<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/OKquake.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/OKquake.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/OKquake.jpg?v=ap&w=980&h=551 800w" > A television reporter takes video as she walks past a damaged building in Cushing, Oklahoma, caused by an earthquake in November 2016. (Jim Beckel/The Oklahoman via AP)

At a Glance For the third year in a row, the number of magnitude 3 or higher earthquakes has gone down in Oklahoma.

The decline began when state officials tightened the rules on fracking in 2015.

The number of quakes has dropped from a record 903 in 2015 to 196 in 2018. For the third year in the row, the number of earthquakes in Oklahoma reaching magnitude 3 or higher has gone down following state officials' request to oil and gas producers to close off wells and limit injection amounts in others.

The decline in the number of quakes began in 2015 when Oklahoma's Corporation Commission tightened rules on fracking after the underground injection of wastewater was linked to earthquakes, according to the Oklahoma Geological Survey.

While state seismologist Jake Walter is confident the number of quakes will continue to dwindle, he added that the quakes should not be expected to end completely anytime soon. Tremors will likely be felt for at least another 10 years “because earthquakes beget earthquakes ," Walter told the Tulsa World.

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“There’s complex interactions among these networks of faults that can continue to propagate the seismicity back and forth, up and down in all directions,” he added.

Through late December, the survey reported 196 quakes of magnitude 3 or stronger, down from 302 in 2017, 623 in 2016 and a record 903 in 2015.

From 2008 to 2013, the state averaged 44 earthquakes of that size every year. And from 1976 to 2007, Oklahoma averaged about one quake of magnitude 3.0 or more each year. That magnitude is strong enough to feel locally but too weak to cause damage.

Seismologists say that 2018 was the fourth straight year that wastewater injection into the ground, which has been linked to the earthquakes, has declined in the 15,000-square-mile “area of interest,” which covers much of central and northwestern Oklahoma and is subject to stricter disposal regulations.

Walter said scientists remain unsure of the precise physics of what causes induced seismicity, including how much wastewater is required to produce a quake.

Corporation Commission spokesman Matt Skinner said no further regulations are imminent, but that seismic events are monitored constantly.

“It’s reasonable to expect other changes and actions, but nothing right now is on the horizon other than the day-to-day business,” Skinner said.