RAYLEIGH-WAVES IN ISOTROPIC VISCOELASTIC MEDIA

In the surface of a linear viscoelastic medium, two types of Rayleigh waves may propagate. One of them, which always occurs, has wave characteristics which are close to those of the corresponding elastic solid. The second surface wave, not present in the elastic case, is possible for certain values of the material parameters, and for a given range of frequencies. Its properties are different from those of the first surface wave, particularly the energy velocity which is closer to the compressional body wave velocity. In this work, the properties of the two wave modes are analysed by using energy considerations. The energy balance for the Rayleigh waves is computed, and the quality factors and energy velocities are calculated as a function of the frequency, of depth, and per unit surface area. The main results indicate that the anelastic properties calculated from energy considerations are close, for practical purposes, to those obtained from the Rayleigh secular equation, i.e. phase velocity and attenuation factors give a good approximation to the dispersive and dissipation characteristics of the waves. In relation to the elastic case, the energy is more evenly distributed with depth, particularly in the v.e. mode. This wave has similar anelastic properties to those of the compressional body wave.