News reports continue to shed light on the damage inflicted on Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear power plant by the magnitude-6.8 earthquake that struck Niigata and Nagano prefectures July 16. Most worrying is a report that the tremors were more than double the quake-design benchmark of the world's largest nuclear-power-generation complex.
What happened at the Kashiwazaki-Kariwa plant has raised doubts about the safety of the nation's 55 power-generation reactors. Power companies must review the capability of their nuclear power plants to withstand seismic tremors under the tougher design guidelines revised by the Nuclear Safety Commission in September. In addition, the government and the commission should not hesitate to further revise plant-design guidelines after taking into consideration the damage wrought by the July 16 earthquake.
The focus of the earthquake was about 9 km northeast of the nuclear power plant and about 17 km below the Sea of Japan. Worryingly, the Meteorological Agency analyzed the distribution of aftershocks and ascertained the possibility that the fault that caused the main quake runs directly beneath the nuclear plant at a depth of 20 km. The approximately 15-km-wide aftershock zone extends some 30 km southeast of the quake's focus. The nuclear power plant lies within this zone.