Orthorhombic anisotropy is typical of naturally fractured reservoirs. This type of anisotropy is caused by the single system of vertical fractures embedded in a horizontally layered medium. Arbitrary orthorhombic elastic anisotropy can be characterized by ten independent parameters, one of which is density. In the best of circumstances, only six of these parameters can be inverted from P wave scattered energy, reliably. Here we access the resolution of S wave inversion from the wavenumber illumination prospective and show that S waves can resolve the rest of the orthorhombic parameters.