Preprints
https://doi.org/10.5194/tc-2021-1
https://doi.org/10.5194/tc-2021-1

  28 Jan 2021

28 Jan 2021

Review status: this preprint is currently under review for the journal TC.

Downhole distributed acoustic seismic profiling at Skytrain Ice Rise, West Antarctica

Alex M. Brisbourne1, Michael Kendall2, Sofia-Katerina Kufner1, Thomas S. Hudson2, and Andrew M. Smith1 Alex M. Brisbourne et al.
  • 1IDP, NERC British Antarctic Survey, Cambridge, CB3 0ET, UK
  • 2Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN, UK

Abstract. Antarctic ice sheet history is imprinted in the structure and fabric of the ice column. At ice rises, the signature of ice flow history is preserved due to the low strain rates inherent at these independent ice flow centres. We present results from a distributed acoustic sensing (DAS) experiment at Skytrain Ice Rise in the Weddell Sea Sector of West Antarctica, aimed at delineating the englacial fabric to improve our understanding of ice sheet history in the region. This pilot experiment demonstrates the feasibility of an innovative technique to delineate ice rise structure. Both direct and reflected P- and S-wave energy, as well as surface wave energy, are observed using a range of source offsets, i.e., a walkaway vertical seismic profile (VSP), recorded using fibre optic cable. Significant noise, which results from the cable hanging untethered in the borehole, is modelled and suppressed at the processing stage. At greater depth, where the cable is suspended in drilling fluid, seismic interval velocities and attenuation are measured. Vertical P-wave velocities are high (VINT = 4029 ± 244 m s−1) and consistent with a strong vertical cluster fabric. Seismic attenuation is high (QINT = 75 ± 12) and inconsistent with previous observations in ice sheets over this temperature range. The signal level is too low, and the noise level too high, to undertake analysis of englacial fabric variability. However, modelling of P- and S-wave traveltimes and amplitudes with a range of fabric geometries, combined with these measurements, demonstrates the capacity of the DAS method to discriminate englacial fabric distribution. From this pilot study we make a number of recommendations for future experiments aimed at quantifying englacial fabric to improve our understanding of recent ice sheet history.

Alex M. Brisbourne et al.

Status: open (until 26 Mar 2021)

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  • RC1: 'Comment on tc-2021-1', Anonymous Referee #1, 01 Mar 2021 reply

Alex M. Brisbourne et al.

Alex M. Brisbourne et al.

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Short summary
How ice sheets flowed in the past is written into the structure and texture of the ice sheet itself. Measuring this structure and properties of the ice can help us understand the recent behaviour of the ice sheets. We use a relatively new technique, not previously attempted in Antarctica, to measure the seismic vibrations of a fibre optic cable down a borehole. We demonstrate the potential of this technique to unravel past ice flow and see hints of these complex signals from the ice flow itself.