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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.
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Delayed Dynamic Triggering and Enhanced High‐Frequency Seismic Radiation From Brittle Rock Damage in 3D Dynamic Rupture Simulations
Abstract Using a novel high‐performance computing implementation of a nonlinear continuum damage‐breakage model, we explore interactions between 3D co‐seismic off‐fault damage, seismic radiation, and rupture dynamics. Our simulations demonstrate that off‐fault damage enhances high‐frequency wave radiation above 1 Hz, reduces rupture speed and alters the total kinetic energy. We identify distinct damage regimes separated by solid‐granular transition, with smooth distributions under low damage conditions transitioning to localized, mesh‐independent shear bands upon reaching brittle failure. The shear band orientations depend systematically on the background stress and agree with analytical predictions. The brittle damage inhibits transitions to supershear rupture propagation and the rupture front strain field results in locally reduced damage accumulation during supershear transition. The dynamically generated damage yields uniform and isotropic ratios of fault‐normal to fault‐parallel high‐frequency ground motions. Co‐seismic damage zones exhibit depth‐dependent width variations, becoming broader near the Earth's surface consistent with field observations, even under uniform stress conditions. We discover a new delayed dynamic triggering mechanism in multi‐fault systems, driven by reductions in elastic moduli and the ensuing stress heterogeneities in 3D tensile fault step‐overs. This mechanism affects the static and dynamic stress fields and includes the formation of high shear‐traction fronts around localized damage zones. The brittle damage facilitates rupture cascading across faults, linking delay times directly to damage rheology and fault zone evolution. Our results help explain near‐fault high‐frequency isotropic radiation and delayed rupture triggering, improving our understanding of earthquake processes, seismic wavefields and fault system interactions.
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- PAR ID:
- 10648448
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 130
- Issue:
- 9
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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