EARTHQUAKES AND JAPAN

null
Tokyo 1923 Japan is riddled with faults and is located at the junction of four tectonic plates. In the last 75 years, the Japanese archipelago or areas immediately offshore have experienced five earthquakes measuring more than eight on the Richter scale; and 17 measuring more than seven on the Richter scale. It is unusual for a year to go by without three or four earthquakes measuring 6.0 or more.

Japan accounts for about 20 percent of the earthquakes of magnitude 6 or greater on the Richter scale. Each day about 1,000 tremors that can be felt are produced in Japan. More than 130,000 quakes were logged in Japan in 2005. Each year nearly ten percent of the energy released in the world in earthquakes is centered around Japan. In the last century Japan has experienced 25 destructive earthquakes. In some places small earthquakes are felt on a weekly and even daily basis. One journalist wrote that "Japan is always living on the edge of one disaster or another."

The Japanese seismic scale is slightly different from the Richter scale used in the United States and elsewhere in the world. The Japanese scale has maximum intensity of 7 and measures earthquake based on the amount of damage caused. The destructive Kobe earthquake in 1995 measured 6.9 on the Richter scale and 7 on the Japanese scale.

For an earthquake to be regarded as major enough to get a name it must destroy at least 100 houses, and measure more than 7 on the Richter scale or have an intensity of more than 5 on the Japanese scale.

Good Websites and Sources: U.S. Geological Survey (USGS) National Earthquake Information Center earthquake.usgs.gov ; Wikipedia article on Earthquakes Wikipedia ; Earthquake severity pubs.usgs.gov ; Collection of Images from Historic Earthquakes Pacific Earthquake Engineering Research Center, Jan Kozak Collection ; World Earthquake Map iris.edu/seismon Most Recent Earthquakes earthquake.usgs.gov ; Earthquake Pamphlet pubs.usgs.gov ; USGS Earthquakes for Kids earthquake.usgs.gov/learn/kids ; Earthquake Preparedness and Safety Surviving an Earthquake edu4hazards.org ; Earthquake Preparedness Guide earthquakepreparednessguide.com ; Earthquake Safety Site earthquakecountry.info

Earthquake Information for Japan Earthquake Information from Japan Meteorological Agency jma.go.jp/en/quake ; F-Net Broadband Seismography Network fnet.bosai.go.jp ; Wikipedia List of Earthquakes in Japan Wikipedia ; Major Earthquakes in Japan in the 20th Century drgeorgepc.com ; Earthquake Engineering and Disaster Prevention: Disaster Prevention Research Institute, University of Kyoto dpri.kyoto-u.ac.jp/web ; Japan Association of Earthquake Engineering jaee.gr.jp/english ; Earthquake Preparedness in Japan Earthquake Preparedness Survey whatjapanthinks.com ; Earthquake Research in Japan: Headquarters of Earthquake Research Promotion jishin.go.jp ; Institute of Geology and Geoinformation unit.aist.go.jp Research Center for Earthquake Prediction, University of Kyoto rcep.dpri.kyoto-u.ac.jp ; Earthquake Research Institute, University of Tokyo eri.u-tokyo.ac.jp ; 1923 Tokyo Earthquake: Great Kanto earthquake of 1923 dl.lib.brown.edu/kanto ; 1923 Tokyo Earthquake Photo Gallery japan-guide.com

Earthquake Mythology in Japan

According to Japanese mythology earthquakes are caused by the thrashing movement of “namazu” (giant catfish), who has the power to generate tremors on both land and sea. One way to prevent earthquakes, the Japanese believe, is to knock the fish on the head with a gourd. After a devastating earthquake in the 1850s many people in Japan put up pictures of a KO'd catfish on the doors of their house for protection.

The first earthquake, the Japanese Creation Myth goes, occurred after the Goddess Susanowo came out of her cave to bring light to the Earth. The eight million dancing deities of nature were so enchanted by her presence that they shook the earth with their exclamations of happiness.

Causes of Earthquakes in Japan

null
The four major plates that merge under Japan are: 1) the Eurasian Plate, 2) the Philippine Sea Plate, 3) the Pacific Plate and 4) the North American Plate. Most earthquakes occur along two plate boundaries near Japan's Pacific coast, where the Eurasian Plate and the Philippine Sea Plate meet and the Eurasian Plate and Pacific Plate collide.

