Today's M5.8 Earthquake in Virginia

john's picture

By now, everyone in the United States knows that significant earthquakes can happen on the east coast.  It might be prudent to recall other major earthquakes that have occurred east of the Rocky Mountains.  These included the M~7.5 earthquakes in New Madrid, Missouri during 1811-1812, the M6.5 Cape Ann earthquake of 1755 that occurred off the coast of Massachusetts, and the M7.3 earthquake the destroyed Charleston, SC on August 31, 1886.

The New Madrid earthquakes reportedly rang church bells in Boston and York, Ontario.  Sidewalks apparently cracked in Washington, DC. 

Today we saw images of frightened people streaming out of buildings, a few of which had moderate damage.  Better to duck, cover and hold on until the shaking stops, then proceed cautiously outside, lest loose masonry fall on one's head causing injuries. 

One question that many are asking is, was that it?  Will there be other earthquakes?  Was this a foreshock of something larger?  At the moment, the best estimate we have is that there is about a 5% chance that this event will be followed by another, larger event within a few days, going by our experience in California.  We see so few earthquakes on the east coast of this size, we have considerably less data to guide us. 

There were a 3 small earthquakes in the general viciinity of today's quake over the past 18 months.  The largest of these was a M3.0 event on October 2, 2010 that was located about 30 miles away.  That small event, which was felt in the Washington, DC area,  could have been a foreshock of today's M5.8 earthquake. 

While we can't know exactly what will happen, it would be wise to consider the recent two destructive earthquakes near Christchurch, NZ.  The first of these, the M7.1 Canterbury event on September 4, 2010, was located 40 km from Christchurch.  While it caused major damage, there were only 2 fatalities associated with it.  The second event, a M6.3 earthquake very near the city, generated much more widespread damage to buildings and almost 200 deaths.  The reason for the greater damage and number of deaths is the close proximity of the epicenter to the city, as well as the fact that the earlier event had weakened many of the buildings that subsequently collapsed. 

Should there be a significant aftershock of today's earthquake, and were it closer to population centers such as Richmond and Washington, the damage could be as large or larger than what we saw today.


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