9526678 Tajima This research is to investigate the seismic structure of the upper mantle transition zone, from 400 to 700 km depth, which is key to understanding the mode of convection within the Earth's mantle as well as the chemical composition of the Earth. In this project, the plan will be to delineate seismic structure of the transition zone associated with Japanese subduction zones using upper mantle (triplicated P and S waveforms recorded at regional stations. Three major issues debated recently will be considered: 1) what velocity anomalies are associated with the subduction zones in the transition zone; 2) whether the subducting slabs flatten at the bottom of the transition zone or extend into the lower mantle; and 3) whether the seismic structure derived for the upper mantle supports a model of chemical layering or one with discontinuities due to temperature-dependent phase transitions approximately at 410 km, and possibly at about 525 km. *** ??
