BACKGROUND:
According to plate tectonic theory, the Earth's crust
is fractured into a number of large tectonic plates, composed of the crust
and upper mantle. The plates have moved very slowly, sliding over the the
Earth's asthenosphere (a partially molten layer in the mantle). This
movement causes a great amount of stress as the plates either bump together,
moves away from, or slide past each other.
The stress from plate motion builds up in rocks until
they break. On the surface of the Earth, the break appears as a fault or
fracture, such as the 1906 rupture in the picture above. When the break
happens, the stress is released as seismic waves, which travel through the
Earth. The larger the break, the greater the release of energy.
In this Post Lab, the students will play the
"Quake, Shake Game," which is a large motor skill activity.
PROCEDURE:
- Review that earthquakes occur when the outer portion of the Earth's
crust, is under stress. Slow movement inside the Earth and from rotating
on its axis, all add stress. Emphasize slow by saying, "much slower
than a turtle walking or the last drop of ketchup from a bottle."
The movement of the Earth's crust is many times slower; it is actually
about the speed at which fingernails grow. To relieve this surface
stress, the Earth experiences volcanoes and/or earthquakes.
Explain that this slow movement will eventually cause breaks in the
crust: earthquakes. When an earthquake occurs, it releases energy in the
form of waves. It is this wave energy that we feel.
- Explain the rules of the "Quake, Shake Game," to the class.
In this game the students will pretend to be earthquakes and will
dramatize the energy released by various earthquakes using their body
movements.
A weak earthquake consists of slight body movement, a moderate
earthquake consists of a little more violent motion than that of a weak
earthquake, and a strong earthquake consists of shaking, rocking, and
rolling.
- Instruct one student be the shake master (similar to "Simon
Says.")
The shake master announces one of the following:
"The surface of the Earth is under a little stress; I am a weak
earthquake."
"The earth is under some stress; I am a moderate earthquake."
"The earth is under a lot of stress; I am a strong
earthquake."
The rest of the class does the appropriate type of shaking. The teacher
acts as the "judge" to observe if the students acted out the
right kind of earthquake.
Change the "Shake Master" as needed.
