VOCABULARY
Fault:
a break or frac-
ture in Earth’s crust
along which movement
has taken place.
Friction:
mechanical resistance to
the motion of objects or bodies that
touch.
Stick-slip movement:
a jerky,
sliding movement along a surface. It
occurs when friction between the two
sides of a fault keeps them from
sliding smoothly, so that stress is
built up over time and then suddenly
released.
Variable:
in a scientific experiment,
the one element that is altered to test
the effect on the rest of the system.
Q
Marking pen
Q
Scales
Q
Pine board, approx. 2.5 cm x 30 cm x 1.8 m (1 in. x 12 in. x 6 ft.)
Q
Several books to support one end of the board
Q
Protractor for measuring angles
Q
1 brick (optional)
PROCEDURE
Teacher Preparation
To assure success, construct the model ahead of time and rehearse the
activity. Then arrange materials for student models in a convenient
place.
A. Introduction
Elicit a definition of
fault
from the class, supplementing students’
information as necessary until the essential elements have been
covered.
Explain to 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 residual 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.
B. Lesson Development
1. Divide the class into working groups of at least four students each.
Distribute one copy of Master 2.1a, 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 (4.5 in. x
11 in.) in size.
b. Wrap one of the strips around the box and secure it around the sides
(not the top and bottom) with two rubber bands. (See diagram.) Weigh
and record box mass.
A G U
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F E M A
40
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E I S M I C
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L E U T H S
