Observations of geoelectric potential have been conducted since 1997 at Ohtawa (Kamioka town, Gifu prefecture) for the purpose of testing VAN method (short-term earthquake prediction), as a collaborative research of Toyama University and RIKEN-IFREQ. The data from Ohtawa station are obtained in excellent condition for geoelectric potential study because of small artificial electric noises. A relatively strong change of geoelectric potential is observed. This is clearly correlated with the timetable of Tateyama railway. That is, the geoelectric potential change is caused by the leakage current from DC train of Tateyama railway. The current travels through more than 16km distance. The geoelectric potential changes caused by the leak current of Tateyama railway may be useful to study a electrical resistivity of the soil and it’s time variation around the area. A time variation of largest amplitude of the rail leak current has been analyzed since April 1998, to obtain the variation of apparent resistivity. So far, there has not been sensible correlation for apparent resistivity variation and an inert seismic activity. In contrast, it is remarkable that the resistance changes gently in a cycle of one year. The gentle variation of resistivity is thought to be caused by annual or seasonal phenomenon. The leakage of the current from DC train is a powerful tool to monitor temporal variation of resistivity structure around the area.
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