Facts and Details

TSUNAMIS IN JAPAN

Damage from 1896 tsunami Japan gave the world the word tsunami.More than 800 tsunamis have been generated in the Pacific in the last century. Some 22 percent of these were generated off of Japan According to geological evidence catastrophic tsunamis like the one that hit Sumatra, Thailand and Sri Lanka in 2004, strike Japan every 400 or 500 years. There have long been worries that a large tsunami on the Pacific coast could kill tens of thousands of people and cause hundreds of billions of dollars in damage. A large earthquake off the east coast of Japan could produce a huge tsunami and people would only have minutes to evacuate even if they are given a warning when the earthquake occurs. This happened in 2011. As bad as it was things could have been worse if a tsunami of that size struck closer to Tokyo or the industrial heart of Japan.

A tsunami is a series of waves produced by an event in the ocean such as an underwater landslide or an earthquake that cases large amounts of seawater to be displaced . Sometimes they can be very large. Catastrophic ones occur a few times a century, Other times they are so small they virtually undetectable.

For a long time tsunamis were erroneously called tidal waves. A tidal wave according to Oxford English Dictionary is a “high water wave caused by the movement of the tide.” It is different from a storm surge a flood of water that occur when water pushed inland by a storm such as a typhoon coincides with a high tide. The word tsunami is derived from the Japanese tsu (“harbor”) and nami (“waves”).

Most tsunamis are comprised of a series of crests and troughs called a “wave train” and have a leading wave followed by crests that push it from behind. Damages is not caused so much by huge wall of water crashing down like a large beach wave but rather by a surge of water than pushes far inland. The waves comes in series, sometimes with many minutes passing from one to the next.

Waves a meter high can severely damage houses. A two-meter-high tsunami can destroy wooden buildings. Often the damage caused by receding waves being sucked to the sea is more severe than that caused by advancing waves. Receding waves can also drag people far out to sea.

The height of a wave can differ significantly depending on the contour of the land areas that are stricken. A narrow creek can funnel such waves, causing them to rise to a height of 10 meters. If the earthquake that generates the waves is nearby the waves come in rapid succession. If the earthquake is farther away the waves can arrive over a period of several hours.

Websites and Resources

tsunami refuge Good Websites and Sources: Wikipedia article on Tsunamis Wikipedia ; Surviving a Tsunami, Lessons from Chile, Hawaii and Japan pubs.usgs.gov ; Tsunami Warning System in Japan jma.go.jp/jma ; Tsunami Warnings from Japan Meteorological Agency jma.go.jp/en/tsunami ; Book: Tsunami: The Underrated Hazard by Edward Bryant. Tsunamis That Struck Japan Major Tsunamis in Japan in the 20th Century tsunami.civil.tohoku.ac.jp ; Major Earthquakes and Tsunamis in Japan in the 20th Century drgeorgepc.com ; 1933 Earthquake and Tsunami pdf file cidbimena.desastres.hn ; 1983 Tsunami drgeorgepc.com ; Report on the 1993 Tsunami nctr.pmel.noaa.gov ; Small Tsunami in 2010 reuters.com ;

Links in this Website: VOLCANOS AND JAPAN Factsanddetails.com/Japan ; MAJOR VOLCANOS AND ERUPTIONS IN JAPAN Factsanddetails.com/Japan ; EARTHQUAKES AND JAPAN Factsanddetails.com/Japan ; EARTHQUAKES AND LIFE IN JAPAN Factsanddetails.com/Japan ; LARGE EARTHQUAKES IN JAPAN Factsanddetails.com/Japan ; KOBE EARTHQUAKE OF 1995 Factsanddetails.com/Japan ; LARGE EARTHQUAKES IN JAPAN IN THE 2000s Factsanddetails.com/Japan ; TSUNAMIS IN JAPAN Factsanddetails.com/Japan

