Rocks are very slowly, but continuously moving and changing shape. Under high temperature and pressure conditions common deep within Earth, rocks can bend and flow. In the cooler parts of Earth, rocks are colder and brittle and respond to large stresses by fracturing.
A fault is a crack across which the rocks have been offset.
- They range in size from micrometers to thousands of kilometers in length and tens of kilometers in depth, but they are generally much thinner than they are long or deep.
- In addition to variation in size and orientation, different faults can accommodate different styles of rock deformation, such as compression and extension.
Not all faults intersect Earth’s surface, and most earthquakes do not rupture the surface. When a fault does intersect the surface, objects may be offset or the ground may get cracked, or raised, or lowered. We call a rupture of the surface by a fault a fault scarp and identifying scarps is an important task for assessing the seismic hazards in any region.