The southern Peru subduction zone is a complex region, marking the transition between the flat slab associated with the Nazca Ridge subduction in the North and a much steeper subduction in the south. The area has been affected by several large earthquakes over the past 20 years, like the Mw 7.2 earthquake that occurred on June 28th 2024 close to the city of Acari, in an area that already ruptured in 2013 and 2018.
Here we use data from 26 seismic stations active from March 2022 to December 2024 as part of the DEEPTrigger project, along with 16 permanent Peruvian stations and 15 permanent Chilean stations, to create a 3-year seismicity catalogue of South Peru. Using PhaseNet for the detection and picking of phases and PyOcto for their association, we obtain a total of 154645 events. These earthquakes are located with NonLinLoc using a new 3D P and S-wave velocity model of the region obtained from full-waveform inversion. They are then relocated using double difference methods with cross-correlation times to obtain precise locations. This allows us to image seismic structures along the subduction zones, thus demonstrating the influence of interseismic coupling and of bathymetric features like the Nazca Ridge on seismicity patterns. We focus in particular on the Acari sequence, which occurred at the edge of the Nazca Ridge. The Mw 7.2 mainshock was preceded by a Mw 6 foreshock on June 16th 2024, with both earthquakes seemingly occurring at the plate interface. We show that both the foreshock and the mainshock activated intraslab seismicity along the whole edge of the ridge down to 100 km depth, thus providing a good example of far-field interactions between deep and shallow regions of the subduction.
How to cite: Chalumeau, C., Sanchez-Reyes, H., Chevrot, S., Lovery, B., Villegas, J.-C., Gonzales, A., Langlais, M., Norabuena, E., Munchmeyer, J., Monteiller, V., Kan, L., Tavera, H., and Socquet, A.: Deep-shallow interactions in the 2024 Acari sequence (South Peru), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16913, https://doi.org/10.5194/egusphere-egu25-16913, 2025.
A well-established characteristic of intermediate-depth earthquakes is that they are deficient in aftershocks to shallow earthquakes of equivalent magnitude. The lack of aftershocks suggests faults within slabs are relatively insensitive to static stress changes on the order of earthquake stress drops. In contrast, some studies have reported significant changes in the frequency of seismicity within slabs following Mw 8-9 megathrust earthquakes, which would imply some level of stress sensitivity to stress transfer at intermediate depths. I will describe work searching for globally consistent signals of earthquake rate-changes within subducting slabs in response to stress transfer using both regional and global earthquake catalogues and outline some implications of our findings for the mechanisms of intermediate-depth earthquake generation.
How to cite: Wimpenny, S. and Craig, T.: Re-Examining Temporal Variations in Intermediate-Depth Seismicity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2270, https://doi.org/10.5194/egusphere-egu25-2270, 2025.
In subduction zones, earthquakes at depths between 60 and 100 km occur within the subducting slab rather than at the slab interface. The presence of fluids resulting from dehydration reactions in the medium is often called to explain the occurrence of these earthquakes, as fluids would favour the rupture (by fluid embrittlement). But the relation between the two processes is yet not fully constrained.
We study the aftershock sequence following the M7.1 2003/05/26 intraslab earthquake which was located off the Miyagi prefecture coast, in Japan, at 70 km-depth. This sequence displays characteristics that are promising for studying the intraslab and the relations between seismicity and fluid pressure (high aftershock rate, rupture of both the crust and the mantle of the slab, expanded instrumentation...).
The analysis of the catalogue of seismicity and focal mechanisms provides information on the principal characteristics of the aftershock sequence (Omori-Utsu law, Gutenberg-Richter law). In particular, the aftershock sequence follows a nearly perfect Omori’s law with a p-exponent depending on depth. This extremely good agreement between the data and the model appears to be due to the absence of large aftershocks, as confirmed by a significant deviation of the frequency-magnitude relationship from the Gutenberg-Richter law at large magnitudes. An application of the ETAS model to the sequence suggests that most of the sequence would be triggered by the M7.1 itself, i.e the aftershocks play no role in triggering more aftershocks. Moreover, the temporal distribution (although it has to be confirmed after Template Matching reevaluation of the catalogue) and inversion of stress field in the small aftershock zone show that, unlike the slab interface, the area inside the slab does not seem to be disturbed by the nearby occurrence of M9 Tohoku-oki earthquake (2011/03/11).
