The Oklahoma Geological Survey said Tuesday it is "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.
Geologists have been studying the cause of hundreds of earthquakes that have shaken the homes and the nerves of residents in central and north-central Oklahoma, where the pace of oil and gas drilling has accelerated in recent years.
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 indicate the earthquakes "are very unlikely to represent a naturally occurring process."
The survey said the "primary suspected source" of the temblors is 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 is more likely the injection in disposal wells of wastewater produced as a byproduct of fracking.
This segment aired on April 22, 2015.