JJJuneuneune,, 200520052005

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P R E S E N T E D B Y:

UNESCO INTERGOVERNMENTAL OCEANOGRAPHIC COMMISSION (IOC)

INTERNATIONAL TSUNAMI INFORMATION CENTRE (ITIC)

LABORATOIRE DE GEOPHYSIQUE, FRANCE (LDG)

U. S. NATIONAL OCEANIC & ATMOSPHERIC ADMINISTRATION (NOAA)

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The purpose of this brochure is to

increase awareness and knowledge of

tsunamis. Please share what you learn;

knowing the right information may save

your life and the lives of those you love.

Left: Computer model of the initial water surfacechanges at the time the July 30, 1995, Chilean tsunamiwas generated. A is Antofagasta, Chile.Right: Computer model of the same tsunami, threehours after it was generated.

The phenomenon we call "tsunami" (soo-NAH-mee) isa series of traveling ocean waves of extremely long lengthgenerated primarily by earthquakes occurring below ornear the ocean floor. Underwater volcanic eruptions andlandslides can also generate tsunamis. In the deep ocean,the tsunami waves propagate across the deep ocean witha speed exceeding 800 kilometers per hour ([km], ~500miles per hour), and a wave height of only a few tens ofcentimeters (1 foot [ft]) or less. Tsunami waves are dis-tinguished from ordinary ocean waves by their great lengthbetween wave crests, often exceeding 100 km (60 miles[mi]) or more in the deep ocean, and by the time betweenthese crests, ranging from 10 minutes to an hour.

As they reach the shallow waters of the coast, the wavesslow down and the water can pile up into a wall of destruc-tion tens of meters (30 ft) or more in height. The effect canbe amplified where a bay, harbor or lagoon funnels thewave as it moves inland. Large tsunamis have been knownto rise over 30 meters (100 ft). Even a tsunami 3–6 meters(m) high can be very destructive and cause many deathsand injuries.

Tsunamis are a threat to life and property for all coastalresidents living near the ocean. During the 1990s, over4,000 people were killed by 10 tsunamis, including morethan 1000 lives lost in the 1992 Flores region, Indonesia,and 2200 lives in the 1998 Aitape, Papua New Guineatsunamis. Property damage was nearly one billion UnitedStates (U.S.) dollars. Although 80% of all tsunamis occur

in the Pacific, they can also threaten coastlines of countriesin other regions, including the Indian Ocean, MediterraneanSea, Caribbean region, and even the Atlantic Ocean. Themost devastating tsunami occurred in December 2004, whena M9.0 earthquake off of northwestern Sumatra, Indonesiaproduced a destructive tsunami that attacked coasts through-out the Indian Ocean, killing 300,000 people, displacing morethan one million people, and causing billions of dollars ofproperty damage.

At the Richard H. Hagemeyer Pacific Tsunami WarningCenter (PTWC), the operational center of the Tsunami WarningSystem in the Pacific (TWSP), scientists monitor seismolog-ical and water level stations throughout the Pacific Basin,evaluate potentially tsunamigenic earthquakes, monitor tsuna-mi waves, and disseminate tsunami warning information. ThePTWC provides international tsunami warning information tonational authorities in the Pacific Basin. Regional WarningCentres are also operating in Japan, French Polynesia, andChile, in addition to the United States. As a result of the 2004great tsunami, tsunami warning systems are now being imple-mented globally, including in the Indian Ocean, Caribbean Sea,Atlantic Ocean, and Mediterranean Sea.

The UNESCO IOC International Tsunami Information Centre,hosted by the U.S., monitors and evaluates the performanceand effectiveness of the TWSP, assists in the establishment ofnew warning systems, and serves as an educational and infor-mation resource in support of the IOC’s Tsunami Programme.

Hilo Harbor, Hawaii, April 1, 1946, Aleutian Islands earthquake.Photo taken from the vessel Brigham Victory of tsunami breakingover Pier 1. The gentleman on the left did not survive. (NOAA)

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PLATE TECTONICSPlate Tectonic theory is based on an earth model char-

acterized by a small number of lithospheric plates, 70 to250 km (40 to 150 mi) thick, that float on a viscous under-layer called the asthenosphere. These plates, whichcover the entire surface of the earth and contain both thecontinents and seafloor, move relative to each other atrates of up to ten cm/year (several inches/year). Theregion where two plates come in contact is called a plateboundary, and the way in which one plate moves relativeto another determines the type of boundary: spreading,where the two plates move away from each other; sub-duction, where the two plates move toward each other andone slides beneath the other; and transform, where thetwo plates slide horizontally past each other. Subductionzones are characterized by deep ocean trenches, and

the volcanic islands or volcanic mountainchains associated with the many subduc-tion zones around the Pacific rim are some-times called the Ring of Fire.

