This megathrust earthquake was a recurrence of the mechanism of the earlier 869 Sanriku earthquake , which has been estimated as having a magnitude of at least 8.4 Mw , which also created a large tsunami that inundated the Sendai plain . Three tsunami deposits have been identified within the Holocene sequence of the plain , all formed within the last 3,000 years , suggesting an 800 to 1,100 year recurrence interval for large tsunamigenic earthquakes . In 2001 it was reckoned that there was a high likelihood of a large tsunami hitting the Sendai plain as more than 1,100 years had then elapsed . In 2007 , the probability of an earthquake with a magnitude of Mw 8.1 – 8.3 was estimated as 99 % within the following 30 years
869 Sanriku earthquake
869 Sanriku earthquake
2011 Tōhoku earthquake and tsunami