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International Strategy for Disaster Reduction
Platform for the Promotion of Early Warning


What is tsunami?
In brief - Recent and historical tsunamis - Tsunami early warning system technique - Tsunami warning systems
- Key tsunami actors & organisations - Research projects - Further reading

Recent and historical tsunamis
Indian Ocean Tsunami on 26 December, 2004

The 9.0 undersea earthquake occurred at 00:58:53 UTC. The earthquake generated a tsunami that was among the deadliest disasters in modern history. The tsunami wreaked devastation along the shores of Indonesia, Sri Lanka, South India, Thailand, Maldives and other countries where waves of up to 30 metres hit the coast. Even areas as far as the coast of East Africa sustained damage and recorded fatalities.
It is estimated that between 228,000 to 310,000 people died as a result of the tsunami, and the count is still rising. The true number will never be known.

Earthquake’s characteristics
The epicentre of the quake was just north of Simeulue Island north-west of Sumatra, Indonesia. It was the strongest recorded earthquake since the 9.5 Great Chilean Earthquake in 1960.
See top ten mega earthquakes at:

New analyses suggested that the magnitude was underestimated with one study estimating it at 9.3 on the Richter scale.



                                                      Tectonic setting of the region. (USGS)

This megathrust earthquake was felt as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore and the Maldives. In northern Indonesia the shaking was felt for up to several minutes. It is estimated that parts of a-1200 km faultline slipped about 15 m along the subduction zone where the India Plate dives under the Burma Plate. The India Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting north-east at an average of 6 cm/year (2 inches/year). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench. At this point the India Plate subducts the Burma Plate, which carries the Nicobar Islands, the Andaman Islands and northern Sumatra.

Tsunami characteristics    
The earthquake induced sudden vertical rise of the seabed by several metres disrupted massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. In some places the tsunami waves reached as far as 2 kms inland and caused terrible destruction in their path. Please see a full-length animation of how the waves traveled at: upload/animation.gif. The animation will show why some countries were more affected than others. The 1,200 km faultline affected by the quake was in a nearly north-south orientation; therefore, the greatest strength of the tsunami waves was in an east-west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had very few casualties despite being a low-lying country.  

Map showing travel times of the Indian Ocean tsunami waves

Normally, you would expect that coasts that have a land mass between them and the tsunami's location of origin are safe but tsunami waves can diffract around land masses. For example, the Indian state of Kerala was hit by the tsunami despite being on the western coast of India. This is also comparable to the western coast of Sri Lanka, which suffered substantially from the impact. Further, distance alone is no guarantee of safety; Somalia was hit harder than Bangladesh despite being much farther away.

The vice-president of the Tsunami Society, Tad Murty, calculated the total energy of the tsunami waves to be about five megatons of TNT which is more than twice the total explosive energy used during all of World War II, and is still much less than the total energy released during the earthquake itself!

Depending on the distance to the epicentre the tsunami waves almost traveled from fifteen minutes to seven hours (for Somalia) to reach the various coastlines. The northern parts of Sumatra were hit immediately, whereas, Sri Lanka and the east coast of India were hit between about 90 and 120 minutes later. The shallow water of the Andaman Sea caused the tsunami waves to travel slower; and therefore Thailand was hit relatively late. Despite the close distance to the epicenter, the waves reached Thailand’s coast about 2 hours after the earthquake.
USGS site to the Indian Ocean earthquake and tsunami

Informative internet links related with the Indian Ocean tsunami

The Papua New Guinea Tsunami on July 17, 1998
  A moderate magnitude 7.1 earthquake with the epicentre in northern New Guinea near the coast triggered an undersea landslide that caused a locally major tsunami, which caused more than 2000 fatalities.
Magnitude 9.5 earthquake in Chile on May 22, 1960

This earthquake was the largest ever instrumentally recorded. The epicenter of the earthquake was 60 meters down below the ocean floor about 100 miles off the coast of Chile out in the Pacific. It took 12 hours for the tsunami waves to reach New Zealand, and 20 hours after the earthquake the waves reached Japan.

Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan
The U.S. Geological Survey published an 18-page booklet. It contains lessons on how to survive a tsunami based on accounts from people who survived the tsunami generated by the largest earthquake ever measured. It also contains an excellent description of what tsunamis are.

Effects of the 1960 Chilean earthquake tsunami in North America
Tad Murty, R.D. Scott, and C Fournier, 2000. A conference paper presented at The Fourth International Congress on Earth Sciences, in Santiago, Chile, August 2000.

The Krakatau eruption in Indonesia on August 26, 1883
  After the explosion and collapse of the volcano, waves were generated that reached 135 feet and destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people.