While the location of the earthquake is within a region known to produce occasional small and moderate earthquakes, known as the Central Virginia Seismic Zone according to this USGS description, the mechanism which causes such earthquakes is not well understood or clearly explained by followers of the conventional tectonic theory.
Note that Virginia and the east coast of the United States are far from any "plate boundaries" (see the USGS map in this previous post) where tectonic theory explains earthquakes as resulting from the buildup of pressure between drifting plates. Note that the post referenced discusses the phenomenon of earthquakes far from plate boundaries.
In his book In the Beginning: Compelling Evidence for Creation and the Flood, Dr. Walt Brown provides an extensive discussion of the mechanisms which cause earthquakes and notes the numerous aspects of earthquakes which the conventional tectonic theories have difficulty in explaining (the book can be read online, and the detailed discussion of earthquake mechanisms begins here).
In discussing earthquakes far from plate boundaries, Dr. Brown writes:
The compression event and earth’s vertical adjustments during and after the flood produced many faults throughout the mantle and crust. Only the weakest faults slip frequently and are considered “plate boundaries.” The entire mantle and crust are being compressed and, as shown in Figure 89, laterally displaced generally toward the Pacific. [See “Magma Production and Movement” on page 149.] Therefore, earthquakes sometimes occur far from plate boundaries.
Today, very slight amounts of slippage frequently occur along faults in the crust and mantle, especially where faults extend from a trench down to the unsteady liquid foundation of the outer core. If, instead of a solid foundation, your home rested on a dense liquid foundation, you can imagine how cracked the walls of your house would be if ripples sometimes pulsed through the liquid or if that foundation rose by the steady addition of dense liquid. Slippage would frequently occur along existing cracks in the walls. Within the mantle, slippage along faults produces more magma, most of which drains into the outer core, adding to its volume and causing more uplift, slippage, and ripples. The mantle is unstable.
Frictional heat generated along faults throughout the mantle conducts slowly into the walls of the fault. Above depths of 410 miles (700 kilometers), local instabilities sometimes arise as heat weakens the solid silicate scaffolding and forms more droplets. Once leaks form, the liquid droplets can escape; their buoyancy forces them upward if they are above the crossover depth or downward if they are below the crossover depth. The scaffolding then will quickly collapse and thereby generate much more heat and melting. Earthquakes—runaway shocks—result.
This explanation is much more scientific than the mechanism offered by the tectonic theory, which postulates a liquid mantle circulating below the crust and occasionally causing earthquakes when slippage occurs between plates, or when pressures build up between plates and they temporarily "unlock." We noted in this previous post that such an explanation is not even truly satisfactory for the activity of the famous San Andreas Fault in California.
Today's unusual Virginia earthquake should provide a good opportunity for greater interest in the cause of earthquakes in general, and of earthquakes far from plate boundaries in particular. Those who examine all the evidence may conclude that the hydroplate theory provides a much better explanation than does the theory of plate tectonics.