A tsunami (from the Japanese meaning harbor wave, the term tidal wave is generally synonymous, but not using science, because tsunamis are not related to the oil) is a series of waves that originate from an earthquake, submarine earthquake, volcanic activity, landslides, meteorite impacts in the sea or close to it.
Lately, the word tsunami (from Japanese tsu "harbor" and nami "wave" or "wave against the port") has now come into use in the Italian language as a synonym for the current tsunami, notably through the misuse of that term by newspapers and television, to the detriment of the Italian word. The meaning of these terms is essentially the same: to indicate a wave anomaly that strikes the coast, regardless of the cause that may have originated. The source, in fact, can often be a submarine earthquake, which, while affecting the bottom of the sea, it is a movement of the earth's crust, so it's just an earthquake. Even so, the word tsunami, however, is in no way linked to any such seismic origin, so much so that it comes to describing even the tsunami wave produced by the impact of a large meteorite with an ocean.
The energy of a tsunami is constant, depending on his height and speed when the wave approaches land, its height increases while its speed decreases. The waves travel at high speeds, without being more or less observable when crossing deep water, but their height can grow up to 30 meters and more when they reach the coastline. The tsunami caused severe destruction on coasts and islands.
Many cities that overlook the Pacific Ocean, mainly in Japan but also in Hawaii, have warning systems and evacuation procedures in the event of a serious tsunami. A potentially tsunami-genic earthquake can be predicted by various institutions in various parts of the world seismology.
At the moment there is no reliable model can correlate the occurrence of an earthquake to the generation of a tsunami. The only way to measure the actual generation of a tsunami is by measuring the sea level. Currently measurements to relay early warnings, with the necessary level of reliability can be made only through the use of systems placed on the seabed and are capable of transmitting real-time acquired data. Due to the speed of propagation of the tsunami on the high waters and, if you want to have at least one hour notice, will be a need to deploy the platform at a distance of about a thousand kilometers from the coast that will be alerted. Of course in this case, the source tsunami-gene will be at a greater distance.Are in progress at the time many experiments to determine a reliable model able to correlate the seismic surveys in the generation of tsunami. None of these systems can fully protect against a tsunami if it is triggered by a phenomenon very close to the coastline as it is not possible to alert the population in time. A significant contribution may be made from the study of small-scale Tsunami (Tsunami baby) and their correlation with seismic events of low intensity, measured directly on the ocean bottom seismic networks in addenda to the land.
Creation, Propagation And Unbreakable
A tsunami forms when you move a large body of water. At present it is believed that a tsunami may be caused by: a strong undersea earthquake, measuring at least 7 (Richter scale), a sharp rise or lowering of the seabed, a slip of the coastal land or underwater, an impact of a meteorite. It should be noted that a strong earthquake is not necessarily cause a tsunami: it all depends on how you change the ocean floor near the fault.
Moving water creates waves propagates gradually and very long (usually a few hundred kilometers) and large duration (several tens of minutes). For comparison the normal waves have wavelengths of a few meters and a duration of only a few seconds: the length, scope and duration of waves of a tsunami are so much higher than those of normal waves, while only heights of the two types of waves can be comparable. When the tsunami event occurs near the coast, it is called "local tsunami".
The speed of a tsunami can reach at 500-1000 km / h in the open ocean until reduced to about 90 mph near the coast.
Some tsunamis can propagate thousands of kilometers. These are generally very long tsunamis of tectonic origin, since they do not slip in the ground water and volcanic explosions usually cause waves of shorter length that instantly disappear.
The destructive force of a tsunami is the quantity of water raised, so an earthquake in the open ocean can be extremely dangerous, because it may be able to lift and move all the water present above the seabed, although only a few centimeters. This huge mass of water coming in near the coast is always a lower seabed and therefore tends to slow down her face making it shorter but rising further. A tsunami wave in open sea is only a few inches high and tens of kilometers long near the coast becomes a wave several centimeters or several meters with a length of several kilometers. No barrier port is able to counter a wave of this kind, in fact the Japanese port of call wave
The waves created by wind, however, only move the masses of water surface, without affecting the seabed, and break the barriers port. This is also why several meters high waves, even tens of meters (many are on the Pacific coast), caused by the wind, do not carry enough water to penetrate inland. Conversely, a one or two meters high tsunami can be devastating, because the amount of water that carries allows him to pour up to hundreds of meters inland if the surface is flat and without artificial or natural obstacles like trees.
