Observation of electric fields in the shallow sea using the stainless steel electrode antenna system

To detect electromagnetic (EM) waves emitted from the seismic active zone where the rock fracture is expected, the ELF/VLF electrode antenna system working in the deep sea has been developed. The minimum detectable signal amplitude at the input of the amplifier is about 7 nV per root Hz, with the electrode span of 2 m. Simultaneous observation of ELF/VLF atmospherics on land and in the sea has been carried out at Usa bay near Kochi city using the ball antenna and the stainless steel electrode antenna. Transfer functions of the amplitude and phase through the seawater layer (15–20 m thick) have been obtained experimentally and compared with the theory. Analysis of the data indicates that the EM pulses can penetrate the sediment layer contained seawater as thick as 20 m.