SEISMIC OBSERVATIONS OF GLACIER DEFORMATION IN GREENLAND

The major outlet glaciers of the Greenland Ice Sheet are the source of a broad range of observable seismic phenomena, ranging from long-period globally observable surface waves from major calving events to high-frequency seismicity observable on seismographs installed near outlet glaciers. We investigated nearly two decades of globally observable events known as glacial earthquakes and found a close link between earthquake occurrence and calving-front behaviour. We found that glacial earthquakes occur at glaciers with grounded or near-grounded termini, an observation that explains the northward progression of glacial earthquakes with time, as calving fronts have retreated. Less is known about high-frequency seismic sources at Greenland's glaciers. To analyze the high-frequency emissions of a major outlet glacier, we use data recorded by a temporary network of six 3-component seismometers, sampling at 100 sps, deployed around Helheim Glacier in East Greenland. We identify thousands of seismic events by analysis of seismogram envelope functions and find the occurrence of these events to be strongly tidally modulated. The pattern of tidal modulation we observe is consistent with geodetic observations of tidal forcing of glacier behaviour. Many of the signals we observe are also highly correlated, suggesting that many of the events emanate from a localized source region and have similar source mechanisms. A better understanding of the full frequency range of glaciogenic seismic signals will aid in understanding calving processes and glacier dynamics more broadly.