Visualizing Strain in Rocks with Interactive Computer Programs

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Geology (42)Strain is a fundamental topic in structural geology, and researchers endeavor to quantify strain in rocks to understand the development of deformation fabrics, and examine strain gradients in folds and fault zones in order to constrain mechanisms of their formation. This CCLI Type I project is providing students in structural geology opportunities to gain confidence gathering and analyzing data from rocks and relating deformation to large-scale structures. The two computer programs and accompanying tutorials being created are providing students with opportunities to determine strain in rocks and an opportunity for them to gain experience in data acquisition and error analysis. Students are also learning about important problems that complicate all attempts to quantify strain, such as ductility contrast between marker object and matrix, initial shape and distribution of marker objects, and area or volume change during deformation. Thus, the value of such exercises goes far beyond training students to measure strain in rocks; these projects also are providing an opportunity for students to critically examine the assumptions and limitations of any attempt to quantify a natural process.Intellectual Merit. Two common methods for estimating strain in rocks are the Rf/Phi and center-to-center methods. Both require making numerous measurements, plotting the results on graphs, and interpreting patterns in the graphs to estimate strain. Students commonly have trouble connecting the objects measured in deformed rocks with the graphs. The programs being created are continuously and instantaneously linking images of the rocks, as deformation is simulated by linear transformations, with the graphs that are used to calculate strain. This approach is giving students a visual link between deformation and the otherwise abstract graphical display. A prototype program is being refined and tutorials are being created to help students become familiar with the Rf/Phi method for determining strain. A second similar program for measuring strain by the center-to-center method and tutorials are also being developed. A third tutorial is for advanced treatments of strain analysis describing how both methods can be used to measure strain in some rocks to partition strain into shape change and area change components. The programs are being written in Java, so they can run on virtually any computer. The tutorials are available as text documents with screen captures of the programs, and as PowerPoint presentations for use in the classroom. Broader Impact. The programs and associated tutorials being developed will impact the teaching of structural geology, a core course taken by nearly all geology majors. The programs and tutorials are improving undergraduate courses in structural geology by fostering a deeper understanding of how commonly used strain methods work. The programs are also being used to demonstrate some basic principles of strain for introductory geology courses. To support wide dissemination and increase the number of geology faculty that are using the programs in their structural geology courses, workshops are being held at national and regional geology meetings. All material is freely available and is downloaded from the Williams College Geosciences and Information Technology web pages.