Bue= text on screen
Green= Graphics
Red= Audio
Tsunamis
Dan—For text on screen, use black unless otherwise indicated, but please feel free to use white instead of black if it shows up better on a
given graphic. Please use Times New Roman for fonts displayed on screen.
Narration
Visuals
Instructions
[1] Comet_rope_wave.jpg
Audio 4.0.wav
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4.0 Propagation
s01p0001.swf
[1] Though it is common to think of waves as
moving water, in deep water, waves are more
flowing energy than moving mass. Think of
whipping a rope attached to a wall up and
down—though waves travel through it, the rope
itself has no net horizontal movement. [2]
Likewise, birds swimming at sea stay put as
waves travel beneath them.
[2]
flickr_seagull_waves.jpg
4.1 Wave Properties
[1]Physicists have described many basic
properties of waves. The most basic parts include
crests, or high points, and troughs, or
depressions. The distance between two
successive crests or troughs is called the
[2]wavelength, or L. Imagine a wave passing a
pier. Marking the difference between a
successive crest and trough would give the
[3]wave height, or H.
[4]Now imagine starting a stopwatch when a
crest passes and stopping it when the next crest
arrives. That time is the [5]period, or T. The
inverse (1/T) of the period is the [6]frequency, f,
or number of wavelengths that pass a fixed point
per unit time. [7]These terms, with the exception
of height, [8]are all related by the equation
Speed(S) = L/T=Lf.
Though all waves possess these basic properties,
different wave types display unique patterns of
properties.
Audio 4.1.wav
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[1]
Comet_wave_properties.jpg
[2] (L)
[3](H)
[4]
Comet_seagull_period.swf
[5] T=
[6]1/f=
[8] Speed (S) = L (meters)/T(sec)=L(meters) x f (1/sec)
[2] Place text to right of “Wavelength”
[3] Place text to right of “Wave Height”
[4] Replace
[5] Place text to left of stopwatch in lower
right.
[6] Add text to left of [5]
[7] Fade all added text
[8] Add text over green water in a place
that looks good to you.
4.1.1 Deep Water Waves
[1] The wind waves familiar to travelers at sea
are deep-water waves, so-called because the
distance to the ocean bottom is greater [2]
(usually far greater) than the wavelength. In this
illustration, you can see how wavelength and
particle motion relate to depth in deep water
waves.
[1] Comet_deepwater_wave.swf
Audio 4.1.1.wav
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[2] Thousands of feet to bottom
[2] Add text and an arrow pointing down
to Davy Jones’s Locker
Wind waves have heights at sea proportional to
their energy; waves with the most energy are
visible as large swell. Water molecules affected
by passing deep-water wind waves have circular
or slightly elliptical orbits that gradually decrease
in diameter with depth. These orbital motions
cease at [3]a depth equal to ½ the wavelength.
Even during a fierce storm the water is placid
below 150 m (500 ft). The bottom of the ocean is
completely unaffected by wind-generated waves.
[3] Add arrow pointing to depth at which
particle motion ceases.
4.1.2 Shallow Water Waves
[1] As deep-water waves approach shore, they
start to “feel bottom” as the motion of the
deepest orbits begins to interact with the
seafloor. They steepen and heighten. Once the
bottom is less than about one-twentieth of their
wavelength, they become shallow-water waves.
[2] In these waves, water particle motion
becomes a long flattened ellipse or a horizontal
oscillation. While wave speed is slowing down,
particle speed accelerates as energy moves from
one form to the other. In other words, shallow
water waves increasingly become moving water,
and not just moving energy.
[3] When waves begin to interact with the
seabed in shallower water, they slow down,
wavelength decreases, and wave height
increases. [4]Eventually, for wind-waves, the
steepness becomes too great and they "break,"
creating the classic curl sought after by surfers.
