Ivan

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Ivan Just when you thought it was safe to go
back into the water We did not go to Ivan,
so Ivan is coming for us! http//www.nhc.noa
a.gov/archive/2004/IVAN_graphics.shtml
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The phenomenon we call a tsunami is a series of
waves of extremely long wavelength and period
generated in a body of water by an impulsive
disturbance that displaces the water. Although
tsunamis are often referred to as "tidal waves"
by English-speaking people, they are not caused
by the tides and are unrelated to them.
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Tsunamis are primarily associated with
earthquakes in oceanic and coastal regions. When
an earthquake occurs, the energy travels outward
in all directions from the source. This can be
illustrated by throwing a pebble into a small,
still pond. The pebble represents a meteorite or
some other energy source, and the pond represents
the ocean. The ripples that travel out in all
directions from the focus, or the point where the
pebble hit the water, represent the energy that
creates a sea wave. Notice how the waves become
larger as they reach shore, where the water is
shallower.
Detecting tsunamis is a very difficult thing to
do. When a wave begins in the deep ocean waters,
it may only have a height of about twelve to
twenty-three inches and look like nothing more
than the gentle rise and fall of the sea surface.
An example of how easy tsunamis are to overlook
is the Sanriku tsunami, which struck Honshu,
Japan, on June 15, 1896.       Fishermen twenty
miles out to sea didn't notice the wave pass
under their boats because it only had a height at
the time of about fifteen inches. They were
totally unprepared for the devastation that
awaited them when they returned to the port of
Sanriku. Twenty-eight thousand people were killed
and 170 miles of coastline were destroyed by the
wave that had passed under them.
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 Tsunamis in deep water can have a wavelength
greater than 300 miles (500 kilometers) and a
period of about an hour. This is very different
from the normal California tube, which generally
has a wavelength of about 300 feet (100 meters)
and a period of about ten seconds. (The period of
a wave is the time between two successive
waves.)       Tsunamis are shallow-water waves,
which means that the ratio between water depth
and wavelength is very small. These shallow-water
waves move at a speed equal to the square root of
the product of the acceleration of gravity
(9.8m/s/s) and the water depth. The deeper the
water, the faster the wave is. For example, when
the ocean is 20,000 feet deep, a tsunami travels
at 550 miles per hour. At this speed, the wave
can compete with a jet airplane, traveling across
the ocean in less than a day.        Another
important factor in considering tsunamis is the
rate at which they lose energy. Because a wave
loses energy at a rate inversely related to its
wavelength, tsunamis can travel at high speeds
for a long period of time and lose very little
energy in the process.
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Panel 1--Initiation Earthquakes are commonly
associated with ground shaking that is a result
of elastic waves traveling through the solid
earth. However, near the source of submarine
earthquakes, the seafloor is "permanently"
uplifted and down-dropped, pushing the entire
water column up and down. The potential energy
that results from pushing water above mean sea
level is then transferred to horizontal
propagation of the tsunami wave (kinetic energy).
For the case shown above, the earthquake rupture
occurred at the base of the continental slope in
relatively deep water. Situations can also arise
where the earthquake rupture occurs beneath the
continental shelf in much shallower water.Note
In the figure the waves are greatly exaggerated
compared to water depth! In the open ocean, the
waves are at most, several meters high spread
over many tens to hundreds of kilometers in
length.
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Panel 2--Split Within several minutes of the
earthquake, the initial tsunami (Panel 1) is
split into a tsunami that travels out to the deep
ocean (distant tsunami) and another tsunami that
travels towards the nearby coast (local
tsunami).The height above mean sea level of the
two oppositely traveling tsunamis is
approximately half that of the original tsunami
(Panel 1). (This is somewhat modified in three
dimensions, but the same idea holds.) The speed
at which both tsunamis travel varies as the
square root of the water depth. Therefore the
deep-ocean tsunami travels faster than the local
tsunami near shore.
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Panel 3--Amplification Several things happen as
the local tsunami travels over the continental
slope. Most obvious is that the amplitude
increases. In addition, the wavelength decreases.
This results in steepening of the leading
wave--an important control of wave run-up at the
coast (next panel).Note also that the deep ocean
tsunami has traveled much farther than the local
tsunami because of the higher propagation speed.
As the deep ocean tsunami approaches a distant
shore, amplification and shortening of the wave
will occur, just as with the local tsunami shown
above.
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Panel 4Runup As the tsunami wave travels from
the deep-water, continental slope region to the
near-shore region, tsunami run-up occurs. Run-up
is a measurement of the height of the water
onshore observed above a reference sea level.
Contrary to many artistic images of tsunamis,
most tsunamis do not result in giant breaking
waves (like normal surf waves at the beach that
curl over as they approach shore). Rather, they
come in much like very strong and very fast tides
(i.e., a rapid, local rise in sea level). Much of
the damage inflicted by tsunamis is caused by
strong currents and floating debris. The small
number of tsunamis that do break often form
vertical walls of turbulent water called bores.
Tsunamis will often travel much farther inland
than normal waves.
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Do tsunamis stop once on land? After run-up, part
of the tsunami energy is reflected back to the
open ocean. In addition, a tsunami can generate a
particular type of wave called edge waves that
travel back-and forth, parallel to shore. These
effects result in many arrivals of the tsunami at
a particular point on the coast rather than a
single wave suggested by Panel 3. Because of the
complicated behavior of tsunami waves near the
coast, the first run-up of a tsunami is often not
the largest, emphasizing the importance of not
returning to a beach several hours after a
tsunami hits.
