IntroductionWhat is tsunami?

A tsunami (pronounced tsooNAH-mee) is a series of waves, made in an ocean or other body of water by an earthquake, landslide, volcanic eruption, or meteorite impact. Tsunamis can cause huge destruction when they hit coastlines. Some people call tsunamis “tidal waves”, but these large waves really have little to do with tides, so the term “tidal wave” does not really suit them.

The term tsunami comes from the Japanese, meaning "harbor" (tsu, 津) and "wave" (nami, 波). There are only a few other languages that have a native word for this disastrous wave. In the Tamil language, the word is aazhi peralai. In the Acehnese language, it is ië beuna or alôn buluëk. On Simeulue island, off the western coast of Sumatra in Indonesia, in the Defayan language the word is semong, while in the Sigulai language it is emong.

Tsunami waves are different from the waves you can usually find rolling into the coast of a lake or ocean. Those waves are made by wind offshore and are quite small compared with tsunami waves. A tsunami wave in the open ocean can be more than 100 km across. That’s roughly the length of 1000 American football fields! Tsunami waves are huge and can travel very quickly, at about 700 km/hr, but they are only about one meter high in the open sea.

Tsunamis are caused by sudden movement of the sea bed, during an earthquake or volcano. The result is a ripple of waves, just as if you dropped a large stone into a pool. Tsunami waves can travel at over 400 miles an hour through deep ocean, but don't usually cause any trouble at that stage to ships or boats. That's because the water is deep and the waves are long. Ships and boats just rise and fall gently - and may have no idea that a Tsunami wave has just passed beneath them.

As a tsunami wave travels into the shallower water near the coast, it slows and grows in height. Even though a tsunami may be barely visible at sea, it may grow to be many meters high near the coast and have a tremendous amount of energy. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide or a series of waves with a maximum height of up to 30 meters.

A few minutes before a tsunami wave hits, the water near shore may move away, exposing the ocean floor. Often the first wave may not be the largest, and additional waves may arrive at the coast every 10 to 60 minutes. They move much faster than a

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person can run. The danger from a tsunami can last for several hours after the arrival of the first wave. Unlike other waves, tsunami waves typically do not curl and break.

Coasts affected by a tsunami will be severely eroded. A tsunami can cause flooding hundreds of meters inland. The water moves with such force that it is capable of crushing homes and other buildings.

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Tsunami wave facts - speed and depth

A tsunami can travel at well over 970 kph (600 mph) in the open ocean - as fast as a jet flies. It can take only a few hours for a tsunami to travel across an entire ocean. A regular wave (generated by the wind) travels at up to about 90 km/hr.

As a tsunami wave approaches the coast (where the sea becomes shallow), the trough (bottom) of a wave hits the beach floor, causing the wave to slow down, to increase in height (the amplitude is magnified many times) and to decrease in wavelength (the distance from crest to crest).

At landfall, a tsunami wave can be hundreds of meters tall. Steeper shorelines produce higher tsunami waves.

In addition to large tsunami waves that crash onto shore, the waves push a large amount of water onto the shore above the regular sea level (this is called runup). The runup can cause tremendous damage inland and is much more common than huge, thundering tsunami waves

Tsunami wave falls as it approaches land, and how the height rises. We can see this in graph below:

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How often do Tsunami waves happen?

Tsunamis happen far more often than most people realise. Hawai sees a small tsunami every year and Alaska, Californai, Oregan, Washington, Japan, Indonesia, Malaysia, Philipines, India and other parts of the world can all expect to experience larger or smaller tsunamis in the future.

The Size of a Tsunami

Tsunamis have an extremely long wavelength (wavelength is the distance between the crest (top) of one wave and the crest of the next wave) -- up to several hundred miles long. The period (the time between two successive waves) is also very long -- about an hour in deep water.

In the deep sea, a tsunami's height can be only about 1 m (3 feet) tall. Tsunamis are often barely visible when they are in the deep sea. This makes tsunami detection in the deep sea very difficult.

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CharacteristicsWhen the wave enters shallow water, it slows down and its amplitude (height)

increases.

The wave further slows and amplifies as it hits land. Only the largest waves crest.

While everyday wind waves have a wavelength (from crest to crest) of about 100 meters (330 ft) and a height of roughly 2 meters (6.6 ft), a tsunami in the deep ocean has a wavelength of about 200 kilometers (120 mi). Such a wave travels at well over 800 kilometers per hour (500 mph), but due to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 meter (3.3 ft). This makes tsunamis difficult to detect over deep water. Ships rarely notice their passage.

As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its velocity slows below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its amplitude grows enormously, producing a distinctly visible wave. Since the wave still has such a long wavelength, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break (like a surf break), but rather appears like a fast moving tidal bore. Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front.

When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant

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time between the wave crests. The first wave to reach the shore may not have the highest run up.

A wave becomes a shallow-water wave when the ratio between the water depth and its wavelength gets very small. Since a tsunami has a large wavelength, tsunamis act as a shallow-water wave even in deep oceanic water. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s2) and the water depth. For example, in the Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200 m/s (about 712 km/hr or 442 mi/hr) with little energy loss even for far distances, while at a water depth of 40 m, the speed is 20 m/s (about 71 km/hr or 44 mi/hr), much slower, but still difficult to outrun.

In deep water, the energy of a tsunami is constant, a function of its height and speed. Thus, as the wave approaches land, its height increases while its speed decreases. While in deep water a person at the surface of the water would probably not even notice the tsunami, the wave can increase to a height of 30 m and more as it approaches the coastline and compresses. Tsunamis can cause severe destruction on coasts and islands, even at locations remote to the source event, where that event itself is not even noticable without instruments.

Tsunamis propagate outward from their source, so coasts in the "shadow" of affected land masses are usually fairly safe. However, tsunami waves can diffract around land masses (as shown in this Indian Ocean tsunami animation as the waves reach southern Sri Lanka and India). They also need not be symmetrical; tsunami waves may be much stronger in one direction than another, depending on the nature of the source and the surrounding geography.

About 80% of tsunamis occur in the Pacific Ocean, but are possible wherever there are large bodies of water, including lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.

