Wei Wang, Satish Singh, Zhikai Wang, Aiguo Ruan, Yong Tang, Jérôme Dyment, Sylvie Leroy, Louise Watremez, Zhaocai Wu, He Li, and Chongzhi Dong

During the Jurassic period, the Gondwana Continent progressively rifted from north to south along three huge transform faults (Davie Fracture Zone (DFZ), Mozambique Fracture Zone (MFZ) and Agulhas-Falkland Fracture Zone (AFFZ)), forming the northern, central and southern continental margins along Mozambique, producing a series of divergent and strike-slip margins. These margins are crucial areas for understanding the evolution of Gondwana as their crustal nature and geometry have strongly impacted the kinematic reconstruction of Gondwana. Especially, the debate about continental or oceanic crust for the Mozambique Coastal Plain (MCP) and North Natal Valley (NNV) at the southern Mozambique margin led to tens of kinematic reconstruction models of Gondwana. Based on the OBS and MCS data results of PAMELA MOZ3/5 Cruises, MCP and NNV were identified as continental crust. This has led the scientific community to reconsider the issue, for example, the opening time of the oceanic basin, the movement direction of rifting, and the intense magmatism during the rifting and break-up of Gondwana.

In June 2021, the Second China-Mozambique Joint Cruise was conducted onboard the R/V “Dayang hao”. Three wide-angle seismic OBS profiles were acquired where 70 four-component OBSs were deployed along profiles DZ02 and DZ04 oriented nearly W-E and DZ01 oriented nearly N-S. Four Bolt air guns with a total volume of 8000 in3 in total were towed at ~100 m behind the R/V “Dayang hao” at ~10 m below the sea surface. The shot interval was 200 m.

Here, we present the tomographic results of P-wave velocity along 442 km long profile DZ02, where 21 OBSs were deployed. It traverses through the Continent Ocean Transition (COT) and extends into the Mozambique ocean basin. Approximately 19,000 P-wave arrivals were manually picked, using the travel-time tomography inversion to get the velocity model. The tomographic result shows an apparent decrease in crust thickness from COT to the ocean basin, and the thickness of the oceanic crust is about 8 km. We also observe high-velocity anomalies up to 7.4 km/s in the lower crust above Moho, suggestive of more primitive melt. We will also present the S-wave velocity model for DZ02.  

How to cite: Wang, W., Singh, S., Wang, Z., Ruan, A., Tang, Y., Dyment, J., Leroy, S., Watremez, L., Wu, Z., Li, H., and Dong, C.: Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13269, https://doi.org/10.5194/egusphere-egu24-13269, 2024.

EGU24-13432 | Orals | TS2.1

Structural Evolution of the Black Sea Basin Using Sectioned Computational Models 

Armagan Kaykun and Russell Pysklywec

The tectonic formation of the Black Sea Basin (BSB) has been an ongoing debate: primarily, there is still not a consensus on whether the basin was rifted as one east-west oriented basin, or as two separate basins named Eastern and Western Black Sea Basins. These interpretations are based largely on deep-sea drilling projects and a growing dataset of seismic information (of variable access for academic use). Supporting the two-basin idea is the semi-parallel ridge and depression geometry of the BSB with NW-SE orientation in the Eastern portion of the Black Sea Basin; and W-E orientation in the Western portion of the Black Sea Basin. On the other hand, interpretations for a single basin are supported by the regional structure of the BSB being aligned with the geodynamic models of the basins rifted as a result of slab roll-back. Complicating the understanding of the basin extension and development is the inferred tectonic inversion to shortening in the region starting in the Late Eocene.

To propose a model to answer ongoing debates, we interpreted 24 long-offset 2D seismic lines acquired by GWL in 2011 in a structural geology context. We focused on the structural elements such as big scale normal faults, reverse faults, and tectonic inversion features to create a basis for our 2D computational models for both east and west portions of the BSB. One important finding was to determine the null points on basin bounding faults where the extensional tectonic movements stopped, and the compressional tectonic movements started. Utilizing the ASPECT geodynamic code, we built 2D computational models parallel to the selected two 2D seismic profiles. We compared our findings in our seismic interpretations with the results to understand the timing and basin-wide distribution of structural highs and the compressional tectonic features that shaped the BSB.

How to cite: Kaykun, A. and Pysklywec, R.: Structural Evolution of the Black Sea Basin Using Sectioned Computational Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13432, https://doi.org/10.5194/egusphere-egu24-13432, 2024.

Many orogenic belts today preserve evidence of past crustal rifting. During the syn-rifting, the crust undergoes thinning, forming rift basins with thick sedimentary deposits. The upwelling of the mantle during this extensional phase increases the geothermal gradient within the basin, affecting the crust and sedimentary rocks.

In this study, we used numerical models to simulate the temperature changes in sedimentary rocks within rift basins during both the active rifting phase and the passive continental margin phase after rifting cessation. We found that under a stretching rate of 0.7 cm per year, after 20 million years of continuous stretching, the geothermal gradient within the basin can reach 50-60°C per kilometer, with sedimentary rocks reaching temperatures as high as 450-500°C. After 20 million years of cooling following the end of stretching, the temperatures of the sedimentary rocks decrease by nearly 100°C, and the geothermal gradient reduces to approximately 30°C per kilometer.

We believe that these phenomena can be correlated with the evolution of the Hsuehshan Range in Taiwan, which experienced a transition from rifting to a passive continental margin. During the rifting phase, the temperatures of the sedimentary rocks within the basin reached high metamorphic temperatures of 450-500°C, as indicated by carbonaceous material Raman spectroscopy (RSCM). As the region entered the passive continental margin phase, the rocks gradually cooled, with a temperature decrease of nearly 100°C prior to the onset of mountain building in Taiwan. Similar high-temperature metamorphic temperatures were obtained through RSCM analysis along the Central Cross-Island Highway and Northern Cross-Island Highway, exceeding the closure temperatures of zircon core tracks. However, some zircon core tracks in certain areas did not yield closure ages, suggesting that the high metamorphic temperatures obtained from RSCM analysis were inherited from previous stretching events rather than occurring during the Penglai orogeny.

How to cite: zheng, M., Lee, Y.-H., and Tan, E.: Numerical modelling of continental margin of the Eurasian Plate Rifting and Tectonic evolution.Causes of the highest metamorphic temperature in the Hsuehshan Range and Backbone Range , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14297, https://doi.org/10.5194/egusphere-egu24-14297, 2024.

EGU24-14808 | Orals | TS2.1

Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup 

Egidio Armadillo, Daniele Rizzello, Pietro Balbi, Alessandro Ghirotto, Davide Scafidi, Guy Paxman, Andrea Zunino, Fausto Ferraccioli, Laura Crispini, Andreas Läufer, Frank Lisker, Antonia Ruppel, Danilo Morelli, and Martin Siegert

Recent sub-ice topography compilations of East Antarctica have imaged a wide sector, spanning from 100° E to 160° E in longitude and from the Oates, George V and Adelie coastlines to 85° S in latitude, which contains numerous low-lying basins of variable size and uncertain origin. The sector shows a Basin and Range style tectonics comprising two major basins of continental proportions, the Wilkes Basin and the Aurora Basin complex, and many smaller basins such as the Adventure, Concordia, Aurora and Vostok trenches. The main longitudinal axes of the basins consistently point towards the South Pole and many exhibit intriguing distinct triangular shapes, sitting within an approximately 2000 x 2000 km fan-shaped physiographic region limited by a semi-circular coast line. We name this region as the East Antarctic Fan shaped Basin Province (EAFBP). To the West, this sector is limited by the intraplate Gamburtsev Mountains (GM) and to the East by the Transantarctic Mountains (TAM) constituting the uplifted shoulder of the Cenozoic West Antarctic Rift System (WARS).

Origins and inter-relationships between these four fundamental Antarctic tectonic units (WARS, TAM, EAFBP, GM) are still poorly understood and strongly debated. Very little is known about the mechanism generating the basins in the EAFBP, their formation time, whether they are all coeval and if and how they relate to Australia basins before Antarctica-Australia rifting. Present genetic hypotheses for some of the basins span from continental rifting to a purely flexural origin or a combination of the two. Also, post-tectonic erosional and depositional processes may have had a significant impact on the present-day topographic configuration.

Here we interpret the EAFBP as the result of a single genetic mechanism: a wide fan-shaped intra-continental extension around a near pivot point at about 135° E, 85° S that likely occurred at the Mesozoic-Cenozoic transition. We discuss evidence from the sub-ice topography and potential field airborne and satellite data. We have applied image segmentation techniques to the rebounded sub-ice topography to semi-automatically trace the first order shape of the sub-ice basins, that we assume to be fault controlled. Then we have fitted the edges of the basins by maximum circles and estimated the best Euler pole identified by their intersection. Potential field anomalies have been taken into account in order to enlighten major discontinuities not revealed by the sub-ice topography.

The reconnaissance of this large sector of East Antarctica as the result of rotational extension may have major implications on global and regional tectonics plate reconstructions, plate deformation assumptions and new tectonic evolutionary models of WARS, TAM, and GM.

How to cite: Armadillo, E., Rizzello, D., Balbi, P., Ghirotto, A., Scafidi, D., Paxman, G., Zunino, A., Ferraccioli, F., Crispini, L., Läufer, A., Lisker, F., Ruppel, A., Morelli, D., and Siegert, M.: Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14808, https://doi.org/10.5194/egusphere-egu24-14808, 2024.

EGU24-14829 | Orals | TS2.1 | Highlight

The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms 

Freysteinn Sigmundsson, Michelle Parks, Halldór Geirsson, Andrew Hooper, Vincent Drouin, Kristín Vogfjörð, Benedikt Ófeigsson, Sonja H. M. Greiner, Yilin Yang, Chiara Lanzi, Gregory Paul De Pascale, Kristín Jónsdóttir, Sigrún Hreinsdóttir, Valentyn Tolpekin, Hildur María Friðriksdóttir, Páll Einarsson, and Sara Barsotti

A 15 km long dike formed rapidly in the Reykjanes Peninsula oblique rift on 10 November 2023 and propagated under the town of Grindavík.  From just before noon on 10 November until midnight, around 25 MW≥4 earthquakes occurred, two of which were of MW~5.2. Three-dimensional ground deformation is well resolved both temporally and spatially with dense Global Navigation Satellite System (GNSS) geodetic observations, which record cumulative displacements up to about 80 cm occurring mostly over 6 hours in the evening of 10 November and continuing at much reduced rates in the following days. Interferometric analysis of synthetic aperture radar images using Sentinel-1, COSMO-SkyMed, and ICEYE satellites records also well the dike deformation, which occurred simultaneously with deflation over the nearby central part of the Svartsengi volcanic system. Geodetic modelling, assuming uniform elastic host rock behavior, infers a dike volume of (130-139)×106 m3, with up to ~8 m dike opening, as well as some strike-slip shear motion. Deflation at Svartsengi in our model is best fit using a spherical point source with a volume decrease of (76-82)×106 m3up until 12 November. The temporal evolution of the dike opening was further modelled using hourly GNSS displacements, allowing better derivation of the temporal evolution of the flow rate into the dike and the contraction volume of the subsidence source. The maximum flow rate into the dike is inferred to be ~9500 m3/s, between 18:00 and 19:00 on November 10. We infer that the massive magma flow into the dike was established with only modest overpressure in the feeding magma body, a sufficiently large pathway opening at the boundary of the magma body, and pre-failure lowering of pressure along the pathway that had occurred through gradual build-up of high tensile stress over the previous eight centuries. This explains the unprecedented fast maximum magma flow rates that we infer. Such high flow rates provide insight into the formation of giant dike swarms under conditions of high tensile stress, and imply a high hazard potential for dike intrusions, considering their potential to transition into eruptions.

 

How to cite: Sigmundsson, F., Parks, M., Geirsson, H., Hooper, A., Drouin, V., Vogfjörð, K., Ófeigsson, B., Greiner, S. H. M., Yang, Y., Lanzi, C., De Pascale, G. P., Jónsdóttir, K., Hreinsdóttir, S., Tolpekin, V., Friðriksdóttir, H. M., Einarsson, P., and Barsotti, S.: The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14829, https://doi.org/10.5194/egusphere-egu24-14829, 2024.

EGU24-14830 | Posters on site | TS2.1

High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif) 

Prokop Závada, Vladimír Cajz, Andrew Kylander-Clark, and David Uličný

A new set of high-precision U-Pb data was acquired for two groups of phonolite bodies emplaced in the volcano-sedimentary sequence of the Cenozoic Eger Rift in Bohemian Massif. The phonolites are located in the western (5 bodies) and eastern (3 bodies) edge of this monogenetic volcanic field, stretched along the central part of the Eger Rift system. The selected phonolite bodies represent lava flows, cryptodomes or extrusive domes emplaced in phreatomagmatic maar-diatremes, remnants of dykes, and a laccolith. The U-Pb dates were acquired using the Laser Ablation Split Stream system at Santa Barbara University geochronology lab, which provides the coupled geochronology and also REE and selected major element geochemistry. Despite the great variety of internal zircon textures from oscillatory zoning to complex patchy patterns with a large range of cathodoluminescence intensity, the groups of spots gained coherent and surprisingly precise ages for each sample. The western group of phonolite bodies, namely the Bořeň, Želenický vrch, Špičák, Hněvín, and Ryzelský vrch display clusters of ages ranging between 33Ma and 36Ma, while zircons of the eastern group of the phonolites, Krompach, Mariánská hora and Luž (Lausche) indicate ages between 30Ma and 32Ma. Terra-Wasserburg diagrams for individual samples revealed remarkable precision marked by errors of only 90-180 thousand years (5 samples) and 300-650 thousand years (2 samples). The U-Pb zircon ages are interpreted to reflect primarily the high-temperature overprint of inherited (and possibly newly crystallized) zircons before emplacement of the phonolite bodies in the upper crust. In addition, titanite grains measured alongside the zircon grains (in another run) either overlap (Bořeň) with the zircon age error on Terra-Wasserburg diagrams (geochrone) or are 2 Ma years younger than corresponding zircon ages (Špičák phonolite body). REE binary diagrams revealed separate clusters of Sm/Nd and also Hf content of the zircons, which can be attributed to different degrees of partial melting of parental magma in the source upper mantle or the lower crust for both groups of sampled phonolites. In summary, the results suggest that U-Pb geochronology using the LASS system is a powerful tool with a great potential for deciphering the evolution of phonolites in the Cenozoic Rift system in Bohemian Massif and possibly other rift systems in the foreland of the Alpine orogeny.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Závada, P., Cajz, V., Kylander-Clark, A., and Uličný, D.: High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14830, https://doi.org/10.5194/egusphere-egu24-14830, 2024.

EGU24-15107 | ECS | Posters on site | TS2.1

The evolution of fault networks during multiphase deformation: An analogue modeling approach 

Jun Liu, Matthias Rosenau, Ehsan Kosari, Sascha Brune, Frank Zwaan, and Onno Oncken

It is well known that triaxial deformation is a common feature of continental tectonics, and is accommodated by complex polymodal fault networks. Field investigations confirm that multiple phases involving time-dependent three-dimensional strain conditions (e.g. constriction, plane, and flattening strain) affect the spatial and temporal interaction of polymodal fault systems. However, a key question remains: How do changing strain conditions affect the reactivation of fault systems that formed during a previous deformation phase? Here, we conduct scaled analogue models with time-dependent boundary conditions to investigate how fault networks evolve under changing boundary conditions, including  reactivation and formation of new faults.

We have developed a setup in which a basal rubber sheet is stretched in one direction, so that longitudinal extension and layer thinning are accompanied by lateral shortening, hence producing triaxial deformation (Liu et al. in revision). According to previous brittle-viscous experiments with this set-up, an increase in longitudinal extension velocity results in a higher coupling between the rubber base and brittle layer, generating increasing transmission of lateral shortening from the base into the brittle layer. We thus induce constriction-to-plane strain conditions in the brittle layer as a function of longitudinal extension velocity by varying the magnitude of lateral contraction. In a new set of experiments, by varying extension velocity either stepwise or continuously, we realize time-dependent kinematic boundary conditions including deformation phases and secular changes, respectively. Digital image correlation (DIC) and photogrammetry (structure from motion, SFM) are employed to track the 3D kinematic surface and topography evolution, respectively.

Preliminary observations show both the formation of new faults and the reactivation of early phase faults through a change from plane to constriction strain. Conversely, a change from constriction to plane strain conditions results in the abandonment of the early phase fault network as it becomes overprinted by fault systems of the subsequent phase. Moreover, early-phase fault systems influence the propagation and linkage of fault populations in subsequent phases. Our analogue models highlight the impact of strain conditions on the overall plan-view geometry of fault populations, providing alternative explanations for complex fault patterns and interactions (e.g. the Jeanne d’Arc basin, the North Træna Basin, and the Beagle Platform).

How to cite: Liu, J., Rosenau, M., Kosari, E., Brune, S., Zwaan, F., and Oncken, O.: The evolution of fault networks during multiphase deformation: An analogue modeling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15107, https://doi.org/10.5194/egusphere-egu24-15107, 2024.

EGU24-15188 | Posters on site | TS2.1

Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia 

Radomír Grygar, Karel Mach, Roman Gramblička, and Tomáš Novotný

The Most Basin is the largest and best-preserved of sedimentary basins formed within the Eger Rift, the easternmost part of the European Cenozoic Rift System. Previous work on the tectono-sedimentary history of the basin and its surroundings has led to an interpretation of two main extensional phases that governed the Oligo-Miocene rift initiation and subsequent evolution. That interpretation has been derived mainly from large-scale considerations of main fault geometries, while a satisfactory support by a large mesoscopic dataset from the basin infill was lacking.

 

Systematic acquisition of mesoscopic structural data in some of the open-cast coal mines operating in the Most Basin has been motivated by prevention of accidents of bucket wheel excavators, threatened by sliding of blocks of mainly clayey sediments. As a result, over 5 thousand mesoscopic measurements were acquired in the Bílina Mine alone and hundreds in other mines over the past 13 years. In the Most Basin, the main coal seam is located close to the base of the basin fill. Open-case mines thus expose a thick overburden and, locally, also the underlying basement. The structural measurements involved the superposition and evolution of mesoscopic structural features in geological time, from Variscan metamorphic rocks through Cretaceous sediments and Oligocene volcanics through the Miocene coals and clastics of the basin fill.

 

Structural analysis of the dataset and statistical comparison of specific regions focused on

spatial and stratigraphic distribution of fault directions and inclination arrays, resulting in interpretation of spatial and stratigraphic distribution of local paleostress. The principal results are as follows:

  • the number of detected mesoscopic fault populations, as well as of interpreted deformation phases decreases upward through the stratigraphic column;
  • orientation of faults generally changes from a dominant E-W and NW-SE strike of population in the pre-Miocene formations into dominant SW-NE up to WSW-ENE strike within the youngest Libkovice Member (Early Miocene);
  • a trend of decreasing fault inclination from older, more consolidated formations to younger ones, most probably linked to rheological (stage of lithification) on brittle deformations;
  • generally, data evaluation of inclination and direction of faults gave generally similar results for the Bílina and Libouš mines, in spite of the 60 km distance between them and their proximity to different leading fault systems (Bílina and Victoria faults in the former case and the Ahníkov and Kralupy faults in the latter);
  • the large dataset of mesoscopic fault-slip data shows a generally more complex picture of possible paleostress evolution than the one derived from the geometries of the main bounding fault systems, due to the influence of local stress fields of normal and transtensional faults. The general picture, however, implies a plausible gradual evolution of extension vector from NNE-SSW to NW-SE orientations. throughout the early Miocene.

 

The Severočeské doly, a.s., supported the long-term acquisition of the structural dataset and its utilization for basic research purposes. This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Grygar, R., Mach, K., Gramblička, R., and Novotný, T.: Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15188, https://doi.org/10.5194/egusphere-egu24-15188, 2024.

EGU24-15268 | Orals | TS2.1

Shallow sources of upper mantle seismic anisotropy in East Africa  

Cynthia Ebinger, Miriam Reiss, Ian Bastow, and Mary Karanja

The East African rift overlies one or more mantle upwellings and it traverses heterogeneous Archaean-Paleozoic lithosphere rifted in Mesozoic and Cenozoic time. We re-analyze XKS shear wave splitting at publicly available stations to evaluate models for rifting above mantle plumes. We use consistent criteria to compare and contrast both splitting direction and strength, infilling critical gaps with new data from the Turkana Depression and North Tanzania Divergence sectors of the East African rift system. Our results show large spatial variations in the amount of splitting (0.1–2.5 s) but consistent orientations of the fast axes within rift zones: they are predominantly sub-parallel to the orientation of Cenozoic rifts underlain by thinned lithosphere with and without surface magmatism. The amount of splitting increases with lithospheric thinning and magmatic modification. Nowhere are fast axes perpendicular to the rift, arguing against the development of extensional strain fabrics. Thick cratons are characterized by small amounts of splitting (≤0.5 s) with a variety of orientations that may characterize mantle plume flow. Splitting rotates to rift parallel and increases in strength over short distances into rift zones, implying a shallow depth range for the anisotropy in some places. The shallow source and correlation between splitting direction and the shape of upper mantle thin zones suggests that the combination of channel flow and oriented melt pockets contribute > 1 s to the observed splitting delays. Enhanced flow, metasomatism, and melt intrusion at the lithosphere-asthenosphere boundary suggest that fluid infiltration to the base of the lithosphere may facilitate rifting of cratonic lithosphere. 

How to cite: Ebinger, C., Reiss, M., Bastow, I., and Karanja, M.: Shallow sources of upper mantle seismic anisotropy in East Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15268, https://doi.org/10.5194/egusphere-egu24-15268, 2024.

EGU24-16081 | Orals | TS2.1

Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport 

Adina E. Pusok, Yuan Li, Richard F. Katz, Tim Davis, and Dave A. May

Geophysical studies along the Main Ethiopian Rift and Eastern Rift in Kenya indicate that strain accommodation is dominated by magmatic intrusion rather than tectonic extension (e.g., Ebinger and Casey, 2001). However, it remains unclear how magmatic extension developed in the Turkana Depression, the low-lying, broadly rifted region separating the Ethiopian and East African plateaus. We investigate the rifting dynamics of the Turkana Depression with two-phase flow numerical models of melt transport through the ductile–brittle lithosphere. These models suggest that the pre-rift rheological structure of the lithosphere exerts a counter-intuitive control on melt extraction, which can explain the character of the Turkana region.

Recent seismic imaging shows that both the Turkana Depression and the uplifted plateaus are underlain by deep-seated, hot, partially-molten, buoyant mantle that ponds below a thinned plate (Kounoudis et al., 2021). Yet, Ogden et al. (2023) estimated the Moho is 10–20 km shallower throughout the Turkana Depression (~20–25 km) than surrounding regions (~35–40 km). Here, we hypothesise that variations in lithospheric strength across the Turkana Depression and the Ethiopian Plateau have influenced magma transport across the lithosphere and rift development (Morley, 1994). 

Our models of melt extraction through the ductile–brittle lithosphere incorporate a new poro-viscoelastic–viscoplastic theory with a free surface (Li et al., 2023), designed and validated as a consistent means to model dykes. We initialise models with a source of partial melt in the asthenosphere and investigate how rheology of the overlying lithosphere impacts melt migration to the surface. Experiments are performed for buoyancy-driven magma transport under no tectonic extension, and for low background tectonic extension rates typical to the Turkana Depression (4 mm/yr; e.g., Knappe et al., 2020). Results indicate that both the rheology of lithosphere and extension rate control the efficiency of magma extraction. Magma transport across a thick, elastic lithosphere is more efficient than across a thin, more ductile lithosphere, and increases with extension. Our results suggest that surface volcanism in the Ethiopian Plateau is more likely to occur compared with the Turkana Depression, and at earlier times. 

References

Ebinger and Casey (2001), Geology, DOI: 10.1130/0091-7613(2001)029<0527:cbimpa>2.0.co;2

Kounoudis et al. (2021), G-cubed, DOI: 10.1029/2021GC009782

Ogden et al. (2023), EPSL, DOI: 10.1016/j.epsl.2023.118088

Morley (1994), Tectonophys., DOI: 10.1016/0040- 1951(94)90170-8

Knappe et al. (2020), JGR: Solid Earth, DOI: 10.1029/2019JB018469

Li et al. (2023), GJI, DOI: 10.1093/gji/ggad173

How to cite: Pusok, A. E., Li, Y., Katz, R. F., Davis, T., and May, D. A.: Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16081, https://doi.org/10.5194/egusphere-egu24-16081, 2024.

EGU24-16240 | ECS | Posters on site | TS2.1

Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years. 

Amber Distelbrink, Grace E. Shephard, Jean-Baptiste P. Koehl, Steffen G. Bergh, and Anouk Beniest

Constraining the evolution of the opening of the northernmost region of the Northeast Atlantic Ocean is of particular importance for understanding the diversity of ocean basin opening dynamics, including the development of oblique margins and shear zones. Accurately determining the timing and kinematics of the motion along the Senja Shear Zone and opening of the Fram Strait is of particular importance for climate research as this region forms the only deep-water gateway between the Northeast Atlantic Ocean and Arctic Ocean. This study combines new and legacy data and presents an analysis of the tectonic evolution of the northern Norwegian passive margin over the past 200 Ma, including integrating structural field observations and plate tectonics models.

Fieldwork took place on the islands of Senja and Kvaløya in Troms County of northern Norway. The field observations reveal four dominant brittle fault groups corresponding to four normal-oblique extension directions: E-W, NNW-SSE, NW-SE, NE-SW. In the Senja Shear Zone, the strike-slip faults are predominantly oriented NNW-SSE to NW-SE. Analysis of existing plate motion models for the region for 200 Ma to present day includes three prominent extension phases in chronological order: E-W, NNW-SSE, and NW-SE.

This study suggests that during the E-W oriented crustal thinning phase, normal faulting and minor strike-slip faulting dominated and gave way to basement-seated strike-slip faults during the NNW-SSE oriented extension phase. The presence of mid-upper crust faulting is argued by fault mineral striation assemblages and hydrothermal alteration. In the NW-SE oriented extensional phase, both normal faults and strike-slip faults were active. Comparisons to existing rigid plate tectonic models for the region suggest a revised deformable plate framework is required, and offers insights into the original thickness of the North-American and European plates and the role of mid-crustal tectonics in the breakup. The role of inheritance, including earlier shear zones and extensional phases will also be discussed. In addition, the present research encourages scientists to digitize analogue maps and data, preventing loss of knowledge during the analogue to digital transition.

How to cite: Distelbrink, A., Shephard, G. E., Koehl, J.-B. P., Bergh, S. G., and Beniest, A.: Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16240, https://doi.org/10.5194/egusphere-egu24-16240, 2024.

EGU24-17089 | Posters on site | TS2.1

The ANR project “FirstMove”: first movements of divergence between future tectonic plates 

Julia Autin, Roxane Mathey, Harmony Suire, Mélanie Ballay, Marc Ulrich, Gianreto Manatschal, Daniel Sauter, Benoît Petri, Marc Schaming, and Luis Somoza Losada

As two tectonic plates drift away, the earlier movements, prior to oceanic crust formation, are ill-constrained. We are convinced that the kinematic models of plate movements could be significantly enhanced by focusing on the divergence before final lithospheric breakup. During this phase of transition several problems arise. Firstly, the classical interpretations of magnetic anomalies are not trustworthy (debated geometry and/or origin of anomalies). Secondly, the movements are more complex than in oceanic domain (polyphase deformation, obliquity, asymmetry). Those particularities occur especially if plate breakup happens in magma-poor conditions where mantle is exhumed at the surface (in about 50% of instances).

We focus on two pairs of conjugate magma-poor rifted margins: the Bay of Biscay and the Australia-Antarctica margins. In these areas, magnetic anomalies are controversial and seafloor formation started with large domains of hyperextended continental crust and exhumed mantle. Thus, the location and age of the LaLOC (landward limit of the oceanic crust) are uncertain. We aim to better define these domains in space, divergence direction and time through geophysical data and localized petrological observations and dating. This project is in its starting phase, it includes 2 PhD thesis. This presentation focuses on the general framework of the project and the preliminary results.

How to cite: Autin, J., Mathey, R., Suire, H., Ballay, M., Ulrich, M., Manatschal, G., Sauter, D., Petri, B., Schaming, M., and Somoza Losada, L.: The ANR project “FirstMove”: first movements of divergence between future tectonic plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17089, https://doi.org/10.5194/egusphere-egu24-17089, 2024.

EGU24-17201 | ECS | Posters on site | TS2.1

Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea 

Chao-Hsun Wang, Ping-Rong Wu, Kenn-Ming Yang, Chih-Cheng Yang, and Bieng-Zih Hsieh

Jieyang Depression is located between the Southern Depression of the Taixinan Basin and the Chaoshan Depression of the Pearl River Mouth Basin in northern South China Sea. A series of NE-SW striking half graben developed in this area from late Mesozoic to early Paleogene, and then another two stages of normal faulting happened during Neogene. The development of these stages of normal faults are separated by the breakup unconformity and a post-rift truncation. The main purposes of this study are to investigate the evolutionary sequences of the multi-stages of normal faults and the truncations during the multi-stages of extension, the spatial distribution of each phase of normal faults, and how the younger normal faults were affected by the pre-existing ones.

The normal faults in the Jieyang Depression can be divided into three types. Type 1 faults are related to the Paleogene half graben formation and only cut through the pre-rift and syn-rift strata. Type 2 normal faults only developed and cut through the post-rift strata. Type 3 normal faults cut through the syn-rift and post-rift strata. In this study, we further divide the Type 2 normal faults into two different kinds. Type 2-1 faults developed above the Paleogene half graben and cut off by the post-rift truncation. Type 2-2 faults developed after the truncation. Type 3 normal faults can be divided into two different kinds as well. Type 3-1 faults developed in the syn-rift stage and yet were reactivated and linked with the faults developing in the later extension. Type 3-2 faults are the Type 2 faults that developed continuously cutting downward into the syn-rift strata.

In terms of spatial distribution, Type 1 normal faults strike NE-SW, forming the half grabens. Most of the Type 2 normal faults are located far away from continental shelf. Type 3 normal faults mostly distribute on the northeast and northwest sides of the study area, close to the continental shelf, and most of them are cut by the post-rift truncation.

As a result, from the late Mesozoic to the early Paleogene, the northern slope of the South China Sea experienced a NW-SE extension. At the end of the Paleogene, the extension ceased, forming the breakup unconformity. In the Neogene, the Jieyang Depression experienced second extension. In this time the extension orientation was NNW-SSE, developing Type 2-1 and Type 3 faults before the post-rift truncation. The subsequent truncation cuts Type 2-1 faults and the upper part of the Type 3 faults. After accumulating new strata above truncation, the third stage of extension happened and Type 2-2 faults developed after the post-rift truncation.

Key words: South China Sea, Jieyang Depression, normal fault, multi-stage extension, truncation

How to cite: Wang, C.-H., Wu, P.-R., Yang, K.-M., Yang, C.-C., and Hsieh, B.-Z.: Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17201, https://doi.org/10.5194/egusphere-egu24-17201, 2024.

EGU24-17395 | ECS | Orals | TS2.1

Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin 

Valentin Rime, Anneleen Foubert, Derek Keir, and Tesfaye Kidane

The Danakil Depression is situated in the northern part of the Afar Depression in Ethiopia and Eritrea and is in an advanced phase of rifting close to continental breakup. It forms the equivalent of a magma-rich margin. As it is currently active and emerged, it offers a unique opportunity to study the processes of formation of these types of passive margins.

We combine seismic reflection data, field data, and remote sensing to constrain the structure and kinematics of this basin. Seismic data reveal the formation of Seaward Dipping Reflectors (SDRs). Surprisingly, field data show that these SDRs are dominated by clastic sediments and only contain relatively minor amount of magmatic material. Paleoshorelines and other proxies allow to quantify uplift and subsidence rates across the basin. These data highlight high spatial variability and allow to better understand the structure and evolution of older, deeply buried passive margins.

How to cite: Rime, V., Foubert, A., Keir, D., and Kidane, T.: Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17395, https://doi.org/10.5194/egusphere-egu24-17395, 2024.

EGU24-17937 | ECS | Posters on site | TS2.1

Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin. 

Alexandra Tamas, Robert E. Holdsworth, Dan M. Tamas, Edward D. Dempsey, Kit Hardman, Anna Bird, John R. Underhill, Dave McCarthy, Ken J.W. McCaffrey, and David Selby

Constraining the age of formation and movement along fault arrays in superimposed basins helps us to better unravel their kinematic history as well as the role of bounding faults or inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) comprises a series of superimposed basins overlying rocks of the Caledonian basement, the pre-existing Devonian-Carboniferous Orcadian Basin and a regionally developed Permo-Triassic North Sea basin system. The IMFB rifting occurred mainly in the Upper Jurassic – Lower Cretaceous after a long period of subsidence followed by localised uplift in its eastern parts due to thermal doming in the central North Sea (in the middle Jurassic). The rift basin later experienced further episodes of regional tilting, uplift and fault reactivation during Cenozoic.

New detailed field observations augmented by drone photography and creation of 3D digital outcrops, coupled with U-Pb geochronology of syn-faulting calcite-mineralised veins are used to constrain the absolute timing of fault movements and decipher the kinematic history of basin opening. It also helps to identify those deformation structures associated with earlier basin-forming events.

Five regional deformation events emerge: Devonian rifting associated with the older Orcadian Basin; Late Carboniferous inversion related to dextral Great Glen fault movements; Permian thermal subsidence with some evidence of minor fracturing; Late Jurassic – Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to many of these events.

How to cite: Tamas, A., Holdsworth, R. E., Tamas, D. M., Dempsey, E. D., Hardman, K., Bird, A., Underhill, J. R., McCarthy, D., McCaffrey, K. J. W., and Selby, D.: Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17937, https://doi.org/10.5194/egusphere-egu24-17937, 2024.

The presentation is based on the results of the research work of the Arktic-2011, Arktic-2014 and Arktic-2022 expeditions and contains the results of analysis of the structure of the sedimentary cover of the Eurasian basin of the Arctic Ocean. For the first time, the entire array of seismic data, including Russian and foreign seismic profiles, was used for tectonic constructions. The results obtained make it possible to reconstruct extensive areas of continental lithosphere development in the Eurasian basin. Based on the analysis of the structure of the sedimentary cover of the Amundsen Basin, four stages of the geological history of the formation of the sedimentary system of the Eurasian basin of the Arctic Ocean are substantiated. During the first (Cretaceous-Paleocene) stage, extensive axis-symmetric epicontinental paleo-basins of the Amundsen and Nansen Basins were formed on the shoulders of the continental rift, which were subsequently separated by seafloor spreading. Evidence of similar riftogenic settings in the second half of the Cretaceous is recorded along the entire periphery of the Arctic basin from Greenland to the Chukchi Rise. The second (Eocene)-spreading stage was characterised by stage accretion of the oceanic crust in the Gakkel Ridge and was accompanied by a gradual expansion of the sedimentary basin up to the present-day boundaries of the Eurasian basin. The third stage (Oligocene-Miocene) of sedimentary flexure corresponded to the accumulation of a thick undisturbed sedimentary cover over the entire Eurasian basin, indicating the temporary cessation of spreading in the Gakkel Ridge and the establishment of a tectonic quiescence regime. Similar conditions at this stage are recorded throughout the periphery of the Arctic basin. The resumption of spreading processes occurred at the fourth (Pliocene-Quaternary) neotectonic stage. As the result of the intensification of spreading processes in the Norwegian-Greenland Basin, tectonic stresses penetrated intothe Eurasian Basin along the axis of the Gakkel Ridge. The distinct morphological division of the Gakkel Ridge into Siberian-Marine and Atlantic segments is explained by the jump-like transmission of tectonic stresses of the North Atlantic, which is also confirmed by the anomalously high tectonic, volcanic and hydrothermal activity of the Gakkel Ridge.

How to cite: Neevin, I., Rekant, P., and Budanov, L.: MODEL OF THE FORMATION OF THE SEDIMENTATION SYSTEM OF THE EURASIAN BASIN OF THE ARCTIC OCEAN AS A BASIS FOR RECONSTRUCTING Its TECTONIC HISTORY, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18255, https://doi.org/10.5194/egusphere-egu24-18255, 2024.

EGU24-19671 | Orals | TS2.1

A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins 

Christian Heine, Ken McDermott, James Eldrett, Colin Grant, and Philip Thompson

The spatio-temporal analysis of rifts and passive margin evolution is often done based on regional case studies, using non-standardized terminology and classification models to characterize crustal boundaries and basin infill. As example, the use of “continent-ocean boundary” to delineate crustal types or “syn-rift” as basin infill characterization has proven to be no longer adequate, given our evolved understanding of passive margins. In general, such local approaches do not lean themselves to aggregate data for global and large-scale comparative analysis and often struggle to reconcile the spatially varying magmatic/weakly magmatic margin architecture in a rift system context. They also do not allow efficient deployment of spatio-temporal data analytic models due to a lack of standardized data classification.

To overcome these limitations, we have designed a novel “data science-ready” data model for crustal architecture that is based on commonly accepted terminologies, can be used independent of input data heterogeneity and can be deployed globally across the whole spectrum of margin types and complex 3D margin geometries/microplate settings. We classify two key crustal boundaries, the oceanward limit of continental crust ("OLCC") and the landward limit of oceanic crust ("LaLOC"), along with several key crustal interfaces, such as the top basement and base crust which are further subdivided into sub-categories. This approach allows us to easily generate standardized data products on rift system scale, which quantitatively describe key parameters relevant to understand lithosphere extension dynamics, such as volumes, ratio, and distribution of continental and magmatic crust, crustal stretching factors, and amount of crustal embrittlement. Coupled with plate kinematic models, these data products allow to build reproducible, extensible, and quantitative models of rift and margin evolution through time and highlight the dynamics of stretching, localization of deformation, the basin infill response, and spatio-temporally varying patterns and types of magmatism.

Applying this data model, we have characterized the crustal architecture of the conjugate South Atlantic passive margins, interpreting more than 100k line-kilometers of 2D and 3D seismic reflection data. Our findings highlight substantial shortcomings of current plate models to reconcile the crustal type distributions in the southern South Atlantic with a tight pre-breakup fit, the temporal emplacement dynamics of SDRs and plume-related magmatism along the whole South Atlantic rift, as well as the localization of deformation and dynamics of basin infill.

How to cite: Heine, C., McDermott, K., Eldrett, J., Grant, C., and Thompson, P.: A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19671, https://doi.org/10.5194/egusphere-egu24-19671, 2024.

EGU24-19853 | Posters on site | TS2.1

Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting 

Marta Pérez-Gussinyé, Yangfan Xin, Tiago Cunha, Raghu Ram, Miguel Andres-Martinez, Dongdong Dong, and Javier Garcia-Pintado

The thermal history of margins controls the development of hydrothermal systems during rifting, diagenetic processes in the sediments and the generation and preservation of hydrocarbons. It also affects the depth of the oceanic gateways formed during continental break-up, thereby influencing ocean circulation and ultimately climate (Brune et al., 2023, Pérez-Gussinyé et al., 2023, Peron-Pinvidic et al., 2019). Observed heat-flow values however, do not always comply with classic rifting models. Here, we use 2D numerical models to investigate the relationship between rifting, sedimentation and thermal history of margins. We find that during the synrift, the basement heat flow and temperature are not only controlled by extension factor, but also by synrift sediment thickness and the evolution of deformation. As this progressively focuses oceanward, the proximal sectors thermally relax, while the distal sectors experience peak temperatures. This time lag is important for wide rifted margins. In the postrift, the lithosphere under the hyperextended margins does not return to its original state, at least for ~100 Myrs after breakup. Instead, it mimics that of the adjacent oceanic plate, which is thinner than that of the original continental plate. This results in heat flow values increasing oceanward at postrift stages where classic rifting theory predicts complete thermal relaxation. Our increased heat-flow estimations, may extend hydrocarbon plays into distal margin sectors and adjacent oceanic crust, previously discarded as immature. Finally, our models indicate that commonly used temperature approximations in basin analysis may strongly differ from those occurring in nature (Pérez-Gussinyé et al., 2024).

 

Brune, S., Kolawole, F., Olive, JA. et al. Geodynamics of continental rift initiation and evolution. Nat Rev Earth Environ 4, 235–253 (2023). https://doi.org/10.1038/s43017-023-00391-3

Pérez-Gussinyé, M., Collier, J., Armitage, J., Hopper, J. R., Sun, Z., and Ranero, C. R., Towards a process-based understanding of rifted continental margins, in Nature Reviews Earth and Environment, 2023, doi: 10.1038/s43017-022-00380-y

Marta Pérez-Gussinyé, Yanfang Xin, Tiago Cunha,  Raghu Ram, Miguel Andrés-Martínez, Dongdong Dong, Javier García-Pintado,Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension, in press, Geol. Soc Spec. Publ., 2024

Peron-Pinvidic, G., Manatschal, G., eta al. Rifted Margins: State of the Art and Future Challenges, Front. Earth Sci., 22 August 2019, Sec. Structural Geology and Tectonics, Volume 7 - 2, https://doi.org/10.3389/feart.2019.00218.

How to cite: Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andres-Martinez, M., Dong, D., and Garcia-Pintado, J.: Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19853, https://doi.org/10.5194/egusphere-egu24-19853, 2024.

EGU24-19947 | ECS | Posters on site | TS2.1

Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling 

Yaoyao Zou, Daniele Maestrelli, Giacomo Corti, Chiara Del Ventisette, Liang Wang, Xiaofan Wan, Yanjie Gao, and Chuanbo Shen

 

Multiple fault populations with different orientations and complex fault patterns can be observed during oblique rifting, conditions which result from a complex rift kinematics which combines dip-slip and strike-slip motion. Although analysis of different natural cases and analog or numerical modeling have shed light on the relations between rift obliquity and the related fault architecture, many aspects of the process remain poorly understood. One of these aspects is related to the existence of pre-existing fabrics in the upper crust, which may further complicate the fault pattern by forcing the development of faults with atypical geometries and orientation.

Here, we performed enhanced-gravity analog models of oblique narrow rifting to characterize the evolution and architecture of rift-related faults developing in a brittle upper crust characterized by inherited fabrics. The models reproduce a rift obliquity of 30° (angle between the rift trend and the orthogonal to the direction of extension), kept constant in all the experiments, and pre-existing vertical fabrics with variable orientation (from 0°, i.e. orthogonal to extension, to 90°, i.e. extension-parallel). Modeling results suggest that inherited fabrics have an important influence on rift-related faulting, with a significant correlation between the intensity of reactivation and their trend with respect to the extension direction. When the pre-existing fabrics trend perpendicular to the extension direction (obliquity 0°), they are strongly reactivated, localizing deformation and promoting the rapid development of faults and grabens perpendicular to the extensional direction. When the pre-existing fabrics trend at moderate obliquity (15°-45°), they are still reactivated and localize deformation causing the development of atypical fault trends and patterns. The degree of reactivation tends to gradually decrease with increasing obliquity; similarly, the influence of pre-existing structures decreases with progressive extension, and the fault pattern and evolution are progressively dominated by extension kinematics and crustal thinning. When the pre-existing fabrics trend at high obliquity (≥ 60°), they have almost no influence on the fault geometry and architecture.

This study has significant implications for explaining the fault geometry and evolution of some natural rift basins worldwide, such as basins of the East African Rift system, the North Sea Rift, and some offshore rift basins in eastern China.

How to cite: Zou, Y., Maestrelli, D., Corti, G., Del Ventisette, C., Wang, L., Wan, X., Gao, Y., and Shen, C.: Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19947, https://doi.org/10.5194/egusphere-egu24-19947, 2024.

EGU24-20162 | ECS | Posters on site | TS2.1 | Highlight

 The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages 

Yafet Gebrewold Birhane, Raphael Pik, Nicolas Bellahsen, Irene Schimmelpfennig, Lydéric France, Jessica Flahaut, Dereje Ayalew, and Gezahegn Yirgu

The Afar depression at the northern end of the East African Rift system is presently experiencing the final stage of continental break-up and progressive onset of steady magmatic spreading. The Magmatic Rift Segments in Afar broadly analogous to those observed within the mid oceanic ridges, offer the opportunity to study both mantle and crustal processes. Investigating the crustal architecture of those magmatic segments represents a key aspect to decipher fundamental parameters that control focussing of magmatic and tectonic activity during the generation of magmatic crust. Here, we present the typical organization of a 32 km long subsegment of the Manda Hararo magmatic rift system, with fissural activities symmetrical to an apparent mid segment magmatic reservoir and establish geochronology of the last eruptive history. We combine field investigations, precise mapping of volcanological and tectonic features, cosmogenic 36Cl exposure dating and geochemical analysis of lavas to constrain the temporal frame and the dynamics of magmatic processes. Our results show that the recent historical volcanic events (~ 500 to 2000 years) are sourced from calderas and fissures representing an alternating sequence of effusive and explosive (block fields) activities related to a coherent rifting episode along a single self-consistent magmatic sub-segment. Those recent fissural flows resurfaced a large portion of the segment and emplaced on older thick pahoehoe flows with a rather long lag-time of about 75 kyr separating the two episodes. Strongly contrasted geochemical signatures are also observed between those two volcanic episodes, with more differentiated and trace elements enriched basalts for the recent one, compared to the older one which are characterized by a unusual depleted signature. These new results for the Central Afar Manda Hararo rift have important implications for: (i) the local hazards along the segments, and (ii) the volcano-tectonic organization of the segment with coexistence of contrasted melt reservoirs on the underlying transcrustal plumbing system.

How to cite: Birhane, Y. G., Pik, R., Bellahsen, N., Schimmelpfennig, I., France, L., Flahaut, J., Ayalew, D., and Yirgu, G.:  The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20162, https://doi.org/10.5194/egusphere-egu24-20162, 2024.

EGU24-20218 | ECS | Posters on site | TS2.1

Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data. 

Louis Gaudaré, Cécile Doubre, Marc Jolivet, Olivier Dauteuil, Samuel Corgne, Raphaël Grandin, Marie-Pierre Doin, and Philippe Durand

Located at the southwestern terminus of the East African Rift System, the Okavango Rift System represents an opportunity to study the propagation of an active rift at its early stages (Gaudaré et al., in review). The Okavango Graben (northern Botswana) is an active half-graben of the Okavango Rift System, which shows normal to dextral strike-slip tectonic displacements of the order of 1 mm per year (Pastier et al., 2017). In addition to the impact of tectonics, large volumes of water (~10 km3 per year) brought in by the annual flood of the Okavango River generate seasonal subsidence of over 2 cm in the graben (Dauteuil et al., 2023). The prevalence of the hydrologic signal over the tectonic signal makes it challenging to provide clear interpretations of the Rift dynamics within the Okavango Graben. The previous studies are based on a network of GNSS stations, providing punctual data on displacements. To quantify the deformation field over the Okavango Graben, we analyze interferometric synthetic aperture radar (InSAR) data produced by the ForM@Ter LArge-scale multi-Temporal Sentinel-1 InterferoMetry service (FLATSIM, Thollard et al., 2021). FLATSIM automatically computes interferograms from Sentinel-1 synthetic aperture radar data and inverts them into displacement time series. The products span from April 2016 to April 2021 with a temporal resolution of 12 days, a spatial resolution of 115 x 115 m and cover the entire Okavango Rift System. We analyze and compare the seasonality of both the interferometric coherences and the InSAR displacement time series. Change detection in the interferometric coherence allows us to delineate flooded surfaces through time in the Okavango Graben, from which we deduce water loadings on the lithosphere and model the corresponding flexural response of the lithosphere. We then compare this response to the spatial distribution of annual vertical oscillations extracted from the displacement time series. Taking these seasonal signals into account, our objective is to estimate the rates of the tectonic subsidence in the Okavango Graben to better constrain the propagation of the East African Rift System at its southwestern end.

Dauteuil, O., Jolivet, M., Gaudaré, L., & Pastier, A.-M. (2023). Rainfall-induced ground deformation in southern Africa. Terra Nova, 00, 1–7. https://doi.org/10.1111/ter.12650

Gaudaré, L., Dauteuil, O., & Jolivet, M. Geomorphology of the Makgadikgadi Basin (Botswana): insight into the propagation of the East African Rift System. Tectonics, in review.

Pastier, A.-M., Dauteuil, O., Murray-Hudson, M., Moreau, F., Walpersdorf, A., & Makati, K. (2017). Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review. Tectonophysics 712–713, 469–481. https://doi.org/10.1016/j.tecto.2017.05.035

Thollard, F., Clesse, D., Doin, M.-P., Donadieu, J., Durand, P., Grandin, R., Lasserre, C., Laurent, C., Deschamps-Ostanciaux, E., Pathier, E., Pointal, E., Proy, C., & Specht, B. (2021). FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service. Remote Sensing, 13(18), 3734. https://doi.org/10.3390/rs13183734

How to cite: Gaudaré, L., Doubre, C., Jolivet, M., Dauteuil, O., Corgne, S., Grandin, R., Doin, M.-P., and Durand, P.: Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20218, https://doi.org/10.5194/egusphere-egu24-20218, 2024.

EGU24-20223 | Posters on site | TS2.1

Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling. 

Thomas Theunissen, Ritske S. Huismans, Delphine Rouby, Sebastian Wolf, and Dave A. May

The magma-poor passive rifted conjugate margins in the Southern Equatorial Atlantic, North Atlantic/Arctic oceans, and Northern Mozambique Channel display en-echelon extensional segments separated by long transform faults (>300 km), influenced by inherited weaknesses. Using advanced 3-D forward geodynamic modeling coupled with surface processes, we investigate the formation of oblique rifts and passive margins. Our focus is on pre-existing weaknesses parallel to the extension direction, exploring the system's sensitivity to various erodibility factors. Key findings include: (1) erodibility within a low to moderate range has limited influence on the morpho-structural evolution of the oblique continental rift, (2) pure-strike slip faults reactivating transform weaknesses result in reduced topography, (3) major catchments sink in the inner corner at the tip of each extensional segments, and (4) hinterland drainage network capture along extensional segments is absent, controlled by isostatic rebound during rift flank drainage divide migration. This study enhances our understanding of the complex interplay between inherited weaknesses, erodibility, and the evolving morphology of oblique rifted margins.

How to cite: Theunissen, T., Huismans, R. S., Rouby, D., Wolf, S., and May, D. A.: Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20223, https://doi.org/10.5194/egusphere-egu24-20223, 2024.

EGU24-20850 | Posters on site | TS2.1

The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search 

Martina Busetti, Alberto Pastorutti, Magdala Tesauro, Carla Braitenberg, Florence Colleoni, and Laura De Santis

The basins composing the 1000-km wide West Antarctica Rift System (WARS), derived from extensional dynamics lasting from the Cretaceous to the Middle Neogene, bear evidence of a peculiar evolution through time: a transition from a diffuse to a localized thinning style and a migration of the focus of deformation, which likely progressed towards the cratonic domains of West Antarctica. Using the current observations, we aim at identifying which inherited starting conditions [1] result in outcomes compatible with the present-time structures and which do not allow so, unless other factors are accounted for.

To this aim, we turn to an extensive grid search in the parameter space, running a large number of forward numerical models to cover the possible permutations of parameters under test. We use the open source Underworld2 code [2] with a simplified scheme of starting conditions and kinematics boundaries, for lithospheric-scale 2-D thermomechanical models. We analyse the results obtained by changing a great number of parameters, including initial geometries of the crust and lithosphere, different rheologies, inherited structures, such as strain-weakening scars and thermal remnants of slabs.

We identify that a high crustal thickness (more than 45 km) is required to accommodate the first rifting phase (170 km ca. of cumulated extension, [3]) without producing crustal necking and eventual ocean formation. Parameters that favour a weaker strength profile, chiefly temperature (due to a thicker crust and/or a shallow lithosphere-asthenosphere boundary), are also required to avoid an early transition to localized deformation, in agreement with previous studies [4]. Smaller scale features, such as partition in multiple sub-basins, require additional factors, such as inherited weak-zone seeds (“scars”) in the crust and mantle, which are likely remnants of previous compressive phases [5].

[1] Perron, P., Le Pourhiet, L., Guiraud, M., Vennin, E., Moretti, I., Portier, É., & Konaté, M. (2021). Control of inherited accreted lithospheric heterogeneity on the architecture and the low, long-term subsidence rate of intracratonic basins. BSGF - Earth Sciences Bulletin, 192. https://doi.org/10.1051/bsgf/2020038

[2] Mansour, J., Giordani, J., Moresi, L., Beucher, R., Kaluza, O., Velic, M., Farrington, R., Quenette, S., & Beall, A. (2020). Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud. Journal of Open Source Software, 5(47), 1797. https://doi.org/10.21105/joss.01797

[3] Brancolini, G., Busetti, M., Coren, F., De Cillia, C., Marchetti, M., De Santis, L., Zanolla, C., Cooper, A.K., Cochrane, G.R., Zayatz, I., Belyaev, V., Knyazev, M., Vinnikovskaya, O., Davey, F.J., Hinz, K., 1995. ANTOSTRAT Project, seismic stratigraphic atlas of the Ross Sea, Antarctica. In: Cooper, A.K., Barker, P.F., Brancolini, G., (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin. Antarctic Research Series, vol. 68, https://doi.org/10.1029/AR068

[4] Huerta, A. D., & Harry, D. L. (2007). The transition from diffuse to focused extension: Modeled evolution of the West Antarctic Rift system. Earth and Planetary Science Letters, 255(1–2), 133–147. https://doi.org/10.1016/j.epsl.2006.12.011

[5] Talarico, F., Ghezzo, C., & Kleinschmidt, G. (2022). The Antarctic Continent in Gondwana: a perspective from the Ross Embayment and Potential Research Targets for Future Investigations. In Antarctic Climate Evolution (pp. 219–296). Elsevier. https://doi.org/10.1016/B978-0-12-819109-5.00004-9

How to cite: Busetti, M., Pastorutti, A., Tesauro, M., Braitenberg, C., Colleoni, F., and De Santis, L.: The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20850, https://doi.org/10.5194/egusphere-egu24-20850, 2024.

EGU24-1801 | Posters on site | TS3.1

Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling 

Eleftheria Papadimitriou and Vassilios Karakostas

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, exhibits the fastest rates of relative plate motion in the Mediterranean. It constitutes an active boundary and comprises five manor fault segments with a total length of nearly 120km, and are characterized by fast long–term rates of displacements of about ~25mm/yr for Kefalonia segments and ~15 mm/yr for Lefkada segments. Strike slip faulting with moment magnitudes Mw up to 7.0 characterizes the largest earthquakes, whereas the five almost along strike faults have been the sites of numerous earthquakes of moment magnitude, Mw, 5.0–7.0 during the past 50 years. The KTFZ in its entire length is much more active at the Mw>6.0 level than a comparable length of either the North Aegean Trough or Corinth rift, which are the most fastly deforming areas in the area of Greece. Alteration of active periods comprising multiple earthquakes with much longer quiescent periods is the mode of strong earthquake occurrence, with prevailing clustering over the period when historical information is available. The fast rate of plate motion, maximum size of earthquakes and relatively short repeat times make these fault segments suitable to seek for recurrence behavior that approaches quasi–periodic and its potential implications to the cyclic mode of seismogenesis. Recurrence of M6.0 earthquakes along nearly the same fault segment is attempted after evaluating the location of the historical events, based on all available macroseismic descriptions. These estimations are then compared with computed simulated catalogs.

The computed depths of earthquakes along the KTFZ are accurate enough to ascertain centroid depths as indicators of the downdip width of seismic faulting. With aftershock relocation we constrained the seismogenic layer in Kefalonia and Lefkada segments equal to 14 km (between depths of 3 and 17 km) and 10 km (between depths of 5 and 15 km) respectively, corresponding to downdip widths of 19 and 12 km, respectively. We compared these constraints with the calculated downdip width from a segment’s length along strike, moment release and relative plate motion ‘assuming’ full seismic coupling. The good correlation between the two support the high degree of coupling along the KTFZ.

Acknowledgments: Funded by the European Union. Views and opions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

 

 

How to cite: Papadimitriou, E. and Karakostas, V.: Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1801, https://doi.org/10.5194/egusphere-egu24-1801, 2024.

EGU24-2188 | ECS | Posters on site | TS3.1

Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model 

Weilun Qin, Rob Govers, Mario D’Acquisto, Natasha Barlow, and Riccardo Riva

Subduction earthquake cycles are known to produce distinctive patterns of crustal motion, providing critical insights into the details of plate interface coupling and rupture behavior. Retrieving these patterns in the Cascadia subduction zone poses a significant challenge, particularly because the 1700 great Cascadia earthquake (Mw>=9.0) occurred more than three centuries ago.

Previous studies of the megathrust earthquake cycle along the Cascadia margin focused on either the geologically constrained coseismic rupture, or on the present-day interseismic coupling patterns based on geodetic observations. There thus is a gap in the comprehensive understanding of the earthquake cycle, particularly in the integration of available geological and geodetic evidence.

Our study aims to bridge this gap and unify the insights preserved in both records. To do so, we develop a three-dimensional viscoelastic earthquake cycle model with realistic slab geometry, crustal thickness, and topography. We simulate the coseismic, postseismic, and interseismic stages of the earthquake cycle by alternately locking and releasing asperities, which are derived from geodetic coupling (Li et al., 2018) and geological rupture (Wang et al., 2013) studies.

Our results show a good match to convergence-parallel interseismic velocities from the geodetic observations of McKenzie and Furlong (2021). Considering the subsidence signal in the geological record, a good fit can be obtained by a combination of coseismic slip and early afterslip. We find that our results are largely determined by the slab geometry, although factors like asperity configurations, downdip limits of the slab-crust interface, and mantle viscosity structure influence the model predictions.

How to cite: Qin, W., Govers, R., D’Acquisto, M., Barlow, N., and Riva, R.: Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2188, https://doi.org/10.5194/egusphere-egu24-2188, 2024.

The 2021 Maduo MS7.4 earthquake occurred in the Jiangcuo fault with left-lateral strike-slip movement. In order to study the movement and deformation characteristics of the Jiangcuo fault before the Maduo earthquake and further analyze the seismogenesis process of the continental strong earthquake, the large-scale strain rate field distribution in western China, the locking degree and the evolution of slip deficit rate of the Jiangcuo fault, and the rupture mechanism of seismogenic fault are analyzed and discussed in this paper using the GPS velocity field on a long time scale and InSAR dynamic velocity field. The results show that: (1) The strain rate field in EW direction shows that the Maduo earthquake is located at the edge of the EW direction strong compression zone of Bayanhar block. The eastern part of the Maduo earthquake is a compression strain accumulation zone, and the western part is a gradual transition from weak compression to tension strain. The results of the maximum shear strain rate field show that the Maduo earthquake is located at the edge and high gradient zone of the high value area of the maximum shear strain rate field. (2) The inversion results of the locking degree show that deep unlocking occurs in some regions in the east and west of the epicenter of the fault during 2015-2021, gradually transitioned to a completely locked state in the middle of the fault, and the focal point of Maduo earthquake is at the edge of the completely locked region in the transition region. The dynamic results from 2015 to 2017 and 2017 to 2019 were basically stable. The whole fracture plane was basically in a state of strong locking, and only partial unlocking with a depth below 15km existed in local areas. From 2019 to 2021, some faults in the east and west of the epicenter have deep and shallow unlocking phenomena, including the overall unlocking of most areas of the western section and the local deep unlocking of the East section of the ruptured fault, while the rapid unlocking of the two sides of the epicenter may contribute to the occurrence of the main earthquake. This work was supported by Science for earthquake resilience (XH23047A).

How to cite: Zhao, J., Yuan, Z., and Wang, Y.: The movement and deformation of the Jiangcuo fault before the 2021 MS7.4 Maduo earthquake reflected by GPS and InSAR data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2226, https://doi.org/10.5194/egusphere-egu24-2226, 2024.

EGU24-2385 | ECS | Posters on site | TS3.1

Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data. 

Chris Milliner, Jean-Philippe Avouac, Saif Aati, James Dolan, and James Hollingsworth

As faults accumulate displacement, they are thought to mature from disorganized and distributed fracture networks to more simplified throughgoing fault structures with a more localized zone of inelastic strain. Understanding the degree of inelastic strain localization holds importance for seismic hazard, as smoother faults are thought to host faster rupture velocities and have different seismic shaking intensities from ruptures along rougher, less mature faults. However, quantifying this evolutionary process of strain localization along major fault systems has been difficult due to a lack of near-field coseismic measurements. Here we test if such an evolutionary process exists by measuring the near-field surface deformation pattern of 17 large (6.0 < Mw < 7.9) continental strike-slip surface ruptures. To do this we use a range of geodetic imaging techniques including, a new 3D optical pixel tracking method, and pixel tracking of radar amplitude data acquired by satellite and UAVSAR platforms. With these geodetic imaging data we measure the total coseismic offset across the surface rupture and difference them from the displacements recorded by field surveys, which we assume captures the on-fault, discrete component of deformation. This differencing allows us to obtain an average magnitude of off-fault deformation for each surface rupturing event, which we compare to a number of known source parameters to test the notion of progressive fault localization. Our results show that progressively smaller amounts of off-fault strain occur along fault systems with higher cumulative displacements, supporting the notion that faults systems localize as they mature. We also find strong correlations of off-fault deformation with the long-term fault slip-rate and the geometrical complexity of the mapped surface rupture, and a moderate correlation with rupture velocity. However, we find a weak-no correlation of off-fault deformation with the fault initiation age and the moment-scaled radiated energy. We also present comparisons of off-fault strain with other known seismic source parameters.

How to cite: Milliner, C., Avouac, J.-P., Aati, S., Dolan, J., and Hollingsworth, J.: Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2385, https://doi.org/10.5194/egusphere-egu24-2385, 2024.

EGU24-2389 | ECS | Orals | TS3.1

Decoding inter-seismic deformation: Insights from viscoelastic modeling 

Hugo Boulze, Luce Fleitout, Emilie Klein, and Christophe Vigny

GPS positioning offers millimetric precision in measuring deformation of the lithosphere during the seismic cycle. In particular, during the post-seismic phase, long-lasting and large-scale deformation are measured. They result from the viscoelastic relaxation in the asthenosphere. Consequently, the post-seismic phase is currently modeled using viscoelastic rheologies (e.g., Maxwell or Burgers viscous models). On the other hand, the inter-seismic phase is mainly modeled using purely elastic models. In particular, coupling models, widely used to quantify the accumulation of deformation on the subduction fault, are therefore used to evaluate earthquake hazard. However, such elastic models fail to explain mid-field deformation without the use of an external hypothesis (e.g., a third plate called sliver).

The study of post-seismic deformation has provided important insights into the rheological properties of the asthenosphere during the post-seismic phase. For example, viscous creep has been found Newtonian since the cumulative post-seismic displacements normalized by the co-seismic offset, as a function of distance to the trench, superimpose very well for earthquakes of different magnitudes [Boulze et al. 2022].

By incorporating these different results and using the backslip theory [Savage 1983], we model the inter-seismic phase using viscoelastic models. We explore the impact on coupling distribution along the Chilean subduction zone, in particular discussing differences with the elastic model in terms of depth and lateral extension. We also examine the impact of viscoelastic models in a region of Chile (Taltal region, 25.2°S) where elastic models currently fail to reproduce deformation in the near-field [Klein et al. 2018]. Finally, we show that a 2-Burgers viscous model is necessary to reproduce deformation in Argentina in 2010, before the Maule earthquake.

How to cite: Boulze, H., Fleitout, L., Klein, E., and Vigny, C.: Decoding inter-seismic deformation: Insights from viscoelastic modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2389, https://doi.org/10.5194/egusphere-egu24-2389, 2024.

We have developed a 3D viscoelastic finite element model to study processes that control the postseismic deformation due to the 2021 M8.2 Chignik, Alaska earthquake. Our model employs a bi-viscous Burgers rheology to represent the viscoelastic relaxation of the upper mantle and the first two years GPS data after Chignik event as constraints.

Initially, we investigated the viscoelastic relaxation mechanism and stress-driven afterslip mechanisms individually. We then attempted to reconcile their contributions by assessing the misfit between observed and simulated displacements. And, it is assumed that the afterslip evolution is governed by rate-strengthening friction. The results show that there exists a substantial misfit between the simulated and the observed value of the optimal model under the viscoelastic relaxation mechanism. Notably, at one observation site in the near-field, the observed displacement exceeds 200 mm, whereas the simulated value only less than 5 mm. Similarly, the optimal solution of simulated value under the afterslip mechanism does not align well with the observed value. Furthermore, we also utilized different frictional properties on updip (0-40 km) and downdip (40-100 km) regions of the coseismic rupture. The preferred misfit in this model is lower than that obtained using the model with a uniform friction parameter, but there is still a discrepancy between the simulated and observed values. These results indicate that neither the afterslip nor viscoelastic relaxation mechanisms alone can fully explain the total postseismic deformation.

Subsequently, we utilized an integrated model to simultaneously extract the contributions from both mechanisms. The combined modeling results indicate that the near-field postseismic displacements are dominated by both mechanisms together. However, in the far-field, deformation is primarily controlled by afterslip, with minimal influence from the viscoelastic relaxation mechanism. The inferred frictional properties on the updip and downdip regions of the coseismic rupture exhibit significant differences, which likely reflect variations in fault zone materials at different depths. And the optimal model supports a viscoelastic rheology for the continent mantle, with a steady-state viscosity is 1×1019Pa•s and the transient viscosity is 1×1018Pa•s. 

How to cite: Dong, P. and Zhao, B.: Afterslip and viscous relaxation on the postseismic deformation following the M8.2 Chignik, Alaska earthquake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2967, https://doi.org/10.5194/egusphere-egu24-2967, 2024.

EGU24-6640 | ECS | Orals | TS3.1

Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake 

Wenqian Yao, Jing Liu_Zeng, Yann Klinger, Guiming Hu, Yanxiu Shao, Xiaoli Liu, Kexin Qin, Zhijun Liu, Zijun Wang, Yunpeng Gao, and Longfei Han

Faults grow through fault lengthening and slip accumulation, which are episodic processes related to the repetition of earthquakes. It is most often recorded in geomorphology. Meanwhile, the activity and seismic hazard of the ‘slow-moving’ faults are often overlooked due to their weak imprints in landforms, especially at their initial formation stage. The 2021 Mw 7.4 Maduo earthquake triggered a ~158-km long surface rupture along the poorly-known and geomorphically subtle Jiangcuo fault, which is one of the distributed faults in the Bayan Har block and splays that merge with the Kunlun Pass fault. The slip rate of the Jiangcuo fault is thus crucial for comprehending how the strain is distributed between the major and subsidy faults in the complete fault system of the Bayan Har block, as well as the broader deformation process at a large scale. In this study, we present three sites where the Jiangcuo fault left-laterally displaces Holocene geomorphic features (e.g., terraces, fans, and channels). Through the detailed interpretations of high-resolution Digital Elevation Models (DEMs), field investigations, and credible Optically Stimulated Luminescence (OSL) dating of displaced geomorphic features, we document an average left-lateral slip rate of 2.1 ± 0.2 mm/yr since ~12 ka of the Jiangcuo fault. Furthermore, we conservatively updated existing slip rates of the large strike-slip faults (East Kunlun fault, Ganzi-Yushu-Xianshuihe fault) bounding the Bayan Har block. Synthesizing the slip rate of the Jiangcuo fault with the updated rates of the bounding faults, our findings suggest that the Jiangcuo fault accommodates ∼10% of the total deformation in the Bayan Har block. This study provides valuable insights into the impact of younger faults on regional deformation processes.

How to cite: Yao, W., Liu_Zeng, J., Klinger, Y., Hu, G., Shao, Y., Liu, X., Qin, K., Liu, Z., Wang, Z., Gao, Y., and Han, L.: Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6640, https://doi.org/10.5194/egusphere-egu24-6640, 2024.

Strike-slip faults of considerable scale play a pivotal role in accommodating crustal deformation resulting from the Cenozoic India-Eurasia collision. The manner in which strike-slip motion is transferred along faults remains a topic of ongoing debate. In this study, we have meticulously compiled millennial strike-slip rates and GPS-derived strike-slip data along the extensive ~1800 km East Kunlun Fault (EKF). Our objective is to discern the slip distribution pattern and evaluate the mode of strike-slip transfer. The findings reveal a segmented pattern of strike-slip activity, characterized by a consistently high strike-slip rate exceeding 10 mm/yr along the central segments. In contrast, the eastern segment exhibits a reduced slip rate, measuring less than 5 mm/yr, and further diminishes to approximately 1 mm/yr along its eastern fault tip zone. Notably, strike-slip drop events occur within the fault bending zone, or in areas where the fault bifurcates, forming a horsetail structure. To complement our observational insights, numerical modeling has been employed to validate that the fault geometry may serve as a crucial controlling factor in the observed variation of strike-slip rates, Additionally, it influences the local stress situation along the fault, further contributing to the earthquake risk along the fault and the associated hazards impacting the local area.

How to cite: Zhang, Y. and Jiao, L.: Mechanism of Strike-slip Transfer along the East Kunlun Fault in Northern Tibet, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7062, https://doi.org/10.5194/egusphere-egu24-7062, 2024.

EGU24-7436 | ECS | Orals | TS3.1

Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data  

Yingfeng Zhang, Sam Wimpenny, Luca Dal Zilio, and Xinjian Shan

Strain partitioning between strike-slip faults within mountain ranges and thrust faults along their margins is a common process that accommodates oblique plate convergence in continental collision zones. In these settings accumulated strain is periodically released by earthquakes on the strain-partitioned fault systems, which threatens the densely populated foreland areas. An extreme earthquake rupture scenario in these settings is that multiple faults rupture simultaneously releasing the built up strain – an example being the 2016 Mw 7.8 Kaikoura earthquake where a cascading rupture occurred on many separate faults with different kinematics. Recent work suggests that such cascading ruptures may occur in fault systems that are coupled in the shallow crust that are being loaded by a deeper, creeping fault.

 

This study focuses on understanding earthquake risks in the northern Qilian strain-partitioned fault system, which is important due to the populated areas nearby. We investigate its 2-D kinematic models using available geodetic measurements under a Bayesian inversion frame. Our results prove that the kinematic models of the northern Qilian strain-partitioned fault system can be well determined, and compatible of the geological measurement and seismicity distribution. In contrast to the frequent thrust earthquakes, any thrust faults are not required to explain the available geodetic data indicating that the short-term geodetic measurements cannot reflect the thrust fault kinematics of the northern Qilian Shan in the geological time-scale. The non-thrust fault involved model also present a highly locked wedge beneath the foreland area, reconciling the supposed historical cascading earthquake ruptures in north Qilian Shan.

How to cite: Zhang, Y., Wimpenny, S., Dal Zilio, L., and Shan, X.: Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7436, https://doi.org/10.5194/egusphere-egu24-7436, 2024.

Geometric complexity plays an important role for a fault’s seismotectonic behavior as it affects the initiation, propagation and termination of an earthquake and influences stress-slip relationships, fault-segment size, and the probability of multi-segment rupture. Consequently, geometric fault complexity is studied intensively and increasingly incorporated into computational earthquake rupture simulations. These efforts reveal a problem: While a natural fault’s geometry may be well quantifiable at the surface (i.e., the fault trace), its down-dip buried portion cannot be well constrained. At this point, it is not clear how this epistemic uncertainty affects the propagation of individual ruptures and a fault’s seismotectonic behavior (e.g., large-earthquake recurrence).

We address this issue computationally with a physics-based multi-cycle earthquake rupture simulator (MCQsim), enabling us to investigate various aspects of rupture propagation and earthquake cycle in a controlled environment (e.g., with well constrained fault geometry). We approximate fault geometric complexity as a 2-D random field using the “random midpoint displacement” method which allows us to represent fault roughness (i.e., incorporate its epistemic uncertainty) while keeping the fault surface trace unchanged. 

Using MCQsim, we create 20kyr-long synthetic earthquake catalogs for strike-slip faults that share the same complex fault surface trace but have different sub-surface fault geometries. We analyze the resulting variations in single-event rupture propagation (i.e., the kinematic source model) and long-term seismotectonic behavior. We find that kinematic source models of individual events differ substantially between different realizations of sub-surface geometry. However, the long-term seismotectonic behavior (e.g., large-earthquake recurrence) does not differ as much and is less sensitive to the epistemic uncertainties of sub-surface fault geometry.

How to cite: Zielke, O. and Mai, P. M.: Exploring the effects of sub-surface fault geometry on rupture propagation and long-term fault behavior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7556, https://doi.org/10.5194/egusphere-egu24-7556, 2024.

EGU24-7990 | ECS | Orals | TS3.1

Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data 

Guoguang Wei, Kejie Chen, and Luca Dal Zilio

The geometry of faults regulates the spatial patterns of interseismic, coseismic, and post-seismic surface deformation. Geodetic techniques can measure these deformation patterns during a seismic cycle and are expected to constrain the geometry of  seismogenic faults. However, the conventional linear inversion of geodetic data is unable to simultaneously estimate the fault slip distribution and the fault geometry. In this study, we propose a Bayesian framework that treats fault geometry as a time-invariant parameter. It can individually use coseismic deformation data or simultaneously utilize interseismic, coseismic, and post-seismic deformation data to invert for both fault slip distribution and non-planar fault geometry. Within this framework, geometry evidence informed by geophysical imaging, geological surveys, and microseismicity forms the basis for establishing the prior probability density function, while geodetic observations constitute the likelihood function. Our methodology provides an ensemble of plausible geometry parameters by sampling the posterior probability distributions of the parameters using Markov Chain Monte Carlo simulation. The performance of the developed method is tested and demonstrated through inversions for synthetic oblique-slip faulting models. Results demonstrate that assuming constant rake can significantly bias fault geometry estimates and data weighting. Additionally, considering the variability of slip orientations allows for plausible estimates of non-planar fault geometry with objective data weighting.We applied the method to the 2013 Mw 6.5 Lushan earthquake in Sichuan province, China. The results reveal dominant thrust slips with left-lateral components and a curved fault geometry, with the confidence interval of the dip angles ranging between 20° and 25° and 56° and 58°. Furthermore, the application of this method to the 2015 Gorkha earthquake in Nepal sheds light on the Main Himalayan Thrust, which serves as the interface between the Indian Plate and Eurasia. This may provide new insights into future seismic potential and topographic growth in the Nepal Himalaya.

How to cite: Wei, G., Chen, K., and Dal Zilio, L.: Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7990, https://doi.org/10.5194/egusphere-egu24-7990, 2024.

EGU24-8280 | ECS | Orals | TS3.1

Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis 

Jin Fang, Tim Wright, Kaj Johnson, Qi Ou, Richard Styron, Tim Craig, John Elliott, and Andy Hooper

Earthquakes release strain energy that has accumulated between seismic events. Measuring strain accumulation rates is critical for understanding earthquake cycle and assessing earthquake potential, with fault slip rates serving as essential inputs for seismic hazard models. However, the Tibetan Plateau has been lacking comprehensive estimates of geologic slip rates on numerous faults. To address this gap, geodetic data have been invoked to derive fault slip (or slip deficit) rates using various methodologies. These include the commonly adopted classic and deformable block modelling approaches (Meade & Loveless, 2009) and the newly developed direct inversion of geodetic strain rates (Johnson et al., 2022), which has the advantage of not requiring blocks to be defined.  A comprehensive comparison of slip rates obtained from these different geodetic methods has been notably absent.

In this study, we focus on the southeastern Tibetan Plateau, utilising Sentinel-1 satellite data from 35 ascending and 32 descending frames spanning the period between 2014 and 2023, along with published GNSS velocities. We constructed high-resolution (1 km) maps of velocity and strain rate fields covering 1.3 million km2. Using these maps, we derived slip rates on newly mapped faults (Styron, 2022) using classic block modelling, “deformable block” modelling, and by the direct inversion of strain rates. Our strain rate fields reveal a partition through focused shear on the Kunlun fault, the Xianshuihe-Xiaojiang fault system, the Longriba fault, the Longmenshan fault possibly influenced by the ongoing postseismic deformation of the 2008 Mw 7.9 Wenchuan earthquake, and the Lijiang-Xiaojinhe fault. On the deforming plateau there is diffuse deformation away from the major faults, with average shear strain and dilatation rates of 14.3 and 13.1 nanostrain/year, compared to 9.4 and 11.1 nanostrain/year in the Sichuan basin (which likely reflects the noise floor in the data). The geodetically-determined slip rates from the three methods generally align with available geologic rates, particularly along-strike variations on the Kunlun fault and the Xianshuihe-Xiaojiang fault system. Our block model consists of 103 blocks bounded by 326 fault sections in the southeastern Tibetan Plateau. The model is constrained by the combined geodetic horizontal velocities from 6617 observation points. Classic block modelling without considering internal strain tends to overestimate slip rates on faults that slip faster than 5 mm/yr, compared to deformable block model that accounts for homogeneous intrablock strain, constituting 5% of the total. The two block models explain approximately 45-50% of the geodetic strain, predicting focused strain on block boundaries even in the absence of observed strain concentrations. By directly inverting strain rates, we suggest that 40-50% of the geodetic strain is attributable to elastic coupling (back slip) on faults, while the remaining can be explained by off-fault distributed moment sources (body forces) in a thin elastic plate. We discuss limitations of different geodetic approaches in modelling deformation (velocities or strain rates) and implications for seismic hazard by comparing the seismic moment release rate from earthquakes and the geodetic moment accumulation rate from our geodetic models.

How to cite: Fang, J., Wright, T., Johnson, K., Ou, Q., Styron, R., Craig, T., Elliott, J., and Hooper, A.: Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8280, https://doi.org/10.5194/egusphere-egu24-8280, 2024.

EGU24-9097 | ECS | Posters on site | TS3.1

Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey 

Nicolas Harrichhausen, Julia de Sigoyer, Yann Klinger, Cengiz Yildirim, Melike Karakaş, and Baptiste Camus

We present preliminary results from a paleoseismic study of the middle branch of the Northern Anatolian Fault (MNAF) in Turkey. Despite low instrumental seismicity and geodetic slip rates (~2.5 mm/yr) relative to the northern branch, historical, archeological, and paleoseismic studies indicate the MNAF has hosted several damaging earthquakes in the last two millennia. Recent geomorphic and bathymetric analyses reveal segmentation of the MNAF that may indicate strain partitioning of normal and strike slip along parallel fault strands. However, it remains uncertain whether these fault segments have ruptured simultaneously. Geologic studies have constrained right-lateral slip rates to between 2 and 5.3 mm/yr, with most results contrasting against the present-day geodetic slip rate of ~2.5 mm/yr. Whether this represents a reduction in strain rate along this branch of the Northern Anatolian fault is not clear. Our study has two main objectives: first, to delineate the earthquake history along the newly identified segment of the MNAF beneath Lake Iznik and map its onshore extensions to the east and west of the lake; second, to determine the right-lateral slip rate of the MNAF across different temporal scales. We will present preliminary results from geomorphic mapping, electromagnetic conductivity and ground penetrating radar surveys, and paleoseismic trenching aimed at achieving these objectives. By further establishing the earthquake history and length of the new branch beneath Lake Iznik, we aim to ascertain whether this segment has ruptured concurrently with parallel and along-strike segments, allowing us to estimate paleo-earthquake magnitudes and maximum rupture lengths. Concurrently, by constraining the slip rate of the MNAF over time, we seek to understand whether slip along this branch has decreased and if this reduction is linked to a subsequent increase in slip rate on either the northern or southern branch of the Northern Anatolian Fault.

How to cite: Harrichhausen, N., de Sigoyer, J., Klinger, Y., Yildirim, C., Karakaş, M., and Camus, B.: Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9097, https://doi.org/10.5194/egusphere-egu24-9097, 2024.

EGU24-9399 | ECS | Posters on site | TS3.1

A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures 

Tristan Montagnon, Sophie Giffard-Roisin, James Hollingsworth, Erwan Pathier, Mauro Dalla Mura, and Mathilde Marchandon

Precise estimation of ground displacement from correlation of optical satellite images is fundamental for the study of natural disasters. In the case of earthquakes, characterizing near-field displacements around surface ruptures provides valuable constraints on the physics of earthquake slip. Recently, image correlation has been used to investigate the degree of slip localization, and how it may vary as a function of geological parameters (such as fault structural maturity), raising the possibility that slip localization (vs distribution) may be predictable, with important implications for seismic hazard assessment.

Current sub-pixel correlation methods (frequency or spatial domain) all rely on the same general approach: they work at a local scale, with small sliding windows extracted from a pair of co-registered satellite images acquired at different times, and they assume a rigid uniform shift between the two correlation windows. However, in the near-field of fault ruptures, where the correlation window spans the fault discontinuity, this hypothesis breaks down, and may bias the displacements. Additional smoothing associated with the correlation window further complicates the interpretation of sharp features in the displacement field, artificially shifting displacement to the off-fault region.

We developed a U-net-based method to solve the sub-pixel displacement estimation problem at a global scale. Such architecture is able to retrieve full scale surface displacement maps, making use of both global and local features, and potentially tackling different noises of the input images. We trained our model with real satellite acquisitions, warped with ultra-realistic synthetic displacement maps representing realistic faults. The model exhibits promising preliminary results, showcasing its capability to retrieve full-scale surface displacement maps with high accuracy. While direct comparisons with other state-of-the-art approaches (COSI-Corr and MicMac) are pending, our findings suggest that our proposed U-net-based approach has the potential to compete or even outperform these correlators. 

How to cite: Montagnon, T., Giffard-Roisin, S., Hollingsworth, J., Pathier, E., Dalla Mura, M., and Marchandon, M.: A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9399, https://doi.org/10.5194/egusphere-egu24-9399, 2024.

Geometrical irregularities of faults drive stress heterogeneities that strongly affect the seismic rupture. Here we analyze the effect of fault topography and remote stresses during the interseismic phase on the static stress pattern around faults and on the onset of failure. The analytical solution is derived using perturbation theory for a defined interface topography. We apply our solution for the static stress field near the East Anatolian Fault and we show that a large stress barrier is developed around the segment that ruptured during the Mw 7.8 Kahramanmaraş Earthquake. Considering stress field conditions that are associated with left-lateral strike slip on the fault, we show how the barrier location is affected by the fault geometry, while the amplitude of stress variations are sensitive to the background stress values and their directions. The solution predicts that the value of the accumulated elastic energy in the host rock around the fault is maximal in the barrier region suggesting that in this area the elastic energy available for potential slip is the largest. We therefore suggest that the length of the ruptured segment and magnitude of the strong Kahramanmaraş Earthquake were greatly influenced by the stress heterogeneity generated by the fault geometry during the long interseismic period. This example of the East Anatolian Fault shows that the geometry of the fault is crucial for the location and the extent of earthquakes along it. We further suggest that the presented analytical approach provides a simple yet powerful new tool for assessing seismic hazards before earthquakes occur.

How to cite: Sagy, A., Morad, D., and Lyakhovsky, V.: Stress, energy, and the onset of failure around geometrically irregular faults: Example from the East Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9615, https://doi.org/10.5194/egusphere-egu24-9615, 2024.

EGU24-9782 | Orals | TS3.1

Detection of slow slip events along the southern Peru - northern Chile subduction zone 

Jorge Jara, Romain Jolivet, Anne Socquet, Diana Comte, and Edmundo Norabuena

Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Southern Peru - Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from $M_w$~5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creeping or where geometrical complexities of the interplate region have been proposed. We finally discuss the potential role of fluids as a triggering mechanism for SSEs in the area. 

How to cite: Jara, J., Jolivet, R., Socquet, A., Comte, D., and Norabuena, E.: Detection of slow slip events along the southern Peru - northern Chile subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9782, https://doi.org/10.5194/egusphere-egu24-9782, 2024.

EGU24-11002 | ECS | Posters on site | TS3.1

Simulating normal fault interactions during complex seismic sequences in the southern Apennines 

Constanza Rodriguez Piceda, Zoë K. Mildon, Yifan Yin, Billy J. Andrews, Claudia Sgambato, Martijn van den Ende, and Jean Paul Ampuero

Active faults with low extension rates can generate large magnitude earthquakes with severe damages, as exemplified in the southern Apennines (Italy) by the Irpinia earthquake (Mw 6.8) in 1980 and the Val D’Agri earthquake (Mw 7.1) in 1857. These earthquakes occur within a network of faults, and geological evidence (e.g. paleoseismic trenching) suggest that earthquake activity varies from decennial to millennial time scales on such fault systems. Therefore, improving our understanding and forecasting capabilities of seismic sequences in these areas is crucial. However, studying fault behaviour in slowly deforming regions can often prove challenging due to the long recurrence intervals and low slip rates of these faults, which results in limited instrumental, historical and paleoseismological records.

To address this issue, we use physics-based numerical models, since they allow for controlled experiments that can span thousands of years with relatively low computational costs, thus they are valuable tools to investigate the causal dynamics between seismic events. Here, we model a system of NW-SE oriented normal faults in the southern Apennines, accounting for the variable slip rates and geometry of the faults. The study region is characterized by areas with variable number of across-strike faults, thus it is suitable to study the effects of fault network geometry (across-and along-strike interaction) on the seismic cycle and earthquake statistics (e.g. recurrence time, coefficient of variation) of a geologically realistic fault network. We use the boundary-element code QDYN which incorporates rate-and-state friction and elastic interactions to examine relevant inputs for seismic hazard assessment, including inter-event time within and between faults, magnitude-frequency distribution, and nucleation location. We are able to simulate spontaneous ruptures following power-law relationships of frequency-magnitude distribution. Differences in the recurrence time (periodic vs. aperiodic cycles) and rupture extent (characteristic vs. non-characteristic seismicity) in the fault planes seem to correlate with the number of faults that exist across strike. Our simulations demonstrate how quasi-dynamic earthquake simulators can provide insights into how fault network geometry impacts earthquake occurrence and seismic hazard assessment.

How to cite: Rodriguez Piceda, C., Mildon, Z. K., Yin, Y., Andrews, B. J., Sgambato, C., van den Ende, M., and Ampuero, J. P.: Simulating normal fault interactions during complex seismic sequences in the southern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11002, https://doi.org/10.5194/egusphere-egu24-11002, 2024.

EGU24-12582 | ECS | Orals | TS3.1

Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating. 

Jenni Robertson, Claudia Sgambato, Gerald Roberts, Zoe Mildon, Joanna Faure Walker, Francesco Iezzi, Sam Mitchell, Athanassios Ganas, Ioannis Papanikolaou, Elias Rugen, Varvara Tsironi, Joakim Beck, Silke Mechernich, Georgios Deligiannakis, Steven Binnie, Tibor Dunai, and Klaus Reicherter

We report the first example where the timing of earthquake slip from in situ 36Cl cosmogenic exposure dating of an active normal fault scarp can be verified using independently 14C dated Holocene coastal notches which are deformed along the strike of the fault. We have remodelled 36Cl data from the active Pisia-Skinos normal fault, Greece, published by Mechernich et al. (2018), which indicates that the fault slip rate fluctuated through time. We model the expected coastal uplift and subsidence induced by slip on the fault using elastic half-space models and surface ruptures observed following the 1981 Pisia-Skinos earthquakes. Coastal uplift is constrained by elevation measurements of Holocene coastal notches that have previously been dated using 14C by Pirazzoli et al. (1994) and agree with time periods consistent with Holocene climate stability. We mapped the elevations and numbers of notches along the strike of the Pisia-Skinos fault, including measurements made underwater for locations where fault slip has submerged the notches below the present-day shoreline. We show that the spatial patterns and timing of uplift and subsidence from the notches agrees with the timing of periods of high slip associated with earthquake clusters and quiescence associated with anti-clusters from the slip histories derived from 36Cl data, and with the uplift and subsidence derived from elastic half-space modelling. In particular, where modelled subsidence is highest, Holocene notches that formed between 6-2 ka can be preserved but are submerged. Notches could form at this time because the 36Cl data show that the Pisia fault had entered a period of relative quiescence with a slip-rate of <0.1 mm/yr, accompanied by uplift from the offshore Strava fault. In contrast, rapid slip on the Pisia fault at 1.4 mm/yr between 2 ka and the present-day did not allow notches to form during this time period in the location of highest subsidence. Our example is the first that independently calibrates the timing of slip derived from 36Cl on a fault plane using 14C dates on a deformed coastline, and is consistent with the idea that slip-rate variations can be measured and should be incorporated into seismic hazard assessment.

How to cite: Robertson, J., Sgambato, C., Roberts, G., Mildon, Z., Faure Walker, J., Iezzi, F., Mitchell, S., Ganas, A., Papanikolaou, I., Rugen, E., Tsironi, V., Beck, J., Mechernich, S., Deligiannakis, G., Binnie, S., Dunai, T., and Reicherter, K.: Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12582, https://doi.org/10.5194/egusphere-egu24-12582, 2024.

The seismic chronicle, derived from the analysis of 14 short sediment cores and three long cores from Lake Iznik (NW Turkey), along with the identification of a subaquatic fault segment belonging to the Middle Strand of the North Anatolian Fault (MNAF), provides insights into both local seismicity and the regional seismic activity over the last 6000 years.

The integration of this seismic chronicle with ground-motion estimations at the core locations for all historical earthquakes, together with the evolution of sedimentation rate through time, allow to discuss the epicentral region and epicentral intensity of each historical earthquake in the western NAF system. This analysis also helps us to discriminate which earthquake is likely to generate an event deposit in the case of several historical earthquake candidate, especially when chronological uncertainty are larges

This approach allows a discussion of the factors influencing the threshold (sedimentation rate, ground motions at different spectral frequencies ) for triggering an event deposit in the Lake Iznik and the type of slope destabilization that can be triggered .

Thanks to these finding and through the established scaling relationship it is then possible to infer a minimum intensity for prehistoric earthquakes recorded in Lake Iznik at a given period.

Combining these data with paleoseismological data from the region allows us to propose a scenario for the long-term seismic cycle of the western NAF system.

How to cite: de Sigoyer, J., Domenge, J., Céline, B., Gastineau, R., Sabatier, P., and Duarte, E.: Information on past seismicity of the western NAF system (Turkey) combining ground-motion models with historical earthquakes and event deposits recorded in the sediments of Lake Iznik (NAF system, Turkey), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12894, https://doi.org/10.5194/egusphere-egu24-12894, 2024.

EGU24-13043 | ECS | Posters on site | TS3.1

PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS) 

Maureen Llinares, Lucilla Benedetti, Ghislain Gassier, and Sophie Viseur

Markov Chain Monte Carlo (MCMC) algorithms are sampling approaches relying on Bayesian inference, theorized in the late 1940s and used in many applications (multi-dimensional integral computations, probability law explorations, inversion problems, etc.). MCMC methods are computationally expensive and many variants have been proposed to optimize them Today, MCMC algorithms are used as inversion tools in different contexts: from receiver functions in seismology . The success and efficiency of those methodologies depends on: the complexity of the forward function, the efficiency of the MCMC strategy and the implementation language. The last MCMC sampler is the No U-Turn Sampler or NUTS (Hoffman and Gelman, 2011), an evolution of the Metropolis Hastings (HMC).

Estimating seismic history along fault scarps from 36Cl profiles is a typical inversion problem. Thus, previous studies have proposed MCMC routines to the forward function described in (Schlagenhauf et al., 2011), to invert 36Cl data and to infer seismic histories on fault scarps  (Beck et al., 2018; Mechernich et al., 2023; Tesson and Benedetti, 2019). The complexity of the forward function implies the necessity of a powerful MCMC sampler such as NUTS (Liesenfeld and Richard, 2008).

Here, we discuss these different approaches and present a new approach, termed as PyMDS, which relies on the NUTS algorithm. We implemented the code in python and performed synthetic tests to evaluate the algorithm ability to retrieve seismic histories.The results for three earthquakes synthetics tests will be presented and show that the algorithm is capable of finding the seismic scenario (ages, slips and slip rate) with a precision of few hundred years on the ages, 10 to 30 cm on the slips and inferior 0.05 mm/yr on the slip rate with a runtime of 4 hours (faster than the previous Fortran code published by Tesson & Benedetti (2019) that required 3 days to complete). We will also present preliminary results obtained on the five sites located on the Velino-Magnola fault system and the implication on seismic cycle. Finally, we will discuss potential improvement and development perspectives, such as the optimization of the forward function, the necessity to invert slips and the parametrization of the NUTS algorithm.

How to cite: Llinares, M., Benedetti, L., Gassier, G., and Viseur, S.: PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13043, https://doi.org/10.5194/egusphere-egu24-13043, 2024.

EGU24-13133 | ECS | Orals | TS3.1

Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities. 

Francesco Iezzi, Marco Francescone, Alberto Pizzi, Anna Maria Blumetti, Paolo Boncio, Pio Di Manna, Bruno Pace, Tommaso Piacentini, Felicia Papasodaro, Francesco Morelli, Marco Caciagli, Massimo Chiappini, Francesca D’Ajello Caracciolo, Valerio Materni, Iacopo Nicolosi, Vincenzo Sapia, and Stefano Urbini

Features such as fault geometry and slip-rates are key inputs to assess the seismic hazard imposed by either ground motion or fault displacement. However, complexities in the geology of faults, such as relay zones and along-strike fault bends, could lead to settings characterized by high segmentation, with multiple splays arranged both along and across strike. In order to assess the seismic hazard associated with such fault sectors, it is necessary to establish whether the 3D shallow deformation is equally spread over the multiple fault splays or the activity tends to localise on specific splays. This problem is enhanced when these faults are located within urban areas, and therefore their surface expression is altered by intense anthropic activity.

Within the framework of a work on the mitigation of the fault displacement hazard associated with the Mt. Marine active normal fault (Central Italy), we have performed two paleoseismological surveys within the town of Pizzoli (about 10 km NW of L’Aquila), where the fault is expressed with several splays arranged both along and across-strike. The trenches were planned to explore (i) potential fault scarps altered by human activity, identified through aerial photographs, LiDAR and fieldwork analysis, and (ii) discontinuities in the stratigraphic record highlighted by geophysical investigations (ERT, GPR) and borehole data.

The paleoseismological surveys intercepted five fault splays arranged across-strike, three synthetic and two antithetic to the main Mt. Marine fault. The fault splays show evidence of multiple Late Pleistocene/Holocene surface-rupturing seismic events, marked by colluvial wedges and infilled fractures. Moreover, we constrained the Late Pleistocene slip-rate of the Mt. Marine fault splays by dating and correlating Late-Pleistocene paleosols found (1) outcropping in the footwall of one of the inner fault splay and (2) in a borehole located just at the hangingwall of the outermost splay.

Our results show that the fault splays exhibit different and variable activity rates, suggesting that fault activity is localized on specific fault splays through space and time with the potential to rupture simultaneously during large earthquakes. Our findings have strong implications on fault-based seismic hazard assessments, as they imply that data collected on one splay may not be representative of the behaviour of the entire fault.

How to cite: Iezzi, F., Francescone, M., Pizzi, A., Blumetti, A. M., Boncio, P., Di Manna, P., Pace, B., Piacentini, T., Papasodaro, F., Morelli, F., Caciagli, M., Chiappini, M., D’Ajello Caracciolo, F., Materni, V., Nicolosi, I., Sapia, V., and Urbini, S.: Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13133, https://doi.org/10.5194/egusphere-egu24-13133, 2024.

Previous studies have constrained the fault slip rates and block geometries of the SoutheasternTibetan Plateau (SETP) with contradictory results due to complex deformation patterns, limited datasets, and subjective choices of block boundaries. In this work, we address the issue of uncertain block geometries by employing an unsupervised machine learning (Euler pole clustering) algorithm that automatically resolves regions that behave as rigid blocks (clusters) using ~1000 GNSS velocity vectors. The optimal clustering results, determined by F-test and Euler-vector overlap analyses, indicate 4 elongated blocks exist in the SETP that are approximately parallel and delineated by a set of arcuate sinistral-slip faults. Our clustering results redefine the kinematicsof the SETP region with new block definitions which elucidate the dominance of sinistral-slipfaults.

How to cite: Xu, R. and Liu, X.: Clustering of GNSS Velocities Using Unsupervised Machine Learning in the Southeastern Tibetan Plateau: Block Identification and the Dominance of Sinistral-slip Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13534, https://doi.org/10.5194/egusphere-egu24-13534, 2024.

EGU24-14326 | Orals | TS3.1

Low-angle normal faulting triggered by fluids 

Carolina Pagli, Alessandro La Rosa, Derek Keir, Gareth Hurman, Hua Wang, Cecile Doubre, Renier Viltres, Martina Raggiunti, and Atalay Ayele

In extensional settings under Andersonian mechanics, low-angle normal faults should not form in favour of steeply dipping normal faults. However, InSAR shows that a seismic sequence including an earthquake with magnitude Mw 5.6 on August 1st, 2023 (NEIC - National Earthquake Information Center) at the northern end of the Afar rift was caused by normal faulting on a low-angle 35° dipping plane. Our best-fit InSAR model shows that the low-angle normal fault occurred on the west margin of the rift axis, it was relatively deep (6.7 km) and it slipped fully seismically, having a geodetic magnitude of Mw 5.66 in agreement with the global seismic recordings (NEIC). Temporally, the faulting occurred at the end of a one-year period (December 2022-December 2023) of increased seismicity in the northern sector of Afar, with swarms of seismicity migrating northward along the rift. The seismic characteristics, fault location and kinematics are consistent with the low-angle normal fault being triggered by fluids that locally could be released by a deep magmatic heat source along the rift axis under high extensional stresses. Our observations show that low-angle normal faults can form in rifting settings, are activated seismically and are likely fluid-induced.

How to cite: Pagli, C., La Rosa, A., Keir, D., Hurman, G., Wang, H., Doubre, C., Viltres, R., Raggiunti, M., and Ayele, A.: Low-angle normal faulting triggered by fluids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14326, https://doi.org/10.5194/egusphere-egu24-14326, 2024.

EGU24-16153 | ECS | Posters on site | TS3.1

Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece) 

Zoe Mildon, Manuel Diercks, Gerald Roberts, Joanna Faure Walker, Athanassios Ganas, Ioannis Papanikolaou, Vassilis Sakas, Jennifer Robertson, Claudia Sgambato, and Sam Mitchell

Loading and deformation during the interseismic period of the earthquake cycle is often considered to be constant for continental faults, therefore assuming that the short-term (annual-decadal) deformation is representative of longer-term deformation. Based on this assumption, geodetically-derived deformation rates are sometimes used to infer the slip-rates and thus seismic hazard of faults. However geological observations indicate that deformation and slip rates are variable over a range of timescales, and we present an observation of variable deformation across an active normal fault occurring on an annual timescale. The Pisia-Skinos normal fault in the Gulf of Corinth, Greece, is a well-known fault which slipped most recently during a sequence of damaging earthquakes in 1981. Using vertical deformation data, available from the European Ground Motion Service (EGMS), we observe uplift/subsidence of the footwall/hangingwall of the Pisia fault between 2016-2021. Of particular interest is our observation that the deformation is not uniform over the 6 year time period, instead there is an up to 7-fold increase in the vertical deformation rate in mid-2019. We hypothesise that this deformation is aseismic as there is no temporally correlated increase in the earthquake activity (M>1). We explore four possible causative mechanisms  for observed deformation; shallow slip, post-seismic after-slip, deep slip on an underlying shear zone, and post-seismic visco-elastic rebound. Our preferred hypothesis is that the transient deformation is caused by centimetre-scale slip in the upper 5km of the Pisia fault zone, based on the magnitude and spatial extent of the deformation. Our results suggest that continental normal faults can exhibit variable deformation over shorter timescales than previously observed, implying that the interseismic period of the earthquake cycle on continental faults may be more variable than previously hypothesised. This also highlights potential pitfalls of using slip rates measured over short-timescales to infer seismic hazard.

How to cite: Mildon, Z., Diercks, M., Roberts, G., Faure Walker, J., Ganas, A., Papanikolaou, I., Sakas, V., Robertson, J., Sgambato, C., and Mitchell, S.: Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16153, https://doi.org/10.5194/egusphere-egu24-16153, 2024.

EGU24-16171 | Orals | TS3.1

Fast stress-loading and -unloading below the seismogenic zone 

Claudia Trepmann, Lisa Brückner, and Fabian Dellefant

At depth just below the seismogenic zone of the continental crust, i.e. at greenschist facies conditions, stresses increase during seismic rupturing within minutes from differential stresses on the order of a few tens of MPa to several hundreds of MPa. These fast stress-loading rates are manifested in characteristic microfabrics in fault rocks (cataclasites and pseudotachylytes) exhumed from these depths. The microfabrics indicate quasi-instantaneous cataclasis of almost all rock-forming minerals including garnet and quartz, as well as mechanical twinning of pyroxenes, amphiboles and titanite. In combination with experiments, the microfabrics can be used as paleo-stress gauges, i.e., paleopiezometers. The characteristic microstructures can occur distributed over the whole width of large-scale thrust faults, as the Silvretta basal thrust in the Central European Alps. There, twinned amphiboles record transient differential stresses of more than 400 MPa in a rock volume to about 300 m above the basal thrust exposed at the contact to the Penninic units of the Engadine window over several tens of km. Fast stress-unloading is indicated by growth of new undeformed quartz grains along cleavage cracks in host quartz generated coeval with seismic rupturing and missing evidence of quartz dislocation creep after pseudotachylyte formation. This fast stress-loading and unloading is recorded in pseudotachylytes, i.e., close to the seismic rupture, whereas at larger distance to the seismic rupture accelerated creep at hundreds of MPa occurs on a longer time scale. 

How to cite: Trepmann, C., Brückner, L., and Dellefant, F.: Fast stress-loading and -unloading below the seismogenic zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16171, https://doi.org/10.5194/egusphere-egu24-16171, 2024.

EGU24-16276 | ECS | Orals | TS3.1

Triggered and recurrent slow slip in North Sulawesi, Indonesia 

Nicolai Nijholt, Wim Simons, Taco Broerse, and Riccardo Riva

Nearby faults interact with each other through the exchange of stress. However, the extent of fault interaction is poorly understood. In particular, closely tied tectonic systems like crustal-scale faults that are right next to subduction zone interfaces are likely to express such interactions. Interactions may lead to slow-slip activity, resulting in episodes of transient surface motion.

Our study concentrates on Northwest Sulawesi (Indonesia), which hosts two fault zones with potential for major earthquakes and tsunamis: the strike-slip Palu-Koro fault and the Minahassa subduction zone. Both fault zones accommodate 4 cm/yr of interseismic relative motion. Thanks to a 20-year-long effort in geodetic monitoring, we are able to identify multiple periods during which surface velocities deviate from their interseismic trend. The most recent episode followed the 2018 Mw7.5 Palu earthquake.

We use a Bayesian methodology with forward predictions of slip on the two fault interfaces to match the observations following the 2018 Mw7.5 Palu earthquake, and infer that both deep afterslip on the Palu-Koro fault and slow slip on the Minahassa subduction interface have caused the observed transient surface motion. This finding represents the first recording of a slow slip event on the Minahassa subduction interface. We also speculate that the subduction interface and the strike-slip fault are likely interacting on a regular basis, affecting the seismogenic potential of both parts of this tectonic system.

How to cite: Nijholt, N., Simons, W., Broerse, T., and Riva, R.: Triggered and recurrent slow slip in North Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16276, https://doi.org/10.5194/egusphere-egu24-16276, 2024.

EGU24-16670 | Orals | TS3.1

Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake 

Rob Govers, Celine Marsman, Femke Vossepoel, Ylona van Dinther, and Mario D'Acquisto

Geodetic data covering different phases of the earthquake cycle provide a great opportunity to improve our understanding of the processes and parameters governing the dynamics at subduction margins. However, quantifying the individual contributions of physical processes such as viscoelastic relaxation, afterslip, and (re)locking throughout the earthquake cycle remains challenging. Moreover, it is relevant to account for these processes within a rheological framework that is consistent over the entire earthquake cycle. We address this using Bayesian inference in the form of an ensemble smoother, a Monte Carlo approach that represents the probability density distribution of model states with a finite number of realizations, to estimate geodynamic model parameters. Prior estimates of the imperfect physical model are combined with the likelihood of noisy observations to estimate the posterior probability density distribution of model parameters.

 

We construct a 2D finite element seismic cycle model with a power-law rheology in the mantle. A priori information, such as a realistic temperature field and a coseismic slip distribution, is integrated into the model. Model pre-stresses are initialized during repeated earthquake cycles wherein the accumulated slip deficit is released entirely. We tailor the last earthquake to match the observed co-seismic slip of the 2011 Tohoku earthquake. The heterogeneous rheology structure is derived from the temperature field and experimental flow laws. Additionally, we simulate afterslip using a thin, low-viscosity shear zone with a Newtonian rheology. We focus on constraining power-law flow parameters for the mantle, and the shear zone viscosity.

 

We assimilate 3D GEONET GNSS displacement time series acquired before and after the 2011 Tohoku earthquake. The data require separate viscoelastic domains in the mantle wedge above and below ~50 km depth, and in the sub-slab mantle. Power-law viscosity parameters are successfully retrieved for all three domains. The trade-off between the power-law activation energy and water fugacity hinders their individual estimation. The wedge viscosity is >1019 Pa·s during the interseismic phase. Postseismic afterslip and bulk viscoelastic relaxation can be individually resolved from the surface deformation data. Afterslip is substantial between 40-50 km depth and extends to 80 km depth. Bulk viscoelastic relaxation in the wedge concentrates above 150 km depth with viscosities <1018 Pa·s. Landward motion of the near-trench region occurs during the early postseismic period without the need for a separate low-viscosity channel below the slab.

How to cite: Govers, R., Marsman, C., Vossepoel, F., van Dinther, Y., and D'Acquisto, M.: Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16670, https://doi.org/10.5194/egusphere-egu24-16670, 2024.

Shallow creep, as a widespread phenomenon in the earthquake cycle, plays an important role in understanding the behavior of faults and seismic hazards. However, it is still under debate whether creeping is an inherent behavior of fault or is a form of afterslip following large earthquakes. The East Anatolian Fault was recently ruptured by the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, providing a unique opportunity to investigate the relation between shallow creep and earthquakes along strike-slip fault. Here, we show the spatial distribution and temporal evolution of creeping segments along the EAF using the InSAR phase-gradient stacking method. We derive the shear-strain rates in three periods – before the 2020 earthquake, between the 2020 and 2023 earthquakes, and after the 2023 earthquake sequence. By comparing the spatial distribution of the interseismic strain rates, the coseismic slip, and the post-seismic strain rates, we document a tight connection between creeping and coseismic slip on the two recent earthquakes. We also investigate the temporal behavior of faults following the two earthquakes using time-series shear strain analysis. The results reveal behaviors of shallow creep on different segments of the EAF with different statuses before the earthquakes. Our results shed new light on understanding the mechanism of creeping and its relation with large earthquakes during the earthquake cycle.

How to cite: Liu, Z. and Wang, T.: Shear-strain rates across the East Anatolian Fault (EAF) response to the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18092, https://doi.org/10.5194/egusphere-egu24-18092, 2024.

EGU24-18562 | Posters on site | TS3.1

Insights into the site-to-site correlation of paleoseismic data  

Nicolás Pinzon and Yann Klinger

Integration of paleoseismic data from multiple sites is important to assess the past fault rupture scenarios and determine an earthquake chronology for the entire fault system. However, the current methods used to combine paleoseismic data are diverse and lack theoretical foundations from a mathematical perspective. We present a method to evaluate and integrate paleoseismic event data from multiple sites into a single earthquake time history. We apply this method to the central-eastern fault sections of the Altyn Tagh Fault using data from ten fault trenches. Applying a Bayesian approach we constructed time-stratigraphic models that yield the probability density functions corresponding to the age of individual earthquakes at each site. Then, our method to integrate these data consists of two main steps: 1) we constructed a rupture pool with all the modeled event ages, and we evaluated the overlapping degree between the site PDFs; 2) For sufficiently contemporary PDFs we combine them by computing the weighted-mean method which emphasizes the overlap in the site earthquake times. The weighted-mean method yields smaller earthquake-time uncertainties compared to the rupture-mean approach and is consistent with the earthquake rupture assumptions behind the integration of paleoseismic data and the probability theory of density functions. This approach helps to clarify the timing and rupture extent of past earthquakes along central-eastern ATF and is essential to improve the earthquake probability assessment for the region.

How to cite: Pinzon, N. and Klinger, Y.: Insights into the site-to-site correlation of paleoseismic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18562, https://doi.org/10.5194/egusphere-egu24-18562, 2024.

Following large earthquakes, postseismic crustal deformations are often observed. They include the afterslip and the viscoelastic deformation of the crust and the upper mantle, activated by the coseismic stress change. In order to predict the future deformations, and the stress change distributions, it is important to divide each deformation. The physical parameters; frictional properties of the fault and the rheological properties are the key to determining the slip behavior, but they are generally unknown.

Data assimilation (DA) studies have attempted to estimate the frictional properties directly from the observational data. DA incorporates the observed data into the physics-based model to construct a more plausible model. When DA works well, we can obtain the physics-based model, including the physical properties, that can quantitatively explain the observed data. The constructed physics-based model can be used to simulate the slip evolution beyond the data period, i.e., prediction of the deformation.

There are two types of DA technique applying to nonlinear system, the sequential method called as Ensemble Kalman filter method (EnKF) and the variational method called as 4DVAR. For the fault system, EnKF is applied to the deformation data to estimate the physical variables (van Dinther et al., 2019, Hirahara and Nishikiori, 2019). 4DVAR is also applied to the afterslip assuming elastic medium to estimate the fault frictional properties (Kano et al., 2015; 2020). If the physics-based model under consideration is linear, the sequential and the variational methods are consistent, but this is not the case for fault systems.

In this presentation, I construct a simple model that include the fault slip that follows the rate- an state- friction law and the viscoelastic deformation. Then I apply both EnKF and 4DVAR, and compare the results to discuss the characteristics of the methods.

How to cite: Ohtani, M.: Numerical experiments on estimating the fault frictional properties and the viscosity from the postseismic deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19405, https://doi.org/10.5194/egusphere-egu24-19405, 2024.

EGU24-20077 | ECS | Orals | TS3.1

Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations 

Floriane Provost, Volkan Karabacak, Jean-Philippe Malet, Jérôme Van Der Woerd, Mustapha Meghraoui, Frédéric Masson, Matthieu Ferry, David Michéa, and Elisabeth Pointal

On February 6, 2023, southern Türkiye was hit by two major earthquakes at 01:17 UTC (Mw 7.8, Pazarcık, Kahramanmaraş) and at 10:30 UTC (Mw 7.6, Elbistan, Kahramanmaraş) leading to severe damages at the complex junction of the Dead Sea Fault (DSF), the Cyprus arc and the East Anatolian fault zone (EAFZ). The ruptures propagated along several known strands of the southwestern termination of the EAFZ, the main Pazarcık and Karasu valley faults and the Çardac-Sürgü fault. The spatial extent of the impacted zone (300 x 300 km) supports the use of satellite images to map ruptures and damages and measure the co-seismic displacement over the whole region. Among the different satellite constellation available nowadays, Sentinel-2 presents the advantages of offering high-resolution images (10 m), global coverage with frequent revisit time and open access policy to the images. We here present the high-resolution mapping of the entire coseismic surface ruptures derived from image correlation of optical Sentinel-2 satellite acquisitions. We further estimated the rupture width, the total and on-fault offset, and of the diffuse deformation obtained a few days after the two mainshocks along the two main ruptures at 50 m resolution along the rupture. The mapping and the estimation of the offset are validated with the location of the rupture and the offset measurements collected on the ground. We found that the ruptures extend over lengths of 310 km and 140 km, with maximum offsets reaching 7.5±0.8 m and 8.7±0.8 m near the epicenters, for the Mw 7.8 and Mw 7.6 mainshocks, respectively. We propose a segmentation of the two ruptures based on these observations, and further discuss the location of potential supershear rupture. The use of optical image correlation complemented by field investigations along earthquake faults provides new insights into seismic hazard assessment.

How to cite: Provost, F., Karabacak, V., Malet, J.-P., Van Der Woerd, J., Meghraoui, M., Masson, F., Ferry, M., Michéa, D., and Pointal, E.: Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20077, https://doi.org/10.5194/egusphere-egu24-20077, 2024.

EGU24-20361 | ECS | Posters on site | TS3.1

3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault 

Adélaïde Allemand, Liqing Jiao, and Yann Klinger

Knowing about the geometry of both (i) ruptured zones during seismic events, and (ii) faults throughout seismic cycles, as well as the evolution of this geometry, is important to understand what is controlling the start and the ending of large earthquakes. In this study, we use 3D Discrete Element Modeling (DEM) in order to simulate a strike-slip fault, formed from an initially homogeneous, intact medium representing brittle rock that is submitted to tectonic loading. Indeed, this numerical method models the crust as an assembly of rigid spheres which are linked by user-defined interactions and reconfigurate very naturally when subjected to loading. Therefore, such approach is adapted to study the evolution of fault geometry through earthquake cycles, since it permits to simulate large displacements of the particles, while avoiding prescribing fault location and geometry, and letting such geometry evolve freely.

A 3D parallelepipedic model is designed and then indefinitely sheared by assigning periodic boundary conditions. The particular feature of our model is the implementation of a healing phenomenon, a key process which allows fractured zones to restrengthen after a slip event. During the simulation, the position of particles and the state of their bonds are recorded at regular time intervals; consequently, the shape and dimension of deformation are evaluated, the evolution of fault geometry is monitored, and the stresses in the domain can be measured. Results show a stick-slip behaviour which can be identified as earthquakes separated by locking periods. In addition, the amount of displacement and the rupture surface can be estimated and enable the computation of a magnitude-like quantity. Thus, earthquake-like events seem to follow a magnitude-frequency relationship, and earthquake-like surface deformations are comparable to observations of ground deformation after real size earthquakes. Eventually, the evolution of the fault geometry during the simulation is also scrutinized.

How to cite: Allemand, A., Jiao, L., and Klinger, Y.: 3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20361, https://doi.org/10.5194/egusphere-egu24-20361, 2024.

EGU24-293 | ECS | Orals | TS3.3

Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya 

Jyoti Tiwari, Surendra S. Bhakuni, Pradeep Goswami, and Anil Tiwari

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.

How to cite: Tiwari, J., Bhakuni, S. S., Goswami, P., and Tiwari, A.: Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-293, https://doi.org/10.5194/egusphere-egu24-293, 2024.

There is a growing interest among seismologists on the nonlinearity of seismic processes, corresponding to the synergetic approach to the development of the Earth as a nonlinear, open, self-organizing system. In the analysis of very complex multi-component geological-geophysical systems, it is important to assess the degree of their nonlinearity based on a set of control parameters. For the analysis of the seismic process, we propose to use seismic-tectonic stress in the Earth's crust and lithosphere as a control parameter. Also, in the analysis of processes releasing tectonic stresses in the form of earthquakes, the synergetic of choosing the initial state becomes important.

To choose the initial state of the Earth's crust and lithosphere, we consider them as an oscillatory block-hierarchical system, interconnected and developing over time but differing in various layers of the Earth's crust – sedimentary, consolidated crust, lower crust, and mantle beneath the Moho boundary, as each layer has its lithological properties and is in different physical conditions, at least due to the change in pressure. Block sizes are determined based on the thickness of the layer, and vertical planes of the block are determined based on the morphology of the layer, as well as the presence of a fault inside the block. Changes in the seismic-tectonic deformation vector indicate a change in the initial state of seismic-tectonic deformation of each block. Thus, for the analysis of the nonlinear seismic process, we obtain a continuous series of changes in seismic-tectonic stresses in different layers and for each block of the layer. Thanks to the known time of deformation changes, as well as the known size of each block, we have an approximation of the nonlinear oscillatory process in the block-hierarchical system of the Earth's crust and lithosphere, manifested as seismicity. Within the designated time interval, the seismic-tectonic deformation process in each block follows a linear law. We have tested our methodological approaches to the analysis of the nonlinear seismic process in the example of the Crimean-Black Sea region. We have processed earthquakes contained in the new catalog of seismic events for the period 1970-2012, recalculated according to the Seismological Bulletins of the USSR and Ukraine. The method of Aki was used to determine the seismic-tectonic deformation regime by constructing averages foci by the signs of the first arrivals of P-waves taken from the bulletins. Time series of changes in seismic-tectonic deformation regimes in different layers of the Earth's crust and lithosphere show that each layer has its peculiarities of deformation but fits into the general context of tectonic processes in the region. One of the interesting features of the tectonic process in the region turned out to be the unexpected variability of regimes and their duration from 2 to 10 years in different areas of the Crimean-Black Sea region. An important consequence of our study is the definition of clear spatial-temporal frameworks for the analysis of the amounts of seismic energy release in each of the blocks, which will improve the quality of seismic risk assessment for individual regions.

How to cite: Shumlianska, L. and Vilarrasa, V.: Approximation of nonlinear seismic processes based on space-time series of changes in seismotectonic deformation regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-641, https://doi.org/10.5194/egusphere-egu24-641, 2024.

The faults and the fault zones are essential to determine the seismotectonic features and the regime of a region and to produce seismic hazard and risk maps. Many geophysical methods, such as seismic, magnetic and gravity are used to determine the location and direction of faults. This study aims to detect potential fault edges located in the south-southwest of Nisyros Island and west of Tilos Island in the southeastern Aegean Sea and to interpret the seismic activity and faulting characterization. To this end, the potential fault edges were initially detected using the total horizontal derivative method on the gravity dataset collected from the WGM2008 database. The obtained spatial locations were combined with the seismicity and the focal mechanisms of the earthquakes. The detected fault has a northeast-southwest orientation with normal faulting. It was proved that this obtained fault is not included in the active faults of the Eurasia database (AFEAD), European Fault - Source Model 2020 (EFSM20) database and the Mineral Research and Exploration General Directorate (MTA) active fault map. Moreover, this observed fault was detected as longer than the fault shown on the National Observatory of Athens (NOAFAULTs) in terms of length. Consequently, it is highly recommended that this potential fault, which produces earthquakes with a moment magnitude greater than 4.0 (on instrumental period) must be added to such fault databases to increase and spread the knowledge of seismological and seismotectonic research.

How to cite: Tamtaş, B. D. and Toktay, H. D.: Seismotectonic interpretation and edge detection of the potential fault on the SE Aegean Sea using the total horizontal derivative method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-785, https://doi.org/10.5194/egusphere-egu24-785, 2024.

EGU24-1278 | ECS | Posters on site | TS3.3

Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia 

Tamar Shikhashvili, Mariam Mariam Bekurashvili, Anzor Giorgadze, Aleksander Razmadze, Onise Enukidze, and Victor Alania

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region (e.g., Cavazza et al., 2023). Inversion of back-arc basins, exhumation, and crustal thickening took place in the far-field zone, forming two orogens, and leading to a convergence between the Lesser Caucasus (LC) and Greater Caucasus (GC). Continuous convergence between the LC and GC caused incremental deformation of the Kura foreland basin (Alania et al., 2023). Our study area is located within the LC-GC convergence zone in the western Kura foreland basin and is represented by the lenticular-shaped compressional basin formed by northward and southward-directed thrusting. 2D seismic reflection profiles revealed the presence of triangle zones at the frontal part of the LC retro-wedge and GC pro-wedge. According to analog, seismic, and sequential kinematic modeling results, the frontal part of the GC is represented by a double wedge-dominated triangle zone and is characterized by the presence of passive, active wedges and passive-forethrust. In the frontal part of the LC orogen, the syn-kinematic (Middle-late Miocene) strata have been deformed and uplifted by passive-back thrusting at the triangle zone. Seismic reflection profiles show north-vergent duplex and structural wedge at the triangle zone beneath the thrust front monocline and is represented by Cretaceous-Paleogene strata. Western part of the triangle zone of the Kavtiskhevi-Akhalkalaki area is introduced by south-vergent imbricated fan (passive-back thrusts). The imbricated fan is characterized by fault-propagation folding. The kinematic evolution of south-vergent fault-propagation folds is related to northward propagating duplex. Recent and historical earthquakes and paleoseismic data indicate that the frontal part of LC and GC is tectonically active (e.g., Stahl et al., 2022; Tsereteli et al., 2016).

 

Reference

Alania, V., et al. (2023). Interpretation and analysis of seismic and analog modeling data of triangle zone: a case study from the frontal part of western Kura foreland fold-and-thrust belt, Georgia. Frontiers in Earth Sciences 11, 1195767.

Cavazza, W., et al. (2023). Two-step exhumation of Caucasian intraplate rifts: a proxy of sequential plate-margin collisional orogenies, Geoscience Frontiers 15, 101737.

Stahl, T. A., et al. (2022). Recent Surface Rupturing Earthquakes along the South Flank of the Greater Caucasus near Tbilisi, Georgia. Bull. Seism. Soc. Am. XX, 1–19.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328-344.

How to cite: Shikhashvili, T., Mariam Bekurashvili, M., Giorgadze, A., Razmadze, A., Enukidze, O., and Alania, V.: Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1278, https://doi.org/10.5194/egusphere-egu24-1278, 2024.

EGU24-1557 | Posters on site | TS3.3

Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia 

Mariam Bekurashvili, Tamar Shikhashvili, and Victor Alania

Our study area, Tbilisi urban area is located in the eastern Achara-Trialeti fold-and-thrust belt. The Achara-Trialeti fold-and-thrust belt, which is one of the good examples of collision-driven far-field deformations, is located within the northernmost part of the Lesser Caucasus orogen and is associated with Arabia-Eurasia convergence. Our interpretation has integrated seismic reflection profiles, several oil wells, and surface geology data to reveal the deformation structural style of the eastern Achara-Trialeti fold-and-thrust belt. Fault-related folding theories were used for seismic interpretation. Seismic reflection data reveal the presence of south-vergent and north-vergent fault-propagation folds, duplexes, and structural wedge. Interpreted seismic reflection profiles, structural cross-section, and recent earthquakes reveal the presence of an active blind thrust fault and structural wedge(s) beneath Tbilisi and the surrounding area. The structural model shows that the 2002 Mw 4.5 Tbilisi earthquake was related to a north-vergent blind thrust and the Kumisi and Teleti earthquakes are related to a north-vergent blind wedge thrust system.

How to cite: Bekurashvili, M., Shikhashvili, T., and Alania, V.: Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1557, https://doi.org/10.5194/egusphere-egu24-1557, 2024.

EGU24-1713 | Posters on site | TS3.3

The Valsugana area (TN, Italy): a structural knot 

Silvana Martin, Laura Montresor, Pina Zambotti, Giovanni Monegato, Guido Roghi, Gianluca Piccin, Alessia Modesti, and Francesco Gosio

In the Valsugana area (Southern Italian Alps) a NE-SW trending pre-permian Southalpine phyllitic basement is intruded by an Early to Middle Permian granitoids (Cima d’Asta,190 km2) and includes volcanic calderas of the Athesian Volcanic Group (125 km2) of the same age, and is locally covered by Upper Permian to Miocene sedimentary sequences. A complex system of faults juxtaposes these different geological domains. In particular, the Permian tectonic structures have been repeatedly reactivated during Mesozoic and Tertiary. The phyllitic basement, which suffered Variscan metamorphism and deformation, and the granitoids were dismembered by NNW-SSW and N-S tectono-magmatic faults associated with the opening of permian calderas. The main tectonic system of this area is the ENE-WSW oriented Valsugana fault system of Middle-Late Miocene age (Heberer et al., 2017 ). The master fault separates the metamorphic basement from the sedimentary sequences (e.g., M. Armentera, M. Civerone and M. Lefre). At the footwall of the master fault, other faults deformed in a compressive to transpressive regime the sedimentary sequences. Some of these are extensional faults were reactivated many times from Triassic to Lower Jurassic. The Valsugana fault system ends against the Permian to Mesozoic Calisio fault to the SW, while it continues to the NE towards Brocon and Cereda Passes (Gianolla et al. 2022). The Valsugana fault system is cut across by the Val di Sella fault of Late Miocene-Pliocene age, oriented c.a. E-W which deformed the northern walls of the Asiago Plateau (Barbieri & Grandesso, 2007), transporting slices of metamorphic basement and Permo-Mesozoic sequences to the north, over the Middle Miocene sandstones and marls of Valsugana. The most recent tectonic system consists of a set of NNW-SSE to N-S faults which cut across the ENE-WSW Valsugana and E-W Val di Sella fault systems. The N-S Grigno-Tolvà fault cuts across the Cima d’Asta magmatic complex from Val Vanoi to the north to Asiago Plateau to the south over XX km, and dislocates the Belluno and Val di Sella thrust faults at the footwall of the Valsugana fault system. All these faults are still seismically active.

Barbieri G. & Grandesso P. (2007) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 082, Asiago.

Heberer B., Reverman R.L., Fellin M.G., Neubauer F., Dunkl I., Zattin M., Seward D., Genser J. & Brack P. (2017) - Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation. International Journal of Earth Sciences (Geologische Rundschau), 106:1557–1580.

Gianolla G., Caggiati M. & Riva A. (2022) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 046, Longarone.

How to cite: Martin, S., Montresor, L., Zambotti, P., Monegato, G., Roghi, G., Piccin, G., Modesti, A., and Gosio, F.: The Valsugana area (TN, Italy): a structural knot, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1713, https://doi.org/10.5194/egusphere-egu24-1713, 2024.

EGU24-1794 | Orals | TS3.3

Disaggregation bands as indicator for active blind faults 

Christian Brandes, David Tanner, Haakon Fossen, Matthias Halisch, and Katharina Müller

The identification of active faults is an important step in the seismic hazard evaluation process. However, this task is often difficult because many faults are unknown, buried below younger sediments. Especially in slowly-deforming intraplate areas with long recurrence intervals between individual seismic events, the detection of hidden blind faults is a major challenge. Furthermore, active faults can undergo long episodes of aseismic creep and thus do not produce typical earthquake-related, soft-sediment deformation structures, which also hinders the detection of these faults. Consequently, there is the demand for a robust universal geological indicator for active blind faults. Based on outcrop studies, we are able to show that disaggregation bands (near-surface deformation bands that develop in unconsolidated sediments due to reorganization of the grain fabric) are such an indicator. Disaggregation bands are developed at several locations in Central Europe and Scandinavia, in near-surface sandy sediments above the tip lines of blind faults. The strike of these bands is parallel to the strike of the underlying faults, which indicates that the disaggregation bands formed as a consequence of fault movement. The disaggregation bands internally show a pore-space reduction and in some cases a clear alignment of elongated grains. The thickness of the disaggregation bands increases with the amount of offset along the bands. Based on these observations, we infer that the bands formed in the process zone of propagating faults due to a shear-related reorganization of the grain fabric that leads to strain-hardening and a growth of the bands into centimetre-thick tabular structures. With analogue shearing experiments we show that disaggregation bands can form at a wide range of deformation speeds, even down to speeds several orders of magnitudes lower than seismogenic fault-slip velocities. Thus, disaggregation bands are key structures that record large parts of the seismic cycle and represent a very suitable indicator for active blind faults, even if the related fault creeps without emitting seismic waves. Disaggregation bands can easily be recognized in outcrops and artificial trenches, and previous studies showed that it is possible to even image them with ground-penetrating radar.

How to cite: Brandes, C., Tanner, D., Fossen, H., Halisch, M., and Müller, K.: Disaggregation bands as indicator for active blind faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1794, https://doi.org/10.5194/egusphere-egu24-1794, 2024.

EGU24-1802 | Posters on site | TS3.3

The shear deformation zone along the KTFZ: implications for faulting properties 

Vasileios Karakostas and Eleftheria Papadimitriou

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, a dextral strike slip transform zone, exhibits the fastest rates of relative plate motion in the Mediterranean. Strong (Mw>6.0) earthquakes associated with the fault segments comprised in KTFZ are frequent as historical information and instrumental record reveals. Four main shocks of this order magnitude, among other earthquakes of Mw>5.0 occurred since 2003 on almost along strike adjacent fault segments, with high aftershock productivity extended far beyond the fault tips forming aftershocks zones remarkably wider than expected of strike slip faulting. This enhanced aftershock seismicity is associated with the shear deformation zone surrounding the mainshock rupture plane. It has been suggested that it results from the reactivation of secondary faults, its width decreases as a power law with cumulative fault displacement being narrower around mature faults than around immature faults. As the structural maturity may have a strong impact on earthquake behavior, such as magnitude, stress drop, distribution of slip, rupture velocity, ground motion amplitude, and number of ruptured segments, as prior studies have suggested, we aim at investigating the shear deformation zone along KTFZ. We used the relocated aftershock seismicity of the four recent (2003 – 2015) strong (Mw>6.0) main shocks that occurred on almost along strike positioned strike slip faults for defining the fault width in conjunction with the fault length, as we have already done in the case of the 2015 Lefkada main shock, and the activation of secondary faults, most probably triggered by stress changes and stress redistribution due to the main shock coseismic slip. Detailed slip models, when available, are engaged for this scope for investigating possible triggering of the secondary fault segments taking part in each seismic excitation, due to the stress transfer, taking also into account the stress sensitivity on the geometry and faulting properties of the minor faults, along with the accurately relocated aftershock seismicity. After the main fault width definition, we investigated the decrease of aftershock frequency and spatial density as a function of distance from the main fault.

Acknowledgments: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

How to cite: Karakostas, V. and Papadimitriou, E.: The shear deformation zone along the KTFZ: implications for faulting properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1802, https://doi.org/10.5194/egusphere-egu24-1802, 2024.

EGU24-2168 | Posters on site | TS3.3

Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review 

Federico Pasquaré Mariotto, Alessandro Tibaldi, Fabio Luca Bonali, Noemi Corti, Martina Pedicini, Babayev Gulam, and Tsereteli Nino

The convergence between the Arabian and the Eurasian plates resulted in the development of the Greater Caucasus (GC) and the Lesser Caucasus fold-and-thrust belts, separated across most of their length by the Transcaucasian depression. The whole sub-horizontal shortening of the Caucasus was quantified at hundreds of kilometers and, according to several studies, reached its maximum rate in the Miocene-Pliocene. At present, convergence between the Eurasian and African-Arabian plates is still active, producing widespread deformation within the mountain belt and in surrounding regions, as testified to by seismological, paleoseismological and GPS data.

Understanding the active tectonics of the Caucasus is of paramount importance for a better assessment of geohazards, especially seismic hazard. Moreover, there is a major concentration of residents in Tbilisi, the capital of Georgia, hosting 1.2 million citizens, and in Baku, the capital of the Azerbaijan Republic, with over 2.3 million citizens; both cities are located in active tectonic basins at the southern foothills of the GC. Hundreds of rural villages are scattered in the mountain regions, and all were built without taking into consideration antiseismic criteria. All the above shows that the Caucasus and Transcaucasus regions are subject to an extreme seismic hazard and risk.

Here, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, structural-geological and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, activeWNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, although swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus.

How to cite: Pasquaré Mariotto, F., Tibaldi, A., Bonali, F. L., Corti, N., Pedicini, M., Gulam, B., and Nino, T.: Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2168, https://doi.org/10.5194/egusphere-egu24-2168, 2024.

EGU24-3078 | Orals | TS3.3 | Highlight

Differences in earthquake size distributions for thrusts and normal faults: the case of Italy 

Michele M. C. Carafa and Matteo Taroni

The earthquake size distribution is characterized by an exponential function determined by the b-value parameter. Previous studies have demonstrated the dependence of the b-value on both the differential stress and tectonic settings. This study proposes a novel approach to categorize earthquakes based on the kinematics of interseismic geodetic strain rates and horizontal stress directions. When combined with other geological or geophysical information, incorporating stress directions and geodetic data enhances seismotectonic models, reducing arbitrariness in delineating seismic zones.

Using the Italian peninsula as a case study, we observe a significantly larger b-value for extensional faults than thrusts, albeit with smaller differences than previously reported. Additionally, our findings reveal that the spatial fragmentation of uniform tectonic regimes can lead to inaccurate b-value estimates for single faults due to the undersampling of earthquake size distribution.

How to cite: Carafa, M. M. C. and Taroni, M.: Differences in earthquake size distributions for thrusts and normal faults: the case of Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3078, https://doi.org/10.5194/egusphere-egu24-3078, 2024.

In this research, we combine seismic and tectonic approaches in an attempt to apply the empirical relationships between fault parameters and earthquake magnitudes aiming to assess the maximum possible magnitude for the prediction of intensity ground motion in the areas close to active faults. The case we study is the Talysh area in southern Azerbaijan with the total area of 3960 km². It stretches to 38054'N northern latitude and 48035'E eastern longitude and spreads to the north through the Alborz mountains of Iran. The earthquakes with a higher depth are concentrated mainly in the central part of the Talysh zone (up to 70 km) and in the southwestern part of the Caspian Sea (up to 55 km), with the local magnitude range of up to M5.5.

The earthquake magnitudes calculated on the basis of the surface fault length were compared with the catalogued magnitudes. As a procedure, (1) a comprehensive catalogue of all available known faults was compiled; (2) earthquake magnitude is then derived from fault length; (3) the resulting fault-length-earthquake-magnitudes were compared by the mathematical difference with catalogued earthquake magnitudes; and (4) as a final, intensity simulation of ground motion on near-fault areas was plotted. The results show the approximate consistence of the calculated fault-length-earthquake-magnitude with the catalogued seismicity. The map shows that the highest intensity areas of VII are observed in the central and western parts of the zone. An intensity VI covers majority of the Talysh zone. The results will contribute to the implementing more solid analyses for advancing seismic hazard analysis. Our research emphasizes the seismotectonic areas in southern Azerbaijan where further comprehensive studies on faults are required.

How to cite: Babayev, G., Aliyev, Y., and Aliyev, M.: Magnitude and intensity simulation of ground motion on near-fault areas: the case of Talysh (southern Azerbaijan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3646, https://doi.org/10.5194/egusphere-egu24-3646, 2024.

EGU24-5338 | ECS | Posters on site | TS3.3

A dynamic identification of continuous discontinuities in geodynamic numerical models 

Valeria Fedeli and Anna Maria Marotta

 Discontinuities affect the Earth’s dynamics, yet the Earth is often represented in geodynamical models as a continuous material. The challenge of representing discontinuities in numerical models has been addressed in several ways in literature. The split node method, originally introduced by Jungels (1973) and Jungels and Frazier (1973) for elastic rheology and then modified by Melosh and Raefsky (1981) to simplify its implementation, allows the introduction of discontinuity into a finite element model by imposing an a-priori slip at a designated node, where the displacement depends on the element which the node is referred to. Originally, this method requires that the discontinuity’s geometry and slip are pre-established.

More recently, Marotta et al. (2020) modify this approach by introducing a coupling factor that indicates the percentage difference between the velocities of the element to which the slip node belongs, while the velocity consistently derives from the dynamic evolution of the system. However, this method still requires the pre-establishment of the discontinuity’s geometry.

We here present a new technique that enables the dynamic identification of the discontinuity’s during the thermomechanical evolution of the system, based on physical parameters and without predefining the slip or the geometry.

We have implemented a new algorithm that identifies one or more discontinuities in a finite-element scheme operating through two phases: nucleation and propagation. Nucleation involves selecting a yield physical property and identifying the potential slip nodes, i.e., nodes on which the chosen physical property exceeds a yield value. The nucleus is then identified as the potential slip node where the chosen property most exceeds the yield. Propagation can be performed by choosing between three approaches of propagation: single simple fault, multiple simple fault and single double fault; and three schemes for the identification of neighboring nodes: grid-bounded, pseudo-free and free. The resulting discontinuity is the line connecting the nucleus and the propagation nodes.  Once the discontinuity has been identified, a coupling factor is introduced and the algorithm continues to operate following the Marotta et al., (2020)’s scheme.

The results of several benchmark tests, performed through both simple and complex finite-elements models, confirm the success of the algorithm in recognizing yield conditions and introducing a discontinuity into a finite-element model and demonstrate the correctness of the propagation’s geometry.

References

Jungels P.H.; 1973: Models of tectonic processes associated with earthquakes. PhD thesis.

Jungels P.H., Frazier G.A. Frazier; 1973: Finite element analysis of the residual displacements for an earthquake rupture: source parameters for the San Fernando earthquake. Journal of Geophysical Research.

Marotta A.M., Restelli F., Bollino A., Regorda A., Sabadini R.; 2020: The static and time-dependent signature of ocean-continent and ocean-ocean subduction: The case studies of Sumatra and Mariana complexes. Geophysical Journal International.

Melosh H.J., Raefsky A.; 1981: A simple and efficient method for introducing faults into finite element computations. Bulletin of the Seismological Society of America.

How to cite: Fedeli, V. and Marotta, A. M.: A dynamic identification of continuous discontinuities in geodynamic numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5338, https://doi.org/10.5194/egusphere-egu24-5338, 2024.

EGU24-6061 | Orals | TS3.3

Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China). 

Martine Simoes, Christelle Guilbaud, Jérôme Van der Woerd, Guillaume Baby, Laurie Barrier, Haibing Li, and Jiawei Pan

The Tibetan Plateau stands as a prominent topographic feature at the Earth’s surface, characterized by intense seismic activity, in particular along the mountain ranges that form its bounding edges. To the northwest, the Western Kunlun Range has received increasing attention since the 2015 Mw 6.4 Pishan earthquake but its kinematics of deformation remain to be properly documented. Here, we analyse the terrace record of active deformation along the Karakash River, where it crosses the Hotan anticline. We date terraces using in-situ produced cosmogenic isotopes, and show that terrace incision and uplift are spatially correlated with blind duplex ramps beneath the anticline. From there, we quantify the overall slip rate of the duplex to be 1.2-2.8 mm/yr over the last ~250 kyr. Our data are not able to resolve the detailed kinematics on each blind ramp and we cannot exclude that several of them are active at places along the anticline. By comparison to the data available west of our study area, we propose that the blind structures all along the foothills of the Western Kunlun range have an overall slip rate of ~2 mm/yr. However, the way this slip rate is to be partitioned on one or several blind ramps is expected to vary along strike, generating a certain structural and kinematic segmentation of active deformation, and from there possibly explaining the moderate recorded seismicity in this region. Because this slip is transmitted upward and forward onto the Mazar Tagh wide and geometrically simple frontal thrust sheet, we question the possibility of large – but rare – earthquakes rupturing this structure. From there, we propose the idea of a bimodal seismicity in the region, as a mirror of the structural segmentation of active faults.

How to cite: Simoes, M., Guilbaud, C., Van der Woerd, J., Baby, G., Barrier, L., Li, H., and Pan, J.: Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6061, https://doi.org/10.5194/egusphere-egu24-6061, 2024.

EGU24-6563 | Orals | TS3.3

Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines 

Deborah Di Naccio, Cinzia Di Lorenzo, Marco Battistelli, Simona Miccolis, Vanja Kastelic, and Michele MC Carafa

In the past decade, seismic hazard assessment has progressively relied on innovative approaches based on seismotectonic models for robust physical-based short-term and long-term estimations. For this reason, consistency and homogenization are crucial in collecting data for a scientifically sounding seismotectonic model, especially when dealing with large amounts of information at different temporal and spatial scales. Additionally, a solid probabilistic approach is needed to correctly explore the uncertainties of the seismotectonic model components (e.g., offset, age, long-term slip rate). In this contribution, we focus on the active tectonics of the central Apennines because they have been repeatedly investigated in past decades, and a significant amount of complementary data is available. In such a case, we can define an innovative fault database for seismic hazard assessment, exploring in a probabilistic sense the deformation data (age and offset) and rate (long-term slip rate). Our approach provides a substantial methodological upgrade to fault-based input for seismic hazard assessment. The proposed methodology can be easily exported to zones with scarce data availability.

How to cite: Di Naccio, D., Di Lorenzo, C., Battistelli, M., Miccolis, S., Kastelic, V., and Carafa, M. M.: Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6563, https://doi.org/10.5194/egusphere-egu24-6563, 2024.

EGU24-6771 | Posters on site | TS3.3

Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia 

Victor Alania, Onise Enukidze, Nino Kvavadze, Anzor Giorgadze, Demur Merkviladze, Alexander Razmadze, and Tornike Xevcuriani

The Greater Caucasus orogen is a typical active double wedge orogen that accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Our study area is a central part of the Greater Caucasus pro-wedge and represented by the Dzirula-Imereti Uplift zone and epicentral area of Racha 1991 (MW=7) and 2009 (MW=6) earthquakes - Southern Slope of Greater Caucasus. Here we present a new structural model based on interpreted seismic profiles and regional balanced cross-sections. Seismic reflection data reveals the presence of a basement structural wedge, fault-related folds, triangle zones, and active- and passive-roof duplexes. The most important observation from our study is that the Dzirula massif is a basement wedge and forms a triangle zone. The Dzirula structure is defined by mid-crustal detachment and a roof thrust, constituting a tectonic wedge with a passive back thrust. The regional balanced cross-sections show that the Racha earthquakes are related to crustal-scale duplexes.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Alania, V., Enukidze, O., Kvavadze, N., Giorgadze, A., Merkviladze, D., Razmadze, A., and Xevcuriani, T.: Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6771, https://doi.org/10.5194/egusphere-egu24-6771, 2024.

EGU24-7249 | Orals | TS3.3

Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt 

Daniele Cheloni, Nicola Angelo Famiglietti, Cristiano Tolomei, Riccardo Caputo, and Annamaria Vicari

On September 8, 2023, a magnitude 6.8 earthquake impacted the High Atlas Mountains in western Morocco, approximately 70 km southwest of Marrakesh, resulting in significant devastation and casualties. This study delves into a comprehensive geodetic dataset, utilizing interferometric synthetic aperture radar (InSAR) measurements to analyze the fault segment accountable for the seismic occurrence. Our findings propose two potential fault scenarios: a transpressive NNW-dipping high-angle fault (70°), associated with the Tizi n’Test alignment, or a transpressive SSW-dipping low-angle fault (22°) linked to the North Atlas Fault, where slip (up to 2.2 m) is observed predominantly in deeper sections of the fault. Although seismic catalogs were inconclusive regarding the dip direction of the fault, evidence from mainshock locations, gravity and heat-flow data, along with modeling, and the active shortening direction, collectively indicate the activation of a low-angle, southwesterly dipping oblique thrust of the North Atlas fault during the 2023 Moroccan earthquake. Integrating interferometric analyses with geological, tectonic, and seismological data could be crucial for resolving ambiguities in satellite-based models. This study therefore underscores the complexity of fault identification and the need for a multidisciplinary approach in understanding seismic events.

How to cite: Cheloni, D., Famiglietti, N. A., Tolomei, C., Caputo, R., and Vicari, A.: Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7249, https://doi.org/10.5194/egusphere-egu24-7249, 2024.

EGU24-7666 | ECS | Orals | TS3.3

Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians). 

Martin Šutjak, Rostislav Melichar, Ivo Baroň, Yi-Chin Chen, Jan Černý, Jia-Jiyun Dong, Václav Dušek, Filip Hartvich, Lenka Kociánová, Tung Nguyen, Matt Rowberry, and Chia-Han Tseng

The Outer Western Carpathians are fractured by several syn-thrust and post-thrust faults. One of them, the Mikulov Fault, has been studied using a combination of surface and subsurface methods. The former comprised the analysis of a LiDAR digital terrain model and aerial photographic interpretation while the latter comprised the analysis of ERT profiles and 2D seismic reflection profiles interpreted with the aid of borehole data. Paleostress analysis has also been used to understand the stress history and progressive development of the fault. By combining these methods it has been possible to define a distinct N-S directed fault zone that intersects or delineates the majority of the Jurassic limestone nappe outliers around the highlands of Pavlov Hills. This almost continuous fault zone runs for several kilometers on the Czech side of the border and extends further south into Austria. The thrusted Jurassic limestone bodies are cut by the fault zone, which tectonically crushed the limestone in its core and the cores of the secondary fault branches. The mapped pattern of the fault zone suggests branching and reattaching with the production of lenticular tectonic slices. Consequently, we interpret the fault as a prominent sinistral shear zone. This is indicated on the surface by block displacement on Svatý kopeček Hill and by the orientation of the accompanying subvertical Riedel shears with identified horizontal lineation. Subsurface kinematic indication derives from the interpretation of a prominent negative flower structure in the deep seismic profiles, just beneath the fault zone. The ERT profiles have revealed that the limestone bodies are tectonically bound by accompanying fault branches. Moreover, paleostress analysis suggest that fault zone activity can be divided into three main stages: (i) NE-SW thrust faults indicate thrusting of the Carpathian accretion wedge over the Bohemian Massif; (ii) NE-SW strike-slip faulting, during which the fault blocks moved along the faults in the direction of propagating wedge; (iii) N-S strike-slip faulting, marking the change in compression direction and transition from thrusting to a strike-slip regime. The main movement along the fault is probably of the late Miocene age and probably continues to the present day.

 

The research was funded by the Grant Agency of the Czech Republic (GC22-24206J).

How to cite: Šutjak, M., Melichar, R., Baroň, I., Chen, Y.-C., Černý, J., Dong, J.-J., Dušek, V., Hartvich, F., Kociánová, L., Nguyen, T., Rowberry, M., and Tseng, C.-H.: Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7666, https://doi.org/10.5194/egusphere-egu24-7666, 2024.

EGU24-7731 | ECS | Posters on site | TS3.3

Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations 

Xianwei Zeng, Chunquan Yu, and Gongheng Zhang

The 2021 MS 6.4 Yangbi earthquake occurred near the southwestern boundary of the Chuandian block in the SE Tibetan Plateau. Previous studies found that the mainshock occurred to the west of the main boundary fault – the Weixi-Qiaohou-Weishan fault, but the detailed seismogenic structure of the Yangbi earthquake sequence remains unclear. Accurate spatiotemporal characteristics of aftershocks and precise fault-zone structure are crucial for a more thorough understanding of the seismogenic structure and nucleation mechanisms of the Yangbi earthquake. Five days after the mainshock, we deployed a dense array with 200 short-period nodal seismometers spaced approximately 2 to 3 km in the vicinity of the Yangbi earthquake source region. In this study, we use the three-month-long continuous recordings of the dense array to study aftershock source parameters and fault-zone structures. We first obtained an earthquake catalog containing 88934 high-resolution event locations and 625 high-quality focal mechanisms. The entire aftershock sequence has a complete magnitude of -0.2, and a b-value of 0.97, with earthquake depths concentrated between 1 and 7 km below sea level. Combining precise aftershock locations and focal mechanisms, we constructed a detailed three-dimensional fault-zone structure model for the Yangbi earthquake sequence. The results reveal significant geometric variations in both strike and dip directions of the main fault. Along the dip direction, a conspicuous flower-like structure is present in the shallow part, transitioning to a listric structure inclined to the southwest at deeper levels. Along the strike direction, a noticeable bend exists in the central part. Several conjugate or intersecting faults are also present around the main fault. One of these faults, intersecting the main fault at a depth of about 4 km and dipping to the northeast, is likely the seismogenic fault of the largest foreshock. Additionally, below the main fault, there is another listric fault which appears to connect to the known Weixi-Qiaohou-Weishan fault at the surface. Our study provides new insight into the mechanism of the 2021 Yangbi earthquake sequence. The 3D fault-zone geometry can potentially be used for dynamic source modeling to better understand the initiation and rupture process of the mainshock.

How to cite: Zeng, X., Yu, C., and Zhang, G.: Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7731, https://doi.org/10.5194/egusphere-egu24-7731, 2024.

EGU24-7828 | Orals | TS3.3

3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia  

Onise Enukidze, Victor Alania, Nino Kvavadze, Alexandre Razmadze, Anzor Giorgadze, and Demur Merkviladze

The Rioni foreland basin system is located between the Lesser Caucasus (LC) and the Greater Caucasus (GC) orogens. Deformation of the Rioni double flexural foreland basin was controlled by the action of two opposing orogenic fronts, the LC retro-wedge to the south and the GC pro-wedge to the north (Alania et al., 2022). The Rioni foreland fold-and-thrust belt (RFFTB) is part of the Greater Caucasus pro-wedge.  Here we show the deformation structural style of the RFFTB based on seismic reflection profiles and serial structural cross-sections. On the basis of serial structural cross-sections, 3-D structural models. 2-3D structural models show that the Rioni foreland is a thin-skinned fold-and-thrust belt and the main style of deformation within the RFFTB is represented by a set of fault-propagation folds, duplexes, and triangle zones. The presence of two detachment levels in the RFFTB raises important questions about the deformation sequence. The serial structural cross-sections show that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. The formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. Recent earthquake data indicate that the RFFTB is still tectonically active and earthquake focal mechanisms within the RFFTB are thrust faults (Tsereteli et al., 2016), and active structures are mainly represented by thrust faults, blind thrusts, and blind wedges. 

Acknowledgments. This work was funded by the Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

References

Alania, V., et al. (2022). Deformation structural style of the Rioni foreland fold-and-thrust belt, western Greater Caucasus: Insight from the balanced cross-section. Frontiers in Earth Science 10, 10968386.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328–344.

How to cite: Enukidze, O., Alania, V., Kvavadze, N., Razmadze, A., Giorgadze, A., and Merkviladze, D.: 3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7828, https://doi.org/10.5194/egusphere-egu24-7828, 2024.

EGU24-8289 | ECS | Orals | TS3.3

Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy) 

Tiziano Volatili, Veronica Gironelli, Lucia Luzi, Paolo Galli, Michele Carafa, and Emanuele Tondi

The Inner Abruzzi region ranks among Italy's highest seismic hazard areas, hosting a system of SW-dipping normal faults historically active with moderate-to-large earthquakes (Mw ≥ 5.5). The L’Aquila earthquake in April 2009 (Mw = 6.3) intensified interest in assessing active fault seismogenic potential. Despite extensive studies, the Maiella Massif's historical seismicity, notably the 1706 and 1933 earthquakes (Mw ~6.8 and 5.9, respectively), causing severe damage, remains elusive. The investigation of historical seismic events, such as the 1706 earthquake within the Maiella area, aligns with the pressing need to identify and characterize potential seismogenic sources of future seismic activity. This task is often hindered by the scarcity of unambiguous evidence or quantitative data at both near-surface and seismogenic depths. Many source hypotheses, possibly related to the 1706 earthquake, are present in the literature. These structures, with different geometrical parameters, depths, and kinematics, characterized the tectonic setting of this region.

This study offers a comprehensive overview of these hypotheses in assessing the 1706 earthquake’s source. Their 3D geometrical representation was modelled, considering the available geological and geophysical information. The resultant seismic scenarios were estimated in terms of macroseismic intensity by calculating peak ground motion values (i.e., PGV, PGA) for each point within the 1706 macroseismic field. This procedure incorporates site amplification effects into the synthetic ground motion calculations at each site within the macroseismic field, coupling a Vs,30 map of the Italian territory. Finally, the determination of the best source model involves assessing the misfit (residuals) between the simulated macroseismic intensities and the observed ones. The accuracy of the simulated macroseismic field in reproducing the real field is evaluated by calculating the residual mean and the root-mean-square error (RMSE).

The study outcomes highlight the complexities in determining the exact source of the 1706 earthquake. Despite detailed modelling efforts, discrepancies in intensity distributions and the absence of recent seismic activity on specific faults pose uncertainties in understanding seismicity in the Inner Abruzzi area. While contributing to the ongoing debate, the research underscores the need for further investigations to better constrain the seismic hazard of this region.

How to cite: Volatili, T., Gironelli, V., Luzi, L., Galli, P., Carafa, M., and Tondi, E.: Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8289, https://doi.org/10.5194/egusphere-egu24-8289, 2024.

EGU24-9839 | ECS | Posters virtual | TS3.3

Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China 

Nianfa Yang and Zonghu Liao

Characterizing the structures of buried faults is inherently challenging due to a lack of data. However, the seismic survey has demonstrated the potential to reveal geometrical features of faults in the subsurface. In this study, we utilized three-dimensional seismic data and its associated attributes of variance, edge detection, and azimuth for investigating the distribution and structural characteristics of the buried faults in the Bohai Basin, eastern China. The results indicate: (1) there are two 7-km NNE strike-slip carbonate faults (F1, F2, in the Figure) dominated in this region, with fault sub-systems of horst and graben, stepped combinations, and "Y"-shaped; (2) F1 fault is approximately 6.5km with a fault damage zone of about 0.75km in width, and F2 fault is about 7.5km with a fault damage zone of 1.0km in width; (3) The width of fault damage zones increases from south to north, with increasing fault displacement. The maximum fault displacements of F1 and F2 are estimated at 420m and 700m, respectively. We argue that fault displacement leads to the growth of fault damage zones, which potentially controls the evolution of fault architecture. The geometrical information from the subsurface may provide crucial insights for understanding the fault mechanisms and associated earthquakes.

Figure 1. (A) Seismic attribute map of edge detection and time structure showing the two carbonate faults (F1, F2); (B) Measured fault displacement and damage zone width along the fault striking direction of F1 and (C) F2.

How to cite: Yang, N. and Liao, Z.: Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9839, https://doi.org/10.5194/egusphere-egu24-9839, 2024.

EGU24-10101 | Posters on site | TS3.3

Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan  

Alessandro Tibaldi, Fabio Bonali, Federico Pasquaré Mariotto, Paolo Oppizzi, Nino Tsereteli, Hans Havenith, Gulam Babayev, and Tomáš Pánek

We present the main features of the frontal structure, known as Kur Fault, of the Plio-Quaternary Kura fold-and-thrust belt in the Greater Caucasus (Azerbaijan). The Kur Fault has been analysed thanks to geological-structural and geomorphological surveys of its whole length, integrated by a relocation of instrumental seismicity, data on historical seismicity, new focal mechanism solutions, and ambient vibration measurements across the fault trace. The in-depth study of the frontal structure can: i) provide insights into the shallow propagation of a regional reverse fault, ii) contribute to a better understanding of the earlier stage of development of a young continent-continent collision, and iii) have implications for seismic hazard assessment because the area is seismically active and hosts the most important infrastructure for energy production in the country. The results show that the fault deforms the surface for a total length of 123 km. The shallow expression is given by four main scarp segments, with a right-stepping arrangement, which have different structural significance; they are represented by an alternation of fault-propagation folds, folds with offset frontal limbs, and shallow faulting. Analyses of the age of deformed deposits and landforms suggest activity from Mid-Late Miocene times to the Holocene. The fault attitude and its reverse kinematics are coherent with the Holocene and present-day state of stress, characterised by a N-S to NNE-SSW horizontal s1, suggesting the capability for seismic reactivation. Earthquake focal mechanism solutions indicate from pure reverse motions to transpressional kinematics in the area. Calculation of potential Mw indicates values in the range 7.5-7.9 if we consider its entire fault length, 6.1-7.2 if we consider the single segments.     

How to cite: Tibaldi, A., Bonali, F., Pasquaré Mariotto, F., Oppizzi, P., Tsereteli, N., Havenith, H., Babayev, G., and Pánek, T.: Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10101, https://doi.org/10.5194/egusphere-egu24-10101, 2024.

EGU24-10669 | Posters on site | TS3.3

Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy) 

Cinzia Di Lorenzo, Michele Carafa, Deborah Di Naccio, and Vanja Kastelic

The large amount of long-term fault slip rate measurements allows for determining the long-term tectonic moment rate for the central Apennines (Italy). Converting the long-term moment rate in seismicity rates requires a correct estimation of the long-term seismic coupling due to aseismic creep, possibly responsible for some of the observed dislocations. Ignoring this issue could induce a gross overestimation of the regional seismic hazard. Consequently, we must quantify the fraction of tectonic deformation released as earthquakes to correctly use the fault-based approach for forecasting long-term seismicity and assessing the seismic hazard of a region. To this aim, we introduce the seismic coupling in the calculation and treat it as a statistical variable. The probabilistic approach also considers the uncertainties in each parameter of active faults (depth of seismicity cutoff, length, and slip rate). The parameters of a regional Tapered Gutenberg-Richter distribution are determined to reproduce the observed earthquake size distribution. We found that about three-quarters of the long-term tectonic moment rate goes into earthquake activity, suggesting a non-marginal role of aseismic deformation for active faults in the central Apennines.

How to cite: Di Lorenzo, C., Carafa, M., Di Naccio, D., and Kastelic, V.: Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10669, https://doi.org/10.5194/egusphere-egu24-10669, 2024.

EGU24-11665 | Posters on site | TS3.3

Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy) 

Rita de Nardis, Alessandro Vuan, Luca Carbone, Donato Talone, Maria Adelaide Romano, and Giusy Lavecchia

Our study extensively explores the analysis of successive swarms and seismic sequences that followed the 2009 L'Aquila mainshock (Mw 6.3) in the southern-central Apennines of Italy—a region historically recognized for seismic events, some reaching ~M7.

The study area is characterized by active fault alignments well-documented in the geological literature. Bounded eastward by the Fucino-Marsicano-Barrea SW-dipping faults and westward by the southern termination of the Ernici NE NNE-dipping fault systems, it is also crosscut by the Villavallelonga-Pescasseroli–San Donato-Val Comino and the innermost right-stepping en-echelon Balsorano-Posta Fibreno sets, as well as the Sora fault.

Despite its active fault systems, the study area exhibits a low level of seismicity, prompting extensive investigation in previous experiments conducted by temporary seismic networks (Bagh et al., 2007; Romano et al., 2013) and more recent contributions by Frepoli et al. (2017). Notwithstanding, the paucity of seismicity, coupled with the deep geometry of faults and their association with historical earthquakes, remains a topic of ongoing debate in the literature.

Through the application of template matching techniques (Vuan et al., 2018) to enhance the available seismic catalog, we unveil previously undetected low-level seismicity with a completeness magnitude ML ~ 0.0. The space-time evolution of the intense seismicity, along with the characterization of each seismic episode, migration velocity, and Vp/Vs ratios, combined with the 3D distribution of seismicity and geological data, revealed both a clear tectonic influence and the role of fluids in seismic processes. This exploration illuminated previously unknown geometric aspects and provided the first evidence of the WNW-ESE deformation zone in the southernmost segment of the Villavallelonga fault at depths ranging from 11 to 15 km. Our results indicate that deeper seismicity (>16 km) suggests an ascending trend of possible mantle-derived CO2.

These findings significantly contribute: (1) to the understanding of tectonic seismic swarms in extensional domains, (2) to provide insights into fluid involvement in seismic processes, and (3) to the discussion of the seismotectonic setting in high seismic-risk areas. The acknowledgment of the value of microseismicity for regional seismotectonic studies serves as a compelling conclusion, underscoring the broader significance of these findings.

 

Bagh, S., Chiaraluce, L. et al. 2007. Background seismicity in the Central Apennines of Italy: The Abruzzo region case study. Tectonophysics, 444,80–92.

Frepoli, A, Cimini, G.B et al., 2017. Seismic sequences and swarms in the Latium-Abruzzo-Molise Apennines (central Italy): New observations and analysis from a dense monitoring of the recent activity, Tectonophysics, 312-329.

Vuan, A., Sugan, M., et al., 2018. Improving the Detection of Low‐Magnitude Seismicity Preceding the Mw 6.3 L’Aquila Earthquake: Development of a Scalable Code Based on the Cross Correlation of Template Earthquakes. BSSA 108, 471–480.

Latorre, D., Di Stefano, R., et al., 2023. An updated view of the Italian seismicity from probabilistic location in 3D velocity models: The 1981–2018 Italian catalog of absolute earthquake locations (CLASS): Tectonophysics, 846, 229664.

Romano, M. A., de Nardis, et al., 2013. Temporary seismic monitoring of the Sulmona area (Abruzzo, Italy): A quality study of microearthquake locations. NHESS, 13, 2727–2744.

How to cite: de Nardis, R., Vuan, A., Carbone, L., Talone, D., Romano, M. A., and Lavecchia, G.: Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11665, https://doi.org/10.5194/egusphere-egu24-11665, 2024.

EGU24-12862 | ECS | Posters on site | TS3.3

Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series 

Renier Viltres, Cécile Doubre, Marie-Pierre Doin, and Frédéric Masson

The present-day tectonics of the northernmost Africa region is dominated by the oblique convergence
between the Nubia and Eurasia plates initiated 35 Ma ago. GNSS-derived velocities indicate that the
relative plate motion of only ~5 mm/yr is accommodated within a wide region involving inland
and offshore tectonic structures, from Morocco to Tunisia and from the Mediterranean Sea to the Sahara
platform. Due to limited and sparse geodetic measurements, the main zones of strain accommodation as
well as the strain partitioning between thrust and strike-slip faults remain unresolved. However, despite
the low strain budget, significant seismicity and destroying earthquakes have been recorded in the region
with five M>6 events nucleated on both inland and offshore faults during the last decade.

To better identify the active inland faults and constrain their interseismic behavior for a better seismic
hazard assessment in northernmost Africa, we used multi-temporal InSAR analysis to produce the first
regional-scale interseismic velocity map of the region. The primary data consists of up to ~8 years of
SAR imagery from the Sentinel-1 satellite constellation for 6 tracks in both the ascending and descending
orbits. The data processing and the generation of InSAR-based time series describing the spatio-temporal
evolution of surface deformation were performed using the New Small Baselines Subset processing chain
(NSBAS, Doin et al. 2011). We followed a three-blocks processing strategy leading to (1) interferograms
generation, (2) phase unwrapping, and (3) time series estimation. Within the first block, interferometric
networks combining image pairs with short and long temporal baselines were defined to mitigate potential
bias introduced by changes in soil properties (e.g., snow, vegetation growth, dunes). Before unwrapping,
interferograms flattening, multi-looking, and atmospheric phase screen (APS) corrections based on the
ECMWF ERA-5 atmospheric model were implemented. The resulting time series of surface displacement
along the line-of-sight direction (LOS) for the 2014-2022 period were decomposed into the near-vertical
and horizontal (E-W) components and expressed into a Eurasia-fixed reference frame using the GNSS
velocities in Billi et al. (2023).

Our estimated deformation maps reveal multi-scale present-day motions, with large- and small-scale
signals suggesting tectonic origin and ground response to anthropogenic activity or landslides, respectively.
The oblique plate convergence involves the interseismic loading of a series of E-W oriented right-lateral
strike-slip inland faults. Between the longitudes ~3°W and ~9°E, this inland deformation is localized
within a 25-75 km wide zone consistent with a unique linear strike-slip fault without any clear uplift related
to thrusting on already mapped transfer structures. The rates and directions of surface displacements
suggest that the shortening component of the Nubia-Eurasia relative plate motion is almost entirely
accommodated by offshore tectonic structures which has an important impact on the assessment of
seismic and tsunamigenic hazards.

 

 

How to cite: Viltres, R., Doubre, C., Doin, M.-P., and Masson, F.: Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12862, https://doi.org/10.5194/egusphere-egu24-12862, 2024.

EGU24-13778 | Orals | TS3.3

Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array 

Wei-Hau Wang, Yi-Shen Lin, Wei-Cheng Huang, and Strong Wen

We employed dense seismic arrays to reveal the seismogenic zones beneath the foreland basin and the foothills in southwestern Taiwan. We used EqTransformer to pick earthquakes and P and S wave arrival time, GaMMA to associate earthquakes, and NonLinLoc to locate the earthquakes. Our results show that the thin-skinned thrust belts were mostly locked above a shallow decollement at a depth of ca. 6 km. Below it, a foreland-dipping seismogenic belt extends from the base of the shallow decollement to a depth of about 15 km, the deep decollement, beneath the coastal plain. We interpret this westward-dipping seismogenic belt as a passive roof duplex by inversion of the pre-existing graben-and-horst structure sliding along a ductile shear zone at a depth of 15 km during the ongoing orogeny.

How to cite: Wang, W.-H., Lin, Y.-S., Huang, W.-C., and Wen, S.: Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13778, https://doi.org/10.5194/egusphere-egu24-13778, 2024.

EGU24-13981 | Posters on site | TS3.3

Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence 

Chung-Hsiang Mu, Ching-Chou Fu, Hao Kuochen, Kuo-Hang Chen, and Kuo-Wei Chen

Our goal is to comprehend fluid circulation within fault zones and its impact by monitoring hydrochemical and hydrophysical aspects across multiple dimensions. We also monitor nearby micro-seismicity and surface deformation. MAGIC (Multidimensional Active fault of Geo-Inclusive observation Center) is located at the Chihshang creeping fault, situated at the boundary of tectonic plates in eastern Taiwan. This fault exhibits aseismic creep at a rate of 2 cm per year, alongside high seismic activity.

The earthquake sequence of 2022 began with a magnitude 6.4 event on September 17 (local time), followed by a magnitude 6.8 earthquake the next day. The epicenters were within the Central Range fault system, positioned to the west of our monitoring network. This presents a significant opportunity to observe co-seismic changes in pore pressure within the footwall and fault zone.

The findings revealed that after the initial earthquake in the adjacent fault system, the pore pressure within the footwall swiftly decreased by nearly 100 cm within 15 hours. Simultaneously, the pore pressure within the fault zone increased by approximately 25 cm during the same period. Subsequently, the footwall's pore pressure continued to decrease with the second earthquake and then slowly recovered. These alterations in pore pressure suggest that fractures underwent both opening and closure during stress migration.

How to cite: Mu, C.-H., Fu, C.-C., Kuochen, H., Chen, K.-H., and Chen, K.-W.: Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13981, https://doi.org/10.5194/egusphere-egu24-13981, 2024.

EGU24-14319 | Posters on site | TS3.3

Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea 

Seongjun Lee, Youngbeom Cheon, Jong-won Han, Sangmin Ha, Jeong-Heon Choi, Yeong Bae Seong, Hee-Cheol Kang, and Moon Son

The 2017 Pohang earthquake (ML 5.4) ranked as the second-largest instrumental earthquake in Korea and the most destructive seismic event. Before this event, the absence of documented instrumental seismic activity and no mapped Quaternary faults near the epicenter raised questions about the paleoseismic history of the region. This study aims to gather and trace evidences of the paleoseismic ruptures along the surface projection of seismogenic fault, reported by previous study, and interpret their implications. To achieve it, we conducted comprehensive paleoseismological investigations, including geomorphic analysis, fieldwork, drilling survey, trench excavation and numerical age dating. Through geomorphic analysis and drilling survey, we identified two lineaments: NNE–SSW-striking Fault-1 and NE–SW to NNE–SSW-striking Fault-2. In the excavation site of fault-1, stratigraphic features and numerical ages indicate that the PE event occurred between 11±1 ka and 2.6±0.1 ka, and then the MRE event activated after 0.17±0.01 ka.  On the other hand, the combined results of two outcrops of Fault-2 show that the MRE and PE of Fault-2 could be constrained to have occurred between 148±7 ka and ca. 40 ka and around 200 ka, respectively. Our findings present that even before the 2017 Pohang earthquake, seismic events causing surface ruptures of moderate to large magnitude have occurred at least three times in this area during the late Quaternary.

This work was supported by a grant (2022-MOIS62-001) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, South Korea).

How to cite: Lee, S., Cheon, Y., Han, J., Ha, S., Choi, J.-H., Seong, Y. B., Kang, H.-C., and Son, M.: Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14319, https://doi.org/10.5194/egusphere-egu24-14319, 2024.

Kvarner area belongs to the External Dinarides fold-and-thrust belt that is characterized by intensive tectonic deformations of a few kilometers thick sedimentary cover of the central part of the Adriatic microplate. The main deformations occurred predominantly during Eocene to Oligocene thin-skinned tectonics, while late-orogenic thick-skinned deformations and wrenching resulted in the exhumation of the orogenic belt. The latter tectonic mechanism is supposed to be still active, but there is no reported evidence of active faults on the surface of predominantly karstic terrain. Nevertheless, seismological data reveal subsurface activity along various fault plane solutions, and crucial evidence of possible active deformations on the surface is expected within stratified superficial deposits in the area. However, stratified Quaternary sediments are rare onshore and on the Kvarner islands but are widespread on the bottom of the surrounding Adriatic Sea. During the targeted high-resolution sub-bottom geoacoustic seismic survey we focused on the zones that are characterized by earthquakes and on the previously arbitrarily recognized regional seismogenic sources. However, only shallow seismic profiles along and across the Vinodol and the NW part of the Velebit channel revealed clear evidence of fault-related deformations of the youngest Quaternary sediments. The fault zone is up to hundreds of meters wide, limited by parallel sub-vertical fault planes, and characterized by deformations of the strata between the planes either in a positive (uplifted) or a negative (downthrown) manner along the strike, which are typical for strike-slip faults. Besides, the disturbed layering of the uppermost well-stratified unit (Late Pleistocene) resembles fluid/sediment escape structures that could be related to strong shaking during prehistorical earthquakes. The fault zone is also tentatively recognized in the onshore bedrock along the strike of the submerged fault, where it appears as an indistinct fractured zone that is more corroded than surrounding bedrock carbonates. Therefore, sub-bottom profiling has been proven to be a useful tool for identifying active faults and should be used as a key method in future seismotectonic research of submerged seismogenic zones.

How to cite: Korbar, T., Hasan, O., Brunović, D., and Markušić, S.: High-resolution seismic imaging of the sub-bottom Quaternary deposits revealed an active fault in the Vinodol-Velebit channel (Kvarner, Croatia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14660, https://doi.org/10.5194/egusphere-egu24-14660, 2024.

To better understand seismotectonic processes and the associated seismic hazards within a region, it is imperative to explore the causality between earthquakes, active tectonics, and individual fault structures. Hypocenter locations represent a well-established method to identify active faults, their spatial geometry and temporal evolution. First motion focal mechanisms provide insights into source processes and fault kinematics, aiding in the reconstruction of seismic strain and seismogenic stress regimes. Waveform modelling is key to refine earth structure models and constrain source process parameters.

Here, we present the challenging case of the seismic sequence of Saint-Ursanne of March and April 2000 in Switzerland, where we applied advanced seismological analyses to reduce uncertainties in hypocenter locations and focal mechanisms, commonly encountered in shallow seismicity. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which has been approved as a site for the development of a deep geothermal project. Our results, combined with geological data, suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the sequence. These new findings provide new insights into the present-day seismotectonic processes of the Jura fold-and-thrust belt (FTB) of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely <0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement. This transpressive regime is confirmed by the ongoing Réclère earthquake sequence, ca. 20 kilometres west of St. Ursanne, which initiated with a reverse event of ML 4.1 on December 24, 2021, and was followed by few aftershocks in January 2022. Seismic activity started again in March 2023 with another ML4.3 reverse event, which activated a left-lateral strike-slip secondary fault just west of the reverse fault. This fault seems to be more active in terms of microseismicity and is responsible for the increased activity over the last years.  

How to cite: Lanza, F. and Diehl, T.: Deciphering seismic sequences with high-precision hypocenter locations, focal mechanisms, and waveform modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14739, https://doi.org/10.5194/egusphere-egu24-14739, 2024.

EGU24-14973 | Orals | TS3.3

Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area 

Barreca Giovanni, Pepe Fabrizio, Sulli Attilio, Morreale Gabriele, Gambino Salvatore, Gasparo Morticelli Maurizio, Grassi Sabrina, Monaco Carmelo, and Imposa Sebastiano

Archaeoseismic analysis performed in Western Sicily point to deformed archeological remains at Lilybaeum, a Punic coastal city founded in 397 B.C. at the Island’s westernmost edge. Starting from the direct observation of deformed ruins, an interdisciplinary work-strategy, which has included field-structural analysis, drone-shot high-resolution aerial photogrammetry, and geophysical prospecting, was employed to investigate whether the identified deformations may represent the ground effects of a previously unknown large earthquake in the area. Among the unearthed remains, some mosaics and a stone-paved monumental avenue show evidence of tectonic deformation being fractured, folded, and uplifted. Trend of folding and fracturing is consistent with the NNW-SSE oriented tectonic max stress axis to which western Sicily is currently undergoing. Displacement along a fracture deforming the Decumanus Maximus together with the finding of a domino-type directional collapse, enable us to interpret the observed deformation as the ground signature of a coseismic slip. Seismic rupture occurred along a previously unmapped deformation front that well fits in the seismotectonic context of Western Sicily. Measured offset, geophysical prospecting, and age-constraints all point to the possibility that a highly-energetic earthquake nucleated in the area following a coseismic rupture along a NE-SW trending back-verging reverse fault towards the end of the IV century A.D. Since seismic catalogs do not provide evidence of such a large earthquake, the latter might represent a missed event in the historical seismic record. This finding provides constraints to redefine the seismic hazard of Western Sicily, a region where recurrence-time intervals for large earthquakes are still unknown.

How to cite: Giovanni, B., Fabrizio, P., Attilio, S., Gabriele, M., Salvatore, G., Maurizio, G. M., Sabrina, G., Carmelo, M., and Sebastiano, I.: Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14973, https://doi.org/10.5194/egusphere-egu24-14973, 2024.

EGU24-15305 | Posters on site | TS3.3

Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy) 

Mara Monica Tiberti, Francesco Emanuele Maesano, Mauro Buttinelli, Pasquale De Gori, Fernando Ferri, Liliana Minelli, Maria Di Nezza, and Chiara D'Ambrogi

In the Central Apennines (Italy), the project RETRACE-3D provided a reliable 3D model of the crust in the area affected by the 2016-17 Amatrice-Visso-Norcia seismic sequence, highlighting that the coseismic rupture at the surface can involve old inherited normal faults while the seismogenic sources lay at depth, possibly reactivating and inverting previous thrust faults, as in the case of the Mw 6.5 Norcia earthquake (30 october 2016). Here we present a 2D gravity model across the Central Apennines, spanning from the Tyrrhenian coast to the Adriatic Sea, aimed at completing and verifying the crustal geometries resulting from the 3D model itself. The cross-section was built integrating different types of data, such as surface geology, hydrocarbon wells, seismic lines, and results from receiver function analysis. It was then checked against gravity anomalies and the velocity distribution from Local Earthquake Tomography (LET), adding further details, and, finally, against seismicity recorded during the 2016-2017 sequence. The results substantiate the reliability of the geometries proposed in the RETRACE 3D model, as they fit well, except for some local misfits, with the other independent data, such as the Bouguer anomalies and the velocity distribution from LET. Furthermore, the integration of different types of data allowed us to describe in detail the structural setting of the Apennine chain also in the surroundings of the RETRACE study area, where the cross-section length exceeds the 3D model, and to add some new elements at seismogenic depths, that exceed those typical of hydrocarbon exploration. In particular, we were able to investigate the nature of the basement top and its relationship with seismotectonics.

How to cite: Tiberti, M. M., Maesano, F. E., Buttinelli, M., De Gori, P., Ferri, F., Minelli, L., Di Nezza, M., and D'Ambrogi, C.: Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15305, https://doi.org/10.5194/egusphere-egu24-15305, 2024.

Outer Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, followed by an Mw 5.1 aftershock 10 minutes later considered as foreshocks, and culminated with the main shock Mw 6.38 on 26 November 2019, preceded by several immediate foreshocks (Mw 2.0-4.4), followed by numerous aftershocks (Mw > 5.0). We model the co-seismic slip distribution using InSAR, permanent and campaign GNSS measurements. Two hypotheses are tested: an earthquake on a thrust plane with direction N160°, and an earthquake on a backthrust. Varying the depth and dip angle for the first hypothesis and only the dip angle for the second, it is concluded that the optimal solution is a blind thrust at a depth of 15 km with an eastward dip of 40°, a maximum slip of 1.4 m and a Mw of 6.38. The GNSS time series obtained after 2020 shows two slow slip events (SSE): the first 200 days after the main shock up to about 26 days, and the second 300 days after the main shock up to about 28 days. We tested three hypotheses: SSE occurred along the basement thrust where the main shock was localised, SSE occurred along the flat formed by the detachment layer of the cover, and SSE occurred along these two faults. It has therefore been concluded that SSE has occurred along the detachment layer or along both the detachment layer and the basement thrust activated during the Mw 6.38 Durres earthquake.

How to cite: Matraku, K., Jouanne, F., and Dushi, E.: The 26 November 2019 Durres earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15944, https://doi.org/10.5194/egusphere-egu24-15944, 2024.

EGU24-16075 | ECS | Posters on site | TS3.3

Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults 

Nino Kvavadze, Victor Alania, and Onise Enukidze

The Caucasus region, which is one of the good examples of collision-driven far-field deformations, is located in the northernmost part of the Arabia/Eurasia collision zone and is classified with moderate seismic activity. Racha region, a part of Greater Caucasus orogen, in particular is characterized with the highest activity. In recent year several moderate earthquakes were observed in the region, notably 2009 September 7 (Mw = 6.0), 2011 August 18 (Mw = 4.8), and also 2024 January, 2 (Mb = 4.4), with depths varying from 10 to 15 km. The strongest event during the instrumental period recorded in Racha was observed in 1991 April 29, with magnitude Mw=7.0 and Depth = 17.2 km. Which was the largest earthquake recorded in the region, causing casualties. This event caused a number of fore- and aftershocks. Following the Racha 1991 earthquake temporary, dense seismic network was installed around the area to study aftershock activity, around 2000 aftershocks of different magnitudes were recorded by this network in total. This data was analyzed in several papers (for example Triep, et al., 1995, Fuenzalida, et al., 1997), including hypocenters and focal mechanisms. Depths of the aftershocks were observed ranging from 0 to 15 km. The mechanism of Racha 1991 main shock was shown to be reverse faulting on a gently sloping (35°) plane. Also, strong earthquake mechanisms show reverse faulting with strike-slip components. This work was oriented to analyze existing earthquake data and see its correlation to a 2-3D structural model created for the area.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Kvavadze, N., Alania, V., and Enukidze, O.: Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16075, https://doi.org/10.5194/egusphere-egu24-16075, 2024.

EGU24-16527 | ECS | Posters on site | TS3.3

First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses 

Giulia Patricelli, Maria Eliana Poli, Emanuela Falcucci, Stefano Gori, Giovanni Paiero, Enzo Rizzo, Andrea Marchesini, and Riccardo Caputo

We present the findings of a multimethodological study made on the Budoia-Aviano Thrust System conducted as part of the NASA4SHA PRIN Project “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy”.

The NW dipping, SW-NE striking Budoia-Aviano Thrust System represents the southeast-verging external front of the Plio-Quaternary Eastern Southalpine Chain, occurring at the front of the western Carnic Pre-Alps, between Polcenigo and Montereale (PN).

The recent activity of the Budoia-Aviano thrust is evidenced by numerous geological and morphostructural features, including the exposure of Mio-Pliocene reliefs emerging from the Last Glacial Maximum alluvial plain, the upwarping of the LGM fan of the Artugna stream, and geomorphic anomalies of the surface hydrographic network (Poli et al., 2014).

Moreover, to identify sites to perform excavation aimed at exploring the Holocene movements of the thrust system, we performed multiscale geophysical investigations, such as Deep Electric Resistivity Tomography, Electric Resistivity Tomography and Ground Penetrating Radar across the entire thrust system. They revealed the presence of a series of possible north-verging shear planes, whose trace seemed to correspond to the more pronounced up-ward convex profile of the Artugna alluvial fan.

Based on geophysical results, two NNW-SSE paleoseismological trenches were excavated along selected GPR profiles. The trenches exposed late LGM-to-Holocene alluvial fan deposition of the Artugna stream. Notably, a paleosoil embedded in alluvial sequence yielded a 14C age interval between 16 Ky and 5 ky BCE.

In both trenches, the entire excavated late Quaternary succession was affected by a set of north-verging reverse planes, coinciding with the discontinuities identified in GPR profiles. In each trench, the total vertical displacement measured across all thrust planes is of about 4.5 meters, resulting from at least three displacement events occurred in the last 7,000 years. Moreover, the involvement of the bottom of the ploughed soil supports the hypothesis of the backthrust being activated during the MW 6.3 Alpago-Cansiglio earthquake (Rovida et al., 2022) as suggested by Galadini et al. (2005).

The integration of paleoseismology, photogrammetry, and high-resolution geophysics enabled the construction of a detailed 3D model of the Budoia-Aviano Thrust System, revealing a 20-meter-wide deformation zone on the hanging wall of the main south-verging Budoia-Aviano Thrust. In the perspective of seismic hazard assessment and regional planning, it is worth to consider the proximity of this active and capable fault to industrial complexes, urban centres, and vulnerable structures characterizing the Budoia and Aviano area.

REFERENCES

  • Galadini, M.E. Poli, Zanferrari, A. (2005). Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy). Geophysical Journal International161(3).
  • M.E. Poli, G. Monegato, A. Zanferrari, E. Falcucci, A. Marchesini, S. Grimaz, P. Malisan, E. Del Pin (2014). Seismotectonic characterization of the western Carnic pre-alpine area between Caneva and Meduno (Ne Italy, Friuli). DPC-INGV-S1 Project.
  • Rovida, M. Locati, R. Camassi, B. Lolli, P. Gasperini, A. Antonucci (2022). Catalogo Parametrico dei Terremoti Italiani (CPTI15), versione 4.0. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/CPTI/CPTI15.4

How to cite: Patricelli, G., Poli, M. E., Falcucci, E., Gori, S., Paiero, G., Rizzo, E., Marchesini, A., and Caputo, R.: First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16527, https://doi.org/10.5194/egusphere-egu24-16527, 2024.

EGU24-17289 | ECS | Orals | TS3.3

Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images 

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

Large strike-slip earthquakes are usually modeled as slip on localized planar fault planes within a homogeneous or layered elastic half-space. However, geodetic fault-slip inversions often show a shallow slip deficit, where the maximum slip is found at a depth of several kilometers with gradually decreasing slip towards the surface. High-resolution satellite images of earthquake surface ruptures also suggest a reduction in on-fault slip, often termed as off-fault damage or distributed deformation. In this study, we refer to this reduction in near-fault deformation as surface absent deformation (SAD). The presence of coseismic SAD, due to off-fault damange and/or compensated for by shallow interseismic fault creep and afterslip, holds significance for earthquake rupture processes, paleoseismology, and earthquake hazard assessments.

In our study, we quantify the SAD along the main ruptures of the magnitude 7.8 and 7.6 Kahramanmaraş earthquakes, which occurred on 6 February 2023 near the Türkiye-Syria border, by mapping coseismic three-dimensional (3D) surface displacements using differential interferometry and pixel tracking of satellite synthetic aperture radar (SAR) images. The two earthquakes had a combined rupture length of approximately 500 km, exhibiting multi-meter surface fault offsets and diverse fault geometries, necessitating high-resolution deformation mapping near and away from the fault. We obtained the SAD distribution by analyzing fault-perpendicular profiles of fault-parallel displacement from the SAR-derived 3D displacements. For each profile, an arctan function was used to predict the near-fault (e.g., 0-5 km) elastic displacement based on the far-field (e.g., 5-50 km) observations, yielding an estimate of the lack of deformation close to the fault (i.e., the SAD). The results reveal a clear correlation between SAD and geometrical complexities along the two co-seismic ruptures. Using this strategy to determine the SAD, we find that about 35% of the surface fault slip is “missing” and expressed as SAD within a distance of 5-7 km from the coseismic surface ruptures. By comprehensively analyzing the interseismic, coseismic, and postseismic deformation in this area, we find that shallow interseismic fault creep and afterslip cannot explain the coseismic SAD and that it appears to be dominated by off-fault damage. Notably, existing research on off-fault damage has been concentrated within a range of only 1-2 km. Our results therefore underscore the significance of extending investigations of off-fault damage to 5-10 km from fault ruptures, and suggest that relying solely on on-fault offset measurements may lead to an underestimation of fault slip rate estimations by as much as one third.

How to cite: Liu, J., Jónsson, S., Li, X., and Klinger, Y.: Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17289, https://doi.org/10.5194/egusphere-egu24-17289, 2024.

EGU24-19541 | Orals | TS3.3

Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy) 

Pierfrancesco Burrato, Andrea Brogi, Paola Vannoli, Martina Zucchi, Umberto Fracassi, Gianluca Valensise, Hsun-Ming Hu, and Chuan-Chou Shen

We explored the behaviour and earthquake potential of an active fault system in the slowly deforming part of southern Tuscany. This region corresponds to the eastern margin of the Siena Basin, a Neogene structural depression that developed during the extensional tectonics that affected the inner northern Apennines. Here, N-, NE- and WNW-trending faults were active during the Zanclean-Latest Quaternary. Clear evidence of the activity of these faults, particularly the most recent WNW-striking ones, is represented by faulted Late Pleistocene-Holocene travertine deposits that preserve also evidence of active seismogenic faulting. Indeed, this area in recent times was mostly interested by low-magnitude seismic sequences that occurred in the uppermost 10 km of the crust, mainly characterized by transcurrent and transtensive faulting mechanisms. However, the historical record includes also damaging earthquakes in the 5.0-6.0 Mw range, such as the 7 August 1414, Mw 5.7, Colline Metallifere, 13 April 1558, Mw 6.0, Valdarno Superiore, and 25 August 1909, Mw 5.3, Crete Senesi events, but, to date, very little is known about the geometry, maximum earthquake potential and slip rate of their causative faults.
In this study, we characterize an active, capable, and seismogenic fault system identified in the saw-cut walls of an active travertine quarry near Serre di Rapolano, a few kilometres south-east of the city of Siena. To document the geometric and kinematic features of the active faults, we carried out a detailed geological and structural field survey of the quarry outcrop, collected samples for U-Th dating and constructed a virtual outcrop model. We found compelling evidence for nearly SW-NE surface-breaking faulting, perpendicular to the main structural fabric of the central and northern Apennines, whose activity extends at least into the Upper Pleistocene. The peculiar geology of the area also suggests that these faults have generated earthquakes associated with surface faulting, namely the occurrence of clastic dykes injected within the fault zones during earthquake-induced liquefaction.
Our results may help to address the current lack of understanding concerning earthquake activity in the slowly deforming region, and improve the current knowledge of the seismotectonic setting of the Siena Basin and the corresponding part of the inner northern Apennines. Our findings hint to a still unexplored tectonic mechanism, which suggests that the earthquakes affecting this part of southern Tuscany may be caused by segments of rather elusive, very long, SW-NE and WNW-ESE lineaments crossing the entire Apennine stack.

How to cite: Burrato, P., Brogi, A., Vannoli, P., Zucchi, M., Fracassi, U., Valensise, G., Hu, H.-M., and Shen, C.-C.: Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19541, https://doi.org/10.5194/egusphere-egu24-19541, 2024.

EGU24-20372 | Orals | TS3.3

FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023) 

Martin Zeckra, Lahcen El Moudnib, Abderrahime Nouyati, and Sebastián Carrasco

The 2023 Mw 6.9 Al Haouz Earthquake in the Moroccan High Atlas mountains is the most recent example of a destructive event in an intraplate setting under the absence of a causative plate boundary. Their large inter-event times in such seismotectonic regimes hinders the study of single focus regions and apparently underestimates their larger seismic hazard potential, leaving local communities unaware of the scale of their exposure to these risks. One major shortcoming in the immediate scientific analysis of this unprecedented earthquake is the lack of (publicly) available seismic waveform recordings in the source area.

An immediate impact is displayed in the source location uncertainty, including a high variability in focal depth estimations. Associating the earthquake origin to a causative fault remains puzzling, bearing in mind the deeper-than-average focal depth of around 32 km. The complex tectonic history of the Atlas mountain chains is depicted in a plethora of active, reactivated and abandoned faults. In addition, prior studies noticed a lithospheric anomaly underneath the High Atlas mountain range, that lacks a classical mountain root. Thus, this event raise questions on the thermo-elastic parameters at depth in order to support a large seismogenic thickness of the crust.

In the immediate aftermath of the Al Haouz, we initiated a rapid-response task force for setting up a temporal seismic network in the High Atlas. Within two weeks, six autonomous seismological stations have been installed between 20 and 80 km from the estimated epicenter. Due to the large degree of destruction, problematic access and absence of major infrastructure in the epicentral region, we relied on autarkic and robust sensors. As a novelty, the stations consisted of SmartSolo® three component 5 Hz geophone sensors. These industrial-level instruments are light-weight and easy to deploy in any terrain. In a compact casing, the passive sensors host digitizer, data storage, GPS and battery life-time of up to 30 days.

Here, we present the first data of this 2 months temporary network. Based on preliminary analysis, we could obtain more than 1000 events recorded on all stations of the network during the 54 recording days. The largest recorded events had an assigned magnitude of ML 4.5. Considering single stations detections as well, we estimate more than 10,000 earthquake detections overall. This catalog will greatly expand the scientific insight into the mechanisms of this exceptional earthquake in the near-future.

Further, through the use of simple geophone sensors this study presents a proof of concept for rapid response installations of temporary aftershock network. These sensor types strongly outperform the fully elaborated counterparts in installation speed, transportability and external requirements for potential installation sites without large drawbacks in data quality.

How to cite: Zeckra, M., El Moudnib, L., Nouyati, A., and Carrasco, S.: FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20372, https://doi.org/10.5194/egusphere-egu24-20372, 2024.

EGU24-20764 | Orals | TS3.3

POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain 

César R. Ranero, Paraskevi Nomikou, Filomena Loreto, Irene Merino, Valentina Ferrante, Danai Lampidou, Elisavet Nikoli, and Serafeim Poulos

The cruise POSEIDON from 10-22 June 2023, mapped the tectonic structure of the region extending from the western Peloponnese across the Ionian Islands. This is one of the most complex and comparatively little evaluated regions, with demonstrated seismic hazard, in the Mediterranean.

The region contains a complex fault system with numerous strands controlling much of the submarine and subaerial relief and with dramatic lateral changes in deformation rates. The fault system has produced large earthquakes, mostly offshore, recorded during the past few decades in the Greek national seismological network. However, the largest recent Mw~6.8-7.0 Kephalonia 1953 event was recorded in few stations available then. This earthquake - possibly the most destructive in recent Greek history - cause the collapse of ~85% of all buildings on Kephalonia Island, ~1k deaths, and ~145k people homeless. However, the 1953 earthquake is poorly understood compared with more recent, albeit less destructive events. The epicentre of the 1953 event is not well constrained, and the location and dimensions of the causative fault are unknown. Likewise, the hypocenter depth of the 1953 event thrust-fault focal mechanism, that occurred E or SE of Kefalonia, is defined from <50 km to <20 km, depending on the analysis. Studies in the islands interpret active shallow thrusting to propose that the 1953 event ruptured the upper 5 km of several shallow faults, but such a rupture cannot explain a Mw~6.8-7.0 even.

The goal of POSEIDON is to define the regional fault system structure and kinematics and to place it in the proper geodynamic context that helps understand hazards and eventually evaluate associated risks. The DEM displays a rugged terrain from the Ionian Islands to the Peloponnese Peninsula, with numerous features that indicate active deformation across the entire region. Major submarine tectonic structures around the islands trend from NE-SW to NNW-SSE, similar to the basins and ranges on the islands. Elongated shallow troughs offshore laterally project to the relief trends on the islands, supporting widespread active faulting.

A further complication in the research area is that the upper-crust fault system, might be located above, or sole into, a mega-thrust plate boundary fault of the Hellenic subduction zone, inferred -in publications- to dip in a NE direction at ~25-40 km depth under the surface. However, the location of a mega-thrust seismogenic zone is yet not well constrained. POSEIDON seismic data image the tectonic features in the crust and integrated with the high-resolution bathymetry allow to define the main faults across the offshore region in unprecedented detail.

Acknowledgements

We acknowledge the professional and dedicated work of the National Institute of Oceanography and Applied Geophysics (OGS-Trieste) technical party and the technical party of the Marine Technology Unit (UTM) from the Spanish National Research Council (CSIC) to make the experiment a success. We also acknowledge the professional and dedicated work of the master, officers and crew of the R/V Laura Bassi during the POSEIDON experiment.

How to cite: Ranero, C. R., Nomikou, P., Loreto, F., Merino, I., Ferrante, V., Lampidou, D., Nikoli, E., and Poulos, S.: POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20764, https://doi.org/10.5194/egusphere-egu24-20764, 2024.

EGU24-63 | ECS | PICO | TS5.2

Harmonic Dynamic of the Earth 

Xianwu Xin

The Harmonic Motion Phenomenon of the Earth is introduced through Experiments: Under the Combined Action of Tidal Force and the Earth's Rotation, Continental Unit Body Segments, like Caterpillars, actively crawl westward on the Mantle. Based on the Force Analysis of the Earth Motion Process and the Generalized Hooke's Law, the Harmonic Motion Equation and the Crustal Motion Equation of the Earth are derived, also the Conversion Equation of Continental Drift Datum has been derived. The Velocity Field of Continent Latitudinal Movement is calculated, and compared with the Measured Value of ITRF2000 station. From the Perspective of Kinematics, it is proved that the Harmonic Motion of the Earth is the Basic Dynamic Mechanism of the crust and inside of the Earth Movement. The Degree of Dominance which this Dynamic Process to Continental Drift is 72% to 97.4%. It's Energy comes from the Rotation Energy of the Earth. Using the results of Motion Calculation to was reconstructed the Proto Ancient Continent, that was it moment of started cracked at before 250 million years. In addition, the Driving Force Equation of the Earth’s Harmonic Motion is derived. Discussed the Driving Force accumulation process and the formation mechanism of Earthquake: The Thrust of the Rock Stratum to the Hindered Portion slowly increases with the Creep between stratus and the Successive Compression each time it from Peak Point to Valley Point. Continuously increase the Elevation and Area of the Compression Zone. When the Driving Forces Accumulation reaches the Limit of the Strength of the Hindered Rock Stratum, sudden movement or Fracture Occurs, and an Earthquake formation. Earthquakes are a Process of Concentrated Energy Release. In High-Temperature and High-Pressure Areas within 700km underground, when Earthquakes, some Rocks melt to form Magma, and driven by Harmonic Motion, enriches westward along Rock Fractures and enters the Ocean Ridges Bottoms and the Below of the Volcano. The Magma of Below the Volcano erupts from the Earth's Surface after increasing Pressure. The Magma at the Bottom of the Ocean Ridge is driven by the Footpath Board Effect and moves upwards along the Cracks, and Condensed on the Surface of the Sidewall, when change the Gaps of the Cracks along with the Ocean Floor Undulating, the Ocean Floor on Both sides of the Ocean Ridge is pushed apart from each other. This kind of process of Ocean Floor Fluctuate Spreading leads to Gradual wear and tear of the Ocean Floor, Ultimately Subducting beneath Land or trenches and returning to the Mantle. In Passive Mantle Convection and Ocean Floor Fluctuate Spreading, the Driven Force of Magma flow is provide by the Earth's Rotation through Fluctuate Processes, magma does not output Power. At last, according to the Driving Force Equation of Earth‘s Harmonic Motion, the Energy Conversion Equation is given. The Total Power of Earth‘s Harmonic Motion is calculated, and compared with the Relevant Measured Values. It is further proved from the Perspective of Dynamics and Energy Conversion: The Harmonic Dynamic Proces of the Earth is the Basic Dynamical Proces of Tectonic Movement.

