When a block of rock drops down in relation to the block of rock beside it, a feature known as a "fault" can be created. A fault is a fracture or break in the Earth's crust where rocks on either side have moved relative to each other. This movement is a result of the forces acting upon the rocks, causing one block to move downward while the adjacent block remains in place. The boundary between the two blocks is called the fault plane, and the location where the rocks have moved is known as the fault line.