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Tsunami HistoryAlthough tsunamis occur most frequently in the Pacific Ocean, they are known

to occur anywhere. Many ancient descriptions of sudden and catastrophic waves exist, particularly in and around the Mediterranean. A large percentage of world cultures share the legend of a Great Deluge or Flood, which may have been inspired by oral histories of real-life tsunamis.

Past World Earthquakes and Tsunami List :

26 Dec 2004 - Indian Ocean tsunami2004 Indian Ocean earthquake. The magnitude 9.0 2004 Indian Ocean earthquake

triggered a series of lethal tsunamis on December 26, 2004, with over one hundred and fifty thousand fatalities, ranging from those in the immediate vicinity of the quake in Indonesia, Thailand and the north-western coast of Malaysia to people thousands of kilometers away in Bangladesh, India, Sri Lanka, the Maldives, and even as far as Somalia in eastern Africa. The death toll from this event makes it the deadliest tsunami in recorded history.

Unlike the Pacific Ocean, there is no organized alert service covering the Indian Ocean. This is in part due to the absence of major tsunami events since 1883 (the Krakatoa eruption) and an emphasis on developing a tropical cyclone warning system.

The tsunami has sparked the largest ever relief efforts, gathering more than $2 billion dollars from all over the world in contributions so far.

5000 BC and beyond

5000 B.C. (and beyond). In the North Atlantic, the Storegga Slide is a major series of sudden underwater land movements resulting in massive tsunami covering much of present-day Scotland.

1650 BC, Santorini, Greece TsunamiSantorini. At some time between 1650 BC and 1600 BC (still debated), the

volcanic Greek island Santorini blew up in a violent eruption, causing a 100m to 150m high tsunami that devastated the north coast of Crete, 70km (45 miles) away, and would certainly have eliminated every timber of the Minoan fleet along Crete's northern shore.

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1755, Portugal1 November 1755 - Lisbon, Portugal. Tens of thousands of Portuguese who

survived the great 1755 Lisbon earthquake were killed by a tsunami which followed minutes later. Many townspeople fled to the waterfront, believing the area safe from fires and falling debris from aftershocks. Before the great wall of water hit the harbor waters retreated, revealing lost cargo and forgotten shipwrecks.

The earthquake, tsunami, and subsequent fires killed some more than a third' so Lisbon's pre-quake population of 275,000. Historical records of explorations by Vasco da Gama and Christopher Columbus were destroyed, and the power and colonial ambitions of the Portuguese Empire were sharply curtailed. 18th century Europeans stuggled to understand the disaster within religious and rational belief systems. Philosophers of the Enlightenment, notably Voltaire, wrote extensively about the Lisbon earthquake and the devastation. The concept of the sublime, as described by philosopher Immanuel Kant in the Observations on the Feeling of the Beautiful and Sublime, took its inspiration from attempts to comprehend the enormity of the Lisbon quake and tsunami.

Many animals sensed danger and fled to higher ground before the water arrived. This is the first documented case of such a phenomenon, which was also noted in Sri Lanka in the 2004 Indian Ocean (Boxing Day) earthquake. Some scientists speculate that animals may have an ability to sense subsonic Rayleigh waves from an earthquake minutes or hours before a tsunami strikes shore.

1883, Krakatoa Volcano26 August 1883 - Krakatoa explosive eruption. The island volcano of Krakatoa in

Indonesia exploded with devastating fury in 1883, blowing its underground magma chamber partly empty so that much overlying land and seabed collapsed into it. A series of large tsunami waves was generated from the explosion, some reaching a height of over 40 meters above sea level. Tsunami waves were observed throughout the Indian Ocean, the Pacific Ocean, the American West Coast, South America, and even as far away as the English Channel. On the facing coasts of Java and Sumatra the sea flood went many miles inland and caused such vast loss of life that one area was never resettled but went back to the jungle and is now the Ujung Kulon nature reserve.

1960, Chili22 May 1960 - Chilean tsunami. The Great Chilean Earthquake, the largest

earthquake ever recorded, off the coast of South Central Chile, generated one of the most destructive tsunamis of the 20th century. It spread across the entire Pacific Ocean, with waves measuring up to 25 meters high. When the tsunami hit Onagawa Japan almost 22 hours after the quake, a tide gauge recorded a wave height of 10 feet above high tide. The number of people killed by the earthquake and subsequent tsunami is estimated to be between 490 to 2,290.

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1964, Alaska, British Columbia27 March 1964 - Good Friday tsunami. After the magnitude 9.2 Good Friday

Earthquake, tsunamis struck Alaska, British Columbia, California and coastal Pacific Northwest towns, killing 122 people. The tsunamis were up to 6 m tall that killed 11 people as far away as Crescent City, California.

EFFECT OF TSUNAMNI IN ANCIENT DAYS

Other historical tsunamis:Other tsunamis that have occurred include the following:

The 1755 Lisbon earthquake, along with the resulting tsunami and fires, led to near total destruction of the Portuguese capital.

One of the worst tsunami disasters engulfed whole villages along Sanriku, Japan, in 1896. A wave more than seven stories tall (about 20 m) drowned some 26,000 people.

1946: An earthquake in the Aleutian Islands sent a tsunami to Hawaii, killing 159 people (only five died in Alaska).

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1958: A very localized tsunami in Lituya Bay, Alaska was the highest ever recorded: more than 500 m (1500 ft) above sea level. It did not extend much beyond the outlet of the fjord in which it occurred, but did kill two people in a fishing vessel.

1976: August 16 (midnight) a tsunami killed more than 5000 people in the Moro Gulf region (Cotabato city) of the Philippines.

1983: 104 people in western Japan were killed by a tsunami spawned from a nearby earthquake.

July 17, 1998: A Papua New Guinea tsunami killed roughly 3,000 people. A 7.1 magnitude earthquake 15 miles offshore was followed within 10 minutes by a tsunami about 12 m tall. While the magnitude of the quake was not large enough to create a tsunami directly, it is believed the earthquake generated an undersea landslide, which in turn caused the tsunami. The villages of Arop and Warapu were destroyed.

