29 Avril 2017
April 28, 2017
By TAKAHIRO TAKENOUCHI/ Staff Writer
Southern Pacific coastal regions are at the greatest risk of earthquakes strong enough to topple buildings over the next 30 years, although almost every area of Japan is in danger, a report showed.
The grim but familiar warning was seen in the National Seismic Hazard Maps for 2017 released by the Headquarters for Earthquake Research Promotion on April 27.
Some city centers in the Pacific coastal areas of the Kanto, Tokai, Kinki and Shikoku regions have probabilities exceeding 80 percent for quakes with an intensity of lower 6 or higher on the Japanese seismic scale of 7 in the next three decades, according to the headquarters.
Naoshi Hirata, chair of the Earthquake Research Committee within the headquarters, said people living outside those high-risk zones should also be wary.
“Please don’t think your area is safe,” said Hirata, a professor of seismology at the University of Tokyo. “Instead, consider every part of Japan to be highly likely to have intense earthquakes.”
The probability maps were based on the locations of active fault lines, previous seismic activity and predictions, and other topographic factors.
The maps are colored according to probabilities as of Jan. 1. Rates between 0.1 percent and 3 percent are classified as “fairly high,” while those at 3 percent and higher are “high.”
Compared with the 2016 data released in June, the sharpest rise in probability for an intensity-6 quake was around the city of Sanyo-Onoda in Yamaguchi Prefecture. It increased by 3.6 percentage points to 17.1 percent.
Ibara in Okayama Prefecture had the largest drop, down 0.65 percentage point to 9.56 percent.
These changes reflect new information obtained from a re-evaluation of active faults in the Chugoku region in July.
The likelihood of a disastrous subduction-zone temblor, such as the long-expected Nankai trough earthquake, increased slightly along the Pacific coast.
By location of city government offices, Chiba has the highest probability among major cities, at 85 percent, followed by Yokohama and Mito at 81 percent each, Kochi at 74 percent, Tokushima at 72 percent, and Shizuoka at 69 percent.
At the site of the Kumamoto city government office, the probability remained at 7.6 percent from last year. Some parts of the Futagawa and Hinagu fault zones that triggered the deadly series of earthquakes in Kumamoto Prefecture in 2016 are still likely to cause strong aftershocks in the area.
The seismic hazard maps can be viewed at the Japan Seismic Hazard Information Station’s website: (http://www.j-shis.bosai.go.jp/map/).