This session brings together modelers and data analysts interested in the physics and computational aspects of earthquake phenomena and earthquake engineering. We welcome contributions spanning all aspects of seismic hazard assessment and earthquake physics - from slow slip events, fault mechanics and rupture dynamics, to wave propagation and ground motion analysis, to the seismic cycle and interseismic deformation and links to long-term tectonics and geodynamics - as well as studies advancing the state-of-the art in the related computational and numerical aspects.
Material interfaces play crucial role in forming seismic wavefield in local surface sedimentary structures and resulting free-surface motion. Multiple reverberations between the free surface and sediment-bedrock interface can lead to resonant amplifications and generation of local surface waves, and consequently to strong site effects of earthquakes.
It is therefore important to properly implement material interfaces in numerical modelling of seismic wave propagation and seismic motion. This has been well known for some time, and several approaches have been developed in variety of numerical methods.
The finite-difference (FD) method is still dominant method in numerical investigations of site effects of earthquakes. It applies relatively simple discretization in space to the material parameters and discretization in space and time to wavefield variables. Therefore, consequences of discretization must be analyzed in time, space, frequency and wavenumber domains.
Interestingly enough, the least attention has been paid to the wavenumber domain. Mittet (2017) and Moczo et al. (2022) recently demonstrated that, due to spatial discretization, a model of the medium must be wavenumber-limited by a wavenumber k smaller than the Nyquist wavenumber. Mittet (2021) and Valovcan et al. (2024) proved that the wavefield (numerically simulated or exact) in a medium limited by wavenumber k can only be accurate up to half this wavenumber. This has significant consequence for practical FD modelling of motion in realistic models of local structures.
We numerically demonstrate a perfect and unprecedented sub-cell resolution (capability to sense the position of interface within a grid cell) of FD modelling based on the wavenumber-limited medium using a finite spatial low-pass filter. The finding that it is possible to use a finite-length filter for wavenumber limitation of the medium is of key importance for the next development of the concept in terms of computational efficiency in modelling site effects.
How to cite: Kristek, J., Valovcan, J., Moczo, P., Kristekova, M., Mittet, R., and Galis, M.: Accuracy of the Finite-difference Modeling of Seismic Motion – Wavenumber Limitation of Medium, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5554, https://doi.org/10.5194/egusphere-egu26-5554, 2026.
This paper presents the quantification of site-city-interaction (SCI) effects on the dynamic response of buildings and free-field motion using domain reduction method. The simulated physics based broadband near-fault ground motion due to Mw6.5 strike-slip earthquake is being utilized to excite the site-city models using domain reduction method. The two step, domain reduction method, is utilized to reduce the exorbitant computational memory and speed as well as measures have been taken to preserve the ground motion characteristics. A building is incorporated in numerical grid as a building block model (BBM) and its dimension, different modes of vibrations and damping are as per the real building. The dynamic response of site-city models is simulated using both the pulse and non-pulse type motions. The analysis of simulated results reveals that the SCI study using realistic earthquake ground motion has caused a reduction of response of building and free field motion in a wide frequency bandwidth as well as its fundamental frequency. An increase of these reductions has been obtained with decrease of building-damping, fundamental frequency and impedance contrast between the BBM and the underlying sediment. A considerable difference in SCI effects is obtained when site-city model is excited with pulse and non-pulse type near-fault ground motions. Detailed study is carried out in order to find out the terms and conditions under which SCI is beneficial to all the buildings of the city.
How to cite: malik, S. and Narayan, J. P.: Quantification of site city interaction effect on Response of building in near fault region using Domain Reduction Method, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10205, https://doi.org/10.5194/egusphere-egu26-10205, 2026.
Over the past two decades, seismic hazard modeling has advanced along two complementary frontiers: empirical probabilistic frameworks, which systematically capture uncertainty through statistical inference, and physics-based simulation platforms, which directly compute ground motions from the governing equations of wave propagation. This project seeks to unify these two worlds by developing an end-to-end integration between OpenQuake and CyberShake, thereby creating a new generation of seismic hazard models that are globally extensible, probabilistically complete, and physically consistent. CyberShake has been under active development for more than a decade, demonstrating its robustness and scientific maturity through extensive implementations in California. It performs a physics-based probabilistic seismic hazard analysis (PSHA), replacing traditional empirical Ground Motion Prediction Equations (GMPEs) with full 3D numerical simulations of seismic wave propagation. Built upon the UCERF2/3 Earthquake Rupture Forecasts, CyberShake computes hazard curves directly from synthetic seismograms generated via Strain Green’s Tensors and thousands of stochastic rupture variations. This approach enables non-ergodic, site-specific hazard estimation and has set a global benchmark for high-fidelity hazard computation. However, its application has remained geographically limited: both the ERF and 3D velocity models were designed specifically for California, requiring extensive datasets that are rarely available elsewhere. Conversely, OpenQuake, developed by the Global Earthquake Model (GEM) Foundation, provides a fully open-source, Python-based framework for probabilistic seismic hazard and risk analysis. It serves as the computational backbone of large-scale hazard models such as the European Seismic Hazard Model 2020 (ESHM20), which integrates decades of regional expertise into a unified and statistical representation. OpenQuake provides a complete probabilistic framework to build Earthquake Rupture Forecasts (ERFs) that combine declustered catalogs, background seismicity, and multi-branch logic trees, ensuring a balanced and uncertainty-aware representation of regional tectonics. Furthermore, its ecosystem extends seamlessly to vulnerability and exposure modules, enabling the translation of hazard into actionable risk assessments and resilience planning.
This project will establish a direct pipeline from OpenQuake’s event-based results to the generation of an ERF compatible with CyberShake’s simulation framework, ensuring moment–rate consistency. By doing so, it will enable CyberShake simulations to be performed for regions beyond California, extending its use to Europe based on the knowledge contained in the ESHM20. The first pilot region is Istanbul, Turkey, a densely populated metropolis located near the western termination of the North Anatolian Fault. Our initial results show that the workflow is already functioning at the prototype level: we have developed a unified 3D velocity model for the Istanbul region by combining available tomographic models with local datasets; generated preliminary event-based rupture catalogs from ESHM20 using OpenQuake; and demonstrated early convergence behavior in hazard curves, indicating that the rupture sampling strategy is statistically robust. These initial results demonstrate the feasibility of the integration approach and indicate that the essential elements needed for a CyberShake-ready ERF are already in place.
How to cite: Riaño Escandon, A. C., de la Puente, J., Danciu, L., and Callaghan, S.: Adapting CyberShake for Europe using OpenQuake-Derived Earthquake Rupture Forecasts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-540, https://doi.org/10.5194/egusphere-egu26-540, 2026.
Reliable physics-based seismic hazard assessment (PB-SHA) requires basin velocity models that accurately reproduce key characteristics of observed seismic wave propagation, which is critical for predicting ground-motion scenarios in complex sedimentary basins. We present a validation study of a three-dimensional basin model with depth-dependent P- and S-wave velocity profiles of the Sulmona Basin (central Italy), developed to represent basin-scale structures relevant for physics-based ground-motion simulations.
The model is implemented in the spectral-element code SPECFEM3D and evaluated through direct comparison of observed and synthetic seismograms at the available stations within the basin. Simulations are performed for selected regional earthquakes, with synthetic waveforms filtered to match the target frequency range of the model. Waveform misfit is quantified using the Pyflex framework, allowing an objective assessment of phase arrival times, waveform similarity, and amplitude differences across multiple stations.
The results show that the model reproduces basin-controlled wave-propagation characteristics, including waveform duration and spatial variability of ground-motion amplitudes. Amplitude variability and waveform agreement primarily reflect the depth-dependent velocity structure and 3D basin geometry, while localized misfits reflect unresolved features and the limited number and spatial coverage of recording sites.
Overall, this validation provides a first quantitative assessment of the Sulmona Basin velocity model, forming a foundation for subsequent work towards physics-based seismic hazard assessment and scenario modelling.
How to cite: May, J. B., Kastelic, V., Carafa, M. M. C., de Nardis, R., and Casarotti, E.: Validation of a 3-D Basin Velocity Model for Physics-Based Seismic Hazard Assessment: The Sulmona Basin, Central Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21376, https://doi.org/10.5194/egusphere-egu26-21376, 2026.
