ANNUAL VARIATION OF Z COMPONENT OF GEOMAGNETIC FIELD

The Z component data of absolute magnetic surrey at 8 stations in Hebei Province and its sdjacent region are used to analyze the annual variation of Z component of geomagnetic field. The result is, for the curve against long oblique line, two peak values were formed before or after April and October in a yeat. The low values are in January, July and December, the lowest one in July every year. Against the maximum amplitude of annual variation of the long oblique line, the variation of various stations is little, showing a sign to gradully increase from south to north, but the annual variation amplitude of each station showed relatively large difference with time. Meanwhile, it is considered that the variation of Z component of each station is different,which was caused mainly by different variation rate of long-term variation in different localities. After these variational characteristics and laws of Z component of geomagnetic field are recognized, the geomagnetic surrey method can play a better role in short-term and imminent earthquake prediction.