EARTHQUAKES ANDTSUNAMIS

An earthquake can be caused by vol-canic activity, but most are generated bymovements along fault zones associatedwith the plate boundaries. Most strongearthquakes, representing 80% of the total

energy released worldwide by earthquakes, occur in sub-duction zones where an oceanic plate slides under a con-tinental plate or another younger oceanic plate.

Not all earthquakes generate tsunamis. To generate atsunami, the fault where the earthquake occurs must beunderneath or near the ocean, and cause vertical move-ment of the seafloor (up to several meters) over a largearea (up to a hundred thousand square kilometers). Shallowfocus earthquakes (depth less 70 km or 42 mi) along sub-duction zones are responsible for most destructivetsunamis. The amount of vertical and horizontal motionof the sea floor, the area over which it occurs, the simul-taneous occurrence of slumping of underwater sedimentsdue to the shaking, and the efficiency with which energyis transferred from the earth’s crust to the ocean water areall part of the tsunami generation mechanism.

sunamis, also called seismic sea wavesor incorrectly tidal waves, are causedgenerally by earthquakes, less com-

monly by submarine landslides, infrequently bysubmarine volcanic eruptions and very rarelyby large meteorite impacts in the ocean.Submarine volcanic eruptions have the poten-tial to produce truly awesome tsunami waves.The Great Krakatau Volcanic Eruption of 1883generated giant waves reaching heights of 40meters above sea-level, killing more than 30,000 people and wiping out numerous coastal villages.

All oceanic regions of the world can experi-ence tsunamis, but in the Pacific Ocean and itsmarginal seas, there is a much more frequentoccurrence of large, destructive tsunamisbecause of the many large earthquakes alongthe margins of the Pacific Ocean.

Tsunami generated by December 26, 2004, M9.0 north-west Sumatra earthquake approaching Hat Rai LayBeach, Krabi, southern Thailand. Foreign touristsscramble for safety in advance of the first of six tsuna-mi waves after venturing out when the water firstreceded (AFP/AFP/Getty Images).

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TSUNAMI: THE RELATIONWITH THE SEISMIC SOURCE

FOCUS

TSUNAMI EARTHQUAKESThe September 2, 1992 earthquake (magnitude 7.2) was

barely felt by residents along the coast of Nicaragua.Located well off-shore, its intensity, the severity of shak-ing on a scale of I to XII, was mostly II along the coast,and reached III at only a few places. Twenty to 70 min-utes after the earthquake occurred, a tsunami struck thecoast of Nicaragua with wave amplitudes 4 m (13 ft) abovenormal sea level in most places and a maximum runupheight of 10.7 m (35 ft). The waves caught coastal resi-dents by complete surprise and caused many casualtiesand considerable property damage.

This tsunami was caused by a tsunami earthquake —an earthquake that produces an unusually large tsunami

relative to the earthquake magnitude. Tsunami earth-quakes are characterized by a very shallow focus, faultdislocations greater than several meters, and fault surfacesthat are smaller than for a normal earthquake.

They are also slow earthquakes, with slippage alongthe fault beneath the sea floor occurring more slowly thanit would in a normal earthquake. The only known methodto quickly recognize a tsunami earthquake is to estimatea parameter called the seismic moment using very longperiod seismic waves (more than 50 seconds / cycle).Two other destructive and deadly tsunamis from tsuna-mi earthquakes have occurred in recent years in Java,Indonesia (June 2, 1994) and Peru (February 21, 1996).

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The earthquake focus is the point in the earth where therupture first occurs and where the first seismic wavesoriginate. The epicenter is the point on the Earth’s sur-face directly above the focus.

The magnitude is a measure of the relative size of anearthquake. A number of different magnitude scalesexist besides the Richter scale, including the momentmagnitude which measures the energy released andgives the most reliable estimate for large earthquakes.An increase in one unit of magnitude corresponds to afactor of 10 increase in seismic wave amplitude, and a30-fold increase in released energy. The momentmagnitude is measurable nearly immediately thanks tothe advent of modern seismometers, digital recording,and real-time communication links. This allows warn-ing centres to provide initial tsunami advisories withinminutes after the earthquake’s occurrence.

