Wednesday's earthquake was an aftershock from the magnitude 5.8 earthquake of August 23, 2011. That previous earthquake startled tens of millions of people in the eastern U.S. and southeastern Canada, and damaged schools and houses in the epicentral area.
Since the 2011 earthquake, more than 450 aftershocks have been recorded. These events were catalogued by the USGS National Earthquake Information Center (NEIC), using data from portable seismographs that were deployed by several organizations immediately after the earthquake.
More than 50 of these aftershocks were large enough to be felt, and 38 were the size of today's earthquake, or larger. Scientists expect that these aftershocks will continue for many months.
Earthquakes in this area are not unprecedented, as they are within the Central Virginia seismic zone. This zone has been identified on USGS seismic hazard maps for decades as an area of elevated earthquake risk.
Although earthquakes are less frequent in the East, their damaging effects can extend over a much larger area as compared to the western United States. The difference between seismic shaking in the East versus the West is due in part to the geologic structure and rock properties that allow seismic waves to travel farther without weakening.
Looking Back to 2011
The earthquake from 2011 was among the largest to occur in this region in the last century. It is estimated that approximately one third of the U.S. population could have felt this earthquake, more than any other earthquake in U.S. history.
Around 148,000 people reported their ground-shaking experiences caused by the earthquake on the USGS "Did You Feel It?" website. Shaking reports came from southeastern Canada to Florida and westward to locations near the Mississippi River.
So what have scientists been up to since 2011? The USGS is engaged in many research projects to help ensure public safety in Virginia and other areas of the eastern U.S. Read a USGS feature story to learn more about the Virginia earthquake in 2011 and see the variety of related science efforts underway.
Start with Science
The USGS is actively studying earthquake hazards worldwide. The President's requested FY14 budget includes a proposed increase in funding to improve earthquake monitoring in the eastern U.S. Expertise at the USGS includes earthquake monitoring and notification, earthquake impact and hazard assessments, geologic mapping and targeted research on earthquake causes and effects.