[1] comet_Wave02.mov
Audio File 4.1.2.wav
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[2] comet_shallowwater_wave.swf
[2]Replace
[3]Replace
[4]Replace
[3]
comet_wave_transition.jpg
[4]
flickr_ocean_swell.jpg
4.1.3 Wave Properties Summary Questions
On the diagram below, match the labels to the wave feature
identified. <Create a diagram with missing labels for crest, trough,
wavelength, wave height.> Drag the terms to the image.
Initial image: comet_wave_properties_blank.jpg
Feedback: Comet_wave_properties.jpg
2, Quiz question: The number of wavelengths that pass a fixed
point per unit of time is the [frequency/period]. The inverse, or
amount of time that passes between successive wave crests, is
the [frequency/period]. [1]
Answer: frequency and period.
3. Interaction: Deep water [wave period/wave height/wave
frequency/wavelength] is directly proportional to the wave’s
energy.
Answer: Wave height.
4. Interaction. Shallow water waves have wavelengths that are
much [less/greater] than the depth.
Answer: greater. Deep water waves that have wavelengths much
greater than the distance to the bottom.
5. When shallow-water waves approach shore, [wave
speed/particle motion] slows, while [wave speed/particle motion]
accelerates, and wave height [increases/decreases].
Answer: wave speed, particle motion, increases.
4.1.4 Wind and Tsunami Waves at Sea
[1] At sea, deep-water wind waves travel slowly
yet produce relatively high crests, as anyone who
has experienced seasickness can attest. [2]Their
wavelengths are usually in the dozens or
hundreds of meters, with 10-20 second periods
and speeds of 1-10 m/s (3.6-36 km/hr, or 3.3 –
33 ft/s) for waves made by winds of 40 km/h (25
mi/hr) or less. Wind waves are commonly 5-10 m
(16-33 ft) high during strong gales, travel 15-20
m/s (49 - 66 ft/s) and reach 25 m (75 ft) high in
hurricane force winds. Wind waves over 30 m
(100 ft) tall are not unknown, but this still pales
Audio file 4.1.3.wav
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[1]
Noaa_wavesatsea.jpg
[2]Deep Water Wind Waves
Wavelength: dozens to hundreds of meters
Period: 10-20 seconds
[2] Fade these statistics onto as they are
mentioned. Use white for the color.
in comparison to the depth of the ocean.
[3]Tsunami waves, on the other hand, have long
periods and wavelengths, low amplitudes, and
very high speeds. Their velocity approaches
those of commercial jets: around 800 km/hr (500
mi/hr), which means they can cover incredible
distances in short times. [4] Their wavelengths
can be up to 650 km(400 mi) long, while typical
periods are 10 minutes to one hour. Yet a
tsunami in open ocean may be only a half a
meter (1.6 ft) high. A ship at sea is unlikely to
notice anything unusual if a tsunami passes
underneath it.
Speed: 1-10 meters/second (3.3-33 ft/sec)
Wave height: (in strong gales) 5-10 meters (16-33 feet)
[3]
Nasa_tsunami_traveltimes.jpg
[4] Tsunami Waves
Wavelength: up to 650 km(400 miles)
Period : 10 minutes to 2 hours
Speed: around 800 km/hr (500 miles/hr)
Wave height (at sea): 0.5 m (1.6 ft)
[3] Replace
[4] Display as mentioned on screen in
white.
4.1.5 Tsunami Properties
Lead-in Interaction: Which type of wave do you think tsunami
waves are?
A. Deep-water waves
B. Shallow-water waves
Feedback: The answer is B.
[1] Believe it or not, tsunamis are shallow water
waves. Water motion associated with the
passage of the wave reaches the seabed even in
deep water because the entire water column has
been forced up over a large area. This makes
tsunami wavelengths much longer than the
depth of the ocean. As we saw, shallow-water
waves form when the distance to the ocean
bottom is generally less than one-twentieth of
their wavelength. Tsunamis can have
wavelengths up to 500 km (300 mi) long—but
the ocean bottom averages only a few kilometers
[1] comet_tsunami_properties.swf
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deep, making them shallow-water waves from
the start.
