Crustal structure beneath South China revealed by deep seismic soundings and its dynamics implications

Since the 1970s, 57 DSS profiles have been carried out in South China. In this paper we collect all DSS profiles in South China, construct the 3-D crust velocity model in the region (100 degrees E similar to 125 degrees E and 18 degrees N similar to 34 degrees N) using robust 3-D Kriging interpolation method. We discuss the spatial distribution of Moho depth and Pn velocity in detail; analyze the relationship between average velocity and thickness in tectonic units; investigate the crust character and the subduction direction of Pacific plate to Eurasian plate. The results show that: (1) the average Moho depth of Yangtze block is about 40 km, the average crust velocity is 6.30 km/s, while the Moho depth of Cathaysia block is about 32 km, the average velocity is 6.24 km/s; (2) Sichuan basin has the same character as continental platforms in the world, Cathaysia block has the character of extended continent, Taiwan has the character of continental arcs; (3) the average Pn velocity is 8.02 km/s in Cathaysia block 7.98 km/s in Taiwan orogen, and 7.94 km/s in Yangtze block, including the fastest 8.02 km/s in Sichuan basin and the slowest 7.75 km/s in east Songpan-Ganzi. Chuandian area and east Songpan-Ganzi is relatively active, while Sichuan basin and Cathaysia block are steady; (4) the subduction direction of Pacific plate to Eurasian plate should be NW-SE.