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ShareMay 1, 2005 — In the Global Seismographic Network, 138 networked stations can pick up quake movement and send instant information to computers around the world. The network has passed its first real-world test: Sensors on seismometers worldwide started moving just a few minutes after the December 26, 2004 Sumatran earthquake started.
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Last December's tsunami was triggered by an earthquake in the Indian Ocean. Experts say the United States has a 1 in 5 chance of a cataclysmic earthquake off the west coast in the next 50 years, one that could trigger our own tsunami. This realization put the scientific community to work, as it now examines the vast amount of information collected from a network of seismic monitors.
When the earthquake and tsunami shook Southeast Asia, it sent seismic waves worldwide.
"They don't happen all that often, but when they do you can see the very devastating effect. It's important that we understand how those earthquakes are generated," says David Simpson, a seismologist at Incorporated Research Institutions for Seismology Consortium in Washington, D.C.
Seismologists may be a step closer to that goal as they examine data from monitors linked together across the world.
Yale University seismologist Jeffrey Park, says, "The Global Seismographic Network, in the case of this earthquake, is going to help us study that process to try to understand a little more about how plate tectonics works and how these huge slabs of rock slide past each other."
The Sumatra earthquake was the first full-scale test of the network to see if it could meet the goals it was designed for. From new seismographs, scientists receive clearer and even real-time information on earthquakes -- for a faster emergency response.
Park says, "It gives a rapid indication when there is something damaging and perhaps devastating happening."
Any one of the 138 networked seismographs can pick up quake movement and send instant information to computers around the world -- sensors on seismometers worldwide started moving just a few minutes after the Sumatra earthquake started.
"This is the first time that the earth has been excited by a really large event," says Simpson, "and it lets us understand something, things about the internal structure that we couldn't see before."
Keeping this technical ear to the ground may help scientists predict quakes and plan ways to withstand them. As seismologists work on better ways to predict the impact of quakes, they say a communications network also needs to be in place to help alert governments and citizens of a threat as it occurs.
A seismograph is an instrument installed in the ground that records and measures the vibrations produced by earthquakes.
If you throw a rock into a pond or lake, waves will ripple outward in all directions from the point where the rock hit the water. The same thing happens during an earthquake: it creates seismic waves of vibrations in the ground that radiate out in all directions. The further these waves are from source of the earthquake, the less energy they have, and the harder they are to detect. Scientists want to detect them, however, because they learn useful things about the Earth's many-layered interior from them.
The Earth's motion during an earthquake must be compared to an object that doesn't move when the ground shakes. That's why a seismograph uses an object -- usually a large electromagnet -- suspended on springs within a case made of fine wire, to keep the object still, while the case around it moves with the ground's motion. (This is similar to the way shock absorbers work in cars.) As the case moves, it produces small electrical signals in the wire coil. These signals are then amplified and stored digitally on a computer, or transcribed onto a recording drum.
But a single seismograph pendulum only detects waves moving in one direction. To get a complete picture of the wave's motions from other directions, modern seismograph stations have three separate instruments to record the different kinds of waves: waves moving north-south and east-west, and the way the ground moves up and down.
The Global Seismograph Network goes one step further, linking 128 seismograph stations in more than 80 countries on all continents to collect and store seismic data from around the world that can be accessed by everyone.
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