Electromagnetic monitoring in the region of seismic activization (on the Gorny Altai (Russia) example)

Abstract

Based on the analysis of the field data of nonstationary electromagnetic soundings with different installations, the evolution of the stressed state of the geological massif in the epicentral region of the destructive 2003 Мw7.3 Chuya earthquake is investigated in the paper. The measurements by these methods were executed in a lot of regular points located at two sites of the western part of the Chuya basin of Gorny Altai (Russian Federation). The field works have been performed for 13 years. We developed a measurement technique using data from the three Transient Electromagnetic Method (TEM) method settings for determination of the resistivity anisotropy coefficient. Interpretation of the field data is carried out based on the inverse problem solution, and further, taking into account the geological structure and seismological data, variations of true electrophysical characteristics of the cross-section (electrical resistivity and resistivity anisotropy coefficient) are analyzed. According to the TEM data acquired in the 1980s, the geoelectric parameters of rocks in the period of low seismic activity were estimated. Comparison of the results of quantitative interpretation of the modern measurements (2004–2016) with those taken before the Chuya event allows tracing a change in the geoelectric parameters of the cross-section in the aftershock period, and on this basis tracking the evolution of the rock massif after the destructive seismic impact.