The Ryukyu subduction zone offshore eastern Taiwan possesses significant seismogenic potential, exemplified by the 1920 M8 earthquake. However, even to date, the scarcity of near-field data leaves the ground motion characteristics of such mega-earthquakes poorly constrained, posing a threat to seismic hazard assessments. To estimate potential ground motions in inland eastern Taiwan from future mega-earthquakes, we simulated an M8 scenario earthquake using characterized source models (CSMs) based on the "Recipe" procedure (Irikura and Miyake, 2011). We employed a 3-D finite-difference method to conduct 1,728 full-waveform simulations, incorporating kinematic fault-rupture parameters, including rupture directivity, rupture speed, source time function, and asperity distribution, along with two recent tomographic velocity models and topography. Synthetic waveforms generated at 4,950 virtual stations (about 1.5 km spacing) were analyzed using RotD50 spectral accelerations (SA) at 1, 3, and 5 s. Detailed analysis highlights two notable characteristics of the dataset: first, rupture speed and directivity primarily govern the spatial variability and intensity of ground motions; second, tests demonstrate that utilizing a Gaussian source time function with periods of 2, 5, and 9 s yields optimal performance for assessing SA at 1.0, 3.0, and 5.0 s, respectively. We further calculated non-ergodic terms based on the CH20 GMM (Chao et al., 2020). The patterns clearly delineate northeastern Taiwan's geological domains: high values in the Ilan area (SA 1.0 s) and Longitudinal Valley (SA 1.0, 3.0, 5.0 s), and low values in the Coastal Range. These patterns mirror the crustal velocity structure, highlighting the dominance of path effects over relatively weak source effects. Consequently, our extensive simulation datasets provide a foundation for refining current GMMs and facilitate the transition toward non-ergodic seismic hazard assessments, thereby improving the accuracy of ground motion predictions for future mega-earthquake scenarios in the region.
How to cite: Hsieh, M.-C., Sung, C.-H., and Yang, Y.-C.: 3-D Seismic Wave Simulations for Non-Ergodic Ground Motion Modeling: Source and Path Variability in an M8 Ryukyu Subduction Scenario, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8902, https://doi.org/10.5194/egusphere-egu26-8902, 2026.
Physics-based earthquake wave propagation and ground motion simulations rely critically on three-dimensional seismic velocity models as inputs. These models may originate from seismic tomography, empirical regional compilations, geological constraints, or hybrid modelling approaches, and are commonly treated as deterministic representations of the subsurface. However, all such velocity models are affected by substantial epistemic uncertainty arising from limited data coverage, modelling assumptions, and methodological choices, and often disagree in overlapping regions. Neglecting this uncertainty obscures how variability in Earth structure propagates into simulated wavefields and ground motion estimates, limiting the interpretability and robustness of physics-based seismic hazard assessments.
We present a probabilistic framework to account for velocity model variability in physics-based ground motion predictions. Rather than selecting a single preferred velocity model, we represent model uncertainty through the fusion of multiple, spatially overlapping velocity models using scalable Gaussian process (GP) regression. Our approach treats existing velocity models as spatially correlated observations of an underlying velocity field and infers a continuous probability distribution that captures both shared structural features and model disagreement. The GP formulation thus preserves spatial coherence across scales and provides an interpretable description of uncertainty in terms of spatial covariance, characteristic length scales, and amplitude variability. This enables the generation of ensembles of physically plausible velocity model realisations for use in wave propagation solvers, thereby producing ground motion predictions that explicitly reflect velocity model uncertainty.
Using our framework and realistic 3D seismic velocity models in a regional case study, we generate an ensemble of velocity model realisations and propagate them through physics-based earthquake simulations. We show that uncertainty in velocity structure alone can produce substantial variability in simulated wavefields and predicted ground motions, even when all other aspects of the simulation are held fixed. These results highlight the sensitivity of physics-based ground motion estimates to uncertain subsurface structure and motivate the need to explicitly incorporate velocity model uncertainty in physics-based earthquake simulations.
While demonstrated here for seismic velocity models, the framework can readily incorporate additional geophysical parameters relevant to earthquake wave propagation, such as density and attenuation. This provides a practical route for incorporating epistemic Earth model uncertainty into physics-based seismic hazard assessment.
How to cite: Scivier, S. A., Koelemeijer, P., Mag, A. M., and Nissen-Meyer, T.: From uncertain velocity models to ensemble-based ground motion simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13780, https://doi.org/10.5194/egusphere-egu26-13780, 2026.
The Gulf of Aqaba (GoA) fault system constitutes the southernmost segment of the Dead Sea Transform Fault (DSTF) and forms a ~180 km long left-lateral strike-slip plate boundary separating the Arabian Plate from the Sinai microplate. As the most seismically active region of the Red Sea, the GoA has hosted multiple large historical earthquakes and poses significant seismic hazards to surrounding coastal communities. Increasing tourism activity and the infrastructural giga-project NEOM of the Kingdom of Saudi Arabia in the vicinity of the GoA, highlight the need for advanced seismic hazard assessment (SHA). However, the offshore nature of the fault system and limited availability of observational data complicate the efforts.
To assess earthquake potential and seismic hazard in the region, we construct multiple realizations of three-dimensional, multi-segment fault models representing alternative configurations of the GoA fault system. We constrain variations in 3D fault geometry with recent high-resolution multibeam imaging and local seismicity, while explicitly accounting for uncertainties in seismogenic depth, initial stress conditions, and fault roughness. Incorporating off-fault plasticity along with realistic topography and bathymetry, we perform dynamic rupture simulations with varying hypocenter locations to investigate mechanically plausible rupture scenarios and the resulting ground motions in the GoA. Our physics-based simulations show that all considered model uncertainties, especially the fault geometry, prestress condition and hypocenter location, can strongly influence rupture dynamics, cascading, and segment interactions, determining how and if rupture propagates across the multi-segment GoA fault system. Beyond characterizing earthquake potential on individual fault segments, the simulations indicate that events as large as Mw 7.6 are possible if rupture extends along the full north–south length of the fault system. The resulting synthetic ground motions show attenuation properties consistent with empirical ground motion models, but display highly heterogeneous spatial patterns, including strong rupture-directivity effects during subshear propagation and pronounced off-fault Mach-front amplification for supershear rupture that significantly enhance ground shaking in coastal communities along this narrow gulf. These results underscore the substantial seismic hazard posed by large, dynamically complex earthquakes in the Gulf of Aqaba region and highlight the value of physics-based simulations in enhancing and complementing seismic hazard assessments.
How to cite: Li, B. and Mai, P. M.: Physics-based assessment of earthquake potential and ground motions in the Gulf of Aqaba, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5925, https://doi.org/10.5194/egusphere-egu26-5925, 2026.
Fault geometrical complexity is a first-order controlling factor on the extent of strike-slip fault surface rupture and earthquake magnitude, and step-over represents a key type of such complexity. The Banquan pull-apart basin along the Tanlu fault zone provides a natural example to investigate how tectonically evolved fault geometry influences dynamic rupture propagation across step-overs. We construct a 3-dimensional fault model that incorporates Y-shaped negative flower structure, connecting faults, and a sedimentary layer within the extensional step-over. The shallow fault geometry is constrained by surface geological observations, and the deep fault structure is informed by analogue experiments of pull-apart basin formation. Spontaneous coseismic dynamic rupture simulations are performed to examine the rupture behavior under these fault geometries. Our results show that when stress perturbation associated with stopping phases at the main fault termination is insufficient to trigger rupture on the secondary fault directly, the presence of connecting faults can act as a bridge to facilitate rupture propagation across the step-over. A deeper connecting fault can generate a stress shadow on the secondary fault, inhibiting local rupture propagation and potentially behaving as a barrier on the secondary fault, whereas shallow connecting faults have little influence on the rupture process. These findings provide insights into rupture jumping behavior in step-overs with similar fault structures and extend the existing interpretation of step-over triggering based on stopping phases with planar fault geometries.
How to cite: Lu, Z. and Hu, F.: Effects of tectonic evolution informed fault geometry on dynamic rupture propagation across step-overs: A case study of the Banquan pull-apart basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4321, https://doi.org/10.5194/egusphere-egu26-4321, 2026.
The northern branch of the North Anatolian Fault (NAF), the Main Marmara Fault (MMF), constitutes one of the most critical seismic hazards in the Eastern Mediterranean. This system currently hosts an ~120-km seismic gap bounded by the Mw 7.4 1912 Ganos and Mw 7.4 1999 İzmit earthquakes, and most recently accommodated the Mw 6.2 April 23, 2025 Marmara Sea Earthquake. The 2025 event ruptured the Kumburgaz segment, a key structural transition zone between the partially creeping Central Marmara Basin to the west and the fully coupled Çınarcık Basin to the east. Given the ~260-year seismic quiescence along this region of the MMF, understanding how the 2025 earthquake, together with the 1912 and 1999 events, has modified the regional stress field is essential for evaluating the likelihood and characteristics of a future large Marmara Sea earthquake.
In this study, we construct three complementary quasi-static block models to quantify stress evolution along the MMF: (1) a cumulative coseismic stress transfer model incorporating the 1912, 1999, and 2025 earthquakes; (2) a coseismic model isolating the effects of the 2025 rupture; and (3) an interseismic loading model constrained by GNSS observations. The two models enable a comparative assessment of static Coulomb stress changes on adjacent fault segments, illuminating how recent and historical ruptures collectively influence present-day stress accumulation patterns.
Building upon the quasi-static results, we generate new 3D dynamic rupture simulations using a 1D crustal velocity structure for the nonplanar multi-segment MMF, explicitly incorporating interseismic stress loading, coseismic stress perturbations, and the partially creeping behavior of the MMF. We further benchmark these new simulations against our earlier dynamic models that assumed a homogeneous velocity structure to evaluate the sensitivity of rupture dynamics to crustal heterogeneity and initial stress conditions.
Our integrated modeling framework reveals that, during a potential future large Marmara earthquake, rupture is likely to propagate westward through multiple MMF segments, while arresting near the eastern entrance of the İzmit Fault. New segmented rupture patterns are also observed as a result of using a 1D crustal structure instead of a homogeneous medium, together with the inclusion of coseismic stress transfer. The findings offer important insights into post-2025, post-1999, and post-1912 stress redistribution, fault-segment interactions, and rupture cascade potential across the Marmara region. Collectively, this work advances the scientific basis for earthquake hazard assessment in one of the world’s most densely populated and tectonically active metropolitan corridors.
How to cite: Korkusuz Öztürk, Y., Konca, A. Ö., and Meral Özel, N.: Integrated Stress Evolution and Multi-Segment Rupture Dynamics of the Main Marmara Fault After the 2025 Mw6.2 Marmara Sea Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1665, https://doi.org/10.5194/egusphere-egu26-1665, 2026.
Seismic waves originate from dynamic rupture propagation in faults. Seen from afar, faults are analogous to shear cracks, and their rupture can be analysed using the tools of fracture mechanics. However, a closer look reveals that faults can also be considered locally as a tribosystem, i.e. as a layered structure which accommodates deformation thought localized shearing in a thin granular layer of fault gouge. These two scales are equally important but are difficult to handle simultaneously in simulations.
In this communication, we propose a novel numerical model where this challenge is addressed. The gouge layer is represented using the Discrete Element Method, where each micrometric gouge grain (about 1 million of them in the present case) is explicitly represented and submitted to Newtonian dynamics, based on the forces it receives from its contacting neighbours. This layer is 2 mm-thick, and is confined between two continuum regions simulated using an explicit Meshfree Method. They receive the elastic properties of country rock, and are prestressed in the normal and tangential directions in order to bring the gouge layer just below its peak strength. The resulting fault system has a total length of 64 cm.
A labquake is then triggered from the central point of the fault, and the weakening rheology of the gouge layer allows it to propagate along two rupture fronts, which exhibit specific properties inherited from the frictional response and structure of the gouge. Inclined Riedel bands spontaneously develop at quasi-periodic intervals in the granular layer, and both rupture fronts propagate by leaps when successively activating slip in these structures. They both transition to a supershear regime after a certain sliding distance.
This model allows for the first time to observe the behaviour and response of the gouge layer as it endures the propagation of a rupture front. Localization patterns and granular complexity render the rupture irregular and heterogeneous, but a moving average in time in the frame of the crack tip allows to recover stress concentrations and slip velocity patterns which are consistent with the Linear Elastic Fracture Mechanics predictions. Il allows to relate gouge frictional response and rupture dynamics without the need to prescribe an arbitrary friction law or to rely on separation of scales.
How to cite: Mollon, G. and Casas, N.: Dynamic rupture of a gouge layer in a meter-sized labquake: a coupled numerical model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12115, https://doi.org/10.5194/egusphere-egu26-12115, 2026.
Sequences of Earthquakes and Aseismic Slip (SEAS) simulations focus on km scale models and consider all phases of faulting from aseismic slip to earthquake nucleation, propagation and termination. Many codes exist that use different approaches to tackle SEAS simulations; however, solutions designed to leverage the potential of GPUs to parallelize and speed up the simulation are limited (although recent examples are emerging such as PyQuake3D). In this work, we propose a GPU parallelized SEAS quasi-dynamic solver written in Julia adopting the Spectral Boundary Integral Method (SBIM). The SBIM approach is optimal for GPUs as it is more memory efficient in respect to other mesh-based solvers, thus enabling to efficiently run high resolution simulations with around 10 million nodes on the fault plane. We rearrange the rate-and-state equations to solve for the slip rate and adopt a slightly modified Newton-Raphson algorithm for root finding. We introduce elastic bulk by using an analytical stress-slip relationship in the Fourier/wavenumber domain. Most of the operations that are carried out in the solver are element wise and thus can be run in parallel on GPUs, significantly cutting down on computation time as the domain resolution increases. While FFT is inherently not fully parallelizable, GPU kernels are available to efficiently perform Fourier transforms on GPUs. Moreover, by using the FFT algorithm, the numerical complexity for calculating the stress is reduced from O(N²) to O(NlogN). To verify the correctness of our solver, we use the BP4-QD benchmark and show comparable results with other outputs hosted by SCEC. We then measure the runtime of the solver on CPU and 2 NVIDIA GPUs, the RTX4060 8GB and the A100 40GB, and show a x5 to x16 speedup for simulations depending on the GPU. Finally, we run the BP4-QD problem on the A100 GPU, decreasing the indicated node spacing and Dc values by an order of magnitude. This simulation yielded 36 events of Mw > 7 and 181 events of Mw between 5 and 6, showing emergence of complexity. Moreover, we observe that the earthquake’s nucleation points are distributed along the edges of the rate-weakening patch. The smaller events are mostly concentrated on the four corners and the two sides parallel to the slipping direction while the bigger events are distributed more uniformly all around the border.
How to cite: Benedetti, G. and Heimisson, E. R.: Accelerating and scaling up SEAS simulations using GPUs in Julia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9901, https://doi.org/10.5194/egusphere-egu26-9901, 2026.
Earthquakes and tsunamis occur on a timescale of seconds and are experienced by humans as sudden devastating disasters. However, the tectonic systems that determine where they occur are shaped over millions of years. Deformation in subduction zones is characterized by visco-elasto-plastic interactions between the accretionary prism featuring splay faults, subducting and overriding plate, asthenosphere, and free surface. To understand the present-day seismicity, earthquake cycle, and splay faulting in particular, these deformation processes need to be considered across all time scales. However, numerical models have not been able to resolve the dynamics across both tectonic and earthquake time scales.
We present a novel numerical modeling technique that simulates fully dynamic earthquake sequences and slow slip events in a subduction zone described by a visco-elasto-plastic rheology. Faults form and evolve spontaneously according to heterogeneous, temperature-dependent material parameters and the local stress field during both the initial 4 million years of subduction and the subsequent seismic phase. We employ an invariant formulation of rate- and state-dependent friction and adaptive time stepping to fully resolve all phases of the seismic cycle.
We generate events covering the slip spectrum from aseismic creep to earthquakes with slip rates in the order of m/s and tens of meters of slip. We find that events are largely characteristic despite the potential for deviating rupture paths in the subduction channel. We find that splay faults need to be sufficiently weak to be activated during a megathrust earthquake, since they cannot accumulate stress over time because velocity-strengthening afterslip relaxes their stresses. Dynamic triggering of a splay fault can lead to an early arrest of the megathrust rupture. Such short-term effects alter the long-term deformation compared to a purely geodynamic model by increasing the importance of one splay fault over others. We also observe that trapped seismic waves significantly change the slip distribution in a similar manner as has been found using a dynamic rupture model.
We conclude that our model successfully combines aspects of established geodynamic models and dynamic rupture models, providing a missing link between the long-term and the short-term. When applying this modeling approach to a complex continental setting, the interaction of multiple faults results in further complexities such as clustering. This highlights the potential and versatility of the method for a wide range of tectonic settings.
How to cite: Koelzer, A., de Vos, M., Gerya, T., and van Dinther, Y.: Bridging the Gap Between Millions of Years and Milliseconds: Modeling Earthquake Sequences, Slow Slip, and Splay Fault Rupture in Subduction Zones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13053, https://doi.org/10.5194/egusphere-egu26-13053, 2026.
