| Abstract: | A combined application of two independent direct current geoelectric methods, potential gradient mapping (PM) and magnetometric resistivity (MMR), is proposed for the investigation of high-resistivity basement structures. From a one-dimensional relation between horizontal electric and magnetic fields (due to currents originating from point electrodes placed on the surface of a two-layered half-space having a high-resistivity basement) several advantages of the combined PM-MMR method are shown for two-dimensional and three-dimensional basement structures. Three-dimensional models have been studied by analogue modeling experiments. This new mapping method embraces two parameters: the horizontal electric conductance map, derived from the ratio of the related electric and magnetic components, and the gradient map of their product. A close relation between structural forms and anomaly maps is obtained by using two orthogonal source-electrode layouts. Based on model results a two-channel measuring instrument was developed. The method and the instrument were tested near Sopron where a gradual deepening of, and faults in, the Paleozoic basement were found. |
