ИСТИНА

Exploration into the natural ULF electromagnetic (EM) fields and noises in the coastal ocean environment is of interest for geophysical studies of continental shelves, ship navigation and underwater communications. These studies are also important both for the problem of monitoring and forecasting tsunami waves in the ocean, and for improving the global tsunami warning system. This warning system should include not only seismic, but also EM equipment capable of distinguishing the signal caused by tsunamis and earthquakes from background natural EM noises. This study examines the electrokinetic (EK) effect as a possible source of EM noise on the oceanic coast. The cause of the EK effect is that the surfaces of pores adsorb ions of certain sign from the electrolyte solution whereas the underground fluid accumulates the excess ions of opposite sign. The EK current is generated due to the ions entrainment with the moving underground fluid. Oceanic waves coming on the shore generate a variable pressure on the seabed thereby producing the motion of the groundwater in the porous rocks of the seabed and coast. We have studied two different reasons for this phenomenon. The first one is the deformation of seabed rocks under the influence of variable wave pressure, which is accompanied by the generation of a pressure gradient of a porous fluid. Another reason, unrelated to the deformation of the porous medium, is due to the pushing of seawater through the pores and cracks connecting the seabed and the coast. The results of this study points clearly to the existence of the low-frequency electric noise caused by EK effect in the seabed and coastal rocks. The amplitude of telluric electric field in a porous medium has been shown to decrease almost exponentially with distance from a shoreline. A penetration depth of the telluric field as a function of wave frequency in the range of 10 - 100 mHz was analyzed.