Orals: Thu, 7 May, 08:30–15:40 | Room G2
Off-fault deformation in surface-rupturing earthquakes can be detected using geodetical methods, but field evidence is rare. Here we present data from the North American-Caribbean Plate boundary, documenting off-fault deformation in the geological record in great detail.
The Motagua Fault in Guatemala is part of the plate boundary between the North American and Caribbean plates. It ruptured in a M7.5 earthquake in 1976, producing a 230 km-long surface rupture with an average slip of about 1 m. At the Estanzuela site, the fault-parallel, elongated topographic depression “Laguneta Los Yajes” is about 2 m lower than its surroundings as revealed by new airborne LiDAR data. It is interpreted as a pull-apart basin, either caused by a fault stepover or by a fault bend. Since it was seasonally filled with water, the surface rupture of the 1976 Earthquake could not be mapped precisely here. We trenched the northern topographic scarp of the depression to investigate the boundary fault but did not encounter a distinct major shear zone. Instead, we found distributed deformation manifested as fractures. Two additional trenches in the center of the depression found the main fault zone and additional structures that accommodate distributed shear. We interpret the fault geometry to be a fault bend rather than a stepover, and we document the evidence for off-fault deformation over 80 m around the main strand at this site. These data shed light on the anatomy of the plate boundary and its associated off-fault deformation.
How to cite: Grützner, C., Niemi, T., Flores, O., Perez Arias, C., Dollens, A., Maurer, J., and Obrist-Farner, J.: The anatomy of a strike-slip plate boundary fault in a pull-apart basin – The Motagua Fault in Guatemala, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8422, https://doi.org/10.5194/egusphere-egu26-8422, 2026.
Current understanding of earthquake rupture and earthquake cycles is largely derived from continental fault systems, implicitly assuming their applicability to oceanic lithosphere. Futhermore, the limited geological and geophysical constraints on large oceanic earthquakes hinder robust assessment of how deformation, fault growth, and stress accumulation takes place in the oceanic lithosphere. The 2012 Mw 8.6 Wharton Basin earthquake, the largest instrumentally recorded strike-slip event, challenged prevailing views of intraplate deformation in the Indian Ocean by rupturing a complex network of faults at high angles to one another. Seismological and geodetic analyses revealed a deep centroid depth, high stress drop, and multi-fault rupture, yet the offshore setting severely limited constraints on fault geometry and rupture propagation. Here, we bridge short- and long-term deformation processes by integrating high-resolution bathymetry, multichannel seismic reflection, and sub-bottom profiler data. We present the surface and near-surface deformation along one of the faults ruptured during the Mw 8.6 earthquake, which runs ESE-WNW and initiates near the epicenter of the Mw 8.2 aftershock. The ~100-km-long fault displays well-preserved dextral offsets accumulated since ~4 - 5 Ma and an en-echelon segmented pattern forming a positive flower structure rooted in the oceanic mantle. We estimate slip rates of ~0.4 to 0.8 mm/yr suggest long recurrence intervals for large intraplate earthquakes. Coulomb stress modelling indicates substantial coseismic stress loading on the N-S fault that subsequently ruptured during the Mw 8.2 earthquake, thus establishing a mechanical relationship between the two events. Overall, our study shows that the oceanic lithosphere can deform slowly and extensively over long time scales, accumulating strain along slow-slipping faults that can produce very large, cascade-style earthquakes. Furthermore, our study offers key inputs for earthquake cycle and dynamic rupture models in oceanic settings by providing geological constraints on fault geometry and slip rates.
How to cite: Rohilla, S., Carton, H., Singh, S., Laurencin, M., Hananto, N., Roharik, M., Qin, Y., Sarkar, S., Noble, M., Hamahashi, M., and Tapponnier, P.: Direct marine geophysical constraints on the rupture of the 2012 Mw 8.6 Wharton basin earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7786, https://doi.org/10.5194/egusphere-egu26-7786, 2026.
On January 5, 2025, the Mw 7.0 Tingri earthquake ruptured the Dingmuco fault in the Xainza-Dinggye rift, Southern Tibet. This event was the largest normal-faulting earthquake recorded in the slowly deforming Southern Tibetan rift system and is among the largest continental normal-faulting earthquakes worldwide. Understanding the mechanics of the Tingri earthquake provides a unique opportunity to understand the regional tectonics and the rupture processes of large continental normal-faulting earthquakes in evolving rift systems.
Here, we combine space geodetic analysis and 3D dynamic rupture simulations to investigate the earthquake. Our geodetic analysis, based on near-fault 3D optical displacement measurements and a joint optical-InSAR-SAR fault slip inversion, indicates oblique normal-left-lateral slip on a west-dipping fault that steepens toward the surface, with an average slip of 1.8 m and a shallow slip deficit of 60%. Both our fault zone width estimates and our geodetic slip model show an increase in slip-obliquity toward the surface, with left-lateral slip reaching the surface more efficiently than dip-slip, a pattern consistent with shallow rake rotation. Our geodetic analysis also reveals 0.5 m of shallow normal slip on a secondary antithetic fault located 20 km west of the main fault, which did not host aftershocks.
Next, we perform 3D dynamic rupture simulations with the open-source software SeisSol, incorporating geodetically constrained main and antithetic fault geometries, heterogeneous initial stress and fast velocity-weakening rate-and-state friction. A preferred dynamic rupture scenario that reproduces the observations suggests pulse-like, subshear rupture, with a modeled average stress drop of 6.3 MPa, higher than the observationally inferred average for normal faulting earthquakes. A strong velocity-weakening behavior at depth, characterized by a large negative stability parameter (a − b) = −0.009, transitioning to velocity-strengthening behavior in the shallowest ~2 km is required to reproduce the observed slip distribution and moment rate release. None of our dynamic rupture scenarios dynamically triggers slip on the antithetic fault. The maximum positive dynamic and static stress changes due to rupture on the main fault occur at shallow depths of the antithetic fault, where it is expected to be governed by velocity-strengthening friction. Together with the shallow geodetically inferred slip and the absence of aftershocks, these results indicate that slip on the antithetic fault might have occurred aseismically. However, future events across the same fault system may involve deeper coseismic slip on both faults. The high stress drop and large shallow slip deficit are characteristics of rupture on an immature fault such as the Dingmuco fault. Our study demonstrates that combining geodetic analysis with dynamic rupture simulations can shed light on the physical processes governing seismic and aseismic slip in continental rift systems.
How to cite: Marchandon, M., Magen, Y., Hollingsworth, J., and Gabriel, A.-A.: Multi-segmented rupture, coseismically-triggered aseismic slip, and shallow rake rotation during the 2025 Mw 7.1 Tingri, South Tibet, earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19796, https://doi.org/10.5194/egusphere-egu26-19796, 2026.
Seismic gaps are fault sections that have not hosted a large earthquake for a long time compared to neighbouring segments, making them likely sites for future large events. The 2025 Mw 7.7 Mandalay (Myanmar) earthquake, on the central section of the Sagaing Fault, ruptured through a known seismic gap and ~160 km beyond it, resulting in an exceptionally long rupture of ~460 km. Here we investigate the rupture process of this event and the factors that enabled it to breach the seismic gap by integrating satellite synthetic aperture radar observations, seismic waveform back-projection, Bayesian finite-fault inversion and dynamic rupture simulations. We identify a two-stage earthquake rupture comprising initial bilateral subshear propagation for ~20 s followed by unilateral supershear rupture for ~70 s. Simulation-based sensitivity tests suggest that the seismic gap boundary was not a strong mechanical barrier in terms of frictional strength, and that nucleation of the earthquake far from the gap boundary, rather than its supershear speed, allowed the rupture to outgrow the gap and propagate far beyond it. Hence, we conclude that the dimension of seismic gaps may not reflect the magnitude of future earthquakes. Instead, ruptures may cascade through multiple fault sections to generate larger and potentially more damaging events.
How to cite: Mai, P. M., Jónsson, S., Li, B., Suhendi, C., Liu, J., Li, D., Delorme, A., and Klinger, Y.: Seismic gap breached by the 2025 Mw 7.7 Mandalay (Myanmar) earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10477, https://doi.org/10.5194/egusphere-egu26-10477, 2026.
On February 6, 2023, two earthquakes of magnitude Mw7.8 and Mw7.6 struck in South Türkiye. The first mainshock occurred along the East Anatolian fault, at the boundary between the Anatolian and Arabian plates, and was followed 9 hours later by a second one on a secondary fault system to the North. The importance of such continental earthquakes and the relatively good data coverage of the region present an unique opportunity to investigate post-seismic deformation.
To study afterslip, corresponding to post-seismic transient aseismic slip, we use a combination of ground deformation measurements, including Sentinel-1 InSAR timeseries (6 tracks covering almost 2 years after the earthquakes) and GNSS (more than 40 permanent stations and 60 campaign sites). The cities of Hassa and Gölbaşı, located on the East Anatolian fault, are investigated in detail using 8 continuous GNSS stations installed across the fault 6 months after the earthquakes.
While the large surface imprint of the surface deformation, with significant displacements more than 200 km away from the fault, and our inability to model it with fault slip points toward the dominance of a visco-elastic processus, clear markers of shallow afterslip are visible. In the Pütürge segment, located at the tip of the first earthquake’s coseismic rupture, InSAR data reveals a cumulative surface offset 20 months after the earthquake of about 10 cm due to shallow afterslip. Other segments affected with afterslip have been identified in the eastern part of the rupture of the second earthquake, accounting for several centimeters of slip over 20 months. Our local GNSS networks in Hassa and Gölbaşı reveal the smaller scale complexity of post-seismic surface deformation near the fault. In Gölbaşı, subsidence of more than 2 cm/year is highlighted in the pull-apart basin, while horizontal GNSS displacements suggest possible shallow aseismic slip happening at the southern end of the basin.
We model afterslip on the fault by jointly inverting InSAR and GNSS data, minimizing the least squares criterion. Afterslip is concentrated around the coseismic rupture zone, accompanied by important aftershock activity. The Pütürge segment appears as a seismic barrier, having stopped both Mw6.8 2020 Elazığ earthquake to the East and Mw7.8 2023 Kahramanmaraş earthquake to the West, possibly because of the fault geometry and/or heterogeneous coupling. Future efforts will be directed towards the evolution of afterslip with time and its interplay with aftershocks, including visco-elastic relaxation models. These results help us better understand the relationship between the different phases of the seismic cycle.
How to cite: Lacroix, C., Rousset, B., Masson, F., Dérand, P., Jolivet, R., Özkan, A., and Yavaşoğlu, H. H.: Afterslip following the 2023 Mw7.8 and Mw7.6 Kahramanmaraş earthquakes: observations and modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13346, https://doi.org/10.5194/egusphere-egu26-13346, 2026.
The 17 August 1999 İzmit (M7.4) and 12 November 1999 Düzce (M7.2) earthquakes ruptured the North Anatolian Fault Zone (NAFZ) in northwestern Türkiye and caused catastrophic damage. The offshore extensions of the central and northern strands of the NAFZ beneath the Sea of Marmara remain seismically active, having produced several Mw≥ 5.0 earthquakes since 2005. In this study, we analyse the spatiotemporal evolution of Coulomb stress changes following the 1999 earthquake doublet and examine their relationship to subsequent moderate earthquakes, including the 2006 Gemlik (Mw5.0), 2019 Silivri (Mw5.7), 2023 Mudanya (Mw5.0), and 2025 Silivri (Mw6.2) events.
Our models indicate that for the 2006 Gemlik and 2023 Mudanya earthquakes, coseismically imposed stress shadows generated by the 1999 ruptures were progressively erased and reversed to positive values by viscoelastic postseismic relaxation in the lower crust and upper mantle. In contrast, at the locations of the 2019 and 2025 Silivri earthquakes, positive coseismic stress changes were substantially amplified by subsequent viscoelastic processes. These results demonstrate that stress perturbations associated with the 1999 mainshocks continue to modulate seismicity along offshore Marmara fault segments over decadal timescales.
In the broader context of the seismic cycle of the Main Marmara Segment, which last ruptured in 1766, the increasing occurrence of moderate-magnitude earthquakes may reflect a transition toward a late-stage, critically stressed regime. Our results suggest that long-lived viscoelastic stress transfer following the 1999 earthquakes has imposed an additional stress load on an already mature seismic cycle, potentially accelerating its progression toward failure. Accounting for such persistent, time-dependent stress interactions is therefore essential for refining time-dependent earthquake hazard assessments in this densely populated region.
How to cite: Nalbant, S. S., Uzunca, F., Utkucu, M., and Durmuş, H.: Viscoelastic Stress Loading Following the 1999 Earthquakes and Late-Stage Seismicity in the Marmara Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11337, https://doi.org/10.5194/egusphere-egu26-11337, 2026.
Seismogenic depth is a fundamental parameter in seismic hazard assessment and is commonly inferred from kinematic approaches that rely on empirically defined thresholds. However, these observational estimates require validation and calibration against physics-based earthquake cycle models. Here we focus on the San Andreas Fault system in California, where high-quality geodetic, seismicity, and geothermal datasets are available. We construct a geodetically derived fault-coupling model for the entire fault system and systematically compare seismogenic depths inferred from fault coupling with those constrained by earthquake depth distributions. Our results show that a geodetic seismogenic depth defined by a coupling ratio of 0.45 provides the closest agreement with the depth enclosing 90% of the observed seismicity. This correspondence is quantitatively consistent with predictions from thermally constrained rate-and-state friction models, although the numerically inferred seismogenic depths are systematically shallower. Along-strike variations in seismogenic depth obtained from all approaches exhibit similar spatial patterns and correlate strongly with geothermal gradients, indicating that temperature is the primary controlling factor. These results establish a quantitative link between seismogenic depths derived from observational constraints and physics-based numerical models, thereby providing a stronger physical basis for incorporating geodetically inferred coupling models into seismic hazard assessments.
How to cite: Xu, X., Zhao, X., and Weng, H.: Discrepancies and controlling factors of rupture depths inffered from geodesy, seismicity and thermally constrained rate-and-state friction models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2700, https://doi.org/10.5194/egusphere-egu26-2700, 2026.
