Following the occurrence of Niigata-Chuetsu-Oki Earthquake on July 16, 2007,
the Tokyo Electric Power Company, Inc. (TEPCO) has received an instruction from
the Nuclear and Industrial Safety Agency (NISA) of the Ministry of Economy, Trade,
and Industry (METI) to ensure safety at the Kashiwazaki-Kariwa
Nuclear Power Station (NPS) [*1].
Currently, TEPCO is conducting operations to confirm the seismic
safety of its safety-significant facilities.
As a part of such operations, TEPCO submits reports on the progress and results of
its geological and geological structure surveys to review boards [*2] of NISA
whenever appropriate. The Company then comes up with summary reports based on the
feedbacks from the review boards. TEPCO announces that it compiled the results of
its geological and geological structure surveys as an interim report, which was
submitted to the NISA on May 12, 2008.
1. Survey results
(1) Land area
Based on the results of our research on the literature, we have conducted a
geomorphologic survey, a subsurface exploration, an underground exploration,
and a boring survey in the land area covered by an approximately 30km radius
from the center of the premise of the NPS.
We have concluded from the results of the surveys that the fault which is
likely to most severely impact the NPS premise is the Nagaoka Plain Western
Rim Fault Zone. We decided that the activities of the Kakuda/Yahiko fault,
the Kihinomiya fault, and the Katagai fault, all of which comprise the Nagaoka
Plain Western Rim Fault Zone, occur independent of each other. However, because
the faults are adjoining each other, we have decided to make a collective safety
evaluation for them in our seismic safety evaluation, considering the possibility
of concurrent activities of the three faults (which, in total, stretches for
about 90km).
(2) Water area
In order to obtain data on seabed topography, geology, and geological structure,
we have conducted a maritime sonic prospecting and a seafloor topography survey
along the area stretching for about 140km along the coast line with the center
point of the premise of the NPS, and the ocean area covered by an approximately
50km radius from the center of the NPS premise.
We have concluded from the results of the surveys that major faults that are
likely to have an impact on the NPS are the Sado Eastern fault, the F-B undersea
fault, the Sado Southern fault, the F-D undersea fault, and the Takada Bay fault.
We are in the opinion that activities of the F-D undersea fault and the Takada Bay
fault occur independent of each other. However, because the faults are close to
each other, we have decided to make a collective safety evaluation for them in our
seismic safety evaluation, considering the possibility of concurrent activities of
the two faults (which, in total, stretches for about 55km).
2. Our future actions
TEPCO plans to continue to evaluate the geology and geological structures within and
surrounding the NPS premise, and use the results of the interim report to proceed with
the operations to confirm the seismic safety of its facilities.
* 1
The instruction of the NISA on ensuring safety at the NPS: "[TEPCO] is to analyze the
seismic observation data obtained during the [Niigata-Chuetsu-Oki] Earthquake, and make a
progress on the confirmation of the seismic safety of its facilities that are important in
terms of security." An excerpt from On Ensuring Safety at the NPS, which Sustained Damages
by Niigata-Chuetsu-Oki Earthquake of 2007, issued on July 16, 2007, Instruction No. 2,
19-07-16.
* 2
The review boards at the NISA of the Ministry of Economy, Trade, and Industry: Nuclear and
Industrial Safety Subcommittee, Advisory Committee for Natural Resources and Energy, the
Resource Energy Research Council; the Subcommittee on Quakeproof Structure and Design and the
Joint Working Group on Earthquake, Tsunami, Geology, and Ground Foundation
 Appendix :
A Summary of the Interim Report on the Results of Geological and Geological Structure
Surveys in Areas Adjoining the NPS (PDF 214KB)
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