The domain of existence of prograde Rayleigh-wave particle motion for simple models

The existence of prograde particle motion for fundamental-mode Rayleigh waves is studied systematically in models of increasing complexity by using an exact expression of the ellipticity. This expression, together with the secular equation for the phase velocity, are useful to find the most relevant parameters for prograde particle motion, namely Poisson’s ratio in the layer and the shear-wave velocity contrast between the layer and the half-space. The density contrast between layer and half-space, and up to a certain degree Poisson’s ratio in the half-space, are usually less important. The domain of existence of prograde Rayleigh-particle motion is specified for typical combinations of parameters.