Slip-rate variations over multiple seismic cycles play a fundamental role in controlling the behaviour of active fault systems, as they are linked to spatio-temporal earthquake clustering and can influence the recurrence patterns of adjacent faults. However, processes that produce slip-rate fluctuations are yet to be fully defined. Despite their importance, the physical mechanisms responsible for such slip-rate fluctuations remain only partially understood. In this study, we investigate whether interactions between neighbouring along-strike brittle faults and their underlying viscous shear zones can generate slip-rate variability associated with synchronous earthquake clustering and fault system synchronization. We focus on nine normal faults and related shear zones within the Central Apennines fault system (Italy), arranged in six along-strike fault pairs characterized by different fault spacings and strike geometries. We integrate cosmogenic 36Cl dating of tectonically exhumed fault scarps with numerical modelling of differential stress transfer between interacting fault–shear-zone pairs. The results identify a mechanism capable of producing simultaneous earthquake clusters, driven by the synchronization of high driving stresses within the viscous shear zones beneath the brittle faults. This behaviour is strongly modulated by along-strike fault spacing and strike variations. In settings with closely spaced fault pairs and limited strike variations, earthquake clusters induce positive differential stress variations on neighbouring shear-zones of sufficient magnitude to induce positive slip-rate variations on their overlying brittle faults. This produces positive feedback mechanism that sustains the occurrence of earthquake clusters that will continue to positively load the neighbouring shear zones. These findings provide new insights into fault system dynamics across multiple timescales and have important implications for seismic hazard evaluation.
How to cite: Iezzi, F., Claudia, S., Roberts, G., Mildon, Z., Robertson, J., Faure Walker, J., Papanikolaou, I., Michetti, A. M., Mitchell, S., Shanks, R., Phillips, R., McCaffrey, K., and Vittori, E.: Structural controls on normal fault synchronization and simultaneous earthquake clustering, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21777, https://doi.org/10.5194/egusphere-egu26-21777, 2026.
Recurrence intervals and magnitude distributions of earthquakes are key parameters in probabilistic and time-dependent seismic hazard assessments, yet they are difficult to constrain because the time window of instrumental and paleoseismic records often capture only a smaller fraction of the earthquake cycle of large earthquakes. Physics-based seismic cycle simulators can help to overcome these limitations by generating synthetic catalogues that span thousands of years, offering valuable insights into the statistical behaviour of fault networks. Despite the increasing use of these simulators, the physical mechanisms governing earthquake timing and size distributions remain incompletely understood, in particular the role of fault interactions and spatial variations in long-term slip rates.
Here we use the boundary-element code QDYN to simulate earthquake cycles on normal fault networks of increasing geological complexity, ranging from simplified two-fault configurations to realistic fault networks derived from field data in the Central and Southern Apennines (Italy). Our results show that both fault geometry and slip-rate variability critically influence earthquake recurrence and magnitude distributions. Networks with multiple across-strike interactions produce more complex seismic sequences, irregular recurrence intervals, and broader ranges of rupture sizes and moment magnitudes (Mw) compared to simpler configurations. Similarly, spatially variable slip-rate profiles promote diverse rupture behaviours, including partial ruptures and slow-slip events, that increase variability in stress redistribution, magnitude-frequency relationships and recurrence times. In contrast, models using uniform slip-rate profiles tend to produce regular recurrence patterns and characteristic earthquake magnitudes. These findings highlight the importance of incorporating realistic fault geometries and spatially variable slip rates in physics-based earthquake simulators used to inform seismic hazard assessments.
How to cite: Rodriguez Piceda, C., Mildon, Z., Andrews, B., Ampuero, J.-P., van den Ende, M., Yin, Y., Sgambato, C., and Visini, F.: Stress interactions in seismogenic faults through the lens of physics-based earthquake cycle simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-477, https://doi.org/10.5194/egusphere-egu26-477, 2026.
Paleoseismology extends earthquake records by documenting geological evidence of past surface-rupturing events, providing constraints for seismic source characterization, and improving the understanding of fault behavior. The reliability of paleoseismological interpretations depends on observational data and analytical methods. Conventional trenching and bedrock-scarp studies face uncertainties, as surface processes can obscure subtle deformation, and chronological correlations between units are often poorly constrained. Ground-based remote and direct sensing techniques now enable centimeter-scale multi-sensor datasets that significantly enhance observation and documentation of paleoseismic evidence.
This study builds on established methodologies to explore the integration of ground-based hyperspectral imaging, LiDAR, photogrammetry, and direct field measurements for improved detection of coseismic deformation, paleoearthquake identification, and 2D–3D reconstructions of fault displacement (for slip-rate estimation). The approach is applied to two active tectonic settings in the western Mediterranean: the Alhama de Murcia Fault within the Eastern Betics (SE Spain), with dominant transpression, and the Southern Fucino Fault System, Central Apennines (Italy), with dominant extension. At first, paleoseismological trenches were studied in alluvial sediments at the Saltador site. Second, an exhumed limestone fault scarp was analyzed at the San Sebastiano site.
At the Saltador site, 13 wall trenches excavated parallel and perpendicular to the fault, together with a natural outcrop, were logged using conventional paleoseismology and combined with remote sensing to reconstruct 2D–3D fault deformation and identify displaced alluvial-channel piercing points for slip-rate estimation. At San Sebastiano, LiDAR and photogrammetric data were combined with direct field measurements (spectroradiometry and Schmidt hammer rebound values) to characterize fault-surface roughness, mineralogical variability, and rock mass properties, to detect progressive scarp exhumation, building on existing 36Cl cosmogenic constraints. Hyperspectral imagery was acquired using an AISA Fenix 1K (400–2500 nm) at the Saltador and SPECIM FX10/FX17 (400–1700 nm) at San Sebastiano. Radiometric correction, co-registration with point clouds, and illumination modeling were performed using the hylite package. Subsequent processing included dimensionality reduction (MNF, PCA) and mineral-sensitive band ratios for lithological and structural discrimination.
The integration of hyperspectral data enhanced paleoseismological interpretations in both study areas by reducing uncertainties in coseismic deformation and surface rupture detection. At the Saltador site, previously unrecognized secondary faults and surface ruptures within alluvial sediments were revealed. Spectral band ratios improved the discrimination of sedimentary facies and erosional contacts, strengthening the identification of piercing points and deformation patterns. At least three paleoearthquake events over the past ~34 ka were confirmed, enabling refined 3D reconstructions of offset deposits and an estimated horizontal slip rate of ~0.2 mm/yr for the studied fault branch.
At San Sebastiano, visible to near-infrared hyperspectral data captured spatial variability in alteration minerals (e.g., hematite–goethite and, possibly, hydrated clay minerals), delineating vertical spectral zones that correspond to 36Cl-dated exhumation clusters, suggesting a link between mineralogical variability and progressive scarp exhumation. Combined with roughness and rock-strength measurements, these results could help to refine scarp exhumation rates, surface-rupturing earthquake sequences, and spatial variability in fault-rock exposure.
Overall, hyperspectral and multi-sensor ground-based techniques can enhance the reliability, reproducibility, and robustness of paleoseismological analyses in complex tectonic settings.
How to cite: Gallego Montoya, J. J., Ortuño, M., Benedetti, L., Kirsch, M., Thiele, S., Garcia-Sellés, D., Riesner, M., García-Meléndez, E., and Ollé-López, M.: Advancing Paleoseismology with Integrated Hyperspectral and Multi-Sensor Approaches: Enhanced Interpretation of Trenches and Active Fault Scarps in Spain and Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19397, https://doi.org/10.5194/egusphere-egu26-19397, 2026.
Earthquake ground motion is inherently directional and governs deformation in near-surface sediments, yet whether this directional information is preserved in geological archives remains poorly constrained. Soft-sediment deformation structures produced by earthquakes (seismites) are widely used to reconstruct past earthquake catalogues but are generally assumed to lack information on seismic-wave direction, limiting their ability to identify seismogenic faults. Here we develop a three-dimensional physical framework integrating numerical simulations with field observations to resolve how different seismic-wave components control deformation anisotropy in water-saturated sediments. We show that horizontally polarized shear waves dominate anisotropic deformation, producing systematically stronger shear and folding on planes oriented perpendicular to wave propagation. This behaviour is quantified using a dimensionless deformation index and fold counts measured on orthogonal profiles. Applying this framework to a well-preserved three-dimensional seismite in the Pamir region, we demonstrate that contrasts in deformation intensity robustly record seismic source direction and enable identification of causative seismogenic faults, together with reconstruction of a sequence of paleo-earthquakes when integrated with chronological constraints. These results establish that near-surface geological deformation can preserve directional information on seismic-wave propagation, opening new opportunities to reconstruct seismic source direction from sedimentary cores and outcrop-scale geological records worldwide.
How to cite: Yang, X., Shi, X., Yang, H., Klinger, Y., Chen, H., Ge, J., Li, F., Liu, X., Yan, Y., and Bai, Z.: Three-dimensional anisotropy of seismite deformation constrains seismogenic fault location, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10546, https://doi.org/10.5194/egusphere-egu26-10546, 2026.
Normal fault systems within extensional domains often create steep mountain fronts and associated colluvial breccia deposits. These deposits hold an archive of long-term fault activity and landscape evolution, yet they are rarely used to quantify fault slip histories due to their complex nature and dating challenges. In this study, we investigate the Zurim Escarpment in northern Israel, focusing on the Sajur Fault, to reconstruct the long-term morphotectonic history from syn-tectonic colluvial breccia units on the hanging-wall. We integrate U-Pb dating of calcite precipitates and luminescence dating of quartz grains within the breccia matrix to constrain the timing of two breccia depositional phases. Dating results constrain the age of the older breccia phase to ~2.5 Ma, and the younger phase to at least 1.2 Ma. The presence of colluvial breccia at ~2.5 Ma indicates that relief had already developed, constraining the minimum age of escarpment formation. Through clast provenance analysis, we link breccia deposition to the progressive exhumation of the fault footwall. This yielded a long-term slip rate of 0.14±0.02 to 0.15±0.02 mm/yr over the past 2.5 million years, lower than short-term rates derived from cosmogenic dating of fault scraps (0.2–0.5 mm/yr). This discrepancy reflects the temporal dependence of fault slip rates calculations, with values decreasing and stabilizing over longer timescales as they capture the full ratio of seismically active periods to intervening quiescent periods. Our results underscore the potential of syn-tectonic colluvial breccia as a long-term archive for fault activity and landscape evolution in carbonate terrains.
How to cite: Shraiber, G., Siman-Tov, S., Matmon, A., Golan, T., Porat, N., Jacobi, Y., and Nuriel, P.: Dating Hanging-Wall Colluvial Breccia to Reconstruct the Long-term Normal Fault Evolution in Carbonate Terrains, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10634, https://doi.org/10.5194/egusphere-egu26-10634, 2026.
The Roccapreturo fault, part of the Middle Aterno Valley Fault system in the central Apennines (Italy), is a key structure for understanding the region’s seismic hazard. Despite evidence of Quaternary activity, its Holocene seismic history remains poorly constrained, with no historical earthquakes directly attributed to this fault. In this study, high- and low-resolution 36Cl cosmogenic nuclide profiles from five sites along the Roccapreturo limestone fault scarp were used to reconstruct the seismic history of this fault. The seismic history was constrained using PyMDS inversion algorithm (Llinares et al., 2025), which relies on Markov Chain Monte Carlo (MCMC) approach to infer the timing and slip of past surface-rupturing earthquakes.
Our results indicate at least five major seismic events over the last ~18,000 years, with coherent clusters at ~5 ka, ~3.5 ka, ~2–3 ka, ~1 ka, and <0.5 ka BP on at least two sites. The most recent event, dated at ~300 years BP, could correspond to a previously unattributed historical earthquake. Slip Rates (SRs) over the Pleistocene, estimated from high resolution profiles, range from 0.1 to 0.4 mm/yr, which is consistent with previous studies (Falcucci et al., 2015; Tesson et al., 2020) and InSAR data (Daout et al., 2023). SRs over the Holocene are higher (~1–2 mm/yr), suggesting temporal variability. The study also discusses methodological advances, including the value of dense sampling, the use of statistical changepoint detection, and the integration of fuzzy statistics to address uncertainties in seismic history derived from 36Cl dataset from limestone fault scarp.
These findings provide new constraints on the seismic behavior of the Roccapreturo fault, highlight the importance of multi-site and high-resolution approaches, and underscore the need for further paleoseismological and historical investigations to refine the seismic hazard assessment in the central Apennines.
How to cite: Llinares, M., Benedetti, L., Gassier, G., and Riesner, M.: Using dense 36Cl profiles to assess the seismic history of the Roccapreturo Fault (Italy) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19344, https://doi.org/10.5194/egusphere-egu26-19344, 2026.
Why do some earthquakes repeatedly rupture discrete fault segments, while others rupture entire
faults? Answering this remains fundamental to improving seismic hazard analysis and, in turn, to
hazard preparedness and mitigation efforts. Over the past two decades, several mechanisms for
rupture termination and propagation have been proposed, including variation in geometric,
structural, and geologic characteristics of faults (Aki, 1979; King and Nabelek, 1985). In this study
we investigated the Eastern Precordillera (EPC) of the Andes Mountain in Argentina which is
classified into three segments: Villicum, Las Tapias, and Zonda–Pedernal (Siame et al., 2002) to
determine whether the historical surface ruptures associated with major earthquakes crossed the
segment boundaries, or whether rupture propagation was arrested by structural asperities
indicating an asperity-controlled behavior. To address this, we conducted a new paleoseismic
investigation at this site to complement and integrated with the preexisting dataset to evaluate the
extent of past surface ruptures in relation to fault geometry and structural segmentation. We have
complied earthquake timing of six earthquakes. Preliminary results suggest that, of the six
identified events, only one earthquake appears to have ruptured across an ~18 km-long segment
gap, including a ~4 km stepover and notable lithologic variation evidence consistent with a multi-
segment rupture event.
How to cite: Arora, S., Cochran, D., Janson, E., Ortiz, G. F., Rimando, J., Brown, N., Villalobos, M., Gomez, R., and Klinger, Y.: One Big Earthquake or Many? Fault Segmentation in the Eastern Precordillera, western Argentina, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22278, https://doi.org/10.5194/egusphere-egu26-22278, 2026.
The timing and size of the past large earthquakes that ruptured active faults are important to better understand seismic processes and time-dependent seismic hazards. A recent study highlights the rarity of ‘overdue’ earthquakes for New Zealand faults, a finding that directly contrasts observations from California, which indicate an unlikely long period of seismic quiescence. Here, we analyze paleoearthquake and historic records from 210 faults globally, including California, to test the international applicability of the findings for the New Zealand faults against a global active fault dataset. By comparing earthquake-elapsed and mean-recurrence data that derive from end-member fault systems, we explore the factors that control the shape of recurrence-interval distributions on different regions, and assess whether existing paleoearthquake and historical data can be used for estimating time-dependent seismic hazard. Our analysis: 1) demonstrates that the regions examined generally behave similarly for interevent and elapsed times, except for California which forms an outlier. This dissimilarity is important as faults in California have been commonly used to inform earthquake forecast models; 2) supports recurrence-interval distributions that are consistent with positively-skewed renewal models; and 3) proposes an improved approach for defining recurrence-interval distributions that involves the closed elapsed times constrained by historic ruptures and their penultimate events.