Three plates move in three directions three miles beneath the streets of Tokyo. The Pacific Plate is the fastest moving. It subducts about four inches a year below the North American Plate and the Philippine Plate. The stress is taken up by strong shallow earthquakes off the east coast of Japan.

The tectonic makeup of Tokyo and surrounding areas is complicated, with two ocean plates subducting below a land plate on which the Japanese archipelago is located. There have been many earthquakes in this area, as both plate-boundary quakes, which are caused by friction between the plates, and inland quakes, which are caused by faults in the plates, can occur.

There are two main types of earthquakes that strike Japan: ocean trench ones, which are caused by oceanic plates pushing down on or moving under land plates; and inland quakes, which occur along fault lines between land plates.

Earthquakes along Eurasian Plate and the Philippine Sea Plate are regarded as particularly dangerous because lots of people live there and a lot of friction build up as the Philippine Sea Plate slides at a rate of 5 millimeters a year under the Eurasian Plate. This boundary passes directly under Shizuoka before making a U-turn at Mt. Fuji and returning to the sea at Sagami Bay off Yokohama, the epicenter of the great 1923 quake.

Many earthquakes that affect Japan originate far out at sea with their epicenters deep under the ocean floor. Others occur deep under the earth’s crust. The Japan Trench, a deep furrow in the sea floor running north to south just off the coast of Japan, is where two plates come together, one sliding beneath the other. The Pacific Plate is moving toward Japan at about 3 ½ inches a year. Its leading edge is crammed under Japan, lifting the country higher. Over time the strain builds until it is released in an earthquake.

Measuring Earthquakes in Japan

Earthquake intensity levels used to be determined based simply on the senses of officials at observatories and the level of destruction they caused. After 1996, however, they have been calculated automatically, based on data collected from observation points across the nation.

Currently, there are about 4,000 observation points. However, the level of tremors varies depending on the ground underneath the different facilities and the local terrain. As a result, agency officials sometimes conduct field surveys after they receive information about damage caused by a quake. "By international standards, Japan has a high density of observation points. But it's still difficult to precisely assess all tremors," Koji Nakamura, assistant section head of the Japan’s Meteorological Agency’s Earthquake and Tsunami Observations Division, told the Yomiuri Shimbun.

Japanese Seismic Intensity Scale

null
leaning building at Kobe in 1995 due
to liquification of soil Seismic intensity refers to the extent to which the shock of an earthquake can be felt. The Japan Meteorological Agency measures the intensity of each temblor and makes the results available to the public. An intensity of 7 is the most violent shock measured by the agency. An earthquake registering that level of intensity could topple most unsecured furniture. It also could cause some reinforced concrete buildings that lack strong earthquake resistance to collapse. The agency has recorded an intensity of 7 only in three quakes--the Great Hanshin Earthquake of 1995, the Niigata Prefecture Chuetsu Earthquake of 2004 and Great East Japan Earthquake in 2011. [Source: Yomiuri Shimbun, April 10, 2012]

There was a time when the agency's officials determined seismic intensity based on bodily sensations they experienced as well as the extent of damage to buildings. But this was changed in 1996, following the Great Hanshin Earthquake. Since then, seismic intensity meters have been used to measure a quake's intensity.In the past, the agency's seismic intensity scale comprised eight different levels, from 0 to 7. In 1996, however, the agency adopted a 10-level scale, dividing levels 5 and 6 into two sublevels--"upper" and "lower."

There are serious concerns about an earthquake with an intensity of 7 striking Tokyo and its neighboring areas. The government has anticipated 18 patterns of seismic activity in the Tokyo metropolitan area. These include one with a focus in the northern part of Tokyo Bay. Seismic studies have shown that the anticipated quake could originate from an underground location closer than previously predicted. This means areas adjacent to Tokyo Bay could be struck by a quake of intensity level 7.

