teletsunami or distant tsunami A tsunami originating from a distant source, generally more than 1000 km away. Far less frequent, but potentially much more hazardous are Pacific-wide or distant tsunamis. These occur when the disturbance that generates the tsunami is sufficiently great. Usually starting as a local tsunami that causes extensive destruction near the source, these waves continue to travel across the entire ocean basin with sufficient energy to cause additional casualties and destruction on shores more than a thousand km from the source. In the last two hundred years, there have been at least seventeen destructive Pacific-wide tsunamis. The most destructive Pacific-wide tsunami of recent history was generated by a massive earthquake off the coast of Chile on May 22, 1960. All Chilean coastal towns between the 36th and 44th parallels were either destroyed or heavily damaged by the action of the tsunami and the quake. The combined tsunami and earthquake toll included 2,000 killed, 3,000 injured, 2,000,000 homeless, and $550 million damage. Off the coastal town of Corral, Chile, the waves were estimated to be 20 meters (67 feet) high. The tsunami caused 61 deaths in Hawaii, 20 in the Philippines, and 100 or more in Japan. Estimated damages were US$50 million in Japan, US$24 million in Hawaii and several more millions along the west coast of the United States and Canada. Distant wave heights varied from slight oscillations in some areas to 12 meters (40 feet) at Pitcairn Island; 11 meters at Hilo, Hawaii; and 6 meters at some places in Japan. A Pacific-wide tsunami today, similar in size to the May 1960 event, could easily have catastrophic consequences.

tidal wave 1. The wave motion of the tides. 2. In popular usage, any unusually high and therefore destructive water level along a shore. It usually refers to either a storm surge or tsunami.

tide The rhythmic, alternate rise and fall of the surface (or water level) of the ocean, and of bodies of water connected with the ocean such as estuaries and gulfs, occurring twice a day over most of the Earth, and resulting from the gravitational attraction of the moon (and, in lesser degrees, of the sun) acting unequally on different parts of the rotating Earth.

tide amplitude One-half of the difference in height between consecutive high water and low water; hence, half of the tidal range.

tide gauge A device for measuring the height (rise and fall) of the tide. Especially an instrument for automatically making a continuous graphic record of tide height versus time. Picture of a Chilean Tide Gauge installed on a pier at Coquimbo bay (latitude 30º South) showing the waterproof case, the solar panel, the flat antenna and the pressure sensor.

tide station A place where tide observations are obtained.

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

travel time map Map showing isochrons or lines of equal tsunami travel time calculated from the source terminal points on distant coastlines. Travel-times (in hours) for the May 22, 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 TWSP and ITSU.

tsunami A series of traveling waves of extremely long length and period, usually generated by disturbances associated with earthquakes occurring below or near the ocean floor. (Also called seismic sea wave and, pospularly, tidal wave.) Also, a series of ocean waves produced by a submarine earthquake, landslide, or volcanic eruption. These waves may reach enormous dimensions and travel across entire ocean basins with little lost of energy. They proceed as ordinary gravity waves with a typical period between 5 and 60 minutes.  Tsunamis steepen and increase in height on approaching shallow water, inundating low-lying areas; and where local submarine topography causes extreme steeping, they may break and cause great damage. Tsunamis have no connection with tides; the popular name is entirely misleading. Destruction along the waterfront of Hilo, Hawaii from the Pacific-wide tsunami generated off the coast of Unimak Island, Aleutian, USA on April 1, 1946

tsunami amplitude Usually measured on a water level record, it is: 1.the absolute value of the difference between a particular peak or trough of the tsunami and the undisturbed water level at the time, 2. half the difference between an adjacent peak and trough, corrected for the change of tide between that peak and trough. It is intended to represent the true amplitude of the tsunami wave at some point in the ocean. However, it is often an amplitude modified in some way by the response of the tide gauge. Mareogram record of a tsunami

tsunami amplitude (maximum) Usually measured on a water level record, it is half the value of the maximum peak-to-trough excursion, corrected for the change of tide between that peak and trough.

