卡里巴水库蓄水引起库区应力场变化影响分析

水库地震是近几年国际上地震学和地球动力学领域研究的热点问题。 作为世界上库容最大的卡里巴(Kariba)水库在其蓄水后库区地震活动性不断增加, 并于1963年9月23日发生M6.1地震, 是世界上公认发生过6级以上水库地震的四大水库之一。 对该水库蓄水引起库区应力场变化进行量化估算, 有助于对特大—大型水库蓄水后库区应力场变化及应力触发地震这一基础性科学问题的深入了解。 本文分别应用解析解和数值解方法对卡里巴水库蓄水引起库区弹性应力场、 不排水和排水孔隙压力变化进行了计算分析。 结果表明, 卡里巴水库蓄水引起M6.1地震震源处孔压变化为0.015~0.22 MPa, 库仑应力变化约0.03~0.17 MPa, 触发了此次地震的发生。

Stress Field Changes after the Impoundment of Kariba Reservoir

In recent years, reservoir induced earthquake (RIE) has drawn more and more attention in both the fields of seismology and computational geodynamics. Kariba reservoir is the world's largest reservoir by the volume of impoundment. After the impoundment of Kariba reservoir, there appeared seismicity around the reservoir region and an M6.1 earthquake happened in September 23, 1963, which is recognized as one of the four RIEs greater than M6.0 around the global. Therefore, it is a good example for quantitative assessment of the stress field changes induced by the impoundment of the large reservoir and investigation of the magnitude of stress changes that can trigger reservoir seismic activities. Adopting analytical solution and finite element method, we first calculated simultaneously the changes of elastic stress and undrained pore pressure induced by water load. After that, the drained pore pressure after the impoundment, which varies with the respect of time, was also introduced. Our primary results reveal that reservoir impoundment increases pore pressure and coulomb stress changes at the hypocenter of this major event. The value of coulomb failure stress changes is around 0.03~0.17 MPa and the pore pressure is about 0.015~0.22 MPa.