关键词: 小震重定位, 活动构造, 双差定位法, 活动断裂, 北京及其邻区

Abstract: We relocated 11796 small earthquakes occurred from 2002 to 2015 in Beijing and its adjacent areas (38°~42°, 113°~120°E). By using the double-difference algorithm, we obtained 9 311 relocated earthquakes. Combined with geological-tectonic characteristics, we analyzed the relationship between spatial distribution characteristic and active tectonics, as well as the revealed tectonic information. The results show that the earthquake relocation has been significantly improved the accuracy of the original location. The focal depth is mainly distributed in 6~16 km. It indicates that the seismogenic layer is mainly located in the upper and middle crust, and the depth of the plain area is deeper than that of the bedrock area. The geographical distribution of small earthquakes is clearly controlled by active tectonics, which are mainly distributed in the Zhangjiakou—Bohai Tectonic Zone, Shanxi Tectonic Zone and North China Plain Fault Depression Zone in late Quaternary active faults, and along the fault zone or different directions of active fracture intersection area is linear or planar distribution. The activity of the fault zones obviously reflected by the small earthquakes activity, for instance, Chenggezhuang—Xiadian—Gu′an fault zone, Tangshan—Cangdong fault zone and the piedmont fault zone of Taihang Mountain, etc. They exhibit prominent segment activity, respectively. To a certain extent, the distribution of small earthquakes can reveal the fault dip, dip angle and extension. The NW trending buried active fault zone may exist along the line from the Erlichangshan fault to the Jiyunhe fault, the NNE—SSW trending active fault may exist in the Wen′an area, and Yongding River fault may extend to the southeast direction and to the Langfang inner plain area.

Key words: Small earthquake relocation, Double-difference algorithm, Active tectonics, Active fault, Beijing and its adjacent area