黄海及其邻近地区的Pn波速度与各向异性

利用中国东部地震台网和ISC 报告1980~2004年的地震走时数据，反演了黄海及其邻近地区的Pn波速度和各向异性，根据岩石层地幔的横向非均匀性分析了区域地质构造的深部特点.Pn波速度的变化与区域地质构造有一定的对应关系，黄海地区上地幔顶部的P波平均速度较高，没有发现明显的低速异常，表明上地幔顶部不存在大范围的地幔扰动.速度异常的分布表明，南黄海东部和西部有可能分属于不同的构造块体，其间的分界大致对应于南北走向的黄海东部断裂带，具有相对较低的Pn波速度.边界东、西两侧的Pn波各向异性存在明显的差异：南黄海西部Pn波的快波方向以北东—北北东方向为主，反映了海区内部扬子块体向北运动产生的构造变形；南黄海东部Pn波的快波方向为南北方向，与黄海东部断裂带的走向基本一致，说明黄海东部和西部之间存在一个深达岩石层地幔的南北向转换边界.结合相关资料估计黄海东部断裂带在中生代时期发生了右旋走滑运动，以响应中国东部郯庐断裂带的大规模左旋剪切以及南黄海扬子块体的向北嵌入.

Pn wave velocity and anisotropy in the Yellow Sea and adjacent region

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.