2014 United Nations

Educational, Scientific and

Cultural Organization

Intergovernmental

Oceanographic

Commission
IOC/BRO/2012/4 Rev.

Original: English

The designations employed and the presentation of the material in this publication do not imply the expression of any opinion 

whatsoever on the part of the Secretariats of UNESCO and IOC concerning the legal status of any country or territory, or its 

authorities, 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. 2014. Tsunami, The Great Waves, Revised Edition.

Paris, UNESCO, 16 pp., illus. IOC Brochure 2012-4. (English.), revised 2014.

Language versions at: http://unesdoc.unesco.org/ulis/cgi-bin/ulis.pl?lin=1&catno=148609

Published by the United Nations Educational, Scientific and Cultural Organization

7 Place de Fontenoy, 75352 Paris Cedex 07 SP, France

Prepared by Intergovernmental Oceanographic Commission of UNESCO - NOAA International Tsunami Information Center, 

1845 Wasp Boulevard, Building 176, Honolulu, Hawaii 96818 U.S.A.

Printed by UNESCO/IOC NOAA ITIC, 2014
1

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.

elevation (m)

Left: Computer model of the initial water surface changes 

at the time the July 30, 1995, Chilean tsunami was 

generated. A is Antofagasta, Chile. Right: Computer model 

of the same tsunami, three hours after it was generated.

THE GREAT

WAVES

(nearly 90%) are generated by great earthquakes or 

earthquake-generated landslides. During the 1990s, over 

4,300 people were killed by 16 tsunamis, including 1100 

lives lost in the 1992 Flores, Indonesia, and 2200 lives in 

the 1998 Aitape, Papua New Guinea tsunamis. Property 

damage was nearly one billion United States (U.S.) 

dollars. Although most tsunamis (>70%) occur in the 

Pacific, they can also threaten coastlines of countries in 

the Indian Ocean, Mediterranean Sea, Caribbean region, 

and the Atlantic Ocean. Since 2000, there have been 14 

tsunamis. The most devastating tsunami ever occurred 

in December 2004, when a M9.1 earthquake off of 

northwestern Sumatra, Indonesia produced a destructive 

tsunami that attacked coasts throughout the Indian 

Ocean, killing 227,000 people, displacing more than one 

million people, and causing billions of dollars of property 

damage. In March 2011, a M9.0 earthquake generated a 

giant local tsunami that overtopped sea walls, claiming 

17,000 lives in Tohoku, Japan.

At the Pacific Tsunami Warning Center (PTWC, USA) 

in Hawaii, the operational centre of the Pacific Tsunami 

Warning and Mitigation System (PTWS), scientists 

monitor seismographic and sea level stations, evaluate 

potentially tsunamigenic earthquakes, and disseminate 

international tsunami advisories to national authorities 

throughout the Pacific and Caribbean. Regional Tsunami 

Service Providers also exist in Japan for the northwest 

Pacific and in Alaska, USA for the northeast Pacific. As a 

result of the 2004 Indian Ocean tsunami, tsunami warning 

systems are now implemented globally, including in the 

Indian Ocean, Caribbean Sea, Northeastern Atlantic 

Ocean, the Mediterranean and connected seas.

The UNESCO IOC International Tsunami Information 

Center, staffed by the USA and Chile, monitors and 

evaluates the PTWS’s effectiveness, helps establish new 

warning systems globally, and serves as an education and 

information resource for the IOC’s Tsunami Programme.

Hilo Harbor, Hawaii, April 1, 1946, Aleutian Islands 

earthquake. Photo taken from the vessel Brigham 

Victory of tsunami breaking over Pier 1. The gentleman 

on the left did not survive. (NOAA)

The phenomenon we call “tsunami” (soo-NAH-mee) is 

a series of traveling ocean waves of extremely long length 

generated primarily by earthquakes occurring below 

or near the ocean floor. Underwater volcanic eruptions 

and landslides can also generate tsunamis. In the deep 

ocean, the tsunami waves propagate across the deep 

ocean with a speed exceeding 800 kilometers per hour 

([km], ~500 miles per hour), and a wave height of only 

a few tens of centimeters (1 foot [ft]) or less. Tsunami 

waves are distinguished from ordinary ocean waves by 

their great length between wave crests, often exceeding 

100 km (60 miles [mi]) or more in the deep ocean, and by 

the time between these crests, ranging from 10 minutes 

to an hour.

As they reach the shallow waters of the coast, the 

waves slow down and the water can pile up into a wall 

of destruction tens of meters (30 ft) or more in height. 

The effect can be amplified where a bay, harbor or lagoon 

funnels the wave as it moves inland. Large tsunamis 

have been known to rise over 30 meters (100 ft). Even a 

tsunami 3–6 meters [m] high can be very destructive and 

cause many deaths and injuries.

