Glacial earthquakes in Antarctica

Little tectonic activity takes place on Earth’s ice-covered, southernmost continent. That makes the area around David Glacier (shown in the figure and located on the inset map) especially interesting because a lot of low-level seismic events have been detected there over the years. Those detections prompted Stefania Danesi and Andrea Morelli of the National Institute of Geophysics and Volcanology in Bologna, Italy, and Stephen Bannister of GNS Science in Lower Hutt, New Zealand, to deploy a portable seismographic array for three months during the austral summer of 2003-04. They recorded more than 6000 events, most of which originated within the ice layer; the remaining 121 were induced by ice-rock interactions as the outlet glacier flowed over the underlying terrain. Those 121 events—all with magnitudes from 1.1 to 2.2—had unusual but similar waveforms and occurred in three main clusters, labeled and shown with stars in the figure. Two loose clusters are situated where the glacier drops 300-400 meters. In contrast, the DW cluster has 75 events located within 2 km², where the glacier flows past a promontory in the basement. The researchers speculate that repeated ruptures of a single asperity at the ice-bedrock interface are responsible for the DW events. The scientists note that this is a new and complex environment for studying fracture dynamics. (S. Danesi, S. Bannister, A. Morelli, Earth Planet. Sci. Lett., DOI:10.1016/j.epsl.2006.10.023, 2006 .)