Japan Earthquake Makes Waves Across the U.S.

Moving ground. From Japan to the United States, "body waves" from the earthquake moved quickly through the earth at a 90˚ angle, shaking the sensors up and down. These were followed by surface waves from the west that swept the sensors an hour after the quake, and waves from the east which hit 2 hours after the quake.
Credit: IRIS

Scientists from seismic monitoring agencies across the globe were shaken out of bed this morning by calls to respond to the devastating earthquake that struck Japan. They immediately predicted tsunamis in Japan and issued warnings. Their next priority was to analyze as many monitoring systems as possible in order to form an accurate picture of how the quake occurred and its potential effects on the rest of the planet.

"It's clearly one of the great earthquakes," says seismologist Robert Woodward of the Incorporated Research Institutions for Seismology (IRIS) in Washington, D.C. "The data have already propagated around the world and people will be continuing to analyze it for months, even years."

Woodward is the director of USArray, a mostly mobile set of seismographs operated by the National Science Foundation that are moved in regions from west to east over a period of several years, collecting data on Earth's motion as it progresses.

It takes 3 hours for surface seismic waves to circle the earth: coming from Japan, the high intensity waves hit USArray from the west an hour after the quake.

Coming from the opposite direction, a second set of waves from the east hit the array 2 hours after the quake.

Currently stretching across the center of the United States, the array can detect earthquakes in the Japan region with a magnitude as low as magnitude 4.0; it was rocked by this morning's magnitude-8.9 quake. Woodward said the quake may soon be upgraded to 9.0 as the multiple agencies tracking it coordinate their data.

The energy from the quake, said Woodward, "caused the planet to ring like a bell." It will continue to ring for months as the full impact of the tragedy becomes clear.