Transcript Tsunami - meteo.units.it

Tsunamis
Overview
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Tsunami - what is it?
Tsunami Formation
What is the Physics behind them?
Warning systems?
Examples of Tsunamis
Animations/Simulations
Conclusion
References
Questions
Tsunami- what is it?
Definition:
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Unusually large wave in a harbour
(Japanese)
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Series of water waves generated by huge
and sudden perturbation
(e.g. earthquakes, slides, volcanoes,
asteroids)
Characteristics:
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Wave period: 2-200 minutes
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Run-up heights: O(10-100 m)
(Flooding of shoreline)
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Speed
Facts
Total energy released by a magnitude
9.0 earthquake exceeds the total
amount of energy consumed in the U.S.
in one month
 Massive release of energy and shift in
mass insignificantly altered the Earth's
rotation
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A tsunami (pronounced sooNAA-mee) is a series of
waves (called a "wave train")
generated in a body of water
by a pulsating or abrupt
disturbance that vertically
displaces the water column.
Tsunami's are also mistakenly
referred to as tidal waves as
they often resemble a tide that
keeps rising, rather than
cresting waves when they reach
shore. However, as they are not
actually related to tides the term
may be misleading, and its use
is discouraged by scientists.
Anthony Liekens 15:30, 28 Dec 2004 (UTC)
Tsunami Formation
Tsunami Formation
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Tsunamis can be generated when the sea floor suddenly displaces the
overlying water vertically.
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Tectonic earthquakes are a kind of earthquake that can cause that.
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When they occur beneath the sea, the water above the deformed area is
displaced from its equilibrium position.
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Waves are formed as the displaced water mass, acting under the force of
gravity, tries to regain equilibrium.
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When large areas of the sea floor elevate or subside, a tsunami can be
created.
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Large vertical movements of the earth's crust can occur at plate
boundaries, at the faults.
Tsunami Formation
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As a tsunami leaves the deep ocean and travels toward the
shallow coast, it transforms.
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A tsunami moves at a speed related to the water depth,
therefore the tsunami slows as the water depth decreases.
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The tsunami's energy flux, being dependent on both its wave
speed and wave height, remains nearly constant.
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As a result, the tsunami's speed decreases as it travels into
shallower water, and its height increases.
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When it reaches the coast, it may appear as a rapidly rising or
a series of breaking waves.
Tsunami Formation
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As a tsunami reaches the shore, it begins to lose energy .
It Slows down and height increases when approaching shallow
coast
Tsunamis reach the coast with tremendous amounts of energy.
Destructive power is due to speed and force with which they
strike the coastal area.
Tsunamis are stronger and retain height longer than waves
generated by wind.
http://observe.arc.nasa.gov/nasa/exhibits/tsunami/tsun_hit2.html
What’s the Physics behind the
Waves………
Warning Systems
PUBLIC WARNING SYSTEM
can you tell if a tsunami is coming?
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The U. S. ESSA operates warning systems.
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Its PTWC in Hawaii is the regional operational center for
tsunami information in the Pacific
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A Tsunami Watch Bulletin is released when an earthquake
occurs with a magnitude of 6.75 or greater on the Richter
scale.
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A Tsunami Warning Bulletin is released when information
from tidal stations indicates that a potentially destructive
tsunami exists.
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This system is not very reliable. For example, Honolulu
was evacuated in 1948 on a false alarm at a cost of more
than $30 million dollars.
Examples of Tsunamis
-The fifth-largest earthquake in a century with magnitude of
26thDec2004 8.9 Richter scale
-struck the coast of the northern Indonesia Island of Sumatra
-triggered tsunamis in Srilanka, India,tourist islands in
Thailand , Maldives, some part of East Africa
1992
The Cape Mendocino quake produced a tsunami that hit
Humboldt Bay within 20 minutes
1964
an earthquake in Alaska produced a destructive tsunami that
inundated Crescent City
Simulations/ Animations
Wave Propagation simulation
http://www.pgc.nrcan.gc.ca/press/images/2003JB002521-animation.gif
Conclusion
Tsunamis…..
 Are uncontrollable phenomenon
 Causes extensive loss of life
 Damage property
 Public warning systems provide some
measures of protection.
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