Earthquakes Recorded in Virginia: A Primer
In the theory of plate tectonics, the earth's outermost layer is
composed of plates that move relative to each other. Most of the
world's earthquakes occur at the plate boundaries. Since places like
the California coast are on a boundary between two plates, they have
many more earthquakes than places like Virginia, which is near the
center of the North American plate (Figure 1a). Yet earthquakes still
occur in Virginia (Figure 1b).
Figure 1: (a) Seismogram of the January 17, 1994 Northridge
earthquake, magnitude 6.8.
(b) Seismogram of the January 22, 1995 Pulaski earthquake,
magnitude 2.9. Both events were recorded on a seismograph in
Virginia has had over 160 earthquakes since 1977 of which 16% were
felt. This equates to an average of one earthquake occurring every
month with two felt each year. Click here
for a summary of the largest earthquakes in Virginia.
The largest earthquake to occur in Virginia is the 1897 magnitude 5.8
Giles County earthquake. This earthquake is the third largest in the
eastern US in the last 200 years and was felt in twelve states. Click
here for a discussion on the
observed effects of this event.
Seismic activity (seismicity) has been
known for several decades to be strongest in and around Giles County
and in central Virginia. This led researchers at the VTSO to
concentrate seismic monitoring stations in these two areas, as shown in
Figure 2, which shows earthquakes (circles, scaled to
magnitude) in and near Virginia from 1774 through 1994.