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Megatsunami, Seiche Tsunamis Evidence shows that megatsunamis, a tsunami more than 100 meters (325ft) high, are possible. These rare events are typically caused by significant chunks of an island collapsing into the ocean, and can be extraordinarily devastating to faraway coastal regions.

Related to a tsunami is a seiche, an underwater, irregular fluctuation or rhythmic rocking of the water level of a lake. Often large earthquakes produce both tsunamis and seiches at the same time and there is evidence that some seiches have been caused by tsunamis.

The highest tsunami wave ever recorded was very localized: caused by a landslide in Lituya Bay, Alaska in 1958, a tsunami more than 500 m high stripped trees and soil from the steep walls of a fjord. By the time the wave reached the open sea, however, it dissipated quickly. The height of the waves was determined more by the topography of the inlet than by the energy generated by the landslide.

Seismic wave

A seismic wave is a wave that travels through the Earth, often as the result of an earthquake or explosion. Seismic waves are studied by seismologists, and measured by a seismograph.

Body Waves Body waves travel through the interior of the Earth. They follow curved paths because of the varying density and composition of the Earth's interior. This effect is similar to the refraction of light waves. Body waves transmit the preliminary tremors of an earthquake but have little destructive effect. Body waves are divided into two types: primary (P) and secondary (S) waves.  

P waves are longitudinal or compressional waves, which means that the ground is alternately compressed and dilated in the direction of propagation. These waves generally travel twice as fast as S waves and can travel through any type of material. Typical speeds are 330m/s in air, 1450m/s in water and about 5000m/s in granite.  

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S waves are transverse or shear waves, which means that the ground is displaced perpendicularly to the direction of propagation, alternately to one side and then the other. S waves can travel only through solids. Their speed is about 58% of that of P waves in a given material.

Surface Waves Surface waves are analogous to water waves and travel over the Earth's surface. They travel more slowly than body waves. Because of their low frequency, they are more likely than body waves to stimulate resonance in buildings, and are therefore the most destructive type of seismic wave. There are two types of surface waves: Rayleigh waves and Love waves.  

Rayleigh waves , also called ground roll, are surface waves that travel as ripples similar to those on the surface of water. The existence of these waves was predicted by John William Strutt, Lord Rayleigh, in 1885. They are slower than body waves.  

Love waves are surface waves that cause horizontal shearing of the ground. They are named after A.E.H. Love, a British mathematician who created a mathematical model of the waves in 1911. They are usually slightly faster than Rayleigh waves. A quick and dirty way to determine the distance from a location to the orgin of a seismic wave is to take the difference of arrival time from the P wave to the S wave in seconds and multiply by 8 kilometers per second.

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Megatsunami

A megatsunami is a rare tsunami more than 100 meters (325ft) high. Aside from some large tsunamis in Alaska, including one 520 m high, the last megatsunami to hit a populated area is believed to have occurred 4,000 years ago. Geologists say it is usually caused by a very large landslide, such as a collapsing island, into a vast body of water such as an ocean or sea.

Megatsunamis can rise to heights of hundreds of meters, travel at 890 km/h in mid-ocean and potentially reach 20 km inland in low-lying regions.

In deep ocean, a megatsunami is barely noticeable. It moves as a vertical shift of only a metre or so throughout the volume of water, with a crest to crest distance of hundreds of kilometers. However the huge amount of energy in the motion of this massive volume generates a much higher wave as it approaches shallow water.

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Underwater earthquakes do not normally generate such large tsunamis unless they also trigger an underwater landslide — typically they have a height of less than ten metres.

Landslides that are large compared to the depth of water hit the water so fast that the displaced water cannot settle before the rocks hit the bottom. This means that the rocks displace the water at full speed all the way to the bottom. If the water is deep, the displaced volume is large and the lower parts are under high pressure. The resulting wave contains large amounts of energy.

Some have conjectured that historic megatsunamis underlie the deluge legends that are common to many cultures throughout the world. However this is unlikely, considering that megatsunamis usually occur without any warning, only hit coastal areas, and do not necessarily occur after a rain.

Tsunami phases and wave form

A tsunami can arrive at a coastline in one of two ways. First, there's the negative wave where the trough of the wave precedes the actual arrival of the crest or 'wave' itself. Here, the common and better known warning sign of an impending tsunami strike is a rapidly receding sea followed by a sudden onrushing body of water traveling inland at high speed. The second form in which a tsunami arrives is the positive wave or crest first. In this case, the warning signs are much more vague if any. The sea will usually start rising immediately rather slowly at first without the receding phase, much more like an on-coming high tide but instead of stopping at tidal level it will keep on rising faster and faster until the crest of the tsunami passes and continues moving inland. Therefore, the second form of tsunami waves are usually more dangerous owing to the fact that it can

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arrive without much warning giving residents less time to prepare and outrun the tsunami. These two types of tsunamis are usually generated simultaneously(in opposing direction of travel) by a megathrust earthquake similar to the 2004 Indian Ocean earthquake.

Retreat-rise cycle (negative wave)

The tsunami was a succession of several waves, occurring in retreat and rise cycles with a period of over 30 minutes between each peak. The third wave was the most powerful and reached highest, occurring about an hour and a half after the first wave. Smaller tsunami continued to occur for the rest of the day.

Rise-retreat-rise cycle (positive wave)

If the crest of a tsunami arrives first, there won't be any recession. The sea level will increase rapidly to inundate everything in the path of the tsunami. This appears to be the case in countries such as Sri Lanka and India that lies to the west of the Andaman-Sumatra fault where the tsunami originates. After the first tsunami wave passed, water will then begin to flow back into the ocean receding at a quicker pace as the second wave arrives.

Tsunami intensity and magnitude scales

As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events.

Intensity scales

The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity

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scale, used in the Pacific. The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula

where Hav is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.

Magnitude scales

The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy. Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale Mt, calculated from,

where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicenter, a, b & D are constants used to make the Mt scale match as closely as possible with the moment magnitude scale.

TSUNAMI CAUSESA tsunami can be generated when convergent or destructive plate boundaries

abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent (constructive) or conservative plate boundaries. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of tsunami.

Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above

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the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

On April 1, 1946, a magnitude-7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 metres (46 ft) high surge. The area where the earthquake occurred is

where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.

