Telluric Currents in the Kurobe Hot Tunnel, Kurobe—Sennindani Hot Dry Rock

Abstract

An observation of telluric current was carried out on 27 November 1978 in the Kurobe Sennindani hot dry rock, utilizing the Kurobe Jobu railway tunnel known as a hot tunnel penetrating through the hot dry rock. The results obtained are as follows: (1) Observed variations of telluric current do not show any characteristics of natural origins but of artificial electric noises or stray current originating probably from some electric power plants within 1.5 km distance and DC-electric cars operating at about 4 km away. (2) Variations with frequency of 4.4 Hz in earth current were found at a low temperature zone (about 15°C), but it disappeared at hot a rock zone (about 70°C). It may follow that earth current of 4.4 Hz-frequency is unable to penetrate into the hot rock zone due to skin effect. Taking 300 to 500 m for the depth of the hot rock zone below the ground, 2 Ω-m of low resistivity of the hot rock zone is obtained by Cag niard equation. The result was discussed, referring to rock characteristics of the high temperature zone. (3) Irregular variations of earth current were in opposite directions at the low and high temperature zones. (4) Long period currents by streaming potential were observed at the hot rock zone. It is estimated that streaming potential was induced by warm and humid wind forming from hot rock walls and fumaroles. © 1983, THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN. All rights reserved.