Quakes linked to oil and gas work

OKLAHOMA CITY — The Oklahoma Geological Survey said Tuesday that it was “very likely” that most of the state’s recent earthquakes were triggered by the subsurface injection of wastewater from oil and natural gas drilling operations.

A statement released by state geologist Richard D. Andrews and Dr. Austen Holland, state seismologist, said the rate of earthquakes and geographical trends around major oil and gas drilling operations that produce large amounts of wastewater indicated the earthquakes were “very unlikely to represent a naturally occurring process.”

The survey said the “primary suspected source” of the temblors was not hydraulic fracturing, or fracking, which is the practice of injecting fluid under high pressure to create cracks in deep-rock formations so natural gas and oil will flow more freely during drilling. It said the source was more likely the injection in disposal wells of wastewater produced as a byproduct of fracking.

The state “considers it very likely that the majority of recent earthquakes, particularly those in central and north-central Oklahoma, are triggered by the injection of produced water in disposal wells,” the statement said.

Earthquake activity in Oklahoma in 2013 was 70 times greater than the rate of earthquakes before 2008.

Geologists historically recorded an average of 1.5 earthquakes of magnitude 3 or greater each year. The state is now recording an average of 2.5 earthquakes of magnitude 3 or greater each day, geologists say.

The U.S. Geological Survey had previously linked wastewater injection to Oklahoma quakes.