SOME CHARACTERISTICS OF SEISMIC ACTIVITY IN CHINA
SHIH CHEN-LIANG HUAN WEN-LIN TSAO HSIN-LINGWu HUAN-YING LIU YAO-PIN HUANG WEI-KING(Institute of Geophysics, Aeademia Sinica)
In this paper we have made a statistical analysis of more than a thousand destructive earthquakes which occurred throughout China, since 1000 A.D. We have examined! certain characteristics of the distributions in time, and space and of the intensities of these strong shocks. The whole country is first divided into 23 seismic zones, each of which being regarded as a single unit in which the processes of strain accumulation and release are taking place. It is found that strong seismic activities in the same zone were always concentrated in some periods, while others were of comparative quiescence. The whole duration from the time of comparative quiescence to that of high activity may be regarded as a single process of strain accumulation and release which again may be divided into four stages. The first stage is that of strain accumulation. This is followed by the stage of accelerating strain release. Then comes the stage of rapid release in which the strain accumulated is almost wholly released. The whole course of activity is completed by the stage of remnant release. In the stage of rapid release, the strain accumulated in some of the seismic zones is released through a single major shock but in others, through several shocks of lower magnitudes. The former is called the type of single major shock and the latter, the type of multiple major shocks. As a statistical result of various seismic zones, the total strain release of this stage appears to be of a certain limited value.In the seismic zones of China, one period of seismic activity may last a few hundred, or even a thousand years, maximum magnitude of earthquakes which occurred in various stages may vary a great deal. Therefore, in seismic regionalization, the activity should not be regarded as a stationary process. The stage to which the activity belongs must be taken into consideration. This will be helpful in obtaining a better estimate of the seismicity and the tendency of earthquake occurrence.