震源应力场与构造应力场

THE STRESS FIELD OF EARTHQUAKE SOURCE AND THE TECTONIC STRESS FIELD

摘要:

每个地震按照双力偶模型所得到的震源应力场,有的反映构造应力场,有的反映转换应力场。凡是在已存在的活动断裂上由粘滑发震的震源机制解而得出的P、B和T轴与构造应力场的最大、中等、最小的压力主轴是对应的,只是略有偏离。分析了岩块相对滑动产生的转换应力场,证明由转换应力场所产生的脆性剪切破裂而发震的震源机制解得出的P、B、T轴则与构造应力场三个主轴方向可以完全不符。通过对具体震例分析表明,当考虑了转换应力场之后可对几个地震区的应力场得到统一的解释。因此,在一个地区根据震源机制解来恢复构造应力场时必须先判明:是构造应力的直接作用下的粘滑或剪切破裂,还是转换应力场所形成的、共轭剪切破裂,前者可直接恢复构造应力场,后者则应经过转换寸能恢复构造应力场。

Abstract:

Some of the stress fields obtained from earthquake mechanism according to double couple model of earthquake represent tectonic stress field, but some of them represent the transformed stress field. The axes P, B, and T obtained from earthquake mechanism correspond with the maxmum, intermediate and minimum principal axes of the tectonic stess respectively if the earthquake was caused by stick-slip mechanism on an acting fault, though there may be a departure from the real directions. The transformed stress field was analysed when blocks of the crust moved relatively. The axes P, B, and T are entirely different from the principal axes of the tectonic stress if the earthquake was caused by transformation stress field. Through analysing several earthquake sequences, it was shown that uniform stress field was obtained from earthquake mechanism when the transformation stress field was taken into account. Therefore, to obtain the tectonic stress field from an earthquake mechanism, it must be clarified that the earthquake was caused by stick-slip or shear fracture due to tectonic stress or caused by conjugate shear fracture due to transformation stress some criteria were given. The tectonic stress could be obtained directly from the former, but some transformations have to be done if the tectonic stress was obtained from the latter.