Seismic wave propagation in cracked porous media

The movement of interstitial fluids within a cracked solid can have a signi ficant effect on the properties of seismic waves of long wavelength propaga ting through the solid. We consider three distinct mechanisms of wave-induc ed fluid flow: flow through connections between cracks in an otherwise non- porous material, fluid movement within partially saturated cracks, and diff usion from the cracks into a porous matrix material. In each case the crack s may be aligned or randomly oriented, leading, respectively, to anisotropi c or isotropic wave speeds and attenuation factors. In general, seismic vel ocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on eit her a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely differ ent effects on seismic wave propagation. A numerical analysis shows that al l models can have an effect over the exploration seismic frequency range.