What is the term used to describe the line along which an earthquake occurs?

The term that describes the line along which an earthquake occurs is a fault. A fault represents a fracture or zone of weakness in the Earth's crust where blocks of the crust have moved past each other. This movement can be a result of stress accumulation due to tectonic activity, and when the stress exceeds the strength of the rocks, an earthquake occurs along this fault line.

The epicenter refers to the point on the Earth's surface directly above where the earthquake originates, but it does not describe the line of the earthquake itself. The focus is the actual location within the Earth where the earthquake starts, which is often along the fault but does not represent the extent of the fault line. A seismic zone refers to a broader area that is prone to seismic activity but does not describe the specific line of movement where an earthquake occurs. Thus, the correct answer provides a precise term for the geological feature associated with the earthquake's origin.