ATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 4.3 Faulting
Near the surface of the earth, rock is brittle and will crack or fracture when placed under great stress by earth movements. Rocks contain many small fractures or joints. When a lot of movement has happened along a fracture it is called a fault. Faults often occur in parallel sets because the stress that produces them operates
over a large area. Pressure and tension make the land either side of the fault move up, down or sideways.
Fault Normal fault
Normal faults Land surface Rock layer
Stretching of crust
Exposed surface called a fault
Movement
(tension/ extension)
When a sloping fault is created and land slips down along one side of it, a normal fault is formed. These are caused by the land being pulled apart (tension), sometimes making a rift valley. The exposed face of the fault is called the fault scarp.
Fig. 8 Exam Diagram: A normal fault
Reverse fault Fault
Land surface Rock layer
Squashing of crust
(compression /
Fig. 9 A normal fault in sedimentary rock in El Salvador Reverse faults Compression Movement Fig. 10 Exam Diagram: A reverse fault
If pressure from earth movements (compression) causes land to move up along a sloping fault line a reverse fault is formed, sometimes making block mountains, for example the Ox Mountains of County Sligo.