Purpose. It is well-known that strong earthquakes are typically accompanied by some phenomena which relate to variations of natural electromagnetic fields. Based on the idea about the mechanism of lithosphere–atmosphere–ionosphere coupling we expect to detect some precursors of strong natural earthquakes in electromagnetic data sets recorded by magnetotelluric instruments far enough from epicenters. Methodology. The temporal changes of power spectral density in the natural electromagnetic field components were analyzed with respect to the earthquakes with a magnitude greater than 5 (M5+) occuring in Europe as well as worldwide. Results. Electrical and magnetic field variations were recorded at three sites located at two lines. The first line was placed along the Tesseyre-Tornquist Zone in Poland and the second one was perpendicular to the first. The observations have been carried out from September 2015 to April 2018. The data were recorded by standard five channels magnetotelluric instruments. The magnetic field components were measured in three orthogonal directions and electrical ones in two horizontal orthogonal directions. The spectra of the electromagnetic field components have been analyzed with respect to earthquakes with M5+ in Europe as well as around the globe. The changes in the intensity of the spectra which can be treated as earthquake precursors have been detected from 24 to 32 hours before the seismic events. The reasons for such effects are also discussed. Originality. The electromagnetic monitoring is typically carried out next to seismically active regions but according to theoretical explanations some of the phenomena are of global origin. We used ordinary magnetotelluric data recorded at mid latitude sites placed far enough from the seismically active regions and we show that a global relationship exists between seismic and electromagnetic events with high probability. Practical significance. Such results can accomplish the information about earthquake precursors.
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