Modifying the original Earthquake Machine
M i c h a e l H u b e n t h a l , L a r r y B ra i l e ,
a n d J o h n Ta b e r
T
he large earthquakes off the coast of Sumatra, with
magnitudes (Mw) of 9.1 and 8.7 in 2004 and 2005,
have recently brought geophysics to the forefront
of the world’s attention. While the awe-inspiring
power of such events makes them a highly engaging topic
for many Earth science students, maintaining this interest
once the video footage of earthquake damage has ended
can be a challenge. Further, the nature of earthquakes
makes it difficult for students to collect, explore, and explain empirical data about earthquakes in the lab. The
Earthquake Machine Lite (EML), a mechanical model of
stick-slip fault systems, can increase student engagement
and facilitate opportunities to participate in the scientific
process. The model can be used to explore causes of earthquakes, distribution of event occurrence in time, distribution of event size, and earthquake prediction.
This article introduces the EML model and an activity that challenges ninth-grade students’ misconceptions
about earthquakes. The activity emphasizes the role of
models as part of the scientific enterprise and the concept
of scientific inquiry as a continuing, creative process of
explaining natural phenomena.
32
The Science Teacher
Over the past four years, the Incorporated Research Institutions for Seismology (IRIS) professional development
workshops (see “On the web,” at the end of this article)
have introduced teachers to the Earthquake Machine.
This model uses a brick, six-foot-long board, bungee
cord, and crank to represent the behavior of a stick-slip
fault system (Hall-Wallace 1998; Ringlein 2005). Assessments of IRIS workshops where the original model was
used revealed that participants enjoyed working with
the model and developed professionally from the experience, but follow-up surveys conducted one year later
revealed that only 15% of workshop participants actually
constructed and used the models when returning to their
classrooms (Hubenthal, Braile, and Taber 2003).
While this original Earthquake Machine provides an accurate, concrete representation of the abstract phenomenon
of earthquake generation, it seems possible that the cumbersome size, cost, and complicated construction makes it
accessible for only the most enthusiastic of Earth science or
physics teachers. Additionally, previous descriptions of the
Earthquake Machine have lacked fully developed exercises
or lesson plans to support teachers’ use of the model with
students. This means that if teachers want to use the original model with students, they need to develop their own
activities. Given their limited experience with the model
and the background content knowledge required to design
such exercises, many teachers from the workshop may
have simply determined that the effort was too great and
abandoned its use. This is unfortunate, as the Earthquake
Machine has tremendous potential to help students develop
deeper understanding of the nature of earthquakes.
Students use the Earthquake
Machine Lite to refine their
ideas about the causes of
earthquakes
To resolve this, we have created a simple, scaled
version of the original Earthquake Machine, resulting
in a scientifically comparable model. The EML version is significantly less expensive, can be assembled by
students, and can be packed as a class set in one large
shoebox (Figure 1, p. 34). To support this new design, a
series of activities have been designed around interesting
questions that can be explored using the model. In keeping with the recommendations of Hall-Wallace (1998),
these questions are broken into small hierarchical segments to enhance concept development for students and
to highlight the strengths and weaknesses of the model.
Significant opportunities for discussion and analysis
of both the process and results of each exercise are also
included. The activity described in this article will help
you and your students begin using the EML. A materials list and instructions for constructing the model are
available online (see “On the web”).
EML in perspective
The simplicity of the EML (Figure 2, p. 35) allows students to visualize the inputs and outputs of a fault system
and explore stick-slip fault behavior. The model’s wooden
block and sandpaper base represent an active fault section.
Students’ pull on the measuring tape attached to the block
is analogous to plate motions. For example, this represents
the downward pull of a subducting slab of lithospheric
plate, which is continuously adding tension to the system.
The rubber band represents the elastic properties of the
surrounding lithosphere, storing potential energy. When
the frictional forces between the block and sandpaper
are overcome, the block lurches forward with a stick-slip
motion. Students get to “experience” an earthquake by
seeing the release of energy stored in the rubber band and
feeling the propagation of seismic waves from an elastic
source (Bolt 2004). Visualizing the energy released by the
slip of the block is further enhanced by the motion of the
model building (Figures 1 and 2), made of strips of lightweight poster board or manila folder material.
