20082008

IOC Brochure 2008-1Original: English

The designations employed and the presentation of the material in this publication do not imply the expression of any opinionwhatsoever on the part of the Secretariats of UNESCO and IOC concerning the legal status of any country or territory, or itsauthorities, or concerning the delimitation of the frontiers of any country or territory.

For Bibliographic purposes, this document should be cited as follows:

Intergovernmental Oceanographic Commission. 2008. Tsunami, The Great Waves, Revised Edition. Paris, UNESCO, 16 pp., illus. IOC Brochure 2008-1. (English.)

Published by the United Nations Educational, Scientific and Cultural Organization7 Place de Fontenoy, 75 352 Paris 07 SP, France

Printed by the U.S. National Oceanic and Atmospheric Administration (NOAA)International Tsunami Information Center, 737 Bishop Street, Suite 2200, Honolulu, Hawaii 96813 U.S.A.

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 tsuna-mi was 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 a 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 60% 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 M9.3 earthquake off of northwestern Sumatra, Indonesiaproduced a destructive tsunami that attacked coasts through-out the Indian Ocean, killing 230,000 people, displacing morethan one million people, and causing billions of dollars ofproperty damage.

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)

At the U.S. NOAA Richard H. Hagemeyer Pacific TsunamiWarning Center (PTWC) in Hawaii, the operational warningcentre of the Pacific Tsunami Warning and Mitigation System(PTWS), scientists monitor seismographic and sea level sta-tions throughout the Pacific, evaluate potentially tsunamigenicearthquakes, monitor tsunamis, and disseminate tsunamiwarning information. The PTWC provides international tsuna-mi warning advisories to national authorities throughout thePacific. Sub-regional warning centres also exist in Japan forthe northwest Pacific and Alaska, USA for the northeast Pacific.As a result of the 2004 great tsunami, tsunami warning sys-tems are now being implemented globally, including in theIndian Ocean, Caribbean Sea, Atlantic Ocean, andMediterranean Sea.

The UNESCO IOC International Tsunami Information Centre,staffed by the USA, Chile and Japan, monitors and evaluatesthe PTWS’s effectiveness, helps establish new warning sys-tems globally, and serves as an education and informationresource for the IOC’s Tsunami Programme.1

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 35,000 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, M9.3 northwestSumatra earthquake approaching Hat Rai Lay Beach,Krabi, southern Thailand. After venturing out when theocean first receded, tourists scramble for safety inadvance of the first of six tsunami waves that hit the coast(AFP/AFP/Getty Images).

T

2

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 tsunamirelative 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. One known method toquickly recognize a tsunami earthquake is to estimate aparameter called the seismic moment using very longperiod seismic waves (more than 50 seconds / cycle).Three other deadly tsunami earthquakes have occurredin recent years off Java, Indonesia (June 2, 1994; July 16,2007) and Peru (February 21, 1996).

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 moment mag-nitude is measurable nearly immediately thanks to theadvent of modern seismometers, digital recording, andreal-time communication links. This allows warning cen-tres to provide initial tsunami advisories within minutesafter 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) 3

The last large tsunami that caused ocean-wide death and destruction in the Pacific wasgenerated 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 Japan.The Great Alaskan Earthquake of 1964 pro-duced deadly tsunami waves in Alaska,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 Pacific 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, Indonesida,Japan, Philippines, southwest Pacific, Chile,Caribbean, eastern Mediterranean, and theU.S. West Coast, can be immediate fortsunamis from nearby earthquakes which takeonly a few minutes to reach coastal areas orless urgent for tsunamis from distant earth-quakes which can take up to a day to hitcoastal areas.

In the open ocean a tsunami is less than a few tens of centimeters (1 ft) high atthe surface, but its wave height increases rapidly in shallow water. Tsunami waveenergy extends from the surface to the bottom in even the deepest waters. Asthe tsunami attacks the coastline, the wave energy is compressed into a muchshorter distance and a much shallower depth, creating destructive, life-threat-ening waves.

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 thenorthwest coast of Sumatra, Indonesia, and Male, Hulule, MaldiveIslands from the December 26, 2004 tsunami that caused ocean-wide destruction. The first wave was not the largest at Sibolga.Vertical axis in meters. (University of Hawaii Sea Level Center,BAKOSURTANAL, Indonesia)

Sibolga, Indonesia

Male, Hulule, Maldives

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-1

210

-1

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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 that tsunami waves will follow.