Examples of tsunami at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilized sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before traveling transoceanic distances.

The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc.)

The 1960 Valdivia earthquake (Mw 9.5) (19:11 hrs UTC), 1964 Alaska earthquake (Mw 9.2), and 2004 Indian Ocean earthquake (Mw 9.2) (00:58:53 UTC) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (Mw 4.2) earthquakes in Japan can

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trigger tsunamis (called local and regional tsunamis) that can only devastate nearby coasts, but can do so in only a few minutes.

In the 1950s, it was hypothesised[who?] that larger tsunamis than had previously been believed possible may be caused by landslides, explosive volcanic eruptions (e.g., Santorini and Krakatau), and impact events when they contact water. These phenomena rapidly displace large water volumes, as energy from falling debris or expansion transfers to the water at a rate faster than the water can absorb. The media dub them megatsunami.

Tsunamis caused by these mechanisms, unlike the trans-oceanic tsunami, may dissipate quickly and rarely affect distant coastlines due to the small sea area affected. these events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay 1958, which produced a wave with an initial surge estimated at 524 metres (1,720 ft). However, an extremely large landslide might generate a megatsunami that can travel trans-oceanic distances, although there is no geological evidence to support this hypothesis.

Most tsunamis are caused by submarine earthquakes which dislocate the oceanic crust, pushing water upwards.

Tsunami can also be generated by erupting submarine volcanos ejecting magma into the ocean.

A gas bubble erupting in a deep part of the ocean can also trigger a tsunami

Earthquake-generated tsunami

An earthquake may generate a tsunami if the quake:

occurs just below a body of water, is of moderate or high magnitude, and displaces a large-enough volume of water.

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Drawing of tectonic plate boundary before earthquake.

Overriding plate bulges under strain, causing tectonic uplift.

Plate slips, causing subsidence and releasing energy into water.

The energy released produces tsunami waves.

2004 Indian Ocean Tsunami

Date December 26, 2004Magnitude 9.3 Mw

Depth 30 km (19 mi)Epicenter location

3°18 ′ 58 ″ N 95°51 ′ 14 ″ E / 3.316°N 95.854°E Coordinates : 3°18 ′ 58 ″ N 95°51 ′ 14 ″ E / 3.316°N 95.854°E

Type Undersea (subduction)Countries/regions affected

Indonesia (mainly in Aceh)Sri LankaIndia (mostly in Tamil Nadu)

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ThailandMaldives

The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra-Andaman earthquake.[3][4] The resulting tsunami itself is given various names, including the 2004 Indian Ocean tsunami, Asian Tsunami, Indonesian Tsunami, and Boxing Day Tsunami.

Origin Time and Epicenter

The great tsunamigenic earthquake occurred on Sunday, 26 December 2004, at 00:58:50 UTC (6:58:50 a.m. local time). The epicenter was at 3.298 N, 95.779 E and its focal depth was very shallow (much less than 33 km - possibly about 10km)

Magnitude and Energy Release

The quake was widely felt in Sumatra, the Nicobar and Andaman Islands, Malaysia, Myanmar, Singapore, Thailand, Bangladesh and India.

According to the U.S. Geological Survey (USGS NEIC (WDCS-D)), the moment magnitude of the earthquake - which is larger than the Richter magnitude - was 9. Such magnitude would make this earthquake to be the fourth largest in the world since 1900 - and the largest since the 1964 Alaska earthquake.

However, on the basis of subsequent analysis of additional seismograms from around the world, scientists at Northwestern University determined the earthquake's magnitude to be 9.3 and not 9.0, as originally estimated. Therefore, the calculated energy release was 1.13 X 10 (raised to the 30 power) dynes-cm , or three times larger than originally thought. The revised estimate makes this earthquake to be the second largest ever instrumentally recorded. The largest earthquake ever recorded, which measured 9.5, was in Chile on May 22, 1960.

Tectonic Setting

The region where the great earthquake occurred on 26 December 2004, marks the seismic boundary formed by the movement of the Indo-Australian plate as it collides with the Burma subplate, which is part of the Eurasian plate. However, the Indo-Australian tectonic plate may not be as coherent as previously believed. According to recent studies

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reported in the Earth and Planetary Science Letters (vol 133), it apears that the two plates have separated many million years ago and that the Australian plate is rotating in a counterclockwise direction, putting stress in the southern segment of the India plate.

For millions of years the India tectonic plate has drifted and moved in a north/northeast direction, colliding with the Eurasian tectonic plate and forming the Himalayan mountains. As a result of such migration and collision with both the Eurasian and the Australian tectonic plates, the Indian plate's eastern boundary is a diffuse zone of seismicity and deformation, characterized by extensive faulting and numerous large earthquakes.

USGS graphic showing the migration of the Indian tectonic plate

The epicenter of the 26 December 2004 earthquake was near the triple point junction of three tectonic plates where major earthquakes and tsunamis have occurred in the past.

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Previous major earthquakes have occurred further north, in the Andaman Sea and further South along the Sumatra, Java and Sunda sections of one of the earth's greatest fault zones, a subduction zone known as the Sunda Trench. This great trench extends for about 3,400 miles (5,500 kms) from Myanmar (Burma) south past Sumatra and Java and east toward Australia and the Lesser Sunda Islands, ending up near Timor. Slippage and plate subduction make this region highly seismic. The volcanoes of Krakatau, Tambora and Toba, well known for their violent eruptions, are byproducts of such tectonic interactions.

In addition to the Sunda Trench, the Sumatra fault is responsible for seismic activity on the Island of Sumatra. This is a strike-slip type of fault which extends along the entire length of the island.

The Burma plate encompasses the northwest portion of the island of Sumatra as well as the Andaman and the Nicobar Islands, which separate the Andaman Sea from the Indian Ocean. Further to the east, a divergent boundary separates the Burma plate from the Sunda plate.

More specifically, in the region off the west coast of northern Sumatra, the India plate is moving in a northeastward direction at about 5 to 5.5 cm per year relative to the Burma plate.

