During the past year, north central Arkansas has been experiencing swarms of earthquakes, off-and-on, which have shook the region with varying magnitude quakes from the 1’s to the 4’s.

Some fear that the New Madrid Fault Zone has something to do with it, while others are convinced that local natural gas wells are the root cause of the earthquake swarms.

Let’s have a look at both possibilities…


Arkansas earthquake swarms and the New Madrid Seismic Fault Zone

Map of the New Madrid Seismic Fault Zone


The New Madrid Seismic Zone technically stretches from southern Illinois across western Kentucky and southeast Missouri, through New Madrid Missouri and south to parts of northwest Tennessee and northeast Arkansas.

The New Madrid Fault Zone is famously known for the earthquakes of 1811 to 1812 and registered four of the strongest earthquakes ever recorded in North America. They are believed to have been magnitude 8 earthquakes with one of them possibly as high as magnitude 8.6, or some say a 9.0 or larger (7-Feb-1812), which destroyed New Madrid, Missouri and rang church bells in Boston and New York City, one thousand miles away.

The New Madrid Fault, also known as the Reelfoot Rift, is located about 25 miles under the ground and is located quite within the North American Plate. The New Madrid Zone is a rift in the plate, but has not split the plate. It is essentially a ‘scar’, a weak zone in the middle of the North American Plate.

The location of the recent Arkansas earthquake swarm activity is about 100 miles to the west southwest of the southernmost tip of the New Madrid Fault earthquake activity that has been recorded over time.

The recent Arkansas earthquakes, reportedly at least 700 of them, have been highly concentrated in an area between Greenbrier and Guy Arkansas, and do not appear to be part of the New Madrid Zone activity, based on simple observations of past earthquake activity and their locations. But, like I said, that’s based simply on observations of past quake activity.

Geologists are saying that the “Guy swarm” might be a ‘naturally occurring swarm’. Or, in other words, basically, they don’t know.


Arkansas earthquake swarms and the Natural Gas Drilling


Another possibility, and one that many locals believe to be true, is that local natural gas wells are the root cause of the earthquake swarms. More specifically, a process called hydraulic fracturing or “fracking”.

Hydraulic fracturing is accomplished by drilling into gas or oil-rich rock formations and applying fluid pressure which extends the fractures through the rock, which in turn releases more of the gas or oil. An estimated 90 percent of the natural gas wells in the US use hydraulic fracturing to produce gas at ‘economical’ rates.

A major source of natural gas in Arkansas is the Fayetteville Shale, an organically-rich rock formation in north-central Arkansas. Drillers there free up the gas by using hydraulic fracturing.

From a February 17 article at huffingtonpost.com, Scott Ausbrooks, geohazards supervisor for the Arkansas Geological Survey said geologists don’t believe the production wells are the problem, but rather the injection wells that are used to dispose of “frack” water when it can no longer be re-used. The wastewater is pressurized and injected into the ground.

According to a Wikipedia report on hydraulic fracturing, The Energy Policy Act of 2005 exempted wells which are hydraulic fractured from being re-classified as injection wells, placing them under federal regulation under the Safe Drinking Water Act which was originally intended to regulate disposal wells.

Reports of ground water contamination have questioned whether the exemption is appropriate. A complete listing of the specific chemical formulation of additives used in hydraulic fracturing operations are not currently made available to landowners, neighbors, local officials, or health care providers. This practice is under scrutiny as well.

Examining a map from the Arkansas Geological Survey which shows the locations of Fayetteville Shale wells, and overlaying a map of  the Guy earthquake swarms, reveal that the location is located at the southern edge of the most concentrated area of natural gas wells.

Not only might the wastewater injection wells be causing the earthquake swarms there, but there remains an open-ended question whether or not the area drinking water may also be affected as well.

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