Tsunamis are a threat to life and property for all coastal 

residents living near the ocean. Globally over history 

through 2014, 245 confirmed tsunamis have caused more 

than 600,000 deaths, with nearly 90% of the casualties 

from local tsunamis that hit within one hour. Most tsunamis 
2

Tsunami generated by December 26, 2004, M9.1 

northwest Sumatra earthquake approaching Hat Rai 

Lay Beach, Krabi, southern Thailand. Foreign tourists 

scramble for safety in advance of the first of six tsunami 

waves after venturing out when the water first receded 

(AFP/AFP/Getty Images).

Plate Tectonic theory is based on an earth model 

characterized by a small number of lithospheric plates, 

70 to 250 km (40 to 150 mi) thick, that float on a viscous 

underlayer called the asthenosphere. These plates, 

which cover the entire surface of the earth and contain 

both the continents and seafloor, move relative to each 

other at rates of up to ten cm/year (several inches/year). 

The region where two plates come in contact is called a 

plate boundary, and the way in which one plate moves 

relative to another determines the type of boundary: 

spreading, where the two plates move away from each 

other; subduction, where the two plates move toward each 

other and one slides beneath the other; and transform, 

where the two plates slide horizontally past each other. 

Subduction zones are characterized by deep ocean 

trenches, and the volcanic islands or volcanic mountain 

chains associated with the many subduction zones 

around the Pacific rim are sometimes called 

the Ring of Fire.

An earthquake can be caused by 

volcanic activity, but most are generated by 

movements along fault zones associated 

with the plate boundaries. Most strong 

earthquakes, representing 80% of the total 

energy released worldwide by earthquakes, 

occur in subduction zones where an oceanic plate slides 

under a continental plate or another younger oceanic 

plate.

Not all earthquakes generate tsunamis. To generate 

a tsunami, the fault where the earthquake occurs must 

be underneath or near the ocean, and cause vertical 

movement of the seafloor (up to several meters) 

over a large area (up to a hundred thousand square 

kilometers). Shallow focus earthquakes (depth less 70 

km or 42 mi) along subduction zones are responsible for 

most destructive tsunamis. The amount of vertical and 

horizontal motion of the sea floor, the area over which 

it occurs, the simultaneous occurrence of slumping 

of underwater sediments due to the shaking, and the 

efficiency with which energy is transferred from the 

earth’s crust to the ocean water are all part of the tsunami 

generation mechanism.

T sunamis, also called seismic sea 

waves or incorrectly tidal waves, are 

caused generally by earthquakes, 

less commonly by submarine landslides, 

infrequently by submarine volcanic eruptions 

and very rarely by large meteorite impacts 

in the ocean. Submarine volcanic eruptions 

have the potential to produce truly awesome 

tsunami waves. The 1883 Great Krakatau, 

Indonesia Volcanic Eruption generated giant 

waves reaching heights of 40 meters above 

sea-level, killing more than 35,000 people and 

wiping out numerous coastal villages.

All oceanic regions of the world can 

experience tsunamis, but in the Pacific Ocean 

and its marginal seas, there are more frequent 

occurrence of large, destructive tsunamis 

because of the many large earthquakes along 

the margins of the Pacific Ocean.

PLATE TECTONICS

EARTHQUAKES AND

TSUNAMIS

 LAND

EARTHQUAKES

SHALLOW

INTERMEDIATE

DEEP

SPREADING

RIDGE TRENCH

TRANSFORM

FAULT MOST TSUNAMI

GENERATED HERE

OCEAN

ASTHENOSPHERE

LITHOSPHERE
3

El Transito, Nicaragua, September 2, 1992. Ninemeter high waves destroyed the town, killing 16 

and injuring 151 in this coastal community of 1,000 

people. The first wave was thought to be small 

providing time for people to escape the destructive 

second and third waves. More than 40,000 people 

were affected by the loss of their homes or means of 

income. (Harry Yeh, Univ. of Washington)

The September 2, 1992 earthquake (M7.2) was barely 

felt by residents along the coast of Nicaragua. Located 

well off-shore, its intensity, the severity of shaking on a 

scale of I to XII, was mostly II along the coast, and reached 

III at only a few places. Twenty to 70 minutes after the 

earthquake occurred, a tsunami struck the coast of 

Nicaragua with wave amplitudes 4 m (13 ft) above normal 

sea level in most places and a maximum runup height 

of 10.7 m (35 ft). The waves caught coastal residents 

by complete surprise and caused many casualties and 

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 

earthquakes are characterized by a very shallow focus, 

fault dislocations greater than several meters, and fault 

surfaces that are smaller than for a normal earthquake. 

They are also slow earthquakes, with slippage along 

the fault beneath the sea floor occurring more slowly than 

it would in a normal earthquake. One known method to 

quickly recognize a tsunami earthquake is to estimate 

a parameter called the seismic moment using very long 

period seismic waves (more than 50 seconds / cycle). 

