Using Models to Develop Deep Understanding of Earthquakes
NICOLE LADUE (email@example.com) is an assistant professor in the Department of Geology and Environmental Geosciences at Northern Illinois University, DeKalb, Illinois; MICHAEL HUBENTHAL (firstname.lastname@example.org) is a senior education specialist at teh IRIS Consortium, Washington DC; and GLENN DOLPHIN (email@example.com) is the Tamaratt Teaching Professor in Geoscience, University of Calgary, Calgary, Alberta.
Earthquakes are a popular topic with both students and teachers. Their unpredictable nature and potentially catastrophic effects command attention and pique curiosity. As instructors, it is common for us to take advantage of earthquakes as seismological "teach-able moments" (www.iris.edu/hq/retm). However, we are also responsible for developing our students' fundamental understanding of "how" and "why" earthquakes occur and how they fit within the larger Earth system.
Research into students' learning (National Research Council, 2000) clearly indicates that accomplishing this task requires more than a few lecture notes on slides. Incorporating hands-on/minds-on learning into an introductory seismology unit has traditionally focused on two activities: the earthquake location lab and hand plotting of epicenters to illustrate plate boundaries. While these two activities enable students to use earthquake data (seismograms and event data) and illustrate seismological concepts (e.g., S waves travel slower than P waves and most earthquakes occur along plate boundaries), they tend to be instructionally inefficient; both could be more efficiently conveyed using alternative methods. Instead, instructors need to develop and deliver instruction that encourages students to think deeply about the earthquakes themselves, to consider more than shaking and damage and explore the underlying physics from local, regional, and global scales to develop an explanatory mental model for these natural hazards.Designing such instruction requires educators who understand more than just the science content, especially given the abstract nature of most topics related to earthquakes. In this article, we highlight advances in our understanding of learners' needs, discuss appropriate pedagogies that encourage students to think deeply about Earth processes, and introduce instructional tools for teaching about abstract earthquake concepts.
Working with Models
Research about how people learn tells us that students benefit from working with models. Models can represent structures and processes in a concrete or abstract way, using static to dynamic relationships (see examplesof models in Table 1, p. 2) (Gilbert, 2011; Boulter and Buckley 2000). Even physical gestures (e.g., when geologists move their hands together with one going under the other to describe subduction) are a type of dynamic physical model. Models can make abstract ideas tangible, and to use models effectively in the classroom we need to: (1) help students map the structures andprocesses from the model to the real world, (2) help them draw inferences about the model, and (3) help them identify the limitations as well as the strengths of the model (Gentner and Smith, 2012). The goal is to support students in identifying the causal mechanisms underlying the structures and processes associated with earthquakes. (See the online extra in this issue by LaDue, Hubenthal, and Dolphin for more on educational research and the challenges of learning about earthquakes.)
A Model Sequence That Builds Abstract Reasoning
Each of the models presented in this special issue has been designed to illustrate several aspects of the elastic rebound theory, an explanation devised by geophysicist Harry Reid in 1910 for how energy is released during an earthquake. Each also addresses specific learner needs. However, each model has its limitations. Therefore, one of the most powerful aspects of this collection of models may be the use of some or all of them in combination. This approach allows students to view the content from different perspectives, to assess the strengths and weaknesses of the various models and therefore refine their own mental model of the concept (Ainsworth, 2006; Harrison and Treagust, 2000). In the pages that follow, we suggest a sequence for implementing the collection of models based on our experiences using them in the classroom and in research (Table 2).
The model sequence can be initiated by engaging students in an evidence-based problem such as the GPS data from the San Andreas fault shown in Figure 1. Begin by orienting students with the axes and, if necessary, data with error bars associated with it. Next, challenge them to summarize this ground motion data, and, like Reid who examined evidence of ground motion before and after the 1906 San Francisco earthquake when formulating his theory (see Dolphin in this issue, The History of Elastic Rebound Theory), propose possible mechanisms, based on their prior knowledge, to explain the data. They may use text and/or sketches to summarize their conclusions.
This approach offers multiple learning benefits. It mirrors the historic development of the theory and engages students in predictions about real data, revealing students' preconceptions while encouraging them to create their own explanatory analogies. This provides feedback to the teacher about how far student conceptions may be removed from the scientific consensus explanation.
Once students have developed a hypothesis explaining the ground motion data, engage them in a discussion about what is in the ground. They may have direct personal experiences with digging, seeing quarries, construction sites, caves or exposed bedrock in outcrops or roadcuts. The ultimate discussion goal is to lead students to recognize that the outer layer of Earth is comprised largely of rocks. Note that GPS stations are installed into this layer of bedrock and that the rocks deep underground are generally quite similar to those we see at or near the surface.
The stage is now set to employ the marble tongs demonstration (see Hubenthal in this issue, Bending Rocks in the Classroom). This demonstration allows students to both see and feel that rocks are indeed elastic, despite their prior experiences with them as rigid objects. Following the use of the tongs, students should reflect on data from the beginning of the earthquake lesson. Ask students to consider how the demonstration might relate to the data and to develop their own explanatory hypothesis for how such data could be generated. Students should meet in small groups to discuss their explanations.
Once students have had an opportunity to refine their initial hypotheses in small groups, the asperity model (see LaDue and Schwartz in this issue, Teaching Fault Aspertities with Spaghetti) can be introduced. This simple model illustrates how stress on rocks can result in deformation of the rocks on either side of the fault. When the stress becomes great enough, the rocks will slip relative to one another. The slip releases built up stress and the rocks return elastically to a relaxed state. After manipulating the model and discussing its strengths and limitations, student groups can reassemble to discuss the implications of the asperity vise for their hypotheses. Do they need to revise their hypotheses to explain the new model they have observed?
Next, teachers can guide students to consider the implications of repetitive cycles of stick-slip processes throughout time using the earthquake machine (see Dolphin in this issue, Modeling the Role of Elasticity in Earthquakes). Similar to the asperity vise, this model illustrates the stick process of elastic rebound along a fault. However, the design allows students to rapidly repeat the process over and over again and collect empirical data about the patterns of earthquake occurrence through time.
Last in the suggested sequence of activities, teachers can summarize learning from the models through an analysis of GPS velocity vectors (see Brudzinski in this issue, Using GPS Velocity Vectors to Illustrate Elastic Rebound). This graphical model of ground movement can show variations in the rate of ground motion. Begin by introducing students to velocity vectors for stations that are relatively close in proximity to a fault. This supports them building a conceptual model of the elastic behavior of rocks in a region surrounding a fault. Once they have incorporated this new understanding into their hypotheses, teachers can align the series of models to elastic rebound theory. If teachers want to add more real world examples of how geologists study these aspects of rock behavior, they can find velocity vectors using tools like those available from UNAVCO (http://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer.html).
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Gentner, D., and Smith, L., 2012, Analogical reasoning: Encyclopedia of human behavior, p. 130.
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