This research involves the systematic mapping of scatterers in the deep mantle, in particular in the bottom 1000 km of the mantle where recent high-resolution tomography revealed unexpected changes in the planform of mantle heterogeneity. The objectives of this research are threefold. First, imaging techniques will be integrated to develop a powerful migration method for studies of lower mantle heterogeneity. Second, additional evidence will be sought for constraints on the postulated change in bulk chemistry in the lower mantle. Preliminary inversions to 1300-km depth suggest limited structures in the upper lower-mantle. This work will continue this work into the bottom third of the mantle. Third, by means of a combination of scattering and transmission tomography, improved understanding will be sought of the structure and dynamics of the base of the mantle. The integration of the techniques of body-wave scattering with those of transmission tomography will better determine that gradients and amplitudes of wave speed variations and thus produce a new class of Earth models that place tighter constraints on the chemical and thermal history of our planet.
