A fractured surface in the Earth’s crust along which rocks have travelled relative to each other. Usually, faults occur together in large numbers, parallel to each other or crossing each other at different angles; these are then described as a fault system. The slope of the fault is known as the dip. Where rocks have moved down the dip there is a normal fault; where rocks have moved up the dip, there is a reverse fault. A thrust fault is a reverse fault where the angle of dip is very shallow and an overthrust fault has a nearly horizontal dip. A fault plane is the surface against which the movement takes place. A tear fault is where movement along the fault plane is lateral. This latter type of fault may be termed a strike-slip fault. Regions, such as the Harz of Germany, that are split by faults into upland horsts or depressed rift valleys are said to be block faulted.
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