大同5.5级地震前的电磁前兆信号

１９７６年唐山地震皮后，上地震引起的电磁信号异常现象开始引起人们的极大关注，我国相继建立了２００多个地震电磁波观测台，并且积累了许多震例资料。同时在国外也发表了一些相关的文章，但大多数文章仅涉及到震前一个台的异常信号或某个频段上的异常信号。

Analysis of the seismo-electromagnetic anomaly before the 5.5magnitude earthquake on 18th October,1989 in Datong,Shanxi Province

Great attention has been drawn to the Seismo-electromagnetic (SEM) waves after the large Tangshan earthquake in 1976.About 200 stations have been established for observation SEM waves at earthquake risk region in China.We have accumulated many predictive data of SEM waves and earthquake Samiles.Similar articles have been published in foreign country,anomaluos signals at single station or in one frequency band were involved in these reports.One of the most prominent abnormal SEM was recorded before the 5.5magnitude earthquake on 18th,October 1989 in Datong,Shaxi Province,as well as three earthquakes(Ms: 5.5)had occurred continuously in three hours.These earthquakes were the greatest at Huabei area in the near decade.We have collected SEM observationdata at 12 stations within the epicentral distance of 200 300km in different frequency bands for two monthes before earthquake till earthquake occurred.Amplitude of anomalous signals changed from small to bigger,and shape of signals changed from undulation to pulses,then quieted.Earthquake would occurs after some days.There were features of SEM befor middle earthquake:(1) long time of anomaly;(2)larger amplitued:(3)wider radiation extent and (4) wider radiation frequency band.Time of appearing SEM anomaly at different stations and in different frequency bands was not synchronous due to complexity of structure on the earth's crust,conduction of fairly inhomogeneous medium and different propagation of SEM from seismic source.