Here's why:

* Fault: A fracture in the Earth's crust where there's been movement.

* Hanging Wall: The block of rock that sits above the fault plane. It's named as if it were hanging from the fault like a picture on a wall.

* Footwall: The block of rock that sits below the fault plane.

When a fault moves downward, it's called a normal fault. This happens when the tectonic forces are pulling the Earth's crust apart. The hanging wall will move down relative to the footwall.

Let me know if you have any other questions!