Instructor Materials: Overview of GPS, Strain, and Earthquakes Module
- Students are able to access and analyze GPS data in order to calculate and interpret ongoing strain in the region between three neighboring GPS stations.
- Students are able to synthesize how calculated local strain is related to regional tectonics and earthquake hazard and risk, and propose mitigation strategies.
Students apply what they have learned about GPS and strain analysis to a new region. They select a triangle of stations in an actively deforming area of interest to them, analyze the strain, and apply their findings to potential earthquake hazards, societal impact, and mitigation strategies. Learn more about assessing student learning in this module.
Note: Although the term GPS (Global Positioning System) is more commonly used in everyday language, it officially refers only to the USA's constellation of satellites. GNSS (Global Navigation Satellite System) is a universal term that refers to all satellite navigation systems including those from the USA (GPS), Russia (GLONASS), European Union (Galileo), China (BeiDou), and others. In this module, we use the term GPS even though, technically, some of the data may be coming from satellites in other systems.
In this opening unit, students develop the societal context for understanding earthquake hazards using the case study of the 2011 Tohoku, Japan, earthquake. It starts with a short homework "scavenger hunt" in which students need to find a compelling video and information about the earthquake. In class, they share some of what they have found and then engage in a series of think-pair-share exercises to investigate both the societal and scientific data about the earthquake.
Students gain an intuitive understanding of strain and deformation through a series of physical model activities using everyday materials such as bungee cords, rubber bands, fabric, index cards, silly putty, sand, and more. Can be run to fill an entire lab session exploring multiple materials or as a shorter exercise using just rubber bands and stretchy fabric. An additional addendum provides mathematical content (vectors, matrices, multidimensional strain) that can be used by instructors interested in more significantly building student quantitative skills.
This unit provides essential background information on GPS (global positioning system) and reference frames. Students learn how to access GPS location and velocity data from the Plate Boundary Observatory (PBO) . They calculate total horizontal motion graphically and mathematically and tie the observed motions to local strain.
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. This unit contains the primary infinitesimal strain analysis for the module. After the instructor demonstrates the method using data from Japan, students closely investigate three different GPS station triangles in three difference tectonic regimes: convergent (USA Pacific Northwest), extensional (Wasatch fault, Utah), and strike-slip (San Andreas Fault, California).
The 2014 South Napa earthquake was the first large earthquake (Mag 6) to occur within the Plate Boundary Observatory GPS network since installation. It provides an excellent example for studying crustal strain associated with the earthquake cycle of a strike-slip fault with clear societal relevance. The largest earthquake in the California Bay Area in 25 years, the South Napa earthquake caused hundreds of injuries and more than $400 million in damages. This activity uses a single triangle of GPS stations, located to the west of the earthquake epicenter, to estimate both the interseismic strain rate and coseismic strain. By the end of the exercise, the students also have direct evidence that considering the recurrence interval on a single fault, which is part of a larger system, is not reasonable.
Students select their own set of three stations in an area of interest to them, conduct a strain analysis of the area between the stations, and tie the findings to regional tectonics and societal impacts in a 5–7 minute class presentation. In larger classes, students may work in pairs to shorten total time needed for presentations. Unit 6, along with an exam question, is the summative assessment for the module.
Making the Module Work
To adapt all or part of the GPS, Strain, and Earthquakes module for your classroom you will also want to read through