The separation of the electromagnetic field at the position of the sources in the magnetotelluric method

P.N. Alexandrov^a*, A.K. Rybin^b**, O.B. Zabinyakova^b***

^aGeoelectromagnetic Research Center, Schmidt Institute of Physics of the Earth,

Russian Academy of Sciences, Troitsk, 108840 Russia

^bResearch Station of the Russian Academy of Sciences in Bishkek, Bishkek, 720049 Kyrgyzstan

E-mail: ^*alexandr@igemi.troitsk.ru, ^**rybin@gdirc.ru, ^***zabinyakova@gdirc.ru

Received April 20, 2017

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Abstract

The theoretical problems of using the magnetotelluric sounding method (MTS) for electromagnetic monitoring of the current geodynamic processes have been considered.

Using the electromagnetic field registered on the Earth's daylight surface, the task has been set to single out the component associated with exogenous sources (ionospheric currents, lighting discharge, etc.) and the field component related to endogenous sources that can be generated by irreversible geodynamic processes in the lithosphere, such as cracking. The direct MTS problem for layered space, which is expressed as the impedances of the upper and lower half-spaces and fields from the sources located in the corresponding areas of space, has been solved. Using the electromagnetic field extension through the horizontally layered medium, a formula showing the relationship between the tangential components of the electromagnetic field registered on the Earth's surface has been determined. In this case, the magnetotelluric impedance depends exclusively on the electromagnetic parameters of the geoelectrical medium. The field from the sources located in the layered space is included additively into this relationship formula.

The approach to solving the direct MTS problem for horizontally layered media on the basis of field extension is not stable terms of calculation. For this reason, the stable algorithm for solving the MTS direct problem with account of electromagnetic fields sources distributed in the lower half-space has been developed. A stable solution of the direct problem for the layered laterally homogeneous arbitrary anisotropic model of geoelectrical medium with electromagnetic field sources distributed in it has been obtained. In this case, the sources can be located in arbitrary places of the layered half-space with the random amplitude and time of occurrence. This solution allows to efficiently implement direct mathematical modeling of the electromagnetic field, thereby providing the necessary theoretical and calculation basis for setting and solving the inverse problem of passive electromagnetic monitoring.

Keywords: passive electromagnetic monitoring, magnetotelluric sounding, modern geodynamic processes

Acknowledgments. The study was supported by the Russian Foundation for Basic Research (project no. 17-05-00844).

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For citation: Alexandrov P.N., Rybin A.K., Zabinyakova O.B. The separation of the electromagnetic field at the position of the sources in the magnetotelluric method. Uchenye Zapiski Kazanskogo Universiteta. Seriya Estestvennye Nauki, 2018, vol. 160, no. 2, pp. 339–351. (In Russian)

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