f Problems in interpretation of resistivity sounding data, distorted by geological noise

The traditional resistivity sounding method deals with isolated sounding sites located casually on profile or area of investigation and executed with logarithmic step in distance growth. This technology has very restricted possibilities. Therefore it has begin to exchange practically simultaneously in different countries into new sounding technology, called multielectrodic sounding, or resistivity tomography, electrical imaging, etc. Its main advantage - more dense survey along profile - is clear visible, while the other - overlapping system of measurements is not so evident. Our group in MSU began to apply multi-electrodic resistivity sounding to overcome distorting influence of geological noise. From the end of the 80-th we have been working in areas with high resistivity contrast along both vertical, and horizontal direction. Such sounding data have different features of distortions or differences from response for horizontally layered models. At that period we developed theory of distortions of DC electric field by deep and near-surface inhomogeneities (Electrical..., 1994) and software to establish VES data distortion with the help of various indicators, noticeable on VES curves. We have found, that more than 70 % of all VES curves are distorted. That means, that the distortions are practically constant features of resistivity sounding. Carrying out the large volumes of VES field data and their interpretation (up to 1000 VES sites a year) we analyzed misfit errors of VES curves interpretation. The average value of misfit error (average RMS or D , where D is dispersion) consists 8-12%, that seems rather high value and needs to be explained.