Modelling frequency‐dependent anisotropy due to fluid flow in bed limited cracks

Abstract

Evidence from a number of measurements support the idea that anisotropy, or shear-wave splitting, exhibits a frequency dependence, that is generally attributed to properties of the microstructure of the rock. This effect is generally assumed to be the result of scattering from oriented inclusions within the rock mass, however there are a number of competing mechanisms that may give rise to this observed frequency dependence. The scale length of the inclusions must be much smaller than the wavelength at which the measurements where conducted, in order for their presence to be observed as an effective anisotropy, and may therefore be insufficient to account for a significant frequency dependence. An alternative mechanism resulting in frequency dependence is the transfer of fluid between the inclusions, assumed to be fluid filled. Using an established model, it is demonstrated that this fluid effect is potentially significant enough to explain observed frequency dependence.