张北6.2级地震的水化前兆异常分析及有关问题讨论

张北地震前、在中期阶段，多井水氡出现负异常变化；短期阶段出现区域水氡差分异常的月频次增加；短临阶段则出现怀来４井水汞的多次突跳。大同地震前多井出现水氡的趋势性正常，是张北地震水化前兆最显著的不同之处。本文分析了张北地震水化方法预报失误的原因。讨论认为，水氡负异常做为中期前兆的信度较低；为提高水化预报地震的效能，必须与其它前兆手段相结合。

ANALYSIS OF THE HYDROCHEMICAL PRECURSORY ANOMALIES AND DISCUSSION OF THE RELATED ISSUES OF ZHANGBEI M6. 2EARTHAQUAKE

Before Zhangbei earthquake,in mid term stage,water radon in many wells showed negative anomalous variation;in short term stage,the monthly frequency of the differential anomalies of regional radon increased;in imminent stage,water mercury in Huailai No. 4 well showed many sudden jumps. Before the Datong earthquake,water radon in many wells showed trend positive anomalies,which is obviously different with the hydrochemical precursors of Zhangbei earthquake. In this paper,the reason of prediction failure by hydrochemical method to Zhangbei earthquake is analyzed. It is considered that the confidence of water radon negative anomalies which are regarded as mid term precursors is low. In order to raise the effectiveness of earthquake prediction by hydrochemical method,the method must be combined with other precursory methods.