I

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. Thisgreat speed

makes it important to be aware of the tsunami as soon as it is generated. Scientists canpredict when a tsunami will arrive at various places by knowing the source characteristicsof the earthquake that generated the tsunami and the characteristics of the seafloor alongthe paths to those places. Tsunamis travel much slower in shallower coastal waters wheretheir 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 modify

the tsunami as it attacks the coastline. When the tsunami hits the coast, often as a wall ofwater, sea levels can rise many meters. In extreme cases, water level has risen to morethan 15 m (50 ft) for tsunamis of distant origin and over 30 m (100 ft) for tsunami wavesgenerated near the epicenter. The first wave may not be the largest in the series of waves.One coastal community may see no damaging wave activity while in another nearby com-munity destructive waves can be large and violent. The flooding can extend inland by onekm (~0.5 mi) or more, covering 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 tsunammis, is helping to extend the documented historicaltsunami record further back in time. As more events are found, better estimates of the fre-quency of occurrence of tsunamis in a region are obtained. During each of the last fivecenturies, there were three to four Pacific-wide tsunamis, most of them generated off theChilean coasts. The tsunami on December 26, 2004 claimed 300,000 lives and causeddamage throughout the Indian Ocean, making it the worst tsunami catastrophe in history.It was also the first known basin-wide destructive tsunami in the Indian Ocean.

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 are measured from the amplitude of waves seen on tide gauges.These data are crucial for creating good inundation and evacuation maps.

Maximum calculated global wave heights from the December 26,2004 tsunami, which were recorded in Antarctica, throughout thePacific Ocean and the Atlantic Ocean in South and North Americaand Canada (NOAA PMEL).

Calculated tsunami travel times for the December 26, 2004 earth-quake off western Sumatra. Each concentric curve represents 30minutes of tsunami travel time. Destructive tsunami hit Indonesiain 15 minutes, Sri Lanka in two hours, and Kenya nine hours afterthe 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, and staffed by the USA, Chile, and Japan, the ITICserves as the information service for the IOC’s International Tsunami WarningSystem (ITSU). The ITSU Secretariat, located in Paris, France, coordinates theactivities of the international tsunami warning and mitigation system. The ITICdirectly serves Member States in the PTWS and other regions by monitoring andrecommending improvements to the tsunami warning systems, helping MemberStates to establish regional and national tsunami warning systems, supportingcapacity building through training programmes in tsunami mitigation, and serv-ing as an information clearinghouse for the promotion of research, and the devel-opment and distribution of educational and preparedness materials to mitigateagainst the tsunami hazard. The ITIC regularly publishes the Tsunami Newsletter,maintains a tsunami library, hosts a Bulletin Board listserve, and conducts theIOC’s Training Programme in tsunamis 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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The IOC is coordinating the implementation of the globaltsunami warning and mitigation system, building upon itsPacific experience to establish warning systems in the IndianOcean, Caribbean, Atlantic, and the Mediterranean. ThePacific Tsunami Warning Center (PTWC) serves as the Pacificwarning centre. This international warning effort became aformal arrangement in 1965 when PTWC assumed the respon-sibility as the operational centre for the PTWS. TheICG/PTWS, presently comprised of 32 Member States, over-sees warning system operations and facilitates coordinationand cooperation in all international tsunami mitigation activ-ities. In 2005, the PTWC and the Japan MeteorologicalAgency (JMA) began cooperatively providing interim warn-ing services for the Indian Ocean, and in 2006, sub-region-ally for the South China Sea of the Pacific.

The initial objective of PTWC is to detect, locate and deter-mine the seismic parameters of potentially tsunamigenicearthquakes occurring in the Pacific Basin or its immediatemargins. To accomplish this, it continuously receives seis-mographic data from more than 150 stations around thePacific through cooperative data exchanges with the U.S.Geological Survey, Incorporated Research Institutions forSeismology Global Seismic Network, International Deploymentof Accelerometers, GEOSCOPE, the U.S. West Coast/AlaskaTsunami Warning Center (WC/ATWC), and other nationaland international agencies running seismic networks.

If an earthquake has the potential to generate a destruc-tive tsunami based on its location, depth, and magnitude, atsunami warning is issued to advise of an imminent tsunamihazard. Initial warnings apply only to areas the tsunami couldreach within a few hours and bulletins include the predictedtsunami arrival times and/or wave heights at selected coastallocations. Communities outside those areas are put into eithera tsunami watch or alert 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 PacificBasin. PTWC receives sea level data from more than 100coastal stations through cooperative data sharing betweenUS agencies, research centers, countries, and internationalnetworks such as the Global Sea Level Observing System(GLOSS). It also receives data from more than 40 DART deepocean sensors in the Pacific and around the world. Tsunamiwarning advisories are disseminated to designated emer-gency officials and the general public by a variety of com-munication methods.

