Why do some buildings fall in earthquakes?
All buildings have a natural, period, or resonance, which is the number of seconds it takes for the building to naturally vibrate back and forth. The ground also has a specific resonant frequency. Hard bedrock has higher frequencies softer sediments. If the period of ground motion matches the natural resonance of a building, it will undergo the largest oscillations possible and suffer the greatest damage. A classroom demonstration follows the animated portion of this video clip.
What are the key features addressed in this animation?
- Frequency of a wave refers to the number of waves that pass through a point in one second
- Period is the amount of time it takes one wave cycle to pass the given point
- Resonance is the tendency of a system to oscillate with greater amplitude at some frequencies than at others
- Resonant frequency of any given system is the frequency at which the maximum-amplitude oscillation occurs.
- All buildings have a natural, period, or resonance, which is the number of seconds it takes for the building to naturally vibrate back and forth.