We conclude from our analyses that this intraslab sequence is characteristic of a very critically stressed crustal and upper mantle volume implying strong faults that are not sensitive to large stress perturbations. Moreover, if fluids are involved, then they are likely to be drained off from the top of the activated volume as suggested by the depth dependence of the Omori-Utsu’s p-value, possibly playing a role in the subsequent occurrence of the 2011 megathrust Tohoku-Oki earthquake which hypocenter is updip this sequence.
How to cite: Costes, L., Marsan, D., and Gardonio, B.: What controls seismicity at intermediate depths in subducting slabs : a study of the M7.1 2003 Miyagi-oki intraslab earthquake sequence, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-476, https://doi.org/10.5194/egusphere-egu25-476, 2025.
The accurate location of intermediate-depth earthquakes has proven to be one of the more enduring problems in global seismic location studies. Complicated in many cases by a paucity of near-field observational data, the determination of accurate source depths for such earthquakes, in particular, has proven to be elusive. As a result, and despite improvements in recorded seismic data density and quality, the distribution and controls of these events remain poorly understood.
Depth phases (near-source surface reflections, e.g. pP, sP, sS) are crucial for the accurate determination of earthquake source depth using global seismic data. However, such phases are often difficult to detect, suffering from low signal-to-noise ratios, are disguised in the direct-wave coda, and often suffer from an ambiguity as to which depth phase has been observed. Here, we draw on the vast expansion of seismic network coverage over the last few decades to develop an approach using adaptive medium-aperture teleseismic arrays to boost the detection, identification, and inclusion of depth phases, for both P and S waves. Our approach leads to a radical increase in the number of depth phases detected, particularly for smaller-magnitude events, down to a magnitude of 4.7. We then assess how the inclusions of increased depth phase observations impacts on the resolution and accuracy of global earthquake location algorithms.
Using data from 30 years of earthquakes along the length of the South American subduction zone, we show the potential for such array-based observation to enhance current global location routines, producing higher-resolution earthquakes catalogues capable of imaging the complex distribution of intraslab seismicity. With this enhanced earthquake catalogue, fine-scale variations in intraslab seismicity are detectable, shedding light on the geodynamic processes behind such earthquakes.
How to cite: Craig, T., Blackwell, A., and Rost, S.: High-resolution relocation of intraslab earthquakes beneath South America using global seismic data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15967, https://doi.org/10.5194/egusphere-egu25-15967, 2025.
Fluid plays a pivotal role in the dynamics of subduction zones and earthquake activity. Recent observations have revealed that some megathrust earthquakes (Mw > 6.8) are followed by abundant aftershocks (Mw > 4), while others of similar magnitude produce few or none. We conducted a series of numerical simulations using MDOODZ 7.0, a geodynamic modeling framework, to systematically investigate the factors controlling subduction zone geometries. By varying key parameters, including plate convergence velocity, the thicknesses of continental and oceanic lithospheres, and the age of the oceanic plate, we identified the conditions that lead to the development of contrasting subduction regimes, specifically flat versus steep subduction geometries. To gain insights on the pore-fluid dynamics in different subduction geometries, we explored the variations in fluid release by coupling the geodynamic models with Perple_X calculations, which allowed us to model the interaction between the evolving fault zones and the dehydration reaction boundaries under varying pressure-temperature conditions. Furthermore, we quantified the amount of fluid released during these reactions and determined their depth within the subduction zone. Our preliminary results suggest that the depth of serpentinite dehydration occurs around ~60 km. These findings will be correlated with regions of increased seismic activity and higher aftershock density.
How to cite: Gunatilake, T., Duretz, T., Moulas, E., Gerya, T., and Candioti, L.: Investigating Fluid Release and Aftershock Activity in Subduction Zones: A Numerical Study Using MDOODZ and Perple_X, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19079, https://doi.org/10.5194/egusphere-egu25-19079, 2025.
