Term Paper_ Tsunami

8/8/2019 Term Paper_ Tsunami

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THENATURAL

DISASTERS


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y This ppt is made by Rohit Maheshwari (btech ,civilengg. IIT Kanpur) in one of geo science course taken

by javed malik.


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ATsunami is a series of waves (called a "wave train")generated in a body of water by a pulsating or abruptdisturbance that vertically displaces the water column

In literal terms, a Tsunami (pronounced soo-NAA-mee) is the Japanese name meaning harbour wavesgiven to large waves that sometimes devastated the

shores and ports of Japan.


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Earthquake

Volcanic Eruption

Landslides

Meteorological Impact

Underwater Explosions


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Oceanic plate is being forceddown into the mantle by platetectonic forces.

As the stuck plate continuesto descend into the mantle the

motion causes a slowdistortion of the overridingplate accumulating seismicenergy

Energy accumulates in theoverriding plate until itexceeds the frictional forcesbetween the two stuckplates. When this happens, theoverriding plate snaps backinto an unrestrained position

Tsunami spreads away

Earthquakes occur when the fault ruptures, suddenly releasing built-up energy.

Not all earthquakes generate tsunamis. the most destructive tsunamis are generated fromlarge shallow earthquakes with an epicenter or fault line near or on the ocean floor.


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Most such landslides aregenerated by earthquakes or

volcanic eruptions.

The 1958 landslide-generatedtsunami in Lituya Bay, Alaska

which produced a wave as highas 1,722 foot (525 meter) wave.


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Volcanoes occur along coastalzones, like in Japan and islandarcs throughout the world, cancause several effects that mightgenerate a tsunami.

Waves are generated by thesudden displacement of watercaused by a volcanic explosion,by a volcano's slope failure, ormore likely by a explosion andcollapse of the volcanicmagmatic chambers.

The eruption of Krakatau inthe Straights of Sunda, between Java and Sumatra, in 1883generated at least three tsunamithat killed 36,417 people.


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Up till now no Historicalexample as such of MeteoriteImpact Tsunami.

Nuclear testing by the UnitedStates in the Marshall Islandsin the 1940s and 1950sgenerated tsunami.


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On the average, 2 tsunamis per year somewhere in the world which causedamage near the source. Approximately every 15 years a destructive, Pacific-

wide major tsunami occurs.

Based on historical data, about 59% of the world's tsunamis have occurredin the Pacific Ocean, 25% in the Mediterranean Sea, 12% in the AtlanticO

cean, and 4% in the IndianO

cean. Most tsunamis occur around the Pacific Rim. The figure given below isof Tsunami world map. The circle marked below represent the source zone.


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NORMAL SEA WAVES TSUNAMI

Wavelength, ranges up to 1 miles. Wavelength rangeshundreds ofmiles .

Few miles an hour up to sixty miles an hour Canattainspeeds ofupto 500 milesanhour.

Generated with the gravitational attraction

due to moon and sun and also due to wind

force.

Generateddueto theearthquake,landslides,volcanoes etc.

These Surface waves energy reach only downto a depth of 10 m or so. The energy passes through the entire watercolumn to the sea bed


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Tsunami is shallow water wave as even in deep ocean ,the ratio of (depth/wavelength ) is very small.

Shallow water waves move at a speed which is equal to the square root of the productof the acceleration of gravity (9.8 m/s2) and the water depth i.e. V =g h.

At 20,000ft depth ,speed of tsunami 880 km/hr ~almost equal to speed of jet aeroplane.

At a water depth of 40 m, the speed is 20 m/s~(still difficult to out run).

Also a wave loses energy at a rate inversely related to its wavelength, so tsunamis cantravel at high speeds for a long period of time and lose very little energy in the process.


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ATsunami behaves fundamentally different in the open ocean and close to the coastin shallow waters. Tsunami in the deep ocean has very long wavelengths and very lowamplitude , which made it almost undetectable.

While approaching the shore the tsunami will slow down in speed and amplitudeswill increase dramatically. This is due to the fact that the tsunamis energy flux, which isdependent on both its wave speed and wave height, remains nearly constant.

Consequently, as the tsunamis speed diminishes as it travels into shallower water, itsheight grows, a tsunami, imperceptible at sea, may grow to 10-50 meters near the coast.


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Tsunamis begin to lose energy by bottom friction and turbulence as they rushonshore, but still Tsunamis reach the coast with tremendousamounts of energy.

While as the wave approaches land, its speed decreases, so it begins to 'pile-up',the wave-front becomes steeper and taller and there is less distance between crests.Run-up height which is the vertical height reached by a tsunami onshoreabove reference sea level increases drastically. The first wave to reach the shore mayor may not have the highest run up

The effect a tsunami/run up height on a coastline depends on the origin of thetsunami, distance from its point of origin, its size, the slope and configuration ofthe sea floor and coastal topography that the tsunami is approaching.


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Since a Tsunami consists of a series of waves, the danger can lastfor many hours. Large tsunamis are generally recorded for a fewdays following the event.


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Destruction of human life.

Destruction of structure and other assets due to movement or overturning;caused primarily because of the ultrahigh impact/drag applied by waves.

Large scale spread of waterborne disease like cholera , fever ,malaria etc.

Corrosion of metallic bodies due to presence of high salt concentration in wavesdecreases their life ultimately leading to failure.

The quality of the ground water sources are affected due to the sudden influx ofseawater brought about by waves and also it is found shallow groundwater in somecoastal areas may remain unsuitable as drinking water after tsunami.

Agriculture affect badly due to due to seawater seepage and subsequent saltaccumulation.


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The first intensity scales used routinely to measure the intensity of tsunami werethe Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iidaintensity scale, used in the Pacific. The latter scale was modified by Soloviev, whocalculated the Tsunami intensity I .