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Seismicity of the Region

Earthquakes originate at two principal tectonic sources in Indonesia. The major tectonic feature in the region is the Sunda Arc that extends approximately 5,600 km between the Andaman Islands in the northwest and the Banda Arc in the east. The Sunda Arc consists of three primary segments; the Sumatra segment, the Sunda Strait Segment and the Java Segment. These locations represent the area of greatest seismic exposure, with maximum earthquake magnitudes of up to 7.75 or even more on the Richter scale (as this latest earthquake with Moment Magnitude 9 indicates - and which occcurred on the Sumatra segment).

The region where the earthquake occurred - and particularly the Andaman Sea - is a very active seismic area. According to the literature (Bapat 1982) from 1900 to 1980, a total of 348 earthquakes were recorded in the area bounded by 7.0 N to 22.0 N and 88.0 E to 100 E. However, only five of these earthquakes in the Bay of Bengal had magnitudes equal to or greater than 7.1 ( ranging from 7.1 to 8.5). Also Sumatra is in the center of one of the world's most seismically active regions. Earthquakes with magnitude greater than 8 struck Sumatra in 1797, 1833, and 1861. Earthquakes with magnitude greater than 7 struck offshore islands in 1881, 1935, 2000, and 2002.

Aftershocks

As of 1 January, 2005, there were about 84 aftershocks with magnitudes ranging from 5.0 to 7.0 in the region of Northern Sumatra and the Nicobar and Andaman Islands. Twenty six (26) of these - including the largest- occurred on 26 December 2004, the same day as the main earthquake. Since 1 January 2005, many more aftershocks have occurred. The aftershocks are expected to continue for several weeks and months. Some of the major aftershocks have occurred in the vicinity of the epicenter of a past earthquake which had occurred on 26 June 1941 and some in the area near the Nicobar Islands where the 1881 earthquake had occurred.

The distribution of afteshocls suggests that the earthquake resulted by the sudden slip of these two plates and that there was a slip as well as an upward thrust of the Burma plate along this boundary.

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Chronological Sequence of Major Aftershocks Along the West Coast of Northern Sumatra and in the Nicobar and Andaman Island Region Following the Major Earthquake on 26 December 2004

MAGNITUDE DATE UTC-TIME LATITUDE LONGITUDE

DEPTH REGION

8.9 2004/12/26 00:58:51 3.298 95.779 10.0 West Coast

of Northern Sumatra

5.9 2004/12/26 01:48:47 5.393 94.423 10.0 West Coast of Northern Sumatra

5.8 2004/12/26 02:15:58 12.375 92.509 10.0 Andaman Islands

6.0 2004/12/26 02:22:02 8.83 92.532 10.0 Nicobar Islands

5.8 2004/12/26 02:34:50 4.104 94.184 10.0 West Coast of Northern Sumatra

5.8 2004/12/26 02:36:06 12.139 93.011 10.0 Andaman Islands

6.0 2004/12/26 02:51:59 12.511 92.592 10.0 Andaman Islands

5.9 2004/12/26 02:59:12 3.177 94.259 10.0 West Coast of Northern Sumatra

6.1 2004/12/26 03:08:42 13.808 92.974 10.0 Andaman Islands

7.3 2004/12/26 04:21:26 6.901 92.952 10.0 Nicobar Islands

5.7 2004/12/26 06:21:58 10.623 92.323 10.0 Andaman Islands

5.7 2004/12/26 07:07:10 10.336 93.756 10.0 Andaman Islands

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5.8 2004/12/26 07:38:25 13.119 93.051 10.0 Andaman Islands

6.5 2004/12/26 09:20:01 8.867 92.382 10.0 Nicobar Islands

6.2 2004/12/26 10:19:30 13.455 92.791 10.0 Andaman Islands

6.3 2004/12/26 11:05:01 13.542 92.877 10.0 Andaman Islands

Crustal Displacements and Rupture

The distribution of the larger aftershocks indicates that the two tectonic plates (the India plate and the Burma subplate) slipped for about 1,200 km along their boundary. The aftershocks extend from northern Sumatra (approximately 3 degrees North Latitude) to the Andaman Islands (approximately 14 degrees north). Therefore, the length of the overall rupture is estimated to be about 1,200 km.

However, the slippage does not appear to be continuous. It appears that it occurred in two phases along two sections of the great fault that parallels the Sunda Trench. The rupture started near the epicenter off the western coast of North Sumatra and progressed - at a fast rate - northward to the Andaman islands along a preexisting major fault. For the first 500-600 km the orientation of the rupture (the quake's strike) was appoximately 320- 330 degrees. Subsequently the rupture continued - at a much slower rate in an approximate North-South direction - for another 500 -600 km along another segment of the northern Sunda fault system. This is probably the same segment that ruptured during the 1941 Andaman Islands earthquake - which also generated a destructive tsunami.

It has been estimated that this megathrust faulting along the India and Burma boundary has resulted in a shift that averaged about 15 meters with maximum slip being 20 meters. The vertical upward movement of the sea floor may have been several meters - possibly as much as 5 meters or more in some places. At some of the islands there may be subsidence while at others there was upthrusting. Field surveys of the islands off Summatra and of the Nicobar and Andaman islands - when completed - will provide better estimates of net crustal movements.

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No Tsunami Warning Issued

The large tsunami which struck 11 of the nations that border the Indian Ocean was a complete surprise for the people living there, but not for the scientists who are aware of the tectonic interactions in the region. Many seismic networks recorded the massive earthquake, but there was no tide gauges or other wave sensors to provide confirmation as to whether a tsunami had been generated. There was no established communications network or organizational infastructure to pass a warning of any kind to the people coastlines.

No Tsunami Warning System exists for the Indian Ocean as there is for the Pacific. The Pacific Tsunami Warning Center in Honolulu had no way of providing warning information to the region. Part of the problem is that most of the countries in the region have underestimated their potential tsunami threat from the Northern end of the Sunda Trench. Review of historical records would have revealed that a very destructive tsunami occurred in 1941, in the same general area. This particular tsunami killed more than 5,000 people on the eastern coast of India, but it was mistaken for a "storm surge". Thousands more must have gotten killed elsewhere in the islands of the Bay of Bengal in 1941, but there has been no sufficient documentation. Unfortunately, no Regional Tsunami Warning System, Preparedness Program, or effective Communications Plan exist for this part of the world.

