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Title: 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 the western Greenland Ice Sheet during a ~35 day period of the 2011 melt season to study changes in ice deformation before, during, and after a supraglacial lake drainage event. During rapid lake drainage, ice flow speeds 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 ice speeds fell to ~150% of winter values and showed nightly peaks in spatial variability. Approximately 95% of all detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagation within near-surface ice (<330 m deep) that generated Rayleigh waves. Icequakes occurring before and during drainage frequently were collocated with the down flow (west) end of the primary hydrofracture through which the lake drained but shifted farther west and outside the lake basin after the drainage. We interpret these results to reveal vertical hydrofracture opening and local uplift during the drainage, followed by enhanced seismicity and ice flow on the downstream side of the lake basin. This region collocates with interferometric synthetic aperture radar-measured speedup in previousmore » years and could reflect the migration path of the meltwater supplied to the bed by the lake. The diurnal seismic signal can be associated with nightly reductions in surface melt input that increase effective basal pressure and traction, thereby promoting elevated strain in the surficial ice.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [4] ;  [4]
  1. Univ. of Washington, Seattle, WA (United States); Los Alamos National Lab., Los Alamos, NM (United States)
  2. Univ. of Washington, Seattle, WA (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Woods Hole Oceanographic Institution, Woods Hole, MA (United States)
  5. Univ. of Tasmania, Hobart, TAS (Australia)
Publication Date:
OSTI Identifier:
1215646
Report Number(s):
LA-UR--14-29056
Journal ID: ISSN 2169-9003
Grant/Contract Number:
NNX08AU82H; ANT-0424589; ARC-1023382; ARC-1023364; FT110100207; AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Earth Surface
Additional Journal Information:
Journal Volume: 120; Journal Issue: 6; Journal ID: ISSN 2169-9003
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; 97 MATHEMATICS AND COMPUTING seismology; cross-correlation; seismic source physics; glaciology; polar science; cold regions; glaciers; statistical signal processing; seismic threshold monitoring; detection theory; supraglacial lakes