Deep Structural Characteristics and Dynamic Processes of the Jishishan Ms 6.2 Earthquake and Its Adjacent Areas

Objectives: On December 18, 2023, the Ms 6.2 earthquake occurred in Jishishan County, Gansu Province. The breeding and occurrence of strong earthquakes are controlled by the regional stress field and the main active fault zone, as well as the deep physical structure and dynamic environment. It is of great significance to study the deep structure characteristics and seismogenic environment in the focal area and its adjacent areas to reveal the causes of strong earthquakes and to carry out the work of earthquake prevention and disaster reduction. Methods: Based on the XGM2019e global gravity field model, the Bouguer gravity anomaly data are processed and analyzed by using wavelet multi-scale analysis and three-dimensional crustal density structure inversion, and the deep structural characteristics and dynamics processes in the study area are analyzed from the perspective of gravity mechanics. Results: The Bouguer gravity anomaly in the focal area and its adjacent areas is a negative anomaly, and the variation range is between –170-–530 mGal. The tectonic movement in the upper and middle crust of this region is active, and a complex phenomenon of high-density and low-density bodies appears inside the crust. This area is in an arc-shaped gravity gradient belt between the Alxa block, Ordos block and the Tibetan Plateau block. The calculation results show that the Tibetan Plateau material migrated eastward under the influence of plate collision and was deposited after being obstructed by the Alxa block and Ordos Basin. Conclusions: The largescale motion adjustment caused by plate movement and the interaction between the deep and shallow parts of the crust have contributed to the frequent earthquakes in this region.