A multi-electrode array for resistivity surveying

Techniques for the interpretation of resistivity data collected over a horizontally layered earth have received a great deal of attention over the years and are now very successful. Even where the strata show some dip or gentle folding, or when other lateral variation occurs, useful results can often be obtained, but problems do arise when the geology departs too far from the horizontally layered model. However, the subsurface structure may be sufficiently uniform in cross-section to be treated as two-dimensional and, as the variation in apparent resistivity at the surface for any such subsurface distribution of resistivity can now be computed, the investigation of subsurface features of this type is in principle feasible. Two major difficulties have to be overcome in developing a practical technique for this purpose, one instrumental and one interpretational. We believe we have solved the first problem: we have also made some progress with the second.