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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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Equivalent Near-Field Corner Frequency Analysis of 3D Dynamic Rupture Simulations Reveals Dynamic Source Effects
Abstract Dynamic rupture simulations generate synthetic waveforms that account for nonlinear source and path complexity. Here, we analyze millions of spatially dense waveforms from 3D dynamic rupture simulations in a novel way to illuminate the spectral fingerprints of earthquake physics. We define a Brune-type equivalent near-field corner frequency (fc) to analyze the spatial variability of ground-motion spectra and unravel their link to source complexity. We first investigate a simple 3D strike-slip setup, including an asperity and a barrier, and illustrate basic relations between source properties and fc variations. Next, we analyze >13,000,000 synthetic near-field strong-motion waveforms generated in three high-resolution dynamic rupture simulations of real earthquakes, the 2019 Mw 7.1 Ridgecrest mainshock, the Mw 6.4 Searles Valley foreshock, and the 1992 Mw 7.3 Landers earthquake. All scenarios consider 3D fault geometries, topography, off-fault plasticity, viscoelastic attenuation, and 3D velocity structure and resolve frequencies up to 1–2 Hz. Our analysis reveals pronounced and localized patterns of elevated fc, specifically in the vertical components. We validate such fc variability with observed near-fault spectra. Using isochrone analysis, we identify the complex dynamic mechanisms that explain rays of elevated fc and cause unexpectedly impulsive, localized, vertical ground motions. Although the high vertical frequencies are also associated with path effects, rupture directivity, and coalescence of multiple rupture fronts, we show that they are dominantly caused by rake-rotated surface-breaking rupture fronts that decelerate due to fault heterogeneities or geometric complexity. Our findings highlight the potential of spatially dense ground-motion observations to further our understanding of earthquake physics directly from near-field data. Observed near-field fc variability may inform on directivity, surface rupture, and slip segmentation. Physics-based models can identify “what to look for,” for example, in the potentially vast amount of near-field large array or distributed acoustic sensing data.
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- Award ID(s):
- 2121568
- PAR ID:
- 10535849
- Publisher / Repository:
- Seismological Society of America
- Date Published:
- Journal Name:
- Seismological Research Letters
- Volume:
- 95
- Issue:
- 2A
- ISSN:
- 0895-0695
- Page Range / eLocation ID:
- 900 to 924
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0220230225
