InSAR observation and inversion of the seismogenic fault for the 2017 Jiuzhaigou MS7.0 earthquake in China

Abstract

An earthquake with MS7.0 occurred in Jiuzhaigou County, Sichuan Province on 8 August 2017. This work derives the coseismic deformation field based on Sentinel-1 SAR images by using the InSAR technique. Then, the coseismic slip distribution is inverted and the static Coulomb stress changes in the aftershock distribution area and surrounding faults are calculated. Finally, we discuss the seismogenic fault of this event. The results show that from the InSAR deformation fields, the Jiuzhaigou earthquake caused crustal deformation with a magnitude of 20 cm in the line of sight direction. The coseismic deformation fields exhibit an asymmetric characteristic. The coseismic slip was dominated by left-lateral strike motion and mainly distributed at depths 4~16 km, with the maximum slip of approximately 77 cm at a depth 9 km. The inverted magnitude is approximately MW6.46. The causative fault did not rupture the surface. Most of the aftershocks occurred in the regions with increases of Coulomb stress change. This earthquake increased the Coulomb stress change on some surrounding faults, such as eastern segment of the Dongkunlun fault, Longriba fault, and Huya fault. The seismic risk of the eastern segment of the Dongkunlun fault should be considered in the future. Our work suggests that the causative fault of the Jiuzhaigou earthquake is the Shuzheng fault, which is presumably the hidden part of the northwestward extension of the Huya fault. And this event was resulted from southeastward motion of the Bayan Har block when blocked by the South China block.