Steel and concrete according to Wikipedia.
Yes
Bingo. If any terrorist wanted to target that damn, ....
In theory you are correct.
But the scale of things in this matter makes setting off an upstream landslide very hard. You would have to organise a pretty large "construction site" to do this. Even in a open democracy like Norway it would be an impossible feat to pull it off unnoticed. In China...
Look,
The Three Gorges is an concrete
gravitational dam, a very safe dam type. It is by nature designed to be overflowed, and it is much less prone to earth quakes than other types (except rock fill dams).
Yes it has its weaknesess, but so have all constructions. Im am not inclined to talk abouth them tough. Just let us say that Im farly confident in the chinese in this matter.
IMHO the "only" real threath to the Three Georges is a war against a foe that can project
high energy specialised power to the site. Terrorist attacks is not an issue, except the unlikely nuclear device.
The environmental effects of The three Georges is another matter ofcourse. Those who are conserned about to this, should not try to make an issue of the possibility of an dam break at the Three Georges.