Terremotos en numeros

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  • Publicado : 23 de marzo de 2011
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La Física de los Terremotos
Japan's terrible earthquake once again makes it painfully clear how fragile our existence is in this planet. We seldom stop to think about this, but we are here asguests. Our impressive power, even our capacity for planetary destruction, pales when confronted with the real power of planetary dynamics. We may have learned to harness the power of energy, and are verygood at describing regular, periodic natural phenomena, but our ability to predict sudden planetary changes is still in its infancy.
The February 27, 2010 magnitude 8.8 earthquake in Chile shortenedthe duration of a day by 1.26 microseconds (a microsecond is one millionth of a second). The 2004 Sumatran 9.1 earthquake shortened the day by 6.8 microseconds. It is estimated that the March 11earthquake in Japan, with magnitude 9.0, shortened the length of the day by a bit more than the Chilean one, about 1.8 microseconds.
The change in day duration is due to a redistribution of Earth's mass.Just as an ice skater can speed up her spin by bringing her arms closer to her body, the shifting of Earth's mass will make it rotate faster. The closer the earthquake is to the equator, the more itwill spin up the Earth. And if the Earth spins a bit faster, days are a bit shorter.
Perhaps even more impressive, initial data indicates that the earthquake shifted the position of Japan's main islandby 8 feet. It also shifted the position of Earth's figure axis (the axis long which Earth's mass distribution is balanced, like the balance axis in a see-saw) by about 6.5 inches (17 centimeters).The figure axis is not the same as the north-south axis, around which Earth rotates in space at about 1,000 mph. They are off by about 33 feet. Earthquakes can't shift the north-south axis; onlyexternal gravitational forces, such as that exerted by the sun, planets or moon on Earth, could.
To put us on our right place, it's possible to compare the energy released in an earthquake to that...