[MIS11-P02] Triggers and scales of mid-17th-century tsunami estimated from tsunami deposits in western Pacific coast, Hokkaido
Keywords:Sector collapse, M8.8 mega earthquake, Tsunami magnitude
Two sandy event layers were discovered from the western pacific coast (Ex. Noboribetsu area). The lower layer was covered by the AD 1640 Ko-d tephra, which is inferred to be originated by the 1640 Hokkaido Komagatake eruption. The upper layer, on the other hand, probably correlated with the common event layer from the Iburi coast, indicates that the mega earthquake along the Kuril trench occurred before AD 1663 and after AD 1640.
Based on the characteristics of historical tsunami deposits and the examination of recent tsunamis, we can estimate the inundation depth of the historical tsunami events. We estimated the scale (Mt: tsunami Magnitude) of two tsunami events by investigation of these deposits. The tsunami caused by the Komagatake eruption is possible that the tsunami affected to Shiraoi, not to Mukawa area. The tsunami deposits in eastern part of Mukawa area yields larger than Mt 8.6-8.7, which values are consistent with the Government’s assumption of 17th century earthquake value, Mt 8.8 along the Kuril Trench.