On Earth-Current Variations caused by the Pressure acting upon the Ground
Oshima, H.
Abstract
Results of the measurement of earth-current variations caused by the pressure acting upon the ground and a possible interpretation are reported in this paper. The pressure was given by trains with steam-engine running on the Joban-line which had not been electrified yet in this measurement. Large changes above 20 mV in the earth-current potential were observed when the train passed by. However，in the specific earth resistivity no change
was found exceeding the relative measuring accuracy，say order of about 10・-２ in the region where the train weight acted upon the ground effectively. Then，these changes observed in the earth-current potential are not able to be interpreted by the change of the specific earth resistivity. Author considers that the earth is formed of semi-infinite porous medium which is filled with water and the electric double layer is formed on the boundary between soil and water. When the pressure act upon the surface of such earth， the water may move through narrow capillary in the soil and streaming-potentials may be generated. The streaming-potential may cause leakage currents in the earth. Calculated potentials according to this consideration show good agreement with observed changes of the earth-current potential. Author，therefore，concludes that the main cause of the earth-current variation generated by the pressure acting upon the ground is streaming-potential and its leakage current in the earth. This problem may have important relation to the earthquake prediction because non homogeneous pressure in the ground may cause thc so-called “Difference of Earth Potentials" by Prof. T. Yoshimatsu.
