Tsunamis

1
Tsunamis
EPS 131Introduction to Physical Oceanography

• Presented by
• Saira Hashmi
• Oct. 14th,2005

2
Overview

• Tsunami - what is it?
• Tsunami Formation
• What is the Physics behind them?
• Warning systems?
• Examples of Tsunamis
• Animations/Simulations
• Conclusion
• References
• Questions

3
Tsunami- what is it?

• Definition
• Unusually large wave in a harbour (Japanese)
• Series of water waves generated by huge and
  sudden perturbation (e.g. earthquakes, slides,
  volcanoes, asteroids)
• Characteristics
• Wave period 2-200 minutes
• Run-up heights O(10-100 m)(Flooding of
  shoreline)
• Speed

4
Tsunami Formation
5
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 cause 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, at the faults.

6
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.
• When it reaches the coast, it may appear as a
  rapidly rising or a series of breaking waves.

7
Tsunami Formation

• 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.

8
Whats the Physics behind the Waves
http//observe.arc.nasa.gov/nasa/exhibits/tsunami/
tsun_hit2.html
9
Warning Systems
10
PUBLIC WARNING SYSTEMcan you tell if a tsunami
is coming?

• The U. S. ESSA operates warning systems.
• Its PTWC in Hawaii is the regional operational
  center for tsunami information in the Pacific
• A Tsunami Watch Bulletin is released when an
  earthquake occurs with a magnitude of 6.75 or
  greater on the Richter scale.
• A Tsunami Warning Bulletin is released when
  information from tidal stations indicates that a
  potentially destructive tsunami exists.
• 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.

11
Examples of Tsunamis
12
Simulations/ Animations
13
Wave Propagation simulation
http//www.pgc.nrcan.gc.ca/press/images/2003JB0025
21-animation.gif
14
Conclusion

• Tsunamis..
• Are uncontrollable phenomenon
• Causes extensive loss of life
• Damage property
• Public warning systems provide some measures of
  protection.

15
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.ht
  m 5 March 2005
• "2004 Indian Ocean earthquake" . "Wikipedia" .
  Online . http//en.wikipedia.org/wiki/2004_India
  n_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/ussl
  av/ 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/ussl
  av/ 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

16
Questions