To study the spatiotemporal patterns of local earthquakes mb < 4.0, a local seismic network of six smoked paper seismographs was installed on the Oaxaca Coast three weeks before November 29, 1978, M=7.8, Earthquake, as part of a Research Project between the Institute of Geophysics of the UNAM and the California Institute of Technology. This study aimed to obtain relevant information on the Oaxaca Seismic Gap proposed by Kelleher et al. (1973). 339 earthquakes were located in this period, with a coda magnitude range of 1.0 to 4.4, most of the seismicity is located between the coastline and the Chacalapa Fault. The depths of the precursors are mainly between 10 and 35 km, basically in the continental crust. We observe an NS alignment of seismicity at 96.6° (east of the earthquake epicenter). Two clusters of seismicity are observed, one 25 km southwest of the epicenter and another 45 km west of the epicenter. Frames of quiescence period centered at the main event epicenter in profiles NS and EW are observed.  Using composite focal mechanisms, an analysis of the variation of previous stresses in the epicentral area of the earthquake is presented.

How to cite: Nunez-Cornu, F. J.: Assessment of Spatiotemporal Stress Associated with the November 29, 1978 M=7.8, Foreshocks in Oaxaca, Mexico, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-584, https://doi.org/10.5194/egusphere-egu25-584, 2025.

Earthquakes occurring along subduction interfaces account for most of the seismic energy released at the Earth's surface. To better understand the mechanisms involved, it is essential to compile an exhaustive catalog of these events. In this study, we have documented 201 M_w7.5+ events between 1900 and 2023 in a catalog called Subquake 2.0 (SQ2). This new catalog represents a significant update to the one published in 2018 by van Rijsingen and colleagues.

We developed an automatic procedure to detect events that are strong candidates for earthquakes nucleated along the subduction interface. This procedure exploits both the ISC-GEM catalog and the Slab2.0 model, taking into account the uncertainties associated with positions, for determining the probability that the event occurred within some specific distance to the slab. Guided by this automatic selection, a thorough and comprehensive bibliographic review of each event allowed us to remove 30 events from the previous release (Subquake 1.0) and add 49 new ones.

The M_w7.5+ subduction earthquake frequency varies little between 1901 and 2023 (one event every 212 days in average), still there are some slight variations. Consistent with previous studies, we identify two bursts of M_w8.5+ events during 1946-1965 and 2004-2011 periods. Furthermore, we confirm that some subduction zones hosted more M_w7.5+ earthquakes than others during the 1901-2023 period. For example, regions such as West Sunda, Japan-Kuril-Kamchatka, Aleutian-Alaska, Central and South America or Melanesia exhibit higher seismic activity levels in contrast to zones like  the Mediterranean, Ryukyus, SE Asia, Tonga-Kermadec, Cascades, Lesser Antilles or South Sandwich on the other.

We assembled the rupture envelopes for 77% of SQ2 events, with more than half involving asperities – defined here as patches that slipped by more than 50% of the maximum estimated slip. This dataset will enable us to carry out a large number of tests on the characteristics of the most/least frequently ruptured zones.

This new database will be soon available through the submap web tool (submap.fr).

How to cite: peyret, M., lallemand, S., arcay, D., and brizzi, S.: New insights from 1901-2023 Mw7.5+ subduction interface earthquakes catalog revisited: SubQuake2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8562, https://doi.org/10.5194/egusphere-egu25-8562, 2025.

Central Chile may not have experienced a major earthquake that ruptured the entire megathrust since 1730. At the same time, this stretch of the Chilean margin hosts major population centers which are endangered by such a future earthquake and the following tsunami. While geodetic techniques are most commonly used to constrain the state of the megathrust and thus the possible extent of future large earthquakes, the analysis of background microseismicity can also deliver valuable information. In previous studies, it was suggested that highly coupled regions on the megathrust exhibit very low seismicity rates and low b-values, but are surrounded by half-ellipses or ‘rims’ of enhanced seismicity. Regions of lower coupling generally exhibit higher seismicity rates and higher b-values, and in some cases show seismicity clusters with swarm-like behavior.

