Earthquake Patterns

Concepts and learning outcomes

Students will understand that:

• Earthquakes may occur repeatedly at the same locations.
  • Scientists examine the average time between ruptures as a useful measurement for assessing the risk the fault presents.
  • The more time that passes between repeated surface ruptures on a single fault, the larger the earthquake.
  • Smaller earthquakes cause less damage each time but occur more often.
• Earthquakes relieve strain that accumulates over time because of plate motion.
  

Time requirements

Vocabulary

Background for teachers

An article in the Undergraduate Engineering Review at the University of Wisconsin-Madison provides detailed information on the cyclic nature of earthquakes. It describes one way to think about the different stages before, during, and after an earthquake (it identifies 5 stages, though there are several other ways scientists divide them). It also gives several case studies about how information from each of these stages could one day be used to predict earthquakes. The reason for the cyclic nature of earthquakes is because the driving forces of plate tectonics never stop.

Read about the Parkfield Experiment. This site describes the scientific background for the experiment, including the tectonic setting at Parkfield, CA, the historical earthquake activity on this section of the San Andreas fault, the monitoring and data collecting activities currently being carried out, and plans for future research. Start by reading the Introduction then click on Background, then on Earthquake Prediction (all on left side). Data are available to view in real-time and download.

For background information to help you demonstrate to students that earthquakes repeat cyclically, go to Parkfield: Earthquake Prediction: A Brief History. This website gives historical background information on Parkfield, CA where six earthquakes have repeated in almost the same spot since 1857. The main point is that the earthquakes at Parkfield are all very similar in size and happen at a surprisingly regular interval (about once every 22 years). The regular pattern and the fact that the time between earthquakes is only a few decades rather than hundreds or thousands of years makes it the perfect place for scientists to study. The web page describes some of the equipment the United States Geological Survey (USGS) uses to study the fault during all stages of the earthquake cycle.

Teacher tip

Activity 2 may be too difficult for some middle school students. The concepts will still be sufficiently covered if only Activity 1 is completed.

Activities 2 and 3 are very similar. They simply use the data from two different locations. Depending upon student ability and time constraints you may want to consider the following options:

• Do Activity 2 together as a class activity so that students fully understand the directions and then have them complete Activity 3.
• Do Activity 2 (or 3) only, and use the other as an optional extension, extra credit, or homework.

Activities

1. Patterns from Parkfield: Students look at the cyclical nature of the Parkfield, California earthquakes.
2. Patterns of Recurrence: Students investigate and graph earthquake occurrences on the Mojave segment of the San Andreas fault in order to see the relationships among fault length, recurrence interval, magnitude, and risk.
3. Recurrence on the Hayward Fault: Students apply what they have learned about patterns of recurrence to patterns along the Hayward Fault.

Resources used