Countries may operate National or Sub-regional Centresto provide more rapid or detailed warnings for regional orlocal tsunamis. The JMA provides local warnings to Japan,and its Northwest Pacific Tsunami Advisory Center providesearthquake and tsunami wave forecasts to countries in thenorthwest Pacific and its marginal seas, the South Chinaregion, and island nations in the North Pacific. The CentrePolynesien de Prevention des Tsunamis in French Polynesia,Chile, and Russia have operated national warning systemsfor decades. Australia, Canada, Colombia, Ecuador, ElSalvador, Indonesia, Korea, Malaysia, New Zealand,Nicaragua, Peru, Philippines, and Thailand continue to improvetheir systems.

In the US, the WC/ATWC warns North America, includingCanada, Puerto Rico and the Virgin Islands, and the PTWCwarns Hawaii, US Pacific interests, and provides interim advi-sories to the wider Caribbean. Through the open and time-ly sharing of data, Warning Centres can provide backup andsupplemental analyses of events should a Centre become dis-abled. The Centres can also serve as focal points for region-al tsunami awareness, education, and other mitigation activ-ities.

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TSUNAMI WARNING CENTERS Information about the IOCThe Intergovernmental Oceanographic Commission

(IOC), a body with functional autonomy within theUnited Nations Educational, Scientific and CulturalOrganization (UNESCO), provides Member States withan essential mechanism for global co-operation in thestudy of the ocean. The IOC assists governments toaddress their individual and collective ocean andcoastal problems through the sharing of knowledge,information and technology and through the coordi-nation of national and regional programs.

The IOC’s functions are to develop, recommend andcoordinate international programs for scientific studyof the oceans and related ocean services; to promoteand make recommendations for the exchange ofoceanographic data and the publication and dissem-ination of scientific investigation results; to promoteand coordinate the development and transfer of marinescience and its technology; to make recommenda-tions to strengthen education and training and to pro-mote scientific investigation of the oceans and appli-cation of the results thereof for the benefit of allmankind. Presently, there are 136 Member States. TheAssembly meets every two years at the UNESCO head-quarters in Paris, France.

The IOC consists of an Assembly, an ExecutiveCouncil, a Secretariat and such subsidiary bodies asit may establish. Under this concept, the Commissionhas created Global and Regional Programmes whichexamine and execute specific projects, or consist ofcommittees composed of Member States interestedin such projects. This is the case for theIntergovernmental Tsunami Warning and MitigationCoordination Groups in the Pacific (PTWS), IndianOcean (IOTWS), Caribbean (CARIBE-EWS), and north-eastern Atlantic and Mediterranean (NEAMTWS).

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 is achievedwhen all persons in vulnerable coastal communities areprepared and respond appropriately, and in a timely man-ner, upon recognition that a potentially destructive tsuna-mi is coming. Timely tsunami warnings issued by a rec-ognized tsunami warning centre are essential. Whenthese warning messages are received by the designat-ed government agency, national tsunami emergencyresponse plans must already be in place so that well-known and practiced actions are immediately taken toevaluate the scientifically-based warning, and commu-nicate an appropriate course of action to ordinary citi-zens. Tsunami preparedness programmes must alreadyhave started so that good decisions can be made with-out delay.

Essential activities of an effective warning system are:- Identification of the tsunami hazard, assessment of risk,and mitigation to reduce wave impact. Tsunami evacu-ation maps which show where flooding is likely are basedon this information.- Issuance of timely warnings. For a distant tsunami, real-time earthquake and sea level monitoring to confirm thegeneration of a destructive tsunami, followed by imme-diate dissemination to the public, is critical. For a localtsunami where there may not be time for an official warn-ing, people must already know a tsunami's natural warn-ing signals and respond immediately.- Continuous and sustained awareness activities.Education is fundamental to building an informed citi-zenry and to ensure that the next generation is equallyprepared. Political support, laws and regulations, andinstitutional responsibility are key.

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

DASE/LDG 8

Left: July 30, 1995,Chilean Tsunami. Model results showingthe maximum runupand 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 mitigated throughcommunity preparedness, timely warnings, effective response, and publiceducation. The U.S. National Tsunami Hazard Mitigation Program is a goodexample of a comprehensive effort to reduce tsunami risks.

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

Ocean-bottom pressure sensors, able to measuretsunamis in the open ocean, are providing important dataon the propagation of tsunamis in deep water, and satel-lite communications have enabled these data to be usedin real time to detect and measure tsunami waves in thedeep ocean. NOAA has pioneered the development andoperation of these tsunami detection buoys over the last20 years. Measurements from these buoys are now help-ing warning centres to issue or cancel warnings and otheralerts with more precision. Numerical modeling methodsare also enabling centres to issue wave forecasts thusgiving customers more information on the expected waveimpact.