Supercomputer Earthquake System Used to Predict Earthquake Aftermaths

In January 2012, the Yomiuri Shimbun reported: A University of Tokyo research team has developed a system that will use a next-generation supercomputer to simultaneously predict tremors, tsunami and movements in the Earth's crust after a massive earthquake occurs. The team, led by Takuto Maeda, an associate professor at the University of Tokyo's Center of Integrated Disaster Information Research (CIDIR), has used the new system on a current-generation supercomputer, which almost succeeded in reconstructing the aftermath of the Great East Japan Earthquake on March 11. [Source: Yomiuri Shimbun, January 31, 2012]

Predictions about tremors, tsunami and crust movements have been made separately in the past. But the system's simultaneous calculations are more likely to predict damage that would have been missed by separate findings, such as how a tsunami might impact an area where the ground level has sunk due to an earthquake. Using the system, the team entered data of the March 11 earthquake, such as its magnitude and location, into the supercomputer. The supercomputer predicted seismic waves would occur throughout the nation within 10 minutes of the earthquake, a massive tsunami hitting coastal areas after about 30 minutes, and the subsiding of the Kanto and Sendai plains.

The system's usability was confirmed by its ability to make predictions that were very close to what occurred in the aftermath of the Great East Japan Earthquake. But the system was restricted by the processing power of the current-generation supercomputer. A large amount of data must be processed to simultaneously calculate crustal movements and tsunami. Current-generation supercomputers lack sufficient storage capacity to process these calculations, and therefore some data was skipped.

Despite this, the team has further developed the system to predict more accurate damage in anticipation for its use on the nation's next-generation supercomputer, known as K, which has a data storage capacity 100 times greater than the current generation, and will be available in autumn. As the system can be used to predict detailed damage caused by multiple disasters, the team is planning to analyze the effect of the simultaneous occurrence of three big earthquakes known as the Tokai, Tonankai and Nankai earthquakes. Meanwhile, the University of Tokyo's Earthquake Research Institute is planning to develop another system for the K supercomputer from April that will analyze urban damage caused by earthquakes and tsunami, such as the collapse of buildings, and predict how certain regions should be evacuated.

Earthquake Prediction in Japan

null
earth movement
measuring devise Japan spends about $110 million a year on earthquake prediction studies. Earthquake monitoring devises include observation wells more than a mile deep, east and west of Tokyo, with meters that can detect movements in the earth's crust.

Japan has been making regular seismic observations since 1885. Groundwater is checked for increased concentrations of radon, which some scientists say is an indicator of an imminent earthquake. Monitoring plate activity is made difficult by the large amount of noise generated by factories, trains and vehicles.

Some Japanese scientist think they can predict the next major earthquake based on the periodic movement of the crust in certain areas of region before an earthquake. A very large earthquake hits the Tokyo on average of once every 69 years. The Japanese are also studying animal behavior as prediction method. Before the Kobe earthquake, fish reportedly swam near the surface of the sea and pigeons and crows flew in crazy patterns.

Laboratory experiments indicate that major fractures of rock are preceded by “pre-slips” in which the rock gives a little before it buckles. Scientists hope to pick up the pre-slips before a large earthquake and give people an advanced warning. Many scientists are skeptical as to whether these pre-slips do indeed exists and if they do exist how they can be distinguished from mundane daily tremors.

The Japanese government's Headquarters for Earthquake Research Promotion is responsible for predicting the occurrence and scale of earthquakes in or around the Japanese archipelago. The headquarters' long-term forecasting method uses records of past quakes.

The urgent earthquake warning system, introduced in 2007, is designed to estimate the intensity of an earthquake through detection of a weak, fast-traveling primary wave that occurs before a more powerful secondary wave. Emphasizing speed, the agency predicts an earthquake's intensity based on the primary information, leading to a margin of error of plus or minus one level, an agency official said. [Source: Masatoshi Imai, Yomiuri Shimbun, December 11, 2010]

Inaccuracies of Short Term Predictions of Earthquakes Based on Primary Waves

In December 2010, the Meteorological Agency issued an urgent earthquake warning, predicting a strong earthquake in the 5 range would occur soon in the Sapporo area. Warnings were issued on television; trains were stopped. But the earthquake turned out to be a minor one, two intensity levels below the one predicted.

