青藏高原东北缘地壳各向异性及其动力学意义

Crustal anisotropy beneath northeastern margin of the Tibetan Plateau and its dynamic implications

利用中国地震科学探测台阵项目二期(ChinaArrayⅡ)81个台站的地震数据,使用时间域反褶积方法提取接收函数,挑选满足要求的高质量Ps震相,通过改进的剪切波分裂计算方法获取了53个台站共130对高质量各向异性参数对.地壳各向异性分析指出,研究区东南部地区地壳各向异性方向为NWW向,与XKS各向异性方向、GPS速度场三者近平行关系,说明该地区在青藏高原向欧亚大陆增生的过程中是一个耦合的连贯变形过程;位于研究区中、北部地区的地壳各向异性方向表现为NEE-SWW或E-W方向,与GPS速度场方向一致,而与XKS结果的偏振方向大角度相交,说明该地区受到青藏高原下地壳塑性管道流的影响,可能存在壳幔解耦作用.

We present anisotropy results using Ps phase in receiver functions, which are computed from the data of 81 seismic stations in northeastern margin of Tibetan Plateau. We use a modified automatic shear-wave splitting method to compute the anisotropic parameters using selected Ps phase. We would like to discuss about dynamic mechanism in this area using crustal anisotropy associated with the result of SKS-splitting and surface constraints like GPS velocity. The result can be summarized as follows. The large delay times imply that the crustal anisotropy is mainly derived from middle to lower crust rather than upper crust. In the southeastern part of the research area, crustal anisotropy agrees well with the result computed form SKS phase and GPS velocity directions trending NWW-SEE or E-W. This result implies a vertically coherent deformation in the area as the directions of crustal anisotropy trend to be perpendicular to the direction of normal stress. In the middle and north part of the research area, the fast polarization direction of crustal anisotropy is NEE-SWW or E-W, parallels the direction of GPS velocity, and differs from the direction of the result of XKS-phase. This result implies that decoupled deformation in this area is associated with middle to lower crustal flow.