9725808 Helmberger This research is a continuation of highly successful work to map details of earth structure by means of seismic tomography and wave-form matching. Significant results include the discovery of ultra-low-velocity zones just above the core-mantle boundary, whole mantle convection, and seismic anisotropy in the earth's inner core. The research continuation will concentrate on the physical shapes and locations of the ultra-low-velocity zones, the characteristics of inner-core anisotropy in terms of strength distribution and orientation, the agreement of tomographic 3-D models with observed wave forms traveling through the structures, and the sharpness of the upper-mantle transition zones, 410 km and 640 km, as a function of tectonic environment. ***
