THE STATISTICAL DISTRIBUTION OF TIME INTERVALS BETWEEN TWO SUCCESSIVE EARTHQUAKES AND ABNORMAL VARIATION OF THE D-VALUE, THE DEGREE OF SEISMIC DANGER PRIOR TO SEVERAL GREATER EARTHQUAKES IN NORTH CHINA

In this paper the statistical distribution of the time interval between two successive earthquakes is discussed, statistically tested, and shown that it obeys Weibull distribution f() =-1exp-(/).Actual calculation results show that in general the seismicoccurence fashionparametre, the p-value, is less than 1.0. This means that the pattern of seismic occurence is successive. Using some results of the reliability theory, the degree of seismic danger function D(t) =1-exp-(t/) is introduced, it is the probability of occurrence of an earthquake in timet. In this paper we let t = 1 day and call D(1) the degree of seismic danger, the D-value. The results indicate that the degree of seismic danger, the D-value showed a significant rising trend before all nine earthquakes of Ms5.8 in North China (1970-1984). The relation between , , D-value and the actual seismic activity, stability of the calculated D-value etc. are discussed. Besides, it is thought that the D-value is a function of stress. The other parametres of reliability theory have similar variations as the D-value.