3-D Crustal Shear Velocity Structure and Azimuthal Anisotropy of the Taiwan Strait and Fujian, SE China

Abstract:

The southeastern margin of China is located at the oblique convergence zone of the Eurasian (ES) plate and the Philippine Sea (PS) plate, which is a typical model in the trench-arc-basin system. The crescent shape of thrust wedge, the mountains in Taiwan, and the different strike angles of this wedges in north and southeastern Taiwan reveal complex tectonic evolution as well as collision and subduction mechanisms. Previous studies have shown that the PS slab has subducted under the ES plate along the Ryukyu trench in the north area of Taiwan. But in the south, the ES plate is subducted under the PS slab. Little work has been done in the region of Taiwan Strait especially the pattern of crustal and upper mantle anisotropy. The dynamic process in this region has been a controversy for a long time. In this study we use about 50 broadband stations (2008) located in Fujian province of mainland China and Taiwan to invert for 3-D shear velocity structure and azimuthal anisotropy in the crust and uppermost mantle in this region from ambient noise tomography in the period band of 5-40 s. The lateral resolution of the 3-D model is about 100 km. Our results reveal a high crustal S-velocity anomaly in the strait and a rotational pattern of crustal azimuthal anisotropy around the strait with SE-NW fast direction in the center of the strait. The fast polarization axes are mainly along NE-SW direction in the central Fujian. The preliminary results are important for understanding the mechanisms of material flow and crustal deformation in the margin of ES plate.