2013年甘肃岷县—漳县M 6.6地震序列精定位研究

采用双差定位法对2013年7月22日甘肃岷县—漳县交界地区M 6.6地震及主震后48小时内388次余震序列进行重新定位,得到350个精定位地震数据。结果表明,余震优势展布以北东向较大倾角的铲状结构为特征,长约12 km,以主震为中心两侧对称分布;震源深度主要集中在4—10 km范围内,但余震震级由10 km左右深度的3—4级向3 km深度之上近地表的2—3级迁移变化;余震分布清晰呈现双层结构,较深层分布在4—10 km深度,而较浅层分布3 km深度之上,2层之间地震分布较少。分析认为,浅层地震可能为本次地震地表破坏较强原因之一。震源深度剖面显示,破裂面向NE倾斜,推测此次地震的发震断裂为临潭—宕昌断裂。

Precise relocation of Minxian-Zhangxian M6.6 earthquake sequence in Gansu Province, 2013

Applying the double-difference algorithm to the Minxian-Zhangxian, mainshock (M6.6) and its 388 aftershocks after 48 hours, Gansu on July 22 2013, we obtained 350 relocated earthquakes. Our results show that the aftershocks are shown as a shovel-shaped structure with a large northeastward dip extending for over 12 km long along the north-west direction and have an approximately symmetrical distribution about a center of the mainshock. The aftershocks are focused at depths of 4-10 km, but they migrate from about 10 km depth to above 3 km depth and their magnitudes range from 3-4 in a deeper layer to 2-3 in a shallower layer. The aftershocks show clearly a double-layer structure, one of which is at 4-10 km depth, while the other is above 3 km depth. There are few events between these two layers. The shallow earthquake layer could be one of causes that made a strong damage in the event. The vertical cross section of aftershock hypocenters shows a northeast tilt of the fault plane, suggesting that the seismogenic fault of this mainshock could be the Lintan-Diachang fault.