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Zipingpu Dam May Have Triggered the Sichuan Quake
bfwebster writes "An article in the Telegraph (UK) raises an interesting question: was the massive (7.9) Sichuan earthquake that wracked China last year and left millions homeless caused by ground stresses following the completion of the Zipingpu dam? As the article notes, 'The 511-ft-high Zipingpu dam holds 315 million tonnes of water and lies just 550 yards from the fault line, and three miles from the epicenter, of the Sichuan earthquake. Now scientists in China and the United States believe the weight of water, and the effect of it penetrating into the rock, could have affected the pressure on the fault line underneath, possibly unleashing a chain of ruptures that led to the quake.'" The Sichuan region is earthquake-prone, but has not seen anything as large as the 7.9-magnitude quake for perhaps millions of years. The Chinese government denies any connection between the dam and the earthquake and seems to be actively obstructing the access of scientists who want to investigate. The article concludes, "There is a history of earthquakes triggered by dams, including several caused by the construction of the Hoover Dam in the US, but none of such a magnitude."
As with all things geological, there are a lot of unknown variables, hence the "could", "might" and other diluting terms.
Engineering is the art of compromise.
Sir Ranulph Fiennes (the famous arctic explorer, among other things) was actually kicked out of the SAS for destroying a dam using stolen explosives. You can google for more detailed accounts of the story, but here's one:
http://www.independent.co.uk/student/career-planning/getting-job/my-first-job-explorer-sir-ranulph-fiennes-was-an-sas-officer-420601.html
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let's say they know dams cause earthquakes. ok, so there will be some minor earthquakes. but 7.9? no one is going to predict anything that large
still, let's assume the dam is still the trigger for the 7.9 earthquake. emphasis on trigger. its going to happen someday anyway
if they never built the dam, we'd be talking about the 7.9 or 8.3 sichuan earthquake of 2031 or 2102
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
not to dodge your sarcasm, but the scientific findings are vague enough to blame the entire quake on Bush bombing people in iraq.
you never know what that one last MOAB will really do what with the butterfly effect and everything.
also if a quake hasn't happened in a million years then it just might be under a lot of stress, that doesn't easily go away.
i thought once I was found, but it was only a dream.
Oh yeah, I was of course sidestepping the issue of "Is the finding ACTUALLY valid." Somewhat like what the chinese government will do, only they probably won't do it with sarcasm. It'd be refreshing if they did though.
Would a 7.9 quake, although large by earthquake standards, even leave evidence that lasted more than, say, 1000 years? You might be able to tell if you took a cross section of the entire fault line, I suppose, but not all fault lines are known. A L.A. city geologist found a previously unknown (but not currently active) fault under the house of a friend of mine when he was having some drainage work done; new ones are discovered all the time.
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
If this is true, then just wait until the Three Gorges begins to top off (it has been filling for years now and has some time to go.)
Maybe they can get this drilling crew on the mission to save the day!
All humour aside, most people have no clue about the energy levels and destructive power available to natural forces, just on our world. (ie:water) Even engineers can fall prey to their preconceptions at times, if they are not diligent. Water is a powerful force, in scale.
Most people perceive the Earth as a solid/stable surface to build on(dig to 'bedrock' for the foundation, etc...), frequently forgetting Earth more resembles a poultry egg: relatively thin shell covering/encasing a liquid center...and just as fragile on scale.
At our most terrible destructive level available technologically to humans today, we are still just 'wannabe' punks in the big picture. Actually, I would argue that communication tech is the most powerful weapon/tech we have devised to date.
*(IAANB) I Am A NASA Brat![clarification of subject line]-just could not pass this one up. And NOT trying to pick on engineers, who have demanding job requirements, but there is a good reason to put erasers on pencils! :-)
Sorry if this was more than you bargained for trying to make a 'funny', but you did raise a valid point! :-)
Down With Slashdot BETA!!! I've been around the corner and seen the oliphant; you can only abuse me from your perspecti
Yes, that's so true. The changes that China has gone through in the last 100 years are staggering. Edgar Snow's Red Star Over China gives a fantastic account of what China was like during the Communist Revolution. It brought them forward a millennia in a few years, spreading education, and raising standards for 100 of millions of poor Chinese peasants. But that still left China far behind what we consider a well developed country. Of course, the Great Leap Forward and Cultural Revolution didn't really help. Then again in the last ten or fifteen years, it's almost as if China has come forward another millennia, where cities like Shanghai are fairly easy to live in as Westerner. The people there are now beginning to resist change for this reason. Want to build a new Maglev line to Hangzhou or high speed rail link to Beijing? The people organised together and forced the government to re-route it via somebody else's neighbourhood. Out in the country though, people still put up with being relocated because their lives haven't changed as fast and are some way behind.
