Considering that the Noto Peninsula Earthquake caused damage not only to wooden houses but also to concrete buildings, the Ministry of Land, Infrastructure, Transport and Tourism has developed an ``earthquake area coefficient'' that discounts the seismic strength of buildings according to regional seismic activity. I learned that they are considering revising it, including making it uniform.
According to the Ministry of Land, Infrastructure, Transport and Tourism, for reinforced concrete buildings and wooden buildings of three or more stories, an "earthquake area coefficient" is set for each region from 0.7 to 1.0, depending on past earthquake activity, and the seismic resistance standard by law is 1.0. The strength is discounted as
Wajima City, Suzu City, Noto Town, and Anamizu Town, which were heavily damaged by the Noto Peninsula Earthquake, have a coefficient of 0.9.
In the 2016 Kumamoto Earthquake, tremors with a seismic intensity of 7 were observed in areas with a coefficient of 0.9, and there have been cases of severe shaking in areas with low coefficients in the past, so experts are not sure what the ``earthquake area coefficient'' should be. There is an ongoing debate between them.
In response to the Noto Peninsula Earthquake, the government is considering revising the ``earthquake area coefficient'' with a view to making it uniform throughout the country, according to interviews with people involved.
In the future, a committee set up by the Ministry of Land, Infrastructure, Transport and Tourism consisting of experts in building structure and design will conduct research and analysis on the relationship between damage from the Noto Peninsula earthquake and earthquake area coefficients, and will compile a report around autumn. Based on the results, the government is expected to proceed with full-scale consideration.
What is “earthquake area coefficient”?
The current "earthquake area coefficient" is a coefficient that discounts the force of earthquakes used in seismic design when constructing buildings, based on the idea that the scale and frequency of earthquakes differ depending on the region. It has been established.
It targets reinforced concrete buildings and wooden buildings of three or more stories, which require precise calculations of the strength of buildings called "structural calculations."
Standard wooden houses of two stories or less are not eligible.
The coefficient is set in 0.1 increments from 0.7 to 1.0 based on past earthquake records and the scale of damage.The coefficient is set at 1.0 in Tokyo and Osaka, while it is 0.9 and 0.8 in Kyushu and Hokkaido. It depends.
Suzu City, Wajima City, Noto Town, and Anamizu Town in Ishikawa Prefecture, which were severely damaged by the Noto Peninsula Earthquake in January this year, all have a rating of 0.9.
Furthermore, in the 2016 Kumamoto Earthquake, buildings were damaged one after another in areas with coefficients of 0.9 and 0.8 within Kumamoto Prefecture.
After this earthquake, various opinions arose from experts regarding the appropriateness of the "earthquake area coefficient," but most of the severe damage was caused by small wooden houses that do not use the earthquake area coefficient, and even steel-framed buildings have a coefficient of As no collapse was confirmed due to the impact of
However, due to the continued occurrence of large-scale earthquakes in areas where the force of earthquakes has been discounted using coefficients, such as the Kumamoto Earthquake and the Noto Peninsula Earthquake, consideration has now been given to revising the system.