Abstract: Since 1968, it has been noted that preseismic variation in electrical field has something to do with both variation of water level in a well and the active fault, therefore it is inferred that observed anomalous electrical field is probably induced by a streaming potential mechanism. In view of inhomogeneous distribution of fluid pressure, fault-valve behavior and the coupled equations of the current density and fluid flow within the Earth′s crust, especially, the observed anomalies in electrical field showed a similar pattern of rapid starting and slow decay, some of these anomalies associated with episodical spouting from borehole or the increase of fluid pressure in wells, it is reasonable to consider that the source of precursory electrical field anomalies is the streaming potential mechanism. Experimental results show that lead electrodes can record precursor in electrical field. Anomalies of either horizontal and/or vertical component in electrical field are observed during and before both the M7.8 Tangshan earthquake of 1976 and the M7.3 Haicheng earthquake of 1975. There are cases showing some strong earthquakes were predicted through analysis of geoelectrical field data both at home and abroad. The geoelectrical field method, which is easy to measure, can be applied in a short-term and impending earthquake prediction.

Key words: Geoelectrical field method, Horizontal and/or vertical component, Streaming potential mechanism, Precursor, Short-term and impending earthquake prediction