According to the USGS website, the largest damaging earthquake in the central Virginia seismic zone occurred in 1875 and was magnitude 4.8.
Central Virginia has experienced a series of minor earthquakes in recent years. Last Oct. 3, a magnitude 2.4 earthquake shook parts of Hanover County. That earthquake hit at 4:17 about 20 miles north of Richmond, according to the National Weather Service. In July 2009, a magnitude 2.3 quake struck near the Henrico-Goochland county line 8 seconds before midnight. Smaller earthquakes that cause little or no damage are felt each year or two. A series of similar minor quakes struck central Virginia in 2003 and 2004.
The most recent quake felt in Maryland was a magnitude 3.6 shaking centered in Germantown, in Montgomery County. Tuesday's magnitude 5.9 quake may have been the strongest on record for Maryland. On March 9, 1828, a quake centered in southwestern Virginia was felt from Pennsylvania to South Carolina, and as far west as Ohio. According to the U.S. Geological Survey, the small town of Mineral, Virginia was was the epicenter of a 5.9 magnitude earthquake earlier this afternoon, making today's quake at least equal in intensity to the State's largest earthquake on record, which the USGS says occurred in Giles County Virginia in 1897.
What is the likelihood of earthquakes in Virginia?
The USGS classified last year's Montgomery county earthquake as a "significant earthquake." Earthquakes in Maryland and Northern Virginia are uncommon but not unprecedented. The largest earthquake on record in Virginia is a magnitude 5.6 in Giles County on May 31, 1897. More recently in the broader area, a magnitude 4.1 earthquake struck Lancaster County, Pennsylvania on April 22, 1984. This Pennsylvania earthquake caused slight damage at Conestoga, Lampeter, Mt Nebo and New Providence and was felt from West Virginia to Connecticut. A series of small, felt earthquakes spanning March to July 1993 occurred near Columbia, Maryland, within 33 km (20 miles) of the July 16, 2010 earthquake. That earthquake was felt widely in central Virginia and in parts of Maryland. The most recent earthquake in this region was a magnitude 2.0 event on May 6, 2008 near Annandale, Virginia.
Note: the "largest earthquake on record" reported in this official USGS statement from 2010 is not misreported; the summary states the largest earthquake on record in Virginia as being 5.6 in Giles county, while the USGS website ranks the Giles County earthquake at 5.9.