Already I've read woowoo claims in comments on articles about the big earthquake that happened in China today.
Somebody claimed that the building of the Three Gorges Dam (resp. the pressures that the filling reservoir is putting on the plates) could have caused the tensions that caused the earthquake in Sichuan today.

I think this is utter bunk and would like to refute them, but I need some help on the numbers... as I'm not a geologist nor a designer of water reservoirs.
See the link above for numbers on the epicentre and depth - the dam was apparently outside the quake area, but that won't shut them up I guess.

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Si tacuisses, philosophus mansisses.

"Half of what I say is meaningless, but I say it so that the other half may reach you."

Let's see if I can get the numbers on the three gorges project.

The capacity of the reservoir is 39.3 cubic km. The area is 1,000,000 sq kilometers (if I read wiki correctly there). This is full capacity, which is not normally used since they need a flood buffer. Add to that the weight of the dam, locks, etc.

But I don't think the problem is going to be the actual pressure by m^2. It might have more to do with the distribution of weight by the dam wall (which, by the way, is an incredible feat of engineering) or the water seeping into the surrounding area.

I also found that the BBC has picked up on that scarecrow: http://news.bbc.co.uk/2/hi/science/nature/1974736.stm
This of course ignores that there have been huge quakes in the area long before the dam was built and that the reservoir isn't even filled yet...

Any thoughts?

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Si tacuisses, philosophus mansisses.

"Half of what I say is meaningless, but I say it so that the other half may reach you."

Hm... did the Himalayas get higher as the dam filled? Could we be about to lose Japan?

People don't understand big numbers I guess.
from: China Daily

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* Never doubt there is Truth; just doubt that you have it!

Oh, yoy...
He bounces around the world talking about tectonic hot spots, mostly Africa, without any regard to being caused by dams.
There are only two mentions of dam caused earthquake, and even those are only related by time which convinced him of a cause and effect.
Typical scare tactic. Report all sorts of gloom and doom on the related subjects to make it sound like the subject is the gloom and doom.

I do see one point in this article (although it's not made clear). A dam built in an active area is more prone to a disaster. But, the cause and effect is the other way around.

And; of course, studying it never hurts.

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Numbers are not case sensitive. (me)

Some things are so ridiculous, they're hardly worth refuting.

The quake was located on a major thrust fault, which is a regional expression of the compression caused by the Indian subcontinent continuing to move into the Asian continent. See the USGS link provided in the other quake thread for details.

Yeah, I have that link too. What the woowoos are saying though is that the reservoir's filling in conjunction with the fault has caused the earthquake.

Which I think is silly, since city growth and housing projects should then have a similar effect. Or the annual flooding before the dam was built.

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Si tacuisses, philosophus mansisses.

"Half of what I say is meaningless, but I say it so that the other half may reach you."

How far is the reservoir from the fault, or from the epicenter of the quake?

Edited to add, if the reservoir was having an impact, we would expect to see an increase in small quakes under and next to the reservoir as it filled. Have there been such an increase? If so, are they related to the fault in question?

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

And shouldn't we have seen increases in earthquake activity along other resevoirs that are on or near fault lines?

What is the relative mass of a filled resevoir compaired to that of the plate, and the force required to move said plate?

And the fact that the quake occured in an area that has had regular and documented quake activity, that occured not only within the expeted timeframe but within expected magnitude (even if higher than "average")... That's like me saying "I have a grandfather clock that chimes every night at midnight. Last night, I put a new lightbulb in the bathroom light fixture. The clock chimed at midnight. The extra power drawn through the lightbulb must have caused a surge that resulted in the clock chiming."

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I'm like one of those idiot savants...well, except for the savant part.
"In order to increase awareness of the homeless, security have been given binoculars."

That's not necessarily true - if the dam was on a solid plate, you could have tilt motion at the edge of the plate & that could be some distance off.

But the weight of even such a dam as this one seems highly unlikely to have produced a quake. It's an unstable area & as shown in the China Daily articles, 5 years ago or more, the local experts were predicting one to come, not because of the dam but simply because it was overdue based on the extended history.

Now if that amount of water had been slid into the fault itself...? Then the woowoo would have a case.

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* Never doubt there is Truth; just doubt that you have it!

Uh, no. Listen to Aurora, the geologist.

I think that claim is absurd, like everybody else said.

But just because the Three Gorges Dam didn't cause an earthquake, doesn't mean it isn't harmless. Millions of people were displaced, thousands of years of culture and archaeological sites flooded, horrid pollution, an entire species of dolphin now extinct. I can't even begin to describe the horror.

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You can't really tell the difference between drunken rambling and sober blogging.

I was talking about an increase in small quakes, like a cluster of small quakes. On that scale, there really isn't such a thing as a solid plate. In between major faults there are all sorts of differing materials, especially in a place as geologically diverse as China.

I recall a paper back in the '70's of a study done at a new dam site in Colorado where they discovered that this actually happens --- that clusters of small quakes can occur as a new dam fills.

What I'd be interested in seeing is a study that shows whether such a cluster, if it occured in China, is physically related to the major fault that had the big quake.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender