瀑布沟库区地震活动及应力场特征

Characteristic of seismicity and stress field of the Pubugou reservoir

摘要:

通过对瀑布沟水库和成都数字遥测地震台网记录的波形数据的研究发现，四川瀑布沟水库库区大量的所谓小震活动皆是爆破成因，从而改变了此前对该库区蓄水前地震活动密集，蓄水后地震活动骤然平静的认识。2009 年11 月水库蓄水后在蓄水区域周边10km 范围内仅发生ML1. 5 以上地震1 次，即2010 年8 月8 日ML1. 7 地震，蓄水前后小震稀少。水库西侧的2 个地震密集区的走滑型地震占较大比例，区域主压应力为NWW 向。水库东、北部区域的地震震源机制解呈多种类型。瀑布沟水库区小震活动总体受区域应力场控制，NWW 向近水平主压应力有利于库区NNW 向中小断裂发生走滑型错动。

Abstract:

By using waveform data from the Pubugou reservoir seismographic network and Chengdu digital telemeter seismographic network，we found lots of small earthquakes in reservoir area are results of explosions． The research has changed the previous understanding that seismicity level is higher before the impoundments rather than after． There was one earthquake with magnitude greater than ML1. 5 within 10km of water area of the Pubugou area after impoundment: ML1. 7 on August 8，2010． In fact，earthquake occurring before or after impoundment is rare． The proportion of strike-slip earthquakes is larger than others in the two clusters which are on the west of Pubugou reservoir，and the direction of principal compressive stress of these clusters is NWW． On the east and north of reservoir the focal mechanisms take on diversity． The small earthquake activity is totally controlled by region stress field，and NWW horizontal principal comprehensive stress may help generate the strike-slip rupture of moderate and small faults with direction of NNW．