Good Websites and Sources on Earthquakes: U.S. Geological Survey (USGS) National Earthquake Information Center earthquake.usgs.gov ; Wikipedia article on Earthquakes Wikipedia ; Earthquake severity pubs.usgs.gov ; USGS Earthquake Frequently Asked Questions earthquake.usgs.gov/learn/faq ; 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 ; Interactive Earthquake Guide guardian.co.uk ; USGS Earthquakes for Kids earthquake.usgs.gov/learn/kids ; Earthquake Preparedness and Safety Surviving an Earthquake edu4hazards.org ; Earthquake Pamphlet pubs.usgs.gov ; Earthquake Preparedness Guide earthquakepreparednessguide.com ; Earthquake Safety Site earthquakecountry.info ;

USGS Earthquake Information for Japan Earthquake Information from Japan Meteorological Agency jma.go.jp/en/quake ; F-Net Broadband Seismography Network fnet.bosai.go.jp ; USGS Japan Earthquake Information earthquake.usgs.gov/earthquakes/world ; Tectonics and Volcanos of Japan volcano.oregonstate.edu ; MCEER Earthquake Engineering on Major Earthquakes in Japan in the 20th Century mceer.buffalo.edu ; Major Earthquakes in Japan in the 20th Century drgeorgepc.com ; Sesimic Hazard Map earthquake.usgs.gov ; Earthquake Density Map earthquake.usgs.gov ; Seismicity Map earthquake.usgs.gov ; Blogs About Japanese Earthquakes blogged.com/topics/japan-earthquake ; Geological Maps aist.go.jp/GSJ ; 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 ;U.S. Embassy Disaster Preparedness Checklist tokyo.usembassy.gov ; U.K. Embassy on Earthquake Preparedness v ; Report on Fastening Furniture pdf file iiasa.ac.at/Research/RAV ;Earthquake Preparedness Guide earthquakepreparednessguide.com ;

Earthquake Research in Japan: Headquarters of Earthquake Research Promotion jishin.go.jp ; Active Fault Research Center unit.aist.go.jp ; Institute of Geology and Geoinformation unit.aist.go.jp ; Tokai Earthquake Prediction from Japan Meteorological Agency jma.go.jp/en/quake_tokai ; Research Center for Earthquake Prediction, University of Kyoto rcep.dpri.kyoto-u.ac.jp ; Earthquake Prediction Research Center, Tokyo University eri.u-tokyo.ac.jp/ ; Earthquake and Science Museums Shinagawa City Disaster Prevention site city.shinagawa.tokyo.jp ; Earthquake Museum (Kita Ward, near the Nishigahara Station on the Naboku subway line), Tokyo Essentials tokyoessentials.com ; Honjo Life Safety Learning Center (Sumida Ward) simulates an earthquake and fire in a 3-D theater. There is also a room that simulates a storm with wind sped of 30 meters per second. Tokyo City PDF file bousai.metro.tokyo.jp

Recent Earthquakes in Japan : USGS Last Earthquake in Japan neic.usgs.gov/neis/last_event/world_japan ; Recent Earthquakes eri.u-tokyo.ac.jp ; Info for the Previous Week jma.go.jp/en/quake ; Major Earthquakes in Japan Wikipedia List of Earthquakes in Japan Wikipedia ; USGS Historic Earthquakes earthquake.usgs.gov/earthquakes/world/historical ;Major Earthquakes in Japan in the 20th Century drgeorgepc.com ; 1923 Tokyo Earthquake: 1923 Tokyo Earthquake Images eas.slu.edu/Earthquake_Center ; Great Kanto earthquake of 1923 dl.lib.brown.edu/kanto ; 1923 Tokyo Earthquake Photo Gallery japan-guide.com ; Earthquake Pictures: Earthquake Image Archive geot.civil.metro-u.ac.jp ; BBC Pictures of 2007 Niigata Earthquake BBC Pictures of 2007 Niigata Earthquake ; Kobe Earthquake Site seismo.unr.edu

Physics of Tsunamis

Tsunamis are caused when there is a movement of land on the ocean floor and this displaces water causing one area of water to be higher than an other. The water at the surface starts to shift downhill and that is what triggers the tsunami. Tsunamis tend to maintain their force as they travel through the deep seas at speeds of a jetliner. While normal waves are movements of water along the surface of the sea tsunamis are forces that move through the sea sort of like a series of dominoes knocking over the dominoes in front of it. When a tsunami strikes a shallow ocean bottom it loses some energy to friction. In the open sea there is nothing to slow it down.

