龙门山断裂带南段横波分裂分析

基于2009年1月—2015年4月芦山地震震源区 (龙门山断裂带南段) 大量地震的双差重定位结果，对固定台站 (BAX, MDS, TQU) 和流动台站 (L131, L132, L134, L135) 周围处于横波分裂窗内的地震记录进行了横波分裂分析.研究结果表明:除台站TQU外，其它台站的快波偏振优势方向与龙门山断裂带的走向基本一致；台站TQU处于前山断裂与一条SE向断裂的交汇处，其偏振方向具有一定的方位性，表明SE向断裂可能是导致台站TQU快波偏振优势方向偏离的原因之一.各台站位于1角区 (入射射线与裂隙面夹角为15°—45°的双叶区域) 和2角区 (入射射线与裂隙面夹角为0°—15°的区域) 的归一化时间延迟结果显示，除台站L135由于缺少震后持续数据外，其余6个台站在1角区内的归一化时间延迟在芦山地震主震后均逐渐减小.另外，从BAX, MDS, L134, L131这几个台站的玫瑰图中可见，芦山地震后快波偏振矢量发生了90°翻转现象，说明各向异性孔隙弹性 (APE) 理论在该研究区的适用性，即该理论可用于监测研究区的区域应力场变化. 

Shear-wave splitting on southern segment of Longmenshan fault zone

The database used in this paper, which is from the earthquake catalog during the period from January of 2009 to April of 2015, has been relocated by double-difference method. Then shear wave splittings recorded at permanent stations BAX, MDS, TQU, and mobile stations L131, L132, L133, L134, L135 on southern segment of Longmenshan fault zone have been analyzed. The results show that, except the station TQU, the preferential directions of fast wave polarization of all the studied stations are parallel to the strike of Longmenshan fault zone, which is similar to previous studies. Moreover, the polarization of station TQU, which is located at the juncture of Qianshan fault and a SE-strike fault, shows an azimuth distribution, suggesting that the SE-strike may be one of the causes of different preferential direction at the station TQU. Then the database was divided into band 1 (double-leafed solid angle between 15° and 45° of ray path with the average crack plane) and band 2 (solid angle within 15° of ray path with the average crack plane). The results show that the normalized time-delays in band 1 have a decreasing trend after the Lushan earthquake except the station L135. 90°-flips in shear-wave polarizations after Lushan earthquake at the stations BAX, MDS, L134 and L131 confirmed the validation of APE (anisotropic pore-elastic) theory, which is applicable to monitor the variation of local stress field in the studied region.