四川锦屏水电站地区的剪切波分裂参数变化

Changes of shear-wave splitting parameters in Jinping hydro-power station, Sichuan

通过分析四川锦屏水电站地区2012年1月至2013年12月库区的地震活动性和木里台的剪切波分裂参数变化,研究了水电站3次大规模蓄水对该地区地震活动性和地壳应力的影响.结果显示:经3次蓄水,该地区的地震活动呈持续增强趋势,最终保持在较高水平,尤其是第二次蓄水之后,地震活动增强最为明显;木里台的快剪切波偏振方向在锦屏水电站3次蓄水前后表现出明显的变化.锦屏水电站在蓄水之前,木里台快剪切波偏振方向的优势取向为北东向,与锦屏山—小金河断裂走向一致;第一次蓄水之后,快剪切波偏振方向则变得较为分散,无明显的优势取向;第二次蓄水之后,快剪切波偏振方向偏转为南东向;第三次蓄水之后,快剪切波偏振方向表现为一致的南东向;慢剪切波延迟时间在第二次蓄水前后明显变短.这些显著的变化说明了锦屏水电站第二次蓄水之后原地小范围内的地壳应力方向迅速改变,地壳应力也随着地震活动的增强而释放.

This paper focused on the influences on the seismic activity and the crustal stress caused by three water storages in Jinping hydro-power station,according to the seismic activity in Jinping hydro-power station and the change of shear-wave splitting parameters of the station MLI from January 2012 to December 2013. The results show that, after three water storages,the seismic activity in this region continued to increase,especially after the second water storage,and finally remained at a high level. Moreover, the polarization direction of fast shearwave at the seismic station MLI also showed significant changes before and after three water storages of the hydro-power station. Before the water storage of Jinping hydro-power station,the predominant polarization direction at MLI seismic station was northeast,which was in agreement with the strike of Jinpingshan-Xiaojinhe fault. After the first storage,the polarization directions are distributed scatteredly. After the second water storage,the predominant polarization direction changed to southeast. And the polarization directions showed the southeast consistently after the third water storage. As for the station MLI, the delay time of slow shear-wave has changed before and after the three storages of Jinping hydro-power station, especially after the second storage the delay time of slow shear-wave decreased obviously. Thus,the seismic activity,the polarization directions of fast shear-wave and the delay time of slow shear-wave changed significantly after the second water storage of Jinping hydro-power station,suggesting that the direction of crustal stress changed quickly in a small region after the second water storage,and the crustal stress also released with the enhanced seismic activity.