TEACHING CLUES AND CUES
Deep-focus earthquakes
produce seismograms
very different from those
produced by shallow-
A. Introduction
Tell students that earthquakes occur in many locations and at different
depths. The study of earthquakes has provided most of what we now
know about the Earth’s structure. The patterns of their locations
provided much of the evidence that led geologists to hypothesize the
existence of plates.
B. Lesson Development
1. Divide the class into the same groups as for Activity One of this
lesson. Give each group one copy of Master 3.4d, Central Japan (two
pages, left and right) and Master 3.4e, Selected Earthquakes Since
1980, Japan. Instruct students to cut the left page of Master 3.4d along
the dotted line and tape it to the right page.
2. Divide the list of earthquakes into as many equal sections as you
have student groups, and assign one section to each group. It is not
necessary to use all the earthquakes. (If you have eight groups, each
will be responsible for 10 quakes.) Instruct students to begin plotting
their assigned quakes from Master 3.4e on the map of Japan by
latitude and longitude, then mark each epicenter with its reference
number, depth, and magnitude. Point out that 10 small squares on their
maps represent one degree of longitude and one degree of latitude.
3. When the first group has located all the quakes on its own section of
the list, it can transfer those locations to the hanging map. Other
groups can follow as they complete their sections. Give these
instructions for transferring data to the hanging map:
a. For each earthquake, take two beads of the same color. Use one
bead to represent the epicenter of each quake and the other bead to
represent its focus.
b. Locate the latitude and longitude of the first quake on the hanging
map. Mark its epicenter and punch a hole all the way through the
cardboard with the nail. Thread dental floss through the small bead
and tie a knot to hold the bead at the correct location. Calculate the
distance below the map at which the large ball will be hung (the depth
of the focus) by letting 1 cm stand for 5 km. The bead representing
earthquake #1 will hang 2 cm below its epicenter. Tie knots to hold
the beads in place.
c. Repeat this procedure until all the quakes have been plotted on the
map. When students have finished, invite them to view this 3-D plot
from many directions.
4. Ask:
focus earthquakes. EPIC and some
of the other non-print media sources
listed in the resources for Units 2
and 3 can provide examples of both
for you to show your students.
Q
What pattern do you see? Where do the earthquakes concentrate?
(on the lower right)
Q
What do you think is happening to the Earth’s crust in this area?
(Old crust is being broken off and pushed under the edges of the
plate, in the process geologists call subduction.)
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