The D.C. area is not particularly known for earthquakes. The area sits near no major fault lines. And both Virginia and Maryland rank in the bottom half of states with the most 3.5+ magnitude earthquakes, according to the U.S. Geological Survey.
Now, a new study may have found the underlying cause behind the 2011 5.8 magnitude earthquake epicentered in Mineral, Virginia that shook the district and put cracks in several D.C. landmarks.
According to a paper published in the Journal of Geophysical Research: Solid Earth, the mantle (the area between the earth's crust and outer core) under the region is periodically breaking off and sinking down into the earth. Because of this, the plate left under the D.C., Maryland and Virginia regions is weakened, making it more likely to slip and cause another earthquake.
In a blog post accompanying the study, researchers explain that this is likely to cause more earthquakes in the area in the future. The reason for this, says University of North Carolina seismologist Berk Biryol, is that "[seismic] zones that are active will continue to be active for some time.”
The paper does not attempt to predict when the next earthquake might hit the area.