Geomorphological study on large tsunamis in coral sea region.

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This projext aims to clarify nateure of historical and prehistorical large tunamis. Southern islands of the Ryukyus are selected for the study area of this study, because tsunami deposits composed of subrecent reef coral fossils enable us to restore timing, location and magnitude of tsunamis by analyses of radiocarbon ages of the fossils and their distribution on land.Field study has been carried out mainly in the Ishigaki and Miyako Islands which have been attacked by destructive tsunami in 1771. Radiocarbon ages of tsunami deposits revealed that the islands have been repeatedly attacked by large tumanis of 1771 scale or bigger than that. It is deduced from the ages and distribution of tsunami deposits that tsunamis prior to 1771 took place about 500,1,1000,1,900,2,400 and 4,000 yr. B.P..