Fault reactivation is a research area within geology and geophysics that focuses on understanding how and why faults that were previously inactive can become active again. This can occur due to changes in the stress regime of the Earth's crust, such as from tectonic forces or human activities like mining or fluid injection. Understanding fault reactivation is important for assessing seismic hazards and risks associated with activities that may trigger fault movement. Researchers in this area study the mechanics of fault movement, the factors that control fault reactivation, and the potential consequences for seismic activity and geologic hazards.