Fault lines are fractures in the Earth's crust where blocks of land have moved relative to each other. These geological features are crucial in understanding seismic activity, as they are often the sites of earthquakes. The movement along these lines can be caused by tectonic forces, leading to significant geological changes over time. In addition to their role in earthquakes, fault lines can also influence the landscape, creating valleys and mountains. Understanding fault lines helps scientists predict seismic events and assess risks in populated areas. Notable examples include the San Andreas Fault in California and the North Anatolian Fault in Turkey.