紫坪铺水库附近都江堰震群小震震源机制解分析

2008年2—4月，位于汶川大震初始破裂点的紫坪铺水库附近发生了一系列的小震活动，它们与汶川地震和紫坪铺水库小震的关系值得研究。本文采用CAP方法，反演了紫坪铺水库7个专用数字地震台站的数据，得到震级大于M_L 1.0的28个震源机制解。结果表明:有19个地震事件集中在紫坪铺水库东南方向的都江堰附近，最大地震为逆冲型，发震机制为逆冲型带走滑分量，少量带正断层分量；从深度剖面看，地震震源深度主要集中分布在地下13km附近区域，都江堰震群丛集在前山断裂带上，其它地震散布在中央断裂带上；发震最大主压应力方向随时间的变化具有从最大主压应力方向变化比较大到趋向一致的演化过程。这些现象说明龙门山断裂带在都江堰附近存在1个凸凹体，形成应力集中点，引发都江堰震群活动，由此迫使龙门山断裂带前山断裂发生逆冲性活动，从而加剧了龙门山断裂带中央断裂的活动，在一定程度上加速了汶川地震的发生。

Analysis on Mechanism of Dujiangyan Earthquake Swarm in the Vicinity of Zipingpu Reservoir

A series of small earthquakes occurred in the vicinity of Zipingpu Reservoir at the beginning of the Wenchuan earthquake from February to April, 2008 and their relationship with the Wenchuan earthquake and the small earthquakes of the Zipingpu reservoir is worth studying. In this paper, the digital seismic data of seven special seismic stations of the Zipingpu reservoir are analyzed by using the CAP method, and 28 focal mechanisms with magnitude greater than M_L1.0 level are obtained. The results show that 19 of these earthquakes are concentrated in the southeast of the Zipingpu Reservoir near Dujiangyan, in which the maximum earthquake is the thrust type, and the others are thrust with strike-slip and normal faulting. The focal depth of the earthquake is mainly distributed at the area above 13km depth, and the Dujiangyan earthquake swarm is concentrated in the front mountain fault zone, the other earthquakes are scattered on the central fault zone. In the change of the maximum main compressive stress direction over time, the change from the maximum main compressive stress direction is great and the trend is consistent. These evidences suggest that there is a convex and concave body in the Longmen mountain fault zone near Dujiangyan, which forms the stress concentration area. When the Dujiangyan earthquake swarm occurred to force the thrust of the Longmenshan fault, it intensified the activity of the central fault of the Longmenshan fault zone and accelerated the occurrence of the Wenchuan earthquake to some extent.