Inversion of high-rate (1 sps) GPS data for rupture process of the 11 March 2011 Tohoku earthquake (Mw9.1)

[1] The space-time fault displacement history of the 11 March 2011 Tohoku (Mw 9.1) megathrust earthquake is obtained by least-squares inversion of high-rate (1 sample per second) GPS ground motions recorded in Japan. Complete near-source time-varying and static ground motions for periods ≥25 s are fit in the inversion using a normal mode formalism to compute the Green functions. The basic rupture pattern is stable for various choices of model parameters and solution smoothing, and excellent fits to the complete seismo-geodetic ground motions are obtained. The preferred solution has concentrations of slip near the trench and hypocenter, with sub-fault source time function durations of ∼30–70 s and maximum slip of ∼60 m. Down-dip slip spreads over a wider area with smaller maximum slip (<∼10–15 m). Inversion of the high-rate GPS data exploits both the timing and total displacement information in the ground motions, yielding stable estimates of the seismic moment (∼4.8 × 1022 Nm; Mw = 9.1) and slip distribution.