2014年10月云南景谷M_S6.6地震序列剪切波分裂参数变化研究

Study of the Change of Shear-wave Splitting Parameters of Jinggu M_S6. 6 Earthquake Sequence in October 2014

采用质点运动判别与偏振法相结合的方法,测定了2014年10月云南景谷MS6.6地震余震序列剪切波分裂参数,得到了4个台站的剪切波分裂参数。快波偏振方向结果显示,这4个台站的快波偏振优势方向均为北北东向和北东向,与区域主压应力轴方向和地表破裂方向一致。4个台站的慢波延迟时间分布在2.24~7.37 ms/km,距离主震震中较近的L5307台站的慢波延迟时间相对较大,这与该台站位于震源区有关。L5309台站在MS5.8强余震前观测到了地震前7天慢波延迟时间突然下降,MS5.9地震前10小时,该台站也观测到慢波延迟时间的突然下降,直到地震发生。由此可见,MS5.8和MS5.9两次强余震发生之前慢波延迟时间都突然下降,表明较大地震发生之前地壳应力的突然增强。

This paper computed the shear wave splitting parameters of aftershock sequence of Jinggu MS6.6,Yunnan in October 2014 with the method of the particle motion discrimination and polarization analysis,and contained shear wave splitting parameters at 4 seismic station.The results of polarization direction of fast shear wave show that the polarization directions of fast shear wave at 4 seismic stations are NNE and NE which is in agreement with the direction of the regional principal compressive stress and the surface fracture.The polarization direction results reflects the diction of regional stress field is NE.The delay time of slow shear wave is in the range of 2.24~7.37ms/km.And the value of the delay time of slow shear wave is large at the seismic station which is near from the epicenter of the mainshock.The results of the change in delay time show that the delay time at L5307 station decreases suddenly one day before the MS5.8 in 6th December.The delay time of slow shear wave still decreased before and after MS5.9 until 7th December.The delay time of slow wave at L5309 station increased before the MS5.8strong aftershock,and decreased suddenly 7 days before the MS5.8 earthquake.The delay time also decreased 10hours before MS5.9 earthquake.Therefore,the delay time of slow shear wave decreased before MS5.8 and MS5.9strong aftershocks,indicating the crustal stress released suddenly before the big earthquakes.