Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
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Application of Two-Dimensional Boundary Condition to Three-Dimensional Magnetotelluric Modeling

3차원 MT 탐사 모델링에서 2차원 경계조건의 적용

  • Han, Nu-Ree (Department of Energy Systems Engineering, Seoul National University) ;
  • Nam, Myung-Jin (Department of Petroleum and Geosystems Engineering, The University of Texas at Austin) ;
  • Kim, Hee-Joon (Department of Energy Resources Engineering, Pukyong National Universiy) ;
  • Lee, Tae-Jong (Geological Research Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Song, Yoon-Ho (Geological Research Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Suh, Jung-Hee (Formerly Department of Civil, Urban and Geosystem Engineering, Seoul National University)
  • 한누리 (서울대학교 에너지시스템공학부) ;
  • 남명진 ;
  • 김희준 (부경대학교 에너지자원공학과) ;
  • 이태종 (한국지질자원연구원 국토지질연구본부) ;
  • 송윤호 (한국지질자원연구원 국토지질연구본부) ;
  • 서정희 (서울대학교 지구환경시스템공학부)
  • Published : 2008.11.30
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Abstract

Assigning an exact boundary condition is of great importance in three-dimensional (3D) magnetotelluric (MT) modeling, in which no source is considered in a computing domain. This paper presents a 3D MT modeling algorithm utilizing a Dirichlet condition for a 2D host. To compute boundary values for a model with a 2D host, we need to conduct additional 2D MT modeling. The 2D modeling consists of transverse magnetic and electric modes, which are determined from the relationship between the polarization of plane wave and the strike direction of the 2D structure. Since the 3D MT modeling algorithm solves Maxwell's equations for electric fields using the finite difference method with a staggered grid that defines electric fields along cell edges, electric fields are calculated at the same place in the 2D modeling. The algorithm developed in this study can produce reliable MT responses for a 3D model with a 2D host.

MT 모델링에서는 송신원을 고려하지 않으므로, 평면파에 대한 배경 매질의 반응을 경계값으로 설정하는 Dirichlet 경계조건을 이용할 때에 그 경계값의 정확한 계산이 매우 중요하다. 이 연구에서는 1차원 배경 매질만을 가정하던 기존의 모델링 알고리듬을 2차원 배경 매질을 고려할 수 있도록 발전시켰다. 1차원 배경매질의 경우 경계값은 해석적으로 계산할 수 있으나, 2차원 구조가 존재하는 경우에는 2차원 모델링을 통해 경계값을 계산하여야 한다. 2차원 모델링의 TM(transverse magnetic) 및 TE (transverse electric) 모드는 3차원 모델링의 입사 전기장의 분극 방향과 2차원 구조의 주향에 따라서 결정된다. 전기장을 셀 모서리에 정의하는 기존의 3차원 모델링 알고리듬과 잘 부합하도록 2차원 모델링에서도 모서리에서 전기장을 계산하였다. 2차원 모델링을 통해 계산된 값을 3차원 모델링의 경계값으로 활용한 결과, 단층 모형 혹은 한 면에 바다를 포함한 모형에 대해 보다 정확한 겉보기비저항 및 위상을 얻을 수 있었다.

Keywords

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