GETSI Teaching Materials >GPS, Strain, and Earthquakes > Unit 5: 2014 South Napa Earthquake and GPS strain
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This module is part of a growing collection of classroom-tested materials developed by GETSI. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
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Unit 5: 2014 South Napa Earthquake and GPS strain

Vince Cronin, Baylor University (Vince_Cronin@baylor.edu)
Phil Resor, Wesleyan University (presor@wesleyan.edu)

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Summary

The 2014 South Napa earthquake was the first large earthquake (Mag 6) to occur within the Plate Boundary Observatory GPS network (now Network of the Americas- NOTA) 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 twenty-five 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 (P198, P200, SVIN), 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. An extension option gives the opportunity to discuss earthquake early warning systems.

Used this activity? Share your experiences and modifications

Learning Goals

Unit 5 Learning Outcomes

Unit 5 Teaching Objectives

  • Affective: Encourage reflection and analysis of societal impacts of earthquakes.
  • Cognitive: Facilitate students' ability to compare interseismic strain with coseismic displacements.

Context for Use

This module was designed for structural geology courses but can also be successfully used in geophysics, tectonics, or geohazards courses or possibly even a physics or engineering course seeking practical applications. Unit 5 assumes that students have already learned to use and analyze results from a GPS Strain Calculator and thus must come after Unit 3: Getting started with GPS data and Unit 4: GPS and infinitesimal strain analysis. In fact, Unit 5 could even be done after Unit 6: Applying strain and earthquake hazard analyses to different regions, which is the summative assessment for the rest of the module (Units 1–4). We have found the 2014 South Napa earthquake example can be a great way to return to and solidify these concepts later in the course and to bring up again the critical importance of understanding ongoing to strain in preparing our society for earthquake hazards.

July 23, 2021 - Data portal issue update: The data portal described in this exercise is having a temporary issue with link integrity. Internet browsers have discontinued the use of FPT sooner than its scheduled termination so the ftp:// links on the GPS station pages are not currently working. NOTA is working to address the issue but it will take some time to complete the transfer to http:// links within all the station pages (>1200). At the moment you can still follow the data portal directions to the point of getting to the station pages. Instead of clicking on the "NAM14 CVS" link you see on the page, use this protocol instead: https://data.unavco.org/archive/gnss/products/position/XXXX/XXXX.cwu.nam14.csv  where XXXX is the 4-letter station name for the station of interest. For example with station P402, the link you would want to use is https://data.unavco.org/archive/gnss/products/position/P402/P402.cwu.nam14.csv.

Description and Teaching Materials

Primary exercise

This exercise helps foster analysis and discussion of the Mw 6.0 August 24, 2014, South Napa earthquake using data from permanent GPS arrays. The information provided could be presented as: (1) an instructor-led discussion or (2) part of a student-centered activity building on the GPS strain analysis process. Use the full resources provided to do the student-centered activity. For the discussion-only option, have the students still do the short homework assignment to learn about the 2014 South Napa earthquake, but then primarily use the presentation to guide a class discussion of the analysis.

We suggest leading this exercise with a short homework assignment in which the students are asked to come to class having gathered data about the 2014 South Napa earthquake. This short pre-assignment is also on slide #2 of the presentation.

  • In preparation for the next lab period, each student should select an aspect of the 2014 South Napa earthquake for which to do some research: seismology, faulting, or damage (pass around a signup sheet with three columns and only enough spaces so that you get an even distribution of topics in the class)
  • Come to class ready to serve as the "expert" on your select topic for your three-person team
  • READ the short background document that was emailed to you

Once in class, run a quick jigsaw activity in which the class is divided into groups of three, with one of each type of "expert." Each student is responsible for bringing the entire team up to speed on the topic she or he researched.

Below are the teaching materials for the unit:

Extension Option—Earthquake Early Warning System

As of 2015, Japan and Mexico have public-alert earthquake early warning systems that can sense initial shaking in one region, identify that an earthquake is underway, and send notices within tens of seconds to people and infrastructure further away that imminent shaking can be expected. The United States does not currently have a fully functional earthquake early warning system, but a prototype has been developed for the Bay Area, called ShakeAlert. It was in operation during the 2014 South Napa earthquake and functioned correctly to send a warning, for example, to the BART (Bay Area Rapid Transit) trains. In happened that no trains were moving because the earthquake occurred in the middle of the night, but had it been daytime, trains would have been slowed or stopped by the time shaking arrived in San Francisco. You can ask students, what types of earthquake risk could be reduced by having 10–100 seconds of warning? After a short discussion, you could then show them the short animation about the ShakeAlert system.
Youtube: ShakeAlert—Earthquake Early Warning. How does it work?
MP4 file: ShakeAlert—Earthquake Early Warning. How does it work? (MP4 Video 26MB Oct7 15)

Teaching Notes and Tips

  • The pre-activity homework provides excellent motivation for the activity, but instructors may need to limit discussion to complete the activity in a single class meeting.
  • Instructors wishing to complete the activity in a single class session may want to have students plot the velocity/offset and strain rate / strain data in advance or provide the plotted data to students so that they can focus on interpretation of the data.
  • The conclusion of the activity is an assessment of earthquake recurrence using GPS observations of interseismic and coseismic deformation.
    • Instructors may want to revisit the Tohoku earthquake using slide 7 from Unit 4 Example interseismic data from Japan (PowerPoint 2007 (.pptx) 11.8MB Dec7 16) to help students develop their understanding of elastic rebound.
    • Physical analogs such as spring-slider models (for example: http://serc.carleton.edu/introgeo/demonstrations/examples/earthquake.html) may also be helpful in developing student intuition.
    • Unit 5 2014 South Napa earthquake presentation (PowerPoint 2007 (.pptx) 29.3MB Dec8 16) slides 22–30 are provided to foster discussion of the earthquake cycle using data from the South Napa earthquake.
    • The simple model used in the activity results in an unrealistically short recurrence interval. Unit 5 2014 South Napa earthquake presentation (PowerPoint 2007 (.pptx) 29.3MB Dec8 16) slides 31–32 are provided to guide discussion of two major shortcomings of the model. Instructors may want to couch this discussion as an example of how we can learn from the failure of models. State-of-the-art earthquake rupture forecasts use GPS data and elastic rebound theory to estimate earthquake probabilities, but incorporate more realistic fault geometries and other underlying assumptions into their models.
  • We provide supporting math materials in Unit 2 for instructors interested in having student take the quantitative analysis to a deeper level. These include vector, matrices, and infinitesimal strain analysis background.

Assessment

Formative Assessment:

Observation of student activity and conversations, individual questioning, and group discussion are excellent ways to conduct formative assessment as the students complete this exercise.

Summative Assessment:

The student exercise is the summative assessment for this unit. Many of the questions have definite right or wrong answers. To receive full credit, students must show their work, where appropriate. Where an open-ended answer is required, students are assessed based on a simple 2-point system.
2 points = correct answer with thorough supporting evidence and/or complete description
1 point = answer not completely correct or lacking thorough supporting evidence or description
0 points = incorrect answer

References and Resources


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This module is part of a growing collection of classroom-tested materials developed by GETSI. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »