The Mediterranean Hellenic Arc subduction zone (HASZ) has generated several Mw>=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 hypocenter 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 Mw~8 scenario resembling the 1303 Crete earthquake. Using along-strike varying initial stresses results in Mw~8.0-8.5 dynamic rupture scenarios with diverse slip rates and uplift patterns. The model with the most heterogeneous initial conditions yields a Mw~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.

We present 3-D spontaneous dynamic rupture earthquake scenarios for the Húsavík–Flatey Fault Zone (HFFZ) in Northern Iceland. We construct three fault system models consisting of up to 55 segments of varying geometric complexity. By varying hypocenter locations, we analyze rupture dynamics, fault interactions and their associated ground motions and observational uncertainties in 79 scenarios. We use regional observations to constrain 3-D subsurface velocities and viscoelastic attenuation as well as fault stress and strength. Our models account for topo-bathymetry, off-fault plasticity and we explore the effect of fault roughness. Our spontaneous dynamic rupture scenarios can match historic magnitudes. We show that the fault system segmentation and geometry, hypocenter locations, initial stress conditions and fault roughness have strong effects on multi-fault rupture dynamics across the HFFZ. Breaking of different portions of the same fault system leads to varying rupture dynamics, slip distributions and magnitudes. All dynamic rupture scenarios yield highly heterogeneous near-field ground motions. We observe amplification from rupture directivity, geometric complexities, and amplification and shielding due to topography. We recover a magnitude-consistent attenuation relationship in good agreement with new regional empirical ground motion models. Physics-based ground motion variability changes with distance and increases for unilateral vs. bilateral rupture. Our study illustrates important ingredients for fully physics-based, regional earthquake scenarios, their respective importance for rupture dynamics and ground motion modeling and how they can be observationally constrained and verified. We entail that dynamic rupture scenarios can be useful for non-ergodic probabilistic seismic hazard assessment, specifically in data-limited regions.

We study the effects of pore fluid pressure (Pf ) on the pre-earthquake, near-fault stress state and 3D earthquake rupture dynamics through 6 scenarios utilizing a structural model based on the 2004 Mw 9.1 Sumatra-Andaman earthquake. As pre-earthquake Pf magnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre-earthquake Pf averages near 97 % of lithostatic pressure, leading to pre-earthquake average shear and effective normal tractions of 4-5 MPa and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co-seismic principal stress rotations and absolute post-seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with larger Pf magnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre-earthquake Pf depth distribution. If Pf follows a sublithostatic gradient, pre-earthquake effective normal stress increases with depth. If Pf follows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate up-dip. This renders constraints on near-trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site-specific measurements to constrain dynamically plausible megathrust strength and Pf gradients.

Despite decades-long debate over the mechanics of low-angle normal faults dipping less than 30°, many questions about their strength, stress, and slip remain unresolved. Recent geologic and geophysical observations have confirmed that gently-dipping detachment faults can slip at such shallow dips and host moderate-to-large earthquakes. Here, we analyze the first 3D dynamic rupture models to assess how different stress and strength conditions affect rupture characteristics of low-angle normal fault earthquakes. We model observationally constrained spontaneous rupture under different loading conditions on the active Mai’iu fault in Papua New Guinea, which dips 16-24° at the surface and accommodates ~8 mm/yr of horizontal extension. We analyze four distinct fault-local stress scenarios: 1) Andersonian extension, as inferred in the hanging wall; 2) back-rotated principal stresses inferred paleopiezometrically from the exhumed footwall; 3) favorably rotated principal stresses well-aligned for low-angle normal-sense slip; and 4) Andersonian extension derived from depth-variable static fault friction decreasing towards the surface. Our modeling suggests that subcritically stressed detachment faults can host moderate earthquakes within purely Andersonian stress fields. Near-surface rupture is impeded by free-surface stress interactions and dynamic effects of the gently-dipping geometry and frictionally stable gouges of the shallowest portion of the fault. Although favorably-inclined principal stresses have been proposed for some detachments, these conditions are not necessary for seismic slip on these faults. Our results demonstrate how integrated geophysical and geologic observations can constrain dynamic rupture model parameters to develop realistic rupture scenarios of active faults that may pose significant seismic and tsunami hazards to nearby communities.

Advances in physics-based earthquake simulations, utilizing high-performance computing, have been exploited to better understand the generation and characteristics of the high-frequency seismic wavefield. However, direct comparison to ground motion observations of a specific earthquake is challenging. We here propose a new approach to simulate data-fused broadband ground motion synthetics using 3D dynamic rupture modeling of the 2016 Mw6.2 Amatrice, Italy earthquake. We augment a smooth, best-fitting model from Bayesian dynamic rupture source inversion of strong-motion data (<1 Hz) with fractal fault roughness, frictional heterogeneities, viscoelastic attenuation, and topography. The required consistency at long periods allows us to quantify the role of dynamic source heterogeneities, such as the 3D roughness drag, from observational broadband seismic waveforms. We demonstrate that 3D data-constrained fully dynamic rupture synthetics show good agreement with various observed ground-motion metrics up to ~5 Hz and are an important avenue towards non-ergodic, physics-based seismic hazard assessment.