Abstract: The relationship between the short-term recurrence anomaly of the induced current of the daily variation of the geomagnetic vertical component (the overlapping anomaly) and the gravity change before two earthquakes is studied. It is found that within half a year after the occurrence of the anomaly, negative gravity anomalies appear near the end of the overlap segment. The direction of the overlapped section of induced current is consistent with that of the high conductivity zone in the upper mantle and crust and the induced current may several thousand amperes. We infer as follows. Some unknown factors lead to “cracks” in the upper mantle and crust, and the deep fluid enters into the “cracks” to form “short-time high conductivity channels”. When the “channels” last for many days, or appear on different days in the same place in a short time, the induced current generates heat in the high resistance area at the end of the overlap section. The thermal expansion of the medium leads to the deformation of the ground above and results in the gravity drop. The horizontal compression of the crust leads to the reduction of the friction resistance between faults at the high stress area and then earthquakes occur.

Key words: Geomagnetic diurnal variation, Induced current, Concentrated distribution, Seismic anomaly, Mechanism