Stressed rock goes through stages of change as the energy within builds up. In the first stage, elastic deformation, the rock will go back to its original shape once the stress is released.
If the stress reaches the rock’s elastic limit, or the point where it can’t go back to its original shape, the rock will be permanently deformed.
This stage of stress is called ductile deformation. Ductile deformation tends to bend layered rock into folds: syncline, or U-shaped; anticline, or bridge-shaped; mono-cline, which looks a little like an escalator; or recumbent, when the fold bends back on itself.
Recumbent folds look something like toothpaste lying on a toothbrush in advertisements.
Rock enters the final stage, fracture, when it is no longer able to bear the stress, and cracks. Fractured rock leads to faults and earthquakes.