Microearthquakes and subglacial conditions

Natural seismic emissions from glaciers have been associated with fracture within rapidly deforming ice, with ice motion over rock beds, and with glacial surges; and analysis of these seismic events can also help determine subglacial conditions.

Using new microearthquake data from an array of passive seismic recording stations on Rutford Ice Stream, West Antarctica, A. M. Smith investigated subglacial conditions in an area previously mapped with seismic reflection surveys and thus known to have subglacial sediments whose porosity varied along the surveys. In previous studies Smith hypothesized that where the ice was underlain by high porosity sediment, deformation of the sediment itself was responsible for the motion of the overriding ice, while over low-porosity sediments, the ice moved mainly by sliding. Smith's current analysis shows that areas underlain by low porosity sediments produce six times more seismic events than high porosity areas, confirming that sliding is much more prevalent over low porosity sediments. He suggests that monitoring microearthquakes can help map ice stream basal conditions over wide areas.

By American Geophysical Union