BACKGROUND:
The first sign of an earthquake is often a sharp thud,
signaling the arrival of compressional seismic waves (P wave). The second
sound and sensation are a rumbling caused by ground rolling from surface
waves.
A geologist in the Valdez, Alaska, 1964 earthquake
described the motion as follows:
"The first tremors were hard enough to stop a
moving person and shock waves were immediately noticeable on the surface of
the ground. These shock waves continued with a rather long frequency which
gave the observer an impression of a rolling feeling rather than abrupt hard
jolts. After about 1 minute the amplitude or strength of the shock waves
increased in intensity and failures in buildings as well as frozen ground
surface began to occur..."
The severity of an earthquake can be expressed in
several ways. The magnitude of an earthquake, or the amount of energy
released can be expressed by the Richter scale. The Modified Mercalli Scale
expresses the intensity of an earthquake's effects in a given locality, as
experienced by people.
PROCEDURE:
- This coloring and word exercise serves as a springboard to begin a
discussion with your students about the sounds caused by an earthquake.
Discuss that there are natural sounds from an earthquake, like
"rumble," but there are also other sounds like
"bang" and "crash" that indicate that something is
falling or breaking.
- Ask the students which sounds should serve as a warning if an
earthquake should occur. This exercise emphasizes to the students how to
evaluate the situation during the earthquake, using all their senses.
For example, by listening to the noise the earthquake makes and
observing shaking objects, they would be able to determine whether an
earthquake is a weak, moderate, or strong event. This will make them
better prepared to take action.
- Instruct the students to color the worksheet, and to think about
sounds made by earthquakes. You may also want students to simulate the
sound of an earthquake "rumble" by having them all softly make
a rumble sound. Practice as a whole group and then have students do a
"rumble wave" (like the waves made by a crowd at a football
game, where the sound gets progressively louder and then softer). This
would simulates the movement of the "energy wave."
