Comparison of an optimized resistivity array with dipole-dipole soundings in karst terrain

Abstract

We report the results of a field comparison of 2D resistivity data collected using both the traditional dipole-dipole array and a new computer-optimized array recently described in literature. The study was conducted at a karst site in eastern Pennsylvania. Computer simulations suggested that for a given line length, the optimal array and the dipole-dipole array would be equally effective at imaging shallow targets but the optimal array would provide better resolution at depth. Our field test results showed that the two arrays imaged karst bedrock topography equally well. When the full grid of 2D lines were combined and analyzed using 3D inversion, however, the optimal array was able to resolve a crosscutting bedrock fracture system that was not visible in the dipole-dipole data. The existence of the fracture system was confirmed by drilling. Because the optimal array requires roughly three times as many measurements per line, we conclude that the optimal array is preferable to traditional dipole-dipole soundings only when the slight improvement in resolution at depth is more important than rapid data collection.