Three Gorges Dam prediction

I don't know if this has been mentioned yet, but I would expect to see more earthquakes in the area of the Three Gorges Dam. When I was in college, I had a professor mention a theory that the reason fault lines creating the continental plates are in certain places is because the sheer mass of the water pressing down on the earth. This works especially well when you take a look at the indopacfic rim.
My prediction is that in the fragile valley that the three gorges dam will flood is going beyond our knowledge of stress that we can put on the earth. While the area will be far smaller than an ocean, or even some of the great lakes of the US, the fast change is pressure could result in major problems in the area. I think the last thing one would want after building the world's largest dam with the largest reservoir would be the possibility of an earthquake. What do you guys think?

Just a quick note on this: From what I can tell, the area that the dam is in is the most geologically stable region of China. Here's a link to a quake risk map....
geology.about.com...

Here's another map that will help you pinpoint the Three Gorges Dam....
www.ibiblio.org...

This area looks as stable as the Canadian Shield.

Originally posted by carlwfbird
When I was in college, I had a professor mention a theory that the reason fault lines creating the continental plates are in certain places is because the sheer mass of the water pressing down on the earth. This works especially well when you take a look at the indopacfic rim.

Proof that should take anything a 'professor' says with a healthy dose of skepticism.

First, the major faults are the boundary of the plates, so in a sense the plates make the faults, not the other way around.

Second, rocks weigh more than water. So the continents are heavier than the oceans for the same volume. So wouldn't the faults then form in the middle of the continents where the weight is the greatest?

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The water above the oceanic tectonic plates does weigh less than rock, but the actual rock of the oceanic plates is heavier than the rock of the continental tectonic plates.

The continents are in general made up of lighter rock material, basically sort of like the sludge that can build up ontop of a pond.

Off the top of my head i think the silting up of the reservoir behind the dam and the waste of all that topsoil will probably be a more likely problem. Large bodies of water do add extra weight, but if the crust is pretty stable there it shouldn't be a problem.
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Dave, Discovery is running a show on the three gorges right now. They too echoed my concern of tectonic activity. The dam actually strattles a fault line. The mountains that the dam is built into actually were created by earthquakes.

ISOSTASY

NEWTON'S 2ND LAW

I give that this is a very stable basin... yet the whole of the basin will sink. The entire plate will become relatively heavier than the other plates. A new equalibrium will be found on the planet. The quake activity will have its seed in the dam... but will be felt abroad.

Noteworthy observation carlwfbird.

Sri Oracle

Ok you guys have got the wrong end of the stick here.

The statement that you would expect to see more earthquakes around the 3 gorges in entirely correct. However it is not for the reasons this "professor" said, I'm not sure what he was a professor of, but it doesn't sound like geology!

Anyway, it is fairly common to get increased seismic activity around major dam projects. The earthquakes tend not to be that big, around 3 - 4 on the richter scale. However India has undergone some 6.3 quakes that have been related to the filling dam building project in the narmada valley.

The reasons why earthquakes are thought to occur in areas which where previously reasonably tectonically quiet are not related to any of the reasons previously stated on this thread. It is thought that upon filling of the resevoir behind the dam, the increased water pressure that occurs in factures and fissures in the rock below and around the mass of water held back by the dam, causes lubrication of fault plains which may have already have been under tectonic strain. However prior to the building of the dam and filling with water the fault lines did not move due to friction of the rocks.

Maybe this is an appropriate time to look at the Sichuan earthquake of 2008. It is being suggested that the large dam only a few hundred metres from the fault that moved was a cause of that quake.
www.telegraph.co.uk...

It seems that the long term impacts of stresses resulting from major engineering works is only now being recognised. In Newcastle, Australia, it seems that 200 years of coal mining may have been the cause of the 1989 earthquake there. news.nationalgeographic.com...
Note that Newcastle was not considered to be a seismic risk for much the same reasons that the Three Gorges Area is considered stable.

It could well be the ultimate man-made disaster if it does fail.