VOCABULARY
Modified Mercalli scale
of 1931:
a qualitative
scale of earthquake
effects that assigns an
P ROC E DUR E
A. Introduction
Ask students on what basis scientists classify earthquakes. Many
students may be aware of the Richter Scale and some may be aware of
the Mercalli Scale. Explain that the Richter Scale is a quantitative
measure of the energy released by an earthquake, while the Mercalli
Scale is a qualitative measure of the amount of damage it does. The
Richter rating is referred to as a quake’s magnitude, and the Mercalli
rating is referred to as its intensity. The original Mercalli Scale was
developed in 1902 by the Italian geologist Giuseppi Mercalli. Wood
and Neumann adapted it to U.S. conditions and introduced the
Modified Mercalli Scale in 1931. Both the Richter and the Mercalli
scales have their uses. Have students give other examples of
quantitative vs. qualitative measurements.
intensity number to the ground
shaking for any specific location on
the basis of observed effects.
Mercalli intensity is expressed in
Roman numerals.
Qualitative:
having to do with
perceived qualities; subjective.
Examples: large, cold.
Quantitative:
having to do with
measurable quantities; objective.
Examples: 10 m long, 5º C.
B. Lesson Development
1. Project the transparency of the Modified Mercalli Scale and
distribute student copies. Share the background information about the
two earthquake scales (back of Master 3.3a) with the class and discuss
the importance of intensity in establishing building codes. Briefly
discuss each of the values assigned on the Mercalli scale. If some
students in the class have experienced an earthquake, ask them to
estimate its intensity from the scale.
2. Have the students compare and contrast the differences between the
two types of measurements. Ask: Why do you think magnitude is
more often reported than intensity? (Most earthquake-prone areas have
equipment already in place to determine magnitudes, so this
measurement can be quickly established. Mercalli ratings are
sometimes not arrived at until several days later, when a full estimate
of the damage can be made.) Point out to students that the lack of
news accounts reporting intensity does not diminish its value to city
planners and engineers.
TEACHING CLUES AND CUES
Have students listen
carefully for significant
phrases in the callers’
reports. They will be
found in the Mercalli scale (Master
3.3a).
It may take class discus-
sion to reach agreement
on the values for some
of the reports. Have
3. Tell students that in this activity they will be using data adapted
from reports of an earthquake that struck California in 1971.
Distribute copies of Master 3.3b, Wattsville Map. Appoint one student
to be Jake Wilde, the television news anchor, and tell the other
students that they are citizens of Wattsville and the surrounding area.
The town has just been struck by an earthquake.
4. Distribute the strips cut from Master 3.3c and have students take
turns reading them in order, starting with the news anchor’s report.
Distribute student copies of the script as well.
5. As each student reads a part, have the other students locate the site
of the report on their maps, scan the Modified Mercalli Intensity
Scale, and mark a Mercalli intensity in pencil next to the location.
6. After the last student has read, have students draw blue lines
enclosing areas with equal intensity ratings to develop an isoseismal
map. (They will be drawing a series of concentric lines.)
students read the descriptions on the
Mercalli scale carefully, and reread
them as necessary, checking with
the script as they proceed.
A G U
/
F E M A
163
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E I S M I C
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L E U T H S