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Background The tsunami that struck New Guinea on
July 17, 1998 was the most devastating tsunami
since the 1976 Moro Gulf, Philippines, tsunami
and may surpass that event (Lockridge and Smith,
1984 Satake and Imamura, 1995). The high
reported runups and the tremendous loss of life
are of great concern to all, including the
international scientific community. Scientists
will closely examine this event in the coming
months, in the ultimate hope of mitigating such
disasters in the future. New Guinea is a
seismically active region, the site of an
arc-continent collision, where tectonic plates
are converging and sliding past each other. The
tectonic boundaries and faulting in this region
are very complex, as shown below.
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The Earthquake The recorded magnitude of the
earthquake was 7.1, and the epicenter was located
in northern New Guinea near the coast. The fault
mechanism from the National Earthquake
Information Center (NEIC) shown by the
red-and-white ball indicates that the earthquake
could have occurred as uplift on a vertical fault
or sliding on a horizontal fault. The inset in
the upper right corner of the figure shows the
location of the epicenter.
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Bathymetry The bathymetry indicates that just
offshore of the northern coast of New Guinea
there is very steep and linear slope. It is
possible that the relatively deep water near
shore contributed to the unusual height of this
tsunami. Shown below is the bathymetry in the
region contoured at 200 m intervals from the
2-minute bathymetric data of Smith and Sandwell
(1997).
In the above figure, black circles indicate
locations for the earthquake determined by the
NEIC, Harvard, and the Earthquake Research
Institute (ERI) at the University of Tokyo.
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The Tsunami At present, too little is known about
the July 17, 1998 earthquake and about the
distribution of run-up to formulate a
quantitative model of the tsunami. The reported
run-ups are unusually large for an earthquake of
magnitude 7.1 (cf. Geist, 1998). Below, a
descriptive or qualitative simulation of the
tsunami is computed by making several assumptions
about the source parameters of the earthquake.
About the Animation The animation shows how the
July 17 tsunami might have looked from a vantage
point above Papua New Guinea. The coastline shown
in the animation is about 550 kilometers (340
miles) long. The animation begins with the
initial wave--which formed almost simultaneously
with the earthquake that triggered the event--and
shows how the initial wave was reflected from the
island. Note other waves traveling east and west
along the coast." This animation does not show
run-up (56 kB)--the maximum elevation the water
reached as it rose above the shoreline. Based on
very preliminary data, this animation is a
"descriptive model" of the tsunami. A more
accurate simulation, or "quantitative model", can
be developed when accurate measurements of the
runup and more information about the earthquake
that triggered the tsunami become
available. http//walrus.wr.usgs.gov/tsunami/PNG.h
tmltsunami
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Survey team report On July 17, 1998 a Mw 7.0
earthquake struck the north central coast of
Papua New Guinea. Following the earthquake a
large tsunami also struck the region. Initial
reports claimed that the wave was between 7 and
10 meters and that up to 3000 persons were killed
or missing. This seemed to be an unusually
damaging tsunami given the size of the
earthquake. Members of the International Tsunami
Survey Team decided that a field survey was
necessary as soon as possible to try and
determine the true value of the maximum run-up
and to accurately map the run-up distribution
along the coast. Upon arrival at the disaster
relief command post in Aitape, the team was
granted full access to the sealed region around
Sissano Lagoon and Sissano Village, the site of
the most deaths and greatest destruction. The
first surveys to the Sissano region confirmed the
7 - 10 m wave reports and even found a place
where the waves were larger - up to 15 m. The
severe damage and extreme wave heights were
confined to a relatively short (40 km) stretch of
coast between Aitape and Sissano Village.
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The survey was conducted by a multinational team
with representatives from Japan, the United
States, Australia, and New Zealand. The team was
broken up into two groups, the Japanese and
everyone else. The Japanese team traveled
overland from Wewak to Aitape measuring run-up
along the way. Japanese team members also
installed seismographs in the region to measure
aftershock activity. The rest of the team
traveled by ship from Wewak to the west stopping
at some of the offshore islands. The two groups
reunited in Aitape before a survey of the Sissano
area was conducted. The boat continued west as
far as Serai Village where run-up values were
seen to diminish considerably. Images of the
aftermath of the Papua 1998 Tsunami http//www.usc
.edu/dept/tsunamis/PNG/random1.html http//www.usc
.edu/dept/tsunamis/PNG/random2.html
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Summary chart presenting observed (top) and
computed (bottom) time series for nine tide gage
stations along the coasts of California and
Oregon. Vertical axes are deviation from
background sea level in cm horizontal axes are
minutes of elapsed time after the main shock,
with a vertical line indicating the computed
arrival time at each station. Bathymetric contour
interval is one kilometer. The dotted line
rectangle denotes the numerical model
computational region. Cape Mendocino is just
south of North Spit, and the solid star marks the
earthquake epicenter. Note that, at Crescent City
(CC), the first wave packet arrives within
minutes of the computed travel time (vertical
line) this is the non-trapped tsunami energy,
which traverses deep offshore water. Three hours
after this first arrival, the largest observed
tsunami wave is recorded at this station this
second tsunami wave packet corresponds to the
trapped edge wave mode.
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1992 EarthquakeComputed vertical crustal
deformation for a single fault plane model.
Heavy, solid contours represent uplift, dashed
subsidence the first solid contour is 0.2 cm,
and all other contours are at 20 cm intervals.
The solid line rectangle delineates the surface
projection of the fault plane (see Generation
Mechanism section in text for fault plane
parameters Gonzalez, et al., 1995), and the
location of the epicenter is indicated by a star
. Note that the uplift region is located in
shallow water near the coast, an optimal location
for generating coastally trapped edge wave modes.

