Source rupture process of the 2011 Tohoku - Oki earthquake derived from the strong - motion records

We reveal the source rupture process using the strong-motion data by the inversion analysis. The derived slip distribution shows one prominently large slip area extending from the hypocentre area to the shallow part of the fault along the trench axis, which is located far off the coastal region extensively damaged by the tsunamis. The shallow main rupture started 60 seconds after the initial break and lasted for as long as 40 seconds. The deeper area between the hypocentre and the coastline experienced the two down-dip ruptures at 20-50 and 70-100 seconds. Distinctive phase observed in the low-frequency velocity waveforms is generated by the rupture of these two areas after 60 seconds. Rupture after 100 seconds propagated southward. Our result suggests that the large extent of the rupture area resulted in large ground motions across wide regions and the shallow large slip triggered the devastating tsunamis.