Rapid characterization of finite fault geometry and slip for large earthquakes is important for mitigation of seismic and tsunamigenic hazards. Saturation of near-source weak motion and problematic integration of strong-motion data into displacements make this difficult in real time. Combining GPS and accelerometer data to estimate seismogeodetic displacement waveforms overcomes these limitations by providing mm-level three-dimensional accuracy and improved estimation of coseismic deformation compared to GPS-only methods. We leverage collocated GPS and accelerometer data from the 2011 Mw 9.0 Tohoku-oki, Japan earthquake by replaying them in simulated real-time mode. Using a novel approach to account for fault finiteness, we generate an accurate centroid moment tensor solution independently of any constraint on the slab geometry followed by a finite fault slip model. The replay of GPS and seismic data demonstrates that robust models could have been made available within 3 min of earthquake initiation.