Tsunami Bulletin Board Email exchange system primarily for tsunami scientists that is used to quickly disseminate ideas and information regarding tsunamis and tsunami research. The Tsunami Bulletin Board has been very useful for helping to rapidly organize post-tsunami surveys and distribute their results, and to plan tsunami workshops and symposia.

tsunami damage Loss or harm caused by a destructive tsunami. More specifically, the damage caused directly Massive destruction in the town of Aonae on Okushiri Island, Japan caused by the regional tsunami of July 12, 1993. by tsunamis can be summarized into the following: 1) deaths and injuries; 2) houses destroyed, partly destroyed, inundated, flooded, or burned; 3) other property damage and loss; 4) boats washed away, damaged or destroyed; 5 ) lumber washed away; 6) marine installations destroyed, and; 7) damage to public utilities such as railroads, roads, electric power plants, water supply installations, etc.  Indirect secondary tsunami damage can be: 1) Damage by fire of houses, boats, oil tanks, gas stations, and other facilities; 2) environmental pollution caused by drifting materials, oil, or other sub stances; 3) outbreak of disease of epidemic proportions which could be serious in densely populated areas.

tsunami dispersion Redistribution of tsunami energy, particularly as a function of its period, as it travels across a body of water.

tsunami earthquake An earthquake that produces an unusually large tsunami relative to the earthquake magnitude (Kanamori,1972 ). Tsunami earth quakes are characterized by a very shallow focus, fault dislocations greater than several meters, and fault surfaces smaller than for normal earthquakes. They are also slow earthquakes, with slippage along their faults occurring more slowly than would occur in normal earthquakes. The last events of this type were 1992 Nicaragua and 1996 Chimbote, Peru.

tsunami generation Tsunamis are generated primarily by tectonic dislocations under the sea which are Tsunami generated by an earthquake caused by shallow focus earthquakes along areas of subduction. The upthrusted and downthrusted crustal blocks impart potential energy into the overlying water mass with drastic changes in the sea level over the affected region. The energy imparted in to the water mass results in tsunami generation which is energy radiating away from the source region in the form of long period waves. Tsunami generated by a landslide   Tsunami generated by a pyroclastic flow

tsunami generation theory The theoretical problem of generation of the gravity wave (tsunami) in the layer of elastic liquid (an ocean) occurring on the surface of elastic solid half-space (the crust) in the gravity field can be studied with methods developed in the dynamic theory of elasticity. The source representing an earthquake focus is a discontinuity in the tangent component of the displacement on some element of area within the crust. For conditions representative of the Earth’s oceans, the solution of the problem differs very little from the joint solution of two more simple problems: the problem of generation of the displacement field by the given source in the solid elastic half-space with the free boundary (the bottom) considered quasi-static and the problem of the propagation of gravity wave in the layer of heavy incompressible liquid generated by the known (from the solution of the previous problem) motion of the solid bottom. There is the theoretical dependence of the gravity wave parameters on the source parameters (depth and orientation). In particular, a very rough estimation of the source energy passing into the gravity wave can be obtained. In general, a portion of it corresponds to the estimates obtained with empirical data. Also, tsunamis can be generated by other different mechanisms such as volcanic or nuclear explosions, landslides, rock falls and submarine slumps.

tsunami hazard The pr obability of th at a t sunami o f a particular size will strike a particular section of coast. Tsunami Hazard There are tens of thousands of kilometers of coastline in the Pacific region, representing portions of at least 23 countries around the rim, and 21 island states. These areas are developing at an accelerating rate with the expansion of harbor and industrial facilities in most locations, and increasing population densities almost everywhere. This element of growth in both population and in frastructure development exposes more people and their homes, buildings, and transportation systems to the onslaught of tsunamis. Since 1992, major local tsunamis have claimed more than 4 ,200 lives and caused hundreds of millions of dollars in property damage.

tsunami hazard assessment For each coastal community, an assessment of the tsunami hazard is needed to identify populations and assets at risk, and the level of that risk. This assessment requires knowledge of probable tsunami sources (such as earthquakes, landslides, volcanic eruption), their likelihood of occurrence, and the characteristics of tsunamis from those sources at different places along the coast. For those communities, data of earlier (historical and paleotsunamis) tsunam is may help quantify these factors. For most communities, however, only very limited or no past data exist. For these coasts, numerical models of tsunami inundation can provide estimates of a reas that will be flooded in the event of a local or distant tsunamigenic earthquake, local landslide.

tsunami impact Although infrequent, tsunamis are among the most terrifying and complex physical phenomena and have been responsible for great loss of life and extensive destruction to property. Because of their destructiveness, tsunamis have important impacts on the human, social and economic sectors of societies. Historical records show that enormous destruction of coastal communities throughout the world has taken place and that the socio-economic impact of tsunamis in the past has been enormous. In the Pacific Ocean where the majority of these waves have been generated, the historic record shows tremendous destruction with extensive loss of life and property. In Japan, which has one of the most populated coastal regions in the world and a long history of earthquake activity, tsunamis have destroyed entire coastal populations. There is also a history of severe tsunami destruction in Alaska, the Hawaiian Islands, and South America, although records for these areas are not as extensive. The last major Pacific-wide tsunami occurred in 1960. Many other local and regional destructive tsunamis have occurred with more localized effects.

