Where is that chunk of crust going?

Vince Cronin
Baylor University
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I introduce students to GPS, frames of reference, and the permanent GPS stations in the EarthScope Plate Boundary Observatory (PBO) in class, and obtain near-real-time data for two stations from UNAVCO. We use simple vector math (developed in class) to compute where one of the stations is going relative to a specified frame of reference. Then we compose a set of procedures, do the analysis again for the other station, compare and discuss the results. They do the computation for a third station of their choosing as homework, with a follow-up classroom discussion.

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This project has been used in an introductory physical geology course that has no prerequisites, in the core course in structural geology, and in graduate courses in structure/tectonics.

Skills and concepts that students must have mastered

Students need to be able to navigate on the web and must be able to use a calculator or a spreadsheet to compute.

How the activity is situated in the course

This is used in association with the plate tectonics discussion in my physical geology course. It can be used as a jumping-off point for a discussion of plate kinematics in a tectonics course.


Content/concepts goals for this activity

I want students to understand how we can measure relative motion on a global, regional or local scale.

Higher order thinking skills goals for this activity

Students need to visualize motion in 3 directions and apply appropriate mathematical concepts/procedures to describe that motion.

Other skills goals for this activity

This project involves obtaining data from the web, performing operations on those data, and developing a hypotheses.

Description of the activity/assignment

Introductory in-class session
I bring a hand-held GPS receiver into class, and present information about how the GPS receiver functions in coordination with the GPS satellites to define a position on Earth. I then talk about high-resolution GPS receivers, and introduce UNAVCO and the EarthScope Plate-Boundary Observatory. We visit the PBO website (http://pboweb.unavco.org) and find time-series data graphed for the motion of a given station (SBCC in Mission Viejo, California) relative to 3 orthogonal axes: north-south, east-west, and up-down. I hand-out paper copies of the data graphs, and we determine the slopes of the data to find the rate of change along each axis. We then use simple trigonometry to determine the length and direction of the 3-D velocity vector for that station. When we finish working on the first station's data together, we jointly write some rules for how to do the analysis. Then we use the rules to do a second analysis in class, working on data from a handout in groups of 2-3 students. The second station is BEMT in Twentynine Palms, California. The rules are refined as necessary and posted on the web. The results for SBCC and BEMT are then compared and discussed.

Homework portion
Students are required to find data for another PBO station and use the rules we developed to determine the velocity vector for that station. A report with the data and results of the analysis is due in the next class session. A sample report may be provided for their reference.

Classroom follow-up session
The results of the various analyses are compared, and questions generated about where various chunks of the lithosphere are going, how fast they are moving, and why they are moving. At the end, students are asked to write a few sentences describing what they would like to do next with the data -- what questions would they like to address through additional research work?

Determining whether students have met the goals

Students have a homework assignment to complete. At the end of the project, students are asked to propose the next question(s) to be addressed using the PBO data and our simple analysis method.

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