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ABSTRACT Fault zones exhibit geometrical complexity and are often surrounded by multiscale fracture networks within their damage zones, potentially influencing rupture dynamics and near-field ground motions. In this study, we investigate the ground-motion characteristics of cascading ruptures across damage zone fracture networks of moderate-size earthquakes (Mw 5.5–6.0) using high-resolution 3D dynamic rupture simulations. Our models feature a listric normal fault surrounded by more than 800 fractures, emulating a major fault and its associated damage zone. We analyze three cases: a cascading rupture propagating within the fracture network (Mw 5.5), a non-cascading main-fault rupture with off-fault fracture slip (Mw 6.0), and a main-fault rupture without a fracture network (Mw 6.0). Cascading ruptures within the fracture network produce distinct ground-motion signatures with enriched high-frequency content, arising from simultaneous slip of multiple fractures and parts of the main fault, resembling source coda-wave-like signatures. This case shows elevated near-field characteristic frequency (fc) and stress drop, approximately an order of magnitude higher than the estimation directly on the fault of the dynamic rupture simulation. The inferred fc of the modeled vertical ground-motion components reflects the complexity of the radiation pattern and rupture directivity of fracture-network cascading earthquakes. We show that this is consistent with observations of strong azimuthal dependence of corner frequency in the 2009–2016 central Apennines, Italy, earthquake, sequence. Simulated ground motions from fracture-network cascading ruptures also show pronounced azimuthal variations in peak ground acceleration (PGA), peak ground velocity, and pseudospectral acceleration, with average PGA nearly double that of the non-cascading cases. Cascading ruptures radiate high-frequency seismic energy, yield nontypical ground-motion characteristics including coda-wave-like signatures, and may result in a significantly higher seismologically inferred stress drop and PGA. Such outcomes emphasize the critical role of fault-zone complexity in affecting rupture dynamics and seismic radiation and have important implications for physics-based seismic hazard assessment. 

The Mediterranean Hellenic Arc subduction zone (HASZ) has generatedseveral Mw>=8 earthquakes and tsunamis.Seismic-probabilistic tsunami hazard assessment typically utilizesuniform or stochastic earthquake models, which may not represent dynamicrupture and tsunami generation complexity. We present an ensemble of ten3D dynamic rupture earthquake scenarios for the HASZ, utilizing arealistic slab geometry. Our simplest models use uniform along-arcpre-stresses or a single circular initial stress asperity. We thenintroduce progressively more complex models varying initial shear stressalong-arc, multiple asperities based on scale-dependent critical slipweakening distance, and a most complex model blending all aforementionedheterogeneities. Thereby, regional initial conditions are constrainedwithout relying on detailed geodetic locking models. Varying hypocenterlocations in the simplest, homogeneous model leads to different rupturespeeds and moment magnitudes. We observe dynamic fault slip penetratingthe shallow slip-strengthening region and affecting seafloor uplift.Off-fault plastic deformation can double vertical seafloor uplift. Asingle-asperity model generates a Mw~8 scenarioresembling the 1303 Crete earthquake. Using along-strike varying initialstresses results in Mw~8.0-8.5 dynamic rupture scenarioswith diverse slip rates and uplift patterns. The model with the mostheterogeneous initial conditions yields a Mw~7.5scenario. Dynamic rupture complexity in prestress and fracture energytends to lower earthquake magnitude but enhances tsunamigenicdisplacements. Our results offer insights into the dynamics of potentiallarge Hellenic Arc megathrust earthquakes and may inform futurephysics-based joint seismic and tsunami hazard assessments. 

Abstract The nonlinear mechanical responses of rocks and soils to seismic waves play an important role in earthquake physics, influencing ground motion from source to site. Continuous geophysical monitoring, such as ambient noise interferometry, has revealed co‐seismic wave speed reductions extending tens of kilometers from earthquake sources. However, the mechanisms governing these changes remain challenging to model, especially at regional scales. Using a nonlinear damage model constrained by laboratory experiments, we develop and apply an open‐source 3D discontinuous Galerkin method to simulate regional co‐seismic wave speed changes during the 2015 M_w7.8 Gorkha earthquake. We find pronounced spatial variations of co‐seismic wave speed reduction, ranging from <0.01% to >50%, particularly close to the source and within the Kathmandu Basin, while disagreement with observations remains. The most significant reduction occurs within the sedimentary basin and varies with basin depths, whereas wave speed reductions correlate with the fault slip distribution near the source. By comparing ground motions from simulations with elastic, viscoelastic, elastoplastic, and nonlinear damage rheologies, we demonstrate that the nonlinear damage model effectively captures low‐frequency ground motion amplification due to strain‐dependent wave speed reductions in soft sediments. We verify the accuracy of our approach through comparisons with analytical solutions and assess its scalability on high‐performance computing systems. The model shows near‐linear strong and weak scaling up to 2,048 nodes, enabling efficient large‐scale simulations. Our findings provide a physics‐based framework to quantify nonlinear earthquake effects and emphasize the importance of damage‐induced wave speed variations for seismic hazard assessment and ground motion predictions. 

