Holocene sea-level change,crustal movement, and coral reef development in the Ryukyu Islands based on C-14 calendar ages

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Large islands in the Ryukyus, such as Okinawa and Ishigaki, whose formative period of coral reefs goes back to 6800-7000 cal BP, have been affected by hydro-isostasy and locally crustal movement, while a small island of Zamami and a large island of Iriomote with younger coral reefs in 4000-5000 cal BP are due to without hydro-isostasy or without locally crustal movement.Holocene coral reefs in Okinawa developed from about 8500 to 6300 cal BP to have formed the first stage of the coral reefs in the tectonically active areas of the southern coast, while after 6300 cal BP the second and the third ones appeared in the inactive areas of the central and northern coasts.Large tsunamis in the southern Ryukyus generated in 1771 (Meiwa Tsunami), and about 500, 1000, 2000, 2400 cal BP probably due submarine thrust and landslide off Ishigaki Island. It is suggested that the Holocene tilting from southeast to northwest in Ishigaki on land is due to submarine thrust movements off Ishigaki. The highest run-up height of the Meiwa Tsunami is assumed to attain about 30-30 m above sea level in Ishigaki Island. Concentration of the tsunami boulders to the northern coasts in Tarama and Kuro Islands with circular coasts is presumed due to diffraction of tsunami waves. Large waves in about 3400 cal BP attacked the eastern coasts of Amami and Okinawa. Reef blocks in the southern Okinawa were moved by large typhoon waves in 1832 and in 1951.