Faults are fractures in earth's crust where rocks on either side of the crack have slid past each other.
sometimes the cracks are small with barely noticeable movement between the rock layers. other faults can also be hundreds of miles long, such as the san andreas fault in california. we classify faults by how the two rocky blocks on either side of a fault move relative to each other. when movement along a fault is the reverse of what you would expect with normal gravity, the fault is called a reverse fault. the hanging wall moves up in relation to the foot wall.