To extend this type of analysis in Central Chile, we applied state-of-the-art automatic approaches, i.e. a deep-learning based picker (EQTransformer) and a novel associator (PyOcto) to available continuous seismic data from Central Chile, covering the years 2014-2023. We thus retrieve a seismicity catalog that comprises >350,000 events, to which we apply relative relocation via hypoDD to retrieve high-resolution sharpened features. We classify the events into different populations corresponding to the main seismogenic regions (plate interface, downgoing slab, upper plate).

In this contribution, we mainly analyze the plate interface seismicity in the catalog in terms of statistical properties and temporal evolution, evaluate the spatiotemporal detection capacity of our approach by retrieving completeness magnitudes, and correlate the retrieved features to existing evidence from other disciplines.

How to cite: Sippl, C., Tassara, A., Moreno, M., Morales-Yáñez, C., and Ruiz, S.: Characterizing the plate interface with microseismicity: Central Chile, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6600, https://doi.org/10.5194/egusphere-egu25-6600, 2025.

Subduction zones host the majority of global earthquakes, from shallow megathrust and outer-rise to deep intraplate earthquakes. Although it is well established that subducting slabs are the primary energy source for most earthquakes, the quantitative relationship between slab dynamics and seismic events remains poorly understood. In this study, we develop a comprehensive 3D geodynamic model of the Izu-Bonin-Mariana subduction system to connect long-term slab dynamics with earthquake activity. Our comparison of the modeled stress state predictions with observed earthquake focal mechanisms reveals that both shallow megathrust and outer-rise earthquakes, as well as deep earthquakes associated with plate bending at the mantle transition zone, can be explained by slab dynamics. However, the intermediate-depth (150-300km) earthquakes remain enigmatic. Additionally, our findings show a notable spatial correlation between the slab’s energy dissipation rate and the distribution of seismic activity. These correlations between model predictions and observed earthquake characteristics underscore the profound connection between earthquakes and the large-scale, long-term dynamics of mantle flow and subduction.

How to cite: Li, Y., Ribe, N., and Jia, Z.: Large-Scale Slab Dynamics as Drivers of Seismicity: Modeling Earthquakes in the Izu-Bonin-Mariana Subduction Zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14114, https://doi.org/10.5194/egusphere-egu25-14114, 2025.

The Taiwan Island is the product of the orogeny: the Philippine Sea Plate has subducted the Eurasia Continent Plate and formed Ryukyu Volcanic Arc in northern and northeastern Taiwan. The Datun Volcano Group (DVG) located in northern Taiwan is the westernmost member of the Ryukyu Volcanic Arc and has the widest extent and largest eruption among the volcanic rock areas. About 1 Ma, compressional stress transformed into extensional stress in northern Taiwan, and magma from the depth erupted to form about 20 younger volcanoes in the same area. During this period, the Taipei Basin gradually formed as a half graben on a normal fault, namely the Shanjiao Fault.

The DVG and the Shanjiao Fault have been identified to be active for micro-earthquake activities and topographical features, respectively, revealed by dense and high-resolution surficial monitoring systems in the DVG area. However, owing to rugged landscape and dense vegetations, geological boreholes are few and shallow (10 to 20 meters) so that the underground structure of the Shanjiao Fault in the DVG area are still unclear. In this study, broad-band seismic sensors cross the presumed fault trace of the Shanjiao Fault were set to collect natural microtremor (0.02–50 Hz) in order to acquire S-wave velocity structure near the potential positions of the Shanjiao Fault. The horizontal-to-vertical spectral ratio (i.e., HVSR) for single-station analysis is applied to reveal different dominant frequency for different volcanic products and the high-resolution frequency wavenumber method (i.e., F-K method) for array-station analysis is applied to reveal boundaries of geological structures.

The resultant dispersion curves derived from the F-K method show that the phase velocity decreases at the frequence of 1.5 Hz from the southern array data, while it increases at 2–3 Hz from the northern array data within the hanging wall of the Shanjiao Fault. In addition, the results of this study also indicate that the stations on thin loose deposits (pyroclastic debris) underlying by lava flow (andesite) show the higher dominant frequency, and these stations are near crater, while the stations farther from the craters have lower dominant frequency with thick loose deposits. And these results are also consistent with the topography revealed by high-resolution digital terrain model of the Datun Mountain area.

