Earthquakes Correlated With Texan Fracking Sites 259
eldavojohn writes "A recent peer reviewed paper and survey by Cliff Frohlich of the University of Texas' Institute for Geophysics reveals a correlation between an increase in earthquakes and the emergence of fracking sites in the Barnett Shale, Texas. To clarify, it is not the actual act of hydrofracking that induces earthquakes, but more likely the final process of injecting wastewater into the site, according to Oliver Boyd, a USGS seismologist. Boyd said, 'Most, if not all, geophysicists expect induced earthquakes to be more likely from wastewater injection rather than hydrofracking. This is because the wastewater injection tends to occur at greater depth, where earthquakes are more likely to nucleate. I also agree [with Frohlich] that induced earthquakes are likely to persist for some time (months to years) after wastewater injection has ceased.' Frohlich added, 'Faults are everywhere. A lot of them are stuck, but if you pump water in there, it reduces friction and the fault slips a little. I can't prove that that's what happened, but it's a plausible explanation.' In the U.S. alone this correlation has been noted several times."
Oh - FRACKING (Score:5, Funny)
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Re:Oh - FRACKING (Score:4, Funny)
The Lone Battlestar State?
Meh. That joke was olmos funny.
Re:Oh - FRACKING (Score:5, Insightful)
Peer review of correlation. Wow. :-)
Fracking probably accelerates seismic disturbance. But I just can't help thinking of yesterday's discussion thread: http://tech.slashdot.org/story/12/10/02/1930257/the-history-of-correlation-does-not-imply-causation [slashdot.org]
"Yep! These sure appear to be co-incident, according to the data!"
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You think maybe earthquakes cause frakking? Or perhaps an oil company exec's decisions cause both frakking AND earthquakes?
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Re: A car analogy... (Score:5, Insightful)
One thing nobody seems to be realizing is that it may very well be ok to decide that this is a risk that's worthwhile.
Occasional small earthquakes vs. massively cheaper natural gas with a thousand year supply and 30% lower emissions than coal? Sign Earth up, peeze.
Re:Oh - FRACKING (Score:5, Insightful)
In many cases, there are important metrics called the "strength of correlation". This is an important consideration when determining a causation. Additionally, there is the necessity of determining alternative causes. For example, when a school does better on some sort of testing after several teachers are fired, it COULD be because those teachers sucked that bad, or it could be directly related to the change in morale with the other teachers, or it could even be related to a change in management style, or a change in classroom size, or any number of other factors.
When one considers that a series of earthquakes are seen that correlate with fracking sites (biggest earthquakes ever recorded, always within 2miles of the site in multiple sites), there is precious little else to consider as likely alternatives other than a very unlikely set of happenstance or coincidence.
It's certainly possible that it's a coincidence, but a strong correlation tends to indicate that this is not the case. Understanding statistics at a deep level will ehlp you understand this more.
ALL surveys show a correlation. Inferring a causation is simply trying to eliminate as many other co-correlations as possible and demonstrating that the original correlation holds up even when other possible causes are removed.
Can you think of other causes for unusually strong earthquakes happening to cluster around fracking sites?
Re:Oh - FRACKING (Score:4, Informative)
The other possible causes are faults.
You seem not to have read the last sentence of the abstract. Allow me: "Testing this hypothesis would require identifying geographic regions where there is interpreted subsurface structure information available to determine whether there are faults near seismically active and seismically quiescent injection wells. "
Re:Oh - FRACKING (Score:5, Insightful)
Can you think of other causes for unusually strong earthquakes happening to cluster around fracking sites?
One possibility (and this is knowing very little about fracking, so I don't know if this actually makes sense) would be that necessary traits of good fracking sites are themselves indicative of higher natural earthquake likelihood. In other words, fracking tends to be easier - and therefore done more often - in places where more earthquakes happen.
Re:Oh - FRACKING (Score:4, Interesting)
It's likely true that good fracking sites would be located in earthquake prone areas. However, what if you can show that the average number of earthquakes has gone up after fracking as compared to before?
Re:Oh - FRACKING (Score:4, Interesting)
Correlation doesn't imply causation, but it often points at it while waggling it's eyebrows meaningfully.
Coupled with other things we know it sure suggests that we should be taking a careful look for causation.
