1082 Carmichael.pdf (30.46 MB)
Seismicity on the western Greenland Ice Sheet: surface fracture in the vicinity of active moulins
journal contribution
posted on 2023-05-18, 11:36 authored by Carmichael, JD, Joughin, I, Behn, MD, Das, S, Matt KingMatt King, Stevens, L, Lizarralde, DWe 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 (<330m 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 previous years and could reflect the migration path of themeltwater 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.
Funding
Australian Research Council
History
Publication title
Journal of Geophysical Research: Earth SurfaceVolume
120Issue
6Pagination
1082-1106ISSN
2169-9003Department/School
School of Geography, Planning and Spatial SciencesPublisher
Wiley-Blackwell PublishingPlace of publication
United States of AmericaRights statement
© 2015. American Geophysical UnionRepository Status
- Open