There are many things that affect the propagation of a tsunami. One major impact is the bathymetry of the seafloor in between the origin of the tsunami and the shoreline which it impacts. The factors of bathymetry can be separated into two major types; those that make the wave have a larger impact, and those that lessen the impact.

  The general detriments to the propagation of a tsunami wave have characteristics of drastically interrupting the sea floor, and therefore taking a portion of the wave’s energy away from it. They essentially cause the wave to dissipate some of its energy before it reaches the shoreline, therefore having a lesser impact on the area. An example of a detriment of a wave is a coral reef. When a tsunami impacts with a coral reef it can cause the tsunami to have a premature break, thereby loosing a portion of its energy. Although this greatly damages the coral reef and the wave does regain some speed after it passes over the reef, it can lower the level of damage to the shoreline. Berms also help to remove some energy from waves. Berms are embankments, and have the general same effect on a tsunami wave as a coral reef. Berms, however, do not get destroyed as easily as coral reefs because they do not have the extensive ecosystem associated with them like coral reefs do. A final example of a detriment to a tsunami wave is a deep trench parallel to the shoreline. This hurts the tsunami wave because when there are drastic changes in the seafloor it removes energy from the wave when the wave interacts with it.

  There are also many enhancements to tsunami waves due to bathymetry. One aspect is trenches that run perpendicular to a shoreline. As opposed to the trenches that run parallel with shore and act as a buffer, the trenches that run perpendicular essentially funnel the wave in towards the shore. It focuses the strength of the tsunami to the portion of the shore that is exactly opposite the opening of the trench. In addition if the seafloor is smooth and gradually slopes up to shallow water the wave will have a larger impact on the shore simply because there is nothing for the wave to interfere with, and limited places for the energy to be dissipated.

  Once the wave reaches shore there is also a series of interactions to be considered when thinking about the potential damage of an area. The coastal topography can either protect and area from most major damage or ensure the destruction of the infrastructure, land, and lives in the area. There are some important aspects of costal topography to consider when looking specifically at Peru and Micronesia. There are again two categories in which topography features can be divided into. Within the first category of protecting the shoreline the topic of bluffs or seaside cliffs that could potentially be present in an area is found. This feature offers significant protection to an area, but is unfortunately hard to replicate except perhaps by a seawall. Luckily Lima, the capitol of Peru, has significant cliffs protecting most of it from a tsunami. Another feature that can protect the shore is mangroves or other densely packed vegetation on the shore. Although this is not as sturdy as cliffs, a large portion of the tsunami’s energy will be dissipated on the vegetation which will significantly help to lower the damage. Finally, levees provide temporary protection for an area as well. They can hold back flood water and provide a barrier that can shield an area. Levees however are not exceptionally sturdy as was seen in New Orleans, and if they are heavily relied on the consequences can be horrific.

  The affect that bathymetry and coastal topography has on the tsunami waves allows for important information to be predicted about future waves. Algorithms can be created using data sets of bathymetry and topography to determine the risk of an area. Other important pieces of information that should be included within the algorithm would be data like past tsunamis, past earthquakes, the magnitude and damage occurred due to them. This coupled with the bathymetry and topography data can be used to determine what areas are at the highest risk so they can be the most prepared and all areas can plan accordingly.

  A tsunami is by nature a global natural disaster. Propagation of tsunami waves most often occurs in open ocean, where the waves can spread to many countries. This was seen in the December 2004 tsunami that spread from Indonesia to parts of Asia and Africa and eventually the Americas. An earthquake that occurs underwater near Japan could create a tsunami that hits not only Japan but Micronesia as well. The ideal warning system must allow for the possibility that a tsunami may originate at a close or far location from the area being studied. At present, the international community is in the process of implementing such a network around the world as priority and funds allow. As a Mission group, we worked to determine the best sensors and sensor placement for the areas which we are studying in reference to the plans already in the works, with the hope that the planned sensors will be put in place soon.

