Southern Arcadia Lake has had 565 earthquakes this year. Thirty events there have been of a 3.0 magnitude or greater, said Austin Holland, research seismologist with the Oklahoma Geological Survey.
He is one of only two seismologists working at OGS. Holland spoke at a town hall meeting at the Waterloo Baptist Church in Edmond. One-hundred of these events have been felt.
“The median depth of earthquakes is about 3.5 miles. This is much below any oil and gas activity that is occurring,” Holland said.
The deepest wastewater injection well is 2 miles in depth. The earthquakes in the Waterloo Road sequence are about 3 miles deep, Holland said. The Waterloo Road swarm has produced 50 felt events and nine events of magnitude 3.0 or greater, he said.
“They started in 2013 and this has really picked up,” Holland said. “They weren’t able to find a fault they previously didn’t know about, but through the earthquakes themselves were able to learn something about fault and the slip movements along that fault.”
A complex fault structure is also being mapped under Liberty Lake in Guthrie, Holland said.
The number of earthquakes in Oklahoma is increasing with 226 magnitude 3.0 earthquakes occurring as of last week in the state just this year, Holland said. Oklahoma is having more 3.0 magnitude earthquakes than the Western U.S. combined. The majority of them are occurring in central Oklahoma, Holland said.
An earthquake can be triggered by other earthquakes, Holland said. Besides natural causes, earthquakes may also be caused by human reservoir impoundment, mining, oil production and fluid injection, Holland said.
“The Langston sequence has been more continuous through time,” Holland said. “But it has had less of these magnitude 3.0 or greater earthquakes.”
Many hands went up when Matt Skinner, spokesman with the Corporation Commission, asked how many people were awakened by an earthquake earlier in the morning.
“I think it is very important to understand that this is not an abstract issue,” Skinner said. “It’s not just a bureaucratic exercise in policy. There are my neighbors in this room. There are my friends in this room.”
One of the earthquakes’ centers was under the home of Tim Baker, pollution abatement manager for the state Corporation Commission.
“As much as I take pride in the professionalism of the people I work with; there is no doubt that it adds a different dimension to your work,” Skinner said.
What is happening is frightening and worrisome, Skinner said. So, the commission is working with OGS and other researchers across the nation, Skinner said.
“Commissioner Murphey’s house has shaken. Commissioner Douglas’ house has shaken,” Skinner said. “…We’re all in this together.”
Many of the new oil and gas exploration testing and monitoring rules that Gov. Fallin signed into law recently are already being done by the industry.
After the 5.6 magnitude earthquake under Prague in 2011, the commission learned there would be 3-dimensional seismic studies done along the fault.
“Researchers were desperate for that kind of data,” Skinner said. This survey is 100 percent confidential in Oklahoma.
“Nobody can see it except the people who paid for it,” Skinner said.
Commissioners asked the oil and gas company if it would be possible to share the information. It has since been made available to scientists researching the earthquakes.
“So there are some bright spots,” Skinner said.
According to a summary for potentially-induced seismicity reported by the OGS:
• No documented cases of induced seismicity have ever come close to the current earthquake rates of the area over which the earthquakes are occurring.
• Long history of oil and gas activity and a large number of wells require detailed research projects to identify induced seismicity.
• The usual simple methods to identify potentially induced seismicity have only produced small numbers of identified cases.
• Potential cases of induced seismicity have been identified both from hydraulic fracturing and disposal wells.
• Hydraulic fracturing only contributes a small amount to the observed rate of earthquakes.
• Disposal wells are thought to be a larger contributor.
source: Oklahoma Geological Survey
TO LEARN MORE about Oklahoma earthquakes, go to the Oklahoma Geological Survey website at http://www.ogs.ou.edu/homepage.php.