REFLECTION AND TRANSMISSION OF QP-QS PLANE-WAVES AT A PLANE BOUNDARY BETWEEN VISCOELASTIC TRANSVERSELY ISOTROPIC MEDIA

We consider the problem of reflection and transmission in two viscoela stic transversely isotropic (VTI) media in contact, with the symmetry axis of each medium perpendicular to the interface. The problem is inv estigated by means of a plane-wave analysis and a numerical simulation experiment. For an incident homogeneous wave, the reflected wave is o f the same type and is also homogeneous, while the other waves are inh omogeneous, that is, equiphase planes do not coincide with equiamplitu de planes. If the transmission medium is elastic, the refracted waves are inhomogeneous of the elastic type, that is, the attenuation vector s are perpendicular to the respective Umov-Poynting vectors (energy di rection). On the other hand, if the incidence medium is elastic and th e transmission medium anelastic, the attenuation vectors of the transm itted waves are perpendicular to the interface. The angle between the attenuation and the real slowness vectors may exceed 90 degrees, but t he angle between the attenuation and the Umov-Poynting vectors is alwa ys less than 90 degrees. As in the anisotropic case, energy flow paral lel to the interface is the criterion for obtaining a critical angle, which exists only in rare instances in viscoelastic media. In fact, fo r this particular example, the transmitted flux of the quasi-compressi onal wave is always greater than zero. To balance energy flux it is ne cessary to consider the interference fluxes between the different wave s (these fluxes vanish in the elastic case). The relevant physical phe nomena are related to the energy flow direction (Umov-Poynting vector) rather than to the propagation direction (real slowness vector). The simulation experiment gives the particle velocity fields caused by a m ean stress source. The results are in good agreement with the plane-wa ve analysis, despite the fact that only a qualitative comparison can b e performed. The presence of the conical wave, which cannot be explain ed with a plane analysis, indicates that, in spite of the absence of a critical angle, some of the refracted energy disturbs the interface.