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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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The First Three Months of Postseismic Deformation of the 29 July 2021 Mw 8.2 Chignik Earthquake Provides New Constraints on the Down‐Dip Extent of Coseismic Slip
Abstract Stress‐based postseismic deformation modeling including afterslip and viscoelastic relaxation usually assumes the coseismic slip distribution and the associated stress perturbation as known. However, that assumption biases the postseismic modeling results by the assumptions that underlie the coseismic models. Importantly, this misses an opportunity to iteratively constrain the coseismic slip model with postseismic observations. We used a broad set of seismic and geodetic data to create multiple coseismic slip models that only differ in the down‐dip extent of the rupture plane and fit the coseismic observations for the July 29, Mw 8.2 Chignik earthquake equally well. We then evaluated the quality of those coseismic slip models based on how well each of them predicts postseismic GNSS displacements using a stress‐driven afterslip model. We find that coseismic slip models that generate afterslip too far down‐dip systematically fail to predict postseismic deformation. We find that the postseismic observations are best predicted by a narrower coseismic slip model that terminates abruptly at its deepest extent. The model predictions improve further if stress‐driven afterslip is combined with a superimposed viscoelastic relaxation response of a 50 km thick elastic lithosphere for the overriding plate and an elastic cold nose to the mantle wedge.
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- PAR ID:
- 10648585
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 130
- Issue:
- 10
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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