HR: 0800h
AN: GP41B-0879    [Abstracts]
TI: Three-Dimensional Topographic Correction in Magnetotelluric Surveys Using Edge Finite-Element Modeling
AU: * Nam, M
EM: nmj@GPL.snu.ac.kr
AF: School of Civil, Urban & Geosystem Engineering, Seoul National University, Shinrim9-dong, Kwanak-gu, Seoul, 151-744 Korea, Republic of
AU: Kim, H
EM: hejkim@pknu.ac.kr
AF: Department of Environmental Exploration Engineering, Pukyong National University, Daeyeon3-dong, Nam-gu, Busan, 608-737 Korea, Republic of
AU: Song, Y
EM: song@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, Gajeong-dong 30, Yuseong-gu, Daejeon, 305-350 Korea, Republic of
AU: Lee, T
EM: megi@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, Gajeong-dong 30, Yuseong-gu, Daejeon, 305-350 Korea, Republic of
AU: Suh, J
EM: suh@GPL.snu.ac.kr
AF: School of Civil, Urban & Geosystem Engineering, Seoul National University, Shinrim9-dong, Kwanak-gu, Seoul, 151-744 Korea, Republic of
AB: We apply a three-dimensional (3D) edge finite-element method (FEM) code developed for computing magnetotelluric (MT) responses to a model having arbitrarily complex topography and subsurface structure. Edge FEM uses a vector shape function at each edge of hexahedral element, satisfying the continuity of the tangential electric field even at conductivity boundaries. The modeling algorithm has been successfully verified for COMMEMI 3D-2 and 2D ridge models. Using a trapezoidal hill model, we investigate a 3D topographic effect on MT responses to know whether it can be reduced by a correction procedure. This correction technique assumes that the topographically distorted subsurface response is equal to the undistorted subsurface response multiplied by a distortion tensor. This tensor is a function of frequency and receiver position, and is calculated by normalizing the impedance for a topographic model having a homogeneous medium with the half-space impedance. The 3D terrain correction procedure reduces distortions caused by the topographic effect and improves the quality of subsurface interpretation. Numerical experiments indicate that although significant MT anomalies can be generated by topographic features, the correction procedure reduces distortions by the topographic effect and improves the quality of subsurface interpretation. Topography-corrected data show more clearly the response of subsurface conductivity structure, making quantitative interpretation more valid.
DE: 0644 Numerical methods
DE: 0903 Computational methods: potential fields (1214)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005