Pn Wave Velocity and Anisotropy in the Yellow Sea and Adjacent Region

Abstract

AbstractUsing arrival times from the 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 geology and 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 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 the large scale sinistral shearing of the Tan‐Lu fault zone in eastern China and the northward motion of the Yangtze block in the southern Yellow Sea.