There is a good example of visible faulting in the Siah Rood Fault Geosite. The Siah Rood fault system accrued in the Eocene Flysch Deposits (about 56 to 33.9 million years ago). One of these faults is more obvious and cut the geological layers. A fault is a fracture or zone of fracture between two blocks of rock. Faults cause the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake -or may occur slowly and silently. Faults may range in length from a few centimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults into three different groups:

1- Normal Fault or Dip-slip in which the block above the fault has moved downward relative to the block below.

2- Reverse (thrust) Fault in which the upper block, above the fault plane, moves up and over the lower block.

3- Strike-slip Fault- a fault on which the two blocks slide past one another.

Siah Rood's Fault is a normal fault. Since this type of faulting occurs in response to extension, they are also called gravity fault.

During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal, vertical, or some arbitrary angle in between.