El Transito, Nicaragua, September 1, 1992. Nine-meter high waves destroyed the town, killing 16 andinjuring 151 in this coastal community of 1,000 peo-ple. The first wave was thought to be small provid-ing time for people to escape the destructive secondand third waves. More than 40,000 people were affect-ed by the loss of their homes or means of income.(Harry Yeh, Univ. of Washington)

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The last large tsunami that caused wide-spread death and destruction was generatedin the Pacific by an earthquake located off thecoast of Chile in 1960. It caused loss of lifeand property damage not only along the Chilecoast, but in Hawaii and as far away as Japan22 hours later. The Great Alaskan Earthquakeof 1964 produced deadly tsunami waves inAlaska, Oregon and California.

In July 1993, a tsunami generated in theSea of Japan killed over 120 people in Japan.

Damage also occurred in Korea andRussia but not in other countries sincethe tsunami wave energy was confinedwithin the Sea of Japan. The 1993 JapanSea tsunami is known as a "regionalevent" since its impact was confined toa relatively small area. For people livingalong the northwestern coast of Japan,the tsunami waves followed the earth-quake within a few minutes.

During the 1990s, destructive region-al tsunamis also occurred in Nicaragua,Indonesia, the Philippines, Papua NewGuinea, and Peru, killing thousands ofpeople. Others caused property dam-age in Chile and Mexico. Some damagealso occurred in the far field in the

Marquesas Islands (French Polynesia) fromthe July 30, 1995, Chilean and February 21,1996, Peruvian tsunamis.

In less than a day, tsunamis can travel fromone side of the ocean to the other. However,people living near areas where large earth-quakes occur may find that the tsunami waveswill reach their shores within minutes of theearthquake. For these reasons, the tsunamithreat to many areas, e.g., Alaska, thePhilippines, Japan, Indonesia and the U.S.West Coast, can be immediate for tsunamisfrom nearby earthquakes which take only afew minutes to reach coastal areas, or lessurgent for tsunamis from distant earthquakeswhich take from three to 22 hours to reachcoastal areas.

In the open ocean a tsunami is less than a few tens of centimeters (1 ft) highat the surface, but its wave height increases rapidly in shallow water.Tsunami wave energy extends from the surface to the bottom in even thedeepest waters. As the tsunami attacks the coastline, the wave energy iscompressed into a much shorter distance and a much shallower depth,creating destructive, life-threatening waves.

n the deep ocean, destructive tsunamis can be small – oftenonly a few tens of centimeters or less in height – and cannotbe seen nor felt on ships at sea. But as the tsunami reach-

es shallower coastal waters, wave height can increase rapidly.Sometimes, coastal waters are drawn out into the ocean justbefore the tsunami strikes. When this occurs, more shoreline maybe exposed than even at the lowest tide. This major withdrawalof the sea should be taken as a natural warning sign thattsunami waves will follow.

213 km 23 km

10.6 km

4000 m

50 m10 m

Depth(meters)7000400020002005010

Velocity(km/h)9437135041597936

Wave length(km)2822131514823

10.6

Tsunami Speed is reduced in shallow water as wave height increases rapidly.

OCEAN-WIDE AND REGIONAL TSUNAMIS

Sea level records of the tsunami recorded at Sibolga on the northwestcoast of Sumatra, Indonesia, and Male, Hulule, Maldive Islands from theDecember 26, 2004 tsunami that caused ocean-wide destruction. Thefirst wave was not the largest at Sibolga. Vertical axis in meters.(University of Hawaii Sea Level Center, BAKOSURTANAL, Indonesia)

Sibolga, Indonesia

Male, Hulule, Maldives

210

-1

210

-1

I

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HOWFAST?

Where the oceanis over 6,000 mdeep, unnoticedtsunami wavescan travel at thespeed of a com-mercial jet plane,over 800 km perhour (~500 miper hour). Theycan move fromone side of thePacific Ocean tothe other in lessthan a day. This

great speed makes it important to be aware of the tsunami as soon as it is generated.Scientists can predict when a tsunami will arrive at various places by knowing the sourcecharacteristics of the earthquake that generated the tsunami and the characteristics of theseafloor along the paths to those places. Tsunamis travel much slower in shallower coastalwaters where their wave heights begin to increase dramatically.

