The current theory, accepted by most geologists, is that the earth has an outer shell made up of six to eight large tectonic plates and many smaller ones. "Tectonic" comes from the Greek world "tekton" which means "builder." These relatively rigid masses of rock slide over the mantle. The mantle is composed of hot, soft rocks underneath the plates. Some geologists suggest that the mantle is in motion and carries the plates along with it.
About the South Asian tsunami:
Near Sumatra Island in Indonesia, there is a complex structure of tectonic plates involving the Burma plate, with the India and Australia plate to the west and the Sunda and Eurasian plates to the east. These plates are continually grinding against each other. They move very slowly -- only at about the rate, on average, that a fingernail grows. Serious problems happen at subduction zones where one plate dives underneath the edge of an adjoining plate. Force builds up -- sometimes over hundreds of years -- until a rupture occurs and generates a violent earthquake. On 2004-DEC-26 -- the day after Christmas -- at 0758 local time (0058 GMT), an unusually powerful rupture occurred which generated a magnitude 9.15 earthquake "about [100 miles] 160 kilometers...off the coast of Indonesia's Sumatra Island at a depth of about [6.2 miles] 10 kilometers...." 3 It was the strongest earthquake anywhere on earth since the magnitude 9.2 quake which hit Prince William Sound, Alaska, in 1964. "The strongest quake on record hit Chile in 1960 and measured 9.5 on the Richter scale." 4 The energy in earthquakes increases by a factor of ten for each one point increase in the open-ended Richter scale.
The earthquake was detected by sensors at earthquake observatories round the world. Quakes approaching 9 on the Richter scale are capable of generating a tsunami. This earthquake sent a sea surge in the Indian Ocean which probably reached speeds of 270 mph (450 km/hr) in open water. After about three hours, it approached Sri Lanka. It slowed down to perhaps 27 mph (45 km/hr) as it neared land, where it was squeezed upwards to produce a wave capable of massive destruction. 3
The first sign from land of a tsunami is that water is sucked away from the beach. In some areas, this tsunami exposed the ocean bottom near the shore, stranding fish. Many villagers rushed to collect the fish, were hit by the sea surge, and killed.
In early 2005-FEB, scientists at NASA said that the earthquake that caused the tsunami disrupted the Earth's rotation and shaved 2.68 microseconds from the length of each day. The North Pole shifted by about one inch. The planet is now slightly less oblate -- that is, not as flattened at the poles. 8
Reducing the death toll from the next tsunami:
It is quite impossible to rearrange tectonic plates, prevent earthquakes, or prevent tsunamis. But there are ways to minimize some of the devastation and loss of life:
Benefits of the motion of the tectonic plates:
It is difficult to talk about the benefits of tectonic plates with the realization that their motion created a tsunami which snuffed out the lives of about 155,000. However, the same shifting of tectonic plates that causes earthquakes and generated the South Asia tsunami is also partly responsible for life on earth.
Dr. Donald J. DePaolo, a geochemist at the University of California, Berkeley, said: "It's hard to find something uplifting about 150,000 lives being lost. But the type of geological process that caused the earthquake and the tsunami is an essential characteristic of the earth. As far as we know, it doesn't occur on any other planetary body and has something very directly to do with the fact that the earth is a habitable planet." 5 If tectonic plates existed elsewhere in the solar system's approximately 70 planets and moons, they would have produced mountain ranges of the type seen on Earth. None have been seen.
Dr. Frank Press, the lead author of "Understanding Earth" 6 and a past president of the National Academy of Sciences, said: "On balance, it's possible that life on earth would not have originated without plate tectonics, or the atmosphere, or the oceans."
Plate movement "builds mountains, enriches soils....concentrates gold and other rare metals and maintains the sea's chemical balance." 7 Plate movement also recycles carbon dioxide, thus regulating the earth's temperature. Evolution of the species is enhanced when the long-term temperature of the earth is stable. 5 Without a relatively constant temperature enhanced by the movement of the tectonic plates, life might not have evolved on earth beyond simple organisms. Having plate tectonics complete the cycle is absolutely essential to maintaining stable climate conditions on earth," Dr. William H. Schlesinger, dean of the Nicholas School of the Environment and Earth Sciences at Duke University said. "Otherwise, all the carbon dioxide would disappear and the planet would turn into a frozen ball." 7
Dr. Jelle Zeilinga de Boer, a geologist at Wesleyan University says that evidence from earlier tsunamis suggests that they can distribute rich sediments from river systems across coastal plains, making the soil richer. He said: "It brings fertile soils into the lowlands. In time, a more fertile jungle will develop."
Robert S. Detrick Jr., a geophysicist at the Woods Hole Oceanographic Institution, said that in spite of the staggering loss of life, "there's no question that plate tectonics rejuvenates the planet." 7
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