The 1771 Great Yaeyama Tsunami (also called 明和の大津波, the Great Tsunami of Meiwa) was caused by the Yaeyama Great Earthquake at about 8 A.M. on April 24, 1771, south-southeast of

Ishigaki Island , also known as ''Ishigakijima'', is a Japanese island south-west of Okinawa Hontō and the second-largest island of the Yaeyama Island group, behind Iriomote Island. It is located approximately south-west of Okinawa Hontō. It is within the ...

, part of the former

Ryūkyū Kingdom The Ryukyu Kingdom, Middle Chinese: , , Classical Chinese: (), Historical English names: ''Lew Chew'', ''Lewchew'', ''Luchu'', and ''Loochoo'', Historical French name: ''Liou-tchou'', Historical Dutch name: ''Lioe-kioe'' was a kingdom in t ...

and now part of present-day

Okinawa is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi). Naha is the capital and largest city ...

, Japan. According to records, 8,439 people were killed on Ishigaki Island and 2,548 on Miyako Island. Shimoji obiiwa1

Earthquake analysis

According to the Japanese government publication ''Rika-Nenpyō'' ( 理科年表) or ''Chronological Scientific Tables'', the epicenter was 40 km south-southeast of

with a magnitude of 7.4. According to the Mamoru Nakamura Laboratory, University of the Ryukyus, the earthquake was due to the activity of the fault east of Ishigaki and it is estimated that the magnitude was 7.5. Further simulation led to the activity of faults in the Ryukyu

oceanic trench Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...

and the magnitude was 8.0. Also, there is a hypothesis that claims the magnitude was 8.5. The depth was . This trench lies between the

Philippine Sea Plate The Philippine Sea Plate or the Philippine Plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part o ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

. The disparity in the amount of recorded shaking (maximum 4 JMA) and the size of the tsunami has led to the interpretation of this event as a

tsunami earthquake In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanamori in 1972. Such events a ...

Damage

Earthquake

It is considered that the earthquake registered an intensity of 4 (on the Japanese scale) in the

Yaeyama Islands The Yaeyama Islands (八重山列島 ''Yaeyama-rettō'', also 八重山諸島 ''Yaeyama-shotō'', Yaeyama: ''Yaima'', Yonaguni: ''Daama'', Okinawan: ''Yeema'', Northern Ryukyuan: ''Yapema'') are an archipelago in the southwest of Okinawa P ...

, and the damage by the earthquake itself was not as serious as the ensuing tsunami.

Tsunami

The dead and missing amounted to 12,000 people, and more than 2,000 houses were destroyed on Ishigaki and

Miyakojima is the largest and the most populous island among the Miyako Islands of Okinawa Prefecture, Japan. Miyako Island is administered as part of the City of Miyakojima, which includes not only Miyako Island, but also five other populated islands. ...

. It has been estimated local agriculture was severely damaged because of sea water invasion and the population decreased to about one third of what it was before the earthquake. On Ishigaki island, the run-up was first estimated around 40 to 80 meters high from historical documents. However, taking into account the rough precision of the measuring instruments at this time and considering geomorphological parameters, the maximal run-up has been re-estimated to ~30m. Following the tsunami, the damage it caused was such that it led to a famine that lasted for 80 years.

Boulders

There are many huge boulders on the coasts of the Yaeyema and Miyako islands that are believed to have been deposited by

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

s. There was a legend that an

islet An islet is a very small, often unnamed island. Most definitions are not precise, but some suggest that an islet has little or no vegetation and cannot support human habitation. It may be made of rock, sand and/or hard coral; may be permanen ...

disappeared, but this has never been verified. This set of rocks are called the ''Ishigaki East Coast Tsunami Rocks''. Among them, Yasura-ufukane, Amatariya–Suuari and Taka-koru sishi have been dragged by the 1771 Meiwa tsunami.

Footnotes