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Correlation *does* imply causation. It just doesn't prove it. In many cases, the correlated act was caused by the other. In others, they are correlated because a third, previously unknown, cause caused both. But again, there is a causal link, just not directly.
Correlation
While... (Score:5, Interesting)
Re:While... (Score:5, Interesting)
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Small earthquakes are also symptoms of larger shifts. You do them no favor by inducing them, or allowing their tap water to ignite as natural gas gets pumped up through aquifers.
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Small earthquakes are also symptoms of larger shifts. You do them no favor by inducing them, or allowing their tap water to ignite as natural gas gets pumped up through aquifers.
Reminds me of someone's pronuciation of this as aqua-fires.
Re:While... (Score:5, Insightful)
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I do get the point: fracking enables earthquakes. The hubris is that they predict, small, trivial little, meaningless earthquakes without knowing about the rest of the system's capacity to be influenced by these events.
Those teensy-weensy little earthquakes are just helping things!
Yes: there's a correlation between fracking and earthquakes. Tell me you can vet any information relating to data suggesting that these iddy-biddy earthquakes are just, well, fine! The theory posited sounds like it's right out of
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Tell me you can vet any information relating to data suggesting that these iddy-biddy earthquakes are just, well, fine!
Let's ask the people in Japan if they prefer a hundred small quakes or one Fukishima. "Just, well, fine" compared to the alternative.
Re:While... (Score:4, Insightful)
Or perhaps a lot of little, benign microquakes that lead to a Fukushima..... or worse.
A lot of microquakes cannot lead to a Fukishima, because a microquake simply cannot generate the energy to cause the tsunami that followed. I get the NWS quake/tsunami warning messages, and there are a LOT of small quakes going on all the time that don't trigger anything close to Fukishima sized events, or "worse".
Nor will a microquake cause buildings to fall down and people to die. A thousand microquakes may cause incremental damage, but that can be fixed in between quakes and the final effect will be ... yawn.
It's PR you're listening to, IMHO.
No, it's common sense and an understanding that the effects of many small events can be much less than the sum total all at once. Want to loan me an iPhone for a demonstration?
Re:While... (Score:5, Interesting)
You are only sort of right. Micro-quakes can allow a fault to shift in a way that triggers a big quake that might not have otherwise happened. These are non-linear dynamic systems. It is possible to both release a small amount of energy from the system while concentrating existing energy in the system into a narrow area.
In addition, energy is injected into regional fault systems in a manner that is itself probably not constant and probably relates to the configuration of the regional system at any time.
Put all together, we do not yet have enough information to tell how fracking may affect large earthquakes, whether positively or negatively.
Re:While... (Score:4, Interesting)
Conservation of energy still applies.
While true, this is immaterial in a non-linear system where energy can be transferred around quite easily. Quakes do not just release energy, they also shift the stresses around, allowing energy to shift between fault lines.
Micro-quakes could simultaneously release energy, and spread the remaining stresses around such that energy cannot be built up into a single large quake. Alternatively, micro-quakes could simultaneously release energy and concentrate the remaining stresses such that even more energy is concentrated into a large quake than would have happened otherwise. Considering how small the energy releases are in small quakes, these second order effects should be much more important than the amount of energy released by the micro-quakes.
Most likely outcome is that such micro-quakes do absolutely nothing of importance to the system. A few hundred or thousand micro-quakes simply would not make a huge difference compared to the amount of energy being concentrated then released in a major quake.
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That may be going a little to far, but the simple fact is: the total energy released in earthquakes represents a constant power input. Fracking may change the timing (for better or worse), but it has no effect whatsoever on the input power, or the total release energy over time.
Sometimes I think there's a group of people who just want power to be expensive: they resent technology and the change it brings, and will look for any excuse to insist that cheap power is bad - not on the merits, but truely because
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I want power to be cheap, I want to be able to use as much electricity as a city now uses.
I do not want to pollute the earth to the point were I cannot hunt or fish anymore. I do not want to pay to cleanup these sites after the companies leave.
How about we use sources of power that per unit energy have less environmental costs? Maybe we even require these folks to clean the water instead of just dumping it.
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Er, the water being unclean is intentional. It is the right mixture to induce fracking. It is not supposed to leak into the water table/river/elsewhere when done correctly. So, as long as we make sure the companies dont cut corners and do fracking correctly, it is all good.
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Let me be more clear.
