Magnetotelluric interpretations in a crustal environment. Semi-annual report, 1 January 1978-30 June 1978. [MIT, January 1 to June 30, 1978] [electronic resource].
- Cambridge, Mass. : Massachusetts Institute of Technology, 1978.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
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- Pages: 208 : digital, PDF file
- Additional Creators:
- Massachusetts Institute of Technology
United States. Department of Energy. Office of Scientific and Technical Information
- Crustal variations in the conductivity and resistivity of the earth cause great complications in the surface distribution of electric currents and fields. At low frequencies the crust can be treated as a thin sheet, and the crustal conductivity variations can be incorporated into the thin sheet conductance variation. In the first model developed in this thesis, the layer below the thin sheet is a layer of finite conductivity. Thus the thin sheet model consists of a thin conducting sheet of variable conductivity over a general layered medium. In the earth the resistive layer below the surface conductive sheet is represented by the lower crust. The resistivity of the lower crust underneath the ocean is expected to be different from the resistivity of the lower crust below the continents. This difference in the lower crust resistivity value is taken into account in the Generalized Thin Sheet model. In this model the thin sheet is treated as an anisotropic thin sheet with different (parallel) conductivity and (perpendicular) resistivity variations. Specific examples in which conductivity and resistivity vary only in one direction were studied. It was found that in a crustal environment, approximation being made, it is possible to get simple analytical solutions for E variations perpendicular to the strike direction. Electric fields measured at a point are influenced not only by the conductivity and the resistivity of the medium at the point of measurement, but also by the electrical properties of the medium a considerable distance away. The method of imbedding was developed in which fields close to the point of measurement are computed at close spacings, while fields farther away are determined at larger spacings. These methods were applied to modelling magnetotelluric measurements on the island of Oahu. 107 figures, 13 tables.
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