云南地区地壳介质各向异性——快剪切波偏振特性

SEISMIC ANISOTROPY OF THE CRUST IN YUNNAN,CHINA:POLARIZATIONS OF FAST SHEAR-WAVES

通过对云南遥测地震台网2000年1月1日—2003年12月31日4年资料的分析,使用剪切波分裂SAM综合分析方法,获得了云南地区10个数字地震台站的快剪切波偏振结果.结果表明,云南地区大部分台站的快剪切波偏振优势方向主要为近N—S或NNW方向;位于活动断裂上的台站的快剪切波偏振优势方向与活动断裂的走向一致;与GPS主压应变方向一致,与区域主压应力方向基本一致;少数台站的快剪切波偏振较为复杂,或与活动断裂的走向及GPS主压应变方向不一致.这样的台站总是位于几个断裂的交会处,反映了复杂的断裂背景和复杂的应力分布特征.快剪切波偏振优势方向代表了原地最大主压应力方向,受到区域应力场和断裂分布等多种因素的控制.

Using January 1, 2000 seismic data recorded by Yunnan Telemetry Digital Seismic Network from to December 31, 2003, the dominant polarization directions of fast shear-waves are obtained at 10 digital seismic stations in this study, which adopts SAM technique, a systematic analysis method on shear-wave splitting. The results show that domi nant directions of polarizations of fast shear-waves at most stations are mainly at nearly N -S or NNW direction in Yunnan. The dominant polarization directions of fast shear-waves at stations located on the active faults are consistent with the strike of active faults, consistent with directions of regional principal compressive strains measured from GPS data, and basically consistent with regional principal compressive stress. Only a few of stations show complicated polarization pattern of fast shear-waves, or are not consistent with the strike of active faults and the directions of principal GPS compressive strains, which are always located at junction of several faults. The result reflects complicated fault distribution and stress field. The dominant polarization direction of fast shear-wave indicates the direction of the in-situ maximum principal compressive stress, which is controlled by multiple tectonic aspects such as the regional stress field and faults,