The water they pump down the well is fine. Then they pump that back up to get it out of the way at that point it is highly polluted. They tend to either shoot that down a used well, or keep it in ponds. Either way it eventually will leak as humans have never built anything that lasts forever.
They will always cut corners, so long as their is money to be made. We must assume that they will and insure against it.
Re:While... (Score:4, Insightful)
We call them "Texas Oil Barons".
For the cost of reinstalling the slave-holding tyrants of Kuwait, we could have instead built a sustainable, biologically derived methane infrastructure that would deliver more gas at less cost than fracking, while creating career jobs on American soil.
But that would drive the price of Texas Oil down. Way down. Which cannot be allowed!
Re:While... (Score:5, Insightful)
Sometimes I think there's a group of people who just want power to be expensive: they resent technology and the change it brings, and will look for any excuse to insist that cheap power is bad - not on the merits, but truely because they don't want to ever have to change their beliefs as the world changes.
And sometimes you WANT to think other people's genuine motivations are somehow malicious so that you don't actually have to analyze the problems with your own.......
More frequent but smaller better? (Score:2)
This was the same thought I had - better to have the fault slip now when it's a barely feelable ~3.0 than to have it work it's way up to a 6.
Then again, maybe the little slips put more pressure on different areas, and might make the 'big one' more likely.
It'd be something for scientists to work out on supercomputers. Maybe we'll deliberately inject wastewater to trigger that 6.0 before it builds up to that 8-9.
More frequent but smaller IS better! ... FTFY (Score:2)
Re:While... (Score:5, Insightful)
Unless, you're releasing a stable fault to freely move that wouldn't have otherwise. Not something I'd want drillers playing with without real data to know for sure.
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Actually, a fault exists where there was movement. Depending on the causes of said movement, there may indeed be the potential for future activity. Or, as is often the case with shallow normal faults in sedimentary rock, the fault could have been caused by the sediment shifting along the plane of bedrock, leaving it in a more stable position than before.
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A stable fault is a fault without torsional pressure.
It's not to say that most faults are stable, but I'm sure some are pretty darn close, especially right at the center of a large continental plate.
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If it moves when you lubricate it, then there was stress on it.
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Or you added stress?
Or you induced a stress in just a small area that now failed and that means more stress is applied to what remains.
It would be nice if you are correct, but we have no such idea and to suggest that is the mechanism is very premature.
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If the earthquakes are indeed caused entirely by injecting water and not by any pent up geological stress then there's nothing to worry about. Unless the oil companies are using nuclear pumps (as in bombs), they won't be putting enough energy into the ground to do any serious damage.
Frakking has some potential issues, but earthquakes aren't one of them. The earthquakes caused by frakking range from irrelevant to beneficial.
Re:While... (Score:5, Interesting)
Way to ignore what I said.
Imagine you have a fault line 100 miles long, now with fracking 90 miles of it slip. The last 10miles are now bearing the loads that were on all 100 miles. Think that might cause a problem?
I am no more a geologist than you, but calling it irrelevant to beneficial when no one knows is highly irresponsible.
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This isn't entirely true. The Richter scale is logarithmic for a reason. Small earthquakes (at least ones as small as they're measuring in these kinds of fracking studies) don't release enough energy to meaningfully change the energy in a large earthquake. But small earthquakes can shift around the stresses such that energy is concentrated into (or diluted away from) regions of a fault. Whether energy will be concentrated/diluted in such manners would be entirely dependent on the configuration of the fa
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If it moves when you lubricate it, then there was stress on it.
Just add Pennzoil.
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Layman thinking here, but it doesn't seem like lube should trigger movement in something that's 'stable' (implying zero net force). If lube triggers movement then it wasn't stable.
WHAT??!!?? (Score:2)
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Don't be apologizing for "defending" fracking. There is nothing wrong with it any more than there is with a million other industrial or mining procedures on which the civilization depends and which would have been equally attacked had the environmentalist movement been around when they were invented.
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Unfortunately the movement wasn't, so now we taxpayers get to pay for fixing it [epa.gov].
Re:While... (Score:4, Insightful)
I agree it is just as terrible as mountain topping, and open pit mining that is not filled after use.
I disagree that civilization must rely on these things. There are better ways, they just cost a little more since they tend to internalize costs.
As we can see from your signature you are a hypocrite. Externalizing costs to the rest of society is no different than any other form of socialism.
