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Last year, there were more tremors measured at magnitude 3 or greater in Oklahoma than anywhere else in the continental U.S. As Frank Morris of member station KCUR reports, the industry that sustains Oklahoma's economy may be to blame.
FRANK MORRIS, BYLINE: Medford, population about 900, is out on the flat, flat prairie of northern Oklahoma. It's the kind of place where people give directions from the four-way stop in the middle of town. It seems pretty sedate, but it's not.
DEA MANDEVILL: Yeah, we are shaking all the time, all the time.
MORRIS: Dea Mandevill is the city manager here. And she says that the afternoon I stopped by, two earthquakes had already rumbled through Medford.
MANDEVILL: Light day (laughter). The day's not over yet. We still have several more hours, so...
MORRIS: Mandevill may be laughing it off, but Austin Holland, the state seismologist, isn't.
AUSTIN HOLLAND: I certainly regret starting smoking again, but there are some days where nicotine and coffee are about what get me through the day.
MORRIS: Holland says that Oklahoma used to have, on average, one or two perceptible earthquakes a year. Now they're averaging two or three a day.
HOLLAND: As far as we know, this has never happened before.
MORRIS: Holland thinks modern oil production techniques are triggering the jump in quakes. A few years back, companies figured out how to drill sideways through layers of shale, and then break, or frack, the rock, releasing a torrent of oil. It sparked a massive boom here, but the technique produces much more water than oil - tens of billions of gallons of very salty, toxic water. The only economical way to dispose of it, Holland says, is to force it deep into the earth.
HOLLAND: That pressure acts as a lubricant. It's not actually the water itself lubricating, but the pressure. And the best way to think about that is an air hockey table.
MORRIS: That's right, air hockey with huge slabs of rock as the pucks. Holland says injecting water near faults can deliver just enough lubricating pressure to set them in motion. It's called induced seismicity.
RYAN LADRA: It was that loud or louder, but it was coming from everywhere. I mean, the walls, the roof.
MORRIS: Ryan Ladra is standing at his parents' battered house describing the Prague earthquake. It happened four years ago, a magnitude of 5.6, the strongest ever recorded in Oklahoma.
LADRA: When it hit, it hit so violent and hard that we thought the house was coming down on top of us.
MORRIS: The house's stone chimney collapsed, striking Ladra's mom, Sandra, who is suing companies that ran nearby wastewater injection wells.
But Kim Hatfield with the Oklahoma Independent Petroleum Association says he's not convinced there's a connection. He says oil companies have been pumping brine down wastewater injection wells for decades. And more than 3,200 of them dot the state.
KIM HATFIELD: You're going to find out that all tornadoes are close to injection wells as well. If a meteor strikes the state of Oklahoma, I'm going to guarantee that it's going to be close to an injection well.
MORRIS: Still, evidence linking injection wells to earthquakes is building. And though the oil industry wields enormous clout in Oklahoma, the agency regulating it is ramping up.
Matt Skinner with the Oklahoma Corporation Commission admits that the agency's never actually denied a permit for a disposal well. He says it's recently closed a few bad ones and is scrutinizing applications for new ones like never before.
MATT SKINNER: When we're saying we're doing everything we can, what we're really saying is we're doing everything we know today. Tomorrow, we may know something more.
MORRIS: Back in Medford, Dea Mandevill says she worries about an earthquake rupturing the big natural gas pipeline here. But then she beams, looking out over the new park the little town's just built with oil boom tax money.
MANDEVILL: We have a new swimming, splash pad, new sidewalks and a new basketball/tennis court.
MORRIS: It illustrates the complex relationship between oil and earthquakes in Oklahoma.
MANDEVILL: You put up with a few things falling off your walls, a few nights being woken up in the middle of the night with the shakes. Overall, it's been good.
MORRIS: You'd take the earthquakes?
MANDEVILL: I'll take the earthquakes for all the benefits that Medford's had so far.
MORRIS: But those benefits are starting to sag a little. With oil prices low, companies are laying off workers here. On the bright side, less oil coming out of the ground would mean less wastewater going back deep down into it and, just possibly, fewer earthquakes. For NPR News, I'm Frank Morris.
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