The number of Oklahoma earthquakes registering a magnitude 3.0 or greater has declined for the third consecutive year after state regulators began directing oil and natural gas producers to close some wells and reduce injection volumes in others.
The number of such quakes began declining in mid-2015 when the state Corporation Commission took action after the quakes were linked to the underground injection of wastewater, according to the Oklahoma Geological Survey.
State seismologist Jake Walter told the Tulsa World he’s optimistic the downward trend will continue, but he said not to expect the temblors to end anytime soon. He said the quakes will likely continue for at least a decade “because earthquakes beget earthquakes.”
“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,” Walter said.
Through late December, the survey reported 196 quakes of magnitude 3.0 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.
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