Earthquake Destruction & Proofing

In an earthquake, the release of energy in the Earth’s crust creates seismic waves, or waves of force, that spread out from the energy release center, or epicenter.  As a wave passes an object on the ground, the ground and object move with the wave a short distance and then spring back, only to be hit by another wave, and another, and another.  This massive shifting of the ground puts great lateral stress on objects such as buildings.  As the stress on the structures that make up the building accumulates, the building eventually fails in numerous locations.  For a small-scale example, glue a cardboard house to another piece of cardboard and then shake it back and forth.  The weakest part of the house (probably the glue in this example) will fail and the house will fall over.  When Earthquakes are powerful enough, they create massive damage to cities such as what happened in Haiti.

There are three types of earht-quake proofing when constructing a house or building: passive damping, diagonalbracing, and base isolation.  Passive damping includes the use of energy-absorbing materials that can deform and take the brunt of the energy rather than the building.  Diagonal bracing is just as it sounds.  Using diaganol bracing in the frame of the building helps to prevent lateral failure.  Base isolation includes isolating the foundation of the building through the use of large rollers and a number of other techniques.  In the case of the rollers, imagine a ball inside of a bowl.  If you shake the bowl back and forth the ball will roll up and down from one rim of the bowl to the next, but not very far relative to its initial position to the ground.  Now imagine this ball connected to the corners of a building’s foundation with “bowls” underneath.  In an earthquake, the ground will shake back and forth, but the building will not move with the ground as easily.  This technique is common in places like Tokyo, but adds to building costs and complexity.  As you can imagine, old and cheap buildings in poor countries do not have the luxury of this earthquake proof construction.

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