Effects of the 26 December 2004 Tsunami in the Bay of Bengal and in the Indian Ocean

Waves of up to 10.5 meters in height struck Northern Sumatra, the Nicobar and Andaman Islands, Thailand, Sri Lanka, India. Destructive waves also struck the Maldives, Somalia, Kenya and the islands off the African coast. The tsunami was recorded by tide gauge stations not only in the Indian Ocean, but in the Pacific as well. In Manzanillo, Mexico, the tide gauge recorded a wave of 2.6 meters.

Eighteen (18) countries bordering the Indian Ocean were affected by the tsunami. These were: Indonesia, Thailand, India, Sri-Lanka, Malaysia, Myanmar, Bangladesh, Maldives, Reunion Island (French), Seychelles, Madagascar, Mauritius, Somalia, Tanzania, Kenya, Oman, South Africa and Australia.

DEATH TOLL -The tsunami had its greatest impact and casualties in Indonesia, Thailand, India, Shri-Lanka, Malaysia, Myanmar, Maldives and Somalia. Eleven (11) countries reported deaths, some in tens of thousands.The death toll thus ar has been reported as 226,566. However, this is an underestimate as thousands are still missing and many more may have been killed in remote islands. More than 1.5 million people were left homeless around the region.

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INDONESIA

Tsunami waves of up to ten meters swamped the smaller outlying islands of Sumatra as well as its northern and western coastal areas - about 100 km (60 mi) from the earthquake epicenter . Hardesh hit was the northern Aceh province. Nearly all the casualties and damage took place within this province. Very heavy damage occurred as far South as Tapatkuan. The waves also propagated around the northern tip of Sumatra into the Straits of Malacca and struck coastal settlements along the northeast coast as far east as Lhokseumawe.

According to the latest official reports (Ministry of Health) 166,320 people were killed, 127,774 are still missing and 655,000 people were displaced in Northern Sumatra. A total of 110 bridges were destroyed, 5 seaports and 2 airports sustained considerable damage, and 82% of all roads were severy damaged. The death toll is expected to rise. The following is a summary of the tsunami impact in Northern Sumatra.

DISASTER CAUSED BY TSUNAMI

THAILAND

Hardest hit was the Southwest coast of Thailand, particularly Phuket and the resort areas of Phi Phi and Khao-Lak. It took about two hours for the first of the tsunami waves to reach the resort of Phi Phi island.

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The arrival of the tsunami was heralded by a recession of the water which exposed the sea bottom for considerable distance, including previously submerged rocks. According to eyewitness reports, the first wave arrived at about 10:30 am local time and it was about 4 meters high. The second wave arrived about 2.5 minutes later and it was 7 meters. The third about 11 meters.The waves destroyed all beachfront hotels, bungalows and other structures at Phi Phi, hurling boats and other floating objects . All electricity and phone lines were cut. The hisghest reported wave was 11.6 meters at Khao-Lak beach.

Thai Government sources reported 5,313 deaths, 8,457 injuries and 4,499 missing, including more than 1,000 foreign tourists. Many of the missing are presumed dead. It is expected that these estimates will be revised upwards.

INDIA

The estimated number of casualties in India is 16,000, but at least 6,000 more are missing. It is expected that the death toll will rise. Hardest hit were the Andaman and Nicobar Islands which were close to the tsunami generating area. Along India's southeastern coast, several villages were swept away, and thousands of fishermen at sea were missing. On the western coast of India' mainland, hardest hit was the state of Tamil Nadu.

Andaman and Nicobar Islands - The tsunami hit hard the Andaman and Nicobar group which comprises of a total of 572 islands of which 38 were significantly inhabited. Entire islands have been The waves literally washed away some of these islands, and there were reports that the island of Trinket had split in two. The Great Nicobar and Car Nicobar were the worst hit among all the southern Nicobar Islands because of their proximity to the earthquake's epicenter and relative low topography. The maximum tsunami wave reached a height of 15m. According to reports one fifth of the population of the Nicobar Islands is said to be dead, injured or missing. Chowra Island lost two thirds of its population of 1,500.

The official death toll is 812, but about 7,000 were reported as missing. The unofficial death toll (including those missing and presumed dead) is estimated to be about 7,000 and expected to rise. On 30 December 2004, four days after the great earthquake, Barren 1 volcano on Barren Island - located 135 kilometres (80 miles) northeast of the capital Port Blair - erupted.

Andhra Pradesh - There was significant loss of life and destruction. The affected districts were Krishna, Prakasam, Nellore, Guntur, West Godavari and East Godavari.

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Kerala - The tsunami killed many people (official toll 168) and caused extensive destruction particularly at Kollam (131 dead), Alappuzha (32) and Ernakulam (5) were also affected.

Pondicherry - In the Union territory of Pondicherry, the affected districts were Pondicherry (107 dead), Karaikal (453 dead). The latest official toll was 560. An estimated 30,000 people were rendered homeless .

Tamil Nadu - The tsunami had a great impact on the state of Tamil Nadu on India's mainland with entire coastal villages destroyed. According to official reports the overall death toll in the state was 7,793. The Nagapattinam district had 5,525 casualties. The latest reported death toll at Velankanni was 1,500. Kanyakumari district has had 808 deaths, Cuddalore district 599, the state capital Chennai 206 and Kancheepuram district 124. The death tolls in other districts were Pudukkottai (15), Ramanathapuram (6), Tirunelveli (4), Thoothukudi (3), Tiruvallur (28), Thanjavur (22), Tiruvarur (10) and Viluppuram (47). The death toll may be significantly higher as many are still missing. The nuclear power plant at Kalpakkam was shut down after sea water rushed into a pump station. No radiation leak or damage to the reactor was reported.

SRI-LANKA

The first of the tsunami waves took a little over two hours to reach Sri-Lanka. A clock on the western side of Sri Lanka at Colombo stopped at 9:20 in the morning, so the tsunami travel time to Colombo (first wave) must have been about 2 hours and 20 minutes. Sri-Lanka's south and east coasts were hardest hit. More than 50,000 people lost their lives - mostly children and the elderly. Most of them (more than 1,200) were in the eastern district of Batticaloa.

