GRACE detects coseismic and postseismic deformation from the Sumatra‐Andaman earthquake

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Abstract
We show that spherical harmonic (SH) solutions of the Gravity Recovery and Climate Experiment (GRACE) are now of sufficient quality to observe effects of co‐seismic and post‐seismic deformation due to the rupture from the Mw = 9.3 Sumatra‐Andaman earthquake on December 26, 2004, and its companion Nias earthquake (Mw = 8.7) on March 28, 2005. The improved GGM 03 SH (Level 2) solutions, and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range‐rate (Level 1) GRACE data. The gravity field disturbance extends over 1800 km along Andaman and Sunda subduction zones, and changes with time following events. Gravity changes may be due to afterslip, viscoelastic relaxation, or other processes associated with dilatation. Satellite gravity measurements from GRACE provide a unique new measure of deformation and post‐seismic processes associated with major earthquakes, especially in areas which are primarily oceanic.