The fault plane is where the action is. It is a flat surface that may be vertical or sloping. The line it makes on the Earth's surface is the fault trace. Where the fault plane is sloping, the upper side is the hanging wall and the lower side is the footwall.
Normal faults form when the hanging wall drops down. The forces that create normal faults are pulling the sides apart, or extensional.
Reverse faults form when the hanging wall moves up. The forces creating reverse faults are compressional, pushing the sides together.
Strike-slip faults have walls that move sideways, not up or down. That is, the slip occurs along the strike, not up or down the dip. In these faults the fault plane is usually vertical, so there is no hanging wall or footwall. The forces creating these faults are lateral or horizontal, carrying the sides past each other.
Jan 8th, 2015
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