Based on the results, the future work of this study will be describing spatial geometry of the Shanjiao Fault by inversion method for propose s-wave velocity structures in the study area.

How to cite: Tseng, C.-H., Chu, P.-Y., Wu, C.-F., and Rau, R.-J.: Shallow geological structures revealed by applying microtremor analysis in volcanic area in northern Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8344, https://doi.org/10.5194/egusphere-egu25-8344, 2025.

Permanent GNSS stations providing high-rate data have become a well-established practice, offering valuable insights into co-seismic displacement and seismic wave propagation during earthquakes. This study focuses on the co-seismic displacements induced by the doublet of earthquakes with magnitudes Mw 7.8 and Mw 7.6 in south-eastern Turkey in February 2023. GNSS data of 1Hz were analyzed to assess both co-seismic and transient deformation in near and far-field.

The analysis includes 1 Hz GNSS data from over 41 continuously operating stations located near the earthquake sequence in southwest Turkey (<500km distance from epicentre), and an additional 54 far-field stations distributed across the Aegean Sea and mainland Greece in a distance of 500 to 1000km from the two earthquakes epicentre. The data are processed using the Precise Point Positioning (PPP) method with Ambiguity Resolution to estimate position time-series and displacement waveforms. The study investigates correlations between the seismic motion and the distance from the epicentre, identifying variations in parameters such as peak ground displacement (PGD) and spectral characteristics of seismic waves across different frequency bands and radial distances.

The results of this study reveal the relationships between seismic parameters and epicentral distance and provide insights into the interplay between static and dynamic interactions associated with large-magnitude seismic events.

The findings contribute to a deeper understanding of the widespread consequences of major earthquakes, extending beyond 1000 km from the epicentre, and support the refinement of seismic hazard assessment and mitigation strategies.

How to cite: Anastasiou, D., Psimoulis, P., Papanikolaou, X., and Tsakiri, M.: Near and far-field deformation from the 2023 Turkey earthquakes using GNSS Data , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18416, https://doi.org/10.5194/egusphere-egu25-18416, 2025.

The tectonics of the Eastern Mediterranean is governed by the convergence of the Eurasian, Nubian and Anatolian plates and characterized by the highest seismic hazard in Europe. Some boundaries between these plates are well defined and localized, such as the Hellenic subduction zone or the North Anatolian Fault (NAF). In contrast, the junction between Nubia and Eurasia near the northwestern end of the Hellenic subduction remains poorly documented, while the transition zone between the western end of the NAF and the normal faults in the Gulf of Corinth is characterized by distributed deformation.

Over the last decades, GNSS measurements have revealed that the Adriatic promontory moves slightly differently from the Nubian plate. This motion is well described by two rigid blocks, Adria and Apulia, which act as indenters pushing into the Alps and the Dinarides towards the north-east. Historically, the Balkan region has been considered a stable part of the Eurasian plate, experiencing negligible strain. However, recent GNSS data show that the entire peninsula undergoes significant deformation resulting in a clockwise rotation towards the Aegean domain, extending as far as central Serbia. Such deformation is outlined by recent earthquakes in Croatia (Petrinja, 2020) and Albania (Durrës, 2019). The style, magnitude, and spatial extent of the distributed deformation across the Dinarides and Albanides remain poorly constrained due to sparse GNSS measurements and the low strain rates expected in these regions.

In this study, we invert for the strain rate tensor over Italy, the Balkans and continental Greece using (i) the combined GNSS velocity field by Pina-Valdes et al. 2021 that offers the best coverage to date and (ii) the Bstrain code published by Pagani et al. 2021 which employs a Bayesian transdimensional approach. Our analysis produces probabilistic continuous maps of the strain rate tensor invariants (e.g. the second invariant and dilatation), vorticity, and interpolated horizontal velocities. We assess these results through statistical indicators derived from their probability density functions (PDFs), and make them openly accessible via an online plateform https://bstrainplotter.univ-lyon1.fr, in agreement with the FAIR principles.

