U.S. earthquake increase tied to disposal well boom

• Earthquakes have increased in places where they usually don%27t happen%2C seismic records show
• The increase seems tied to pressurized deep disposal wells putting pressure on quake faults
• Most deep wells don%27t trigger quakes%2C but experts call for better monitoring to detect rare problems

A boom in earthquakes seems to have accompanied the U.S. energy boom, geologists reported Thursday. They are finding an increase in temblors that appear tied to wastewater from energy drilling that is injected deep underground, putting pressure on quake faults.

In a study out today that provides the strongest link to date between wastewater wells and quakes, seismologists and geologists say U.S. earthquakes have become roughly five times more common in the past three years. They warn about inadequate monitoring of deep wastewater disposal wells that are setting off these small quakes nationwide.

There are more than 30,000 such deep disposal wells nationwide. They're increasingly used as mile-deep dumping grounds for fluids left over from the more shallow hydraulic fracturing, or "fracking," wells responsible for surging U.S. natural gas production. The earthquakes have been linked to the wastewater wells but not the fracking drilling wells themselves.

Earthquakes near Dallas, Oklahoma City and Youngstown, Ohio, in the past half-decade have been tied to wastewater "injected" at high pressure thousands of feet underground near quake faults. A National Research Council report last year cautioned that such deep disposal wells raise risks for triggering quakes.

"Clearly it is happening. Earthquakes have been happening in some unusual parts of the United States," says U.S. Geological Survey geophysicist William Ellsworth. "At this point, we do not know if all or just some part of that increase is attributable to industrial activities like wastewater injection."

More than 300 significant earthquakes, ones above magnitude 3, occurred nationwide from 2010 to 2012, a rate of about 100 a year compared with a past average of 21 per year, says the report in the journal Science.. Of the suspected "induced" quakes near deep wastewater wells, none has exceeded magnitude 5.6, Ellsworth says, "and no one has been killed in one of those quakes." Quakes of that strength, however, can cause structural damage.

Earthquake experts have understood that over-pressurized disposal wells can stress earthquake faults and trigger quakes since the 1960s, says earthquake seismologist Cliff Frolich of the University of Texas-Austin, who was not part of the new studies. "I think they are making the correct argument here. While most (deep) injection wells aren't a problem, the records are pointing to a real increase near some."

In particular, waste fluids injected deep underground at high pressure appear to have loaded faults to near a "tipping point" for quakes, according to Columbia University researchers. One study led by seismologist Nicholas van der Elst of Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., suggests that some Midwestern temblors appear tied to distant aftershocks from large earthquakes worldwide, such as Japan's massive earthquake in 2011. Such quakes in turn set off faults under pressure from disposal wells.

"This phenomena has been known about for decades and it is exceedingly rare, so it is all about managing risk," says Steve Everley of Energy in Depth, a fracking industry organization based in Washington. "It's important to note these are not fracking wells where you see this seismicity, but deep disposal wells, so it is not hydraulic fracturing at work here."

A related University of California-Santa Cruz study finds that geothermal projects near Southern California's Salton Sea raised earthquake risks near the famed San Andreas fault from 1981 to 2011. Energy plants there inject water more than a half-mile underground in the region into geothermal fields, generating steam that provides 650 Megawatts of power yearly.

Since most disposal wells don't seem to trigger quakes, one solution, Ellsworth says, would be to institute better monitoring of immediate seismic activity and sudden pressure changes during disposal operations. Both are signs of faults being pressured by waste fluids and might indicate to well operators they need to ease off or halt injection efforts. "We also need a system that keeps regional differences in mind with respect to earthquake risk," Frolich says. "A magnitude-6.0 quake in West Texas wouldn't bother anyone, it seems, but one in Dallas would be disastrous."