Source Parameters and Slip Distribution of the 2023 Mw 6.0 Jishishan (Gansu, China) Earthquake Constrained by InSAR Observations

Objectives: On 18 December 2023, an Mw 6.0 earthquake struck Jishishan county (Gansu, China). It is the largest earthquake ever recorded in the Lajishan fault zone at the northeastern margin of the Tibetan Plateau since modern seismicity has been recorded and is of great importance to determine seismogenic fault geometry and refined slip distribution for assessing future seismic hazards in the Lajishan fault zone region. Methods: We used Sentinel-1A synthetic aperture radar (SAR) images to acquire coseismic surface deformation and used them as a constraint to invert the fault geometry and refined slip distribution. Finally, we analysed the regional seismic risk based on the static Coulomb failure stress change (ΔCFS). Results: The InSAR 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 ~6.5 cm for ascending track, and the maximum LOS uplift deformation ~7.2 cm for descending track. Source modeling results show that the coseismic surface displacements of this event can be explained well using either east- or west-dipping fault geometries. Conclusions: Based on aftershock and coseismic landslide distributions, we prefer to the east-dipping fault model as the seismogenic fault of the event, i.e. this earthquake occurred on a NNW-trending, east-dipping, blind thrut fault. Stress loading in the region indicates that future attention should be paid in (1) the entire section of the South Laji Mountain fault,（ 2） the NWW-trending segments of the North Laji Mountain fault and its NNW-trending segments south of the epicentre, and (3) the segments east of the epicentre of the northern margin of western Qinling fault and Daotanghe-Linxia fault.