Near-surface seismic anisotropy in Antarctic glacial snow and ice revealed by high-frequency ambient noise

Ambient seismic recordings taken at broad locations across Ross Ice Shelf and a dense array near West Antarctic Ice Sheet (WAIS) Divide, Antarctica, show pervasive temporally variable resonance peaks associated with trapped seismic waves in near-surface firn layers. These resonance peaks feature splitting on the horizontal components, here interpreted as frequency-dependent anisotropy in the firn and underlying ice due to several overlapping mechanisms driven by ice flow. Frequency peak splitting magnitudes and fast/slow axes were systematically estimated at single stations using a novel algorithm and compared with good agreement with active source anisotropy measurements at WAIS Divide determined via active sources recorded on a 1 km circular array. The approach was further applied to the broad Ross Ice Shelf (RIS) array, where anisotropy axes were directly compared with visible surface features and ice shelf flow lines. The near-surface firn, depicted by anisotropy above 30 Hz, was shown to exhibit a novel plastic stretching mechanism of anisotropy, whereby the fast direction in snow aligns with accelerating ice shelf flow.

Automated summary

Ambient seismic recordings in Antarctica reveal time-variable resonance peaks in near-surface firn layers, resulting from trapped seismic waves. The splitting of these peaks on the horizontal components indicates frequency-dependent anisotropy in the firn and underlying ice caused by overlapping mechanisms driven by ice flow. A novel algorithm was used to estimate the splitting magnitudes and axes, which were compared with active source anisotropy measurements, showing good agreement. The study also discovered a novel plastic stretching mechanism of anisotropy in the near-surface firn, where the fast direction aligns with accelerating ice shelf flow.