[2] Replace with graphic
[2]The wavelength of a tsunami is set by the
width of rupture on the sea floor, since the initial
deformation of the sea surface copies the seismic
deformation below. Because one part of the
ocean floor generally moves up and another
down, [3]this represents the horizontal distance
from the crest to the trough of a wave, which is
½ the wavelength. [4]The wavelength determines
the period of the wave through the relationship
period = wavelength divided by wave speed. For
shallow water waves, the wave speed depends
on depth according to the formula
[5]Speed(v)=√𝑔𝑑 , where g is the acceleration of
gravity and d is the depth. Thus the width of the
deformation and the depth of the water are the
key factors in determining tsunami period. Notice
wave speed is independent of wavelength,
depending only on [6] gravity and [7]depth.
[7]As mentioned in the Initiation section, the
initial wave height of a tsunami [8]is also set by
the amount of uplift or dropdown on the
seafloor. Because water isn’t very compressible,
it’s a close relationship. One meter of uplift on
the seafloor will typically yield about a one meter
wave height above the rupture.
[2]
comet_tsunami_wavelength.jpg
[3]Draw a line from crest of wave to
nearby trough.
[4]Display equation
[3] ½ Wavelength
[5] Add to right or below [4], wherever it
fits best.
[6] Highlight g
[4]Period (P) = Wavelength (L) / Speed (v)
[7] Highlight d
[5] Speed (v)=√𝑔𝑑
[7] Fade all added text.
[8]Add an arrow reaching from base of
uplifted seafloor to top of uplifted water.
4.1.6 Tsunami Particle Movement
[1] As shallow water waves, tsunami wave speed
is inversely related to particle motion. [2] In deep
water when waves are traveling fast, each
individual particle moves only a few meters
horizontally at most. [3] In shallow water, as
waves slow down, particles move much farther
and the tsunami becomes a movement of water
en masse.
Audio file 4.1.5.wav
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You might think of this in terms of energy
absorbed per water molecule. [4]In the deep
ocean, there are many water molecules between
the seafloor and the surface to transmit the
energy of a passing wave, so each individual
molecule doesn’t move far. This changes at
shore, where the energy is concentrated
vertically and horizontally. [5]In very shallow
water, there are many fewer water molecules
between the surface and the bottom. Even as the
wave slows down, individual water molecules
speed up and run far up the shore before the
wave’s energy is spent.
[4] Add many more “water particles”
(white dots) all over diagram. Highlight
deep water area where there will be more
between surface and bottom
[2] Highlight deep water particle motions
[3] Highlight shallow-water particle
motions
[1]
Comet_tsunami_particles.jpg
4.1.7 DART buoy observations for a real tsunami
[5] Highlight fewer molecules in shallow
water at shore and how they move
farther.
[1] DART buoys deployed by NOAA monitor the
oceans and measure tsunami waves at sea. These
buoys measure passing tsunamis by sensing
pressure changes at the bottom of the
ocean.[2]Here are some DART buoy data for the
2010 Chilean tsunami. In the bottom graph at far
left, you can see the seismic surface wave arrive
before the big initial spike of the tsunami.
Audio file
[1] Display
[1]
noaa_DARTII_Buoy.jpg
[2]
Comet_dart_data.jpg
4.1.8 Summary Questions
1. Indicate whether each of the following are typical tsunami
wave values or deep-water wave values for waves at sea:
1. Period: 15 minutes
2. Wavelength: 100 meters
3. Wave height: 5 meters
4. Speed: 30 km/hr
Use drop down boxes.(Tsunami wave or Deep-water wave)
1. Tsunami wave
2. Deep-water wind wave
3. Deep-water wind wave
4. Deep-water wind wave
2. Why are tsunamis considered to be shallow-water waves?
A. Because their wavelengths are much greater than the
ocean’s depth
B. Because their wavelengths are much less than the
ocean’s depth
C. Because their wave heights are much greater than the
[2] Replace
ocean’s depth
D. Because their wave heights are much less than the
ocean’s depth
Feedback: The correct answer is A. Like wind waves approaching
shore, tsunamis are shallow-water waves because their
hundreds-kilometer long wavelengths are much greater than the
ocean’s depth.
