Background InformationOn July 16, 2007 a number of earthquakes struck the seas of Japan. There were two main earthquakes a 6.8 magnitude earthquake and a 6.6 magnitude earthquake. Figure 1 Shows the location of the 6.6 earthquake. The 6.6 earthquake was an oblique thrust fault and had occurred 13 hours prior to the bigger 6.8. The 6.6 was a shallow earthquake most likely caused by the deformation of the Okhotsk plate. The 6.8 quake originated at a depth of 350km and about 130km off the coast of Japan. The earthquake originating at such a depth suggests that it was cause by deformation of the Pacific plate rather then the Okhotsk plate. It is because of this that the 6.8 quake is not believed to be an aftershock of the first 6.6 quake. The 6.6 magnitude earth was experienced as the more intense of the two earthquakes. This is because it was a shallow earthquake and it had less earth to travel through resulting in less loss of energy.
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Figure 1. Earthquake Location
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Figure 2. Mercalli Intensity Scale



Earthquake Damage SummaryFigure 2 shows the Mercalli intensity experienced from the quake, and also shows the Niigata area clos
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Figure 4. Traditional Style Building
e to the yellow zone. The higher intensity can be attributed to Japans poor soil. It is sandy soil that can easily exhibit liquefaction during shaking. The liquefaction leads to major damage to many of the structures in the area. Not only during this earthquake but also previous earthquakes. The last major quake to hit the Niigata area occurred in October of 2004 and resulted in a cost of $30 billion dollars. The 2007 quake lead to major damage to building, roads and to be covered later, the nuclear plant located there. Leading to an estimated $5-$10 billion dollars and 10 deaths. The Niigata area shown in figure 2 just north of the star, experienced a large amount of damage. The buildings in Niigata were built in the more traditional style of Japan, with wooden structure and tile. These type of buildings do not withstand earthquakes as well as more modern ones would. The heavy tile roofs and weak structure of the traditional buildings pose not match for the strength of the earthquake and most were damaged or completely collapsed. Figure 4 shows a traditional style building that has completely collapsed under the weight of the tile roof.

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Figure 3. Compromised Soil Foundation

The more stable, modern, buildings were not spared in the earthquake, however. As a result, of the liquefaction foundations of many buildings were compromised. Figure 3 shows an example of settling soil under a foundation. Liquefaction lead to the majority of the damaged sustained by the earthquake. Business and industry sectors were hit hard. The violent shaking damaged underground utilities disrupting business. To add to the disruption roads and bridges were damaged. The liquefaction had unsettled many of the slopes in the area. The roads and bridges located on or near these unstable slopes were left cracked beyond use.









Nuclear Power Plant Damage
Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) is the worlds largest nuclear facility. KKNPP is comprised of seven
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Figure 5. Kashiwazaki-Kariwa Nuclear Power Plant
reactors and is shown in Figure 5. After the earthquake occurred many buildings were damaged or destroyed. Roads buckled and cracked. The business in the Niigata area came to a stand still. KKNPP was the only building being closely watch by the news. Being the worlds largest nuclear facility also means that they serve a large portion of Japans population, about 30%. A shutdown of the plant would affect a huge portion of the population.

When KKNPP was built seismic activity was a concern of the bulding process. The facility was built with two levels of intensity in mind. An operating intensity which would allow the facility to still operate during a quake and still be elastic enough to withstand. The second level is a shutdown intensity where the plant would shutdown. Motion sensors were put around KKNPP to sense the level of movement and determine which level of action to take. When the earthquake hit KKNPP only 3 of the reactors were online and 1 was in the process of being brought back online. The intensity of shaking had exceeded more then twice the expected intensity of shaking when the facility was built. This lead to all the reactors shutting down. Initial reports indicated that there was only a minimal amount of damage to the facility. A small amount of radioactive material was said to have been exposed to the environment, with little to no consequence. The news had blown this fact out of proportion initially. Ultimately, the shutdown of the reactors for repairs and clean up lead to billions in revenue loss for the company.

Conclusion The Moderate quake lead to large amounts of damage through liquefaction. The loose soil of japan was unable to support the structures built on them and many of the foundations in the affected area were compromised. After seeing the large consequences of the quake, it was seen as a wake up call. When Niigata was struck by a 6.8 on the Richter scale, the KKNPP was designed to resist such seismic wave only this time it did not hold as it was designed for. This quake was not the largest to hit Japan, but the damage shows how ill prepared even newer buildings are. Also, it shows just how easy a quake can interrupt everyday business and affect so many people, even those far from the quake. Hopefully the vulnerabilities made apparent in this quake can be remedied before the next major quake.



Resources
http://www.power-technology.com/projects/kashiwazaki/

http://www.grmcat.com/images/Niigata-Chuetsu-Oki-Japan-Report.pdf
http://news.bbc.co.uk/2/hi/asia-pacific/6900156.stm
http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007ewa8/#summary
http://www.ens-newswire.com/ens/jul2007/2007-07-16-04.asp
http://www.nytimes.com/2007/07/16/world/asia/16cnd-japan.html?_r=1