Coseismic deformation field of the Jishishan Ms6.2 earthquake based on InSAR observations

Abstract On 18 December 2023 (Beijing time), an Ms6.2 earthquake struck Jishishan County (Gansu, China). It is the largest earthquake ever recorded in the Lajishan fault zone, located at the northeastern margin of the Tibetan Plateau, since the advent of modern seismic recording. This event is crucial for determining the seismogenic fault geometry and refining the slip distribution, which are essential for assessing future seismic hazards in the Lajishan fault zone region. The coseismic deformation field was derived using both ascending and descending Sentinel-1A data in this article, and the Bayesian inversion method was applied to determine the source parameters of the seismogenic fault and its slip characteristics. The results show that the coseismic displacements were dominated by uplift deformation for both ascending and descending tracks, with the maximum line-of-sight (LOS) uplift deformation approximately 72 mm for the ascending track and approximately 88mm for the descending track. Source modelling results show that the coseismic surface displacements of this event can be explained well using either east- or west-dipping fault geometries. The event has a northwest-dipping fault with a dip of 50.57°, a strike of 323.2° and a rake of 65.79°, indicating that this earthquake is a thrust event with a dextral slip component. By analysing the geometric and kinematic characteristics of the main active faults in the surrounding areas, we found that the Jishishan earthquake occurred in the southern margin of the Lajishan fault, and the east section of the Lajishan fault may be a straddle structure between the Nanshan fault, the west section of the Lajishan fault and the West Qinling fault.