Fault is a fracture of huge rocks caused by the earth movement or tectonic forces. But trench is an excavation in the ground caused by man's digging, river erosion, earth movement and other environmental factors.
See the difference through their photos below:
A fault in the Grands Causses as seen from Bédarieux, France. The left side moves down while the right side moves up. The warping of the rock layers on the right is likely due to drag folding.
A trench made for gas main
Have you seen the difference? Can you tell us more differences between fault and trench?