Contribution of satellite gravimetry to understanding seismic source processes of the 2011 Tohoku‐Oki earthquake

The 2011 great Tohoku‐Oki earthquake, apart from shaking the ground, perturbed the motions of satellites orbiting some hundreds km away above the ground, such as GRACE, due to coseismic change in the gravity field. Significant changes in inter‐satellite distance were observed after the earthquake. These unconventional satellite measurements were inverted to examine the earthquake source processes from a radically different perspective that complements the analyses of seismic and geodetic ground recordings. We found the ‘average’ slip located up‐dip of the hypocenter but within the lower crust, as characterized by a limited range of bulk and shear moduli. The GRACE data constrained a group of earthquake source parameters that yield increasing dip (7–16° ± 2°) and, simultaneously, decreasing moment magnitude (9.17–9.02 ± 0.04) with increasing source depth (15–24 km). The GRACE solution includes the cumulative moment released over a month and demonstrates a unique view of the long‐wavelength gravimetric response to all mass redistribution processes associated with the dynamic rupture and short‐term postseismic mechanisms to improve our understanding of the physics of megathrusts.