The 1605 Keichō earthquake () occurred at about 20:00 local time on 3 February. It had an estimated magnitude of 7.9 on the

surface-wave magnitude The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This mag ...

scale and triggered a devastating

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, ...

that resulted in thousands of deaths in the Nankai and Tōkai regions of

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. It is uncertain whether there were two separate earthquakes separated by a short time interval or a single event. It is referred to as a

tsunami earthquake In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater Seismic magnitude scales, magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanam ...

, in that the size of the tsunami greatly exceeds that expected from the magnitude of the earthquake.

Background

The southern coast 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 ...

runs parallel to the

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, ...

, which marks 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 ...

beneath the Eurasian plate. Movement on this

convergent plate boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

leads to many earthquakes, some of them of megathrust type. The Nankai megathrust has five distinct segments (A-E) that can rupture independently, the segments have ruptured either singly or together repeatedly over the last 1,300 years. Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them although in the

1707 Hōei earthquake The struck south-central Japan at around 13:45 local time on 28 October. It was the largest earthquake in Japanese history until it was surpassed by the 2011 Tōhoku earthquake. It caused moderate-to-severe damage throughout southwestern Hons ...

all segments are thought to have ruptured at once. In 1854 there were two earthquakes a day apart and there were similar earthquakes in 1944 and 1946. In each case, the northeastern segment ruptured before the southwestern segment. In the 1605 event, there is evidence for two distinct earthquakes, but they are not distinguished by all historical sources and some seismologists suggest that only the Nankai segment of the megathrust ruptured.

Earthquake

There are very few reports of shaking associated with this earthquake, with most historical records only mentioning the tsunami. This has led seismologists to interpret this as a 'tsunami earthquake', probably involving a slow rupture velocity causing little observed shaking while generating a large tsunami.

Tsunami

The records of this tsunami are quite sparse but the maximum wave heights are larger than those recorded for either the 1707 Hōei or 1854 Ansei Nankai tsunamis in areas on the south coast 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 ...

where they can be compared. The regional extent of this tsunami is supported by the discovery of

tsunami deposit A tsunami deposit (the term tsunamiite is also sometimes used) is a sedimentary unit deposited as the result of a tsunami. Such deposits may be left onshore during the inundation phase or offshore during the 'backwash' phase. Such deposits are use ...

s on the northeastern part of the

Kii Peninsula The is the largest peninsula on the island of Honshū in Japan and is located within the Kansai region. It is named after the ancient Kii Province. The peninsula has long been a sacred place in Buddhism, Shinto, and Shugendo, and many people wou ...

and at

Lake Hamana is a brackish lagoon in Shizuoka Prefecture, Japan. Formerly a true lake, it is now connected to the Pacific Ocean by a channel. As an internal body of water, it is considered Japan's tenth-largest lake (by area). It spans the boundaries of th ...

correlated to this event. Victims of the tsunami were also reported from

Kyushu is the third-largest island of Japan's Japanese archipelago, four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa Island, Okinawa and the other Ryukyu Islands, Ryukyu (''Nansei'') Ryukyu Islands, Islands ...

Damage

There is no reported damage associated with the earthquake itself. At least 700 houses were washed away at

Hiro Hiro may refer to: People * Hiro (given name), includes lists of people with the given name * Hiro (photographer) (1930–2021), Japanese-born American photographer * Hiro (singer) (born 1991), French singer * Hiroko Shimabukuro (born 1984), Japa ...

in present-day

Wakayama prefecture is a prefecture of Japan located in the Kansai region of Honshu. Wakayama Prefecture has a population of 876,030 () and a geographic area of . Wakayama Prefecture borders Osaka Prefecture to the north, and Mie Prefecture and Nara Prefecture to ...

and 80 at

Arai __NOTOC__ Arai may refer to: Places * Arain, Armenia * Arai, Niigata, Japan * Arai, Shizuoka, Japan People *Arai (surname) Companies * Arai Helmet (アライ), a Japanese motorcycle helmet manufacturer * ARAI (Automotive Research Association of ...

in what is now

Shizuoka prefecture is a Prefectures of Japan, prefecture of Japan located in the Chūbu region of Honshu. Shizuoka Prefecture has a population of 3,555,818 and has a geographic area of . Shizuoka Prefecture borders Kanagawa Prefecture to the east, Yamanashi Pref ...

Castles A castle is a type of fortified structure built during the Middle Ages predominantly by the nobility or royalty and by military orders. Scholars usually consider a ''castle'' to be the private fortified residence of a lord or noble. This i ...

were reported destroyed or damaged at Tahara on the

Atsumi Peninsula The is a peninsula in southern Aichi Prefecture, central Honshū, Japan. Geography It has an approximate length of east-west, separating Mikawa Bay (to the north) from the Pacific Ocean to the south, with Ise Bay lying to its west. It fa ...

; the main keep of

Kakegawa Castle is a ''hirayama''-style Japanese castle. It was the seat of various ''fudai daimyō'' clans who ruled over Kakegawa Domain, Tōtōmi Province, in what is now central Kakegawa, Shizuoka Prefecture, Japan. Background Kakegawa Castle is located a ...

was also destroyed. The total number of casualties is uncertain as records are incomplete and contradictory, but estimates are in the order of thousands.

References

{{DEFAULTSORT:1605 Keicho Nankaido earthquake Tsunamis in Japan 1605 in Japan 1605 in Asia 1600s earthquakes 1605 disasters Tsunami earthquakes Earthquakes of the Edo period

Background

Earthquake

Tsunami

Damage

See also

References