Energy Production Causes Big US Earthquakes 211
ananyo writes "Natural-gas extraction, geothermal-energy production and other activities that inject fluid underground have caused numerous earthquakes in the United States, scientists have reported in a trio of papers in Science (abstracts here, here and here). Most of these quakes have been small, but some have exceeded magnitude 5.0. They include a magnitude-5.6 event that hit Oklahoma on 6 November 2011, damaging 14 homes and injuring two people."
Re:But ... But ... But ... (Score:5, Informative)
No amount of frakking nor drilling adds any energy to the system. All the energy in the system was put there by geology, and all of that energy will be released via some earthquake. You might change the timing (or location), but you'll have no effect on the total energy released over time.
Though if we knew a whole lot more about this, it's interesting to contemplate deliberately triggering earthquakes in the least damaging places and times to shed that energy safely, but somehow I doubt such a plan would end well in practice.
Size of Quakes Correlates With Water Used (Score:5, Informative)
Now, scientists have known that geothermal power plants cycling water from underground can cause small quakes. But Brodsky's research actually matches the amount of water moved to the frequency of the quakes.
However, they're still not sure what causes the larger quakes. The hypothesis is that the really big ones might be triggered by other unrelated tremors.
So what van der Elst wanted to know was: "What prompts that slip?" Sometimes it's just all that water building up. However, he discovered that in three cases in the past decade — in Oklahoma, in Colorado and in Texas — the trigger was yet another earthquake, a really big one, thousands of miles away. In each case, the large earthquakes set up large seismic waves that traveled around the surface of the earth "kind of like ripples," van der Elst says. "You can even see them on seismometers, going around the world multiple times."
Source: http://www.npr.org/2013/07/11/200515289/wastewater-wells-geothermal-power-triggering-earthquakes [npr.org]
Re:But ... But ... But ... (Score:2, Informative)
Did you reply to the right post?
My position is: don't confuse proximate causes with root causes. It's often unwise to poke a pile of unstable explosives with a stick, but it's equally unwise to think you're safe as long as no one pokes it. The important problem is the pile of explosives!
It's a bit humble to presume that the *human* geologic activity in the crust (introducing large amounts of special chemicals at high pressure, removing other chemicals, replacing it all with yet another set of chemicals) is in no way capable of disrupting the plates on their own. We simply dont know enough about what's going on down there, it could very well be that our activity is destabilizing an otherwise very stable arrangement that wouldn't have ever resulted in an earthquake. The only inevitable earthquakes are ones at the plate edges where plate movement causes elastic stress to build and release. Most of these reports are about earthquakes far from traditional fault lines.
Re:But ... But ... But ... (Score:4, Informative)
That pressure can add a whole lot of energy to an already unstable fault line
Going by http://en.wikipedia.org/wiki/Richter_magnitude_scale [wikipedia.org], quakes that cause minor damage to poorly constructed buildings tend to be in the .5+ kilotons range.
For the record, the 2011 east-coast earthquake that caused pretty minor damage was a 6.0 earthquake, at about 15kt / the equivalent of the Hiroshima atomic bomb.
Im not too worried about fracking pumps introducing that much energy into the system, especially when the largest ever "fracking induced" earthquake clocked in at 3.7 on the richter, which equates to about 0.0045kt / 5 orders of magnitude less than that; the average appears to be around 3.0 on the richter, which is about 1/10th of even that strength.
Re:change over time (Score:5, Informative)
Ah, I actually RTFA : "the annual number of earthquakes record at magnitude 3.0 or higher in the central and eastern United States has increased almost tenfold in the past decade â" from an average of 21 per year between 1967 and 2000 to a maximum of 188 in 2011. " I don't think one needs a statistical test for those data. The trend is pretty clear.
You RTFA, and managed to miss that this is unrelated to fracking? I work in the oil and gas industry, so include me among the biased I guess, but I also understand oil and gas production so I'm here to tell you that it is injecting wastewater into fault lines that is causing earthquakes. Not fracking, not oil production, not gas production, but what we call "disposal wells."
In many areas of the USA, water is a scarce commodity, so there aren't any injection wells even though there is lots of fracking.
In many areas of the USA, there is water injection going on in order to "wash out" remaining oil in old formations. These wells are not hydraulically fractured shale formations (the "controversial" process). This has been going on for nearly 100 years.
A Geophysicist I know who works for a large independent oil & gas producer maintains that it has been known for about 20 years that injection wells can cause earthquakes by lubricating fault lines. Extensive testing was done during fracturing at multiple sites and the study was not able to find any data supporting a link between fracking and earthquakes. The instruments used were geophones, which are ultra-sensitive accelerometer devices normally purposed for analyzing formations by echolocation.
All of the comments I see so far clearly didn't click links.. the links mention geothermal production and water injection, the summary indicates that somehow natural gas is extracted by pumping fluid in the ground. That is only true for oil production. In natural gas production our aim is to deliquify wells so that the water isn't exerting backpressure on the gas production, slowing it down and eventually stopping it altogether. Disposal wells are only sometimes used, to get rid of the nasty, brackish, useless water produced from all kinds of hydrocarbon wells.