Subsurface Detection

The various responses of Earth materials to electric fields of different types permits additional characterization of the subsurface. Natural and artificial signals at a variety of different frequencies can be observed to travel through different parts of Earth. Measurements are made of how the signals are modified in their paths, and then models are constructed which try to emulate this behavior. Often these techniques are most useful where the extension of a geological body with distinctive electrical properties is sought in the subsurface. Metallic ore deposits or ion-rich pollutant plumes are good examples. Measurements of electrical resistivity, the resistance of a material to passing a current of electricity, have been used for decades in the oil industry to help locate oil- or gas-bearing rock units.