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Several regularly recurring moderate-size earthquakes motivated dense instrumentation of the Parkfield section of the San Andreas fault, providing an invaluable near-fault observatory. We present a seismo-geodetic dynamic inversion of the 2004 Parkfield earthquake, which illuminates the interlinked complexity of faulting across time scales. Using fast-velocity-weakening rate-and-state friction, we jointly model 3D coseismic dynamic rupture and the 90-day evolution of postseismic slip. We utilize a parallel tempering Markov chain Monte Carlo approach to solve this non-linear high-dimensional inverse problem, constraining spatially varying prestress and fault friction parameters by 30 strong motion and 12 GPS stations. From visiting >2 million models, we discern complex coseismic rupture dynamics that transition from a strongly radiating pulse-like phase to a mildly radiating crack-like phase. Both coseismic phases are separated by a shallow strength barrier that nearly arrests rupture and leads to a gap in the afterslip. Coseismic rupture termination involves distinct arrest mechanisms that imprint on afterslip kinematics. A backward propagating afterslip front may drive delayed aftershock activity above the hypocenter. Analysis of the 10,500 best-fitting models uncovers local correlations between prestress levels and the reference friction coefficient, alongside an anticorrelation between prestress and rate-state parameters b−a. We find that a complex, fault-local interplay of dynamic parameters determines the nucleation, propagation, and arrest of both, co- and postseismic faulting. This study demonstrates the potential of inverse physics-based modeling to reveal novel insights and detailed characterizations of well-recorded earthquakes.
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Afterslip on Conjugate Faults of the 2020 Mw 6.3 Nima Earthquake in the Central Tibetan Plateau: Evidence from InSAR Measurements
ABSTRACT Afterslip could help to reveal seismogenic fault structure. The 2020 Mw 6.3 Nima earthquake happened in a pull-apart basin within the Qiangtang block, central Tibetan plateau. Previous studies have explained the coseismic and early (<6 mo) postseismic deformation by rupture and afterslip on a normal fault bounding the western side of the basin. Here, we resolved the 19-month Interferometric Synthetic Aperture Radar-measured sequences of postseismic displacements that revealed a second postseismic displacement center ~12 km to the east of the main fault. Fitting the postseismic displacement requires afterslip on both the main fault and an antithetic fault that probably forms a y-shaped pair of conjugate faults in a negative flower structure. Stress-driven afterslip models suggest that the required afterslip on the antithetic fault could be triggered by coseismic rupture of the main fault or by a simultaneous rupture on the antithetic fault. The afterslip on both faults occurred mainly up-dip to the coseismic slip and has released moment ~15%–19% of that by the coseismic rupture. These results provide insights into active extension in the central Tibetan plateau and highlight the complex nature of fault rupture and afterslip.
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- Award ID(s):
- 2013656
- PAR ID:
- 10425726
- Date Published:
- Journal Name:
- Bulletin of the Seismological Society of America
- ISSN:
- 0037-1106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Several regularly recurring moderate‐size earthquakes motivated dense instrumentation of the Parkfield section of the San Andreas fault (SAF), providing an invaluable near‐fault observatory. We present a seismo‐geodetic dynamic inversion of the 2004 Parkfield earthquake, which illuminates the interlinked complexity of faulting across time scales. Using fast‐velocity‐weakening rate‐and‐state friction, we jointly model coseismic dynamic rupture and the 90‐day evolution of postseismic slip in a 3D domain. We utilize a parallel tempering Markov chain Monte Carlo approach to solve this non‐linear high‐dimensional inverse problem, constraining spatially varying prestress and fault friction parameters by 30 strong motion and 12 GPS stations. From visiting 2 million models, we discern complex coseismic rupture dynamics that transition from a strongly radiating pulse‐like phase to a mildly radiating crack‐like phase. Both coseismic phases are separated by a shallow strength barrier that nearly arrests rupture and leads to a gap in the afterslip, reflecting the geologic heterogeneity along this segment of the SAF. Coseismic rupture termination involves distinct arrest mechanisms that imprint on afterslip kinematics. A backward propagating afterslip front may drive delayed aftershock activity above the hypocenter. Trade‐off analysis of the 10,500 best‐fitting models uncovers local correlations between prestress levels and the reference friction coefficient, alongside an anticorrelation between prestress and rate‐state parameters . We find that a complex, fault‐local interplay of dynamic parameters determines the nucleation, propagation, and arrest of both, co‐ and postseismic faulting. This study demonstrates the potential of inverse physics‐based modeling to reveal novel insights and detailed characterizations of well‐recorded earthquakes.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0120220247