Three other deadly tsunamis from tsunami earthquakes 

have occurred in recent years off Indonesia (June 2, 1994; 

July 16, 2007; October 25, 2010) and Peru (February 21, 

1996).

The earthquake focus is the point in the earth where the 

rupture first occurs and where the first seismic waves 

originate. The epicenter is the point on the Earth’s 

surface directly above the focus.

The magnitude is a measure of the relative size of an 

earthquake. A number of different magnitude scales 

exist besides the Richter scale, including the moment 

magnitude which measures the energy released and 

gives the most reliable estimate for large earthquakes. 

An increase in one unit of magnitude corresponds to 

a factor of 10 increase in seismic wave amplitude, and 

a 30-fold increase in released energy. The moment 

magnitude is measurable nearly immediately thanks to 

the advent of modern seismometers, digital recording, 

and real time communication links. This allows warning 

centres to provide initial tsunami advisories within 

minutes after the earthquake’s occurrence.

TSUNAMI EARTHQUAKES TSUNAMI: THE RELATION

WITH THE SEISMIC SOURCE

SEA SURFACE

SEA SURFACE

SEA SURFACE

SEA SURFACE

SEA FLOOR

SEA FLOOR

SEA FLOOR

SEA FLOOR

FAULT

EARTHQUAKE
4

OCEAN-WIDE AND LOCAL TSUNAMIS I

n the deep ocean, destructive tsunamis can be small – often 

only a few tens of centimeters or less in height – and cannot 

be seen nor felt on ships at sea. But as the tsunami reaches 

shallower coastal waters, wave height can increase rapidly. 

Sometimes, coastal waters are drawn out into the ocean just 

before the tsunami strikes. When this occurs, more shoreline may 

be exposed than even at the lowest tide. This major withdrawal 

of the sea should be taken as a natural warning sign that tsunami 

waves will follow.

In the open ocean a tsunami is less than a few tens of centimeters (1 ft) high 

at the surface, but its wave height increases rapidly in shallow water. Tsunami 

wave energy extends from the surface to the bottom in even the deepest waters. 

As the tsunami attacks the coastline, the wave energy is compressed into a 

much shorter distance and a much shallower depth, creating destructive, lifethreatening waves. As shown in this figure, tsunamis are a series of waves that 

can be destructive for hours. Although not depicted, the 1st wave may not be 

the largest.

Sea level records of the tsunami recorded at 

Sibolga on the northwest coast of Sumatra, 

Indonesia, and Male, Hulule, Maldive Islands 

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, 

BIG, Indonesia) 

The last large tsunami that caused significant 

ocean-wide death and destruction in the Pacific 

was generated by an earthquake located off the 

coast of Chile in 1960. It caused loss of life and 

property damage not only along the Chile coast, 

but in Hawaii and as far away as Japan and the 

Philippines 22 hours later. On March 11, 2011, a 

deadly local tsunami in Japan caused USD 233 

billion in damage, USD 100 million in Hawaii 

and California, and one death each in California, 

USA and Jayapura, Papua, Indonesia. The 

Great Alaskan Earthquake of 1964 

produced deadly tsunami waves in 

Alaska, Oregon and California. 

In July 1993, a tsunami generated 

in the Sea of Japan killed 208 people 

in Japan. Damage also occurred in 

Korea and Russia but not in other 

countries since the tsunami wave 

energy was confined within the Sea 

of Japan. The 1993 tsunami is known 

as a “local or regional event” since its 

impact was confined to a relatively 

small area. For people living along 

the northwestern coast of Japan, 

the local tsunami waves followed the 

earthquake within a few minutes.

Since the 1990s, there have been 31 

deadly tsunamis that have killed more 

than 250,000 people, with 227.000 

occurring in 14 countries in 

the December 26, 2004 Indian 

Ocean tsunami. The tsunami 

sources were located in Latin 

America (Mexico, Nicaragua, 

Costa Rica, Peru, Chile), North 

America (Canada, USA), Japan, the Philippines, 

Indonesia, the Pacific Islands (Papua New 

Guinea, Solomon Islands, Vanuatu, Samoa), 

the Caribbean (Haiti), and the Mediterranean 

(Turkey).