Slow slip events (SSEs) are usually observed in elongated transitional zones between the seismogenic and creeping regions of the subduction zones, with the potentials to trigger large subduction earthquakes. Geodetic observations of SSEs in the Cascadia subduction zone (Michel et al., 2019) reveal contrasting complexities of rupture segmentations in the northern and southern segments separated by 44°N, with the northern segment preferring longer ruptures and the southern part preferring shorter ruptures. However, it remains unclear what mechanisms control the observed contrasting rupture segmentations of SSEs. Additionally, understanding the mechanisms behind the rupture complexities of SSEs can provide physical insights into the processes governing characteristic or complex earthquakes. Here, we conduct numerical simulations of SSE cycles along an elongated fault with a finite width W , which is governed by the rate-and-state friction with velocity-strengthening. We find that the rupture complexities of SSEs on a fault – classified as characteristic ruptures, complex ruptures, or creeping – depend on two non-dimensional ratios Lnuc/W and Lc/W, where Lnuc is the critical nucleation length and Lc is the critical cohesive zone length. When Lnuc/W is larger than 0.5, the fault keeps creeping and cannot produce any SSEs, which is consistent with previous theoretical predictions of 0.5 to 1. In addition, we find that runaway characteristic ruptures are enabled if the fault satisfies the energy balance condition between the energy release rate G0 and the fracture energy Gc,, G0 = Gc, derived from the three-dimensional theory of dynamic fracture mechanics that accounts for finite rupture width (Weng and Ampuero, 2022). If G0 < Gc, ruptures prefer to arrest in a short distance and form complex events. This work proposes that a wide spectrum from creeping to characteristic ruptures is controlled by two length ratios in the framework of fracture mechanics, providing new physical insights into the mechanisms of SSEs.
References:
Michel, S., Gualandi, A., & Avouac, J.-P. (2019). Similar scaling laws for earthquakes and Cascadia slow-slip events. Nature, 574(7779), 522–526. https://doi.org/10.1038/s41586-019-1673-6
Weng, H., & Ampuero, J.-P. (2022). Integrated rupture mechanics for slow slip events and earthquakes. Nature Communications, 13(1). https://doi.org/10.1038/s41467-022-34927-w
How to cite: Shi, Y. and Weng, H.: Rupture Complexities of Slow Slip Events Controlled by Fault Friction Mechanics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12196, https://doi.org/10.5194/egusphere-egu26-12196, 2026.
Reservoir-induced seismicity (RIS) is a critical concern in geo-engineering, arising from the coupled interactions among in-situ stress, fluid flow, and fault mechanics, associated with reservoir impoundment. Improving our understanding of earthquake dynamics is therefore essential for elucidating the dynamics of rupture processes at RIS. In particular, understanding fault reactivation and the transition from quasi-static aseismic slip to dynamic rupture is crucial, as the nucleation phase may provide valuable information for detecting pre-seismic signals and estimating earthquake magnitudes.
We develop a novel two-dimensional, fully coupled poro-visco-elasto-dynamic finite-element model (implemented in COMSOL) to simulate RIS under reservoir impoundment in extensional tectonic settings. The porous medium is represented as a Kelvin–Voigt poro-visco-elastic solid to capture elastic deformation and intrinsic damping, while inertial effects are included to resolve rupture dynamics and seismic wave propagation. The fault is modeled as non-penetrating surfaces enforced using an augmented Lagrangian contact formulation and governed by rate-and-state friction, where fault deformations are tolerated by using a virtual thin layer capability.
Model results show that when frictional and hydromechanical conditions permit fault reactivation, slip may become unstable and transition into a coseismic event, with rupture propagating along the fault in asymmetric two–crack-tip–like slip pattern emanating from the hypocenter. Rupture propagation speed is higher in the stiffer rock than in the softer one. Preferential flow induced by the reservoir impoundment forces the rupture nucleation earlier. Porosity and permeability of the fault damage zone decrease with depth (higher than that of the ambient rock at the upper part of the fault), providing the conduit for fluid flow over the fault and promoting longer rupture lengths at RIS.
These findings highlight the critical role of mechanical and hydraulic properties in controlling nucleation and rupture processes in RIS, with important implications for the design and management of reservoir impoundment.
How to cite: Zhou, X. and Katsman, R.: Reservoir Induced Seismicity Modelled Using a Fully Coupled Poro-Visco-Elasto-Dynamic Model with Frictional Contact and Rate-and-State Dependent Friction: Dynamics of Spontaneous Coseismic Rupture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2242, https://doi.org/10.5194/egusphere-egu26-2242, 2026.
Modeling earthquake rupture dynamics often requires stochastic approaches to address the impracticality of obtaining analytical solutions for asymmetric many-body systems. Following Langevin's approach, we propose a stochastic dynamic model for the earthquake rupture process, where complexity in degrees of freedom is reduced by introducing a random force to account for uncertainties in fault plane heterogeneity and structural collisions. In this coarse-grained framework, the random term captures unresolved heterogeneity and interactions at a macroscopic system scale; it does not assert that rupture at the scale of specific fault patches is inherently random. Treating the tectonic process as a Coulomb friction process allows this Langevin equation to be viewed as a stochastic variant of Newton’s second law, attributing physical significance to the sample paths.
However, applying a zero-dimensional (0-D) stochastic framework to complex faulting raises a critical conceptual challenge: can a model lacking explicit spatial dimensions reproduce the highly heterogeneous energy distribution observed in nature? Intuition suggests that the exponential slip distribution derived from a 0-D process may not exhibit tail behavior sufficient to satisfy the standard asperity criterion, where a small fraction of the fault area releases most of the seismic energy. To validate the physical basis of the model, we first examine the spectral properties of the synthetic velocity fluctuations. Results demonstrate that the model output is not arbitrary white noise; rather, the velocity spectra exhibit a Lorentzian form characterized by a single corner frequency. This spectral structure indicates that system memory is governed by a characteristic timescale determined by the load ratio, reflecting a competition between frictional dissipation (which erases memory) and external driving (which sustains motion).
Furthermore, we evaluate the steady-state slip distribution derived from the corresponding Fokker–Planck equation against empirical scaling relations for asperities. Adopting the criterion which defines an asperity as regions where slip exceeds 1.5 times the average, and using squared slip as an upper-bound proxy for energy release under elastic loading, we calculate the theoretical energy concentration. The model predicts that the top ∼22% of the statistical "area" contributes ∼81% of the total energy. This theoretical prediction lies within the 20–30% range observed empirically for asperity area fractions. These findings suggest that the concentration of energy in asperities can emerge from stochastic frictional dynamics, arising from the exponential tail of the slip distribution without explicit modeling of spatial heterogeneity.
How to cite: Wu, T.-H. and Chen, C.-C.: Emergence of asperity-like energy concentration in a stochastic Langevin framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15721, https://doi.org/10.5194/egusphere-egu26-15721, 2026.
The amount of geodetic surface displacement observations from GNSS and InSAR has been growing in recent years yet exploring the model space of corresponding sub-surface deformation remains a complicated and computationally expensive exercise. This is especially the case when there is more than one source and is further complicated when there is a variety in source types, such as combinations of on-fault slip and off-fault mantle flow. While analytical solutions exist for a variety of deformation types within elastic half-spaces (such as fault slip, tensile dislocation, volumetric strain, expansion/contraction) the optimization of source parameters beyond single source models is computationally burdensome due to the need to extensively search with forward passes of the numerical solutions. In most kinematic modelling exercises, the strategy is to assume geometries of sources and solve for magnitude parameters in inversions or to let a Finite Elements simulation evolve from a starting static displacement. Furthermore, there is no effective way to blindly discover the number of sources along with their respective modes of deformation.
Here we demonstrate a solution to these problems that uses surrogate cuboid anelastic deformation sources and sparsity. Cuboid surrogates, that are trained on analytical solutions of anelastic deformation in a half-space, provide a versatile parametrization capable of approximating a wide range of deformation styles - from volumes to faults - by collapsing the thickness towards a near-planar geometry. Once trained, the model can be run in inversion mode so that parameters of the source, such as centroid, length, width, depth, and strain tensor can be optimized by means of a back-propagated loss between the measured surface displacement and surrogate model prediction. Multiple sources can be added trivially, and a sparse solution found with an approximately sparse optimization strategy.
By replacing repeated forward evaluations with a trained surrogate model, the proposed framework enables rapid optimization directly from observed deformation fields without the need for assuming the types of deformations or number of sources. This combination of a flexible cuboid-based source representation and efficient surrogate modelling offers a practical route towards scalable discovery of sub-surface deformation features.
How to cite: Çökerim, K. and Bedford, J.: Versatile Surrogate Inversion of Deformation Sources, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14752, https://doi.org/10.5194/egusphere-egu26-14752, 2026.
This study investigates rupture directivity effects on source spectra of small-magnitude earthquakes in Central Italy, based on a dataset comprising 18,994 waveforms from 656 shallow crustal events recorded between 2008 and 2018. The Generalized Inversion Technique (GIT) is employed to isolate frequency-dependent source characteristics. Apparent Source Spectra (AppSS) exhibit clear azimuthal variations, indicating the presence of directivity effects, particularly in events associated with higher standard deviations. The source spectra are analyzed using multiple empirical models, allowing for the estimation of seismic moment and stress drop for 138 events. Model performance is evaluated through residual analysis across a frequency range of 0.5–25 Hz. Our findings indicate that the ω² source model fitting on the plateau (ωest²) provides a better fit to the observed spectra for the selected events in the dataset. Comparison with previous studies confirms the reliability of the spectral estimates and modeling approach. For the two selected events, spatial maps of ground motion are presented, offering valuable insights into the regional variability of shaking. The study results underscore the importance of incorporating rupture directivity in ground motion models, thereby reinforcing the robustness of empirical predictive approaches and their relevance for improving seismic hazard assessments.
