The spectrum of fault slip

Eliza Richardson, David Pearson, Casey Moore, Jeff Marshall

Summary

This is one component of the Seismogenic zone Experiment Mini Lessons

This mini lesson consists of two items:

1. A powerpoint mini-lecture to give background information about geodetically-detected slow slip events (SSEs) in subduction zone settings. Source parameters are explained vis-a-vis ordinary earthquakes and also a brief explanation of how to read GPS time series data plots. The lecture is designed to lead up to the problem set students will complete. However, the background lecture material can also stand alone from the problem set.

2. A problem set in which students work with GPS data to calculate source parameters of actual slow slip events. They are asked to construct hypothetical time series plots given a description of an earthquake or slow slip event. This problem set should be used concurrently with the background mini-lecture.

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Learning Goals

  • Students will know that subduction zones release energy in rapid earthquakes as well as in slower ruptures
  • Students will practice analyzing time series data from geodetic instruments.
  • Students will know the strengths and limitations of different types of instrumental data (e.g. why do we use GPS rather than seismic data to study creeping faults?)
  • Students will be able to calculate earthquake source parameters from known scaling relationships
  • Students will be able to use GPS data to infer the duration and slip magnitude of a slow slip event
  • Students will be able to sketch what GPS time series data should look like given a hypothetical earthquake or slow slip at a particular location.

Context for Use

  • upper level geophysics
  • upper level structural geology
  • upper level seismology / geodynamics
  • tectonics

Description and Teaching Materials

SSEs v. earthquakes as recorded by GPS
  • Background lecture for The Spectrum of Fault Slip minilesson (PowerPoint 2007 (.pptx) 2.5MB Feb26 15) background minilecture: geodetic comparison of ordinary earthquake, SSEs
  • Student Handout Problem Set for The Spectrum of Fault Slip minilesson (Acrobat (PDF) 689kB Feb26 15)
  • problem set: comparing geodetic data recording an ordinary earthquake v. an SSE. Students make hypothetical sketches of geodetic time series data, calculate slip vectors, calculate magnitude, compare rupture durations of the two kinds of slip events. Uses published data, also freely available data from UNAVCO and USGS. The files here involve the student handout version of the problem set plus the UNAVCO-produced reference page explaining how to read time series plots plus the answer key.

Teaching Notes and Tips

Three points here:

  1. The background lecture may stand alone, but the problem set will be much more difficult for the students without the lecture.
  2. The problem set involves assessing by hand so it is not necessarily scalable to a large class unless you are lucky enough to have TAs or other grading help.
  3. My suggestion for the problem set is to tell students to show their work by using a straightedge and pencil to mark their measurements and do their arithmetic right on the GPS time series data that's given to them in the problem set file. My intention is for students to practice the method of interpreting the data and making calculations, as opposed to this being an exercise in curve-fitting methods. In other words, I ask students to eyeball a best fit line to the GPS time series data and show their work. That way, if they get slightly different numbers from my answers given in the key, I can follow their calculations through and check that they did it the right way, which is what I think is important here. This is real data after all. You may feel differently. For an advanced class or if students work in groups, adding a discussion of measurement uncertainty could be an add-on, but I don't explicitly include such a discussion in this problem set.


Assessment

Students will turn in a problem set in which they will be asked to handle authentic data, make some measurements and calculations, and answer follow-up questions

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