How to cite: Xin, X.: Harmonic Dynamic of the Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-63, https://doi.org/10.5194/egusphere-egu24-63, 2024.

Fold-and-thrust belts (FTBs) evolve over a mechanically weak basal décollement that separates overlying intensely deformed rocks from the underlying less deformed or undeformed rocks. Although fold-and-thrust belts are often considered laterally cylindrical in nature, a closer inspection reveals remarkable variations in structural style (e.g., fold geometry) both along and across the strike of mountain belts. Using crustal scale thin-sheet laboratory experiments, this study focuses on the role of laterally varying coupling strength of the basal décollement on the evolution of structural styles in natural FTBs. In this study, we used a rectangular slab of silicon putty, a linear viscous material, of uniform thickness in all experiments to simulate the crustal section and the models were deformed at a uniform convergence velocity of ~7.649 × 10-5 ms-1. Analyses of experimental results show remarkable changes in the wedge growth with the introduction of along strike variations in décollement strength. The segment of the deforming wedge over weakly coupled décollement propagates at a faster rate towards the frontal direction compared to the laterally continuous segment over a strongly coupled décollement, leading to an overall sinuous geometry of the deformation front. In contrast, an approximately linear deformation front represents a condition of uniform along-strike coupling strength at the basal décollement. Based on our experimental results, we argue that the broad arcuation of the mountain front along the eastern margin of the Zagros fold-thrust belt (i.e., Fars arc region) might have resulted due to along strike variations in the décollement strength, while the occurrence of a linear deformation front from the central to western margin of the fold-and-thrust belt represents a segment of the wedge with a uniform coupling strength at the basal décollement. Our experimental results can be carefully used to explain the cause of strike-wise segmentation of tectonic processes in orogenic belts, variations in topography and earthquake activities.   

How to cite: Roy, S., Willingshofer, E., and Bose, S.: Influence of lateral variations of décollement strength on the structure of orogenic wedges: insights from experimental viscous wedge models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3310, https://doi.org/10.5194/egusphere-egu24-3310, 2024.

With the wide application of high-quality three-dimensional (3-D) seismic volumes in hydrocarbon exploration, it has been found that a special type of fault system, i.e., conjugate strike-slip fault system, is often developed in the Cratonic basins (e.g., Tarim Basin, Sichuan Basin, and Ordos Basin in China). They not only can directly indicate the principal stress direction, but also play a crucial role in controlling the transport and formation of hydrocarbons in the basin. Analysis of 3-D seismic data revealed that the Tarim Basin exhibited typical X-shaped (symmetrical) and asymmetrical (two sets of faults differing greatly in number) conjugate strike-slip fault systems. However, there is a lack of analogue models on the geometries and progressive evolution of conjugate strike-slip faults, as well as a poor understanding of the mechanisms of asymmetric conjugate strike-slip fault systems. Additionally, previous experiments have not been compared with such natural examples.

Based on the structural analysis of strike-slip faults in the Tarim Basin using seismic reflection data, we used three sets of symmetric (rectangular shape) and two sets of asymmetric (parallelogram shape) rubber basement models to investigate the geometries and progressive evolution of conjugate strike-slip faults. In this study, our research successfully modelled the kinematic and geometric evolution of different types of conjugate strike-slip fault systems, and found that they have the same acute angle and that the direction of their angular bisectors is parallel to the direction of contraction. In symmetric models, we observed the development of numerous typical X-shaped conjugate strike-slip faults were developed. Conversely, the development of two sets of faults in the asymmetric models showed an asymmetry, i.e., one set of faults was more obviously developed than the other, and with the degree of asymmetry increased, the asymmetry was even more obvious. Furthermore, we analysed the stress state of the models using the Mohr space and inferred that the stress state of the model changed from the strike-slip in the early stages to the extension in the later stages.

We proposed two synoptic models, namely, the symmetric conjugate strike-slip fault system (SCSFS) model and the asymmetric conjugate strike-slip fault system (ACSFS) model, for conjugate strike-slip fault systems based on the results of the different models. The models and experimental results were compared with natural examples of the two sets of strike-slip fault systems in the Tabei uplift in China’s Tarim Basin, which exhibited many strong similarities in their structural geometries, and they also provided further insight into the mechanisms of strike-slip faults in the Tabei uplift. These synoptic models proposed based on the analogue models may provide useful templates for the seismic interpretation and mechanism of different types of conjugate strike-slip fault systems in nature and for inferring the orientation of the maximum principal stress.

How to cite: Xiao, K. and Tong, H.: Analogue modelling of conjugate strike-slip faults in the Cratonic basin: A case from the Tarim Basin, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3751, https://doi.org/10.5194/egusphere-egu24-3751, 2024.

Fault evolution is influenced by multiple factors, including the reactivation of pre-existing structures, stress transmission within ductile detachment layers, and the growth, interaction, and connection of newly formed fault segments. In the same stress field, displacement vectors of fault strikes, dip-slip vectors, and subtle fractures accommodate strain distributed everywhere. This study employs PIV analysis and model reconstruction to simulate oblique extensional fault systems formed at four different angles. Simulation modelling indicates that oblique extensional reactivation of pre-existing structures controls the linear arrangement of fault segments in the overlying strata. Arcuate faults can be classified into linear master fault segments controlled by pre-existing structures, curved splay faults in termination zones, and normal fault segments responding to regional stress fields. Along-strike displacement is regulated by linear segments within the master strike-slip fault, while progressive bending of splay faults, relay ramps' dislocation, and inclined displacements are regulated by relay ramps within the overlap zone. Small-angle (15°) oblique extension favours the formation of fault segments with distinct step-like features, leading to additional relay ramps. In contrast, high-angle (60°) oblique extension often results in the development of more continuous fault segments. As faults continuously evolve, new fault segments tend to deviate from the control of pre-existing structures, concentrating more on the development of planar and continuous master faults. Finally, we compared the established model with the transtensional fault system within the intraplate rift system in eastern China, demonstrating that the oblique extension angle controls the composite characteristics of the overlying strata faults.

How to cite: Wang, Y. and Yu, F.: The Linkage Evolution of Strike-Slip Faults with Normal Faults—Insights from Analogue Modelling at Various Oblique Extension., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4813, https://doi.org/10.5194/egusphere-egu24-4813, 2024.

EGU24-6667 | ECS | PICO | TS5.2

Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting:  

Mouad Ankach, Mohamed Gouiza, and Khalid Amrouch

The Atlas fold and thrust belt extend from the Atlantic rifted margin of Morocco to Tunisia over a distance of 2500km. Before its inversion in the Cenozoic to the present, the Atlas system evolved initially as a rift basin that opened simultaneously with the Atlantic rift in the west and the Tethys in the north, during the upper Triassic-Jurassic period.

The Western High Atlas is believed to be influenced by the Atlantic Ocean (also known as the Atlantic domain), where the Triassic to Early Jurassic strata are considered to be syn-rift, while the Middle Jurassic to Cretaceous deposits are labelled as post-rift. In contrast, the Marrakech High Atlas (MHA), Central High Atlas (CHA), Middle Atlas (MA), and the Eastern High Atlas (EHA) are assumed to be influenced by the Tethys Ocean (also known as Tethyan domain), where the Triassic to Jurassic sediments are considered to be syn-rift. This implies that the Mesozoic rifting along the Atlas was diachronous, making it difficult to determine the exact timing and kinematic of crustal stretching. Constraining the extensional phases in the Atlas system is crucial for understanding how the Atlas crust was stretched and thinned. Our work aims to quantify the magnitude and regional kinematic of stretching in the Atlas system using various methods, namely, thickness variation method, subsidence analysis and palinspatic reconstruction of 2D cross-sections.

Our preliminary results indicate that the maximum stretching factor (beta factor) in the Atlas is β = 1.25; and that crustal thinning did not exceed 20%, based on tectonic subsidence analysis. While the palinspatic restoration suggest that the Moroccan Atlas system underwent approximately a uniform stretching with β = 1.11 in EHA (Midelt-Errachidia area), β = 1.08 in CHA (Imilchil area), and β = 1.12 in the East Marrakech High Atlas (EMHA: Demnat area). These values indicate that the Moroccan Atlas crustal thickness has been thinned by 9% in EHA, 8% in CHA, and 11% in EMHA. In addition, the geological context of the High and Middle Atlas regions, where the estimated shortening is reported to be less than 20%, the stretching factor (β) was calculated based on the crust thickness. The initial crustal thickness (IC) of the Meseta block, which constitutes one of the Atlasic rift shoulders, considered an undeformed area, served as a reference. Accounting for the observed shortening, the final crustal thickness was deduced by subtracting the reported shortening value representing 7.8 km from the observed crustal thickness (39 km), resulting in a β value of 1.25, which is consistent with the result obtained from the subsidence analysis.

Keywords: Atlas system, extension, stretching factor, Thinning factor,

 

 

 

How to cite: Ankach, M., Gouiza, M., and Amrouch, K.: Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting: , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6667, https://doi.org/10.5194/egusphere-egu24-6667, 2024.

EGU24-6869 | ECS | PICO | TS5.2 | Highlight

Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning 

Giacomo Mastella, Fabio Corbi, Jonathan Bedford, Elvira Latypova, Federico Pignalberi, Marco Scuderi, and Francesca Funiciello

Despite considerable progress in monitoring natural subduction zones, key aspects of megathrust seismicity remain puzzling, mainly due to the temporally incomplete and spatially fragmented available record. Scaled seismotectonic models yield valuable insights by spontaneously creating multiple stick-slip cycles in controlled, downscaled three-dimensional laboratory replicas. Here we report recent progress in analog modeling of the megathrust seismicity, particularly focusing on a meters-scale elasto-plastic model featuring a frictionally segmented, granular fault that mimics the subduction channel at natural subduction zones. We showcase how by employing analog materials under low-stress conditions, the potentialities of monitoring can be maximized using three diverse techniques: 1)  Precise monitoring of surface spatial deformation over time is achieved through digital image correlation techniques, mirroring a uniformly distributed dense geodetic network spanning land to trench in real subduction zones. 2) A Micro-Electro-Mechanical (MEMS) accelerometric network, emulating a seismic network, captures seismic wave propagation at the model surface. 3) Embedded piezoelectric sensors within the granular analog fault capture near-field acoustic signatures of frictional instabilities. These diverse monitoring techniques allow for investigating the consistency between continuous seismic activity and surface deformation data, offering insight into both micro and macroscopic features of analog seismic cycles. At the macroscopic level, the models' frictional behavior can be numerically reproduced via rate and state numerical simulations, considering earthquake fault slip as a nonlinear dynamical process dominated by a single slip plane. At smaller scales, the model accounts for complexities in fault slip emerging from grain interactions, reflecting nonlinearities that arise when considering faults as distributed three-dimensional volumes. These fundamental attributes, coupled with their capacity to create extensive catalogs of small labquakes, make scaled seismotectonic models exceptional apparati for employing Machine Learning (ML) in comprehending multi-scale spatiotemporal seismic processes. Cutting-edge Deep Learning methods are employed to predict the spatiotemporal evolution of surface deformation, where regression algorithms not only forecast timing but also the propagation and magnitude of analog earthquakes across diverse spatiotemporal scales. Given that one of the monitoring systems used in seismotectonic analog models mimics a geodetic-like network in nature (GNSS data-Global Navigation Satellite Systems), an attempt to generalize the promising outcomes achieved in the laboratory to natural subduction faults is proposed.  Such promising avenues emphasize the potential for ML to bridge the gap between laboratory experiments and real-world seismic events. These initial findings, combined with advancements in the instrumentation of fault laboratories in nature and expanding data reservoirs, reinforce the belief that ML can significantly augment our understanding of the multiscale behaviors of natural faults.

How to cite: Mastella, G., Corbi, F., Bedford, J., Latypova, E., Pignalberi, F., Scuderi, M., and Funiciello, F.: Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6869, https://doi.org/10.5194/egusphere-egu24-6869, 2024.

EGU24-7785 | ECS | PICO | TS5.2

Haromonic Curvature and Bedding Uncertainty Across Scales 

David Nathan, Mario Zelic, Eun-Jung Holden, Daniel Wedge, and Christopher Gonzalez

Observations of geological structures are often made at different scales and often can cross multple orders of magnitude. This attribute of scale though is often not explicitly incorporated into the workflow of geological modeling and is usually treated as data preparation or sampling bias. The spectral properties of the discrete Laplacian operator, when applied to reconstructed surfaces from implicit modeling though offer a potential means of bridging this gap, when also combined with appropriate directional statistical anaysis. We present an example of how bedding orientation measurements from a 1:5000 scale surface map and drillhole bedding orientation picks from borehole televiewer images can be integrated using the manifold harmonics of the Laplacian operator and a mixture of von-Mises Fisher probability distributions. This provides automated insights for sampling for modeling and also possible kinematic and tectonics processes.

How to cite: Nathan, D., Zelic, M., Holden, E.-J., Wedge, D., and Gonzalez, C.: Haromonic Curvature and Bedding Uncertainty Across Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7785, https://doi.org/10.5194/egusphere-egu24-7785, 2024.

This study investigates a fold-and-thrust belt (FTB) beneath the South Yellow Sea Basin, a noteworthy petroleum exploration target, featuring a basement high and a detachment layer. In the central basin, magnetic anomalies reveal the development of the basement high. Seismic reflection data, in conjunction with drilling information, disclose the presence of the Lower Silurian Gaojiabian Formation, exceeding ~500 m, acting as a low-cohesion detachment layer. However, the impact of these features on regional structures and the resulting hydrocarbon preservation conditions remains uncertain. This study explores the kinematic characteristics and deformation localization associated with the basement high and intermediate detachment using four sandbox models and particle velocity analysis within the FTB framework. Model 1, the reference, utilized pure quartz sand without either feature. Model 2 examined the role of the intermediate detachment using glass microbeads, revealing a limited effect in generating typical thin-skinned FTB. Model 3 considered the basement high and found that it strongly influenced the deformation regime of the wedge. Model 4 examined both features and suggested their combined influence on FTB deformation processes. In Model 2, lacking a pre-existing basement high, the intermediate detachment did not contribute to FTB deformation. In Model 3, lacking an intermediate detachment, deformation propagated along the surface of the basement high upon reaching its edge. In Model 4, shortening propagated upward along the edge of the basement high and then into the intermediate detachment, producing comparable structural geometry to the prototype, including both thick- and thin-skinned FTBs in nature. The results indicate that in the central South Yellow Sea Basin, structural layers between the basement high and detachment are likely to experience weak deformation; thus, favorable hydrocarbon preservation conditions can be anticipated in this region. This study holds significant importance in guiding future petroleum exploration efforts in the central South Yellow Sea Basin.

How to cite: Zhang, P., Fu, Y., and Yan, B.:  Influence of Basement High and Detachment on the Kinematics of a Fold-and-Thrust Belt in the Central South Yellow Sea Basin with Implications for Hydrocarbon Preservation: Insights from Analog Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8859, https://doi.org/10.5194/egusphere-egu24-8859, 2024.

EGU24-10540 | ECS | PICO | TS5.2

Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models  

Afonso Gomes, Filipe Rosas, Nicolas Riel, João Duarte, Wouter P. Schellart, and Jaime Almeida

Ophiolites are exposed remnants of oceanic lithosphere that are critical to our understanding of the structure, composition, and evolution of oceanic plates.

Some ophiolites (e.g., some Tethyan-type ophiolites) originate in the oceanic forearc of an intra-oceanic subduction system (i.e., in the overriding plate). If the trailing edge of the subducting oceanic lithosphere is connected to a continental passive margin, then that passive margin may also be subducted (beneath the forearc and proto-ophiolite) once all the oceanic lithosphere is “consumed” at the trench. The subduction of the continental passive margin means that a buoyant continental crust will underthrust the oceanic forearc (i.e., proto-ophiolite). This crust goes through a burial-exhumation cycle, and as it exhumes it can drag and detach the tip of the overlaying oceanic forearc, creating an ophiolite klippe. The exhumation-emplacement process is, however, still not fully understood, particularly regarding the constraints imposed by the forearc itself. For example, the detachment of the tip of the forearc (ophiolite) from the remainder of the plate should, at least in part, be controlled by the mechanical properties of the forearc (i.e., presumably the tip of a “weak” forearc will detach more easily than the tip of a “strong” forearc).

Present-day intra-oceanic subduction forearcs (i.e., present-day model-types for Tethyan-type ophiolites) experience significant chemical alteration induced by the circulation of metamorphic fluids originating from the dehydration of the underlying subducting plate. This chemical alteration occurs mostly in the form of serpentinization of forearc peridotites, leading to a substantial weakening of the forearc lithospheric mantle. The circulation of these fluids, and hence the serpentinization process, is thought to occur primarily along preexisting deeply rooted fault systems, further weakening these strain-localizing structures, although some diffuse alteration probably also occurs. It is then reasonable to assume that the paleo forearcs that originated Tethyan-type ophiolites were also subject to these chemical and mechanical alterations, which are then expected to have affected the ophiolite emplacement process.  

Here we present novel 2D and 3D dynamic numerical models that investigate the role of forearc weakening on ophiolite emplacement processes. Specifically, we test different mechanical weakening patterns, i.e., localized (serpentinized faults) vs homogeneous (diffuse serpentinization) weakening.

Preliminary results suggest that prior serpentinization of the forearc has a critical control on ophiolite emplacement. Furthermore, differing degrees of forearc serpentinization, as well as serpentinization distribution patterns, result in different tectonic regimes of ophiolite emplacement.

 

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and through scholarship SFRH/BD/146726/2019.

How to cite: Gomes, A., Rosas, F., Riel, N., Duarte, J., P. Schellart, W., and Almeida, J.: Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10540, https://doi.org/10.5194/egusphere-egu24-10540, 2024.

EGU24-12208 | PICO | TS5.2

Numerical and analogue modelling of boudinage under non-coaxial shear strain 

Filipe Rosas, Afonso Gomes, Jaime Almeida, João Duarte, Nicolas Riel, and Wouter Schellart

The recognition of different boudinage patterns is of key importance to the unravelling of the tectono-metamorphic evolution of different domains in different tectonic contexts and at different considered spatio-temporal scales.

The main reason for this is twofold: (1) Boudins tend to preserve the relic metamorphic conditions that characterize deformation prior to the one recorded by matrix fabrics and associated mineral associations. (2) Specially under shear deformation regimes, quarter-structure geometric patterns comprising rotated boudins and folded matrix planar fabrics, can be used to determine the shear sense of the later (sin-boudinage) deformation.

In the present work, we present preliminary numerical and analogue modelling results of boudinage, under non-coaxial (shear strain) deformation. We specifically investigate the potential influence of three main parameters on the genesis of different (boudins-folds) quarter structures patterns: i) the viscosity contrast between the boudin and the matrix; ii) the original position of the non-equidimensional boudin; and ii) the assumed (bulk) shear strain rate.

We proceed by presenting a preliminary comparison of our results with archetypical natural examples of boudinage, in different tectonic-structural contexts and at different scales, further illustrating the potential value of these type of structures in the unravelling of the deformation history in different situations.

Acknowledgements

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

How to cite: Rosas, F., Gomes, A., Almeida, J., Duarte, J., Riel, N., and Schellart, W.: Numerical and analogue modelling of boudinage under non-coaxial shear strain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12208, https://doi.org/10.5194/egusphere-egu24-12208, 2024.

EGU24-12468 | ECS | PICO | TS5.2

Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems  

Nemanja Krstekanic, Ernst Willingshofer, Antoine Auzemery, Liviu Matenco, and Jasper Smits

In subduction systems, asthenospheric flow, generated by subducting slabs, is considered as one of the key forces contributing to the deformation of the overlying lithosphere. Previous analogue modelling studies predominantly focused on understanding the kinematics and dynamics of subduction roll-back-driven asthenospheric flow, without looking at the influence of that flow on upper-plate deformation due to the modelling setups or methodological limitations. We developed a novel analogue modelling approach where gravity-driven asthenospheric flow represents the main driver for upper plate deformation. Volume-constant flow within the deformation box is achieved by an inlet-outlet system. In the models, we gradually increase the setup complexity from single-layer asthenosphere-only models to 4-layer asthenosphere-lithosphere models to test flow velocity distribution and its sensitivity to the outlet size, model thickness and rheological stratification of the model, as well as the transfer of deformation from the asthenosphere to the overlying lithosphere. Furthermore, we study the effects of the inherited lithospheric structures, such as weak zones representing old sutures, on deformation transfer. The results are compared with the Pannonian-Carpathians system of south-eastern Europe, where the large Pannonian back-arc basin formed during the Miocene retreat of the Carpathians slab.

For the methodological approach, the results show that asthenospheric flow can be fully controlled by the inlet-outlet system by adjusting the outlet size, which provides an efficient mechanism for the deformation of the overlying mechanically stratified lithosphere. The models also demonstrate that the back-arc extension is initiated farther away from the asthenospheric flow origin (i.e., the outlet in the models or slab-roll back in nature). The subsequent deformation propagates in two directions, towards the flow origin, and farther away from it, both directions controlled by the shape of an indenter located laterally to the subduction zone. Most of the back-arc extension and the lithospheric thinning are accommodated in the area farther to the “slab” due to the strain shadow effect of the indenter. The indenter also contributes significantly to the strain partitioning in its closer proximity where a complex pattern of bi-directional extension, transtensional, strike-slip and transpressional deformation forms. The weak zones accommodate the onset of back-arc extension or act as transfer zones between areas with different extension rates, depending on their orientation relative to the asthenospheric flow. These models show several similarities with the Pannonian-Carpathians system, where most of the Pannonian lithospheric thinning is located at a significant distance from the subducting Carpathians slab, bypassing the Transylvanian-Apuseni area. This extension started by reactivation of the Neotethys suture zone, while the Mid-Hungarian Fault zone transferred the deformation between areas of higher extension to the south and lower extension to the north. Furthermore, several triangular-shaped sub-basins within and at the margin of the Pannonian Basin are radially located around the Moesian NW corner, similar to our modelling results. The complex pattern of the bi-directional extension and strike-slip observed in the models were recorded by the Carpathians-Balkanides orocline in the vicinity of the Moesian indenter.

How to cite: Krstekanic, N., Willingshofer, E., Auzemery, A., Matenco, L., and Smits, J.: Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12468, https://doi.org/10.5194/egusphere-egu24-12468, 2024.

EGU24-13464 | ECS | PICO | TS5.2

A new geodynamic model of the Azores archipelago: preliminary results 

Jaime Almeida, João Duarte, Filipe Rosas, Rui Fernandes, Fernando Geraldes, Luis Carvalho, and Ricardo Ramalho

The Azores archipelago is an integral part of the Macaronesian geographic region (which also includes the volcanic archipelagos of Madeira, Selvagens, Canaries and Cape Verde). This region, located in the centre of Atlantic Ocean, has its individual islands spread around a triple junction, which has been suggested to affected by a plume-ridge interaction (Storch et al., 2020; Beier et al., 2022). One of the major questions surrounding its history concern the why/how the Terceira Rift (i.e., the NW-SE oriented connection between the mid-ocean ridge and the Gloria Fault Zone) was formed.

To explore this issue, we have run sets of 3D viscoelastoplastic models for the region using the state-of-the-art modelling code LaMEM (Kaus et al., 2016). As our objective was to evaluate how the geological data and the suggested evolution for the region fit geodynamic constraints. We based our numerical models on previously established evolutionary models for the region, such as the leaky transform model (Madeira and Ribeiro, 1990).

Preliminary results hint that the formation of the Terceira Rift could be formed as the result of a shift in the regional tectonic forcing, which we attribute to the collision between the Iberian and Eurasian plates. Furthermore, our results suggest that a strong rheological contrast in the region was required to ensure the localization of deformation. Models without this feature tended to maintain a simple E-W connection between the Gloria Fault Zone and the southern part of the mid-ocean ridge.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through projects GEMMA (https://doi.org/10.54499/PTDC/CTA-GEO/2083/2021) and national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

 

References

Beier, C. et al. (2022) ‘The submarine Azores Plateau: Evidence for a waning mantle plume?’, Marine Geology, 451, p. 106858. Available at: https://doi.org/10.1016/j.margeo.2022.106858.

Kaus, B.J.P. et al. (2016) ‘Forward and Inverse Modelling of Lithospheric Deformation on Geological Timescales’, NIC Series, 48, pp. 978–3.

Luis, J.F. and Miranda, J.M. (2008) ‘Reevaluation of magnetic chrons in the North Atlantic between 35°N and 47°N: Implications for the formation of the Azores Triple Junction and associated plateau’, Journal of Geophysical Research: Solid Earth, 113(B10). Available at: https://doi.org/10.1029/2007JB005573.

Madeira, J. and Ribeiro, A. (1990) ‘Geodynamic models for the Azores triple junction: A contribution from tectonics’, Tectonophysics, 184(3–4), pp. 405–415. Available at: https://doi.org/10.1016/0040-1951(90)90452-E.

Storch, B. et al. (2020) ‘Rifting of the oceanic Azores Plateau with episodic volcanic activity’, Scientific Reports, 10(1), p. 19718. Available at: https://doi.org/10.1038/s41598-020-76691-1.

How to cite: Almeida, J., Duarte, J., Rosas, F., Fernandes, R., Geraldes, F., Carvalho, L., and Ramalho, R.: A new geodynamic model of the Azores archipelago: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13464, https://doi.org/10.5194/egusphere-egu24-13464, 2024.

Eastern Sichuan fold belt, a prolific hydrocarbon province in China, shows the similar fold styles to the Swiss Jura Mountain fold belt, which’s therefore called as Jura-type fold by Chinese geologists. However, it’s still a matter of geologist’s debate on the formation mechanism of the eastern Sichuan fold belt.

To unravel how this type of fold trains form, a systematic scaled 2D contractional analogue experiments with composite materials were conducted. Silica-sand represents the overburden with added mica-flakes, and a stiff plasticine interlayer introducing different mechanical anisotropies. Viscous silicone rubber represents the salt detachment. The following 3 main issues have been investigated: 1) what type mechanical stratigraphy can form the fold train during lateral contraction; 2) what are the mutual interaction between faulting and folding during the formation process of detachment fold; 3)what are kinematics and its related strain distribution patterns for a detachment fold system.

The modelling results indicate that the presence of a stiff plasticine layer is the key perquisite for the formation of a concentric fold train for the following reasons: 1) it encourages the shortening to be periodically accommodated by sinusoidal-symmetric buckle folds at the inceptive folding stage; 2) it can keep the break-thrust ramps from being activated with further shorting delaying the development of faulted detachment folds at the later folding stage. As for silicone detachment, it mainly plays a role in the amplification of detachment folds via the redistribution of ductile material between the syncline and anticline domain.

DIC strain data show that the main sections of detachment fold-the limbs, especially in the forelimb, and the hinge are easily strained. More specifically, the normal faults and breakthrusts can form in the anticlinal hinge and limbs, respectively, when the detachment fold cannot be tightened any more. However, the strain is not easily accumulated in the syncline domain.

Our modelling result together with the latest interpretation of seismic reflection suggest that the eastern Sichuan fold belt is a result of faulted detachment folds, mainly controlled by the competence contrast within the overburden and the thickness of both the weak viscous detachment and strong brittle overburden.

Keywords: Eastern Sichuan Basin; Analogue modelling; DIC; Fold-thrust belt; Detachment fold

How to cite: Feng, G., Adam, J., Chen, S., and Wang, X.: Key controlling factors on the formation of Jura-type fold in eastern Sichuan Basin, South China: insights from analogue modelling with optical strain monitoring (Digital Image Correlation), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13637, https://doi.org/10.5194/egusphere-egu24-13637, 2024.

EGU24-13652 | ECS | PICO | TS5.2

Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling 

Nuno Rodrigues, Filipe Rosas, Nicolas Riel, Jaime Almeida, Afonso Gomes, and João Duarte

Continental collision occurs when two continents are dragged towards each other by the pull of the attached subducting oceanic lithosphere. Previous geodynamic modeling studies of collisional systems focused on first-order processes (such as coupled/decoupled regimes, continental delamination, slab break-off dynamics) and regional or even local scale dynamics (e.g., exhumation of HP/UHP rocks, surface topography). However, continuous subduction of continental lithospheric mantle after the onset of collision and long-term dynamics of continental subduction remains poorly constrained. Long-term continental subduction bears major geodynamic implications for the evolution of past and present collision zones.

To this aim, we use the geodynamic code LaMEM to perform high-resolution (2048 × 512) 2D buoyancy-driven numerical models, coupled with phase diagrams to account for density changes, of continued continental subduction with conditions that favor flake tectonics. We investigate the role of lower crust rheology to assess which rheological scenarios allow continental flaking and, thus, continued subduction of continental lithospheric mantle.

Our preliminary results exhibit long-term continental subduction, due to decoupling of the lower crust from the subducting continental mantle and/or density changes. This separation allows the deformation to be transmitted onto the overriding plate, with the emplacement of the subducting plate crust onto the overriding plate spanning more than 350 km and lasting over 100 Myr.

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and through scholarship UI/BD/154679/2023.

How to cite: Rodrigues, N., Rosas, F., Riel, N., Almeida, J., Gomes, A., and Duarte, J.: Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13652, https://doi.org/10.5194/egusphere-egu24-13652, 2024.

The deformation associated with the evolution of fold-thrust tectonic (FTT) wedge has been in the focus of research due to their association with hydrocarbons resources. Analogue sandbox modelling has been proven to be useful in characterizing FTT wedge. However, it is less convenient to interpret the influence of complex boundary conditions and material rheological parameters and to derive the stress distribution pattern from the analogue models. Nonetheless, these challenges can be accomplished competently by means of an exact numerical equivalence of those analogue models. Therefore, we undertook a numerical replication of the analogue sand-box with an absolute identical set up. This makes the attempt unique from earlier approaches, where lengths, rheology, and/or cohesive strengths were likely varied for converging the solutions in codes. Here, propagation parallel profile of sandbox experiments is numerically modelled in a 2-dimensional (2D) space with a plain strain assumption. For simplicity, the models are devoid of complex geological phenomena such as isostasy, pore fluid pressure and surficial processes. The present model enforces an elastoplastic constitutive relationship having exactly same rheology as our sand-box model. The model comprises cover material resting over a rigid decollement with frictional interaction. The cover material is subjected to asymmetrical push from one end as in physical experiment. With the identical rheology, dimensions, and geometry our numerical model successfully produced comparable results with our physical sandbox models. The measured kinematic attributes of the wedge such as taper angle, wedge width, thrust spacing, displacement along thrust from our numerical model are found in good agreement both qualitatively and quantitively with their analogue counterparts. The dynamics of deformation has also been investigated by extracting the magnitudes of stresses from each node of the numerical mesh of the present models.  From the dynamic analysis, the spatial distribution of stresses revealed that within a deforming wedge all the stress parameters are maxed periodically at a certain distance away from the pushing end boundary. The position of maximum stress is found consistent with the zone localized failure. Monitoring the periodic peaks of stress approximate the location of failure, in return leading to measure the thrust spacing. Furthermore, empirical relationships for stress distribution within a collisional wedge have been successfully developed from the observed stress distribution patterns. With the help of these relationships, mathematical expressions were developed for predicting 2D curvature of a thrust plane within a tectonic wedge. 

How to cite: Behera, A. and Bhattacharjee, D.: The dynamics of fold-thrust tectonic wedge: An insight from impeccable simulation of Physical Sandbox Experiment with Finite Element Model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14388, https://doi.org/10.5194/egusphere-egu24-14388, 2024.

EGU24-14511 | PICO | TS5.2

Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China 

Jingbo Zhang, Sixian Chen, and Zonghu Liao

Abstract

Accurate understanding and identification of faults architecture is crucial in seismic data interpretation and earthquake analysis, where fault slip surfaces may interact with damage rocks, forming damage zones with a width larger than hundred meters. We use machine learning (ML) to show 10 kinds of seismic attributes from a seismic survey could be applied in identification and quantification of fault damage zone in northeast Sichuan Basin, China. The results indicate: (1) Six seismic attributes provide highest contribution to the fault characterization, including root mean square amplitude attributes, azimuth angle attributes, reverse attributes, original attributes, chaotic body attributes and ant body attributes; (2) The application of SHAP (SHapley Additive exPlanations) algorithm improves the model's accuracy, as the loss value (Mean Square Error , MSE) of the test data is restored from 17.86% to 16.03%; (3) Width estimation from the kernel density estimation algorithm (KDE) show the fault damage zone ranges from 0.3 to 1.2 km. Our work provides new insights into the interpretation of fault architecture in the subsurface, and we argue the geometrical parameters of the fault damage zone is significant for understanding the evolution of fault and earthquake simulations.

Keywords:  Fault damage zone; Seismic interpretation; Machine learning (ML); Geometrical parameters

Figure1.The seismic attributes of the actual work area entered into the model and the model calculation results: (A) Original attributes of the work area. (B) Variance attribute of the work area. (C) Results calculated by the ML model

Figure2. Thermal diagram presents the structure of the fault damage zone: (A) A vertical line perpendicular to the fault orientation correction; (B) indicates the fault range with a thermal index greater than 1.572; (C) indicates a fault range with a thermal index greater than 2.065; (D) indicates a thermal index greater than 2.401 fault range. The width of the damage zone could be estimated by these figures.

 

Figure3. Descriptive diagram of fault damage zone width. Fault_1 represents the direction of fault width with thermal index greater than 1.572; Fault_2 represents the direction of fault width with thermal index greater than 2.065; Fault_3 represents the fault width trend map with thermal index greater than 2.401

How to cite: Zhang, J., Chen, S., and Liao, Z.: Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14511, https://doi.org/10.5194/egusphere-egu24-14511, 2024.

EGU24-16472 | PICO | TS5.2

How the rigidity of the subducting plate affects the geometry of accretionary prisms? 

Laetitia Le Pourhiet, Alexis Gauthier, Nadaya Cubas, Julie Tugend, and Geoffroy Mohn

Simulations of accretionary prisms are most of the time realized either using a simplified set up that cannot account for the evolution of temperature with the growth of the prism nor deformable basement or using a very large size simulation of the complete subduction zone using a larger resolution locally. The first method is over-simplified and discards the possibility to study crustal scale accretionary prism, the second method is very costly numerically.  

Here, we present simulations of accretionary prisms that use 1/ heatflux as boundary condition allowing the temperature at the base of the model to evolve as the accretionary prism grows and 2/ flexural deformation of the basement in response to the growth of the accretionary prism. This new boundary condition is very cheap to compute as we implemented it by solving analytically the flexure equation using sinus decomposition and image method.  

We then present a set of numerical simulations of crustal scale accretionary prism with particular focus on the geometry of the subducting basement in order to better understand how the alternation between period of subduction erosion and accretion affects the geometry of the accretionary prism and its thermal history as a function of the rigidity of the subducting plate. We compare our simulations with a set of east-west trending seismic profiles located southwest of Taiwan showing along strike structural variations of the accretionary prism.    

How to cite: Le Pourhiet, L., Gauthier, A., Cubas, N., Tugend, J., and Mohn, G.: How the rigidity of the subducting plate affects the geometry of accretionary prisms?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16472, https://doi.org/10.5194/egusphere-egu24-16472, 2024.

EGU24-17730 | ECS | PICO | TS5.2

Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India 

Uma Narayan M, Surendra Kumar Sahu, Rishikesh Bharti, and Archana M Nair

The continual modification of the topography due to varied processes results in diverse and dynamic terrain. Landscape evolution studies can link the effect of small-scale topographic quantities on long-term landscape evolution. In this study, the evolutionary pattern of the Dibang basin, located at the limb of the Eastern Himalayan Syntaxis stretch along the active tectonic region of northeast India is analysed using the stream power incision model (SPIM). SPIM is an empirical power law equation linking erosion with channel area and bed slope.  With constant tectonic forcing and homogeneous physical properties, river profiles deviate from linearity and exhibit convexity (indicating uplift) and concavity (indicating erosion) in their longitudinal profiles. These deviations indicate the transient responses of the river profile due to tectonics. Here, the landscape is modelled assuming that the Dibang River lying close to the mountain front shows bedrock properties. The evolved topography is seen to exhibit an erosion-dominated landscape with a rapid decrease in the mean elevation. The profile of the Dibang River exhibits a concave-convex-concave shape, indicating that the river channel is in a state of disequilibrium. The steepness index is observed to be varying across the Dibang basin with higher values in the middle and upper right parts of the basin. The χ plot also reveals the transient nature of the river profile.

How to cite: Narayan M, U., Sahu, S. K., Bharti, R., and Nair, A. M.: Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17730, https://doi.org/10.5194/egusphere-egu24-17730, 2024.

EGU24-18656 | PICO | TS5.2

Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting 

Martin Staněk, Prokop Závada, and Ondřej Krýza

The Reykjanes Peninsula (RP) in southwestern Iceland represents a zone of oblique rifting where the divergent boundary of the Mid-Atlantic ridge is offset to the eastern Iceland along a left-lateral transform fault - the South Iceland Seismic Zone (SISZ). RP and the SISZ represent regions of the most abundant earthquake activity on Iceland, development of fissure arrays and occasional lava eruptions. A series of earthquake swarms at RP in the 2021-2023 period indicates development of distributed fracture networks along ENE direction of the transform fault and two new fissure arrays trending NE divided by a gap in seismicity. In the last 3 years, the volcanic activity culminated two times in volcanic eruptions, bringing magmas from Moho depth at 15 km.

Inspired by the recent tectonic activity at RP, we conducted a series of analogue experiments consisting of a silicone magma chamber embedded in a photoelastic gelatine crust. The aim of our study is to constrain the links between the depth level of the magma chamber, the crustal scale fracture arrays, faults, magma pathways, superficial fractures and the location of related potential volcanic activity in a transform setting. Inducing strike slip deformation of the system, we explored the influence of shape and orientation of the magmatic chamber on the evolution and pattern of progressively developed fractures along the central shear domain. During the experiment, we captured the stress fringe patterns in the fractured gelatine. The surface deformation was traced by a stereoscopic digital image correlation (DIC) system employing two high-speed LaVision cameras. Analog magma spreading was traced using fluorescent dye mixed to the silicone or into the gelatine interlayer.

Modelling results show that decoupling of the crust above the magma reservoir in strike-slip setting produces a domain with higher vorticity bounded by a conjugate set of tensional fractures. The largest open fractures initiate at and propagate from the intersection of the principal strike-slip fault plane with the vertical contact of the magma chamber and the surrounding crust. Including other open fractures, the orientation of the fracture set is oblique (~ 60°) to the fault plane. With formation approximately coeval to those of the fractures, fine wrinkles at the crust surface are observed with orientation of ~ 120° with respect to the fault plane.

How to cite: Staněk, M., Závada, P., and Krýza, O.: Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18656, https://doi.org/10.5194/egusphere-egu24-18656, 2024.

Abstract: The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U‒Pb‒Hf isotope, whole-rock geochemistry, Sr‒Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U‒Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr‒Nd, and Lu‒Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to −5.1) and εHf(t) (−6.7 to −1.2) values, high Rb/Y and Th/La ratios, slight Nd‒Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic‒intermediate rocks from the western margin of the Yangtze Block commonly show high K2O/Na2O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area.

Keywords: Potassium-enriched intrusive rocks; Southwestern Yangtze Block; Fractional crystallization; Lithospheric mantle; Sediment melt

How to cite: Jiang, X. and Lai, S.: Petrogenesis of Neoproterozoic high-K intrusion in the southwestern Yangtze Block, South China: Implication for the recycled subducted-sediment in the mantle source, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-253, https://doi.org/10.5194/egusphere-egu24-253, 2024.

EGU24-330 | Orals | GD4.1

The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau 

Ebru Şengül Uluocak, Russell N. Pysklywec, Andrea Sembroni, Sascha Brune, and Claudio Faccenna

Post-subduction tectonics can involve a wide range of spatiotemporal processes associated with regional and large-scale upper mantle forces. To better understand the interaction between these forces in collisional settings, we focus on active mantle dynamics beneath the East Anatolian Plateau, a well-documented segment of the Arabian-Eurasian continental collision zone. In detail, we use state-of-the-art instantaneous thermomechanical models by combining the advantages of 3D numerical modeling with high-resolution imaging techniques. We analyze the model’s outputs, such as 3D stress-strain and temperature variations of upper mantle convection and reconcile them with numerous geological and geophysical observations. Our results show prominent northward-directed channel flow in the mantle that cuts across the plateau and surroundings, from the Arabian foreland to the Greater Caucasus domain. This result reproduces and elucidates the proposed ~SW-NE-oriented Anatolian Background Splitting pattern and recent seismic low-ultra low-velocity anomalies. We argue that this large-scale upper mantle flow constitutes the engine for the long-wavelength dynamic topography (~400 m) in the region and promotes the relatively small-scale convection pattern by supporting intraplate rift tectonics in the extensional Van Lake zone.

How to cite: Şengül Uluocak, E., Pysklywec, R. N., Sembroni, A., Brune, S., and Faccenna, C.: The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-330, https://doi.org/10.5194/egusphere-egu24-330, 2024.

  Yanshanian magmatic rocks are widely distributed in the northern margin of the South China Sea and the continental margin of South China. These magmatic rocks are generally believed to have been formed by the subduction of the Paleo-Pacific plate to the South China Plate from Late Jurassic to Early Cretaceous. Due to the small number of wells drilled to the basement, most predecessors have studied on the distribution range, origin and tectonic setting of Yanshanian magmatic rocks by geophysical means(magnetic anomalies and seismic data). At present, The reported ages of basement magmatic rocks in the Pearl River Mouth Basin are mainly concentrated in Zhu 1 Depression and Panyu Low Uplift, and there is no petrological evidence in other regions.Baiyun Depression, as the largest hydrocarbon generating depression in the Pearl River Mouth Basin, has important oil and gas significance. In order to better define the spatial and temporal distribution of Yanshanian magmatic rocks, nearly 30 basement drilling samples in the periphery of Baiyun Depression and 8 onshore outcrop samples were collected. The genesis and tectonic significance of Yanshanian magmatic rocks are discussed through 76 thin sections, 7 U-Pb zircons dating, 26 major elements analysis, 16 trace elements analysis and 4 Sr-Nd-Pb isotope analysis.The results show that the magmatic rocks in the study area are concentrated in the J3-K1 and mainly developed S-type granite. These magmatic rocks are basically derived from the crust, and a few magmatic rocks or a small amount of mantle-derived materials are mixed in. The trace element discrimination diagram indicates that all samples belong to volcanic island arc type granite. The distribution curve of rare earth elements shows that light rare earth elements are enriched and heavy rare earth elements are low and stable.According to the above results, these magmatic rocks are part of the NE-trending continental margin magmatic arc formed by subduction and accretion of the paleo-Pacific plate to the South China Plate during the Yanshanian.Combined with the previous research results, it is believed that the extensional action caused by subduction and retreat of the Paleo-Pacific plate migrated to the ocean direction in the late stage of tensile rupture, and magmatism also migrated to the ocean, so the intrusion time of the magmatic rocks from continental to marine along the NW-SE direction gradually became late.This study adds important petrological evidence to clarify the genesis and tectonic setting of Yanshanian magmatic rocks in the northern margin of the South China Sea and the South China continent, and also has important application value for oil and gas exploration of buried hills in the Pearl River Mouth Basin.

How to cite: lu, F. and zhao, J.: Genesis and Tectonic Setting of Yanshanian Magmatic Rocks in the Northern Margin of South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-339, https://doi.org/10.5194/egusphere-egu24-339, 2024.

EGU24-568 | ECS | Posters on site | GD4.1

Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement? 

Nikola Stanković, Taras Gerya, Vladica Cvetković, and Vesna Cvetkov

Oceanic obduction and ophiolite emplacement are processes which result in positioning of more dense oceanic lithosphere on top of less dense continental crust. It is known that obduction is related to the closure of oceanic realms, however exact mechanisms that lead to the obduction of these ophiolite rocks, and more importantly, their permanent emplacement onto the continental crust is still controversial.

Although many mechanisms for ophiolite emplacement have been proposed, there have been substantial difficulties in modelling the ophiolite emplacement by means of numerical simulations. Creating physically viable simulations of the ophiolite emplacement is of paramount importance for better understanding of the process itself. There have been some notable successful attempts. For example, [1] succeeded in emplacing ophiolites by artificially reversing the velocity conditions once the ophiolite block is already obducted. More recently, [2] have shown that continental extrusion mechanism, which is a result of the activation of subducted continental crust at higher P-T conditions, can account for the emplacement of far-travelled ophiolites.

In this communication, we report interim results of our attempt to explain spontaneous emplacement of large ophiolite blocks by means of trans-lithospheric diapirism of continental crust. This phenomenon has recently been modelled [3] in the context of continental collision and the formation of the European Variscides. However, in this study, we produce a spontaneously induced intra-oceanic subduction. This model involves a retreating subduction with trench reaching the passive continental margin, leading to the continental subduction under very young oceanic lithosphere. Consequently, subducted crust is activated in deeper regions and forms a diapiric upward flow. This trans-lithospheric diapirism reaches the surface, thus separating the already obducted parts of the oceanic lithosphere from the rest of the oceanic domain, resulting in permanent ophiolite emplacement.

The presence of crustal rocks in such deep environments of ultra-high pressure certainly leads to their metamorphism. In the scope of our simulations we are monitoring the P-T paths of relevant crustal markers and propose rough estimates of the P-T conditions of metamorphic peak. For the calculations of the numerical simulations we utilize marker-in-cell method with conservative finite differences [4].

 

[1] T. Duretz, P. Agard, P. Yamato, C. Ducassou, E. B. Burov, and T. V. Gerya, “Thermo-mechanical modeling of the obduction process based on the oman ophiolite case,” Gondwana Research, vol. 32, pp. 1-10, 2016.

[2] K. Porkoláb, T. Duretz, P. Yamato, A. Auzemery, and E. Willingshofer, “Extrusion of subducted crust explains the emplacement of far-travelled ophiolites,” Nature Communications, vol. 12, no. 1, p. 1499, 2021.

[3] P. Maierová, K. Schulmann, P. ’Štípská, T. Gerya, and O. Lexa, “Trans-lithospheric diapirism explains the presence of ultra-high pressure rocks in the european variscides,” Communications Earth & Environment, vol. 2, no. 1, p. 56, 2021.

[4] T. V. Gerya and D. A. Yuen, “Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties,” Physics of the Earth and Planetary Interiors, vol. 140, no. 4, pp. 293-318, 2003.

How to cite: Stanković, N., Gerya, T., Cvetković, V., and Cvetkov, V.: Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-568, https://doi.org/10.5194/egusphere-egu24-568, 2024.

EGU24-700 | ECS | Posters on site | GD4.1

The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints 

Noémie Bosc, Delphine Bosch, Mélody Philippon, Mélanie Noury, Olivier Bruguier, Lény Montheil, Douwe van Hinsbergen, and Jean Jacques Cornée

The British Virgin Islands (BVI) is a NE-SW trending archipelago located in the northeastern corner of the Caribbean plate. Exposing volcanic arc rocks, it is located at the junction between the old arc of the Greater Antilles to the Northwest and the active arc of the Lesser Antilles to the South. The BVI are a key location to study the geodynamical evolution of the northeastern boundary of the Caribbean plate. In order to understand its significance into the overall Caribbean evolution, a set of 16 igneous samples from seven islands was studied for petrology, geochemistry (major and trace elements, and Pb-Sr-Nd-Hf isotopes), thermobarometry (Al-in-hornblende) and U-Pb geochronology on accessory minerals (zircon, titanite and apatite). The studied rocks show a typical volcanic arc signature and correspond to a calc-alkaline series, differentiated along a NE/SW gradient. Trace elements patterns show strong negative HFSE anomalies and LILE enrichments. ɛHfi are homogeneous ranging from +11.4 to +14.1 typical of a MORB-type mantle. Magmas were thus originated from a homogeneous mantle corresponding to the mantle wedge, with participation of a slab component. The slab component contribution is estimated to be less than 2% and is dominated by aqueous fluids, except for Peter and Norman Islands. U-Pb ages emphasize an active magmatic period spanning between ~43 Ma and ~30 Ma along a NE-SW younging gradient. This age range and strong geochemical similarities with arc lavas exposed in St Martin and St Barthélémy suggest that the BVI represent the northern continuity of the Eo-Oligocene extinct branch of the Lesser Antilles arc. Crystallization depth of the studied plutonic bodies, estimated by thermobarometric constraints, supports a NE-SW increasing emplacement depth from ~7km to ~13km. The oldest plutonic bodies at NE thus experienced less total exhumation than the youngest plutonic bodies at SW (maximum rate of ~2.2 mm/yr at SW and minimum rate of ~0.2 mm/yr at NE). From Eocene to Oligocene it has been recently demonstrated that the block from Puerto Rico-Virgin Islands (PRVI) rotated 45° counter clockwise (Montheil et al., 2023). Previous thermochronological data shows that the BVI exhumation occurred synchronously along the archipelago between ~25 and ~21 Ma (Román et al., 2021). Together these observations suggest a regional tilt of the BVI block that occurred between plutons crystallisation and their exhumation at ~2 km depth. We propose that the tilting and the fast exhumation of the BVI, that are synchronous with counterclockwise rotation of the PRVI block, are the consequence of subduction locking generated by the Bahamas bank accretion to the northeastern Caribbean plate.

How to cite: Bosc, N., Bosch, D., Philippon, M., Noury, M., Bruguier, O., Montheil, L., van Hinsbergen, D., and Cornée, J. J.: The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-700, https://doi.org/10.5194/egusphere-egu24-700, 2024.

EGU24-1044 | ECS | Orals | GD4.1

The role of hydration-induced processes in the deformation of the North China craton 

Açelya Ballı Çetiner, Oğuz Göğüş, Jeroen van Hunen, and Ebru Şengül Uluocak

Numerous previous studies have been conducted in the North China Craton to investigate its anomalously thin lithosphere, high magmatism, and extensional tectonics along its eastern margin. Based on petrological analyses it has been suggested that the cratonic mantle lost its root (~100 km) with multiple tectonic processes during the late Jurassic – Early Cretaceous. The weakening and erosion of the North China craton is often attributed to its high water content and lower viscosity of the lithosphere associated with the movement and position of the Paleo-Pacific plate. However, other mechanisms and control parameters for the craton destruction have been proposed, and the thinning of the North China craton remains an enigmatic process.

To have a better understanding of the dynamics of the lithospheric deformations beneath the North China Craton that changes over time, we conducted a series of 2D geodynamic models. Specifically, we investigate the impact of hydration-induced processes on the lithosphere and the overriding plate and focus on parameters such as external tectonic forcing, the rheology and the strength of the overriding plate. Moreover, the effect of the angular position of the oceanic plate, and the existence of the mid-lithosphere discontinuities was also examined. Our results reveal that the destruction of North China Craton is more complex and heterogeneous than is often assumed in modelling studies. Furthermore, we find that without significant weakening, the mantle lithosphere is unlikely to delaminate. Extensive hydrous weakening may account for this, but external tectonic forcing in combination with non-linear rheology and eclogitization of the lower crust may have played an important role too.  

How to cite: Ballı Çetiner, A., Göğüş, O., van Hunen, J., and Şengül Uluocak, E.: The role of hydration-induced processes in the deformation of the North China craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1044, https://doi.org/10.5194/egusphere-egu24-1044, 2024.

EGU24-3010 | ECS | Posters on site | GD4.1

Thermo-mechanical models on the missing forearc basement in Taiwan 

Chih-Hsin Chen, Eh Tan, Shu-Huei Hung, and Yuan-Hsi Lee

Taiwan is located at the edge of the Eurasian plate and borders the Philippine Sea plate. The Philippine Sea plate is moving northwestward at a speed of 70 to 80 mm/yr and is converging with the Eurasian plate, forming the Luzon arc and the Taiwan orogenic belt. However, in the middle section of the Taiwan orogenic belt, the Luzon arc is directly adjacent to the edge of the Eurasian continental margin, and the forearc basement is missing. This phenomenon of missing forearc basement is also widely observed in similar plate convergence zones. Previous studies have suggested that this forearc basement has subducted between the Philippine Sea plate and the Eurasian plate. In order to explore the mechanism of forearc basement subduction, we used thermal-mechanical coupled numerical simulations combined with geological data to simulate the dynamic mechanism of forearc basement subduction in the middle section of the Taiwan orogenic belt.

 

The simulation results show that when the subducting plate transitions from oceanic crust to continental crust, the continental crust has a lower density and is not easily subducted. The huge mass formed by the orogeny blocks the Philippine Sea plate from moving northwestward, causing the forearc crust to bend concavely and form a forearc basin. The basin begins to accumulate a large amount of sedimentary material. Later, the center of the basin breaks to form the Longitudinal Valley fault, the island arc to the east of the basin thrusts over the forearc basement, pushing the basin sediment to uplift rapidly, and finally the forearc basement subducts below the Philippine Sea plate.

 

This model explains the mechanism for the missing forearc basement, the timing of the formation of the Longitudinal Valley fault, and the dramatic up and down movements recorded in the sedimentary rocks of the Coastal Mountains. It also explains the spatial pattern of the surface heatflow.

How to cite: Chen, C.-H., Tan, E., Hung, S.-H., and Lee, Y.-H.: Thermo-mechanical models on the missing forearc basement in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3010, https://doi.org/10.5194/egusphere-egu24-3010, 2024.

EGU24-4122 | ECS | Orals | GD4.1

Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective 

Xin Zhou, Nicolas Coltice, and Paul Tackley

Subduction initiation (SI) creates new subduction zones and provides driving forces for plate tectonics, being a key process of theplate tectonic regime on Earth. Although SI has been extensively studied in 2D regional numerical models, obtaining a global perspective on SI remains elusive. Geological observations and plate reconstructions both suggest that SI is coeval with the global or local plate reorganizations. The tectonic plate reorganizations are marked by rapid changes of plate motions occurring over a few million years and are recurrent throughout Earth’s history.  One of the most well-known plate reorganization events occurred at approximately 53-47 Ma ago, characterized by the bending of Hawaii-Emperor Seamount Chain. Simultaneously, several SI events occurred in the Pacific Plate, such as Izu-Bonin-Mariana (~52 Ma) and Tonga-Kermadec (~50 Ma). The relationship between SI and plate reorganizations, as well as their collective impacts on continental evolution, is poorly understood. It is also unclear whether these processes are dominated  by a “top-down” or “bottom-up” mechanism. This study is committed to exploring the interaction between SI and plate reorganizations using 3D global mantle convection models. We reproduce SI coeval with plate reorganizations in these numerical models. We analyze the changes of stress distribution in the lithosphere during the plate reorganizations and their effects on SI. A variety of different interplays between SI and tectonic plates reorganizations have been identified based on their chronology and driving mechanisms. We also investigate their influences on the supercontinental breakup and assembly. Two major plate reorganization events, occurring at 100 Ma and 50 Ma ago respectively, are used to compare with the numerical modeling results. The effects of key parameters, such as lithosphere thickness and strength, will be examined. Plate reconstruction models will also be included to study the interaction between SI and plate reorganizations in the future.

How to cite: Zhou, X., Coltice, N., and Tackley, P.: Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4122, https://doi.org/10.5194/egusphere-egu24-4122, 2024.

Subduction initiation remains one of the least understood global processes of plate tectonics.  Prominent models have been cast in terms of two broad classes: “spontaneous” cases due to lithospheric gravitational instabilities and “induced” cases due to forced plate convergence. Yet gravitationally unstable lithosphere is old, strong, and difficult to begin to bend into a subduction zone and convergent forces necessary to begin subduction are often too large given the plates involved. These models also consider the asthenospheric mantle as passive, even though relative motion between slabs and the asthenosphere has long been regarded as a strong control on subduction dynamics. Here I propose that subduction-transform edge propagator (STEP) faults can initiate subduction depending on the absolute motion of the STEP fault with respect to the asthenosphere. STEP faults form where subduction zones end and the subducting plate tears forming a down flexed transcurrent plate boundary at the surface shearing against the adjacent rear arc lithospheric plate. However, STEP faults are not simple transcurrent boundaries. Absolute motion of the down flexed STEP fault edge with respect to the surrounding asthenosphere can produce a strong “sea anchor” force that either continues to bend the edge downward, initiating subduction, or opposes slab bending, inhibiting subduction. In the south Pacific, the southern end of the New Hebrides Trench and the northern end of the Tonga Trench are type-example STEP faults with opposite senses of dip but both moving northward with respect to the asthenosphere. The northward dipping New Hebrides STEP fault moves northward in a mantle reference frame creating a strong asthenospheric flow against the STEP fault edge, inducing active subduction at the Matthew-Hunter trench. In contrast, the Tonga STEP fault dips southward but also has a northward component of motion with respect to the mantle. Asthenosphere thus flows southward beneath the down flexed Tonga STEP fault edge opposing further bending.  Subduction does not initiate at the Tonga STEP fault despite a ~100 Myr age contrast between the Pacific and north Fiji and Lau basin lithospheres. Since absolute plate motions reflect the sum of all forces acting on the entire lithospheric plate, a strong sea anchor mantle force may be generated at a STEP fault edge, initiating subduction (or inhibiting it), even where lithosphere is old, strong, and resists bending and without requiring large convergent forces between plates, overcoming these objections to previous models.

How to cite: Martinez, F.: Subduction initiation (or not) due to absolute plate motion at STEP faults: The New Hebrides vs. the Tonga examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4189, https://doi.org/10.5194/egusphere-egu24-4189, 2024.

The migration and character of magmatism over time can provide important insights into the tectonic evolution of an orogen. We present evidence for three separate episodes of compositionally distinct granitoid magmatism associated with the Acadian orogenic cycle in the eastern and southern Newfoundland Appalachians. The interpretations are based on new zircon U-Pb ages, geochemical data, and Sr-Nd-Hf-O isotopic data for 18 samples from 15 Silurian and Devonian granitoid plutons, combined with previously published data. The three episodes outline hinterland and foreland-directed migration trends and represent subduction (435-420 Ma), syn-collision (415-405 Ma), and post-collision (395-370 Ma) settings in the Acadian orogenic cycle. The Silurian plutons (435-420 Ma) consist mainly of quartz diorite, tonalite, granodiorite, monzogranite, and syenogranite, with high-K calc-alkaline and enriched Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -5 to -2; εHf[t] = -3 to -1; δ18O = +6 to +8). They are interpreted to record the subduction of oceanic lithosphere of the Acadian seaway that separated the leading edge of composite Laurentia represented by the Gander margin and Avalonia. The Early Devonian plutons (415-405 Ma), containing more voluminous monzogranite and syenogranite, have calc-alkaline to high-K calc-alkaline features, adakite-like compositions, and more-depleted Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -6 to 0; εHf[t] = +1 to +3; δ18O = +5 to +6). This stage occurs mostly to the northwest of the Silurian, indicating a regional scale northwestward (hinterland-directed) migration of magmatism with a rate of > 9 km/Ma. The migration is interpreted to be related to the progressive shallow underthrusting of Avalonia beneath the Gander margin (composite Laurentia) at least as far as 90 km inboard. The Middle to Late Devonian plutons (395-370 Ma) consists mainly of monzogranite, syenogranite, and alkali-feldspar granite, which are silica- and alkali-rich with large negative Eu anomalies. These rocks are concentrated along both sides of the Dover - Hermitage Bay fault zone, which represents the boundary between Avalonia and composite Laurentia, to the southeast of the Silurian-Early Devonian igneous rocks. This stage of magmatism represents a foreland-directed (retreating) migration. The Early Devonian and Middle to Late Devonian magmatism were separated by a gap between 405 and 395 Ma, and recorded an evolution from (high-K) calc-alkaline to alkaline compositions, which is ascribed to partial delamination of Avalonian lithospheric mantle in a post-collisional setting.

How to cite: Wang, C., Wang, T., Cees, V. S., Hou, Z., and Lin, S.: Evolution of Silurian to Devonian magmatism associated with the Acadian orogenic cycle in Newfoundland Appalachians: Evidence for a three-stage evolution characterized by episodic hinterland- and foreland-directed migration of granitoid magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4216, https://doi.org/10.5194/egusphere-egu24-4216, 2024.

Convergent continental margins are the major sites for the formation, differentiation, preservation, and destruction of continental crust. This article focuses on the Mesozoic crustal modification history of northeastern China from a magmatic perspective. During Mesozoic times, NE China was influenced by three convergent systems, namely the Paleo-Asian Ocean (PAO) regime to the south, the Mongol-Okhotsk Ocean (MOO) regime to the northwest, and the Paleo-Pacific Ocean (PPO) regime to the east. This study comprehensively synthesizes information on Early Triassic to Early Cretaceous magmatic rocks. We unravel the spatiotemporal effects of the above-mentioned convergent regimes by evaluating the migration of major magmatic belts and other geological and geophysical evidence. The PAO regime is confined to the southernmost part of NE China and exerted influence during pre-late Late Triassic times. The MOO regime-related magmatism lasted until the early Early Cretaceous and occurred throughout the Great Xing’an Range and adjacent regions. The spatial effect of the PPO did not exceed the eastern margin of the Songliao Basin until the Early Jurassic; low-angle to flat subduction of the PPO slab led to the westward migration of continental arc front in the Middle Jurassic and the waning of PPO regime-related magmatism in the Late Jurassic. Since the earliest Cretaceous, the rollback and retreat of the PPO slab became the predominant geodynamic control in NE China, but the superposition of the MOO regime played a role during the early Early Cretaceous. Employing whole-rock Nd and zircon Hf isotope spatial imaging, this study elucidates that, although the pre-Mesozoic lithospheric heterogeneity provides first-order control, the Mesozoic crustal architecture of NE China was further carved by Mesozoic tectonics. Retreating subduction (slab rollback) and post-collisional lithospheric delamination resulted in the prolonged extensional background and crustal growth (rejuvenation); on the contrary, low-angle subduction and syn-collisional compression could cause transient periods of ancient crust reworking. Our results also estimate the high altitude of the Great Xing’an Range and adjacent regions in the Early Cretaceous. This study opens new possibilities to explicitly document crustal modification processes in fossil orogens from a magmatic perspective.

How to cite: Huang, H., Wang, T., and Guo, L.: Crustal modification influenced by multiple convergent systems: Insights from Mesozoic magmatism in northeastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4240, https://doi.org/10.5194/egusphere-egu24-4240, 2024.

EGU24-4319 | Posters virtual | GD4.1

Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians 

Uros Stojadinovic, Marinko Toljić, Branislav Trivić, Radoje Pantović, Danica Srećković-Batoćanin, Nemanja Krstekanić, Bojan Kostić, Miloš Velojić, Jelena Stefanović, Nikola Randjelović, and Maja Maleš

Among the many examples observed worldwide, the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians represents an excellent area for a process-oriented study on the interplay between tectonics, sedimentation, and magmatism in continental back-arc basins above evolving subducted slabs. The TMC is a segment of the larger Late Cretaceous Apuseni-Banat-Timok-Srednogorie (ABTS) magmatic belt, formed in response to the subduction of the Mesozoic Neotethys oceanic lithosphere beneath the Carpatho-Balkanides of south-eastern Europe. However, despite many qualitative studies, the quantitative link between the subducted slab's mechanics and the overlying basins' evolution is less understood. Within the scope of the newly funded TMCmod project, supported by the Science Fund of the Republic of Serbia (GRANT No TF C1389-YF/PROJECT No 7461), coupled field and laboratory kinematic and petrological investigations will be focused on creating a conceptual definition of the TMC geodynamic evolution, by combining near-surface observations with the known evolution of the subduction system. This definition will be subsequently validated through analogue modelling and integrated into a coherent geodynamic model of tectonic switching in basins driven by the evolution of subducted slabs. The new geodynamic model coupling the TMC basin with its Neotethys subduction driver will quantitatively advance the strategy of prospecting and exploration of world-class porphyry copper-gold deposits, which have been actively exploited in this region for more than a century. Furthermore, reconstructed regional kinematic evolution will improve seismic hazard assessment during industrial and societal infrastructure planning and construction.

How to cite: Stojadinovic, U., Toljić, M., Trivić, B., Pantović, R., Srećković-Batoćanin, D., Krstekanić, N., Kostić, B., Velojić, M., Stefanović, J., Randjelović, N., and Maleš, M.: Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4319, https://doi.org/10.5194/egusphere-egu24-4319, 2024.

Previous subduction thermal models are inconsistent with the values of forearc heat flow (50-140 mW/m2) and global P‒T conditions of exhumed rocks, both suggesting a shallow environment 200~300°C warmer than model predictions. Here, we revaluate these problems in Kuril-Kamchatka using 3-D thermomechanical modeling that satisfies the observed subduction history and slab geometry, while our refined 3-D slab thermal state is warmer than that predicted by previous 2-D models and better matches the observations involving exhumed rock records. We show that warmer slabs create hierarchical slab dehydration fronts at various forearc depths, causing fast and slow subduction earthquakes. The multilayered subduction regime and a large downdip thermal gradient of > 5°C/km beneath Kuril-Kamchatka indicate a stratified characteristic effect on slab dehydration efficiency. We conclude that fast-to-slow subduction earthquakes all play a key role in balancing plate coupling energy release on megathrusts trenchward of high P‒T volcanism.

How to cite: Zhu, W. and Ji, Y.: Reestimated slab dehydration fronts in Kuril-Kamchatka using updated three-dimensional slab thermal structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4972, https://doi.org/10.5194/egusphere-egu24-4972, 2024.

Oceanic Core Complexes (OCCs) are peridotite and serpentinite rich geological features, commonly located at the external intersections of slow-spreading mid-oceanic accreting ridges (MORs) with transform faults (TFs). The peridotites of these complexes are commonly considered to derive from the upper mantle while the serpentinites are attributed to chemical weathering that affected rock-mass during its ascent through the lithosphere. Description of cores drilled into OCCs commonly describes in detail the various peridotites but ignores the serpentinites, which are considered secondary additions. However, this presumption seems flawed due to the absence of high-pressure rocks such as eclogites, therefore it seems that the origin of the various peridotite minerals were formed concurrently with the serpentinites from pyroxenes under constrains of moderate geological pressures and temperatures, and various availabilities of H2O.

The intersections between slow MORs and TFs, where most OCCs occur, are characterized by steep thermal gradients and by distinct density contrasts. The thermal gradients in the upper crust of the MOR axial rift are nearly 1300/km, due to the shallow depth of the upper mantle there. The density of the fresh basaltic lava at the MOR is ca. 2700 kg/m3, because the temperature of the fresh basalt is some 1100oC. However, the density of the older basalt that builds the older plate across the transform fault is 2900 kg/m3. It is plausible that at fast-spreading MORs the plate juxtaposed against the active spreading rift would still be warm and its density would too light to initiate the spontaneous subduction. Tectonic experiments showed that at least 200 kg/m3 density contrast between lighter and denser crustal slabs would be sufficient to initiate spontaneous subduction. Furthermore, geochemical experimentation shows that under 500oC temperatures, namely at depths of ca. 4 km under the MOR, minerals of the pyroxene group in the oceanic basalts, are likely to be altered either into peridotites under dry conditions or into serpentinites under wet constraints at such temperature. These constraints suggest that the serpentinites in OCCs are generic and not erosional features, and their light densities and plasticity could have generated the diapiric ascent of the OCCs. The density contrast between the fresh and the old basalts, juxtaposed at the ridge – transform junctions, could take place if the spreading rate of the MOR is slow and the older slab has the time required to cool and reach the density of 2900 kg/m3.

 Keywords: Ridge-transform intersection, oceanic core complexes, spontaneous subduction, peridotites, serpentinites, diapirs.

How to cite: Mart, Y.: Oceanic core complexes: Serpentinite diapirs at slow ridge - transform fault intersections?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5261, https://doi.org/10.5194/egusphere-egu24-5261, 2024.

EGU24-5274 | ECS | Orals | GD4.1

Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling 

Christian Schuler, Boris Kaus, Eline Le Breton, and Nicolas Riel

The geodynamic evolution of the Alpine-Mediterranean area is complex and still subject to ongoing debate. The Adriatic microplate motion is of particular interest as it is influenced by three distinct subduction systems: the Alpine subduction in the north, the Dinaric-Hellenic subduction in the east, and the Calabrian-Apenninic subduction in the west. Additionally the system is influenced by the northward movement of the African continent, which further contributes to the geodynamic complexity of the region.

In this study, 3D thermomechanical simulations of the Alpine-Mediterranean region are performed using the code LaMEM (Kaus et al., 2016). The simulations employ a viscoelastoplastic rheology and an internal free surface to investigate the internal dynamics of the mantle. The initial plate configuration for the simulations is based on the kinematic reconstructions of Le Breton et al. (2021) at 35 Ma. The objective is to identify the controlling factors that drive the motion of the Adriatic microplate. This is achieved by investigating the role of various model parameters, such as the thermal structure of the lithosphere, the geometry and strength of the continental margin, the mantle viscosity, brittle parameters of the crust and the location of crustal heterogeneities.

Results show that Adria undergoes two distinct phases of plate motion over the past 35 million years. Between 35 Ma and 20 Ma, the African plate moves northward, pushing Adria in the same direction. However, once the Hellenic slab rolls back from the east and the Calabrian and Apenninic slabs roll back from the west, the Adriatic microplate decouples from the African plate, resulting in an anticlockwise rotation of Adria. Overall, this study provides valuable insights into the parameters that affect subduction dynamics in the Mediterranean and the independent motion of the Adriatic microplate.

Kaus, B. J. P., A. A. Popov, T. S. Baumann, A. E. Pusok, A. Bauville, N. Fernandez, and M. Collignon, 2016: Forward and inverse modelling of lithospheric deformation on geological timescales. Proceedings of NIC Symposium.

Le Breton, E., Brune, S., Ustaszewski, K., Zahirovic, S., Seton, M., & Müller, R. D. (2021). Kinematics and extent of the Piemont–Liguria Basin–implications for subduction processes in the Alps. Solid Earth, 12(4), 885-913.

How to cite: Schuler, C., Kaus, B., Le Breton, E., and Riel, N.: Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5274, https://doi.org/10.5194/egusphere-egu24-5274, 2024.

Fluid release from dehydration reactions and subsequent fluid migration in the subducting slab control the distribution of fluids in subduction zones, impacting many subduction processes, such as intraslab earthquakes, megathrust earthquakes, episodic slip and tremor, mantle wedge metasomatism, and arc-magma genesis.  Previous numerical models of two-phase flow indicate that compaction-pressure gradients induced by the dehydration reactions could drive updip intraslab fluid flow near the slab surface (Wilson et al., 2014). However, how the initial hydration in the incoming oceanic mantle prior to subduction impacts the updip fluid flow has not been investigated. Here, we use a 2-D two-phase flow model to investigate this effect under various initial slab-mantle hydration states and slab thermal conditions, the latter of which impact the depth extent of the stability of hydrous minerals. We especially focus on quantifying the lateral shift between the site of dehydration reactions and the location at which the fluids reach the slab surface due to their updip migration within the slab. The modeling results show that the most favourable path for updip flow is the antigorite dehydration front, the spatial extent of which depends on the slab-temperature and the thickness of the hydrated slab mantle. Our models predict that slab-derived fluids can travel over tens of km updip within the slab before reaching the slab surface. Such updip migration is more likely in warm(ish)-slabs, in which the formation of the antigorite dehydration front in the slab mantle does not require deep hydration of the incoming oceanic mantle prior to subduction.

How to cite: Cerpa, N. and Wada, I.: Role of degree and depth extent of slab-mantle hydration in controlling the intraslab fluid flow upon dehydration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6007, https://doi.org/10.5194/egusphere-egu24-6007, 2024.

EGU24-6290 | Orals | GD4.1

Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography? 

Jifei Han, Nick Rawlinson, Hrvoje Tkalčić, Caroline Eakin, Mike Coffin, and Joann Stock

Subduction is a key process in both the recycling and creation of new oceanic crust, the exchange of water between the Earth, oceans and atmosphere, and the distribution of earthquakes and volcanoes. However, the formation of new subduction zones - or subduction initiation - remains a poorly understood process. Macquarie Island, which lies along the Macquarie Ridge Complex (MRC) that forms the transpressional boundary between the Australian and Pacific plates in the southwest Pacific, is one location on Earth where subduction initiation is thought to be taking place. Several studies have suggested that the northern and southern segments of the MRC may be experiencing incipient subduction, but it is unclear what is happening in the central section, which includes Macquarie Island.


Indirect evidence for at least incipient subduction beneath Macquarie Island includes (i) ophiolite (oceanic crust) being exposed above sea level; (2) extreme topography, with Macquarie Island lying  ~5 km above the surrounding ocean basin; (3) thrust faults on either side of the island. To help investigate whether subduction may have been initiated in the neighborhood of Macquarie Island, we analyze teleseismic body wave data recorded by a network consisting of land stations and oceanic bottom seismometers deployed between October 2021 and November 2022. We extract teleseismic P-wave arrival time residuals across the combined array from ~20 events with epicentral distances between 30 and 90 degrees and invert them using FMTOMO to obtain 3-D P-wave velocity anomalies in the upper mantle. Preliminary results indicate that higher velocities are present to the east of the MRC in the vicinity of Macquarie Island, although further refinement is required before a detailed interpretation is possible.

How to cite: Han, J., Rawlinson, N., Tkalčić, H., Eakin, C., Coffin, M., and Stock, J.: Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6290, https://doi.org/10.5194/egusphere-egu24-6290, 2024.

The spinel phase (wadsleyite, ringwoodite) in the mantle transition zone (MTZ), can contain up to 1–2 wt% of water. However, whether these water reservoirs in the MTZ are filled is debated and, as the result, water content estimates in the MTZ range from less than 1 to up to 11 surface oceans (Ohtani, 2021 and references therein). I test water stability in the MTZ numerically by using 2D hydro-thermomechanical-chemical upper-mantle scale models with phase transitions and water diffusion and percolation in the mantle. Initial conditions correspond to a hydrated stagnant slab segment placed on top of 660 km discontinuity. Numerical model predicts that water diffusion from thermally relaxing slab triggers development of cold hydrous plumes from the slab surface, which are driven by the water-induced buoyancy (Richard and Bercovici, 2009). These plumes rise to and interact with olivine-spinel transition at 410 km. Positive Clapeyron slope of this transition causes cold plume upwellings to spread under it until their temperature rises enough to allow hydrated material to cross the transition. This crossing triggers aqueous fluid release, which rapidly rises upward in form of porosity waives. Relatively low water content and cold temperature of the wet plumes rising from stagnant slabs in the mantle transition zones may suppress hydrous melting above the 410 km discontinuity, thereby disabling the transition-zone water filter effect (Bercovici and Karato, 2002) at this boundary. Based on the results of experiments, we conclude that, due to the intrinsic positive buoyancy of hydrated mantle compared to dry rocks, mantle transition zone can only serve as a transient water reservoir. The duration of water residence mainly depends on the characteristic thermal-chemical relaxation time of subducting slabs in the mantle transition zone. Therefore, average water content in this zone should mainly depend on the average amount of water brought into it by subducting slabs globally during the characteristic relaxation time.

 

References

Bercovici, D., Karato, S., 2003. Whole-mantle convection and the transition zone water filter. Nature, 425, 39–44.

Ohtani, E., 2021. Hydration and Dehydration in Earth's Interior. Annual Review of Earth and Planetary Sciences, 49, 253-278.

Richard, G.C., Bercovici, D., 2009. Water-induced convection in the Earth’s mantle transition zone. J. Geophys. Res. 114, B01205.

How to cite: Gerya, T.: Is mantle transition zone a water reservoir? Yes, but only transient, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6602, https://doi.org/10.5194/egusphere-egu24-6602, 2024.

EGU24-6689 | Orals | GD4.1

Hoop Stresses in Free Subduction on a Sphere 

Neil Ribe, Stephanie Chaillat, Gianluca Gerardi, Alexander Chamolly, and Zhonghai Li

Because Earth's tectonic plates are doubly curved shells, their mechanical behavior during subduction can differ significantly from that of flat plates. We use the boundary-element method to study free (gravity-driven) subduction in 3-D spherical geometry. The model comprises a shell with thickness h and viscosity η1 subducting in a viscous planet with radius R0. Our focus is on the magnitude of the longitudinal normal membrane stress (`hoop stress'), which has no analog in Cartesian geometry. Scaling analysis based on thin-shell theory shows that the resultant (integral across the shell) of the hoop stress obeys the scaling law Tφ ∼ (η1h W/R0) max(1, cotθ) where θ is the colatitude and W is the velocity of the shell normal to its midsurface that is associated with bending. We find that the state of stress in the slab is dominated by the hoop stress, which is 3-7 times larger than the downdip stress. Because the hoop stress is compressive, it can drive longitudinal buckling instabilities. We perform a linear stability analysis of a subducting spherical shell to determine a scaling law for the most unstable wavelength, which we compare with observed shapes of trenches in the Pacific ocean. 

How to cite: Ribe, N., Chaillat, S., Gerardi, G., Chamolly, A., and Li, Z.: Hoop Stresses in Free Subduction on a Sphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6689, https://doi.org/10.5194/egusphere-egu24-6689, 2024.

The dynamics of subducting lithosphere with an embedded continental fragment is complex, with rapid changes in plate kinematics, mantle flow and uplift of the overriding plate as the fragment impacts the trench. However, the sequence and timing of the effects is often difficult to constrain, leading to uncertainties in the exact causes for particular subduction zones. We conducted 2D and 3D numerical modelling of subduction with Underworld2.0 to investigate the interactions between the subducting lithosphere and an embedded continental fragment, the Eratosthenes Seamount in the Cyprus subduction zone. Due to the uncertainty in the size of the continental crust around the Eratosthenes Seamount, we varied the size of the fragment from 200 km to 400 km (trench perpendicular) and compared to 3D model with a fixed seamount. The 3D model matches the regional seismic tomography models that show the absence of lithosphere on the subducting slab ahead of the continental fragment. In all the models, the subduction zone first develops as expected as the continental fragment approaches the trench. As the fragment contacts the trench at 6.5 Ma, the first uplift in Anatolia is experienced. However, the pace of uplift increases dramatically at 450 ka as the slab tear develops and the mantle flow pattern changes. The observed uplift rate before 450 ka is 0.07 mm/yr while after 450 ka, the uplift rate increases to 3.21 – 3.42 mm/yr. The model that best matches the size of the fragment is 200 km with a rate of 0.04 mm/yr before 450 ka and 1.76 mm/yr after 450 ka. The reference uplift rate from the model without the slab break-off from 450 ka is only 0.02 mm/yr.  The models demonstrate that the slab tear and break-off caused by the impact of the Eratosthenes Seamount causes the uplift observed and in particular is responsible for the more rapid uplift rates observed since 450 ka in the Central Taurides. 

How to cite: Clark, S. and Lou, P.: The Acceleration of Uplift in the Central Taurides due to Continental Fragment Collision in the Subduction Zone of the Eastern Anatolian Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7174, https://doi.org/10.5194/egusphere-egu24-7174, 2024.

EGU24-7864 | Orals | GD4.1

Folding of subducting slabs controls their deep thermal structures in the mantle transition zone  

Fanny Garel, Nestor Cerpa, Hana Čížková, Xavier Vergeron, Diane Arcay, Serge Lallemand, and Cécilia Cadio

The thermal structure of slabs is thought to be a key parameter for deep-focus earthquakes in subduction zones, since most proposed mechanisms, such as transformational faulting, dehydration reactions or shear instabilities, are controlled by temperature. However, the classical (shallow) thermal parameter "phi", associated to the downward advection of isotherms and approximated as slab age x sinking velocity (Kirby et al., 1996), does not explain deep-focus seismicity occurring in relativelty “hot” subduction zones, e.g. under Bolivia.

 

On the other hand, the various morphologies if subducting slabs imaged by seismic tomography reveal reveal the diversity of slab deformation histories in the transition zone as they reach the high-viscosity lower mantle, e.g. folding, deflection, vertical piling.

 

Using numerical models of subduction dynamics, we propose here to characterize the spatio-temporal evolution of deep thermal structures of subducted slabs throughout various subduction scenarios. We investigate how the maximum depth reached by a given isotherm vary through time (up to 200 km for a given subduction zone). In particular, we evidence the key control of the history of slab-folding in the transition zone (folding amplitude and frequency), associated to e.g. slab viscosity and buoyancy.

 

Hence the past dynamics of subduction zones, in addition to present-day subduction parameters, has to be taken into account to predict slabs thermal structures.

 

This work is part of ANR project RheoBreak (ANR-21-CE49-0009).

How to cite: Garel, F., Cerpa, N., Čížková, H., Vergeron, X., Arcay, D., Lallemand, S., and Cadio, C.: Folding of subducting slabs controls their deep thermal structures in the mantle transition zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7864, https://doi.org/10.5194/egusphere-egu24-7864, 2024.

EGU24-8053 | Posters on site | GD4.1 | Highlight

Gibraltar subduction zone is invading the Atlantic 

Joao C. Duarte, Nicolas Riel, Filipe M. Rosas, Anton Popov, Christian Schuler, and Boris J.P. Kaus

Subduction initiation is a cornerstone of the Wilson cycle. It marks the turning point in an ocean’s lifetime, allowing its oceanic lithosphere to be recycled back into the mantle. However, forming new subduction zones in Atlantic-type oceans is challenging, as it commonly involves the action of an external force, such as the slab pull from a nearby subduction zone, a far-field compression or the impact of a mantle plume. Notwithstanding, the Atlantic Ocean already has two fully developed subduction zones, the Lesser Antilles and the Scotia arcs. These subduction zones have been forced from the nearby Pacific subduction zones. The Gibraltar Arc is another place where a subduction zone is invading the Atlantic. This corresponds to a direct migration of a subduction zone that developed in the dying Mediterranean basin. Nevertheless, few authors consider the Gibraltar subduction zone as still active because it has significantly slowed down in the last millions of years. Here, we present new 3D buoyancy-driven geodynamic models, using the code LaMEM, that reproduce the first-order evolution of the Western Mediterranean, show how the Gibraltar Arc may have formed and test if it is still active. The numerical simulations are validated using geological and geophysical data. The results suggest that the Gibraltar arc is still active and will propagate further into the Atlantic after a period of tectonic quiescence. The models also show how a subduction zone starting in a closing ocean (the Ligurian) can migrate on its own into a new opening ocean (the Atlantic) through a narrow oceanic corridor. Subduction invasion is likely a common mechanism for introducing new subduction zones in Atlantic-type oceans and a fundamental process in the recent geological evolution of Earth.

 

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). JCD also acknowledges FCT a CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002 (https://doi.org/10.54499/CEECINST/00032/2018/CP1523/CT0002).

How to cite: Duarte, J. C., Riel, N., Rosas, F. M., Popov, A., Schuler, C., and Kaus, B. J. P.: Gibraltar subduction zone is invading the Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8053, https://doi.org/10.5194/egusphere-egu24-8053, 2024.

EGU24-8155 | ECS | Posters on site | GD4.1

Insights into Asymmetric Back-Arc Basin Formation in the Mariana Trough at 17°N from Traveltime Tomography 

Helene-Sophie Hilbert, Anke Dannowski, Ingo Grevemeyer, Christian Berndt, Shuichi Kodaira, Gou Fujie, and Narumi Takahashi

The Mariana Trough is the youngest back-arc basin in a series of basins and arcs that developed behind the Izu-Bonin-Mariana subduction zone in the western Pacific. In addition to active seafloor spreading, the Mariana Trough also exhibits a pronounced asymmetry, with the spreading axis closer to the Mariana Arc. The formation and development of this back-arc basin and its predecessor is controlled by a complex interplay of temporal mantle heterogeneities, subduction dynamics of the Pacific Plate and large-scale tectonics since ~50 Ma. Here, we present new insights into the development of the central Mariana Trough at ~17°N from analyses of a 2-D P-wave traveltime tomography together with high-resolution bathymetric data. The refraction and wide-angle reflection data have been recorded by R/V KAIYO (JAMSTEC) on 41 ocean bottom seismometers (OBSs) along a 250 km profile in 2003. The results allow a subdivision of the Mariana Trough into different stages of back-arc basin opening and seem to imply a transition from symmetric rifting to asymmetric seafloor spreading. Fast-velocities in the lower crust in the rifting domain indicate that magma generation and crust formation was highly affected by hydrous melting from the subducting slab during this stage. This slab contribution decreases with the onset of active seafloor spreading due to a change in mantle flow and hence seems to be accompanied by a tectonic rearrangement of the eastern side of the basin.

How to cite: Hilbert, H.-S., Dannowski, A., Grevemeyer, I., Berndt, C., Kodaira, S., Fujie, G., and Takahashi, N.: Insights into Asymmetric Back-Arc Basin Formation in the Mariana Trough at 17°N from Traveltime Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8155, https://doi.org/10.5194/egusphere-egu24-8155, 2024.

EGU24-8282 | ECS | Orals | GD4.1 | Highlight

A twisted ribbon of subducted lithosphere beneath southeast Anatolia and its seismotectonic implications 

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

Forensic analysis of the geological architecture in the aftermath of destructive earthquakes is an essential step to identify controlling structures that need to be monitored. Here we suggest the sequence of events during the February 2023 Turkey–Syria earthquakes was driven by the roll back of a twisted ribbon of subducted lithosphere beneath southeast Anatolia. We assume that the February 2023 Turkey–Syria earthquakes were short-term manifestations of a longer-term tectonic process. To investigate, we built a three-dimensional (3D) mesh frame defining the geometry of subducted Tethyan lithosphere in the Eastern Mediterranean, using the UU-P07 global tomography model, and where appropriate, earthquake hypocentre sets from the Global Centroid Moment Tensor project (GCMT) and from the International Seismic Centre (ISC). The 3D model of the subducted Tethyan lithosphere exhibits three variably twisted ribbons. The Cyprus ribbon is subducted to ~280 km depth and is ~120 km wide, and it twists and curls parallel to its length by ~20 degrees anticlockwise.

The geometry prior to subduction can be estimated by floating the mesh back to the surface using the Pplates program. The process of subduction can be visualised by incorporating the floated mesh into a 2D+time tectonic reconstruction from 125 Ma to the present. This leads to the inference that the ribbons are associated with slab tearing during roll back of the Tethyan lithosphere, due to the accretion of the Lycian block and the Cyprus promontory. The twisting motions can be related to a lateral push sideways caused by anticlockwise vertical axis rotation of the Arabia indenter during opening of the Red Sea rift and the Gulf of Aden. We suggest that the Anatolian lithosphere is being stretched by ongoing differential roll back caused by drag of the Cyprus ribbon through the asthenosphere underlying southeast Anatolia. This motion continually triggers failure along strike-slip faults while facilitating the continued indentation of Arabia. Seismotectonic analysis of aftershock sequences highlights the underlying geodynamics.

How to cite: Yeung, S., Lister, G., Spakman, W., Göğüş, O., Forster, M., Simmons, A., and Jelsma, H.: A twisted ribbon of subducted lithosphere beneath southeast Anatolia and its seismotectonic implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8282, https://doi.org/10.5194/egusphere-egu24-8282, 2024.

EGU24-8760 | ECS | Orals | GD4.1

Mantle Oxidation Driven by the Redox Dynamics of the Mariana-Type Subduction 

Wenyong Duan, James Connolly, Peter van Keken, Taras Gerya, and Sanzhong Li

Oceanic plates descending into subduction zones transport a significant amount of oxidized material to both the subduction zone and the Earth's deeper layers (Wood et al. 1990). However, the specific mechanism of mass transfer and the corresponding flux released at different depths remains unclear. Through the use of numerical modeling and a coupled geochemical database, we examined redox dynamics in subduction zones, particularly focusing on Mariana-type subduction zones, representative of the modern plate tectonic regime (Yao et al., 2021).

Our findings highlight two primary mechanisms in the mantle oxidation processes related to subduction. Firstly, desulfurization enables subduction fluids to carry substantial oxidation fluxes into the sub-arc mantle. Mass balance calculations emphasize the sufficiency of these fluxes in oxidizing both the arc magma and mantle wedge, with the hydrated mantle being the primary fluid contributor, followed by the altered oceanic crust. Secondly, partial melting of slab-top rocks, where Fe3+-rich melts from sediments and altered oceanic crust play a predominant role in the oxidation of the back-arc mantle. Importantly, during Mariana-type subduction, the majority of oxidation fluxes penetrate the deeper mantle with subducting slabs. According to our models, we illustrate that during the modern era of plate tectonics, the oxidation fluxes generated by Mariana-type subduction zones had a significant global impact on Earth's mantle redox evolution and the oxygenation of our planet.

References

Wood, B. J., Bryndzia, T., Johnson, K. E. Mantle oxidation state and its relationship to tectonic environment and fluid speciation. Science 248, 337-345 (1990).

Yao, J., Cawood, P. A., Zhao, G., Han, Y., Xia, X., Liu, Q., Wang, P. Mariana-type ophiolites constrain the establishment of modern plate tectonic regime during Gondwana assembly. Nat. Commun. 12(1), 4189 (2021).

How to cite: Duan, W., Connolly, J., van Keken, P., Gerya, T., and Li, S.: Mantle Oxidation Driven by the Redox Dynamics of the Mariana-Type Subduction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8760, https://doi.org/10.5194/egusphere-egu24-8760, 2024.

EGU24-8783 | Posters on site | GD4.1

Unveiling parental compositions in Andean-type intrusions through magma mingling zones 

Daniel Gómez Frutos and Antonio Castro

An important task in petrology is the successful identification of the parental that birthed the magmas constituting the continental crust. Among these, an intermediate parental to subduction related magmas, often referred to as Andean-type, has been determined experimentally in various works. However, identification of a natural rock matching the model compositions has not been accomplished. This difficulty arises primarily from prolonged cooling times, leading to large-scale fractionation and impeding the preservation of the parental magmas. In this regard, quenching becomes a valuable phenomenon, precluding differentiation and thereby preserving the initial compositions. This highlights the relevance of magma mingling zones, a common feature of Andean-type batholiths, as optimal places to probe for parental compositions. Following these considerations, a new set of geochemical analyses from the Gerena magma mingling zone, an Andean-type intrusion in southwest Iberia, is presented to address this problematic. Sampling focused on dark bodies, presumed to be mafic to intermediate in composition. Interestingly, combined evidence from major, trace element and Sr and Sm isotopes suggest that the smaller dark bodies have undergone precluded differentiation. Moreover, according to geochemical modelling their composition can reproduce the neighbouring granites and cumulates through differentiation. These findings emphasize the importance of magma mingling zones as valuable sources of information and shed new light in the identification of the parental composition to Andean-type magmatism.

How to cite: Gómez Frutos, D. and Castro, A.: Unveiling parental compositions in Andean-type intrusions through magma mingling zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8783, https://doi.org/10.5194/egusphere-egu24-8783, 2024.

        The East Kunlun orogenic belt represents a typical accretionary orogenic belt and has undergone an evolutionary process from the Proto-Tethys to the Paleo-Tethys oceans. The Late Triassic period witnessed the East Kunlun transitioning into the post-collisional extensional tectonic setting. However, there is ongoing debate regarding the dynamic mechanism responsible for the post-collisional extension. This study conducts the lithological, geochronological, and geochemical characteristics of the Yeniugou gabbros to shed light on the dynamic mechanism. Zircon geochronology suggests that the gabbros formed in the Late Triassic, ca. 207–209 Ma. Furthermore, the positive εHf (t) values (0.1–5.7), the relatively high values of Mg# (42.2–59.4), as well as the elevated contents of the compatible element (V, Cr, Co, Ni), suggest a mantle source with the contributions from asthenospheric mantle constituents. Additionally, gabbros are enriched in LREE and LILEs (Rb, Ba, Th, U, Sr), and depleted in HFSEs (i.e., Nb, Ta, Ti, Zr), suggesting the incorporation of arc-related enrichment components. The higher values of La/Sm, Th/Yb, Th/La, and lower values of Ba/Th, Ba/La, and Lu/Hf indicate that the enriched components are derived from the melting of the terrigenous sediment. The higher Zr/Y ratios, Nb contents, moderate Zr, Y contents, and the positive correlation between clinopyroxene Alz and TiO2, imply that these rocks were formed within an extensional tectonic setting, where upwelling of asthenospheric mantle caused partial melting of metamorphosed lithospheric mantle. Our new investigations support the interpretation that E-KOB experienced the thickening lithospheric delamination during the Late Triassic.

How to cite: Zhang, B., Dong, Y., Sun, S., and He, D.: Petrogenesis and tectonic implications of the late Triassic gabbro in southern East Kunlun Orogenic Belt, northern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10243, https://doi.org/10.5194/egusphere-egu24-10243, 2024.

EGU24-10304 | Orals | GD4.1

Dynamics of subducting slabs and origin of deep-focus earthquakes 

Hana Čížková, Jakub Pokorný, Craig Bina, and Arie van den Berg

Most earthquakes are associated with subduction zones. While earthquakes occur on very short time scales, they reflect thermal conditions and stress state attained in the subducted slab during its long term evolution. The source models of deep earthquakes thus might provide unique information about stress distribution in subduction zones which could be used to constrain geodynamic models.  

In the Tonga region, ordinary deep (620-680 km) earthquakes exhibit down-dip compressional stresses as expected, but unusually deep (≥680 km) earthquakes have unique focal mechanisms with vertical tension and horizontal compression. Here we employ geodynamic slab models to investigate the effects of the phase transitions and rheology on the stress and thermal state in Tonga slab in the transition zone and shallow lower mantle and we discuss its relation to deep earthquakes. We show that the direct buoyancy effects of the endothermic transition at 660 km depth are overprinted by bending-related forces and resistance from the more viscous lower mantle transmitted by a strong slab up-dip. The stress pattern that best fits seismogenic stresses is found for the cold plate (150 Myr old) and a viscosity increase at 1000 km depth. An abrupt change in stress orientations occurs as the slab temporarily deflected by the endothermic phase transition penetrates the shallow lower mantle while the fold in the flat-lying part tightens.

How to cite: Čížková, H., Pokorný, J., Bina, C., and van den Berg, A.: Dynamics of subducting slabs and origin of deep-focus earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10304, https://doi.org/10.5194/egusphere-egu24-10304, 2024.

EGU24-10345 | ECS | Orals | GD4.1

Subduction initiation, propagation and progression recorded along the Sulu and Celebes seas (SE Asia) 

Patricia Cadenas Martínez and César R. Ranero

The inception of a subduction system delineates the birth of a destructive plate boundary that constrains the closure of Earth´s oceans. Material and structures of the transient stage between the reactivation of a passive margin and the establishment of a self-sustaining subduction zone are rarely-preserved in the geological record of fossil subduction zones, and natural examples of currently ongoing subduction initiation are scarce. Reported Cenozoic fossil examples have been interpreted to illustrate successive immature stages of plate rupture, underthrusting and the formation of a volcanic arc, all prior to the formation of a mature self-sustained subduction zone. However, many uncertainties about the processes and the kinematics of subduction initiation remain, due to the scarcity- and lack of recent studies- of examples recording the plate rupture and decoupling, the transition to underthrusting, and the formation of the mega-thrust fault.

We use seismic images to study active subduction initiation and plate-boundary propagation in the Sulu and Celebes seas located in SE Asia. The two basins formed in Paleogene to Lower Miocene time and since possibly late Miocene, a phase of contractional deformation has led to the creation of the subduction trenches. The Sulu Trench is growing and laterally propagating along the SE margin of the Sulu Sea basin, and the Cotobato and North Sulawesi trenches propagate along the northeastern and southern margins of the Celebes Sea basin.

We reprocessed and interpreted >4857 km of 2D seismic reflection profiles that image the structure across three active trenches and the regions where the trenches are laterally propagating and display likely related deformation. We identified and mapped subduction-related structural domains of the downing and overriding plates. The megathrust plate boundary reaching the surface separates a trench filled with turbidites from the thrusts sheets of accretionary prisms, overlain with a forearc basin. The images show pre-existing faults and first-order seismo-stratigraphic horizons along the continental margins away from the trench, and the deformation structures associated to their reactivation and possibly linked to either lateral propagation of the subduction trenches or perhaps the local formation of a new trench.

The images illustrate the transition from diffuse deformation to two decoupled plates and to along-strike structural variations of subduction-related structural domains. We show for the first time how the three trenches record the spatial variability of currently active deformation associated to stages of passive margin reactivation, subduction initiation, propagation and progression. These results provide novel insights to further investigate and constrain unsolved questions about the initiation and development of subduction zones.

How to cite: Cadenas Martínez, P. and R. Ranero, C.: Subduction initiation, propagation and progression recorded along the Sulu and Celebes seas (SE Asia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10345, https://doi.org/10.5194/egusphere-egu24-10345, 2024.

EGU24-10454 | Orals | GD4.1

Compaction pressure goes global: Investigating fluid release and flow in subduction zones worldwide 

Peter E. van Keken, Cian R. Wilson, and Geoff A. Abers

Subduction of oceanic slabs causes the influx of fluids through hydrated phases. Fluids are released by metamorphic dehydration reactions particularly when the slab comes in contact with the hot mantle wedge at depths greater than ~80 km. Fluid release can be diverse and occur at different depths inside the oceanic slab with sediments and uppermost oceanic crust generally dehydrating before the serpentinized mantle and gabbroic sections.

Significant progress has been made in recent years on geophysical imaging of subduction zones that highlight the thermal structure, the location of metamorphic dehydration reactions, and the presence of fluids in slab and mantle wedge (e.g., Kita et al., Tectonophysics, 2010; van Keken et al., Solid Earth, 2012; Shiina et al., GRL, 2013; Pommier and Evans, Geosphere, 2017, Abers et al., Nature Geoscience, 2017). In a complimentary fashion, geodynamical modeling provides first principles constraints on how fluids are released and transported.

Using a simplified modeling geometry, Wilson et al. (EPSL, 2014) showed the importance of compaction pressure gradients as an oft cited, but also frequently ignored, driving force for fluids in the slab. The inclusion of compaction pressure gradients causes the fluids to both be driven from their source to the arc and flow up in part parallel to the slab surface, explaining to at least some extent geophysical observations.

We have modeled the effects of compaction pressure gradients in a global set of subduction zone models (van Keken and Wilson, PEPS, 2023) and show that focusing of the fluids below the typical arc location (at where the slab is at about 100 km depth) is a common feature and that therefore the compaction pressure effects, along with the geometry of the cold corner in the mantle wedge, can naturally explain the position of the arc above subduction zones globally.

How to cite: van Keken, P. E., Wilson, C. R., and Abers, G. A.: Compaction pressure goes global: Investigating fluid release and flow in subduction zones worldwide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10454, https://doi.org/10.5194/egusphere-egu24-10454, 2024.

EGU24-10800 | ECS | Orals | GD4.1

Gravimetric signature of subducted slabs’ deep thermal structures. 

Xavier Vergeron, Cécilia Cadio, and Fanny Garel

At subduction zones, cold lithospheric plates dive deep into the hotter Earth’s mantle. Earthquakes can occur at depths of hundreds of kilometers in these cold subducted slabs, apparently related to their thermal structures. Seismic tomography provides a first-order information on slab morphology but cannot discriminate « cold » from « warm » slabs partly due to the inhomogeneous repartition of seismic sources and surface sensors. This study investigates the potential of the gravity data from the GOCE mission to infer deep slabs’ inner thermal structures (> 200 km depth). Thermal structures of slabs with various morphologies are derived from dynamic subduction zones models. We convert temperature field into density assuming mineralogical phases at thermodynamical equilibrium for pyrolite mantle using HeFESTo model (Stixrude and Lithgow-Bertelloni 2011). We then use the freeware DynG3 (Cadio et al. 2011) to predict surface and CMB deflections due to slab dynamic sinking – depending on the radial mantle viscosity – and calculate the corresponding synthetic signals (geoid, gravity disturbance, gravity gradients). Our parametric study considers various radial mantle viscosity profiles, slab morphologies and slabs inner thermal structures (SITS). As expected, geoid and gravity gradients are sensitive to density anomalies at different depth ranges. We highlight linear relationships between both these signal for a given viscosity profile and a given slab’s morphology :

  • First, the colder an isothermal slab, the higher the geoid and gravity gradients anomalies.

  • Second, for a given shallow temperature, the colder the deep slab (>500 km), the lower the gravity gradient anomaly and the higher the geoid anomaly.

This last, counter-intuitive, result is explained by the fact that the long wavelength component associated to deep density anomaly overprints, for colder slabs, the short wavelength component associated to surface deflection. Thus, for a known viscosity profile and slab morphology, both shallow (~ 200-500 km depth) and mean slab thermal structures could be inverted from the combination of geoid and gravity gradients anomalies.

How to cite: Vergeron, X., Cadio, C., and Garel, F.: Gravimetric signature of subducted slabs’ deep thermal structures., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10800, https://doi.org/10.5194/egusphere-egu24-10800, 2024.

Subduction zone plate boundary shear zones are often heterogenous, polyrheological units with a block-in-matrix structure analogous to exhumed mélanges. Field study of these units reveal extreme variability in block and matrix lithologies, geometries, and internal structures. Subduction zone plate interfaces are host to a wide range of slip magnitudes and velocities, including some of the largest earthquakes on our planet.

Previous studies on the mechanical behaviour of these mélange units in shear zones have shown that the material properties of the blocks and matrix, as well as the proportions of each, strongly influence the rheological behaviour of the zone. Analysis of the Osa Mélange in SW Costa Rica has also shown that blocks may be weakened by alteration and brecciation, and/or the matrix strengthened by diagenesis/metamorphism, such that the blocks become weaker than their surrounding matrix at shallow depths of subduction. Rheological inversion may also occur at greater depths by processes such as heterogenous dehydration of serpentinite. Such an inversion of the typically-envisaged rheological relationship can have a profound influence on the distribution of stresses, location of ruptures, and the resultant slip behaviour. 

Using COMSOL Metaphysics, we conducted a systematic series of finite element numerical experiments of simple-shear in models consisting of one or multiple inclusions. The geometry, arrangement, number, and material properties of these inclusions were varied systematically — as was the material properties of the surrounding matrix — and the magnitude and location of von Mises stress minima and maxima were recorded. These experiments assessed varying the Young’s Modulus of blocks and matrix from Eblock > Ematrix to Ematrix > Eblock in comparison to varying block proportion, block aspect ratio, block angularity, block rotation angle, and the difference in Poisson’s ratio between the blocks and the matrix. 

Our data shows that the difference in Young’s Modulus between the blocks and the matrix has a greater influence on the magnitude and structure of the stress field than any other studied factor and that weak blocks in a strong matrix lead to significantly greater accumulated stresses in all geometrical configurations. Whether the blocks or matrix are expected to yield first will depend on the interplay between the difference in strength and the difference in Young’s Modulus of the two materials. In the inverted rheological relationship, failure in one block leads to greater increases in the stresses in neighbouring blocks than in the normal rheological relationship.

Clustered failure of blocks in a subduction channel has been proposed as a causal mechanism for non-volcanic tremor, with the accompanying accelerated strain being analogous to slow slip events. Rheological inversion markedly increases the likelihood that blocks fail before the matrix and that failure of one block triggers a cascade of similar failure events. This study demonstrates the significance of rheological inversion to considerations of the mechanics of subduction zone plate boundary shear zones.

How to cite: Clarke, A., Vannucchi, P., and Morgan, J.: Weak Blocks in a Strong Matrix: Exploring parameter-spaces for the biggest controls on subduction interface mechanics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11199, https://doi.org/10.5194/egusphere-egu24-11199, 2024.

EGU24-12008 | ECS | Posters on site | GD4.1

On The Timing of Collision Induced Slab Break-Off and Polarity Reversal 

Erkan Gün, Philip Heron, Russell Pysklywec, Gültekin Topuz, and Oğuz Göğüş

The subduction process is the main driver of tectonic plate movements and can carry different-sized, thick crustal materials (i.e., continents, oceanic plateaux, seamounts, volcanic arcs) to the subduction trenches through the consumption of oceanic plates. The arrival of these allochthonous terranes to the subduction channel and their accretion to the overriding plate (fully or partly) can often halt the subduction process. Such a subduction-choking event is usually followed by slab break-off or polarity reversal if an ocean-ocean subduction setting is present. While these two types of post-subduction termination events are well-documented in the literature, their timing following a collision is often overlooked.

Here, we present an extensive compilation of scientific literature that shows slab break-off and subduction polarity reversal (flip) events following a collision can happen in a very short time interval. Evidence from contemporary and paleo-subduction zones (i.e., Ontong Java Plateau, Taiwan/Ryukyu Arc, Banda Arc, Philippine Trench, Caribbean Oceanic Plateau, Central Apennines, India-Asia collision) suggests that these major subduction dynamic changes can occur, on average, in 2.5 to 4.5 Myr. The findings of our numerical subduction models are in accordance with the literature and demonstrate that the required time for collision-induced break-off and polarity flip can be as short as ~2 Myr. Our recent numerical modeling work, focusing on allochthonous terranes (microcontinents and oceanic plateaux), explains a potential mechanism for these fast geodynamic events. The slab pull force can stretch and weaken the trench side of drifting terranes. Following arrival in the subduction channel, this weakened portion of terranes is easier to break, yielding a fast detachment of subducting slabs.

How to cite: Gün, E., Heron, P., Pysklywec, R., Topuz, G., and Göğüş, O.: On The Timing of Collision Induced Slab Break-Off and Polarity Reversal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12008, https://doi.org/10.5194/egusphere-egu24-12008, 2024.

EGU24-12731 | Orals | GD4.1

The Seismic Expression and Tectonomagmatic Evolution of Subduction Termination along the Anatolian Margin  

Jonathan Delph, Mary Reid, Daniel Portner, Susan Beck, A. Arda Ozacar, W. Kirk Schleiffarth, Michael Darin, Donna Whitney, Michael Cosca, Christian Teyssier, Nuretdin Kaymakci, and Eric Sandvol

The geological expression of subduction termination is poorly understood due to overprinting during the collisional stage of the Wilson Cycle. The Anatolian domain of the eastern Mediterranean represents a modern system where spatial variability can be interpreted in terms of the transition from subduction to collision. Convergence in the west is accommodated by the subduction of the last remnants of Neotethyan oceanic lithosphere, while in the east, the margin has transitioned to complete continent-continent collision. In central Anatolia, however, the expression of convergence is complicated by the underthrusting of small continental fragments and attenuated continental lithosphere. By investigating variations in the geological expression of convergence across this system, we can investigate the processes that accompany the transition from subduction to collision.

Spatially variable tectonomagmatic and seismic characteristics along the Anatolian margin reflect this transition. Seismic images reveal a disjointed and disaggregating subducting slab beneath central Anatolia that interacts with, and in some cases induces, mantle flow. This spatially corresponds with Miocene-to-recent volcanism that is sourced from very shallow depths (<60 km) and has a southwestward younging pattern to the initiation of magmatism. Primitive melts in the region contain metasomatized lithospheric mantle and asthenosphere signatures resulting from the long-lived subduction history of the margin combined with recent slab rollback and mantle upwelling around the subducting slab edge based on seismic images. Superimposed on regional magmatic trends, local spatiotemporal patterns show subtle southward and westward younging and/or broadening, perhaps associated with thermomagmatic erosion of the lithosphere along relict structures and/or slab edge-induced flow. Conversely, seismic images in eastern Anatolia reveal a nearly uniform mantle flow and no discernable evidence for subduction. Interestingly, magmatic patterns in central and eastern Anatolia bifurcate in the early to mid-Miocene, interpreted as the time when a vertical slab tear developed along the once continuous Tethyan slab. These results indicate that expressions of subduction termination can be very heterogenous along the strike of a margin.

How to cite: Delph, J., Reid, M., Portner, D., Beck, S., Ozacar, A. A., Schleiffarth, W. K., Darin, M., Whitney, D., Cosca, M., Teyssier, C., Kaymakci, N., and Sandvol, E.: The Seismic Expression and Tectonomagmatic Evolution of Subduction Termination along the Anatolian Margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12731, https://doi.org/10.5194/egusphere-egu24-12731, 2024.

EGU24-12869 | Posters on site | GD4.1

Deep lithospheric controls on the formation and evolution of the East Anatolian Fault Zone and Anatolia-Arabia-Africa Triple Junction 

Jonathan Delph, Michael Darin, Donna Whitney, Michael Cosca, Christian Teyssier, Tuna Eken, Nuretdin Kaymakci, Mary Reid, and Susan Beck

The North and East Anatolian Fault Zones represent plate-bounding transform faults that enable the westward tectonic escape of the Anatolian Plate away from the Arabian-Eurasian collisional zone. These fault zones are both capable of hosting large (Mw > 7) seismic events, as most recently demonstrated by the extremely damaging February 2023 Kahramanmaraş earthquake sequence. This earthquake sequence highlighted that plate boundary forces in this area are distributed over a very broad region, however what controls the location, distribution, and character of this plate-bounding strike-slip system remains enigmatic. To better understand potential contributions to deformation, we compare seismic images of the lithosphere (e.g., crustal and lithospheric mantle thickness and velocity) to deformational features and seismicity near the EAFZ, as well as further west where it joins with the Anatolia-Arabia-Africa (A3) triple junction along the southeastern margin of the Anatolian escape system. We interpret that although controls on surface deformation are commonly linked to stress in the brittle upper crust, the complex deformation and seismicity patterns in this region are likely related to variations in the location and extent of the strong lithospheric mantle of the Arabian plate, which currently underthrusts Anatolia as far north as the Sürgü-Çardak fault zone (~50 km). In addition, the Arabian lithospheric mantle extends at least as far west as at least the central Adana Basin, coincident with a zone of relatively deep (>30 km) strike-slip seismogenesis that has produced Mw > 6 earthquakes. By investigating the relationship between recent geological deformation since the inception of the East Anatolian Fault (ca. 5 Ma) and the modern record of seismic structure and seismicity, we infer that the Sürgü-Çardak fault zone and its associated near-orthogonal bend reaching into the Adana Basin will be the future southeastern boundary of the Anatolian Plate escape tectonic system.

How to cite: Delph, J., Darin, M., Whitney, D., Cosca, M., Teyssier, C., Eken, T., Kaymakci, N., Reid, M., and Beck, S.: Deep lithospheric controls on the formation and evolution of the East Anatolian Fault Zone and Anatolia-Arabia-Africa Triple Junction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12869, https://doi.org/10.5194/egusphere-egu24-12869, 2024.

EGU24-14322 | ECS | Posters on site | GD4.1

The metamorphic dehydration of subducted metabasalts in the Catalina Schist: Does epidote record fluid production at the depths of deep slow slip and tremor? 

Peter Lindquist, Cailey Condit, William Hoover, and Victor Guevara

Dehydration reactions in the subducting slab have been suggested as a fluid source for high pore fluid pressures that are inferred in the environment that hosts deep slow slip and tremor in subduction zones. Using petrography, major and trace element geochemistry, and petrologic modeling, we study the record of dehydration reactions in exhumed metabasalt from the Catalina Schist in southern California, USA to explore potential sources of the fluids that produce high pore fluid pressures at the plate interface. The Catalina Schist comprises tectonic slices that were underplated in a subduction zone at lawsonite blueschist to amphibolite facies conditions. Metabasalts from the epidote-amphibolite facies unit here represent a coherent section of oceanic crust that was underplated during subduction at ~550°C and ~1 GPa, and are  ~100 m structurally below an ultramafic-metasedimentary mélange unit interpreted to be a paleosubduction interface from ~35 km paleodepth. Previous thermodynamic modelling suggests that epidote minerals may be common reaction products during prograde dehydration reactions along typical warm subduction geotherms, particularly at the conditions of slow slip and tremor. We therefore focus on epidote textures and trace-element compositions to provide insights into the metamorphic reactions experienced by these metabasalts, and by extension reconstruct the dehydration history of this subducted slab. Pairing these analyses with phase equilibrium modeling, we estimate the P-T path experienced by these metabasalts and the conditions at which epidote may be growing or reacting out. Epidote textures vary significantly across outcrops and appear in various settings including: epidote-rich veins and vein-like dehydration networks, and porphyroblastic epidote in surrounding host rocks. Oscillatory zoning in synkinematic epidote porphyroblasts further suggests episodic growth under varying conditions or fluid compositions. Variations in the major element and trace element geochemistry of epidote across these domains, coupled with petrologic modeling helps to reveal the metamorphic reactions that occurred in these rocks, and allows us to begin quantifying the volumes of fluids that may be released during prograde metamorphism near the conditions of deep slow slip and tremor.

How to cite: Lindquist, P., Condit, C., Hoover, W., and Guevara, V.: The metamorphic dehydration of subducted metabasalts in the Catalina Schist: Does epidote record fluid production at the depths of deep slow slip and tremor?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14322, https://doi.org/10.5194/egusphere-egu24-14322, 2024.

Elastic/viscoelastic dislocation theory is a fundamental tool in computing crustal deformation due to fault motion, not only for instantaneous coseismic deformation but also for gradual postseismic and interseismic deformation. Expressing the kinematic interaction between the subducting and overriding plates by dislocation along the plate interface, our group has developed a crustal deformation model due to plate subduction, named "dislocation model for plate subduction" (Matsu'ura & Sato 1989, GJI), which is a generalization of Savage's back slip model (Savage, 1983, JGR), including the effect of deformation due to steady plate subduction. Hashimoto et al. (2004, PAGEOPH) demonstrated that the pattern of uplift rates in and around Japan computed by this model shows excellent coincidence to the observed free-air gravity anomalies. Fukahata and Matsu‘ura (2016, GJI), using the 2D model, explained the physical mechanism of island-arc uplift, trench subsidence, and outer rise uplift by combining the effects of lithospheric rotation and gravity.

   In this study, we develop a 3D numerical model and compute vertical displacement rates in a subduction zone caused by steady slip along a plate interface, in which the trench axis has a bend convex toward the island arc. Computation results show that the island arc lithosphere significantly subsides around the bend, and that the subsidence is larger for a larger bend angle.

   This subsidence can be physically understood by mass deficit in the island arc lithosphere, as explained below. When a plate subducts along a trench with a bend convex toward the island arc, mass excess inevitably occurs in the subducting slab, which can be understood from an analogy of a tablecloth draped at a corner of a table. In the dislocation model, the motion of plate subduction is expressed by displacement discontinuity along the plate interface. The displacement discontinuity, which is equivalent to a force system of a double couple, requires two surfaces that sandwich a fault to move in exactly opposite directions each other, which results in mass deficit in the island arc, because mass excess occurs in the subducting slab.

   Along the main Japanese islands, we observe significant invasions of negative free-air gravity anomalies into the forearc around the Hidaka Trough, the Kanto Plain, and the Bungo Channel, which correspond to the junctions of the trench axes. In brief, these forearc negative free-air gravity anomalies can commonly be understood by the above mechanism. We also observe similar invasions of negative free-air gravity anomalies around the Arica bend, South America, and Cascadia, though the signals of negative gravity anomalies are smaller in these regions, reflecting gentler changes of the strikes of the trench axes.

How to cite: Fukahata, Y. and Mori, Y.: 3-D Numerical Simulation of Island Arc Deformation based on the Dislocation Model for Plate Subduction and its Insight into Topographic Evolution of Island Arcs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14479, https://doi.org/10.5194/egusphere-egu24-14479, 2024.

EGU24-14482 | ECS | Posters on site | GD4.1

An alternative mode of slab deformation in the mantle transition zone: segmentation and stacking 

Keqing Li, Jiashun Hu, Yida Li, Hao Zhou, and HaiJiang Zhang

The contradiction of high subducting plate speed (ranging from 4-9 cm/yr on Earth’s surface) and slow slab sinking rate (about 1-2 cm/yr in lower mantle) is intimately related to the subduction dichotomy of strong plates and weak slabs. The significant difference in the two rates indicates significant slab deformation in the mantle transition zone. However, the way and mechanism by which this deformation occurs have not been fully understood. Slab buckling has been frequently invoked to explain the deformation, but it is insufficient to accommodate the large difference in slab sinking rates across the mantle transition zone, even if an extremely low yield stress  100 MPa is applied.

Using 2-D numerical models that incorporate composite viscosity and grain size evolution, we propose a new mode of slab evolution, slab segmentation and stacking, to accommodate the differential slab sinking rates between the upper and lower mantle. The segmentation of slab is facilitated by the serpentinization of the normal faults at the outer rise and the grain size evolution, confirming the results of earlier studies (Gerya et al., 2020). More interestingly, we find periodic tearing and stacking of slab when it encounters the high viscosity lower mantle. Stacked slabs slowly sink in the lower mantle, while periodic slab tearing hinders stress transimission upward, allowing shallow plates to subduct at a higher rate. This model not only explains the high plate subduction rate observed at present day, but also the thickening of slab in the lower mantle. In addition, it provides a mechanism for slab to tear in the mantle transition zone, and thus may explain the enigmatic slab geometry beneath the Izu-Bonin-Mariana subduction zone.

How to cite: Li, K., Hu, J., Li, Y., Zhou, H., and Zhang, H.: An alternative mode of slab deformation in the mantle transition zone: segmentation and stacking, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14482, https://doi.org/10.5194/egusphere-egu24-14482, 2024.

EGU24-14498 | ECS | Posters on site | GD4.1

Numerical modelling of dynamic fluid-rock reactions in subduction settings 

Kevin Wong, Alberto Vitale Brovarone, Simon Matthews, Guillaume Siron, Valeria Turino, Adam Holt, and Andrew Merdith

At subduction zones, geophysical and petrological observations suggest that forearc mantle wedges may be serpentinised by fluids released from the devolatilization of subducting slabs [1]. This pervasive serpentinisation of the wedge may be a substantial source of abiotic hydrogen (H2) and methane (CH4): gases with the potential to feed extremophile microorganisms in the deepest parts of the continental lithosphere that overlie the wedge. Characterisation of mantle wedge serpentinisation is therefore paramount to constraining the limits within which this deep biosphere can exist. However, the geochemical and geodynamical controls on wedge serpentinisation remain a subject of immense uncertainty. The magnitude of H2 and CH4 concentrations and fluxes generated from wedge serpentinisation are therefore poorly constrained at present.

Owing to the inaccessibility of the mantle wedge, constraints on H2 and CH4 generation within the mantle wedge must be predicted through geochemical models. In this contribution we present the preliminary results of an ongoing modelling study into mantle wedge serpentinisation. Our approach utilises the Deep Earth Water model [2] to calculate fluid-rock reactions at relayed pressure-temperature conditions in the wedge, which are dictated by geodynamical models of subduction zone thermal structure [3]. The resultant fluids of prior reactions are used as reactant fluids for subsequent reactions at new pressures and temperatures; a chain of individual reactions therefore simulates the whole-scale serpentinisation of a column of mantle rock by slab fluid as the fluid migrates upwards through the wedge. By recording the composition of the overall mantle column at each pressure-temperature step, the introduction of new fluid to the resultant column provides a time element, which we use to track the evolution of bulk mantle mineralogy as subduction progresses.

Our preliminary results suggest that a heavily serpentinised layer forms rapidly at the slab-wedge interface, thereby strongly shielding the overlying mantle from significant alteration. Over more time steps, while bulk mantle density continues to decrease with time and increasing serpentinisation, our model suggests that new fluid does not significantly alter the mineralogical composition of the bulk mantle as observed within the first few time steps, and H2 and CH4 concentrations remain invariant throughout the column. However, the rate at which this fluid equilibration is achieved is strongly dependent on the initial conditions applied to the model. Our approach therefore provides a means to test multiple different parameters on H2 and CH4 generation at subduction zones, with scope for investigating the impact of variable fluid-rock ratio, initial mantle wedge and slab fluid compositions, and mantle wedge thermal structure.

[1] Vitale Brovarone et al., 2020. Nature Comms. 11(1), 3880.
[2] Sverjensky et al., 2014. Geochim. Cosmochim. Acta 129, 125-145.
[3] Holt and Condit, 2021. Geochem. Geophys. Geosyst. 22(6), e2020GC009476.

How to cite: Wong, K., Vitale Brovarone, A., Matthews, S., Siron, G., Turino, V., Holt, A., and Merdith, A.: Numerical modelling of dynamic fluid-rock reactions in subduction settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14498, https://doi.org/10.5194/egusphere-egu24-14498, 2024.

EGU24-14820 | Orals | GD4.1

Subduction dynamics and overriding plate deformation 

Wouter P. Schellart

Many subduction zones on Earth experience active overriding plate deformation. Most experience extension, resulting in the formation of a backarc basin (e.g. East Scotia Sea, North Fiji Basin, Aegean Sea), while some experience shortening, resulting in a massive cordilleran mountain range (e.g. Andes). It is unclear why some overriding plates experience shortening and others extension, and why extension occurs more frequently than shortening. Numerical geodynamic simulations of subduction are presented investigating the control of slab width and subduction depth on overriding plate deformation. The numerical models demonstrate that shortening only occurs at very wide subduction zones that have subducted into the lower mantle, while overriding plate extension occurs more frequently, taking place both for narrow and intermediate size subduction zones throughout their evolution, and for wide subduction zones in the early (upper mantle) stage of their evolution as well as near their lateral slab edges during the middle stage of their evolution. The model results are compared with a global dataset of all active subduction zones on Earth (about 51,600 km of subduction zones), providing an explanation for the present-day deformation style at these subduction zones. In particular, the comparison between models and the global dataset provides an explanation for the more frequent occurrence of extension in the overriding plate compared to shortening.

How to cite: Schellart, W. P.: Subduction dynamics and overriding plate deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14820, https://doi.org/10.5194/egusphere-egu24-14820, 2024.

EGU24-15803 | ECS | Posters on site | GD4.1

Slab window geodynamics: towards an integrated understanding of upper mantle dynamics and observations 

Jorge Sanhueza, Attila Balázs, Taras Gerya, Gonzalo Yáñez, and W. Roger Buck

The generation of a slab window impacts the spatio-temporal evolution of subduction zones and promote complex mantle flow pattern where slabs once descended. The origin of slab windows is attributed to processes such as mid-ocean ridge subduction, slab tearing and/or break-off. The interaction between mid-ocean ridges and trenches is a common process affecting the geodynamic history of the margins around the Pacific, at least, during the Cenozoic and generated several modern slab windows. These intriguing features have notable effects on the upper mantle where temperature anomalies develop due to the asthenospheric upwelling and complex toroidal flow patterns through and around slab windows. There are profound effects on the overriding plate for the surface heat flow, geochemistry and spatial distribution of magmatic activity, seismicity and topographic relief. However, these manifestations evolve through space and time depending on the ridge axis-trench geometry, inducing the continuous slab window opening during its subduction.

In this contribution, we derived a simplified expression for the slab window angle and then conducted 3D geodynamic modeling to link slab windows dynamics with geochemical and geophysical observables. The numerical models were conducted with fixed geometries in steady-state (using finite elements), compared with time-dependent solutions (using the I3ELVIS code) and then compared with observations from modern slab windows along the eastern Pacific. The analytical solution for the plan projection of the slab window depends on three parameters: the ratio between the half-spreading rate to the velocity of the overriding plate, the subduction angle and the obliquity of the ridge axis respect to the trench.

Fast spreading or slow plate convergence promotes a wide (> 90°) slab window while slow spreading or fast convergence narrows this gap (< 90°). The slab dip and ridge obliquity have a second order control on the plan projection of the slab window but affect the existence of a steady-state solution. The implementation of this geometry into 3D steady-state models was used to generate a novel methodology to estimate mantle/melt upwelling and temperature anomalies in the upper mantle for a wide range of tectonic settings. Preliminary results on 3D time-dependent models reproduce a self-consistent opening of the slab window by only imposing spreading at the mid-ocean ridge and a subduction velocity with respect to the overriding plate. The ratio and absolute magnitude of these velocities controls the timing of the opening as well as the lateral and depth extent of the subducting plates. This timing also influences the development of upwelling and toroidal flow patterns around the slab edges. Finally, observations in modern slab windows along the eastern Pacific are consistent with the temperature and velocity field of the models. Variations in temperatures in the upper mantle are consistent with mantle shear wave speeds anomalies, while the flow field is correlated with the azimuthal anisotropy. In terms of magmatism, variables degrees of melting are consistent with the generation of tholeiitic to alkaline magmas in backarc areas.

How to cite: Sanhueza, J., Balázs, A., Gerya, T., Yáñez, G., and Buck, W. R.: Slab window geodynamics: towards an integrated understanding of upper mantle dynamics and observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15803, https://doi.org/10.5194/egusphere-egu24-15803, 2024.

EGU24-15924 | Posters on site | GD4.1

The Mussau Ridge and Trench – news from an infant subduction zone 

Philipp Brandl, Christoph Beier, Leon Waßmund, Jacob Geersen, and Felix Genske

The Mussau Trench between Papua New Guinea and the Federated States of Micronesia is considered as the type locality for induced subduction initiation through transference. Despite its significant role for studying and understanding global plate tectonic cycles, little is known about its tectonic  geomorphology, lithostratigraphy, and geodynamic evolution. During research expedition SO299 DYNAMET with the German RV SONNE, the morphology and shallow structure of the Mussau Ridge was mapped along its entire length and sampled at representative locations. At the central segment, the ridge was visually mapped and stratigraphically sampled using the ROV. Here we present the first results from petrology, geochemistry and structural mapping of the ridge. Preliminary glass major and trace element data indicate a depleted MORB-like nature of the exposed crust that is in agreement with previous findings. Stratigraphically, lavas (layer 2A) and sheeted dykes (layer 2B) of the oceanic igneous crust are exposed. Whole rock trace element and radiogenic isotopes analyses are currently underway to further constrain the geochemical character of the crust and its associated mantle sources. Initial results from hydroacoustic and visual mapping indicate the presence of an active thrust system based on pristine fault scarps and large rubble piles lacking any sediment cover. However, shape and structure of the ridge vary along strike, and only the central portion holds indications for tectonic uplift. In the south and in the north, the ridge shows evidence for a strong lateral shear component. We combine the obtained results into an initial model of the tectonic evolution of the ridge and how this fits into regional plate tectonic models.

How to cite: Brandl, P., Beier, C., Waßmund, L., Geersen, J., and Genske, F.: The Mussau Ridge and Trench – news from an infant subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15924, https://doi.org/10.5194/egusphere-egu24-15924, 2024.

EGU24-16152 | Posters on site | GD4.1

Balance of solid and fluid transfers near the updip limit of the seismogenic zone at the scale of all subduction zones in a revised kinematic framework 

Serge Lallemand, Michel Peyret, Diane Arcay, Nestor Cerpa, and Arnauld Heuret

The nature and amount of sediments transferred from one plate to the other near the subduction interface partly determine the tectonic and seismogenic regime of a margin. Examination of over 500 multichannel seismic lines has enabled us to build a global database of subduction zone front characteristics at unprecedented spatial resolution. The total thickness of sediments in the trench below the deformation front, as well as that of the subduction channel at a distance from the trench, combined with other indices, such as the tectonic regime of the forearc or the migration of the volcanic front, are used to revisit the accretionary or erosional character of active margins.

The integration of our observations over the last million years has been achieved in parallel with a revision of the kinematics of subduction zones, taking into account deformation at the front of the thrust plate. Indeed, subduction zones are often the site of distributed or localized deformation up  to several hundred kilometers away from the plate boundary. Taking the "arc sliver zone » deformation into account yields a more accurate estimate of the effective long-term slip velocities (modulus, azimuth) on the subduction interface, which is fundamental to properly estimate material flow transiting towards the mantle.

Preliminary conclusions, based on ∼3/4 of sufficiently documented subduction zones, show a predominance of the erosive character of subduction over the last million years. The flux of solid sedimentary matter through the shallow part of the subduction channel is approximately 1.5 km3/yr, and that of pore fluids 0.4 km3/yr. Some subduction zones, such as the Aegean-Cyprean one, are characterized by exceptional solid flux in the channel, whereas the fluid flux is comparatively moderate. This is because channel sediments are compacted even before being subducted. Indeed, porosity has a major influence in estimating these fluxes, maximum porosity in the channel being reached when there is neither accretion nor tectonic erosion. Overall, fluid flux in the channel is greater under erosive margins, due both to the higher rate of subduction and often higher porosity. The data are displayed over 260 transects across subduction zones thanks to the Submap web-tool (www.submap.fr).

How to cite: Lallemand, S., Peyret, M., Arcay, D., Cerpa, N., and Heuret, A.: Balance of solid and fluid transfers near the updip limit of the seismogenic zone at the scale of all subduction zones in a revised kinematic framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16152, https://doi.org/10.5194/egusphere-egu24-16152, 2024.

EGU24-16410 | ECS | Orals | GD4.1 | Highlight

H2 formation in subduction zone 

Alexis Gauthier, Tiphaine Larvet, Laetitia Le Pourhiet, and Isabellle Moretti

Dihydrogen (H2) is a promising decarbonized energy source, but traditional artificial production methods emit CO2 and/or consume a lot of energy. However, there are natural sources of H2 on Earth originating from diverse geochemical processes. A recent study above the Nazca plate subduction in the Andes, detected variations in the H2 emanation function on the slab dip angle. This H2 release is likely the result of peridotite hydration in the mantle wedge, notably through serpentinization. The water required for peridotite hydration is sourced from dehydration of the subducting plate as it sinks into the Earth's mantle.

This study aims to understand the influence of slab dip angle on H2 production in the mantle wedge using the pTatin2D code. Fluid circulation were implemented based on two principles:

  • The hydration and dehydration capacity of rocks under varying pressure and temperature conditions is predicted using tables from the thermodynamic software PerpleX.
  • The velocity of free water is equivalent to that of surrounding rocks, with a vertical component related to percolation.

Numerical simulations show that in the case of flat subduction, the mantle hydration zone, where H2 is produced, is wide and extending up to 500 km from the trench. On the other hand, in the case of a steep subduction, the zone is narrower, and is located between the trench and the volcanic arc. Magma formation competes with H2 generation for the use of water released from the subducting plate. During the transition from steep to flat subduction, the mantle hydration zone undergoes widening while the volcanic zone migrates significantly away from the trench. This transition may also trigger oceanic crust melting, resulting in a shift in magma composition before the volcanism intensity diminishes and then disappears.

How to cite: Gauthier, A., Larvet, T., Le Pourhiet, L., and Moretti, I.: H2 formation in subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16410, https://doi.org/10.5194/egusphere-egu24-16410, 2024.

EGU24-17659 | ECS | Posters on site | GD4.1

Dynamics of Plateau Growth: Geodynamic Modeling of the East AnatolianPlateau Uplift Through Double Subduction Processes 

Uğurcan Çetiner, Jeroen van Hunen, Andrew P. Valentine, Oğuz H. Göğüş, and Mark B. Allen

The Turkish–Iranian Plateau was formed by the collision between the Arabian and
Eurasian plates, commencing along the Bitlis-Zagros suture in the Late Eocene (~30-
35 Ma). This region, commonly partitioned into the East Anatolian Plateau and the
Iranian Plateau, is associated with significant differences in terms of lithospheric
structure despite an overall average of ~2 km. The geodynamic evolution of East
Anatolia is represented by a double subduction system, where the two branches of
Neo-Tethys were subducting beneath Eurasia, constantly accumulating accretionary
material that forms the bulk of the plateau today (i.e., East Anatolian Accretionary
Complex). Seismic evidence demonstrates that the region has unusually thin MOHO
(~35 km around Lake Van region) while the whole area is formed mostly by oceanic
(accretionary) material and is underlain by no or very thin mantle lithosphere. The
uplift of East Anatolia is attributed to slab break-off and slab peelback (delamination),
combined with crustal shortening. However, the intricate plate dynamics arising from
such a double subduction system, controlling plateau formation remains unclear.
Here, we conducted 2D numerical experiments and comparative model sets indicate
that, in a double subduction system like Eastern Anatolia, the mechanisms of slab
break-off and peelback heavily depend on the rheology of the subducting plates and
the coupling between the overlying and subducting plate along the trenches. In cases
of strong coupling between subducting and overlying plates, we observed an
amalgamation of the two subducting plates as they converge, potentially resulting in
a break-off as a single blob, depending on plate rheology. Conversely, in models with
weaker coupling along the trenches, peelback along the northern slab creates a thin
lithosphere along the accretionary prism, such as in the evolution of the Eastern
Anatolian Plateau. Our results highlight the important interaction between the
subduction systems where rheological constraints of the lithosphere, among other
model parameters, exert a first-order control for plateau formation.

How to cite: Çetiner, U., van Hunen, J., Valentine, A. P., Göğüş, O. H., and Allen, M. B.: Dynamics of Plateau Growth: Geodynamic Modeling of the East AnatolianPlateau Uplift Through Double Subduction Processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17659, https://doi.org/10.5194/egusphere-egu24-17659, 2024.

EGU24-17823 | Posters on site | GD4.1

Influence of the fluid pressure ratio on accretionary wedge evolution over long timescales 

Derek Neuharth, Whitney Behr, Adam Holt, and Jonas Ruh

Accretionary wedges are regions of off-scraped and underplated sediment and oceanic crustal materials formed along subduction zones. Many modeling studies investigate accretionary wedge mechanics on a crustal scale, or on a larger scale using kinematic boundary conditions. However, in fully dynamic systems subduction velocity can change through time in response to variations in large-scale subduction dynamics (e.g., as the slab travels rapidly through the upper mantle vs. slower sinking through the transition zone). How this time-dependence affects an evolving accretionary wedge and subduction interface properties, and the resulting effect on subduction speeds, is not well understood.

To understand how accretionary wedges evolve during different stages of subduction, we develop fully dynamic 2D subduction models using the finite element code ASPECT. The visco-plastic model setup consists of a dense subducting plate and a buoyant overriding plate coupled with a 6-km thick wet quartzite sediment interface. A fluid pressure ratio profile is prescribed within the sediment that varies from 0.4 at the surface to 0.9 at depths greater than 4-km. Between 50 to 100 km depth, the fluid pressure ratio is linearly tapered from 0.9 to 0. We run models for 30 Myr where we vary 1) the initial sediment thickness, 2) frictional strength, and 3) the depth needed to reach the maximum fluid pressure ratio. We explore how these parameters affect the thickness of the accretionary wedge, the amount of sediment that enters the subduction channel, and the resulting subduction speed.

Preliminary results suggest that an accretionary wedge will initially frontally accrete as the wedge thickens. Over time, the faults forming these slivers are rotated towards vertical and moved towards the subduction zone along a basal decollement. Eventually, a second decollement forms along the overriding plate interface and links to the first decollement through backthrust faulting, creating a series of accretionary wedge blocks that are underthrust into the subduction interface. Increasing the depth to the maximum fluid pressure ratio leads to a larger accretionary wedge, and a deeper basal decollement. A deeper decollement results in greater sediment underplating due to the backthrust faulting, resulting in more sediment within the subduction interface.

How to cite: Neuharth, D., Behr, W., Holt, A., and Ruh, J.: Influence of the fluid pressure ratio on accretionary wedge evolution over long timescales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17823, https://doi.org/10.5194/egusphere-egu24-17823, 2024.

EGU24-18222 | ECS | Posters on site | GD4.1

Variability of lower continental crust constrained by drill core data of the Ivrea Zone (DIVE project DT-1B, Ornavasso, Val d’Ossola, Italy) 

Alexia Secrétan, Sarah Degen, Luca Pacchiega, Jörg Hermann, and Othmar Müntener

The estimates of the chemical composition of the lower continental crust ranges from predominantly mafic to felsic. The Ivrea Zone in the Southern European Alps provides insight into this variability, featuring a pre-Permian mostly felsic lower crust modulated by additions of mafic rocks during Permian underplating. The Ivrea zone is an ideal location to examine major, trace, and volatile elements over the full range of proposed lower crustal compositions. Our study presents whole-rock data derived from a drill core of the first hole (DT-1B) of the ICDP-funded project DIVE (Drilling the Ivrea-Verbano Zone). The drilled section spans nearly 600 m, representing an upper part of the Ivrea lower continental crust. Logging of the drill core showed that biotite-gneisses (Qtz + Pl + Bt ± Gt ± Kfs ± Sil – 75 vol%) and metamafic rocks (Amp + Pl + Qtz ± Px ± Bt ± Gt – 21 vol%) are the main rock types with minor calcsilicate rocks (Cc + Gt + Px + Ttn + Qtz + Pl ± Amp – 2 vol%), and some minor pegmatites (2 vol%). Both targeted and grid sampling strategies aimed to minimize sampling bias, providing a reliable basis for understanding the Ivrea lower continental crustal composition and extrapolating the results toward a realistic assessments of the LCC composition in general.

Amphibolite facies metasediments (34 samples) range from calc-silicates to pelites and psammites, exhibiting a wide range of major element compositions (32 - 89 wt.% SiO2; 0.5 - 5.8 wt.% K2O; 0.35 - 0.54 Mg#). Metamafic rocks (16 samples) cover a more restricted compositional range (43 - 57 wt.% SiO2; 0.1 - 5 wt.% K2O; 0.3 - 3 wt.%; 0.36 - 0.61 Mg#). Most mafic rocks are LREE enriched, but a few resemble MORB-like compositions. A preliminary comparison of the bulk rock estimate of the entire drill core relative to the integrated composition derived from geological maps indicates that deviations between the two approaches are considerable, ranging from <10% up to 30% difference for major elements (calculated bulk vs compiled data from the literature: 62.8 vs 57.6 wt.% SiO2; 2.3 vs 1.95 wt.% K2O; 0.47 vs 0.50 Mg#). Results also indicate that fluid-mobile elements are mostly conservative with respect to potential protoliths. The chemical variability points to a possible origin of sediments derived from an accretionary wedge. The evaluation of bulk trace element ratios (i.e., Th/La, Sm/La, Nb/K2O) suggests that the drilled sequence likely originated from (Paleozoic?) turbidites. Subduction of sediments and accretion to the lower continental crust are the most likely processes to explain the predominance of metasediments in this part of the Ivrea lower continental crust.

How to cite: Secrétan, A., Degen, S., Pacchiega, L., Hermann, J., and Müntener, O.: Variability of lower continental crust constrained by drill core data of the Ivrea Zone (DIVE project DT-1B, Ornavasso, Val d’Ossola, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18222, https://doi.org/10.5194/egusphere-egu24-18222, 2024.

EGU24-18579 | ECS | Posters on site | GD4.1

Complex subduction and mantle dynamics induced by along-strike variations in overriding plate structure 

Pedro José Gea Jódar, Ana M. Negredo, Flor de Lis Mancilla, Jeroen van Hunen, and Magali Billen

Subduction zones are intrinsically three-dimensional and present a huge variability in observables along the trench, such as deformation style of the overriding plate, trench velocity, slab depth and mantle flow patterns. Geodynamic models commonly rely on factors such as external mantle flow and/or along-strike variations in the properties of subducting slabs to account for these variations in the trench-parallel direction, often ignoring the role of the overriding plate, which has been proven to strongly affect subduction dynamics. In this work, we investigate through self-consistent 3D subduction models how along-strike variations in the overriding plate structure can induce along-strike variations in subduction dynamics and mantle flow. Our results show that variations of the overriding plate thickness along the trench-parallel direction result in large along-strike variations of the trench retreat velocities, leading to highly arcuated trenches. This difference in trench retreat velocities along the trench induce complex mantle flow patterns, with the toroidal flow cells that surround the slab converging below the thin part of the overriding plate. Due to this complex mantle flow, regions of maximum localised extension are found within the thin portion of the overriding plate. Overall, our results contribute to a better understanding of seismic anisotropy observations at subduction zones on Earth.

How to cite: Gea Jódar, P. J., Negredo, A. M., Mancilla, F. D. L., van Hunen, J., and Billen, M.: Complex subduction and mantle dynamics induced by along-strike variations in overriding plate structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18579, https://doi.org/10.5194/egusphere-egu24-18579, 2024.

EGU24-19448 | ECS | Posters on site | GD4.1

Bending-related faulting, hydration, and mantle serpentinization in the incoming Cocos Plate at Middle America Trench: Evidence from wide-angle seismic refraction data 

Yuhan Li, Ingo Grevemeyer, Adam Robinson, Timothy J. Henstock, Milena Marjanović, Anke Dannowski, Helene-Sophie Hilbert, and Damon A.H. Teagle

At subduction zones, the bending of incoming plates and associated extensional stresses resulted in strong fault activity in the crust and upper mantle. The severe fracturing of the subducting slab in the trench outer rise facilitates the entrain of seawater into the lithosphere, leading to the serpentinization of peridotite in the upper mantle. Therefore, subduction zones are an important setting, nurturing material exchange between the hydrosphere and the solid earth, affecting the water cycle.

To investigate the behavior of the subducting plate, during the experiment conducted aboard RRS JAMES COOK in the Guatemala Basin where the Cocos plate enters the Middle America Trench, we collected a wide-angle seismic refraction profile and coincident multi-channel seismic profile. Here, we present a seismic velocity model derived from a joint refraction and reflection seismic tomography using 10,508 crustal refraction arrivals, 6,533 Moho reflection arrivals, and 7,769 upper mantle refraction arrivals recorded by 37 ocean-bottom-seismometers. The spacing of instruments is ~7.5 km on the unaltered incoming plate and decreases to half of that from the outer rise into the trench. The results show that the unaltered oceanic crust is ~5-6 km thick and features a typical two-layer oceanic structure, ranging from ~4-5 km/s at the basement top to ~7 km/s at the bottom of the crust. Closer to the trench, at ~70 km away, we observe a prominent velocity reduction with lower-crustal velocities dropping to <6.8 km/s, indicating a strong impact of bend-faulting and/or hydration of the crust. However, the onset of normal faulting is observed in the coincident seismic reflection profile at ~100 km away from the trench axis. The observed faulting may indicate an evolutionary process with the progressive development of bending-related faults. At the outer rise, a seamount rising ~1 km above the seafloor is characterized by extremely low crustal velocities of only <6.5 km/s at the bottom of the crust, suggesting that the seamounts facilitate hydration. Further east, the lower crustal velocities are reduced to ~6.5-6.7 km/s beneath the outer trench wall. In the upper mantle, velocity reduction is observed ~100 km away from the trench axis and reaches its minimum beneath the seamount at the outer rise with ~7.2 km/s, which may indicate up to ~20% of mantle serpentinization. Based on our velocity modeling results, we conclude that the intensity of bend-related faulting, hydration, and mantle serpentinization is not only controlled by the distance from the trench axis but also by seamounts ventilating the oceanic crust.

How to cite: Li, Y., Grevemeyer, I., Robinson, A., Henstock, T. J., Marjanović, M., Dannowski, A., Hilbert, H.-S., and Teagle, D. A. H.: Bending-related faulting, hydration, and mantle serpentinization in the incoming Cocos Plate at Middle America Trench: Evidence from wide-angle seismic refraction data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19448, https://doi.org/10.5194/egusphere-egu24-19448, 2024.

EGU24-19465 | Posters on site | GD4.1

Parametric study for self-sustained Andean-type subduction speed 

Jamison Assunção, Nicolas Riel, Andrea Piccolo, and Victor Sacek

The relation between subduction dynamics, plate rheology and geometry is still not well understood. To numerically assess how subduction convergence velocity develops, a wide range of simulations is required to quantify any correlation between physical parameters and kinematic behavior of a subduction system. In this study, we performed a set of 2D numerical simulations designed to better constrain the range of rheological and geometrical conditions necessary to model subduction dynamics. We used the parallel numerical code LaMEM to simulate thermo-mechanical convection. In addition, we coupled these numerical simulations with MAGEMin to compute a self-consistent mineral assemblage of the asthenospheric mantle and the plates, and we parameterized the lower mantle using a linear equation, following the Clapeyron slope from Faccenda and Zilio (2017). The modeled region is 9300 km wide and accounts for both the upper and whole lower mantle. We consider an Andean type subduction system where our baseline scenarios are defined by a partially subducting oceanic plate beneath a continental plate. Once the simulation starts, the subducted portion of the oceanic plate triggers the subduction thanks to a weak zone between the lower and upper plate. The subduction is sustained by the negative buoyancy of the lower plate with respect to the surrounding mantle. We aim to simulate subduction dynamics that exhibit convergence velocities and long term behavior, including lower mantle penetration, similar to what is observed in nature. We investigate the role of the length of the subducting plate, the geometry of its composing lithological units, and the viscosity of the asthenosphere and the lower mantle. We find that the subduction velocity is inversely correlated with the non subduction length of the oceanic plate, and that a less viscous asthenospheric mantle increases the subduction speed. 

How to cite: Assunção, J., Riel, N., Piccolo, A., and Sacek, V.: Parametric study for self-sustained Andean-type subduction speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19465, https://doi.org/10.5194/egusphere-egu24-19465, 2024.

EGU24-19667 | ECS | Posters on site | GD4.1

Dynamical evolution of forearc subsidence controlled by slab geometry 

Francisco Bolrão and Wouter Schellart

The forearc is the region of the overriding plate (OP) that physically interacts with the subducting plate (SP) and is expected to record critical information about subduction dynamics. A way to access such information is through its topography, which presents a wide variability across the natural prototypes. Some forearcs show a peculiar topography characterised by a forearc high next to the trench and a forearc basin in between this high and the magmatic arc (e.g. Alaska, Java, Central Chile). Previous studies have proposed that such topographic signature is a consequence of the gradient of the vertical component of the suction force along the plate interface (e.g., Hassani et al. 1997, Chen et al. 2017). 
Our study focuses on the role of several subduction parameters in shaping the topography of the forearc, namely the OP and SP thicknesses, OP viscosity, and slab dip angle. To carry out this investigation, we developed a series of buoyancy-driven and isoviscous models using analogue techniques, where we applied a stereoscopic particle image velocimetry technique to monitor the topography of the forearc.
So far, we have analysed the impact of the OP thickness, which shows a negative correlation with the magnitude of the forearc basin. Thicker OPs constrain trench retreat, which forces the SP to move trenchward,with subduction occurring mostly through down-dip slab sinking. Consequently, the suction force created at the plate interface by hinge retreat will decrease, resulting in shallower forearc basins. Moreover, the wavelength of the forearc basin is also affect, with thicker OP producing wider basins. Such observation suggests that the previously proposed mechanism that shapes the forearc topography is correlated with the subduction partitioning so that the magnitude of the forearc basin increases as the subduction is increasingly accommodated by slab retreat.

How to cite: Bolrão, F. and Schellart, W.: Dynamical evolution of forearc subsidence controlled by slab geometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19667, https://doi.org/10.5194/egusphere-egu24-19667, 2024.

EGU24-20470 | Orals | GD4.1

Storage and fate of volatiles in the shallow mantle: Insights from fluid mobile elements and light element (B, Li) isotopes in serpentinites 

Ivan Savov, Samuele Agostini, CeesJan DeHoog, William Osborne, Andrew McCaig, Detlef Rost, Jeff Ryan, Roy Price, Dyonisis Foustoukos, Haiyang Liu, and International Ocean Discovery Program Expedition 399 Sci. Party

We will present whole rock and mineral chemistry insights into the systematics of light elements (B, Li) and their isotopes during the serpentinization processes at both divergent and convergent plate margins. For the divergent plate case we have selected Site 1309D and some from the recently drilled (IODP Expedition 399, Atlantis Massif, Mid-Atlantic Ridge 30N) Site 1601C as the deepest in situ gabbo-peridotite drill cores ever recovered from the ocean floor. The downcore variation in fluid mobile elements and the vast Sr and light element isotope fractionations highlight the important role of seawater infiltration and seawater-crust interactions taking place at depth. However, it appears that the role of seawater is gradually diminishing with depth, where rather unaltered lithologies may still be involved in active metamorphic (hydration) reactions. For the convergent plate margin serpentinization we have selected to present the fascinating case of the Mariana serpentinite mud “volcanism” in the W. Pacific. Several key cores were recovered during ODP Legs 125 and 195, as well as during the IODP Expedition 366. The rocks and fluids at these forearc sites also show very large downcore elemental and isotope fractionations. In contrast to the oceanic intraplate sites, these are associated with fluids produced by metamorphic dehydration reactions occurring at blueschist and amphibolite facies conditions as a consequence of subduction of old and cold Pacific slabs. We will attempt to contrast the different tectonic settings and speculate on the importance of variously hydrated ocean crust as a volumetrically important carrier of volatiles from the surface to the deep mantle and back. Serpentinites may be important to kick-start subduction initiation.

How to cite: Savov, I., Agostini, S., DeHoog, C., Osborne, W., McCaig, A., Rost, D., Ryan, J., Price, R., Foustoukos, D., Liu, H., and Ocean Discovery Program Expedition 399 Sci. Party, I.: Storage and fate of volatiles in the shallow mantle: Insights from fluid mobile elements and light element (B, Li) isotopes in serpentinites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20470, https://doi.org/10.5194/egusphere-egu24-20470, 2024.

EGU24-20684 | ECS | Posters on site | GD4.1

Subduction polarity reversal facilitated by plate coupling during arc-continent collision 

Zaili Tao and Jiyuan Yin

Subduction polarity reversal usually involves the break-off or tearing of downgoing plates (DPs) along the continent-ocean transition zone, in order to provide space for the overriding plate (OPs) to descend. Here we propose that subduction polarity reversal can also be caused by DP-OP coupling and that it can account for the early Paleozoic geological relationships in the West Kunlun Orogenic Belt (WKOB). Our synthesis of elemental and isotopic data reveals transient (~5 Myr) changes in the sources of the early Paleozoic arc magmatism in the southern Kunlun terrane. The early stage (530–487 Ma) magmatic rocks display relatively high εNd(t) (+0.3 to +8.7), εHf(t) (−3.6 to +16.0) values and intra-oceanic arc-like features. In contrast, the late-stage (485–430 Ma) magmatic rocks have predominantly negative εNd(t) (−4.5 to +0.3), εHf(t) (−8.8 to +0.9) values and higher incompatible trace elements (e.g., Th), similar to the sub-continental lithospheric mantle (SCLM) beneath the Tarim Craton. This abrupt temporal-spatial variation of arc magmatism, together with the detrital zircon evidence, indicate that subduction polarity reversal of the Proto-Tethys Ocean occurred in a period of ~10 Ma, consistent with migration of the magmatic arc. This rapid polarity reversal corresponds with the absence of ultra-high-pressure metamorphic [(U)HP] and post-collisional magmatic rocks, features normally characteristic of the slab break-off or tearing. Numerical modeling show that this polarity reversal was caused by plate coupling during arc-continent collision without slab break-off and tearing. This prevented rebound of the positively buoyant relic rocks and asthenosphere upwelling. This model successfully explains the early Paleozoic orogenesis in the WKOB and may be applied elsewhere where post-collisional magmatic and (U)HP rocks are absent.

How to cite: Tao, Z. and Yin, J.: Subduction polarity reversal facilitated by plate coupling during arc-continent collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20684, https://doi.org/10.5194/egusphere-egu24-20684, 2024.

EGU24-21046 | ECS | Orals | GD4.1

On the iron isotope systematics of subducted oceanic gabbros 

Alex Churchus, Oliver Nebel, Yona Jacobsen, Xueying Wang, Massimo Raveggi, Marianne Richter, and Roland Maas

Oceanic gabbros represent a voluminous part of oceanic crust and are to a large degree cumulative mineral assemblage composed of olivine-pyroxene-feldspar and iron oxides. As such, oceanic gabbros represent a large Fe isotope reservoir in the global Fe cycle. During recycling into the mantle, oceanic gabbros undergo metamorphic reactions but are often considered a small contributor to the subduction component in arcs (e.g., slab-derived fluids) due to their relatively dry and refractory nature. Instead, fluids released from serpentinite as a result of slab devolatisation are considered to be the main source of deep mantle wedge fluids and considerably contribute to arc-lava chemistry and the redox state of metasomatised mantle wedge. However, serpentinite-derived fluids will, by default, pass through overlying gabbroic sequences when ascending to the mantle wedge with a potentially considerable contribution to the Fe isotope budget of the mantle wedge and arc lavas.

Here, we investigate the Fe isotopic signature of gabbroic rocks exposed on the seafloor along the Southwest Indian Ridge and collected during IODP scientific ocean drilling expedition leg 118 from the Atlantis Bank Gabbro Massif (IODP Site 735B). Site 735B is composed of intrusive lower crustal and upper mantle rock exhumed to the surface by detachment faulting. Iron was chemically leached, simulating passing fluids, with both leachate and residue analysed for their Fe isotope composition. Our samples display large variation in isotopic composition ranging from mantle to extreme values of δ57Fe = -0.07 to +0.68‰ (relative to IRMM-524a) for the leachate, and MORB-like δ57Fe = -0.1 to +0.21‰, for the residue, respectively. Our results imply that the leached isotopically heavier Fe from oceanic gabbros can be a significant contributor to the Fe isotope composition of the subduction component in arcs and counterbalance the light Fe isotopes derived from serpentinites. Considering the oxidation state of Fe in magnetite, this may further add to the oxidized nature of arc lavas. If such fluids remain in the mantle, they can potentially be a very heavy Fe isotope reservoir, which may explain some exotic signatures observed in ocean island lavas or transition zone diamond inclusions. Gabbroic residues deprived of any such leachate resembles Fe isotope signatures of the upper mantle and MORB and thus does not change the Fe isotope composition of the mantle significantly after subduction. 

How to cite: Churchus, A., Nebel, O., Jacobsen, Y., Wang, X., Raveggi, M., Richter, M., and Maas, R.: On the iron isotope systematics of subducted oceanic gabbros, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21046, https://doi.org/10.5194/egusphere-egu24-21046, 2024.

EGU24-990 | ECS | Posters on site | GD9.1

Quirquincho and Pampeano-Chaqueño Highs: forebulge or Palaeozoic structures? 

Valentina Cortassa, Robert Ondrak, Stefan Back, Cecilia del Papa, and Eduardo Rossello

The Andean Foreland Basin in the Chaco-Pampean Plain of North-West Argentina is thought to have been tectonically inactive during the Cenozoic. However, re-interpreted industry seismic-reflection data and borehole information document a complex tectonic history in the subsurface at least until Palaeogene times. Data synopsis and re-analysis reveal two regionally extensive and approximately NW-SE-oriented basement highs beneath the flat present-day surface, the Quirquincho (or Rincón Caburé) High and the Pampeano-Chaqueño High. These large geological structures were described previously, but the mechanism that elevated these features relative to the surrounding stratigraphy and the timing of uplift has remained elusive.

This study documents and describes of the Quirquincho and Pampeano-Chaqueño Highs and their relationship to the depocenters around and the sedimentary successions of the Chacoparanaense, Salta Rift and Andean Foreland Basins. We studied palaeo-basin morphology, stratigraphy, stratal terminations and distance to the Andes to unravel viable mechanisms that influenced the genesis of the two structural highs. The work presented is based on the re-interpretation of a large set of subsurface information (2D seismic-reflection profiles and well reports) using a regional approach that considers the Chacoparanaense, Salta Rift and Andean Foreland Basins as a complex lateral arrangement of basins varying in activity through time, depending on their relative location concerning orogens and rifted ocean margins.

Our research reveals that the Quirquincho and Pampeano-Chaqueño Highs were elevated features from the Late Palaeozoic to the Palaeogene, strongly influencing the deposition of Mesozoic and Palaeogene sediments. The tectonic mechanism controlling the rise of the Quirquincho and Pampeano-Chaqueño Highs was initially flexural deformation in the foreland of the Gondwanide orogen in the Permian, subsequently influenced in the Mesozoic by the opening of the Southern Atlantic Ocean.

How to cite: Cortassa, V., Ondrak, R., Back, S., del Papa, C., and Rossello, E.: Quirquincho and Pampeano-Chaqueño Highs: forebulge or Palaeozoic structures?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-990, https://doi.org/10.5194/egusphere-egu24-990, 2024.

EGU24-5394 | ECS | Orals | GD9.1

Comprehensive two-dimensional structural-geological model of the Nazca Ridge subduction zone 

Sara Ciattoni, Federico Cella, Stefano Mazzoli, Miller Zambrano, Robert Butler, Stefano Santini, Antonella Megna, and Claudio Di Celma

The Nazca Ridge's thickened subduction beneath the South American continental margin (10° to 15° S) is characterised by a flat-slab configuration. This peculiar geological setting strongly influences upper plate dynamics, significantly impacting stress distribution and seismicity in the South American plate. However, the effects of the Nazca Ridge subduction on the Peruvian forearc and Andean Cordillera development remain subjects of extensive debate. In this study we thoroughly investigate the general structure of the Nazca Ridge subduction zone producing an integrated two-dimensional structural-geological model of the south-Peruvian Andes. Combining surface geological data and geophysical information from existing literature, we delineated the crustal structure up to a depth of about 130 km along a ca. 1000 km-long transect, encompassing the Peruvian Forearc System and the Andean Cordillera. In order to improve the characterization of geological features and validate the model, we carried out forward modelling of the Bouguer anomaly in the region, integrating four distinct datasets. Subsequently, we formulated a two-dimensional density model to reproduce the observed gravity field, taking into consideration the petrological properties of the materials and the P-T condition in each area of the crustal section. The geometry of the structures was assessed by choosing the configuration that, honouring the geological and geophysical constraints upon which the initial model was based, also allowed maximising the fit between observed Bouguer anomaly values and the values computed during the forward modelling process. Our exhaustive approach allowed us to obtain a comprehensive model of the Nazca Ridge subduction zone, accurately defining both the deep lithosphere-asthenosphere system and shallow geological structures. This contribution will substantially enhance the ongoing debate on the tectonic evolution and geodynamics of Andean orogeny.

How to cite: Ciattoni, S., Cella, F., Mazzoli, S., Zambrano, M., Butler, R., Santini, S., Megna, A., and Di Celma, C.: Comprehensive two-dimensional structural-geological model of the Nazca Ridge subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5394, https://doi.org/10.5194/egusphere-egu24-5394, 2024.

EGU24-5730 | ECS | Posters on site | GD9.1

Combining local earthquake tomography and petrological models to constrain wavespeeds in the subducting Nazca Plate 

Nazia Hassan, Sally Henry, and Christian Sippl

Intermediate-depth seismicity in Northern Chile shows a pattern which is distinct from a conventional double seismic zone (DSZ) setting. While two distinct seismicity planes are present in the updip part of the slab, there is a sharp transition to a highly seismogenic cluster of 25–30 km thickness at 80-90 km depth, extinguishing the gap between the two seismicity planes. As seismic velocities can be used to constrain mineralogy and fluid content, characterizing seismic wavespeeds of this subduction zone segment using local earthquake tomography can provide important constraints on the mineralogical processes that produce the seismicity pattern seen here.

We used the catalog of Sippl et al. (2018), which contains arrival time data from permanent stations of IPOC (Integrated Plate Boundary Observatory Chile), complemented by several temporary deployments spanning shorter time sequences. The catalog contains more than 100,000 earthquakes and 1,200,404 P- and 688,904 S-phase picks for the years 2007 to 2014. In order to use the best available picks for tomography, we limit our analysis to events that have more than 14 P-arrivals as well as more than 7 S-arrivals, leading to a total of 8883 events with 213,908 P- and 99466 S-arrivals.

Parallelly, we also attempt to obtain an estimate of the possible mineral compositions at the depths and P-T conditions relevant to our study in the DSZ setting. For this, we assume a simple model where the upper plane of the DSZ is considered to be evolving from MORB-like composition and the lower plane of the DSZ from depleted-mantle composition. These global average compositions are then fed into Perple X (Connolly & Kerrick, 1987) as starting compositions and pseudosections of possible mineral assemblages are constructed for P-T conditions significant to this study. We calculate the theoretical Vp and Vp/Vs values for those P-T conditions using the same software.

We present 3D models of P- and S-wavespeeds from the Northern Chile forearc between about 20.4° S and 22.5° S, as well as images of ray coverage, relocated seismicity, and synthetic resolution tests. Tomography models for different choices of grid spacing and damping-smoothing parameters are compiled and compared to derive the optimal settings for the inversion. The seismic velocity distribution obtained through tomography is compared with the aforementioned theoretical wavespeeds to narrow down the range of possible reactions occurring at depth.

How to cite: Hassan, N., Henry, S., and Sippl, C.: Combining local earthquake tomography and petrological models to constrain wavespeeds in the subducting Nazca Plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5730, https://doi.org/10.5194/egusphere-egu24-5730, 2024.

EGU24-5819 | ECS | Orals | GD9.1

Structure and geometry of the Chilean subduction zone near Copiapó (~27°S) based on an amphibious seismic refraction experiment 

Arne Warwel, Dietrich Lange, Anke Dannowski, Sara Aniko Wirp, Eduardo Contreras-Reyes, Ingo Klaucke, Marcos Moreno, Juan Diaz-Naveas, and Heidrun Kopp

The subduction of the oceanic Nazca plate beneath the continental South American plate shapes the Chilean margin and is known to generate large megathrust earthquakes. Our study focuses on the region defined by the pre-collision and subduction of the Copiapó Ridge with the Chilean margin at ~27°S. This area has been a seismic gap since 1922, and little is known about the geometry and deep structures of the incoming plate, the overriding plate, and the processes related to the subduction of the Copiapó Ridge. 

We model the seismic structure in the region by using wide angle seismic data from a recent amphibious seismic refraction experiment. Thereby, we utilize seismic signals from both offshore airgun-shots and onshore mining blasts. Overall, we use 36 Ocean-Bottom-Seismometers and 10 temporal seismic land stations along an approximately 420 km long profile ranging from more than 300 km offshore up to more than 100 km landwards.

Our P-wave velocity model images the geometry and velocity structure of the incoming oceanic plate, including three seamounts belonging to the Copiapó Ridge, the marine and continental forearc, and the upper part of the downgoing slab. The model shows an oceanic crust with hardly any sediment cover (generally less than 10 m) and an average oceanic Moho depth of about 6.2 – 6.9 km below the seafloor, which increases to over 10 km below the seamounts of the Copiapó Ridge. The velocities beneath the seamounts are similar or slightly slower compared to the adjacent upper oceanic crust (Vp ranging from 3.5 to 6 km/s). This suggests that the Copiapó Ridge was predominantly formed by extrusive processes. In addition, the velocity model reveals a significant thinning (to less than 4 km) of the oceanic crust landwards of the trench axis.

Together with recently acquired bathymetry data, we will compare our findings to other studies north and south of the Copiapó region and discuss the structural and geometric along-strike variations of the northern Chilean subduction zone.   

How to cite: Warwel, A., Lange, D., Dannowski, A., Wirp, S. A., Contreras-Reyes, E., Klaucke, I., Moreno, M., Diaz-Naveas, J., and Kopp, H.: Structure and geometry of the Chilean subduction zone near Copiapó (~27°S) based on an amphibious seismic refraction experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5819, https://doi.org/10.5194/egusphere-egu24-5819, 2024.

EGU24-5820 | Orals | GD9.1

Spanning the Arc: Margin Geometry and Topography Control Upper Plate Deformation in the Central Andean Subduction Zone 

Bernd Schurr, Armin Dielforder, Lukas Lehmann, and Claudio Faccenna

Subduction zone forearcs deform transiently and permanently due to the frictional coupling with the converging lower plate. Transient stresses are mostly the elastic response to the seismic cycle. Permanent deformation is evidenced by forearc topography, upper plate faulting, and earthquakes; its relation to the megathrust seismic cycle is debated. Here we study upper plate seismicity, interplate earthquake slip vectors, and the GNSS strain field in the northern Chile subduction zone to deduce the stress field and to separate elastic and permanent strain. We find that seismicity is distributed unevenly and that high seismicity rates concur both with a break in the forearc topography and tectonics of the Coastal Cordillera and the onset of a change in subduction obliqueness. Earthquakes in the South American crust under the sea and the Coastal Cordillera show a remarkably homogenous north-south, i.e., trench-parallel, compressional stress field. The trench-parallel compression above the plate coupling zone, almost perpendicular to plate convergence direction, may be explained by strain resulting from a change in subduction obliqueness due to the concave shape of the plate margin, which we demonstrate by investigating inter-plate earthquake slip vectors. From these, we derive a strain rate estimate (-5×10e-8 /a) and compare it to one derived from upper plate earthquakes (-8×10e-9 /a). We argue that the dominance of trench-parallel compressive stresses over trench-perpendicular ones is due to canceling of the latter by tensional gravitational stresses due to the topographic gradient between the Andes and the Nazca trench. Based on the distribution of the type of faulting we investigate the trench-perpendicular stress field with a force-balance model. The observed deep strike-slip earthquakes, expression of trench-perpendicular tension, require the deepest extent of the megathrust to be very weak.

How to cite: Schurr, B., Dielforder, A., Lehmann, L., and Faccenna, C.: Spanning the Arc: Margin Geometry and Topography Control Upper Plate Deformation in the Central Andean Subduction Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5820, https://doi.org/10.5194/egusphere-egu24-5820, 2024.

EGU24-6860 | ECS | Orals | GD9.1

Phase stability and metamorphic reactions related to intraplate seismicity in the Nazca Plate 

Martin Riedel, Andrés Tassara, Nicole Catalán, and Rodolfo Araya

Subduction zones are complex geotectonic environments where multiple processes interact resulting in different kinds of seismicity. Among them is intermediate depth intraplate seismicity, which occurs within the subducting plate in conditions that should favor ductile shear rather than fragile faulting. A high variability in focal mechanisms and spatial distribution has been observed globally for this kind of events. In some subduction zones a double seismicity zone develops while in others not. Moreover, these earthquakes may occur in dry and hydrated conditions. Therefore, there is no consensus on the process that originate them.

In the context of hydrated subductions, such as is the Chilean case, the influence of fluids liberated through the metamorphism of the slab is generally considered as the main triggering factor. It is therefore important to know at what pressure and temperature and between which mineral associations these reactions occur.

Hacker et al. (2003) compiled information on average mineralogy and whole rock composition to create phase diagrams which have allowed the study of dehydration reactions and intraplate seismicity around the world. However, their work is based on data from the FAMOUS area in the Atlantic Ridge for the MORB and the Semail ophiolite for ultramafic rocks, which do not correlate to compositions in the Nazca Plate.

To better constrain the conditions on which dehydration reactions take place within the Nazca slab, we used PERPLE_X to calculate pseudosections with geochemical data more representative of it. We created a simple model of the plate consisting of a top layer with MORB compositions from drilled and dredged samples for the crust and a bottom layer with ultramafic rock compositions obtained from ophiolites from a geotectonic context consistent with that of the Nazca Plate. We then coupled the pseudosections with a kinematic thermal model of the Chilean subduction zone to create profiles of stable mineral associations and hydration gradient along the subducted slab.

We observe that, for constant PT, hydrated mineral stability is mainly controlled by the initial (pre-subduction) slab hydration percentage and in a much lesser extend by slab composition. For areas where slab hydration is constrained by geophysical data, we tested different slab compositions and found that modelling with data from Nazca Plate layer 2 basalts and a mid ocean ridge type ophiolites provides the best fit to seismic data. It appears that intraplate seismicity nucleates along areas with strong hydration gradients, i.e. where dehydration reactions occur. We then extrapolated these compositions to the rest of the plate and with the assumption that the correlation observed between hydration gradient and intraplate seismicity hypocenters is maintained along the margin, we estimated hydration percentages along 5 latitudinal profiles.  Although further work remains to improve our seismic catalogues and spatial resolution of the thermal model, preliminarily it seems that the Nazca Plate is more hydrated in northern Chile (~2.5%) and less to the south (~1%) and that the Chilean double seismicity zone only occurs where hydration is above ~2%.

How to cite: Riedel, M., Tassara, A., Catalán, N., and Araya, R.: Phase stability and metamorphic reactions related to intraplate seismicity in the Nazca Plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6860, https://doi.org/10.5194/egusphere-egu24-6860, 2024.

The use of machine-learning based tools for phase picking and association is in the process of revolutionizing the field of seismicity analysis, leading to the simplified creation of “deep” seismicity catalogs often containing 10s or 100s of thousands of events. Having such catalogs as an available resource opens the field for novel ways of combining seismicity information with other types of datasets. At the same time, the sheer amount of data poses challenges for the visualization as well as joint analysis with other constraints.

In this contribution, I want to explore different ways of using and visualizing large seismicity catalogs, using a range of different recently compiled earthquake catalogs from the Chilean margin as showcase examples. Moreover, I attempt to find efficient ways of cross-plotting seismicity data from “deep” catalogs with other datasets such as interplate coupling maps, seismic velocity distributions, temperature models or inferred mineralogy maps.

How to cite: Sippl, C.: Using large microseismicity catalogs to constrain subduction zone processes – examples from the Chilean margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7484, https://doi.org/10.5194/egusphere-egu24-7484, 2024.

EGU24-7958 | ECS | Posters on site | GD9.1

Towards 3D attenuation tomography of the Northern Chile forearc 

Ignacio Castro-Melgar and Christian Sippl

In subduction zones, intermediate-depth earthquakes typically occur in two discrete layers, delineating an upper and a lower seismicity plane with a separating aseismic or minimally seismic region, a phenomenon named Double Seismic Zone (DSZ). However, the seismicity pattern in Northern Chile features two parallel planes of seismic activity only in the shallower section of the slab. Around depths of 80–90 km, the seismicity undergoes a transition to a significantly seismogenic zone approximately 25–30 km thick, effectively connecting the initial seismicity planes. This variation presents a distinct form of intraslab seismicity that deviates from the traditional DSZ structure and prompts further investigation into its underlying mechanisms and implications for regional seismic hazard assessment. Insights derived from this region's seismicity could provide pivotal constraints and enhance our understanding of the complex interplay between geological processes, mineral transformations, and fluid migrations in shaping subduction zone seismicity.

The attenuation of seismic waves in a rock volume is a property that is highly sensitive to the presence and concentration of fluids as well as spatial variations of temperature. As intermediate-depth seismicity is thought to originate from dehydration processes in the downgoing slab, along-strike or along-dip changes in slab seismicity should have a signature in seismic attenuation of the slab as well as the overlying mantle wedge. We hence aim at better understanding the aforementioned seismicity configuration in Northern Chile by acquiring a 3D image of its attenuation signature. 

The primary dataset for our analysis comes from the seismic stations of the Integrated Plate boundary Observatory Chile (IPOC) network in Northern Chile's forearc, augmented by additional data from different temporary deployments. Using the extensive seismicity catalog of Sippl et al. (2023), we have about 180,000 events at over 50 seismic stations at our disposal from the period 2007 to 2021; we select only the high quality traces for the analysis. The rays are traced in a 3D velocity model. We invert the spectral ratios obtained with the coda normalization method to obtain total-Q values. We present images of the 3D attenuation structure of the Northern Chile Forearc between 21ºS and 23ºS, which are obtained with measurements of the coda normalization method using the Multi-Resolution Attenuation Tomography algorithm (Sketsiou et al., 2021).

How to cite: Castro-Melgar, I. and Sippl, C.: Towards 3D attenuation tomography of the Northern Chile forearc, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7958, https://doi.org/10.5194/egusphere-egu24-7958, 2024.

EGU24-8006 | ECS | Posters on site | GD9.1

Towards a 3D integrated geophysical model of Northern Chile 

Dominika Godová and Christian Sippl

The South American active margin is one of the most important and well-studied subduction zones on the Earth. In the last decade, our knowledge about the geometry of its respective constituent parts in Northern Chile has been significantly expanded thanks to seismicity data from a large network of permanent seismic stations. That calls for an effort to summarize these diverse constraints in a single 3D model, which can be validated and optimized using satellite gravity data.

Integrated geophysical modelling is primarily based on gravity data, which bring information about different crustal density inhomogeneities and their sources. As an inverse geophysical problem, gravity modelling is ambiguous, and therefore it is necessary to include geometry constraints from other geophysical data as well as geological information. Different types of seismic data offer the most commonly used constraints due to their depth range and the relatively well-described relation between seismic velocities and densities.

We aim to compile a 3D integrated geophysical model for Northern Chile in the IGMAS+ software, based on gravity data of the global gravitational (or geopotential) model EIGEN-6C4, which include terrestrial, satellite and altimetry data to a high degree and order of spherical harmonic expansion. As the main geometry constraints of the model, we use the newest available seismicity catalogs in the study area together with crustal thickness values from receiver functions. Starting with the geometries of previously published density models in the area of the Central Andes, especially those located at least partly in Northern Chile, we will modify these models guided by the geometry constraints from seismic data and will also use regional and global models of crustal and lithospheric interfaces, such as the top of basement in sedimentary areas, plate interface geometry, depth to continental Moho, and the lithosphere-asthenosphere boundary (LAB). Densities of the modeled bodies will be selected based on previously published models or estimated from seismic velocities. We also plan to study the gravity effect of the different geometries deduced from different generations of seismic data.

Our contribution provides an overview of evidence compiled in previous studies and adds new information on the deep lithospheric structure of the North Chilean margin by integrating them into a single model.

How to cite: Godová, D. and Sippl, C.: Towards a 3D integrated geophysical model of Northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8006, https://doi.org/10.5194/egusphere-egu24-8006, 2024.

We derive a co-seismic slip model of the 2015 Mw 8.3 Illapel, Chile earthquake constrained by line-of-sight displacements from Sentinel-1 interferograms. Greens functions are calculated with 3D finite element models (FEMs). The FEMs simulate a non-uniform distribution of elastic material properties and a precise geometric configuration of the irregular topographical surface. The rupturing fault follows the curvilinear Peru-Chile Trench and Slab1.0. The optimal model that inherits heterogeneous material properties, provides a significantly better solution than that in a homogenous domain at the 95% confidence interval. The best-fit solution for the domain having a non-uniform distribution of material properties reveals a triangular slip zone. Slip is concentrated near the trench with a dip-slip up to 7.75 m, giving rise to a moment magnitude of Mw8.22 in general agreement with the seismological estimate. This methodology allows us to integrate multiple datasets of geodetic observations with seismic tomography, to achieve a better understanding of seismic ruptures within crustal heterogeneity and fault curvature.

How to cite: Tung, S. and Masterlark, T.: Revisit the coseismic slip model of the 2015 Mw 8.3 Illapel, Chile earthquake with curvilinear fault rupture, finite element model, and InSAR observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8443, https://doi.org/10.5194/egusphere-egu24-8443, 2024.

EGU24-8472 | ECS | Orals | GD9.1 | Highlight

Crustal Deformation Associated with the Seismic Cycle in the Central Andes from InSAR and GNSS Geodetic Time Series 

Bertrand Lovery, Anne Socquet, Mohamed Chlieh, Marie-Pierre Doin, Mathilde Radiguet, Juan Carlos Villegas-Lanza, Juliette Cresseaux, and Philippe Durand

The Central Andes subduction has been the theater of numerous large earthquakes since the beginning of the 21th Century, notably the 2001 Mw8.4 Arequipa, 2007 Mw8.0 Pisco, and 2014 Mw8.1 Iquique earthquakes. A better knowledge of the interplate coupling distribution and seismic cycle in this area is thereby fundamental for improving our understanding of large earthquakes segmentation, and ultimately improving our knowledge of the seismic potential in the area. Interseismic models from inversions of 80 GNSS velocities in Central and South Peru (12–19°S) on a 3-D slab geometry indicate that the locking level is relatively high and concentrated between 20 and 40-km depth. Locking distributions indicate a high spatial variability of the coupling along the trench, with the presence of many locked patches that spatially correlate with the seismotectonic segmentation. Our study confirms the presence of a creeping segment where the Nazca Ridge is subducting, we also observe a lighter apparent decrease of coupling related to the Nazca Fracture Zone (NFZ). However, since the Nazca Ridge appears to behave as a strong barrier, the NFZ is less efficient to arrest seismic rupture propagation. Considering various uncertainty factors, we discuss the implication of our coupling estimates with size and timing of large megathrust earthquakes considering both deterministic and probabilistic approaches. We estimate that the South Peru segment, from the Nazca Ridge to the Arica bend, could have a Mw=8.4-9.0 earthquake potential depending principally on the considered seismic catalog and the seismic/aseismic slip ratio (Lovery et al., 2024).

We use large-scale InSAR Sentinel-1 time series, processed in the frame of the FLATSIM-Andes project (Thollard et al., 2021), encompassing the Central Andes (7–26°S) on the 2015-2021 period. These InSAR data provide a useful complementarity to the GNSS data, with a higher spatial resolution in exchange for a lower temporal resolution. Subsequently, it allows to better define the contours of the asperities, or the maximum locking depth. We modelled the effects of non-tectonic processes such as solid earth tides (SET), ocean tide loading (OTL), and ionospheric electronic content (TEC) on the ramps in range and azimuth, in order to measure ground deformation in a stable reference frame, with sufficient accuracy for large-scale tectonic applications, allowing vertical and horizontal decomposition.

In order to perform joint inversions of GNSS and InSAR interseismic velocities, we also develop finite element models of the subduction zone with more complex viscoelastic rheology (Maxwell and Burger laws). Viscoelastic models are expected to produce a broader displacement, with horizontal displacements extending further inland. Higher magnitudes of deformation in the late-stage of the interseismic period and a shallower optimal locking depth have also been reported for viscoelastic models. These features are key factors to make the link between short-term and long-term deformation, and to discriminate the slip on the slab interface from internal deformation. We investigate the viscoelastic effects associated with the great 2001 Mw8.4 Arequipa earthquake, in order to assess its impact on the interseismic loading estimate on the subduction megathrust.

How to cite: Lovery, B., Socquet, A., Chlieh, M., Doin, M.-P., Radiguet, M., Villegas-Lanza, J. C., Cresseaux, J., and Durand, P.: Crustal Deformation Associated with the Seismic Cycle in the Central Andes from InSAR and GNSS Geodetic Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8472, https://doi.org/10.5194/egusphere-egu24-8472, 2024.

EGU24-8641 | ECS | Posters on site | GD9.1

Joint inversion for Vp, Vs, and Vp/Vs of subduction zone in northern Chile 

Zixin Chen, Haijiang Zhang, and Lei Gao

We collected earthquake waveform data recorded by permanent seismic stations in northern Chile from 2014 to 2019 to construct a new earthquake catalog, and integrated them with the previous catalog data. In total, the new catalog consisted of 536342 P and 453920 S arrival times from 52165 earthquakes and 245 stations. We resolved Vp, Vs, and Vp/Vs models and seismic locations for northern Chile by using a new version of double-difference seismic tomography method based on Vp/Vs model consistency constraint (Guo et al., 2018). The new velocity models provide a refined structure of the subducting slab down to 350 km.

The earthquake relocations reveal a distinct double seismic zone in northern Chile, but the gap between the two seismic planes disappears at a depth of approximately 100 km and replaced by a concentration of seismic cluster. Under this intermediate-depth seismic cluster, several isolated small seismic clusters remain. The tomography results indicate a strong correlation between seismicity distribution and high-velocity anomalies. The subducting Nazca Plate presents stripe-like high-velocity anomalies with clear segmentations, potentially related to the weakening at the outer-rise of the trench. Furthermore, our Vp/Vs model indicates that the upper seismic plane exhibits high Vp/Vs anomalies, which may indicate the presence of fluids released from dehydration reactions of various hydrous minerals. In contrast, lower seismic plane and deep seismic clusters are associated with low Vp/Vs anomalies, which could be related to supercritical fluids. Additionally, the enhanced seismicity and velocity anomalies in the region of 21-22ºS along the strike suggest a potential influence of the subduction of the Iquique Ridge of the Nazca Plate.

How to cite: Chen, Z., Zhang, H., and Gao, L.: Joint inversion for Vp, Vs, and Vp/Vs of subduction zone in northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8641, https://doi.org/10.5194/egusphere-egu24-8641, 2024.

EGU24-9019 | ECS | Posters on site | GD9.1

The IPOC catalog goes deep: preliminary results 

Nooshin Najafipour, Jorge Antonio Puente Huerta, Christian Sippl, Javad Kasravi, Jonas Folesky, and Bernd Schurr

Northern Chile is one of the most seismogenic regions on the planet, and has been monitored by a permanent network of seismic stations since 2007. We here present a first step towards a new, more complete seismicity catalog for this region, leveraging modern deep-learning based algorithms for phase picking and association.

We first assessed the performance of EQTransformer, a deep learning based phase picker, in detecting and phase picking seismic data from the Northern Chile Subduction Zone by comparison with a large, meticulously handpicked dataset. We found that the "INSTANCE" model within SeisBench yielded the best performance for our study area. Through systematic threshold variations, we determined the optimal values using Precision-Recall curves (0.4 for event detection, 0.1 for P and S picks). Subsequently, we applied GaMMA, identified as the best performing phase associator in synthetic tests, coupled with NonLinLoc for initial event location. One of GaMMA's key operational criteria is the association threshold, where we required a minimum of five seismic phases to define an event, which yielded a high reliability in the phase association process. Moreover, we refined the catalog by automatically identifying and removing duplicate events. All associated events were consecutively relocated in a 1D and a 2D velocity model, using the VELEST and simul2000 algorithms. Events with disproportionally high RMS residuals as well as single picks with high residuals were removed in the process. In a final step, events were relocated with a double-difference approach.

A first application of this combined approach for the year 2020 yielded 2,838,080 P and S picks in the picking stage, with a total of 83,194 events after association and relocation. This is a nearly tenfold increase in event numbers compared to the IPOC catalog of Sippl et al. (2023), which contains 8,716 events for the same time interval.

In this contribution, we present results from a larger-scale application of our procedure to several years of IPOC data, and compare retrieved geometries as well as event numbers to the previously published IPOC catalog. Our findings demonstrate the potential of modern deep-learning algorithms in the creation of larger and more complete earthquake catalogs. Moving forward, our goal is to extend this preliminary catalog to span the entire 15 years of IPOC operation, facilitating in-depth analysis of regional processes.

How to cite: Najafipour, N., Puente Huerta, J. A., Sippl, C., Kasravi, J., Folesky, J., and Schurr, B.: The IPOC catalog goes deep: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9019, https://doi.org/10.5194/egusphere-egu24-9019, 2024.

EGU24-9376 | Posters on site | GD9.1

Joint Tomographic Inversion of the Pampean Flat Slab: Insights from Extensive Archived Seismic Data 

Ariane Maharaj, Steve Roecker, Diana Comte, Mauro Saez, Sol Trad, Gustavo Ortiz, and Martin Fernadez

The Andean Margin hosts alternating regions of “flat” and “normal” subduction, which includes the Pampean flat slab that extends from central Chile to Argentina. The discovery of an unusual travel time anomaly beneath the high Andes above the flat slab motivated a study to investigate the lithosphere in this region. Leveraging extensive archived seismic data from both Chile and Argentina, we performed a large-scale joint inversion of P and S body wave arrival times from earthquakes, and surface wave dispersion measurements from earthquakes and ambient noise. We created 3D Vp, Vs and Vp/Vs models using at least an order of magnitude more data than previous studies with about an 80% reduction in grid spacing. Our models corroborate results from previous studies: (1) a high velocity, high Vp/Vs region associated with a cool, slightly hydrated and depleted mantle above the flat slab, and (2) a low velocity structure beneath the high Andes interpreted as an overthickened crustal root, with our results showing that the root extends to just above the flat slab. Curiously, our models also reveal two low velocity zones within and below the flat slab seismic zone that have not been previously reported. Notably, the decrease in velocity is more pronounced in Vp than Vs. We postulate that the eastern low velocity anomaly is likely due to hot asthenosphere heating the slab, although no melting is occurring as the Vs is not significantly reduced. The western low velocity anomaly, which spatially correlates with the Juan Fernandez Ridge (JFR), we postulate is either due to the presence of supercritical fluids trapped within the JFR or an increase in silica content possibly linked to petit spot volcanism.

How to cite: Maharaj, A., Roecker, S., Comte, D., Saez, M., Trad, S., Ortiz, G., and Fernadez, M.: Joint Tomographic Inversion of the Pampean Flat Slab: Insights from Extensive Archived Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9376, https://doi.org/10.5194/egusphere-egu24-9376, 2024.

EGU24-11322 | ECS | Orals | GD9.1 | Highlight

What repeating earthquakes can tell us about postseismic slip and fluid circulation in the Ecuadorian subduction zone 

Caroline Chalumeau, Hans Agurto-Detzel, Louis De Barros, and Philippe Charvis and the Rapid Response Team of the 2016 Pedernales Earthquake

The Ecuador-Colombia subduction zone is a complex and spatially heterogeneous region that hosts both shallow aseismic slip and large megathrust earthquakes, and where both  inter-seismic and post-seismic seismicity have been linked to aseismic slip. Repeating earthquakes, which are the result of repeated loading and failure of single asperities on a fault, are a valuable tool in studying aseismic slip as well as in monitoring the evolution of fault properties over time. In this study, we search for repeating earthquakes within one year of aftershocks following the April 16th, 2016 Mw 7.8 Pedernales earthquake, and we analyze their relationship to afterslip and the evolution of their source properties. 

We calculate waveform cross-correlation coefficients (CC) on 4762 catalog events, and use a threshold CC of 0.95 to sort events into preliminary families, which are then completed using template-matching and relocated using HypoDD. In total, 376 earthquakes were classified into 62 families of 4 to 15 earthquakes. Additionally, the magnitudes, corner frequencies and stress drops of 136 repeaters were determined using spectral ratios.

We find an increase in the recurrence time of repeating events with time after the mainshock, highlighting a possible timeframe for the afterslip’s deceleration. However, repeating earthquakes appear to concentrate around the areas of largest afterslip release, where afterslip gradient is the highest. This suggests that while most repeating aftershocks are linked to afterslip release, the afterslip gradient may play a bigger role in determining their location than previously thought. We also find that repeaters in the region near the trench are unusual, in that their stress drops are anomalously low and systematically decrease over the postseismic period, hinting at a potential increase in pore fluid pressure in this region over time. 

How to cite: Chalumeau, C., Agurto-Detzel, H., De Barros, L., and Charvis, P. and the Rapid Response Team of the 2016 Pedernales Earthquake: What repeating earthquakes can tell us about postseismic slip and fluid circulation in the Ecuadorian subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11322, https://doi.org/10.5194/egusphere-egu24-11322, 2024.

EGU24-11363 | Orals | GD9.1 | Highlight

Tectonics and exhumation processes in the northern Andes 

Audrey Margirier, Manfred R. Strecker, Stuart N. Thomson, Peter W. Reiners, Ismael Casado, Sarah George, and Alexandra Alvarado

The Cenozoic growth and uplift of the Andes has been strongly influenced by the subduction dynamics and the superposed effects of climate. Previous studies have shown that the arrival of oceanic ridges and slab flattening triggered regional uplift and exhumation in Peru and Chile. Recent studies suggest that the subduction of the Carnegie Ridge below the Ecuadorian Andes controlled the formation of a crustal sliver moving northward. However, the timing of the ridge’s arrival at the trench and its effect on topographic growth remain unclear.

New geo-thermochronological data allows us to investigate the possible role of ridge subduction in prompting the growth of the Ecuadorian Andes and to pinpoint the timing of the Carnegie Ridge subduction. Time-temperature inverse modeling of this new thermochronological dataset constrained two cooling phases in the Western Cordillera. The first phase occurred after the emplacement of intrusions, likely associated with magmatic cooling. The second phase began ~6 Ma, coinciding with the last cooling phase observed in the Eastern Cordillera and is likely to be associated with exhumation of the Western Cordillera. Based on our results and existing geological cross-sections we propose that recent crustal shortening and rock uplift led to exhumation of Ecuadorian Andes at ~6 Ma. We suggest that the onset of Carnegie Ridge subduction at ~6 Ma increased the coupling at the subduction interface, promoting shortening and rock uplift in the region.

How to cite: Margirier, A., Strecker, M. R., Thomson, S. N., Reiners, P. W., Casado, I., George, S., and Alvarado, A.: Tectonics and exhumation processes in the northern Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11363, https://doi.org/10.5194/egusphere-egu24-11363, 2024.

EGU24-12727 | Posters on site | GD9.1

Characterizing past earthquakes through historical observations and logic tree approximation 

Ignacia Calisto, Rodrigo Cifuentes, Javiera San Martín, Javiera Alvarez, Lisa Ely, Breanyn MacInnes, Jorge Quezada, and Daniel Stewart

Characterizing the spatial distribution of ruptures from historical and recent earthquakes is key to understanding the seismic cycle of large earthquakes in subduction zones, and thus to assessing the potentialrisks associated with future earthquakes. Central Chile (35°S - 38°S) has been continuously affected by large earthquakes, such as the 2010 Maule (Mw 8.8) and the 1835 earthquakes witnessed by Robert Fitzroy (HMS Beagle captain). Here, we identify the rupture pattern and tsunami propagation of the 1751, 1835, and 2010 mega-earthquakes, events that overlapped in central Chile, by  compiling historical records and applying robust statistical tools. We used an adaptation of a logic tree methodology to generate random sources of slip distribution for each event, constrained by tsunami and deformation data. We find that the three events studied have different slip peaks. The 1751 earthquake has the largest slip with a maximum patch of ∼ 26 m, while the 2010 and 1835 earthquakes reach slips of ∼ 16 m and ∼ 10 m, respectively. Our results show that a part of the segment between 36◦S and 37◦S was consistently affected by large earthquakes, but with different slip and depth. The northern part of the segment accumulated energy for at least 300 years and was released by the 2010 earthquake. This work provides important information for identifying rupture patterns between historical and recent earthquakes, and highlights the importance of extending the time scale of earthquake slip distribution analyses to multiple cycles to describe both earthquake characteristics and their spatial relationship, and thus gain a better understanding of seismic hazard.

How to cite: Calisto, I., Cifuentes, R., San Martín, J., Alvarez, J., Ely, L., MacInnes, B., Quezada, J., and Stewart, D.: Characterizing past earthquakes through historical observations and logic tree approximation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12727, https://doi.org/10.5194/egusphere-egu24-12727, 2024.

EGU24-12800 | ECS | Posters on site | GD9.1

Interaction between historical earthquakes in the seismic gap of central Chile and the Marga-Marga crustal Fault: The seismic potential of the Valparaiso region. 

Javiera Álvarez, Ignacia Calisto, Jorge Crempien, Joaquín Cortés, Claudio Faccenna, and Rodolfo Araya

The characterization of the spatial distribution of historical earthquake ruptures in a seismic segment plays a fundamental role in our understanding of the seismic cycle of significant earthquakes and in assessing the potential hazards associated with future events of this nature.

Due to its tectonic behavior, Chile has been impacted by megathrust earthquakes of considerable magnitude, such as the Valdivia 1960, Maule 2010, and more recently, the Illapel 2015 events. However, there are certain areas where no large earthquakes have occurred and are thus considered to be in a seismic gap. Despite experiencing some significant events, they do not manifest the required energy release properties and depth to compensate the accumulated friction. All these earthquakes, which represent varying stages of the seismic cycle, interact with different geological characteristics of the segment. This is evident in the central zone of Chile, specifically in the Valparaíso region, which has been in a seismic gap since the last major surface-rupturing earthquake of 1730.

During the Maule 2010 and Illapel 2015 earthquakes, rupture occurred only in the southern and northern segments in the mentioned area. Despite seismic activity in 1822, 1906, 1985, and 2017, and the presence of the Marga-Marga crustal fault in Viña del Mar, the energy release has not been sufficient to trigger the expected seismic sequence. It is worth noting that the fault is dangerously located in the most densely populated and frequented area of the city of Viña del Mar, presenting a threat to the surrounding population greater than what could be expected from a subduction earthquake itself.

This research aims to identify and quantify the interaction between the subducting and the Marga-Marga faults in order to assess the potential seismic activity in the area, considering that the crustal earthquakes caused by faults such as Marga-Marga are potentially more destructive than subduction earthquakes of equal magnitude. A relevant precedent is the interaction between the rupture of the Maule 2010 earthquake and the active fault segment of Pichilemu, which triggered a seismic swarm in 2011.

To achieve this, a study was conducted to characterize the slip associated with tsunamigenic events that occurred in the Central Chile segment in 1730, 1906, and 1985. The study revealed deformation patterns, indicating that the last shallow movement occurred in 1730, followed by deep patterns along the coast for subsequent events. Historical data was collected, and a stochastic modeling methodology was applied to comprehensively reconstruct the events. The Coulomb stress transmission between the Marga-Marga fault and subduction events, such as the one in 1906, was then characterized using the newly acquired information from historical deformation to identify potential activation zones of the crustal fault. Currently, efforts are underway to implement a methodology that uses computational simulation tools to visualize the impact of a coseismic event, such as the one in 1730, on the crustal fault and the surrounding region. The aim is to understand the past behavior of the region to be prepared for potential future activations.

How to cite: Álvarez, J., Calisto, I., Crempien, J., Cortés, J., Faccenna, C., and Araya, R.: Interaction between historical earthquakes in the seismic gap of central Chile and the Marga-Marga crustal Fault: The seismic potential of the Valparaiso region., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12800, https://doi.org/10.5194/egusphere-egu24-12800, 2024.

EGU24-12834 | Posters on site | GD9.1

Lower plate retreat and opening of a Cretaceous forearc basin, Northern Andes 

Andreas Kammer, Camilo Andrés Betancur, and Camilo Conde

The tectonic setting of the Northern Andes is delineated fundamentally by a western oceanic terrane that was juxtaposed to the continental margin along the now fossilized interandean Romeral suture since the Early Cretaceous. This constellation and the connection to the Caribbean Large Igneous province have been attributed to a far-travelled and now partially subducted, formerly coherent terrane with a trailing edge represented by the Panama-Choco block. A former disconnection between oceanic terrane and South American plate may, however, be contended by considering continental provenance data of siliciclastic and volcanic rock units and a widely distributed geochemical arc signature of the effusive rock series. Moreover, the emplacement of the basic igneous sequences was strongly controlled by extensional tectonics and subduction correlates in its lifetime with the production of oceanic crust, suggesting a coupling between intrusive activity and convergence. In this contribution, we examine apparently conflicting structural deformations that may be reconciled, however, with the opening of a forearc basin and a deformational imprint that affected extensively the continental margin, supposing the existence of a subduction system composed of two continentward dipping slabs.

How to cite: Kammer, A., Betancur, C. A., and Conde, C.: Lower plate retreat and opening of a Cretaceous forearc basin, Northern Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12834, https://doi.org/10.5194/egusphere-egu24-12834, 2024.

EGU24-12909 | ECS | Posters on site | GD9.1

Microplate behaviour of the Andes during co- and early postseismic phases of the seismic cycle 

Mara A. Figueroa, Franco S. Sobrero, Demián D. Gómez, Robert Smalley Jr., Michael G. Bevis, Dana J. Caccamise II, and Eric Kendrick

The Central and South-Central Andes form a “two-sided” mountain belt bounded by distinct zones of convergence in the western forearc and eastern foreland flanks. Previous geodetic studies of interseismic deformation in the Bolivian Subandes and the Argentine Precordillera found that the forearc to foreland velocity field decayed too slowly to be explained purely by elastic shortening driven by locking of the Nazca megathrust. The velocity field is more precisely explained if elastic deformation is augmented by eastward displacement of the entire Andes. Here, we extend the earlier interpretation of interseismic motion and argue that foreland décollements can participate in the co- and postseismic phases of the earthquake deformation cycle associated with the Nazca megathrust. These findings have direct implications in estimating recurrence interval, slip rate, and probabilistic seismic hazard analysis on both sides of the orogen.

How to cite: Figueroa, M. A., Sobrero, F. S., Gómez, D. D., Smalley Jr., R., Bevis, M. G., Caccamise II, D. J., and Kendrick, E.: Microplate behaviour of the Andes during co- and early postseismic phases of the seismic cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12909, https://doi.org/10.5194/egusphere-egu24-12909, 2024.

EGU24-13804 | Orals | GD9.1

3D-time slab deconstruction and ore deposit localization in South America 

Nipaporn Nakrong, Marnie Forster, Wim Spakman, Hielke Jelsma, and Gordon Lister

Here we present a 3D-time reconstruction of the tectonic evolution of the Nazca and South American plates. The geometry of subducted slabs was modelled down to a depth of ~1950km using UU-P07 global tomographic model. Our approach integrated geochronological records, geological history, and seismotectonic data. Furthermore, our proposed slab models incorporated both velocity and temperature gradients to determine the mid-slab surface accurately. To reconstruct these slabs with minimal distortion back to the Earth's surface, we employed a reverse engineering method. The positions of potential tears in the subducted slabs can then be recognized by the induced distortions. We identified at least three down-dip tears, which significantly influence subduction behaviour. We then integrated the floated or pre-subducted slabs into a 2D-time tectonic reconstruction and tracked the subduction interface over time. Our reconstruction reveals that the pre-subducted slabs accurately mimic the shape of the Andes during the Oligocene-Miocene boundary. However, the remnants of slabs subducted before that time are no longer connected to the entire slab. To the north of the Nazca tear, which coincides spatially with the Nazca fracture zone, the continuous slab has subducted to a depth of ~1950km. To the south, the downgoing slab has been segmented into three distinct zones, with tears localized along the two arms of the extrapolated Juan de Fernández ridge and the inferred Challenger fracture zone. Moving from north to south, the slab in these zones detached at some point after 22Ma, 15Ma, and 12Ma, respectively. Each slab segment exhibits variations in geometry, with flat slab and steep slab portions, as well as differences in penetration depth. Notably, the location of the Nazca down-dip tear coincides with the initial location of the eastward spanning of the Cu belts.

How to cite: Nakrong, N., Forster, M., Spakman, W., Jelsma, H., and Lister, G.: 3D-time slab deconstruction and ore deposit localization in South America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13804, https://doi.org/10.5194/egusphere-egu24-13804, 2024.

EGU24-13893 | ECS | Posters on site | GD9.1

Stochastic Strong-Motion Simulation of Valparaiso 1985 Mw 8.0 Chile Earthquake 

Rogelio Torres and Sergio Ruiz

In recent years, several historical earthquakes have been studied in Chile to understand the seismotectonic context and anticipate the ground motion of these natural phenomena. One of the first great earthquakes documented by the Global Digital Seismographic Network (GDSN) occurred on March 3, 1985, off the coast of Valparaiso, with a moment magnitude (Mw) 8.0.

Several researchers have modeled the slip distribution at the seismic source, obtaining satisfactory results and fits, mainly at low frequencies and in far field. However, a discrepancy has been observed between the areas of maximum slip and the accelerations recorded in the near field.

In this study, the code proposed by Ruiz and Otarola (2016) was employed to stochastically generate synthetic accelerograms capable of accurately replicating the accelerations observed during near-field ground motion. This approach provides a realistic simulation of earthquake characteristics, source, path, and site.

The importance of generating synthetic accelerograms extends to critical sectors such as civil engineering, geophysics, construction, and urban planning. These simulations play a critical role in understanding ground behavior, predicting large seismic movements, and improving the development of earthquake-resistant structures. Furthermore, in the fields of construction and urban planning, synthetic accelerograms are essential for assessing the vulnerability of specific areas, diversifying applications in industry, and facilitating a more resilient design approach for future seismic events.

The results obtained by generating synthetic accelerograms can replicate the spectral and temporal shape, in agreement with the records provided by the National Seismological Center (CSN) network. Stochastic simulations have been run both in rocky environments and in areas with site effects.

How to cite: Torres, R. and Ruiz, S.: Stochastic Strong-Motion Simulation of Valparaiso 1985 Mw 8.0 Chile Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13893, https://doi.org/10.5194/egusphere-egu24-13893, 2024.

EGU24-14050 | Posters on site | GD9.1

Nature of asperities and barriers along the Chilean megathrust unveiled by an integrated analysis of seismicity, gravity, geodetic locking and wedge geometry 

Andres Tassara, Christian Sippl, Martin Riedel, Catalina Castro, and Favio Carcamo

Asperities inside the seismogenic zone of subduction megathrust are regions where specific frictional properties allow a stick-slip behavior characterized by the accumulation of slip deficit over decades to centuries and its sudden release during earthquakes. Despite its major role on the occurrence of the most devastating earthquakes and tsunamis on the planet, the physical nature of asperities and their limiting barriers is still unclear. This is partially due to an, often, ambiguous interpretation of individual geophysical proxies that are theoretically connected with the frictional structure of the megathrust at quite different time scales, ranging from 100-102 yrs (seismicity patterns, geodetic locking, Vp/Vs and MT anomalies) to 105-107 yrs (coastal geomorphology, forearc wedge geometry and associated basal friction, magnetic and gravity anomalies). If transient phenomena, like slow slip events (SSEs) or stress shadows created by previous earthquakes, do not dominate the seismogenic behavior of the megathrust, then short- and long-term frictional proxies should coincidently illuminate the location of asperities and barriers. Moreover, this would imply that the nature of this features must be connected to the geology structure of both converging plates, with strong implications to seismic hazard assessment. A number of previous studies have explored a combination of several geophysical proxies for megathrust frictional structure, most of them along the Chilean margin. Here we expand over the work of Molina et al. (2021) and Sippl et al. (2021) by performing an integrated analysis of gravity anomalies, friction from critical wedge theory, geodetic locking and seismicity patterns for the entire 4000-km long Chilean megathrust. Particularly, we use available (micro)seismicity catalogues to compute maps of the b-value of the frequency-magnitude relationship. This parameter contributes with an independent short-term proxy for the stress state of the megathrust and we treat it as an additional continuous field into a principal component analysis (PCA) similar to Molina et al. (2021) that aims to quantify the main spatial correlation between the proxies. We will also test other techniques to measure the degree of spatial correlation, like AI-based pattern recognition methods. This integrated analysis will also consider rupture length of historical earthquakes over the last 500 yrs and slip distribution of instrumental earthquakes and SSEs. This will allow us to test contrasting hypothesis about the nature of seismic asperities and barriers along the Chilean megathrust and elsewhere.

How to cite: Tassara, A., Sippl, C., Riedel, M., Castro, C., and Carcamo, F.: Nature of asperities and barriers along the Chilean megathrust unveiled by an integrated analysis of seismicity, gravity, geodetic locking and wedge geometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14050, https://doi.org/10.5194/egusphere-egu24-14050, 2024.

EGU24-17042 | ECS | Posters on site | GD9.1

Search for repeaters in the central part of the Chilean subduction zone  

Audrey Chouli, Lucile Costes, David Marsan, Jannes Münchmeyer, Sophie Giffard-Roisin, and Anne Socquet

Repeating earthquakes, corresponding to the rupture of the same asperity over time at more or less regular intervals, can be used to estimate the slip rate on a subduction plate interface. The purpose of this work is to build a catalog of repeaters for the central part of the Chilean subduction zone, extending from 24°S to 33°S latitude and centered on the Copiapo seismic gap. As a basis for our study, we used the seismicity catalog from the Centro Sismológico Nacional (CSN).

The similarity between waveforms gives a good criterion to assign earthquakes to a similar asperity. To measure it, we calculated for each pair of events the coherency, correlation and associated time lag between the vertical components of their P waves, on a 5 s window starting 1 s before the P arrival. We tested different frequency bands (1-4 Hz, 3-12 Hz, 5-20 Hz, ...) and kept each time the one with the best coherency value. We selected all pairs of earthquakes with coherency higher than 0.95, at three or more stations. To ensure a stable measurement, we imposed that the time lags from cross-correlation and coherency differ by less than 0.01 s. To verify that the earthquakes of a repeaters family take place at the same location, we relocated the events using a double-difference method and created clusters based on both coherency and location similarity. As coherency values are calculated on a 5 s window, we relocate the centroids of the events, i.e. the center of mass of the rupture. To estimate the surface rupture, we calculate the rupture radius based on the seismic moment and stress-drop values (Eshelby 1957), estimating the stress-drop and seismic moment with SourceSpec (Satriano 2023).          

As preliminary results, we found 347 families, mostly located between 30-60 km deep, and between 29-33.5°S. Almost no repeaters were found before 2015 due to the lack of available stations. Obtained families contain a few events, with 11 earthquakes in the biggest one. We compared the obtained repeaters with the coupling along the plate interface.  Most repeaters are located at the transition between strong and low coupling zones in the Illapel area, making a circle shape around the deep part of the Illapel coseismic slip. Furthermore, we investigated the evolution of the number of repeaters with time in different areas and found potential aseismic slip marked by repeaters' activity consistent with previous observations, such as before the 2017 Valparaiso sequence (Ruiz et al., 2017) or after the Atacama sequence (Klein et al., 2021).

In order to obtain more complete repeaters families, we created a new machine learning based earthquake catalog for the study area with SeisBench (Woollam et al., 2022), using data from permanent and temporary networks in Northern and Central Chile. We are currently applying our analysis to this new catalog.

How to cite: Chouli, A., Costes, L., Marsan, D., Münchmeyer, J., Giffard-Roisin, S., and Socquet, A.: Search for repeaters in the central part of the Chilean subduction zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17042, https://doi.org/10.5194/egusphere-egu24-17042, 2024.

EGU24-20233 | ECS | Orals | GD9.1 | Highlight

Structural control on aseismic and seismic slip interactions during the 2020 SSE in the Atacama region, Chile. 

Diego Molina, Jannes Münchmeyer, Mathilde Radiguet, Anne Socquet, and Marie-Pierre Doin

While subduction earthquakes are widely recognized for releasing seismic slip, aseismic slip can also be hosted on the megathrust by the occurrence of postseismic phase or Slow Slip Events (SSEs). SSEs have been reported along several subduction zones, preferably on the deeper zone and usually lasting months or even years (Draguert et al., 2001). Notably, in the Chilean subduction zone, deep SSEs have been observed in only a reduced area in Central Andes, specifically close to the Copiapo city. Recent studies report that this area is prone to host regular SSEs with a recurrence time of ~5 years and variable duration (Klein et al., 2021), which was confirmed by a new detected SSE in 2020 and 2023.

Notably, during the 2020 SSE, a seismic crisis with a main shock of Mw 6.9 took place on the zone (September 2020), likely provoking an interaction between the different slip modes.  In this work, we attempt to enhance the characterization of the temporal and spatial pattern-evolution of the SSE to elucidate whether there was a trigger mechanism for the seismic crisis or if the earthquake affected the SSE evolution.

To describe the seismic behavior of the area, we recur to the analysis of distinct data sets. On one hand, GNSS stations deployed by different institutions are used to characterize the temporal evolution and amplitude of the 2020-SSE and respective seismic crisis. On the other hand, the spatial pattern is recovered by InSAR data recorded by Sentinel-1 mission. Additionally, a seismicity catalogs coming from machine learning approach is used to investigate aseismic-seismic interactions.

Our analysis shows that the 2020 SSE triggered the seismic sequence in September of that year. We also observed that the aseismic deformation migrates, resulting in a total cumulative slip pattern similar to another SSE detected in 2014. Remarkably, our study evidences a clear segmentation along dip and strike affecting both, aseismic and seismic slip, which correlates with gravity anomalies.

This study suggests a tectonic control on the slip behavior characterizing the area and highlights the cinematic between slow and fast earthquakes hosted along the plate interface.

 

 

How to cite: Molina, D., Münchmeyer, J., Radiguet, M., Socquet, A., and Doin, M.-P.: Structural control on aseismic and seismic slip interactions during the 2020 SSE in the Atacama region, Chile., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20233, https://doi.org/10.5194/egusphere-egu24-20233, 2024.

EGU24-20700 | ECS | Posters on site | GD9.1

From regional to local structures imaged by seismic tomography at the Atacama seismic gap, Central-Northern Chile (24.5-29°S) 

Nicolás Hernádez-Soto, Matthew Miller, Marcos Moreno, Dietrich Lange, Anne Socquet, Christian Sippl, and Diego González-Vidal

Between 2020 and 2022 the ANILLO+DEEPtrigger (Y6+XZ) Seismic Network, comprising 108 seismic stations, operated for eighteen months in Northern-Central Chile (24.5°S - 29°S). Employing Deep Learning (EQTransformer, Mousavi et al., (2022)) and Phase Association (GaMMA, Zhu et al. (2021)) algorithms, we identified over 30,000 seismic events in an area with a notable absence of moderate-to-large events in the past century, since the 1922 M8.5 Atacama earthquake.  
From the initial catalog, we selected a well-distributed subcatalog of 1000 earthquakes, consisting of 26,570 P- and 22,109 S-wave arrival times, by selecting for events with an optimal spatial distribution, small residuals, and abundant P- and S-arrivals. These selected events served as input for VELEST (Kissling et al., 1994) to compute a new 1-D velocity model representative of this region by minimizing the subset residuals. To reduce both residuals and location errors associated with the seismicity, we relocated the entire catalog using staggered tomographic inversions based on SIMUL2000 (Thurber & Eberhart-Phillips, 1999), simultaneously inverting for seismic velocity models and hypocentral parameters within the iterative damped least squares method. Following the proposed method, we gradually increased model complexity, transitioning from 2-D Vp and Vp/Vs to ultimately a 3-D fine Vp and Vp/Vs solution with low node separation.
Next, synthetic resolution tests were conducted to assess the reliability of the spatial limits and boundaries within the solutions. In this context, distinctive patterns were identified for each profile of the three-dimensional model, revealing enhanced horizontal and vertical resolution in the central region beneath the network. Conversely, a decline in resolution was noted at the peripheries, primarily attributable to reduced station coverage causing poorer seismic event relocations.
Our results reveal both regional and local patterns. We observed a mantle wedge with vertical thicknesses ranging from ~35km in the southernmost profiles less than 25 km in the northern region, consistent with previous seismic tomography observations in northern Chile (Pastén-Araya et al., 2021). The Vp/Vs ratio and Vp values allow us to discern the distribution of the hydrated slab, which, spatial correlated with seismicity, provides evidence of irregular dehydratation processes along both dip and strike directions.
Relocated seismicity exhibits some noteworthy features. Shallower crustal sesmicity is predominantly related to high rates of mining activity. In the subduction areas, the most prominent cluster is located at depths of 20-50 km, delineating the seismogenic zone. At greater depths, double and even triple seismic bands add structural complexities to the observations.
From 26.5°S to 29.5°S, between 20 km and ~75 km depth, seismicity predominantly aligns with the interplate contact defined by SLAB2 (Hayes et al., 2018). In contrast, northward from 26.5°S, our deepest seismicity, situated between 75 and 125 km depth, diverges from SLAB2, depicting a steeper dip angle.
Lastly, we recommend integrating OBS and back-arc stations, whose data would improve off-shore and back-arc resolution, contributing to a more comprehensive understanding of seismotectonic environments. Non-supervised Deep Learning results can provide exceptional databases for tomographic studies, yielding residuals similar to human-picked databases but within shorter timeframes.

How to cite: Hernádez-Soto, N., Miller, M., Moreno, M., Lange, D., Socquet, A., Sippl, C., and González-Vidal, D.: From regional to local structures imaged by seismic tomography at the Atacama seismic gap, Central-Northern Chile (24.5-29°S), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20700, https://doi.org/10.5194/egusphere-egu24-20700, 2024.

EGU24-20861 | Orals | GD9.1

The effect of subduction relief on megathrust slip properties in Ecuador, constraints from gravity anomalies and seismic tomography 

Michele Paulatto, Yueyu Jiang, Audrey Galve, Mireille Laigle, Andreas Rietbrock, Monica Segovia, and Sandro Vaca

The subduction margin in Ecuador is dominated by the subduction of the Carnegie Ridge and associated oceanic plate relief. This region is also affected by complex slip behaviour including aseismic deformation, slow slip, and large earthquakes. We present new seismic and gravity data collected as part of the HIPER campaign in 2020 and 2022, covering the subduction margin at the northern edge of the Carnegie Ridge. Traveltime tomography of dense active source wide-angle seismic data from a trench perpendicular profile reveals the structure of this part of the margin. The slab crust thickens from 7.5 km at the western end of the profile to 15 km at the eastern end. The profile crosses two seamounts (Atacames seamounts), one currently impinging onto the margin (AS2) and the other already buried beneath the accretionary prism (AS1). The seamounts have low P-wave velocity roots and are associated with gravity anomaly highs. The forearc is uplifted in front of the subducted seamount AS1 and is affected by gravitational collapse in its wake. In the area affected by the seamounts, the interseismic plate coupling is reduced to almost zero likely because of the fracturing and disruption of the forearc and lubrication induced by enhanced fluid input. Further downdip the profile extends into the rupture area of the 2016 M7.8 Pedernales earthquake. This part of the plate interface is more laterally homogeneous and characterised by higher Vp. Our results confirm that rugged plate relief is associated with reduced interseismic coupling and that megathrust earthquake rupture areas tend to have high Vp and laterally homogeneous properties.

How to cite: Paulatto, M., Jiang, Y., Galve, A., Laigle, M., Rietbrock, A., Segovia, M., and Vaca, S.: The effect of subduction relief on megathrust slip properties in Ecuador, constraints from gravity anomalies and seismic tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20861, https://doi.org/10.5194/egusphere-egu24-20861, 2024.

We performed (U-Th-Sm)/He apatite and zircon thermochronology (AHe and ZHe, respectively) on basement rocks from the Central Taurides, southern Turkiye to constrain its Tertiary >2000m surface uplift history. The samples were collected from the Alanya and Antalya units exposing in the southern part of the Central Taurides. The Alanya Massif represent a Late Cretaceous HP/LT eclogite to blueschist facies metamorphic pile whereas the Antalya Unit shows a relatively coherent stratigraphy consisting mainly of Triassic sandstones together with Permian and Jurassic limestones that are exposed as tectonic windows below the Alanya Massif. The AHe ages from the Alanya Massif cluster in with Early Oligocene (ca. 30 Ma), Early Miocene (ca. 20 Ma) and Late Miocene (ca. 8 Ma) ages. Apatites from one of the sandstone samples from the Antalya Unit gave also a Late Miocene age (ca. 9 Ma), consistent with the cooling ages of the tectonically overlying metamorphic rocks. In contrast, apatites from a sandstone sample exposed in the north show old, dispersed ages suggesting that they escaped from tectonic burial during the Eocene nappe stacking. ZHe ages from one of the metamorphic samples gave a ca. 30 Ma age; indistinguishable from its apatite ages. Our new AHe and ZHe age data indicate that, during Late Eocene nappe tectonics, the Alanya Massif and the underlying Antalya Unit was buried enough to reset the AHe and ZHe ages. Following the compressional regime, during the Early Oligocene, the Alanya Massif was subjected to a fast exhumation, possibly through an extensional detachment. This post-contractile-tectonic exhumation continued episodically during the Early Miocene until just prior to the Miocene transgression. The final Late Miocene exhumation ages are noteworthy and overlaps well with the beginning of the surface uplift of the southern margin of the Anatolian plateau. The new thermochronological data from the Central Taurides suggest that the extension of the southern margin of the Anatolian Plateau had already started in the Early Oligocene, predating the Arabia-Anatolia collision. The extension could have been triggered by the roll-back of the until then intact Bitlis-Cyprus-Hellenic slab, which created a widespread Oligo-Miocene extensional regime on the overriding Anatolian margin.

How to cite: Aygül, M., Uysal, I. T., Sobel, E. R., Okay, A. I., and Glodny, J.: New (U-Th-Sm)/He low-temperature apatite and zircon thermochronology ages reveal episodic Tertiary exhumation and uplift of the Central Taurides, southern Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1527, https://doi.org/10.5194/egusphere-egu24-1527, 2024.

The Oligocene-to-present tectonic history of the western Mediterranean region is characterized by the ESE-ward roll-back of isolated Alpine and Neo Tethys oceanic slab fragments that determined the spreading of two diachronous back-arc basins: the Liguro-Provencal Basin between 30 and 15 Ma and the Tyrrhenian Sea between 10 and 2 Ma. Such geodynamic events induced the fragmentation and dispersal of the Alpine chain through the formation and migration of microplates and terranes, making the debate on the nature, origin, and evolution of such crustal blocks vivid since the 1970s. For instance, it is commonly accepted that the Corsica-Sardinia microplate rotated counterclockwise (CCW) by at least 50° during Oligo-Miocene and that the Calabro-Peloritan, Kabylies and Alboran blocks drifted hundreds of kms on top of nappe piles ESE-ward, SE-ward and SW-ward, respectively. These blocks, know all together as AlKaPeCa, presently form isolated and enigmatic igneous/metamorphic terranes stacked over the Meso-Cenozoic sedimentary successions of the Apennines and Maghrebides. Besides back-arc basins widths and ages, no other kinds of geologic/geophysical data from Corsica-Sardinia microplate or AlKaPeCa terranes constraining their drift magnitudes exist. On the other hand, drift timing may be properly documented by paleomagnetic vertical-axis rotations obtained from different age rocks, and such data usefully complement ages derived from back-arc basins.

We paleomagnetically sampled the Meso-Cenozoic sedimentary cover of the Calabrian (Longobucco sequence) and Peloritan (Longi-Taormina sequence) terranes and the mid-late Eocene continental Cixerri Formation of SW Sardinia. In addition, we re-evaluated previous paleomagnetic results from the whole Corsica-Sardinia microplate and considered the robust Serravallian-Pleistocene dataset from the Calabrian block. Such data indicate a novel rotation and drift history in the western Mediterranean region (Siravo et al., 2021; 2022). The South Sardinia, Peloritan and Calabrian blocks belonged to the “Greater Iberia plate” before mid-Oligocene (<30 Ma) dispersal, as they all show its characteristic paleomagnetic fingerprint (middle Cretaceous 30°-40° CCW rotation). Rifting of the Liguro-Provencal between 30 and 21 Ma induced 30° CCW rotation of both South Sardinia and Calabria blocks, whereas the Peloritan block, located further south, was passively drifted SE ward at the non-rotation apex of a Paleo Appennine-Maghrebides orogenic salient. South Sardinia plus the adjacent Calabrian block and North Sardinia-Corsica blocks assembled in the early Miocene and rotated 60° CCW as a whole between 21 and 15 Ma. After 10 Ma ago the Calabrian block detached from south Sardinia following the opening of the Tyrrhenian Sea and rotated 20° clockwise (CW), at the apex of a Neo Appennine-Maghrebides Arc. On the other hand, the Peloritan terrane rotated 130° CW on top of the Sicilian Maghrebides, along the southern limb of the orogenic salient.

 

REFERENCES

Siravo, G., Speranza, F., & Macrì, P. (2022). First Pre‐Miocene Paleomagnetic Data From the Calabrian Block Document a 160 Post‐Late Jurassic CCW Rotation as a Consequence of Left‐Lateral Shear Along Alpine Tethys. Tectonics, 41(7), e2021TC007156.

Siravo, G., Speranza, F., & Mattei, M. (2023). Paleomagnetic evidence for pre‐21 Ma independent drift of South Sardinia from North Sardinia‐Corsica:“Greater Iberia” vs. Europe. Tectonics, e2022TC007705.

How to cite: Siravo, G. and Speranza, F.: Paleomagnetism of the Peloritan, Calabrian and South Sardinia blocks unveils a Greater Iberia plate and its mid Oligocene-early Miocene breakup    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1733, https://doi.org/10.5194/egusphere-egu24-1733, 2024.

EGU24-2454 | Orals | GD9.2

Multiengine-driving Tethyan evolution 

Zhong-Hai Li

Tethys tectonic system has experienced a long-term evolution history, including multiple Wilson cycles; thus, it is an ideal target for analyzing plate tectonics and geodynamics. Tethyan evolution is typically characterized by a series of continental blocks that separated from the Gondwana in the Southern Hemisphere, drifted northward, and collided and accreted with Laurasia in the Northern Hemisphere. During this process, the successive opening and closing of multistage Tethys oceans (e.g., Proto-Tethys, Paleo-Tethys, and Neo-Tethys) are considered core parts of the Tethyan evolution. Herein, focusing on the life cycle of an oceanic plate, four key geodynamic processes during the Tethyan evolution, namely, continental margin breakup, subduction initiation (SI), Mid-Ocean Ridge (MOR) subduction, and continental collision, were highlighted and dynamically analyzed to gather the following insights. (1) Breakup of the narrow continental margin terranes from the northern Gondwana is probably controlled by plate subduction, particularly the subduction-induced far-field stretching. The breakup of the Indian continent and the subsequent spreading of the Indian Ocean can be attributed to the interactions between multiple mantle plumes and slab drag-induced far-field stretching. (2) Continental margin terrane collision-induced subduction transference/jump is a key factor in progressive Tethyan evolution, which is driven by the combined forces of collision-induced reverse push, far-field ridge push, and mantle flow traction. Moreover, lithospheric weakening plays an important role in the occurrence of SI. (3) MOR subduction is generally accompanied by slab break-off. In case of the considerably reduced or temporary absence of slab pull, mantle flow traction may contribute to the progression of plate subduction. MOR subduction can dynamically influence the overriding and downgoing plates by producing important and diagnostic geological records. (4) The large gravitational potential energy of the Tibetan Plateau indicates that the long-lasting India-Asia continental collision requires other driving forces beyond the far-field ridge push. Further, the mantle flow traction is a good candidate that may considerably contribute to the continuous collision. The possible future SI in the northern Indian Ocean will release the sustained convergent force and cause the collapse of the Tibetan Plateau. Based on the integration of these four key geodynamic processes and their driving forces, a “multiengine-driving” model is proposed for the dynamics of Tethyan evolution, indicating that the multiple stages of Tethys oceanic subduction provide the main driving force for the northward drifting of continental margin terranes. However, the subducting slab pull may be considerably reduced or even lost during tectonic transitional processes, such as terrane collision or MOR subduction. In such stages, the far-field ridge push and mantle flow traction will induce the initiation of new subduction zones, driving the continuous northward convergence of the Tethys tectonic system.

How to cite: Li, Z.-H.: Multiengine-driving Tethyan evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2454, https://doi.org/10.5194/egusphere-egu24-2454, 2024.

EGU24-3712 | Orals | GD9.2

Quantitative Sn-wave Attenuation Beneath the Tibetan Plateau and Lithospheric Rheology 

Lian-Feng Zhao, Xiao-Bi Xie, Xi He, and Zhen-Xing Yao

Sn wave, a regional seismic phase, propagates horizontally in the uppermost mantle and is sensitive to lateral variations in mantle lid thickness, temperature, and melt. The physical properties of the lithosphere can be indicated by Sn propagation efficiency or attenuation. The inefficient Sn propagation has been typically used to describe the regions with high-temperature anomalies in the uppermost mantle and infer the subduction front of the Indian lithosphere in the north Tibetan plateau. Here we collect 122,481 tangential-component digital seismograms, isolate the geometric spreading and attenuation for SH-type Sn wave, and construct a broadband uppermost mantle shear wave attenuation model in the Tibetan region. Beneath the central and north parts of the Tibetan plateau the Sn waves are strongly attenuated, while relatively weaker attenuation can be observed in the perimeter of the plateau, i.e., the Himalaya mountains in the south, Tarim and Qaidam basins and Eastern Kunlunshan terrain in the north, and Sichuan basin in the east. These weak attenuation regions are likely where the old crustal fragments were deposited during the collision between the Indian and Asian plates. In contrast, strong Sn attenuation likely indicates local lithospheric delamination in central and eastern Tibet. Furthermore, the correlation between strong Sn and Lg attenuation zones reveals the potential mantle upwelling with deep heat sources invading the crust.

How to cite: Zhao, L.-F., Xie, X.-B., He, X., and Yao, Z.-X.: Quantitative Sn-wave Attenuation Beneath the Tibetan Plateau and Lithospheric Rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3712, https://doi.org/10.5194/egusphere-egu24-3712, 2024.

     The collision between the Indian and Eurasian plates in the Cenozoic eras resulted in the formation of the world's largest and highest plateau. The intensive collision, subduction, and related deep dynamic processes led to significant crustal shortening, uplifting, and expansion of the Plateau, accompanied by eastward extrusion of plateau materials. The southeastern Tibetan Plateau (SETP) is one of the most important channels for escaping plateau materials. The widespread existence of crustal weak material flow in the SETP has become widely accepted. However, previous research has mostly been limited to two-dimensional profiles or spaced data measurement points. Therefore, obtaining reliable and high-resolution geophysical models of the lithosphere is crucial for understanding the deformation mechanisms of the plateau.

    Our three-dimensional resistivity model shows unprecedented resolution of the Simao Block of the Indochina Block, offering new insights into the material transport and deformation mechanisms of the SETP. Two consecutive large-scale high-conductivity anomalies observed in the middle-lower crust are speculated to be partial melting associated with crustal flow. The rigid lithosphere separated by significant strike-slip faults on the SETP may be pulled by ductile materials flow, where plastic flows in the middle-lower crust drive the rigid blocks to extrude and escape along the boundary faults, thus dominating the deformation of the lithosphere. The large-scale delamination of the continental lithosphere leads to upwelling of the asthenosphere along mechanically weak areas. Upwelling hot materials continue to heat the entire crust, and the expanding and diffusing lower crust further accelerates partial melting and plastic flow in the middle-lower crust.

How to cite: Ye, G., Sang, W., Wei, W., Jin, S., Lei, Q., and Dong, H.: Preliminary Results of Material Transport Model of Rigid Block Extrusion Driven by Crustal Flow Beneath the SE Tibetan Plateau: insights from high-resolution 3-D Magnetotelluric Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4844, https://doi.org/10.5194/egusphere-egu24-4844, 2024.

The Lhasa Terrane in southern Tibet is widely recognized as having separated from the northern margin of Gondwana with a Precambrian basement and undergoing a protracted and intricate evolution. Abundant Early Cretaceous volcanic rocks are present in the central Lhasa subterrane, Tibet, playing an essential role in models aimed at comprehending the tectonic-magmatic evolution and mantle-crust interaction of this terrane. In this study, we present a well-preserved section of Zenong Group volcano-sedimentary sequence in Eyang, Xainza area within the central Lhasa subterrane. Our new data combined with existing literature data indicate that there was an extensive period of magmatism (approximately 140 Ma to 102 Ma) throughout the Early Cretaceous in the central Lhasa subterrane, reaching its peak around 113 Ma with remarkable compositional diversity.

However, the composition of Early Cretaceous volcanic rocks in the central Lhasa subterrane underwent a temporal transition from high-silica rhyolites to dacites and andesites, exhibiting a reverse cyclicity. Moreover, the intermediate rocks from the upper section display elevated whole rock εNd(t) and zircon εHf(t) values, as well as decreased 87Sr/86Sr ratios compared to the high-silica rocks from the lower section. These observations collectively suggest: (a) involvement of open-system processes encompassing mantle-derived magmas and ancient crustal-derived materials; (b) an increasing contribution of mantle sources in the magma genesis; (c) variable magma origins with distinct petrogenetic histories rather than a uniform source involving assimilation-fractional crystallization processes.

The high-silica rhyolites from the bottom of the Eyang section display characteristics of fractional crystallization and exhibit varying zircon εHf(t) values (−16.7 to −7.8), negative εNd(t) values (−13.7 to −13.1), highly variable initial Sr isotopic compositions, and radiogenic Pb isotopic signatures, indicating that a combined process of magma mixing (involving crustal-derived felsic melts and mantle-derived mafic melts) followed by fractional crystallization was primarily responsible for their formation. The dacitics from the upper part of the Eyang section show higher εHf(t) values (−9.9 ~ +0.5) and εNd(t) values (−10.6 to −9.5) than the high-silica rhyolites, suggesting that these dacitic rocks were also largely derived from anatexis of ancient crustal material with more involvement of mantle-derived magmas. The andesites exhibit more enriched Sr-Nd-Hf isotopic compositions compared to the contemporaneous dacitics, as well as less radiogenic Pb isotopic compositions, suggesting their likely derivation from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments.

We propose that the high-silica rhyolites in the lower section of the Xainza area (≥ ca. 120 Ma) are associated with slab roll-back, while the dacites and andesites in the upper section (≤ca. 120 Ma) are linked to slab break-off during southward subduction of Bangong-Nujiang Ocean lithosphere. Furthermore, it is evident that the ancient basement of the central Lhasa subterrane underwent localized reworking by mantle-derived melts.

How to cite: Huang, Y., Zhao, Z., and Zhu, D.-C.: Compositional and tectonomagmatic evolution of Early Cretaceous magmatism in the central Lhasa suberrane, Tibet: Implications from the Zenong Group volcanic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4877, https://doi.org/10.5194/egusphere-egu24-4877, 2024.

EGU24-5416 | ECS | Posters on site | GD9.2

Mantle transition zone anomalies beneath Iberia and NW Maghreb 

Joan Antoni Parera Portell, Flor de Lis Mancilla, José Morales, and Jordi Díaz

The 410 and 660 discontinuities are predicted to be the result of isochemical phase changes in olivine. The differing Clapeyron slope of the reactions, though, leads to opposite 410 and 660 behaviour for a same temperature variation, with cold and hot mantle anomalies resulting in a thicker or thinner transition zone (MTZ), respectively. Here we use more than 56500 high-quality P-wave receiver functions obtained from 881 broadband seismic stations to locate anomalies in the MTZ beneath Iberia and NW Maghreb. We obtained robust maps of the 410 and 660 discontinuity depth thanks to the combined measurements of several 3D depth migrations using regional and global P-wave tomography models, and used these maps to calculate the MTZ thickness. Our results reveal several large-scale anomalies in the region mostly linked to the thermal effects of cold subducted slabs, but we also found evidence for significant chemical heterogeneity in the MTZ. The Gibraltar-Alboran and Alpine-Tethys slabs cause a continuous MTZ thickening along the Mediterranean coasts. Accompanying the slab anomalies are up to three areas with a low-velocity layer (LVL) located at the top of the 410 discontinuity, which provide evidence for partial melting coinciding with an MTZ enriched in water due to slab dehydration reactions. A similar LVL is also found at the top of the lower mantle where the Alpine-Tethys slab pushes the 660 discontinuity downwards. Mantle upwelling occurs at the back of the Gibraltar-Alboran slab, where we find the thinnest MTZ in the region. Upwelling hot materials seem to travel SW following a toroidal flow along the southern boundary of the slab and cause the 410 discontinuity to deepen significantly. Even though the MTZ thickness remains near-standard, the 410 also deepens in a more discontinuous manner beneath the Atlas Mountains. The active anorogenic volcanism in the Western Mediterranean correlates remarkably well with the LVL on top of regions with sunken 410, possibly pointing at a MTZ source for the melts.

How to cite: Parera Portell, J. A., Mancilla, F. D. L., Morales, J., and Díaz, J.: Mantle transition zone anomalies beneath Iberia and NW Maghreb, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5416, https://doi.org/10.5194/egusphere-egu24-5416, 2024.

The Central Asian Orogenic Belt (CAOB) is one of the largest orogenic collages in the world, and preserves important records of accretionary orogeny and Phanerozoic continental growth. The Yili Block is one microcontinent in southwest of CAOB, 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 conclude that the southward subduction of the Junggar Ocran beneath the Yili Block, but the Silurian magmatism is rarely reported.

Mafic dikes preserve a considerable amount of geological information about geodynamics, crustal evolution and transformation of the regional stress field. Multi-period basic dikes, including Neoproterozoic and Carboniferous, are exposed in the northern margin of the Yili Block, which record important information about the transformation process of regional tectonic system. Recently, we have identified early Silurian diabase dikes in the Precambrian metamorphic rocks in the Wustu area, Wenquan County, northern margin of Yili Block. This paper reports zircon U-Pb age and Lu-Hf isotopic compositions, whole-rock geochemistry and Sr-Nd isotopic compositions for the Wustu diabase dikes and its surrounding rocks. One diabase sample yielded a zircon U-Pb age of 442±7 Ma with positive εHf(t) values (+3.0~+9.1), and its surrounding rock sample (leucogranite) yielded a zircon U-Pb age of 901±3 Ma. The diabase samples have high TFe2O3 contents (8.34%~9.81%) and K2O+Na2O contents (5.72%~6.86%), low MgO contents (3.69%~4.38%) and TiO2 contents (1.69%~2.00%) and belong to the high-K calc-alkaline series. The samples are enriched in the large ion lithophile elements (LILEs, such as Rb, Th, U and K) and have negative anomalies in the high-field-strength elements (HFSEs, e,g. Nb, Ta and Ti), with low Nb/Th ratios (0.13~1.16), Nb/La ratios (0.42~0.45) and high Zr/Hf ratios (39.6~42.2). They also have high initial 87Sr/86Sr ratios (0.707369~0.708637) and positive εNd(t) values (+1.9~+3.6). Our results indicate that they were sourced from a metasomatic sub-continental lithospheric mantle, which mainly composed of spinel iherzolite and garnet iherzolite. The trace element contents and its ratios, such as Zr (212×10-6~242×10-6), Hf (5.16×10-6~6.02×10-6), Nb (6.69×10-6~9.24×10-6), Ta (0.60×10-6~0.81×10-6), Zr/Y (5.21~6.82) and Hf/Th (0.69~0.91), indicate that the diabase dikes formed in an extensional setting during the early Silurian. Finally, we propose that the extensional tectonic setting maybe relate to the change of the subducted slabs angle or tectonic regime transition induced by the collage of the Aktau-Wenquan continental domain to the Yili Block in the end of Ordovician.

How to cite: Chen, Y., Wang, M., Zhu, S., and Cao, M.: The Early Silurian diabase dikes in the northern margin of the Yili Block, southwestern CAOB: insight into rift-related magmtism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6914, https://doi.org/10.5194/egusphere-egu24-6914, 2024.

Although the arc magmatism before collision has been considered as the main mechanism to the continental crustal growth and vertical geochemical fractionation for many years, the syn-collision magmatism related to the melting of accumulation in the base of arc could be an important contribution to crustal net growth and fractionation. Hence, the syn-collision magmatism could be an ideal object to research the continental crustal maturation and stratification. The arc magmatism could be controlled by the connecting magmatic reservoir in different depth and the experimental data show that the arc magma could be polybaric fractionation. However, the detail fractional phase in different level is not clear. Therefore, we selected the Early Eocene mafic rock series in the Tengchong Block, southwestern extension of Tibet, to reveal the detail magmatic evolution process. The rocks include hornblendite, hornblende (Hb) gabbro and diorite with different mineral assemblages, which is the syn-collision magmatism related to the Indian-Asian continental collision. These rocks have zircon ages of ca. 54Ma, and similar whole rock Sr-Nd and zircon Hf isotopes, indicating they are coeval and congenetic. In contrast to the isotopic composition, the major elements of the suits are variable, such as SiO2 contents of 48.72-61.49 wt.%, MgO contents of 12.02-2.69wt.%. The clinopyroxene (cpx) is mainly enclosed in the hornblende in the samples and part of the Hb could be the products of the replace reaction associated with cpx and others could be direct crystallization from the magma. The crystallization parameters calculation results show that the clinopyroxenes have high pressures of 2.4-10.7kbar with average of 7.6kbar and temperatures of 1006-1208°C with average of 1154°C. The hornblende crystallized at the pressures of 2.2-7.8kbar with average of 3.8kbar, and temperatures of 776-875°C with average of 827°C. In addition, the plagioclases in the all samples have three types, including high An core, low An rim with overgrowth rim as type I, low An core, high An mantle low An rim with overgrowth rim as type II, low core with overgrowth rim as type III. The homogeneous in-situ Sr isotopes show the compositions variation from the core to rim could be resulted from the process of dissolution and reprecipitation during the batches recharging of homogeneous magma. Therefore it could conclude that the primary magma of the Eocene mafic rocks could be fractionated in the lowermost crust, and the major crystallization phase dominated by clinopyroxene and forming the pyroxenite as the base of the arc. Then the evolution mafic magma emplace and form a mafic reservoir in the middle crust according to the assembly of batches of magma and finally occurring the further fractionation that the hornblende-dominated accumulation forming the hornblendite and the hornblende and plagioclase accumulation forming the Hb-gabbro and diorite. This polybaric fractionation within the continental crust during syn-collision could lead to the melt transition from mafic to granitic and further strengthen the crustal maturation and stratification.

Supported by National Natural Science Foundation of China [Grant Nos. 42272052 and 41902046], Fundamental Research Funds [Grant No. 300102273102]

How to cite: Zhao, S., Wen, T., and Fang, X.: Polybaric and multistage fractionation of syn-collision mafic magma in continental arc: constraints from the Eocene mafic rocks in the Tengchong Block, southeastern extension of Tibet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6939, https://doi.org/10.5194/egusphere-egu24-6939, 2024.

EGU24-6941 | ECS | Orals | GD9.2

Machine Learning unravels the protracted role of India-Eurasia collision in the uplift of the Tibetan plateau 

Zhikang Luan, Jia Liu, Johnny ZhangZhou, Qunke Xia, and Eero Hanski

The Tibetan Plateau, Earth's largest and highest plateau, boasts an extraordinarily thick continental crust (60-80 kilometers) and an average elevation exceeding 4000 meters. Unraveling the plateau's uplift history, vital for comprehending Earth's Cenozoic history and its environmental impacts, has long been a subject of debate. While prior studies predominantly attribute the plateau's formation to the India-Asia collision, 45-59 million years ago, its timing and underlying mechanisms remain contentious. Airy isostasy as a response to crustal thickening during the Indian-Asian collision was considered the main factor for the uplift of the Gangdese terrain, the important portion of the Tibetan. Trace elemental ratios, e.g. Sr/Y and (La/Yb)n ratios, of the bulk magmatic rocks were the main geochemical indexes to recover the thickening history. However, the resultant crustal thickness and the consequent geodynamics recovered by different indexes remain controversial. Here, we compile the geochemical data for the volcanic rocks from global young arcs and continental orogens and built a supervised Machine Learning model to estimate crustal thickness. The reliability of this new model was tested, and the crustal thickening history of Gangdese terrain was recovered with it. The results reveal that the Gangdese terrane maintained a global-average thickness during the early stage of the India-Asia collision, which was not sufficient to support the uplift to >3000 m, as revealed by the recent paleoaltimeter data, through Airy isostasy.  This challenges the conventional belief of rapid uplift due to crustal thickening upon the Indian-Asian collision. Instead, our results suggest a protracted uplift process that parallels crustal thickening, reshaping our understanding of this iconic geological feature.

 

How to cite: Luan, Z., Liu, J., ZhangZhou, J., Xia, Q., and Hanski, E.: Machine Learning unravels the protracted role of India-Eurasia collision in the uplift of the Tibetan plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6941, https://doi.org/10.5194/egusphere-egu24-6941, 2024.

EGU24-8570 | ECS | Orals | GD9.2

Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey)  

Ezgi Sağlam, Turgut Duzman, Cemre Ay, Aral Okay, Gültekin Topuz, Gürsel Sunal, Ercan Özcan, Demir Altıner, Aynur Hakyemez, Jia-Min Wang, and Andrew RC Kylander-Clark

During the Late Cretaceous, a 2700 km long magmatic arc extended from the Lesser Caucasus through the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans. We studied the arc volcanic rocks in three regions of the Western Pontides, and compared them to the other arc magmatic rocks from the Lesser Caucasus, Eastern Pontides and Balkans. Prior to the onset of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data indicate that magmatism in the Lesser Caucasus, Pontides and Balkans started during the Turonian (ca. 93 Ma), peaked in the middle Campanian (80–78 Ma), and subsequently became rare and sporadic after the late Campanian (ca. 75 Ma). The arc magmatism, characterized by typical subduction signatures, was mainly of middle to high-K calc-alkaline affinity. Late Cretaceous volcanism occurred in a submarine and extensional environment. Along the whole belt, the arc volcanic rocks are overlain by Maastrichtian to Paleocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The geochemistry of the Maastrichtian volcanic rocks is more diverse compared to the older arc volcanic rocks, including alkaline and calc-alkaline basalts, as well as adakitic dacites. The coeval initiation of arc magmatism along the 2700-km-long magmatic arc is associated with the acceleration of Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of suprasubduction-zone ophiolites and sub-ophiolite metamorphic rocks in Anatolia. The end of the magmatic activity in the arc is associated with a marked decrease in the convergence rate during the Campanian.     

How to cite: Sağlam, E., Duzman, T., Ay, C., Okay, A., Topuz, G., Sunal, G., Özcan, E., Altıner, D., Hakyemez, A., Wang, J.-M., and Kylander-Clark, A. R.: Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8570, https://doi.org/10.5194/egusphere-egu24-8570, 2024.

EGU24-8893 | ECS | Orals | GD9.2

A missing Cretaceous magmatic arc of Neo-Tethys in Iran 

Yiyang Lei, Yang Chu, Bo Wan, Wei Lin, Ling Chen, Guangyao Xin, and Morteza Talebian

Magmatic arcs are generally considered to be the direct record of subduction zone. Magmatic activity can start with subduction initiation until the end of oceanic subduction. In the Neo-Tethys tectonic domain, arc magma gaps in Alps and Iran prove that arc magmatism and oceanic subduction are not always coupled.

Unlike the Alps, where arc magmatism is absent, or the Gangdese, where arc magmatism is continuous, Iran exhibits an intermittent arc magma record. Since the subduction of the Neo-Tethys Ocean in the Jurassic, Iran has recorded two phases of magmatic activities: the Middle Jurassic (200-140 Ma, with a peak at ~170 Ma) and the Eocene (55-25 Ma, with a peak at ~40 Ma), which are attested by the age peaks of detrital zircons from Mesozoic-Cenozoic clastic rocks. The Cretaceous magma record is sparse, but Cretaceous detrital zircons are abundant (120-65 Ma, with a peak at ~90 Ma). Regarding this mismatched age record of detrital zircons and magmatic rocks, we choose the Makran forearc basin deposits as the target because it receives thick detritus from Eurasia to form a tens of kilometer thick sedimentary sequence. We conducted a detrital zircon study from the Makran to explore the magmatic evolution of the Iranian Tethys zone.

Euhedral zircon grains, obvious oscillatory zoning, low zircon Th/U>0.1, and trace element geochemistry indicate Cretaceous magmatic zircons sourced from the continental magmatic arcs rather than ophiolites. Positive zircon Hf isotopes excludes the source region of the Gangdese arc which is more depleted. We further used machine learning to confirm our provenance results, that reveal Cretaceous (120-65 Ma) magmatism by the Neo-Tethys Ocean subduction in Iran.

The decreasing trend of Cretaceous zircons U-Pb in Late Cretaceous to Pliocene strata indicates gradual denudation of the Cretaceous magmatic arc from deep to shallow. Cretaceous zircon peaks disappears abruptly in the Pliocene rocks, implying that the Cretaceous magmatic arc was completely denuded. Thus, we confirm that since the subduction initiation, magmatic activity was continuous in Iran but the “missing” was due to the denudation process. This works also highlights the importance of comprehensive analysis before discussing subduction geodynamics based on the record of magmatic outcrops.

How to cite: Lei, Y., Chu, Y., Wan, B., Lin, W., Chen, L., Xin, G., and Talebian, M.: A missing Cretaceous magmatic arc of Neo-Tethys in Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8893, https://doi.org/10.5194/egusphere-egu24-8893, 2024.

The Ediacaran to Cambrian in the northwest Yangtze Block, has long been considered to be formed in a passive margin. Wells and seismic data, however, show that a Lower Cambrian thick siliciclastic rock succession occurs in the northwest Sichuan Basin, the provenance of which has not received attention from previous workers. In this study, we first propose that an Early Cambrian foreland basin was formed in the northwest Yangtze Block. Stratigraphic correlation shows a distinct stratigraphic absence from the Lower Cambrian to Devonian in the Bikou terrane, implying an orogeny might take place from NW to SE. A regional seismic profile shows a wedge stratigraphic geometry of the Lower Cambrian from NW to SE, further indicating a typical structure of a foreland basin. Field outcrops show an overall coarsening-upwards siliciclastic succession of the Lower Cambrian. The petrological analysis of siliciclastic rocks presents an immature feature implying a proximal source. Paleocurrent measurements of siliciclastic rocks point to dominant SE-vergent orientations. The age spectra of detrital zircon U-Pb dating of the Canglangpu Formation show a dominant Early Cambrian age of ca. 530 Ma, together with some positive ɛHf(t) values, indicating that the detrital zircon grains from the Lower Cambrian were derived from a northwest proximal juvenile continental arc and older crust. Therefore, the northwest Yangtze Block experienced a tectonic transition from an Ediacaran passive margin to an Early Cambrian foreland basin. The formation of the Early Cambrian foreland basin appears to have been strongly influenced by an orogenic loading northwestward. Here, this previously-overlooked orogenic event is named as the Motianling orogeny. The origin of the Early Cambrian orogeny may be related to subduction of the Proto-Tethys ocean beneath the northwest Yangtze Block, resulted in continental collision and uplift of northwest microterranes that provided siliciclastic sediments to fill the foreland basin southeastward.

How to cite: Gu, Z., Jian, X., and Watts, A.: Tectonic evolution of an Early Cambrian foreland basin in the northwest Yangtze Block, South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9027, https://doi.org/10.5194/egusphere-egu24-9027, 2024.

EGU24-9628 | ECS | Orals | GD9.2

Kinematics of Intra-Plate Strike-Slip Earthquakes in an Oblique Convergent Setting  : Insights from the Eastern Himalayan and Indo-Burman Plate Boundary Systems 

Dibyajyoti Chaudhuri, Rupak Banerjee, Sankha Subhra Mahanti, Ajay Kumar, and Supriyo Mitra

North-East India comprises a part of the eastern extremity of the Alpine-Himalayan Belt and is one of the most rapidly deforming regions owing to its unique geological setup. The tectonics of this region is dominated by oblique convergence between two nearly perpendicular plates and results in a zone of distributed deformation. This region is associated with a large number of intra-plate strike-slip and oblique-slip (thrust) earthquakes which are not related to any of the plate boundaries. In this study we model the source mechanisms of five recent strong-to-moderate earthquakes (5.5≥Mw≤6.0) using teleseismic P and SH waveforms inversion and use source directivity and back-projection of the high-frequency energy from multiple teleseismic arrays for the largest event, to isolate the fault plane from the auxiliary plane. We then combine these mechanisms with results from previous studies of earthquake source and GPS geodetic velocity vectors and the GPS-derived strain field to build a kinematic model for this region. The depth distribution of the earthquakes reveals that they occur in the lower crust of the underthrusting Indian Plate. The oblique-thrust and thrust events are the result of compressive stresses in the inner arc of the flexed Indian Plate. The oblique convergence of the Indian Plate with respect to Tibet and the slab pull force from the subduction of the Indian Plate beneath Burma combined together are responsible for the strike-slip earthquakes. The region north of the Dauki Fault in the vicinity of the Kopili Fault Zone deforms through dextral strike-slip faulting and anti-clockwise rotation of blocks along NW-SE trending transverse structures. The transitional crust of the Bengal Basin has several NE-SW trending paleorifts which manifest sinistral strike-slip motion and clockwise rotation. The GPS velocity vectors and the strain field indicate that throughout most of the region north of the Dauki Fault there is a strong coupling between the surface deformation and the earthquake faulting whereas towards the south in some areas the coupling is weaker. The strike-slip events in the Indo-Burman Ranges probably occur due to a complex interplay between the trench-normal slab pull forces and lateral shear forces set up by the strike parallel components of the interplate coupling resistance and the mantle drag forces.

How to cite: Chaudhuri, D., Banerjee, R., Mahanti, S. S., Kumar, A., and Mitra, S.: Kinematics of Intra-Plate Strike-Slip Earthquakes in an Oblique Convergent Setting  : Insights from the Eastern Himalayan and Indo-Burman Plate Boundary Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9628, https://doi.org/10.5194/egusphere-egu24-9628, 2024.

EGU24-11578 | Orals | GD9.2 | Highlight

Crustal Structure in the Central Tethys Realm 

Vahid Teknik, Hans Thybo, and Irina Artemieva

The central Tethys realm including Anatolia, Caucasus and Iran is one of the most complex geodynamic settings within the Alpine-Himalayan belt. We calculate the depth to magnetic basement and the average crustal magnetic susceptibility, which is sensitive to the presence of iron-rich minerals, to interpret its present structure and the tecto-magmatic evolution. The data demonstrates that the structural complexity increases from the Iranian plateau into Anatolia.

In Iran, our data reveals the presence of hitherto unknown sedimentary basins and we identify two unknown parallel Magmatic-Ophiolite Arcs hidden by the sedimentary cover in eastern Iran. Based on the width of the magmatic anomalies we find that the paleo-subduction zone at the Urmia-Dokhtar Magmatic Arc (Neo-Tethys subduction structure at Zagros) was steeply dipping (> 60°) in the SE and, in contrast, it had shallow dip(< 20°) in the NW part.

Our results for Anatolia demonstrate exceptional variability of crustal magnetization with smooth, small-amplitude anomalies in the Gondwana realm and short-wavelength high-amplitude variations in the Laurentia realm. Poor correlation between known ophiolites and magnetization anomalies indicates that Tethyan ophiolites are relatively poorly magnetized, which we explain by demagnetization during recent magmatism. We analyze regional magnetic characteristics for mapping previously unknown oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by tectono-magmatic events. By the style of crustal magnetization, we distinguish three types of basins and demonstrate that many small-size basins host large volumes of magmatic rocks within or below the sedimentary cover. We map the width of magmatic arcs to estimate paleo-subduction dip angle and find no systematic variation between the Neo-Tethys and Paleo-Tethys subduction systems, while the Pontides magmatic arc has shallow (∼15°) dip in the east and steep (∼50°–55°) dip in the west. We recognize an unknown, buried 450 km-long magmatic arc along the western margin of the Kırşehir massif formed above steep (55°) subduction. We propose that lithosphere fragmentation associated with Neo-Tethys subduction systems may explain high-amplitude, high-gradient crustal magnetization in the Caucasus Large Igneous Province. Our results challenge conventional regional geological models, such as Neo-Tethyan subduction below the Greater Caucasus, and call for reevaluation of the regional paleotectonics.

References:

Teknik V., Thybo H., Artemieva I.M., Ghods A., 2020, Crustal density structure of NW Iranian Plateau. Tectonophysics, 792, 228588, doi: 10.1016/j.tecto.2020.228588.

Teknik, V., Artemieva, I. M., & Thybo, H. 2023. Geodynamics of the central Tethyan belt revisited: Inferences from crustal magnetization in the Anatolia-Caucasus-Black Sea region. Tectonics, 42, https://doi.org/10.1029/2022TC007282.

How to cite: Teknik, V., Thybo, H., and Artemieva, I.: Crustal Structure in the Central Tethys Realm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11578, https://doi.org/10.5194/egusphere-egu24-11578, 2024.

EGU24-12661 | ECS | Posters on site | GD9.2

Interpretation of crustal structure and hydrocarbon potential of the South Caspian and Kura basins, Azerbaijan  

Nazim Abdullayev, Fakhraddin Kadirov, Ibrahim Guliyev, Shalala Huseynova, Arzu Javadova, Bakir Maharramov, and Abdulvahab Mukhtarov

The South Caspian Basin and Kura basin have had a complex tectonic and stratigraphic history and characterized by different thermal regimes. The basins are a genetically linked system created in a Mesozoic extensional setting with a complex Cenozoic sedimentary filling.

The study presents a new interpretation of the regional geodynamic history and crustal structure based on the new geological and geophysical data. New insights at the South Caspian Basin and Kura basin formation, evolution, and hydrocarbon potential were achieved by integrating published structural maps into the tectonostratigraphic framework delineating these basins and geothermal data, including onshore and offshore borehole temperature measurements, geothermal gradients, and heat flow data. The gravity and magnetic data were used to understand the regional geological model.

For the first time geological evolution of the offshore the South Caspian Basin and onshore Kura Basin were linked within a single map set. Delineating and linking these basins allow novel understanding the geodynamic history of the Black Sea and Caspian regions. The study reveals several specific regions including “cold” South Caspian basin with a 20 km thick sedimentary succession and less than 10 km crustal thickness, “intermediate” Lower Kura basin, and “warm” Kura basin (including Yevlakh Agjabadi depression) with less than 10 km thick sedimentary succession and the crustal thickness of 20 to 25 km. According to the proposed evolution history the basins adjacent to the South Caspian basin involves Mesozoic island arc extension origin followed by subsequent development in Jurassic, with possible additional rifting in Eocene and flexural overprint in Tertiary.

The South Caspian basin contains the dynamic petroleum systems with the prolific Oligocene-Miocene source rocks characterized with proved hydrocarbon potential increasing basinwards.

Inherited tectonic boundaries between the South Caspian and Kura Basins such as the West Caspian Fault zone serve as markers for hydrocarbon prospectivity. The crustal parameters control the distribution of temperature gradients within the basins and hence hydrocarbon generation. Isothermal surfaces are displaced: depth of the surfaces changes across the boundary between the continental crust of the onshore Kura Basin and the different “oceanic-type” crust of the South Caspian basin. This boundary is located at around 500 km where isothermal values are abruptly displaced downwards by about 4 km. A sharp increase in depth of the 120°C isotherm along the boundary has significant implications for the thermal maturity of the source rocks. Rapid burial rates of the offshore South Caspian basin together with the low geothermal gradient have delayed the maturation of organic matter in the source rocks, making the South Caspian basin the location of one of the world’s deepest active petroleum systems. Thus, in deep and prospective offshore South Caspian hydrocarbon generation occurs at greater depth compared to onshore areas, characterized by a more limited hydrocarbon potential. The difference in maturity of onshore and offshore source rocks could play a role in segregating hydrocarbon prospective areas.

How to cite: Abdullayev, N., Kadirov, F., Guliyev, I., Huseynova, S., Javadova, A., Maharramov, B., and Mukhtarov, A.: Interpretation of crustal structure and hydrocarbon potential of the South Caspian and Kura basins, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12661, https://doi.org/10.5194/egusphere-egu24-12661, 2024.

EGU24-14740 | ECS | Orals | GD9.2 | Highlight

Strong Variability in the Thermal Structure of Tibetan Lithosphere 

Bing Xia

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 a 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.: Strong Variability in the Thermal Structure of Tibetan Lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14740, https://doi.org/10.5194/egusphere-egu24-14740, 2024.

EGU24-15423 | ECS | Posters on site | GD9.2 | Highlight

Relocated Earthquakes Confined to the Upper Crust in the Southern Tibet 

Gaochun Wang, Hans Thybo, and Irina M. Artemieva

We have located a total of 202 local earthquakes, based on the data recorded by the Hi-CLIMB seismic stations from 2002-2005, in the southern Tibet. The focal depths of all relocated earthquakes, in the Lhasa terrane, are shallow than 30km, however, the depths can extend to 50km under Himalaya, although there are many earthquakes deeper than 80 km according to the catalogue.  The absence of the earthquakes of the lower crust, in Lhasa terrane, implying a brittle upper crust lying on a soft felsic lower crust. Moreover, the focal depths, in Himalaya, show a low angle (~12°) of subducted Indian lower crust. The focal mechanisms show that the normal faults are the main type of the crustal deformation, which indicate the dominant direction of the extension is approximately east-west, in Lhasa terrane. The strike-slip faults played a regulatory role between normal faults. The thrust faults are only occurred in the south of STDS. The calculated mechanisms correlate well with the surface geology features. Our new results suggest that the whole crust of the Himalaya is brittle and prone to triggering earthquakes under the northward convergence of the Indian plate. However, the lower crust of the Lhasa terrane may be soft, felsic and stable floating above the mantle, under a brittle upper crust which is easier to collapse.

How to cite: Wang, G., Thybo, H., and Artemieva, I. M.: Relocated Earthquakes Confined to the Upper Crust in the Southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15423, https://doi.org/10.5194/egusphere-egu24-15423, 2024.

EGU24-15623 | ECS | Orals | GD9.2

Locked Frontal and Lateral Ramps on the Main Himalayan Thrust beneath NW Himalaya illuminated by precisely located seismicity 

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

The Kashmir ‘seismic gap’ in NW Himalaya, between the 1905 Kangra and 2005 Muzaffarabad earthquake rupture zones, has been replete with moderate-to-small earthquakes. GPS geodetic measurements across the Himalayan-arc reveal arc-normal convergence of ~11 mm/yr, which reduces towards the foreland in the India-fixed reference frame. In 2013 the Jammu And Kashmir Seismological NETwork (JAKSNET), and later the Himachal Pradesh Seismological NETwork (HiPSNET) was established to study the seismological characteristics of this ‘seismic gap’. Using continuous waveform data from these networks an earthquake catalog has been created using the Regressive ESTimator (REST) algorithm. Following this, seismic phases were manually picked from ~1100 earthquake records to determine the accurate arrival-times. A subset of these events based on the quality of picked phases are relocated using a probabilistic Non-Linear Location (NLL) method. These earthquakes have magnitudes between 0.5 and 4.5, and are distributed throughout the crust, with the majority concentrating at shallow (<25 km) depth. These shallow earthquakes are concentrated beneath the Higher Himalaya with lateral variations south of the Kishtwar window and to a region to its east. In arc-normal cross-section, the hypocenters lie on and above the MHT and the depth increases hinterlandward. Two distinct clusters of seismicity with increasing depth coincides with the mid-crustal frontal ramp observed in Vs structure beneath the Kishtwar window. The arc-parallel cross-section shows two eastward dipping hypocenter-clusters on and above the MHT. The one west of the Kishtwar window coincides with the lateral ramp observed in the Vs model. We conjecture that the one to the east also illuminates a similar transverse structure within the Himalayan wedge. Comparison of our hypocentral distribution with GPS velocities across this region reveal a frictionally locked shallow segment of the MHT, with the down-dip unlocking-zone highlighted by the across-arc clustering of seismicity beneath the Higher Himalaya. The locked-to-creep transition occurs immediately north of the mid-crustal frontal-ramp. We compute strain-rate from the sparse GPS data which reveals a predominant NE-SW compression and high strain-rates in regions of clustered shallow-seismicity. We are in the process of further refining the hypocentral locations using a double-difference relocation method, results of which will be presented. 

How to cite: Shamim, S., Ghosh, A., Mitra, S., Priestley, K., Sharma, S., and Wanchoo, S. K.: Locked Frontal and Lateral Ramps on the Main Himalayan Thrust beneath NW Himalaya illuminated by precisely located seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15623, https://doi.org/10.5194/egusphere-egu24-15623, 2024.

EGU24-18337 | ECS | Posters on site | GD9.2

New scenario for structural segmentation and subduction modeling in Makran (Iran and Pakistan) 

Peyman Namdarsehat and Wojciech Milczarek

The Makran subduction zone is located in southeastern Iran and southern Pakistan. It was formed by the subduction of part of the oceanic crust of the Arabian Plate beneath the Eurasian Plate. In the eastern part of this zone, the convergence rate, coastal uplift and seismicity are higher than in the western part of this zone. In addition, there are a larger number of Quaternary volcanoes in the western part due to a subduction arc of the oceanic lithosphere. The study of the velocity vectors shows that the asymmetric pressure impressed the Makran and in addition a number of tectonic evidences were attributed to different dip angles of subduction. The results indicate that the segmentation of the Makran is influenced by two key factors: asymmetric pressure, resulting in varying convergence rates, and different subduction dip angles. These factors are identified as the origin parameters that contribute to the formation of two distinct blocks with contrasting structures. Based on the considerations made in this study, subduction in the Makran was modeled. And a new structural segmentation was presented in this zone. The results indicate a propagation of the eastern boundary of the Lut block in Makran. The model presented in this paper was able to show the tectonic problems of the Makran and furthermore demonstrate the discrepancy between the tectonic features of the western and eastern blocks of the Makran.

How to cite: Namdarsehat, P. and Milczarek, W.: New scenario for structural segmentation and subduction modeling in Makran (Iran and Pakistan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18337, https://doi.org/10.5194/egusphere-egu24-18337, 2024.

EGU24-19538 | Posters on site | GD9.2

Crustal structure of the Dinarides: new insights from the receiver functions and ambient noise tomography  

Josip Stipčević, Tena Belinić Topić, Stéphane Rondenay, and Petr Kolínský

The Dinarides, located at the eastern edge of the Adriatic Sea, are the focus of ongoing geophysical research due to their complex tectonic characteristics and distinctive structural transition zones. Prior investigations have identified a two-layered crust with variable thickness, featuring a transitional zone between Dinaric and Pannonian crust. Recent studies have introduced the concept of a deep-seated Dinaric crustal root, marked by a discernible transition to shallower crust along the northern edge.

This study includes two complementary research approaches to advance our understanding of the Dinarides' crustal structure: receiver function analysis and ambient noise tomography. The P receiver function method was applied to 123 seismic stations across the broader Dinaric area, involving 1234 teleseismic earthquakes recorded from 2016 to 2023. Results are presented through cross-sectional CCP stacking images, offering a comprehensive visualization of the converted Ps phase crucial for mapping significant crustal discontinuities. Additionally, seven years of continuous data, recorded from 2016 to the end of 2022 at 121 seismic stations, were utilized to calculate phase velocities of surface waves. Eikonal tomography was applied to both Rayleigh and Love waves, with local dispersion curves independently inverted for each surface wave type. The outcomes provide distributions of vertically and horizontally polarized shear-wave velocities, presented as maps at various depths and cross-sectional profiles, contributing to an in-depth exploration of shear-wave velocities across the entire region.

The results reveal intriguing insights: a pronounced high-velocity anomaly beneath the Dinarides at shallower depths, a significant low-velocity anomaly in the mid-crust beneath the Dinarides for vertically polarized shear waves, and a distinct, localized thick low-velocity anomaly beneath the NW Dinarides for horizontally polarized shear waves. These findings collectively suggest complex variations in crustal thickness and seismic properties, particularly thickening crust toward the Southern and Inner Dinarides.



How to cite: Stipčević, J., Belinić Topić, T., Rondenay, S., and Kolínský, P.: Crustal structure of the Dinarides: new insights from the receiver functions and ambient noise tomography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19538, https://doi.org/10.5194/egusphere-egu24-19538, 2024.

EGU24-21398 | Orals | GD9.2

Fault rupture mapping of the February 6, 2023 earthquake sequence, eastern Türkiye 

Jiannan Meng, Timothy Kusky, Walter D. Mooney, Erdin Bozkurt, Mehmet Nuri Bodur, and Lu Wang

The powerful earthquake that struck eastern Türkiye on February 6th 2023 is the most devastating earthquake of the past century in the region. Here we present our first-hand field measurements of the ground offsets and the high resolution (centimeter level) drone-mapped surface ruptures 10 days after the first shock. It is clear that the initial rupture was on the Dead Sea fault zone (DSFZ), yet maximum displacements and energy release (Mw 7.8) occurred 24 sec later when rupture transferred to the East Anatolian fault zone (EAFZ). Seven hours later, a Mw 4.5 aftershock at the junction of the EAFZ with the east-west striking Çardak-Sürgü fault (Ç-SF) triggered the second large (Mw 7.5) earthquake, causing another round of the damage in the region. The maximum ground offsets are around 47.5 kilometers away from the epicenter in this event on the EAFZ. The surface ruptures directly cut young basins and mountains, as well as activating some pre-existing surfaces. Our observation provides important data on surface deformation during large continental strike-slip earthquakes, rupture propagation mechanisms, and how slip may be transferred between complex fault systems. We also provide insight into how slip along linked fault systems accommodates global plate motions.

How to cite: Meng, J., Kusky, T., Mooney, W. D., Bozkurt, E., Bodur, M. N., and Wang, L.: Fault rupture mapping of the February 6, 2023 earthquake sequence, eastern Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21398, https://doi.org/10.5194/egusphere-egu24-21398, 2024.

EGU24-304 | ECS | Posters on site | SM4.17

Extracting 3-dimensional co-seismic displacement using InSAR techniques 

Dmitry Sidorov-Biryukov and Dragana Đurić

Synthetic-aperture radar (SAR) has emerged as a dependable data source across various disciplines, particularly in geophysics. Its utility extends to applications such as fault zones assessment, surface rupture extent estimation, and evaluation of potential infrastructure damage. A key advantage of SAR data in remote sensing for seismology lies in its reliability, as it operates independently of the day/night cycle and weather conditions within the designated area of interest. This characteristic enhances its efficacy in providing consistent and uninterrupted observations for seismic monitoring and analysis. This study proposes a slightly modified methodology for extracting three-dimensional movements of the terrain by leveraging ascending and descending synthetic-aperture radar (SAR) images acquired both pre- and post-event. The approach aims to contribute to a more comprehensive understanding of geophysical dynamics by analyzing SAR data in both orbital configurations, providing insights into the spatial and temporal aspects of co-seismic deformation. 
A seismic event investigation was conducted, focusing on the magnitude 6.9 earthquake that occurred in Indonesia on August 5, 2018. This seismic event was attributed to a shallow thrust fault located on or near the Flores Back Arc Thrust. The study utilized Sentinel-1 data for Differential Interferometric Synthetic Aperture Radar (DInSAR) processing and phase unwrapping, employing conventional procedures. The three-dimensional displacement extraction method was applied to the processed data, and the resulting image underwent a comprehensive analysis. The findings reveal a maximum displacement of 0.35 meters in the north-south direction, 0.125 meters in the east-west direction, and an uplift of approximately 0.68 meters.

How to cite: Sidorov-Biryukov, D. and Đurić, D.: Extracting 3-dimensional co-seismic displacement using InSAR techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-304, https://doi.org/10.5194/egusphere-egu24-304, 2024.

EGU24-1304 | Posters on site | SM4.17

Dynamic rupture process of the 2018 Hokkaido Mw6.6 earthquake, Japan 

Wenbo Zhang and Zhangdi Xie

The Mw6.6 earthquake occurred in the Higashi-Geizen area of Hokkaido, Japan, on September 5, 2018, at a depth of 37 km, which exceeds the depth of the brittle-ductile boundary between the crust and the upper mantle and produces strong damage at the surface. In order to study the seismic tectonics of the source region of the Hokkaido earthquake and the physical mechanism that generates strong ground motions, this paper investigated the dynamics of this earthquake, and attempts to invert the dynamic rupture process based on a kinematic source model. First, the kinematic model of the Hokkaido earthquake was used to analyze and calculate the shear stresses on the fault plane, and it was found that the rupture process basically followed the slip-weakening friction law. Based on this result, an initial dynamic source model was built. Then the dynamic rupture process of the earthquake was inverted by the trial-and-error method. Our results show that the dynamic source rupture process of the Hokkaido earthquake was dominated by strike-slip in the rupture initiating area, and at first propagated toward NE and then toward SW. Finally propagated toward the up-dip direction of the fault plane, producing thrust rupture at the bend of the fault. At the location of thrust rupture, the slip rate and total slip reach their maximum values. Combined with the analysis of kinematic and dynamic inversion results, it is inferred that the region is a strong motion generation zone (SMGA). The strong-ground motions generated from the SMGA mainly caused this earthquake disaster.

How to cite: Zhang, W. and Xie, Z.: Dynamic rupture process of the 2018 Hokkaido Mw6.6 earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1304, https://doi.org/10.5194/egusphere-egu24-1304, 2024.

Fast and slow earthquakes represent distinct modes of energy release during tectonic fault rupture. While laboratory stick-slip experiments have observed both fast and slow slips, limitations in sampling rates have obscured detailed insights into fault thickness variation. Specifically, the underlying reasons for a single fault exhibiting different slip modes have remained elusive. In this study, we conducted ring shear experiments employing an ultrahigh sampling rate (10 MHz) to shed light on the contrasting physical processes between fast and slow slip events. Our findings reveal that slip durations varied from dozens to hundreds of milliseconds. Fast slip events exhibit continuous large-amplitude Acoustic Emission (AE) signals alongside complex variations in sample thickness: a brief compaction pulse during rapid stress release, succeeded by sample dilation and thickness vibrations. As the slip concludes, the sample thickness initially undergoes slow compaction, followed by dilation preceding the nucleation of subsequent slip events. Conversely, during slow slip events, shear stress reduction coincides with intermittent bursts of low-amplitude AE and sample dilation. Fast and slow slips have similar AE spectra. Detailed observations of thickness variations during slips indicate that dilation occurs in both fast and slow slips, aligning with natural observations of coseismic dilatation. This study offers insights into the mechanisms governing fault slips during fast and slow earthquakes, potentially explaining their impact on stress redistribution and structural reorganization within faults.

How to cite: Ge, Y., Hu, W., and Gou, H.: Concordant Dilatancy in Stick-Slip Events and Fast/Slow Earthquakes: Insights from High-Resolution Studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2509, https://doi.org/10.5194/egusphere-egu24-2509, 2024.

Ancient plate tectonic processes (e.g., continental collisions) can generate deformation deep into the lithosphere, highlighted by seismological imaging showing mantle lithosphere heterogeneities (thought to be scarring from past events). As the mantle lithosphere is the largest (and often strongest) component part of a tectonic plate, it has the potential to control tectonic deformation at the surface. A number of numerical modelling studies indicate the closure of ancient plate boundaries could generate latent deep structures that could be ‘perennially’ reactivated in intraplate settings - dominating shallow geological features in activating tectonics in plate interiors. This work has often been linked to large-scale tectonic processes such as continental rifting and orogenesis. However, in order to fully understand such ‘bottom-up’ influences on plate tectonic processes, it is important to analyse such mechanisms in more ‘actualistic’ models (e.g., finding evidence in present-day tectonics) rather than applying to ancient activity (e.g., to events millions of years ago).

Here, we analyse the present-day intraplate earthquake database for any scenarios where deep latent lithosphere structures could drive shallower seismic events. Case studies for intraplate earthquakes of Central China, North America, Scotland, and Africa are presented using a new visualisation software we’ve developed to handle large amounts of seismic events. A potential present-day example of this theoretical deep trigger of shallow earthquakes is examined in detail, with careful attention given to the inherent uncertainty of this work. Finally, we highlight the difficulty in understanding the rheology and composition of latent structures deep in the lithosphere, and whether they can be passive or active in present-day tectonics.

 

How to cite: Heron, P. and Wan, C.: Reactivation of mantle lithosphere scars: deep sutures inducing shallow intraplate earthquakes? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3284, https://doi.org/10.5194/egusphere-egu24-3284, 2024.

The geometry of long strike-slip faults often includes local deviations from the general fault orientation, commonly known as restraining and releasing bends. As earthquake ruptures propagate along the fault, these bends experience either an increase or decrease of stress, influencing the rupture dynamics. While it is well established that these geometric features can dramatically affect rupture parameters such as propagation velocity, style, and extent, the exact dynamics and mechanics of the rupture-bend interaction are not yet clear. Here, we present direct experimental observations of the interaction of shear ruptures with restraining and releasing bends of different angles, deviating from a planar interface by up to 30 degrees. We trigger dynamic ruptures that spontaneously propagate along matching interfaces between two loaded PMMA plates and image ruptures at the area of the bends with an ultra-high-speed camera, operating at a rate of million frames per second. By applying Digital Image Correlation on the imaged frames, we produce high-resolution, full-field maps of the evolution of displacements, particle velocities, and stresses as the ruptures propagate through the bends. While all ruptures reach the bends as self-healing slip pulses propagating at sub-Rayleigh velocities, different bend geometries have different effects on the ruptures. These include arresting the ruptures, transitioning them into supershear and crack-like ruptures, and triggering secondary ruptures and back-propagations. These results can illuminate the complex dynamics that evolve around restraining and releasing bends during earthquakes and can be used for calibrating earthquake models and refining earthquake hazard assessments.

How to cite: Gabrieli, T. and Tal, Y.: The effects of restraining and releasing fault bends on the propagation of shear ruptures: direct experimental measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4586, https://doi.org/10.5194/egusphere-egu24-4586, 2024.

EGU24-4795 | Posters on site | SM4.17

Interaction between aseismic slip phenomena in a collision orogen 

Kate Huihsuan Chen, Satoshi Ide, Wei Peng, I-Chu Hua, Chieh-Chih Chen, and Ya-Ju Hsu

Using continuous seismological data of Central Weather Administration (CWA) Seismographic Network and Broadband Array in Taiwan for Seismology (BATS), we applied the envelope correlation method of Mizuno and Ide (2019) to identify tectonic tremors in Taiwan 2012 to 2022. With a large number of seismic stations used in this study and removal of short-lasted events (< 10 s), we successfully detected ~7000 events. Except for the tremor zone previously observed at southern Central Range, we reported the new tremor “hotspots” across the mountain range of the island, over a distance of 200 km. Different from the fluid-rich environment previously established for tremors in subduction zones, the newly discovered tremor zones in Taiwan coincide with the spots with high geothermal heat flux, indicating that the temperature effect may be the common mechanism for tremor generation in a mountain belt of Taiwan.

Other than tectonic tremors, several seismic phenomena are believed to be driven by aseismic slip process such as repeating earthquakes and earthquake swarms. The three catalogs may provide new insight into the controls of quasi-periodic aseismic slip and the role of deep fluid in their generation mechanism. We found that only < 5% of repeating earthquakes and swarms are located in 5 km of the tremor clusters, indicating that the deep-seated tremors might be engineered differently, comparing with the shallower repeaters and swarms. The spatial association is only observed underneath the southern Central Range, where the shallow swarms (< 15 km) and deep tremors (20-50 km depth) are likely interactive. We found 69-80% tremors and 86-96% swarm events occurred at the lower ground water level, respectively. This is contradictory with opposite clamping effect of hydrological/tidal stresses on thrust faulting (tremor) and normal faulting (swarm) slip. We hypothesized that in the lower crust where the thrust-faulting tremors are generated, the vertical fluid mobility could be easily elevated during the decreasing ground water level under the condition of near-lithostatic pore-fluid pressure. The upward migration of fluids may play an important role in the occurrence of swarm activities above the tremors. The continuous magnetotelluric monitoring at the location of active swarms will help us to confirm and further establish the temporal variation of fluid flow. 

How to cite: Chen, K. H., Ide, S., Peng, W., Hua, I.-C., Chen, C.-C., and Hsu, Y.-J.: Interaction between aseismic slip phenomena in a collision orogen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4795, https://doi.org/10.5194/egusphere-egu24-4795, 2024.

EGU24-5165 | ECS | Posters on site | SM4.17

Machine learning based Pseudo-Dynamic rupture generator for geometric rough faults 

Tariq Anwar Aquib, David Castro Cruz, Jagdish Vyas, and Paul Martin Mai

Accurately predicting the intensity and variability of strong ground motions from future large earthquakes is crucial for seismic hazard analysis. While kinematic ground motion simulations are computationally efficient and can be conditioned to inferred source-inversion models of past events or ensemble statistics of rupture-model databases, they rely on predefined spatiotemporal evolution of slip. In contrast, dynamic rupture simulations solve for a physically self-consistent slip evolution under prescribed stress and friction laws on the fault, yet, they are still computationally expensive. A practical compromise, therefore, is a physics-compatible source model embedded in a kinematic approach (i.e., Guatteri et al., 2004), referred to as the Pseudo-Dynamic (PD) approach.

Geologic features, such as small-scale fault roughness influence the rupture process, generating realistic high frequency radiation with  decay characteristics (Mai et al., 2017). Presently, most PD models are based on rupture simulations of planar faults (with the notable exception of Savran and Olsen, 2020). Additionally, these models rely on 1-point and 2-point statistics between source parameters, which may not adequately capture nonlinear relationships between kinematic rupture parameters.

In this study, we develop a Machine Learning (ML) framework involving Fourier Neural operators (FNO) (Li et al ., 2020) to learn the interdependencies between earthquake source parameters. We train our model using 21 dynamic simulations of rough faults (15 for training, 6 for testing; all from Mai et al., 2017). Our generator initiates with a stochastic final slip (Mai and Beroza, 2002) and a slip-constrained hypocentre location (Mai et al., 2005). The local slip evolution is described by a regularized Yoffe source time function (STF) characterized by rupture onset time, slip, peak time and rise time.

Dynamic rupture simulations show correlation between rupture speed and the gradient of fault roughness, with rupture deceleration in regions of positive roughness gradients, coinciding with fault areas of increased shear stress. Therefore, we establish rupture speed as a function of stress drop computed from 2D final slip and relate peak slip velocity to the estimated rupture speed. Assuming a Yoffe STF, we then compute rise time and the time of peak slip velocity, enabling a full spatiotemporal earthquake source characterization that accounts for dynamic rupture on rough faults. For the stochastic slip, we also demonstrate an approach to model roughness correlated with stress drop. Our PD rupture generator reproduces the mean and standard deviation of ground motion models for different intensity measures in simulations of M 6.0-7.0 strike slip scenarios. This outlines a new PD source modelling approach suitable for broadband physics-based probabilistic seismic hazard analysis.  

How to cite: Aquib, T. A., Cruz, D. C., Vyas, J., and Mai, P. M.: Machine learning based Pseudo-Dynamic rupture generator for geometric rough faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5165, https://doi.org/10.5194/egusphere-egu24-5165, 2024.

EGU24-5657 | Orals | SM4.17

Seismicity, Segmentation and Structure of the Blanco Transform Fault System in the Northeast Pacific 

Dietrich Lange, Yu Ren Ren, and Ingo Grevemeyer

The Blanco transform fault system (BTFS) in the northwest off the coast of Oregon is highly segmented and one of the newly evolving transform faults. While for most transform systems, no high-resolution seismological data is available, the BTFS was instrumented with a dense network of 54 ocean-bottom-seismometer stations in 2012-2013.  We use one year of ocean-bottom-seismometer data from the Blanco Transform OBS Experiment (network code X9) to compare the seismicity with high-resolution multibeam bathymetry, aeromagnetic, and gravity datasets to study the seismotectonics of the BTFS. 

We determine P and S-phase arrivals using a new machine learning picker trained on OBS data to create a high-resolution local seismicity catalogue. We compare seismicity catalogues based on different picking algorithms and event associators, including an automated phase picker for OBS data (PICKBLUE) using the hydrophone and seismometer channels. 

In total, we locate ~9.000 local events, which reveal lateral deformation along the BTFS in very high detail, including smaller step-overs, transtensional structures, and focused seismicity along the fault trace and several ~15 km long aseismic segments along the BTFS. At segments where the BTFS is linear, most seismicity is very concentrated to the transform fault, suggesting that the deformation is within +/-7 km of the fault trace and, hence, very focused. Furthermore, we will present vp and vp/vs velocity models, which reveal the three-dimensional structure of the BTFS and compare the seismicity with seismic velocities.  

The local seismicity indicates substantial along-strike variations, indicating different slip modes in the eastern and western BTFS. Seismic slip vectors suggest that the eastern BTFS is a mature transform fault system accommodating the plate motion. At the same time, the western BTFS is immature as its re-organization is still ongoing.

The available datasets provide no evidence of either transform faults or fracture zones around the BTFS before 2 Ma, supporting that there were no pre-existing transform faults before the initiation of the BTFS. Therefore, we suggest that the BTFS developed from two broad transfer zones instead of pre-existing transform faults. 

Furthermore, we applied the deep learning phase picker, to analyse an extensive OBS dataset over three years, including a total of 225 OBS deployments (network codes: 7D, X9, and Z5) deployed offshore the south-central Cascadia subduction zone, south of the BTFS. As a result, ~7000 well-constrained local events were derived, providing new insights into offshore fault dynamics and the segmentation of the Gorda ridge  South of the BTFS.

 

How to cite: Lange, D., Ren, Y. R., and Grevemeyer, I.: Seismicity, Segmentation and Structure of the Blanco Transform Fault System in the Northeast Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5657, https://doi.org/10.5194/egusphere-egu24-5657, 2024.

EGU24-6184 | ECS | Orals | SM4.17

The Frictional Strength and Stability of Spatially Heterogeneous Fault gouges 

Job Arts, André Niemeijer, Martyn Drury, Ernst Willingshofer, and Liviu Matenco

Along-fault lithological heterogeneity is observed in all fault zones that cross-cut compositional layering. Modelling studies of fault rupture nucleation, propagation and arrest often assume that the fault mechanical behaviour is governed by either the rheologically weakest phase or by homogeneous gouge mixtures of the juxtaposing lithologies. However, the effects of spatial heterogeneity on fault gouge composition and hence its frictional behaviour are not well understood.

In this study, we conducted friction experiments to understand how material mixing and clay-smearing in fault gouges affect the frictional strength and stability of claystone-sandstone juxtaposing faults. Simulated mechanically contrasting fault gouges (Ten Boer claystone and Slochteren sandstone) were derived from the Groningen gas field in the northeast of the Netherlands, an area affected by induced seismicity. We conducted velocity stepping tests in a rotary shear configuration to facilitate substantial shear displacement, essential to study mixing and clay-smearing in large offset faults. Experiments were performed under normal stresses ranging between 2.5 and 10 MPa, imposed velocities ranging between 10 and 1000 µm/s, and under drained conditions. We introduced spatial heterogeneity by segmentation of the simulated gouge in claystone and sandstone patches.

Our mechanical data shows displacement-dependent changes in sliding friction and its rate-dependence. Clay smearing and shear localization on foliation planes cause transient weakening of the gouge and a shift from velocity-weakening to velocity-strengthening behaviour. Progressive shearing leads to juxtaposition of sandstone segments that are separated only by a thin clay smear. We propose that the associated increase in friction is caused by lithology mixing at the interfaces between the clay smear and the bulk Slochteren sandstone gouge, and by the disruption of continuous Y-shears. Progressive shearing does not lead to a decrease in the rate-sensitivity parameter (a-b), suggesting that, although affected by quartz and feldspar grains, deformation remains localized on phyllosilicate foliation planes.

Our results show that fault friction and its rate-dependence are not simply governed by the weakest lithology along a fault plane, nor that they can be simply represented by a homogeneous mixture of the juxtaposing lithologies. Detailed knowledge of the stratigraphic layering in combination with the fault offset is required to predict the macroscopic frictional behaviour of heterogenous fault gouges.

How to cite: Arts, J., Niemeijer, A., Drury, M., Willingshofer, E., and Matenco, L.: The Frictional Strength and Stability of Spatially Heterogeneous Fault gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6184, https://doi.org/10.5194/egusphere-egu24-6184, 2024.

EGU24-7887 | ECS | Orals | SM4.17

Studying the Viability of Kinematic Rupture Models and Source Time Functions with Dynamic Constraints 

Maria Eugenia Locchi, Francesco Mosconi, Mariano Supino, Emanuele Casarotti, and Elisa Tinti

Earthquake is one of the greatest natural hazards and a better understanding of the physical processes causing earthquake ruptures is required for appropriate seismic hazard assessment. Kinematic modelling is a standard tool for providing paramount information about the complexity of the earthquake rupture process and for making inferences on earthquake mechanics. Despite recent advances, kinematic models are characterized by uncertainties and trade-offs among parameters (related to the non-uniqueness of the problem). It has been shown that, for the same earthquake, source models obtained with different methodologies can exhibit significant discrepancies in terms of slip distribution, fault planes geometry and rupture time evolution.

One of the crucial assumptions in kinematic modelling on causative faults is the source time function, because it contains key information about the dynamics. Such function is nonetheless one of the most poorly observationally constrained characteristics of faulting. Recently, slip velocity time histories have been studied with laboratory earthquakes, and it has been observed that a systematic change of mechanical properties and traction evolution corresponds to a change in the shape of slip velocity. However, in kinematic inversions this function is a-priori assumed using simplified shapes, although functions compatible with rupture dynamics should be preferred.

In this work, we run a series of forward and inverse modelling to investigate the effect of the assumed slip velocity function on the ground motion and on the inverted slip history on the fault plane. We generate spontaneous dynamic models and use their ground motion as real events, inverting these data with kinematic models. Kinematic inversions have been conducted using both single-time and multi-time windowing. Uncertainties have been investigated assuming four different source time functions (i.e., triangular, box, regularized-yoffe and exponential functions). In this way we examine how the slip velocity function influences the slip distribution on the fault plane, and test if the inferred kinematic parameters (rise time and rupture velocity) are consistent with the dynamic models. Also, for a dense grid of phantom receivers, we examine the variability of the peak ground velocity (PGV) of synthetic seismograms up to 1 Hz. The latter have been obtained with forward models assuming the same slip distribution, rise time and rupture velocity but changing the source time functions.

Finally, we use the retrieved kinematic history on the pseudo-dynamic models to examine how different kinematic assumptions lead to a variability in the shear stress evolution. We focus on dynamic parameters such as breakdown work, stress drop, and Dc parameter. Our results provide a glimpse of the variability that kinematic source time functions (dynamically consistent or not) might have when used as a constraint to model the earthquake dynamics.

How to cite: Locchi, M. E., Mosconi, F., Supino, M., Casarotti, E., and Tinti, E.: Studying the Viability of Kinematic Rupture Models and Source Time Functions with Dynamic Constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7887, https://doi.org/10.5194/egusphere-egu24-7887, 2024.

EGU24-8773 | Orals | SM4.17

Stress heterogeneity and its relation to geology during the 2016-2017 central Italy earthquake sequence 

Patricia Martínez-Garzón, Men-Andrin Meier, Federica Lanza, Cristiano Collettini, and Georg Dresen

Quantifying the stress field variability at different wavelengths and how it evolves over time has important implications for the development of earthquake sequences. As small earthquakes occur more frequently than larger ones, their focal mechanisms are essential to create larger catalogs, that allow to statistically quantify the kinematics of earthquake sequences within a region and the preferential orientations of co-seismic strain release. Inverting earthquake focal mechanisms is widely used to infer a number of stress-related parameters characterizing a crustal volume, including the orientation of the principal stress axes, maximum horizontal stress, and the relative magnitudes of the principal (stress ratio R) and horizontal stresses (APHI). If resolution allows, these stress parameters can be employed to quantify stress variability and heterogeneity in different rock volumes. Here we studied the 2016-2017 Central Italy seismic sequence that is characterized by the occurrence of three mainshocks: the Mw 6.0 Amatrice, Mw 5.9 Visso and Mw 6.5 Norcia. These major events nucleated on normal faults with kinematics consistent with the regional stress field. Taking advantage of a high-resolution catalog generated with deep learning and containing ~56.000 focal mechanisms, we calculated the distribution of stress parameters over small crustal volumes activated during the sequence and resolved the variability of the stress field during three different time periods punctuated by the three largest events. We found a change in the local trend of SHMax with better defined orientations consistent with the regional stress field towards the SE of the Amatrice mainshock, and larger variability to the NW where also Visso and Norcia mainshocks ruptured. These changes in SHMax trend also coincide with a contrast in the APHI parameter quantifying the relative magnitude of the horizontal stresses. The area between the Amatrice, Visso and Norcia epicenters displayed the lowest APHI (i.e. representing a normal faulting stress regime where SV >> SHMAX) and the lowest relative magnitude of the S2 (SHMax in the case of normal faulting). Furthermore, an increase in the APHI parameter is observed at depths below 8 km, reaching transtensional and strike-slip stress regimes in some local volumes. The area surrounding the rupture of the Amatrice mainshock displays the largest deviations from the regional stress over the entire analysed time period, indicating a stress anomaly driven by the properties of the medium or stress heterogeneities caused by static stress transfer that are persisting over the one-year time span of the catalogue. The observed local stress deviations from the regional stress field can help illuminating dominant local loadings affecting the deformation pattern.

How to cite: Martínez-Garzón, P., Meier, M.-A., Lanza, F., Collettini, C., and Dresen, G.: Stress heterogeneity and its relation to geology during the 2016-2017 central Italy earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8773, https://doi.org/10.5194/egusphere-egu24-8773, 2024.

EGU24-9095 | Orals | SM4.17

Modeling the along-fault variability of slow earthquakes in subduction zones based on a combined Maxwell Viscoelastic and damaging rheology 

Sina Massoumi, Véronique Dansereau, Jérôme Weiss, Michel Campillo, and Nikolai M. Shapiro

Slow earthquakes are transient events detected with geodetic (slow slip) and/or seismic (low-frequency earthquakes and tremors) observations that release energy over a period of hours to months, i.e., much longer than regular earthquakes. These events are observed in several subduction at a specific range of depths and with their properties, such as strength, duration, recurrence interval, and predominance of either slip or seismic components varying along the subduction interface. In this study, we investigate slow earthquakes based on numerical modeling by applying a combined Maxwell viscoelastic and damaging rheology. Unlike conventional rate and state modeling practices utilizing infinitely thin fault assumptions with fault friction laws, our approach incorporates a finite fault thickness through a damage mechanism and suitable failure criteria. Our model directly predicts a geodetically observable slow displacement, while rock damaging rate is considered as a proxy to seismic tremors.

We run a set of numerical simulations to systematically explore the effects of model parameters such as viscosity, yield stress, and healing time on slow slip and tremors. We then incorporate along-fault variations in temperature, pore pressure, and permeability rate to infer changes in viscosity, yield stress, and healing time. The model successfully reproduces the observed synchronous episodes of slow slip and tremors in the initial stage. We show that decreasing strength and healing time results in reducing the recurrence intervals between these episodes and the amplitude of slow slip. Conversely, decreasing viscosity leads to a larger recurrence time and increased amplitude. After introducing the along-fault variability of main mechanical parameters, the model successfully predicts tremor concentration in the downdip zone which can be explained by the influence of high pore pressure in the yield stress profile as a function of depth. The capacity of the model to reproduce some patterns seen in observations underscores its capacity to capture the physics of slow earthquakes, emphasizing its potential to improve our understanding of seismic phenomena in subduction zones.

How to cite: Massoumi, S., Dansereau, V., Weiss, J., Campillo, M., and Shapiro, N. M.: Modeling the along-fault variability of slow earthquakes in subduction zones based on a combined Maxwell Viscoelastic and damaging rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9095, https://doi.org/10.5194/egusphere-egu24-9095, 2024.

EGU24-9837 | Orals | SM4.17 | Highlight

A search for dilation in low frequency earthquake waveforms 

Jessica Hawthorne, Amanda Thomas, Lois Papin, Hui Huang, and Samuel Cavendish

The fault zone process that creates slow earthquakes remains unclear, but one proposed mechanism to limit slip speeds depends on shear-induced dilatancy and the resulting pore pressure changes.  This process would imply that the fault zone dilates during slow earthquakes.  So in this study, we search for the signature of dilation in the focal mechanisms of tremor’s low frequency earthquakes (LFEs).

It is, however, difficult to directly observe dilation in LFE waveforms.  The paths travelled by LFEs’ 1-10 Hz seismic waves are complex, and Earth structure is poorly known at the short wavelengths of interest.   This complexity makes it difficult to disentangle path effects from source properties.  Thus we look for differences in the seismic waves created by two groups of LFEs: groups of events that are in the same location but occur at different times.  The earlier events are smaller and thought to rupture through more solid, low-permeability fault rock and thus may have large dilation, while the later events rupture areas that have recently slipped and thus may have smaller dilation.

In our initial analysis, we stack and analyse waveforms of LFEs identified in Cascadia by Bostock et al (2015).  However, we identify no significant difference in the waveforms or any significant trends in the polarisation of the difference.  Preliminary results suggest that the early and late LFEs have waveforms that differ by less than 1-2%.  

That zero to minimal difference could indicate that there is no dilation.  Perhaps early and late LFEs are exclusively shear slip, and shear-induced dilatancy does not limit LFE slip speeds.  However, it is also possible that dilation is simply small.  The early, potentially large-dilation LFEs could have a dilation-to-shear slip moment ratio of 0.05, and the later, potentially small-dilation LFEs have a dilation-to-shear ratio of 0.04.   Such dilation would be large enough to significantly affect LFE slip rates but would not be visible with our current data and techniques.

In our continuing work, then, we seek to decrease the uncertainty in our observations by identifying and stacking more LFEs and by extracting more information from seismograms including many LFEs.

How to cite: Hawthorne, J., Thomas, A., Papin, L., Huang, H., and Cavendish, S.: A search for dilation in low frequency earthquake waveforms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9837, https://doi.org/10.5194/egusphere-egu24-9837, 2024.

EGU24-10095 | ECS | Posters on site | SM4.17

Static and Quasi-Static Inversion of Fault Slip During Laboratory Earthquakes 

Feyza Arzu, Cedric Twardzik, Barnaby Fryer, Jean-Paul Ampuero, and François Passelègue

Inferring from seismological data the spatio-temporal distribution of slip during earthquakes remains a challenge due to the large size, non-uniqueness and ill-posedness of the inverse problem. Consequently, finite source inversion usually relies on simplifying assumptions. Moreover, in the absence of ground truth source data, the evaluation of the performance of source inversion is only possible through synthetic tests.

To address these concerns and test the viability of the inversion methods used for natural earthquakes, laboratory earthquakes offer a valuable alternative. They enable us to work with "simulated real data" and provide a relatively well-constrained solution. Here, we employ a biaxial apparatus capable of reproducing shear rupture along a rectangular fault separating two PMMA blocks. Both normal and shear stresses are initially increased up to the target normal stress using external pressure pumps, assuming a fixed shear to normal stress ratio of 0.3. Subsequently, the shear stress is increased until instabilities occur at a peak friction of 0.4. During each seismic rupture, we measure the acceleration at 20 receivers along the fault. The acceleration data are integrated twice into displacements, and then used to invert for the slip history, which is compared to direct measurements using laser sensors placed through the fault. For a static inversion of final slip, predictions are computed using Okada's formulation and the posterior probability density function of the slip history is obtained using a Metropolis algorithm. We will also report on results of quasi-static inversion. The adoption of a probabilistic approach provided a range of solutions, essential for assessing the uncertainty in our results and addressing the issue of non-uniqueness. Ultimately, the obtained results will offer insights into inversion methods, presenting their strengths and limitations more realistically than when using artificially generated synthetic datasets.

How to cite: Arzu, F., Twardzik, C., Fryer, B., Ampuero, J.-P., and Passelègue, F.: Static and Quasi-Static Inversion of Fault Slip During Laboratory Earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10095, https://doi.org/10.5194/egusphere-egu24-10095, 2024.

EGU24-10195 | ECS | Orals | SM4.17

Identifying uncataloged low-frequency earthquake sources with deep learning 

Jannes Münchmeyer, Sophie Giffard-Roisin, Marielle Malfante, William Frank, Piero Poli, David Marsan, and Anne Socquet

Tectonic faults exhibit a wide spectrum of processes releasing stress: from fast earthquakes to slow deformation. Mapping smaller-scale slow deformation directly is challenging because of the limited signal-to-noise ratio of geodetic recordings. Instead, we need to rely on other telltale signs of slow deformation. Low-frequency earthquakes (LFEs) are such signs: a class of seismically observable signals that coincide with slow deformation.

However, detecting LFEs is challenging due to their emergent nature and generally low magnitude. The most common method for LFE detection is template matching. Due to the need for waveform templates, this method is specific to a set of LFE sources and seismic stations. This limitation renders the template matching unable to discover uncataloged sources or detect LFEs in regions without prior known LFE activity.

Here, we present a novel, deep learning method for detecting LFEs. Our method detects phase arrivals from LFEs, allowing to detect them with a workflow closely modeled after a standard earthquake detection workflow. In contrast to template matching, the deep learning method is substantially more flexible and can generalise to unknown LFEs and even across world regions. We apply our method to a diverse set of regions, including regions with previously known LFE activity, such as Cascadia and Nankai, and without known LFE activity, such as Northern Chile.

How to cite: Münchmeyer, J., Giffard-Roisin, S., Malfante, M., Frank, W., Poli, P., Marsan, D., and Socquet, A.: Identifying uncataloged low-frequency earthquake sources with deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10195, https://doi.org/10.5194/egusphere-egu24-10195, 2024.

EGU24-11935 | ECS | Orals | SM4.17

Modeling 3D dynamic rupture and arrest of spontaneous fluid-induced microearthquake 

Francesco Mosconi, Elisa Tinti, Emanuele Casarotti, Alice-Agnes Gabriel, Luca Dal Zilio, Antonio Pio Rinaldi, Ravil Dorozhinskii, 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 modelling of microearthquakes induced by fluid injection is also relevant for studying rupture propagation following a stimulated nucleation. The ERC-Synergy project FEAR (Fault Activation and Earthquake Ruptures) in the Bedretto Underground Laboratory (Swiss Alps) at approximately 1500m depth offers a unique opportunity to investigate fluid-induced micro-events on broadband seismic arrays. In this study, we leverage this opportunity to perform dynamic ruptures caused by fluid injection on a target pre-existing fault (50m x 50m), generating a Mw ≤ 1 seismic event. We conduct fully dynamic rupture simulations coupled with seismic wave propagation in 3D using a linear slip-weakening constitutive law, implemented on the supercomputer Leonardo (CINECA) with a multi-GPU distributed system.

Stress field and fault geometry are constrained by in-situ characterization, allowing us to minimize the a priori imposed parameters. We investigate the dynamics of rupture propagation and its arrest for a target Mw < 1 induced earthquake with spatially heterogeneous stress drops caused by pore pressure changes and different constitutive parameters (i.e., critical slip-weakening distance, Dc, dynamic friction). We explore different homogenous conditions of frictional parameters, and we show that the spontaneous arrest of a propagating rupture following a dynamic instability is possible in the modeled stress regime by assuming a high fault strength parameter S, that is high ratio between strength excess and dynamic stress drop characterizing the fault before injection. The arrest of rupture propagation in our modeled induced earthquakes depends on the heterogeneity of dynamic parameters caused by the spatially variable effective normal stress, which controls the on-fault spatial increment of fracture energy Gc. Furthermore, in faults with high S values (i.e., low rupturing potential), we find that even minor variations in Dc (from0.45 to 0.6 mm) have a substantial effect on the rupture propagation and on the ultimate size of the earthquakes. Our results show that modest variations of dynamic stress drop determine the rupture mode, distinguishing self-arresting from run-away ruptures. Studying dynamic interactions (stress transfer) among slipping points on the rupturing fault provides insights on the dynamic load and shear stress evolution at the crack tip. The inferred spatial dimension of the cohesive zone in our crack models is roughly ~0.3-0.4m, with a maximum slip of ~0.6cm. Finally, analyzing the radiated synthetic waveforms, we examine the differences in the high-frequency content of simulated waveforms between self-arresting and run-away earthquakes and provide an estimation of the source parameters obtained through the spectral inversion. This estimation is then compared with source parameters of the dynamic forward models.

Our results suggest that several features inferred for accelerating dynamic ruptures differ from those observed during rupture deceleration in a self-arresting earthquake caused by the spatial gradients of normal stress and pore-pressure. These results related to rupture arrest integrate those obtained with spatial variations of the initial stress, highlighting the role of the heterogeneities of stress drop and Gc.

How to cite: Mosconi, F., Tinti, E., Casarotti, E., Gabriel, A.-A., Dal Zilio, L., Rinaldi, A. P., Dorozhinskii, R., and Cocco, M.: Modeling 3D dynamic rupture and arrest of spontaneous fluid-induced microearthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11935, https://doi.org/10.5194/egusphere-egu24-11935, 2024.

EGU24-13605 | Posters on site | SM4.17

Source of the 2023 Morocco Earthquake (Mw6.8) inferred by analysis of Seismic and Geodetic Data 

Bento Caldeira, Elisa Buforn, Rui Oliveira, Mourad Bezzeghoud, José Borges, and Ines Hamak

On September 8, 2023, at 22:11 UTC, a seismic event of magnitude Mw6.8 (according to the USGS) occurred near the village of Talat N’Yaaqoub, Al Haouz province, in the High Atlas region of Morocco. This earthquake had a profound impact, violently shaking the entire area within a radius of over 70km from the epicentre. More than 78,000 buildings were severely damaged, resulting in approximately 5,600 injuries and around 3,000 fatalities. A considerable portion of the affected population resides in buildings seismically vulnerable and limited access to resources for mitigating such risks. This incident stands out as a significant earthquake in a region characterized by a low deformation rate and generally considered to have low seismic activity. Testimonies collected by CSEM reveal that the seismic vibrations were felt not only in the High Atlas but also by people in a wider area extending to Algeria, southern Spain, and Portugal.

This study presents the preliminary results obtained from a comprehensive investigation of the earthquake's source. The analysis is based on the interpretation of seismic and geodetic data, employing a combination of the following methods: (1) inversion of the seismic moment tensor to determine fault plane geometry and hypocenter depth, (2) waveform inversion using a finite source model to assess spatiotemporal slip distribution, (3) modeling of surface strain field produced by the slip distribution model. The validation of the rupture model was performed by comparing the synthetic surface deformation field with the observed field obtained through the geospatial InSAR method.

Acknowledgement: The work was supported by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 - ICT (Institute of Earth Sciences).

How to cite: Caldeira, B., Buforn, E., Oliveira, R., Bezzeghoud, M., Borges, J., and Hamak, I.: Source of the 2023 Morocco Earthquake (Mw6.8) inferred by analysis of Seismic and Geodetic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13605, https://doi.org/10.5194/egusphere-egu24-13605, 2024.

EGU24-13905 | ECS | Posters on site | SM4.17

New slow slip events along the Hikurangi margin detected using wavelet analysis 

Andrea Perez-Silva, Ting Wang, and Laura Wallace

Along the Hikurangi margin, where the Pacific plate subducts beneath the Australian plate, slow slip events (SSEs) have been detected at both shallow and deep depths. With the aim of improving the SSE catalog along the Hikurangi margin, we use a wavelet-based method developed by Ducellier et al. (2022) to detect SSEs recorded by the GPS sites operated by the GeoNet network. We apply wavelet decomposition to the east component of the GPS stations along Hikurangi. To do so, we consider two transects, transect 1 and transect 2 that target the shallow and deep SSE regions, respectively.
We take equally spaced points along the transects and group stations within a 50-km radius of a given point. Then we apply wavelet decomposition to each station within the radius. We then stack each detail over all stations within the radius and sum the stacked details at each level of decomposition. We find that SSEs are best distinguishable in levels 5, 6 and 7 for shallow SSEs and levels 7, 8 and 9 for deep SSEs. We then define a displacement threshold of one standard deviation of the stacked details. To define an SSE, we consider the stacked details below the displacement threshold that are followed by stacked details above the displacement threshold, following Ducellier et al. 2022. Considering the stacked details along transect 1, which targets shallow SSEs, we find 54 SSE detections from 2005 to 2023. Of those, 20 have been reported in previous work, which leaves 34 potential new SSE detections. The stacked details along transect 2, which runs close to the deep SSE region, indicate 15 SSE detections over the same period; six of which were previously reported and nine potential new detections. We then geodetically model the new SSE detections using the software TDEFNODE (McCaffrey 2009) to study their spatial and temporal distribution along the margin.

How to cite: Perez-Silva, A., Wang, T., and Wallace, L.: New slow slip events along the Hikurangi margin detected using wavelet analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13905, https://doi.org/10.5194/egusphere-egu24-13905, 2024.

EGU24-15181 | Posters on site | SM4.17

Unravelling the intraplate 2019 Broome earthquake in the North West Shelf, Australia, through 3D CMT analysis 

Sima Mousavi, Babak Hejrani, and Meghan S. Miller

The July 14, 2019 Broome earthquake, with a magnitude of 6.6, was a significant seismic event in the North West Shelf (NWS) region of Western Australia where the dynamics of earthquakes are not well-understood. This study examines the focal mechanisms, centroid time, and locations of the Broome earthquake and its aftershocks using Centroid Moment Tensor (CMT) analysis.

The NWS is located in an intraplate tectonic setting where the dynamics of earthquakes are not well-understood. The region has a complex history of fault activity, and it transitions from an active collisional plate boundary in the north to a passive continental margin in the west. These tectonic regimes have generated seismic zones along the plate interface and reactivated older faults.

The Broome earthquake, a strike-slip event, exhibited a dominant NNE-SSW maximum horizontal stress orientation, prevalent across the NWS and responsible for numerous regional earthquakes. Despite the NWS's seismic activity, focal mechanism studies have been limited due to sparse seismic stations, significant azimuthal gaps, and considerable distances between stations and earthquake locations.

We utilized CMT inversion with a high-resolution 3D AusREM velocity model of the region. This method offers enhanced accuracy in determining earthquake source parameters at frequency up to 0.1 Hz, which allows us to study smaller magnitude events, which pose challenges for traditional 1D models.  

The results reveal primarily strike-slip faulting with considerable non-double-couple components, indicating complex rupture processes beyond planar assumptions. The 25-58% double-couple percentages highlight significant deviation from standard seismic models, underlining the NWS's geological complexity.

How to cite: Mousavi, S., Hejrani, B., and Miller, M. S.: Unravelling the intraplate 2019 Broome earthquake in the North West Shelf, Australia, through 3D CMT analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15181, https://doi.org/10.5194/egusphere-egu24-15181, 2024.

EGU24-15566 | ECS | Orals | SM4.17

Surface displacement and source parameters of the 2020 Zagreb, Croatia earthquakes 

Marija Mustać Brčić, Jinyin Hu, Marijan Herak, Hrvoje Tkalčić, and Thanh-Son Pham

On 22 March 2020 at 5:24 UTC, a MW 5.4 earthquake occurred on the outskirts of Zagreb and was followed by a MW 5.0 aftershock at 6:01 UTC on the same day. These moderate-magnitude events resulted in ground motion at the edge of detectability with satellite data but caused considerable damage in Zagreb’s historic centre. To illuminate the seismic sources, we compute the ground motion and invert seismic data using a state-of-the-art Bayesian inversion method that accounts for uncertainties in the data and in the Earth structure model. We compare the results to a well-established technique that uses a large number of hand-picked first-motion polarities.

Sentinel-1 Interferometric Wide data both from the ascending and descending orbit is obtained and processed using the European Space Agency SNAP toolbox. The resulting images show a phase difference of about 2π corresponding to ground displacement of 3 cm. The hypocentre and centroid locations of the events suggest that both were initiated at a depth of around 10 km, the rupture propagated upward, and most of the energy was released at a depth of 4 to 5 km. The shallow depth of the earthquakes possibly led to measurable surface displacement and resulted in considerable damage in the epicentral area and the centre of Zagreb.

How to cite: Mustać Brčić, M., Hu, J., Herak, M., Tkalčić, H., and Pham, T.-S.: Surface displacement and source parameters of the 2020 Zagreb, Croatia earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15566, https://doi.org/10.5194/egusphere-egu24-15566, 2024.

The study of earthquake rupture complexity plays a crucial role in assessing and mitigating seismic hazards.
Among the earthquake source parameters, the rupture velocity is generally unknown and assumed as a fixed percentage (60%-90%) of the shear wave velocity, although it controls the rupture duration, directivity, amplitude, and frequency content of the radiated wavefield. The rupture velocity is indeed the key parameter that determines the earthquake rupture length and indirectly the stress release, through the seismic moment. The observed large variability of stress drop estimates (over three orders of magnitude) can be partly related to the uncertain estimate of the rupture velocity and its possible heterogeneity or scaling with magnitude.

In this study, we tackle the specific problem of estimating earthquake rupture velocity, together with other characteristic source parameters, using a time-domain technique, applied to a 24-event dataset of micro-seismic events occurring in The Geysers area in California, USA. We propose a methodology that combines P and S half-pulse durations to infer independent estimates of the rupture radius and speed of microearthquakes assuming a circular fracture surface. For this aim a previous technique, that uses the P- and S-wave log-displacement curves as a function of the time along the seismogram has been used to measure attenuation-corrected, average P and S half-durations and plateau levels from a set of recorded earthquake waveforms. Refined estimations of seismic moment, rupture radius, and velocity allowed to determine accurate estimations of the stress release. Results show that rupture velocity is not constant but increases with magnitude in the explored range, reaching in 16 cases supershear speed values. Noteworthy, a self-similar, constant stress drop scaling is obtained only if a variable rupture velocity with magnitude is used for rupture radius and stress release determinations. The possibility of extremely fast ruptures (super-shear) occurring in the considered geothermal area can be attributed to the effect of lubrication and/or pore pressure increase due to massive volumes fluids injected under high pressure in the subsoil, to exploit the energy resources of the geothermal reservoir.

This work paves the way for a deeper comprehension of the physical and geological conditions determining the nucleation, propagation, and arrest of the fracture in crustal rock volumes with different faulting mechanisms, and offers a new and interesting approach for a more complete and accurate earthquake source parameters estimation through a time domain technique.

How to cite: Lambiase, A., Nazeri, S., Longobardi, V., and Zollo, A.: Rupture Velocity Estimation and Source Parameter Analysis of Micro-Seismic Events at The Geysers, California, USA, Applying A Time-Domain Technique, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16185, https://doi.org/10.5194/egusphere-egu24-16185, 2024.

EGU24-16697 | ECS | Posters on site | SM4.17

Estimating source parameters by dynamic source inversion of apparent source time functions or spectra 

Lubica Valentová K. and František Gallovič

In dynamic source inversions, observed waveforms are used to infer frictional parameters on a fault, obtaining a rupture model constrained by both data and physics. Assuming a slip-weakening friction law, Bayesian dynamic rupture inversions of regional waveforms have already been performed for several large events (e.g., Gallovič et al., 2019;  Gallovič, et al., 2020; Kostka, et al., 2022). On the other hand, apparent source time functions (ASTF) or apparent source spectra are commonly used to estimate source parameters (corner frequency, stress drop, etc.) under the assumption of simplified source models (e.g., Brune source). The ASTFs can be inferred from observed waveforms by, e.g., empirical Green’s function deconvolution (Plicka et al., 2022), and characterize a station-specific source radiation free of path and site effects. Employing the ASTFs or apparent source spectra at each receiver instead of the full (low-frequency) waveforms in Bayesian dynamic source inversion is a promising way of surpassing the simplifying assumptions on the rupture process and radiation in earthquake source analyses.

 

Here we inspect the performance of the Bayesian dynamic source inversion applied to ASTFs and apparent source spectra on a series of synthetic tests. As a target model, we assume a Mw 6.2 dynamic source model on a 30x14km fault embedded in a 1D layered medium. The model parameters of the slip-weakening friction law are heterogeneous on the fault. The inversion is performed using the fd3D_tsn_pt code (Premus et al., 2020) with the same parametrization as the target dynamic model. The posterior dynamic model samples are used to assess the reliability of various kinematic or dynamic parameters, such as rupture size, duration, corner frequency, or static stress drop, including their uncertainty, when inverting ASTFs, apparent source spectra, or full waveforms. The synthetic tests reveal which of the source parameters can be estimated reliably using each dataset and which are biased due to the settings of the McMC sampling process. Finally, a real-data application of the ASTF dynamic source inversion for the 2010 Mw 6.9 deep earthquake in East China is shown.

How to cite: Valentová K., L. and Gallovič, F.: Estimating source parameters by dynamic source inversion of apparent source time functions or spectra, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16697, https://doi.org/10.5194/egusphere-egu24-16697, 2024.

For more than a decade, earthquakes induced by natural gas extraction have been a significant societal concern in Groningen, the Netherlands. Their occurence underlines the importance of understanding earthquake source characteristics and the development of suitable and accurate characterization methods. In this study we (i) estimate the source characteristics of ten relatively strong induced events (magnitude > 2 ML) and (ii) analyse the rupture propagation of these events. The determination of the source characteristics (aspect i) involves the estimation of centroid-moment tensors (CMT) by means of an iterative workflow based on the Hamiltonian Monte Carlo algorithm. Importantly, this approach allows us to quantify the uncertainties of the model parameters (hypocenter, origin time, and moment tensor components) as the Markov Chain asymptotically approaches the posterior probability of these model parameters. The Bayesian inference problem is paired with geological prior knowledge of the Groningen subsurface (i.e., a detailed 3D velocity model and the know fault geometry). For the rupture propagation analysis (aspect ii), we employ the Empirical Green's Function method and exploit the dense sampling of the wavefield in Groningen resulting from the extensive seismic network in the region. This analysis allows us to estimate the directivity and speed of the ruptures, as such giving insight into the kinematics of the ten selected earthquakes.

 

We find that the lateral coordinates of the estimated centroids (posterior means) are consistent with the available Groningen fault map. Furthermore, the depths are mainly distributed in the vicinity of either the top or bottom of the gas reservoir. In terms of source mechanisms, the earthquakes are predominantly explained by double-couple sources featuring normal faulting. After conversion of the mean of the ensemble of moment tensors to strike, dip, and rake, we obtain values consistent with the known fault geometry. As for the rupture propagation analysis, our results indicate that these earthquakes display a relatively minor directivity effect. In spite of the minimal effect, however, the rupture directions are mostly consistent with the strike derived from both the MTs and the available fault map. 

How to cite: Weemstra, C. and Masfara, L. O. M.: Probabilistic centroid moment tensor inversion and rupture analysis of incuded seismic events in the Groningen gas reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18600, https://doi.org/10.5194/egusphere-egu24-18600, 2024.

A secondary zone of surface uplift (SZU), located from 200 to 400 kilometers landward of the trench, has been measured after several megathrust earthquakes. The SZU reached a few centimeters hours to days after the 2011 Mw 9.1 Tohoku (Japan) and 2010 Mw 8.8 Maule (Chile) earthquakes. One interpretation is that this SZU is universal, driven by volume deformation around the slab interface (van Dinther et al. 2019). Indeed, published coseismic finite-fault models for these events do not reproduce the measured SZU.

Here, we build on the case of the SZU to understand if, and how, our prior assumptions on the forward model can prevent us (or allow us) to make the most out of our dataset. In particular, we investigate under which assumptions the SZU can, or cannot, be predicted with fault slip. We show the SZU cannot be reproduced with coseismic finite-fault models that neglect 3D elastic heterogeneities in lithospheric structure. In contrast, we can recover the SZU with fault slip if elastic heterogeneities associated with the subducting slab are accounted for, as opposed to assuming homogeneous or layered elastic lithospheric structures. The SZU may therefore result from slip on the slab interface, downdip of the main coseismic patch. We suggest SZU might be caused by rapid afterslip, but a deformation of the volume around the fault cannot be ruled out.

Reference: van Dinther, Y., Preiswerk, L. E., & Gerya, T. V. (2019). A Secondary Zone of Uplift Due to Megathrust Earthquakes. Pure and Applied Geophysics, 176(9), 4043–4068. https://doi.org/10.1007/s00024-019-02250-z

How to cite: Ragon, T. and Simons, M.: Assumptions on elastic structure in finite-fault models: the case of the secondary zone of uplift measured after megathrust earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19335, https://doi.org/10.5194/egusphere-egu24-19335, 2024.

EGU24-19510 | ECS | Posters on site | SM4.17

Towards automated rapid earthquake dynamics characterization:  a proof of concept based on the 2024 Mw7.4 Noto Peninsula, Japan, earthquake 

Thomas Ulrich, Alice-Agnes Gabriel, and Fabian Kutschera

Rapid earthquake source characterization following an earthquake is crucial for effective emergency response and risk management. It may help for example in warning of potential secondary hazards like tsunamis or aftershocks or may guide resource allocation towards efficient coordination of rescue operations. The United States Geological Survey (USGS) provides routinely generated kinematic models based on teleseismic body and surface wave data, CMT solutions, and scaling relationships (Hayes, 2017). For the most significant earthquakes, models can be iteratively updated based on available data, such as strong motion or geodetic data (Goldberg, 2022). Nevertheless, in most cases, such automatically derived source characterization is limited to static slip. Yet, a characterization of rupture kinematics or dynamics would be beneficial as well. 

We here propose a workflow for the automated generation of earthquake dynamic rupture scenarios based on the fault slip distribution of a given kinematic model, and we present a proof of concept based on the 2024 Mw7.4 Noto Peninsula, Japan, earthquake. Our workflow, here based on the USGS model,  consists of retrieving the fault slip associated with the kinematic model, automatically generating a mesh and the input files, and running a set of dynamic rupture scenarios, informed by the stress change of the kinematic model. We plan to explore a limited parameter set, from which a preferred scenario could be selected, based on the fit to the input slip distribution, the fit to routinely inferred moment rate release, or to other available datasets, such as teleseismic, geodetic, or strong motion data. 

We expect such routinely derived dynamic rupture scenarios to be beneficial in the emergency response phase, for example, to better assess the potential damage to structures. More generally, such systematic source characterization could feed earthquake source databases, and therefore contribute to improving earthquake hazard assessment and the overall understanding of tectonic processes.

How to cite: Ulrich, T., Gabriel, A.-A., and Kutschera, F.: Towards automated rapid earthquake dynamics characterization:  a proof of concept based on the 2024 Mw7.4 Noto Peninsula, Japan, earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19510, https://doi.org/10.5194/egusphere-egu24-19510, 2024.

EGU24-20029 | Orals | SM4.17 | Highlight

Insight on along-dip fault transition zone rheology through LFE clustering  

Zaccaria El Yousfi, Baptiste Rousset, Mathilde Radiguet, and William B. Frank

Active faults present a wide spectrum of slip behaviors, from fast earthquakes, transient slow slip events to steady creep. Although each fault has its own specificities, the distribution of these behaviors is dictated by the evolution of depth-dependent pressure and temperature conditions to first order. In most of the subduction zones, transient slow slip events, accompanied by tectonic tremors and Low Frequency Earthquakes (LFEs), are located in the transition zone, between the updip seismogenic zone and the downdip steadily creeping zone. 

When present, tremors and LFEs are unique tools to monitor in detail the slip behavior in the transition zone. Previous studies analyzed the spatio-temporal clustering of tremors and LFEs (Wech et Creager, 2011, Rubin et Armbruster, 2013, Frank et al., 2013), and revealed that the properties of tremors/LFE bursts evolve with increasing depth: long recurrence intervals and long-lasting bursts occur close to the seismogenic zone while short recurrence intervals and short-lasting bursts happen deeper, close to the continuously creeping zone. These observations were made in various regions and tectonic contexts, including Cascadia (Wech and Creager, 2011), Nankai (Obara et al., 2011) and Mexico (Frank et al., 2013) for subduction zones, and the San Andreas strike-slip fault (Shelly et al., 2017).

In this study, we aim to gain insight on the rheological properties of the transition zone by a systematic analysis of the LFEs clustering properties in different regions and tectonic contexts. To do so, we analyze with similar methods LFE catalogs obtained with template matching, for Mexico (Frank et al., 2013), Nankai (Kato et al., 2020), Cascadia (Sweet et al., 2019) and Parkfield (Shelly et al., 2017).

We analyze the clustering properties of the LFE families (asperities), by computing the auto-correlation spectra of LFE catalogs for single families, and stacking them for bins along depth. This spectrum shows the density of recurrence of LFE bursts, and we observe a clear variation of maximum recurrence intervals between 100 and 10 days along depth for all regions. Additionally, we calculated and compared LFE burst recurrences using the cumulative LFE time series derivative, from which we retrieved prominent bursts, and using other clustering methods such as DBSCAN. Finally, we compile the results from different regions and compare them with the along depth pressure-temperature  conditions of these faults (Behr and Bürgmann, 2021) to have a rheological insight on these observations made using LFEs.

How to cite: El Yousfi, Z., Rousset, B., Radiguet, M., and Frank, W. B.: Insight on along-dip fault transition zone rheology through LFE clustering , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20029, https://doi.org/10.5194/egusphere-egu24-20029, 2024.

EGU24-20899 | Orals | SM4.17 | Highlight

Heat flow in the Nankai forearc, SW Japan, derived from BSR and drilling: Possible effect ofseamount subduction on earthquakes 

Masataka Kinoshita, Rie Nakata, Kazuya Shiraishi, Yohei Hamada, and Yoshitaka Hashimoto

In the central to western Nankai Trough. a series of dense seismic reflection surveys were conducted in 2018-2020 (Nakamura et al., 2022 GRL). They show impressive topographic features of the subducting plate boundary, including a subducting seamount in the Hyuga-Nada region and off Cap Muroto. Compiled seismic dataset was used for picking BSRs (bottom-simulating reflectors), which define a boundary between the hydrate-rich formation above and a gas-bearing layer below. The heat flow values are calculated from these BSR depths and the average thermal conductivity between the seafloor and BSR. The short wavelength variations are filtered out and the obtained heat flow values are regionally averaged ones. The result was then merged with the existing heat flow data (surface, borehole and BSR-derived) in this area.

Heat flow is highest near the trough axis off Cape Muroto (near the central Nankai Trough), which is interpreted as the fluid seepage along the decollement. In the forearc region, heat flow varies between 50-70 mW/m^2, On the forearc area off Muroto, the bathymetry is characterized by a large landward embayment including the trough axis and deformation front. Within 20 km landward from the deformation front, heat flow is ~80 mW/m^2 in this embayed area, whereas it is 40-60 mW/m^2 on either side of embayment. Further landward, we found a low heat flow (~30mW/m^2) region above the subducted seamount. We propose that the heat flow is affected by the subduction of seamount.

In Hyuga-Nada forearc, the westernmost portion of the Nankai Trough region off eastern Kyushu, the Kyushu-Palau Ridge (KPR) is obliquely subducting toward N30W since several Ma B.P. Heat flow marks a sharp contrast at KPR; to the east it is 50-100mW/m2 to the east and 25-40mW/m2 to the west. The transition from high to low heat flow occurs in only 20 km across KPR. Higher heat flows of 100 mW/m2 to the east are located near the axis of Nankai Trough, similar to those reported off Muroto. Lower heat flow to the west is attributed to the subduction of older West Philippine Basin. Near the KPR we observed a ‘bowl-shape’ negative heat flow anomaly; heat flow outside is ~45mW/m2, whereas it is ~25 mW/m2 above the subducted KPR.

We hypothesize these local low heat flow close to subducted seamounts in 2 models. The first is that the subducted seamount was already cooled down by the downward fluid flow (recharge) after it was formed as the opening of Shikoku Backarc basin (15-25 Ma). The second is that the seamount subduction caused a stress contrast between the leading and trailing sides, encouraging a poroelastic fluid flow in the sediment above seamount. Through numerical simulations we found either model is possible to explain the observation. However, considering a frequent occurrence of low-frequency tremors around the seamount in Hyuga-Nada, we favor the latter model, because the fluid flow can reduce the effective stress, leading to the occurrence of seismic activities. We further discuss these mechanisms.

How to cite: Kinoshita, M., Nakata, R., Shiraishi, K., Hamada, Y., and Hashimoto, Y.: Heat flow in the Nankai forearc, SW Japan, derived from BSR and drilling: Possible effect ofseamount subduction on earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20899, https://doi.org/10.5194/egusphere-egu24-20899, 2024.

EGU24-20904 | ECS | Orals | SM4.17

The Balance Process in Subduction Zones 

Cristián E. Siegel, Patricio Toledo, Sebastián Riquelme, Raúl Madariaga, and Jaime Campos

The subduction zone seismic-cycle is a complex phenomena with individual earthquakes as clearer manifestations. Although earthquakes are fundamentally space-extended, they are inferred to be material ruptures mostly considered as points in space. Nevertheless, in the temporal dimension, because they are plate-velocity dependent, it is less clear that they can be considered as point processes. Therefore, when considering this plate velocity in the balance analysis and assuming a locally homogeneous stochastic process hypothesis along coarse-graining upscaling it is possible to get a picture that makes sense of the whole seismic-cycle. This picture has emergent properties not available from purely seismic events, but that are more and more frequently recognized from geodetic and satellite observations, such as distant interactions and slow slip events. Taking advantage of the instrumentation installed at northern Chile, which makes use of both temporary and permanent stations from the National Seismological Center and IPOC it has been possible to obtain a well detailed picture of the seismic cycle between 2007 and 2023, that is consistent with representations obtained from geodesical measurements. We also obtain this representation for 49-year ISC catalog. We discuss possible applications of this seismic cycle representation.

How to cite: Siegel, C. E., Toledo, P., Riquelme, S., Madariaga, R., and Campos, J.: The Balance Process in Subduction Zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20904, https://doi.org/10.5194/egusphere-egu24-20904, 2024.

SM5 – Real-time and Time-dependent Seismology

EGU24-586 | ECS | Posters virtual | SM5.2

Delineation of microseism noise sources in the Indian Ocean. 

Gyanasmita Pradhan, Ramakrushna Reddy, and Paresh Nath Singha Roy

Microseisms are the continuous oscillations of the earth originated from the interaction of ocean waves with the solid earth. It is divided into two types, primary microseism and secondary microseism. Primary microseisms are generated by the interaction of ocean waves in the shallow coastal part and secondary microseisms are generated due to the interaction of two waves traveling opposite towards each other in the deeper or shallower part. Secondary microseism is also known as double frequency microseism band which is divided into two parts, long period double frequency microseism band and short period double frequency microseism band.

We have taken data from IRIS DMC for ten seismic stations of the year 2018. Our study area is on the Indian Ocean. Indian ocean is considered as one of the global sources of microseism noise. In comparison to the North Indian Ocean, the Southern Ocean generates very strong amplitudes of microseism noise. Storm activity of Southern Ocean is very hazardous and destructive. In addition to that, the Antarctic circumpolar current brings warm water to the Ocean. Therefore, every year it experiences multiple cyclones which play a major role in the generation of microseism noise.

In this study, we are using the frequency-dependent polarization analysis method. Our aim is to understand the spatial variation of noise and their possible sources. Power spectral density (PSD) is calculated using the spectral covariance matrix. Diagonal elements of the matrix represent the power spectra of each component (EW, NS, and Z). For analysing the spatial variation of PSD, we have used the vertical component (Z). We have observed higher PSD in the stations that are present close to the Southern Ocean and comparatively lower amplitudes are observed in the stations far away from the Southern Ocean. Back azimuth is used to determine the dominant source direction of the noise. From our results, major source direction of noise is from the Southern Ocean while minor sources are from Bay of Bengal and Arabian Sea. Clear seasonal variation in the source direction is not observed but seasonal variation in the number of polarized signals is observed indicating maximum polarized signal in the winter season and minimum polarized signals in the summer season. Combined results of spatial variation of PSD and back azimuth analysis help us to better understand the noise sources.  

How to cite: Pradhan, G., Reddy, R., and Singha Roy, P. N.: Delineation of microseism noise sources in the Indian Ocean., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-586, https://doi.org/10.5194/egusphere-egu24-586, 2024.

EGU24-2797 | Orals | SM5.2

Analysis of seismic noise sources in an open pit mining environment. 

Jordi Diaz, Montserrat Torne, Martin Schimmel, Susana Rodríguez, David Martí, Mario Ruiz, Helena Seivane, Pilar Sánchez-Pastor, and Diego Davoise

We present the characterization of the seismic ambient noise wavefield in the open-pit Riotinto mine (southern Spain), in the mainframe of a collaborative research project aiming to use the ambient noise wave field to monitor structural subsurface changes in near real-time. Noise characterization is based on a dense seismic network of 30 stations located along a 1-km long segment of a tailings dam. We first describe the most frequent transient signals detected, including local and distant earthquakes, blasting, and vehicles. The time variations in the amplitude of the 10-40 Hz frequency band are then used to define three phases of activity during the recording period. The highest amplitudes are directly related to the regrowth of the dam wall carried out to properly store the constantly increasing amount of tailings. In the third phase, the seismic noise is dominated by the deposition of tailings into the deposit, allowing the use of seismic data to monitor in detail the evolution of the deposition process. The detailed knowledge of the sources of noise in the Riotinto mine provides the basis for developing ambient noise seismic interferometry methods to monitor the physical properties of the subsurface of this and other open-pit mining areas.

This research is part of the R+D+I project CPP2021 009072 funded by MCIN/AEI/10.13039/501100011033 (Ministry of Science, Innovation and Universities/State Innovation Agency) with funds from the European Union Next Generation/PRTR (Recovery, Transformation, and Resilience Plan).

How to cite: Diaz, J., Torne, M., Schimmel, M., Rodríguez, S., Martí, D., Ruiz, M., Seivane, H., Sánchez-Pastor, P., and Davoise, D.: Analysis of seismic noise sources in an open pit mining environment., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2797, https://doi.org/10.5194/egusphere-egu24-2797, 2024.

EGU24-4190 | ECS | Posters on site | SM5.2

Monitoring Spatiotemporal Seismic Velocity Changes Using Seismic Interferometry and Distributed Acoustic Sensing in Mexico City 

Yang Li, Mathieu Perton, Francisco J. Sánchez-Sesma, and Zack Spica

Mexico City, the most populated city in the Americas, undergoes significant seismic hazards. Conventional seismometers often suffer from limited spatial density, restricting detailed observations in urban areas. In contrast, Distributed Acoustic Sensing (DAS) can convert standard telecommunication fiber-optic cables into dense seismic arrays, providing great potential for high-resolution spatiotemporal monitoring. Therefore, we installed a DAS interrogator in Mexico City in May 2022 in a long-term fashion to collect data for observational studies in the region. The fiber crosses the city from south to north along a 29-kilometer path following the subway track. The dataset comprises 2266 channels with a 12.8-m spacing and a 200-Hz sampling rate. 

On Sep. 19, 2022, a Mw7.6 earthquake occurred in Michoacán, approximately 450 km away from the City. Exactly 37 years after the great 1985 Mw8.1 event. The DAS system provided high-quality, ultra-dense, yet unique data for this earthquake in particular. One of the goals of this study is to assess the earthquake-induced changes in the sedimentary basin material properties. For this endeavor, we employ seismic interferometry on the ambient noise field of DAS data and the stretching method to monitor seismic velocity variations in Mexico City. Our analysis reveals a velocity drop following the 2022 Mw7.6 earthquake in some city areas. The results indicate that DAS can effectively monitor the velocity variations in urban environments, offering valuable insights for urban hazard assessment.

How to cite: Li, Y., Perton, M., Sánchez-Sesma, F. J., and Spica, Z.: Monitoring Spatiotemporal Seismic Velocity Changes Using Seismic Interferometry and Distributed Acoustic Sensing in Mexico City, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4190, https://doi.org/10.5194/egusphere-egu24-4190, 2024.

EGU24-4644 | Posters on site | SM5.2

Probing the SAA Depth Range using ML-measured short-period dispersion 

Hsiao-Ming Chang, Yuan-cheng Gung, Wu‐Yu Liao, Kai-Xun Chen, Chun-Fu Liao, Ban-Yuan Kuo, Ying-Nien Chen, and En‐Jui Lee

In this study, we aim to explore the depth range of stress-aligned anisotropy (SAA) in Taiwan. Our recent works have shown that the near-surface SAA is consistent with shear-wave splitting studies employing local earthquakes. However, it contrasts with SWS studies using deep phase (SKS) and the shallow crustal Vs anisotropy model derived from noise-derived broad-band (4-20 s) Rayleigh waves. This suggests that SAA is likely confined to the uppermost crust. Despite micro-cracks assumed to be fully closed with increasing ambient stress at depths, the depth range of the SAA mechanism remains unclear.

Our approach involves noise tomography using short-period (1-10 s) Rayleigh waves enhanced by the multicomponent stacking technique. To measure the dispersion of the isolated fundamental mode Rayleigh waves accurately and effectively, we employ a modified machine learning algorithm based on the algorithm proposed by Yang et al.(2022) We employ the Recurrent-Residual U-Net (R2U-Net) developed by Liao et al. (2021) for training. The model training data consists of dispersion diagrams from CCFs derived in various regions, including Taiwan, Japan, and the South Island of New Zealand. Approximately six thousand data are included in the training stage.

With the obtained dispersion data, we apply the wavelet-based multi-scale inversion technique to derive 3D models of Vs and Vs anisotropy. In this inversion process, the results from prior studies by Lee et al. (2023) serve as a priori constraint for the uppermost section of the model.

 

 

How to cite: Chang, H.-M., Gung, Y., Liao, W., Chen, K.-X., Liao, C.-F., Kuo, B.-Y., Chen, Y.-N., and Lee, E.: Probing the SAA Depth Range using ML-measured short-period dispersion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4644, https://doi.org/10.5194/egusphere-egu24-4644, 2024.

EGU24-5425 | ECS | Orals | SM5.2

Monitoring two-phase fluids in geothermal fields using seismic noise interferometry 

Pilar Sánchez-Pastor, Sin-Mei Wu, Ketil Hokstad, Bjarni Kristjánsson, Vincent Drouin, Cécile Ducrocq, Gunnar Gunnarsson, Antonio Rinaldi, Anne Obermann, and Stefan Wiemer

Harvesting geothermal energy often leads to a pressure drop in reservoirs that promotes the formation of steam. In some reservoirs, steam coexists with liquid water forming two-phase fluids, as happens in the Hengill geothermal field. This field is located in a triple junction of three large tectonic features in Iceland, 30 km east of the capital Reykjavik. The accumulation of steam in the top part of the reservoir forms a so-called steam cap. While steam caps are valuable energy resources, they also alter the reservoir thermodynamics and entail diverse risks such as land subsidence. Therefore, monitoring the steam content in reservoirs is essential for both operational and economic perspectives. However, this is an inherently challenging task and quantifying the steam content from indirect and surface-based measurements is still an unsolved matter.

Here, we present a new method for indirectly sampling the steam content in the subsurface using the ever-present seismic background noise. We analyse the seismic velocity changes in the area, estimate the land subsidence via Interferometric Synthetic Aperture Radar (InSAR) and work with in situ borehole data. We observe a consistent annual velocity drop in the Hengill geothermal field and establish a correlation between the velocity drop and steam buildup. This study introduces seismic noise interferometry as a powerful tool for monitoring two-phase fluids in the crust with minimal infrastructure, only one seismic station. Beyond geothermal sites, the methodology could extend to diverse geological settings, such as volcanoes, CO2 storage sites, hydrocarbon reservoirs, among others.

How to cite: Sánchez-Pastor, P., Wu, S.-M., Hokstad, K., Kristjánsson, B., Drouin, V., Ducrocq, C., Gunnarsson, G., Rinaldi, A., Obermann, A., and Wiemer, S.: Monitoring two-phase fluids in geothermal fields using seismic noise interferometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5425, https://doi.org/10.5194/egusphere-egu24-5425, 2024.

The understanding of microseism-source characteristics has become increasingly important, particularly in the context of retrieving Green's functions, which play a crucial role in various fields of seismology. This study aims to elucidate the characteristics of microseismic sources, encompassing seasonal variations in the activity of primary and secondary microseisms, along with periodic changes observed in microseismic peaks. The analysis involved data from seven stations carefully selected from the Korean Meteorological Administration seismic network, each with over 10 years of continuous data. Employing cross-correlation techniques, we calculated Empirical Green's Functions (EGFs) between 17 station pairs. The averaged spectra of the calculated EGFs revealed two primary peaks, concentrating energy distribution around 18 seconds and in the period range of 2-5 seconds, aligning with the peaks associated with Primary and Secondary microseism. We then categorized spectral energy distribution data into less than and more than 10 seconds, aiming to discern distinct characteristics associated with the two microseismic peaks. Subsequently, we examined average temporal energy variations for each microseism, generating, we say, spectral-time series data by summing and averaging separated energy in the period direction, and calculating energy variations for each period using a multi-filtering technique (MFT). Observing prominent dominant changes with a 1-year period in both Primary and Secondary microseisms, we noted additional periodic variations with 6 months, 3 months, and 2 months in Secondary microseism. Specifically focusing on 1-year period changes, Primary microseism displayed dominance during the summer, with lower energy levels in the winter across the entire area. For Secondary microseism, 1-year period changes often showed the lowest values in the summer and the highest values in the winter. Additionally, in Secondary microseism, maximum or minimum values were observed in the spring and autumn, resembling patterns observed in Primary microseism. Simultaneously, we reconstructed the dominant period of ocean gravity waves from Wave Watch III to explore the effect on microseisms around the stations used in this study. Comparing this data with calculated the spectral time series data of Primary and Secondary microseisms revealed not only a match in the 1-year period but also in detailed phases below 1 year. This implies a close relationship between microseisms around the Korean Peninsula and ocean activities, prompting future research to delve into detailed periodic changes, correlate them with ocean activities, and identify their underlying causes.

How to cite: Jang, Y. and Lee, W.: Microseismic Characteristics: Seasonal Variations, Periodic Changes, and Oceanic Influences in the Korean Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7251, https://doi.org/10.5194/egusphere-egu24-7251, 2024.

Karst disasters pose a substantial threat to geological environmental stability, resulting in ground collapse and groundwater contamination. To determine the spatial distribution of karst terrain, high-resolution underground imaging is essential. However, traditional synchronous observation systems struggle to achieve high-density spatial sampling due to limitations in instrument quantity. In this study, we conducted short-term synchronous and asynchronous ambient noise observations in a deserted parking lot in Hangzhou, China, to overcome the limitations of insufficient sampling density. We performed the first-round observation on one half of the parking lot for around 24 hours, followed by an immediate relocation of the stations to the other half for the second-round ~24-hour observation. Additionally, 29 fixed stations were placed outside the parking lot to continuously record ambient noise.

The imaging results of noise source distribution indicate that high-frequency noise sources exhibit significant non-uniform distribution during the daytime, which could affect the accuracy of the retrieved surface waves. To address this, we propose using the similarity of cross-component cross-correlation functions to select only data segments with stronger in-line noise sources, thereby enhancing the reliability of synchronous cross-correlation functions. Furthermore, we utilized the cross-component cross-correlation stacking method to suppress higher-mode surface waves and reduce their impact on the accuracy of the computation of asynchronous cross-correlation functions. Applying the ambient noise source-receiver interferometry method to the synchronous cross-correlation functions, we successfully retrieved the surface waves between asynchronous stations. In total, we obtained 66,472 pairs of cross-correlation functions, comprising 38,416 synchronous pairs and 28,056 asynchronous pairs. We extracted phase velocity dispersion curves of the fundamental mode surface wave for station pairs within the parking lot and utilized the direct surface wave tomography method to obtain the subsurface 3D shear-wave velocity structure.

The inversion results revealed the presence of two distinct low-velocity anomalies in the northeastern and southwestern parts of the site at depths around 40 m, which align with the location and depth of karst caves obtained from drilling data, confirming the reliability of the inversion results. Furthermore, we uniformly subsampled half of the data to simulate the case of insufficient station quantity, and the inversion model exhibited less apparent responses to the low-velocity anomalies, emphasizing the necessity of dense array observations. This study demonstrates that the combined observations of synchronous and asynchronous ambient noise can be utilized for high-resolution imaging of karst characteristics.

How to cite: Liu, Y. and Xia, J.: Short-term synchronous and asynchronous ambient noise tomography in urban areas: Application to Karst investigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7746, https://doi.org/10.5194/egusphere-egu24-7746, 2024.

EGU24-8004 | ECS | Orals | SM5.2

Results from WINES: Wind turbIne Noise assEsSment in the Italian site candidate for “Einstein Telescope”, the third-generation gravitational wave detector. 

Giovanni Diaferia, Carlo Giunchi, Irene Molinari, Marco Olivieri, Fabio Di Felice, Andrea Contu, Domenico D'Urso, Luca Naticchioni, and Davide Rozza

The area in the municipalities of Lula, Bitti, and Onanì in Sardinia (Italy) is a candidate for hosting the “Einstein Telescope” (ET, the third-generation gravitational wave detector), given the extremely low level of natural and anthropogenic seismic noise at this site. For the same unique characteristics of this area, the multi-disciplinary geophysical far-field observatory “Faber” (PNRR-Meet project) will be set up.

However, the strength and persistence of wind make this area exceptionally favorable for the exploitation of wind energy, as testified by the nearby Buddusò wind park that, consisting of 69 turbines and about 130 MW of total installed power, is the largest in Italy.

It is well known that wind turbines are an important source of seismic noise between 1 and 10 Hz, posing a relevant concern for noise contamination of ET as it will operate in the same frequency range.

In the context of the seismic characterization of such a candidate site, the WINES experiment (Wind turbIne Noise assEsSment in the Italian site candidate for the Einstein Telescope) provided a two-month-long passive seismic recording of nine broad-band stations placed at increasing distances from the Buddusò wind park. The aim of the experiment was the evaluation of the noise generated by the wind park in terms of amplitude, spectral content, and decay with distance, in relation to the wind park operation.

Analyzing the frequency spectra at all stations, the spectral imprint of the wind park manifests through sharp, well-defined spectral peaks at 3.4, 5.0, 6.8, and 9.4 Hz, even in conditions of absent or moderate wind speed (0-3 m/s). With stronger winds (>20 m/s), all spectra increase their amplitude by an order of magnitude, and the sharpest and most persistent peaks are found at 3.5, 5.2, and 6.8 Hz. In both wind conditions, the amplitude of such peaks decreases with distance, being clearly distinguishable up to 5-6 km from the wind park. We use these spectral peaks to derive an empirical relationship for their amplitude vs. distance, highlighting a well-behaved exponential decay that translates into a two-orders-of-magnitude decrease within 10 km distance.

Lastly, considering the assumption that the generated seismic noise propagates as Rayleigh waves, the continuous recordings along the array have been used for the estimation of the direction of noise arrival at each station. Signal coherence allows the recovery of this information for stations within 5 km from the wind park, showing a dominant back-azimuth of the incoming signal that is fully compatible with the position of the wind park with respect to each station.

How to cite: Diaferia, G., Giunchi, C., Molinari, I., Olivieri, M., Di Felice, F., Contu, A., D'Urso, D., Naticchioni, L., and Rozza, D.: Results from WINES: Wind turbIne Noise assEsSment in the Italian site candidate for “Einstein Telescope”, the third-generation gravitational wave detector., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8004, https://doi.org/10.5194/egusphere-egu24-8004, 2024.

EGU24-8272 | ECS | Posters on site | SM5.2 | Highlight

Mapping glacier structure in inaccessible areas from turning seismic sources into a dense seismic array 

Ugo Nanni, Philippe Roux, and Florent Gimbert
Understanding glaciers structural heterogeneity is crucial for assessing their fate. Yet, places where structure changes are strong are often inaccessible for direct instrumentation, such as in crevasses fields. To overcome this limitation, we introduce an innovative technique that transforms seismic sources, here generated by crevasses, into virtual receivers using source-to-receiver spatial reciprocity. We demonstrate that phase interference patterns between well-localized seismic events can be leveraged to retrieve phase velocity maps using seismic Michelson interferometry. The obtained phase velocity exhibit sensitivity to changes in glacier structure, offering valuable insights into the origins of mechanical properties changes, with spatial resolution surpassing traditional methods by a factor of four. In particular, we observe sharp variations in phase velocity related to strongly-damaged subsurface areas and indicative of a complex 3-D medium. Applying this method more systematically and in other contexts will enhance our understanding of the structure of glaciers and other seismogenic environments.

 

How to cite: Nanni, U., Roux, P., and Gimbert, F.: Mapping glacier structure in inaccessible areas from turning seismic sources into a dense seismic array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8272, https://doi.org/10.5194/egusphere-egu24-8272, 2024.

EGU24-8313 | ECS | Posters on site | SM5.2

Mantle Transition Zone (MTZ) beneath the contiguous US revealed by ambient noise cross-correlations 

Yongki Andita Aiman, Yang Lu, and Götz Bokelmann

Understanding the nature of the Mantle Transition Zone (MTZ) can foster our knowledge about the dynamics of the Earth, especially related to the vertical heat and mass exchange between the upper and the lower mantle. The MTZ, characterized by seismic-velocity discontinuities at depths of 410 km and 660 km, is conventionally studied using seismic waves emitted by earthquakes. However, this approach suffers from a typically uneven distribution of earthquakes, biases in earthquake location, and the complexity of earthquake processes.

In this study, we used body waves retrieved from ambient noise correlations to map the mantle transition zone beneath the US. We analyzed cross-correlation functions from more than 3500 seismic stations, including the EarthScope USArray stations during its deployment time frame between 2004 and 2013. We obtained clear short period (<10 s) P410P and P660P reflection phases by using a stacking strategy that considers global noise wave field data selection. This allows us to image the MTZ at an unprecedented high resolution, providing new constraints that can shed light on the tectonic history and the mantle dynamics in this area.

How to cite: Aiman, Y. A., Lu, Y., and Bokelmann, G.: Mantle Transition Zone (MTZ) beneath the contiguous US revealed by ambient noise cross-correlations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8313, https://doi.org/10.5194/egusphere-egu24-8313, 2024.

EGU24-8529 | ECS | Posters on site | SM5.2

Sensitivity of coda correlation wavefields to spatio-temporal variations of microseism noise sources 

Mahsa Safarkhani, Sven Schippkus, and Céline Hadziioannou

Previous research suggests that continuous seismic noise records can effectively extract information about the properties of the Earth's subsurface. The coda of the correlation wavefield between station pairs shows sensitivity to crustal heterogeneity and has been described as a multiple scattering signal. These signals allow to monitor variations in dv/v to detect weak changes in the medium at depth. Oceanic regions, which are highly effective in generating microseisms, play a crucial role in the distribution of seismic energy sources. In Green's function estimates from cross correlations, highly asymmetric correlation wavefields are common due to non-homogeneous source distributions.

This study focuses on the impact of oceanic noise sources on the coda of the correlation wavefield between station pairs. We utilized ambient seismic noise interferometry to retrieve the correlation wavefields between some master stations throughout Europe and the Gräfenberg array located in Germany, in the microseism frequency range. We then applied cross-correlation beamforming to these correlation wavefields. This identifies the source direction for correlation wavefields over a three-year period, allowing us to compare variations in source direction and seasonality with results from raw data beamforming. We find dominant source directions towards the north-northwest of Gräfenberg in winter (with slowness expected for surface waves) and towards the south in summer (with slowness expected for body waves) in the raw data and throughout the coda of the correlation wavefields up to lapse times of one hour. This is in contrast to the diffuse wavefield expected from classical seismic interferometry and demonstrates that higher-order correlations, which are computed during the correlation beamforming of correlation functions, do not improve the degree of scattering in the correlation wavefield coda when persistent, isolated noise sources are present. Additionally, the findings demonstrate notable correlation between the seasonal incidence of microseisms and the very late coda of the correlation wavefields, raising questions about the current understanding of the correlation wavefield coda.

How to cite: Safarkhani, M., Schippkus, S., and Hadziioannou, C.: Sensitivity of coda correlation wavefields to spatio-temporal variations of microseism noise sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8529, https://doi.org/10.5194/egusphere-egu24-8529, 2024.

EGU24-8922 | ECS | Posters on site | SM5.2 | Highlight

Monitoring seismic velocity changes at Campi Flegrei (Naples) using seismic noise interferometry - Do we see precursors of the future volcanic activity? 

Marcel van Laaten, Jozef Müller, and Ulrich Wegler

Campi Flegrei is a volcanic field located in the immediate vicinity of the densely populated area of Naples, Italy. Since 2005, the area has been experiencing a new bradyseismic crisis, i.e., a slow uplift of the subsurface caused by rising fluids in the subsurface. The uplift is accompanied by earthquake activity that has been steadily increasing for years, culminating in the strongest earthquake (ML 4.2) in the last 40 years on September 27, 2023. Such uplift and earthquakes can cause changes in seismic velocity and are often succeeded by a volcanic eruption. In this study, we utilize seismic noise to calculate velocity changes at different levels/frequencies over a 7-year period using passive image interferometry. The observed long-term velocity decrease of 1.39 % near the surface over the period from 2016 to 2023 can be explained by a volume increase of the hydrothermal system at the depth of 3 km. In 2023, the Campi Flegrei underwent several phases of velocity change. After a period of minor velocity changes, there was a gradual 0.7 % increase in velocity starting in May. Following the onset of the earthquake swarm in August, the velocity slowly decreased once again.

How to cite: van Laaten, M., Müller, J., and Wegler, U.: Monitoring seismic velocity changes at Campi Flegrei (Naples) using seismic noise interferometry - Do we see precursors of the future volcanic activity?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8922, https://doi.org/10.5194/egusphere-egu24-8922, 2024.

EGU24-10391 | ECS | Posters on site | SM5.2

Mapping large-scale deep soil moisture variation using ambient seismic noise 

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 scientific 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 Central-Southern Europe with ambient seismic noise. It is the first time that the seismic method has been applied to map soil moisture at a regional scale using an ordinary seismic network setup. The 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.: Mapping large-scale deep soil moisture variation using ambient seismic noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10391, https://doi.org/10.5194/egusphere-egu24-10391, 2024.

EGU24-10427 | Orals | SM5.2

A natural pump-probe experiment reveals nonlinear elastic properties along the Irpinia Fault, Southern Apennines 

Nicola D'Agostino, Stefania Tarantino, Piero Poli, Maurizio Vassallo, Gerardo Ventafridda, Gaetano Festa, and Aldo Zollo

The conventional picture of the earthquake cycle implies that rupture is reached by progressive stress buildup until reaching fault’s failure strength. Alternatively, the failure strength may be altered by changes in pore pressure and/or properties of fault rocks. This last scenario may be associated with significant modifications of the elastic properties of the crust potentially detectable with seismological tools. Natural oscillatory stress sources (tides, seasonal and multiannual) can thus be      exploited to probe the time-dependent response of active fault zones to stress variations at various temporal and spatial scales and investigate time-dependent variations of its elastic properties (Delorey et al., 2021). A multidisciplinary (seismology, geodesy, geochemistry) study is carried out along the Irpinia Fault System (IFS, Southern Apennines) to investigate the response of the crust to hydrological forcing associated with      phases of recharge/discharge of karst aquifers in terms of time-dependent variations of its elastic and hydraulic properties. Charge/discharge phases of the karst aquifers in the Apennines cause significant seasonal and multi-annual strain transients (Silverii et al, 2019), that modulate the secular, tectonic deformation (~3 mm/yr extension across the Apennines). It has been previously observed that these seasonal and multi-annual transients correlate with the seismicity rate (D’Agostino et al, 2018) and seismic velocity variations (Poli et al., 2020). Recent studies (Silverii et al., 2016; D’Agostino et al., 2018) have shown the high sensitivity of the IFS to hydrological stresses reflected in a complex, time-dependent response of deformation and seismicity. We performed a natural pump-probe experiment to assess the non-linear behavior of the seismogenic volumes in response to non-tectonic deformations. Seasonal horizontal strains associated with the discharge and recharge of karst aquifers are used as the “pump”. Coda wave interferometry demonstrates to be a powerful tool to probe time-dependent crustal elastic properties. We computed seismic velocity variations using empirical Green's functions reconstructed by autocorrelation on continuous 14-year-long time series of ambient noise. We analyzed two different sites (co-located GPS and seismic stations), near and afar the IFS. We found that velocity variations are significant (∼0.2%) near IFS and not significant farther away from IFS. We compared the velocity variations near IFS with the time series of Caposele spring discharge, temperature, horizontal deformation and seismicity rate. Our observations are coherent at seasonal and multi-annual scales and can be explained by the same mechanism. At the time of the maximum peak of the discharge spring, representing a proxy of the hydraulic head, the seismic wave velocity is minimum, the dilation of crust is maximum and related to the opening of pre-existing cracks’ system. The background microseismicity occurrence is favored by the hydrologically-related dilatation, superimposed on the ongoing tectonic extension. From the comparison between hydrological strain variations and velocity changes, we estimate a strain sensitivity of velocity change of ~-10^3 typical of worn crustal material and in good agreement with laboratory experiments.  This nonlinear elasticity regime suggests the presence of a multi-fractured and damaged crust subject to periodic seasonal phases of weakening/healing, potentially affecting earthquake nucleation processes.

How to cite: D'Agostino, N., Tarantino, S., Poli, P., Vassallo, M., Ventafridda, G., Festa, G., and Zollo, A.: A natural pump-probe experiment reveals nonlinear elastic properties along the Irpinia Fault, Southern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10427, https://doi.org/10.5194/egusphere-egu24-10427, 2024.

EGU24-10482 | ECS | Posters on site | SM5.2

Distinguishing between Medicanes and common seasonal storms using microseism 

Alfio Marco Borzì, Vittorio Minio, Raphael De Plaen, Thomas Lecocq, Flavio Cannavò, Giuseppe Ciarolo, Sebastiano D'Amico, Carlo Lo Re, Carmelo Monaco, Marco Picone, Giovanni Scardino, Giovanni Scicchitano, and Andrea Cannata

Microseism, the most continuous seismic signal on the Earth generated by the interaction between the hydrosphere, the atmosphere, and the solid Earth, is a useful tool for acquiring information about climate change. Indeed, several authors dealt with the relationship microseism-sea state and microseism-cyclonic activity, considering in particular tropical cyclones, hurricanes, typhoons, and recently Medicanes (small-scale tropical cyclones that occur in the Mediterranean Sea). In this study, we analyze, from a seismic point of view, several meteorological events that occurred in the Mediterranean Sea during the period November 2011 - February 2023. In particular, we consider 9 Medicanes and 4 more common storms. Despite the marked differences between them, each of these events caused heavy rainfall, strong wind gusts, violent storm surges with significant wave heights usually greater than 3 meters, and damage along the exposed coast. Occasionally, these events caused deaths and injuries. In this work, we analyzed the seismic signal recorded by 104 seismic stations, installed along the Italian, Maltese, Greek, and France coastal areas, and 15 seismic stations, installed in the Etnean area used only to perform array analysis. We deal with the relationships between the considered meteorological events and the features of microseism in terms of spectral content, space-time variation of the amplitude, and source locations tracked using two different methods (a grid search approach based on seismic amplitude decay and array techniques). By comparing the positions of the microseism sources, obtained from our analysis, with the areas of significant storm surges, retrieved from hindcast data, we observe that the microseism locations are in agreement with the actual locations of the storm surges for 10 out of 12 events analyzed (two Medicanes present very low intensity in terms of meteorological parameters and the microseism amplitude does not show significant variations during these two events). In addition, we also carried out two analyses that allowed us to obtain both the seismic signature of these events, by using a method that exploits the coherence of continuous seismic noise, and their strength from a seismic point of view, called Microseism Reduced Amplitude. By integrating the results obtained from these two methods, we can “seismically” distinguish Medicanes and common storms. Consequently, we demonstrate the possibility of creating a novel monitoring system for Mediterranean meteorological events by incorporating microseism information alongside with other techniques (e.g. wave buoy, wave gauge, and High-Frequency coastal radar) commonly used for studying and monitoring meteorological phenomena. In addition, since the seismometers were among the first geophysical instruments installed, it is possible to digitize old seismograms and examine historical data shedding new light on extreme weather events in a climate change scenario.

How to cite: Borzì, A. M., Minio, V., De Plaen, R., Lecocq, T., Cannavò, F., Ciarolo, G., D'Amico, S., Lo Re, C., Monaco, C., Picone, M., Scardino, G., Scicchitano, G., and Cannata, A.: Distinguishing between Medicanes and common seasonal storms using microseism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10482, https://doi.org/10.5194/egusphere-egu24-10482, 2024.

EGU24-10645 | ECS | Orals | SM5.2

Improved Spatial Autocorrelation Method for Dispersion Imaging of Ambient Seismic Noise 

Chaoqiang Xi, Ya Liu, and Hao Zhang

The determination of shear (S) wave velocities within near-surface earth layers holds paramount significance in the realms of hazard assessment and geotechnical applications. In the fields of geophysics and civil engineering, ambient noise surface wave methods have garnered considerable attention due to their effectiveness in determining shear wave velocities within near-surface layers, particularly in densely populated urban areas. The spatial autocorrelation (SPAC) method, introduced in 1957 for the analysis of ambient noise dispersion, has maintained enduring relevance and widespread utilization within the realm of engineering geophysics in recent years[Aki 1957; Hayashi et al.,2022].

However, the dispersion energy generated using the SPAC (Spatial Autocorrelation) method is susceptible to contamination, especially at high frequencies, resulting from the occurrence of 'crossed' artifacts[Cheng et al.,2023]. The presence of these 'crossed' artifacts leads to the intersection and distortion of dispersion energy within the frequency–velocity domain[Xi et al.,2021]. These artifacts emerge from the simultaneous fitting of both inward and outward propagating cylindrical wavefields, encapsulated within the Bessel function. To mitigate the impact of these artifacts, we advocate for the exclusive fitting of the outward propagating cylindrical wavefield. To achieve this, a combination of the spatial autocorrelation coefficient and its Hilbert transform is employed, facilitating the construction of the outward propagating cylindrical wavefield.

In our proposed improved SPAC method, we replace the Bessel function with the Hankel function for fitting the constructed outward propagating cylindrical wave. Both synthetic and real-world field examples substantiate the efficacy of the proposed method in enhancing the accuracy of surface wave multimode dispersion measurements. This modification not only eliminates the 'crossed' artifacts but also underscores the robustness of our approach in refining the precision of dispersion analysis, particularly in scenarios involving complex wavefields and varying geological conditions.

Aki, K., 1957. Space and time spectra of stationary stochastic waves, with special reference to microtremors. Bulletin of the Earthquake Research Institute, 35(3), 415–456.

Cheng F, Xia J, Xi C. Artifacts in High-Frequency Passive Surface Wave Dispersion Imaging: Toward the Linear Receiver Array. Surveys in Geophysics, 2023: 1-31.

Hayashi K, Asten M W, Stephenson W J, et al. Microtremor array method using spatial autocorrelation analysis of Rayleigh-wave data. Journal of Seismology, 2022, 26(4): 601-627.

Xi C, Xia J, Mi B, et al. Modified frequency–Bessel transform method for dispersion imaging of Rayleigh waves from ambient seismic noise. Geophysical Journal International, 2021, 225(2): 1271-1280.

How to cite: Xi, C., Liu, Y., and Zhang, H.: Improved Spatial Autocorrelation Method for Dispersion Imaging of Ambient Seismic Noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10645, https://doi.org/10.5194/egusphere-egu24-10645, 2024.

EGU24-11436 | ECS | Posters on site | SM5.2

Three-dimensional deep crustal structure of the Moncuni ultramafic massif (Western Italian Alps) imaged by ambient noise tomography 

Martina Raggiunti, Douglas Stumpp, Paola Baccheschi, Fabio Villani, Matteo Lupi, Geneviève Savard, Vincenzo Sapia, Marina Pastori, Alessandra Smedile, Alessandra Sciarra, Sara Lovati, Marco Massa, Andrea Antonioli, Pamela Roselli, and Roberto Tonini

The intermediate-depth earthquakes usually occur at depths between 40-300 km, and are commonly related to deformation along and within the subducting plate. Promising but contrasting mechanisms of their seismic failure are proposed to model their generation and associated deformation processes, including ductile shear instability, dehydration embrittlement and failure of dry rocks. This work exploits one of the best examples worldwide of exposed sources of intermediate-depth earthquakes to better understand their nucleation environment. The study area consists of the Moncuni ultramafic massif (Southern Lanzo Massif, Western Italian Alps), a peridotite and gabbro section considered as a dry remnant of the Tethyan oceanic lithosphere subducted, during the Alpine orogeny, and then exhumed without experiencing ductile deformation and metamorphism. Moncuni geological units are extensively crossed by a network of pseudotachylytes (geological product of seismic slip associated to earthquakes), that locally preserve high-pressure minerals, suggesting an intermediate-depth seismic environment origin.

In this study, we want to better understand the nucleation environment of intermediate-depth earthquakes by peeking into the deeper structure of the ophiolitic peridotite and gabbro of the Moncuni area. We are performing a Nodal Ambient Noise Tomography (NANT), which allows crustal imaging based on the measurement of short-period surface wave dispersion curves between pairs of seismic stations. The used dataset was acquired by installing a temporary seismic network with 197 three-component nodal geophones over 250 km2 area surronunding the Moncuni massif and operating for about one month.

To perform the ambient noise data processing, we followed the procedure of Bensen et al. (2007). Before using the data, we accomplished a careful data quality analysis by checking the possible occurrence of some perturbations, monitoring several parameters like recording time, and sensor absolute position and stability. We also computed power spectral density curves for each node to investigate the occurrence of anthropogenic noise, and to select the optimal frequency band to use for the NANT. NANT is being performed extracting the empirical Green's functions (EGFs) cross-correlating time series of noise recorded at pairs of stations, so using the frequency-time analysis (FTAN) as proposed in Bensen et al., (2007), we have produced a huge amount of dispersion curves, and we applied a machine learning approach, deep convolutional neural networks, to perform automatic picking and to attribute a quality picking score. We evaluate as reliable picks with a score > 0.7. Conversely, the picks with a score < 0.7 were checked and manually corrected. The dispersion curves will be used to construct a shear-wave velocity model of the study area, allowing us to obtain a detailed image of the deep structure of the Moncuni massif with the goal of understanding whether these earthquakes originate in presence of fluids or in dry oceanic slab.

How to cite: Raggiunti, M., Stumpp, D., Baccheschi, P., Villani, F., Lupi, M., Savard, G., Sapia, V., Pastori, M., Smedile, A., Sciarra, A., Lovati, S., Massa, M., Antonioli, A., Roselli, P., and Tonini, R.: Three-dimensional deep crustal structure of the Moncuni ultramafic massif (Western Italian Alps) imaged by ambient noise tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11436, https://doi.org/10.5194/egusphere-egu24-11436, 2024.

EGU24-14919 | ECS | Posters on site | SM5.2

Improving dispersion measurement using weighted stacking based on polarization analysis 

Bo Guan and Jianghai Xia

Retrieving surface waves using linear arrays is becoming gradually popular in urban areas with abundant anthropogenic noise [Mi et al., 2020]. Dispersion measurements can be problematic due to the presence of off-line noise sources. We use the polarization analysis of three-component noise recordings to estimate the back-azimuth and intensity of sources for linear arrays. The noise segment where the source locates in the stationary-phase zones (SPZs) is retained and the noise cross-correlation function (NCF) is weighted according to the source intensity. In this way, we obtain accurate virtual shot gathers and dispersion images.

A single three-component seismic station can simultaneously record vertical, north, and east displacements. The back-azimuth and intensity of a noise source within a time segment can be estimated by the relationship between the vertical-horizontal cross-spectra [Takagi et al., 2018]. In practical applications, we remove the mean and trend of the raw three-component noise recordings and divide them into multiple segments. We use the polarization analysis for each segment to locate the orientations and intensities of the noise sources. We then average the results obtained at multiple stations in a linear array to obtain more robust results. We retain the noise segments where the noise sources are distributed in the SPZs and perform weighted stacking of their NCFs according to the intensities of the noise sources in these segments to obtain the final NCF and perform the subsequent dispersion measurement. We use a synthetic experiment and two field examples to demonstrate the superiority of our proposed method. After using the proposed method, the NCFs become more accurate with a higher signal-to-noise ratio, and the trend of the dispersion energy is more continuous.

 

Takagi, R., Nishida, K., Maeda, T. & Obara, K., 2018. Ambient seismic noise wavefield in Japan characterized by polarization analysis of Hi-net records. Geophysical Journal International, 215, 1682–1699. doi:10.1093/gji/ggy334

Mi, B., Xia, J., Bradford, J.H. & Shen, C., 2020. Estimating near-surface shear-wave-velocity structures via multichannel analysis of Rayleigh and Love waves: an experiment at the Boise hydrogeophysical research site. Surveys in Geophysics, 41, 323–341. doi:10.1007/s10712-019-09582-4

How to cite: Guan, B. and Xia, J.: Improving dispersion measurement using weighted stacking based on polarization analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14919, https://doi.org/10.5194/egusphere-egu24-14919, 2024.

EGU24-15768 | ECS | Posters on site | SM5.2

Sub-daily seismic velocity changes as indicator for large vulnerable groundwater reservoirs 

Richard Kramer, Yang Lu, Qingyu Wang, and Götz Bokelmann

We use an adapted approach for long-distance high temporal resolution monitoring to investigate the daily and sub-daily behavior of seismic velocity changes. We analyze four years of continuous data from AlpArray and other local networks throughout the Central-Southern Europe. Focusing on the 1 Hz frequency we calculate seismic velocity changes based on coda wave interferometry. Our results show that we can observe a consistent periodic behavior with periods of 24 h and 12 h, with a focus primarily on the latter. We attribute these changes predominantly to variations in atmospheric pressure. These changes manifest through loading effects on the unsaturated zone and alterations in the water bodies below that.  By analyzing the spatial variations of this two-cycle-per-day behavior we found a strong correlation with extensively karstified water-bearing formations. This connection may contribute to the hydrological characterization of the near-subsurface in central Europe identifying large water reservoirs.

How to cite: Kramer, R., Lu, Y., Wang, Q., and Bokelmann, G.: Sub-daily seismic velocity changes as indicator for large vulnerable groundwater reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15768, https://doi.org/10.5194/egusphere-egu24-15768, 2024.

Ambient seismic noise is a useful tool to monitor the crust and shallow subsurface, with application cases that vary widely, including for example fault zone, volcano, and groundwater monitoring. Classic ambient-noise monitoring applications are based on observing changes in seismic velocity, or changes in cross-correlation waveforms. Here, we explore the possibility of monitoring crustal attenuation (both viscous and scattering) with ambient seismic noise.

Attenuation monitoring is envisioned to be an immensely useful complement to velocity monitoring, because it is sensitive to the material properties of the subsurface, and can be used together with seismic velocities to monitor the crust, for example to track crustal fluids. However, short-term measurements of attenuation from ambient seismic noise may suffer biases due to the variability of natural ambient seismic noise sources. This is of particular concern when working with the ocean-generated primary and secondary microseismic noise, which provide energy to monitor the crust at several kilometer depth, but have sources that vary strongly and rapidly.

To examine the limitations imposed by oceanic seismic noise source variability quantitatively, we first investigate the temporal behavior of Rayleigh wave attenuation coefficient α, as well as Coda-Q of ambient noise cross-correlations, at broadband seismic stations in Switzerland and in the Hengill region of Iceland, over 12 and 2.5 years, respectively. These parameters have previously been used to study crustal attenuation with ambient noise and have been shown to yield geologically meaningful information as long as long-term and array averaging is performed, which makes the observations more robust with respect to noise source variability (Soergel et al., 2020, Magrini et al., 2021).

Second, we simulate ambient noise cross-correlations with secondary microseism source models based on ocean wave hindcasts. To generate the synthetic ambient noise cross-correlations, we consider the spatiotemporal variation of the noise source spectra as well as realistic seismic wave propagation computed using the spectral element technique.

Based on the simulated and observed time series of α and Coda-Q, we evaluate the effect of noise source variability on the attenuation parameters. In this way, we intend to estimate the presence and severity of noise source bias. We consider this as a necessary step towards regional ambient noise-based attenuation monitoring.

 

 

Soergel, D., Pedersen, H. A., Stehly, L., Margerin, L., Paul, A., & AlpArray Working Group. (2020). Coda-Q in the 2.5–20 s period band from seismic noise: Application to the greater Alpine area. Geophysical Journal International, 220(1), 202–217. https://doi.org/10.1093/gji/ggz443

 

Magrini, F., Boschi, L., Gualtieri, L., Lekić, V., & Cammarano, F. (2021). Rayleigh-wave attenuation across the conterminous United States in the microseism frequency band. Scientific Reports, 11(1), Article 1. https://doi.org/10.1038/s41598-021-89497-6

 

How to cite: Ermert, L., Obermann, A., and Boschi, L.: Towards ambient noise attenuation monitoring: Time-varying noise source effects on noise-based attenuation estimates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16014, https://doi.org/10.5194/egusphere-egu24-16014, 2024.

EGU24-16682 | ECS | Posters on site | SM5.2

Determination of the shallow S-wave velocity structure and sedimentary thickness offshore central Chile using distributed acoustic sensing. 

Clara Vernet, Trabattoni Alister, Diane Rivet, and Marie Baillet

Distributed acoustic sensing (DAS) provides an attractive solution for ocean-bottom seismological instrumentation by providing a dense and long-distance measurement of the deformation of the ground along offshore submarine fiber-optic cables. This study reports analyses made on records acquired with a network located along the Chilean margin. We focus onto the analysis of the structure of the shallow crust, in particular, the sedimentary layer of the overlying crust, whose lateral variations suggest strong contrasts of the sedimentary recharge of the slab.

The POST experiment was carried out from October 27 to December 3, 2021 on a fiber-optic cable connecting the city of Concón (100km northwest of Santiago) to La Serena. Using strain-rate recordings for twenty local and regional earthquakes, we estimated both the thickness and shear wave velocity of sediments. We used jointly (1) travel time delays between the direct P-wave and converted Ps at the bedrock/sediment interface that were estimated from manual picks and (2) coda wave interferometry. This later was done by identifying the phase velocities of the fundamental Rayleigh wave mode on frequency-wavenumber (FK) diagrams over 2km linear arrays along the fiber in the 0.3 to 7Hz frequency band. Each dispersive curve and travel time delays between the direct and converted wave were then jointly inverted to create a 2D S-wave velocity (Vs) structure of the sedimentary layer under the fiber.

Our results show significant differences in thickness and in Vs along the cable. Two basins are observed, including the Valparaiso Forearc Basin separated by the Punta Salinas Ridge and another basin limited by a thin sedimentary layer with Vs of a few hundred m/s. In the extreme northern part of the cable, a thin layer of unconsolidated Quaternary sediments is on top of a deeper compacted sediments with faster Vs. The developed methodology comforts the potential of DAS for subsurface imaging purposes. Moreover, accurate modeling of the subsurface could be used to correct the location of earthquakes on the \iber sensors.

How to cite: Vernet, C., Alister, T., Rivet, D., and Baillet, M.: Determination of the shallow S-wave velocity structure and sedimentary thickness offshore central Chile using distributed acoustic sensing., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16682, https://doi.org/10.5194/egusphere-egu24-16682, 2024.

EGU24-16974 | Posters on site | SM5.2

Ambient noise interferometry to investigate temporal changes in the São Jorge Island (Azores) subsurface structure associated with the 2022 seismic crisis.  

Graça Silveira, Joana Carvalho, Martin Schimmel, Virgílio Mendes, Nuno Dias, Susana Custódio, João Fontiela, Stephen P. Hicks, and Ana Ferreira

In March 2022, a seismic crisis was declared in São Jorge Island. Despite the regular seismotectonic activity observed in the Azores Central Group, São Jorge has not exhibited significant activity since the crisis associated with an eruption in 1964. Between the fall of 2021 and the end of 2022, approximately 12,000 earthquakes (magnitudes up to ML 3.8) have been recorded, with the seismicity and geodetic modelling pointing to a magmatic intrusion. Intrusions cause gas release, fluid circulation, and pressure perturbations in the subsurface volcanic system that often induce changes in seismic velocity. Here, we probe spatial-temporal changes in the seismic velocity structure beneath São Jorge using ambient noise interferometry.

In this study, we analyzed data continuously recorded between January 2021 and December 2022 by two permanent stations (PMAN and ROSA) operated by the Instituto Português do Mar e da Atmosfera (IPMA) to investigate the presence of subsurface structural changes in response to the seismic crisis. Data were cut into 1-hr length files and filtered between 1 and 3 Hz for autocorrelation, and between 0.1 and 1.0 Hz for cross-correlation. We applied the Phase Auto- and Cross-Correlation (PAC and PCC) method to the filtered data. This method is based on phase coherence and is amplitude-unbiased. PAC and PCC functions were then linearly stacked over three days to achieve a stable noise response. To infer changes in the velocity structure, we analyzed the waveform similarity values for different time lag windows. We compared the waveform similarity results with meteorological data and ground deformation inferred from GPS. Additionally, relative velocity changes have been estimated. 

The two analyzed stations exhibit different waveform-similarity results. Preliminary interpretation of PMAN results (closer to the island center) show, in the second half of 2022, a very slight recovery of the waveform similarity at shorter lag times (shallower depths) that decreases again in the fall of the same year. Globally, data from this station exhibits a more systematic decorrelation when the crisis was declared, most likely due to perturbations in the seismic structure between < 8 - 10 km and deeper than 15 km. 

This work is a contribution to RESTLESS (DOI:10.54499/PTDC/CTA-GEF/6674/2020) and GEMMA (DOI:10.54499/PTDC/CTA-GEO/2083/2021). It was also funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).



How to cite: Silveira, G., Carvalho, J., Schimmel, M., Mendes, V., Dias, N., Custódio, S., Fontiela, J., Hicks, S. P., and Ferreira, A.: Ambient noise interferometry to investigate temporal changes in the São Jorge Island (Azores) subsurface structure associated with the 2022 seismic crisis. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16974, https://doi.org/10.5194/egusphere-egu24-16974, 2024.

EGU24-17146 | Orals | SM5.2 | Highlight

New perspectives on crustal imagery leveraging offshore submarine fiber optic cables 

Diane Rivet, Gauthier Guerin, Clara Vernet, Alister Trabattoni, and Marie Baillet

Distributed acoustic sensing transforms fiber-optic cables into giant and very dense seismic networks. Although less sensitive to ground motion than traditional networks, they offer new possibilities for passive imaging and temporal monitoring, especially in hardly accessible locations such as the seafloor. From two case studies - in South of France, on a 42km long cable off-shore Toulon and in Central Chile on the northern leg of the Concón landing site of the GTD telecom cable - we explore the capability to perform passive imagery using ambient seismic noise and coda waves.

Despite a higher instrumental noise level and uneven ground coupling, underwater telecom cables can record the microseismic noise. This may be strong microseismic noise generated locally, or microseismic noise amplified by the resonance of the water column. The recorded microseismic noise at the seafloor allows a better understanding of its generation and provides high resolution images of shallow crustal structures.

From the observation of ocean gravity waves and microseismic noise, we highlight the strong localization of seismic noise sources near the coast, which can be highly variable over short time scales.  Due to the localized nature of the noise sources, and because it is not always possible to average the noise recorded over long periods of time (months, years), conventional methods for ambient noise imagery show significant discrepancies in velocity estimates, up to 30%, especially at greater depths. We present here a method that minimizes the errors due to highly localized sources by carefully correcting the apparent velocities from the azimuth of the sources.

In seismic areas, in addition to microseismic noise, it is possible to expand the frequency content toward higher frequencies using seismic coda. Coda waves are dominated by multi-diffracted surface waves on local heterogeneities. The spatial distribution of their energy is more isotropic. Using dispersion curves stacked over the coda of several earthquakes, we image the shallow crustal structure of the sediments. This innovative approach opens up new horizons for structural imaging and monitoring.In coastal environments, the distribution of noise sources must be systematically studied in order to obtain reliable results.

How to cite: Rivet, D., Guerin, G., Vernet, C., Trabattoni, A., and Baillet, M.: New perspectives on crustal imagery leveraging offshore submarine fiber optic cables, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17146, https://doi.org/10.5194/egusphere-egu24-17146, 2024.

EGU24-17324 | Orals | SM5.2

Ambient seismic noise tomography for mineral exploration in the Irish Midlands  

Trond Ryberg, Corinna Roy, Christian Haberland, Kacie Wellington, and Conor Moynihan

Europe set out its goals for decarbonization in the EU Green Deal, which includes reducing net greenhouse gas emissions by relying more on renewable energy and green technologies. One goal of the EU project VECTOR (https://vectorproject.eu) is to test and develop passive, non-disruptive exploration methods to investigate Europe‘s raw material potential.

We test the application of passive seismic imaging in the Irish midlands, which contain potential areas for zinc mineralization, one of the multiple raw materials needed for green energy technologies. More specifically, we apply ambient noise tomography to image the Earth’s subsurface and assess the utility of this technique for mineral exploration at depth:

Thus, 210 temporary, continuously running digital seismic stations were deployed in the Irish midlands (north of Collinstown) in an area of ~8 x ~6 km, and recorded ambient noise data for ~6 weeks. We then extracted Rayleigh wave group velocities in the frequency range 0.625 – 10 Hz by cross-correlating the data (~42517 time series in total) and using the FTAN method. In the first step we used 1% of the data (long offsets) in a stochastic, transdimensional, hierarchical Monte Carlo search with Markov Chains to derive a three-dimensional shear wave velocity model. In the second step, we added shorter offsets, which did not lead to any significant changes in the 3D model.

The velocity model shows distinct velocity anomalies down to approximately 1.6 km depth that correspond to features also seen in reflection seismic profiles provided by Teck Ireland Ltd, a subsidiary of Teck Resources Limited, that owns the project area and is an Associated Partner of VECTOR. This demonstrates the potential of low-cost passive seismic methods to investigate the Earth’s subsurface compared to expensive active seismic methods. We used synthetic 3D Checkerboard tests to assess which areas of the model are well resolved and we will further compare our models with other data sets, for example, petrophysical borehole data available in this area.

How to cite: Ryberg, T., Roy, C., Haberland, C., Wellington, K., and Moynihan, C.: Ambient seismic noise tomography for mineral exploration in the Irish Midlands , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17324, https://doi.org/10.5194/egusphere-egu24-17324, 2024.

EGU24-17499 | ECS | Posters on site | SM5.2

Ambient noise characteristics of the Chung-Liao Tunnel area in National Highway No. 3 

Ting-Yu Lin, Ying-Nien Chen, and Ruey-Juin Rau

    Under a uniform scattered wave field, the continuous recording of Cross-Correlation Functions (CCF) between monitoring stations can be approximated by the Green's function between these stations. Therefore, passive seismic noise interference techniques can be employed to monitor changes in the structural properties of the Earth. The Zhongliao Tunnel in the southern section of National Highway No. 3 cuts through two significant active structures, the chishan Fault and the Chekualin Fault. In order to investigate the impact of fault activity on the tunnel's structure, our laboratory deployed a dense array composed of 33 portable seismometers around the Zhongliao Tunnel starting in 2020, conducting seismic observations for an entire year. With an average station spacing of less than 1 kilometer in this dense array, there is a chance to obtain high-frequency Green's functions, enabling monitoring of shallow structures. However, non-uniform distribution of noise energy may cause differences between interference waveforms and real Green's functions. Therefore, this study focuses on the spatiotemporal characteristics of background high-frequency signals, aiming to clarify their sources as a foundation for future research. Through Power Spectral Density (PSD) analysis of the stations, we observed energy drops at night in the range of 1-12Hz , possibly attributed to body waves or surface waves generated by vehicular traffic on the highway. To identify the distribution of noise sources, the research area was subdivided into 121 grid points as potential signal sources. Surface wave and body wave energy decay characteristics were fitted separately to the spatial distribution of that energy, revealing that the predominant seismic mode is surface waves, and the most likely noise source is located at the tunnel entrance, unevenly distributed on the highway. Furthermore, an analysis of the amplitude asymmetry in the cross-correlation functions between stations indicated that the high-frequency signals originate from the tunnel entrance. As there are no specific conditions near the tunnel entrance that can autonomously generate high-frequency signals, we speculate that these signals are still caused by vehicles on the highway. When seismic waves propagate around the tunnel, the velocity structure causes energy to focus at the tunnel entrance, radiating outward. In the future, we will use Eikonal tomography to analyze the velocity structure beneath the array and conduct waveform simulations to test this hypothesis.

How to cite: Lin, T.-Y., Chen, Y.-N., and Rau, R.-J.: Ambient noise characteristics of the Chung-Liao Tunnel area in National Highway No. 3, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17499, https://doi.org/10.5194/egusphere-egu24-17499, 2024.

EGU24-18041 | ECS | Posters on site | SM5.2

Teleseismic body wave phase extracted from ambient noise interferometry constrains the secondary microseism sources of Northern Hemisphere 

Yajian Gao, Andreas Rietbrock, Michael Frietsch, Hans Agurto-Detzel, Sofia-Katerina Kufner, Edmond Dushi, Besian Rama, Damiano Koxhaj, Bernd Schurr, and Frederik Tilmann

Dense seismic networks are ideally suited to detect daily or even hourly variations of the global secondary microseism via ambient noise cross-correlation beamforming (CCBF) and backprojection (BP) in the slowness-backazimuth domain. We combine the seismic recordings from Hi-net in Kyushu (HINET) network, Southern California Seismic Network (SCSN), and the Large-N AlbaNian TectonIcs of Continental Subduction (ANTICS) network to capture 3-hourly and daily northern hemisphere secondary microseism variations during 2022-2023. We calculate stable ambient noise CC with 300 s lag and 24 substacks per day. In the secondary microseism period band, 1-10s, we detect clear and vigorous high apparent velocity P phase (> 8 km/s) arrivals in 3-hourly and daily stacks for these networks. Both the 3-hourly and daily stacks show clear temporal amplitude and delay time changes in station-pair-distance and symmetry changes of causal and acausal branches, indicating the active evolution of ambient noise source location and strength. For ANTICS, the strongest energy patch emerges with back-azimuth (BAZ) 280°-330° and slowness around 8-10 s/deg. Further two energy patches appear with BAZ 90°-135° and slowness of 4-6 s/deg as well as 0° BAZ and slowness of 5-7.5 s/deg . We back-project the energy from the beamforming to the source location based on IASP91 velocity model assuming the propagation of teleseismic energy as direct P wave (including Pdiff, PKiKP and PKIKP). The back-projection results reveal that the strongest energy comes from the North Atlantic covering a broad arc-shape area (from the northeast coast of the US to the west coast of the UK, and from the south of Greenland and Iceland down to 45°N). The two other energy patches with much higher apparent velocities originate from the south Indian Ocean and the north Pacific near the Aleutian Islands. The 3-hourly and daily changes are tracked and recovered by the CCBF and BP approach for all three networks. The secondary microseism variations in the north Pacific could be improved by the SCSN and HINET whereas the north Atlantic is constrained by ANTICS and SCSN. Some small-scale autumn storms near the Japanese trench are also detected and tracked. Our results are consistent with existing wave height maps and provide a new and cheap observation for hindcasting of the state of the coupling of oceans and the solid earth. 

How to cite: Gao, Y., Rietbrock, A., Frietsch, M., Agurto-Detzel, H., Kufner, S.-K., Dushi, E., Rama, B., Koxhaj, D., Schurr, B., and Tilmann, F.: Teleseismic body wave phase extracted from ambient noise interferometry constrains the secondary microseism sources of Northern Hemisphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18041, https://doi.org/10.5194/egusphere-egu24-18041, 2024.

EGU24-18405 | ECS | Posters on site | SM5.2

Matched Field Processing of train vibrations for opportunistic surface wave tomography 

Théo Rebert, Thomas Bardainne, Caifang Cai, Thibaut Allemand, and Hervé Chauris

Railways are exposed to geotechnical hazards such as sinkholes or subsidence because they encounter many geological settings. Railway subsurface imaging is thus important in order to detect small anomalies in the elastic properties of the upper 50 meters of soils. Seismic interferometry applied on train induced signals is a promising technique, and previous works have shown clear Rayleigh waves and reflections in the retrieved Green’s functions. However, extracting the dispersion curves of the reconstructed Rayleigh waves in a automated and robust way with high-resolution is challenging.

We study a continuously acquired dataset consisting of a dense array of five lines of accelerometers deployed parallel to 120 m of track. We use Matched Field Processing (MFP) to recover a high-resolution S-wave velocity model of the subsurface. The workflow begins by correlating signals in time windows when the train is outside the array, to ensure nearly planar wavefronts before the interferometry step. However, using only trains far from the array discards the measurements associated to the train crossing the array which have a very high signal-to-noise ratio but are difficult to model. We observe experimentally that train crossings the array generate correlations compatible with the isotropic and uncorrelated source distribution hypothesis used in passive seismology. Under this assumption, we correlate signals when the train is directly next to the sensors. Combined with correlations for the train in the far-field, this allows to track the Rayleigh dispersion curve in the very high frequencies (> 50 Hz). This broadband dispersion curve extraction, along with the balanced azimuthal coverage of our image due to the source diversity, is helpful for reliable imaging of shallow structures ranging from the bottom of the ballast to the bedrock. Since array methods are robust, and trains are repeatable sources, this paves the way for reliable monitoring of the subsurface with unprecedented temporal and spatial resolution.

How to cite: Rebert, T., Bardainne, T., Cai, C., Allemand, T., and Chauris, H.: Matched Field Processing of train vibrations for opportunistic surface wave tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18405, https://doi.org/10.5194/egusphere-egu24-18405, 2024.

EGU24-18648 | ECS | Posters on site | SM5.2

Reduction of seismic noise with depth - Characterisation of ambient seismic noise for surface and borehole stations at three candidate sites of the Einstein Telescope 

Michael Frietsch, Thomas Forbriger, Carlo Giunchi, Matteo Di Giovanni, Luca Naticchioni, and Andreas Rietbrock

The next generation gravitational wave detector Einstein Telescope (ET) is planned to be built at a depth of about 200 m to 300 m to significantly reduce the influence of ambient seismic noise with respect to current surface detectors. Three candidate sites for ET are currently under investigation: Sardinia (Italy), Lausitz (Germany), and the Euregio Meuse-Rhine (EMR, Netherlands, Belgium, Germany). Broadband downhole and surface seismometers have been installed at all three sites over the last couple of years which now allows the comparison of seismic noise levels and reduction with depth. Furthermore, we include the Sos Enattos mine in Sardinia, as an additional reference location. We see a significant reduction in seismic noise with depth over a broad frequency range above 1 Hz and below 0.1 Hz. The most significant noise reduction is observed in the frequency band between 3 to 30 Hz for which all sites reach a noise level below 10-7 m2 s-4 Hz-1 at depth. For the Lausitz and EMR sites we measure a reduction of seismic noise with depth of up to 40 dB while Sardinia shows an exceptionally low seismic noise above 2 Hz even below the NLNM but shows the smallest improvement with depth because noise levels are remarkably low at the surface. The noise can be attributed to various sources such as anthropogenic and ocean generated microseisms. The EMR and Lausitz sites show a clear reduction of seismic noise during nights and weekends. The day/night and week/weekend dynamic of cultural noise is not very pronounced for the Sardinia site. Our favoured explanation for the extremely low noise level in Sardinia is therefore the low level of anthropogenic noise. However, the ocean generated microseism is strongest at the Sardinia site due to the Mediterranean Sea that is located only a few tens of kilometers from the candidate site location. The exceptionally low ambient noise level in Sardinia at above 2Hz exposes the self-noise of the Trilium Slimline borehole seismometer and the noise floor of the CENTAUR digitizer as the limiting factor at frequencies above 4 Hz. 

How to cite: Frietsch, M., Forbriger, T., Giunchi, C., Di Giovanni, M., Naticchioni, L., and Rietbrock, A.: Reduction of seismic noise with depth - Characterisation of ambient seismic noise for surface and borehole stations at three candidate sites of the Einstein Telescope, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18648, https://doi.org/10.5194/egusphere-egu24-18648, 2024.

EGU24-19994 | ECS | Posters on site | SM5.2

Assessing similarity in continuous seismic cross-correlation functions using hierarchical clustering 

Alexander Yates, Corentin Caudron, Philippe Lesage, Aurélien Mordret, Thomas Lecocq, and Jean Soubestre

Passive seismic interferometry has become a popular technique towards monitoring subsurface activities in a variety of settings. This includes active volcanoes and geothermal fields spanning a large range of temperatures (25C to 250C) in Belgium and Iceland. The method depends on the relative stability of background seismic sources in order to make repeatable measurements of subsurface properties. Such stability is typically assessed by examining the similarity of cross-correlation functions through time. Thus, techniques that can better assess the temporal similarity of cross-correlation functions may aid in discriminating between real subsurface processes and artificial changes related variable seismic sources.

In this work, we apply agglomerative hierarchical clustering to cross-correlation functions computed using seismic networks at volcanoes. These include Piton de la Fournaise volcano (La Réunion island) and Mt Ruapehu volcano (New Zealand). Clustering is then used to form groups of cross-correlation functions that share similar characteristics and also, unlike common similarity measures, the method does not require a defined reference period. At Piton de la Fournaise, we resolve distinct clusters that relate both to changes in the seismic source (volcanic tremor onset) and changes in the medium following volcanic eruptions. At Mt Ruapehu, we observe a consistency to cross-correlation functions computed in the frequency band of volcanic tremor, suggesting tremor could be useful as a repeatable seismic source. 

Our results demonstrate the potential of hierarchical clustering as a similarity measure for cross-correlation functions, suggesting it could be a useful step towards recognizing structure, or complex patterns, in seismic interferometry datasets. This can benefit both decisions in processing and interpretations of observed subsurface changes.

How to cite: Yates, A., Caudron, C., Lesage, P., Mordret, A., Lecocq, T., and Soubestre, J.: Assessing similarity in continuous seismic cross-correlation functions using hierarchical clustering, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19994, https://doi.org/10.5194/egusphere-egu24-19994, 2024.