3. True or false: Tsunami waves cause water particle movement
all the way to the bottom of the ocean.
Answer: True
4. As tsunamis approach shore, their waves [slow down/speed
up] while the water molecules affected by their passing [move
faster /move slower] and travel [longer/shorter] distances.
Answer: slow down, move faster, longer. Eventually, wave slows
from up to 800 km/hr to 50km/hr (500 mi/hr to 30 km/hr), but
the moving particles become a current running far up the shore.
4.2 Tsunami Modeling
[1]Before or during a tsunami, scientists can use
seismic data, buoy and tide gauge data,
bathymetric data, and tsunami models to help
them predict which coasts are most in danger.
Like weather forecasters, they run these data
through models that use different numerical
techniques to solve similar tsunami propagation
equations. The solutions to these equations
forecast wave height. They can also look at
historical records of nearby earthquakes and
what sort of waves they generated, and
sometimes this information can be plugged into
models. This is particularly true in the Pacific
Ocean, where good data have been kept ocean-
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comet_tsu_center1.jpg Insert picture into print version
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wide for 100 years, and for many centuries
before that in Japan.
[2] Tsunami forecast models use two basic
boundary conditions to drive the model
calculations: initial sea level perturbation, and
the bathymetric/elevation configuration. The
initial sea level perturbation is derived from
earthquake source parameters including rupture
length, width, depth, strike, dip, slip, and
moment. The bathymetric/elevation
configuration accounts for the shape of the sea
floor.
[2] Replace
[2]
comet_tsu_center4.jpg
The science of tsunami modeling is young and
developing rapidly. As with all models, the
solutions are approximations only.
4.2.1Energy directivity
[1]When tsunamis propagate, they don’t do so
evenly like the ripples ringing a pebble tossed
into a pond. For one, the ocean is a much bigger
place. [2]Over the distances tsunamis travel, the
bottom is uneven and the ocean is filled with
obstacles that can steer, disrupt, speed, or slow
waves. [3]For another, tsunami triggers aren’t
rounded like pebbles. They’re often unevenly
shaped or oblong, since fault ruptures can be
hundreds of kilometers long.
[4]When tsunamis emanate from earthquakes
from such long ruptures, most of the energy is
directed perpendicular to the fault. As a result,
the waves often seem “beamed” in one
direction, particularly if the tsunami wavelength
[1]comet_pond_wave.swf
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[3]Replace
[2]
Comet_southeast_asia.jpg
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[3] usgs_IOT_watermodel.mov
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produced by a given earthquake is less than the
rupture length. [5] In 2004, India and Sri Lanka
felt the full strength of the tsunami because they
were perpendicular to the rupture in the east
Indian Ocean. The southeastern Indian Ocean, on
the other hand, received only weak waves
because it was in a “shadow zone”. [6]The Alaska
earthquake of 1946 “beamed” its waves
southeast toward Chile and the Southern Ocean.
[4] Pmel_IOT_simulation.mov
[5]
[6] Replace
science_IOT_amplitude.jpg
[6]
wcatwc_EAleutians.jpg (Note in msdb this is 1946)
4.2.2 Reflection
[1]Just like light, tsunamis reflect off surfaces
they encounter. In this series of animations, you
can see what happens to ideal waves when they
strike a flat object.
[1] Wcatwc_tsunami_initiation2.mov
[2]Here is an image of the rise from the Indian
Ocean bottom up to the Maldives and Sri Lanka.
The steep surface makes an excellent reflector,
as you can see in [3]this movie.
[2]
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[4]Reflections can create complex and
unpredictable wave patterns. In this movie of
the 2006 Kuril Island tsunami, you can see how it
reflects off the [5]Emperor seamounts and the
[6]Hawaiian Ridge, generating complex wave
patterns elsewhere.