These findings enable a detailed tectonic and geodynamic analysis of the region, grounded in a refined knowledge of surface deformation. We delimit the various tectonic styles based on the strain rate tensor's principal directions and highlight key features through representative cross-sections. This provide insights, for example, on the along-strike segmentation of the strain rates along the Apennines, the continuous arc-shaped compressive limit to the north and east of the eastern Alps, and a marked zero divergence line continuous from the Albanides region to the Hellenic subduction zone. 

How to cite: Métois, M., Lasserre, C., Meridi, A., Henriquet, M., and Bodin, T.: Bayesian estimation of surface strain rates in the peri-Adriatic, Balkans and Aegean region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5477, https://doi.org/10.5194/egusphere-egu25-5477, 2025.

This study investigates the kinematic behavior and deformation patterns of the Psathopyrgos normal fault in the Western Gulf of Corinth (GoC) using space geodetic techniques such as InSAR and GNSS time-series analysis. The Psathopyrgos fault is the main onshore tectonic structure of the north-dipping fault system and is located near the western tip of GoC (Tsimi et al. 2007). The crustal extension across the Corinth rift increases from east to west and reaches its maximum value in the western GoC where the Psathopyrgos fault is located.  Our analysis covers the period from 2016 to 2022 and leverages LiCSBAS, an open-source package, for InSAR time series analysis with the N-SBAS method. We combine our InSAR results with GNSS velocities in order to obtain a more accurate estimation of the deformation field. Through the InSAR time-series analysis, the E-W fault trace of the Psathopyrgos fault was mapped in detail as the ground motion pattern is affected by the long-term displacement of the fault. An offset across the fault trace was detected in the LOS position time series. The Up-Down component of InSAR confirms the LOS findings thus indicating a mainly vertical component of motion and shows an average velocity offset of 4.5 mm/yr between the two blocks across the fault, i.e., the footwall and the hanging-wall. This geodetic evidence confirms the creeping behavior of the fault. The E-W cross-sections of the InSAR velocity data also show contrasting patterns of motion. The E-W component of InSAR reveals a right-lateral slip along the western segment of the fault. An additional finding was provided by the examination of the time-series of the pixels that are located on the hanging wall of the Psathopyrgos fault. These pixels include offsets related to possible co-seismic or passive slip of Psathopyrgos fault because of the 17 February 2021 M5.3 offshore earthquake (Zahradnik et al. 2022). The offset in the time-series was about 0.01 m. The geodetic data indicate a possible surface rupture or passive slip along the Psathopyrgos fault plane, together with continuous motion that could relate to migration of fluids and aseismic creep. These new findings suggest a combination of slip history including fault rupture, aseismic creep, and fluid migration, thus, contributing to a better understanding of the interseismic and co-seismic dynamics of the Psathopyrgos active fault.

Tsimi, Ch., Ganas, A., Soulakellis, N., Kairis, O., and Valmis, S., 2007. Morphotectonics of the Psathopyrgos active fault, western Corinth rift, central Greece. Bulletin of the Geological Society of Greece, vol. 40, 500-511 http://dx.doi.org/10.12681/bgsg.16657  .

Zahradník, J., Aissaoui, E. M., Bernard, P., Briole, P., Bufféral, S., De Barros, L., et al. (2022). An atypical shallow Mw 5.3, 2021 earthquake in the western Corinth rift (Greece). Journal of Geophysical Research: Solid Earth, 127, e2022JB024221. https://doi.org/10.1029/2022JB024221

How to cite: Tsironi, V. and Ganas, A.: Characterizing deformation processes along the Psathopyrgos fault, western Gulf of Corinth through InSAR and GNSS time-series analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5905, https://doi.org/10.5194/egusphere-egu25-5905, 2025.

