FOCAL MECHANISM OF KEY MONITORING AREA OF THREE GORGES RESERVOIR BEFORE AND AFTER IMPOUNDMENT
三峡水库重点监视区蓄水前后震源机制研究

By use of the data from digital telemetered seismic network of induced earthquake monitoring system in the Three Gorges area from 2000 to 2006,the focal mechanisms in key monitoring area of the Three Gorges reservoir are calculated.The results show that the focal mechanism parameters of earthquakes before impoundment are strike-slip-reverse fault, the maximum horizontal principal compressive stress is near EW while P axis elevation is small,i.e. P axis is near horizontal,it is consistent with the regional principal compressive stress; the focal mechanism parameters of earthquakes after impoundment are strike-slip-normal,P axis elevation is near vertical,the directions of maximum horizontal principal compressive stress axis are mussy and are not controlled by regional principal compressive stress.This state implies that the complex focal mechanisms may be correlated with the complex seismogenic mechanisms of the induced earthquake.