Mapping the ice-bed interface characteristics of Rutford Ice Stream, West Antarctica, using microseismicity

Flow dynamics of the ice streams that drain the Antarctic Ice Sheet are heavily influenced by processes at the bed. Natural seismic activity generated beneath an ice stream is associated with the motion of the ice over its bed and can be used to map both the characteristics of the ice-bed interface and to understand these basal processes. Basal microseismicity was recorded over a 34 day period on Rutford Ice Stream, West Antarctica, using 10 three-component geophones 40 km upstream of the grounding line. Around 3000 microseismic events were located in discrete spatial clusters near the ice-bed interface. The activity of each cluster varies with time, and the source mechanism for the events is interpreted as subhorizontal, low-angle faulting, slipping in the ice flow direction. Cluster locations are interpreted as “sticky spots” of stiff basal sediment at the ice-bed interface, where ice movement is accommodated by stick-slip basal sliding. The sticky spots occur in areas where independent active-source seismic surveys show low porosity sediments at the bed. We show that the sticky spots probably accommodate only a small amount of the total basal motion. Our results suggest that most of the ice stream basal motion is accommodated by aseismic deformation of soft, dilatant basal sediment, or by a well-lubricated, stiffer bed.

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