| Abstract: | In all electrical methods (EM, MT, DC), a theoretical one-to-one relation links the apparent resistivity diagram at a station with the local distribution of the resistivities in a tabular earth. Unfortunately, the actual field diagrams derive from a few measurements of limited accuracy and the one-to-one relation vanishes. Calculating the distribution of the earth resistivities from the field diagrams is thus an undetermined problem, which experience has shown to be partly controlled by approximate laws of “equivalence”. The use of these rough rules can produce only a very restricted number of the resistivity distributions that correspond to calculated diagrams which do not differ from a given field curve by more than a tolerable discrepancy. On the other hand, the full set of such “equivalent” solutions is given automatically by a computer program. Tests made on field examples prove that a few geological data generally reduce the wide range of undetermination. |
