Magnitude of quake predictions upgraded

December 23, 2012

Probability of major quake in Kanto rises sharply

The Yomiuri Shimbun

http://www.yomiuri.co.jp/dy/national/T121222003036.htm

The government has upgraded the probability of a powerful earthquake--lower 6 on the Japanese seismic intensity scale of 7, or stronger--to hit cities in the Kanto region within 30 years, with Mito at 62 percent and Chiba at 75 percent.

The Earthquake Research Committee of the government's Headquarters for Earthquake Research Promotion released an earthquake probability map for the first time in two years.

Taking into consideration the effect of the Great East Japan Earthquake, the committee upgraded the magnitude of earthquakes predicted in waters off the quake-hit regions, compared with the 2010 map.

The committee predicted a quake with a maximum magnitude of 8 could occur off Ibaraki Prefecture or the Boso Peninsula--where plate boundary deformations associated with earthquakes remain. The probability of being hit by large quakes grew dramatically, mainly in the coastal areas of the Kanto region, at 62.3 percent in Mito and 75.7 percent in Chiba.

The probability is also high along the Nankai Trough--which stretches from off Shizuoka Prefecture to the Shikoku and Kyushu regions--where magnitude-8 quakes, such as the Tonankai and Nankai earthquakes, have repeatedly occurred. The map indicated Shizuoka had an 89.7 percent possibility and Tsu, 87.4 percent.

The map shows the probability of the country's future earthquakes with an intensity of lower 6 or stronger in the next 30 years beginning Jan. 1 next year.

The map has been produced since 2005, excluding 2011. The committee, which is currently reviewing measures to predict quakes following last year's Great East Japan Earthquake, released the provisional version Friday.

As regions with a low probability of quakes have been hit by major quakes, the committee is working to improve the accuracy of the map.

The committee said it plans to release a revised map based on new measurements as early as next year.