三峡水库重点监视区蓄水前后震源机制研究

FOCAL MECHANISM OF KEY MONITORING AREA OF THREE GORGES RESERVOIR BEFORE AND AFTER IMPOUNDMENT

利用2000～2006年三峡工程诱发地震监测系统数字遥测地震台网监测数据,对其水库重点监视区内震源机制进行了解析。结果表明,蓄水前震源机制为走滑-逆断性质,水平最大主压应力方向近东西向,P轴仰角较小,近水平,与区域主压应力一致;蓄水后震源机制为走滑-正断性质,水平最大主压应力方向各异,P轴仰角较大,明显不受区域应力场控制,这种现象可能与水库诱发地震成因机制的复杂性有关。

By use of the data from digital telemetered seismic network of induced earthquake monitoring in the Three Gorges area from 2000 to 2006, the focal mechanisms in key monitoring area of the Three Gorges system reservoir are calculated. The resuhs 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.