The 684 Hakuho earthquake took place in Japan in 684, and is described in the history book '' Nihon Shoki'' from the 8th century. The earthquake took place on 29 November, 684, in 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. Tenmu's re ...

(

Tenmu period The Temmu period is a chronological timeframe during the Asuka period of Japanese history. The Temmu period describes a span of years which were considered to have begun in the 1333rd year of the Yamato dynasty.Murray, David. (1894). , citing Wil ...

). It caused the under-sea inundation of approximately of

rice fields A paddy field is a flooded field of arable land used for growing semiaquatic crops, most notably rice and taro. It originates from the Neolithic rice-farming cultures of the Yangtze River basin in southern China, associated with pre-Aust ...

. A number of great

interplate earthquake An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move past ...

s have occurred along the

Suruga Trough The is a trough that lies off the coast of Suruga Bay in Japan, forming part of the Nankai Trough, the latter being responsible the source of many large earthquakes in Japan's history. Both mark the boundary of the Philippine Sea Plate subductin ...

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, wh ...

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

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

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 The Tōkai earthquakes () are major earthquakes that have occurred regularly with a return period of 100 to 150 years in the Tōkai region of Japan. The Tōkai segment has been struck by earthquakes in 1498, 1605, 1707, 1854, and 1923. Given the hi ...

taking place in eastern Japan, and an example of

Nankai earthquakes The are major megathrust earthquakes that affect the Nankaidō (Southern Sea Circuit) region of Japan, west of the Tōnankai region (Southeastern Sea) and Tōkai region (Eastern Sea), and are caused by ruptures in the Nankai zone of the Nanka ...

taking place in western Japan. The Hakuho earthquake is the oldest recorded Nankai earthquake. The earthquake is associated with strong ground motion, and damaged a broad area. It affected the

capital city A capital city or capital is the municipality holding primary status in a country, state, province, Department (country subdivision), department, or other subnational entity, usually as its seat of the government. A capital is typically a city ...

Asuka Asuka may refer to: People * Asuka (name), a list of people * Asuka (wrestler), professional wrestler * Asuka (wrestler, born 1998), professional wrestler also known as Veny outside of Japan Places In Japan * , an area in Yamato Province (now ...

, and caused a

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 explo ...

. 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 move ...

in the

plain In geography, a plain 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 as plateaus or uplands ...

of the

Kōchi Prefecture is a prefecture of Japan located on the island of Shikoku. Kōchi Prefecture has a population of 757,914 (1 December 2011) and has a geographic area of 7,103 km2 (2,742 sq mi). Kōchi Prefecture borders Ehime Prefecture to the northwest and ...

. The welling of water was disrupted in the

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

s of the island of

Shikoku is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), '' ...

, and the springs of the

Kii Peninsula The is the largest peninsula on the island of Honshū in Japan. It is named after the ancient Kii Province. Overview The area south of the “ Central Tectonic Line” is called , and is home to reef-like coral communities which are amongst ...

in the island of

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island separ ...

. 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 syste ...

. The Japanese unit shiro is equivalent to 15.13

acre The acre is a unit of land area used in the imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imp ...

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

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* * * {{Japan-hist-stub 684 7th century in Japan 7th-century earthquakes