Body Wave Study Of Crustal And Upper Mantle Velocity Structure In South China

The southern part of China is in the place where Eurasian Plate,Indian OceanPlate and Pacific Ocean Plate piece together,being the front edge of the SoutheasternEurasian Plate,it is the most active area of crustal and upper mantle activation inEurasian Plate.Besides,the South China Block plays an important role in the Eurasianand even the World plate pattern，so learning the three-dimension velocity sturcture inthis area is quite meaningful for the tectonic history and dynamic background ofSouth China Block and other Blocks around.The seismic data we use in this study is selected from China Earthquake DataCenter, China Earthquake Networks Center (CENC) and International SeismologicalCenter (ISC),finally we got32104and33403proper events in the local region forP&S respectively,and picked up433201P arrivals,406041S arrivals for the seismictomography within12°N～36°N，100°E～124°E,down from10km～120km.Thefollowing part is what we learned from this study of1°×1°three-deminsion velocitystructure in crustal and upper mantle with four profiles:The thickness of Songpan-Ganzi Block in the west of Longmen-Shan Fault ismuch bigger than the Sichuan Basin,in where the thickest part could be60km,andmaterial partial melting could be observed in the lower curst;the low velocity anomalyemerge in the lower crust of Sichuan Basin could have some relationship with plasticdeformation;and the motion and velocity structure in crust and upper mantle ofSichuan and Yunnan is controlled by the important local faults:XianshuiheFault,Anninghe Fault,Xiaojiang Fault,Chenghai-Ailaoshan-Redriver Fault,the crustalmaterials escape from Tibet Plateau move to the southeast along these faults.The distinct low velocity anomaly in crust lying in the coastal area of Southeastand South China could caused by the upwelling mantle material,but some high velocity anomaly happen beneath Nanling and Wuyi region might show thecharacteristic of intracontinent collision orogen in South China,and the low velocityanomaly beneath Moho layer in Hainan Island could be seen as the proof of plume.The comprehensive exist of hot fluid activity under Taiwan and Luzon regionwhich caused by the subduction of Eurasian Plate and Philippine Sea Plate lead twovelocano arc between Taiwan Island and Luzon Island arc,the subduction make thecrust grow thick and mountine uplift in Taiwan meanwhile cause the low velocityanomaly beneath Luzon Island arc,and the asthenosphere upwelling cause the lowvelocity anomaly in the Northeast of Taiwan.