AZLE –– While the earthquake swarm rattling the Azle and Reno area seems to have slowed, many residents say they are still concerned about the tremors that began in early November.
There have been more than 20 since then, according to the U.S. Geologic Survey. That’s so many that longtime resident Dwayne Harris, 83, has marked each quake on calendars that now hang in the family living room.
He has marked nearly three dozen, although that includes some too small to be registered by the USGS.
"It has to be the wastewater they forced back into the ground that caused it," said Harris.
Injection wells dump wastewater from the hydraulic fracturing process back into the ground.
Hayden Chasteen, a geology professor at Tarrant Community College who worked in the oil and gas industry for nearly a decade, says it's likely something about the injection sites started the tremors.
"If you've already got a fault present underneath the ground, and somehow that water gets in there,” he said. “Then you are going to push it apart and cause that lubrication, which causes the earthquake.”
In other places, such as Oklahoma, Arkansas and Ohio, studies have linked earthquakes to injection sites. Dr. Won-Young Kim researched one injection well that was linked to more than 100 tremors near Youngstown, Ohio in 2011 and 2012.
"The injection well was shut down, and seismicity disappeared," he said.
News 8 obtained Texas Railroad Commission statistics on injection sites in the Azle and Reno area.
There are four primary injection wells closest to most of the earthquakes. Each is permitted through the commission to dump anywhere from 10 to 25,000 barrels of wastewater each day. None of these wells have received any recent inspection violations.
Commission staff recently inspected other wells in Tarrant and Parker counties too. Only one, run by Finley Resources, was found to have a pressure leak late last year, which resulted in it temporarily being shut down. The commission said operators are working to get it back in compliance.
One of the well operators, XTO Energy, told News 8 it hadn't voluntarily cut back on how much wastewater was dumped into its site. A spokeswoman did say the site routinely dumps less than what is permitted by the state.
At a public meeting on the earthquakes in Austin last month, commissioners said the agency would only act if a definitive link is identified.
"We need to dig deeper to see if there is a fault we were unaware of, or if there is some linkage," said Chairman Barry Smitherman at the time.
Southern Methodist University scientists have installed seismic monitoring devices in the area, but full study results are unlikely to be known for another six to eight months.
The commission has vowed to hire a seismologist, and is currently reviewing more than 20 applications.