Studies of Oklahoma’s Largest Earthquake Included in Seismology Journal

By SEAN MURPHY | June 26, 2017

Oklahoma’s largest recorded earthquake affected geological structures both above and below ground last year, but experts caution there still is much that scientists don’t know the 5.8-magnitude temblor that struck near Pawnee.

Ten separate academic studies into the Sept. 3 quake will be included in an upcoming issue of Seismological Research Letters, an internationally recognized peer-reviewed journal.

Thousands of earthquakes have been recorded in Oklahoma in recent years, with many linked to the underground injection of wastewater from oil and natural gas production

Oklahoma Geological Survey Director Jeremy Boak said the number of quakes larger than 4.0 magnitude has dropped dramatically so far this year, but it’s still not clear what caused several large quakes last year that were above 5.0 magnitude.

“I guess I’d have to say (the Pawnee quake) fits into the pattern of all the earthquakes we’ve been having,” Boak said in an interview with The Associated Press. “It’s bigger than any of the others, but nobody’s found the smoking gun that says this is an induced earthquake or this is a natural earthquake.”

Before 2009, Oklahoma averaged one magnitude 3.0 earthquake a year. The number of quakes above 3.0 spiked to more than 900 in 2015 and dropped to 623 last year. Boak said if the number of quakes remains at the same rate this year, there would be about 250 or 260 at the end of 2017. The decline is likely a combination of a reduction in the amount of wastewater being injected into the ground as oil prices fell, along with directives from state regulators to reduce injections in earthquake-prone areas, Boak said.

Among the studies conducted into the Sept. 3 quake is one by researchers at Oklahoma State University that documented above-ground features called sand blows that are caused when water-saturated sands spurt to the surface through cracks in the ground.

The process, called soil liquefaction, can cause significant problems in larger quakes by causing structures likes homes or buildings to sink into the ground or gas lines to rupture, Boak said.

Art McGarr, a geophysicist with the U.S. Geological Survey in Menlo Park, California, noted that all of the studies are very preliminary and it’s too early to discern what impact they will have on improving scientists’ understanding of earthquakes.

“I don’t know what the future holds,” McGarr said. “I think there’s a lot more earthquake activity yet to come in Oklahoma.”

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