De Broglie wavelengths Contents: de Broglie wavelengths Example 1 Whiteboards
Lecture 6: Tsunami Waves › rjmitch › L6_tsunamis.pdf · What does “feeling” bottom have to...
Transcript of Lecture 6: Tsunami Waves › rjmitch › L6_tsunamis.pdf · What does “feeling” bottom have to...
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Lecture 6: Tsunami Waves
Key Questions1. What are four sources for tsunami waves?
2. What are the wavelength, period, velocity, frequency, height relations for a wave?
3. What does “feeling” bottom have to do with the height amplification of a wave?
4. What are typical wavelengths and speeds for tsunami waves?
5. What three methods does NOAA use to mitigate tsunamis?
6. What is DART?
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Magnitude 6.9 - SOUTHERN QINGHAI, CHINA(depth of 6.2 miles)
India-Asia continent-continent plate convergence
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Source unknown
Tsunami Hazards
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Figure 6.B
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A tsunami wave is created by some impulsive disturbance.
There are four possibilities.
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1. Submarine earthquake
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1. Submarine earthquake
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2. Submarine landslide
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Failure of the Nooksack Delta could cause a tsunami
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3. Volcanic landslide
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4. Asteroid impact
The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest mass extinctions
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L = wavelength
H = heightcalm water surface
seafloor
d = depth to the seafloor
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L = wavelength
H = heightcalm water surface
seafloor
d = depth to the seafloor
Wave Period = T = time for one wave length to pass a point
LVelocity = v = T1Frequency = f = T
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L = wavelength
H = height
seafloor
d = depth to the seafloor
Velocity ~~ g x d works if d < L/10
g = acceleration of gravity 9.81 m/s2
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L = wavelength
H = height
A tsunami wave can have a wavelength (L) on the order of 100s of kilometers
and velocities as high as 800 km/hr!
Seattle Spokane450 km
Lperiod = T = v450 km
750 km/hr= = 0.60 hr
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L = wavelength
H = height
Seattle Spokane450 km
Deep in the ocean the wave height may only be 1 meter or so.
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Shoaling (wave amplification)
Rotating particles start sensing the seafloor when
depth = d = L2
d
where L is the wavelength
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Shoaling (wave amplification)
when waves “feel” the bottom, they slow down
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Shoaling (wave amplification)
when waves slow down, the wavelength gets shorter
Lthe period stays constant = T = v
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Shoaling (wave amplification)
wavelength gets shorter and the wave gets higher
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Shoaling (wave amplification)
If the wave becomes too high it will break when
HL
17
H
≥
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Note: tsunami waves don’t break—their wave lengths are too long!
misconception
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L = wavelength
H = height
Seattle Spokane450 km
Deep in the ocean the wave height may only be 1 meter or so.
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
1) Use computer models to produce inundation maps showingworse-case scenarios.
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
1) Use computer models to produce inundation maps showingworse-case scenarios.
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
2) Use the maps to educate the public.
Modeling predicts that a Cascadiasubduction zone earthquake may produce a tsunami that will arrive in Bellingham Bay about 2.5 hours after the EQ
Note: It would take about 20 minutes to reach the coast of Washington
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
2) Use the maps to educate the public.
Modeling predicts that a Cascadia subduction zone earthquake may produce a tsunami wave having an amplitude of 2-4 meters.
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
2) Use the maps to educate the public.
The tsunami will flood most of the Nooksack River delta and lower flood plain.
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
2) Use the maps to educate the public.
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Tsunami Mitigation
2) Use the maps to educate the public.
Note: It would take about 20 minutes for a tsunami from a Cascadia subduction zone EQ to reach the coast of Washington
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Tsunami Mitigation
2) Use the maps to educate the public.
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Tsunami Mitigation
2) Use the maps to educate the public.
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Earthquakes in the subduction zone along the Aleutian Islands also pose a risk.
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Earthquakes in the subduction zone along the Aleutian Islands also pose a risk.
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3:45 min
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Earthquakes in the subduction zone along the Aleutian Islands also pose a risk.
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March 28, 1964 Prince William Sound, Alaska
About 4 hrs to reach Neah Bay
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Tsunami Mitigation
NOAA has taken a three-pronged approach:
3) A sophisticated detection system to warn the public.
DART® (Deep-ocean Assessment and Reporting of Tsunamis
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