What’s causing the earthquakes?

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http://www.thesuntimes.com/news/x1914252734/What-s-causing-the-earthquakes

What's causing the earthquakes?

By Louis Short/ Co-Editor

The Sun-Times

Fri Oct 30, 2009, 01:06 PM CDT

Cleburne County, Ark. -

Relatively minor earthquakes around Quitman in Cleburne County and Greenbrier in

Faulkner County have hit over 15 times within the past two weeks and

seismologists are taking notice. The quakes have ranged from 2.5 to 3.0 in

magnitude and no damage has been reported. Why are they happening?

A couple of the quakes have hit near Quitman and Higden. The first one near

Cleburne County hit October 14 just after 11 p.m. and was located six miles

north, northwest of Quitman. It registered a 2.8.

A second quake near Cleburne County hit October 16 around 2:20 p.m. about seven

miles south, southwest of Higden and it too registered a 2.8.

White County has had at least one quake as well. Others have occurred in the

state, but the focus is in the Greenbrier area. Over 80 people in the Greenbrier

area reported to the US Geological Survey that they felt a quake that took place

Sunday just before 10 p.m. It registered 2.9 in magnitude. At least one person

reported feeling her house shake and seeing her ceiling fans sway.

Caruso, a geophysicst with the US Geological Survey in Golden, Colorado

told the Sun-Times the quakes are highly unusual. " Quakes this size happen all

the time in California and it's not noticed, but when they happen in Arkansas,

it's a big deal. "

Do all the small earthquakes mean a big one is looming? " It's hard to say if

these are a precursor of anything to come. We don't predict earthquakes. "

Caruso said earthquakes in the United States aren't deemed significant unless

they hit the 4.0 mark on the Richter scale. " Every earthquake is unique.

Normally anything above a three in magnitude is felt and anything above a four

causes damage. "

He said the recent quakes are probably not associated with the New Madrid Fault

Line. " Fault lines have cracks that come off them that can cause quakes

themselves. "

Is the gas drilling that's taking place with the Fayetteville Shale causing the

quakes? " I can't say if that's the case there. "

For a more detailed answer in regards to drilling being associated with the

quakes, Caruso turned us to the University of Arkansas at Little Rock.

Induced seismicity, or earthquakes caused by man, is being investigated. " It is

possible oil and gas drilling could be causing the earthquakes, but we are not

100 percent confident of that, " said Dr. Haydar Al-Shukri, director of the

Arkansas Earthquake Center at UALR. " We have not seen this much activity in the

past, but we cannot say, at this time, that it is drilling related. This is an

abnormal increase. "

He further explained the definition of induced seismicity. " Induced seismicity

are earthquake cluster(s) that are activated or triggered by human activities,

such as impoundment of large reservoirs behind high dams, geothermal power

generation, secondary oil recovery, deep underground mining, removal of large

volumes of rock during surface quarrying; fluid extraction as in petroleum

production, and fluid injection.

" To my knowledge, I have not seen a scientific paper or article that reported an

earthquake of magnitude larger then 5.5. Usually induced activity intends to

occur in large number and small magnitude. Also this type of activity does not

seem to be related to a single fault in the region. "

Al-Shukri said seven seismic stations were installed within a three to four mile

radius of Enola earlier this year. " Those stations are being used to study

induced seismicity, which is due to fluid being put into the ground for the

drilling of wells. "

He said his department is still processing data to try to determine the cause of

the quakes. " In addition to our data, we will retrieve information from the oil

and gas industry in the region to see what their activity is. We are retrieving

good, high quality date from the area. "

Al-Shukri said they will analyze the information over the next few months to

have a better conclusion. Once a conclusion has been reached, the public may not

necessarily be privy to the information. " The Arkansas Oil and Gas Commission,

Arkansas Geological Survey, and the drilling companies will determine what

information will be released. "