Abstract: The anomalies are caused by the propagation or weakening of fault segments in short-termto imminent stages before an earthquake. The results of experiments and numerical simulationhave shown that the disturbant stress field accompanying by the short-term to imminant stage is afour-quadrant pattern for mean stress and an eight-petaline pattern for maximum shear stress.Inorder to judge the applicability of the mentioned patterns,a series of numerical models have beenstudied.It is found that no matter how complicated the fault system and the stress field are,thedisturbant stress field,basically,keeps the patterns,if the propagation or weakening has oc-curred along a fault.This result provides us a basis to distinguish the possibly coming instablefault.Meanwhile,the distortion of the disturbant stress field in complicated tectonic settingshould not be neglected.

Key words: Seismogenic fault, Anomaly recognition, Spatial distribution chacteristic, Stress field.Numerical simulation

摘要： 在地震短临阶段异常是由局部断层扩展或弱化引起。实验与数值模拟结果曾得到与之相伴的是平均应力扰动场的四象限分布和最大剪应力扰动场的八瓣式分布。为检验此结果的普适性作了进一步的研究。结果表明不论区域构造及其基本应力场如何复杂,这种四象限分布与八瓣式分布型式不变,这为最终判定失稳区提供了依据。与此同时,在复杂构造情况下这种应力扰动场的畸变也不容忽视。

关键词: 发震断层, 异常识别, 空间分布特征, 应力场, 数字模拟