Japan Geoscience Union Meeting 2023

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[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS16] Tsunami deposit

Tue. May 23, 2023 3:30 PM - 4:45 PM 106 (International Conference Hall, Makuhari Messe)

convener:Masaki Yamada(Department of Geology, Faculty of Science, Shinshu University), Takashi Ishizawa(International Research Institute of Disaster Science, Tohoku University), Koichiro Tanigawa(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), RYO NAKANISHI(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Takashi Ishizawa(International Research Institute of Disaster Science, Tohoku University), RYO NAKANISHI(Atmosphere and Ocean Research Institute, The University of Tokyo)

4:30 PM - 4:45 PM

[MIS16-11] Maximum sizes of paleo-tsunamis, earthquakes, and storms inferred from coastal boulder deposit

★Invited Papers

*Kenta Minamidate1,2, Kazuhisa Goto2 (1.Graduate School of Science, Tohoku University, 2.Department of Earth and Planetary Science, The University of Tokyo)


Keywords:Coastal Boulder Deposits, Storm Deposit, Natural Hazards, Tropical Cyclone, Tsunami

What is the maximum size of a coastal hazards such as tsunami and storm wave that has ever occurred? This is one of the most important information for coastal disaster prevention, but it is not easy to answer to this question. Depositional pattern of sandy sediments, which are the main target of researches on tsunami and storm deposits, varies greatly depending not only on the complexity of the transport process but also on the source conditions. Therefore, it is difficult to estimate the scale of the event simply from information such as the thickness of the sediments. On the other hand, coastal boulder deposits weighing from several tons to more than several hundred tons are useful as proxies to record the size of past extreme wave events because large wave forces are required to transport them and their motions can be described by relatively simple dynamic equations. As an example, we have conduct numerical computation constrained by the distribution of storm boulders on Kudaka Island, Japan, to estimate the maximum sizes of typhoon-associated storm waves and tsunamis since the formation of the fringing reef in the island (Minamidate et al., 2020; 2022). The series of studies is based on the premise that the present-day spatial distribution of the boulder field is formed by the cumulative effect of all waves that have impacted the region in the past, regardless of whether they were tsunamis or typhoon waves, and that no event has disrupt this distribution. Furthermore, once the maximum size of a tsunami or storm wave is estimated, the maximum size of the wave-source events such as earthquake and typhoon that caused the wave event can also be constrained. This opens up the possibility of extracting information on the maximum size of events from coastal boulder deposits in other regions such as the Pacific Ocean, Atlantic Ocean, and Caribbean Sea, where coastal boulders have been reported but have not been used for hazard size estimation.