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DESIGN for disaster: As a quake rumbles through a metropolitan area, a kind of natural selection determines which buildings will survive. A structure whose long axis is parallel to ground motion 1 will sway less than another whose axis is perpendicular. Where such buildings are joined 2, one wing sways more than the other, and a rupture occurs. Likewise, a tower rising from a lower structure 3 may fracture at the point of connection.

"Soft" supports, such as in a building whose first story is composed of only tall columns, can be the recipe for destruction 4. Here both buildings sway the same amount, but A remains intact because it flexes as a unit. In building B, most flexing takes place in the soft first story, and the structure fails. 'A building can resonate with the frequency of the ground waves, like a child on a swing being pushed higher and higher. The force applied at the bottom may be multiplied as many as five times at the top and result in destruction 5.
Buildings close to one another that begin to sway may collide 6, a phenomenon known as pounding. Because their masses are so great, even a slight touch can be disastrous.

In designing for survival in earthquake-prone areas, architects are paying more attention to local geology. Solid rock foundations 7 transmit seismic waves as short, sharp jolts. Uncompacted substrata 8, such as the ancient lake bed under Mexico City, transmit rocking motions similar to those produced by an ocean swell. A building can be "tuned" so that it will not resonate with the ground wave and destroy itself.

Built on rock, a relatively tall building 9 has extra reinforcement at the joints where one structural member meets another. This construction allows strength with flexibility-under the stress of an earthquake the building will flex like a tree or an airplane wing. On soft ground a short, stiff building 10 will not resonate to long ground waves. Diagonal members brace the structure, adding rigidity.

Even though a building 11 is strong enough to survive ground oscillations (arrows, lower right) of a quake, its innards could become a deadly shambles. On the top floor the unbraced ceiling panel carrying heating and cooling ducts collapses. A floor below, the sprinkler system ruptures, and the partition falls. 

On the second floor unsecured banks of computers topple. Bookcases on the first floor fall like dominoes; a file cabinet reels with force enough to send a person flying. Distortions in the building may jam the doors, trapping people inside. In the basement a huge gasfired boiler and a generator are shorn from their cradles. Rolling like loose cannon, they tear gas lines and unleash the most feared secondary effect of a quake-fire. Though the building codes in California and some other western states require quake-resistant construction, only a few communities-let alone states-east of the Rockies have adopted such codes.

Rubber and steel plates (top) partly isolate a structure from a concrete slab shaking at earthquake frequency at the Earthquake Simulator Laboratory in Berkeley, California. The technique, employed in an office building in southern California (bottom), awaits the challenge of a major quake.