전기비저항탐사에서 음의 겉보기 비저항

초록

In the resistivity method, the potential difference between two grounded electrodes is measured and this canbe positive or negative. The apparent resistivity and the potential difference have the same polarity. Since the electricfield is the gradient of the potential, the polarity of the potential difference depends on the direction of the electric field.If the direction of the vector connecting two grounded electrodes is the same to that of the electric field, the measuredpotential difference and the apparent resistivity become positive. If the opposite is the case, they become negative. Ingeneral, the primary electric field and the vector connecting two potential electrodes have the same direction in a surfaceresistivity method. In this case, the measured potential difference is always positive because the primary electric field isgreater than the secondary field. Therefore, the apparent resistivity is always positive if noise is free and topography isflat. The secondary field component, however, can be greater than the primary field component along the vector connectingtwo potential electrodes in the cross-hole resistivity method. Furthermore, if the secondary electric field and the vectorconnecting two potential electrodes have an opposite direction, the apparent resistivity become negative. Consequently,the apparent resistivity may be negative in the region where the primary electric field component along the vectorconnecting two potential electrodes is very small.

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