Most moderate and large earthquakes (M > ~4.5) occur when two bodies of rock slide rapidly past each other on a fault in the Earth's crust. We have recently discovered a class of earthquakes that we believe, based on analysis thus far, to result instead from the rapid sliding of glacial ice over the glacier bed. These glacial earthquakes occur in Alaska, Antarctica, and Greenland, with the vast majority of the earthquakes occurring at the rapidly moving outlet glaciers that drain ice from the Greenland Ice Sheet. The earthquakes we have detected to date have magnitudes of about 4.7-5.1. The size of the earthquakes can also be characterized by the product of the sliding mass and the sliding distance in each earthquake; these mass-sliding products are typically in the range 0.1 - 2.0 x 1014 kg-m. A mass-sliding product of this magnitude might be produced by, for example, the displacement of 10 km3 of ice over 10 m. We are currently conducting research to obtain better constraints on the processes by which glacial earthquakes occur and to gain a better understanding of the ways in which glacial earthquakes contribute to the overall deformation occurring within outlet glaciers.
Participants in this project at Columbia/LDEO are Göran Ekström, Meredith Nettles, and Morten Langer. Participants at other institutions include Victor Tsai (Harvard University) and the Helheim 2006 research team.
Meredith Nettles, Lamont-Doherty Earth Observatory of Columbia University, copyright ©2006, all rights reserved. Last modified: June 1, 2006 (MN)