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Distant Tsunami Animation http//www.pmel.noaa.gov
/tsunami/Mov/andr1.mov Inundation of Aonae
during Hokkaido-Nansei-Oki Tsunami
http//www.pmel.noaa.gov/tsunami-hazard/vasily.mpg
http//www.pmel.noaa.gov/animations/Aonae.all.mp
g
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As part of the U.S.National Tsunami Hazard
Mitigation Program (NTHMP), the DART Project is
an ongoing effort to develop and implement a
capability for the early detection and real-time
reporting of tsunamis in the open ocean. DART is
essential to fulfilling NOAA's national
responsibility for tsunami hazard mitigation and
warnings. Project goals are 1) Reduce the loss
of life and property in U.S. coastal
communities.2) Eliminate false alarms and the
high economic cost of unnecessary
evacuations.DART stations are sited in regions
with a history of generating destructive tsunamis
to ensure early detection of tsunamis and to
acquire data critical to real-time forecasts.
Buoys shown on the accompanying map represent an
operational array scheduled for completion in
2003.
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A DART system consists of a seafloor bottom
pressure recording (BPR) system capable of
detecting tsunamis as small as 1 cm, and a moored
surface buoy for real-time communications. An
acoustic link is used to transmit data from the
BPR on the seafloor to the surface buoy. The data
are then relayed via a GOES satellite link to
ground stations, which demodulate the signals for
immediate dissemination to NOAA's Tsunami Warning
Centers and PMEL. http//www.pmel.noaa.gov/tsunam
i/Dart/Flash/CODEframe4DART.html
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• Important Facts to Know about Tsunamis
• Tsunamis that strike coastal locations in the
  Pacific Ocean Basin are most always caused by
  earthquakes. These earthquakes might occur far
  away or near where you live.
• Some tsunamis can be very large. In coastal areas
  their height can be as great as 30 feet or more
  (100 feet in extreme cases), and they can move
  inland several hundred feet.
• All low-lying coastal areas can be struck by
  tsunamis.
• A tsunami consists of a series of waves. Often
  the first wave may not be the largest. The danger
  from a tsunami can last for several hours after
  the arrival of the first wave.
• Tsunamis can move faster than a person can run.
• Sometimes a tsunami causes the water near the
  shore to recede, exposing the ocean floor.
• The force of some tsunamis is enormous. Large
  rocks weighing several tons along with boats and
  other debris can be moved inland hundreds of feet
  by tsunami wave activity. Homes and other
  buildings are destroyed. All this material and
  water move with great force and can kill or
  injure people.
• Tsunamis can occur at any time, day or night.
• Tsunamis can travel up rivers and streams that
  lead to the ocean.

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• If you are on land
• Be aware of tsunami facts. This knowledge could
  save your life! Share this knowledge with your
  relatives and friends. It could save their lives!
  
