Seismic Structure of Marine Sediments and Upper Oceanic Crust Surrounding Hawaii

We present models of compressional and shear velocity structure of the oceanic sediments and upper crust surrounding the Hawaiian islands. The models were derived from analysis of seafloor compliance data and measurements of Ps converted phases originating at the sediment-bedrock interface. These data were estimated from continuous broadband ocean bottom seismometer acceleration and pressure records collected during the Plume-Lithosphere Undersea Mantle Experiment, an amphibious array of wideband and broadband instruments with an aperture of over 1,000 km. Our images result from a joint inversion of compliance and Ps delay data using a nonlinear inversion scheme whereby deviation from a priori constraints is minimized. In our final model, sediment thickness increases from 50 m at distal sites to over 1.5 km immediately adjacent to the islands. The sedimentary shear velocity profiles exhibit large regional variations. While sedimentary structure accounts for the majority of the compliance signal, we infer variations in shear velocity in the uppermost bedrock on the order of ±5%. We also require relatively high values of Poisson's ratio in the uppermost crust. Lower crustal velocities are generally seen to the north and west of the islands but do not appear well correlated with the Hawaiian Swell bathymetry. A region of strong low velocity anomalies to the northeast of Hawaii may be associated with the Molokai fracture zone.