Preliminary Observations on the Niigata-Chuetsu Oki, Japan, Earthquake of July 16, 2007
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EERI Special Earthquake Report — September 2007 Learning from Earthquakes Preliminary Observations on the Niigata-Chuetsu Oki, Japan, Earthquake of July 16, 2007 Three days after the Niigata-Chuetsu EERI), Stephen Dickenson (also numerous ground failures as far Oki earthquake, EERI and GEER with GEER), Curt Edwards, Anshel away as the Unouma Hills, located (Geo-Engineering Earthquake Re- Schiff, Alex Tang, and Yumei Wang. approximately 50 km inland. connaissance) deployed a joint The ASCE team received assistance In Niigata prefecture, the JMA seis- team of engineers and emergency from the Japanese Society of Civil mic intensity was 6+ (IX in MMI) in management experts to document Engineers (JSCE). The JSCE team Kariwacho, Kashiwazaki City, and geotechnical effects; the perfor- members included Jorgen Johans- Nagaoka City; it was the same in mance of the Kashiwazaki-Kariwa son and Hiroyuki Yanagawa. Ohzuna-machi in Nagano prefec- nuclear power plant; the perfor- The EERI-GEER team and the pub- ture. The downtown Kashiwazaki mance of other structures, bridges, lication of this Learning from Earth- City K-NET site recorded a PGA of ports and harbors, and lifelines; and quakes report were supported by 0.67g. The earthquake resulted in the response and recovery. The the National Science Foundation 11 fatalities and nearly 2,000 injur- EERI-GEER team, with the assis- through Grants #CMII-0323914 and ies. Close to ,00 residential struc- tance of the Japanese Association #CMII-0131895. A greatly expanded tures collapsed — almost exclusive- for Earthquake Engineering (JAEE), companion web report can be found ly old bamboo and stuccoed post- was led by Robert Kayen of the at www.eeri.org or www.gees.usc. and-lintel structures with heavy U.S. Geological Survey and Santi- edu/GEER. Readers of this report kawara tile roofs. Many of these ago Pujol of Purdue University, and can download a linked dynamic collapses were associated with dis- included Brian Collins of the USGS; Google Earth map file at http:// placements on the slopes of sand Scott Ashford, Stephen Dickenson, walrus.wr.usgs.gov/infobank/n/ dune deposits or with liquefied and Yohsuke Kawamata of Oregon nii07jp/html/n-ii-07-jp.sites.kmz to ground. There was damage to gas, State University (with partial support view sites discussed below, includ- water, and electricity infrastructure from the Pacific Earthquake Engi- ing many additional photos. and to the world’s largest nuclear neering Research Center); Scott J. power plant, the Kashiwazaki- Brandenberg of UCLA; Norm Abra- Introduction Kariwa facility. The power plant was hamson, Lloyd Cluff, Joseph Sun, in a region of high isoseismal inten- and Ben Tsai of PG&E; Haruo Hay- The M6.6 Niigata-Chuetsu Oki earth- sity, as inferred from the observed ashi, Norio Maki, and Laurie John- quake struck at 0:3 am local time damage patterns in the area. son of Kyoto University; Mark Yash- on July 6, 2007, along the west insky of Caltrans; with contributions coast of Honshu Is- from Peter Yanev; Renee Lee of land, Japan. It was Arup; Kit Miyamoto of Miyamoto followed by a se- International; Yasuo Tanaka and quence of after- Hidetaka Koumoto of Kobe Univer- shocks that were sity; Kohji Tokimatsu of Tokyo Insti- felt during the en- tute of Technology; Toshimi Kabeya- tire time of the re- sawa, Kim Yousok, Kazuo Konagai, connaissance ef- Toshikazu Kabeyasawa, and Toshi- fort. The event had nori Kabeyasawa of Tokyo Univer- a shallow focal sity; Nanako Marubashi and Toshi- depth of 0 km and katsu Ichinose of the Nagoya Insti- struck in the Japan tute of Technology; Keiko Tamura of Sea immediately Niigata University; and the staff of offshore from Kari- the Research Center for Urban Safe- wa (see Figure ). ty and Security (RCUSS). The team The quake affected also coordinated lifelines investiga- an approximately tions with a team from the American 00 km-wide area Society of Civil Engineers (ASCE) along the coastal Technical Council on Lifeline areas of southwes- Earthquake Engineering (TCLEE), tern Niigata prefec- Figure 1: Location and aftershock map of Niigata in-cluding Mark Yashinsky (also with ture and triggered Chuetsu Oki event. EERI Special Earthquake Report — September 2007 of which were within 50 km. The accelerograms obtained at station NIG08 (close to the fault plane and within the area where damage was more severe) show low-frequency content, suggesting features associ- ated with liquefaction in foundation soils below the instrument. Whereas there was no observed sign of lique- faction at the ground surface, the spiky trace of the acceleration rec- ord is consistent with the known be- havior of sandy soils undergoing cy- clic mobility in undrained loading. Acceleration response spectra com- puted for a damping coefficient of 5% are