Teleseismic S-Wave Coda Autocorrelation and vp/vs Distribution over the Antarctic Icesheet.

Accurate characterization of the compressional to shear (P-to-S) wave-speed ratio (vp/vs) within the Antarctic Ice Sheet (AIS) is crucial for understanding its internal structure,mechanical stability, and vulnerability to a changing climate. In this study, we apply autocorrelation to steeply-arriving P and S waves and their subsequent reverberations from distant earthquakes, i.e., teleseismic coda, to reveal their reflectivity within the ice sheet, which enables the estimation of vp/vs from P- and S-wave reflection onsets. By incorporating shear wave reflections retrieved from S-wave coda, in addition to those obtained from P-wave coda autocorrelation, we significantly expand the vp/vs dataset across Antarctica. This enhancement leads to 28 new, reliable vp/vs estimates, nearly doubling the number of previously resolved sites to a total of 61, and improving spatial coverage, including the remote interiors, particularly in East Antarctica. The updated vp/vs map reveals distinct regional contrasts: East Antarctica shows relatively ratios close to the standard value of 2.0 for isotropic ice, while West Antarctica exhibits greater variability, with elevated vp/vs values around 2.1 to 2.2 in central regions and lower values toward the coastal margins. Synthetic modeling indicates that the higher vp/vs values result from reduced shear-wave velocities in the lower ice layer, driven by anisotropy and the presence of partial melt or interstitial water. These findings suggest that elevated geothermal flux in West Antarctica promotes warmer, fluid-affected basal ice where physical and thermal processes together influence the seismic structure of the ice sheet.