Displacement on a fault in the crust results in crustal shortening or crustal extension?

• A. Shortening
• B. Extension
• C. Both
• D. None

Answer: (A)

Displacement on a crustal fault reflects the stress that built it. When the forces are compressional, blocks on opposite sides of the fault push toward each other, so relative movement shortens the horizontal dimensions of the crust (the hanging wall moves up relative to the footwall, and the crust thickens vertically). That is crustal shortening. If the regime were extensional, the blocks would pull apart and you’d get crustal extension, such as with a normal fault. So, under typical compressional conditions, shortening is the expected outcome.