The kinematic rupture process of the 2011 Mw 9.0 Tohoku earthquake is inverted with an elliptical-patches method, using a genetic algorithm, for the purpose of rapid and robust estimation of the source parameters of a mega-earthquake. We use the ground-displacement field provided by a continuous GPS network and the ground-velocity field recorded by acceleration networks. In addition to the typical inversion procedure in which a data duration long enough to cover the whole rupture process is used, inversions based on shorter signals, giving an incomplete view over the ground shaking sequence, are also carried out. How fast can a robust estimation of the source parameters be obtained? Using the elliptical approximation, we find that robust solutions of Mw ~ 9.0-earthquakes are rather quickly obtained regardless of the frequency band and the elliptical patch description. It is also confirmed that, because of the absence of off-shore recording stations on the east side of the fault, some uncertainties in the rupture process cannot be completely removed. In fact, at the very low frequencies considered, the western part of the fault (deeper portion) contributes more significantly to the recorded signals than does the other end close to the trench. This problem also prevents refinement of the description of the rupture process, in particular when using more than one ellipse.