北京及其邻区小震重定位与活动构造分析

摘要

使用双差定位法对北京及其邻区(38°～42°N,113°～120°E)范围内2002年1月～2015年1 2月的11 796个小震进行重新定位,获得9 311个重定位结果,结合北京及其邻区地质构造特征,分析了小震空间分布特征与活动构造的关系及其揭示的信息.结果表明:重新定位结果显著提高了原始定位结果的精度.震源深度主要分布在6～16 km,显示孕震层主要位于中上地壳,且平原区的震源深度比基岩山区深.小震的空间分布明显受活动构造控制,主要分布在晚第四纪活动断裂发育的张家口-渤海构造带、山西断陷盆地带和华北平原断拗区内,并多沿活动断裂(带)呈线状分布或在不同方向活动断裂交会区呈面状分布.小震活动可明显反映断裂(带)的活动性,如程各庄-夏垫-固安断裂带、唐山-沧东断裂带、太行山山前断裂带等均呈明显的分段活动性.小震分布在一定程度上也可以揭示断裂的倾向、倾角及其延伸展布情况.沿二十里长山断裂至蓟运河断裂一线可能存在地下贯通的NW向隐伏活动断裂带,过文安地区可能存在走向为NNE-SSW的隐伏活动断裂带,永定河断裂可能延伸至平原区内部,到达廊坊一带.%We relocated 11 796 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.