Gravitational gradient changes following the 2004 December 26 Sumatra-Andaman Earthquake inferred from GRACE

It has been demonstrated that the Gravity Recovery And Climate Experiment (GRACE) spaceborne gravimetry data are capable of observing coseismic gravity changes resulting from great earthquakes, such as the 2004 December 26 SumatraAndaman event (Mw 9.19.3). Here, we show for the first time that refined deformation signals from the 2004 December 26 SumatraAndaman Earthquake (Mw 9.19.3) together with the 2005 March 28 Nias earthquake (Mw 8.6) can be revealed by deriving the full gravitational gradient tensor from GRACE monthly gravitational field. The GRACE-inferred coseismic gravitational gradient changes agree well with coseismic slip model predictions. Since the high-frequency contents in gravitational field variation can be amplified by deriving the gravitational gradients, the GRACE-derived coseismic gravitational gradient changes clearly delineate the fault lines, locate significant slips, and better define the extent of the coseismic deformation.