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Just as bad as topping or leaving a pit unfilled?
What can anyone even say to you people?
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Do you not know what happens in those situations or do you hate a clean environment?
Mountain topping means filling in valleys and headwaters of rivers. It means polluting the properties down stream. It means someone makes a fortune will depriving others of fish and game and wild areas and unpolluted property.
An unfilled pit mine, like say a copper mine fills will rain water, that becomes highly polluted and eventually then drains into the ground water.
What someone can say to us people is that they will pay
Re:While... (Score:5, Insightful)
I understand it fine. Here is the externality that occurred in my area:
They fracked an old NatGas well, to do so they pumped water + some relatively safe stuff down the well. Then they pumped that stuff back up, it was now of course highly polluted with various hydrocarbons. Then they dumped the waste water off at a water treatment plant meant for human waste not industrial waste. The water was not properly treated and ended up in our reservoir that our drinking water comes from.
What would you call that?
What would you call the end result of abandoned open pit mine that is full of poisoned water? What would you call the result of mountain topping with the loss of headwaters of streams to both filling and what streams are left being too polluted for fish to live in?
Modern mining practices are one exercise in externalizing costs after the other. They specialize in externalizing as much costs as possible.
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they dumped the waste water off at a water treatment plant meant for human waste not industrial waste. The water was not properly treated and ended up in our reservoir that our drinking water comes from. What would you call that?
A multimillion dollar lawsuit. So you are saying that a specific company heavily polluted your drinking water and you can prove it? And you are not besieged by lawyers camping on your front lawn hoping for a percentage of the large damages that you are likely going to be en
Re:While... (Score:4, Insightful)
br.Go the USA!!!
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No matter what, why the hell should they not pay to clean their own waste up?
This is getting silly. Of course they should. The fact of the case may be completely different but lets work with what you said. They claim they effectively outsourced the cleanup of the water to the waste water company. The waste water company denies that their contract covers that. Ok so far?
So how does this have anything to do with the fracking process as opposed to any other industrial activity that produces w
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I bet he externalizes the cost of posting to Slashdot to his parents.
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I am personally under the impression that is has some long-term consequences are far as ground water safety, and several other issues.
In general, fracking sites have a bad history of conservationism, as far as I'm aware. I don't have a problem with energy production methods, provided they internalize the costs of the environmental damage, chemical disposal, etc. Dumping them into the air/water/ground is not a long-term viable solution and simply doing it in the short term because "this one issue is so sma
You are correct Sir (Score:2)
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I'm not defending fracking, per se, isn't it better to have a bunch of small earthquakes than one big one?
Presuming that the small ones are not a precursor to a big one, sure, why not?
I assume the "Best" option of not doing shit that causes earthquakes is off the table...
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Perfect example: If you're a commoner in America, major campaign finance reform is the "best" solution to, for lack of a more accurate term, rampant bribery in our election process; however, if you're a politician receiving these obscene amounts of bribes, er, 'donations,' then "best" is probably not a word you would use when talking about legislation that would se
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There have been unusually large numbers of (largish) quakes everywhere in the last few years. The hypothesis is that the big Indonesian one shook everything up and we're still feeling the effects.
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I'm not defending fracking, per se - msauve
I am not one of the sceptics - Mojib Latif
I have black friends - most anyone who discusses race.
What if it was called... (Score:2)
I'm not defending fracking
I'm wondering why fracking needs defending the first place... Let's just agree that if it had been named horizontal drilling, nobody would have considered it a threat :)
Is there a chance I'm right about this?
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Nope.
The reality is the reason it needs defending is because it follows the standard practices of mining. Extract resources and leave the mess for the taxpayer to pay for.
Privatize the profits, socialize the losses. Sure they use the excuse that often these costs are individually quite low, filling in one headwater or poisoning one well, but in total we see the truth. Personal responsibility is not something the mining industry wants. Look at the BP spill for a good example. They tried to pawn off the probl
Yup. (Score:2)
Re:While... (Score:5)
That should be Who are you.
It's called climate change. Didn't you get the memo? And, this is just a wee bit off topic. Don't you think?
Global? I don't know if this was an attempt at a straw man argument, or not. Regardless, if you actually read the GP's post, you'll see that his point is that maybe releasing mini earthquakes is a good thing. Just like having controlled burns in heavily wooded areas is a good measure to take to avoid wild fires later on. All he did was ask a question -- a valid question that merits an answer.