Tsunami waves usually strike in a train of a dozen or more waves rather than a single wave with each wave slightly weaker that the one in front of it. The distance between the swells can be a be a kilometer or more.

Tsunamis waves generally radiate out in directions opposite from the seismic disturbance. They are distinguished from coastal waves in that can be very long and move at very high speeds. A single wave from a tsunami can be 160 kilometers long and move across the ocean at 965 kilometers per hour.

Tsunamis move like sound waves through the water and get slower and more powerful at the surface as they move through shallow water. When they approach the coast the slow dramatically as their wavelength shortens, causing them to rise up dramatically because of the enormous volume of water that piles up in the shallow water. The top travels at fast speed which increases its height.

A super powerful tsunami can move at 900kph in deep water, producing only a ripple at the surface, not even noticed by ships in the open sea. It slows to 300kph at the continental shelf and then suddenly rises to 20 meters when it hits the shore at 35 kph, potentially killing thousands. When a wave slows it does not lose energy it simply rearranges it. In many case the full energy of a tsunami is not released until it hits something.

When the water off the coast is very deep, tsunamis come a shore like a high tide that just keeps coming and coming. When the water is shallow large violent, breaking waves are more likely. When trains of waves hit shallow water the leading waves slows down first and the waves behind them slow down less rapidly and pile on from behind, shortened the distance between the waves and adding to the height of the leading waves. Hours after an earthquake tsunamis loose energy because of friction over the rough sea bottom and/or the dissipation of energy over long distances.

Causes of Tsunamis

Tsunamis can be caused by earthquakes, earthquake-induced landslides, non-earthquake landslides caused by water from aquifers, volcanic eruptions, and collapsing sea cliffs and explosions on volcanic islands, volcanic eruptions or meteor or asteroid impacts. The most common and destructive tsunamis are caused by earthquakes.

Large tsunamis are typically the result of quakes known as subduction earthquakes. They're the most powerful earthquakes on the planet, and they occur at plate boundaries, where one tectonic plate is grinding inexorably beneath another. When the bottom plate suddenly lurches deeper, a colossal amount of energy is released, unleashing the sorts of massive earthquakes and calamitous tsunamis that hit the Indian Ocean in 2004 and the coast of Japan in March 2011. Generally an earthquake of 7.5 of larger is needed to deform the sea bottom enough to displace enough water to produce tsunamis wave pulses that can travel long distances across the ocean. These earthquakes typically occur along thrust faults, where an ocean plate is thrust under a continental plate, dragging it down until the fault ruptures, causing an earthquake that cause the sea floor to rise.

Volcanic eruptions, the collapse of volcanic features and huge profusions of ash are all capable of producing a tsunami. The volcanic explosion of Krakatau in Indonesia and the collapse of its caldera produced 130-foot-high waves and killed 36,0000 people. There are concerns about specific volcanos triggering huge landslides that could generate tsunamis over 1000 feet high.

Landslides caused by earthquakes, rock falls or ice falls can produce enormous local tsunamis. Places that are vulnerable to these events include the unstable flanks of volcanos and continental shelves with huge deposit of sediments. Some of the largest tsunamis have been generated by earthquake-induced landslides. These can occur after any large earthquake, say 6.5 on the Richter scale and above. An earthquake in Lutuya Bay, Alaska in 1958 caused a massive rock fall that generated a tsunami that was 1,720 feet high, 267 feet higher than the Empire State Building. Fortunately it struck a wilderness area and did not travel across the sea to Japan or Hawaii.