How to cite: Xhafaj, E., Vitrano, L., Pacor, F., Sgobba, S., and Lanzano, G.: Characterizing Earthquake Rupture Directivity Using Apparent Source Spectra: A Case Study from Central Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3583, https://doi.org/10.5194/egusphere-egu26-3583, 2026.
The excitation and propagation of multiple wave types, including seismic waves, ocean acoustic waves, and tsunamis triggered by earthquakes within the oceanic wavefield, constitute a problem of substantial scientific and practical challenge for both fundamental geophysical understanding and hazard assessment. While various numerical approaches have been proposed to model these full-coupled wavefields, the role of realistic seafloor topography in modulating wave propagation remains underexplored.
We present a novel earthquake-tsunami coupled simulation approach based on the spectral-element method (SEM), leveraging its robustness and accuracy in representing arbitrary fluid-solid interface geometries. The approach is quantitatively validated through comparisons of simulated permanent seafloor deformation and sea-surface displacement time series with benchmark finite-difference method (FDM) solutions, yielding an excellent correlation coefficient of 0.998 and negligible errors. Furthermore, we construct two distinct numerical models: one incorporating realistic seafloor topography and another assuming an idealized flat seafloor to investigate the effects of bathymetry on oceanic wavefield. Our analyses reveal that complex bathymetry profoundly alters the propagation of both seismic and tsunami waves, modifying amplitudes, arrival times, and spatial distribution patterns. By systematically separating the contributions of the overlying seawater and the underlying seafloor topography, we clarify their individual influences on the composite oceanic wavefield. We also investigate how variations in earthquake source location affect wave propagation waves, underscoring the necessity of accurate bathymetric representation for offshore events.
This SEM-based earthquake-tsunami coupling framework offers a robust tool for comprehensively understanding the oceanic wavefield under gravity and holds considerable promise for advancing earthquake and tsunami risk evaluation, especially when combined with seismological observational data.
How to cite: Hou, X., Zhang, L., and Xu, Y.: Coupled simulation of earthquake and tsunami by spectral-element method and effects of bathymetry on oceanic wavefield, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15953, https://doi.org/10.5194/egusphere-egu26-15953, 2026.
Understanding the physical mechanisms governing aftershock patterns and their evolution in fault networks is crucial for interpreting seismic catalogues and improving physics-based seismic hazard assessment. Here, we develop a mechanics-based modeling framework based on the discrete fracture network approach to explicitly simulate mainshock rupture, coseismic stress changes, and aftershock generation in complex 3D fault networks. The fault system that we model comprises a primary strike-slip fault surrounded by a network of thousands of secondary faults with sizes following a power-law distribution. Dynamic rupture nucleates within a localized patch on the primary fault and propagates spontaneously at a sub-Rayleigh speed, producing a Mw 7.6 mainshock. The model captures aftershock triggering driven by radiated seismic waves and/or permanent stress redistribution, and quantifies their combined effect using Coulomb failure stress changes. Fault slip is governed by a linear slip-weakening friction law, where the critical slip distance is varied over orders of magnitude to explore its influence on breakdown-zone size, fracture-energy dissipation, and rupture propensity on secondary faults. The simulations capture key emergent characteristics of aftershock sequences: spatially, aftershocks cluster within positive Coulomb stress lobes and are suppressed within stress shadows, with additional localization near fault intersections; statistically, the cumulative frequency–magnitude distributions follow Gutenberg–Richter scaling over a broad magnitude range. Importantly, the synthetic catalogues consistently exhibit a two-branch frequency–magnitude scaling behavior, in which the lower-magnitude branch is dominated by partial ruptures and premature arrest, whereas the higher-magnitude branch corresponds to self-sustained ruptures whose moment magnitudes scale with fault area and are therefore more strongly constrained by fault network geometry. We further show that the transition between these regimes is governed by fault criticality and fracture energy dissipation, providing an alternative mechanics-based explanation for the commonly observed roll-off in frequency–magnitude distribution. Overall, our framework mechanically connects fault network structure and rupture dynamics to explain aftershock statistics, enabling physics-based interpretation of seismic catalogues and supporting improved seismic hazard assessment.
How to cite: Pan, W., Zhang, Z., and Lei, Q.: Mechanics-based simulation of aftershock sequences in complex 3D fault networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15115, https://doi.org/10.5194/egusphere-egu26-15115, 2026.
Earthquake nests are defined as volumes of intense intermediate-depth seismicity which are isolated from any surrounding seismic activity. The high seismic activity within these earthquake nests occurs continuously and thus sets them apart from other seismic sequences such as earthquake swarms or aftershocks. These intermediate-depth earthquakes cannot be explained by the same causes as shallow earthquakes. Instead, they are often linked to slab detachment (e.g. in the Hindu Kush).
To constrain the conditions at which these large intermediate-depth earthquakes occur, numerical models are required to better understand their tectonic environment. Here, we use two-dimensional thermomechanical models with a nonlinear visco-elasto-plastic rheology were to determine the deformation state and the controlling mechanisms of the detachment process.
In this study, we focus on the question how the viscosity ratio (ηlith /ηlc) between the lithosphere and the lower crust and the depth dlc to which lower crust may have been subducted influence the subduction process. Both is poorly constrained for the Hindu Kush. To this end, we varied the viscosity ratio ηlith /ηlc between 0.01 and 1000 and the subduction depth of the lower crust dlc between 160 km and 240 km. We obtained detachment depths ranging from 110 km to 470 km, which fall within the range of the Hindu Kush earthquake nest, extending up to 280 km. The deformation behaviour from the 264 models can be classified into five different regimes based on stress, strain rate, detachment depth, and coupling between subducting and overriding plate. The five regimes represent the dependency of the detachment depth (ddet) to its viscosity ratio (ηlith /ηlc). Detachment in regime two is enhanced via shear heating and detachment in the other regimes occurs via necking. The relationship between lower crustal depth and detachment depth varies by model category. This variability reflects the complex influence of the “lubrication effect” of a weak lower crust and the limitation of subduction depth governed by its rheological properties.
How to cite: Weiler, T., Piccolo, A., Spang, A., and Thielmann, M.: Effects of the lower crust on slab detachment – a case study in the Hindu Kush, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14664, https://doi.org/10.5194/egusphere-egu26-14664, 2026.
Precursory signals preceding large earthquakes are commonly attributed to the acceleration of localized slip during rupture nucleation, yet their spatial expression in the surrounding medium remains poorly constrained. Here, we model the evolution of off-fault strain during earthquake nucleation governed by rate-and-state friction. Our results show that strain accumulates gradually during the early nucleation phase and then accelerates sharply, exceeding a threshold of ε ~ 10-7—comparable to natural strain levels and detectable by modern strainmeters and geodetic instruments—tens to hundreds of days before instability, depending on the uncertainty in the characteristic slip distance Dc and effective normal stress σeff. Approximately 0.7 times the nucleation duration prior to failure, the strained region (ε > 10-7) extends to distances exceeding one nucleation length away from the fault and spans most of its entire length. We further show that σeff controls both the magnitude and spatial distribution of strain, whereas Dc primarily influences the spatial extent of the strained region. Assuming a representative value for the sensitivity of seismic velocity changes to strain (η ≈ 104), the predicted strain amplitudes correspond to ~0.1%-100% changes in seismic velocity, well above the detection limits of ambient-noise monitoring. A comparison between strain footprints and seismic wavelengths further suggests that analysis of short-period noise (T = 0.1 - 1 s) would be most favorable for identifying these precursory signals. Together, these findings directly link nucleation theory to observable field-scale precursors and provide a physics-based framework for precursor identification in natural fault systems.
How to cite: Zhang, L., Ampuero, J.-P., and Romanet, P.: Linking off-fault strain to rate-and-state friction nucleation: Implications for monitoring precursory velocity changes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2376, https://doi.org/10.5194/egusphere-egu26-2376, 2026.
UrgentShake is an urgent computing system developed by OGS (National Institute of Oceanography and Applied Geophysics) for the rapid generation of physics-based ground shaking scenarios. It employs a distributed architecture across High-Performance Computing (HPC) and cloud infrastructures to perform numerical simulations in near real-time, providing reliable estimates of ground motion following significant seismic events in Northeastern Italy, thereby supporting decision-making by emergency management authorities.
Although primarily designed for rapid response to earthquakes, UrgentShake’s flexible architecture also makes it suitable for non-real-time applications, such as Civil Protection exercises and risk analyses. In these contexts, a single realization of a specific seismic source is not sufficient; instead, a suite of plausible scenarios is needed to define median, minimum and maximum estimates of ground shaking and potential impacts.