The ML 6.2 Petrinja earthquake, which struck on December 29, 2020, is one of the most significant continental earthquakes in central Europe in recent years, following previous major events in Central Italy and Albania. This earthquake, along with the magnitude 5.5 event in Zagreb earlier in March 2020, resulted in substantial loss of life and extensive damage to infrastructure, highlighting the region's high seismic hazard. Historical records reveal a consistent pattern of seismic activity in the Petrinja area, characterized by the activation of NW-SE right-lateral faults linked to the Pannonian basin dynamics. Following the Petrinja earthquake, a comprehensive survey was conducted by the Croatian Geological Survey in collaboration with European geologists and engineers, utilizing conventional and advanced satellite and airborne technologies such as GNSS (Global Navigation Satellite System),(Unmanned Aerial Systems (UAS), Airborne Laser Scanning (ALS) and InSAR (Interferometric Synthetic Aperture Radar) to assess environmental impacts. The study's findings underscore the importance of understanding active fault systems and suggest enhanced cooperation between scientists to address the complex seismic risk in the region. The research emphasizes the need for an in-depth analysis of fault behaviour to develop effective risk mitigation and disaster preparedness strategies.

How to cite: Kordić, B. and Maslač, J.: Impact and Insights from the 2020 Petrinja Earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8617, https://doi.org/10.5194/egusphere-egu25-8617, 2025.

Slovenia is located on an active convergent boundary between the Adriatic microplate and the Eurasian plate, characterized by compressive active fault systems and moderate seismicity. Relatively high seismic hazard in W Slovenia is related to the Dinaric Fault System of dextral strike slip faults. After the Idrija fault, second most important is more than 100 km long Raša Fault. Its activity has been estimated in previous geomorphological studies and the slip rate is estimated at about 0.7 mm/year. Due to its length, relatively large earthquake magnitudes are expected in the albeit less likely scenario of the entire fault trace activation.

Raša Fault runs through carbonate and siliciclastic rocks. The geomorphological trace of the Raša fault is well expressed through prevailing carbonate rocks, while difficult to follow through siliciclastic rocks. Quaternary deposits are generally thin and mainly present along the river and some streams crossing the fault.  The broader area is characterized by a complex regional geologic setting, overprint of various tectonic phases, low levels of deformations, high level of erosion and the influence of both karstic and slope mass processes, making it difficult to identify and characterize the fault solely by means of structural geologic and tectonic geomorphological mapping. Therefore, we employed an extensive GPR and ERT survey to support the seismotectonic characterization at several locations along the fault with supposed favorable characteristics of Quaternary sediments for further paleoseismological investigations. Both methods were consistent in delineating lateral and vertical changes in sediment composition, along with strike-slip fault related level of bedrock and sediment deformation. Overall, high amplitude GPR reflections resulted from bedrock and coarse alluvial sediments, and attenuated with the increasing clay/water content in the sediments limiting the depth of investigations, which was resolved with the ERT. The attenuated GPR signal along with an abrupt termination of reflectors was useful to delimit potential zones of highly fractured media, which in term result in a decrease of ERT determined resistivity. The Raša fault core zone is nicely visible with both methods, and is characterized by a low resistivity anomaly in ERT and by attenuation and abrupt termination of GPR reflections, extending from the overlaying alluvial sediment deposits to greater depths in the bedrock. Combining both methods we got a better insight related to the fault zone location and its extension bellow the Quaternary cover, as well as in some cases within the deposits. Moreover, general information about the sedimentological and hydrogeological characteristics  was obtained, contributing to characterization of candidate sites for consecutive paleoseismological investigations. Our study contributes valuable new data on the near-surface deformation along the active Raša Fault and demonstrates the successful integration of geophysical techniques into the study of active faults within this complex environment.

How to cite: Rupar, L., Jamšek Rupnik, P., Gostinčar, P., Jež, J., Placencia Gomez, R. E., Atanackov, J., Zajc, M., and Gosar, A.: High-resolution geophysical investigation for the seismotectonic characterization of the Raša Fault, SW Slovenia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12786, https://doi.org/10.5194/egusphere-egu25-12786, 2025.

The western structural boundary of the Makran Subduction Zone (MSZ) corresponds to the Minab–Zendan–Palami (MZP) dextral strike-slip fault system, a critical transitional zone that accommodates the velocity gradient between the Zagros and western Makran regions. This study investigates the kinematic behavior and mechanisms of the MZP fault system to enhance our understanding of fault dynamics and their implications for seismic hazards and subduction-zone processes. Continuous monitoring is essential to advance our knowledge of this complex fault system. However, the existing GPS network lacks the density \ necessary for effective fault monitoring. To address this knowledge gap, Synthetic Aperture Radar (SAR)-based analysis is well-suited for studying the MZP fault system. This study applies the Small Baseline Subset (SBAS) method to a decade of SAR data from the ascending path (57) of Sentinel-1A (2014–2024). The results detect and quantify subtle crustal deformations and fault kinematics with high precision. We classified the fault system motions based on their displacement characteristics. In conclusion, this research makes significant contributions to the fields of geodesy and geodynamics by refining our understanding of fault systems at tectonic boundaries and providing critical insights for seismic hazard assessments in this tectonically complex and seismically active region.

