Earthquake 'swarm' rattles Arkansas town and its residents

CNN ^ | 12/13/2010 | Dave Alsup,

[FromLori]

The Arkansas Geological Survey is trying to unravel a mystery: What is causing earthquakes in the town of Guy, Arkansas?

Since September 20, the community of 549 residents north of Little Rock has experienced an almost constant shaking from 487 measurable earthquakes.

"We've had 15 today including a 3.1 (magnitude) from this morning," Scott Ausbrooks, geohazards supervisor for the Geological Survey, said Monday. "These are shallow quakes between two and eight kilometers (between one-and-a-quarter and five miles) below the surface."

While earthquakes aren't unusual in the Southeast state, the frequency is.

"This time last year we had 39 quakes total for the entire state," said Ausbrooks.

Most of the quakes in the swarm -- a localized surge of earthquakes with all of them about the same magnitude, according to the United States Geological Survey -- are so small they go unnoticed. The largest, a 4.0 on October 11, caused the only documented damage, cracking a window at a visitor's center to a state park.

[Gondring]

There’s a 2003 USGS pub with the GIS data of historical seismicity of the central US (Mississippi valley, basically), IIRC, but I can’t recall the authors. I’ll let you know if I find it.

Of course, the old data in it is sketchy.

[epithermal]

Actually they have the most current data here (assuming my 30 second look at the site is correct!):

http://earthquake.usgs.gov/research/data/

And, you can download a file of well locations here (Excel format):

http://www.geology.ar.gov/home/fayetteville_play.htm

I usually use the crippled version of GlobalMapper that the USGS gives away free here:

http://mcmcweb.er.usgs.gov/drc/dlgv32pro/

It will import comma separated value files which you can make from the Excel file of wells and the txt files of earthquakes. Assuming you can tell what the projections are for each data set, it may even provide a useful map! I may play with it tomorrow.

Now I am going to go look for DRG topo files for Arkansas.

[SunkenCiv]

Thanks FromLori.

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[rdl6989]

Yep, that was my first thought. I hope we’re wrong.

[gleeaikin]

I have said several times that I think we will have one more world class earthquake or volcano before the earth settles down for another quieter period of around 70 years. It seems at least in the past few centuries that every 100 years there is a period of about 30 years when there are more and greater earthquakes and volcanos. I think this cycle is not quite over.

[FourPeas]

Brick homes are a common thing in the Arkansas/Oklahoma area.

[FourPeas]

Brick homes are a common thing in the Arkansas/Oklahoma area.

[epithermal]

I think this is a case of intracratonic rifting being caused by fracing ;>). Let me know what you think of this: I found 20 injection wells in the Arkansas Geologic Survey data and plotted them here along with the nearby 2009 earthquakes. The injection wells are the light bulbs in the red squares. The earthquakes are the red crosses:

Then I took the screen dump of recent earthquakes around Guy from the AGS site and plotted the nearby injection well locations:

[Gondring]

What about pre-recent earthquakes?

Correlation based on geology of predisposition of both gas content and tectonic activity?

I think it’s the timing that’s the key...did the earthquakes pre-date the drilling?

[epithermal]

With that kind of logic you will never be allowed into the Green Church. ;>) They do have a list of all historical earthquakes, but I am not sure it includes the smaller ones. I will take a look at it today. It would be fun to make an animated Gif of a time lapse of earthquakes in the area.

One thing I find interesting about the maps I posted is the scale of the area with recent activity versus the location of injection wells. I find it hard to believe that those two wells could have been responsible for such a large region of seismic activity.

[Gondring]

Heh. Both churches consider me a heretic.

I suspect you’ll find the dataset biased by the lack of earlie observations—no sensitive detectors might make it seem quiet in earlier times.

[epithermal]

OK, this is making me a little mad because I can't seem to find the recent data for earthquakes around the shale play. Anyway, I took the historical earthquake data off the Arkansas Geological Survey site and divided it up based on the earliest drilling I found in the shale play starting with one well in 2001. I divided up the earthquakes between pre 2001 (light bulbs) and post 2000 (red crosses):