Characteristic of S-wave Splitting of the 2017 Jiuzhaigou M_S7.0 Earthquake Sequence

This paper combination aspect ratio method and the polarization analysis method to measure the S-wave splitting parameters of M_S7.0 earthquake sequence occurred in Jiuzhaigou area, Sichuan Province: polarization direction of fast S-wave and the delay time of slow S-wave of the earthquake sequence. Finally, we got the S-waves splitting results at 6 stations, the results show: there are two dominant polarization directions (NNE and EW) of fast S-wave at stations L6202 in dense aftershock area. One month after the main-shock, with the stress release caused by aftershocks, the dominant polarization directions of fast S-waves at station L6202 adjusted from EW to NNE. Due to the complex geological structure of the area and the stress adjustment after the main shock, there is no obviously dominant polarization direction of fast shear waves at station L5111. The dominant polarization direction of fast S-waves is in NNE at station L5112, which is consistent with the strike of Minjiang fault. The dominant polarization direction of the fast S-waves is in NNE at station JZG, located in the eastern of the aftershocks dense area, which is consistent with the strike of Tazang fault. The dominant polarization directions of the fast S-waves are approximate EW, in agreement with the direction of the regional principal compressive stress, at stations L5110 and L5113 located in the southern of the aftershocks dense area. Furthermore, the time delay of slow S-wave is in the range of 1.2~5.0 ms/km. The time delay of slow S-wave at stations L6202 and L5112 is obviously more than at stations JZG, L5110, suggesting the stress accumulation in the dense aftershocks area is stronger than other area.