9. Faults

This chapter takes you to the amazing world where a block of rock mass moves past another such block along a plane of separation called fault. A fault is an elongated zone of high shear stress along which two blocks of adjacent rocks have been offset. It is thus a discontinuity or anisotropy due to which the rock loses its cohesion. Being a plane, a fault can be described in geometric terms such as dip and strike. The orientation of stresses acting upon a fault surface controls the geometry of the fault. Rubbing of two blocks of rock masses not only leaves behind a variety of signatures on or in close vicinity of the fault surface but may also genetically modify the host rocks. During fieldwork, a geologist is sometimes surprised to note that in some areas a fault has concealed one or a few beds while in other areas it has got a few other beds repeated. In brief, a fault is able to do or undo many things to the rocks of an area that sometimes leave a field geologist baffled!