Surface Deformation and Hazard Analysis after the 2023 Ms 6.2 Earthquake in Jishishan, Gansu Province Based on InSAR and Optical Imagery Interpretation

Objective: On 18th December 2023, an Ms 6.2 earthquake struck Jishishan County, Linxia Prefecture, Gansu Province, China. It triggered significant building damage and induced numerous coseismic landslides, resulting in severe casualties and substantial socio-economic losses. The acquisition of post-earthquake surface deformation and disaster distribution information is of great guiding significance for disaster assessment and postdisaster reconstruction. Methods: Firstly, surface coseismic deformation information was obtained using interferometric synthetic aperture radar (InSAR). And, high-resolution optical imagery was employed for visual interpretation near the epicenter. Subsequently, seismic disaster extraction was performed based on co-seismic deformation information from InSAR and visual interpretation information from high-resolution optical images. Finally, the extracted seismic disaster information was statistically analyzed, and potential factors contributing to its formation were briefly analyzed. Results and Conclusions: The earthquake resulted in an approximately elliptical uplift between two faults to the northeast of the epicenter, with long and short axes measuring approximately 22.5 km and 15 km, respectively. The maximum uplift approached 8 cm, consistent with characteristics of thrust-type seismic motion. The earthquake destroyed 1 506 buildings near the epicenter, mainly affecting self-built rural houses made of brick, wood, and earth structures. The epicentral distance was primarily distributed within a range of 5 to 25 km, and the azimuths were predominantly between 0° to 30° and 330° to 360°. A total of 4 996 coseismic landslides were interpreted near the epicenter, primarily distributed within a range of 5 to 30 km distance to the epicenter, with azimuths between 0° to 60° and 330° to 360°, predominantly comprising small-scale loess landslides. Among these, the surface of the large landslide in Zhaizi Village exhibited 208 cracks and 73 landslides and collapses, posing significant safety hazards. The area affected by the flowslide in Zhongchuan Township was about 456 982.10 m², destroying 158 buildings and 4 569 m of roads. The earthquake did not cause severe surface disasters within 5 km of the epicenter, indicating that the most severely affected areas may not necessarily concentrate around the micro-epicenter, which is closely related to the direction of seismic wave propagation and regional geological conditions.