Downhole distributed acoustic seismic profiling at Skytrain Ice Rise, West Antarctica
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Published:2021-07-23
Issue:7
Volume:15
Page:3443-3458
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ISSN:1994-0424
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Container-title:The Cryosphere
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language:en
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Short-container-title:The Cryosphere
Author:
Brisbourne Alex M.ORCID, Kendall MichaelORCID, Kufner Sofia-KaterinaORCID, Hudson Thomas S., Smith Andrew M.ORCID
Abstract
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, 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=3984±218 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 travel times 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.
Funder
Natural Environment Research Council
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Water Science and Technology
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