Earthquake and volcano

The highest mountain is Mt. Fuji. You can see the Suruga Bay on the left side and the Akashi Mountains in the background.
The highest mountain of the Amagi Mountains is called Manzaburo-dake(1406m).
Plate structure surrounding Japan
Source:National Research Institute for Earth Science and Disaster Prevention
Omuro-yama (580m) is a typical example of scoria-producing volcano in a suburb of Ito. This picture was taken in the cherry blossom season.

In winter we have an especially good view of Mt. Fuji (3776m) from my house on the Amagi Mountains, because the winter weather is super fine on the Pacific Ocean side of the Japanese archipelago. The strong north-west wind, which comes down from Siberia, absorbs moisture from the Sea of Japan and drops heavy snow on the north-western side of the mountains. Then the dried out wind blows on over the Pacific coast.

Mt. Fuji is a symbol of good luck and if you can dream of Mt. Fuji in your first dream of the New Year, you will have a happy and lucky year, according to the old saying in Japan. However, this peaceful photo of Mt. Fuji also shows the very place where a catastrophic natural hazard might occur in the near future.

While Mt. Fuji lies on the North-American Tectonic Plate, the Izu Peninsula, from where I took this photo, belongs to the Filipino Plate. The Filipino Plate is about 30 to 40 km thick. It moves towards the North-American plate at approximately 4cm per year and is thrust underneath the latter. The border of these two plates forms here the Suruga Trough - the northern most section of the Nankai Trough - which starts from the coast on this picture. This section of the Nankai Trough caused huge earthquakes every 150 years in the past and the next one is approaching, say experts.

Japan is unfortunately notorious for its frequent and damaging earthquakes. "Earthquake, thunder, fire and father" were four terrific things in the feudal Japan. Now, "father" is no longer fearsome but only a poor creature, while "earthquake" is as dangerous as before. Japan belongs to the countries rich in earthquakes, because it lies along the borders of at least four different tectonic plates: Pacific Plate, Filipino Plate, North American Plate and Eurasian Plate.

The Izu Peninsula, together with its adjacent areas in the north, the Hakone and Tanzawa Mountains, has a different origin from the rest of the Japanese islands. The Izu Peninsula was originally an island on the Filipino Plate. Izu collided against Honshu Island about a million years ago, but could not move underneath the continental plate, because it was too big and became instead part of Honshu. On both sides of the Izu Peninsula the Filipino Plate continues to move underneath two continental plates and causes heavy earthquakes both along the Sagami Trough - Kanto earthquakes - as well as the Suruga trough - Tokai earthquakes.

While the Filipino Plate slides below the North American Plate, the Pacific Plate moves further below and underneath the Filipino Plate. At the west of the Suruga Trough, the Filipino Plate is thrust underneath the Eurasian Plate. The geographical situation is thus very complex around the Izu Peninsula. The latest Tokai Earthquake occurred along the Suruga Trough in 1854. Since then 154 years have already passed and the next mega-earthquake can occur at any time.

The Sagami Trough caused many earthquakes as well, including the Great Kanto Earthquake in 1923. While the danger of a Tokai earthquake is imminent, the interval of Kanto earthquakes is thought to be 200 years and it is believed that we are now in a relatively quiet period so a mega earthquake will not occur in the immediate future. However, earthquakes with smaller magnitude but shallow epicenter - therefore they can cause severe damage - can occur in the near future.

Apart from these earthquakes caused by plate tectonic reasons, there occasionally occur so-called earthquake swarms offshore of Ito. These are coupled with movements of magma and volcanic eruptions. The latest earthquake swarm occurred in April 2006. The one before was accompanied by the eruption of a submarine volcano just in front of Ito city on 9th July 1989. This was the first ever eruption in the history of Izu and the volcano was named as "Teishi kaikyu".


"Teishi kaikyu" erupted in front of the citizens of Ito.
Source: Japan Meteorological Agency

It was feared that the eruption might frighten tourists. But, two days after the eruption a beautiful pop singer attempted suicide and grabbing the exclusive interest of media so the adverse effect on tourism was kept to the minimum. The celebrity scandal had a much greater magnitude than the modest eruption of a submarine volcano.

 2008.12.30