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.