I listened to the bit on the VA quake yesterday and quickly wanted to give some info. I am a licensed professional geologist and I live in Chicago. The United States Geological Survey set the quake at 5.8. Which is a moderate sized quake. The focus of the quake (the point at which th quake actually occurs below the epicenter) was at a depth of 3.7 miles. It's unusual but not unheard of. VA is near the middle of a tectonic plate and considered stable. However, 400 million years ago when the Appalachian mountains were being built it was a zone of active subduction. This created many passive faults in the area. Matter of fact 99 percent of all faults are dormant or inactive. The quake was too deep to be human induced. An old fault probably got reactivated to compensate for the Earth's constant movement elsewhere. I have a podcast on my blog about the subject in more detail. It's in 2 parts totaling about 4.5 minutes at migeweb.org/wordpress on the podcast page. I hope this helps.

Steve