technical matters as well as the aspect of management."

Right after the temblor hit, water started leaking from the spent fuel pool at the No. 6 reactor and a transformer fire started at the No. 3 reactor that burned for about two hours. Tepco eventually reported 63 problems at the complex, including low-level radiation leaks.

News reports blamed the slowness in extinguishing the fire on swamped telephone lines and weak safety guidelines from the central government. It was also reported that the facility lacked the proper equipment to fight a blaze of this type.

Assurances from utilities and government agencies that reactors can be made quake-proof face mounting skepticism, because Tepco and other utilities are no strangers to the act of concealing shortcomings.

In March, 12 utilities owned up to 97 incidents of nuclear plant-related malpractice. The most serious involved Tepco and Hokuriku Electric Power Co., which had failed to report reactor control rod accidents leading to uncontrolled criticality accidents. Skeptics wonder how well Japan's 55 nuclear plants can perform in the widely expected eventuality of the Big One.

In 2005, the Cabinet office's Central Disaster Prevention Council calculated a 30 percent chance of a massive earthquake in Tokyo within the next decade, and a 70 percent chance within 30 years.

Records show that over the past century, Japan has experienced an average of one magnitude-7 or greater quake yearly.

An earlier version of this story had erroneously cited the magnitude of potential future quake as magnitude 6.8. In fact the figure should have been magnitude 8. We regret the error.