本世纪华东地区两种不同空间分布类型的地震活动性分析

综合分析本世纪以来华东地区地震资料相对可靠的中强地震活动，发现前后两阶段有着不同的空间分布类型。第１阶段地震活动集中在苏鲁近海、菏泽一带及大别山地区，呈环状分布。而１９７１年以来的第２阶段中强地震全都分布在菏泽至溧阳北西向一线的东北一侧，并呈网络性分布。其中已经发生的３次６级以上地震都分布在上阶段较少地震活动的苏南至长江口及邻近海域。同时分析研究了各阶段地震活动特点，以及由于受北东、北西向构造控制影响，所划分华东地区三大部分地震活动在两阶段出现的震场迁移。最后指出该地区目前应重点注意苏南至长江口及邻近地区的地震活动。

ANALYSIS FOR TWO TYPES OF SPACE DISTRUBUTIONS OF EAST CHINA SEISMICITY IN 20 CENTURY

Based on the seismic data of east China, the moderate seismicity of the region since early 20 century has analysed. The different distrubution typs of seismicity in two stages had been discovered. In the first stage, seismicity had been in the Jiangsu and Shandong off sea, and the zone of Heze and Dabishan, distrubuting as loop. In the second stage after 1971, all moderate earthqukes have distrubuted in NE side of a line of NW orientation from Heze to Liyang, distrubuting as a network. Three earthquakes of M S≥6.0 occurred in the south Jiangsu, Yangtse river mouth and adjacent sea region where seismicity was very weak in the first stage. The characters of seismicities of various stages and the controll effect of NE and NW structures on seismicity and epicentre migration are researched. It is indicated that the seismicities of south Jiangsu, Yangtse river mouth and adjacent area should emphatically monitored at present.