INDEX FOR ACTIVENESS AND QUIETNESS OF MEDIUM AND SMALL EARTHQUAKES BEFORE MAIN EVENT IN HENAN AND ITS NEIGHBORING REGION

the nonlinear ZL curves of seismicity in different regions of Henan and its vicinity from 1970 are discussed with accumulative frequency method. The ZL values before M≥5 earthquakes are all calculated.The results show that the activeness (or quietness) anomalies begin 1 to 2 years before an earthquake, and end within one year before the event, concentrating to 0-4 month before. The quantitative index for anomalies and earthquake type are presented.