BACKGROUND:
The energy released during an earthquake causes the
ground to shake. If you are close to the epicenter of a moderate quake, the
shaking is more severe than if you were farther away. Scientists have
developed many scales to measure the intensity of earthquakes. Two common
ones are the Richter Scale and Modified Mercalli Scale. The Richter Scale
measures the size of the waves produced by the earthquake, hence the energy
it releases. The Richter Scale is absolute; seismologists will derive the
same Richter magnitude wherever they measure the earthquake. The Modified
Mercalli Scale describes what a person feels during an earthquake. This
scale is relative; it changes depending on how far you are away from the
epicenter.
PROCEDURE:
- Read the book, Three Earthquake Dolls. Discuss with
students the energy produced during each earthquake. The Tangshan
earthquake in northeastern China was a 7.8 magnitude killed
240,000. The Lisbon earthquake was a 9.0 magnitude and killed
100,000. This earthquake would have had the most energy
released. The New Madrid earthquake was a 8.0 and killed
very few.
- Have your students examine the worksheet of the shaking boy. Tell the
students that the boy is experiencing an earthquake. Ask them if they
think the earthquake is strong, moderate, or weak. Be sure to have them
justify their answers. The earthquake probably is a strong one because
the bird in the tree is startled by the shaking of the tree. In a very
strong earthquake it will be difficult for people to stand up. However
most earthquakes are small, so hopefully children will never have to
experience such a quake.
- The boy is being shaken by an earthquake as he is walking through a
forest. Ask the children if he is safe. When a person is in the open
country with no telephone poles or overhead wiring, he/she is basically
safe. The tree in this picture is too far away to harm the boy if it
were to fall down. If the boy were at home, however, he should seek
shelter under a strong structure like a heavy desk to protect himself
from falling objects. If he were outside near his home, he should stay
away from overhead wiring and not run inside. Some children have been
taught to "duck and cover." However, during an earthquake they
may attempt to do just that, move from outside to inside in order to
"duck" and be "covered" by the table they practiced
with. Emphasize with the students that they must think during an
earthquake in order to make decisions that will keep them safe during
the shaking.
- Some children think that the Earth opens up and swallows people during
an earthquake, as it is often depicted on television. An earthquake,
however, is caused by stress within the outermost layers of the Earth.
Some cracks may appear on the ground after an earthquake, but they are
small, and rarely if ever threaten people. The seismic waves traveling
through buildings may create enough energy to destroy an building.
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