At Trincomalee in the northeast, the tsunami reached more than 2 km (1.25 mi) inland killing about 800 people. In the neighboring Amparai district alone, more than 5,000 people died. The naval base at Trincomalee was reported to be submerged. About 3,000 more people died in Mullaitivu and Vadamaradchi East. A train, known as the "Sea Queen", while traveling between Colombo and Galle, with 1,600 passengers on board, was struck and derailed by the tsunami. Only about 300 of the passengers survived. More than one and a half million people were displaced in Shri-Lanka and the death toll is expected to rise.

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HIGEHT OF TSUNAMI THAT OCCOURED IN 2004

Tsunami Wave Heights and Tsunami Travel Times

Tsunami waves varied in height. Maximum reported height was reported as being 10.5 meters, A detailed report on tsunami wave distribution for different of the stricken areas througout the Indian Ocean is being compiled from reports of eyewitnesses and other sources. A list of tsunami wave heigts as recorded by tide stations will be provided. However, most of the tide stations that recorded the tsunami are at distant locations. It is not known at this time whether any tide gauge stations closer to the tsunami generating area recorded the tsunami. An effort is being made to locate such records from tide stations that were not destroyed by the tsunami - if such stations exist,

Tsunami travel times for different areas in the Bay of Bengal and throughout the Indian Ocean are being compiled. Travel times of the first tsunami wave after the earthquake: Sumatra 10 minutes ,Thailand: 1 Hour, Sri Lanka: 2 hours, India: 2 Hours, East Africa: about 7 Hours.

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PENINSULA OF ACEP MEULABOH IN NORTHERN SUMATRA - one of the hardest hit by the tsunami areas.

TSUNAMI DrawbackIf the first part of a tsunami to reach land is a trough (called a drawback) rather

than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas.

A drawback occurs because the tectonic plate on one side of the fault line sinks suddenly during the earthquake, causing the overlaying water to propagate outwards with the trough of the wave at its front. It is also for this reason that there would not be any drawback when the tsunami travelling on the other side arrives ashore, as the tectonic plate is "raised" on that side of the fault line.

Drawback begins before the wave's arrival at an interval equal to half of the wave's period. If the slope of the coastal seabed is moderate, drawback can exceed hundreds of meters. People unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed. During the Indian Ocean tsunami, the sea withdrew and many people went onto the exposed sea bed to investigate. Pictures show people walking on the normally submerged areas with the advancing wave

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in the background. Few survived.

Tsunami Warning SystemsMany cities around the Pacific, notably in Japan but also in Hawaii, have

warning systems and evacuation procedures in the event of a serious tsunami. Tsunamis are predicted by various seismologic institutes around the world and their progress monitored by satellites.

Bottom pressure recorders with buoys as communication links are used to detect waves which would not be noticed by a human observer on deep water. The first rudimentary system to alert communities of an impending tsunami was attempted in Hawaii in the 1920s. More advanced systems were developed in the wake of the April 1, 1946 and May 23, 1960 tsunamis which caused massive devastation in Hilo, Hawaii. The United States created the Pacific Tsunami Warning Center in 1949, and linked it to an international data and warning network in 1965.

One system for providing tsunami warning is the CREST Project (Consolidated Reporting of Earthquakes and Tsunamis) implemented on the West coast (Cascadia),

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Alaska, and Hawaii of the United States by the USGS, NOAA, the Pacific Northwest Seismograph Network, and three other university seismic networks.

Tsunami prediction remains an imperfect science. Although the epicenter of a large underwater quake and the probable tsunami arrival times can be quickly calculated, it is almost always impossible to know whether massive underwater ground shifts have occurred, resulting in tsunami waves. As a result, false alarms are common.

The topography of the sea floor can however give a guidance on safe spots. For example, vertical disturbance on ocean bed infested with mountains are less like to lead to destructive Tsunami. This is because a possible tsunami will partially or completely collapse in the middle of the ocean if it encounters a mountain on its journey to the dry land.

No system can protect against a sudden tsunami. A devastating tsunami occurred off the coast of Hokkaido in Japan as a result of an earthquake on July 12, 1993. As a result, 202 people on the small island of Okushiri lost their lives, and hundreds more were missing or injured. This tsunami struck just three to five minutes after the quake and most victims were caught while fleeing for higher ground and secure places after surviving the earthquake.

While there remains the potential for sudden devastation from a tsunami, warning systems can be effective. For example if there were a very large subduction zone earthquake (magnitude 9.0) off the west coast of the United States, people in Japan, for example, would have a little more than 12 hours (and likely warnings from warning systems in Hawaii and elsewhere) before any tsunami arrived, giving them some time to evacuate areas likely to be affected.

Signs and warnings

Despite a lag of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken completely by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general populace living around the ocean. Tsunami detection is not easy because while a tsunami is in deep water it has little height and a network of sensors is needed to detect it. Setting up the communications infrastructure to issue timely warnings is an even bigger problem, particularly in a relatively poor part of the world.

Tsunami are much more frequent in the Pacific Ocean because of earthquakes in the "Ring of Fire", and an effective tsunami warning system has long been in place there. Although the extreme western edge of the Ring of Fire extends into the Indian Ocean (the point where this earthquake struck), no warning system exists in that ocean. Tsunamis there are relatively rare despite earthquakes being relatively frequent in Indonesia. The last major tsunami was caused by the Krakatoa eruption of 1883. It should be noted that

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not every earthquake produces large tsunamis; on March 28, 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.

In the aftermath of the disaster, there is now an awareness of the need for a tsunami warning system for the Indian Ocean. The United Nations started working on an Indian Ocean Tsunami Warning System and by 2005 had the initial steps in place. Some have even proposed creating a unified global tsunami warning system, to include the Atlantic Ocean and Caribbean.

The first warning sign of a possible tsunami is the earthquake itself. However, tsunami can strike thousands of kilometres away where the earthquake is only felt weakly or not at all. Also, in the minutes preceding a tsunami strike, the sea often recedes temporarily from the coast. Around the Indian Ocean, this rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as 2.5 km (1.6 mi) of exposed beach, with fatal results.[45] However, not all tsunami causes this 'disappearing sea' effect. In some cases, there are no warning signs at all. The sea will suddenly swell without retreating surprising many people and giving them little time to flee.

