Not so many years ago, earthquake science was no more relevant to Oklahoma than marine biology. But these days the state is shaking way more often than California, and giving many people there an unwanted crash course in seismology.
Last year, Oklahoma had 585 earthquakes with a magnitude 3.0 or greater (big enough for people to easily feel) -- almost three times as many as California had and up from an average of just two a year before 2009. Not coincidentally, that's when oil and gas drillers began injecting wastewater from fracking operations into thousands of underground wells. In the past week alone, Oklahomans have felt the earth move eight times -- which is probably eight times more than nature intended them to. It's enough to get officials, even in a drilling-friendly state, to take action to manage wastewater wells.
The phenomenon isn't mysterious. Geologists have known for many decades that when pressure underground is changed -- when people inject water, for example, or extract geothermal energy - - latent earthquakes can be triggered. While the great majority of fracking-wastewater wells have no such effect, some -- especially those in which great volumes of water reach crystalline basement rock that lies close to a fault -- induce earthquakes that otherwise might not have happened for hundreds of years.
There's also a whole lot more shaking going on in Arkansas, Colorado, New Mexico, Ohio, Texas and Virginia, too. But the most tremors have been reported in Oklahoma.
So far, the injuries to humans and damage to chimneys and foundations from the uptick in seismic activity have been mostly minor. But scientists aren't able to predict this seismicity, or whether it is likely to continue to grow in frequency and strength.
What's most scary is that no one knows exactly how big quakes could get in the mid-continent. In 2011, one Oklahoma quake registered magnitude 5.7. And 1,300 years ago, the geological record shows, an area that is now within the state withstood a quake of magnitude 7-- far more powerful than anything anticipated by local building codes.
For the moment, it's not even clear whether the problems are caused by individual wells or a bunch of them applying pressure in concert. Sometimes well injections can trigger earthquakes miles away, and sometimes the effect is delayed by months or even years.
Yet there are ways to manage the threat, U.S. Geological Survey scientists Arthur McGarr and William Ellsworth and several colleagues argue in an article in Science last week. It would be wise, for example, to keep wastewater wells away from cities. And it's important to monitor seismicity more precisely. By finding out exactly where small quakes are happening, it may be possible to map any larger faults that wastewater injection is nudging to life. At the same time, oil and gas drillers should report publicly where they're drilling wells, how much water they're injecting and how deeply.
Then regulators can keep an eye on any trouble using a so- called traffic-light approach: If seismicity in a certain area reaches a threshold magnitude, injections are slowed. Colorado officials tried this successfully last year with a well that had triggered unaccustomed shaking near Greeley. In some cases, a well may need to be shut down -- as the Oklahoma Corporation Commission did with a well near Cherokee after a 4.1 magnitude quake earlier this month.
The oil and gas industry has every reason to want to track and manage the problem: Injection wells aren't cheap, and no one wants to drill one that can't be used.
To the extent that drillers can learn to clean and re-use their fracking water (up to a million gallons for every wellhead) they'll be able to ensure they maintain a reliable water supply -- and stop shaking things up so much above ground.
Mary Duenwald writes on energy, health care and science for Bloomberg News.