What term describes the area in a fault zone that remains stationary while the opposite side moves?

The term that describes the area in a fault zone that remains stationary while the opposite side moves is the footwall. In geological terms, when a fault forms, the hanging wall is the block of rock that sits above the fault plane and can move downward relative to the footwall, which is the block of rock that remains stable or moves less while the hanging wall shifts.

Understanding the relationship between the footwall and hanging wall is crucial in the study of tectonic activity and how earthquakes occur. The stability of the footwall is significant as it provides a reference point for measuring the movement of the hanging wall, which can be indicative of stress accumulation along the fault line. The other terms, like fault line and epicentre, refer to different concepts in geology; the fault line is simply the boundary between two tectonic plates, and the epicentre is the point on the Earth's surface directly above where an earthquake originates.