The 1854 Tōkai earthquake was the first of the Ansei great earthquakes (1854–1855). It occurred at about 09:00 local time on 23 December 1854. It had a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 8.4 and caused a damaging

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, ...

. More than 10,000 buildings were destroyed and there were at least 2,000 casualties. It was the first of the three Ansei great earthquakes; the

1854 Ansei-Nankai earthquake The 1854 Nankai earthquake occurred at about 16:00 local time on 24 December. It had a magnitude of 8.4 and caused a damaging tsunami. More than 30,000 buildings were destroyed and there were at least 3,000 casualties. It was the second of the ...

of similar size hit southern

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 ...

the following day.

Background

The southern coast of Honshu 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 1300 years. Megathrust earthquakes on this structure tend to occur in pairs, with a relatively short time gap between them. In addition to the two events in 1854, there were similar earthquakes in 1944 and 1946. In each case the northeastern segment ruptured before the southwestern segment.

Damage

Diana Wreckage Illustrated London News 1856

Much of central Japan experienced seismic intensities of 5 (on the JMA scale). Damage from this earthquake was particularly severe in the coastal areas of

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 ...

from

Numazu is a city located in eastern Shizuoka Prefecture, Japan. , the city had an estimated population of 189,486 in 91,986 households, and a population density of 1,014 persons per km2. The total area of the city is . Geography Numazu is at the n ...

Tenryū River The is a river in central Honshū, Japan. With a length of , it is Japan's ninth longest river. Its source is Lake Suwa in the Kiso Mountains near Okaya in Nagano Prefecture. It then flows through Aichi Prefecture and western Shizuoka Prefec ...

, with many houses being damaged or destroyed. On the east side of the

Izu Peninsula The is a mountainous peninsula with a deeply indented coastline to the west of Tokyo on the Pacific Ocean, Pacific coast of the island of Honshu, Japan, the largest of the four main islands of Japan. Formerly known as Izu Province, Izu peninsu ...

, Shimoda was hit by the tsunami one hour after the earthquake. A series of nine waves struck the city, destroying 840 houses and claiming 122 lives. '' Diana'', the flagship of the visiting Russian admiral, Yevfimy Putyatin, in Japan to negotiate what would become the

Treaty of Shimoda The Treaty of Shimoda (下田条約, ''Shimoda Jouyaku'') (formally Treaty of Commerce and Navigation between Japan and Russia 日露和親条約, ''Nichi-Ro Washin Jouyaku'') of February 7, 1855, was the first treaty between the Russian Empire, a ...

, was spun round 42 times on its moorings and was so badly damaged that it sank in a later storm. At

Suruga Bay Suruga Bay (駿河湾, ''Suruga-wan'') is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of a straight line from Omaezaki Point to Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honsh� ...

, on the west side of the Izu Peninsula, the village of Iruma was destroyed and a 10 m high sand dome was deposited, on which the village was later reconstructed.

Characteristics

Earthquake

The rupture area, magnitude and epicenter have been estimated from seismic intensity measurements, information about tsunami arrival times and evidence of co-seismic uplift/subsidence.

Tsunami

In most of the affected areas, run-up heights were in the range of 4–6 m. However, at Iruma, run-up heights of 13.2 and 16.5 m have been measured, much higher than most of the surrounding area. This and the deposition of the unusual sand dome, with an estimated volume of 700,000 m³, is interpreted to have been caused by the effects of resonance in the V-shaped Suruga bay.

References