Two-Dimensional Magnetotelluric Interpretation by Finite-Element Method

유한요소법에 의한 MT 법의 2차원 해석

  • Kim, Hee-Joon (Department of Environmental Exploration Engineering, Pukyong National University) ;
  • Choi, Ji-Hyang (Department of Energy System Engineering, Seoul National University) ;
  • Han, Nu-Ree (Department of Energy System Engineering, Seoul National University) ;
  • Lee, Seong-Kon (Groundwater & Geothermal Resources Division, Korea Institute of Geoscience & Mineral Resources) ;
  • Song, Yoon-Ho (Groundwater & Geothermal Resources Division, Korea Institute of Geoscience & Mineral Resources)
  • 김희준 (부경대학교 환경탐사공학과) ;
  • 최지향 (서울대학교 에너지시스템공학부) ;
  • 한누리 (서울대학교 에너지시스템공학부) ;
  • 이성곤 (한국지질자원연구원 지하수지열연구부) ;
  • 송윤호 (한국지질자원연구원 지하수지열연구부)
  • Published : 2008.05.31

Abstract

Magnetotelluric (MT) methods are widely applied as an effective exploration technique to geothermal surveys. Two-dimensional (2-D) analysis is frequently used to investigate a complicated subsurface structure in a geothermal region. A 2-D finite-element method (FEM) is usually applied to the MT analysis, but we must pay attention to the accuracy of so-called auxiliary fields. Rodi (1976) proposed an algorithm of improving the accuracy of auxiliary fields, and named it as the MOM method. Because it introduces zeros into the diagonal elements of coefficient matrix of the FEM total equation, a pivoting procedure applied to the symmetrical band matrix makes the numerical solution far less efficient. The MOM method was devised mainly for the inversion analysis, in which partial derivatives of both electric and magnetic fields with respect to model parameters are required. In the case of forward modeling, however, we do not have to resort to the MOM method; there is no need of modifying the coefficient matrix, and the auxiliary fields can be elicited from the regular FEM solution. The computational efficiency of the MOM method, however, can be greatly improved through a sophisticated rearrangement of the total equation.

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