共和7.0级地震前地下流体前兆的动态演化特征

使用40个地下流体观测点的资料,对1990年4月26日青海省共和M_S7.0地震的前兆动态特征进行了系统研究.结果表明:(1)地震带内观测点的水氡趋势异常及水化、水位群体异常及频次异常与断层平均形变速率呈同步变化.地下流体群体异常频次的累加值曲线在地震前表现为指数加速变化图形.(2)震源外围240km范围内的水氡中短期趋势上升异常,表现为由震源逐渐向外围扩散的特点.在短临阶段各测点水氡的异常变化基本同步.(3)流体短临前兆出现明显的起伏加剧和层次现象,突出的表现是流量、断层气日变化在临震阶段出现3次加剧,且异常幅度一次高于一次.

DYNAMIC EVOLUTION CHARACTERISTICS OF GROUND FLUID PRECURSORS BEFORE THE GONGHE MS7.0 EARTHQUAKE 1990 IN QINGHAI PROVINCE

The dynamic evolution characteristics of ground fluid precursors of the M_S7.0 Gonghe earthquake on April 26,1990 in Qinghai Province are systematically studied, by using the ground fluid data of 40 observation stations. The results are following:(1) The mean deformation rate of faults in seismic belt were synchronous with the cluster anomaly frequency of the ground fluid and the trend anomalies of radon content in groundwater. The curves of the deformation rate of fault and the accumulative frequency of the ground fluid cluster anomalies changed acceleratly in a law of index.(2) The acceleration and rising stage of medium-term tendency anomalies of the radon data, which were obtained from the observation stations within 240 kilometers of the focus of the M_S7.0 Gonghe earthquake showed transmission feature from the focus to the periphery. The anomalies in short-impending term of the radon data appeared synchronously.(3) The ground fluid precursors showed clearly aggravation of fluctuation and hierarchy pattern. It is obvious that the change of daily mean values of fault product gases and flow of groundwater showed three hierarchies with anomalous amplitude which are higher and higher each in the impending earthquake stage.