tsunami causes

7/31/2019 Tsunami Causes

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ThinkQuest Team 01724 (Oct 04 May 05)

Tsunami:

Magnitude of Terror

Causes


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Contents

Plate Tectonics

Tsunami Formation

Indian Ocean Earthquake


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Causes

Plate Tectonics


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Plate Tectonics

In the 20th century, a German meteorologist named AlfredWegener proposed the Continental Drift Theory whichstates that the surface of the Earth actually consisted ofplates which were in constant slow motion.

By the 1950s, the theory was later improved to become theTheory of Plate Tectonics which is widely accepted today.

According to this theory, the Earths surface is broken intoeight major plates and several other smaller ones. The

edges of these plates are known as the plate boundaries,and are areas with intense geologic activity, e.g. earthquakes,volcanic activities and folding of the crust.

These plates are continuously in motion, forming sites of

convergence, divergence and sliding.


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Plates of The World


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Plate Tectonics

Plate tectonics is a combination of two earlier ideas, namelythe Continental Drift Theory and sea-floor spreading.

It states that the earth was actually made up of a hugecontinent many hundreds of millions of years ago, calledPangaea, which broke up into smaller continents to form

the continents today. Sea floor spreading is the creation ofnew oceanic crust at

divergent plate boundaries where two plates move apartfrom each other, allowing magma from the mantle to wellup and cool, forming new sea floor.


7/20ThinkQuest Team 01724 (Oct 04 May 05)

Elastic Rebound Theory

DefinitionElastic rebound theory states that as tectonic plates moverelative to each other, elastic strain energy builds up alongtheir edges in the rocks along fault planes.

As the plates are moving against each other, stress (elastic

strain energy) is gradually build up along the plates' edges.Since the plates are huge and their edges can span thousandsof kilometers, great amount of energy can be stored.

When there is a sudden release of large amount of storedenergies, an earthquake occurs.



Causes

Tsunami Formation



Tsunami Formation

DefinitionTsunamis are defined as extremely large ocean wavestriggered by underwater earthquakes, volcanic activities orlandslides.

The word tsunami was coined from the Japanese word "", translating to "harbor wave" in English.

Tsunamis are sometimes referred to as "tidal waves" by thegeneral public, which is a misnomer as tsunamis areunrelated to the tides.

Tsunamis normally occur in Pacific Ocean, and arerelatively rare in areas surrounding the Indian subcontinent.

The December 26th tsunami disaster is an example of a

tsunami which was triggered by an earthquake.



Tsunami Formation

Tsunamis are characterized as shallow-water waves due totheir long periods and wavelengths.

A wind-generated wave might have a period of ten secondsand a wavelength of 150 meters, but it is possible for atsunami to have a wavelength more than 100 kilometers anda period on the order of one hour, with a wavelength of only

a few centimeters. Tsunamis behave like shallow-water waves.

Shallow-water waves move at speeds equivalent to thesquare root of the product of the acceleration of gravity andthe water depth i.e.

In the Pacific Ocean, where the depth of water is about 4000

meters, tsunamis travel at about 200 m/s. Because the rate of energy loss by the wave is inversely

proportional to its wavelength, tsunamis not only spread athigh speeds, they can also travel large distances with littleenergy loss.



Tsunami Formation

Tsunamis can be generated when the sea floor suddenlydisplaces the overlying water vertically.

Tectonic earthquakes are a kind of earthquake that can causedthat.

When they occur beneath the sea, the water above the deformedarea is displaced from its equilibrium position.

Waves are formed as the displaced water mass, acting under theforce of gravity, tries to regain equilibrium.

When large areas of the sea floor elevate or subside, a tsunamican be created.

Large vertical movements of the earth's crust can occur at plateboundaries.

These boundaries are called faults.

For example, at the boundaries of the Pacific Ocean, denseroceanic plates slip under the less dense continental plates in aprocess known as subduction.

Subduction earthquakes are particularly effective in generatingtsunamis because they provide much force and disturbancesdeep underwater.



Tsunami Formation

As a tsunami leaves the deep ocean and travels toward theshallow coast, it transforms.

A tsunami moves at a speed related to the water depth,therefore the tsunami slows as the water depth decreases.

The tsunami's energy flux, being dependent on both itswave speed and wave height, remains nearly constant.

As a result, the tsunami's speed decreases as it travels intoshallower water, and its height increases.

Because of this shoaling effect, a tsunami, unobvious at sea,may heighten to several meters or more near the coast.

