From: Andy Soos, ENN
Published August 24, 2011 10:30 AM

The Great Virginia Earthquake

Nowadays when a disaster strikes the cell phones react. A magnitude 5.8 earthquake struck the National Capital Area on Tuesday, August 23, at 1:51p.m. (EDT), causing moderate shaking and potentially significant damage, and was felt throughout Northern Virginia and neighboring areas. No casualties are expected. Immediately cell phones throughout the area were jammed as everybody called out checking on friends and loved ones as well as what happened. The earthquake occurred near Louisa and Mineral, Va., approximately 100 miles southwest of Washington, DC. It was a shallow earthquake, and shaking was recorded all along the Appalachians, from Georgia to New England. There have been several aftershocks. Such an earthquake is unusual but not unprecedented for the east coast.

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There have been other earthquakes in the recent history of Virigina, it is just that they are normally not felt so far off.  Also, luckily, damage was minimal.  

On December 9, 2003, a magnitude 4.5 event occurred near Farmville, about 30 miles west of Richmond, Virginia, and was felt strongly across Virginia. Tremors were reported in North Carolina, the District of Columbia, and suburban Maryland, eastern West Virginia, southern Pennsylvania, and portions of the Delmarva Peninsula.  

There was a 5.9 Virginia earthquake in 1897 with aftershocks continuing through June 6, 1897.

An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the Richter scale.

The 2011 Virginia earthquake occurred in the Central Virginia Seismic Zone, which has produced earthquakes in the past. The most notable was an earthquake that occurred in 1875 that scientists believe was about a magnitude 4.5.

The earthquake was felt so widely because it was a shallow earthquake, and geologic conditions in the eastern U.S. allow the effects of earthquakes to propagate and spread much more efficiently than in the western United States.

Western rock is relatively young, which means it absorbs a lot of the shaking caused by earthquakes. Thus, western earthquakes result in intense shaking close to the epicenter, but fade more quickly the farther the earthquakes travel.

In the eastern United States, on the other hand, the rock is far older, and so earthquakes can have a much larger and more widespread impact. Earthquake energy can therefore spread farther and have a greater impact.

This brings to mind what to do when an earthquake strikes.  Stay as safe as possible during an earthquake. Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimize your movements to a few steps to a nearby safe place and if you are indoors, stay there until the shaking has stopped and you are sure exiting is safe.  Find a sturdy location such as a doorway or under a desk.  If outdoors, stay there and away from any structure that might collapse.

Those who felt the earthquake can go online and report their observations on the USGS Did You Feel It? website. Over 10,000 reports of felt shaking have already been received from more than 3400 zip codes all over the eastern United States.

For further information:  http://www.usgs.gov/newsroom/article.asp?ID=2898&from=rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+UsgsNewsroom+%28USGS+Newsroom%29&utm_content=Google+Reader

Photo:  USGS  http://www.clarkedailynews.com/wp-content/uploads/2010/10/se100210d_ciim.jpg

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