Here's why:

* Lithosphere: The Earth's outer layer, composed of the crust and the uppermost part of the mantle. It's relatively rigid and brittle.

* Fracture: A break or crack in a material.

* Fault: A fracture in the Earth's crust where there has been movement.

Faults are where the Earth's tectonic plates interact. The movement along these fractures can cause earthquakes, volcanic activity, and the formation of mountains.