Physical Insight into the Elastic Brewster's Angle

Light (EM) waves are transversely polarized and thus share properties with elastic shear waves. In particular, optical waves reflecting from an interface experience changes in their polarization. Brewster’s angle occurs for light reflecting from an interface such as air over a glass plate. This angle is the angle—for a particular polarization—where energy is entirely transmitted, and thus has zero reflectivity. The polarization where this occurs, in terms of the seismic nomenclature, is the SV polarization—or transverse polarization in a plane normal to the reflecting interface. In the elastic case of a seismic SV wave interacting with a solid/solid boundary, there are four resultant waves, and thus the situation is far more complex. This result occurs because of mode conversion from SV waves upon both reflection and transmission to P-waves. One of the motivations in addressing a physical insight of the Brewster’s angle phenomena is to expand our understanding of that the value of angle jB for an incident SV wave is, for most contrasts in P- and S-impedances, nearly constant. The sensitivity of this angle to contrasts in physical properties, as small as the variations may be, could prove useful in the interpretation of many rock parameters, including anisotropy.