When it reaches the coast, it may appear as a rapidly risingor falling tide or a series of breaking waves.



Tsunami Formation

As a tsunami reaches the shore, it begins to lose energy

whereby part of its wave energy is reflected offshore, while

the shoreward-propagating wave energy is dissipated

through friction and turbulence.

In spite of this, tsunamis still reach the coast with

tremendous amounts of energy



Causes





Statistics

Date : 26 December 2004

Origin Time : 00:58 53 s UTC

Latitude/Longitude : 3.267 North / 95.821 EastDepth : 10 km

Magnitude : 9.0

Locality : 255 km SSE of Banda Aceh, Northern

Sumatra



Official Report

U.S. Geological Survey, National Earthquake Information Center

World Data Center for Seismology, Denver

The devastating megathrust earthquake of December 26, 2004,occurred on the interface of the India and Burma plates and wascaused by the release of stresses that develop as the India plate

subducts beneath the overriding Burma plate. The India plate begins its descent into the mantle at the Sunda trench,

which lies to the west of the earthquake's epicenter.

The trench is the surface expression of the plate interface between theAustralia and India plates, situated to the southwest of the trench, andthe Burma and Sunda plates, situated to the northeast.

At region of the earthquake, the India plate moves northeast at a rateof about 6 cm/year relative to the Burma plate.

This results in oblique convergence at the Sunda trench.



Official Report

This motion is partitioned into thrust-faulting, which occurson the plate-interface and involves slip directedperpendicular to the trench, and strike-slip faulting, whichoccurs several hundred kilometers to the east of the trenchand involves slip directed parallel to the trench.

The December 26 earthquake occurred as the result of

thrust-faulting. Preliminary locations of larger aftershocks following the

megathrust earthquake show that approximately 1200 km ofthe plate boundary slipped as a result of the earthquake.

From the size of the earthquake, it is likely that the averagedisplacement on the fault plane was about 15 meters.

The sea floor overlying the thrust fault would have beenuplifted by several meters as a result of the earthquake.



Comparison

For comparison, the world's largest recordedearthquakes have been listed below.

They have all been megathrust events, occurring whereone tectonic plate subducts beneath another.

These include: 1960 Chile earthquake (Magnitude 9.5)

1964 Prince William Sound, Alaska earthquake(Magnitude 9.2)

1957 Andreanof Islands, Alaska (Magnitude 9.1) 1952 Kamchatka earthquake (Magnitude 9.0)


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References


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Reference

[Online] . http://pubs.usgs.gov/publications/text/historical.htm [1 February 2005] "Elastic Rebound" . "Pacific Earthquake Engineering Research Center" . [Online] .

http://peer.berkeley.edu/~jrodgers/EQDef/eqdef2.htm [5 March 2005]

"2004 Indian Ocean earthquake" . "Wikipedia" . [Online] .http://en.wikipedia.org/wiki/2004_Indian_Ocean_Earthquake [20 February 2005]

"Tsunami" . "Wikipedia" . [Online] . http://en.wikipedia.org/wiki/Tsunami [20February 2005]

"USGS Earthquake Hazards Program-Latest Earthquakes" . "US Geological Survey" .

[Online] . http://earthquake.usgs.gov/eqinthenews/2004/usslav/ [5 March 2005] "26 December 2004 Tsunam" . "National Institute of Oceanography, India" . [Online] .

http://www.nio.org/jsp/tsunami.jsp [5 March 2005]

"Tsunami!: The WWW Tsunami Information Resource" . "Earth and Space Sciences(Geology and Geophysics) at UW" . [Online] .http://www.ess.washington.edu/tsunami/toc.html [5 March 2005]

"Sumatra Earthquake 26 December 2004" . "British Geological Survey" . [Online] .http://www.earthquakes.bgs.ac.uk/latest_info.htm ]

"USGS Earthquake Hazards Program-Latest Earthquakes" . "US Geological Survey" .

[Online] . http://earthquake.usgs.gov/eqinthenews/2004/usslav/ [5 March 2005] "26 December 2004 Tsunam" . "National Institute of Oceanography, India" . [Online] .

http://www.nio.org/jsp/tsunami.jsp [5 March 2005]

"Tsunami!: The WWW Tsunami Information Resource" . "Earth and Space Sciences(Geology and Geophysics) at UW" . [Online] .http://www.ess.washington.edu/tsunami/toc.html [5 March 2005]

"Sumatra Earthquake 26 December 2004" . "British Geological Survey" . [Online] .http://www.earthquakes.bgs.ac.uk/latest_info.htm

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