Unit 2 Risk at Transform Plate Boundaries
This unit builds on what students have learned about transform fault hazards to introduce the idea of risk. Students examine earthquake risk along the San Andreas Fault in San Francisco by examining public school sites around the city. Students calculate relative risk (risk = hazard probability x vulnerability x value) due to earthquake hazards at five sites, analyze different seismic hazard scenarios, communicate risks to stakeholders, and evaluate possible responses to seismic hazards. Students conclude with a summative assessment in which they reflect on the value of earthquake forecasts and warnings in mitigating risk.
This unit addresses several overarching goals of the InTeGrate program including analyzing geoscience-related grand challenges facing society (impact of natural hazards), developing students' ability to address interdisciplinary problems and use authentic geoscience data, and improving students' geoscientific thinking skills (interpretation of multiple data sets).
Unit 2 Learning Objectives (and areas in the unit where objectives are addressed)
- Students will relate earthquake damage to rock/soil type and distance from epicenter.
- Students will identify factors that contribute to building damage associated with earthquakes, and they will describe potential strategies to mitigate seismic damage to buildings.
- Students will evaluate information about seismic hazard, building construction, and population to quantify risk on the Pacific/North America plate boundary near San Francisco.
Context for Use
Unit 2 builds on ideas from Unit 1 (Hazards at Transform Plate Boundaries), adding the ideas of risk and risk mitigation to seismic hazards associated with transform plate boundaries. Students are expected to come to the activity with the following background:
- Familiarity with the basic tenets of plate tectonics and the general characteristics of plate boundaries. One suggested activity is Using Google Earth to Explore Plate Tectonics, by Laurel Goodell.
- Familiarity with the concept of earthquake magnitude.
- Completion of the prework assignment (which could be incorporated into class time if a longer time is available).
This unit is designed for introductory-level geology courses, including physical geology and geologic hazards, but is also appropriate for any course studying plate tectonics.
Unit 2 is designed for a 50-minute class period, with additional pre-class work designed to help students visualize patterns of damage from the 1906 great earthquake. In class, students are expected to work in large groups (for activity 1) and pairs or small groups (for activity 2), and can access the data necessary for the activities in one of two ways:
- Using printed maps and data sheets (provided).
- Using a computer equipped with Google Earth and a web browser. Necessary files can be downloaded from the links below.
This unit is suitable for most class sizes if enough students are available for at least 4 or 5 student groups for activity 2.
If used for a longer period (e.g. 75-minute lab), the prework and in-class work can all be completed in one session. Internet access is required for prework.
Description and Teaching Materials
USGS data sources for some Google Earth layers are currently not working due to changes at the USGS web site. While they are being repaired, please use the paper maps version of the activity.
If Google Earth is available:
- Students explore San Francisco 1906 earthquake information (KMZ File 747kB Feb20 20) and fill out the following sheet:
- Unit 2 prework sheet (Microsoft Word 2007 (.docx) 25kB Sep20 14)
- PDF version of worksheet (Acrobat (PDF) 66kB Sep22 14)
If Google Earth is not available:
- Paper maps Word version (Microsoft Word 2007 (.docx) 6.4MB Sep22 14)
- PDF of paper maps (Acrobat (PDF) 9MB Sep22 14)
The prework is intended to take about 30 minutes, not including any time necessary for students to become familiar with Google Earth.
Outline of In-Class Work
Before the class begins, the instructor will assign students to groups of three to five individuals for the day's activities. Although these groups are only strictly necessary for tasks 3, 4 and 5, it will save time if students are already placed in groups at the beginning of class.
- [~10 min] The instructor solicits student responses to question 3 from the prework ("Suppose that local fire and rescue crews had to prioritize which of the areas in the "Strong Shaking Case Studies" layer to search first for earthquake survivors and casualties. Which area should get priority? Why?"). The instructor then briefly introduces the concept of calculated seismic risk as a combination of seismic hazard, vulnerability to damage, and value. In the case of the activities described here, the value term is assessed in terms of human casualties (or, alternatively, the number of human lives protected from harm by a reduction in risk). This is an ideal opportunity to highlight the reasons that geologists are continually updating their assessments of natural hazards: more and more people are living near plate boundary zones with earthquake potential of trends in the number of people affected by seismic activity through time).
