Seismoelectric Effect Associated with Rayleigh Wave Propagation

—In the scope of Frenkel’s equation, an analytical solution is obtained for pore pressure and electrokinetically induced electric field caused by the Rayleigh surface wave propagation in a poroelastic fluid-saturated medium. The problem is solved in the frequency domain with the allowance for the boundary condition on the Earth’s surface. It is shown that the solution can be represented in the form of a sum of two waves, the first prevailing in the near-surface layer and rapidly decaying with depth, and the second covering a much greater depth interval and associated with longitudinal component of the Rayleigh wave. The rate of exponential decay of the first wave with depth is determined by the skin depth which, in turn, depends on the permeability coefficient of a poroelastic medium and on a number of other parameters. As a result, vertical component of the electric field associated with the first wave is highly sensitive to the change in the permeability of the surface layer, which opens the possibility of its determination from the observed seismoelectric signal. The first wave creates the dominant part of the electrokinetic effect on the surface. In accordance with the Helmholtz-Smoluchowski equation, we derived the expressions for the vertical and horizontal components of the electric field strength. Based on the estimated parameters of the Rayleigh wave recorded in the region of Mt. Wrangell, Alaska after the M = 9.0 Sumatran 2004 earthquake, the expected amplitudes of the vertical component of the coseismic electric field are found to range between dozens of µV/m and tenths to units of V/m. It is shown that the amplitudes and the skin depth for this component substantially depend on the permeability coefficient of the medium.