Map Analysis of a Restraining Bend
The goal is for students to study the map and recognize the geometric relationships and geomorphic expression of a restraining bend along a strike slip fault.
This is used in a required undergraduate structural geology course.
Skills and concepts that students must have mastered
Students must be familiar with the concept of strike slip faults, but may not necessarily need to be familiar with restraining and releasing bends. If slightly modified, it could be used as a more exploratory exercise.
How the activity is situated in the course
This is a short in class activity that is done in pairs, a class period or two after they have completed a short experiment and discussion of strike slip faults, restraining bends, and releasing bends. The purpose is to revisit concepts that they explored in a previous session. In the past I have not given offset direction, and have had students deduce whether the fault is left lateral or right lateral; however, I've since added in a short hands-on demo that illustrates the deformation more effectively so I've shortened this exercise into a reinforcement activity.
Content/concepts goals for this activity
Map analysis and observation
Higher order thinking skills goals for this activity
This is a very simple exercise, but it requires students to use map observations (uplift, fault geometry) to think about the stresses that are occurring and how those relate to the topography of the landscape.
Other skills goals for this activity
working in small groups
Description and Teaching Materials
This is a short in class exercise designed to reinforce student understanding of fault mechanisms, and uplift associated with resistant fault bends in strike-slip systems.
Student Handout for Catalina Fault Zone Activity (Acrobat (PDF) 319kB Jun18 12)
Catalina Fault Zone Activity (PowerPoint 2007 (.pptx) 5.6MB Jun18 12)
Teaching Notes and Tips
Students may be confused by the fact that the area to the south of the restraining bend does not appear to be uplifted; it is, but the majority of the deformation is seen on the north side of the fault. For a more in depth discussion of this region, please refer to:
M.R. Legg, C. Goldfinger, M. J. Kamerling, J. D. Chaytor and D. E. Einstein. Morphology, structure and evolution of California Continental Borderland restraining bends. Geological Society, London, Special Publications 2007; v. 290; p. 143-168
After the group work, I collect the written responses from each pair. We then discuss the activity as a class. I review the written responses, looking for key points: Did they correctly identify the topographic high (Catalina Island) to the north of the fault? Did they correctly identify the restraining bend, and did they indicate that compressive forces were causing uplift at that location?
References and Resources