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Tsunami Formation






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.

                                                                           Tsunami Causes

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


There are 10 main tsunamigenic regions in the Pacific Ocean. These regions 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.

                                                  Map of Regions

Both of the countries examined in this study are located in the equatorial 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 resultThe 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 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.

                                             Peru Map

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.

                                  Damage Percentage

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.


                                          Map of Micronesia

In summary, there are 2 main causes of tsunamis: earthquakes 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.




Annotated Bibliography



Graphic for banner on this page from http://www.noaa.gov/tsunamis.html



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