TEPCO: Active fault found in seabed off nuclear plant (Dec. 7, 2007)

The Yomiuri Shimbun

Tokyo Electric Power Co. on Wednesday said it found a 23-kilometer-long active fault
in the Sea of Japan off the Kashiwazaki-Kariwa nuclear power plant, which was
damaged in the Niigata Prefecture Chuetsu Offshore Earthquake in July.

According to TEPCO, the fault was found in the seabed about 18.5 kilometers from the
shore where the plant is located, and it likely caused the powerful earthquake.
The company reported the discovery at a panel meeting of the Economy, Trade and
Industry Ministry’s Nuclear and Industrial Safety Agency held Wednesday.

TEPCO will continue to examine the active fault near the plant, reviewing the scale of
predicted earthquake.

In 1981, when TEPCO applied for permission to set up the power plant, it only found
part of the active fault. TEPCO reported it was eight kilometers long, concluding it was
a fold fault, which is soil deformation with low activity. The ministry confirmed the
content of the report.

In 2003, adopting a new seismographic observation that the fold
fault is also part of an active fault, TEPCO reviewed its past examination of the area.
Although TEPCO recognized that the fault might be 20 kilometers long, it concluded it
was not necessary to review the scale of seismic activity that the fault could cause.
TEPCO had not previously released the results of the 2003 review.

However, the latest examination discovered that the fault was an active one, urging
TEPCO to prepare for an earthquake on a larger scale than it initially expected.
An official of TEPCO’s nuclear plant management department said: “We couldn’t tell
the fault was an active one in the 1981 examination. When we reviewed it in 2003, we
thought it wouldn’t affect the station in the level of earthquake we expected, and
therefore we concluded it wasn’t necessary for us to release the content of the review.”

(Dec. 7, 2007)