File Name: what is tsunami and its causes .zip
Known tsunamis of volcanic origin are reviewed and classified according to their causes.
The tsunami that affected the coasts of the Indian ocean on December 26, claimed close to lives, mainly on the island of Sumatra, Indonesia, which suffered overwhelming devastation. This article asks whether a tsunami warning system is needed in the Indian Ocean, where the probability of experiencing a similar catastrophe is very small. In addition, other alternatives, including land use planning and education focused on tsunami risk management, are presented. Their application could considerably reduce financial and human losses if a disaster of this nature was to occur again. Keywords: tsunami, natural hazard, hazard, vulnerability, risk management, warning system, land use planning, education.
The tsunami science and engineering began in Japan, the country the most frequently hit by local and distant tsunamis. The gate to the tsunami science was opened in by a giant local tsunami of the highest run-up height of 38 m that claimed 22, lives.
In , the same area was hit again by another giant tsunami. Relocation of dwelling houses to high ground was the major countermeasures. The tsunami forecasting began in In , the Chilean Tsunami damaged the whole Japanese Pacific coast. The height of this tsunami was 5—6 m at most. The countermeasures were the construction of structures including the tsunami breakwater which was the first one in the world. Since the late s, tsunami numerical simulation was developed in Japan and refined to become the UNESCO standard scheme that was transformed to 22 different countries.
In , photos and videos of a tsunami in the Japan Sea revealed many faces of tsunami such as soliton fission and edge bores. The tsunami devastated a town protected by seawalls 4. This experience introduced again the idea of comprehensive countermeasures, consisted of defense structure, tsunami-resistant town development and evacuation based on warning.
The Sumatra Earthquake and Indian Ocean Tsunami gave us a vivid description of menace of major tsunamis. It also suggested that tsunami science and engineering were inevitable to save human society, industries, and natural environment.
An answer can be found in Japan. Japan is the country the most frequently hit by tsunamis in the world. The experiences are well documented and are continued as the local legends. In , the tsunami science started when the Meiji Great Sanriku Tsunami claimed 22, lives. An idea of comprehensive countermeasures was officially introduced after the Showa Great Sanriku Tsunami. The major works taken after this tsunami, however, were the relocation of dwelling houses to high ground and tsunami forecasting that started in The Chilean Tsunami opened the way to the tsunami engineering by elaborating coastal structures for tsunami defense.
The Japan Sea Earthquake Tsunami that occurred during a fine daytime cleared the veil of actual tsunamis. The Hokkaido Nansei-Oki Earthquake Tsunami led to the practical comprehensive tsunami disaster prevention used at present, in which three components, defense structures, tsunami-resistant town development and evacuation based on warning are combined. The present paper briefs the history of tsunami research in Japan that supports countermeasures.
On the next day, the Ansei-Nankai Earthquake followed at the west side of the Peninsula. The two earthquakes generated tsunamis that gave heavy damages in the wide area. The height of tsunami was 5 m on an average with locally high value of 10 m.
The construction of coastal dike was quite rare before The highest tsunami run-up height was 38 m at Ryori Shirahama in Iwate Prefecture.
This resulted in the death toll of 22, After this tsunami, several villages were relocated to high ground at private expenses of individual person or village leaders. In an article about the Meiji-Sanriku event published by the CEDP, earthquake was mentioned as one of forerunning phenomena of tsunami. After , there was a hot academic debate about the generation mechanism of this tsunami. Because of the extremely weak ground shaking, many researchers doubted an earthquake but underwater eruption or landslide as the origin of the tsunami.
The key to the solution was the tide records showing quite a long wave period. Only the large fault motion could explain the generation of such a long wave. In around , researchers understood that a fault motion of earthquake was the cause of tsunami. After the Kanto Earthquake that devastated the Tokyo Area, the central government fully led the restoration of the metropolis.
At the same time, the central government and academic society participated in drafting countermeasures against earthquake and tsunami. The Showa Great Sanriku Tsunami was the first major tsunami under the modern knowledge and the modern system. In the early morning on March 3rd, , 37 years after the Meiji event, another major tsunami struck the Sanriku Region.
The maximum run-up height was 29 m at Ryori Shirahama. Most of coastal villages on the Sanriku Region suffered devastating damages again. Because the ground shaking was strong this time, many residents were awaken and evacuated to high ground; however, the death toll reached 3, The CEDP proposed a total system of tsunami disaster mitigation three months later.
Relocation of dwelling houses to high ground: This is the best measure against tsunami. Coastal dikes: Dikes against tsunamis may become too large, and financially impractical. Tsunami-resistant areas: If the tsunami height is not so high in a busy quarter, solid concrete buildings are to be built in the front line of the area.
Buffer zone: Dammed by structures, a tsunami inevitably increases its height. In order to receive the flooding thus amplified, rivers and low-lands are to be designated as buffer zone to be sacrificed. Tsunami watch: Because it takes 20 minutes for a tsunami to arrive at the Sanriku coast, we may detect an approaching tsunami and prepare for it. Tsunami evacuation: The aged, children and weak should be evacuated to safe higher ground where they could wait for about one hour. Ships more than a few hundred meters offshore, should move farther offshore.
Memorial events: Holding memorial services, erecting monuments, etc. This idea proposed by researchers who worked in the field survey after the tsunami covers major necessary items in the tsunami prevention.
