Animation shows Costa Rican quake rocking ground underneath U.S.
U.S. residents didn't feel quake because ground under U.S. moved only fractions of inch.
Wed, Sep 05, 2012 at 05:23 PM
A new animation shows the shockwave from the 7.6 magnitude earthquake that struck Costa Rica on Sept. 5 arriving and reverberating through the ground beneath the United States.
The visualization was made by scientists at Incorporated Research Institutions for Seismology (IRIS) and shows the Earth slowly moving up and down. Red spots show seismometers moving upward; the darker the hue, the higher they are moving up. The opposite goes for blue.
The visualization shows how earthquakes create waves of motion through the Earth's crust, just as a pebble tossed into a pond creates a ripple. "But in this case, the pond is North America," said John Taber, head of outreach for IRIS.
People couldn''t feel the quake this far away from Costa Rica in North America because the ground only moved a fraction of an inch, and the wave traveled relatively slowly, Taber told OurAmazingPlanet.
There are 400 seismometers in the array and they are mostly clustered in the Mississippi River valley but will eventually be moved around the entire country to provide scientists with a "CAT scan of the Earth," Taber said.
Seismic waves travel at different speeds through different rock types. "By measuring them, we can learn more about the structures beneath the ground," Taber said.
Data collected by these instruments helps to paint a clearer picture of the rift beneath the Mississippi River Valley in what's known as the New Madrid fault system. This rift was responsible for the 1811-1812 New Madrid earthquakes, and may cause temblors in the future.
The Costa Rica quake originated 87 miles (140 kilometers) west of the capital San Jose, and was centered 25 miles (40 km) below the Earth's surface, according to the U.S. Geological Survey.
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