Seismicity on the western Greenland Ice Sheet: surface fracture in the vicinity of active moulins

We analyzed geophone and GPS measurements collected within the ablation zone of thewestern Greenland Ice Sheet during a ~35 day period of the 2011 melt season to study changes in icedeformation before, during, and after a supraglacial lake drainage event. During rapid lake drainage, ice flowspeeds i...

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Bibliographic Details
Published in:Journal of Geophysical Research: Earth Surface
Main Authors: Carmichael, JD, Joughin, I, Behn, MD, Das, S, King, MA, Stevens, L, Lizarralde, D
Format: Article in Journal/Newspaper
Language:English
Published: Wiley-Blackwell Publishing 2015
Subjects:
Engineering
Geomatic Engineering
Geodesy
Greenland
Rapid Lake
Ice Sheet
Online Access:https://doi.org/10.1002/2014JF003398
http://ecite.utas.edu.au/101688
Description
Summary:We analyzed geophone and GPS measurements collected within the ablation zone of thewestern Greenland Ice Sheet during a ~35 day period of the 2011 melt season to study changes in icedeformation before, during, and after a supraglacial lake drainage event. During rapid lake drainage, ice flowspeeds increased to ~400% of winter values, and icequake activity peaked. At times >7 days after drainage,this seismicity developed variability over both diurnal and longer periods (~10 days), while coincident icespeeds fell to ~150% of winter values and showed nightly peaks in spatial variability. Approximately 95% ofall detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagationwithin near-surface ice (<330m deep) that generated Rayleigh waves. Icequakes occurring before andduring drainage frequently were collocated with the down flow (west) end of the primary hydrofracturethrough which the lake drained but shifted farther west and outside the lake basin after the drainage. Weinterpret these results to reveal vertical hydrofracture opening and local uplift during the drainage, followedby enhanced seismicity and ice flow on the downstream side of the lake basin. This region collocates withinterferometric synthetic aperture radar-measured speedup in previous years and could reflect the migrationpath of themeltwater supplied to the bed by the lake. The diurnal seismic signal can be associated with nightlyreductions in surface melt input that increase effective basal pressure and traction, thereby promoting elevatedstrain in the surficial ice.

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