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The massive Tohoku-Oki earthquake of a moment magnitude (Mw) of 9.0 occurred on 11 March, 2011 off the Pacific coast of the Northeastern Japan. The mass redistribution in and around the focal region associated with this earthquake was studied using the gravity changes detected by Gravity Recovery and Climate Experiment (GRACE) satellite. After the 2004 Sumatra-Andaman and the 2010 Central Chile (Maule) earthquakes, the present study presents the third case of clear detection of coseismic gravity changes by GRACE. The observed gravity changes were dominated by decrease over the back-arc region of ∼7 μGal or less. This reflects, to a large extent, coseismic crustal dilatation of the landward plate. They agree well with the changes calculated with the Green's function for the realistic earth using fault parameters inferred from coseismic crustal movements. The spatial patterns of the gravity changes of these earthquakes are very similar because they are all shallow angle reverse faulting at convergent plate boundaries. We found linear relationship between gravity decreases and seismic moments.
Matsuo et al. (Fri,) studied this question.