ASSESSMENT OF EARTHQUAKE SEQUENCE TYPES BY MEANS OF THE APPARENT SEISMIC WAVE AMPLITUDE RATIO VARIANCE

Having analyzed one by one 16 different earthquakes taking place in nine provinces of eastern China and off their coasts, this paper proposes a method of assessing their sequence types, especially the foreshock sequence by means of the apparent seismic wave amplitude ratio variances of S and P waves.The results are as follows. As far as the apparent seismic wave amplitude ratio variance is concerned, the foreshock sequence is smaller than 0.25; the cluster sequences range between 0.26 and 0.50 and the after-shock sequence as well as the foreshock-major shock-after shock type sequence greater than 0.55. For normal earthquake activity, the variance of apparent seismic wave amplitude ratio is about the same as that of the cluster sequence. If we combine all variances into pairs and make F tests between them, we can find that in most cases, there exist marked discrepancies between the variances of different types of earthquake sequences. On the other hand, no obvious discrepancies between Sequences of the same type have been observed. By means of the method of cumulative scores in statistics, accuracy rate of 85.8% at a confidence level α=0.05 and 88.3% at. α=0.10 have been obtained.