The d¿collement beneath the Barbados accretionary complex is a gently dipping shear zone 10--40 m thick within which slippage occurs between the overlying sediments of the accretionary wedge and the underthrust sediments on the subducting tectonic plate. The density and seismic velocity of the d¿collement, derived from modeling of tuned seismic P wave reflections from its top and base, are very low and indicate high porosity sustained by above-hydrostatic pore pressure. Previous modeling assumed that the d¿collement is isotropic. Here we investigate whether neglecting anisotropy might bias the interpretation. Likely causes of anisotropy are aligned cracks and aligned pores and grains within the clays. Unrecognized anisotropy might cause misestimation of porosity, and confusion of P -- S -- P mode converted waves with the tuned P wave reflections. Horizontal cracks within the d¿collement would cause lower vertical velocity than in an isotropic material with the same porosity; this reduces the interpreted porosity, but by only a few percent, because crack density is limited by the observed finite strength of the d¿collement. P -- S -- P mode-converted waves would be caused by anisotropy due to nonhorizontal alignment within the d¿collement or in the accretionary wedge above. Appreciable P -- S -- P conversion requires anisotropy too great to be caused by aligned cracks alone. A d¿collement of aligned anisotropic clay particles gives appreciable mode conversion when 50% of the clay particles are within 30¿ of perfect alignment. Reflections for incidence angles up to ~26¿ from a strongly anisotropic d¿collement zone with horizontal alignment are indistinguishable from those from an isotropic zone.