BACKGROUND:
As discussed in the Pre Lab, the damage caused by earthquakes is
dependent on the intensity of the earthquake and the type of ground a
structure is built on. A third factor is the materials used in a
building’s construction. In earthquake country, unreinforced building
materials like brick are not suitable, because these structures are
weak. It takes little energy to cause the mortar to break loose, causing
the building to collapse. Materials like wood are much more resistant to
earthquake shaking, because these structures are flexible. A seismic
wave can easily pass through a wood structure with little breakage.
Another factor in determining resistence to earthquake damage is the
shape of a building. Students will see in this exercise that a shape
with a large base and a smaller top (like a pyramid) is the most
resistant of high structures. A cylinder or high standing rectangle is
not resistant to shaking.
This lab illustrates the intensities of different earthquakes by
having the students experiment with different shapes on the shaker
boards. Because we cannot accurately simulate the Richter or the
Modified Mercalli scales, the students will make their own relative
scales, which they will name it after themselves. The key concept is
that the harder the shaking the higher the intensity and magnitude of
the earthquake.
PROCEDURE:
- Explain the factors that contribute to earthquake damage. Emphasize
that the shape and construction of a building are important factors.
- Have the students work in groups of four. For Exercise I, each group
will construct a simple shaker table. Each group will need a shaker
board, a handful of marbles, a plastic container lid, and toy blocks or
their equivalent. Have the students place the marbles in the plastic
top. The marbles will act as ball-bearings in the experiment. Next, have
them balance the shaker board on top of the marbles. This completes the
shaker table. The board should be about 12 to 18 inches in length and at
least ½ inch thick.
- Explain that for each type of motion, the same student will perform
the shaking for all four building shapes. Have the students record their
names next to their type of motion on the worksheet. Have the students
practice the different types of motion before they conduct the
experiments. "Slow-long motion" means to move the board in the
long direction slowly. "Quick-long motion" means moving the
board in the long direction quickly. "Slow-short" and
"quick-short" mean slow and fast motions in the short
direction, respectively. As much as possible, try and get the groups to
move the boards similar amounts and speeds.
- Instruct the students to build 4 differently shaped structures (i.e.,
rectangle, triangle, sphere, cylinder) on their tables. Have each
student "shake" the table at their assigned intensity. The
students should record if the shapes are resistant (do not fall),
semi-resistant (does not fall easily), or not resistant (falls
immediately). Their conclusions may vary because of the shape(s) they
test, as well as how the students move the boards.
- During the experiment, the students should quickly realize that
intensities B and D (both quick) represent a high number on the
student's scale, while A and C represent a low number.
- In Exercise II, the students try to stack 3 Styrofoam cups so that
they will resist a slow-long earthquake. They can put the cups up or
down. They may have trouble drawing the cups. Help them by suggesting an
easy way to draw the cups: cup up; cup down; side view (cup up); side
view (cup down); top view (cup up); two view (cup down).
- Remember that the relative shaking of the boards is dependent on the
student. It is important for students to recognize the relative nature
of quantifying an earthquake. The Richter Scale is a mathematical
representation of the intensity of an earthquake, but your students
cannot simulate this.
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