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Tsunami
Formation and Sensor Placement
Alan
Foreman
Tsunamis: Generation
and Propagation
Tsunamis, often incorrectly referred to as tidal waves, are generated
in a
variety of ways. Regional uplifting along the seafloor (earthquakes) is
the
most common cause of tsunamis, and tends to generate tsunamis that
result in
enormous amounts of destruction and that may travel for thousands
of miles
before stopping (Alaska Sea Grant 2005). Underwater
landslides, which occur
when large masses of sediment shift along the seafloor, are another
common
cause of tsunamis. The tsunamis generated by landslides tend to be
relatively
localized and typically do less damage than the earthquake
generated tsunamis.
Finally, volcanoes and local landslides along the coast can
generate tsunamis
as well. These tsunamis are highly localized, however, and
generally affect
only a central area.
The "lifetime" of a tsunami can be divided up into three stages:
generation,
propagation, and runup. (Comer 1978) Of these, we are most
concerned with the
first two. In our study we will be trying to best monitor the
generation of
tsunamis, and, after they are generated, understand the direction
of tsunami
propagation.
The
power of a tsunami is highly dependent on two factors: seafloor
morphology and tide. The shape of the ocean floor alters
the height of the
tsunami by changing the ratio between the wavelength and the
wave height of
a tsunami. In general, the ratio of wavelength to
wave height decreases as
the wave travels into shallower water, causing the tsunami to
grow in size
(Smith 2005). The tide also plays a role in the
damage a tsunami will do to
an area: at high tide the tsunami will be able to do much more
damage than
at low tide.
Tsunamis: Peru and
Micronesia
are Alaska-Aleutians, Central America, South America, New
Zealand-Tonga, New
Guinea-Solomon I, Indonesia, Philippines, Japan,
Kuril-Kamchatka, and Hawaii
(Gusiakov 2005). The countries that we are examining in
this study are Peru
and Micronesia, which fall in the South America and New
Guinea-Solomon I
regions, respectively.
humid zone. This zone has the highest rate of sedimentation, accumulation
roughly 76% of the sediments flowing into the ocean. This increased
sedimentation results in a higher rate of ocean floor slumping, which in turn
results in a higher potential for tsunami generation (Gusiakov 2005).
The probability of tsunami generation is further increased in the South
American region by the location of the fault line running along the South
American coastline. The source of earthquakes along in the South American
region (the fault line) is located very close to the coastline, and as a result
many of the earthquakes along the fault have a large potential of being
tsunamigenic. (Gusiakov 2005) This potential is further increased by the high
slope gradient between the Peru-Chile trench and the nearby Cordilleras
Mountains, which results in an increase in the amount of erosion and sediment
going into the nearby ocean.
The chart below shows the
relative damage of the tsunamis that occurred
in each region over the past century. The black
sections of the graph are
the percentage of highly damaging tsunamis that occurred in
each region.
Both the South American and New Guinea and Solomon I regions
have relatively
high percentages of damaging earthquakes, indicating that
these are both
high-risk areas. These regions are believed to be at such high
risk that
Gusiakov classifies them as being in the "red" category, or
highest risk
area.
Because Peru and
Micronesia are both developing nations and because both fall
under the "high risk" category, many experts believe that it
will be impractical
to design a system built only to issue warnings when completely certain
of
tsunami
risk. Instead, it will be much more effective to build a
system which
will respond when there is any large danger of a tsunami (Woo and
Aspinall
2005). This is in large part because, as developing
countries, both Peru and
Micronesia have relatively high population densities. A high
population density
centered along the coastline causes each nation's
government to be more concerned
with massive loss of human life than the economic
cost of a few false alarms.
Furthermore, if possible, sensor headquarters
should be placed in a position so
as to warn the cities with the highest
population densities first.
and underwater landslides. Each contributes to the potential of
tsunami generation in a region, and can result in major damage
to an area. For our study, which examines the South American
and New Guinea and Solomon I regions, we must monitor both the
fault lines along each country and examine the areas with the
highest rate of sedimentation in order to best achieve our goal
of tsunami detection.
Bibliography
Photo
Credits
Graphic
for banner on this page from http://www.noaa.gov/tsunamis.html
Page
last updated by aforeman at 11/1/2005 9:22:16 PM