There have been more than 500 magnitude 3.0 or greater earthquakes in Oklahoma this year, up significantly from 109 in 2013 and just 35 in 2012, according to U.S. Geological Survey officials.
As of Monday, there were 549 of the higher magnitude quakes in 2014, with 19 being magnitude 4.0 or greater.
USGS officials focused on magnitude 3.0 or greater quakes because the smaller the magnitude, the more potential there is for missing an event, USGS Geophysicist Robert Williams said.
The USGS is looking into the increase in earthquakes, mostly occurring in central and north-central Oklahoma, he said.
“Starting probably in 2009, we started to notice the jump in earthquakes, even though it was small back then, relative to 2014,” Williams said.
A new scientific group focused on studying induced seismicity has been formed. There probably are six to 10 researchers working on the issue, with about four or five working full time now, according to Williams.
“This group, along with others from academia, have published a number of papers — eight or so papers in the last couple of years in peer review journals — that point toward water in disposal wells injected deep under ground as contributing to the cause of earthquakes in Oklahoma.”
A USGS statement released in May, in collaboration with the Oklahoma Geological Survey, indicated the likelihood of injection wells contributing to the seismicity and noted a higher chance of earthquakes, Williams said.
“Because, the more small earthquakes you have generally leads to the occurrence of more large earthquakes,” he said. “So the possibility of a damaging earthquake is higher in the last couple years.”
As part of its continued monitoring of the situation, the USGS has deployed a few more seismographs in the region, according to Williams.
“We’re monitoring the situation, trying to understand what’s going on,” he said. “We’ve also been funding researchers outside of the USGS to study the problem over the last three years or so.”
The researchers are being funded through a competitive grant program renewed on a yearly basis by the USGS, Williams said.
“Most of the activity that we think is related to injection wells is in Oklahoma,” he said. “It’s not a new problem. Seismologists have known about if you inject or withdraw fluids from the earth’s surface, there’s a pretty long history of, in some cases, that process causing earthquakes.
“And it goes back 50 years or so to seeing this and monitoring it. It’s not the first time seismologists have seen this activity before.”
Williams said there also has been a burst of earthquakes in the past year, just across the border, in south-central Kansas, near Harper and Conway Springs, Kan.
“It was an area that had virtually no earthquakes historically and has had a number of them recently,” he said.
The Kansas earthquakes are related to new injection wells in south-central Kansas that came on line in 2012 and 2013, Williams said.
USGS officials think the oil and gas production activity in south-central Kansas and north-central Oklahoma is related to the same oil play, he said.
“It’s a similar formation that they’re going after to extract oil and gas,” Williams said. “It just happens to be at the border.”
There also has been some earthquake activity in Arkansas and Texas believed to be related to injection wells, he said.