The change of diatom flora showed that the Pacific coast of eastern Hokkaido rose at least 0.5m through the decades after a abnormally large tsunami in 17th century. The uplift produced an upward transition from tidal-flat mud to forest peat at an estuary previously after the invasion of the tsunami. Volcanic-ash layers show that the uplift began before 1667 and probably ended by 1694. Beneath the uplifted area, which extends at least 70km along the Kuril trench, oceanic crust subductys beneath the Kuril arc at depths of 60-80km. The simulation of crustal deformation suggests that shallow rupture seaward of the coarst along hundreds of kilometers of the Kuril trench probably generated the tsunami and the rupture triggered deep afterslip that raised the coast.
