As with travel-time based velocity analysis methods, the primary purpose for
waveform inversion is to find a velocity model for imaging. However, waveform
inversion needs to match data phase and amplitude, not just travel-times, and
the examples in this report show that inverting for just velocity can be
dangerous when density variations are significant. A possible solution is the
joint inversion of density and velocity as proposed by Tarantola (1984).
Further research is needed to determine whether seismic data typically contain
the information necessary to constrain both fields.