Oklahoma Earthquake Swarm Linked to Wastewater Injection by Fracking Industry

Oklahoma had more earthquakes than California in 2014. A new study suggests that the increase in earthquakes in Oklahoma is associated with wastewater wells used by the oil and gas industry.

Katie Keranen, professor of geophysics at the Cornell University, who conducted the study, said that earthquakes in Oklahoma account for nearly half of all seismicity occurring in central and Eastern U.S. Many of these earthquakes occurred in areas with high levels of water disposal.

Oklahoma has already registered 240 earthquakes of magnitude 3.0 or higher since the beginning of 2014, The Guardian reported. Scientists are now attributing these induced earthquakes to a handful of wastewater wells used by the fracking industry.

Hydraulic fracturing or fracking is a technique designed to obtain gas and oil from shale rock. The process involves drilling down into the earth's surface followed by injecting water, sand and chemicals at high pressure to release gas from the rocks. The wastewater is then injected into subsurface wells to avoid contaminating water sources.

Man-made earthquakes have been known for decades. Impoundment of water in reservoirs, surface and underground mining and even injection of water in underground disposal tanks can lead to tremors.

The Oklahoma earthquake swarm was a result of water disposal from oil and gas drilling operations, USA today reported.

"Induced seismicity is one of the primary challenges for expanded shale gas and unconventional hydrocarbon development. Our results provide insight into the process by which the earthquakes are induced and suggest that adherence to standard best practices may substantially reduce the risk of inducing seismicity," said Keranen in a news release. "The best practices include avoiding wastewater disposal near major faults and the use of appropriate monitoring and mitigation strategies."

According to the researchers, around 20 percent of the central U.S. earthquakes in a swarm can be triggered by water disposal at just four of highest-volume disposal wells in Oklahoma. The earthquake swarm covered an area of nearly 2,000 square kilometers.

Researchers also found that the earthquakes can be induced at a radius of about 30 km, which is way beyond the existing 5 kilometer criteria for detecting earthquake.

"Earthquake and subsurface pressure monitoring should be routinely conducted in regions of wastewater disposal and all data from those should be publicly accessible. This should also include detailed monitoring and reporting of pumping volumes and pressures," said Keranen. "In many states the data are more difficult to obtain than for Oklahoma; databases should be standardized nationally. Independent quality assurance checks would increase confidence."

Last year, the U.S. Geological Survey and Oklahoma Geological Survey said that they are conducting a collaborative research to see what was causing the rise in seismic activity in Oklahoma.

The study is published in the journal Science.