1854 Ansei-Tōkai earthquake
Encyclopedia
The 1854 Ansei-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
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....

 of 8.4 and caused a damaging tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

. More than 10,000 buildings were completely destroyed and there were at least 2,000 casualties.

It was the first of the three Ansei Great Earthquakes; the 1854 Ansei-Nankai earthquake
1854 Ansei-Nankai earthquake
The 1854 Ansei-Nankai earthquake occurred at about 16:00 local time on 24 December, 1854. It had a magnitude of 8.4 and caused a damaging tsunami...

 of similar size hit southern Honshu
Honshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...

 the following day.

Background

The southern coast of Honshu runs parallel to the Nankai Trough
Nankai Trough
The Nankai Trough is a submarine trough located south of Japan's island of Honshū, extending approximately 900 km offshore. In plate tectonics, the Nankai Trough marks a subduction zone that is caused by subduction of the Philippine Sea Plate beneath Japan, part of the Eurasian plate...

, which marks the subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 of the Philippine Sea Plate beneath the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

. Movement on this convergent plate boundary leads to many earthquakes, some of them of megathrust type
Megathrust earthquake
Megathrust earthquakes occur at subduction zones at destructive plate boundaries , where one tectonic plate is forced under another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes ...

. 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

Much of central Japan experienced seismic intensities of 5 (on the JMA scale
Japan Meteorological Agency seismic intensity scale
The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan and Taiwan to measure the intensity of earthquakes. It is measured in units of...

). Damage from this earthquake was particularly severe in the coastal areas of Shizuoka Prefecture
Shizuoka Prefecture
is a prefecture of Japan located in the Chūbu region on Honshu island. The capital is the city of Shizuoka.- History :Shizuoka prefecture was formed from the former Tōtōmi, Suruga and Izu provinces.The area was the home of the first Tokugawa Shogun...

 from Numazu
Numazu, Shizuoka
is a city located in eastern Shizuoka Prefecture, Japan. As of 2009, the city has an estimated population of 205,636 and a population density of 1,100 persons per km². The total area was 187.11 km².- Geography:...

 to Tenryu River
Tenryu River
The is a river arising from Lake Suwa in Okaya, Nagano Prefecture, grazing Aichi Prefecture and flowing through western Shizuoka Prefecture in central Honshū, Japan. With a length of , it is Japan's ninth longest river.-Geography:...

, with many houses being damaged or destroyed.

On the east side of the Izu Peninsula
Izu Peninsula
The is a large mountainous peninsula with deeply indented coasts to the west of Tokyo on the Pacific coast of the island of Honshū, Japan. Formerly the eponymous Izu Province, Izu peninsula is now a part of Shizuoka Prefecture...

, Shimoda
Shimoda, Shizuoka
is a city and port in Shizuoka, Japan.As of 2010, the city had an estimated population of 25,054 and a population density of 242 persons per square kilometer...

 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 a visiting Russian admiral, Putyatin
Yevfimy Putyatin
Yevfimy Vasilyevich Putyatin was a Russian admiral noted for his diplomatic missions to Japan and China which resulted in the signing of the Treaty of Shimoda in 1855.-Early life:...

, 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
Suruga Bay is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of an imaginary line joining Omaezaki Point and Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honshū to the southwest and west and the Izu Peninsula to the east.-Geology:Suruga...

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

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.
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 Iruma bay.
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