Geodetic constraints on the mechanism of glacial earthquakes

Columbia University, New York NY

Investigators

Abstract

Nettles OPP-0612609 The Principal Investigators request support for research to be carried out with a pilot field experiment in summer, 2006 at Helheim Glacier, East Greenland to obtain an understanding of the mechanisms by which glacial earthquakes are generated and their relation to glaciological and climatological processes. A new class of earthquakes occurring at glaciers in Alaska, Antarctica, and Greenland was identified in 2003 by Ekstrom. Teleseismic analysis indicates that these glacial earthquakes are the result of rapid sliding of the glacial ice over the glacier bed. Little is understood about the mechanism by which glacial earthquakes occur, but recent observations indicate a relationship with the hydrological cycle at glaciers and ice sheets. The number of earthquakes that occur on Greenland is strongly seasonally modulated, with the largest number of events occurring during the late summer months. A rapid increase in the number of earthquakes at outlet glaciers across Greenland since approximately 2000 suggests a link to large-scale climate change. This research consists of two parts: 1) a field deployment of Global Positioning System (GPS) stations on Helheim Glacier to obtain direct measurements of the displacement transients associated with glacial earthquakes, the logistical costs for which will be funded separately; and 2) integrated, interdisciplinary analysis of recorded GPS, seismic, and glaciological data using state-of-the-art techniques from each field to obtain an understanding of the mechanism by which glacial earthquakes occur. Seismic analyses will provide long-wavelength estimates of the earthquake source characteristics, while the geodetic observations will provide detailed information about the timing and pattern of deformation within the glacier. A combined analysis of these datasets will result in geophysically consistent models of the deformation process, which will then be studied in the context of glaciological observations of the background glacier behavior and time-varying melting rates to evaluate the hypothesis that surface melting is linked to the generation of glacial earthquakes. Intellectual Merit. This research will lead to a greatly improved understanding of the processes controlling glacial earthquakes, a previously unknown geophysical phenomenon. It will also provide insight into modes of glacier deformation and possible connections between glacial earthquake activity and global climate change. Broader Impacts. The results will be important for glaciologists and climatologists in addition to geodesists and seismologists. The understanding of glacial earthquakes developed as a result of this study will allow remote-sensing seismic data to be used as a glaciology tool and studies of global change, while also leading to improved knowledge of the response of the solid Earth to transient deformation events at or near the surface of the Earth.