Abstract: The M_S5.6 and 6.1 earthquakes occurred on May 24th and 30th, 2014 in Yingjiang area, Yunnan Province, respectively. We measured the shear wave splitting parameters: the polarization direction of fast shear wave and the delay time of slow shear wave of the Yingjiang earthquake sequence by the combined method of the particle motion discrimination and the polarization analysis. Finally,we obtained the shear waves splitting parameters at 4 seismic stations. The results show the dominant polarization direction of fast shear wave is NS at stations KAC and MNO around the focal region, which is in agreement with the direction of the regional principal compressive stress. The polarization direction of fast shear wave at station MNO became in disorder and that of KAC deflected after the M_S6.1 earthquake. The average delay time of slow shear wave at the 4 stations is in the range of 1.50~4.47 ms/km. The average delay time is greater than 4.0 ms/km at stations KAC and MNO near the mainshock, which suggests the closer to the mainshock, the greater the degree of anisotropy. The delay time of slow shear wave reduced suddenly at station MNO before the M_S6.1 earthquake, implying the crustal stress released in the focal region before the mainshock.

Key words: Shear wave splitting, Polarization direction of fast shear wave, Delay time of slow shear wave, The 2014 Yingjiang M_S6.1 Earthquake Sequence