Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

Many recent Antarctic seismic structure studies use Rayleigh wave data and thus determine only the SV structure. Love waves provide greater resolution for shallow structure, and coupled with Rayleigh waves, can constrain radial anisotropy by comparing vertically (V-SV) and horizontally (V-SH) polarized shear velocities. In this study, we jointly analyze Rayleigh and Love wave phase and group velocities from ambient noise to develop a new radially anisotropic velocity model for West and Central Antarctica with an improved shallow crustal resolution using all broadband data collected in Antarctica over the past 20 years. Group and phase velocity maps for Rayleigh and Love waves are estimated and inverted for shear wave velocity structure using a Monte Carlo method. We determine a new sediment distribution map that reveals a thick sedimentary basin (similar to 4 km) beneath the Southeastern Ross Embayment. Sediment thicknesses at interior basins such as the Polar Subglacial Basin and Bentley Subglacial Trench are modest (<1.5 km), suggesting that these basins are sediment-starved. The shallow crust as well as the mid-to-lower crust in several places shows strong positive anisotropy (V-SH > V-SV), likely due to lattice preferred orientation of mica-bearing rocks. However, large regions of the mid-to-lower crust show negative anisotropy, likely due to lattice preferred orientation of plagioclase. The uppermost mantle is characterized by strong positive radial anisotropy (4%-8%) in West Antarctica, with the largest anisotropy beneath the Transantarctic and Whitmore Mountains, likely resulting from horizontal olivine preferred orientation due to tectonic activity. Plain Language Summary The crust and upper mantle structure of Antarctica have been poorly understood until recent studies, due to the remote location and thick ice cover. Seismic anisotropy, the directional dependence of seismic wave propagation, represents a probe to understand the deformation history of the crust and mantle. In this study, we use all broadband seismic records collected in Antarctica over the past 20 years to investigate the shear wave radial anisotropy structure. In addition, the improved shallow resolution allows us to determine a new continental-scale sediment thickness map, which reveals a thick sediment layer beneath the Southeastern Ross Embayment. Basins on the interior of the continent show limited sediment cover, likely due to sediment-starved conditions through much of their history. We find positive anisotropy (V-SH > V-SV) in the shallow crust and a few places in the mid-to-lower crust, likely due to the orientation of the mica-bearing rocks. Much of the lower crust shows negative anisotropy (V-SH < V-SV), likely due to the lattice preferred orientation of plagioclase. The uppermost mantle generally has positive anisotropy, with the largest magnitudes beneath the Transantarctic and Whitmore Mountains, where it likely results from the tectonic activity.