SCGSN Nov-96

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Sri Lanka Earthquake Tsunami Warning Training
Program
Session IV.4 Tsunami Generation And Propagation
April 6, 2006 CETRAC, Sri Lanka
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Topics covered

• What causes tsunami
• How they propagate

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Tsunami Generators
Underwater Landslides
Underwater Landslides
Earthquakes
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The Sumatra-Andaman Eathquake
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Courtesy Miho Aoki, Univ of Alaska
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Grand Banks Slide of 1929
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The Big Island (Hawaii) Slides
Heights up to 400m, inland up to 7km
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Seafloor Stability Numerous process can trigger
slope failure

• Earthquakes
• Rapid deposition and oversteepening
• Increase pore pressure (e.g., hydrate
  dissociation)

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Landscape Seascape Evolution
Todays morphology is Tomorrows stratigraphy
Hazard assessment Onshore/offshore
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Underwater Landslides
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How fast do tsunami travel?What kind of wave
are they?
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Tsunami waves have far greater period, faster
speed, and longer wavelength than beach waves
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Unlike regular waves, tsunami reach all the way
to the sea bottom. --You cant out dive a tsunami.
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Tsunami slow and grow as they near the coast. In
deep water V500 mph They come ashore about 30 -
50 mph. Still -- Cant outrun one to high ground.
Tsunami steepen in shallow water, but generally
do not become steep enough to break.
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Seismic and Tsunami Waves
Seismic Waves 20,000 mph Tsunami Waves 500 mph
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Tsunami Waves propogate across the Indian Ocean
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Seismic data give evidence that an earthquake has
occurred but NOT if that earthquake triggered a
tsunami. Data from ocean sensors are needed to
determine for certain if a tsunami is
approaching.
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Some capabilities

• Seismic networks provide important data to
  Earthquake Tsunami Centers, but
• Data from a single stations cannot locate
  earthquakes
• Tsunami warning Earthquake location requires
  data from many stations spread over 1000s of
  kilometers
• Buoys provide direct evidence of tsunami, seismic
  stations do not

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Conclusions
numerous mechanisms can trigger Tsunami
education and awareness can save many lives low
recurrence interval - so Tsunami occurrence is
RARE, but devastating when they do occur we are
trying to identify areas of the seafloor
susceptible to slope failure