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Bahr et al. 1993
Bahr, K., Olsen, N. and Shankland, T.J. (1993). On the combination of the magnetotelluric and the geomagnetic depthsounding method for resolving an electrical conductivity increase at 400 km depth. Geophysical Research Letters 20: doi: 10.1029/93GL02134. issn: 0094-8276.

The simultaneous use of two different passive electromagnetic (EM) sounding techniques for resolving the upper mantle electrical conductivity structure is emphasized: The geomagnetic (GM) method uses magnetic field variations at periods between 3 hours and 600 hours, yielding penetration depths between 300 km and 1000 km. The magnetotelluric (MT) method is applied to field variations at periods between a few seconds and 16 hours and yields penetration depths between a few km and 600 km. This is an extension of both methods, using additional Dst-data for MT and additional Sq-data for GM. In application to field data from Western Europe the resulting overlap of the target depths includes electrical conductivity increase from 10-2 S/m at 300 km to 1 S/m at 700 km depth while a single conductivity jump at either 400, 500, or 700 km cannot explain the broadband data. Although the olivine to spinel transition is a possible explanation of the conductivity enhancement at 400 km depth, another mineralogy could also occur. This conductivity increase has not been resolved in other sub-continental profiles and lateral heterogeneity is probable in this depth range. ¿American Geophysical Union 1993

BACKGROUND DATA FILES

Abstract

Keywords
Electromagnetics, Electromagnetic theory, Geomagnetism and Paleomagnetism, Geomagnetic induction, Geomagnetism and Paleomagnetism, Time variations, diurnal to secular, Tectonophysics, Composition and state of the Earth's interior
Journal
Geophysical Research Letters
http://www.agu.org/journals/gl/
Publisher
American Geophysical Union
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