Characteristics of Vertical Earth Potential Difference Signals

Abstract

A modified measurement method to observe the electric earth potential difference is proposed with regard to the reduction of the unnecessary signals induced by artificial and natural earth current sources. With this method, the potential difference is measured as the voltage between two electrodes that are buried at vertically different positions below the ground surface. We examined this method at four observatories with different measurement conditions and discussed the characteristic features of the three types of the observed signals. (1) With the variation of the geomagnetic fields, the horizontal earth potential difference signals appear according to its induced current. The vertical signals, however, do not because of no induced vertical current. To be sure to realize this effect, the observation area must be sufficiently level. (2) After heavy rain fall the characteristic quasiperiodic pulse signals appear extremely rarely. No horizontal potential difference signals could be found when measured together with the vertical signals. (3) Pulse signals appear with the exactly same period that might be caused by artificial current source from structures and buildings. Consequently, to use this vertical observation method effectively, we should choose a location where the ground surface is as level as possible and as far as possible from current source points.