4.5-magnitude aftershock rattles DC region

The USGS has announced a 4.5-magnitude quake emanating from the epicenter as Tuesday’s 5.8-magnitude earthquake that rattled the U.S. East Coast. It took place today (August 25) at at 1:08 a.m. EDT (5:08 UTC). USGS is reporting that the earthquake is coming from a depth of three miles (five kilometers).

Location with respect to nearby cities:
8 km (5 miles) S (170 degrees) of Mineral, VA
13 km (8 miles) SE (135 degrees) of Louisa, VA
31 km (20 miles) NE (48 degrees) of Columbia, VA
59 km (36 miles) NW (320 degrees) of Richmond, VA
133 km (82 miles) SW (216 degrees) of Washington, D.C.

Map Centered at 37°N, 80°W (USGS)

An aftershock of this size is good news. Earthquakes typically happen in series, with smaller quakes preceding and following a larger one. For example, the March 2011 9.0-magnitude earthquake in Japan was preceded by a 7-magnitude quake a couple of days prior to the big one. Until the whole series occurs, there’s no way to know which are the foreshocks and which are the aftershocks. So some of us wondered, silently, if a larger quake were ahead for the Washington, D.C. region. This aftershock suggests that it’s not likely.

In fact, there have have been a total of seven earthquakes around the Mineral, Virginia epicenter since August 22. Last night’s 4.5 and Tuesday’s 5.9 were simply the largest of those seven. Here’s the whole list of seven Virginia earthquakes in the past few days.

Bottom line: A 4.5 magnitude aftershock rattled the Virginia and Washington, D.C. region on August 25 at 1:08 a.m. EDT (5:08 UTC). Like the larger 5.9 magnitude quake of August 23, the epicenter was near Mineral, Virginia.

More from USGS on today’s Virginia and D.C. region aftershock

Earthquakes in central Virginia seismic zone from USGS

Do you live near an earthquake hazard zone?

How animals at National Zoo reacted to August 23 D.C. earthquake

August 25, 2011

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Deborah Byrd

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