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Materials needed
1. a rectangular plastic bin -- something 10 x 14 inches works
well, and about 6 inches deep.
2. sand; you'll need about 20 pounds
3. a bucket of water
4. a brick
5. an electric sander
6. bungee cords
7. a stop-watch
Procedure
Strap the sander to the bin using the bungee cords. You want the
vibrating part of the sander to be in contact with one side of
the bin. Make sure it's on good and tight! Fill the bin with enough
sand to make a layer about 3 inches deep. Place the brick (simulated
building) upright in the sand. Now, turn on the sander and use
the stop-watch to measure how long it takes the brick to fall
over. You might want to reset the brick and re-run your "earthquake"
a few times.
Now, for fun, put enough water in the bin to make the sand moderately soggy. Repeat your experiment, and see what happens! Did the brick fall over faster than before?
Results or What causes earthquakes?
It takes a lot of energy to move the surface of the Earth, even a small fraction of it! Earthquakes can be caused by the same upwellings of heat that cause volcanoes, but most are caused by collisions or slippage between the large floating plates of Earth's crust. These tectonic plates are sometimes moving apart, building up stress for a long time until suddenly, the fault snaps with terrible energy.
We can't avoid earthquakes, but it is important to try to minimize the loss of life and property. Since quakes shake buildings, builders try to use designs that will absorb some of the motion. A tall building that will sway a little bit in a earthquake will survive better than one that is very rigid. It's also important for the building to have a very secure foundation in the Earth. If the building rests on sand, the vibrations of the quake will "liquefy" the ground beneath the building. Then, watch out!