2. As
you point to each of the figures, 1 through 6, read the
accompanying text aloud to the class.
3. Divide the class into working groups of three to five students each.
Distribute paper for covering desks, clay, knives, rollers (if available),
and one copy of Master 2.3e, Sag Pond Template, to each group. Give
these directions:
a. Pat or roll two clay patties, one white and one red, to a thickness of
about 1 cm (.3 in.). Using the template provided, trim the patties to fit
within the confines of the circle marked on the grid, then remove them.
b. Now make two sag pond peat deposits, one white and one blue, each
0.5 cm thick and sized according to the small sag pond template at the
upper left of the grid.
c. Place the large white layer on the grid template between A-B and
C-D as outlined. Place the blue clay sag pond deposit on top of this first
layer, aligning the long axis of the sag pond layer with fault line E-F,
and centering it between A-B and C-D. Out both layers along the fault
line E-F. Lift the A-B side and raise it to the position marked Offset
Line.
d. Place the red layer of clay over the offset layers and center a second
sag pond deposit (the white one), as in the stop above. Cut (or trench,
as geologists say) all the clay patties along line A-D. Carefully separate
the sides so you have a good cross-section view and draw a cross
section of each side. Compare the layers on the two sides of the fault
A-D.
C. Conclusion
Build a class discussion around these questions:
Q
How is the principle of superposition applied in this activity?
Q
How is the principle of crosscutting relationships applied in this
activity?
Q
How is the principle of uniformitarianism applied in this activity?
Q
What does the difference in thickness and spacing of the peat layers on
the two sides of the fault indicate? (that the terrain has been disturbed)
Q
In what year do we know an earthquake occurred on this fault? (1857)
PART TWO
D
ITCH
C
REEK
P ROC E DUR E
A. Introduction
Tell students: By using age-dating methods on peat deposits and very
old stream channels, geologists can determine earthquake recurrence
intervals dating back several thousands of years. The shorter its recur-
rence interval, the more likely an area is to experience an earthquake in
your lifetime. This activity is another illustration of the principles you
saw in the last one. Like the previous activity, it is based on a
generalized model of a strike-slip fault.
A G U
/
F E M A
71
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E I S M I C
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L E U T H S
