Limiting apparent-resistivity values for dipping-bed earth models

Consideration is given to some special features of normalized apparent-resi stivity (NAR) curves, resulting from the deployment of Wenner electrode arr ays on the surface above dipping earth structures. Limiting values of the p otential are derived when a direct-current source is located at points on t he surface above a simple two-region dipping-bed earth model and their infl uence on corresponding NAR curve characteristics is investigated. Particula r attention is given to the exploitation of such features to provide a new and direct approach to model parameter estimation, either as an alternative to traditional curve-matching techniques or as a source of supporting info rmation when other earth model characterization methods have been employed. Throughout, the emphasis is on the single-dipping-bed model, but applicati on to more complex structures is discussed, including examples of two dippi ng beds, dipping dikes and more general tilted unconformities.