Wednesday, August 24, 2011
East Coast Earthquakes Are Felt More Widely Than West Coast Earthquakes of the Same Size
Yesterday's 5.8 earthquake in Virginia was felt over a huge area: as far away as Canada, North Carolina, Georgia and Michigan.
In fact, earthquakes on the East Coast are felt more widely than similar-size earthquakes on the West Coast.
East Coast earthquakes are typically felt in a wider area than those in California. That's because the Earth's crust is more solid in the East, and it carries seismic waves better than in the more fractured West Coast crust.
CNN quotes Rowena Lohman - assistant professor of geophysics and tectonics at Cornell University - to explain:
The West Coast is a much more active region, with earthquakes, volcanoes and high rates of deformation overall and with a relatively warm, "squishy" young crust compared with the old, "cold" rock material underneath the East Coast. This means that the seismic waves that radiate outward from an earthquake in California are absorbed much more and are not felt as strongly as they would be for a similar earthquake here on the East Coast.
Scientists often say that the East Coast "rings like a bell" after an earthquake, with the seismic waves remaining strong over long distances, whereas in California the seismic waves are absorbed relatively quickly, so their effect is more like the thud you'd hear if you rang a wooden bell.
And LiveScience notes:
The shaking was felt over such a large area ... largely because the eastern part of the North American continent is different than the West Coast, where quakes are more common.
"The crust is different in the east than in the west," United States Geological Survey (USGS) earthquake geologist David Schwartz told LiveScience. "It's older and colder and denser, and as a result, seismic waves travel much farther in the east than in the west."
Additionally, said Andy Frassetto of the Incorporated Research Institutions for Seismology, the sediments along the east coast can make quakes feel stronger.
"The sediments of the coastal plain along the eastern seaboard can trap waves as they propagate and produce a minor amplification of the shaking," Frassetto told LiveScience.