Japan Atomic Power Co. overlooked for seven years data from its sonic survey of 2005 finding that a fault running under its Tsuruga nuclear power plant in Fukui Prefecture could trigger an earthquake more serious than anticipated, a government-affiliated researcher alleged Wednesday.
The data's importance was confirmed through recent re-examination by a team of researchers at the National Institute of Advanced Industrial Science and Technology.
Earlier in March, Yuichi Sugiyama, leader of the team, said the Urazoko fault under the plant is at least 35 km long and could trigger a magnitude 7.4 quake. Earlier predictions had estimated the fault could produce a temblor releasing less than half that amount of energy.
The research team estimated the length of the Urazoko fault by combining other faults connected to it, and the magnitude based on the assumption that the fault would cause a total displacement of more than 3 meters if it becomes active.
The government's Earthquake Research Committee and Japan Atomic Power earlier estimated that the Urazoko fault, including other faults connected to it, is 25 km long.
Japan Atomic Energy has failed to provide the data for studies undertaken by an expert panel launched in 2008 by the Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry.