Abstract
AbstractSeismic studies of glaciers yield insights into spatio-temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice. These methods enable direct monitoring of the bed in ways that complement other geophysical techniques, such as geodetic or ground penetrating radar observations. In this work, we report on the analysis of passive seismic data collected from the interior of the North East Greenland Ice Stream, the Greenland ice sheet's largest outlet glacier. We record thousands of basal earthquakes, many of which repeat with nearly identical waveforms. We also record many long-duration glacial tremor episodes that migrate across the seismic network with slow velocities (e.g. ~4–12 m s−1). Analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity. We suggest that both processes are produced by shear slip at localized asperities along the bed. The transition between discrete and quasi-continuous slipping modes may be driven by pore-water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till.
Highlights
Ice streams are responsible for discharging the majority of ice from ice sheets into the ocean (Rignot and others, 2008)
The processes by which ice stream slip occurs are influenced by a complex interaction of factors including basal topography, subglacial drainage networks, water pressure, debris entrained in basal ice, substrate material properties, overburden pressure, driving stress and heat flow
In this study we report findings from passive seismic data recorded during a field campaign to the Greenland ice sheet (GIS) on the Northeast Greenland Ice Stream (NEGIS)
Summary
Ice streams are responsible for discharging the majority of ice from ice sheets into the ocean (Rignot and others, 2008). As the ice approaches the ocean the speed of ice flow increases by 2–3 orders of magnitude relative to the ice-sheet interior and forms distinct bands of (∼50–200 km) wide fast-flowing ice. Most modern and historically documented ice streams tend to be located in modest topographic depressions, form low-angle surfaces The processes by which ice stream slip occurs are influenced by a complex interaction of factors including basal topography, subglacial drainage networks, water pressure, debris entrained in basal ice, substrate material properties, overburden pressure, driving stress and heat flow. The dynamic interaction of these factors on the small to medium scale gives rise to the macroscopic velocity field of all glaciers, and can result in transient phenomena such as kinematic waves (Weertman, 1962; Van de Wal and Oerlemans, 1995), surging glaciers (Clarke, 1987; Sharp, 1988), drainage network reorganization (Nienow and others, 1998), basal water pressure fluctuations (Stearns and others, 2008) and outburst floods (Walder and Costa, 1996). Long-term macroscopic evolutionary trends, such as thinning and thickening of the ice, or the growth and stagnation of entire ice streams (Alley and others, 1994), are on the whole driven by dynamic interaction of many small-scale components
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