Fault systems are geological structures that consist of a series of fractures or zones of weakness within the Earth's crust. These faults can vary in size and orientation and are caused by tectonic forces acting on the Earth's crust. Fault systems play a key role in the movement and deformation of the Earth's crust, and are responsible for earthquakes, mountain building, and other geological phenomena. Studying fault systems can help scientists better understand the processes of plate tectonics, seismic activity, and the formation of mountain ranges.