shown in Figure 2. The seven-unit Kashiwazaki-Kariwa Nuclear Power Plant is located about 6 km from the epicenter determined Figure 2: Acceleration response spectra for a damping coefficient of 5%. From by the Japan Meteorological Agency top to bottom: NIG016, NIG017, NIG018, NIG019. The left panel is the EW com- (JMA) for this event and was instru- ponent, the middle panel is the NS component, the right panel is the Z compo- mented at 99 locations. The motions nent. The horizontal axes represent frequency, in Hz, and the vertical axes at 33 locations with a new sensor represent absolute acceleration as a fraction of the acceleration of gravity. system were recorded, but the re- cordings at the other 66 older instru- The team recorded the spatial posi- cific plates). The moment magnitude ment locations, including two free- tion and severity of ground failure of the mainshock of this event was field down-hole arrays and most of and structural damage using digital estimated to be 6.6 using teleseis- the structural arrays, were lost with mapping techniques. GPS data, mic data (USGS) and 6.7 using re- the exception of the peak values. site logs, and digital pictures are gional data. The Japan Meteorologi- The ground motion data on the old archived in a Google Earth database cal Agency assigned a magnitude of system could not automatically mentioned in the preface; it contains 6.8 to the mainshock. transmit due to communication con- a comprehensive explanation of gestion, and aftershocks triggered The Niigata earthquake was a bur- each site for use as a supplement to the recorders and overwrote the buf- ied reverse-slip earthquake, with a this newsletter insert. The database fer containing the mainshock record- hypocenter estimated at a depth of was constructed as the reconnais- ings. The 33 recordings of the new 8 km (NRI ESDP, 2007). Two po- sance progressed, and proved use- system included 27 from a majority tential planes of faulting are unre- ful for planning visits to unexplored of the reactor and turbine buildings solved, as aftershock locations fell areas. Niigata Prefecture has built a and one 4-depth free-field array at on both planes. The rupture length 3D buildings layer for Kashiwazaki the service hall (see Figure 3). The is estimated to be 30 km and the City in Google Earth that was useful data indicate a large range in the down-dip fault width is estimated to for identifying critical facilities. High- foundation motions for the EW com- be 22 km for both planes. The in- resolution laser-mapped data sets ponent, with PGA values ranging ferred location of the hypocenter is of the most significant structural and over a factor of two (322-680 gals). at the northeast end of both planes, geotechnical damage features were The NS component shows more and the rupture is inferred to have also collected for preservation using similar values (267-311 gals). The progressed from the northeast the USGS’s terrestrial LiDAR (light large variation in the EW component toward the southwest. Slip models detection and ranging) system. values cannot be explained by sim- for both rupture planes show a sin- ple -D site effect differences. Re- gle strong asperity in the western cordings from aftershocks show a Seismological Aspects end of the rupture. The maximum large variation in the site response, Niigata is located in a subduction computed slip is 3.5m. with larger motions for the northern zone near the boundary between the The Japanese nationwide strong units (5,6,7) for some aftershocks Amur plate and the Okhotsk plate motion network, K-NET, recorded and larger motions for the southern (two relatively small plates that lie the earthquake at 390 stations, 20 units (, 2, 3, 4) for other aftershocks. between the larger Eurasia and Pa- 2 EERI Special Earthquake Report — September 2007 Figure 3: Peak accelerations (cm/sec/sec) in and around Unit 1 (source: TEPCO, 2007). The observed varia- general settings: riverbank deposits, tion in the PGA am- beach deposits, dune sand, and plification is corre- placed fill. Along the Sabaishi River, lated with epicentral azimuth, indi- liquefaction and lateral spreading cating that strong 3-D wave propa- features were observed over ap- gation effects are contributing the proximately 5 km from the river large variability of the ground mo- mouth. River deposits near the sea Figure 4: Pipe breaks due to sep- tions over short distances. The large liquefied and settled severely at the aration of two halves of Kashiwa- range of PGA values on the EW Kashiwazaki wastewater treatment zaki Wastewater Treatment Plant. component shows the need for multi- facility separating two plant build- ple recordings at NPP sites to reliably ings (Figure 4). Upriver, liquefaction determine the input ground motions resulted in settlement of the levee damage, all of it within one kilometer for the structures. embankment near the Kai-Un Bridge, of the mouth of the river.