Coseismic fault model of the 2017 M_W 6.5 Jiuzhaigou earthquake and implications for the regional fault slip pattern

On August 8, 2017, an M_W 6.5 earthquake occurred in Jiuzhaigou County, Sichuan Province, China, on the eastern margin of the Qinghai–Tibet Plateau. This study investigates the coseismic deformation field and fault model with ascending and descending Sentinel-1 synthetic aperture radar (SAR) images, aftershock distribution, and elastic half-space dislocation model. The regional fault slip pattern is then quantitatively examined using the boundary element method. The results show that the ascending and descending interferometric synthetic aperture radar (InSAR) coseismic deformation fields display an overall NNW–SSE trend, with more significant deformation on the southwest side of the fault. The coseismic fault geometry is divided into NW and SE sub-faults with strikes of 162.1° and 149.3°, respectively. The coseismic fault slip is dominated by a left-lateral strike-slip movement with an average rake of −2.31°, mainly occurring at a depth of 0–13.04 km with a shape of an approximately inverted triangle. The fault slip features two peak slip zones, with a maximum of 1.39 m. The total seismic moment is 6.34 × 10¹⁸ N·m (M_W 6.47). The boundary element calculation quantitatively indicates that the regional fault slip pattern may be mainly attributable to the changing strike and dip. The strike changes from NNW–SSE to nearly NS direction, and the dip gradually decreases from the Jiuzhaigou earthquake fault in the north to the Huya fault in the south. With these characteristics, the Huya and the Jiuzhaigou earthquake faults form the eastern boundary of the Minshan uplift zone and accommodate the accumulated deformation.