Tsunami hazard maps are constructed for past tsunamis
or for the most likely tsunami source. In the Sendai plain
before the 2011 Tohoku tsunami, tsunami hazard maps
and other countermeasures were prepared for an M~8
earthquake, which was estimated to occur with 99% probability
in the next 30 years (see The 2011 Tohoku earthquake
and tsunami section). The predicted inundation area
was, for the most part, within 1 km from the coast, and
much smaller than the actual tsunami inundation area of
the 2011 M= 9.0 earthquake which was up to 5 km. The
distribution of the 869 Jogan tsunami deposits, however,
was similar to the inundation area of the 2011 Tohoku tsunami.
The hazard maps need to consider such infrequent
gigantic earthquake and tsunamis.