Structure of areas with basement rocks outcrops in the Uimonskaya depression of the Gorniy Altay based on electrical survey data using three-dimensional modeling

Relevance. Significant development of tourist infrastructure in the Gorniy Altai, associated with the construction of hotels, campsites, guest houses, new communications, roads, as well as the reconstruction of existing ones. In this relation the tasks of search, exploration and additional exploration of deposits of building materials, ore minerals by geophysical methods are relevant. Knowledge about the structure of the upper part of the section is required for mapping aquifers in order to drill demanded hydrological wells. In addition, since Gorniy Altai belongs to the territories of high seismic hazard, it is important to identify seismic-generating fault structures for correct seismic zoning. Aim. To clarify the deep and near-surface structure of the Uimonskaya depression using electrical exploration methods. Studies of the geoelectric structure of the depression began in 2011 with depth soundings by transient electromagnetic and vertical electric soundings. In 2018, an electrotomography method was added in several areas of the trough to build detailed models of the upper part of the section. Depths to the basement according to transient electromagnetic and vertical electric soundings data in the western and central part of the depression, away from the mountain frame, reach 500 m, and in the eastern part – up to 1000 m, and in some areas there are bedrock outcrops on the day surface, the structure and origin of which are still unclear. Results. The paper presents geoelectric models based on the data of the electrotomography method of one of the sites with bedrock outcrops, for verification and refinement of which numerical three-dimensional modeling was performed. According to the results of the electrotomography method, it was established that the bedrock outcrops observed on the day surface are not a subsurface high resistivity heterogeneity of small size. It is an object going to a depth of more than 45 m with inclined and subvertical lateral boundaries. Harmonization of the results of all used methods – transient electromagnetic, vertical electric soundings and electrotomography – allowed substantiating the models of the general geoelectric structure of the study area and assuming the existence of an extended intermountain cofferdam in the western part of the trough, partially extending to the surface. These results can be useful not only for solving the above-mentioned applied problems, but also important for specialists of geological directions when considering the stages of formation of the depression, which refers to the fundamental problems of geodynamics, structural geology and neotectonics of the entire Gorniy Altai.