The ability of megathrust fault segments to generate devastating interplate earthquakes (and triggered tsunamis) has been long recognized as partially controlled by one or more factors related to the plate tectonics configuration of subduction zones. However, there is still debate regarding the actual contribution of each factor and possible combinations of them that could favor the occurrence of large earthquakes. We investigated (Crisosto and Tassara, GRL2024) the relationship between the seismogenic behavior of megathrusts segments at a global scale and various subduction parameters (subducting plate age and roughness, slab dip, convergence speed and azimuth, distances to closest ridge and plate boundary). For each of 157 trench-perpendicular transects covering most of the subduction zones worldwide we estimate one value of the afford mentioned parameters and one b-value of the frequency magnitude relationship (Gutenberg and Richter, 1946) that parameterizes the relative amount of large to small earthquakes. For this we use the ISC global seismicity catalogue between 1900 and 2022 considering events located less than 10 km around the SLAB2.0 model (Hayes et al., 2018) and computed the b-value for each transect implementing the b-positive estimator (van der Elst, 2021), which helps avoiding contamination of the estimates by transient changes during aftershock sequences. With this dataset we performed a parametric approach by implementing three decision tree‐based Machine Learning (ML) algorithms to predict the b‐value as a non‐linear combination of subduction variables. Using the Shapley Additive exPlanation (SHAP) values to interpret the ML results, we observe that plate age and subduction dip are the most influential variables, as also noticed by previous authors (e.g. Nishikawa and Ide, 2014). However, our results contradict these previous views because we observe that older, not younger slabs, that are associated to shallow‐dipping plates correlates with low b‐values, pointing to higher megathrust stress (using the b-value as a stressmeter, as proposed by Schoerlemer et al., 2005). This pattern is attributed to the higher rigidity of older plates, increasing flexural strength that opposes to bending, generating a shallow penetration angle, increasing the frictional interplate area and therefore augmenting the likelihood of larger earthquakes. These findings shed light on the complex dynamics of seismic activity on a global scale and provide valuable information for understanding the megathrust earthquake behavior and its hazard assessment worldwide
How to cite: Tassara, A. and Crisosto, L.: Relating Megathrust Seismogenic Behavior and Subduction Parameters via Machine Learning at Global Scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17108, https://doi.org/10.5194/egusphere-egu25-17108, 2025.
The Balkans Peninsula is one of the most seismic areas in Europe, with destructive earthquakes causing significant damage and fatalities in recent decades. Recent seismic activity (Mw 6+), occurring in diverse tectonic settings, reflects the complexity of the regional geodynamic setting. Despite efforts, the Balkans remains poorly instrumented compared to other European regions.
The latest study of the regional kinematics [1], based on a combination of GNSS velocity fields, indicates that most of the peninsula is expected to move at very low velocities ranges, well below 1 cm/yr. Large areas remain devoted of GNSS stations, and the overall network is too sparse to identify deformation associated with each individual active structures. While InSAR has been used locally for coseismic or anthropogenic displacement studies, no regional-scale study has yet quantified long-term interseismic velocities.
Our aim is to take advantage of a new InSAR dataset processed by the FLATSIM service [2] based on Sentinel-1 data over the western Balkans. FLATSIM interferograms, displacement time series and velocity maps are available over the region, covering 360 000 km². With a ground resolution of 240 m and 6-12 days temporal resolution, this dataset is used to better quantify the current deformation. From the FLATSIM displacement time series, we initially separate the linear, seasonal, and, where necessary, coseismic components for each track. We then reference the InSAR velocity maps (the extracted linear components) into an ITRF14 reference frame [3], adapting the approach of [4]. This allows us to produce the first large-scale InSAR velocity field for the Balkans Peninsula, referenced in ITRF14 , with very limited use of GNSS data.
We then analyze serial profiles of LOS velocities across major active structures in the region. This reveals, with unmatched resolution, tectonic deformation patterns related, for example, to the Dinaric thrusts , or to lithospheric processes across the eastern Balkans, where a 150 km-long wavelength North-South velocity gradient exceeding 1 cm/yr is observed north of the Gulf of Corinth, over Central Macedonia and Thessaly regions.