Tsunami Information Bulletin Message issued by PTWC to advise participants of the occurrence of a major earthquake in the Pacific or near-Pacific area, with the evaluation that a potentially destructive Pacific-wide tsunami was not generated.

tsunami magnitude Mt  tsunami magnitude Mt Measurement of the overall physical size of a tsunami, defined in terms of instrumental tsunami-wave amplitudes. Tsunami magnitude is defined by: Mt =log2H as revised by Iida, Cox, and Pararas-Carayannis (1967), where H is the maximum run-up height or amplitude on a coastline near the generating area. Other tsunami magnitude scales have been proposed, also based on maximum run-up height. Abe defined two different tsunami magnitude amplitudes. His first tsunami magnitude (1979) is: Mt =logH +B where H is the maximum single crest or trough amplitude of the tsunami waves (in meters) and B a constant. The second definition (1981) is: Mt =logH +alogR +D where R is the distance in km from the earthquake epicenter to the tide station along the shortest oceanic path, and a and D are constants.

tsunami numerical modeling Often the only way to determine the potential run ups and inundation from a local or distant tsunami is to use numerical modeling, since data from past tsunamis is usually insufficient. Models can be initialized with potential worst case Estimated Tsunami Inundation at Iquique-Chile, based on numerical model results. scenarios for the tsunami sources or for the waves just offshore to determine corresponding worst case scenarios for runup and inundation. Models can also be initialized with smaller sources to understand these verity of the hazard for the less extreme but more frequent events. This information is then the basis for creating tsunami evacuation maps and procedures. At present, such modeling has only been carried out for a small fraction of the coastal areas at risk. Sufficiently accurate modeling techniques have only been available in recent years, and these models require training to understand and use correctly, as well as input of detailed bathymetric and topographic data in the area being modeled. Numerical models have been used inrecent years to simulate tsunami propagation and interaction with land masses. Such models usually solve similar equations but often employ different numerical techniques and are applied to different segments of the total problem of tsunami propagation from generation regions to distant areas of runup. For example, several numerical models have been used to simulate the interaction of tsunamis with islands. These models have used finite difference, finite element, and boundary integral methods to solve the linear long wave equations. These models solve these relatively simple equations and provide reasonable simulations of tsunamis for engineering purposes. Historical data are very limited for most Pacific coastlines. Consequently, numerical modeling may be the only way to estimate the potential risk to those areas from the tsunami hazard. Techniques now exist to carry out this assessment. Computer programs and training necessary to perform this modeling need to be transferred to all Pacific countries at risk through programs such as the IOC/ITSU Tsunami Inundation Modeling Exchange.

tsunami observation Notice, observation or measurement of sea level fluctuation at a particular point in time caused by the incidence of a tsunami on a specific point.

tsunami period Amount of time that a tsunami wave takes to complete a cycle. Tsunami periods typically range from 5 minutes to 2 hours.

tsunami period (dominant) Difference between the arrival time of the highest peak and the next one measured on a water level record.

tsunami preparedness Readiness of plans, methods, procedures and actions taken by government officials and the general public for the purpose of minimizing potential risk and mitigating the effects of future tsunamis. The appropriate preparedness for a warning of impending danger from a tsunami requires knowledge of areas that could be flooded (tsunami inundation maps) and knowledge of the warning system to know when to evacuate and when it is safe to return.

tsunami propagation Tsunamis travel outward in all directions from the generating area, with the direction of the main energy propagation generally being orthogonal to the direction of the earthquake fracture zone. Their speed depends on the depth of water, so that the waves undergo accelerations and decelerations in passing over an ocean bottom of varying depth. In the deep and open ocean, they travel at speeds of 500 to 1,000 kilometers per hour (300 to 600 miles per hour). The distance between successive crests can be as much as 500 to 650 kilometers (300 to 400 miles); however, in the open ocean, the height of the waves is generally less than a meter (3 feet) even for the most destructive teletsunamis, and the waves pass unnoticed. Variations in tsunami propagation result when the propagation impulse is stronger in one direction than in others because of the orientation or dimensions of the generating area and where regional bathymetric and topographic features modify both the wave form and rate of advance. Specifically tsunami waves undergo a process of wave refraction and reflection throughout their travel. Tsunamis are unique in that the waveform extends through the entire water column from sea surface to the ocean bottom. It is this characteristic that accounts for the great amount of energy propagated by a tsunami. Model of the tsunami propagation in the southeast Pacific, nine hours after its generation. Source: Antofagasta, Chile (30 July, 1995)

tsunami risk The probability of a particular coastline being struck by a tsunami times what is exposed to tsunami damaged and casualties along that coast. In general terms, risk is the hazard times the exposure.

