Wednesday, March 02, 2011

Arkansas shaken by numerous earthquakes ( www.thecypressti)

John G. Winder, The Cypress Times
Published 03/01/2011 - 3:27 p.m. CST Arkansas quake registers 4.7 on the Richter Scale. Largest in over 35 years. ABOUT THE AUTHOR

John G. Winder


One town plagued for months by swarm of earthquakes

GREENBRIER, AR – Greenbrier, in central Arkansas experienced the strongest earthquake that state has felt in over 35 years. The quake hit a approximately 11 pm Sunday night and centered just northeast of Greenbrier which is about 40 miles from Little Rock. More than 800 earthquakes have hit the area since September of last year in what is being called the Greenbrier earthquake swarm.

According to the US Geological Survey website the quake which was felt as far away at Ft. Smith Arkansas and Memphis, Tennessee struck 4 miles northeast of Greenbrier. It registered a 4.7 on the Richter scale and occurred at a depth of 2.4 miles. Eighteen minutes later another quake measuring 3.8 struck at a depth of 2.6 miles and was located 3 miles north-northeast of Greenbrier.

On February 18, 2011 a 4.1 magnitude quake was recorded 3 miles north-northeast of Greenbrier and the USGS noted that the quake was part of an earthquake ‘swarm’ that began on February 15.

The USGS says the earthquake ‘swarm’ is continuing and no cause has been determined. During this active ‘swarm’ period as many as two dozen quakes have registered in a single day.

From the USGS:

“This earthquake is part of a swarm of earthquakes that began on Tuesday February 15, 2011 and is continuing. This area is slightly south of and most likely related to similar activity (known as the Guy earthquake swarm) of hundreds of small earthquakes near Guy, Arkansas from August 2010 to present. Central Arkansas has a history of earthquake activity with a swarm of thousands of earthquakes smaller than magnitude 4.5 to 4.7 in the early 1980s and another swarm in 2001 (known as the Enola earthquake swarms). The Center for Earthquake Research and Information (CERI) at the University of Memphis and the Arkansas Geological Survey (AGS) have deployed a local seismic array in the Greenbrier-Enola, Arkansas, area to augment regional seismic stations to carefully monitor this situation. USGS scientists have been working with their AGS and CERI colleagues. 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.”

One of the “human activities” that is coming under scrutiny is the region’s extensive natural gas drilling industry.

However, geologists from the University of Arkansas at Little Rock say they have found a previously undetected fault line capable of producing large magnitude earthquakes.