Discussion on shear-wave splitting of the June 24， 2012 Ninglang-Yanyuan M_S5.7 earthquake

On June 24 2012， an earthquake with M_S5.7 happened in the junction of Ninglang in Yunnan Province and Yanyuan in Sichuan Province. This paper chose the seismic data recorded by the station LGH from September 2008 to September 2013 to analyze shear-wave splitting of the Ninglang-Yanyuan M_S5.7 earthquake. The regional stress characteristics and the stress changes before and after the earthquake are obtained preliminarily from the change of shear-wave splitting parameters with time. The polarization results of fast shear-wave at the station LGH show that there are two polarization directions， i.e.， NE and SE， which are consistent with the strike of the faults in the studied area. There is a visible change in the delay time of slow shear-wave during the observational five years， especially before and after the M_S5.7 earthquake. One year before the earthquake， the delay time of slow wave slowly increased， suggesting the stress accumulation. Till one month before the earthquake， the delay time of slow wave decreases rapidly， indicating the stress in the crust releases rapidly with the earthquake occurrence.