Crustal P-wave velocity structure and layering beneath Zhujiangkou-Qiongdongnan basins, the northern continental margin of South China Sea
南海北部珠江口—琼东南盆地地壳速度结构与几何分层

Base on stack velocity spectrum dataset of 14 near-vertical deep reflection profiles in the Zhujiang River estuary-Qiongdongnan basin in the continental margin of northern South China Sea, we use Dix formula to transform the corresponding stack velocities into the crustal-layer-velocities (in TWT domain) and convert the layer velocities into the depth domain by time-depth transformation scheme. Integrating all the crustal velocity models, we analyze the spatial variation of P wave velocity in different depths and the stratified geometry of crust in the Yinggehai and Qiongdongnan basin area in the continent margin of northern South China Sea. The results demonstrate that the kinematic structure of Qiongdongnan basin can be divided into 4~8km thick sediment layer (Vp is 1.7~4.7 km/s), 4~10 km thick upper crust (Vp is 5.2~6.3 km/s), about 5 km thick normal lower crust (Vp is 6.4~7.0 km/s) and about 2~6 km thick anomalous lower crust with high velocity (>7.0 km/s). The existence of anomalous lower crust layer with high velocities >7.0 km/s can be considered as seismic signature of the underplating at the lower crust bottom induced by lithosphere extension in South China and its continental margin, or the residual mafic layer of the extended Cathaysia lower crust. Integrating the related geophysical sounding results, we construct the depth images of Moho and the lithosphere bottom across the continent of South China and the continental slope of South China Sea, which reveals the lithosphere thinning across continental South China and the continental margin of the South China sea.