While this model accurately simulates the strain energy that slowly accumulates in rock surrounding a locked
fault that is released in a sudden slip event, a process
known as the elastic rebound theory, it is ultimately a simplification of a complex Earth system (Bolt 2004). Such
simplifications must be understood to interpret the model
accurately. Therefore the relationship between the model
and reality should be clearly emphasized to students. This
is particularly important for high school–aged students,
who often think of physical models as copies of reality
rather than representations (Grosslight et al. 1991). For
example, students should discuss how the fault plane of
the model is horizontal due to the materials it is created
from, and that such faults do not exist in nature.
Not only does the model provide a physical perspective
on the generation of earthquakes, it also illustrates the
concept of an earthquake’s magnitude (Mw), and how the
Mw can be calculated based on the physical features of the
fault (Figure 3, p. 36). In our model, the length and width
of the fault section that slips during an event (represented
by the dimensions of the block of wood) as well as the
January 2008
33
Figure 1
The EML.
Building cut from file folder
4" x 4" wood blocks with
sandpaper glued to bottom
Rubber band
Belt sandpaper
Fabric measuring tape
Redefining an
earthquake activity
The following activity challenges students’ misconceptions about earthquakes, emphasizes the role of models as
part of the scientific enterprise, and highlights the concept
of scientific inquiry as a continuing, creative process of
explaining natural phenomena.
Establishing students’ current understandings
If you teach in a region where seismic hazard is low,
most students will have little personal experience with
earthquakes. For these students, the concept of the
ground suddenly beginning to tremble is largely unimaginable and fearful. Conversely, if you teach in a
seismically active area, your students may have extensive
personal experience with earthquakes. Still, the sudden
and frightening nature of experiencing an earthquake
can limit an observer’s ability to critically and carefully
develop an understanding of the event. Therefore for
most students, the very nature of earthquakes makes
them discrepant events.
Various media outlets represent earthquakes as mysterious events generated by unseen, uncontrollable forces deep beneath our feet. Media images show only that
that in a few seconds these forces can destroy everything
we believe permanent. Therefore, students as young
as third grade conclude that an earthquake is destruction, injury, and confusion, and the causes are unknown
(Ross and Shuell 1993). As students mature and receive
instruction about earthquakes and plate tectonics, most
34
The Science Teacher
David Tuttle
rigidity of Earth materials
(represented by the elasticity of
the rubber band) are constant
for every event generated.
The only factor that can vary
is the displacement or slip of
the fault. As a result, there is
a direct correlation between
the amount of slip of the block
and the moment magnitude
of the event. While aspects of
the mathematical relationship
discussed in Figure 3 (p. 36)
may be premature for some
students’ experience, all students will physically see this
relationship by noting how
much the “building” on top
of the block moves in relation
to the amount the block slips.
The further the block slips, the
more energy is released, and
the more violently the building shakes.
come to relate seismic activity to movement along plate
and fault boundaries. This concept of earthquakes seems
to stick with students—the vast majority of students enrolled in introductory college geology courses still associate the movement of tectonic plates with earthquakes
(Barrow and Haskins 1996; DeLaughter et al. 1998;
Libarkin et al. 2005).
While student definitions appear accurate at the
surface, it is quite likely that they lack a depth of understanding. This can be seen in the Delaughter et al.
study (1998), which found that the vast majority of
undergraduate students used plates or plate tectonics
when defining an earthquake. However, when these
same students were asked to explain why earthquakes
occur where they do, only 41% referred to the presence
of nearby faults or plate edges. These findings are consistent with previous research showing that children can
express scientifically acceptable statements while maintaining misconceptions (Cohen and Kagan 1979) and
can recite correct concept definitions without any true
understanding (Hoz et al. 1987).
Naïve beliefs and shallow understandings such as
these can present major obstacles to learning if instruction does not identify and address them explicitly (Snow
1989). An affinity-diagramming activity (Ray 1999) can
be used to help students identify their current beliefs before exploring them in the laboratory. Begin by asking
students to write their response to the question “What is
an earthquake?” on sticky notes. Then divide students
R e d e f i n i n g E a r t h q u a ke s a n d t h e E a r t h q u a ke M a c h i n e
Figure 2
photo courtesy of the authors
Students can visualize the inputs
and outputs of a fault system and
experience the release of seismic
waves from an elastic source.
into groups of five to eight; the first participant reads one
of his or her notes and places it on a flipchart. If other students have similar ideas, their notes are read and posted
near the original. Continue to call and sort ideas until all
notes are posted on the flipchart. Allow notes to be moved
as the group refines the relationships between their ideas
and arrives at a consensus on one definition that includes
the entire group’s ideas. This definition should be written
on the flipchart and serve as the group’s starting definition of an earthquake.
