DALLAS — Ancient faults in Oklahoma have been reactivated by seismic activity over the past five years, raising the risk of a major earthquake in regions where oil and gas is produced by hydraulic fracturing, according to a new
"The recent increased seismicity poses an elevated earthquake hazard to the infrastructure, communities and regional population," according to a preliminary version of the report for publication by the American Geophysical Union.
While researchers from the U.S. Geological Survey took part in the study, the report is not considered an official USGS paper. The lead author of the study is Dan McNamara, U.S. Geological Survey research geophysicist.
The research cited previous studies noting the effects of hydraulic fracturing or "fracking" of tight shale formations to release oil and gas, but did not specifically cite the process as the cause of the quakes. The purpose of the study was to identify increased risk of earthquakes for the insurance industry and government agencies, according to the report.
However, Bob Jackman, a petroleum geologist in Tulsa who has attributed earthquakes to the oil and gas industry for years, called the report the missing piece of the puzzle, according to The Tulsa World.
"The science is settled," Jackman said. "The debate is over. These are man-made earthquakes."
Oklahoma had 585 earthquakes of magnitude 3.0 or greater in 2014, more than the previous 35 years combined.
The study describes ancient, high-angle faults under Oklahoma that would have stayed dormant for tens of thousands of years had the seismic activity of the past five years not occurred.
Researchers have found as many as 12 different fault zones capable of producing a large, 5 to 6 magnitude earthquake.
The reactivated faults originally formed about 300 million years ago and are well known as geological formations that trap oil and gas, according to the report.
In November 2011, Oklahoma suffered a 5.6 magnitude quake centered near Prague, Okla., that damaged more than a dozen homes and several businesses.
While Oklahoma recorded more earthquakes than California in 2014, building codes in Oklahoma for seismic events are not as stringent as California's.
"If this is the new norm, then we need to get on board with how to design bridges that can possibly withstand the earthquake, whenever that might come," Department of Transportation Director Mike Patterson told the state Transportation Commission in 2014 after more than 1,300 earthquakes were recorded in the first three months of the year.
In the Jones, Okla., region more than 420 earthquakes have been recorded since 2010, the report said.
"This cluster of earthquakes has been previously linked to fluid migration from high-rate disposal wells (averaging about 1,000,000 barrels/month) located about 20 km SSW in southeast Oklahoma City," the report said. "Relocated earthquake depths (1-10 km) are within large disposal formations and in the deeper basement structures."
After the Prague earthquake, a "complex intersection of reactivated fault segments" were identified, the report said.
"Currently, the USGS National Seismic Hazard Map Project (NSHMP) does not include human-induced seismicity, and therefore, likely underestimates earthquake hazard in the region," the report said.
The Oklahoma Legislature on March 11 outlawed any local restrictions on oil and gas drilling in the state. The measure is designed to keep regulation of oil and gas production in the hands of the Oklahoma Corporation Commission. Local governments are still allowed to regulate road use and noise under the bill.
