Abstract:On December 18, 2023, an MS6.2 earthquake occurred in Jishishan County, Gansu Province. The ascending and descending Sentinel-1A SAR satellite images were selected and the differential interferometric synthetic aperture radar (D-InSAR) technology was used to obtain the co-seismic deformation field of the earthquake. The results show that the long axis direction of co-seismic deformation field in the line of sight (LOS) direction is NW-SE, and the deformation is positive, indicating an approach towards the satellite and revealing surface uplift. The maximum deformation in the LOS direction of ascending and descending tracks is 12 and 9 cm, respectively. Subsequently, the co-seismic slip distribution was inverted using the steepest descent method with ascending and descending deformation data as constraints. The inversion results show that both the SW-dipping and NE-dipping fault models fit the observed values of InSAR co-seismic deformation field well, indicating that the MS6.2 earthquake is a combined thrust/strike-slip faulting type. The tectonic background and aftershock distribution in the study area were discussed to solve the controversies on the seismogenic fault and its dipping direction of the event. It is inferred that the seismogenic fault of the Jishishan MS6.2 earthquake is a hidden fault striking NW-SE and dipping SW, with a strike of approximately 148.4°, a dip angle of 52°, and a slip angle of approximately 130°, possibly a branch fault of the Jishishan east margin fault. Additionally, the co-seismic Coulomb stress model shows that the eastern section of Lintan-Tanchang fault, the eastern section of Lenglongling fault, the western section of Haiyuan fault, the western section of Lajishan southern margin fault, and the Guide fault are located at the positive-negative transition zone of co-seismic Coulomb failure stress change (ΔCFS), which should be given attention.
