A 5.8 MW earthquake struck the Piedmont region of Virginia, and was felt by more people than any other quake in U.S. history.

The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. M_w  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (M_L ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.

On August 23, 2011, a magnitude 5.8 earthquake hit the Piedmont region of the U.S. state of Virginia at 1:51:04 p.m. EDT. The epicenter, in Louisa County, was 38 mi (61 km) northwest of Richmond and 5 mi (8 km) south-southwest of the town of Mineral. It was an intraplate earthquake with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. Several aftershocks, ranging up to 4.5 M_w in magnitude, occurred after the main tremor.

The Piedmont is a plateau region located in the Eastern United States. It is situated between the Atlantic Plain and the Blue Ridge Mountains, stretching from New York in the north to central Alabama in the south. The Piedmont Province is a physiographic province of the larger Appalachian Highlands physiographic division and consists of the Piedmont Upland, and the Piedmont Lowlands sections.

Virginia, officially the Commonwealth of Virginia, is a state in the Southeastern and Mid-Atlantic regions of the United States between the Atlantic Coast and the Appalachian Mountains. The state's capital is Richmond and its most populous city is Virginia Beach. Its most populous subdivision is Fairfax County, part of Northern Virginia, where slightly over a third of Virginia's population of more than 8.8 million live.