TSUNAMI CLASSIFICATION

Characteristics of the
Tsunami Phenomena

A tsunami travels outward from the source region as a series of waves. Its speed depends upon the depth of the water, and consequently the waves undergo accelerations or decelerations in passing respectively over an ocean bottom of increasing or decreasing depth. By this process the direction of wave propagation also changes, and the wave energy can become focused or defocused. In the deep ocean, tsunami waves can travel at speeds of 500 to 1,000 kilometers per hour. Near shore, however, a tsunami slows down to just a few tens of kilometers per hour. The height of a tsunami also depends upon the water depth. A tsunami that is just a meter in height in the deep ocean can grow to tens of meters at the shoreline. Unlike familiar wind-driven ocean waves that are only

disturbance of the sea surface, the tsunami wave energy extends to the ocean bottom. Near shore, this energy is concentrated in the vertical direction by the reduction in water depth, and in the horizontal direction by a shortening of the wavelength due to the wave slowing down.

Tsunamis have periods (the time for a single wave cycle) that may range from just a few minutes to as much as an hour or exceptionally more. At the shore, a tsunami can have a wide variety of expressions depending on the size and period of the waves, the near-shore bathymetry and shape of the coastline, the state of the tide, and other factors. In some cases a tsunami may only induce a relatively benign flooding of low-lying coastal areas, coming onshore

similar to a rapidly rising tide. In other cases it can come onshore as a bore - a vertical wall of turbulent water that can be very destructive. In most cases there is also a drawdown of sea level preceding crests of the tsunami waves that results in a receding of the shoreline, sometimes by a kilometer or more. Strong and unusual ocean currents may also accompany even small tsunamis.

Destruction from tsunamis is the direct result of three factors: inundation, wave impact on structures, and erosion. Strong tsunami-induced currents have led to the erosion of foundations and the collapse of bridges and seawalls. Flotation and drag forces have moved houses and overturned railroad cars. Tsunami associated wave forces have demolished frame buildings and other structures. Considerable damage also is caused by the resultant floating debris, including boats and cars that become dangerous projectiles that may crash into buildings, piers, and other vehicles. Ships and port facilities have been damaged by surge action caused by even weak tsunamis. Fires resulting from oil spills or combustion from damaged ships in port, or from ruptured coastal oil storage and refinery facilities, can cause damage greater than that inflicted directly by the tsunami. Other secondary damage can result from sewage and chemical pollution following the destruction. Damage of intake, discharge, and storage facilities also can present dangerous problems. Of increasing concern is the potential effect of tsunami drawdown, when receding waters uncover cooling water intakes associated with nuclear plants.

air-coupled tsunami

Synonym for atmospheric tsunami

atmospheric tsunami

Tsunami-like waves generated by a rapidly moving atmospheric pressure front moving over a shallow sea at about the same speed as the waves, allowing them to couple.

internal tsunami

Tsunami wave manifested as an internal wave and traveling along a thermocline.

local tsunami

A tsunami which its destructive effects are confined to coasts within a hundred km, of the source, usually an earthquake and sometimes a landslide.

microtsunami

A tsunami of such small amplitude that it must be observed instrumentally and is not easily detected visually.

near-field or local tsunami

A tsunami from a nearby source, generally less than 200 km away. A local tsunami is generated by a small earthquake, a landslide or a pyroclastic flow.

Numerical Modeling: snapshots of the water surfaces 10 minutes after the initiation of the submarine landslide of the pyroclastic flow (on the South-East part of Monserrat Island)
 

 

Pacific-wide tsunami

A tsunami capable of widespread destruction, not only in the immediate region of its generation, but across the entire Pacific Ocean

1960 Damaged caused by the May 22,
1960 Chilean Tsunami

paleotsunami

Research on paleotsunamis, events occurring prior to the historical record, has recently been taking place in a few regions around the Pacific. This work is based primarily on the collection and analysis of tsunami deposits found in coastal areas, and other evidence related to the uplift or subsidence associated with nearby earthquakes. In one instance, the research has led to a new concern for the possible future occurrence of great earthquakes and tsunamis along the northwest coast of North America. In another instance, the record of tsunamis in the Kuril-Kamchatka region is being extended much further back in time. As work in this field continues it may provide a significant amount of new information about past tsunamis to aid in the assessment of the tsunami hazard.

regional tsunami

A tsunami capable of destruction in a particular geographic region, generally within about 1000 km of its source. Regional tsunamis also occasionally have very limited and localized effects outside the region.

Most destructive tsunami can be classified as local or regional, meaning their destructive effects are confined to coasts within a hundred km, or up to a thousand km, respectively, of the source -- usually an earthquake. It follows that the majority of tsunami related casualties and property damage also come from local tsunami. Between 1975 and 1998 there have been at least eighteen in the Pacific and its adjacent seas resulting in significant casualties and/or property damage.

Table of recent local and regional tsunamis
Date			Source Location		Est. Lives Lost
29	Nov	1975		Hawaii, USA		2
17	Aug	1976		Philippines		*8,000
18	Jul	1979		Indonesia		540
12	Sep	1979		New Guinea		100
12	Dec	1979		Colombia		500
26	May	1983		Sea of Japan		100
2	Sep	1992		Nicaragua		168
12	Dec	1992		Flores Is., Indonesia		1,000
12	Jul	1993		Okushiri Is., Japan		230
3	Jun	1994		Java, Indonesia		222
4	Oct	1994		Shikotan Is., Russia		11
14	Nov	1994		Philippines		74
9	Oct	1995		Manzanillo, Mexico		1
1	Jan	1996		Sulawesi, Indonesia		9
17	Feb	1996		Irian Jaya, Indonesia		110
23	Feb	1996		Peru		12
17	July	1998		Papua New Guinea		2,500
* May include earthquake casualties

For example, a regional tsunami in 1983 in the Sea of Japan or East Sea, severely damaged coastal areas of Japan, Korea, and Russia, causing more than $800 million in damage, and more than a hundred deaths. Then, after nine years without an event, eleven locally destructive tsunamis occurred in just a seven-year period from 1992 to 1998, resulting in over 4,200 deaths and hundreds of millions of dollars in property damage. In most of these cases, tsunami mitigation efforts in place at the time were unable to prevent significant damage and loss of life. However, losses from future local or regional tsunamis can be reduced if a denser network of warning centers, seismic and water-level reporting stations, and better communications are established to provide a timely warning, and if better programs of tsunami preparedness and education can be put in place.
 

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.

 

Table of major Pacific teletsunamis registered after 1800
Date			Source Location	Est. Lives Lost
20	Feb	1835	Chile	2
7	Nov	1837	Chile	62
13	Aug	1868	Chile	*25,000
10	May	1877	Chile	500
15	Jun	1896	Sanriku, Japan	22,000
31	Jan	1906	Colombia-Eduador	500
17	Aug	1906	Chile	-
7	Sep	1918	Kuril Is., Indonesia	47
11	Nov	1922	Chile	100
3	Feb	1923	Kamchatka, Russia	2
2	Mar	1933	Sanriku, Japan	3,000
1	Apr	1946	Aleutianas Is., U.S.A.	179
4	Nov	1952	Russia	-
9	Mar	1957	Aleutianas Is., U.S.A.	5
22	May	1960	Chile	2,000
28	Mar	1964	Alaska, U.S.A.	112
4	Feb	1965	Aleutianas Is., U.S.A.	-
* May include earthquake casualties

 

tsunami earthquake

An earthquake that produces an unusually large tsunami relative to the earthquake magnitude (Kanamori, 1972). Tsunami earthquakes 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.