The first historically documented description of a tsunami can be found in the Bible, where he quotes the passage of the Jews through the Sea of Reeds (or Sea Rush), identified with a certain degree of uncertainty with the area of the Red Sea far from Port Said. The Jews crossed the strait (a lagoon, most likely) was favored, according to some historians , the sudden withdrawal of water caused by the explosion of the volcano on the Greek island of Thera (now Santorini) around 1627 BC, as well as the next rising wave that swept back to the Egyptians. In 426 BC, the greek historian Thucydides described a tsunami, in his work on the Peloponnesian War, assuming that it - most probably - was triggered by an undersea earthquake. In 365 AD, the tsunami that destroyed Alexandria in Egypt was described by the Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19). The estimate of victims is approximately 50,000 dead. On February 4, 1169 a tsunami had 20,000 victims in Catania.On May 5, 1202 in a scrolling area of the faults of the eastern Mediterranean caused a tsunami that devastated Greece, Turkey, Egypt, Sicily, Syria and Israel. From the historical record shows that the victims were approximately 1,200,000, estimates that, if confirmed, to project this cataclysm at the top of catastrophic events. The Lighthouse of Alexandria, built in the Hellenistic period, was shot down by the waves generated by an earthquake off the coast of Crete in 1309. In its place on the peninsula Rabat el Tin, was built a strong following. The Greek and Italian coasts, in particular, were affected by the tsunami on 9-11 January 1693 (60,000 deaths). We should also mention the tsunami that ended the devastation caused by fire caused by the earthquake in Lisbon in 1755. The wave caused the deaths of at least 55,000 people in the Lusitanian capital and at least another 10,000 in Morocco. Calabria was hit by a tsunami in 1783 that had 1,500 victims.
Tsunami Run-up with more, or the maximum height reached by a tsunami wave, occurred in Alaska on July 7, 1958, in the bay called Lituya Bay: the monstrous wave reached the height of 525 meters would been able to cover plenty of the Taipei 101 (Taiwan), one of the tallest buildings in the world. However, the case of Lituya Bay can not be described as a veritable tsunami because it was created by a submarine earthquake, but by a huge landslide of earth: an entire mountain had fallen into the sea, raising the huge mass of water .The tsunami occurred before the astonished eyes of the occupants of three boats: two of them were swept away by the wave and were never found. However on the third vessel was present a man who witnessed the whole scene: it is the only eyewitness to the wave of 525 meters. On the Web there are many photographs of the effects of wave Lituya Bay, who left the ravaged landscape, carrying away trees and rocks, he even tore off the blades of grass and earth. However, the wave has not been able to climb over the mountains surrounding the bay and therefore can not be considered the most destructive wave ever recorded: the tsunami in 2004, the Indian Ocean, had a height much smaller force but a much higher.
Yet another terrible tsunami devastated the Hawaiian Islands following the terrible earthquake that ravaged the May 22, 1960 Chile
Another was the devastating tsunami occurred off the coast of Hokkaido, Japan, as a result of an earthquake, July 12, 1993. As a result, two hundred and two people on the tiny island of Okushiri killed, and hundreds more were injured or missing.
The worst incident is that of the Indian Ocean tsunami of December 26, 2004, which caused hundreds of thousands dead, injured and homeless.
More recently, 17 July 2006 a tsunami struck the coasts of Java, Indonesia: 547 people died and 233 were injured.
On September 30, 2009 a tsunami struck the southern islands of Samoa in the Pacific: the provisional budget is more than 100 victims.
On October 25, 2010 a tsunami strikes again, Indonesia, following an earthquake of magnitude 7.7. Killed more than 300 people
'S March 11 2011 tsunamis are devastating some of Japan and surrounding areas after an earthquake of magnitude 8.9.
In the rest of the world
It was built to install an early warning system and evacuation from tsunami on the beaches of Phuket and Krabi. Following the catastrophic events of December 26, 2004, when a tsunami generated by an earthquake on the ocean floor caused profound devastation and hundreds of thousands of victims in several countries bordering the Andaman Sea and Indian Ocean, the Royal Thai Government unanimously approved a proposal to immediately intervene to prevent such disasters and has made a systematic program for the evacuation of coastal areas in the provinces on the Andaman Sea of Thailand. The evacuation program included installation of a public system of early warning and an indication of the assembly and evacuation routes for shorter from the beach area. In a pilot project, an early warning system was installed at three strategic points along the beach of Patong.
Next, the installation of early warning systems has been achieved in each of the six provinces of southern Thailand, including Krabi. The data on the intensity of a possible wave caused by a hypothetical earthquake or tsunami will be processed and sent immediately to the alarm system and satellite in the event that there is a high probability of occurrence of a tsunami, an immediate alarm will be launched high-risk areas around Thailand.
Warning and alarm systems consist of sirens, flashing red lights, well-recorded audio messages into various languages, will enter service immediately. The alarm system will be supported by radio stations (FM 169696) and automatic sending of more than 20 million SMS messages.
The Thai Meteorological Agency, a complete system, installed in late 2007, three abyssal stations in the Andaman Sea to the real-time measurement of the tsunami, in order to prevent the possible reoccurrence of the population likely to induce false alarms Coast to doubt the effectiveness of the system. Alarms are generated only on the basis of seismic data should in fact be regarded as merely "probable tsunami warnings" and not as true alarms.
On 26 December 2004, the violent earthquake that struck the coasts of Thailand and Indonesia did not cause, guilty of an effective warning to the coasts of India and Sri Lanka, where the destructive tidal wave came after about four hours, causing some 40,000 victims. There would be plenty of time to notify, by radio, local police, sms and television, people living in coastal villages, to cause them to flee on foot just 500 meters from the coast. The personal injury would have been much milder. Something did not work, even in the absence of previous close in time, but four hours in an alarm could be issued also incomplete by the authorities, who instead were left uncertain about what to do. The seismological observatories around the world should have been studded with great alarm the authorities of the Asian country, warning that the wave, you already know the size and extreme danger, would come within a few hours and southern India on Ceylon, after crossing the Bay of Bengal quickly.