Shear Wave Splitting Analysis of the 31 March 2006 Qian'an M5.0 Earthquake Sequence

The Qian'an M5.0 earthquake occurred on March 31,2006 in the center of Songliao basin is the largest earthquake in the last 40 years in Jilin province.This paper analyzes shear-wave splitting using waveform data of Qian'an M5.0 earthquake sequence recorded by Lao-Yingtai station of Jilin Digital Seismic Network.The results show that the dominant polarization of fast shear wave is in NNE direction and does not consist with the maximum principal compression stress direction,which indicate that the earthquake is related with the region stress field adjustment.The time delay of shear wave splitting is 0.02s-0. 38s.After main shock,the time delay of shear wave splitting dropped apparently which may reflects the release of the principal compression stress.