Active source electromagnetic surveying of the ocean crust

An electromagnetic profiling system is under development at the Scripps Institution of Oceanography. The goal of the development is to provide vertical sections of electrical conductivity under the ocean crust to a depth of a few kilometers. The method is an outgrowth of successful profiling experiments in which the electromagnetic source consists of an electric dipole dragged on the sea floor, and several electric receivers also on the sea floor are spaced out at various distances from the source. The electromagnetic signals propagate down from the source into the crust, laterally through the rocks and then up to the receiver. Direct propagation through the water is avoided by use of such high frequency signals that practically complete absorption of the water signals occur. The system is most sensitive for detection of layers that have a low conductivity compared to their surroundings.