EGU24-480 | ECS | Posters on site | GM2.1

Probabilistic optimal transport-driven inversion of the 2012 Palisades rockfall seismic source 

Rebeca Ursu, Mark Naylor, Hui Tang, and Jens M. Turowski

During rockfall events, the seismic waves are generated in response to the time-varying normal and tangential forces between the Earth and colliding and sliding mass. These forces carry information about the nature of the generative seismic source; hence, the source dynamics can be estimated. Several studies have used forward modeling to determine the amplitude and duration of these forces and, implicitly, the source process that could generate the observed seismic waves. Through running multiple forward models, the force history inversion involves adjusting the force amplitude and duration to minimize the misfit between the proposed source model, convoluted with the force-impulse Green’s functions, and the observations. In the Bayesian framework, the normal likelihood function is traditionally used to measure the misfit between the observed and predicted waveforms with respect to amplitude. However, the normal likelihood function is insensitive to the potential misalignment of the waveforms in time. Moreover, the relevant parameter space often exhibits multiple local minima, which may lead to a convergence to a minimum that does not present the global optimum. Optimal transport distances-driven exponential likelihoods were recently proposed as alternatives thanks to their ability to capture the time structure of the signals. We employed a Metropolis-Hastings sampling strategy in the probabilistic framework to reconstruct the 2012 Palisades rockfall seismic source using two implementations of the Wasserstein distance-based exponential likelihood function. The first implementation transforms between density functions, which are always positive and integrate to one. Therefore, it requires the transformation of the signals into probability density functions, which is done here via a modified graph-space transform scheme. The second method is applied directly to the signals. We evaluated the robustness of the two implementations of the Wasserstein distance-based exponential likelihood function in simulating the source characteristics with respect to the normal likelihood. Preliminary results show that contrary to the expectations, using optimal transport distances-driven exponential likelihoods leads to negligible improvement in the fit to the observed waveform.

How to cite: Ursu, R., Naylor, M., Tang, H., and Turowski, J. M.: Probabilistic optimal transport-driven inversion of the 2012 Palisades rockfall seismic source, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-480, https://doi.org/10.5194/egusphere-egu24-480, 2024.

EGU24-1972 | ECS | Orals | GM2.1 | Highlight

Do earthquakes cause more damage in the summer? 

Eldert Fokker, Elmer Ruigrok, and Jeannot Trampert

Shallow soft sedimentary layers overlaying harder bedrock are known to amplify ground motion generated by earthquakes. Such an amplification occurs when seismic waves travel from high impedance (density times wave speed) to low impedance layers. Large impedance contrasts can lead to substantially larger earthquake damages. As the impedance contrast determines the amplification factor, variations in shallow shear-wave speed contribute directly to changes in site amplification.

Seasonal temperature fluctuations have been shown to induce shear-wave speed variations and, hence, affect site amplification factors. This naturally leads to the question: is the strength of earthquake damage season dependent? In this study we model by how much seasonal temperature variations affect site amplification. The site-specific physical properties determine whether site amplification is more pronounced during summer or winter. For parameters from the Groningen region of the Netherlands, affected by the gas extraction induced seismicity, we expect in the summer a relative increase in amplification of 8% with respect to the amplification factor in the winter.

How to cite: Fokker, E., Ruigrok, E., and Trampert, J.: Do earthquakes cause more damage in the summer?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1972, https://doi.org/10.5194/egusphere-egu24-1972, 2024.

EGU24-3399 | ECS | Orals | GM2.1

Enhancing debris flow warning through seismic feature selection and machine learning model comparison 

Qi Zhou, Jens turowski, Hui Tang, Clément Hibert, Małgorzata Chmiel, Fabian Walter, and Michael Dietze

Machine learning can improve the accuracy of detecting mass movements in seismic signals and extend early warning times. However, we lack a profound understanding of the limitations of different machine learning methods and the most effective seismic features especially for the identifcation of debris flows. This contribution explores the importance of seismic features with Random Forest and XGBoost models. We find that a widely used approach based on more than seventy seismic features, including waveform, spectrum, spectrogram, and network metrics features, suffers from redundant input information. Our results show that six seismic features are sufficient to perform binary debris flow classification with equivalent or even better results., e.g., the Random Forest and XGBoost models achieve improvements over the benchmark of 0.09% and 1.10%, respectively, when validated on the ILL12 station. Considering models that aim to capture patterns in sequential data rather than information in the current time window, using the Long Short-Term Memory algorithm does not improve the binary classification performance over Random Forest and XGBoost models. However, in the early warning context, the Long Short-Term Memory model performs better and more consistently detects the initiation of debris flows. Our proposed framework simplifies seismic signal-driven early warning for debris flows and provides a proper workflow that can be used for detecting also other mass movements.

How to cite: Zhou, Q., turowski, J., Tang, H., Hibert, C., Chmiel, M., Walter, F., and Dietze, M.: Enhancing debris flow warning through seismic feature selection and machine learning model comparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3399, https://doi.org/10.5194/egusphere-egu24-3399, 2024.

EGU24-3861 | ECS | Posters on site | GM2.1

Capturing the short-term dynamics of outlet glaciers:  insights from seismic monitoring on Sermeq Kujalleq in Kangia, Greenland 

Janneke van Ginkel, Ana Nap, Adrien Wehrlé, Fabian Walter, and Martin Lüthi

Sermeq Kujalleq in Kangia, also known as Jakobshavn Isbræ, a major outlet glacier of the Greenland Ice Sheet, exhibits a flow speed higher than 30 m/day near the terminus. Basal sliding, iceberg calving, and subglacial hydraulics play pivotal roles in ice flow dynamics of this outlet glacier, and understanding these processes is crucial for predicting the impact of outlet glaciers on the Earth system in a changing climate.

 Seismic and geophysical field campaigns were conducted in 2021, 2022 and 2023 in the region of Sermeq Kujalleq in Kangia. The project has the aim to monitor the dynamic behavior of such a fast-flowing outlet glacier and its interaction with the surrounding shear margins. Shallow borehole seismic sensors and self-sufficient seismic boxes were deployed in multiple arrays on the fast-moving ice stream and its margin. The sensors capture seismic sources and monitor subglacial conditions and spatiotemporal variabilities throughout the ice mass. An on-rock broadband seismometer near the terminus records iceberg calving activity ideally complementing observations of a Terrestrial Radar Interferometer operating simultaneously.

 Here we report on first results of a seismic analysis that provides insights into details of ice dynamic variations of Sermeq Kujalleq. Power spectrograms of the 2023 upstream arrays feature a 4-day tremor-like signal between 2.5 and 6 Hz. This phenomenon was not observed for other calving events and was missing in the 2022 record. Beamforming techniques are employed to constrain the source location of this tremor as well as other seismic events. Potentially this multi-day tremor signal corresponds to the ice stream response to a major calving event. Additionally, beamforming and spectral analysis provide insights into hydraulic cycles of the glacier, such as widespread diurnal water drainage and the activity of moulins. By comparing these seismic observations with ice flow speed and satellite images we aim at understanding the details of short-term perturbations to ice flow, which may influence larger-scale ice stream dynamics.

How to cite: van Ginkel, J., Nap, A., Wehrlé, A., Walter, F., and Lüthi, M.: Capturing the short-term dynamics of outlet glaciers:  insights from seismic monitoring on Sermeq Kujalleq in Kangia, Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3861, https://doi.org/10.5194/egusphere-egu24-3861, 2024.

EGU24-5306 | ECS | Posters on site | GM2.1

Quantifying snout marginal bedload export from alpine glaciers 

Eva Wolf, Michael Dietze, and Stuart Lane

Bedload export from Alpine glaciers by rivers is a geomorphological process of increasing interest given the high retreat rates of temperate ice masses in the context of global warming. Access and measurement difficulties make it very poorly known and contradictory hypotheses exist about how it might respond to receding glaciers. In subglacial channels, bedload transport is a key mechanism for evacuating one of the products of glacial erosion. It likely constrains glacial erosion rates as removal of the products of erosion is needed so as to yield fresh bedrock for further erosion. Environmental seismology may be a valuable tool in understanding rates of subglacial bedload export.
Previous studies have considered subglacial bedload export in glacial forefields using seismic sensors and tracked particles moving underneath the ice sheet. We are taking former studies forward and extend the monitoring of bedload export detecting coarse grain impacts using seismometers right at the glacial terminus. The project aims to determine diurnal as well as seasonal sediment export quantities and compare results among different field sites.
We studied subglacial bedload export for the Otemma and Arolla glacier in Valais, Switzerland in the summer of 2023 by installing two seismic stations (PE-6/B geophones) close to each glacier terminus throughout the melt season. These four-month records of seismic signals were processed using fluvial inversion algorithms of the eseis package implemented in R. The algorithm is refined with wave propagation- and ground properties determined through active seismic experiments as well as measured grain size distributions from field sampling. We are able to separate turbulent water noise and bedload noise in the seismic signal and estimate water stage as well as bedload transport rates. Results are validated by comparing the water stage estimates to measurements from a discharge gauging station. Over a full season, we compare the behaviour of the two different glaciers regarding sediment export taking into account their size, orientation, elevation and other factors. We relate the detected bedload export events to meteorological conditions and shifts in seasonal melt processes from snow melt to ice melt.
The results of this study help to get a clearer picture of diurnal as well as seasonal patterns of bedload export from glaciers, impacting downstream riverbed erosion and deposition in the light of increasingly rapid glacier melt. These geomorphological processes are of interest for different infrastructural facilities such as hydropower plants.

How to cite: Wolf, E., Dietze, M., and Lane, S.: Quantifying snout marginal bedload export from alpine glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5306, https://doi.org/10.5194/egusphere-egu24-5306, 2024.

EGU24-5821 | Orals | GM2.1

Global observations of an up to 9 day long, recurring, monochromatic seismic source near 10.9 mHz associated with tsunamigenic landslides in a Northeast Greenland fjord 

Paula Koelemeijer, Rudolf Widmer-Schnidrig, Kristian Svennevig, Stephen Hicks, Thomas Forbriger, Thomas Lecocq, Anne Mangeney, Clément Hibert, Niels Korsgaard, Antoine Lucas, Claudio Satriano, Robert Anthony, Aurélien Mordret, Sven Schippkus, Søren Rysgaard, Wieter Boone, Steven Gibbons, Kristen Cook, Sylfest Glimsdal, and Finn Løvholt and the VLPGreenland team

We report the discovery of an unprecedented, monochromatic low-frequency seismic source arising from the fjords of North-East Greenland. Following a landslide and tsunami event in Dickson fjord on 16 September 2023, the seismic waves were detected by broad-band seismometers worldwide. Here we focus on a detailed analysis of the long-period seismic signal, while a reconstruction of the dynamics of the landslide is presented by Svennevig et al. in session NH3.5. 

Both frequency and phase velocity of the waves are consistent with fundamental mode Rayleigh- and Love-waves. However, the decay rate of these waves is much slower than predicted for freely propagating surface waves so that we infer a long-lasting and slowly decaying source process. Although the 16 September 2023 event was by far the largest, analysis of historical seismic data has revealed five other previously undetected events, all with a fundamental frequency between 10.85 and 11.02 mHz. The signal of the largest two events initially decayed with a quality factor, Q close to Q=500, which increased to Q=3000 within the first 10 hours and could thus be detected for up to nine days. The smaller four events had a slow decay-rate (Q>1000) for their entire duration. In comparison, the global average attenuation of Rayleigh waves at these frequencies is Q=117 for PREM, thus precluding a single, impulsive source for these signals.

Gleaning archives of optical and SAR satellite images reveals that at least four out of six events could be associated with landslides in Dickson fjord, the two others remain unresolved. However, such rapid transient events cannot explain the long duration of the radiated seismic waves. Our modelling of the largest event shows that a transversal seiche in Dickson fjord, excited by a landslide induced tsunami, can account for both the monochromatic low frequency signal as well as its seismic signal amplitude and radiation pattern. However, the seiche modelling results in Q values lower than 250 and hence the seiche needs to be continuously driven for the entire duration of the observed seismic signal. Thus, a full understanding of the source process that produces the monochromatic signal remains enigmatic.

How to cite: Koelemeijer, P., Widmer-Schnidrig, R., Svennevig, K., Hicks, S., Forbriger, T., Lecocq, T., Mangeney, A., Hibert, C., Korsgaard, N., Lucas, A., Satriano, C., Anthony, R., Mordret, A., Schippkus, S., Rysgaard, S., Boone, W., Gibbons, S., Cook, K., Glimsdal, S., and Løvholt, F. and the VLPGreenland team: Global observations of an up to 9 day long, recurring, monochromatic seismic source near 10.9 mHz associated with tsunamigenic landslides in a Northeast Greenland fjord, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5821, https://doi.org/10.5194/egusphere-egu24-5821, 2024.

EGU24-5947 | ECS | Posters on site | GM2.1

Low-cost raindrop sizing with piezoelectric sensor: A mechanical approach 

Chi-Ling Wei and Li-Pen Wang

Raindrop size distribution (DSD) is a key factor to derive reliable rainfall estimates. It is highly related to a number of integral rainfall variables, such as rain intensity (R), rain water content (W) and radar echo (Z) and thus can contribute to a range of hydrological and meteorological applications, such as rainfall-induced landslide warnings and radar rainfall calibration. Disdrometers are commonly used to measure DSDc. Well-known disdrometer sensors include JWD, Parsivel and 2DVD . These sensors may have their own strengths and weaknesses, but their costs are all much higher than that of widely-deployed catching gauges (e.g. tipping bucket and weighing gauges). This makes it infeasible to have a widespread, or dense, DSD monitoring network. To address this issue, our ultimate goal is to develop a lightweight and low-cost disdrometer with descent accuracy.

In this work, we have prototyped a disdrometer with a piezoelectric cantilever. It is not new to use piezoelectric materials as rain sensors because of its low cost and low maintenance. It is however not trivial to ‘calibrate’ this type of sensors, and various calibration methods have been proposed in the literature. However, whereas most of these sensors associate received signal with rainfall properties directly (via statistical or machine learning approaches), we propose to formulate the drop sensing process as a ‘mechanical’ problem. More specifically, we first form a physical model that can well simulate the signal response of continuous excitation force on a piezoelectric cantilever based on an existing theoretical model. We then analytically derive the inverse function of the model which can obtain the excitation force directly from the measured signals. The derived force-time signal is found to linearly associate with DSD and can also be used for other purposes including kinetic energy analysis.

In spite of the sound underlying theory, the real-world signal is far from perfect, containing a considerable amount of noise. Additionally, as our physical model requires conducting differentiation and second-order differentiation, to which the impact of noise is even destructive. Although we have made efforts to improve the quality of signal from the source, it does not fully solve the problem because the physical model is highly sensitive to signal gradients. To effectively deduce the impact of noise, we then introduced various signal ‘noise’ models, which were reported to well resemble the behavior of real-world signal noises, to train a machine learning (ML) model, such that the actual excitation force function can be derived from various weather conditions.

To verify the proposed sensor and signal processing model, we have set up lab experiments using an in-house device with micropumps and high-voltage raindrop detachment devices to control the required size, drop location, and timing of the drops. Preliminary results from a given range of drop sizes have shown the potential of the proposed sensor and ML-based signal processing model to well derive drop sizes from our experimental device. We plan on further testing our sensor outdoor and compare the measurements with those collected from a co-located Parseval2 disdrometer.

How to cite: Wei, C.-L. and Wang, L.-P.: Low-cost raindrop sizing with piezoelectric sensor: A mechanical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5947, https://doi.org/10.5194/egusphere-egu24-5947, 2024.

EGU24-6218 | ECS | Orals | GM2.1

High resolution observations of tide induced icequake activity at the Astrolabe glacier grounding zone 

Tifenn Le Bris, Guilhem Barruol, Florent Gimbert, Emmanuel Le Meur, and Dimitri Zigone

Cryoseismology, which records ice-induced seismic activity, is emerging as a powerful tool for studying the grounding zone - a critical spatio-temporal area where outlet glaciers grounded on the continent starts floating and interacting with the ocean underneath. The SEIS-ADELICE project supported by the French Polar Institute (IPEV) aims to characterise the dynamics of the Astrolabe glacier in Terre Adélie (East Antarctica), from its grounded part to its terminus in the ocean. Over the past 3 years, we deployed broad-band seismometers both at the grounding zone and on stable ice around the glacier, along with ocean bottom seismometers (OBS) close to the glacier terminus. In January 2023, the recording system was complemented by a dense array of 50 seismic nodes over the grounding zone. This allowed us to cover spatial scales from metres to several kilometres, providing a high-resolution observation of tidal forcing on the floating tongue and its repercussions on the glacier behaviour. The seismic records contain a wide range of signals, including icequakes, accepted to result from the brittle deformation of the ice. Although the seismic patterns at the different stations show clear modulation of icequakes by tidal cycles, their phasing with the tide depends on the location of the sensors, whether they are grounded or floating and on their distance from the active part of the glacier. This highlights the importance of the network typology and its proximity to the grounding line when characterising icequake occurrence patterns. Local icequakes detected at the grounding line exhibit a consistent occurrence during both rising and falling tides, with the peak activity observed during high tide. Source location analysis reveals that events are distributed across both the grounding line and the lateral shear zones of the glacier which are under strong stress from the ice-ocean interactions during tides.

How to cite: Le Bris, T., Barruol, G., Gimbert, F., Le Meur, E., and Zigone, D.: High resolution observations of tide induced icequake activity at the Astrolabe glacier grounding zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6218, https://doi.org/10.5194/egusphere-egu24-6218, 2024.

EGU24-6613 | Orals | GM2.1

Tracking baleen whale calls in the Lower St. Lawrence Seaway, Canada, using land seismometers   

Yajing Liu, Eva Goblot, and Alexandre Plourde

The Lower St. Lawrence Seaway (LSLS) is part of a major marine shipping corridor in eastern Canada, and also an essential feeding ground for fin whales and blue whales. Understanding the whale migration and habitat usage in the LSLS is critical for informing conservation policies that minimize noise pollution and risk of collision to the whale populations. In this study we utilize continuous recordings of six broadband seismometers located on the north and south shores of the St. Lawrence River to characterize the frequency range, recurrence interval and duration of fin and blue whale calls. We further use the whale call detections to quantify their spatial and temporal variations along the LSLS between February 2020 and January 2022, with the caveat that the detection range at these land stations is probably limited to a few kilometers due to energy loss along the seismic wave travel paths through multiple interfaces. We identified higher whale call detection rates at stations near the northwest of St. Lawrence Gulf than the upstream Estuary, suggesting possible influences of ocean currents and ice conditions. Whale calls are detected year around, with majority in the fall/winter months (September to February), implying seasonal and annual variations that may be influenced by climate change. We are currently analyzing recordings from a temporary deployment of 48 nodal seismometers, at 10-km average spacing, along the shorelines of the LSLS between September-October 2023, to further quantify the spatial patterns of whale calls and identify possible linkages to coastal bathymetry, ocean currents and preferential diets for the baleen whales.

How to cite: Liu, Y., Goblot, E., and Plourde, A.: Tracking baleen whale calls in the Lower St. Lawrence Seaway, Canada, using land seismometers  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6613, https://doi.org/10.5194/egusphere-egu24-6613, 2024.

The EarthScope Transportable Array (TA) in Alaska has been a unique seismic network since about 2014 because most stations are equipped with environmental sensors to record pressure, temperature, and wind (speed and direction). We will summarize some physical insights of near-surface properties in Alaska that can be gained from the combined analysis of seismic and environmental sensors. We also point out a possible effect of the thick sea ice on the climate in the North Slope region that faces the polar ocean.

First, the combined analysis of seismic data and pressure data allows us to separate two distinct types of seismic noise; one is the ordinary seismic noise, consisting of propagating body and surface waves, and the other is the deformation caused by the local pressure loading. This loading effect is observed at many stations when surface pressure becomes high. It can be confirmed based on two pieces of evidence; one from high coherence between seismic and pressure data and the other from the phase difference between pressure and vertical seismic displacement. By selecting data from a high-pressure range, we can apply the compliance method, similar to the compliance method applied to ocean bottom observations (e.g., Webb and Crawford, 1998). We will show a map of shallow rigidity variations for the depth range of 50-100m.

Second, the combined analysis of temperature and seismic noise allows us to identify the major effects caused by near-surface melting, primarily in the permafrost area. Some stations show a thousand-fold increase of horizontal noise in summer at 0.01-0.03 Hz in comparison to the frozen state. This anomalous horizontal noise can be seen at low frequency (< 0.1 Hz) and is undoubtedly related to tilt effects as its amplitude increases towards lower frequency.

Third, seasonal variation in horizontal noise shows a rapid increase in summer due to melting but the way the noise level returns to the frozen (low-noise) state varies from station to station. For most stations, this return occurs well after the surface temperature becomes negative in September or October. But some stations require time until March of next year to return to the low noise level. These data suggest that the melt layer remains at depth for a long time even after temperature drops below freezing, perhaps developing a sandwiched molten layer between the developing ice from the surface and the underlying permafrost ice.

How to cite: Tanimoto, T.: New Perspectives on the Shallow Environment in Alaska from co-located seismic, pressure, temperature, and wind sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6637, https://doi.org/10.5194/egusphere-egu24-6637, 2024.

EGU24-7490 | Posters on site | GM2.1 | Highlight

August 2023 Slovenian flood anatomy from national seismometer network data analysis 

Michael Dietze, Mateja Jemec Auflič, Sašo Petan, and Nejc Bezak

Excessive and sustained rainfall can trigger regional floods with a large propagation range. Their non-linear onset, rapid evolution and massive impact make prediction, mitigation and posteriour anatomy efforts difficult.

The atmospheric low “Petar” that struck Europe in early August 2023 was one drastic example of such flood triggering rain events. It was able to gain abundant moisture and heat over an exceptionally warm Mediterranean Sea, before it moved to continental Europe, crossing Slovenia, Austria, and Germany. It caused severe flooding as a result of locally more than 350 mm rain within less than two days. We focus on Slovenian examples, where the event was perceived the most devastating natural hazard in the last decades.

Here, we follow a seismic approach to study the spatially contrasting effects of the rain signal from available FDSN data (SL network). We study the time variant spectral signatures of reaches in steep mountain, graded upland and wide basin landscapes across northern Slovenia and exemplarily invert the seismic data for key flood parameters: water level and debris flux, and propagation velocity. We discuss the detection range of existing earthquake seismometer networks and the potential to improve those with respect to flood quantification. Our analysis highlights the compound effects of channel geometry, event magnitude and network density for flood detection and signature consistency.

How to cite: Dietze, M., Jemec Auflič, M., Petan, S., and Bezak, N.: August 2023 Slovenian flood anatomy from national seismometer network data analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7490, https://doi.org/10.5194/egusphere-egu24-7490, 2024.

EGU24-7576 | ECS | Orals | GM2.1

Constructing a New Catalogue of Greenland's Iceberg Calving Events through Seismic Data Analysis and Machine Learning 

Selina Wetter, Clément Hibert, Anne Mangeney, and Eléonore Stutzmann

The Greenland ice sheet, a critical component of the global climate system, has played a substantial role in rising sea level, marked by a fourfold increase in mass loss due to iceberg calving between 1992-2000 and 2000-2011. Through the quantification of the spatio-temporal changes in Greenland’s ice mass loss resulting from iceberg calving, we gain a deeper understanding of the impacts of climate change.

The mass loss related to calving icebergs can be estimated by combining mechanical simulation of iceberg calving and inversion of seismic data. Seismic signals are generated by the time-varying force produced during iceberg calving on marine-terminating glacier termini. These events, known as glacial earthquakes, are recorded by the Greenland Ice Sheet Monitoring Network at tens of kilometres from the source.

However, differentiating these signals from tectonic events, anthropogenic noise, and other natural noise is challenging due to their complex frequency content (1-100s), multi-phase waveforms and low amplitude. To overcome this difficulty, we use a detection algorithm based on the Short-Time Average over Long-Time Average (STA/LTA) method and combine it with machine learning (Random Forests). By training the machine learning algorithm on seismic event catalogues containing more than 400 earthquakes and glacial earthquakes each, our approach is apt for identifying glacial earthquakes. Applying this methodology to continuous data offers the possibility to uncover smaller and previously undetected events. As a result, we present a comprehensive catalogue spanning several years and discuss its relevance and reliability. The generated catalogue allows us to develop new methods to better understand the spatio-temporal evolution of the ice-calving activity in the region. Among these, we will initially focus on locating and inverting the force of the largest events, providing a basis for testing new machine learning approaches for the characterisation of the source. This includes extracting properties like the iceberg volume and shape from both large and smaller events, ultimately advancing our understanding of Greenland's ice mass loss dynamics.

How to cite: Wetter, S., Hibert, C., Mangeney, A., and Stutzmann, E.: Constructing a New Catalogue of Greenland's Iceberg Calving Events through Seismic Data Analysis and Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7576, https://doi.org/10.5194/egusphere-egu24-7576, 2024.

EGU24-8208 | ECS | Orals | GM2.1

Icequake source location using seismic data in Dålk Glacier, East Antarctica 

Shun Zhao, Zheyi Cao, Yuanyuan Gu, Chen Lv, Zhitu Ma, Tong Hao, Gang Qiao, Benfeng Wang, and Rongxing Li

Icequakes are closely associated with glacier movement and rupture, and their temporal and spatial distribution patterns can portray the dynamics of glaciers. In this study, we used the seismic data recorded by 34 short-period Smartsolo seismometers deployed in Dålk Glacier, East Antarctica for about 60 days to detect and locate icequakes. The array was deployed at the edge of the Dålk Glacier and across the grounding line previously generated by satellite observations. The recorded data were strongly affected by Antarctica storms and we selected two days with little wind noise for preliminary analysis. Using time-frequency analysis and particle motion, we found that the seismic events are either dominated by body waves or surface waves, which likely correspond to deep icequakes or near-surface crevasse icequakes. Since the propagation of surface waves is easier to analyze and possible detections of crevasse icequakes are more likely to be verified from satellite images, we chose to focus on surface wave signals in this preliminary analysis. We first filtered records to 5-20 Hz and manually examined records with clear surface wave arrivals. We then produced templates using these events to scan through our records. We successfully identified 89 events within the two-day period. Lastly, these signals were located using a grid-search approach for their latitudes and longitudes, together with an average group velocity for each event. Nearly half of the incidents were concentrated on the edges of rock outcrops, which suggests they were generated by the relative movement between the glacier and outcrops. The other half of the events was found in the eastern region, where a large number of surface crevasses were observed on satellite imagery. In addition, the optimal velocity from the grid search is ~2.8 km/s for events from the North and West, while the optimal velocity for events from the East is ~1.8 km/s. The difference in wave velocity suggests the existence of a boundary between rock and ice at a depth of about 100-150m within or near our seismometer array. By analyzing the amplitude variations of incidents in different directions recorded at various stations, we observed that this boundary is within our array and its location and geometry can be estimated. Compared to the grounding line predicted from satellite observations, our result shows that the boundary is offset to the East by ~100 m. The reason for this discrepancy will be further discussed in the meeting.

How to cite: Zhao, S., Cao, Z., Gu, Y., Lv, C., Ma, Z., Hao, T., Qiao, G., Wang, B., and Li, R.: Icequake source location using seismic data in Dålk Glacier, East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8208, https://doi.org/10.5194/egusphere-egu24-8208, 2024.

EGU24-8304 | Posters on site | GM2.1

Water table height maps prediction from passive surface-wave dispersion using deep learning 

José Cunha Teixeira, Ludovic Bodet, Agnès Rivière, Marine Dangeard, Amélie Hallier, Alexandrine Gesret, Amine Dhemaied, and Joséphine Boisson Gaboriau

Monitoring underground water reservoirs is challenging due to limited spatial and temporal observations. This study presents an innovative approach utilizing supervised deep learning (DL), specifically a multilayer perceptron (MLP), and continuous passive-Multichannel Analysis of Surface Waves (passive-MASW) for constructing 2D water table height maps. The study site, geologically well-constrained, features two 20-meter-deep piezometers and a permanent 2D geophone array capturing train-induced surface waves. For each point of the 2D array, dispersion curves (DCs), displaying Rayleigh-wave phase velocities (VR) across a frequency range of 5 to 50 Hz, have been computed each day between December 2022 and September 2023. In the present study, these DCs are sampled in wavelengths ranging from 4.5 to 10.5 m in order to focus the monitoring on the expected water table depths. All VR data around one of the two piezometers is used to train the MLP model. Water table heights are then predicted across the entire geophone array, generating daily 2D piezometric maps. Model's performance is tested through cross-validation and comparisons with water table data at the second piezometer. Model’s efficiency is quantified with the root-mean-square error (RMSE) and the coefficient of determination (R²). A R² is estimated above 80 % for data surrounding the training piezometer and above 55 % for data surrounding the test piezometer. Additionally, the RMSE is impressively low at 0.03 m at both piezometers. Results showcase the effectiveness of DL in generating predictions of water table heights from passive-MASW data. This research contributes to advancing our understanding of subsurface hydrological dynamics, providing a valuable tool for water resource management and environmental monitoring. The ability to predict 2D piezometric maps from a single piezometer is particularly noteworthy, offering a practical and efficient solution for monitoring water table variations across broader spatial extents.

How to cite: Cunha Teixeira, J., Bodet, L., Rivière, A., Dangeard, M., Hallier, A., Gesret, A., Dhemaied, A., and Boisson Gaboriau, J.: Water table height maps prediction from passive surface-wave dispersion using deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8304, https://doi.org/10.5194/egusphere-egu24-8304, 2024.

EGU24-9067 | ECS | Posters on site | GM2.1

Seasonal variations in sediment transport from ice sheet terminus through a proglacial forefield. A case study from Leverett glacier, Western Kalaallit Nunaat (Greenland).  

Marjolein Gevers, Stuart N. Lane, Floreana Miesen, Davide Mancini, Matthew Jenkin, Chloé Bouscary, Faye Perchanok, and Ian Delaney

Current climatic warming is causing accelerated melt of the Greenland Ice Sheet. Whilst the changing hydrological response is well known, the sediment export as well as the geomorphic changes in the proglacial area remain uncertain.  

Here we present records of sediment transport from melt seasons 2022 and 2023 in the proglacial area of Leverett glacier, a land terminating glacier outlet on the Western part of the Greenland Ice Sheet. The proglacial area here is very well denifed by a waterfall cutting through bedrock functioning as terminal gauge, which allows for the installation of hydrological stations. These hydrological gauging stations, containing turbidity and pressure sensors, allow for estimation of discharge and suspended sediment concentrations over the melt season. Variations in bedload transport can be analysed using the sesimic data obtained from the geophones placed on the river bank close to the hydrological gauging stations. To convert the recorded seismic data into bedload flux, a Fluvial Inversion Model is used, which is calibrated using active seismics surveys and the water stage data from the hydrological gauging stations.

The dataset allows us to investigate the relationships between bedload, suspended sediment, and water discharge from the Leverett glacier as well as sediment transport and deposition in the proglacial area. We observe several spring events in the first half of July, where suspended sediment concentration and water discharge increase simultaneously at the start of the melt season. During the first half of August, we observe a clear dilution signal, where increase in water discharge coincides with a decrease in suspended sediment concentration From insights about the relationship between water and sediment discharge from the ice sheet, we can speculate about the sediment export response to increased water discharge from the Ice Sheet.

How to cite: Gevers, M., Lane, S. N., Miesen, F., Mancini, D., Jenkin, M., Bouscary, C., Perchanok, F., and Delaney, I.: Seasonal variations in sediment transport from ice sheet terminus through a proglacial forefield. A case study from Leverett glacier, Western Kalaallit Nunaat (Greenland). , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9067, https://doi.org/10.5194/egusphere-egu24-9067, 2024.

Groundwater storage monitoring is now one of the most promising application of seismic interferometry techniques. In steep mountain environments, where drilling wells is particularly challenging, the use of seismic stations to retrieve relative seismic velocity changes could fundamentally advance our understanding of groundwater dynamics. However, very few studies have looked at seismic velocity variations at the scale of a single steep topography unit. Here, we estimate velocity variations from six stations covering a distance of 3.5 km on a single mountain ridge in the county of Hualien, Taiwan. One station was placed at the top of a ridge (900m elevation), two at the mid-slope of the topography and two others at the bottom (200m elevation), near the river banks. The aim is twofold: Determining how homogenous these velocity changes are and understanding the possible impact of topography on groundwater variations in a mountainous setting. Results from auto-correlations and cross-correlations are compared with meteorological data and other geophysical analysis. We identify the average hydrological dynamics of the ridge unit and connect the residual velocity changes to local site characteristics and upstream weather conditions.

How to cite: Illien, L., Kuehn, J., Andermann, C., and Hovius, N.: Monitoring groundwater dynamics in a mountain ridge using seismic interferometry: Influence of topography, local subsurface structure and meteorological conditions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9608, https://doi.org/10.5194/egusphere-egu24-9608, 2024.

EGU24-9822 | ECS | Posters on site | GM2.1

Intermediate-depth icequakes at Greenland’s fastest outlet glacier: evidence for englacial thrust faulting? 

Ana Nap, Fabian Walter, Martin P. Lüthi, Adrien Wehrlé, Janneke van Ginkel, Andrea Kneib-Walter, and Hugo Rousseau

In traditional glacier flow laws and consequently glacier models, a widely used assumption is that the ice behaves as a non-Newtonian viscous fluid that slides either across hard bedrock or via deforming subglacial till. Elastic effects and brittle deformation within the ice are often neglected for simplicity, as even ubiquitous surface crevasses are difficult to capture in numerical schemes. While there is ample seismological evidence that stick-slip motion plays a significant role in basal sliding of both alpine and polar glaciers, similar evidence is lacking for brittle deformation within the ice mass itself. Instead, it is commonly assumed that the ice moves and deforms in a purely viscous or ductile manner, which may not be an accurate representation of reality.

Here, we present observations of high-frequency (>50Hz) signals of intermediate-depth seismic sources occurring along the fast ice-stream of Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), Greenland’s fastest flowing outlet glacier. The waveform characteristics of these events closely resemble the known characteristics of waveforms associated with basal stick-slip events, making them easily distinguishable from the more prevalent icequake signals generated by surface crevasse opening and propagation. However, differences in P and S wave arrival times as well as probabilistic source locations show that these events occur at ~170-400 m depth, whereas at those locations the glacier has a total depth of approximately 2000 m. Hence, these events cannot be caused by stick-slip motion at the base of the glacier, but must originate from englacial dislocations such as e.g., thrust faulting. Hundreds of these englacial icequakes are observed at several seismic arrays that were temporarily deployed in 2022 and 2023 along the fast ice-stream of Sermeq Kujalleq. Using waveform clustering and source mechanism analysis, we discuss the role of these events in ice dynamics and in particular englacial deformation.

 

How to cite: Nap, A., Walter, F., Lüthi, M. P., Wehrlé, A., van Ginkel, J., Kneib-Walter, A., and Rousseau, H.: Intermediate-depth icequakes at Greenland’s fastest outlet glacier: evidence for englacial thrust faulting?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9822, https://doi.org/10.5194/egusphere-egu24-9822, 2024.

EGU24-10147 | ECS | Posters on site | GM2.1

Uncovering Stick-Slip Events: Denoising Cryoseismological Distributed Acoustic Sensing Data with an Autoencoder 

Johanna Zitt, Patrick Paitz, Fabian Walter, and Josefine Umlauft

One major challenge in cryoseismology is that signals of interest are often buried within the high noise level emitted by a multitude of environmental processes. Specifically, basal sources such as stick-slip events often stay unnoticed due to long travel paths to surface sensors and accompanied wave attenuation. Yet, stick-slip events play a crucial role in understanding glacier sliding and therefore, it is of great interest to investigate their spatio-temporal evolution, across the entire glacier from its ablation to its accumulation zone.
Distributed Acoustic Sensing (DAS) is a technology for measuring strain rate by using common fiber-optic cables in combination with an interrogation unit. This technology enables us to acquire seismic data over an entire glacier with great spatial and temporal resolution. To unmask stick-slip events, new techniques are required that effectively and efficiently denoise large cryoseismological DAS data sets. 
Here, we propose an autoencoder, a type of deep neural network, which is able to separate the incoherent environmental noise from the temporally and spatially coherent signals of interest (e.g., stick-slip events or crevasse formations). We trained the autoencoder in order to denoise a DAS data set acquired on Rhonegletscher, Switzerland, in July 2020. Due to the highly active and dynamic cryospheric environment as well as non-ideal cable-ground coupling the collected DAS data are characterized by a low signal to noise ratio compared to classical point sensors.
Several models were trained on a variety of data subsets, differing in recording positions (ablation or accumulation zone), event types (stick-slip event or surface event) and the quantity of training events. We compare and discuss the denoising capabilities of these models with several metrics, such as inter-channel coherence, similarity between seismometer and DAS recordings, and visual assessment. This evaluation is conducted while considering different data types in a qualitative and quantitative manner. All models show an increase in inter-channel coherence of the seismic records after denoising. Further, all models uncover previously undetected stick-slip events, whereby models trained on manually picked training data perform better than models trained on randomly picked training data. We believe that the application of our models can improve the understanding of basal stick-slip information in cryoseismological DAS datasets, potentially uncovering previously hidden information.

How to cite: Zitt, J., Paitz, P., Walter, F., and Umlauft, J.: Uncovering Stick-Slip Events: Denoising Cryoseismological Distributed Acoustic Sensing Data with an Autoencoder, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10147, https://doi.org/10.5194/egusphere-egu24-10147, 2024.

EGU24-10347 | Orals | GM2.1 | Highlight

The seismic signature of skiing 

Heiner Igel, Sophie Brass, Fabian Lindner, Koen Van Noten, Raphael de Plaen, Joachim Wassermann, Felix Bernauer, and Thomas Lecocq

In March 2023 the annual winter school SKIENCE (www.skience.de) was held in the Bavaria alps, south-east of Munich. The topic was environmental seismology with a focus on seismic monitoring using ambient seismic noise. The winter school had strong practical training aspects. Prior to the meeting 12 5Hz nodes (SmartSolo) were deployed in the valley near Bayrischzell with the goal to explore local structure and site effects using interferometric methods. During the midweek free afternoon the 12 SmartSolo nodes were installed on both sides of a slalom run with several gates through which participants of the winterschool skied one after each other. First inspection of the data showed that clear signals of the skiers could be identified. Here, we report on attempts to use the seismic data records to recover the tracks of the skiers as moving seismic sources. Questions associated with this experiment are at which points in the tracks seismic energy is generated, where exactly the incoming signals propagate and with what velocities, and how well the source locations can be backprojected. A simple theoretical model is used to develop the inversion tools to recover the moving sources.   

How to cite: Igel, H., Brass, S., Lindner, F., Van Noten, K., de Plaen, R., Wassermann, J., Bernauer, F., and Lecocq, T.: The seismic signature of skiing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10347, https://doi.org/10.5194/egusphere-egu24-10347, 2024.

EGU24-10380 | Orals | GM2.1

Observing ice-bed weakening on a fast flowing glacier with seismic noise interferometry and unsupevised clustering. 

Léonard Seydoux, Ugo Nanni, Lucien Goulet, Thomas Pauze, and Andreas Köhler
Glacier flow instability often results from changes at the ice-bed interface. However, understanding these processes is challenging due to limited access to the glacier bed. Our study focuses on Kongsvegen glacier in Svalbard, which shows signs of an upcoming rapid flow event. To investigate the potential causes of such acceleration, we installed 20 seismometers along the glacier flowline, from the surface down to 350 m near the ice-bed interface. We combined our seismic monitoring with measurements of surface velocity, basal water pressure, and basal sediment deformation.
First, we performed seismic noise interferometry between stations located along the glacier flowline with inter-station distances ranging from 1 to 12 km. We observed a multi-year decrease in seismic velocity, with a seasonal signal superimposed, showing a melt-season decrease in seismic velocity of 2 to 4%. We compared our observations with 1D models and concluded on the presence of damaged basal ice and/or a weakening of the subglacial sediments. This indicates a mechanical weakening of the ice-bed interface, promoting further glacier acceleration.
Second, we conducted unsupervised clustering of seismic waveforms using a novel approach based on a deep scattering network. Doing so, we observed a yearly increase in surface crevasses concomitant with an increase in basal events, likely indicating stick-slip and/or basal crevasses. This increase is particularly visible during winter, where the number of events steadily increases from year to year. We suggest that, in response to an initial glacier acceleration, new crevasses have opened, providing access pathways for surface meltwater to the base of the glacier, affecting the ice-bed coupling. This mechanism represents a positive hydro-mechanical feedback that fuels further acceleration and crevassing, potentially having wider implications for triggering glacier-wide instabilities, increasing short-term sea-level rise, and local hazards.

 

How to cite: Seydoux, L., Nanni, U., Goulet, L., Pauze, T., and Köhler, A.: Observing ice-bed weakening on a fast flowing glacier with seismic noise interferometry and unsupevised clustering., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10380, https://doi.org/10.5194/egusphere-egu24-10380, 2024.

EGU24-10525 | ECS | Posters on site | GM2.1

Deep Embedded Clustering of a Cryo-Data-Cube 

Julia Peters, Felix Roth, and Josefine Umaluft

Cryoseismological records consist of numerous signals generated by various sources within or surrounding glacial ice, including icequakes, water flow, avalanches, rockfalls, wind, or precipitation. This results in a notably high noise level within the data, posing a significant challenge in detecting and distinguishing individual seismic events and sources.

Our research employs Deep Embedded Clustering (DEC) to address this challenge, focusing on the analysis of a Distributed Acoustic Sensing (DAS) dataset acquired on Rhonegletscher (Switzerland) in 2020.

To visualize and efficiently streamline the DEC processing of this substantial volume of data, we reorganize the numerous continuous DAS channels as a 3D data cube featuring the three dimensions: time, space, and frequency. The DEC approach involves first transforming high-dimensional seismic data into a more manageable lower-dimensional latent space using an autoencoder. This transformation is vital in emphasizing the essential characteristics of the data, thereby enabling more effective clustering. Subsequently, the DEC algorithm autonomously categorizes these seismic signals into distinct clusters based on their unique spatio-temporal characteristics, without the prerequisite of manual annotation.

The primary aim of this approach is to utilize DEC for the effective mapping of clearly defined spatio-temporal clusters within cryoseismological records. This approach is geared towards achieving a more nuanced understanding of the various sources contributing to these records and their complex dynamics. By successfully segregating these clusters, the aim is to reveal new insights into the complex processes and interactions in glacial environments.

Both the DAS data and the clustering results can be explored interactively using the data cube viewer Lexcube. Come find us at the poster stand!

How to cite: Peters, J., Roth, F., and Umaluft, J.: Deep Embedded Clustering of a Cryo-Data-Cube, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10525, https://doi.org/10.5194/egusphere-egu24-10525, 2024.

EGU24-11086 | ECS | Posters on site | GM2.1

Support vector regression-based model for the prediction of surface displacement and vibration using meteorological data 

Chi En Hi, Kate Huihsuan Chen, Wei Peng, Wan-Ru Huang, Hsiang Han Chen, Ko Chih Wang, and Kuo En Ching

Can we use environmental data to predict changes in surface displacement fields? Do severe weather events alter the near-surface geomechanical properties? The seasonal variations in GPS time series and crustal seismic velocities have been frequently observed at different study areas. Such variation has been tied closely to the cyclic hydrological loads [e.g., Costain et al., 1987; Heki, 2003; Roth et al., 1992], which its association with tectonic deformation remains debated. Using the 15 years meteorological, geodetic, and seismic data recorded in southern Taiwan (near Chaozhou fault where the background seismicity level is low), we aim to explore the possibility of predicting surface displacement and vibration using climatic variables (time series of temperature, precipitation, and wind velocity) and groundwater levels. Here the Support Vector Regression (SVR) model is developed for the prediction of the GNSS and seismic signals, while 15-yr datasets are divided into groups of 75%  and 25% datasets for model calibration and testing. When the predicted surface displacement is compared with the real data, the R-square values reach 95%, indicating the applicability of SVR model on long-term surface deformation prediction. In the future, long-term prediction model will be conducted to target several extreme weather events in Taiwan.

How to cite: Hi, C. E., Chen, K. H., Peng, W., Huang, W.-R., Chen, H. H., Wang, K. C., and Ching, K. E.: Support vector regression-based model for the prediction of surface displacement and vibration using meteorological data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11086, https://doi.org/10.5194/egusphere-egu24-11086, 2024.

EGU24-11562 | ECS | Posters on site | GM2.1 | Highlight

How trees sway and what it tells us about their overall vitality 

Jana Roth, Karin Mora, Djamil Al-Halbouni, Ronny Richter, Teja Kattenborn, Sebastian Johannes Wieneke, Ana Bastos, Alexandra Weigelt, Christian Wirth, and Josefine Umlauft

Changing climate, especially the increase in frequency and intensity of extreme events such as heat waves and droughts, poses a significant challenge to the biosphere, threatening biodiversity overall and specifically exacerbating tree mortality. Countermeasures and management actions often prove insufficient due to delayed visual indicators of tree stress. 

Real-time monitoring of physiological and structural changes in tree characteristics and related abiotic parameters, such as sap flow, leaf angle, or soil moisture, plays a crucial role in tracking the trees’ overall vitality. However, conventional monitoring approaches are often expensive, require high maintenance and are therefore not feasible on a larger spatio-temporal scale.     

In a groundbreaking approach, we propose to measure the seismic oscillation generated by tree sway under specific weather conditions, potentially reflecting tree vitality. Specifically, oscillations are related to material properties of leaves, branches, and trunks, which change when they become dry. Seismic measurements offer scalability and low maintenance, making them viable for extensive spatio-temporal coverage. Through integrated observations from dense seismic arrays, direct tree trait measurements, and meteorological parameters collected at the research arboretum (ARBOfun) during autumn 2023, we successfully isolated the seismic fingerprint of tree sway.

However, the unique nature of this novel data introduces challenges, for example noise from human and animal activities, allowing for only time series snapshots. To overcome these challenges, we explored various time series and frequency related analysis methods to separate the tree signal from other influences.

How to cite: Roth, J., Mora, K., Al-Halbouni, D., Richter, R., Kattenborn, T., Wieneke, S. J., Bastos, A., Weigelt, A., Wirth, C., and Umlauft, J.: How trees sway and what it tells us about their overall vitality, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11562, https://doi.org/10.5194/egusphere-egu24-11562, 2024.

EGU24-13007 | Orals | GM2.1 | Highlight

Assessing the seismic signature of turbulent flow and intense bedload transport from designed laboratory experiments 

Florent Gimbert, Maarten Bakker, Marco Piantini, Alain Recking, and Michael Lamb

The field of fluvial seismology has undergone significant advances over the past decade. The development of dedicated physical theories and their applications in various contexts have allowed separating the respective contributions of turbulent flow and bedload transport, such that physical parameters like flow depth and sediment flux may be inferred from seismic observations. However, the quantitative link between signal characteristics (amplitude, frequency) and the underlying physics yet involves simplified considerations that do not necessarily apply to more complex situations, such as for example under rough flow conditions or during extreme floods.

In this talk I will present results from laboratory experiments that we designed specifically in order to quantify the seismic signature of flow turbulence and intense bedload transport under a range of conditions using force sensors coupled to the river bed. On one hand, I will show that existing theory regarding turbulent flow properly captures the main characteristics of the seismic source, but that additional dependencies on flow conditions and particle-wake development need to be included for more accurate predictions. On the other hand, I will show that existing theory regarding bedload transport fails at capturing the main characteristics of the seismic source under intense bedload transport conditions associated with complex changes in internal flow dynamics. In this case the seismic source appears to be a decreased function of solid concentration, as opposed to an increased function such as considered in current theories, which we suggest is due to grain impacts being agitation-controlled rather than bed-roughness controlled. Finally, I will discuss possible ways towards building more generic theories of ground motion induced by sediment transport.  

How to cite: Gimbert, F., Bakker, M., Piantini, M., Recking, A., and Lamb, M.: Assessing the seismic signature of turbulent flow and intense bedload transport from designed laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13007, https://doi.org/10.5194/egusphere-egu24-13007, 2024.

EGU24-13208 | Posters on site | GM2.1 | Highlight

Analysis of Precursors and Collapse of June 15, 2023, Brienz/Brinzauls Rockslide in Switzerland: Integrating Seismic and Remote Sensing Observations 

Sibashish Dash, Michael Dietze, Fabian Walter, Marcel Fulde, Wandi Wang, Mahdi Motagh, and Niels Hovius

The early detection of slope instability and the monitoring of frequent hazard processes in mountainous regions is of paramount importance due to their sudden occurrence, and the risk of causing numerous fatalities and significant economic damage. The recent collapse of the Brienz/Brinzauls rockslide on June 15, 2023, in an active, deep-seated mountain slope deformation complex in Switzerland, provides a unique opportunity to investigate the evolution of precursors leading up to the collapse. Early identification of accelerating rockmass enabled us to set up a network of five broadband seismometers, strategically deployed to systematically record seismic signals in close proximity, reducing information loss due to attenuation of seismic waves. 

The internal rock damage dynamics in the displacing rock mass were interacting with external seasonal forcings, such as snow melt and rainfall, for years preceding the collapse at approximately 21:38:00 UTC on June 15, 2023. Seismic events of various types have been detected in the entire landslide complex, characterised by the recurrence of identical seismic events that aggregate prominently within the most rapid compartment, referred to as the "Insel," positioned directly above the village of Brienz. This study aims to investigate the influence of seasonal forcings on accelerating the rate of displacements and to understand how the nature of detected precursors changes over time. We systematically examine the feedback loop between seasonal triggers and gravity-driven internal rock damage under changing stress conditions during fluctuations in compartment velocity. Initially, events exhibit accelerations following periods of precipitation, but subsequently, a runaway acceleration in seismic events was noted even during dry periods. The locations detected reveal communication between the upper and lower parts of the “Insel” mass in the build-up to the main collapse. From June 1 onward, there is a consistent and gradual increase in the mean spectral power of the recurring seismic events, with a rapid escalation observed in the three days leading up to the collapse. Interestingly, on the final day preceding the main collapse, a significant decrease in the mean spectral power was identified. To complement seismic observations, the spatial and temporal changes in pre-failure slope instability for the period 05.2014-06.2023 were also analyzed using Sentinel-1 synthetic aperture radar (SAR) data using a multi-temporal interferometric (MTI) approach. MTI analysis indicates several patches of instability and surface deformation on the slope, along with signs of significant surface displacement of a few centimetres per year, also manifesting in the village of Brienz. To facilitate automatic detection and classification, we apply data science methods to various statistical seismic attributes of the identified precursors. This study contributes to advancing our understanding of the mechanisms leading to rockslide collapses, with the potential to significantly enhance warning system effectiveness.

How to cite: Dash, S., Dietze, M., Walter, F., Fulde, M., Wang, W., Motagh, M., and Hovius, N.: Analysis of Precursors and Collapse of June 15, 2023, Brienz/Brinzauls Rockslide in Switzerland: Integrating Seismic and Remote Sensing Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13208, https://doi.org/10.5194/egusphere-egu24-13208, 2024.

EGU24-13569 | Orals | GM2.1

Validation of seismic bedload saltation model: From laboratory flume to field-scale experiments 

Wei-An Chao, Chi-Yao Hung, and Yu-Shiu Chen

Reliable bedload flux estimations are necessary for a variety of applications such as sedimentation engineering, flood risk mitigation and river restoration. Several seismic physical models with considering different bedload transport mechanisms have been proposed, which provided an opportunity to have quantitative observation in practical. However, a lack of direct measurements of bedload fluxes in field application cause a challenge for the validation of seismic models. In the practical application, the bedload impact kinematics (elasticity and velocity) and particle dynamics assumed in models are crucial for achieving high accuracy in bedload inversion. In-situ seismic parameters such as shear-wave velocity and seismic quality factor are also required to reduce the uncertainty in model prediction. Thus, this study first conducts bedload transport experiments in a flume laboratory to understand the kinematics and mechanics of particle transport by using the smart rock embedded with accelerometer and gyroscope, geophone and hydrophone. For the field-scale experiments, we further studied distributed acoustic sensing (DAS) measurement during the experiments, which can record the dynamic strain in fiber optic cable under riverbed. Both case of laboratory flume and field-scale experiments, we will evaluate the performance of the different physical models by comparing in-situ measurements of bedload mass and impact forces recorded by the smart rock. In the case of field experiment, we adopted the active and passive seismic surface wave exploration to investigate the properties of wave propagation and attenuation. The effect of the process of rolling and/or sliding particles, as opposed to saltating particles, contributing in seismic signal generation, was also explored.   

How to cite: Chao, W.-A., Hung, C.-Y., and Chen, Y.-S.: Validation of seismic bedload saltation model: From laboratory flume to field-scale experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13569, https://doi.org/10.5194/egusphere-egu24-13569, 2024.

EGU24-13722 | ECS | Posters on site | GM2.1

Investigating bedload transport in mountain rivers through seismic methods: the new monitoring station in the Solda River (South Tyrol, Italy) 

Marco Piantini, Matthias Bonfrisco, Rudi Nadalet, Roberto Dinale, Gianluca Vignoli, Gianluca Antonacci, Silvia Simoni, Fabrizio Zanotti, Stefano Crema, Marco Cavalli, Alessandro Sarretta, Velio Coviello, and Francesco Comiti

Bedload transport plays a key role in the morphodynamics of mountain rivers by regulating erosion and aggradation processes. However, it is still challenging to estimate and predict bedload transport rates with reliability because of a complex interplay between different types of sediment supply, hydrological forcing, and fluvial morphologies. In the last two decades, passive sensors recording the seismic signals generated by coarse particles impacting the riverbed have been proposed to provide a continuous indirect measure of bedload transport. Among them, geophone plates and seismometers have been demonstrated to be valid tools.

Here, we present the preliminary results from the new monitoring station of Stilfserbrücke/Ponte Stelvio designed and built to monitor both water and sediment fluxes in the Solda River (Italian Alps). The station, mainly financed through two ERDF 2014-2020 projects of the Autonomous Province of Bolzano South-Tyrol, is part of the operational gauging network of the Civil Protection Agency of Bolzano (Italy). Bedload transport is indirectly monitored by sixteen geophone plates covering the downstream side of a consolidation check dam. The signal associated with the vibrations generated by particle impacts on the steel plates is recorded continuously with a sampling frequency of 5 kHz. In order to calibrate the instruments, direct bedload measurements have been carried out through an innovative bridge-like structure (BLS) consisting of an electronically controlled mobile trap. The collected samples have been sieved by hand to characterize their grain size distribution. At the end of summer 2023 we have also explored the possibility to additionally monitor the river with seismometers installed on the left bank at the monitoring station. We have analyzed the signal from the geophone plates by counting the number of times its amplitude exceeds a preselected threshold expressed in volts (i.e. the impulses, Rickenmann et al., 2014), and by computing its power (Coviello et al., 2022). The best correlation is found between impulses (threshold of 0.04 V) and the bedload transport rates of particles larger than 22 mm, with a power law regression characterized by a coefficient of determination (R2) of 0.85 and a low root mean square error (RMSE) of 3.3 kg/min against peak bedload transport rates reaching 41 kg/min.

These findings pave the way towards ensuring the continuous quantification of coarse sediment transport in the Solda River, allowing for the evaluation of the impact of glacier retreat and slope instabilities associated with global warming on river dynamics. Finally, the simultaneous use of seismometers may provide a unique opportunity to test existing theoretical models on bedload-induced ground vibrations through the indirect measurements provided by the geophone plates.

References

Coviello, V., Vignoli, G., Simoni, S., Bertoldi, W., Engel, M., Buter, A., et al. (2022). Bedload fluxes in a glacier-fed river at multiple temporal scales. Water Resources Research, 58, e2021WR031873.

Rickenmann, D., Turowski, J.M., Fritschi, B., Wyss, C., Laronne, J., Barzilai, R., Reid, I., Kreisler, A., Aigner, J., Seitz, H. and Habersack, H. (2014), Bedload transport measurements with impact plate geophones: comparison of sensor calibration in different gravel-bed streams. Earth Surf. Process. Landforms, 39: 928-942.

How to cite: Piantini, M., Bonfrisco, M., Nadalet, R., Dinale, R., Vignoli, G., Antonacci, G., Simoni, S., Zanotti, F., Crema, S., Cavalli, M., Sarretta, A., Coviello, V., and Comiti, F.: Investigating bedload transport in mountain rivers through seismic methods: the new monitoring station in the Solda River (South Tyrol, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13722, https://doi.org/10.5194/egusphere-egu24-13722, 2024.

Solid Earth Sciences:SE07 Faults and Earthquakes: Networks, Precursors, Monitoring Systems and Numerical Modelling Techniques

Research on new methods and equipment for seismological monitoring of glaciers on the Qinghai-Tibet Plateau

Lei Zou1, Richard Games2, ……

1 SmartSolo Inc., China

2 SmartSolo Inc., Huston, USA

Abstract: Glacier seismology combines the advantages of glaciology and seismology to form a young interdisciplinary subject. Icequakes are vibrations produced during the movement and breakup of glaciers, ranging from small squeaks to sudden ruptures or slides equivalent to earthquakes (MW7). According to the location and mechanism of icequake occurrence, icequakes can be divided into five types: surface fissures, stick-slip movement, iceberg calving, subglacial flow, and hydraulic fracturing. In addition to traditional seismological methods, icequake research can also be conducted using multidisciplinary methods such as GPS, numerical simulation, and glacier physical properties. Icequake research can further explore the occurrence process and risk assessment of ice avalanches. We review advances in glacier seismology.

Our users use SmartSolo scientific instruments to successfully analyze ice avalanche events through vibration signals by observing multi-parameter glacier environment and climate changes, combined with seismological observation instruments. Provide a new and effective monitoring method for glacier seismic monitoring. It enriches the process observation and risk assessment methods of ice avalanche occurrence, and the combination of multiple parameters further improves the accuracy and effectiveness of ice avalanche event monitoring.

How to cite: Gamez, R. and Zou, L.: Research on new methods and equipment for seismological monitoring of glaciers on the Qinghai-Tibet Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13798, https://doi.org/10.5194/egusphere-egu24-13798, 2024.

EGU24-13859 | ECS | Orals | GM2.1 | Highlight

An overview of environmental seismology used to study the internal structure of the North East Greenland Ice Stream  

Emma Pearce, Dimitri Zigone, Andreas Fitchner, Coen Hofstead, Joachim Rimpot, Johannas Brehmer-Moltmann, and Olaf Eisen

In 2022 a network of 23 seismometers and Distributed Acoustic Sensing (DAS) fibre optic cable were deployed on the North East Greenland Ice Stream (NEGIS). Using a combination of environmental seismology methods, we were able to gain a comprehensive understanding of the ice streams internal structure, giving insight into its past and present dynamics.  

From ambient noise recording, we utilise the 9-component correlation tensors associated with all station pairs.  We derived dispersion curves for Rayleigh and Love wave group velocities with usable data in the frequencies from 1 to 25 Hz. These data are then inverted to obtain shear wave velocity measurements for the top 150 m of the ice stream using an MCMC approach. We reveal variations in the radial anisotropy for both the along and across-flow components.

Alternative methods of passive seismology were explored, such as using the seismic signal from an airplane landing. The recorded signals by the surface DAS cable displayed exceptional clarity, revealing at least 15 visible wave propagation modes, including various Rayleigh and pseudo-acoustic waves within the frequency range of 8 to 55 Hz.

Seismic While Drilling (SWD) methods utilising the noise from ice core drilling and cutting at NEGIS were investigated as an unconventional signal at the borehole camp. While not successful in this instance, recommendations for future deployments were provided to optimize the utilisation of these techniques.

These methods collectively offer insight into the layering of snow, firn, and ice within the ice stream, indicating the presence of seismic anisotropy. Demonstrating the effectiveness of short-duration (2-3 weeks) seismic deployments in glaciology.  

How to cite: Pearce, E., Zigone, D., Fitchner, A., Hofstead, C., Rimpot, J., Brehmer-Moltmann, J., and Eisen, O.: An overview of environmental seismology used to study the internal structure of the North East Greenland Ice Stream , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13859, https://doi.org/10.5194/egusphere-egu24-13859, 2024.

EGU24-14117 | ECS | Posters on site | GM2.1

Probing relation between rainfall pattern and seismic detected water-and-sediment events 

Guan-Syun Huang and Wei-An Chao

Southern Taiwan often experienced abundant monsoon seasons during seasonal transitions, and monsoons and typhoons controlled the rainfall patterns to be complex and varied, resulting the high intensity, prolonged duration, and high concentration. The aforementioned rainfall characteristics can increase the risk of water-and-sediment-related disasters.  To explore the correlation between rainfall patterns and water-and-sediment events, this study employs micro-seismic monitoring network, and the selected Putanpunuas River in southern Taiwan as a case study site. Frequent landslides in the middle and upper watershed supply the river with stable source of sediment materials. Consequently, during the periods with strong precipitation, our study site the shows high susceptibility of water-and-sediment events.  The seismic network comprises one station (BNAR) on the right bank and two stations (BNAL, BNAS) on the left bank downstream of the Putanpunuas River, and an additional station (BNAF) at the confluence of the Putanpunuas River and the Laonong River.  By conducting a series of spectrogram analysis, the average power spectral density (PSD) time series of each station can be computed. Then, we further quantified the seismic signal characteristic parameters for each water-and-sediment events.  This study initially employs various machine learning algorithms (Decision Tree, KNN, K-means, Auto-sklearn) to develop an optimized model for identifying water-and-sediment events, classifying different types of events, such as flooding (FD), debris flooding (DFD) and debris flow (DF), then providing a 4-year-length (2019~2023) catalog of water-and-sediment events.  Rainfall data including hourly precipitation and LiDAR estimated rainfall are collected from the rain gauge stations nearby study area. Using a certain definition (e.g., 4 mm/hr threshold for picking start time) of rain episodes, we calculated total number of episodes and established a rain episodes catalog.  The aforementioned datasets allow us to probe the relationship between rainfall patterns and water-and-sediment events, aiding in inferring the main rain episodes characteristics associated with water-and-sediment events . The  results of this study can be applied to predict potential water-and-sediment event types in Putanpunuas River using rainfall information as input. This can facilitate relevant early warning operations, reducing the societal impact of water-and-sediment disasters.

Key words : Rainfall Patterns, Rain Episode, Micro-seismic monitoring network, Putanpunuas River, Water-and-Sediment Events, Machine Learning

How to cite: Huang, G.-S. and Chao, W.-A.: Probing relation between rainfall pattern and seismic detected water-and-sediment events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14117, https://doi.org/10.5194/egusphere-egu24-14117, 2024.

EGU24-14125 | ECS | Posters on site | GM2.1

Studying field-scale dam breach due to overtopping by using seismic signals 

You-Lin Hou, Wei-An Chao, Chi-Yao Hung, Su-Chin Chen, and Tzu-Yao Chang

A dam is the natural damming of a river by the geohazards, such as landslides and debris flows. When the dam materials are eroded or washed away due to scour, erosion, and/or an increasing in water level of dam lake, leading dam breach and catastrophic outburst of flooding, which affect the downstream area. Therefore, real-time monitoring of dam failure would facilitate relevant early warning message for the impending floods. The conventional approach using image-based analysis and hydrological measurements is for providing timely warnings of breach; however, landslide dams often occur in mountainous areas, where the methods may face limitations of in-situ measurement. Additionally, the observations of landslide dam breach process are rare and cause the large uncertainties in scientific research. Hence, this study utilizes seismic signals to study the overtopping breach process of field-scale dams. Seismic signals serve as a monitoring tool while simultaneously monitoring the seismic characteristics of overtopping failure in the field-scale dams. In fact, there is a scarcity of observed seismic signal records related to dam breach process in field. Even if some observational data is available, there is a lack of corresponding image analysis or hydrological information for comprehensive discussions. Thus, this study aims to observe and understand overtopping failure through a series of field-scale dam breach experiments. In this study, we first investigate the time-frequency characteristics of seismic power spectral density (PSD) corresponding to the dam breaches primarily involves retrogression erosion, longitudinal and lateral erosion, and the stabilization period. Then, the results of photographic analysis (surface flow velocity, breach geometry), discharge measurements and the time-frequency characteristics of PSD are integrated to discuss the phenomena associated with dam breach. Finally, a series of comparison between compacted and non-compacted dams for PSD spectrogram patterns. The time-series of mean PSD and flow discharge data for the compacted dam exhibit a single-peak and short-term signal duration. Notably, the mean PSD time-series recorded by the seismic station located at the left bank showed a similar trend with flow discharge. Furthermore, during the retrogression erosion period, significant high-frequency PSD energy can be observed only in a case of the compacted dam. In contrast, the PSD energy for the non-compacted dam is concentrated in a relatively lower frequency range (between 10 to 30 Hz). The PSD and flow time series data for the non-compacted dam present a bimodal shape with longer time duration. Based on the flow velocity of breach notch, both in the compacted and non-compacted dams, the maximum velocity occurred during the transition from longitudinal to lateral erosion. In practical application, the results of seismic characteristics for the non-compacted dam case can be applied to the monitoring of dams formed by natural landslides in the field. Our results not only advance in understanding of the field-scale dam breach process but also can be directly applied to breach flooding warnings.
Key words : field-scale dam breach experiments, overtopping breach, power spectral density, time-frequency characteristic

How to cite: Hou, Y.-L., Chao, W.-A., Hung, C.-Y., Chen, S.-C., and Chang, T.-Y.: Studying field-scale dam breach due to overtopping by using seismic signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14125, https://doi.org/10.5194/egusphere-egu24-14125, 2024.

EGU24-15165 | Orals | GM2.1

Investigating Rainfall-Driven Resonance Frequency Changes in a Natural Rock Formation 

Juliane Starke, Laurent Baillet, Eric Larose, Antoine Guillemot, and Laurence Audin

Rainfall, temperature variations, and chemical processes are well-known drivers of rock erosion. The impact of rainfall on rocks is not well-understood yet but may impact the mechanical properties (including damage, rigidity, deformation) of the rock. In this study, we exhibit the effect of rainfall events on the resonance frequency of a rock column.

Resonance frequencies of structures have been utilized to monitor rock columns due to their sensitivity to changes in the rock apparent rigidity (1). For instance, daily temperature changes induce stress variations in the rock column, resulting in a daily cycle of resonance frequency changes (thermal-acousto-elasticity, 2).

This research involves long-term monitoring of the first resonance frequency of a 50 m high limestone cliff covering the Chauvet cave in the Ardèche plateau, SW France, exposed to climatic solicitations including daily solar radiation, air temperature fluctuations, and rain events. The rock column was equipped with seismic and meteorologic stations and monitored continuously during three years.

To demonstrate the effect of rainfall events on the mechanical properties of the rock, we calculated the resonance frequency depending only on air temperature and solar radiation, using a simple bivariate linear regression. The regression provides well-fitting results for dry periods but shows larger deviations during most rainy periods. This indicates that rain has an effect on the changes in rock resonance frequency. Identifying and quantifying these changes would be a key factor in understanding the evolution of damage.

 

1) Bottelin, P., Baillet, L., Larose, E., Jongmans, D., Hantz, D., Brenguier, O., ... & Helmstetter, A. (2017). Monitoring rock reinforcement works with ambient vibrations: La Bourne case study (Vercors, France). Engineering Geology, 226, 136-145.

2) Guillemot, A., Baillet, L., Larose, E., & Bottelin, P. (2022). Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems. Geophysical Journal International, 231(2), 894-906.

How to cite: Starke, J., Baillet, L., Larose, E., Guillemot, A., and Audin, L.: Investigating Rainfall-Driven Resonance Frequency Changes in a Natural Rock Formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15165, https://doi.org/10.5194/egusphere-egu24-15165, 2024.

EGU24-15365 | Posters on site | GM2.1

Automatic Monitoring of Seismogenic Slope Failure Activity at Brienz (Switzerland) Using Distributed Acoustic Sensing and Semi-Supervised Learning 

Jiahui Kang, Fabian Walter, Patrick Paitz, Johannes Aichele, Pascal Edme, Andreas Fichtner, and Lorenz Meier

Distributed Acoustic Sensing (DAS) represents a leap in seismic monitoring capabilities. Compared to traditional single-seismometer stations, DAS measures seismic strain at meter to sub-meter intervals along fiber-optic cables thus offering unprecedented temporal and spatial resolution. Leveraging the resolution of DAS enables us to monitor and detect seismogenic processes in the domain of hazardous mass-movements, including catastrophic rock avalanches.

Here, we present a semi-supervised neural network algorithm for screening DAS data related to mass movements at the Brienz landslide in Eastern Switzerland, which partially failed on 15 June 2023. A DAS interrogator connected to a 10 km-long dark fiber provided by Swisscom Broadcast AG near the landslide recorded seismic data from 16 May to 30 June 2023, with a sampling frequency of 200 Hz and a channel spacing of 4m. During a test period from June 1 to June 19, 2023, a total of 634 characteristic waveforms potentially related to slope failures, including the 15 June 2023 event, were detected, along with vehicle and other anthropogenic noise sources with characteristic diurnal and weekday/weekend variations.

For information extraction, we selected a subset of adjacent DAS channels, which include cable sections that were parallel to the failure event trajectory and thus particularly sensitive to mass movement activity. To facilitate efficient processing, we downsampled the data to 20 Hz, considering that slope failure events predominantly excite seismicity at below 10 Hz. We conceptualize the DAS data as a series of images representing consecutive strain rate data in the two dimensions of time and space. To bring out signal coherence between DAS channels, we transform the waveforms into cross-spectral density matrices (CSDM’s) which serve as the input image for unsupervised feature learning using an autoencoder (AE). Leveraging the features learned from the AE, we focus on activity classification using approximately 1500 samples. As ground truth for the slope failure class, we utilize concurrent Doppler radar data. The radar provides an event magnitude, which scales with failure volume and the number of individual rockfalls. Furthermore, the radar provides a measure of the moving mass’s trajectory length and front speed. The radar detected 516 slope failures during the test period.

Our algorithm captures 41.09 % of the slope failures recorded by the Doppler radar. The undetected events mainly have low radar magnitudes suggesting that they are associated with mass movements generating reduced seismic activity. Among the slope failure-type signals detected by DAS, 87.85% are also present in the radar catalogue. Interference from vehicle or human-triggered seismic waves, deteriorating the signal-to-noise ratio significantly, poses a challenge for our algorithm to differentiate between slope failures and those activities. Our study thus provides a benchmark for future natural hazard monitoring and suggests that using existing fiber optic infrastructure has a high potential for early warning purposes.

How to cite: Kang, J., Walter, F., Paitz, P., Aichele, J., Edme, P., Fichtner, A., and Meier, L.: Automatic Monitoring of Seismogenic Slope Failure Activity at Brienz (Switzerland) Using Distributed Acoustic Sensing and Semi-Supervised Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15365, https://doi.org/10.5194/egusphere-egu24-15365, 2024.

EGU24-15794 | ECS | Orals | GM2.1 | Highlight

Monitoring subsurface changes in a quick clay area during extreme weather 

Charlotte Bruland, Andreas Köhler, Anna Maria Dichiarante, Volker Oye, and Ivan Van Bever

Some of the more densely populated areas in Norway are in potential quick clay zones. When disturbed, the structure of quick clay can suddenly collapse, and behave and flow as a liquid, potentially having disastrous impact over large areas One of the triggering factors for quick clay slides is heavy rainfall. Here, we focus on passive seismic data from two Raspberry shake sensors located in an urban area in Oslo, Norway with quick clay in the subsurface. Using coda wave interferometry, near-surface velocity variations are estimated during the extreme weather ”Hans” (August 2023).

We compute auto-correlations and single station cross-correlations of anthropogenic seismic noise (> 1 Hz) over a two-year period leading up to ”Hans”. We observe environmental velocity fluctuations well correlated with air temperature, precipitation and the water level in a nearby river. In particular, freezing and thawing produces strong changes in seismic velocity (up to 4 %). Disregarding freezing, we see the largest change in seismic velocity following the heavy rainfall associated with ”Hans”. This extreme event is associated with a sharp velocity drop anti-correlated with pore pressure. The surface wave-coda is sensitive to changes in shear wave velocity, which in turn can be used to detect changes of the subsurface properties. Therefore, observed velocity variations at the site could have potential for monitoring and early warning of quick clay instabilities.

How to cite: Bruland, C., Köhler, A., Dichiarante, A. M., Oye, V., and Van Bever, I.: Monitoring subsurface changes in a quick clay area during extreme weather, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15794, https://doi.org/10.5194/egusphere-egu24-15794, 2024.

EGU24-16742 | ECS | Posters on site | GM2.1

Detection and localisation of wadi flow events utilizing seismic sensors 

Robert Krüger, Michael Dietze, Xabier Blanch, Jens Grundmann, Issa El-Hussain, Ghazi Al-Rawas, and Anette Eltner

In Oman, the frequency of flash floods has significantly increased in recent years. This phenomenon is correlated with climate change, resulting in an intensification of the atmospheric water cycle. Consequently, a further escalation of flash floods can be anticipated in the future. In Oman, the issue of flash floods is exacerbated by the frequent occurrence of tropical cyclones. Furthermore, the rapid expansion of urban areas, in some cases extending directly into wadis, coupled with the advancing sealing of the ground and insufficient drainage systems, leads to an increased risk of flooding. This is accompanied by substantial property damage and recurring loss of life.

Despite the growing danger posed by flash floods, there is currently no early warning system for precise prediction of these events in Oman. To establish such a system, densely distributed networks for rainfall and water level measurements would be required. However, due to the challenging topography and vastness of the country, implementing such networks is currently not feasible.

Recent studies have shown that seismic sensors could be used for measuring flow conditions. Further, seismic networks could be utilized to detect and track extreme flow events. The increasing availability of low-cost seismic sensors opens up the possibility of instrumenting previously ungauged wadi systems. However, the question remains if seismic networks can pick up smaller flow events and flow events happening in multiple smaller catchments at the same time.

In this study we used flow data from wadi gauge stations in the Al-Batinah Region (NW Oman) and data from broadband seismometers of the Earthquake Monitoring Center to research how flow events of various sizes can be detected by seismic networks. Initial results suggest that flow regimes in wadi systems offer favourable conditions for detection, as they mainly change between flow and no flow conditions. As the amplitude of seismic signals decreases with distance from the source, detection range is limited by background noise. To overcome this, low-cost seismic sensors have recently been installed in a wadi system together with camera based river gauges. Further work utilizing this data is currently ongoing.

How to cite: Krüger, R., Dietze, M., Blanch, X., Grundmann, J., El-Hussain, I., Al-Rawas, G., and Eltner, A.: Detection and localisation of wadi flow events utilizing seismic sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16742, https://doi.org/10.5194/egusphere-egu24-16742, 2024.

EGU24-17219 | ECS | Posters on site | GM2.1

Towards seismic monitoring of terrestial ecosystems: an exploratory data analysis of the SeisSavanna dataset 

Rene Steinmann, Tarje Nissen-Meyer, Fabrice Cotton, Frederik Tilmann, and Beth Mortimer

Our planet experiences ongoing unrest across various scales, from human footsteps to the powerful forces of volcanic eruptions and megathrust earthquakes. Seismic sensors, typically employed for geophysical studies, record diverse phenomena, including ground vibrations caused by the movement of terrestrial animals, known as footfall signals. The recently released SeisSavanna dataset comprises approximately 70,637 footfall signals from 11 different species in the African savanna. Consequently, ground-based vibrations might represent an underexplored sensory mode for continuously monitoring habitat usage and undisturbed animal behavior. To gain a deeper understanding of footfall signals, we conduct exploratory data analysis on the SeisSavanna dataset. Utilizing a scattering transform, we capture the distinctive features of footfall signals, creating a high-level and interpretable data representation for subsequent analyses. Seismogram atlases and clustering enable us to group similar types of footfall signals and investigate the signal-altering path and site effects, providing a comprehensive overview of the entire dataset. Moreover, this data-driven approach serves as a quality check for the species labels retrieved from co-located camera traps with a limited angle of view.

How to cite: Steinmann, R., Nissen-Meyer, T., Cotton, F., Tilmann, F., and Mortimer, B.: Towards seismic monitoring of terrestial ecosystems: an exploratory data analysis of the SeisSavanna dataset, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17219, https://doi.org/10.5194/egusphere-egu24-17219, 2024.

EGU24-17786 | Orals | GM2.1

Monitoring the mechanics of mountain permafrost using ambient noise seismology 

Antoine Guillemot, Eric Larose, Laurent Baillet, Agnès Helmstetter, Xavier Bodin, and Reynald Delaloye

Since last decades, coda wave interferometry (CWI) from ambient seismic noise has become an efficient method to probe continuous temporal changes of mechanical properties of the subsurface and crust. This method has successfully been used for environmental seismology issues, in a view of investigating the response of subsurface to environmental changes, in particular hydrological and thermal forcings (2). More, it has contributed to monitoring instabilities such rock slopes or landslides (3). Applying these methods to permafrost is then relevant to assess and monitor its mechanical response to environmental forcings.

As lobate or tongue-shaped superficial landforms composed of frozen rock debris, active rock glaciers are widespread features of mountain permafrost (4), potentially causing emerging hazards linked to permafrost thawing and debris flows.

Passive seismic instrumentation has been deployed for several years at Gugla, Tsarmine (Valais, Switzerland) and Laurichard (Hautes-Alpes, France) rock glaciers.

CWI has been applied to compute daily averaged dV/V (or relative change in velocity of the surface waves). For the three sites studied, seasonal variations of shear stiffness have been measured, associated with freeze-thawing cycles (5) (6). We located these daily fluctuations in depth by using a 1D coda wave inversion scheme. We also tracked water-induced power spectral density (PSD) and we detected microseismic events, highlighting the role of water inputs in changing the mechanical state, thus accelerating the whole rock glacier body. Also, we developed a viscoelastic model to explain the seasonal variability of the kinematics of rock glaciers. Combined with other geophysical methods, environmental seismology paves hence the way to deeply understand the mechanical response of mountain permafrost landforms to thermo-hydrological forcings.

 References

  • Richter, T., Sens‐Schönfelder, C., Kind, R., & Asch, G. (2014). Comprehensive observation and modeling of earthquake and temperature‐related seismic velocity changes in northern Chile with passive image interferometry. Journal of Geophysical Research: Solid Earth, 119(6), 4747-4765
  • Le Breton, M., Bontemps, N., Guillemot, A., Baillet, L., & Larose, É. (2021). Landslide monitoring using seismic ambient noise correlation: challenges and applications. Earth-Science Reviews, 216, 103518.
  • Haeberli, W., Hallet, B., Arenson, L., Elconin, R., Humlum, O., Kääb, A., ... & Mühll, D. V. (2006). Permafrost creep and rock glacier dynamics.Permafrost and periglacial processes, 17(3), 189-214.
  • Guillemot, A., Helmstetter, A., Larose, É., Baillet, L., Garambois, S., Mayoraz, R., & Delaloye, R. (2020). Seismic monitoring in the Gugla rock glacier (Switzerland): ambient noise correlation, microseismicity and modelling.Geophysical Journal International, 221(3), 1719-1735. https://doi.org/10.1093/gji/ggaa097
  • Guillemot, A., Baillet, L., Garambois, S., Bodin, X., Helmstetter, A., Mayoraz, R., and Larose, E.: Modal sensitivity of rock glaciers to elastic changes from spectral seismic noise monitoring and modeling, The Cryosphere, 15, 501–529, https://doi.org/10.5194/tc-15-501-2021, 2021.

How to cite: Guillemot, A., Larose, E., Baillet, L., Helmstetter, A., Bodin, X., and Delaloye, R.: Monitoring the mechanics of mountain permafrost using ambient noise seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17786, https://doi.org/10.5194/egusphere-egu24-17786, 2024.

EGU24-17787 | Posters on site | GM2.1

(Multi)annual variations in the microseism of the Northern Atlantic 

Lars Wiesenberg, Sunke Schmidtko, and Thomas Meier

Microseism is one of the biggest parts of ambient seismic noise and has a huge effect on seismic measurements on almost every regular broad band seismometer, but especially in coastal areas. Generally, microseism describes the interaction of water waves and the seafloor. Its variation over time is from huge interest. It is often used on short-period scales to investigate local weather effects, like storm events or seasonal variations. In this work, we are investigating variations in the microseism of the Northern Atlantic on multiannual scales. For that reason, we utilize up to 50 years of seismic data from several onshore stations across Central and Northern Europe. The focus is on secondary microseism of the Northern Atlantic which is normally sensitive at periods of ≈10 to 5 s. It is estimated over two-hour segments of seismic data, separately. Secondary microseism is post processed to eliminate effects of data gaps or outliers before lowpass filtering for the periods of interest. Besides of a dominant peak at one year period, secondary microseism shows also distinct variations at several year of periods. These variations clearly correlate with the North-Atlantic-Oscillation Index (NAO), not only visually, but also quantitatively and might therefore be relatable to climate variations affecting the North Atlantic.

How to cite: Wiesenberg, L., Schmidtko, S., and Meier, T.: (Multi)annual variations in the microseism of the Northern Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17787, https://doi.org/10.5194/egusphere-egu24-17787, 2024.

Predicting bedload transport is a key element of water-related hazard assessment and hydraulic engineering applications. However, knowledge of bedload transport processes remains limited, particularly in steep mountain streams. Previous studies have revealed that bedload transport rates in mountain streams exhibits a large spatio-temporal variability for given flow conditions. This results from the direct influence of streambed structure on bedload transport, where sediment movement, in turn, interacts with streambed evolution. Furthermore, variations in sediment availability contribute to the spatio-temporal bedload variability. The complex interactions between water flow, bedload transport, and bed structure are not yet fully understood. In this work, systematic flume experiments were conducted to investigate the acoustic signal responses of impact plate geophone systems generated by bedload particles impacting on the flume bed during experimental flows in the transitional regime. The experiments varied in the grain size distribution of the transported particles and the bed material, and the compactness and the water content of the flume bed. Geophones were installed on the underside of steel plates flush with the flume bed both upstream and downstream to effectively capture the changes in vibration signals generated by the moving bedload mass impacting on the bed. Triaxial force sensors were utilized to measure the impact forces of the bedload particles on the bed material layer. Pore-water pressure sensors were embedded at different depths in the bed material to measure the change in pore-water pressure in the bed under the influence of the bedload mass. Flow velocities and depths of the moving bedload mass were recorded using a binocular high-speed camera and were analyzed with an image processing method. The observed vibration signals and fluctuating forces were used to calculate the characteristic parameters of bedload transport using calibrated relationships and seismic theory. In addition, a high-precision Digital Elevation Model (DEM) of the bed was constructed using the photography and 3D modeling techniques. The results of this work show that geotechnical material parameters of the bed such as compactness, compression modulus, and grain size distribution may affect the changes of bed structure caused by bedload transport This in turn influences the spatio-temporal variability of the transport rate. The findings of this work may help to explain the variability of the bedload transport process in mountain streams.

How to cite: Chen, Z., Badoux, A., and Rickenmann, D.: Quantitative measurement of bedload transport variability with acoustic monitoring systems: Insight from controlled laboratory flume experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18262, https://doi.org/10.5194/egusphere-egu24-18262, 2024.

EGU24-18668 | Posters on site | GM2.1

Bedload sediment dynamics in two contrasting alpine glacier headwater catchments 

Simon Cook, Darrel Swift, Kristen Cook, Christoff Andermann, Michael Dietze, William Wenban, and Rory White

Glaciated landscapes are showing an amplified reaction to global climate change. Glacial streams are the primary conveyor belts of the incipient sediment cascade, implementing the export of glacially scoured sediment to lower reaches, where the exported sediment controls fluvial geometry, valley floor evolution and ecosystem functioning, water reservoir lifetime and energy production in several alpine countries. Despite that importance, especially of the coarse bedload fraction, there is a striking lack of knowledge about the timing, magnitude and control factors of bedload flux in glacial streams. This is predominantly due to the difficulties to obtain such flux data by classic empirical approaches that require direct in-stream sampling. Here, we pursue a seismic approach to bedload transport quantification, where geophysical sensors are installed along the banks of glacial streams that continuously record ground motion caused by both the turbulent flow of the stream and coarse particle impact on the river bed. We installed small geophone networks along straight reaches of streams draining the glacierised catchments of Oberaargletscher and Steingletscher in Switzerland and recorded the target signals for several days in August 2022, when the melt driven, diurnal river stage fluctuated significantly. River level, turbidity and stream geometry were also observed. Ground parameters for the inverse seismic-model approach were determined using an active seismic survey. We present results of the instrumentation concepts, parameter estimation and data inversion. This allows a discussion of the temporal variability, non-linearity and site-specific nature of hydraulic and sediment transport patterns in catchments where sediment export is dominated by glacial processes.

How to cite: Cook, S., Swift, D., Cook, K., Andermann, C., Dietze, M., Wenban, W., and White, R.: Bedload sediment dynamics in two contrasting alpine glacier headwater catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18668, https://doi.org/10.5194/egusphere-egu24-18668, 2024.

EGU24-20192 | ECS | Orals | GM2.1

Boulder-induced Turbulence Drives Shift in Seismic Frequency 

Ron Nativ, Jonathan Laronne, Jens Turowski, Jui-Ming Chang, Ci-Jian Yang, Niels Hovius, Wen-Sheng Chen, and Wen-Yen Chang

Turbulent flows capable of mobilizing sediments, despite being studied over the past 100 years, continue to constitute an elusive process. In environmental seismology, seismic waves generated by the interplay of surface processes and the Earth offer a key to unraveling the dynamics of river processes. We studied the seismic signals emitted during floods in two tributaries with large boulders. Early findings indicated an unusually high dominant seismic frequency, reaching 2-4 times the frequency observed in nearby channels with smoother beds. Consistent anomalous high-frequency content during times without sediment transport prompts our hypothesis that turbulence is the key process driving the frequency shift. We hypothesized that the most energetic turbulent eddies, dominating the signal, decrease in size in response to the boulder-influenced constrained flow geometry, and we argue that this effect possesses a first-order control on the frequency shift. A frequency scaling law with boulder spacing, approximating boulder-induced eddy size, shows good agreement with our field data. The dynamics of the eddies under changing flow velocity are well predicted by a power law function of seismic frequency with water depth. The trend breaks at the onset of bedload transport, indicating that energy is dissipated through the partitioning between turbulence and sediment transport. Our study emphasizes that seismic frequency effectively records the dominant morphology and fluvial processes, revealing the intricate interaction between roughness and seismic energy.

How to cite: Nativ, R., Laronne, J., Turowski, J., Chang, J.-M., Yang, C.-J., Hovius, N., Chen, W.-S., and Chang, W.-Y.: Boulder-induced Turbulence Drives Shift in Seismic Frequency, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20192, https://doi.org/10.5194/egusphere-egu24-20192, 2024.

SM6 – Seismic Imaging (from near-surface to global scale, incl. methodological developments)

EGU24-753 | ECS | Orals | SM6.1

Surface-wave attenuation and phase-velocity maps using the AlpArray seismic network: implications for crustal heterogeneity 

Henrique Berger Roisenberg, Fabio Cammarano, Lapo Boschi, Fabrizio Magrini, and Irene Molinari

The Apennines-Alps-Carpathians-Dinarides orogenic belt results from complex geodynamic processes, manifesting as pronounced crustal heterogeneities across much of Europe. This geotectonic setting has been extensively studied in order to unveil the processes underlying its formation and evolution. Several geophysical methods such as deep reflection and refraction seismic surveys, receiver function analysis, gravimetry studies, local earthquake tomography, and more recently ambient-noise tomography have been applied to this region. The dense and homogeneous coverage of recently deployed seismic stations in this area, such as the AlpArray Seismic Network, offers unprecedented seismic coverage enabling high-resolution tomographic imaging. However, one of the main challenges when studying the Earth’s crust is to interpret unambiguously the role of fluids, composition, and temperature. Seismic velocities are not sufficient alone for resolving these properties. On the other hand, seismic wave attenuation is more sensitive to the physical conditions of the crust and mapping its variations is indeed important for a better understanding of the dissipative mechanisms which act in the lithosphere. Therefore, we decided to apply to our study region a novel method, that is capable of sampling the crust at high resolution compared to other earthquake-based methods, to estimate attenuation from the seismic ambient noise. We also performed new phase-velocity measurements with unprecedented resolution, to complement our attenuation measurements, providing a more robust interpretation of the area.

Two years of continuous data from 749 broadband seismic stations, densely deployed throughout the Alps-Apennines-Carpathians-Dinarides orogenic system, were used to compute Rayleigh-wave phase velocities and attenuation coefficients from seismic ambient noise. The excellent seismic coverage allows us to measure phase velocities at shorter surface-wave periods compared to previous studies (down to 3s). Preliminary results indicate that the spatial variations in Rayleigh-wave velocities correlate with known geological features, such as the relatively low-velocities of Cenozoic basins (Po’ plain, Molasse basin, Rhine graben) and the relatively high-velocity crust (Apennines, Alps, Bohemian massif, Dinarides). Attenuation maps between 3 and 20 seconds were computed and are the first of their kind for the study region. Preliminary results show a clear anomaly pattern of seismic attenuation related to the Po’ plain and the Apennines. The correlation between attenuation coefficients and phase velocities presents an intriguing pattern, still under debate, that is consistent with what has been observed in previous studies using the same methodology in the United States. Combining the new constraint on seismic attenuation to phase velocity results enables us to improve interpretation on temperature and composition of the crust, including the role of fluids. These results also provide an indirect constraint on the current rheological properties of the crust.

How to cite: Berger Roisenberg, H., Cammarano, F., Boschi, L., Magrini, F., and Molinari, I.: Surface-wave attenuation and phase-velocity maps using the AlpArray seismic network: implications for crustal heterogeneity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-753, https://doi.org/10.5194/egusphere-egu24-753, 2024.

EGU24-1075 | ECS | Orals | SM6.1

3D crustal shear wave velocity structure in northeast India from joint inversion of receiver function and Rayleigh wave group velocity 

Aakash Anand, Kajaljyoti Borah, Sourav Mandal, and Dipok Bora

In this study, we computed the Rayleigh wave group velocity tomography of northeast India (NEI) to a higher resolution of 2°×2° for a 15 to 80-second period. The group velocity dispersion obtained from the tomography was inverted using two ways – (a) inversion for every 0.2 degree of the study area to estimate the 3-D shear wave velocity, which overcome the constraint of sparse seismic station coverage in a few segments of the study region,(b) Joint Inversion of the computed dispersion with the  Receiver Function from 22 stations spread across NEI, covering all major geological features, to deduce the shear wave velocity structure. Moho geometry showed significant variation in the region, with IBR (~ 43–62 km) and Himalaya (~ 40–53  km) showing deeper Moho; Assam Valley (~ 33–38 km), Shillong Plateau (~ 30–32 km) and Bengal Basin (~ 37 km) being comparatively shallower. Moho beneath Shillong Plateau is found to be the shallowest (~ 30 km). For stations, TAWA, RUPA, ITAN, and TZR significant back azimuthal variation in shear wave velocity structure is observed. The average crustal shear wave velocity Vs beneath Shillong Plateau (Vs ~ 3.16-3.27 km/s) and Assam Valley (Vs~3.14-3.35 km/s) is found to be lower than the average crustal Vs (~3.75 km/s) beneath the Indian shield. Shillong Plateau and proximal Assam Valley stations showed low uppermost mantle shear wave velocity (Vsn ~ 4.0-4.1 km/s), which might be attributed to factors such as rock composition, grain geometry, higher temperature or the presence of partial melt.The eastern segment of the Assam Valley is not in conformity with the western segment, as evident from the DIBR station at the eastern edge of Assam Valley which doesn’t show this decreased Vsn.Thus indicating prima facia towards different geodynamics along the eastern and western segment of the Assam valley, which might be attributed to the role played by the uplifted, uncompensated Shillong Plateau and/or the Kopli Fault. Relatively higher Vsn (~ 4.2-4.6 km/s) observed beneath the IBR stations can be associated with the deeper moho (~ 43–62 km). Thus the improvised Moho geometry, crustal velocities structure, Vsn could be crucial in understanding the geodynamics of the region and could provide better constraint on the quantification of seismic hazards in the region.

How to cite: Anand, A., Borah, K., Mandal, S., and Bora, D.: 3D crustal shear wave velocity structure in northeast India from joint inversion of receiver function and Rayleigh wave group velocity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1075, https://doi.org/10.5194/egusphere-egu24-1075, 2024.

EGU24-2333 | ECS | Posters on site | SM6.1

A perfectly matched layer for first- and second order time-domain wave equation 

Arash Rezaei Nevisi and Thomas Bohlen

The simulation of wave propagation is an essential part of several cutting-edge geophysical techniques, such as Full-Waveform Inversion (FWI) and Reverse Time Migration (RTM). Due to constraints in computational resources and memory capacity, wave propagation simulations are typically conducted within truncated media. In order to effectively absorb unwanted reflected waves at the boundaries of these simulations, specialized boundary layers are implemented. The Perfectly Matched Layer (PML) is widely acknowledged as a commonly employed technique in the field of seismology for its effectiveness as an absorbing boundary layer.

Conventional PML suffers from some well-known drawbacks, including instabilities in long-time simulations and inadequate absorption in cases involving grazing incident and evanescent waves. These limitations can hinder the accuracy and reliability of numerical modeling of seismic wave propagation. CFS-PML (Complex Frequency Shifted Perfectly Matched Layer) addresses the limitations of traditional PML approaches and offers improved absorption and stability in numerical modeling. The CPML technique is widely regarded as highly effective when applied in the context of first-order systems of equations. Nevertheless, this method is not specifically designed for application in second-order displacement formulations. In such cases, alternative numerical techniques, such as finite-element methods and spectral-element methods, have demonstrated greater suitability. Previous studies have primarily focused on expanding the first-order formulation to the second-order.

Another approach that to incorporate the CFS technique in the wave conventional PML is using ADEs (auxiliary differential equations). The ADE-CFS-PML method incorporates ADEs to drive wave equations equipped with PML in a more simple and straightforward manner than recursive convolution approach.

Our contribution is to develop a general scheme that not only satisfies the first-order (velocity-displacement) staggard-grid system, but can easily incorporate in second-order wave equation and address the drawbacks of conventional PML effectively. The proposed scheme demonstrates comparable performance to CPML while avoiding the need for recursive convolution operations. Instead, it introduces the PML into the wave equation through ADEs, which is easily implementable, efficient, and compatible with existing codes and simplifies the implementation process.

Our proposed scheme for implementation of the ADE-CFS-PML method has been tested on benchmark models with complex geological structures and has shown excellent performance by demonstrating its effectiveness in absorbing grazing incident waves and maintaining stability in long-term simulations. It effectively dampens grazing incidence waves and remains stable for long-term simulations. The scheme is suitable for large 3D models due to its on-the-fly computation capabilities, and its memory efficiency, since the coefficients are only varying in the PML area and are constant in the interior media.

Overall, it offers an improved method for numerical modeling in various media and PDE orders, while addresses the limitations of traditional PML approaches. The proposed scheme demonstrates enhanced absorption and stability, making it a valuable tool for seismic wave propagation studies and other applications in geophysics and physics.

How to cite: Rezaei Nevisi, A. and Bohlen, T.: A perfectly matched layer for first- and second order time-domain wave equation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2333, https://doi.org/10.5194/egusphere-egu24-2333, 2024.

EGU24-3393 | Posters on site | SM6.1

Preliminary Results of P-wave tomographic imaging beneath Sulawesi, Indonesia 

Pepen Supendi, Nicholas Rawlinson, Jifei Han, Sri Widiyantoro, and Dwikorita Karnawati

The island of Sulawesi is located within a complex tectonic region at the confluence of the Eurasian, Indo-Australian and Philippine plates. The recent geological history in the area reflects the ongoing subduction, extension, obduction, and collision of continental fragments. The island consists of four elongated arms (the north, east, southeast, and southern arms) that are composed of distinct lithological assemblages. Based on local and regional earthquake travel-time tomography, we present a new 3-D P-wave velocity model of the crust and upper mantle beneath Sulawesi. We used the Fast Marching Tomography (FMTOMO) package to retrieve 3-D P-wave velocity variations relative to a 1-D starting velocity model based on ak135. The catalogue and phase data were taken from the Agency for Meteorology, Climatology, and Geophysics (BMKG) of Indonesia for the period 2018 through to 2023, recorded by 126 seismic stations in Sulawesi and its neighbourhood. Our preliminary results reveal clear evidence of subducted slabs as indicated by high-velocity anomalies penetrating into the mantle along the Molucca Sea Collision Zone and to the north of Sulawesi; we also see a low-velocity anomaly beneath volcanoes located at the eastern end of the North Arm of Sulawesi.

How to cite: Supendi, P., Rawlinson, N., Han, J., Widiyantoro, S., and Karnawati, D.: Preliminary Results of P-wave tomographic imaging beneath Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3393, https://doi.org/10.5194/egusphere-egu24-3393, 2024.

EGU24-4249 | ECS | Posters virtual | SM6.1

Africa's Lithospheric Architecture with Multi-mode Body Wave Imaging 

Jean-Joel Legre and Tolulope Olugboji

Africa’s lithosphere hosts the longest-lived cratons on our planet and records a rich and diverse tectonic history: plate subduction to the North, a long rift system in the East, the super swell in the South, and a record of continental breakup to the West. However, gaps remain in our current efforts to study its lithospheric layering due to sparse coverage and noisy short-term seismic deployments. Here, we present a body-wave dataset and model assessment products for investigating Africa’s lithosphere (ADAMA). We address the challenge of lithospheric imaging on the continent using sparse and noisy teleseismic body wavefields, i.e., receiver functions and SS precursors. The latter extends lithospheric illumination in regions without station coverage. In both cases, we explore novel denoising approaches: (1) CRISP-RF (Clean Receiver Function Imaging with Sparse Radon Filters), which uses sparse Radon transforms to interpolate the sparse receiver function data and eliminate incoherent noise, and (2) FADER (Fast Automated Detection and Elimination of Echoes and Reverberations), which deconvolves thin-layer reflections buried in long-period SS precursors. We improve constraints on bulk crustal structure and lithospheric layering, e.g., from H-k stacking, following CRISP-RF denoising. We extend spatial sampling and detections of lithospheric layering by jointly interpreting receiver functions and SS precursors following cepstral deconvolution of long-period SS precursor waveforms. Our final model, ACE-ADAMA-BW (Africa’s Continental Layering Evaluated with ADAMA’s Body Waves), will improve 3-D resolution of lithospheric layering spanning the cratons (West Africa, Tanzania, Congo, Kaapvaal, Zimbabwe), rifts (Gourma, East African Rift System) and basins (Taoudeni, Goo, Congo) of Africa.

How to cite: Legre, J.-J. and Olugboji, T.: Africa's Lithospheric Architecture with Multi-mode Body Wave Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4249, https://doi.org/10.5194/egusphere-egu24-4249, 2024.

EGU24-4339 | ECS | Posters on site | SM6.1

Crust and Upper Mantle S Wave Velocity Structure in Turkey Based on Ambient Noise Tomography 

Peng Wang, Juqing Chen, and Xiaofei Chen

Turkey belongs to the initial collision stage of the Tethys tectonic domain. The western part of Turkey experiences the subduction of the African plate, while the eastern part suffers the collision with the Arabian plate. In addition, extensive volcanic activity and tectonic uplift are also distributed in this region. To understand the relationship between these surface phenomena and underground structure, it is necessary to obtain reliable and precise velocity structure in the region. We collect continuous waveform data from 688 stations in the region and obtain Rayleigh wave dispersion curves for periods between 4 and 100 s based on frequency-Bessel transform dispersion analysis. We then perform quasi-Newton inversion to calculate the S wave velocity structure between 0 and 200 km. Subsequently, the reliability of the results is verified using a model validation method based on waveform simulation. Our results elucidate the layered structure and distribution of the lithosphere asthenosphere boundary beneath the region, which is of great significance for a profound understanding of the tectonic evolution process in the region. At the same time, it also provides reliable data support for subsequent waveform inversion and earthquake mechanism research in the region.

How to cite: Wang, P., Chen, J., and Chen, X.: Crust and Upper Mantle S Wave Velocity Structure in Turkey Based on Ambient Noise Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4339, https://doi.org/10.5194/egusphere-egu24-4339, 2024.

EGU24-4417 | ECS | Posters on site | SM6.1

Teleseismic Traveltime Tomography of Sulawesi, Indonesia 

Lintang Kesumastuti and Simone Pilia

Located in the eastern region of Indonesia, Sulawesi exhibits a distinctive K-shaped configuration due to the Cretaceous to present day tectonic interaction of the Indian-Australian, Sunda, and Philippine plates. This tectonic interaction has delineated two main tectonic provinces of Sulawesi: the Western Sulawesi Province, including the South and North Arms with large plutono-volcanic rocks generated during the Paleogene, and the Eastern Sulawesi Province, comprising the East and Southeast Arms characterized by the ophiolite complex and metamorphic belt emerging after the Early Miocene collision between the northern part of the Australian continental plate and the North Arm of Sulawesi. The present configuration of Sulawesi is attributed to the Sulawesi Orogeny, the attachment of eastern Sulawesi and Buton-Tukang Besi as well as Banggai-Sula Islands by subduction, accretion, and collision that led to the development of two major active tectonic structures in Sulawesi: the left-lateral Palu-Koro strike-slip fault to the west and the Celebes Sea subduction zone to the north.

We present preliminary P-wave tomographic images of the crust and upper mantle beneath Sulawesi, obtained by exploiting teleseismic earthquake data. Passive-seismic data are recorded by approximately 89 seismic stations of the Agency for Meteorology, Climatology, and Geophysics (BMKG) network running from January 2020 to July 2023. We employ an adaptive stacking technique to extract relative P-wave traveltime residuals from nearly a thousand teleseismic events recorded across the network. The relative arrival-time residuals from first-arriving, core and reflected P phases are then utilized to map 3-D P-wave perturbations using an inversion technique implemented in FMTOMO.

The final tomographic model reveals several distinct features, including a south-dipping, high-velocity anomaly beneath northern Sulawesi that we associated to the subducting slab of the Celebes Sea. 

How to cite: Kesumastuti, L. and Pilia, S.: Teleseismic Traveltime Tomography of Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4417, https://doi.org/10.5194/egusphere-egu24-4417, 2024.

EGU24-4597 | Posters on site | SM6.1

The SHIELD’21 deep seismic profile across Ukraine 

Tomasz Janik, Vitaly Starostenko, Anna Murovskaya, Wojciech Czuba, Piotr Środa, Tamara Yegorova, Paweł Aleksandrowski, Oleksandra Verpakhovska, Katerina Kolomiyets, Dmytro Lysynchuk, Tetiana Amashukeli, Dariusz Wójcik, Victor Omelchenko†, Olga Legostaeva, Dmytro Gryn, and Serhii Chulkov

Carried out in 2021, the wide-angle reflection-refraction (WARR) SHIELD’21 profile crosses, from SW to NE, the main tectonic structures of Ukraine. It has targeted the crustal and uppermost mantle structure underlying the Archaean and Paleoproterozoic crystalline complexes of the Ukrainian Shield and the adjacent platformal areas. To the SW of the Ukrainian Shield, the crystalline basement is overlain by Vendian through Paleozoic strata of the Volhyno-Podolian Homocline, plunging at its SW end below the Carpathian belt and its Neogene foredeep. To the NE, the crystalline cratonic basement is covered by Devonian and Carboniferous successions of the Dnieper-Donets rift basin. The ~650 km long SHIELD’21 profile is a northeasterly extension of the RomUkrSeis profile carried out in 2014 and running from Romania to the southwestern part of the Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile provided high-quality seismic records. The main recorded seismic waves are refractions of P- and S-waves in the sedimentary layer, crystalline basement, middle and lower crust and uppermost mantle, as well as reflections from crustal boundaries, the Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times allowed us to build a velocity model not only for the P-, but also for S-waves and Vp/Vs ratio. The model reveals that over the entire thickness of the crust, the Vp in the crystalline basement nowhere exceeds 6.85 km/s, which – particularly in the context of the lower crust – represent low values, but similar to those known from the other nearby deep seismic profiles (e.g. TTZ-South, and DOBRE-4). Patterns of crustal boundaries combined with velocity differences across them, permit hypothesizing on Proterozoic large-scale subhorizontal extensional faulting in the crystalline upper crust. A prominent dome-like structure in the lower crust may represent a longitudinal section of a major duplex resulting from Paleoproterozoic overthrusting to the NW, comparable to those interpreted on the TTZ-South profile (Janik et al., 2022). The Moho shows strong variability of a depth (~32-50 km), and is underplated by lenticular horizontal ca. 10 km thick high velocity mantle bodies with Vp>8.36 to 8.40 km/s, also present deeper in the upper mantle of Vp between 8.15 and 8.25 km/s. The Moho is prominent and marked by the Vp velocity contrast of c. 1.4 to 1.8 km/s between the upper mantle and lower crust. It is characteristically undulated with successive downward and upward bends, with the amplitude locally exceeding 15 km and wavelength of the order of 150 to 250 km. A similar Moho undulation form was described along the DOBRE-4 profile and was interpreted as Mesozoic(?) buckle mega-folds (Starostenko et al, 2013).

 

  • Janik, T. et al. (2022). TTZ-South, Minerals, 12, 112, doi.org/10.3390/min12020112
  • Starostenko, V. et al. (2013). DOBRE-4, Geophys. J. Int. 195, 740–766, doi.10.1093/gji/ggt292
  • Starostenko, V. et al. (2020). RomUkrSeis, Tectonophysics, 794, 228620, doi.org/10.1016/j.tec to.2020.228620

How to cite: Janik, T., Starostenko, V., Murovskaya, A., Czuba, W., Środa, P., Yegorova, T., Aleksandrowski, P., Verpakhovska, O., Kolomiyets, K., Lysynchuk, D., Amashukeli, T., Wójcik, D., Omelchenko†, V., Legostaeva, O., Gryn, D., and Chulkov, S.: The SHIELD’21 deep seismic profile across Ukraine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4597, https://doi.org/10.5194/egusphere-egu24-4597, 2024.

EGU24-4699 | ECS | Posters on site | SM6.1

Full-waveform inversion of the OBS data from the Japan Trench area affected by the petit-spot volcanism 

Andrzej Górszczyk and Yousef Amirzadeh

Petit-spot volcanoes, recently discovered volcanic structures, have significantly enriched our understanding of intraplate volcanism, particularly occuring in response to plate flexure during subduction. Discovery of these volcanoes in the vicinity of the Japan Trench marked a milestone showcasing the profound impact of tectonic processes on the intraplate volcanism and supporting the existence of small-degree melts at the base of the lithosphere.

One of the key question marks surrounding the petit-spot volcanoes is the extraction and ascent of melts to the seabed that would required development of lithospheric-scale fractures. As for now, no physical model has been devised to validate this hypothesis. The complexities involved in understanding the intricate genesis of petit-spot volcanism underline the need for its further investigation with innovative approaches.

In 2017 Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out an active seismic survey to investigate the geological setting impacted by petit-spot volcanism in the trench-outer-rise region of the Japan Trench. During the survey 40 ocean-bottom seismometers (OBS) were deployed at 2 km intervals along an 80-km long 2D receiver profile, coupled with the firing of 983 air-gun shots at 100 m intervals along an extensive 100-km shooting profile. The resulting dataset creates an opportunity for in-depth analysis of subsurface and holds the potential for constructing a high-resolution velocity model with full-waveform inversion (FWI).

In this work we use first arrival traveltime tomography and time-domain acoustic FWI to reconstruct P-wave velocity model at the wavelet resolution. We push the inversion up to 8 Hz, which allows us to delineate sharp velocity contrasts within the incoming plate that are likely related to the petit-spot volcanism phenomenon occurring in this region. The resulting velocity model promises to contribute to our comprehension of intraplate volcanism, offering a perspective on the broadening of our understanding the underlying processes causing intraplate volcanism.

How to cite: Górszczyk, A. and Amirzadeh, Y.: Full-waveform inversion of the OBS data from the Japan Trench area affected by the petit-spot volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4699, https://doi.org/10.5194/egusphere-egu24-4699, 2024.

EGU24-4874 | ECS | Posters on site | SM6.1

Earth structure from P-wave coda autocorrelation using particle swarm optimization 

Jinju Zhou and Hrvoje Tkalčić

Teleseismic P-wave coda autocorrelation has been increasingly applied to subsurface structure detection and has shown potential for inverting subsurface velocity models. However, it has yet to be extensively investigated in terms of inversion and practical field data application strategy and initial model dependence. Compared with the receiver function, teleseismic P-wave coda autocorrelation can be used to invert the subsurface velocity model using only single-component data. This will significantly improve the application areas and reduce the costs of passive source seismology methods. Here, we propose a new inversion scheme for teleseismic P-wave coda autocorrelation based on the particle swarm optimization.

 

The teleseismic P-wave coda autocorrelations are binned according to the ray parameters and then stacked to construct the observed waveforms. Our featured method, the particle swarm optimization, is then used to find the velocity model that minimizes the fitting error to the observed waveforms. It is a global optimization algorithm that simulates the feeding of a natural population. Each particle in the population has two parameters: position and velocity. The optimization space is a multi-dimensional space comprising various stratum thicknesses and velocities. Thus, a particle's position in the optimization space represents a set of parameters for the subsurface velocity distribution. We assume that the maximum number of layers within the crust above the mantle (a homogeneous half-space) is 10. The thickness of each layer ranges from 0 to 10 km, and if the thickness of a layer is 0 km, this corresponds to a reduction of one layer. The method thus allows the number of layers within the crust to be obtained by inversion without a priori information. Together with the P-wave velocity of each layer (including the mantle), the optimization space is 21-dimensional.

 

While we still assume horizontal layers, our method is capable of inverting a wide range of crustal models, including those containing surface sedimentary layers, upper crustal low-velocity layers, and lower crustal low-velocity layers, among others. Notably, the method does not require prior knowledge of the number of layers in the model, making it highly robust. Furthermore, field data tests demonstrate the method's potential for practical application.

How to cite: Zhou, J. and Tkalčić, H.: Earth structure from P-wave coda autocorrelation using particle swarm optimization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4874, https://doi.org/10.5194/egusphere-egu24-4874, 2024.

EGU24-4967 | ECS | Posters on site | SM6.1

The mid-crustal low-velocity zones in Iceland revealed by multimodal surface wave 

Sen Zhang and Xiaofei Chen

The evolution of the Icelandic crust has been significantly influenced by magmatism associated with the Icelandic hotspot and the Mid-Atlantic Ridge. The spreading mid-ocean ridge and fissure swarms create favorable conditions for magma migration, feeding active volcanic activities on the surface. Previous receiver function studies have reported the mid-crustal low-velocity zone (MCLVZ) as a crucial characteristic. However, it is absent in the previous model representing the overall features of Iceland. Recently, the frequency-Bessel transform method (F-J method) has been proposed, enabling the effective extraction of multi-mode dispersion curves from ambient noise data. We collect continuous seismic data from the HOTSPOT network in Iceland for 2 years, as well as other supplementary data, covering the main regions of Iceland. Using the F-J method, we extract multi-mode dispersion curves of 0.02-0.4 Hz. Subsequently, we obtain an Icelandic average Vs model, including an MCLVZ with an amplitude of 3%. Moreover, through the analysis of local region data, we identify MCLVZs in the western fjords and the central volcanic zone of Iceland. Our results supplement the previously lacking MCLVZ feature in the Icelandic average structure, suggesting the presence of MCLVZs in both volcanic and non-volcanic regions of Iceland. The elevated temperature and partial melting associated with the volcanic activity may be not the sole reasons for MCLVZs. Further research on the distribution of MCLVZs in Iceland is needed in the future.

How to cite: Zhang, S. and Chen, X.: The mid-crustal low-velocity zones in Iceland revealed by multimodal surface wave, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4967, https://doi.org/10.5194/egusphere-egu24-4967, 2024.

EGU24-5241 | ECS | Posters on site | SM6.1

Advancing seismic imaging: Fresnel volume migration in anisotropic and anelastic media 

Niklas Kühne, Felix Hlousek, Stefan Buske, Hui Ding, and Maximilian Schulze

Advanced seismic imaging techniques play a crucial role in generating reliable, high-resolution subsurface images across diverse applications, such as exploring hydrocarbons and minerals, characterizing geothermal reservoirs, and selecting sites for radioactive waste disposal. In this study we present the extension of the seismic imaging technique, Fresnel volume migration (FVM), to anisotropic and anelastic media.

A wavefront construction method for 3D anisotropic (TTI) velocity models was employed to compute the Green's functions required for FVM. This wavefront construction method was further developed by calculating complex traveltime fields (t*) for predefined quality factor (Q) models, describing the anelastic attenuation of seismic waves. Subsequently, these resulting traveltime fields (t*) were used in the migration process to facilitate the corresponding anelastic compensation of the amplitudes.

The developed method was applied to synthetic 2D data and a real 3D dataset obtained over the "Asse" salt structure in Lower Saxony, Germany (2020). The migration with anelastic compensation demonstrated a correct enhancement of amplitudes in the synthetic data. Furthermore, the application of the anisotropic FVM to the real 3D dataset resulted in a significant improvement in the imaging quality of reflectors throughout the area surrounding the salt structure.

Our findings underscore the pivotal role played by considering both anisotropy and anelastic attenuation in complex 3D models for achieving a reliable and high-resolution subsurface image using the further developed FVM approach. The latter lays the foundation for subsequent quantitative analyses of reflectors and hence supporting dependable geological interpretations.

How to cite: Kühne, N., Hlousek, F., Buske, S., Ding, H., and Schulze, M.: Advancing seismic imaging: Fresnel volume migration in anisotropic and anelastic media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5241, https://doi.org/10.5194/egusphere-egu24-5241, 2024.

EGU24-5347 | ECS | Posters on site | SM6.1

Investigating the Subsurface of the Iranian Plateau using Adjoint Tomography: A 3D Seismic Velocity Model 

Abolfazl komeazi, Ayoub Kaviani, and Georg Rümpker

A 3D seismic velocity model of the Iranian plateau was constructed using adjoint tomography. The initial model used in this study is taken from a previous adjoint noise tomography investigation in the region, and was refined through the inversion of waveforms recorded at seismic broadband stations from 320 local/regional earthquakes for which a Centroid-Moment-Tensor (CMT) has been computed. The synthetic waveforms were calculated using the spectral-element method (SEM) through a mesh of 12 million grid points representing the Iran region. The model parameters were iteratively updated by Newton's method, using misfit and Hessian kernels to minimize the difference between observed and synthetic waveforms. The forward and adjoint simulations were computed on the HRL GPU-cluster in Frankfurt, requiring a total of 6720 simulations and approximately 13,000 node hours to achieve the final model after 11 iterations. Comparison of the synthetic waveforms produced by the proposed model to the observed waveforms for a subset of selected earthquakes indicates improved fit in the period range of 10-50 seconds confirms the model's ability to accurately predict actual waveforms. The identification of previously undetected anomaly features beneath the Iranian plateau was also observed, which could be attributed to geological features with sufficient data coverage and resolution.

How to cite: komeazi, A., Kaviani, A., and Rümpker, G.: Investigating the Subsurface of the Iranian Plateau using Adjoint Tomography: A 3D Seismic Velocity Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5347, https://doi.org/10.5194/egusphere-egu24-5347, 2024.

The Southeast Coastal Areas of China (SCAC) is part of the Cathaysia block, the convergence area of the Eurasian, Pacific and India-Australian plates. The Cathaysia and the Yangtze blocks collided and merged into the South China block in the Neoproterozoic. These areas have experienced complex geological evolution and multiple periods of intense magmatic events since the Paleozoic, mainly manifested as a large number of Paleozoic and Mesozoic granitic rocks and Cenozoic mafic magmatism. Large-scale structural deformation caused by emplacements is very strong to the stratum reconstruction, forming a series of faults with different scales and directions. The development of large-scale fault systems has led to the potential risk of strong earthquake disasters in the region. In addition, the urban agglomeration with its dense population, is located in SCAC. Thus, seismic risk assessment and seismic research are very urgent and critical. The high-resolution crustal structure model is especially necessary for understanding the geological processes and seismic hazards in and around the areas. We collected ambient noise data from fixed and temporary seismic stations in the SCAC, and used the frequency-Bessel transform (F-J) method to extract Rayleigh wave dispersion curves and performed multimodal ambient noise dispersion curves inversion. We constructed a 3D high-resolution S-wave velocity model for this area. Specifically, we extracted reliable multimodal dispersion curves (up to the 8th higher-order in some sub-areas) with a broad frequency band range (0.03Hz-0.65Hz). Preliminary results show a widespread mid-crustal low-velocity zone, and we will further discuss the crustal structural anomalies and their related tectonic implications and evolution mechanisms.

How to cite: Li, H., Chen, X., and Cai, H.: Shear‐Wave Velocity Structure beneath Southeast Coastal Areas of China from the F-J Multimodal Ambient Noise Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5355, https://doi.org/10.5194/egusphere-egu24-5355, 2024.

EGU24-6980 | ECS | Posters on site | SM6.1

JointNet: A multimodal deep-learning-based approach for joint inversion of Rayleigh wave dispersion and ellipticity 

Xiang Huang, Ziye Yu, Weitao Wang, and Fang Wang

Joint inversion of multiple datasets is an effective approach for high-precision imaging of the crustal and upper mantle velocity structures. In this study, we propose a novel deep learning-based method called JointNet for jointly inverting Rayleigh wave phase velocity and ellipticity data to obtain high-precision shear wave velocity models. JointNet, a multimodal deep neural network, is designed to analyze these independent physical parameters and generate outputs that include a velocity model and layer thicknesses. The network is trained using a large dataset of randomly generated 1D models along with their corresponding calculated phase velocities and ellipticities. Our tests using synthetic and observed data demonstrate that JointNet produces inversion results that are highly comparable to those obtained through a Markov Chain Monte Carlo-based method. This indicates that the network effectively captures the nonlinear relationship between phase velocity, ellipticity data, and the 1D Vs model. In addition, JointNet eliminates the need for prior information input and significantly reduces the computational time for inversion compared to traditional nonlinear methods. Training using synthetic data based on a global model ensures its wide applicability in various regions with different velocity structures. Furthermore, JointNet can be readily adapted to incorporate additional datasets, such as receiver functions, to further enhance imaging resolution. Essentially, JointNet can also function as a novel inversion framework for more extensive model inversion studies.

How to cite: Huang, X., Yu, Z., Wang, W., and Wang, F.: JointNet: A multimodal deep-learning-based approach for joint inversion of Rayleigh wave dispersion and ellipticity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6980, https://doi.org/10.5194/egusphere-egu24-6980, 2024.

EGU24-7001 | ECS | Posters on site | SM6.1

Ambient noise tomography of Mount Isa, Northern Queensland in Australia 

Ao Chang and Craig O'Neill

The Mount Isa region in Northern Australia is a world-class mining complex, yielding significant combined outputs of lead, silver, copper and zinc. This zone consists of sedimentary layers from lower to middle Proterozoic era with a mix of bimodal volcanic rocks and plutonic formations. A significant crustal structure, known as the Gidyea Suture zone, exists within the Mt Isa succession, and its geological history and association with the mineralisation at Mt Isa are unclear.  Previous surveys highlighted the distinct geophysical characteristics of region, in terms of magnetic and gravity anomalies, magnetotellurics conductivity anomalies, and structural features from deep seismic refraction. The characteristics of the mid-crustal zone has been implicated in mineralisation models, and imaging mid to deep crustal structures is important for mineral exploration. In this depth zone, passive seismic surveys show apparent advantages due to their low cost and continuous recording, when contrasted with active seismic surveys, or indeed earthquake tomography in this typically low-activity seismic zone.  In this study, we use the legacy noise data collected from 53 3-component temporary seismic sensors with 50km spacing covering the Mount Isa area deployed from June 2009 to March 2011, and perform ambient noise tomography (ANT) to model the shear wave velocity (Vs) crustal structure. 681 cross-correlations (CCs) of recordings over two weeks between each pairwise stations are used to calculate the empirical Green’s function (EGF) to construct the impulse wavefield. The dispersion curves of the fundamental mode of Rayleigh surface waves are extracted from vertical components of the CCs. Separating the fundamental mode from the other higher modes in the group-velocity map is usually hard to identify. A modified frequency-time analysis (FTAN) based on the global seismology code CPS is used for digitising dispersion curves here. Then the dispersion curve is inverted using a bespoke Markov-Chain Monte Carlo approach to build 1D Vs profiles, which are finally used to construct a 3D shear wave velocity model across the area of interest. We discuss the comparison of the legacy passive seismic data to the results of other geophysical measurements, to provide a new understanding of terrane evolution and crustal structure of Northern Queensland.

How to cite: Chang, A. and O'Neill, C.: Ambient noise tomography of Mount Isa, Northern Queensland in Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7001, https://doi.org/10.5194/egusphere-egu24-7001, 2024.

EGU24-7020 | ECS | Posters on site | SM6.1

The research of early arrival waveform inversion and its application in imaging the shallow fault zone structure 

Xiaona Ma, Weitao Wang, Shanhui Xu, Wei Yang, and Yunpeng Zhang

Waveform inversion is a robust geophysical tool for reconstructing subsurface structures, involving an iterative process that begins with an initial model and utilizes complete information from observed data to update the target model. However, its wide field applications have been impeded by challenges such as strong nonlinearity, nonconvexity of the misfit function, and complexity of the propagation medium. To mitigate these issues and enhance the linearity and simplicity of the inversion process, we employ early arrival wavefields to construct misfit function that promotes  global convergence.

High-resolution structure imaging of active faults within urban areas is vital for earthquake hazard mitigation, so we perform a seismic survey line crossing the Pearl River Estuary Fault (PREF) in Guangzhou, China. First, ten shots of a new and environmentally friendly gas explosion source are excited with about 1 km spacing and recorded by 241 nodal short-period seismometers with an average spacing of 60 m. Then, based on these acquisition data, we adopt waveform inversion to explore the kinematic and dynamic information of early arrival wave-fields to recover the subsurface structures. Here, the early arrival wavefields were defined as those events that arrived within a few periods of the first arrivals. The inversion results indicate that while the low-velocity zone (LVZ) in depth surrounding the PREF is 2.5 km in width and extended to 0.7 km, another LVZ of 1.5 km in width and extended to 0.7 km in depth is surrounded by the Beiting-Nancun fault. We observe that the analysis of evolution and activities of the fault systems reveal no historical earthquakes in our study area; we interpret that the two LVZs controlled by the faults are probably attributed to the fluid dynamics, sediment source, and fault motion at different geological times, rather than fault-related damage zones.

Summarily, the results can provide significant basis for earthquake prevention and hazard assessment in Guangzhou. The finding also shows that the waveform inversion can effectively explore the fine structure of active faults in urban area with dense linear array and spare active source excitations. This acquisition and inversion methods should have broad applications in other cities.

How to cite: Ma, X., Wang, W., Xu, S., Yang, W., and Zhang, Y.: The research of early arrival waveform inversion and its application in imaging the shallow fault zone structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7020, https://doi.org/10.5194/egusphere-egu24-7020, 2024.

EGU24-8000 | ECS | Orals | SM6.1

Experimental Design for Seismic Mass Movement Monitoring 

Dominik Strutz, Tjeerd Kiers, Cedric Schmelzbach, Hansruedi Maurer, and Andrew Curtis

Mass movements are a significant natural hazard and are expected to increase in frequency as global temperatures rise and extreme weather events become more common. The close observation of mass movements can be essential to minimise their adverse effects on society. The efficient use of the available surveying equipment and resources is important when monitoring mass movements. This is because they are often located in inaccessible terrain, and observing them over months or years can be expensive.

A deployment pattern and number of sensors (henceforth, the experimental design) can often be optimised to substantially decrease the uncertainty of scientific results that can be inferred from the observed data. We have developed a novel method to optimise the design of seismic node layouts and fibre-optic based Distributed Acoustic Sensor (DAS) cable pathways for monitoring seismic events. We use it to design surveys to focus on slope instability-induced seismicity.

Our general Bayesian experimental design framework can take into account prior information on event locations, subsurface seismic velocity models, the nonlinearity of the physics governing seismic traveltimes, different models of attenuation, and the directional sensitivity of different sensor types (e.g. the inline sensitivity of fibre-optic cables). The introduction of a likelihood that a travel-time measurement will be made at a given station for a given seismic event allows us to account for the effect of attenuation on the observed data, and the angular dependence of one-component measurements such as DAS.

We show that we can efficiently design seismic node installations, give quantitative recommendations for DAS cable layouts, and show the feasibility of optimising hybrid designs combining both measurement types. We benchmark the experimental design algorithms using an effectively exhaustive data set collected at the Cuolm da Vi slope instability (Swiss Alps, near Sedrun, in Central Switzerland). The data set includes recordings from over 1000 seismic nodes, in a hexagonal grid with roughly 28m receiver spacing over the slope’s surface, of which each recorded data from over 100 dynamite shots spread across the slope. This extremely dense deployment provides the unique opportunity to choose nearly arbitrary designs (i.e. subsets of the nodes) and then test those designs by using them to locate the explosions for which we know the location. By averaging the performance of the probabilistic source location inversions over all dynamite shots, the performance of optimised, heuristic and random experimental designs can be compared.

The same design methods can be applied to seismic source localisation in many different contexts, such as locating microseismic events, and other scenarios, such as infrasound source location.

How to cite: Strutz, D., Kiers, T., Schmelzbach, C., Maurer, H., and Curtis, A.: Experimental Design for Seismic Mass Movement Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8000, https://doi.org/10.5194/egusphere-egu24-8000, 2024.

EGU24-8390 | ECS | Posters on site | SM6.1

Imaging the Crust and Upper Mantle in the Southern Central Mediterranean with Joint Ambient Noise and Earthquake Surface Wave Tomography 

Felix Eckel, Amr El-Sharkawy, Graziella Barberi, Luciano Scarfì, Horst Langer, Sergei Lebedev, and Thomas Meier

Surface wave tomography has proven to be a very powerful tool for discerning complex crustal and upper mantle structures since it bypasses the necessity for local seismic sources and crustal corrections. This study presents a refined 3D model encompassing the crust and uppermost mantle in Southern Italy and the broader southern Central Mediterranean region, achieved through the joint inversion of ambient noise and earthquake data.

Our dataset comprises 11,900 phase velocity dispersion curves, spanning 2 to 100 seconds, derived from ambient noise cross-correlations. Additionally, we incorporate 81,000 phase velocity curves covering 8 to 250 seconds, obtained through inter-station cross-correlations and averaging over single earthquake measurements. A thorough quality control process ensures the reliability of both datasets, which are seamlessly integrated using a correction factor derived from inter-station paths with overlapping measurements.

Azimuthally anisotropic Rayleigh wave phase velocity maps are computed using a regularized least-square approach. These maps, showcasing directional variations in wave velocities, serve as the foundation for our 3D model. The inversion process employs a stochastic particle swarm optimization algorithm, enhancing the robustness and accuracy of the final model.

The resulting 3D velocity model brings to light significant subsurface features, notably the subducted Calabrian and Hellenic slabs, alongside the identification of a delaminated high-velocity anomaly beneath Sicily. Additionally, the model captures details such as the transition from the Ionian Lithosphere to the Calabrian Slab, deformation of the Adriatic Lithosphere, and the dynamic flow of the asthenosphere beneath the Tyrrhenian Sea.

How to cite: Eckel, F., El-Sharkawy, A., Barberi, G., Scarfì, L., Langer, H., Lebedev, S., and Meier, T.: Imaging the Crust and Upper Mantle in the Southern Central Mediterranean with Joint Ambient Noise and Earthquake Surface Wave Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8390, https://doi.org/10.5194/egusphere-egu24-8390, 2024.

EGU24-8837 | ECS | Posters on site | SM6.1

Direct image inversion of multimodal dispersion spectra and its application to deep seismic reflection data 

Qi Liu, Xiaofei Chen, and Wenbin Guo

Nowadays multimodal dispersion spectra can be easily obtained from surface wave data, but sometimes they are actually intractable for the traditional curve-based inversion methods due to the existences of mode-kissing phenomenon and uneven mode-energy distribution. We developed a new spectrum inversion method to circumvent these possible curve-related troubles by directly minimizing the image dissimilarity between the observed and synthetic dispersion spectra. Wherein the synthetic spectrum would be straightforwardly calculated by the Generalized Reflection and Transmission Coefficient method. The new inversion method could rapidly obtain a stable and reliable subsurface velocity structure, even without curve-extracting and mode-identifying in data processing, because it could exploit dispersion energy distribution features to constrain further the velocity structure. As an example of application, we applied this method to deep seismic reflection data in Beijing, and resolved a 2-D S-wave velocity profile above 200 m depth. The strong consistency of structural features between the inversed results of the new and traditional methods shows that the former is effective and practical for realistic data.

 
 

How to cite: Liu, Q., Chen, X., and Guo, W.: Direct image inversion of multimodal dispersion spectra and its application to deep seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8837, https://doi.org/10.5194/egusphere-egu24-8837, 2024.

EGU24-8963 | Orals | SM6.1

3D Least-squares Migration of Receiver Function 

Pengfei Zuo and Yunfeng Chen

Receiver function (RF) imaging is a crucial method that employs converted teleseismic waves to characterize discontinuities in the Earth's interior. The proliferation of dense areal seismic arrays has necessitated developing advanced imaging techniques to effectively utilize the increasing seismic data. In this study, we develop a 3D regularized least-squares migration (LSM) method for RF imaging, which allows for imaging subsurface structures using teleseismic waves incident from arbitrary directions. We employ the Split-step Fourier algorithm to solve the acoustic wave equation, resulting in the construction of forward and adjoint operators for wavefield propagation. These operators facilitate the transformation of the seismic migration into an inverse problem in a least-squares sense, which enables suppressing the strong acquisition footprints and compensating for inadequate illumination. Tikhonov regularization is performed to generate preconditioned images with higher resolution than standard migration algorithms. To assess the performance of the proposed method, we conduct synthetic experiments by simulating teleseismic recordings using the SPECFEM3D code. The input model incorporates undulated and step Moho interfaces. The obtained migration images demonstrate that the capability of the developed LSM method to accurately recovers the 3D geometry of the Moho interfaces. The current study only considers the P-to-S converted waves, and future research will focus on utilizing free-surface multiples to obtain higher-resolution subsurface structures.

How to cite: Zuo, P. and Chen, Y.: 3D Least-squares Migration of Receiver Function, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8963, https://doi.org/10.5194/egusphere-egu24-8963, 2024.

EGU24-9514 | ECS | Posters on site | SM6.1

Multi-parameter Receiver Function Modeling: Application to the Subduction Zones of Cascadia and the Central Andes 

Wasja Bloch, Bernd Schurr, Claudio Faccenna, Frederik Tilmann, Pascal Audet, and Michael Bostock

Receiver functions are a powerful tool to image lithospheric stratigraphy. For flat lying structures, receiver functions can be stacked azimuthally to achieve high signal-to-noise ratios and h-κ-stacks allow to estimate the depth of interfaces (h) and P-to-S wave velocity ratio of the hanging layers (κ). For dipping layers, characteristic for the slab structure in a subduction zone forearc, these methods fail, because the moveout of phases arriving from different azimuths violates the basic assumptions of these methods.

We here present a simple routine to simultaneously search for the depth of the top of slab and of the oceanic Moho, for strike and dip of the downgoing slab, as well as for the S-wave velocities and the P‑to-S wave velocity ratios of multiple layers of the overriding and downgoing plates in subduction zone forearcs. Our approach is based on the recent Python port PyRaysum of Frederiksen and Bostock's classic (2000) code for modeling ray-theoretical plane body-wave propagation in dipping anisotropic media, and on SciPy's simulated annealing global parameter search.

We applied the routine to hundreds of azimuthally-dependent receiver function sections from the subduction zones of Cascadia (North America) and the central Andes (South America) and retrieved laterally coherent station measurements of the depth and orientation of the top of the subducting slab and the subducting Moho, with only weakly constrained seismic velocities. In Cascadia, we interpolated a regional slab model through fitting of regularized spline surfaces. Small scale structures that are not present in previous slab models can be resolved, e.g. under Olympic Peninsula (Cascadia) and Mejillones Peninsula (northern Chile). Where the receiver functions are more complex than can be accounted for by our model, the labeling of the modeled receiver function phases and comparison to the observed receiver functions allows us to confidently interpret the additional subsurface complexities and reconcile them with our interpretations.

How to cite: Bloch, W., Schurr, B., Faccenna, C., Tilmann, F., Audet, P., and Bostock, M.: Multi-parameter Receiver Function Modeling: Application to the Subduction Zones of Cascadia and the Central Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9514, https://doi.org/10.5194/egusphere-egu24-9514, 2024.

EGU24-9868 | ECS | Orals | SM6.1

Receiver function modelling of the lithosphere beneath the Sinai Subplate, west of the Dead Sea fault system 

Pousali Mukherjee, Nadav Wetzler, Ittai Kurzon, and Yuval Tal

The Sinai subplate in the eastern Mediterranean region separates the African and Arabian plates, and is demarcated on the east by the Dead Sea fault (DSF). The shallow and deep crustal Vs and Vp/Vs variations of the eastern Sinai subplate beneath Israel, as well as mantle properties, are not well constrained. With the recent development of the regional seismic network, we present new geophysical observations beneath the Sinai subplate. We focus on the crustal and mantle structure using receiver functions (RF) to image the lithosphere beneath the eastern Sinai subplate, including backazimuth variations. Around 250 teleseismic earthquakes greater than magnitude 6.0 from 2018-2023 are used for our analysis. The obtained receiver functions reveal negative conversions from basin structure, and positive phases from the sediment layer and Moho discontinuity, with backazimuth variations. RF computation is followed by inversion for investigating the shear velocity and Vp/Vs variations across depth, from shallow depths in the crust, extending to deep crust and mantle. An extensive Moho variation under the area is observed by integrating findings from this study and prior investigations. RF and inversion profiles reveal additional insights into seismic boundaries in the crust and mantle beneath the region. The lithospheric architecture beneath the eastern Sinai subplate highlights variations in crust and mantle properties beneath the region, along profiles stretching from north-west to south-east direction beneath the Sinai subplate, and along the strike of the DSF. This work enhances our understanding of the underlying lithosphere beneath the region and offers valuable insights into the evolution of the Sinai subplate and Dead Sea basin zone.

How to cite: Mukherjee, P., Wetzler, N., Kurzon, I., and Tal, Y.: Receiver function modelling of the lithosphere beneath the Sinai Subplate, west of the Dead Sea fault system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9868, https://doi.org/10.5194/egusphere-egu24-9868, 2024.

EGU24-10073 | Posters on site | SM6.1

Global SV wave upper mantle model. 

stephanie durand, yanick ricard, fabien dubuffet, and eric debayle

We present the latest update of the global SV model developed by our team, in Lyon. It is based on the waveform modeling of more than 3 millions Rayleigh waves recorded since 1976. The tomographic model is built using the same automated scheme as was presented in Debayle et al., GRL 2016, while the number of data has increased by a factor larger than 2. For each seismogram, we obtain a path average shear velocity and quality factor model, and a set of fundamental and higher-mode dispersion and attenuation curves from 40s to 250s. We incorporate the resulting set of path average shear velocity models into a tomographic inversion. Due to the drastic increase of data, this second step of inversion became too computationally costly. We rewrote it so that the largest matrix to invert has now a size (number of geographical point)**2 instead of (number of data)**2. Thanks to these improvements we reduced the correlation lengths from 4 deg down to 1deg.  We will focus in several geographical areas and geological objects, to emphasize the improvement in precision of this new model. We will also present our new online tool (https://fascil.univ-lyon1.fr/) available to explore this tomographic model and to compare with existing ones.

How to cite: durand, S., ricard, Y., dubuffet, F., and debayle, E.: Global SV wave upper mantle model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10073, https://doi.org/10.5194/egusphere-egu24-10073, 2024.

The oblique convergence between the Caribbean and North American plates produces the tectonic complexity of Hispaniola Island. The western region is characterized by high topography bounded by dominantly reverse and oblique-slip faults along the edges of the uplifted mountain ranges, while the eastern part is lower in elevation and no important active faults are identified. This work analyzes the seismic data (Profiles A and D) obtained during the CARIBE NORTE project (2009) in the frame of the current MICROSIS-I (2020-2021-1A4-043) and GEOCIBAO-RS (2023-1-1A4-0627) projects. A seismic array of vertical and three-component land stations registered both profiles along N-S and W-E seismic transects of 425 and 450 km, respectively. The seismic sources used in these lines corresponded to three marine shooting lines (LM1N, LM1S for Profile A and LM4, for Profile D), land borehole explosions 1 Ton (S1, S2, and S3), and one earthquake that occurred during the registering period.

We constrained the seismic structure of the Dominican Republic by the inversion of wide-angle seismic travel-time data for the previous 2D P-wave velocity model of both profiles. The results show marked differences between the western and eastern regions of the island. In the eastern zone, the Moho discontinuity rises to 24 km deep, increasing towards the island's interior with a maximum depth value of approximately 30 km in the west and central part of the transect. A structure dipping 18º towards the eastern interior of Hispaniola Island was identified up to 120 km deep from the analysis and relocation of an earthquake that occurred on April 11, 2009, using the CARIBE NORTE temporary seismic network.

How to cite: Núñez, D. and Córdoba, D.: Crustal and uppermost mantle velocity structure beneath the Cordillera Central and Cordillera Oriental, Dominican Republic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10118, https://doi.org/10.5194/egusphere-egu24-10118, 2024.

EGU24-10916 | ECS | Posters on site | SM6.1

SeimicWaves.jl: an efficient yet user-friendly Julia package for Full-Waveform Inversion on multi-xPUs 

Giacomo Aloisi, Andrea Zunino, and Andreas Fichtner

This work focuses on creating efficient and user-friendly tools for seismic tomography using Full-Waveform Inversion (FWI) methods. FWI has proven effective in providing detailed images of the Earth's subsurface. Despite its success, challenges persist due to its high computational costs and complexity, limiting its widespread application in research and education.

To fill the gap between theory and practice, we present efficient, easy-to-use, and scalable finite-difference-based solvers for FWI in the Julia programming language developed in the open-source package SeismicWaves.jl (part of HMCLab, a framework to perform Bayesian inversion and optimization for geophysical problems), which enable non-experts to conduct numerical experiments and address real applications with seismic data. Our device-agnostic solvers can be distributed on multiple devices (multi-xPUs), providing users with different parallelization options fitting diverse use cases.

Rigorous tests and synthetic inversions validate the solvers' correctness, offering insights into both the potentials and pitfalls of the method. Benchmark tests evaluating memory throughput, crucial for the memory-bound algorithms under study, reveal that our solvers achieve high memory throughput (up to 90% of peak) on modern GPUs and exhibit good weak scaling on distributed systems.

In conclusion, by leveraging advancements in software and hardware from the scientific computing community, our research addresses both computational and complexity challenges of FWI, making it a viable and efficient method for educational and research purposes in seismic tomography.

How to cite: Aloisi, G., Zunino, A., and Fichtner, A.: SeimicWaves.jl: an efficient yet user-friendly Julia package for Full-Waveform Inversion on multi-xPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10916, https://doi.org/10.5194/egusphere-egu24-10916, 2024.

EGU24-11052 | ECS | Posters virtual | SM6.1

3D Crustal Imaging of North-East India and Indo-Burmese Subduction Zone 

Anurima Mishra, Satish Maurya, William Kumar Mohanty, and Mohan Gollapally

We present a high-resolution 3D shear wave velocity (Vsv) model for the North-East India Region (NER) and Indo-Burmese Subduction Zone (IBSZ) down to an 80 km depth by inverting a new and extensive Rayleigh wave dispersion dataset. We retrieved vertical component dataset of more than 900 seismic events recorded by 26 global and regional seismic broadband networks. We picked and analyzed ~20,000 paths of Rayleigh wave fundamental mode group velocity dispersion curves across a wide period range of 4-70s. The methodology involved a two-step inversion approach: a 2D continuous regionalization incorporating azimuthal anisotropy was utilized to produce tomographic images from the local velocity dispersion curves. Subsequently, a Markov Chain Monte Carlo scheme within a trans-dimensional Bayesian framework was employed for the inversion process. The resulting 2D tomograms of the regionalized dispersion data at different periods and the subsequent inverted 3D model are consistent with the velocity values associated with the known geologic features, accurately outlining the primary tectonic boundaries in the study area. The region under study encompasses the Bengal basin (BB), Shillong plateau (SP), Mikir Hills, Assam-Brahmaputra-valley (BV), North-Eastern Himalayas, Indo-Burma ranges (IBR) and western Myanmar. Sediment thickness is highest in the southern delta region (18-22km), increasing from west to east towards the northern part of the BB and thinnest at the Dauki fault zone (8-10km). Crustal thickness under BB varies widely, from 33-46km. The velocity model reveals an undulating mantle and higher upper-crustal shear wave velocity (Vsv~3.3-3.6km/s) under the SP than its surrounding regions. Moho thickness varies across the region: ~33km in Garo Hills, ~38km in Assam valley, and ~42km beneath the Lesser Himalayan foredeep. There is a clear eastward dipping subduction geometry along ~22°N from under BB towards the Central Myanmar Basin (CMB) (at ~95°E). Sediment thickness in the CMB varies from 10-12km. The Main Himalayan Thrust (MHT) depth is ~18km under the Arunachal Himalaya, which moving northward dips down to ~28km under the Greater Himalaya. The crustal thickness at the syntaxial corner and BV is significantly greater than its surficial topography. The maximum crustal thickness of ~52km is on the southern IBR, along its eastern side.

 

 

Keywords: Crustal Structure, North-East India, Indo-Burma subduction zone, Rayleigh wave, group velocity, 3D shear wave velocity model, Bayesian inversion.

 

How to cite: Mishra, A., Maurya, S., Mohanty, W. K., and Gollapally, M.: 3D Crustal Imaging of North-East India and Indo-Burmese Subduction Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11052, https://doi.org/10.5194/egusphere-egu24-11052, 2024.

EGU24-11129 | Orals | SM6.1

How resolving are teleseismic forward and backscattered teleseismic P to S converted waves? 

Alexandrine Gesret, Emile Denise, and Ali Janbein

The Receiver Function (RF) technique, that aims to isolate P to S teleseismic converted waves, is largely used to image seismic discontinuities at depth. In particular, in subduction zones, the subducting crust has often be identified on RF as a Low Velocity Layer (LVL) embedded between the mantle of the overriding plate and the mantle of the subducting lithosphere.

The arrival times and polarities of the forward Ps and backscattered Pps and Pss converted waves at the top and bottom of a LVL are sensitive to the backazimuth and ray parameter of the teleseismic events. We first demonstrate on a synthetic study that the thickness, the Vp/Vs ratio and the dip of a LVL can be retrieved by inverting the arrival times and polarities of these converted waves for a good azimuthal coverage. The Bayesian formalism allows us to also quantify the uncertainties associated to these inverted parameters.

In several subduction zones, a high Vp/Vs ratio inside the oceanic crust has been estimated from the arrival times of the forward and backscattered P to S converted waves at the top and bottom of the LVL. In order to check if the signal periods associated to common filters could lead to an overestimation of the Vp/Vs ratio, we compute the wavelet response in conversion for a LVL typical of an oceanic crust. This multiscale analysis allows to illustrate that the LVL characteristics can be misinterpreted for the common frequency range due to interferences between the converted waves at the top and at the base of the LVL. For example, for a common dominant period of about 3s, the Vp/Vs of a typical oceanic crust will be largely overestimated and its thickness underestimated since a period smaller than 1s is required for a reliable interpretation. Indeed the true characteristics of a layer can be retrieved only if the ratio between the dominant period and the time delay (between the converted waves at the top and bottom of the LVL) is smaller than 1. This allows us to quantify, for the three kind of waves (Ps, Pps and Pss), the resolvable thickness of a LVL with respect to the Vp/Vs ratio and to the Vp velocity for a given signal period.

The approach is finally applied to a real data example of teleseismic events recorded at a 3-component seismometer in order to reliably constrain the dip, the Vp/Vs ratio and the thickness of the oceanic crust at the top of the Hellenic subduction.

How to cite: Gesret, A., Denise, E., and Janbein, A.: How resolving are teleseismic forward and backscattered teleseismic P to S converted waves?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11129, https://doi.org/10.5194/egusphere-egu24-11129, 2024.

EGU24-11364 | ECS | Orals | SM6.1

Seismic 3D imaging at the Bedretto Underground Laboratory (Switzerland): active seismic cross-hole tomography using fat rays 

Miriam Schwarz, Hansruedi Maurer, Anne Obermann, and Stefan Wiemer and the BedrettoLab Team

The Bedretto Underground Laboratory for Geosciences and Geoenergies (BedrettoLab), operated by ETH Zurich, is a unique research facility providing optimal conditions for conducting experimental research on understanding the responses of the deep underground when stimulating it. Our experiments were performed in a Geothermal Testbed in the BedrettoLab. It includes six monitoring boreholes, ranging from 250 to 400 m length. They are equipped with multiple instruments including seismic sensors (geophones, accelerometers and acoustic emission) and active seismic sources (piezoelectric transducers). In addition, two stimulation boreholes are used to access the underground. A fault zone is crossing the boreholes in the volume of interest, which is one of the main targets of our investigations.

Advanced knowledge of the spatial distribution of the seismic velocities (i.e. elastic properties) is essential for several purposes, including, for example, geological and geotechnical characterizations of the rock volume, locating microseismicity caused by the hydraulic stimulations, and performing active seismic monitoring experiments. For that purpose, we have compiled a comprehensive active seismic travel time data set. As seismic sources we considered borehole sparker shots and the permanently installed piezoelectric transducers. The seismic waves were recorded with hydrophone streamers and the permanently installed seismic sensors. This resulted in roughly 45’000 travel time picks.

Here, we present first results of a 3D P-wave velocity tomography. Even with this relatively large data set, the ray coverage within the volume of interest is still relatively incomplete, when using classical (infinitesimally thin) rays. Therefore, we considered a fat ray approach, with which the finite bandwidth of seismic waves can be approximated more realistically. We will compare the classical ray-based tomography (high frequency approximation) with results from the fat ray tomography (frequency dependent). The resulting tomograms can be compared with borehole image logs.

How to cite: Schwarz, M., Maurer, H., Obermann, A., and Wiemer, S. and the BedrettoLab Team: Seismic 3D imaging at the Bedretto Underground Laboratory (Switzerland): active seismic cross-hole tomography using fat rays, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11364, https://doi.org/10.5194/egusphere-egu24-11364, 2024.

EGU24-11392 | ECS | Posters on site | SM6.1

Upper-mantle velocity structures and anisotropy under the Mongol-Baikal region 

Hanting Wu and Zhouchuan Huang

The Mongol-Baikal region is located in the western segment of the Central Asian Orogenic Belt. This area experienced multiple periods of extensive compression starting from the Proterozoic. In the Cenozoic, the study region was modified by neotectonics, featuring large extensional rifting (the Baikal rift zone) and plateau uplift (the Hangai Dome). However, the deep mechanisms of the onset of rifting and doming are still debated. We performed high-resolution 3-D P-wave tomography under the southwestern Baikal and western Mongolia. The images show distinct low-velocity anomalies under the Baikal Rift at ~60 km depth, the Hangai Dome at ~200 km depth, and beneath the Siberian craton. This may indicate that potential mantle flows ascended from the deep Siberian MTZ to shallower levels, influencing the rifting of the Baikal rift zone and the lithospheric process of the Hangai Dome. We then further determined the seismic anisotropy of the upper mantle under western Mongolia using SKS splitting measurements. The study region is dominated by NW-SE trending fast polarization directions (FPD), which indicates consistent compressional and transitional stress among the whole study area. Small delay times in the Hangai Dome spatially coincide with the low-velocity anomalies, supporting remarkable asthenosphere upwelling. However, the local Hangai upwelling did not affect the general anisotropic structures significantly, indicating that the lithospheric process only occurred in a limited area.

References

Wu, H., Huang, Z., 2022. Upper mantle anisotropy and deformation beneath the western Mongolian Plateau revealed by SKS splitting. Tectonophysics 835, 229376. https://doi.org/10.1016/j.tecto.2022.229376

Wu, H., Huang, Z., Zhao, D., 2021. Deep structure beneath the southwestern flank of the Baikal rift zone and adjacent areas. Physics of the Earth and Planetary Interiors 310, 106616. https://doi.org/10.1016/j.pepi.2020.106616

 

How to cite: Wu, H. and Huang, Z.: Upper-mantle velocity structures and anisotropy under the Mongol-Baikal region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11392, https://doi.org/10.5194/egusphere-egu24-11392, 2024.

EGU24-11469 | Orals | SM6.1

Seismic Thermography 

Sergei Lebedev, Javier Fullea, Yihe Xu, and Raffaele Bonadio

What is next in seismic tomography? In this presentation, we make a case that a key future direction is the inversion of seismic data directly for temperature within the Earth. We term this emerging branch of seismic imaging Seismic Thermography. Variations in temperature are of great interest because they indicate the thickness and, consequently, mechanical strength of the lithosphere and density variations and convection patterns in the sub-lithospheric mantle. Seismic tomography maps seismic-velocity variations in the mantle, which depend on temperature. Temperatures and the lithospheric structure and thickness are, thus, often inferred from tomography. Tomographic models, however, are non-unique solutions of inverse problems, regularized to ensure model smoothness or small model norm, not plausible temperature distributions. For example, lithospheric geotherms computed from seismic-velocity models typically display unrealistic oscillations, with improbable temperature decreases with depth within shallow mantle lithosphere.

It is more accurate to invert seismic data directly for temperature and avoid the errors due to the intermediate-model non-uniqueness. Because seismic-velocity sensitivity to composition is weaker than to temperature, we can use computational petrology and thermodynamic databases to invert seismic data primarily for temperature, with reasonable assumptions on composition and other relevant properties and with additional inversion parameters such as anisotropy.

Here, we apply thus defined Seismic Thermography to the thermal imaging of the lithosphere, asthenosphere and the lithospheric thickness using surface waves. Conductive geotherms and standard compositions fit the data from Precambrian continents and from Britain and Ireland, which we use as examples. Exotic compositions and temperature profiles can also be mapped, when required by the data, using specially defined components of the parameterisation. The accuracy of the models depends critically on the accuracy of the extraction of structural information from the seismic data. Random errors have little effect but correlated errors of even a small portion of 1% can affect the models strongly.

Seismic Thermography builds on the techniques of seismic tomography and relies on computational petrology but it is emerging as a field with its own scope of goals, technical challenges and methods. It is producing increasingly accurate models of the Earth and important inferences on its dynamics and evolution.

How to cite: Lebedev, S., Fullea, J., Xu, Y., and Bonadio, R.: Seismic Thermography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11469, https://doi.org/10.5194/egusphere-egu24-11469, 2024.

EGU24-12010 | ECS | Posters on site | SM6.1

Refinement of tomographic models in the Western Mediterranean region through full waveform inversion 

Paula Herrero-Barbero, Martin Schimmel, David Martí, Lion Krischer, and Ramon Carbonell

Accurate imaging of crustal structures necessitates sophisticated inverse modeling utilizing extensive waveform data, including high-frequency signals from minor seismic events, an aspect traditionally underused in full waveform inversion (FWI). Integrating these intricate elements into novel tomographic models using FWI for the Western Mediterranean region, we address the challenge of enhancing model resolution while acknowledging the increased computational demands associated with inversion, an endeavor made feasible only through High-Performance Computing (HPC).

This study incorporates new considerations by comparing diverse reference models and updating a substantial dataset of earthquakes spanning the time interval from 2007 to 2022. While station deployment in the Mediterranean region is notably dense, the uneven geographical distribution of ray coverage from far-field waveforms necessitates the inclusion of lower magnitude earthquakes (M<4.5). This demands the determination of additional moment tensor solutions not readily available in public databases, alongside efforts to enhance signal-to-noise ratios. Our approach employs an iterative multiscale FWI approach, initially prioritizing the inversion of lower frequencies (period band of 100-120 s), and as the model refines, higher frequencies are progressively incorporated. The final goal is targeting a minimum period of 12 seconds or less. This incremental strategy aims to continuously enhance waveform fitting throughout each iteration, facilitated by an intensive computational workflow.

This contribution centers on the technical construction of the model, primarily focusing on S-velocity, and provides a comprehensive discussion of the employed data processing methods. We address the benefits, limitations and uncertainties inherent in this approach. Recognizing the pivotal role of higher-resolution velocity models in precise forward waveform modeling, we anticipate that the advancement of these inversion strategies will also contribute to refining earthquake-induced shake maps at regional to local scales. This research is funded by the Horizon Europe Project DT-GEO: A Digital Twin for GEOphysical extremes (ID 101058129).

How to cite: Herrero-Barbero, P., Schimmel, M., Martí, D., Krischer, L., and Carbonell, R.: Refinement of tomographic models in the Western Mediterranean region through full waveform inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12010, https://doi.org/10.5194/egusphere-egu24-12010, 2024.

EGU24-13737 | ECS | Posters on site | SM6.1

Lithospheric Imaging of Northern Taiwan Using Teleseismic Full Waveform Inversion: from Volcanic Reservoirs to Plate Boundaries 

Li-Yu Kan, Hao Kuo-Chen, Sebastien Chevrot, Jean-Claude Sibuet, Cheng-Horng Lin, and Vadim Monteiller

The tectonic of northern Taiwan is in a post-collisional stage and has undergone a subduction polarity flip between the Eurasian Plate (EP) and Philippine Sea Plate (PSP). The shallow crust of northern Taiwan features the Tatun Volcano Group (TVG) and the Turtle Island magma reservoirs, with their proximity to Taipei metropols highlighting the volcanic risks to densely populated regions and critical infrastructure. However, it is challenging to image all these structures from the surface down to several hundred kilometers depth with classical passive tomographic approaches. Here, we present tomographic models of density, P-wave velocity (Vp), S-wave velocity (Vs), and the Vp/Vs ratio beneath northern Taiwan, obtained by inverting complete teleseismic waveforms from 18 P and 9 SH events recorded by 175 broadband stations from the Formosa Array and the permanent stations. In our final model, the plate boundary between EP and PSP is clearly depicted as a west-dipping plane, consistent with the western boundary of slab seismicities. Our model identifies two distinct low-velocity, high VP/VS bodies beneath the TVG and Turtle Island, indicative of underlying magma reservoirs. The reservoir beneath the TVG is beaker-shaped, extending from a depth of 6 to 20 kilometers. The reservoir beneath Turtle Island, located on the island’s eastern side, is larger than TVG's but less well defined due to sparse station coverage. The crust north of the Hsueshan Range is thinner, likely related to the post-collisional delamination of the lower crust. This process leads to increased mantle heat flow, providing the heat source for the TVG. With the new 3-D model, we also relocate the local events by utilizing a nonlinear location method, in order to improve their spatial accuracy and get better constraints on the seismogenic structure.

How to cite: Kan, L.-Y., Kuo-Chen, H., Chevrot, S., Sibuet, J.-C., Lin, C.-H., and Monteiller, V.: Lithospheric Imaging of Northern Taiwan Using Teleseismic Full Waveform Inversion: from Volcanic Reservoirs to Plate Boundaries, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13737, https://doi.org/10.5194/egusphere-egu24-13737, 2024.

EGU24-15474 | Orals | SM6.1

Adaptive mesh joint inversion using seismic body and surface wave data: Method and Application 

Ying Liu, Hongjian Fang, Huajian Yao, and Haijiang Zhang

Seismic tomography using body or surface wave data is a powerful tool to explore the structure of Earth’s interior structure. In recent decades, joint inversion of seismic body and surface wave data has been widely employed to investigate seismic velocities of the Earth’s lithosphere and asthenosphere. Benefited from the complementary sensitivities of different datasets, seismic velocities determined by joint inversion generally exhibit higher resolution and accuracy. Regular mesh (cell or grid) is commonly used in seismic tomography. As data distribution is uneven in most cases, regularization techniques are implemented in regular mesh seismic tomography method to stabilize ill-posed problems. Despite the selection of appropriate regularization parameters, it is also challenging to achieve multiscale resolution in regular mesh joint inversion method. In this study, we developed a joint inversion method using adaptive irregular mesh according to the real data distribution based on Poisson-Voronoi cells. Synthetic tests show that the newly developed method can better resolve multi-scale structures without regularizations. We applied this method to a dataset with seismic arrays in different scales. The newly determined multiscale velocity model reveals distinct features particularly in areas with dense data distribution.

How to cite: Liu, Y., Fang, H., Yao, H., and Zhang, H.: Adaptive mesh joint inversion using seismic body and surface wave data: Method and Application, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15474, https://doi.org/10.5194/egusphere-egu24-15474, 2024.

EGU24-15579 | ECS | Orals | SM6.1

Long-range fiber-optic earthquake sensing by active phase noise cancellation 

Sebastian Noe, Dominik Husmann, Nils Müller, Jacques Morel, and Andreas Fichtner

We introduce a novel fiber-optic environmental deformation sensor operating on active phase-noise cancellation (PNC). Networks with PNC have been established over the last decade by national metrology institutes to enable state-of-the-art frequency dissemination of atomic clock signals. Utilizing this infrastructure, PNC sensing exploits recordings of a compensation frequency that arises in the frequency dissemination. As the recording operates simultaneously with the metrological service, the existing phase-stabilized metrological networks can be co-used with minimal effort as environmental sensors. The compatibility of PNC sensing with inline amplification enables the interrogation of cables with lengths beyond 1000 km, potentially contributing to earthquake detection and early warningsystems in the oceans.

In a practical application, we analyze the recordings of a magnitude 3.9 earthquake in eastern France on a 123 km fiber-optic link between Bern and Basel, Switzerland. Through spectral-element seismic wavefield simulations, we compute the theoretical compensation frequency time series on the in-line strain rates resulting from the seismic wavefield and compare it to the observations. Simulations account for the complex cable geometry and topography. Observed and computed recordings match for periods above 3 s.

As simulations appear to explain the data, we further deploy a moment tensor inversion for the same event. This involved computing Green’s functions for all moment tensor components based on the full waveform. Comparing the inversion results to conventional source solutions from public earthquake databases yields a good fit, despite relying on a single data trace only, suggesting that PNC can be used for quantitative seismology. We discuss the detection of other earthquakes with this instrument and future research directions, including tomography.

How to cite: Noe, S., Husmann, D., Müller, N., Morel, J., and Fichtner, A.: Long-range fiber-optic earthquake sensing by active phase noise cancellation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15579, https://doi.org/10.5194/egusphere-egu24-15579, 2024.

EGU24-16138 | ECS | Orals | SM6.1

3D Attenuation Tomography of the Kashmir ‘Seismic Gap’ in NW Himalaya 

Amarjeet Kumar, Dibyajyoti Chaudhuri, Supriyo Mitra, Sunil Kumar Wanchoo, and Keith Priestley

Lateral variation in seismic-energy attenuation is necessary to unravel the tectonic and thermal structure of the lithosphere, and to quantify ground-motion from future earthquakes. We study the 3D variations in intrinsic, scattering and body-wave attenuation across the Kashmir ‘seismic gap’ in the NW Himalaya, which is among the least studied segments of the Himalayan arc. This region is situated between the rupture zones of the 1905 Kangra earthquake (M ∼ 7.9) and the 2005 Muzaffarabad earthquake (Mw ~ 7.6), and spans the meizoseismal zone of the 1555 Kashmir earthquake (Mw ∼ 8.0). Over the last five centuries, this region has accumulated sufficient strain-energy to drive a future mega-thrust earthquake of similar magnitude. 

We use 507 local earthquake (Mw ≥ 2) waveform data recorded by the Jammu And Kashmir Seismological NETwork between 2013 to 2017. These earthquakes have been re-located using the non-linear location algorithm. Intrinsic attenuation is calculated using coda waves modeled as a composite of multiple forward-scattered energies in a diffusive regime (Qc ~ Qi). The exponential decay of the coda-wave envelopes are used to invert for the intrinsic attenuation using sensitivity kernels, whose parameters like albedo and extinction length are computed using the Multiple Lapse Time Window Analysis (MLTWA). Scattering attenuation is imaged using peak delay-time method, which is a direct measure for multiple forward-scattering. The body wave (P- or S-wave) attenuation is computed using the coda-normalization method, by taking the ratio of the measured direct and coda wave energies, which depends only on Q, thereby using a linearized inversion. 

The preliminary results show a spatial variation in frequency dependent 3D scattering, absorption, and body-wave attenuation, which are related to the different geologic/tectonic features across the NW Himalaya. These results will be jointly interpreted with local S-wave velocity models to understand the tectonic and thermal structure of the lithosphere.

How to cite: Kumar, A., Chaudhuri, D., Mitra, S., Wanchoo, S. K., and Priestley, K.: 3D Attenuation Tomography of the Kashmir ‘Seismic Gap’ in NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16138, https://doi.org/10.5194/egusphere-egu24-16138, 2024.

EGU24-16784 | Orals | SM6.1

Evidence for the Partial Melt Beneath the Central Anatolia Elucidated from Frequency Dependent Shear Wave Attenuation 

Tuna Eken, Gizem Izgi, Peter Gaebler, Tülay Kaya-Eken, and Tuncay Taymaz

The Central Anatolian Plateau, featuring volcanic provinces, serves as a significant transition zone between compressional deformation in the east and an extensional regime in the west. The Central Anatolian Fault Zone acts as the demarcation between the Kırşehir Block to the north and the Anatolide-Tauride block to the south within the plateau. A comprehensive understanding of physical properties, particularly seismic attenuation in the crustal volume of this region, offers insights into the potential sources of past and present geodynamic events, contributing to the observed deformation. In our study, we adopt a non-empirical coda wave modeling approach to separately analyze intrinsic and scattering attenuation. This involves a fitting process between observed and synthetic coda wave envelopes for each earthquake across multiple frequency bands. Utilizing acoustic radiative transfer theory with assumptions of multiple isotropic scattering, we forward model synthetic coda-wave envelopes for local earthquakes. Our findings highlight the dominancy of intrinsic attenuation over scattering attenuation, suggesting the presence of thick volcanic rocks with relatively high attenuation values beneath Central Anatolia. The spatial distribution of attenuation at various frequencies distinctly identifies the Kırşehir Massif with its considerable high attenuating character. Our results, coupled with earlier seismological and geo-electrical models suggests the possibility of partial melt beneath much of the Central Anatolian Volcanic Province. Zones with elevated fluid content exhibit dominant intrinsic attenuation. Toward the southeast, a gradual decrease in observed attenuation aligns with the Central Tauride Mountains, where high altitude is believed to have evolved following slab break-off and subsequent mantle upwelling.

How to cite: Eken, T., Izgi, G., Gaebler, P., Kaya-Eken, T., and Taymaz, T.: Evidence for the Partial Melt Beneath the Central Anatolia Elucidated from Frequency Dependent Shear Wave Attenuation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16784, https://doi.org/10.5194/egusphere-egu24-16784, 2024.

EGU24-17918 | Orals | SM6.1

3D imaging of Rayleigh wave mantle attenuation with uncertainty quantification 

Ana M.G. Ferreira and William Sturgeon

We present global 2-D maps of frequency-dependent attenuation based on a huge dataset of ~10 million Rayleigh wave amplitude measurements. We incorporate fundamental mode and up to 4th overtone measurements over a period range of 35-200 s to ensure sensitivity in both the uppermost mantle and in the transition zone. In order to isolate intrinsic anelastic attenuation structure, we account for source, path and receiver effects on the amplitude data. Most prominently, we account for focusing/defocusing effects along the ray-path using complementary phase velocity maps. Following the removal of outliers based on strict data selection criteria, the resulting dataset is inverted using a least-squares approach along with a thorough exploration of model regularisation.

Our maps show a strong correlation between attenuation and surface tectonics up to periods of T~100 s, with low attenuation beneath the continents and high attenuation beneath the oceans. Our maps also show a commonly observed age progression trend in ocean basins, with lower attenuation beneath older oceanic crust. In particular, our maps delineate all major global cratons, including some separation between the Congo and Kalahari cratons in Africa, as well as the reletively small North China craton between T~40-100 s. The East Pacific Rise, western North American and hotspots correlate with high attenuation up to T~100s, but then correspond to low attenuation regions at periods greater than T~180 s. As to be expected, uncertainties are higher in regions of poor data coverage (e.g., southern hemisphere and oceans).

We then, for the first time, jointly invert frequency-dependent Q-curves for 1D profiles of shear-attenuation using the Monte-Carlo based Neighbourhood Algorithm. We discuss the implications of our resulting 3D model in terms of mantle temperature and composition anomalies.

How to cite: Ferreira, A. M. G. and Sturgeon, W.: 3D imaging of Rayleigh wave mantle attenuation with uncertainty quantification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17918, https://doi.org/10.5194/egusphere-egu24-17918, 2024.

EGU24-18839 | ECS | Orals | SM6.1

Downscaling Tomographic Images with Generative Neural Networks 

Théo Santos, Thomas Bodin, Ferréol Soulez, Yann Capdeville, and Yanick Ricard

In seismic tomography, only waveforms up to a minimum period are observed, preventing to resolve scales smaller than a minimum wavelength. As a result, seismic tomography is only able to recover effective mediums, which are smoothed versions of the studied structures. A true small-scale structure can be related to its corresponding effective medium through the homogenization theory of wave propagation.

Geodynamics is able to model small-scales structures, providing useful a priori information about the Earth structures. In this study, we aim to combine small-scale a priori information and the homogenization theory to downscale tomographic images, i.e. find the small-scale realistic models equivalent to the observed smooth images. It requires an appropriate parametrization of the small-scale models, that takes into account the a priori information.

We propose to carry out this parametrization with a Generative Neural Network. After the training, the network can generate models that are statistically similar to the training set – in this context, a set of small-scale models, corresponding to the a priori structures. This parameterization integrates the prior, as it is learned during the training. It also has the advantages to be low-dimensional, computationally quick, and avoid strong non-linearities relationships between parameters and the data.

The network is then utilized in an inverse framework to dowscale a given tomographic image.

To test this methodology, we train the network on geodynamical simulations of the mantle, the marble-cake models. For a given synthetic smoothed effective tomographic image, we plug the network into a Bayesian framework, using a McMC to explore the space of marble-cake models that are equivalent to the tomographic image for long period waves.

How to cite: Santos, T., Bodin, T., Soulez, F., Capdeville, Y., and Ricard, Y.: Downscaling Tomographic Images with Generative Neural Networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18839, https://doi.org/10.5194/egusphere-egu24-18839, 2024.

EGU24-21544 | ECS | Orals | SM6.1

High-Resolution 3D Imaging of Crustal and Upper Mantle Structure in the Alps from Full Waveform Inversion of Teleseismic P Waves 

Najmieh Mohammadi, Stephen Beller, Vadim Monteiller, and Stéphane Operto

The northward movement of the African and European plates since the Late Cretaceous has led to the slanted subduction of the Tethys oceanic lithosphere beneath the Adriatic microplate, followed by an asynchronous continental collision between the European plate and continental microplates (Iberia and Adria) during the Cenozoic. This dynamic interaction has given rise to the creation of intensely deformed mountain chains, encompassing the Alps, Apennines, Dinaric, and Carpathian ranges. Furthermore, the convergence of these colliding continental plates triggers crustal shortening, playing a substantial role in the development of orogenic systems and mountains. This process has accreted crustal regions with distinctive properties, resulting in the formation of intricate and varied tectonic units. The objective of this study is to develop high-resolution seismic models of the crust and upper mantle in the Alps, considering P-wave velocity (VP), S-wave velocity (VS), and density. This is achieved with Full Waveform Inversion (FWI) method, utilizing teleseismic earthquakes recorded by the European permanent seismological broadband stations and supplemented by data from temporary stations, including AlpArray, SWATH-D, and CIFALPS2. We employed a semi-automated data selection method, incorporating a rigorous process to ensure data quality. We built a P-wave dataset for Full Waveform Inversion (FWI) that encompasses approximately 91 teleseismic events, whose magnitude (MW) range from 6 to 7.4. These events are characterized by depths less than 20 km or exceeding 120 km. We used the AK135 velocity model as the initial model in our inversion process and applied iterative inversions on the Z, N, and E components of P-waves. The P-waves were filtered within the 6-25 second period range. The optimization algorithm utilized the limited-memory BFGS. The time windows considered during the inversion process were set to 40 seconds (20 seconds before the P-onset). We derived comprehensive models for VP , VS, and density beneath the Alps, enabling us to investigate the lithospheric and upper mantle structures beneath the Western, Central, and Eastern Alps simultaneously. Our models effectively capture key Alpine features, including the thick low-velocity sedimentary basins of Molasse Basin (MB), the Po Basin (PB), and the Southeast-France Basin (SFB), alongside the high-velocity Ivrea body (IB). Moreover, we identify small high-velocity anomalies in the Central and Eastern Alps along the Periadriatic line, corresponding with Permian magmatic rocks observed in these areas. Our model depicts the underthrusting of the low-velocity European crust beneath the Ivrea body mantle wedge in the southwestern Alps and investigates its variation along the strike of the Alps. Additionally, we prepare a Moho topography map from the VS model by considering the iso-velocity of 4.3 km/s as a prox

How to cite: Mohammadi, N., Beller, S., Monteiller, V., and Operto, S.: High-Resolution 3D Imaging of Crustal and Upper Mantle Structure in the Alps from Full Waveform Inversion of Teleseismic P Waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21544, https://doi.org/10.5194/egusphere-egu24-21544, 2024.

EGU24-3066 | Orals | SM6.2

Testing multiple ambient noise methodologies to map the basement of small-scale sedimentary basins 

Jordi Diaz, Sergi Ventosa, Martin Schimmel, Mario Ruiz, Albert Macau, Anna Gabàs, David Martí, Özgenç Akin, and Jaume Verges

The potential of different ambient noise methodologies to map the geometry of a small-scale sedimentary basin has been tested using data acquired in the Cerdanya Basin (eastern Pyrenees). We present results based on a 1-year long broad-band deployment covering a large part of the Eastern Pyrenees and a 2-month long high-density deployment covering the basin with interstation distances around 1.5 km. The explored techniques include autocorrelations, ambient noise Rayleigh wave tomography, horizontal-to-vertical spectral ratio, and band-pass filtered ambient noise amplitude mapping. The basement depth estimations retrieved from each of these approaches, based on independent datasets and different implicit assumptions, are consistent, showing that the deeper part of the basin is located in its central part, reaching depths of 600-700 m close to the Têt Fault trace bounding the Cerdanya Basin to the NE. The results show also that when high-density seismic data are available, HVSR and ambient noise amplitude analysis in a selected frequency band are useful tools to quickly map the basement of a sedimentary basin. On the other hand, surface wave tomography, more complex to obtain, provides detailed information on the 3D velocity structure. Besides this methodological aspect, our results help to improve the geological characterization of the Cerdanya Basin and will provide further constraints to refine the seismic risk maps of an area of relevant tourism and economic activity.

How to cite: Diaz, J., Ventosa, S., Schimmel, M., Ruiz, M., Macau, A., Gabàs, A., Martí, D., Akin, Ö., and Verges, J.: Testing multiple ambient noise methodologies to map the basement of small-scale sedimentary basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3066, https://doi.org/10.5194/egusphere-egu24-3066, 2024.

EGU24-3527 | ECS | Posters on site | SM6.2

Body wave retrieval from seismic ambient noise: results validation workflow within a known velocity model 

Ali Riahi, Alexandre Kazantsev, Eleonore Stutzmann, Martin Schimmel, Jean-Paul Montagner, Mark Noble, and Jean-Philippe Metaxian

We estimated the Empirical Greens Functions (EGF) from ambient noise cross-correlations using a dense array of 3C broadband seismometers deployed above an anticline structure hosting an underground gas storage in France. In total, 580 recording locations are available. Several array configurations have been used, some of the seismometers being moved to new locations every day. The survey duration was of 16 days, with around 2 days of recording per location, and a typical interstation distance of 400 meters.

Our methodology uses polarization characteristics to separate body and surface waves. The approach uses the imaginary part of ZR+RZ cross-coherency (Z: vertical; R: radial) to enable the distinct reconstruction of diving P-waves. In order to enhance the signal-to-noise ratio of the retrieved P-wave, we employed common-offset bin-stacking over all virtual sources and receivers, with an offset bin of 50 meters. Subsequently, we assessed the stability of the extracted P-wave by computing a separate common-offset bin-stack for each recording day and each station couple azimuth interval. The consistent moveout of the extracted P-wave, regardless of various station couple azimuths and recording days, suggested that there was no significant source distribution bias in our EGFs.

In the next step, by using the P-wave window from the common-offset bin-stack as a template, we selected only the individual station pairs for which the correlation coefficient between the EGF and the template was above 0.8. This resulted in rejecting about 95% of the station couples. Around 7000 P- arrival times were picked from the selected EGFs in a semi-manual way. The accuracy of these arrival times was validated against the Eikonal solution for the first arrival within the “known” 3D velocity model of the site, based on active seismic and well logging data.

Finally, a 3D tomography based on the picked arrivals allowed us to invert for a P-velocity model up to a depth of around 700 meters. The consistency and the limits of the comparison between this inverted model and the known model are discussed.

How to cite: Riahi, A., Kazantsev, A., Stutzmann, E., Schimmel, M., Montagner, J.-P., Noble, M., and Metaxian, J.-P.: Body wave retrieval from seismic ambient noise: results validation workflow within a known velocity model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3527, https://doi.org/10.5194/egusphere-egu24-3527, 2024.

EGU24-4428 | ECS | Orals | SM6.2

Characterizing the Seafloor Sediment Layer Using Teleseismic Body Waves Recorded by Ocean Bottom Seismometers 

HyeJeong Kim, Hitoshi Kawakatsu, Takeshi Akuhara, and Nozomu Takeuchi

Kim et al. (2023; JGRse) presents an approach to better characterize the P-wave and S-wave velocity structure of the seafloor sediment layer using ocean bottom seismometers. The presence of low-velocity seafloor sediment layers influences the observed seismic record at the seafloor over a broad frequency range, such that detailed knowledge of this sediment structure is essential to predict its effect on teleseismic records. We use the radial component of teleseismic P waves and autocorrelation functions of the radial, vertical, and pressure components of teleseismic P and S waves to obtain sediment layer models using the Markov chain Monte Carlo approach with parallel tempering. Synthetic tests show that the body waves constrain the P- and S-wave impedances and travel times and the P- to S-wave velocity ratio of the sediment layers. The proposed method resolves thin layers at a high resolution, including the uppermost thin (∼50 m to a few hundred meters) low S-wave velocity layer. Real data applications at sites across the Pacific Ocean that are coincident with previous in situ studies demonstrate the effectiveness of this method in characterizing the seafloor sediment unit. Furthermore, we widely apply the methodology to data from various OBS arrays in the Pacific to estimate in-situ sediment structures. The sediment models show multiple layers in some regions, including the top water-saturated layer with low S-wave velocity and high Vp/Vs values. The scaling relationship of Vp/Vs to Vp shows higher values than the previously discussed ones (e.g., Brocher, 2005; Hamilton, 1979). Furthermore, the sediment layer model constrained from the body waves exhibits agreement in predicted Rayleigh wave admittance with the sediment model from the Rayleigh wave admittance (Bell et al., 2015). The sediment models characterized by this new approach will allow us to more accurately predict and correct the effects of sediment layers in generating P- and S-wave reverberations. Additionally, in this presentation, we will discuss how the in-situ high-Vp/Vs multi-layer sediment model differs in predicting the reverberation effects on receiver function analysis for ocean bottom seismometers.

How to cite: Kim, H., Kawakatsu, H., Akuhara, T., and Takeuchi, N.: Characterizing the Seafloor Sediment Layer Using Teleseismic Body Waves Recorded by Ocean Bottom Seismometers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4428, https://doi.org/10.5194/egusphere-egu24-4428, 2024.

EGU24-7809 | ECS | Orals | SM6.2

Seismic interferometry applied to microseismic monitoring networks in mountain areas 

Ilaria Barone, Alessandro Brovelli, and Giorgio Cassiani

Seismic interferometry using ambient seismic noise is a powerful technique to constrain shear-wave velocities at different scales. Microseismic monitoring is essential to ensure the safety of industrial operations, including hydrocarbon extraction, gas storage and geothermal production. Microseismic monitoring involves recording seismic vibrations continuously, in order to identify and locate local earthquakes. However, most of the recorded seismic signals is ambient noise, that could be used to infer the shear-wave velocities in the area, thus allowing a more accurate location of the seismic events.

This study aims at applying seismic interferometry to ambient noise recorded by two small microsesimic monitoring networks in Switzerland, deployed around geothermal wells. The processing workflow for each station pair includes different steps as (1) cross-correlation of the raw seismic records, (2) analysis of the zero-crossings of the cross-spectra, (3) picking of the dispersion curve and (4) depth inversion. Due to the sparse nature of the seismic networks, surface wave tomography was not applied. Considerations on the topography effects, on the lateral variability of velocities and on the possible resonance effects due to the valley geometry will be done.

How to cite: Barone, I., Brovelli, A., and Cassiani, G.: Seismic interferometry applied to microseismic monitoring networks in mountain areas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7809, https://doi.org/10.5194/egusphere-egu24-7809, 2024.

EGU24-8975 | Orals | SM6.2

Passive seismic imaging for CO2 geological storage in the Sudret area of Gotland, Sweden 

Zhihui Wang, Christopher Juhlin, Peter Hedin, Mikael Erlström, and Daniel Sopher

Carbon capture and storage (CCS) is a strategy that can be employed to reducing human impact on climate change In the 21st century. Geological storage has been currently considered the most promising strategy. It is reported that there is a large theoretical capacity to store CO2 in the Precambrian sedimentary succession of the Baltic Basin.

 

To aid in surveying and evaluating the potential storage reservoirs in the Baltic Sea, a seismic survey was performed over similar geology in the Sudret area of Gotland. Part of the survey consisted of 14-hours passive data, recorded along a 2.8 km profile with 10m receiver spacing and 1ms sample rate using 329 5Hz SmartSolo nodal units in the vicinity of two boreholes that had been drilled earlier.

 

We retrieved body wave and surface wave virtual shot gathers after applying signal separation and cross correlation calculations. For the body waves, conventional seismic data processing was conducted to obtain a stacked profile; for the surface waves, we could determine the dispersion curve in the frequency range 0.5 to 5.5 Hz and inverted these curves to obtain a velocity model from the ground surface down to c. 1500m depth.

 

Both the body waves and surface waves provide a high quality and high resolution image of the top of the Ordovician formation and have a good consistency with active seismic data in the same location. Moreover, they revealed some reliable deep geological information which active data cannot provide because of the limited source energy. Compared with active seismic exploration, passive seismic is friendly to the environment and cost effective. In some cases, it is an important complementary or alternative method to active seismic for CO2 storage and monitoring.

How to cite: Wang, Z., Juhlin, C., Hedin, P., Erlström, M., and Sopher, D.: Passive seismic imaging for CO2 geological storage in the Sudret area of Gotland, Sweden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8975, https://doi.org/10.5194/egusphere-egu24-8975, 2024.

EGU24-9327 | ECS | Orals | SM6.2

Ambient noise tomography for geothermal exploration: the central Vienna basin, Austria 

Clément Estève, Yang Lu, Götz Bokelmann, and Jeremy Gosselin

The Vienna Basin (VB) is currently the main target area for deep geothermal exploration in Austria. Knowledge of the subsurface heavily relies on active seismic reflection that are expensive and logistically demanding. Affordable geophysical prospecting methods are needed to reduce subsurface uncertainty. Over the recent years, seismic ambient noise tomography (ANT) has proven to be a cost-effective and environment-friendly exploration technique. Here, we present an ANT of the central Vienna Basin revealing the shear-wave velocity structure of the top 5 km beneath the surface. We deployed an array of ~100 seismic nodal instruments during 6 weeks over summer 2023. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic ambient noise and employed transdimensional Bayesian tomography to invert for isotropic group velocity maps at periods ranging from 0.8 to 5.5 s. We then extracted Rayleigh and Love group velocity dispersion curves from the group velocity maps at all locations and jointly inverted them for shear-wave velocity as a function of depth using a transdimensional Bayesian framework. We discuss features observed in our 3D shear-wave velocity model relevant to geothermal exploration.

How to cite: Estève, C., Lu, Y., Bokelmann, G., and Gosselin, J.: Ambient noise tomography for geothermal exploration: the central Vienna basin, Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9327, https://doi.org/10.5194/egusphere-egu24-9327, 2024.

EGU24-13498 | ECS | Orals | SM6.2

Real-time Ambient Seismic Noise Tomography of the Hillside IOCG Deposit 

Tim Jones, Gerrit Olivier, Bronwyn Murphy, Martin Gal, Nick Smith, Brooke North, Darren Burrows, Lachlan Cole, Craig Went, and Steven Olsen

We use ambient noise tomography (ANT) to image the Hillside Iron-Ore-Copper-Gold (IOCG) deposit at prospect-scale, leveraging Fleet's direct-to-satellite technology for real-time data analysis. Our results capture aspects of the deposit's known geology, including depth of cover, structures linked to mineralisation, and the mineralised host rock, and identifies several new features, including the behavior of key structures down to 1 km depth and lithological variation that underlies the Hillside deposit. Results are compared to existing magnetic, gravity, induced-polarization and drilling data. An analysis of model convergence rates with respect to environmental noise conditions (signal-to-noise ratio) shows that real-time analysis can reduce data collection at the site to within 50% of traditional deployment times. We conclude by commenting on the efficacy of ANT for IOCG exploration more broadly.

How to cite: Jones, T., Olivier, G., Murphy, B., Gal, M., Smith, N., North, B., Burrows, D., Cole, L., Went, C., and Olsen, S.: Real-time Ambient Seismic Noise Tomography of the Hillside IOCG Deposit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13498, https://doi.org/10.5194/egusphere-egu24-13498, 2024.

In the last decade, passive seismic techniques have found use in the mineral exploration sector. In particular, ambient noise tomography is a low cost viable option that can outperform competing geophysical methods when imaging down to a few kilometers depth. However, at present it does not belong to the core approaches (e.g. magnetic, gravity, etc.) mainly due to a lack of experience in the industry. Novel approaches often go through a period of testing where the industry is familiarized with the technique and expectations are "adjusted". In order to speed up this testing period, an extensive review of the technique and its capabilities for real geological settings is required.

In this work, we build geological models of well known mineral deposits and generate ambient noise cross correlation functions (ccfs) for synthetic deployments. The ccfs are then used in a state of the art fully probabilistic ambient noise tomography to assess the strengths and weaknesses of this technique. This work will allow the industry to better understand the methods capabilities and adjust their expectations for exploration purposes. 

How to cite: Gal, M., Oliver, G., Lecocq, T., and Gunner, G.: Assessing the Accuracy and Feasibility of Ambient Noise Tomography for Copper Exploration: Insights from Synthetic Data Generation with Realistic Geological Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13672, https://doi.org/10.5194/egusphere-egu24-13672, 2024.

EGU24-16563 | ECS | Orals | SM6.2

Imaging of sediment-hosted Cu deposits using ambient noise tomography: a case study of the Kansanshi Cu-mine, Zambia. 

Tobermory Mackay-Champion, Nicholas Harmon, Sekelo Mutelekesha, Mulenga Chanda, Thomas Hudson, John-Michael Kendall, and Michael C Daly

Improved passive seismic imaging of sedimentary basins plays a crucial role in improving our understanding of basin inversion tectonics and sedimentary-hosted mineral systems. The Central African Copperbelt of Zambia and the Democratic Republic of Congo is hosted in the Neoproterozoic Katangan sedimentary basin and accounted for 8.8% of global copper production in 2021 (World Economic Forum, 2024). Despite this, the tectonic evolution of the basin in Northern Zambia is currently unclear, significantly hampering our understanding of the Cu, Co and Ni mineralisation in that area. To investigate the geodynamics that shaped this region, and to assess the suitability of MEMS-accelerometers for passive seismic imaging of sedimentary basins, an array of nodal accelerometers was deployed around the Kansanshi Mine (NW Zambia), previously Africa’s largest Cu mine. Surface wave phase velocities in the mine and surrounding area were analysed using ambient noise tomography, with average Rayleigh wave phase velocities ranging from 3.05 +/- 0.2 km/s at 3 s period to 3.5 +/- 0.15 at 6 s period. The S-wave velocity at points of particular interest was examined using iterative non-linear inversions of surface wave dispersion curves constructed from the tomography results. These S-wave profiles provide new insight into the structural configuration of the Kansanshi copper mine and show that the mine overlies a large thickness of sediments from which the copper could be scavenged. This study illustrates the efficacy of performing ambient noise tomography on MEMS-accelerometer data to investigate the structures controlling the inversion of sedimentary basins and the formation of sedimentary-hosted metal deposits at a local to regional scale.

How to cite: Mackay-Champion, T., Harmon, N., Mutelekesha, S., Chanda, M., Hudson, T., Kendall, J.-M., and Daly, M. C.: Imaging of sediment-hosted Cu deposits using ambient noise tomography: a case study of the Kansanshi Cu-mine, Zambia., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16563, https://doi.org/10.5194/egusphere-egu24-16563, 2024.

EGU24-18794 | ECS | Orals | SM6.2

Subsurface characterization using downhole passive Distributed Acoustic Sensing data in the Groningen gas field 

Wen Zhou, Anna Stork, Jan van Elk, Ari David, Hanneke Paulssen, and Annemarie Muntendam-Bos

This study presents passive downhole Distributed Acoustic Sensing (DAS) measurements conducted in the Groningen gas field, Netherlands, for subsurface and induced seismicity monitoring. The optical fiber installation, completed in Sept 2015, was partially cemented behind the inner casing along a deviated well (~3800 m), extending into the sandstone reservoir at temperatures ranging from 100-110 degrees Celsius. In Nov 2022, we interrogated the optical fiber utilizing a 10 m gauge length and 1 m sampling spacing.

Within this setup, most DAS traces exhibit the lowest self-noise floor in the frequency range of 0.1 to 30 Hz. Noteworthy is the absence of visible differences between cemented and uncemented sections. Strong ambient seismic noise is observed in the near-surface unconsolidated sediment at approximately 800 m depth. Noise cross-correlation (CC) analysis is performed for DAS channels and DAS seismometer pairs. Surface wave signals in the 0.1 to 1 Hz range are identified in DAS-seismometer CCs, displaying amplitude and polarization changes with depth, following Surface wave theory.

Induced seismicity is also recorded, with wavefields of events exhibiting clear amplitude variations along the fiber, strongly correlating with sonic logging. Our findings suggest that downhole DAS has the potential to characterize the subsurface with high resolution.

How to cite: Zhou, W., Stork, A., van Elk, J., David, A., Paulssen, H., and Muntendam-Bos, A.: Subsurface characterization using downhole passive Distributed Acoustic Sensing data in the Groningen gas field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18794, https://doi.org/10.5194/egusphere-egu24-18794, 2024.

EGU24-19600 | ECS | Posters on site | SM6.2

Seasonal variations in seismic velocities within the Swiss Jura using Ambient Noise Interferometry 

Michaïl Henry, Geneviève Savard, Francisco Muñoz, and Matteo Lupi

In recent years, seismic ambient noise interferometry has become a promising non-invasive time-lapse monitoring tool for near-surface studies. Indeed, researches have revealed that the coda of ambient noise cross-correlations can detect subsurface velocity changes (dv/v) as small as 0.01%. Seismic interferometry applications have been demonstrated for monitoring natural processes (groundwater cycle, volcano eruption dynamics) and human operations affecting the subsurface (e.g. geothermal, wastewater disposal). In such applications investigating human-induced effects, careful consideration must be given to site-specific natural background fluctuations to confidently determine if observed velocity changes can be attributed to human interventions. 

An upcoming Enhanced Geothermal System will be developed in the Swiss Jura mountains. Before seismic interferometry can be deployed to monitor geothermal operations, it is important to understand seasonal variations of the noise field. Hence, we are conducting a seismic interferometry study to investigate natural dv/v fluctuations in the area of the future geothermal plant. Using four years of continuous seismic data (August 1, 2017 to June 1, 2021) recorded by four triaxial high-gain broadband stations part of the Swiss national seismic network, we are applying both the moving window cross-spectral (MWCS) and stretching techniques across multiple cross-components. The objective is to quantify the range and magnitude of seasonal seismic velocity changes in the subsurface. Furthermore, our investigations involve exploring correlations between observed velocity changes and specific environmental factors, such as precipitation, groundwater level variations, and temperature fluctuations.

 

How to cite: Henry, M., Savard, G., Muñoz, F., and Lupi, M.: Seasonal variations in seismic velocities within the Swiss Jura using Ambient Noise Interferometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19600, https://doi.org/10.5194/egusphere-egu24-19600, 2024.

In this study, the detection of buried objects in GPR images using the deep learning-based Faster R-CNN and YOLOv5 methods and their classification according to their geometric shapes are investigated. Buried objects in the near surface may have different geometric shapes. Such objects can be imaged using Ground Penetrating Radar (GPR). As research materials, a rectangular prism-shaped aluminum-coated box and a cylindrical rod are used for laboratory measurements. A simulated underground model has been created in a laboratory environment, and GPR measurements have been performed. A radar device is designed for measurements using a Vector Network Analyzer (VNA) and a Vivaldi antenna pair. The scenarios for the measurements in the laboratory environment are modeled in the gprMax program, and synthetic GPR images are generated. The dataset consists of both actual measurements and synthetic data. Deep learning-based Faster R-CNN and YOLOv5 methods are popular techniques used for object detection in images. The GPR images used for training in these methods are augmented by using flipping and resizing techniques, and the dataset is expanded. Subsequently, hyperbolic structures of objects in GPR images are labeled as "rectangular" and "cylindrical" based on their geometric shapes. The training process is then carried out using these methods, resulting in the detection of buried objects in GPR images with high accuracy and classification based on their geometric shapes as "rectangular" and "cylindrical". The performances of the two different methods are compared, revealing that Faster R-CNN achieved higher accuracy, while the YOLOv5 method exhibited faster detection.

How to cite: Apaydın, O. and İşseven, T.: Detection and classification of near-surface buried objects in GPR images with deep learning-based Faster R-CNN and YOLOv5 methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-382, https://doi.org/10.5194/egusphere-egu24-382, 2024.

EGU24-1014 | ECS | Orals | SM6.4

Mapping basalt lava flows at Dive Ghat (Pune, India) using multichannel analysis of surface wave (MASW) technique 

Rashi Rashi, Rahul Dehiya, Sudipta Sarkar, and Raymond Duraiswami

Lava-flow structure and morphology provide insights into eruption styles, emplacement mechanisms, and post-emplacement alterations like weathering. However, the challenge lies in quantifying subsurface structures of buried lava flows beneath soil and vegetation cover. We present a case study of lave flow mapping employing seismic methods from the Dive Ghat region of Pune, situated in the Deccan Volcanic Province. Seismic data was collected using a 48-channel engineering seismograph with 1m receiver spacing and 2m shot spacing via a sledgehammer source. The seismic profile is taken parallel (roughly 4 m away) to the approximately 10 m vertical exposed section, which is used for cross-validation of the flow geometry, and it shows the presence of roughly six inches of red bole layer overlaying on a highly weathered basalt. The observed data is analyzed through refraction and multichannel analysis of surface wave (MASW) techniques. The refraction method yielded a high-resolution P-wave velocity model in the near subsurface with P-wave velocity (Vp) ranging from 0.3–4.5 km/s. However, the refraction method fails to image highly weathered basalt, which is expected as no critically refracted wave will be generated from the top of a low-velocity layer. The MASW method delivered a horizontally smeared S-wave velocity model where S-wave velocity (Vs) varies from 0.15–2.2 km/s. The subsurface S-wave model has a low-velocity layer of around 0.7 km/s Vs velocity embedded between 8.5–14m, which correlates to a red bole layer and underlying fractured basalt formed through weathering. Furthermore, a Vp-Vs cross plot is calculated to characterize different seismic units in velocity sections. The results obtained in this study may serve as an analogue to map near-surface flow geometry in unexposed sections in the Deccan Volcanic Province region. The MASW method successfully imaged the buried red bole layer and underlying weathered zone, which is crucial for agriculture due to its organic content. The imaging also holds implications for slope stability studies, emphasizing the importance of seismic characterization for hazard zonation, especially concerning the red bole and fractured basalt.

How to cite: Rashi, R., Dehiya, R., Sarkar, S., and Duraiswami, R.: Mapping basalt lava flows at Dive Ghat (Pune, India) using multichannel analysis of surface wave (MASW) technique, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1014, https://doi.org/10.5194/egusphere-egu24-1014, 2024.

EGU24-3609 | ECS | Orals | SM6.4

HVSR analysis to investigate a possible correlation to a gas shallow reservoir in a mud volcanic field: the case of Nirano (MO). 

Albachiara Brindisi, Dario Albarello, Nicolò Carfagna, and Enrico Paolucci

Multiple studies highlight the evidence of a trough within the low-frequency range in HVSRs measurements performed over a gas field and attribute it to the presence of a hydrocarbon reservoir (Lambert et al., 2007; Saenger et al., 2007; Panzera et al., 2016). To explain the natural emission of low-frequency signals Saenger et al. (2007) and Lambert et al. (2007) consider hydrocarbon-reservoir related microtremor, assuming that the reservoir itself acts as a (secondary) source of low-frequency seismic waves by a resonant amplification effect. Furthermore, Panzera et al. (2016) observe that the minimum is identified by an “inverse eye-shaped” feature in the Fourier spectra, related to an amplitude increase in the vertical component of motion due to a velocity inversion. This study focuses on the investigation of the spectral anomaly described above at Nirano mud volcano field, conducted through the analysis of the results obtained by seismic arrays and three directional velocimetric stations (HVSR) deployed in the site. After a cluster analysis carried out on HVSRs have been identified 3 groups of measurements, one of which include HVSRs located in the caldera-like basin area, marked by a minimum in the seismic spectrum at 0.53 Hz. The joint inversion procedure based on Genetic Algorithms of the HVSR curves and the Rayleigh waves dispersion curve shows that the minimum is well reproduced even without a velocity inversion. This proves that it is not uniquely correlated to the mechanisms proposed above and that, therefore, it may be linked to a stratigraphic effect that unites all the measurements concentrated in the group under examination or to the surface wave model used.

References

Lambert M., Schmalholz S. M., Saenger E. H. and Podladchikov Y. Y.; 2007: Low-frequency anomalies in spectral ratios of single-station microtremor measurements: Observations across an oil and gas field in Austria. In SEG Technical Program Expanded Abstracts 2007 (pp. 1352-1356). Society of Exploration Geophysicists.

