VOCABULARY
Amplitude:
a measure-
ment of the energy of a
wave. Amplitude is the
displacement
ACTIVITY TWO
R
ICHTER
M
AGNITUDE
RA T I ONA L E
To determine Richter magnitude, we need to know both the maxi-
mum wave amplitude as recorded on the seismogram and the distance
between the seismograph station and the earthquake, which can be
calculated by finding the lag time.
F OCU S QU E S T I ON S
How do scientists determine the size of an earthquake?
OB J E C T I V E S
Students will:
1. Interpret seismograms to calculate Richter magnitude.
2. Compare Richter magnitudes from several seismograph stations for
the same earthquake.
MA T E R I A L S
Q
Transparency made from the first page of Master 3.3d, Five
Seismograms
Q
Overhead projector
Q
Transparency marker
Q
Copies of Master 3.3d, Five Seismograms (simplified) (3 pages),
one set for every two students
Q
Copies of Master 3.3e, Distance, Magnitude, Amplitude, one for
every two students
Q
Paper and pencils or pens
Q
Rulers or straightedges
Q
Transparency made from Master 3.3e, Distance, Magnitude,
Amplitude
of the medium from zero or the
height of a wave crest or trough from
a zero point.
Duration:
the length of time that
ground motion at a given site shows
certain characteristics. Most earth-
quakes have a duration of less than
one minute in terms of human
perceptions, but waves from a large
earthquake can travel around the
world for hours.
Lag time:
the difference between
the arrival time of P waves (T
p
) and
S waves (T
s
).
Magnitude:
a number that charac-
terizes the size of an earthquake by
recording ground shaking on a
seismograph and correcting for the
distance to the epicenter of the
earthquake. Magnitude is expressed
in Arabic numbers.
Richter magnitude:
the number that
expresses the amount of energy
released during an earthquake, as
measured on a seismograph or a
network of seismographs, using the
scale developed by Charles Richter
in 1935.
Seismogram:
the record of earth-
quake ground motion recorded by a
seismograph.
Q
Transparency made from back of Master 3.3d (page 2), Richter
Data Table, Answer Key
P ROC E DUR E
A. Introduction
Tell students that Richter magnitude is a quantitative measure that is
related to the amount of energy released during the earthquake and is
not attracted by factors such as population, building materials, or
building design. Ask them to name some other kinds of quantitative
measures (minutes, hours, centimeters, dollars). Be sure they under-
stand the distinction between quantitative and qualitative description.
B. Lesson Development
1. Divide students into pairs. Give each pair a ruler and copies of
Master 3.3d, Five Seismograms, and Master 3.3e, Distance,
A G U
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F E M A
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E I S M I C
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L E U T H S