- [~10 min, optional] Students work as a class to hypothesize what the effects of an earthquake similar to the 1906 San Francisco earthquake would be if that earthquake struck San Francisco today. Specifically, what hazards would have greater effects, and what would have smaller effects in the present-day city? Potential examples could include damage to bridges and freeway overpasses (as seen in the Loma Prieta earthquake) that were not present in 1906; improved fire control and building codes since 1906; damage to communication infrastructure that is much more important to San Francisco than it was in 1906; denser population than in 1906. Possible discussion prompts include:
- "Suppose that an earthquake similar to the 1906 earthquake were to strike San Francisco today. In what ways might a city like San Francisco be better equipped to save lives and property after an earthquake, compared to 1906? What about modern cities could make earthquake response efforts more difficult?"
- "Imagine that you lived in San Francisco now, and that an earthquake like the 1906 earthquake had just happened. Your house has not been destroyed, but your life has been affected by the earthquake in other ways. How might your everyday life—your commute to work, your ability to get food and help to your friends, your lines of communication with the outside world—be affected by a major earthquake?"
- [~15 min] Certain factors leave some buildings vulnerable to damage. After a brief instructor-led summary of earthquake-safe design, students examine a set of red background images from this PowerPoint (PowerPoint 2007 (.pptx) 5.8MB Apr2 15) to assess the possible factors that can increase or decrease risk of property damage. Slides with black backgrounds are intended to help students identify ways in which seismic, geological, and construction parameters can influence a building's earthquake safety. The images with red backgrounds show pairs of buildings damaged by earthquakes. These are intended to illustrate differences in each of the major factors that affect a building's response to an earthquake. Construction, ground type, and topography, in particular, are important. The slideshow is designed so that the instructor can choose a few (2-3) of the red background images for a think-pair-share activity, in which students first try individually to identify the factors responsible for the earthquake damage in the photograph. Students then discuss their analyses within their small groups, so that each group reaches a consensus. The instructor then polls the class about their analyses (a show of hands will work, although this would be relatively easy to adapt as a clicker question).
- [~ 15 min] The class now applies its knowledge of earthquake hazard probability (Unit 1) and building vulnerability factors (previous activity) by using Google Earth to look at the relative risk at five school campuses. Small groups of students evaluate the seismic risk at one of five school campuses in San Francisco using Google Earth. Directions are included on a worksheet. An alternative version of this activity uses maps and photographs instead of Google Earth. Student teams will elect a note-taker, a Google Earth navigator, and a spokesperson.
- Students use hazard maps to assess strong shaking (%g) and liquefaction potential (high/med/low) at the school sites.
- Students assess landslide risk (high/med/low) based on LIDAR-derived topography around the schools.
- We have created a scaled-down version of the FEMA Rapid Visual Screening protocol for assessing seismic safety. The basic assessment categories include construction type (unreinforced masonry) and presence of "soft" stories. Assessment is based on Google Street View photos.
- The value of each school is based on the number of students in each school.
- Risk scores are calculated as hazard x vulnerability x value. Additional detail on the calculation is given in the worksheet.
- San Francisco Earthquake Hazards (KMZ File 3.8MB Feb20 20) Google Earth KMZ (Note: schools labeled A-E are intended for this activity. Two alternates are labeled F and G. These are intended for use in large classes where additional groups could examine different schools.)
- Paper maps (Acrobat (PDF) 16.2MB Jan23 15) and demographic statistics (Excel 2007 (.xlsx) 41kB Jan23 15) (PDF version (Acrobat (PDF) 35kB Jan23 15)) for the non-Google-Earth version of the activity
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