Tsunamis Preethi Ganapathy Physical Oceanography November 20, 2007

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

Physics of Tsunamis Tsunamis have very long wavelengths and periods Tsunamis have very long wavelengths and periods Equations of motion: Equations of motion: –  x=  x 0 sin(kx±ωt) –  y= -  y 0 cos(kx±ωt) Vertical amplitude:  y 0 =  x 0 kH Vertical amplitude:  y 0 =  x 0 kH Velocities: Velocities: –V x =  x 0 (±ωt)cos(kx±ωt) –V y =  x 0 kH(±ωt)cos(kx±ωt) Energies: Energies: –U=2ρLg  x 0 2 kH 2  –T= 2ρLω 2  x 0 2 ω 2  H/k Dispersion Relation: ω 2 =gHk 2 Dispersion Relation: ω 2 =gHk 2

Physics of Tsunamis Dispersion Equation shows: Dispersion Equation shows: –Phase velocity: v p =ω/k =√(gh) –Group velocity: v g =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 Earthquakes Landslides Landslides Volcanism Volcanism Cosmic Impact Cosmic Impact

Causes of Tsunamis Tsunami from Earthquakes Most common cause of Tsunamis Most common cause of Tsunamis Subduction of plate causes transfer of energy to water during rupture Subduction of plate causes transfer of energy to water during rupture Water rushes landward and seaward Water rushes landward and seaward Cited from [4]

Causes of Tsunamis Tsunamis due to landslides may be caused by earthquakes Tsunamis due to landslides may be caused by earthquakes Volcanic eruptions can cause sudden displacement of water Volcanic eruptions can cause sudden displacement of water Tsunamis caused by cosmic impact could cause massive destruction 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. 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 A wave more than seven stories tall (about 20 m) drowned some 26,000 people. One of the worst tsunami disasters engulfed whole villages along Sanriku, Japan, in 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). 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. 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. 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. 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. 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, F Behroozi and N Podolefsky, Eur. J. Phys. 22, Thorne K S Applications of Classical Physics chapter 15 (available in pdf form in the site of Caltech) of the University of Washington Religion and Spiritual Beliefs Resource,