How to cite: Mouslopoulou, V., Nicol, A., Howell, A., and Griffin, J.: Why closed seismic cycles matter for time-dependent seismic hazard: Lessons from global paleoearthquake records , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8066, https://doi.org/10.5194/egusphere-egu26-8066, 2026.
Faults are ubiquitous structures, ranging in length from millimeters to thousands of kilometers, with significant variations in permeability that regulate regional fluid flow, solute transport, seismicity, and hydrothermal circulation within the crust. Measurement of in situ fault permeability is challenging due to drilling difficulties and the risk of hydraulic fracturing. Moreover, existing scaling laws of laboratory permeability or fracturing intensity within faults are site-specific, highlighting the need for universal laws. Furthermore, damage zone permeabilities (kDZ) normalized to the protolith permeability (kNDZ) are typically high, while normalized fault core permeability (kNC) varies. We analyzed 752 in situ injection tests and 967 geomechanical experiments on seven faults with shear displacements (D) ranging from 1 to 5 m in the Asmari–Jahrum Formation (AJF), Iran. The AJF database was supplemented with 334 kDZ and 64 kNC datasets from the literature, covering 245 faults and spanning nine orders of magnitude in D. We quantified the hydraulic roles of fault cores as conduits (kNC>1) or barriers (kNC<1) based on porosity changes. We also developed kNC scaling laws using displacement divided by fault core thickness within a fuzzy-logic framework. A universal kNDZ law was established using distance from the fault core, damage zone thickness, and geomechanical parameters through kriging analysis. The universal material- and fault-dependent kNDZ and kNC laws indicate variations up to ten orders of magnitude in permeability. These findings enhance our understanding of fault hydrology and offer predictive tools for estimating fault permeability.
How to cite: Akbariforouz, M., Zhao, Q., Zheng, C., and Faulkner, D.: Scaling of Permeability Within Faults Across Nine Orders of Magnitude of Displacement , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3242, https://doi.org/10.5194/egusphere-egu26-3242, 2026.
Understanding how sand–fines mixtures respond cyclically is crucial for assessing liquefaction risks and how soil stiffness decreases under seismic forces. Fines, especially low-plasticity clays, greatly influence the buildup of excess pore pressure and strain during cyclic loading. However, their mechanical role at moderate fines levels is not yet fully understood.
This study presents findings from a series of stress-controlled undrained cyclic triaxial tests performed on clean sand and sand–clay mixtures. The base material consisted of a uniformly graded sand combined with low-plasticity kaolinite clay, with fines content of 10% and 15% by dry weight. In order to accurately determine the full role of fines content on the mechanical response, grading entropy coordinates where calculated for each mixture.
Cyclic loading involved applying a sinusoidal deviator stress of constant amplitude under undrained conditions. Throughout the tests, axial strain development and excess pore pressure were continuously monitored. Liquefaction was identified using two complementary criteria: (i) initial liquefaction, indicated by the complete loss of effective stress caused by excess pore pressure, and (ii) strain-based criteria, which relied on different double-amplitude axial strain thresholds.
The results demonstrate that higher fines content slows the development of excess pore pressure and delays the onset of liquefaction compared to clean sand. Both sand–clay mixtures showed less strain accumulation during initial cyclic loading, due to changes in pore space compressibility and drainage caused by low-plasticity clay. Nevertheless, at higher strain levels, significant cyclic softening, notable stiffness loss, and increased residual pore pressures were observed.
The findings emphasise the dual role of low-plasticity fines: moderate fines levels can improve cyclic resistance, while higher fines contents may weaken the granular framework and hinder effective stress transfer. The study underscores the importance of detailed analysis of void ratio and soil structure for accurately assessing the cyclic behaviour and liquefaction potential of sand–fines mixtures.
How to cite: Jagodnik, V., Bekir Afacan, K., Leak, J., and Marušić, D.: The Dual Role of Low-Plasticity Fines in the Cyclic Behaviour of Sand–Clay Mixtures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19444, https://doi.org/10.5194/egusphere-egu26-19444, 2026.
A growing body of geophysical observations, numerical simulations, and theoretical studies indicates that the evolution of the internal structure of fault zones strongly influences fault slip behavior. However, the theoretical frameworks most commonly used to describe fault stability—such as rate-and-state friction—were originally formulated to represent frictional sliding at idealized laboratory interfaces, in which the fault is treated as an effectively two-dimensional boundary with implicitly prescribed contact-scale processes. As a result, these models do not explicitly account for the space–time evolution of fault-zone structure, including damage, granular reorganization, and fluid-mediated processes. Moreover, the state variables used to represent contact evolution are phenomenological and are only weakly constrained by seismological observations, limiting the ability of these formulations to be rigorously applied across spatial and temporal scales.
Here, we propose an experimentally derived theoretical framework that reformulates fault stability in terms of internal variables directly linked to elastic-wave observables. Using double direct shear experiments on gouge layers under controlled boundary conditions, we combine mechanical measurements with active ultrasonic probing. Full waveform inversion is employed to reconstruct one-dimensional profiles of shear modulus and attenuation across the entire sample during normal and shear loading, stable sliding, and stick–slip events.
Ultrasonic waves induce only a small perturbation in strain and therefore probe the linearized constitutive response of the system without modifying its internal state. In this context, effective elastic stiffness and attenuation can be treated as internal variables that encode the evolving fabric and organization of the fault zone. The inverted profiles reveal spatially localized regions within the gouge where elastic properties evolve during slip instabilities, enabling a data-driven identification of the dynamically active fault region, distinct from the mechanically inactive surrounding material.
Based on these observations, we reframe the classical stiffness competition problem that defines the criteria for slip instability entirely in terms of observable quantities. Specifically, we propose to substitute the phenomenological state variable with the retrieved effective viscoelastic properties. Because elastic wave propagation obeys the same governing equations across laboratory and geophysical scales, this framework provides a physically grounded pathway for connecting laboratory experiments, numerical models, and seismological imaging of natural faults. More broadly, it represents a step toward a theory of fault mechanics grounded in seismological observables and geologically relevant fault-zone structures.
How to cite: De Solda, M., Mastella, G., Mauro, M., Guglielmi, G., and Scuderi, M. M.: Seismic imaging in the laboratory: Reframing fault stability using elastic-wave observables, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19479, https://doi.org/10.5194/egusphere-egu26-19479, 2026.
Constraining the timing of large subduction earthquakes remains a fundamental yet unresolved problem in seismic hazard assessment. Although paleoseismic records from many subduction margins suggest predominantly quasi-periodic recurrence of great earthquakes, the large variability observed among different segments and regions raises the question of whether such patterns reflect intrinsic megathrust behavior or, instead, the limitations of the available records. Here we investigate the robustness and interpretability of earthquake recurrence metrics by combining global paleoseismic datasets with scaled seismotectonic models of the subduction megathrust seismic cycle.
We characterize earthquake recurrence using two complementary statistics: burstiness (B), which quantifies the degree of periodicity and clustering of inter-event times, and the memory coefficient (M), which captures temporal correlations between consecutive recurrence intervals. Mapping paleoseismic records from multiple subduction zones onto the M–B plane reveals that most segments exhibit quasi-periodic behavior (B < 0), but span a wide range of memory values, from strongly negative to strongly positive. Notably, this diversity shows no systematic dependence on subduction rate, earthquake rate, or record length, and adjacent segments along the same margin may occupy markedly different regions of the M–B plane.
To assess whether this apparent variability reflects differences in fault dynamics or observational bias, we analyze long, continuous earthquake sequences generated by scaled seismotectonic models. Despite large contrasts in asperity number, size, and along-strike strength heterogeneity, experimental sequences cluster within a relatively narrow domain of the M–B plane. Through controlled subsampling tests, we show that catalog incompleteness, limited along-strike coverage, and short observation windows can substantially shift M and, to a lesser extent, B.
The analysis of experimental data provides useful constraints on the limits of our ability to infer long-term earthquake recurrence from paleoseismic records, with important implications for probabilistic seismic hazard assessment.
How to cite: Corbi, F., Latypova, E., Mastella, G., Funiciello, F., Brizzi, S., and Guastamacchia, S.: Burstiness and memory of large subduction earthquakes: insights from paleoseismology and analogue modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14323, https://doi.org/10.5194/egusphere-egu26-14323, 2026.
Identifying frictionally locked regions of subduction megathrusts from geodetic observations remains a challenging task in tectonic geodesy. Natural geodetic records typically capture only a fraction of seismic cycles, restricting our ability to assess temporal variations in interseismic coupling and their relationship to frictionally locked regions on subduction interfaces, commonly referred to as asperities. Clarifying this relationship is important, because interseismic coupling is widely used as an indicator of seismic potential, but coupled regions may include both mechanically locked asperities and surrounding unlocked regions.
Scaled seismotectonic models provide an effective framework to investigate these processes, by simulating hundreds of seismic cycles within a short time interval under controlled laboratory conditions, with predefined asperity distributions and high-resolution deformation monitoring.
Here, we explore the spatiotemporal variability of interseismic coupling, coseismic slip and their connection to predefined asperities using Foamquake, a well-established 3D seismotectonic model, which simulates megathrust seismic cycles.
Through kinematic inversions of surface deformation, we derive cycle-by-cycle maps of interseismic coupling and coseismic slip and analyse their statistical behavior across models with different asperity configurations and applied normal stress. Our results show pronounced cycle-to-cycle variability in interseismic coupling, even within asperity regions, with highly coupled areas systematically extending beyond the asperity boundaries. Coseismic slip shows a positive but highly scattered correlation with preceding interseismic coupling, suggesting that while coupling is a necessary condition for large slip, it alone does not determine rupture magnitude.
How to cite: Latypova, E., Bedford, J., Corbi, F., Mastella, G., Funiciello, F., Guastamacchia, S., and Pardo, S.: When subduction changes its grip: cycle-to-cycle variability in interseismic coupling and coseismic slip, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18093, https://doi.org/10.5194/egusphere-egu26-18093, 2026.
Seismotectonic analogue models provide a valuable complement to seismological, geodetic and paleoseismological-geomorphological approaches for investigating the earthquake cycle. Physical models mainly made with elastic and frictional materials, allow the simulation of multiple seismic cycles under controlled laboratory conditions. Such physical models can reproduce interseismic, coseismic and postseismic deformation. However, all those models include a pre-existing fault, and thus do not necessarily model realistic fault geometries. As a consequence, the influence of geometric complexity—such as fault segmentation, bends, and step-overs—on rupture dynamics and seismic cycle behaviour remains poorly explored in those seismotectonic models.
Here, we present a new analogue seismotectonic model of a strike-slip fault system that allows complex fault geometries to emerge and evolve while producing multiple seismic cycle. The experimental setup consists of two juxtaposed horizontal PVC plates separated by a straight velocity discontinuity, with one plate fixed and the other moving at constant velocity, simulating a vertical basement fault. The overlying medium is composed of three granular layers: a basal layer of rubber pellets that stores elastic strain, an intermediate rice layer that exhibits stick–slip behavior and represents the seismogenic crust, and an upper frictionally stable sand layer mimicking a non-seismogenic shallow crust.
Surface deformation is monitored with photographs acquired every 2 seconds, corresponding to 25 μm of displacement for the basal plate , and processed using image correlation and dense optical flow methods. Seismic events are detected when surface displacement exceed the imposed basal plate displacement. In addition, recordings made with a high-speed camera at 100 frames per second capture transient surface deformation during rupture propagation. A total of 23 high-speed sequences, each lasting 10 seconds, document coseismic surface deformation associated with earthquake propagation.
We explore the potential of this experimental setup to investigate how rupture characteristics—such as rupture velocity, nucleation and arrest processes— may depend on the evolution of fault geometry and associated off-fault deformation. By quantifying the spatiotemporal distribution of surface deformation and seismic events along evolving fault networks, this approach allows us to investigate how fault segments are activated, temporarily locked, or interact throughout successive stages of the seismic cycle. Moreover, we examine how interseismic deformation reflects the evolving mechanical state and geometry of the fault system, and how this state influences subsequent earthquakes.
How to cite: Demange, L., Souloumiac, P., Maillot, B., Hebaz, S.-E., and Klinger, Y.: Earthquake rupture in a strike slip experiment , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10939, https://doi.org/10.5194/egusphere-egu26-10939, 2026.
Strike-slip shearing is widespread in the brittle crust and is typically expressed as segmented rupture zones with characteristic spacing. Yet, the key factors controlling this geometric pattern remain poorly understood. In this study, we use discrete element method (DEM) simulations to systematically explore the fundamental physical and tectonic controls on fault segment spacing in strike-slip systems. Our results show that spacing is influenced by both physical and tectonic factors. Physically, spacing increases with crustal thickness and strength, but decreases with density and gravitational acceleration. A near-linear relationship emerges between the ratio of spacing length to thickness and the ratio of strength to the combined effects of density, gravity, and thickness. Tectonically, spacing is reduced by increasing thrust components but enlarged by extensional components. Pre-existing weak zones strongly localize rupture, while surface topography modulates rupture propagation, with segments preferentially forming in lower-elevation areas. These results offer new insights into the mechanics of segmented strike-slip ruptures on Earth and other planetary bodies and provide a framework for better assessing natural hazard risks.
How to cite: Jiao, L., Jiao, Y., and Zhang, Y.: DEM Modelling-Based Insights into the Controlling Factors of Strike-Slip Fault Segmentation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15813, https://doi.org/10.5194/egusphere-egu26-15813, 2026.
Strike-slip continental faults often show complex geometries, inherited from their past history. More particularly, they display branches, bends, and steps, also referred to as geometric asperities. Thus, far from being straight-lined, continental strike-slip faults are characterised by disconnected and misaligned sections, whose length and separating distance vary as the faults mature in time.
The presence of those discontinuities (or complexities) along the fault could affect earthquake rupture dynamics; indeed, the extensional or compressional nature of these discontinuities results in stress heterogeneities along the fault system. In addition, depending on the degree of development of the latter, the deformation at fault complexities can show various levels of localisation, balancing between fault segments well connected by fractures and fault portions dominated by damaged zones where the deformation is distributed. As a consequence, fault complexities often act as nucleation- or end-points for seismic ruptures.
In order to study the effect of fault geometry on earthquake ruptures, we developed a 3D numerical model of an evolving continental strike-slip fault, based on the Discrete Element Method (DEM).
