试论地震前兆

发生构造地震的必要条件为地应力σ上升时,断裂长度 c 增大:dc>0,((?)σ)/((?)c)>0,此时岩体应力—应变曲线的斜率为正;或者是地应力不变而岩体强度下降使断裂长度增大:dc>0,((?)σ)/((?)c)=0,此时岩体应力—应变曲线的斜率为零。在这两种情况下,断裂均进行稳态扩展,称之为异常阶段。发生构造地震的充分条件为断裂长度增大时地应力又转为明显减小:dc>0,((?)σ)/((?)c)<0,此时老体应力—应变曲线的斜率变为负,断裂扩展失稳,称之为地震前兆。

A DISCUSSION ON SEISMIC PRECURSOR

The essential condition of a tectonic earthquake is that the fracturelength(?)c increases with the rising stress σ,i.e.dc>0,■In this case,the slope of stress-strain curve of the rock is positive.Inother case,the fracture length c increases with the decreasing rock stre-ngth when the earth's stress is constant.At that time,the slope of stress-strain curve of the rock is zero.In these two cases,which are calledanomaly stage,the fracture extends steadily.The ample condition of a tectonic earthquake is that the stress turnsto decrease obviously when the fracture length c increases: dc>0,■In that case,the slope of stress-strain curve of rock is negativeand the fracture extends unsteadily.This is called the seismic precursor.