A U.S. Geological Survey research team has linked oil and natural gas drilling operations to a series of recent earthquakes from Alabama to the Northern Rockies. The researchers say the spike in earthquakes since 2001 near oil and gas extraction operations is “almost certainly man-made.” The research team cites underground injection of drilling wastewater as a possible cause.
The authors of a study published by the Seismological Society of America found that the frequency of earthquakes started rising in 2001 across a broad swath of the country between Alabama and Montana. In 2009, there were 50 earthquakes greater than magnitude-3.0, the abstract states, then 87 quakes in 2010. The 134 earthquakes in the zone last year is a sixfold increase over 20th-century levels.
The USGS authors said they do not know why oil and gas activity might cause an increase in earthquakes but a possible explanation is the increase in the number of wells drilled over the past decade and the increase in fluid used in the hydraulic fracturing of each well. The combination of factors is likely creating far larger amounts of wastewater that companies often inject into underground disposal wells. Scientists have linked these disposal wells to earthquakes since as early as the 1960s. The injections can induce seismicity by changing pressure and adding lubrication along faults.
The U.S. Energy Information Administration reports that between 1991 and 2000, oil and gas companies drilled 245,000 wells in the U.S. compared to 405,000 wells between 2001 and 2010 – a 65 percent increase. As an example of how much more fracking fluid is used, New York state’s review of oil and natural gas drilling regulations in 1988 assumed that companies would use between 20,000 and 80,000 gallons of fluid for hydraulic fracturing per well. The state’s 2011 review of regulations for natural gas drilling in shale formations assumed that companies would use 2.4 million to 7.8 million gallons of fluid per well – a 100-fold increase.
The USGS report is likely to be of particular interest in California where earthquakes are a part of life largely as a result of the 810-mile long San Andreas Fault. An Environmental Working Group (EWG) investigation recently discovered that companies are engaged in hydraulic fracturing, mostly for oil, in a number of counties throughout California, including several directly above the fault line. It is unclear how the companies are disposing of their wastewater.
“With gasoline prices at $4 a gallon, there’s pressure to rush ahead with drilling, but the USGS report is another piece of evidence that shows we have to proceed carefully,” said Dusty Horwitt, EWG's Senior Counsel and chief natural resources analyst.