Topographic effects in resistivity surveys.

The nature and significance of topographic-effect resistivity anomalies are discussed and a two-dimensional, finite element computer technique is described that provides a means for: (1) analyzing the nature of these anomalies, (2) correcting apparent resistivity data for topographic effects, and (3) incorporating topography in interpretative models. The effects of slope length and slope angle on the shapes and amplitudes of these anomalies for a valley, a ridge and a slope were studied. A technique for correcting apparent resistivity for topographic effects uses the finite element program to compute the correction factors. The accuracy of these corrections depends upon how closely the actual case approximates an ideal two-dimensional model. Examples are given to show how topographic effects produce anomalies that can lead to erroneous interpretations.