Crossposted with TheGreenGrok.
In recent years oil and gas production has been on the rise in the United States. So have minor earth shakes. Is there a link?
A new study (PDF) by the U.S. Geological Survey fingers increased energy production in the midcontinental United States for the recent uptick in magnitude3 or higher earthquakes.
Earthquakes of Magnitude 3 or Greater Way Up in Recent Years
Just how much has seismicity increased? Here are the numbers of earthquakes of magnitude 3 or greater over the past few decades:
Considered "minor," magnitude 3 quakes are rarely strong enough to do damage but typically large enough to be felt.
Interestingly, over the same period that the number of these types of quakes has been rising, the United States has seen a rather sizable increase in the extraction of oil and gas.
So is oil and gas production causing the uptick in the country's shaking? Could it be that the increase in earthquakes is specifically tied to the growing practice of using hydraulic fracturing (fracking) to release oil and gas from shale and other tight formations? And what about the high-pressure injection of wastewater from the production into geologic formations at a mile or more beneath the Earth's surface?
Caveats in Connecting the Dots Too Quickly
In a recently released abstract for an upcoming study, government scientists credit the seismicity to oil and gas activities: "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.
In an article on the Interior Department's website, David J. Hayes, the department's deputy secretary, sounds a different cautionary note, writing:
- "USGS's studies do not suggest that hydraulic fracturing, commonly known as 'fracking,' causes the increased rate of earthquakes. USGS's scientists have found, however, that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells."
- "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."
- "We also find that there is no evidence to suggest that hydraulic fracturing itself is the cause of the increased rate of earthquakes."
The good news for now is that there's no evidence that either extraction or disposal activities have given rise to a major earthquake (with a magnitude of seven or above). Nevertheless, I wouldn't be surprised if there are folks in America's heartland who are wondering if the oil and gas companies are doing things right. Sleep tight.
Additional Reading
"Is the Recent Increase in Felt Earthquakes in the Central U.S. Natural or Manmade?" - Interior Department article
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End Notes
Midcontinent is defined here
as 85 degrees to 108 degrees West, 25 degrees to 50 degrees North, or
the area roughly bracketed from Ohio to Colorado and North Dakota to
Texas.
The magnitude of an earthquake is a measure of its size based on the amplitude of the seismic wave it generates. Because the value is logarithmic, small differences in magnitude numbers are a lot bigger than they might look: "each whole number increase in magnitude represents a tenfold increase in measured amplitude." Earthquakes measuring 8 or above are considered "great" quakes; major quakes are in the 7 to 7.9 range; 6 to 6.9 quakes are considered "strong." (More here.)
The numbers here are an annual average.
One of the largest quakes to hit the U.S. midcontinent -- with a magnitude of 5.6 -- was excluded from the study. The USGS has indicated that it was natural, but it appears to still be under investigation.