An approach to determine equivalent solutions to the geoelectrical 2D inversion problem

The equivalence problem in geoelectrical data interpretation is a well-known fact. Generally, the equivalence analysis is implemented into 1D data inversion software but completely neglected in 2D data interpretation. In this paper, we present a practical approach to the problem of equivalence in a 2D data inversion. A 1D interpretation with equivalence analysis of the data is used to generate different starting models for a 2D inversion. At suitable locations, sounding curves are extracted from the 2D data set and inverted. Calculation of equivalent 1D results is carded out at each sounding point. The different resulting models are connected laterally to form different starting models for a 2D inversion of the complete 2D data set. Our 2D inversion results, similar in terms of data fit, but very different regarding the resulting resistivity distributions, enforce the necessity to carry out equivalence analysis in 2D data interpretations. It is shown that the implementation of a 1D interpretation of a 2D data set of predominantly layered structures provides a suitable way to introduce a first-order equivalence analysis to the problem in 2D. (C) 2004 Elsevier B.V. All rights reserved.