Earthquakes can modify the Earth's gravity field by deforming the Earth's layers and by changing the density of rocks through dilation and compression of crust and mantle material. Such changes were detected after the 2004 Sumatra-Andaman earthquake by the Gravity Recovery and Climate Experiment (GRACE) satellite, which has previously been used to monitor dynamics such as changes in ground water storage on land masses, exchanges between ice sheets or glaciers and the oceans, and fluctuations in ocean currents. Ogawa and Heki studied GRACE data following this earthquake and found signatures of extensive post-seismic creep along the main rupture. The authors also saw evidence for slow recovery of gravity field changes, possibly induced by simultaneous diffusion of mantle water while post-seismic slip occurs. They expect that such a self-healing system of earthquake-induced gravity changes, which introduces a new role of water in the mantle, would significantly reduce the amount of permanent shifts of the Earth's rotation axis by earthquakes.

Title: Slow Postseismic Recovery of Geoid Depression Formed by the 2004 Sumatra-Andaman Earthquake by Mantle Water Diffusion

Authors: Ryoko Ogawa: Division of Earth and Planetary Science, Graduate School of Science, Hokkaido University, Sapporo, Japan;
Kosuke Heki: Department of Natural History Science, Faculty of Science, Hokkaido University, Sapporo, Japan

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029340, 2007

2. Recent trends in Arctic Ocean mass distribution

Satellite-detected declines in salinity and bottom pressure in parts of the Arctic Ocean indicate that a reversal of the polar oceans circulation may be under way. The spatial distribution and magnitude of these trends suggest a shift from a clockwise to a counterclockwise pattern
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Contact: Peter Weiss
pweiss@agu.org
202-777-7507
American Geophysical Union
16-Apr-2007