In this model, an initially intact medium is subjected to a strike-slip tectonic regime and, thanks to the DEM capability to explicitly describe progressive failure mechanisms, it evolves through different stages of deformation that eventually lead to the emergence of a structure presenting complexities similar to that of natural faults. We are thus able to analyse the relationship between fault maturity and fault geometry. In addition, multiple local ruptures occur along the fault. Therefore, we can characterise the evolution of the earthquake cycles with geological history: on one hand, for each earthquake, we explore how the rupture is spatially affected by fault complexities; on the other hand, we look at the way successive earthquakes progressively modify the geometry of the fault system. Finally, we compare those observations with natural cases.
How to cite: Allemand, A., Klinger, Y., and Scholtès, L.: Insights into fault evolution and rupture dynamics in a strike-slip context from 3D Discrete Element models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10956, https://doi.org/10.5194/egusphere-egu26-10956, 2026.
Major fault systems are inherently complex, including geometric features such as multiple interacting fault segments and variations in strike, dip, and depth. Fault geometries can be effectively reconstructed through field observations and seismic monitoring. Many studies have demonstrated that this geometric complexity plays an important role in controlling the initiation, arrest, and recurrence of both seismic and aseismic slip. In particular, 3D variations in fault geometry cannot be neglected.
However, the vast majority of slip-dynamics models are conducted on planar faults due to algorithmic limitations. To overcome this restriction, we develop a 3D quasi-dynamic slip-dynamics model capable of simulating arbitrarily complex fault geometries. In boundary-element methods, the elastic response to fault slip is computed through the multiplication of a dense matrix with a slip rate vector, which are computationally expensive. We accelerate these calculations using hierarchical matrices (H-matrices), reducing the computational complexity from O(N^2) to O(NlogN), where N is the number of elements. The H-matrix parameters provide explicit control over the trade-off between computational efficiency and accuracy.
In our framework, fault geometry is fully arbitrary and discretized using triangular elements. Fault slip is governed by rate-and-state friction laws and loaded by either stressing rates or plate rate. This approach enables efficient simulation of the spatiotemporal evolution of slip and stress on complex fault systems over multiple earthquake cycles.
We validate the model against analytical solutions for static cracks and through a numerical benchmark (SCEC SEAS BP4). Finally, we apply the method to a realistic fault system with complex geometry that was reactivated during the 2023 Kahramanmaraş–Türkiye earthquake doublet. The results highlight the model’s ability to generate complex earthquake sequences driven solely by fault geometry, without including additional complexities such as rheological, frictional, or fluid-interaction effects.
How to cite: Almakari, M., Cheng, J., Bhat, H., Lecampion, B., and Peruzzo, C.: FASTDASH: an implementation of 3-D earthquake cycle simulation on complex fault systems using the boundary element method accelerated by H-matrices, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18883, https://doi.org/10.5194/egusphere-egu26-18883, 2026.
Seismic hazard models increasingly rely on detailed active fault databases to explicitly represent earthquake sources and their complex geometries. However, transforming fault-based information into consistent and physically plausible inputs for probabilistic seismic hazard analysis (PSHA) remains a non-trivial and often fragmented task. We present NEXTQUAKE, a modular MATLAB tool designed to bridge this gap by converting an active fault database into a complete, internally consistent seismic hazard input. The first core component of NEXTQUAKE generates a comprehensive catalog of earthquake ruptures starting from the geometry of an active fault system. The algorithm constructs single-fault and multi-fault ruptures while enforcing physical plausibility through a fault-to-fault and subsection-to-subsection connectivity framework. Multi-fault ruptures are generated only among geometrically and kinematically connected faults, dramatically reducing the combinatorial space and ensuring realistic rupture scenarios. Each rupture is described in terms of geometry, area, and magnitude, and is encoded through a sparse subsection–rupture incidence matrix that enables efficient downstream processing. The second component performs an inversion to estimate the expected occurrence rates of all generated ruptures. The inversion integrates geological and geophysical constraints, such as long-term slip rates, and provides a self-consistent set of rupture rates compatible with the fault database. This step allows the direct use of fault-based information within probabilistic frameworks without relying on simplified or ad hoc assumptions. Finally, the third component of NEXTQUAKE translates the rupture catalog and associated rates into fully compliant input files for OpenQuake, enabling seamless integration with state-of-the-art PSHA engines. By automating the entire workflow, NEXTQUAKE offers a transparent, reproducible, and extensible framework for fault-based seismic hazard modeling. NEXTQUAKE is particularly suited for regional-scale applications and for exploring the impact of rupture connectivity assumptions on seismic hazard results.
How to cite: Valentini, A.: NEXTQUAKE: a MATLAB tool to transform an active fault database into seismic hazard input, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11056, https://doi.org/10.5194/egusphere-egu26-11056, 2026.
The Central Apennines (Italy) are characterized by moderate seismicity and active fault systems capable of generating damaging earthquakes. However, the limited duration of historical and paleoseismic records restrict our understanding of long-term fault behaviour. In this study, we use the Multi-Cycle Earthquake Rupture Simulator (MCQsim) to construct a 3D model of 42 active normal faults and to generate multiple 100,000-year-long synthetic earthquake catalogues. We systematically vary key model parameters, including dynamic friction and fault strength heterogeneity, to assess their influence on earthquake occurrence rates, magnitudefrequency distributions, and rupture scaling.
The simulations reproduce the regional Gutenberg–Richter trend and show magnitude–average slip and magnitude–rupture area relationships consistent with empirical scaling laws and the available historical catalogue. Seismic productivity and rupture characteristics are most sensitive to variations in dynamic friction and fault heterogeneity. Although uncertainties arise from simplified fault geometries and assumptions about seismogenic depth, the overall agreement between synthetic and observed seismicity suggests that MCQsim effectively captures key aspects of long-term fault-system behaviour. These results indicate that physics-based synthetic earthquake catalogues can improve constraints on earthquake recurrence and rupture scenarios, providing valuable input for probabilistic seismic hazard assessment in regions characterized by moderate seismicity, complex active fault systems, and sparse observational data.
How to cite: Saghatforoush, K., Pace, B., Verdecchia, A., Visini, F., Novell, O. G., Zielke, O., and Peruzza, L.: Exploring Fault Behaviour and Seismic Hazard in the Central Apennines through Earthquake Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4289, https://doi.org/10.5194/egusphere-egu26-4289, 2026.
Probabilistic Seismic Risk Analysis (PSRA) integrates seismic hazard with the vulnerability of exposed assets; however, the full propagation of uncertainties across this chain is still rarely examined. Although uncertainties affect hazard, vulnerability, and exposure models, most studies only partially address them, and end-to-end assessments remain limited. Epistemic uncertainty, arising from incomplete knowledge, is commonly represented through logic trees, which encode alternative modelling assumptions (e.g., recurrence models, maximum magnitudes) and define a discrete probability distribution over mutually exclusive options.
Previous studies suggest that hazard-related uncertainties often dominate seismic risk estimates, but few studies quantify this systematically, and is largely based on case studies from California. Within the TREAD project (tread-horizon.eu), we extend this understanding by applying a comprehensive framework to evaluate multiple sources of epistemic uncertainty using Italy, an earthquake-prone region, as both a national and regional case study.
We employ two alternative logic-tree structures: an area-source model with 540 branches and a combined fault-based plus smoothed-seismicity model with 243 branches. These configurations allow us to isolate the impact of choices related to slip rates, ground-motion models, scaling relations, recurrence behaviour, maximum-magnitude values, completeness methodologies, and site-specific assumptions.
Risk calculations are performed using the OpenQuake Engine, with structural economic losses adopted as the risk metric. Our results indicate that the dominant sources of epistemic uncertainty vary with the return period, implying that priorities for data acquisition and scientific investment should depend on the intended application of the risk results. Although ground-motion models often represent the largest contributor to epistemic uncertainty, our findings show that this assumption does not hold consistently across regions or return periods.
How to cite: Montejo, J., Silva, V., and Pace, B.: Influence of sources of epistemic uncertainties in hazard modeling on risk assessment: a regional assessment in Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3229, https://doi.org/10.5194/egusphere-egu26-3229, 2026.
Probabilistic seismic hazard analysis (PSHA) traditionally assumes time-invariant Poisson processes over mainshocks, while removing aftershocks through non-objective declustering procedures. This may underestimate seismic hazard, as recent sequences demonstrate significant ground-shaking contributions from aftershocks. Models for cluster correction (e.g., Marzocchi and Taroni, 2014; MT14) incorporate aftershock productivity but maintain temporally constant rates. While these models improve hazard estimates, the temporal persistence of conditioning effects in long-term forecasts remains poorly quantified.
This study investigates how long-term SimplETAS-based seismic hazard is affected by forecast initialization time, considering two scenarios: (i) an unconditional PSHA, i.e. not conditioned on a specific earthquake sequence, and (ii) a conditional PSHA initialized immediately after the 2009 L’Aquila earthquake sequence. We aim to assess whether 50-year PSHA remains consistent across different initialization times, which is typically assumed sufficient for the stationarity of the hazard process.
We employ the SimplETAS algorithm to generate two sets of 100,000 synthetic catalogs spanning 50 years: one set starting in 2024 (unconditional) and one starting immediately after the 2009 L’Aquila seismic sequence (conditional). For each earthquake in the synthetic catalogs, we assign a plausible seismogenic structure and compute fault-to-site distances for ground motion prediction using the GMPEs. Hazard curves are calculated empirically as the fraction of catalogs exceeding given PGA thresholds, without relying on the Poisson distribution. We analyze four Italian cities with varying seismicity levels: L’Aquila, Reggio Calabria, Firenze, and Milano. In the unconditional scenario, we compute 50-year hazard curves for all four cities. In the conditional scenario, we compute hazard curves for the same four cities to identify a conditioning effect only on the affected site of L’Aquila. Additionally, for that site, we quantify the temporal decay of conditioning by computing hazard curves over multiple time windows (1, 5, 10, and 50 years) and comparing them with the corresponding unconditional PSHA.
Unconditional PSHA shows good agreement with the reclustered version of the official Italian seismic hazard model (MPS19_cluster) across all four cities and different return periods, corroborating the use of SimplETAS-based approach for long-term PSHA, and the suitability of the MT14's PSHA correction across different return periods. The results of the conditional analysis reveal that L’Aquila exhibits differences of about 10-20% between conditional and unconditional PSHA even over the 50-year window, while Firenze, Milano, and Reggio Calabria remain essentially unchanged. The temporal decay analysis at L’Aquila shows how conditioning effects progressively decrease over longer periods, though the average effect remains detectable in a 50 years time window.
How to cite: Pane, A., Visini, F., Mancini, S., and Marzocchi, W.: Is long-term PSHA time-dependent? Insights from SimplETAS model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1855, https://doi.org/10.5194/egusphere-egu26-1855, 2026.
Posters on site: Wed, 6 May, 14:00–15:45 | Hall X2
Earthquake-induced soil liquefaction poses significant risks to urban infrastructure in seismically active regions. Recent events, notably the 2011 Christchurch earthquake in New Zealand, demonstrate that liquefaction-induced damage can exceed that from ground shaking. This emphasises the need for scalable liquefaction hazard assessment tools. Traditional assessment methods that rely on cone penetration tests (CPT) and standard penetration tests are impractical for large-scale applications (e.g., regional hazard mapping or insurance portfolio analysis). This research develops a machine learning (ML) model that serves as a cost-effective proxy for traditional geotechnical testing.
Using CPT data from the New Zealand Geotechnical Database (NZGD), this study implements the state-of-practice Boulanger and Idriss (2016) methodology to calculate Liquefaction Potential Index (LPI) values for 5,879 unique locations across five Holocene geological units in New Zealand (i.e., windblown, human-made, estuary, river, and swamp deposits). ML models were trained separately for each geological unit to predict CPT-derived LPI, using three primary features: earthquake magnitude (Mw 5.0-8.0), peak ground acceleration (PGA) (0.05-1.2g), and groundwater table depth (0.5-15.0m). For each CPT location, the LPI was recomputed under sampled Mw-PGA-GWT combinations to create an expanded training set spanning plausible hazard and groundwater states. Using this training dataset, several ML methods were initially tested (i.e., gradient boosting, XGBoost, LightGBM, neural network, support vector machine), finally selecting LightGBM based on the best accuracy-training time trade-off.
Model performance varied by geological unit: windblown deposits were captured well, achieving R2= 0.854, whereas river deposits reached only R2= 0.555, despite the latter having more training data. This finding demonstrates that depositional homogeneity, rather than data volume, can be more influential on ML performance in geotechnical applications. Feature importance analysis revealed balanced contributions to influencing predictions (i.e., magnitude: 33.7%, PGA: 34.5%, groundwater table depth: 31.8%), indicating the need to represent groundwater variability rather than treating shaking intensity as the sole dominant control. Validation against analytical LPI calculations for a synthetic scenario representing fully saturated conditions (Mw = 6.5, PGA = 0.4g, GWT = 0m) yields moderate agreement (R2= 0.491). The models tend to produce more conservative estimates for LPI < 5 and slightly underpredict for LPI > 40, likely reflecting systematic biases in the training data distribution, where extreme cases are underrepresented. Real-world application was also assessed by comparing predicted patterns with observed liquefaction manifestations during the 2011 Christchurch event from NZGD, independent of the training dataset. Comparisons observed good qualitative agreement with known high-susceptibility areas in eastern Christchurch, including zones near the Avon River and coastal margins. The proposed framework provides a scalable alternative to traditional CPT-based assessments, particularly for large-scale regional applications.
How to cite: Tami, D., Gentile, R., Prabhu, S., and Carenzo, M.: Machine Learning for Liquefaction Hazard Mapping: A Case Study for New Zealand , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3040, https://doi.org/10.5194/egusphere-egu26-3040, 2026.