Economic impact OF TSUNAMI

The impact on coastal fishing communities and fisher folk, some of the poorest people in the region, has been devastating with high losses of income earners as well as boats and fishing gear. In Sri Lanka artisanal fishery, where the use of fish baskets, fishing traps, and spears are commonly used, is an important source of fish for local markets; industrial fishery is the major economic activity, providing direct employment to about 250,000 people. In recent years the fishery industry has emerged as a dynamic export-oriented sector, generating substantial foreign exchange earnings. Preliminary estimates indicate that 66% of the fishing fleet and industrial infrastructure in coastal regions have been destroyed by the wave surges, which will have adverse economic effects both at local and national levels.

But some economists believe that damage to the affected national economies will be minor because losses in the tourism and fishing industries are a relatively small percentage of the GDP. However, others caution that damage to infrastructure is an

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overriding factor. In some areas drinking water supplies and farm fields may have been contaminated for years by salt water from the ocean.

Both the earthquake and the tsunami may have affected shipping in the Malacca Straits by changing the depth of the seabed and by disturbing navigational buoys and old shipwrecks. Compiling new navigational charts may take months or years.

Countries in the region appealed to tourists to return, pointing out that most tourist infrastructure is undamaged. However, tourists were reluctant to do so for psychological reasons. Even resorts on the Pacific coast of Thailand, which were completely untouched, were hit by cancellations.

Environmental impact OF TSUNAMI

Beyond the heavy toll on human lives, the Indian Ocean earthquake has caused an enormous environmental impact that will affect the region for many years to come. It has been reported that severe damage has been inflicted on ecosystems such as mangroves, coral reefs, forests, coastal wetlands, vegetation, sand dunes and rock formations, animal and plant biodiversity and groundwater. In addition, the spread of solid and liquid waste and industrial chemicals, water pollution and the destruction of sewage collectors and treatment plants threaten the environment even further, in untold ways. The environmental impact will take a long time and significant resources to assess.

According to specialists, the main effect is being caused by poisoning of the freshwater supplies and the soil by saltwater infiltration and deposit of a salt layer over arable land. It has been reported that in the Maldives, 16 to 17 coral reef atolls that were overcome by sea waves are totally without fresh water and could be rendered

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uninhabitable for decades. Uncountable wells that served communities were invaded by sea, sand and earth; and aquifers were invaded through porous rock. Salted-over soil becomes sterile, and it is difficult and costly to restore for agriculture. It also causes the death of plants and important soil micro-organisms. Thousands of rice, mango and banana plantations in Sri Lanka were destroyed almost entirely and will take years to recover. The United Nations Environment Programme (UNEP) is working with governments of the region in order to determine the severity of the ecological impact and how to address it. UNEP has decided to earmark a US$1,000,000 emergency fund and to establish a Task Force to respond to requests for technical assistance from countries affected by the tsunami. In response to a request from the Maldivian Government, the Australian Government sent ecological experts to help restore marine environments and coral reefs—the lifeblood of Maldivian tourism. Much of the ecological expertise has been rendered from work with the Great Barrier Reef, in Australia's northeastern waters.

Could Tsunami deaths have been prevented?

Many scientists had been warning of the risks of a severe Tsunami in the region, and continue to warn of future Tsunami risks. The 2004 Tsunami was caused by a major shift in part of a well-known fault line. The result was an increased pressure on other parts of the fault, making further earthquakes more likely.

We never know when a major earthqake will happen. Tsunami waves travel very fast, and it is impossible to provide warnings for those very close to the earthquake zone which generates the wave. However, it is certainly possible to provide other coastal areas further away with adequate time for many people to get out of danger by moving to higher ground.

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Tsunami warning systems are now in place across the region most affected in December 2004 and were used during a recent tremor (April 2005). If they had been working earlier, it is possible that many tens of thousands of lives would have been saved.

CONCLUSION Human societies face disasters from time to time. In these times of emergencies it becomes necessary for the civic authorities and the people to respond in a way that will help the affected people.

Disaster like tsunami can occur with warning or without warning .Whatever it may be, for some hours the community and local health personnel have only themselves to fall back upon, till outside assistance arrives. This period is normally of 48 to 72 hours and is called the “Rescue” phase.

The basic aim of any disaster management plan is:

1. To prepare the community to handle the disaster in the first 48 hours till outside help does not reach the affected area.

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2. To have an effective and appropriate system in place to provide assistance to the affected people.

Once the disaster strikes it is necessary to evaluate the situation. It has to look the consequences of the disaster. Another major function of the local committee for disaster management is to coordinate with different levels to avoid confusion and chaos.

The assessment is to be undertaken in the following way:

A. GENERAL INFORMATION Assessment of the no. of homeless, Estimation of the type, extent and seriousness of the material damage, Information of isolated villages, Information of people cut off from their families, Forecasts as to how the natural phenomena responsible for the disaster will

develop.

B. REQUESTS FOR ASSISTANCE Machines for clearing rubble, Means of transport, fuel, Shelters Blankets, clothing, boots, raincoats, Food, tools, batteries, containers, materials Persons specializing in rescue work

C. REQUESTS MADE BY THE LOCAL HEALTH Health equipment and material, Medicaments, Any health personnel required, Suitably equipped hospitals to which patients may be sent who cannot be

looked after on the spot, Means and organisation for evacuating the injured and the sick.

Post recovery phase also becomes important after the initial rescue and help. This is the period (usually after 2 to 3 days) when outside help starts and when reality of disaster begins to sink in affected population.

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Rapid steps must be taken to establish a system of continuous contact with the families stricken by the disaster.

Disaster will organise itself to deal with the post-disaster period (rehabilitation phase), assigning responsibilities in various fields like:

Water supply, food , means of survival, Transport and highway maintenance, communications and information, Public works, building Sanitation, Health, Public law and order,

Taking care of the dead including animals

BIBLOGRAPHY

For completion of this project on TSUNAMI we have referred to various sources that are:

Newspaper cut outs Magazines Books on environment www.Encyclopedia.com

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PHOTO GALLARY

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