Quantitative Analysis of Tsunami Disasters by The Jogan Earthquake

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Mode of sediment transport by the 869 Jogan earthquake tsunami was estimated by analogy with grain-size composition and facies of the tsunami deposit. In addition, initial hydraulic condition of tsunami-induced currents was sedimentologically evaluated to increase knowledge on behavior of tsunami run-ups. Landward fining of the sand layer that comprises the Jogan tsunami deposit was clearly identified on the basis of the grain-size analysis by the laser-diffraction gram-size analyzer. This is consistent with the results from our hydraulic experiments of sediment transport and deposition of tsunamis. It is clarified that mode of fining of sedimentary layer can be treated as important criteria that reflect the energy dissipation of tsunami run-ups. These criteria may provide physical- geographic condition for theoretical understandings of formation of coastal topography. In addition, they may give us indispensable knowledge on developments of urban and industrial infrastructures of coastal areas.Changes in foraminiferal assemblages after the 2004 Indian Ocean tsunami were clearly demonstrated by the micropaleontological analysis of sediment samples collected from the southwest coast of Thailand. This implies that traces of turbidity currents induced by tsunami backwashes can be preserved in submarine sedimentary environments. Therefore history of tsunami occurrence is possible to uncover based on sediment excavation on the ocean. These results were presented and gained scientific attention in the XXIV General Assembly of IUGG that was held in Perugia, Italy, in July 2007, as an actual example of tsunami disaster and sedimentation.