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Crystal orientation fabric (COF) describes the intrinsic anisotropic nature of ice and is an important parameter for modeling glacier flow. We present the results of three‐component active‐source seismic observations from the Whillans Ice Stream (WIS), a fast‐flowing ice stream in West Antarctica. Surface‐wave dispersion analysis, ray tracing, and traveltime inversion of compressional (P) and shear (S) waves reveal the presence of transversely isotropic ice with a vertical axis of symmetry (VTI) beneath approximately 65 m of isotropic firn. The ice stream is characterized by weak anisotropy, involving an average ice thickness of approximately 780 m. The analysis indicates that about 95% of the ice mass is anisotropic, and the crystalline caxes span within an average broad cone angle of 73 ± 10° with respect to the vertical axis. Moreover, the mean temperature T(below the firn) estimated from seismic data is −15 ± 5°C. These data do not show evidence of englacial seismic reflectivity, which indicates the lack of abrupt changes in the COF. The presence of azimuthal anisotropy due to transversely compressive flow or fractures aligned along a preferential direction is also excluded. We suggest that the observed VTI ice structure is typical of large ice streams in regions where basal sliding and bed deformation dominate over internal glacial deformation. We analyze multicomponent seismic data acquired on the Whillans Ice StreamThe analysis reveals that the ice mass below the firn is VTIWe derive the average temperature and mean COF properties of the ice column

We simulate two-phase fluid flow using a stress–strain relation based on Biot’s theory of poroelasticity for partial saturation combined with the mass conservation equations. To uncouple flow and elastic strain, we use a correction to the stiffness of the medium under conditions of uniaxial strain. The pressure and saturation differential equations are then solved with an explicit time stepping scheme and the Fourier pseudospectral method to compute the spatial derivatives. We assume an initial pressure state and at each time step compute the wetting- and non wetting-fluid pressures at a given saturation. Then, we solve Richards’s equation for the non wetting-fluid saturation and proceed to the next time step with the updated saturations values. The pressure and saturation equations are first solved separately and the results compared to known analytical solutions showing the accuracy of the algorithm. Then, the coupled system is solved. In all the cases, the non-wetting fluid is injected at a given point in space as a boundary condition and capillarity effects are taken into account. The examples consider oil injection in a water-saturated porous medium.

Abstract: In many cases, geological formations are composed of layers of dissimilar properties whose thicknesses are small compared to the wavelength of the seismic signal, as for instance, a sandstone formation that has intra-reservoir thin mudstone layers. A proper model is represented by an anisotropic (transversely isotropic) and viscoelastic stress–strain relation. In this work, we consider a sandstone reservoir, such as the Utsira formation, saturated with CO2 and use White’s mesoscopic model to describe the energy loss of the seismic waves. The mudstone layers are assumed to be isotropic, poroelastic and lossless. Then, Backus averaging provides the complex and frequency-dependent stiffnesses of the transversely isotropic (TI) long-wavelength equivalent medium. We obtain the associated wave velocities and quality factors as a function of frequency and propagation direction, while the synthetic seismograms are computed with a finite-element (FE) method in the space-frequency domain. In this way, the frequency-dependent properties of the medium are modeled exactly, without the need of approximations with viscoelastic mechanical models. Numerical simulations of synthetic seismograms show results in agreement with the predictions of the theories and significant differences due to attenuation and anisotropic effects compared to the ideal isotropic and lossless rheology. [Copyright &y& Elsevier]