Geoelectrical survey of structures closed in depth by two dipping discontinuities

Alfano's integral equation method, previously used to calculate VES theoretical curves in parallel or diverging dipping planes including an indefinite conductive medium (open structures), was applied to calculate VES theoretical curves in closed structures, i.e. when the conductive medium is limited in depth. The theoretical curves, as calculated for various cases, show slopes steeper than the corresponding two-layers curves and resistivity asymptotic values equal to those of the resistive layer; their trends can be used to evaluate the dips of contacts. Two surveys, carried out on similar superficial situations in the Appennines area, have been interpreted by means of the new theoretical curves, and have shown different structural situations in depth.