Testing plate tectonics in the Gulf of California

Paul Umhoefer
Northern Arizona University
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Summary

This is a simple exercise to use real-world data from recent large earthquakes so that students can test for themselves if plate tectonics "works" in the Gulf of California. The Gulf of California is fairly straightforward for most predicted behavior of an oblique-divergent plate boundary, but there are some intriguing differences between the earthquakes and what textbooks claim.

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Learning Goals

Content & Concept goals: - using GeoMapApp - finding data from earthquake catalogs - plotting selective data from earthquake catalogs

Higher order thinking goals: - critique of classic textbook models - comparison of real earthquakes along a simple active plate boundary to what is predicted from textbooks - evaluation of exceptions to the classic model - evaluation of earthquakes that are substantially away from the main plate boundary - evaluation of quality of data - comparison of the location of the same earthquake from two different earthquake catalogs, and determining which location is closest to the true epicenter given the simplest interpretation

Context for Use

Audience: Introductory class in Geology of any kind that presents principles of plate tectonics

Skills and concepts that students address: Assignment can be adapted to higher level classes.

Use of Exercise in Introductory class: This exercise is designed as a homework exercise with a follow up discussion in a moderate to large introductory class. It can easily be used as part of a lab, or it can be a group exercise embedded within a lecture with follow up discussion in the same class session.

Description and Teaching Materials

Assignment handout (Microsoft Word PRIVATE FILE 26kB Apr3 07)

Bathymetry map of the southern half of the Gulf of California: Download the KMZ File (KMZ File 1MB Feb20 09) or use the jpg image at right

Bathymetry map of the southern half and mouth of the Gulf of California: Download the KMZ File (KMZ File 1.9MB Feb20 09) or use the jpg image at right

Teaching Notes and Tips

  • Instructors should familiarize themselves with the data website (see resources below) ahead of time so that they can be ready to help students navigate the interface when they go in to find the data that they will be plotting.
  • This activity provides a great opportunity to talk to students about the fact that the models we make of how the Earth works are always imperfect. In this case, theory would hold that 100% of the seismicity would be on the transform plate boundary or the spreading ridge when in reality, a small but significant percentage of it happens away from either. If the class and the instructor have sufficient background this can lead to a discussion of how this does or doesn't fit with accepted theory and what the current state of thinking is on the subject.

Assessment

Students turn in the plot that they have annotated with the earthquake data together with their interpretation of the patterns present in the data and their answers to the questions on the Assignment handout.

References and Resources