云南地区SKS波分裂研究

A study on SKS splitting beneath the Yunnan region

根据云南数字地震台网和云南流动地震台网的台站，以及中国国家数字地震台网（CNDSN）腾冲台和昆明台，共计47个台站记录到的远震SKS波震相，计算了各个台站下方的各向异性，讨论并分析了各向异性层的深度、厚度、起因，进一步探讨了与青藏高原东南缘地区地球动力学有关的一些问题．从得到的结果来看，云南北部的各向异性的快波偏振方向呈南北向，逐渐过渡到南部的近东西向，整体来看，有一旋转的趋势．分析表明各向异性层主要分布于上地幔，时间延迟在0．58—1．88s，厚度在67，216kin之间．青藏高原存在垂直向隆升变形和东西向拉张变形外，地幔物质还向东南运移．

SKS shear waves recorded at 47 stations, which are located in Yunnan and involve Yunnan digital seismograph network, Yunnan temporary seismometer arrays, and China National Digital Seismograph Network （CNDSN）, are used to analyze the direction and extent of seismic anisotropy. Furthermore, some problems related to the dynamics of the Qinghai-Tibetan plateau are discussed. It is demonstrated that delay times vary from 0.58 to 1.88s and fast wave polarization directions are present at stations with nearly N-S in northern Yunnan and gradually rotate to W-E in southern Yunnan. The shear wave splitting is mainly due to the anisotropy in the upper mantle whose thickness is between 67km and 216km. It is possible that the collision of the India and Eurasia plates resulted in not only crustal thickening and subsequently the E-W extension beneath the Qinghai-Tibetan plateau, but also mantle material flow southeastward.