Pseudo-interface Rayleigh wave on a permeable porous medium/vacuum interface

It is well known that the Rayleigh wave propagating along a permeable plane boundary of a poroelastic half-space may have a high-frequency cutoff beyond which the corresponding Rayleigh pole is absent. The present study investigates the specific features of the surface wave propagation during transition through this cut-off frequency. Using a set of experimentally determined mechanical parameter values for water-saturated sintered glass beads in the framework of Biot's theory, this theoretical investigation indicates the following. The Rayleigh wave upper cut-off frequency may occur within a physical frequency range over which the characteristic wavelength far exceeds typical pore size. Beyond the cut-off frequency, the Rayleigh pole migrates onto the non-principal, in other words, unphysical, Riemann sheet. As a consequence, during this transition, the Rayleigh wave transforms into a pseudo-interface wave and radiates part of its energy into the interior of the half-space in the form of P2-wave motion.