Lateral and topographic effects in geoelectric soundings

Several two-dimensional structures are modelled for vertical electrical soundings in arrays parallel and perpendicular to the strike of the structure. The models are a horst and a graben within a three-layer medium, a cliff over two layers, and heterogeneities around the electrodes. Apparent resistivity curves are shown for different model parameters and different distances to the two-dimensional structures. Some of the features on the shape of these curves are inflections that may be misinterpreted as fictitious layers, of slopes greater than 45°; some features are simply anomalous peaks. One-dimensional interpretation of a two-dimensional graben model has been performed, in order to show typical errors when 2D structures are interpreted as one-dimensional. A real case corresponding to a landfill near Barcelona and showing strong lateral and topographic effects is presented. This represents combined effects of the above theoretical 2D models.