Analysis of principles of equivalence and suppression in resistivity sounding technique

Abstract

The principles of equivalence and suppression in resistivity sounding technique are phenomena where different resistivity models may produce resistivity curves that are essentially the same. The understanding of these phenomena could be of great importance in using resistivity sounding technique for citing boreholes in places underlain by Basement Complex rocks. In such areas, it would be difficult to identify the fractured/weathered bedrock from the sounding interpretation. This is because the resistivity of the weathered layer is usually intermediate between those of the adjacent layers (i.e. residual overburden) on top and the fresh bedrock below. Therefore, it is important to analyse the problems of suppression and equivalence in resistivity sounding data for estimating thickness and resistivity of the subsurface layers. Several resistivity models were generated ranging from two-layer to five-layer models to investigate these phenomena. The apparent resistivity curves were plotted for these models. The results show that the problems of suppression and equivalence exist in resistivity sounding data. Hence, geophysicists should not make any a priori quantitative inferences using the shape of the resistivity sounding curve.