Federal and Oklahoma authorities are warning that people in and around Oklahoma City are at much greater risk from earthquakes than they were four years ago, possibly because of oil and gas drilling-related activities.
"They're more at risk than they were four years ago," said seismologist Bill Leith of the U.S. Geological Survey. "These don't look like normal earthquake sequences."
Earthquakes are now six times more likely in central Oklahoma, said Leith, the agency's senior science adviser for earthquake and geologic hazards.
USGS, along with the Oklahoma Geological Survey, issued a warning this week that called the increase in central Oklahoma an "earthquake swarm."
The involvement of the state Geological Survey represents the closest any state official has come to saying earthquakes have been "induced" by deep injection of wastewater from drilling.
"The whole community realizes some of them are induced," Oklahoma Geological Survey Director Randy Keller said yesterday. "It's a question of which ones."
More than 200 earthquakes of magnitude 3.0 or larger have rattled central Oklahoma since 2009, according to USGS. That's about 40 a year. Before that, there were usually one to three a year.
The agency's analysis suggests "wastewater disposal" may be "a contributing factor" in the surge. The statement does not cite oil and gas production by name, but Keller noted, "That's where the big volume is."
Researchers have been finding increased links between earthquakes and drilling wastewater disposal in Oklahoma for years. Leith said USGS did the release to let people in central Oklahoma know that there is an increased risk and that the agencies are working on it.
Leith said the point was not to link specific earthquakes to specific wells, but to address the general increased danger posed by earthquakes.
For example, both Leith and Keller said building codes might need to be strengthened, or "tweaked."
If the idea was to get the word out in Oklahoma, it does not appear to have worked. A search did not show that the statement was covered by general-circulation newspapers in Oklahoma or the state's television news outlets.
Attempts yesterday to reach Oklahoma Gov. Mary Fallin (R) and Oklahoma City Mayor Mick Cornett (R) were not successful.
A 'swarm' of quakes
The joint statement points to a broad swath of earthquakes across Oklahoma being induced, including some in the Oklahoma City suburbs that even researchers have not widely attributed to "induced seismicity."
The statement specifically refers to the series of earthquakes known as the "Jones swarm" in the eastern Oklahoma City suburbs, where seismologists have detected hundreds of small quakes but have not publicly linked them to injection.
The analysis also pointedly includes the largest recorded earthquake in the state, a magnitude-5.7 rupture in November 2011, as part of the whole central Oklahoma swarm.
The origins of that quake, centered near Prague, have been hotly debated. When researchers at USGS, Columbia University and Cornell University earlier this year issued a peer-reviewed paper linking the quake to two nearby injection wells, Keller's agency issued a position paper rejecting their conclusions (EnergyWire, March 27).
Keller said yesterday that his agency was not endorsing the idea that the Prague quake was triggered by oil and gas waste injection.
"The Prague event needs to be separated from these other, smaller ones," he said.
By contrast, Leith specifically cited the study on the Prague quake, authored by Katie Keranen at Cornell, as evidence of a change in the state's underground dynamics.
Keller did say that some of a spate of quakes near Enid in recent weeks may be related to injection. Some of the state's highest-volume injection wells are located in the area.
"The timing suggests that some of them are induced," Keller said.
Shaky political ground
Scientists have known for decades that underground injection of fluid can lubricate faults and unleash earthquakes.
The practice of hydraulic fracturing has not been linked to damaging earthquakes. But fracking does create millions of gallons of salty, toxic wastewater. Most of it eventually gets injected underground into deep disposal wells. There are thousands of such wells all over Oklahoma.
Researchers have linked such deep injection wells to earthquakes in Arkansas, Texas, Ohio and Colorado. More "Earth-friendly" procedures, such as geothermal energy production and carbon sequestration, can also set the earth rumbling.
But the question of whether oil and gas activities cause earthquakes is politically fraught, especially in places where drilling is vital to the economy, like Texas and Oklahoma.
In 2012, when USGS scientists first pointed to connections between oil and gas activities and a "remarkable" spate of quakes in the middle of the country, the No. 2 official in the Interior Department stepped in to say concerns about drilling were "premature" (EnergyWire, April 12, 2012). USGS is part of the Interior Department.
U.S. EPA's study of drilling and man-made earthquakes, begun in 2011, appears to be in permanent limbo (EnergyWire, July 22).
Even in states where researchers have linked quakes to injection, many agencies have ignored the issue when updating drilling and underground injection rules (EnergyWire, March 25).
Colorado's top geologist angrily dismissed USGS researchers as "cowboys" when they suggested that a damaging 2011 earthquake in the state was linked to injection (EnergyWire, Dec. 3, 2012).
Oklahoma officials have continued to allow injection into the active fault near Prague. But more recently, the Oklahoma Corporation Commission put limits on a new injection well in southern Oklahoma when earthquakes occurred nearby shortly after it began injecting (EnergyWire, Oct. 2).