Thin crème brûlée rheological structure for the Eastern California Shear Zone

Shaozhuo Liu, Zheng-Kang Shen, Roland Bürgmann, Sigurjon Jonsson

Research output: Contribution to journalArticlepeer-review

Abstract

Since the occurrence of the 1992 CE Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes in the Mojave Desert (California, USA), postseismic deformation following both earthquakes has been intensively studied, and models with a strong crust overlying a low-viscosity mantle asthenosphere have been favored. However, we recently found that the near-field postseismic transients after the two earthquakes have lasted longer than previously thought, which requires a revision of the postseismic modeling. Our new modeling results based on the revised postseismic transients show that: (1) the effective viscosity of the lower crust beneath the Mojave region at the decadal time scale is ~2 × 1020 Pa·s (transient viscosity ~2 × 1019 Pa·s), i.e., only ~5 times that of the underlying mantle asthenosphere, and (2) the transient viscosity of the upper mantle exhibits a time-dependent increase, providing fresh geodetic evidence for frequency-dependent rheology (e.g., Andrade or extended Burgers rheology). The inferred transient rheology for the first year agrees well with that obtained for the July 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquakes ~180 km north of the two Mojave events. Our modeling results support a thin crème brûlée model for the Eastern California Shear Zone (part of the Pacific-North America plate boundary) in which both the lower crust and the upper mantle exhibit ductility at decadal time scales.
Original languageEnglish (US)
JournalGeology
DOIs
StatePublished - Oct 7 2020

Bibliographical note

KAUST Repository Item: Exported on 2020-12-14
Acknowledged KAUST grant number(s): BAS/1/1353–01–01
Acknowledgements: We appreciate constructive reviews by Greg Hirth, Fred Pollitz, and James Jackson. We thank Sylvain Barbot for sharing the Unicycle code; Rongjiang Wang for his guidance on the PSGRN/PSCMP software; and Xiaohua Xu and Kang Wang for sharing their rupture models. Liu acknowledges support from the Institute of Geology, China Earthquake Administration. This study was funded by King Abdullah University of Science and Technology (KAUST, Saudi Arabia) award BAS/1/1353–01–01. This is Southern California Earthquake Center publication 10779.

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