A simple, cheap, and easy slider block model

Seth Stein, Department of Earth and Planetary Sciences

Northwestern University, Evanston IL 60208

Carol Stein, Department of Earth and Environmental Sciences

University of Illinois at Chicago, Chicago IL 60607

A common demonstration for teaching about earthquakes is a slider block model, in which an object is pulled across a surface by an elastic. Due to the difference between static and dynamic friction, steady loading produces a series of discrete slip events, analogous to earthquakes. This demonstration is especially useful now that GPS data can be used to observe strain accumulation before earthquakes, which corresponds to the elastic stretching before the block slips.

Organized instructors have nicely prepared models with a crank loading device to provide steady loading. However, less organized instructors like ourselves often want a simple, though less elegant, model that can be prepared quickly. However it can be hard to to find a combination of materials that give the desired stick-slip behavior. Only certain combinations of the block weight, elastic constant, and friction coefficient work.

After trying a variety, we found that one such combination is a piece of a yoga mat, soap bar, and ordinary rubber band. These are easily acquired and carried to lectures.

For a quicktime movie of the model, click here

The mathematics of the model are illustrated below (Stein & Wysession, Fig. 5.7-21).

GPS data showing strain accumulation (Stein & Wysession Fig. 4.5-13)