Earthquakes

[|Earthquake] - a trembling or a shaking movement of the Earth's surface. Earthquakes occur where the stress exceeds the capacity of Earth materials to support it, most often found at the boundaries of the tectonic plates.

seismic waves

[|vibration] - or oscillation - quick moving back and forth (or up and down) about a point of equilibrium. The vibration may be periodic (having a pattern) or random. Something that is vibrating may shake at the same time.

Shake-and-vibe testing

Shake table

[|Seismometer] or seismograph - an instrument that measures motions of the ground, including those generated by earthquakes, nuclear explosions, and other sources. Records of seismic waves called seismograms allow to map the interior of the Earth, and locate and measure the size of those different sources

A demonstration of how vibration affects buildings - concurrent shake table testing of two building models. The right model rests on base isolators, the left one is fixed to the platen. (image at right)
 * What's the problem?**
 * **Ask** -
 * **Imagine** -
 * **Design, Build** -
 * **Improve** -

> stress, capacity, support, boundaries, seismometer, seismic waves, periodic, random, vibration, shake, frequency, Hertz, amplitude, model, base, isolation, fixed
 * That's engineering**
 * period - the time it takes a vibrating object to go back and forth completely
 * frequency - the number of back-and-forth movements in one second is its frequency, measured in Hertz (Hz)
 * amplitude - the farthest possible distance from the equilibrium point
 * vibration - a fast movement back and forth
 * Engineering ideas**

Challenges for you to work on...
 * Do It**
 * [|how soil affects the stability] - explore how building on different types of surfaces—clay, gravel, sand, soil—will affect a structure’s stability.
 * [|seismometer] - this machine measures sound waves moving the trough the air. Noises are made by vibrations,


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