Introducing the need for and role of a model
“Today we want to explore your definition of an earthquake in the lab. Does this sound safe or possible?” Using questions such as this, establish the need for models,
as well as their role in the scientific enterprise. Questioning should lead students to understand that some
models allow scientists and students to explore large and
dangerous things, such as earthquakes, in a safe way.
Examples of common models that fit this reasoning,
such as model airplanes, can enrich student understanding and highlight how a model can allow us to learn
about certain aspects of reality (e.g., the shape and dimensions of an airplane, aerodynamics) but may also be
unlike reality in some ways (e.g., how the engines operate, how well the airplane actually flies) and may allow
insights unavailable in the real world.
Using the model to collect new information
Several studies (Duschl et al. 1992; Nottis 1995; Ross and
Shuell 1993) have established that traditional instruction
methods are not enough to allow students to construct coherent explanations about the causes of earthquakes, nor
to reduce students’ misconceptions about earthquakes.
Therefore the hands-on, inquiry-oriented approach of the
EML presents a nontraditional opportunity for students
and teachers. By developing a preliminary definition of an
earthquake, students have already clarified their current
cognitive framework. Information gained from working
with the model must fit into students’ working definition
of an earthquake, or else that definition must be modified
to accommodate the new information. Working in groups
of two or three, students explore the model, record their
observations, and compare these against their current assumptions (see the student lab worksheet, Figure 4, p. 36).
Exploring the model in this way establishes a firm foundation that will allow students to use the EML to collect
and analyze empirical data in future exercises.
Reflecting on the exercise
Following the exercise, many hands will respond to the
question “How many groups have modified their definitions of an earthquake as a result of the lab activity?” In
the small groups used for the affinity-diagramming exercise, students should examine the differences between
their original and new definitions. Then the class should
discuss what caused their responses to change. During
this discussion, explicitly emphasize the relationship between students’ experiences and the creative, continuous
process of generating new scientific knowledge. This
discussion should also cover the role of the model as a
method of generating new insights and understandings.
For a quick summative assessment of the lesson, show a
few seconds of CNN video footage of earthquake effects
on a building (see “On the web”). Students can use their
new definitions of earthquakes to explain the footage in
a brief written summary. Summaries should show a more
in-depth and accurate understanding of earthquakes and
their effects on humans.
Conclusions and extensions
The EML is an inexpensive, easy-to-build, scientifically
accurate representation of a stick-slip fault system that
will greatly enhance student engagement with and the
level of inquiry of a unit on earthquakes. This modified
model along with the activity presented represent a novel
method to help students increase their understanding of
the mechanics of earthquake generation, explore the role
of models in the scientific enterprise, and gain experience
with scientific inquiry as a continuing, creative process. A
detailed lesson plan, keyed to the American Association
for Advancement in Science benchmarks and including
guiding questions throughout the activity, is available
online (see “On the web”). Also available is a second
EML activity emphasizing the collection of empirical
data about the frequency of event occurrence and energy
release. Once collected, this data can be compared with
global earthquake data, allowing students to explore the
randomness of earthquake occurrence in time and eventsize distribution. n
January 2008
35
R e d e f i n i n g E a r t h q u a ke s a n d t h e E a r t h q u a ke M a c h i n e
Figure 3
Figure 4
Background equations for
understanding the EML.
Student lab worksheet: Redefining an
earthquake.
Seismic moment (Mo) is a measure of the size of an earthquake
based on the physical characteristics of the fault and can be
determined either from seismograms or fault dimensions.
Mo = L x W x D x µ or Length x Width x Displacement (Slip) x
Rigidity (index of an elastic body’s resistance to shear). L, W,
and D are given in cm; for typical Earth’s crust, the rigidity is
usually assumed to be ~3.2 x 1011 dynes/cm2.
Directions: Position the block at one end of the sandpaper.
Using a slow, steady pulling motion, pull the measuring tape
through the eyelet until the block moves at least five times.
1.Draw three comic strip frames depicting what a video camera
inside the paper office building might have recorded when
the block moved a small slip, medium slip, and big slip.
