20世纪云南地区Ms≥5.0级地震活动的基本特征

在对云南地区地震目录完整性和均匀性分析的基础上，系统总结和分析了20世纪云南地区Ms≥5．0级地震活动时、空、强分布的基本特征。有以下主要认识：（1）6．7级以上大震存在十年尺度的活跃－平静交替活动过程；（2）50年左右的大震复发周期；（3）5级以上地震活动的时、空分布具有很大的随机性，5－6级地震活动不存在活跃期和平静期之分；Ms≥5．0级地震有约2．6次／年的期望年发生率，每年发生0．8－4．5次Ms≥5．0级地震的自然概率是68．3％；（4）6级以上地震具有空间丛集特征，云南全区80％的6级以上地震只分布在全区20％左右的面积上；（5）以金沙江－红河断裂带为界，6．7级以上大震成组地在滇西和滇东交替活动；（6）5级以上地震活动的b值为0．69。

Basic Characteristics of Seismicity with Ms≥5.0 in Yunnan in the 20th Century

The basic features of time,space and strength distributions on earthqua ke occurrence with Ms≥5.0 in Yunnan in the 20 century have systematically been summarized and analyzed based on the study of the completeness and uniformity o f earthquake catlogue. Some basic understandings have been obtained as follows: (1) there existed the cycle of activation-guiet on ten-year scale for the ear thquakes with Ms≥6.7; (2) large earthquake reoccurrence period; (3) highly ran domicity on the time-space distribution for the earthquakes with Ms≥5.0, no cy cle of activation-quiet for the earthquakes with Ms 5～6, and annual occurrence rate of about 2.6 times and 68.3% probability of occurring 0.8～4.5 times per year of the earthquakes with Ms≥5.0; (4) space clustering of the earthq uakes with Ms≥6.0,80% of which only occurred in the about 20% of Yunnan area; (5) alternation activity of earthquakes with Ms≥6.7 in group in the West Yunna n and the East Yunnan divided by the Jingshajiang River-Red River fault; (6) the b-values for the earthquakes with Ms≥5.0 were 0.69.