We then perform a standard 3D decomposition of the LOS velocity field. There, we use the 2D GNSS velocity field provided by [1], along with a newly refined velocity dataset interpolated from its original dataset, based on a Bayesian transdimensional estimation (Bstrain code, [5]). The horizontal component is estimated either as an eastern component, fixing the northern component at that given by the interpolated GNSS field, or using the azimuth of this GNSS field as the direction of the horizontal component. This 3D decomposition highlights the added value of InSAR in providing spatially continuous data and unveils new insights, in particular regarding horizontal velocity field, where the localization of transtension in the inner Albanides is clearly refined. Finally, the richness of the dataset leaves many more motions to explore, including landslides, basins or aquifers [6], or induced by anthropogenic activities [7].
References:
[1] Piña‐Valdés et al. (2022), 10.1029/2021JB023451
[2] Thollard et al. (2021), 10.3390/rs13183734
[3] Altimimi et al. (2016), 10.1002/2016JB013098
[4] Lemrabet et al. (2023), 10.1029/2022JB026251
[5] Pagani et al. (2021), 10.1029/2021JB021905
[6] Serpelloni et al. (2018), 10.1002/2017JB015252
[7] Métois et al. (2020), 10.5194/se-11-363-2020
How to cite: Meridi, A., Métois, M., Lasserre, C., Doin, M.-P., and Durand, P.: Active Straining of the Balkans Peninsula: insights from spatial geodesy (InSAR and GNSS) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11094, https://doi.org/10.5194/egusphere-egu25-11094, 2025.
The Amorgos-Santorini region (Hellenic Volcanic Arc, Greece), suffered the most powerful earthquake in the Mediterranean in the 20th century (1956, Mw ~7.5). This event caused casualties, severe damage and a large tsunami. The epicentral area is offshore and is characterized by several basins bounded by submarine faults accommodating back-arc extension and the Anatolian extrusion. Recently, the Amorgos fault was identified as the causative fault of the 1956 Amorgos earthquake. However, the characteristics of this fault, such as its detailed geometry, segmentation and kinematics remain unclear and debated. Using new high-resolution bathymetric data and sediment cores, we present a detailed mapping of this fault and its neighbors.
The Amorgos fault is composed of three segments separated by relay zones. Taking into account the onshore geology, where E-W striking late Miocene normal faults are mapped, the segmentation could be controlled by structural heritage. Offshore, all but the southernmost segments of the Amorgos fault exhibit cumulative scarps of at least 700 m in relief. The segments strike NE-SW, except for the northern one that displays a curved structure in its middle, at 60° with respect to the main fault (E-W striking).
The central segment, where evidences of the 1956 earthquake rupture were found, is composed of several secondary faults that offset young geomorphic features at the seafloor (such as mass-wasting scars) with purely normal kinematics. In comparison, the curved northern segment shows fewer secondary faults, none of them offsetting the numerous mass-wasting scars observed along its trace. We also find here secondary NE-SW faults that are crosscutting its cumulative scarps, and are offsetting the Last Glacial Maximum wave-cut platform by up to 5 meters, testifying for their recent activity. These observations question the role of the northern E-W striking segment in the accommodation of the present-day stress regime (NW-SE extension), that may be now inactive, or activated as a strike-slip fault, although we do not observe markers laterally offset. We discuss how the geometry and segmentation of the Amorgos fault can impact the rupture propagation, especially in relation to the 1956 earthquake and morphology of the nearby faults.
How to cite: Palagonia, S., Leclerc, F., Larroque, C., Feuillet, N., Nomikou, P., Schmidt, S., and Escartin, J.: Fault segmentation, geometry and recent activity in the epicentral area of the 1956 Mw 7.5 Amorgos earthquake (Greece), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16612, https://doi.org/10.5194/egusphere-egu25-16612, 2025.
