Plate Tectonic - Earthquakes (4)
 Lab 

   
OBJECTIVES:
  • Comparing the relative differences between high and low intensity earthquakes.
  • Testing how different shapes react during an earthquake
VOCABULARY:
  • intensity
  • Mercalli Scale
  • not resistant
  • resistant
  • Richter Scale
  • semi-resistant
MATERIALS:
  • Shaker Boards
  • marbles
  • large plastic container lids
  • Styrofoam cups
  • building sets

Students determine the damage caused by seismic waves.


San Francisco, 1906

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:

  1. Explain the factors that contribute to earthquake damage. Emphasize that the shape and construction of a building are important factors.
      
  2. 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 ˝ inch thick.
      
  3. 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.
      
  4. 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.
      
  5. 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.
      
  6. 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).
      
  7. 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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