Panzera F., Sicali S., Lombardo G., Imposa S., Gresta S. and D’Amico S.; 2016: A microtremor survey to define the subsoil structure in a mud volcanoes area: the case study of Salinelle (Mt. Etna, Italy). Environmental Earth Sciences, 75, 1-13.

Saenger E.H., Torres A., Rentsch S., Lambert M., Schmalholz S.M. and Mendez-Hernandez E.; 2007: A hydrocarbon microtremor survey over a gas field: Identification of seismic attributes. 77th SEG meeting, San Antonio, Texas, USA, Expanded Abstracts, 1277–1281.

How to cite: Brindisi, A., Albarello, D., Carfagna, N., and Paolucci, E.: HVSR analysis to investigate a possible correlation to a gas shallow reservoir in a mud volcanic field: the case of Nirano (MO)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3609, https://doi.org/10.5194/egusphere-egu24-3609, 2024.

EGU24-3801 | Posters on site | SM6.4

3D reflection seismic surveying and borehole DAS measurements to image the sedimentary structure in the Sudret area of Gotland, Sweden 

Christopher Juhlin, Bojan Brodic, Mikael Erlström, Peter Hedin, Daniel Sopher, Zhihui Wang, and Zbigniew Wilczynski

Reflection seismic data were acquired in the Sudret area of Gotland in the time window 6 to 13 November, 2023. Objectives of the survey were to obtain images of the subsurface down to the Precambrian basement in the vicinity of two coreholes that had been drilled earlier down to about 800 m. These images would provide a better understanding of the sedimentary strata and local structure near these holes. For these purposes a sparse 3D survey was acquired that covered a c. 300 m by 700 m rectangular area with high fold, including the locations where the boreholes were drilled. A longer c. 2.8 km 2D profile was also acquired adjacent to the 3D survey that ran roughly in the N-S direction. In addition, distributed acoustic sensing (DAS) measurements were performed in the two coreholes. We report here on some results from the 3D survey and from the DAS measurements.

A Bobcat source with a 500 kg weight drop hammer with base plate was used as a source and 410 5Hz nodal units were available for recording. In total, 704 receiver locations were occupied with acquisition along 19 source lines, implying that 294 units had to be moved during the survey and that the source lines had to be shot twice. DAS data were recorded over the depth interval 17 m above sea level to 475 m below sea level in the Nore-1 corehole. In Nore-2 the depth interval was 17 m above sea level to 720 m below sea level. The fiber optic cable was sampled at 2.45 m intervals and data were recorded at a sampling frequency of 4000 Hz. Due to borehole irregularities it was not possible to get the fiber optic cables all the way to the bottom of the coreholes.

Numerous semi-continuous reflection horizons are observed in the c. upper 500 ms after stacking. A particularly strong reflection at 350 ms likely originates from the top of the Ordovician. Cambrian sandstones are also reflective, as well as shallow sandstone layers in the upper 150 ms. Normal moveout (NMO) velocities are relatively constant at about 3500 m/s. However, depth conversion using this velocity places the reflectivity deeper than what is expected from the cores. The DAS data allow the vertically propagating P-wave velocity to be measured at 3100 m/s. Using this velocity for depth conversion provides more reasonable depths to the main horizons. Since the NMO velocities are largely controlled by the horizontal velocity of the rock the difference between these and the DAS velocity can be explained by the rocks in the area having significant anisotropy (about 10%).

How to cite: Juhlin, C., Brodic, B., Erlström, M., Hedin, P., Sopher, D., Wang, Z., and Wilczynski, Z.: 3D reflection seismic surveying and borehole DAS measurements to image the sedimentary structure in the Sudret area of Gotland, Sweden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3801, https://doi.org/10.5194/egusphere-egu24-3801, 2024.

In seismic exploration, three-dimensional near-surface tomography is key to solving complex statics problem and is an important prerequisite for migration imaging. To this end, this paper starts with the principles of ray tracing theory and tomographic inversion methods. Based on a comprehensive comparative analysis of the advantages and disadvantages of traditional ray tracing methods and numerical algorithms for tomographic inversion, using the first arrival times in three-dimensional seismic data, a high-precision three-dimensional ray tracing method based on multi-retracing technology and a tomographic inversion method constrained by prior information such as small refraction and micro logging throughout the process are proposed. First, this paper use near-surface survey information such as micro logging and small refraction to constrain the establishment of an initial velocity model and constrain tomographic inversion to improve the vertical inversion accuracy of the model. Secondly, to address the loss of shallow layer information due to excessive shot-to-detector distances, this paper introduces a virtual detector point technique. By adding one or more virtual detector points between known shot points and detector points within a close offset range, the density of rays at near offsets is increased, thereby improving the lateral tomographic imaging accuracy of the near-surface. At the same time, various constraints are introduced during the inversion process, including the range of velocity restriction, inversion slowness correction size constraints, internal iteration number constraints of tomographic inversion, dual-grid inversion, velocity extrapolating and smoothing, etc., greatly improving the accuracy of inversion and the quality of tomographic imaging. Given the large computational volume of three-dimensional data and the high memory consumption of large sparse matrices, this paper employs compressed storage and tomographic matrix solving techniques, greatly saving memory space and enhancing computational efficiency. The test results on theoretical models and actual data show that the ray tracing method used in this paper provides essentially correct ray propagation paths, consistent with geological laws. The final inversion results effectively reveal the velocity and thickness of near-surface low-speed layers and deceleration layers, demonstrating the correctness and effectiveness of the inversion method proposed in this paper.

Keywords: Velocity modeling, Ray tracing, Tomographic inversion, Micro logging, Small refraction

How to cite: cheng, R.: Method for near-surface three-dimensional velocity modeling based on first-arrival, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4659, https://doi.org/10.5194/egusphere-egu24-4659, 2024.

EGU24-5159 | Posters on site | SM6.4

Adaptive Mesh-free Approach for Gravity Inversion 

Yan Liu, Yao Huang, and Qingtian Lü

We proposes a method of gravity inversion based on an adaptive mesh-free approach by using a modified radial basis function . It can parametrize the density distribution by using a mesh-free approach. The subsurface space is generally discretized into regular grid cells, while mesh-free methods can avoid the expensive mesh generation and manipulation required in traditional approaches. Scattered points are introduced in most mesh-free methods to discretize the given equations. To deal with the problem of unstructured nodal discretization, we use a mesh-free discretization strategy to establish a mapping of subsurface grid cells to a cloud of discrete points. The nodes are adaptively refined during the inversion process to better recover abnormal bodies. In addition, the hybrid basis function and the modified radial basis function are used to improve the accuracy and stability of the solution. We verify the effectiveness of the proposed method by using several synthetic and empirical tests.

How to cite: Liu, Y., Huang, Y., and Lü, Q.: Adaptive Mesh-free Approach for Gravity Inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5159, https://doi.org/10.5194/egusphere-egu24-5159, 2024.

EGU24-7978 | ECS | Orals | SM6.4

Integrated model-data observations of water flow dynamics across bedrock and vegetation variations of a mountainous hillslope 

Sebastian Uhlemann, Luca Peruzzo, Chunwei Chou, Kenneth Williams, Stijn Wielandt, Chen Wang, Nicola Falco, Yuxin Wu, Brad Carr, Philip Meldrum, Jonathan Chambers, and Baptiste Dafflon

Hydrological processes in mountainous watersheds, and how soil, bedrock, and plants interact are still poorly understood. Through a dense network of soil moisture and temperature sensors, high resolution electrical resistivity tomography monitoring, and weather data we assess the above and below-ground processes driving the hydrological response of a hillslope during snowmelt and summer monsoon. The monitoring transect covers different bedrock and vegetation types, with a steep upper part characterized by shallow bedrock and covered by pine trees, and a gentle lower part underlain by colluvium and covered mostly by grass and veratrum. Coupling the monitoring data with a simplified hydrological model, we observe several important hydrological processes that show how variations in bedrock and vegetation type change subsurface flow patterns, allowing us to answer how subsurface flow pathways differ between shallow and deep bedrock units, and to assess the interactions between vegetation, bedrock types and subsurface flow dynamics. 

While on the steep section, characterized by thin soil and shallow bedrock, we observe mostly shallow and rapid lateral flow, on the gentle slope underlain by colluvium vertical flow is prevailing. Timelapse resistivity patterns indicate that for shallow bedrock, fractures and tree roots may provide preferential flow pathways into deeper bedrock units during snowmelt, which may provide means to mitigate summer drought conditions. Shading of the trees seems to further mitigate drought conditions by limiting evaporation of summer monsoon rainfall, leading to less drying of the shallow soil layer. In the lower, gentle part of the profile snowmelt is contributing to vertical flow recharging the aquifer, while in the summer upwelling groundwater is providing moisture to sustain plant growth. 

These observations show that variations in bedrock and vegetation pose a strong control on hillslope hydrology, creating spatially complex flow patterns. These results highlight the spatial heterogeneity of hydrological processes in mountainous watersheds, which need to be understood to predict how watersheds respond to disturbances.

How to cite: Uhlemann, S., Peruzzo, L., Chou, C., Williams, K., Wielandt, S., Wang, C., Falco, N., Wu, Y., Carr, B., Meldrum, P., Chambers, J., and Dafflon, B.: Integrated model-data observations of water flow dynamics across bedrock and vegetation variations of a mountainous hillslope, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7978, https://doi.org/10.5194/egusphere-egu24-7978, 2024.

EGU24-8256 | Posters on site | SM6.4

Using ambient noise to study the co-seismic and post-seismic velocity changes of the 2021 Yangbi MS 6.4 earthquake in Yunnan, China 

Yanru An, Weitao Wang, Wei Yang, Haikun Jiang, Jun Yang, Xiaobin Li, and Rui Pan

Seismic velocity change is a good indicator reflecting the stress state variation of the underground media. Therefore, seismogenic process could be effectively revealed by the velocity change calculation. Based on the seismic ambient noise interferometry, we study the co-seismic velocity change and post-seismic recovery process of the 21 May 2021 MS6.4 Yangbi earthquake using the continuous records from 16 stations within 50km of the epicenter. The results show that the relative velocity changes between the station pairs (dv/vpair) decrease significantly after the mainshock. The amplitude ranges from -0.29% to -0.02% and decreases with the increase of station spacing. The relative velocity changes of each station (dv/vstation) obtained by linear regression range from -0.16% to -0.02%, and are generally negatively correlated with the epicenter distance. It is notable that the measured co-seismic velocity changes are mainly originated from the shallow media (≤2km). Such changes are considered to be caused by both static and dynamic strain, but the primary controlling factor is rock fragmentation and large-scale adjustment of stress produced by strong ground motion. In addition, dv/vstation located at the northern stations far from the epicenter have the largest drop values, demonstrating that they are more sensitive to stress disturbances. This may be related to the distribution of thermal fluids below these stations. The results of velocity changes indicate that around the study area the seismic velocity reached its minimum value within a few days after the mainshock. The value then gradually recovered, reaching the pre-seismic level around August, which characterizes the healing process of broken rocks. In this study, ambient noise interferometry has been effectively applied to measure the velocity changes during and after the Yangbi earthquake, and the results show that co-seismic velocity changes are jointly controlled by various factors including the fracture degree of the fault zone, dynamic strain, and the existence of fluids.

How to cite: An, Y., Wang, W., Yang, W., Jiang, H., Yang, J., Li, X., and Pan, R.: Using ambient noise to study the co-seismic and post-seismic velocity changes of the 2021 Yangbi MS 6.4 earthquake in Yunnan, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8256, https://doi.org/10.5194/egusphere-egu24-8256, 2024.

EGU24-9128 | ECS | Posters on site | SM6.4

Optimal Experimental Design strategies for geoelectrical monitoring of fluid transport processes 

Nino Menzel, Sebastian Uhlemann, and Florian M. Wagner

Electrical resistivity tomography (ERT) offers noninvasive monitoring capabilities for a wide range of environmentally relevant subsurface processes. Its sensitivity to fluid content and temperature changes positions it as an important tool for capturing dynamic processes such as the transport of groundwater pollutants, CO2 or radionuclides. Particularly crucial is its ability to achieve this without intrusively accessing to the site, making it highly valuable in closed repositories like high-level radioactive waste (HLW) storage sites.

In highly sensitive and complex environments, as in the case of closed repositories, it is critical to maximize the information content of the planned (geo)physical measurements while keeping the costs to a minimum. Several past studies presented approaches to optimize both the sensor positions and the measurement configurations of ERT surveys for static or moving targets in the subsurface. This study extends Optimal Experimental Design (OED) strategies for geoelectrical measurements using information of active time-dependent transport processes in the subsurface. We present three different approaches for process monitoring and apply them to a simulated diffusive-advective transport process in a synthetic model over several time steps. The methods aim at focusing the survey only on the relevant part of the model, in this case the model region that is affected by the transport process. All presented approaches account for uncertain model input parameters by introducing an uncertainty factor in the ranking function. We present a purely model-driven and a purely data-driven active time-dependent OED approach. The first method utilizes the already acquired data from previous time steps to create predictive focusing masks for the next data set, the latter purely relies on model predictions to focus the survey. Moreover, we delineate a hybrid approach using both the simulated transport distance and the already acquired datasets. All three OED methods are compared to each other as well as to datasets that were acquired using standard electrode configurations.

The results of our synthetic study show that the adaptively designed, time-dependent OED approaches result in increased image quality compared to both standard surveys as well as time-independent OED methods. For slow transport processes or small monitoring intervals, the purely data-driven approach is most suitable, since no model predictions, and thus no possible model parametrization uncertainties, are incorporated. For faster transport processes or monitoring strategies with larger acquisition intervals, the strategies that (partly) incorporate model predictions provide the most promising results.

How to cite: Menzel, N., Uhlemann, S., and Wagner, F. M.: Optimal Experimental Design strategies for geoelectrical monitoring of fluid transport processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9128, https://doi.org/10.5194/egusphere-egu24-9128, 2024.

EGU24-9793 | ECS | Orals | SM6.4

Geoelectrical monitoring of tree-soil water interactions at urban sites  

Johannes Hoppenbrock, Malkin Gerchow, Matthias Beyer, Vera Hörmann, Mona Quambusch, Michael Strohbach, and Matthias Bücker

The impact of climate change is increasingly restricting water availability in the soil, posing a significant challenge in urban areas where plants have to deal with limited space and sealed surfaces hinder rainwater infiltration. However, the amount of plant-available soil moisture plays a crucial role in plant vitality and is therefore important for ecosystem health. In urban environments, obtaining information on soil moisture is challenging. Commonly used methods, such as soil-moisture sensors, are often not applicable or do not provide a spatially resolved picture of soil moisture.

Within the context of the interdisciplinary project CliMax, we explore the applicability of geophysical methods to characterize soil moisture in the rhizosphere in urban areas. Over the past year, monthly monitoring Electrical Resistivity Tomography (ERT) measurements were conducted at nine different tree locations in Braunschweig, Germany, characterized by diverse tree species and degrees of sealing of the surface. Additionally, temporally and spatially higher-resolution measurements were selectively taken. Various time-lapse inversion approaches implemented in the open geophysical inversion library pyGIMLi were tested and applied. Furthermore, Time-Domain Reflectometry (TDR) soil-moisture sensor data from different depths are available at each site, allowing calibration of ERT results with respect to soil moisture.

The time-lapse inversion reveals well-resolved variation in soil moisture over the observed period, distinguishing between weather fluctuations and the influence of trees on the water balance. The water uptake is evident through increased resistivity values directly beneath the trees. Our study indicates that, depending on tree species and degree of sealing, the investigated urban trees predominantly extract water from the upper 1-4 meters. This finding is substantiated at specific locations by the data from deployed soil-moisture sensors.

How to cite: Hoppenbrock, J., Gerchow, M., Beyer, M., Hörmann, V., Quambusch, M., Strohbach, M., and Bücker, M.: Geoelectrical monitoring of tree-soil water interactions at urban sites , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9793, https://doi.org/10.5194/egusphere-egu24-9793, 2024.

EGU24-11360 | Posters on site | SM6.4

Trace Modelling: A Quantitative Approach to the Interpretation of Ground Penetrating Radar Profiles 

Antonio Schettino, Annalisa Ghezzi, and Luca Tassi

Classical analysis of radar profiles generally relies on a visual inspection and interpretation of profiles and sometimes on inverse modelling of the acquired data. Both methods suffer severe limitations due to the antenna resolution, thereby preventing the identification of tiny structures, especially in forensic applications. Here we describe a forward modelling technique, which allows to reproduce individual traces (A-scans) of radar profiles through superposition of Ricker wavelets. The method allows to detect ultra-thin layers, well beyond the Ricker and Rayleigh vertical resolution of GPR antennas. This approach starts from an estimation of the instrumental uncertainty of common monostatic antennas and takes into account of the frequency-dependent attenuation, which causes spectral shift of the dominant frequency acquired by the receiver antenna. The forward modelling procedure loads a single trace from a radar profile and allows to build a synthetic A-scan by fitting a sequence of Ricker wavelets with user-defined amplitude, polarity, and arrival time to the acquired trace. The resulting synthetic trace can be used to create a reflectivity diagram that plots reflection amplitudes and polarities versus depth. Often a reflectivity diagram shows intervals bounded by reflectors of opposite polarity, associated with layers having higher or lower velocity than the surrounding material, respectively. These intervals may result from very subtle features that represent interesting survey targets, for example buried bones, small cracks, thin lens of liquid contaminants, etc. and could be confused with individual reflectors through the simple visual inspection of a radar profile. Our quantitative approach can be used in several applications of GPR methods, especially in forensic, paleontological, civil engineering, heritage protection, and soil stratigraphy applications.

How to cite: Schettino, A., Ghezzi, A., and Tassi, L.: Trace Modelling: A Quantitative Approach to the Interpretation of Ground Penetrating Radar Profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11360, https://doi.org/10.5194/egusphere-egu24-11360, 2024.

EGU24-12013 | Posters on site | SM6.4

Measuring and modelling seismic surface-wave dispersion variations in various hydrogeological contexts 

Ludovic Bodet, Ramon Sanchez Gonzalez, José Cunha Teixeira, Marine Dangeard, Alexandrine Gesret, and Agnès Rivière

Pressure (P) or shear (S)-wave velocity models of the near-surface can be simultaneously estimated along coincident arrays from P-wave refraction tomography and surface-wave (SW) dispersion inversion methods. Over the past decade, this approach has been integrated into the hydrogeophysics toolbox to image spatial variations of VP/VS (or Poisson) ratio, as its evolution is strongly associated with water content (or saturation) contrasts. The relevance of this method has been verified in various Critical Zone (CZ) observatories, each with distinct hydrogeological characteristics such as continuous multi-layered hydrosystems or fractured environments with strong discontinuities. It has also proven successful in other contexts and application scales, including a hydrothermal site or partially saturated glass beads in a laboratory experiment. However, we identified two major issues: (1) the combined use of P-wave traveltime tomography and SW dispersion inversion involves distinct characteristics of the wavefield and different assumptions about the medium, providing VP and VS models with different sensitivity, resolution, investigation depth, and posterior uncertainties; (2) the involved inversion processes use a small number of layers that cannot properly describe the continuous variations of subsurface hydrological properties. In particular, we noted that VP/VS (or Poisson) ratio was only consistent with strong saturation contrasts and often faced difficulties in retrieving water content variations in the unsaturated zone. This underscores the need to use petrophysical approaches to build alternative forward models and improve inversion processes. Adapted rock physics models have thus recently been developed to take capillary suction effects into account in the effective stress of the soil. In this study, we first present several datasets obtained from various contexts in which SW dispersion variations have been observed and related to changes in water content and/or water table depths. We then suggest using the previously cited rock physics models to simulate these data and show how it helps in understanding the involved hydrofacieses and processes. We finally address the relevance of surface-wave dispersion inversion approaches involving such forward models and discuss the possible use of additional attributes of the seismic wavefield to constrain interpretations.

How to cite: Bodet, L., Sanchez Gonzalez, R., Cunha Teixeira, J., Dangeard, M., Gesret, A., and Rivière, A.: Measuring and modelling seismic surface-wave dispersion variations in various hydrogeological contexts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12013, https://doi.org/10.5194/egusphere-egu24-12013, 2024.

EGU24-12370 | ECS | Posters on site | SM6.4

Minimum entropy constrained cooperative inversion with application to electrical resistivity, seismic and magnetic field and synthetic data 

Anton H. Ziegon, Marc S. Boxberg, and Florian M. Wagner

Interpreting independent geophysical data sets can be challenging due to ambiguity and non-uniqueness. To address this, joint inversion techniques have been developed to produce less ambiguous multi-physical subsurface images. Recently, a novel cooperative inversion approach that uses minimum entropy constraints has been proposed. The major feature of this approach is that it can produce sharper boundaries inside the model domain. We implemented this approach in an open-source software framework and systematically investigated its capabilities and applicability on electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and magnetic data.

First, we conducted a synthetic 2D ERT and SRT data study to demonstrate the approach and investigate the influence of the equations’ parameters that must be calibrated as well as to justify extensions of the method. The results show that the use of the joint minimum entropy (JME) stabilizer outclasses separate, conventional smoothness-constrained inversions and provides improved images.

Next, we used the method to analyze 3D ERT and magnetic field data from Rockeskyller Kopf, Germany. Independent inversion of the magnetic field data already suggested a subsurface volcanic diatreme structure, but the joint inversion using JME not only confirmed the expected structure, but also provided improved details in the subsurface image. The multi-physical images of both methods are consistent in many regions of the model as they produce similar boundaries. Due to the sensitivity of the ERT measurements to hydrogeological conditions in the subsurface, some structures are only visible in the ERT data. These features seem not to be enforced on the magnetic susceptibility model, which highlights another advantage and the flexibility of the approach.

However, the results of both the synthetic and field data use cases suggest that careful parameter tests are required prior to cooperative inversion to obtain a suitable hyperparameters and reference model. Our work implies that minimum entropy constrained cooperative inversion is a promising tool for geophysical imaging provided that proper settings are chosen while it also identifies some objectives for future research to improve the approach.

How to cite: Ziegon, A. H., Boxberg, M. S., and Wagner, F. M.: Minimum entropy constrained cooperative inversion with application to electrical resistivity, seismic and magnetic field and synthetic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12370, https://doi.org/10.5194/egusphere-egu24-12370, 2024.

EGU24-12500 | ECS | Posters on site | SM6.4

High-resolution 4D GPR data acquisition strategy to monitor fast and small-scale subsurface flow processes 

Sophie Stephan, Conrad Jackisch, Jens Tronicke, and Niklas Allroggen

High-resolution measurement techniques for distributed and fast soil water dynamics could advance the understanding of subsurface infiltration processes on the plot scale when it can combine high spatial and temporal resolution with a high repeatability of the measured data.

Ground-penetrating radar (GPR) is a promising geophysical tool to image and quantify subsurface flow processes in a non-invasive fashion. In the literature, different strategies to collect time-lapse GPR data have been presented. However, so far, no standardized data acquisition and analysis strategy has been established to monitor subsurface changes related to water infiltration and to compare the outcomes of different experiments.

Here, we present a 4D-GPR measurement strategy to monitor infiltration experiments by combining an irrigation pad (to simulate moderate rain fall events) with a manually operated 3D GPR measurement platform (equipped with a two-channel GPR antenna array and positioning guides). For investigating the repeatability and resolution limits of our measurement strategy, we conducted a systematic field experiment with two recurrent irrigations at two nearby spots at a selected field plot. Our results show that we can reliably monitor non-uniform subsurface flow processes with a spatial resolution < 5 cm and a temporal resolution below 10 minutes.

Because of these so far unreached spatial and temporal resolution capabilities we consider our 4D-GPR measurement strategy as a first step toward a standardized strategy for monitoring infiltration processes. Furthermore, such detailed knowledge about the resolution and repeatability limits of 4D-GPR measurements opens new options for further interpretation approaches, for example without assumptions about a horizontally stratified subsurface model.

How to cite: Stephan, S., Jackisch, C., Tronicke, J., and Allroggen, N.: High-resolution 4D GPR data acquisition strategy to monitor fast and small-scale subsurface flow processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12500, https://doi.org/10.5194/egusphere-egu24-12500, 2024.

Hydrothermal and natural degassing geological systems present various hazards. Monitoring them is crucial to understanding their behavior, assessing risks comprehensively, and mitigating potential impacts on both the environment and human safety. Electrical resistivity, which is closely related to water content, gas content, and fluid temperature, is a key parameter for studying these systems. However, existing mathematical relationships, such as Archie's law, have limitations, particularly in their applicability to a wide range of petrophysical and thermodynamic properties. Linking the observed variations in measured resistivity to variations in the dynamics of the hydrothermal or natural degassing system under investigation is not straightforward.

 

The aim of this study is to establish a numerical relationship between petrophysical and thermodynamic input variables and resistivity data obtained from geoelectrical field surveys. This numerical relationship could predict changes in the electrical resistivity distribution based on variations in simulated petrophysical and thermodynamic values over time. Comparison between predicted and field resistivity data would ultimately validate the current dynamic state of the system, providing a powerful monitoring tool.

 

To this end, two 3D petrophysical and thermodynamic numerical models for two natural degassing systems were constructed by 3D electrical resistivity tomography surveys using constraints derived from different types of data (e.g., geological, geochemical and/or hydrogeological data). The models were validated through the comparison of predicted temperature, pressure, and gas flow distributions with field survey data. We then trained a Random Forest algorithm to predict the resistivity values for each cell of the models using the petrophysical and thermodynamic parameters of each cell as input and the field resistivity values as the target variable.

 

The results obtained for both models on the test data demonstrate the effectiveness of the Random Forest algorithm in successfully predicting resistivity values. This predictive capability, which allows adjustments to the system’s petrophysical and thermodynamic parameters until the predicted resistivity aligns with newly observed values, could shed light on the ongoing dynamics within the system, thereby enhancing its understanding through geophysical monitoring. The developed methodology could be a powerful addition to resistivity monitoring in active geological systems.  

How to cite: Carbonari, R., Salone, R., and Di Maio, R.:  Predicting Electrical Resistivity in Hydrothermal and Natural Degassing Geological Systems through petrophysical and thermodynamic data: a machine learning approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14573, https://doi.org/10.5194/egusphere-egu24-14573, 2024.

EGU24-15191 | ECS | Posters on site | SM6.4

Constraining Vp and Vs structures using the dispersion of surface and leaky waves 

Caiwang Shi, Xiaofei Chen, and Zhengbo Li

The dispersion curves of surface waves have been widely used for the retrieval of subsurface structures. Because the surface-wave dispersion is not sensitive to Vp, classical dispersion inversion can only retrieve Vs structures. To retrieve Vp, the dispersion of guided-P waves, which belong to leaky waves, should be considered. Due to the difficulty in forward modeling, the quantitative analysis of the leaky-wave dispersion curves has been rarely reported. In this study, we first derive the sensitivity analysis method of the leaky-wave dispersion based on previously proposed the semi-analytical spectral element method. Then the quantitative sensitivity analysis of leaky-wave dispersion curves is carried out, which confirms the ability of guided-P wave dispersion to constrain the velocity structures. With the theoretical analysis, we propose a joint inversion method based on surface and guided-P wave dispersion curves, which can simultaneously retrieve Vp and Vs. To verify the effectiveness, the proposed joint inversion has been applied to different kinds of field data including ocean bottom seismometer data with active sources and the seismic data of Nevada in the United States in 2008. Both of the inversion tests show that the joint inversion of surface- and leaky-wave dispersion can effectively constrain the velocity structure of Vp and Vs at the same time, which helps to obtain more complete and accurate models than the traditional surface wave dispersion inversion.

How to cite: Shi, C., Chen, X., and Li, Z.: Constraining Vp and Vs structures using the dispersion of surface and leaky waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15191, https://doi.org/10.5194/egusphere-egu24-15191, 2024.

Exploring the shallow crustal structure of Mars can offer valuable insights into the planet’s geological evolution and climate history. The ambient wavefield data and marsquake records from NASA’s InSight mission have enabled the characterization of both fine-scale near-surface structures (less than 200 meters) and large-scale crustal structures (greater than a few kilometers) on Mars. However, the exploration of intermediate-scale structures has remained limited. In this study, we introduce a novel varying-parameter approach that integrates principal component analysis with receiver function techniques. This method allows for the effective extraction of P-wave particle motions across various frequencies from the InSight low-frequency marsquake data, facilitating the inversion for the S-wave velocity structure within the topfew kilometers beneath the lander. Our resulting models reveal a distinct discontinuity at a depth of approximately 0.7 km, marked by a sharp increase in S-wave velocity from about 1.4 km/s to roughly 1.9 km/s. This discontinuity is characterized by a sharp transition, approximately 0.1 km thick, rather than a wider gradient zone. Our models are generally consistent with existing data on Mars’ near-surface and large-scale crustal structures, effectively bridging these datasets. When combined with previous geological and seismic observations, the newly identified discontinuity may signify the top of less affected basaltic bedrock, and the overlying structures are interpreted as a composite of Noachian- to early Hesperian-aged sediments and Hesperian to Amazonian basalts. These insights provide new perspectives on the stratification at the InSight landing area, enhancing our understanding of Martian geological history.

How to cite: Wang, X., Chen, L., and Wang, X.: Shallow Crustal Structures of Mars Beneath the InSight Landing Site Revealed by Frequency-Dependent P-wave Particle Motions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15635, https://doi.org/10.5194/egusphere-egu24-15635, 2024.

EGU24-16128 | ECS | Orals | SM6.4

Imaging large-scale geological structures using Deep ERT: a case study on the Booze Val-Dieu block in Belgium 

Yannick Forth, Hadrien Michel, David Caterina, Joost Hase, Andreas Kemna, Nils Chudalla, Florian Wellmann, Bjorn Vink, and Frédéric Nguyen

The geophysical investigation of geologic structures is an essential prerequisite for the preparatory phase of large subsurface construction projects like caverns or tunnels and to study structural geology. This type of investigation is crucial to guide boreholes for relevant ground truth, knowledge of the local geology, or to adjust the position of underground constructions.

Typical approaches to image large structures are seismic reflection surveys or Airborne Electromagnetic surveys (AEM). However, seismic surveys might fail due to an absorbing soft top layer or steeply inclined layers. AEM surveys generally are poorly adapted to applications in urbanized areas. To overcome these issues, another method for large-scale subsurface imaging is the application of Deep Electrical Resistivity Tomography (Deep ERT), a recent approach where employing separated injection and measurement systems allows for large injection dipoles that retrieve information from depth.

We conducted a Deep ERT campaign in the framework of the E-TEST project for the investigation for a suitable location for the Einstein Telescope, a gravitational wave observatory consisting of a set of subsurface laser interferometers in a triangular shape at a depth around 300 m. Here, we present the results from a 2D Deep ERT survey in Val Dieu, Belgium with a total length and maximum injection dipoles of 7,5 km and a total of 14040 measured datapoints. We show the challenges during preparation, performance and data processing and discuss its capability in imaging large and deep geological structures.

How to cite: Forth, Y., Michel, H., Caterina, D., Hase, J., Kemna, A., Chudalla, N., Wellmann, F., Vink, B., and Nguyen, F.: Imaging large-scale geological structures using Deep ERT: a case study on the Booze Val-Dieu block in Belgium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16128, https://doi.org/10.5194/egusphere-egu24-16128, 2024.

EGU24-17357 | ECS | Orals | SM6.4

Comparison of data-driven and physics-driven surface wave inversion 

Xinhua Chen, Jianghai Xia, Yu Hong, and Jingyin Pang

In near-surface investigations, the advent of massive seismic data has ushered in the application of deep learning (DL) techniques for surface wave inversion to attain the shear-wave velocity (Vs). While the efficiency of DL inversion surpasses that of classic physics-driven methods, its broader attributes remain underexplored. Our study delves into a comparative analysis of DL inversion versus physics-driven inversion, focusing on three key aspects: anti-noise ability, stability, and generalization.

In numerical experiments, we employ the neighborhood algorithm (NA) (Wathelet, 2008) as a representative of physics-driven inversion, and a convolutional neural network (CNN) constructed for near-surface investigations (Chen et al., 2022) as a representative of data-driven inversion. In addition to comparing the two methods, we also explore the characteristics of joint inversion using Rayleigh-wave dispersion curves (DCs) and Love-wave DCs in the three above aspects. To quantitatively evaluate inversion results, we calculate the root mean square error and relative error of both DCs and Vs. The assessment of anti-noise performance involves applying NA and CNN to DCs with varying noise levels. To gauge stability, we introduce errors in compressional-wave velocity (Vp) and density, examining their effects on inversion precision. Lastly, to assess generalization, we use NA and CNN to invert DCs whose Vs exceeds the range of the training dataset by different percentages.

Our findings reveal that DL inversion has a higher anti-noise ability compared with NA. Both methods demonstrate high stability, with errors in Vp and density exerting a slight impact on inversion results, aligning with surface wave inversion characteristics. Compared with physics-driven inversion, generalization is a unique feature of data-driven inversion. The experimental results indicate that the CNN can predict Vs models that are not included in the training dataset although this ability is somewhat limited. Furthermore, like physics-driven inversion, joint inversion enhances all three examined aspects for data-driven inversion. This analysis of characteristics can guide the selection of inversion methods for surface wave applications in near-surface investigations.

 

References:

  • Wathelet M., "An improved neighborhood algorithm: parameter conditions and dynamic scaling," Geophysical Research Letters, vol. 35, no. 9, pp. 2008, doi: 10.1029/2008GL033256.
  • Chen X., Xia J., Pang J., Zhou C., and Mi B., "Deep learning inversion of Rayleigh-wave dispersion curves with geological constraints for near-surface investigations," Geophysical Journal International, vol. 231, no. 1, pp. 1-14, 2022, doi: 10.1093/gji/ggac171.

How to cite: Chen, X., Xia, J., Hong, Y., and Pang, J.: Comparison of data-driven and physics-driven surface wave inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17357, https://doi.org/10.5194/egusphere-egu24-17357, 2024.

EGU24-17729 | ECS | Orals | SM6.4

Optimizing Full Waveform Inverse Problems: A Combined Data and Model approach 

Arnaud Mercier and Hansruedi Maurer

Full Waveform Inversion (FWI) has emerged as a groundbreaking tool in geophysics, offering unprecedented resolution in subsurface imaging. However, its broader application is often limited by substantial computational demands, especially in 3D elastic applications. This research addresses this critical barrier by introducing a novel approach that optimizes both data (source-receiver layout) and model (model parameterization) spaces, thereby reducing computational overhead and extending FWI's applicability. The interdependence between data and model spaces is a key factor to optimize FWI. We believe that both spaces must be simultaneously optimized to enhance the efficiency of FWI. This optimization is particularly crucial for intensive FWI problems but is also expected to make FWI accessible to a broader range of users, including those with limited computational resources.

We combine principles from Optimal Experimental Design (OED) and Compact Full Waveform Inversion (CFWI). Selecting only the most relevant source-receiver pair ensures a minimal, yet informative data set. By using a wavelet representation of the model, it is possible to easily tune the compression of the model based on the local resolution. The outcome of our data-model approach is a source-receiver layout that maximize the resolution of a compressed representation of the model.

Initial results with applications focused on synthetic 2D acoustic problems shows that the data-model approach allow for a significant reduction in both source-receiver pairs (≈ 50%) and model parameters (≈ 90%), whilst retaining 90% of the information content. Compare to classical OED criterion, our approach posses a lower time complexity by about 2 order of magnitude (O (m) vs O (mn2)). The significant speed up enables optimizing for sources and receivers independently, leading to further optimized layouts.

The data and model compression enables the use of Gauss-Newton optimization algorithm, leveraging faster convergence and greater flexibility. Benefits of this algorithm includes the possibility to optimize source-receiver layouts not only prior to fieldwork, but also during the inversion. At each stage of the inversion process, the most relevant data points are effectively identified and retained. This selection significantly reduces both computational and memory requirements. An additional benefit of this approach is the straightforward implementation of targeted OED, enabling optimization of the source-receiver layout for specific subsurface targets.

Key aspects to ensure a reliable and efficient data-model approach include evaluating the prior model's influence, examining the effects of compression ratio, resolving ambiguities in survey layout and model parametrization, and refining source and receiver positioning. We will present initial results and  highlight its potential benefits to significantly reduce the computational load of FWI.

How to cite: Mercier, A. and Maurer, H.: Optimizing Full Waveform Inverse Problems: A Combined Data and Model approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17729, https://doi.org/10.5194/egusphere-egu24-17729, 2024.

The application of Electrical Resistivity Tomography (ERT) for the investigation of architectural heritage has numerous limitations. In most cases, we are referring to historic stone buildings and monuments built from limestone, sandstone, or granite blocks, where many features may complicate the interpretation of electrical resistivity data. First of all, there is incomplete or missing information about principles of building construction and the materials used. Another challenge is the heterogeneity of the masonry as a material due to the presence of many joints between the stone blocks, which may be filled with cementitious materials or be completely or partially empty. For medium-scale studies with limited penetration depth, the presence of air in the joints between stone blocks may affect the electrical resistivity distribution and interfere with the detection of the archaeologically relevant anomalies associated, in particular, with the presence of air cavities. Systematic studies of the applicability of the Electrical Resistivity Tomography in such blocky structures are lacking. In this study, the effect caused by masonry geometry was assessed using numerical 3D modelling of the electrical resistivity distribution in a simplified blocky structure consisting of rows of masonry blocks by incorporating joints between them. The purpose is to study how the presence of air-filled joints affects the ability of the ERT method to detect voids in masonry structures depending on the position and size of these voids. The analysis of numerical models provides insights to facilitate the interpretation of ERT results in historical monuments and other structures constructed from stone blocks.

How to cite: Pugacheva, P. and Allam, H.: Application of 3D Forward Modelling to Improve the Interpretation of Electrical Resistivity Tomography Results in Architectural Heritage Monuments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18216, https://doi.org/10.5194/egusphere-egu24-18216, 2024.

EGU24-19047 | Posters on site | SM6.4

Statistical analyzes of the shapes of marine sand dunes off the Opal Coast (Eastern English Channel) 

Virginie Gaullier, François Schmitt, and Muriel Laurencin

Numerous very high-resolution seismic lines (Sparker/single-channel seismic reflection) were acquired in the Eastern Channel, along the the Opal Coast, between the Bay of Somme and Cape Gris-Nez, during the oceanographic missions GEOBAS (2016-2020), TREMOR 1 (2014), TREMOR 2 (2017) and MARCOPALE (2023). In this sector, numerous sandy banks are observed, especially the Bassure of Baas. These geophysical data were analyzed as part of the TURBODUNES project, by comparing two reflectors, respectively the sea floor and the base of the dunes (corresponding to the top of the deformed Cretaceous and Eocene bedrocks). The difference between the two signals makes it possible to identify areas with dunes and areas where dunes are absent. Assuming a constant boat speed, the extraction of signals provides spatial information on the height of the dunes. We carry out analyzes of these signals using different methods, including Fourier spectral analysis, empirical mode decomposition and structure functions. Empirical mode decomposition is a method which allows a one-dimensional series to be decomposed into a sum of several series, called “modes”, each having a characteristic wavelength. This makes it possible to quantitatively characterize the shape of the dunes via different modes, each having a wavelength ranging between 25 and 400 m. The lines for which dunes are absent nevertheless have profiles with strong multi-scale variability, with scale-invariant Fourier spectra with a slope of -2, for scales between 2.5 m and approximately 1 km.

How to cite: Gaullier, V., Schmitt, F., and Laurencin, M.: Statistical analyzes of the shapes of marine sand dunes off the Opal Coast (Eastern English Channel), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19047, https://doi.org/10.5194/egusphere-egu24-19047, 2024.

EGU24-19778 | ECS | Orals | SM6.4

Source- and receiver-coupling effects for time-domain Full Waveform Inversion 

Hagen Söding, Hansruedi Maurer, and Thomas Fechner

Tomographic techniques have been an indispensable tool for tackling manifold problems in earth and environmental sciences. For wavefield techniques, like seismics and ground penetrating radar, full waveform inversions offer powerful tools for extracting the full waveform information content to obtain high-resolution subsurface images. Although mostly applied to deeper targets (exploration scale), near-surface full waveform information holds a strong potential to analyse the often more complicated subsurface structures both in imaging and monitoring applications. Due to the complexity of the very shallow subsurface, source- and receiver coupling often exhibit substantial variations and can thus not be neglected. Maurer et al. (2012) showed that this problem can be addressed in frequency domain full waveform inversions by including source- and receiver coupling terms as additional unknowns into the inversion workflow. However, there are inherent trade-offs between the source- and receiver coupling factors. This is irrelevant for frequency-domain full waveform inversions, but this problem needs to be addressed for time-domain inversion problems.

In our contribution we present two possible options to make source- and receiver coupling inversions also applicable in time-domain problems, using either a parameterized source wavelet or a sparsity regularisation approach. We demonstrate our novel methodology with a synthetic study and with an application to an acoustic seismic full waveform inversion on a CCS study from the Digimon project from Svelvik, Norway.

 

References:

Hansruedi Maurer, Stewart A. Greenhalgh, Edgar Manukyan, Stefano Marelli, Alan G. Green; Receiver-coupling effects in seismic waveform inversions. Geophysics 2012;; 77 (1): R57–R63. doi: https://doi.org/10.1190/geo2010-0402.1

How to cite: Söding, H., Maurer, H., and Fechner, T.: Source- and receiver-coupling effects for time-domain Full Waveform Inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19778, https://doi.org/10.5194/egusphere-egu24-19778, 2024.

EGU24-358 | ECS | Posters on site | SM6.5

Ambient noise tomography of Popocatépetl volcano, México 

Leonarda I. Esquivel-Mendiola, Marco Calò, Arturo Iglesias, Josué Tago, and José Luis Macías

Popocatépetl volcano is among Mexico’s most risky due to its proximity to populated areas. Since its reactivation in 1994, several geophysical studies have been performed to understand the eruptive history, volcanic activity, and associated hazards. Although several seismic studies were carried out using permanent and temporal seismic network records, the internal structure of Popocatépetl volcano is still unclear.

In this work, we propose the first 3D velocity model of Popocatépetl volcano, describing the whole edifice inverting group velocity dispersion curves. We used data recorded at 39 broadband seismic stations installed in different epochs. We computed ambient noise cross-correlations, which were computed using two methods to increase the information for the modeling. Our results suggest the presence of a mushroom-shaped Popocatépetl’s system composed of two high shear wave velocity regions, the first one located at 5-0 km a.s.l., the second one located at 4-7 km b.s.l., and a narrow ‘pipe-like’ conduit connects both. The shallow high velocities are related to old and young volcanic structures due to mixed magmatic materials, which are affected by an intense degassing process that increases the magma viscosity and crystal content. The deepest reservoir is interpreted as a magmatic body that is confined due to the lithostatic pressure. The intermediate region is considered a narrow pipe conduit, where there is a low-velocity layer at the same depth. Moreover, our model reveals evidence of buried volcanic paleo-structures and the remains of ancient collapses generated by previous eruptions.

How to cite: Esquivel-Mendiola, L. I., Calò, M., Iglesias, A., Tago, J., and Macías, J. L.: Ambient noise tomography of Popocatépetl volcano, México, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-358, https://doi.org/10.5194/egusphere-egu24-358, 2024.

EGU24-3069 | Posters on site | SM6.5

3-D Intrinsic Attenuation Tomography of La Palma island (Canary Islands) using Ambient Seismic Noise 

Iván Cabrera-Pérez, Luca D'Auria, Jean Soubestre, Edoardo del Pezzo, Janire Prudencio, Jesús M. Ibáñez, María Jiménez, Germán D. Padilla, José Barrancos, and Nemesio M. Pérez

Seismic attenuation plays a vital role in geothermal exploration due to its direct association with the fluid content of reservoirs. In this study, we obtained the first attenuation model of La Palma island (Canary Islands) for geothermal exploration, applying a novel local-scale ambient noise attenuation tomography technique. Data from 44 seismic stations underwent meticulous processing. The initial stages involved preprocessing ambient noise data via standard normalization techniques, bandpass filtering and cross-correlation to retrieve the Empirical Green's functions (EGFs). For each EGF we retrieve the intrinsic attenuation  across various frequencies using the lapse-time dependence method, in which intrinsic attenuation is measured as a function of the coda window length for different onsets of the ambient-noise cross-correlation coda (Calvet and Margerin, 2013). Subsequently, 2-D spatial intrinsic attenuation maps for different frequencies were generated through linear inversion using sensitivity kernels (Del Pezzo and Ibáñez, 2020). Finally, we inverted the 2-D spatial intrinsic attenuation maps to derive 1-D depth profiles of intrinsic attenuation. The results unveiled distinct high-attenuation anomalies which releveled a possible hydrothermal zone  beneath the southern part of La Palma island. Comparative analyses with previous resistivity studies (Di Paolo et al., 2020), S-wave velocity research (Cabrera-Pérez et al., 2023), and density models (Montesinos et al., 2023) further corroborated these findings, underscoring the significance of ambient noise attenuation tomography in geothermal exploration.

References:

Cabrera-Pérez, I. et al. Geothermal and structural features of La Palma island (Canary Islands) imaged by ambient noise tomography. Sci. Reports 13, 12892 (2023)

Calvet, M. & Margerin, L. Lapse-time dependence of coda q: Anisotropic multiple scattering models and application to the pyrenees. Bull. Seismol. Soc. Am. 103, 1993–2010 (2013).

Del Pezzo, E. & Ibáñez, J. M. Seismic coda-waves imaging based on sensitivity kernels calculated using an heuristic approach. Geosciences 10, 304 (2020).

Di Paolo, F. et al. La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion. Sci. reports 10, 1–8, DOI: 10.1038/s41598-020-75001-z (2020).

Montesinos, F. G. et al. Insights into the magmatic feeding system of the 2021 eruption at Cumbre Vieja (La Palma, Canary Islands) inferred from gravity data modeling. Remote. Sens. 15, 1936 (2023)

How to cite: Cabrera-Pérez, I., D'Auria, L., Soubestre, J., del Pezzo, E., Prudencio, J., Ibáñez, J. M., Jiménez, M., Padilla, G. D., Barrancos, J., and Pérez, N. M.: 3-D Intrinsic Attenuation Tomography of La Palma island (Canary Islands) using Ambient Seismic Noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3069, https://doi.org/10.5194/egusphere-egu24-3069, 2024.

EGU24-4185 | ECS | Posters on site | SM6.5 | Highlight

Fiber seismic tomography of the Long Valley volcanic system 

Ettore Biondi, Weiqiang Zhu, Jiaxuan Li, Ethan Williams, and Zhongwen Zhan

High-resolution tomographic imaging of the subsurface structures beneath volcanic systems is fundamental to better assess their hazard and potentially estimate the amount of eruptive materials. However, obtaining such images represents a major challenge for multiple reasons. The significant velocity contrasts commonly present within volcanic systems require accurate wave simulations or traveltime modeling to correctly account for wavefield triplications and ray bending. Moreover, station coverage and temporary deployments usually cannot achieve the requirements needed to meet high-resolution imaging targets.

We demonstrate how distributed acoustic sensing (DAS) data recorded on existing telecommunication fiber cables and employed within an accurate and efficient matrix-free Eikonal tomography workflow can overcome these limitations. Specifically, we produce high-resolution tomographic images of the Long Valley caldera system in California, which in recent years has been undergoing significant inflation and seismic unrest. Our results reveal a distinct separation between the large magma chamber at approximately 10 km depth and the shallow crust. We interpret this separation as an upper-crust lid confining the pressurized volcanic fluid released through the crystallization of the magma reservoir over time. 

Our study highlights the potential of DAS for advancing volcano science; from providing insights into subsurface structures to monitoring dynamic processing due to fluid and magma movements through these complex systems.

How to cite: Biondi, E., Zhu, W., Li, J., Williams, E., and Zhan, Z.: Fiber seismic tomography of the Long Valley volcanic system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4185, https://doi.org/10.5194/egusphere-egu24-4185, 2024.

EGU24-6321 | ECS | Posters on site | SM6.5

Dynamic and static strain sensitivity of seismic velocity variations at Ischia Island, southern Italy  

Stefania Tarantino, Piero Poli, Maurizio Vassallo, and Nicola D'Agostino

Ischia Island is the westernmost, active volcanic complex of the Campanian plain (Southern Italy, Civetta et al., 1991). A long-term depressurization (Sepe et al., 2007) in the local hydrothermal system is causing deflation and contraction (Trasatti et al., 2019) of the surrounding volcanic edifice. In 2017 a Mw 3.9 shallow earthquake occurred in Casamicciola, in the northern part of the island, causing landslides and several collapses (Nappi et al., 2018). Here we present seismic velocity variation measurements δv/v over 8 years (2016-2023) for variable coda waves time lapse using empirical Green's functions reconstructed by autocorrelation of seismic noise recorded at local velocimeters. We compared velocity variations time series with the temporal evolution of the strain, obtained from displacements measured at the GPS network deployed on the island.  We focused on short-term velocity variations caused by the earthquake and on the long-term trend of δv/v measurements. This latter shows to be related to the deformation mechanism affecting the volcanic edifice. We found high values in both dynamic and static strain sensitivity of velocity variations with appreciable differences on the island, reflecting the anisotropic pattern of depressurization. This also proves a significant non-linearity in the elastic properties of the local volcanic materials. The joint use of geodetic methods and ambient noise monitoring revealed a remarkable sensitivity of δv/v to depressurization processes and its potential to enhance our understanding of the dynamics of the magmatic system.

References

Civetta, L., Gallo, G., & Orsi, G. (1991). Sr- and Nd-isotope and trace-element constraints on the chemical evolution of the magmatic system of Ischia (Italy) in the last 55 ka. Journal of Volcanology and Geothermal Research, 46(3–4), 213–230. https://doi.org/10.1016/0377-0273(91)90084-D

Nappi, R., Alessio, G., Gaudiosi, G., Nave, R., Marotta, E., Siniscalchi, V., Civico, R., Pizzimenti, L., Peluso, R., Belviso, P., & Porfido, S. (2018). The 21 August 2017 Md 4.0 Casamicciola Earthquake: First Evidence of Coseismic Normal Surface Faulting at the Ischia Volcanic Island. Seismological Research Letters, 89(4), 1323–1334. https://doi.org/10.1785/0220180063

Sepe, V., Atzori, S., & Ventura, G. (2007). Subsidence due to crack closure and depressurization of hydrothermal systems: a case study from Mt Epomeo (Ischia Island, Italy). Terra Nova, 19(2), 127–132. https://doi.org/10.1111/j.1365-3121.2006.00727.x

Trasatti, E., Acocella, V., Di Vito, M. A., Del Gaudio, C., Weber, G., Aquino, I., Caliro, S., Chiodini, G., de Vita, S., Ricco, C., & Caricchi, L. (2019). Magma Degassing as a Source of Long‐Term Seismicity at Volcanoes: The Ischia Island (Italy) Case. Geophysical Research Letters, 46(24), 14421–14429. https://doi.org/10.1029/2019GL085371

How to cite: Tarantino, S., Poli, P., Vassallo, M., and D'Agostino, N.: Dynamic and static strain sensitivity of seismic velocity variations at Ischia Island, southern Italy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6321, https://doi.org/10.5194/egusphere-egu24-6321, 2024.

EGU24-9403 | ECS | Posters on site | SM6.5

Utilizing Diffractions as a Tool to Study the Volcano-Tectonic Processes at the Christiana-Santorini-Kolumbo Volcanic Field 

Lisa Ischebeck, Jonas Preine, and Christian Hübscher

The interplay between volcanism and tectonics gives rise to a spectrum of geological phenomena, including eruptions, earthquakes, mass failures, and tsunamis, posing significant threats to both local and global environments. Seismic data interpretation serves as a crucial tool for reconstructing past volcanic-tectonic interactions, offering insights into potential precursors and triggers for future events. However, the inherent complexity of volcanic-tectonic regions often poses challenges for seismic imaging and interpretation, particularly regarding the delineation of faults, as well as the identification of volcanic structures, volcanic products, and mass transport events.

In this study, we explore the frequently overlooked diffracted wavefield as a tool to aid seismic interpretation of volcano-tectonic structures. Wave diffraction occurs at geodynamically important features like faults, erosional surfaces or other small-scale scattering objects and encodes information on a sub-wavelength resolution. Our approach models and adaptively subtracts the reflected wavefield from the un-migrated seismic data before we focus the separated diffractions to generate diffraction-energy images. We will present two seismic profiles from the Christiana-Santorini-Kolumbo volcanic field, one of the most active volcano-tectonic fields in Europe. These profiles cross major rift basins, complex fault zones, volcanic edifices, and mass-transport deposits. Our derived diffraction images provide a unique window into the subsurface, highlighting important small-scale heterogeneities. We observe that diffractions cluster at geodynamically important subsurface structures, such as faults, volcanic cones, as well as distinct unconformities within the rift basins. Diffractions also cluster at seismic subunits previously interpreted as eruptive products such as ignimbrites and lava flows, as well as mass-wasting deposits. In contrast, we observe that little diffraction occurs in sedimentary strata interpreted to be the result of hemipelagic background sedimentation. Thus, this study strongly advocates for the integration of diffraction energy images into the standard practice of seismic data analysis and interpretation in the context of volcano-tectonic interactions.

How to cite: Ischebeck, L., Preine, J., and Hübscher, C.: Utilizing Diffractions as a Tool to Study the Volcano-Tectonic Processes at the Christiana-Santorini-Kolumbo Volcanic Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9403, https://doi.org/10.5194/egusphere-egu24-9403, 2024.

EGU24-9449 | ECS | Posters on site | SM6.5 | Highlight

Seismic Imaging of Submarine Volcanoes and Volcanic Ridges at the Southeastern Azores Plateau 

Annalena Friedrich, Christian Hübscher, Jonas Preine, Christoph Beier, Anthony Hildenbrand, Paraskevi Nomikou, and Pedro Terinha

There is an ongoing debate about the water depths to which explosive submarine volcanism is possible. In this study, we present high-resolution reflection seismic data from cone-shaped intraplate volcanoes on the southeastern Azores Plateau that indicate explosive submarine volcanism at water depths greater than 2 km. In addition, the data illustrate the early stages of volcanic ridge evolution at similar water depths, which were mainly formed by fissure eruptions. The volcanic cones are ca. 4 km wide and 500 m high above the ocean floor. They are characterised by stratified flanks that are onlapped by sub-horizontal, hummocky high-amplitude reflections. We interpret the layered flanks as evidence of rather unconsolidated volcanic deposits from submarine explosive eruptions, where the magma emerging from the seafloor was fragmented by expanding volatiles. Guided by diffraction imaging, we interpret the high-amplitude reflections as the top of lava flows from effusive eruptions, that postdated the explosive eruptions. Distinct upward-bent reflections beneath the volcanic cones are interpreted to be velocity pull-ups caused by the presence of dense, high p-wave velocity material in the central part of the volcanic cones. We apply depth-stretching to correct for these artefacts and to access the true geometry of the volcanic cones and the underlying features. Upward concave reflections within the basaltic basement might represent funnel shaped conduits or diatremes. The seismic signature of a volcanic ridge between two of the volcanic cones suggests that stacked effusive eruptions dominated its evolution. Both the cones and ridges superimpose hemipelagic sediments, which in turn overlie the basaltic basement. Hence, the evolution of the volcanic features postdated the main magmatic evolution of the western part of the eastern Azores Plateau that started in the middle Miocene. Generally, our study sheds new light on the complex volcanic evolution of the southeastern Azores Plateau and highlights the potential of seismic imaging as a tool for submarine volcanology.

How to cite: Friedrich, A., Hübscher, C., Preine, J., Beier, C., Hildenbrand, A., Nomikou, P., and Terinha, P.: Seismic Imaging of Submarine Volcanoes and Volcanic Ridges at the Southeastern Azores Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9449, https://doi.org/10.5194/egusphere-egu24-9449, 2024.

EGU24-11079 | Posters virtual | SM6.5

Near-surface effects in seismic wavefields at Krafla volcano (NE Iceland): characterization and mitigation.  

Regina Maass, Christopher J. Bean, and Ka Lok Li

Seismic imaging of small-scale geological features in volcanic regions is challenging due to the often heterogeneous subsurface, causing extensive wave scattering and limited coherence in the wavefields. A well-known example that illustrates this problem is the unexpected encounter of magma at 2.1 km depth at Krafla (NE Iceland) during geothermal drilling in 2009. Despite numerous geophysical studies, the magma body remained undetected prior to drilling. In the summer of 2022, we deployed ~100 short-period seismic nodes in a reflection seismic configuration at Krafla. Using the known reflector as a guide, our goal is to investigate and enhance seismic imaging in complex geological settings. Analyses of ~300 local earthquakes (magnitudes < 1.5) show that the wavefields at Krafla are largely dominated by wave scattering and reverberations within the uppermost ~100m of the subsurface, causing little coherency in the data even among neighbouring stations spaced at 30 meter intervals. Using auto – and cross-correlation techniques, we address the reverberations and construct transfer functions characterising the seismic response of the sites at each station. This is followed by time-dependent deconvolution. The deconvolved wavefields show increased coherency, as the influence of the near-surface could be considerably reduced. Coherent phases emerge in the wavefields which were previously obscured by reverberating waves. Different imaging techniques such as common-depth-point (CDP) binning and stacking will be applied to the cleaned wavefields in order to resolve potential layer boundaries and magma pockets, ultimately improving our understanding of the Krafla geothermal system.

How to cite: Maass, R., Bean, C. J., and Li, K. L.: Near-surface effects in seismic wavefields at Krafla volcano (NE Iceland): characterization and mitigation. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11079, https://doi.org/10.5194/egusphere-egu24-11079, 2024.

In 1978, seven seismic reflection profiles were acquired through a joint venture between Agip and Enel to explore geothermal resources in the Campi Flegrei caldera. These vintage profiles reflect the technological limitations of that era: sparse shot points, limited channels, low bandwidth and dynamic range, resulting in a low signal-to-noise ratio, especially near volcanic structures. Despite these limitations, they can offer invaluable insights in Campi Flegrei, where obtaining new seismic data is impractical due to urbanization, environmental concerns, and intensified volcanic hazards.

This presentation shares the outcomes of a reprocessing aimed at enhancing profile signal-to-noise ratio. Given acquisition geometry and data quality, contemporary seismic processing methods like pre-stack depth imaging, reflection tomography, and full-waveform inversion are impractical. The reprocessing adapted to data quality limitations, utilizing time-domain algorithms. It involved assigning a crooked line geometry, conventional common-midpoint (CMP) processing, and less conventional common reflection surface (CRS) processing. CRS stacking, not reliant on stacking velocity estimation, improves seismic imaging quality. P-wave velocity models were reconstructed along the profiles through tomography algorithms applied to picked first arrivals. Post-stack time migration and depth conversions with vertical stretching were applied to CDP/CRS stacks.

Despite limitations, these depth images, tied to exploration wells and geophysical logs, can significantly contribute to understanding the near-surface structure of this dynamic region and its structural and stratigraphic relations with the sedimentary Volturno Plain to the North.

How to cite: Bruno, P. P. G. and Cardillo, C.: Results from reprocessing the vintage 1978 ENI-ENEL seismic reflection profiles acquired on the onshore of Campi Flegrei, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11650, https://doi.org/10.5194/egusphere-egu24-11650, 2024.

EGU24-13907 | Posters on site | SM6.5

Crustal structure in the Tengchong Volcanic Area based on the H-κ-c method 

Yingying Zhang and Yanru An

The Tengchong volcano is the most famous active intraplate volcano in Southwest China, which has been dormant for hundreds. The significant seismicity, active geothermal activities and gas emissions are all indicate that the volcanoes still have potential for future eruptions. However, the origin of the Tengchong volcano is still on debate, which is strongly depend on the structure underneath. Here we employ a recently developed H-κ-c method to characterize the crustal structure with its thickness and the Vp/Vs ratio of the Tengchong volcanic area. A total of 4,040 receiver functions are obtained from 9 permanent seismic stations, providing an overall good coverage in both distance and azimuth of the analyzed data. After removing the back azimuthal effects of dipping Moho and/or crustal anisotropy, our results are more robust and highlight local variations. The crustal thickness increases from south to north, ranging from 33.5 to 41.9 km with an average of 37.6 km. The crustal thickness beneath stations RHT is thicker than the surrounding stations, suggesting a possible local crustal depression beneath this station. The Vp/Vs ratios vary from 1.75 to 1.79 and the average value is 1.76 with a standard deviation of 0.015. Stations with high Vp/Vs values indicate partial melting magma chambers in the crust beneath those stations.

How to cite: Zhang, Y. and An, Y.: Crustal structure in the Tengchong Volcanic Area based on the H-κ-c method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13907, https://doi.org/10.5194/egusphere-egu24-13907, 2024.

EGU24-16182 | Posters on site | SM6.5 | Highlight

Seismic attenuation structure of the lower crust upper mantle under El Hierro island (Spain) 

Janire Prudencio, Eduardo A. Díaz-Suárez, Aitor Cid, Ithaiza Dominguez-Cerdeña, Iván Cabrera, Carmen Del Fresno, and Jesús M. Ibáñez

The origin of the Canary Islands has been under debate for the last decades. The hotspot hypothesis as the origin of the islands was abandoned long ago, however, there are still theories that partially incorporate this idea. The scientific community widely accepts none of these models and the recent volcanic eruptions of El Hierro and La Palma once again question these theories. 

In order to confirm the structure and to explain the diversity of the eruptive processes observed in the Canarian archipelago, we return to El Hierro island to obtain a high-resolution seismic attenuation tomography, as it has proven to be more sensitive to the presence of magma as shown in Mt. Etna (Castro-melgar et al., 2021). Thus, we have analyzed the same database that García-Yeguas et al. (2014) used in the velocity tomography and we have obtained a new tomographic model of El Hierro island that confirms the existence of an intermediate chamber as observed in Tenerife and La Palma which could feed the 2011 eruption.

The lack of high attenuation anomalies in the central part of the island is already observed in the velocity tomography results obtained by García-Yeguas et al. (2014). In addition, Montesinos et al. (2005) identified high-density anomalies in the same zone, where Sainz-Maza et al. (2017) also observed high gravity values. These results could demonstrate the existence of a dense core in the center of the island related to the oldest volcanism of El Hierro and diverting the magma intrusions to the outer zone of the island as the 2011 Tagoro eruption.

How to cite: Prudencio, J., Díaz-Suárez, E. A., Cid, A., Dominguez-Cerdeña, I., Cabrera, I., Del Fresno, C., and Ibáñez, J. M.: Seismic attenuation structure of the lower crust upper mantle under El Hierro island (Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16182, https://doi.org/10.5194/egusphere-egu24-16182, 2024.

EGU24-17405 | Posters on site | SM6.5

Magma storage quantified under Aluto volcano, Ethiopia, using probabilistic tomography 

Corinna Roy, Andy Nowacki, Andrew Curtis, and Brian Baptie

Rift volcanoes worldwide present significant hazards to people from eruptions but also provide resources such as geothermal energy. Aluto volcano in the Ethiopian rift is a hotspot for geothermal power exploitations, despite significant periods of deformation in the last 15 years.

Various geophysical imaging methods have been applied to Aluto to obtain a detailed 3D image of the hydrothermal reservoir and the location, geometry, and size of possible magma bodies. However, the models give a single or narrow range of answers without the possibility for the exploration of uncertainties arising from the data and assumptions.

Here we address this current limitation for the seismic data by performing a fully nonlinearized joint inversion of local seismic P- and S-wave travel times, and surface wave dispersion data between 0.5 Hz and 2 Hz from empirical Green's functions, for the location of earthquakes and the velocity of the subsurface. The combination of data types helps reduce the range of permitted models.

We use a reversible-jump Markov chain Monte Carlo approach to incorporate prior information and, from our data, retrieve the posterior probability of earthquake parameters and seismic velocity in a Bayesian sense. This provides rigorous distributions of the covariance of the earthquake and velocity parameters.

Our 3D seismic models display areas of elevated Vp/Vs ratio at 2-6 km depth under the caldera, interpreted as areas of partial melt. The hydrothermal reservoir shows in our results as lower Vp/Vs. This is in good agreement with the previous resistivity models from the magnetotelluric study of Samrock et al. 2020. However, while Samrock et al. observed two zones of partial melt, our model suggests that the lower and upper melt zones are connected.

To go one step further, we developed a workflow to link seismic velocities to melt fraction estimates by combining the posterior distributions of seismic velocity and thermodynamic modeling. We conclude that the melt fraction under Aluto is between 3 and 7 % at 5 km depths, and the melt volume is approximately 0.37 km3.

How to cite: Roy, C., Nowacki, A., Curtis, A., and Baptie, B.: Magma storage quantified under Aluto volcano, Ethiopia, using probabilistic tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17405, https://doi.org/10.5194/egusphere-egu24-17405, 2024.

EGU24-17692 | ECS | Posters on site | SM6.5 | Highlight

A detailed view of the magmatic plumbing system beneath Askja Volcano, Iceland, from ambient noise tomography  

Joseph Fone, Tom Winder, Nicholas Rawlinson, Robert White, and Bryndís Brandsdóttir

The volcano Askja in the Northern Volcanic Zone (NVZ) of Iceland last erupted in 1961 and has been steadily deflating from the 1970s until August 2021 when GPS and InSAR measurements confirmed that it had begun re-inflating. The NVZ has hosted a network of seismic stations operated by the University of Cambridge Volcano Seismology group since 2006. In the summer of 2023, this network has been augmented by 12 three component nodes that will record for ~2 months in addition to 10 broadband instruments that will be left for a year in or around the caldera of Askja with an average station spacing of ~1-2 km. The combination of the long-term recordings from the backbone network during deflation and the more recent short-term dense recordings will provide a unique dataset to examine how this switch from deflation to inflation may effect the seismic velocity structure beneath the volcano, thereby providing new insight into the underlying magmatic system. In this study, we present preliminary results from the application of ambient noise tomography to this dataset to try and image any changes in the magmatic system, which will involve stacking different periods of ambient noise cross-correlations to obtain two sets of dispersion curves that are sensitive to the subsurface velocity structure beneath Askja prior to and following the switch to reinflation in August 2021. This allows us to produce 3D models of shear wave velocity that can be compared to help elucidate changes in the plumbing system that occurred due to this switch. The dense deployments in the caldera have the advantage of allowing us to measure dispersion curves to high frequencies due to the short interstation distances, which is expected to yield more information on shallow subsurface structure where GPS and InSAR measurements appear to indicate that the source of the inflation is concentrated.

How to cite: Fone, J., Winder, T., Rawlinson, N., White, R., and Brandsdóttir, B.: A detailed view of the magmatic plumbing system beneath Askja Volcano, Iceland, from ambient noise tomography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17692, https://doi.org/10.5194/egusphere-egu24-17692, 2024.

EGU24-18404 | ECS | Posters on site | SM6.5

Nodal Local Earthquake Tomography of La Soufrière Volcano, Guadeloupe 

Elliot Amir Jiwani-Brown, Geneviève Savard, Filippo Barsuglia, Alberto Rosselli, Federico Fischanger, Catherine Truffert, and Matteo Lupi

La Soufrière is an active andesitic stratovolcano lava dome at 1467 m elevation. It is the most recently eruptive centre of the Guadeloupe archipelago in the eastern Caribbean Sea. Previous activity has consisted of effusive, explosive magmatic, and phreatic eruptions. Many hazards are associated with La Soufrière volcano, including explosive blasts, pyroclastic flows, acid degassing and contamination of groundwater sources. Since 1992, increased seismic and fumarolic activity at La Soufrière has raised the alert level to yellow, peaking with a volcanically triggered ML 3.7 earthquake in 2018.  

In the framework of the MEGaMu project, innovative geophysical subsurface imaging methods are deployed at La Soufrière to produce a high-resolution model of the volcanic edifice at up to ~1 km depth to improve our understanding of the volcano’s shallow structure. In October 2023, we deployed an array of 48 3-component 5 Hz nodal geophones around the base of the volcanic massif and the summit crater, recording continuous passive seismic data at a sampling of 250 Hz for one month. An electrical resistivity campaign was conducted at the same time, providing an outstanding opportunity to compare the derived 3D seismic velocity model with a 3D electrical resistivity model on a similar scale. In this study, we apply seismic ambient noise tomography using data from our temporary nodal network and nearby existing broadband stations to produce Rayleigh wave group velocity maps and a 3D model of shear wave velocity. This model is interpreted with the 3D resistivity model to determine the extent of the shallow hydrothermal system and known fault zones crossing the volcanic massif. Such a multi-scale and multi-physics geophysical prospection approach greatly helps in reducing subsurface uncertainty in the interpretation of geophysical datasets.

We use new nodal technologies and up-to-date applications of seismic passive noise tomography to analyse Rayleigh wave shear-velocity dispersion data from a nodal seismic network of 48 3-component units, and generated 2D group velocity maps at different periods, and 3D depth insertion of shear wave velocities. We compare this to a 3D electrical resistivity, carried out simultaneously with seismic deployment, to better constrain the subsurface plumbing system based on comprehensive geophysical methodologies.

How to cite: Jiwani-Brown, E. A., Savard, G., Barsuglia, F., Rosselli, A., Fischanger, F., Truffert, C., and Lupi, M.: Nodal Local Earthquake Tomography of La Soufrière Volcano, Guadeloupe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18404, https://doi.org/10.5194/egusphere-egu24-18404, 2024.

EGU24-496 | ECS | Orals | TS5.1

Rayleigh and Love Wave Tomographic Imaging of Heterogeneous Crust in a magmatic rift: the Turkana Depression, East Africa 

Martin Musila, Francesco Civilini, Cynthia Ebinger, Ian Bastow, Rita Kounoudis, Finnigan Illsley-Kemp, and Chris Ogden

Theory and geoscientific observations demonstrate that plate stretching, heating, faulting, active and frozen magma intrusions, and extrusive eruptive products are consequences of mantle upwelling mechanism driving continental rifting. Problematic to this picture is the lack of consensus on how, when and where these processes modify the crust’s thermal and mechanical structure. We use data from East Africa’s 300-km wide Turkana Depression to investigate how the superposition of these rift processes and the spatial migration of the active plate boundary through time within one geodynamic setting modify the crust’s structure. Utilizing ambient noise seismic methods and data from the 34 station Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) seismic network, we invert for Rayleigh and Love tomographic models and overlay results with our local earthquakes crustal splitting results. Preliminary results show that regions that experienced Eocene flood magmatism have localized high Vs of > 3.4 km/s at mid-lower crustal depths implying that flood magmatism is fed by unknown localized centers and/or dike swarms. Quaternary eruptive centers with Vs < 3.4 km/s at mid-lower crustal depths are punctuated and irregularly spaced suggesting that bottom-up mantle upwelling influence their location. Regions with superposed Cretaceous-Paleogene and Miocene-Recent rift phases have persistent low velocities (Vs ≥ 3.8 km/s) to the mid-crust with thinner crust (~ 20 km); the active Miocene-Recent rift structures are oblique to the largely inactive Cretaceous-Paleogene rift structures implying no reactivation of pre-existing structures during modern-day rifting.

How to cite: Musila, M., Civilini, F., Ebinger, C., Bastow, I., Kounoudis, R., Illsley-Kemp, F., and Ogden, C.: Rayleigh and Love Wave Tomographic Imaging of Heterogeneous Crust in a magmatic rift: the Turkana Depression, East Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-496, https://doi.org/10.5194/egusphere-egu24-496, 2024.

EGU24-608 | ECS | Posters on site | TS5.1

Miocene to Quaternary Seismic Stratigraphy and Tectonic Evolution of the Marine Area Between Çandarlı Bay and Lesbos Basin, Northeastern Aegean Sea 

İrem Elitez, Tuba İslam, Derya İpek Gültekin, and Cenk Yaltırak

This study focuses on the marine area located between Çandarlı Bay and Lesbos Basin in the Northeastern Aegean Sea. The high quality multibeam bathymetry data, their processing and interpretation with the onshore structures and an integrated interpretation with seismic reflection profiles allowed to map the offshore active faults, to prepare the seismic stratigraphy and to evaluate the tectonic evolution of the marine area between Çandarlı Bay and Lesbos Basin. In addition, thickness maps were generated from seismic reflection profiles and seismic stratigraphic units were correlated with the Foça-1 well to reveal the characteristics of the deposited strata in this region. The seismic stratigraphic units were also compared with onshore geological units.

Five major seismic stratigraphic units were identified and all of which are compatible with each other from the Çandarlı Bay to the Gulf of Izmir. The findings suggest continuous sedimentation from the Burdigalian (Lower Miocene) to the present day. A predominantly volcaniclastic sequence deposited in the Burdigalian-Serravalian period rests on basement rocks. This unit is overlain by Tortonian clastics and carbonates interbedded with volcanic rocks. Tortonian sediments are followed by about 300-500 m thick clastics and anhydrites, which were deposited in an environment corresponding to the Messinian salinity crisis in the Mediterranean Sea. The post-Messinian unit is of Pliocene age and starts with upper Miocene limestones at the base and transitioning upwards into clastic rocks. The stratigraphy concludes in the upper part with a Quaternary unit, which is mainly composed of fine-grained clastics and has been influenced by sea-level changes.

The study area is dominated by both NW-SE and NNW-SSE-striking normal faults and two distinct tectonic phases have been identified. The first phase spans from the Miocene to the end of the upper Miocene and is characterized as a supra-detachment basin associated with the development of core complexes in the region. These faults do not extend to the surface in seismic sections and are indicative of an early-stage tectonic activity. The homogeneity of the sediment thickness suggests a slowdown in tectonic activity during the Tortonian-Messinian period. In the Plio-Quaternary period, the sediment thicknesses indicate uplift in the surrounding region. Additionally, the bathymetric traces of faults shaping the Lesbos Basin to the west of Çandarlı Bay indicate the presence of a new tectonic system.

How to cite: Elitez, İ., İslam, T., Gültekin, D. İ., and Yaltırak, C.: Miocene to Quaternary Seismic Stratigraphy and Tectonic Evolution of the Marine Area Between Çandarlı Bay and Lesbos Basin, Northeastern Aegean Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-608, https://doi.org/10.5194/egusphere-egu24-608, 2024.

The seismically active Andaman-Sumatra subduction zone hosts a prolonged back-arc basin, with the Andaman Sea encompassing several volcanoes, notably the active Barren volcano and the dormant Narcondam volcano. Metamorphic features like the Alcock Rise and Sewell Rise are prominent in this region, experiencing oblique subduction between the Indo-Australian and Eurasian plates alongside backarc seafloor spreading. This convergence has led to significant crustal-scale fault systems like the Great Sumatra Fault, the Andaman Nicobar Fault, and the Sagaing faults. Due to limited geophysical datasets, particularly offshore Narcondam, we utilized three reflection lines (Line 1: 30 km, Line 2: 36 km, and Line 3: 36 km) derived from industry and corresponding satellite gravity data to complete the objectives of this study. We employed F-K and parabolic Radon filtering methods on the seismic data, eliminating noise and seawater multiples from the lengthy east-west 2D seismic profile lines. Subsequently, semblance-based conventional processing techniques were applied to visualize the subsurface. The water depths in the basin range from 1262 to 1554 meters along the profile, with the thickest sediment (~2.35 km) observed at CDP-2877 on Line 1. Satellite gravity data aided in deciphering the crustal architecture of the study area using gravity modeling. The crust's nature beneath Narcondam remains a subject of debate, whereas below Alcock Rise, some authors suggest either oceanic or island arc crust. Our integrated geophysical approach, encompassing gravity modeling, seismic interpretation, and focal mechanism solutions, pivots in evaluating evidence related to the paleo ANF. This comprehensive method allowed for an in-depth examination of the crustal architecture and upper mantle structure beneath both Narcondam Island and the northern part of Alcock Rise. The interpreted seismic section along with the focal mechanism interpretation in the basin indicates the presence of the Paleo ANF, spanning the basin and extending to the Moho. Its significance lies in facilitating fluid migration and influencing depocenter variation during the basin's evolution.

How to cite: Srivastav, H., Ghosal, D., and Kumar, P.: Evidence of Paleo ANF and crustal architecture beneath the Narcondam: Insights from High-Resolution Reflection Seismic Data and Gravity modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3317, https://doi.org/10.5194/egusphere-egu24-3317, 2024.

Subsurface fault zones play an important role in fluid flow. However, the quantitative research regarding fault damage zones based on conventional seismic attributes is challenging. Therefore enhancing the interpretation of subsurface fault zones using advanced workflows is a priority. We try to highlight these apparent fault zone arrays using 3D seismic data from the M17 prospect. Based on the dip-steering cube computed from the original seismic data, several conditioning approaches were co-used with multiple seismic attribute calculations and a supervised neural network. The computed hybrid attributes based on these methods have enhanced the images of the fault zone arrays. We propose five basic types of fault zone architecture regarding the fault zone arrays based on quantitative analysis via the hybrid attributes and previous research. The fault zone types correspond to different linkage types, representing different evolution stages of fault zone growth. This research has implications for understanding the architecture and growth of related fault zone arrays.

How to cite: cui, L., dong, D., and huang, Y.: Insights into Fault Zone Architecture and Growth Based on Enhanced Image of Fault Zone Arrays Using Hybrid Attributes  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3512, https://doi.org/10.5194/egusphere-egu24-3512, 2024.

EGU24-3916 | ECS | Posters on site | TS5.1

Seismic Attenuation Imaging in the Western Part of the North Anatolian Fault Zone 

Wei-Mou Zhu, Luca De Siena, Lian-Feng Zhao, David G. Cornwell, Xiao-Bi Xie, Simona Gabrielli, Aqeel Abbas, Xi He, Lei Zhang, Panayiota Sketsiou, Stella Lamest, and Zhen-Xing Yao

Colossal and devastating earthquakes are typically associated with the slip and rupture of fault zones. Fault zone imaging is challenging yet crucial to understand fault structure and behavior, and consequently hazard assessment and mitigation. Seismic attenuation imaging provides constraints on the fault zone structure that are independent of seismic velocity imaging. Here, we image the S-wave total attenuation (Qs) structure of the western part of the North Anatolian Fault Zone (NAFZ) using data recorded by the DANA (Dense Array for North Anatolia) array. The area of interest is divided into three distinct regions by the northern and southern segments of the NAFZ, which extends from north to south: the Istanbul Zone to the north, the Armutlu Block in between, and the Sakarya Terrane to the south, respectively. The Armutlu Block exhibits much higher attenuation compared to the other two regions. The anomaly body has an attention value of 0.0008 with a notable 3D distribution pattern: It extends from 30.2°E to 30.6°E and around roughly 40.6°N following the northern strand of the NAF and shows a west-east trend, dipping deeper into the crust to the east from depths of 5 to 15 km. Combining previous geological, geodetic, micro-seismicity, and other geophysical observations, we inferred that the high values are a sign of fluid pathways. Micro-seismicity and strain distributions around the Armutlu Block are in line with the assumption fluids migrate through cracks and increased permeability attributed to the background stress, particularly residual stress after the 1999 M7.4 Izmit earthquake and M7.2 Düzce earthquake.

This research is supported by the National Natural Science Foundation of China (U2139206, 41974061, 41974054) and the Special Fund of China Seismic Experimental Site (2019CSES0103). The first author has also been financially supported by the China Scholarship Council (202204910302).

How to cite: Zhu, W.-M., De Siena, L., Zhao, L.-F., G. Cornwell, D., Xie, X.-B., Gabrielli, S., Abbas, A., He, X., Zhang, L., Sketsiou, P., Lamest, S., and Yao, Z.-X.: Seismic Attenuation Imaging in the Western Part of the North Anatolian Fault Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3916, https://doi.org/10.5194/egusphere-egu24-3916, 2024.

EGU24-4302 | ECS | Posters on site | TS5.1

Imaging of Main Himalayan Thrust in Central Seismic Gap using seismic interferometry   

Saneesh Ali T S, Sandeep Gupta, Sudesh Kumar, Krishnavajjhala Sivaram, and Vishal Rawat

The Main Himalayan Thrust (MHT) demarcates the boundary between the underthrusting Indian Plate and the overriding Himalayan orogeny. Stress accumulation on the MHT due to the underthrusting of the Indian Plate leads to the occurrence of bigger earthquakes in the Himalayas. It is, therefore, imperative to understand the MHT's geometry in different Himalayan segments. Furthermore, how this geometry varies along the Himalayan arc while taking into account the uneven distribution of earthquakes offers a comprehensive insight into earthquake nucleation in the region. The central seismic gap is one of the most significant segments of the Himalayas, which is considered a potential region for the proposed great earthquake in the future. This study focuses on defining the MHT geometry by constructing a 3-D model within the central seismic gap using the seismic interferometry technique.  We analyzed the data sets obtained from 159 broadband stations spread across the area to construct a comprehensive three-dimensional geometry of MHT. The different arc normal cross-sections highlight variations in the MHT's geometry along the arc in the central seismic gap.

Keywords: Main Himalayan Thrust, seismic interferometry, central seismic gap, crustal imaging.

How to cite: Ali T S, S., Gupta, S., Kumar, S., Sivaram, K., and Rawat, V.: Imaging of Main Himalayan Thrust in Central Seismic Gap using seismic interferometry  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4302, https://doi.org/10.5194/egusphere-egu24-4302, 2024.

EGU24-4975 | Posters on site | TS5.1

Deep borehole based subsurface geophysical monitoring network: TELLUS Project 

Yeonguk Jo, Sehyeok Park, and Changhyun Lee

We introduce a comprehensive strategy to monitor subsurface fault behavior and associated geophysical environment (e.g., micro-seismicity, stress, groundwater), using a deep borehole based monitoring system. This study provides an in-depth overview of the TELLUS (The Earth Login Leverage for Underground Signal) project, with its individual monitoring system tracking subsurface fault movements with high precision by deploying borehole seismometers, and gathering important data on various geophysical properties.

This paper details site selection process and characterizations, the operational framework on monitoring system installations, and the potential of deep borehole monitoring approach in advancing subsurface-related geophysical studies. We conducted extensive review of the distributions of major fault systems in the south-eastern part of South Korea. Subsequently, we strategically selected and arranged candidates for monitoring system installations. Total of six TELLUS deep borehole monitoring systems were installed in the vicinity of the major faults (Yangsan and Ulsan fault).

In the TELLUS observatories, preliminary monitoring data is being collected in real time, and this is establishing a foundation for a more precise understanding of the behavior of subsurface faults and the related geophysical environment. It would be expected that the comprehensive analysis of these datasets will further elucidate the intricate subsurface geophysics. This enhanced understanding promises to contribute substantially to our seismic risk assessment capabilities and to the broader field of geoscience research, offering new insights into earthquake prediction and geophysical phenomena.

How to cite: Jo, Y., Park, S., and Lee, C.: Deep borehole based subsurface geophysical monitoring network: TELLUS Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4975, https://doi.org/10.5194/egusphere-egu24-4975, 2024.

EGU24-6400 | ECS | Posters on site | TS5.1

Accurate seismic phase picking using High-Order Statistics: the case study of the Irpinia Seismic Array in Southern Italy 

Giovanni Messuti, Mauro Palo, Silvia Scarpetta, Ferdinando Napolitano, Francesco Scotto di Uccio, Paolo Capuano, and Ortensia Amoroso

Fault imaging and characterization of crustal structures, along with source parameter estimation, strongly depend on reliable direct seismic wave arrival times. To lower the detection threshold of small earthquakes and improve the quality of fault imaging, dense arrays of seismic stations are being installed more and more frequently in different parts of the world. Given the rising number of new, denser seismic networks and the growing demand for high-quality seismic catalogs, the use of automatic techniques is crucial to efficiently process and analyze the vast amount of seismic data, contributing to the advancement of seismic research and monitoring capabilities.

The Irpinia fault system (Southern Italy) hosted in 1980 the M 6.9 earthquake and is currently monitored by the Irpinia seismic network (ISNet), which is composed of 31 seismic stations covering an area of about 100x70 km2 along the Campania-Lucania Apennine chain. ISNet was integrated by 200 seismic stations grouped in small-aperture arrays of 10 stations during the 1-year DETECT project (DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging). DETECT focused on the acquisition of a unique multiparametric dataset and aimed to monitor and image the fault system during the inter-seismic phase fostering at the same time the collaboration among various institutions.

The use of seismic arrays, in a region characterized by high seismic hazard, presents a unique opportunity to introduce a novel technique that accurately reveals the first arrivals of seismic phases of small earthquakes. We examined 226 micro-earthquakes, with magnitude ranging from -0.27 to 2.28, detected by the seismic arrays during the first six months of the DETECT project (September 2021 - February 2022). We present a novel approach that utilizes high-order statistics (HOS), computed on the vertical components of waveforms, to identify P-wave arrival times and provide reliability measurements for our predictions. The advantage of the arrays’ geometry enabled the integration of the HOS technique with a criterion designed to select the optimal onsets. The proposed methodology incorporated over 3,300 additional P-wave arrival times into the existing catalog. Furthermore, semblance measurements among traces recorded at the same array highlighted the superior quality of the selected picks compared to the existing ones.

This work is partially supported by project TOGETHER - Sustainable geothermal energy for two Southern Italy regions: geophysical resource evaluation and public awareness financed by European Union – Next Generation EU (PRIN-PNRR 2022, CUP D53D23022850001).

How to cite: Messuti, G., Palo, M., Scarpetta, S., Napolitano, F., Scotto di Uccio, F., Capuano, P., and Amoroso, O.: Accurate seismic phase picking using High-Order Statistics: the case study of the Irpinia Seismic Array in Southern Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6400, https://doi.org/10.5194/egusphere-egu24-6400, 2024.

EGU24-6580 | Orals | TS5.1 | Highlight

Seismic imaging of crustal fault systems 

CharLotte Krawczyk

The construction of geodynamic and reservoir models requires - as many other applications - the knowledge of fault signatures and fracture systems.  In general, structural images of the subsurface rely on sampling and experiment design, wavefield components retrieved, as well as coherence and focusing potential of the data recorded in different geological settings.  Nonetheless, direct geophysical images of especially sub-/vertical or inactive faults are still hampered by fracture complexity and associated diffuse wavefields.  Furthermore, back-tracing weak signals to their originating location remains one of the challenges for high-resolution imaging.  While petrophysical and mechanical rock properties characterize the hosting material as such, they can provide at the same time assistance in fault or horizon tracking, respectively, and may allow pattern identification, for instance by machine learning tools.

In the overview presented, we will discuss different examples from recent active and passive seismic surveys covering both sedimentary and hardrock environments using either dense or sparse seismic and fibre-optic arrays.  These experiments are adapted to investigation depths between some km and only few 10s of metres scale, encompassing geodynamic, geothermal, hazard and critical zone investigations.  Thereby, the wide applicability of seismic methods for imaging and characterizing distinct horizons, transitional zones, and fault systems is emphasized.

How to cite: Krawczyk, C.: Seismic imaging of crustal fault systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6580, https://doi.org/10.5194/egusphere-egu24-6580, 2024.

EGU24-7098 | ECS | Posters on site | TS5.1

Shallow velocity structure of the Tainan frontal thrust based on Eikonal tomography 

Tzu-Cheng Yang, Ying-Nien Chen, and Ruey-Juin Rau

    We deployed a dense array of 173 seismometers covering a 30 by 40 km2 area in the Tainan frontal thrust of southwestern Taiwan from February to June 2021. The seismic array with an inter-station distance of about 2 km, spanned from west to east, across four major tectonic regimes: Anping Plain, Tainan Tableland, Dawan Lowland, and Chungchou Tableland. Structurally, the Houchiali Fault separates the Tainan Tableland and Dawan Lowland, while the right-lateral Hsinhua Fault is located 5 kilometers northeast of the Houchiali Fault. For the Eikonal tomography analysis, we included data from ten BATS (Broadband Array in Taiwan for Seismology) stations, five stations from CWASN (Central Weather Administration Seismographic Network), and one station from TSMIP (Taiwan Strong Motion Instrumentation Program). These stations were strategically positioned at distances ranging from 40 to 80 kilometers away from the dense array, with azimuths between 45° to 140° and 270° to 360°. We then calculated the cross-correlation function (CCF) between 173 seismometers and these stations. These results were subsequently used by beamforming to measure the relative surface wave arrival times. To perform Eikonal tomography, we calculated the surface wave propagation of the ambient noise and the shallow velocity structure for each period between 4 and 10 seconds. Our result shows that the velocity on Tainan Tableland is almost uniform, which is probably due to the gently folded character of the underneath Tainan anticline. Meanwhile, a low-velocity zone of approximately 2.5 by 2.5 km2 with a 4s period was revealed northeast of the Houchiali Fault and southwest of the Hsinhua Fault, with a shear-wave velocity of approximately 0.5 km/s. Upon reaching the Hsinhua Fault to the northeast, the velocity increases five times to 2.5 km/s. For the 4s period, the average velocity in this region is approximately 1.5 km/s, however, the velocity distribution does not conform with the regional velocity models. This suggests the presence of potentially unexamined small-scale structures in this area. Furthermore, this area encountered strong shaking from three local or regional moderate earthquakes that occurred in 1946, 2010, and 2016 respectively. Coincidentally, the low-velocity zone aligns roughly with the soil liquefaction sites caused by these three events.

How to cite: Yang, T.-C., Chen, Y.-N., and Rau, R.-J.: Shallow velocity structure of the Tainan frontal thrust based on Eikonal tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7098, https://doi.org/10.5194/egusphere-egu24-7098, 2024.

EGU24-7099 | ECS | Posters on site | TS5.1

Three-dimensional shallow velocity structure beneath the urban agglomerations revealed by methane source and dense array 

Yunpeng Zhang, Liwei Wang, Weitao Wang, Shishuo Liu, Xiuwei Ye, Wei Yang, Shanhui Xu, and Xiaona Ma

The three-dimensional (3D) velocity structure beneath urban agglomerations is an important data for urban construction planning and earthquake hazard risk assessment. Combining a short-period dense array with the active source can enable us to conduct high-resolution imaging of shallow structures, with a short observation time. With the increasing limitations on the usage of explosives, we have developed a new type of active source, the methane source, which has been proven to be environmentally friendly, efficient, safe, and economical. It produces seismic waves by rapidly releasing high-pressure air in borehole by igniting oxygen and methane with the reaction products of carbon dioxide and water, and can be applied to various complex terrains to detect small-scale subsurface structures, particularly in cities and fault zones.

To obtain the high-resolution structure beneath the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), we deployed a dense array consisting of 6,172 short-period stations, and carried out 63 active source excitations using new methane green sources in 2020. Using the manually picked 16,885 first-arrival phases from 63-shots methane sources, we present the first high-resolution 3D shallow P-wave velocity structure (above 1.5 km depth) in the central area of the GBA. The obtained results show that (1) the velocity images have a good correspondence with the regional topography and shallow lithology distribution. The depression area presents a low Vp distribution, while the uplift area with high Vp anomalies, which corresponds to clastic sedimentary rocks, granites, and metamorphic rocks, respectively. (2) The velocities have a strong anomaly on both sides of the Guangcong fault, Shougouling fault, Zhujiangkou fault, and Baini-Shawan fault. Among them, the Shougouling fault has the strongest controlling effect, making the velocity images show obvious differences between the north and south side along the fault at different depths. (3) The cross-fault velocity profiles show that regional faults control the distribution and burial depth of sedimentary layers. Our study shows that combination using of new green methane source and dense short-period array is an effective method to detect the shallow velocity structure and fault system under urban agglomerations.

How to cite: Zhang, Y., Wang, L., Wang, W., Liu, S., Ye, X., Yang, W., Xu, S., and Ma, X.: Three-dimensional shallow velocity structure beneath the urban agglomerations revealed by methane source and dense array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7099, https://doi.org/10.5194/egusphere-egu24-7099, 2024.

EGU24-7510 | ECS | Posters on site | TS5.1

Seismic insights into the structure of the Balmuccia Peridotite within the Ivrea Verbano Zone 

Damian Pasiecznik, Andrew Greenwood, and Florian Bleibinhaus

In the Ivrea Verbano Zone (IVZ) Italy, which is characterized with lower-crustal rocks and fragments of upper mantle rocks, a high-resolution seismic survey is conducted across the Balmuccia Peridotite. This study is in preparation of a proposed deep scientific drilling project which focuses on targeting mantle rocks and understanding the region's complex geology. Specifically, we target characterizing structures within the peridotite body.

The seismic survey employs a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 10 m along three sub-parallel receiver lines spaced 40-80 m apart. Vibroseis source points are at 22 m stations along a 2.2 km line utilizing a 12-140 Hz 10 s linear sweep with 3 s listening time. The survey aims to explain the seismic characteristics of the peridotite body and its relation to the surrounding geological structures.

The P-wave traveltime tomography reveals a range of seismic velocities within the peridotite from 6 to 8 km/s, with a mean velocity of ca. 7 km/s. These variations reflect the heterogeneity of the peridotite, influenced by the presence of fractures and faults. Notably, the higher velocities observed are consistent with findings from laboratory studies on small-scale samples from the area. The reflection seismic analysis shows subvertical reflectors that coincide with the peridotite boundaries mapped at the surface. These reflectors come together at a depth of 0.175 km b.s.l., suggesting that the peridotite has a lens-like structure. In addition, several features within the peridotite suggest a highly fractured body. Nevertheless, limitations in the imaging process do not allow for a thorough interpretation of the area below the imaged lens-shaped body. A deep reflector is identified at approximately 1.3 km depth. This feature potentially marks the top of the Ivrea Geophysical Body (IGB), aligning with previous geophysical estimations.

How to cite: Pasiecznik, D., Greenwood, A., and Bleibinhaus, F.: Seismic insights into the structure of the Balmuccia Peridotite within the Ivrea Verbano Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7510, https://doi.org/10.5194/egusphere-egu24-7510, 2024.

EGU24-7896 | ECS | Posters on site | TS5.1

Physics-informed neural networks for 3D seismic travel time tomography 

Shaobo Yang and Haijiang Zhang

Seismic travel time tomography is a widely used technique to image the Earth’s interior. Recently, there have been growing interests in employing deep learning for seismic tomography, and physics-informed neural networks (PINNs) are attractive for their integration of physical information into the networks and their greater stability compared to conventional neural networks. PINNs have been successfully used in 2D tomography, including cross-hole tomography (Waheed et al., 2021) and surface wave phase velocity tomography (Chen et al., 2022). However, 3D seismic tomography based on PINNs has not been developed. Here we propose a novel method for 3D travel time tomography based on PINNs and show its effectiveness using both synthetic and real data. The network consists of two branches, one taking in the 3D coordinates of a pair of source and receiver for fitting observed travel times and another taking in the receiver location for predicting velocities. The loss function also consists of two terms, the data fitting residual term and the Eikonal equation residual term. In this way, the two branches are connected using the Eikonal equation loss function term. After training, the network can simultaneously reconstruct the travel time fields and estimate the subsurface velocities. Our method is tested using synthetic and real travel time data for seismic network in Parkfield, California. Compared to traditional travel time tomography methods, this approach offers many advantages, including meshless modeling, no need for regularization and independent on the initial velocity models.

How to cite: Yang, S. and Zhang, H.: Physics-informed neural networks for 3D seismic travel time tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7896, https://doi.org/10.5194/egusphere-egu24-7896, 2024.

EGU24-8875 | ECS | Posters on site | TS5.1

Body wave seismic attenuation tomography of the crust in the Sichuan-Yunnan Region, China 

Jiachen Wang, Haijiang Zhang, Jing Hu, and Ying Liu

   The Sichuan-Yunnan Region is located at the southeastern margin of the Tibetan plateau in southwest China. Determining the structure of southeaster margin of the Tibetan plateau is very important for understanding the eastward growth of the plateau. At present, most of seismic tomography studies are focused on resolving multiscale velocity anomalies of the crust and mantle. However, seismic attenuation structure of the crust and upper mantle in the Sichuan-Yunnan Region is less studied, which can be used to better understand the temperature regime and the distribution of partial melting. In this study, based on a high-resolution community velocity model of the crust and uppermost mantle in this area (Liu et al., 2021), we determined body wave attenuation structure in the Sichuan-Yunnan region using data from 350 stations and 9837 seismic events observed between 2010 and 2013 (Figure 1).

 

Figure 1. Distribution of seismic events (red circles) and stations (blue triangles) in the Sichuan-Yunnan region.

    Q value is a reduction to a dimensionless form of the more usual measures of attenuation (Knopoff, 1964. Body wave attenuation tomography typically needs to extract a parameter called t* from the displacement or velocity spectrum in the frequency domain to calculate Q using the following equation:

     

    Here the influence of frequency on Q was not considered. Using the measured absolute t* values, the attenuation structure was then determined with the following relationship between t* and Q:

    For the Sichuan-Yunnan region, we constructed three-dimensional Qp and Qs models with a horizontal spatial grid interval of 0.4° × 0.4°. Our attenuation models exhibit a high consistency with large-scale features in previous researches. In the shallow depths (<20 km), inside the Chuan-Dian diamond block, it exhibits high Q anomalies, which may be related to the high density and low porosity characteristics of the Emeishan Large Igneous Province (ELIP). Previous studies suggest the presence of high Vp and Vs anomalies in the same zone (Liu et al., 2021). In comparison, most of the fault zones show low Q anomalies, indicating that fractures and fluids in the crust can increase the attenuation of seismic waves. At deeper depths (20-40 km), the ELIP still maintains a high Q anomaly, and separates two clear stripes of low Q anomalies along the Lijiang-Xiaojinhe Fault and Xiaojiang Fault. This suggests the existence of partial melting along the two fault zones that could be caused by upwelling of hot mantle materials. In addition, high Q values are observed in the Yangtze craton and Sichuan Basin, corresponding to stable tectonic block and weak tectonic activity.

How to cite: Wang, J., Zhang, H., Hu, J., and Liu, Y.: Body wave seismic attenuation tomography of the crust in the Sichuan-Yunnan Region, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8875, https://doi.org/10.5194/egusphere-egu24-8875, 2024.

EGU24-9088 | ECS | Posters on site | TS5.1

Seismogenic structure of the 2021 Ms6.4 Yangbi earthquake by seismic tomography based on the variation of information  

Yuqi Huang, Haijiang Zhang, Jing Hu, ying liu, Ji Gao, and Max Moorkamp

Seismic tomography is a useful tool to obtain the velocity structure of the Earth's interior. Compared with the Vp and Vs models, the Vp/Vs model is of great significance for studying the properties of subsurface structure, such as fluid saturation and porosity.  However, due to different data quality and quantity for P- and S-wave, Vp and Vs models generally have different resolutions and uncertainties, leading to some artifacts in the Vp/Vs model. Tryggvason and Linde (2007) proposed to use the structural similarity in Vp and Vs models to better constrain the Vp/Vs model. However, the clustering relationship between Vp and Vp/Vs models is not optimized, which limits the further geological interpretations based on velocity models. In this study, we aim at developing a new seismic tomography method based on the variation of information for Vp and Vp/Vs models. This method follows joint inversion of magnetotelluric and gravity data based on the variation of information (Moorkamp, 2022), which can improve the clustering relationship between electrical resistivity and density.
 The 2021 Ms6.4 Yangbi earthquake is located at the intersection of the Red river fault and the nearly north-south trending Lijiang-Dali fault system on the southwestern boundary of the Sichuan-Yunnan block. This earthquake has the classic characteristic of a "foreshock-mainshock-aftershock" sequence. In this study, we have developed a new seismic tomography method based on the variation of information to couple the Vp/Vs model with the Vp model to obtain more reliable Vp, Vs, and Vp/Vs models in the source region of the Yangbi earthquake. Our results show that the foreshocks occur in structures with low Vp, high Vs and low Vp/Vs, while the main shock occurs in the area with high Vp, high Vs and low Vp/Vs. Based on the cross-plot analysis and petrophysical experimental data, we suggest that long-term stress accumulation causes shearing in areas with high quartz content at a depth of 10km. 

How to cite: Huang, Y., Zhang, H., Hu, J., liu, Y., Gao, J., and Moorkamp, M.: Seismogenic structure of the 2021 Ms6.4 Yangbi earthquake by seismic tomography based on the variation of information , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9088, https://doi.org/10.5194/egusphere-egu24-9088, 2024.

EGU24-9340 | Orals | TS5.1 | Highlight

Dike-like structures control the unrest in Campi Flegrei 

Anna Tramelli and Marco Calò

The occurrence of seismicity in active calderas causes great concern as it is one of the main precursors for the volcanic eruptions.

Campi Flegrei is one of the largest known active calderas and its historical unrests are characterized by a high number of low to moderate magnitude earthquakes usually associated with soil uplifts reaching several centimeters or even meters within each cycle.

The last unrest started in 2006 and is currently accompanied by a large sequence of events localized beneath the Soflatara-Piscarelli system, together with the increment of gas emission in Piscarelli and strong variations of several geochemical and geophysical parameters.

Here we show two classes of seismic models generated using passive methods that employed both Earthquakes and Ambient Noise recorded from 2005 till March 2022.

These models enabled us to demonstrate, for the first time, the existence of vertically elongated high P-wave velocity bodies beneath Pisciarelli, Pozzuoli, and a resurgent formation situated offshore. The most evident dike-like structures are positioned at the border of the resurgence dome involved in the uplift, indicating that the peripheral structures regulate the upward fluid migration, contributing to the ongoing unrest.   

How to cite: Tramelli, A. and Calò, M.: Dike-like structures control the unrest in Campi Flegrei, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9340, https://doi.org/10.5194/egusphere-egu24-9340, 2024.

In the northern Los Angeles area, the interaction of complex tectonics and sedimentary structures has a significant influence on the attenuation characteristics of the crust. The region is also characterized by partially fluid-saturated crust and seismic sequences that promote intense fracturing. Modelling high-frequency seismic attenuation to image fine-scale crustal features and gain insight into the driving mechanisms of the seismicity is a powerful tool for seismic hazard assessment across this densely populated area.

We develop the first high-resolution 3D seismic attenuation model across the Chino and San Bernardino basins using 5,300 three-component seismograms from local earthquakes (M<3.6). The events were recorded by 410 nodal stations deployed along eight linear arrays during the 2017-2020 Basin Amplification Seismic Investigation experiment and 10 Southern California Seismic Network broadband stations. We present peak delay and coda-attenuation tomography in 6-12 and 12-24 Hz frequency bands (with horizontal and vertical grid spacings of 3 km and 1 km) as proxies of seismic scattering and absorption, respectively.

The attenuation models show distinct scattering contrasts in the uppermost 10 km of the crust across two major faults in the northern edge and in the middle of the Chino basin, suggesting variations in fracture intensity in the basement. Low scattering values characterize the crustal block bounded by these two faults, while high scattering coincides with zones of seismicity indicating highly fractured fault-rocks, such as the areas across the Cucamonga, Fontana, and San Andreas faults. The N-S pattern of high absorption and seismicity migration associated with the 2019 Fontana seismic sequence suggests potential groundwater movement across the fault into a buried intensely fractured zone in the basement that we interpret was once an elevated part of the Perris Block. Low scattering values beneath the Chino basin in the source region of the seismic sequence may confirm the presence of fluid-saturated rocks and increased pore pressure. The attenuation results allow the small-scale characterization of fractured basement rocks and fluid migration pathways, and show a heterogenous pattern of seismic wave amplification beneath the region.

How to cite: Nardoni, C. and Persaud, P.: Imaging Fracture Networks beneath the Los Angeles Metropolitan Area using High-Frequency Seismic Attenuation Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9648, https://doi.org/10.5194/egusphere-egu24-9648, 2024.

EGU24-12789 | Posters on site | TS5.1

Imaging the crustal structure of the Central Pyrenees using Seismic Interferometry 

Ruth Soto, Juvenal Andrés, Anna Gabàs, Fabián Bellmunt, Albert Macau, Pilar Clariana, Carmen Rey-Moral, Félix Rubio, Esther Izquierdo-Llavall, Tania Mochales, Emilio L. Pueyo, and Conxi Ayala

The Pyrenees constitute a natural laboratory where hundreds of geological and geophysical data have been acquired during the last decades. It represents a roughly E-W oriented doubly vergent orogen formed during the Alpine Orogeny. Deep seismic reflection data obtained during the 80s revealed its crustal architecture that resulted from the subduction of the Iberian plate under the European lithosphere at its central part.

In this work we applied seismic interferometry to the same passive dataset through two different techniques aiming to construct two independent images of the Central Pyrenean lithosphere, to enhance the current knowledge of the area. The main objectives are to compare them and correlate the obtained results with previous data. Data were acquired within the IMAGYN project along a NE-SW 70 km-long profile extending from the Southern Pyrenees (Pedraforca and Cadí Units, northern Iberia) to the northern part of the Axial Zone, close to Ax-les-Thermes (France). Data came from three to five months of continuous recording from an almost linear array of 43 seismic stations (being 17 and 26 broadband and short-period stations, respectively). The two applied techniques are (1) the global-phase seismic interferometry (GloPSI), using continuous recordings of teleseismic (30 < epicentral distance < 95⁰) and global earthquakes (> 120⁰ epicentral distance), and (2) the use of continuous ambient seismic noise recordings through autocorrelation. Despite both methods rely on different energy sources, they are complementary and use static receivers. In the first method (GloPSI), we extracted global phases (PKP, PKiKP and PKIKP) and their reverberations within the lithosphere. The selected phases were autocorrelated and stacked to construct a high-resolution pseudo zero-offset reflection image. The second approach provided an approximation to the zero-offset reflection response of a single station. Results reveal features that can be correlated in both reflection images. The crust-mantle boundary is mapped as a relative flat interface at approximately 35-40 km depth. Crustal interfaces detected at 15 and 25 km depth can be related to the Conrad discontinuity and other compositional changes within the crust.

(This work is part of the project “High-resolution imaging of the crustal-scale structure of the Central Pyrenees and role of Variscan inheritance on its geodynamic evolution” (IMAGYN), PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033)

How to cite: Soto, R., Andrés, J., Gabàs, A., Bellmunt, F., Macau, A., Clariana, P., Rey-Moral, C., Rubio, F., Izquierdo-Llavall, E., Mochales, T., Pueyo, E. L., and Ayala, C.: Imaging the crustal structure of the Central Pyrenees using Seismic Interferometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12789, https://doi.org/10.5194/egusphere-egu24-12789, 2024.

EGU24-13950 | ECS | Posters on site | TS5.1

Retrieving Seismic Reflective Waves from DAS VSP: a Case Study from MiDAS Project 

Zhuo-Kang Guan, Hao Kuo-Chen, Chun-Rong Chen, and Kuo-Fong Ma

The Longitudinal Valley in eastern Taiwan situated at the boundary between the Philippine Sea Plate and the Eurasian Plate, making it one of the significant seismogenic regions in Taiwan. In 2018, a magnitude 6.4 earthquake occurred offshore of Hualien, at the northern end of this valley. More than 4,000 aftershocks received over following two weeks beneath the Longitudinal Valley. Surprisingly, Hualien City and the Milun Fault, situated near the epicenter, did not experience notable aftershocks. However, they did display evident co-seismic deformation during the mainshock. Milun fault Drilling and All-inclusive Sensing (MiDAS) project aims to establish a comprehensive and long-term monitoring system, which involves three boreholes encompassing the fault for both surface and subsurface geoscientific observations. This study utilized a 700-meter DAS (Distributed Acoustic Sensing) setup within the borehole A of the MiDAS project to conduct VSP (Vertical Seismic Profiling) experiments. Additionally, electrical logging and surface reflection seismic data were gathered.  According to the 2D reflection seismic profile, the results depicted a gently sloping stratum on the northwest side arching towards the southwest. Most layers tapered beneath the Milun Terrace, and the fault-induced stratigraphic disturbance was not clearly discernible, making it challenging to determine if the layers were intersected by the fault. However, pronounced folding structures were evident beneath the terrace, correlating with areas of intense co-seismic deformation. From the VSP experiment, the data exhibited pronounced P-waves and Tube waves, suggesting the presence of fluids around the casing rather than rocks or cement. After data processing, the P-wave velocity correlated well with the downhole sonic logging data. Also, reflection signals with two-way travel times ranging from 0.27 to 0.45 seconds were observed in both seismic profiles. This suggests that the VSP effectively resolved reflection signals from depths of 340 to 612 meters. These signals displayed a high resemblance to lithology indicators such as Gamma ray and resistivity, confirming the authenticity of the separated reflection signals obtained from shallow depth, lower signal-to-noise ratio data.

How to cite: Guan, Z.-K., Kuo-Chen, H., Chen, C.-R., and Ma, K.-F.: Retrieving Seismic Reflective Waves from DAS VSP: a Case Study from MiDAS Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13950, https://doi.org/10.5194/egusphere-egu24-13950, 2024.

Neotectonic movements pose significant hazards and hold crucial scientific and social relevance, notably in seismic hazard assessment and subsurface utilization. In regions like northern Germany, a presumed aseismic region, understanding these processes remains limited because many faults are buried under sediments. Despite confirmed neotectonic activity, the specifics of these processes and associated structures remain largely unknown.

Improving our understanding of neotectonic activity requires investigations of recently-active fault zones, such as the Osning Fault System (OFS) in North Rhine-Westphalia, Germany. Using near-surface geophysics becomes crucial in this endeavour, which so far were not used at the OFS.

The OFS stands out as a site of recent and historical seismic activity, experiencing several large earthquakes over the past four centuries. Notably, major earthquakes in 1612 and 1767 with intensities ranging from VI to VII on the MSK scale, emphasize the seismic significance of the OFS. Unlike other faults in the region, the faults of the OFS reach the basement and the fault zone dips north-eastward. Furthermore, the former iceload from Scandinavia influenced the fault system by facilitating glacial isostatic adjustment, which subsequently enabled fault reactivation. The complex nature of the fault system spans various geological phases, prompting a comprehensive investigation approach to understand its regional neotectonic evolution.

Our geophysical and geological approach integrates high-resolution 2D P- and SH-wave reflection seismics and retrodeformation of previously-published cross-sections. This is complemented by surface geological maps and limited drilling information. Our aim is to identify and interpret fault geometry and kinematics.

While P-wave seismic surveys used for imaging of deep structures often lack high-resolution in the shallow subsurface, the integration of SH-wave reflection seismics compensates for this limitation, offering enhanced resolution, especially at the near-surface. The survey involved three P-wave profiles employing a hydraulically-driven vibrator vehicle and four SH-wave profiles utilizing an electro-dynamic micro-vibrator with varying source point spacing.

These seismic profiles successfully delineate fault structures within the Cretaceous formations, revealing previously unidentified extensions of the OFS. Although the P-wave profiles inadequately image the Quaternary layers, there are indications that the faults extend into this formation. The SH-wave profiles, with their superior resolution in the near-surface due to lower wave velocities, confirm these assumptions, revealing further faulting and deformation features within the Quaternary sediments. Interpretation and fault imaging are further enhanced by full waveform inversion of P- and S-wave data, testing of different migration methods for the S-wave data, and seismic attribute analysis.

Retrodeformation and balancing of existing cross-sections and the interpreted seismic profiles allows the fault geometry and kinematics to be assessed. We determined which adjustments were necessary to make the profiles more geologically plausible. This combined geophysical and geological approach enabled a more comprehensive interpretation and understanding of the local fault geometry and the neotectonic evolution of the OFS.

How to cite: Wadas, S., Tanner, D., and Polom, U.: The structure and neotectonic evolution of the Osning Fault System in Germany derived from near-surface P- and SH-wave reflection seismics and retrodeformation modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15033, https://doi.org/10.5194/egusphere-egu24-15033, 2024.

EGU24-15578 | Posters on site | TS5.1

Scattering and absorption imaging of the Nesjavellir (Iceland) geothermal area 

Paolo Capuano, Ferdinando Napolitano, Luca De Siena, Thorbjorg Ágústsdóttir, Vala Hjörleifsdóttir, Mauro Palo, and Ortensia Amoroso

Detailed imaging of the elastic and anelastic properties of the crustal structures of geothermal regions is crucial from a scientific and industrial standpoint. The Hengill volcano region is the most productive high-temperature geothermal region in Iceland, located in the southwestern region of Iceland (30 km east of Reykjavík). To the north of the Hengill volcano is the Nesjavellir geothermal subfield, which lies within the Hengill fissure swarm trending N30°E.

Scattering and absorption measurements have proven reliable proxies for the spatial extension of faults, thrusts and fluid reservoirs across tectonic, volcanic and hydrothermal settings. Scattering marks tectonic interactions and lithological contrasts due to wave-trapping mechanisms that increase energy across the earthquake coda. Fluid content is, instead, the primary controller of seismic absorption. Rock physics studies and numerical simulations have proven the sensitivity of this parameter to strain rate and pore space topology.

The present work aims to provide the first 3D images of seismic scattering and absorption accross the Nesjavellir geothermal area at different frequency bands, measured through peak delay mapping and coda-attenuation tomography, respectively. Manually picked seismic events that occurred between November 2017 and December 2022, recorded by three permanent and temporary seismic networks, have been used to provide the first attenuation imaging of this geothermal area.

The preliminary results show, firstly, the stability of the peak delay and coda attenuation results as the analysis parameters change. The 3D scattering and absorption imaging show that the well-resolved areas of the Hengill region are characterized by high scattering, coinciding with highly-fragmented fissures at the surface. High absorption anomalies mark the Nesjavellir geothermal sub-field, mainly between 4 and 6 km depth, where seismic tomographies highlight high Vp/Vs.

The work is supported by project TOGETHER - Sustainable geothermal energy for two Southern Italy regions: geophysical resource evaluation and public awareness financed by European Union – Next Generation EU ( PRIN-PNRR 2022, CUP D53D23022850001).

How to cite: Capuano, P., Napolitano, F., De Siena, L., Ágústsdóttir, T., Hjörleifsdóttir, V., Palo, M., and Amoroso, O.: Scattering and absorption imaging of the Nesjavellir (Iceland) geothermal area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15578, https://doi.org/10.5194/egusphere-egu24-15578, 2024.

EGU24-16491 | ECS | Posters on site | TS5.1

The Attenuation and Scattering Signature of Fluid Reservoirs and Tectonic Interactions in the Central-Southern Apennines (Italy)  

Donato Talone, Luca De Siena, Giusy Lavecchia, and Rita de Nardis

The intricate tectonics of Central-Southern Italy, characterized by its complex fault network and sparse seismicity distribution, have posed a significant challenge to understanding the region's seismic hazard, its three-dimensional structural assessment, and the role of fluids in the seismic release. Conventional geophysical techniques, often limited by low seismicity rates, have struggled to provide a comprehensive picture of the crustal structures, and a coherent geophysical model of the area is still absent. Leveraging the last decade’s expanded detection capabilities of the Italian seismic network, we were able to make up for this lack and employed seismic attenuation and scattering tomography methods to produce complete 3D attenuation models of the crust.

By analyzing the energy loss of seismic waves as their propagation through the crust, the study revealed a pervasive pattern of high attenuation zones that extend along the entire Apenninic Chain, particularly concentrated in Southern Italy. The distribution of these anomalies aligns closely with the regional fault structures suggesting a strict relationship with the fracture level due to the tectonic processes. In contrast to the bigger anomalies, the study also identified prominent low attenuation and scattering volumes corresponding to the Fucino and Morrone-Porrara fault systems. These are likely regions of accumulated stress where the locked seismic energy release contributes to the high seismic hazard. Furthermore, the study identified a previously undetected high-attenuation region beneath the Matese extensional system, indicating a potential source of both deep and shallow circulation of fluid. Another anomaly was detected near the L'Aquila 2009 seismogenic area, suggesting a regional distribution of fluid-rich areas.

The findings of this study provide unprecedented insights into the tectonic interactions and fluid sources of Central-Southern Italy, with significant implications for seismic hazard assessment, fluid exploration, and the development of effective mitigation strategies for this geologically active region.

How to cite: Talone, D., De Siena, L., Lavecchia, G., and de Nardis, R.: The Attenuation and Scattering Signature of Fluid Reservoirs and Tectonic Interactions in the Central-Southern Apennines (Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16491, https://doi.org/10.5194/egusphere-egu24-16491, 2024.

EGU24-16588 | ECS | Orals | TS5.1

Ambient noise based seismic imaging of the Tuscan Magmatic Province, Italy 

Konstantinos Michailos, Geneviève Savard, Elliot Amir Jiwani-Brown, Domenico Montanari, Michele d'Ambrosio, Gilberto Saccorotti, Davide Piccinini, Nicola Piana Agostinetti, Riccardo Minetto, Marco Bonini, Chiara Del Ventisette, Francisco Muñoz, Juan Porras, and Matteo Lupi

The Tuscan Magmatic Province (TMP) is the result of several geodynamic events associated with the formation of the Apennines orogen and the Tyrrhenian Basin. Previous studies highlighted different aspects of the TMP, characterised by a complex geology, a thin continental crust, low seismicity rates, and locally high heat flow rates (e.g., Larderello-Travale and Amiata geothermal fields). Despite numerous active and passive seismic investigations in the past, the knowledge of the crustal structure across the broader TMP region is limited, particularly when considering its spatial coverage. To tackle this problem, we use ambient noise tomography and waveform data from the TEMPEST temporary seismic network and permanent seismometers. The TEMPEST network operated from late 2020 to late 2021, comprising 30 broadband seismometers, augmenting the existing permanent seismometer network.

Here we analyse Rayleigh wave group-velocity dispersion data from all seismic stations of our composite seismic network of 62 seismometers and generate 2-D maps of group velocities at different periods. We observe relatively low group velocities that may represent possibly two plutonic bodies in the region (i.e., Larderello and Mt Amiata). To further constrain the volume of the plutonic bodies, we intend to perform a series of inversions to estimate the variation of shear-wave velocity with depth. Our approach showcases the effectiveness of ambient noise tomography in unravelling crustal structures in geologically complex regions such as the Tuscan Magmatic Province, Italy, and its implications for geodynamic and tectonophysics studies.

How to cite: Michailos, K., Savard, G., Jiwani-Brown, E. A., Montanari, D., d'Ambrosio, M., Saccorotti, G., Piccinini, D., Agostinetti, N. P., Minetto, R., Bonini, M., Del Ventisette, C., Muñoz, F., Porras, J., and Lupi, M.: Ambient noise based seismic imaging of the Tuscan Magmatic Province, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16588, https://doi.org/10.5194/egusphere-egu24-16588, 2024.

EGU24-17959 | ECS | Orals | TS5.1

Assessing the geometry and topology of a fault network along the Northern North Sea rift margin: insights from broadband 3D seismic reflection data 

Edoseghe Edwin Osagiede, Casey Nixon, Rob Gawthorpe, Atle Rotevatn, Haakon Fossen, Christopher A-L. Jackson, and Fabian Tillmans

Recent advances in seismic reflection acquisition and processing technologies have led to a general improvement in the resolution of seismic reflection data, allowing for better imaging of subsurface structures, particularly fault networks. Leveraging high-resolution, broadband 3D seismic reflection data from the northern North Sea, we, for the first time, investigate how the geometrical and topological properties of the Late Jurassic normal fault network vary spatially along the rift margins. We also discuss the factors that may have influenced the spatial variability of the rift fault network properties. Our results reveal that normal faults closer to the North Viking Graben exhibit dominant N-S and NE-SW strikes that are sub-parallel to the graben axis and associated step-over zone, whereas those farther from the graben, exhibit an additional NW-SE strike, resulting in a complex fault network. We identify two broad topological domains within the fault network: 1) dominated by isolated (I-) nodes, partially connected (I-C) branches, low fault density, and connectivity, and 2) dominated by abutting (Y-) nodes, fully connected (C-C) branches, moderate to high fault density and connectivity. These topological domains correlate with previous sub-division of the rift margin in the northern North Sea into platform and sub-platform structural domains, respectively. There is also a positive correlation between the spatial variability of the fault orientations, density, and connectivity, highlighting the relationship between normal fault network geometry and topology. We conclude that variation in the amount of relative strain, the presence of pre-existing structures, accommodation zone- and fault damage zone-related deformation are among the main factors that influence the spatial variation of fault network properties both at a regional and local scale. This study provides a new, but complementary way of characterising large-scale structural domains in rift systems. Additionally, our assessment of fault network topology provides important insights into the connectivity of rift-related normal faults, which have implications when considering the integrity of structural traps and subsurface fluid flow related to hydrocarbon and geothermal reservoirs, and CO2 storage.

How to cite: Osagiede, E. E., Nixon, C., Gawthorpe, R., Rotevatn, A., Fossen, H., Jackson, C. A.-L., and Tillmans, F.: Assessing the geometry and topology of a fault network along the Northern North Sea rift margin: insights from broadband 3D seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17959, https://doi.org/10.5194/egusphere-egu24-17959, 2024.

EGU24-18014 | Orals | TS5.1

Passive seismic survey across the fault-zone of Introdacqua, central Italy: the subsurface geological structure role on the site amplification pattern  

Marta Pischiutta, Alessia Mercuri, Federico Fina, Francesco Salvini, Luca Minarelli, Giovanna Cultrera, and Giuseppe Di Giulio

In this work we perform a detailed passive seismic survey in proximity of a shear zone in the Introdacqua area, central Italy, around the permanent seismic station IV.INTR of the Italian seismic network RSN. This station is located on a prominent ridge (width of about 200 m, relative height of about 240 m), and is affected by a clear directional amplification between 1 and 3 Hz, with maximum amplification along N160° azimuth, as shown by HVSRs calculated using both seismic events and ambient noise recordings (CRISP database, www.crisp.ingv.it). This effect was confirmed by 11 ambient noise measurements performed nearby station IV.INTR in the framework of an agreement with the Italian Civil Protection. Since the maximum amplification occurs parallel to the topography elongation, it is not explainable through the topo-resonant model (e.g. Géli et al. 1988).

In this work, to better investigate the anomalous seismic response, as well as the areal extension of the directional effect, we implement an array of further 32 ambient noise measurement points, including a larger area around the topography. We find that the directional effect along N160° azimuth is gathered only at measurement sites close to IV.INTR, disappearing when increasing distances (over 300 m). A detailed structural geological survey suggests the presence of intensely fractured rocks produced by a fault located close to station IV.INTR, fractures strike being concentrated around N70°-80° azimuth, transversally to the directional effect. This is in agreement with several literature papers suggesting that across fault zones directional amplification is transversal to the prevailing fracture strike (e.g. Pischiutta et al., 2023, and references therein).

The Introdacqua study case suggests that anomalous amplification patterns can be found on topography as an effect of the subsurface geological structure, rather than being produced by the sole convex shape. Since topographic irregularities and rock fractures often coexist in tectonically active zones, this is a key point to interpret amplification at sites with pronounced topography. For this reason, Introdacqua was chosen as a test-site in the of the ongoing INGV-GEMME international project, whose aim is the study of the seismic site response in complex 3D geological and morphological settings, and the deep investigation of the wave propagation by using 3D numerical modeling, to provide guidelines for future site characterization.

How to cite: Pischiutta, M., Mercuri, A., Fina, F., Salvini, F., Minarelli, L., Cultrera, G., and Di Giulio, G.: Passive seismic survey across the fault-zone of Introdacqua, central Italy: the subsurface geological structure role on the site amplification pattern , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18014, https://doi.org/10.5194/egusphere-egu24-18014, 2024.

EGU24-18800 | ECS | Orals | TS5.1

 The TEst Site IRpinia fAult (TESIRA) project. Initial Findings from Active-Source Seismic Experiments 

Giuseppe Ferrara, Pier Paolo Gennaro Bruno, Luigi Improta, Stefano Maraio, David Iacopini, Vincenzo Di Fiore, and Paolo Marco De Martini

The scientific project TESIRA (TEst Site IRpinia fAult), funded in 2021 by the University of Naples “Federico II”, aims, through the integration of a multivariate dataset, to achieve a high-resolution 3D geophysical imaging of the shallow structure of the southern branch of the 1980 Ms=6.9 Fault at Pantano San Gregorio Magno (SA). The set of data acquired during the project life-span included: a microgravimetric survey; 3D and 2D Electrical Resistivity measurements; aeromagnetic and GPR surveys by drone; a CO2 surface degassing measurement and a full-waver electric investigation.

Specifically, the active-source seismic dataset acquired at Pantano consists of four high- to very-high resolution seismic profiles spanning a total length of 3150 m and a high-resolution seismic volume covering an area of 12.5 acres. The seismic experiment's location was strategically chosen to illuminate key features of the Pantano basin affected by coseismic surface faulting, such as the rupture during the November 23,1980 Irpinia earthquake and the southern segment of the Pantano-San Gregorio Fault System (PSGM).

We share the early findings obtained through standard Common Depth Point processing and post-stack depth migration. Even at this initial stage, the results offer a clear picture of the intricate 3D structure of the basin, revealing a complex pattern of the carbonatic basement resulting from active faulting. Additionally, the seismic images underscore the evident influence of active faulting on the basin's formation and recent sedimentation. Future analyses, including full-waveform inversion and post-stack depth migration, are planned to enhance the imaging of this critical sector in the southern Apennines. Although seismic data present the highest resolution among the geophysical datasets at Pantano, their integration with the extensive data collected during the TESIRA project will facilitate a reliable interpretation of the complex basin subsurface, useful to improve our understanding of the interplay between active surface faulting and recent basin growth pattern.

How to cite: Ferrara, G., Bruno, P. P. G., Improta, L., Maraio, S., Iacopini, D., Di Fiore, V., and De Martini, P. M.:  The TEst Site IRpinia fAult (TESIRA) project. Initial Findings from Active-Source Seismic Experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18800, https://doi.org/10.5194/egusphere-egu24-18800, 2024.

EGU24-19431 | ECS | Orals | TS5.1 | Highlight

Multi-scale investigation of the InSight landing site, on Mars, using one-station seismology 

Sebastian Carrasco, Brigitte Knapmeyer-Endrun, Ludovic Margerin, Eleonore Stutzmann, Martin Schimmel, Keisuke Onodera, Sabrina Menina, Wanbo Xiao, Zongbo Xu, Cedric Schmelzbach, Manuel Hobiger, and Philippe Lognonné

The internal structure of a planet provides constraints for understanding its evolution and dynamics. In November 2018, the InSight spacecraft landed on Mars and deployed a set of geophysical instruments, including one seismological station. In this work, the subsurface structure at the InSight landing site (ILS) is explored, from the shallow subsurface to crustal depths, by applying single-station seismological techniques (SST) on martian ambient vibrations and seismic events data.

The shallow subsurface at the ILS, in the order of meters, is investigated using the horizontal-to-vertical spectral ratios (HVSR) from the coda of martian seismic events. Assuming a fully diffuse wavefield, a nonlinear inversion using the conditional Neighbourhood Algorithm (NA) allowed to map the shallow subsurface at the ILS. Due to the non-uniqueness problem, different sets of models are retrieved. The 8 Hz HVSR peak can be explained by a Rayleigh wave resonance due to a shallow high-velocity layer, while the 2.4 Hz trough is explained by a P-wave resonance due to a buried low-velocity layer. The kilometer-scale subsurface was constrained by Rayleigh wave ellipticity measurements from large martian seismic events. The ellipticity measurements (0.03-0.07 Hz) were jointly inverted with P-to-s Receiver Functions and P-wave lag times from autocorrelations, to provide a subsurface model for the martian crust at the ILS. The joint inversion allowed the thickness and velocities of a new surface layer, previously proposed only conceptually, to be constrained by multiple seismological data. The HVSR in the 0.06-0.5 Hz frequency range from the coda of S1222a, the largest event ever recorded on Mars, suggests a gradual transition from shallow to crustal depths and consolidates the group of shallow subsurface models with the largest shear-wave velocities as the most compatible with the crustal structure.

A comprehensive multi-scale model of the ILS subsurface is proposed. The ILS is characterized by the emplacement of a low-velocity regolith/coarse ejecta layer over a high-velocity Amazonian fractured lava flow (~2 km/s, ~30 m thick). A buried Late Hesperian-Amazonian sedimentary layer is deposited below (~450 m/s, ~30 m thick), underlain by a heavily weathered Early Hesperian lava flow. The latter overlays a thick, likely Noachian sedimentary layer that extends to a depth of 2-3 km. This shallow structure forms the first crustal layer derived from the joint inversion. Deeper crustal layers are consistent with other reported ILS models, with intracrustal discontinuities at 8-12 km and 18-23 km depth. The Moho depth at the ILS is found at 35-45 km depth. Shear-wave velocities above ~20 km depth are lower than 2.5 km/s, slower than in other regions of Mars, suggesting a higher alteration due to local processes or a different origin of the upper crust at the ILS. The proposed model is consistent with the geologic history of Mars and other independent observations, confirming the great potential of SST for multi-scale investigation of, e.g., other planetary bodies or understudied regions on Earth.

How to cite: Carrasco, S., Knapmeyer-Endrun, B., Margerin, L., Stutzmann, E., Schimmel, M., Onodera, K., Menina, S., Xiao, W., Xu, Z., Schmelzbach, C., Hobiger, M., and Lognonné, P.: Multi-scale investigation of the InSight landing site, on Mars, using one-station seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19431, https://doi.org/10.5194/egusphere-egu24-19431, 2024.

EGU24-20377 | ECS | Posters on site | TS5.1

High-resolution crosshole seismic imaging of glacial sediments by full-waveform inversion 

Sarah Beraus, Daniel Köhn, Thomas Burschil, Hermann Buness, Thomas Bohlen, and Gerald Gabriel

During the Quaternary, glaciers shaped the Alpine region by excavating deep valleys and refilling them with the sediments that they transported. One such overdeepened valley is the Tannwald Basin (ICDP site 5068_1), which was created by the Rhine Glacier in what is thought to have been several glaciations. The sediments found in such valleys thus provide climate archives and tell us about the landscape evolution if we understand the sedimentation processes that took place.

To study these glacial sediments in terms of their small-scale structure and deposition, we acquired P- and S-wave seismic crosshole data using high-frequency borehole sources. While the pressure field was recorded by a 24-station hydrophone array, the S-waves excited by horizontally and vertically polarizing sources, respectively, were recorded by an 8-station 3C geophone string.  

Since the S-wave data is quite complex, we directly apply elastic mono-parameter full-waveform inversion (FWI). This mitigates the phase misidentification problem in deriving an S-wave model from phase picks. In preparation for the inversion, we rotate the data into a ray-based coordinate system so that the SV-wave dominates on the vertical component and the SH- wave dominates the horizontal component. We then invert the vertical component of the SV-dataset and the transverse component of the SH-dataset using the appropriate parameterization. We apply a global correlation norm and preconditioning to ensure proper and fast converge of the inversion. In addition, we use the multistage approach to deal with the non-linearity of the problem. Anisotropic Gaussian filtering of the gradients as a function of the S-wave wavelength at higher frequency stages pushes the vertical resolution of our model below 1 m. This represents a significant improvement over surface seismic and traveltime tomography methods. A comparison with the lithology known for one of the boreholes shows an impressive correlation. Thus, our approach can bridge the gap between traditional surface seismic imaging and borehole methods.

In future research, we will repeat this approach for the SH-dataset. In the case of structural similarity, but a systematic difference in the S-wave velocities, this will provide us with evidence of seismic anisotropy, which will then need to be further characterized and quantified. From this, we will be able to infer the sedimentation processes that will help us to understand the evolution of the Alpine landscape. Eventually, FWI of the P-wave data will provide a more comprehensive, high-resolution image of the subsurface at the drill site.

How to cite: Beraus, S., Köhn, D., Burschil, T., Buness, H., Bohlen, T., and Gabriel, G.: High-resolution crosshole seismic imaging of glacial sediments by full-waveform inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20377, https://doi.org/10.5194/egusphere-egu24-20377, 2024.

EGU24-415 | ECS | Orals | TS8.1

The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana 

Antomat Avelino de Macedo Filho, Alisson Oliveira, Valdecir Janasi, and Maria Helena Hollanda

Extensive igneous activity, currently identified from NE Brazil and western Africa to the Falkland Islands and South Africa, preceded the fragmentation of the Western Gondwana supercontinent in the Early Cretaceous. The Paraná-Etendeka Magmatic Province (PEMP) is characterized by continental basaltic flows and igneous plumbing systems in SE South America and its African counterpart. In NE Brazil, dyke swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). A prominent feature of EQUAMP is the Rio Ceará-Mirim dyke swarm, an arcuate igneous plumbing system approximately 1,100 km in length. Aeromagnetic data suggests that the Rio Ceará-Mirim dykes stretch from the corner of South America to the northwest border of the São Francisco Craton. At this point, the dykes shift orientation to the NNW, extending towards the south, where they appear to connect with the Transminas dyke swarm (northern PEMP). The apparent continuity of dykes as a single entity would constitute a massive transcontinental swarm of about 2,300 km. A similar relationship is observed for the Riacho do Cordeiro (southern EQUAMP) and Vitória-Colatina (northern PEMP) dykes, indicating continuity across the São Francisco Craton of about 1,600 km. This study, supported by new petrological, geochemical, isotopic, and geochronological data, combined with geophysical and geodynamical analyses, demonstrates that the Transminas and Vitória-Colatina dyke swarms share the same composition and age as the Rio Ceará-Mirim and Riacho do Cordeiro dyke swarms, respectively. The set of new evidence supports a genetic connection between the PEMP and EQUAMP. Therefore, they can be collectively referred to as a single large igneous province related to the early stage of the South Atlantic rifting process in the West Gondwana realm: The South Atlantic Magmatic Province.

How to cite: Avelino de Macedo Filho, A., Oliveira, A., Janasi, V., and Hollanda, M. H.: The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-415, https://doi.org/10.5194/egusphere-egu24-415, 2024.

EGU24-1934 | ECS | Posters on site | TS8.1

The hypothesis of a lost Cenozoic “Himalandia” between India and Asia 

Liang Liu, Lijun Liu, Jason Morgan, Yi-Gang Xu, and Ling Chen

            The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83˚E and 88˚E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55±5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation.

How to cite: Liu, L., Liu, L., Morgan, J., Xu, Y.-G., and Chen, L.: The hypothesis of a lost Cenozoic “Himalandia” between India and Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1934, https://doi.org/10.5194/egusphere-egu24-1934, 2024.

EGU24-2317 | Posters on site | TS8.1

Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific 

Gabi Laske, Grace Atkisson, Sujania Talavera Soza, John Collins, and Donna Blackman

The OHANA experiment comprises a 15-month deployment of 25 broadband ocean bottom seismometers (OBSs) in the northeast Pacific Ocean, about halfway between Hawaii and the North American west coast. The primary objective of this project is to explore the crust, lithosphere and asthenosphere in a 600~km wide region west of the Moonless Mountains, covering mainly 40-to-50 Myr old Pacific lithosphere. A fundamental question to be addressed is whether this particular area has the signature of a typical oceanic lithosphere that has a normal plate cooling history. Alternatively, we seek evidence for a previously proposed reheating process, e.g. resulting from small-scale shallow-mantle convection. 

The new data enhance seismic imaging in a regional as well as in a global context. Regionally, short-period ambient noise and long-period earthquake-derived Rayleigh wave dispersion provide the centerpiece for imaging the crust and upper mantle. In  a top-down approach,
we start with the assembly and analysis of ambient-noise cross-correlation functions between 5 and 25 s. We present an initial assessment of high signal-to-noise quality cross-correlation functions. We derive path-averaged dispersion curves for the fundamental mode and present tomographic images from initial inversions. 

Furthermore, our cross-correlation functions contain prominent waveforms from overtones that can help improve resolution as a function of depth.

How to cite: Laske, G., Atkisson, G., Talavera Soza, S., Collins, J., and Blackman, D.: Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2317, https://doi.org/10.5194/egusphere-egu24-2317, 2024.

EGU24-2624 | ECS | Posters on site | TS8.1

Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean  

Yiming Luo, Jian Lin, Zhiyuan Zhou, Fan Zhang, Xubo Zhang, and Jinchang Zhang

We investigated the impacts of the Kerguelen and Amsterdam-St. Paul (ASP) hotspots on mantle evolution and crustal accretion of nearby spreading ridges in the Southeastern Indian Ocean. Gravity analysis revealed enhanced magmatism and thickened crust along the ridge caused by the Kerguelen and ASP hotspots. By employing plate motions derived from the GPlates global plate reconstruction model, along with the ASPECT 3-D mantle convection code, we presented a comprehensive depiction of the ridge-dual hotspot system, which has been relatively underexplored in previous research. Model results indicated that the Kerguelen hotspot had a significantly greater influence on mantle temperature and ridge crustal thickness compared to the ASP hotspot. Furthermore, there is evidence suggesting a potential interaction between the dual hotspots, leading to the migration of ASP plume materials towards the Kerguelen plume.

How to cite: Luo, Y., Lin, J., Zhou, Z., Zhang, F., Zhang, X., and Zhang, J.: Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2624, https://doi.org/10.5194/egusphere-egu24-2624, 2024.

EGU24-2711 | ECS | Orals | TS8.1

Links between large volcanic eruptions, basal mantle structures and mantle plumes 

Annalise Cucchiaro, Nicolas Flament, Maëlis Arnould, and Noel Cressie

As part of mantle convection, mantle plumes rise from the deep Earth, leading to volcanic eruptions during which large volumes of mafic magma are emplaced at Earth’s surface over a few million years. In 1971, Jason Morgan showed that seamount chains could be used to calculate the absolute motion of tectonic plates above fixed mantle plumes. This ground-breaking work notably led to the study of the relationship between Earth’s deep interior and its surface. Mantle plumes have been critical to constrain absolute plate motions in Earth’s recent geological past, with the development of both fixed-hotspot and moving-hotspot plate-motion models. Recent studies also revealed a statistical link between large volcanic eruptions and basal mantle structures in space and time, suggesting that large volcanic eruptions, mantle plumes, and hot basal structures are intrinsically connected. In these studies, mantle plumes were considered as the implicit process connecting volcanic eruptions at the surface to hot basal mantle structures. Geodynamic models suggest that mantle plumes are generated by two large antipodal hot basal mantle structures, up to ~1,200 km thick, and shaped by subducted oceanic crust through time. Here, we systematically compare three volcanic-eruption databases, four global tomographic models, and six reconstructions of past global mantle flow, to investigate the spatio-temporal links between volcanic eruptions, hot basal mantle structures, and modelled mantle plumes from 300 million years ago to the present day. We find that large volcanic eruptions are spatially closer to fixed and moving hot basal mantle structures than to modelled mantle plumes, because mantle plumes cover an area that is five orders of magnitude smaller than the area covered by hot basal mantle structures. The strength of the spatial-statistical relationships is largest between volcanic eruptions and modelled mantle plumes and, overall, it is larger between volcanic eruptions and moving basal mantle structures than between volcanic eruptions and fixed basal mantle structures.  This suggests that large volcanic eruptions are preferentially associated with mantle plumes generated from the interior of mobile basal mantle structures, which is in sharp contrast to previous studies that suggested mantle plumes are generated from the edges of fixed basal mantle structures.

How to cite: Cucchiaro, A., Flament, N., Arnould, M., and Cressie, N.: Links between large volcanic eruptions, basal mantle structures and mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2711, https://doi.org/10.5194/egusphere-egu24-2711, 2024.

EGU24-4020 | ECS | Orals | TS8.1

Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction 

Björn Heyn, Grace Shephard, and Clint Conrad

Between about 130 and 75 Ma, the Arctic was impacted by widespread and long-lived volcanism known as the High Arctic Large Igneous Province (HALIP). HALIP is a very unusual large igneous province because it exhibits prolonged melting over more than 50 Myr with pulses of activity, an observation that is difficult to reconcile with the classic view of large igneous provinces and associated melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a large igneous province has been questioned, and alternative mechanisms have been invoked to explain at least part of the volcanism. However, the Arctic also exhibits a very complex and time-dependent tectonic history that includes cratons, continental margins and rifting, all of which are expected to interact with the rising plume and affect its melting behaviour.

 

Here, we use 2-D numerical models that include melting and melt migration to investigate a rising plume interacting with a lithosphere of variable thickness, i.e. an extended-basin-to-craton setting. Models reveal significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30-40 Myr, but only if feedback between melt and mantle convection is accounted for. In particular, we find that melt migration transports heat upwards and enhances local lithospheric thinning, resulting in a more heterogeneous distribution of melting zones within the plume head underneath the Sverdrup Basin. Once the thicker continental and cratonic lithosphere move over the plume, plume material is deflected from underneath the Greenland craton and can then re-activate melting zones below the previously plume-influenced Sverdrup Basin, even though the plume is already ∼500 km away. Hence, melting zones may not represent the location of the deeper plume stem at a given time. Plume flux pulses associated with mantle processes, rifting of tectonic plates or magmatic processes within the crust may alter the timing and volume of secondary pulses and their surface expression, but are not required to generate pulses in magmatic activity. Hence, we propose that the prolonged period of rejuvenated magmatism of HALIP is consistent with plume impingement on a cratonic edge and subsequent plume-lithosphere interaction. Based on melt fractions, our models suggest that HALIP magmatism should exhibit plume-related trace element signatures through time, but potentially shifting from mostly tholeiitic magmas in the first pulse towards more alkalic compositions for secondary pulses, with regional variations in timing of magma types.

How to cite: Heyn, B., Shephard, G., and Conrad, C.: Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4020, https://doi.org/10.5194/egusphere-egu24-4020, 2024.

The India-Asia convergence has persisted since the onset of collision at ~55 Ma, indicating the driving forces of Indian indentation do not disappear on continental collision in the convergence process. What drives ongoing India-Asia convergence? This puzzle cannot be well resolved by the traditional theory of plate tectonics and the concept of Wilson Cycle. Consequently, questions concerning the primary driving force of the ongoing India-Asia convergence and the magnitude of this force still await an answer. Previous works have proposed multiple candidates for the primary driver of India-Asia convergence, including the continental subduction of the Indian lithosphere under Tibet, oceanic subduction at the Sumatra-Java trench, as well as the basal drag exerted by the mantle flow on the base of Indo-Australia plate. Here we present global geodynamic models to investigate the driving forces behind the India-Asia convergence, which produce good fits to the observed motions, stresses and strains within the Indo-Australia plate. On this basis, we quantitatively calculate the magnitude of effective forces of boundary forces (slab pull and ridge push) and basal drag. We conclude that the Sumatra-Java subduction is the primary driver of the ongoing India-Asia convergence. Indo-Australia plate motion is driven at the Sumatra-Java trench, impeded along the Himalaya, which could increase the shear stress within the plate. Different from the recent emphasis on the basal drag as a dominant driving force for the India-Asia convergence, this study shows that basal drag acts as the resisting force for the northeastward motion of the giant Indo-Australia plate, though it serves as a driver in some local regions.

 

How to cite: Zheng, Q. and Hu, J.: Driving forces for the ongoing India-Asia convergence: insight from global high-resolution numerical modeling of mantle convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4314, https://doi.org/10.5194/egusphere-egu24-4314, 2024.

EGU24-4754 | Orals | TS8.1

Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots 

Barbara Romanowicz, Federico Munch, and Utpal Kumar

With recent progress in resolution in global seismic mantle imaging provided by numerical wavefield computations using the Spectral Element Method and full waveform inversion, Jason Morgan’s suggestion from over 50 years ago that mantle plumes may be rooted at the core-mantle boundary (CMB) has been confirmed. Yet the imaged plumes present intriguing features that contrast with the classical thermal plume model and should inform our understanding of mantle dynamics. Among other features, they are broader than purely thermal plumes, and do not extend straight from the CMB to the corresponding hotspot volcanoes, but they are frequently deflected horizontally in the extended transition zone (400-1000 km depth), so that their lower mantle location can be significantly offset (as much as a 1000 km) from their surface expression. They appear to be thinner in the upper mantle. This, together with similar horizontal flattening observed in subduction zones suggests a change in the radial viscosity structure of the mantle that may occur deeper than usually assumed to be related to the 660 km phase change. The fattest plumes have been shown to be anchored within the perimeter of the large low shear velocity provinces (LLSVPs) and an increasing number of them appear to house mega-ultra low velocity zones within their roots.  Moreover, in the upper mantle, they appear to be associated with regularly spaced low velocity channels aligned with absolute plate motion.

We discuss these features in the light of recent regional imaging updates in the south Atlantic and beneath Yellowstone, contrasting the corresponding mantle plumes, and in particular showing mounting evidence that the LLSVPs are not compact “piles” extending high above the CMB, but rather a bundle of thermo-chemical plumes feeding secondary scale convection in the top 1000 km of the mantle.

How to cite: Romanowicz, B., Munch, F., and Kumar, U.: Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4754, https://doi.org/10.5194/egusphere-egu24-4754, 2024.

EGU24-6247 | ECS | Posters on site | TS8.1

Slab dynamics in the mantle: a back-to-basics approach 

Abigail Plimmer, Huw Davies, and James Panton

Subduction is one of the most fundamental processes on Earth, linking the lithosphere and mantle and is a key driving force in mantle circulation. Despite this, and the advancement of geophysical methods which allow us to better understand mantle dynamics, our understanding of slab behaviour is still limited. The Earth is a very complex system, and so conclusions regarding slab dynamics are also sensitive to the interplay between countless processes acting within the mantle. 

There is much to learn about slab sinking in the mantle from considering a single 'perfect' plate, such that the dynamics can be isolated from any pre-established or distal processes. We present a range of 3D spherical mantle circulation models which evolve from the initial condition, driven by a 'perfect' plate at the surface. Each of these plates comprises a rectangular geometry, bound by a subduction zone on one side, a spreading ridge on the opposite side, and two tranform faults on the adjacent edges. We vary the geometry of the plate, both in terms of the length of the subducting trench, and the distance from the trench to the ridge, and vary the plate velocity.

We will report the slab behaviour in terms of plate geometry, mantle properties, and plate velocity, focussing on the evolution of downwellings, upwellings and other mantle structures in response to mantle circulation models driven solely by a single plate at the surface.

How to cite: Plimmer, A., Davies, H., and Panton, J.: Slab dynamics in the mantle: a back-to-basics approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6247, https://doi.org/10.5194/egusphere-egu24-6247, 2024.

EGU24-6549 | ECS | Posters on site | TS8.1

Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models 

Taiwo Ojo, Joshua Guerrero, Chad Fairservice, Pejvak Javaheri, and Julian Lowman

We implement an innovative method of plate identification for the purpose of evaluating plate motion in numerical mantle convection models. Our method utilizes an existing tool,  Automatic Detection Of Plate Tectonics (ADOPT), which applies a tolerance (threshold) algorithm to elevation maps, to detect candidate plate boundaries at the surface of 3-D spherical mantle convection models. The logarithm of the strain-rate field yields a well-defined elevation map where local maxima lineations indicate spreading centres, zones of convergence, transform faults or diffuse deformation zones. For the plates found by ADOPT’s analysis, we determined rotation (Euler) poles implied by the velocities  within  the plate interiors. Subsequently, we examined the velocity field of each model plate for its agreement with rigid motion about the Euler poles.  We apply our method to snapshots taken from three previously published mantle convection calculations that appear to generate plate-like surface behaviour. Self-consistently generated model plates were obtained by combining a highly temperature-dependent viscosity with a yield stress that adds a strain-rate dependence to the viscosity, thus allowing for both intra-plate low strain-rate and weakening along tightly focussed plate boundaries. We generally identify more (and smaller) rigid plates for low yield stress or low threshold. Strong agreement of the surface velocities with rigid-body rotation around Euler poles is found for many of the plates identified; however, some plates also exhibit internal deformation. Regions that show a departure from rigidity can be decomposed into subsets of rigidly moving plates. Thus, the identification of a mantle convection model's maximally rigid plate surface may require plate boundary detection at both low and high thresholds. We suggest that as global mantle convection models superficially converge on the generation of plate boundary network similar to those observed with plate tectonics (including transform fault generation), testing for plate rigidity through the determination of Euler poles can serve as a quantitative measure of plate-like surface motion.

How to cite: Ojo, T., Guerrero, J., Fairservice, C., Javaheri, P., and Lowman, J.: Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6549, https://doi.org/10.5194/egusphere-egu24-6549, 2024.

EGU24-6630 | Posters on site | TS8.1

Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability 

Ya-Nan Shi and Jason Morgan

Delamination of continental lithospheric mantle is now well-recorded beneath several continents. However, the fate of delaminated continental lithosphere has been rarely noted, unlike subducted slabs that are reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5  horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500-700 km depths beneath former Gondwana, with the slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2-4×106 km3, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

How to cite: Shi, Y.-N. and Morgan, J.: Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6630, https://doi.org/10.5194/egusphere-egu24-6630, 2024.

EGU24-7075 | Orals | TS8.1

Absence of surface volcanism and the indeterminate evidence for continental mantle plumes 

Simone Pilia, Giampiero Iaffaldano, Rhodri Davies, Paolo Sossi, Scott Whattam, and Hao Hu

There are rare occurrences on Earth where mantle plumes intersect with continents, resulting in surface volcanism.Unlike their more common counterparts in oceanic lithosphere, where the ascent of melts is facilitated by a thinner lithosphere, identifying continental plumes is challenging. Surface volcanism, traditionally a key indicator of mantle plumes, may play a diminished role in regions characterized by complex tectonics and variations in lithospheric thickness.

Eastern Oman provides an excellent example where a continental mantle plume has remained undetected due to the absence of current surface volcanism. The region exhibits evidence of intraplate basanites, although with an age of ~35-40 Ma. Given their geochemical signature, these alkaline rocks likely originated from a mixture of melts from a plume-derived source and those from a lithosphere-derived component. Using P- and S-wave arrival-time residuals from distant earthquakes, we image a new mantle plume in eastern Oman, which we name the Salma plume. This continental plume is revealed in our 3-D P- and S-wave tomographic models as a 200 km low-velocity conduit extending to at least the base of the upper mantle, and located below the area of Tertiary intraplate volcanism. Despite experiencing minimal shortening since the Paleogene, the shallow-marine sediments of the Salma Plateau in eastern Oman reach elevations exceeding 2000 meters. Ongoing uplift, indicated by elevated Quaternary marine terraces, suggests that the plateau is still rising. The present uplift rate is modest but maps of residual topography show a positive trend in eastern Oman that can be associated to the presence of a plume.

Incorporating a geodynamic perspective, our analysis of noise-mitigated Indian plate motion relative to Somalia reveals that India underwent a constant-velocity reorientation of approximately 15˚  from 48 to 30 Ma, concurrent with the arrival of the plume head beneath eastern Oman. We quantitatively demonstrate that increased asthenospheric flow induced by the plume flux in eastern Oman, adjacent to the Indian plate in the Eocene, may be responsible for deflecting the Indian plate path, as indicated in kinematic reconstructions.

The consequence of ignoring a plume in Oman is that we were unable to understand many of the enigmatic observations from plume impingement at ~40 Ma. Our study underscores the potential of combining seismology, geology, geochemistry, and geodynamics to be a more effective approach for detecting continental plumes than relying solely on surface volcanism, and has transformed our understanding of the tectonic evolution of the area and beyond.

How to cite: Pilia, S., Iaffaldano, G., Davies, R., Sossi, P., Whattam, S., and Hu, H.: Absence of surface volcanism and the indeterminate evidence for continental mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7075, https://doi.org/10.5194/egusphere-egu24-7075, 2024.

EGU24-7255 | Orals | TS8.1

Short-period (400 kyr) pulsation of the Réunion plume 

Vincent Famin, Xavier Quidelleur, and Laurent Michon

Many hotspots worldwide display evidence of fluctuating magmatic emplacement rates in their history, at periods of 1-20 Myr, indicative of changing melt production within underlying mantle plumes. Here we report unprecedentedly short fluctuations of magmatic activity in the Réunion hotspot, emblematic because it started with the Deccan traps suspected to have caused the Cretaceous-Paleogene mass extinction. Using K-Ar geochronology, field observations, and geomorphology, we reconstructed the volcanic history of La Réunion and Mauritius islands, the two latest manifestations of the Réunion hotspot. Our reconstruction reveals coeval magmatic activity pulses and rest intervals for the two islands over the past 4 Ma. The period of these pulses, of ~400 kyr, is an order of magnitude shorter than any fluctuation found on other hotspots. Given the distance between La Réunion and Mauritius (~230 km), this synchronous short-period pulsation of the Réunion hotspot cannot stem from the lithosphere (≤70 km thick), and must be attributed to deeper plume processes. Moreover, this ~400 kyr periodicity coincides with the recurrence time of magmatic phases in the Deccan traps, suggesting that the pulsation began with the initiation of the hotspot. We propose that the Réunion plume is regularly pulsing with a periodicity of ~400 kyr, possibly since the Cretaceous-Paleogene transition, thus delivering extremely short-period waves of magma to the surface, synchronous over hundreds of kilometers. Understanding the geodynamic causes of this superfast beat of the Réunion plume is the objective of the four-year project “Plum-BeatR”, funded by the Agence Nationale de la Recherche (ANR- 23-CE49-0009), starting in 2024.

How to cite: Famin, V., Quidelleur, X., and Michon, L.: Short-period (400 kyr) pulsation of the Réunion plume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7255, https://doi.org/10.5194/egusphere-egu24-7255, 2024.

Plate tectonics plays a pivotal role in shaping the Earth's surface and is intricately linked to internal processes, including the subduction of cold slabs and the ascent of hot mantle plumes. Statistical analyses have unveiled a strong correlation between the distribution of large igneous provinces (LIPs) over the past 320 Ma and two large low-velocity provinces (LLVPs) beneath Africa and the Pacific Ocean. Consequently, hypotheses have emerged suggesting the long-term stability of these LLVPs. However, numerical modeling challenges this notion, suggesting that these basal mantle structures are mobile. To resolve these debates, we attempt to study these basal mantle structures from the evolution of intermediate-scale thermochemical anomalies. We report such an intermediate-scale thermochemical anomaly beneath the NW Pacific Ocean based on existing tomographic models and use paleogeographically constrained numerical models to study its evolution. Considering different plate configurations in North Pacific, our models consistently show that this anomaly was separated from the Perm anomaly by the subduction of the Izanagi slab in the Cretaceous. After the separation, it generated a mantle plume, inducing an oceanic plateau that got subducted beneath Kamchatka in Eocene. This scenario is consistent with multiple lines of evidence, including the seismic anomaly in the lower mantle, a seismically detected megameter-scale reflector that coincides with the subducted oceanic plateau and changes in Pacific Plate motion that correlated with the Eocene trench-plateau collision. We propose that intermediate-scale low velocity structures constantly undergo segregation and coalescing, and are sources of plumes that lie outside the two major LLVPs. Merging of the reported anomaly with the Pacific LLVP suggests the latter is still under assembly.

How to cite: Zhang, J. and Hu, J.: Segregation of thermochemical anomaly and associated deep mantle plume outside the large low-velocity provinces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8432, https://doi.org/10.5194/egusphere-egu24-8432, 2024.

EGU24-8563 | ECS | Orals | TS8.1

UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region 

Maria Tsekhmistrenko, Ana Ferreira, and Miguel Miranda

We present initial tomographic findings from the ERC-funded UPFLOW (Upward mantle flow from novel seismic observations) project, showcasing results from a large-scale passive seismology experiment conducted in the Azores-Madeira-Canaries region between July 2021 and September 2022. Recovering 49 out of 50 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area with an average station spacing of ~150-200 km, we analyze approximately ~8000 multi-frequency (T ~2.7-30 s) body-wave travel time cross-correlation measurements derived from UPFLOW OBS data and over 120 teleseismic events. A preliminary P-wave tomographic model is presented, offering insight into the region's mantle dynamics.

Furthermore, by integrating UPFLOW's OBS data with global seismic data from both temporary and permanent stations, we expand the dataset to around 600,000 multifrequency measurements. This comprehensive dataset is employed to construct a global P-wave model, providing enhanced resolution throughout the entire mantle column beneath the Azores-Madeira-Canaries region. A comparative analysis with existing global tomography models is performed, and we discuss the geodynamical implications of our new, high-resolution model.

How to cite: Tsekhmistrenko, M., Ferreira, A., and Miranda, M.: UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8563, https://doi.org/10.5194/egusphere-egu24-8563, 2024.

EGU24-8567 | Orals | TS8.1

Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic 

Alexander Koptev and Sierd Cloetingh

The North Atlantic region is a prime example of the interaction between plate tectonic movements and thermal instabilities in the Earth’s mantle. The opening of the Labrador Sea/Baffin Bay and the North Atlantic, the widespread volcanism and the localized uplift of the topography in Greenland and the North Atlantic are traditionally attributed to the thermal effect of the Iceland mantle plume. However, several prominent features of the region – the temporal synchrony of magmatism and break-up events, the symmetrical configuration of the Greenland-Iceland-Faroe Ridge, and the diachronous domal uplift of the North Atlantic rifted margins – have inspired alternative, “non-plume” views. According to these, the North Atlantic Igneous Province (NAIP) and Iceland magmatism originate from plate tectonic processes sourced in the shallow upper mantle, at odds with the unequivocal presence of deep-seated low-velocity seismic anomalies beneath Iceland and the isotopic signatures of plume-derived melts in Cenozoic magmatic units.

We resolve apparent contradictions in the observations and reconstructions and reconcile end-member concepts of the Late Mesozoic-Cenozoic evolution of the North Atlantic realm. We show that simultaneous Paleocene (~62-58 Ma) magmatism in Western Greenland/Baffin Island and the British Isles, which together form the NAIP, is driven by two processes accidently coinciding in time: 1) the propagation of the Labrador Sea/Baffin Bay spreading axis has overlapped with the ~100-80 Ma dated segment of the Iceland hotspot track near the West Greenland margin, while 2) the actual tail of the Iceland plume has reached the eastern continental margin of Greenland, allowing a horizontal flow of hot plume material along corridors of relatively thinned lithosphere towards Southern Scandinavia and Scotland/Ireland. In this framework, the subsequent formation of the symmetrical Greenland-Iceland-Faroe Ridge can be coherently explained by the continuous supply of hot plume material through an established channel between Eastern Greenland and the British Isles. In contrast to the Scotland/Ireland region, the South Norway continental lithosphere remains too thick to enable localized uplift of the topography and melting immediately after plume lobe emplacement at ~60 Ma. Therefore, the development of topographic domes in Southern Scandinavia only started ~30 Myr later in the Oligocene as a consequence of increasing ridge-push compression that built up during the opening of the Norwegian-Greenland Sea.

The evolution of the North Atlantic region shows that a thermal anomaly that has been hidden below a thick lithosphere for tens of Myr without signs of excessive magmatism can be re-initialized (or “re-awakened”) by the lateral propagation of spreading ridges or by the tapping of its source beneath thinner segments of the overlying lithosphere due to horizontal plate movements. We dub this type of Large Igneous Province (LIP) as LIP-Dornröschen (LIP-Sleeping Beauty). We hypothesise that the term LIP-Dornröschen may be applicable to a broad family of LIPs, including Precambrian and oceanic LIPs. This means that the interpretation of the timing of LIP formation from the perspective of mantle dynamics should be treated with caution, as there may be delays between the timing of upwelling in the mantle and detectable magmatic manifestations at or near the Earth’s surface.

How to cite: Koptev, A. and Cloetingh, S.: Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8567, https://doi.org/10.5194/egusphere-egu24-8567, 2024.

EGU24-9504 | ECS | Orals | TS8.1

Depth dependence of mantle plume flow beneath mid-ocean ridges 

Sibiao Liu, Fan Zhang, Lei Zhao, Xubo Zhang, and Jian Lin

Hotspot-related anomalies observed in mid-ocean ridge systems are widely interpreted as the result of upwelling mantle plumes interacting with spreading ridges. A key indicator of this interaction is 'waist width', which measures the distance of plume flow along the ridge. Current scaling laws for waist width, premised on a gradual decrease in plume temperature along the ridge, often overlook sub-ridge longitudinal thermal variations, potentially biasing width measurements at various depths. In this study, we refined waist width measurements by tracking the material flow and its thermal diffusion from the plume source in plume-ridge interaction models. These non-Newtonian viscoplastic models integrate ridge spreading, lithospheric cooling with hydrothermal circulation, and mantle dehydration. Model results show that the hot plume initially boosts upwelling from the deep mantle to near the dehydration zone, followed by a slowdown and lateral spread across and along the ridge. In addition to strongly correlating with plume flux and spreading rate, the pattern and distance of plume flow vary with depth. At deeper depths, the plume expands radially in a pancake-like thermal pattern with shorter along-ridge distances, while shallower, it shows an axial pipe-like dispersion over longer distances, forming a concave structure. This is shaped by the cooling of the plume material during the phase of decelerated upwelling and along-ridge dispersion within the dehydration zone and cooling of the oceanic lithosphere associated with plate spreading. Estimates of plume buoyancy flux, derived from both material- and isotherm-tracking waist widths, show significant variations at different depths, suggesting that understanding depth-dependent plume dynamics beneath mid-ocean ridges is crucial for reconciling the observed discrepancies in buoyancy flux estimates.

How to cite: Liu, S., Zhang, F., Zhao, L., Zhang, X., and Lin, J.: Depth dependence of mantle plume flow beneath mid-ocean ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9504, https://doi.org/10.5194/egusphere-egu24-9504, 2024.

EGU24-9647 | Posters virtual | TS8.1

Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data 

Nirjhar Mullick, Vivek Kumar, Gokul Saha, Shyam S. Rai, and Thomas Bodin

Mantle plumes play major role in modifying the continental lithosphere producing rifts and massive amounts of basaltic volcanism as the anomalously hot mantle undergoes decompressive melting. If conditions are favourable the rift may widen and a new ocean is formed. During the break up of Eastern Gondwana at ~ 130 Ma, the Kerguelen mantle plume influenced the separation of India from Antarctic and Australian plates and generation of the Eastern Indian Ocean. Eastern India-Bangladesh region (83-94ºE, 21-26ºN) carries imprints of the plume activity in the form of the Rajmahal and Sylhet traps and their subsurface expression in Bengal basin and extensive lamproytes. Existing geophysical studies of the region are mainly crustal scale and do not explicitly refer to the Kerguelen plume activity providing geophysical evidence for the same. We present here lithospheric shear velocity structure of the region up to a depth of ~ 175 km by trans-dimensional Baysian inversion of Rayleigh group velocity dispersion data (7-100s at 1º X 1º resolution). Using the same, we investigate the influence of the Kerguelen plume on the lithosphere of the Eastern India-Bangladesh region that comprises the Eastern India craton, the Bengal basin, the Bhrahmaputra basin, Bangladesh and the Shillong- Mikir plateau.

How to cite: Mullick, N., Kumar, V., Saha, G., Rai, S. S., and Bodin, T.: Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9647, https://doi.org/10.5194/egusphere-egu24-9647, 2024.

EGU24-10288 | Posters on site | TS8.1

Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions 

Adrien Vezinet, Blas Barbera, Alexander V. Sobolev, Valentina G. Batanova, Charbel Kazzy, and Aleksandr V. Chugunov

Melt inclusions hosted in highly magnesian olivine crystals have proven invaluable for probing the composition of the mantle through time since their geochemical signature is reflecting that of parental melt. Additionally, the geochemical study of melt inclusions has shown to be more suited to identify the heterogeneity in the magma from which they crystallized, particularly the chemically depleted domains [1, 2]. Here, we will present new major, minor & trace elements, H2O contents and Sr-isotope signature of more than 300 olivine-hosted naturally quenched melt inclusions from Pu’u Wahi (910 yr-old) and Puʻu Mahana (ca. 50 kyr-old), two ash cones associated with Mauna Loa, the largest shield volcano of the Hawai’ian seamount chain. In order to have a high degree of confidence in the geochemical proxies, Sr-isotope and trace elements analyses were conducted through laser ablation split stream (LASS) protocol on top of EPMA and Raman (for H2O contents) analytical spots. Preliminary results in our new set of inclusions show the presence of high (Sr/Ce)N inclusions, previously interpreted as indicating either gabbro influence in the source of the plume [3] or interactions between plagioclase-rich cumulates and percolating mantle-derived melts [4]. Further, “ultra-depleted melts”, UDM, indicated by K2O contents < 0.1 wt.% identified in [1], have also been re-identified in this new set of inclusions (not analyzed for Sr-isotope yet). 87Sr/86Sr of non-UDM inclusions ranges from 0.70361±0.00025 to 0.70427±0.00025, i.e. analogous to the most recent TIMS values [4, 5]. Additional LASS analyses will be conducted before the meeting. The full set of analyses will be confronted to published results on the same volcano [1, 3-6] and integrated in a larger framework of interactions between mantle plume and consequences for plate tectonic.

References:

  • Sobolev, A.V., et al., Nature, 2011. 476(7361).
  • Stracke, A., et al., Nature Geoscience, 2019. 12(10).
  • Sobolev, A.V., et al., Nature, 2000. 404(6781).
  • Anderson, O.E., et al., Geochemistry, Geophysics, Geosystems, 2021. 22(4).
  • Reinhard, A., et al., Chemical Geology, 2018. 495.
  • Sobolev, A.V., et al., Nature, 2005. 434(7033).

How to cite: Vezinet, A., Barbera, B., Sobolev, A. V., Batanova, V. G., Kazzy, C., and Chugunov, A. V.: Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10288, https://doi.org/10.5194/egusphere-egu24-10288, 2024.

EGU24-10507 | ECS | Posters on site | TS8.1

The density and viscosity of a bilithologic plume-fed asthenosphere 

Jia Shao and Jason Morgan

Pyroxenites are generated by the subduction of sediments and oceanic basalts into the deep mantle. These rocks, together with the larger volume fraction of their surrounding mantle peridotites make up a lithologically heterogeneous two-component mantle, sometimes called a ‘marble-cake’ or ‘plum-pudding’ mantle. Geochemical and petrological observations have shown that pyroxenites play a significant role in the genesis of oceanic island basalts (OIB). However, the consequences of preferential pyroxenite melting on bulk mantle properties have yet to be systematically explored. For example, how does the plume melting process modify a plum-pudding mantle’s bulk density and viscosity? This question could be very important, in particular if the asthenosphere is formed by material from upwelling, melting plumes.

To explore the above questions, we use the thermodynamic software Perple_X to determine densities for different degrees of depleted (i.e. partially melted) peridotites and pyroxenites. We then include these relations into a one-dimensional numerical simulation code for the upwelling and pressure-release melting of a potentially wet multi-component mantle. We investigate the density changes associated with the melting of this idealized mantle’s pyroxenites and peridodites, and also the viscosity change by assuming that the reference viscosity of pyroxenite is 10-100 times that of dry peridotite at similar P-T conditions, since the peridotite’s olivines are the weakest large volume-fraction minerals in the upper mantle. We have explored the effects of mantle temperature, initial water contents, initial fractions of pyroxenites and peridotite, peridotite solidi, and the thickness of the overlying lithosphere which will affect the depth-interval of upwelling and melting. Preliminary results show that significant density and viscosity changes should take place during plume upwelling and melting. ~30% partial melting of pyroxenite would lead to a net bulk density reduction of 0.3%, comparable to the thermal buoyancy associated with a ~100° temperature increase. As long as the surrounding peridotites do not melt, the mixture’s aggregate viscosity will remain that of wet peridotitic mantle; after the peridotites have melted a percent or so, the aggregate viscosity will increase 10-100-fold to that of dry peridotite. This could lead to the formation of a 10-100x asthenospheric viscosity restitic hotspot swell root. Eventual peridotitic melting will reduce the density of the more depleted peridotites relative to fertile peridotite as originally noted by Oxburgh and Parmentier (1977), but to a lesser degree than the density reduction associated with the preferential removal of pyroxenites by their partial melting. A dynamical consequence is that the asthenosphere is likely to be strongly stratified by density, with its most pyroxenite-depleted materials likely to rise to form a layer along the base of the overlying oceanic lithosphere. 

How to cite: Shao, J. and Morgan, J.: The density and viscosity of a bilithologic plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10507, https://doi.org/10.5194/egusphere-egu24-10507, 2024.

EGU24-10967 | ECS | Posters on site | TS8.1

From plumes to subduction network formation and supercontinent break-up 

Michaël Pons, Stephan V. Sobolev, Charitra Jain, and Elodie Kendall

The evolution of modern plate tectonics is described by the Wilson cycle, which portrays the dynamics of the supercontinental cycle through the interaction of the oceanic plate with the continental plate over periods of hundreds of millions of years. This cycle is characterized by a phase of supercontinent assembly and enhanced orogenic collision, followed by a phase of supercontinent fragmentation and dispersal, as shown by the geological record. The dynamics of the Wilson cycle is intrinsically linked to mantle convection and subduction dynamics. While the assembly phase appears to follow a degree-2 mantle convection style, the mechanism responsible for supercontinent fragmentation is still debated. We hypothesize that the dispersal phase is mostly governed by trench roll-back from subductions and mantle plumes. To test this hypothesis, we have built a series of 2D and 3D geodynamic models of the Earth on a global scale using the ASPECT code. We have tested different scenarios in which we prescribe the distribution of the supercontinent Rodinia at 1Ga or Pangea at 250 Ma and let the models evolve self-consistently.  In some model variants, the strength of the supercontinent and that of the surrounding oceanic area is changed. We will present our preliminary results and discuss the dynamics of continental dispersal and its link to subduction and mantle dynamics. In particular, 3D models will demonstrate how regional plume-induced retreating subduction zones evolve into a global network of subduction zones and tectonics plate boundaries which ultimately leads to the break-up of the supercontinent.

How to cite: Pons, M., V. Sobolev, S., Jain, C., and Kendall, E.: From plumes to subduction network formation and supercontinent break-up, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10967, https://doi.org/10.5194/egusphere-egu24-10967, 2024.

While the temperature drop across the thermal boundary layer (TBL) at the base of the mantle is likely > 1000 K, the temperature anomaly of plumes, which are believed to rise from that TBL is only up to a few hundred K. Reasons for that discrepancy are still poorly understood. It could be due to a combination of (1) the adiabat inside the plume being steeper than in the ambient mantle, (2) the plume cooling due to heat diffusing into the surrounding mantle as it rises, (3) the hottest plume temperature representing a mix of temperatures in the TBL, and not the temperature at the core-mantle boundary (CMB), (4) plumes not directly rising from the CMB due to chemically distinct material at the base of the mantle, (5) a plume-fed asthenosphere which is on average warmer than the mantle adiabat, reducing the temperature difference between plumes and asthenospheric average. Here we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere towards the lower mantle, reaching about 1023 Pas above the basal TBL, consistent with geoid modelling and slow motion of mantle plumes. With a mineral physics-derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, e.g. 1280 K temperature difference at the CMB reduces to about 835 K at 200 km depth. In 2-D cartesian models, plume temperature drops more strongly and is rather time variable due to pulses rising along plume conduits. In contrast, 3-D models of isolated plumes are more steady and, after about 10-20 Myr after the plume head has reached the surface, their temperatures remain rather constant, with excess temperature drop compared to an adiabat for material directly from the CMB usually less than 100 K. This extra temperature drop is small because plume buoyancy flux is high. Hence the above points (2) and (3) do not contribute much to reduce temperature of isolated 3-D plumes. In our models, the asthenosphere is on average about 200-400 K hotter than the mantle beneath, due to plume material feeding into it. While this appears to reduce the plume temperature anomaly, a resulting cooler mantle adiabat also corresponds to an even stronger temperature drop in the basal TBL, offsetting that effect. In the Earth, plumes are likely triggered by slabs and probably rise preferrably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet-like, as the 2-D models, or temperature at their source depth is less than at the CMB.

How to cite: Steinberger, B. and Roy, P.: Why are plume excess temperatures much less than the temperature drop across the core-mantle boundary?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11566, https://doi.org/10.5194/egusphere-egu24-11566, 2024.

EGU24-11719 | Orals | TS8.1

Prospects of Neutrino Oscillation Tomography of the Earth  

Veronique Van Elewyck, Joao Coelho, Yael Armando Deniz Hernandez, Stephanie Durand, Nobuaki Fuji, Edouard Kaminski, Lukas Maderer, Eric Mittelstaedt, and Rebekah Pestes

Much has been learned about the deep Earth through a combination of geophysical constraints, theories of Earth’s formation, and seismic measurements. However, such methods alone cannot directly resolve the full structure of the inner Earth, e.g. in terms of matter density, composition and temperature distributions.

Complementary information about Earth’s interior can be provided by small, nearly massless elementary particles called neutrinos that propagate through the Earth. Neutrinos exist in different flavours and are known to experience a quantum phenomenon of flavour oscillation as they propagate. With an extremely small chance of interacting with matter, neutrinos can travel long distances through very dense materials (e.g., the Earth’s core). For atmospheric neutrinos of energy ~GeV crossing the Earth, the flavour oscillation patterns are distorted due to coherent forward scattering on electrons along their path. Measuring the flavour, energy and angular distributions of such neutrinos therefore provides sensitivity to a new observable of geophysical interest: the electron number density in the layers of matter traversed.

After a short introduction to the concepts of neutrino oscillation tomography, we will discuss the potential of this method to address open questions concerning inner Earth's structure and composition (such as the amount of light elements in the core and the nature of LLSVPs), the status of sensitivity studies, and the perspectives opened by the next generation of atmospheric neutrino detectors.

How to cite: Van Elewyck, V., Coelho, J., Deniz Hernandez, Y. A., Durand, S., Fuji, N., Kaminski, E., Maderer, L., Mittelstaedt, E., and Pestes, R.: Prospects of Neutrino Oscillation Tomography of the Earth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11719, https://doi.org/10.5194/egusphere-egu24-11719, 2024.

The Rajmahal Traps is one of the two major Large Igneous Provinces (LIPs) that erupted in the Indian subcontinent in the Mesozoic. The trap was the product of activity at the Kerguelen hotspot, located in the Indian Ocean, that initiated around 117 Ma. Earlier studies on the eruption location of the Rajmahal trap show that its location does not coincide with the present-day location of the Kerguelen Hotspot. This difference in the paleo-locations could be the result of mantle dynamics beneath the Indian Ocean during the Cretaceous and has been explained with concepts such as the multiple diapir-single plume model, the migration pathway of the hotspot beneath the mantle, and the complex plume-ridge interaction.

In this study, we use paleogeographic reconstruction software GPlates to reconstruct the paleogeography of the Rajmahal Traps on the Indian subcontinent plate in an Antarctica fixed reference frame since 117 Ma to pin-point the paleo-location of the Kerguelen hotspot and eruption location of the Rajmahal trap along with the tectonic changes that the Indian Ocean was encountering. The mantle structure below the Indian Ocean was further studied using publicly available P-wave tomography data. The paleogeographic reconstruction linked to the mantle structure hints towards the presence of a tree-like hotspot-plume structure beneath the Kerguelen hotspot where a deep-seated single plume feeds into various fissures at the surface which are active at different points in time.

Our kinematic analysis for the Indian Plate reveals significant changes in the velocity of the plate since the Cretaceous at specific points in time in response to tectonic activities initiated by the plumes present in the Indian Ocean. These activities that link to changes in the velocity include interactions with the Morondova plume (velocity increase at 90 Ma) and Reunion hotspot (velocity increase between 78 – 62 Ma), and other processes like continental collision (velocity decrease at 56 Ma and between 50-43 Ma) and slab pull (velocity increase at 56 Ma). Using this new velocity profile, we have developed a revised velocity model for the drift of the Indian subcontinent since the Cretaceous.

How to cite: Guleriya, S., Beniest, A., and Tiwari, S. K.: Change in eruption location in Kerguelen hotspot and Kinematic Reconstruction of Rajmahal Trap:  Implications for Cretaceous to present day Geodynamics of Indian plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11883, https://doi.org/10.5194/egusphere-egu24-11883, 2024.

EGU24-12584 | Orals | TS8.1

Robust hotspot origin far from LLSVP margins 

John Tarduno

W. Jason Morgan’s seminal development of plate tectonic theory set the foundation for current investigations of mantle convection and the nature of deep mantle plumes. More recently, hotspots have been proposed to occur at the edges of stationary African and Pacific large low shear velocity provinces (LLSVPs) and that this has a special significance in terms of plume/hotspot generation. The basis for this proposed global correlation has in turn been challenged, and whether LLSVPs edges are the sites of initial mantle plume formation debated. A different approach is to consider hotspots with the greatest buoyancy flux because to be successful, any global model should be able to explain their origin. In all analyses of buoyancy flux, the Pacific’s Hawaiian hotspot, which figured prominently in Jason’s early papers, stands out above all others. However, paleomagnetic and age-distance relationships indicate that the Hawaiian hotspot originated >1500 km N of the Pacific LLSVP and subsequently drifted to its edge where it may have become anchored. The hotspot with the highest buoyancy flux in the Atlantic is Iceland, which is far from the African LLSVP. Iceland represents the youngest of three past episodes of extraordinary volcanism affecting the North Atlantic-Arctic region, namely the North Atlantic Tertiary Volcanic Province, the High Arctic Large Igneous Province, and the Siberian Traps. This recurrent volcanism spanning more than 250 million years requires either drift of a single pulsing plume, or separate plumes, generated far from the edge of the proposed stationary African LLSVP. Thus, the nature and histories of these robust hotspots in the Pacific and Atlantic imply an origin distinct from stationary LLSVPs.  

How to cite: Tarduno, J.: Robust hotspot origin far from LLSVP margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12584, https://doi.org/10.5194/egusphere-egu24-12584, 2024.

EGU24-13570 | Orals | TS8.1

Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate 

Colleen Dalton, Timothy Herbert, Douglas Wilson, and Weimin Si

The rate of ocean-crust production exerts control over mantle heat loss, sea level, seawater chemistry, and climate. Reconstructing ocean-crust production rates back in time relies heavily on the distribution of present-day seafloor age. Different strategies to account for the incomplete preservation of older seafloor have led to differing conclusions about how much production rates have changed since the Cretaceous, if at all. We have constructed a new global synthesis of ocean-crust production rates along 18 mid-ocean ridges for the past 19 Myr at high temporal resolution.  We find that the global ocean-crust production rate decreased by ~37% from its maximum during 19-15 Ma to its minimum during 6-4 Ma. Our ability to resolve these changes at a statistically significant level is due to the availability of many new plate reconstructions at high temporal resolution and our use of an astronomically calibrated magnetic time scale with small uncertainties in reversal ages. We show that the reduction in crust production occurred because spreading rates slowed down along almost all ridge systems. While the total ridge length has varied little since 19 Ma, some fast-spreading ridges have grown shorter and slow-spreading ridges grown longer, amplifying the spreading-rate changes. The change in crust production rate skews the seafloor area-age distribution toward older crust, and we estimate that sea level may have fallen by as much as 32-37 m and oceanic heat flow may have been reduced by 6%. We also show, using a simple model of the carbon cycle, that the inferred changes in tectonic degassing resulting from the crust-production changes can account for the majority of long-term surface-temperature evolution since 19 Ma.

How to cite: Dalton, C., Herbert, T., Wilson, D., and Si, W.: Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13570, https://doi.org/10.5194/egusphere-egu24-13570, 2024.

EGU24-13786 | ECS | Posters on site | TS8.1

Counterflow and entrainment within a buoyant plume-fed asthenosphere 

Xianyu Li, Jia Shao, Guanzhi Wang, Yanan Shi, and Jason Morgan

Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere (cf. Morgan et al., Terra Nova, 2007) implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Such asthenosphere would instead be mostly removed by accretion into overlying oceanic lithosphere, both at mid-ocean ridges where a ~60-km compositional lithosphere forms due to the melt-induced dehydration of upwelling peridotitic mantle, and later with the thermal growth of  overlying oceanic lithosphere. When an oceanic plate subducts, the lower (hot) side of a subducting slab entrains a 10– 30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal ‘freezing’ onto the slab as by mechanical downdragging.  

Here we use 2-D numerical experiments to investigate the dynamics of entrainment and counterflow at subduction zones. We explore situations with both stable subduction geometries and slab rollback. Due to its low viscosity, a plume-fed asthenosphere is particularly likely to be stratified in its internal density, with variable amounts of plume melt-extraction leading to variable pyroxenite fractions and associated vertical density stratification within a bilithologic ~80-90% peridotite, ~10-20% pyroxenite asthenosphere. While this type of vertical density stratification appears to lead to similar predicted entrainment by subducting slabs, it will generate more complex patterns of asthenospheric counterflow that involve shallower and time-dependent counterflow behind the subducting slab.

How to cite: Li, X., Shao, J., Wang, G., Shi, Y., and Morgan, J.: Counterflow and entrainment within a buoyant plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13786, https://doi.org/10.5194/egusphere-egu24-13786, 2024.

EGU24-13826 | ECS | Posters on site | TS8.1

Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context 

Isadora Page, Ben R. Mather, Nicole Januszczak, Michele Anthony, and R. Dietmar Muller

Nickel-Copper (Ni-Cu) sulphide deposits are a diverse class of deposits, formed during the cooling and crystallisation of metal-rich mafic to ultramafic magmas. Despite sharing several key ore-forming processes, many of these deposits form in contrasting geologic environments and periods. The objective of this research project is to investigate the spatial and temporal distribution of Ni-Cu sulphide deposits in a mantle convection and plate tectonic context, and to explore the influence of different mantle and tectonic parameters on their origins and occurrence. We first determine the location of these deposits in relation to relevant geologic and tectonic features through time, including subduction zones, large igneous provinces (LIPs), and mantle plumes. Using a 1 billion year plate model we extract key parameters relating to subduction, as well as the spatio-temporal distribution of LIPs through time. Employing an associated geodynamic model, we identify model mantle plumes and quantify their key properties. Preliminary findings indicate that certain mantle plumes associated with deposits exhibit increased plume flux in the upper mantle preceding deposit formation, and that many deposits are spatially associated with LIPs throughout their formation history. For several deposits located in convergent margin settings, we have identified a notable spike in subduction volume and convergence rate during a 50-100 million year period prior to the onset of mineralisation. While the angle of the subducting slab is highly variable throughout the evolution of these deposits, several deposits are associated with a distinct steepening of the subducting plate in the lead-up to deposit formation. The findings of this study aim to contribute new insights into the dynamic processes governing the genesis of magmatic Ni-Cu sulphide deposits. These insights aid in our understanding of the interplay between mantle dynamics, plate tectonics, and deposit formation, and hold implications for future critical mineral exploration.

How to cite: Page, I., Mather, B. R., Januszczak, N., Anthony, M., and Muller, R. D.: Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13826, https://doi.org/10.5194/egusphere-egu24-13826, 2024.

EGU24-13939 | ECS | Posters on site | TS8.1

Numerical exploration of the dynamics of the subduction plate boundary channel  

Guanzhi Wang, Jason P. Morgan, and Paola Vannucchi

The plate ‘interface’ at subduction zones has often been idealized as a single fault with ‘asperities’, however there is increasing evidence that plate boundary motions typically occur across a ~100-1000m channel or shear zone. Here we investigate the dynamics of slip in a mechanically heterogeneous plate boundary shear zone, and will typically use periodic boundary conditions to model the channel at a ~m-scale.  In contrast to most previous numerical studies, we imagine that this shear zone is embedded within finite strength wall-rock associated with the downgoing and overriding plates that themselves are capable of subduction-related deformation, for example during bend-faulting of the lower-plate or a forearc deformation event. We first look at how stress-concentrations can form by the clogging of strong blocks in a channel with a weaker matrix. We find that the strength of the surrounding wall-rock will play a key role in the channel’s response to a clogging event. In general, a clogging event can be mitigated by failure of surrounding relatively weak wallrock along the edges of a subduction channel in the conceptual process put forward by von Huene et al. (2004) to drive basal erosion of the forearc. We also consider cases where metamorphic transitions have led to the existence of weaker blocks within a stronger matrix. In this case, frequent tremor-like failure of the weak blocks can coexist with rarer earthquake failure of the stronger surrounding matrix.  Finally we explore the mechanical effects of channel widening and narrowing events that will invariably lead to a component of local pressure-driven flow within a subduction shear channel. Numerical snapshots and videos are used to visualize these potential modes of subduction shear zone deformation.

How to cite: Wang, G., P. Morgan, J., and Vannucchi, P.: Numerical exploration of the dynamics of the subduction plate boundary channel , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13939, https://doi.org/10.5194/egusphere-egu24-13939, 2024.

EGU24-14528 | Posters on site | TS8.1

Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins 

Jialei Qiu, Nadia Padavini, Paola Vannucchi, and Jason Morgan

Both dynamic topography and seismic tomography have played crucial roles in providing invaluable insights into the Earth's interior structure and geological processes. Here we explore to what degree dynamic topography within ocean and back-arc basins can be correlated with the upper mantle seismic structure that has been imaged in recent high-resolution global models.

To explore the global ocean dynamic topography associated with subsurface mantle convection, we need to remove the influences of known contributing factors to seafloor relief such as the cooling of the ocean floor and the thickness of the ocean crust and sediments. We developed a series of scripts in PyGMT and MATLAB to do this, based on seafloor ages in GPLATES and sediment/crust information in CRUST1.0. With these corrections for near-surface structure, we obtained global average residual-depth values that serve as a basis for analyzing global subsurface structures linked to the asthenosphere and upper mantle, which we then compare to the vertically averaged shear-wave seismic structure above the transition zone. Our preliminary study highlights that the significant ~km-difference in dynamic topography between the Philippine back-arc basin and the Lau-Tonga backarc appear to be linked to a major difference in asthenosphere thickness and density beneath these two regions.

How to cite: Qiu, J., Padavini, N., Vannucchi, P., and Morgan, J.: Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14528, https://doi.org/10.5194/egusphere-egu24-14528, 2024.

EGU24-16479 | Posters on site | TS8.1

H, He, and seismic evidence for a bilithologic plume-fed asthenosphere  

Jason P. Morgan and W. Jason Morgan

Chemical diffusion in the mantle has typically been viewed to play a negligible role in geodynamic processes.  However, diffusion rates for water (H) and helium (He) are large enough that they lead to observable differences between pyroxenite-rich melting associated with ocean island volcanism (OIB) and more peridotite-rich melting associated with mid-ocean ridge basalts (MORB). Laboratory measurements of diffusion rates of H and He at ambient mantle temperatures in olivine are of order ~10 km/1.7Gyr for He and ~250 km/1.7 Gyr for H. If the mantle is an interlayered mixture of recycled oceanic basalts and sediments surrounded by a much larger volume of residual peridotites, then chemical diffusion can shape the mantle in two important ways.  Hydrogen will tend to migrate from peridotites into adjacent pyroxenites, because clinopyroxene has a much stronger affinity for water than the olivine and orthopyroxene that form the bulk of mantle peridotites. Therefore pyroxenite lithologies will typically have twice or more the water content of their surrounding damp peridotites. This will strongly favor the enhanced melting of pyroxenites that is now mostly agreed to be a common feature of the OIB source. Radiogenic 4He will have the opposite behaviour — it will tend to migrate from where it is produced in recycled incompatible-element-rich (e.g. U and Th-rich) pyroxenites into nearby, larger volume fraction, but U+Th-poorer peridotites, while the radioisotopes of Ar and Ne that are also produced by the decay of the incompatible elements K, U, and Th will diffuse much less, and thus remain within their original pyroxenite source.  This effect leads to lower 4He/21Ne and 4He/40Ar ratios in OIB in comparison to the predicted values based on the mantle’s bulk geochemistry, and complementary higher 4He/21Ne and 4He/40Ar ratios in the MORB source that is formed by the plume-fed asthenospheric residues to OIB melt extraction at plumes.

 The recent observation of a 150-km-deep positive shear velocity gradient (PVG) beneath non-cratonic lithosphere (Hua et al., 2023) is further evidence for the initiation of pyroxenitic melting at this depth within the asthenosphere. It also implies that lateral temperature variations at this depth are quite small, of order +/- 75°C. This near uniformity of temperatures near both mantle plumes and mid-ocean ridges is, in turn, strong evidence in favor of the hypothesis that the asthenosphere is fed by mantle plumes. We propose that two filtering effects occur as plumes feed the asthenosphere, removing both the hottest and coldest parts of upwelling plume material. First, the peridotite fraction in the hottest part of upwelling plume material melts enough for it to dehydrate, thereby transforming this fraction into a more viscous and buoyant hotspot swell root that moves with the overlying plate, not as asthenosphere. Second, since plume material is warmer than average mantle, it is more buoyant, creating a natural density filter that prevents any cooler underlying mantle from upwelling through it. These rheological and density filters make the asthenosphere sampled by melting at mid-ocean ridges have a more uniform temperature than its typical underlying mantle.

How to cite: Morgan, J. P. and Morgan, W. J.: H, He, and seismic evidence for a bilithologic plume-fed asthenosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16479, https://doi.org/10.5194/egusphere-egu24-16479, 2024.

EGU24-17078 | ECS | Orals | TS8.1

Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite 

Mateo Esteban, Alexander Sobolev, Valentina Batanova, Adrien Vezinet, Evgeny Asafov, and Stepan Krasheninnikov

Meimechite (i.e., rare high MgO and TiO2 ultramafic rocks) concluded the Permo-Triassic Trap magmatism ca. 250 Ma-ago, known as a Siberian Large Igneous Province (SLIP) in the Meimecha-Kotui region, northern Siberia (e.g. [1]). In addition to their elevated MgO contents, meimechite’s melts display almost no crustal contamination, making them ideally suited to investigate the mantle source of the SLIP. Formerly, two opposing models were evoked for the origination of the meimechite: i) the hottest phanerozoic mantle plume [1] or ii) water fluxing of the asthenospheric mantle in a long-lived subduction zone [2]. Based on an extended analytical workflow we will shed new light on the source of these unusual rocks.

Here we present new results for more than 300 olivine-hosted homogenized melt inclusions from Siberian meimechite including major, minor and trace elements, water and Sr-isotopes contents (EPMA, LA-ICP-MS and Raman spectrometry) along with the chemical composition of their host olivine (EPMA, LA-ICP-MS). When encountered, spinel inclusions were analysed by EPMA for major element abundances.

We show that the Siberian meimechite crystallised from a highly magnesian (MgO > 22 wt%) parental melt deficient in H2O compared to Ce and K concentrations, which was degassed of most of its CO2 and likely part of its H2O while rising to shallower depths. Three independent geothermometers (Mg-Fe and Sc-Y olivine melt and Al olivine-spinel) confirm the high crystallisation temperature of the Siberian meimechite, ca. 1400oC. Furthermore, the calculated potential temperatures (over 1500oC) imply a mantle plume origin of the Siberian meimechite and, consequently, of the SLIP.

Initial 87Sr/86Sr values of melt inclusions reveal heterogeneous populations ranging from 0.7022±0.0002 to 0.7039±0.0004 suggesting mixing between at least two depleted mantle components. The less depleted group has an average Bulk Silicate Earth (BSE) model age of 876±88 Ma, whereas the more depleted group is significantly older with an average model age of 1716±76 Ma. All source components display significantly fractionated proxies of continental crust extraction (Nb/U, Th/U and Ce/Pb [3]), indicating major events of continental crustal formation and deep recycling of residual lithosphere before the Proterozoic Eon.

References:

[1] – Sobolev, A.V., et al., Russ. Geol. Geophys., 2009 and references therein. [2] – Ivanov, A.V., et al., Chem. Geol., 2018. [3]- Hofmann, A.W. et al. EPSL, 1986.

How to cite: Esteban, M., Sobolev, A., Batanova, V., Vezinet, A., Asafov, E., and Krasheninnikov, S.: Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17078, https://doi.org/10.5194/egusphere-egu24-17078, 2024.

EGU24-17341 | ECS | Orals | TS8.1

The Influence of Mantle Plumes on Plate Tectonics 

Ingo L. Stotz, Berta Vilacís, Jorge N. Hayek, Sara Carena, Anke Friedrich, and Hans-Peter Bunge

Our understanding of plate tectonics and mantle convection has made significant progress in recent decades, yet the specific impact of mantle plumes on plate tectonics remains a topic of controversy. The motions of the Earth’s lithosphere serves as a powerful lens into the dynamic behavior of the asthenosphere and deeper mantle, helping to untangle such controversies. Surface observations, therefore, provide important constraints on mantle convection patterns through space/time. Among these observations, the record of plate motion changes stands out, as it enables the geographical identification of torque sources. Consequently, surface observations provide essential constraints for theoretical models and numerical simulations.

The analytical Poiseuille flow model applied to upper mantle flux in the asthenosphere offers a robust and testable prediction: Poiseuille flow induced plate motion changes should coincide with regional scale mantle convection induced elevation changes. Mantle plumes can generate such pressure driven flows, along with intraplate magmatism and induce buoyancy-driven uplift that leaves an imprint in the sedimentary record.

Here, I will present a synthesis of geological and geophysical observations, supported by analytical calculations, to illustrate that a significant number of plate motion changes can be attributed primarily to torques originating from mantle plumes.

How to cite: Stotz, I. L., Vilacís, B., Hayek, J. N., Carena, S., Friedrich, A., and Bunge, H.-P.: The Influence of Mantle Plumes on Plate Tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17341, https://doi.org/10.5194/egusphere-egu24-17341, 2024.

Models depicting the plate kinematic development of the Indian Ocean have a range of applications including in paleogeographic studies and in formulating and testing ideas about plume/plate interactions. Until now, these applications have been forced to tolerate egregious model/observation inconsistencies concerning the relative motion history of India and Madagascar. Whilst the Phanerozoic record of these motions begins with ∼90 Ma basalts that erupted along a narrow rift basin, all modern plate kinematic models for the Indian Ocean predict hundreds of kilometres of relative motions, in diverse and conflicting senses, over several tens of millions of years prior to the eruptions. The diversity of these predicted motions suggests they are artefacts that arise from differing approaches taken to modelling the development of the eastern and western parts of the ocean, rather than a reflection of insufficient or absent geological observations. In this contribution, I present a new model for the early plate kinematic development of the Indian Ocean that is constrained by observational evidence for relative plate motion azimuths in the Enderby and western Bay of Bengal basins and by explicitly maintaining a rigid mid- and early Cretaceous Indo-Malagasy body. This approach requires the model to feature two small tectonic plates between the continental margins of eastern India and East Antarctica. The older of the two, Mandara, is an intraoceanic plate in the Enderby Basin that may have formed in relation to delivery of excess melt from the Kerguelen plume to the basin's mid-ocean ridge. The younger plate, Vasuki, in the western Bay of Bengal Basin, also accommodated plume-related melt at its boundaries, in its case from the Marion and possibly also the Crozet plume. The model shows this plate transporting Sri Lanka ∼800 km southwards along the eastern Indian continental margin to its present location. The model also requires the presence of around half a million square kilometres of continental crust beneath the Kerguelen Plateau, which lies within the range of published observation-led estimates of its extent. Neither the absence of evidence for relative motions between India and Madagascar prior to ∼90 Ma, nor the modelled Euler rotation pole's location afterwards, are consistent with suggestions that traction forces related to the ascent of the Marion plume drove the mid-Cretaceous onset of subduction in the western Neotethys.

