Final answer:
A thrust fault is formed by compressional stress during mountain-building events; it occurs when the hanging wall block is pushed over the footwall block, seen in mountain belts like the Appalachian Mountains.
Step-by-step explanation:
A thrust fault is formed by compressional stress, which accommodates horizontal shortening of the crust during mountain building events. Compressional stress leads to rocks being pushed together and results in the creation of features such as thrust faults, particularly during tectonic collisions like those that have shaped mountain belts. By contrast, tensional stress would pull rocks apart, leading to the formation of normal faults, and is commonly associated with rifting zones. Shear stress, involving horizontal movements in opposite directions, would give rise to strike-slip faults.
In the context of mountain building and the formation of thrust faults, compressional stress can cause the hanging wall block of a fault to move up and over the footwall block. This action is evident in structures like the Copper Creek Thrust Fault in the Appalachian Mountains, which were formed as a result of the collision between the African and North American tectonic plates during the Pennsylvanian period.
Occasionally, you might observe features typically associated with compression, such as anticlines and synclines, in regions of tensional stress. This could be the result of local compressive forces acting perpendicular to the larger-scale tensional forces of a rifting zone, which may occur along structures such as the Ramapo Fault.