Stepovers between fault segments are a key structural control on rupture propagation, often determining whether ruptures terminate or cascade into large, multi-segment earthquakes. These dynamics critically influence earthquake magnitude and seismic hazard. Theoretical models, in particular the rupture-tip equation of motion for elongated ruptures (Weng & Ampuero, 2019), describe rupture growth along planar faults of finite widths. However, they do not account for the potential of rupture jumping across geometric discontinuities or frictional barriers. In this study, we use 2.5D dynamic rupture simulations with the spectral element method (SEM2DPACK software) to determine how the critical distance Hc for rupture jumping across stepovers in elongated fault systems of two parallel normal faults depends on prestress level S’ and seismogenic width W (Fig. a). We simulate dynamic rupture on a primary fault and record the resulting stress perturbations on a locked secondary fault. The critical stepover distance Hc is determined by computing the strength excess required for Coulomb failure on the secondary fault over a static process zone Lc. This approach is validated by complete dynamic rupture simulations in a selected set of fault stepover cases. For two co-planar faults we find a Hc/W ~ 1/S’n scaling relationship with n=2 for short Hc (near-field) and n=1/2 for large Hc (far-field) (Fig. b), consistent with dynamic nucleation thresholds with stepovers. For non-co-planar faults we find a Hc/W ~ 1/S’n scaling relationship with n=1 for near-field transitioning to n=2 for far-field (Fig. c). This transition is governed by the angular dependence of the stopping phase emitted by rupture arrest on the primary fault and the resulting dynamic trigger. These scaling relationships for co-planar and non-co-planar faults will be incorporated into the rupture-tip equation of motion, extending its applicability to segmented fault systems. The updated framework will improve assessment of rupture potential in complex fault networks, such as the 2023 Kahramanmaraş sequence (strike-slip), the 2010 Maule earthquake (subduction zone), and the 2016 Kaikōura earthquake (multifault rupture), as well as for induced earthquakes (e.g., the Groningen gas field). Particularly, extrapolating our results suggests that faults with small W need to be highly critically stressed to jump over even short distances (e.g., >94% stressed to jump over 300 m in Groningen’s 300 m wide gas reservoir). Since fault slip is expected to occur locally before reaching such high averaged stresses, this implies that rupture jumping in induced seismicity settings with small W is highly unlikely. These findings contribute to a unified theory of rupture propagation incorporating complex segmented systems.
How to cite: van der Heiden, V., Weng, H., Ampuero, J.-P., and van Dinther, Y.: Rupture Jumping Across Fault Stepovers: An Extension of Rupture-Tip Theory of Elongated Earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20257, https://doi.org/10.5194/egusphere-egu26-20257, 2026.
Developing numerical models of faulting in the upper crust remains a challenge due to limitations in numerical algorithms and problems in choosing realistic constitutive models. This results in strong limitations when trying to model the strain and stress fields, and elastic and plastic energy release (i.e. stress times strain), under realistic parametrization obtained from lab experiments, particularly regarding mechanical and chemical weakening that leads to localization as observed in nature.
Here we explore applications of the Geotechnical Particle Finite Element Method (P-FEM), a large-deformation numerical tool developed to capture detailed progressive failure and fracturing using a non-local formulation.
P-FEM allows modelling localized shear bands that naturally emerge independent of mesh discretization, both in thickness and orientation. Moreover, continuous remeshing in a Lagrangian framework enables modeling of large deformations, and techniques used to minimize numerical diffusion help produce realistic localized shear/fault zone patterns.
The elastoplastic constitutive models can be calibrated using multi-method lab tests (e.g. monoaxial, triaxial, Brazilian, oedometer, etc.) to include complex non-linear effects, such as strain weakening and softening, poroelasticity, strength envelopes with a cap (i.e. porosity collapse in compression), and mechano-chemical degradation. This allows for realistic simulations of geo-materials with contrasting properties, including non- or weakly-cohesive fault gouges, weak porous rocks, and stronger brittle frictional-plastic materials.
After an overview of the method, we will show how P-FEM is particularly suited for investigating deformation in the upper crust including (i) fault nucleation and growth in mechanically layered materials, (ii) the interplay between faulting and folding in thrust belts, and (iii) the development of fault damage and/or process zones in materials with heterogeneous mechanical properties.
How to cite: Bistacchi, A., Ciantia, M., Castellanza, R., Mittempergher, S., and Agliardi, F.: Modelling complex fault systems with the Particle Finite Element Method (P-FEM), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21171, https://doi.org/10.5194/egusphere-egu26-21171, 2026.
Oblique displacement in continental tectonic setting often leads to complex fault systems that incorporate both dip-slip and strike-slip motion, with fault geometry and seismic activity developing across subsequent earthquake cycles. Understanding how boundary conditions influence fault growth, rupture dynamics, and off-fault deformation is an ongoing challenge in tectonics and earthquake physics. In this study, we are using three-dimensional discrete element models to analyze the evolution of continental fault systems under oblique boundary conditions.Specifically, we employ a numerical sandbox that represents the continental crust as a brittle layer where deformation can localize as a result of fracture nucleation, propagation and coalescence, without any a priori assumptions on its spatio-temporal evolution. Transtensional and transpressional loadings are applied through combined normal and shear components of deformation. Our simulations show cyclic stick-slip behavior, defined by periods of elastic responses followed by fault ruptures. Thanks to the model’s capability, we analyze the evolution of the emerging fault geometry, the ruptures extent, as well as slip partitioning throughout the simulated earthquake cycles. Particular emphasis is placed on the spatial distribution of damage, the development of fault-related topography on the surface, and the role of obliquity in controlling rupture propagation. Our findings show strong relationships between imposed boundary conditions, fault system configuration, and seismic rupture characteristics.
How to cite: Dwivedi, A., Klinger, Y., and Scholtès, L.: 3-D Discrete Element Modeling of Continental Fault System Evolution Under Oblique Boundary Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12056, https://doi.org/10.5194/egusphere-egu26-12056, 2026.
Since Reid formulated the elastic rebound theory in the early 20th century to describe earthquakes in brittle faulting, fault systems have been widely represented by spring–slider models, both in theoretical frameworks and laboratory experiments. From a different perspective, structural geology has long documented fault systems as geometrically complex structures, reflecting the heterogeneous physical properties of different lithologies. These systems are characterised by multiple slip surfaces and secondary fault splays and comprise large volumes of highly damaged rocks. Such damaged volumes are effectively part of the loading medium that is commonly conceptualised, in simplified models, as an elastic spring.
Over the past decades, a wealth of seismological and geodetic observations has shown that these damaged crustal volumes actively deform inelastically during the seismic cycle, rather than merely storing elastic energy. In parallel, numerical models indicate that off-fault damage can account for a significant portion of the earthquake energy budget. Together, these observations challenge the classical representation of the fault loading medium as purely elastic.
Here, we integrate observations spanning outcropping fault-zone descriptions, seismicity catalogues, and laboratory observations to explore how the earthquake loading medium could be more realistically defined and described in natural fault systems. We focus on well-studied seismogenic normal faults in Italy, namely the Gubbio and Norcia faults, where a long-standing and extensive knowledge of the involved lithologies is combined with a high-resolution fault image obtained by both high-quality outcrop exposure and enhanced seismological catalogues, and where the involved rocks have been extensively studied in the laboratory. By adopting this interdisciplinary perspective, we aim to better constrain the nature of the loading medium toward a better estimation of the forcing imbalance that is fundamental to earthquake nucleation.
How to cite: Giorgetti, C. and Collettini, C.: How to define the earthquake loading medium: an interdisciplinary approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18225, https://doi.org/10.5194/egusphere-egu26-18225, 2026.
During an earthquake, the frictional resistance of a fault suddenly drops to release the elastic energy that has been accumulating over decades to centuries. In addition to the steady increase of stress on faults due to tectonics, external perturbations have been shown to modulate the fault behavior over a wide range of time scales. The spring block slider model following rate-and-state friction framework with velocity-weakening behavior undergoing periodic perturbations has been known to host complex stick-slip events ranging from fast earthquakes to slow earthquakes, making it a good analog of a simple fault. Accurate characterization of system state and tidal forcing parameters is critical for understanding the triggering mechanisms and ultimately improving seismic hazard assessment. In this work, we employ ensemble-based data assimilation techniques to carry out state and joint state-parameter estimation in a tidal modulated spring slider. We perform twin experiments to estimate the tidal perturbation parameters such as period and amplitude. In this scenario, we compare the iterative ensemble Kalman smoother (I-EnKS) with ensemble Kalman filter (EnKF) variants for joint state-parameter estimation. Using the smoothed estimates, we assess forecast quality by evaluating prediction accuracy over multiple recurrence intervals. To account for model uncertainties, we incorporate additive stochastic forcing to examine its effect on state-parameter estimation and forecast accuracy.
How to cite: Shanmugasundaram, B., Bhat, H., and Jolivet, R.: Quality evaluation of assimilation-based forecast of rate-and-state governed fault analog, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19222, https://doi.org/10.5194/egusphere-egu26-19222, 2026.
Strike-slip faults accommodate plate motion through a coupled spectrum of abrupt seismic rupture and distributed, aseismic creep that coexist and interact within the same fault system. Yet the surface expression of these behaviours remains poorly constrained, largely because the short-term physics of frictional instability and the long-term construction of fault-zone morphology are rarely observed within a single framework. Here, we address this gap using seismotectonic analogue experiments designed to isolate how velocity-dependent (velocity-weakening and velocity-strengthening) and neutral frictional regimes govern both transient and cumulative deformation in strike-slip systems. The experiments reproduce hundreds of analogue earthquake cycles along a laboratory strike-slip fault system to build topography while simultaneously measuring shear force, acoustic emissions, and full-field surface displacements. By systematically modifying fault material properties and boundary conditions, we analyse their mechanical and geometric consequences.
We argue that the distinction between velocity-weakening, neutral, and strengthening friction is not merely a control on whether earthquakes occur but also organizes fault-zone architecture. In the velocity-weakening zone, deformation is expected to concentrate episodically into narrow, migrating shear bands that imprint discontinuous, step-like surface relief. In contrast, velocity-strengthening and velocity-neutral regimes should promote diffuse surface strain, topographic gradients, and a cumulative memory of stable slip. Investigating the interaction between these regimes provides a mechanical explanation for natural strike-slip faults that often display coexisting seismic segments and creeping sections. By linking fault frictional heterogeneity to measurable surface deformation patterns, we aim to contribute to presenting a mechanical and morphological framework for strike-slip fault evolution.
How to cite: Willingshofer, E., Kosari, E., Wassens, L., and van Dinther, Y.: Velocity-Dependent Friction and Its Role in the Evolution of Surface Deformation and Topography in Strike-Slip Fault Systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19393, https://doi.org/10.5194/egusphere-egu26-19393, 2026.
Understanding earthquake site effects in fault-controlled geological settings remains a key challenge for seismic hazard assessment, particularly in intramontane basins affected by active normal faulting. In these settings, fault-zone site effects are expected due to the abrupt contact between thick soft and/or granular sedimentary basin-fill and the carbonate bedrock, which is characterized by highly variable fracture intensity and orientation.
In this study, we present the results of a multidisciplinary investigation aimed at characterizing fault-related site effects along the Monte Morrone fault system, a major Quaternary normal fault bounding the eastern margin of the Sulmona intramontane basin (Central Apennines, Italy) and recognized as a key seismogenic structure in the region.
A passive seismic survey was conducted at three sites located along the fault zone: Eremo di Sant’Onofrio, Roccacasale North, and Roccacasale South. The two Roccacasale sites are structurally located within the fault core and damage zone of the Monte Morrone fault system, characterized by intense deformation and pervasive fracturing. Ambient noise data were acquired and processed using the Horizontal-to-Vertical Spectral Ratio (H/V) technique to investigate resonance frequencies and potential directional amplification effects. Where suitable reference conditions were identified, the data were further analyzed using the Standard Spectral Ratio (SSR) technique to provide a more robust estimate of relative amplification.
Geophysical observations were integrated with detailed structural and geomechanical field measurements. These include fault architecture mapping, fracture density and fracture orientation analysis, and in-situ rock mass characterization through Schmidt hammer rebound measurements. The combined dataset highlights significant lateral variations in seismic response between the investigated sites, which can be directly related to the features of the fault-zone structures, damage intensity, and rock mass stiffness. Directional amplification patterns observed in H/V are consistent with the dominant orientation of fault-related discontinuities, suggesting a strong structural control on local seismic response.
Our results are consistent with previous studies documenting fault-controlled site effects and directional amplification within active fault zones in the central Apennines (e.g., Pischiutta et al., 2013, Vignaroli et al., 2019), and further emphasize the role of fault-core properties and damage-zone architecture in modulating seismic ground motion. These findings support the growing evidence that structural heterogeneities within regional fault zones play a key role in controlling seismic wave propagation and site effects, even at rock sites traditionally considered mechanically homogeneous. Our results suggest that fault cores and associated damage zones should be treated as mechanically distinct domains, characterized by stiffness contrasts and velocity anisotropies capable of modifying the amplitude, frequency content, and directionality of seismic ground motion.
From an application perspective, the multidisciplinary dataset presented here provides further evidence of the importance of correctly representing fault zones in two-dimensional subsurface models for numerical simulations of local seismic response. Explicitly considering the internal architecture of faulted rock masses, rather than assuming uniform "bedrock" conditions, can significantly improve ground motion modeling and help reduce uncertainties in seismic microzonation studies in tectonically active regions.
References
Vignaroli et al., 2019 Domains of seismic noise... BEGE, doi.org/10.1007/s10064-018-1276
Pischiutta et al., 2017. Structural control on the directional.. EPSL, doi:10. 1016/j.epsl.2017.04.017
How to cite: Pizzi, A., Giallini, S., Simionato, M., Puricelli, C., and Pagliaroli, A.: Integrating Structural, Geomechanical, and Passive Seismic Data to Investigate Site Effects along an Active Normal Fault Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21225, https://doi.org/10.5194/egusphere-egu26-21225, 2026.
Over the past few decades, reconstructing paleoseismic sequences using in situ cosmogenic 36Cl exposure ages has proven effective in numerous countries and regions, greatly enhancing our quantitative understanding of active faults (Akçar et al., 2012; Benedetti et al., 2002; Goodall et al., 2021; Mitchell et al., 2001; Mouslopoulou et al., 2014). However, in China, where normal fault bedrock exposures are typically rich in quartz, 10Be is the optimal nuclide for dating fault scarps, offering a better fit to the local geological context than 36Cl. Despite this, only a handful of 10Be studies have reconstructed earthquake slip histories for large events (M>7) using the relationship between exposure ages and height on cumulative scarps (Lunina et al., 2020; Shen et al., 2016).
This study investigates the bedrock fault scarp at Duyu, situated along the Huashan Piedmont Fault (HPF)—the source of the AD 1556 M 8½ earthquake—using 10Be concentration profiling to identify paleoearthquake events. Our analysis confirms a strong earthquake occurred prior to the 1556 event, dated to 3092 ± 383 years ago. This finding bridges a significant gap in the paleoseismic record for this interval, which was previously undetected by traditional trenching methods. The HPF exhibits a quasi-periodic recurrence pattern with an estimated interval of 2623 ± 383 years. During the late Holocene, the fault maintained a vertical slip rate of 2.0 to 2.7 mm/yr, with individual events generating coseismic vertical displacements of 6 ± 0.5 m. These results demonstrate the value of in situ10Be exposure dating as a robust method for reconstructing the seismic histories of normal faults in tectonically similar regions globally.
How to cite: Yin, J., Xu, W., Shi, W., Chen, J., and Caffee, M.: 10Be-Based indentification of Paleoearthquake event on the Huashan Piedmont Fault, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6377, https://doi.org/10.5194/egusphere-egu26-6377, 2026.
The high integrated brittle strength of cratons with a cool and thick lithosphere protects cratonic interiors from tectonic deformation. High strain rates (>10-15 s-1) at plate boundaries facilitate enhanced faulting. However, cratons are not immuned from seismic activities. Intraplate earthquakes have caused more fatalities than interplate earthquakes. For example, the 1556 Huaxian earthquake (M 8.0), the deadliest earthquake in human history that killed 830,000 people, occurred in the middle of continental China. Seismic quiescent may in some stable continent relate to short instrumental histories (< ~150 years) with respect to the earthquake cycles (>104 years) and the limited resolution of geodetic surveys for fault motions in stable cratons. The extremely long earthquake cycles in stable continents make it hard to be detected due to surface erosional processes, particularly for those ‘one-off’ events. Classical seismic hazard estimation based on slip deficit calculations may not apply to earthquakes in stable continents when the last destructive earthquake occurred in history is unknown. To quantify the impact of seasonal hydrological cycles on seismicity in stable cratons, we integrate seismic catalogs with GRACE(-FO) data, borehole water levels, precipitation records, and InSAR observations from the Pilbara and Yilgarn cratons in Australia. Our analysis tests whether seismic responses to hydrological stress are consistent across cratons and assesses whether these perturbations induce temporary or permanent changes in craton stability.
How to cite: Yang, H. and Zhao, S.: Could Surface Precipitations Destabilize a Craton?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8590, https://doi.org/10.5194/egusphere-egu26-8590, 2026.
Probably the most impressive geological feature of active fault zones hosted in carbonate rocks is the presence of several hundreds of meters thick damage zones, often composed of in-situ shattered rocks (ISRs, i.e. rocks fragmented into clasts < 1 cm in size). Despite their abundance, it remains unknown how ISRs form (during the propagation of seismic ruptures?), and how their presence affects (1) the propagation of individual mainshock seismic ruptures, (2) the near field wave radiation and associated strong ground motions, and (3) the evolution in space and time of aftershock seismic sequences. In this contribution, we will present preliminary results of a three-year Ph.D. project aimed at addressing these issues through an integrated field geology and numerical modelling approach.
We exploit existing and newly acquired field geology data on fault damage zone distributions in the Central Apennines (Italy), and perform dynamic rupture earthquake sequence simulations with SeisSol (https://seissol.org). The fully-dynamic individual earthquake simulations with SeisSol rely on the discontinuous Galerkin method, which allows treating complex 3D geological structures, nonlinear rheologies (including off-fault plastic yielding) and high-order accurate propagation of seismic waves (Käser et al., 2010). The earthquake modelling simulations integrate laboratory-derived frictional constitutive laws with simplified and realistic representations of fault zone geometry and surface topography. Currently, our study is focused on the 25 km long Campo Imperatore fault system in the Gran Sasso Massif area (Italian Central Apennines) where the damage zones are pronounced and well mapped (Demurtas et al., 2016; Fondriest et al., 2020).
We aim at using the dynamic rupture earthquake modelling simulations to discuss the formation and distribution of ISRs with respect to (1) the maximum magnitude (Mw 7.0) of the earthquake associated with the studied fault, (2) fault geometry (length, presence of step overs, fault bends, etc.), (3) topographic effects (valleys, etc.), and (4) lithology (limestones, dolostones, etc.) of the wall rocks. This approach is expected to identify the physical, geological, and loading conditions controlling seismic rupture propagation and the development of fault damage zones. The physically based, fully dynamic 3D simulations will also provide estimates of earthquake source parameters (e.g., fracture energy and seismic moment release rate) and synthetic seismograms (strong ground motions), which will be compared with seismological and strong-motion data from earthquakes in the Central Apennines.
References
Demurtas, M., Fondriest, M., Balsamo, F., Clemenzi, L., Storti, F., Bistacchi, A., & Di Toro, G. (2016). Structure of a normal seismogenic fault zone in carbonates: The Vado di Corno Fault, Campo Imperatore, Central Apennines (Italy). Journal of Structural Geology, 90, 185–206. https://doi.org/10.1016/j.jsg.2016.08.004
Fondriest, M., Balsamo, F., Bistacchi, A., Clemenzi, L., Demurtas, M., Storti, F., & Di Toro, G. (2020). Structural Complexity and Mechanics of a Shallow Crustal Seismogenic Source (Vado di Corno Fault Zone, Italy). Journal of Geophysical Research: Solid Earth, 125(9), e2019JB018926. https://doi.org/10.1029/2019JB018926
Käser, M., Castro, C., Hermann, V., & Pelties, C. (2010). SeisSol – A Software for Seismic Wave Propagation Simulations. In High Performance Computing in Science and Engineering, Garching/Munich 2009 (pp. 281–292). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-13872-0_24
How to cite: Dreier, D., Marchandon, M., Fondriest, M., Gabriel, A.-A., and Di Toro, G.: Formation of Fault Damage Zones in Carbonates and Their Role in the Seismic Cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10254, https://doi.org/10.5194/egusphere-egu26-10254, 2026.
The classical earthquake cycle is commonly described as alternating between long periods (decades to centuries) of interseismic locking and brief episodes (seconds) of coseismic rupture. However, increasingly dense geodetic observations from recent megathrust earthquakes reveal a more complex spectrum of transient deformation processes that challenge this binary framework. The New Georgia Group in the Solomon Islands provides a unique natural laboratory to investigate these processes, where the Woodlark Basin subducts beneath the Solomon Arc and has generated large megathrust earthquakes, including the 1936 Mw 7.9 and 2007 Mw 8.1 events.
The close proximity of the islands to the trench allows Porites corals to serve as high-resolution recorders of vertical ground motion. While coral morphology has long been used to identify coseismic uplift, we introduce a novel approach that combines coral morphology with stable isotope analysis (δ¹³C and δ¹⁸O) to quantify relative sea-level (RSL) variations at annual resolution. We first assess the robustness of the relationship between coral water depth and δ¹³C using 141 new samples collected across a range of depths formed within the same time interval. For depths between 170 and 110 cm below sea level, δ¹³C exhibits a strong linear correlation with water depth (R² = 0.982), while shallower samples display a non-linear response.
We then apply this RSL proxy to a 692-sample coral time series spanning 1928–2012 and validate the reconstructed RSL against available tide-gauge records. The 2007 Mw 8.1 earthquake is clearly resolved, with coral morphology recording ~70 cm of coseismic uplift expressed as a pronounced die-down surface, accompanied by a δ¹³C excursion exceeding 2‰. The 1936 Mw 7.9 event is similarly captured by a distinct δ¹⁸O anomaly, with postseismic relaxation observed consistently along two independent drilling transects.
Beyond discrete coseismic signals, the record reveals multi-year to decadal periods of uplift and subsidence that we interpret as complex interseismic deformation. In particular, we identify intervals consistent with slow slip activity during 1955–1964, 1977–1986, and 1999–2002. These results demonstrate that stable isotope measurements in corals provide a powerful bridge between instrumental geodesy and paleoseismology, enabling a continuous, high-resolution view of subduction-zone deformation and stress evolution across the full earthquake cycle.
How to cite: Karaesmen, M. E., Lavier, L., and Taylor, F.: High-resolution Coral Geodesy in the Solomon Islands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15880, https://doi.org/10.5194/egusphere-egu26-15880, 2026.
Active normal faults in the Central Apennines accommodate ongoing crustal extension and have generated significant earthquakes (up to Mw ~7) during historical and instrumental times. However, several fault systems, including the Gran Sasso fault system (GSFS), lack documented surface-rupturing earthquakes, raising questions about their structural maturity, role in accommodating the extension in this region, and their potential to generate future large-magnitude events.
Here, we investigate the relationship between fault geometry, cumulative displacement, and slip rate along the Gran Sasso fault system located 19km north of L’Aquila, a system consisting of two major normal faults with an overall length of ~46 km. These include(i) the Campo Imperatore fault, consisting of two segments measuring roughly 20 km and 8 km, and (ii) the Assergi fault, which extends about 18 km along the western flank of the Gran Sasso massif. Both faults exhibit a consistent average W-E orientation with secondary structure tending WNW-ESE. Our aim is to assess the structural maturity and seismic significance of the GSFS within the broader Apennine fault network.
Using high-resolution Pleiades satellite imagery combined with existing geological maps and field observation, we mapped in detail the active fault trace and identified displaced geomorphic markers. The analysis focuses on two main fault segments, the Campo Imperatore and Assergi segments, along which a well-preserved Holocene fault scarp is continuously expressed. Scarp height was measured accurately along strike using several complementary approaches, including field-based observations, topographic profiles extracted from high-resolution DEMs, and the automated ScarpLearn algorithm (Pousse et al., 2022), which identifies and quantifies fault scarp morphology together with associated uncertainties. Preliminary results indicate that vertical displacement varies between ~2 and 16 m, locally reaching up to ~20 m along the Campo Imperatore segment. These results are analyzed in relation to fault architecture to assess how geometric complexities, such as relay zones and step-overs, influence displacement distribution along strike
Field investigations and detailed mapping along the Campo Imperatore fault allowed the identification of three key sites where fluvial terraces and glacial moraines are displaced and can be used as geomorphic markers of fault slip. Samples were collected for ^36Cl cosmogenic exposure dating of these surfaces. When combined with measured offsets, these exposure ages provide constraints on average late Quaternary slip rates and on the long-term activity of the fault, under the assumption that the dated surfaces record cumulative displacement since their abandonment.
How to cite: delleci, H., Benedetti, L., Riesner, M., Di Toro, G., Fondriest, M., and Montoya, J. G.: Linking Fault Geometric Complexity and Cumulative Displacement with Seismic Behavior: Insights from the Gran Sasso Fault System (Central Apennines, Italy), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17057, https://doi.org/10.5194/egusphere-egu26-17057, 2026.
Western Anatolia represents one of the most active continental extensional domains within the Alpine–Himalayan orogenic system. Ongoing NNE–SSW extension has produced a system of E–W–trending grabens and half-grabens controlled by active normal faults. These basins provide natural laboratories to investigate the interaction between fault-controlled deformation, sedimentary basin evolution, and seismic hazard. A key characteristic of such extensional basins is the presence of thick, unconsolidated basin fills overlying competent basement rocks. This strong mechanical contrast promotes seismic wave trapping and amplification, leading to prolonged ground-motion duration and increased shaking intensity. Similar basin-related effects have been documented in other extensional and transtensional settings worldwide (e.g., the Basin and Range Province, Central Apennines, and the Aegean region), highlighting their importance for seismic risk in densely populated areas.
The Büyük Menderes Graben is one of the largest and most mature extensional basins in Western Anatolia and hosts several major population centers. Paleoseismological investigations carried out on the main basin-bounding normal faults reveal repeated surface-rupturing earthquakes during the Holocene. These data show that fault segmentation, fault length, and basin geometry play a primary role in controlling earthquake magnitude, rupture characteristics, and recurrence patterns. At a regional scale (~100 km), several active faults have the potential to generate moderate to large earthquakes (Mw ~6.0–7.1). The combined effects of distributed fault deformation and basin amplification imply that seismic hazard in extensional provinces cannot be assessed solely based on proximity to individual faults. Instead, an integrated approach that considers fault interaction, basin geometry, and site effects is required.
In this study, trench-based paleoseismological investigations were carried out along the İncirliova, Umurlu, and Atça segments forming the northern margin of the Büyük Menderes Graben (BMG). In trenches excavated along all three segments, strong evidence was obtained for Holocene earthquakes that produced surface faulting. Preliminary findings suggest that the 22 February 1653 Menderes Valley earthquake (Ms6.7) may have originated from the İncirliova Segment, whereas the 20 September 1899 Menderes Valley earthquake (Ms6.9) was likely generated by the Umurlu and Atça Segments.
This study synthesizes active tectonic observations, paleoseismological trench data, and basin-scale geological constraints from the Büyük Menderes Graben to highlight how extensional basins amplify seismic risk beyond simple fault-based models. The results have broader implications for seismic hazard assessment in other active continental rift and graben systems worldwide, particularly where rapidly growing urban areas are built on young sedimentary basins.
How to cite: Kürçer, A., Çal, Ç., Yalvaç, O., Gürsoy, H., and Elmacı, H.: Active Tectonics and Paleoseismology of an Extensional Basin: Implications from the Büyük Menderes Graben (Western Anatolia, Türkiye), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19316, https://doi.org/10.5194/egusphere-egu26-19316, 2026.
The Yingjing-Mabian-Yanjin tectonic blet (YMYTB) serves as a critical boundary structure between the southeastern margin of the Tibet Plateau and the Sichuan Basin. Although seismicities has been frequent since the late Quaternary, the activity of individual faults within the tectonic belt remains unclear, introducing significant uncertainty in understanding and assessing the current regional crustal deformation patterns and seismic hazards. Particularly, the southern segment of the tectonic belt near the Leibo fault has experienced the 1216 Mahu M7 earthquake and several strong earthquake swarms of magnitude 6 or above. However, research on this fault zone is limited, and there is still a lack of reliable evidence to determine its most recent activity period and its relationship with nearby major earthquakes.
To address this issue, this study conducted paleoseismic trenches on the northern, central, and southern branches of the Leibo fault, based on the interpretation of high-resolution remote sensing imagery and field geological-geomorphological investigations. The following conclusions were drawn:
(1) Based on paleoseismic event identification markers, three, three, and five paleoseismic events were revealed on the three branch faults, respectively. Dating results of radiocarbon samples constrained the occurrence times of the three paleoseismic events on the northern branch fault to 21,190–20,590 BC (EP1), 20,550–12,120 BC (EP2), and after 12,090 BC (EP3). The timings of the three strong seismic activities on the central branch fault were 7,400–6,320 BC (EY1), 5,690–2,620 BC (EY2), and 2,220 BC–170 AD (EY3). The occurrence times of the five surface-rupturing seismic events on the southern branch fault were 14,660–9,300 BC (ES1), 9,270–7,560 BC (ES2), 600–640 AD (ES3), 740–1,440 AD (ES4), and 1,650–1,900 AD (ES5). The paleoseismic results indicate that all branch faults of the Leibo fault zone are Holocene active faults.
