Coseismic and postseismic deformation of the 2011 tohoku-oki earthquake constrained by GRACE gravimetry

Spaceborne gravimetry data from the Gravity Recovery And Climate Experiment (GRACE) are processed using spatio-spectral Slepian localization analysis enabling the high-resolution detection of permanent gravity change associated with both coseismic and postseismic deformation resulting from the great 11 March 2011 Mw 9.0 Tohoku-Oki earthquake. The GRACE observations are then used in a geophysical inversion to estimate a new slip model containing both coseismic slip and after-slip. The GRACE estimated moment for the total slip, up to the end of July 2011 is estimated as (4.59 ± 0.49) × 10²² Nm, equivalent to a composite Mw of 9.07 ± 0.65. If the moment for the Tohoku-Oki main shock is assumed to be 3.8 × 10²² Nm, the contribution from the after-slip is estimated to be 3.0 × 10 ²¹-12.8 × 10²¹ Nm, in good agreement with a postseismic slip model inverted from GPS data. We conclude that GRACE data provide an independent constraint to quantify co-and post-seismic deformation for the Tohoku-Oki event.