Mapping upper mantle flow beneath French Polynesia from broadband ocean bottom seismic observations

Upper mantle structures and flow related to the South Pacific Superswell and to the associated short-lived hotspots are investigated using seismic stations deployed in French Polynesia. Beside island stations, broadband ocean bottom seismometers ( BBOBS) have been deployed between the various Polynesian archipelagos to investigate the oceanic upper mantle "unperturbed'' by thickened crust or hotspot activity. We investigate seismic anisotropy measured at BBOBS stations and found it rather similar to that from island stations. This confirms the ability of OBS to be used for anisotropy purposes and suggests some homogeneity in the upper mantle pervasive deformation. The two OBS installed on the head of the Society hotspot provide different anisotropy signatures than most of the other French Polynesian stations: one is "isotropic'' to SKS waves and the other provides a fast split direction normal to the average value observed in this area, suggesting a more complex mantle flow induced by the plume upwelling. Citation: Barruol, G., D. Suetsugu, H. Shiobara, H. Sugioka, S. Tanaka, G. H. R. Bokelmann, F. R. Fontaine, and D. Reymond ( 2009), Mapping upper mantle flow beneath French Polynesia from broadband ocean bottom seismic observations, Geophys. Res. Lett., 36, L14301, doi:10.1029/2009GL038139.