Effects of the density perturbation in scattering

The influence of density variation on scattering is investigated in terms of attenuation, coda level, and apparent frequency shift. The influence of density variations is to produce more scattered energy than for velocity perturbations alone with a consequently higher coda level. The temporal decay of the coda is reduced, so that high perturbations in density are associated with a long duration of coda. These effects are particularly important for media with small-scale heterogeneity. Thus inversions for heterogeneity parameters, based on the character of precursors and coda of seismic phases penetrating deep into the Earth, need to take into account the nature of the density variations as well as wave speed variations.