On December 18, 2023, a M_W6.0 earthquake struck Jishishan County, Gansu Province, China. This earthquake occurred in southeastern Gansu, within the northern segment of the North-South Seismic Belt, a critical area forming part of the northeastern margin of the Qinghai-Xizang Plateau. The region is intersected by several active fault zones, including the East Kunlun fault, Qilian-Haiyuan fault, Altyn Tagh fault, and West Qinling fault. Jishishan County lies on sedimentary strata at the junction of the Loess Plateau and the Qinghai-Xizang Plateau, where significant site amplification effects on the western edge of the Loess Plateau can exacerbate surface damage. The Jishishan Mountains, located in the easternmost segment of the Qilian Mountains, form part of the northern margin of the Qinghai-Xizang Plateau. This region has undergone significant continental crustal thickening due to the ongoing collision between the Indian and Eurasian plates. As the plateau continues to push northward and expand laterally, large-scale left-lateral strike-slip faults and thrust fault zones have developed. The Jishishan Mountains, trending northwest-southeast （NNW−SSE）, are bounded by faults on both sides, exhibiting evidence of thrusting and strike-slip motion. Consequently, investigating the coseismic surface deformation field, geometric parameters of the seismogenic fault, and stress field disturbances induced by fault rupture is of paramount importance.

In this study, Interferometric Synthetic Aperture Radar （InSAR） technology was employed to process Sentinel-1A SAR images covering the epicentral region. Shuttle radar topography mission （SRTM） data of National Aeronautics and Space Administration （NASA）, with a 30-meter DEM resolution, were utilized for image coregistration and removing topographic phase contributions. Precise Orbit Ephemerides （POE） data from the European Space Agency （ESA） were used to correct orbital errors, while atmospheric corrections were performed using the Generic Atmospheric Correction Online Service for InSAR （GACOS） to minimize atmospheric noise. The final step involved geocoding the output, which generated coseismic surface deformation fields in the line of sight （LOS） direction for both ascending and descending tracks of the Jishishan earthquake.

The spatial distribution of aftershock hypocenters, based on clustering patterns near the main fault, allowed for clear delineation of the fault plane’s geometric structure. A single plane was used to model the seismogenic fault in this study. By using a dislocation model in an elastic half-space, coseismic surface displacements and the double-difference relocation algorithm for the earthquake sequence were then inverted to determine fault geometry parameters and non-uniform fault slip distributions.

The results indicate that the 2023 Jishishan earthquake was a reverse fault event on a buried fault, with maximum surface displacements of 7.0 cm and 6.8 cm observed in the ascending and descending tracks, respectively. Joint fitting of small-earthquake fault planes and inversion of fault geometry parameters show that the seismic source depth is primarily concentrated between 6 and 15 km. The fault trends northeast, strikes at 323°, and dips at 50°. Rupture is predominantly concentrated at depth of 4−11 km, with a maximum slip of 0.2 m occurring at 5.7 km depth. The earthquake likely occurred on the southern edge of the Lajishan fault, which is characterized as a NNW-trending, east-dipping thrust fault.

The distributed slip model suggests that primary rupture occurred at depth between 0 and 8 km, with significantly reduced slip observed at 10 km, implying that coseismic rupture may have triggered deeper aftershocks. The seismogenic fault mechanism is predominantly thrust-dominated. Additionally, deep fault structures inferred from aftershocks show slight variations in dip angle between deeper and shallower sections, as observed in InSAR surface deformation. Near the surface, the fault dip angle becomes shallower, indicating a decrease in dip from depth to the surface-consistent with the potential bending geometry of deep thrust faults. Consequently, a depth of 10 km was selected for calculating Coulomb stress disturbances.

Analysis of Coulomb failure stress changes （ΔCFS） in the surrounding area induced by the 2023 Jishishan earthquake reveals positive ΔCFS values at both ends of the seismogenic fault. The distribution of Coulomb stress changes indicates that several fault segments are in a stress-loaded state （with ΔCFS exceeding 10 kPa）, including the entire southern segment of the Lajishan south margin fault; the WNW-trending segment of the Lajishan north margin fault and its NNW-trending segment south of the epicenter; the North margin fault of the West Qinling; and the segment of the Daotanghe-Linxia fault east of the epicenter. These areas exhibit relatively high seismic hazard and warrant continuous monitoring.