A study of seismic anisotropy of Wenchuan earthquake sequence

Using seismic data of the aftershock sequence of the 2008 Wenchuan earthquake recorded by seismic stations in the seismic source and circumjacent areas, with the systemic analysis method of shear-waves splitting, this paper analyzes the anisotropic characteristics in the crust along and around the Longmenshan fault belt, where occurred the Wenchuan earthquake, and obtains the directions of the principal compressive stress field in the crust and their spatial distribution. The results show the following spatial difference: approximately taking Anxian area as a boundary, the polarization directions of fast shear-waves at stations located at the northeast segment of Longmenshan fault belt are in the northeast direction, consistent with the strike of the faults. However, the polarization directions of fast shear-waves at stations located at the southwest segment are in the northwest direction, which is perpendicular to the strike of the faults. This Pattern also indicates that the southwest segment of the Longmenshan fault is a thrust fault, and the northeast segment a strike-sill) one. In this study, the Polarization directions of fast shear-waves are scattered at stations near the intersection area of the Xianshuihe fault, the Longmenshan fault and the Xiaojiang fault. It may be attributed to the local complex geology structure around the seismic source area, and is consistent with the characteristic of the complex direction of the principal compressive stress in this zone.