Credit: SPbU An essential preliminary to building and construction or resource extraction is studying the geological structure of the site. One of steps of this process is geophysical investigation. This provides a continuous overview of the geological horizons rather than just data on points: boreholes. The standard methods of geophysics help successfully solve this problem in comparatively simple conditions. Yet the classical direct current methods may lead to serious inaccuracy if we have to investigate geologically complex structures with thin layers of sandy and clayey soils. Among the most popular methods in geoelectrical survey is electrical resistivity tomography (ERT). It is a geophysical method for imaging subsurface structures by electrical resistivity measurements made at the surface or in boreholes. It allows geologists to 'see' various rock formations as they have different resistivity. Yet the electrical resistivity tomography can also result in serious inaccuracy in measuring geologic layer thickness, and therefore lead to a considerable increase in values.