Closer fault study raises Kyushu quake threat

by Kazuaki Nagata

Staff Writer

The possibility of Kyushu being hit by a magnitude 6.8 or stronger temblor within 30 years is between 30 to 42 percent under newly revised criteria, a recent report by the government’s earthquake research panel shows.

The Headquarters for Earthquake Research Promotion under the Education, Culture, Sports, Science and Technology Ministry released the report Friday. It outlined quake scenarios based on major active faults in Kyushu under the stricter criteria.

When looking at specific areas, the report said northern Kyushu faces a 7 to 13 percent chance of being hit by a magnitude 6.8 or stronger quake in 30 years’ time, whereas central Kyushu faces an 18 to 27 percent chance and southern Kyushu a 7 to 18 percent possibility.

In 2010, the government changed the criteria for calculating earthquake probability based on active faults after a deadly 2007 magnitude 6.8 temblor hit Niigata Prefecture.

The old criteria only looked into active faults longer than 20 km, which could cause a magnitude 7.0 earthquake, but the new guideline requires that the government check those longer than 15 km that could cause a magnitude 6.8 quake.

The new criteria also include active seabed faults, while the old criteria only considered those on land. The criteria were revised because even under 7.0 can cause serious damage, as was the case when the magnitude 6.8 quake hit the Niigata area.

This is the first time the research panel released a report based on the new criteria.

The report also looked at the active Nishiyama fault zone that runs from central Fukuoka Prefecture to about 40 km offshore, noting it has the potential to cause a magnitude 7.9 to 8.2 temblor.

There are about 28 active faults that might cause a 6.8 quake, the report showed. An earlier estimate pointed to only eight active faults in Kyushu that posed a 7.0-plus quake threat.