Washington (CNN) -- A strong earthquake in Virginia shut down a nearby nuclear power plant Tuesday afternoon and sent out seismic waves felt by millions from Georgia to northern New England. Three aftershocks were reported by Tuesday evening. No major injuries or extensive damage were reported after the 5.8-magnitude earthquake, which struck about 40 miles northwest of Richmond. The quake prompted evacuations of office buildings and the precautionary closing of monuments in the nation's capital. A surge in calls by cell-phone users after the event affected service in many areas, federal officials said. Aftershocks of magnitude 2.8 and 2.2 were recorded later in the afternoon, followed by one of 4.2 just after 8 p.m. ET, officials said. More aftershocks are possible in the coming weeks. "It's one of the largest that we've had there," U.S. Geological Survey seismologist Lucy Jones said of the quake. Most federal buildings in Washington had reopened by late Tuesday afternoon, but officials were taking all precautions before giving the all-clear to some of its most iconic structures. The U.S. Capitol was cleared for employees to come back to get their belongings, but inspectors asked people to limit their time inside the building while engineers continue to work around the complex. A helicopter inspected the Washington Monument, and it was found to be structurally sound, the National Park Service said. But a secondary inspection revealed cracking in the stones at the top of the monument. Structural engineers on Wednesday will determine the best way to repair the monument before it is reopened, the agency said. The grounds have been reopened except for an area about 100 feet outside the plaza.