I N T R O D U C T I O N
3
In the first lesson, students will learn about the
movement of earthquake waves in our Earth and on its
surface. It was the study of this movement, by
Mohorovicic, Lehmann, and others, that developed
our current understanding of the interior of the Earth.
Activities illustrate the movement of P and S waves.
Background material on Love and Rayleigh waves is
also provided.
The second lesson in Unit 3 is built around
biographical sketches of three individuals who made
major contributions to our knowledge of the Earth’s
inner structure: the German meteorologist Alfred
Wegener, who amassed evidence for the controversial
theory of continental drift; the Croatian seismologist
Andrija Mohorovicic, who demonstrated the existence
of the discontinuity between crust and mantle that
bears his name; and the Danish seismologist Inge
Lehmann, who demonstrated the existence of the inner
core. A timetable of other relevant discoveries is
included as teacher background material.
Lesson 3 begins with a pair of activities that contrast
the two systems most commonly used to characterize
earthquakes—the Modified Mercalli scale, which
assigns a number on the basis of observed effects, and
the Richter scale, which assigns a number on the basis
of instrument readings. Students draw isoseismals on a
map in the first activity. In the second they compare
Richter magnitudes from several seismograph stations
for the same earthquake. In the third activity, they
practice reading seismograms.
Lesson 4 has three parts, moving from the worldwide
distribution of earthquakes to one seismically active
area of Japan and then home to the United States. At
all three stages, students plot actual earthquake data in
order to gain an experiential understanding of where
earthquakes occur. In the second activity they
construct a plot in three dimensions. Most students
will be surprised to learn that earthquakes are
everyday occurrences on a global scale, and that they
may originate from foci as deep as 700 km inside the
Earth—1/9 of the way to its center.
Like the previous unit, this one offers a variety of
experiences in scientific observation, computation, and
the application of social science principles. It also
presents factual information that will stand students in
good stead as consumers of media information and as
future property owners.
Social studies teachers may be especially interested in
the second lesson of this unit. Mathematics teachers
will find applications of algebra and geometry in many
of the others. The lessons in this unit can stand on their
own, but taken together, they provide an excellent
preparation for learning to mitigate the effect of
earthquakes on the human environment, in Unit 4.
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