# Modelling an earthquake: Teachers' notes

Students use a brick and sandpaper to model the characteristics of earthquakes. They record the amount of slip produced each time the brick moves, and the force before and after each slip.

## Learning objectives

Students will:

• compare the relative frequencies of slip size with real earthquake data
• observe force build up, slippage and release over several slip cycles
• compare this with the pattern of stress build-up and release in different earthquake models.

## Notes

This arrangement with a force meter provides a steady increase in tension in the string, equivalent to stress building up in a seismic fault. The pulley can be clamped to a corner of the bench, or could be screwed onto the plank or runway to provide an integral unit.

The area of the brick in contact with the plank represents the fault and is a constant size. You may need to experiment with different combinations of brick and sandpaper to get the best effect: the brick shouldn't move as soon as you start to turn the pulley but should 'go' suddenly.

You may prefer to use sandpaper on the bottom of the brick, too, and to use bungee cord in place of the string attached to the brick.

Task A focuses on the relationship between how often earthquakes occur and their size. Students should find that the slip size can vary considerably from one 'slip' to another.

Task B is an additional task about using a model to predict when an 'earthquake' will occur and what determines how big it is likely to be. It can really only be done with access to data logging equipment with suitable force sensors, because it is too difficult to establish reliable values of forces by looking at the reading on a force-meter as the brick suddenly jerks then stops. If this is not possible, preliminary observations of the force before slippage should still allow students to establish that the force reading can vary quite considerably from one 'slip' to another.

## Resources needed

Each group will need:

• SEP pulley for earthquake simulation (see note above)
• A plank or a dynamics runway
• A brick
• Coarse sandpaper, plus adhesive tape or G-clamps to stick it onto the plank
• A force meter (eg 0-20 N, 0-50 N)
• Metre rule or tape measure – needs to have mm markings
• Temporary adhesive putty or double-sided tape to stick the ruler down (optional)
• Straw pointer, plus something to stick it onto the brick
• Graph paper
• Eye protection
• Activity: modelling an earthquake

This is one, relatively simple, approach to modelling an earthquake. There are other, similar modelling activities, such as those previously developed by Chris King and the Earth Science Teachers' Association (ESTA) and by Ross Stein for the United States Geological Survey (USGS).

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