Department of Earth and Environmental Sciences
Most people living in the eastern U.S. probably think of places like California and Japan when they hear the word “earthquake.” But last year’s magnitude 5.8 earthquake in Virginia was a stark reminder that large and damaging earthquakes do occur in the eastern United States. And when eastern U.S. earthquakes occur, their effects can be quite dramatic compared to earthquakes of the same magnitude in the western United States. Here’s why:
Because of the difference in the structure of the Earth’s crust beneath the eastern U.S. versus the western U.S., seismic waves propagate more efficiently in the East than in the West. This difference is due to the fact that the crust beneath the East is older, warmer, and more solid than the crust underlying the West. The result of this difference is that when an earthquake of a given magnitude occurs in the eastern United States it is felt (and causes damage) over a much wider area than if that same size earthquake were to occur in the western United States.
This can be dramatically seen in the figure below, which shows areas where the Virginia earthquake was reported as being felt, as compared to areas where a magnitude 6 earthquake in California was reported as felt. The Virginia earthquake, although similar in size to the California quake (actually a bit smaller), was felt over an area about six times as large as that of the California earthquake.
This difference in the efficiency of seismic wave propagation, coupled with the fact that the region surrounding the Virginia quake is so densely populated, results in a surprising conclusion:
It is quite likely that the Virginia earthquake was felt by more people than any other earthquake in the history of the United States!
So even though earthquakes are obviously more frequent in California than they are in the East (due to California being on the plate boundary between the North American and Pacific plates), earthquake shaking and damage are nonetheless very real phenomena in the eastern United States.
If you felt this earthquake, please tell us your story by submitting a comment here.
References and Additional Reading:
For additional information about the Virginia earthquake, and more about the differences between eastern versus western U.S. earthquakes, see:
Learning from the 2011 Virginia Earthquake, Congressional briefing testimony of J.W. Horton, Congressional Hazards Caucus, March 29, 2012, www.hazardscaucus.org/briefings/horton-eqeast0312.pdf.
Mineral Virginia Earthquake Illustrates Seismicity of a Passive-Aggressive Margin, E. Wolin, S. Stein, F. Pazzaglia, A. Meltzer, A.L. Kafka, and C. Berti (2012), Geophysical Research Letters, 39(L02305), doi:10.1029/2011GL050310, www2.bc.edu/alan-kafka/ Virginia_082311/Virginia_GRL.pdf.
The Enigma of Why a Magnitude 5.8 Earthquake Occurred in Virginia, A.L. Kafka, akafka.wordpress.com/2011/12/27/the-enigma-of-why-a-magnitude-5-8-earthquake-occurred-in-virginia.