  Tsunamis are caused in three ways. The most common, and usually most devastating, are earthquakes. Underwater landslides can also cause tsunami waves, as they abruptly distort the sea floor morphology. Finally, tsunamis can be caused by meteor impacts over open water; however, these are infrequent enough that our team did not specifically plan this cause.
  Once a tsunami or landslide occurs, the strength of the wave once it reaches land is determined by several factors. The sea floor morphology will either channel or dissipate the wave’s energy. The more mountainous features underwater, the more the wave will be disrupted and the tsunami wave will be smaller. Coral reefs work to dissipate wave energy in this way. At high tides, a tsunami will be much larger than at a low tide. Areas with higher sedimentation rates have more rock shifting during the earthquake or tsunami, resulting in larger waves.

  Our team looked at several methods of tsunami detection. The two main proposed methods were remote satellite sensing and buoys utilizing a bottom-pressure recorder. Satellites can “see” the tsunami waves as they propagate across open water. A satellite happened to be over the Indian Ocean at the time of the Sumatran tsunami and pictures taken from the satellite showed how the tsunami wave moved around the world. While this data was very useful in reconstructing the event after it occurred, it was not part of the warning system. The particular satellites that have the instruments that can detect tsunamis are not in geosynchronous orbit and there are not enough of them to ensure that a satellite would be within range at the point in time when a tsunami would occur. The data gathered from the satellite in the Sumatran tsunami was not accessed until several hours after the earthquake hit, much too long for it to be useful during an evacuation. Currently, the Global Earth Observation System of Systems (GEOSS) project is planning for such a sensing network of satellites that measure many different things that would be put in place over the next ten years. However, our team has determined that a more immediate, accessible method of detection is needed.

  At present, the most effective warning system utilizes DART II (Deep-ocean Assessment and Reporting of Tsunamis) buoys designed and monitored by the National Oceanic and Atmospheric Administration (NOAA). These “buoys” consist of two main parts – the bottom package and the buoy. The bottom package consists of a Bottom Pressure Recorder (BPR) which uses a quartz-crystal resonator that can detect changes in bottom pressure and water height within millimeters. There is also a thermometer to counteract the influence of temperature on the pressure readings. There is a tilt sensor, a battery and a transmitter that connects the bottom package to a surface buoy (Meinig, 2005). We propose to add to the DART II buoy a seismometer to the bottom package to gather additional earthquake data.
  The surface buoy is a 2.5 meter diameter fiberglass foam disk buoy that displaces 4000 kg of water (National Data Buoy Center). It has two electronic systems in case one system malfunctions or fails. It also includes a receiver to receive transmissions from the bottom package and a transmitter to send the data to GOES GPS satellites, from where it is sent to warning centers. The buoy is capable of two-way communication. We propose that a short-wave radio transmitter also be added to the DART II buoy that could send the data to a site on land close to the buoy. That way, the time delay that results from sending the information to the international warning center is eliminated and the area about to be hit will have a few extra minutes to begin preparing.
  Generally, the BPR will continuously monitor the pressure and record fifteen second averages, which are sent together in a single transmission every six hours. This is known as “standard mode.” When a tsunami occurs, the buoy detects high pressures and enters “event mode.” The above-average pressure rating for the fifteen second interval is sent immediately as message #0 via satellite, and then pressure readings are continually sent detailing the 15 second intervals every few minutes until the algorithms within the buoy determine that the tsunami parameters identifying a tsunami are no longer met. It takes from three to five minutes from when the first abnormal pressure reading is made to when the satellite transmission reaches a warning center (Meinig, 2005).
  The DART design has been tested rigorously and currently has a 96% success rate at data return since 1998 (National Data Buoy Center). It can detect differences of less than a millimeter in water column height, and has a reporting delay of three minutes (Meining, 2005).
DART I system diagram, excluding our suggested improvements of a short-wave radio transmitter and a seismometer. Diagram from http://www.ndbc.noaa.gov/Dart/dart.shtml

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