This research involves the utilization of revolutionary improvements in seismic data, due to the Global Seismic Network and PASSCAL portable seismometer campaigns, in order to resolve mantle structure by means of body wave and surface wave techniques. Considerable progress has been made in mapping out lateral variations in seismic velocity in the mantle, demonstrating the active dynamic processes going on beneath the earth's surface. This research combines long-period surface wave inversion, travel-time tomographic imaging, and detailed whole record modeling. An intercomparison of models independently derived from these varied techniques involving totally different data sets show great complexity but, fortunately, some agreement. The major goal is to reconcile disagreements where resolvable. The major issues to be addressed are upper-mantle heterogeneity and its extension into the transition region (down to 670 km) and connections to lower mantle structures. The long-wavelength circum-Pacific down-willing region needs to be localized into more discrete continuous seismic structures with reliable estimates of P and S anomalies and their sharpness. Zones of slab buckling and abrupt thickening that are so abundant in dynamic models should be identifiable seismically. Similarly, the large-scale slow structures beneath Africa and mid-Pacific, although well established near the CMB, are less well defined at shallower depths where models vary greatly. The results are important as input to geochemical, mineral physical, and geodynamic models of the earth.
