SOME CHARACTERISTICS OF RECENT EPISODIC SEISMICITY IN THE MAINLAND OF CHINA
Fu Zhengxiang Cheng Yan (Center for Analysis and Prediction, State Seismological Bureau)
The strong shallow earthquake sequences which occurred recently in the Chinese continent may be divided into some active and quiet seismic episodes by using the Fisher method of cluster analysis, and the charateristics and the mechanism of these episodes are preliminarily discussed. The results show:(1) there were three active seismic episodes (1913-1937, 1944-1955, 1966-1976) with a time scale of a few tens of years for the process of strong earthquake activity in the Mainland of China since 1900.(2) the areas of energy release of strong shocks within the three episodes migrated orderly from Northwest China, Southwest China to North China.(3) in other two areas (the southern edge of Himalayas erogenic zone and the boundary of North Pacific plate) adjacent to the Chinese continent, their episodic seis-micity might be reflections of episodic movements of India and Pacific plates. The ups and downs of seismicity in the Chinese continent may be strongly controlled by episodic plate movements, and also probably affected by episodic variations in the earth's rotations.