The most powerful earthquake to strike North Texas in five years rocked south Wise County early Tuesday night.
The 3.6 magnitude earthquake was centered in Briar, but shockwaves were felt as far north as Boyd and rattled residents in Newark and across the northern stretch of Eagle Mountain Lake. It was the 10th earthquake to strike in the vicinity since Nov. 5 and the fifth to be centered in Wise County, according to the U.S. Geological Survey (USGS). Five more have occurred in neighboring Parker County since early November.
Homeowners described the rumbles as a force striking their house.
“It felt like something hit and shook the whole house,” said Karissa Mosely of Newark.
“It was a pretty hard jolt here,” said Lisa Anderson of Boyd. “The walls and bookcases rattled pretty good.”
The first quake hit Wise County at 9:54 p.m. Tuesday, Nov. 5. It was a 2.3 magnitude earthquake according to USGS. A 2.8 magnitude earthquake struck one mile west of Briar ar 2:30 a.m. Monday, Nov. 11. Then three hit last Tuesday, a 2.5 magnitude in Briar at 11:57 a.m., a 2.8 magnitude five minutes later between Briar and Newark and then the 3.6 at 6:40 p.m. in Briar.
A study completed by the Institue for Geology at University of Texas at Austin found wastewater disposal or injection wells as the probable cause of these earthquakes.
Cliff Frohlich, associate director of the Institute for Geology at University of Texas at Austin, started re-investigating the phenomenon a few years ago after several earthquakes occurred in the Metroplex and Cleburne in 2008 and 2009.
The man-made earthquakes aren’t being caused by drilling for oil and gas but rather from disposing of the wastewater used in “fracking” a well.
“There is a long history of man-made earthquakes,” Frohlich said. “When you inject enough fluids into a deep well, there’s always a chance to cause an earthquake.”
Natural gas in the Barnett Shale and other formations is trapped in rock called shale. The gas is freed by pumping water at an extremely high pressure into the shale to splinter it. The process is called hydraulic fracturing, or fracking, and it was perfected in the 1980s by engineers working for George P. Mitchell in Wise County.
It requires millions of gallons of water to frack one well. The water is mixed with sand and a chemical mixture. The chemicals, which include a host of molecules, some toxic, represent about 1 percent of the total volume used in hydraulic fracturing. After the fracking occurs, the water is sucked out of the well and hauled off in large tankers. The tankers then transport the wastewater to a disposal/injection well.
The shale is located between 6,500 and 8,500 feet below the surface. The disposal wells inject the wastewater to an average depth of 12,300 feet and potentially into fault lines. Tanker trucks run around the clock in Wise County disposing of wastewater from fracking.
The Texas Railroad Commission currently permits 32 active commercial injection wells in Wise County. Injection wells in Wise County disposed of approximately 2.9 million barrels of wastewater every month last year. That amounts to 121.8 million gallons per month, or 1.46 billion gallons of wastewater per year, injected into the ground beneath Wise County.
“There has never been an earthquake reported in Dallas,” Frohlich said. “That’s about 150 years of history. Then an injection well starts up and within six weeks you had an earthquake (in 2008).”
In the past few years, such earthquakes have been seen also in Oklahoma, Colorado and several other states throughout the middle of the continent where disposal wells are in use. They have almost all been between a magnitude of 3 and 4.
Earthquakes occur when faults in the Earth slip and slide against one another.
“The Earth’s crust is riddled with small faults,” Frohlich said.
These faults are normally locked due to friction and don’t move, but when you add millions of gallons of water, the faults can shift and move.
“It’s like an air hockey table,” Frohlich said. “When the air is turned off, the puck doesn’t move. But once you add the air, the puck starts to move around.”
The number of earthquakes of magnitude 3 or greater occurring in the mid-continent region of the United States has increased sixfold in 2011 over 20th century levels, according to USGS.
Ed Ireland, executive director of the Barnett Shale Energy Education Council, said scientists have observed seismic activity around disposal wells but have not proven whether it’s a random correlation or a real connection.
“It’s important to remember that most of the time these don’t cause earthquakes,” Frohlich said. “There are tens of thousands of injection wells in Texas, and we’ve only had a handful of earthquakes caused by them.”
There is no reference map of every single, small fault line in the Earth. So until an earthquake is triggered, it’s unknown if an injection well is disposing of water into a fault that could trigger a quake.
“There is a need for more research,” Frohlich said.
The most powerful earthquake to ever hit Texas occurred in 1931 in the tiny West Texas town of Valentine just west of Marfa, according to USGS. The 5.8 magnitude quake collapsed brick and adobe buildings and caused landslides in mountains as far away as Big Bend and New Mexico.