Geophysical Constraints on Glacial Earthquakes in Greenland and Implications for Glacier Dynamics

Abstract:

Gigaton-scale calving events at large outlet glaciers in Greenland generate seismic surface waves similar in amplitude to those from M 5 tectonic earthquakes. These glacial earthquakes provide a form of ground-based remote-sensing tool for the Greenland Ice Sheet, with increasing utility as understanding of the events improves. The number of glacial earthquakes occurring in Greenland has increased steadily since the early 1990s, when our observing record begins; 2012 and 2013 saw record numbers of glacial earthquakes in Greenland. Patterns of earthquake occurrence in space and time are closely linked to changes in glacier dynamics, including variations in the grounding state of the calving front. Event occurrence is strongly seasonally modulated, following seasonal patterns of ice-front retreat at individual glaciers. Seismological observations combined with geodetic, meteorological, and glaciological information demonstrate that glacial-earthquake ice-loss events are a primary control on short-term velocity variability at marine-terminating outlet glaciers. Glacial-earthquake source parameters derived from waveform modeling using a centroid--single-force approach agree well with independent estimates of changes in glacier geometry from satellite remote-sensing data and field observations. As for tectonic earthquakes, however, the full glacial-earthquake source process is more complex than that represented by such a long-period approximation. The seismological observing capacity in Greenland has improved dramatically in recent years, beginning to allow more detailed investigation of the time history of forces active during glacial earthquakes. Improved knowledge of the glacial-earthquake force history and source process will provide greater insight into calving processes and dynamic glacier behavior.