Radial Anisotropy and sediment thickness of West and Central Antarctica estimated from Rayleigh and Love wave velocities

Abstract:

Seismic surface wave velocities determined from ambient noise correlation provide valuable information of the distribution of seismic anisotropy in the crustal and uppermost mantle structure in greater detail, revealing the deformation history of the crust and mantle. Whereas most former studies of Antarctic seismic anisotropy focus on azimuthal anisotropy, here we use Rayleigh and Love wave phase and group velocities to constrain radial anisotropy, the difference between the speeds of vertically and horizontally polarized shear waves. Since Love waves are more sensitive to shallow structure than Rayleigh waves, models of crustal velocity can be further improved, allowing identification of slow velocity sediments. In this presentation, we highlight results that constrain both the radial anisotropy and sediment thickness of West and central Antarctica. In this work, we use all available broadband data collected in Antarctica over the past 18 years, including data from recent temporary arrays. From these data, group and phase velocity maps for both Rayleigh and Love waves are obtained and are then inverted for shear wave velocity structure using a Monte Carlo inversion method. From the new 3D velocity model, a new sediment distribution map is obtained, in which thick sediments (~ 5 km) in the western Ross Embayment extending south to the southern Siple Coast are found. At interior basins such as the Polar Subglacial Basin and Bentley Trench, Sediment thicknesses are modest (< 1.5 km), suggesting that Antarctic interior basins have been sediment-starved and lack thick sedimentary deposits. Beneath the Ellsworth-Whitmore Mountains, the whole crust shows strong positive anisotropy, likely due to horizontal fabric developed during the rotation of this terrain into its current location. For most of the upper to middle crust in West Antarctica, positive anisotropy is found, likely due to mineral orientation resulting from extension along the West Antarctic Rifting System. The uppermost mantle shows strong positive radial anisotropy (6 -8%), typical for normal upper mantle structure due to the lattice preferred orientation of olivine, with strongest anisotropy observed along the Transantarctic Mountain front and Whitmore Mnts, likely resulting from horizontal olivine LPO due to tectonic activity.