Counts of U.S. earthquakes of magnitude 3.0 or greater, 1973-2012, in the region between 108W-85W and 25N-50N. Tamino / USGS

By Deborah Zabarenko, Environment Correspondent; Editing by Marilyn W. Thompson and Philip Barbara
17 April 2012

(Reuters) – The number of earthquakes in the central United States rose "spectacularly" near where oil and gas drillers disposed of wastewater underground, a process that may have caused geologic faults to slip, U.S. government geologists report.

The average number of earthquakes of magnitude 3 or greater in the U.S. midcontinent - an area that includes Arkansas, Colorado, Oklahoma, New Mexico and Texas - increased to six times the 20th century average last year, scientists at the U.S. Geological Survey said in an abstract of their research.

The abstract does not explicitly link rising earthquake activity to fracking - known formally as hydraulic fracturing - that involves pumping water and chemicals into underground rock formations to extract natural gas and oil.

But the wastewater generated by fracking and other extraction processes may play a role in causing geologic faults to slip, causing earthquakes, the report suggests.

"A remarkable increase in the rate of (magnitude 3) and greater earthquakes is currently in progress," the authors wrote in a brief work summary to be discussed Wednesday at a San Diego meeting of the Seismological Society of America.

"While the seismicity rate changes described here are almost certainly manmade, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production," the abstract said.

From 1970 through 2000, the rate of magnitude 3 or greater quakes was 21 plus or minus 7.6 each year, according to USGS figures. Between 2001 and 2008, that increased to 29 plus or minus 3.5.

But the next three years saw the numbers increase "much more spectacularly," said Arthur McGarr, of the geologic survey's Earthquake Science Center in California: 2009 had 50, 2010 had 87 and 2011 had 134 such events.

"We don't know why, but we doubt that it's a natural process, because in nature, the only time you see such a big increase is during an aftershock sequence (with a series of quakes) or in a volcanic setting where you often get swarms of earthquakes due to magmatic activity," McGarr said by telephone.

When swarms of quakes occurred in Colorado and Oklahoma last year, the U.S. Environmental Protection Agency asked the geologic survey to investigate possible links to energy extraction in the area.

Among other sites, they examined an August 2011 earthquake centered around Trinidad, Colorado, near the New Mexico border, that registered a magnitude of 5.3, said McGarr, a co-author of the abstract.

That quake "turned out to be really close to two of the highest injection volume waste water disposal wells in the field," McGarr said. "So that gives us quite a strong hint that these earthquakes are being triggered by these wastewater disposal facilities." […]

Human-made earthquakes reported in central U.S

By Tamino
7 April 2012

A new study by scientists from the U.S. Geological Survey, not yet published but scheduled to be presented at the upcoming annual meeting of the Seismological Society of America, reports a dramatic increase in earthquakes of magnitude 3.0 or greater over a large area of the U.S. More interestingly, the report states that the increase is “almost certainly man-made,” and attributes it to oil and gas production.

Since I’m a data junkie, I retrieved some data on earthquake occurrences in the study region. The data I retrieved are from only one of the catalogues used in the USGS study, and I haven’t applied the control measures used by the study authors, so my numbers don’t theirs match exactly — but it should at least give us an idea whether or not there is an obvious increase in earthquakes as dramatic as reported.

Annual counts of earthquakes of magnitude 3.0 or greater looks rather like, well, a hockey stick. […]

Deja Vu

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