Transcript Tsunami: Magnitude of Terror

Tsunami:
Magnitude of Terror
Causes
ThinkQuest Team 01724 (Oct 04 – May 05)
Contents
• Plate Tectonics
• Tsunami Formation
• Indian Ocean Earthquake
ThinkQuest Team 01724 (Oct 04 – May 05)
Causes
Plate Tectonics
ThinkQuest Team 01724 (Oct 04 – May 05)
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.
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Plates of The World
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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.
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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.
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Causes
Tsunami Formation
ThinkQuest Team 01724 (Oct 04 – May 05)
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.
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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
square 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.
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Tsunami Formation
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Tsunamis can be generated when the sea floor suddenly
displaces the overlying water vertically.
Tectonic earthquakes are a kind of earthquake that can caused
that.
When they occur beneath the sea, the water above the deformed
area is displaced from its equilibrium position.
Waves are formed as the displaced water mass, acting under the
force 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
boundaries.
These boundaries are called faults.
For example, at the boundaries of the Pacific Ocean, denser
oceanic 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.
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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.
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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
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Causes
Indian Ocean Earthquake
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Indian Ocean Earthquake
Statistics
• Date : 26 December 2004
Origin Time : 00:58 53 s UTC
Latitude/Longitude : 3.267° North / 95.821° East
Depth : 10 km
Magnitude : 9.0
Locality : 255 km SSE of Banda Aceh, Northern
Sumatra
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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 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.
ThinkQuest Team 01724 (Oct 04 – May 05)
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.
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Comparison
• For comparison, the world's largest recorded
earthquakes have been listed below.
• They have all been megathrust events, occurring where
one tectonic plate subducts beneath another.
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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
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[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 [20
February 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)