Japan’s Meteorological Agency has issued 17 urgent warnings as of December 2010. However, in seven cases, the quakes turned out to measure 4 or below on the intensity scale. On the other hand, the agency did not issue a warning in seven cases in which the quakes turned out to be lower 5 or stronger. [Source: Masatoshi Imai, Yomiuri Shimbun, December 11, 2010]

null
Kobe 1995 Short term predictions based on weak primary waves that precede the main shock have significantly improved over the years, but can still be off the mark. On December 2, 2010, for example, Japan’s Meteorological Agency issued an urgent warning predicting that an earthquake registering lower 5 or higher on the Japanese seismic intensity scale of 7 would soon hit Sapporo and other nearby cities. The earthquake's epicenter was in the central part of the Ishikari region of Hokkaido. [Ibid]

Masatoshi Imai of the Yomiuri Shimbun wrote: “The agency corrected itself soon after, announcing the quake had been a 3. But the next day, the Sapporo District Meteorological Observatory announced the intensity level was believed to have been 4 and lower 5 in certain areas. Explaining why an agency official said: "According to the seismic intensity meter, the quake was a 3. But we have a limited number of observation points [in this area], so it's difficult to accurately determine the intensity near the epicenter immediately after the quake." [Ibid]

“The agency issued the urgent warning after an observation point in Eniwa, Hokkaido, detected a primary wave of the quake at 6:44 a.m. on Dec. 2. The agency projected the quake would measure between 4 and lower 5, and issued the warning 8.5 seconds later. About one minute later, the agency concluded that the quake had been a 3, based on data collected from dozens of observation points. However, the observatory's field survey the next day showed the quake had broken windows at some schools and caused a landslide at a golf course in Kiyota Ward, Sapporo. Using the agency's criteria for determining seismic intensity, the observatory announced the quake had measured 4 to lower 5 in some areas.”

“An earthquake that struck Fukushima Prefecture in September was similar to the case in Sapporo. Shortly after the agency issued an urgent warning, it announced the quake had measured as a 4. The following day, the agency announced that quake was believed to have been a lower 5 in some areas, after confirming that some roads had been cracked because of the earthquake.” [Ibid]

"The current urgent earthquake warning system has limitations. But I don't want people to dismiss the information as inaccurate," said Katsumasa Abe, professor emeritus of the University of Tokyo. "I urge people to continue paying attention to the information, as it may save their lives. At the same time, the Meteorological Agency must improve the system," Abe said. [Ibid]

Earthquake Monitors in Japan

null
monitoring instruments Japan’s Meteorological Agency is responsible for monitoring earthquakes. The Matsuhiroo Seismological Observatory, which is mainly consists of tunnels containing of earthquake observation devices in a mountains in Nagano Prefecture, can detect earthquakes and nuclear tests from around the globe.

The Japanese government is currently installing underground seismometers between a dozen and several hundred meters underground as part of its set up to give scientists a better idea of when big quakes are likely to occur plus offer instaneous warnings when earthquakes occur. When the system is completed in 2014, major active faults in 110 locations nationwide will be monitors.

Ground meters that are designed to pick up such pre-slips have been placed all over the Tokai area to pick up signs of a potentially dangerous earthquake there. If one or two meters show anomalies schoolchildren may be sent home. If three occur the country is put on high alter and police, soldiers and firefighter are put on high alert to act immediately and the Prime Minister will go on television to announce that an earthquake is imminent.

More than 1,000 permanent GPS instruments have installed throughout Japan have discovered episodic, slow-slip events along subduction zones. Maps have been produced that show where large earthquakes are most likely to occur. In addition, a number of stress meters have been installed in the area straddling Aichi and Shizuoka Prefectures in attempt to predict or at least get a warning of powerful Tokai earthquake.

Yet, with all this, more than two decades after Tokyo established an Earthquake Assessment Committee no public warning of an earthquake has ever been issued.

See Earthquake Warnings

Image Sources: Mostly Earthquake Research Institute, University of Tokyo (Japan pictures), USGS (non-Japan pictures) except Tokyo 1923 (J.B. Macelwane Archives, St. Louis University) and Kobe 1995 (Kobe University)

Text Sources: New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated January 2013