It revived in See Section 7. The central government made the restoration plan based on the above proposal. The basic policy was that cities could be restored at the original location surrounded by sea walls but the tsunami-resistant areas and buffer zones should be prepared, and fishing villages should be basically relocated to high ground. In , a tsunami warning organization was founded for the Sanriku coast. A tsunami forecasting chart was drafted empirically. By the Meteorological Business Act enacted in , the forecasting system was made to cover the whole coast of Japan.
On May 23rd, in Japanese local time , an earthquake occurred off Chilean coast. The tsunami generated by the earthquake attacked the Japanese coast on the next morning. Coastal residents in Japan did not feel any ground shaking. The Japan Metrological Agency did not issue a tsunami warning.
Thus, the residents were suddenly attacked by the tsunami. The economic damage was 2. The wave period of the Chilean Tsunami was from 40 minutes to 1 hour, longer than that of near-field tsunamis that was usually 5 to 20 minutes.
Its initial profile in the direction to Japan had the wave length longer than km. Even if short components were included in the initial profile, they were more easily scattered by or trapped around islands and sea mounts during the travel over the Pacific Ocean. In addition, short components retarded due to dispersion effect and then long components arrived first. The tsunami height, 3 to 6 m, was not so high in comparison of such near-field tsunami as the Meiji and Showa Tsunamis. In order to judge whether the dispersion effect is non-negligible for a far-field tsunami or not, Kajiura theoretically introduced a criterion.
Judged with this criterion, the linear long wave theory including the Coriolis force and dispersion effect expressed with longitude-latitude coordinates is used for the Chilean Tsunami. Imamura et al. Kajiura 2 also discussed the energy transfer from the sea bottom to the water in relation to the duration of the bottom movement. If the duration is less than several minutes, the deformation may be considered to be abrupt as far as the tsunami is concerned.
However, if the movement is completed in a few second, the energy transferred to the compressional water waves might be larger than the tsunami energy. His theoretical results are broadly known as the basis of the current tsunami research. Shore protection works started in and were legally authorized under the Seashore Act enacted in In , the Ise Bay typhoon generated a storm surge with the amplitude of 3. This storm surge yielded the most serious damages to Nagoya area.
Coastal embankments made of soil with solid covers only on the seaside surface were completely washed away by overflowing sea water. After this experience, the design standard was revised. Three surfaces seaward slope, landward slope and crown of soil embankment should be armored by concrete. By the Chilean Tsunami, serious damage occurred in the areas that had been believed safe for the past near-field tsunamis. A good example is the area at the bottom of the Ofunato Bay, Iwate Prefecture.
This area was hazardless for the past near-field tsunami and was being developed as the industrial and urbanized areas. The long Ofunato Bay became resonant to long wave period of the Chilean Tsunami, producing the largest inundation at the bottom of the bay. The response of bays in the Sanriku Region to the near- and far-field tsunamis was first cited by Watanabe. Major defense countermeasures after this tsunami consisted mainly of the construction of seawalls and coastal dikes, because the tsunami height was 5—6 m at most.
Seawalls were made of concrete and coastal dikes had front, top and back covered with concrete, applying the experience of the Ise Bay typhoon. It should be mentioned that the first tsunami breakwater was constructed at the mouth of the Ofunato Bay, where the maximum water depth was 38 m. The effect of this breakwater was investigated through numerical simulation. This was the first stage of computer in the tsunami science and engineering. In addition, it should also be mentioned that an international cooperation of tsunami warning was started after the Chilean Tsunami.
Fortunately, its tsunami height was not higher than the crown height of just completed structures, and there were no damages. But unfortunately, many person including coastal residents became to believe that there would be no threat of tsunami in the future, forgetting such huge tsunamis as the Meiji and Showa events.
Although rare, tsunamis have the potential to cause considerable loss of life and injury as well as widespread damage to the natural and built environments. The objectives of this review were to describe the impact of tsunamis on human populations in terms of mortality, injury, and displacement and, to the extent possible, identify risk factors associated with these outcomes. This is one of five reviews on the human impact of natural disasters. Data on the impact of tsunamis were compiled using two methods, a historical review from to mid of tsunami events from multiple databases and a systematic literature review to October of publications. Analysis included descriptive statistics and bivariate tests for associations between tsunami mortality and characteristics using STATA There were , deaths range ,, and 48, injuries range 45,, as a result of tsunamis from to
PDF | On 26th of December , Sri Lanka experienced, perhaps its most devastating natural disaster through a impact of a Tsunami. The Tsunami, a | Find.
Official websites use. Share sensitive information only on official, secure websites. A tsunami can kill or injure people and damage or destroy buildings and infrastructure as waves come in and go out.
The main cause of tsunami generation in the Mediterranean Sea is tectonic activity associated with strong earthquakes. However, tsunami waves are also generated by landslides. From a compilation of 32 reliable cases of landslide tsunamis it comes out that most of them were caused by subaerial landslides or marine slides induced mainly by earthquakes and less frequently by volcanic eruptions. Others were caused by gravitative landslides or marine slides.
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Often a tsunami wave warns of its arrival with roaring and rumbling from the ocean, but sometimes a rising wall of water approaches silently and imperceptibly. A.Anthony S. 19.12.2020 at 19:41
Tsunamis are caused by violent seafloor movement associated with earthquakes, landslides, lava entering the sea, seamount collapse, or meteorite impact.Rialigevo 21.12.2020 at 08:48
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