Northwest Croatia is a seismically active region located at the junction of the Eastern Alps, Internal Dinarides, and the Tisza mega block of the Pannonian Basin System. The area is shaped by the slow convergence of the Adriatic microplate and Eurasian plate (3–4.5 mm/year), driving complex Cenozoic tectonics and Pliocene-Quaternary transpressive fault activity. Among the active faults, the Sveta Nedelja Fault (SNF) is particularly understudied, despite its seismogenic potential. Positioned along the southern front of Mt. Žumberak, the SNF separates Triassic-Cretaceous carbonates in the north from Miocene basin deposits in the south.
Geomorphological analysis was conducted to investigate the structural characteristics and tectonic activity of the Sveta Nedelja Fault (SNF). The study included the construction of swath profiles perpendicular to the fault strike to examine variations in topography and identify gradients indicative of structural deformation. Detailed mapping and analysis of drainage patterns, particularly in the Konšćica sub-basin, were performed to assess fault-related geomorphic features such as vertical steps, knickpoints, and convex stream profiles.
Reconstruction of second-order drainage systems across the fault was undertaken to estimate potential displacements and identify alignments of streams and wind-gaps. This approach provided insights into both long-term tectonic processes and recent activity associated with the fault. These methods collectively aimed to delineate fault kinematics and assess its impact on regional landscape evolution. Future work will focus on quantifying deformation rates, employing age dating, geophysical and paleoseismological methods to better constrain the timing and extent of Quaternary fault activity. These findings are critical for understanding the neotectonic evolution of the Žumberak region and assessing seismic hazards, particularly in light of the 2020 Zagreb and Petrinja earthquakes, which underscore the urgent need for comprehensive seismic hazard assessments in Northwest Croatia.
How to cite: Maslač Soldo, J., Jamšek Rupnik, P., Matoš, B., and Kordić, B.: Pliocene to Quaternary activity of the Sveta Nedelja Fault in Northwest Croatia as revealed by geomorphological analyses , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20375, https://doi.org/10.5194/egusphere-egu25-20375, 2025.
Located within the active continental collision between the Adriatic microplate and Eurasia, Albania is an earthquake-prone country with one of the highest seismic hazard in Europe. A stark reminder of this was the occurrence of the Mw=6.4 Durrës earthquake in November 2019, which caused 51 fatalities and heavily damaged infrastructure in the port town of Durrës. Despite this, the country’s seismicity and velocity structure still remain poorly constrained. Our recent ANTICS large-N deployment aims to fill this knowledge gap by producing a high-quality seismic dataset from 382 temporary stations densely distributed along the southern half of the country during 2022-2024. Here we present the results of the processing of the continuous waveforms in order to extract a new catalogue of earthquakes and the inversion of a local velocity model for the region. Our semi-automatic workflow incorporates the detection and association of phases based on a fully automatic AI-based picker and associator (PhaseNet, HEX), the inversion of a 1D local velocity model for both P- and S-phases including station corrections terms, and the relocation of the entire catalogue using our newly derived velocity model and station corrections.
A total of 38 m phases were initially detected, of which 1.6 m were successfully associated to produce a catalogue of 18k events between October 2022 and May 2023. Magnitudes (ML) vary between -1.0 to 4.5, with a magnitude of completeness of 1.5. The seismicity is concentrated in clusters and along major known structures, with hypocentres mostly occurring between 5 and 25 km depth. Two particular clusters are noteworthy for their productivity and higher magnitudes. The first one affected the town of Klos, in the northern centre of the country during mid January 2023. Up to 700 events per day were recorded during this sequence that lasted for two weeks starting on the 13 of January 2023. The mainshock magnitude was ML=4.5, with up to 12 earthquakes with ML>3.0 during the sequence. Seismogenic depths were constrained between 5 to 20 km depth, and the sequence can be spatially related to a NW-striking normal fault which is also supported by the mainshock focal mechanism. The second cluster occurred during March 2023 nearby the town of Erseke, in the south-east of the country. Up to 800 events per day were detected during this sequence that lasted for ten days between 23 of March and 2 of April 2023. The magnitude of the mainshock was ML=4.3, with up to seven earthquakes with ML>3.0 during the sequence. Seismogenic depths were constrained between 3 to 17 km depth, and the cluster is spacially associated to a NNE-striking oblique normal fault which is corroborated by the focal mechanism of the mainshock. Overall, in terms of number of earthquakes, our catalogue represents a 17-fold improvement over the local Albanian catalogue, which is manually picked and uses only the permanent stations. The detected seismicity highlights the active nature of shallow seismogenic sources in Albania, and could be used to update seismic hazard maps in the region.
