Department of Geomagnetism

This study represents a new view on the 1D magnetotelluric problem on a layered half-space. Emphasis is put on the physical aspect of the matters. No wave effects are allowed and the electric field undergoes subsequent decay with the rate depending on the conducting properties of the subsurface. It is also claimed that the magnetic field inside a layer is produced by local currents according to Ampère’s law. The presented analysis led to explicit formulas for apparent resistivity and impedance phase – the key characteristics of the magnetotelluric research – as functions of frequency. This is significant because understanding of these behaviours can help in interpretation of measured data – in other words, it can help to "read" the sounding curves. It is shown that as to how the apparent resistivity reacts on a change in local resistivity by increase or decrease, the impedance phase reacts on the same factor by change of its curvature. This finding is a base for design of a straightforward method to recover physical parameters of the model. Once properties of the sounding curves are known, the layered half-space in question can be easily reconstructed.

Computed apparent resistivity and phase difference between the electric and magnetic fields for Half-space 1 consisting of 3 layers (1000 m, 100 Ωm; 3000 m, 1000 Ωm; 2000 m, 10 Ωm) and substratum (100 Ωm). The violet curves are obtained by using Wait’s recursion formula, the green ones are obtained by explicit formulas as the results of this study. The presented dependences embody abrupt changes which reflect sharp transitions in physical conditions on interfaces between the layers whose resistivities are marked in orange. The smooth recursive solution provides a basis for validation of the present approach.

In the period 17/09 - 24/09/2016 additional magnetotelluric measurements were carried out on the selected positions in Belianske Tatras and Spišská Magura mountains.

These measurements were accomplished in the framework of bilateral cooperation with Geophysical Institute of the Czech Academy of Sciences.