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USGS Researchers Lead International Team Investigating Damage Caused by Offshore Earthquake Near World's Largest Nuclear Power Plant in Japan
On July 16, 2007, a magnitude 6.6 earthquake occurred off the coast of Japan near the world's largest nuclear power plant. The M=6.6 mainshock of the Niigata Chuetsu Oki earthquake struck in the Japan Sea near the west coast of Honshu at 10:13 a.m. local time, with a shallow estimated focal depth of 10 km (details posted at http://earthquake.usgs.gov/eqcenter/recenteqsww/
The site that sustained the highest seismic intensity was the Kashiwazaki-Kariwa Nuclear Power Station of the Tokyo Electric Power Co. (TEPCO), with seven independent reactors and a total output of 8,200 MW. This facility is heavily instrumented with strong-motion recorders, which captured the highest-amplitude motions ever recorded at a nuclear power plant. Ground-level and reactor-floor shaking was as high as 0.68 g (1 g is approx 9.81 m/s2, the acceleration due to gravity at the Earth's surface), and the accelerations at the top of steam turbines and reactor roofs were twice as high.
Critical structures at the power plant appeared to have performed well, in view of the intensity of the shaking and the damage to the ground surrounding the reactors, including extensive ground settlement and evidence of liquefaction near the waterfront. Although shutdown of the reactors proceeded safely, some secondary damage did occur, and the plant remains shut down for ongoing inspection and repair. Outside the power plant, the earthquake strongly shook the nearby city of Kashiwazaki, resulting in 11 fatalities and nearly 2,000 injuries. Approximately 1,100 residences collapsed, almost all of them old houses with wood and clay walls and heavy clay-tile roofs.
The earthquake reconnaissance of the Niigata event, begun only hours after the quake, was a combined effort by U.S. and Japanese engineers. From the United States, the National Science Foundation (NSF) supported the investigations of the Earthquake Engineering Research Institute (EERI) and the Geo-Engineering Earthquake Reconnaissance (GEER). The Japanese participants were from academia, the Japanese Society of Civil Engineers, and the Japan Association for Earthquake Engineering. The NSF reconnaissance-team leader for the combined EERI-GEER effort was USGS researcher Robert Kayen. USGS Mendenhall Postdoctoral Research Fellow Brian Collins was an investigator in the study and led the capture of critical terrestrial lidar (light detection and ranging) data at damage sites (for more information about terrestrial lidar, see "Land-Based Lidar Mappinga New Surveying Technique to Shed Light on Rapid Topographic Change" (USGS Fact Sheet 2006-3111). USGS researcher Clint Steele managed the data organization and produced multimedia Google Earth maps for the investigation report (download maps [176 KB KMZ, requires Google Earth application] from URL http://walrus.wr.usgs.gov/infobank/n/nii07jp/html/n-ii-07-jp.sites.kmz). During the investigation, USGS scientists participated in interviews with the Japanese print media.
The first reconnaissance team was organized and sent to the affected region within 48 hours after the earthquake, and in the following weeks, several other teams joined the effort to assess structural damage and soil effects at the nuclear power plant and surrounding cities. The teams quantified the spatial extent and amplitude of ground failures, soil liquefaction, and landslides, as well as damage to bridges, piers, ports and harbors, lifeline systems, and critical structures.
The reconnaissance effort was conducted largely from vehicles and covered most of the roads in the damaged region. Each vehicle carried teams equipped with handheld two-way radios, digital cameras, maps, computers for recording site logs, and Global Positioning System (GPS) units for recording the routes the teams traveled and the locations of sites where they collected data. During the fieldwork, the researchers merged their data into a common database so that they could generate Google Earth displays of all the observations on dynamic, multilayered digital maps. Individual data layers could be selected to create damage-specific maps, for example, a map showing only liquefaction damage. By using Google Earth to display and observe the damage they had mapped, the teams were able to identify unexplored areas for reconnaissance, discern spatial trends in the observations, and discover any errors in the GPS logs and recorded observations. The city of Kashiwazaki already had a file of three-dimensional views of the city's buildings available as a layer in Google Earth (check "3D Buildings" in list of Google Earth layers); the team used this layer to identify the locations of critical facilities, such as schools, water- and wastewater-treatment plants, municipal-waste incinerators, and ports, which they then visited for further data collection. In the USGS office in Menlo Park, California, Clint Steele took the dataset compiled by researchers in the field and added links to their photographs and written descriptions of each site, creating a Google Earth file (download file [176 KB KMZ, requires Google Earth application] from URL http://walrus.wr.usgs.gov/infobank/n/nii07jp/html/n-ii-07-jp.sites.kmz) that allows all interested viewers, researchers and the public, to take virtual tours of the damage zone.
Much of the damage from the Niigata earthquake was associated with geotechnical problems, that is, problems related to the physical response of rock and soil to the shaking. For example, evidence of soil liquefaction was seen in various settings: riverbank deposits, beach deposits, dune sand, and placed fill. Soil liquefaction affected structures severely, triggering a transformer fire and simultaneously damaging the fire-suppression system at the nuclear power plant, as well as closing the Kashiwazaki wastewater-treatment plant. Ground settlement caused by liquefaction broke large water mains and gas conduits, damaged bridge abutments, and compromised ports and harbors. Landslides caused by the earthquake consisted of shallow translational slides, debris slumps, and deep-seated rotational slides. Where transportation lines crossed areas of steep terrain, landslides blocked or destroyed whole sections of roadways and railways.
For more information on the earthquake and the investigation, see the detailed 230-page "Investigation of the M6.6 Niigata-Chuetsu Oki, Japan, Earthquake of July 16, 2007" (USGS Open-File Report 2007-1365), which describes the seismologic, geotechnical, and structural aspects of the damage caused by the earthquake, as well as the effectiveness of the emergency response and recovery.
Engineers and scientists participating in the investigations were from Oregon State University (Scott Ashford, Steve Dickenson, and Yohsuke Kawamata); the University of California, Los Angeles (UCLA, Scott Brandenberg); Purdue University (Santiago Pujol, EERI coleader); the Japanese Association of Earthquake Engineers (Toshimi Kabeyasawa, Nanako Marubashi, and Yousok Kim); Kobe University (Yasuo Tanaka and Hidetaka Koumoto); the Tokyo Institute of Technology (Kohji Tokimatsu); the Pacific Gas and Electric Co. (Norm Abrahamson, Ben Tsai, Lloyd Cluff, and Joseph Sun); the California Department of Transportation (Mark Yashinsky); Kyoto University (Laurie Johnson); and a private consulting firm (Peter Yanev).
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