What's the Story?

Dzl52B5.mpg
Click for 1.3 MB MPEG video of two slip events on a table top.

Example of two "earthquake" slip events.


Click for 0.1 MB WMV video showing pen used to pull rubber bands and point to tape measure.


Click for 0.2 MB WMV video of two slip events on stretch fabric.

How could pulling a block of wood with a string of rubber bands have anything
to do with earthquakes?

There are no rubber bands in the Earth, but all solids are elastic, including
the Earth's crust.

The outer hard shell of the earth is broken into about dozen major plates. 
The plates can glide along at a few cm per year over the materials below
them. Earthquakes are not generated at this lower boundary because
at 80 km depth the high temperature and pressure allows the rocks to 
slowly and permanently deform.

At shallow depths, however, along the faults that form the boundary between
the plates, the rocks bend and deform as the plates move past one another. 
They store elastic energy that is eventually released in an earthquake.