MODULE MATERIALS - Infinitesimal strain analysis using GPS data:
Module for structural geology or geophysics course

The premise of the module is to have students work with GPS velocity data from three stations in the same region that form an acute triangle. By investigating how the ellipse inscribed within this triangle deforms, students learn about strain, strain ellipses, GPS, and how to tie these to regional geology and ongoing hazards. The calculations can be done as a "black box" using provided Excel or Matlab calculators (most typical) or students can be asked to do the calculations or coding themselves (see extensions section below).

Basic module

About one week including lab period and some lecture/class time

ALL of the Basic Module files bundled (v: May 9 2013) [zip; 42Mb] or download individually below…

Presentation: Intro to GPS (v: Dec 22 2012) [pptx; 14Mb] This PowerPoint provides a basic introduction to what GPS is, how it works, and how to start reading and interpreting data output from GPS stations in EarthScope's Plate Boundary Observatory (PBO).

Document: Strain Introduction NEW DOCUMENTS (v: May 9 2013)
For instructors [docx; 4Mb] [pdf; 1.5Mb]
For students [docx; 4Mb] [pdf; 1.5Mb]
These documents give a more intuitive introduction to strain than is offered in some structural geology text books and is designed to dovetail with other documents in this module.

Exercise: Finding location and velocity data for PBO GPS stations (v: May 9 2012) [docx; 3Mb] [pdf; 1Mb] This short exercise can be done as a homework after a short introduction. The explanation walks students through finding and accessing GPS location and velocity data through the PBO site and plotting the net horizontal velocities. The final pages of the document are data recording sheets.

Presentation: Using velocities from a triangle of GPS sites to investigate crustal strain (v: Mar 20 2013) [pptx; 4Mb] This PowerPoint provides a basic introduction to how a triangle of velocities from GPS stations can be used to determine the different components of infinitesimal strain that are occurring in the region between the sites.

Activity: GPS strain analysis (v: May 9 2013)
[docx; 9Mb] [pdf; 1Mb] Students use a strain calculator to determine the different components of strain at three example sites (Coastal Cascadia, Wasatch Fault, and San Andreas) in the PBO network. Can be done individually or in teams as a class-wide "jig-saw" activity. Site-specific instructor's notes included.

Excel Calculator: Strain within triangle of GPS sites (v: Dec 22 2012) [xlsx] Matlab version (v: Jan 11 2013) [m] These simple calculators intake GPS station location and velocity data and output components of infinitesimal strain (translation, rotation, extension, etc). Excel version is more "black box" whereas Matlab is better for courses intending to investigate the underlying mathematics and coding process.

Document: Explanation of calculator output (v: May 9 2013) [docx; 1.5Mb] [pdf] This document helps students walk through interpreting the meaning of the calculator output.

Super short version

One lab period only, emphasizing San Andreas

Activity: GPS and strain on the San Andreas (v: Nov 15 2012) [docx; 3Mb] [pdf] This version was modified from the Basic Module by Anne Egger (Central Washington University) to use in the strike-slip portion of her structural geology course. She reports that the students finished relatively quickly. Next time she will probably integrate a similar use of GPS data into each of the three course sections related to: compressional, extensional, and strike-slip settings or do a "jig-saw" activity similar to the "GPS Strain Analysis Activity" above—either using sites from a variety of different tectonic settings or by having different student groups look at different triangles around the San Andreas. She pulled slides from "Introduction to GPS" and "Using triangle of GPS velocities" presentations to orient the students and then produced this activity document.

Extension options

Related activities to go into more depth

Activity: Physical models of strain NEW DOCUMENT (v: March 20 2013) [docx; 6.5Mb] [pdf; 0.5Mb] This lab activity is a great one for helping students gain intuitive understanding of a variety of structural geology processes and features. They use simple materials such as stretchy fabric and silly putty to investigate different types of strain and consider the relationship between velocity vectors and strain. When testing the module in his own class, Vince had the students do this activity early in the semester prior the rest of the Basic Module above.

Research Project: Calculating and interpreting strain at student-selected site (v: Oct 2012) [docx] – revised version coming soon Students select their own triangle of GPS stations, use the calculator to determine the different components of strain occurring in that location, tie their findings to known regional geology, and present findings in 5-minute presentation. This project is an in-depth summative evaluation that opens the opportunity for class conversations about challenges and benefits of using multiple data sets (ex. GPS data and quaternary fault index). Includes detailed evaluation rubric.

The following files allow much greater exploration of the back ground theory, math, and computer programing involved in the strain calculations

Infinitesimal Strain Primer (v: Sept 2012) [docx] - revised version coming soon
This document is intended for a faculty member, graduate student, or advanced undergraduate. It walks the reader through the theory and math behind 1-, 2-, and 3-D analysis of infinitesimal strain.

Algorithm for computing infinitesimal strain (v: Sept 2012) [docx] Explains the steps needed to generate one's own infinitesimal strain calculator – would be particularly useful if one wants students in an advanced geophysics course to learn the inner workings of the otherwise "black box".

Mathematical review (v: Sept 2012) [zip]
Series of handouts that review the math relevant to strain calculations and GPS data: vectors, matrices, dot product, eigenvalues, and eigenvectors.