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Tsunamis

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  1. Tsunamis Preethi Ganapathy Physical Oceanography November 20, 2007

  2. Tsunamis Tsunami: “Tsu”=Harbor, “Nami”=Wave • Physics of Tsunamis • Causes of Tsunamis

  3. 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

  4. 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

  5. Causes of Tsunamis Tsunamis from • Earthquakes • Landslides • Volcanism • Cosmic Impact

  6. 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]

  7. 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

  8. 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]

  9. References • Margaritondo, G Eur. J. Phys. 26, 401 • F Behroozi and N Podolefsky, Eur. J. Phys. 22, 225 • 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). • http://geology.com/articles/tsunami-geology.shtml • www.geophys.washington.edu/tsunami/general/physics/physics.html of the University of Washington • http://www.ringsurf.com/online/2411-what_causes_a_tsunami_.html • Religion and Spiritual Beliefs Resource, http://www.important.ca/tsunami_history.html