August 24, 2008
Kendall Owens
Times Herald, Forrest City, Arkansas
A small earthquake in Lee County Wednesday was a rarity for the region, and scientists say that it originated from a fault which has not seen much activity in years.
According to a story from the Associated Press, two earthquakes struck Northeast and Eastern Arkansas late Wednesday night, neither of them causing any damage. The first struck at 10:36 p.m., with an epicenter about eight miles east of Hayne and 10 miles northeast of Marianna. The quake had a magnitude of 2.6 on the Richter Scale. The second occurred an hour later at 11:35 p.m., with an epicenter about five miles southwest of Cooter, Mo., and five miles north-northeast of Blytheville, and was a 2.7 magnitude earthquake along the New Madrid fault.
According to Dr. Haydar Al-Shukri with the Applied Science Department at the University of Arkansas at Little Rock, the earthquake in Lee County was both small and uncommon and occurred along a fault line that has yet to found.
“This was a small earthquake, but it’s very uncommon to see events happening in this area. We know that this area has been struck by major earthquakes in the past, and we have found at least three instances where evidence can be found of those major events, but there have been very few actual earthquakes that generated in that area over the last 10 to 15 years,” said Al-Shukri.
Al-Shukri said that evidence has been found in areas along the St. Francis River and to the south of Marianna which consists of sand blows or areas where subsurface sand has been blown up through the surface during an earthquake.
“We’ve been able to find at least three locations where sand blows were caused by earthquake events. Two of the locations are to the east of Haynes along both the east and west sides of the St. Francis River. We’ve also found evidence south of Marianna of an earthquake which was at least a 7.2 magnitude event and occurred about 5,000 years ago, so the fault that is in that area has produced some major events in the past,” he said.
He also said that researchers are continuing to search the area for other evidence of earthquake events in hopes of establishing a chronological timeline which could indicate when the next event might occur.
“As geologists, we examine things that happen over millions of years. Right now, we’re still working to determine how frequently events have occurred, and the way that we do that is by determining when separate events have happened and establishing a chronological timeline using those event,” said Al-Shukri. “Right now, we’re looking at a very short time frame, and we’ll need more information before we can determine the period between major events, but we do know that there have been at least two or three major events in the past.”
The fact that the Mississippi River also runs through the area depositing sand and silt makes research a little more difficult.
“We look primarily for evidence of sand blows because they are an excellent source of information, but with the Mississippi running through that area, there are lots of places where there are sand deposits that originated from the river,” he said. “We study all of the locations, and through our research we are able to determine whether its a sandy area that was caused by the river or is in fact evidence that sand and sediment was ejected during an earthquake event. What basically happens is that during a major earthquake, there is liquification which occurs, and when that matter erupts through the surface, the sand is expelled along with any water from dikes which leaves these sandy patches on the surface.”
In an interview with the Times-Herald last year, Al-Shukri said that the evidence found in Lee County could not have been generated by the New Madrid Seismic Zone, which caused earthquakes between December of 1811 and February of 1812. The largest earthquake during that time was a 7.9 magnitude quake on the Richter scale.
The New Madrid Seismic Zone is 150 miles long and stretches from Cairo, Ill., south through Missouri and into west Tennessee before ending near Marked Tree and Blytheville.
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