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ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

AUDIE CORNISH, HOST:

And I'm Audie Cornish. The oil and gas industry is creating earthquakes. The U.S. Geological Survey will soon confirm that with new data from the Midwest. Researchers also found that these manmade quakes are happening more often than originally thought. They've briefed NPR's Christopher Joyce on their findings, and he has this report.

CHRISTOPHER JOYCE, BYLINE: Press your hands together as if you're praying. Where the palms meet is a fault. Push them together and they'll stay together. But if you push one hand forward hard enough, bam, they slip. That's an earthquake. Some force pushes the fault out of balance, and it slips. There's stress on innumerable faults like this on our continent, but seismologists like Bill Ellsworth, from the U.S. Geological Survey, started seeing something odd about 12 years ago.

BILL ELLSWORTH: One thing we had begun to notice was there were an unusual number of earthquakes occurring in the middle of the country.

JOYCE: Not a place known for quakes. They were small, usually just over Magnitude 3. Then, in 2009, the shaking got much more frequent.

ELLSWORTH: After that time, things really began to take off. That was really what caught our attention. It is really quite surprising.

JOYCE: Surprising, in that in 2009, there were 50 quakes a year in the mid-continent, 87 the next year and 134 last year. This is so unusual that Ellsworth and other seismologists suspected it wasn't natural - they suspected the oil and gas industry. Gas drilling is on the rise around the country, especially hydraulic fracturing. Hydrofracking uses billions of gallons of water a year to crack deep rock and release natural gas. Some have suspected that fracking was causing quakes, but evidence in several parts of the country points to waste water wells, where companies dump used frack water. Ellsworth thinks his data confirm that.

ELLSWORTH: We find no evidence that fracking is related to the occurrence of earthquakes that people are feeling. We think that it's more intimately connected to the waste water disposal.

JOYCE: Ellsworth says most of these new quakes are clustered around places where there are waste wells. Waste wells have been around for decades. In fact, there are tens of thousands of waste wells in the country - but very few quakes. But what's changed is that the gas industry is using and disposing of more water. Waste wells are often deeper than gas drilling wells. They go down into basement rock where faults are more common. And while the quakes are small, Ellsworth says they can happen anywhere.

ELLSWORTH: There are stresses that can produce earthquakes basically everywhere in the crust. And in most of the regions of the U.S., earthquakes don't happen because the stresses are not changing. But if we have a way of unlocking them, such as by pumping fluid into an area where there is a preexisting fault, it's possible that we can trigger earthquakes.

JOYCE: These waste wells are filled with water pumped down at very high pressures. Seismologist Cliff Frohlich, at the University of Texas, says that water affects a fault the way air does a puck in an air hockey game.

DR. CLIFF FROHLICH: The minute you put air on, it floats - the puck still weighs the same, but there's no friction that keeps it from going horizontally. The same thing can happen on a fault.

JOYCE: The high water pressure basically separates a fault that's locked in place; the fault moves and creates a quake. The more scientists study these manmade quakes, the more they find. Frohlich has studied a swarm of 183 small quakes near Dallas that took place in 2008 and 2009. That's right next to one of the largest oil and gas plays in the country. And Frohlich suspects that it's not just waste wells creating quakes. In some areas, the amount of oil and gas taken out of the earth has changed the local geology. He looked at two quakes near the town of Alice, Texas - one in 1997, the other in 2010. Since the 1930s, the area has produced 100 million barrels of oil and nearly three trillion cubic feet of gas.

FROHLICH: Sometimes quakes caused when you remove things from underground. I mean, there are quakes related to mining - you're changing the stress field with the material you remove, and that puts stress on a fault, and you get an earthquake.

JOYCE: Frohlich notes - somewhat reassuringly - that so far, manmade quakes have not been any bigger than natural earthquakes in a region. Christopher Joyce, NPR News.

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