1707 Hōei earthquake

The 1707 Hōei earthquake happened at 14:00 local time on 28 October 1707. It was one of the largest earthquakes in Japanese history.

Background
The southern coast of Honshu runs in the same direction as the Nankai Trough. This marks the place where the Philippine Sea Plate moves under the Eurasian Plate. Movement on this boundary causes many earthquakes; some of them are megathrust earthquakes. The Nankai megathrust has five parts (A-E) that can break one by one. The different parts have broken either one at a time or all together many times over the last 1,300 years. This kind of quake often happens in pairs with a relatively short time between them. In addition to the two earthquakes in 1854, there were similar earthquakes in 1944 and 1946. Each time, the north-eastern part broke before the southwestern part. In 1707, the earthquakes were either at the same time, or close enough together so that writing from that time do not describe them separately.

Damage
29,000 houses were destroyed and more than 5,000 people were killed. The earthquake caused at least one major landslide in Shizuoka. This landslide was one of the three largest in Japan and is called the Ohya Landslide. It covered an area of 1.8 km2 with an estimated volume of 120 million m3. In the Nara Basin, the earthquake made the soil behave like a liquid.

Characteristics
Earthquake
There were two other very large earthquakes: the 1854 Ansei-Tōkai and Ansei-Nankai earthquakes. The 1707 was stronger than both. Several observations show that the Hōei earthquake was bigger. At Cape Muroto, Kōchi, a cliff was raised up about 2.3 m in 1707, but just 1.5 m in 1854.  In the Kawachi Plain area, the earthquake was around 6 - 7 on the JMA scale. Also, the amount of damage and height of the water from tsunami showed the strength of the earthquake. There are also records of tsunami at distant locations, such as Nagasaki and Jeju-do, South Korea.

Tsunami
The tsunami that followed the earthquake raised water along the coast. Along the southwestern coast of Kōchi, the average increase in sea level was 7.7 m. In some places it rose up to 10.2 m

Connection to Mount Fuji eruption
Changes in stress caused by large earthquakes may be enough to cause volcanic eruptions, when the magma system of the volcano is close to a critical state. The great earthquake in 1707 may have changed pressure in the magma under Mount Fuji and might have caused the last eruption of Mount Fuji 49 days later.

Related pages
Hōei eruption of Mount Fuji

References

Category:Tsunamis
Category:1707
Category:Earthquakes in Japan
Category:18th century in Japan
Category:1700s in Asia