Crustal thickness and Poisson's ratios of South China revealed from joint inversion of receiver function and gravity data

Abstract

Crustal thickness and Poisson's ratio are two important parameters for understanding the crustal structure, composition, and deformation of the South China block. Due to the complicated crustal structure and poor signal-to-noise ratio of teleseismic data at dozens of stations in South China, the receiver-function H–κ stacking produces large uncertainty and deviation when estimating these two crustal parameters. In this paper, we improve the technique of the joint inversion of receiver function and gravity data and utilize it to improve the estimates of crustal thickness and Poisson's ratio in South China. We calculate the receiver functions of 245 permanent seismic stations from the teleseismic data recorded during 2013–2015 and then carry out the joint inversion on the receiver functions and the complete Bouguer gravity anomalies data. The joint inversion reduces the uncertainty of each single-method inversion and enhances the accuracy of estimation. Our results demonstrate that the crustal thickness, ranging 26.1–46.5 km, is large in the NW (38–46.5 km) and small in the SE (26–34 km) with a NNE-trending gradient zone along the line of Yichang–Jishou–Baise in central South China. The crustal Poisson's ratio, ranging 0.20–0.31, is high (0.28–0.31) in most of the northern South China, intermediate (0.26–0.29) around the eastern coastal area, very low (0.20–0.24) within the Jiangnan orogenic belt and around the southern coastal area, and slightly low (0.22–0.26) in other places. With the constraints of previous geological and geophysical studies, we suggested that the notable low-value belt of crustal Poisson's ratio (between the lines of Shitai–Jiujiang–Yiyang–Jishou–Baise and Shaoxing–Jiangshan–Pingxiang–Yongzhou–Guigang–Beihai) represents the possible suture zone between Yangtze and Cathaysia sub-blocks in South China during the Neoproterozoic.