High-resolution Vs tomography of South China by joint inversion of body wave and surface wave data

Abstract

To take advantage of complementary strengths of earthquake body wave data and surface wave data from both earthquake and ambient noise sources, we have jointly used them to determine a high-resolution 3D Vs model of the lithosphere in South China by the joint inversion algorithm of Zhang et al. (2014). For body wave data, we assembled P- and S-wave arrival times for 40,028 earthquakes during the period of 2008/10–2018/06 recorded by 676 stations in South China. For surface wave dispersion dataset, it includes Rayleigh wave phase velocity maps at periods of 8–70 s and group velocity maps at periods of 8–50 s from Shen et al. (2016). Due to the complementary strengths of the two data types, the resolution of the jointly inverted Vs model has improved compared to the separately inverted models. The joint inversion model can also fit both data types at a similar level compared to separate inversions. In comparison with previous models, the new velocity model better delineates the sedimentary basins in the shallow crust and high velocity root in the lithosphere beneath the Sichuan basin, as well as better resolves the velocity variations between western and eastern Yangtze craton, thin lithosphere beneath eastern Yangtze craton and Cathaysia block, and helps us to better understand the mechanism of the lithosphere thinning. From the correlation between high velocity anomalies in the middle crust and the distribution of Neoproterozoic basalt samples, we propose the amalgamation suture between the Yangtze craton and Cathaysia block is along the eastern segment of the Jiangshan-Shaoxing fault and the west margin of the Jiangnan orogen volcanic rocks. Our new joint inversion model is useful for constructing a community velocity model and for better understanding the complex tectonics of the South China block.