1. Teaching Aids Service by KRRC Information Section

2. What determines if a rock Folds (bends) or faults (breaks)? Type of force applied Pressure Temperature Rock (mineral) composition

3. Three Major Types of Directed Stress Compression Extension Shear

4. Compression Action of oppositely directed forces acting towards each other at the same time

5. Tension Action of coinciding and oppositely directed forces acting away from each other

6. Shear Action of coinciding and oppositely directed forces acting parallel to each other across a surface

8. Brittle Deformation (Rupture) As the applied force is increased, the rock undergoes little change until it suddenly breaks Usually along a zone of weakness

10. Brittle Versus Ductile Some rocks are naturally brittle Some rocks are naturally ductile A rock that is brittle at shallow depths can be ductile at greater depths

11. Factors that Affect Deformation Temperature Pressure Strain rate Rock type The variation of these factors determines whether a rock will fault or fold

12. How Rocks Fracture Joints Faults

13. Faults: These are fractures created by tectonic processes along which there has been relative movement of the blocks past each other. Regardless of size, all faults are classified by the direction of relative movement (which is called slip)

16. Fault Terminology Fault Plane: It is the planar surface or fracture along which relative displacement of blocks takes place during the process of faulting. When it is non-planar the same surface is known as fault surface. The fault plane may be vertical, inclined or horizontal. Dip: The dip of the fault is its inclination with the horizontal as measured in a vertical plane at right angles to the strike of fault. It is measured both in terms of direction and dip.

18. Hade: The hade of the fault is the angle which the fault makes with the vertical. In other words it is the complementary to the dip angle. Throw: It is the vertical displacement of dip separation measured in a direction perpendicular to the strike of the fault in a vertical plane. Heave: It is the horizontal component of dip separation measured in a direction perpendicular to the strike of the fault in a vertical plane.

19. The Walls The two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the hanging wall occurs above the fault plane and the footwall occurs below the fault. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall hanging above him. Net Slip Slip: It is defined as relative displacement of any two points that were formerly contiguous to each other as measured along a fault plane. Dip Slip: The displacement of any two points along the dip is known as dip slip. Strike Slip: The displacement of any two points along the strike is known as strike slip.

23. Rake: Rake is a term related to slickensides, it is used to express angular relationship of slickensides or some other line with the fault plane. Fault Line: is the surface trace of a fault, the line of intersection between the fault plane and the Earth's surface. Fault Zone: Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane. Shear Zone: It is a zone on either side of which major faulting has taken place. It is a tabular zone of some thickness that may be extending to any depth and breadth and is characterized with intensive displacement. Fault Gouge and Fault Breccia.

26. Recognition of faulting Faults are fractures along which there is relative sliding movement of the blocks in opposite directions on either side. We recognize them by various criteria: 1) Layers of different types and ages of rock units sit side- by-side 2) Abrupt topographic discontinuities of landforms 3) Depressions along the fault trace (broken rock is more easily eroded) 4) Scarps or cliffs 5) Sudden shifts of drainage courses. 6) Abrupt changes in vegetation patterns. 7) Presence of fault gauge and fault breccia

28. Classification of faults The apparent movement of the disrupted blocks along the fault plane. The direction of slip Dip-slip faults – Normal – Reverse Strike-slip faults – Right-lateral – Left-lateral Oblique-slip faults

29. Types of Faults Normal Fault: A fault in which hanging wall has apparently moved down with respect to the foot wall is known as a Normal fault. These faults develop where two blocks of rock are pulled apart. These are also known as gravity faults. Horst : is the raised fault block bounded by normal faults or graben. A horst is formed from extension of the Earth's crust. The raised block is a portion of the crust that generally remains stationary or is uplifted while the land has dropped on either side.

30. Hanging wall Foot wall

31. Normal Fault footwall hanging wall footwall Before After

32. Normal Fault hanging wall footwall

33. Graben: is a depressed block of land bordered by parallel faults. A graben is the result of a block of land being downthrown producing a valley with a distinct scarp on each side. Graben often occur side-by-side with horsts. Horst and graben structures are indicative of tensional forces and crustal stretching.

34. Grabens are produced from parallel normal faults, where the hanging wall is downthrown and the footwall is upthrown. The faults typically dip toward the centre of the graben from both sides. Horsts are parallel blocks that remain between graben; the bounding faults of a horst typically dip away from the centre line of the horst. Single or multiple graben can produce a rift valley.

35. Rift Valley

37. Hanging wall Foot wall

38. Reverse Fault footwall hanging wall footwall hanging wall Thrust faults: Thrust faults are low-angle reverse faults. Nappes: This term have been used for extensive blocks that have been transported to great distances, often ranging to several hundred kilometers, along a thrust plane. Thrust Fault

39. Strike-slip Faults Motion of the fault blocks is parallel to the strike direction There are 2 types Right-lateral Left-lateral

41. Left-lateral Strike Slip Fault left-lateral If you were to stand on the fault and look along its length, this is a type of strike-slip fault where the left block moves toward you and the right block moves away.

42. Right-lateral Strike Slip Fault right-lateral If you were to stand on the fault and look along its length, this is a type of strike-slip fault where the right block moves toward you and the left block moves away.

43. San Andreas Fault (right-lateral)

44. Displacement both vertically and horizontally

47. Joints Cracks in rocks along which there has been no appreciable displacement.

48. Nature of joints: Open or closed Attitude: Dip and strike may be described either independently or with respect to the rock in which they occur. Classification (a) Spatial relationship (b) Geometry (i) Strike joints (ii) Dip joint (iii) oblique joints

50. Genesis Tension joints Compression joints Shear Joints

51. Joints in Igneous Rocks Sheet joints Mural Joints Columnar Joints

52. Giants Causeway - Ireland Columnar jointing results when basalt or (other igneous rocks) cools from the outside in causing shrinkage and the development hexagonal joints