A possible mechanism for elastic wave propagation in porous rocks

Porous rocks are widely spread in the Earth's crust. They are an object investigated in a wide range of frequencies from ultrasound to seismic. A nontrivial property of mountainous rocks, including porous ones, is the fact that the logarithmic damping decrement does not depend on the frequency, which in turn is equivalent to the zero dispersion of velocity at the linear frequency dependence of the damping coefficient. This phenomenon clearly contradicts the widely accepted relaxation mechanism, under which the damping is necessarily accompanied by velocity dispersion, and the damping coefficient nonlinearly depends on the frequency.