Laboratory Analogs of Faults

Jackie Langille
,
University of North Carolina Asheville
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Summary

This activity utilizes a sandbox analog model (Dell Castello and Cooke, 2008) which is used to create normal faults or a foreland propagating fold and thrust belt. For the normal fault portion of the activity, students investigate the progression of normal fault generation and accumulation of offset. During the thrust fault portion of the activity, students evaluate (1) the initiation angles of thrust faults, (2) compare that to the final angles to understand how fault angles rotate with progressive thrust propagation, and (3) they visualize how the critical slope angle is involved in the initiation of younger thrust faults. In addition, they conceptualize methods utilized to evaluate the magnitude of fault offset, and vertical and horizontal shortening. Here I provide a copy of the laboratory assignment that I use.

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Context

Audience

This laboratory assignment is used in my Structural Geology undergraduate course.

Skills and concepts that students must have mastered

Students should be familiar with basic structures and tectonic processes, foreland propagating thrust faults, critical slope angle, etc.

How the activity is situated in the course

This activity is a laboratory assignment done in the second half of the semester, after we have discussed extensional and compressional settings.

Goals

Content/concepts goals for this activity

  • Conceptualize fault initiation and evolution in compression and extension settings
  • Quantitative methods for evaluating fault offset
  • Quantitative methods for evaluating shortening and extension

Higher order thinking skills goals for this activity

Students use there measurements and observations to conceptualize the mechanisms involved in rift or fold and thrust belt settings.

Other skills goals for this activity

Students work in groups to collect data as the experiment progresses.

Description of the activity/assignment

This activity utilizes a sandbox analog model which is used to create normal faults and a foreland propagating fold and thrust belt. For the normal fault portion of the activity, students investigate the progression of normal fault generation and accumulation of offset. During the thrust fault portion of the activity, students evaluate (1) the initiation angles of thrust faults, (2) compare that to the final angles to understand how fault angles rotate with progressive thrust propagation, and (3) they visualize how the critical slope angle is involved in the initiation of younger thrust faults. In addition, they conceptualize methods utilized to evaluate the magnitude of fault offset, and vertical and horizontal shortening.

This activity is motivated by and utilizes a sandbox model from:

Dell Castello, M., and Cooke, M., 2008, Watch faults grow before your very eyes in a deformational sandbox: Journal of Geoscience Education, v. 56, p. 324-333.

Tips for the activity: I place a sheet of sandpaper under the sand on one side of the compression experiment to test the outcomes with varying basal friction. For the extension portion, I attach separate metal sheets to the stationary wall and the moving wall, under the sand. These sheets are joined by elastic fabric. To save money, mix non-toxic paint powder into basic sand to get colored sand.

Determining whether students have met the goals

Students complete a laboratory assignment.

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