S-wave velocity structure of upper and middle crust beneath the Three Gorges reservoir dam and adjacent region

A 3-D S-wave velocity structure of upper and middle crust beneath the Three Gorges reservoir dam and in adjacent region was reconstructed by means of the seismic tomography using the absolute Sg-arrivals from the earthquakes observed by the Three Gorges seismic network. Main research results of the crustal structure are as follows.①The lithology of the Huangling anticline is highly solidified, with uniformity and integrity. Its buried depth is not less than 14 km. ②The rock strata of the Zigui basin are consistent with that of its marginal region, so their velocity structures are the same. The depth distribution and velocity structure characteristics of the Zigui basin and its adjacent areas depended on the intensity of the tectonic deformation.③The partially molten substances, located in upper and middle crust and intruded from upper mantle,mainly distribute beneath the Zigui basin, as well as nearby the Peishi region.④The crystalline basement was constructed inhomogeneously, its top and bottom boundary, and the basement thickness and corresponding velocity structure, show significant regional variation.⑤The velocity gradient zone is generally consistent with the gravitational gradient zone.