Scientists as recently as January thought that what they’re informally calling the “Guy-Greenbrier Fault” spanned 3.7 miles, but now estimate it to be 6 to 7.5 miles long.The potential power of an earthquake along this fault could reach up to 6.0 on the Richter Scale and could cause significant damage at the epicenter. Why are we experimenting with fracking and injection wells? The truth is the chemicals used in fracking are designed to prop open the rock. The industry calls it "slickwater fracking." They lubricate and make "slippery" the formations and cause mini explosions in the strata when they frack. Then the gas companies need to get rid of the millions of gallons of toxic wastewater so they inject that back into the strata at high pressure. Why are they risking lives in such a seismically sensitive area? Could the faultline actually be longer than 7.5 miles? We have friends in Mountain View who feel earthquakes from Greenbrier/Guy even if they are below 3.0 on the Richter Scale? It would probably take more money and research to discover this information, but why experiment with human lives in the meantime.
Ausbrooks said the length is a concern because a longer fault could trigger bigger earthquakes.
Theoretically, if an entire 3.7-mile fault were to rupture, it could trigger a magnitude-5.0 to magnitude-5.5 earthquake. A 6-mile fault, meanwhile, could trigger a magnitude-5.5 to magnitude-6.0 quake.Ausbrooks said a magnitude-6.0 quake releases 32 times more energy than a magnitude-5.0 quake.In general, poorly built structures begin to sustain structural damage with magnitude-5.5 quakes, Ausbrooks said. Structures at the epicenter of such a quake would have broken windows and cracked masonry, he said, and the quake would be felt outside the state.
A magnitude-4.7 quake struck Feb. 27 roughly three miles from Greenbrier, and was Arkansas’ largest earthquake in about 35 years. It was one of hundreds that have been felt in the area since September.
Scientists, including those at the state geological survey and at the Center for Earthquake Research and Information at the University of Memphis, discovered the Guy-Greenbrier Fault by tracking the pattern of recent seismic activity in the area. The scientists then confirmed the fault’s existence by using imaging of the subsurface obtained from companies operating in the shale. The companies hadn’t noticed the fault because “it’s much deeper than what they are concerned about,” Ausbrooks said. The center says on its website that they are concerned there is a risk of triggering more and larger earthquakes if the injection wells continue to operate.
The Arkansas Oil and Gas Commission weighs in on the issue of the two injection wells on March 29th. Ausbrooks discussed the two injection wells:
“The theory is that the well increases the ... pressure in the rock formation sufficiently to overcome friction, to allow the fault to move, which generates the earthquake,” Ausbrooks said. Ausbrooks said the fault is deep and old. Its last vertical movements are believed tohave been 400 million years ago, he said. The fault doesn’t cut to the surface, and the uppermost part is about 8,000 to 10,000 feet deep. Clarita’s well is 7,800 to 10,900 feet deep while Chesapeake’s is 5,700 to 6,200. The Clarita well is “injecting at the same layer of rock” that the fault cuts up into, Ausbrooks said. Operators of the well are arguing that the earthquakes are occurring because of natural causes. Clarita said in a release last week that the quakes began before its well was operational. The general area - northern Faulkner County - has seen natural seismic activity in the past, including a series of small quakes that began in 1982 in Enola, which is about 10 miles away from the current swarm. However, the Enola earthquakes originated from a different fault than the current swarm, Ausbrooks said. Ausbrooks said there were “no known earthquakes in this Guy-Greenbrier swarm area” before the first of the two wells went into operation.Please come out to the AOGC meeting on March 29th. We must make a statement to the commissioners and our government. Any reasonable person would agree that we must err on the side of caution.
Since the injections stopped Thursday, “we’re still seeing micro-seismicity,” Ausbrooks said. He added that Arkansas saw a “couple of” magnitude-1 and magnitude-2 quakes on Tuesday. “There’s no reason why that shouldn’t continue for a period of time.” Scientists at the center in Memphis and with the survey are basing their research on a 1960s case in Denver that showed injection wells could cause earthquakes. Ausbrooks said that the quakes diminished dramatically after the injections were stopped and started once the injections began again. However, the largest quakes struck about two years after the injections stopped, he said.
“Once you start that pressure front moving out [through the rock], it takes time for it to dissipate and to move out.”
Ausbrooks said he couldn’t comment on what the survey’s position is on a potential link between the wells and the seismic activity because it is awaiting the March 29 hearing.
Read the Arkansas Democrat Gazette article here.