1854 Ansei-Tōkai earthquake
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| Date | December 23, 1854 |
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| Magnitude | 8.4 ML |
| Epicenter | 34°00′N 137°48′E / 34.0°N 137.8°ECoordinates: 34°00′N 137°48′E / 34.0°N 137.8°E |
| Areas affected | Japan, Tōkai region |
| Tsunami | yes |
| Casualties | >2,000 |
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 of 8.4 and caused a damaging tsunami. 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 of similar size hit southern Honshu the following day.
The southern coast of Honshu runs parallel to the Nankai Trough, which marks the subduction of the Philippine Sea Plate beneath the Eurasian Plate. Movement on this convergent plate boundary 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.
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 from Numazu to Tenryu River, with many houses being damaged or destroyed.
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