Using THEMIS Images of Mars Graben in a Structural Geology Course
Barbara J. Tewksbury
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Students use Mars THEMIS images of normal faults to learn to recognize features of normal faults systems that are typically obscured on Earth by erosion and/or deposition and to calculate displacement and estimate regional extension based on features in the images.
The activity as written is for a structural geology course. The activity would be very easy to modify, however, so that it could be done by students who have very little background in structural geology. For students with less background, the activity could be modified to introduce needed terminology. With such minor modifications, this activity could, in fact, be used in introductory geology.
Skills and concepts that students must have mastered
This activity is written assuming that students know the general terminology for normal fault systems (graben, horst, relay ramp, hangingwall block, heave, throw, dip, etc.). The exercise also is written assuming that students can figure out how to use trig to solve for fault heave and throw.
How the activity is situated in the course
Content/concepts goals for this activity
On Earth, even young, active normal faults are modified rapidly by erosion and deposition, obscuring the surface expression of features. On Mars, by contrast, one can find relatively pristine normal fault features in which very little modification has occurred. Mars normal faults offer an ideal opportunity for students to study the features of real normal fault systems in map view, rather than simply in stylized map-view diagrams in textbooks, and to gain experience in recognizing features in a pristine setting that students can transfer to studying normal fault systems on Earth. Mars images also allow students to do simple calculations of fault slip and regional extension that help them put into perspective the kinematics of normal fault systems.
Higher order thinking skills goals for this activity
- Collection and analysis of data
- Assessment of assumptions
- Evaluation of uncertainties
Other skills goals for this activity
Description of the activity/assignment
Before class, students complete a homework assignment that familiarizes them with accessing and downloading Mars THEMIS images and in which they download images of normal faults in the Ceraunius Fossae of northern Tharsis. In class, I start with a short discussion about how THEMIS images are obtained, why the images are in strips, what resolution means, and so on. Students then examine their Mars images and identify normal fault features. Students determine the range of graben widths and then calculate throw for one fault using shadow width to calculate graben depth. Students then calculate heave for the same fault, assuming a fault dip of 60°. Students then do a back-of-the-envelope calculate to estimate crustal extension along a line across several graben. Students finish the activity by considering the impact of their assumptions on their results and evaluate the validity of their back-of-the-envelope calculation of extension. At the very end, we look at research results from several studies that have carefully calculated extension in Ceraunius Fossae.
Determining whether students have met the goals
Summaries of their work written during the activity plus their ability at a later date to apply what they have learned in this activity to other problems.
More information about assessment tools and techniques.
Teaching materials and tips
I have listed supporting references in the downloadable materials.