During her trip to Indonesia, German Chancellor Angela Merkel will visit the site of the GITEWS tsunami early warning system - a joint project with the potential to save millions of lives.
The software compares incoming information with thousands of possible scenarios saved on the hard drive.
Because the earthquake zone is not far from the coast, tsunami flood waves can reach shore as early as 30 to 40 minutes after a quake. In the case of a tsunami, that would give people in Indonesia - on the main islands, at least - around 30 minutes to get to high gound.
Tsunamis are also often confused with storm surges, even though they are quite different phenomena. As well as travelling at high speeds, tsunamis can also travel large distances with limited energy losses. Tsunamis have great erosion potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. In 1995 the National Oceanic and Atmospheric Administration (NOAA) began developing the Deep-ocean Assessment and Reporting of Tsunamis (DART) system. An undersea earthquake in the Indian Ocean on 26th December 2004 produced a tsunami that caused one of the biggest natural disasters in modern history. As the tsunami propagates across the ocean, the wave crests can undergo refraction (bending), which is caused by segments of the wave moving at different speeds as the water depth along the wave crest varies. So a tsunami with a height of 1 m in the open ocean where the water depth is 4000m would have a waveheight of 4 to 5 m in water of depth 10 m. Capable of inundating, or flooding, hundreds of metres inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures.
The data were taken by a radar altimeter on board the satellite along a track traversing the Indian Ocean when the tsunami waves had just filled the entire Bay of Bengal.
A numerical model was used to replicate the generation and propagation of the tsunami and it shows how the waves propagated around the world's ocean basins. The term "tidal wave" is misleading; even though a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the tides. These stations give detailed information about tsunamis while they are still far off shore.


GITEWS (German Indonesian Tsunami Early Warning System) is a network made up of various types of sensors specifically designed to fit the geographical conditions in the Indian Ocean. Information from the seismographs, the GPS trackers and the coastal stations reaches a data center - the warning center - in the Indonesian capital city, Jakarta.
For tsunamis that are generated by underwater earthquakes, the amplitude of the tsunami is determined by the amount by which the sea-floor is displaced. As a tsunami leaves the deep water of the open-ocean and travels into the shallower water near the coast, it transforms. In the deep ocean, a tsunami has a small amplitude (less than 1 metre) but very long wavelength (hundreds of kilometres). Due to the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines. If you read the "The physics of a tsunami" section, you will know that a tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows. Refraction and diffraction of the waves meant that the impact of the tsunami was noticed around the world and sea-level monitoring stations in places such as Brazil and Queensland also felt the effect of the tsunami.
The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. However, during the Indian Ocean tsunami of December 26th 2004, the Jason satellite altimeter happened to be in the right place at the right time. The surface buoy then radios the information to the Pacific Tsunami Warning Center (PTWC) via satellite.
Emergency tsunami procedures have been planned right down to the evacuation of the coast in three test regions. Luckily, the plates moved horizontally and not vertically like they did in the great tsunami of 2004. Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. On its arrival on shore, the height of the tsunami varied greatly, depending on its distance and direction from the epicentre and other factors such as the local bathymetry.
Depending on whether the first part of the tsunami to reach the shore is a crest or a trough, it may appear as a rapidly rising or falling tide.


Each station consists of a sea-bed bottom pressure recorder which detects the passage of a tsunami. The system has considerably improved the forecasting and warning of tsunamis in the Pacific. There, a computer rapidly calculates in which direction a tsunami would go and how high its flood wall would be.
The tide gauge at Cocos Island observed the tsunami on December 26th 2004 as it passed by the island, as shown in these observations made during December.
Please listen to your local radio and TV announcements or call 1300 TSUNAMI (1300 878 6264) for latest warning information. Tsunamis may reach a maximum vertical height onshore above sea level, often called a run-up height, of tens of metres.
Thailand was also struck about two hours later, despite being closer to the epicentre, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast. Similarly, the wavelength and period of the tsunami are determined by the size and shape of the underwater disturbance. One problem with this kind of satellite data is that it can be very sparse - some satellites only pass over a particular location about once a month, so you would be lucky to spot a tsunami since they travel so quickly. This large vertical displacement of the sea-floor generated the devastating tsunami, which caused damage over such a large area around the Indian Ocean.
The data shown are the differences in sea surface height from previous observations made along the same track 20-30 days before the earthquake, showing the signals of the tsunami.
Because of this shoaling effect, a tsunami that is unnoticeable at sea, may grow to be several metres or more in height near the coast.



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