The 684 Hakuho earthquake took place in Japan in 684, and is described in the history book ''

Nihon Shoki The or , sometimes translated as ''The Chronicles of Japan'', is the second-oldest book of classical Japanese history. It is more elaborate and detailed than the , the oldest, and has proven to be an important tool for historians and archaeol ...

'' from the 8th century. The earthquake took place on 26 November 684 (

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

), in the 13th year of the reign of

Emperor Tenmu was the 40th Emperor of Japan,Imperial Household Agency (''Kunaichō'') 天武天皇 (40) retrieved 2013-8-22. according to the traditional order of succession. Ponsonby-Fane, Richard. (1959). ''The Imperial House of Japan'', p. 53. He ascended ...

( Tenmu period). It caused the under-sea inundation of approximately of rice fields.

Tectonic setting

A number of great interplate earthquakes have occurred along the Suruga Trough and

Nankai Trough The is a submarine trough located south of the Nankaidō region of Japan's island of Honshu, extending approximately offshore. The underlying fault, the ''Nankai megathrust,'' is the source of the devastating Nankai megathrust earthquakes, ...

, off the southwestern coasts of Japan. These earthquakes are associated with the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of 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 of ...

. These recurring earthquakes take place at intervals of one or two centuries. These earthquakes take place in pairs, with an example of Tōkai earthquakes taking place in eastern Japan, and an example of Nankai earthquakes taking place in western Japan. The Hakuho earthquake is the oldest recorded Nankai earthquake.

Earthquake

The earthquake was associated with strong ground motion, and damaged a broad area. It affected the

capital city A capital city, or just capital, is the municipality holding primary status in a country, state (polity), state, province, department (administrative division), department, or other administrative division, subnational division, usually as its ...

of Asuka, and caused a

tsunami A tsunami ( ; from , ) 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 underwater explosions (including detonations, ...

. There was

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...

in the

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

of the Kōchi Prefecture. The welling of water was disrupted in the

hot spring A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...

s of the island of

Shikoku is the smallest of the List of islands of Japan#Main islands, four main islands of Japan. It is long and between at its widest. It has a population of 3.8 million, the least populated of Japan's four main islands. It is south of Honshu ...

, and the springs of the Kii Peninsula in the island of

Honshu , historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...

. In this earthquake, the sea reportedly "swallowed up" 500,000 shiro of cultivated land in

Tosa Province was a province of Japan in the area of southern Shikoku. Nussbaum, Louis-Frédéric. (2005). "''Tosa''" in . Tosa bordered on Awa to the northeast, and Iyo to the northwest. Its abbreviated form name was . In terms of the Gokishichidō syst ...

. The Japanese unit shiro is equivalent to 15.13

acre The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...

s. The governor of this province reported the sinking of many ships by a "high-rising great tide" which accompanied the earthquake. He was describing a

, using the then-used term "oshio". Regarding the flooding, the ''Nihon Shoki'' reports that the local people had never experienced a disaster of this type. A corresponding Tōkai earthquake may have occurred in 684, but is not clearly recorded in primary sources. The next known Nankai earthquake took place in 887.

References

Notes

Sources

* * * {{Japan-hist-stub Hakuhō earthquake Hakuhō earthquake Hakuhō earthquake