7. Ask students to compare the world map you have just distributed
with the stacked transparencies. Ask:
Q
Can you detect any relationship between the locations of
earthquakes below 40 km and the outlines of Earth’s plates? (These
earthquakes occur under the continents on the landward side of
plate boundaries.)
Q
Do all the earthquakes occur at or near plate boundaries? (Some
earthquakes occur in places that seem unrelated to plate
boundaries.)
Q
Were any of the students correct in judging where earthquakes
occur most frequently, at the beginning of class?
8. Ask students to note how earthquakes are distributed among the
four geographic areas: north latitude/west longitude, north latitude/east
longitude, south latitude/west longitude, and south latitude/east
longitude. Ask them to speculate on the reasons for this distribution.
(The northeast quadrant has the highest concentration of quakes. The
main portion of the Ring of Fire is in this quadrant.)
TEACHING CLUES AND CUES
Don’t tell students how
to calculate the total;
challenge them to find a
way. One procedure
9. Remind students that the eight tables represent earthquakes that
occurred on just eight days. Ask them to count the total number of
quakes and estimate how many earthquakes occur each year. (Students
should calculate that more than 15,000 significant earthquakes occur
each year.)
10. Ask students where the world’s most powerful earthquakes have
occurred. Record their hypotheses, then place the transparency of
Master 3.4b on top of the others as a check. Ask students to predict
where major earthquakes will occur in the future.
C. Conclusion
Sum up in a discussion. Ask the class:
is for each group to report the
numbers on its map (Tables 1
through 8), then for students to add
the numbers and average them. The
average of 42 quakes a day, multi-
plied by 365, yields a figure of
15,630.
Q
Are people who live near the boundaries of major tectonic plates the
only ones who have to worry about earthquakes? Why or why not?
(No. The majority of earthquakes occur along plate boundaries, but
some quakes do occur within the plates.) Invite students to speculate
about the causes of intraplate earthquakes and faulting.
Q
Does the amount of damage an earthquake does depend only on its
magnitude? (No. Population density, soil conditions, building types,
and other factors determine the amount of damage. Students will
learn more about these factors in subsequent units.)
ADA P T A T I ON S AND E X T E N S I ON S
1. Obtain copies of Preliminary Determinations of Epicenters and have
students plot other kinds of data on fresh copies of the map, such as:
a. Earthquakes having magnitudes greater than magnitude 5 for (1) the
world; (2) a particular region of the country, or (3) a particular state or
local area.
b. Earthquakes that have caused the greatest damage or loss of life.
A G U
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F E M A
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