C13D-04
Sounds of the deep: Passive microseismic monitoring of the base of ice streams.

Monday, 14 December 2015: 14:25
3007 (Moscone West)
Emma Clare Smith1, Andrew Smith1, Robert S White2, Alan F Baird3, J Michael Kendall3 and Alex Brisbourne1, (1)NERC British Antarctic Survey, Cambridge, United Kingdom, (2)University of Cambridge, Bullard Laboratories - Department of Earth Sciences, Cambridge, United Kingdom, (3)University of Bristol, School of Earth Sciences, Bristol, United Kingdom
Abstract:
Ice sheets discharge the majority of their mass though fast flowing ice streams and outlet glaciers and the flow dynamics of these features are heavily influenced by conditions at the base. Passive monitoring of microseismic icequake signals generated beneath ice streams are 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. These signals can be inverted for source location, source mechanism and magnitude, amongst other properties, to give spatial and temporal information about the active basal dynamics of a moving ice stream. Since the first dedicated microseismic survey on ice was undertaken in the 1960s, the use of passive microseismic monitoring to investigate the base of ice streams and glaciers has become more commonplace and the utilisation of information contained in these signals increasingly varied and complex.

We present a summary of the present state of passive microseismic monitoring of the base of ice streams with a focus on recent findings from Rutford Ice Stream, West Antarctica. We have located around 3000 microseismic events, in discrete spatial clusters near the ice-bed interface. The source mechanism for the events is interpreted as sub-horizontal, 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. We show that the location of these events, historically difficult to accurately determine, can be better constrained by synthetic modeling to investigate the source of errors in location. In addition to this we show that shear wave splitting in the signals can be used to determine properties of the ice fabric of Rutford Ice Stream, which informs both the deformation history and the future response of that ice to the stresses induced by ice flow.

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