Press Releases 2013

At the public hearing regarding earthquake and Tsunami held by the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry (at the time) on August 10, 2012, the necessity of a more detailed examination of Yasuda Layer^*1 including its age was pointed out. In response to this, a geological survey was performed for the purpose of defining the age of Yasuda Layer.

(Previously announced on August 23, 2012)

From September 2012, boring investigation was performed in 3 areas (7 locations) including the area within the power station site and the samples obtained (volcanic ash and fossil) were analyzed. As a result, Yasuda Layer was confirmed to have been formed in the middle Pleistocene^*2 though previously it was considered to have been formed sometime during the period from the late Pleistocene to the middle Pleistocene^*3.

Based on this evaluation results and the fact that all the faults found under the power station site^*4 stop within Yasuda Layer, it has been determined that the faults have been inactive since approx. 200,000 years ago after Yasuda Layer.

We will continue investigation and analysis and will perform evaluation as necessary in the case that new standards of active fault evaluation are established.

End

Attachment: Outline of the geological survey on the age of Yasuda Layer under Kashiwazaki-Kariwa Nuclear Power Station (PDF 921KB)
Reference: Report on the geological survey on the age of Yasuda Layer under Kashiwazaki-Kariwa Nuclear Power Station (PDF 44.6MB)

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*1 Yasuda Layer
A geological layer which lies under Kashiwazaki Plain and its surrounding area.
Considering that all the faults under the power station site stop within Yasuda Layer, the age of the layer is used as a guide of active fault evaluation.
*2 Formed in the middle Pleistocene
Based on the results of the survey performed this time, Yasuda Layer was confirmed to have been formed sometime during the period from approx. 300,000 years ago to approx. 200,000 years ago.
*3 Formed sometime during the period from the late Pleistocene to the middle Pleistocene
Yasuda Layer was previously considered to have been formed sometime during the period from approx. 240,000 years ago to 120,000-130,000 years ago considering that Atatorihama Tephra (formed approx. 240,000 years ago) is included in the layer.
*4 Faults found under the power station site
A total of 23 faults such as α,βfaults, F, V, L type faults and (1),(2)faults have been found under Kashiwazaki-Kariwa Nuclear Power Station.