向家坝水电站蓄水前后库区地震活动特征

对比向家坝库区蓄水前后地震活动特点，结合库尾段地震时序与库水位的变化关系及震中区地层岩性、构造特征等，认为发生在库尾段的地震属于构造型水库诱发地震。地震震中呈北西向密集条带状分布，虽然地表没有明显的控震构造，但不排除在2 km之下存在隐伏断层的可能。该区段位于马边-盐津断裂带的中段，水库蓄水前地震活动十分微弱，蓄水后发生不同于以往的地震活动。

Seismicity Characteristics of Xiangjiaba Reservoir Region before and after the Impoundment

We analyze the seismicity characteristics of Xiangjiaba reservoir region before and after the impoundment, as well as the relationship between the seismic sequence in the last segment and the reservoir water level, combined with the lithological and structural features of the epicenter area. We find that the earthquakes occurred in the last segment of Xiangjiaba reservoir are structural reservoir-induced earthquakes. These earthquakes are distributed in a NW direction. Although no obvious surface rupture zones are formed, there may be hidden faults 2 km below the surface. This area is located in the middle section of the Mabian-Yanjin fault zone, and shows very low levels of natural seismic activity prior to the impoundment of reservoir. However, after impoundment, the frequency and intensity of seismicity increased in this area.