VISUALIZING STRUCTURE CONTOURS WITH SKETCHUP: FROM STRIKE AND DIP TO CROSS-SECTION CONSTRUCTION

The use of structure contours to interpret maps and cross-sections is an example of a fundamental geologic concept rooted in 3D visualization. Students typically learn how to solve specific structure contour problems using 2D projections, but many fail to link the solution to the underlying 3D geometry. 3D models can help students visualize structure contours, and Trimble SketchUp is a particularly useful application for making them because it is relatively easy to learn and free.

I created a sequence of models that shows how to use structure contours to 1) test if a contact is planar, 2) determine the strike and dip of planar beds, 3) find the true thickness of stratigraphic units, 4) solve the 3-point problem, 5) determine the depth of a target unit, 6) estimate displacement across faults, and 7) create cross-sections. I also made a dynamic component (which required SketchUp Pro to make but can be used by anyone with the free version) that can be used to quickly generate structure contours for a planar surface with arbitrary strike and dip. The user can also specify the interval and elevation range of the structure contours, and the exact position of the surface. I wrote a tutorial that describes how to generate artificial topography, import a digital elevation model of an area of interest, create a planar surface or a sequence of surfaces, make a simple geologic map, add structure contours, and create a cross-section in a 3D environment.

Many structural geology courses rely on classic lab manuals containing simple problems for students to solve. SketchUp can be used to recast these classic exercises into 3D models. One of the most exciting aspects of creating 3D models with SketchUp, however, is the ability to generate a host of new problems with minimal effort; such exercises are otherwise very time consuming to create.

Models can be disseminated directly as electronic SketchUp (.skp) files, which students can explore and modify. SketchUp models can be exported as COLLADA digital asset exchange (.dae) files, and incorporated into an iBook as interactive 3D models using iBooks Author for IOS devices. The .dae files can also be uploaded to Sketchfab, a web service designed to publish and display interactive 3D models. Once uploaded to Sketchfab, the models may be embedded in a webpage where anyone with a WebGL enabled browser can view them.