To address this need, a feasibility study was conducted to demonstrate the potential integration of UrgentShake with CyberShake, a physics-based platform for seismic hazard modeling that simulates many rupture scenarios. CyberShake simulations for a representative earthquake scenario were performed using the Graves and Pitarka stochastic rupture generator and the Anelastic Wave Propagation code on HPC resources at the Barcelona Supercomputing Centre. By generating multiple independent source realizations with varying nucleation points, fault geometries and rupture characteristics, this proof of concept illustrates how source-related uncertainties can be incorporated into UrgentShake to produce robust ground shaking scenarios. These scenarios can support Civil Protection training and preparedness activities while enabling physics-based damage assessments to inform risk analyses.
How to cite: Zuccolo, E., Zamora, N., and Scaini, C.: UrgentShake for Scenario-Based Ground Motion Simulations: Integrating Multiple Source Realizations with CyberShake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4273, https://doi.org/10.5194/egusphere-egu26-4273, 2026.
The Eastern Adriatic region has been historically affected by strong destructive earthquakes, including the M6.4 1667 Dubrovnik earthquake, the M6.6 1905 Shkodra event, and the M6.4 2019 Durrës earthquake. Some of those destructive events are associated with the Scutari-Pec Fault System (Albania). This tectonic structure extends sub-parallel to the coastline, in the SW-NE direction, through the Dinaride-Hellenide transition. This fault system corresponds to a compressive and transform fault system near the Adriatic Sea that changes the tectonics to an extensional regime towards the East. The distribution of focal mechanisms of microseismicity recorded in the region (Serpelloni et al, 2007) evidences the complex tectonics (Grund et al., 2023).
As part of the German SPP project DEFORM, we plan to simulate 3D dynamic earthquake scenarios to study the rupture propagation of large earthquakes across the Scutari-Pec Fault System. We apply the open-source SeisSol code to generate synthetic seismograms up to frequencies of 2 Hz. We will specifically investigate the effect of variability of locking depth as a crucial parameter for determining the earthquake potential of the fault system. Ground motion for dynamic rupture scenarios with characteristics similar to the destructive reported events will be estimated, in particular for the most populated cities located within 50 km of the central fault system. This presentation is a first step toward these goals and aims to provide relevant information for such simulations, which may complement seismic hazard assessment in the region.
How to cite: Abril, C. and Gabriel, A.: Towards physic-based ground-motion simulations for the Scutari-Pec Fault System, Eastern Adria, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18857, https://doi.org/10.5194/egusphere-egu26-18857, 2026.
Physics-based approaches are increasingly recognized as essential for improving seismic hazard assessment, however, no fully physics-based probabilistic seismic hazard analysis (PSHA) exists for the Italian territory. This gap is particularly relevant in the Po Plain area in northern italy, where deep sedimentary deposits strongly amplify seismic waves and prolong shaking, even for moderate-magnitude events. In this context, broadband ground-motion simulations represent a key requirement for capturing both long-period basin effects and high-frequency scattering. In this study, we generate synthetic seismograms spanning the engineering-relevant 0.1–10 Hz bandwidth using a hybrid approach that combines deterministic low-frequency (<1 Hz) simulations with stochastically generated high-frequency (1–10 Hz) ground motion. The low-frequency component (<1 Hz) is computed using the SPECFEM3D Cartesian code, which implements the spectral element method to solve the full seismic wave equation in complex 3D media. A central goal of this work is the validation of the 3D MAMBo velocity model (Molinari et al., 2015). We test the model using several earthquakes and compare its performance against alternative candidate 1D and 3D velocity models, highlighting the critical role of a detailed 3D representation of basin geometry and major velocity discontinuities. The synthetic seismograms are quantitatively evaluated using time–frequency misfit and goodness-of-fit metrics. Our results show that the 3D characterization significantly improves the agreement with observed waveform shapes and durations, and they provide a foundation for future refinement of the regional velocity model. The resulting broadband synthetics are suitable for seismic-hazard analysis and engineering applications in the densely populated and economically important Po Plain. Overall, this study outlines a pathway toward fully physics-based probabilistic seismic hazard analysis (PSHA) in northern Italy, grounded on validated 3D structure and physics-based broadband ground-motion simulations.
How to cite: Saturnino, C., De Siena, L., and Molinari, I.: Toward physics-based PSHA study in northern Italy: 3D velocity model validation and broadband seismic signals synthesis., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2980, https://doi.org/10.5194/egusphere-egu26-2980, 2026.
The 2016 Mw7.8 Kaikoura earthquake presents one of most challenging natural events to model dynamically, with up to 21 faults involved in the full rupture, according to geological measurements of surface rupture ( e.g. Litchfield et al. 2018). However, most studies using static displacement observations do not resolve individual fault activation and their temporal connectivity at some parts of the fault range (e.g. Hamling et al. 2017), as suggested by the near-source strong motion data (REF). A more recent complete aftershock catalog provides improved seismological constraints on the rupture kinematics, offering new insights into the fault geometry and faulting mechanisms (Chamberlain et al. 2021). These advances motivate a re‑examination of the mysterious multi-fault rupture with complete seismological observation and physics-based dynamic rupture modeling for to better understand the governing mechanisms of multi-fault ruptures.
Compared to kinematic source inversions, dynamic modeling is a powerful numerical tool to compute realistic cases of earthquake occurrence due to complex ruptures. Yet, for earthquakes involving multiple interacting faults, even state-of-the-art dynamic models can lead to fundamentally different physical interpretations. On one hand, the corresponding dynamic modeling setup heavily depends on prior knowledge of the full system geometry, as well as on the stress-state and velocity model of the medium. On the other hand, due to the nonlinear nature of the problem, several models can produce similar results. Results show that for relatively simple ruptures, involving one or two fault planes, the solution is stable. However, when the rupture involves several faults, even minor changes to the dynamic setup result in instability and non-uniqueness of the solution.
To gain insight into how such extreme fault complexity controls rupture evolution, we perform the dynamic modeling of the 2016 Mw7.8 Kaikoura earthquake using the open-access SeisSol package. We use the New Zealand 3D velocity model and compare two different geometries. The first geometry uses the NZ Community Fault Model, while the second is based on a previously published rupture model (Ando & Kaneko 2018). For the first geometry, we analyze whether the rupture actually used secondary faults to continue its path, or if subsequent rupture was triggered by the generated wavefield. For the second geometry, we investigate the impact of rupture bifurcation onto two faults and assess whether this process generates identifiable seismic phases in the wavefield.
We analyze both dynamic scenarios using near-field and regional strong-motion records, which are expected to capture hidden features of the rupture. We further compare the simulated rupture evolution with previously published high-resolution earthquake catalogs to identify rupture patterns and evaluate potential changes in the stress field before and after the event. Our results highlight both the strengths and inherent ambiguities of dynamic rupture modeling for complex multi-fault earthquakes and provide new constraints on the physical processes governing the Kaikoura rupture.
How to cite: Caballero-Leyva, E., Li, D., Ando, R., and Benites, R.: Impact of Fault Geometry in dynamic modeling simulations: The case of the 2016 Mw7.8 Kaikoura., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3216, https://doi.org/10.5194/egusphere-egu26-3216, 2026.
Earthquake rupture propagation speed is an essential source factor that largely controls hazard and risk. However, measuring rupture speeds of natural earthquakes is often challenging and ambiguous. Near-fault seismic waveforms (recorded within several km) are believed to have high capability for resolving rupture process. In this study, we probe the feasibility of using near-fault data signatures to directly infer rupture speeds in continental strike-slip earthquakes.
To thoroughly understand near-fault features, we synthesize the near-fault seismic waves for kinematic source models on a strike-slip fault under different rupture speeds in a 3D medium. We identify the dependence of velocity waveform and particle motion on rupture speed in both amplitude and shape. In addition, we compare our results with the analytical solution with steady-state constant rupture speed. The discrepancies between the kinematic model and the analytical model indicate the contribution of radiation from different configurations. With inspecting the near-fault dataset of eight M>7 strike-slip earthquakes, we find that instead of dealing with the velocity waveforms with multiple high-frequency spikes, the features of the particle motion shape are easier to identify. Then we apply the particle-motion-based criterion to identify signatures associated with supershear, subshear, and other complexities such as multiple rupture fronts and initial-stage rupture phase. Our study highlights the further application of near-fault seismic data in studying earthquake sources.
How to cite: Yao, S., Yang, H., Bhat, H., and Aochi, H.: Rupture Speed Signatures of Near-fault Particle Motion in Large Strike-slip Earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7716, https://doi.org/10.5194/egusphere-egu26-7716, 2026.
