A STUDY OF GEOMAGNETIC ANOMALIES BEFORE THE DATONG 6.1 EARTHQUAKE

Before the Datong 6.1 earthquake, geomagnetc precursory anomalies showed a regular distribution along certain structures in time, space and ε emplitude.Among them, the boundary line of anomaly of low-point move-ment of daily variation formed a closed ring along yanshan-Yingshan fault zone, the piedmont fault zone of Taihang mountain, Qinling fold fault zone and South-North seismic zone.The precursory anonalies of mobile geomagnetic observation, telluric current, deformation, bydrochemistry, groundwater and terrestrial stress, were on two belts, Beiging-Huhehote and Beijng-Handan, obviously showing a band-like distribution.The region concentrated with these anomalies is just one part of Yanshah fault zone and the piedmont fault zone of Taihang mountain through which the boundray line of low-point movement of daily variation passed, but the precursory anomalies far from the boundary line were obvrously decreased.This indicates that, in the crustal blocks which were separated by some tectonic zones, movement to a certain extent may take place beforc an earthquake, resulting in variatron of physical property of media in some tectonic znoes.Furthermore, prior to the Datong earthquake, these precursory anomalies showed the characteristics of mid-term, short-term and imminent precursors in time series.