Negative Apparent Resistivity in Resistivity Method

전기비저항탐사에서 음의 겉보기 비저항

  • 조인기 (강원대학교 자연과학대학 지구물리학과) ;
  • 김정호 (한국지질자원연구원 탐사개발연구부) ;
  • 정승환 (한국지질자원연구원 탐사개발연구부) ;
  • 서정희 (서울대학교 공과대학 지구환경시스템공학부)
  • Published : 2002.08.01

Abstract

In the resistivity method, the potential difference between two grounded electrodes is measured and this can be positive or negative. The apparent resistivity and the potential difference have the same polarity. Since the electric field 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 measured potential difference and the apparent resistivity become positive. If the opposite is the case, they become negative. In general, the primary electric field and the vector connecting two potential electrodes have the same direction in a surface resistivity method. In this case, the measured potential difference is always positive because the primary electric field is greater than the secondary field. Therefore, the apparent resistivity is always positive if noise is free and topography is flat. The secondary field component, however, can be greater than the primary field component along the vector connecting two potential electrodes in the cross-hole resistivity method. Furthermore, if the secondary electric field and the vector connecting 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 vector connecting two potential electrodes is very small.

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