Recent Earthquakes Recorded at the VTSO
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
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
Click here for waveforms, figures,
and location information.
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
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