Near surface structure of the South China Block by ambient noise tomography

Previous research indicated that the South China Block is formed by the collision between the Yangtze Craton and the Cathasyia Block (e.g. Zheng et al. 2006). However, due to the lack of dense seismic array, details of the structure in the South China Block hadn't been well understood. Now by using two-years continuous recordings from July 2014 to June 2016 at 154 stations in South China, we can acquire high-resolution subsurface images and structural variations through ambient noise tomography. The study area is located between 112°E-120°E and 25°N-33°N. Surface waves extracted from ambient seismic noise are used to construct group velocity dispersion maps, and Rayleigh wave group velocity maps at short periods(8-40s) are calculated by inversion. Tomography results of 8-16s are well correspondent to the surface structure of the South China Block. Low-velocity structures such as Jianghan Basin, Subei Basin are clearly shown in velocity maps. The Rayleigh wave velocity near the Moho is approximately shown in tomography results of 20-25s. The high-velocity anomaly below the Jianghan Basin demonstrates that the Moho depth here is shallow. In contrast, the strong low-velocity anomaly below Subei Basin indicates a deep Moho depth. These results show the change of the Moho depth in the South China Block from west to east. Besides, according to the tomography results of 30-40s, there is a strong high-velocity anomaly block at southeast of the South China Block below the Moho, which may be a small intruded block. By using ambient noise recording from dense array, we get high resolution of crust and uppermost mantle structures in the study area, which can provide evidences for better understood of tectonic movement in the South China Block.