This research is to investigate the transition zone structures in the upper mantle with emphasis on the 400 km and 670 km discontinuity. Recent advances in mineral physics have given a new urgency to the accurate characterization of elastic structure for such boundaries, as well as to the search for other discontinuities. By using broad band seismograms for a number of deep focus earthquakes, and incorporating a suite of reflected and converted phases with varying ray parameters, the work will separate the effects of wave speed and density contrast, as well as measuring sharpness. The results have important implications for global geodynamics and mantle convection, the driving force of the crustal plates.
