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Russian Geology and Geophysics

2014 year, number 10

GEOMAGNETIC INDUCTION RESPONSES OF ANISOTROPIC CONDUCTING MANTLE

V.V. Plotkin
A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: MagnesiowГјstite, lower mantle, conductivity anisotropy, induction, three-component records of geomagnetic variations, observatories, horizontal components of electric field

Abstract

Phase change of dielectric magnesiowьstite in the lower mantle may leave signatures in geomagnetic records of the globally distributed array of observatories. The related features appear in EM induction responses of lower mantle, which are studied theoretically. The surface EM field corresponding to a response of the earth with conductivity anisotropy in a mantle spherical layer is presented as the sum of the magnetic and electric modes. Equations for the fields of both modes and their relationship in a weakly anisotropic earth are obtained by the perturbation method. The two field modes are analyzed jointly and separately to characterize the conductivity tensor of the anisotropic lower mantle. The tensor elements corresponding to the tangential components of the field can be estimated from the magnetic mode alone recorded currently by the global network of geomagnetic observatories. For the tensor data to be complete, observatory data on lateral variations of the electric field are required in addition to three-component geomagnetic records.

DOI: http://dx.doi.org/10.1016/j.rgg.2014.09.009