HOW BIG?Offshore and coastal features can determine the size and impact of tsunami waves. Reefs,bays, entrances to rivers, undersea features and the slope of the beach all help to modifythe tsunami as it attacks the coastline. When the tsunami reaches the coast and moves

inland, the water level can rise many meters. In extreme cases, water level has risen tomore than 15 m (50 ft) for tsunamis of distant origin and over 30 m (100 ft) for tsunamiwaves generated near the epicenter. The first wave may not be the largest in the seriesof waves. One coastal community may see no damaging wave activity while in anothernearby community destructive waves can be large and violent. The flooding can extendinland by 300 m (~1000 ft) or more, flooding large expanses of land with water and debris.

HOW FREQUENT?Since scientists cannot predict when earthquakes will occur, they cannot determine exact-ly when a tsunami will be generated. However, by looking at past historical tsunamis, sci-entists know where tsunamis are most likely to be generated. Past tsunami height mea-surements are useful in predicting future tsunami impact and flooding limits at specificcoastal locations and communities. Paleotsunami research, in which scientists look forsediments deposited by giant tsunamis, is helping to extend the documented historical tsuna-mi record further back in time. As more events are found, better estimates of the frequencyof occurrence of tsunamis in a region are obtained. During each of the last five centuries,there were three to four Pacific-wide tsunamis, most of them generated off the Chilean coasts.The tsunami on December 26, 2004 claimed 300,000 lives and caused damage through-out the Indian Ocean, making it the worst tsunami catastrophe in history. It was also thefirst known basin-wide destructive tsunami in the Indian Ocean.

Maximum calculated global wave heights (cm) from the December26, 2004 Indian Ocean tsunami. Waves were recorded on sea levelgauges in Antarctica, and along the coasts of South and North Americaand Canada in both the Pacific and Atlantic Oceans (NOAA PMEL).

During post-tsunami field surveys, inundation and runup measurements are takento describe the tsunami effects. Inundation is the maximum horizontal distanceinland that a tsunami penetrates. Runup is the maximum vertical height abovemean sea level that the sea surface attains during a tsunami. Actual tsunamiwave heights can be measured from the amplitude of the wave signals seen onsea level or tide gauge instruments.

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Calculated tsunami travel times for the December 26, 2004earthquake off western Sumatra. Each concentric curve repre-sents 30 minutes of tsunami travel time. Destructive tsunami hitIndonesia in 15 minutes, Sri Lanka in two hours, and Kenyanine hours after the earthquake (NOAA PMEL).

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The Wave. Painting by Lucas Rawah of Aitape, done to commemoratethe July 17, 1998, Papua New Guinea event. A magnitude 7.1 earth-quake is thought to have triggered a submarine landslide generatinga tsunami that destroyed entire villages along the Aitape coast.

International Tsunami Information Centre (ITIC) Located in Honolulu, Hawaii, the ITIC serves as the information service forthe IOC’s Tsunami Programme. The ITIC’s responsibilities include monitor-ing and recommending improvements to the international tsunami warningsystem, helping Member States to establish regional and national tsunamiwarning systems, supporting technology transfer through training programmesin tsunamis, and serving as an information clearinghouse for the promotionof research, and the development and distribution of educational and pre-paredness materials to mitigate against the tsunami hazard. The ITIC regu-larly publishes the Tsunami Newsletter, maintains a tsunami library, hosts aBulletin Board listserve, and conducts the IOC’s Training Programme intsunamis and tsunami warning systems.

Kodiak, Alaska. The March 27, 1964, tsunamicaused 21 deaths and $30 million U.S. dollarsin damage in and near the city of Kodiak.

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TInformation about the IOC

The Intergovernmental Oceanographic Commission (IOC),a body with functional autonomy within the United NationsEducational, Scientific and Cultural Organization (UNESCO),provides Member States with an essential mechanism forglobal co-operation in the study of the ocean. The IOC assistsgovernments to address their individual and collective oceanand coastal problems through the sharing of knowledge, infor-mation and technology and through the coordination of nation-al and regional programs.

