Crustal and uppermost mantle structure beneath Tristan da Cunha using surface wave phase velocity from horizontal components OBS ambient seismic noise

Abstract

SUMMARY We applied ambient noise tomography on data from an ocean bottom seismometer (OBS) experiment around Tristan da Cunha in the South Atlantic, in order to determine the crust and uppermost mantle shear velocity structure beneath this region. The determination of the orientation of the horizontal seismometer components allowed to perform ambient noise cross-correlation with all three components of 19 broad-band OBSs and two land stations. We extracted the phase velocity dispersion curves from the first higher mode Rayleigh waves and fundamental mode Love waves at periods of 3–8 s, which were only observed in the radial and transverse components, respectively. Following the two-steps inversion of surface wave tomography, we finally obtained a 3-D shear velocity model around Tristan da Cunha. Our results concur with previous studies in this region. The 3-D shear velocity model documents that there is a shallow conduit of low shear velocity underneath the volcanic archipelago, extending to at least ∼25 km depth. This conduit in the lithosphere may represent the magmatic plumbing system. We also observe indications for low shear velocities in the uppermost mantle beneath the seamounts in the southwest of the island, in an area where the deeper Tristan mantle plume is assumed.