Final answer:
Geologists monitor faults to understand and predict earthquakes, ensure safety for infrastructure, and inform geological planning for engineering projects.
Step-by-step explanation:
Geologists monitor changes along a fault because the motion along fault zones is crucial for understanding and predicting earthquakes. The Earth's tectonic plates move continuously, but this movement is not always smooth. The creeping motion of these plates against each other builds up stress in the Earth's crust, which can be released in the form of sudden, violent slippages, causing earthquakes. Moreover, monitoring can inform infrastructure planning, especially in the petroleum, mining, and engineering industries, to prevent disasters and maintain the safety of engineering structures. By studying the deformation within the crust, geologists can contribute valuable insights into the behavior of deformed rocks and ensure proper geological planning is considered in engineering projects.