Why Was Virginia's Earthquake Felt All The Way in Canada?

Today's 5.8 magnitude earthquake centered in Virginia. So why are there reports of tremors being felt as far away as Canada, North Carolina, Georgia and Michigan? According to the U.S. Geological Survey (via Live Science), it's because the East Coast experiences quakes differently than the West Coast, where they are more common:

"The crust is different in the east than in the west," 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.

NPR has more specifics on the east-west comparison:

California is a tectonically active area. The state is situated along the San Andreas Fault, where the North American and Pacific tectonic plates meet.

Virginia sits about smack in the middle of the North American plate, where "intra-plate seismicity" — that is, seismic activity within a plate itself, rather than at a plate boundary — causes the occasional earthquake.

According to USGS, earthquakes that take place to the east of the Rocky Mountains are felt over 10 times a longer distance than those to the west. Virginia is classified at "moderate" risk for earthquakes.

USA Today reported seismologist Karen Fischer of Brown University as saying that earthquakes of this magnitude are unusual but not unheard of:

Virginia is not on an active earthquake fault and is roughly in the middle of the North American continental crustal plate, she says. But it has residual fault scars left over from 200 million to 300 million years ago, when it was an earthquake zone, at the time when the Atlantic Ocean rifted apart from Europe.

. . .

"We are just seeing pressure build up and release on those scars," Fischer says. "There is a lot of debate on exactly what is going on down there and exactly how quakes this big happen in this kind of crustal zone."

According to USGS, there have been about 200 earthquakes in Virginia since 1977. Tuesday afternoon's earthquake ties for the largest with the largest quake ever experienced on 1897 at 5.8 magnitude.