How to cite: Eagles, G.: A new model of plate kinematics describing the early development of the Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17862, https://doi.org/10.5194/egusphere-egu24-17862, 2024.

EGU24-18017 | Orals | TS8.1

Flexural Pumping and the Origins of Petit-Spot Volcanism 

Paola Vannucchi, Yanan Shi, Ting Yang, Gou Fujie, and Jason P. Morgan

Most volcanic activity on Earth is linked to well-known processes like plate tectonics and mantle plumes, typically through mechanisms such as flux-melting in subduction zones and decompression-melting at ridges and mantle plumes. However, recent discoveries point to a different origin for some intraplate volcanism, a key example being 'Petit-Spots'—small volcanic mounds that erupt on incoming plates near subduction zones. Here we propose that flexural pumping, occurring as the subducting slab unbends, transports fluids released by intra-slab dehydration to the slab's base where these fluids induce flux-melting in the warm slab base and asthenosphere beneath the slab. Counterflow in the buoyant asthenosphere beneath the subducting plate further expands the region of petit-spot volcanism. This mechanism not only explains the origin of petit-spot volcanism but also suggests a broader conceptual model for generating low-degree melts in the oceanic asthenosphere.

How to cite: Vannucchi, P., Shi, Y., Yang, T., Fujie, G., and Morgan, J. P.: Flexural Pumping and the Origins of Petit-Spot Volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18017, https://doi.org/10.5194/egusphere-egu24-18017, 2024.

EGU24-18296 | ECS | Posters on site | TS8.1

How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland. 

Raffaele Bonadio, Sergei Lebedev, David Chew, Yihe Xu, and Javier Fullea

The extensive Paleocene magmatism of the British and Irish Tertiary Igneous Province (BITIP)—a part of the North Atlantic Igneous Province (NAIP)—was accompanied by significant uplift and exhumation, as evidenced by geothermochronological and other data. The enigmatic origins of the volcanism and uplift are debated. The Iceland Hotspot reached the North Atlantic at that time and could probably supply anomalously hot asthenospheric material to the volcanic areas of NAIP, but they were scattered over a broad area thousands of kilometres across. This motivates alternative, non-plume explanations.

Here, we obtain a map of the lithosphere-asthenosphere boundary (LAB) depth in the region using thermodynamic inversion of seismic surface-wave data. Love and Rayleigh phase velocity maps in broad period ranges were computed using optimal resolution tomography with direct model error estimation and supplied the data for the inversion.

Our results reveal a consistently thinner-than-average lithosphere beneath the Irish Sea and surroundings, encompassing northern Ireland and western Scotland and Wales. The Paleocene uplift, BITIP volcanism and crustal underplating are all located in the same regions, which are underlain, consistently, by anomalously thin lithosphere.

The previously unknown lithospheric anomalies we discover yield a new insight into how the Iceland Plume could cause volcanism scattered over the vast NAIP. Plume material is likely to have flowed into pre-existing areas of thin continental lithosphere, whose thickness was then reduced further by the erosion by the hot asthenosphere. The thinning of the lithosphere and the presence of hot asthenosphere beneath it can account for the uplift, volcanism and crustal underplating. The localisation of the plume material in scattered thin-lithosphere areas, such as the circum-Irish-Sea region, can explain the wide scatter of the volcanic fields of NAIP.

How to cite: Bonadio, R., Lebedev, S., Chew, D., Xu, Y., and Fullea, J.: How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18296, https://doi.org/10.5194/egusphere-egu24-18296, 2024.

The X-discontinuity at 300 km beneath the Hawaiian hotspot has been hypothesized to require at least 40% basalt, a figure that would far exceed the plume's buoyancy and thus be irreconcilable with initial entrainments.
We had previously explored the potential for large basalt accumulations to form over time by simulating a section of the plume conduit, with known quantities of basaltic material flowing in as discrete heterogeneities. For entrainments of 10-20%, we had estimated average accumulations of 20-25% at ~300 km depth.
While this simplified setting recreated segregation of the denser material, it did not feature a realistic plume. On the other hand, employing mechanical mixture compositions hamper quantitative analyses of the recycled basalt.

I have overcome this issue by developing a novel implementation to the ASPECT code.
My advancement features a mechanical mixture composition (82% harzburgite — 18% basalt) for both the background mantle and the plume. The recycled material is then added to the self-consistent rising plume in the form of compositionally distinct basaltic heterogeneities. By combining these two approaches, I was able to successfully reproduce and quantify material segregation while keeping an accurate plume composition.

Preliminary results, conducted in a 2000 km * 1000 km 2D domain, with entrainments of 10-20%, and a maximum resolution of 0.98 km in the heterogeneities, show average basalt accumulations of 20-22% around 300 km depth. Occasional, transient peaks at 31% and 35% can be observed for plumes incorporating 15% basalt. Over the model time (20 Ma), the denser material tends to sink between 360-660 km depth, generating large average accumulations of 35-40%. 

This new strategy not only opens promising scenarios by overcoming long-standing model limitations, but also reinforces the potential for mantle plumes to accumulate more denser material than classically thought, shedding further light on the controversial link between the X-discontinuity and the Hawaiian plume activity.

How to cite: Monaco, M.: A Novel Implementation to Simulate Basalt Segregation in the Hawaiian Mantle Plume Overcomes Model Limitations and Elucidates the Origin of the X-discontinuity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18845, https://doi.org/10.5194/egusphere-egu24-18845, 2024.

EGU24-19459 | ECS | Posters on site | TS8.1

Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges 

Raghu Ram Gudipati, Marta Pérez-Gussinyé, and Javier García-Pintado

Classic models of continental rifting predict that after continental break-up, the extended lithosphere returns to its original thermal state (McKenzie, 1978). At this time, the heat-flow should decrease from the proximal margin sectors, where the radiogenic crust is still relatively thick, towards its distal sectors, where the crust has extensively thin and the thermal lithosphere thickness approximates that of the adjacent untinned continental lithosphere. This should occur after approximately ~50 Myr for 120 km thick continental lithosphere (McKenzie, 1978). Although, good quality heat flow data is very scarce along margins, some of them, such as the Voring basin, show instead increasing heat flow towards the distal margin sectors ~60 Myr after break-up (Cunha et al., 2021). Recent numerical models have suggested, instead, that the lithosphere under the hyper-extended continental margins, does actually not return towards its original thermal thickness, instead it acquires a thickness which is similar to that of the adjacent plate, resulting in higher heat-flow towards the distal margins at ~80-100 Myr after break-up (Perez-Gussinye et al., 2023). In those models, the delay in thermal relaxation under the hyper-extended margins is caused by small-scale convections cells, a process which also prevents the oceanic lithosphere to infinitely cool and is responsible for the flattening of the oceanic bathymetry at old ages. Interestingly, the models show that the delay in thermal relaxation under both the hyper-extended rifted margins and the old oceanic crust increases with decreasing rifting and spreading velocity, such that is most obvious in ultra-slow margins and adjacent oceanic basins (Perez-Gussinye et al., 2023). Here we use updated 2D numerical models which include the thermal consequences of serpentinisation, melting and melt emplacement to understand the thermal evolution of oceanic plates and compare the resulting plate structure, heat-flow and bathymetry with the observations from seismic LAB structure, and global heat-flow and bathymetry databases.

 

References

Cunha, T.A., Rasmussen, H., Villinger, H. and Akinwumiju, A.A., 2021. Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea. Geosciences, 11(5), p.190.

McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary science letters, 40(1), pp.25-32.

Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andrés-Martínez, M., Dong, D. and García-Pintado, J., 2024. Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension. Geological Society, London, Special Publications, 547(1), pp.SP547-2023.

How to cite: Gudipati, R. R., Pérez-Gussinyé, M., and García-Pintado, J.: Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19459, https://doi.org/10.5194/egusphere-egu24-19459, 2024.

EGU24-19570 | ECS | Orals | TS8.1

The tectonic evolution of the western North American margin since the Devonian 

Andres Felipe Rodriguez Corcho, Sabin Zahirovic, Michele Anthony, Dene Tarkyth, Christopher Alfonso, Maria Seton, Dietmar Muller, Bruce Eglington, and Basil Tikoff

The western North American margin records multiple phases of rifting and convergence, resulting from the interaction between western Laurentia, rifted continental fragments, and intra-oceanic terranes originating in the Panthalassa and Pacific oceanic plates. Quantitative plate reconstructions of this margin have prioritised diverging interpretations regarding the subduction polarities of eastern Panthalassa terranes during Jurassic to Cretaceous times. These discrepancies arise from the reliance on either seismic tomography or surface geology as the first-order constraint for determining subduction polarity. We present an updated tectonic reconstruction for western North America from the Devonian to present day. In this new model, we reconcile geological histories based on surface geology, geochronology, paleomagnetism and isotopic data, with interpretations of seismic tomography. The new reconstructions account for the tectonic evolution of the Alaska orocline, western Canada and western United States (US) and south-western (SW) North America, which have not been implemented in detail in previous tectonic models. Our model suggests that most of the terranes of western North America were rifted off Laurentia and Baltica during Devonian to Triassic extension and trench-retreat. Following back-arc rifting and opening, many of the terranes (e.g. Insular, Intermontane, Angayucham) experienced an intra-oceanic phase before accreting to the continental margin of North America at different times, between Early Triassic to Late Cretaceous times. The model illustrates the collision of the Angayucham Terrane, counterclockwise rotation and orocline formation in Alaska during the middle Jurassic. In western US and SW North America, the model showcases Jurassic to Cretaceous extension and rifting. Extension starts first in western US (170-145 Ma) and is then propagated south, causing the opening of the Bisbee Basin (161-105 Ma). The model also captures the Late Cretaceous collision of the Insular Terrane, which triggered transpression, terrane translation for thousands of kilometers and clockwise rotation in western US during Late Cretaceous to Paleogene times. Our updated model highlights the importance of surface geology in constraining the polarity of ancient subduction zones interpreted from seismic tomography.

How to cite: Rodriguez Corcho, A. F., Zahirovic, S., Anthony, M., Tarkyth, D., Alfonso, C., Seton, M., Muller, D., Eglington, B., and Tikoff, B.: The tectonic evolution of the western North American margin since the Devonian, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19570, https://doi.org/10.5194/egusphere-egu24-19570, 2024.

Geodynamicists have long proposed that mantle convection creates dynamic topography — a long-wavelength, low-amplitude signal extending beyond plate tectonics. This predicts transient vertical Earth surface movement of 1–2 km across thousands of horizontal kilometers at any location, including continental interiors. Despite these claims, experts working on local observations, using the multitude of high-resolution geological, sedimentological, and geomorphological data, face challenges in finding clear evidence to unequivocally support dynamic models of whole mantle convection, including the plume mode. Moreover, regional-scale stratigraphic techniques, such as sequence stratigraphy, which enabled hydrocarbon exploration, invoke unconformities on multiple scales but, from their far-field perspective, render correlation to distinct geodynamic events difficult.

To circumvent this scaling and correlation problem, I propose to reverse the stratigraphic perspective to an outwards-directed view. This approach requires a theoretical geodynamic framework and the identification of tectonic events (center, near field), such as magmatic arcs, flood basalts, or uplifted domes, followed by outward-directed geological mapping of regional-scale stratigraphic unconformities —predicted by theory— to distal regions. This approach is analogous to the way in which paleoseismologists examine so-called event horizons, i.e., unconformities in the stratigraphic record adjacent to fault scarps that preserve a record of the Earth's surface at the time of earthquake rupture.

This event-based stratigraphic mapping method (EVENT-STRAT) enables analysis of geological events on geological maps compiled at regional to continental scales. The technique connects local work into a continent-scale framework, allowing identification of transient patterns related to dynamic mantle-derived events. The EVENT-STRAT mapping method is designed to visualize geological effects resulting from both the plate and the plume mode of mantle convection. The toolbox consists of the hiatus mapping method (Friedrich 2019, Geological Magazine) and the event-based stratigraphic framework mapping (e.g., Friedrich et al. 2018, Gondwana Research). The upcoming EVENT-STRAT mapping method involves multiple polygonal stacking to analyze various stratigraphic event horizons, such as hiatus surfaces and unconformities. The most significant current challenge is to add the high-precision stratigraphic data compiled on local chronostratigraphic charts to continent-scale geological maps. This effort requires the attention of geological surveys on international scales seeking to compile theory-based geodynamic-stratigraphic parameters on the next generation of global and continent-scale geological maps.

How to cite: Friedrich, A. M.: Geodynamic Stratigraphy — Defining the Need for Mapping Strategies to link Models of Mantle Dynamics to Surface Processes on Geological Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19837, https://doi.org/10.5194/egusphere-egu24-19837, 2024.

EGU24-649 | ECS | Posters on site | GD6.1

A lower crust shear zone favors delamination and continental subduction in the Apennines 

Irene Menichelli, Irene Bianchi, and Claudio Chiarabba

Understanding the physical characteristics and structure of the lithosphere is crucial in unraveling the evolution of mountain belts. In this study, we present detailed Vs profiles of the Apennine lithosphere that shed light on a controversial aspect of continental subduction: the intricate process of crustal delamination from the descending plate. Through an accurate analysis of a dense teleseismic Receiver function data set (comprising over 15,000 teleseismic events), we find that the delamination of continental lithosphere is facilitated by the development of a low Vs shear weak zone within the mid-lower crust.

Utilizing a Reversible-jump Markov chain Monte Carlo (RjMcMC) approach for computing 1D Vs models across the central Apennines, we mitigate the reliance on a-priori information, thus enhancing the robustness of the final solution.
We observe a double Moho beneath the outer regions of the current mountain range, indicating the gradual development of a shallow interface. This incipient formation of the double Moho finds a mature-stage equivalent in the backarc, where crustal thinning and magmatism ensued following the re-establishment of the shallow Tyrrhenian Moho.

Proposing a novel scenario for Apennine subduction, we hypothesize that the onset of delamination occurs in the forearc, necessitating a longer thermal rebalancing. This hypothesis suggests that sustained continental subduction can persist if it develops at mid-lower crustal depths within weak rheology inhibiting the slab break-off process.
Our findings present a new perspective on continental subduction and offer prognostic insights into the long-term evolution of the Apennines over the next 7-10 million years.

How to cite: Menichelli, I., Bianchi, I., and Chiarabba, C.: A lower crust shear zone favors delamination and continental subduction in the Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-649, https://doi.org/10.5194/egusphere-egu24-649, 2024.

EGU24-1098 | ECS | Posters on site | GD6.1

Crustal Structure across the Northern Scandinavian margin along the Senja OBS Profile  

Rafet Ender Alemdar, Metin Kahraman, Alexey Shulgin, Asbjorn Breivik, Irina Artemieva, and Hans Thybo

The Senja onshore-offshore seismic profile is located in the northwestern part of Fennoscandia, extending from onshore Norway into the North Atlantic Ocean. The Fennoscandian lithosphere has been formed by the amalgamation of terranes and microcontinents to an Archean core, primarily during the Palaeoproterozoic. The later Sveconorwegian (Grenvillian) and Caledonian orogenies had strong effect on the western part of Fennoscandia. The Scandia Mountain range extends along the west coast with elevation up to 2500 m, mainly coinciding with the surface outcrops of Caledonian deformed crust. Its location far from any active plate boundary makes this mountain range enigmatic. The offshore continental part of Fennoscandia experienced a long post-Caledonian extensional period for more than 200 My, and it now forms a continental shelf below sea level extending to the continent to ocean transition.

We present a crustal-scale seismic profile along the NW-SE striking Senja OBS Profile in northern Scandinavia between 12°E and 20°E. This profile covers both offshore and onshore domains over a total distance of ~300 km across the Norwegian shelf in the North Atlantic Ocean, Senja Island, and mainland Norway. Airgun shots from the vessel Hakon Mosby were used as sourced for the refraction/wide-angle reflection survey. The dataset includes recordings on 5 ocean bottom seismometers (OBS) on the shelf, slope, and oceanic environment, complemented by 68 onshore stations at 1.3-kilometre intervals. We present a seismic p-wave velocity model derived by ray-tracing modelling of P-wave arrivals along the profile.

The model includes a deep sedimentary basin extending to ~10 kilometres depth with velocities between ca. 2 km/s and 5.10 km/s, which gradually thickens from the coast to its maximum thickness of 10 km about 25 km from the coast. This deep sedimentary basin is very wide (approximately 8 km). Further offshore the sedimentary cover of the shelf and oceanic environment is relatively thin. The upper crustal velocity below the sedimentary sequence has velocities of ~ 6.0 km/s.

 

How to cite: Alemdar, R. E., Kahraman, M., Shulgin, A., Breivik, A., Artemieva, I., and Thybo, H.: Crustal Structure across the Northern Scandinavian margin along the Senja OBS Profile , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1098, https://doi.org/10.5194/egusphere-egu24-1098, 2024.

EGU24-2015 | ECS | Orals | GD6.1

Craton Formation by Underplating and Development of the MLD: Evidence from Bayesian Surface Wave Inversion  

Alistair Boyce, Thomas Bodin, Stephanie Durand, Dorian Soergel, and Eric Debayle

Craton formation and evolution remains enigmatic because observations from long and short period seismic waves and geochemical data are inconsistent. For example, both internal layering and radial anisotropy are poorly constrained. By inverting cratonic Rayleigh and Love surface wave dispersion curves for shear-wave velocity and radial anisotropy using a flexible Bayesian scheme, we show that these inconsistencies can be reconciled. Our methodology does not require any vertical smoothing and only includes anisotropic layers where necessary to fit the data. Results show all cratons possess a positively radially anisotropic upper lithospheric layer that is best explained by Archean underplating. An isotropic layer lies beneath, likely indicative of two-stage craton formation. We find a variable amplitude low velocity zone (LVZ) may exist within the upper anisotropic layer of up to 9 of 12 cratons studied. This LVZ is well correlated to observed Mid-Lithospheric Discontinuities (MLDs). Our results suggest the MLD is best explained by post formation modification within cratons.

How to cite: Boyce, A., Bodin, T., Durand, S., Soergel, D., and Debayle, E.: Craton Formation by Underplating and Development of the MLD: Evidence from Bayesian Surface Wave Inversion , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2015, https://doi.org/10.5194/egusphere-egu24-2015, 2024.

Since the Early Mesozoic, extensive Cretaceous intraplate volcanism, cratonic lithospheric thinning, and widespread crustal deformation have been documented in Northeast (NE) Asia. Global plate reconstruction models and paleo-magnetic data suggest a highly complex subduction system under NE Asia since the early Mesozoic, with proposed Mesozoic models including continuous subduction of the Izanagi plate and possible subduction of intra-oceanic arcs and early Cenozoic subduction of an active spreading ridge. Although subduction is a critical factor impacting continental deformation, the interactions between deep dynamic processes and surface tectonic responses remain debated. Based on a systematic investigation of seismic tomography, plate reconstruction, and igneous rock data, we present a new model of continental co-deformation with a multistage subduction history involving the Proto-ocean, Izanagi, and Pacific plates in Northeast Asia. The high-resolution mantle seismic structures were ascertained using a novel global tomographic inversion based on adaptive inversion mesh refinement and regional velocity perturbation constraints from 298,725 hand-picked and > 16 million arrival times of multiple P-wave phases (e.g., P, pP (pwP), PP, PcP, Pdiff, PKP, PKiKP) which were recorded by the 4,107 temporary and permanent stations in Northeast Asia. The unprecedented data reveal new integrative views on the geometry and behavior of mantle high-velocity anomalies associated with a sequence of oceanic lithosphere subduction events. The extensive compilation of dated volcanic samples provides strong constraints on past subduction events. Positions of remanent slabs derived from a multistage subduction history were reconstructed using the ages of initial subduction and slab sinking rates, where the geographical distribution of remnant slabs observed in our tomographic model helps to define the plate reconstruction history since the Early Mesozoic. The inferred multi-plate subduction configuration with slab advance, rollback, stagnation, break-off, and foundering, together with implied slab dehydration, should have resulted in various degrees of fluid-rock interactions among the slabs, the asthenosphere, and the continental lithosphere. We argued that fluid intrusions and mantle flow have played crucial roles in episodic intraplate volcanism and craton lithosphere thinning in different subduction stages. The Early Cretaceous intraplate volcanism, the ancient cratonic lithospheric thinning, and the crustal deformation have been caused mainly by a successive effect of the Proto oceanic plate and Izanagi slab subduction, but less by the Pacific plate subduction. These findings provide a systematical framework for understanding the co-evolution of the continental lithosphere with deep mantle dynamics in NE Asia and also serve as an excellent illustration of how the Earth's interior works.

How to cite: Wang, Z., Liu, L., Fu, Y., and Zhao, L.: Tomographic evidence on multistage plate subduction in Northeast Asia: Implications for lithospheric deformation and intraplate volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2673, https://doi.org/10.5194/egusphere-egu24-2673, 2024.

EGU24-3139 | ECS | Orals | GD6.1

A rock density model for geodynamic and tectonic studies of the Southern Benue Trough in Nigeria from a tailored gravity data 

Ojima Apeh, Robert Tenzer, Luan Pham, Elochukwu Moka, Emmanuel Onah, Victus Uzodinma, and Elijah Ebinne

The application of gravity data in mapping of the Earth’s subsurface has steadily been on the increase globally. Gravity information is more often used to understand mechanisms associated with rock formations, interpret underground faulting and fracturing zones as well as estimating depths of underlying geological structures. A rock density mapping could be used to estimate mineral deposits, differentiate lithofacies, understand the general dynamics of heat flow, interpret geomorphologies, and determine the size and characteristics of different types of rocks in the Earth’s crust. Recently, there is a growing trend of applying an apparent density mapping technique for the estimation of rock densities from gravity data. In this study, we compute a high-resolution tailored Bouguer gravity data over the Southern Benue Trough of Nigeria and use approximate rock density ranges of some common rock types and existing geological/geophysical information to understand geodynamic processes and tectonic events predominant within the study area. We further apply the inverse density deconvolution filter (i.e., the apparent density mapping technique) to a computed short-wavelength gravity component (realized from a gravity separation approach) in order to estimate rock densities. According to our estimates, the rock densities within the study area vary between 2.50 and 2.74 g/cm3, with minimum density values attributed to volcano-sedimentary deposits along the Cameroon Volcanic Line and maximum density values at the eastern and southern parts associated with mafic igneous rocks. A comparison of estimated rock densities with available in-situ rock density data showed slightly higher rock density estimates in most cases than the in-situ rock density values at 50 sample locations. However, estimated rock densities are within the range of density variations of sedimentary and basement rocks predominant in the study area. Our gravity and density maps reveal the geometry of main geological structures dominated by sedimentary basins, igneous intrusions, uplifts, volcanoes, and diapirs occurring within the study area. Folds, faults, and fractures forming ridges and troughs in different directions (mostly NE-SW) are also manifested in those maps. The compiled maps could identify these subsurface geological structures as well as reveal different erosion patterns and landforms characteristic of the study area. The revealed patterns of crustal deformations within the study area demonstrate compressional and extensional tectonic events which may have possibly led to the faulting and fracturing systems with thermal and chemical variations among ores and gangue minerals in the area. These findings confirm the different geomorphic processes and structural deformations well-known about the study area. In conclusion, we point out that a rock density model could be an essential tool for studying geodynamic processes and tectonic events in a region since it can demonstrate mechanisms of tectonic events, patterns of deformation regimes, and mineral prospectivity of such an area.

 

Keywords: gravity; rock densities; tectonics; geodynamics; density inversion; mineral deposits

How to cite: Apeh, O., Tenzer, R., Pham, L., Moka, E., Onah, E., Uzodinma, V., and Ebinne, E.: A rock density model for geodynamic and tectonic studies of the Southern Benue Trough in Nigeria from a tailored gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3139, https://doi.org/10.5194/egusphere-egu24-3139, 2024.

Since last 1960’s, the plate tectonics has been played a main role for the study on the Earth’s evolution and global tectonics, but mostly focused on the global divergence and convergence, and focused on the continental margin—subduction and collision. However, the plate tectonics cannot resolve all of the tectonic evolution and reconstruction of the global evolution, like non-rigid blocks and continental lithospheric deformation; and mountain building within the continent; large scales deformation and tectonics in the continental interiors and so on. Thus, “Intracontinental Tectonics and Orogeny” has been studied. 

Globally, there are lots of tectonics or deformation types have been found and the intracontinental mountain building and the orogeneses have been classified, like types of the Alice Spring in Australia, the Tianshan in Asia and the Pyrenees in Europe. They are with different orogenic frameworks including deformation, magmatism, sedimentation and metamorphism. Also, they have formed in different tectonic backgrounds, such as on the reworking orogenic belt, intracontinental rift-basin deformation, and multiple-stage orogeny between the continental blocks, and linkages to plate tectonics and non-plate tectonics in mechanism and dynamics.  

How to cite: Wang, Y., Liu, S., and Gong, M.: Classification of intracontinental (intraplate) orogeny based on tectonics and its evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3525, https://doi.org/10.5194/egusphere-egu24-3525, 2024.

EGU24-4613 | ECS | Posters on site | GD6.1

Mantle discontinuities beneath Arctic ocean and Aleutian-Alaska subduction zone 

Ye Yuan, John Keith Magali, and Christine Thomas

We investigate the properties of mantle discontinuities beneath the Arctic ocean and the Aleutian-Alaska subduction zone with underside reflections of PP and SS waves. The depth distributions of the 410-km and 520-km discontinuities suggest a relatively normal mantle transition zone beneath the Arctic ocean and a cold mantle transition zone with the subducted Pacific plate beneath Aleutian-Alaska subduction. The depth of the 660 km discontinuity shows normal behavior beneath the Arctic Ocean. However, the detection of deep reflectors with opposite polarities in depth range of 720~770 km beneath the eastern Aleutians introduces additional complexity for explaining the slab morphology.  We test several plausible compositions using mineralogical modeling along a subduction geotherm. The deep reflectors are interpreted as mid-ocean ridge basalt (MORB) crust associated with the Pacific slab that may deform or buckle at the bottom of the mantle transition zone beneath the eastern Aleutians.  Meanwhile, an uplifted 660-km discontinuity observed in the adjacent Alaska region suggests a different subduction depth, where the slab may penetrate the 410-km discontinuity but does not reach the 660-km discontinuity,  consistent with previous regional studies. Our observations thus depict a complex slab geometry along the Aleutian-Alaska trench, that is, the slab  may reach the top of the lower mantle beneath eastern Aleutian but remains at the base of the transition zone underneath central Alaska.

How to cite: Yuan, Y., Keith Magali, J., and Thomas, C.: Mantle discontinuities beneath Arctic ocean and Aleutian-Alaska subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4613, https://doi.org/10.5194/egusphere-egu24-4613, 2024.

EGU24-4710 | Posters on site | GD6.1

The Lithosphere Structure Of Bohai Bay Basin: Combining Gravity, Geoid, And Topography Data 

Jing Ma, Wanyin Wang, Hermann Zeyen, and Zhongsheng Li

The Bohai Bay Basin, located in northeast China, is a Meso-Cenozoic strike-slip extensional basin. A lot of research work carried out in Bohai Bay Basin, has shown that there is a huge potential of oil and gas resources. However, the proportion of known oil and gas reserves to the total estimated resources is not high, which means that this area still has broad exploration prospects. Although oil and gas resources are mainly distributed in sedimentary basins, their enrichment degree is largely influenced by the structure and development of the lithosphere. Based on lithospheric local isostasy theory and thermal conduction principle linked to temperature dependence of rock densities, the three-dimensional deep structure of the lithosphere under the Bohai Bay Basin is calculated by using geoid and gravity anomalies, topographic and existing geological-geophysical data. The results show that the lithosphere-asthenosphere boundary of Bohai Bay Basin gradually rises from the western onshore to the eastern offshore area from 90 to 110 km. The thinnest lithosphere is found under the Bozhong Depression in the southeast of the Bohai Bay Basin. It is concluded that the thinning of the lithosphere in the Bohai Bay Basin is closely related to the subduction of the Meso-Cenozoic Pacific plate, which led first to thickening followed by delamination of the North China Craton lithosphere, and then the magma upwelling led to slow uplift of the Earth’s surface and continuous stretching of the lithosphere. At the same time, favorable conditions of temperature, pressure, chemistry and structure were provided for the formation of oil and gas. In this wqy, the Bohai Bay basin developed into the present oil-rich basin. This study provides a new perspective for understanding the deep structure and hydrocarbon resource control mechanisms of Bohai Bay Basin.

How to cite: Ma, J., Wang, W., Zeyen, H., and Li, Z.: The Lithosphere Structure Of Bohai Bay Basin: Combining Gravity, Geoid, And Topography Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4710, https://doi.org/10.5194/egusphere-egu24-4710, 2024.

Despite numerous geophysical observations on Hindu Kush, fine structures of mantle discontinuities remain less explored. By stacking near-source SdP phases from large datasets, we conducted systematic imaging of mantle discontinuities beneath Hindu Kush. Compared with the IASP91 model, we find an abrupt topographic transition of the 410-km discontinuity (410) from uplifts of up to 41 km within the subducting slab to depressions of less than 20 km near the slab edge, as well as a slightly depressed 660-km discontinuity (660) with depths of 660-668 km, and a fluctuant 300-km discontinuity (300) with depths of 264-337 km. We suggest that the sinking Indian slab elevates the 410 due to its cold interior, and deepens it near the slab edge by the hot mantle upwelling of slab-entrained mantle escaping below the slab, but has almost no impacts on the 660. Moreover, the fluctuant 300 can be explained by the coesite to stishovite phase transition in the eclogite-rich mantle within the subduction zone. When considered alongside other studies, our seismic results offer new insights into subduction dynamics of the Indian slab.

How to cite: Cui, Q., Zhou, Y., Gao, Y., and Liu, L.: Deep dynamics of subducting Indian slab revealed by mantle discontinuity structures beneath Hindu Kush from SdP observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4912, https://doi.org/10.5194/egusphere-egu24-4912, 2024.

Olivine and its polymorphs are the dominant minerals in the upper mantle and transition zone. The olivine phase transitions, determined primarily by pressure and temperature, control mantle discontinuities and influence mantle dynamics. Pressure is a first-order control on olivine phase transition and relates primarily to depth; therefore, it is commonly used to interpret the depths of mantle discontinuities. However, mantle dynamic models predicted stress levels of 100-300 MPa or as high as 1 GPa. Previous work has provided a complete picture of how such stresses would affect the positions where mineral reactions occur (and hence large-scale mantle structure). In this work, we plan to focus on the feedback between pressure and stress on the olivine phase transition at grain scale, and then the results can be extrapolated and upscaled to mantle scale deformation.

 

We use the Open Phase Studio software based on the phase field model to simulate olivine phase transitions. The phase field model uses order parameters to distinguish different phases and describe their evolution. The parameter value of 1 indicates the bulk of the phase, and a value of 0 indicates the absence of this phase and is a smooth function of position. The smooth transition of a phase parameter indicates a diffuse interface between phases. The total free energies, interface properties, and microstructure control the phase field evolution. Open Phase Studio considers the Helmholtz free energies of each phase and uses their elastic energies to account for the pressure and stress effects on phase evolution. This software currently focuses on models of alloys, but appropriate values for silicates can be input. As a foundation, we first consider an Al-Li alloy to understand the behaviour of models. Then, we input olivine thermodynamic data via temperature-composition (T-x) phase diagrams for olivine composition and their elastic moduli to test the phase transition under different stress boundary conditions. We present our preliminary results here.

How to cite: Lu, L. and Wheeler, J.: Grain-scale simulation of olivine phase transition under stress: implications for mantle discontinuities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5239, https://doi.org/10.5194/egusphere-egu24-5239, 2024.

The La Réunion hotspot is one of the best examples of a primary plume, manifested as intraplate volcanism, a linear chain of volcanos with age progression, a large igneous province and geochemical anomaly. In this study, we investigate the mantle transition zone structure in and around the La Réunion Island using 3D migration of P-Receiver functions to decipher the effect of the plume on the Mantle Transition Zone(MTZ) and its architecture. Results indicate a thin MTZ beneath Madagascar, its western side, the eastern and south-eastern side of La Réunion sampling the oceanic region, in terms of a depressed 410 km and elevated 660 km discontinuity. A thin MTZ suggests high-temperature anomalies within, caused by the plume. Interestingly, we detect a depressed 410 km discontinuity exactly beneath the La Réunion hotspot and a broader depression of the 660 km discontinuity in and around it. These maiden results shed light on the high-temperature anomalies in the mid mantle, probably sourced from the La Réunion plume and provide evidence for Majorite-garnet (Mj) to Perovskite (Pv) phase transformation at the 660 km discontinuity. We postulate that the conduit of the La Réunion plume has initially hit the 660 km discontinuity and got horizontally spread at this depth and further progressed to the 410 km discontinuity as a columnar structure.

How to cite: Bommoju, Dr. P. R.: Inference of a plume conduit in and around the LaRéunion Island from 3D Migration of Ps conversionsfrom the Mantle Transition Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5520, https://doi.org/10.5194/egusphere-egu24-5520, 2024.

EGU24-6651 | ECS | Orals | GD6.1

A Global View of Upper Mantle Stratification: CRISP-RF 

Sayan Swar, Tolulope Olugboji, Ziqi Zhang, Steve Carr, Jean-Joel Legre, Canberk Eckmecki, and Mujdat Cetin

Abstract:

Our planet’s mantle is the largest rock-layer by volume. Across its old and stable Archean and Proterozoic terranes, seismological evidence suggests ubiquitous, spatially variable, and puzzling discontinuities, within, across and beneath the upper mantle lithosphere (~50- 350 km). A variety of explanations have been proposed, including phase transformations, melting and compositional anomalies, anisotropy, and elastically accommodated grain. To evaluate these, and other models, it is crucial to improve our threshold for detecting such discontinuities especially in reverberant and noisy environments. Here, we present a new method for sifting through the echoes and reverberations: CRISP-RF (Clean Receiver function Imaging with Sparse Radon Filters). With a global dataset of Ps converted waves, we use CRISP-RF to isolate hard-to-detect wave conversions buried in reverberations and noise. This refined, high-resolution, global view of upper mantle stratification will ensure robust evaluation of proposed models of upper mantle structure, evolution, and dynamics.

How to cite: Swar, S., Olugboji, T., Zhang, Z., Carr, S., Legre, J.-J., Eckmecki, C., and Cetin, M.: A Global View of Upper Mantle Stratification: CRISP-RF, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6651, https://doi.org/10.5194/egusphere-egu24-6651, 2024.

The continental mid-lithospheric discontinuity (MLD) has been widely detected within most cratons, with the dominant depth of 70-100 km and a significant drop of shear-wave velocity of 2-12%. However, the formation mechanism and corresponding strength of the MLD are widely debated, which may strongly affect the roles of MLD on craton evolution. In this study, we have conducted systematic numerical models with hydrated blocks generation routine to simulate the formation of MLD. Model results indicate that the MLD may be induced by the accumulation of hydrous minerals within cratonic lithosphere, and acts as a water collector during craton evolution. Further on, we focus on the roles of MLD in craton evolution. Based on the comparison among variable mechanisms, the viscosity of MLD may vary from the relatively high viscosity induced by wet olivine to the rather low viscosity induced by antigorite. Thus, systematic numerical modeling has been conducted with the MLD of contrasting strengths, i.e. the wet olivine-induced MLD or antigorite-induced MLD, to investigate the effects of MLD on the craton instability under variable tectonic regimes (stable, extension, compression, mantle flow traction, or mantle plume). Model results indicate that the wet olivine-induced MLD could not lead to lithospheric delamination under all the tested tectonic regime. In contrast, the weak antigorite-induced MLD could localize large strain and decouple the overlying and underlying lithosphere significantly; despite this, the lithospheric delamination requires additional conditions. Craton destruction only occurs with the connection of the weak antigorite-induced MLD and the sub-plate asthenosphere during craton extension or mantle plume activity. The partial melting process during large amount of extension or upwelling of mantle plume with high temperature anomaly and large size is a key condition. In addition, the depleted cratonic lithospheric mantle with low density would increase the intrinsic buoyancy of lithosphere, and inhibit the lithospheric delamination and craton destruction. Therefore, the effect of MLD on the craton destruction is not as significant as previously considered in the models, which requires additional strict conditions that are not widely satisfied on the Earth. This may explain the general stability of most cratons with widespread MLDs.

How to cite: Fu, H.-Y. and Li, Z.-H.: Formation mechanism of continental mid-lithosphere discontinuity and its effects on craton instability under variable tectonic regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7017, https://doi.org/10.5194/egusphere-egu24-7017, 2024.

EGU24-7153 | ECS | Posters on site | GD6.1

A new method for constraining crustal Vp/Vs ratio using P and S wave multiples 

Fanchang Meng, Chunquan Yu, and Xianwei Zeng

The ratio between compressional and shear wave speeds (Vp/Vs) in the Earth's crust is crucial for gaining a better understanding of its chemical composition and geological evolution history. Many studies employed H-κ stacking of receiver functions to estimate the crustal Vp/Vs ratio. However, the Vp/Vs ratio obtained from H-κ stacking can be biased due to lateral variations in crustal structures and/or incorrect absolute wave speed assumption. In this study, we propose a novel method to estimate the crustal Vp/Vs ratio using P and S wave multiples near receivers, that is the PpPmp (where m represents the Moho) and SsSms phases. The absolute arrival times of PpPmp and SsSms are sensitive to crustal thickness and wavespeeds, but the ratio of their arrival times is most sensitive to the crustal Vp/Vs ratio. We first verify the new method using synthetic tests on various crustal models. Synthetic results show that in the presence of lateral variation in crustal structure, the new method gives more accurate Vp/Vs ratios than the conventional H-κ stacking of receiver functions. We further validate the new method using field data recorded by the broadband station HYB in the eastern Dharwar Craton. Our data analysis involved preprocessing and manual selection of teleseismic events. Ultimately, the observed PpPmp and SsSms phases from 351 teleseismic events were used to calculate the Vp/Vs ratio beneath the HYB station, resulting in a value of 1.737±0.016. We find that this value is comparable to research results obtained by previous researchers using receiver function inversion (Zhou et al., 2000). Our new method for estimating crustal Vp/Vs ratio can potentially to applied to many other regions of tectonic importance.
This study is supported by National Natural Science Foundation of China (43/K22431006).

How to cite: Meng, F., Yu, C., and Zeng, X.: A new method for constraining crustal Vp/Vs ratio using P and S wave multiples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7153, https://doi.org/10.5194/egusphere-egu24-7153, 2024.

Knowledge of elastic properties of the Earth's crust provide important constraints on its chemical composition, isostasy and tectonic evolution. However, accurate determination of crustal properties beneath sedimentary basins is challenging. This challenge mainly arises from interference caused by sedimentary reverberations, which may either mask desired signals or cause significant bias in parameter estimates. Some studies attempted to remove the sediment effect by applying wavefield downward continuation or resonance filters to conventional receiver functions, but successful applications were limited. Recently, a novel method utilizing Pn and its multiples, named as PnPn, has been developed and proven effective in imaging the Moho beneath sedimentary basins. Arrival times of Pn multiples are sensitive to crustal thickness (H) and P wave speed (Vp). In contrast, arrival times of converted phases in receiver functions are most sensitive to crustal thickness and Vp/Vs ratio. In this study, we apply a joint analysis of the newly developed Pn multiple method and conventional receiver functions to investigate the sedimentary and crustal structures of the northern Ordos basin along a west-east trending profile. We first apply a multi-frequency receiver function waveform fitting technique to constrain the shallow sediment structure. Then, we combine receiver functions and Pn multiples to determine the thickness, Vp and Vp/Vs ratio of the crystalline crust. Our results show that the interior of the Ordos basin is characterized by thick sediments, with the maximum thickness reaching 4.6 km. The sediment thickness shoals toward the eastern margin of the Ordos basin. The sediment structure in general is consistent with previous findings from active source studies and is of higher resolution than previous passive source studies. For the crystalline crust beneath the northern Ordos basin, the absolute Vp ranges from 6.45 to 6.57 km/s and the Vp/Vs ratio ranges from 1.73 to 1.78. These values suggest an overall intermediate crustal composition beneath the northern Ordos basin, in contrast to felsic crustal composition beneath the eastern North China Craton. The crustal thickness in the interior of the northern Ordos basin is remarkably flat, approximately 40 km, closely aligning with the Airy model. However, a deviation from Airy isostasy of approximately 5 km in crustal thickness is observed at the eastern margin of the Ordos basin, which could be due to increased bulk density of the crust accompanying the thinning of low-density sedimentary layer.

How to cite: Yin, W. and Yu, C.: Sedimentary and crustal structures beneath the northern Ordos basin constrained by receiver functions and Pn multiples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7369, https://doi.org/10.5194/egusphere-egu24-7369, 2024.

EGU24-7989 | Posters on site | GD6.1

Mantle Transition Zone structure beneath the Central and Eastern European region based on P-to-S Receiver Function analysis 

Dániel Kalmár, Konstantinos Michailos, Laura Petrescu, György Hetényi, Götz Bokelmann, and AlpArray and PACASE Working Groups

The depths of mineralogical phase transitions in the mantle (at ~410 and ~660 km depth) offer crucial insights into the thermal conditions of the mantle transition zone and, by extension, the upper mantle's state and circulation. Our approach involves conducting P-to-S receiver function analysis to determine the mantle transition zone's thickness and the absolute depths of the ~410 km and ~660 km discontinuities in the Central and Eastern European region.

Our workflow meticulously attends to each step, starting from data download, quality control, and culminating in the calculation of P-to-S receiver functions. We use data from multiple sources, including the AlpArray and AdriaArray Seismic Networks, the PACASE, Carpathian Basin, and South Carpathian Project temporary seismic networks, as well as the permanent stations of the Hungarian National Seismological network and of the neighboring countries. This analysis covers the time period from 2002 to 2023, involving over 860 seismological stations. Our extensive dataset, consisting of approximately 2 million three-component waveforms and over 120,000 high-quality P-to-S radial receiver functions, coupled with dense piercing-point coverage, allows us to achieve unprecedented resolution.

We present Common Conversion Point cross-sections migrated with a 3D tomographic velocity model underneath the Alps, Carpathians, and the Pannonian Basin. Additionally, we aim to offer new insights into the mantle transition zone's thickness beneath intriguing regions (e.g., Vrancea zone, Alpine Tethys Ocean zone, Eastern Alps–Pannonian Basin transition zone). For a precise understanding of geodynamic processes such as slabs, mantle plumes, and volcanism, it is imperative to accurately map these boundaries.

How to cite: Kalmár, D., Michailos, K., Petrescu, L., Hetényi, G., Bokelmann, G., and Working Groups, A. A. P.: Mantle Transition Zone structure beneath the Central and Eastern European region based on P-to-S Receiver Function analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7989, https://doi.org/10.5194/egusphere-egu24-7989, 2024.

EGU24-8696 | Posters on site | GD6.1

Mapping the Moho in the Bohemian Massif and the Western Carpathians with P-receiver functions 

Hana Kampfová Exnerová, Jaroslava Plomerová, Luděk Vecsey, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

We present the Moho depths in the Bohemian Massif and Western Carpathians derived from P-to-S receiver functions calculated from broad-band P-coda waveforms from teleseismic events recorded at temporary and permanent stations operated in a region within 10–23º E and 47.5–52º N during last two decades. By the Zhu and Kanamori method (2000) and the Ps time delays (Kvapil et al., 2021), we process data collected from running AdriaArray Seismic Network (since 2022), PACASE experiment (2019 – 2022), AlpArray Seismic Network (2015 – 2019) and its complementary experiment AlpArray-EASI (2014 – 2015), as well as from previous passive seismic experiments in the region – BOHEMA I-IV (2001 – 2014), PASSEQ (2006 – 2008) and EgerRift (2007 – 2013). By applying different methods, we aim at upgrading the current knowledge of the crust in the broader surroundings of the European Alps (Michailos et al., 2023), the Pannonian Basin (Kalmar et al., 2019), and the Carpathians. Locally, differences between Moho depth from individual methods could highly exceed 5 km, thus reflecting various sensitivities of individual methods to the local complex structure. An extended amount of data and regionally combined evaluation provide a homogeneous estimate of Moho depths, particularly for the usage in deep Earth studies, e.g., in applying crustal corrections in the upper mantle tomography of Central Europe.

How to cite: Kampfová Exnerová, H., Plomerová, J., Vecsey, L., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: Mapping the Moho in the Bohemian Massif and the Western Carpathians with P-receiver functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8696, https://doi.org/10.5194/egusphere-egu24-8696, 2024.

EGU24-9487 | ECS | Orals | GD6.1

A new global crust model: ECM24 

Biao Lu, Mark van der Meijde, Islam Fadel, Mirko Reguzzoni, Lorenzo Rossi, Daniele Sampietro, Fabio Cammarano, and Jordi Julia

Despite 160 years of probing the world crust, due to lack of seismic and ground gravity observations, there are still white spots in the worlds' crustal thickness map. The crustal structure in those regions is among the least understood of the Earth's continental areas, and variations in basic but fundamental parameters - such as crustal thickness - are still poorly constrained over large areas. Recent research has shown that satellite gravity-based crustal modeling in regions with limited seismological coverage can provide unique insights in crustal thickness and underlying geodynamical processes.

In almost all of these cases the gravity signal related to crustal structure is isolated by applying 3 different corrections: topography, sediments, and upper mantle structure. Of these three, the upper mantle correction is least well addressed. It doesn’t account for any lateral inhomogeneity upper mantle composition close to the crust-mantle boundary. As a result, satellite gravity data reductions for upper mantle structure are a source of uncertainty.

Our new model includes a new state-of-the-art upper mantle correction. By combining satellite gravity and seismic tomography, we have formulated a new methodology to integrate potential field data inversions, tomographic modelling, and petrolophysics into a single inversion scheme. Our crustal thickness model ECM24 has therefore more accurate crustal thickness values, is seismically fitting better than previous models, and is also very consistent with gravity observations.

How to cite: Lu, B., van der Meijde, M., Fadel, I., Reguzzoni, M., Rossi, L., Sampietro, D., Cammarano, F., and Julia, J.: A new global crust model: ECM24, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9487, https://doi.org/10.5194/egusphere-egu24-9487, 2024.

EGU24-9631 | Posters on site | GD6.1

European and Siberian lithospheric thermo-chemical heterogeneity and density structure. 

Alexey Shulgin and Irina Artemieva

We present a new combined model for the density structure of the lithospheric upper mantle beneath Europe and Siberia, based on a 3D tesseroid gravity modeling. Our results are based on the EuNaRho model (Shulgin & Artemieva, 2019) complimented by similar modeling approach for Siberia. For Siberia modeling is preformed based on a detailed crustal structural database SibCrust (Cherepanova et al., 2013) constrained by regional seismic data. The presented residual lithospheric mantle gravity anomalies are derived by removing the 3D gravitational effect of the crust. Later, these anomalies are converted to lithosphere mantle in situ densities. To evaluate chemical heterogeneities of the lithospheric mantle, thermal effects are removed based on the global continental thermal model TC1 (Artemieva, 2006). The resulting density model at SPT conditions shows a highly heterogeneous structure of the cratonic lithospheric mantle, and distinct change at the transition between different tectonic units. We speculate on the origin of these anomalies.

How to cite: Shulgin, A. and Artemieva, I.: European and Siberian lithospheric thermo-chemical heterogeneity and density structure., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9631, https://doi.org/10.5194/egusphere-egu24-9631, 2024.

EGU24-9813 | Orals | GD6.1

Seismic evidence favoring depletion of Precambrian lithosphere and partial melt at the base of tectonic plates 

Eric Debayle, Yanick Ricard, Durand Stéphanie, and Thomas Bodin

Most global tomographic studies of the upper mantle and their thermochemical interpretations have focused on shear velocity (Vs). Shear attenuation has a different sensitivity to temperature, composition and melt content and therefore provides complementary constraints on the origin of seismic heterogeneities. In the upper mantle, shear attenuation is negligibly dependent on major element chemistry and exponentially dependent on temperature.

Here, we first simultaneously interpret two recent global Vs and Qs models, which are obtained from the same Rayleigh-wave dataset, at the same resolution and using the same modelling approach. Comparison with mineralogical data suggests that partial melt occurs within the LVZ and down to 150–200 km beneath mid-ocean ridges, major hotspots and back-arc regions. A small part of this melt (less than 0.3%) remains trapped within the oceanic LVZ.

Melt is mostly absent under continental regions. In these regions, we observe high seismic velocity keels extending to depths that often exceed 200 km. The thermochemical interpretation of our global shear velocity models requires mineralogical depletion and a decrease of compositional density beneath Precambrian cratons. These conditions ensure their preservation for billions of years in a convective mantle, in agreement with mantle xenoliths suggesting that high viscous keels formed early in the history of cratons.

 

How to cite: Debayle, E., Ricard, Y., Stéphanie, D., and Bodin, T.: Seismic evidence favoring depletion of Precambrian lithosphere and partial melt at the base of tectonic plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9813, https://doi.org/10.5194/egusphere-egu24-9813, 2024.

EGU24-9864 | Orals | GD6.1

Effects of variations in density and effective viscosity of the mantle lithosphere on the distribution of intraplate earthquakes in western and central Europe  

Judith Bott, Magdalena Scheck-Wenderoth, Ajay Kumar, Mauro Cacace, Sebastian Noe, and Jan Inge Faleide

The distribution of seismicity in intracontinental western and central Europe is not well understood despite evidence for tectonic forces and glacial isostatic adjustments to partially affect local stress and strain relationships. Our region of interest, located between the northern Alpine Deformation Front and the southwestern margin of Fennoscandia, is well differentiated into seismically quiet domains (e.g., most of Ireland, the southern North Sea and the Paris Basin region) and elongated zones of increased seismicity, such as across mainland Britain and the European Cenozoic Rift System. Some inherited zones of crustal weakness have been suggested to control the observed clustering of active deformation, but the majority of earthquakes in the region cannot unequivocally be mapped to specific crustal discontinuities. To investigate potential effects of upper mantle heterogeneities on the lateral distribution of earthquakes across stable western and central Europe, we have derived thermal field variations from a continent-scale tomographic shear-wave velocity model by using a Gibbs's free energy minimization approach. This way we find that seismicity in this intraplate region is largely limited to areas that exhibit a temperature-controlled low-density layer in the uppermost lithospheric mantle and preferentially clustered above large lateral gradients in upper mantle effective viscosity. We propose that the spatial correlations between mantle low-density bodies and crustal seismicity reflect gravitational instabilities due to buoyancy forces within the mantle lithosphere. In addition, lateral contrasts in temperature and related effective viscosity seem to foster localized deformation within the shallow mantle which imposes differential loading of the overlying crust and earthquake clustering.

How to cite: Bott, J., Scheck-Wenderoth, M., Kumar, A., Cacace, M., Noe, S., and Faleide, J. I.: Effects of variations in density and effective viscosity of the mantle lithosphere on the distribution of intraplate earthquakes in western and central Europe , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9864, https://doi.org/10.5194/egusphere-egu24-9864, 2024.

EGU24-11165 | Posters on site | GD6.1

Cratons are not all that stable! 

Hans Thybo

Cratons are usually considered ‘old and stable’ geological units and, therefore, the do not receive as much consideration by geophysical data acquisition as active tectonic regions. However, abundant evidence shows that ‘stable’ cratons are modified substantially during their existence as demonstrated by geophysical data imaging cratonic lithosphere in several cases:

(1) The Baltic Shield formed during the Svecofennian orogeny c. 1.7 Ga and its western parts were reworked by the Sveconorwegian/Grenvillian orogeny. Recent geophysical interpretations image a large body of crustal material in eclogite facies beneath the present Moho in the central shield. This body probably formed after the initial cratonization (Buntin et al., 2021).

(2) The isopycnicity hypothesis proposes that a trade-off between composition and temperature of the lithospheric mantle maintains constant topography in cratons (Jordan, 1978) based on kimberlite data from South Africa. However, gravity data from Siberia shows that kimberlite pipes solely modify cratons in isostatic equilibrium (Artemieva et al., 2019). Therefore, kimberlite sampling is nonrepresentative, and the real composition of most cratonic mantle lithosphere is unknown.

(3) Strong seismic anisotropy is observed in many cratons and is commonly attributed to the mantle due to frozen-in lithospheric features or asthenospheric flow. Recently it was demonstrated that a major part of the anisotropy resides in the crust of the Kalahara craton and that the fast axes are parallel to the strike of major dyke swarms and orogenic fabric (Thybo et al., 2019). This finding indicates significant craton modification by magmatic intrusion.

(4) Modification by external stresses and induced magmatism may even split existing cratons.  Integrated interpretation of existing data and geodynamic modelling show that a linear sequence of volcanic harrats in the Arabian craton potentially represents the formation of a new plate boundary (Artemieva et al., 2022). It is probable that the extension in the northern Red Sea rift will jump to the volcanic lineament, which eventually will develop into new ocean spreading and effectively split the existing craton.

References

Artemieva, I.M.., Thybo, H. & Cherepanova, Y, 2019. Isopycnicity of cratonic mantle restricted to kimberlite provinces. Earth Plan. Sci. Lett. 505, 13-19, doi:10.1016/j.epsl.2018.09.034 (2019).

Artemieva, I.M., Yang, H., Thybo, H. Incipient ocean spreading beneath the Arabian shield, Earth-Science Reviews, 226, 103955 (2022)

Buntin, S., Artemieva, I.M., Malehmir, A., Thybo, H. et al. Long-lived Paleoproterozoic eclogitic lower crust. Nat Commun 12, 6553 (2021).

Jordan, T. Composition and development of the continental tectosphere. Nature 274, 544–548 (1978)

Thybo, H., Youssof, M. & Artemieva, I.M. Southern Africa crustal anisotropy reveals coupled crust-mantle evolution for over 2 billion years. Nat Commun. 10, 5445 (2019)

How to cite: Thybo, H.: Cratons are not all that stable!, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11165, https://doi.org/10.5194/egusphere-egu24-11165, 2024.

Sedimentary and crustal thickness constraints are important for a wide range of geological and geophysical applications, including: a) measuring dynamic topography; b) calculating heat flow; c) generating seismic tomographic models; d) improving predictions of resource distribution; and e) accurately assessing seismic hazards. In this contribution, we present the methodology and preliminary results of an ongoing study to improve sedimentary and crustal thickness constraints in the continental realm. Active-source seismic experiments and well data provide high-accuracy constraints for total sedimentary thickness. Interpolation between sedimentary thickness measurements is undertaken using a minimum curvature gridding algorithm. We investigate the impact of varying the grid resolution across a range of sedimentary basins, and demonstrate that a high-resolution grid (e.g., ~ 0.03 degrees) is crucial in order to capture lateral heterogeneity. We define crustal thickness as the vertical distance between the base of the sediment (i.e. top basement) and the Moho. Our new sedimentary thickness estimates constrain the top basement while measurements from a new publication of active- and passive-source seismic data are used to constrain Moho depth. Resulting crustal thickness estimates show relatively thin crust beneath a number of continental sedimentary basins. We investigate whether our new estimates of sedimentary and crustal thickness can improve predictions of surface heat flow. Our results demonstrate that constraints of the outermost layers of the Earth are important for understanding the interaction between crust, lithosphere and asthenospheric mantle.

How to cite: Holdt, M. and White, N.: Global Sedimentary and Crustal Thickness Constraints: Implications for Lithosphere-Asthenosphere Dynamics., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11624, https://doi.org/10.5194/egusphere-egu24-11624, 2024.

EGU24-12307 | Orals | GD6.1 | Highlight

Broad variability in craton reworking 

Irina M. Artemieva

Cratons are commonly considered as stable parts of continents that can survive a long-term interaction with mantle convective instabilities, basal drag and plate tectonic processes. However, geochemical evidence, geophysical observations and numerical modeling question their long-term stability and suggest heterogeneous modification with possible partial destruction of cratonic lithosphere. Cratonic modification may be identified either from a significant reduction in lithospheric thickness or from densification of cratonic lithospheric mantle e.g. through melt-metasomatism. Both characteristics can be identified through geophysical modeling, such as joint interpretation of thermal and gravity data. The examples from the cratons of Eurasia, South Africa, Greenland and Antarctica demonstrate various degrees of lithosphere reworking by mantle convection and plate tectonics processes. Sharp lithosphere thinning across Greenland possibly marks the Iceland plume passage (10.1016/j.earscirev.2018.10.015) which can hardly be identified from seismic observations (10.1029/2018JB017025). In contrast, the cratonic Siberian LIP region preserves a thick lithosphere, but with a fertile mantle (10.1016/j.epsl.2018.09.034). Similarly thick but fertile lithosphere is present below the southern Africa cratons (10.1016/j.gr.2016.03.002, 10.1016/j.gr.2016.05.002) and in parts of the North China craton (10.1029/2020JB020296), where spatially limited geochemical data have earlier been interpreted as lithosphere destruction by the Mesozoic Pacific plate subduction. Indeed, the lithosphere of West Antarctica has been essentially destroyed by the Mesozoic Phoenix plate subduction, most likely in the back-arc settings (10.1016/j.earscirev.2020.103106). In contrast, the India plate subduction produced heterogeneous pattern in lithosphere thinning below Tibet (10.1029/2022JB026213). Continental regions, typically considered to be stable cratons, may have also essentially lost their cratonic signature, such as cratonic East Antarctica (10.1016/j.earscirev.2022.103954) and the East European craton with strong variations in both lithosphere thickness (10.1016/j.earscirev.2018.11.004) and mantle density (10.1029/2018JB017025). The observed broad variability in the present-day cratonic lithosphere structure precludes unique interpretations of past interactions of the cratons with mantle convection and plate tectonics processes, and indicates the existence of various types and multiple phases of such interactions, controlled by lithosphere rheology.

How to cite: Artemieva, I. M.: Broad variability in craton reworking, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12307, https://doi.org/10.5194/egusphere-egu24-12307, 2024.

EGU24-12342 | Orals | GD6.1

Deformation of Western Anatolia under the effect of the Hellenic Trench and the North Anatolian Fault 

Tülay Kaya-Eken, Akinori Hashima, and Haluk Özener

The Anatolian Plate, surrounded by the Eurasian, African and Arabian plates, represents a great laboratory for geoscientists with its all complicated tectonic settings. The region is located at a widely spread active tectonic deformation zone that has primarily been controlled by the African plate subduction beneath the Hellenic Trench and the movement of the North Anatolian Fault Zone (NAFZ). The effect of crustal thinning due to the extensional regime gave rise to the formations of horst and graben systems leading to large earthquakes (e.g. The Mw7.0 2020 Samos earthquake) with normal faulting mechanisms in western Türkiye. A precise evaluation of tectonic deformation process and the potential seismic risk in this area requires a comprehensive understanding of the quantitative impact of both the Hellenic subduction and the NAFZ to the surface movement. To distinguish these individual contributions, we examine the published regional GPS data along Greece-Türkiye region. Considering a basic elastic-viscoelastic layered earth model, our first step is to estimate the contribution of the NAFZ to the GPS velocity at each station under various average slip rare conditions. We then perform an inversion on the residual velocities obtained by subtracting the calculated velocity from the observed data. This inversion allows us to derive the subduction rate along the Hellenic Trench. Our modelling indicates an optimal slip rate of <35 mm/yr that identifies the NAF zone and an average subduction rate of about 40 mm/yr for the the Hellenic Trench. These results suggest the significance of both the Hellenic Trench slab rollback and the NAFZ movement highlighting their essential roles in the observed deformation beneath this region.

How to cite: Kaya-Eken, T., Hashima, A., and Özener, H.: Deformation of Western Anatolia under the effect of the Hellenic Trench and the North Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12342, https://doi.org/10.5194/egusphere-egu24-12342, 2024.

EGU24-13677 | Posters on site | GD6.1

Lithospheric Structure beneath Northeastern Tibet Plateau and Sichuan Basin revealed by S-Receiver Function Imaging  

Yaoyang Zhang, Ling Chen, Yinshuang Ai, Hui Fang, and Gang Wang

    Based on the seismic data of 60 portable stations and 90 permanent CEA stations in the northeastern Tibet Plateau and adjacent regions, we utilized the wave equation post-stack migration method of S-receiver function to image the lithospheric structure of northeastern Tibet Plateau and the Sichuan Basin.

Fig. 1 Distribution of the seismic stations and imaging profile

    The imaging results show that the Moho in the northeastern Tibet Plateau is deeper than 50 km, and it gradually becomes shallow along the profile to the southeast until reaches about 45 km below the Sichuan Basin. The negative anomaly signals corresponding to the Lithosphere and Austhenosphee Boundry (LAB) are obvious in most areas, but under the Sichuan Basin, there are many strong negative anomaly signals in the migration images of different frequencies. In general, the LAB along the profile is undulating and discontinuous: The lithosphere is deeper in the southern Qilian Orogenic Belt, up to ~200 km, with no significant change at the boundary between the Qilian Orogenic Belt and the western Qinling Orogenic Belt. The lithosphere gradually thinned to ~150 km beneath the western Qinling Orogenic Belt, with a step of ~100 km at the tectonic boundary between the Qinling Orogenic Belt and the Songpan-Garze block, and the signal intensity is obviously weakened. LAB was maintained at this depth level until near the Longmenshan Fault, and the lithosphere thickened again to ~190 km after entering the Sichuan Basin. Moreover, there are two discontinuities within the lithosphere of the Sichuan Basin, with depths of ~100 km and ~140 km, respectively, and the latter becomes shallower to ~110 km in the western margin of the Sichuan Basin. Our observations of mid-lithospherci discontinuity (MLD) beneath the Sichuan Basin provide further evidence that the cratonic lithospheric mantle is generally stratified.

Fig. 2 The migration results of the profile

    It is proposed that the lithospheric thinning along the eastern margin of the Songpan-Garze Block may be related to the eastward flow of hot mantle materials beneath the eastern Tibet Plateau. Blocked by the Ordos block and the Sichuan Basin, which have preserved the ancient and rigid craton roots, the eastward flow of mantle materials from the Tibet Plateau will turn to the west of the two blocks. A small part of the blocked mantle material migrates eastward to the Qinling Orogenic Belt, while most of it migrates southward clockwise along the mantle flow path to the west of the Sichuan Basin. The lithosphere in the eastern margin of the Songpan-Garze block, heated by the mantle flow, will be subjected to thermochemical erosion and destruction in the process of collision with the Yangtze craton, and is more likely to be delaminated, resulting in significant thinning and destruction under long-term action.

How to cite: Zhang, Y., Chen, L., Ai, Y., Fang, H., and Wang, G.: Lithospheric Structure beneath Northeastern Tibet Plateau and Sichuan Basin revealed by S-Receiver Function Imaging , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13677, https://doi.org/10.5194/egusphere-egu24-13677, 2024.

EGU24-14107 | ECS | Orals | GD6.1

Deformation of the northeastern Tibetan Plateau and adjacent areas: Evidence from MT array data 

Haoxiang Yin, Sheng Jin, and Gaofeng Ye*

The uplift and growth of the Tibetan Plateau is an essential geologic issue. The closure of the Neo-Tethys Ocean and northward subduction of the Indian Plate formed the Tibetan Plateau and influenced the strain on its northeastern margin. We obtained the lithospheric electrical structure by inversion of MT array data collected at the Alxa and Ordos blocks neighboring the northeastern Tibetan Plateau. It shows the Ordos Block has noticeable electrical differences between the north and south parts. The northern lower crust to the upper mantle characterized large-scale low-resistivity anomaly, while the south is a stable craton block. The retreat of the Paleo-Pacific Plate caused the North China Craton to be in a tensional environment. With the northward subduction of the Indian lithosphere, the Tibetan Plateau continues to grow in a northeastern direction, resulting in an intensification of the subduction of the Alxa Block to the Ordos Block, and the north Ordos Block was pried up and in a weak state. The Asian asthenosphere became active under the influence of Indian lithospheric subduction. It jumped over the rigid Alxa and southern Ordos blocks to deform the northern part of the Ordos Block and form the large-scale partial melting. Since partial melt is more viscous than rigid blocks, it better equilibrates crustal deformation, resulting in flatter topography.

How to cite: Yin, H., Jin, S., and Ye*, G.: Deformation of the northeastern Tibetan Plateau and adjacent areas: Evidence from MT array data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14107, https://doi.org/10.5194/egusphere-egu24-14107, 2024.

The thermal state of the Earth’s interior is a key factor in controlling various geological processes. However, our knowledge of the geotherm and its temporal and spatial variability is usually poorly constrained, as it is typically based on point-wise data. Specifically, for the lower continental crust (LCC), data on rock’s thermal properties are scarce, and therefore temperature estimates are uncertain.

 

We collect new data and provide new insights in this domain, realized in the frame of project DIVE (Drilling the Ivrea-Verbano zonE; www.dive2ivrea.org), which aims at a better understanding of the physical and chemical evolution and formation of the LCC. The first borehole in Ornavasso (DT-1B) has been successfully completed and reached a depth of 578.5 m with 100% core recovery; it provides continuous drill cores of mainly felsic metasedimentary and metamafic lithologies. The second borehole in Megolo di Mezzo (DT-1A) is ongoing and planned to be completed in Spring 2024.

 

The first results on the thermal characterization of lower crustal rocks are based on 17 fresh cores from DT-1B, sampling all the lithologies present in the borehole. We performed continuous, high-resolution (2 mm) thermal conductivity (TC) measurements using an Optical TC Scanner (Popov et al., 1999), profiling over 10 metres of rock cores in total. Our results show that TC can exhibit large variations even within a given lithology, as a result of mineralogical variability, indicating that this approach provides more representative results compared to conventional methods (e.g. needle-probe technique). We also measured the concentrations of heat producing elements (U, Th, K) using powder-based gamma spectrometry, and use (spectral) gamma borehole logs to evaluate the variability of heat production (A) in the borehole. The correlation of both TC and A with other petrophysical properties is analyzed.

 

Based on the new measurements, we investigate the consequences on LCC geotherms. The small-scale TC variations affect heat flow calculations and have implications for their uncertainty. These are quantified through model calculations as part of an upscaling procedure employing harmonic averaging. We aim to quantify the effect of continuous TC profiling and how our approach influences the level of uncertainties by applying many realizations of heat flow calculations. The probability distribution of heat flow can be determined by using Bullard’s approach (Bullard 1939; Beardsmore & Cull, 2001) and by randomly selecting rock’s thermal property data while calculating the geotherm. Further samples from DT-1B and a new set of samples from DT-1A will provide a representative dataset for the LCC.

 

 

References

 

Beardsmore, G. R. (Graeme R., & Cull, J. P. (James P. (2001). Crustal heat flow: a guide to measurement and modelling. Cambridge University Press.

 

Bullard, R. (1939). Heat flow in South Africa. Mon. Not. R. Astr. Soc., Geophys, 173, 229–248.

 

Popov, Y. A., Pribnow, D. C., Sass, J. H., Williams, C. F., & Burkhardt, H. (1999). Characterization of rock thermal conductivity by high-resolution optical scanning. Geothermics, 28(2), 253–276.

How to cite: Lemke, K. and Hetényi, G.: Thermal characterization of the lower continental crust: first results from the DT-1B borehole of project DIVE (Ivrea-Verbano zone, Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14356, https://doi.org/10.5194/egusphere-egu24-14356, 2024.

EGU24-14363 | Posters on site | GD6.1

Crustal S-wave 3D azimuthal anisotropy beneath the southern Sichuan-Yunnan block of SW China from multiple seismic arrays 

Yuan Gao, Ying Li, Huajian Yao, Jianhui Tian, Yuanyuan V Fu, and Qiong Wang

The southern Sichuan-Yunnan block (SYB) is intersected by the NW-striking Honghe faults (HHF) and the nearly NS-trending Xiaojiang faults (XJF), providing an excellent zone for exploring severe crustal deformation and complicated tectonic movement. However, the crustal-mantle deformation mechanisms are still controversial, partially due to the lack of detailed information. With ambient noise data from several temporary seismic arrays and regional permanent seismic stations, we applied the direct surface wave tomography to obtain S-wave velocity and azimuthal anisotropy simultaneously. The crustal S-wave structures show complex heterogeneity both horizontally and vertically, relating to geologic settings and large faults. In the mid-lower crust, there are two significant low-velocity anomalies with strong azimuthal anisotropy, with the NNW-SSE direction near the northwest end of HHF and the NE-SW direction around the mid-south segment of XJF, respectively. The fast axis within the SYB shows approximately in the N-S direction, which differs from those in the low-velocity zones on its east and west sides. Therefore, we consider the ductile deformation in the mid-lower crust is more likely restricted by large faults. At the end of the wedged intersection, the southward mid-lower crustal flow could be blocked by the HHF, resulting in the weak materials distributed along the faults rather than crossing over at large-scale. Combining other independent studies, we conclude that there may be different deformation between the crust and the lithospheric mantle. This 3-D model provides important constraints for the regional deformations and plate tectonics of the large boundary faults [supported by NSFC Projects 42074065 & 41730212].

How to cite: Gao, Y., Li, Y., Yao, H., Tian, J., Fu, Y. V., and Wang, Q.: Crustal S-wave 3D azimuthal anisotropy beneath the southern Sichuan-Yunnan block of SW China from multiple seismic arrays, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14363, https://doi.org/10.5194/egusphere-egu24-14363, 2024.

EGU24-15642 | Posters on site | GD6.1

Tectono-metamorphic interaction between the upper mantle and lower crust during continental rifting in the western Betic Cordillera 

Károly Hidas, Juan Díaz-Alvarado, Luis González-Menéndez, Antonio Azor, and Antonio Pedrera

Recent geological mapping in the Ronda peridotites (Betic Cordillera, S Spain) has unveiled a consistent field correlation between lower crustal metamorphic units and specific tectono-metamorphic domains of the ultramafic massif. Mylonitic and highly tectonized spinel ±garnet peridotites (i.e., Grt-Spl mylonite and Spl tectonite domains) –that are considered to originate from a thick continental lithosphere– are in contact with garnet-bearing gneisses (i.e., kinzigites of the Jubrique unit) along a narrow but continuous mylonitic shear zone. Phase equilibrium calculations indicate that these metamorphic rocks align with an initial continental setting characterized by normal crustal thicknesses, which underwent two melting events. The first melting occurred at the base of the lower crust, while the second one took place at shallower crustal conditions and led to a more restricted melt production. By contrast, the spinel ±plagioclase peridotites (i.e., Pl-tectonite domain) –that are stable only at shallowest mantle levels within a highly extended continental lithosphere– are consistently found exposed in contact with heterogeneous granites and migmatites that form part of the Guadaiza crustal unit. According to new thermodynamic modeling, this migmatitic series record a single melting event characterized by a moderate melt production at the base of an extremely thin continental crust. The systematic correlation observed between the crustal metamorphic units and specific ultramafic domains of the Ronda peridotites –consistently overlaying the mantle rocks– indicates that their juxtaposition primarily resulted from the severe extension of the continental lithosphere.

Previous and new U-Pb radiometric dating of zircons from gneisses, migmatites, and heterogeneous granites show that extensional processes, crustal anatexis, and melt stagnation occurred at around 280 Ma. Considering the structural position and correlation between mantle and crustal rocks, these radiometric ages suggest that a Permian high-temperature / low- to medium-pressure event uniformly affected the crustal units over the Ronda peridotites. This event coincided with the formation of characteristic ultramafic mineral assemblages in the Ronda massif, providing evidence for the interaction between upper mantle rocks and lower- to mid-crustal metamorphic rocks during that period.

This research received funding from the Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación (AEI, MICINN, Spain) under the grant no. PID2020-119651RB-I00/AEI/10.13039/501100011033.

How to cite: Hidas, K., Díaz-Alvarado, J., González-Menéndez, L., Azor, A., and Pedrera, A.: Tectono-metamorphic interaction between the upper mantle and lower crust during continental rifting in the western Betic Cordillera, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15642, https://doi.org/10.5194/egusphere-egu24-15642, 2024.

EGU24-17843 | Orals | GD6.1

Detached Tonga slab in the mantle transition zone imaged by stress variations of deep-focus earthquakes 

Pavla Hrubcová, Ghazaal Rastjoo, and Václav Vavryčuk

Tonga is a part of Tonga-Kermadec, the 2,550 km long subduction system in SW Pacific. It represents a convergent plate boundary and the outcome of the Pacific plate submerging underneath the Australian plate. The Tonga slab subducts steeply into the mantle and is the fastest converging and the most seismically active deep subduction system in the world. In the mantle transition zone, especially at depths greater than 500 km, the geometry of the slab becomes complex, forming separated slab segments. Moreover, it undergoes strong deformation and sharp bending in the north, which results in significantly different course of the southern and northern Tonga slab.

We focused on the mantle transition zone in the southern part of Tonga (south of latitude 22°S). We performed stress analysis by inverting focal mechanisms of deep earthquakes available in the Global Centroid Moment Tensor catalog. We focused on depths ranging from 400 to 680 km, where seismic activity forms two subparallel bands of events, in the west and east. We revealed two distinct stress regimes that characterize this deep Tonga double seismic zone and distinguish two slab segments. The stress orientation in the eastern slab segment matches the down-dip compressional stress regime of the subducting slab. However, the stress orientation of the western slab segment is different, with the maximum compression in the vertical direction. This suggests that the western slab segment is no longer connected to the subducting slab. Such findings are also supported by the horizontal westward detachment of the western slab segment at 520 km depth and by substantially different fault orientations in both slab segments. This points not only to the retention of the southern Tonga slab in the mantle transition zone but also to its detachment at the base of the upper mantle with a remnant slab no longer connected to the younger actively subducting slab.

How to cite: Hrubcová, P., Rastjoo, G., and Vavryčuk, V.: Detached Tonga slab in the mantle transition zone imaged by stress variations of deep-focus earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17843, https://doi.org/10.5194/egusphere-egu24-17843, 2024.

EGU24-17947 | ECS | Posters on site | GD6.1

Multi-scale Potential Field Modelling to Delineate the Lithosphere Structure below the Eastern Indian Shield and its Tectonic Implications   

Sumanta Kumar Sathapathy, Munukutla Radhakrishna, and Yellalacheruvu Giri

The Precambrian terrains of the Eastern Indian Shield (EIS) comprise of Bundelkhand, Singhbhum, and Bastar cratons with intervening Proterozoic mobile belts such as Central Indian Tectonic Zone, Eastern Ghat Mobile Belt, Singhbhum Mobile Belt and Chotanagpur Granite Gneissic Complex. This region is also characterised by the presence of Proterozoic Mahanadi Rift, Chhattisgarh and Vindhyan Basins with significant coverage of Indo-Gangetic Plain sediments in northern part. In this study, we present the results of a seismically well-constrained 2-D multi-scale geopotential modelling to delineate lithosphere structure across different Precambrian terrains of the EIS. The joint interpretation of the potential field data reveals that i) mobile belts are bounded by the deep crustal faults with denser crust, ii) presence of thick underplated crust below Singhbhum craton, Singhbhum Mobile Belt, Chotanagpur Granite Gneissic Complex and the surrounding rift basin, iii) localised Moho upwarp at a depth of ~36-37 km below the Proterozoic basins, iv) the Lithosphere-Asthenosphere Boundary (LAB) varying between 90-200 km below the EIS region. The distinct crustal structure along with relatively deeper LAB (130-200 km) below the mobile belts suggests the Proterozoic amalgamation and lithosphere reworking. Below the Singhbhum craton, LAB is observed at a depth of ~145-155 km, which is comparatively thinner with respect to other cratonic areas elsewhere. The observed crustal underplating and thinner LAB below the Singhbhum craton indicate the lithosphere erosion and magmatic upwelling caused by the major Paleo-Mesoproterozoic and early- Cretaceous Large Igneous Province (LIP) events.  

How to cite: Sathapathy, S. K., Radhakrishna, M., and Giri, Y.: Multi-scale Potential Field Modelling to Delineate the Lithosphere Structure below the Eastern Indian Shield and its Tectonic Implications  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17947, https://doi.org/10.5194/egusphere-egu24-17947, 2024.

EGU24-18927 | Orals | GD6.1

Crustal Structure of the Lofoten Shelf, NE North Atlantic,along the Silver-Road refraction profile 

Metin Kahraman, Hans Thybo, Irina Artemieva, Alexey Shulgin, Peter Hedin, and Rolf Mjelde

The Lofoten continental shelf is located at the edge of the Baltic Shield in the northeastern North Atlantic Ocean. It was formed during continental break up in early Eocene associated with intense magmatism, leading to large intrusions and basaltic volcanic rocks now hidden below Cenozoic sediments. The Lofoten shelf is relatively narrow.

We present results of ray tracing model of seismic refraction/wide-angle reflection data along the offshore Silver Road profile across the Lofoten Shelf at the northeastern Baltic Shield. The ~300km long WNW/ESE trending offshore section between 63oN and 71oN profile is perpendicular to the coastline and extends a ~300km onshore section. Wide-angle seismic data obtained from air gun shots from the vessel Hakon Mosby along the whole offshore profile were recorded by 16 ocean bottom seismometers on the shelf, slope and oceanic environment as well as by 270 onshore seismic stations.

The new offshore crustal velocity - depth model covers the anomalous and heterogeneous transition from shelf to oceanic lithosphere around the North Atlantic Ocean. The results will test existence of crustal root and magmatic intrusions along the offshore profile.

How to cite: Kahraman, M., Thybo, H., Artemieva, I., Shulgin, A., Hedin, P., and Mjelde, R.: Crustal Structure of the Lofoten Shelf, NE North Atlantic,along the Silver-Road refraction profile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18927, https://doi.org/10.5194/egusphere-egu24-18927, 2024.

The faceting behaviour of olivine controls many properties on the grain surface such as diffusion and storage.  This behaviour and its effects are poorly understood due to the difficulty of examining them and the many controls that are on this paper.  In this talk I shall present a thermodynamic model of olivine faceting and how it is controlled by temperature, pressure, iron, grain size and water content.  In turn I shall discuss how this faceting then controls other important properties such as storage of water on the grain boundaries and how these are perhaps an overlooked sink in the Earth’s mantle.

How to cite: Muir, J.: Olivine faceting and water storage: A complex dynamic anisotropic sink, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2395, https://doi.org/10.5194/egusphere-egu24-2395, 2024.

A connected set of singularity points is called the singularity line. Along this line, the slowness surfaces (or phase velocity surfaces) of different wave modes coincide. For anisotropic models, the singularity lines are mostly known in transversely isotropic media (Crampin and Yedlin, 1981). Recently, it was shown that they also can be defined in the special types of orthorhombic media: degenerate (Stovas et al, 2023b) and pathological (Stovas et al, 2023a). Singularity line can also exist in the low symmetry anisotropic models, monoclinic and triclinic (Khatkevich, 1963; Vavrycuk, 2005; Roganov et al, 2019).

In this paper, we focus on singularity lines in monoclinic media with a horizontal symmetry plane. We define the singularity lines in all coordinate planes, and in vertical planes of arbitrary azimuthal orientation. Since the monoclinic anisotropic model can be considered as the transversely isotropic medium with a vertical symmetry axis being perturbed with the multiple azimuthally non-invariant fracture sets, identification of singularity lines can give additional constraints in inversion of seismic data for fracture prediction. The singularity lines being converted into the group velocity domain results in continuous bands in the group velocity surface (traveltime surface) shaping the lacunas for S1 wave and internal refraction cones for S2 wave associated with strong anomalies in wave amplitudes.

The singularity directions satisfy the following polynomial equations (Alshits, 2004; Roganov et al., 2019), , where  are the third-order polynomials given by the elements of the Christoffel matrix. Resolving this system of equations, we define the conditions (in terms of stiffness coefficients) for existence of singularity lines in vertical planes. The Sylvester criterion is applied to control the physical realizable model. Mostly, the obtained models have singularity lines formed by S1 and S2 waves, while one model has singularity line composed of S1S2 and PS1 legs connected by the triple PS1S2 singularity point.

 

 

References

Alshits, V.I., 2004, On the role of anisotropy in crystalloacoustics, In: Goldstein R.V., Maugin G.A. (eds) Surface Waves in Anisotropic and Laminated Bodies and Defects Detection. NATO Science Series II: Mathematics, Physics and Chemistry, vol 163. Springer, Dordrecht.

Crampin, S., and M. Yedlin, 1981, Shear-wave singularities of wave propagation in anisotropic media, J. Geophys., 49, 43–46.

Khatkevich, A.G., 1963 Acoustic axes in crystals, Sov. Phys. Crystallogr. 7, 601–604.

Stovas, A., Roganov, Yu., and V. Roganov, 2023a, On pathological orthorhombic models, Geophysical Prospecting, 71(8), 1523- 1539.                                                                    

Stovas, A., Roganov, Yu., and V. Roganov, 2023b, Degenerate orthorhombic models, Geophysical Journal International, accepted for publication.                  Roganov, Yu., Stovas, A., and V. Roganov, 2019, Properties of acoustic axes in triclinic media, Geophysical Journal, 41(3), 3-17.                                                    Vavrycuk, V., 2005, Acoustic axes in triclinic anisotropy, The Journal of the Acoustical Society of America 118, 647-653.

How to cite: Stovas, A.: Singularity lines for monoclinic media with a horizontal symmetry plane, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2468, https://doi.org/10.5194/egusphere-egu24-2468, 2024.

How continental plate boundary faults develop with depth has been under debate. We inverted SKS shear wave splitting data along the San Andreas Fault (SAF) into two layers of anisotropy using a Bayesian inversion. While the two layers are statistically required, the fast polarization directions of the upper layer do not match the strike of the SAF as previously reported. To capture the lithospheric shear zone, we progressively decrease the upper limit of the delay time of the upper layer. In northern California where SAF strikes 140-150, the upper layer fast directions get close to these azimuths when the delay time is reduced to ~0.5 s. In southern California where the SAF strikes 120-130, the upper layer fast directions capture the SAF with delay times of a similar magnitude. For olivine LPO with vertical shear plane, these delay times translate to a anisotropy layer of 40 km thickness, or a depth of 70 km from the surface, assuming the seismogenic zone in the crust is too localized to influence the SKS splitting. This depth coincides with the depth of lithosphere-asthenosphere boundary independently estimated. The lower-layer fast directions are in between the absolute plate motion directions of the American and the Pacific plates, or at least agree with that predicted from surface wave study in northern California. We picture a vertical continental shear zone widening to at least 200 km at the bottom of the lithosphere, transitioning to a horizontal shear regime in the asthenosphere driven by plate motions. This architecture of continental shear zone is consistent with our understanding of the rheology of crust and mantle.

How to cite: Kuo, B.-Y., Peng, C.-C., and Wang, P.-C.: Structures of the continental shear zone beneath the San Andreas Fault inferred from two-layer modeling of SKS splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3339, https://doi.org/10.5194/egusphere-egu24-3339, 2024.

The seismic moment tensor, which represents the equivalent body-force system of the seismic source (Backus and Mulcahy, 1973), may exhibit non-double couple components (NDCs) when the earthquake occurs on a planer fault if the source medium is anisotropic (Aki and Richards, 1981; Kawasaki and Tanimoto, 1981). Kawakatsu (1991, GRL) reported that the NDCs of the moment tensors for shallow earthquakes from the Harvard CMT catalog (Dziewonski et al.,1981; predecessor of GCMT) exhibit a systematic characteristic dependent on faulting types. Specifically, the sign of NDC on average systematically switches between normal-faulting and reverse-faulting. The average NDC parameter ε (Giardini, 1983) is negative for thrust faulting and positive for normal faulting. This behavior can be explained if the source region is transversely isotropic with a vertical symmetry axis (radially anisotropic). In fact, the transverse isotropy model of PREM at a depth of 24.4 km predicts the observed systematic NDC pattern, although the magnitude is slightly underestimated, indicating the potential to enhance our understanding of the lithospheric transverse isotropy using the NDC of the moment tensors.

To investigate the lithospheric transverse isotropy structure utilizing the NDCs of the moment tensors, we propose a novel inversion scheme, building upon the approaches employed by Vavrycuk (2004) and Li, Zheng, et al. (2018) for deep and intermediate-depth earthquakes, but with necessary modifications to address shallow sources (Kawakatsu, 1996, GJI). Synthetic tests conducted under conditions of random faulting indicate the potential to constrain the S-wave anisotropy (ξ) and the fifth parameter (ηκ; Kawakatsu, 2016, GJI). However, in realistic scenarios where a predominant stress regime influences earthquake occurrence to limit the diversity of faulting types, a significant correlation between these two parameters is anticipated, especially in regional-scale cases. Preliminary application of this method to real data sourced from the GCMT catalog suggests that the lithospheric transverse isotropy of PREM serves as a suitable initial model. However, some adjustments may be necessary, particularly regarding the fifth parameter, to enhance the model's fidelity in representing observed NDCs of the moment tensors.

How to cite: Kawakatsu, H.: Characterizing Lithospheric Transverse Isotropy via Non-double Couple Components of Moment Tensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3697, https://doi.org/10.5194/egusphere-egu24-3697, 2024.

The continental lithosphere of the Iranian plateau is complicated by a multitude of tectonic processes resulting from the convergence between the Arabian and Eurasian plates. In order to investigate the deformation mechanisms of the uppermost mantle, this study presents a radial anisotropy model beneath the Iranian Plateau constructed by long period (10-100 s) Rayleigh and Love waves from ambient noise data. The broadband Rayleigh and Love signals are extracted from continuous data recorded by 88 seismic stations using a double-beamforming algorithm. Due to utilizing long period surface waves, we apply finite-frequency ambient noise tomography to generate two-dimensional dispersion maps. These phase velocity maps are consistent with those obtained from conventional methods. Finally, we invert Rayleigh and Love local phase velocity dispersion curves using a Bayesian Markov chain Monte Carlo inversion method. The obtained radial anisotropy model shows negative values in Central Iran suggesting a horizontal character of the minerals likely due to a channelized asthenospheric flow in the upper mantle.

How to cite: Movaghari, R. and Yang, Y.: Uppermost mantle radial anisotropy based on double-beamforming of ambient noise cross correlation beneath Iranian plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3769, https://doi.org/10.5194/egusphere-egu24-3769, 2024.

Complex tectonics and significant crustal anisotropy are observed at the intersection of the Red River Fault (RRF) and the Xiaojiang Fault (XJF) in the southern Sichuan-Yunnan block, in the SE Tibetan Plateau. The fast S polarization of upper crustal anisotropy varies from NW-SE in the west to NE-SW in the east near the Yimen region. However, small-scale anisotropic structures remain challenging due to limited measurements. Using two years of seismic data from the temporary linear HX Array and permanent stations, this study employed machine learning to construct a high-precision earthquake catalog for S-wave splitting, revealing the upper crustal anisotropy. The new catalog has nearly twice as many earthquakes as the China Earthquake Networks Center. The seismicity is concentrated in the Yimen region with various strike-slip faults, which has a strong correlation with high- and low-velocity boundaries, especially near the edge of the low-velocity zone. Spatial variations in upper crustal anisotropy along the HX Array correspond to geological structures and regional stress. Despite a dominant NE-SW PFS (i.e., fast S-wave polarization) in the Yimen region, stations show dual dominant directions with high values of DTS (i.e., delay times between split S-waves), indicating intricate tectonic and stress interactions. The middle segment of the RRF shows significantly lower DTS values than either side, along with a vertically distributed earthquake swarm, possibly indicating locked structures with high seismic hazard. A comparison between the upper and whole crustal anisotropy reveals consistent deformation within blocks and nearly orthogonal deformation near the RRF and the XJF. The boundary faults likely play a crucial role in influencing the crustal anisotropy both horizontally and vertically. The faults like the Shiping-Jianshui and the Puduhe, running parallel to the RRF and the XJF, are believed to affect the crustal structure. This study highlights that microseismic detection enhances earthquake catalog completeness, providing insights into detailed structures [supported by NSFC Projects 42074065 & 41730212].

How to cite: Li, Y., Gao, Y., and Tian, J.: Microseismic records based on machine-learning reveal the crustal anisotropy beneath the southern Sichuan-Yunnan block in the SE Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4528, https://doi.org/10.5194/egusphere-egu24-4528, 2024.

EGU24-7126 | ECS | Posters on site | GD7.1

Seismic anisotropy of the crust and upper mantle beneath eastern Pamir 

Changhui Ju, Junmeng Zhao, Qiang Xu, and Guohui Li

The East Pamir seismic experiment (8H) was conducted in the eastern Pamir and the adjacent Tarim Basin from August 2015 to May 2017. Utilizing seismograms from the 8H network and nine permanent seismic stations operated by the China Earthquake Administration, we computed shear wave splitting parameters through cluster analysis of the minimum energy method. A total of 452 high-quality individual SKS-splitting measurements were obtained at 39 seismic stations. Given the predominant availability of events with a back-azimuth (BAZ) around ~110° and the absence of a broad range of BAZ values, we opted for a single-layer anisotropic model to interpret the measurements.

The upper mantle seismic anisotropy structure in the Western Himalayan Syntaxis (WHS) exhibits distinctive regional characteristics in various regions. Group A comprises 15 stations situated near the Alai Valley and the Tien Shan with a northeast-oriented Fast Polarization Direction (FPD), aligned with the strike of the orogen and the Absolute Plate Motion (APM) azimuthal direction (~80°) of the Eurasian plate. This group exhibits relatively larger Delay Time (DT) and may be originated from the oriented arrangement of olivine crystals in the mantle lithosphere of the Eurasian continent during the northward subduction of the Indian continent. Group B consists of 21 stations located in the eastern Pamir and adjoining Tarim Basin, demonstrating a curved orientation. While this orientation contradicts the APM direction, it approximately parallels the trend of large-scale surface structures. Combining these observations with previous imaging results, we propose that during the northward advancement of the Indian continent, mantle material flow (escape) in the Pamir-Hindu Kush region formed seismic anisotropy structures similar to those in the Western Himalayan Syntaxis (WHS).

How to cite: Ju, C., Zhao, J., Xu, Q., and Li, G.: Seismic anisotropy of the crust and upper mantle beneath eastern Pamir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7126, https://doi.org/10.5194/egusphere-egu24-7126, 2024.

EGU24-8306 | ECS | Posters on site | GD7.1

Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis 

Lin Liu, Stephen Gao, Kelly Liu, Sanzhong Li, and Youqiang Yu

In contrast to many prior studies that relied on station-averaged shear-wave splitting (SWS) measurements and sparsely distributed stations, this study takes advantage of the recent deployment of broadband seismic stations at intervals of less than 50 km to explore the intricate seismic azimuthal anisotropy between the dynamic Tibetan Plateau and the stable North China Craton. Our analysis encompasses 6,409 high-quality individual SWS measurements from 465 closely spaced stations located along the boundary of the northeastern Tibetan Plateau and the western North China Craton. Notably, twenty of these stations show splitting parameters with a π/2 periodicity based on azimuthal variations, indicating a complex double-layer horizontal anisotropy structure. The anisotropy of the upper layer is linked to ductile flow in the middle-to-lower crust originating from the Tibetan Plateau. This flow encounters the rigid lithosphere of the Alxa Block, leading to a bifurcation into northeastward and southeastward directions. The anisotropy in the lower layer, exhibiting fast orientations in an NW-SE direction, is consistent with the observed one-layered anisotropy and aligns with the absolute plate motion (APM) of the Eurasian plate. The coherence in the spatial distribution of splitting parameters indicates that the predominant source of observed anisotropy is asthenospheric flow. This mantle flow exhibits a southeastward orientation beneath the Alxa block, transitioning to an almost eastward direction along the thinner lithospheric passage between the Ordos and Sichuan cratonic keels. This pattern unveils the influence of cratonic edges in modulating localized mantle flow systems.

How to cite: Liu, L., Gao, S., Liu, K., Li, S., and Yu, Y.: Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8306, https://doi.org/10.5194/egusphere-egu24-8306, 2024.

EGU24-8694 | Orals | GD7.1

A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves  

Luděk Vecsey, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Splitting of shear waves proves their propagation within an anisotropic medium. Frequently used methods of evaluating of upper mantle anisotropy search for two parameters - the delay time of the slow split shear wave and the polarization direction of the fast split shear wave. The parameters retrieved by the standard methods such as energy minimization on the transverse component of the shear waveforms or eigenvalue of cross-correlation matrix suffer from e.g., ubiquitous noise, errors in sensor orientation and numerous so-called ‘null splits’ or unrealistically large values. However, well-resolved splitting parameters from core-mantle refracted shear SK(K)S phases are limited to relatively narrow fans of back azimuths. Such incomplete back-azimuth coverage prevents modelling anisotropic structures with symmetry axes oriented generally in 3D, i.e., with tilted axes, to be compatible with 3D anisotropic models from independent observables.  Generally used averages of time delays and polarization pairs lead to simplified models of the upper mantle, which concentrate on modelling the present-day flow in the sub-lithospheric mantle.

Therefore, we propose a new method directly exploiting variations in width and orientation of particle motion (PM) of split shear waves, which allows measuring anisotropic characteristics for a larger amount of waveforms and improves azimuthal coverage in a region. We characterize the PM by two parameters, the PM width and the PM orientation. At each station, we plot the normalized width of the PM as a ratio of lengths of the minor to major axes in dependence on back-azimuths. Variations of the PM width with back-azimuth exhibit oscillations with several extremes of different amplitudes. Such behaviour results from wave propagation through the anisotropic upper mantle. One of the advantages of the method is that the width of the PM is invariant of potential mis-orientation of sensors.

We test the PM method on a set of SKS waveforms recorded at a subset of stations included in several recent or running passive seismic experiments (EASI, AlpArray, PACASE, AdriaArray). The stations form a band of about 200km broad running from the western Bohemian Massif through the Eastern Alps to the Adriatic Sea. Stations characterized by similar variations of the PM parameters group into sub-regions, which are compatible with the main tectonic features of the whole region. The formation of such lithospheric blocks of similar anisotropic signals is in agreement with 3D self-compatible anisotropic models of the mantle lithosphere domains derived from independent observables. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows anisotropic model of the upper mantle derived from 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise.

How to cite: Vecsey, L., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8694, https://doi.org/10.5194/egusphere-egu24-8694, 2024.

EGU24-8851 | Orals | GD7.1

Constraining D" seismic anisotropy with reflections and splitting 

Christine Thomas and Angelo Pisconti

Detection of D" anisotropy is usually carried-out with shear wave splitting analysis. To constrain azimuthal anisotropy and infer mineralogy and deformation style, a number of crossing paths is necessary. Here we use an approach that utilises the polarity of P- and S- wave reflections from the D" discontinuity, compared with the main phases P and S, and combines these measurements with ScS splitting results. Using deformation scenarios for a number of lower(most) mantle candidate materials, we calculate the reflection coefficient for P and S-wave reflections and ScS splitting predictions. From our modelling, a clear distinction between different anisotropic media is possible by using both types of observations together. Furthermore, the approach allows to use only a single direction to distinguish between different scenarios. We apply the method to the Central/South Atlantic and South Africa, across the border of the large-low seismic velocity province (LLSVP). Shear wave splitting observations suggest that anisotropy is present in this region of the mantle, in agreement with previous studies that partially sampled this region. Modelling the observations with lattice preferred orientation and shape preferred orientation of materials expected in the D" region, we find two domains of mineralogy and deformation: sub-horizontally aligned post-perovskite outside the LLSVP, beneath the South and Central Atlantic, which is replaced by up-tilted aligned bridgmanite within the LLSVP beneath South Africa.

How to cite: Thomas, C. and Pisconti, A.: Constraining D" seismic anisotropy with reflections and splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8851, https://doi.org/10.5194/egusphere-egu24-8851, 2024.

EGU24-8905 | Posters on site | GD7.1

Anisotropic structure of the central European lower crust from ambient noise inversion 

Jiří Kvapil, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Previous research of the Bohemian Massif (BM) crust with the use of ambient noise tomography (ANT) indicates a transversely isotropic structure of the lower crust (Kvapil et al. 2021). In this study, we have developed a new approach for evaluations of localised seismic anisotropy by travel time integration method.

The method calculates synthetic Rayleigh (vertical ZZ correlation) and Love (transverse TT correlation) velocities and derives the vSH/vSV from the initial 3D isotropic vSV model. The higher ratio of measured vSH/vSV to synthetic vSH/vSV indicates the existence of velocity anisotropy in the lower crust of the BM in the reference ANT model (Kvapil et al., 2021). The new method evaluates azimuthal variations of the synthetic parameters due to heterogeneities reflecting local geology effects and corrects the observed velocity ratios. Then the 1D stochastic joint (ZZ, TT) inversion is applied to retrieve the depth dependence of the velocity ratio. We use cross-correlation of ambient noise and earthquake data from seismic stations included in the AlpArray, PACASE, and Adria Array passive seismic experiments and data from the PASSEQ experiment, which complement the sparse coverage in the northern part of the BM.

Seismic anisotropy records the stress/strain conditions of each originally independent tectonic microplates during the formation of the BM crust. We demonstrate that synthetic modelling over the reference isotropic velocity model is an efficient tool for extracting radial and azimuthal shear velocity anisotropy in the lower crust directly from Rayleigh and Love wave dispersion curves. Regions with consistent parameters of seismic anisotropy correlate well with the major tectonic units of the BM. We show that variations in azimuthal and radial anisotropy of the lower crust on a regional scale can provide constraints for the reconstruction of geodynamic processes during the formation of the BM. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows an anisotropic model of the upper mantle derived from a 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves.

How to cite: Kvapil, J., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: Anisotropic structure of the central European lower crust from ambient noise inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8905, https://doi.org/10.5194/egusphere-egu24-8905, 2024.

EGU24-8928 | Posters on site | GD7.1

Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif 

Helena Žlebčíková, Jaroslava Plomerová, Luděk Vecsey, and AlpArray Working Groups

Teleseismic body waves recorded during passive seismic experiments allow us to investigate isotropic velocities of the Earth’s upper mantle in a great detail, on scales of tens of kilometres. However, most of the tomography studies neglect the body-wave anisotropy completely or limit it either to azimuthal or radial anisotropy. We have developed a code called AniTomo for coupled anisotropic-isotropic travel-time tomography of the upper mantle (Munzarová et al., Geophys. J. Int. 2018) which allows for inversion of relative travel-time residuals of teleseismic P waves simultaneously for 3D distribution of P-wave isotropic-velocity perturbations and anisotropy of the upper mantle. We assume weak anisotropy of hexagonal symmetry with either ‘high-velocity’ axis a (lineation) and low velocity (b,c) plane or ‘low-velocity’ axis b and high velocity plane (a,c) (foliation) that is oriented generally in 3D. Such an approach of searching for orientation of the symmetry axes freely in any direction is unique and more general in comparison with the published methods that usually assume only horizontal or vertical orientation of the high-velocity symmetry axis. The code represents a step further from modelling homogeneously anisotropic blocks of the mantle lithosphere (e.g., Vecsey et al., Tectonophysics 2007; Plomerová et al., Solid Earth 2011) towards modelling anisotropy arbitrarily varying in 3D. We present complementary studies of anisotropic structure of the mantle lithosphere in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise. 

We have applied the AniTomo code on P-wave travel time deviations recorded during passive seismic experiments AlpArray-EASI (2014-2015) and AlpArray Seismic Network (2016-2019) to image the upper mantle large-scale anisotropy beneath the western part of the Bohemian Massif and the Eastern Alps. We interpret the P-wave tomography results along with results of splitting parameters from core-mantle refracted shear waves at 240 broad-band stations in about 200 km broad and 540 km long band along 13.3° E longitude. The code allows to control the depth variations and an extent of the fabric. The joint inversion/interpretation allows for distinguishing which type of the models (a-axes model or b-axis model) approximates better the anisotropic structure.

The derived anisotropic-velocity models of the mantle lithosphere cluster into domains with boundaries coinciding with boundaries of the main tectonic sub-regions. These domains are compatible with domains inferred from a joint interpretation of directional variations of P-wave travel-time residuals and SKS-wave splitting parameters. The coincidence of boundaries of the anisotropic models of the mantle lithosphere domains with main tectonic features, correlation of the anisotropy depth extent with the LAB models as well as a decrease of anisotropy strength in the sub-lithospheric mantle support fossil origin of the directionally varying component of the detected anisotropic fabrics of the continental mantle lithosphere.

How to cite: Žlebčíková, H., Plomerová, J., Vecsey, L., and Working Groups, A.: Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8928, https://doi.org/10.5194/egusphere-egu24-8928, 2024.

EGU24-9012 | ECS | Posters on site | GD7.1

Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves  

Rupak Banerjee, Frederik Tilmann, Supriyo Mitra, Tuna Eken, Keith Priestley, and Sunil Wanchoo

Recent enhancement in instrumentation in the northwest (NW) Himalaya provides an unprecedented dataset to study the deformation due to the Indo-Eurasia convergence. The NW Himalaya is unique in terms of hosting a seismic gap and a flat-ramp geometry at its decollement. We determine azimuthal  seismic anisotropy using core refracted shear waves (SKS) and interpret the results to develop insight about the prevailing geodynamics. Here, 459 raypaths with moment magnitude (Mw) >= 5.5, recorded at 15 seismographs of the J&K Seismological NETwork (JAKSNET), operational between 2013 and 2022, are used. To avoid contamination from direct S and SKiKS phases, we analyze the data within the epicentral distance range of 90°-125°, filtered at 0.04-0.2 Hz. We perform a 2-D grid search over the splitting parameters (delay time and fast axis azimuth) and compute their optimum values, for which the energy of the transverse component is minimum (MTE) after correcting for the inferred splitting. Simultaneously, the Rotation Correlation (RC) method is employed to calculate the delay time and fast axis azimuth corresponding to the maximum correlation coefficient between the splitting-corrected horizontal components. We use selection criteria based on the quality factor and the signal-to-noise ratio (SNR) to determine the measurements to be used for station averaging. The quality factor depends on the similarity of results obtained from the RC and MTE methods, hence helps in avoiding subjective interpretation about the quality of the measurement. The non-null splitting measurements passing these selection criteria are then used for station averaging applying the circular mean method and the energy map stacking method. We observe mostly N-S to NE-SW trending fast axes azimuths (13 of 15 stations); this direction corresponds to the absolute plate motion of India in a no-net rotation frame. The two remaining stations show average NW-SE fast directions, which are parallel to the mountain front, but also these stations show somewhat contradictory single splitting measurements, and one of those two anomalous stations is located very close to stations with NE-SW fast measurements, so we will not interpret these. The mean delay times range from 1.5-3.3 s, with the majority of the stations exhibiting > 2s split time being situated on the foreland basin deposits of the Sub-Himalaya. The high absolute Indian plate motion of 51 mm/yr appears to align the upper mantle olivine beneath the orogeny and NE oriented fast axes track the mantle flow manifested by the basal shear of the plate motion. To complement the SKS data, which are dominated by results with eastern backazimuths and corresponding initial polarisation, we further measured splitting for direct S-wave with the reference station method. Here, the correlation between the horizontal traces of the target and reference stations is maximised after correcting the target trace with trial splitting parameters and differences in gain; the reference station trace has previously been corrected for SKS splitting. We will present direct S splitting measurements from 370 events with Mw>=5.5 and distance within 40°-80° with an interstation spacing of <120 km.

How to cite: Banerjee, R., Tilmann, F., Mitra, S., Eken, T., Priestley, K., and Wanchoo, S.: Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9012, https://doi.org/10.5194/egusphere-egu24-9012, 2024.

EGU24-12689 | Orals | GD7.1

Full waveform anisotropic tomography of the transition zone beneath the south west Pacific 

Dorian Soergel, Utpal Kumar, Nicolas Valencia, and Barbara Romanowicz

The presence of ponding slabs at the base of the mantle transition zone (600-700 km) has been well known for a long time and can be explained by the changes in material properties related to phase changes around this depth. However, recent tomographic studies have shown the presence of slabs stagnating at larger depths of around 1000 km. While geodynamic simulations and experiments provide different insights, seismic tomography is crucial to constrain these geodynamic models. More specifically, seismic anisotropy is of particular interest to understand the dynamics of the mantle because of its sensitivity to the flow of mantle material.

The south-west pacific zone is an area with a very complex tectonic setting, with several subduction zones in a relatively small area, illuminated by a very high level of seismicity. It is thus of particular interest to understand the dynamics of the extended transition zone. As such, it has been the object of numerous tomographic studies, including high-resolution full-waveform tomography. In most cases, these studies only invert for radial anisotropy, as azimuthal anisotropy is generally more difficult to measure. However, azimuthal anisotropy is equally important as radial anisotropy and a proper interpretation in terms of mantle flow requires both. We present updated results of a full-waveform inversion of the region including azimuthal anisotropy recovered from body and surface waveforms and XKS-splitting data.

How to cite: Soergel, D., Kumar, U., Valencia, N., and Romanowicz, B.: Full waveform anisotropic tomography of the transition zone beneath the south west Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12689, https://doi.org/10.5194/egusphere-egu24-12689, 2024.

EGU24-12788 | ECS | Posters on site | GD7.1

P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy) 

Rosalia Lo Bue, Francesco Rappisi, Marco Firetto Carlino, Elisabetta Giampiccolo, Ornella Cocina, Brandon Vanderbeek, and Manuele Faccenda

Mount Etna (Italy), renowned for its persistent eruptive activity, is a hazardous volcano shaped by the intricate interplay between magma uprising and a complex tectonic and geodynamic context. Despite extensive monitoring, seismic tomography encounters challenges in accurately depicting the shallow-intermediate P-wave velocity structures, primarily due to the common assumption of isotropy. This study discards such simplification, employing a novel methodology (Vanderbeek and Faccenda, 2021) to simultaneously invert for perturbations to P-wave isotropic velocity and three additional anisotropic parameters (i.e., magnitude of hexagonal anisotropy, azimuth, and dip of the symmetry axis).

By analysing the seismicity recorded in the Mt. Etna area from 2006 to 2016, we constructed 3D anisotropic P-wave tomography models to better constrain the crustal structure of Etna volcano within the framework of its local tectonic setting. The revealed anisotropy patterns are consistent with the structural trends of Etna, unveiling the depth extent of fault segments. We identify a high-velocity volume, deepening towards northwest, recognized as the collision-related subducting foreland units (i.e. Hyblean foreland carbonate slab; Firetto Carlino et al., 2022) that appear to confine a low velocity anomaly, hypothesized to be the expression of a deep magmatic reservoir. A likely tectonic-origin discontinuity affects the subducting units, facilitating the transfer of magma from depth to the surface. This geological setting may explain the presence of such a very active basaltic strato-volcano within an atypical collisional geodynamic context. 

This research improves our understanding of the dynamics governing magma and fluid ascent beneath the volcanic edifice and emphasises the importance of considering anisotropy in seismic investigations. It contributes to our framework for understanding volcanic processes and mitigating associated risks.

 

VanderBeek, B. P., & Faccenda, M. (2021). Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations. Geophysical Journal International, 225(3), 2097-2119.

Firetto Carlino, M., Scarfì, L., Cannavò, F., Barberi, G., Patanè, D., & Coltelli, M. (2022). Frequency-magnitude distribution of earthquakes at Etna volcano unravels critical stress changes along magma pathways. Communications Earth & Environment, 3(1), 68.

How to cite: Lo Bue, R., Rappisi, F., Firetto Carlino, M., Giampiccolo, E., Cocina, O., Vanderbeek, B., and Faccenda, M.: P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12788, https://doi.org/10.5194/egusphere-egu24-12788, 2024.

EGU24-13005 | Orals | GD7.1

Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography 

Ebru Bozdag, Ridvan Orsvuran, Lijun Liu, and Daniel Peter

Earth’s upper mantle and lithosphere show significant evidence for anisotropy related to deformation and composition. First-generation GLAD (GLobal ADjoint) models (GLAD-M15 (Bozdag et al. 2016), GLAD-M25 (Lei et al. 2020), GLAD-M35 (Cui et al. submitted)) are radially anisotropic in the upper mantle. Starting from GLAD-M25, we performed 25 conjugate gradient iterations and constructed model GLAD-M50-AZI by including azimuthal anisotropy in the parameterization of the inverse problem. We inverted azimuthally anisotropic normalized parameters Gc’ and Gs’ simultaneously with vertically and horizontally polarized shear waves beta_v and beta_h, respectively. Due to our parameterization, our data set consists of only minor- and major-arc Rayleigh and Love waves from 300 globally distributed earthquakes. GLAD-M50-AZI captures plate motions globally well, which are also supported by the transverse isotropy, specifically at the subducted slabs and mid-ocean ridges. Furthermore, it approaches continental-scale resolution in regions with good data coverage depicting smaller-scale tectonic and flow patterns, giving us a chance to have a more detailed and unified view of the anisotropy globally. In the next step, we explore how anisotropy derived from seismic tomography compares to geodynamical modeling observations to have better insight into mantle dynamics. We perform numerical simulations to compute synthetic seismograms and full-waveform inversion on Texas Advanced Computing Center’s Frontera system. 

How to cite: Bozdag, E., Orsvuran, R., Liu, L., and Peter, D.: Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13005, https://doi.org/10.5194/egusphere-egu24-13005, 2024.

EGU24-13585 | ECS | Orals | GD7.1

Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs 

Poulami Roy, Bernhard Steinberger, Manuele Faccenda, and Juliane Dannberg

Seismic anisotropy, which involves directionally dependent wave propagation, is likely to occur in the lowermost few hundreds km of the mantle, especially at the edges of Large Low Shear Velocity Provinces (LLSVPs). This anisotropy may be indicative of significant deformation, potentially due to mantle flow interacting with the sides of these provinces or the generation of mantle plumes. In this study, we investigate subducted slab induced plume generation from an LLSVP boundary and the flow behaviour of the lower mantle using compressible 2-D and 3-D mantle convection models in the geodynamic modeling software ASPECT combined with mantle fabric simulation in ECOMAN. In our geodynamic simulation, we assume that the LLSVPs are chemically distinct piles with intrinsically high viscosity. We use the Clapeyron slope of the phase transition from Bridgmanite to post-Perovskite from the previous mineralogical study by Oganov & Ono (2004) in the mantle fabric calculation. Modeling lattice preferred orientation of Bridgmanite and post-Perovskite in the lower mantle reveals that the lower mantle is overall isotropic except the regions of plume conduits and the surroundings of the subducted slab where vertically polarized shear wave (Vsv ) is faster. The generation of anisotropy are caused by the accumulation of high finite strain in these regions. The bottom 300 km of the lower mantle is characterized by fast horizontally polarized shear wave (Vsh ) beneath the subducted slab which deflects to fast Vsv at the margins of the LLSVPs due to the rheological contrast between the highly viscous LLSVP and less viscous ambient mantle. Our result shows that six possible slip systems [100](010), [100](001), [010](100), [001](100), [110](-110) and [-110](110) of Bridgmanite and the slip system [100](001) of post-Perovskite can produce a fast Vsv in the plume generation zones where post-Perovskite transforms to Bridgmanite and fast Vsh at the base of the subducted slab where post-Perovskite is preserved in the D”. However, our models do not show anisotropy inside of the LLSVPs and the subducted slab, possibly because of their high viscosity. Our findings are comparable with the previous seismic observations beneath the Iceland plume where Vsv > Vsh and the slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean where Vsh > Vsv .

How to cite: Roy, P., Steinberger, B., Faccenda, M., and Dannberg, J.: Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13585, https://doi.org/10.5194/egusphere-egu24-13585, 2024.

EGU24-14416 | Orals | GD7.1

Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array. 

Ratna Mani Gupta, Hsin-Hua Huang, Po-Fei Chen, Cheng-Horng Lin, and Cheng-Chien Peng

The Taiwan orogenic belt originates from the collision between the Philippine Sea Plate (PSP) and the Eurasian Plate (EU) with a subduction polarity reversal. The reversal around northern Taiwan creates a complex geodynamic process from subduction waning to post-collision extension. We study the deformation fabric with the shear wave splitting (SWS) method to unravel this tectonic complexity using multiple core phases (PKS, SKS, and SKKS, hereafter XKS). Prevailing SWS research acknowledged the presence of orogen-parallel anisotropy. However, recent studies with numerical modeling and coherency analysis suggested that the anisotropy source is in the asthenosphere. A recent dense seismic array (Formosa Array) of 148 seismic stations in northern Taiwan enables us to revisit this debate with improved spatial and back azimuthal coverage of the SWS measurements. The results show distinct variations in fast direction (Φ) from different back-azimuths and a much larger average delay time (dt) of ~2 sec compared to that derived from local subduction events (at 100-250 km depth). Application of the Fresnel zone and spatial coherency analysis also support an asthenospheric source for the observed anisotropy. The findings emphasize the need for depth-source analysis of anisotropy to better elucidate the responsible mechanisms of complex tectonic settings.

How to cite: Gupta, R. M., Huang, H.-H., Chen, P.-F., Lin, C.-H., and Peng, C.-C.: Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14416, https://doi.org/10.5194/egusphere-egu24-14416, 2024.

EGU24-14883 | ECS | Posters on site | GD7.1

Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km 

John Keith Magali, Christine Thomas, Jeffrey Gay, Angelo Pisconti, and Sebastien Merkel

There is growing evidence, both from a modelling perspective and seismic observations, that seismic anisotropy in the lower mantle is localized around penetrating slabs where large straining is anticipated. It is believed that the high stresses experienced near the slab activate dislocation creep mechanisms that drive the crystallographic preferred orientation (CPO) of bridgmanite aggregates. Still, deformation mechanisms in bridgmanite remain enigmatic. In recent years, deformation experiments in bridgmanite subjected to mantle temperatures and pressures suggest that its microstructures evolve with pressure, providing another perspective on the debated structure and deformation in the lower mantle. Using this information, we develop a numerical technique that calculates pressure-dependent large-scale seismic anisotropy in a pyrolitic mantle with variable velocity gradients. As a first test, we use the method to predict seismic anisotropy by calculating anisotropic reflection coefficients of underside reflections off a depth corresponding to 50 GPa where pressure-induced slip transitions in bridgmanite are expected. For this, we consider two simple deformation styles: (1) uni-axial compression, akin to vertically penetrating slabs, and (2) simple shear associated with corner-type flows. Finally, we demonstrate a multiscale approach that calculates large-scale seismic anisotropy from a fully time-dependent thermo-chemical model of free subduction with latent heating and phase transitions. The result is a long-wavelength equivalent azimuthal and radial anisotropy maps that are actually comparable to a seismic tomography model. We demonstrate how such an approach can create discontinuities in anisotropy at ~1000 km and provide insights as to how it relates to the heterogeneous distribution of the 1000-km discontinuity.

How to cite: Magali, J. K., Thomas, C., Gay, J., Pisconti, A., and Merkel, S.: Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14883, https://doi.org/10.5194/egusphere-egu24-14883, 2024.

EGU24-15225 | ECS | Orals | GD7.1

Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods 

Brandon VanderBeek, Gianmarco Del Piccolo, and Manuele Faccenda

The Cascadia subduction system is an ideal location to investigate the nature of mantle flow and associated driving forces at a convergent margin owing to the dense network of on- and off-shore seismic instrumentation. While numerous shear wave splitting and tomography studies have been performed with these data, they have produced conflicting views of mantle dynamics collectively referred to as the Cascadia Paradox. On the overriding plate, splitting observations are consistent with large-scale 3D toroidal flow while off-shore splitting patterns are more easily explained by 2D plate-driven flow. Either geometry is difficult to reconcile with seismic tomographic models that image a fragmented Juan de Fuca slab descending beneath the Western USA. However, these observations offer only an incomplete image of Cascadia mantle structure. Shear wave splitting provides a depth integrated view of anisotropic fabrics making inferences regarding the 3D nature of mantle deformation difficult. Prior high-resolution body wave tomography typically neglects anisotropic effects which can in turn yield significant isotropic imaging artefacts that complicate model interpretation. To overcome these limitations, we invert P-wave delay times for a 3D hexagonally anisotropic model with arbitrarily oriented symmetry axes using the reversible jump Markov chain Monte Carlo algorithm. This stochastic imaging approach is particularly well-suited to the highly non-linear and under-determined nature of the anisotropic seismic tomography problem. The resulting ensemble of solutions allows us to rigorously assess model parameter uncertainties and trade-off between isotropic and anisotropic heterogeneity. We investigate whether the fragmented nature of the subducted Juan de Fuca slab is a well-resolved feature and to what extent its geometry trades off with anisotropic parameters. In light of our new 3D anisotropic model, we re-evaluate the Cascadia Paradox and attempt to reconcile disparate views of Western USA mantle dynamics.

How to cite: VanderBeek, B., Del Piccolo, G., and Faccenda, M.: Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15225, https://doi.org/10.5194/egusphere-egu24-15225, 2024.

EGU24-16887 | ECS | Posters on site | GD7.1

The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria) 

Dustin Lang, Rebecca Kühn, Rüdiger Kilian, Hannah Pomella, and Michael Stipp

The interpretation of seismic data in orogens is usually difficult to decipher as structural information is limited to surface and borehole data. Seismic interpretations very much depend on the elastic wave velocity model, which in the simplest case is a function of rock composition. Seismic velocities can also be anisotropic, i.e. depend on the wave propagation direction inside the rock. Seismic anisotropy can be subdivided into intrinsic (crystallographic preferred orientation (CPO)) and extrinsic (shape preferred orientation, compositional layering or fractures) anisotropy. Microstructures in thin section scale have an impact not only on millimeter-scale but also on larger anisotropies in the field such as meter- to kilometer-scale folds. Here we explore the effect of microstructure (mainly folding and crenulation) on the homogenization of seismic anisotropy from samples of millimeter to thin section scale.

The investigated samples are phyllosilicate- and graphite-rich samples (Innsbruck quartzphyllite and Bündner schist) from the N-S running Brenner Base Tunnel Project (NW-Tauern Window). Phyllosilicate-rich sections with layers of different composition and structure were selected from drill core samples of the exploration tunnel. The CPO of phyllosilicates and graphite from 1.5 – 3.5 mm thick cylinders was measured using high energy X-ray diffraction at DESY (Hamburg, Germany) and the ESRF (Grenoble, France). Pole figure data was directly extracted using single peak fitting. The CPO of quartz was determined by using EBSD. Seismic velocities for each sample were computed using µXRF-based modal composition and single crystal stiffness tensors. We measured the smallest representative volume element which we consider to be undisturbed by microstructural effects. Therefore, we estimate an upper bound of expected intrinsic velocity anisotropies. Thin section-scale anisotropies were modeled from the upper bound anisotropy and the observed microstructure, i.e., small-scale folding. Computed velocities were compared to Vp-anisotropy measurements on the drill cores.

The velocity anisotropy is primarily governed by the content and distribution of phyllosilicates and graphite. Given the crystal symmetry and the low single crystal elastic anisotropy, phases such as feldspar, quartz or calcite can be considered as irrelevant with respect to seismic anisotropies. The simulation of a crenulation cleavage has a stronger impact than centimeter-size folding: The crenulation cleavage reduces the anisotropy for example from 14 % to 12 %. Centimeter-size folding with observed interlimb angles of 140° in contrast is negligible.

The effect of microstructures like centimeter-scale folds and crenulation has only a limited impact on anisotropies of foliated rocks during homogenization from millimeter to thin section-scale. We assume that during homogenization to a larger scale, the effect of folding with small interlimb angles or different fold axes within the homogenized volume will have a stronger influence on seismic anisotropy.

How to cite: Lang, D., Kühn, R., Kilian, R., Pomella, H., and Stipp, M.: The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16887, https://doi.org/10.5194/egusphere-egu24-16887, 2024.

EGU24-17055 | ECS | Orals | GD7.1

Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau.  

Arijit Chakraborty, Monumoy Ghosh, Siddharth Dey, Shubham Sharma, Sankar N. Bhattacharya, and Supriyo Mitra

The Indian Lithosphere has been shaped by multiple tectonic processes, which include break-up from the Gondwana Supercontinent, traversing over the Reunion and Kerguelen hotspots, collision with Eurasia, and underthrusting beneath the Himalaya and Tibetan Plateau. Seismic velocity structure and radial anisotropy of the lithosphere preserves imprints of these  tectonic processes and related deformation. We perform joint-modeling of fundamental-mode Rayleigh (LR) and Love (LQ) wave group-velocity dispersion, for periods between 10 and 120s, to obtain radially anisotropic shear-wave velocity structure across India, Himalaya and Tibet. 1D path-average dispersion curves, computed for ~14700 regional earthquake-receiver raypaths, has been passed through systematic quality control of signal-to-noise ratio (>3), elimination of multipathed energy using polarization analysis, and removal of overtone interference, by synthetic tests. These 1D dispersion data are combined through a tomographic formulation to obtain 2D maps. The tomographic parametrization is done using  4906 nodes as apex of triangular elements of side 1°. LR and LQ fundamental-mode group-velocity dispersion data at these nodes are the observation input to the joint inversion. The inversion is done in 2-steps, first by parameterizing the model as isotropic layers and using an isotropic inversion scheme to obtain the best fitting Vs model; second using this output Vs model into an anisotropic inversion scheme, implemented using Genetic Algorithms (GA). GA exhaustively searches the model-space composed of Vsh, Vph and Xi[Vsh^2/Vsv^2] as free parameters. The fit to both LR and LQ datasets significantly improve in the anisotropic inversion. 

 

Results are presented as 2D depth-slice maps and cross-sections constructed using bilinear interpolation. The main findings from our models are lateral variation in the voigt-average Vs beneath the Tibetan Plateau at depth between 80-140 km. Western Tibet has high Vs and positive Xi, while Central-Eastern TIbet has Low Vs and negative Xi. From cross-sections across both regions, we infer that the dip and underthrusting of the Indian Plate beneath Tibet has lateral variation. The high Vs and positive anisotropy in Western Tibet indicates a shallow underthrusting of the Indian lithosphere up to the Tarim Basin, with simple-shear deformation. Where as, the lower Vs and negative anisotropy in Central-Eastern Tibet is a result of partial-underthrusting of India at a steeper-angle up to the Bangong-Nujiang Suture, and pure-shear deformation of thickened Tibet Lithosphere beneath North-Central Tibet. A negative anisotropy signature along the Reunion volcanic track is observed between 100 and 160 km depth. We infer this to be the signature of  Reunion hotspot volcanism in the Indian lithosphere caused by the vertical ascent of a huge volume of melt arising from the plume-head. Similar observations are also made beneath the track of the Kergulean hotspot. 

How to cite: Chakraborty, A., Ghosh, M., Dey, S., Sharma, S., Bhattacharya, S. N., and Mitra, S.: Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17055, https://doi.org/10.5194/egusphere-egu24-17055, 2024.

EGU24-17743 | Orals | GD7.1

Predicting seismic anisotropy in the upper mantle using supervised deep-learning 

Andrea Tommasi, Nestor Cerpa, Fernando Carazo, and Javier Signorell

Both elastic and viscoplastic behaviors of the Earth’s upper mantle are highly anisotropic, because olivine, which composes 60-80% of the mantle, has a strong intrinsic anisotropy and develops strong crystal preferred orientations (CPO). Predicting the evolution of anisotropy with strain is essential to: (1) probe indirectly the deformation in the mantle based on seismic measurements and (2) accounting for the deformation history when simulating the long-term dynamics of the Earth. However, traditional micro-mechanical approaches to model the evolution of CPO-induced elastic and viscous anisotropies are too memory-costly and time-consuming for coupling into geodynamical simulations. To speed up the prediction of seismic anisotropy in the mantle, we developed deep-learning (DL) surrogates trained on a synthetic database built with viscoplastic self-consistent simulations of texture evolution of olivine polycrystals in typical 2D geodynamical flows. A first challenge was the choice of memory-saving representations of the CPO. Training the DL models on the evolution of the elastic tensor components avoided the need of storing the CPOs. However, the major challenge has been to prevent error compounding in a recursive-prediction scheme – where a model prediction at a given time step becomes the input for the next one - to evaluate the anisotropy evolution along a flow line. We implemented multilayer feed-forward (FFNN), ensemble, and transformer neural networks, obtaining the best efficiency/accuracy ratio for the FFNN. The results highlight the importance of (1) the standardization of the outputs in the training stage to avoid overfitting in predictions, (2) the statistical characteristics of the strain histories in the training database, and (3) the influence of non-monotonic strain histories on error propagation. Predictions for complex unseen strain histories are accurate, much more time-efficient and memory-costly than the traditional micro-mechanical models. Our work opens thus new avenues for modeling the strain-controlled evolution of mechanical anisotropy in the Earth’s mantle. This work was supported by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation programme [grant agreement No 882450 – ERC RhEoVOLUTION.

How to cite: Tommasi, A., Cerpa, N., Carazo, F., and Signorell, J.: Predicting seismic anisotropy in the upper mantle using supervised deep-learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17743, https://doi.org/10.5194/egusphere-egu24-17743, 2024.

EGU24-18148 | ECS | Orals | GD7.1

Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging 

Gianmarco Del Piccolo, Rosalia Lo Bue, Brandon Paul VanderBeek, Manuele Faccenda, Ornella Cocina, Marco Firetto Carlino, Elisabetta Giampiccolo, Andrea Morelli, and Joseph Byrnes

Trans-dimensional inference identifies a class of methods for inverse problems where the number of free parameters is not fixed. In seismic imaging these methods are applied to let the data, and any prior information, decide the complexity of the models and how the inferred fields partition the inversion domains. Monte Carlo trans-dimensional inference is performed implementing the reversible-jump Markov chain Monte Carlo (rjMcMC) algorithm; the nature of Monte Carlo exploration allows the algorithm to be completely non-linear, to explore multiple possibilities among models with different dimensions and meshes and to extensively investigate the under-determined nature of the tomographic problems, showing quantitative evidence for the limitations in the data-sets used. Implementations of this method overcome the main limitations of traditional linearized solvers: the arbitrariness in the selection of the regularization parameters, the linearized iterative approach and in general the collapse of the information behind the solution into a unique inferred model.

We present applications of the rjMcMC algorithm to anisotropic seismic imaging of Mt. Etna with P-waves. Mt. Etna is one of the most active and monitored volcanoes in the world, typically investigated under the assumption of isotropic seismic speeds. However, since body waves manifest strong sensitivity to seismic anisotropy, we parametrize a multi-fields inversion to account for the directional dependence in the seismic velocities. Anisotropy increases the ill-condition of the tomographic problem and the consequences of the under-determination become more relevant. When multiple seismic fields are investigated, such as seismic speeds and anisotropy, the data-sets used may not be able to independently resolve them, resulting in non-independent estimates and corresponding trade-offs. Monte Carlo exploration allows for the evaluation of the robustness of seismic anomalies and anisotropic patterns, as well as the trade-offs between isotropic and anisotropic perturbations, key features for the interpretation of tomographic models in volcanic environments. The approach is completely non-linear, free of any explicit regularization and it keeps the computational time feasible, even for large data-sets.

How to cite: Del Piccolo, G., Lo Bue, R., VanderBeek, B. P., Faccenda, M., Cocina, O., Firetto Carlino, M., Giampiccolo, E., Morelli, A., and Byrnes, J.: Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18148, https://doi.org/10.5194/egusphere-egu24-18148, 2024.

EGU24-21240 | Posters on site | GD7.1

Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation 

Jan Philipp Kruse, Georg Rümpker, Frederik Link, Thibault Duretz, and Harro Schmeling

We utilize three-dimensional geodynamic models to predict XKS-splitting in double subduction scenarios characterized by two outward-dipping slabs. These models are highly applicable in various realistic settings, such as the central Mediterranean. Our primary focus is on the analysis of XKS-splitting, a key geophysical observable used for inferring seismic anisotropy and mantle flow patterns.Our models simulate the concurrent subduction of two identical oceanic plates separated by a continental plate. The variation in the strength of the separating plate causes a transition from a retreating to a stationary trench. The models offer detailed insights into the temporal evolution of mantle flow patterns, particularly the amount of trench-parallel flow induced by this specific type of subduction.In the subsequent step, we employ the well-known D-Rex model to estimate Crystallographic Preferred Orientation (CPO) development in response to plastic deformation resulting from mantle flow. Based on the D-Rex model results, which incorporate the full elastic tensor of a deformed multiphase polycrystalline mantle aggregate, we derive synthetic apparent splitting parameters and splitting intensities at virtual receivers placed at the surface using multiple-layer anisotropic waveform modeling. To identify regions with pronounced depth-dependent variations of anisotropic properties, particularly the fast polarization directions, we define a complex anisotropy factor dependent on the apparent splitting parameters and splitting intensities.Finally, using the apparent splitting parameters, we conduct two-layer model inversions at selected locations characterized by a large complex anisotropy factor. The two-layer model provides apparent splitting parameters as a result of analytical waveform modeling for two anisotropic layers. We observe that while several models can effectively explain the apparent splitting parameters, only a subset can accurately reproduce the depth-dependent anisotropic properties. Our findings unequivocally demonstrate that a classical XKS-splitting analysis can effectively identify areas characterized by complex anisotropy and provide accurate approximations of the depth-dependent variations of anisotropic properties within these regions. However, caution is warranted when interpreting results obtained through inversion based on a two-layer analysis.

How to cite: Kruse, J. P., Rümpker, G., Link, F., Duretz, T., and Schmeling, H.: Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21240, https://doi.org/10.5194/egusphere-egu24-21240, 2024.

EGU24-322 | ECS | Posters virtual | GD10.2

Joint long-period P and S velocity inversion for Earth's mantle based on deep learning 

Jun Su, Christine Houser, and John Hernlund

Many large-scale structures in the mantle have been proposed to explain seismic observations and constrain geodynamic models. While the geophysical community cannot agree on the morphology and nature(s) of large low shear velocity provinces (LLSVPs) due to the difference in approaches, decorrelated P and S velocity anomaly (dVno longer proportional to dVS), inherently associated with changes in composition and/or phase, can help examine geodynamic models and imply the thermal/chemical evolution of the mantle. To further apply the inference to finer structures and to improve the precision for quantitative mineral physical implications, it is necessary to build a new seismic dataset for P and S waves measured in a self-consistent manner.

In this study, we trained a phase-picking model using code modified from EQTransformer (Mousavi et al., 2020). Our training dataset includes 65,298 traces, where teleseismic P and S arrivals are manually picked at the long-period (~20 sec) onset. Based on the machine-learning architecture proven useful for seismicity at local to regional distances, we managed to reproduce the manual picking results by machine and extend the picking catalog for seismic data to the present. We also conduct tomographic inversion for the global mantle to obtain a three-dimensional velocity model for both P and S waves. The new model has a higher resolution, allowing interpretations to understand geodynamics better.

How to cite: Su, J., Houser, C., and Hernlund, J.: Joint long-period P and S velocity inversion for Earth's mantle based on deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-322, https://doi.org/10.5194/egusphere-egu24-322, 2024.

EGU24-557 | ECS | Orals | GD10.2

Temporal Record of Plume-Ridge Interaction in the North Atlantic: Interdisciplinary Insights from IODP Expedition 395C 

Callum Pearman, Nicky White, John Maclennan, and Chia-Yu Tien and the IODP Expedition 395 science party

The Icelandic mantle plume is regarded as one of the most significant mantle upwellings on Earth, however the dynamics of its interaction with the surrounding asthenosphere and mid-oceanic ridge systems in the North Atlantic are poorly understood. The clearest manifestation of this plume-ridge interaction are the Reykjanes V-shaped ridges and V-shaped troughs (VSRs and VSTs) that straddle the Reykjanes Ridge axis south of Iceland. These time-transgressive linear features are particularly well exposed by short-wavelength gravity data and are thought to represent the progressive sampling of thermal asthenospheric pulses that horizontally advect away from the Icelandic mantle plume conduit. The Reykjanes Ridge therefore acts as a ‘window-sampler’ into the temporal and spatial dynamics of plume outflow. International Ocean Discovery Program (IODP) Expedition 395C drilled into two VSR and VST pairs along a plate-spreading flow line approximately 600 km south of Iceland in summer 2021. Over 400 m of basalt was recovered, which represents a magmatic record over 15 Ma of plate spreading at a fixed distance from the mantle plume conduit. We present Nd isotopic analysis of recovered whole-rock that reveals a linear isotopic evolution from ƐNd of 7.5 to 10.5 over 14 Ma (n = 50), which implies that the ‘plume-like’ enriched component of the mantle source has been progressively diluted by mixing with depleted upper mantle material. This evolution occurred synchronously with the entire timeframe of VSR formation as defined by free-air gravity anomalies, and a long-wavelength increase in crustal thickness implied by wide-angle seismic experiments. It is therefore apparent that the dynamics of plume-ridge interaction are directly interlinked with changes in magmatism, structural tectonics and crustal production. Furthermore, major and trace elements of both whole-rock and glass samples have been measured, by multiple analytical techniques, revealing distinct compositions between and within boreholes. These observations can be understood in terms of temporal changes in the depth and degree of melting. In summary, petrological, petrophysical and geochemical analysis of this rock core in conjunction with consideration and modelling of wide-angle seismic surveys, gravity and bathymetric data can be used to develop a quantitative understanding of the dynamics of plume-ridge interaction, test hypotheses for the formation of VSRs, and constrain the temporal evolution of the North Atlantic mantle domain.

How to cite: Pearman, C., White, N., Maclennan, J., and Tien, C.-Y. and the IODP Expedition 395 science party: Temporal Record of Plume-Ridge Interaction in the North Atlantic: Interdisciplinary Insights from IODP Expedition 395C, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-557, https://doi.org/10.5194/egusphere-egu24-557, 2024.

EGU24-1275 | ECS | Posters on site | GD10.2

Enhanced subduction flux during the assembly of Pangea recorded by global intracontinental magmatism 

Qian Chen, He Liu, Andrea Giuliani, Tim Johnson, Luc Doucet, Lipeng Zhang, and Weidong Sun

Plate tectonics drives the compositional diversity of Earth’s convecting mantle through subduction of lithosphere. In this context, the role of evolving global geodynamics and plate (re)organisation on the spatial and temporal distribution of compositional heterogeneities in the convecting mantle is poorly understood. We test the hypothesis that an increase in the cumulative length of subduction zones associated with supercontinent assembly triggered geochemical enrichment of the convective mantle globally, in particular since the emergence of protracted, cold, deep subduction in the late Neoproterozoic. We compiled the trace element and Nd isotopic compositions of intracontinental basalts formed over the last billion years (1000 Myr).  After careful filtering to eliminate samples with evidence for crustal contamination, the data show that intracontinental basalts formed before 300 Ma exhibit supra-chondritic initial 144Nd/143Nd values. Those with sub-chondritic initial 144Nd/143Nd values become common only after 300 Ma, broadly coeval with the global appearance of kimberlites with geochemically enriched isotopic signatures. We attribute these step-changes in the sources of intraplate magmatism to a rapid increase in the supply of deeply subducted lithosphere due to increased peri-continental subduction during the assembly of Pangea.

How to cite: Chen, Q., Liu, H., Giuliani, A., Johnson, T., Doucet, L., Zhang, L., and Sun, W.: Enhanced subduction flux during the assembly of Pangea recorded by global intracontinental magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1275, https://doi.org/10.5194/egusphere-egu24-1275, 2024.

EGU24-2139 | ECS | Orals | GD10.2

Geodynamic-mineralogical predictions of mantle transition zone seismic structure 

Isabel Papanagnou, Bernhard S. A. Schuberth, Christine Thomas, and Hans-Peter Bunge

A main objective in geodynamics is to create models that provide quantitative information to other Earth science disciplines. In order to assess the validity of the underlying assumptions and chosen input parameters related to different geodynamic hypotheses, it is crucial to test these models against observations. In this, thermodynamic models of mantle mineralogy represent an essential tool. On the one hand, they enable the linking of temperature fields from mantle circulation models (MCMs) to seismic observations. On the other hand, they provide critical information on material behaviour in response to changing temperature and pressure conditions that occur over time within such mantle convection simulations. Some of the most interesting aspects in this context relate to mineral phase transitions and associated dynamic effects on mantle flow.

The mantle transition zone (TZ) in particular is expected to influence vertical mass flow between upper and lower mantle as it hosts a complex set of mineral phase transitions as well as an increase in viscosity with depth. Still, neither its seismic structure nor the associated dynamic effects have conclusively been constrained. The seismic discontinuities at around 410 and 660 km depth (‘410’ and ‘660’) have classically been related to phase transitions between olivine polymorphs, the pressure of which is modulated by lateral temperature variations. The resulting topography of these discontinuities is seismically visible and can thus potentially provide insight on temperature and phase composition at depth. Besides the olivine phase changes, the disassociation of garnet may additionally impact the 660 at higher temperatures. However, the volume of material affected by this garnet transition and its dynamic implications have not yet been quantified.

Here, we present hypothetical realizations of TZ seismic structure and major discontinuities based on the 3-D temperature field of a published MCM for a range of relevant mineralogies, including pyrolite and mechanical mixtures (MM). Systematic analysis of these models provides a framework for dynamically informed interpretations of seismic observations and gives insights into the potential dynamic behaviour of the TZ. Using our geodynamic-mineralogical approach we can identify which phase transitions induce specific topographic features of 410 and 660 and quantify their relative impact. Areal proportions of the garnet transition at the 660 are ∼3 and ∼1 per cent for pyrolite and MM, respectively. This proportion could be significantly higher (up to ∼39 per cent) in a hotter mantle for pyrolite, but remains low (< 2 per cent) for MM. In pyrolite, both slabs and plumes are found to depress the 660 —with average deflections of 14 and 6 km, respectively— due to the influence of garnet at high temperatures indicating its complex dynamic effects on mantle upwellings. Pronounced differences in model characteristics for pyrolite and MM, particularly their relative garnet proportions and associated topography features, could serve to discriminate between the two scenarios in Earth.

How to cite: Papanagnou, I., Schuberth, B. S. A., Thomas, C., and Bunge, H.-P.: Geodynamic-mineralogical predictions of mantle transition zone seismic structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2139, https://doi.org/10.5194/egusphere-egu24-2139, 2024.

The temperature at Earth’s core-mantle boundary (CMB) is a key parameter to understand the dynamics of our planet’s interior. However, it remains poorly known, with current estimate ranging from about 3000 K to 4500 K and more. Here, I introduce a new approach based on joint measurements of shear-wave velocity, VS, and quality factor, QS, in the lowermost mantle.  Lateral changes in both VS and QS above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, Tref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from VS and QS should be equal gives a constraint on Tref. Correcting Tref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, TCMB. This approach further relies on the presence of post-perovskite (pPv) phase in the deep mantle and on the fact that VS-anomalies are affected by the geographical distribution of phis phase. As a result, the inferred Tref is linked to the temperature TpPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to VS and QS measured beneath Central America and the Northern Pacific suggest that for TpPv = 3500 K, TCMB lies in the range 3470-3880 K with a 95 % likelihood. Additional measurements in various regions, together with a better knowledge of TpPv, are needed to determine a precise value of TCMB with this method.

How to cite: Deschamps, F.: Estimating the temperature at the core-mantle boundary from measurements of shear-wave velocity and seismic attenuation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2497, https://doi.org/10.5194/egusphere-egu24-2497, 2024.

The study of the Earth’s interior has been traditionally based on seismological and geodynamic modelling, the first one providing important information about its present-day structure, composition and state, while the second about its dynamics and compositional evolution. Seismological and geodynamical modelling are very often conducted independently, which creates mechanical and geometrical inconsistencies across the models, hampers the interpretation of seismic observations in terms of geodynamic processes and enhances the non-uniqueness of geodynamic model predictions.

An alternative approach is combining computational seismology and geodynamics with mineral physics, which provides a comprehensive understanding of the Earth's interior processes, seismic behavior, and material properties. In this multidisciplinary methodology, the geodynamic flow calculations are used to compute the rock elastic properties as a function of strain-induced mantle fabrics through micro-mechanical models of crystal aggregate deformation, and of the local P-T conditions with thermodynamically self-consistent models of mantle mineralogy. The obtained seismic mantle structure is then used for seismological synthetics, such that specific hypotheses on mantle dynamics can be tested directly against seismic data. Examples from the South American, North American, and the Central Mediterranean convergent margins will be discussed.

Finally, I will introduce ECOMAN, a recently developed, open-source software package that is intended to overcome the computationally intensive nature of this approach and the lack of a dedicated and comprehensive computational framework for modelling strain-/stress-induced rock fabrics and testing the effects of the resulting mechanical (elastic and viscous) anisotropy on seismic imaging and mantle convection.

How to cite: Faccenda, M.: Constraining Mantle Convection Patterns by Joint Geodynamic and Seismological Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5439, https://doi.org/10.5194/egusphere-egu24-5439, 2024.

Mantle convection causes the most important contribution to the geoid and dynamic topography. With high resolution tomography models and numerical simulation methods solving the governing equations of mantle convection, the model geoid can fit well compared to observation. However, if wave speed variations are converted to density variations assuming both are due to temperature variation in the entire mantle, there is still a large discrepancy between the present dynamic topography predicted by mantle flow and that induced from observations: Especially large negative topography is predicted in cratons, contrary to observations. In order to improve the fit of model dynamic topography compared to observations, chemical density anomaly in earth’s lithosphere need to be included. In this study, we will combine these with lateral viscosity structure and study the effect on model dynamic topography and geoid, and investigate which density models would yield a good fit. In the sublithospheric mantle, under the assumption that the density anomalies are thermally induced from temperature variation in the mantle, we use temperature-dependent viscosity. We also include thermo-chemical density anomalies in the Large low-shear-velocity provinces (LLSVPs) in the lowermost mantle to compute their effect on the model geoid and dynamic topography. Our overall objective is a better constraint on the Earth’s interior structure, by achieving good fits of both dynamic topography and geoid to their observations, to provide as a good reference for the Earth’s study.

How to cite: Cui, R., Steinberger, B., and Fang, J.: Modeling geoid and dynamic topography from tomography-based thermo-chemical mantle convection with temperature- and depth-dependent viscosity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5452, https://doi.org/10.5194/egusphere-egu24-5452, 2024.

The effects of pressure and temperature on the phase transformation of olivine to wadsleyite and then ringwoodite within the mantle is well understood. However, the extent to which stress affects this phase transformation is not clear. Understanding how stress influences the kinetics of the olivine to spinel phase transformation and the mechanism in which it does so at grain scale, will have broader implications for mantle dynamics. Deformation experiments using Mg2GeO4 have been used as an approximate analogue for fayalite as it transforms from olivine to ringwoodite at lower pressures and temperatures rather than the conditions found at d410 (Vaughan, 1981). This enables the use of larger samples than possible for the silicate system, and allows for extensive microstructural investigations. This session aims to discuss high pressure deformation experiments on Mg2GeO4 (olivine) during the transformation to ringwoodite using a Griggs-type, solid medium, deformation apparatus. These experiments expand on (Vaughan 1984) which linked kinetics of the reaction in a model that matches other stressed reactions in the mantle (Wheeler, 2020). Experiments were conducted at a range of confining pressures 0.8 - 1.2 GPa at a fixed temperature of 900 °C and a strain rate of 10-6 /s. The four samples were deformed to finite strains ranging from 10 to 45 %. The aim of the conditions chosen was to apply varying amounts of differential stress and therefore differing the σ1 stress on the sample as a whole. Samples were characterised down to the level of individual interfaces using Electron Backscatter Diffraction (EBSD) to understand the physical mechanism of the reaction and the kinetics that govern it.

How to cite: Akhtar-Lewis, S.: Effects of Stress on the Olivine–Spinel Phase Transformation in the Mantle: Griggs-Type Deformation Experiments Using Mg2GeO4 as an Analogue., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6130, https://doi.org/10.5194/egusphere-egu24-6130, 2024.

EGU24-6325 | ECS | Posters on site | GD10.2

Assessment of geodynamic predictions with surface-wave tomography in the Pacific upper mantle accounting for full 3D resolution and robust uncertainties. 

Franck Latallerie, Paula Koelemeijer, Andrew Walker, James Panton, and Huw Davies

Surface-waves carry important information about upper mantle structure, especially in poorly sampled areas such as oceanic regions. Surface-wave tomography models can be used to assess geodynamic simulations by comparing observed and predicted structures. However, surface-wave data are noisy and sparse resulting in tomography models being noisy and blurred pictures of the Earth's structure. As a result, tomography models can hardly be compared directly to geodynamic predictions which aim to predict the true structure of the Earth. Although challenging, assessing geodynamic simulations with surface-wave tomography requires accounting for full 3D resolution and robust uncertainties.

In this study, we present a workflow to quantitatively assess geodynamic model predictions using surface-wave tomography. Specifically, we measure dispersion data for paths crossing the Pacific ocean and estimate data uncertainties including measurement and theoretical errors. We use a finite-frequency forward theory to linearly relate data to the three-dimensional Vsv structure in the upper mantle. Subsequently, we apply the SOLA (Backus-Gilbert-style) method in 3D to control and produce the full three-dimensional resolution and robust model uncertainties together with the Vsv tomography model. Equipped with this, we assess predictions for the Pacific upper mantle from a set of geodynamic simulations based on different input parameters.

Preliminary results highlight physical parameters of mantle convection influencing significantly the misfit between observed and predicted structure in the Pacific upper mantle; and, for quantitative parameters, inform us on values that provide the best fits.

How to cite: Latallerie, F., Koelemeijer, P., Walker, A., Panton, J., and Davies, H.: Assessment of geodynamic predictions with surface-wave tomography in the Pacific upper mantle accounting for full 3D resolution and robust uncertainties., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6325, https://doi.org/10.5194/egusphere-egu24-6325, 2024.

EGU24-6554 | ECS | Posters virtual | GD10.2

Mid-mantle imaging through a reverberant transition zone: A CRISP-RF approach 

Steve Carr and Tolulope Olugboji

On a planet that dissipates heat through whole mantle convection, no sharp changes in elastic properties are expected in the mid-mantle: ~750-1300 km. Yet, a growing number of seismic studies continue to document evidence of discontinuities across these depths. Compared to the upper mantle, the global prevalence and causal origins of such features remain relatively enigmatic. Here, we investigate mid-mantle layering beneath two large seismic arrays (US and Alaska) using high-resolution Ps-converted waves. The challenge is that top-side reflections (reverberations) from the mantle transition zone interfere with and contaminate desired mid-mantle conversions and make their interpretation difficult. In the past, the slowness slant stack (vespagram) approach has been used. We extend the resolution of this stacking scheme using a newly developed sparsity-promoting, non-linear, CRISP-RF technique (Clean Receiver function Imaging with Sparse Radon Filters). Preliminary results suggest that CRISP-RF can isolate high-frequency (0.5Hz) mid-mantle body wave conversions buried within transition zone reverberations. With our filtered Ps-RFs and machine learning, we will present tighter constraints on mid-mantle layering (depth, sharpness, spatial variation)  exploring important implications for its origin.  

How to cite: Carr, S. and Olugboji, T.: Mid-mantle imaging through a reverberant transition zone: A CRISP-RF approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6554, https://doi.org/10.5194/egusphere-egu24-6554, 2024.

EGU24-7341 | Orals | GD10.2 | Highlight

Chocolate in the marble cake: the fate of eclogite and pyroxenite during mantle convection and melting 

Romain Tilhac, Carlos Garrido, Stephan König, and María Isabel Varas-Reus

The presence of lithologies derived from recycled oceanic lithosphere in the convective mantle is an expected consequence of subduction. Geochemical studies have provided compelling evidence of the contribution of recycled eclogite and pyroxenite in the mantle source of oceanic basalts, particularly ocean island basalts (OIB). However, identifying their signatures in mid-ocean ridge basalts (MORB) is challenging due to more intricate melting and mixing processes. Furthermore, the use of elemental and isotopic proxies of different geochemical affinities provides contrasting pictures on their source heterogeneity. Understanding the role of pyroxenite and eclogite during partial melting bears critical information regarding the fate of recycled lithospheric material, the dynamics and timescales of mantle convection and the thermal regime of mid-ocean ridges.

We present a numerical approach based on the thermodynamically constrained Mixed-Source Melting model (MSM3), enabling a coherent assessment of the role of recycled lithologies. Within a comprehensive plate tectonic cycle, the MSM3 model simulates the two-stage recycling of eclogites derived from subducted oceanic crust in a marble-cake mantle.

  • Stage 1 corresponds to the formation of secondary pyroxenite from the hybridization of high-degree eclogite-derived melts interacting at high pressure with peridotite in the convective mantle.
  • Stage 2 corresponds to the formation of MORB in a triangular melting regime from the adiabatic decompression melting of a 3-lithology source of peridotite, pyroxenite and residual eclogite obtained from stage 1.

To tackle the diversity of geochemical proxies applied to oceanic basalts, MSM3 recovers melt and residual compositions in terms of major elements and sulfur, as well as any lithophile and chalcophile trace elements and isotope systems. This is achieved thanks to the integration of melting models with pMELTS calculations constrained by a thermodynamic parametrization specific to pyroxene-rich lithologies (Melt-PX), calculations of sulfur concentration at sulfide saturation (SCSS), and composition-dependent partition coefficients. To take into account the inherent variability of most parameters (e.g., potential temperature, source proportions, sulfur contents) and avoid arbitrary choices, we use a stochastic approach by running the MSM3 model as an inversion based on adaptative Monte Carlo simulations.

We here demonstrate the flexibility of this approach, even for systems controlled by sulfides. We show that, over potential temperatures ranging between 1280 and 1420 ºC, the generation of 0-10% of pyroxenitic heterogeneities from subducted eclogite, and the contribution of both eclogite and pyroxenite in the melting regime of MORB produce 20-95 % of the melts aggregated at the ridge. Such proportions correspond to up to 30 times the proportion of these lithologies in the mantle. This over-contribution is controlled by the melting regime properties and is enhanced or attenuated by the mass balance specific to the elements and isotope systems considered (concentrations, partitioning behavior, modal evolution of the main host minerals in the different lithologies). In other words, the more-fusible pyroxenite and eclogite act as chocolate in the marble-cake mantle, giving the dominant flavor to its melting products, although different geochemical proxies may "taste" it differently.

How to cite: Tilhac, R., Garrido, C., König, S., and Varas-Reus, M. I.: Chocolate in the marble cake: the fate of eclogite and pyroxenite during mantle convection and melting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7341, https://doi.org/10.5194/egusphere-egu24-7341, 2024.

EGU24-8992 | Posters on site | GD10.2

Imaging deep subducted lithosphere beneath the Indian Ocean with seismic source array recordings 

Christine Thomas and Björn Holger Heyn

The D" region, located just above the core-mantle boundary (CMB), is a geologically interesting region that has been imaged using both tomographic and reflection techniques. However, reflection studies often rely on array analysis techniques, and the lack of suitable seismic arrays in the oceans has left large areas of D" unmapped. One notable area, that is currently sparsely sampled, is beneath the Indian Ocean, where ancient subducted lithosphere has been imaged near the CMB in global tomography studies. We take advantage of the long-running history of five GEOSCOPE stations located in the western Indian Ocean and Antarctica, to investigate the possibility of using source arrays to detect P-wave reflections from the discontinuity above the D" layer. Despite restricting the selected earthquakes around Indonesia to a 120 km depth range and implementing several source normalization techniques, source-array stacks (i.e., source vespagrams) were difficult to interpret. We infer that this complication arises from differing earthquake depths, violating the plane wave assumption made when constructing these stacks. Therefore, we extend our method to a source-array scatter imaging method, which we call source migration, that does not rely on travel-times calculated for a plane wave. Using this technique in conjunction with source normalization, we found clear evidence for a D" P-wave reflector at four of the six GEOSCOPE stations considered in the study. The depth of the reflector for our imaged region varies between 190 km above the CMB beneath the Great Australian Bight and 220 to 270 km beneath the Indian Ocean west of Australia. Our determined depth in the northern portion of our study area is consistent with previous studies of D" depths using S-waves. We suggest that our D" reflections are the result of the previously imaged subducted lithosphere in the region and find that this lithosphere likely thins to the southeast. Additionally, our work more broadly indicates that the long-running history of single global seismic stations combined with source array techniques may be utilized to compliment and extend previous work imaging D" using conventional receiver-array techniques.

How to cite: Thomas, C. and Heyn, B. H.: Imaging deep subducted lithosphere beneath the Indian Ocean with seismic source array recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8992, https://doi.org/10.5194/egusphere-egu24-8992, 2024.

EGU24-10944 | ECS | Orals | GD10.2

Constraining global mantle circulation models with global seismic observations 

William Sturgeon, Ana M.G. Ferreira, James Panton, and J. Huw Davies

In order to improve our understanding of mantle flow, we require a joint collaboration between all fields of Earth Sciences. Seismic tomography provides key information on the current state of the mantle and therefore can constrain mantle circulation models. We present high-resolution (degree-60) global models of frequency-dependent phase and group velocity measurements from huge a huge dataset of ~47 million Rayleigh and Love waves. These include fundamental mode measurements, which are sensitive to the uppermost mantle and up to 6th overtone, adding sensitivity to the transition zone, covering a period range of 16-375 s. We also present global models of mantle attenuation (degree-20), made from ~10 million Rayleigh wave amplitude measurements, including fundamental and up to 4th overtone measurements (35-275 s). All seismic maps presented also have associated uncertainty maps, which are essential for robust interpretation but also for multidisciplinary interpretations of mantle circulation models.

We constrain 3D mantle circulation models, known as TERRA models, at the present day. In order to do this, we construct 1D profiles of velocities and density from a suite of TERRA models on a 2x2 degree grid. Forward modelling of each 1D profile using MINEOS provides global predictions of seismic observables at all seismic wave periods, including phase velocity and group velocity. A misfit can then be calculated between the seismic models and predictions from the suite of TERRA models. This provides constraints on which TERRA models are most Earth-like, which will improve our understanding of mantle flow.

How to cite: Sturgeon, W., Ferreira, A. M. G., Panton, J., and Davies, J. H.: Constraining global mantle circulation models with global seismic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10944, https://doi.org/10.5194/egusphere-egu24-10944, 2024.

EGU24-11588 | ECS | Posters on site | GD10.2

Modelling the global geodynamic and seismological consequences of different phase boundary morphologies.  

Gwynfor Morgan, J. Huw Davies, Bob Myhill, James Wookey, and James Panton

Throughout Earth’s mantle, several significant phase transitions occur, with the Ol→Wd and Rw→Brm+Pc reactions (exothermic and endothermic respectively) producing large discontinuities in Earth’s seismic velocity structure at 410 and 660km depth respectively (‘410’ & ‘660’). The equilibrium depth of these reactions is sensitive to temperature, and the resulting topography has been observed with various seismic phases. Numerical modelling from the 1980s onwards has suggested that the topography on endothermic phase transitions can stagnate downwellings and even layer mantle convection for extreme Clapeyron slopes or density changes. The thermodynamic properties of the post-spinel reaction make it unlikely that slabs would stagnate due to effects associated with phase transitions. At cooler temperatures the post-spinel reaction splits into two reactions (Rw + Ak → Ak + Pc → Brm + Pc) which seems to explain well aspects of the observed topography of the ‘660’ discontinuity. It has been suggested that this second reaction (which has a more extreme Clapeyron slope than the post-spinel reaction) could stagnate downwellings. Recently, Ishii et al (2023) suggested that the post-garnet reaction (Gt → Brm + Cor [+ St]) is in fact univariant, producing a sharp reaction that is endothermic for cooler temperatures and exothermic at higher temperatures – and that this may contribute to slab stagnation. Here, we test these slab stagnation mechanisms using realistic mineral physics and whole-mantle convection models (MCMs).

The lack of anti-correlation between the topography of the ‘410’ and ‘660’ discontinuities does not match simple theory if they are controlled solely by temperature variations across the post-olivine and post-spinel reactions respectively. Previous work has shown that the calculated topography on the discontinuities can be markedly different for various single-composition mantles generated from MCMs (Papanagnou et al, 2022). Here we will explore the impact of laterally varying chemistry generated in thermochemical MCMs on global discontinuity topography.

How to cite: Morgan, G., Davies, J. H., Myhill, B., Wookey, J., and Panton, J.: Modelling the global geodynamic and seismological consequences of different phase boundary morphologies. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11588, https://doi.org/10.5194/egusphere-egu24-11588, 2024.

EGU24-11790 | Orals | GD10.2

Thermo-compositional model of the South African cratonic mantle obtained from seismic and gravity data 

Magdala Tesauro, Mikhail Kaban, and Mohammad Youssof

Xenolith data reveal lateral and vertical compositional variations of the upper mantle of the Precambrian cratons, indicating a different degree of refertilization with respect to the most depleted mantle in iron components, characterizing the oldest Archean cratons. The South African cratonic region is composed of the Kaapvaal and Zimbabwe craton, both of Archean age, having deep and fast lithospheric roots, which are likely depleted in heavy constituents. In contrast, there exist regions, such as the Limpopo belt, a terrane that was trapped between the Kaapvaal and Zimbabwe cratons during their collision (2.6–2.7 Ga), and Bushveld Complex, an area characterized by intraplate magmatism occurred 2.05 Ga, whose negative velocity anomalies in the upper mantle, indicate a more fertile composition due to metasomatism. To unravel the origin of these anomalies and link them to the tectonic history of the area, we apply an integrative technique based on a joint interpretation of the seismic tomography and gravity data, which can discern temperature and compositional variations. To this aim, we combine the global surface seismic tomography model [1] with the embedded regional model [2], derived from teleseismic tomographic inversion of the S-body wave dataset recorded by the Southern African Seismic Experiment. The combined seismic model is inverted for temperature, assuming an initial composition, representative of a refertilized upper mantle [3], using a mineral physics approach [4]. The composition and temperature of the upper mantle are iteratively changed, increasing progressively the amount of iron depletion, to fit the residual density, obtained from the joint inversion of the residual gravity and residual topography. The great advantage of using both the gravity field and residual topography lies in their different dependence on the distribution of density heterogeneities (depth and size). In a second type of inversion we included the GOCE gravity gradient [5]. The obtained results show that the most depleted lithosphere is confined at depth lower than 100 km, generating a temperature higher than ~200, with respect to that of a refertilized lithosphere. The Southeastern Terrane of the Kaapval craton are characterized by thicker and more depleted cratonic roots than the Zimbawe craton. The presence of a depleted mantle below the cratonic crust may indicate that the crust and mantle have been connected since the craton formation. These results, related to the different structures and properties of the upper mantle, improve our understanding of the evolution of the South African cratonic lithosphere.

References

[1] Schaeffer and Lebedev, 2013. https://doi.org/10.1093/gji/ggt095

[2] Youssof et al., 2015. http://dx.doi.org/10.1016/j.epsl.2015.01.034

[3] Griffin et al., 2004. doi:10.1016/j.chemgeo.2004.04.007

[4] Conolly, 2005. doi:10.1016/j.epsl.2005.04.033

[5] Kaban et al., 2022. doi.org/10.1007/s00024-021-02925-6

How to cite: Tesauro, M., Kaban, M., and Youssof, M.: Thermo-compositional model of the South African cratonic mantle obtained from seismic and gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11790, https://doi.org/10.5194/egusphere-egu24-11790, 2024.

EGU24-12417 | Posters on site | GD10.2

Quantifying mantle mixing through configurational Entropy 

Cedric Thieulot, Erik van der Wiel, and Douwe van Hinsbergen

Geodynamic models of mantle convection provide a powerful tool to obtain insights into the structure and composition of the Earth’s mantle that resulted from a long history of differentiating and mixing. Comparing such models with geophysical and geochemical observations is challenging as these datasets often sample entirely different temporal and spatial scales. Here, we explore the use of configurational entropy, based on tracer and compositional distribution on a global and local scale. We show means to calculate configurational entropy in a 2D annulus and find that these calculations may be used to quantitatively compare long-term geodynamic models with each other. The entropy may be used to analyze, with a single measure, the mixed state of the mantle as a whole and may also be useful to validate numerical models against local anomalies in the mantle that may be inferred from seismological or geochemical observations.

How to cite: Thieulot, C., van der Wiel, E., and van Hinsbergen, D.: Quantifying mantle mixing through configurational Entropy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12417, https://doi.org/10.5194/egusphere-egu24-12417, 2024.

EGU24-14060 | ECS | Orals | GD10.2 | Highlight

Constraining LLSVPs initial conditions and heating scenarios from simulations of mantle convection with heterogeneous thermal conductivity 

Joshua Guerrero, Frédéric Deschamps, Wen-Pin Hsieh, and Paul Tackley

New insights from models of thermo-chemical mantle convection featuring heterogeneous thermal conductivity indicate that heat-producing element (HPE) enrichment in large low shear velocity provinces (LLSVPs) significantly impacts the long-term stability of these regions. Because the internal heating rate was more significant in the past, thermal conductivity's influence on thermal buoyancy (and bulk erosion) must have also been more substantial. As a consequence, the initial volume of the LLSVPs may have been significantly larger than their present-day volume. In numerical models, the evolution and stability of LLSVPs are often initiated by considering a dense and uniformly distributed layer on top of the core-mantle boundary. From energy balance calculations, a thin layer of LLSVP material (small mantle volume fraction) supports more HPE enrichment than a thicker layer (larger mantle volume fraction) to maintain the mantle's heat budget. For example, an initial layer thickness of 160km (~3% mantle volume) implies present-day HPE enrichment factors up to ~70 times the ambient mantle heating rate. This should be compared with more conservative factors of 10 to 20 for similar dense layer thicknesses employed in previous studies of thermochemical pile stability. Thus, HPE enrichment may have been significantly underestimated in earlier models of LLSVP evolution. Conversely, and assuming that LLSVPs formed from a much larger reservoir, HPE enrichment may be overestimated based on the present-day LLSVP volume. Our study considers LLSVPs with a primordial geochemical reservoir composition (consistent with an undegassed 4He/3He signature and HPE enrichment). We examine models of thermo-chemical mantle convection models with time-dependent internal heating rates and HPE enrichment (implied by the initial dense layer thicknesses). In this new context, we re-examine, in particular, the impact of a fully heterogeneous lattice thermal conductivity (derived from conductivity measurements of upper and lower mantle minerals). Furthermore, in light of recent developments with radiative conductivity, we also examine the added effect of a strongly temperature-dependent radiative conductivity component on the stability of LLSVPs. Using LLSVPs' present-day volume and core-mantle boundary coverage as a constraint, we recover potential initial conditions, heating scenarios, and thermal conductivity for an Earth-like model.

How to cite: Guerrero, J., Deschamps, F., Hsieh, W.-P., and Tackley, P.: Constraining LLSVPs initial conditions and heating scenarios from simulations of mantle convection with heterogeneous thermal conductivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14060, https://doi.org/10.5194/egusphere-egu24-14060, 2024.

EGU24-14786 | ECS | Orals | GD10.2

Global full-waveform inversion reveals previously undetected positive wave speed anomalies beneath the Pacific Ocean 

Thomas Schouten, Lars Gebraad, Sebastian Noe, Anna Gülcher, Sölvi Thrastarson, Dirk-Philip van Herwaarden, and Andreas Fichtner

Seismic tomography, a critical tool for studying Earth's interior structure and dynamics, has revealed positive seismic wave speed anomalies in the mantle that are commonly interpreted as slabs, the remnants of subducted lithosphere. However, classical travel-time tomography relies on the inversion of travel times of a few easily identifiable body wave phases along ray paths or volumetric sensitivity kernels, which is strongly dependent on the geometry of seismic sources and receivers. Since both of these are primarily clustered on modern convergent plate boundaries, the resulting tomographic resolution is highly variable across the mantle. Full-waveform inversion (FWI) attempts to reduce this dependence by fitting whole seismograms, thereby including many reflected and refracted body wave phases to enhance the volumetric sensitivity of the inversion.

Here, we analyse a new global tomographic model constructed using FWI. The mantle structure imaged in this model reveals significantly more positive seismic wave speed anomalies in the mantle when compared to travel-time tomography, particularly in regions with low seismic activity and limited station coverage. Notably, FWI detects positive wave speed anomalies with slab-like morphologies at ~1000 km depth beneath the Pacific Ocean that fall outside the coverage of classical travel-time tomography. We demonstrate the sensitivity of FWI to wave speed anomalies below the western Pacific using forward wavefield modelling. Importantly, we find that these newly imaged positive wave speed anomalies do not correspond to reconstructed subduction zones in existing global plate reconstructions.

Our work challenges the widespread assumption that positive wave speed anomalies (exclusively) represent subducted slabs, highlighting potential gaps in either global plate reconstructions or the current understanding of the nature of seismic anomalies in the mantle.

How to cite: Schouten, T., Gebraad, L., Noe, S., Gülcher, A., Thrastarson, S., van Herwaarden, D.-P., and Fichtner, A.: Global full-waveform inversion reveals previously undetected positive wave speed anomalies beneath the Pacific Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14786, https://doi.org/10.5194/egusphere-egu24-14786, 2024.

Subducted slabs provide the primary driving force for mantle convection, and the slab strength directly controls the transfer of the forces between the slab and the lithospheric plates at the surface. The analysis of subducted slab viscosity structure has been one of the main concerns in geodynamics over the past few decades. Previous studies, using the topography, gravity or geoid as crucial observations, have provided some constraints on the viscosity of subduction plates (Bessat et al., 2020; Hager, 1984; Moresi & Gurnis, 1996). However, slab viscosity constrained by surface topography and gravity data is significantly lower than that suggested by mineral physics laboratory experiments. It is unclear whether the free-slip top boundary condition used in many previous studies affects the inverted slab viscosity with gravity or geoid data.

In this study, we develop 2-D free-surface subduction models that can generate realistic topography by a modified "sticky-air" method using Underworld2 software (Moresi et al., 2019), and we compare the computed topography and gravity in our free-surface subduction models with observations to constrain the subducting slab viscosity. We investigate the influence of slab viscosity at the bending region and below the bending region on the topography and the gravity, respectively. Our model results support relatively weak slabs (20-120 times more viscous than the upper mantle) at the bending region, consistent with previous studies with a free-slip top boundary. The viscosity of the slab below the bending region barely affects the surface topography and gravity field, and both strong and weak slabs fit the observed topography and gravity field, suggesting that extra independent observations are needed to constrain the deep slab viscosity. Besides, in this study, we also find the comprehensive relations between subduction interface viscosity, surface topography and gravity anomaly, and trench motion. Models with trench advance have significantly low topography and gravity above the volcanic arc, contradicting subduction zone observations. Together with present trench motion observations and previous studies, we support the idea that the trench retreats under normal single-slab subduction conditions.

 

Bessat, A., Duretz, T., Hetényi, G., Pilet, S., & Schmalholz, S. M. (2020). Stress and deformation mechanisms at a subduction zone: insights from 2-D thermomechanical numerical modelling. Geophysical Journal International, 221(3), 1605–1625. https://doi.org/10.1093/gji/ggaa092

Hager, B. H. (1984). Subducted slabs and the geoid: Constraints on mantle rheology and flow. Journal of Geophysical Research: Solid Earth, 89(B7), 6003–6015. https://doi.org/10.1029/JB089iB07p06003

Moresi, L., & Gurnis, M. (1996). Constraints on the lateral strength of slabs from three-dimensional dynamic flow models. Earth and Planetary Science Letters, 138(1–4), 15–28. https://doi.org/10.1016/0012-821X(95)00221-W

Moresi, L., Giordani, J., Mansour, J., Kaluza, O., Beucher, R., Farrington, R., et al. (2019, February 18). underworldcode/underworld2: v2.7.1b (Version v2.7.1b). Zenodo. https://doi.org/10.5281/ZENODO.2572036

How to cite: Deng, L. and Yang, T.: Constraining subducting slab viscosity with topography and gravity fields in free-surface mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16119, https://doi.org/10.5194/egusphere-egu24-16119, 2024.

EGU24-16771 | ECS | Posters on site | GD10.2

Trace element and bulk chemistry of plumes and ridges in geodynamic simulations 

James Panton, Huw Davies, and Paul Beguelin

Volumetrically, the most important magmatic source on Earth is beneath mid-ocean ridges, from which mid-ocean ridge basalts (MORBs) are sourced. Second to this is plume related magmatism, the source for ocean-island basalts (OIBs). Decades of geochemical analysis have discerned that MORBs exhibit low isotopic variation, which is interpreted to mean that their source is globally homogeneous at an ocean basin (and possibly global) scale. OIBs, however, exhibit strong isotopic variation not just spatially, but even temporally, indicating a compositionally heterogenous source region. Global scale numerical geodynamic models, driven by reconstructed plate motions, generate both plume and ridge structures at which melting occurs, similar to Earth, however it is not known how well dynamic models can re-create the first-order observation that ridge lavas are typically homogenous compared to plume lavas.

Using the 3D spherical mantle convection code, TERRA, constrained by plate motion reconstructions spanning 1Gyr of Earth’s history, ridge and plume structures are simultaneously generated. The location of ridges is known from the input plate reconstruction model, while plumes are identified using the simulated temperature and radial velocity fields and a combination of K-means and density-based clustering. Using our approach, we can not only compare the properties of ridges and plumes, but can also compare the properties of ridges across different ocean basins and of individual simulated mantle plumes. Analysis of the bulk composition and melting age of tracer particles associated with ridges and plumes allows us to better interpret the history of material found in these regions. We analyse the U ratio to see if recent (~600 Ma) changes in the subducted U flux are evident in differences in the U composition of plume and ridge material.

How to cite: Panton, J., Davies, H., and Beguelin, P.: Trace element and bulk chemistry of plumes and ridges in geodynamic simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16771, https://doi.org/10.5194/egusphere-egu24-16771, 2024.

EGU24-17413 | ECS | Orals | GD10.2 | Highlight

Neutrino oscillations investigation of the base-of-the-mantle structure: simulation tools and preliminary results 

Rebekah Pestes, Joao Coelho, Yael Deniz Hernandez, Stéphanie Durand, Nobuaki Fuji, Eric Mittelstaedt, and Véronique Van Elewyck

The origin of Large Low-Velocity Provinces (LLVPs) at the base of mantle remains a mystery, but particle physics may be able to provide another piece of the puzzle. Using a phenomenon known as neutrino oscillation, atmospheric neutrino experiments are sensitive to the electron number density inside the Earth, which is complementary to the information seismology can provide. In order to reveal lateral heterogeneities in density and chemical composition such as those expected for LLSVPs across the Earth’s lower mantle, we have developed a numerical method that allows us to compute the sensitivity of neutrino oscillation data to 3D Earth structure. Based on this approach, we will present some preliminary assessment of the potential resolving power of ongoing and future neutrino experiments.

How to cite: Pestes, R., Coelho, J., Deniz Hernandez, Y., Durand, S., Fuji, N., Mittelstaedt, E., and Van Elewyck, V.: Neutrino oscillations investigation of the base-of-the-mantle structure: simulation tools and preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17413, https://doi.org/10.5194/egusphere-egu24-17413, 2024.

EGU24-1383 | ECS | PICO | CR5.1

Basal debris at an Antarctic ice rise revealed by seismic amplitude-vs-angle analysis.  

Ronan Agnew, Alex Brisbourne, Adam Booth, and Roger Clark

Reconstructing past ice sheets is important for understanding the response of modern ice sheets to changes in climate. The evolution of the Weddell Sea Sector’s grounding line since the last glacial maximum (LGM) to its present position remains ambiguous; previous authors have proposed hypotheses both of monotonic grounding line retreat and of rapid grounding line retreat followed by readvance. However, distinguishing these scenarios with current observations remains difficult. To explore these scenarios, we report seismic measurements of basal properties at KIR, an ice rise in the Weddell Sea Sector, West Antarctica. A three-component seismic survey enabled detection of the compressional (P) wave reflection and the converted (PS) wave reflection (an incident P wave converted to a shear wave at the base-ice reflector) from the base of KIR. Amplitude-vs-angle (AVA) analysis aims to constrain the physical properties (namely density, seismic velocity, by measuring the variation of reflectivity with incidence angle at the reflector. By jointly inverting the AVA responses of the PP wave reflection and the PS reflection, we increase the confidence in the interpretation of the base-ice properties. 

Analysis of PP and PS AVA responses at KIR indicates that the reflection arises from a material with a P wave velocity of 4.03 ± 0.05 km/s, an S wave velocity of 2.16 ± 0.06 km/s and a density of 1.44 ± 0.06 g/cm3; these properties are consistent with a reflection from a layer of entrained basal debris, with 20-30% debris by volume. The observed properties are not indicative of interference at a thin layer, as observed beneath glaciers elsewhere. The absence of deeper subglacial reflections indicates a poorly-defined boundary between this basal debris layer and the underlying subglacial material, which we therefore propose consists of frozen sediments . If this interpretation is correct, the presence of a debris layer overlying basal frozen sediment indicates a potential retreat/readvance scenario for KIR. A possible scenario is a previous episode of flow during which KIR may have been weakly grounded as an ice rumple, followed by grounding on the lee side of the bathymetric high and subsequent freezing of subglacial sediments. However, the origin of such a homogeneous and debris-rich layer remains unclear. The indication of a reflection from a basal debris layer raises questions about whether conventionally interpreted basal reflections can truly be considered as such, and whether these interpretations may mask the true nature of the underlying subglacial material. This ambiguity may be most effectively reconciled by borehole sampling.

How to cite: Agnew, R., Brisbourne, A., Booth, A., and Clark, R.: Basal debris at an Antarctic ice rise revealed by seismic amplitude-vs-angle analysis. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1383, https://doi.org/10.5194/egusphere-egu24-1383, 2024.

EGU24-4532 | ECS | PICO | CR5.1

Conductive textile electrodes for time-efficient ERT surveys performed in coarse-blocky mountain environments 

Mirko Pavoni, Jacopo Boaga, Alexander Bast, Matthias Lichtenegger, and Johannes Buckel

Electrical resistivity tomography (ERT) is one of the most accurate geophysical techniques to distinguish between frozen and unfrozen ground in permafrost areas. Performing the measurements, however, requires considerable logistics and time efforts. This is mainly due to the fact that optimal galvanic contact between the electrodes and the ground surface is necessary to collect reliable ERT datasets. Therefore, the traditional steel-spike electrodes must be steadily coupled between the boulders and wet with salt water on coarse blocky surfaces. To further decrease the contact resistances, sponges soaked in salt water can be inserted between the spike and the surface of rocks. Nevertheless, this traditional coupling system is particularly time-consuming, making it challenging to collect several ERT survey lines in a single workday in mountain environments. Recently developed conductive textile electrodes were applied to facilitate the deployment of ERT arrays in rock glacier environments. Instead of hammering the steel spikes, the conductive textile electrodes can be easily pushed between the boulders and wet with less water (compared to the sponges). Consequently, this new electrode approach decreases the time needed to prepare an ERT array. In this work, we evaluate the performance of the textile electrodes by comparing these with the traditional electrode approach, considering common investigation lines. This comparative test has been carried out in three test sites, which present different lithologies, surface characteristics and using different electrode spacing. The collected datasets were statistically analysed with robust regression analysis and Wilcoxon rank-sum test to examine the accuracy and significant differences between the two electrode systems regarding contact resistances, injected electrical current, measured apparent resistivities, reciprocal error, and inverted resistivity values. The obtained results demonstrate that conductive textile electrodes are suitable to collect reliable ERT datasets and, consequently, applying this approach in future ERT measurements performed in high mountain environments with coarse blocky surfaces (e.g. rockfall deposits, blocky slopes, or rock glaciers) would allow to acquire more survey lines (e.g. realisation of pseudo-3D geometries) extending the characterisation of the subsurface.

How to cite: Pavoni, M., Boaga, J., Bast, A., Lichtenegger, M., and Buckel, J.: Conductive textile electrodes for time-efficient ERT surveys performed in coarse-blocky mountain environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4532, https://doi.org/10.5194/egusphere-egu24-4532, 2024.

EGU24-5435 | PICO | CR5.1

Demonstrating a large UAV for Antarctic environmental science 

Tom Jordan and Carl Robinson

Airborne survey is one of the most important observational techniques in environmental science. This is especially true in polar settings where access is challenging and observational requirements, such as ice sounding radar, in situ study of turbulent atmospheric processes, cloud cover, or requirements for high resolution potential field data, limit use of satellite data. Although critical, airborne survey using traditional platforms, such as the versatile twin otter aircraft operated by the British Antarctic Survey (BAS), come with a relatively high logistical, financial, and environmental (CO2) footprint. Larger UAV’s offer an alternative, but as yet un-realised, lower impact platform to deliver the same, if not more scientific data.

Through the Innovate UK SWARM project BAS is collaborating with Windracers to trial their large (10 m wing span) Ultra UAV as a platform for environmental science. Making use of the large (700 L/max 100 kg), easily accessible payload bay and a series of interchangeable payload floors this trial will be carried out in February/March 2023. The science payloads will include: Atmospheric (turbulence probe), environmental (hyperspectral and visual cameras), cryosphere (600-900 MHz accumulation radar), and potential field geophysics (gravity/magnetic sensors). The missions, between 10 and 330 km long, will be flown beyond visual line of sight (BVLOS) of the operator using the Distributed Avionics autopilot, including take-off and landing, which will be overseen by an in-field safety pilot.

Here we present the first results of this trial, including our experience integrating BVLOS UAV operations with traditional aircraft in an Antarctic context and initial results and lessons learned from the four trailed instrument suites. Our demonstration will be an important milestone in the transition to widespread use of larger UAVs for environmental science. We will discuss how the reduced environmental and logistical impact can open up new opportunities in Antarctic and beyond.

How to cite: Jordan, T. and Robinson, C.: Demonstrating a large UAV for Antarctic environmental science, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5435, https://doi.org/10.5194/egusphere-egu24-5435, 2024.

EGU24-5751 | ECS | PICO | CR5.1

Firn Density Distribution and Annual Snow Water Equivalent Estimates from Ground Penetrating Radar 

Akash Patil, Christoph Mayer, and Matthias Braun

Abstract: Accurate estimation of glacier volume-to-mass conversion relies on a thorough understanding of firn density, both in-depth and over time. Ground-penetrating radar (GPR) serves as a suitable geophysical tool to trace internal reflection horizons (IRHs) and estimate the physical properties of different layers. Our goal is to characterize the IRHs as annual layers and ascertain the spatial firn density-depth profile in the accumulation zone of the Aletsch glacier.

The process involves identifying IRHs from radargrams and iteratively selecting the annual layers by excluding unreasonable layer structures. For an accurate estimation of firn density distribution, it is necessary to derive the velocity-depth profile of electromagnetic waves within the firn zone. The common mid-point (CMP) method was applied to track the velocity distribution within the firn body. Additionally, a method was introduced to estimate the velocity-depth profile for longer GPR profiles by backtracking the calculated velocity from the CMP gather.

To validate IRHs as annual firn layers, we utilized annual accumulation measurements at a nearby stake for Snow Water Equivalent (SWE) estimation. The resulting firn density-depth profile was compared to different firn densification models, considering regional meteorological information. This approach enables us to determine a reliable density-depth function for bulk SWE computations. The study also addresses uncertainties associated with selecting IRHs as annual layers and enhances the application of local volume-to-mass estimates.

How to cite: Patil, A., Mayer, C., and Braun, M.: Firn Density Distribution and Annual Snow Water Equivalent Estimates from Ground Penetrating Radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5751, https://doi.org/10.5194/egusphere-egu24-5751, 2024.

EGU24-7654 | ECS | PICO | CR5.1

Coupling Solid Earth and ice temperature models to estimate geothermal heat flow 

Judith Freienstein, Wolfgang Szwillus, Marion Leduc-Leballeur, Giovanni Macelloni, and Joerg Ebbing

Geothermal heat flow (GHF) is a key element of Solid Earth-cryosphere interactions. However, polar regions as Antarctica are only sparsely covered with heat flow determinations from boreholes, so one must rely on interpolation or regression models of GHF (e.g. machine learning) from other sources to derive a regional map. Interpolation/regression of GHF in this manner depends strongly on the available sparse boreholes, which can distort the resulting regional map.

Additional information can be gained from the SMOS (Soil Moisture and Ocean Salinity) satellite by inferring ice temperature profiles with a Bayesian inversion from remote sensing microwave radiometer data. This retrieval uses geothermal heat flow as a free parameter so that it provides a posterior distribution of the GHF needed to explain the ice temperature profiles.

We aim to reconcile geophysical geothermal heat flow models with the ice temperature profiles and improve the estimates of GHF with this coupling.

We use stationary thermal modelling where we force the ice temperature and lithospheric temperature model to converge at the base of the ice. Using stochastic inversion, we estimate the thermal parameters in the lithosphere. The posterior distribution of the retrieval as constraint for the GHF is included as prior distribution to the inversion to the stationary thermal modelling so that the GHF with the highest likelihood can be estimated.

With our approach, we can evaluate a GHF distribution that both explains the ice temperature and lithospheric temperature models and covers large parts of Antarctica.

How to cite: Freienstein, J., Szwillus, W., Leduc-Leballeur, M., Macelloni, G., and Ebbing, J.: Coupling Solid Earth and ice temperature models to estimate geothermal heat flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7654, https://doi.org/10.5194/egusphere-egu24-7654, 2024.

EGU24-8245 | ECS | PICO | CR5.1

Sensitivity Study for Seismic Waves Guided in an Ice Pack: Influence of the Frequency Content and Snow Layer Thickness Covering the Ice 

Hooshmand Zandi, Ludovic Moreau, Ludovic Métivier, and Romain Brossier

Studying Arctic sea ice is essential as it plays an important role in climate regulation, influencing weather
patterns, as well as impacting the local ecosystems and living conditions of people. Among different
methods for collecting data and studying sea ice, seismology has proved to be an efficient way to extract
the ice properties, from which the mechanical behavior of sea ice can be explored. Seismic data recorded on
sea ice, using 3-component geophones, are used as a starting point to derive useful information regarding
the ice. To devise an efficient inversion method for deriving ice properties, an effective tool would be
necessary to generate synthetic data in a way that encompasses the physics of sea ice. While there are
approximate solutions to wave propagation problem in a floating ice layer based on plate theory, which is
based on the assumptions of homogeneity of the ice layer and valid at low values of frequency×wavelength,
numerical counterparts such as wavenumber integration method and finite element method have been
also used to to create synthetic waveforms. The numerical methods have shown the limitations of these
approximate solutions in modeling wave propagation; nonetheless, the effects of these limitations on the
estimations of the location of icequakes and thickness of ice need to be investigated.

In this study, these limitations are explored. To do this, two possible scenarios that can happen in
practice are taken into account: (1) when there is high-frequency content in the source generating the
seismic data, and (2) when the physical model includes a snow layer overlying the ice layer. First, we
will show the limitations of the approximate solutions for these two cases by comparing the waveforms,
derived from these approximate solutions, with those of a numerical method at a given distance from
the source. The numerical used here is spectral element method. Then, the effects of these limitations
on the estimations of icequake location and ice thickness are explored in an inversion process, in which
synthetic data are created using the approximate solutions. Results indicate that when there are high-
frequency content in the data and a snow layer on top of the ice, the use of the approximate solutions
to generate synthetic data introduces bias in the estimation of ice thickness and source-receiver distance
in the inversion process. This bias is in the form of underestimations, smaller ice thicknesses and smaller
source-receiver distances. Furthermore, to tackle the biases associated with the inversion method based on
the approximate solutions, a novel strategy is adopted, where a database of simulations using the proposed
numerical method is built for various models of ice and snow. Here the inversion comprises of searching
in the database to find the best ice thickness and source-receiver distance for each icequake. In addition,
the database-based inversion reduces the computational cost. Thanks to this inversion strategy, and
using real data recorded on sea ice, the ice thicknesses along different source-receiver paths are estimated
efficiently, from which a 3D map of ice thickness is constructed.

How to cite: Zandi, H., Moreau, L., Métivier, L., and Brossier, R.: Sensitivity Study for Seismic Waves Guided in an Ice Pack: Influence of the Frequency Content and Snow Layer Thickness Covering the Ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8245, https://doi.org/10.5194/egusphere-egu24-8245, 2024.

EGU24-9857 | ECS | PICO | CR5.1

Broadband Spectral Induced Polarization in Permafrost Peatlands of Northern Sweden  

Madhuri Sugand and Andreas Hördt

Permafrost peatlands, located in the Arctic and high mountain regions, are typically known to be ice-rich. This is primarily linked to significant water content and often oversaturation, a characteristic property of peat soil. The current understanding of the effects of human-induced climate warming suggests that these regions are approaching a climatic tipping point with substantial permafrost thaw expected in the coming decades. Ice content is an important parameter for modelling permafrost evolution and at present limited studies exist that determine its in-situ spatial distribution in such areas.

The geophysical method known as high-frequency induced polarisation (HFIP) is advantageous for cryohydrological research in these environments. This method can capture the frequency-dependent polarisation of ice (also termed dielectric relaxation peak), which occurs within the range of 100 Hz to 100 kHz and is expressed by complex resistivity. Therefore, by analysing the spectral behaviour of this complex resistivity within the target frequency range the distribution and quantity of ice can be estimated.

The results from the latest field campaign conducted at Storflaket mire and Stordalen mire in Abisko, Sweden, are presented. Two-dimensional HFIP profiles were measured to resolve the near-surface unfrozen layer (no-ice) and the underlying frozen layer (ice-bearing). The measurements were performed in late summer when the depth of the unfrozen layer was at its maximum. Field data are inverted as independent frequencies to obtain the spectral variation of complex resistivity. No-ice and ice-bearing regions are classified by the presence of the relaxation peak. Subsequently, a two-component mixture model, with one component as ice and the second as the surrounding matrix, is applied to determine ice content distribution. Boundary constraints and starting parameters are chosen using the spectral analysis of the inverted complex resistivity. The model accuracy is evaluated using unfrozen layer probing and a permafrost core extracted along the HFIP profile. The HFIP-derived ice content distribution is consistent with unfrozen layer probing, i.e., the classification of no-ice and ice-bearing regions is successful. The model tends to underestimate ice content percentages compared to permafrost core laboratory measurements. This discrepancy can be explained since laboratory measurements are based on gravimetric water content and assumes all pore-water is frozen. However, it is known that residual pore-water is present in these soils even below 0°C. Additionally, it is observed that the model performs well when the ice content percentage is 10% or greater and its applicability might be limited in scenarios where the ice content is less than 10%.

The latest results are discussed in comparison with previous findings from Heliport, a permafrost mire also located in Abisko. In the Heliport study, HFIP successfully resolved the complex resistivity and ice content distribution on a larger scale. Building on the field knowledge gained at Heliport, this study incorporates improvements in electrode configuration setup, data acquisition speed, and minimising cable-earth coupling effects. The findings contribute to the understanding of the induced polarisation of permafrost peatlands, which is an underexplored area from a geophysical perspective.

How to cite: Sugand, M. and Hördt, A.: Broadband Spectral Induced Polarization in Permafrost Peatlands of Northern Sweden , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9857, https://doi.org/10.5194/egusphere-egu24-9857, 2024.

EGU24-10814 | ECS | PICO | CR5.1

Analysis of H/V spectral ratio curves from passive seismic data acquired on glaciers worldwide 

Julien Govoorts, Koen Van Noten, Corentin Caudron, Bergur Einarsson, Thomas Lecocq, Sylvain Nowé, Finnur Pálsson, Jonas Pätzel, and Harry Zekollari

Estimations of bedrock topography below glaciers and ice thickness are vital for quantifying freshwater availability for surrounding populations and understanding the contribution of melting glaciers to sea-level rise in the context of global warming. While active seismology is commonly used for ice thickness estimation, the utilization of passive methods remains relatively rare. Passive seismology solutions offer cost-effectiveness, non-invasiveness and continuous monitoring capabilities that present valuable benefits in glaciological research.

Over the past two decades, numerous seismic stations have been deployed on glaciers worldwide for various purposes. Through passive seismology approaches, these seismic stations could show their potential as new sources of ice thickness measurements and feed the related database. For this purpose, we analyzed data of 3-components seismic sensors from different deployments as well as data from open access databases, such as IRIS, employing the Horizontal-to-Vertical Spectral Ratio (HVSR) technique. HVSR has been predominantly used in microzonation studies to determine site effects and the thickness of sediments in sedimentary basins.  Even though the use of this technique in glacial seismology is quite new, HVSR has been already utilized to estimate in-situ ice thickness, to retrieve the basal properties or to detect cavities under the ice.

Our primary objective is to demonstrate the potential of the HVSR technique to retrieve in-situ ice thickness on different glaciers. Subsequently, we will compare the HVSR results with different data sources including models, ground-penetrating radar or active seismology. By performing this comparison we evaluate the limitations of the HVSR method in an icy environment. We investigate these limitations by studying the effect of other natural agents such as wind on the H/V amplitude and fundamental frequency retrieved from the HVSR curves. Having a global understanding of these influences will eventually help deciphering variations in continuous H/V monitoring.

How to cite: Govoorts, J., Van Noten, K., Caudron, C., Einarsson, B., Lecocq, T., Nowé, S., Pálsson, F., Pätzel, J., and Zekollari, H.: Analysis of H/V spectral ratio curves from passive seismic data acquired on glaciers worldwide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10814, https://doi.org/10.5194/egusphere-egu24-10814, 2024.

EGU24-11300 | PICO | CR5.1

Icequakes beneath Thwaites Glacier eastern shear margin  

Emma C. Smith, Ronan Agnew, Adam D. Booth, Poul Christoffersen, Eliza J. Dawson, Lucia Gonzalez, Marianne Karplus, Daniel F. May, Nori Nakata, Andrew Pretorius, Paul Summers, Slawek Tulaczyk, Stephen Vietch, Jake Walter, and Tun Jan Young

The stability of Thwaites Glacier, the second largest marine ice stream in West Antarctica, is a major source of uncertainty in future predictions of global sea level rise. Critical to understanding the stability of Thwaites Glacier, is understanding the dynamics of the shear margins, which provide important lateral resistance that counters basal weakening associated with ice flow acceleration and forcing at the grounding line. The eastern shear margin of Thwaites Glacier is of interest as it is poorly topographically constrained, meaning it could migrate rapidly, causing further ice flow acceleration and drawing a larger volume of ice into the fast-flowing ice stream.  

In this study, we present an analysis of ~4000 icequakes, recorded over a two-year-period on a broadband seismic array deployed across the eastern shear margin of Thwaites Glacier. The array consisted of seven three-component seismometers, deployed around a central station in a circle, roughly 10 km in diameter.  We use an automated approach to detect and locate “high-frequency” seismic events (10-90 Hz), the majority of which are concentrated in clusters around the ice-bed interface on the slow-moving side of the shear margin, as opposed to within the ice-stream itself. The event waveforms exhibit clear shear-wave splitting, indicative of the presence of an anisotropic ice fabric, likely formed within the shear margin, which is consistent with published radar studies from the field site. Initial analysis of the split shear-waves suggests that they can be used to better constrain the region's ice fabric, and likely used to infer past shear margin location and assess the future stability of this ice rheology.

How to cite: Smith, E. C., Agnew, R., Booth, A. D., Christoffersen, P., Dawson, E. J., Gonzalez, L., Karplus, M., May, D. F., Nakata, N., Pretorius, A., Summers, P., Tulaczyk, S., Vietch, S., Walter, J., and Young, T. J.: Icequakes beneath Thwaites Glacier eastern shear margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11300, https://doi.org/10.5194/egusphere-egu24-11300, 2024.

EGU24-11386 | PICO | CR5.1

Towards a unified description of the count rate – snow water equivalent relationship in cosmic-ray neutron sensing 

Benjamin Fersch, Markéta Součková, Paul Schattan, Nora Krebs, Jannis Weimar, Carsten Jahn, Peter Martin Grosse, and Martin Schrön

The observation of near-ground cosmogenic neutrons enables the monitoring of various water storage variations at the land surface at the field scale including soil moisture and the water content of snow layers. The parabolic neutron-count versus soil moisture function is quite uniform among different locations, and soil types and requires typically a one-time-only in situ reference observation. For the detection of snowpack water equivalent (SWE) variations by cosmic-ray neutron sensing such a uniform approach has so far not been developed. Therefore, the establishment of new cosmic-ray snow monitoring sites requires substantial in situ measurements for obtaining the local relationship of SWE amounts and neutron count rates. Observations suggest that the relationship is quite uniform for grass-vegetated locations which is different to what is found for stony ground.

Within the framework of the research unit Cosmic Sense, we generated extensive in situ measurements of snow water equivalent and cosmogenic neutron count rates at various sites with differing elevations in the German and Austrian Alps. From these data, we investigate commonalities among the site conditions and if the varying patterns of the relationships can be reasonably explained by physical reasons and therefore be modeled with a unified approach.

How to cite: Fersch, B., Součková, M., Schattan, P., Krebs, N., Weimar, J., Jahn, C., Grosse, P. M., and Schrön, M.: Towards a unified description of the count rate – snow water equivalent relationship in cosmic-ray neutron sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11386, https://doi.org/10.5194/egusphere-egu24-11386, 2024.