How to cite: Namdarsehat, P. and Milczarek, W.: Decade-Long InSAR Time-Series (2014–2024): Fault Kinematics and Seismic Hazards across the Minab–Zendan–Palami Fault System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17525, https://doi.org/10.5194/egusphere-egu25-17525, 2025.

The Pokupsko earthquake in Oct. 1909 (Ms 5.7) and, more recently, the Petrinja earthquake in Dec. 2020 (Mw 6.4), both occurring along the same Petrinja-Pokupsko Fault system, induced soil liquefaction phenomena in the alluvial plain of the Kupa river (Croatia). While surface evidence of liquefaction was limited in the 1909 event, the 2020 earthquake triggered more extensive and well-developed liquefaction features along the riverbanks. These features included sand blows, fissures, ground settlements, and lateral spreading, highlighting the increased susceptibility of the alluvial deposits to seismic shaking in the 2020 event. 

The use of remote sensing techniques enhances the understanding of the spatial distribution of liquefaction occurrences and their subsequent impacts. 
Drone surveys and a high-resolution Digital Elevation Model (0.5 m resolution) reveal that liquefaction is concentrated within the lowest Holocene terrace and specific areas shaped by fluvial processes. Of particular note is the higher density of sand blows observed in the convex sections of river meanders and the increased lateral spreading at the inflection zones of meanders, where point bar formations become tightened.
Lateral spreading along the Kupa river can also be mapped and quantified from optical image correlation of high-resolution aerial images (30 cm resolution) taken before and after the 2020 Petrinja earthquake. These data show that lateral spreading locally exceeds 1 m of displacement toward the river and is generally confined to within 200 m of the riverbanks. 

On a smaller scale, geological and geotechnical surveys in different sites along the Kupa river point to other conditions influencing liquefaction occurrences and their effects. Soundings and sampling have shown that all sand blows originate from point bars buried between 3 m and 6 m below the surface covered by silty sediments. The soil strength and the thickness of this covering sediment layer are key parameters controlling the occurrence of sand blows. In addition, OSL and 14C dating indicate possible paleo-liquefaction for a sand dyke sealed below the upper part of the aforementioned cover. 

This combined approach facilitates the identification and detailed characterization of the areas most susceptible to liquefaction in 2020 and historically along the Kupa river. However, in these regions, the surface cover may impede the emergence of liquefied soils to the surface or mask their presence.

How to cite: Moiriat, D., Maslač Soldo, J., Henriquet, M., Wacha, L., Hürtgen, J., Louis, K. J., Nguyen, L., Gelis, C., Benz-Navarette, M., Reiffsteck, P., Luong, T.-A., and Belić, N.: Characterisation at different scales of earthquake-induced soil liquefaction along the Kupa river (Croatia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6914, https://doi.org/10.5194/egusphere-egu25-6914, 2025.

