Estimating the hazard resulting from great earthquakes on active subduction megathrusts is plagued with difficulties, yet it is necessary in populated areas proximal to active subduction. In practice, we are increasingly including knowledge of the physical fault system and mechanics into estimations of seismic hazard, aided by rapid advances in understanding the diverse spectrum of megathrust behavior. In general, statistical approaches to estimating hazard are hampered by the paucity of observed data and deterministic approaches involve large uncertainty. In Taiwan and New Zealand, megathrust‐hazard estimates are further complicated by the relatively short history of seismic observations and lack of any historical, local, or regional great earthquakes to use as analogs. Thus, it is useful to consider what insights can be gained from observations of the 2011 Mw 9.0 Tohoku‐Oki earthquake, Japan.