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利用有限元方法,在三峡水库172m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172m水位相对于蓄水前库首区地壳8km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,容易促使断裂失稳错动而引发地震活动。
Using the finite element method, a three-dimensional linear elastic finite element model of the Three Gorges Reservoir Area is established in the background of the Hujiaping MS4.1 earthquake occurring after the 172m impoundment of the Three Gorges Reservoir. The equivalent stress field of the 172m water level relative to the depth of 8km crust in the first reservoir area before the impoundment is calculated, which is basically consistent with the anomaly distribution characteristics of the flow gravity field over the same period. On this basis, comparing the change of equivalent stress field after water impounding with that of Hujiaping MS4.1 earthquake, it is found that the earthquake occurred on the gradient zone of increasing and decreasing area of equivalent stress. The analysis shows that the obvious change of equivalent stress in such a lot is the site where the stress and strain accumulate and the tectonic activity is strong. In addition, the northern tip of the Xiannushan fault can easily lead to the fault instability and lead to the earthquake activity.