Slow Earthquakes Beneath the Greenland Ice Sheet

Harvard University, Cambridge MA

Investigators

Abstract

The Principal Investigator will investigate a group of highly anomalous magnitude~5 earthquakes that he has recently detected in Greenland. The earthquakes belong to a new class of seismic events associated with glaciers discovered in early 2003. The previously unknown earthquakes on Greenland generate long-period seismic surface waves that are recorded well on globally distributed seismic stations. The earthquakes have previously gone undetected because they do not generate the high-frequency seismic waves on which traditional earthquake detection and location methodologies are based. Beyond a few basic characteristics, little is known about these sources of seismic radiation. Preliminary results indicate that the seismic waves are inconsistent with tectonic faulting, but instead consistent with sudden and massive glacial sliding. If the events are caused by rapid glacial motion, they will represent a new and distinct mode of glacial behavior. The Principal Investigator will make use of data from global seismic stations as well as seismic stations on Greenland to improve the characterization of the new class of earthquakes. In particular, our detection algorithms will be improved and extended, and applied to continuous waveform data to develop a catalog of events for the last ten years. Modification of the algorithm and the inclusion of data from Greenland will lower the detection magnitude threshold and reduce the location uncertainty, allowing a better geographic correlation with glacial features and morphology. The seismic source model will be refined to allow evaluation of different physical models for the earthquake source. The results from the proposed seismological analysis will form the basis for an evaluation of future research opportunities, including geodetic and seismic campaign work on Greenland, and theoretical modeling. Intellectual Merit. This research will lead to a detailed characterization of the phenomenon of slow earthquakes beneath the Greenland ice sheet. The analysis will address first-order questions about the fundamental nature of the new class of glacial earthquakes, and will explore various physical explanations for their occurrence. Since almost nothing is currently known about these events, the proposed research will result in new knowledge about seismic sources and the seismic behavior of glaciers. Broader Impacts. Current results strongly suggest that the newly discovered earthquakes are caused by sudden sliding of large portions of the glacier in a manner not previously described or observed. The Principal Investigator will develop and test this and alternative explanations for the observed earthquakes. If the glacial-sliding explanation is confirmed, this result is likely to have a significant influence on the understanding of glacial movement and dynamics.