This research is to study seismic surface wave propagation in the Pacific Ocean Basin. First, surface-wave dispersion will be investigated over a number of "aseismic" ridges and plateaus, including the Nazca, Cocos and Hawaiian Ridges; the goal will be to obtain precise mapping of the crust-mantle interface, as well as of the extent of the low-velocity zone under the chains. This will put substantial constraints on the thermo-mechanical interaction between the moving oceanic plate and the fixed plume during the formation of the island, and, in the case of the Hawaiian chain, on the process of "healing" of the plate downstream from the hotspot. The second investigation will be of upper mantle anisotropy, in particular with the goal of determining whether the anisotropy required in the seismic asthenosphere by recent surface wave observations is of the polarization or azimuthal type. This bears directly on the composition and crystalline layout of the asthenosphere and on the processes of accretion upon cooling at the base of the seismic lithosphere.
