三峡水库蓄水后全位移场变化的数值模拟

NUMERICAL SIMULATION OF TOTAL DISPLACEMENT FIELD CHANGE AFTER IMPOUNDMENT OF THREE GORGES RESERVOIR

利用有限元数值模拟方法,计算了三峡水库蓄水后全位移场的变化:蓄水至135 m水位后,出现了巴东、牛口、归州和新滩镇4个全位移极值区;172 m水位试验性蓄水后,4个极值区沿长江两岸范围进一步扩大,量值也有所增加。将蓄水后全位移场变化与同期地震活动对比发现,伴随135 m水位蓄水发生的4次ML≥2.5地震分布在高桥断裂南段与巴东极值区的交汇部位;172 m水位蓄水以来发生的14次ML≥2.5地震主要分布在巴东和新滩镇全位移极值区附近。分析认为,三峡水库蓄水造成上地壳表层全位移场的梯度带是垂向上强烈的剪切活动带,同时也是垂向剪应变能较大和构造活动强烈的地带,易于诱发水库地震。

Using the numerical simulation by finite element method, the total displacement field change after Three Gorges reservoir impounding was calculated. We found out that there four extreme areas of total displacement appeared as Badong, Niukou, Guizhou and Xintan town after the water level reached 135 m. When water level cuts and tries impoundment to 172 m, the four extreme areas further expanded along the Yangtze river and the values also increased. We contrasted and analyzed the seismic activity and the total displacement field changes after the reservoir impounding to 135 m, and found out that four ML≥2.5 earthquakes occurred in the intersection part of the south section of the Gaoqiao fault and Badong extreme area went with the 135 m water level impounding. 14 ME 2.5 earthquakes mostly occurred near the Badong and Xintan town total displacement extreme area, after the 172 m water level impounding. The analysis suggests that the gradient zone of total displacement field of the upper crust surface is the active strong shear belt in the vertical direction. It＇ s also the belt where the vertical shear strain energy is large and the tectonic activity is strong. It＇ s easy to induce the reservoir earthquake.