Earthquakes magnitude 3.0 and greater have dropped for the fourth straight year in Oklahoma.
There were 62 such quakes in 2019, down from 203 a year ago and the peak of 903 in 2015, according to Oklahoma Geological Survey data. The state’s only 4.0 quake this year was a 4.5 in May near Medford, which tied for the state’s 13th largest ever.
Oklahoma hasn’t been below 100 for 3.0 quakes in a year since prior to 2013, which until 2019 also was the last time the state experienced a single 4.0 in a year. The most 4.0s in a year was 27 in 2015.
However, the state’s quake hazards remain elevated, with the seismicity rate well above the historical average of two or three 3.0s a year. The last time that average hit was in 2008 with two.
The U.S. Geological Survey updated its long-term hazard model in late November, placing Oklahoma at a 4% to 19% of a slight or greater damaging earthquake in 100 years. The scientists used a methodology to exclude induced seismicity, writing that its rapid changes in short time spans wasn’t appropriate for far future projections.
Scientists point to deep wastewater disposal wells as the catalyst for Oklahoma’s unprecedented man-made earthquakes. A 15,000-square-mile area in central and western Oklahoma is under restrictions designed to curtail disposal into the deepest wells to limit induced seismicity.
Four of the state’s five largest quakes have happened in the past decade, including a 5.7 near Prague in 2011. A state appeals court in November affirmed a district court’s decision to certify a class-action lawsuit against oil and gas companies.
There are petitions in state district courts seeking class-action status for the 5.8 and 5.0 quakes in 2016 near Pawnee and Cushing, respectively.