[7]Here is another example—the 2009 Samoan
Tsunami. Notice the many reflections,
particularly off the coast of California.
[8] In this marigram of the 2004 Indian Ocean
tsunami, you can see waves reflected from Sri
Lanka and the Maldives islands at the Cocos
Islands in the East Indian Ocean.
{3] Replace; pause narration to let the
movie play.
wcatwc_IOT_bath2.jpg
[3] usgs_sum2TNW_small.mov
[4] Pmel_kuril_2_small.mov
[5] Emperor Seamounts
[6] Hawaiian Ridge
[4] Replace; let movie play to end before
continuing
[5] Label Emperor Seamounts to their
right.
[6] Label Hawaiian Ridge to their right
[7] Replace; let movie play to end before
continuing.
[7] PMEL_Samoa_propagation.mov
[8]
cocos.tif Remove “probable” from graphic if easy
[8] Replace
4.2.3 Refraction
[1]Refraction is the change in the direction of
wave movement due to a change in wave speed.
These changes in wave speed happen because
waves slow down in shallow water. When one
part of a wave is in shallower water than another
part, the wave bends. [2]For example, in this
illustration of a wave passing by a spit of land as
it nears the coast, you can see that the wave
turns toward the peninsula. [3]Here is a real
refraction of wind waves off Waikiki Beach in
1946.
Refraction can create some very interesting
effects—like channeling. [4]In the Indian Ocean
tsunami, you can see how mid ocean ridges
seemed to channel tsunami waves down their
length. This is a refraction effect. At a mid-ocean
ridge, the speed decrease will be highest in the
center of the ridge since it is shallowest there.
Hence the ridges seem to funnel tsunami waves
along them.
[1] wave_refraction.swf
[2]
comet_shore_refraction.jpg
[3]
[5]In this example, you can see how the 2006
Kuril Island tsunami was guided toward shore by
the Mendocino Fracture Zone off the coast of
northern California.
ngdc_1946alaska_refraction.jpg
[4]
Audio 4.2.3.wav
science_IOT_amplitude.jpg
[5]
noaa_cal_coast_small.gif
4.2.4 Convergence
[1]When a drop falls in water, its waves spread
out evenly in concentric circles. As they travel,
their amplitudes drop as their energy is spread
through a larger surface area in accord with the
law of conservation of energy. [2]But now
imagine wrapping the plate around a spherical
object like Earth. If a drop fell on the water at its
north pole, the waves would spread outward and
lose height until they reached the equator. But as
the waves continued on toward the South Pole,
they would begin converging. As a result, the
waves would again grow taller.
[3]Similarly, a drop released just above a waterfilled pie plate will produce an expanding wave
front that will diminish in amplitude as it travels
from the center. After reflection from the rim,
the wave front will converge at the center and
produce a high-amplitude spike.
Scientists have seen this effect with tsunamis.
The 1960 Chilean tsunami occurred in the far
southeast section of the Pacific Ocean. Japan,
almost half the way around the globe,
experienced large waves due in part to
[1] comet_ripples.mov
Waves moving outward only at 25 % speed
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[2] Comet_convergence.swf
[3] Replace
[3] comet_ripple_convergence.mov
1.5 wave cycles at 25%
convergence.
4.2.5 Friction
[1]Friction acts as a drag force that wears waves
down. It doesn’t slow them directly, but instead
drains their energy. Some of the energy is
reflected to sea, further reducing wave energy at
shore. Wave height drops, and in shallow water
friction breaks waves down into overlapping
waves of many different frequencies. These wear
down faster too. In the deep ocean, friction has a
miniscule effect on tsunamis.
[1] Comet_wave_friction.swf
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[1]spectra_at_2points.swf
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[2] comet_pond_wave.swf
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[3]
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4.2.7 Dispersion
[1]Earthquakes and underwater landslides
generate waves of many different lengths.
