Using GPS data to analyze crustal strain -or- Where is the boundary between the Pacific and North American plates?
The San Andreas fault in California is typically called upon to mark the boundary between the Pacific and North American plates. This activity tests this assumption by investigating crustal strain in southern California. Part A has students analyze by hand GPS time-series data from three stations in southern California, and plot a strain ellipse that characterizes the crustal strain in the triangular area defined by the three stations. Part B introduces students to Matlab code that does the same thing, and sets them loose to plot numerous strain ellipses to in the larger study area. Part C has students interpret their results in the context of the boundary between the Pacific and North American plates, and compare their results to other data such as seismicity and recently active faults.
Context for Use
Students worked on it in the 3-hour lab session, which included an introduction to Matlab, and then completed the report on their own for submission the following week. This was an excellent application of Matlab which some students had used before, and others with no Matlab experience got a manageable dose. Materials include graph paper, tracing paper, and computer access (student laptops).
Description and Teaching Materials
The lab session starts out with an brief introduction to strain and the plate tectonic setting of southern California.
Students then work through Part A, which has step-by-step instructions on how to choose three appropriate GPS stations, interpret and plot the GPS data, and sketch a strain ellipse describing the strain within the triangular area defined by the three stations. Excellent resources for this portion are UNAVCO module's PowerPoint presentations on "Intro to GPS" and "Using triangle of GPS velocities to determine strain," available at:http://www.unavco.org/edu_outreach/resources/gps-strain/majors-gps-strain/module-materials/module-materials.html
For Part B, students are given an introduction to Matlab, and then instructed how to use the Matlab code to draw multiple strain ellipses across the study area.
Part C has students interpret their results in relationship to the plate boundary setting, and also compare their results to trends of recent seismicity, active faults in the area, and long-term average plate motion in the area. Some of these these are included in the handout, as well as in a kmz file to explore with Google Earth.
- Student Handout for Southern California Crustal Strain Activity (Microsoft Word 2007 (.docx) 3.2MB Feb24 13)
- Google Earth layers for Crustal Strain Exercise (KMZ File 6.9MB Feb24 13)
- Instructor notes for Southern California Crustal Strain Activity (Microsoft Word 2007 (.docx) 34kB Feb24 13)
- Example of strain ellipse map for the study area (Acrobat (PDF) 129kB Feb24 13)
- Matlab code for Crustal Strain in southern California activity (Zip Archive 218MB Feb25 13)
Teaching Notes and Tips
References and Resources