HR: 0830h
AN: S11F-0357    [PDF]
TI: Elastic wave velocities anisotropy and dispersion in cracked rocks
AU: * Gueguen, Y
EM: gueguen@geologie.ens.fr
AF: Laboratoire de Geologie, ENS PARIS, 24 rue Lhomond, Paris, 75005 France
AU: Schubnel, A
EM: schubnel@geologie.ens.fr
AF: Laboratoire de Geologie, ENS PARIS, 24 rue Lhomond, Paris, 75005 France
AU: Schubnel, A
EM: schubnel@geologie.ens.fr
AF: Lassonde Institute, 170 College Street, Toronto, on M5S 3E3 Canada
AB: In the static regime (when cracks do not propagate), the simplest hypothesis that can be made is to neglect crack interactions. In fact, we show that such hypothesis takes better into account the interactions than most interactive models (especially the self-consistent and Hudson's approaches) because of the geometrical compensation of interactions that exist when cracks are distributed randomly or in parallel. Kachanov's [1993] non interactive model of solids with many cracks enables us to predict elastic wave velocity anisotropy for non-randomly orientated distribution of cracks. In the transversely isotropic case, we show that P wave anisotropy and S wave birefringence can be very different in the dry and saturated regimes. This model also enables us to quantify the damage in a rock in terms of crack density, as well as preferential orientation of the crack distribution and saturation using laboratory elastic wave velocity measurement data. Predictions are in agreement with microstructural analysis up to crack densities higher than 0.5. By coupling such a model to poroelasticity, we can also predict dispersion between high frequency and low frequency measurements in the saturated regime due to "squirt flow" mechanisms. Dispersion is lower when cracks are not parallel. However, when they are parallel, dispersion can be very high and therefore elastic wave velocity anisotropy observed on the field (at low frequency, i.e.$<$1KHz) can be very different than the one observed in the laboratory (at high frequency, i.e. ~ 1MHz). S wave birefringence is particularly sensitive to saturation and thus to frequency.
DE: 3025 Marine seismics (0935)
DE: 3909 Elasticity and anelasticity
DE: 5102 Acoustic properties
DE: 5144 Wave attenuation
DE: 7203 Body wave propagation
SC: Seismology [S]
MN: 2003 Fall Meeting