By comparing the occurrence times of paleoseismic events on each branch fault, it is determined that the Leibo fault zone has experienced at least 10 surface-rupturing paleoseismic events since the Late Pleistocene. The corresponding age ranges are 21,190–20,590 BC (E1), 14,600–9,300 BC (E2), 12,090–11,820 BC (E3), 9,270–7,560 BC (E4), 7,400–6,320 BC (E5), 5,690–2,620 BC (E6), 2,220 BC–170 AD (E7), 600–640 AD (E8), 740–1,440 AD (E9), and 1,650–1,900 AD (E10). The paleoseismic history of the Leibo fault zone reveals that the strong seismicities of the three branch faults exhibit significant spatial independence and temporal clustering, indicating that the branch faults of the Leibo fault zone are independent seismogenic structures.
(3) Based on historical earthquake records and paleoseismic research results, this study proposes that the seismogenic structure of the 1216 Mahu M7 earthquake is the southern branch of the Leibo fault. Additionally, the Leibo fault likely participated in the rupture of the 1935–1936 Mabian M6¾ earthquake swarm.
(4) By collecting and analyzing the magnitudes of strike-slip earthquake events that generated surface ruptures in western China since 1920, it is inferred that the lower limit of the magnitudes of paleoseismic events revealed on the Leibo fault zone is 6.5. Furthermore, based on the fault length and empirical relationship, it is estimated that the Leibo fault has the capability to generate earthquakes with magnitudes of 7.0 or higher.
How to cite: Sun, H.: Late Quaternary Strong Earthquake History of the Leibo Fault on the southeastern margin of the Tibetan Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21381, https://doi.org/10.5194/egusphere-egu26-21381, 2026.
The Roccapreturo Fault (RF) is a 9 km-long NW-SE normal fault forming one of the major segments of the Middle Aterno Valley Fault system, located 20 km south of L’Aquila in the Central Apennines (Italy). Despite its clear seismogenic potential, no earthquakes have been documented in historical sources. Large earthquakes on such structures typically have time intervals of several millennia, making paleoseismology crucial for constraining their long-term seismic behavior. The RF exhibits 150–250 m-high triangular facets and a 10 m-high semi-vertical fault scarp that cuts the Cretaceous limestone sedimentary sequence and delineates the main fault trace. North of Roccapreturo village, Quaternary colluvial deposits and alluvial fans feed a small intermontane basin, bounded by a 25-m-high ridge most probably related to the cumulative displacement along an antithetic fault subparallel to the main fault. We excavated two paleoseismological trenches across this antithetic fault, where a refined sedimentary record enhances the preservation of coseismic deformation. An additional trench was excavated ~1 km south, at the base of the main fault scarp.
Trenches were logged using standard stratigraphic, structural, and event-identification criteria. Event ages were constrained through radiocarbon dating of 23 bulk-sediment and charcoal samples. To complement conventional trench analysis, we implemented an integrated workflow combining conventional paleoseismology with pixel-based image enhancement. This approach exploits multi-temporal orthophotography datasets acquired at different spatial resolutions and times. Photogrammetric products (orthomosaics, true- and false-color RGB composites, 3D textured point clouds, and raster derivatives) were integrated into a georeferenced multi-layer stack to support post-field interpretation and independent validation of trench observations.
In the trenches across the antithetic fault, the basal stratigraphy consists of fine-grained marsh deposits faulted and folded against fractured and brecciated limestone bedrock. These units are overlain by clast-supported colluvial sequences containing wedges that record cumulative vertical displacements of up to ~70 cm, defining multiple paleoearthquake horizons. Three to four surface-rupturing events were identified in the antithetic fault trenches, with clustered ages of 0–1.7 ka, 4–8 ka, 8–13 ka, and 15–21 ka. In contrast, the trench excavated at the base of the main scarp preserves only a single recent event within colluvial deposits, consistent with the youngest event recorded in the antithetic fault trenches.
Previous studies along the main RF focused on cosmogenic dating of the bedrock scarp, estimating Middle Pleistocene slip rates of 0.2–0.3 mm/yr, and on trenching at alluvial-fan intersections. Two Holocene surface-rupturing events (2–8 ka) were identified, indicating a recurrence of about 2 ka and magnitudes up to Mw 6.5. The earthquake events that yielded in our trenches correlate well with previous results, extending the seismic record of the RF into the Late Pleistocene. Together, these results are crucial for constraining the timing and recurrence of surface-rupturing events and for assessing the role of antithetic faults in accommodating distributed deformation within the fault system. In addition, integrating image-enhancement techniques improves the visualization of subtle deformation and stratigraphic relationships, reduces interpretative uncertainty, and provides a scalable, reproducible framework that effectively complements classical paleoseismological trenching.
How to cite: Riesner, M., Gallego-Montoya, J., Benedetti, L., Pucci, S., Cinti, F. R., Boncio, P., Pantosti, D., Testa, A., Ferry, M., Baize, S., and Pace, B.: Paleoseismology of the Roccapreturo Fault (Central Apennines): Insights from Antithetic Fault Trenching and Image-Enhanced Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17450, https://doi.org/10.5194/egusphere-egu26-17450, 2026.
The central Apennines (Italy) are characterized by active normal faulting that is largely clustered in space and time, as documented by both historical and paleoseismic records. The 2016-2017 central Italy earthquake sequence, comprising a series of Mw 5 to Mw 6.5 events within half a year, exemplifies this behavior. Over longer timescales, 36Cl dating of Holocene fault scarps reveals earthquake clustering in the Fucino basin. Although the central Apennines have dense geodetic and seismological observations, these instrumental datasets only cover a small portion of the seismic cycle. This raises fundamental questions about how representative the present-day deformation signals are of long-term tectonic loading and seismic hazard. Here, we address the following questions: How representative is the current geodetic signal over multiple earthquake cycles in an area characterized by a dense fault network? How do surface velocities evolve through the earthquake cycle, and how does the spatial and temporal distribution of earthquakes relate to this evolution?
We combine new InSAR observations with newly developed seismo-thermo-mechanical models with an invariant rate-and-state friction (STM-RSF) and a visco-elasto-plastic rheology in a geodynamic framework. This fully dynamic earthquake cycle model resolves the inter-, post- and co-seismic periods, as well as cumulative deformation over several seismic cycles. We build on previous STM modeling in the central Apennines (Fonteijn et al., in prep). Faulting is localized on pre-defined weak zones from geology and the Fault2SHA active faults database, but can also occur outside the weak zones.
We analyzed InSAR time-series to study interseismic surface deformation in the central Apennines. We detect significant short wavelength velocity variations across faults of 0.5 to 2 mm/yr, which could possibly be explained by bookshelf faulting. Additionally, we simulated an earthquake sequence of six large normal-faulting earthquakes over ~8000 years in the central Apennines. These earthquakes occur on different normal faults in sequence before faults are reactivated, with rupture on one fault transferring stresses to adjacent faults. We also find rupture of a spontaneously arising antithetic fault and accumulated vertical displacement shows block-faulting behavior. We assess the variability of interseismic surface displacements and compare with InSAR interseismic displacements. Preliminary results show significant variations in vertical velocities in both duration and intensity over 8000 years, with alternating periods of subsidence and uplift in the orogen. This new modelling approach for the first time allows for a comparison of surface displacements over multiple earthquake cycles with short-term geodetic observations. The outcome of this study will have important implications for how to use geodetic data for seismic hazard assessment.
How to cite: Pathier, E., Fonteijn, M., Koelzer, A., Socquet, A., van Veenhuizen, N., and van Dinther, Y.: Assessing the longevity and stationarity of surface velocities for seismic hazard in the central Apennines (Italy) by combining InSAR and fully dynamic earthquake cycle modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20817, https://doi.org/10.5194/egusphere-egu26-20817, 2026.
The 2023 Turkey earthquake sequence generated widespread off-fault deformation. Recent 3D InSAR analyses of the doublet sequence show that ~35% of coseismic slip was accommodated by off-fault deformation extending up to 5 – 7 km from the fault (Liu et al., 2025). These observations, coined Absent Surface Displacement (ASD), may highlight the complex interplay between off-fault deformation, geometric fault complexity, and near-surface off-fault material properties. Quantifying how such deformation patterns emerge, and whether numerical earthquake models can capture their spatial organisation, remains an open question.
In this study, we investigate the relationship between InSAR-derived ASD patterns from the MW 7.8 Kahramanmaraş rupture and synthetic off-fault plastic strain fields, which represent distributed inelastic yielding of the surrounding medium under dynamic rupture loading. This is generated in a suite of six different 3D dynamic rupture simulations with non-associative off-fault Drucker-Prager plasticity. These models extend on those presented in Gabriel et al. (2023) and incorporate varying on-fault frictional and structural complexities, such as fault roughness or fault waviness, variable fracture energy through different frictional parameters, and supershear initiation rupture speeds. We analyse fault-normal profiles along the geometrically complex rupture trace, and explore approaches for quantifying along-strike variability in inelastic yielding regions, plastic strain distribution and deformation asymmetry. Our analysis focuses on exploring whether off-fault plasticity can serve as a proxy for ASD and how geometric complexities and different dynamic rupture model ingredients influence the distribution and magnitude of off-fault deformation. This work provides an initial step toward constraining the consistency between observed and modelled near-fault deformation, and toward improving the representation of off-fault processes in physics-based earthquake rupture simulations.
How to cite: Preca Trapani, R., Klinger, Y., Marchandon, M., Hok, S., Scotti, O., and Gabriel, A.-A.: Quantifying Off-Fault Plastic Strain in 3D Dynamic Rupture Models: Insights from the 2023 Kahramanmaraş Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1206, https://doi.org/10.5194/egusphere-egu26-1206, 2026.
The 2010 Mw 8.8 Maule earthquake is one the largest and the best-instrumented megathrust ruptures worldwide, with extensive seismic and geodetic observations spanning its interseismic, coseismic, and postseismic phases, making it an exceptional case for understanding how a subduction interface relaxes and recouples after a great earthquake. In this study, we investigate the spatio-temporal evolution of seismicity with a focus on moderate-to-large seismic events (M ≥ 6) that occurred between 2010 and 2022 in the northern half of the Maule rupture and analyze how their deformation patterns reflect postseismic stress redistribution. While shallow aftershocks dominated the first two years following Maule, later seismicity concentrated around the margins of the main slip patch, where both afterslip and Coulomb stress changes were greatest. Only three M ≥ 6 earthquakes recorded in this interval generated measurable surface deformation: the 2012 Mw 7.1 Constitución, 2017 Mw 6.9 Valparaíso, and 2019 Mw 6.8 Pichilemu earthquakes. GNSS trajectory modeling combined with InSAR observations were used to characterize their coseismic deformation fields and invert for slip on the megathrust, revealing rupture patches consistent with independent constraints on Maule coupling and coseismic slip. The Constitución earthquake activated a deep asperity down-dip of the Maule high-slip zone, in a region that accumulated stress during early postseismic relaxation; the Valparaíso rupture occurred within a strongly coupled segment north of the Maule rupture that experienced enhanced loading and was preceded by a slow-slip episode; and the Pichilemu earthquake ruptured a shallow zone that underwent rapid afterslip before gradually re-locking. Together, these earthquakes demarcate a decade-long transition from afterslip-dominated deformation to the re-establishment of heterogeneous coupling along the megathrust, revealing that the Maule rupture continued to control regional tectonics long after the mainshock. These findings emphasize that moderate-magnitude events are key markers of ongoing stress redistribution and must be included to fully resolve the postseismic stage of the seismic cycle in one of the most active seismogenic subduction zones on Earth.
How to cite: Monge, C., Moreno, M., and Becerra-Carreño, V.: Postseismic evolution and megathrust re-coupling revealed by the spatio-temporal distribution of seismicity after the 2010 Maule earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1323, https://doi.org/10.5194/egusphere-egu26-1323, 2026.
The Kamchatka subduction zone marks one of the most tectonically active regions in the world. Along the Kuril-Kamchatka Trench, the dense, cold Pacific plate subducts beneath the Okhotsk plate, accommodating a shortening rate of ~80 mm/yr along a direction almost perpendicular to the trench. Numerous tsunamigenic earthquakes have been documented along this subduction zone, including the 1952 Mw 8.8-9.0 megathrust earthquake that remains one of the largest events ever recorded by modern instruments. Similar megathrust events are suspected to have occurred in 1737 and 1841, although the observations from those times are scarce. On 29 July 2025, a Mw 8.7-8.8 earthquake occurred offshore Kamchatka, generating a tsunami that traveled across the Pacific. The 2025 epicenter lies less than 40 km from that of the 1952 earthquake and is accompanied by an aftershock distribution of comparable extent. The 2025 event therefore presents a rare opportunity to study the megathrust rupture on the Kamchatka plate interface using modern satellite-based geodesy.
We analyzed coseismic deformation of the 2025 Kamchatka earthquake using InSAR from multiple satellites and GNSS. InSAR images show deformation concentrated in the southern Kamchatka Peninsula, with amplitudes increasing progressively from inland areas toward the coast. The GNSS station on Paramushir Island recorded the maximum GNSS displacement, with seaward horizontal and downward vertical motions of ~1.7 m and ~0.2 m, respectively. Slip inversions suggest that the rupture propagated unilaterally from the epicenter to the southwest for ~480 km, broadly consistent with the aftershock distribution. The coseismic slip extended downdip to a depth of ~46 km, where the satellite-based geodetic data provide sufficient resolution. However, we found that inland geodetic measurements are insensitive to near-trench slip. Therefore, we generated three geodetic slip models with extreme, moderate, and zero shallow slip, and used DART tsunami observations to evaluate them. As a result, the model with zero shallow slip best reproduces the tsunami arrival times at DART stations, supporting the absence of significant near-trench rupture during the mainshock. The main rupture was confined to depths of 13-46 km, with a peak slip of ~9 m and a geodetic moment magnitude of Mw 8.7. The updip shallow portion of the 2025 rupture zone and the northern adjacent section may pose an elevated tsunami risk due to stress transfer. This work further underscores the crucial role of seafloor observations, as inland data typically offer limited insight into the shallow slip behavior of subduction interfaces.
How to cite: Tang, C.-H., Fukushima, Y., Okada, Y., and Mizutani, A.: Limited near-trench slip of the 2025 Mw 8.7-8.8 Kamchatka earthquake from geodetic and tsunami data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1374, https://doi.org/10.5194/egusphere-egu26-1374, 2026.
