Examining All the Factors

Students explore several interactive web sites to gather information which will enable them to compare the seismicity and potential level of earthquake damage for five different locations in the San Francisco Bay Area. Working in teams, they will demonstrate their knowledge and understanding that the level of earthquake damage is a result of multiple factors.

Materials / Preparation

Computers with Internet connections

Each student will need a copy of:

• Data Record Sheet
• Earthquake Hazard Analysis Activity
• Earthquake Hazards Student Web Page which includes the links to the activities described here.

Alternative: If classroom computer access is not available, all the maps could be printed out on a color printer. Note that What's the Probability? has a clickable map but all the information from clicking is also found in a table at the end of the page. The only problem is that not all segments are labeled (they are color coded, and the colors may be hard to read on a printout). The teacher may want to hand label the printouts with segment names before photocopying.

Grouping

Groups of four

Teacher tips

Review the student activities 1906 Scenario Earthquake Scenario and What's the Probability? You may also want to read Four Earthquake Scenarios for a brief description of the four main earthquake scenarios mentioned in this activity.

This activity may be compressed to fit within a single class period or fleshed out to be a more creative culminating activity spanning several periods with a substantial writing component for a final report.

Procedures

1. Hand out a copy of the Earthquake Hazard Analysis Activity to each student. Read through the Scenario. Emphasize to students that they will be given five sites in the San Francisco Bay Area. As the Bay Area is prone to earthquakes, their job is to determine which of these sites is seismically the safest. The five sites are; Palo Alto, San Francisco, Antioch, Pittsburg and Rohnert Park.
2. Review with students the factors that are important to consider when trying to predict potential earthquake damage in an area. Students should recall factors such as: proximity to the fault, magnitude of the earthquake, length of the rupture, soil composition, liquefaction, frequency and patterns of earthquakes.
3. Read through the Specific Task of the Earthquake Hazard Analysis Activity that the students will be responsible for and explain that there is a list of several websites to explore, but to begin their research, they should gather some specific data.
   a. Pass out copies of the Data Record Sheet.
   b. Explain the concept of earthquake probabilities to the students. Be sure that the students recognize that these probabilities describe the likelihood of a specific event (earthquake on a specific segment of a specific fault) over a specific timeframe (30 years). A 100% chance of an earthquake means that there will absolutely, positively be a magnitude 6.5 earthquake in the next 30 years, while 0% means that there is not even the slightest chance
4. Have students go to What's the Probability, which is accessible from the Earthquake Hazards Student Web Page. Ask students to observe the estimates of the probability of a major earthquake occurring on each of the major Bay Area faults. Students should click on a colored fault segment and look at the three boxes near the top of the screen. A fault name, estimated magnitude, and probability will appear. The fault name is the name of the colored segment they clicked on. The magnitude shown is the magnitude of the earthquake that would occur if this segment ruptured. The probability is the likelihood that this segment will slip in the next 30 years. [Note that the Maacama, West Napa, and Monte Vista thrust faults do not have predicted magnitudes/probabilities.]
   a. Have students explore the magnitudes and probabilities of different faults.
   b. Ask students, "Do you think the probability of a smaller earthquake, say magnitude 5 on the Hayward fault, would be higher or lower than the estimates on this web site?" (Answer: much higher because smaller earthquakes happen more often). "Do you think that the probability of a magnitude 6.5 earthquake in the next 5 years on the Hayward fault would be higher or lower?" (Answer: Lower).
5. Share the brief descriptions of the Four Earthquake Scenarios with your students. Using the map that they are exploring, have them record the magnitude and probability for each of these four scenarios.
6. Have groups navigate to the 1906 Scenario Earthquake Scenario website which is accessible from the Earthquake Hazards Student Web Page.
   a. The first page on the web site shows the predicted shaking intensity IF the 1906 earthquake were to happen again. What is the probability of that happening in the next 30 years? (See information on the table they just completed.)
   b. Red colors are areas that will experience stronger shaking and lighter green and blue colors will experience less shaking intensity. Encourage students to remember the factors that affect shaking intensity (earthquake magnitude, distance from earthquake rupture, rock type).
   c. Each of the five potential sites in which the students can select to live is indicated by a thick rectangle. For each site, zoom in by clicking on the center of the box. Zoom in again. You should now see the rectangle surrounding a few city blocks. The names of each city are written on the top of each web page. Zoom out by using the BACK button on the web browser or clicking on the words "Zoom Out" on the bar on the right.
   d. Demonstrate the Liquefaction susceptibility option. This map answers the question: "If strong shaking occurs here, how likely is it that there will be soil liquefaction?" An area that never experiences strong shaking will not have liquefaction, even though this map indicates that it is susceptible.
   e. Remind your students that some earthquakes would cause lots of damage if they happen, but have only a small chance of happening during their lifetime. They might be better off preparing for a smaller earthquake that is more likely to occur. That is the trade-off they will have to think about.
7. Once students understand how the site works, have them record the name of the city and the predicted shaking intensity for each site for each of the four earthquake scenarios. Have the students record the liquefaction susceptibility for each of the five sites, remembering to zoom in all the way on each one.
8. Once the students have completed the Data Record Sheet, they can use this data to complete their report. Additional websites to explore are listed at the bottom of the Earthquake Hazard Analysis Activity sheet.
9. Determine the amount of class time you would like your students to use for the completion of their reports. To bring this activity to a close, have students share their decisions and the rationale for their choices with the rest of the class.

Resources used

How do scientists determine earthquake probabilities?
http://quake.usgs.gov/~dalessio/DLESE/EQ/scenarios_aboutprobabilities.html

Modified Mercalli Intensity Scale
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-008-814

What's the Probability?
http://quake.usgs.gov/~dalessio/DLESE/EQ/scenarios.html

1906 Scenario Earthquake Scenario
http://quake.usgs.gov/~dalessio/DLESE/EQ/index.html

Four Earthquake Scenarios
http://quake.usgs.gov/~dalessio/DLESE/EQ/scenarios_about.html