Two assumptions are made here: first, rays traveling through the subsurface
are confined to the vertical plane that contains the sources and
receivers (a 2-D assumption).
Second, no lateral velocity variation exists in the region of the
analysis
(a time-processing assumption). However, some treatment to
lateral inhomogeneity is applied in the NMO correction stage.
Violating
the first
assumption will degrade the anisotropic processing result and
generally
reduce the degree of
anisotropy measured. Therefore, measurements from out-of-plane
reflections will not be mistaken
for anisotropy (Lynn et. al., 1991).
If anything, measurements from out-of-plane reflections will lower
the value of 
due to the lower NMO velocities associated with
out-of-plane reflections. Violating the second assumption will result
in errors similar to those encountered using isotropic time processing in
areas of lateral inhomogeneity. These errors are dependent on the degree of lateral
inhomogeneity, and as is likely here, such errors are expected to be small.