A fault is a fracture or zone of fractures between two blocks of rock where one side has moved relative to the other. A fault divides the rock into a hanging wall and footwall. There are three major types of faults: normal faults, where the hanging wall has dropped down relative to the footwall; strike-slip faults, where the blocks move horizontally parallel to the strike of the fault; and oblique-slip faults, where there is both vertical and horizontal displacement at an angle. Faults can cause problems for civil engineering projects because the crushed rock in the fault zone is weak, unstable, and permeable.

1. Description and
Classification of Faults
Dr. P. Sarathbabu M.Sc. B.Ed. Ph.D.
Department of Geology
Acharya Nagarjuna University

2. A fault is a surface or narrow zone in the earth's crust
along which one side has moved relative to the other in a
direction parallel to the surface or zone.
A fault divides the rocks it cuts into two fault
blocks
Hanging wall for the bottom surface of the upper
fault block.
Footwall for the top surface of the lower fault
block.

4. Three major Faults

5. Normal Fault

6. • Based on the orientation of the relative displacement, or
slip i.e., the net distance and direction that the hanging
wall block has moved with respect to the footwall block
Dip-slip fault: slip is approx. parallel to the dip of
the fault surface
Strike-slip fault: slip is ~ horiz., parallel to the strike
of the fault surface
Oblique-slip fault: slip is inclined obliquely on the
fault surface
• Strike: It may be defined as the trend of the formed by intersection of fault
plane and horizontal plane

7. Strike-Slip Fault

8. Strike: It may be defined as the trend of the formed by intersection of
fault plane and horizontal plane
Dip: The dip is the angle between fault plane and horizontal surface

10. Significance of Faults
• Along a fault zone, highly crushed and sheared rocks are
met with.
• These zones being weak, unstable and highly
permeable, pose expensive problems in civil engineering
constructions, such as dams, reservoirs, tunnels and
highways