The functions of the IOC are to develop, recommend andcoordinate international programs for scientific study of theoceans and related ocean services; to promote and make rec-ommendations for the exchange of oceanographic data andthe publication and dissemination of scientific investigationresults; to promote and coordinate the development and trans-fer of marine science and its technology; to make recom-mendations to strengthen education and training and to pro-mote scientific investigation of the oceans and application ofthe results thereof for the benefit of all mankind. 129 MemberStates are currently part of the IOC. The Assembly meetsevery two years at the UNESCO headquarters in Paris, France.

The IOC consists of an Assembly, an Executive Council, aSecretariat and such subsidiary bodies as it may establish.Under this concept, the Commission has created Global andRegional Programmes which examine and execute specificprojects, or consist of committees composed of MemberStates interested in such projects. This is the case for theInternational Coordination Group for the International TsunamiWarning System (ICG/ITSU).

TSUNAMI WARNING CENTERSThe IOC is coordinating the implementation of the global

tsunami warning and mitigation system, building upon itsexperiences in the Pacific to establish warning systems for theIndian Ocean, Caribbean Sea, and the Mediterranean Sea.The Richard H. Hagemeyer Pacific Tsunami Warning Center(PTWC) serves as the international warning center for thePacific. This international warning effort became a formalarrangement in 1965 when PTWC assumed responsibility asthe operational center for the Tsunami Warning System in thePacific. The ICG/ITSU, presently comprised of 27 MemberStates, oversees warning system operations and facilitatescoordination and cooperation in all international tsunamimitigation activities. Since April 2005, the PTWC and JapanMeteorological Agency (JMA) have been cooperatively pro-viding interim warning services for the Indian Ocean.

The initial objective of PTWC is to detect, locate and deter-mine the seismic parameters of potentially tsunamigenic earth-quakes occurring in the Pacific Basin or its immediate mar-gins. To accomplish this, it continuously receives seismographicdata from more than 150 stations around the world throughcooperative data exchanges with the U.S. Geological Survey,Incorporated Research Institutions for Seismology, InternationalDeployment of Accelerometers, GEOSCOPE, the U.S. WestCoast/Alaska Tsunami Warning Center (WC/ATWC), and othernational and international agencies running seismic networks.

If an earthquake has the potential to generate a destructivetsunami based on its location, depth, and magnitude, a tsuna-mi warning is issued to warn of an imminent tsunami hazard.Initial warnings apply only to areas the tsunami could reach with-in a few hours and bulletins include the predicted tsunami arrivaltimes at selected coastal communities within those areas.Communities located outside those areas are put into either atsunami watch or advisory status.

Warning centre scientists then monitor incoming sea leveldata to determine whether a tsunami has occurred. If a sig-nificant tsunami with long-range destructive potential is detect-ed, the tsunami warning is extended to the entire Pacific or

Indian Basin. PTWC receives sea level data from more than100 stations through global data exchanges with the U.S.National Ocean Service, WC/ATWC, the University of HawaiiSea Level Center, Chile, Australia, Japan, Russia, FrenchPolynesia, and other international sources. Tsunami warn-ings, watches, and information bulletins are disseminated toappropriate emergency officials and the general public by avariety of communication methods.

Countries may operate National or Regional Centres to pro-vide more rapid or detailed warnings for regional or localtsunamis. The JMA provides local warnings to Japan, and itsNorthwest Pacific Tsunami Advisory Center provides regionaltsunami wave forecasts to Russia, Korea, China, Philippines,Indonesia, Papua New Guinea, and to the North Pacific forevents in the Japan Sea and northwest Pacific. The CentrePolynesien de Prevention des Tsunamis provides regionalwarnings in French Polynesia. In the US, the WC/ATWC warnsAlaska, the U.S. West Coast and Canada, and PTWC provideswarnings locally to Hawaii, regionally to US Pacific interests,and assists warning authorities in Puerto Rico. Chile, Peru, andRussia have operated national warning systems for decades.

The IOC believes that sustainable regional warning systemsmust be built through international, multilateral cooperation.Free and open data and information exchange is paramountas the system should be owned by and provide services toevery country in the region. While national centres may joint-ly operate international detection networks, each nation mustbe responsible for issuing its own national tsunami warningsand for protecting its own population. National warning cen-tres must therefore build strong links with emergency pre-paredness agencies so that warnings ultimately reach all house-holds. Warning centres can also serve as backups shouldanother centre become disabled, and can be focal points forawareness, education and other mitigation activities.

