This project proposes to perform high resolution mapping of seismic anisotropy across the Lau basin active back-arc system. The project will apply a variety of advanced analysis techniques to data from recent experiments in the Tonga-Fiji region to better resolve the anisotropic structure of the Lau back arc basin and address specific questions concerning mantle flow within such a system. Anisotropic analyses combining data from land seismic stations and an ocean bottom seismometer (OBS) deployment will provide good coverage of the basin. S-wave splitting analyses will help map regions of consistent anisotropic fast directions. This information on regionalization will be used to aid in inversions for Pn and surface wave azimuthal anisotropy. Advanced techniques to be used include stacking of splitting results, use of 2-station travel time information for Pn measurements, and surface wave techniques specifically designed for making inter-station phase velocity measurements where station spacing is small. The final mapping of anisotropy will be used to answer such questions as what is the size, direction, and depth extent of anisotropy and how does this vary across the backarc basin? What is the relationship of seismic anisotropy with processes associated with the backarc-spreading center and subduction of the Pacific plate?