Wave theory, simulation and determination of gas-hydrate content in sediments (revised)

We present a Biot-type theory for wave propagation through gas-hydrate saturated media at all frequency ranges, including the effects of attenuation, partial saturation, and effective pressure. The differential equations are suitable to compute synthetic seismograms in inhomogeneous media. An amplitude versus angle analysis of the bottom-simulating reflector allows us to infer qualitative information about the concentration of gas hydrates, saturation of gas, and grain cementation. We estimate quantitatively the concentration and saturations from log and vertical seismic profile (VSP) data and traveltime reflection tomography, based on the Biot-Gassmann equation to model the seismic velocity. Finally, we obtain the P-wave quality factor by attenuation tomography, which constitutes an additional technique to obtain information about the presence of fluids and structure of the porous media.