Magnetotelluric Responces of Three-Dimentional Bodies in Layered Earths

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The electric and magnetic fields scattered by a three-dimensional inhomogeneity in a conducting earth result largely from current-gathering, a boundary polarization charge phenomenon that becomes increasingly important as frequency falls. Boundary charges cause normalized electric field magnitudes, and thus tensor apparent resistivities and magnitudes of vertical admittance elements, to remain anomalous as frequency approaches zero. However, these E-field distortions below certain frequencies are essentially in-phase with the incident electric field. In addition, secondary magnetic field amplitudes over a body ultimately decline in proportion to the layered host impedance. It follows that tipper element magnitudes and all MT function phases become ... continued below

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Wannamaker, Phillip E.; Ward, Stanley H. & Hohmann, Gerald W. November 1, 1982.

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  • Geothermal Energy Program (U.S.)
    Publisher Info: DOEEEGTP (USDOE Office of Energy Efficiency and Renewable Energy Geothermal Tech Pgm)
    Place of Publication: United States

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The electric and magnetic fields scattered by a three-dimensional inhomogeneity in a conducting earth result largely from current-gathering, a boundary polarization charge phenomenon that becomes increasingly important as frequency falls. Boundary charges cause normalized electric field magnitudes, and thus tensor apparent resistivities and magnitudes of vertical admittance elements, to remain anomalous as frequency approaches zero. However, these E-field distortions below certain frequencies are essentially in-phase with the incident electric field. In addition, secondary magnetic field amplitudes over a body ultimately decline in proportion to the layered host impedance. It follows that tipper element magnitudes and all MT function phases become minimally affected at low frequencies by an inhomogeneity. Resistivity structure in nature is a collection of inhomogeneities of various scales, and the small structures in this collection can have MT responses as strong as those of the large structures. Hence, a severe distortion due to current-gathering in any nearby, small-scale geological noise can be superimposed to arbitrarily low frequencies upon the apparent resistivities and vertical admittance magnitudes of buried targets. On the other hand, the MT responses of small and large bodies have frequency dependencies that are, in general, separated as the square of the geometric scale factor distinguishing the different bodies.

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  • Report No.: DOE/ID/12079-87
  • Grant Number: DE-AC07-80ID12079
  • DOI: 10.2172/893412 | External Link
  • Office of Scientific & Technical Information Report Number: 893412
  • Archival Resource Key: ark:/67531/metadc882781

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  • November 1, 1982

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  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 7, 2016, 4:49 p.m.

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Wannamaker, Phillip E.; Ward, Stanley H. & Hohmann, Gerald W. Magnetotelluric Responces of Three-Dimentional Bodies in Layered Earths, report, November 1, 1982; United States. (digital.library.unt.edu/ark:/67531/metadc882781/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.