A review of the 2011 Tohoku-Oki earthquake (Mw 9.0): Large-scale rupture across heterogeneous plate coupling

The 2011 Tohoku-Oki earthquake ruptured a large source region, which included areas with a range of past M 7 to M 8 earthquakes, varying stress accumulation, and different structural features. This megathrust event was substantially larger than anticipated in this region, though there were indications that the sequences of events in recent times were insufficient to relieve the full accumulated strain in the relatively rapid subduction of the Pacific plate. The source process time of about 150. s included rupture of an area of very large slip (30 to 60. m) on the shallow portion of the megathrust, updip of the hypocenter. The area of large slip produced large amplitude low-frequency radiation, while the dominant high-frequency radiation was generated from deeper sources down-dip of the hypocenter. Real-time information systems in Japan were able to issue timely warnings of the strong shaking and tsunami, but the complicated pattern of rupture growth led to an underestimate in the initial estimates of magnitude and tsunami threat. Variations in the plate coupling and heterogeneities of physical properties in the megathrust zone characterize the different source areas that ruptured together during the earthquake. Tomographic images of shear-wave and bulk-sound speeds show subtle changes of physical properties that may be associated with coupling condition and present clues for understanding the rupture process of this Mw 9 earthquake, which combined the source areas of many past earthquakes.