Stick-Slip Movement (FEMA Activity 2.1)

Learning Objectives:
1. Students will model the frictional forces involved in the movement of a fault 2. Students will measure movement, calculate averages, and plot and graph information. 3. Students will compare and contrast the variables of fault strength and potential energy.

Materials, equipment and/or facilities:
Seismic Sleuth Master 2.1a, Stick-Slip Data Sheet Sandpaper sheets: grit 60, 120, and 400 Scissors Strapping tape Sugar cubes Thumbtacks Large paper clips Meter stick String Dowel or empty paper towel tube Marking pen Scales Pine board (1"x12"x6') Protractor Brick

Sequence and duration of each part of lesson:
To assure success, construct the model ahead of time and rehearse the activity. Then arrange materials for studetn models in a convenient place.

Introduction (10 minutes)
Elicit a definition of a fault from the class, supplementing studetns' information as necessary until the essential elements have been covered.

Explain to the students that when an earthquake occurs and movement begins on a fault plane, the movement will not proceed smoothly away from the focus. Any change in the amount of friction along the fault will cause the fault movement to be irregular. This includes changes along the length of the fault and with depth, changes in rock type and strength along the fault, and natural barriers to movement, such as changes in the direction of the fault or roughness over the surface of the fault plane.

Rupture along a fault typically occurs by fits and starts, in a type of sporadic motion that geologists call stick-slip. As energy builds up, the rock on either side of the fault will store the energy until its force exceeds the strength of the fault. When the residula strength of the fault is exceeded an earthquake will occur. Movement on the fault will continue until the failure reaches an area where the strength of the rock is great enough to prevent further rupture. In this manner, some of the energy stored in the rock, but not all of it, will be released by frictional heating on the fault, the crushing of rock, and the propagation of earthquake waves.

Lesson Development (30 minutes):
1. Divide the class into working groups of at least four students each. Distribute one copy of Stick-Slip Data Sheet to each group. Tell students that they are going to model a process, record data for each trial, and then vary the process, changing only one variable at a time.

2. Allow groups to assemble their materials, then give these directions:

a. Fold each piece of 120-grit sandpaper in half lengthwise and cut, to produce eight strips of sandpaper, each 11.5 cm x 28 cm in size.
b. Wrap one of the strips around the box and secure it around the sides (not the top and bottom) wiuth two rubber bands. Weigh and record box mass.
c. Tape the seven remaining strips of 120-grit sandpaper into one long strip. (Be sure to use tape only on the back of the sandpaper.) Now attach the sandpaper lengthwise down the cetner of the pine board, using two thumbtacks at each end and being sure the sandpaper is drawn tight.
d. Attach one paper clip to one of the rubber bands around the box.
e. Tie one end of the string onto another paper clip and place a mark on the string about 1 cm from the clip. Use one rubber band to joing the paper clip on the box with the paper clip on the string. Tie the free end of the string around the dowel or paper towel roll.
f. Tape the meter stick onto the sandpaper strip on the board.
g. Position the box at one end of the board so it is centered on teh sandpaper. Use books to raise the other end of the board approximately 10 cm. Measure and record the height.
h. Gently roll the string onto the dowel until the string lifts off the paper and becomes taut. Note the location of the mark on the string rrelative to the meter stick. Take care to keep the dowel in the same position during rolling and measurement.
i. Continue to roll the string onto the dowel until the box moves. The box should move with a quick jumping motion. Record the new location of the mark on the string (the distance the box moved) on the data table. Continue rolling up the string and recording jump distance until the box hits the meter stick. The meter stick can be pulled upwards to allow the box to continue to be pulled.
j. Subtract the beginning measurement from the ending measurement or add up the jump measurements to find out how far the box moved. Divide by the number of jumps to calculate an average jump distance.