梯级水坝的地震触发级联效应:以溪洛渡和向家坝水库为例

Cascade effects of triggered earthquakes of cascade dams:Taking Xiluodu and Xiangjiaba reservoirs as examples

本文研究了溪洛渡和向家坝水库蓄水后的级联效应对周围应力场的扰动,建立了梯级水库联合蓄水的三维孔隙弹性耦合模型,应用有限元方法计算孔隙压力场、弹性应力场和断层上库仑应力的变化.结果表明:(1)震群的时空分布与孔隙压力增加的区域存在明显的一致性;(2)水库蓄水在2014年4月永善M_(L)5.1地震和8月永善M_(L)5.2地震震源处造成的ΔCFS分别为:0.67 kPa和10.87 kPa,说明蓄水对两者具有促进作用,且对后者促进作用更为明显;(3)溪洛渡蓄水引起的弹性应力场变化在前期对向家坝库尾地震具有一定的触发作用,但向家坝水库蓄水增加的孔隙压力占据主导作用,孔隙压力变化可达1.0 kPa;(4)库区内烟峰断层南段和莲峰断层中段地震危险性增大,而玛瑙断层受水库蓄水的影响较小.

This study investigates the perturbations of the surrounding stress field caused by the cascade effect of Xiluodu and Xiangjiaba reservoirs after impoundment and a three-dimensional pore-elastic coupling model of the impoundment of cascade reservoirs are established.The finite element method calculates the pore pressure field,elastic stress field,and variation of Coulomb stress on local faults.The results show that:(1)The spatial distribution of the earthquake cluster is obviously consistent with the area where the pore pressure increases;(2)TheΔCFS at the epicenters of the April 2014Yongshan M_(L)5.1earthquake and the August 2014Yongshan M_(L)5.2earthquake imparted by the reservoirs are:0.67kPa and 10.87kPa,respectively,indicating that impoundment promotes these two earthquakes at different levels,and the latter is more significant;(3)The elastic stress field change imparted by the impoundment of Xiluodu reservoir has an impact on the Xiangjiaba reservoir in the early stage.However,the earthquakes between two reservoirs are possibly triggered by the latter.The Xiangjiaba reservoir increases the pore pressure in its upstream part by 1.0kPa;(4)The impoundment of the reservoirs increases the seismic risk of the southern section of the Yanfeng fault and the middle section of the Lianfeng fault,while the Manao fault is less affected.