滇西北中强震前震级频度分布与G—R关系式的偏离特征

DEVIATION OF MAGNITUDE FREQUENCY DISTRIBUTION OF EARTHQUAKES FROM GUTENBERG -RICHTER RELATION BEFORE MEDIUM AND STRONG EARTHQUAKES IN NORTH-WEST YUNNAN

本文利用 Ｓ． Ｏｋｕｄａ 等根据 Ｋｕｌｌａｃｋ Ｌｅｉｂｌｅｒ 平均信息给出的表示实际地震震级－ 频度分布与古登堡－ 里克特 （ Ｇ－ Ｒ） 关系式偏离的量度 Ｃ， 研究了滇西北自１９８５ 年７ 月有速报目录以来的中强震前 Ｃ 值偏离特征， 结果表明： Ｃ 值一般在０１３４ － ０１５７ 之间， 中强震前 Ｃ值显著减小（ Ｃ≤ Ｃｏ ， Ｃｏ ＝ ０１３５ 为自组织临界点） ， 对应率为６／７ ＝ ０８６ ， 概括率为６／８ ＝０７５ ， 且首次临界点到发震的时间绝大部份在４ 个月之内， 表明 Ｃ 值异常可作为一个较好的短临预报指标推广使用， 文章还根据 Ｃ 值的变化对１９９６ 年２ 月３ 日丽江７０ 级大地震孕育过程提出了相应的解释。

This paper studies the deviation of magnitude frequency distribution before the medium and strong earthquakes occurred in North west Yunnan since rapid earthquake catalogue was made in July, 1985, using the C showing deviation of practical magnitude frequency distribution from Gutenberg-Richter relation and given by S. Okuda according to Kullback-Leibler Information. The results show that C value generally came between 0.134 and 0.157 and reduced obviously before the medium and strong earthquakes (C≤C o, C o=0.135 for threshold value), with the corresponding rate of 6/7=0.86 and the summarizing rate 6/8=0.75, which shows the C value might be a good index for short-impending earthquake prediction. And also, the author gives explanation of the preparation process of the M 7.0 Lijiang earthquake on Feb. 3, 1996 according to variation in c value.