Are these wave and ray equations precisely equivalent? No. Equation (1) can
be made to approximate dispersion relations that have a horizontal symmetry
plane. Approximate it both in the neighbourhood of the *z* axis for
conventional seismic and VSP data, and in the neighbourhood of the *x* axis
for cross-hole data. Likewise Equation (2) will then be a good paraxial
approximation in the neighbourhood of both the *z* and the *x* axes.

1/13/1998