Large areas of faulting occur in the Earth's crust due to the movement of tectonic plates. The Earth's crust is made up of several plates that move slowly over time. When two plates move towards each other, they collide and create stress along their boundaries. This stress builds up until the rocks along the boundary break and move suddenly, creating a fault. Faults can also occur when plates move apart or slide past each other.
The type and extent of faulting depend on the movement and nature of the tectonic plates involved. For example, when two plates move towards each other and one is forced beneath the other, a subduction zone is formed, and faults occur both along the boundary and within the overriding plate. These faults can be very long and deep and can cause large earthquakes.
Similarly, when two plates move apart, they create a rift valley, and faults occur along the boundaries of the plates. These faults can also be very long, and as the plates move apart, new faults can form and old ones can widen.
In summary, large areas of faulting occur in the Earth's crust due to the movement of tectonic plates, which create stress along their boundaries. When this stress becomes too great, the rocks break, and faults are formed. The extent and type of faulting depend on the movement and nature of the plates involved.