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Measuring Earthquakes
ACTIVITY OVERVIEW
MODEL
I
Students model how a seismograph records earthquakes as they explore the relationship between earthquakes and plate boundaries.
KEY CONCEPTS AND PROCESS SKILLS
(with correlation to NSE 5–8 Content Standards)
1.
Creating models is one way to understand and communicate scientific
information. (Inquiry: 1)
2.
The continents are part of large lithospheric plates that have moved over
geological time and continue to move at a rate of centimeters per year.
(EarthSci: 1, 2)
3.
The movement of the earth’s plates can produce earthquakes and volcanoes,
and result in the formation of mountains over geological time. (EarthSci: 1)
KEY VOCABULARY
earthquake
plates
Richter scale
seismograph
seismogram
fault (optional)
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Activity 43 • Measuring Earthquakes
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
Scoring Guide: GROUP INTERACTION (GI)
1
Transparency 43.1, “Earthquake Strength”
1
overhead projector
For each group of four students
*
1
seismograph model
1
black marker
4
sheets of plain paper
8
toothpicks
For each student
*
1
pair of safety goggles
1
Scoring Guide: GROUP INTERACTION (GI) (optional)
*Not supplied in kit
This activity provides an opportunity to assess students on their ability to work in
groups. You can use the GROUP INTERACTION (GI) Scoring Guide to assess students’ ability to work as a group and respectfully consider each other’s ideas. Masters for Scoring
Guides can be found in Teacher Resources III: Assessment.
SAFETY
Remind students to pay attention to the other people and objects in the vicinity when
moving the different parts of the seismograph model. If students have long fingernails that could potentially scratch the hands of other students, demonstrate how to
hold the seismograph so that nails are pointed away from the hands of other group
members.
TEACHING SUMMARY
Getting Started
1.
Introduce the seismograph model.
Doing the Activity
2.
(GI ASSESSMENT) Students model earthquakes.
Follow-Up
3.
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Apply observations from the model to plate tectonics.if this works)
Measuring Earthquakes • Activity 43
BACKGROUND INFORMATION
Earthquakes
An earthquake is the sometimes violent vibration of the earth’s surface that follows a
release of energy in the earth’s lithosphere. This energy can be generated by a sudden
dislocation of segments of the lithosphere, by a volcanic eruption, or even by manufactured explosions. The largest earthquakes, and many smaller ones, are a result of
movements within the rocks of the lithosphere. The tectonic plates that form the outer
surface of the earth continue to move. Sometimes the movement is gradual, while at
other times, the plates are locked together, unable to release accumulating energy.
Eventually the plates break free, causing an earthquake.
The lithosphere may first bend and then, when the stress exceeds the strength of the
rocks, break and “snap” to a new position. In the process of breaking, vibrations
called seismic waves are generated. These waves travel outward from the source of the
earthquake along the surface and through the earth at varying speeds, depending on
the material through which they are moving. Earthquakes can be destructive in many
ways. Earthquakes that occur beneath the ocean floor sometimes generate tsunamis,
like the one that affected southeast Asia in December 2004. Other earthquakes can
cause landslides or liquefaction of the soil.
The region where an earthquake’s energy originates is known as the focus, with the
focus of most earthquakes occurring in the earth’s crust or upper mantle. Deep earthquakes may originate up to 700 kilometers (435 miles) below the suface, which is still
only 10% of the depth to the center of the earth’s core. Earthquakes are also commonly located by their epicenter, which is the point on the earth's surface directly
above the focus.
A fracture in the earth’s surface, along which two blocks of the crust have slipped, is
known as a fault. Faults are usually described by how the blocks move in relation to
each other. Geologists have found that earthquakes tend to reoccur along faults,
which reflect zones of weakness in the earth's crust and which are often found on or
near tectonic plate boundaries.
Scientists use machines called seismographs to measure earthquakes. A seismograph
is designed to address that fact that when the ground moves, so does the seismograph. These machines usually contain a large suspended mass (which tends to
remain at rest) attached to a recording structure. A seismograph records the difference in motion between the earth’s surface and the suspended mass. Since a single
seismograph can only record motion in a single direction, most sites contain several
seismographs (including one that can measure vertical motion).
REFERENCES
Shedlock, Kaye M., and Pakiser, Louis C. (1994) Earthquakes. Washington, D.C.: U.S.
Geological Survey.
U.S. Geological Survey. (August 17, 2005) Earthquake Hazards Program: Earthquakes:
Frequently Asked Questions (website). U.S. Department of the Interior. Retrieved August
2005 from earthquake.usgs.gov/faq/plates.html
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Activity 43 • Measuring Earthquakes
TEACHING SUGGESTIONS
GETTING STARTED
1. Introduce the seismograph
model.
Ask students if any of them have experienced an
earthquake. If so, have the student describe what it
felt like. (If you are in an earthquake-prone area, it
is likely that many students will want to share their
experiences. You may want to limit this discussion
to no more than 5 minutes.) If no one in your class has
experienced an earthquake, you may want to share
the following U.S. Geological Survey description:
“Generally, during an earthquake you first will
feel a swaying or small jerking motion, then a
slight pause, followed by a more intense rolling
or jerking motion. The duration of the shaking
you feel depends on the earthquake's magnitude, your distance from the epicenter, and the
geology of the ground under your feet.”
Use the Student Book introduction to review the
concept of a seismograph and a seismogram.
DOING THE ACTIVIT Y
2.
