Geologists say that they have confirmed what many have suspected for years: a swarm of earthquakes that rattled central Oklahoma was the direct result of fracking and wastewater injection.

The study by a team of geologists from Cornell University, the University of Colorado, Columbia University and the United States Geological Survey released last week makes a direct link between high-pressure wastewater injection at four hydraulic fracturing sites southeast of Oklahoma City to a swarm of 2,547 small earthquakes near the small town of Jones.

According to the study, fracking and wastewater injection is responsible for a 22,900 percent increase in magnitude 3.0 or higher earthquakes in the state since 2008. Prior to that, Oklahoma typically saw, on average, one magnitude 3.0 earthquake per year.

Click here for a pre-and-post 2009 map of earthquakes in Oklahoma from the USGS (Note: PDF)

"It really is unprecedented to have this many earthquakes over a broad region like this," says study co-author Geoffrey Abers of Cornell University. "Most big sequences of earthquakes that we see are either a main shock and a lot of aftershocks or it might be right at the middle of a volcano in a volcanic system or geothermal system. So you might see little swarms but nothing really this distributed and this persistent."

Oklahoma is now the second-most active state for quakes in the lower 48 states, trailing only California.

Fracking and wastewater injection are two distinct parts of the same process. Fracking involves injecting a potent and toxic brew of water and chemicals into a layer of oil or gas-producing shale formations underground, breaking up the rock and releasing the hydrocarbons—which are then sucked back up to the surface along with the water and chemicals. This process can generate earthquakes, but the quakes are typically small—most cannot be felt and are very rarely greater than magnitude 3.

Wastewater injection, though, is the real problem child—for a number of environmentally nasty reasons, but in this case particularly for generating larger earthquakes. The wastewater from fracking operations is separated from the valuable oil and natural gas and then injected at high pressure back into wells deep underground. Scientists say that the wastewater injection process can, in essence, pry apart rock layers and act as a lubricant on deeply-buried and otherwise stable faults, triggering potentially strong and damaging earthquakes in places that probably aren't used to them.

A powerful magnitude 5.6 quake linked to wastewater injection struck central Oklahoma in November of 2011, destroying 14 homes and injuring two people.

In general, the oil and natural gas energy industry has mostly stuck by the position that there is no direct scientific link between wastewater injection at fracking sites and earthquakes. And there hasn't been an increase in earthquake activity at many of the nation's 30,000 deep injection wells, including in North Dakota's busy Bakken Shale formation.

But for years, scientists have known—or at least strongly suspected—that injecting fluids deep underground can trigger earthquakes. In August of 1967, a series of magnitude 5.0+ earthquakes believed to have been caused by the injection of liquid waste into a borehole at the Rocky Mountain Arsenal outside of Denver caused millions of dollars in damage.

Last month, Colorado state regulators ordered a 20-day stoppage of operations at an injection well in Weld County northeast of Denver after a magnitude 2.6 quake was recorded in the area. The same area was hit by a magnitude 3.4 quake in May.

The earthquake problem is being seen all across the west, often in places that have rarely—if ever—had earthquakes before. And that's bad news for some property owners as seismic building regulations in many of the areas now undergoing a fracking boom aren't as strong as those in states where naturally-occuring quakes are common.

In the normally seismically-stable Texas, wastewater injection is suspected in a swarm of over 300 mostly small but unnerving earthquakes around a fracking site northwest of the Dallas-Fort Worth metroplex. One homeowner in Reno, Texas, says that the quakes have cracked his walls and wrecked his toilets, among other things—but his insurance company refuses to pay for the damage because they say the earthquakes were man-made.

"An earthquake in this part of the country was the furthest thing from my mind," said David Hull, who lived most of his adult life in North Texas without ever feeling a tremor. "But they're here."

Earthquakes with suspected links to fracking and wastewater injection have also been felt in New Mexico, Ohio, Kansas, and other states and provinces across the U.S. and Canada.

In California, which certainly doesn't need yet another trigger for earthquakes, a bill in the state legislature would put a freeze on wastewater injection and fracking operations in the state until research shows it can be done without triggering earthquakes. Geologists think that there could be as much as 15 billion barrels of oil in the Monterey Shale formation in the San Joaquin Valley that can only be accessed via fracking.

Back in Edmond, Oklahoma, a nervous overflow crowd gathered at a town hall meeting last month to discuss the increase in earthquakes in their area. The town was rattled by an early-morning magnitude 3.5 quake in late June, and many in the audience asked why fracking operations in their area haven't been shut down as a result.

They were told by officials that under state law fracking operations can't be unilaterally shut down without a legal justification.

The subject of fracking and wastewater injection is a touchy one in Oklahoma, as nearly a quarter of all jobs in the state are tied to the oil and natural gas industry.

In Nature, Oklahoma Geological Survey seismologist Austin Holland—who was not a part of the new study—says that the results need to spark a larger social and political discussion in the state about the costs of fracking:

"Just how important is it to produce oil and gas in Oklahoma, and are we willing to deal with the issues of these disposal wells in order to produce the oil and gas that we are accustomed to producing?"

Image via PBS.org