A magnitude 4.5 earthquake centered near the Cumberland-Powhatan County border shook Central Virginia at 3:59 pm EST December 9, 2003. Below is a map showing the epicenter of the earthquake. In Farmville, two distinctive vibrations lasting about ten to fifteen seconds total could be felt in the Natural Sciences Department (Stevens Hall) at Longwood University. Also heard by some observers was a bang that preceded the rumbling. The latter is caused by the transition of seismic waves in the ground to sound waves in the air.
Above is the seismograph reading from a station at the University of Maryland in College Park. You can clearly see the quake begin a little before 4 pm (right side of graph, in black) and continue for a bit over two minutes (left side of the graph). The most intense vibrations can be seen coming 40-50 seconds after 4 pm. Who felt our earthquake? Below is a map of perceived intensity of the quake by zip code based on nearly 7,000 witness' accounts of the earthquake (I submitted one twelve minutes after the quake; weak earthquake, no damage; 23909 supplied 22 reports).
Is this some dire warning that the end is near? Hardly. Central Virginia is one of two active earthquake zones in Virginia (the other is in Southwest Virginia) and small earthquakes are common. However, temblors that can be felt at the surface are relatively rare. The last earthquake that could be felt at the surface in Farmville hit Buckingham County in 1998. Earthquakes are common events where faults exist beneath the surface. The Piedmont of Virginia is riddled with fractures and faults that run roughly parallel to the Blue Ridge mountains. These fault are the result of ancient tectonic processes (roughly 200 million years ago) that compressed and then pulled apart the rocks of the Piedmont. Slippage of blocks of the Piedmont along those faults created long thin valleys that filled with sediments called Triassic Basins. Those blocks continue to slip, causing earthquakes. The quake of 1998 was centered at the edge of the Farmville Triassic Basin in Buckingham County. Tuesday's earthquake appears to have been near the western edge of the Richmond Triassic Basin in western Powhatan County.
Created December 9, 2003
Updated December 12, 2003