Lesson 6: Earthquakes and Tsunamis
During the next several weeks we'll be learning about the hazards associated
with specific geologic processes such as earthquakes (as in San Francisco, 1906, at right), volcanic eruptions, floods,
and landslides. Each chapter we'll study provides some background on the underlying geologic processes, looks at how the hazards they create impact human activities and at what steps we can take to minimize the loss of lives and damage to property.
This week we'll examine two phenomena—earthquakes and tsunamis—that are often closely related. You'll learn how seismologists measure and locate earthquake foci using seismograms, the strategies they are using to forecast the likely times and locations of future earthquakes, and what steps society can take to avoid or mitigate the damage and loss of life that quakes—and the tsunamis that often accompany them in coastal areas—are likely to cause.
As you read through the discussion of earthquakes and tsunamis in our text and work through the online Earthquake exercise it will be helpful to take notes so that you can keep track of major points and have that information available when we use it later in the semester. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz described at the bottom of the page.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Predict which of the seismic waves generated by an earthquakeP, S, or surface wavesare likely to arrive first at a distant seismic station and which characteristics of the earthquake its P-S delay and wave amplitude can be used to determine.
- Distinguish normal, reverse, and strike-slip faults in cross-sections or block digagrams and tell which type of stress (extensional, compressive, or shear) is associated with each type of fault.
- Explain why longer periods of repose along a fault might be expected to produce larger earthquakes in light of the elastic rebound model.
- Distinguish between an earthquake's magnitude and its intensity, and explain how differences in distance, direction, focus depth, or substrate materials are likely to affect the shaking produced by a given earthquake. (Note: Do not worry about the differences between moment and Richter magnitudes; just be sure that you understand what property of an earthquake magnitude describes, and how quakes with different magnitudes differ in the amounts of energy they release and ground motion they produce at a given distance.)
- Predict which types of earthquake effects (such as liquefaction, landslides, and tsunamis) might pose the greatest threats to the populations of large cities, coastal areas, or mountainous areas and explain his or her rationale.
- Decide whether a set of given observations is better suited for making a long-term (conditional probability) or a short-term (forecast) earthquake prediction, and explain how the data are related to the prediction.
- Contrast the different ways in which a tsunami can be generated and describe how tsunamis change as they move from the open-ocean to nearshore areas.
- Outline five strategies we can use to minimize tsunami hazards and suggest which strategy or strategies might be most appropriate in a specific situation.
Reading and Browsing Assignment
- Read Chapters 6 and 7 and focus on the topics outlined in the learning objectives above.
- Take a few minutes to browse through the IRIS educational resources site. In the "Teaching About Earthquakes" section you'll find some cool animations of seismic waves as well as several informative video lectures on faulting and earthquakes.
- California is one of the most seismically active places in the world. You can see a near-real time map of the the past week's earthquake activity in the state by visiting the Recent Earthquakes Map. (Click on a quake and see what happens!) Also, check out the California Earthquake Forecast map based on recent aftershock activity. Finally, to see what's up at College of the Siskiyous check out the online record of the campus seismometer.
- Finally, to learn more about tsunamis and about what National Oceanic and Atmospheric Administration is doing to detect and warn about them check out NOAA's tsunami site.
Exercise 6: Earthquake (Due by 9:00 AM on 26-Sep-2010)
After you have read the chapter and are comfortable with the concepts outlined in the learning objectives above, point your browser to Virtual Courseware's Earthquake exercise.
- Under "Main Activities" on the first screen, click "Travel Time" and work through the exercise by following the instructions and using each tool in sequence to construct a travel time diagram. Like the earlier radiometric dating exercise you worked on this one uses Java applets that may take a little while to load, so be patient. At the end of the first part of the exercise return to the main screen (you do not need to save your results from the first part.)
- Next, work through the "Epicenter and Magnitude" exercise (third button under "Main Activities") which shows you how to calculate a Richter magnitude. At the end of this part of the exercise you will be asked if you want to take a quiz. Click yes, fill in your name, and enter 1823490 as your class code. (Write this number down now so that you have it when you go to the Earthquake site.) Complete the 10-question quiz. When you are done you will be able to review your score, and the program will automatically post a copy of it to a file that I will access next Monday (26-Sep-11). (You may want to print a copy of the page that shows your certificate and quiz results and keep it until I confirm your score by posting it to our class gradebook.)
- When you've finished both parts of the exercise (Travel Time and Epicenter & Magnitude) and taken the quiz, you'll be finished with Exercise 6. Have funthis is a very cool way to learn about how seismologists determine the locations and magnitudes of earthquakes.
Quiz 6: Earthquakes and Tsunamis (Due by 9:00 AM on 26-Sep-2010.)
After you feel you have met the learning outcomes outlined above, please complete Quiz 6 in the Etudes "Assignments, Tests, and Surveys" area. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around the basics of earthquakes and tsunamis pretty well and are ready to move on to a more detailed look at volcanism and volcanic hazards next week.