The Oklahoma Geological Society says it is "very likely" that most of the state's recent earthquakes have been triggered by the subsurface injection of wastewater from oil and natural gas drilling operations.

The society investigated dozens of earthquakes in central and north-central Oklahoma. It said Tuesday that, based on seismicity rates and geographical trends following major oil and gas operations that produce a lot of wastewater, the rates of earthquakes are "are very unlikely" to be the result of a naturally occurring process.

The society said the "primary suspected source" is not hydraulic fracturing, or fracking, but wastewater injections.

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 magnitude 3 or greater earthquakes each day.