2.Was the shaking of the building a cause or a result of the
block moving?
3.Describe the sequence or steps leading up to the model
building shaking.
4.Where did the energy come from that made the block
move? Where might this same energy come from in the
Earth to create an earthquake?
5.After using the EML, refine your definition of an earthquake
based on the model.
6.What did this model allow you to see that you do not
think you would be able to see if looking at a real fault?
7.How might this model be like/unlike an actual fault and
earthquake?
8.How would you modify the model so that it no longer
stored energy? How do you think your modification would
impact the model’s overall operation?
9.What aspects of the model do you think could be measured
quantitatively? Describe how you could do this.
Moment magnitude (Mw) is based on the concept of seismic
moment where constants in the equation have been chosen so
the moment magnitude scale correlates with other magnitude
scales. Mw = (2/3) x log10 (Mo) – 10.7.
(From Stein and Okal 2005)
Michael Hubenthal ([email protected]) is an education specialist
and John Taber ([email protected]) is the education and outreach program manager, both at IRIS Consortium in Washington, DC: Larry
Braile ([email protected]) is a professor and department head in
the Department of Earth and Atmospheric Sciences at Purdue University in West Lafayette, Indiana.
References
Barrow, L., and S. Haskins. 1996. Earthquake knowledge and experiences of introductory geology students. Journal of College Science Teaching 26: 143–146.
Bolt, B. 2004. Earthquakes. 5th ed. New York: W.H. Freeman.
Cohen, M.R., and M.H. Kagan. 1979. Where does the old moon go?
The Science Teacher 46(8): 22–23.
DeLaughter, J., S. Stein, C. Stein, and K. Bain. 1998. Preconceptions
abound among students in an introductory Earth science course.
Eos Transactions 79(36): 429–36.
Duschl, R., M. Smith, S. Kesidou, D. Gitomer, and L. Schauble. 1992. Assessing student explanations for criteria to format conceptual change
learning environments. Paper presented at the annual meeting of the
American Educational Research Association, San Francisco.
Grosslight, L., C. Unger, E. Jay, and C.L. Smith. 1991. Understanding models and their use in science: Conceptions of middle and
high school students and experts. Journal of Research in Science
Teaching 28: 799–822.
Hall-Wallace, M. 1998. Can earthquakes be predicted? Journal of
Geoscience Education 46: 439–49.
Hoz, R., Y. Tomer, D. Bowman, and R. Chayoth. 1987. The use of
concept mapping to diagnose misconceptions in biology and Earth
sciences. In Proceedings of the Second International Seminar: Misconceptions and Educational Strategies in Science and Mathematics, ed.
J.D. Novak, 215–256. Ithaca, NY: Cornell University.
Hubenthal, M., L. Braile, and J. Taber. 2003. Assessing the IRIS
professional development model: Impact beyond the workshop.
Eos Transactions 84(46). Fall Meeting Supplemental Abstract
ED21C-1223.
Libarkin, J., S Anderson, J. Dahl, M. Beilfuss, and W. Boone. 2005.
36
The Science Teacher
Qualitative analysis of college students’ ideas about the Earth:
Interviews and open-ended questionnaires. Journal of Geoscience
Education 52: 17–26.
Nottis, K. 1995. The effective use of analogies in Earth science.
Ph.D. diss., University of New York at Buffalo.
Ray, R.G. 1999. The facilitative leader: Behaviors that enable success.
Upper Saddle River, NJ: Prentice-Hall.
Ringlein, J. 2005. Connecting earthquakes and violins. The Science
Teacher (72)8: 24–29.
Ross, K., and T.J. Shuell. 1993. Children’s beliefs about earthquakes.
Science Education 77(2): 191–205.
Snow, R.E. 1989. Toward assessment of cognitive and conative structure in learning. Educational Researcher 18(9): 8–14.
Stein, S., and E. Okal. 2005. The 2004 Sumatra earthquake and
Indian Ocean tsunami: What happened and why. The Earth Scientist 21(2): 6–11.
On the web
CNN video footage: www.cnn.com/TECH/9509/japan_seismology
EML materials list and instructions: www.iris.edu/edu/EQlite
Activity1.htm
EML animations and lesson plans: www.iris.edu/about/ENO/
aotw/archive/1
IRIS professional development workshops: www.iris.edu/edu/PD.htm