The rock does not open up. Students may have the misconception that they may be swallowed in an earthquake. It is important not to reinforce this in any way. It is along faults that earthquakes occur. The direction of fault movement varies dependent upon the forces working within the crust.
Normal faults result from tension forces.
This is the predominant type of fault that occurs in Utah. The mountains are forced up by the pressure released and the valley is dropped down. Typically, the valley drops more than the mountains are pushed up. Reverse faults result from compression forces. These faults often occur in areas of folding in mountain belts.