A logarithmic function is the popular model of temporal evolution of afterslip, derived from the rate-and-state friction law (RSF) under the steady-state assumption (Marone+1991JGR). Relaxing this assumption, self-accelerating aseismic slip is predicted prior to subsequent decay even with velocity velocity-strengthening setting (i.e., a–b> 0; PerfettiniAmpuero2008JGR). The only natural observation example of such an accelerating stage of afterslip following large earthquakes is the case of the 2003 Tokachi-oki earthquake (M 8.0) in Japan, presented by Fukuda2009JGR (F09) with the data analysis performed by LarsonMiyazaki2008EPS (LM08). They reported that the early postseismic deformation emerged ~1 hour after the mainshock. We revisit this earthquake’s early postseismic deformation with a modern kinematic GNSS processing workflow by Gipsy-X v2.3 because many default and/or recommended settings and products have evolved from the time when these previous works were carried out. This revisit will align the Tokachi-oki case with other earthquake cases analyzed by GNSS processing strategies closer to ours than LM08’s.
Among all the parameters/settings of GNSS processing we tested, the most impactful parameter was the position random walk (RW) parameter. We tested a wide range of values from 1 to 1e-5 m/sqrt(s) for this parameter with switching to the white noise during the mainshock and the M 7.1 largest aftershock (1.3-h later). Comparing our test results with F09’s dataset, the largest mismatch was found between the mainshock and the 7.1 largest aftershock when we attempted to reproduce F09’s cumulative displacements. During this interevent window, F09’s dataset shows tiny deformation, while our solutions show significant deformation. On the other hand, our test solutions exhibit the acceleration at similar timings as F09’s, with the RW parameter same as F09’s (1e-5 m/sqrt(s)), but our cumulative displacements are much smaller than F09’s after the largest aftershock coseismic step was removed. This is because of a trade-off between early postseismic deformation and the largest aftershock step, caused by the very tight RW not allowing sites to move other than at the coseismic timing. Therefore, we recommend careful testing position RW parameter to accurately resolve early postseismic deformation, rather than taking a value introduced in other studies. With our test results, we concluded that no parameters could satisfactorily reproduce the early postseismic deformation presented in F09; in other words, the acceleration of early afterslip reported in F09 was absent in our solutions. Our results imply that the transition between the interseismic and postseismic stage of velocity strengthening faults would happen within several minutes at the longest, implying that the very beginning of afterslip is concurrent with the dynamic ruptures of the mainshock.
How to cite: Itoh, Y., Twardzik, C., Vergnolle, M., and Maubant, L.: Revisiting the early postseismic deformation of the 2003 Tokachi-oki earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2471, https://doi.org/10.5194/egusphere-egu26-2471, 2026.
The spatio-temporal variations of the Earth’s gravity field recorded by satellites have been shown to provide unique insight into mass redistributions during and after major subduction-zone earthquakes, and to reveal anomalous signals preceeding two great ruptures, attributed to rapid aseismic deformations of subducted plates. Understanding these gravity signatures is important for studying subduction system dynamics throughout the earthquake cycle and for improving regional seismic risk assessment. Physics-based numerical simulations are therefore needed in order to model pre- to post-seismic satellite gravity signals, taking into account the 3D structure of the subducting zone, including lateral heterogeneities in the mantle rheology and lateral variations in crustal thickness. In this study, we apply a novel numerical approach to simulate gravity perturbations induced by fault dislocations in a 3D viscoelastic Earth using a Spectral-Infinite-Element (SIE) method, implemented in the SPECFEM-X numerical code. Considering examples of dislocation within a subducted slab, we examine the sensitivity of the surface gravity signals to 3D slab geometry and material structure, including the effects of low-viscosity layers, mantle wedge and cold nose. This approach enables us to investigate the sources of the pre-seismic gravity anomalies prior to the 2011 Mw 9.1 Tohoku earthquake through realistic 3D Earth models and state-of-the-art simulation setups. The findings of this study underscore the importance of numerical simulations in gravitational geodesy as well as in seismic hazard assessment.
How to cite: Parla, R., Panet, I., Gharti, H. N., Martin, R., Remy, D., and Plazolles, B.: Numerical Modelling of Fault-Slip-Induced Satellite Gravity Signals in a 3D Viscoelastic Earth: Application to the Japanese Subduction System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11580, https://doi.org/10.5194/egusphere-egu26-11580, 2026.
The spatial distribution and deformation characteristics of coseismic surface rupture zones are fundamental to understanding the rupture behavior of strong earthquakes. They provide critical insights for predicting the extent, scale, and degree of deformation of future events, which is of great significance for assessing the magnitude of potential seismic hazards.
The December 3, 1915, M7.0 Sangri earthquake in the Woka Graben (northern Cona-Woka Rift) is the region’s most recent major seismic event. Historical records place the epicenter near Zangga, identifying the Eastern Boundary Fault (EBF) as the primary seismogenic structure. However, its remote, high-altitude location and coarse legacy satellite imagery have left details undocumented and source parameters poorly constrained. To address this, we integrated UAV-derived centimeter-scale Digital Surface Models (DSM), orthomosaics, and field investigations. This enabled multi-scale, multi-perspective analysis of fault traces, surface rupture geometry, and coseismic deformation.
Refined mapping reveals that the seismogenic EBF manifests as a continuous, single-branch structure with a total length of approximately 60 km. The fault trace is well-defined and can be divided into northern and southern segments by the Delimuqu River. The northern segment extends ~29km in a nearly N-S direction with a westward dip, while the southern segment extends ~31 km with a NNE strike and a NW dip. A distinct coseismic surface rupture zone, ~35 km in length, developed primarily along the entire northern segment and the northern part of the southern segment of the EBF. Field measurements revealed a maximum coseismic vertical displacement of ~2.1m.
Furthermore, we utilized a MATLAB-based displacement measurement program to perform quantitative extraction of cumulative offsets and Cumulative Offset Probability Density (COPD) analysis across 225 investigation sites, yielding an average coseismic vertical displacement of ~0.79 m. Additionally, a fault scarp diffusion age modeling program was employed to constrain the extent of the coseismic surface rupture based on morphological degradation. Analysis of 362 measurement sites via COPD indicated an average diffusion age of 2.05 ± 0.88 kt for the coseismic scarps. The integration of spatial distributions for minimum mean diffusion ages and cumulative vertical displacements allowed us to quantitatively define the coseismic surface rupture length to ~32 km. This result is in excellent agreement with the ~35 km length derived from remote sensing interpretation, validating the reliability of the estimated rupture scale. Using empirical scaling relationships based on the obtained rupture length and the average/maximum vertical displacements, we re-estimated the earthquake magnitude to be Mw 6.71~6.84, highlighting the high seismic potential of the EBF. This study fills a critical gap in the detailed investigation of the coseismic surface rupture of the 1915 Sangri earthquake and underscores the significant utility of high-resolution topographic data in active tectonics research.
How to cite: Qiao, J., Sun, H., and Wang, X.: Coseismic Surface Deformation Characteristics of the 1915 M7.0 Sangri Earthquake in Tibet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11605, https://doi.org/10.5194/egusphere-egu26-11605, 2026.
The 2025 M 7.7 Myanmar earthquake affected over 30 million people across Myanmar and the broader Asian region. The earthquake caused over 5,000 fatalities, injured thousands, and left several hundred people missing. Damage extended across Myanmar, Thailand, and China, with strong shaking felt throughout Southeast Asia. The rupture propagated for over 450 km, one of the longest strike-slip earthquake ruptures worldwide, cutting through densely populated and economically important regions of central Myanmar. However, the ongoing military coup and subsequent civil conflict between the central army and People’s Defence Forces (PDFs) severely limited rescue operations and ground-based field investigations. As a result, the assessment of rupture characteristics and, slip distribution, remains limited due to gaps in ground observations.
In this study, we investigate rupture characteristics and coseismic offsets using ground-based field survey data integrated with remote-sensing observations and social media-derived felt reports and rupture information. Near the northern rupture termination, which coincides with an active conflict area, we mapped rupture patterns using newly updated Google Earth imagery, validated through reports of rupture posted by locals on social media (Facebook). Along the inferred 1839 M7+ rupture segment, details of the surface rupture were documented using unmanned aerial vehicle (UAV) and tape-and-compass surveys. In the restricted regions controlled by the central army, from Nay Pyi Taw to the southern rupture termination, coseismic offsets were measured using tape-and-compass methods only.
Slip amounts measured from ground-based surveys south of Mandalay systematically underestimate offsets determined from remote sensing, suggesting a significant fraction of the deformation occurred beyond a few meters of the main fault zone. Nonetheless, our mapping indicates that the 2025 surface rupture partially or fully overlapped multiple earlier historical Sagaing fault ruptures, including those in 1839 (Mw 7+), 1956 (Mw 7.1), 1929 (Mw ~7.0), 1930 (Mw 7.3) and 2012 (Mw 6.8). The observed macroseismic effects are comparable to those inferred for the 1839 Ava earthquake, which was poorly understood due to limited historical data. These ground-based data provide critical insights into the rupture behaviour over multiple earthquake cycles of fault segments that, at least in 2025, are inferred to have produced supershear rupture.
How to cite: Aung, L. T., Min, S., Htay, K. N., Mann, T. N., Maung, C. S., Kyaw, H. A., Kyaw, A., Yun, S.-H., and Meltzner, A. J.: Surface rupture characteristics and macroseismic effects of the 2025 Mw 7.7 Sagaing fault earthquake in central Myanmar, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19962, https://doi.org/10.5194/egusphere-egu26-19962, 2026.
Reliable real-time earthquake source characterization requires the rapid selection of solutions from competing algorithms while minimizing false alarms. To address this challenge, Jozinović et al. (2024) have proposed a ground-motion-envelope-based goodness-of-fit approach that ranks candidate source solutions using amplitude ratios and cross-correlation between observed and predicted waveform envelopes. In its current implementation, however, this approach relies on the ground motion envelope prediction model of Cua (2005), which is limited to small-to-moderate sized earthquakes.
In this work, we explore the benefits and limitations of replacing this empirical model with envelopes derived from machine-learning-generated broadband (up to 50 Hz) synthetic waveforms (Palgunadi et al., 2025). These synthetics are generated using a conditional denoising diffusion model, conditioned on preliminary source parameters (magnitude, hypocentral distance, depth), and site effects. For large magnitude events, we superpose point-source synthetics to produce realistic finite-fault rupture waveforms using the SWEET workflow (Colosimo, MSc thesis).
We find that the diffusion-based synthetics extrapolate realistically across a broader magnitude range and reproduce observed envelope characteristics as well as, or even better than, the empirical prediction model. This capability has the potential to enable earlier and more reliable identification of correct source solutions, reduce magnitude and location bias, and improve robustness for larger events.
How to cite: Colosimo, F. A., Jozinović, D., and Böse, M.: Improving Real-Time Earthquake Source Characterization Using Diffusion Model Based Broadband Envelope Synthetics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20840, https://doi.org/10.5194/egusphere-egu26-20840, 2026.
We investigated the geometry and the kinematics of the Sındırgı fault, which was activated during the two M6+ earthquakes (10.08.2025 and 27.10.2025) and their aftershocks. We analyzed all available seismographs from KOERI (Kandilli Observatory and Earthquake Research Institute) and AFAD (Disaster and Emergency Management Authority) to identify fault geometry, earthquake locations, and focal mechanisms. We analyzed P-wave initial polarities and arrival times of a total of 43 M4+ earthquakes including two mainshocks (waveforms from KOERI and AFAD). Fault plane solutions as well as the accurate hypocenter locations indicate that the majority of the mainshocks and the aftershocks activated a south dipping fault. The results indicate an average strike of 110 ± 5.6°, a dip of 61.6 ± 4.4°, and rake a rake -124.6 ± 2.3°. Additionally, we investigated inter-seismic slip rates using 2D dislocation model analyzing the GNSS velocity field. We transformed the most recent velocity field into Anatolian-fixed reference frame. We decomposed GNSS velocities into fault-parallel and fault-perpendicular components and applied 2D arctan curve fitting to simultaneously determine the slip rates and the fault locking depths. Bootstrap error analysis was performed (1σ) to assess error bounds. The lateral motion is nearly negligibly small; however, fault-perpendicular velocities indicate the extension along the Sındırgı fault at 2.34 ± 0.69 mm/y slip rate. Inter-seismic slip rates suggest a rake of -95.2°, a nearly pure normal fault, which is consistent with average mainshock-aftershock rakes. In this context, GNSS-derived interseismic slip rates are capable of forecasting the extensional kinematics of the Sındırgı fault that generated two predominantly normal-faulting M 6+ earthquakes in 2025.
How to cite: Yavuz, S. C., Çelik, R. N., and Bulut, F.: Interseismic Slip Rates of the Sındırgı Fault Forecast Extensional Kinematics During the 2025 M6+ Earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23007, https://doi.org/10.5194/egusphere-egu26-23007, 2026.
Posters virtual: Wed, 6 May, 14:00–18:00 | vPoster spot 1a
EGU26-21372 | ECS | Posters virtual | VPS30
Dynamic Triggering and Effects of Crust Heterogeneities on Propagating Waves due to the 2025 Mw 7.7 Myanmar EarthquakeWed, 06 May, 14:09–14:12 (CEST) vPoster spot 1a
We investigate the heterogeneity of the Indian subcontinent using seismic recordings from the Mw 7.7 Myanmar earthquake that occurred on 28 March 2025. This event was recorded by broadband stations across India. These variations in waveforms at different stations highlight the influence of radiation pattern, crustal structure, wave-propagation paths, and local site conditions. Sedimentary basins, characterized by relatively soft sediments, are known to amplify seismic energy and modify ground motion characteristics, often resulting in enhanced shaking. Understanding these effects is essential for assessing seismic hazard.
We use time-series data from approximately 88 seismic broadband stations provided by the National Centre for Seismology (NCS), India. We apply frequency spectrum analysis, horizontal-to-vertical spectral ratio (HVSR) analysis, and surface wave dispersion analysis. The frequency spectrum helps identify frequency bands where seismic energy is amplified while HVSR analysis is used to estimate the site’s fundamental resonance frequency and the corresponding amplification factor. Surface wave dispersion analysis provides shear-wave velocity information, which is crucial for characterizing near-surface geological conditions.
Together, these analyses help us to understand the influence of local geological conditions at the receiver sites and contributes to a better analysis of regional seismic wave propagation and site-specific ground motion characteristics across the Indian subcontinent.
How to cite: Gupta, S., Silwal, V., and Bora, S. S.: Dynamic Triggering and Effects of Crust Heterogeneities on Propagating Waves due to the 2025 Mw 7.7 Myanmar Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21372, https://doi.org/10.5194/egusphere-egu26-21372, 2026.
