TULSA, Okla. (AP) — The number of Oklahoma earthquakes registering a magnitude of 3.0 or greater is on pace to decline for the fourth straight year after state regulators began directing oil and natural gas producers to close some wells and reduce injection volumes in others.

The U.S. Geological Survey indicates that 27 earthquakes have already been recorded in 2019, down from 97 by this time last year and 144 in the first half of 2017, the Tulsa World reported.

Oklahoma's Corporation Commission began imposing volume restrictions on oil companies' disposal wells in mid-2015, after the quakes were linked to the underground injection of wastewater. Some well operators have evaded the limits by plugging back wells into shallower formations or moving activity into other areas.

Numerous lawsuits have been filed in recent years accusing the oil companies of triggering earthquakes.

Oklahoma's short-term hazard levels in some areas are similar to active regions in California, according to the USGS.

"If you take the last five years and compare the number of 3.0s in Oklahoma relative to the number of 3.0s in California, Oklahoma has had more earthquake activity than the state of California," said Oklahoma Seismologist Jake Walter.

A USGS spokesman said the federal agency didn't create a 2019 forecast and the agency is doubtful to do another one any time soon.

"The reason is because that induced seismicity has been decreasing every year since we did our first forecast back in 2015-2016, and as such, we're moving on to different priorities," said Drew LaPointe, a USGS public affairs specialist. "The long-term forecast we'll be releasing in the next few weeks for 2019 mentions this decrease in activity as well, but not in great detail."

Walter noted USGS' perspective signifies a lack of federal interest in long-term monitoring the frequency of earthquakes in the central U.S.

The USGS prediction for 2018 revealed an expansion of the area that is considered to be at a higher risk.

"So unless it gets updated, that document isn't representative of the seismic hazard as it exists today," Walter said.

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Information from: The Oklahoman, http://www.newsok.com

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