According to the

formula

Where Hav is the average wave height along the nearest coast.

Intensity and Magnitude Scale

The first magnitude scale that genuinely calculated a magnitude for a tsunami, was theML scale proposed by Murty & Loomis based on the potential energy. Difficulties in

calculating the potential energy of the tsunami mean that this scale is rarely used.In this formula :- h is the maximum tsunami-wave amplitude (in m) measured by a tidegauge at a distance R from the epicenter, a, b & D are constants


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ATsunami warningsystem (TWS) is a system to detect Tsunamis and

issue warnings to prevent loss of life and property. It consists of two equallyimportant components:

Anetwork of sensors to detect tsunamis.

Acommunications infrastructure to issue timely alarms to permitevacuation of coastal areas.

International Warning Systems (IWS)

1. Pacific Tsunami Warning System (established 1968).

2. Indian Ocean Tsunami Warning System (established 2005).3. North Eastern Atlantic, Mediterranean, and Connected SeasTsunami Warning System(established 2005).

4. Caribbean Sea and Adjacent Regions Tsunami Warning

System (established 2006)


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The PTWS mainly consists of two Tsunami warning centers: The Pacific Tsunami WarningCenter (PTWC) in Hawaii and the Alaska Tsunami Warning Center (ATWC) in Alaska. PTWCserves as the operational headquarters of the Pacific tsunami warning system

PTWC provides warnings for Pacific basin teletsunamis to almost every country around thePacific rim and to most of the Pacific island and after the Indian Ocean Tsunami in 2004 ,PTWC has extended its warning guidance to the Indian ocean also

While WC/ATWC's area of responsibility are Alaska, British Columbia, Washington,

Oregon, and California.

PTWS issue alerts 10-20 minutes after the event. It makes use of more than 150 seismic stationsaround the world to locate potentially tsunamigenic earthquakes, and accesses nearly 100 sea levelstations globally to verify the generation and evaluate the severity of a tsunami.


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Detection and prediction of tsunamis using sensors is only half the work of the system. There equal

importance is the ability to warn the populations of the areas that will be affected.

Depending on the seismic data, PTWC will issue the following typeof bulletins/warnings:

Tsunami Warning Message: This is the highest and most serious level of tsunami notification.Warningsare issued when there is imminent threat of a tsunami or confirmation of a tsunami wave. Whencommunities are issued a warning, local emergency plans should be activated and public safety actionstaken

Tsunami Advisory: The second highest level of tsunami alert. Advisories are issued due to the threat of atsunami that has the potential to produce strong currents dangerous to those in or near the water.Significant inundation is not expected for areas under Advisory but coastal regions prone to damage dueto strong currents may be at risk.

Tsunami Watch Message: This is notification based on early seismic information that provides advancedalerting to areas thatcould be impacted if a tsunami has been generated.

Tsunami Information Bulletin (TIB): Issued when a large earthquake has occurred and to adviseregarding the potential for tsunami. In most cases a TIB indicates there is no threat of a destructivetsunami affecting the issuing Tsunami Warning Center'sArea of Responsibility.

All tsunami warning systems feature multiple lines of communications (such as SMS, e-mail, fax, radio,and telex) enabling emergency messages to be sent to the emergency services and armed forces, as well

to population alerting systems (e.g. sirens).


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Severe ground shaking from local earthquakes may cause tsunamis.

Athunderous boom may be heard followed by a roaring noise as of a jet plane or

a noise akin to the periodicwhop-whop of a helicopteror a whistling sound.

Some time as a tsunami approaches shorelines, water may recede from the coast,

exposing the ocean floor, reefs and fish.

Large quantities of gas may bubble to the water surface and make the sea look as

if it is boiling, the water in the waves may be unusually hot.

Animals have ability to sense subsonic Rayleigh waves from an earthquake

minutes or hours before a tsunami strikes shore. The behavior of an animal subject

to changes in these conditions.


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Building Artificial Wall- Some countries has implemented an extensive

program of building up to 4.5m (13.5 ft) high in front of populated coastalareas and have built floodgates and channels to redirect the water fromincoming tsunamis. The wall built helps in slowing down and moderatingthe height of the tsunami.

Tree cover on the Shoreline - Some locations in the path of the 2004

Indian Ocean tsunami escaped almost unharmed because Tsunami's energygot weak by a belt of trees such as coconut palms and mangroves. Forexample the village of Naluvedapathy in India's Tamil Nadu region sufferedminimal damage and few deaths as the wave broke up on a forest of almost 1lakh trees planted along the shoreline.

Plantations could offer a much cheaper and longer-lasting means oftsunami mitigation than the costly and environmentally destructivemethod of erecting artificial barriers.

Elevate coastal homes Elevate coastal homes and avoid living inbuildings within 200 meters of the high tide coastline as most tsunami

waves are less than 3 meters.


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Know the height of your home /hotel above sea level and its distance from thecoast.

Avoid Homes and small buildings located in low-lying coastal areas as they arenot designed to withstand tsunami impacts rather move to High, multi-story,reinforced concrete hotels.

Pre-prepared with the evacuation plan.Be familiar with the tsunami natural warning signs.

If you are at the beach or near the ocean and you feel the earth shake, moveimmediately to the higher ground and DO NOT wait for a tsunami warning to beannounced. As a regional tsunami from a local earthquake could strike some areasbefore a tsunami warning could be announced.

Stay away from rivers and streams that lead to the ocean.If you are on boat and tsunami warning had already announced , then movedeeper toward ocean rather than coming to port.

A tsunami is a series of waves with the time period vary from several minutes toas long as 1 hour. So after one wave do not assume that the danger is over. The next

wave may be larger than the first one. Better to stay out of the area.


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Term Paper_ Tsunami

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