This research is a continuation of investigations of the region of the earth just above the core-mantle boundary (CMB) region known as D". These include: identifying/mapping out small to medium-scale strong lateral variations in heterogeneity beneath the Pacific; mapping variable D" discontinuity structure and seismic wave speed anisotropy; discovering a variable thin (5-40 km) ultra-low velocity (10% slow) layer at the CMB; and probing seismic structure of the outermost core. This project will address in increasing detail the systematics of D" anisotropy. In addition to documenting patterns in travel time splits of D" traversing shear waves, there is compelling evidence for geographical systematics in waveform irregularities. These features will be mapped and related to lower mantle heterogeneity for the well-sampled D" regions beneath Alaska, the northern Pacific, the Caribbean, Eurasia, and India/Indian Ocean. One of the goals is to better understand the relationship that subducting slabs may have with D" anisotropy and structure.