tsunami source Point or area of tsunami origin, usually the site of an earthquake, volcanic eruption, or landslide that caused large-scale rapid displacement of the water to initiate the tsunami waves.

tsunami velocity or shallow water velocity The velocity of an ocean wave whose length is sufficiently large compared to the water depth (i.e., 25 or more times the depth) can be approximated by the following expression: c =Sqrt(gh) Where: c is the wave velocity g the acceleration of gravity h the water depth. Thus, the velocity of shallow-water waves is independent of wave length L. In water depths between ½L and 1/25 L it is necessary to use a more precise expression: c =Sqrt((gL/2π )[tanh(2 π h/L)]) Wave Height and Water Depth: in the open ocean a tsunami is less than afew feet high at the surface, but its wave height increases rapidly in shallow water. Tsunami wave energy extends from the surface to the bottom in the deepest waters. As the tsunami attacks the coastline, the wave energy is compressed into am much shorter distance creating destructive, life threatening waves.

Tsunami Warning Bulletin Warning message issued throughout the Pacific based on confirmation that a tsunami has been generated that poses a threat to the population in part or all of the Pacific. A Tsunami Warning will be followed by additional bulletins with updated information until it is cancelled.

tsunami wave length The horizontal distance between similar points on two successive waves measured perpendicularly to the crest. The wave length and the tsunami period give an information on the tsunami source. For tsunami generated by earthquakes, typical wave length range from 20 to 300 km. For tsunami generated by landslide, the wave length range from hundreds of meters to tens of kilometers.

tsunami zonation (tsunami zoning) Designation of distinctive zones along coastal areas with varying degrees of tsunami risk and vulnerability for the purpose of disaster preparedness, planning, construction codes, or public evacuation.

tsunami zoning (tsunami zonation) Designation of distinctive zones along coastal areas with varying degrees of tsunami risk and vulnerability for the purpose of disaster preparedness, planning, construction codes, or public evacuation.

tsunamic Having features analogous to those of a tsunami or descriptive of a tsunami.

tsunamigenic Having generated a tsunami: a tsunamigenic earthquake, a tsunamigenic landslide.

TWSP Tsunami Warning System in the Pacific. Seismic data used by PTWC in support of the TWSP Tsunami warning systems in the Pacific can be classified by two related factors: 1) the type of tsunami they are prepared to warn against - from local to distant, and 2) the area of responsibility (AOR) they warn for each type of tsunami - sub-national, national, regional, or international. The Pacific-wide system operated by PTWC provides an international warning about onehalf to one hour after the occurrence of the earthquake, and is effective for communities located at least several hundred kilometers from the source region. Regional systems, such as those operated by the USA, Japan, the Russian Federation, France, and Chile, provide primarily domestic warnings within about 10-15 minutes of the earthquake and are effective for communities located at least a hundred kilometers from the source region. Local systems operated by Japan, Chile and United States of America are capable of providing a warning in about 5 minutes or less to give some measure of protection to communities located within a hundred kilometers of the source. Just as important as issuing warnings, are issuing rapid cancellations to warnings when no significant waves are found to exist, and informational messages for large but not potentially tsunamigenic earthquakes. Centers that operate the tsunami warning systems include: the Pacific Tsunami Warning Center at Ewa Beach, Hawaii, USA; the West Coast /Alaska Tsunami Warning Center at Palmer, Alaska, USA; the Russian Federation tsunami warning centers at Petropavlovsk-Kamchatskiy, Kurilskiye, and Sakha-links; the Japanese tsunami warning centers at Sapporo, Sendai, Tokyo, Osaka, Fukuoka, and Naha; the French Polynesia Tsunami Warning Center at Papeete, Tahiti, and the National Tsunami Warning System of Chile headquartered at Valparaiso. Certain other Member States have also recently established or improved their seismic and/or water level instrumentation and analysis capabilities as the basis for national tsunami warning systems.