Quake questions answered

Posted: August 24, 2011

FEARING ANOTHER terrorist attack just weeks before the 10th anniversary of 9/11, workers poured from office buildings in big East Coast cities just before 2 p.m. yesterday, only to learn that an earthquake had struck the region.

The 5.8-magnitude temblor that struck near Mineral, Va., about 50 miles northwest of Richmond, was the biggest to hit the East Coast in 67 years, and one of the strongest ever recorded in the region.

The quake could be felt as far away as South Carolina, Maine and Martha's Vineyard, where President Obama is vacationing, as well as Detroit and Toronto, said a spokeswoman for the U.S. Geological Survey.

The quake wasn't a disaster, but it sure raised plenty of questions. We answer a few:

Q: First of all, is everyone OK?

A: Yes. The quake caused a few injuries in Washington, but the worst damage in Philly was a few cracked windows in Center City high-rises and debris falling from a some buildings in the area. City Hall, plenty of office buildings and the Capitol in Harrisburg were evacuated. SEPTA trains were delayed as the tracks were inspected, and several large employers sent their workers home early, so really, the worst damage here was a hellish early commute.

Q: Could an earthquake as strong as yesterday's center on Philadelphia?

A: It could, but it isn't likely, said earth scientist Jane Dmochowski of the University of Pennsylvania. Philadelphia is far from a plate boundary, where the vast majority of earthquakes occur, she said. If one does strike, the Red Cross says, stay inside. If this were a bigger quake, those millions of people who ran outside yesterday would have been much more likely to get hurt or killed.

Q: Will there be aftershocks?

A: One already has occurred, and more are expected in coming weeks.

Q: Was this quake connected to the 3.0-magnitude earthquake that struck Northeast Philly in May?

A: No, the U.S. Geological Survey spokeswoman said. Minor quakes occur in the Northeast fairly frequently, but they often aren't strong enough to be felt.

Q: Why was the Virginia quake felt so far away, while tremors from those in the West Coast don't travel so far?

A: In general, Earth's crust is more dense on the East Coast, and seismic waves travel faster in denser rock, Dmochowski said.

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