GPS, Strain, and Earthquakes

Vince Cronin (Baylor University)
Phillip Resor (Wesleyan University)

Technical Advisors: Bill Hammond and Corné
Kreemer (University of Nevada Reno)
Editor: Beth Pratt-Sitaula (UNAVCO)

This material was developed and reviewed through the GETSI curricular materials development process.

This material was developed and reviewed through the GETSI curricular materials development process. This rigorous, structured process includes:

team-based development to ensure materials are appropriate across multiple educational settings.
multiple iterative reviews and feedback cycles through the course of material development with input to the authoring team from both project editors and an external assessment team.
real in-class or field camp/course testing of materials in multiple courses with external review of student assessment data.
multiple reviews to ensure the materials meet the GETSI materials rubric which codifies best practices in curricular development, student assessment and pedagogic techniques.
created or reviewed by content experts for accuracy of the science content.

This page first made public: Dec 9, 2016

Summary

Understanding how the Earth's crust deforms is crucial in a variety of geoscience disciplines, including structural geology, tectonics, and hazards assessment (earthquake, volcano, landslide). With the installation of numerous high precision Global Positioning System (GPS) stations, our ability to measure this deformation (strain) has increased dramatically, but GPS data are still only rarely included in undergraduate courses, even for geoscience majors. In this module students analyze GPS velocity data from triangles of adjacent GPS stations to determine the local strain. Students learn about strain, strain ellipses, GPS, and how to tie these to regional geology and ongoing societal hazards. A case study from the 2014 South Napa earthquake helps students make connections between interseismic strain and earthquake displacements.

Show more about Online Teaching suggestions

Webinar about teaching this module: Addressing Earthquake Hazards with LiDAR, GPS, and InSAR in Upper-level Undergraduate Courses

For introductory-level treatment of GPS and plate motions, please see Measuring the Earth with GPS - Unit 2

Strengths of the Module

Most structural geology courses only cover finite strain (generally through the analysis of deformed fossils), missing the rich opportunity to investigate ongoing strain (infinitesimal strain) now measurable through methods such as GPS. This module introduces geoscience majors to Plate Boundary Observatory (PBO) GPS data in order to study infinitesimal strain and connect it to broader tectonic settings and hazards.

The earlier units help ground the students in the societal impact of earthquakes and give them an opportunity to explore strain and deformation through a variety of physical models ranging from Silly Putty® to drywall compound. This affective and intuitive introduction to strain provides a firm foundation from which to learn about strain quantitatively.

Students work with GPS velocity data in sets of 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 data, and how to connect these to regional geology and hazards. The calculations can be done using provided Excel or Matlab calculators (most typical) or students can be asked to do the calculations or coding themselves.

The Unit 6 summative assessment has the students select a set of three GPS stations in an area of interest to themselves. For many students this is their first experience with "research" and possibly their first time giving an oral presentation. Despite initially being daunted by this idea, students generally end up doing well on it and gaining notable confidence with GPS data.