The breaking and sliding surface between blocks of crust is called a fault. Faults are fractures in the Earth's crust where rocks have broken and moved. They can be caused by a variety of forces, including earthquakes, volcanic eruptions, and the movement of tectonic plates. Faults can be either vertical or horizontal, and they can range in size from a few meters to hundreds of kilometers.

When rocks on either side of a fault move, they can create a variety of features, including:

* Scarps: These are steep cliffs that form when one side of a fault moves up or down relative to the other side.

* Grabens: These are valleys that form when a block of crust sinks between two faults.

* Horsts: These are mountains that form when a block of crust rises between two faults.

Faults can also be a source of earthquakes. When rocks on either side of a fault move suddenly, they can release a tremendous amount of energy. This energy can travel through the Earth in the form of seismic waves, which can cause damage to buildings and infrastructure.

Faults are an important part of the Earth's geology. They play a role in the formation of mountains, valleys, and other landforms. They also help to release energy from the Earth's interior, which can prevent the buildup of pressure that can lead to earthquakes.