Regional gravity decrease after the 2010 Chile earthquake indicates large-scale internal mass re-distribution

We report small but detectable, sudden changes in the GRACE satellites’ trajectory (relative speed between two satellites) after the earthquake in Maule, Chile on 27 February 2010 that can be used to delineate the shift in the Earth’s gravity field. The gravity anomaly of -5 µGal with a spatial scale of 500 km was found east of the epicenter after the earthquake. Our estimate of long-wavelength gravity changes based on coseismic models indicates that the interior deformation (mostly associated with intrinsic density change and characterized with negative anomaly) exceeds the surface deformation (causing positive anomaly) in the total gravity change at such spatial scale. Our results suggest a substantial role of large-scale gravity observations on deciphering changes of the Earth’s interior during great earthquakes by filling in the (seldom-observed) long wavelength spectrum of earthquakes as a complement to surface geodetic measurements and seismic data.