Effects of Marine Geologic Structure on the Propagation of Extremely Low Frequency Underwater Electromagnetic Waves

In the study of the propagation characteristics of extremely low frequency (ELF) electromagnetic waves in the oceanic environment, a five-layer medium channel model, consisting of the “air layer-seawater layer-sediment layer-rock layer-asthenosphere”, was developed by integrating marine geological layer structures and electromagnetic inversion data. The impacts of the marine geological structure on the propagation of submarine ELF electromagnetic waves were analyzed, and the simulation results were validated with the offshore test data. The results indicate that the highly conductive sediment layer and the asthenosphere, along with the less conductive rock layer in marine geology, jointly form a waveguide effect. Once the ELF electromagnetic waves excited above the seabed penetrate the sediment layer accompanied by a relatively larger amount of loss, their energy will be confined to the rock layer. As a consequence, these waves can travel a longer horizontal distance with lower loss. In marine areas, the thicker the sediment and rock layers, the greater the propagation loss.