Characteristics of the Variation of Cross Fault Short-Baseline and Short-Range Leveling in Western Yunnan Earthquake Test Site Before Lijiang M_S7.0 Earthquake

Results of analysis of variation of cross fault short-baseline and short-range leveling in Western Yunnan Earthquake Test Site (WYETS), results show that among five observation stations of cross fault short-baseline and short-range leveling in WYETS before the Lijiang MS7.0 Earthquake occurred in February 1996 only Yongsheng observation station (epicentral distance 82 km) located at Chenghai fault shows great variation about one year before the earthquake. And the nearest observation station, Lijiang (epicentral distance 42 km); presents great coseismic variation, but does not show obvious anomalous variation before the earthquake. There are no significant variations related to the earthquake at the other three observation stations. Two methods are used in analysis of the observed data and some valuable results have been obtained.

丽江7.0级地震前后滇西实验场的重力异常变化特征

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。

丽江7.0级地震滇西实验场区跨断层短基线短水准测量的变化特征

通过对滇西实验场区跨断层短基线、短水准测量的计算分析表明：１９９６年２月丽江７０级地震前，滇西实验场区５个跨断层短基线、短水准测量的测点中，只有位于程海断裂带上的永胜测点（震中距８２ｋｍ）在震前１年左右出现巨变异常，而距震中最近的丽江测点（震中距４２ｋｍ），震前并没有显著的异常变化，但却有很大的同震变化。其它３个测点看不出与该次地震有明显联系的变化。尝试性地进行了两种计算，可能对孕震地区的判断有一定的参考价值。