Soon after the John Hancock Tower in Boston was built it was discovered that there was a very real danger of it tipping over in a high wind. To prevent this, a large (approx. 40 tons) weight suspended on springs was placed at the top floor of the building. If the tower swayed in one direction, the inertia of the weight would halt it and swing it back. This allowed the tower to sway slightly in the wind, but prevented it from overbalancing and toppling.

Incidentally, the engineers had initially worried about the building toppling in the direction of its broad side, and had taken steps during construction to prevent this. The surprise came afterward when it was discovered that the real danger was in the buiding falling along its narrow side, which necessitated the weights in the top floor.

Back in college I did an internship at WZLX radio in the 42ns floor of the Hancock. During storms you could hear the building creeeeeak back and forth. Creepy.

Here’s a site that talks about some of the techniques of keeping skyscrapers from falling over in earthquakes:

http://www.nd.edu/~quake/case.studies/mhivcs.html

http://www.nd.edu/~quake/case.studies/act.html

–sublight.