Magnitude 5.8 - VIRGINIA
2011 August 23 17:51:04 UTC
- This event has been reviewed by a seismologist.
|Depth||6 km (3.7 miles)|
|Location Uncertainty||horizontal +/- 2.3 km (1.4 miles); depth +/- 3.1 km (1.9 miles)|
|Parameters||NST= 22, Nph= 23, Dmin=50 km, Rmss=0.44 sec, Gp= 79°,|
M-type=centroid moment magnitude (Mw), Version=B
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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 Washington D.C. area. Minor damage reported in parts of Delaware, southeastern Pennsylvania and southern New Jersey. Very strongly felt (VII) at Boston, Bumpass, Kent Store, Louisa, Mineral, Rhoadsville and Summerduck. 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.
The Virginia earthquake of 2011 August 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, December 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 (average depth about 8 km). They have had diverse focal mechanisms and have occurred over an area with length and width of about 120 km, 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. The dimensions of the individual fault that produced the 2011 August 23 earthquake will not be known until longer-term studies are done, but other earthquakes of similar magnitude typically involve slippage along fault segments that are 5 - 15 km long.
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 100 km (60 mi) 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 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).
Shown are the main shock (star) and aftershocks (red circles) greater than about magnitude 1.0 recorded through May 2, 2012. It is estimated that there were about 450 aftershocks greater than M1.0 from August 24, 2011 to May 2, 2012. These earthquakes were located by the USGS National Earthquake Information Center (NEIC) using data provided by portable seismographs deployed by Virginia Polytechnic Institute (Virginia Tech), Columbia University Lamont- Doherty Earth Observatory, University of Memphis Center for Earthquake Research and Information, Lehigh University, IRIS (Incorporated Research Institutions for Seismology (IRIS), Cornell University, and USGS. A couple hundred of the aftershocks greater than about M1.7 were felt locally. Many more aftershocks smaller than M1.0 (and unlikely to have been felt) have likely occurred in the epicentral area during this time, but the data have not been thoroughly analyzed for events this small.
Scientific & Technical Information
- Global CMT Project Moment Tensor Solution
- USGS/SLU Regional Moment Tensor Solution
- USGS WPhase Moment Tensor Solution
- Phase Data
- Theoretical P-Wave Travel Times
- Energy and Broadband Solution
- Groundwater-Level Response to Virginia Earthquake, August 23, 2011
- Strong Motion data for the Virginia earthquake from CESMD
- Preliminary Earthquake Report
- Southeast U.S. Seismic Network