Living in Earthquake Country (6-12)
Overview of the box
Concepts and Standards
Lessons:
1 Earthquake damage
2 Faults are at fault:
Where earthquakes occur
3 Earthquake patterns
Activities:
1 Patterns from Parkfield
2 Patterns of recurrence
3 Recurrence on the
Hayward Fault
4 Seismic waves
5 A whole lot of shakin’
goin’ on!
6 Landslides, liquefaction,
and structural failure
7 Examining all the factors
Online resources
Student Web Page

Extras:
Lessons that use the
Rapid Earthquake Viewer
Teaching Boxes Home
Lesson 3: Earthquake Patterns

Activity 1

Patterns from Parkfield

Materials / Preparation

  • Blocks of foam rubber to illustrate strike-slip faults – see Why do Earthquakes Happen?
  • LCD projector OR overhead projector. If using the overhead, print out Parkfield: Earthquake History and make a transparency that includes the chart and seismogram image. These images show the similarity and pattern of earthquakes in Parkfield, CA

Grouping

Small group and then whole class

Teacher tip

Specific tips are embedded in the procedures below.

Procedures

  1. Open this lesson with a quick activity that demonstrates how earthquakes occur. Guide students through the activity Why do Earthquakes Happen? in which they will experience two foam rubber "plates" sticking as they move past each other and then the sudden movement when that pressure is released. Discuss what happens. Remind them that this is a model of what happens at a strike-slip fault.
  2. Ask students what they think scientists can learn from studying past earthquakes. After a brief discussion, let them know that they will be taking a quick look at an interesting study area of the San Andreas fault (a strike-slip fault) in Parkfield, California.
  3. Share the history of Parkfield, Ca. from the teacher resource site:Parkfield: Earthquake Prediction: A Brief History. Emphasize that 6 damaging earthquakes have happened in Parkfield since 1857.
  4. Project only the seismograms that are shown at the bottom of the screen at Parkfield: Earthquake History. Point out that these are seismograms of three earthquakes that occurred at Parkfield, California along the same fault in 1922, 1934, and 1966. What do you notice? What does that similarity tell us?
    Teacher tip: A seismogram is essentially a fingerprint of an earthquake, so the similar seismograms indicate that these earthquakes were about the same size and occurred in about the same location. For students who have studied earthquake location and magnitude, get them to justify their answers in terms of the similar time between P and S wave arrival and nearly identical wave amplitude. P-Waves arrive at the left edge of the seismogram, S-waves arrive where the label 1934 points, and the largest amplitude waves are surface waves. You will go into more detail about seismic waves in Lesson 4.
  5. Look at the dates when earthquakes occurred in the past. Is there a pattern?
    Based on the chart of dates, ask students to estimate when the next earthquake should occur.
    Teacher tip: The average interval is 22 years and this is what scientists used. There is regularity in the occurrences of Parkfield earthquakes – they do not occur at random times. The time between earthquakes at Parkfield is more predictable than almost any other location on earth.

    a. Inform the students that scientists used the pattern in the dates to forecast that an earthquake would occur between 1988 and 1993. How was that date derived? Did the seismologists act like magicians and pull the date from out of a hat? Wouldn’t they have some scientific basis for the forecast date? What could it have been?
    Teacher tip: Remind students of the activity that they did with the foam plates and how the pressure built up to a certain pressure and then was released.

    b. Explain that an earthquake did occur in 2004, not in the time span of ’88-‘93 as forecast. Does this change the pattern, negate the pattern? Is it still in the realm of following a pattern? Do you think this would be true for other faults?
    Teacher tip: The time between earthquakes varies between 12 and 38 years at Parkfield, which means that a prediction using the 22-year average might be off by more than a decade. That may seem like a long time to a young student, but, as the next two activities in this Lesson show, some faults have earthquakes once every several hundred or even thousands of years apart, making them much harder to predict in our own lifetimes.

  6. Tell the students that in the next activity they will be exploring patterns of earthquakes on other areas of the San Andreas Fault.

Resources used

Why do Earthquakes Happen?
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-008-818

Parkfield: Earthquake History
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-008-819

Parkfield: Earthquake Prediction: A Brief History
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-008-809

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