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Will
tsunami destruction get us an early warning system? Last Sunday's underwater quake, which the U.S. Geological Survey put at magnitude 9.0 in the Richter scale, was the biggest since 1964, when a 9.2-magnitude temblor struck Alaska, also touching off a tsunami. There were at least a half-dozen powerful aftershocks and even one of magnitude 7.3. Enzo Boschi, the head of Italy's National Geophysics Institute, likened the quake's power to detonating a million atomic bombs the size of those dropped on Japan during World War II and said the shaking was so powerful it even disturbed the Earth's rotation. The earthquake occurred at a spot where the Indian Ocean plate is gradually being forced underneath Sumatra -- which is part of the Eurasian plate -- at about the speed at which a human fingernail grows, according to David Booth, a seismologist at the British Geological Survey. Ninety-five percent of the world's seismic activity happens in the Pacific, which is why Sunday's devastation around the Indian Ocean was such a surprise. If it had happened on land, it would have caused massive devastation, but the effects, most likely, would have been fairly local. Instead, the shock wave -- spreading from beneath the ocean floor -- sent a giant bulge of water six miles above. The ripple effect quickly spread, reaching Sri Lanka in two hours, the coast of India in three hours and the eastern-most parts of Africa in six. Tsunami means "harbour wave" in Japanese. Caused by an earthquake beneath the sea floor, it is a series of waves that is caused by it. Even though tsunamis are primarily associated with earthquakes in oceanic and coastal regions, landslides, volcanic eruptions, nuclear explosions, and even impacts of objects from outer space (such as meteorites, asteroids, and comets) can also generate tsunamis. It can drop 200 billion gallons of water on a shoreline in a minute. Scientists say it is one of nature's most massive killers. Tsunamis are not caused by the tides and are unrelated to the tides; although a tsunami striking a coastal area is influenced by the tide level at the time of impact. A tsunami will lose little energy as it grows. Hence in very deep water, it will travel at high speeds and great transoceanic distances with limited energy loss. For example, when the ocean is 20,000 feet (6100 m) deep, unnoticed a tsunami travels about 550 miles per hour (890 km/hr), the speed of a jet airplane. And it can move from one side of the Pacific Ocean to the other side in less than one day. Since the Pacific Coast is deemed more liable to the most amount of tsunami occurrences -- countries in the region have websites dedicated to informing its residents on how to react in the event of any. As a tsunami leaves the deep water of the open sea and spreads into the more shallow waters near the coast, it undergoes a transformation. Since the speed of the tsunami is related to the water depth, as the depth of the water decreases, the speed of the tsunami diminishes. The change of total energy of the tsunami remains constant. Therefore, the speed of the tsunami decreases as it enters shallower water, and the height of the wave grows. Because of this "shoaling" effect, a tsunami that was imperceptible in deep water may grow to be several feet or more in height. In extreme cases, water level can rise to more than 50 feet (15m) for tsunamis of distant origin and over 100 feet (30m) for tsunami generated near the earthquake's epicentre. One coastal area may see no damaging wave activity while in another area destructive waves can be large and violent |
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