Corporate Information

Press Release (Jul 19,2007)
Observation Record of the Seismic Activity at the Kashiwazaki-Kariwa Nuclear Power Station during the Niigata-Chuetsu-Oki Earthquake
The Tokyo Electric Power Company, Inc. (TEPCO) has collected and sorted 
the seismic observation data recorded during the Niigata-Chuetsu-Oki 
Earthquake (magnitude: 6.8, distance from the seismic epicenter: 16km, 
distance from seismic center: 23km) that hit the Kashiwazaki-Kariwa NPS 
on July 16th, 2007 in order to conduct seismic observation data analyses 
and impact evaluation on seismic safety.

We announce the results of the seismic data collected for all seven units 
at the Kashiwazaki-Kariwa NPS, including those for units 1, 5 and 6, which 
had been previously announced.

At the Kashiwazaki-Kariwa NPS, in addition to the existing seismographs 
that were installed in the buildings of units 1, 5, and 6 and on the site 
ground (67 in total), new seismographs (30 in total) have been installed 
in all seven units and have been functional since April of 2007.

During the course of data collection following the earthquake, we confirmed 
that among the seismic data collected from the 63 existing seismographs, 
seismic wave profile data had disappeared.

However, we believe sufficient analyses will be possible based on maximum 
acceleration data found in the existing seismographs for the main quake; 
all data for the main quake is available from the newly installed seismographs 
for all units, and subsequent data for the aftershocks are available from 
both existing and newly installed seismographs.

The data disappeared due to the fact of that the seismic record for the main 
quake had been overwritten by that of the aftershocks. The data was overwritten 
because data could not be transmitted to the server located in Tokyo due to 
congestion on the communication channel coupled with the consecutive occurrence 
of numerous aftershocks.

Similar problems occurred during the Noto Peninsula earthquake that hit the Shika 
NPS of Hokuriku Electric, and TEPCO was planning to replace seismographs, including 
those of KK (for unit 1 in 2007 and for units 5 and 6 in 2008.)

In light of this incident, we will immediately replace all seismographs in addition 
to registering this incident on the NUCIA (NUClear Information Archives) database 
for the purpose of informing other utilities.

We will continue collecting seismic data of the aftershocks as well as analyzing 
the seismic records, and confirm the seismic safety of facilities that are of 
high safety importance.

Reference1:The observed seismic acceleraion at the Kashiwazaki-Kariwa Nuclear
           Power Plant during the Niigata Earthquake
Reference2:Layout of seismograph installations
Reference3:Image of seismic observation system
back to page top

to TOP