(GI ASSESSMENT) Students model
earthquakes.
Demonstrate how to set up the seismograph model
and then explain how to use the model to produce a
seismogram. The model requires a large surface to
support all of the moving parts. If you do not have
large tables available, you may want to have students work with the model while sitting on the
floor. In either case, remind students to be aware of
the location of other students and to use the model
correctly and safely.
You may also want to review seating arrangements
so that each role is conducted properly. The illustration after Procedure Step 2 of the Student Book illustrates how students can work together to use the
seismograph model. The two people pushing Plates
A and B (the Plate Holders) should be seated next to
each other. The Data Recorder should sit at a right
angle on their right-hand side (so that the paper
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tray is easily pulled). The Observer should sit on
their left-hand side. This ensures that no one is
facing Plate B as it is pushed away from the Plate B
Holder.
Some students may be concerned that they will not
be able to conduct their role properly, but use this as
an opportunity to explain this as the reason that
each student will perform his or her role two times
in a row. Each group of four will conduct a total of
eight trials, and every student will have a chance to
produce two seismograms by pushing Plate B twice.
Although it is the Data Recorder who will ensure
that the seismogram is recorded, the actual data
will be a result of the Plate B Holder pushing the
model and breaking the toothpick. It is not necessary for every trial to produce valid data (i.e. a
“good” seismogram).
Distribute the materials and have students complete the Procedure. You may wish to assess how
well students are working together using the GROUP
INTERACTION (GI) Scoring Guide.
Remind students to write their observations of the
seismograph model, the seismogram, and the force
required to break the toothpick in their science
notebooks. Encourage them to compare their observations to previous trials.
FOLLOW-UP
3.
Apply observations from the model to plate
tectonics.
Have students take a few minutes to discuss Question 1 in their groups. Then, hold a full class discussion of Questions 1 and 2 and review the model.
Display Transparency 43.1, “Earthquake Strength,”
and point out that there are different ways of measuring the strength of an earthquake. One approach
is quantitative and the other qualitative. Introduce
or review the Richter scale, which is used to quantitatively rate the strength, or magnitude, of an
earthquake at the point where the rocks break, and
the Mercalli scale, which is used to qualitatively
rate the damage done, or intensity, of the earthquake at a particular place on the surface. Each
increase of 1 on the Richter scale is equal to a
Measuring Earthquakes • Activity 43
30-fold increase of released energy. Point out that
there is a general correspondence between the
Richter and Mercalli scales. However, an earthquake with a higher Richter value can do little or no
damage if it occurs far enough away and vice
versa—an earthquake with a lower Richter value
can do considerable damage if it occurs very close
by. Ask, Did your seismograms provide you with
enough information to compare the strength of your
“earthquakes?” Answers will vary. Some students
may observe that the wavy line was more pronounced when the “earthquake” was more intense,
while others may not see any significant relationship, except that a wavy line (vs. a straight line)
was recorded when the “earthquake” occurred
(when the toothpick broke).
2. a. What did each half of the seismograph model
represent?
A plate on the earth’s surface.
b. What did the toothpick represent? (Hint: Reread
the introduction to this activity.)
Underground rock. When rock layers that
are “stuck” together by the high pressures
beneath the earth’s surface, they tend to
resist motion until a critical force is applied.
c. When did an “earthquake” occur? It occurred
when:
• the Data Recorder began pulling the paper tray.
• Plate B was first pushed.
• the toothpick broke.
The “earthquake” occurred when the toothpick broke.
Ask, How can modeling earthquakes help you understand plate tectonics? Explain that the movement of
the lithospheric plates requires enormous amounts
of energy and that this energy can build up. When
it is released all at one time, this energy causes
earthquakes. This explains the frequency of earthquakes along plate margins.
d. What type of plate movement did you simulate?
• plates colliding
• plates sliding past each other
• plates pulling apart
The activity simulated plates sliding past
each other.
SUGGESTED ANSWERS TO QUESTIONS
1.
3.
What similarities and differences did you
observe among your group’s 8 seismograms?
Student responses will vary. In general, several
of the seismograms should show a straight line,
followed by one or more waves, and again more
of the straight line. This corresponds to the initial pulling by the Data Recorder (when there
was no plate movement), followed by the breaking of the toothpick as Plate B was pushed past
Plate A, and finally a straight line again as the
sudden motion ended.
Students are likely to have seismograms with
varied kinds of data, including situations in
which very little data was recorded (the pen was
no longer touching the paper), the mark went
off the paper (an extremely violent movement
of the plates), a single straight line (either
because the Data Recorder forgot to say “Start,”
or because the Plate B Holder could not break
the toothpick before the length of paper ran
out), and so on.
Describe what the seismogram looked like
a. when there was little or no movement
It recorded a straight line.
b. when the toothpick broke.
It recorded one or more wavy lines that were
perpendicular to the straight line.
4.
This activity modeled an earthquake
occuring along a plate boundary. What
do you think are the strengths and weaknesses of this
model?
Strengths of this model include the sudden
“earthquake” motion that occurs when the
toothpick snaps, the recording of this movement
as a seismogram, and “earthquakes” resulting
from the movement of “sliding plates.” Weaknesses of this model include the use of people’s
hands to move the plates and the paper, the use
of a toothpick to provide resistance instead of
rock, and the lack of quantitative data.
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©2012 The Regents of the University of California
Earthquake Strength
Issues and Earth Science • Transparency 43.1
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