In less than a day, tsunamis can travel from one 

side of the Pacific to the other. However, people 

living near areas where large earthquakes occur 

may find that the tsunami waves will reach their 

shores within minutes. For these reasons, the 

tsunami threat to many areas, e.g., Caribbean, 

Indonesia and Makran source areas, Pacific 

Ring of Fire, and Eastern Mediterranean, can 

be immediate from local tsunamis that take only 

a few minutes to reach coastal areas or less 

urgent from distant tsunamis that can take up 

to a day to arrive. 200 km 20 km

10 km

4000 m

50 m

10 m

Depth

 (m)

7000

4000

2000

200

50

10

Velocity

(km/h)

950

700

500

150

80

40

Wavelength

(km)

300

200

150

50

20

10

Sibolga, Indonesia 

Male, Hulule, Maldives 

2 

1 

0 

-1 

2 

1 

0 

-1 

Tsunami Speed is reduced in shallow water as wave height increases rapidly.
5

Where the ocean 

is over 6,000 m 

deep, unnoticed 

tsunami waves can 

travel at the speed 

of a commercial 

jet plane, over 800 

km per hour (~500 

mi per hour). They 

can move from one 

side of the Pacific 

Ocean to the other 

in a day and across 

the Indian Ocean in 

12 hrs. 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 source characteristics of the 

earthquake that generated the tsunami and the characteristics of the seafloor along the 

paths to those places. Tsunamis travel much slower in shallower coastal waters where their 

wave heights begin to increase dramatically.

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 of water, sea levels can rise many meters. In extreme cases, water level has risen 

to more than 15 m (50 ft) for tsunamis of distant origin and over 30 m (100 ft) for tsunami 

waves generated 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 community destructive waves can be large and violent. The flooding can extend 

kilometers (~0.5 mi) inland or more, flooding large expanses of land with water and debris.

Since scientists cannot predict when earthquakes will occur, they cannot determine 

exactly when a tsunami will be generated. However, by looking at past historical tsunamis, 

scientists know where tsunamis are most likely to be generated. Past tsunami height 

measurements are useful in predicting future tsunami impact and flooding limits at specific 

coastal locations and communities. Paleotsunami research, in which scientists look for 

sediments deposited by giant tsunamis, is helping to extend the documented historical 

tsunami record further back in time. As more events are found, better estimates of the 

frequency of 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 227,000 lives and caused 

damage 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.

HOW 

FAST?

HOW BIG?

HOW FREQUENT?

Maximum calculated global wave heights (cm) from the December 26, 

2004 Indian Ocean tsunami. Waves were recorded on sea level gauges 

in Antarctica, and along the coasts of South and North America and 

Canada in both the Pacific and Atlantic Oceans (NOAA PMEL).

Calculated tsunami travel times for the December 26, 2004 

earthquake off western Sumatra. Each concentric curve 

represents 30 minutes of tsunami travel time. Destructive tsunami 

hit Indonesia in 15 minutes, Sri Lanka in two hours, and Kenya 

nine hours after the earthquake (NOAA PMEL).

Since the 1992 Nicaragua tsunami, International Tsunami Survey Teams (ITST) 

have assisted countries with post-tsunami field surveys. Survey scientists 

collect inundation and runup data, and eyewitness accounts, crucial for creating 

safe evacuation maps. Inundation is the maximum horizontal distance inland 

that a tsunami penetrates. Runup is the maximum vertical height above mean 

sea level that the tsunami reaches. Actual heights are measured from wave 

amplitudes on tide gauges. The IOC ITST Post-Tsunami Field Survey Guide 

(2014) gives guiding principles and data collection best practices.
6

International Tsunami Information Center (ITIC)

Located in Honolulu, Hawaii, and staffed by the USA and Chile, the ITIC 

is the oldest information centre serving the UNESCO Intergovernmental 

Oceanographic Commission (IOC)’s Global Tsunami Warning and Mitigation 

System. The IOC Tsunami Unit located in Paris, France, coordinates the 

global system. The ITIC directly serves Member States in the PTWS and 

other regions by monitoring and recommending improvements to the 

tsunami warning systems, helping Member States to establish regional and 

national tsunami warning systems, supporting capacity building through 

training programmes in tsunami mitigation, and serving as an information 

clearinghouse for the promotion of research, and the development and 

distribution of educational and preparedness materials to mitigate against 

the tsunami hazard. The ITIC regularly publishes the Tsunami Newsletter, 

maintains a library, hosts the Tsunami Bulletin Board listserve, and conducts 

the ITIC Training Programme in tsunami warning systems.

The Great Alaska Earthquake of March 27, 

1964 generated a tsunami which caused 21 

deaths and $30 million US dollars in damage 

in and near the city of Kodiak.

The Wave. Painting by Lucas Rawah of Aitape, done to commemorate 

the July 17, 1998, Papua New Guinea event. A M7.1 earthquake is 

thought to have triggered a submarine landslide generating a tsunami 

that destroyed entire villages along the Aitape coast.
7

Information about the IOC

 The Intergovernmental Oceanographic Commission 

(IOC), a body with functional autonomy within 

the United Nations Educational, Scientific and 

Cultural Organization (UNESCO), provides Member 

States with an essential mechanism for global 

co-operation in the study of the ocean. The IOC 

assists governments to address their individual and 

collective ocean and coastal problems through the 

sharing of knowledge, information and technology 

and through the coordination of national and 

regional programs.

