丽江7.0级地震前后滇西实验场的重力异常变化特征

THE VARIATION CHARACTERISTICS OF GRAVITY ANOMALY IN THE EARTHQUAKE PREDICTION TEST SITE IN WESTERN YUNNAN BEFORE AND AFTER THE M 7 0 LIJIANG EARTHQUAKE

１９９６年２月３日，在云南省西北部的丽江县境内发生了一次Ｍｓ７０级强烈地震。此次地震前后滇西实验场重力网共进行２７期流动重力观测，其重力变化的总体特征为：１震中附近地区的丽江—剑川—洱源一带震前为下降变化，下降变化的幅值平均约３０×１０－８ｍｓ－２左右，震后重力变化继续下降；２距震中稍远一点的渡口附近地区震前为持续上升变化，累计上升变化的最大幅值达１２３×－８ｍｓ－２，震后重力变化下降，但下降变化的幅值不大，且永仁—南华一带的重力变化还在继续上升；３距震中较远的保山附近地区震前为持续上升背景上的下降变化，下降变化的最大幅值为６８×１０－８ｍｓ－２，震后还在继续下降，但昌宁—云县一带出现了局部上升变化。震前，根据前２６期资料显示的重力变化。

A strong earthquake of Ms 7 0 occurred in Lijiang county, northwestern Yunnan province on Feb 3, 1996 The 27 mobile gravity measurements were carried out in the gravity network in EPTSWY before and after the event and the general characteristics of gravity variation are obtained as follows: 1 decrease variation in gravity appeared from Lijiang to Jianchuan to Eryuan near the epicenter before the event with the average varied value of about 30×10 -8 ms -2 and the decrease variation in gravity remained after the event; 2 continuous increase variation occurred near Dukou slightly far away from the epicenter, with the maximum cumulative varied value of 123×10 -8 ms -2 , and decrease variation in gravity occurred after the event, but with low varied value and the variation in gravity from Yongren to Nanhua still remained incontinuous increase; 3 the decrease variation on the background of continuous increase occurred near Baoshan far away from the epicenter, with the maximum decrease varied value of 68×10 -8 ms -2 and remained after the event, but local increase variation appeared from Changning to Yunxian The prediction before th earthquake has been made to a certain extent according to the variations in gravity in the first 26 survey data