Discriminating between true and pseudo-anisotropic ground using azimuthal resisitivty soundings

In an azimuthal resistivity sounding, ground resistivity is measured as a function of both depth and azimuth. The resultant distribution of apparent resistivity recorded at a particular electrode spacing is indicative of the nature of the subsurface at that associated depth of investigation. An elliptical pattem of apparent resistivity implies that the surveyed ground might be electrically anisotropic. Fractured rock constitutes a hydraulically anisotropic medium. Hydrogeologists drawan analogy between these two properties and so employ azimuthal resistivity soundings to identify and then characterise fracture induced anisotropy. Fracture systems are of considerable importance to hydrogeologists as they can represent significant sources of groundwater and have considerable implications as regards waste disposal, groundwater protection and contaminant transport.