长江三峡库区秭归杨林桥镇震群成因

The genesis of the Yanglinqiao small earthquake swarm, Zigui, Three Gorges Reservoir region

对三峡数字地震台网记录的2016年3—6月三峡工程库区秭归库段杨林桥镇小震群进行双差精定位,通过Snoke方法计算该震群中较大地震的震源机制解,并结合野外宏观调查等方法,分析震源参数的时空变化特征。结果表明:杨林桥镇小震群密集分布在2 km×3 km矩形范围内,有较明显的展布方向,但与邻近的仙女山断裂、九畹溪断裂和天阳坪断裂走向不一致;震群距长江干流超过10 km,与三峡水库无水利联系,无相关性;震群展布方向上有岩溶洞分布,且降雨丰富,初步判断成因类型为岩溶塌陷型。

The small earthquake swarm was recorded by the Three Gorges Digital Seismic Network during March and June, 2016. Analysis work such as double difference location, focal-mechanism solutions and field survey were carried out on larger events in order to determine source parameters and their spatiotemporal variation. The results indicate that the small earthquake events manly distribute in a 2 km×3 km area in Yanglinqiao, with an obvious spreading direction different from the strike direction of Xiannvshan fault, Jiuwanxi fault and Tianyangping fault. Besides, the small earthquake swarm locates more than 10 km away from stem stream of the Yangtze River, and has no water relation with Three Gorges Reservoir. Taking into consideration that there are karst caves distributed on the earthquake swarm distribution area and the rainfall is rich; the small earthquake swarm may attribute to karst collapse events.