3. Overview
• Tsunami - what is it?
• Tsunami Formation
• What is the Physics behind them?
• Warning systems?
• Examples of Tsunamis
• Animations/Simulations
• Conclusion
• References
• Questions
4. 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
6. 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.
7. 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.
8. 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.
11. PUBLIC WARNING SYSTEM
can 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.
13. 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
