A
thrust fault is a type of
fault, or break in the Earth's crust with resulting movement of each side against the other, in which a lower stratigraphic position is pushed up and over another. This is the result of compressional forces.
Another name for high angle thrust fault is reverse fault. The difference between a thrust and a reverse fault is in their influence. A reverse fault occurs primarily across lithological units whereas a thrust usually occurs within or at a low angle to lithological units. It is because of this that it is often difficult to recognize thrusts because their deformation and dislocation can be difficult to detect when they occur within the same rocks without appreciable offset of lithological contacts.
If the angle of the fault plane is low (generally less than 20 degrees from the horizontal) and the displacement of the overlying block is large (often in the kilometer range) the fault is called an overthrust. Erosion can remove part of the overlying block, creating a fenster (or window) when the underlying block is only exposed in a relatively small area. When erosion removes most of the overlying block, leaving only island-like remnants resting on the lower block, the remnants are called klippen (singular klippe).
If the fault plane terminates before it reaches the earth's surface, it is referred to as a blind thrust fault. Because of the lack of surface evidence, blind thrust faults are difficult to detect until they rupture. The destructive 1994 quake in Northridge, California was caused by a previously-undiscovered blind thrust fault.