Earthquake nests are defined as volumes of intense intermediate-depth seismicity which are isolated from any surrounding seismic activity. The high seismic activity within these earthquake nests occurs continuously and thus sets them apart from other seismic sequences such as earthquake swarms or aftershocks. Among the known earthquake nests, the Hindu Kush earthquake nest is the most active and has produced a large earthquake (MW ≥7) every 10-15 years. The intermediate-depth seismicity in this nest extends to a larger depth (up to 250 km) than in other earthquake nests and it is characterized by a bimodal distribution with an earthquake gap at approximately 150 km depth. Despite the depth of these earthquakes, they pose a significant seismic hazard. The continuous seismic activity is commonly related to subducting and detaching slabs.  
To understand the physical mechanisms and the tectonic environment of this intermediate-depth earthquake nest, we aim to conduct data-driven numerical simulations. These will determine the deformation state in the Hindu Kush and the controlling mechanisms of the detachment process. These data-driven models require two main ingredients: 1) a synopsis of existing data and 2) an understanding of the impact of model parameters (e.g. the rheology of crust, lithosphere and mantle). 
We used the open-source Julia package GeopyhscialModelGenerator.jl to create a synopsis of existing datasets of earthquake locations, seismic tomographies, Moho topographies and other datasets that will serve as the basis for the three-dimensional models.   
Based on this synopsis, we constructed 2D thermomechanical models incorporating a non-linear visco-elasto-plastic rheology to investigate the deformation state of a detaching slab and the underlying mechanisms controlling the detachment process. This analysis includes the effects of the subducted lower crust as well as the rheological properties of the eclogitized lower crust and the lithospheric mantle.
First results show that slab detachment depends on the viscosity ratio between the lower crust and lithosphere. Deeper initial depths of the lower crust, generate shorter detachment times. The detachment times increase linearly for shallower initial depths and the detachment time offset is smaller for increasing viscosity ratios. Increasing viscosity ratios create higher ratios of detachment depth to initial depth. The depth ratio offset is higher for larger viscosity ratios and shallower initial lower depths. The depth ratio varies by about 20% of the initial depth which is in the range of the Hindu Kush's earthquake nest. 

How to cite: Weiler, T., Piccolo, A., Spang, A., and Thielmann, M.: How to generate deep earthquakes in the Hindu Kush? - A data driven modelling approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6856, https://doi.org/10.5194/egusphere-egu25-6856, 2025.

The Mw 6.4 Petrinja earthquake, which struck Croatia on December 29, 2020, is among the most powerful earthquakes recorded in the slowly deforming region of Eastern Europe. In areas of low tectonic strain, limited seismic monitoring and the sporadic occurrence of strong earthquakes often hinder detailed analyses of coseismic ruptures preventing the scientific community to fully understand the processes governing these moderate and destructive events. In particular, it's not clear whether those continental earthquakes follow the same scaling laws than the ones occurring on mature faults, hence the need to better understand the source of these events.

Seismic source inversions and InSAR-based models from multiple studies indicate that the coseismic rupture of the Petrinja earthquake results from a single patch of right-lateral slip. On the other hand, we showed in a previous study that discontinuous surface ruptures and slip inversions of near-field geodetic benchmarks suggest rather along-strike complexities of the fault slip (Henriquet et al., 2023). To better constrain the slip distribution of the Petrinja earthquake, we leverage dense near field measurements from optical image correlation and numerous geodetic benchmarks together with InSAR data. We first assess the sensitivity of the model to each dataset to show that slip patterns are overall consistent to first order, although significant differences appear along dip, mainly depending on the distance between the fault trace and the considered measurements. We then jointly invert all the displacement data to provide a robust solution of the coseismic slip. The results confirm that the coseismic slip occurred on a near-vertical strike-slip fault at shallow depths, less than 10 km, with significant slip extending to the surface locally. It also indicates that fault bending near Kriz influenced the rupture propagation, as the largest slip, exceeding 3 meters, was concentrated in the northwestern section at depths of less than 5 km and that a deeper slip of smaller amplitude is required by the data to the southeast. This along-strike variation in slip depth and amplitude also correlates with changes in aftershocks rate and average depth (Herak et al., 2023), which confirms that the Petrinja fault is not a straight, mature fault system. This complexity in the slip distribution is in agreement with the large stress drop values obtained by seismological studies (Lončar et al., 2024). In conclusion, this study offers new insights into the seismogenic source of the Petrinja earthquake and highlights the value of combined displacement fields in improving source models of moderate intracontinental earthquakes.

How to cite: Henriquet, M., Métois, M., Kordić, B., Hollingsworth, J., Cavalié, O., Lasserre, C., Baize, S., and Benedetti, L.: Unraveling the complex rupture of the 2020 Mw 6.4 Petrinja Earthquake (Croatia): insights from joint inversion of geodetic benchmarks, InSAR and optical correlation data., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8048, https://doi.org/10.5194/egusphere-egu25-8048, 2025.