云南小湾水库蓄水后P波速度结构的双差地震层析成像研究

P-wave Velocity Structure after the Xiaowan Reservoir Impounding by Double-difference Tomography

摘要:

联合小湾水库库区及其附近11249个地震的P波绝对到时、相对到时数据，利用双差地震层析成像方法反演得到小湾水库蓄水后2008年12月16日~2011年6月30日和2011年7月1日~2016年12月31日2个时间段内库区及其附近的地震重定位结果和三维P波速度结构。结果表明，蓄水后黑惠江段和小湾水库回水澜沧江段地震的增多与水库蓄水有关。由于水体渗透导致孔隙压变化，并随着时间的推移孔隙压变化朝着更深的部位扩散，地震震源深度也随之向深部扩散，进而导致介质变化和P波速度降低。蓄水回水至澜沧江保山段后该区域地震增多，P波速度下降，库水渗透作用为主控因素，该区域地下一定深度的地质构造有利于库水的快速渗透。初步判定2015年10月30日云南昌宁M_S5.1地震余震序列是与蓄水有关的柯街断裂上的构造地震。同时，也存在着与蓄水相关性不大的属于构造地震的活动，如云南施甸一带历来地震多发，施甸2010年6月1日M_L4.8、2012年9月11日M_S4.7地震序列均属于构造地震，与水库蓄水无关。

Abstract:

The Xiaowan reservoir is the leading reservoir of cascade hydropower station in the middle and lower reaches of the Lancang river,lying in an area of active tectonics. In this paper,we used both absolute arrival time and relative arrival time of 11249 earthquakes around the Xiaowan reservoir during two periods after impounding:December 16,2008 to June 30,2011 and July 1,2011 to December 31,2016,and with the double-difference seismic tomography method. Finally,we obtained the P-wave velocity structure and relocation of earthquakes in the Xiaowan reservoir area. We found that the increased earthquakes in the Heihuijiang river and backwater section of the Xiaowan reservoir are related to the reservoir impoundment. The pore pressure changes due to the infiltration of the water body,and the pore pressure changes to the deeper part with the change of time,which leads to the change of medium and the decrease of P-wave velocity. There are more earthquakes in the Lancang river after the return of water storage to the Baoshan section of the Lancang river. It causes the P-wave velocity to drop. Reservoir water infiltration is the main control factor. And the aftershock sequence of the Channing M_S5.1 earthquake on October 30,2015 is tectonic earthquake that is related to the water storage. At the same time,there is an activity which is not related to the water storage. The Shidian region always has earthquakes,which are tectonic earthquakes and have nothing to do with reservoir storage.