2011 Virginia Earthquake

Date: August 23, 2011 • Location: Louisa County, United States

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. Mw was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Before Hanks and Kanamori (1979), Kanamori (1977) developed Mw scale for large earthquakes above 7.5. Thus Mw and M are not the same mathematically even though they are considered the same. Similar to the local magnitude/Richter scale (ML) 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.