Abstract. Tsunamigenic earthquakes pose considerable risks, both economically and socially, yet earthquake and tsunami hazard assessments are typically conducted separately. Earthquakes associated with unexpected tsunamis, such as the 2018 Mw  7.5 strike-slip Sulawesi earthquake, emphasize the need to study the tsunami potential of active submarine faults in different tectonic settings. Here, we investigate physics-based scenarios combining simulations of 3D earthquake dynamic rupture and seismic wave propagation with tsunami generation and propagation. We present time-dependent modeling of one-way linked and 3D fully coupled earthquakes and tsunamis for the ∼ 100 km long Húsavík–Flatey Fault Zone (HFFZ) in North Iceland. Our analysis shows that the HFFZ has the potential to generate sizable tsunamis. The six dynamic rupture models sourcing our tsunami scenarios vary regarding hypocenter location, spatiotemporal evolution, fault slip, and fault structure complexity but coincide with historical earthquake magnitudes. Earthquake dynamic rupture scenarios on a less segmented fault system, particularly with a hypocenter location in the eastern part of the fault system, have a larger potential for local tsunami generation. Here, dynamically evolving large shallow fault slip (∼ 8 m), near-surface rake rotation (± 20∘), and significant coseismic vertical displacements of the local bathymetry (± 1 m) facilitate strike-slip faulting tsunami generation. We model tsunami crest to trough differences (total wave heights) of up to ∼ 0.9 m near the town Ólafsfjörður. In contrast, none of our scenarios endanger the town of Akureyri, which is shielded by multiple reflections within the narrow Eyjafjörður bay and by Hrísey island. We compare the modeled one-way linked tsunami waveforms with simulation results using a 3D fully coupled approach. We find good agreement in the tsunami arrival times and location of maximum tsunami heights. While seismic waves result in transient motions of the sea surface and affect the ocean response, they do not appear to contribute to tsunami generation. However, complex source effects arise in the fully coupled simulations, such as tsunami dispersion effects and the complex superposition of seismic and acoustic waves within the shallow continental shelf of North Iceland. We find that the vertical velocity amplitudes of near-source acoustic waves are unexpectedly high – larger than those corresponding to the actual tsunami – which may serve as a rapid indicator of surface dynamic rupture. Our results have important implications for understanding the tsunamigenic potential of strike-slip fault systems worldwide and the coseismic acoustic wave excitation during tsunami generation and may help to inform future tsunami early warning systems. 

Abstract The 2023 Turkey earthquake sequence involved unexpected ruptures across numerous fault segments. We present 3D dynamic rupture simulations to illuminate the complex dynamics of the earthquake doublet. Our models are constrained by observations available within days of the sequence and deliver timely, mechanically consistent explanations of the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, heterogeneous fault offsets, locally strong shaking, and fault system interactions. Our simulations link both earthquakes, matching geodetic and seismic observations and reconciling regional seismotectonics, rupture dynamics, and ground motions of a fault system represented by 10 curved dipping segments and embedded in a heterogeneous stress field. The Mw 7.8 earthquake features delayed backward branching from a steeply branching splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral Mw 7.7 earthquake are explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous earthquake. Our models explain the northward deviation of its eastern rupture and the minimal slip observed on the Sürgü fault. 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multifault systems. 

Physics-based dynamic rupture simulations are valuable for assessing the seismic hazard in the Cascadia subduction zone (CSZ), but require assumptions about fault stress and material properties. Geodetic slip deficit models (SDMs) may provide information about the initial stresses governing megathrust earthquake dynamics. We present a unified workflow linking SDMs to 3D dynamic rupture simulations, and 22 rupture scenarios to unravel the dynamic trade-offs of assumptions for SDMs, rigidity, and pore fluid pressure. We find that margin-wide rupture, an earthquake that ruptures the entire length of the plate boundary, requires a large slip deficit in the central CSZ. Comparisons between Gaussian and smoother, shallow-coupled SDMs show significant differences in stress distributions and rupture dynamics. Variations in depth-dependent rigidity cause competing effects, particularly in the near-trench region. Higher overall rigidity can increase fault slip but also result in lower initial shear stresses, inhibiting slip. The state of pore fluid pressure is crucial in balancing SDM-informed initial shear stresses with realistic dynamic rupture processes, especially assuming small recurrence time scaling factors. This study highlights the importance of self-consistent assumptions for rigidity and initial stresses between geodetic, structural, and dynamic rupture models, providing a foundation for future simulations of ground motions and tsunami generation. 

