POWER POINT PRESENTATION

Submitted by Sony.S Physical Science

NATURAL DISASTER

TSUNAMI

CONTENTS

What is tsunamitsunami sourcestsunami locationstsunami propagationtsunami warningEffects of tsunami

What is Tsunami?When mass movement, such as an earthquake or landslide, suddenly displaces a large amount of water from its equilibrium state a disastrous wave called a tsunami can form. Tsunami literally translates from Japanese to harbor wave but are often call tidal waves because small, distant-source tsunamis resemble tidal surges.

BANDA ACEH, INDONESIA: June 23, 2004 A satellite image of the waterfront area of Aceh province's capital city before the tsunami.

BANDA ACEH, INDONESIA: December 28, 2004 An image taken after the tsunami shows destroyed housing and the shoreline nearly wiped out.

Tsunami SourcesEarthquakes (e.g. Sumatra, 2004: >200,000 people killed; Papa New Guinea, 1998: ~3,000 people killed)Volcanic eruptions (e.g. Krakatoa, 1883: tsunamis killed 30,000 people; Santorini, 2002).Mass Movement (e.g. Alaska, 1958: waves up to 518 m high formed in Lituya Bay).

Extraterrestrial Impacts - large impacts have the potential to create enormous tsunamis.

Tsunami SourcesEarthquakes that suddenly uplift or down-drop the sea floor generate tsunamis. Generally such surface deformation is largest for reverse and normal faulting earthquakes, and small for transform faulting events thus the potential for tsunamis is lower for strike slip faults (e.g. the Balleny earthquake 1998 did not generate a tsunami). In general tsunami are generated by reversal faults.

Tsunami GenesisTsunamis are caused by events that drastically and suddenly shift a large volume of water.From Plummer McGeary Carlson

Tsunami EarthquakesSome earthquakes have generated very large tsunamis for their size. These events are called tsunami earthquakes.Analysis of seismograms from these events suggest that they are the result of low-frequency seismic energy.These earthquakes present a problem for tsunami warning systems

Tsunami EarthquakesOne way to identify these events is to compare Ms to MwMs ~ 20 seconds periodMw ~ 100-200 seconds periodSince the signals are enriched in long periods the magnitude is unusually larger than the Ms estimate.

Describing TsunamisTsunami wave height is the height of the wave at the shore.Tsunami run-up height is the maximum height that the wave reaches on land.

Tsunami LocationsLarge subduction zones produce the most tsunamis. The Pacific, rimmed with subduction zones, has the most tsunamis.Pacific ~ 80%Atlantic ~ 10%Elsewhere ~ 10%

Tsunami PropagationTsunamis are most devastating near the earthquake. They are larger and strike the region soon after the earthquake.They also travel across entire oceans and cause damage and death thousands of miles from the earthquake.

Local Tsunami DamageDamage close to the tsunami is usually more devastating. Even small events can generate locally high waves. (For example in a bay the waves can be focused and increase their amplitude, a landslide triggered by an earthquake in a fiord in Alaska in 1958 created waves with a run-up up to 518 m high).The warning time can be dramatically short.

Tsunami WarningBecause tsunamis travel relatively slowly, we have a chance to warn distant regions of potential tsunamis.These efforts provide strong arguments for real-time earthquake monitoring.Alerts are issued routinely by cooperating governments.

Tsunami WarningAs soon as an earthquake of magnitude >6.5 is located in the sea the alarm start.Using computer simulations and maps like the one in the following slide scientists forecast the time of arrival in different locations.The use of Buoy and tide gauges help to verify the effective presence of a tsunami, the alarm is given.

Protecting Yourself (Tsunami)Move to higher ground.Wait until authorities give the go ahead to return to low-lying regions.Watch for surges of water in rivers and streams near the coast.If you feel a strong earthquake, dont wait for a formal warning.

Rivers & Lakes

Shaking & Rivers & LakesTsunamis are an ocean phenomena, but any large body of water can be at risk if a larger part of its water is suddenly displaced.Collapsing river banks or lake bluffs can be hazardous to anyone on the water and disrupt river traffic, which can impact local economies.

SeichesThe sloshing of closed bodies of water during an earthquake is call a seiche.Large earthquakes have produced seiches observed over large areas.Although seiches have produced waves with a height of a few feet, damage was minimal.

Landslide in lakesA much more serious hazard is a landslide that it a lake in particular artificial basins. In this case the wave generated can overtop the dam and/or cause the dam failure. The results can be devastating (e.g. Longarone, Italy, 1963, 1917 people killed)

Tsunami disaster

Tsunami disaster

Effects of tsunami

Effects of tsunami

Effects of tsunami