• If you are in school and you hear there is a
  tsunami warning, you should follow the advice of
  teachers and other school personnel.
• If you are at home and hear there is a tsunami
  warning, you should make sure your entire family
  is aware of the warning. Your family should
  evacuate your house if you live in a tsunami
  evacuation zone. Move in an orderly, calm and
  safe manner to the evacuation site or to any safe
  place outside your evacuation zone. Follow the
  advice of local emergency and law enforcement
  authorities.
• If you are at the beach or near the ocean and you
  feel the earth shake, move immediately to higher
  ground, DO NOT wait for a tsunami warning to be
  announced. Stay away from rivers and streams that
  lead to the ocean as you would stay away from the
  beach and ocean if there is a tsunami. A regional
  tsunami from a local earthquake could strike some
  areas before a tsunami warning could be
  announced.

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• If you are on land
• Tsunamis generated in distant locations will
  generally give people enough time to move to
  higher ground. For locally-generated tsunamis,
  where you might feel the ground shake, you may
  only have a few minutes to move to higher ground.
  
• High, multi-story, reinforced concrete hotels are
  located in many low-lying coastal areas. The
  upper floors of these hotels can provide a safe
  place to find refuge should there be a tsunami
  warning and you cannot move quickly inland to
  higher ground. Local Civil Defense procedures
  may, however, not allow this type of evacuation
  in your area. Homes and small buildings located
  in low-lying coastal areas are not designed to
  withstand tsunami impacts. Do not stay in these
  structures should there be a tsunami warning.
• Offshore reefs and shallow areas may help break
  the force of tsunami waves, but large and
  dangerous wave can still be a threat to coastal
  residents in these areas. Staying away from all
  low-lying areas is the safest advice when there
  is a tsunami warning.

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• If you are on a boat
• Since tsunami wave activity is imperceptible in
  the open ocean, do not return to port if you are
  at sea and a tsunami warning has been issued for
  your area. Tsunamis can cause rapid changes in
  water level and unpredictable dangerous currents
  in harbors and ports.
• If there is time to move your boat or ship from
  port to deep water (after a tsunami warning has
  been issued), you should weigh the following
  considerations
• Most large harbors and ports are under the
  control of a harbor authority and/or a vessel
  traffic system. These authorities direct
  operations during periods of increased readiness
  (should a tsunami be expected), including the
  forced movement of vessels if deemed necessary.
  Keep in contact with the authorities should a
  forced movement of vessel be directed.
• Smaller ports may not be under the control of a
  harbor authority. If you are aware there is a
  tsunami warning and you have time to move your
  vessel to deep water, then you may want to do so
  in an orderly manner, in consideration of other
  vessels. Owners of small boats may find it safest
  to leave their boat at the pier and physically
  move to higher ground, particularly in the event
  of a locally-generated tsunami. Concurrent severe
  weather conditions (rough seas outside of safe
  harbor) could present a greater hazardous
  situation to small boats, so physically moving
  yourself to higher ground may be the only option.
  
• Damaging wave activity and unpredictable currents
  can effect harbors for a period of time following
  the initial tsunami impact on the coast. Contact
  the harbor authority before returning to port
  making sure to verify that conditions in the
  harbor are safe for navigation and berthing.

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• Earthquake Assignment (Due next Thursday)
• Do the Travel Time exercise (print map and
  journal to turn in)
• Do the Epicenter Magnitude exercise (print
  map and journal to turn in)
• Do the Assessment (print Certificate and
  assessment scores) Registration number is 476231
• http//www.sciencecourseware.com/eec/Earthquake/

Turn off Pop-up Blocker!
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• Earthquake Prediction
• What constitutes a useful earthquake prediction?
• Has there ever been a useful prediction?

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One well-known successful earthquake prediction
was for the Haicheng, China earthquake of 1975,
when an evacuation warning was issued the day
before a M 7.3 earthquake. In the preceding
months changes in land elevation and in ground
water levels, widespread reports of peculiar
animal behavior, and many foreshocks had led to a
lower-level warning. An increase in foreshock
activity triggered the evacuation warning.
Unfortunately, most earthquakes do not have such
obvious precursors. In spite of their success in
1975, there was no warning of the 1976 Tangshan
earthquake, magnitude 7.6, which caused an
estimated 250,000 fatalities.
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• Methods of Earthquake Prediction
• Animal behavior
• Seismic Gaps
• Monitoring precursory phenomena

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Seismic gapA seismic gap is a section of a fault
that has produced earthquakes in the past but is
now quiet. For some seismic gaps, no earthquakes
have been observed historically, but it is
believed that the fault segment is capable of
producing earthquakes on some other basis, such
as plate-motion information or strain
measurements.
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It has been shown that humans can trigger
earthquakes by pumping water into fault
zones. Should we use this method to trigger
small earthquakes in a controlled fashion so as
to prevent a large earthquake in a populated
area?