Recent Earthquakes Recorded at the VTSO

Near Charlottesville, VA: 22 Sept. 2001

A magnitude 3.2 earthquake occurred at 12:01 EDT on Saturday, Sept. 22, 2001. The epicenter was near Shadwell, VA, just east of Charlottesville. The focal depth was within a few kilometers of the surface, and this produced a strong acoustic signal that local officials attributed to an aircraft in transonic flight.

In fact, such explosive sounds are frequently associated with shallow earthquakes in eastern North America. Unlike the situation in California, the rocks in the upper few kilometers of the Earth's crust in the east are extremely efficient transmitters of high frequency seismic energy, and a proportion of this energy is converted to ordinary sound waves when the seismic waves reach the Earth's surface.

This earthquake was in most respects typical of the earthquakes that occur within the central Virginia seismic zone. This is an area of the Virginia Piedmont that has long been recognized as an area of increased seismic activity in the central Appalachians. The earthquakes occur at depths from near surface to approximately 20 km. The largest known shock in central Virginia occurred in 1875, with probable epicenter in Goochland County. The magnitude was in excess of 5.0, and the shock caused structural damage and considerable panic in Richmond, and in the epicentral area.

In more recent times, a magnitude 4.0 shock occurred on August 17, 1984. The epicenter was approximately 15 miles to the southeast of Charlottesville. This was a much stonger event that the shock on Sept. 22, 2001. It was felt from Washington, DC to the North Carolina border, and from Staunton, VA to Norfolk.

Click here for waveforms, figures, and location information.


Two felt events near Galax, VA: 30 Oct. 97


Central Virginia: Culpeper Basin

The Mesozoic faulting (both onshore and offshore) is the youngest large scale faulting episode to affect our region. However, the relationship between the Mesozoic faults and modern earthquake activity is not clearly understood. In some areas further to the northeast, particularly in New York and New England, it appears that the Mesozoic features are spatially correlated with the earthquake activity. However, in Virginia the Mesozoic features do not show such a correlation. In fact, the recent Manassas and Culpeper earthquakes are the first such events that can be considered potentially associated with this class of feature. The epicenters of both shocks appear to be near the borders of the Culpeper basin, but the instrumental data are not sufficient to identify the actual faults. Both were very minor events, and are not necessarily associated with mapped faults.

Maps are made using the U.S. Census Bureau Tiger Mapping service, accessible from http://tiger.census.gov.
Last updated 26 September 2001
Comments/Suggestions to vtso@vt.edu