STEVE INSKEEP, HOST:
Oklahoma is completing a record year of earthquakes. That one state has experienced more than 5,000.
LINDA WERTHEIMER, HOST:
INSKEEP: Five thousand earthquakes so far this year. Researches have linked the quakes to oil production. Some of the earthquakes have struck North America's largest commercial crude oil storage center in Cushing, Okla. And Joe Wertz of StateImpact Oklahoma went there.
JOE WERTZ, BYLINE: This little patch of prairie in northeastern Oklahoma is one of the most important places in the U.S. energy market.
MIKE MOELLER: We're in amongst about 18 tanks here of various sizes, aywhere from 350,000 barrels to 575,000 barrels.
WERTZ: That's Mike Moeller of Enbridge Energy. He walks through the tank farm and worries about all the industry-linked earthquakes. These tanks were built to national standards that account for some shaking, but they weren't constructed with serious earthquakes in mind. That's because, historically, Oklahoma never had many. That's changed. 2014 was a record. This year, there will likely be even more. Last month, a 4.5-magnitude earthquake struck a few miles away. Moeller says it triggered inspections at the Enbridge tank farm.
WERTZ: Did they find anything?
MOELLER: Nope. We've not experienced any issues, any deformations or releases that were caused because of an earthquake.
WERTZ: This is where domestic crude enters the energy market. The massive hub in Cushing is dotted with hundreds of airplane hanger-sized tanks that hold an estimated 54 million barrels of oil. No earthquake damage has been reported yet. But the possibility is a matter of national security.
DANIEL MCNAMARA: I have had conversations with Homeland Security. They're concerned about the tanks mostly.
WERTZ: That's Daniel McNamara with the U.S. Geological Survey. He says the faults underneath the oil hub could be primed for more severe shaking. His research centers on a series of earthquakes recorded last year. Those quakes and the faults that produced them are strikingly similar to the ones that created the largest quake ever recorded in Oklahoma.
MCNAMARA: In fact, it's all part of the same general fault system.
WERTZ: That 5.6-magnitude quake occurred in 2011 near an Oklahoma town called Prague. The two places have something else in common.
MCNAMARA: The wastewater injection.
WERTZ: Oil and gas production creates a lot of toxic wastewater. To keep it from contaminating drinking water, oil companies inject the fluid into underground disposal wells. That can put pressure on faults, causing them to slip, which scientists say is responsible for Oklahoma's massive earthquake spike. Officials worry if a strong quake hits Cushing it would damage the oil hub and disrupt the U.S. energy market. Back in Cushing, Moeller opens the door to Enbridge Energy's control center.
MOELLER: One might describe this as the fishbowl.
WERTZ: It's like tank farm mission control. Two men sit behind banks of screens that flash sensor readouts and pipeline data. When an earthquake strikes, they can dispatch inspectors or flip a switch to move oil out of a leaky tank.
MOELLER: They go to the USGS site, look at the maps, look at the guidance that's given there, the data that's recorded.
WERTZ: Control center operators ordered inspections after that strong quake last month. State regulators shut down and limited injection at nearby disposal wells. McNamara, the USGS scientist, says that was smart. They did the same thing last year, too. McNamara says that seemed to slow the shaking, at least for a while. The earthquake activity near the oil hub resumed when the wells came back online. For NPR News, I'm Joe Wertz in Oklahoma City.
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