 The functions of the IOC are to develop, recommend 

and coordinate international programs for scientific 

study of the oceans and related ocean services; 

to promote and make recommendations for the 

exchange of oceanographic data and the publication 

and dissemination of scientific investigation results; 

to promote and coordinate the development and 

transfer of marine science and its technology; to 

make recommendations to strengthen education 

and training and to promote scientific investigation 

of the oceans and application of the results thereof 

for the benefit of all mankind. In 2014, 147 countries 

were Member States of the IOC. The Assembly 

meets every two years at the UNESCO headquarters 

in Paris, France.

 The IOC consists of an Assembly, an Executive 

Council, a Secretariat and such subsidiary bodies 

as it may establish. Under this concept, the 

Commission has created Global and Regional 

Programmes which examine and execute specific 

projects, or consist of committees composed of 

Member States interested in such projects. This is 

the case for the Intergovernmental Tsunami Warning 

and Mitigation Coordination Groups in the Pacific 

(ICG/PTWS), Indian Ocean (ICG/IOTWS), Caribbean 

(ICG/CARIBE-EWS), and Northeastern Atlantic and 

Mediterranean (ICG/NEAMTWS).

The IOC coordinates the global tsunami warning and 

mitigation system that covers the Pacific Ocean, Indian 

Ocean, Caribbean, Northeastern Atlantic Ocean, and the 

Mediterranean. The Pacific system, established in 1965 in 

response the 1960 M9.5 earthquake and deadly tsunami, 

is the oldest. The ICG/PTWS, encompassing 46 Pacific 

countries, oversees warning system operations and facilitates 

coordination and cooperation of international tsunami 

mitigation activities. The PTWC serves as the primary Tsunami 

Service Provider (TSP), with the Japan Meteorological Agency 

(JMA) Northwest Pacific Tsunami Advisory Center (NWPTAC) 

acting since 2006 as a regional TSP, and interim South China 

Sea TSP with PTWC. In the Indian Ocean, the PTWC and the 

JMA provided interim services from 2005-2013 until Australia, 

India, and Indonesia assumed roles as permanent TSPs. In 

the Caribbean, PTWC has been the interim TSP since 2006.

The initial objective of a tsunami warning or advisory centre 

is to detect, locate and determine the seismic parameters of 

potentially tsunamigenic earthquakes occurring in its area 

of responsibility. To accomplish this, PTWC continuously 

receives seismographic data from more than 500 stations 

around the world through cooperative data exchanges with the 

U.S. Geological Survey, Incorporated Research Institutions for 

Seismology Global Seismic Network, International Deployment 

of Accelerometers, GEOSCOPE, and other national and 

international agencies running seismic networks.

If an earthquake has the potential to generate a destructive 

tsunami based on its location, depth, and magnitude, a tsunami 

warning is immediately issued to advise of an imminent tsunami 

threat. Initial warnings may apply only to the nearest areas 

the tsunami could reach and messages include the predicted 

tsunami arrival times and/or wave heights. Coastal forecasts 

exceeding 0.3 m in height with strong water currents can cause 

significant damage and death as waves crush structures and 

floating debris become battering rams.

Warning centres then monitor incoming sea level data to 

determine whether a tsunami has occurred. If a significant 

tsunami with destructive potential is detected, warning areas 

are extended. PTWC receives sea level data from more than 

600 coastal stations through cooperative data sharing between 

US agencies, research centres, countries, and international 

networks such as the Global Sea Level Observing System 

(GLOSS). It also receives data from more than 60 deepocean or DART sensors around the world. These data enable 

accurate forecasts to be done. In Japan, GPS wave gauges 

provide offshore sea surface heights of oncoming tsunami. 

Warnings are then disseminated to designated emergency 

agencies and the general public by a variety of communication 

methods.

Countries may operate National or Sub-regional Centres to 

provide more rapid or detailed warnings for regional or local 

tsunamis. In the Pacific, the JMA provides local warnings to 

Japan, and its NWPTAC provides forecasts to countries in 

the Northwest Pacific, South China, and North Pacific island 

nations. The Centre Polynesien de Prevention des Tsunamis 

in French Polynesia, Chile, and Russia have operated national 

warning systems for decades. Australia, Canada, Colombia, 

Ecuador, El Salvador, Indonesia, Korea, Malaysia, Mexico, 

New Zealand, Nicaragua, Peru, Philippines, Samoa, Solomon 

Islands, Thailand, Tonga, and Vietnam have improved their 

systems since 2004.

In the US, the US National Tsunami Warning Center (NTWC) 

warns North America, including Canada, and the PTWC warns 

Hawaii, American Samoa, Guam and the Northern Mariana 

Islands. Through the open and timely sharing of data, Warning 

Centres can provide backup and supplemental analyses of 

events should a Centre become disabled. The Centres can 

also serve as focal points for regional tsunami awareness, 

education, and other mitigation activities.