Seismologists, studying the dynamics of earthquakeswith broad band seismometers (20 to 0.003 Hertz), are for-mulating new methods to analyze earthquake motion andthe amount of energy released. Where the traditionalRichter (surface wave) magnitude of earthquakes is not

accurate above 7.5, the seismic moment andthe source duration are now used to betterdefine the amount of energy released and thepotential for tsunami generation. Real-timedetermination of the depth of the earthquake,type of faulting, and extent, direction and speedof rupture will significantly improve the warn-ing centres’ ability to identify the likelihood ofa threatening tsunami.

In the last decade, paleotsunami researchhas extended the historical tsunami record toimprove risk assessments. Tsunami depositfield studies and laboratory wave tank experiments arenow helping engineers design tsunami-resistant struc-tures through knowledge of how tsunami waves impactcoasts and scour and erode building foundations.

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 has beenissued.

RUN-UP MAXIMUM

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WHAT YOU SHOULD DO

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

Share this knowledge with your relatives 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 just as you would stay away fromthe beach and ocean if there is a tsunami. A tsuna-mi from 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.

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

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

by earthquakes. These earthquakes might occur far away ornear where you live. While earthquakes occur in all oceanbasins around the world, most do not generate tsunamis.

� Some tsunamis can be very large. In coastal areas their heightcan be as great as 10 m or more (30 m in extreme cases), andthey cause impacts like flash floods. Later waves are oftenfull 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 several hoursafter the arrival of the first wave. Tsunami waves typically donot 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 the shoreto 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, andhomes and buildings destroyed. All this material and water movewith 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 as dan-gerous on coasts not facing the source of the tsunami.

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 to deep water. Small boat own-ers may find it safest to leave their boat at the pierand physically move to higher ground, particular-ly in the event of a locally-generated tsunami.Concurrent severe weather conditions (rough seasoutside of the harbor) could present a greater haz-ardous situation to small boats, so physically mov-ing 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: Photograph of tsunami effects andeddies formed behind the breakwater at Tahauku Bay in the MarquesasIslands, French Polynesia, several thousand kilometers away from thetsunami source. Right: Currents in Tahauku Bay based on numericalmodeling 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 complete-ly razed coastal towns and

villages, leaving behind onlysand, mud, and water (mid-

dle) where once there hadbeen thriving communities of

homes, offices, and greenspace (top). (DigitalGlobe

QuickBird 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 thattsunami waveswould return inminutes to inun-date the shoreline.(Honolulu Star-Bulletin)

Pagaraman, BabiIsland, Indonesia,

December 12, 1992.Tsunami washedaway everything

leaving only whitebeach sand. Seven

hundred peoplewere killed by the

earthquake andensuing tsunami.

(Harry Yeh, Univ. ofWashington)

12

International TsunamiInformation Center

Illustrations and layout by Joe Hunt Design, Honolulu, Hawaii, and ITIC Background images and wave logo courtesy of Aqualog, France

IntergovernmentalOceanographicCommission

International Tsunami Information CenterA UNESCO/IOC - NOAA Partnership737 Bishop Street, Suite 2200Honolulu, Hawaii 96813, U.S.A.Tel: <1> 808-532-6422Fax: <1> 808-532-5576E-mail: itic.tsunami@unesco.orghttp://ioc3.unesco.org/itic http://www.tsunamiwave.info

United NationsEducational, Scientific and

Cultural OrganizationIntergovernmental Oceanographic Commission (IOC)United Nations Educational, Scientific and CulturalOrganization (UNESCO)1, rue Miollis75 732 Paris Cedex 15, FranceTel: +33 1 45 68 39 83Fax: +33 1 45 68 58 12http://ioc-unesco.org/http://www.ioc-tsunami.org/

ACKNOWLEDGMENTSTHE PREPARATION OF THIS BROCHURE WAS SUPPORTED BY:Intergovernmental Oceanographic Commission (IOC) of UNESCOThe International Tsunami Information Center: A UNESCO/IOC - NOAA Partnership Department Analyse Surveillance Environnement, FranceU.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA)

TECHNICAL GUIDANCE PROVIDED BY:The International Tsunami Information Center: A UNESCO/IOC - NOAA Partnership, http://www.tsunamiwave.infoDepartment Analyse Surveillance Environnement, France, http://www-dase.cea.frU.S. NOAA 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. NOAA National Ocean Service, http://www.nos.noaa.govU.S. NOAA National Geophysical Data Center, http://www.ngdc.noaa.govU.S. NOAA Pacific Marine Environmental Laboratory, http://www.pmel.noaa.govServicio Hidrográfico y Oceanográfico, Chile, http://www.shoa.clSchool of Ocean & Earth Science & Technology, University of Hawaii, http://www.soest.hawaii.edu

FURTHER INFORMATION ON IOC TSUNAMI WARNING AND MITIGATION SYSTEMS, TSUNAMIS, AND THE ITIC MAY BE OBTAINED FROM:

20082008