|National Cathedral in D.C. closed temporarily for damage inspection|
Photo from CNN.com
Courtesy of the National Cathedral
Thanks to the magnitude 5.8 earthquake in the D.C. area today, we now know that there is a town called Mineral, Virgina! It had a population of 424 in the 2000 census, and is probably going to have a lot more people there tonight! During its heyday in the early part of the 20th century, there were 15 gold mines located within two miles of the town, as well as a zinc and lead mine. Mineral is only 5 miles from the epicenter of today's earthquake. It is 38 miles northwest of Richmond. According to the USGS, the quake was at a very shallow depth, 6 km, 3.7 miles (other estimates go up to 7 miles).
There is a neat video of the seismic waves from the quake crossing the IRIS seismometer array here. Gives a good feel for how long this earthquake was (>20 seconds).
National Park Service
|Seismicity map of eastern North America showing epicenters of|
quakes from 1928-1981. From Zoback and Zoback 1981.
Earthquakes occur in the eastern U.S. because ancient plate boundaries are being reactivated by today's stresses. During the past half billion years, the crust underlying the east coast has been the site of two major geologic episodes. Between ~450-250 million years ago, Africa collided with North America to form Pangea, the supercontinent. Then, beginning about 200 million years ago, the present day Atlantic ocean began to form as Pangea broke up. About 200 million years ago, further rifting led to the opening of the present-day Atlantic. This episode is referred to as the Mesozoic rifting event. Mesozoic rifts are exposed in rocks in Connecticut and Massachusettes and around the New york City area, and are believed to be buried beneath sediments along the continental margins of the eastern U.S. This summary taken from here.
Here's an interview with Rowena Lohman of Cornell in which she speculates on the role that glacial rebound may have east coast earthquakes.
And, here's an interview about the animals in the Washington Zoo that addresses the question about whether or not animals anticipate these events.
For a technical overview, see Zoback and Zoback, "State of Stress and Intraplate Earthquakes in the United States," Science, 213p. 96, 1981. Updated in M.L. Zoback and M. Zoback, "Lithosphere Stress and Deformation, Treatise on Geophysics, 6, 353-273, Editor-in-Chief, Gerald Schubert, Academic press, in publication.
Added 8/27/11: Here's the USGS analysis of the earthquake and a good Wiki article.