TSUNAMI WARNING CENTRES
8

An effective tsunami warning system reaches all persons in 

danger before the wave hits

DEEP-OCEAN ASSESSMENT AND 

REPORTING ON TSUNAMIS (DART)

INDEPENDENT 3 COMPONENT 

BROAD -BAND SEISMIC STATION

April 1, 1946. People flee as the tsunami attacks downtown Hilo, Hawaii. The tsunami struck 

without warning 4.5 hours after being generated by a M8.1 Aleutian Islands earthquake 3500 km 

to the north, and resulted in the start of the US Seismic Sea Wave Warning System (now PTWC) in 

1949. (Bishop Museum Archives).

An effective tsunami early warning system is achieved 

when all persons in vulnerable coastal communities are 

prepared and respond appropriately, and in a timely 

manner, upon recognition that a potentially destructive 

tsunami is coming. Timely tsunami warnings issued by a 

recognized tsunami warning centre are essential. When 

these warning messages are received by the designated 

government agency, national tsunami emergency 

response plans must already be in place so that well-known 

and practiced actions are immediately taken to evaluate 

the scientifically-based warning, and communicate an 

appropriate course of action to ordinary citizens. Tsunami 

preparedness programmes must already have started so 

that good decisions can be made without delay.

Essential activities of an effective warning system are:

- Identification of the tsunami hazard, assessment of 

risk, and mitigation to reduce wave impact. Tsunami 

evacuation maps that show where flooding is likely are 

based on this information.

- Issuance of timely warnings. For a distant tsunami, realtime earthquake and sea level monitoring to confirm 

the generation of a destructive tsunami, followed by an 

immediate warning to the public, is critical. For a local 

tsunami where there may not be time for an official 

warning, people must already know a tsunami’s natural 

warning signals and respond immediately.

- Continuous and sustained awareness activities. 

Education is fundamental to building an informed 

citizenry and to ensure that the next generation is equally 

prepared. Political support, laws and regulations, and 

institutional responsibility are key.

 DATA

SIGNAL

ACOUSTIC

DATA SIGNAL

PRESSURE

SENSOR

DATA

PROCESSING MODULE

WARNING

CENTER

VIA SATELLITE

NOAA/PMEL

RADIO TRANSMITTER

SOLAR

PANEL
9

Tsunami Research Activities

Although a tsunami cannot be prevented, its impact can be mitigated 

through community preparedness, timely warnings, effective response, 

and public education. The U.S. National Tsunami Hazard Mitigation Program 

is a good example of a comprehensive effort to reduce tsunami risks.

Since the 2004 Indian Ocean tsunami, there has been 

great progress in tsunami research. Post-tsunami surveys 

provided detailed and comprehensive data sets that 

have improved our understanding of tsunamis and thus 

our ability to mitigate losses from tsunamis. Scientists 

can numerically model tsunami generation, open ocean 

propagation, and coastal runup.

Real-time data from ocean-bottom pressure sensors 

and offshore GPS wave buoys are now helping tsunami 

warning centres to issue or cancel warnings and other 

alerts more quickly and accurately. Since the 1990s, 

NOAA has pioneered the development and operation of 

deep-ocean tsunami detection buoys. Using numerical 

modeling, centres are now able to calculate wave 

forecasts and the expected coastal impact. In Japan, GPS 

wave buoys have been in operation since 2008. During 

the 2011 Japan tsunami, a 6-m tsunami was detected off 

Kamaishi, Japan. The JMA used these data to upgrade its 

tsunami warning for Japan.

Seismologists, studying the dynamics of earthquakes 

with broad band seismometers (20 to 0.003 Hertz), are 

formulating new methods to analyze earthquake motion 

and the amount of energy released. Where the traditional 

Richter (surface wave) magnitude of earthquakes is 

not accurate above 7.5, the seismic moment (Mw) and 

the source duration are now used to better define the 

amount of energy released and the potential for tsunami 

generation. Real-time determination of earthquake depth, 

type of faulting, and extent, direction and speed of rupture 

are significantly improving the warning centres’ ability to 

identify the likelihood of a threatening tsunami.

Since the 1990s, paleotsunami and tsunami deposit 

field research has extended the historical tsunami record 

to improve risk assessments. Post-tsunami structural 

engineering studies, together with laboratory wave tank 

experiments, are helping engineers design tsunamiresistant structures through knowledge of how waves 

impact coasts and scour and erode building foundations. 

As a result, tsunami building design provisions are 

planned for inclusion in the 2018 International Building 

Code.

Tsunami inundation models, defining the extent of 

coastal flooding, are an integral aspect of tsunami hazard 

and preparedness planning. Using worst-case inundation 

scenarios, these models are critical to defining evacuation 

zones and routes so that coastal communities can be 

evacuated quickly when a tsunami warning is issued.

11 March 2011 Japan Tsunami. Left: Computed 

model (red line) compares well with observed 

runup (black) and inundation height (blue). 

