In some areas, severe earthquake damage is the result of liquefaction of soil. In the right conditions, the violent shaking from an earthquake will make loosely packed sediments and soil behave like a liquid. When a building or house is built on this type of sediment, liquefaction will cause the structure to collapse more easily. During the Loma Prieta earthquake, the Oakland International Airport's main runway suffered severe damage due to liquefaction - cracks measuring up to 3 feet wide were found.
To help it withstand earthquakes, the new San Francisco International Airport uses a bunch of advanced building technologies. One of these technologies involves giant ball bearings.
As you can see, airports located in earthquake-prone areas have several safety issues to consider, such as:
- The integrity of the buildings and terminals
- The integrity of the control tower
- The integrity of the runways
The 267 columns that support the weight of the airport each ride on a 5-foot-diameter steel ball bearing. The ball rests in a concave base that is connected to the ground. In the event of an earthquake, the ground can move 20 inches in any direction. The columns that rest on the balls move somewhat less than this as they roll around in their bases, which helps isolate the building from the motion of the ground. When the earthquake is over, gravity pulls the columns back to the center of their bases. This takes care of the folks waiting for a departing flight, but what about the people that are on arriving flights?
As we've mentioned, runways can suffer some pretty serious damage due to liquefaction, so a plane landing just after an earthquake could have quite a treacherous runway to maneuver. If the people in the control tower feel the earthquake and can radio the pilot, the plane could divert and avoid landing at all. But if a plane happens to be landing just as the first shock of an earthquake hits, it's not a big problem. The plane's landing gear is designed to handle big shocks from hard landings, so you can ride out the earthquake in comfort.