THE LONG-TERM ACTIVITY OF LARGE EARTHQUAKE AREAS

After the analysis of the parameters time,space,and intensity of seismic activity in seismic areas of some large historical earthquakes of M7 in the inland areas of China,it was found that in many large earthquake areas,after the elapse of several decades,or hundreds of years to even nearly one thousand years,there was still activity of many small earthquakes; sometimes intermediate strong earthquakes occurred; and even recurrent large earthquakes which were comparable to the main shocks also occurred. Here,according to the statistical analysis of seismic areas of 17 earthquakes of M8 and 37 earthquakes of M7,we have proposed the concept of long-term activity in a large earthquake area. This conepet was supported by observational facts in large earthquake areas after establishment of local seismic networks one after another in the middle of the 60's and particularly since 1970. In this paper,besides briefly discussing the physical significance of the long-term activity,the practical significance of such long-term activity in seismic trend predication was further illustrated by some concrete facts.