The graphs above illustrate four idealized models of earthquake recurrence for a fault that bounds two plates that are in steady motion with respect to each other.

bulletPerfectly Periodic

In this model an earthquake always happens when the stress level reaches the same high value and during the earthquake the stress always drops to the same low value.   All of the earthquakes have the same slip and they are equally spaced in time.

bulletTime Predictable

In this model an earthquake always happens when the stress level reaches the same high value.  The slip during each earthquake is variable, so the stress level after each earthquake is not always the same.  Once the slip in one event has been measured, then it is known that the next event will happen when exactly this amount of plate motion has occurred.

bulletSlip Predictable

In this model the stress always drops to the same level after an earthquake.  Once an earthquake has occurred, then one knows that the slip during the next earthquake will be equal to the plate motion that has subsequently occurred.  The longer the time since the last event, the larger the next event will be.


There are some rare faults segments that move by creep rather than large earthquakes.  This appears to be the case for the San Andreas fault where is passes through Hollister, California.  The fault moves by a series of creep events and each year the total slip from creep is the same as the amount of relative plate motion.

The next page give instructions for an experiment using blocks of wood and strings of rubber bands to see which, if any, of these models applies to wooden blocks being pulled by a string of rubber bands. 

Here are some factors to experiment with.  What effect does changing from one block to two stacked blocks have?  Experiment with and without the sandpaper surface of the block in contact with the table or floor.  Try rubber band strings with different lengths.