Abstract: Through study of the relation between magnetic storm and seismicity, the authors have found that there is a better corresponding relation between the maximum variation amplitude ratio of the vertical component of magnetic storm and moderate and strong earthquakes. On the divisional statistics of the data observed for 10~ 20 years in North China, Southwest China and Northwest China, the best time period of the ratio anomaly of maximum variation amplitude in each region before earthquake date can be obtained. When seismogenic process reaches the short and imminent stage, the time index for earth-quake occurrence can be provided by the above-mentioned method. As for the prediction of the epicentral region concerned, it is found that before earthquake occurrence, the daily variation amplitude of magnetic storm Z near the epicenter is obviously greater than that of other regions, which breaks the regular rule that the daily change of normal magnetic storm increased with the higher of latitude, and appeared difference with each region. Ac-cording to the method mentioned above, earthquakes occurred in 1 993 in North China have been tested.

Key words: Magnetic storm, Geomagnetic vertical component, Geomagnetic daily change, Prediction index