Microearthquakes and subglacial conditions

Ten passive seismic recording stations were deployed in a 9 km by 6 km array on Rutford Ice Stream, West Antarctica, to detect microearthquakes from the ice stream bed. The array covered an area where a varying distribution of basal sedimentary conditions had been identified from seismic reflection surveys and interpreted as areas of both basal sliding and subglacial sediment deformation. The passive seismic experiment was designed to give an independent confirmation of this interpretation, as basal sliding is believed to be associated with the release of more acoustic energy than a deforming bed. The results show that this is the case, basal sliding producing six times more events. This confirms that the spatial pattern of basal conditions does indeed reflect the distribution of different ice flow mechanisms. It also shows that microearthquake monitoring can be a valuable new technique for mapping ice stream basal conditions over wide areas.