DYNAMIC EVOLUTION CHARACTERISTICS OF GROUND FLUID PRECURSORS BEFORE THE GONGHE M S7.0 EARTHQUAKE 1990 IN QINGHAI PROVINCE
LIU Yaowei ZHANG Yuansheng (Earthquake Research Institute of Lanzhou, SSB, Lanzhou 730000)
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.