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April 1, 1946. People flee as a tsunami attacksdowntown Hilo, Hawaii (Bishop Museum Archives)

DATASIGNAL

ACOUSTIC

DATA S

IGNAL

PRESSURESENSOR

DATAPROCESSING

MODULE

WARNINGCENTER

VIA SATELLITE

NOAA/PMEL

DEEP-OCEAN ASSESSMENT ANDREPORTING ON TSUNAMIS (DART Project)

INDEPENDENT 3 COMPONENT BROAD -BAND SEISMIC STATION

An effective tsunami early warning system isachieved when all persons in vulnerable coastal com-munities are prepared and respond appropriately, andin a timely manner, upon recognition that a potentiallydestructive tsunami is coming. Timely tsunami warn-ings issued by a recognized tsunami warning centreare essential. When these warning messages arereceived by the designated government agency,national tsunami emergency response plans mustalready be in place so that well-known and practicedactions are immediately taken to evaluate the scien-tifically-based warning, and communicate an appro-priate course of action to ordinary citizens. Tsunamipreparedness programmes must already have start-ed so that good decisions can be made without delay.

Essential activities of an effective warning system are:- Identification of the tsunami hazard, assessment ofrisk, and mitigation to reduce wave impact. Tsunamievacuation maps which show where flooding is likelyare based on this information.- Issuance of timely warnings. For a distant tsunami,real-time earthquake and sea level monitoring to con-firm the generation of a destructive tsunami, followedby immediate dissemination to the public, is critical. Fora local tsunami where there may not be time for an offi-cial warning, people must already know a tsunami's nat-ural warning signals and respond immediately.- Continuous and sustained awareness activities.Education is fundamental to building an informed cit-izenry and to ensure that the next generation is equal-ly prepared. Political support, laws and regulations,and institutional responsibility are key.

An effective tsunami warning system reachesall persons in danger before the wave hits

DASE/LDG

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LEFT: July 30, 1995,Chilean Tsunami.Model results showingthe maximum run-upand inundation relativeto the normal sea leveland shoreline (whiteline) at Tahauku Bay,Hiva Hoa, in theMarquesas Islands,French Polynesia. Twosmall boats sunk inTahauku Bay as aresult of this event.

BELOW: Model of thetsunami in the south-east Pacific, nine hoursafter its generation.

Tsunami Research Activities

★

Although a tsunami cannot be prevented, its impact can be mitigatedthrough community preparedness, timely warnings, effectiveresponse, and public education. The U.S. National Tsunami HazardMitigation Program is a good example of a comprehensive effort toreduce tsunami risks.

With the broad availability of relatively inexpensive yetpowerful computers and desktop workstations, there isgrowing interest and activity in tsunami research. Usingthe latest computer technology, scientists can numericallymodel tsunami generation, open ocean propagation, andcoastal runup.

Ocean-bottom pressure sensors, able to measuretsunamis in the open ocean, are providing important dataon tsunami propagation in deep water, and satellite com-munications have enabled the data to be used in real timeto detect and measure tsunami waves in the deep ocean.NOAA’s Pacific Marine Environmental Laboratory pio-neered development of these tsunami detection buoysand the numerical modeling tools required to operationallyestimate coastal impact. By the end of 2005, at leastseven DART buoys will be in operation in the north andeast Pacific and available for use by the tsunami warningcentres. Better equipment and numerical modeling meth-ods help scientists better understand tsunami generation.

Seismologists, studying the dynamics of earthquakeswith broad band seismometers (20 to 0.003 Hertz), are for-mulating new methods to analyze earthquake motion and

the amount of energy released. Where thetraditional Richter (surface wave) magnitude ofearthquakes is not accurate above 7.5, theseismic moment and the source duration arenow used to better define the amount of ener-gy released and the potential for tsunami gen-eration. Real-time determination of earthquakedepth, type of faulting, and extent and direc-tion of slippage will significantly improve thewarning centres’ ability to identify the likelihoodof a threatening tsunami.

Tsunami generation is initiated by the three-dimensional deformation of the ocean bottom due to faultmovement. Better characterizations of the earthquakefault mechanism will produce more realistic numericalmodels of propagation, runup, and inundation.

Tsunami inundation models, defining the extent of coastalflooding, are an integral aspect of tsunami hazard andpreparedness planning. Using worst-case inundation sce-narios, these models are critical to defining evacuationzones and routes so that coastal communities can beevacuated quickly when a tsunami warning is issued.

