2. General Tsunami Terms: A... to Tr...

This section contains the general terms used in tsunami mitigation and in tsunami generation and modelling. PART 1: A-TR.

A sea-surface wave that has become so steep (wave steepness of 1/7) that the crest outraces the body of the wave  and  it  collapses  into  a  turbulent mass on shore or over a reef. Breaking usually occurs when the water depth is less than 1.28 times the wave height. Roughly, three kinds of breakers can be distinguished, depending primarily on the gradient of the bottom: a) spilling breakers (over nearly flat bottom) which form a foamy patch at the crest and break gradually over a considerable distance; b) plunging breakers (over fairly steep bottom gradient) which peak up, curl over with a tremendous overhanging mass and then break with a crash; c) surging breakers (over very steep bottom gradients) which do not spill or plunge but surge up the beach face. Waves also break in deep water if they build too high while being generated by the wind, but these are usually short-crested and are termed whitecaps.

An offshore or onshore structure, such as a wall, water gate, or other in-water wave-dissipating object that is used to protect a harbour or beach from the force of waves.

Sea wall with stairway evacuation route.

Sea wall with stairway evacuation route used to protect a coastal town against tsunami inundation in Japan. Photo courtesy of River Bureau, Ministry of  Land, Infrastructure and Transport, Japan.

Water gate used to protect against tsunami waves on Okushiri Island, Japan.

Water gate used to protect against tsunami waves on Okushiri Island, Japan. The gate begins to automatically close within seconds after earthquake shaking triggers its seismic sensors.  Photo courtesy of ITIC.

By analogy with a molecule, a “glob” of fluid within the fluid mass that has a certain integrity and life history of its own; the activities of the bulk fluid being the net result of the motion of the eddies.

Eddies generated by the interactions of tsunami waves as they hit the coast of Sri Lanka.

Eddies generated by the interactions of tsunami waves as they hit the coast of Sri Lanka, 26 December 2004.  Photo courtesy of Digital Globe.

Estimated time of arrival (ETA)
Time of tsunami arrival at some fixed location, as estimated from modeling the speed and reftaction of the tsunami waves as they travel ftom the source. ETA is estimated with very good precision if the bathymetry and source are well known (less than a couple of minutes).  The first wave is not necessarily the largest, but it is usually one of the first five waves.

Evacuation map 
A drawing or representation that outlines danger  zones and designates limits beyond which people must be evacuated to avoid harm from tsunami waves.

Inundation and Evacuation Map created for the coastal town of Pucusana, Peru.

Inundation and Evacuation Map created for the coastal town of Pucusana, Peru.

Elevated platform used for tsunami evacuation in Okushiri Island, Japan.

Elevated platform used for tsunami evacuation that also serves as a high-elevation scenic vista point for tourist. Okushiri Island, Japan.  Photo courtesy of ITIC.

             Emergency shelter building, Kisei, Mie Prefecture, Japan.

Emergency shelter building that also acts as community centre and Museum for Disaster Prevention. Kisei, Mie Prefecture, Japan. The building is 22-m high, has five floors covering 320 m2 , and holds 500 persons.  Info courtesy of  http://www.webmie.or.jp.

Historical tsunami data
Historical data are available in many forms and at many locations. These forms include published and unpublished catalogs of tsunami occurrences, personal narratives, marigraphs, tsunami amplitude, run-up and inundation zone measurements, field investigation reports, newspaper accounts, film or video records.

A seiche may be initiated by a standing wave oscillating in a partially or fully enclosed body of water.  May be initiated by long period seismic waves (an earthquake), wind and water waves, or a tsunami.

Seismic sea wave
Tsunamis are sometimes referred to as seismic sea waves because they are most often generated by earthquakes.

Travel time
Time required for the first tsunami wave to propagate ftom its source to a given point on a coastline.

Travel time map
Map showing isochrons or lines of equal tsunami travel time calculated ftom the source outwards toward terminal points on distant coastlines.

Travel times for 22 May 1960 Chile tsunami crossing the Pacific basin.

Travel times (in hours) for the 22 May 1960 Chile tsunami crossing the Pacific basin. This tsunami was extremely destructive along the nearby coast of Chile, and the tsunami also caused significant destruction and casualties as far away as Hawaii and Japan. The awareness and concern raised by this Pacific-wide tsunami ultimately led to the formation of the PTWS.



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Regional Disaster Information Center (Latin America & the Caribbean)

A database of Spanish language materials focused on tsunami preparedness.
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Post-Tsunami Survey:
El Salvador Summary Video

Learn the basics of a post-tsunami survey.

TsunamiTeacher USA
Tsunami Basics

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Learn the basics of tsunamis. Available in English and Samoan.

Tsunamis on the Move

Tsunami Awareness Poster

Awareness poster available in English, Chinese, French, Japanese, Korean, Portuguese, Singalese.


Global Hazard Maps

Posters of Tsunami Sources, Significant Earthquakes and Significant Volcanic Eruptions. Also Tsunami Sources Icosohedron Globe.

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Tsunami, The Great Waves

Available in English, Spanish, French and Chinese.


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Tsunami Glossary

Available in English, Arabic, Spanish, French and Bahasa. 



Where the First Wave Arrives in Minutes

Available in English, Bahasa, Spanish and French.


DVD copies for PC and Macintosh computers are available free of charge from the ITIC, Hawaii (itic.tsunami@noaa.gov).

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