Geological observations show that fault surfaces are complex at both large scales (fault segmentation) and small scales (surface roughness). These geometric complexities strongly influence earthquake rupture behaviour, including slip, rupture speed, rise time, and peak slip velocity. Understanding how these rupture parameters are related to each other is essential for improving understanding of earthquake rupture physics and for developing synthetic rupture models that reproduce realistic dynamic behaviour within kinematic frameworks. Although earlier studies have examined these correlations, the effect of small-scale fault roughness is still not well understood. Therefore, this study focuses on understanding how fault roughness affects correlations among rupture parameters.
To address this problem, we use the dynamic rupture dataset of Mai et al. (2018), which includes twenty-one rupture models with different roughness realizations, roughness amplitudes, and hypocentre locations. Because dynamic slip-velocity functions have complex shapes, we simplify them by fitting the regularized Yoffe function proposed by Tinti et al. (2005). From these fits, we extract key kinematic parameters. We then examine correlations among eight parameters: slip, peak slip velocity, acceleration time, rise time, rupture speed, strike, dip, and rake.
Our results show that slip is positively correlated with rise time, but it does not show clear correlations with other rupture or geometry parameters. Peak slip velocity is negatively correlated with both acceleration time and rise time, and positively correlated with rupture speed. Importantly, as fault roughness increases, the correlation between peak slip velocity and rupture speed becomes weaker. Acceleration time is also negatively correlated with rupture speed, and this correlation also decreases with increasing fault roughness. In contrast, the geometry parameters strike and dip do not show significant correlations with any rupture parameters. Overall, fault roughness mainly affects the relationships between only two pairs of rupture parameters, whereas the correlations among other parameter pairs are not strongly affected.
Our findings provide important constraints for developing synthetic rupture models that can generate realistic high-frequency seismic radiation consistently with radiation of dynamic ruptures propagating on rough faults.
How to cite: Vyas, P. K. and Galis, M.: Influence of Fault Roughness on Earthquake Rupture Parameters Correlations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9624, https://doi.org/10.5194/egusphere-egu26-9624, 2026.
This study investigates the influence of surface-water-level fluctuations on seismicity in the upper crust, using the historic Dead Sea as a natural laboratory. We apply a validated 2D poro-elasto-plastic coupling model in COMSOL Multiphysics. The model integrates coupled hydro-mechanical processes, including pore-pressure evolution, plastic strain localization, and permeability changes, to capture the interaction between surface loading and fault stability. Given reported challenges in capturing hydro-mechanical coupling and scaling behaviour in natural systems using the rate-and-state friction (RSF) formulation, this study adopts an alternative modelling framework that does not explicitly incorporate RSF. The study focuses on applying the model to reconstruct earthquake occurrence patterns associated with Dead Sea water-level variations over the past two millennia. Results demonstrate a strong correlation between relatively rapid water-level changes and increased seismic activity, highlighting the critical role of hydrological forcing in earthquake triggering. These findings provide new insights into reservoir-induced seismicity and underscore the importance of incorporating surface water dynamics into seismic hazard assessment.
How to cite: Belferman, M. and Agnon, A.: Hydro-Mechanical numerical Modeling of Water-Level-Induced Seismicity: Insights from Historic Dead Sea Fluctuations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22999, https://doi.org/10.5194/egusphere-egu26-22999, 2026.
Aseismic creep is widely recognized to influence earthquake rupture, but whether its role remains stationary in different earthquakes is poorly understood. In this study, we integrate GNSS/InSAR observations along the Xianshuihe fault in eastern Tibet and identify six aseismic creeping sections, which have been partially or fully involved in historical earthquakes. The creep exhibits spatiotemporal transient behavior. Using interseismic fault locking as a constraint, we performed 3D dynamic rupture simulations of the Xianshuihe fault. We demonstrate that aseismic creep exerts a dual role in earthquake rupture. On the stabilizing side, creeping sections terminate rupture propagation, with earthquakes that nucleate and are absorbed within the creeping zones further reinforcing their function as stable rupture barriers. Conversely, under favorable local stress conditions and modulated by transient aseismic slip migration and hypocenter location, creeping sections could promote rupture propagation, rendering their impact on rupture non-stationary in different earthquakes. These findings provide a plausible explanation for the pronounced variability of rupture segmentation and cascading on the geometrically simple Xianshuihe fault, and highlight the importance of incorporating both stabilizing and destabilizing effects of aseismic creep into seismic hazard assessments.
How to cite: Li, Y. and Shan, X.: Uncovering the stabilizing and destabilizing roles of aseismic creep in earthquake rupture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4671, https://doi.org/10.5194/egusphere-egu26-4671, 2026.
The Tianzhu seismic gap is an important segment of the Haiyuan fault system. In recent decades, earthquakes have occurred on most fault segments within this region, whereas the Jinqianghe–Maomaoshan fault has not experienced a major earthquake for an extended period. Given that this fault segment is widely regarded as having elevated potential seismic hazard, we conduct three-dimensional dynamic rupture and strong ground motion simulations using the curved grid finite difference method.To effectively constrain model input parameters, interseismic locking coefficients and slip deficit distributions inverted from InSAR and GPS observations are used to impose physically based constraints on the heterogeneous initial stress conditions along the fault. Simulation results indicate that the spatial distribution of locked regions plays a critical role in controlling rupture extent. Under locking-constrained conditions, scenario earthquakes with moment magnitudes of Mw 7.3–7.4 and maximum slip of approximately 5.5 m are generated. Further analyses show that larger accumulated slip deficits tend to promote higher earthquake magnitudes, whereas the surface seismic intensity does not exhibit a monotonic response to slip deficit.These results suggest that the Jinqianghe–Maomaoshan fault segment may be associated with elevated potential seismic hazard.
How to cite: Ren, B., Wang, W., and Qiu, H.: Dynamic Rupture and Ground Motion Simulations of Potential Earthquake on the Tianzhu Seismic Gap, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10413, https://doi.org/10.5194/egusphere-egu26-10413, 2026.
Seismic simulations are essential for ground motion characterization and seismic hazard mitigation. However, achieving accurate seismic modelling requires highly refined computational grids, which impose severe memory and computational challenges. Traditional seismic solvers based on single-precision floating-point 32-bit (FP32) arithmetic, suffer from excessive memory consumption, low-memory access efficiency and limited computational efficiency. In contrast, half-precision floating-point 16-bit (FP16) halves memory usage and effectively doubles memory access efficiency, making it attractive for large-scale seismic simulations. However, direct application of FP16 to classical elastic wave equations is challenging due to overflow and underflow caused by the wide dynamic range of physical variables. In this work, we reformulate the elastic wave equations by introducing three dimensionless scaling constants, Cv, Cs, and Cp, and derive an FP16-based elastic wave equation. Furthermore, we provided a practical strategy for determining these constants based on the source time function, ensuring that velocity and stress variables remain within the representable range of FP16. To maintain FP32-level accuracy, a mixed-precision strategy using “FP16 storage and FP32 arithmetic” is adopted. From a computational perspective, we further exploit the Scalable Vector Extension (SVE) on ARM architectures to accelerate stencil-based computations. However, effectively combining FP16 with SVE introduces additional challenges, including stencil restructuring for vectorization and data layout mismatches arising from “FP16 storage and FP32 arithmetic”. To overcome these challenges, this study develops three complementary seismic solvers on the ARM architecture: an FP16-based solver, an SVE-accelerated solver, and an FP16–SVE hybrid solver that integrates memory efficiency with vectorized computation. All three solvers are implemented, systematically validated, and benchmarked using both synthetic test cases and real earthquake simulations. Numerical results demonstrate near-identical agreement with a reference FP32 solver across diverse seismic scenarios. In particular, the FP16–SVE hybrid solver reduces memory consumption by approximately 50% and achieves up to a threefold speedup, delivering more than a 2.3× acceleration in real-world earthquake simulations. These results highlight the strong potential of the proposed FP16–SVE approach for enabling large-scale, high-efficiency, and near-real-time seismic simulations and earthquake hazard assessment on ARM-based platforms.
How to cite: Wang, W., Ren, B., Zheng, J., and Zhang, Z.: A High-Efficiency and Low-Storage Algorithm for Seismic Simulation Using Half Precision and Scalable Vector Extension on ARM Platforms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11804, https://doi.org/10.5194/egusphere-egu26-11804, 2026.
The Statewide California Earthquake Center (SCEC) sequence of earthquake and aseismic slip (SEAS) group has regularly developed and published benchmarks along the years to follow recent development in the modeling of sequences of aseismic slip and earthquakes, as well as progress in numerical methods. These benchmarks, as well as the results from the different groups are publicly available at: https://strike.scec.org/cvws/seas/. It provides both reference solutions for code verification and a framework for systematic comparison of different modeling approaches. Every group is welcomed to join this Community driven comparison.
Recent efforts have focused on adding physics to better reproduce earthquake cycle by considering 2-dimensional fault (Jiang et al., 2022), improve our understanding of fluid injection processes (Lambert et al., 2025), and the effect of free surface and dipping fault (Erickson et al., 2023).
