Electrokinetic effect provided by long oceanic waves coming on shore

Abstract

Electrokinetic effect (EK) caused by long oceanic waves in porous water-saturated rocks of seabed and shore is examined theoretically. One possible reason for this effect is the motion of groundwater due to the volume deformation of porous rocks by oceanic waves coming on shore. The same mechanism is responsible for seismoelectric effect observed during seismic waves passage through ground-recording station. In this study, we examine another mechanism in which the wave-produced variable pressure on the seabed plays a role of a piston pushing seawater through the seabed rocks into sandy or porous rocks of the seashore thereby exciting the EK effect. To estimate this effect, we first consider a long gravity wave and then solve 2D‑problem on the pressure variations produced by this wave on the bottom. This solution is used to describe groundwater filtration in porous rocks subjected to the variable pressure of seawater. The EK current and telluric electric field in a porous medium are derivable through the pressure gradient of porous fluid. 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. A role played by EK effect in the generation of ULF natural electromagnetic noise in coastal zone was discussed.