Science and technological developments: article

The technique of quantitative estimation of the static shift distortion with the use of magnetic field of controlled source
1 St. Petersburg Branch of Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation Russian Academy of Sciences 2 Geological Institute FRC “Kola Science Center of the Russian Academy of Sciences”
Journal: Science and technological developments
Tome: 98
Number: 4
Year: 2019
Pages: 5-18
UDK: 550.372+550.379
DOI: 10.21455/std2019.4-1
Аnnotation file
Bibliographic list
Keywords: sounding, controlled sources, static shift distortion, Baltic shield
Аnnotation: Static distortions are known abroad under the term “static shift distortions”. They have a strong influence on the results of deep electromagnetic soundings with both natural (AMT-MTS) and control (CSAMT) sources. The main cause of static distortion is the local, in comparison with the electromagnetic wavelength in the ground, heterogeneity of the upper half-space. Static distortion is frequency-independent in nature and manifests itself in a parallel shift of the apparent electrical resistivity curves relative to the resistivity scale. Moreover, the shape of the apparent resistivity, non-existent information about the model of the section, is preserved, but ideas about the depths of the location of the layers and about the magnitude of their electrical conductivity change. To date, many methods have been developed to account for static shift. But they all have a qualitative, phenomenological character. In this paper, a quantitative method for correcting staticshift distortions is proposed. The technique is based on the use of the apparent resistivity curve of a control source, normalized by the value of the total horizontal magnetic field. The use of magnetic measurements with induction coils that do not have a galvanic connection with the Earth allows one to quantitatively calculate static shift distortions by comparing the magnetic field with apparent resistance curves normalized by the total electric field or by the value of the total input impedance. The proposed methodology is applicable only for control source frequency soundings of CSAMT. Nevertheless, it allows you to correct the MTS and AMT curves measured on the same setup and with the same sensors in the low-frequency region, outside the wave zone, where the CSAMT method loses its sounding functions. The results of experimental work are presented that justify the applicability of the new method on the example of control source soundings.