This is a brief summary of our knowledge of the earth's interior. Plate tectonics is the continual slow movement of the tectonic plates, the outermost part of the earth. This motion is what causes earthquakes and volcanoes and has created most of the spectacular scenery around the world. The Story of Plate Tectonics Click on this image to see a larger version. A fault is a fracture or zone of fractures between two blocks of rock.
Faults allow the blocks to move relative to each other.
This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.