EGU24-11729 | ECS | PICO | CR5.1

A physically-based fractal model for predicting the electrical conductivity in partially saturated frozen porous media 

Haoliang Luo, Damien Jougnot, Anne Jost, Aida Mendieta, and Luong Duy Thanh

Macro-scale transport properties (e.g., electrical conductivity, effective excess charge density and hydraulic conductivity) can be conceptualized as capillary bundle models, in which the pore structure of porous medium is viewed as a bundle of capillary tubes of varying sizes. This approach can be used to understand and address the relationship between the petrophysical properties and the geometry of soil phases. When the temperature of porous medium decreases below the freezing temperature, the soil physical properties (transport properties) change drastically. This is attributed to the complexity of the heterogeneous formation of ice in the porous medium. Therefore, understanding better pore ice formation from microscale insights is crucial to describe the evolution of electrical conductivity with temperature in frozen porous medium. In this study, we consider that capillary radius and tortuous length follow fractal distributions, and that total conductance at the microscale scale is determined by the Gibbs-Thomson and Young-Laplace effects as well as by the surface complexation model. A new capillary bundle model is then proposed using an upscaling procedure, which considers the effects of both bulk and surface conductions. Based primarily on an electrical resistance apparatus and the NMR method, a series of laboratory experiments are carried out to study the influence of initial water saturation and salinity on electrical conductivity under unfrozen and frozen conditions. Additionally, the rationality and validity of the proposed model were successfully verified with published data in the literature and experimental data of this study. Our new physically-based model for electrical conductivity opens up new possibilities to interpret electrical and electromagnetic monitoring to easily infer changes in key variables such as liquid water content and moisture gradients.

How to cite: Luo, H., Jougnot, D., Jost, A., Mendieta, A., and Thanh, L. D.: A physically-based fractal model for predicting the electrical conductivity in partially saturated frozen porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11729, https://doi.org/10.5194/egusphere-egu24-11729, 2024.

EGU24-12583 | PICO | CR5.1

Locating subglacial cavities and investigating basal conditions on glaciers with ambient seismic noise: toward acquisition optimization. 

Eric Larose, Noelie Bontemps, Antoine Guillemot, and Laurent Baillet

Subglacial cavities may trap a considerable quantity of liquid water, causing devastating outburst floods in densely populated mountain areas. Both active and passive geophysical methods are employed for the glacier-bedrock interface and intra-glacial characterization, including Ground Penetrating Radar (GPR), refraction seismic, borehole measurements, and surface nuclear magnetic resonance (SNMR). 

Ambient seismic noise can be collected by light and dense arrays at a relatively moderate cost, and allows to access some mechanical properties of the glacier, including the detection and localization of ice cavities and, possibly, basal detachment, taking advantage of spectral anomalies in the horizontal-to-vertical-spectral ratio (HVSR) and in the Vertical-to-Horizontal spectral ratio (VHSR). Specifically, a peak in the VHSR indicates a low impedance volume beneath the surface [1,2]. As a simple picture, we can refer to the “bridge” vibrating mode, where the vertical displacement in the middle of the bridge largely dominates other components of the movement.  Antunes et al. [2] furthermore noticed that the VHSR gives information about seismic energy anomalies generated by fluids in reservoirs since the wavefield is polarized mainly in the vertical direction.
In this work, we apply the HVSR and VHSR techniques to locate a subglacial water-filled cavity in the Tête Rousse glacier (Mont Blanc area, French Alps), using 15 days of data collected in may, 2022 [3]. The results also confirm the general basal conditions of the glacier suggested by other methods, locating temperate areas of the glacier where basal detachments are possible.

We evaluate the optimal seismic noise record duration to obtain a reliable and stable mapping of the VHSR over the glacier to properly locate the main cavity (or secondary cavities). In our case, results suggest that 6 days of record are enough to detect and locate a cavity

 

[1] Saenger, E-H. et al: A passive seismic survey over a gas field: Analysis of low-frequency anomalies, Geophysics, 74 (2), O29–O40 (2009).

[2] Antunes V. et al: Insights into the dynamics of the Nirano Mud Volcano through seismic characterization of drumbeat signals and V/H analysis. Journal of Volcanology and Geothermal Research, 431 (2022).

[3] A. Guillemot, N. Bontemps, E. Larose, D. Teodor, S. Faller, L. Baillet, S. Garambois, E. Thibert, O. Gagliardini, C. Vincent: Investigating Subglacial Water-filled Cavities by Spectral Analysis of Ambient Seismic Noise : Results on the Polythermal Tête-Rousse Glacier (Mont Blanc, France), Geophys. Res. Lett. accepted (2024). DOI:10.1029/2023GL105038

How to cite: Larose, E., Bontemps, N., Guillemot, A., and Baillet, L.: Locating subglacial cavities and investigating basal conditions on glaciers with ambient seismic noise: toward acquisition optimization., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12583, https://doi.org/10.5194/egusphere-egu24-12583, 2024.

The Totten Glacier is a fast moving glacier that serves as a major outlet of the East Antarctic Ice Sheet. During December 2018 and January 2019, we deployed a 12 station broadband seismic array near the grounding zone of the Totten Glacier. We observed a significant number ( > 10,000) of repeating basal stick-slip icequakes across the region. Much of this seismic activity was dominated by higher frequency events (20-75 Hz) similar in size and temporal character (“bursty”) to those found in previous studies, such as those on the Rutford Ice Stream and Greenland Ice Sheet. Additionally, we observe a large number of repeating events dominated by lower frequencies (< 10 Hz) that have larger magnitudes and longer inter-event time than the high-frequency seismic activity. We will provide an overview into both the temporal and spatial variability of this seismic activity and discuss implications for fast flow in the region.

How to cite: Winberry, P.: Repeating Glacier Seismicity Near the Totten Glacier Grounding Zone., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12865, https://doi.org/10.5194/egusphere-egu24-12865, 2024.

EGU24-13124 | ECS | PICO | CR5.1

Exploring englacial hydrology with surface nuclear magnetic resonance 

Laura Gabriel, Marian Hertrich, Raphael Moser, Christophe Ogier, Hansruedi Maurer, and Daniel Farinotti

The amount and distribution of liquid water inside a glacier are relevant for its dynamics, related natural hazards or for sediment transport. Experimentally investigating the glacier's hydrology is challenging because of restricted accessibility, investigation depth, material properties, and environmental factors. In addition, the subglacial drainage network is highly dynamic and undergoes diurnal and seasonal changes.

This contribution investigates the application of surface nuclear magnetic resonance (SNMR) to characterize the liquid water distribution within Swiss Alpine glaciers. Analogous to magnetic resonance imaging (MRI) in medicine, SNMR utilizes an oscillating magnetic field to excite nuclear spins of hydrogen atoms within water molecules. The subsequent spin relaxation is then analyzed, providing insights into the probed material. In simpler terms, this process allows us to directly detect liquid water in ice and gain information on its spatial distribution.

We conducted a first SNMR field survey on Rhonegletscher in the summer of 2023. During this survey, we tested various measurement configurations, including separate-loop measurements and the application of noise-compensation loops. The latter proved crucial for subsequent data processing. After carefully optimizing the processing scheme, we extracted SNMR signals in several recordings despite the poor signal-to-noise ratio. The results were compared to 1D forward-modelled data, suggesting that the average water content in the survey area lay between 0.7 and 1.2 %. In addition, we could show that a homogenous water distribution over the entire ice column cannot explain the observed data and that we need to consider more complex subsurface models including at least one additional water layer. Specifically, our ongoing research aims to identify which configurations of the subglacial water distribution (e.g., homogenous water distribution vs layered water-ice structure resulting from an englacial water channel) are distinguishable experimentally. Moreover, the study seeks to optimize measurement design and data processing methodologies to acquire information more efficiently, and effectively handle the expected low signal-to-noise ratios.

In future field campaigns, we intend to deploy SNMR for selected glaciological case studies within the Swiss Alps. A primary focus will be on efficiently detecting water pockets that may pose a potential risk of downstream flooding upon rupture. Similarly, we want to investigate the extent to which we can distinguish cold from temperate ice.

How to cite: Gabriel, L., Hertrich, M., Moser, R., Ogier, C., Maurer, H., and Farinotti, D.: Exploring englacial hydrology with surface nuclear magnetic resonance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13124, https://doi.org/10.5194/egusphere-egu24-13124, 2024.

EGU24-13663 | ECS | PICO | CR5.1

 Assessing the rate of ice fracture using co-located geophysical surveys on the Brunt Ice Shelf, Antarctica 

Emma Pearce, Oliver Marsh, Alex Brisbourne, and Thomas Hudson

The rate of fracture-induced ice instability is an important factor contributing to uncertainties in sea level projections used for global flood mitigation planning. While the occurrence of ice fracturing at critical stress thresholds is well-documented, the detailed mechanisms controlling fracture timing, rate, and orientation are not fully understood. This gap is particularly evident in differences in fracture behaviour across varying ice types, such as meteoric ice and ice mélange. Observations on the Brunt Ice Shelf reveal a unique behaviour, where rifts deviate from the pathway predicted by the principal stresses to avoid thick blocks of meteoric ice. Their growth rate is significantly reduced when required to cross through these blocks. This stands in contrast to observations on other ice shelves, such as Larsen C, where rift propagation is slower in marine ice bands.

Here we use co-located geophysical methods, seismic and ground-penetrating radar (GPR), to assess the fracture pattern and dynamics and the relationship to ice properties at the leading edge of two active rifts, Halloween Crack and Chasm 2, on the Brunt Ice Shelf.

By determining the depth of seismic events using P to Rayleigh wave amplitude ratios, we estimate a theoretical maximum dry crevasse depth—the depth at which fracturing can occur without the presence of englacial water. Additionally, GPR data are used to precisely locate rift terminations and identify refrozen layers associated with seawater intrusion into the firn layer. Combining these data, we provide new insight into the mechanisms controlling fracture propagation within the Brunt Ice shelf. The synthesis of observations from Chasm 2 and Halloween Crack contributes to a comprehensive understanding of fracture mechanics, enhancing our knowledge of regional-scale ice dynamics.

How to cite: Pearce, E., Marsh, O., Brisbourne, A., and Hudson, T.:  Assessing the rate of ice fracture using co-located geophysical surveys on the Brunt Ice Shelf, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13663, https://doi.org/10.5194/egusphere-egu24-13663, 2024.

EGU24-13683 | ECS | PICO | CR5.1

Testing four Sentinel (1 and 2) and MODIS Fractional Snow Cover products for the evaluation of five Alpine Cosmic Ray Neutron Sensing sites 

Nora Krebs, Paul Schattan, Valentina Premier, Abraham Mejia-Aguilar, and Martin Rutzinger

Above-ground cosmic ray neutron sensing (CRNS) is an emerging technique for the investigation of dynamics in soil moisture, snow water equivalent (SWE), and vegetation at a spatial scale of several hectares. The measurement principle is based on the moderation of natural secondary cosmogenic neutrons by hydrogen atoms. On the earth surface hydrogen atoms are mainly bound in water molecules. However, at complex research sites the signal distinction between various water sources remains challenging. Especially in alpine terrain and at elevated topography, hydrological features are linked in an intricate patchwork, hampering signal discrimination. Satellite observations offer valuable complementary surface information and are commonly provided at a spatial resolution that meets the integrated footprint area of the CRNS detector. In this study we investigate if the interpretation of the CRNS signal can be enhanced by the use of remote sensing products. We compare three readily available fractional snow cover (FSC) products based on Sentinel (1 and 2) and MODIS and one reference FSC Sentinel-2 scene-based machine learning product at the approximate footprint resolution of CRNS, comprising a circular area of 250 m radius. The performance of all four products is assessed at five CRNS sites in the Austrian and Italian Alps that represent a variety of environmental properties, ranging from flat to steep topography, from low to high elevation and from sparse to abundant vegetation cover. At three sites, the presence and absence of snow can be validated by local snow height measurements. The analysis shows that remote sensing snow cover information can be extracted on around 80% of the analyzed days, demonstrating the use of FSC products for the estimation of snow cover duration and timing. Comparing the four products shows overall agreements and allows to deduce product-specific thresholds for the distinction of snow-covered and snow-free situations. Further, pairing remote FSC observations with neutron count measurements provides a first indication on the complexity of local hydrogen pool dynamics and consequent requirements on the calibration routine for ambient water monitoring with CRNS. We conclude that satellite-based FSC products can be used to fortify the choice of CRNS observation location and period prior to the detector installation and for a robust and viable first-order assessment of expected CRNS site conditions. Remote sensing FSC products and CRNS measurements hold complementary data that can mutually benefit snow observations and should be explored further in the future.

How to cite: Krebs, N., Schattan, P., Premier, V., Mejia-Aguilar, A., and Rutzinger, M.: Testing four Sentinel (1 and 2) and MODIS Fractional Snow Cover products for the evaluation of five Alpine Cosmic Ray Neutron Sensing sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13683, https://doi.org/10.5194/egusphere-egu24-13683, 2024.

EGU24-14420 | PICO | CR5.1

Using seismic and gravity data to constrain subglacial seafloor stratigraphy in the vicinity of the Kamb Ice Stream grounding line, Ross Ice Shelf, Antarctica 

Andrew Gorman, Gary Wilson, Huw Horgan, Gavin Dunbar, Caitlin Hall, Jenny Black, Bob Dagg, Matthew Tankersley, and Laurine van Haastrecht

The sedimentary units beneath the Ross Ice Shelf in the vicinity of the Kamb Ice Stream grounding line on the Siple Coast of the eastern Ross Ice Shelf play an important role in evaluating past advances and retreats of grounded ice in West Antarctica through the Quaternary. This region is an ongoing focus for drilling efforts that involve melting through the ice shelf and recovering sediments from beneath the seafloor. Seismic (and to a lesser extent gravity) methods have played a critical role in establishing a stratigraphic framework for these sediment sampling endeavours. Approximately 73 km of seismic data have been collected in this region during three seasons since early 2015, complemented by finely sampled gravity transects and a coarser regional gravity grid. Data acquisition provides localised coverage of the sub-ice-shelf ocean and sediments in a region where ROSETTA-Ice airborne-gravity data identified a gravity low. Seismic acquisition parameters have varied from survey to survey, but all involve explosive charges frozen into a hot-water-drilled holes that are recorded by conventional geophones buried in the firn. Such an acquisition configuration provides imaging of the ice shelf and underlying geological units. Processed seismic data show a mostly flat layered seafloor lying beneath the ocean cavity with at least 200 m of sub-horizontally layered sedimentary strata containing several mappable unconformities that are identified as distinct reflective horizons in the seismic data as well as reflection terminations and pinchouts in overlying and underlying units. These unconformities could correspond to past glacial erosion episodes as the position of the grounding line in this region has migrated landward and oceanward. Gravity modelling suggests that the thickness of the sedimentary basins in the region are variable beyond what we see in the shallow (few hundred metre) penetration of the seafloor.

How to cite: Gorman, A., Wilson, G., Horgan, H., Dunbar, G., Hall, C., Black, J., Dagg, B., Tankersley, M., and van Haastrecht, L.: Using seismic and gravity data to constrain subglacial seafloor stratigraphy in the vicinity of the Kamb Ice Stream grounding line, Ross Ice Shelf, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14420, https://doi.org/10.5194/egusphere-egu24-14420, 2024.

EGU24-15907 | PICO | CR5.1

Long-term refraction seismic monitoring: a reliable method to detect ground ice loss at mountain permafrost sites 

Christin Hilbich, Bernd Etzelmüller, Ketil Isaksen, Coline Mollaret, Sarah Morard, Cécile Pellet, and Christian Hauck

Geophysical monitoring becomes more and more popular in permafrost environments due to its remarkable success to detect permafrost thawing and spatio-temporal changes in the ground ice content. Mostly geoelectric methods such as Electrical Resistivity Tomography (ERT) are applied due to the strong differences in the electrical properties between frozen and unfrozen state. However, seismic properties also change markedly upon freezing/thawing and time-lapse refraction seismic tomography (RST) has been shown to be applicable to permafrost over smaller time scales (e.g., Hilbich 2010). The reason why only few studies employ long-term seismic monitoring in permafrost is probably due to the higher logistical effort required.

At two Swiss permafrost monitoring sites (Schilthorn and Stockhorn) yearly RST surveys are conducted using the same setup for more than 15 years, in addition to standard borehole temperature, climatic and ERT measurements (www.permos.ch). The monitoring aim is to image the interannual changes of the thickness of the active layer as well as differences in ice content within the permafrost layer below.

Additional long-term observations are available from RST (and contemporary ERT) surveys from several mountain permafrost sites in Norway that were initially conducted to characterise permafrost conditions around boreholes drilled in 1999/2008 (Juvvasshoe/Jotunheimen), and 2007/2008 (Iskoras/Finnmark, Guolasjavri/Troms, and Tronfjell, cf. Isaksen et al. 2011, Farbrot et al. 2013). These surveys were repeated with the same geometry in 2019 after 11 years in northern Norway, and after 8 and 20 years in southern Norway. As for the Swiss sites, temperatures from all these boreholes show a clear warming trend over the last 1-2 decades (Etzelmüller et al, 2020, 2023).

We here present the observed long-term changes in electrical resistivity and seismic P-wave velocity based on a) annually repeated measurements in the Swiss Alps, and b) on long-term repetition in northern and southern Norway. The geophysical changes are related to the observed borehole temperature increase during the same period (Etzelmüller et al. 2023) and analysed with respect to climate-induced thawing. We evaluate the advantages and disadvantages of seismic monitoring compared to the more standard ERT monitoring. Finally, the results are also analysed with respect to their suitability for future ERT-seismic joint inversion approaches in a monitoring context.

 

References

Etzelmüller B, Guglielmin M, Hauck C, Hilbich C, Hoelzle M, Isaksen K, Noetzli J, Oliva M and Ramos M 2020. Twenty years of European mountain permafrost dynamics—the PACE legacy. Environ. Res. Lett. 15 104070 DOI 10.1088/1748-9326/abae9d

Etzelmüller B, Isaksen K, Czekirda J, Westermann S, Hilbich C, Hauck C 2023. Rapid warming and degradation of mountain permafrost in Norway and Iceland. The Cryosphere. 17.5477-5497.10.5194/tc-17-5477-2023.

Farbrot H, Isaksen K, Etzelmüller B, Gisnås K 2013. Ground Thermal Regime and Permafrost Distribution under a Changing Climate in Northern Norway. Permafrost Periglac.,24(1):20-38. https://doi.org/10.1002/ppp.1763

Isaksen K, Ødegård RS, Etzelmüller B, Hilbich C, Hauck C, Farbrot H, Eiken T, Hygen HO, Hipp T 2011. Degrading mountain permafrost in southern Norway - spatial and temporal variability of mean ground temperatures 1999-2009. Permafrost Periglac.,22(4):361-377, https://doi 10.1002/ppp.728.

Hilbich C 2010. Time-lapse refraction seismic tomography for the detection of ground ice degradation, The Cryosphere, 4, 243–259, https://doi.org/10.5194/tc-4-243-2010, 2010.

How to cite: Hilbich, C., Etzelmüller, B., Isaksen, K., Mollaret, C., Morard, S., Pellet, C., and Hauck, C.: Long-term refraction seismic monitoring: a reliable method to detect ground ice loss at mountain permafrost sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15907, https://doi.org/10.5194/egusphere-egu24-15907, 2024.

EGU24-16320 | PICO | CR5.1

Quieting of hydraulic tremor: sudden changes in frictional conditions in subglacial channels 

Małgorzata Chmiel, Nicoletta Caldera, Fabian Walter, Gerrit Olivier, Daniel Farinotti, Alberto Guadagnini, Dominik Gräff, Manuela Köpfli, and Florent Gimbert

The state and evolution of subglacial channels strongly impact glacier motion and as a result the mass balance of flowing ice bodies. Yet, the subglacial environment is difficult to access and thus often poorly constrained over significant temporal and spatial scales. This limits our understanding of complex subglacial hydraulic processes and consequently ice dynamics.

Seismology can help overcome these observational constraints, providing new insights into fundamental processes in the cryosphere, such as frictional sliding and subglacial water flow. However, different seismogenic processes of the cryosphere often overlap in both time and space. Differentiating between them and interpreting associated seismic signals require appropriate methodological and instrumental approaches.

Here, we investigate subglacial channel dynamics at the Rhone glacier (Switzerland) over one month in the summer of 2020, focusing on periods coinciding with glacier sliding episodes. To this end, we leverage the sensitivity of near-bed borehole geophones combined with seismic interferometry and beamforming techniques.

We show that the hydraulic tremor, generated by turbulent water flow and resulting pressure variations acting against the subglacial channel bed and walls, acts as a dominant, stable, and coherent noise source. Beamforming analysis reveals the directional stability of the hydraulic tremor and points toward the junction of two subglacial hydraulic channels from which stick-slip asperities originate. The analysis also reveals instances of sudden hydraulic tremor quieting, in agreement with previous observations before and after seismogenic sliding episodes. We explain this quieting as sudden changes in frictional conditions within the subglacial channel corresponding to a rapid transition between a fully and partially filled channel. We discuss channel properties (geometry and bed conditions) that are needed to satisfy the physical conditions for the frictional quieting mechanism. Our analysis offers new insights into the complex mechanical interactions between ice, water, and bed properties and the hydraulic control of glacier sliding.

How to cite: Chmiel, M., Caldera, N., Walter, F., Olivier, G., Farinotti, D., Guadagnini, A., Gräff, D., Köpfli, M., and Gimbert, F.: Quieting of hydraulic tremor: sudden changes in frictional conditions in subglacial channels, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16320, https://doi.org/10.5194/egusphere-egu24-16320, 2024.

EGU24-17134 | ECS | PICO | CR5.1

Lightweight In-Situ Analysis of snow density and accumulation 

Johanna von Drachenfels, Helle Astrid Kjær, and Josephine Lindsey-Clark

A critical factor in accurate Surface Mass Balance predictions of the Greenland Ice Sheet is the availability of spatially and temporally extensive snow accumulation data (Montgomery et al., 2018). Currently, this data remains deficient due to incomplete geographical coverage and poor temporal resolution (Sheperd et al., 2012).

An innovative approach to expanding the existing dataset is the utilization of the LISA box: a portable Lightweight In-Situ Analysis system designed for fast and straightforward snow and ice core measurements (Kjær et al., 2021), which speeds up the delivery of the results. With the LISA box, the sample cores are melted, and continuous flow analysis of chemical impurities and conductivity in the meltwater reveals annual peaks and climatic horizons. This information allows for dating of the single ice and snow layers. The registration of the melt speed furthermore permits the determination of the layer thickness, while the layer density can be inferred with an additional measurement of the meltwater flowrate. By combining these insights, past accumulation rates, as indicated by the volume of annually deposited snow, can be reconstructed.

Here we present updates to the existing LISA box enhancing its abilities to further analyse for density variations in snow and firn cores.

How to cite: von Drachenfels, J., Kjær, H. A., and Lindsey-Clark, J.: Lightweight In-Situ Analysis of snow density and accumulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17134, https://doi.org/10.5194/egusphere-egu24-17134, 2024.

EGU24-17421 | PICO | CR5.1

Lake ice seismicity: seismic and acoustic observations 

Cedric Schmelzbach, Christoph Wetter, Simon Stähler, John Clinton, Zinan Lyu, Maria Mesimeri, and Frédérick Massin

Seismic events (icequakes) associated with floating ice sheets on lakes are a frequently observed phenomenon. We find at our study site on the frozen Lake St. Moritz in the Swiss Alps typically a clear diurnal pattern with hundreds to thousands of icequake signals per hour during night time, while the rate of observed events during daytime is about two orders of magnitude smaller. The seismicity rate shows a significant correlation with temperature changes. It is therefore assumed that the generation of the ice quakes is related to melting and freezing processes as well as the extension and contraction of the ice. Potentially the seismicity rate is also moderated by loading and unloading due to human activities on the ice and/or lake level changes.

These ice quakes generate seismic waves that propagate through the thin ice sheet as plate waves modulated by the air and water half-spaces above and below the ice (quasi-guided waves). One member of this wave-type family, the quasi-Scholte waves, are characterised by distinct dispersion that can be observed with seismic sensors on the ice. Furthermore, the seismic waves traveling through the ice couple into the air leading to audible seismo-acoustic signals. One particularity of the ice-air coupling is a so-called coincidence phenomenon. The particular velocity-frequency combination where the seismic wavelength in the ice matches the apparent acoustic wavelength in the air leads to a resonance phenomenon. Observation of the related coincidence frequency allows us, for example, to infer on the ice thickness from the acoustic observations with a low cost microphone above the ice only. Recording the acoustic signals with small microphone arrays enables additionally, for example, locating the source of the seismo-acoustic signal.

Combined observations of the seismic and acoustic signals provide new insights into the seismicity of lake ice which has rarely been studied in the past. The seismo-acoustic signals have the potential to provide information about the ice properties such as thickness and ice quality as well as waxing and waning processes of ice sheets. These observations are relevant for safe operations on the ice but also to complement other remote-sensing observations with autonomous in situ seismo-acoustic measurements for climate studies.

How to cite: Schmelzbach, C., Wetter, C., Stähler, S., Clinton, J., Lyu, Z., Mesimeri, M., and Massin, F.: Lake ice seismicity: seismic and acoustic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17421, https://doi.org/10.5194/egusphere-egu24-17421, 2024.

EGU24-17767 | PICO | CR5.1

Glaciological characterization of Little Dome C: Influence of ice flow on the future Beyond Epica – Oldest Ice Core drilling project 

Robert Mulvaney, Carlos Martín, Catherine Ritz, Luca Vittuari, Massimo Frezzotti, and Olaf Eisen

An ice core is being drilled near Little Dome C, a small promontory about 30km downstream from the summit of Dome C, to extract a continuous record of climate over the last 1.5 million years. Present and past ice flow conditions are important to interpret the ice core because the surface velocity at the drilling site is about 40 mm/yr and the oldest ice in the record was deposited in the surface about 10km upstream of the drilling site. Here we explore newly acquired and existing geophysical data to describe present ice flow and investigate signs of past changes. We present new GNSS data that describes the subtle but complex local surface velocity, and ApRES radar data that provides englacial strain-rates along the flow path from the summit of Dome C and bulk englacial crystal orientation fabric. Ice currently flows from Dome C summit along the ridge to Little Dome C, even though a subtle uphill slope, but basal conditions are variable along the path due to the strong basal topography. Of special interest is an ice unit in contact with the bedrock with variable thickness up to about 300m that is vertically stagnant and produce a strong radar reflection.  This basal unit is not present in an area of strong melting about 5km upstream from the drilling site. The crystal orientation fabric reflects the ice flow horizontal extension along the path and changes with depth on ice flow properties following climatic transitions and, more intriguing, indicate a possible change in ice flow extension at the beginning of the Holocene. We aim to facilitate detailed ice flow models to better interpret the ice core data.  

How to cite: Mulvaney, R., Martín, C., Ritz, C., Vittuari, L., Frezzotti, M., and Eisen, O.: Glaciological characterization of Little Dome C: Influence of ice flow on the future Beyond Epica – Oldest Ice Core drilling project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17767, https://doi.org/10.5194/egusphere-egu24-17767, 2024.

EGU24-17917 | PICO | CR5.1

Using received laser signal intensity to measure snow and ice surface properties automatically  

Alexander Prokop, Florian Tolle, Jean-Michelle Friedt, and Eric Bernard

In the context of climate warming it is a common scientific goal to study and monitor surface and volume changes of glaciers and melting dynamics of its snow and ice. Therefore several measurement techniques exist to track permanently ice melting e.g. DGPS stations on glaciers, Smart stake, and snow and ice depth measurements via e.g. ultrasonic depth sensors to create time series of snow and ice loss or gain. None of the existing methods measure if actually liquid water is present and melting occurs, this is later concluded by interpretation of the geometric data. The capability of the laser sensor to do so via the reflectance value, in fact the received signal intensity, we consider as a big advantage and worth investigating further as a direct measure of snow or ice melt that helps not only to analyze glacier dynamics but is also important e.g. for providing reliable ground truth data for satellite remote sensing. When melting of snow and ice occurs, water changes the reflectance properties as due to absorption of the laser in water, only a portion of the laser is reflected. This allows determining if liquid water is present at the surface measured. We present the data collected in the last 2 melting seasons of the Austre Lovénbreen glacier near Ny Alesund, Svalbard. We show how we classify wet snow and wet ice hours with confidence and are able to compute melting rates. The single point measurement is put into context to area wide LiDAR measurements and melting dynamics of the glacier are analyzed. The data was verified against visual inspections from automatic cameras, data from an automatic weather station both located in the glacier catchment and ice melt was measured in close proximity with a SmartStake station.

How to cite: Prokop, A., Tolle, F., Friedt, J.-M., and Bernard, E.: Using received laser signal intensity to measure snow and ice surface properties automatically , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17917, https://doi.org/10.5194/egusphere-egu24-17917, 2024.

EGU24-18177 | ECS | PICO | CR5.1

Applying Cosmic-Ray Neutron Sensing in Highly Heterogeneous Conditions: Monitoring Snow Water Equivalent in Periods with Partial Snow Coverage 

Paul Schattan, Jan Schmieder, Markus Köhli, Christine Fey, and Martin Schrön

Cosmic-Ray Neutron Sensing (CRNS) constitutes an emerging method for monitoring soil moisture and snow dynamics at intermediate spatial scales of several hectares. In complex environments such as mountain regions, however, the presence of areas with a high contrast of hydrogen content was found to cause a hysteresis in the relationship between neutron counts and water equivalent. A simulation study using the newly developed hierarchical scenario tool YULIA (Your URANOS Layer Integration Assistant) for the Monte-Carlo neutron simulation model URANOS was conducted to quantify the effect of snow-free areas on above-ground neutron sensing of the snow water equivalent (SWE). It was found that the size and distance of the snow free patches have the largest impact on the neutron flux. The simulations also showed a sensitivity of the signal towards soil moisture and SWE. Correction functions were developed and validated with observed CRNS measurements and LiDAR based distributed SWE maps. The main aim of the correction procedure is to estimate SWE under partly snow-covered conditions. Furthermore, also the soil moisture of the snow-free areas can be inferred if the SWE distribution is known. The latter can be used for other high-contrast CRNS applications like monitoring soil moisture in the presence of ponding water.

How to cite: Schattan, P., Schmieder, J., Köhli, M., Fey, C., and Schrön, M.: Applying Cosmic-Ray Neutron Sensing in Highly Heterogeneous Conditions: Monitoring Snow Water Equivalent in Periods with Partial Snow Coverage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18177, https://doi.org/10.5194/egusphere-egu24-18177, 2024.

EGU24-18639 | PICO | CR5.1

Stick-slip imaging through the GPR phase: Turning  temperate ice 'noise' into signal 

Johannes Aichele, Christophe Ogier, and Barthélémy Anhorn


Ground Penetrating Radar (GPR) is a major tool to investigate, map and monitor polar ice sheets and alpine glaciers. Alpine glaciers are often composed of temperate ice, which has significantly different backscatter properties from cold ice. Radar attenuation is much stronger in temperate ice than in cold ice, because the radar signal encounters strong scattering in temperate ice. 
A major candidate for this scattering is the presence of liquid water inclusions, which are much smaller than the radar wavelength. The large contrast between water and ice dielectric permittivity would explain the diffuse radar scattering in temperate ice. Indeed, recent numerical modelling of the radar signal in temperate ice confirmed the contribution of liquid water inclusions on the scattering of the radar signal (Ogier, 2023). 
Here, we investigate if the strong scattering caused by liquid water inclusions, which is usually treated as noise, can be in fact exploited to unravel dynamic processes inside the glacier. This strong scattering results in large radar phase variations in space, which remain constant over short timescales (hours - days), during which the glacial water content remains constant. During that timescale, however, the mountain glacier might experience sudden internal deformation due to intermittent sliding at the glacier base, also called glacier stick-slip.  This deformation might be resolved using difference imaging and the spatio-temporal properties of the radar phase.
We numerically model radar wave propagation throughout temperate ice (i.e. with the presence of liquid water inclusions) before and after an idealized glacier deformation and show, that through phase difference imaging the internal movement of the sub-wavelength scatterers can be mapped. 
Finally, we discuss how this novel type of monitoring could be applied in the field, which is planned for spring 2024.

 

Ogier, Christophe, Dirk-Jan van Manen, Hansruedi Maurer, Ludovic Räss, Marian Hertrich, Andreas Bauder, and Daniel Farinotti. 2023. “Ground Penetrating Radar in Temperate Ice: Englacial Water Inclusions as Limiting Factor for Data Interpretation.” Journal of Glaciology, September, 1–12. https://doi.org/10.1017/jog.2023.68.

How to cite: Aichele, J., Ogier, C., and Anhorn, B.: Stick-slip imaging through the GPR phase: Turning  temperate ice 'noise' into signal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18639, https://doi.org/10.5194/egusphere-egu24-18639, 2024.

EGU24-19098 | PICO | CR5.1

Observing glacier bed topography: the H/V spectral method applied on a dense seismic array as a simple alternative to radar 

Florent Gimbert, Neil Ross, Tifenn Le Bris, Guilhem Barruol, Tun Jan Young, Samuel Doyle, Stephen Livingstone, Andrew Sole, Adrien Gilbert, Ryan Ing, Liz Bagshaw, Mike Prior-Jones, and Laura Edwards

Accurate knowledge of glacier bed topography is critical for quantifying ice volumes and modelling ice and subglacial hydrology dynamics. Bed topography observations are traditionally obtained from airborne and ice penetrating radar, which offers the crucial advantage of recovering the detailed glacier structure over a range of scales. A main difficulty with radar, however, is that waves can be strongly scattered and attenuated by englacial heterogeneities, in particular by water inclusions, which can potentially limit the applicability of the technique under certain conditions.

Here we present a case study on Isunguata Sermia, West Greenland, where we conducted an ice penetrating radar survey together with dense seismic array acquisitions from 87 nodes spread over a 1 km2 area. We show that, in the area of investigation, radar observations were only partially successful in identifying the ice-bed interface, likely due to the thick warm ice, presence of some surface water and near-surfacing crevassing and other englacial structures. The H/V analysis performed over the seismic array yielded surprisingly coherent estimates of ice thickness, along with its spatial variation along and across the glacier. These findings raise questions about the interpretation of traditional radar measurements under certain glacier conditions, and how dense seismic arrays could retrieve bed topography more systematically. 

How to cite: Gimbert, F., Ross, N., Le Bris, T., Barruol, G., Young, T. J., Doyle, S., Livingstone, S., Sole, A., Gilbert, A., Ing, R., Bagshaw, L., Prior-Jones, M., and Edwards, L.: Observing glacier bed topography: the H/V spectral method applied on a dense seismic array as a simple alternative to radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19098, https://doi.org/10.5194/egusphere-egu24-19098, 2024.

EGU24-20308 | ECS | PICO | CR5.1

“Determination of Hydric Potencial through Geoelectric and Piezometric methods in the Ichickcollcococha Wetland, Pachacoto Hydrographic Unit, Cordillera Blanca, Perú.”  

Leila Maribel Mamani, W. Harrinson Jara, Velnia Chacca Luna, Juan C. Torres, Helder Mallqui, Manuel Cosi, Cristian Quispe, and Milagros Aquino

Abstracts

High-Andean bofedales are vegetated wetlands that play a crucial role in the context of climate change by facilitating the capture of carbon dioxide and regulating water. However, global warming has led to the glacial retreat of major snow-capped peaks, such as the Pastoruri Glacier, resulting in water scarcity that directly impacts these ecosystems. Hence, there is a pressing need to study them. This research aims to characterize the physical structure of the Ichickcollcococha bofedal, located in the Pachacoto Hydrographic Unit in the southern sector of the Cordillera Blanca, Peru. The objective is to determine its water storage potential during periods of high precipitation and drought. The study employs the Vertical Electrical Sounding (VES) geophysical prospecting method, corroborated by vibrating wire piezometers installed in the Ichickcollcococha bofedal. This method allows for a detailed analysis of the subsurface resistive properties, generating geo-electric profiles that detail the internal structure of the bofedal.

Three horizons have been identified: the upper layer is loosely composed of organic material (vegetation, cushioned bofedales) with high moisture content, reaching a depth of approximately 1.5 meters and average resistivity values around 431 Ohm.m. The second layer extends to a depth of 11 meters with resistivities of 67 Ohm.m, corresponding to organic materials such as peat and saturated sands. The third horizon, with estimated depths of 80 meters and resistivities around 1301 Ohm.m, corresponds to underlying limestone rock. The data obtained from the Ichickcollcococha bofedal align with characteristic values of glacial-origin peat bogs.

The findings of this study provide a comprehensive understanding of the internal characteristics of the Ichickcollcococha bofedal, highlighting its contribution to the knowledge of its internal dynamics and its implications for the water potential of high-Andean bofedales. Furthermore, the results offer valuable information for modeling and water resource management.

Keywords: Bofedal, Hydric potential, geoelectric method, VES.

How to cite: Mamani, L. M., Jara, W. H., Chacca Luna, V., Torres, J. C., Mallqui, H., Cosi, M., Quispe, C., and Aquino, M.: “Determination of Hydric Potencial through Geoelectric and Piezometric methods in the Ichickcollcococha Wetland, Pachacoto Hydrographic Unit, Cordillera Blanca, Perú.” , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20308, https://doi.org/10.5194/egusphere-egu24-20308, 2024.

EGU24-21232 | ECS | PICO | CR5.1

Quantifying Ground Ice in Tien Shan and Pamir Permafrost: A Comprehensive Petrophysical Joint Inversion Study Applying the electrical Geometric Mean Model  

Tamara Mathys, Christin Hilbich, Coline Mollaret, Christian Hauck, Tomas Saks, Ryksul Usubaliev, Bolot Moldobekov, Zhoodarbeshim Bektursunov, Muslim Azimshoev, Hofiz Navruzshoev, and Martin Hoelzle

Central Asian Mountain regions (Tien Shan and Pamir) are expected to be significantly impacted by climate change, affecting water availability and natural hazards. The cryosphere plays a crucial role in many watersheds of the region by providing water for hydropower station, irrigation, and domestic use downstream. At the same time, retreating glaciers and thawing permafrost increase the risk of natural hazards. Therefore, cryosphere monitoring systems are necessary to provide baseline data for estimating future water availability and detecting dangerous hazard zones. Despite the large areas underlain by permafrost in the Tien Shan and Pamir Mountain ranges, data on permafrost distribution, characteristics and evolution are scarce. However, quantitative estimations of permafrost subsurface components, especially water and ice contents, are needed to evaluate the consequences of current climate change on mountain permafrost environments.

Recent field-based investigations have emphasised the coupled use of geophysical techniques, e.g., by employing the Petrophysical Joint Inversion scheme (PJI, Wagner et al., 2019) that combines electrical resistivity and seismic refraction p-wave velocity data to estimate the four phases present in the subsurface (volumetric contents of air, water, ice, and rock). The traditional PJI implementation relies on Archie’s law (Archie, 1942) as one of the primary petrophysical equation to link resistivity to porosity and water content. Archie's law is generally considered valid when electrolytic conduction dominates, a condition that is not universally justified for dry and coarse blocky substrates and landforms in mountainous terrain. Recognizing this limitation, Mollaret et al. (2020) introduced the electrical Geometric Mean Model as an alternative implementation in the PJI. The Geometric Mean Model  assumes random distributions of the four phases and offers the advantage of including the fractions of ice and air in the petrophysical equation for resistivity, which are not present in Archie’s law. In this study, we assess the feasibility and effectiveness of using the Geometric Mean Model within the PJI framework across an extensive geophysical dataset comprising 22 profiles in Central Asia (Kyrgyzstan and Tajikistan). Our research encompasses diverse landforms, including moraines, rock glaciers, talus slopes, and fine-grained sediments. Our goals are to (i) evaluate the performance of the Geometric Mean Model in comparison to Archies law across different landforms and (ii) address the existing data gap concerning mountain permafrost and ground ice contents in the Central Asian region.

References

Archie, G. E. (1942). The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics. Transactions of the AIME, 146(01), 54–62. https://doi.org/10.2118/942054-G

Mollaret, C., Wagner, F. M., Hilbich, C., Scapozza, C., & Hauck, C. (2020). Petrophysical Joint Inversion Applied to Alpine Permafrost Field Sites to Image Subsurface Ice, Water, Air, and Rock Contents. Frontiers in Earth Science, 8, 85. https://doi.org/10.3389/feart.2020.00085

Wagner, F. M., Mollaret, C., Günther, T., Kemna, A., & Hauck, C. (2019). Quantitative imaging of water, ice and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data. Geophysical Journal International, 219(3), 1866–1875. https://doi.org/10.1093/gji/ggz402

How to cite: Mathys, T., Hilbich, C., Mollaret, C., Hauck, C., Saks, T., Usubaliev, R., Moldobekov, B., Bektursunov, Z., Azimshoev, M., Navruzshoev, H., and Hoelzle, M.: Quantifying Ground Ice in Tien Shan and Pamir Permafrost: A Comprehensive Petrophysical Joint Inversion Study Applying the electrical Geometric Mean Model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21232, https://doi.org/10.5194/egusphere-egu24-21232, 2024.

SM7 – Crustal Fluids and Seismicity (incl. induced & triggered seismicity, volcano seismology

EGU24-1877 | ECS | Orals | SM7.1

Cascading ruptures on near-orthogonal strike-slip faults controlled by simple shear: Insights from the 2019 Cotabato earthquake quartet, Philippines 

Yu Jiang, Hongyu Zeng, Wan-Lin Hu, Zhangfeng Ma, Judith Hubbard, and Shengji Wei

Near-orthogonal ruptures within the elastic crust cannot be explained by the classic Mohr-Coulomb theory. Instead, simple shear is a promising hypothesis to explain near-orthogonal ruptures, and we test this hypothesis on the 2019 Cotabato earthquake sequence. In 2019, an earthquake quartet struck the Cotabato province on Mindanao island, Philippines: Mw6.4 on October 15 (EQ1), Mw6.6 on October 29 (EQ2), Mw6.5 on October 31 (EQ3), and Mw6.8 on December 15 (EQ4). This was the first documented earthquake quartet involving four similar-size moderate strike-slip events in such a short period. The sequence ruptured the Sindangan-Cotabato-Daguma Lineament, which was formed during the collision of the Sundaland-Eurasia Plate and the Philippine Mobile Plate in the Late Miocene and has not hosted any large earthquake in the past century. We initially estimated the fault orientation by surface wave relocation of M>4.7 events, and then retrieved the fault slip distributions of the major earthquakes using Interferometric Synthetic Aperture Radar (InSAR) images. The geodetic inversion reveals that EQ1, EQ2, and EQ4 ruptured the NW-trending M’Lang and Makilala-Maulungoon faults, while EQ3 ruptured the NE-trending Makilala fault. Near orthogonal (88°-93°) nature between the NW-trending faults (EQ1/EQ4) and the NE-trending fault (EQ3) can be explained by the rotation of the conjugate faults due to simple shear since ~7 Myr. We find that the stepover widths between the near-parallel faults associated with EQ1, EQ2, and EQ4 may have limited the dynamic triggering of EQ2 and EQ4. Coulomb stress transfer models suggest that the coseismic slip of EQ1, EQ2, and EQs 1+2 could have triggered EQ2, EQ3, and EQ4, respectively. Fault orientation rotation modelling reveals the fault starting the near-orthogonal cascading sequence is the one accommodating the majority of the rotation, possibly because of the instability associated with rotations. Our study suggests that the shallow segments of the M’Lang and Makilala-Maulungoon faults did not fail, and that these remain a potential seismic hazard.

How to cite: Jiang, Y., Zeng, H., Hu, W.-L., Ma, Z., Hubbard, J., and Wei, S.: Cascading ruptures on near-orthogonal strike-slip faults controlled by simple shear: Insights from the 2019 Cotabato earthquake quartet, Philippines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1877, https://doi.org/10.5194/egusphere-egu24-1877, 2024.

This study delves into the phenomenon of dynamic triggering of earthquakes in Yunnan, China, a region renowned for its abundant geothermal activity. Through an extensive analysis spanning from 2006 to 2021, we unveil the impact of 13 distant M>6 earthquakes on seismic clusters in the region, emphasizing the unique clustering of these seismic events at specific fault-related locations. Advanced methods, including the Epidemic-Type Aftershock Sequence (ETAS) model, were employed to identify the spatiotemporal patterns of seismic activity before and after these distant M>6 earthquakes.

Noteworthy observations highlight the preferential distribution of earthquake clusters at specific fault-related locations, such as fault ends, bends, intersections, and fault step-overs. Some earthquake clusters exhibit clear fluid diffusion processes, validated by increased water temperature in nearby wells. The applied ETAS model underscores a high proportion of forced seismic activity, elucidating the subtle relationship manifested as delayed triggering effects.

The results of our study emphasize the association of dynamic triggering with specific fault-related locations, emphasizing the potentially significant role of subsurface geothermal fluids in this process. This research deepens our understanding of seismic activity patterns in the Yunnan region, revealing the intricate interplay between distant M>6 earthquakes, fault dynamics, and geothermal fluid activity.

How to cite: Wang, Z., Lei, X., and Ma, S.: Dynamic Triggering of Earthquakes in Yunnan, China: Insights into the Influence of Distant M>6 Earthquakes and Geothermal Fluids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2644, https://doi.org/10.5194/egusphere-egu24-2644, 2024.

EGU24-3876 | Posters on site | SM7.1

The role of anti-repeating earthquakes in seismic sequences and swarms 

Simone Cesca, Peter Niemz, Torsten Dahm, and Satoshi Ide

Repeating earthquakes have overlapping rupture patches, similar focal mechanism and magnitudes. They are often detected based on highly similar waveforms using template matching techniques, which help to reconstruct complex sequences and swarms. Here, we investigate earthquakes with highly anti-correlated waveforms. Such poorly known observation implies the occurrence of reversed seismogenic processes at close hypocentral locations. We introduce the terms true and quasi anti-repeating earthquakes to denote cases affecting the same rupture patch or neighboring patches, respectively. We report about a number of observations of anti-repeating earthquakes in different environments, such as volcano, induced and intermediate-depth seismicity, and then review conceptual models to explain them. Some of these observations occurred during seismicity unrests, in the form of seismic sequences and swarms. Both true and quasi anti-repeating earthquakes are indicators for stress perturbation transients or local stress heterogeneities, often controlled by fluid migration processes. Therefore, their analysis may help the identification and tracking of fluids in the subsurface.

How to cite: Cesca, S., Niemz, P., Dahm, T., and Ide, S.: The role of anti-repeating earthquakes in seismic sequences and swarms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3876, https://doi.org/10.5194/egusphere-egu24-3876, 2024.

EGU24-4636 | Orals | SM7.1

Geometry and mechanics of a complex fault system from deep analysis of seismic sequences within the Irpinia Near Fault Observatory 

Gaetano Festa, Francesco Scotto di Uccio, Grazia De Landro, Luca Elia, Maddalena Michele, Titouan Muzellec, Antonio Scala, Claudio Strumia, Mariano Supino, Greg Beroza, Giovanni Camanni, Lauro Chiaraluce, Nicola D'Agostino, Matteo Picozzi, and Aldo Zollo

The Irpinia Near Fault Observatory is a dense instrumented infrastructure monitoring the normal fault system of the Irpinia region, in the Southern Apennines (Italy). The area is one of the highest seismic hazard regions in Italy; nevertheless, the background seismicity rate is low, with about 4000 earthquakes detected in the last 15 years of network operation, with a magnitude of completeness of 1.1. Thus, understanding the fault system mechanical state requires high quality data and advanced tools for seismicity location and characterization, along with new monitoring systems, able to catch the earthquake signals at or below the noise level.  

In this study, we investigated the geometrical and mechanical properties that can be inferred from the (micro)seismic sequences occurred during the network operation. The seismic catalogs enhanced through the use of machine learning and similarity-based techniques, and double-difference event relocation show that the events define kilometric-scale structures, sub-parallel to the main faults that generated the M 6.9, 1980 Irpinia earthquake. We estimated the stress release and the rupture area of the events within the sequences, showing that the static stress transfer is the main mechanism of triggering of the events within the sequences. The seismicity delineates slip-driven alignments that can be associated with fault roughness. In the case of the major sequence, the event distribution might also indicate the occurrence of an aseismic deformation episode, too small to be detected by surface GNSS instruments. 

Finally, we also analyzed the seismicity recorded along the 1-year DETECT experiment, during which 200 velocimetric stations were deployed as a constellation of seismic arrays, within Irpinia Near Fault Observatory region. We discovered that deep seismicity mainly occurs in sequences, with most events having a magnitude smaller than the unity. When jointly analyzed with the 3D P-wave tomographic model, these sequences illuminate a SW-dipping, previously unknown, segmented fault with a total length of more than 30 km. This structure could be causative for a future M6+ event, depending on the rupture ability to overcome the geometrical stepover on the fault. 

How to cite: Festa, G., Scotto di Uccio, F., De Landro, G., Elia, L., Michele, M., Muzellec, T., Scala, A., Strumia, C., Supino, M., Beroza, G., Camanni, G., Chiaraluce, L., D'Agostino, N., Picozzi, M., and Zollo, A.: Geometry and mechanics of a complex fault system from deep analysis of seismic sequences within the Irpinia Near Fault Observatory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4636, https://doi.org/10.5194/egusphere-egu24-4636, 2024.

EGU24-4933 | ECS | Posters on site | SM7.1

Seismicity under a dormant volcano: unveiling active crustal faulting beneath Piton des Neiges, La Réunion 

Lise Firode, Zacharie Duputel, Valérie Ferrazzini, and Olivier Lengliné

Earthquakes occur regularly in the vicinity of La Réunion's two main hotspot volcanoes, Piton des Neiges and Piton de la Fournaise. While earthquakes at Piton de la Fournaise volcano are clearly linked to its volcanic activity, the seismicity beneath Piton des Neiges is not well understood. However, except during eruptive periods, we often record more seismic events at Piton des Neiges than at Piton de la Fournaise. This study aims to better capture this seismicity to understand the nature and causes of the activity beneath Piton des Neiges, a volcano that has been dormant for 27,000 years. We improve previously available seismicity catalog by using template matching, double relocation and focal mechanism determination. Results indicate that the seismicity is primarily concentrated on a northeast-dipping reverse fault located in the oceanic crust beneath the volcanic edifice. We also identify secondary seismicity clusters with the same orientation in the vicinity of the main fault. Seismicity occurs continuously since the installation of the first seismological stations in the vicinity of Piton des Neiges in 1999. Although occasional periods of increased swarm-like activity are observed in 2011 and 2018, they do not correlate with markers of deep magma transfers that are often observed prior to the eruptions of the Piton de la Fournaise. These variations in seismic activity are limited to the main reverse fault and might be associated with periods of creeping activity. Our findings suggest that the seismic activity beneath Piton des Neiges is likely caused by regional tectonic stress and edifice loading on pre-existing faults, rather than from deep magma transfers. This conclusion is supported by the presence of various reverse faults with similar orientation and the lack of correlation between seismicity fluctuations and deep magmatic activity.

How to cite: Firode, L., Duputel, Z., Ferrazzini, V., and Lengliné, O.: Seismicity under a dormant volcano: unveiling active crustal faulting beneath Piton des Neiges, La Réunion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4933, https://doi.org/10.5194/egusphere-egu24-4933, 2024.

Seismic hazard can be quantified by using probabilities. Modern seismic forecasting models, such as Operational Earthquake Forecasting (OEF) systems, allow us to quantify short-term variations of such probabilities. These probabilities change indeed with time and space, in particular after strong seismic events. However, the short-term seismic hazard could also change during seismic swarms, e.g. sequences with several small/medium size events. The goal of this work is to quantify these changes by both using the Italian OEF system, and estimating the variations of the b-value parameter in Gutenberg-Richter frequency-magnitude distribution. We focus our attention on three seismic swarms that occurred in Central Italy during October-November 2023. Our results indicate that the short-term variations of seismic hazard are limited, less than an order of magnitude. The b-value variations are also not significant. Our conclusion is then that, with the currently available models and catalogs, occurrence of seismic swarms does not significantly affect the short-term seismic hazard.

How to cite: Spassiani, I. and Taroni, M.: The effect of seismic swarms on short-term seismic hazard and Gutenberg-Richter b-value temporal variation. Examples from Central Italy seismic activity durign October-November 2023., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5490, https://doi.org/10.5194/egusphere-egu24-5490, 2024.

EGU24-5498 | Orals | SM7.1

Exploring Mayotte’s magmatic plumbing system using the variety and geometry of its seismicity 

Lise Retailleau, Jean-Marie Saurel, Ian W. McBrearty, Gregory C. Beroza, Gaspard Farge, Anthony Lomax, and Wayne C. Crawford

The seismic sequence off the coast of Mayotte island, in the Comoros archipelago, preceded and accompanied the large submarine volcanic eruption and birth of the volcano Fani Maoré. While this sequence has slowed down and the eruption has stopped, it is still active and captures the deep complex system of this new volcano and its evolution. The seismicity is separated in two clusters. The distal cluster is located about 25 km South-East of Mayotte and has been associated with the magma propagation towards the surface. The proximal cluster, about 10 km East of Mayotte, suggests the presence of several magmatic reservoirs and conduits. 

We built a new catalog using deep learning methods from land and ocean bottom seismometers data from 2019 to 2023. We locate this seismicity using NonLinLoc and a 1D velocity model developed in 2020 specifically for this seismic sequence. We analyze the volcano-tectonic and long period earthquakes spatio-temporal patterns as well as their mechanism to understand the volcanic system. We compare this analysis with recent modeling studies that suggest interactions between reservoirs.

How to cite: Retailleau, L., Saurel, J.-M., McBrearty, I. W., Beroza, G. C., Farge, G., Lomax, A., and Crawford, W. C.: Exploring Mayotte’s magmatic plumbing system using the variety and geometry of its seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5498, https://doi.org/10.5194/egusphere-egu24-5498, 2024.

EGU24-5624 | Posters on site | SM7.1

Investigating the relationship between the presence of active seismicity and the displacement of the eastern flank of Piton de la Fournaise, La Réunion.  

Olivier Lengliné, Lise Firode, Zacharie Duputel, and Valérie Ferrazzini

Geodetic observations indicate a seaward displacement of the eastern flank of Piton de la Fournaise volcano on La Réunion Island. Previous studies have suggested that the this displacement could be the result of a sheared sill. However, the location of the sill inferred from InSAR data is currently inconsistent with the distribution of earthquakes observed at greater depth. However, other results have attributed the current distribution of seismic activity beneath the eastern flank to the combined effect of overpressure in the magma chamber and loading of the volcanic edifice. The aim of the our study is to investigate the relationship between these two phenomena: the presence of active seismicity and the displacement of the eastern flank of Piton de la Fournaise. With this purpose, we enhance the characterization of seismic activity using template matching, double-difference relocation and focal mechanisms determination. We then explore the link between the spatio-temporal evolution of the seismicity and the displacement of the eastern flank. Additionally, we evaluate the impact of the velocity model to determine if we can reconcile hypocenter locations with the destabilization structure inferred from InSAR.

How to cite: Lengliné, O., Firode, L., Duputel, Z., and Ferrazzini, V.: Investigating the relationship between the presence of active seismicity and the displacement of the eastern flank of Piton de la Fournaise, La Réunion. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5624, https://doi.org/10.5194/egusphere-egu24-5624, 2024.

An intense earthquake swarm has persisted for more than three years within a 20 km × 20 km area beneath the northeastern tip of the Noto Peninsula, central Japan since November 2020. The largest magnitude for each year from 2021 to 2023 increased to 5.1, 5.4, and 6.5 by the end of 2023. On January 1st, 2024, an M7.6 earthquake rupture nucleated within the swarm area and propagated bilaterally toward ENE and WSW directions along multiple faults. Globally, it is rare that the long-lasting seismic swarm preceded such a large event. We have analyzed the long-term continuous seismic waveforms to create a more precise earthquake catalog associated with this earthquake sequence. Based on this catalog, we have explored the spatial-temporal evolution of the seismicity before the M7.6 event. Note that the foreshock sequence, including a M5.7 event, started approximately 1 hour before the M7.6 event close to the hypocenter. The M7.6 nucleated from the deepest side of one of numerous planer clusters that were dominantly dipping toward the southeast direction. Several previous studies using seismic and geodetic data suggest that the long-lasting earthquake swarm has been driven by upward fluid flow along pre-existing cracks/faults in the crust (e.g., Nishimura et al. 2023). Especially, Kato (2024, doi:1029/2023GL106444) recognized a rapid upward migration of the immediate aftershocks following the 2023 M6.5 and M5.9 events and implied fault-valve behavior that might be driven by upwelling of crustal fluids along the intensely fractured and permeable fault zones via the dynamic ruptures. If fluids could migrate along pre-existing faults, fault strength would be reduced by lubrication. In addition, the long-lasting intense seismicity and slow deformations detected by GNSS network have partially released the accumulated elastic stress in the swarm area, resulting in stress loading onto nearby fault segments. The strength of the faults gradually decreased, and the stress was partially released over three years, which may have triggered the latest M7.6 earthquake.

How to cite: Kato, A. and Nakagawa, S.: The long-lasting earthquake swarm leading up to the 2024 M7.6 Noto-Hanto earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7349, https://doi.org/10.5194/egusphere-egu24-7349, 2024.

EGU24-8106 | Posters on site | SM7.1

Elastic and inelastic properties of the Pollino (Italy) seismogenic volume 

Ferdinando Napolitano, Ortensia Amoroso, Luca De Siena, Simona Gabrielli, and Paolo Capuano

The Pollino area, one of the largest seismic gaps in Italy, was struck between 2010 and 2014 by a long-lasting seismic sequence. More than 10,000 small-to-medium earthquakes occurred as a swarm-like sequence and, to a lesser extent, as  aftershocks following the two largest events: a ML 4.3 on 28 May 2012 and a ML 5.0 on 25 October 2012. A slow slip event began about three months before the strongest earthquake. 

Our study focuses on this complex sequence and the recent advancements obtained by our group in terms of crustal structure characterization and fault imaging. We integrate the most recent findings in terms of 3D scattering and absorption imaging, high sensitivity to fluid content, deformed fractured structures, and impermeable layers, with already achieved seismic and focal mechanism tomographic results and available geological information for the area. 

High absorption topping the western Pollino seismic volume appears pressurized between the low-Vp/Vs and low-scattering San Donato metamorphic core and a deep basement. This high absorption volume is also characterized, at the same depth, by an excess of fluid pressure, mapped by applying the focal mechanism tomography, where clusters of events of similar waveforms occurred. These events were caused by a slow slip event, similar to the transient deformation event, and favored by pore-pressure increases in fluid-saturated fault networks. 

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

How to cite: Napolitano, F., Amoroso, O., De Siena, L., Gabrielli, S., and Capuano, P.: Elastic and inelastic properties of the Pollino (Italy) seismogenic volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8106, https://doi.org/10.5194/egusphere-egu24-8106, 2024.

EGU24-9592 | ECS | Orals | SM7.1

Illuminating active fault zones at Campi Flegrei Caldera (Southern Italy) from high-precision earthquake locations 

Francesco Scotto di Uccio, Anthony Lomax, Jacopo Natale, Titouan Muzellec, Gaetano Festa, Sahar Nazeri, Vincenzo Convertito, Antonella Bobbio, Claudio Strumia, and Aldo Zollo

The Campi Flegrei caldera, located to the west of the city of Naples, is one of the most active and urbanized volcanic areas in the world, also hosting an eruptive episode in historical times. This area periodically experiences notable unrest episodes which include ground deformations and seismic swarms, as in the recent 1982-1984 crisis. During the past decade, the central portion of Campi Flegrei caldera underwent a sustained and continuous ground uplift reaching rates of 15 mm/month, along with an increase in the rate, maximum magnitude and spatial extent of seismicity especially in the last two years, culminated with the occurrence of an Md 4.2 earthquake on 27th September 2023.

In this study, we compute high-precision earthquake locations using multi-scale, source-specific station corrections and waveform coherence. We relocated ~8.3 k earthquakes between 2014 and 2023, resulting in hypocentral uncertainties less than ~ 100 meters and thus assessing the spatiotemporal evolution of the earthquakes during the current crisis. We show that the integration of the station corrections and the coherence-driven, cross-correlation weighted stack of the probabilistic locations for nearby events (< 2km) strongly improves the location accuracy for target earthquakes. Relocated hypocentres allow us to clearly show with unprecedented detail the complexity of the kilometric-size fault structures activated in response to the increasing rate of the ground uplift phenomenon. Most of the seismicity is clustered along identifiable segments concentrated in a shallow region around the Solfatara-Pisciarelli area, where epicentres define an ~1x1 km, horseshoe-shaped structure, opened and deepening toward the northeast.  In contrast, the deepest offshore seismicity, between 3-5 km depth, appears to fit and approximate the downward propagation of the previously identified south-western caldera inner ring fault. Relocated seismicity appears coherent with the fracture zones activated during the 1982-84 unrest episode. However new sectors of activity have been identified during the present unrest, including the one at the eastern boundary, which hosted the largest Md 4.2 event caused by a km-size rupture within the shallow (3 km) volcanic sedimentary layer. Given the size of the structures mapped in this study and the source parameters estimated for the main event, these faults can accommodate earthquakes of moment magnitude up to 5.0, both around the Solfatara and the offshore, south of Pozzuoli, significantly increasing the hazard in the area.

How to cite: Scotto di Uccio, F., Lomax, A., Natale, J., Muzellec, T., Festa, G., Nazeri, S., Convertito, V., Bobbio, A., Strumia, C., and Zollo, A.: Illuminating active fault zones at Campi Flegrei Caldera (Southern Italy) from high-precision earthquake locations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9592, https://doi.org/10.5194/egusphere-egu24-9592, 2024.

EGU24-9932 | Orals | SM7.1

Volcano-Tectonic seismicity during the 2021-2023 unrest phase at Vulcano island (Italy) and its connection with the regional geodynamic context 

Ornella Cocina, Graziella Barberi, Giovanni Barreca, Susanna Falsaperla, Luciano Scarfì, and Salvatore Spampinato

The island of Vulcano, in the South-Eastern Tyrrhenian Sea (Southern Italy), is the southernmost out-of-water part of a larger submerged volcanic edifice of the Aeolian archipelago. Since its last explosive eruption (1888-1890), relevant episodes of volcanic unrest unfollowed by eruptive activity have been documented. These episodes were characterized by notable increase in geochemical parameters, ground deformation, and local seismicity related to fluid dynamics within the shallower part of the hydrothermal system. Volcano-Tectonic (VT) seismicity located on the island did not play a major role during these unrest phases, except for the 1985 and 1988 seismic sequences that preceded and accompanied a significant increase in temperature and gas flux at the fumaroles causing a depletion of the shallow hydrothermal source. 

The last phase of unrest occurred from mid-September 2021 to December 2023. A climax in high temperature, CO2 flux, fumarolic gas emissions, ground deformation together with LP and VLP seismicity was achieved in early November 2021. In the following months, after a period of stability of the major anomalies, a gradual decrease was observed. Conversely, VT seismicity showed a moderate increase in the time intervals 30/10/2021-31/12/2021, 31/03/2022-30/04/2022 and 04/12/2022-31/12/2022.

In this work, the application of the tomoDDPS algorithm to relocate the seismicity occurred from January 2020 to December 2022, points to the identification of three seismogenic volumes. The space-time distribution and energy release of the relocated seismicity together with waveform correlation analysis enabled us to infer a connection between the unrest process and the activation, at different depth ranges, of a NW-SE trending wrench faults system and associated NE-SW structures. 

How to cite: Cocina, O., Barberi, G., Barreca, G., Falsaperla, S., Scarfì, L., and Spampinato, S.: Volcano-Tectonic seismicity during the 2021-2023 unrest phase at Vulcano island (Italy) and its connection with the regional geodynamic context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9932, https://doi.org/10.5194/egusphere-egu24-9932, 2024.

EGU24-9984 | Posters on site | SM7.1

High-Resolution Analysis of the 2023 Seismic Swarm Offshore Malta 

Francesco Grigoli, Simone Cesca, Gian Maria Bocchini, Sebastiani D'Amico, and Matthew Agius

In January-February 2023 a seismic sequence took place in the Central Mediterranean Sea,  ~90 km south of the island of Malta, and ~200 km from the coast of Sicily. The seismicity started in Mid January, in a region that experienced only sparse seismicity in the past. In the following days several M4+ events occurred. The largest earthquake, with moment magnitude Mw 5.3, took place a couple of weeks after the unrest onset, on January 30. The seismicity continued for several weeks, before fading down. Later seismicity was observed and still going on. This recent, unusual seismicity offers a unique opportunity to investigate seismogenic processes in this region with unprecedented detail. However, analyzing seismic sequences in offshore environments presents significant challenges due to the absence of optimal seismic monitoring conditions. These limitations compromise the effectiveness of conventional data analysis techniques, hindering the characterization of offshore seismic sequences. We tackled these limitations through the adoption of advanced, waveform-based seismic data analysis techniques that allow to investigate offshore seismic sequences, with the aim to provide insights into their origin. We combine full-waveform based detection and template matching methods to enhance the detection of events, advanced location techniques based on Distance Geometry Solvers (DGS), and probabilistic waveform-based methods for seismic source characterization. We combine the seismic source analysis for the 8 largest earthquakes in the sequence, with magnitude exceeding ML 4.5, with waveform-based and statistical analysis of the seismicity. About 500 events are identified. Their locations map a narrow lineament extending ~NW-SE. Full moment tensors for the largest events identify normal faulting mechanisms with a similar orientation, and shallow centroids of ~5 km depth. This result, combined with a waveform similarity analysis, suggests a predominant mechanism for the entire sequence. Using different seismicity indicators we classify the 2023 sequence as a seismic swarm. Indeed, the largest events in the sequence occur weeks after the unrest onset. Compared to previous seismicity, the sequence was outstanding in terms of maximum magnitude, seismicity rate and moment rate. While normal faulting earthquakes are not unusual in the Central Mediterranean, they differ from the few focal mechanisms previously proposed for the swarm focal region, which has important implications, considering that normal faulting earthquakes at shallow depth pose a tsunami hazard in the region.

How to cite: Grigoli, F., Cesca, S., Bocchini, G. M., D'Amico, S., and Agius, M.: High-Resolution Analysis of the 2023 Seismic Swarm Offshore Malta, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9984, https://doi.org/10.5194/egusphere-egu24-9984, 2024.

EGU24-10191 | ECS | Posters on site | SM7.1

A detailed earthquake catalog using Machine Learning-based methods for Tuscany, Italy 

Juan Porras, Konstantinos Michailos, Genevieve Savard, Domenico Montanari, Gilberto Saccorotti, Marco Bonini, Davide Piccinini, Nicola Piana-Agostinetti, Chiara Del Ventisette, and Matteo Lupi

Seismic activity in Tuscany, Italy, is driven by the interplay between complex tectonics and local geological processes. Fluid-driven seismic sequences may occur in high-enthalpy geothermal regions, such as the Larderello-Travale Geothermal Field (LTGF), the oldest and among the most productive geothermal systems of the world. To better understand the regional tectonic setting, we build a detailed seismic catalog of earthquake hypocenters and magnitudes from a composite seismic network consisting of 30 temporary stations deployed in Tuscany in the framework of a temporary experiment (TEMPEST), during a period of one year (from September 2020 to September 2021) and 30 permanent seismic stations from the Istituto Nazionale di Geofisica e Vulcanologia (INGV).

We applied an automated processing routine including a machine learning (ML) phase picker, PhaseNet, and the Gaussian Mixture Model Association (GAMMA) algorithm, a sequential earthquake association and location workflow. We initially obtain nearly 1 million P-phases and 2 million S-phases, yielding in around 5 thousand detected events. We then located the events with NonLinLoc and applied a quality factor metrics to filter out potential false detections (22%) and recognize the high quality solutions which represents 30% of the initial 5 thousand locations with moment magnitudes (Mw) ranging between 0.5 to 2.9, and depths generally shallower than 15 km. Further steps involve the location analysis of the remaining events from the initial catalog. Moreover, we will apply relative earthquake location methods to better constrain already evident seismicity clusters. We also plan to calculate focal mechanisms from first-motion polarities and Moment Tensor (MT) inversion to investigate the earthquake sources in the highlighted tectonic features.

This work represents the starting point of the project “Multidisciplinary and InteGRated Approach for geoThermal Exploration” (MIGRATE). The goal of MIGRATE is to streamline passive seismic exploration methods for the investigation of geothermal resources, while addressing relevant scientific questions. This will result in the development of an automatized end-to-end tool to prospect the upper crust and identify potential geothermal targets.

How to cite: Porras, J., Michailos, K., Savard, G., Montanari, D., Saccorotti, G., Bonini, M., Piccinini, D., Piana-Agostinetti, N., Del Ventisette, C., and Lupi, M.: A detailed earthquake catalog using Machine Learning-based methods for Tuscany, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10191, https://doi.org/10.5194/egusphere-egu24-10191, 2024.

EGU24-10844 | ECS | Orals | SM7.1

Fluid-driven swarms and mainshock-aftershocks sequences in the Ubaye Region (Western Alps). 

Marion Baques, Louis De Barros, Maxime Godano, Clara Duverger, and Hervé Jomard

The Ubaye Region, located in the French Western Alps, is one of the most seismically active regions in France. It is regularly hit by mainshock-aftershocks sequences (1959, ML5.3), seismic swarms (2003-2004), and complex sequences (2012-2015) characterized by successive mainshocks clustered in time and space. This diversity of seismic behaviour highlights the complex processes at play in this area. To improve our understanding of these processes, we compile a regional catalogue of existing focal mechanisms, completed by 100 new calculated focal mechanisms of aftershocks following the 07/04/2014 mainshock (ML5.1). We reconstruct the stress-state orientation for different periods and sub-areas. We found that it is constant in time and space, and consistent to previous published values focusing on swarm periods in this area. We then calculate the fluid-pressure needed to trigger the events. Most of them (65%) need fluid-overpressure between 15 and 40 MPa (17-to-40% of the hydrostatic pressure) with a median value of 24%. Moreover, even the largest earthquakes, like the mainshocks in the 2012-2015 sequence, appear to be triggered by fluid-pressure, similarly as events within swarm sequences. While fluid-overpressure decreases with time in an aftershock sequence, it  varies randomly at high levels during a swarm sequence. Therefore, based on a fault-valve model, we propose that: 1) the fluids trapped in the fault plane tend toward lithostatic pressure and trigger the mainshock rupture and 2) part of the aftershocks are induced by the diffusing fluid-pressure. On the contrary, swarms need external, likely deep, fluid-pressure feedings. Fluid-pressure is likely to be a common triggering mechanism of the seismicity in the Ubaye Region, even if the involved processes should differ to explain the different types of seismic sequences.

How to cite: Baques, M., De Barros, L., Godano, M., Duverger, C., and Jomard, H.: Fluid-driven swarms and mainshock-aftershocks sequences in the Ubaye Region (Western Alps)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10844, https://doi.org/10.5194/egusphere-egu24-10844, 2024.

EGU24-12026 | ECS | Posters on site | SM7.1

Fault (re)activation and fluid-induced seismicity: an example from the Val d'Agri intermontane basin (southern Italy) 

Alessio Lavecchia, Vincenzo Serlenga, Marilena Filippucci, Tony Alfredo Stabile, Giacomo Prosser, and Andrea Tallarico

The occurrence of fluid-induced, moderate-to-large earthquakes in several locations around the globe sparked interest in the relationships between fluids and seismicity over the last few years. Several studies suggest variations of the stress state of rocks, due to the increase or drop of the pore fluid pressure, can be a mechanism that can trigger earthquakes in the presence of fluid phases. In this scenario, the Val d’Agri represents a precious case study where the effect of fluids on seismic activity can be observed. In this region, wastewater reinjection reactivated the Costa Molina blind thrust in the eastern sector of the Val d’Agri, where present-day seismicity was almost absent. A few kilometers SW from this cluster, seasonal water loading from the artificial Pertusillo reservoir generates further seismic activity within the buried carbonatic platform. The formation and evolution of the faults generating seismicity are still a matter of debate, especially in the compressional/extensional tectonic setting that characterizes the southern Apennines geological history. Consequently, the distribution of the seismic potential in the region is largely unconstrained.

We built up a numerical, thermo-mechanical model to identify the principal mechanisms that generated the present-day tectonic setting observed in the Val d’Agri and the surrounding region, and to assess the seismic hazard characterizing this area. We suggest the presence of a major dècollement layer that decouples deformation between the sedimentary cover and the crystalline basement, represented by the Triassic Burano Formation. Our model quantifies the stress field and estimates Coulomb stress values in the Val d’Agri crust, allowing us to assess the potential of the rocks to generate earthquakes. We suggest that Coulomb stress values are positive in a large part of the crust, and therefore that fluid injection may be particularly effective for the reactivation of buried structures, especially within the carbonatic platform at a depth between 2 and 6 km.

How to cite: Lavecchia, A., Serlenga, V., Filippucci, M., Stabile, T. A., Prosser, G., and Tallarico, A.: Fault (re)activation and fluid-induced seismicity: an example from the Val d'Agri intermontane basin (southern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12026, https://doi.org/10.5194/egusphere-egu24-12026, 2024.

EGU24-13232 | ECS | Posters on site | SM7.1

Improving template matching detections using a Convolutional Neural Network 

Dario Jozinović, Tania Toledo, Verena Simon, and Toni Kraft

The use of template matching to detect previously missed small earthquakes is widespread in seismology, due to its power in searching for similar signals. The newly detected earthquakes improve understanding of the geology, seismo-tectonics and seismogenesis of the area explored. The usefulness of template matching has sparked the development of many software tools (e.g. QuakeMatch; Toledo et al., 2024) that allow seismologists to easily apply them to their area of interest. 

Like every detection technique, the performance of template matching shows a tradeoff between sensitivity and false detection rate that is dependent on the choice of the detection threshold. The value of the correlation coefficient between two earthquake signals is highly dependent on several properties such as the distance of the earthquake from the station, the noise level at the station, the magnitude of the earthquake, the focal mechanism of the earthquake, etc, making the selection of a specific correlation coefficient threshold hard. To detect a larger number of earthquakes, researchers often use a lower correlation coefficient detection threshold and manually inspect the detected events to classify them as true events (Toledo et al., 2024). This is, however, a tedious task, especially when using a large number of templates. To reduce the human workload, which can be especially important during evolving earthquake sequences, we employ a Convolutional Neural Network (CNN) to discriminate between earthquakes and noise using the template matching detections as input. We use the data from several microearthquake natural and induced Swiss sequences (Simon et al., 2024, in prep.), to train and test the developed CNN model. Our CNN model uses single-station 3-component waveforms of any length and outputs an earthquake detection score. We demonstrate that the developed CNN can be used to significantly reduce the human workload with high accuracy, allowing the use of low correlation coefficient value thresholds for template matching detections. Furthermore, we show the implementation of the method inside the QuakeMatch software (Toledo et al., 2024).

 

How to cite: Jozinović, D., Toledo, T., Simon, V., and Kraft, T.: Improving template matching detections using a Convolutional Neural Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13232, https://doi.org/10.5194/egusphere-egu24-13232, 2024.

EGU24-13642 | ECS | Posters on site | SM7.1

Understanding the Marianas’ 2007 volcanic earthquake swarm: A perspective from fundamental quantities 

felipe orellana-rovirosa and jason phipps morgan

In this project I am trying to understand the mechanics of the 2007 Marianas earthquake-swarm region and surrounding vicinity; located in the asthenosphere and lithosphere of the Marianas microplate above the subducting Pacific plate. The earthquake swarm exhibited seismicity for almost 2 years, with events occurring from depths of 300 km and up to the surface, right underneath the Marianas arc currently-active basaltic volcanoes.
My approach is to estimate the magnitudes of mechanical variables (forces per unit area, forces per unit volume) that control the evolution of this system. These forces are evaluated for the swarm region, where the ambient rock is heavily fractured and intruded by migrating magmas, thus altered and weakened. From continuum-mechanics momentum equation, the specific terms under consideration are the elastic, viscous and inertial forces. These are evaluated as characteristic magnitudes, following approximated scaling forms of their analytical expressions. Additionally and alternatively, I am carrying out separate assessments of the viscous and elastic forces using visco-elastic (VE) theory (Kelvin-Voigt and Maxwell VE models).
For comparison, I am also carrying out the corresponding estimates for Japan’s Mt. Yake (1998) volcanic earthquake swarm, and also, for a typical continental crustal seismogenic environment.  
Importantly, the deformation of the system is very different when-and-where earthquakes are occurring, than at other times and locations. For this reason, my assessment distinguishes  two regimes: (i) short length-scales and short duration Co-Seismic, and (ii) long-length-scale and long duration A-/Inter-Seismic background. It is for these two time frames that I estimate the stress-strain and forces per unit volume. Additionally, associated energies and energy density-rates are also estimated, and finally the energy budget of the co-seismic and inter-seismic frameworks are studied.

How to cite: orellana-rovirosa, F. and phipps morgan, J.: Understanding the Marianas’ 2007 volcanic earthquake swarm: A perspective from fundamental quantities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13642, https://doi.org/10.5194/egusphere-egu24-13642, 2024.

EGU24-13982 | Orals | SM7.1

Earthquake swarms of complex seismotectonic features in West Texas, USA. 

Savvaidis Alexandros, Huang Guo-Chin, and Lomax Anthony

As part of the intraplate tectonic regime within the continental US, the seismicity rate in Texas is expected to be low. However, the seismicity rate in West Texas has steadily increased since 2009, and significantly accelerated since 2020 with the Texas Seismological Network (TexNet) reporting (http://catalog.texnet.beg.utexas.edu) 49 M≥4 earthquakes (all after 2020) and 3 M≥5 earthquakes (all after 2022).

Two of the largest of these events, M5.4 (2022-11-16, 21:32:44 UTC) and M5.2 (2023-11-08, 10:27:49 UTC) are part of the Coalson Draw sequence, and very close to each other (separated by <3km epicentral distance). They occur in the shallower part of seismicity defining a complex seismogenic structure apparently spanning ~5 km in depth and stretching across the basin-basement interface at about 5 km depth. Using a multi-scale precise, probabilistic location algorithm (NonLinLoc-SSST-coherence) and waveform moment tensor inversion, we resolve the complex seismogenic structure as composed of a series of possibly linked, approximately east-west normal faulting systems with varying but sub-parallel fault geometries.

Only ~11km to the northwest of the Coalson Draw sequence, the earlier M4.9 (2020-03-26, 15:16:27 UTC) Mentone earthquake sequence includes the first M4+ events to occur in the Delaware Basin. In contrast to the Coalson Draw sequence, all available source mechanisms for the Mentone sequence are similar while relocated seismicity forms a WSW-ENE trending, steeply south dipping plane over a depth interval of ~2 km around or above the basement, suggesting a relatively simple and uniform fault geometry.

How to cite: Alexandros, S., Guo-Chin, H., and Anthony, L.: Earthquake swarms of complex seismotectonic features in West Texas, USA., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13982, https://doi.org/10.5194/egusphere-egu24-13982, 2024.

EGU24-14605 | Orals | SM7.1 | Highlight

Growing an ocean island: high-precision seismicity reveals a multi-faceted magma intrusion during the 2022 São Jorge, Azores seismic crisis 

Stephen P. Hicks, Pablo J. Gonzalez, Rui Fernandes, Ana Ferreira, Ricardo Ramalho, Neil Mitchell, Anthony Lomax, Fernando Carrilho, Susana Custódio, Nuno Afonso Dias, João Fontiela, Virgilio Mendes, Arturo M. Garcia, Augustin Marignier, Rui Marques, Miguel Miranda, Octavio Melo, Adriano Pimentel, Graça Silveira, and Maria Tsekhmistrenko and the and the rest of the Sao Jorge investigation group

The central islands of the Azores Archipelago in the North Atlantic straddle a diffuse zone of dextral transtension between the African and Eurasian plates, providing an ideal setting for studying the interplay between tectonics and magmatism. São Jorge is a narrow island dominated by a westward progression of past basaltic fissure eruptions, where fault zones act as volcanic rifts. After two inland eruptions with significant socioeconomic impact in 1580 and 1808, the most recent probable eruption occurred offshore in 1964, after two years of seismic activity. In March 2022, a seismic crisis began on São Jorge (magnitudes up to ML 3.8). 

Our analyses of InSAR and GNSS data are consistent with a dike intrusion that stalled at 2 km depth below sea level. Here, we use seismicity to probe the space-time evolution of the intrusion. The unique geography and near-coastal position of seismicity yield inherently uncertain locations. To address this, we supplemented on-land stations with 6 ocean-bottom seismometers (OBSs) around the island later in the crisis. We use NLL-SSST-coherence, a location method ideal for changing station density, to exploit later OBS data to form robust source-specific station terms that allow precise relocation of the earlier part of the seismic sequence when coverage was sparser. In a final step, we combine waveform coherence and location uncertainty stacks to enhance hypocenter location precision to <100m. 

Relocations of ~12,000 earthquakes show precursory, weak seismicity that started ~6 months before, starting offshore, south of São Jorge before migrating to shallower depth beneath the centre of the island. The main seismic crisis on 19 March 2022 started at shallower (<8 km) depth and moved north-westward and deeper before concentrating in the central zone at ~10 km depth. Intriguingly, nearly all the seismicity is located west of and deeper than the modelled dike intrusion, suggesting the intrusion was largely aseismic. Nevertheless, the agreement between the strike of the dike and the seismicity lineations suggests that the pre-existing Pico do Carvão Fault Zone guided melt ascent in the crust. However, moment tensors from polarity and waveform inversion show double-couple left-lateral strike-slip faulting along planes striking obliquely (by ~20°) to the dike and seismicity lineation, evidencing high fluid/melt pressures. The overall b-value is high (~2).

Interpreting both the seismicity and near-field GNSS displacements, we discuss the intrusion’s evolution along the preexisting fault zone, particularly focussing on potential magmatic inflow and drainage beneath the main dike intrusion.

We are grateful to the UK Ocean Bottom Instrument Consortium (OBIC) and SEIS-UK teams for providing the instrumentation and installation services. This work was also supported by Portuguese FCT/MCTES through the project GEMMA (https://doi.org/10.54499/PTDC/CTA-GEO/2083/2021).

How to cite: Hicks, S. P., J. Gonzalez, P., Fernandes, R., Ferreira, A., Ramalho, R., Mitchell, N., Lomax, A., Carrilho, F., Custódio, S., Dias, N. A., Fontiela, J., Mendes, V., Garcia, A. M., Marignier, A., Marques, R., Miranda, M., Melo, O., Pimentel, A., Silveira, G., and Tsekhmistrenko, M. and the and the rest of the Sao Jorge investigation group: Growing an ocean island: high-precision seismicity reveals a multi-faceted magma intrusion during the 2022 São Jorge, Azores seismic crisis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14605, https://doi.org/10.5194/egusphere-egu24-14605, 2024.

EGU24-14803 | Posters on site | SM7.1

Studies of recent seismo-volcanic activity in the Gegham volcanic ridge (Armenia)  

Lilit Sargsyan, Elya Sahakyan, Hovnatan Demirchyan, Gevorg Navasardyan, Mikayel Gevorgyan, and Khachatur Meliksetian

Armenia, SE Turkey and NW Iran are located in the central part of the Arabian lithosphere collision zone, a region, which experiences N–S shortening and E–W extension accompanied by intense faulting, strong earthquakes and active volcanism. The Gegham volcanic ridge (GVR) is located in the center part of the Neogene-Quaternary volcanic belt formed within the territory of the Armenian Highland. The duration of volcanism within the Gegham Ridge spans from the Late Miocene to the Holocene. The GVR in central Armenia represents one of the densest clusters of individual monogenetic volcanoes in the world.

The study area of the Gegham Volcanic Ridge is located between the system of the Gegham Ridge Fault (GF1) and the Gavaraghet Fault (GF2).

The faults in the axial part of the Gegham ridge (GF1) represent structures of fracturing related to eruptions of numerous Quaternary volcanoes. The Gavaraghet Fault (GF2) related to a few historical and recent earthquakes is the most active one in the Gegham Fault system.

During the period of 2014-2018, earthquake swarms were recorded in the area of the Gegham Volcanic Ridge. Further studies of the relationship between tectonic and volcanic processes will contribute to the assessment of the volcanic hazard for this area. Beyond its importance for natural hazard assessment, the volcanically young Gegham Ridge also holds great potential as a source of geothermal energy.

Seismic activity in the study area was recorded using data from the advanced and dense seismic network installed recently. This network equipped by full-broad band (permanent and temporary) stations has been developed since 2012 and covers both the study region and adjacent areas.

Seismic activity of this area is manifested in the form of small-size earthquakes. Earthquake epicenters tend to concentrate in volcanic vents, as well as near active faults areas. The depths of earthquakes are up to 25 km.

In this study, source mechanisms of earthquakes were investigated using digital waveform data recorded by seismic stations of the Armenian seismic networks (included the 3 temporary seismic stations). The focal mechanisms of a set of earthquakes that occurred within 2022-2023 were constructed with high reliability, based on the polarity of the first motion of the P-wave.

All data were relocated using local and regional seismic network data with the aim to reduce main parameter uncertainties in the catalogue, used in the current study. 

How to cite: Sargsyan, L., Sahakyan, E., Demirchyan, H., Navasardyan, G., Gevorgyan, M., and Meliksetian, K.: Studies of recent seismo-volcanic activity in the Gegham volcanic ridge (Armenia) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14803, https://doi.org/10.5194/egusphere-egu24-14803, 2024.

EGU24-17086 | Posters on site | SM7.1

b-value variations preceding the mainshock of the 2023 Kahramanmaraş earthquakes 

João Fontiela and Helena Seivane

The analysis of the precursory behavior has been growing in the last decades around the paradigm of earthquake prediction. Amongst the plethora of precursors, the b-value has been deemed as a proxy for the state of stress on a seismogenic source. On 6th February 2023 a mainshock of Mw 7.8 followed by another event of Mw 7.5 within a few hours of difference hit Kahramanmaraş region. Both events occurred on different fault zones of the East Anatolian Fracture Zone (EAFZ). While the first one struck the Pazarcik segment on the main segment of the EAFZ, the second event did it on the Sürgü-Misis fault zone at the west of the EAFZ. In a context of complex rupture behavior, a stress redistribution and transient stress caused by the first event are two of the likely triggering mechanisms of the second event. Our b-value analysis relies on the earthquake catalog from AFAD in the period from early 2015 till the previous moments of the first event on February 2023. To homogenize magnitude reported we excluded Md (few events) and convert Ml to Mw using an empirical relation. As the seismicity along the EAFZ is high, and to avoid statistical bias caused by earthquake clusters, we declustered the earthquake catalog. After assessing the magnitude of completeness to guarantee that the catalog gathers the minimal quality requirements, we examined the temporal evolution and the spatial distribution of b-value. Concerning temporal evolution, we detected that 40 days before the mainshock a sudden decrease of the b-value from 0.85 until its minimum 0.5 on the event’s day. With regard to the spatial distribution of b-value, mainshock’s epicenter is on an elongated region with general strike NE-SW and minimum b-value of 0.76.  

Work supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds, UIDB/04683/2020 (ICT) and UIDP/04683/2020 (ICT)

How to cite: Fontiela, J. and Seivane, H.: b-value variations preceding the mainshock of the 2023 Kahramanmaraş earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17086, https://doi.org/10.5194/egusphere-egu24-17086, 2024.

The 2016 Central Italy seismic sequence occurred within an area dominated by normal-fault systems present along the Apennines. The sequence began with the Mw6.0 Amatrice event on the 24 August 2016, followed by the Mw5.9 Visso event on the 26 October 2016 and then, four days later, the Mw6.5 Norcia event. In this study, we aim at modeling the seismicity of this complex earthquake sequence in order to determine the location of highly-pressurized fluids under the studied area through swarms occurring during the sequence. To do so, we take advantage of a high-resolution earthquake catalog based on arrival times derived using a deep-neural-network-based picker. As a first step, we apply a density-based clustering approach to group earthquakes into dense clusters. The majority of the resulting clusters highlight distinct fault planes which indicates an activation of a complex fault network. We further define a 4-dimensional seismicity model based on the « Epidemic-Type-Aftershock- Sequence » (ETAS) model, in which we introduced an earthquake detection probability to accommodate observed rapid fluctuations in earthquake detection throughout the sequence. By computing the ratio between the observed and ETAS-modeled rates of high-density clusters, we can identify candidate seismic swarms. To evaluate their consistency, we compute the weighted index of the largest seismic event and the magnitude difference between the largest and the 4th-largest earthquakes occurring within a target candidate. Furthermore, to analyze their migration behavior, eigenvectors are computed to identify primary and secondary directions, and swarm earthquakes are projected onto these directions, in which we fit a linear regression model. Observed slope values are compared to those from a distribution of simulated slopes generated by 1000 random shuffling, and statistical significance is assessed. The results reveal among the 40 seismic swarms, 29 of them show significant migration with a significance level of 95%. Migration velocity is determined by components representing velocities along primary and secondary directions, measured in kilometers per day based on slope and earthquake count. Our swarms exhibiting significant migration suggest the implications of variations in pore fluid pressure influenced by structural complexity and intense faulting in the region. Before Norcia mainshock, we observe that swarms are detected in shallow depth with z = [0;5] km, whereas after the mainshock, swarms are found deeper with z > 8 km where the detachment plane is located.

How to cite: Xiang, L. and Marsan, D.: Analysis of the 2016 Central Italy earthquake sequence by using a refined earthquake catalog , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18406, https://doi.org/10.5194/egusphere-egu24-18406, 2024.

EGU24-18706 | Posters on site | SM7.1

Advancing Seismic Event Detection: Integrating Machine Learning with Waveform-Stacking Techniques 

Marius Paul Isken, Torsten Dahm, Sebastian Heimann, Jannes Münchmeyer, Simone Cesca, and Peter Niemz

In the realm of seismic and microseismic event detection and localization, our research marks a significant step forward by integrating machine learning with advanced waveform-stacking techniques for detecting, locating and characterising seismic events. This integration is crucial for unravelling the complex spatio-temporal patterns of seismicity sequences. Our study addresses the challenges posed by noise-dominant microseismic events, which are typically overlooked by conventional detection methods.

Building upon the foundational work on migration and stacking, we have developed an automated, data-driven method utilising a neural network trained in seismic phase arrival identification. This approach, underpinned by stacking and migration techniques, is enhanced by the incorporation of a spatial octree to precisely and efficiently localise seismic sources. These enhancement gives insights into complex seismic sequences, such as volcanic swarms and regional tectonic sequences.

The software framework facilitates extensive feature extraction, such as local and moment magnitudes, enabling the study of seismic events across various scales and tectonic settings. This is exemplified in our validation studies using data from the Eifel region, Germany, and the Reykjanes Peninsula, Iceland. These regions, known for their diverse seismic activities including tectonic earthquakes and fluid-induced swarm activity, provide a rich dataset for testing our method's efficacy in different geological contexts.

Our research contributes to the session's overarching goal of understanding the physical processes behind complex seismic sequences. By enhancing detection and localization capabilities, we aim to offer new perspectives and tools for the geophysical community to investigate the triggering mechanisms of these sequences with unprecedented resolution.

How to cite: Isken, M. P., Dahm, T., Heimann, S., Münchmeyer, J., Cesca, S., and Niemz, P.: Advancing Seismic Event Detection: Integrating Machine Learning with Waveform-Stacking Techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18706, https://doi.org/10.5194/egusphere-egu24-18706, 2024.

EGU24-4438 | Orals | SM7.2

Very long-period observations at Piton de la Fournaise volcano, La Réunion 

Zacharie Duputel, Lucile Costes, Valérie Ferrazzini, and Olivier Lengliné

Volcanoes often exhibit very long period (VLP) signals, with periods ranging from 2 to 100 seconds. Due to their very long wavelengths, these waveforms are not strongly affected by volcano structural heterogeneities and provide invaluable insights into dike and magma properties that are not easily accessible though other observations. Historically, only a few VLP events have been recorded at the Piton de la Fournaise, primarily associated with collapses in the summit caldera in 1986, 2002 and 2007. However, since 2010, the monitoring network has evolved significantly and it is now equipped with several broadband stations, allowing a wide range of signals to be recorded. In this study, we show that VLP events are quite common at Piton de la Fournaise. Specifically, we identify swarms of VLP events during eruptions and during magma injections preceding eruptions. Source analysis of VLP events during eruptions indicates the resonance of the dike during sudden decreases in magma flow. Pre-eruptive VLP waveforms exhibit significant differences from those observed during eruptions, pointing to a distinct source process as the dike propagates laterally toward the volcano flank.

How to cite: Duputel, Z., Costes, L., Ferrazzini, V., and Lengliné, O.: Very long-period observations at Piton de la Fournaise volcano, La Réunion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4438, https://doi.org/10.5194/egusphere-egu24-4438, 2024.

EGU24-4796 | ECS | Orals | SM7.2

The role of magma intrusions on faulting mechanisms during pre-eruptive seismic swarms in the Reykjanes Peninsula 

Felix Rodrigo Rodriguez Cardozo, Jochen Braunmiller, Taha Sadeghi Chorsi, Gerardo Mendo Pérez, Vala Hjörleifsdóttir, Kristín Jónsdóttir, Yesim Cubuk Sabuncu, Glenn Thompson, Stephen McNutt, Jacqueline Dixon, Timothy Dixon, and Rocco Malservisi

In March 2021, a fissure eruption in Fagradalsfjall marked the onset of the first volcanic activity in over 800 years on the Reykjanes Peninsula, Iceland. Since then, three more fissure eruptions occurred in August 2022, July 2023, and December 2023. Intense seismic swarms that included Mw≥ 4.0  earthquakes preceded all eruptions. Concurrently with swarm activity, large surface deformations related to magma intrusions were observed by Interferometric Synthetic Aperture Radar (InSAR), and Global Navigation Satellite System (GNSS) data. Ground displacements exceeded the deformation expected from earthquakes by far, suggesting the intrusion process was primarily aseismic. However, the intrusions may have influenced the prevalent earthquake faulting style in the pre-eruptive swarms. For instance, seismic moment tensors before and during the early 2021 swarm indicate that right-lateral bookshelf faulting along roughly north-south trending strike-slip faults dominated seismic deformation. This changed to more northeast-southwest oriented oblique-normal to normal faulting mechanisms for the later swarms consistent with graben formation after a dyke intrusion. Seismic moment release during the 2021 seismic swarm, which included ten relatively large Mw 5+ earthquakes, was larger than for subsequent swarms, where only a few events reached Mw 5. This may indicate that the 2021 intrusion, which marked a reawakening of volcanic activity, may have triggered bookshelf faults close to failure that might have otherwise ruptured in the near term due to the underlying oblique rifting.  The transition of source mechanisms toward oblique and normal faulting during the later swarms, though, may reflect an active role of the intrusion processes on fault orientation of triggered seismicity rather than simply inducing seismicity on pre-existing faults. 

How to cite: Rodriguez Cardozo, F. R., Braunmiller, J., Sadeghi Chorsi, T., Mendo Pérez, G., Hjörleifsdóttir, V., Jónsdóttir, K., Cubuk Sabuncu, Y., Thompson, G., McNutt, S., Dixon, J., Dixon, T., and Malservisi, R.: The role of magma intrusions on faulting mechanisms during pre-eruptive seismic swarms in the Reykjanes Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4796, https://doi.org/10.5194/egusphere-egu24-4796, 2024.

EGU24-4959 | Posters on site | SM7.2

Implementation of machine learning approaches to monitor pre-eruptive swarms at Piton de la Fournaise volcano 

Marine Menager, Zacharie Duputel, Lise Retailleau, Valérie Ferrazzini, and Ian McBrearty

Eruptions of Piton de la Fournaise volcano (Reunion Island, France) are preceded by intense pre-eruptive seismicity swarms characterized by hundreds, or even thousands of micro earthquakes (magnitude < 2). These volcano-tectonic events are triggered by the upward migration of magma toward the surface and their location provides important information regarding the future eruption location. Yet, regarding the large number of earthquakes, it is difficult to locate them all during seismicity swarms. Hence, we have implemented an approach at the Piton de la Fournaise Volcano Observatory (OVPF-IPGP) based on machine learning to automatically detect and locate these events.. First, we use PhaseNet to pick P and S waves from 17 seismic stations installed on and around the volcano. Then, phase association and source location are done using a Graph Neural Network (GNN) approach called GENIE (Graph Earthquake Neural Interpretation Engine). To implement GENIE specifically at Piton de la Fournaise, we trained the code with seismic stations and velocity models used by OVPF-IPGP to monitor the volcano.. After phase association, we perform a final hypocenter localization using the probabilistic approach of NonLinLoc. To study the results quality, we compare origin time and source location to the OVPF manual catalog as well as a catalog resulting from template matching and double-difference relocation. In particular, we focus on pre- and syn-eruptive time-periods for multiple eruptions since 2014 in order to investigate the effect of elevated seismicity rate and eruptive tremor on the performance of the workflow. We also assess to what extent the quality of the resulting automatic locations are sufficient to provide an indication of the future eruption site without expert manual input.

Applying this approach allows us to improve the monitoring of the seismicity at Piton de la Fournaise volcano. A work in progress is to implement the same approach over the entire island of La Réunion, which will enable the monitoring of other active areas in the region.

How to cite: Menager, M., Duputel, Z., Retailleau, L., Ferrazzini, V., and McBrearty, I.: Implementation of machine learning approaches to monitor pre-eruptive swarms at Piton de la Fournaise volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4959, https://doi.org/10.5194/egusphere-egu24-4959, 2024.

EGU24-6379 | ECS | Posters on site | SM7.2

Long-term evolution of continuous seismic signals at Piton de la Fournaise volcano inferred from the network covariance matrix. 

Emmanuel Caballero-Leyva, Nikolai Shapiro, Cyril Journeau, Léonard Seydoux, Jean Soubestre, and Andrés Barajas

Continuous seismic signals recorded in the vicinity of active volcanoes are composed of seismic waves generated by a variety of internal and environmental sources and propagating through different parts of the plumbing system. This implies that these signals are very sensitive to the state of the plumbing system. A change in the volcanic activity affects the properties of the seismo-volcanic sources while a change in the plumbing structure affects the media through which the seismic waves propagate. Network-based analysis of continuous seismic records has been developed to incorporate information from multiple stations simultaneously. Here we use an approach based on the network covariance matrix that combines an ensemble of inter-station cross-correlations. We compute the width of the eigenvalue distribution of this matrix at a given frequency in a moving time window, resulting in a compact time-frequency representation of continuously recorded seismic wavefield.

 We apply this analysis to ten years (2013-2023) of continuous seismic data from the Piton de la Fournaise volcano located in la Réunion, France. The resulting spectral width distributions indicate that continuous signals are characterized by multiple narrow spectral peaks, which are observed during co-eruptive tremors as well as during periods without visible volcanic activity. We propose a normalization process to enhance these peaks in both the frequency and time domains. We observe numerous spectral peaks in the 1-3 Hz frequency band that remain nearly constant for extended periods (weeks to months). We observe a distinct difference in the spectral peak distribution between co-eruptive and quiet periods, as well as significant variations during long-standing eruptions. Locations of sources of the co-eruptive signals correlate well with the eruption sites. The inter-eruptive signals seem to originate from a combination of environmental and weak internal sources, and changes in their spectral properties might reflect the medium changes after major eruptions.

How to cite: Caballero-Leyva, E., Shapiro, N., Journeau, C., Seydoux, L., Soubestre, J., and Barajas, A.: Long-term evolution of continuous seismic signals at Piton de la Fournaise volcano inferred from the network covariance matrix., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6379, https://doi.org/10.5194/egusphere-egu24-6379, 2024.

EGU24-7488 | ECS | Orals | SM7.2

Temporal enrichment of the seismic record of the 2018 eruption at Sierra Negra using deep neural networks 

Sophie Butcher, Andrew Bell, Stephen Hernandez, Peter La Femina, James Grannell, and Mario Ruiz

The 2018 eruption at Sierra Negra volcano, Galapagos Islands, was accompanied by 8.5 metres of caldera subsidence and intense seismicity, resulting from deflation of a shallow sill-like magma reservoir at ~2 km depth. High-precision hypocentre locations from manually picked phase arrivals show that earthquake sources are tightly constrained within a complex, multi-stranded trapdoor fault system (TDF) above the sill. However, the incompleteness of this high-precision catalogue leaves outstanding questions about the spatio-temporal evolution of seismicity through the eruption, and how it relates to deformation and magma efflux.

Here we present the results of an automated workflow to streamline the production of a ‘temporally-enriched’ seismic catalogue for 2018 eruption at Sierra Negra. We initially utilise PhaseNet, a deep-neural-network-based automatic phase picker, to identify events missing from the initial manually picked catalogue, expanding the detections from 1,618 to 9,871 events. Our catalogue identifies more events in the immediate aftermath of the Mw5.4 earthquake that initiated the eruption, and new small magnitude events (< ML2.0) in the period more than 72 hours after the eruption onset. We then use a template matching approach to further supplement these detections. Specifically, these events fill gaps in the catalogue where tremor amplitudes make manual event detection more difficult. Hypocentre locations for newly detected events are also constrained to the TDF zone, however there is more variety in depth estimates. This has implications for how we consider the TDF with depth, and allows us to consider other potential sources of seismicity in the system.

Our workflow offers an efficient method of producing ‘temporally-enriched’ catalogues at Sierra Negra, and can be readily adapted for the sparse seismic network that remains during the current inter-eruptive phase. However, our experience at Sierra Negra suggests that applying automated earthquake detection and location methods can be challenging in volcanic settings, and requires careful parameterization and quality control.

How to cite: Butcher, S., Bell, A., Hernandez, S., La Femina, P., Grannell, J., and Ruiz, M.: Temporal enrichment of the seismic record of the 2018 eruption at Sierra Negra using deep neural networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7488, https://doi.org/10.5194/egusphere-egu24-7488, 2024.

EGU24-10597 | ECS | Orals | SM7.2

Linking volcanic tremor amplitude to drone records of lava lake level changes during the 2021 Geldingadalir eruption, Iceland 

Alea Joachim, Eva P. S. Eibl, Daniel Müller, and Thomas R. Walter

On March 19, 2021, an effusive eruption lasting for six months began in the Geldingadalir valley on the Reykjanes peninsula, in the southwest of Iceland. This eruption was characterised by episodic lava effusion from 2 May to 18 September and changing eruptive behaviour. Here, we analyse five of such effusion episodes of 8 June 2021 by using drone video data acquired over the active crater lake together with volcanic tremors that were recorded by a seismometer located at 5.5 km distance from the active vent. We are thus able to study each of the five episodes in terms of tremor amplitude evolution and its frequency spectrum, and compare it with the timing, height and dynamics of the lava lake, its bubbling and crater overflow. We observe a slow rise of the lava lake by 25.1 to 26.2 metres within 6.15 ± 2.35 minutes, followed by a rapid fall of the lava lake surface to its previous level within 1.6 ± 0.12 minutes. In contrast, the quiescence period in the tremor lasts ~ 10.12 ± 0.68 minutes followed by another 2.55 ± 0.2 minutes of tremor. Thus, the duration of tremor generation is shorter than the time required for the lava lake to reach its maximum height. Furthermore, the tremor amplitude reaches its maximum after the lava lake has started to sink. We discuss the volcanic tremor generation in relation to lava lake elevation and related processes.

How to cite: Joachim, A., Eibl, E. P. S., Müller, D., and Walter, T. R.: Linking volcanic tremor amplitude to drone records of lava lake level changes during the 2021 Geldingadalir eruption, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10597, https://doi.org/10.5194/egusphere-egu24-10597, 2024.

EGU24-11254 | ECS | Posters on site | SM7.2

Understanding unrest and dynamic triggering processes on Sierra Negra, Galápagos Islands. 

Eleanor Dunn, Chris Bean, Ivan Lokmer, and Andrew Bell

Dynamic earthquake triggering refers to the phenomenon where local seismic activity is induced by dynamic stress disturbances, originating from teleseismic earthquakes. An understanding of dynamic triggering on volcanoes offers a window into volcano stress states and seismicity initiation. Sierra Negra, a basaltic shield volcano situated on Isabela Island, Galápagos, has been the site of recurring episodes of dynamic triggering. Sierra Negra features a large elliptical summit caldera with a trap-door fault system and a magma reservoir extending 2km below the surface. Sierra Negra experienced an eruption in June 2018, characterized by a sequence of pre-eruption inflation, co-eruption deflation, and post-eruption inflation. The occurrence of dynamic earthquake triggering at Sierra Negra was observed in response to high magnitude teleseismic events from 2010 to 2018. The frequency of dynamically triggered earthquakes correlates with the increasing inflation of the magma reservoir. In this study, we aim to answer two questions: 1) How confident are we that the seismicity on Sierra Negra is dynamically triggered? And, 2) What is the location of these dynamically triggered events? Random simulations are used to calculate the likelihood that triggered events are related to teleseismic arrivals rather than being representative of local seismic activity. Results show that for the pre-2018 eruption, the likelihood that events are dynamic triggering is very high, compared to post-2018 eruption where events are more likely to be representative of local seismic activity. We only have access to a single station (VCH1) on Sierra Negra meaning the single-station location method must be used to locate all dynamically triggered events. To test and refine this method, 79 known seismic events are located using a full network from April 2018 – December 2018. Rotation of the 3-component VCH1 into the RTZ (radial-transverse-vertical) coordinate system is used to calculate the back-azimuth and the P-wave to S-wave delay is used to calculate the distance between event and station. 21 unknown dynamically triggered events are located in and around the caldera using this method. Looking forward we hope to understand the relationship between the location and timing of dynamic triggering, and its potential use in understanding volcano unrest state.

How to cite: Dunn, E., Bean, C., Lokmer, I., and Bell, A.: Understanding unrest and dynamic triggering processes on Sierra Negra, Galápagos Islands., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11254, https://doi.org/10.5194/egusphere-egu24-11254, 2024.

EGU24-11355 | ECS | Posters on site | SM7.2

Characterisation and locations of volcanic high frequency tremor above 10 Hz on Mount Etna 

Maurice Weber, Christopher Bean, Patrick Smith, Ivan Lokmer, Luciano Zuccarello, Silvio De Angelis, Jean Soubestre, and Vittorio Minio

When it comes to volcanic tremor, low frequency signals (below 5 Hz) are well investigated. Such tremor signals can usually be linked to magma movement or gas fluctuations. However, little is known about seismic tremor signals on Mount Etna above 10 Hz. Hence, a large field campaign targeting high frequencies was undertaken in the summer of 2022. It consisted of the deployment of six dense circular arrays ranging from 30 to 200 m apertures of seismic nodes installed around the summit craters. It led to the detection of tremor bands between 10 and around 20 Hz as well as the typical tremor signals below 5 Hz.

The tremor is detected with good coherency at stations within one array (despite an extreme level of scattering) in good agreement with the energy distribution in the average amplitude spectra of the array. The high frequency tremor varies strongly in intensity over time periods of one hour and re-occurs several times throughout the deployment period of almost a week. In contrast the tremor below 5 Hz is relatively constant. This suggests that the high frequency tremor could be a separate signal due to a process that may not yet be fully understood.

Localisations of these tremor episodes point to or near the Bocca Nuova Summit Crater which was actively degassing at the time. Interestingly, high frequency seismic tremor is matched in time very well by a narrow 3.5-5 Hz acoustic band. While the match in time clearly suggests a connection between the two signals, the different frequencies indicate two different but linked processes happening simultaneously. The acoustic signal implies degassing processes. Later during the deployment tremor episodes are found which are accompanied by much weaker acoustic signals (if at all present) suggesting gases might not necessarily be involved in generating the detected seismic tremor at all.

In summer 2023 we undertook a complementary second deployment of seismic, acoustic and optical camera data in the Bocca Nuova summit area. Once again, we find tremor below 5 Hz, however high frequency characteristics are different to the previous year with tremor bands less dominant than before and much more constant over time. More than one acoustic band is found as well, also constant over time. In this second data set we use camera recordings of the crater activity as a proxy for degassing activity to try and understand the precise origin of these seismic and acoustic volcanic signals.

How to cite: Weber, M., Bean, C., Smith, P., Lokmer, I., Zuccarello, L., De Angelis, S., Soubestre, J., and Minio, V.: Characterisation and locations of volcanic high frequency tremor above 10 Hz on Mount Etna, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11355, https://doi.org/10.5194/egusphere-egu24-11355, 2024.

EGU24-11934 | ECS | Posters on site | SM7.2

Multi-scale seismic imaging and related seismicity patterns of Krafla volcano and its geothermal system 

Elisabeth Glück, Titouan Muzellec, Stephane Garambois, Jean Vandemeulebrouck, Þorbjörg Ágústsdóttir, Egill Árni Guðnason, and Anette Mortensen

Krafla, one of the five central volcanoes of the Northern Volcanic Zone in NE-Iceland, last erupted during the Krafla Fires in the 70s and 80s. During the same period, a geothermal power plant was built within Krafla caldera, first operated in 1978. Both scientific and industrial interest led to an increase of knowledge of the complex system through systematic exploration with a wide variety of geophysical methods including seismic and electromagnetics coupled with borehole information.
Among them, a local seismic network operated by Landsvirkjun and Iceland GeoSurvey, comprising 12 permanent broadband stations, has been continuously recording seismic data since 2013. We supplemented this network in June 2022 with a dense network of 98 nodes, resulting in two arrays, one large-scale, the other small-scale, operating in parallel.
Here we present multi-scale 3-D velocity models for P-, S- and surface waves, independently derived for both networks through local earthquake and ambient noise tomographies. These models offer a glimpse into the subsurface structures of the volcanic system by utilizing various types of waves that are responsive to distinct rock/fluid properties and depths. The relocated and clustered seismic activity, documented by both permanent and temporary networks, underscores active structures pinpointed through tomography. With this we hope to strengthen the understanding of the connected volcanic and geothermal systems. Indeed, both the seismicity and strong velocity anomalies are located at similar depths as the magma batch that was drilled into with the IDDP1.

How to cite: Glück, E., Muzellec, T., Garambois, S., Vandemeulebrouck, J., Ágústsdóttir, Þ., Guðnason, E. Á., and Mortensen, A.: Multi-scale seismic imaging and related seismicity patterns of Krafla volcano and its geothermal system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11934, https://doi.org/10.5194/egusphere-egu24-11934, 2024.

Recent advances in machine learning offer a new way for Earth Scientists to make predictions about geological subsurface properties. In particular, methods based on Fourier Neural Operators (FNOs) are increasingly being used as a substitute for conventional approaches based on numerical forward modelling and inversion, at a fraction of the computational cost. Most importantly, FNOs have been shown to predict accurate 2D and 3D forward modelling simulations of seismic waves up to several hundred times faster than physics-based solvers after training.

In synthetic volcanic settings to date, FNOs have been applied successfully to both the forward and inverse problem, capturing the fine-scale velocity structure of heterogeneous models. However, transferring the successful performance of simulation-trained FNOs to make accurate predictions from field-gathered seismic data is yet to be achieved. In order to accomplish this for volcanological data, training models would need to contain representative small-scale velocity heterogeneities and topography in order to produce highly scattered codas in the synthetic seismograms.

This research presents work in progress on simulation-to-real applications of FNOs using field-gathered seismic data from offshore sedimentary basin settings as a testbed environment. Historical seismic survey datasets from Atlantic sedimentary basins are often supplemented with alternative geophysical surveys and site-specific geological constraints. Combining seismic borehole and stratigraphic logs with regional seismic datasets provides a link between field-gathered seismic waveforms, stratigraphy and depth-dependent, small-scale fluctuations in seismic velocity. This in turn enables the creation of synthetic velocity models and seismograms with field-derived properties, centring the collation of data for real-world machine learning applications in the numerical domain. We aim to bring insights gained from training FNOs on a better understood seismic environment to volcanic contexts in future work.

How to cite: Totten, E., Bean, C., and O'Brien, G.: Predicting near-surface seismic data and velocity models using synthetically-trained deep learning methods: applications in data-rich environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12228, https://doi.org/10.5194/egusphere-egu24-12228, 2024.

EGU24-13020 | Orals | SM7.2

Dynamics of the Popocatépetl Volcano, Mexico, revealed by Machine Learning-Based Seismic Catalogs 

Karina Bernal-Manzanilla, Marco Calò, Karina Eloisa Rodríguez García, Daniel Martínez Jaramillo, and Sébastien Valade

Popocatépetl, one of Mexico's most active volcanoes, poses significant risks to the dense populations in its vicinity. Effective monitoring of its seismic activity is crucial for understanding and mitigating these hazards. This study employs data collected with a network of 19 seismic stations surrounding the volcano, combined with machine learning techniques and spatial coherence methods, to generate comprehensive seismic catalogs spanning from 2019 to the present. Our automated workflow includes the identification and localization of long period (LP) events, tremors, and volcano-tectonic (VT) earthquakes.

For this purpose, an improved classification model based on Support Vector Machines was developed to distinguish LP events and tremors within continuous recordings. Their locations were determined using a cross-correlation-based method. Additionally, the VT earthquake catalog was compiled using deep learning-based models for phase picking, followed by standard location methods. Our findings not only corroborate trends observed in manual analyses at the volcano's observatory but also uncover additional events, highlighting trends in the volcano’s dynamics not observed before.

To showcase the use of these catalogs, we will present a multiparametric analysis integrating seismic data with thermal anomalies, SO2 emissions, and GPS measurements. This research not only deepens our comprehension of volcanic processes but also underscores the transformative role of technology in geophysical research.

 

Research supported by the program UNAM-DGAPA-PAPIIT: IN103823.

How to cite: Bernal-Manzanilla, K., Calò, M., Rodríguez García, K. E., Martínez Jaramillo, D., and Valade, S.: Dynamics of the Popocatépetl Volcano, Mexico, revealed by Machine Learning-Based Seismic Catalogs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13020, https://doi.org/10.5194/egusphere-egu24-13020, 2024.

EGU24-13932 | ECS | Posters on site | SM7.2

Spectral energy distribution of Nevado del Ruiz Volcano seismicity near eruptive events 

Yuly Paola Rave-Bonilla, Mel Rodgers, Félix Rodríguez-Cardozo, Jochen Bruanmiller, and John Makario Londoño

Volcano seismology is a key contributor for assessing the activity status of volcanoes and forecasting future eruptive behaviour. One measurement that may indicate a change in the volcanic behaviour is a temporal change in the spectral content, or frequency distribution, of seismic waveforms. Significant changes in frequency distribution have been observed at Soufrière Hills, Montserrat; Telica Volcano, Nicaragua; Redoubt Volcano, Alaska USA, and at other volcanoes prior to volcanic eruptions. Identification of such changes in spectral energy could indicate changes in volcanic activity, and hence be used in forecasting, as well as to investigate the physical processes behind eruptive processes. With the objective of identifying possible changes in the spectral energy distribution of the seismic sources of the Nevado del Ruiz Volcano (NRV) prior to eruptions, we analysed the spectral energy of volcano tectonic (VT), low frequency (LF) and hybrid seismic events during 2012, when the NRV had two Volcanic Explosivity Index (VEI) 2 eruptions on May 29th and June 30th. We analysed nearly 27,000 events and implemented a semi-automatic pre-processing pipeline in ObsPy for selecting the optimal stations and seismograms based on the signal-to-noise ratio and proximity to seismic clusters. Then, we cut the seismograms to isolate the seismic signals and bandpass-filtered the data before calculating metric such as dominant frequency, ratio of high to low spectral energy. In this work, we present preliminary results on the temporal changes in spectral energy of the seismic events at NRV and whether this could be linked, along with other geophysical measurements, with changes to eruptive behaviour.

How to cite: Rave-Bonilla, Y. P., Rodgers, M., Rodríguez-Cardozo, F., Bruanmiller, J., and Londoño, J. M.: Spectral energy distribution of Nevado del Ruiz Volcano seismicity near eruptive events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13932, https://doi.org/10.5194/egusphere-egu24-13932, 2024.

EGU24-14227 | ECS | Posters on site | SM7.2

The ongoing seismological research for the Central-Southern Aeolian Islands (CAVEAT project), Italy, from dense terrestrial seismic arrays 

Ivan Granados-Chavarria, Francesca Di Luccio, Marco Calò, Matteo Lupi, Mimmo Palano, Daniela Famiani, Federica Magnoni, Antonio Scaltrito, Laura Scognamiglio, Anna Tramelli, Andrea Ursino, Tullio Ricci, and Alessandro Marchetti

One of the tasks of the multidisciplinary project CAVEAT “Central-southern Aeolian islands: Volcanism and tEAring in the Tyrrhenian subduction system” was to deploy a dense seismic network composed by 120 wirelesss nodes, which were deployed for approximately 2 months on three islands of the Aeolian volcanic archipielago.

The main goals of this data acquisition are to:

  • detect and locate the shallow weak seismicity related to both volcanic and tectonic activity,
  • perform regional and local tomographic studies based on both passive methods and ambient noise cross-correlations (previously done for Lipari, Calò et al., 2023) to constrain the crust structure
  • characterize the source mechanisms.

In this work we show the details of the data acquisition strategy and the preliminary analyses of the continuous ambient noise records, to reconstruct the shallow structure of the Aeolian Arc. This study is part of the INGV Pianeta Dinamico project 2023-2025 CAVEAT “Central-southern Aeolian islands: Volcanism and tEAring in the Tyrrhenian subduction system” (grant no. CUP D53J19000170001) supported by the Italian Ministry of University and Research “Fondo finalizzato al rilancio degli investimenti delle amministrazioni centrali dello Stato e allo sviluppo del Paese, legge 145/2018.

How to cite: Granados-Chavarria, I., Di Luccio, F., Calò, M., Lupi, M., Palano, M., Famiani, D., Magnoni, F., Scaltrito, A., Scognamiglio, L., Tramelli, A., Ursino, A., Ricci, T., and Marchetti, A.: The ongoing seismological research for the Central-Southern Aeolian Islands (CAVEAT project), Italy, from dense terrestrial seismic arrays, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14227, https://doi.org/10.5194/egusphere-egu24-14227, 2024.

EGU24-15278 | Orals | SM7.2

Self-supervised learning for the exploration of continuous seismic records at the Fani Maoré submarine volcano (Mayotte) 

Clément Hibert, Joachim Rimpot, Lise Retailleau, Jean-Marie Saurel, Jean-Philippe Malet, Germain Forestier, Jonathan Weber, Tord S. Stangeland, Antoine Turquet, and Pascal Pelleau

Continuous seismological observations provide valuable information to deepen our understanding of processes occurring in both aerial and submarine volcanoes. However, the wealth of the seismicity recorded near volcanoes makes exhaustive exploration of these seismological chronicles very complex and time-consuming. In this study, we present a systematic analysis of two months of seismological records using a self-supervised learning (SSL) approach for the unsupervised clustering of continuous seismic data acquired by ocean bottom seismometers deployed in the vicinity of the Fani Maoré volcano (Mayotte). The proposed clustering process allows the identification of individual seismic events, seismic crisis and tremors that would be challenging to observe using conventional approaches. We show that our approach detects and classifies both known and new events, including two eruptive sequences previously unknown. We also demonstrate the potential of self-supervised methods for the analysis of seismological records, providing a synoptic view and facilitating the discovery of insightful yet rare events. This approach has numerous applications in exploring various seismological datasets, simplifying analysis while making it more comprehensive.

How to cite: Hibert, C., Rimpot, J., Retailleau, L., Saurel, J.-M., Malet, J.-P., Forestier, G., Weber, J., Stangeland, T. S., Turquet, A., and Pelleau, P.: Self-supervised learning for the exploration of continuous seismic records at the Fani Maoré submarine volcano (Mayotte), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15278, https://doi.org/10.5194/egusphere-egu24-15278, 2024.

EGU24-16604 | Orals | SM7.2

Differential phase analysis for volcanic tremor detection and source location. 

Andres Barajas, Nikolai Shapiro, and German Prieto

We present observations showing that during episodes of volcanic tremors, the phase of inter-station cross-correlations becomes stable. We propose a new quantity, the phase coherence, to identify the differential phase stability in recordings obtained from a single pair of stations, which is extrapolated to the seismic network. Then, we present a new approach based on the estimation of differential travel times through the differential phase measurements, to locate the sources of tremors occurring at the end of 2015 at the Klyuchevskoy Volcanic Group in Kamchatka, Russia. We present evidence supporting the existence of two types of activity happening simultaneously during the tremor episode: the main tremor source, originating from a region located between 7 and 9 km depth under the main volcanoes, and the widespread occurrence of weak low-frequency earthquakes occurring at random locations. We show how the phase coherence and the differential phases can be used to provide information on the stability of the tremor source position and to estimate its location.

How to cite: Barajas, A., Shapiro, N., and Prieto, G.: Differential phase analysis for volcanic tremor detection and source location., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16604, https://doi.org/10.5194/egusphere-egu24-16604, 2024.

EGU24-17156 | ECS | Posters on site | SM7.2

Seismic Investigation of the Ojos del Salado Volcano, Chile: The Highest Altitude Volcano in the World 

Louisa Murray-Bergquist, Ayon Garcia Pina, Martin Thorwart, Christopher Ulloa, Janneke van Ginkel, Lisanne van Huisstede, Richard Wessels, and Anouk Beniest

The Ojos del Salado Volcano in Chile is the highest altitude volcano in the world, but has not been visibly active since 1993, when steam was observed rising from near the summit. Since then the volcano has been considered dormant, however, it is unclear if it could become active again, and if so, what the ramifications would be. Little is known about the size and structure of the magma chamber, or its potential interaction with hydrothermal fluids and whether this is the heat source of the nearby hydrothermal lake, Laguna Verde.

The region surrounding the volcano is very arid, but due to the cold climate at such high-altitude there are some remnant glaciers and permafrost from the last glacial maximum. Summer meltwater from these cryosphere features contributes to the water budget of the valley below, which adds to the importance of understanding the extent of remaining permafrost and the interactions between local volcanism and the cryosphere that could increase the rate of melting.

In this study we combine InSAR data with local seismicity to investigate local crustal deformation and seismic activity at the Ojos del Salado Volcano. A small seismic array, deployed in 2022, measured seismicity in the vicinity of the volcano and acted as a pilot for the 2024 campaign and network design. A dense network of geophones was deployed on the volcano’s flanks in early 2024. We present the first results of the analysis of the data from this denser network, and the pilot study, which already showed seismicity in the vicinity of the volcano. From this analysis we gain insight into the level of activity of the Ojos del Salado Volcano, local deformation patterns and the style of faulting which is also an indication of potential fluid pathways that could link the volcano to the hydrothermal lake. With this information we can better understand the interaction between this unique volcano and the local cryosphere.

How to cite: Murray-Bergquist, L., Garcia Pina, A., Thorwart, M., Ulloa, C., van Ginkel, J., van Huisstede, L., Wessels, R., and Beniest, A.: Seismic Investigation of the Ojos del Salado Volcano, Chile: The Highest Altitude Volcano in the World, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17156, https://doi.org/10.5194/egusphere-egu24-17156, 2024.

In this study we utilize 3D numerical models to simulate seismic resonances in a volcanic edifice, arising from the interaction between an externally excited wavefield and a magma chamber-conduit system. The resultant wavefield holds the potential to provide significant insights into the properties of the magmatic system. Contrary to previous assumptions that required an internal source, our findings show that the magma chamber and conduit efficiently capture the incident wavefield of both P- and S-waves, excited by a high-frequency (~10 Hz) earthquake located within the edifice. Due to multiple internal reflections off the boundaries of the chamber and the conduit, prolonged reverberations occur, which are guided along the conduit. Temporal and spectral analyses of synthetic seismograms illustrate that the size of the magma chamber and the width of the conduit are critical in determining the magnitude and dominant frequencies of the seismic resonances. Specifically, models with larger magma chambers and wider conduits consistently yield larger resonance amplitudes at distinct frequencies. At greater distances from the conduit, an intensified scattered wavefield with a broad frequency range indicates the presence of a substantial magma chamber within the volcanic edifice. Resonance frequencies reach up to 23 Hz, underscoring significant frequency shifts. In general, these externally initiated resonances may appear as tremor-like signals at seismic stations on the edifice, accompanying more conventional seismic events in its proximity.

How to cite: Rümpker, G. and Limberger, F.: Numerical modeling predicts seismic resonances in the magma chamber-conduit system due to wavefield capturing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20804, https://doi.org/10.5194/egusphere-egu24-20804, 2024.

EGU24-21112 | Orals | SM7.2

High-Resolution Seismic Methods for Geothermal Exploration and Monitoring across the Hengill volcanic area 

Anne Obermann, Bettina Goertz-Allmann, Pilar Sanchez-Pastor, Peidong shi, Sin-Mei Wu, and Vala Hjórleifsdóttir

Hengill volcano and its associated geothermal fields represent Iceland's most productive harnessed high-temperature geothermal fields, where energy is provided by cooling magmatic intrusions connected to three volcanic systems. The crustal structure in this area is highly heterogeneous and shaped by the intricate interplay between tectonic forces and magmatic/hydrothermal activities, making detailed subsurface characterization challenging. In the Northern part of the Hengill geothermal field, super-hot geothermal resources have been spotted that are currently considered for geothermal exploration.

Over the past years, we have studied the site in great detail, and acquired high-quality datasets from a 40+broadband seismic station array, a dense 500+ station nodal array and distributed acoustic sensing data from a fibre line crossing the area. We compare the results that we obtained from various seismic imaging methods e.g., earthquake tomography, ambient noise methods and discuss their potential and limitation to enable high-resolution seismic methods for exploration and monitoring of geothermal plays in such complex volcanic environments.

How to cite: Obermann, A., Goertz-Allmann, B., Sanchez-Pastor, P., shi, P., Wu, S.-M., and Hjórleifsdóttir, V.: High-Resolution Seismic Methods for Geothermal Exploration and Monitoring across the Hengill volcanic area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21112, https://doi.org/10.5194/egusphere-egu24-21112, 2024.

EGU24-22030 | ECS | Posters on site | SM7.2

Grid-search method for STA/LTA parameters tuning: an application to Stromboli Explosion Quakes  

Andrea Di Benedetto, Anna Figlioli, Antonino D’Alessandro, and Giosue’ Lo Bosco

The collection of a significant catalog of seismo-volcanic data involves the selection of relevant parts of raw signals, that can be automatized by using the Short-term over Long-term Average (STA/LTA) method. Since it is parametric, the common approach to the choice is the adoption of literature-suggested parameters. To overcome these limitations, we propose a methodology for the automatic selection of STA/LTA parameters able to optimize the extraction of local events from a seismo-volcanic raw signal. The parameters are found by a grid search over an index named Quality-Numerosity Index (QNI) that measures the accordance in the automatic cuts and the consequent quantity of triggered seismo-volcanic events with the ones suggested by a human expert. The method was applied in the volcano domain, for the specific application of Explosion Quake signals extraction in Stromboli Volcano. Experiments have been conducted selecting a subset of the dataset as training where to search for the best parameters, which were subsequently adopted in a test set. The results demonstrate that the selected parameters significantly improve the quality of the extraction when compared to those extracted by adopting the parameters indicated in the literature.

How to cite: Di Benedetto, A., Figlioli, A., D’Alessandro, A., and Lo Bosco, G.: Grid-search method for STA/LTA parameters tuning: an application to Stromboli Explosion Quakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22030, https://doi.org/10.5194/egusphere-egu24-22030, 2024.

EGU24-468 | ECS | Posters on site | ERE5.1

Injection Rate effects on failure of a saturated gouge-filled fault failure: Dilation vs. Diffusion 

Pritom Sarma, Einat Aharonov, Renaud Toussaint, and Stanislav Parez

Understanding the underlying mechanisms controlling earthquake triggering by fluids has become increasingly important in recent decades, driven largely by observations that link subsurface fluid injections to subsequent nearby earthquakes. It is clear that understanding and predicting fluid-induced triggering is required in many energy-related activities (e.g. geothermal energy, CO2 injection), as well as for naturally triggered events. One of the main open questions is the effect of fluid-injection rate. Usually the ‘effective stress law’ is invoked to predict the failure of fluid-saturated granular or porous media. This law assumes that in fluid-pressurized faults the instantaneous value of pore pressure controls fault strength and failure. But recent laboratory results (Passelègue et. al., 2018) suggest that the level of pressure by itself cannot describe the full mechanics. These experiments show that the rate of fluid injection is also important: slower injections lead to failure at lower pressures than fast injection rates. 

 

We shall present results from a coupled hydromechanical-discrete element model that simulates the response of a pre-stressed, fully saturated fault, filled with a granular fault gouge, subject to fluid injection at different rates. Our simulation results find similar rate-dependence as seen in the laboratory experiment, i.e. that slow injection causes failure at lower fluid pressure than faster injection. Several mechanisms can be theorized to explain these observations, and we explore the two main end-member cases, dilation-driven and diffusion-driven rate-dependence, by comparing theoretical predictions for the poro-elastic response of the layer vs. pore-pressure diffusion. Our theoretical analysis provides upper and lower bounds to the numerically observed  rate dependence, suggesting the reason why the effective stress law is an insufficient approximation for failure of material exposed to pore fluid injection, when the pore-pressure injection rate is varied.

How to cite: Sarma, P., Aharonov, E., Toussaint, R., and Parez, S.: Injection Rate effects on failure of a saturated gouge-filled fault failure: Dilation vs. Diffusion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-468, https://doi.org/10.5194/egusphere-egu24-468, 2024.

EGU24-3259 | Orals | ERE5.1

Predicting observed induced seismicity due to production in the Hverahlid, SW Iceland, geothermal field 

Vala Hjörleifsdóttir, Kristín Jónsdóttir, Halldór Geirsson, Ásdís Benediktsdóttir, and Sigríður Kristjánsdóttir

The Hverahlíð geothermal field, located in the fissure swarm of Hengill volcano, SW Iceland, has been producing steam and geothermal fluids for the Hellisheiði geothermal power plant (303 MWe, 210 MWth), since late 2016.  A total of 7 geothermal wells in the field (HE-21, -26, -53, -54, -60, -61 and -66) have been producing up to 150 kg/s of steam and 60-70 kg/s of separated liquid.  The combined extraction from the wells is limited by the size of the steam pipeline connecting the field to the power plant.  

Within months of the initiation of production an increase in seismicity was noted within the field.  This is in contrast to the nearby Hellisheiði geothermal field, ~2 km away, which has experienced very little induced seismicity since commission in 2006, despite more than twice as high mass extraction rates and higher deformation rates.  Since early 2018 a total of 8 events with M> 2.5 have occurred in the field.  The latest of these events occurred in November 2022 with M 3.2. The seismicity largely does not line up on faults and is relatively evenly distributed throughout what is considered the top of the geothermal reservoir (Kristjánsdóttir et al 2019).

Currently a second pipeline connecting the geothermal field with the power plant is in construction and with the commission, planned for fall 2024, an increase in mass extraction rates from the Hverahlíð geothermal field  of ~30% is expected.

In this presentation we compare the observed location, seismicity rates and Mmax values to those expected from different models of earthquake triggering.  We furthermore predict the expected increase in seismicity rates due to the increase in production rates and the increase in seismicity that will be felt by the neighboring community of Hveragerði.

How to cite: Hjörleifsdóttir, V., Jónsdóttir, K., Geirsson, H., Benediktsdóttir, Á., and Kristjánsdóttir, S.: Predicting observed induced seismicity due to production in the Hverahlid, SW Iceland, geothermal field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3259, https://doi.org/10.5194/egusphere-egu24-3259, 2024.

EGU24-3789 | Posters on site | ERE5.1

Characteristics for b-value of induced seismicity in Southeast of Sichuan Basin, China 

Mengyu Xie, Yunxiao Zhao, and Lingyuan Meng

Due to abundant shale gas buried beneath Southeast of Sichuan Basin, China (SBC), hydraulic fracturing operations are implemented since 2008. And large-scale shale gas mining began in December 2014. A rapid increase in the rate of seismicity in SBC since 2015, including the 16 December 2018 MS5.7, the 3 January 2019 MS5.3, the 17 June 2019 MS6.0, the 8 September 2019 MS5.4, the 18 December 2019 MS5.2, the 16 September 2021 MS6.0 and the 6 April 2022 MS5.1 earthquakes. Those earthquakes have caused much damages and many injures, which attracts a lot of attention from society and researchers. The related studies show that seismicity in SBC are induced by or related to hydraulic fracturing operation (Meng et al, 2019; Lei et al, 2019). In this work, we try to study the characteristics of local seismicity and explore the spatiotemporal characteristics of b-value in G-R relation to gain insight into the possible dynamic processes beneath the induced seismicity and assess the seismic hazards. The preliminary results indicate that the average b-value decrease from 1.17 to 0.75 when the 16 September 2021 MS6.0 earthquake occurred. And there is a substantial reduction of b-value before the 8 September 2019 MS5.4 earthquake. Moreover, the temporal variations for b-values don’t show a common pattern.

 

This study was supported by the Science for Earthquake Resilience (XH22011YA), “Real-time analyze characteristics of earthquake sequence by b-value and waveform” and National Natural Science Foundation of China (41974068), “Seismicity for Shale Gas Hydraulic Fracturing Stimulation”.

 

Lei X L, Wang Z W, Su J R. 2019. The December 2018 ML 5.7 and January 2019 ML 5.3 Earthquakes in South Sichuan Basin Induced by Shale Gas Hydraulic Fracturing. Seismological Research Letters, 90(3), 1099-1110, doi: 10.1785/0220190029.

Meng L, McGarr A, Zhou L, Zang Y. 2019. An Investigation of Seismicity Induced by Hydraulic Fracturing in the Sichuan Basin of China Based on Data from a Temporary Seismic Network. Bulletin of the Seismological Society of America, 109(1), 348–357, doi: 10.1785/0120180310.

How to cite: Xie, M., Zhao, Y., and Meng, L.: Characteristics for b-value of induced seismicity in Southeast of Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3789, https://doi.org/10.5194/egusphere-egu24-3789, 2024.

EGU24-5646 | ECS | Posters on site | ERE5.1

On the triggering mechanism of fault-slip bursts during deep underground excavation 

Wenbo Pan, Zixin Zhang, Shuaifeng Wang, Chenxi Zhao, and Qinghua Lei

To meet the target of net-zero emissions by 2050, six times more mineral inputs are required in 2040 than today. However, with the depletion of mineral resources in the shallow subsurface, mining at great depth is inevitable. Furthermore, the rapid development of urban systems, transport networks, and hydropower plants also impose an increased demand of deep underground excavation. These deep mining or tunneling activities are, however, confronted with the risk of induced earthquakes and rockbursts. For example, during the Gotthard Base Tunnel construction at great depths of up to 2.5 km in the Swiss Alps, extensive regional earthquakes with magnitudes reaching up to Mw 2.4 were recorded. Accompanying some of these earthquake events, intense rockbursts occurred at the Faido Multifunction Station. So far, it remains poorly understood the triggering mechanisms of these rockburst events and their relationship with the induced earthquakes. Here, we develop a novel three-dimensional coupled seimo-mechanical model which can capture the rupture of a seismogenic fault zone, the redistribution of stress field, the propagation of seismic waves, and the occurrence of coseismic rockbursts in a tunnel located a few hundred meters away from the hypocenter (i.e., in the near-field of the earthquake fault). We investigate the competing roles of static and dynamic triggering in generating these fault-slip burst events and find that static stress changes play a much more dominant role than dynamic waves. The results and insights derived from our research have important implications for understanding and predicting catastrophic rockbursts during deep underground excavation for various geoenergy or geoengineering applications, ranging from critical mineral extraction and nuclear waste disposal to underground energy storage and civil infrastructure development.

How to cite: Pan, W., Zhang, Z., Wang, S., Zhao, C., and Lei, Q.: On the triggering mechanism of fault-slip bursts during deep underground excavation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5646, https://doi.org/10.5194/egusphere-egu24-5646, 2024.

EGU24-5696 | ECS | Orals | ERE5.1

Picoseismic response of hectometer-scale fracture systems to stimulation under the Swiss Alps, in the Bedretto Underground Laboratory 

Anne Obermann, Martina Rosskopf, Virginie Durand, Katrin Plenkers, Kai Bröker, and Nima Gholizadeh Doonechaly

We performed a series of hydraulic stimulations at 1.1 km depth in the Bedretto underground laboratory in the Swiss Alps. The goal was to achieve an unprecedented detailed and profound understanding of hydromechanical and seismic processes during hydraulic reservoir development with a dense multi-sensor monitoring network. With our seismic network that includes various sensor types with different sensitivities, we succeeded in characterizing induced seismicity down to the pico-seismicity level (Mw<-4), thus illuminating details of a complex fracture network more than 100 m from the injection locations. Here, we present the experiments and seismic catalogs as well as a comparative analysis of event number per injection, magnitudes, b-values, seismogenic index and reactivation pressures.

During a first-order data analysis, we could make the following observations: 

-        We find that the ultra-high frequency seismic network with custom-made AE sensors, allows us to observe seismicity over 3 orders of magnitude scale. Thanks to collocated accelerometers and acoustic emission sensors, AE sensors could be calibrated in-situ and adjusted moment magnitudes could be implemented into the seismic catalog. 

-        The volume impacted by the stimulations in different intervals differs significantly with a lateral extent from a few meters to more than 150 m. Most intervals activated multiple fractures. Only during the stimulation of an interval located next to a dominant shear zone, an extended single fracture was activated, which is likely attributed to the dominant shear zone in this area. The seismic clouds typically propagate upwards towards more permeable, shallow depth on parallel dipping planes that are consistent with the stress field and seem to a large extent associated with preexisting open fractures.

-        It is worth noting the strong correlation between the propagation patterns observed in the seismic events and the hydromechanical observations, specifically in terms of the strain and pressure data obtained from Distributed Strain Sensing (DSS), the Fiber Bragg Grating (FBG) and the pore pressure sensors that form part of the multi-component borehole monitoring system. 

-        This experiment confirms the diversity in seismic behavior independent of the injection protocol. Some intervals showed rapidly increasing seismicity that is spatially restricted to the volume in direct vicinity of the injection point, while others have seismicity extending as far as 150 m away from the injection point.

-        The reactivation pressures hint at hydraulic shearing as the dominant process, since the elastic fracture opening appears to be mostly aseismic.

-        The seismicity shows no distinct deviation from “normal” behavior with regard to Gutenberg Richter or McGarr. 

We have the opportunity to analyze the seismic data jointly with a multitude of other geophysical observables, such as strain and pressure, to allow more insights into the correlation of slow fracture opening and aseismic deformation processes. In future studies, the existence of these multi-disciplinary observations will allow us to put more constraints on the processes responsible for the diversity observed in seismicity.

How to cite: Obermann, A., Rosskopf, M., Durand, V., Plenkers, K., Bröker, K., and Gholizadeh Doonechaly, N.: Picoseismic response of hectometer-scale fracture systems to stimulation under the Swiss Alps, in the Bedretto Underground Laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5696, https://doi.org/10.5194/egusphere-egu24-5696, 2024.

EGU24-6443 | ECS | Orals | ERE5.1

What are the alternative pumping strategies to stimulate areservoir without triggering distant faults? 

Bérénice Vallier, Renaud Toussaint, Marwan Fahs, Clément Baujard, Albert Genter, Eirik Grude Flekkøy, and Knut Jørgen Måløy

In the context of deep reservoir exploitation, it is necessary to enhance reservoir permeability before exploitation. One method to achieve this is by conducting stimulations through fluid injection, which increases pore pressure, reduces the effective normal stress and allows dilatant shear and porosity increase along small fractures in the reservoir, in the vicinity of the injection well. The pore pressure diffuses throughout the reservoir and can also sometimes reach distant faults that are critically stressed, with a risk to trigger seismicity along these. The model we propose aims to decrease the effective normal stress reduction caused by pressure disturbance along such distant faults, which can cause the rupture of critically stressed distant faults and induce seismic activity. This work investigates an alternative pumping method to stimulate a reservoir without triggering distant faults. To achieve this, a numerical model based on the finite difference method has been developed to solve the diffusion equation of pressure disturbances. The simplifying assumption is that the domain is isotropic and homogeneous. The 2D domain represents the fault plane and permeable damaged zone embedded in less permeable rock. To validate the numerical model, the numerical distant pressure disturbances are compared to analytical solutions developed from the Green's function of the diffusion equation. The numerical model investigates the impact of a time-dependent oscillating injection strategy on near-well and distant pressure disturbances, in comparison to other tested methods, to minimize induced seismicity. The results suggest that the oscillating pumping strategy has the potential to significantly reduce induced seismicity on distant faults. Future research will involve developing mitigation strategies using more complex models that incorporate realistic fault geometries and operational conditions.

How to cite: Vallier, B., Toussaint, R., Fahs, M., Baujard, C., Genter, A., Flekkøy, E. G., and Måløy, K. J.: What are the alternative pumping strategies to stimulate areservoir without triggering distant faults?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6443, https://doi.org/10.5194/egusphere-egu24-6443, 2024.

EGU24-8026 | ECS | Orals | ERE5.1

Pseudo-prospective forecasting of induced and natural seismicity in the Hengill geothermal field 

Vanille Ritz, Leila Mizrahi, Victor Clasen Repollés, Vala Hjörleifsdóttir, Antonio Pio Rinaldi, and Stefan Wiemer

The Hengill geothermal field, located in southwest Iceland, is host to the Hellisheiði power plant, with its 40+ production wells and 17 reinjection wells. Located on a tectonically active area, the field experiences both natural and induced seismicity associated to the power plant operations. To better manage the risk posed by this seismicity, the development of robust and informative forecasting models is paramount.

In this study, we compare the forecasting performance of a model developed for fluid-induced seismicity (the Seismogenic Index model) and a class of well-established statistical models (Epidemic-Type Aftershock Sequence). The pseudo-prospective experiment is set up with 14 months of initial calibration and daily forecasts for a year. In the timeframe of this experiment, a dense broadband network was in place in Hengill, allowing us to rely on a high quality relocated seismic catalogue. The seismicity in the geothermal field is characterised by four main clusters, associated with the two reinjection areas, one production area an area with surface geothermal manifestations but where no operations are taking place. We show that the models are generally well suited to forecast induced seismicity, despite some limitations, and that a hybrid ETAS  model accounting for fluid forcing has some potential in complex regions with natural and fluid-induced seismicity.

How to cite: Ritz, V., Mizrahi, L., Clasen Repollés, V., Hjörleifsdóttir, V., Rinaldi, A. P., and Wiemer, S.: Pseudo-prospective forecasting of induced and natural seismicity in the Hengill geothermal field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8026, https://doi.org/10.5194/egusphere-egu24-8026, 2024.

EGU24-8044 | Orals | ERE5.1

Presenting a new holistic robust approach for predicting geo-failures in complex underground engineering projects 

Majid Khan, Xueqiu He, Dazhao Song, Zhenlei Li, Xianghui Tian, and Umair Khan

The exploration of geo-resources in complex geological provinces poses significant challenges, often resulting in severe geological disasters with economic losses and fatalities. Fractured rocks, pre-existing fractures, and excavation-induced fractures contribute to the complexity of these disasters. Despite numerous studies, understanding the coupling mechanism of induced seismicity and geological deformations in such complex mining environments remains unclear. This study introduces the "Acousto-Frac Model," a novel, cost-effective, and robust geophysical approach designed to comprehensively understand experimental microseismicity and reveal such a mechanism. Traditionally, physical models and numerical simulations have been employed for dynamic disaster prediction in underground coalmines. However, these methods are often neither cost-effective nor robust. The Acousto-Frac Model offers an innovative methodology for mapping induced fracture networks through Acoustic Emission (AE) experiments conducted on coal and rock samples. This approach tracks each AE event, constructs networks of induced fractures, identifies geological lineaments, and predicts zones prone to failure/disasters.

To implement the model, AE and rock mechanics testing systems were utilized to conduct experiments on coal and rock samples under uniaxial loading. The proposed model successfully identified weak zones, predicting general deformation propagation directions. Moreover, the 3D crack growth theory and the criterion for microcrack density were employed to analyze the fracture transformation process, ranging from small-scale microfractures to large-scale microfractures and from local deformation to complete damage for the coal and rock samples subjected to uniaxial loading.

The study further leverages Single Link Cluster (SLC) simulations and b-value theory to characterize the spatiotemporal response of microearthquakes, including b-value, spatial correlation length (ξ), and information entropy (H). Notably, the results indicated that at the onset of initial loading (15%), the spatial correlation length (ξ) exhibited an upward trend, while the b-value remained comparatively stable. These parameters showed a significant change trend before the buckling failure of coal and rock samples, suggesting that, in combination with the proposed model, spatial correlation length (ξ), b-value, and information entropy (H) provide a new and robust method for complete deformation evaluation and the prediction of geo-material failure. This innovative method, while a panacea for imaging the entire fracturing phenomenon, provides insights with widespread implications for academic researchers and industry practitioners. It serves as a valuable tool for predicting geological failures in global underground engineering excavations, offering a comprehensive and cost-effective solution for the mapping of induced seismicity and geological deformations in underground mines.

How to cite: Khan, M., He, X., Song, D., Li, Z., Tian, X., and Khan, U.: Presenting a new holistic robust approach for predicting geo-failures in complex underground engineering projects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8044, https://doi.org/10.5194/egusphere-egu24-8044, 2024.

A thorough understanding of geological and hydraulic fracturing aspects can offer significant insights into the physical mechanisms governing earthquakes. In this study, we conducted seismic monitoring near a hydraulic fracturing well-pad in the southern Sichuan Basin. The monitoring adopts a dense seismic array that consists of 60 three-component stations, and last for a duration of 53 days. Accordingly, we resolved and located over 1,000 events (-1.43<M<2, Mc=-0.72). Most events (~ 70%) distributed near the southwest direction of the injection wells, delineating a series of NE-SW trending structures. Our high-resolution hypocenter locations and statistical analysis reveal two distinctive clusters: (i) one linearly-distributed cluster characterized by larger magnitudes, deeper focal depths and a b value (1.09) comparable to tectonic earthquakes; (ii) one relatively scattered cluster with smaller magnitudes, shallower depths and a higher b value (1.29). We speculate that deeper events are more consistent with seismicity occurring on pre-existing fault(s), whereas shallower events occur within a fracture network.

The detailed structures are further evaluated with resolved focal mechanisms and 3D seismic reflection imaging. The deeper events unanimously support a right-lateral, steep strike-slip fault, consistent with the fault geometry depicted by high-resolution hypocenter locations. In comparison, focal mechanisms of the shallower earthquakes are more complex and diverse, showing a mixture of normal fault and strike-slip events. In the vicinity of the two clusters, seismic reflection data indicates a ~3 km-length fault that strikes in approximately north-south (NS) orientation. Therefore, we suggest that the damage zone along the NS fault enhanced the connectivity and provided additional hydraulic channel for fluid migration during shale gas extraction. Overall, the distinct characteristics of the two earthquake clusters could be well-explained by their spatial proximity to the fault zone: shallower earthquakes occur on dense fractures near the main fault, whereas the deeper cluster occur on a distant small-scale fault. This study sheds light on the complex relationship between hydraulic fracturing, geological factors, and earthquake occurrence, and may assist strategy development toward risk mitigation of HF-induced seismicity.

How to cite: Zhang, F., Wang, R., Chen, Y., and Yu, H.: Pre-existing Fault Regulates the Distribution and Behavior of Hydraulic Fracturing-Induced Seismicity in southern Sichuan, China , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8812, https://doi.org/10.5194/egusphere-egu24-8812, 2024.

EGU24-8850 | Orals | ERE5.1

Microseismic event analysis using multi-technology sensors at the Quest CCS site 

Bettina Petra Goertz-Allmann, Nadège Langet, Alan Baird, Kamran Iranpour, Daniela Kühn, Jerome Vernier, Estelle Rebel, and Steve Oates

Microseismic monitoring plays a crucial role in assessing the effectiveness and integrity of Carbon Capture and Storage (CCS) projects. By the detection of microearthquakes we can gain real-time insights into the pressure and stress perturbation due to injection operations, aiding in the detection of potential leakage and ensuring the long-term viability of carbon sequestration efforts.

At the Quest CCS site in Alberta, Canada, CO2 injection into a 2 km depth saline reservoir is ongoing since 2015 at a rate of one million tonnes per year.  Several hundreds of small-magnitude seismic events have been located in the Precambrian basement below the reservoir.  A spatio-temporal analysis of seismicity reveals clustered as well as more diffuse distributions of events.  At the Quest site various microseismic monitoring technologies are in place including a downhole 8-level 3-component geophone string, temporary surface nodes arranged in mini-arrays, and downhole optical distributed acoustic sensing (DAS) fiber. The site offers an ideal opportunity to compare and combine the different setups with respect to event detection thresholds and location uncertainties. We demonstrate the importance of advanced signal and array processing techniques and highlight the advantages and disadvantages of different sensor technologies.

How to cite: Goertz-Allmann, B. P., Langet, N., Baird, A., Iranpour, K., Kühn, D., Vernier, J., Rebel, E., and Oates, S.: Microseismic event analysis using multi-technology sensors at the Quest CCS site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8850, https://doi.org/10.5194/egusphere-egu24-8850, 2024.

EGU24-9417 | ECS | Posters on site | ERE5.1

Preliminary analysis of seismic attenuation and heterogeneities in Weiyuan Shale Gas Field: Coda Q and Peak delay time analysis 

Aqeel Abbas, Luca De Siena, Hongfeng Yang, Simona Gabrielli, and Wei-Mou Zhu

During hydraulic fracturing (HF) stimulation in unconventional reservoir development, seismic attenuation significantly affects high frequency microseismic data. Analyzing attenuation parameters, including scattering and absorption, provides valuable insights into reservoir properties and changes that result from HF injections. These attenuation parameters were mapped in 3D using the MuRAT (multi-resolution seismic attenuation tomography) software with a dataset of approximately 32,000 events over two years in the Weiyuan shale gas field (WSGF). Firstly, the coda quality factor Qc (intrinsic absorption), which quantifies coda wave energy loss, is calculated at large lapse time in three frequency bands (3, 6 and 9 Hz). Subsequently, we measure the peak delay time, the time lag between the direct S-wave onset and the highest amplitude arrival. Our preliminary results show that Qc has strong absorption at lower frequencies in specific volumes compared to higher frequencies. Meanwhile, peak delay times indicate consistently stronger scattering along the Weiyuan anticline and Molin fault structures across all frequency bands. We propose that the observed strong absorption is associated with the reservoir and injected fluid, while scattering is linked to pre-existing structural heterogeneities and unmapped faults.

How to cite: Abbas, A., De Siena, L., Yang, H., Gabrielli, S., and Zhu, W.-M.: Preliminary analysis of seismic attenuation and heterogeneities in Weiyuan Shale Gas Field: Coda Q and Peak delay time analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9417, https://doi.org/10.5194/egusphere-egu24-9417, 2024.

The occurrence of induced moderate to strong earthquakes is generally believed to be the reactivation of pre-existing faults of a certain size due to stress disturbances caused by the industrial activities. Therefore, pre-existing faults in the crust are already subjected to the background tectonic stress field, and different orientations of faults experience different stress state. Therefore, evaluating the risk of faults slipping with different orientations under the tectonic stress field is the basis for guiding industrial construction design to reduce induced seismic risk.

The Luxian County shale gas field is one of the four shale gas development areas in southern Sichuan, China. In this study, we conduct a fault slip risk analysis based on the distribution of the three-dimensional (3D) faults in Luxian County shale gas field . Luxian County is situated in the southwestern part of the Huayingshan fold belt, nestled between the steep Gufoshan anticline and the Luoguanshan anticline, with a broad and gentle Fuji syncline in between. The region exhibits extensive development of faults and fractures. Since the extensive implementation of hydraulic fracturing related to shale gas extraction in this region in 2019, there has been a noticeable increase in seismic activity.

In this study, we interpret the 3D fault planes in Luxian County based on seismic reflection profiles. Based on the collection of in-situ stress and formation pressure data, we establish the background tectonic stress field in the Luxian shale gas field and calculate the critical pore pressure increment required for the slipping of 3D fault planes under the background tectonic stress field, as well as the fault slip tendency. Furthermore, we construct a 3D fully coupled poroelastic finite element model to calculate the static Coulomb stress perturbation that injection operations might cause on faults. Considering the uncertainty of stress field and fault orientations, based on the Monte Carlo method, the potential of fault reactivation is calculated. Our research  provides a mechanical basis for the seismic hazard analysis of the Luxian shale gas development area, serving as an excellent example for conducting seismic hazard analysis in shale gas development fields.

How to cite: Yang, X., Tao, W., Lu, R., and Zhang, W.: Three-Dimensional Fault Slip Risk Analysis in a Shale Gas Development Area: A Case Study of the Luxian Shale Gas Field, Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10264, https://doi.org/10.5194/egusphere-egu24-10264, 2024.

EGU24-10650 | ECS | Orals | ERE5.1

Modelling of Strasbourg 2019-2020 seismicity crisis induced by geothermal operations 

Arezou Dodangeh, Renaud Toussaint, Marwan Fahs, Eirik Flekkøy, and Knut Jørgen Måløy

The risk of induced and triggered seismicity is often present in deep geothermal resources exploitation. These facilities allow exploiting practical and green energy resources.
There are many regions with high geothermal capacity, such as Alsace, France. In Vendenheim, north of Strasbourg, the Geoven plant project was expected to extract geothermal energy from the Robertsau fault by circulating fluid at depth.
Two clusters of humanly perceivable seismicity occurred in 2019-2020, one of them close to wells and other one at the Robertsau area at 5km to the south. A question was raised about a possible link between these seismic events and wells activities of Geoven site. A large distance with no earthquakes between the injection wells and the southern cluster was reason for disagreement between scientific experts and the company in charge about the link between the injection and the seismicity on this cluster.
Our objective is studying such a possible connection with numerical modeling through a simple methodology based on fluid/solid deformation and mechanical coupling. In addition, we aim at modelling the pressure perturbation during the time resulting from the history of the injection flux and comparing it with measured data.
The methodology has 3 steps: 1. Structural plan: extracting the geometry of the fault and tectonic stresses  2. Mechanical stability: the stresses on the fault are evaluated and the risk of earthquake triggering is analyzed based on Mohr-Coulomb  criterion. 3. Pore Pressure: a quasi 2D pressure diffusion equation with the proper injection parameters is solved for modeling pressure perturbation in the area due to water injection/extraction.
According to the results, the fault is strong enough in the northern cluster area and slip can happen only by high activation pressure. However, slip and micro-earthquakes resulted from large pressure increase near the wells, which is necessary for permeability increase to improve the transmissivity of  the reservoir. On the other hand, the fault is in the weakest state around the southern cluster, because the pressure required for sliding drops sharply. Indeed, with low amount of pressure increase, slip occurs. Our simulation shows that, the triggered earthquake is expected at this point, due to large enough pressure increase. But between these two clusters, not only is the fault resistant based on its orientation, but also the pore pressure increase is notlarge enough for slip. This explains, the distance of 5km between the two clusters, and absence of earthquakes in between.
Also, we simulated the pressure perturbation in the wells resulting from real injection regime data, during 85 days of operation in Geoven site in 2020, and compare it with real pressure change.
In conclusion, the lowest activation pressure in comparison to other parts can be observed around the southern cluster, which is coherent with the fault and stress tensor geometry implying a weak state in this location. Also, we identify a physical mechanism showing that earthquakes in that zone were possibly triggered by pore pressure perturbation resulting from the Geoven operation.

How to cite: Dodangeh, A., Toussaint, R., Fahs, M., Flekkøy, E., and Måløy, K. J.: Modelling of Strasbourg 2019-2020 seismicity crisis induced by geothermal operations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10650, https://doi.org/10.5194/egusphere-egu24-10650, 2024.

EGU24-11053 | ECS | Posters on site | ERE5.1

Monitoring induced seismicity in urban environment: assessing the performance of low-cost stations within Dense Semi-permanent Seismic Networks 

Riccardo Minetto, Olivier Lengliné, Marc Grunberg, Mathieu Turlure, Antoine Schlupp, Jérôme Vergne, Hélène Jund, and Jean Schmittbuhl

Obtaining high-resolution seismic catalogs from seismic data requires long-term monitoring and a sufficient number of sensors. Permanent seismic networks are usually limited to a small number of sensors, while very dense seismic networks (thousands of sensors) are typically installed for a limited period of time (days to a few weeks) and represent a large investment.

In the framework of the PrESENCE project, we test the performance of a Dense Semi-permanent Seismic Network (DSSN) deployed in an urban environment (Strasbourg Eurométropole). This network, made up of Raspberry Shake seismographs, allows to record data over long periods (years) and from dozens of sites, thanks to the use of low-cost seismic stations operated by non-seismologists.

The study aims to determine the advantages and limitations of these stations in urban environment, especially for the monitoring of induced seismicity. This is done by quantifying their impact on magnitude of completeness and location accuracy, as well as their contribution in detecting events with techniques such as template matching. The analysis was carried out on data recorded from January 2018 to September 2023 in the Strasbourg (France) area, which includes a seismic crisis that culminated in a M3.6 earthquake that led to the closure of the Geoven deep geothermal energy site operated by Fonroche-Geothermie. We conclude that these low-cost stations have provided a significant and valuable impact on the induced seismicity monitoring.

How to cite: Minetto, R., Lengliné, O., Grunberg, M., Turlure, M., Schlupp, A., Vergne, J., Jund, H., and Schmittbuhl, J.: Monitoring induced seismicity in urban environment: assessing the performance of low-cost stations within Dense Semi-permanent Seismic Networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11053, https://doi.org/10.5194/egusphere-egu24-11053, 2024.

EGU24-11193 | ECS | Posters on site | ERE5.1

Process-based understanding of induced seismicity: a key step for public acceptance of geothermal power plants in urbanized areas  

Sofia Bressan, Giorgio Cassiani, Antonio Fuggi, and Alessandro Brovelli

Over the last century, the Earth's climate has been significantly impacted by the increasing levels of greenhouse gases in the atmosphere. To contrast this dangerous trend, the European Commission has committed approximately 17.5 billion euros to shift away from fossil fuels and embrace clean, sustainable energy sources. The ambitious goal is to achieve a substantial reduction of at least 55% in greenhouse gas emissions by 2030, while simultaneously boosting the use of renewable energy sources by approximately 40%. In this socio-cultural context, geothermal energy emerges as an promising, sustainable, and renewable resource that could potentially satisfy the world's escalating energy demand. Nevertheless, despite its considerable advantages, geothermal energy faces a challenge due to insufficient public backing. Among the main causes of this reluctance are the concerns about possible triggering of seismic events during geothermal operations. Recent studies reveal that more than half of anthropogenic activities leading to induced earthquakes are associated with the extraction or injection of underground fluids.

This phenomenon necessitates a detailed examination of the complex interplay between various physical and chemical factors influencing the subsurface dynamics. The complexities of induced seismicity go beyond singular mechanistic explanations. Temperature, volume, and multi-phase nature of the fluid have important physical-chemical implications for stimulated rock volume. These behaviors are well known to the scientific community, which has conducted multidisciplinary research to emphasize that the development of anthropogenic seismic events does not result from a single mechanism but from the interaction of multiple factors, such as perturbations of the stress state, changes in pore pressure, the interactions between pre-existing structures in the area or the dynamic weakening of seismogenetic faults. Despite extensive multidisciplinary research, the coexistence and influence of these processes on earthquake development remain unclear. Addressing this knowledge gap is crucial for developing effective prediction and mitigation strategies.

What are the most recent theories on the generation of anthropogenic earthquakes? Can physics-based models help us better understand the mechanics behind these events and mitigate their development?

This abstract aim is to collect and summarise the most recent information on anthropogenic earthquakes associated with geothermal activities. This review will be the basis for a three-year PhD programme that will evaluate existing theories, compare proposed approaches, and determine the most viable avenues for developing prediction or mitigation techniques. The methodology will involve a comprehensive analysis, starting with structural and geophysical assessments, followed by numerical modelling to improve understanding of the underlying fluid and rock mechanics. The objective will be to develop effective and understandable strategies to address the problems associated with geothermal-induced seismicity.

How to cite: Bressan, S., Cassiani, G., Fuggi, A., and Brovelli, A.: Process-based understanding of induced seismicity: a key step for public acceptance of geothermal power plants in urbanized areas , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11193, https://doi.org/10.5194/egusphere-egu24-11193, 2024.

EGU24-11558 | ECS | Orals | ERE5.1

Fluid-induced earthquake nucleation controlled by shear-induced compaction and dilation 

Luca Dal Zilio, Paul Selvadurai, Taras Gerya, Jean-Paul Ampuero, Elisa Tinti, Massimo Cocco, Frédéric Cappa, Stefan Wiemer, Domenico Giardini, and the FEAR team

The conventional understanding of tectonic faults primarily categorizes them based on frictional behavior: stable due to velocity-strengthening (VS) behavior, or unstable owing to velocity-weakening (VW) that lead to seismic ruptures. This classification has traditionally led to the assumption that VS faults are unlikely candidates for earthquake nucleation. However, emerging evidence from recent laboratory experiments and field studies is challenging this simplistic view, pointing towards a more complex mechanism. In this study, we utilize a hydro-mechanically coupled fault model, which integrates VS friction governed by rate-and-state friction laws with dynamic weakening influenced by poroelastic effects. A key aspect of our findings is the impact of fluid injection on the mechanical state of the fault. This process decreases the effective normal stress and frictional resistance, initially paving the way for the propagation of an aseismic, slow-slip event. The transition from aseismic to seismic slip on VS faults hinges on the balance between shear-induced dilation and compaction. These opposing mechanisms respectively lead to a decrease and an increase in pore-fluid pressure, dictating the balance between fault stability or instability. Our results show that when the effect of compaction-induced pressurization surpasses the initial dilatancy phase, it enables the propagation of dynamic rupture as a solitary pore-pressure wave. Conversely, when dilation predominates over compaction, an aseismic slow-slip event propagates through the fault, maintaining stability and preventing rapid seismic activity. These findings advance our understanding of seismic risk associated with VS faults. They are especially relevant in the context of fluid injection practices in geothermal energy production and CO2 storage, demonstrating how such activities might activate faults that are considered nominally stable. Additionally, our results underscore the critical need for more experimental and theoretical investigations into shear-induced compaction as an efficient mechanism for fault self-pressurization, which plays a key role in leading to seismic instabilities.

How to cite: Dal Zilio, L., Selvadurai, P., Gerya, T., Ampuero, J.-P., Tinti, E., Cocco, M., Cappa, F., Wiemer, S., Giardini, D., and FEAR team, T.: Fluid-induced earthquake nucleation controlled by shear-induced compaction and dilation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11558, https://doi.org/10.5194/egusphere-egu24-11558, 2024.

EGU24-12822 | ECS | Orals | ERE5.1

Frictional Properties of Simulated Fault Gouges subject to Normal Stress Oscillation and Implications for Induced Seismicity 

Bowen Yu, Jianye Chen, Christopher J. Spiers, and Shengli Ma

Under critical conditions where fault slip exhibits self-sustained oscillation in experiments, effects of normal stress oscillation (NSO) on fault strength and stability remain uncertain, as do potential effects of NSO on natural and induced seismicity. In this study, we employed double direct shear testing to investigate the frictional behavior of a synthetic, near velocity-neutral (VN) fault gouge (characterized by self-sustained oscillation under quasi-static shear loading), when subjected to NSO at different amplitudes and frequencies. During the experiment, fault displacement and gouge layer thickness were measured. Transmitted ultrasonic waves were also employed to probe grain contact states within the gouge layer. Our results show that fault weakening and unstable slip can be readily triggered by oscillations, depending on oscillation frequency and amplitude. Interestingly, an amplified shear stress drop and weakening effect were observed when the oscillation frequency fell in a specific range (0.01–0.1Hz). No such effects were seen in a velocity-strengthening gouge. Analysis of transmitted ultrasonic waves in the test on the VN gouge reveals the presence of fault dilatation, accompanied by unstable slip and weakening. By extending an existing microphysical model (the "CNS” model), to account for elastic effects of NSO on gouge microstructure and grain contact state, the mechanical and wave data obtained in our experiment on the VN gouge was reproduced. Assisted by the microphysically-based friction model, resolving the instability criterion of a velocity-neutral fault under perturbation is crucial for understanding and thus predicting the fault behaviors of certain scenarios, like periodic gas storage in deep reservoirs.

How to cite: Yu, B., Chen, J., Spiers, C. J., and Ma, S.: Frictional Properties of Simulated Fault Gouges subject to Normal Stress Oscillation and Implications for Induced Seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12822, https://doi.org/10.5194/egusphere-egu24-12822, 2024.

EGU24-12860 | Orals | ERE5.1

Forecasting and characterizing induced seismicity at the Utah FORGE EGS site 

Federica Lanza and Stefan Wiemer and the DEEP Team

Managing induced seismicity risk is an absolute must to enable the widespread use of deep geothermal technologies, and thus contribute to the transformation towards a sustainable and low-carbon energy sector. A full-scale application of real-time monitoring and forecasting of induced seismicity was tested in April 2022, during a three-stage hydraulic stimulation in a deep granite heat reservoir of low permeability at the Utah FORGE EGS site. During the stimulation, a total of ~1600 m3 pressurized fluids were injected into the target reservoir of ~2.4 km depth to generate fracture networks and improve reservoir permeability for heat extraction. Stage 3 had the most complete monitoring network and thus was used to test the components of an Adaptive Traffic Light System (ATLS). The test produced very positive results, although the data stream was lost early into the stimulation.

Here, we further characterize and perform a retrospective forecasting of post-processed data related to the induced seismicity recorded during stage 3 of the 2022 stimulation at FORGE site. We first investigate the geometrical distribution of the seismicity and discuss it in the context of the stress field at FORGE injection site. The statistical inference indicates that the distribution of the seismicity lies on a plane sub-parallel to the Sv - SHmax and orthogonal to SHmin, and with strike orientation rotated 10o counterclockwise with respect to the N25oE average orientation of SHmax. The analysis seems to indicate that seismicity is induced by a tensile fracture, although we cannot completely rule-out seismic activity on a pre-existing fault. Gutenberg-Richter b-value variations in space are compatible with large magnitude events occurring at the edges of the earthquake propagating front. We further investigate the possible fracturing mechanisms triggered by the injection operation by fitting three plausible physical models: (1) a high-pore pressure diffusion model, (2) an aseismic crack model, and (3) a penny-shaped tensile crack model as the causative process of the recorded seismicity. The analysis of the seismicity evolution alone allows us to fit the three considered scenarios to the data independently, however we cannot exclude a combination of the three processes acting together. Through pseudo-retrospective forecasting, we then replay the induced seismicity as it was happening in real-time. We demonstrate that even if the physical processes are complex and likely difficult to disentangle using the seismicity alone, a simple empirical statistical seismicity rate forecasting model has stable predictability of hydraulic fracturing.

How to cite: Lanza, F. and Wiemer, S. and the DEEP Team: Forecasting and characterizing induced seismicity at the Utah FORGE EGS site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12860, https://doi.org/10.5194/egusphere-egu24-12860, 2024.

EGU24-13824 | ECS | Posters on site | ERE5.1

The QuakeMatch Toolbox: Using waveform similarity to enhance the analysis of microearthquake sequences at Swiss geothermal projects  

Tania Toledo, Verena Simon, Toni Kraft, Veronica Antunes, Marcus Herrmann, Tobias Diehl, and Linus Villiger

 

Many Swiss microearthquake sequences have been analyzed using relative location techniques. While these methods have often been effective in identifying active fault planes and the tectonic processes driving the seismic activity, several sequences present a limited number of located events. This limitation often hampers the detailed analysis of their space-time evolution, seismicity patterns, and driving mechanisms. 

 

To address this challenge, we introduce a nearly automatic workflow that combines established seismological analysis techniques to enhance the completeness of detected and located earthquakes within a sequence. Starting with a manual catalog (magnitude of completeness, Mc ≈ 1.0−1.5 ML), we compile a template set and conduct a matched filter analysis on a single station with the highest signal-to-noise ratio (SNR). This approach enables the detection of events with local magnitudes ML < 0.0, with waveform similarity further leveraged to determine consistent magnitudes for these detections. The enhanced catalog is statistically analyzed to obtain high-resolution temporal evolutions of the Gutenberg−Richter a- and b-values, and consequently, the occurrence short-term probability of larger events. Finally, strong events are relocated by the double-difference technique, typically improving the final number of relocated events by a factor of 2-5. 

 

The proposed workflow significantly improves the analysis of the spatiotemporal behavior of natural and induced microearthquake sequences. Notably, we employ it for semi real-time monitoring of commercial and scientific fluid-injection projects. The QuakeMatch workflow is implemented in Python and PostgreSQL. We discuss the capabilities of QuakeMatch through examples involving induced microearthquake sequences associated with various geothermal projects monitored by the Swiss Seismological Service within the GEOBEST2020+ project. 

How to cite: Toledo, T., Simon, V., Kraft, T., Antunes, V., Herrmann, M., Diehl, T., and Villiger, L.: The QuakeMatch Toolbox: Using waveform similarity to enhance the analysis of microearthquake sequences at Swiss geothermal projects , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13824, https://doi.org/10.5194/egusphere-egu24-13824, 2024.

EGU24-13991 | ECS | Posters on site | ERE5.1

Earthquake behaviors for moderate to strong induced events are controlled by high-velocity bodies near shale reservoirs in southern Sichuan basin, China 

Jian Xu, Junlun Li, Haijiang Zhang, Wen Yang, Yuyang Tan, Chang Guo, Siyu Miao, and Zhengyue Li

Moderate to strong earthquakes have been induced worldwide by shale gas development. However, it is still unclear what factors control the occurrence and magnitude of moderate to strong earthquakes induced by hydraulic fracturing. By using a permanent local seismic network and a temporary dense seismic network, we reliably determined the source attributes of dozens of earthquakes with magnitudes M>3, and importantly, a high-resolution shear-wave velocity model is obtained for studying the detailed seismogenic structure of an unconventional oil/gas field using ambient noise tomography. These earthquakes are found to occur close to the target shale formations in depth, and along high seismic velocity boundaries. Especially, the 2018 Xingwen 5.7 and 2019 Gongxian 5.3 induced earthquakes nucleated around the edges of high velocity zones. These two M>5 earthquake magnitudes as well as co-seismic slip distributions are further determined jointly by seismic waveforms and InSAR data and are found correlated with the high velocity zones along the fault planes. Thus, the distribution of high velocity zones near the target shale formations, together with the stress state modulated by hydraulic fracturing controls induced earthquake behaviors and is critical for understanding the seismic potentials associated with hydraulic fracturing.

How to cite: Xu, J., Li, J., Zhang, H., Yang, W., Tan, Y., Guo, C., Miao, S., and Li, Z.: Earthquake behaviors for moderate to strong induced events are controlled by high-velocity bodies near shale reservoirs in southern Sichuan basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13991, https://doi.org/10.5194/egusphere-egu24-13991, 2024.

EGU24-14139 | ECS | Orals | ERE5.1

Deciphering Seismogenic Patterns in Hydraulic Fracturing: A Machine Learning Approach in the Southern Montney Play 

Bei Wang, Honn Kao, Hongyu Yu, Ge Li, Ramin M.H. Dokht, and Ryan Visser

The burgeoning development of hydraulic fracturing (HF) for unconventional resource extraction has been paralleled by a rise in injection-induced earthquakes (IIEs), posing significant seismic hazards. A critical challenge in mitigating these hazards is the accurate assessment of the seismogenic potential and earthquake productivity of individual HF pads. We addresses this challenge by analyzing over 35,000 earthquakes in the Southern Montney Play (SMP), Western Canada, from 2014 to 2022, and associating them with 357 HF pads.

 

We employed the eXtreme Gradient Boosting (XGBoost) machine-learning algorithm, integrating fifteen geological and operational factors to evaluate their influence on IIE occurrence and intensity. We also utilized Shapley Additive Explanations (SHAP) values for a nuanced interpretation of the model outputs, providing insights into the relative importance and interaction of these factors.

 

Our analysis reveals that the cumulative injected volume and the location of HF pads within the Fort St. John Graben (FSJG) are the primary determinants of seimogenic potential (occurrence of IIE). In contrast, the number of HF stages targeting the Lower Middle Montney formation, cumulative volume from preceding injections, and the HF pad's location within the FSJG predominantly influence the seismogenic productivity (number of IIE). These findings suggest that both operational and geological factors are critical in determining the seismogenic productivity of HF pads. The XGBoost model demonstrated high predictive accuracy (R2 ~0.90), although its performance is constrained by the dataset's size and potential overfitting issues.

 

The study challenges the conventional understanding that proximity to known faults is a major factor in IIE occurrence, instead highlighting the significance of cumulative injection volumes and specific geological settings. The analysis also underscores the complex interplay between various factors, such as the correlation between the location fo the HF pads and the targed formation during HF stimulations, which may influence seismogenic patterns.

 

Overall, our result provides a comprehensive assessment of the factors influencing seismogenic behavior in HF-related IIEs, paving the way for more accurate forecasting of IIE activity levels for individual HF pads in the SMP. The findings have significant implications for seismic hazard assessment and risk mitigation strategies in regions undergoing HF operations. The application of machine learning in this context not only enhances our understanding of induced seismicity but also demonstrates the potential of such techniques in addressing complex geoscientific challenges.

How to cite: Wang, B., Kao, H., Yu, H., Li, G., M.H. Dokht, R., and Visser, R.: Deciphering Seismogenic Patterns in Hydraulic Fracturing: A Machine Learning Approach in the Southern Montney Play, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14139, https://doi.org/10.5194/egusphere-egu24-14139, 2024.

EGU24-14828 | ECS | Orals | ERE5.1

Spatio-temporal evolution of hypocenters and moment tensors derived from time-reverse imaging 

Claudia Finger, Katinka Tuinstra, Peter Niemz, Peidong Shi, Laura Ermert, and Federica Lanza

The location and focal mechanism of microseismicity induced during fluid injection experiments in geothermal wells can be used to infer the extent of fracturing and the orientation of the local stress field. Passive seismic instrumentation is typically deployed at the surface and in boreholes around the injection site to monitor microseismic activity. Recent methodological advancements enable locating the often thousands of seismic events in a timely fashion. However, the determination of focal mechanisms is often limited to a selected number of larger-magnitude events.

 

Time-Reverse Imaging (TRI) exploits the time-invariancy of the elastic seismic wavefield to propagate the seismic wavefield backwards in time from seismic stations through an adequate velocity model. Under ideal conditions, the wavefield will converge on the initial source location at the origin time. The excellent location accuracy for events with signal-to-noise ratios smaller than one and the capability of determining the moment tensor for each locatable event has been demonstrated in controlled synthetic and real studies. Numerous improvements and adaptations have been proposed to augment the resulting image volume used to identify individual seismic events. TRI is a promising one-stop solution for analyzing microseismicity but has two major disadvantages: (1) the computation time needed to simulate the high-frequency elastic wavefield prohibits the analysis of continuous hours or days of microseismic recordings, and (2) the identification of individual seismic events from TRI image volumes is susceptible to overestimating the number of seismic events due to noisy images.

 

Alterations of the TRI concept based on pre-computed Green’s functions exist and provide a near-real time solution but require compromises in terms of location accuracy and minimal signal-to-noise ratio. The focal mechanism cannot be identified yet with these types of methods. Thus, the main challenge of applying TRI is reducing the needed computational time, while retaining most beneficial capabilities. This balancing act requires a careful analysis of possible compromises through careful scaling of simulation parameters.

 

Here, we apply TRI to synthetic seismic recordings created with the sensor setup deployed during the injection experiment in April 2022 at the UtahFORGE test site. A combined elastic velocity model of the complex site geology is used with a network including real locations of fiber optic cables, deep and shallow borehole sensors, and nodal seismic sensors. This synthetic data is used to demonstrate the accuracy gain of using multiple types of sensors and the speed gain of using characteristic functions applied to the seismic recordings prior to back propagation. Accuracy and speed are compared for synthetic and real test cases to optimize their trade-off. Finally, instead of individually picking seismic events, we demonstrate the usefulness of interpreting the spatio-temporal evolution of hypocenters and moment tensors directly from the TRI results.

How to cite: Finger, C., Tuinstra, K., Niemz, P., Shi, P., Ermert, L., and Lanza, F.: Spatio-temporal evolution of hypocenters and moment tensors derived from time-reverse imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14828, https://doi.org/10.5194/egusphere-egu24-14828, 2024.

EGU24-14916 | Posters on site | ERE5.1

The Impact of Injection Protocol and Stress Preconditioning on the Hydro-Mechanical Response of the Crystalline Rock 

Mohammadreza Jalali, Paul Selvadurai, Elena Spagnuolo, Men-Andrin Meier, Luca Dal Zilio, Nima Gholizadeh Doonechaly, Kai Bröker, Julian Osten, Martina Rosskopf, Anne Obermann, and Florian Amann and the FEAR Team

Hydraulic stimulation has been extensively utilized in the geothermal industry as the primary technique to create and develop an efficient heat exchanger in a low-permeable reservoir rock. This technique entails high-pressure fluid injection under various injection schemes to perturb the local stress field at both borehole and reservoir scales, leading to permanent permeability enhancement of the stimulated volume through shear dislocation and dilation. These stress disturbances can also potentially trigger and/or induce seismicity in the reservoir and beyond. Understanding how different injection protocols serve as a preconditioning tool and their impact on the hydro-mechanical response of the stimulated volume would enhance our understanding of geothermal reservoir enhancement and induced seismicity mitigation.

In the preparatory phase of the FEAR (Fault Activation and Earthquake Rupture) project in Bedretto Underground Laboratory (Switzerland), various injection protocols were utilized to understand the hydro-mechanical responses of the stimulated volume as well as earthquake rupture processes such as nucleation and premonitory slip. The adopted injection protocols include a) constant pressure injection for a specific time followed by step-rate injection and b) constant pressure withdrawal for a specific time followed by step-rate injection. In both protocols, an approximately equal amount of water (~3000 liters) was injected over the stimulation phase. Each injection protocol was associated with the pre- and post-characterization tests such as HTPF (hydraulic tests on pre-existing fractures) tests. Hydro-mechanical response of the host rock during these tests was monitored using various pressure, strain, and acoustic emission sensors in the injection and monitoring boreholes.

At first glance, there appears to be no significant difference in the hydro-mechanical responses as well as the seismicity pattern of these two injection protocols, yet deeper investigation mostly based on the strain data reveals that strategy a) produced more heterogeneity in strain rate on the fiber-optic array whereas b) produced a more homogenized response. Numerical modelling and an experimental campaign in the laboratory are now underway to better understand the underlying mechanisms producing this response with the aim to best select a proper injection protocol for the goal of the FEAR project.

How to cite: Jalali, M., Selvadurai, P., Spagnuolo, E., Meier, M.-A., Dal Zilio, L., Gholizadeh Doonechaly, N., Bröker, K., Osten, J., Rosskopf, M., Obermann, A., and Amann, F. and the FEAR Team: The Impact of Injection Protocol and Stress Preconditioning on the Hydro-Mechanical Response of the Crystalline Rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14916, https://doi.org/10.5194/egusphere-egu24-14916, 2024.

EGU24-15394 | Orals | ERE5.1

Microseismic monitoring and insights of rupture mechanism from China's pilot EGS project in Gonghe, Northwestern China 

Hao Zhang and the Hao Zhang, Institute of Geomechanics, Chinese Academy of Geological Sciences

Enhanced Geothermal Systems (EGS) are effective means of developing hot dry rock (HDR) type geothermal resources, transforming low porosity and permeability rock masses deep underground into artificial geothermal reservoirs with high permeability through reservoir stimulation. EGS systems can economically extract a considerable amount of thermal energy over the medium to long term to be utilized for power generation. The development and research of EGS has been ongoing internationally for over 40 years. However, at present, the development of EGS is still in the stage of on-site experimental research and development, and its commercial development still faces many challenges. China, like many other countries, is in need of developing deep geothermal resources to meet its energy demands. In 2017, a well named GR1 with a temperature of 236°C was drilled to a depth of 3705m in the Gonghe Basin of Qinghai Province. Recognizing the potential of HDR resources, the China Geological Survey launched an exploration and production project in Gonghe Basin in 2019. Following several critical technological breakthroughs, the first power generation test of HDR was successfully conducted in the Gonghe Basin in 2022. This study offers a detailed introduction to the localization of microseismic events that occurred during thermal reservoir stimulation at different stages of development. By analyzing these microseismic events, we can evaluate the effectiveness and volume scale of artificial thermal reservoir transformation. In addition, we assess the development of natural fractures utilizing data from 3D seismic attributes of the granite, imaging logging, etc. We conclude by discussing implications for successful geothermal development of the specific geological conditions present at the Gonghe HDR field, based on the localization results of microseismic data and the distribution of natural fractures in the field.

How to cite: Zhang, H. and the Hao Zhang, Institute of Geomechanics, Chinese Academy of Geological Sciences: Microseismic monitoring and insights of rupture mechanism from China's pilot EGS project in Gonghe, Northwestern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15394, https://doi.org/10.5194/egusphere-egu24-15394, 2024.

EGU24-15485 | ECS | Posters on site | ERE5.1

Microseismic monitoring and characteristic analysis for underground coal mining: A case study from Xiaobaodang coal mine, China 

Zhichao Yu, Yuyang Tan, Kaige Gao, Yiran Lv, and Cindy He

Coal mining disrupts the stress equilibrium of the surrounding rock mass, and the rock mass cracks as a result of the changes in the stress field, releasing strain energy and causing microseismic events. Monitoring seismicitiy during coal mining is critical for ensuring safe production and preventing geological disasters. In this study, we deployed 29 surface seismic nodes above an underground coal mine in the Yulin region of Shaanxi Province, China, to monitor the mining operation for 665 hours. A large number of microseismic events have been detected from continuous monitoring data, and analyzed using event clustering, source location, and mechanism estimate. The results show that (1) the frequency and intensity of microseismic events are related to underground mining working conditions; (2) the temporal and spatial locations of the microseismic sources may be utilized for real-time tracking the location of the underground coal mining face; and (3) three rupture mechanisms of tension rupture, implosion rupture, and shear rupture reflect the triggering mechanisms of the coal pillar failure, roof breakage and movement and fault slip. 

How to cite: Yu, Z., Tan, Y., Gao, K., Lv, Y., and He, C.: Microseismic monitoring and characteristic analysis for underground coal mining: A case study from Xiaobaodang coal mine, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15485, https://doi.org/10.5194/egusphere-egu24-15485, 2024.

EGU24-15621 | ECS | Orals | ERE5.1

Machine learning based real-time microseismic monitoring and stimulated fracture characterization at the Utah FORGE Geothermal site 

Peidong Shi, Ryan Schultz, Federica Lanza, Luca Scarabello, Laura Ermert, and Stefan Wiemer

In April 2022, a three-stage hydraulic stimulation was performed in a deep granite heat reservoir of low permeability at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). During the stimulation, around 1600 m3 pressurized fluids were injected into the target reservoir of ~2.4 km depth aiming at creating fracture networks and improving reservoir permeability for heat extraction. Microseismic monitoring is required to assess the stimulation efficiency and manage the induced earthquake risk during the stimulation. We perform near-real-time microseismic monitoring in a playback mode at the third stage of the stimulation where three deep monitoring boreholes equipped with three-component geophone chains were in operation. We apply machine learning (ML) techniques in combination with waveform back projection approaches to automate the microseismic event detection, increase microseismic event location accuracy, and promote the real-time capability of the monitoring workflow. Due to a lack of labeled datasets for model training or transfer learning, we devise a rescaling technique to tune the continuous microseismic recordings of high sampling rates that enables the application of existing ML models pre-trained on tectonic earthquakes. Our benchmark tests show that the proposed rescaling approach achieves high precision and accuracy in detecting microseismic events and picking their phase arrivals.

With the proposed workflow, we compiled a high-resolution microseismic catalog containing around 36, 000 microseismic events with magnitudes of –3.0 to 0.5. Detected events are relocated using a double-difference relocation method and waveform cross-correlation-based arrivaltime refinement. We cluster the detected microseismic events according to their spatial distributions and identify the dominant stimulated fracture planes with principle component analysis of the different event clusters. The spatial distribution of the detected events nicely depicts the stimulated fracture networks which can be used to design the trajectory of the future production well. We analyze the spatio-temporal evolution of the induced microseismic events during and after the stimulation to illuminate the rupturing mechanisms responsible for the induced fracture networks. Induced microseismic events are analyzed together with the injection data to quantify the induced earthquake hazard and the hydraulic stimulation efficiency. The proposed microseismic monitoring workflow and the corresponding analysis provide more insights into the fracturing dynamics and the potential induced earthquake hazard in the Utah FORGE geothermal site, and would benefit the operation of other enhanced geothermal systems.

How to cite: Shi, P., Schultz, R., Lanza, F., Scarabello, L., Ermert, L., and Wiemer, S.: Machine learning based real-time microseismic monitoring and stimulated fracture characterization at the Utah FORGE Geothermal site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15621, https://doi.org/10.5194/egusphere-egu24-15621, 2024.

EGU24-16552 | ECS | Posters on site | ERE5.1

Passive monitoring of a deep geothermal reservoir in the Strasbourg area by interferometric approaches using ambient seismic noise. 

Flavien Mattern, Jérôme Vergne, Jean Schmittbuhl, and Dimitri Zigone

We present preliminary results of ambient seismic noise monitoring near the deep geothermal reservoir at the Vendenheim site north of Strasbourg in France. From November 2019 to mid 2021, various operations led to an intense induced seismic swarm with several events of magnitudes above 3.0Mlv. This crisis is also characterized by the presence of an isolated swarm ~5km south of the geothermal site as well as the occurrence of the maximum magnitude event (3.9Mlv) 6 months after the cease of injection tests. Understanding these remote and delayed triggering mechanisms is essential for the successful development of future deep geothermal projects. We use ambient seismic noise correlations betweens pairs of sensors from a composite network of 137 permanent and temporary stations in the area. In particular, we intend to monitor the evolution of the upper crust around the reservoir by studying velocity variations and coda waveforms decorrelation in different frequency bands.

At high frequencies (1-3Hz), velocity variations appear to be correlated with fluctuations of the water table elevation. Strong decorrelations in waveform coda are also observed during holidays, suggesting changes in anthropogenic noise sources illumination. At low frequencies (3-6s), apparent variations of velocity and decorrelation with mainly an annual periodicity are observed, but could be associated with seasonal variations in the position of the sources of the second microseismic peak. This study shows that in order to observe temporal variation in the properties of deep geothermal reservoirs with ambient noise coda wave interferometry, it is necessary to understand and model variations in the subsurface layers and in the sources of ambient seismic noise.  

How to cite: Mattern, F., Vergne, J., Schmittbuhl, J., and Zigone, D.: Passive monitoring of a deep geothermal reservoir in the Strasbourg area by interferometric approaches using ambient seismic noise., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16552, https://doi.org/10.5194/egusphere-egu24-16552, 2024.

EGU24-16938 | ECS | Orals | ERE5.1

Stress and Strain Changes in Response to Reservoir Water Level Variations – A Case Study of the Enguri High-Head Arch Dam in the Caucasus 

Thomas Niederhuber, Birgit Müller, Malte Westerhaus, Andreas Rietbrock, Jakob Weisgerber, Thomas Röckel, Nasim Karamzadeh, Nino Tsereteli, Nazi Tugushi, Mirian Kalabegishvili, David Svanadze, and Frank Schilling

Hydropower facilities utilize the potential energy of water to generate electricity, with maximum efficiency achieved when there is a significant topographic gradient between reservoir and turbines. Therefore, high dams are typically built in regions with rugged topography, often associated with (frequently combined) erosion, folding or displacement along fault zones, leading to juxtaposed different material properties.

At the Enguri Arch Dam in Georgia, extensive limestone formations from the Cretaceous and Jurassic were thrust southward, resulting in a topography difference exceeding 1000 m between the southward-extending Rioni Basin and the contiguous mountain ranges. The reservoir extends about 25 km to the north. There, nearby mountains reach heights of 3000 m and more. As part of the ongoing crustal shortening process, multiple fault systems have emerged, including prominent SW-NE trending thrust faults, steep strike-slip faults, and to a minor extend normal faults.

The Enguri valley carves into the surrounding mountains, reaching an elevation of 280 m above sea level at the dam site. These substantial topographic variations between hilltops and valleys establish a variable initial stress field characterized by lateral heterogeneity in both magnitude and orientation. The initial stress conditions were determined using borehole imaging data and hydraulic fracturing tests, while the mechanical properties of the subsurface materials were evaluated using mechanical tests on core samples.

The Enguri high-head Dam has a construction height of 271 m and the Jvari-reservoir reaches at full level more than 510 m above sea level. Geodetic GNSS and seismic stations were installed to evaluate the impact of the annual water level changes of about 100 m on the surrounding area.

The subsurface information on stress conditions and material properties was used to create an elastic 3D model of the area. The modelling results were compared with field observations to gain a better understanding of the dynamic processes in the area. In a first step the initial stress field was simulated. Loads were applied to simulate the water level changes. Modelled and observed displacements indicate that rising water level causes the west bank to move north-west, while the east bank moves south-east. Furthermore, both banks of the valley show a downward movement. Conversely, when the water level decreases, the effect is reversed. Variations in water level induce changes in the shear stress and changes in Coulomb Failure Stress (ΔCFS) calculated for different fault orientations. They reveal an increased seismic potential during low water levels, aligning with first seismic observations.

How to cite: Niederhuber, T., Müller, B., Westerhaus, M., Rietbrock, A., Weisgerber, J., Röckel, T., Karamzadeh, N., Tsereteli, N., Tugushi, N., Kalabegishvili, M., Svanadze, D., and Schilling, F.: Stress and Strain Changes in Response to Reservoir Water Level Variations – A Case Study of the Enguri High-Head Arch Dam in the Caucasus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16938, https://doi.org/10.5194/egusphere-egu24-16938, 2024.

EGU24-18907 | ECS | Orals | ERE5.1

The duration of injection protocol likely controls the maximum magnitude of induced earthquakes 

Mohammad JA Moein, Cornelius Langenbruch, and Serge Shapiro

High-pressure fluid injection into subsurface is often carried out to enhance the permeability of deep geothermal reservoirs. The operation sometimes triggers induced earthquakes that may be as large as natural earthquakes. Novel injection protocols such as cyclic injection schemes have been proposed to mitigate the risk of inducing larger events. Currently, the of impact cyclic injection schemes on the maximum magnitude Mmax is not fully understood. Here, the working hypothesis  is that the pore-pressure diffusion is the dominant triggering mechanism of induced events and the maximum induced earthquake scales with the pressure-perturbed fault size. We developed a first-order hydrogeological model and simulated the fluid injection into a porous rock with an embedded large-scale fault zone. Different injection scenarios were implemented, and the pressure-perturbed fault size was computed and translated to the maximum induced earthquake magnitude. The numerical models showed that the duration of the injection protocol plays an important role and likely controls the occurrence of larger-magnitude events. Our numerical models can provide significant insight into the effectiveness of mitigation strategies during the engineering of Enhanced Geothermal Systems and underground storage reservoirs.

How to cite: Moein, M. J., Langenbruch, C., and Shapiro, S.: The duration of injection protocol likely controls the maximum magnitude of induced earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18907, https://doi.org/10.5194/egusphere-egu24-18907, 2024.

EGU24-18935 | Posters on site | ERE5.1

The contribution of pore fluid pressure to earthquakes induced in St. Gallen geothermal field, Switzerland 

Raffaella De Matteis, Bruno Massa, Guido Maria Adinolfi, Ortensia Amoroso, Toshiko Terakawa, and Vincenzo Convertito

In July 2013, a sequence of more than 340 earthquakes was induced during the deep geothermal drilling project close to the city of St. Gallen in Switzerland. Induced seismicity represents a disadvantage during sub-surface geoenergy operations, so understanding the underlying triggering mechanisms is crucial for mitigating the seismic hazard.  To this end, we investigate the role of fluids and elastic stress transfer as driving mechanisms of the St. Gallen seismic sequence. Following the underlying idea of the Focal Mechanism Tomography technique, we estimate the excess pore fluid pressure at the hypocenters of earthquakes from the analysis of their focal mechanisms. The uncertainties on the focal mechanism parameters, friction coefficient and rock density are taken into account using a Monte Carlo approach to calculate the effect on the estimated excess pore pressure. The results indicate that, in addition to Coulomb static stress change, high-pressure fluids had a primary role in the earthquake triggering. Unlike what is observed in other geothermal fields, the value of the calculated excess pore fluid pressure is higher than the injection pressure for approximately half of the earthquakes. This can likely be attributed to the accidental release of overpressured gas (gas kick) that occurred during field operations when the seal to a gas reservoir was broken.

 

This work has been supported by PRIN-2017 MATISSE project (No. 20177EPPN2), funded by Italian Ministry of Education and Research.

 

How to cite: De Matteis, R., Massa, B., Adinolfi, G. M., Amoroso, O., Terakawa, T., and Convertito, V.: The contribution of pore fluid pressure to earthquakes induced in St. Gallen geothermal field, Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18935, https://doi.org/10.5194/egusphere-egu24-18935, 2024.

EGU24-20416 | Orals | ERE5.1

Comparing water-disposal and CO2-storage induced earthquakes 

Cornelius Langenbruch and Serge Shapiro

To date, only several small-scale CO2 storage projects, injecting about 1 Mt of CO2 per year, exist worldwide. Induced seismicity has been recorded during operation. Overall, magnitudes of the seismic events are small (below M=3). Nevertheless, there is the concern that future large-scale projects will induce significantly larger magnitudes, like it is observed for basin-scale waste-water disposal. For instance, large-scale water disposal in Oklahoma and Kansas (USA) induced thousands of widely felt M3+ earthquakes with a maximum magnitude of M=5.8. We analyze seismicity and injection data from CO2-storage projects including Quest (CA), Decataur (USA), In-Sahla (Algeria), Otway (AUS) and Gorgon (AUS). We compute the normalized seismic response of the subsurface to injection of a unit volume of CO2 using the Seismogenic Index (SI) and compare it to water-disposal case studies. We find that the SI at CO2-storage sites is smaller compared to water-disposal cases. It indicates a lower seismic hazard per injected volume of CO2. We discuss physical processes that could explain our observations and show how earthquake magnitude probabilities can potentially be upscaled, considering CO2 storage volumes needed in the future.

How to cite: Langenbruch, C. and Shapiro, S.: Comparing water-disposal and CO2-storage induced earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20416, https://doi.org/10.5194/egusphere-egu24-20416, 2024.