How to cite: Agurto-Detzel, H., Rietbrock, A., Tilmann, F., Dushi, E., Rama, B., and Schurr, B.: New insights into the local seismicity and velocity structure of Albania from the application of an AI-based earthquake detection workflow on a large-N seismic dataset, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17241, https://doi.org/10.5194/egusphere-egu25-17241, 2025.
Posters on site: Tue, 29 Apr, 14:00–15:45 | Hall X3
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 Mw7.5+ 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 Mw7.5+ 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 Mw8.5+ events during 1946-1965 and 2004-2011 periods. Furthermore, we confirm that some subduction zones hosted more Mw7.5+ 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.
How to cite: Cai, Y. and Bürgmann, R.: Surface Loading and Seismicity in Subduction Zones: Linking Stress Changes to Fault Failure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5798, https://doi.org/10.5194/egusphere-egu25-5798, 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 Louisville seismic gap associated with the subduction of the Louisville Ridge (LR) along the Tonga-Kermadec trench is a globally prominent feature. Due to the lack of near-field seismic monitoring, the earthquake potential and seismic behavior in this region have long been an enigma. In this study, we investigate the micro-earthquake activity of the Louisville seismic gap and its southern erosive area using a local network of ocean bottom seismometers. Over 6 months of offshore network deployment, our local catalog reaffirms the existence of the Louisville seismic gap at magnitudes ranging from Mw ~2.5 to 5.5. Furthermore, the width of the seismic gap revealed by our local catalog is much wider than the subducting seamount itself but aligns well with the flexural moat of the LR, indicating that additional features than just topographic relief control the occurrence of seismic gaps. To the south of the seismic gap, seismicity distribution over the forearc is not evenly distributed but shows a patchy characteristic dominated by three earthquake clusters that correspond well with morphological forearc depressions, and a deforming upper plate middle prism is revealed by upward migrated aftershock sequences. Given the widespread small relief highs in the subducting plate, we link the patchy seismicity to the occurrence of topographic anomalies, which might enhance fracturing along the base of the upper plate and ultimately contribute to basal erosion. Additionally, seismicity reveals deformation of the outer rise along trench-parallel normal faults with depths ranging from 5 to 25 km, indicating a highly faulted and hydrated downgoing plate, nurturing down-dip extensive intermediate-depth earthquakes, outlining a double seismic zone that is controlled by dehydration embrittlement.
How to cite: Liu, Y., Lange, D., and Grevemeyer, I.: Micro-Seismicity to the South of the Louisville Ridge-Tonga Trench Collision Zone: New Insight into Processes Controlling Seismic Gaps and Subduction Erosion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3652, https://doi.org/10.5194/egusphere-egu25-3652, 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 Sava Fault, a prominent structure within the Periadriatic Fault System in the Slovenian Southern Alps, plays a key role in the deformation partitioning of the Adria–Europe collision zone. However, many aspects of its activity remain inadequately constrained, including its slip rate and seismic history. In this study, we employed an interdisciplinary approach to investigate the late Quaternary activity of a short section of the fault, combining high-resolution lidar and photogrammetric digital elevation models, remote sensing analysis, geomorphological and structural-geological mapping, near-surface geophysics including electrical resistivity tomography and ground-penetrating radar, and optically stimulated luminescence dating.
Our results reveal subtle geomorphic indicators of fault activity and near-surface deformation, despite the challenges posed by dense vegetation, intense surface processes, and low slip rates. We estimate a slip rate of 1.8 ± 0.4 mm/a for the last 27 ka, exceeding previous long-term geomorphological and recent GNSS estimates, suggesting temporal variability in fault behavior. This variability aligns with observations from the Dinaric Fault System in the northwestern Dinarides, suggesting possible regional deformation patterns.