An asteroid three of four miles in diameter crashing into the Atlantic Ocean could produce a tsunami large enough to wash over New York City and climb up the Appalachian mountains. A 53-mile-wide asteroid that landed in the Chesapeake Bay 35 million years is believed to have produced waves that were thousands of feet high. One that landed on land 65 million years is believed to have kicked up enough debris to cause the climate to change and the dinosaurs to become extinct.

Power of a Tsunami and Tsunami Water

According to the New York Times, “The power of a tsunami comes from straightforward physics. An earthquake suddenly pushes part of the sea floor up or down. That changes the height of the water above it — what physicists call potential energy — and the potential energy quickly changes into the kinetic energy of the tsunami waves.” [Source: New York Times

“In addition to the damage that a tsunami can inflict along coastlines in particular countries, it can also have an effect on the entire earth. The planet’s oceans are very heavy, applying enormous pressure to the ocean crust. When the distribution of that pressure is shifted, as it is during an earthquake, it can induce wobbles in the earth’s rotation.” [Ibid]

“It takes a lot of force just to keep water in place. More than three million cubic yards of concrete hold back the water behind Hoover Dam on the Nevada-Arizona border. At its base, the pressure of the water reaches 45,000 pounds per square foot. In that case, however, the enormous power of water is put to positive use: to generate electricity.”

On the force of the water generated by tsunamis the New York Times reported: “A typical bathtub holds 40 gallons or so of water. That is 330 pounds. A cubic yard of it, filling what at first glance seems a modest volume of 3 feet by 3 feet by 3 feet, weighs nearly 1,700 pounds, as much as the Smart micro car. And when water is moving at 30 or 40 miles an hour, like the tsunami that inundated northern Japan on Friday, the heaviness of water turns deadly. Imagine 1,700 pounds hitting you at that speed, and each cubic yard of water as another 1,700 pounds bearing down on you. The destructiveness of a tsunami is not just one runaway car, but a fleet of them. [Source: New York Times]

“That’s exactly the analogy to use,” Philip N. Froelich, a professor of oceanography at Florida State University, told the New York Times. “And by the time you’re talking about a wall of water that’s 10 meters high, if that wave is two miles long into the ocean, it’s basically like a hundred tanks coming across you. Even though it’s a fluid, it operates like a solid hammer.”

“Water does not act quite the same way as speeding cars,” the New York Times reported. “As a fluid, it can slip around some objects like round columns, while slamming full force when a large wall is in its way. It also gathers debris — dirt, cars, trees — as it flows. Those added projectiles can create more destruction as they crash into other objects. Even if the wave only comes up to the knees, the force is enough to knock a person down.”

Dangerous Tsunamis

It is difficult to predict the likelihood of a dangerous tsunami simply on the magnitude of earthquake. A lot of factors come into play: the kind of earth quake, where on the ocean floor it occurs, the depth of water, the distance from coastal areas, the configurations of harbors and bays and the topography of the land where a tsunami comes a shore.

A dangerous tsunami is more likely to develop in deep water than in shallow water. It is also more likely to develop if the movement of earth is large but concentrated in an small area rather than spread out over a large area. Destructive tsunami often occur where the water is channeled either in the sea or by land and focused on one area.

Generally an earthquake of a magnitude of more than 8.5 on the Richter scale is necessary to produce tsunamis that affect areas long distances away from the epicenter of an earthquake. Smaller earthquakes can generate powerful local tsunamis. But even large earthquakes do not necessarily produce large tsunamis. The worst tsunamis often occur when there is a huge vertical movement on ocean floor, causing sudden, large displacement of water. This contrasts to dangerous land earthquake which often have violent horizontal movements that cause violent shacking over a large area.

Obviously tsunamis are most dangerous when they hit places with a lot of people. Hotels and houses are built along beaches and harbors are particularly vulnerable. Coral reefs, marshes, forests and mangroves act as natural buffers. When they are removed or disturbed they remove obstacles that can slow a tsunami down.

