지구물리 (Journal of the Korean Geophysical Society)

한국지구물리·물리탐사학회 (Korean Society of Earth and Exploration Geophysicists)
권호 표지

2차원 이방성 구조의 MT 반응

MT response on the two dimensional anisotropic structure

  • 발행 : 19990000
PDF 다운로드
⟨ 이전 논문 다음 논문 ⟩

초록

상부맨틀이나 하부지각의 고전도층(HCL)에서 나타나는 고이방성은 MT 탐사에 큰 영향을 미칠 수 있다. 본 연구에서는 고이방성 매질이 MT 반응에 미치는 영향을 고찰하기 위한 모델연구를 수행하였다. 각각의 균질한 암체의 전기적 성질은 대칭적인 전기전도도 텐서로 주어지며 모델링을 위한 기본방정식은 전기장과 자기장 성분이 결합되어진 주파수 영역 분산 방정식으로 주어진다. 이방성 매질에서는 전기장의 왜곡에 의해 항상 4성분의 임피던스가 존재하며, 2차원 구조에서는 대각선 성분, 특히 YY성분의 임피던스가 증가한다. 어떤 경우에는 서로 이방성 주향이 다른 매질의 상호작용에 의해 TM 모드의 위상이 90° 이상으로 증가하고 겉보기비저항이 낮아지는 현상이 발생한다. GB 분리법은 광역적인 반응을 추출하는데 이용될 수 있으나, 심부의 이방성의 영향을 크게 받는다. 이상의 모델연구의 결과를 BC87자료에 적용하여 현장자료에서의 이방성 효과를 고찰하였다.

Magnetotelluric responses may be affected by strong anisotropy of the high-conductivity layers (HCL) in the upper mantle or lower crust. We have studied two-dimensional anisotropy MT modelling to examine the effect of high anisotropic media. Electrical properties of a homogeneous anisotropic body are defined by a symmetric conductivity tensor and the problem is described by coupled diffusion equation in the frequency domain. In two-dimensional anisotropic environments, diagonal elements of the impedance tensor have higher values than those in isotropic environments. In some cases, TM mode phases reach more than 90°and apparent resistivities decrease for some frequency range because of telluric distortion. GB decomposition may be used to recover regional responses, but can be affected by the regional anisotropic effect. Considering these results, BC87 dataset was interpreted with a modified anisotropic model.

키워드

참고문헌

  1. Geophysical Journal International v.130 Electrical anisotropy and conductivity distribution functions of fractal random networks and of the crust: the scale effect of connectivity Bahr, K.
  2. Journal of Applied Geophysics v.29 A study of static shift removal from magnetotelluric data Beamish, D.;Travassos, J. M.
  3. Geophysics v.47 An eigenstate formulation of the manetotelluric impedance tensor Eggers, D. E.
  4. Journal of Geophysical Research v.B no.93 Decomposition of magnetotelluric impedance tensors in the presence of local three-dimensional galvanic distortion Groom, R. W.;Bailey, R. C.
  5. Geophysics v.56 Analytic investigations of the effects of near-surface three-dimensional galvanic scatterers on MT tensor decompositions Groom, R. W.;Bailey, R. C.
  6. Geophysics v.53 Static shift of magnetotelluric data and its removal in a sedimentrary basin environment Jones, A. G.
  7. Journal of Geomagnetism and Geoelectricity v.45 The BC87 Dataset: Tectonic Setting, Previous EM Results, and Recorded MT Data Jones, A. G.
  8. Journal of Geomagnetism and Geoelectricity v.45 Decomposition and Modelling of the BC87 Dataset Jones, A. G.;Groom, R. W.;Kurtz, R. D.
  9. Electrical methods in Geophysical Prospecting Keller, G. V.;Freschknecht. F. C.
  10. Geophysical Journal International v.113 The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle Kurtz, R. D.;Craven, J. A.;Niblett, E. R.;Stevens, R. A.
  11. Geophsical Journal International v.120 Coincident conductive and reflective middle and lower crust in southern British Columbia Marquis, G.;Jones, A. G.;Hyndman, R. D.
  12. Geophysical Journal International v.115 Magnetotelluric response of anisotropic 2-D structures Osella, A. M.;Martinelli, P.
  13. Geophysical Journal International v.128 Finite-difference modelling of magnetotelluric fields in two-dimensional anisotropic media Pek, J.;Verner, T.
  14. Geophysical Prospecting v.19 Magnetotelluric effect of dipping anisotropies Reddy, I. K.;Rankin, D.
  15. Geophysics v.40 Magnetotelluric response of laterally inhomogeneous and anisotropic structure Reddy, I. K.;Rankin, D.
  16. Geophysical Journal International v.130 Estimating galvanic-distortion magnetic fields in magnetiotellurics Smith, J. T.
  17. Geophysics v.50 The magnetotelluric impedance tensor properties with respect to rotations Spitz, S.
  18. Geophysics v.52 Magnetotelluric strike rules Zhang, P.;Roberts, R. G.;Pederson, L. B.