三峡水库蓄水后等效应力场的数值模拟和胡家坪MS4.1地震的孕震机理*
吴建超1,2,陈蜀俊1,2,蔡永建1,2,李 恒1,2,雷东宁1,2,余 松1,2,

(1.中国地震局地震研究所,湖北 武汉 430071; 2.武汉地震工程研究院,湖北 武汉 430071; 3.吉林省有色金属地质勘查局607队,吉林 长春 132105)

有限元; 数值模拟; 等效应力场; 梯度带; 三峡水库

Numerical Simulation of Equivalent Stress Field after the Impoundment of the Three Gorges Reservoir and the Seismogenic Mechanism of Hujiaping MS4.1 Earthquake
WU Jian-chao1,2,CHEN Shu-jun1,2,CAI Yong-jian1,2,LI Heng1,2,LEI Dong-ning1,2,YU Song1,2,QIAO Yue-qiang1,2,CHEN Zi-hua1,LIU Fan-zhen3

(1.Institute of Seismology,CEA,Wuhan 430071,Hubei,China)(2.Institute of Earthquake Engineering in Wuhan,Wuhan 430071,Hubei,China)(3.Group 607 in Nonferrous Metals Geological Exploration Bureau of Jilin Province,Changchun 132105,Jilin,China)

finite element; numerical simulation; equivalent stress field; gradient zone; Three Gorges Reservoir

备注

利用有限元方法,在三峡水库172 m试验性蓄水后发生胡家坪MS4.1地震的大背景中,建立了三峡库首区三维线弹性有限元模型。计算得到了172 m水位相对于蓄水前库首区地壳8 km深度处的等效应力场,与该地区同期流动重力场异常分布特征基本一致。在此基础上,将蓄水后等效应力场的变化与胡家坪MS4.1地震对比后发现,本次地震发生在等效应力递增区与递减区的梯度带上。分析认为,这样的地段等效应力变化明显,是应力应变积累和构造活动强烈的部位,加之处于仙女山断裂的北端段,容易促

Using finite element method,we established a 3D linear elastic finite element model of the head area of the Three Gorges Reservoir after the Hujiaping MS4.1 earthquake occurred after the 172 m level experimental impoundment.Then we calculated and obtained the equivalent stress field under 172 m water level and that in 8 km depth in the head area of the Three Gorges before impoundment,which are consistent with the distribution characteristics of contemporaneous flowing gravity field abnormality in this area.On this basis,we compared the equivalent stress field changes after the impoundment with the Hujiaping MS4.1 earthquake,and found that this earthquake occurred in the gradient zone between the increasing zone and decreasing zone of the equivalent stress.We analyzed that the equivalent stress varied distinctly in the gradient zone,where the stress and strain was accumulated and tectonic activity was intense.In addition,the gradient zone is located in the north section of the Xiannushan Fault,which is easy to make fault instable and move to induce the seismic activity.