闽南粤东沿海北西向断裂构造的近代活动性与应力场的探讨

An Approach to Activities of NW Faults and Recent Tectonic Stress Field on South Fujian and East Guangdong

通过对闽南粤东沿海地区NW向断裂构造与沉积建造、地貌特征、地形变、热震效应和地球物理特征等关系分析,确定本区的NW向断裂带是仅次于NE向的长乐—诏安断裂带的又一组活动性较强的断裂带。由于不同时期构造应力场的差异,使NW向断裂经历了张性(或张扭性)—压性(或压扭性)—张性(或张扭性)三次断裂性质的转变。晚第三纪以来,本区主要受菲律宾板块的挤压作用,应力方向由NW向转为NWW向,造成NW向断裂张裂性质的增强,火山喷发,中基性岩脉的侵入,地貌上表现为以断块作用为主的断块隆起和断陷盆地。并在收集各种资料的基础上,建立了本区的有限模型,结果发现与NW向断裂构造的方向和性质具有很好的一致性。区域应力场方向为300°,而从节理统计,和震源机制及实测资料等求得的最新一期应力场分别为300°,280～300°及290～317°。从而说明本区的应力场是晚新生代应力场的继续和发展。

Through an analysis of the relationship between the faults on south Fujian and East Guangdong and the sedimentary formation, geomorphological features,land deformation, geothermal heat, earthquakes and geophysical characteristics, the NW faults are considered a set of strongly active structrral zones second only to the Changle Zhaoan NE—trending fault, The NW faults control over the formation and development of the quaternary basins , the distribution of geothermal heat and the direction of land deformation. The NW faults, being seisrnical structures of middle-small seisms, often bear relation to earthquakes. Due to variation of the tectonic stress field in different periods, the mechanical properties of the NW faults undergo three times of transformation, that is, from tensoshear to compresso-shear, then to tenso-shear again. Since Mid Tertiary, the studying region has mainly been compressed by the philipine sea plate. Because of the change of direction of the stress from NW to NWW, the tensile properties of the NW faults are intensified, resulting in the eruption of volcanoes and the formation of fault-block mountains and basins. In order to determine the appropriate and precise distribution of the present tectonic stress field, a model of finite element analysis is constructed according to the various data available. After several ways of possible exerted which roughly represent the forces exerted to the region by the surrounding areas are considered, the distribution of the regional tectonic stress is got. Using this model, we further analyse the feature of the faults and the zones where earthquakes often occur. The result shows that the data of the analysed model are corresponding to the direction and feature of the NW faults and that the direction of the regional compressive stress is 300°. Meanwhile, the data gained by means of statistics of the focal mechanisms, joint structures show that the direction of the regional compressive stress is 280--300°. In comparision with the above two data, it can be seen that there are quite few differenees between them. This indicates that in this region the present stress field is the continuity and development of the late cenozoic one.