ABSTRACT Frictional heating during earthquake rupture raises the fault-zone fluid pressure, which affects dynamic rupture and seismic radiation. Here, we investigate two key parameters governing thermal pressurization of pore fluids – hydraulic diffusivity and shear-zone half-width – and their effects on earthquake rupture dynamics, kinematic source properties, and ground motions. We conduct 3D strike-slip dynamic rupture simulations assuming a rate-and-state dependent friction law with strong velocity weakening coupled to thermal-pressurization of pore fluids. Dynamic rupture evolution and ground shaking are densely evaluated across the fault and Earth’s surface to analyze the variations of rupture parameters (slip, peak slip rate, rupture speed, and rise time), correlations among rupture parameters, and variability of peak ground velocity. Our simulations reveal how variations in thermal-pressurization affect earthquake rupture properties. We find that the mean slip and rise time decrease with increasing hydraulic diffusivity, whereas mean rupture speed and peak slip-rate remain almost constant. Mean slip, peak slip-rate, and rupture speed decrease with increasing shear-zone half-width, whereas mean rise time increases. Shear-zone half-width distinctly affects the correlation between rupture parameters, especially for parameter pairs (slip, rupture speed), (peak slip-rate, rupture speed), and (rupture speed, rise time). Hydraulic diffusivity has negligible effects on these correlations. Variations in shear-zone half-width primarily impact rupture speed, which then may affect other rupture parameters. We find a negative correlation between slip and peak slip-rate, unlike simpler dynamic rupture models. Mean peak ground velocities decrease faster with increasing shear-zone half-width than with increasing hydraulic diffusivity, whereas ground-motion variability is similarly affected by both the parameters. Our results show that shear-zone half-width affects rupture dynamics, kinematic rupture properties, and ground shaking more strongly than hydraulic diffusivity. We interpret the importance of shear-zone half-width based on the characteristic time of diffusion. Our findings may inform pseudodynamic rupture generators and guide future studies on how to account for thermal-pressurization effects. 

Abstract The Mediterranean Hellenic Arc subduction zone (HASZ) has generated several 8 earthquakes and tsunamis. Seismic‐probabilistic tsunami hazard assessment typically utilizes uniform or stochastic earthquake models, which may not represent dynamic rupture and tsunami generation complexity. We present an ensemble of ten 3D dynamic rupture earthquake scenarios for the HASZ, utilizing a realistic slab geometry. Our simplest models use uniform along‐arc pre‐stresses or a single circular initial stress asperity. We then introduce progressively more complex models varying initial shear stress along‐arc, multiple asperities based on scale‐dependent critical slip weakening distance, and a most complex model blending all aforementioned heterogeneities. Thereby, regional initial conditions are constrained without relying on detailed geodetic locking models. Varying epicentral locations in the simplest, homogeneous model leads to different rupture speeds and moment magnitudes. We observe dynamic fault slip penetrating the shallow slip‐strengthening region and affecting seafloor uplift. Off‐fault plastic deformation can double vertical seafloor uplift. A single‐asperity model generates a 8 scenario resembling the 1303 Crete earthquake. Using along‐strike varying initial stresses results in 8.0–8.5 dynamic rupture scenarios with diverse slip rates and uplift patterns. The model with the most heterogeneous initial conditions yields a 7.5 scenario. Dynamic rupture complexity in prestress and fracture energy tends to lower earthquake magnitude but enhances tsunamigenic displacements. Our results offer insights into the dynamics of potential large Hellenic Arc megathrust earthquakes and may inform future physics‐based joint seismic and tsunami hazard assessments. 

Near-field earthquake ground motions characterized by strong velocity pulses can cause extensive damage to buildings and structures. Such pulses were identified during the Mw 7.8 and Mw 7.5 earthquake doublet of the 2023 Turkey seismic sequence, potentially contributing to the extensive damage it caused. Therefore, a better understanding and characterization of pulse properties (e.g. period and amplitude) and their underlying physical factors are crucial for earthquake-resistant design. In this study, we characterize the velocity pulses reported in observed records and synthetic waveforms generated by a three-dimensional (3D) dynamic rupture simulation of the Mw 7.8 event. We observed significant variability in the pulse properties of the observed records in near-fault regions, particularly regarding their orientations. This variability was not fully captured by the dynamic rupture simulation. Our results indicate that directivity effects are not the only factors influencing pulse characteristics in this earthquake doublet. While site effects (e.g. basin effects) may influence pulse characteristics at some stations, local heterogeneities in slip amplitude, orientations, and fault geometries can be critical in generating or influencing pulse properties in this earthquake doublet.