The aim of the ICEDISC (Ice dynamics investigations with seismological components) project was to investigate the subglacial drainage system using seismic noise analysis techniques. By focusing on the source of seismic waves, the properties of glacial ice were studied – including ice sheet thickness and the structure of its base.
Spectral analysis of seismic records from the Greenland ice sheet revealed that water plays a key role in the occurrence and frequency of seismic generating processes. It was found that water pressure from moulins determined the frequency and strength of water-generated seismic noise. Moulins are vertical shafts formed in the glacier by surface water percolating through a crack in the ice.
A parallel study analysed seismograms of faraway earthquakes in place of man-made events such as explosions, air guns or hammer blows. The results revealed the existence of a subglacial sediment layer, at least 80 m thick. This finding was in line with recent numerical modelling exercises and observations that suggested the presence of a 'soft bed', which could have a significant impact on ice sheet flow.
ICEDISC provided new insights into glacier dynamics and hydraulics. The discovery of a thick glacial sediment layer must be taken into consideration in models of ice sheet flow and global sea-level rise. In addition, the project has demonstrated that ice sheet and glacier properties can be derived from passive seismic recordings.
As seismic wave propagation depends to some extent on the state of the glacier, noise-derived seismic velocities can be used to monitor the stability of steep glaciers. This will enable villages and tourist resorts to receive advanced warning of the bursting of glacial lakes and collapse of steep glaciers, which have claimed thousands of lives in the past.
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