For those of you who were interested, the earthquake occured in the Central Virginia Seismic Zone.
It isn't clear at this point if it occured on the Lakeside or Spotsylvania fault, but it is most likely one of the two.
It could be on another as-of-yet undiscovered faults as well, since faults in the eastern US aren't mapped very well, but the earthquake happend real close to the two mentioned faults.