ast 2005 1. 2 tsunami dan kelley dept. oceanography dalhousie university dan.kelley@dal.ca

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Tsunami•Dan Kelley•Dept. Oceanography•Dalhousie University•Dan.Kelley@Dal.Ca

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QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

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1. Background

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harbour ("tsu", 津 ) wave ("nami", 波 or 浪 )

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•Students can easily find material on the 2004 event, and ...

•... they would find that interesting, so ...

•... class time could be directed otherwise ... maybe on learning wave Physics :-)

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2. Wave Physics

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•Shallow- versus deep-water waves [what does “shallow” mean?]

•Wave speeds depends on geometry [contrast shallow- and deep-water cases]

•Mathematics = a good thing (™ M. Stewart)

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AST 2005AST 2005Shallow- & deep-water waves

There are many implications of these flow patterns

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“Shallow-water” wave theory applies if wavelength greatly exceeds water depth, λ>>H

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Shallow-water wave speed ... mathematical

fun

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A traveling wave has

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AST 2005Momentum Equation

Water acceleration

Accel. due to gravity

Tilt of ocean surface

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AST 2005Water-conservation Equation

Heaving velocity of ocean surface

Water depth

Convergence of water

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If then

Thus wave speed is

Wave equation

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AST 2005Summarizing the above, if

then wave speed is

get H from bathymetric

chartUse C to predict

wave arrival time

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3. “Shallow” shallow-water case

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AST 2005Wave refraction into shallow water

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Trust me, I could go on with the beach case ... AST2006

perhaps?

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4. “Deep” shallow-water case

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AST 2005Seismic Forcing has

500 km

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1300km

Forcing region

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2h8h

2h

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5. Student Exercise

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Ray-path & wave-front calculation

Ideas, and thus exercise, has applications to Electricity & Magnetism, etc.

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Wave front from distributed source (cf. antenna theory)

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Refracting wave front with varying water depth

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Diagram by Ramzi Mirshak, Dalhousie PhD candidate

Assign each student a dot. Group results yield wave fronts. (Richardson’s scheme.)

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Lewis Fry Richardson 1881-1953

•Working alone, took several months to make a terribly inaccurate 6-hour forecast of Munich weather•Idea for numerical weather prediction: roomful of people doing calculations (“cpu”) and handing back and forth slips of paper (“bus”).•"Big whorls have little whorls that feed on their velocity, and little whorls have smaller whorls and so on to viscosity."

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6. Tsunami Impact

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Local Impact

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•Laurentian slope earthquake, magnitude 7.2•Tsunami of 7m @ southern Nfld•28 deaths

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History•c. 1600BC Tsunami devastated Crete

[Atlantis?]

•1883 Krakatoa volcanic explosion -- 40m tsunami

•1964 (Good Friday) -- 6m wave, killed 121 people in Alaska/BC and 11 in California

•2004 Indian Ocean -- killed 270,000 people

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Conclusions•Use Tsunami to motive a study of wave

physics

•Wave physics is an EASY and FUN way to learn calculus ... why wait until university to see DEs ... why wait to see partial derivatives?