OKLAHOMA CITY (AP) -- Regulators and scientists say the number of 3.0 magnitude or stronger earthquakes in Oklahoma is declining.
The Oklahoma Geological Survey reports the number of quakes of at least that magnitude during 2017 was 294 through mid-December, compared to 624 total during 2016.
The geological survey has said the number began declining in mid-2015 after the state Corporation Commission began directing oil and gas producers to close some wells and reduce injection volumes in others.
The directive came after the quakes were linked to the underground injection of wastewater from their operations.
Geological Survey hydrogeologist Kyle Murray told The Oklahoman that researchers are learning a "trifecta" of injecting wastewater too quickly, injecting too much and too close to basement rock makes injection wells more prone to causing earthquakes.