thinkquest team 01724 (oct 04 – may 05) tsunami: magnitude of terror causes

ThinkQuest Team 01724 (Oct 04 – May 05)

Tsunami: Magnitude of TerrorCauses


Contents

• Plate Tectonics

• Tsunami Formation

• Indian Ocean Earthquake


Causes

Plate Tectonics


Plate Tectonics• In the 20th century, a German meteorologist named Alfred

Wegener proposed the Continental Drift Theory which states that the surface of the Earth actually consisted of plates which were in constant slow motion.

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

• According to this theory, the Earth’s surface is broken into eight 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.


Plates of The World


Plate Tectonics• Plate tectonics is a combination of two earlier ideas, namely

the Continental Drift Theory and sea-floor spreading. • It states that the earth was actually made up of a huge

continent many hundreds of millions of years ago, called Pangaea, which broke up into smaller continents to form the continents today.

• Sea floor spreading is the creation of new oceanic crust at divergent plate boundaries where two plates move apart from each other, allowing magma from the mantle to well up and cool, forming new sea floor.


Elastic Rebound Theory• Definition

Elastic rebound theory states that as tectonic plates move relative to each other, elastic strain energy builds up along their 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 thousands of kilometers, great amount of energy can be stored.

• When there is a sudden release of large amount of stored energies, an earthquake occurs.


Causes

Tsunami Formation


Tsunami Formation• Definition

Tsunamis are defined as extremely large ocean waves triggered by underwater earthquakes, volcanic activities or landslides.

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

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

• Tsunamis normally occur in Pacific Ocean, and are relatively 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 to

their long periods and wavelengths.• A wind-generated wave might have a period of ten seconds

and a wavelength of 150 meters, but it is possible for a tsunami to have a wavelength more than 100 kilometers and a 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 the squa

re root of the product of the acceleration of gravity and the 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 at high speeds, they can also travel large distances with little energy loss.


Tsunami Formation• Tsunamis can be generated when the sea floor suddenly displaces

the overlying water vertically.• Tectonic earthquakes are a kind of earthquake that can caused th

at. • When they occur beneath the sea, the water above the deformed ar

ea is displaced from its equilibrium position. • Waves are formed as the displaced water mass, acting under the fo

rce of gravity, tries to regain equilibrium.• When large areas of the sea floor elevate or subside, a tsunami can

be created. • Large vertical movements of the earth's crust can occur at plate bo

undaries. • These boundaries are called faults. • For example, at the boundaries of the Pacific Ocean, denser oceani

c plates slip under the less dense continental plates in a process known as subduction.

• Subduction earthquakes are particularly effective in generating tsunamis because they provide much force and disturbances deep underwater.


Tsunami Formation

• As a tsunami leaves the deep ocean and travels toward the shallow 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 its wave speed and wave height, remains nearly constant.

• As a result, the tsunami's speed decreases as it travels into shallower 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 rising or 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

Indian Ocean Earthquake


Indian Ocean Earthquake

Statistics

• Date : 26 December 2004Origin Time : 00:58 53 s UTCLatitude/Longitude : 3.267° North / 95.821° EastDepth : 10 kmMagnitude : 9.0Locality : 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, occur

red on the interface of the India and Burma plates and was caused 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 the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast.

• At region of the earthquake, the India plate moves northeast at a rate of 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 occurs

on the plate-interface and involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers to the east of the trench and 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 of the plate boundary slipped as a result of the earthquake.

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

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


Comparison• For comparison, the world's largest recorded earthquak

es have been listed below. • They have all been megathrust events, occurring where

one tectonic plate subducts beneath another.

These include: • 1960 Chile earthquake (Magnitude 9.5) • 1964 Prince William Sound, Alaska earthquake (Magn

itude 9.2) • 1957 Andreanof Islands, Alaska (Magnitude 9.1) • 1952 Kamchatka earthquake (Magnitude 9.0)


References


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

p://peer.berkeley.edu/~jrodgers/EQDef/eqdef2.htm [5 March 2005] • "2004 Indian Ocean earthquake" . "Wikipedia" . [Online] . http://en.wikipedia.org/wi

ki/2004_Indian_Ocean_Earthquake [20 February 2005] • "Tsunami" . "Wikipedia" . [Online] . http://en.wikipedia.org/wiki/Tsunami [20 Februa

ry 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

thinkquest team 01724 (oct 04 – may 05) tsunami: magnitude of terror causes

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