Following the occurrence of the Niigata-Chuetsu-Oki Earthquake on July 16, 2007, the 
Tokyo Electric Power Company, Inc. (TEPCO) 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]. 
In response to this, TEPCO submitted an interim report on the results of the geological 
survey in areas adjoining the NPS to NISA on May 12, 2008. 

Subsequently, this interim report was revised mainly with respect to assessment of 
active faults in areas adjoining the NPS, in light of feedback from the national 
council[*2]. The revised report, which additionally includes the results of geological 
and tectonic evaluation of the NPS site and its adjoining areas, was submitted to NISA 
today. 

At the same time, TEPCO submitted a supplementary document to its previous report 
on the revision of the design-basis seismic motion for the Kashiwazaki-Kariwa NPS, 
which was submitted to NISA on September 22. As suggested by NISA's notification 
on the issues to be incorporated into the seismic safety evaluation[*3], this 
supplementary report describes the evaluation results of the exceedance probability 
of the design-basis seismic motion.

1. Brief outline the reports (see appendices for their summaries) 
(1) Report on geological survey results
    The estimated length of the F-B fault that takes account of uncertainties has been 
    changed to approximately 36 km. Major additions to the initial report are (i) the
    results of geological and tectonic evaluation of the NPS site and its adjoining 
    areas, (ii) the fact that no indications of activity of the Madonosaka and other 
    faults are observed at the NPS site and its adjoining areas, and (iii) assessment 
    results suggesting that there are no active faults or folds that should be 
    considered in seismic design. 

(2) Supplementary report on the design-basis seismic motion 
    The results of the evaluation of the exceedance probability of the design-basis 
    seismic motion show that the probability of occurrence of any seismic motion in 
    excess of the defined design-basis seismic motion is about once every 10,000 to 
    100,000 years. 

For reference purposes, TEPCO evaluated the confirmation seismic motion that has been 
defined in consideration of the draft view of the Nuclear Safety Commission (NSC)[*4]. 
The results show that the properties of the confirmation seismic motion are roughly 
the same as those of the design-basis seismic motion Ss-2, which has been obtained 
from the results of the seismic motion evaluation using the fault model of an earthquake 
that could be caused by the F-B fault. 

2. Our future actions 
In consideration of the survey results compiled into these reports, TEPCO will continue 
the seismic safety evaluation of its facilities, based on the design-basis seismic motion. 

- Appendices 
  (Appendix 1) 
   Summary of the Report on the Geology and Tectonics of the Kashiwazaki-Kariwa NPS Site 
   and its Adjoining Areas (PDF 86.4KB)
  (Appendix 2) 
   Summary of the Supplementary Report on the Analysis of Seismic Observation Data Acquired 
   at the Kashiwazaki-Kariwa NPS during the 2007 Niigata-Chuetsu-Oki Earthquake and the 
   Design-Basis Seismic Motion (PDF 282KB)

*1 Instruction to ensure safety at the Kashiwazaki-Kariwa NPS 
   "[TEPCO] should continue the analysis of the seismic observation data obtained during 
   the [Niigata-Chuetsu-Oki] Earthquake and the confirmation of the seismic safety of its 
   safety-critical facilities."

   An excerpt from "On Ensuring Safety at the Kashiwazaki-Kariwa Nuclear Power Station, 
   which Sustained Damages by the 2007 Niigata-Chuetsu-Oki Earthquake," issued on July 
   16, 2007 (NISA No. 2, 19-07-16) 

*2 National council 
   Joint Working Group on Earthquake, Tsunami, Geology, and Ground Foundation under the 
   Seismic and Structural Design Subcommittee, Nuclear and Industrial Safety Subcommittee, 
   Advisory Committee for Natural Resources and Energy 

*3 Notification on the issues to be incorporated into the seismic safety evaluation 
   "[TEPCO] should define the design-basis seismic motion Ss, based on seismic motion 
   that considers source characteristics and subsurface structural characteristics and 
   should refer to the exceedance probability of the design-basis seismic motion that 
   has been defined considering uncertainties."

   An excerpt from "Issues to Be Incorporated into the Seismic Safety Evaluation of 
   Nuclear Power Stations in Light of the Niigata-Chuetsu-Oki Earthquake," issued on 
   September 4, 2008 (NISA No. 10, 20-08-29) 

*4 Draft view of NSC 
   "[TEPCO] should define, in addition to the design-basis seismic motion, the confirmation 
   seismic motion using a fault model based on the F-B fault and confirm the validity of 
   the design-basis seismic motion. For evaluation, the recipe for strong motion prediction 
   proposed by the Headquarters for Earthquake Research Promotion in 2008 should be used 
   for setting fault parameters. However, in setting stress drops and the number and location 
   of asperities, the data obtained during the Niigata-Chuetsu-Oki Earthquake should be 
   used as much as possible." 

   An excerpt from the "Draft View on the Review by the Nuclear and Industrial Safety 
   Agency on the Formulation of the Design-Basis Seismic Motion for the Kashiwazaki-Kariwa 
   Nuclear Power Station," issued by the Investigatory Advisory Board on Assessment of 
   Seismic Safety on September 25, 2008