August 23, 2011 Earthquake: Louisa County, Maryland, Washington D.C., Virginia, United States

Ref #1053:

Moderately heavy damage (VIII) occurred in a rural region of Louisa County southwest of Mineral. Widespread light to moderate damage occurred from central Virginia to southern Maryland including the District of Columbia area. Minor damage reported in parts of Delaware, southeastern Pennsylvania and southern New Jersey. Very strongly felt (VII) at Boston, Bumpass, Kents Store, Louisa, Mineral, Rhoadsville and Sumerduck. Felt strongly in much of central Virginia and southern Maryland. Felt throughout the eastern US from central Georgia to central Maine and west to Detroit, Michigan and Chicago, Illinois. Felt in many parts of southeastern Canada from Montreal to Windsor.

Tectonic Summary

The Virginia earthquake of 2011 Aug 23 occurred as reverse faulting on a north or northeast-striking plane within a previously recognized seismic zone, the "Central Virginia Seismic Zone." The Central Virginia Seismic Zone has produced small and moderate earthquakes since at least the 18th century. The previous largest historical shock from the Central Virginia Seismic Zone occurred in 1875. The 1875 shock occurred before the invention of effective seismographs, but the felt area of the shock suggests that it had a magnitude of about 4.8. The 1875 earthquake shook bricks from chimneys, broke plaster and windows, and overturned furniture at several locations. A magnitude 4.5 earthquake on 2003 Dec 9 also produced minor damage.

Previous seismicity in the Central Virginia Seismic Zone has not been causally associated with mapped geologic faults. Previous, smaller, instrumentally recorded earthquakes from the Central Virginia Seismic Zone have had shallow focal depths (avg depth ~8km). They have had diverse focal mechanisms and have occurred over an area with length and width of about 120km, rather than being aligned in a pattern that might suggest that they occurred on a single causative fault. Individual earthquakes within the Central Virginia Seismic Zone occur as the result of slip on faults that are much smaller than the overall dimensions of the zone.

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100km from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500km from where it occurred, and sometimes causes damage as far away as 40km.

Ref #12997:

total economic losses from the earthquake were about $200-$300 million, including millions of USD in damage to the National Cathedral, Armed Forces Retirement Home, and Washington Monument in Washington D.C., as well as damage to almost 600 residential properties.

The shaking was felt by approximately one-third of U.S. population [...] caused minor damage as far away as Charleston, South Carolina, ~600km from the epicenter. The shaking caused the first ever shutdown of a U.S. commercial nuclear power plant at the North Anna nuclear power facility located about 23km northeast of the epicenter.

Ref #12998:

MMI VIII damage in the epicentral area

The only factor mitigating damage in this earthquake was the brief (<3 s) duration of strong shaking

Ref #12999:

estimated residential property damage in Louisa County at $18.3 million (USD)[...] total estimate of private property damage in the epicentral region was $21.4 million [...] Damage to businesses, churches, and nonprofits in Louisa County was estimated at $1.5 million in Sept 2011, and damage to public structures was estimated at $66.2 million, including $63.8 million to replace two schools