南海北部陆缘地震带的活动性与发震机制

Activity and triggering mechanism of seismic belt along the northern South China Sea continental margin

南海北部陆缘地震带是一条板内地震活跃带,对其进行研究对于华南沿海的防震减灾和南海北部的新构造活动研究具有重要意义。通过地震活动性分析发现,该地震带可以划分为闽南―粤东、阳江、雷琼3个地震活跃区和珠江口地震弱活动区。结合区域构造背景分析发现,印藏碰撞导致的华南地块往E―SEE向运动并且该区东侧菲律宾海板块高速向NW向运动是该地震带的主要构造背景;二者的高速碰撞以及华南地块与西南、南侧块体的挤压剪切产生了巨大的应变能,这些应变能通过区内的滨海断裂带与壳内低速层进行传递、调整。在受挤压、剪切影响强烈的东、西部区域,除了在NW向与NE向的小规模断裂交会部位形成小震密集区之外,还在NW向断裂与滨海断裂带的交汇区域产生应力、应变积累,引发大震、强震。而在中部受影响较弱的珠江口区域,局部断裂稀疏,因而未出现小震密集区,并且大震、强震空缺。

The continental margin seismic belt（CMSB） of northern South China Sea（SCS） is an active intraplate seismic zone. Research on the CMSB has significant importance in earthquake prevention and disaster reduction,and in understanding the neotectoics of the northern SCS.By seismicity analyzing,we suggest that the CMSB can be divided into seismically active zones of Southern Fujian-Eastern Guangdong,Yangjiang,and Leizhou-Hainan,and less active zone of the Pearl River area. The E-SEE-wards moving of South China（SC） block induced by the extrusion of Indo-Tibet collision,and the NW-wards moving Philippine Sea（PHS） Plate constituent the major tectonic setting of seismicity in the CMSB.Collision of SC and PHS, as well as shearing-compression along the west and south boundaries of SC block,generated great strain energy.This energy was conveyed and balanced with the Literal Faults zone（LFZ） and low velocity layer in curst as conduits.In those areas affected strongly by shearing-compression in both west and east parts of the CMSB,seismicity concentrated at the intersection of NW-and NE-trending local faults,and great earthquakes occurred at the intersection of NW-trending faults and LFZ.The Pearl River mouth area,however,suffered less shearing-compression,and had only scattered earthquakes of mid-low magnitude and no earthquake with M≥6.0 documented.