RUN-UP MAXIMUM

ATUONA

BAY

TAH

AU

KU

BAY

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THE FACTS• Tsunamis that strike coastal locations are almost always caused

by earthquakes. The earthquakes might occur far away or nearwhere you live. While earthquakes occur in all ocean basinsaround the world, most do not generate tsunamis.

• Some tsunamis can be very large. In coastal areas theirheight can be as great as 10 m or more (30 m in extremecases), and they cause impacts like flash floods. Laterwaves are often full of debris.

• All low lying coastal areas can be struck by tsunamis.

• A tsunami consists of a series of waves with crests arrivingevery 10 to 60 minutes. Often the first wave may not be thelargest. The danger from a tsunami can last for severalhours after the arrival of the first wave. Tsunami waves typ-ically do not curl and break, so do not try to surf a tsunami!

• Tsunamis can move faster than a person can run.

• Sometimes a tsunami initially causes the water near theshore to recede, exposing the ocean floor.

• The force of some tsunamis is enormous. Large rocks weigh-ing several tons, along with boats and other debris, can bemoved inland hundreds of meters by tsunami wave activity,and homes and buildings destroyed. All this material andwater move with great force, and can kill or injure people.

• Tsunamis can occur at any time, day or night.

• Tsunamis can travel up rivers and streams from the ocean.

• Tsunami can easily wrap around islands and be just asdangerous on coasts not facing the source of the tsunami.

Be aware of tsunami facts.This knowledge could save your life!

Share this knowledge with yourrelatives and friends.It could save their lives!

- If you are in school and you hear there is a tsuna-mi warning, you should follow the advice of teach-ers and other school personnel.

- If you are at home and hear there is a tsunami warn-ing, make sure your entire family is aware. Preparea family emergency plan beforehand so that every-one knows what to do. Your family should evacu-ate your house if you live in a tsunami evacuationzone. Move in an orderly, calm, and safe mannerto the evacuation site or to any safe place outsideyour evacuation zone. Follow the advice of localemergency and law enforcement authorities.

- If you are at the beach or near the ocean and youfeel the earth shake, move immediately to higherground. DO NOT WAIT for a tsunami warning to beannounced. Stay away from rivers and streams thatlead to the ocean as you would stay away from thebeach and ocean if there is a tsunami. A tsunamifrom a local earthquake could strike some areasbefore a tsunami warning can be announced.

- Tsunamis generated in distant locations will gen-erally give people enough time to move to higherground. For locally generated tsunamis, where youmight feel the ground shake, you may only have afew minutes to move to higher ground.

- High, multi-story, reinforced concrete hotels arelocated in many low-lying coastal areas. The upperfloors can provide a safe place to find refuge shouldthere be a tsunami warning and you cannot movequickly inland to higher ground. Local Civil Defenseprocedures may, however, not allow this type ofevacuation in your area. Homes and small buildingslocated in low-lying coastal areas are not designedto withstand tsunami impacts. Do not stay in thesestructures should there be a tsunami warning.

- Offshore reefs and shallow areas may help breakthe force of tsunami waves, but large and danger-ous waves can still be a threat to coastal residentsin these areas. Staying away from all low-lyingcoastal areas is the safest advice when there is atsunami warning.

WHAT YOU SHOULD DO

Oga Aquarium,Akita Japan.Parking lot ofaquarium isflooded strand-ing car duringthe May 26,1983, JapanSea tsunami.(Takaaki Uda,Public WorksResearchInstitute,Japan)

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Since tsunami wave activity is imperceptible inthe open ocean, do not return to port if you are atsea and a tsunami warning has been issued foryour area. Tsunamis can cause rapid changes inwater level and unpredictable dangerous currentsin harbors and ports.

If there is time to move your boat or ship fromport to a location where the water is more than400m deep (and after you know a tsunami warn-ing has been issued), you should weigh the fol-lowing considerations:

- Most large harbors and ports are under the con-trol of a harbor authority and/or a vessel traffic sys-tem. These authorities direct operations duringperiods of increased readiness, including the forcedmovement of vessels if deemed necessary. Keepin contact with the authorities should a forcedmovement of vessels be directed.

