华东地区现代地壳应力场及地震断层错动性质

CONTEMPORARY CRUSTAL STRESS FIELD AND FEATURE OF EARTHQUAKE FAULT SLIP IN EAST CHINA

使用143组中、小地震单震震源机制解和17组小区域综合机制解资料,统计分析了华东地区的现代构造应力场特征。华东地区现今处在NEE向(80°左右)主压、NNW向(350°左右)主张应力场的控制下;主应力作用方式以水平和近水平为主。在应力场方向和作用方式基本一致的背景上,不同地震构造分区存在一些差异,这些差异可能与相应区域主要活动断裂的主体分布方向有关,可能表征了现存构造对地震错动特征的影响和控制作用。现代中、小地震震源机制解,历史中、强地震和现代有感地震最内等震线长轴方向等资料显示华东地区地震主要沿NE,NW2个方向破裂错动,兼有NNE,NEE,NWW或近EW方向。以走滑和近走滑方式为主,兼有少量斜向滑动。地震断层的错动方式存在某些分区差异。华东地区历史中、强地震以NE向破裂错动为主,而现代中强地震在陆域以NW-SE为主,海域NE,NW兼有。

Statistic analysis has been made on the characteristics of the contemporary tectonic stress field of East China based on 143 sets of single focal mechanical solutions of moderate and small earthquakes and on 17 sets of composite focal mechanism solutions. Results show that the stress field of East China exhibits a NNE (about 80°) oriented principal compression and NNW (about 350°) principal tension, and the principal stresses are mainly horizontal or near-horizontal. In the context of basically consistent orientation and action mode of stress field, there are some variations in the stress field among different seismotectonic regions, which are possibly related to the distribution of major active faults in the respective regions. This indicates that fault slip may be dominated or affected by existing tectonics. The feature of earthquake fracture and the orientation of fault slip of contemporary earthquakes in East China have been analyzed with data of focal mechanism solutions of contemporary moderate and small events, and of the orientations of major axis for innermost isoseismal of historical and contemporary events and so on. It indicates that the earthquake fractures of East China extend at large in NE and NW directions, and sometimes with NNE, NEE, NWW, or near EW directions. The movements of earthquake faults are mainly of strike-slip or near strike-slip with oblique-slip component. There exist some regional variations in the movement of earthquake faults. The historical moderate and strong events in East China exhibit mainly a NE trending slip, while the modern events show the NW-SE trending slip on the land and NE and NW trend slip in the sea area.