Gravity inversion for deep crust-mantle interface in Three Gorges region

In order to better understand the fluctuation of deep crust-mantle interface in Three Gorges region, we performed the gravity inversion by using Parker-Oldenburg iterative inversion method. During the inversion, we used the existing map of Three Gorges complete Bouguer gravity anomaly(1:500000) and a new map of Three Gorges dam complete Bouguer gravity anomaly (1:200000), as well as results of deep seismic sounding and tomography. The inversion result shows that the Moho depth between Badong and Zigui is about 42 km, the depth of middle crustal interface in Jianghan plain and its surrounding area lies in the range of 21—25 km, and the overall morphology of the deep interface and the surface geology presents an overpass-like structure. The middle crust beneath Three Gorges dam is about 9 km thick, being the thinnest part of the middle crust in this region, which is possibly related to the shallow low-density body in Huangling anticline area. Earthquakes always occur in the upper crust, so there exists close relationship between seismic activity and deep crust-mantle interface fluctuation. For example, the Zigui M_S5.1 earthquake took place in the place where the gradient changes of Moho and middle crustal interface were most significant, indicating that deep structure has important effect on regional seismic activity.