关键词: 地震活动性, 震源机制, 断裂活动, 首都圈地区

Abstract: In this paper,the relation of time,space and intensity characteristics,as well as focal mechanisms of earthquakes to fault activity in Beijing area has been analyzed.A tectonic deformation model for the upper crust of this region is developed in this paper in the light of the quantitative analysis of fault activity.The results show that the earthquakes in this region are distributed mainly along the NWW direction,forming a concentration belt of earthquakes.In addition,several earthquakes of above magnitude M_S 4.5 occurred along the NE-or NEE-trending faults.These two sets of fault form a conjugate fault system,on which earthquakes occur alternately in different active periods,and the average release rate of creep energy corresponds to the occurrence of one M_S 4.2 earthquake per year.The crust of Beijing region can be divided in to the Yanshan,North Shanxi,Taihangshan and Central Hebei blocks,which have an irregular boundary along the NWW direction.Under the action of the NEE-directed principal compressive stress,these NWW-arranged blocks were easily activated,resulting in concentration belts of earthquake of a certain scale along block boundaries.Moreover,earthquakes of above magnitude M_S 4.5 occurred along the conjugated NE-or NEE-trending faults.

Key words: seismic activity, focal mechanism, fault activity, Beijing region