Geotechnical Problems in the 2007 Niigata-ken Chuetsu-oki Earthquake

The Niigata-ken Chuetsu-oki earthquake (M_j=6.8) occurred on July 16, 2007, affected the coastal areas of the southwestern Niigata prefecture, including Kashiwazaki city and Kariwa village, most of which were located on or near the sand dunes that run parallel to the coastline. The peak ground accelerations recorded were as large as 6.7 m/s² in Kashiwazaki city and 12.2 m/s² in the Kashiwazaki-Kariwa nuclear power plant. The damage to the city caused by ground shaking, however, appeared to be limited to very old buildings whereas that caused by ground failure extended to both old and new buildings as well as many infrastructures in alluvial deposits and sand dune slopes. The operation of the Kashiwazaki-Kariwa nuclear power plant was automatically shutdown and all the critical structures seemed to be in good condition; however, a fire broke out around a house electric transformer and many non-critical structures as well as incidental components such as pipes and ducts were damaged, retarding the re-operation of the plant. The major cause of the damage including the fire at the site seemed to be not only the near field strong ground motions but also the settlements of backfill around the critical buildings.