10 Lecture 16 Faulting and Folding Greg Anderson Today's lecture discusses how rocks deform and break when placed under stress. This is important information in its own right, but is particular important in terms of the earthquake lectures to come in Lectures 17 and 18.
Stress is force divided by area.
This stress is the same in all directions, and is due to the weight of overlying rock. Imagine squishing some clay in between your fingers - you are applying a directed stress to the clay, in the direction of the line connecting your fingers through the clay. The result is the clay squishes flat. In rock, directed stress is usually due to tectonic forces. If you place a rock under very high confining stresses, it will not do much but compact, except that some of the minerals making up the rock may change form to other minerals.