normal fault graben fault reverse fault thrust fault block mountain tear (slip) fault dome structures horizontal structures uniclinal structures
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Fault line: A fracture in the earth’s surface.
Fault plane: The plane along which the faulted block of rock moves upwards or downwards.
Fault scarp: A step/cliff or cliff-like feature on the earth’s surface caused by faulting.
Faulted structures
Faulting occurs when rocks are put under stress at divergent, convergent or transform plate boundaries. Compression, tension and shear forces lead to fractures/fault lines forming along a line of weakness in the surface rock of the earth’s crust. A flat body of rock is then laterally displaced, sunken or lifted up, relative to the surrounding terrain. This can be recognised on sedimentary rock surfaces where the strata are displaced at the fault line. Fault lines can run for hundreds of miles or they can be very short, only affecting a small area.
Faults resulting from tension
Normal fault A normal fault is formed at a divergent plate boundary when tension in the earth’s crust causes it to stretch and become thinner. When the crust eventually fractures, one block of land will be displaced, moving downwards (Fig. 4.6).
Fault scarp Fault line
Footwall Hanging wall Fault plane
Normal fault: tension force – one section of the crust slips downwards
Fig. 4.6 Normal fault. Graben fault
When tension causes two parallel faults, the large block of land in between may slip downwards. A rift valley is formed, with steep escarpments at either side. Death Valley in California and the Rhine Rift Valley in Germany are examples of this type of fault (Fig. 4.7).
Plateau
Fault scarp Fault line
Rift valley
Fault plane
Parallel faults
Graben fault: tension force – central block of crust sinks Fig. 4.7 Graben fault.
