Wave propagation in poro-acoustic media

Some ocean sediments may be modeled as pore-elastic media with relatively high slow-wave speeds and relatively low shear-wave speeds [N.P. Chotiros, ''Biot model of sound propagation in water-saturated sand'', J. Acoust. Sec. Amer. 97, 199-214 (1995)]. This singular limit may be handled efficiently by allowing the shear modulus to vanish so that shear waves are ignored. This approach reduces the number of equations and permits a relatively coarse numerical grid. The equations of pore-acoustic media are remarkably similar to the equations of acoustic media. The equations of motion are a vector generalization of the variable density wave equation of acoustics [P.G. Bergmann, ''The wave equation in a medium with a variable index of refraction'', J. Acoust. Sec. Amer 17, 329-333 (1946)]. The interface conditions resemble the acoustic conditions for continuity of pressure and particle velocity. The energy-flux integrals of pore-acoustics and acoustics are also similar.