Interior Deputy Secretary David Hayes yesterday issued a lengthy statement designed to dampen public concern raised by an upcoming federal report that explores a link between oil and natural gas drilling and a spate of earthquakes across the middle part of the country.

At issue is the abstract of a yet-to-be-published study led by William Ellsworth, a U.S. Geological Survey geophysicist based in Menlo Park, Calif., titled "Are Seismicity Rate Changes in the Midcontinent Natural or Manmade?"

Ellsworth and a team of researchers concluded that a series of earthquakes in the middle of the country since 2001 "are almost certainly manmade," and that a possible culprit may be the reinjection of water and other waste fluids associated with drilling activity.

The abstract, which Ellsworth is expected to discuss at the Seismological Society of America's annual meeting in San Diego next week, 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 represent a sixfold increase over 20th-century levels (EnergyWire, March 29).

The rise in seismic activity corresponds to a nationwide surge in shale drilling, which requires disposal of millions of gallons of wastewater for each well. According to the federal Energy Information Administration, shale gas production grew, on average, nearly 50 percent a year from 2006 to 2010.

"This is very peculiar, what's going on," Ellsworth said in an interview last month with EnergyWire.

But Hayes cautioned in a blog post yesterday on Interior's website that reports of "new scientific evidence of a link between unconventional oil and gas production here in the United States, and seismic activity" are premature. And he took issue with "a number of news articles" on the issue that he said "varied greatly" in accuracy.

"While it appears likely that the observed seismicity rate changes in the middle part of the United States in recent years are manmade, it remains to be determined if they are related to either changes in production methodologies or to the rate of oil and gas production," he wrote. "We also find that there is no evidence to suggest that hydraulic fracturing itself is the cause of the increased rate of earthquakes."

A more cautious approach

But that has not stopped some critics from using the abstract to lobby for a more cautious approach to the development of unconventional shale oil and gas.

"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," Dusty Horwitt, senior counsel and chief natural resources analyst at Environmental Working Group, said in a statement this month about the USGS abstract. "We can't afford multi-million-dollar water pollution cleanups or earthquakes that could pose risks to homes and health."

The EWG statement also implicated hydraulic fracturing as a contributing factor to the earthquakes, and noted that the abstract "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."

EWG, according to the statement, conducted an investigation that found "companies are engaged in hydraulic fracturing, mostly for oil, in a number of counties throughout California, including several directly above the fault line."

Indeed, in a separate paper to be presented at the San Diego conference by University of Memphis seismologist Stephen Horton, researchers concluded that a magnitude-5.6 earthquake near Oklahoma City in November was "possibly triggered" by nearby waste injection wells. There are 181 injection wells in the Oklahoma county where the November earthquake happened (EnergyWire, March 29).

But Hayes stressed in his blog post that the earthquakes analyzed in the USGS abstract are relatively small, and that "there have been no conclusive examples linking wastewater injection activity to triggering of large, major earthquakes even when located near a known fault."

Click here to read Hayes' blog post.

Streater writes from Colorado Springs, Colo.