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An Interpretive Analysis of Magnetotelluric Response for a Three-dimensional Body Using FDM  

Han Nuree (서울대학교 공과대학 지구환경시스템공학부 물리탐사연구실)
Lee Seong Kon (한국지질자원연구운)
Song Yoonho (한국지질자원연구운)
Suh Jung Hee (서울대학교 공과대학 지구환경시스템공학부 물리탐사연구실)
Publication Information
Geophysics and Geophysical Exploration / v.7, no.2, 2004 , pp. 136-147 More about this Journal
Abstract
In this study, the characteristics of magnetotelluric (MT) responses due to a three-dimensional (3-D) body are analyzed with 3-D numerical modeling. The first model for the analysis consists of a single isolated conductive body embedded in a resistive homogeneous half-space. The second model has an additional conductive overburden while the other conditions remain the same as the first one. The analysis of apparent resistivities shows well that the 3-D effects are dominant over some frequency range for the first model. Two mechanisms, current channeling and induction, for secondary electric fields due to the conductive body are analyzed at various frequencies: at high frequencies induction is more dominant than channeling, while at low frequencies channeling is more dominant than induction. Tippers have a strong relation to the position of anomalous body and the real and imaginary parts of induction vector also indicate the position of anomalous body. off-line conductive anomaly sometimes causes severe problem in 2-D interpretation. In such case, induction vector analysis can give information on the existence and location of the anomalous body. Each parameter of the second model shows similar responses as those of the first model. The only difference is that the magnitude of all parameters is decreased and that the domain showing the 3-D effects becomes narrower. As shown in this study, the analysis of 3-D effects provides a useful and effective means to understand the 3-D subsurface structure and to interpret MT survey data.
Keywords
3-D MT modeling; apparent resistivity; phase; secondary field; tipper; induction vector;
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