Oklahoma saw more than 100 earthquakes just in the past seven days. You read that right: Oklahoma.
The temblors were joined by other kinds of shifts this week. In two firsts, the state's officials acknowledged its spike in quakes is likely caused by oil and gas industry's underground injections of wastewater; and the federal government released a comprehensive analysis of the phenomenon, punctuating the risks for energy-producing states.
The man-made quakes, known as "induced seismicity," aren't confined to Oklahoma. The new U.S. Geological Survey report identifies 17 zones across states including Colorado, Ohio, Arkansas, and Texas that show increased tremors.
Oklahoma's key role in the U.S. oil and gas boom might explain public officials' reluctance to connect it with the concurrent boom in newly discovered fault lines. "So many of our jobs depend on [oil and gas]," Kristy Yager, a spokesperson for Oklahoma City, told National Geographic last year. "It's a difficult position to be in."
But the problem's grown too big to ignore. As its newly launched website notes, Oklahoma experienced quakes at a rate 600 times the historical average, "very likely triggered by the injection of produced water in disposal wells."
The latest developments confirm that quakes from energy activity are neither a temporary blip nor a regional anomaly. Here are 5 key questions and answers about the issue:
So, wastewater disposal has been linked to quakes. What's the connection with fracking, exactly?
During hydraulic fracturing, fluid and sand are pumped at high pressure into shale formations to release oil and gas. That isn't the process most closely associated with quakes—rather, it's the injection wells used to dispose of water after drilling. Some of the wastewater stored deep underground was used for the drilling itself, but the majority of it is "produced" water that came up along with oil and was separated out.
Make no mistake: Fracking itself has been linked to quakes, too. "There are plenty of known cases" where drilling caused earthquakes, says Amberlee Darold, research seismologist with the Oklahoma Geological Survey. "Generally, they're just not felt."
Fracking has caused a handful of documented felt earthquakes also, but "it's not considered an ongoing hazard," Darold says. "Injecting water into the ground and changing the dynamics of the pressures on faults—that's something that's not fully understood."
California gets earthquakes all the time. Why don't we hear about man-made quakes there?
Even though California is both quake-prone and home to thousands of oil and gas wells, it hasn't seen a link between the two. The reason is a combination of regulations and geology, says Jason Marshall, chief deputy director of the California Department of Conservation.
Decades-old state rules govern the pressure at which water is injected into the ground. In addition, Marshall said, the water that's being injected is going back into specially designated zones, such as existing oil fields, that have already been depleted of water. The effect is of restoring pressure that was lost.
In states such as Oklahoma, the water that's pumped out "is not injected back where it came from," says Bill Ellsworth, who co-authored the new USGS report. "It's put into a different [rock] formation, a formation that's never been tampered with before." That helps drillers squeeze out more oil, but it also can cause quakes. (Read more about fracking's potential water impact on California here and here.)
Are there other industry activities that might be causing quakes?
California does see some induced quakes—from geothermal energy production, which also involves injecting water underground. Indeed, the rising number of man-made earthquakes has implications that go beyond just wastewater injection.
Geothermal energy has touched off thousands of earthquakes—most of them too small to be felt, but some in the 4.0 range, according to the U.S. Department of Energy. Quakes are also a potential concern with carbon dioxide injection, which is being used to help recover oil and sequester carbon underground.
What else don't we know about induced quakes?
A fair amount. Darold noted that in Oklahoma, work is under way to better understand the Arbuckle formation, where most of the water is being injected, and to better understand faults beneath the state. (A preliminary map of them was released this week.)
More than typical earthquake pattern, where a main shock is preceded and followed by smaller ones, Darold said, Oklahoma is seeing more quake "swarms"—a series of temblors with no obvious main shock that can last months. Her agency is studying this.
"We by no means know where all the faults are in the state, and a lot of these earthquake swarms are delineating faults that were previously unknown," Darold said.
Oklahoma finally acknowledged the link. What now?
With more widespread agreement on the problem and its likely cause, it's not clear whether new regulations or other measures will stop or reduce the rumbling.
"This is definitely hopeful," said Johnson Bridgewater, director of the Sierra Club's Oklahoma chapter, said of the state's shift in messaging. But in terms of action, he said, he's seen "nothing significant in terms of actual changes on the ground." His group wants a moratorium on injections in 16 counties.
Ellsworth advocates improvements in three areas: a better system for detecting quakes while they're still small; more timely and complete reporting from drillers on injection activities; and better understanding of the conditions underground.
His agency is working to bring the science "down into more human terms," Ellsworth says, "so that people will have a chance [to] prepare for what we see is the potential for something stronger."