Right: Maximum wave amplitude along the 

northern Tohoku coast. At sea, the model 

shows up to 11-m amplitudes around the 

epicenter (star), and up to 7-m at nearshore 

GPS buoys (white circle). At the coast, 

local maximum runup heights 15-40 m were 

measured in many places. 

Computed sea 

surface elevations

show excellent

agreement with

the observed

GPS buoy data 

(Y. Yamazaki and 

K.F. Cheung, 

Univ. of Hawaii).
10

- If you are in school and you hear there is a tsunami 

warning, you should follow the advice of teachers 

and other school personnel.

- If you are at home and hear there is a tsunami 

warning, you should make sure your entire 

family is aware of the warning. Prepare a family 

emergency plan beforehand so that everyone 

knows what to do. Your family should evacuate 

your house if you live in a tsunami evacuation 

zone. Move in an orderly, calm, and safe manner 

to the evacuation site or to any safe place outside 

your evacuation zone. Follow the advice of local 

emergency and law enforcement authorities.

- If you are at the beach or near the ocean and you 

feel the earth shake strongly or for a long time, 

move immediately to higher ground. DO NOT 

WAIT for a tsunami warning to be announced. 

Stay away from rivers and streams that lead to 

the ocean as you would stay away from the beach 

and ocean if there is a tsunami. A tsunami from 

a local earthquake could strike before a tsunami 

warning can be announced.

- Tsunamis generated in distant locations will 

generally give people enough time to move to 

higher ground. For locally generated tsunamis, 

where you might feel the ground shake, you may 

only have a few minutes to move to higher ground.

- High, multi-story, reinforced concrete hotels are 

located in many low-lying coastal areas. The 

upper floors can provide a safe place to find 

refuge should there be a tsunami warning and 

you cannot move quickly inland to higher ground. 

Local Civil Defense procedures may, however, not 

allow this type of evacuation in your area. Homes 

and small buildings located in low-lying coastal 

areas are not designed to withstand tsunami 

impacts. Do not stay in these structures should 

there be a tsunami warning.

- Offshore reefs and shallow areas may help 

break the force of tsunami waves, but large and 

dangerous waves can still be a threat to coastal 

residents in these areas. Staying away from all 

low-lying coastal areas is the safest advice when 

there is a tsunami warning.

WHAT YOU SHOULD DO

Be aware of tsunami facts.

This knowledge could save your life!

Share this knowledge with your 

relatives and friends. It could save their 

lives!

THE FACTS

• Tsunamis that strike coastal locations are almost always caused 

by earthquakes. The earthquakes might occur far away or near 

where you live. While earthquakes occur in all ocean basins 

around the world, most do not generate tsunamis.

• Some tsunamis can be very large. In coastal areas their height 

can be as great as 10 m or more (30 m in extreme cases), and 

they cause impacts like flash floods or strong storm surge. Later 

waves 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 arriving every 

5 to 60 minutes. Often the first wave may not be the largest. The 

danger from a tsunami can last for several hours after the arrival 

of the first wave. Tsunami waves typically 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 the shore to 

recede, exposing the ocean floor.

• The force of some tsunamis is enormous. Large rocks weighing 

several tons, along with boats and other debris, can be moved 

inland hundreds of meters by tsunami wave activity, and homes 

and buildings destroyed. All this material and water 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 as dangerous 

on coasts not facing the source of the tsunami.

Oga Aquarium, 

Akita Japan. 

Parking lot 

of aquarium 

is flooded 

stranding car 

during the May 

26, 1983, Japan 

Sea tsunami 

(Takaaki Uda, 

Public Works 

Research 

Institute, Japan).
11

Since tsunami wave activity is imperceptible in 

the open ocean, do not return to port if you are at 

sea and a tsunami warning has been issued for 

your area. Tsunamis can cause rapid changes in 

water level and unpredictable dangerous currents in 

harbors and ports.

- If there is time to move your boat or ship from 

port to a location in deep water (50-300 m deep, 

depending on local conditions), and after you 

know a tsunami warning has been issued, you 

should weigh the following considerations:

- Most large harbors and ports are under the control 

of a harbor authority and/or a vessel traffic system. 

These authorities direct operations during periods 

of increased readiness, including the forced 

movement of vessels if deemed necessary. Keep 

in contact with the authorities should a forced 

movement of vessels be directed.

- Smaller ports may not be under the control of 

a harbor authority. If you are aware there is a 

tsunami warning, be sure you have enough time 

to motor your vessel safely into deep water. Small 

boat owners may find it safest to leave their boat 

at the pier and physically move to higher ground, 

particularly in the event of a locally-generated 

tsunami. Concurrent severe weather conditions 

(rough seas outside of the harbor) could present 

a greater hazardous situation to small boats, so 

physically moving yourself to higher ground may 

be the only option.

- Damaging wave activity and unpredictable 

currents can affect harbors for hours following the 

initial tsunami impact on the coast. Contact the 

harbor authority before returning to port making 

sure to verify that conditions in the harbor are safe 

for navigation and berthing.

