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Impedances for induction soundings of the Earth's mantle

Semenov V., Shuman V.

Acta Geophysica

2010

Vol. 58, no. 4

527-542

Determination of impedances is necessary in order to eliminate some shortcoming of our knowledge about structures of the exciting source fields and their fickleness. The experimental impedances for induction soundings result from the impedance boundary conditions or heuristic models. The simplified models give just a rough idea of their domain of applicability. Impedances can depend on many factors, including the exciting field structures of several source types which are present in the period range of the mantle soundings (10&sup4;-4×10&sup8; s). The problem in the mantle investigations arises if impedances measured by different methods have to be jointly inverted in order to essentially prolongate the analyzed period range and hence to increase the reliability and depth of induction soundings on land. The subject of our work is an analysis of the known magnetotelluric and magnetovariation impedances to suggest a physically substantiated approach for their joint inversions.

The fundamental relations of impedance type in general theories of the electromagnetic induction studies

Shuman V., Kulik S.

Acta Geophysica Polonica

2002

Vol. 50, nr 4

607-618

This paper considers a number of important aspects of the modern theory of electrical conductivity in application to magnetotelluric and magnetovariation methods. Attention is paid to insufficient argumentation of the known attempt to carry out deep geomagnetic sounding by applying a truncated version of accurate impedance ratio, as it was done by Rytov and Leontovich for harmonic fields of natural and controlled origin. We propose a new approach to the problem of processing data from magnetotelluric and magnetovariational methods of studies that is based on the concept of scalar conditions of impedance type that enables us to simplify and unify an experiment in which the measurements are completely and unambiguously conducted in terms of input impedance.