The temblor was a 4.5, the biggest of at least seven aftershocks in the area.
Tuesday's quake was centered in Mineral, Virginia, but it was felt across several states.
Engineers headed back to the Washington Monument on Thursday after more cracks were found in the top of the building. A four-foot long crack was found just after the quake.
The monument has been closed indefinitely.
Meantime, officials in Washington say they saw the difficulty of evacuating from the nation's capital during an emergency. When the earthquake hit, traffic was snarled for miles in downtown Washington as employers released workers early and at the same time.
Traffic lights malfunctioned, and several streets were closed as crews surveyed reports of damage. Trains were overloaded and slowed by speed restrictions imposed after the quake.
The Associated Press contributed to this report.