- Smaller ports may not be under the control of aharbor authority. If you are aware there is a tsuna-mi warning, be sure you have enough time to motoryour vessel safely into deep water. Small boatowners may find it safest to leave their boat at thepier and physically move to higher ground, par-ticularly in the event of a locally-generated tsuna-mi. Concurrent severe weather conditions (roughseas outside of the harbor) could present a greaterhazardous situation to small boats, so physicallymoving yourself to higher ground may be the onlyoption.

- Damaging wave activity and unpredictable cur-rents can affect harbors for a period of time fol-lowing the initial tsunami impact on the coast.Contact the harbor authority before returning toport making sure to verify that conditions in theharbor are safe for navigation and berthing.

July 30, 1995 , Chilean Tsunami. Left: An observation of the tsunamieffects behind the breakwater at Tahauku Bay in the Marquesas Islands,French Polynesia, several thousand kilometers away from the tsunamisource. Right: Currents in Tahauku Bay based on numerical model-ing of the Chilean tsunami. The modeling reproduces the same kindsof ocean currents seen in the photo.

IF YOU ARE ON A SHIP OR BOAT

Banda Aceh, Sumatra,Indonesia. The tsunami of

December 26, 2004 com-pletely razed coastal towns

and villages, leavingbehind only sand, mud,

and water (middle) whereonce there had been thriv-

ing communities of homes,offices, and green space

(top). (DigitalGlobeQuickBird satellite

imagery, US Navy photo)

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As dangerous as tsunamis are, they do not happenvery often. You should not let this natural hazarddiminish your enjoyment of the beach and ocean.

But, if you think a tsunami may be coming, the groundshakes under your feet, the ocean recedes out to seaexposing the sea bottom, you hear the train-like roarof the tsunami, or you know that there is a warning,tell your relativesand friends, and

MoveQuicklyInland andto HigherGround!

North Shore ofOahu, Hawaii.During the tsunamigenerated by theMarch 9, 1957,Aleutian Islandearthquake, peoplefoolishly searchedfor fish on theexposed reef,unaware that tsuna-mi waves wouldreturn in minutes toinundate the shore-line. (Honolulu Star-Bulletin)

Pagaraman, BabiIsland, Indonesia,December 12, 1992.Tsunami washedaway everythingleaving only whitebeach sand. Sevenhundred peoplewere killed by theearthquake andensuing tsunami.(Harry Yeh, Univ. ofWashington)

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ACKNOWLEDGMENTSTHE PREPARATION OF THIS BROCHURE WAS SUPPORTED BY:UNESCO, Intergovernmental Oceanographic CommissionUNESCO IOC International Tsunami Information CentreLaboratoire de Geophysique, FranceU.S. Department of Commerce, National Oceanographic and Atmospheric Administration

TECHNICAL GUIDANCE PROVIDED BY:International Tsunami Information Centre, http://www.tsunamiwave.infoLaboratoire de Geophysique, France, http://www-dase.cea.frU.S. National Weather Service

Richard H. Hagemeyer Pacific Tsunami Warning Center, http://www.prh.noaa.gov/ptwcWest Coast / Alaska Tsunami Warning Center, http://wcatwc.arh.noaa.gov

U.S. National Ocean Service, http://www.nos.noaa.govU.S. National Geophysical Data Center, http://www.ngdc.noaa.govU.S. Pacific Marine Environmental Laboratory, http://www.pmel.noaa.govServicio Hidrografic y Oceanografic, Chile, http://www.shoa.clSchool of Ocean & Earth Science & Technology, University of Hawaii, http://www.soest.hawaii.edu

FURTHER INFORMATION ON TSUNAMI WARNING SYSTEMS,ICG/ITSU, ITIC, AND TSUNAMIS MAY BE OBTAINED FROM:

International Tsunami Information Centre737 Bishop St., Suite 2200Honolulu, HI 96813 USATel: <1> 808-532-6422, Facsimile: <1> 808-532-5576EMAIL: itic.tsunami@noaa.gov http://ioc.unesco.org/itsu, http://www.tsunamiwave.info

UNESCO, Intergovernmental Oceanographic Commission1, rue Miollis75732 Paris Cedex 15 FranceEMAIL: p.pissierssens@unesco.org

Printing of this booklet sponsored by the State of HawaiiCoastal Zone Management Program... partnering to reduce the risks of tsunami hazards.

Illustrations and Layout by Joe Hunt Design, Honolulu, Hawaii, and ITIC Background images and wave logo courtesy of Aqualog, France@ UNESCO IOC ITIC, Revised and Reprinted, June, 2005

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