Though these waves mostly travel the same
speed, waves of longer wavelength travel a bit
faster than those of shorter wavelength. Over
long distances, the waves tend to sort
themselves out, with the longest waves in the
front and shorter ones in the rear. [2]The same is
true for water dropped into a pan—as the ripples
spread, the longest wave travels fastest and it is
followed by waves of shorter wavelength that
never catch up with the waves in front. [3]Here is
a real example showing two wind wave groups
traveling out of the North Pacific in March.
Tsunamis are subject to dispersion as well,
meaning waves of longer length will outstrip
those of shorter length the farther a tsunami
travels. Though dispersion is an important
phenomenon among wind waves, tsunamis have
such long wavelengths that their dispersion is
very small.
Noaa_dispersion.png
4.2.8 Summary Questions
1. Which of the following are data used by tsunami warning
centers to forecast tsunami danger to coasts around an ocean
basin? (select all that apply)
A. Tsunami models
B. Seismic Data
C. Bathymetric Data
D. Meteorological data
E. Historical Data
F. Tide gauge data
G. DART buoy data
Feedback: The answers are A, B, C, and E, F, and G.
Meteorological data is not generally used because tsunami wave
travel in deep ocean is generally unaffected by weather.
2. Tsunamis generated by earthquakes with long rupture zones
tend to “beam” [more of/less of] their energy in one direction.
Answer: more of
3. When tsunamis strike an islands, continental coasts, or large
seamounts, some of their energy [reflects/refracts/] off it.
Answer: Reflect. Tsunami waves refract when they encounter
shallower water.
4.How does refraction change the direction of waves?
A.
B.
C.
D.
Part of the wave slows.
The water becomes deeper.
Land obstructs the motion of the wave.
The earth’s curvature distorts the wave shape.
Answer: A. Shallow water slows waves, causing refraction. Waves
entering deeper water would experience less refraction, not
more. Obstructing land would reflect waves, and the curvature of
the earth does not affect refraction one way or the other.
5. Convergence causes waves to [gain/lose] height after they
travel more than one-quarter of the distance around the globe.
Answer: gain
6. How does friction affect waves? (Select all that apply).
A. It causes them to steepen
B. It shortens the wavelength
C. It wears them down
D. It causes them to break into overlapping waves of many
frequencies.
Answer: C, D
7. Interaction: Dispersion causes waves of different wavelengths
to sort themselves out by wavelength from [largest/smallest] in
front to [largest/smallest] in back.
Answer: The answer is largest in front and smallest in back,
because higher wavelength waves travel faster.
4.3 Unit 4 Summary Interaction
1.
The following are travel times (in Eastern Standard Time
– consider changing to UTC) for a real tsunami that
struck the Pacific basin on 2:34 a.m. Eastern Time. Click
and drag each location to its proper position on the map,
and then choose the area of the map you think most
likely to have generated the tsunami.
American Samoa, 2:51 p.m.
Auckland, New Zealand 3:56 p.m.
Brisbane, Australia, 6:10 p.m.
Davao, Philippines, 12:27 a.m., next day
Ensenada, Mexico 3:16 p.m.
Hachinohe, Japan, 12:09 a.m. next day
Hilo, Hawaii, 4:05 p.m.
Hualien, Taiwan, 1:26 a.m., next day
Kodiak, Alaska, 8:35 p.m.
Papua New Guinea, 8:23 p.m.
Petropavlovsk, Russia, 10:33 p.m.
Santa Barbara, California, 3:31 p.m.
Sydney, Australia, 4:46 p.m.
[learner moves them to appropriate locations on the map]
When all the cities have been moved, ask
“Now, remembering the tsunami struck at 2:34 a.m. Eastern
Time, where do you think it most likely originated?”
Feedback:
No, that’s incorrect. Try again.
or
Yes, that’s correct. The tsunami you just analyzed was the 2010
Chilean tsunami, which struck Chile at 2:34 A.M. on Feb. 27, 2010
near Santiago, Chile.
Consider including the Chile travel time map at the end.