Of course, preventing flooding of flood plains wrecks the ecology and in many cases has resulted in the severe degradation of the arable land downstream.
A more sensible solution would be to not build towns and cities in flood plains. But it's a bit late for that.
"Software is too expensive to build cheaply"
Paleoseismology as you described is actually quite difficult. In the case of the San Andreas, you can't really look at off-set streams and such. You can rarely discern more than one or two events along such offsets, and once you do, it is very difficult to determine the age of the offset. You can get the amount that it's moved, yes, but not the timing. Worse, since you don't know the timing, you don't know if the offset is from one or more events.
The way it's done for strike-slip faults like the San Andreas is to look at a cross-section perpendicular to the fault, looking for layers of material off-set (or suddenly changing thickness, etc.) along the fault. The best way to date those layers is through carbon-14 dating of organic material, which can give you accuracy only within ~1-200 years - and that's assuming that the organic material you date is not from elsewhere, is not from 200 year old trees, etc. If an event offsets every layer from the bottom up to a certain point, you date the top layer that it cuts through to get a maximum age, and the layer that it didn't cut through is the minimum age.
You can imagine the difficulty and ambiguous nature of this. The individual layers that you have to recognize and date are on the scale of centimeters to decimeters - I've seen some of the areas that were used, the famous one being along Pallet Creek which is along the San Andreas northeast of LA (I have a picture of it - well, it is a picture of a girl standing in front of it - here: http://www.flickr.com/photos/penguinchris/3037578910/) Here, luckily there was constant, relatively rapid deposition of material. In most places this is not the case, so any record of movement on the fault is eroded away.
For the San Andreas, we have a partial record going back ~1500 years. There really is no reliable way to reach back further than that - the record isn't normally visible in older rock units. Looking at the larger-scale structures is interesting by itself but doesn't tell you anything about when specifically there was movement. The fault system in the Sichuan region is fairly well understood - it is a kind of combination strike-slip/thrust fault (see http://quake.mit.edu/~changli/wenchuan.html for some nice diagrams.) But I want to call BS on the idea that they have any idea how frequently major earthquakes have happened there - and even if they do, the idea that it is "perhaps millions of years" since the last one is ridiculous no matter what.
And then, when you *do* figure out a approximate year for an earthquake, how do you determine how big it was? Again, extremely difficult! The best estimates come from comparing old written records of destruction with those from modern earthquakes - nothing scientific at all!
What's being done extensively with the San Andreas is physics-based computer modeling - we have some idea of the force building up, and combining that with records of historical earthquakes we can make an estimate of a major earthquake every ~150 years. But even for this, the best-studied earthquake area, it's not much more than a guess.
I don't know as much about the Teton fault (other than that it is a normal fault, not a thrust fault as you stated ;) ) but I'll comment on the idea of a "magnitude 7 earthquake every 400-700 years." These kinds of estimates are based on the very difficult work I described earlier (and I'm not sure how much has been done for the Teton fault) and whatever geologist came up with that would probably admit it is a simple guess without much to base it on. I mean, think of it - is knowing there's a large earthquake every 400-700 years really all that useful anyway?
By the way, I assume any dating of the Teton fault would be done this way: when new patches of rock are exposed along the fault as you described, they start getting hit by cosmogenic radiation. By measuring the amount of cosmogenic radio isoto
>Dams prevent catastrophic, uncontrolled flooding by buffering the surge in a lake and letting it out slowly.
As long as they're big enough. If they're not, a rapidly increasing flood of water, that if left uncontrolled might rise at 2 feet an hour, flooding many houses, could be turned into a 20 foot high wall of water, debris, and rock from washed-out dams that kills 145 people rather than just destroying a bunch of houses.
Every "flood control structure" on that river got ripped out. A flood that had almost the same rainfall 40 years earlier didn't kill anyone because it took two hours to go from heavy runoff to full flood. My friends that were down in the canyon in the 1976 flood said the front wave of the flood was moving at about 60mph and consisted mostly of a mass of mobile homes (with the occupants still in them.)
Nostalgia's not what it used to be.