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Science 4 August 2006:
Vol. 313. no. 5787, pp. 658 - 662
DOI: 10.1126/science.1128661
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Reports

Crustal Dilatation Observed by GRACE After the 2004 Sumatra-Andaman Earthquake

Shin-Chan Han,1* C. K. Shum,1 Michael Bevis,1 Chen Ji,2 Chung-Yen Kuo1

We report the detection of an earthquake by a space-based measurement. The Gravity Recovery and Climate Experiment (GRACE) satellites observed a ±15-microgalileo gravity change induced by the great December 2004 Sumatra-Andaman earthquake. Coseismic deformation produces sudden changes in the gravity field by vertical displacement of Earth's layered density structure and by changing the densities of the crust and mantle. GRACE's sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements. The GRACE observations provide evidence of crustal dilatation resulting from an undersea earthquake.

1 Geodetic Science, Department of Geological Sciences, Ohio State University, 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, OH 43210–1398, USA.
2 Department of Earth Sciences, University of California at Santa Barbara, Santa Barbara, CA, USA.

* To whom correspondence should be addressed. E-mail: han.104{at}osu.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)