Objectives An earthquake with Ms 6.2 occurred in Jishishan County, Gansu Province on December 18, 2023. The epicenter is located at the Lajishan fault zone, which plays an important role in adjusting regional tectonic deformation. Therefore, it is important to research the crustal deformation of this earthquake.

Methods We collect coseismic and preseismic Sentinel-1 single look complex images covering the study area, and use differential interferometric synthetic aperture radar (InSAR) and small baseline subset technology to obtain the coseismic and interseismic deformation, respectively. Furthermore, both interseismic InSAR and global navigation satellite system observations are integrated to obtain the high-accuracy and high-resolution three-dimensional deformation field. Subsequently, we invert the slip distribution of the seismogenic fault using the steepest descent method program with the constraint of coseismic deformation. The fault model is constructed based on 3D electrical structure, aftershocks, and InSAR deformation field. In addition, we invert the dextral strike slip rate, dip slip, and locking depth of the seismogenic fault with the constraint of three-dimensional deformation.

Results Both ascending and descending coseismic InSAR deformation exhibit symmetrical elliptical uplift with a maximum uplift of 8.9 cm along the radar line of sight direction, indicating a thrust earthquake, and there is no obvious surface rupture. The seismogenic fault is mainly characterized by reverse movement and did not rupture the surface, and the peak slip is 0.24 m at the depth of 13.4 km. The geode⁃tic moment is about 1.93×10¹⁸ N·m, corresponding to Mw 6.1 event. The dextral strike slip rate and dip slip rate of the seismogenic fault are about 1.9 mm/a and 2.4 mm/a, respectively. The locking depth of the seismogenic fault is about 16.8 km, close the the depth of this earthquake.

Conclusions The seismogenic fault may be a SWW-dipping hidden fault near the southern segment of the northern Lajishan fault, which thrusts towards the basin direction and parallel to the Lajishan fault. The main seismogenic fault may be southern segment of the SWW-dipping northern Lajishan fault. This main thrust fault and the NEE dipping back-thrust fault jointly uplift when the earthquake occurs. The static Coulomb stress calculation result indicates that the future seismic risk of the southern section of the northern Lajishan fault, the southern end of the southern Lajishan fault, the central and southern sections of the Daotanghe-Linxia fault, and the western end of the northern west Qinling fault cannot be ignored. This earthquake is the result of a regional stress regulation under the the northeast expansion of the Tibet Plateau.