Constructing the Optimal Model of the Geoelectric Section Using Vertical Electrical Sounding Data: Case Study of the Central Part of the Garm Research Area

Abstract

In geophysical studies, particularly when searching for precursors of earthquakes, there are problems of investigating the geoelectric structure of the medium at the observation point and its changes over time. This paper develops an approach to solving these problems based on the long-term medium monitoring data using the vertical electrical sounding (VES) method. The sounding was carried out daily for 12 years (from April 1979 to May 1992) in the central part of the Garm research area using a stationary multielectrode array. The data are used to construct about 4000 individual VES curves, which are then used to construct 36 10-day average curves for solving the inverse problem within a horizontally layered model using the IPI package. Four-, five-, six-, and seven-layer models of the geoelectric section are constructed based on the interpretation of the solutions. These models are compared by different criteria of their quality. As a result, a four-layer model is selected, which can be considered the best in the sense of minimizing the residual of the solution of the inverse problem, a horizontally layered approximation of the real (average for the seasons of the year) geoelectric section. A comparison of the available geological and geophysical data with each other and with the results of solving the VES inverse problem shows that the four-layer model of the section is in good agreement with the data of geological (drilling, geological mapping), geoelectric (transient electromagnetic sounding (TEM), profile VES), and other studies performed at the observation point.