ERT Interpretation - Now you See it, now you Don't, now What?

ERT is an established technique for imaging 2D targets. ERT studies in areas of complex geology need careful planning so that local lateral variations and anisotropy do not distort or even mask the response of the targets to be located. ERT orientation must be chosen and, if possible, different orientations used to investigate the ground properly. However field conditions, available space, buildings, infrastructure and access to land use, can restrict the orientation and the length of the ERT profiles. The expansion of urban areas to old mining areas needs the location of abandoned shafts and underground works. Often there are no records of old mining activities and ERT can assist in the location of those works. Herein it is demonstrated that local geological conditions and space restrictions limiting the geophysical survey can distort and mask ERT response of old mining structures and, as shown, it is even possible to miss the targets completely. It is also proposed to use the square root of the ratio of model resistivities, obtained from the different ERT orientations, as a further tool for the diagnosis of 2D targets in anisotropic media.