Tsunamis
Preethi Ganapathy
Physical Oceanography
November 20, 2007
Tsunamis
Tsunami: “Tsu”=Harbor, “Nami”=Wave
• Physics of Tsunamis
• Causes of Tsunamis
Physics of Tsunamis
• Tsunamis have very long
•
wavelengths and periods
Equations of motion:
– x= x0sin(kx±ωt)
– y= - y0cos(kx±ωt)
• Vertical amplitude: y0= x0kH
• Velocities:
– Vx= x0(±ωt)cos(kx±ωt)
– Vy= x0kH(±ωt)cos(kx±ωt)
• Energies:
– U=2ρLg x02kH2
– T= 2ρLω2x02 ω2 H/k
• Dispersion Relation: ω2=gHk2
Physics of Tsunamis
• Dispersion Equation shows:
– Phase velocity: vp=ω/k =√(gh)
– Group velocity: vg=dω/dk =√(gh)
– √H Speed and wavelength adjust to keep
period constant
– Increase in height due to conservation of
energy
Causes of Tsunamis
Tsunamis from
• Earthquakes
• Landslides
• Volcanism
• Cosmic Impact
Causes of Tsunamis
Tsunami from Earthquakes
• Most common cause of Tsunamis
• Subduction of plate causes transfer of
energy to water during rupture
• Water rushes landward and seaward
Cited from [4]
Causes of Tsunamis
• Tsunamis due to landslides may be caused
by earthquakes
• Volcanic eruptions can cause sudden
displacement of water
• Tsunamis caused by cosmic impact could
cause massive destruction
Tsunami History
•
The 1755 Lisbon earthquake, along with the resulting tsunami and fires, led to near total
destruction of the Portuguese capital.
•
One of the worst tsunami disasters engulfed whole villages along Sanriku, Japan, in 1896. A wave
more than seven stories tall (about 20 m) drowned some 26,000 people.
•
1946: An earthquake in the Aleutian Islands sent a tsunami to Hawaii, killing 159 people (only
five died in Alaska).
•
1958: A very localized tsunami in Lituya Bay, Alaska was the highest ever recorded: more than
500 m (1500 ft) above sea level. It did not extend much beyond the outlet of the fjord in which it
occurred, but did kill two people in a fishing vessel.
•
1976: August 16 (midnight) a tsunami killed more than 5000 people in the Moro Gulf region
(Cotabato city) of the Philippines.
•
1983: 104 people in western Japan were killed by a tsunami spawned from a nearby earthquake.
•
July 17, 1998: A Papua New Guinea tsunami killed roughly 3,000 people. A 7.1 magnitude
earthquake 15 miles offshore was followed within 10 minutes by a tsunami about 12 m tall. While
the magnitude of the quake was not large enough to create a tsunami directly, it is believed the
earthquake generated an undersea landslide, which in turn caused the tsunami. The villages of
Arop and Warapu were destroyed.
Cited from [7]
References
1. Margaritondo, G Eur. J. Phys. 26, 401
2. F Behroozi and N Podolefsky, Eur. J. Phys. 22, 225
3. Thorne K S Applications of Classical Physics chapter 15 (available in pdf form in the
site www.pma.caltech.edu/Courses/ph136/yr2002/index.html of Caltech).
4. http://geology.com/articles/tsunami-geology.shtml
5. www.geophys.washington.edu/tsunami/general/physics/physics.html of the University
of Washington
6. http://www.ringsurf.com/online/2411-what_causes_a_tsunami_.html
7. Religion and Spiritual Beliefs Resource, http://www.important.ca/tsunami_history.html