中国东部大陆的地震构造应力场
SEISMO-TECTONIC STRESS FIELD IN EAST CHINA
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摘要: 根据1973—1982年期间,中国东北、华中和华南地区的1211次离散分布小震的P波初动方向数据,用格点尝试法求出23个分区内,地震的综合断层面解的P、B、T轴,结合其他作者以前得到的华北地区和鄂尔多斯地块周围地区的主应力轴方向结果,对中国东部大陆地区(105°E以东)构造应力场的方向特征作了归纳和分析。 本区应力场方向的总体特征是:平均P轴方向基本水平,并呈由西部陆地中心向沿海的放射状分布;平均T轴方向水平,并沿向东凸出的弧形线呈环状分布。这一总体特征说明,本区构造运动的力源不象是位于区内的局部力源。本区地震皆发生在地壳内,并且绝大部分震源机制解显示出直立断层的走滑运动,由此推断,本区与地震有关的构造形变基本是地壳内的水平形变。汾渭地堑南段平均P轴直立,显示张性构造运动。 尽管应力场显示出明显的总体特征,但全区地震活动分布很不均匀,这说明控制地震活动差异的主要因素可能是构造差异,而不是力场的差异。Abstract: On the basis of P wave first motion data of 1211 micro-earthquakes which were widespread over northeastern, central and southern part of the continent of eastern China during 1973—1982, we have used the grid testing method to deduce the mean P, B and T axis corresponding to composite fault plane solutions for each of 23 subregions. Combined with the results of principal stress axes studies of 23 additional sub-regions in North China and around the Ordos Massif, which were obtained previously by other authors, the features of the seismo-tectonic stress field have been analysed more completely for the continent of eastern China (to the east of 105°E).The overall features of stress field are as follow: the mean P axes are nearly horizontal and orientate radially from the central part of the continent to eastern coastal region; the mean T axes are horizontal and lie along arcs which are convex eastwards. This indicates that the stress field here is not likely to be generated by some local sources within this region. Since all earthquakes of this region have occurred in the crust and most of them showed vertical strike slip faulting, it is inferred that the dominant deformation associated with the earthquake occurrence is of horizontal type. The vertical mean P axis in the southern part of Fen-Wei Graben indicates tensional tectonic movement there.Although the stress field shows clearly the overall feature, the seismic activity is inhomogeneous in the whole area. This implies that differences in regional seismic activity may be attributed to differences in the tectonic provinces rather than differences in stress field.
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