Thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If the angle of the fault plane is lower (often less than 15 degrees from the horizontal) and the displacement of the overlying block is large (often in the kilometer range) the fault is called an overthrust or overthrust fault. Erosion can remove part of the overlying block, creating a fenster (or window) – when the underlying block is exposed only in a relatively small area. When erosion removes most of the overlying block, leaving island-like remnants resting on the lower block, the remnants are called klippen (singular klippe). Blind thrust faults If the fault plane terminates before it reaches the Earth's surface, it is called a blind thrust fault. Because of the lack of surface evidence, blind thrust faults are difficult to detect until rupture. The destructive 1994 earthquake in Northridge, Los Angeles, California, was caused by a previously undiscovered blind thrust fault. Because of their low dip, thrusts are also difficult to appreciate in mapping,