Faults are of major interest both in structural geology, tectonics, in engineering geology and rock mechanics. The interest in faults and fault zones is practical as well as scientific and aestethic due to the following reasons: Faults and associated structures form the major discontinuities in the Earth´s upper crust and are largely responsible for the design and shape of the great mountain belts. These structures highly influence the characteristics and behaviour of:
• rock mass
• hydrogeology and hydrology
• morphology and land surface.
A fault or fault zone is a planar dislocation along which there has been displacement of the rocks on one side relative to those on the other side. This includes fracture zones and shear zones. Faults may also be defined as fracture surfaces or zones along which rock masses have moved relative to each other. Faulting may result in the disintegration of the adjacent host rocks by fracturing (“cataclasis”), and the formation of fault rocks, particularly fault gouges and cataclasites.
Understanding faults is useful in the design for long-term stability of dams, tunnels, buildings, and power plants, as well as for their effect on population centers and infrastructure. Study of faults helps in understanding mountain-building and deformation processes – studies that have many times turned out to have practical value. Faults are extraordinarily important in rock engineering. The extreme complexity of faults makes their geotechnical investigation and characterization difficult. The technical problems related to faults include their substantial heterogeneity with regard to the internal structure, mineralogical composition, mechanical and hydrological properties as well as stress distribution.