  We develop a representation of reverse-time migration in terms of Fourier
integral operators the canonical relations of which are graphs. Through the
dyadic parabolic decomposition of phase space, we obtain the solution of the
wave equation with a boundary source and homogeneous initial conditions using
wave packets. On this basis, we develop a numerical procedure for the reverse
time continuation from the boundary of scattering data and for RTM migration.
The algorithms are derived from those we recently developed for the discrete
approximate evaluation of the action of Fourier integral operators and inherit
from their conceptual and numerical properties.
