Determining the Character of Subglacial Sediments in the Ice‐Bedrock Interface Zone of Antarctica Using Horizontal‐to‐Vertical Spectral Ratios (HVSRs) of Seismic Ambient Noise

Abstract Interactions between the Antarctic Ice Sheet and the underlying solid Earth occur within the ice‐bedrock interface zone (IBIZ), containing structures of sediments and rocks that strongly influence ice sheet dynamics. Existing insights into the Antarctic IBIZ come primarily from interpretations of airborne geophysical data and active seismic measurements, which require significant logistics. Passive seismic methods provide a lower cost, lower resolution alternative for subglacial mapping, with the potential for continuous remote monitoring. Here, we utilize horizontal‐to‐vertical spectral ratios (HVSRs) of seismic ambient noise to infer the presence of subglacial low‐velocity zones generated by unlithified sediments or porous, water saturated sedimentary rocks, using existing data from over 80 broadband stations across Antarctica. From 1‐D forward modeling, we identify a decrease in synthetic HVSR peak frequencies dependent on the thickness and S‐wave velocity () of the low‐velocity zone unrelated to seismic wavefield conditions. This sensitivity in HVSR peak frequencies is validated by the agreement between synthetic and observed HVSRs at Antarctic stations with independent prior constraints on subglacial structure. Our observed HVSR analysis additionally reveals a widespread seasonality in observed HVSR amplitudes between 0.2 and 1 Hz that correlates with sea ice evolution and the modulation of secondary microseism energies in the Southern Ocean. From the decrease in observed HVSR peak frequencies, we infer the likelihood of subglacial low‐velocity zones across Antarctica along major passive seismic transects, mapping to key subglacial sedimentary basins. We provide practical recommendations for future HVSR applications to infer subglacial low‐velocity zones reliably.