Tsunamis

Presented by:Saira HashmiOct. 14th,2005

EPS 131Introduction to Physical

Oceanography

Overview

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: 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

Tsunami Formation

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.

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.

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.

What’s the Physics behind the Waves………

http://observe.arc.nasa.gov/nasa/exhibits/tsunami/tsun_hit2.htm

l

Warning Systems

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.

Examples of Tsunamis

26thDec2004 -The fifth-largest earthquake in a century with magnitude of 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

[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

Questions