Pn wave velocity and anisotropy in the Yellow Sea and adjacent region
黄海及其邻近地区的Pn波速度与各向异性

Using arrival times from seismic stations in eastern China and the ISC earthquake report during 1980~2004,we inverted Pn wave velocity and anisotropy beneath the Yellow Sea and adjacent region.Deep features of regional geology and tectonics were discussed on the basis of lateral heterogeneity of uppermost mantle.Pn velocity variations are correlated with regional geological tectonics.Averagely,the uppermost mantle beneath the Yellow Sea region has fast Pn velocities,which implies a lack of apparent thermal activity in the upper mantle.Separated Pn velocity anomalies in the western and eastern Yellow Sea regions indicate that they are attributed to different tectonic blocks,and between these two regions there is a relatively slow Pn velocity zone,roughly corresponding to the N-S oriented eastern Yellow Sea fault zone.Moreover,strong anisotropy is observed in the eastern and western Yellow Sea regions.Pn anisotropy in the west shows an NE or NNE oriented fast direction,reflecting the tectonic deformation caused by the northward motion of the Yangtze block in marine areas.However,the fast direction of Pn anisotropy in the east is N-S oriented,parallel to the eastern Yellow Sea fault zone.It suggests an N-S oriented transform boundary in the uppermost mantle between the western and eastern Yellow Sea.We infer that the eastern Yellow Sea fault zone had a dextral shearing in Mesozoic time,responding to a large scale sinistral shearing of the Tanlu fault zone in eastern China and the northward motion of the Yangtze block in the southern Yellow Sea.