Geophysical processes and biosphere: article

Аnnotation: Previously, the authors carried out a unique experiment on long-term continuous precision monitoring of crustal resistance variations in a highly seismic region. The measurements were carried out using precision equipment every day for 12 years on a stationary multi-electrode VES setup, including 18 spacings. The result of this experiment can be considered as a VES profile of a special type, in which, instead of a linear coordinate, the sounding date changes from picket to picket. This profile contains over 4000 pickets. As a result of this profile inversion, long-term time series of resistivity variations at different depths were constructed. To estimate the accuracy of resistivity reconstruction in each layer, a series of numerical experiments was carried out. In the course of these experiments, synthetic time series of resistivity variations in different layers of the section were first constructed, simulating real resistivity variations. Then the direct VES problem was solved for them, and time series of apparent resistivity were constructed. Pseudorandom noise with properties similar to real noise was added to these series. After that, the inverse VES problem was solved and the accuracy of restoring the original synthetic resistivity series was estimated. In the present work, the experimental series of time variations of resistivity in four layers of the geoelectric section, obtained in this experiment, are analyzed. These series, lasting about 10 years, have been reconstructed with an accuracy unprecedented for field soundings. The decomposition of resistivity series into seasonal and residual (flicker-noise) components has been carried out, and their statistical characteristics have been evaluated. The dependence of the amplitude of seasonal effects on the depth of the layer has been studied. The power-law parameter of the spectra for the flicker-noise components is calculated, and its systematic decrease is found as the spacing AB for apparent resistivities and depth for resistivity increases. The possibility of changing the resistivity under the influence of nearby shallow seismic events, as well as the processes of their preparation, is discussed. Earthquakes are considered, the sources of which were located in the immediate vicinity of the probed volume or even partially captured it (the ratio of the linear size of the source to the epicentral distance is at least 0.5). The presence of resistivity variations in the lower layers of the geoelectric section, which are synchronous with seismic events, has been demonstrated, but their significance needs further study.