Shear wave velocity and radial anisotropy structures beneath the central Pacific from surface wave analysis of OBS records

Abstract The central Pacific plate is an ideal area to study the dynamics of the lithosphere-asthenosphere system, as this region is far away from other dynamics systems, such as subduction zones and volcanic hotspots of mantle plumes, and has experienced simple oceanic evolution. In this study, we collect three-component continuous seismic data and differential pressure gauge data recorded by 15 broadband ocean bottom seismometers (OBSs) from the NoMelt experiment. We process continuous seismic noise data to obtain phase velocities of the fundamental (6-30 s) and first high (5-11 s) mode Rayleigh waves and fundamental mode Love waves (5-12 s). We apply a two-plane-wave method to teleseismic Rayleigh waves to obtain the fundamental mode phase velocities at 20-150 s periods, and apply high-resolution linear Radon transform to teleseismic Love waves to obtain phase velocities for the fundamental mode Love waves at 28-48 s periods. Then, we jointly invert the average phase velocities of Rayleigh and Love waves to construct 1-D isotropic shear wave velocity and radial anisotropy from the seafloor to 150 km depth beneath the NoMelt region. Our 1-D model shows a low velocity zone (LVZ) beneath a high velocity lid. By comparing our results with the predictions of partial melt models, we suggest the LVZ is attributed to the presence of a small amount of melt in the asthenosphere. Strong radial anisotropy (5-6%) is observed in the crust. But the mantle lithosphere is characterized by weak radial anisotropy (