UPDATE: Strongest Aftershock to Date Rocks Central Virginia

Aftershocks

Aftershocks are common following an earthquake, especially one of this magnitude. They will all be weaker than the mainquake and have epicenters in the close vicinity of the epicenter of the original, but not necessarily in the exact same place.

Aftershocks can last for days, however the rate of aftershocks decreases quickly over time. And they are generally unpredictable.

More info on aftershocks can be found here.

August 25, 2011

UPDATE

Central Virginia experienced another aftershock at 1:07:50am Thursday morning. According to the United States Geological Survey (USGS), the 4.5 magnitude tremor had an epicenter approximately five miles south of the Town of Mineral (37.940°N, 77.896°W).

Residents from Fluvanna County said they felt a large rumble. Albemarle County and Charlottesville residents also reported feeling the aftershock.

Click here to read the USGS report on the fifth aftershock.

A little more than an hour later, the sixth aftershock was recorded by the USGS at 2:37:31am Thursday. The 2.3 magnitude quake had an epicenter seven miles southwest of Mineral.

More info on the sixth aftershock can be found here.

A seventh aftershock hit at 11:27:47am Wednesday. The 2.4 magnitude quake had an epicenter four miles south of Mineral. Read the USGS report here.



August 23, 2011

According to the United States Geological Survey, a 5.8 magnitude earthquake shook Central Virginia shortly before 2pm Tuesday. It was the second largest ever recorded in Virginia. Only the 5.9 magnitude quake on May 31, 1897 in Giles County measured higher on the Richter Scale.

Aftershocks of 2.8, 2.2 and 4.2 were recorded Tuesday at 2:46pm, 3:20pm and 8:04pm respectively, all with an epicenter within miles of the original quake. A fourth aftershock of 3.4 magnitude was recorded at 12:45am Wednesday.

The original earthquake was felt at 1:51:04 pm at the epicenter in Louisa County just five miles southwest of the Town of Mineral (37.936°N, 77.933°W). It had a depth of 3.7 miles.

The epicenter was:

- 5 miles southwest of Mineral

- 18 miles northeast of Columbia, VA

- 22 miles east of Lake Monticello

- approx. 30 miles east of Charlottesville

View the USGS report here.

At 2:46:50 pm, a 2.8 magnitude aftershock was felt in Louisa. According to the USGS, the epicenter was five miles southwest of the Town of Mineral and approximately one mile from the center of the original earthquake (37.931°N, 77.935°W). Read the USGS report on the first aftershock here.

At 3:20:26 pm, a 2.2 magnitude aftershock was recorded approximately eight miles southwest of Mineral. Read the USGS report here.

At 8:04:36 pm, a 4.2 magnitude aftershock once again hit near the Town of Mineral. According to the USGS, the epicenter was approximately six miles south of Mineral along Route 522/Cross County Road (37.917°N, 77.891°W). You can find the USGS report on the strongest aftershock so far, here.

At 12:45:26 am Wednesday, a 3.4 magnitude aftershock was recorded seven miles south of Mineral (37.925°N, 77.994°W). It had a depth of three miles. Information on the fourth aftershock can be found here.

There's a chance there were even more aftershocks, but the USGS hasn't received more detailed data from a network it relies on for larger number of local seismographs that record ground movements caused by earthquakes.

"For the size earthquake that occurred, I think the number of aftershocks so far has been remarkably low," said Amy Vaughan, a geophysicist with the USGS Earthquake Information Center in Colorado.

Typically, the larger the quake, the longer and the greater extent of aftershocks. Shallow earthquakes like the one in Virginia also tend to generate numerous aftershocks, said Don Blakeman, another geophysicist at the Earthquake Information Center. But it's rare to have an aftershock of comparable size to the initial event.

It's also possible that people closest to the epicenter could feel much smaller aftershocks that the agency wouldn't necessarily be able to confirm immediately, aftershocks that don't register at all, or ones that people just think are happening, Blakeman said.

U.S. officials say there is no threat of a tsunami along the East Coast as a result of the quake. The National Weather Service's West Coast and Alaska Tsunami Warning Center said the epicenter was far enough inland that it didn't threaten to trigger a tsunami on the coast.

The earthquake was felt throughout Central and Northern Virginia, in Washington DC, Philadelphia, New York City and as far north as Rhode Island.


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