Our findings advance the understanding of fault dynamics and deformation processes in this low-strain environment, highlighting the seismic hazard potential of the Sava Fault. They also emphasize the importance of modern high-resolution remote sensing techniques and interdisciplinary approaches in studying faults with subtle geomorphic expressions. These results provide a foundation for future paleoseismological investigations to constrain the seismic history of the fault and refine regional seismic hazard assessments.
Reference: Jamšek Rupnik, P., Atanackov, J., Horn, B., Mušič, B., Zajc, M., Grützner, C., Ustaszewski, K., Tsukamoto, S., Novak, M., Milanič, B., Markelj, A., Ivančič, K., Novak, A., Jež, J., Žebre, M., Bavec, M., Vrabec, M. 2024. Revealing subtle active tectonic deformation: integrating lidar, photogrammetry, field mapping, and geophysical surveys to assess the Late Quaternary activity of the Sava Fault (Southern Alps, Slovenia). Remote sensing, 16, 9: 33 p. DOI: 10.3390/rs16091490.
How to cite: Jamšek Rupnik, P., Atanackov, J., Horn, B., Mušič, B., Zajc, M., Grützner, C., Ustaszewski, K., Tsukamoto, S., Novak, M., Milanič, B., Markelj, A., Ivančič, K., Novak, A., Jež, J., Žebre, M., Bavec, M., and Vrabec, M.: Interdisciplinary investigation of late Quaternary activity of the Sava Fault in the Slovenian Southern Alps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7549, https://doi.org/10.5194/egusphere-egu25-7549, 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. and the Branko Kordić: 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 Hindu Kush locates in the seismic zone of the Tibetan Plateau at the collision region of the Eurasian plate and the Indian Ocean plate. Earthquakes are frequent here, but a few relevant studies on earthquake anomalies was found. The Mw 6.4 Hind Kush earthquake occurred on January 11, 2024, with the epicenter near the Karakum Desert. On the basis of this earthquake, this study collected the microwave brightness temperature (MBT) data from AMSR2 instrument in the research area (), so as to analyze the potential anomaly before the mainshock. The general background and random meteorological disturbance were subtracted from the original MBT images, obtaining MBT residual images during the seismogenic year by the spatio-temporally weighted two-step method.
Based on the MBT residual images at 10.65 GHz horizontal polarization, we found a significant positive MBT anomaly appeared in the eastern part of Karakum Desert, on the immediate west of the epicenter, from three days before and two days after the earthquake. The temporal characteristics of the positive MBT anomaly could be described in sequence as: pre-EQ rising, near-EQ enhancing, co-EQ peaking, after-EQ persisting and dissipating eventually. Combining the multi-source remote sensing data such as surface temperature, microwave polarization difference index, soil moisture, rainfall and snowfall, it was found that the positive MBT anomaly was influenced not only by surface temperature, but also mainly by dielectric constant changes caused by soil moisture and tectonic stresses. On January 8 (3d before the EQ), the MBT anomaly appeared in the eastern part of the Karakum Desert. Especially from January 10 (1d before the EQ) to January 13 (2d after the EQ), Soil moisture was relatively stable, but the microwave polarization difference index and MBT still showed significant anomalies. Through the multi-parameter long-term series analysis in the eastern part of the Karakum Desert, it is also confirmed that there were anomalies in MBT and dielectric constant before and after the earthquake. The deep P-hole particles activated by in-situ stress before the earthquake were transferred to the Quaternary caprock along the stress gradient, reducing the local dielectric constant. Afterwards, the microwave radiation was further amplified by the surface sand layer, ultimately leading to an increase in MBT. In addition, it was found that there were locally high CH4 concentration anomalies near the epicenter one day before the earthquake, which was probably related to the fault stress during the impending earthquake period. This study has important reference significance for identifying microwave brightness temperature anomalies during the seismogenic period and earthquake early warning in the Hindu Kush region.
How to cite: Ding, Y., Wu, L., and Qi, Y.: Characteristics and Mechanism of MBT Anomaly of Karakum Desert Related with the January 11, 2024 Hindu Kush Mw 6.4 Earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6231, https://doi.org/10.5194/egusphere-egu25-6231, 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.