Tsunami Detection

Tsunami detection is very difficult. Scientists use seismometers, sensitive devices used to detect earth movements and measuring earthquakes; tide gauges, that measure changes in the water surface level; and wave-sensing buoys. Water level gauges cost between $5,000 and $20,000 depending on the sensitivity the instruments and the quickness of their communication ability.

The most effective technology are deep ocean instruments called tsunameters than detect passing waves and transmit the information to satellites via buoys at the surface. They cost $250,000 a piece and require $50,000 a year for maintenance. As of 2005 there were only seven of them in operation.

In an efforts to create a global tsunami warning system, tsunami detection devices have been placed around the world on ocean floors at depths of up to 5,400 meters. Scientist have extensively mapped the ocean floor with the aim of finding out where potential tsunami-inducing areas are.

Tying the system together is a communication network that can relay data to a central data base and then disseminate the information quickly to places where the tsunamis may strike.

The world’s largest tsunami research center is run by Oregon State University. Composed of a hanger-size building with a 111-meter-long, 90-centimeter-deep wave pool, it is used mainly to study the effect of large tsunamis on buildings and infrastructure in coastal areas. Tests involve crashing waves on models in various landscapes with the goal of helping planners figure out where to place buildings, plan evacuation routes and design buildings and infrastructure. .

Tsunami Warnings and Escaping a Tsunami

If a very low tide occurs after an earthquakes, it means that a tsunami is approaching fast. During a tsunami the waves can keep coming. If you make it to high ground stay there for at least six hours.

Whether you can escape from the ensuing tsunami after feeling an earthquake's jolt is the difference between life and death. Shigeo Takahashi, director of the Asia-Pacific Center for Coastal Disaster Research at the Port and Airport Research Institute, told the Yomiuri Shimbun, “You must 'escape vertically' and, after evacuating, don't leave until your safety is confirmed."

"Even if you run, a high-speed tidal wave will catch up with you at ground level," said Shigeo Takahashi, director of the Asia-Pacific Center for Coastal Disaster Research at the Port and Airport Research Institute. "You should use a car or anything-whatever means available-to escape [as fast as possible] to higher ground. If there is no higher ground nearby, you should go to a strong-looking building or a pedestrian bridge." Such a building should be, at the very least, more than three stories, he added.

A tsunami warning system for the Pacific Ocean has existed for decades. Headquartered in Hawaii, it issues warnings to 26 nations and was set up in 1965 after devastating tsunamis in Chile and Alaska in the early 1960s. The system analyzes earthquake data from several seismic networks. The information is fed into a computer and models predict were tsunamis might form and strike, and predictions and warnings are dispatched to affected areas. As new data comes in the information is updated. Hawaii is outfit with sirens to warn people of approaching tsunamis.

Where Tsunamis Occur

About 85 percent are tsunami are produced in the Pacific Ocean. Most are generated in the Pacific rim because more undersea earthquakes are generated there than anywhere else. More than 800 tsunamis have been generated in the Pacific in the last century. Some 22 percent of these were generated off of Japan

Tsunami occur much less frequently in the Atlantic Ocean and Indian Ocean. But they the do occur there. One in 1945 killed several hundred people in Bombay. Another in 1762 ravaged a large part of what is now Bangladesh and other parts of the Bay of Bengal.

Between 1992 and late 2004 there were 17 major tsunamis, with 11 of them in the Pacific. They killed a total of 4,000 people.

Videos of the Tsunami

Collections of Tsunami Video

Video of Geology of 2011 Tsunami

Video of 2011 Earthquake in Northern Japan

Video of Tsunami Waves and Whirlpools

Video of Tsunamis Waves Coming Ashore

Video of Boats and Cars Tossed by Tsunami

Video of Tsunamis Hitting Towns

Video of Tsunami Hitting Sendai Area

Video of Tsunami Hitting Minamisanriku

Video of Tsunami Flooding

Video of Tsunami Survivors

Video of Tsunami Survivor Stories

Image Sources: USGS, Tokyo University, YouTube,

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

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© 2008 Jeffrey Hays

Last updated January 2013