TEACHING CLUES AND CUES
In the EPIC Data Base,
times are given in 24-
hour Universal Time
(UT) and carried out to
A. Introduction
From the other activities in this lesson, students have discovered
where earthquakes occur worldwide and how seismologists locate
them. Ask the class where earthquakes occur on the North American
continent. Most of them will probably name California. Accept this,
but try to elicit other locations as well. Some may be aware of the New
Madrid, Missouri, earthquakes in the 19th century, or of other
earthquakes close to home.
Remind students that earthquakes sometimes occur where volcanoes
are present. Ask: Where on the North American Continent are
volcanoes found? Students will probably identify the western United
States. Tell them that at one time volcanoes erupted in the eastern part
of the continent. The famous Palisades, a line of steep cliffs along the
Hudson River in New York and New Jersey, were caused by volcanic
activity. Tell students that in this activity they will use selected data
from the U.S. Geological Survey to plot the locations of earthquakes
of magnitude 4 or larger that occurred during 1990 on the North
American continent.
B. Lesson Development
1. Divide the class into groups of three or four students each.
2. Distribute copies of Master 3.4g, the blank map, and the epicenter
strips. Review latitude and longitude if necessary.
3. Have students plot the locations of the epicenters on their maps.
Give these directions:
a. As you locate each point, mark it with a small dot. Then write the
depth and magnitude of the earthquake next to it in small numbers.
b. When you finish, transfer your data to one of the three
transparencies of Master 3.4g, using the colored pens to code for
magnitude. Green will represent magnitude 4, blue magnitude 5, and
red magnitude 6 or greater. Mark each earthquake with an X in the
appropriate color.
4. When all the data have been plotted, stack the transparencies on the
overhead so you can display them simultaneously. Ask students to
comment on the pattern they observe, and compare it with their
findings in Activity One. Do they see a similar pattern? They should
see once again that earthquakes occur primarily near plate boundaries
(for the U.S., on the west coast) but are not limited to those areas. Is
there a pattern to the depth of the earthquakes? (The deepest quakes
occur at plate margins under continents. This pattern may not be
evident in this data.)
C. Conclusion
Remind students that these data are for one year only, and only for
earthquakes of magnitude 4 or greater. Have them discuss what they
would need to prepare an earthquake risk map for building codes or
insurance rates. (The obvious answer will be more data, but point out
to students some of the things they have already learned about
eight places—210117.90, for
example, which would be approxi-
mately 9:01 pm. In Master 3.4f they
have been shortened to four places
(2101).
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