What is Fault in Geology?
A fault is a fracture or region of fractures between two blocks of rock. Faults enable the blocks to pass relative to every other. This motion may appear rapidly, in the form of an earthquake - or may also happen slowly, in the shape of creep.
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| Figure 1 Types of faulting in tectonic earthquakes, Publisher Encyclopædia Britannica, 2015 |
Faults may additionally vary in size 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 attitude in between.
Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip alongside the fault to classify faults. Faults which move along the direction of the dip airplane are dip-slip faults and described as either ordinary or reverse (thrust), depending on their motion. Faults which cross horizontally are regarded as strike-slip faults and are categorized as both right-lateral or left-lateral. Faults which exhibit each dip-slip and strike-slip action are recognized as oblique-slip faults.
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