P-wave attenuation by slow-wave diffusion is a significant loss mechanism
at seismic frequencies. This effect is known as mesoscopic loss,
because it is a consequence of fluid flow at mesoscopic- scale inhomogeneities.
These are larger than the pore size but smaller than the wavelength,
typically tens of centimeters, and are due to local variations in
lithological properties or to patches of immiscible fluids. Basically,
a P-wave traveling in a porous medium induces a fluid-pressure gradient
in regions of different properties, such as patches saturated with
different fluids, generating slow P-waves, which diffuse away from
the interfaces separating the fluids. This mechanism can be explained
by the combined effect of mesoscopic-scale inhomogeneities and mode
conversion at interfaces. We consider a periodically stratified medium
and perform numerical experiments to determine the P-wave quality
factor in partially saturated rocks. The modeling method is an iterative
domain-decomposition 2D finite-element algorithm for solving Biot
equations of motion in a parallel computer, which is a requirement
to run the numerical experiments at seismic frequencies. The simulated
pulses show evidence of the mesoscopic-loss mechanism, and the quality
factors estimated with the spectral-ratio and frequency-shift methods
are in good agreement with the theoretical values predicted by the
White theory. Errors in the estimation of the quality factor are
less than 5% (spectral ratio) and 3% (frequency shift).