Here's why:
* Normal faults: These occur when the hanging wall (the block of rock above the fault) moves downwards relative to the footwall (the block below the fault). This downward movement causes the crust to stretch and thin.
* Crustal shortening: This occurs when the crust is compressed, causing rocks to fold and buckle. This is typical of reverse faults or thrust faults, where the hanging wall moves upwards relative to the footwall.
In summary:
* Normal faults = Extension
* Reverse/thrust faults = Shortening
Think of it like this: imagine pulling a piece of elastic apart. That's what normal faulting does to the crust.
