The federal government informed jittery Oklahoma residents, who have endured a stunning spike in earthquakes during the past few years, of something most of them already suspected — the risk of a damaging earthquake has dramatically increased, partly because of oil and gas drilling.
In an unusual move, the U.S. Geological Survey (USGS) and the Oklahoma Geological Survey issued a warning to state residents on Monday, informing them of a dramatically higher risk of a damaging magnitude 5.5 or greater earthquake than previously assumed. This higher risk needs to be taken into account when determining building codes, the USGS said.
In a statement, the agencies said that the record number of earthquakes that have struck Oklahoma recently, with a 50% increase in the number of earthquakes of magnitude 3.0 or greater since October 2013 alone, is likely related to changes in energy production practices in the state.
Specifically, the agencies, which conducted studies of the state's earthquake history, said the injection of wastewater deep underground in order to dispose of liquid waste from oil and gas drilling activities, or for other oil and gas production purposes, has helped elevate the background rate of earthquakes in Oklahoma.
The statistics of recent earthquakes in Oklahoma, which is not traditionally thought of as a seismically active state, are staggering. Between 1978 and 1999, the USGS said, there were an average of 1.6 earthquakes of magnitude 3.0 or larger each year in Oklahoma. Yet from October 2013 through April 2014, there were 183 earthquakes of magnitude 3.0 or greater.
Since 2009, the organizations found, there were 20 magnitude 4.0 to 4.8 quakes in Oklahoma, plus one of the two largest recorded earthquakes in state history — a magnitude 5.6 earthquake that occurred near Prague, Oklahoma, on Nov. 5, 2011, that damaged homes and a historic building.
Wastewater injection wells have been linked to earthquakes in other states as well, including Ohio and Arkansas, the agencies said.
Energy companies use such wells for various purposes, including the disposal of waste liquids generated during oil and gas production. Injecting such waste underground tends to be cheaper than disposing of it above ground in treatment plants.
Wastewater injection is also used as a means of enhancing the production of oil and natural gas. Steam, carbon dioxide and water can be injected into an oil or gas well in order to add pressure to that well and improve engineers' ability to recover those resources. This is known as enhanced oil or gas recovery.
The problem with wastewater injection methods, the USGS and the Oklahoma Geological Survey found, is that pumping the liquids into underground rock formations can cause pressure to build on an undiscovered fault or a fault that was already stressed, thereby causing earthquakes. Some scientists and environmental advocates say earthquakes triggered by wastewater injection can be thought of as manmade earthquakes, although they involve a mix of natural and manmade factors.
According to the joint statement released on Monday, wastewater injection has been a "likely contributing factor" to the earthquake swarm during the past few years. The statement said:
"This phenomenon is known as injection-induced seismicity, which has been documented for nearly half a century, with new cases identified recently in Arkansas, Ohio, Texas and Colorado. A recent publication by the USGS suggests that a magnitude 5.0 foreshock to the 2011 Prague, Okla., earthquake was human-induced by fluid injection; that earthquake may have then triggered the mainshock and its aftershocks. OGS studies also indicate that some of the earthquakes in Oklahoma are due to fluid injection. The OGS and USGS continue to study the Prague earthquake sequence in relation to nearby injection activities."
Injection wells can also be used to dispose of waste materials from drilling using hydraulic fracturing, or "fracking," but the USGS did not cite fracking in its statement.
However, the oil and gas industry objects to being blamed for the Oklahoma earthquakes.
“Granted, we’ve not seen this level of seismic activity in Oklahoma in the last 60 to 80 years and before that we don’t have a record. It causes us all concern, but the rush to correlate this activity with our industry is something we don’t believe is necessarily fair,” Brian Woodward, the vice president of regulatory affairs for the Oklahoma Independent Petroleum Association, told the AP.