Geophysical research: article

A.G. Grigoryan
D.V. Likhodeev
Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences, Moscow, Russia
Journal: Geophysical research
Tome: 22
Number: 3
Year: 2021
Pages: 5-25
UDK: 550.344.385
DOI: 10.21455/gr2021.3-1
Full text
Keywords: Earth's magnetic field, anomalous variations of the geomagnetic field, geodynamic processes, preparation of large seismic events, deep fluid-dynamic systems, regional seismicity
Аnnotation: Variations in the geomagnetic field (solar-diurnal, bay-like, etc.) caused by external sources, such as ionospheric currents in the E layer, currents flowing in the upper atmosphere, contain important information about geodynamic processes in the earth's crust. In order to estimate the change in the geological environment, the parameter N(A) was used – the ratio of the amplitudes of intensity variations of the geomagnetic field caused by an external source and measured synchronously at different stations. The calculated parameter N(A) makes it possible to estimate the spatial and temporal changes in the local response of the geomagnetic field as well as changes in electrical conductivity, to identify zones of most active development of the geodynamic process, and so to determine the areas of preparation of the foci of large earthquakes. It is shown that for the system of se-lected observation points in the Republic of Armenia, the changes in the parameter N(A) are mainly caused by the induced component of the geomagnetic field. Using bay-like variations with periods of 10–25, 25–60, 60–90 min as well as Sq variations for 1986–1993, anomalous changes in the local geomagnetic field were de-tected, reflecting the activation of various geodynamic processes at different depths of the earth's crust and upper mantle within the studied territory of the Republic of Armenia. The precursors of two strong earthquakes – the Paravan earthquake (M=5.3, 13.05.1986) and Spitak earthquake (M=7.0, 07.12.1988) were revealed. The method was also applied in the area of the Elbrus volcanic center at the Baksan and Kuban observation points. Bay-like variations with periods of 10–25, 25–60 min and Sq variations were studied for the period 2011–2013. Small values of the anomalies in the N(A) parameter indicate insignificant changes in the electromagnetic parameters in the area of observation points, which indicates weak variations in the fluid regime of the geological environment in the Elbrus volcano area and is confirmed by the data of other observations. Studies of local changes in the pa-rameter N(A) make it possible to control the processes in the geological environment associated with the stress-strain state and dynamics of the fluid regime. This is important for the search of precursors of earthquakes and volcanic eruptions.
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