Geodetic observations detecting coseismic displacements and gravity changes caused by the Mw=9.0 Tohoku-Oki earthquake

This paper reports coseismic displacements and gravity changes caused by the Tohoku-Oki earthquake (Mw 9.0), as observed respectively using GPS in Japan and China and its surrounding area, and as observed by GRACE. To interpret geodetic observation data, we must choose a reasonable model among the slip models presented for the event. For this purpose, we first calculated the displacements using three slip models from USGS, UCSB, and ARIA respectively, with different dislocation theories. Then we compared the results with the displacements observed in Japan and China. Results show that the modeled coseismic displacements calculated using the slip model of Wei et al. (ARIA) and the spherically layered dislocation theory under the PREM model agree well with the observed ones, indicating that the Earth's layer-structural and curvature effects should be considered. Then, we computed the coseismic geoid and gravity changes on the earth surface and at a space-fixed point using the three slip models and the spherically layered dislocation theory. Results show that the maximum coseismic geoid change reaches 2.5 cm and that the coseismic gravity changes are about -1000-600 mu gal for a solid Earth. Furthermore, we processed GRACE data to extract coseismic changes with decorrelation and a Gaussian filter of 350 km. The gravity changes observed by GRACE were dominated by a decrease over the back-arc region, with -5 mu gal reflecting coseismic crustal dilatation of the landward plate, which agrees well with the theoretically modeled values from the three finite fault models. After the 2004 Sumatra-Andaman and 2010 Central Chile (Maule) earthquakes, this study presents the third case of clear detection of coseismic gravity changes by GRACE.