Introduction to Modeling Faults
Summary
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Context
Audience
200-level undergraduate course, "Introduction to Geologic Structures." This course is a pre-requisite for most upper-level undergraduate geoscience courses in the core curriculum, including Structural Geology. It has a pre-requisite of an introductory level Geology course.
Skills and concepts that students must have mastered
Students need to be familiar with fault types, such as strike-slip, normal, and reverse, and with related terminology, such as footwall and hanging wall.
How the activity is situated in the course
This is an introduction to the map patterns indicating the presence of one or more faults. Students have seen maps of angular unconformities, so this activity is designed to help them distinguish different kinds of discontinuities in map patterns.
Goals
Content/concepts goals for this activity
Students will be able to recognize faults on geologic maps
Students will be able to distinguish faults from unconformities on geologic maps
Higher order thinking skills goals for this activity
Students will recognize that similar map patterns can be formed by different kinds of faults and fault motion.
Other skills goals for this activity
3D spatial visualization
Description and Teaching Materials
Working in groups of 3, students assemble 3-4 layers of Play-Doh "stratigraphy." Every student has their own Play-Doh, which they purchase as part of their course materials. I have each group do the following:
1. Construct a Play-Doh model of dipping layers, cut by a vertical fault,
Make the fault perpendicular to the strike of the dipping layers. Move one side of the fault horizontally (strike-slip motion). Examine and describe the resulting map pattern. See photos below.
Dextral:
Sinistral:
2. Construct a Play-Doh model of dipping layers, cut by a vertical fault.
Make the fault perpendicular to the strike of the dipping layers. (You can use the same model as for the first exercise.) Move the side that is closest to you up. Erode ~1 centimeter of the uplifted block. Examine and describe the resulting map pattern. See photos below.
3. Construct a Play-Doh model of dipping layers, cut by a reverse fault.
Make the fault such that its strike is perpendicular to the strike of the dipping layers. Move the hanging wall upward.Erode ~1 centimeter of the uplifted block. Compare the resulting map pattern to the map pattern for the strike-slip fault in the previous model. See photos below.
Following these exercises, I also show the students a model of a fenster ("window") in the hanging wall of a thrust fault. See the photo at the top of this page.
Science of Learning: Why It Works
Three-dimensional models can help to improve students' understanding of geological phenomena. Physical models, such as playdough models, serve as analogies to geological features and geologic maps. Analogies support the development of spatial thinking skills by allowing the student to draw from their knowledge and apply it to new cases (e.g., Gentner 1983). For example, students can reason from what they can experience when carving off pieces of playdough to how erosion will reveal geological structures). Analogical learning also applies to "mapping" -- that is, relating -- the features of models onto real world phenomena (e.g., this layer of playdough corresponds to a layer of sandstone). Physical models provide analogies to real-world phenomena, support cognitive offloading, and promote spatial accommodation.
Practice constructing spatial analogies can help students develop the mental models that allow them to recognize new cases of familiar concepts in the field. When instructors provide accurate physical models of geologic features, students can self-assess their understanding by comparing their mental model -- or their own physical model -- to the instructor's physical model. When students make their own physical models, these models serve as a means of "inscription," in much the same ways that mapping and sketching do: they allow for students to record their conceptual understanding of a natural phenomenon (Mogk and Goodwin, 2012). However, unlike mapping and sketching, a playdough model allows for this record to be three-dimensional, like the phenomenon itself, which can reduce the cognitive demands inherent in the process of inscription by reducing the need to generate a 2D representation of 3D space (Newcombe, 2012). In addition, physical models support spatial accommodation: when a student compares their (mental or physical) model of a phenomenon or region to their instructor's model and recognizes a difference between the models, the student is prompted to revise their mental model (Davatzes et al., 2008). When the change required is spatial the student may use the feedback directly to revise the model. When the change is significant, the student may need to completely discard their old model and construct a new one. Playdough models of geological structures can thus serve as the basis for improved mental models.
Teaching Notes and Tips
Dental floss slices through Play-Doh with minimal smearing.
Assessment
Student understanding is not formally assessed in this activity, but is an essential pre-requisite for many of the subsequent course activities, including homework and lab exercises.
References and Resources
Davatzes et al. (2018). Learning to form accurate mental models. Eos, 99, https://doi.org/10.1029/2018EO091643. Published on 07 February 2018.
Gentner, D. (1983). Structure-mapping: A theoretical framework for analogy. Cognitive Science, 7(2), 155–170.
Mogk and Goodwin (2012). Learning in the field: Synthesis of research on thinking and learning in the geosciences, in Earth and Mind II: A synthesis of research on thinking and learning in the geosciences, edited by Kim A. Kastens and Cathryn A. Manduca. GSA Special Paper 486:131-163. DOI: 10.1130/2012.2486(24)
Newcombe, N. S. (2012). Two ways to help students with spatial thinking in geoscience. Geological Society of America Special Papers, 486, 85-86.