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posted by Fnord666 on Wednesday January 10 2018, @05:43AM   Printer-friendly
from the if-Oklahoma-is-a-rockin... dept.

Arthur T Knackerbracket has found the following story:

In Oklahoma, reducing the amount of saltwater (highly brackish water produced during oil and gas recovery) pumped into the ground seems to be decreasing the number of small fluid-triggered earthquakes. But a new study shows why it wasn't enough to ease bigger earthquakes. The study, led by Ryan M. Pollyea of Virginia Tech in Blacksburg, Virginia, was published online ahead of print in Geology this week.

Starting around 2009, saltwater disposal (SWD) volume began increasing dramatically as unconventional oil and gas production increased rapidly throughout Oklahoma. As a result, the number of magnitude 3-plus earthquakes rattling the state has jumped from about one per year before 2011 to more than 900 in 2015. "Fluids are basically lubricating existing faults," Pollyea explains. Oklahoma is now the most seismically active state in the lower 48 United States.

Previous studies linked Oklahoma SWD wells and seismic activity in time. Instead, Pollyea and colleagues studied that correlation in space, analyzing earthquake epicenters and SWD well locations. The team focused on the Arbuckle Group, a porous geologic formation in north-central Oklahoma used extensively for saltwater disposal. The earthquakes originate in the basement rock directly below the Arbuckle, at a depth of 4 to 8 kilometers.

The correlation was clear: "When we plotted the average annual well locations and earthquake epicenters, they moved together in space," says Pollyea. The researchers also found that SWD volume and earthquake occurrence are spatially correlated up to 125 km. That's the distance within which there seems to be a connection between injection volume, fluid movement, and earthquake occurrence.


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  • (Score: 1) by khallow on Wednesday January 10 2018, @04:56PM

    by khallow (3766) Subscriber Badge on Wednesday January 10 2018, @04:56PM (#620511) Journal

    I thought the energy ratio was 10x per 1.0 delta, where did you get 32 from?

    Energy goes up as 10^1.5 (which is almost a factor of 32) per one delta. It's the motion that goes up by a factor of 10. The interesting thing is that the power law seems to apply well to the frequency of earthquakes, which decline by similar amounts as one increases in the magnitude scale. Stuck faults tend to decline in frequency by a factor of 10, while slippery faults (and the Oklahoma situation) tend to decline as a factor of 30. That has the consequence that large earthquakes are far more likely on stuck faults than on slippery ones and far larger numbers of small earthquakes happen on the slippery faults.

    The real news here is that earthquake frequency in Oklahoma has declined dramatically over the past couple of years. That indicates to me that the real problem is not lubrication of existing faults as claimed in the story, but the energy input from pumping pressured water underground.