# Subduction Zone Earthquakes

#### Summary

While working in groups to facilitate peer tutoring, students manipulate a hands-on, physical model to better comprehend several characteristics of subduction zone earthquakes. By plotting earthquake epicenters on the simulated overriding plate, students observe the difference between focus and epicenter. The model also provides opportunities for students to interact with the data to determine the relationships between distance from the trench, focus depth, and earthquake magnitude. Furthermore, the model allows students to explore the relationship between subduction angle and the locations of earthquake epicenters.

## Learning Goals

Students will understand:

- The difference between earthquake focus and epicenter
- That the deepest earthquakes are farthest from the trench.
- That most earthquakes occur on only one side of the trench.
- The relationship between subduction angle to earthquake epicenters
- That there is no relationship between earthquake magnitude and earthquake position or depth.

## Context for Use

This model can be used in a variety of instructional settings including large lecture classes and small laboratory classes, and can be used in either a unit on plate tectonics or earthquakes. Student manipulation of the model requires more than one person, thus it works best when students are grouped together.

## Teaching Materials

Each student model consists of the following materials:

- One legal-size (8.5 x 14) piece of paper labeled Oceanic Lithosphere" showing a trench at one end, a series of earthquake foci, and a depth scale along one edge. (See handout.) Earthquake magnitudes are denoted by size of the symbol and are categorized as small, medium, and large.
- One 8.5 x 11 piece of clear transparency film labeled "Continental Lithosphere".
- Two transparency markers (different colors).

Subduction Zone Earthquakes Templates (Acrobat (PDF) 85kB Apr29 08)

During a lecture, have the students hold the transparency level while allowing the paper to hang downwards at any angle. The paper represents the descending oceanic crust and the transparency represents the overriding plate. Students use the marker to plot the locations and magnitudes of each earthquake, and then use that information to answer instructor-led questions concerning the relationships between earthquake magnitude, position, and depth.

## Teaching Notes and Tips

Students will be tempted to complete this exercise with both the paper and the transparency lying flat on their desk. This geometry will yield correct answers but will not simulate either the geometry of the descending plate or the relationship between focus and epicenter.

## Assessment

Several different assessment techniques can be used depending on time and the needs of your class.

- If you have a personal response system, you can ask conceptest questions that focus on epicenter location or magnitude distribution. (See Reference and Resource section for conceptest questions that assess this model.)
- By walking around the class, the instructor can observe how well the groups comprehend the underlying concepts and ask individual students to explain their conceptual understanding.
- A short quiz could be given at the end of the class.
- Students could complete a worksheet containing questions about subduction zone earthquakes.
- Students could write a 'minute paper' explaining the distribution of subduction zone earthquakes.

## References and Resources

ConcepTest questions used with this model: