Characteristics of shear-wave splitting for the 2013 Lushan M_S7.0 earthquake sequence

This paper measured the shear-wave splitting parameters, the polarization direction of fast shear-wave and the time delay of slow shear-wave, by using the seismic data recorded by the stations in the focal region and its adjacent areas of the M_S7.0 Lushan earthquake on April 20, 2013. And then the shear-wave splitting results from 40 seismic stations were obtained, which indicates the crustal anisotropy in the studied area. The results show that the dominant polarization directions of fast shear-waves are in NE in the rupture zone, which is consistent with the strike of the major axis of aftershocks distribution. The dominant polarization directions of fast shear-waves in the west of Shuangshi--Dachuan fault are in NW in agreement with the directions of the regional principal compressive stress. And the dominant polarization directions of fast shear-waves, near Yingjing fault are in NW, which is consistent with the strike of Yingjing fault. It is also shown that the dominant polarization directions of fast shear-waves at the stations TQU and BAX around the rupture zone are in NE direction before the main shock, and the dominant polarization directions at the station TQU are almost in EW after the main shock, and the variation of polarization directions before and after the main shock is not obvious at the station BAX, which indicates the polarization directions of fast shear-waves are controlled by Longmenshan fault zone before the main shock, and mainly affected by tectonic stress field after the main shock. Furthermore, the time delay of slow shear-wave is in the range of 1.25—5.40 ms/km for all the stations, but more than 3.0 ms/km in the region with dense aftershocks coverage, reflecting strong anisotropy in the source area. After the main shock, the delay time decreased continuously, suggesting the stress field became stable gradually in the source region.