Japan’s Earthquake Research Committee has released the 2020 seismic hazard map for the country, which shows the probabilities of an earthquake measuring at least a lower six, for geographic points throughout Japan. A “lower six” is the third-highest level on the Japanese seismic intensity scale of seven.
The report shows that Mito City, in Ibaraki prefecture, had the highest probability (81%) of a strong quake occurring sometime in the next 30 years, followed by Tokushima City, in Tokushima prefecture, and Kochi City, in Kochi prefecture, both at 75%. Overall, the committee concluded that the probability of a power earthquake happening over the next 30 years remains high on the Pacific coast of Japan.
The 2020 seismic forecasts are based on an underlying assumption of the high probability of two major offshore earthquakes occurring sometime in the next 30 years. The first is a quake with a magnitude eight that is forecast to occur with 80% probability along the Chishima Trench off the coast of Nemuro, Hokkaido. The second is a quake with a magnitude of eight to nine that is forecast to occur with a probability of 70% to 80% along the Nankai Trough off of the central to southwestern coast of the main island of Honshu and the smaller island of Shikoku.
The updated 2020 map shows at least a 26% probability of a major quake occurring in the eastern part of Hokkaido, as well as the Pacific side of the Kanto region, Tokai region and Kinki and Shikoku regions.
Japanse Shindo Scale
The Japan Meteorological Agency uses a seismic scale called the Shindo scale that measures the degree of shaking in the event of an earthquake. This scale ranges from 0 to 7 and measures the size or energy of the temblor at its source.
|Seismic intensity||Human perception and reaction||Indoor situation||Outdoor situation|
|0||Imperceptible to people, but recorded by seismometers.||–||–|
|1||Felt slightly by some people keeping quiet in buildings.||–||–|
|2||Felt by many people keeping quiet in buildings.
Some people may be awoken.
|Hanging objects such as lamps swing slightly.||–|
|3||Felt by most people in buildings.
Felt by some people walking. Many people are awoken.
|Dishes in cupboards may rattle.||
Electric wires swing slightly.
|4||Most people are startled.
Felt by most people walking. Most people are awoken.
|Hanging objects such as lamps swing significantly,
and dishes in cupboards rattle.
Unstable ornaments may fall.
Electric wires swing significantly. Those driving vehicles may notice the tremor.
|5 Lower||Many people are frightened and feel the need to hold onto something stable.||Hanging objects such as lamps swing violently.
Dishes in cupboards and items on bookshelves may fall.
Many unstable ornaments fall.
Unsecured furniture may move,
and unstable furniture may topple over.
In some cases, windows may break and fall. People notice electricity poles moving. Roads may sustain damage.
|5 Upper||Many people find it hard to move.
Walking is difficult without holding onto something stable.
|Dishes in cupboards and items on bookshelves are more likely to fall.
TVs may fall from their stands, and unsecured furniture may topple over.
Windows may break and fall, unreinforced concrete-block walls may collapse, poorly installed vending machines may topple over, automobiles may stop due to the difficulty of continued movement.
|6 Lower||It is difficult to remain standing.||Many unsecured furniture moves and may topple over. Doors may become wedged shut.||
Wall tiles and windows may sustain damage and fall.
It is impossible to remain standing or move without crawling.
People may be thrown through the air.
|Most unsecured furniture moves, and is more likely to topple over.||
Wall tiles and windows are more likely to break and fall. Most unreinforced concrete-block walls collapse.
|7||Most unsecured furniture moves and topples over, or may even be thrown through the air.||
Wall tiles and windows are even more likely to break and fall. Reinforced concrete-block walls may collapse.
2020 Seismic Hazard Map
The national seismic hazard map has been calculated since 2018, and the forecast probabilities are calculated by evaluating the record of earthquakes that have occurred in the past, as well as the characteristics and ease of shaking of the terrain at specific locations throughout the country.
The 2020 edition is based on detailed survey results of the ground in the Kanto region and detailed topographical information in each region, in addition to records of aftershocks from the Great East Japan Earthquake of 2011. As a result of this new data, the probability of an earthquake in the Kanto region as a whole has been downgraded, compared to 2018, while the probability of a temblor off the coast of Tohoku is now seen to be higher.
You can access the English version of the 2020 seismic hazard map for Japan to zoom in on specific locations in Japan.
|Probability of an earthquake with an intensity of a “lower six” or above on the Japanese Shindo scale occurring in the next 30 years|
|City||Prefecture||Probability %||Increase or Decrease
v. 2018 Assessment in %
Source: 2020 Japan Seismic Hazard Map
Lead photo: iStock 1198160706, March 20, 2011 in Fukushima Soma area the aftermath of the M9 earthquake