关键词: 地震活动性, 时序演化, 震场迁移, 华东地区

Abstract: Located in the southern part of the broad North China, the East China displays a relatively independent seismic activity in the region. The strong earthquakes occurred in this area in the past century displayed a good ordering and systematicness. Basing on these features, we analyze further the characteristics of seismic events of the past 30 years in time sequence and spatial migration. We find that in time sequence there are two episodes of seismic activity with similar evolution process in this area. The first episode occurred from 1970 to 1987, consisting of the stages of pre release, accelerative release, major release and remnant release of energy. These 4 stages made up a relatively complete evolution process of seismic activity. The second episode began from the late 1988, and has not been terminated till now. At present the stages of pre-release and accelerative release of energy of this episode have been completed. Comparing the spatial distribution of seismic events within these two episodes, we find that the main seismic areas of the first episode were distributed from southwest Shandong Province to the middle parts of Jiangsu and Anhui Province, as well as from the western part of the southern Jiangsu Province northeast-ward to the coastal area of middle Jiangsu Province. The main seismic areas of the second episode were distributed from southwest Shandong Province to the sea area of 124? meridian line, and the intersection of Zhejiang, Jiangsu and Shanghai areas. It seems that the spatial distributions of seismic events of the two episodes were characterized by good regionalization, and they were not overlapping each other. This may indicate the eastward migration of the main seismic areas in East China. The results of this study will be helpful to the analysis of seismic tendency and the assessment of potential strong earthquake area in East China.

Key words: Seismic activity, Time sequence variation, Migration of seismic area, East China