CSAMT and MT-AMT Static Shift Correction by Means of the Total Horizontal Magnetic Field

Abstract

“Static shift” appear as the frequency-independent influence on results of EM soundings made with natural or controlled sources. Static shift distortion displaces apparent resistivity curves usually down for several orders and appear as the main reason of false results. In this paper we propose the quantitative method of “static shift” correction. The use of the total horizontal magnetic field measurements in the field of controlled source frequency sounding is the base of this technique. The use of magnetic measurements with induction coils, free of galvanic connection with the ground, made possible to calculate quantitatively the static shift distortions. Experiment on control source sounding with spacing up to 25 and 50 km between transmitter and receiver is implemented for to study the static shift in the Kovdor area (Kola Peninsula). Apparent resistivity curves, calculated by the total electric field \( \left( {\rho E_{tot} } \right) \) happened to be shifted in some measuring points down up to 300–500% compare to apparent resistivity curves calculated by the total magnetic field (\( \rho H_{tot} \)). Impedance curves (\( \rho Z_{tot} \)) shifted dawn up to 900–2500% compare to \( \rho H_{tot} \). After corrections the anomalous lowering of apparent resistivity disappeared and the area of Yona-Belomorian craton happened to be homogeneous in accordance with geological presupposition.