Following the occurrence of the Niigata-Chuetsu-Oki Earthquake on July 16, 2007, 
the Tokyo Electric Power Company, Incorporated (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 safety-significant facilities at the site.
 
We hereby announce the content of the interim report on the results of geological 
and geological structure surveys around the NPS premise, which was submitted to 
the agency on May 12, 2008, and the content of another report on the formulation 
of the design-basis seismic motion at the Kashiwazaki-Kariwa NPS based on the analysis 
of seismic observation data acquired at the time of the 2007 Niigata-Chuetsu-Oki 
Earthquake, which was submitted to the Nuclear and Industrial Safety Agency on 
May 22, 2008.
 
1. Content of the Reports
(1) Active faults that were considered in formulating the design-basis seismic 
    motion based on the results of geological survey. 

    Taking into consideration uncertainties involved in safety evaluation, the 
    following major active faults in the NPS premise were considered in formulating 
    the design-basis seismic motion:
    The F-B fault (34km, M7.0); the Nagaoka Plain Western Rim Fault Zone (91km, M8.1), 
    which we assumed would move concurrently with the Kakuda/Yahiko fault, the 
    Kihinomiya fault, and the Katagai fault, all of which had been previously assumed 
    to move independent of each other; and the concurrent movement of the F-D fault 
    and the Takada Bay fault (55km, M7.7).
 
(2) Results of seismic observation data analysis.

    We have determined that the Niigata-Chuetsu-Oki Earthquake generated larger 
    earthquake motions in comparison with other earthquakes of the same scale.  
    This was because earthquake motions were amplified due to the effects of the 
    thickness and inclinations of sedimentary layers, and also because earthquake 
    motions were amplified due to the old bended structure [*] in the underground 
    of the NPS. The impact of the earthquake on the NPS therefore became more 
    significant.  
    In addition, we have discovered that the degree of earthquake motion amplification 
    differs between the side of units 1 through 4 and the side of units 5 through 7 due 
    to the effects of the old bended structure under the ground of the NPS premise.  
    Specifically, we have determined that earthquake motions become intensified about 
    2 times on the side of units 1 through 4 in comparison with the side of 
    units 5 through 7.
    [*] Bended structure refers to bending and bowing of a stratum.

(3) Formulation of the design-basis seismic motion.
    In formulating the design-basis seismic motion, we have considered the findings on 
    amplification of earthquake motions based on the results of seismic observation data, 
    such as the difference in the degree of earthquake motion amplification between the 
    side of units 1 through 4 and the side of units 5 through 7, in order to formulate 
    the design-basis seismic motion on the free surface of the base stratum caused by 
    earthquakes at the F-B fault and the Nagaoka Plain Western Rim Fault Zone, both of 
    which would have a major impact on the NPS premise. In this way, we have determined 
    that the peak ground acceleration of the design-basis seismic motion on the free 
    surface of the base stratum is 2,280 Gal on the side of units 1 through 4, and 
    1,156 Gal on the side of units 5 through 7.
    Based on these figures, we considered the attenuation of earthquake motions from 
    the free surface of the base stratum to reactor buildings, and evaluated the 
    earthquake motions on the base mats of reactor buildings, which have an ultimate 
    effect on the NPS's major safety-related facilities. The peak ground acceleration 
    turned out to be about 660-830 Gal on the side of units 1 through 4, and about 
    540-660 Gal on the side of units 5 through 7.
    TEPCO will implement construction works on all 7 units in order to enhance seismic 
    safety of the facilities. Specifically, the construction will enable the facilities 
    to withstand a shaking of 1,000 Gal [**] on the base mat of reactor buildings. 
    [**] We have set 1,000 Gal as the standard for improved earthquake resistance by 
         considering earthquake motions generated by the design-basis seismic motion 
         on the base mat of each unit of reactor buildings, as well as an elevated 
         version of the earthquake motions observed on the base mat of reactor 
         buildings at the time of the Niigata-Chuetsu-Oki Earthquake.  
         The level of the earthquake motion is equivalent to 1.5 times the peak 
         ground acceleration observed at the base mat of all reactor buildings at 
         the time of the Niigata-Chuetsu-Oki Earthquake.
 
2. Future actions.
   The design-basis seismic motion which we formulated at this time will be reviewed 
   by review panels [*2] of the Nuclear and Industrial Safety Agency of the Ministry 
   of Economy, Trade, and Industry (METI), among others. By taking the progress of 
   the reviews into consideration, TEPCO will continue to confirm the seismic safety 
   of the Kashiwazaki-Kariwa NPS. In addition, we will reflect the outcomes of reviews 
   at the panels on the construction works to improve seismic safety of the NPS.  
   We plan to explain our findings to the Niigata Prefectural Government and have it 
   reviewed. At the same time, TEPCO will continue to communicate to the local community 
   as well as the public about the situation of the Kashiwazaki-Kariwa NPS after 
   the Niigata-Chuetsu-Oki Earthquake, including the progress of the construction works 
   to improve the earthquake-resistant safety of the NPS. 

Appendix
* A Report on Analysis of Seismic Observation Data Obtained at the Time of the 2007 
  Niigata-Chuetsu-Oki Earthquake at the Kashiwazaki-Kariwa Nuclear Power Station,  
  and the Formulation of the Design-basis Seismic Motion (Summary)(PDF 536KB)
 

[* 1]
The instruction of the Nuclear and Industrial Safety Agency on ensuring safety at 
the Kashiwazaki-Kariwa Nuclear Power Station:
"On Analysis of Seismic Observation Data Obtained at the Time of the 2007 
Niigata-Chuetsu-Oki Earthquake at the Kashiwazaki-Kariwa Nuclear Power Station, 
and Evaluation of Potential Effects on Seismic Safety," issued on July 16, 2007, 
Instruction No. 1, 19-07-16.
1. Analysis of Seismic Observation Data Obtained at the Time of the 2007 
   Niigata-Chuetsu-Oki Earthquake.
2. Confirmation of Seismic Safety of Safety-significant Facilities after the 2007 
   Niigata-Chuetsu-Oki Earthquake. 
 
The instruction of the Nuclear and Industrial Safety Agency on ensuring safety at 
the Kashiwazaki-Kariwa Nuclear Power Station: "[TEPCO] is to analyze the seismic 
observation data obtained during the [Niigata-Chuetsu-Oki] Earthquake, and make 
progress on the confirmation of the seismic safety of safety-significant 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, Instruction No. 2, 19-07-16.

[*2]
The review boards at the NISA of the Ministry of Economy, Trade, and Industry: The 
Joint Working Group on Earthquake, Tsunami, Geology, and Ground Foundation; the 
Seismic and Structural Design Subcommittee of the Nuclear and Industrial Safety 
Subcommittee under the Advisory Committee for Normal Resources and Energy.

Please also refer to this material on this topic.(PDF 458KB)