Borehole analysis using stereographic projection

Eric Nelson
,
Colorado School of Mines
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Summary

Advanced stereonet project using unoriented core structural data. The project gives practice in plotting small circles and in rotations.

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Context

Audience

I use the problem in an advanced applied structural geology course, however it could be used in a basic structural geology course to challenge students.

Skills and concepts that students must have mastered

Stereographic projection, with some lecture/reading material on plotting small circles and doing stereonet rotations.

How the activity is situated in the course

Stand-alone exercise in a section where we study stereonet methods in analyzing borehole and core data.

Goals

Content/concepts goals for this activity

Stereonet methods using unoriented core data; stereonet rotation; forward fold modeling

Higher order thinking skills goals for this activity

This is a difficult project to even know how to begin if students are not guided carefully through it. However, it can be assigned as an open-ended project where they must come up with a solution. (I originally solved this problem as a consultant).

Other skills goals for this activity

This might be appropriate for group or team assignment, where more than one head can be applied toward a solution.

Description of the activity/assignment

Preparation requires lecture and/or reading material on stereonet methods in plotting small circles, and on making stereonet rotations along small circles. In lab, students are given a description of the problem, along with a schematic cross section on the blackboard showing how the dip of the eastern fold limb is not constrained, but how the orientation of cross beds in an unoriented core are the only data available to help constrain the dip of the fold limb. Students are then given a while (~20 minutes) to think about and discuss how a solution can be made. An open class discussion follows, and then I guide the students through the answer. An alternative method is to let the students take a week to think about and solve the problem with little or no help.

Determining whether students have met the goals

By analyzing their stereonet solution.

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