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USGS: The Arkansas Earthquake Swarm

 

NOTE:  You’ll find an update to this blog, with details of a fresh 4.7 mag. quake on 2/28/2011 HERE.

 

 

# 5325

 

 

Although they’ve been happening off and on since 2009, in recent weeks the swarm of small to moderate earthquakes occurring in central Arkansas has received a good deal of publicity. 

 

Yesterday, a moderate 4.1 magnitude temblor rattled the region, one of the largest of the hundreds of quakes that have struck over the past 6 months.

 

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More than 70 earthquakes (Magnitude 1.0+) have been recorded over the past 7 days in south-central U.S., including an unusual 3.5 quake that shook the Alabama Gulf coast yesterday and was felt in the panhandle of Florida.

 

While understandably unnerving for residents, these quakes are not necessarily a harbinger of something bigger in store for the region.  Earthquake swarms often appear, persist for months or even years, and then recede never having caused a significant event.

 

Scientists can’t discount that a larger quake might occur, of course.

 

Which is why it is incumbent upon everyone living in a seismically active area to be prepared for an earthquake (see FEMA Asks: Are You Earthquake Prepared?)

 

Most U.S. residents automatically think of the Pacific coast and Alaska as seismic hotspots, but earthquakes are not unheard of in New England, the Great Lake States, or even in the deep South.

 

The USGS map below shows that most of the United State’s population lives in a seismically active region.

 

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Later this Spring, 8 mid-west states will hold their very first Great Central U.S. ShakeOut at 10:15am on April 28th.

 

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Yesterday, the USGS released this update on the Arkansas swarm.

 

 

Nearly 60 Small to Moderate Earthquakes Strike Arkansas and Are Widely Felt


Released: 2/18/2011 5:12:12 PM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192

Nearly 60 small and moderate earthquakes struck Arkansas since Feb. 15, 2011, the most recent a magnitude 4.3 earthquake this morning 37 miles away from Little Rock. Many of the earthquakes are large enough to be felt.

 

“These earthquake swarms are not that unusual for the region,” said Harley Benz, scientist in charge at the U.S. Geological Survey National Earthquake Information Center. “Central Arkansas has a history of earthquake activity with a swarm of thousands of earthquakes smaller than magnitude 4.5 in the early 1980s and another swarm in 2001, known as the Enola earthquake swarms.”

 

Citizens are encouraged to report any experience feeling the earthquake(s) at the USGS Did You Feel It? website. The earthquake swarm that began Tuesday may continue. This area is slightly south of and most likely related to similar ongoing activity involving hundreds of small earthquakes near Guy, Ark., from August 2010 to present.

 

Scientists do not know why swarms start, why they stop, or how long to expect them to last. The possibility of a larger earthquake cannot be discounted, but none of the other swarms have caused any reason to expect a future earthquake large enough to cause significant damage in central Arkansas.

 

USGS scientists have been working with their partners at the Center for Earthquake Research and Information (CERI) at the University of Memphis and the Arkansas Geological Survey (AGS) to carefully monitor this situation. They have deployed a local network of stations – an array – that measure seismicity in the Greenbrier-Enola area to augment regional seismic stations. The CERI and AGS array and personnel are the best source of the most current information about the new earthquake swarm. The AGS and CERI are investigating whether the earthquakes occur naturally or are related to human activities.

 

Earthquake swarms are common east of the Rocky Mountains; other Central or Eastern U.S. swarms, however, have not involved as many small earthquakes as the central Arkansas swarms. Most of North America east of the Rocky Mountains has infrequent earthquakes that can strike anywhere at irregular intervals. The causes of earthquakes are not understood well enough to reliably make short-term predictions.

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