Magnitude 5.9 Earthquake Rattles Pentagon

WASHINGTON, Aug. 23, 2011 — Oper­a­tions con­tin­ued at the Pen­ta­gon despite the mag­ni­tude 5.9 earth­quake cen­tered in Min­er­al, Va., today.

A “shakemap” of the Aug. 23, 2011, cen­tral Vir­ginia mag­ni­tude 5.9 earth­quake.
U.S. Geo­log­i­cal Sur­vey graph­ic
Click to enlarge

The Nation­al Mil­i­tary Com­mand Cen­ter in the build­ing “main­tained the watch, and there was no loss of com­mu­ni­ca­tions,” said Navy Cmdr. Patrick McNal­ly, a spokesman for the Joint Staff.

Some pho­tos were knocked off walls in the build­ing dur­ing the mid-after­noon quake, and a water pipe on the building’s third floor burst, but plant engi­neers were able to stop the del­uge, Pen­ta­gon Force Pro­tec­tion Agency offi­cials said.

Many offices did evac­u­ate the build­ing, but offi­cials gave the all-clear to return after about 15 min­utes.

The earth­quake occurred at a depth of about 1 kilo­me­ter, about 27 miles east of Char­lottesville, 34 miles south­west of Fred­er­icks­burg and 39 miles north­west of Rich­mond, all in Vir­ginia.

The last time a mag­ni­tude 5.9 earth­quake hap­pened in Vir­ginia was in Giles Coun­ty, near Blacks­burg, in May 1897, accord­ing to the U.S. Geo­log­i­cal Sur­vey.

Though it’s not as well known as the San Andreas seis­mic zone in Cal­i­for­nia, there is a seis­mic zone in cen­tral Vir­ginia. The near­est tec­ton­ic plate bound­aries, which tend to gen­er­ate large and more fre­quent earth­quakes, are in the cen­ter of the Atlantic Ocean and in the Caribbean Sea, USGS offi­cials said.

The cen­tral Vir­ginia seis­mic zone has known faults, offi­cials added, but prob­a­bly has many unde­tect­ed small­er and deeply buried faults. Because of these faults, peo­ple in cen­tral Vir­ginia have felt small earth­quakes and suf­fered dam­age from a few larg­er ones since at least 1774, accord­ing to the U.S. Geo­log­i­cal Sur­vey.

In 1875, a mag­ni­tude 4.8 earth­quake struck in the cen­tral Vir­ginia zone. Every year or two, small­er earth­quakes hap­pen in the region.

East Coast earth­quakes are less fre­quent than West Coast tem­blors, but they tend to be shal­low­er, and there­fore, they can be felt over a larg­er region, USGS offi­cials said.

East of the Rocky Moun­tains, an earth­quake can be felt over an area as much as 10 times larg­er than a sim­i­lar mag­ni­tude earth­quake on the West Coast. Today’s mag­ni­tude 5.9 earth­quake could be felt as far away as Geor­gia, the Car­oli­nas, Ten­nessee, Ohio, Illi­nois, New York and Mass­a­chu­setts.

U.S. Depart­ment of Defense
Office of the Assis­tant Sec­re­tary of Defense (Pub­lic Affairs)

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