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

Abstract

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 (VSV) and horizontally (VSH) 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 (∼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 (VSH > VSV), 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.

Shear Wave Splitting Across Antarctica: Implications for Upper Mantle Seismic Anisotropy

“…However, there is considerable variability in $$\delta t$$ within regions of both thicker and thinner lithosphere (Figure S5 in Supporting Information S1); therefore, it is prudent not to place undue importance on the small difference in $$\delta t$$ of 0.4 s. Nevertheless, this observation is consistent with the Zhou et al. (2022) model of radial anisotropy in west and central Antarctica, which shows stronger radial anisotropy on average in the uppermost mantle beneath WANT and TAM compared to the interior of EANT. Therefore, the spatial patterns of both azimuthal and radial anisotropy observed in Antarctica may suggest that regions with recent tectonic activity and thinner lithosphere have stronger contributions from sub‐lithospheric mantle anisotropy compared to regions characterized by prolonged tectonic quiescence.…”

“…Within central and West Antarctica, Zhou et al. (2022) finds the strongest positive radial anisotropy in the TAM uppermost mantle.…”

“…Recently, Zhou et al. (2022) attributed strong positive radial anisotropy (4%–8%) found throughout much of WANT's uppermost mantle to the preferred orientation of olivine due to tectonic activity.…”

“…Notably, when compared to broader WANT, Zhou et al. (2022) found the largest magnitudes of uppermost mantle radial anisotropy beneath the Whitmore Mountains.…”

Basement Topography and Sediment Thickness Beneath Antarctica's Ross Ice Shelf

“…The throughgoing trends imply regional continuity of crustal structure and a common tectonic development of the Ross Sea and RIS regions. Our sediment thicknesses are compatible with those determined by (a) eight active‐source seismic surveys (Figure 3b), for which the median misfit is 470m (Table S1 in Supporting Information ), and (b) surface wave dispersion indicating 2–4 km of sediment under the RIS, similar to our range, with the maximum beneath Crary Ice Rise (Zhou et al., 2022). Three additional western RIS seismic profiles report up to several kilometers of sediment, in general accordance with our results (Beaudoin et al., 1992; Stern et al., 1991; ten Brink et al., 1993).…”