云贵高原东南部地壳各向异性初步研究

Crustal Anisotropy in the Southeast of the Yunnan—Guizhou Plateau,China

云贵高原东南部地区位于贵州西南部及广西西北部。我们选用中国地震科学台阵一期在广西、贵州区域内的50个流动台站记录的2011年6月至2013年3月的地震波形资料,运用剪切波分裂系统分析方法(SAM),得到了可用于分析的10个台站地震资料,获得剪切波分裂参数即快剪切波偏振方向和慢剪切波时间延迟。结果表明,云贵高原东南部地区的地壳各向异性呈现南北分区的特点。广西西北部地区的快剪切波优势偏振方向为NW—SE,与华南地块主压应力方向一致。贵州西南地区位于扬子板块和华南褶皱系右江褶皱带的过渡带,其快剪切波优势偏振方向近NE—SW,与华南地块主压应力方向近似垂直,反映出区域内复杂的构造背景及应力环境。将云贵高原东南部慢剪切波时间延迟与川滇地块以及华夏地块东南部对比可知,云贵高原东南部地壳介质各向异性程度更接近于华南地块。

Using seismic data recorded by 50 stations of the China Seismic Array during June 2011 to March 2013 in the study area which located in Southwestern Guizhou and Northwestern Guangxi, we got 10 seismic stations for data analysis by the shear-wave splitting snalysis method （SAM）, and obtained shear-wave splitting parameters beneath the Southeastern Yunnan--Guizhou Plateau, which are the polarization of fast shear waves （PFS） and time delay of slow shear-wave. The results show that there is an apparent difference in the northern and southern areas. The PFS in Northwest Guangxi is NW-- SE, which is consistent with principal compressive stress of the South China block. South- west Guizhou is located in transitional zone of Youjiang fold belt of South China fold sys- tem and Yangtzi plate, the PFS in this area exhibits NE--SW direction, which is perpen- dicular to principal compressive stress of the South China block and probably affected by a series of north-east trending faults in this place. It also shows that southwestern Guizhou has a complex regional principal compressive stress and local geological structure. By com- paring the time delay of slow shear-wave in southwest Yunnan--Guizhou plateau with Si- chuan--Yunnan block and southeastern Cathaysia block, the crustal seismic anisotropy in Southwest Yunnan-Guizhou Plateau is similar to the South China block.