Earthquake rates in Oklahoma are down, when compared with 2015, but officials cannot say if the rate is down permanently.
"Steps to reduce wastewater injection were a necessary and prudent step for Oklahoma to take. But the reduction has been taking place for only a few months. It would be premature to conclude that long-term earthquake activity has gone down permanently based on short-term data," U.S. Geological Survey Geophysicist George Choy said. "Whether a decrease is a temporary statistical fluctuation or a permanent trend cannot be established in the few months that have passed. Even at a decreased rate, seismicity could go on for years."
There was a 16.9 percent decrease in magnitude 3.0 or greater earthquakes — down from 463 to 387 — recorded in the state between Jan. 1 and June 29, when compared to the same period in 2015, USGS records show.
However, quakes in 2016 have exceeded the numbers recorded between Jan. 1 and June 29 each year, from 2011 through 2014.
"The rate of magnitude 3.0 and greater earthquakes is down below what we had last year, and it seems to be slowing. You can never be sure where it's going to go, so it's hard to predict, except sort of crudely," Oklahoma Geological Survey Director Jeremy Boak said in June. "As far as I can tell, the main reason that the earthquake rate is down would probably be the million-barrel-a-day reduction in injection in the wells we've been able to track that are in the earthquake area, and injecting into the Arbuckle group.
"As I say, big uncertainties in what the rate will do, but it looks like things are better than they have been."
Earthquakes measuring magnitude 4.0 or greater are down slightly, with 10 recorded between Jan. 1 and June 29, compared to 12 during the same period of 2015, USGS records show. A magnitude 5.1 quake occurred this year, becoming the largest temblor recorded since 2011.
The magnitude 5.1 earthquake, centered at Waynoka on Feb. 13, was the strongest earthquake ever recorded in Northwest Oklahoma.
“This morning’s earthquake is likely the third largest earthquake in Oklahoma state history,” said Robert Williams, USGS Earthquake Hazards Program Central & Eastern U.S. coordinator, on the day of the quake.
The strongest earthquake on record in Oklahoma is a magnitude 5.6 centered in Prague that damaged 200 buildings in November 2011. A magnitude 5.5 was recorded in El Reno in 1952.