(3)The Yaeyama Earthquake Tsunami (April 24, 1771, M 7.4)

This earthquake is thought to have occurred south of Ishigakijima Island. The seismic ground motion was slight, and a seismic intensity of 4 in JMA scale is estimated on the island. The earthquake was accompanied by a large tsunami estimated at slightly less than 30 m high, which devastated the Yaeyama Islands and the Miyako Islands. The tsunami caused extensive damage, and is called the Yaeyama Earthquake Tsunami. This tsunami is said to have begun with an unusually low tide. The earthquake that caused this tsunami is theorized to have been a large landslide on the sea floor near the Nansei Islands Trench, or to have been a low-frequency earthquake. Accounts differ regarding the extent of damage, but 9,400 people drowned in the Yaeyama Islands and 2,463 drowned in the Miyako Islands. Houses were completely collapsed and some were washed away by the tsunami. About 2,200 houses were collapsed in the Yaeyama Islands, and at least 800 were completely collapsed in the Miyako Islands. Some villages on Ishigakijima Island were completely destroyed. Since there were no reports of damage other than on the Yaeyama Islands and the Miyako Islands, this tsunami probably had strong directivity.