Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations

S. K. Kufner; J. Wookey; A. M. Brisbourne; C. Martín; Thomas S Hudson; J. M. Kendall; A.M. Smith

doi:10.1029/2022JF006853

Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations

S. K. Kufner^*
, J. Wookey
, A. M. Brisbourne
, C. Martín
, Thomas S Hudson
, J. M. Kendall
, A.M. Smith

^*Corresponding author for this work

Research output: Contribution to journal › Article (Academic Journal) › peer-review

13 Citations (Scopus)

Abstract

The crystal orientation fabric of glacier ice impacts its strength and flow. Crystal fabric is therefore an important consideration when modeling ice flow. Here, we show that shear-wave splitting (SWS) measured with glacial microseismicity can be used to invert seismic anisotropy and ice fabric, if represented in a statistical sense. Rutford Ice Stream (RIS) is a fast-flowing Antarctic ice stream, a setting crucial for informing large-scale ice sheet models. We present >200,000 SWS measurements from glacial microseismicity, registered at a 38-station seismic network located ∼40 km upstream of the grounding line. A representative subset of these data is inverted for ice fabric. Due to the character of SWS, which accumulates along the raypath, we include information on the depth structure from radar measurements. We find that the following three-layer configuration fits the data best: a broad vertical cone fabric near the base of RIS (500 m thick), a thick vertical girdle fabric, orientated perpendicular to flow, in the middle (1,200 m thick), and a tilted cone fabric in the uppermost 400 m. Such a variation of fabric implies a depth-dependent strength profile of the ice with the middle layer being ∼3.5 times harder to deform along flow than across flow. At the same time, the middle layer is a factor ∼16 softer to shear than to compression or extension along flow. If such a configuration is representative for fast-flowing ice streams, it would call for a more complex integration of viscosity in ice sheet models.

Original language	English
Article number	e2022JF006853
Journal	Journal of Geophysical Research: Earth Surface
Volume	128
Issue number	3
Early online date	8 Mar 2023
DOIs	https://doi.org/10.1029/2022JF006853
Publication status	Published - 15 Mar 2023

Bibliographical note

Funding Information:
This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR-1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript.

Funding Information:
This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR‐1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript.

Publisher Copyright:
© 2023. The Authors.

Keywords

anisotropy
Antarctica
ice fabric
ice stream
icequakes
shear wave splitting

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10.1029/2022JF006853Licence: CC BY

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Cite this

@article{e9b19084ca524740a6aeaa0d0a8edd01,

title = "Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations",

abstract = "The crystal orientation fabric of glacier ice impacts its strength and flow. Crystal fabric is therefore an important consideration when modeling ice flow. Here, we show that shear-wave splitting (SWS) measured with glacial microseismicity can be used to invert seismic anisotropy and ice fabric, if represented in a statistical sense. Rutford Ice Stream (RIS) is a fast-flowing Antarctic ice stream, a setting crucial for informing large-scale ice sheet models. We present >200,000 SWS measurements from glacial microseismicity, registered at a 38-station seismic network located ∼40 km upstream of the grounding line. A representative subset of these data is inverted for ice fabric. Due to the character of SWS, which accumulates along the raypath, we include information on the depth structure from radar measurements. We find that the following three-layer configuration fits the data best: a broad vertical cone fabric near the base of RIS (500 m thick), a thick vertical girdle fabric, orientated perpendicular to flow, in the middle (1,200 m thick), and a tilted cone fabric in the uppermost 400 m. Such a variation of fabric implies a depth-dependent strength profile of the ice with the middle layer being ∼3.5 times harder to deform along flow than across flow. At the same time, the middle layer is a factor ∼16 softer to shear than to compression or extension along flow. If such a configuration is representative for fast-flowing ice streams, it would call for a more complex integration of viscosity in ice sheet models.",

keywords = "anisotropy, Antarctica, ice fabric, ice stream, icequakes, shear wave splitting",

author = "Kufner, \{S. K.\} and J. Wookey and Brisbourne, \{A. M.\} and C. Mart{\'i}n and Hudson, \{Thomas S\} and Kendall, \{J. M.\} and A.M. Smith",

note = "Funding Information: This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR-1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript. Funding Information: This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR‐1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript. Publisher Copyright: {\textcopyright} 2023. The Authors.",

year = "2023",

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doi = "10.1029/2022JF006853",

language = "English",

volume = "128",

journal = "Journal of Geophysical Research: Earth Surface",

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T1 - Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations

AU - Kufner, S. K.

AU - Wookey, J.

AU - Brisbourne, A. M.

AU - Martín, C.

AU - Hudson, Thomas S

AU - Kendall, J. M.

AU - Smith, A.M.

N1 - Funding Information: This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR-1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript. Funding Information: This work was funded by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. The authors thank the staff at Rothera Research Station and BAS Logistics for enabling the fieldwork associated with this project and the BEAMISH field team (2018/2019) for acquiring the passive seismic data. Seismic instruments were provided by NERC GEF (Loan 1017), BAS, and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by the National Science Foundation's Seismological Facilities for the Advancement of Geoscience (SAGE) Award under Cooperative Support Agreement EAR‐1851048. We thank three anonymous reviewers and the editors for thoughtful comments that significantly improved this manuscript. Publisher Copyright: © 2023. The Authors.

PY - 2023/3/15

Y1 - 2023/3/15

N2 - The crystal orientation fabric of glacier ice impacts its strength and flow. Crystal fabric is therefore an important consideration when modeling ice flow. Here, we show that shear-wave splitting (SWS) measured with glacial microseismicity can be used to invert seismic anisotropy and ice fabric, if represented in a statistical sense. Rutford Ice Stream (RIS) is a fast-flowing Antarctic ice stream, a setting crucial for informing large-scale ice sheet models. We present >200,000 SWS measurements from glacial microseismicity, registered at a 38-station seismic network located ∼40 km upstream of the grounding line. A representative subset of these data is inverted for ice fabric. Due to the character of SWS, which accumulates along the raypath, we include information on the depth structure from radar measurements. We find that the following three-layer configuration fits the data best: a broad vertical cone fabric near the base of RIS (500 m thick), a thick vertical girdle fabric, orientated perpendicular to flow, in the middle (1,200 m thick), and a tilted cone fabric in the uppermost 400 m. Such a variation of fabric implies a depth-dependent strength profile of the ice with the middle layer being ∼3.5 times harder to deform along flow than across flow. At the same time, the middle layer is a factor ∼16 softer to shear than to compression or extension along flow. If such a configuration is representative for fast-flowing ice streams, it would call for a more complex integration of viscosity in ice sheet models.

AB - The crystal orientation fabric of glacier ice impacts its strength and flow. Crystal fabric is therefore an important consideration when modeling ice flow. Here, we show that shear-wave splitting (SWS) measured with glacial microseismicity can be used to invert seismic anisotropy and ice fabric, if represented in a statistical sense. Rutford Ice Stream (RIS) is a fast-flowing Antarctic ice stream, a setting crucial for informing large-scale ice sheet models. We present >200,000 SWS measurements from glacial microseismicity, registered at a 38-station seismic network located ∼40 km upstream of the grounding line. A representative subset of these data is inverted for ice fabric. Due to the character of SWS, which accumulates along the raypath, we include information on the depth structure from radar measurements. We find that the following three-layer configuration fits the data best: a broad vertical cone fabric near the base of RIS (500 m thick), a thick vertical girdle fabric, orientated perpendicular to flow, in the middle (1,200 m thick), and a tilted cone fabric in the uppermost 400 m. Such a variation of fabric implies a depth-dependent strength profile of the ice with the middle layer being ∼3.5 times harder to deform along flow than across flow. At the same time, the middle layer is a factor ∼16 softer to shear than to compression or extension along flow. If such a configuration is representative for fast-flowing ice streams, it would call for a more complex integration of viscosity in ice sheet models.

KW - anisotropy

KW - Antarctica

KW - ice fabric

KW - ice stream

KW - icequakes

KW - shear wave splitting

UR - https://www.scopus.com/pages/publications/85151089411

U2 - 10.1029/2022JF006853

DO - 10.1029/2022JF006853

M3 - Article (Academic Journal)

AN - SCOPUS:85151089411

SN - 2169-9003

VL - 128

JO - Journal of Geophysical Research: Earth Surface

JF - Journal of Geophysical Research: Earth Surface

IS - 3

M1 - e2022JF006853

ER -

Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations

Abstract

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Keywords

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Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations

Abstract

Bibliographical note

Keywords

Access to Document

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