Stop hyperventilating, and attempt to have a logical, rational discussion of the potential benefits or problems of various forms of energy production. Don't be so obtuse.
Maybe after the "big" earthquake (Score:2)
They can use natural gas generators until FEMA shows up.
Correlation is not causation! (Score:2, Insightful)
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Well, in this case, you have a strong case for cause.
While the actual cause of the earthquakes is tectonic and geological stresses, the fracking provides lubrication for these events to occur. Without said lubrication, the quakes don't happen until stresses achieve sufficient strength to move without it. (Eg, major earthquake.)
In this context, the lubrication does indeed incite movement, but the energy for the movement coms elsewhere.
This sort of semantic argument reminds me of schoolkids saying "they didn'
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Why woud you assume the fracking is acting as lubrication instead of just adding some stress to the situation that is already there?
Honestly I don't think we know enough to say what the possible cause or even nature of the relationship would be.
Re:Correlation is not causation! (Score:5, Insightful)
Reservoirs (Score:2)
And yet nothing will be done in the long run (Score:3, Insightful)
Oh please, they could prove beyond a shadow of a doubt that fracking, or some part of its process, causes earthquakes, there won't be the slightest change in procedure. After all, that oil's not going to sell itself sitting in the ground there.
Does money ride on an action being taken? If yes, it's absolutely irrelevant what the effects are of it being done, it's going to be done.
Re:And yet nothing will be done in the long run (Score:5, Insightful)
Talk about projection. No one thinks that simply except for you.
Fracking is neither good nor bad, just poorly used and improperly regulated. Apply the cleanwater act and many peoples reservations about it would be greatly reduced. Force them to disclose what is in their fracking fluids and how they dispose of the hydrocarbon laced wastewater and even more folks would be put at ease. Force all hydrocarbon well operations to case the borehole the entire length and again objections would be reduced.
Giving them a free pass on normal regulation, require no disclosure and allow them to select which holes are cased and which are not while shifting any environment cost onto the tax payer is what causes so many objections.
Why is stating that natural gas is less bad than coal but worse than nuclear not true?
In other news... (Score:5, Funny)
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Exactly. The amount of prostitution and drug use has risen dramatically where fracking sites are located.
Not to mention pollution, noise, water contamination, and bar fights.
Though in reality, the local population doesn't get to partake in the upswing in employment because the people running the sites are brought in from elsewhere.
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Those people brought in don't buy things? Everything from houses to clothes to food? More people employed in an area means more economic activity, regardless of where the new employees come from. Your other points about violence, drug use, and other forms of crime are perfectly valid of course.
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Sure they do, but almost all of it is temporary. The real profit goes to places far away. The costs however will be at that location forever. If anything goes bad, the little mining company set up for that site will declare bankruptcy the parent organization will wash its hands of the place and the taxpayer will be stuck with the bill.
For somethings like nuclear power just because of the scale that is the only way it can be, for little natural gas wells this is not the case.
Re:In other news... (Score:4, Insightful)
As far as jobs, this is pretty selectively applied. Windmills will create many construction and long term maintenance jobs. Hydrogen fueling station will create many construction jobs. Niether requires us to pay for fuel at levels that support $70 per barrel, or condemn peoples property for a pipeline, or pollute. There are many ways to work. Some people, like hitmen, have no problems if the jobs are unethical. Others od.
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That means employment causes earthquakes.
Damn you greeny extremists!! (Score:4, Funny)
Clearly, if we were just allowed to dump wastewater into local rivers and streams, none of these earthquakes would have had to happen. Why are environmentalists objectively pro-earthquake?
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I believe he was being sarcastic.
Better question, why are they not required to treat the wastewater to the same standards as when they received it?
Then they could dump it into rivers. The problem is they want to just dump this toxic water, which is polluted from the well.
Is asking someone to pay to cleanup their own mess anti-progress? To me it sounds like personal responsibility.
Don't fuck with Mother Nature! (Score:2)
What happened to earth having a fragile ecosystem?
Why is the search for oil so important, that we will risk destroying parts of this fragile ecosystem just to get more?
How much corporate greed are we going to allow before we say enough?
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The same reason we kill people with drone warfare, install puppet dictators, export rediculous legislation, and arrest grannies wth unsecured wifi.
