A tsunami is one of the most formidable and destructive natural phenomena that our planet can experience. This geological tidal wave is most often caused by underwater or coastal earthquakes with a magnitude greater than 7.5. They are generated at shallow depths and are usually located in subduction zones, where two tectonic plates converge and one is forced beneath the other.
A tsunami can also occur as a result of an underwater volcanic eruption or landslide. In any case, these events, associated with the abrupt displacement of a significant mass of water, generate large tidal waves. They move with astonishing speed (up to 800 km/h) for several hundred kilometers across the ocean surface.
As they approach the coast, the speed of these waves decreases, and the height increases sharply, reaching several hundred meters. Huge rogue waves hit the coast, destroying and washing away everything in its path. Therefore, understanding the nature of tsunamis and finding warning methods are crucial to effectively protect people living in coastal areas.
Tsunami protection methods
Since it is impossible to accurately predict events that cause tsunamis, minimizing the consequences of their effects is an extremely important task. The effectiveness of its solution largely depends on the ability to detect tsunamis immediately after their formation and quickly alert the population in the danger zone.
The Pacific Tsunami Warning Center (PTWC) was created in 1965 to warn people of danger. The center’s main functions include detection, localization, and determination of tsunami characteristics. The center’s work is based on the interaction of a complex network of seismic stations and sea buoys. This ocean network constantly monitors earthquakes that can cause tsunamis, as well as sea level changes that signal the approach of a large wave. In the event of an undersea earthquake of magnitude 7.5 or greater, the situation is immediately assessed to determine the potential for a tsunami. The following tools are used to monitor earthquakes and tsunamis:
- seismometers installed on the seabed or in underwater caves to minimize the interference of external noise and pressure fluctuations on the reading of seismic waves;
- the DART buoy system which records the pressure on the ocean floor (about 5 km). One of the buoys, equipped with a hydrophone, is located at depth, while the other buoy, with a deep pressure recorder, is located on the surface and is connected to a satellite. Thus, a pair of buoys records changes in water pressure and remotely transmits data via satellite;
- tide gauges installed in bays, inlets and harbors. These devices record changes in sea level and wave activity in the bay, as well as resonant effects characteristic of tsunami wave formation;
- harbor tide gauges that track the propagation of tsunamis.
Information for tsunami monitoring is also provided by other types of equipment – GPS sensors installed on buoys, satellites, devices that allow analysis of the electronic content of the ionosphere, etc.
Warning system
If a large magnitude earthquake occurs underwater, it is immediately assessed to determine whether it could cause a tsunami. In this case, data centers quickly analyze the information and send alerts to state and local authorities. They then transmit a tsunami warning to the public through sirens, text messages and other mass media. This allows every resident of the region located in a potentially dangerous area to take the necessary measures to ensure safety.
Statistics and catalogs
Earthquakes and tsunamis are unpredictable, but they always occur in seismically active zones with irregular periods. Therefore, the collection of statistical data and cataloguing of events that have already occurred is the first tool for assessing the danger in the region.
Protective structures
One of the points of the seismic risk management protocol is to plan and build tsunami-resistant infrastructure. For many years, the construction of walls, dams and other barrier structures has been invested in the regions most affected by the tsunami (Japan, Alaska and Hawaii). This made it possible to reduce the impact of waves on coastal settlements and their infrastructure.
Evacuation
Government agencies in countries at risk of tsunamis should develop evacuation plans. The tsunami protection program also includes regular exercises that are conducted with the population. This makes it possible to ensure that people are able to respond correctly to alerts and effectively protect themselves in the event of a tsunami threat.
Any measures taken to protect the population of coastal cities from tsunamis will be effective. It is important to remember that earthquakes and tsunamis are natural disasters, and no matter how advanced civilization becomes, nature can always be stronger.