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利用断裂力学观点前已得出震级 M、区域剪切应力值τ_O,震源破裂半径 a 之间的关系式.通过求 a 和 M 可算出应力值τ_O,用求小震平均断层面解的方法可求出应力场的方向.本文计算和讨论了1976年11月7日云南省盐源地区6.9级地震前后该地区应力场随时间的变化,并与邻区作了比较,结果如下:1.盐源地震前,邻近的中甸地区的τ_O 值比云南省其它地区高出4倍.2.盐源地区1976年以后τ_O 值明显增高,且此时小震的平均应力场方向与主震应力场方向基本一致.从而可以看到震前应力场的变化.分析讨论了测定τ_O 的误差和引起误差的原因.提出了利用单台和多台对不同地区的τ_O值进行比较的可能性和误差.
The relationship between the magnitude M, the shear stress value τ_O and the source rupture radius a has been obtained before using the viewpoint of fracture mechanics. By calculating a and M, the stress value τ_O can be calculated. The direction of the stress field is obtained.This paper calculates and discusses the change of stress field in the area before and after the MS 6.9 Yanyuan area on November 7, 1976, and compares it with the adjacent areas. The results are as follows: 1. Before the earthquake, the value of τ_O in Zhongdian area was 4 times higher than other areas in Yunnan province.2 The τ_O value of Yanyuan area increased obviously after 1976, and the direction of the average stress field and the stress field Which can be seen the change of the stress field before the earthquake.Analysis and discussion of the error of the τ_O and the reason of the error are given.The possibility and error of comparing the τ_O values of different regions with single and multiple units are proposed.