The holy doctrine of "don't fuck with the money."
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Why is the search for oil so important, that we will risk destroying parts of this fragile ecosystem just to get more?
When there was a really really large amount of money to be made obtaining it, that can conveniently be partially distributed to the people responsible for deciding whether we should risk destroying parts of this fragile ecosystem.
The US government has demonstrated on several occasions that it's perfectly willing to fight wars for oil as well (regardless of what you think of the latest Iraq War, the earlier Gulf War was without serious question over oil).
You mean to say... (Score:2, Insightful)
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Correlation is not causation? Give me a break! (Score:4, Insightful)
The people tagging this story with "correlation is not causation" are a perfect example of what Slate is talking about this week on how silly this meme has become. Ok, so are you saying that the frakking does not cause the earthquakes? What, is it the other way around? No, I'm guessing it's a mythical third factor causing both. Some mystery force is causing both the frakking and the earthquakes. Maybe birds. Who knows? But nothing something correlated!
People, the correlation thing is nice and all, but can we please not forget Occam's rasor? The frakking causing the earthquakes really is the simplest explanation, digging out the correlation argument is just as logical as closing your eyes and singing la-la-la. Proving correlation does not prove causation, but it is a necessary step in doing so, not a logical no-no. Even the scientist quoted in the article is aware of the distinction. There is no "gotcha!" here.
Thank you, Slate. I really had not realized how silly this had become.
But!! MONEY!!!! (Score:2)
They are making a lot of money!! Don't let things like large scale damage to property and possible loss of life or other environmental concerns interfere with their god-given right to make money!
How long was there denial of the connection between smoking and cancer? Money at stake... much denial resulted.
Global warming? Same thing... still going on
A separation of church and state needs to happen... and by church I mean money... that *IS* their god after all.
Greasing the wheel (Score:2)
So, instead of one big quake releasing energy built up over a long time, we have a series of small quakes. This is a good thing.
Wastewater, not fracking (Score:2)
Good Thing ? (Score:2)
IANAG, and i'm no fan of fracking for many reasons,
but inducing small earthquakes seems like a good thing to me.
faults build up pressure, and one way or another that pressure is going to release.
it seems better if it releases in smaller, more frequent events than less frequent but large ones.
This whole thing just seems backwards ... (Score:2, Funny)
I think I'll run out and replace the oil in my Jeep with some good old H2O!! 20 mpg here I come!!!
Re:Correlation - Causation? (Score:5, Funny)
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> What is rule #1 in statistics? "Correlation does not equal causality."
Yes, you do fail stats.
When a man-made event clearly proceeds some other event, then correlation does imply causation. This is the entire basis of experimental science.
Unless you can show that the earthquakes in the future are somehow causing fracking in the past, then it is causation. If that's the case, then I'm sure there are a couple of Nobel Prizes in it for your discovery of time-travel.
Re:Stats Fail (Score:5, Insightful)
When A is correlated with B, there are 3 possibilities. A causes B, B causes A, or both B and A are caused by a third factor C.
So are you claiming that earthquakes cause fracking? Or are you claiming that some unknown third factor causes both earthquakes and fracking? If you don't have any plausible suggestions for either, causation seems like the most likely explanation.
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This case, the "third factor" DOES make sense. Hear me out here.
Natural gas deposits (the reason for the fracking) form from decomposing organic deposits trapped between shale or salt layers. This gas formation creates pressure (the reason for the earthquakes.)
So, the third factor is natural gas deposits.
The incidence of earthquakes will positiviely correlate to natural gas deposits. The incidence of fracking will correlate to natural gas deposits.
The result is a positive correlation between earthquakes an
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You could look at places with natural gas deposits that are not being fracked to see how their earthquake incidence compares to areas without gas deposits.
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Earthquakes from natural gas do occur, and have been recorded from pre-fracking periods. The phenomenon has already been studied.
http://www.springerlink.com/content/uq662g4351676m63/ [springerlink.com]
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When A is correlated with B, there are 3 possibilities. A causes B, B causes A, or both B and A are caused by a third factor C.
Seems like 5 to me.
A causes B
B causes A and B is cyclical (or we're time traveling)
B and A are both caused by C
B is caused by C and A is caused by D, C and D are unrelated
B and A self-contained events with no direct external cause and no relationship to each other