Crustal stress field in the focal area of M_S7.0 Jiuzhaigou，Sichuan，earthquake by shear wave splitting

This paper discussed the seismic activity in the focal area after Jiuzhaigou M_S7.0 （M_W6.5） earthquake on August 8, 2017, and calculated the shear wave splitting parameters by using the seismic waveform data from four temporary seismic stations in Jiuzhaigou area, then analyzed the characteristic change of crustal stress in the focal area. After the M_S7.0 Jiuzhaigou earthquake, the seismic activity was significantly enhanced in the focal area on August 8, 2017. Until after 22 August 2017, the seismic activity dropped slightly; correspondingly, the magnitude of the aftershocks also became smaller, concentrating below M_S2.0. The results of the polarization directions of fast shear wave at four seismic stations in the focal area show that the polarization directions are approximately east-west, which reveals the direction of the regional stress field in Jiuzhaigou area is approximately east-west. Meanwhile, the average value of the time delay of slow shear wave in the studied area is 5.04 ms/km, and after Jiuzhaigou earthquake the time delay of slow shear wave decreased, which reflects the release and adjustment of the crustal stress with the aftershocks occurrence. And thus the stress field in the crust tends to be stable at the end of August.