Building Resonance: Structural stability during earthquakes

5min 31s Novice

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.

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Keypoints:

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.

Related Animations

Highly generalized animation reflects the arrivals of P, S, and surface waves to 3 closely spaced buildings. Exaggerated movement of the buildings reflects the relative motion recorded by the seismograms.

Animation Novice

A seismic hazard is the probability that earthquake shaking of a certain intensity will occur in a given geographic area, within a given window of time.  From that, risks can be assessed and included in mitigation efforts. Let's compare them.

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Magnitude and intensity are both related to the size of an earthquake, but they each measure different aspects. One is measured using seismometers; the others is felt. Let's use a lightbulb as an analogy.

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Related Videos

The BOSS model is an effective way to show how buildings of different heights respond to seismic waves. All buildings have a natural frequency.

Video Novice

This video lecture shows John Lahr (USGS Seismologist Emeritus) describing the BOSS experiment that models oscillations of different height buildings.

Video Novice

John Lahr, US Geological Survey Seismologist, demonstrating a cheap and kid-friendly version of the BOSS model that shows how buildings of different height oscillate during earthquake shaking.

Video Novice

Related Lessons

All buildings have a natural frequency of oscillation or resonance frequency. When seismic waves shake the ground beneath a building at its resonance frequency, the structure will begin to sway back and forth. This concept can be demonstrated in the classroom using the BOSS Model Lite as a discrepant event demonstration to engage students in earthquake-engineered buildings.

Lesson Novice

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