IF YOU ARE ON A SHIP OR BOAT

July 30, 1995, Chilean Tsunami. Left: Eddy formed behind the breakwater at 

Tahauku Bay in the Marquesas Islands, French Polynesia, several thousand 

kilometers away from the tsunami source. Right: Currents in Tahauku Bay 

based on numerical modeling of the Chilean tsunami. The modeling reproduces 

the same kinds of ocean currents seen in the photo. (F. Schindele CEA/DASE)

Banda Aceh, Sumatra, 

Indonesia. The tsunami of 

December 26, 2004 completely 

razed coastal towns and 

villages, leaving behind only 

sand, mud, and water (middle) 

where once there had been 

thriving communities of 

homes, offices, and green 

space (top). (DigitalGlobe 

QuickBird satellite imagery, US 

Navy photo)

400

200

200 400 (metre) 600

0

0

1 m/s
12

Onagawa, Japan, March 11, 2011. 

The tsunami attacked eastern Japan 

~25 minutes after the earthquake, 

crushing homes, flooding 4th-floor 

buildings, and inundating inland up to 

6 km. Tsunami warnings broadcast on 

television and radio in three minutes 

were followed immediately by sirens 

to evacuate. Thanks to pre-event 

preparedness that identified hazard 

zones, practiced evacuation to safety, 

and educated schools and the public, 

lives were saved. Nearly 17,000 people 

died, but representing only ~5% of 

the exposed population. Nonetheless, 

as in previous tsunamis, a 

disproportionate number of casualties 

were the elderly, women, and young 

children. (L. Kong, ITIC)

North Shore of Oahu, 

Hawaii. During the 

tsunami generated 

by the March 9, 

1957, Aleutian 

Island earthquake, 

people foolishly 

searched for fish 

on the exposed 

reef, unaware that 

tsunami waves 

would return in 

minutes to inundate 

the shoreline. 

(Honolulu StarBulletin)

As dangerous as tsunamis are, they do 

not happen very often. You should not 

let this natural hazard diminish your 

enjoyment of the beach and ocean. But, if you 

think a tsunami may be coming, the ground 

shakes strongly or for a long time under your 

feet, the ocean recedes out to sea exposing 

the sea bottom, you hear a train-like roar, or 

you know that there is a warning, tell your 

relatives and 

friends, and

Move Quickly 

Inland and to 

Higher Ground!
United Nations Educational, Scientific and Cultural Organization (UNESCO) 

Intergovernmental Oceanographic Commission (IOC)

7 Place de Fontenoy

75352 Paris Cedex 07 SP, FRANCE

Tel: +33 1 45 68 39 84

Fax: +33 1 45 68 58 12

http://ioc.unesco.org

http://www.ioc-tsunami.org/

Illustrations and layout by Joe Hunt Design, Honolulu, Hawaii, and ITIC

Background images and wave logo courtesy of Aqualog, France

International Tsunami Information Center

A UNESCO/IOC – NOAA Partnership

1845 Wasp Boulevard, Building 176

Honolulu, Hawaii 96818, U.S.A.

Tel: +1 808 725 6050

Fax: +1 808 725 6055

E-mail: itic.tsunami@noaa.gov

http://www.tsunamiwave.info

W W W.TS U N A M IWAVE.IN F O

NI TERNATIONAL TSUNAMI INFORMATION CENTER

United Nations

Educational, Scientific and

Cultural Organization

Intergovernmental

Oceanographic

Commission

ACKNOWLEDGMENTS

 

THE PREPARATION OF THIS BROCHURE WAS SUPPORTED BY:

Intergovernmental Oceanographic Commission (IOC) of UNESCO

International Tsunami Information Center (ITIC): UNESCO/IOC – NOAA Partnership

Department Analyse Surveillance Environnement (DASE), France

U.S. Department of Commerce, National Oceanographic and Atmospheric Administration (NOAA)

TECHNICAL GUIDANCE PROVIDED BY:

International Tsunami Information Center: UNESCO/IOC – NOAA Partnership, http://www.tsunamiwave.info

Department Analyse Surveillance Environnement, France, http://www-dase.cea.fr

U.S. National Weather Service

Pacific Tsunami Warning Center (PTWC), http://ptwc.weather.gov

U.S. National Tsunami Warning Center (US NTWC), http://ntwc.arh.noaa.gov 

U.S. National Ocean Service, http://www.nos.noaa.gov

U.S. National Geophysical Data Center, http://www.ngdc.noaa.gov

U.S. Pacific Marine Environmental Laboratory, http://www.pmel.noaa.gov

Servicio Hidrográfico y Oceanográfico, Chile, http://www.shoa.cl

School 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:
2014 United Nations

ucational, Scientific and

Cultural Organization

Intergovernmental

Oceanographic

Commission