To follow up these developments, the SCEC SEAS group is designing two new benchmarks, that will be released to the community soon:
[1] A generalization of our benchmark about fluid injection (BP6) from a 2-dimensional domain to 3-dimensional domain. In this benchmark pore fluid diffuses along a 2-dimensional fault, modifying the effective normal traction through one-way hydromechanical coupling. The fluid is injected for 10 hours on a rate strengthening faut and then shut off. The benchmark is designed to admit an analytical formulation for pore fluid diffusion while avoiding numerical singularities that may occurred with point source injection. For this reason, fluid is injected along a Gaussian profile.
[2] An updated version of our previous dipping fault benchmark (BP3), in a two-dimensional medium with a free surface. Previous version assumed that the normal traction along the fault was constant. This is obviously a strong assumption, because the normal traction should increase with depth. However, this has proven to be difficult to simulate numerically as the system is going stiffer with lower normal traction. This benchmark therefore aims at providing a more realistic simulation of a dipping fault with a free surface by introducing depth dependent normal traction while also testing the ability of different numerical code to circumvent the problem of stiffness. This benchmark will be a joint benchmark with CRESCENT (Cascadia Region Earthquake Science Center).
This contribution will present the design of these forthcoming benchmarks and will provide an opportunity for the community to discuss about future benchmarks and directions for SEAS code comparison efforts.
How to cite: Romanet, P., Dunham, E., Erickson, B., Kim, T., Lambert, V., and Thakur, P.: The future Community-Driven SCEC SEAS Code Comparisons for [1] Three-Dimensional fluid injection and [2] a Two-Dimensional dipping fault with variable normal traction., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12099, https://doi.org/10.5194/egusphere-egu26-12099, 2026.
The main objective of this study is to identify clusters of seismic records with similar Fourier Amplitude Spectrum (FAS) shapes that can be associated with different tectonic domains, path attenuation properties, and site effects in Southern Italy. The analyzed dataset consists of FAS of S-wave windows, computed in the 0.5–25 Hz frequency range from accelerometric and velocimetric records available from EIDA and ITACA for 1349 events and 502 stations, with focal depths up to about 40 km.
We analyzed residuals between empirical FAS-based ground-motion models (GMMs), using ITA18 as reference, and observed spectral amplitudes through a mixed-effects regression framework. This allows us to decompose the total residuals into systematic contributions due to source (between-events term, δBe), path (systematic differences in attenuation, δWes), and site (site-to-site term, δS2S) effects, which are then grouped into clusters.
For the source terms δBe, four clusters are identified. Two of them are particularly interesting: one shows systematic amplification with increasing frequency, while the other shows systematic deamplification at high frequencies. The spatial distribution of the corresponding events highlights the Gargano and southeastern Sicily as regions characterized by amplified spectral amplitudes, whereas northeastern Sicily and the Aeolian area exhibit deamplified amplitudes. Additional insights are obtained by examining the dependence of these clusters on magnitude and focal depth; this analysis reveals that one of the source-related clusters is composed exclusively of shallow events (depth ≤ 10 km), which display distinctive spectral behaviors in specific crustal and volcanic domains.
For the path residuals δWes, four clusters are also recognized, revealing systematic differences in wave propagation across distinct crustal structures. The systematic site terms δS2S are grouped into three clusters: one identifies stations largely unaffected by significant soil amplification, while the other two show, respectively, systematic amplification and deamplification across the whole frequency band, with the clearest separation at intermediate frequencies (about 3–8 Hz).
These results provide a regional framework for ground-motion characterization in Southern Italy, supporting the identification of reference stations and of areas with distinct source and attenuation properties. This work is preparatory to future large-scale and local-scale Generalized Inversion Technique (GIT) studies aimed at the characterization of ground motion for shallow-crustal events and at the definition of key input parameters for earthquake simulations. In particular, the source-related clusters associated with volcanic areas reveal spectral features that deviate from classical ω² source models, pointing to processes likely controlled by complex fluid–rock interactions.
How to cite: Morasca, P., D'Amico, M. C., and Spallarossa, D.: Cluster Analysis of Fourier Amplitude Spectra Residuals for Ground Motion Characterization in Southern Italy., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12340, https://doi.org/10.5194/egusphere-egu26-12340, 2026.
Rotational ground motions have recently emerged as an important and independent observable in seismology, driven by advances in rotational seismometers and the growing availability of high-quality rotational datasets. These observations provide new insights towards understanding near-source and near-surface wave propagation beyond traditional translational measurement. To model rotational components, several analytical approaches have been proposed in the recent past. However, these formulations are typically restricted to idealized source representations and simplified Earth models, limiting their applicability to realistic geological settings accounting for three-dimensional complexities.
Finite-element modeling techniques provide a powerful alternative by enabling the simulation of seismic wavefields in complex media by incorporating heterogeneous velocity structures, layered stratigraphy, surface topography, and finite-fault earthquake sources. Despite this capability, commonly used ground motion simulation codes have not yet been adapted to compute rotational ground motions. In this study, we extend the spectral finite-element code SPECFEM3D to internally compute and output rotational ground motions alongside conventional translational components. The numerical implementation is validated against analytical solutions for two benchmark cases: (i) a homogeneous half-space and (ii) a three-layered velocity model, demonstrating excellent agreement in both amplitude and waveform characteristics. Following validation, the modified code is used to simulate rotational ground motions for a range of realistic scenarios, including layered representations of the subsurface and finite-fault source models. These simulations are used to investigate the generation and propagation characteristics of rotational motions and to examine their spatiotemporal relationship with translational ground motions. Differences in amplitude and propagation behavior between rotational and translational components are particularly analyzed in the present work.
Finally, we assess the potential implications of rotational ground motions for earthquake engineering by evaluating their relative amplitudes and propagation patterns under different source and structural conditions. The results provide a framework for identifying the source characteristics and conditions under which rotational components of ground motion may become significant and potentially influence structural response. These findings contribute to an improved understanding of whether, and under what circumstances, rotational ground motions should be considered in seismic analysis and earthquake-resistant design practice.
Keywords: Rotational ground motions, Seismic wave propagation, Numerical modeling, Earthquake engineering
How to cite: Dhabu, A. C., Hejazi Nooghabi, A., and Hadziioannou, C.: Propagation Characteristics of Rotational Ground Motions in Layered Earth Media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17597, https://doi.org/10.5194/egusphere-egu26-17597, 2026.
Earthquake cycle modeling has enabled to reproduce the full spectrum of slip rates observed along fault segments, and refine our understanding of seismic cycle dynamics. However, key parameters controlling the occurrence of shallow slow slip events (SSE) such as those observed along strike-slip fault segments remain unclear, due to rare worldwide observations and the lack of long-lasting observations covering all phases of the seismic cycle. Here, we apply rate and state friction quasi-dynamic 1D models to explain the ensemble of observations along the Izmit segment of the North Anatolian Fault in Türkiye. This fault segment ruptured in 1999 with the magnitude 7.6 Izmit earthquake, and has been since then widely studied, providing constraints on most of the phases of the seismic cycle, from mainshock amplitude and recurrence times to afterslip logarithmic decay, and the occurrence of shallow SSEs. GNSS, InSAR and creepmeters geodetic data associated with seismological and paleoseismological data enable to describe the cumulative displacement during all phases of the seismic cycle. The comparison between model predictions and the observational time scales led to an optimal set of frictional models. First, the mainshocks maximum slip of ~6 m and return times of about ≥200 yrs are explained by an unstable seismogenic layer below 5.5 km depth with a thickness of 9.5 km and with frictional parameters a-b of about -0.004. The decadal afterslip, well constrained by a pair of campaign GNSS stations located on both sides of the fault, is mostly due to a stable layer located between 5.5 and 1.3 km depth, the lower limit being compatible with the aftershocks sequence limit. We compared model slip predictions and GNSS time series by computing Green's functions for a layered elastic half space medium. Model parameters for this intermediate layer explaining the observed relaxation time have frictional parameters a-b and critical distance of about 0.005 and 8 km, respectively. Finally, a shallow layer from the surface to 1.3 km depth with either a gradient of frictional parameters with depth or constant negative frictional parameters is needed to generate shallow SSEs 20 yrs after the main earthquakes. The shallow layer depth extent being compatible with the Izmit Quaternary sedimentary basin may suggest a key role of the sediments frictional properties to allow a velocity weakening behavior. Models with a gradient of apparent frictional properties throughout the basin may suggest the importance of pore-pressure variations as a function of the fault gouge depth.
How to cite: Doubre, C., Estelle, N., Baptiste, R., Matt, W., and Yoshihiro, K.: Postseismic and shallow slow slip events on the Izmit segment of the North Anatolian Fault controlled by depth-dependent frictional variations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10178, https://doi.org/10.5194/egusphere-egu26-10178, 2026.
