Joint Inversion of Rupture across a Fault Stepover during the 8 August 2017 Mw 6.5 Jiuzhaigou, China, Earthquake

Author:

Zhang Yong1,Feng Wanpeng23,Li Xingxing4,Liu Yajing5ORCID,Ning Jieyuan1,Huang Qinghua1

Affiliation:

1. School of Earth and Space Science, Peking University, Beijing, China

2. Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou, China

3. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China

4. School of Geodesy and Geomatics, Wuhan University, Wuhan, China

5. Department of Earth and Planetary Science, McGill University, Montréal, Canada

Abstract

Abstract The 8 August 2017 Mw 6.5 Jiuzhaigou earthquake occurred in a tectonically fractured region in southwest China. We investigate the multifault coseismic rupture process by jointly analyzing teleseismic, strong-motion, high-rate Global Positioning System, and Interferometric Synthetic Aperture Radar (InSAR) datasets. We clearly identify two right-stepping fault segments and a compressional stepover based on variations in focal mechanisms constrained by coseismic InSAR deformation data. The average geometric parameters of the northwest and southeast segments are strike = 130°/dip = 57° and strike = 151°/dip = 70°, respectively. The rupture model estimated from a joint inversion of the seismic and geodetic datasets indicates that the rupture initiated on the southeastern segment and jumped to the northwestern segment, resulting in distinctive slip patches on the two segments. A 4-km-long coseismic slip gap was identified around the stepover, consistent with the aftershock locations and mechanisms. The right-stepping segmentation and coseismic rupture across the compressional stepover exhibited by the 2017 Jiuzhaigou earthquake are reminiscent of the multifault rupture pattern during the 1976 Songpan earthquake sequence farther south along the Huya fault system in three successive Ms∼7 events. Although the common features of fault geometry and stepover may control the similarity in event locations and focal mechanisms of the 2017 and 1976 sequences, the significantly wider (~15 km) stepover in the 1976 sequence likely prohibited coseismic rupture jumping and hence reduced seismic hazard.

Publisher

Seismological Society of America (SSA)

Subject

Geophysics

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