Spatial distribution of shear wave splitting of the upper crust in the central South China block

Seismic anisotropy of the upper crust beneath the eastern of south China block has been studied by shear wave splitting analysis of local earthquakes recorded by the HN Array and the National Seismic network. The dominant fast directions at majority stations are nearly east-west direction, which are basically consistent with regional maximum compressional stress. Combined the upper crustal anisotropy for North China Block, this study inferred that the westward subduction of the western Pacific plate and Philippine plate is the essential tectonic setting of the upper crust anisotropy in eastern China, which showed the east-west direction of tectonic stress. The obvious regional difference of polarization direction beneath Sulu-Dabie orogenic belt and Jiangnan orogenic belt revealed the complicated characteristics of crustal structure and stress distribution under the interaction between sub-blocks. This study suggested that the complex patterns of upper crustal anisotropy may be attributed to diversity of tectonic features. The seismic anisotropy of Jianghan basin revealed the multi-scale stress field in the sedimentary basin. Moreover, the rock composition contributes to the seismic anisotropy of upper crust. The widely distributed metamorphic rocks in the east of the Cathaysia block lead to obvious differences of the polarization between the east and west Cathaysia blocks.