* Tectonic Plates: The Earth's outer layer is broken into large, moving pieces called tectonic plates. These plates "float" on the hot, semi-molten layer below (the mantle).

* Plate Boundaries: Where these plates meet, there are three main types of boundaries:

* Convergent boundaries: Plates collide, causing one to slide under the other (subduction) or crumple together (mountain building).

* Divergent boundaries: Plates move apart, allowing magma to rise and form new crust.

* Transform boundaries: Plates slide past each other horizontally.

* Faults: The movement of tectonic plates along these boundaries creates stress on the rock. When the stress becomes too great, the rock breaks, creating a fault.

Think of it like this: Imagine you have a piece of paper. If you push the edges together, it will buckle and eventually tear. The tear is like a fault, and the pushing is like the tectonic plates.

Therefore, the movement of tectonic plates along their boundaries is the primary force that causes faults.