SM8 – Seismic Hazard (earthquake forecasting, engineering seismology, seismic and multi-hazard assessment)

EGU24-621 | Posters on site | SM8.1

Temporary Strong Ground Motion Observation in Damaged Areas of  The 2023 Kahramanmaraş Earthquake 

Pinar Duran, Hiroaki Yamanaka, Nobuo Takai, Masayuki Yoshimi, Seiji Tsuno, Ozgur Tuna Ozmen, Oguz Ozel, Deniz Caka, Aysegul Askan, Hiroe Miyake, Kosuke Chimoto, Towa Ono, and Mehmet Safa Arslan

ABSTRACT: We have conducted a temporary observation of earthquake ground motion of aftershocks of the 2023 Kahramanmaras earthquake in southern Turkey in the damaged areas for an acquisition of basic data to understand the earthquake damage. Strong motion accelerometers were installed at 21 stations in Pazarcik, central parts of Kahramanmaras and Adiyaman provinces, Iskenderun and Antakya in Hatay province. One of the stations in each area was selected in a mountain area as a reference station. The characteristics of the observed ground motion are investigated by spectral ratios of the stations to those at the reference stations. The site amplifications are not significantly different in Pazarcik. Most of the site effects in the damaged areas in the other regions are characterized with the large amplifications at frequencies less than 1 or 2 Hz. In particular the site effects are so significant in the damaged areas in Iskenderun, Antakya and Samandag.

 

Keywords: The 2023 Kahramanmaraş earthquake, temporary strong motion observation, strong motion records, aftershock, basin effects, site effects

How to cite: Duran, P., Yamanaka, H., Takai, N., Yoshimi, M., Tsuno, S., Ozmen, O. T., Ozel, O., Caka, D., Askan, A., Miyake, H., Chimoto, K., Ono, T., and Arslan, M. S.: Temporary Strong Ground Motion Observation in Damaged Areas of  The 2023 Kahramanmaraş Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-621, https://doi.org/10.5194/egusphere-egu24-621, 2024.

EGU24-872 | ECS | Posters on site | SM8.1

Verification Of Large Scale Dynamic Soil Model Tests Through Numerical Analysis 

Aslı Çark and Esra Ece Bayat

This study presents numerical evaluation of large scale dynamic soil testing in a new laminar soil container setup. A dry sand sample was instrumented with embedded accelerometers and linear variable differential transformers (LVDT) connected to the container from an outside frame. The large scale soil sample was tested under dynamic sinusoidal and earthquake motions generated on the shaking table. The measured accelerations and LVDT data were processed and the free motion of the sand sample in the middle of the container at different depths was investigated. One dimensional site response of the soil sample was compared with a 1D soil model prepared in site response analysis software program DEEPSOIL v7.0. The results demonstrated that the measured accelerations in good agreement with the computed site response output data.

How to cite: Çark, A. and Bayat, E. E.: Verification Of Large Scale Dynamic Soil Model Tests Through Numerical Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-872, https://doi.org/10.5194/egusphere-egu24-872, 2024.

The future is already a reality with effective cases of effective prevention in Umbria obtained with seismic microzonation investigations (MS). Seismic prevention is important for achieving essential levels of civil protection safety throughout the territory and for increasing resilience to natural disasters. If in an emergency the management of the same has problems or there are decisions delayed by 1-2 days or worse still wrong, because they were made in the absence of knowledge, these then have repercussions on the lives of many people for years.

From the 1990s to 2015, the execution of studies and applications of the knowledge achieved applied to building and urban planning interventions made it possible to reduce the macroseismic intensity caused by the 2016 earthquakes in central Italy from 1 to 3 degrees in Umbria. Analyzes highlighted this by comparing the occurred values of the ICMs with the values of the ICMs deriving from the recorded PGAs.

The recent eartquakes of March 9, 2023 confirmed how important MS investigations are. Since 2014, the city of Umbertide has had detailed seismic microzonation investigations which were further developed in 2022 by the regional Geological Section. The damage caused by the seismic events of 9 March 2023 demonstrated how the MS investigations had already defined the framework of the expected amplifications and damage that would have occurred also through the calculation of the HSM parameter for the different areas. This parameter, starting from the FA values (amplification factors) calculated in the MS studies and the basic seismic hazard of the investigated territory, estimates the "integrated" seismic hazard level (basic hazard and lithostratigraphic amplification effects) of the different parts of the territory with simplified and advanced analyzes for seismic risk assessments, given the vulnerability of the buildings. The processing procedures allow uniform values to be obtained on a national scale and therefore also allow uniform assessments.

The detailed seismic microzonation investigations carried out at various times and methods, if carried out according to the criteria of the guidelines, obtain concordant results: the damage that occurred and the macroseismic intensity detected in the event of a seismic event are both consistent with the previous seismic amplifications identified with detailed seismic microzonations; in the event of a seismic event, the availability of online products of detailed seismic microzonation and the presence of personnel specialized in its use makes it possible to shorten the time required for decisions such as the declaration of a state of emergency (which happened); territorial management through the HSM value indicates the zones and inhabited areas at risk of damage by type of buildings and this value was found to be consistent with the picture of damage occurred with seismic events.

All these analyzes and evaluations, even retrospective with respect to the seismic events taken into consideration, confirm how the detailed seismic microzonation investigations and the application of the HSM value are an effective risk prevention for correct management and planning of the territory and of the emergency.

How to cite: Motti, A.: Seismic prevention from the multiple utilities of detailed seismic microzonation investigations: expected amplifications, damage occurred, correlated intensities, land management using the HSM parameter, declaration of a state of emergency., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2347, https://doi.org/10.5194/egusphere-egu24-2347, 2024.

EGU24-3265 | Orals | SM8.1

Ground Motion Models for rock sites in South Korea 

Seonjeong Park

Ground motion models (GMMs) play a pivotal role in both deterministic and probabilistic seismic hazard assessments, which are essential for identifying the seismic safety of nuclear power plants. In regions with abundant seismic data, especially strong earthquake records, GMMs could be empirically derived. However, in areas like South Korea with scarce strong earthquake records, development of empirical GMMs is impractical, leading to the utilization of alternative methods such as stochastic simulations. There have been a few GMMs developed in South Korea, all of which relied on stochastically simulated motions. In this study, GMMs are developed for rock sites in South Korea using the hybrid empirical method (HEM) suggested by Campbell (2003). Western United States (WUS) is selected as a host region and five Next Generation Attenuation (NGA)-West2 GMMs are used as GMMs of the host region. The seismological parameters employed in the simulation, including effective point source distance, source and path duration, and path attenuation, duly encompass the findings of recent studies. The high-frequency spectral attenuation parameters, kappa, utilized as site attenuation parameters in ground motion simulations for the target region, are estimated in this study. It is primarily estimated using the classical method proposed by Anderson and Hough (1984). Additionally, the estimation process considers the standardized procedure and the recommended lower bound magnitude decisions put forth by Ktenidou et al. (2013) and Van Houtte et al. (2014), respectively. Since the shear wave velocity for bedrock is considered to be 760 m/s in South Korea, the site amplification functions have been applied with reference to this velocity for both the host and target regions. The adjustment factors obtained from simulated ground motions in both the host and target regions are applied to adjust NGA-West 2 Ground Motion Models (GMMs). Derived GMMs are for magnitudes from 5.0 to 7.5 and rupture distances from 10 to 500 km. Median GMMs are provided with aleatory standard deviations. Predictive GMMs are compared with observed ground motions from the available earthquake records for moment magnitudes 5.0 and 5.5. The notable advantages of the GMMs developed in this study are as follows: Distinct from previous researches utilizing stochastic methods, the implementation of HEM served to complement the limitations inherent in stochastic approaches such as lack of near-source ground motion characteristics. Defining the sites where GMMs are employed at Vs30 = 760m/s enables the derivation of seismic motions applicable to rock layers having Vs30 of 760m/s. Since aleatory standard deviations are quantitatively defined, they can serve as the sigma parameter within GMMs in Probabilistic Seismic Hazard Analysis (PSHA).

How to cite: Park, S.: Ground Motion Models for rock sites in South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3265, https://doi.org/10.5194/egusphere-egu24-3265, 2024.

EGU24-3720 | ECS | Posters on site | SM8.1

Uncertainty Projected Mapping: A Bayesian tool for generating site response maps with statistically significant resolutions    

Anirban Chakraborty, Hiroyuki Goto, and Sumio Sawada

Site response maps are mostly proxy-based. The map resolutions are driven by the resolutions of the digital elevation model. Although high-resolution maps are seemingly more enriched with local information, these details are not always supported with in-situ data. The high-resolution maps are reliable only when the in-situ data supports it. Without in-situ data available, a low-resolution map might be more reliable. Depending on the availability of in-situ data, a site response map with spatially varying map resolutions would better represent the actual ground conditions. In this study, we introduce uncertainty projected mapping (UPM) to generate statistically significant map resolutions. UPM is Bayesian-based and considers the statistical significance of differences in neighborhood values in determining the posterior site response. The study area is in Osaka, Japan, where dense borehole data from the Kansai Geo-informatics Network is available. In the Bayesian framework of UPM, the site responses estimated using 1D seismic ground response analysis at this borehole network constitute the likelihood. In the first case study, a non-informative prior (uniform) is employed to generate the posterior UPM site response map. The UPM map shows the presence of statistically significant map resolutions, which in-situ data can explain. In the second case study, the available proxy-based site responses are employed as an informative prior to generate the posterior UPM map. The results show that proxy-based site responses have been updated only at meshes with in-situ data. However, these updates also show statistically significant resolutions explainable by the in-situ data. The results of both case studies show that the statistically significant map resolutions of the UPM site response map better represent the in-situ data.   

How to cite: Chakraborty, A., Goto, H., and Sawada, S.: Uncertainty Projected Mapping: A Bayesian tool for generating site response maps with statistically significant resolutions   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3720, https://doi.org/10.5194/egusphere-egu24-3720, 2024.

EGU24-3831 | Orals | SM8.1

Research on the foreshock characteristics of earthquakes in Chinese Mainland using waveform envelope method 

Yanyan Han, Yang Zang, Mengyu Xie, and Lingyuan Meng

Regarding foreshocks, it is believed that the percentage of the mainshock events with observable foreshocks is very low. But a recent study suggests that 15%–43% of large mainshocks have at least one foreshock. That is to say, if we can effectively identify foreshocks, it can help us carry out short-term and imminent earthquake forecasting, which is of great significance to the local people.

To identify the foreshock, the first step is to understand the characteristics. For example, the low b-value of the foreshock sequence, the cumulative number of foreshock sequences satisfying the anti-Omori law,  the foreshock sequences having similar focal mechanism solutions, and having the characteristics of migration towards the mainshock. Among them, the low b-value of foreshock sequence is widely recognized as a typical feature of foreshocks. However, this method is mainly based on the earthquake catalogs, and requires the number of earthquakes to meet the calculation conditions. Actually, it is difficult to obtain the b-value results in a short time after the earthquake.

In this study, we selected the foreshock event waveform recorded by the station closest to the earthquake epicenter and obtained the envelope function of the waveform. Each peak of the envelope can be regarded as an earthquake event. The amplitude and time of the function peak correspond to the magnitude and time of the earthquakes. Similar to the G-R relationship, the β-value, corresponding relationship between magnitude and peak number, is preliminarily obtained.

For all the M≥6.0 earthquakes with foreshocks in Chinese Mainland since 2010, we calculate the β-values of foreshocks and mainshocks using waveform envelope method. Most β-values of the foreshocks and mainshocks are calculated except the Yushu mainshock for its unsatisfactory data quality. In addition, we also apply this method to the M≥5.0 earthquakes occurred in Chinese mainland since 2022. The results indicate that the β-values of foreshocks are all lower than its mainshocks. If the β-value is less than 0.7, the earthquake can be considered as a foreshock. The β-value could also provide us with some hints about the magnitude and time interval between the foreshock and mainshock.

How to cite: Han, Y., Zang, Y., Xie, M., and Meng, L.: Research on the foreshock characteristics of earthquakes in Chinese Mainland using waveform envelope method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3831, https://doi.org/10.5194/egusphere-egu24-3831, 2024.

EGU24-3971 | Posters on site | SM8.1

Earthquake Ground motion senarios for three cities in Bulgaria 

Dimcho Solakov, Stela Simeonova, and Plamena Raykova-Tsankova

Earthquakes are the deadliest of the natural disasters affecting the human environment, indeed catastrophic earthquakes have marked the whole human history. Global seismic hazard and vulnerability to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to effects of strong earthquakes. Additionally, the uncontrolled growth of mega cities in highly seismic areas is often associated with the construction of seismically unsafe buildings and infrastructures, that are undertaken with an insufficient knowledge of the regional seismicity and seismic hazard.

The territory of Bulgaria represents a typical example of high seismic risk area in the eastern part of the Balkan Peninsula. Over the centuries, Bulgaria has experienced strong earthquakes. At the beginning of the 20th century (from 1901 to 1928) five earthquakes with magnitude larger than or equal to MS=7.0 occurred in Bulgaria. However, no such large earthquakes have occurred in Bulgaria since 1928, which may induce non-professionals to underestimate the earthquake risk. Bulgaria contains important industrial areas that face considerable earthquake risk. Moreover, the seismicity of the neighboring countries, Greece, Turkey, former Yugoslavia and Romania influences the seismic risk in Bulgaria.

The assessment of seismic hazard and generation of earthquake scenarios is the first link in the prevention chain and the first step in the evaluation of the seismic risk. The use of earthquake scenarios in combination with modern methods of seismic engineering can reduce, to a great extent, the damage and casualties from a strong earthquake.

In the present study deterministic and probabilistic earthquake scenarios for the cities of Sofia, Plovdiv, Varna, Ruse and Veliko Tarnovo are presented. The basic approach used for the creation of ground motion maps incorporate in GIS mode the source-geometry, earthquake occurrence model, the strength of the earthquake sources, and the appropriate attenuation relations.

Earthquake scenarios are a powerful tool to support disaster management decisions. Successful preventive measures and planning of post-earthquake activities are based on scenarios of expected damage, destruction and casualties from predicted strong seismic impacts. The implementation of the earthquake scenarios into the policies for seismic risk reduction will allow focusing on the prevention of earthquake effects rather than on intervention following the disasters.

How to cite: Solakov, D., Simeonova, S., and Raykova-Tsankova, P.: Earthquake Ground motion senarios for three cities in Bulgaria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3971, https://doi.org/10.5194/egusphere-egu24-3971, 2024.

EGU24-6413 | Posters on site | SM8.1

Seismic microzonation study of Santo Domingo, Santiago de los Caballeros and Barahona  metropolitan cities  (Dominican Republic) using combined methods of reflection/refraction of surface waves and microtremor records 

Diego Córdoba Barba, Claudia Germoso, Omar González, Senén Sandoval, Thais Montoya, Modesto Martínez, Miguel Souffront, and María Belén Benito

The Dominican Republic has high seismicity, due to the position of the Hispaniola Island, right in the interaction between the North American and Caribbean tectonic plates. More specifically, on the northern edge of the Caribbean plate, where seismicity is especially intense, causing the entire island to be affected by a high seismic hazard. In this tectonic context, a seismic data acquisition campaign has been carried out in several cities of the Dominican Republic to determine site effects and to carry out seismic microzonation studies. These studies have been carried out within the framework of the research projects MICROSIS-I (seismic microzoning in urban areas of the Dominican Republic, based on active and passive seismic) and “KUK ÀHPÁN: Integrated Regional Study of Structure and Evolution 4D of the Lithosphere in Central America”. Implications in the Calculation of Seismic Hazard and Risk”).

In the present study, a campaign of urban noise recording the horizontal-to-vertical (H/V) components spectral ratio and the spatial autocorrelation (SPAC) methods was carried out, in order to extract valuable information about the fundamental frequency peaks and geological shallow structure Vs30 and the bedrock interface under the investigated urban areas of Santo Domingo (East) Santiago de los Caballeros and Barahona cities.

Investigations were performed on 10x10 km dense grid with two broad band 120s seismic stations, five short period (1s) three components short period seismic stations and 36 single channel seismic stations provided with 4.5 Hz vertical component seismometers.

The computed H/V curves suggest the existence of multiple interfaces within the geological structure below the studied cities. The fundamental frequency of resonance varies between 0.3–10.1 Hz. Some H/V curves in the South of Santo Domingo, the bedrock sites are generally characterized by flat spectra whatever the geological nature of bedrock interface. The observed resonance peaks were interpreted according with the available geological information.

In addition of those studies, a Multichannel Analysis of Surface Waves (MASW) experiment of some 40 km has been carried out with a land streamer of 16 three component 4.5 Hz geophones and an active source of surface waves providing Rayleigh and Love waves along de main geological structures identified in the both studied cities. The combination of that methodology, the SPAC and the H/V methods, provided the Shear-wave velocity (VS) and time-averaged shear-wave velocity to 30 m depth (VS30). Values obtained from the above methods were combined and plotted for averaging the site’s Vs30 and layered models and the bedrock interface.

With these new results, we performed a step forward toward the understanding of ground motion propagation in the studied cities and future studies will be done to constrain the bedrock depth in order to build realistic velocity profiles for those cities.

How to cite: Córdoba Barba, D., Germoso, C., González, O., Sandoval, S., Montoya, T., Martínez, M., Souffront, M., and Benito, M. B.: Seismic microzonation study of Santo Domingo, Santiago de los Caballeros and Barahona  metropolitan cities  (Dominican Republic) using combined methods of reflection/refraction of surface waves and microtremor records, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6413, https://doi.org/10.5194/egusphere-egu24-6413, 2024.

EGU24-7445 | ECS | Orals | SM8.1

Automatic Determination Of P-Wave Arrival Time Using The Initial Power Of The P-Wave: A Case Study In Western Java 

Kadnan Kadnan, Dede Djuhana, Djati Handoko, and Nelly Florida Riama

Determining the arrival time of P waves is crucial in the context of earthquake early warning. Accuracy and calculating time play an important role in the earthquake parameter prediction. By using the initial power of the P-wave (IPP), STA/LTA, and artificial neural network, the arrival time of the P wave has been determined. 4,482 earthquake signals which occurred between 2021 to 2023 in the western of Java obtained by accelerometer were carefully investigated. The arrival time calculated by using Initial of P-wave (IPP) then compared with traditional STA/LTA picking and artificial neural network (ANN). Interestingly, IPP method can reduce background noise better than the other implying very clear P-wave to be proceed. It is found that IPP method exhibit less deviation, higher accuracy, and more precise suggesting candidate to apply as earthquake early warning system. This research contributes the reliability of seismic monitoring, thereby enhancing our ability to provide timely and accurate earthquake predictions for enhanced public safety.

How to cite: Kadnan, K., Djuhana, D., Handoko, D., and Florida Riama, N.: Automatic Determination Of P-Wave Arrival Time Using The Initial Power Of The P-Wave: A Case Study In Western Java, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7445, https://doi.org/10.5194/egusphere-egu24-7445, 2024.

EGU24-7493 | ECS | Posters on site | SM8.1

Application of ground motion model (GMM) considering rupture directivityto earthquake early warning (EEW) system in Taiwan 

Chin-Ting Weng, Chun-Hsiang Kuo, Hsin-Hua Huang, and Shu-Hsien Chao

          Taiwan is situated in Circum-Pacific Seismic Belt, located on the boundary between the Eurasian Plate and the Philippine Sea Plate. Therefore, it is necessary to evaluate the ground motion intensity in various seismic designs or seismic disaster assessments. Ground motion model (GMM) is employed for this purpose. In addition, earthquake early warning (EEW) system detects seismic activity in real-time and sends alert, providing people with a few seconds of warning before the arrival of damaging seismic waves, i.e., S-waves. Ground motions result in an increase in peak ground values (e.g. PGA and PGV) during a large magnitude earthquake, especially for the region near the forward rupture direction. Most of current GMMs do not consider the effect of rupture directivity, and thus ground motions in the direction of forward rupture propagation may be significantly underestimated. Accordingly, this study utilizes a GMM with consideration of a rupture directivity function (Chao et al. 2020; Convertito et al. 2012) to predict PGA and PGV for several local earthquakes with magnitude larger than 5.5. We estimate rupture direction (Jan et al. 2018) and then apply the above GMM incorporating rupture directivity effect to predict ground motions near real-time for an EEW system in Taiwan. Our aim is to enhance the accuracy of predicting ground motions, especially for the region near the forward rupture direction in which more critical damages are expected in comparison to the opposite direction.

How to cite: Weng, C.-T., Kuo, C.-H., Huang, H.-H., and Chao, S.-H.: Application of ground motion model (GMM) considering rupture directivityto earthquake early warning (EEW) system in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7493, https://doi.org/10.5194/egusphere-egu24-7493, 2024.

EGU24-7933 | ECS | Posters on site | SM8.1

Seismic noise measurements in the city of Trieste in order to plan an urban seismic network 

Federico Parentelli, Philippe Turpaud, Simone Francesco Fornasari, Deniz Ertuncay, Arianna Cuius, Giovanni Costa, and Veronica Pazzi

The seismic motion can be modified by local geological conditions, which can cause changes in the amplitude, frequency, and duration of earthquake’s seismic waves. For this reason, alongside an assessment of a large scale basic seismic hazard, it is of primary importance to evaluate a local seismic hazard, which takes into account the geological and geomorphological features that characterize the studied area.

Sediments and soft soils, through resonance phenomena, and topography, through focus effects, collaborate to modify seismic waves, usually causing amplification. In Italy, these site effects, since 2008, are commonly investigated by the seismic microzonation, which could be divided into three levels, gradually increasing in details.

The first microzonation level is developed by a work of collection of geological and geophysical data available for the study area, with the addition of some seismic noise measurements. The result is a MOPS chart (Homogeneous Microzone in Seismic Perspective), which divides the land in areas that, theoretically, should behave in a similar way from a seismic point of view. Regarding the city of Trieste, up to now, it is only available a first level microzonation, dated back 2016.

In this work the results of a seismic noise measures campaign carried out in the city of Trieste during the 2022 summer are presented. 32 measurements were carried out in the different homogeneous microzones defined for the city of Trieste, in key positions of the CLE chart (Emergency Boundary Condition), furthermore taking into account the geological, geomorphological, hydrogeological features, and the university building positions.

The goal were multiples. The first one was the estimation of soil amplification in the city of Trieste, analysed according to the horizontal to vertical spectral ratio (H/V) techniques developed by Nakamura. The second goal was to verify the homogenous behaviour of the MOPS, and the results show that the hypothesis of homogenous microzone in the seismic perspective is not always verified. In many examples inside the same homogeneous microzone the seismic behaviour could be highly different. The MOPS seem to be a good instrument as a general first-level evaluation, but they do not appear to be enough accurate for a site-effect detailed evaluation. Lastly, putting all the collected information together, the noise measurement campaign had the goal to find the best sites to settle a seismic monitoring network inside the University buildings, therefore a map of the proposed sites is presented.

How to cite: Parentelli, F., Turpaud, P., Fornasari, S. F., Ertuncay, D., Cuius, A., Costa, G., and Pazzi, V.: Seismic noise measurements in the city of Trieste in order to plan an urban seismic network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7933, https://doi.org/10.5194/egusphere-egu24-7933, 2024.

EGU24-8138 | ECS | Posters on site | SM8.1

Evaluation of the effectiveness of the second level microzonation abacuses for the municipalities located in the Friuli Venezia Giulia (Italy) plain 

Perla Taverna, Chantal Beltrame, Gabriele Peressi, Giovanni Costa, and Veronica Pazzi

The local geological conditions have a significant influence on seismic waves; these differences are referred to as the "local site effect," and they must be taken in consideration when estimating the seismic effects on buildings and urban planning. In fact, local conditions could affect the seismic shaking of an area and modify the seismic wave in terms of amplitude, frequency and duration.

In a very simplified approach to account for the influence of local conditions on ground shacking, according to the Eurocode 8 (EN-1998 2004), five ground types (from A to E) can be identified and used. According to this approach, an outcrop seismic bedrock is a layer characterized by Vs ≥ 800 m/s and correspond to the class A. The thickness and the shear waves velocity of the layer covering the seismic bedrock are the two factors that influence the amplification of a harmonic horizontal motion from the seismic bedrock to the surface. Thus, the equivalent/weighted average shear-wave velocity from the ground to the seismic bedrock depth H is used as a proxy for the seismic soil characteristics to design the appropriate site-dependent elastic response spectrum for structures. In a less simplified approach, the Seismic Microzonation (SM) studies aims at identifying and mapping at the urban scale the ground amplification in order to identify zones with homogeneous seismic behaviour and to assign to different areas a numerical value of expected shaking useful for the seismic design of structures. The Italian second level SM aims at quantifying the seismic amplification factor (AF) by means of abacuses for areas that can be schematised thanks to a 1D subsoil model (alluvial plain).

In this work the study area is the Friuli Venezia Giulia plain municipalities and the response spectra derived applying the AF values (both from abacuses and numerical simulations) have been compared to those obtained by the Italian Building regulation that apply the Eurocode 8 approach. In general, the smoothed seismic response spectra obtained by the numerical simulations are the highest (in the 82,5% of the total sites). In other minor cases, the spectra from abacuses are higher than the numerical simulation and only in 2 sites the spectra from the Italian regulation are higher than the abacuses and the seismic response ones. Moreover, the Tc values obtained by the by Italian regulation simplified approach underestimate the amplification for short periods of time and overestimate it for longer periods. This is highlighted especially in the soil category E.

How to cite: Taverna, P., Beltrame, C., Peressi, G., Costa, G., and Pazzi, V.: Evaluation of the effectiveness of the second level microzonation abacuses for the municipalities located in the Friuli Venezia Giulia (Italy) plain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8138, https://doi.org/10.5194/egusphere-egu24-8138, 2024.

EGU24-8329 | ECS | Posters on site | SM8.1

Comparison between the seismic amplification values obtained from the Italian second-level microzonation (SM2) abacuses and numerical simulation 

Chantal Beltrame, Perla Taverna, Gabriele Peressi, Giovanni Costa, and Veronica Pazzi

The Italian second level seismic Microzonation (SM2) aims to solve the uncertainties of the first level with new studies and gives a numeric estimate of seismic amplification through simplified methods. Seismic amplification occurs when the seismic waves reach a site composed at the top by a low velocity and loosened layer and, at the bottom, by a high velocity (Vs > 800 m/s) and rigid layer. SM2 is a simplified approach that can be applied only to 1D subsoil model (i.e., homogenous parallel layers). It consists of several tables of correspondences, called seismic abacuses, that allow to obtain two different seismic amplification factors (AF) values expected at the site: AFa and AFv. AFa corresponds to the low period amplification factor and is determined around the proper period for which there is the maximum acceleration response, whereas AFv corresponds to the amplification factor over long periods for which the maximum pseudo-speed response is obtained. These abacuses were obtained for specific lithologies of sediment cover (i.e., silt, that consists of all cohesive lithologies, sand and gravel), for established shear waves trend (i.e., constant, maximum or intermediate slope), for established peak ground acceleration at site (i.e., ag = 0.06 g, 0.18 g, 0.26 g) and for established range of seismic bedrock depth (5 m – 150 m) and for velocity of Vs30 or Vs equivalent (150 m/s – 700 m/s). Since the abacuses are thought to be applied for the whole national territory and are not site dependent, this study aims to understand if the seismic amplification factors obtained from these abacuses are representative of the actual values obtained from numerical simulation concerning the Friuli Venezia Giulia plain and if they under/overestimate the seismic hazard. Data has been collected from the Italian National Civil Protection repository and analyzed to obtain the necessary parameters to enter the abacuses. With the same data, several numerical simulations were carried out to obtain the site seismic amplification factors. The results were analysed from different perspectives: soil category obtained from Italian regulation, lithology cover soil, slope of the shear wave velocity - depth curve, and depth of the seismic bedrock. The AF obtained from seismic numerical simulations are higher with respect to the those from abacuses; the AF obtained from silt soils have the highest values; the AF from abacuses are greater than the AF obtained from simulations except for the sites where the slope of shear wave velocity - depth curve is considered maximum, i.e., where the seismic bedrock is shallow. Lastly, apart from some isolated values, the AFa ranges for sites characterized by a seismic bedrock depth lower than 30 m and higher than 30 m, are 1 to 3 and 2 to 5, respectively, while the AFv ranges are 1 to 2 and 1.25 to 4.5, respectively. In general, it is noted that abacuses underestimate the local seismic site effects except for the sites that have a shallow seismic bedrock. Moreover, there were identified no trends between abacuses AF and the ones from numerical simulations.

How to cite: Beltrame, C., Taverna, P., Peressi, G., Costa, G., and Pazzi, V.: Comparison between the seismic amplification values obtained from the Italian second-level microzonation (SM2) abacuses and numerical simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8329, https://doi.org/10.5194/egusphere-egu24-8329, 2024.

EGU24-8502 | Posters on site | SM8.1

Probabilistic Seismic Hazard Assessment of Sweden 

Björn Lund, Niranjan Joshi, and Roland Roberts

Sweden is a low-seismicity, stable continental region where seismic hazard assessment is non-trivial. Diffuse seismicity, low seismicity rate, few large magnitude earthquakes and little strong motion data makes it difficult to estimate recurrence parameters and determine appropriate attenuation relationships. Here we present a probabilistic seismic hazard assessment of Sweden based on a recent earthquake catalogue which includes earthquakes with magnitudes ranging from -1.4 to 5.9. The large number of events enables recurrence parameters to be calculated also for smaller source areas, in contrast to previous studies, and with less uncertainty. We use recent ground motion models developed specifically for stable continental regions, including Fennoscandia, and calculate hazard using the OpenQuake engine. The results are presented in the form of mean peak ground acceleration (PGA) maps at 475 and 2500 year return periods, hazard curves for four seismically active areas in Sweden and deaggregation for the area of highest hazard. We find the highest hazard in the northernmost part of the country, in the post-glacial fault province. This is in contrast to previous studies, which have not considered the high seismic activity on the post-glacial faults. We find relatively high hazard along the northeast coast and in southwestern Sweden, whereas the southeast and the mountain region to the northwest have low hazard. For a 475 year return period we estimate the highest PGAs to be 0.04 0.05g, in the far north, and for a 2500 year return period it is 0.1-0.15g in the same area. Significant uncertainties remain to be addressed with regards to the intraplate seismicity in Sweden and surroundings, such as the homogenization of magnitude scales, the occurrence of large events in areas with little prior seismicity and the uncertainties surrounding the potential for very large earthquakes on the post-glacial faults in northern Fennoscandia.

How to cite: Lund, B., Joshi, N., and Roberts, R.: Probabilistic Seismic Hazard Assessment of Sweden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8502, https://doi.org/10.5194/egusphere-egu24-8502, 2024.

EGU24-8562 | ECS | Posters on site | SM8.1

Seismic ground shaking by historical earthquakes in the Firenze metropolitan area 

Najmeh Ayoqi and Emanuele Marchetti

The seismic vulnerability assessment of a complex metropolitan area depends on the seismic source, wave propagation, and site amplification, as well as seismic response of single edifices. As a first step to evaluate the seismic vulnerability of Firenze, we computed the seismic ground motion on rigid bedrock of the 1919, 6.3 Mw Mugello earthquake in Tuscany, Italy, through a stochastic finite-fault technique (EXSIM) in conjunction with the Python framework.

The theoretical shake maps, evaluated at epicentral distances ranging between 10 and 100 km, is computed from 360 synthetic waveforms and corresponding Fourier acceleration spectrum, pseudo-spectral acceleration, peak ground acceleration, and peak ground velocity in the high-frequency range (f > 1 Hz). Synthetic waveform analysis is performed to investigate the model dependance on the various input parameters and corresponding confidence levels.

Comparison between model results and shake maps obtained from historical damages was used to validate the analysis and discuss the relation between expected damages and the main seismogenic area around the city. This study is performed in the framework of the HGP project (CUP:B55F21007810001) funded within the Next Generation EU program.

How to cite: Ayoqi, N. and Marchetti, E.: Seismic ground shaking by historical earthquakes in the Firenze metropolitan area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8562, https://doi.org/10.5194/egusphere-egu24-8562, 2024.

EGU24-8935 | ECS | Posters on site | SM8.1

Microtremor analysis in the central Longitudinal Valley, eastern Taiwan 

Jui Chang, Cheng-Feng Wu, and Ruey-Juin Rau

Eight days after the 2022 MW 7.0 Chihshang earthquake, we installed 58 short-period seismic stations in Yuli, Longitudinal Valley for a month-long measurement, and 72 stations around the earthquake rupture zones for short-term measurements. The region covers approximately 35 square kilometers, and encompasses the structures from west to east: Central Range Fault, Yuli Fault rupture zone and Chihshang Fault, a segment of the Longitudinal Valley Fault. An alluvial plain covers the topographic lows from the Central Range to Longitudinal Valley while terraces surround the river west of the Central Range Fault. We used horizontal-to-vertical spectral ratio (HVSR) analysis within the frequency range of 0.2 to 20 Hz for data processing, the region can be classified into six major categories from west to east: Category A, located in Central Range; Category B, at the terraces; Category C, situated in the plain west of the Yuli fault rupture zone; Category D, located proximal to the Yuli Fault rupture zone; Category E, located in the plain east of Yuli fault; and Category F, found in the plain east of Chihshang Fault and in the Coastal Range. Our results show that B, C and F have peak amplitudes of around 4.5 within dominant frequency (f0) range of 1.5-2.5 Hz, 2-3 within f0 range of 0.7-1.5 Hz and 3-5.5 within f0 range of 5-13 Hz, respectively. The locations of Categories B and C align with the position of Central Range fault line. Category F, located along the western boundary along the Chihshang Fault separated from the other five categories and exhibits a noticeable f0. On the other hand, A, D, and E exhibit less pronounced dominant frequencies. Category D is positioned at the center of the alluvial layer and is distributed around the rupture zone of Yuli Fault, showing high similarity in HVSR curve across numerous stations, with unclear dominant frequencies. As a result, the HVSR results in the central Longitudinal Valley are mostly related to the tectonics and topographic units in this region.

How to cite: Chang, J., Wu, C.-F., and Rau, R.-J.: Microtremor analysis in the central Longitudinal Valley, eastern Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8935, https://doi.org/10.5194/egusphere-egu24-8935, 2024.

EGU24-9154 | ECS | Orals | SM8.1

Croatian strong motion database: ground motion prediction equations tests 

Iva Lončar, Davor Stanko, and Snježana Markušić

Recent significant seismic events, namely the Zagreb MW5.3 and Petrinja MW6.4 earthquakes in 2020, have highlighted the critical need for enhanced seismic hazard assessment. To facilitate a more accurate assessment of seismic hazard, it is imperative to refine and adjust input parameters. Ground Motion Prediction Equations (GMPEs) assume a pivotal role in this aspect. However, the accurate allocation of GMPEs for specific regions necessitates an extensive database comprising strong motion (SM) recordings. This proves challenging for areas characterized by moderate seismic activity, such as Croatia. In response to this challenge, we have established the first systematic SM digital database, continually updated to address this gap. While the BSHAP database (Salic et al., 2017) was formally recognized as the initial Croatian strong motion database, it primarily contained analogue waveforms, often falling short of satisfactory quality standards. Our database confines its scope to the geographical boundaries of 41.2°N – 47.7°N and 12.5°E – 20.5°E. Comprising over 150 good-quality recordings from 2020 to the present day, with magnitudes equal to or surpassing 3.5, this database serves as a valuable resource. In this study, we tested various widely used Ground Motion Prediction Equations (GMPEs) to define the most suitable models. The findings of this investigation lay the foundation for further GMPE development tailored to the Croatian SM database, leveraging the Hybrid Empirical Method (HEM).

 

 

References:

Salic, R., Sandikkaya, M.A., Milutinovic, Z. et al. BSHAP project strong ground motion database and selection of suitable ground motion models for the Western Balkan Region. Bull Earthquake Eng 15, 1319–1343 (2017). https://doi.org/10.1007/s10518-016-9950-3

How to cite: Lončar, I., Stanko, D., and Markušić, S.: Croatian strong motion database: ground motion prediction equations tests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9154, https://doi.org/10.5194/egusphere-egu24-9154, 2024.

EGU24-9397 | ECS | Orals | SM8.1

Variability in Anelastic Attenuation: Examining Temporal and Spatial Influences on Ground Motion Characteristics in Central Italy 

Simona Gabrielli, Aybige Akinci, Carolina Gutierrez, Javier Ojeda Vargas, Sebastian Arriola, and Sergio Ruiz

In recent decades, Central Italy has faced several seismic sequences, such as the one of the 2016-2017, started with the Amatrice mainshock (Mw6.2) in August 2016, followed by the Visso (Mw5.9) and Norcia (Mw6.5) earthquakes in October 2016 (hereafter AVN). Given the region's frequent seismic activity and heigh seismic risk, the use of ground-motion simulations becomes crucial for seismic risk assessment and earthquake engineering applications. Ground motion characteristics have been already investigated in the area for the Mw6.2 Amatrice and Mw6.5 Norcia earthquakes, using stochastic and numerical approaches.

Moreover, to predict ground motion from hypothesized events, it is fundamental to define the attenuation characteristics of the area and the relationship with the ground motion models.

In this study, we investigate the variability of seismic wave attenuation in strong-ground motion simulation in the Central Apennines, employing stochastic simulations. Initially, we compute the quality factor Q values for the region, deriving the total attenuation Q as a function of frequency for the 2016-2017 seismic sequence. To visualize the variation of the attenuation, a 2D kernel-based imaging of coda-Q space is applied, confirming an increment in attenuation during the AVN sequence in the fault plane zones.

Then, we incorporate the acquired frequency-dependent Q values as input parameters into the simulations of ground motion. This methodology replicates stochastically strong-ground motion at high frequencies, reproducing horizontal and vertical accelerograms and using as input information from the source (stress drop, rupture time, slip distribution and radiation pattern). The estimations are then correlated and validated against observed peak ground accelerations and spectral accelerations for the Amatrice and Norcia fault planes, followed by a comparison with the ground motion prediction equations used for the region.

How to cite: Gabrielli, S., Akinci, A., Gutierrez, C., Ojeda Vargas, J., Arriola, S., and Ruiz, S.: Variability in Anelastic Attenuation: Examining Temporal and Spatial Influences on Ground Motion Characteristics in Central Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9397, https://doi.org/10.5194/egusphere-egu24-9397, 2024.

EGU24-9728 | ECS | Orals | SM8.1

Ground motion prediction using Physics-Informed Symbolic Learning (PISL) 

Xianwei Liu, Su Chen, Lei Fu, Xiaojun Li, and Fabrice Cotton

Ground Motion Models (GMM) are an essential component in seismic hazard analysis. In recent years, Machine Learning (ML) methods have made significant progress in advancing GMM research. However, their effectiveness is hindered by certain limitations. Firstly, some ML methods, such as neural networks, lack interpretability, which poses challenges for researchers and engineers. Secondly, these methods may have limited extrapolation capabilities and may struggle to accurately capture data distribution characteristics when predicting scenarios beyond the scope of the training data. To address these shortcomings, we propose a physics-informed symbolic learning (PISL) approach for constructing GMMs. Symbolic learning extracts an interpretable expression from data using sparse regression. To tackle sparse data issues in the near-field of large earthquakes, we have introduced a near-field saturation factor into the model. This factor contains physics information and guides the model to accurately capture near-field saturation properties even with limited data. We used the NGA-West2 database to develop GMMs for Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Pseudo-Spectral Acceleration (PSA) within the period range of 0.01s-10s. The study conducted comparative analyses using Mw-scaling, RJB-scaling, and VS30-scaling cases with empirical regression models. Model stability was assessed through residual calculations and standard deviation analysis. The results indicate that our model predictions are comparable to those of classical empirical models, with no significant differences in residual distribution and standard deviations. The extrapolation ability of the symbolic learning approach was validated using seismic events outside the training data, including the Wenchuan earthquake and Turkey earthquake. In conclusion, the method described above integrates physical knowledge and data-driven approaches, simplifying the equations while achieving similar results. Symbolic learning methods then provide a new perspective for the application of ML in engineering seismology.

How to cite: Liu, X., Chen, S., Fu, L., Li, X., and Cotton, F.: Ground motion prediction using Physics-Informed Symbolic Learning (PISL), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9728, https://doi.org/10.5194/egusphere-egu24-9728, 2024.

EGU24-10355 | ECS | Posters on site | SM8.1

Site effects and their relationship with geological structure in Tainan, Taiwan 

Chih Yang Yang, Ruey Juin Rau, and Cheng-Feng Wu

Tainan area is one of the areas have the highest risk of earthquake disasters in Taiwan. This research focuses on the microtremor characteristics and site effect of the Tainan Plain, the tableland, lowland and the foothills regions. We analyze the predominant frequency, amplification and fragility index of the seismic stations. Horizontal-to-vertical spectral ratio (HVSR) is used for the evaluations of site effect, and the data used are the micro-tremor received by the 173 single stations placed in the Tainan area from March to June 2021, and the duration of each station is 1-3 months. We used the stratigraphy borehole data as the initial model, f-k and HV-INV methods to obtain the velocity model in this area, and combined this velocity model with H/V to estimate the interface thickness. This is then used to compare different geological structures showing different site effect. The results at this stage point out that the stratum in the Tainan area contains two predominant frequencies, 0.2 Hz and 1~3 Hz respectively. Between them, the frequency of 0.2 Hz is dominant in the plain and the lowland areas. The stations above the tableland and the hills are dominated by 1~3 Hz, and their amplification is 2~3 times larger than that of the plain area. This illustrates that the site effect in the area is controlled by local geological conditions, and when seismic waves approach tableland and hills that the amplifications become stronger due to the site effect. However, the maximum value of PGA and the destroyed houses observed in the 2016 Mw 6.4 Meinong earthquake were found in the lowland area. This may be due to the multiple reflection signals observed in this area. We will sum up the fragility index for the entire interested frequency bands hoping to understand the overall geological strength of Tainan. In addition, we will compare the HVSR differences between the daily microtremor and the earthquake strong ground motion. If there is a certain relationship between them, we can use daily microtremor to estimate amplification and predominant frequency when earthquakes strike, and use this to evaluate the severity of disasters that may occur in different geological environments.

How to cite: Yang, C. Y., Rau, R. J., and Wu, C.-F.: Site effects and their relationship with geological structure in Tainan, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10355, https://doi.org/10.5194/egusphere-egu24-10355, 2024.

EGU24-11465 | Orals | SM8.1

Ground Motion Prediction Equations for the Campi Flegrei volcanic area 

Antonio Scala, Pasquale Cito, Claudio Strumia, Francesco Scotto di Uccio, Gaetano Festa, Iunio Iervolino, Aldo Zollo, Vincenzo Convertito, Luca Elia, Antonio Emolo, Antonella Bobbio, and Antonio Giovanni Iaccarino

Ground Motion Prediction Equations (GMPEs) are semi-empirical relationships commonly used to model ground motion intensity measures, such as peak ground accelerations (PGA) and velocity (PGV) and pseudo-spectral amplitudes (SA) at a specific site, conditional to earthquake parameters such as magnitude, source-site distance, and local site amplification effects. They are used for several seismological and earthquake engineering applications, such as probabilistic seismic hazard and rapid response (ShakeMap) analyses.

In the last decade, the very densely populated volcanic area of Campi Flegrei in Southern Italy, has experienced an intense seismic activity, related to the inner-caldera resurgency and ground uplift, with more than eight-thousand recorded events. During the last two years, both the uplift rate and the seismic activity accelerated, leading to the occurrence of about forty events with duration magnitude between 2.5 and 4.2 whose shaking has been well perceived by the population. Some of these earthquakes showed ground motion intensity (i.e., spectral pseudo-acceleration, SA), leading to non-negligible seismic actions on structures at specific natural vibration periods. Nevertheless, even structures located at less than few km from the source did not sustain significant damage.

Due to the strong discrepancy between observed and predicted data using literature GMPEs for Campi Flegrei, in this work, ad-hoc GMPEs were calibrated for PGA, PGV and 21 SA at periods T  in the range [0.01s 10s] . Data come from the largest magnitude events (38) occurred in the last two years, and recorded at thirty-four accelerometric and/or velocimetric stations located at epicentral distance Repi < 40 km. The events were re-located with a probabilistic, non-linear approach and the moment magnitude was computed from displacement spectrum amplitudes. Results indicate that the re-calibrated GMPEs expect larger PGA and PGV very close to the source (Repi < 5 km) and a higher attenuation at larger distances with respect to the existing attenuation relations for Italian volcanic areas.

The retrieved GMPEs for the Campi Flegrei caldera have been used to map the minimum magnitude of close-by earthquakes expected to exceed code-mandated design (elastic) seismic actions on structures; so-called strong earthquakes. This minimum magnitude is found in the range 4.1-5.1, depending on the ground motion intensity measure, for sites located within or in proximity of the caldera and earthquakes occurring at epicentral distances smaller than 1km.

How to cite: Scala, A., Cito, P., Strumia, C., Scotto di Uccio, F., Festa, G., Iervolino, I., Zollo, A., Convertito, V., Elia, L., Emolo, A., Bobbio, A., and Iaccarino, A. G.: Ground Motion Prediction Equations for the Campi Flegrei volcanic area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11465, https://doi.org/10.5194/egusphere-egu24-11465, 2024.

EGU24-12618 | ECS | Orals | SM8.1

Using Supervised Machine Learning Algorithms for Ground Motion Prediction: A Comparison with the Traditional functional form Approach in Central Italy 

Abel Daniel Zaragoza Alonzo, Miller Zambrano, Lucia Luzi, and Emanuele Tondi

The ground motion intensity measures are often obtained using Ground-Motion-Prediction-Equations (GMPEs) or more in general referred to Ground Motion Models (GMMs), which are empirical mathematical equations that relate the ground motion toseismological parameters (e.g., magnitude, source-to-site distance,focal depth and the average shear-wave velocity in the uppermost 30 m, Vs30). GMPEs are worldwide used as a tool for seismic hazard assessment and seismic design, usually derived from past earthquakes records through linear regression and predefined functional forms.

In the last 20 years, the application of artificial intelligence in earth sciences has been significatively applied to solve nonlinear problems that cannot be explained by empirical approaches.

The last seismic events in central Italy, including the earthquakes in L'Aquila (2009) and the Amatrice-Visso-Norcia sequence (2016-2018), have provided a substantial dataset comprising approximately 34,000 waveforms, contributing to the creation of a robust and accurate database(central Italy dataset).

In this work, we leverage the valuable data compiled by their work for the calibration of prediction models based on supervised Machine Learning (ML) to predict and evaluate the ground motion intensity measures and comparison the result with an existing GMPE currently used in Italy (ITA18).

Several ML regression algorithms are systematically examined and validated, the XGBoost algorithm is identified as the optimal choice, offering a balanced performance in terms of error minimization, interpretability, and computational efficiency. The evaluation encompasses the estimation of diverse Intensity Measures (IMs), such as Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Acceleration Response Spectra at 5% damping (SA) across different time periods (e.g., 0.1 second, 1.0 second, and 2.0 seconds). The ML model developed in this research demonstrates high accuracy, exhibiting notable improvements compared to the Italian Ground Motion Prediction Equation (GMPE). These advancements suggest the model's efficacy in enhancing seismic hazard assessment. Moreover, the versatility of this model extends beyond the study area, as it can be applied to various worldwide geological contexts, provided seismic data is available. The outcomes of this work not only contribute to refining local seismic risk evaluations but also offer valuable insights for seismic studies in diverse global regions.

How to cite: Zaragoza Alonzo, A. D., Zambrano, M., Luzi, L., and Tondi, E.: Using Supervised Machine Learning Algorithms for Ground Motion Prediction: A Comparison with the Traditional functional form Approach in Central Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12618, https://doi.org/10.5194/egusphere-egu24-12618, 2024.

EGU24-12949 | Posters on site | SM8.1

Hamlet: An Application for Seismic Hazard Model Evaluation and Testing 

Richard Styron, Yufang Rong, Kendra Johnson, Marco Pagani, Kirsty Bayliss, and Christopher Brooks

Reliable seismic hazard modeling requires careful calibration to the datasets used to create the model. Additionally, assessing the performance of an existing model involves statistical comparisons to data not used in model construction. However, despite the benefits of such statistical evaluations, comparing a model with the observed data is inherently challenging due to the following reasons:

1) A probabilistic seismic hazard model is essentially a structured collection of 105-108 unique potential earthquake ruptures and the occurrence rates and ground motion fields associated with each rupture. Seismological or geological observations usually include much smaller samples of earthquakes (in the order of 103-104) and active faults (in the order of 101-102), and the data are usually incomplete.

2) To construct a model from such observations, various assumptions and processing are involved (e.g., Poisson time independence of modeled seismicity, declustering of seismic catalogs, and modeling earthquake occurrence based on fault slip rates).

To facilitate model evaluations, we developed Hamlet (Hazard Model Evaluation and Testing), an application designed to process seismic hazard models and perform rigorous statistical comparisons between the model and observations efficiently and flexibly. Hamlet performs the M-, N-, S-, and L-tests recommended by the Center for the Study of Earthquake Predictability (CSEP) and other statistical comparisons (e.g., maximum earthquake magnitudes and seismic moments) by generating a large number of simulated earthquake catalogs of the same duration as an observed seismic catalog, mitigating many of the concerns about differences between the model and the observations. Hamlet can perform statistical comparisons both over the entire model domain and within equal-area hexagonal spatial cells of user-specified size, to better constrain the spatial differences in model performance. Moreover, Hamlet can subset a seismic source model by subregion, logic tree branch, and source type and perform the tests for the subset. This is particularly useful during model construction, as it allows the modeler to understand and adjust how individual components of the model perform.

We have used Hamlet to analyze over 30 hazard models to gauge the applicability of different tests and evaluations to a variety of cases (e.g., seismic hazard models with different characteristics), and to test some widely used assumptions in hazard models to identify which work and which do not. Hamlet is a work in progress, and we are continually adding features and evaluations. Functionality in development or for consideration for the future includes matching the most similar rupture in the source model to each earthquake in an observed seismic catalog, and statistical evaluations against a seismic catalog with different durations for different magnitude ranges. We are also exploring testing of predicted ground motion values and loss (risk) for observed events.

How to cite: Styron, R., Rong, Y., Johnson, K., Pagani, M., Bayliss, K., and Brooks, C.: Hamlet: An Application for Seismic Hazard Model Evaluation and Testing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12949, https://doi.org/10.5194/egusphere-egu24-12949, 2024.

EGU24-13175 | ECS | Orals | SM8.1

Assessment of liquefaction susceptibility under complex stratigraphic conditions: the case of Terre del Reno (FE) 

Silvia Giallini, Carolina Fortunato, Pietro Sirianni, Anna Baris, Maria Chiara Caciolli, Stefania Fabozzi, Iolanda Gaudiosi, Marco Mancini, Luca Martelli, Giuseppe Modoni, Massimiliano Moscatelli, Luca Paolella, Maurizio Simionato, Rose Line Spacagna, Francesco Stigliano, Daniel Tentori, and Chiara Varone

The phenomenon of liquefaction is nowadays sufficiently understood in terms of phenomenology and predisposing conditions. However, a better assessment of liquefaction risk is necessary to mitigate its effects and guide land-use planning choices, particularly in the context of post-earthquake reconstruction.

This evidence comes from some recent events (e.g., New Zealand, 2010-2011; Emilia-Romagna 2012; Palu, 2018), in which liquefaction induced effects were, in some instances, considerably more severe than expected. This is the case of Terre del Reno (Emilia-Romagna region, Italy) which experienced significant liquefaction phenomena during the 2012 Emilia-Romagna earthquake sequence, characterized by two main events: Mw 6.1 and 5.9. In this area sand eruptions, settlements, lateral spreading, and ground fractures were observed, resulting in extensive and irregularly distributed damage to structures and infrastructure.

This study deals with the evaluation of liquefaction susceptibility and development of liquefaction hazard map in complex stratigraphic condition through an integrated method and multilevel approach. The study area is characterized by complex geologic conditions and abrupt slope changes, typical of riverbank-channel systems.

The analysis of liquefaction potential was conducted using simplified semi-empirical methods. The safety factor against this phenomenon was estimated at different depths, relying on  soil properties obtained from penetrometric tests and seismic input. In addition to the calculation of liquefaction potential, the study also addressed the phenomenon of lateral spreading due to liquefaction. To date, the delimitation and representation of area prone to lateral spreading is not yet ruled by guidelines for the mitigation of liquefaction risks. Therefore, this study employed an empirical methodology based on original criteria and procedures to establish the perimeter of such areas.

The cross-analysis between the prediction of indicators of liquefaction potential and the evidence of damage found following the May 20, 2012 earthquake (Mw 6.1) showed a clear correlation between slope and damage frequency, suggesting the possibility of applying an empirical method to define the probability of lateral spreading occurrence.

How to cite: Giallini, S., Fortunato, C., Sirianni, P., Baris, A., Caciolli, M. C., Fabozzi, S., Gaudiosi, I., Mancini, M., Martelli, L., Modoni, G., Moscatelli, M., Paolella, L., Simionato, M., Spacagna, R. L., Stigliano, F., Tentori, D., and Varone, C.: Assessment of liquefaction susceptibility under complex stratigraphic conditions: the case of Terre del Reno (FE), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13175, https://doi.org/10.5194/egusphere-egu24-13175, 2024.

The Koyna-Warna seismic region located in western Indian state of Maharashtra, encompassing the south-western part of the Deccan Volcanic Province, reveals prolific seismicity attributed to both intraplate tectonism and reservoir-triggered activities. The 1967 Koyna earthquake of MW 6.3 marked the largest reported instance of Reservoir-Induced Seismicity, resulting in the destruction of the town of Koynanagar; subsequently, the 1993 Killari earthquake of MW 6.2 claimed thousands of lives with enormous structural damages in Latur district with maximum intensities of IX and VIII respectively. This, therefore, underscores the imperative need for seismic hazard assessment to enhance earthquake disaster preparedness and risk mitigation. Both areal and tectonic sources in two hypocentral depth ranges of 0-25 km and 25-70 km along with 15 Ground Motion Prediction Equations including 6 Site-specific Next Generation Spectral Attenuation models pertaining to Koyna-Warna, Kutch and Central India seismogenic sources have been incorporated to deliver Probabilistic Peak Ground Acceleration (PGA) of Koyna-Warna region at firm rock condition varying from 0.05-0.48g for 10% probability of exceedance in 50 years. Extensive Geotechnical and Geophysical investigations combined with Topographic Gradient data in high-altitude areas have provided the effective shear wave velocity distribution, classifying the region into ten site classes viz. E/F (≤180m/s), D4 (180-240m/s), D3 (240-280m/s), D2 (280-320m/s), D1 (320-360m/s), C4 (360-440m/s), C3 (440-520m/s), C2 (520-620m/s), C1 (620-760m/s) and B (760-1500m/s), leading to a detailed seismic hazard modelling of the ancient holy city of Nashik, the fourth largest city in the state of Maharashtra. 2D nonlinear site response analysis using PLAXIS 2D has been performed for the city, which amplified the bedrock PGA by a factor ranging from 1.75 to 3.18 times, thus generating surface-consistent hazard in the range of 0.14-0.25g. The estimated PGA has further been used for the holistic microzonation integrating multiple geo-hazard themes viz. Surface-consistent Probabilistic PGA, Liquefaction Potential Index (LPI), Site Class, Geomorphology and Geology which categorized the city into five zones based on Seismic Hazard Index (SHI) namely ‘low (0.00<SHI≤0.20)’, ‘moderate (0.20<SHI≤0.40)’, ‘high (0.40<SHI≤0.60)’, ‘very high (0.60<SHI≤0.80)’ and ‘severe (0.80<SHI≤1.00)’. Structural damage potential modelling through “Capacity Spectrum Method”-based SELENA considering ten model building types has yielded Damage Probability in terms of five damage states which predicted that the majority of Unreinforced Masonry type buildings (URML) will experience ‘complete’ damage and others (A1, RS2, C1L, C1M, C1H, C3L, C3M, C3H and HER) will sustain ‘slight to moderate’ damage levels when exposed to the estimated surface-consistent probabilistic seismic hazard scenario of the city. Human casualties has also been speculated for three distinct periods of a day viz. “Night”, “Day” and “Commuting” times thereof. This model is believed to contribute significantly to the seismic-resilient urbanization process by providing precise disaster management and mitigation recommendations for the city of Nashik.

How to cite: Biswas, A. and Nath, S. K.: Surface-consistent Probabilistic Seismic Hazard, Microzonation and Damage Potential Modelling for the City of Nashik, Maharashtra, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14663, https://doi.org/10.5194/egusphere-egu24-14663, 2024.

EGU24-14872 | Posters on site | SM8.1

Seismic Site Effects of Horizontal-to-Vertical Spectral Ratios for the Strong-Motion Stations in Taiwan 

Che-Min Lin, Chun-Hsiang Kuo, and Jyun-Yan Huang

The resonant frequency and site amplification of Horizontal-to-Vertical Spectral Ratio (HVSR) for a site have become common and useful site parameters. The present site database for the strong-motion stations of TSMIP (Taiwan Strong Motion Instrumentation Program) in Taiwan only included conventional parameters, including the averaged shear-wave velocity (VS) of the upper 30 meters (VS30), the depth to the horizons of shear-wave velocity larger than 1.0 km/s (Z1.0), and the high-frequency decay parameter (kappa; κ0). In order to complete the HVSR-based site parameters of the database, the earthquake-based HVSR (eHVSR) and microtremor-based HVSR (mHVSR) are conducted for the TSMIP stations within the site database based on the standard procedures suggested by recent studies. The characteristics of eHVSRs and mHVSRs for different VS30-based site classifications are evaluated and discussed. The relationships between HVSR-based parameters, including resonant frequency and amplification, and conventional parameters are systematically assessed. Although the differences between eHVSR and mHVSR are non-negligible for some stations, the results still show high correlations between their derived site parameters and realistic site conditions. The HVSR-based site parameters of the TSMIP stations would be reliable for further studies of strong motion prediction and simulation, seismic hazard analysis, etc, in Taiwan.

How to cite: Lin, C.-M., Kuo, C.-H., and Huang, J.-Y.: Seismic Site Effects of Horizontal-to-Vertical Spectral Ratios for the Strong-Motion Stations in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14872, https://doi.org/10.5194/egusphere-egu24-14872, 2024.

The complex physics of earthquake rupture, wave propagation and site effects are simplified and modelled into generic Ground-Motion Models (GMMs) for use in seismic hazard and risk assessment. However, the complexity of geology and seismicity in Europe leads to a high variability in the ground motion prediction compared to observed data. Recent GMMs partially resolved this variability by regionalising their model and adapting to the specificity of each region. We focus this study on the apparent anelastic attenuation variability, to understand the underlying physics of wave propagation in the crust and better model the variability in GMMs. The regionalisation model used in the recent European Seismic Hazard Maps 2020 (ESHM20) divides Europe in several polygons, each with a specific apparent anelastic coefficient adjustment. This model has certain limitations due to ambiguity in the criteria to define these polygons, which have led to non-reproducible maps and geologically diverse regions being grouped into a single large polygon, especially in France. Two hypotheses have been made to improve the current regionalisation. Firstly, France was divided following the contrast of Rayleigh wave velocity in the ambient noise tomography of France. Secondly, a null hypothesis was defined where no prior geological information is used, and Europe is simply regionalised into a regular grid. Linear mixed-effects regressions were performed on the pan-European ground-motion dataset, complemented with a French dataset, to quantify the apparent anelastic attenuation variability. The regionalisation based on Rayleigh wave velocity captures attenuation variability better than the current model for France. However, the grid-based regionalisation is more accurate in the representation of the attenuation variability which leads to keep this choice as the best regionalisation. Analyses of variance statistics confirmed this result. The size of the grid was also discussed based on these statistical tests and the number of records. The apparent anelastic attenuation variability captured on a regular grid can now be examined for a physical meaning producing this variability and improve the parametrisation of GMM.

How to cite: Georges, P., Kotha, S. R., and Chaljub, E.: Improving the representation of apparent anelastic attenuation variability in regionalised Ground Motion Models in Europe with a focus in mainland France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15213, https://doi.org/10.5194/egusphere-egu24-15213, 2024.

EGU24-15663 | ECS | Orals | SM8.1

The Comparison of the 2020 European and the Finnish Seismic Hazard Models at Two Nuclear Power Plant Sites in Finland  

Amir Sadeghi-Bagherabadi, Ludovic Fülöp, and Annakaisa Korja

Finland, which is characterized by very low seismicity, does not have a national seismic hazard map. However, site specific Probabilistic Seismic Hazard Assessments (PSHAs) for critical infrastructure, including nuclear power plants (NPPs), have been conducted. The sophisticated 2020 European Seismic Hazard Model (ESHM20) offers several advancements that could influence seismic hazard work in stable continental regions like Finland.  As part of the SEISMIC RISK collaborative project involving the University of Helsinki, VTT Technical Research Centre of Finland, and the Geological Survey of Finland, a national PSHA model has been developed. The model is based on a Fennoscandian earthquake catalogue – FENCAT, compiled from Nordic national catalogues based on the observations from the national seismic networks. This allows for calculation of the recurrence parameters with lower magnitudes than the ESHM20. Although a preliminary comparison reveals only minor local differences at hazard levels, a more detailed examination at critical infrastructure sites is necessary.

We have compared the regional hazard results obtained within the SEISMIC RISK project and hazard values of the ESHM20 at two NPP sites in Finland. Four criteria from the literature, compiled by Douglas et al. (2023), were employed for assessing the differences between the seismic hazard models. To this end, the mean, median, and 16th and 84th fractiles for the ESHM20 were obtained from the European Facilities for Earthquake Hazard and Risk (EFEHR) database hosted by EPOS–Seismology.

A visual inspection of the hazard curves initially indicated consistently higher mean hazards from the Finnish model at the NPP sites compared to ESHM20. The lognormal distributions of the hazard models were estimated, and the differences were assessed for the return periods of 106, 104, 5000, 2475, and 475 years using the four criteria. The distributions revealed a significantly smaller standard deviation for the Finnish model than for the ESHM20. When comparing the two models, the mean Annual Frequency of Exceedance (AFE) changed by over 25% for the ground-motions corresponding to AEFs ≤ 10-4 and by more than 35% for ground-motions corresponding to 10-6 AFE. These findings underline the significant differences between the models. 

In summary, a minimum of two out of the four criteria are met at one of the NPP sites, and at the other NPP site, three out of four criteria are satisfied. This further highlights the significance of the differences between the ESHM20 and the Finnish hazard model. Nevertheless, while the observed change in hazard between the Finnish hazard model and the ESHM20 can be deemed substantial, it does not justify the use of the Finnish hazard model for the longer return periods. Further investigations, such as site-specific hazard assessments, are necessary for the return periods relevant to NPPs. 

 

 

 

Douglas, J., Crowley, H., Silva, V., Marzocchi, W., Danciu, L., & Pinho, R. (2023). Methods for evaluating the significance and importance of differences amongst probabilistic seismic hazard results for engineering and risk analyses: A review and insights. EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-991 

How to cite: Sadeghi-Bagherabadi, A., Fülöp, L., and Korja, A.: The Comparison of the 2020 European and the Finnish Seismic Hazard Models at Two Nuclear Power Plant Sites in Finland , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15663, https://doi.org/10.5194/egusphere-egu24-15663, 2024.

The geometry and soil conditions at a site can strongly influence the ground shaking induced by an earthquake and an important part of seismic hazard assessment is therefore to characterize such site effects. At stiff sites and for weak ground motions, the soil response behaves linearly, however, for larger ground motions and softer sites the site response becomes nonlinear and thus more challenging to assess. Because recordings of such strong shaking are rare, nonlinear soil parameters are often defined from laboratory measurements and numerical simulations. However, the increase of available ground motion data, in particular from sites with recordings from both weak and strong motions, has increased the possibility of deriving nonlinear site parameters directly from empirical data. In this study, we take advantage of the comprehensive KiK-net network in Japan, consisting of stations with recording instruments at both surface and at depth. We use the surface-to-depth ratios of each event recorded by each station, to systematically capture the empirical effects of nonlinear soil response on the local response. Station-specific parameters for the degree of nonlinearity and PGA thresholds for the onset of nonlinear behaviour are then derived and the statistical correlation between these parameters and a selection of geotechnical and geological indicators are investigated. Our results show that - although finding site parameters suitable for predicting nonlinear site effects remains challenging as the nonlinear soil-behaviour is largely site-specific - proxies describing the depth to bedrock, sediment thickness and characterization of the shallowest part of the soil layer display a certain degree of potential for prediction.

How to cite: Loviknes, K., Bergamo, P., Cotton, F., and Fäh, D.: Assessment of the correlation between site-specific nonlinear soil behavior for Japanese KiK-net stations and geological, geotechnical parameters , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16964, https://doi.org/10.5194/egusphere-egu24-16964, 2024.

EGU24-17792 | ECS | Orals | SM8.1

Seismic Deformations due to 2023 Nepal Earthquake Sequence using Satellite Remote Sensing Techniques 

Sandeep Kumar Mondal, Rishikesh Bharti, and Kristy Tiampo

The seismic activity in the Himalayan region results from the ongoing collision between the Indian and Eurasian tectonic plates. The Himalayan thrust zone, comprising critical fault zones like the Main Central Thrust (MCT), Main Boundary Thrust (MBT), and Main Frontal Fault (MFF), is highly seismically active, leading to numerous moderate-to-high magnitude earthquakes annually. Nepal, situated in one of the world's most seismically active continental collision orogenic belts, has experience numerous devastating earthquakes in its history. Earthquakes can result in wide-ranging devastation that includes other, cascading natural disasters, including avalanches, landslides and glacial lake outburst floods (GLOFs). The present study aims to identify ground surface deformations associated with the 2023 Nepal earthquake sequence using C-band radar interferometry from the ESA Sentinel-1A/B synthetic aperture radar (SAR) datasets. The earthquake sequence includes a mainshock (Mw 5.7 triggered at a hypocentre depth of 32.6 km) on November 3, 2023, followed by an aftershock (Mw 5.3 triggered at a hypocentre depth of 10 km) on November 6, 2023. The mainshock's influence radius, determined using shake maps from the USGS earthquake catalog, is 57 km. Because the aftershock's influence radius of 51 km which is smaller than that of the mainshock, we use that as the study radius. Differential interferometric SAR (DInSAR) is employed for this region, utilizing co-seismic single-look complex (SLC) datasets acquired on October 25 and November 6, 2023, respectively. The DInSAR analysis reveals a maximum reliable (regions with coherence ≥ 0.4) and atmospherically-corrected ground deformation of -79 mm. The most significant ground deformations are observed around the Sisne Himal glacial region and the mountain slopes of the Ragda region. Other areas with ground deformations are identified over the mountain slopes of the Guthi Chaur region. The topographic slope of these regions is ≥35° except for Sisne Himal glacial region as observed through ALOS PALSAR high-resolution terrain corrected digital elevation model (DEM) at 12.5m ground resolution. Analysis of pre- and co-seismic coherence images revealed decreased co-seismic coherence in certain locations within the influence radius. These areas are further investigated for soil liquefaction/cyclic mobility using the Temporal Difference Liquefaction Index (TDLI) using Landsat-8 and -9 datasets of October 27 and November 4, 2023 respectively. TDLI detects changes in soil moisture content after an earthquake event. The observed ground deformations indicate potential earthquake-induced slope failures including some of the locations with liquefaction/cyclic mobility susceptibility. This emphasises the importance of monitoring such vulnerable areas for enhanced seismic risk assessment and disaster preparedness.

How to cite: Mondal, S. K., Bharti, R., and Tiampo, K.: Seismic Deformations due to 2023 Nepal Earthquake Sequence using Satellite Remote Sensing Techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17792, https://doi.org/10.5194/egusphere-egu24-17792, 2024.

EGU24-17952 | ECS | Orals | SM8.1

“Evaluation of the near field effects trough numerical modeling: the case of Norcia (Italy)” 

Maria Chiara Caciolli, Silvia Giallini, Alessandro Pagliaroli, Massimiliano Rinaldo Barchi, Roberto De Franco, Gabriele Fiorentino, Marco Mancini, and Massimiliano Moscatelli

The near field condition in seismic events is characterized by its immediate proximity to the seismic source, and is widely proven that ground motion near a causative fault (Near field) can differ significantly from typical ground motion observed at greater distances (far field).

Features of near-fault ground motion are high vertical accelerations and the occurrence of high-amplitude, long-duration (2–5s) pulses observed in velocity–time and displacement–time histories aligned with the fault's normal direction. These features and the other effects linked to this condition are critical factors in causing potential damage to structures as the seismic motion in the near-field can subject structures to seismic demands that differ from the design criteria, primarily in terms of intensity and the nature of ground motion.

As the seismic hazard quantifies the ground motion expected at a given site, understanding and predicting near-field effects are vital for seismic hazard assessment, structural design, and risk mitigation in the areas where near-field conditions occur.

This study aims to investigate the near-field effects in seismic events by employing two-dimension numerical simulations carried out with FLAC 2D Finite Difference Code, to reproduce the features observed during a real earthquake occurred.

The selected area is the Norcia plain, one of the intermountain basins widely present in Central Italy—a context of significant interest due to its association with high seismic hazard and high exposure in urban agglomerations. Several active seismic stations have recorded the last important seismic sequence (Central Italy 2017-2018) in particular the third and largest event on 30th October (6.5 Mw), whose epicenter was located close to Norcia (4 km). The validity of near-field conditions for this event has already been established by previous studies.

Other scientific studies have been carried out in this direction in similar geological contexts with other software and the advancing here proposed is performing simulations using a non-horizontal interface geometry to apply the seismic input, with both horizontal and vertical components. The simulations consider a geological and tectonic model with few variables changing to provide a comprehensive understanding of how results may be affected by the knowledge of the geological and geotechnical setting, gained from basic studies.

This study could have important implications to suggest an updating of the seismic code and the general approach in the seismic design of structures located in the near field domain, for a careful and reliable assessment of seismic risk.

How to cite: Caciolli, M. C., Giallini, S., Pagliaroli, A., Barchi, M. R., De Franco, R., Fiorentino, G., Mancini, M., and Moscatelli, M.: “Evaluation of the near field effects trough numerical modeling: the case of Norcia (Italy)”, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17952, https://doi.org/10.5194/egusphere-egu24-17952, 2024.

Rajasthan, in northwestern India, lies within the Western Indian Shield's tectonic block. The state's landscape is dominated by the extensive Thar desert with diverse sand dunes, alluvial deposits, and areas featuring felsic lava flows, granitic plutons, and mafic lavas. The Aravalli range extends northeast-southwest, subducting beneath the Himalayan arc, marked by numerous parallel active faults. In the southwest, the Cambay Graben forms a rift zone with steep faults, and the north-south trending Konoi Fault at Jaisalmer is linked to intraplate seismicity. Although, Rajasthan is not classified as a high to very high-risk zone according to Bureau of Indian Standards, the emergence of unconventional seismic sources, such as induced seismicity related to anthropogenic activities like mining and reservoir-induced seismicity, underscores the evolving nature of seismic risks. The surrounding region of the state jolted time and again by several devastating earthquakes viz. 1935 Quetta earthquake of Mw 7.7 in Pakistan, 2001 Bhuj earthquake of Mw 7.6 in Gujrat and 1938 Satpura-valley earthquake of Mw 6.2 in Madhya Pradesh with MM Intensities ranging between V–VIII. Moreover, Rajasthan's increasing urbanization and infrastructure development necessitate a thorough assessment of surface-level seismic hazard in the area to safeguard lives, property, and critical infrastructure. By considering seismicity patterns, fault networks, and similarities in focal mechanisms, 12 areal seismogenic sources and additional active tectonic features were identified across various hypocentral depth ranges (0–25 km, 25–70 km and 70–180 km), and utilizing 15 Ground Motion Prediction Equations, including 6 Site-specific Next-Generation Spectral Attenuation models specific to West Central Himalaya, Kutch Region, and Central India tectonic provinces, yielded probabilistic Peak Ground Acceleration (PGA) at engineering bedrock ranging from 0.08 to 0.42 g. A exhaustive geophysical and geotechnical field investigations at 600 sites have been carried out to determine the effective shear wave velocity, ranging from 223 to 956 m/s, leading to the classification of the region into nine site classes: D4, D3, D2, D1, C4, C3, C2, C1, and B. Systematic 2D non-linear site response analysis has been performed using “PLAXIS 2D” and subsequently convolution of absolute site amplification factor with PGA on firm rock condition resulted in a surface-consistent hazard ranging from 0.10 to 0.68 g. A comprehensive seismic hazard microzonation study have also been presented for four major cities, namely Jaipur, Jaisalmer, Jodhpur, and Udaipur, taking into account their significant population and cultural heritage. The findings from this study will be crucial for earthquake hazard and risk assessments of the region.

How to cite: Singh, P. and Nath, S. K.: Seismic Site Characterization of Rajasthan, India with special emphasis on Seismic Hazard Microzonation study for few major populated cities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18652, https://doi.org/10.5194/egusphere-egu24-18652, 2024.

A spectral decomposition approach is applied to separate the site amplification, path attenuation, and source parameters of earthquakes that occurred in Madagascar between 2011 and 2013. Concerning source parameters, the stress drop is derived from the source spectra, fitting the Brune model. Our findings indicate an increase in stress drop with magnitude, ranging from 0.001 to 0.1 MPa. Additionally, the results unveil a consistent attenuation curve diminishing with distance, characterized by a swift decay at higher frequencies below the 1/R^2 decay function. The frequency-dependent behavior of the estimated quality factor for S waves suggests rapid damping and slow dissipation.Regarding site amplification, a robust agreement is noted between resonance frequency obtained through GIT and the H/V spectral ratio. Furthermore, we explore the correlation between site amplification and geological characteristics such as sediment depth and lithology.

How to cite: Ravoson, M. and Razafindrakoto, H. N. T.: Application of Spectral Decomposition approach to examine the attenuation, source parameters, and site effects in Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19444, https://doi.org/10.5194/egusphere-egu24-19444, 2024.

EGU24-19554 | ECS | Posters on site | SM8.1

Slow-Slip Earthquakes observations in Costa Rica and their Potential Impact on Seismic Hazard Assessments 

Mario Arroyo Solórzano, Fabrice Cotton, Graeme Weatherill, Jorge Jara, and Álvaro González

Costa Rica is located at a subduction margin in a complex tectonic setting where four tectonic plates (Caribbean, Coco, Nazca, and Panama) interact, and large earthquakes are generated. Slow-Slip earthquakes (SSEs) are defined as a seismic activity that involves the gradual and aseismic release of tectonic stress. Therefore, SSEs play a very complex role in the seismic cycle, representing a crucial element to be considered in seismic hazard assessment. These events are a common feature in subduction regimes and have been reported in most of the well geodetically instrumented subduction zones worldwide. In northern Costa Rica, shallow and deep SSEs have been identified at the Nicoya peninsula, and recently, shallow SSEs were also documented in the southern part of the country at the Osa peninsula. Here, we present a synthesis and compilation of SSEs observations in Costa Rica based on an in-depth review of previous studies, aiming to delve into potential implications and explore possible viable ways to incorporate it in seismic hazard assessments. We accomplished this by identifying differences among patches inside the subduction segments where occur or not SSEs, evaluating the coupling factors, and considering the observations of recurrence intervals to infer slip deficit values. Based on the previous analysis, we summarized the main findings regarding possible implications of the SSEs occurrence in Costa Rica for seismic hazard purposes. A significant result from the comparison with the 2022 Costa Rica seismic hazard model is that the non-quantification of SSEs in PSHA may be conducting to overestimations, particularly in subduction margins near the coast, as in the case of Costa Rica.

How to cite: Arroyo Solórzano, M., Cotton, F., Weatherill, G., Jara, J., and González, Á.: Slow-Slip Earthquakes observations in Costa Rica and their Potential Impact on Seismic Hazard Assessments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19554, https://doi.org/10.5194/egusphere-egu24-19554, 2024.

EGU24-20762 | ECS | Orals | SM8.1

Accounting for earthquake rates’ variability through Uniform Rate Zone forecasts in the 2022 Aotearoa New Zealand Seismic Hazard Model 

Pablo Iturrieta, Matthew Gerstenberger, Chris Rollins, Russ Van Dissen, Ting Wang, and Danijel Schorlemmer

The distribution of earthquakes in time and space is clustered and may exhibit a non-stationary behaviour. The impacts of non-stationarity are further amplified when the observation window is short compared to the timescales of the underlying tectonic process, such as in regions of low-seismicity. This can preclude a robust statistical analysis for PSHA models, which commonly assume stationary Poisson models. We investigate the performance of forecasts for PSHA, such as smoothed-seismicity models (SSM), with respect to the available training data. We design bootstrap experiments for multiple pairs of consecutive training/forecast windows of a catalogue to: (i) analyse the lowest available amount of training data for which SSM performs spatially better than the least-informative Uniform Rate Zone (URZ) model; (ii) characterise the temporal variability of rates in terms of their over-dispersion and non-stationarity. The results show rate variability up to 10 times higher than predicted by Poisson forecasts, and demonstrate the impact of non-stationarity when assuming a constant mean rate derived during a training period for forecasting purposes. Analytical distributions are used to describe rate variability, which are conditioned on the information available from a training period. Furthermore, we devise a data-driven method based on strain-rate maps to spatially delineate URZs, under the assumption that the strain-rates field is related to the time scales of earthquake occurrence and interaction. For each URZ, a rate temporal distribution is inferred from the training events within it. We provide forecasts for the update of the New Zealand Seismic Hazard Model that have increased rates by up to 10 times higher in extensive low-seismicity regions compared to optimised SSMs. The new forecasts are implemented as negative-binomial distributions in the hazard integral. For a 10% exceedance probability in 50 years, the use of URZ with rate variability descriptions increases the expected PGA by up to 0.16 g in low seismicity regions (e.g. Auckland, Dunedin) compared to SSM. Our results highlight the relevance, as well as the feasibility, of incorporating analytical formulations of seismicity that go beyond the inadequate stationary Poisson description of seismicity.

How to cite: Iturrieta, P., Gerstenberger, M., Rollins, C., Van Dissen, R., Wang, T., and Schorlemmer, D.: Accounting for earthquake rates’ variability through Uniform Rate Zone forecasts in the 2022 Aotearoa New Zealand Seismic Hazard Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20762, https://doi.org/10.5194/egusphere-egu24-20762, 2024.

EGU24-21465 | Orals | SM8.1

Exceedance of probabilistic seismic hazard maps in Italy 

Pasquale Cito, Antonio Vitale, and Iunio Iervolino

Seismic hazard maps deriving from probabilistic seismic hazard analysis (PSHA) collect the intensities, in terms of one ground motion intensity measure (𝐼𝑀), that, at each site taken individually, have the same probability of being exceeded in a time interval or, equivalently, exceedance return period. In the case of Italy, there are three authoritative nationwide PSHA studies that can be currently considered of interest. Given the return period, they provide hazard maps that can differ even significantly in some areas of the country. This contribution pertains to the assessment of the fractional area of Italian territory where 𝐼𝑀 values from hazard maps have been exceeded, at least once, due to seventy-one historical mainshocks that occurred in the country from 1117 to 1968. Ground shaking data for such events were derived from a recently developed large database of ShakeMap inferred from macroseismic intensity data. Such database is not complete, with the Italian catalogue (Catalogo Parametrico dei Terremoti Italiani; CPTI) counting more than two thousand mainshocks in that time interval, yet it is, to date, the highest level of information on shaking data due to historical events. For each hazard model, the exceedance area was quantified considering hazard maps with four return periods, that is, 50yr, 475yr, 975yr and 2475yr, and three 𝐼𝑀𝑠, that is, peak ground acceleration and pseudo-spectral acceleration associated to a vibration period of 0.3s and 1s. It was found that, based on the available regional shaking estimates for historical earthquakes in Italy, the fraction of the country exposed to at least one exceedance, in almost one thousand years, is comparable, given return period and 𝐼𝑀, for all the hazard models, despite their apparent differences. Such comparability was also found when considering instrumental, rather than historical, earthquakes that occurred in Italy in a continuously monitored time interval spanning twelve years. In this case, the exceedance area was quantified considering ShakeMap data for nineteen mainshocks that occurred from 2008 to 2019 according to CPTI, and therefore the dataset can be deemed complete. Thus, the fraction of the country possibly subjected to exceedance of 𝐼𝑀 values from hazard maps according to ShakeMap estimates was also compared with its expected value from PSHA, something that depends only the return period the maps refer to. It was found that, for each return period, the estimated fractional exceedance area in the available twelve years is one order of magnitude lower (or slightly less) than the expected value according to all PSHA studies.

How to cite: Cito, P., Vitale, A., and Iervolino, I.: Exceedance of probabilistic seismic hazard maps in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21465, https://doi.org/10.5194/egusphere-egu24-21465, 2024.

Earthquake catalogues, vital for understanding earthquake dynamics, often grapple with incompleteness across varying time scales. Our research pioneers an innovative strategy to seamlessly integrate time-varying incompleteness into the Epidemic-Type Aftershock Sequence (ETAS) model. Leveraging the Bayesian prowess of inlabru package in R programming language, which is based on the Integrated Nested Laplace Approximation (INLA) method, we not only capture uncertainties but also forge a robust bridge between short-term to long-term gaps in records of earthquakes.

Our methodology, a fusion of the ETAS model and inlabru, provides a comprehensive framework that adapts to diverse scales of incompleteness. We address the complex nature of seismic patterns by considering both short-term gaps in early aftershocks (minutes to a few days) and long-term irregularities (years to centuries) in historical earthquake data records. Technically, the short-term incompleteness period arises from seismic network saturation during periods of high activity, resulting in the underrecording of small events, while the long-term incompleteness originates from sparse network coverage and inability to detect events over extended time. Bayesian foundation of inlabru enriches the model with posterior distributions, empowering us to navigate uncertainties and refine seismic hazard assessments. By utilising a combination of simulated synthetic data and real earthquake catalogues, our results showcase the impact of this approach on the ETAS model, markedly improving its predictive accuracy across various temporal scales of incompleteness.

In this study, we present an initiative in seismicity modelling that bridges temporal gaps, allowing the ETAS model to evolve with the ever-changing landscape of earthquake data incompleteness. This research not only enriches our understanding of spatiotemporal seismicity patterns but also lays the groundwork for more resilient and adaptive aftershock forecasting, ultimately equipping decision-makers with more reliable information about seismic hazards, and enhancing community resilience in the face of earthquakes.

How to cite: Kamranzad, F., Naylor, M., and Lindgren, F.: Bridging time scales for comprehensive ETAS modelling to accommodate short-term to long-term incompleteness of seismicity catalogues, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-401, https://doi.org/10.5194/egusphere-egu24-401, 2024.

EGU24-634 | ECS | Posters on site | NH4.3

Mapping micro-seismicity around a nuclear power station in stable South Africa through machine learning 

Wade van Zyl, Diego Quiros, and Alastair Sloan

Ground motion caused by near-source seismic waves from shallow earthquakes can be dangerous to vital infrastructure such as nuclear power plants. South Africa is a stable continental region (SCR), however significant seismicity is known to occur. Nearby Cape Town, and the Koeberg Nuclear Power Station, historical sources record an earthquake with a potential magnitude of 6.5 in 1809. On September 29th, 1969 the magnitude 6.3 Ceres-Tulbagh earthquake affected an area less than 100 kilometers of the Koeberg Nuclear Power Station. These events emphasize the need to take the potential seismic hazard in this area seriously. Previous research has shown that the source zones of historic and even prehistoric SCR earthquakes are frequently related with enhanced microseismicity over hundreds or even thousands of years. This study seeks to investigate possible source zones for the 1809 event, and possible sources of future damaging earthquakes, by establishing whether earthquakes can be detected on regional structures. To accomplish these goals, we deployed 18 3-component seismographs over a 40-by-35-kilometer area near the Koeberg Nuclear Power Station. The network, which covered the Colenso fault zone, was also near the postulated Milnerton fault, the Ceres-Tulbagh region, and the Cape Town area. The network recorded for three months between August and October 2021. We looked for seismicity around known structures, like the Colenso fault, using supervised machine learning algorithms like PhaseNET, traditional STA/LTA algorithms, and manual inspection in addition to unsupervised machine learning algorithms such as Density-based spatial clustering of applications with noise (DBSCAN) and Bayesian Gaussian Mixture Models (BGMMs). We found 35 occurrences dispersed throughout our research area. These events appear to be organized into three broad groups, the first being an offshore cluster outside of the study region, and the second being a scattered cluster between the Colenso fault system and the postulated Milnerton Fault. The third concentrates on the Colenso Fault system, implying that it may be active. Additional results from our research show that traditional methods like STA/LTA are far less accurate at detecting micro-seismic events than manual inspection of waveform data and machine learning (i.e., where the unsupervised and supervised machine learning algorithms get combined to form an earthquake identification tool).

How to cite: van Zyl, W., Quiros, D., and Sloan, A.: Mapping micro-seismicity around a nuclear power station in stable South Africa through machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-634, https://doi.org/10.5194/egusphere-egu24-634, 2024.

EGU24-2615 | ECS | Orals | NH4.3

What do seismic clusters tell us about fault stability? 

Davide Zaccagnino, Filippos Vallianatos, Giorgios Michas, Luciano Telesca, and Carlo Doglioni

Seismic activity clusters in space and time due to stress accumulation and static and dynamic triggering. Therefore, both moderate and large magnitude events can be preceded by smaller events and also seismic swarms can occur without being succeeded by major shocks – which represents the vast majority of cases.

Unveiling if seismic activity can forewarn mainshocks, being somewhat distinguished by swarms, is an issue of crucial importance for the development of short-term seismic hazard. The analysis of thousand clusters of seismicity before mainshocks in Southern California and Italy highlights that the surface over which selected seismic activity spreads is positively correlated with the magnitude of the impending mainshock, as well as the cumulative seismic moment, the number of earthquakes, the variance of magnitude and its entropy, while no significant difference is observed in the duration, seismic rate, and trends of magnitudes and interevent times between foreshocks and swarms. Our interpretation is that crustal volumes and fault interfaces host more and more correlated seismicity as they become unstable, and some properties of seismic clusters may mark their state of stability. For this reason, large mainshocks tend to occur in more extended correlated regions and because of the scaling of maximum magnitudes with the size of unstable faults. Considering this, the recording of more numerous and energetic cluster activity before mainshocks than during swarms is also reasonable.

In recent years, our ability to track seismic clusters has improved outstandingly, so that their structural and statistical characterization can be performed almost in real time. Therefore, it may be possible to compare the current features of the active seismic cluster with the cumulative distribution functions of past seismicity. However, we would like to stress that foreshocks should not be considered as precursors in the sense that neither they forewarn mainshocks, nor they are physically different from swarms: the precursor is not in seismic activity itself, but in the development of mechanical instability within crustal volumes.

How to cite: Zaccagnino, D., Vallianatos, F., Michas, G., Telesca, L., and Doglioni, C.: What do seismic clusters tell us about fault stability?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2615, https://doi.org/10.5194/egusphere-egu24-2615, 2024.

From October to December 2019, the provinces of Cotabato and Davao del Sur in the Philippines experienced an earthquake sequence that involved five M~6 (Mw 6.4, 6.6, 5.9, 6.5, and 6.7) inland earthquakes. A deep-neural network-based phase picker, PhaseNet, was used to obtain the seismic phases of earthquake waveforms of stations within 200 km from the area of the events for 80 days from October 16 to December 31, 2019. The acquired seismic phases were initially associated and located using the Rapid Earthquake Association and Location (REAL). Subsequently, the initial hypocenter locations were adjusted through relocation utilizing VELEST, with further refinement achieved through a relative relocation technique hypoDD. By employing these methodologies, we successfully created an earthquake catalog that contains ~5,000 earthquakes for the corresponding period. The number of determined earthquakes through this method surpassed the ~3,000 event count reported in the original catalog by DOST-PHIVOLCS which depended solely on manually selected seismic phases. The spatial distribution of the relocated hypocenters reveals two seismic alignments: one trending in the SW-NE direction, parallel to the existing mapped active faults, and the other in the NW-SE direction. These lineaments intersect near the location of the Mw6.4 event, suggesting the presence of a conjugate fault or cross fault. The created earthquake catalog illuminates the spatial and temporal evolution of seismicity following each significant event, offering insights into the detailed patterns that characterize the clustering of aftershocks.

How to cite: Sawi, P., Kita, S., and Bürgmann, R.: Machine-Learning-based Relocation Analysis: Revealing the Spatiotemporal Changes in the 2019 Cotabato and Davao del Sur Earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3482, https://doi.org/10.5194/egusphere-egu24-3482, 2024.

EGU24-3569 | ECS | Posters on site | NH4.3

Testing the Potential of Deep Learning in Earthquake Forecasting 

Jonas Köhler, Wei Li, Johannes Faber, Georg Rümpker, and Nishtha Srivastava

Reliable earthquake forecasting methods have long been sought after, and so the rise of modern data science techniques raises a new question: does deep learning have the potential to learn this pattern? 
In this study, we leverage the large amount of earthquakes reported via good seismic station coverage in the subduction zone of Japan.  We pose earthquake forecasting as a classification problem and train a Deep Learning Network to decide, whether a timeseries of length ≥ 2 years will end in an earthquake on the following day with magnitude ≥ 5 or not.
 
Our method is based on spatiotemporal b value data, on which we train an autoencoder to learn the normal seismic behaviour. We then take the pixel by pixel reconstruction error as input for a Convolutional Dilated Network classifier, whose model output could serve for earthquake forecasting. We develop a special progressive training method for this model to mimic real life use. The trained network is then evaluated over the actual dataseries of Japan from 2002 to 2020 to simulate a real life application scenario. The overall accuracy of the model is 72.3%. The accuracy of this classification is significantly above the baseline and can likely be improved with more data in the future.

How to cite: Köhler, J., Li, W., Faber, J., Rümpker, G., and Srivastava, N.: Testing the Potential of Deep Learning in Earthquake Forecasting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3569, https://doi.org/10.5194/egusphere-egu24-3569, 2024.

EGU24-3684 | Posters on site | NH4.3

Stress Shadows: Insights into Physical Models of Aftershock Triggering 

Jeanne Hardebeck and Ruth Harris

Why some aftershocks appear to occur in stress shadows, regions of Coulomb stress decrease due to a mainshock, is an open question with implications for physical and statistical aftershock models. New machine-learning focal mechanism catalogs make it possible to study the fault orientations of aftershocks occurring in the stress shadows, and test competing hypotheses about their origins. There are three main hypotheses: (1) Aftershocks appear in shadows because of inaccuracy in the computed stress change. (2) Aftershocks in the shadows occur on faults with different orientations than the model receiver faults, and these unexpected fault orientations experience increased Coulomb stress. (3) Aftershocks in the shadows are triggered by dynamic stress changes. We test these three hypotheses on the 2016 Kumamoto and 2019 Ridgecrest sequences. We test Hypothesis 1 through many realizations of the stress calculations with multiple mainshock models, multiple receiver fault orientations based on background events, and a range of coefficients of friction. We find that numerous aftershocks are consistently in the stress shadows. To test Hypothesis 2, we consider whether the individual event focal mechanisms receive an increase of Coulomb stress. Again, we perform many realizations of the stress calculation, this time with receiver fault orientations based on the focal mechanism and its uncertainty. Many of the aftershocks in the shadows consistently show a Coulomb stress decrease on the planes of their focal mechanisms. These results imply that aftershocks do occur in stress shadows, many on fault planes receiving a decrease in static Coulomb stress, contrary to Hypotheses 1 and 2. We test Hypothesis 3 by investigating the modeled dynamic stress changes on the individual event focal mechanisms. Preliminary results show that while the amplitude of the dynamic Coulomb stress change is generally lower on the aftershock nodal planes than on the planes of background events, the amplitude of the dynamic normal stress change is often 20%-100% higher. This suggests a dynamic triggering mechanism related to changing fault strength.

How to cite: Hardebeck, J. and Harris, R.: Stress Shadows: Insights into Physical Models of Aftershock Triggering, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3684, https://doi.org/10.5194/egusphere-egu24-3684, 2024.

With earthquake disasters inflicting immense devastation worldwide, advancing reliable prediction models utilizing diverse data paradigms offers new perspectives to unlock practicable prediction solutions. As reliable earthquake forecasting remains a grand challenge amidst complex fault dynamics, we employ combined finite-discrete element method (FDEM) simulations to generate abundant laboratory earthquake data. We propose a multimodal features fusion model that integrates temporal sensor data and wavelet-transformed visual kinetic energy to predict laboratory earthquakes. Comprehensive experiments under varied stress conditions confirm the superior prediction capability over single modal approaches by accurately capturing stick slip events and patterns. Furthermore, efficient adaptation to new experiments is achieved through fine-tuning of a lightweight adapter module, enabling generalization. We present a novel framework leveraging multimodal features and transfer learning for advancing physics-based, data-driven laboratory earthquake prediction. As increasing multi-source monitoring data becomes available, the established modeling strategies introduced here will facilitate the development of reliable real world earthquake analysis systems.

How to cite: Gao, K.: Laboratory earthquake prediction via multimodal features, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3745, https://doi.org/10.5194/egusphere-egu24-3745, 2024.

EGU24-4379 | ECS | Orals | NH4.3

Magnitude correlation exposes hidden short-term earthquake catalog incompleteness 

Paola Corrado, Marcus Herrmann, and Warner Marzocchi

Current models used for earthquake forecasting assume that the magnitude of an earthquake is independent of past earthquakes, i.e., the earthquake magnitudes are uncorrelated. Nevertheless, several studies have challenged this assumption by revealing correlations between the magnitude of subsequent earthquakes in a sequence. These findings could significantly improve earthquake forecasting and help in understanding the physics of the nucleation process.

We investigate this phenomenon for the foreshock sequence of the first 2019 Ridgecrest event (Mw6.4) using a high-resolution catalog; choosing this foreshock sequence has been guided by a low b-value (~0.68 ± 0.06 after converting local magnitudes to moment magnitudes) and a significant magnitude correlation, even when considering only earthquakes above the completeness level estimated with different methods. To disregard incomplete events in the b-value estimation, we apply the b-positive approach (van der Elst 2021), i.e., using only positive magnitude differences; those magnitude differences are uncorrelated and we obtain a markedly higher b-value (~0.9 ± 0.1). Apparently, the foreshock sequence contained substantial short-term aftershock incompleteness due to a Mw4.0 event.

We observe a similar behaviour for whole Southern California after stacking earthquake sequences. Finally, we generate synthetic catalogs and apply short-term incompleteness to demonstrate that common methods for estimating the completeness level still result in magnitude correlation, indicating hidden incompleteness.

Our findings highlight that (i) existing methods for estimating the completeness level have limited statistical power and the remaining incompleteness can significantly bias the b-value estimation; (ii) the magnitude correlation is the most powerful property to detect incompleteness, so it should supplement statistical analyses of earthquake catalogs.

How to cite: Corrado, P., Herrmann, M., and Marzocchi, W.: Magnitude correlation exposes hidden short-term earthquake catalog incompleteness, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4379, https://doi.org/10.5194/egusphere-egu24-4379, 2024.

EGU24-4958 | Posters on site | NH4.3

Unraveling the Preparatory Processes of the 2023 Kahramanmaraş MW7.8-7.6 Earthquake Doublet 

Fengling Yin and Changsheng Jiang

Within a span of 9 hours on February 6, 2023, two significant earthquakes, with magnitudes of Mw7.8 and Mw7.6, struck the southeastern part of Türkiye and the northern region of Syria, resulting in significant casualties and widespread economic losses. The occurrence of such intense earthquakes in rapid succession on adjacent faults, especially within a highly complex intraplate region with a multi-fault network, poses a rare phenomenon, presenting new challenges for seismic hazard analysis in such areas. In order to investigate whether the preparatory processes for the Mw7.8-7.6 earthquake doublet could be identified on a large spatial scale prior to the seismic events, we employed a data-driven approach for b-value calculation. The difference in b values from the background values (Δb) in a reference period were used as inputs, and the Cumulative Migration Pattern (CMP) method, quantitatively describing the migration of seismic activity, was utilized to calculate the corresponding probability distributions. The results indicate a widespread phenomenon of decreasing b-values in the study area over a decade before the occurrence of the earthquake doublet, revealing a significant enhancement of differential crustal stress over a large region. Additionally, despite not being the region with the most pronounced decrease in b-values, there is a distinct high probability distribution of CMP near the nucleation points of the earthquake doublet, indicating a spatial and temporal "focus" of increased crustal differential stress in the study area, unveiling the preparatory process of the earthquake doublet. This study reveals quantifiable migration patterns over a long-time scale and a large spatial extent, providing new insights into the evolution and occurrence processes of the 2023 Kahramanmaraş Mw7.8-7.6 earthquake doublet. Moreover, it offers potential clues for seismic hazard analysis in such intraplate regions with multiple fault systems.

How to cite: Yin, F. and Jiang, C.: Unraveling the Preparatory Processes of the 2023 Kahramanmaraş MW7.8-7.6 Earthquake Doublet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4958, https://doi.org/10.5194/egusphere-egu24-4958, 2024.

EGU24-5516 | ECS | Posters on site | NH4.3

Asperity distribution and earthquake recurrence time based on patterns of forerunning earthquakes. 

Venkata Gangadhara Rao Kambala and Piotr Senatorski

Abstract. Due to the long recurrence time of the largest earthquakes and the short time covered by seismic catalogues, the potential for the strongest earthquakes in a given region should be estimated based both on combined seismological and geodetic observations, as well as on the developed seismicity models. At the same time, the asperity model, which is a general view of earthquake occurrence in seismic zones, still requires refinement and more solid empirical support.

In this study, we use new data science methods to analyze and interpret various data from selected subduction and collision zones, including Japan, Chile, and Himalaya-Nepal regions. First, we estimate the expected recurrence times of large earthquakes within a given magnitude range as functions of the Gutenberg-Richter’s b values, for  the assumed maximum magnitude and seismic moment deficit accumulation rate due to the tectonic plate movement. Second, we show seismicity patterns and underlying asperity structures using graphs representing the forerunning and afterrunning earthquakes, which are strictly defined based on the location of earthquakes in time and space, as well as their sizes.

In particular, we propose a method to estimate the rupture areas and magnitudes of possible megathrust earthquakes based on seismicity from the last few decades. We use the graph characteristics to distinguish among different seismicity patterns and scenarios. We also argue that changes in these features over time and space can be used to forecast seismicity forecasting.

 

Keywords: Earthquake forecasting, Gutenberg-Richter law, Recurrence time, Asperities, Forerunning earthquakes.

How to cite: Kambala, V. G. R. and Senatorski, P.: Asperity distribution and earthquake recurrence time based on patterns of forerunning earthquakes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5516, https://doi.org/10.5194/egusphere-egu24-5516, 2024.

EGU24-5878 | Posters on site | NH4.3

Forecasting Strong Subsequent Earthquakes in Japan Using NESTORE Machine Learning Algorithm: preliminary results  

Stefania Gentili, Giuseppe Davide Chiappetta, Giuseppe Petrillo, Piero Brondi, Jiancang Zhuang, and Rita Di Giovambattista

NESTORE (Next STrOng Related Earthquake) is a machine learning algorithm for forecasting strong aftershocks during ongoing earthquake clusters. It has already been successfully applied to Italian, Greek and Californian seismicity in the past. A free version of the software in MATLAB (NESTOREv1.0) is available on GitHub. The method is trained on the region under investigation using seismicity characteristics. The obtained region-specific parameters are used to provide the probability, for the ongoing clusters, that the strongest aftershock has a magnitude greater than or equal to that of the mainshock - 1. If this probability is greater than or equal to 0.5, the cluster is labeled as type A, otherwise as type B. The current version of the code is modular and the cluster identification method is based on a window approach, where the size of the spatio-temporal window can be adjusted according to the characteristics of the analyzed region.

In this study, we applied NESTORE to the seismicity of Japan using the Japan Meteorological Agency (JMA) catalogue from 1973 to 2022. To account for the highly complex seismicity of the region, we replaced the cluster identification module with software that uses a stochastic declustering approach based on the ETAS model.

The analysis is performed in increasing time intervals after the mainshock, starting a few hours later, to simulate the evolution of knowledge over time. The analysis showed a high prevalence of clusters where there are no strong earthquakes later than 3 hours after the mainshock, leading to an imbalance between type A and type B classes.

NESTORE was trained with data from 1973 to 2004 and tested from 2005 onwards. The large imbalance in the data was mitigated by carefully analyzing the training set and developing techniques to remove outliers. The cluster type forecasting was correct in 84% of cases.

 

Funded by a grant from the Italian Ministry of Foreign Affairs and International Cooperation and Co-funded within the RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan - NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005) and by the NEar real-tiME results of Physical and StatIstical Seismology for earthquakes observations, modeling and forecasting (NEMESIS) Project (INGV).

How to cite: Gentili, S., Chiappetta, G. D., Petrillo, G., Brondi, P., Zhuang, J., and Di Giovambattista, R.: Forecasting Strong Subsequent Earthquakes in Japan Using NESTORE Machine Learning Algorithm: preliminary results , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5878, https://doi.org/10.5194/egusphere-egu24-5878, 2024.

EGU24-6037 | Orals | NH4.3

Why is  b=1? 

Ian Main and Gina-Maria Geffers

The exponent b of the log-linear frequency-magnitude relation for natural seismicity commonly takes values that are statistically indistinguishable from b=1.  There are some exceptions, notably with respect to focal mechanism and for volcanic and induced seismicity, but it is possible these could be explained at least in part by variability in the dynamic range of measurements between the minimum magnitude of complete reporting and the maximum magnitude, especially where the dynamic range of the statistical sample is small.  However, in laboratory experiments and in discrete element simulations a wide range of b-values for acoustic emissions are consistent (after accounting for systematic differences in the transducer response) with systematic variations in the range  as the stress intensity factor increases from its minimum to its maximum, critical value.  The question remains: why is  an attractor stationary state for large-scale seismicity?  Previous attempts to answer this question have relied on a simple geometric ‘tiling’ argument that is inconsistent with the spatial distribution of earthquake locations, or a hierarchical ‘triple-junction’ model that has not been validated by observation.  Here, we derive a closed analytical solution for the maximum entropy -value, conditional on the assumption that earthquake magnitude scales linearly with the logarithm of rupture area. In the limit of infinite dynamic range, the solution is .  The maximum entropy -value converges to this value asymptotically from above as dynamic range increases for large systems at steady state.  This is in contrast to a previous maximum entropy solution based on analysing the spectrum in ‘natural time’ of earthquake catalogues, where larger samples with greater dynamic range lead to a divergence from .  The new theory is consistent with the trend in b-value convergence from above towards an asymptotic limit of in b=1.027±0.015 at 95% confidence from the global CMT earthquake frequency-moment catalogue for data since 1990.

How to cite: Main, I. and Geffers, G.-M.: Why is  b=1?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6037, https://doi.org/10.5194/egusphere-egu24-6037, 2024.

EGU24-6097 | Orals | NH4.3

The performance of the Foreshock Traffic Light System for the period 2016-2024 

Laura Gulia, Stefan Wiemer, Emanuele Biondini, Bogdan Enescu, and Gianfranco Vannucci

Strong earthquakes are followed by countless smaller events, whose number decays with time: a posteriori, we call them aftershocks. Sometimes, this sequence is interrupted by a larger event, and the “aftershocks” turn out to be foreshocks. In 2019, Gulia and Wiemer have proposed traffic light tool, named the Foreshock Traffic Light System (FTLS), that can discriminate between foreshocks and aftershocks, by monitoring the size distribution of events closely. The model successfully passed the first near real-time test (Gulia et al., 2020). A new version of the code, that can run in real-time, has been recently developed; since testing is the essence of the scientific method and is fundamentally important in seismicity forecast evaluation, we here show the performance of the new version of the FTLS through pseudo-prospective and, when possible, real-time tests on the available seismic sequences between 2016 and 2024.

How to cite: Gulia, L., Wiemer, S., Biondini, E., Enescu, B., and Vannucci, G.: The performance of the Foreshock Traffic Light System for the period 2016-2024, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6097, https://doi.org/10.5194/egusphere-egu24-6097, 2024.

EGU24-6346 | Posters on site | NH4.3

Characterizing clusters with strong subsequent events in Central Italy using RAMONES 

Piero Brondi, Stefania Gentili, Matteo Picozzi, Daniele Spallarossa, and Rita Di Giovambattista

Italy is a country affected by strong seismic activity due to the collision between the African and Euro-Asian plates. In such an area, it often happens that a first strong earthquake (FSE) is followed by a subsequent strong event (SSE) of similar magnitude. In recent years, several studies have attempted to analyze the correlation between the occurrence of a possible SSE in an area and the spatio-temporal distribution of the stress drop on the same area. In this work, we have investigated this relationship in Central Italy by using the Rapid Assessment of MOmeNt and Energy Service (RAMONES), which provides source parameters for events that have occurred in the area since 2007. Using 12900 ML≥2 events available in the RAMONES catalog and a window-based clustering method, we obtained 25 clusters between 2009 and 2017 with magnitude of the FSE greater or equal to 4. Among them are also the clusters corresponding to the L'Aquila earthquake (2009) and the Amatrice earthquake (2016). Looking at the magnitude difference between the FSE and the strongest SSE (DM), it is less than or equal to 1 in 64% of the cases and greater than 1 in 36%. In the first case, we labelled the cluster as type A, in the second case as type B. By analyzing the ratio between seismic energy and seismic moment provided by RAMONES over the entire duration of the cluster, we found that almost all A clusters correspond to a maximum change in apparent stress over time larger than the one of B clusters. To a first approximation, this observation also proves to be true when analyzing the seismicity before the strongest SSE or at the first SSE. These preliminary results are therefore encouraging for future use in forecasting SSEs in Central Italy.

Funded by the NEar real-tiME results of Physical and StatIstical Seismology for earthquakes observations, modeling and forecasting (NEMESIS) Project (INGV).

How to cite: Brondi, P., Gentili, S., Picozzi, M., Spallarossa, D., and Di Giovambattista, R.: Characterizing clusters with strong subsequent events in Central Italy using RAMONES, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6346, https://doi.org/10.5194/egusphere-egu24-6346, 2024.

Exploring the potential relationship between an earthquake’s onset and its final moment magnitude (Mw) is a fundamental question in earthquake physics. This has practical implications, as rapid and accurate magnitude estimation is essential for effective early warning systems.

This study employs a novel approach of a hybrid Convolutional Neural Network (CNN) - Recurrent Neural Network (RNN) models to estimate moment magnitude from just the first two seconds of source time functions (STFs), which is significantly shorter than the entire source duration. We use STFs of large earthquakes from the SCARDEC database, which applies a deconvolution method on teleseismic body waves, considering only events with a Mw > 7 and an initial STF value smaller than 1017 Nm/s to avoid potential bias. Additionally, we incorporate STFs from physics-based numerical simulations of earthquake cycles on nonplanar faults, varying in roughness levels and fault lengths. These simulations exhibit substantial variability in earthquake magnitude and slip behavior between events. The reported methodology uses the information contained in the initial characteristics of the STF, its temporal derivative, and the associated seismic moment, capturing the valuable insights present in the initial energy release about the final moment magnitude.

For the simulated data, the CNN-RNN model demonstrates a good correlation between the initial 2 seconds of the STF and the final event magnitude. Correlation coefficients close to 0.8 and root mean squared errors (RMSE) around 0.25 for magnitudes between 5 and 7.5 showcase the model’s ability to learn and generalize effectively from diverse earthquake scenarios. While results for natural earthquakes from the SCARDEC database remain promising (RMSE of 0.27), the correlation coefficient is lower (0.31), suggesting a weaker relationship than simulated data. This discrepancy might be attributed to the narrower band of magnitudes (7 to 7.5) within SCARDEC data used here, potentially limiting the model’s ability to discern subtle variations and establish a stronger correlation. Further, as an earthquake's fractional duration, 2 sec/source duration, increases, the model's error consistently decreases as expected. Finally, most predictions fall within a narrow range of 1% error, and nearly 90% of samples across diverse durations satisfy a set 5% error threshold. This consistent performance of the hybrid CNN-RNN model across varying source durations, magnitude ranges, and fault characteristics underscores the model's adaptability and robustness in handling diverse earthquake scenarios. While we mostly use here STFs from simulated earthquakes, continuous learning and refinement against reliable and diverse STFs obtained from teleseismic data, when available, are key to enhancing the potential of these CNN-RNN models for a better understanding of the onset-magnitude correlation in natural earthquakes.

How to cite: Rodda, G. K. and Tal, Y.: Analyzing Earthquake's Onset-Magnitude Correlation Using Machine Learning and Simulated and Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7459, https://doi.org/10.5194/egusphere-egu24-7459, 2024.

EGU24-8744 | ECS | Posters on site | NH4.3

Exploring the 2019 Ridgecrest seismic data with unsupervised deep learning  

Sarah Mouaoued, Michel Campillo, and Léonard Seydoux

We analyze the seismic data continuously recorded in the vicinity of the Mw7.4 2019 Ridgecrest earthquake with an unsupervised deep learning method proposed by Seydoux et al. (2020), in search of seismic signatures of physical signatures of the earthquake preparation phase. We downloaded data from the 3 different stations B918, with a 100 Hz sampling frequency, SRT and CLC with a 40 Hz sampling frequency. Using a scattering network combined with an independent component analysis, we define stable waveform features and cluster the continuous signals extracted from a sliding window before proposing cluster-based interpretations of the seismic signals. We also further discuss our results with external datasets such as independently-obtained seismicity catalogs in the area. We also investigate a manifold-learning-based representation (UMAP) of the data in 2D from the scattering network. According to our first results merged with a catalog analysis we are able to separate various events from the noise and identify several types of seismicity and noises. 

How to cite: Mouaoued, S., Campillo, M., and Seydoux, L.: Exploring the 2019 Ridgecrest seismic data with unsupervised deep learning , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8744, https://doi.org/10.5194/egusphere-egu24-8744, 2024.

EGU24-8786 | Orals | NH4.3

A Machine Learning-based Method for Identifying Segmented Fault Surfaces Through Hypocenter Clustering 

Ester Piegari, Giovanni Camanni, Martina Mercurio, and Warner Marzocchi

We present a method for automatically identifying segmented fault surfaces through the clustering of earthquake hypocenters without prior information. Our approach integrates density-based clustering algorithms (DBSCAN and OPTICS) with principal component analysis (PCA). Using the spatial distribution of earthquake hypocenters, DBSCAN detects primary clusters, which represent areas with the highest density of connected seismic events. Within each primary cluster, OPTICS identifies nested higher-order clusters, providing information on their quantity and size. PCA analysis is then applied to the primary and higher-order clusters to assess eigenvalues, enabling the differentiation of seismicity associated with planar features and distributed seismicity that remains uncategorized. The identified planes are subsequently characterized in terms of their location and orientation in space, as well as their length and height. By applying PCA analysis before and after OPTICS, a planar feature derived from a primary cluster can be interpreted as a fault surface, while planes derived from high-order clusters can be interpreted as fault segments within the fault surface. The consistency between the orientation of illuminated fault surfaces and fault segments, and that of the nodal planes of earthquake focal mechanisms calculated along the same faults, supports this interpretation. We show applications of the method to earthquake hypocenter distributions from various seismically active areas (Italy, Taiwan, California) associated with faults exhibiting diverse kinematics.

How to cite: Piegari, E., Camanni, G., Mercurio, M., and Marzocchi, W.: A Machine Learning-based Method for Identifying Segmented Fault Surfaces Through Hypocenter Clustering, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8786, https://doi.org/10.5194/egusphere-egu24-8786, 2024.

Seismic swarms are characterized by intense seismic activity strongly clustered in time and space and without the occurrence of a major event that can be considered as the mainshock. Such intense seismic activity is most commonly associated with external aseismic factors, as pore-fluid pressure diffusion, aseismic creep, or magmatic intrusion that can perturb the regional stresses locally triggering the observed seismicity. These factors can control the spatiotemporal evolution of seismic swarms, frequently exhibiting spatial expansion and migration of event hypocenters with time. This phenomenon, termed as earthquake diffusion, can be highly anisotropic and complex, with earthquakes occurring preferentially along fractures and zones of weakness within the heterogeneous crust, presenting anisotropic diffusivities that may locally vary over several orders of magnitude. The efficient modelling of the complex spatiotemporal evolution of seismic swarms, thus, represents a major challenge. Herein, we develop a stochastic framework based on the well-established Continuous Time Random Walk (CTRW) model, to map the spatiotemporal evolution of seismic swarms. Within this context, earthquake occurrence is considered as a point-process in space and time, with jump lengths and waiting times between successive earthquakes drawn from a joint probability density function. The spatiotemporal evolution of seismicity is then described with an appropriate master equation and the time-fractional diffusion equation (TFDE). The applicability of the model is demonstrated in the 2014 Long Valley Caldera (California) seismic swarm, which has been associated with a pore-fluid pressure triggering mechanism. Statistical analysis of the seismic swarm in the light of the CTRW model shows that the mean squared distance of event hypocenters grows slowly with time, with a diffusion exponent much lower than unity, as well as a broad waiting times distribution with asymptotic power law behavior. Such properties are intrinsic characteristics of anomalous earthquake diffusion and particularly subdiffusion. Furthermore, the asymptotic solution of the TFDE can successfully capture the main features of earthquake progression in time and space, showing a peak of event concentration close to the initial source of the stress perturbation and a stretched relaxation of seismicity with distance. Overall, the results demonstrate that the CTRW model and the TFDE can efficiently be used to decipher the complex spatiotemporal evolution of seismic swarms.

Acknowledgements

The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 00256). 

How to cite: Michas, G. and Vallianatos, F.: Spatiotemporal Evolution of Seismic Swarms in the light of the Continuous Time Random Walk Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9184, https://doi.org/10.5194/egusphere-egu24-9184, 2024.

EGU24-9366 | ECS | Orals | NH4.3

Deep Learning for Higher-Order Aftershock Forecasting in Near-Real-Time 

Leila Mizrahi and Dario Jozinović

The use of machine learning (ML) methods for earthquake forecasting has recently emerged as a promising avenue, with several recent publications exploring the application of neural point processes. Such models, in contrast to those currently applied in practice, offer the flexibility to incorporate additional datasets alongside earthquake catalogs, indicating potential for enhanced earthquake forecasting capabilities in the future. However, with a forecasting performance that currently remains similar to that of the agreed-upon benchmark, the Epidemic-Type Aftershock Sequence (ETAS) model, the black-box nature of ML models poses a challenge in communicating forecasts to lay audiences. The ETAS model has stood the test of time and is relatively simple and comprehensively understood, with few empirically derived laws describing aftershock triggering behavior. A main drawback of ETAS is its reliance on large numbers of simulations of possible evolutions of ongoing earthquake sequences, which is typically associated with long computation times or resources required for parallelization.

In this study, we propose a deep learning approach to emulate the output of the well-established ETAS model, bridging the gap between traditional methodologies and the potential advantages offered by machine learning. By focusing on modeling the temporal behavior of higher-order aftershocks, our approach aims to combine the interpretability of the ETAS model with the computational efficiency intrinsic to deep learning.

Evaluated using commonly applied metrics of both the ML and earthquake forecasting communities, our approach and the traditional, simulation-based approach are shown to perform very similarly in describing synthetic datasets generated with the simulation-based approach. Our method has two major benefits over the traditional approach. It is faster by several orders of magnitude, and it is not susceptible to being influenced by the presence (or absence) of individual 'extreme' realizations of the process, and thus enables accurate earthquake forecasting in near-real-time.

How to cite: Mizrahi, L. and Jozinović, D.: Deep Learning for Higher-Order Aftershock Forecasting in Near-Real-Time, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9366, https://doi.org/10.5194/egusphere-egu24-9366, 2024.

EGU24-10426 | Posters on site | NH4.3

Unraveling the dynamics of the 2021 Arkalochori foreshock swarm: a fusion of machine-learning models and non-extensive statistical physics 

Filippos Vallianatos, Vasilis Kapetanidis, Andreas Karakonstantis, and Georgios Michas

On 27 September 2021, a significant Mw=6.0 earthquake struck near Arkalochori village in central Crete, Greece, about ~25 km south-southeast of Heraklion city. Remarkably, an extensive seismic swarm lasting nearly four months preceded the mainshock, activating structures near its hypocenter. In this work, we investigate the foreshock swarm by leveraging waveform data from seismological stations of the Hellenic Unified Seismic Network (HUSN) that were operational on Crete Island during its occurrence. Our approach involves the utilization of the EQ-Transformer machine-learning model, pre-trained with a diverse dataset comprising ~50,000 earthquakes sourced from the INGV bulletin (INSTANCE dataset). We employ a sophisticated methodology that incorporates a Bayesian Gaussian Mixture Model (GaMMA) to associate automatically picked P- and S-wave arrival times with event origins. Subsequently, the events are located using a local velocity model. Our findings reveal the detection and precise location (ERH < 1 km, RMS < 0.2 s) of over 3,400 events in the activated area between late May and 26 September 2021, showcasing a substantial increase compared to existing catalogs derived from routine analysis using conventional methods. The spatiotemporal distribution of the foreshock seismicity is examined to unveil migration patterns, potentially linked to fluid dynamics and pore-pressure diffusion. Furthermore, we explore the evolution of seismicity concerning different structures activated during the seismic swarm, with a particular focus on the final days leading up to the mainshock. Finally, our results are subjected to analysis through non-extensive statistical physics methods, providing a comprehensive understanding of the complex dynamics culminating in the Arkalochori earthquake sequence.

Acknowledgements

We would like to thank the personnel of the institutions participating to the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) for the installation, operation and management of the seismological stations used in this work. The present study is co-funded by the Special Account for Research Grants (S.A.R.G.) of the National and Kapodistrian University of Athens.

How to cite: Vallianatos, F., Kapetanidis, V., Karakonstantis, A., and Michas, G.: Unraveling the dynamics of the 2021 Arkalochori foreshock swarm: a fusion of machine-learning models and non-extensive statistical physics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10426, https://doi.org/10.5194/egusphere-egu24-10426, 2024.

Our research aims to investigate the three recent and powerful earthquakes in the Ionian Sea region which occurred on January 26, 2014, November 17, 2015, and October 25, 2018, of magnitude Mw 6.1, Mw 6.0, and Mw 6.6 respectively using the complexity theory and the non-extensive statistical physics (NESP).

The scaling properties that have been observed in the three aftershock sequences of the recent strong earthquakes that took place in the region of Ionian islands are presented. To analyze the evolution of three aftershock sequences, we plotted the cumulative number of aftershocks N(t) over time. Additionally, we used a modified version of Omori's law to study the temporal decay of aftershock activity.

Based on non-extensive statistical physics, the analysis of interevent times distribution suggests that the system is in an anomalous equilibrium, with a crossover from anomalous (q>1) to normal (q=1) statistical mechanics for large interevent times. The obtained values of q indicate that the system has either one or two degrees of freedom. Furthermore, the migration of aftershock zones can be scaled as a function of the logarithm of time. This scaling is discussed in terms of rate-strengthening rheology, which governs the evolution of the afterslip process.

Acknowledgements

The present study is co-funded by the Special Account for Research Grants (S.A.R.G.) of the National and Kapodistrian University of Athens.

How to cite: Pavlou, K., Vallianatos, F., and Michas, G.: Spatio-temporal evolution and scaling laws analysis of the recent three strongest earthquakes in the Ionian Sea region during the period 2014-2019., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11734, https://doi.org/10.5194/egusphere-egu24-11734, 2024.

EGU24-13405 | ECS | Posters on site | NH4.3

Pseudo-prospective earthquakes forecasting experiment in Italy based on temporal variation of the b-value of the Gutenberg-Richter law. 

Emanuele Biondini, Flavia D'Orazio, Barbara Lolli, and Paolo Gasperini

The analysis of space-time variations of the b-value of the frequency-magnitude distribution of earthquakes can be considered an important indicator in understanding the processes that precede strong earthquake events. Variations in b-value can provide valuable information on the stress state and probability of earthquake occurrence in a specific geographical region. By analyzing spatial variations in b-value, changes in local tectonic conditions can be identified, highlighting areas where seismic risk may increase. Similarly, the analysis of temporal variations in b-value can reveal patterns preceding seismic events, providing a possible precursor signal. Such variations could be the result of complex geological processes, such as the progressive accumulation of stress along active faults or the presence of underground fluids that influence fault dynamics. In fact, as it has been observed in many cases, the b-value tends to descend in the preparatory phases of a strong earthquake, and it increases suddenly after the mainshock occurrence.

To evaluate such a hypothesis, in this work, an alarm-based forecasting method that uses b-value space-time variations as a precursor signal is implemented. The forecasting method has been retrospectively calibrated and optimized for the period 1990-2011 to forecast Italian shallow earthquake (Z<50 km) of magnitude larger than 5.0.

The method has been than applied pseudo-prospectively over the period 2011-2022 and the forecasting skills have been assessed using specific test and statistics for alarm-based models. Such forecasting skills have been also compared with those of another alarm-based earthquake forecasting model that use the occurrence of potential foreshock as precursor signal.

How to cite: Biondini, E., D'Orazio, F., Lolli, B., and Gasperini, P.: Pseudo-prospective earthquakes forecasting experiment in Italy based on temporal variation of the b-value of the Gutenberg-Richter law., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13405, https://doi.org/10.5194/egusphere-egu24-13405, 2024.

EGU24-13573 | Posters on site | NH4.3

A Bayesian transdimensional approach to estimate temporal changes in the b-value distribution without truncating catalogs 

Marine Laporte, Stéphanie Durand, Blandine Gardonio, Thomas Bodin, and David Marsan

The frequency/magnitude distribution of earthquakes can be approximated by an exponential law whose exponent is the so-called b-value. The b-value is routinely used for probabilistic seismic hazard assessment. In this context we propose to estimate the temporal variations of the b-value together with its uncertainties. The b-value is commonly estimated using the frequentist approach of Aki (1965), but biases may arise from the choice of completeness magnitude (Mc), the magnitude below which the exponential law is no longer valid. Here we propose to describe the full frequency-magnitude distribution of earthquakes by the product of an exponential law with a detection law. The latter is characterized by two parameters, μ and σ, that we jointly estimate with b-value within a Bayesian framework. In this way, we use all the available data to recover the joint probability distribution for b-value, μ and σ. Then, we extend this approach for recovering temporal variations of the three parameters. To that aim, we randomly explore with a Markov chain Monte Carlo (McMC) method in a transdimensional framework a large number of time variation configurations of the 3 parameters. This provides posterior probability distributions of the temporal variations in b-value, μ and σ.  For an application to a seismic catalog of far-western Nepal, we show that the probability distribution of the b-value remains stable with larger uncertainties during the monsoon period when the detectability decreases significantly . This confirms that we can see variations in the b-value that are independent of variations in detectability. Our results can be compared with the results and interpretations obtained using the b-positive approach. We hope that further applications to real and experimental data can provide statistical constraints on the b-value variations and help to better understand the physical meaning behind these variations.

How to cite: Laporte, M., Durand, S., Gardonio, B., Bodin, T., and Marsan, D.: A Bayesian transdimensional approach to estimate temporal changes in the b-value distribution without truncating catalogs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13573, https://doi.org/10.5194/egusphere-egu24-13573, 2024.

EGU24-14304 | Posters on site | NH4.3

Comparative Analysis of Seismic Clustering: Deterministic Techniques vs. Probabilistic ETAS Model 

Giuseppe Falcone, Ilaria Spassiani, Stefania Gentili, Rodolfo Console, Maura Murru, and Matteo Taroni

Short-term seismic clustering, a crucial aspect of seismicity, has been extensively studied in literature. Existing techniques for cluster identification are predominantly deterministic, relying on specific constitutive equations to define spatiotemporal extents. Conversely, probabilistic models, such as the Epidemic Type Aftershock Sequence (ETAS) model, dominate short-term earthquake forecasting. The ETAS model, known for its stochastic nature, has been employed to decluster earthquake catalogs probabilistically. However, the challenge arises when selecting a probability threshold for cluster identification, potentially distorting the model's underlying hypothesis.
This study aims to assess the consistency between seismic clusters identified by deterministic window-based techniques specifically, Gardner-Knopoff and Uhrhammer-Lolli-Gasperini and the associated probabilities predicted by the ETAS model for events within these clusters. Both deterministic techniques are implemented in the NESTOREv1.0 package and applied to the Italian earthquake catalog spanning from 2005 to 2021.
The comparison involves evaluating, for each event within an identified cluster, both the probability of independence and the expected number of triggered events according to the ETAS model. Results demonstrate overall agreement between the two cluster identification methods, with identified clusters exhibiting consistency with corresponding ETAS probabilities. Any minor discrepancies observed can be attributed to the fundamentally different nature of the deterministic and probabilistic approaches.
This research is supported by a grant from the Italian Ministry of Foreign Affairs and International Cooperation.

How to cite: Falcone, G., Spassiani, I., Gentili, S., Console, R., Murru, M., and Taroni, M.: Comparative Analysis of Seismic Clustering: Deterministic Techniques vs. Probabilistic ETAS Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14304, https://doi.org/10.5194/egusphere-egu24-14304, 2024.

Challenges in Aftershock Forecasting

The probabilistic evaluation of aftershock activity relies on two empirical rules: the Gutenberg–Richter law (GR law) and the Modified Omori law (MO law). An important issue arises in aftershock observation, particularly when regarding the technical aspects of seismic monitoring, where smaller earthquakes are more challenging to detect than larger ones.  In cases where records of smaller seismic events are absent, the b value of the GR law and the K value of the MO law tend to be underestimated. This study was conducted to develop a model that corrects underestimation of these parameters based on main shock information.

 

Data and Methodology

Seismic source data from the Japan Meteorological Agency were used, including the main shock – aftershock sequence magnitudes, latitude and longitude of the epicenter, and occurrence times. Using data for the periods immediately after the main shock to 3 hours, 1 day, 30 days, and 90 days, calculations were performed on data to ascertain the K value of the MO law and the b value of the GR law. The objective was to investigate the relation between these parameters and the main shock magnitude (hereinafter, M0). Based on these relations, methodologies for correcting parameters were explored.

 

Results and Discussion

  • Relation between M0 and parameters

Significant negative correlation was found between the M0 and the b value, with larger M0 values associated with smaller b values. Furthermore, correlation was stronger for b values closer to the immediate aftermath of the main shock. This strong correlation suggests that larger M0 values are more likely to result in the omission of weaker seismic events from the data. The omission of earthquakes is particularly noticeable immediately following occurrence of the main shock. Similarly, a tendency was observed for the K value to be underestimated immediately after the main shock, when M0 is larger.

  • Parameter corrections

We introduce new parameters, b' and K', defined as shown below.

Larger values of b' and K' indicate underestimation of parameters at 3 hours after the main shock compared to 1 day after the main shock. Using these parameters, we perform linear regression analysis with M0 as the independent variable and b' and K' as dependent variables to estimate 1 day post-main-shock parameters from the 3 hours post-main-shock values.

The precisions of the estimated values are compared as shown in Figure 1.

Figure1:The precisions of the estimated values

Estimation of b shows superior accuracy compared to that obtained using earlier methodologies and conventional approaches used by the Japan Meteorological Agency. Estimated values of K show that systematic errors have been improved with the methodology used for this study. Using these corrected parameters, Figure 2 presents a comparison of the predicted aftershock numbers from 3 hours to 1 day after the main shock with the actual values. As the figure shows, on average, the methodology used for this provides favorable accuracy of predictions.

Figure2:The accuracy of Aftershock Predictions

How to cite: Hashimoto, R. and Kuzuha, Y.: Advancement of Aftershock Distribution Prediction Model Following a Main Shock – Examining Parameter Correction Methods for Predictive Formula Parameters Based on Main Shock Information –, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14398, https://doi.org/10.5194/egusphere-egu24-14398, 2024.

EGU24-15724 | Orals | NH4.3

Detect and characterize swarm-like seismicity 

Luigi Passarelli, Simone Cesca, Leila Mizrahi, and Gesa Petersen

Tectonic earthquake swarms exhibit a distinct temporal and spatial pattern compared to mainshock-aftershock sequences. Unlike the latter ones, where the earthquake sequence typically starts with the largest earthquake that triggers an Omori-Utsu temporal decay of aftershocks, earthquake swarms show a unique increase in seismic activity without a clear mainshock. The largest earthquake(s) in a swarm sequence often occur(s) later, and the sequence consists of multiple earthquake bursts showing spatial migration. This erratic clustering behavior of earthquake swarms arises from the interplay between the long-term accumulation of tectonic elastic strain and short-term transient forces. Detecting and investigating earthquake swarms challenges the community and ideally requires an unsupervised approach, which has led in recent decades to the emergence of numerous algorithms for earthquake swarm identification.

In a comprehensive review of commonly used techniques for detecting earthquake clusters, we applied a blend of declustering algorithms and machine learning clustering techniques to synthetic earthquake catalogs produced with a state-of-the-art ETAS model, with a time-dependent background rate mimicking realistic swarm-like sequences. This approach enabled the identification of boundaries in the statistical parameters commonly used to distinguish earthquake cluster types, i.e., mainshock-aftershock clusters versus earthquake swarms. The results obtained from synthetic data helped to have a more accurate classification of seismicity clusters in real earthquake catalogs, as it is the case for the 2010-2014 Pollino Range (Italy) seismic sequence, the Húsavík-Flatey transform fault seismicity (Iceland), and the regional catalog of Utah (USA). However, the classification obtained through automated application of these findings to real cases depends on the clustering algorithm utilized, the statistical completeness of catalogs, the spatial and temporal distribution of earthquakes, and benefits of a posteriori manual inspection. Nevertheless, the systematic assessment and comparison of commonly used methods - benchmarked in this work to synthetics catalogs and real seismicity – allows the community to have clear and thorough guidelines to identify swarm-like seismicity.

How to cite: Passarelli, L., Cesca, S., Mizrahi, L., and Petersen, G.: Detect and characterize swarm-like seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15724, https://doi.org/10.5194/egusphere-egu24-15724, 2024.

Determining mainshocks from an ongoing seismic sequence poses a challenge for real-time hazard assessment. This study aims to address this issue by analyzing temporal variations in the b-value derived from the Gutenberg-Richter law, with a focus on moderate-to-large events in Yunnan province, southwest China. Yunnan is well known to experience frequent earthquakes due to the convergence of the Indian and Eurasian tectonic plates, along with its complex subsurface geological structure and active fault zones. Earthquake data were analyzed from the Unified National Catalog over the period from January 2000 through December 2022 and the magnitude of completeness is 1.4. We selected seismic sequences where the mainshock magnitudes were above 5. We employed a temporal b-value calculation approach, utilizing a minimum of 10 years of seismic data and including earthquakes within 20 km from the mainshock hypocenter. We used the long-term average b-value preceding the mainshock as the reference. Specifically, we compared the temporal b-value variation calculated for the one-month period following each mainshock to the reference b-value. In total, we investigated 23 sequences in the region. The b-value increased by 10% or more for 4 sequences and by <10% for 3 sequences. Three sequences showed b-value reduction. Insufficient data prevented analysis of 13 other sequences. To conclude, assessing temporal b-value variations is an active research topic to evaluate ongoing earthquake sequences. By testing the application in Yunnan, our b-value is able to help us identify a few mainshock-aftershock sequences. However, we also observe controversial cases. This limitation poses challenges to rapidly determine mainshocks in operational decision-making applications.

How to cite: Lau, T. L. and Yang, H.: Evaluating the Utility of b-Value for Discriminating Foreshocks and Mainshocks in Yunnan, southwest China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16739, https://doi.org/10.5194/egusphere-egu24-16739, 2024.

EGU24-17178 | ECS | Posters on site | NH4.3

Towards a Deep Learning Approach for Data-Driven Short-Term Spatiotemporal Earthquake Forecasting  

Foteini Dervisi, Margarita Segou, Brian Baptie, Ian Main, and Andrew Curtis

The development of novel deep learning-based earthquake monitoring workflows has led to a rapid increase in the availability of earthquake catalogue data. Earthquake catalogues are now being created by deep learning algorithms at significantly reduced processing times compared to catalogues built by human analysts and contain at least a factor of ten more earthquakes. The use of these rich catalogues has been shown to have led to improvements in the predictive power of statistical and physics-based forecasts. Combined with the increasing availability of computational power, which has greatly contributed to the recent breakthrough in the field of artificial intelligence, the use of rich datasets paired with machine learning workflows seems to be a promising approach to uncovering novel insights about earthquake sequences and discovering previously undetected relationships within earthquake catalogues.

Our focus is on employing deep learning architectures to produce high-quality earthquake forecasts. Our hypothesis is that deep neural networks are able to uncover underlying patterns within rich earthquake catalogue datasets and produce accurate forecasts of earthquakes, provided that a representative dataset that accurately reflects the properties of earthquake sequences is used for training. We use earthquake catalogue data from different geographical regions to build a time series of spatiotemporal maps of past seismicity. We then split this time series into training, validation, and test datasets in order to explore the ability of deep neural networks to capture patterns within sequences of seismicity maps and produce short-term spatiotemporal earthquake forecasts.

We assess the performance of the trained deep learning-based forecasting models by using metrics from the machine learning and time-series forecasting domains. We compare the trained models against a null hypothesis, the persistence model, which assumes no change between consecutive time steps and is commonly used as a baseline in various time series forecasting settings. The persistence null hypothesis has been proven to be a very effective model due to the fact that when only background seismicity is observed, there is very little change between consecutive time steps. We also evaluate the relative performance of different deep learning architectures and assess their suitability for dealing with our specific problem. We conclude that deep learning techniques are a promising alternative to disciplinary statistics and physics-based earthquake forecasting methods as, once trained, deep learning models have the potential of producing high-quality short-term earthquake forecasts within seconds. This realisation can influence the future of operational earthquake forecasting and earthquake predictability. 

How to cite: Dervisi, F., Segou, M., Baptie, B., Main, I., and Curtis, A.: Towards a Deep Learning Approach for Data-Driven Short-Term Spatiotemporal Earthquake Forecasting , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17178, https://doi.org/10.5194/egusphere-egu24-17178, 2024.

EGU24-17967 | Orals | NH4.3

The Effect of Data Limitations on Earthquake Forecasting Model Selection 

Marta Han, Leila Mizrahi, and Stefan Wiemer

In our recent study, we have developed an ETAS-based (Epidemic-Type Aftershock Sequence; Ogata, 1988) time-dependent earthquake forecasting model for Europe. Aside from inverting a basic set of parameters describing aftershock behaviour on a highly heterogeneous dataset, we have proposed several model variants, focusing on implementing the knowledge about spatial variations in the background rate inferred by ESHM20 already during the inversion of ETAS parameters, fixing the term dictating the productivity law to specific values to balance the more productive triggering by high-magnitude events (productivity law) with their much rarer occurrence (GR law), and using the b-positive method for the estimation of the b-value.

When testing the model variants, we apply the commonly used approach of performing retrospective tests on each model to check for self-consistency over long time periods and pseudo-prospective tests for comparison of models on one-day forecasting periods during seven years. While such pseudo-prospective tests reveal that some models indeed outperform others, for other model pairs, no significant performance difference was detected.

Here, we investigate in more detail the conditions under which performance differences of two competing models can be detected with statistical significance. Using synthetic tests, we investigate the effects of a catalog’s size and the magnitude range it covers on the significance of model performance difference. This will provide insight into whether recording many small events can, in this sense, replace having a large enough dataset of higher-magnitude events. Furthermore, due to the underrepresentation (or absence) of high-magnitude earthquakes in both training and testing data, both the models and tests are prone to overfitting to small events, potentially resulting in forecasts that underestimate both productivity of sequences with a high-magnitude main event and probabilities that a larger earthquake will follow such an event. We focus on defining metrics that highlight these properties as they are often of interest when applying time-dependent forecasting models to issuing operational earthquake forecasts.

How to cite: Han, M., Mizrahi, L., and Wiemer, S.: The Effect of Data Limitations on Earthquake Forecasting Model Selection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17967, https://doi.org/10.5194/egusphere-egu24-17967, 2024.

EGU24-20167 | ECS | Orals | NH4.3

Identification of Earthquakes and Anthropogenic Events in Madagascar 

Hoby N.T. Razafindrakoto and A. Tahina Rakotoarisoa

Earthquake catalog is a key element in seism hazards. However, it may be contaminated by non-natural earthquake sources. Hence,
This study aims to discriminate natural and non-natural earthquakes through machine learning techniques and spatio-temporal distribution of the events. 
First, we propose a Convolutional Neural Network based on spectrograms to perform the waveform classification. It is targeted to applications in Madagascar. The approach consists of three main steps: (1) generation of the time–frequency representation of ground-motion recordings (spectrogram); (2) training and validation of the model using spectrograms of ground shaking; (3) testing and prediction. To measure the compatibility between output predictions and given ground truth labels, we adopt the commonly used loss function and accuracy measure. Given that the spatial distribution of the seismic data in Madagascar is non-uniform, we perform two-step analyses. First, we adopt a supervised approach for 6051 known events in the central part of Madagascar. Then, we use the outcome for the second step of training and perform the prediction for non-categorized events throughout the country. The results show that our model has the potential to separate earthquakes from mining-related events. For the supervised approach, among the 20% used for testing, 97.48% and 2.52% of the events give correct and incorrect labels, respectively. These pre-trained data are subsequently used to perform predictions for unlabeled events throughout Madagascar. Our results show that the model could learn the features of the classes even for data coming from different parts of Madagascar.
From the analyses of the spatio-temporal patterns of seismicity, we also found evidence of induced earthquakes associated with the heavy-oil exploration in Tsimiroro, Madagascar with an increase in the rate of earthquake occurrence in 2022.

How to cite: Razafindrakoto, H. N. T. and Rakotoarisoa, A. T.: Identification of Earthquakes and Anthropogenic Events in Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20167, https://doi.org/10.5194/egusphere-egu24-20167, 2024.

EGU24-12 | ECS | Posters on site | NH9.1 | Highlight

Understanding fatal landslides on a global scale: insights from topographic, climatic, and anthropogenic perspectives 

Seckin Fidan, Hakan Tanyas, Abdullah Akbas, Luigi Lombardo, David N. Petley, and Tolga Gorum

Landslides are a common global geohazard that lead to substantial loss of life and socio-economic damage annually. Landslides are becoming more common due to climate change and anthropogenic disturbance, threatening sustainable development in vulnerable areas. Previous studies on fatal landslides have focussed on inventory development; spatial and temporal distributions; the role of precipitation and/or seismic forcing; and human impacts. However, their climatological, topographic, and anthropogenic characterization on a global scale has been neglected. Here, we present the association of natural and anthropogenically induced landslides in the Global Fatal Landslide Database (GFLD) with topographic, climatic, and anthropogenic factors, focusing on their persistent spatial patterns. The majority of natural (69.3%) and anthropogenic (44.1%) landslides occur in mountainous areas in tropical and temperate regions, which are also characterized by the highest casualty rates per group (66.7% and 43.0%, respectively). However, they significantly differ in terms of their morphometric footprint. Fatal landslides triggered by natural variables occur mostly in the highest portions of the topographic profile, where human disturbance is minimal. As for their anthropogenic counterpart, these failures cluster at much lower altitudes, where slopes are gentler, but human intervention is greater due to a higher population density. Our results demonstrate that fatal landslides have a heterogeneous distribution on different macro landforms characterized by different topographic, climatic, and population conditions. Our observations also point towards land cover changes being a critical factor in landscape dynamics, stressing human pressure as a discriminant cause/effect term for natural vs. human-induced landslide fatalities.

How to cite: Fidan, S., Tanyas, H., Akbas, A., Lombardo, L., Petley, D. N., and Gorum, T.: Understanding fatal landslides on a global scale: insights from topographic, climatic, and anthropogenic perspectives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12, https://doi.org/10.5194/egusphere-egu24-12, 2024.

EGU24-1451 | ECS | Posters on site | NH9.1

A vulnerability framework for a global flood catastrophe model 

Conor Lamb, Izzy Probyn, Oliver Wing, James Daniel, Florian Elmer, and Malcolm Haylock

In recent years the precision and skill of global flood hazard models has increased dramatically. This, alongside developments allowing for hazard model conversion to stochastic event sets and the open-sourcing of catastrophe modeling software, have opened up the possibilities of developing detailed and skillful global flood catastrophe models; assessing not just average risk but also the possible impacts of major flood events and the probability distribution of annual losses. In order to realize these possibilities, it is necessary to develop a global vulnerability framework that appropriately represents the state of the art in vulnerability modeling whilst being flexible to user inputs and faithfully representing uncertainties. 

Here, we present a framework for implementing a flexible vulnerability module within a global flood catastrophe model. Vulnerability curves are derived for a variety of occupancies (residential, commercial, industrial), for both building and contents losses. The mean loss ratio curves are derived from literature and commercial datasets before being normalized and fit to a family of logarithmic functions of depth, which can be adjusted for varying property characteristics. Uncertainty distributions are parameterised using a 4 parameter beta model and derived from a large insurance claims dataset (~2 million claims). 

Finally, using the same large claims dataset, we explore the event-level correlation of the quantiles sampled within our uncertainty distribution. Specifically, we evaluate the extent to which the quantiles sampled of the uncertainty distribution, in a Monte Carlo approach, should be clustered for each event. This is vital for correctly estimating the losses from rare, high-impact events and allows for a realistic representation of vulnerability uncertainty in aggregate loss estimates. 

How to cite: Lamb, C., Probyn, I., Wing, O., Daniel, J., Elmer, F., and Haylock, M.: A vulnerability framework for a global flood catastrophe model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1451, https://doi.org/10.5194/egusphere-egu24-1451, 2024.

EGU24-1669 | ECS | Posters on site | NH9.1

A Comprehensive Review of Coastal Compound Flooding Literature 

Joshua Green, Ivan Haigh, Niall Quinn, Jeff Neal, Thomas Wahl, Melissa Wood, Dirk Eilander, Marleen de Ruiter, Philip Ward, and Paula Camus

Compound flooding, where the combination or successive occurrence of two or more flood drivers leads to an extreme impact, can greatly exacerbate the adverse consequences associated with flooding in coastal regions. This paper reviews the practices and trends in coastal compound flood research methodologies and applications, as well as synthesizes key findings at regional and global scales. Systematic review is employed to construct a literature database of 271 studies relevant to compound flood hazards in a coastal context. This review explores the types of compound flood events, their mechanistic processes, and synthesizes the definitions and terms exhibited throughout the literature. Considered in the review are six flood drivers (fluvial, pluvial, coastal, groundwater, damming/dam failure, and tsunami) and five precursor events and environmental conditions (soil moisture, snow, temp/heat, fire, and drought). Furthermore, this review summarizes the trends in research methodology, examines the wide range of study applications, and considers the influences of climate change and urban environments. Finally, this review highlights the knowledge gaps in compound flood research and discusses the implications of review findings on future practices. Our five recommendations for future compound flood research are to: 1) adopt consistent definitions, terminology, and approaches; 2) expand the geographic coverage of research; 3) pursue more inter-comparison projects; 4) develop modelling frameworks that better couple dynamic earth systems; and 5) design urban and coastal infrastructure with compound flooding in mind. We hope this review will help to enhance understanding of compound flooding, guide areas for future research focus, and close knowledge gaps.

How to cite: Green, J., Haigh, I., Quinn, N., Neal, J., Wahl, T., Wood, M., Eilander, D., de Ruiter, M., Ward, P., and Camus, P.: A Comprehensive Review of Coastal Compound Flooding Literature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1669, https://doi.org/10.5194/egusphere-egu24-1669, 2024.

Translation of geoscience research into tangible changes, such as modified decisions, processes or policy in the wider world is an important yet notably difficult process. Co-RISK is an accessible (i.e. open access, paper-based, zero cost) ‘toolkit’ for use by stakeholder groups within workshops, which is intended to aid this translation process. It is given a robust basis by incorporating paradox theory from organisation studies, which deals with navigating the genuine tensions between industry and research organizations that stem from their differing roles. Specifically designed to ameliorate the organizational paradox, a Co-RISK workshop draws up ‘Maps’ including key stakeholders (e.g. regulator, insurer, university) and their positionality (e.g. barriers, concerns, motivations), and identifies exactly the points where science might modify actions. Ultimately a Co-RISK workshop drafts simple and tailored project-specific frameworks that span from climate to hazard, to risk, to implications of that risk (e.g. solvency). The action research approach used to design Co-RISK (with Bank of England, Aon, Verisk), its implementation in a trial session for the insurance sector and its intellectual contribution are described and evaluated. The initial Co-RISK workshop was well received, so application is envisaged to other sectors (i.e. transport infrastructure, utilities, government).  Joint endeavours enabled by Co-RISK could fulfil the genuine need to quickly convert the latest insights from environmental research into real-world climate change adaptation strategies. 

 

https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1251/

How to cite: Hillier, J. K. and van Meeteren, M.: Co-RISK: A tool to co-create impactful university-industry projects for natural hazard risk mitigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1684, https://doi.org/10.5194/egusphere-egu24-1684, 2024.

EGU24-2009 | ECS | Orals | NH9.1

Considering aftershock-induced damage accumulation in seismic loss assessments 

Corentin Gouache and Adélaïde Allemand

This work outlines a methodology developed for considering aftershock-induced damage accumulation in seismic loss assessments. In particular, it adapts this methodology to the case of reinforced concrete (RC) frames in mainland France and incorporates it to an already-developed seismic loss assessment model.

The methodology consists in dividing the RC buildings into sub-categories of buildings, depending on parameters influencing the vulnerability of the structures. For each category, a set of discrete damage states is defined. For each state Di, fragility functions are derived, enabling to compute the probability of transitioning to another damage state Di+1, knowing the intensity of the ground motion. Therefore, this methodology allows to estimate the final damage state reached by a structure submitted to a series of ground motions.

In order to do so, the pool of French RC buildings is analysed so as to create realistic and general models of RC frames. Ground motions are selected from an open database, following some criteria. Fragility functions are then derived (for each type of building) by applying numerous ground motions to the models and assessing the probabilities of reaching each damage state. The methods for constructing those fragility functions are evaluated from the literature. The choice of relevant parameters measuring damage and measuring ground motion intensity is also scrutinized.

How to cite: Gouache, C. and Allemand, A.: Considering aftershock-induced damage accumulation in seismic loss assessments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2009, https://doi.org/10.5194/egusphere-egu24-2009, 2024.

EGU24-5951 | ECS | Posters on site | NH9.1

Three-dimensional analysis of air temperature of the Hualien M6.9 earthquake based on the tidal forces 

Xian Lu, Weiyu Ma, and Zhengyi Yuan

The Hualien M6.9 earthquake on September 18, 2022 was calculated based on the additional tectonic stress caused by celestial tidal-generating forces (ATSCTF) model. The period of celestial tidal-generating forces was the time background of the air temperature calculation, and the air temperature variation of three-dimensional layered before and after the Hualien earthquake was studied combined with the air temperature data from the National Center for Environmental Prediction (NCEP) of United States. According to the changes of ATSCTF, the Hualien earthquake occurred within the Period B among the three periods: Period A, Period B, and Period C. The air temperature stratification changes during these three periods were calculated separately, and the results showed that on September 12 in Period B, a temperature increase phenomenon began to occur near the epicenter of the Hualien earthquake. On September 13, the air temperature increase anomaly was significant, and the amplitude and area of the temperature enhancement anomaly increased. On September 14th and 15th, the anomaly gradually weakened and disappeared, and the change of the air temperature anomaly followed the seismic thermal anomaly law caused by tectonic movement: the air temperature closer to the land’s surface had a greater anomaly amplitude and a wider anomaly range; as the altitude increases, the air temperature gradually decreases, and the range of anomalies gradually reduces until it disappears. Meanwhile, there were also high temperature anomalies on September 4 and 5 in the Period A, as well as October 1 to October 4 in the Period C. However, the amplitude and area of the warming anomalies in the upper atmosphere were larger than those near the land surface, which did not conform to the seismic thermal anomaly law caused by tectonic movements and did not belong to the seismic thermal anomalies. In addition, the solar geomagnetic KP index in the study area was relatively low during Period B, indicating that it was in a calm period of solar geomagnetic.

How to cite: Lu, X., Ma, W., and Yuan, Z.: Three-dimensional analysis of air temperature of the Hualien M6.9 earthquake based on the tidal forces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5951, https://doi.org/10.5194/egusphere-egu24-5951, 2024.

EGU24-7652 | ECS | Posters on site | NH9.1

A semi-automatic natural language tool to minimize systematic biases in geo-hydrological disaster datasets in tropical Africa 

Bram Valkenborg, Olivier Dewitte, and Benoît Smets

The high susceptibility to geo-hydrological hazards in tropical Africa and their impacts remain poorly documented in existing disaster databases. Only impactful events with high attention are manually reported, creating systematic biases. Natural Language Processing has the potential to automate the documentation of geo-hydrological disasters. This research focuses on developing a semi-automated tool to extract information from online press and social media posts. Fine-tuned Large Language Models perform a series of tasks, such as question-answering, zero-shot classification, and near-entity recognition, to extract information from these online sources. A three-step approach is proposed for the detection of events: (1) filtering posts or articles on their relevancy, (2) extracting information on the location, timing, and impact and (3) merging and sorting information to document identified events into a structured disaster database. Shortcomings compared to a manual approach remain. These mainly relate to the complexity of the text or toponymic ambiguity when geocoding events. The tool is therefore complementary to other information-gathering approaches. These new sources of information will improve our understanding of the distribution of disasters related to geo-hydrological hazards, especially in data scarce context. Future work will combine this semi-automated tool with remote sensing and citizen science data, to further reduce systematic biases in disaster datasets.

How to cite: Valkenborg, B., Dewitte, O., and Smets, B.: A semi-automatic natural language tool to minimize systematic biases in geo-hydrological disaster datasets in tropical Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7652, https://doi.org/10.5194/egusphere-egu24-7652, 2024.

EGU24-7875 | ECS | Orals | NH9.1

Advancing drought detection and management using ML enhanced impact-based drought indexes 

Martina Merlo, Matteo Giuliani, Yiheng Du, Ilias Pechlivanidis, and Andrea Castelletti

Drought is a slowly developing natural phenomenon that can occur in all climatic zones and propagates through the entire hydrological cycle with long-term socio-economic and environmental impacts. Intensified by anthropogenic climate change, drought has become one of the most significant natural hazards in Europe. Different definitions of drought exist, i.e. meteorological, hydrological, and agricultural droughts, which vary according to the time horizon and the variables considered. Just as there is no single definition of drought, there is no single index that accounts for all types of droughts. Consequently, capturing the evolution of drought dynamics and associated impacts across different temporal and spatial scales remains a critical challenge.

In this work, we first analyze different state-of-the-art standardized drought indexes in terms of their ability in detecting drought events at the pan-European scale, using hydro-meteorological variables from the E-HYPE hydrological model and forced with the HydroGFD v2.0 reanalysis dataset over the period 1993-2018. The findings suggest the need of adjusting the formulation of traditional drought indexes to better capture and represent drought-related impacts. Specifically, here we use the FRamework for Index-based Drought Analysis (FRIDA), a Machine Learning approach that allows the design of site-specific indexes to reproduce a surrogate of the drought impacts in the considered area, here represented by the Fraction of Absorbed Photosynthetically Active Radiation Anomaly (FAPAN). FRIDA builds a novel impact-based drought index combining all the relevant available information about the water circulating in the system identified by means of a feature extraction algorithm.

Our results reveal a general pattern among different indexes, that Southern England, Northern France, and Northern Italy are the regions with the highest number of drought events, whereas the areas experiencing longest drought durations are instead the Baltic Sea region and Normandy. Clustering the 35,408 European basins according to dominant hydrologic processes reveals that the variables mainly controlling the drought process vary across clusters. Similarly, we obtain diverse correlation between standardized drought indexes and the FAPAN in different clusters. Numerical results also show that, in one of the worst cases (cluster 10), the FRIDA index increases the correlation with FAPAN from 0.16 to 0.69. Lastly, the FRIDA indexes are computed for different climatic projections to investigate future trends in drought impacts.  Results show divergence with respect to the trends of the standardized drought indexes, with correlation values below 0.30. In conclusion, these findings can contribute in advancing drought-related climate services by enabling the analysis of projected drought impacts.

 

How to cite: Merlo, M., Giuliani, M., Du, Y., Pechlivanidis, I., and Castelletti, A.: Advancing drought detection and management using ML enhanced impact-based drought indexes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7875, https://doi.org/10.5194/egusphere-egu24-7875, 2024.

EGU24-8660 | ECS | Orals | NH9.1 | Highlight

Assessing landslide risk on a Pan-European scale 

Francesco Caleca, Luigi Lombardo, Stefan Steger, Ashok Dahal, Hakan Tanyas, Federico Raspini, and Veronica Tofani

Assessing landslide risk is a fundamental step in planning prevention and mitigation actions in mountainous landscapes. To date, most landslide risk analyses address this topic at the scale of a slope or catchment. Whenever the scale involves regions, nations, or continents, the landslide risk analysis is hardly implemented. To test this theoretical framework, we present a practical case study, represented by the European landscape. In this contribution, we take the main Pan-European mountain ranges and provide an example of risk assessment at a continental scale. We consider challenges like cross-national variations landslide mapping and digital data storage. A two-stepped protocol is developed to identify areas more prone to failure. With this initial information, we then model the possible economic consequences, particularly in terms of human settlements and agricultural areas, as well as the exposed population. The analytical protocol firstly results in an unbiased landslide susceptibility map, which is combined with economic and population data. The landslide risk is presented in both the spatial distribution of possible economic losses and the identification of risk hotspots. The latters are defined through a bivariate classification scheme by combining the landslide susceptibility and exposure of human settlements. Ultimately, the exposed population is represented during the two sub-daily cycles across the study area.

How to cite: Caleca, F., Lombardo, L., Steger, S., Dahal, A., Tanyas, H., Raspini, F., and Tofani, V.: Assessing landslide risk on a Pan-European scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8660, https://doi.org/10.5194/egusphere-egu24-8660, 2024.

EGU24-9197 | Orals | NH9.1 | Highlight

A global stochastic flood risk model for any climate scenario 

Oliver Wing, Niall Quinn, Malcolm Haylock, Conor Lamb, Rhianwen Davies, Nick Sampson, Izzy Probyn, James Daniell, Florian Elmer, Johannes Brand, and Paul Bates

Modelling flood hazards at large scales – both uniform frequency hazard maps and event simulations whose frequency varies in space – is a relatively new scientific endeavour. Data and computation constraints have historically necessitated either a more local focus to modelling efforts, or the building of proof-of-concept global-scale models whose fidelity inhibits most practical applications.

Here, we present a global climate-conditioned flood catastrophe model; the culmination of decades of research into scaling inundation modelling, the incorporation of climate change, and synthetic event generation. 30 m resolution global maps representing fluvial, pluvial, and coastal flooding for given return periods were simulated using a hydrodynamic model with sub-grid channels whose inputs were defined using regional flood frequency analyses. Change factors from climate model cascades were flexibly used to perturb the local flood frequency a given flood map represents. Separately, a 10,000-year-long set of synthetic events were simulated using a conditional multivariate statistical model fitted to global fluvial-pluvial-coastal reanalysis data. The empirical return period of a given event is used to sample the corresponding flood map return period in order to build a long synthetic series of floods.

With a global exposure model built using a top-down approach – downscaling capital stock models to high-resolution satellite-derived land-use and building height data – and a global vulnerability model derived from an extensive review of modelling and engineering literature, we demonstrate the calibration and validation of the global risk model. We also show the software challenges overcome to run this model, as well as to enable end-users to flexibly calculate the flood risk of their own exposures in the Oasis Loss Modelling Framework.

How to cite: Wing, O., Quinn, N., Haylock, M., Lamb, C., Davies, R., Sampson, N., Probyn, I., Daniell, J., Elmer, F., Brand, J., and Bates, P.: A global stochastic flood risk model for any climate scenario, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9197, https://doi.org/10.5194/egusphere-egu24-9197, 2024.

EGU24-9533 | Posters on site | NH9.1

Modeling inland flooding caused by tropical cyclones in the US using AI-based synthetic events 

Nans Addor, Natalie Lord, Balaji Mani, Thomas Loridan, Naoki Mizukami, Jannis Hoch, and Malcolm Haylock

Tropical cyclones (TCs) are a key driver of flooding in the US. Here we present a modeling approach to simulate their associated inundation footprint under present and future climate and generate the hazard data necessary to run a CAT model. 

We developed an AI-based model called RainCyc that learns from the TC rainfall fields dynamically generated by the WRF model as well as from observations. RainCyc is orders of magnitudes faster than WRF, meaning that orders of magnitude more events can be simulated for the same computational cost. This is essential to capture the tail of the distribution, i.e., to generate synthetic events over a period longer than the longest return period of interest. Future boundary conditions for RainCyc are provided by the CESM2-LENS ensemble, which covers the 21st century under SSP370 levels of warming using 50 model realizations started from slightly perturbed initial conditions.

The rainfall fields produced by RainCyc are used to simulate inland flooding, i.e., pluvial and fluvial. The inundation footprint for each event is generated by sampling from flood hazard maps simulated by the LISFLOOD hydraulic model. The sampling for pluvial is informed by RainCyc precipitation, while for fluvial, it relies on hydrological simulations driven by the FUSE and mizuRoute models. FUSE is a frugal rainfall-runoff model that is run at 10km over a domain encompassing each event to generate its associated runoff. This runoff is then provided to the vector-based routing model mizuRoute to generate flow time series from which peak flow is extracted and used to sample fluvial hazard maps.

We present this modeling framework and test it for thousands of years of synthetic events under present and future climate. We benchmark the hydrological simulations for historical events using runs from other models, including GloFAS. We also test the ability of the framework to generate synthetic events spanning the intensities covered by hazard maps for a wide range of return periods.

How to cite: Addor, N., Lord, N., Mani, B., Loridan, T., Mizukami, N., Hoch, J., and Haylock, M.: Modeling inland flooding caused by tropical cyclones in the US using AI-based synthetic events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9533, https://doi.org/10.5194/egusphere-egu24-9533, 2024.

Understanding the relationship between extreme temperature events and health outcomes necessitates integration of hazard and impact data. International databases of societal impacts from disasters serve as an important data source for empirical cross-country analyses. Yet, detailed and precise estimations of the hazard magnitude of these impact records are often lacking. Physical metrics play a pivotal role in, for instance, statistical analyses and exposure assessments.

In bridging this gap, our work leverages recent advancements in geocoding of disaster records alongside high-resolution meteorological datasets to construct an inventory of a diverse range of health-related climate metrics. Our global analysis spans over 200 records of extreme temperature disasters from the past fifty years. By doing so, we unveil insights into the properties of these disastrous heat- and cold-waves. We furthermore explore differences across space, time, metrics, and data sources. This work highlights the potential of utilizing this integrated approach to extract meaningful information from historical disaster records in global databases, aiding climate resilience and public health strategies.

How to cite: Lindersson, S. and Messori, G.: Quantifying health-related climate metrics of extreme temperature disasters: An international analysis over five decades, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9798, https://doi.org/10.5194/egusphere-egu24-9798, 2024.

EGU24-10060 | ECS | Posters on site | NH9.1

The Impact of El Niño-Southern Oscillation on Tropical Cyclone Risks 

Juner Liu, Simona Meiler, David N. Bresch, and Carmen B. Steinmann

The El Niño-Southern Oscillation (ENSO) is the most important inter-annual signal of climate variability on the planet. It affects many natural hazards including tropical cyclones (TCs), known for causing severe economic losses and many fatalities. Although research efforts have examined ENSO’s influence on TC characteristics including frequency and intensity in different basins, the transfer of these findings to global TC risk assessments has yet to be undertaken. This covers aspects such as damage to physical assets and the number of people affected. However, this is complicated by many uncertainties, such as landfall location (heterogeneous distribution of exposures) and vulnerability definitions. To bridge this gap, we assess TC risks on physical assets and affected people under ENSO’s influence and quantify related sources of uncertainty on a global scale.

We analyze TC risks during El Niño and La Niña years, using three types of TC datasets: the International Best Track Archive for Climate Stewardship (IBTrACS), probabilistic tracks generated by a random walk algorithm (IBTrACS_p), and synthetic TCs generated by a statistical-dynamical TC model (MIT). Furthermore, we quantify the sensitivity of input variables, such as the ENSO threshold, and assess uncertainties arising from TC landfall location using uniform exposure values. The outcomes regarding ENSO-conditioned TC risks can potentially improve seasonal TC risk prediction, thus benefiting policymakers and the insurance industry alike. Additionally, the results contribute to more balanced and diversified (multi-)hazard risk portfolios by accounting for ENSO as an important common modulator of spatially compounding hazards.

How to cite: Liu, J., Meiler, S., Bresch, D. N., and Steinmann, C. B.: The Impact of El Niño-Southern Oscillation on Tropical Cyclone Risks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10060, https://doi.org/10.5194/egusphere-egu24-10060, 2024.

EGU24-10905 | ECS | Posters on site | NH9.1

Flooding Under Climate Change in Small Island Developing States 

Leanne Archer, Jeffrey Neal, Paul Bates, Natalie Lord, and Laurence Hawker

Small Island Developing States are a group of 57 island nations and territories which are some of the most at-risk places to the impacts of climate change globally, particularly from changes in hydrometeorological hazards such as flooding. Despite this, little research has quantified present day flood hazard and population exposure in small islands, let alone how this may change as global temperatures continue to rise. Until now, this was due to the insufficient data to produce high-resolution flood hazard and population exposure estimates for a wide range of possible scenarios at such a large scale. Following the release of Fathom’s Global Flood Model 3.0, in this work we combine global flood hazard estimates for coastal, fluvial, and pluvial flood hazard at ~30m flood model resolution to estimate present day population exposure to flooding across all 57 small islands. We also investigate how flood hazard and population exposure changes under three climate scenarios: two plausible climate change scenarios (SSP1-2.6 and SSP2-4.5), and a plausible worst-case climate scenario (SSP5-8.5). We assess how present day flood hazard and exposure differs across the island typologies, and how these are projected to change under the different climate change scenarios. We also compare population exposure with vulnerability metrics to explore how population exposure to flooding and vulnerability interact. The results of this analysis aim to improve understanding regarding the range of plausible estimates of current and future population exposure to flooding in Small Island Developing States. These results will help inform adaptation to more extreme flood risk in Small Island Developing States under current and future climate change.

How to cite: Archer, L., Neal, J., Bates, P., Lord, N., and Hawker, L.: Flooding Under Climate Change in Small Island Developing States, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10905, https://doi.org/10.5194/egusphere-egu24-10905, 2024.

EGU24-13847 | Posters on site | NH9.1

Development of a Comprehensive Exposure-at-Risk Map for Europe: Integrating Coinciding Natural Hazards and Exposure Metrics 

James Daniell, Andreas Schaefer, Judith Claassen, Johannes Brand, Timothy Tiggeloven, Bijan Khazai, Trevor Girard, Annika Maier, Benjamin Blanz, Nikita Strelkovskii, Jaroslav Mysiak, Marleen de Ruiter, Wiebke Jaeger, and Philip Ward

The development of an Exposure-at-risk map for Europe that encompasses multiple coinciding natural hazards builds upon many previous attempts and existing portals such as TIGRA, TEMRAP, ESPON, JRC DRMKC, and GIRI to name a few, which have primarily focused on examining a few single hazards and limited exposure.
The novelty of this approach lies in its integration of a myriad of hazards into a single, cohesive framework. The European Hazard Map is constructed using data from various sources, covering geophysical hazards (earthquakes, volcanoes, landslides), meteorological hazards (winds, convective storms, storms), hydrological hazards (river/pluvial floods), climatic overlaps (bushfires, droughts), and biological hazards. These hazards are modelled using both stochastic and probabilistic methods as well as historical reanalysis, offering a robust and comprehensive view of potential risks.
The exposure component of this map is constructed around a handful of key Europe-wide metrics, encompassing aspects crucial to the European multi-sector context. These include tourism-based metrics such as domestic and international expenditure, hotel statistics, employment figures, as well as broader economic indicators like capital stock (particularly focusing on buildings), GDP, and critical infrastructure related to transport and energy. Additionally, agricultural production and seasonal population variations are factored in. These metrics are pivotal in assessing the potential impact of various hazards, including but not limited to earthquakes, tsunamis, winds, floods, landslides, tornadoes, hail, droughts, and bushfires.
This map has been developed as part of the MYRIAD-EU project, a multi-hazard initiative, and is built using open data sources and risk analytics within the project. A significant feature of this map is its ability to demonstrate temporal and spatial overlaps. This capability allows for the visualization of combined events or the combined impact of different exposure-hazard overlaps, depending on whether the output is stochastic or probabilistic. The interface of this map serves as a crucial gateway to the MYRIAD-EU multi-hazard software scorecard approach. It also plays a pivotal role in identifying overlapping hazards within the EU, enabling better preparedness and response strategies.
In summary, this Exposure-at-risk map for Europe is a significant advancement in the field of hazard assessment and risk management. It integrates a multitude of hazards and exposure metrics, offering a comprehensive and detailed view of potential risks across Europe. This map is not only a tool for current risk assessment but also a foundation for future research and development in this critical area of study.

How to cite: Daniell, J., Schaefer, A., Claassen, J., Brand, J., Tiggeloven, T., Khazai, B., Girard, T., Maier, A., Blanz, B., Strelkovskii, N., Mysiak, J., de Ruiter, M., Jaeger, W., and Ward, P.: Development of a Comprehensive Exposure-at-Risk Map for Europe: Integrating Coinciding Natural Hazards and Exposure Metrics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13847, https://doi.org/10.5194/egusphere-egu24-13847, 2024.

EGU24-13864 | Orals | NH9.1

Connecting the dots: teleconnection of global floods and their association with climate variability 

Yixin Yang, Long Yang, Qiang Wang, and Gabriele Villarini

A fundamental question in global hydrology is how global floods behaved in the past and are expected to behave in the future. Previous site-specific analyses might offer locally relevant insights, but little is known about how floods are connected in space and time as well as their synchronous responses to climate variability at the global scale. Here we carry out empirical analyses based on a comprehensive dataset of annual maximum flood peak series from 4407 stream gaging stations. We establish the link between any two stream gages if their annual maximum flood peak discharges are significantly correlated and the dates of their occurrences are sufficiently close (using event synchronization and complex network). Our results identify notable remote links of annual flood peak series over western Canada/US (e.g., upper Missouri River basin), northern Europe (e.g., Kemijoki River basin), southern China (e.g., middle Yangtze River basin), and northern South America (e.g., Amazon River basin). Annual flood peak series are linked to their local neighbors (within a distance of 4500 km) over eastern United States, central Europe, and eastern Australia. Remote links highlight the spatial dependence of riverine floods at the global scale. These links are dictated by the oscillation of dominant climate modes over the Pacific Ocean (e.g., El Niño Southern Oscillation, Pacific Decadal Oscillation) and their resultant anomalous atmospheric circulation patterns. Local flood clusters are more responsive to region-specific atmospheric forcings. The complex flood network plays an important role in regulating the dynamic behaviors of flood hazards. Our results offer new insights into global flood hydrology and their connections with large-scale climate forcings.

How to cite: Yang, Y., Yang, L., Wang, Q., and Villarini, G.: Connecting the dots: teleconnection of global floods and their association with climate variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13864, https://doi.org/10.5194/egusphere-egu24-13864, 2024.

Floods constantly occur in San Miguel de Ibarra's urban setting each year. Situated on the slopes of the Imbabura volcano, an integral component of the UNESCO Global Geopark Imbabura, this Ecuadorian city boasts an invaluable cultural and natural heritage. However, it has experienced multiple adverse impacts due to the overflow of rivers and streams. In 2022, an inventory of floods was compiled for the Geopark, revealing the persistent recurrence of this phenomenon within the city. Consequently, it became imperative to gather historical and contemporary data from diverse sources such as public institutions (GAD Ibarra 2023), digital newspapers, social networks, and aerial imagery (IGM 2014) to discern patterns and establish correlations related to these occurrences (SNGRE 2023).

In this way, the acquired information spanning the period from 1965 to the present, insights were gained into the distribution of flood-prone zones and their correlation with paleochannels. Additionally, discernment was achieved regarding alterations in land-use planning attributable to urban expansion in the city, which, in turn, contributes to the heightened susceptibility to floods. This meticulous analysis unveiled specific areas within the city consistently affected by such hazards, elucidating these events' characteristics and the ensuing damage to both public and private properties. The current publication presents preliminary findings utilized in the estimation of flood risk.

Keywords: Paleochannels, floods, Ibarra, Imbabura, Imbabura UNESCO Geopark

References:

GAD Ibarra (2023) Cartography of Ibarra canton at several scales

IGM (2014) Cartography of Ibarra canton 1:5.000

IGM (2023) Historical imagery of flights in Ecuador at several scales

SNGRE (2023) Data Base Events SNGRE. Period 2010 to 2023

How to cite: Torres-Ramírez, R.: Paleochannels and their correspondence with floods in the 21st century. Case study of Ibarra city, Imbabura, Ecuador., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14423, https://doi.org/10.5194/egusphere-egu24-14423, 2024.

Abstract: The incidences of earthquakes in the north Indian state of Uttarkhand are broadly associated with the presence of active fault viz. Main Central Thrust and Alaknanda Fault in the north, Moradabad Fault and Himalayan Frontal Thrust in the southern margin, Martoli Thrust and Indus Suture in the eastern, Mahendragarh Dehrdun Fault in the west. Uttarakhand falls under Seismic Zone IV and V and has been struck by several devastating earthquakes viz. 1905 Kangra earthquake of MW 7.8, 1991 Uttarkashi earthquake of MW 6.8 and 1999 Chamoli earthquake of MW 6.5 with maximum MM Intensity of IX observed in near-source region causing widespread damage and destruction in the study region. Uttarakhand region has undergone unprecedented development and population growth, emphasizing the importance of analysis of Seismic Hazard to ensure safe and secure progress in this seismically vulnerable region. Consideration of seismicity patterns, fault networks and similarity in the style of focal mechanisms yielded 10 areal seismogenic sources with additional active tectonic features in 0-25km, 25-70km, and 70-180km hypocentral depth ranges, along with 15 Ground Motion Prediction Equations for the tectonic provinces of Uttarakhand region yielding Probabilistic Peak Ground Acceleration (PGA) at engineering bedrock  seen to vary from 0.36g to 0.63g for 475years of return period which places the region in the moderate to high hazard zone necessitating a case study for site-specific seismic characterization of the region. Seismic site classification has been done based on an enriched geophysical, in-situ downhole, geotechnical database and surface geoscience attributes comprising of Geology, Geomorphology, Landform and Topographic Gradient derived shear wave velocity categorizes the region into Site Classes E, D4, D3, D2, D1, C4, C3, C2, C1, B and A. Using the input ground motion at bedrock level obtained from stochastic simulation for the near-source earthquakes, nonlinear site response analyses have been performed using PLAXIS-2D software package wherein site amplification has been mapped which is seen to vary in the range of 1.02 to 2.86. Surface-consistent probabilistic seismic hazard in terms of Peak Ground Acceleration (PGA) for a return period of 475 years has been assessed for the study region by convolving site amplification with bedrock hazard thus predicting a variation of PGA in the range of 0.51-1.61g. Additionally, assessment of liquefaction potential of the terrain and seismic hazard microzonation have been done for Dehradun city to identify areas with varying level of ground shaking and its associated liquefaction phenomenon during earthquakes, enabling the development of site-specific building codes and land-use regulations. The results of this investigation are expected to play vital roles in the earthquake–related disaster mitigation and management of the region.

How to cite: Bind, A. P. and Nath, S. K.: Site-specific Seismic Hazard Assessment of Uttarakhand, India with special emphasis on Liquefaction Potential  modelling of the terrain and Seismic Hazard Microzonation of Dehradun City, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14677, https://doi.org/10.5194/egusphere-egu24-14677, 2024.

EGU24-16095 | ECS | Posters on site | NH9.1

Do catchment characteristics drive extreme discharge tail behavior in the Meuse catchment? Insights from 1,040 years of synthetic discharge data.  

Anais Couasnon, Laurène Bouaziz, Ruben Imhoff, Hessel Winsemius, Mark Hegnauer, Niek van der Sleen, Robert Slomp, Leon van Voorst, and Henk van den Brink

Understanding extreme discharge behavior is of importance for flood design and risk management. For example, estimates of large extreme discharge return periods such as the 100-year return period or higher are often needed as a basis for flood hazard maps or dike design. Yet, frequency analysis based on decade-long discharge records show a large uncertainty for these frequencies, among others due to the statistical uncertainty from the distribution parameters.  This is not the case for the shape parameter, a key parameter that describes the upward or downward curvature of the tail of the distribution and thus an indicator of extreme discharge behavior. 

This study provides robust estimates of the shape parameter by using the 1,040 years of synthetic daily discharge generated for the Meuse catchment as part of the EMfloodResilience project from the Interreg Euregio Meuse-Rhine program. The spatially-distributed hydrological model wflow_sbm, calibrated and validated for the Meuse catchment, is forced with 16 synthetic climate ensembles of 65 years representative for the current climate from the physically-based KNMI regional climate model RACMO climate model at a daily and hourly time step. The annual maxima (AM) from hydrological years (Oct-Sep) are retrieved from these continuous time series, and a GEV distribution is fit to the AM. We observe a clear spatial pattern of the shape parameter across the Meuse catchment. Using this large dataset of shape parameters, we also review the possible reasons for the different tail behavior obtained with respect to rainfall statistics, catchment characteristics and river systems following the In doing so, we aim to bridge the extreme value statistical modelling with our current understanding of the extreme hydrological signatures present in the catchment.

How to cite: Couasnon, A., Bouaziz, L., Imhoff, R., Winsemius, H., Hegnauer, M., van der Sleen, N., Slomp, R., van Voorst, L., and van den Brink, H.: Do catchment characteristics drive extreme discharge tail behavior in the Meuse catchment? Insights from 1,040 years of synthetic discharge data. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16095, https://doi.org/10.5194/egusphere-egu24-16095, 2024.

EGU24-16556 | ECS | Posters on site | NH9.1

Coastal flood risks in Europe in the context of sea-level rise: methods and preliminary results from the CoCliCo project 

Vincent Bascoul, Rémi Thiéblemont, Jeremy Rohmer, Elco Koks, Joël De Plaen, Daniel Lincke, Hedda Bonatz, and Goneri Le Cozannet

Present days and future coastal flooding is a key concern for Europe due to sea-level rise, storm surges and the importance of infrastructure at risk in low-lying areas. To support adaptation, information on future risks such as people exposed and economic damages are required. The CoCliCo project aims to contribute responding to this need by informing users about coastal risks via an open-source web platform. This platform aspires to improve decision-making on coastal risk management and adaptation in Europe.

Here, we present the methods used in CoCliCo to compute risks and provide early results of risk calculations at the European scale. The results take the form of costs calculated for different flooding scenarios on different infrastructures (residential buildings, roads...) as a function of flood water levels. Flood water levels are determined for each infrastructure based on flood modelling. Then, using vulnerability curves, a damage associated with the type of infrastructure as a function of the water level is assigned. The damage ratio then is used to calculate the cost of flooding. Coastal risk can also be presented in social terms, by assessing the number of people potentially affected by flooding. The results are illustrated for two case studies: Dieppe and Hyère in France using detailed flood modelling and complemented by preliminary results for Europe. Our results are compared results from with previous studies.

Finally, flood risk projections will be presented for several return periods at different scales and for different integrated scenarios considering climate change and associated socio-economic pathways as well as different adaptation options. These results will be made available on the CoCliCo platform.

How to cite: Bascoul, V., Thiéblemont, R., Rohmer, J., Koks, E., De Plaen, J., Lincke, D., Bonatz, H., and Le Cozannet, G.: Coastal flood risks in Europe in the context of sea-level rise: methods and preliminary results from the CoCliCo project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16556, https://doi.org/10.5194/egusphere-egu24-16556, 2024.

Tropical cyclones are events responsible for the costliest meteorological catastrophes. On average per year over the last decade, they have affected 20 million people, with estimated economic losses US$51.5 billion (Krichene et al., 2023). These consequences reduce the economic growth of the affected countries (Berlemann & Wenzel, 2018). Take Jamaica, for instance, where annual damages caused by tropical cyclones are estimated at 0.5%, reaching up to 10% of the Gross Domestic Product (Adam & Bevan, 2020).

The climatology of tropical cyclone, defined as characteristics averaged over years, controls parameters like tracks, intensification, number of storms, all crucial for induced hazards (winds, precipitation, storm surge and waves). In recent years, anomalous tropical cyclones have impacted the coasts worldwide. In 2023, hurricane Otis, without precedent, rapidly intensified off the coast of the coast of Acapulco (Mexico), resulting in at least 52 deaths and estimated damage exceeding 10 billion USD. The track of tropical cyclone Kenneth struck areas of Mozambique where no previous tropical cyclone had impacted before, resulting in 45 casualties and $100 million in damage (Mawren et al., 2020). The future of tropical cyclones is impregnated with uncertainty and is a matter of concern, which have motivated the recent advance in this topic. Several authors asseverate an increase in intensity, reduce in frequency (Bloemendaal, et al., 2022; T. Knutson et al., 2020; T. R. Knutson et al., 2010), and their poleward displacement (Studholme et al., 2022). However, the global study of the displacement of tropical cyclones and their characteristics due to the migration of storms has not been integrated into large-scale adaptation planning.

This study identifies regions affected by the displacement of storms in the North Atlantic at the municipal administration level. Analysing characteristics under two climatology periods—a baseline climate (1980-2017) and a future high-emission climate scenario, Shared Socioeconomic Pathway SSP8.5 (2015-2050)—we used synthetic tracks (Bloemendaal, et al., 2022) generated with a model based on STORM  (Bloemendaal et al., 2020). Four Global Climate Models (CMCC, CNRM, EC-Earth, and HadGEM3) were examined to evaluate uncertainty, focusing on frequency, intensity, and critical parameters such as size, translation speed, track complexity, residence time in front of the coast, and relative direction to the shoreline.

This study identifies hotspots where tropical cyclone characteristics are spatially displaced, increasing the exposure to tropical cyclones in these regions. For example, the Canary Islands in Spain show that hurricanes of category 1, in present conditions, have a return period of 215 years, reducing to 62 years in the SSP8.5 scenario. This is in line with the recent records, the Hermine storm in 2022 almost impacted their coasts. The results raise questions about our public policies for future adaptation. In areas historically unaffected and unprepared for tropical cyclones, the corresponding government may lack and require prevention systems for tropical cyclones, such as warning alarms, reducing subsidies for coastal development or implementing disaster relief policies. 

How to cite: Odériz, I. and Losada, I.: Implications of the displacement of tropical cyclones for public policies in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17338, https://doi.org/10.5194/egusphere-egu24-17338, 2024.

EGU24-17738 | ECS | Orals | NH9.1

Complex emergencies: drivers of the humanitarian impacts of climate-related disasters 

Ellen Berntell, Nina von Uexkull, Tanushree Rao, Frida Bender, and Lisa Dellmuth

Climate-related disasters such as floods, droughts and storms often pose significant threats to human livelihoods, especially in developing countries. The extreme weather events often lead to destroying of shelter, harming of crops and livestock as well as fueling of conflicts, and the threat to human livelihoods are likely to increase due to climate change. While we know that climate change and conflict interact and reinforce each other, less is known in the context of natural disasters and disaster aid. In this paper we address this gap by studying how hazard severity, disaster exposure and drivers of vulnerability interact to produce humanitarian impacts, and if the delivery of emergency disaster aid alleviates these impacts. We do this by generating meteorological hazard severity measurements based on the reanalysis dataset ERA5, comparable across different climate-related disaster types, allowing us to study drivers of vulnerability to climate-related hazards. Secondarily, we study the role of aid allocation on limiting disaster mortality and displacement, with the results having broad implications for the understanding of disaster impacts and aid effectiveness.

How to cite: Berntell, E., von Uexkull, N., Rao, T., Bender, F., and Dellmuth, L.: Complex emergencies: drivers of the humanitarian impacts of climate-related disasters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17738, https://doi.org/10.5194/egusphere-egu24-17738, 2024.

EGU24-17751 | ECS | Orals | NH9.1 | Highlight

A New Method to Compile Global Multi-Hazard Event Sets 

Judith Claassen, Elco E. Koks, Timothy Tiggeloven, and Marleen C. de Ruiter

This study presents a new method, the MYRIAD-Hazard Event Sets Algorithm (MYRIAD-HESA), that compiles historically-based multi-hazard event sets. MYRIAD-HESA is a fully open-access method that can create multi-hazard event sets from any hazard events that occur on varying time, space, and intensity scales. In the past, multi-hazards have predominately been studied on a local or continental scale, or have been limited to specific hazard combinations, such as the combination between droughts and heatwaves. Therefore, we exemplify our approach by compiling a global multi-hazard event set database, spanning from 2004 to 2017, which includes eleven hazards from varying hazard classes (e.g. meteorological, geophysical, hydrological and climatological). This global database provides new scientific insights on the frequency of different multi-hazard events and their hotspots. Additionally, we explicitly incorporate a temporal dimension in MYRIAD-HESA, the time-lag. The time-lag, or time between the occurrence of hazards, is used to determine potentially impactful events that occurred in close succession. Varying time-lags have been tested in MYRIAD-HESA, and are analysed using North America as a case study. Alongside the MYRIAD-HESA, the multi-hazard event sets, MYRIAD-HES, is openly available to further increase the understanding of multi-hazard events in the disaster risk community. The open-source nature of MYRIAD-HESA provides flexibility to conduct multi-risk assessments by, for example, incorporating higher resolution data for an area of interest.

How to cite: Claassen, J., Koks, E. E., Tiggeloven, T., and de Ruiter, M. C.: A New Method to Compile Global Multi-Hazard Event Sets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17751, https://doi.org/10.5194/egusphere-egu24-17751, 2024.

EGU24-17874 | ECS | Orals | NH9.1

An evaluation of the use of regional climate model data applied to extreme precipitation in the Meuse basin 

Leon van Voorst, Henk van den Brink, and Anais Couasnon

Understanding of hydrological and meteorological extremes is essential for flood risk management and flood protection. A primary focus in these professions is adequate estimation of extreme events that correspond to large return periods. Hydrological and meteorological observations only go back several decades, complicating frequency analysis of these large extremes. Capturing the tail behaviour of extremes is particularly challenging with such short records, resulting in high uncertainty of large precipitation and discharge extreme estimates.

This study proposes an alternative strategy for hydrological and meteorological frequency analysis. Long timeseries obtained from regional climate models are used to replace short observational datasets, leading to a substantial reduction of the statistical uncertainty of meteorological and hydrological extreme estimates. The approach was tested in the Meuse basin as part of the EMFloodresilience project, evaluating meteorological extremes from 16 synthetic ensembles of 65 years from the RACMO regional climate model (forced by the EC-EARTH global climate model). Hydrological extremes are analysed in a subsequent study from Rijkswaterstaat and Deltares, by forcing the wflow discharge model with the RACMO climate model dataset.

The study results reveal that bias-corrected model data is climatologically comparable to observational averages and extremes, exhibiting similar GEV location and scale parameters. Revealing a previously unexamined range of extremes, the model data offers a more plausible method to estimate the tails of annual extremes and likely provides a better estimate of the corresponding GEV shape parameter. Spatially, the model-derived parameter shows greater consistency across different sub-catchments of the Meuse basin compared to observations, suggesting a more robust insight in the tail behaviour of extremes. Additionally, a distinct separation between GEV distributions of summer and winter events is observed, indicating a transition in magnitude dominance from winter to summer maxima and possibly the presence of a double population. The existence of such a double population is difficult to obtain from observations, but can have an enormous impact on the return values of summer extremes. This emphasizes the need for further research on this area for adequate flood management.

How to cite: van Voorst, L., van den Brink, H., and Couasnon, A.: An evaluation of the use of regional climate model data applied to extreme precipitation in the Meuse basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17874, https://doi.org/10.5194/egusphere-egu24-17874, 2024.

EGU24-18718 | ECS | Orals | NH9.1

When one becomes many: Including complex channel systems in large scale flood models 

Laurence Hawker, Jeffrey Neal, Michel Wortmann, Louise Slater, Yinxue Liu, Solomon H. Gebrechorkos, Julian Leyland, Philip J. Ashworth, Ellie Vahidi, Andrew Nicholas, Georgina Bennett, Richard Boothroyd, Hannah Cloke, Helen Griffith, Pauline Delorme, Stuart McLelland, Andrew J. Tatem, Daniel Parsons, and Stephen E. Darby

Over 70% of flood events recorded in the past two decades in the Global Flood Database and WorldFloods dataset have occurred in locations where complex channel systems occur. Here we define complex channel systems as parts of the river network that diverge, such as bifurcations, multi-threaded channels, canals and deltas. Yet, large scale flood models have, until now, used only single-threaded networks due to the lack of a river network that reflects complex channel systems . Therefore, these large-scale models fundamentally misrepresent the physical processes in these often highly populated areas, leading to sub-optimal estimates of flood risk.

Using the new Global River Topology (GRIT) dataset, a global bifurcation and multi-directional river network (Wortmann et al. 2023), we extend the river channel bathymetry estimation routine of Neal et al. (2021) to model multi-channels with LISFLOOD-FP. We compare the multi-thread model results to observations and to previous versions of LISFLOOD-FP using a single-threaded river network in the Indus, Mekong and Niger rivers at 1 arc second (~30m). By using GRIT, we find marked improvements in model results, observing better connectivity to areas of the floodplain that are far from the main channel and more channel floodplain interactions in wetlands. This work paves the way to further our understanding of global flood risk and to finally consider the diverse, evolving nature of geomorphologically active river networks. As this work progresses, we will continue to model a typology of bifurcations and multi-directional rivers to help further our understanding of the significance of complex river systems.

Neal, J., Hawker, L., Savage, J., Durand, M., Bates, P., & Sampson, C. (2021). Estimating river channel bathymetry in large scale flood inundation models. Water Resources Research57(5), e2020WR028301.

Wortmann, M., Slater, L., Hawker, L., Liu, Y., & Neal, J. (2023). Global River Topology (GRIT) (0.4) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.7629908

How to cite: Hawker, L., Neal, J., Wortmann, M., Slater, L., Liu, Y., Gebrechorkos, S. H., Leyland, J., Ashworth, P. J., Vahidi, E., Nicholas, A., Bennett, G., Boothroyd, R., Cloke, H., Griffith, H., Delorme, P., McLelland, S., Tatem, A. J., Parsons, D., and Darby, S. E.: When one becomes many: Including complex channel systems in large scale flood models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18718, https://doi.org/10.5194/egusphere-egu24-18718, 2024.

EGU24-20386 | ECS | Orals | NH9.1

Slow-moving landslide exposure increases with population pressure 

Joaquin Vicente Ferrer and Oliver Korup

Slow-moving landslides can cause damage to structures and infrastructure and result in thousands of casualties, if they fail catastrophically. Landslide motion may accelerate after prolonged rainfall, and with alterations to their surface hydrology caused by urbanization. As populations grow in mountainous regions, there will be more direct interactions between communities expanding onto landslides. Yet, the lack of systematic data has precluded a global overview of exposure. We address this by compiling a global database of 7,764 large landslides (>0.1 km2 in area) reported to be slow-moving. Here, we assess the presence of human settlements in 2015 and estimate exposure across IPCC regions with projected landslide risk. We estimate that 9% of landslides in a given basin are occupied by human settlements. On 1195 km2 slow-moving landslides, settlement footprints total 55 km2 and cover an average of 12%, relative to the landslide area. We show regional influences of exposure to floods, average steepness, and urbanization on exposure across basins. Our estimates of exposure in East Asia (EAS) show the most credibility across regions facing growing landslide and flood risk by the IPCC. Apart from Central Asia, we find that urbanization in a basin increases the relative number of landslides inhabited. Furthermore, we find that regions with mountain risks projected to increase have highest uncertainty in our assessment.

How to cite: Ferrer, J. V. and Korup, O.: Slow-moving landslide exposure increases with population pressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20386, https://doi.org/10.5194/egusphere-egu24-20386, 2024.

EGU24-20522 | ECS | Orals | NH9.1

Global assessment of human exposure to sea-level rise to 2300 

Jack Heslop, Robert Nicholls, Caridad Ballesteros Martinez, Daniel Linke, and Jochen Hinkel

The PROTECT project [1] includes a probabilistic integrated assessment of global population exposure to coastal flood hazard under climate-induced sea-level rise (SLR) over the next three centuries (to 2300). The assessment synthesises present-day datasets on population distribution [2], low lying coastal elevations [3] and extreme tides [4] with probabilistic projection datasets of population [5] and sea level [6] to 2300. For the scenarios considered (SSP1-2.6 & SSP2-4.5) and at a global scale, the median human exposure to coastal flood hazards grows substantially but then peaks in the early 2200s and subsequently slowly declines by 2300, despite continued rise in sea level.

Previous assessments have primarily focussed on shorter timeframes [2], typically to 2100, while it is widely acknowledged that even if temperatures are stabilised, sea levels are almost certain to continue to rise for many centuries [7][8][9]. Stakeholder workshops carried out with practitioners under the umbrella of PROTECT [10] and literature reviews [11][12] highlight the importance of extending sea-level rise information beyond 2100, to support strategic coastal adaptation and management, land-use planning, and critical infrastructure design.

Recent advancements in long term socio-economic modelling [13][5] now provide projections of global population and GDP at country level to 2300. These have already been applied to long-term risk assessments for other climate sectors [13][5][14].

For this assessment, the global coastline was split into ~29,000 segments, each assigned an extreme tide curve (from the COAST-RP dataset [4]) and a hypsometric curve, generated from a global terrain model [3] and present-day population distribution [2]. The hypsometric curves aggregate the total land-area and population at each elevation, including consideration of hydraulic connectivity to the coastline. This gives the land area and population that would be exposed at a given coastal flood level (up to 20mAMSL) for each coastal segment.

When sea-level scenarios [6] (SSP1-2.6 & SSP2-4.5) and socio-economic data [5] are combined, the human exposure and land area exposure to coastal flood hazard under a chosen extreme tide return period (or the annual average based on the event-exposure curve) is calculated.

This approach facilitates efficient computations, sampling across probabilistic data, and providing robust statistics at a high spatial resolution compared to traditional methods. The outputs at each coastal segment can be aggregated to sub-national, national, or the global scale.

In this analysis, it is found that the median exposure of people to coastal flood hazards increases fivefold to a peak in the early 2200s and subsequently slowly declines to 2300 in both SSPs, despite the continued rise in sea level. For the 80th percentile population exposure grows even more (10- to 11-fold) but then stabilises rather than declines. These results reflect the interplay of sea level and demography with fall in global population in the latter half of the assessment period and are contrary to conventional wisdom. This analysis shows that in addition to sea-level rise, it is important to consider demographic trends when considering coastal futures.

Figure 1. Probabilistic annual average global population exposure to coastal flood hazard

References exceed the word limit so not included

How to cite: Heslop, J., Nicholls, R., Ballesteros Martinez, C., Linke, D., and Hinkel, J.: Global assessment of human exposure to sea-level rise to 2300, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20522, https://doi.org/10.5194/egusphere-egu24-20522, 2024.

EGU24-21315 | Orals | NH9.1

Wildfire Risk Assessment under present and future climate at national scale: a pan european approach 

Farzad Ghasemiazma, Giorgio Meschi, Andrea Trucchia, and Paolo Fiorucci

The authors present a framework designed to model wildfire risk and the future projection of wildfire risk patterns, also in view of climate change scenarios. The adopted modeling framework is inherently multi scale, giving results at national scale, after a data gathering process developed at regional / supranational scale. The risk assessment comprises the computation of susceptibility, hazard, exposures, and damage layers. Machine learning techniques are used to assess the wildfire susceptibility and hazard at regional level, analogously to [1, 2]. To this end, a two-models approach has been adopted. The first model, based on the Random Forest Classifier, is trained at pan-European level to capture the climate variability of the European continent and related fire regimes. Building upon the outcome of this model, a wildfire susceptibility map representative for the historical
conditions at pan-European level is produced and used in input of a second machine learning model, to provide results at national level. The strength of this model lies in using high-resolution downscaled climate data and annual temporal resolution, with the objective of computing a high resolution annual susceptibility map for the specific region. This approach facilitates the generation of annual outcomes for both historical and future conditions, using the climate projections available in the ISIMIP framework. The result of five different climate models and three climate change scenarios have been used to estimate the average annual losses due to wildfires. The wildfire hazard has been evaluated through empirical approaches, building a wildfire hazard classes map combining fuel type/severity maps with wildfire susceptibility. Then, a burning probability is estimated for each hazard class: a statistical analysis on historical wildfires at pan-European level has been performed in order to retrieve the annual relative burned area per hazard class. The method allows to estimate the average annual probability to be affected by a fire given a wildfire event. Several exposed elements were used to estimate the losses ranging from infrastructure to forest and roads: Global Earthquake Model [3] provides a dataset featuring economic values under both present and future conditions across five categories of infrastructures at European level. JRC, OpenStreeMap, and Copernicus provide information on the presence of roads and forests. Empirical vulnerability functions establish a link between severity maps, the presence of exposed elements, and their economic value, leading to the estimation of potential damage maps. The assessment of average annual losses involves coupling spatial information on average annual probability with potential damage maps. This approach allows for the evaluation of average values across various future timeframes associating a variance accounting for both the year to year and climate models’ variability. Results have been produced at national level for several countries characterized by different wildfire regimes, land cover and climate, such as Croatia, Romania and Bulgaria.

How to cite: Ghasemiazma, F., Meschi, G., Trucchia, A., and Fiorucci, P.: Wildfire Risk Assessment under present and future climate at national scale: a pan european approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21315, https://doi.org/10.5194/egusphere-egu24-21315, 2024.

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