最大主应力σ_1等值线分布与唐山7.8级地震的关系

RELATIONSHIP BETWEEN THE PLAN DISTRIBUTION OF THE ISOLINES OF MAXIMUM MAIN STRESS σ1 AND TANGSHAN EARTHQUAKE WITH M7.8

对唐山大震前最大主应力σ_1的等值线平面图进行分析,可以看出:从1976年4月前后开始,所圈定的等值线图的椭圆长轴的方向由北北东方向转为北东东方向。震中区的高值应力σ_1值达到5×98.0665kPa以上。异常面积区域可达1×10~6km^2以上。

The contour diagram of the maximum main stress σ1 before the large Tangshan earthquake has been analyzed in this paper. It shows that the NNE direction of long axis of the contour line has been tured to NEE around April, 1976. The highest stress σ1 was higher than 5×98.0665kPa. The anomalous area was large than 1×106km2.