Tuesday, March 1, 2011
Central Arkansas' recent earthquake swarm not the first
While the recent earthquake swarm near Guy, Arkansas made national news, it's certainly not the first. There have been hundreds of small quakes in the Faulkner County area in 2010 and 2011. Thanks to new gas drilling in the area, the debate on what's causing the ground to shake rages on. Not only is the debate getting louder, so is the intensity of the earthquakes.
A 4.7 magnitude earthquake was felt in neighboring states at 11:00pm on February 27, 2011. My wife was sitting on the couch in our Jonesboro, Arkansas home when she heard the wood floors make a sound as if someone was walking across them. Within seconds the couch shook just enough to make her say "what was that." That earthquake got everyone's attention. It was the largest quake in the Guy/Greenbrier area in recent history and the largest since 1976 according to the U.S.G.S. in Arkansas.
The big question is why is the ground shaking. Many residents in the area are concerned about natural gas drilling in the area. Companies use a process called hydraulic fracturing or "frac'ing" to release natural gas deposits in the Fayetteville Shale rock that lies mostly underneath Faulkner, White, and Cleburne Counties. Water is pumped at high pressures into the rock which breaks up the rock and stimulates the release of natural gas. There have been some concerns from environmental groups that the fluids can create unsafe groundwater and create seismic disturbances. It's not out of the question. Cleburne, Texas had its first earthquake in its 140 history on June 2, 2009. Frac'ing was recently introduced to the area. While many of the quakes in Cleburne were small (2.8 magnitude or smaller), it created a debate about the environmental impact of the mining technique.
Back in Arkansas, the Guy earthquake swarm is not the first in the area and happened long before anyone drilled into the Fayetteville Shale. In 2001, a 4.1 magnitude quake shook the same area. Several smaller aftershocks followed. In the early 1980's Enola, Arkansas a few miles away was the epicenter of the Enola Earthquake Swarm. Hundreds of earthquakes shook the area, all similar to the tremors residents a few miles away are feeling now.
Scientists aren't sure why these quakes keep on happening. One common theory is that the earthquakes are the result of pressure being released from fluids beneath the ground. The good news is that it's likely groundwater and not lava. The bad news is that we may never know if the quakes are made by man or Mother Nature.
Arkansas Earthquake History (USGS)
Arkansas Geological Survey: Earthquakes (State of Arkansas)
Center for Earthquake Research and Information (CERI - Memphis)