Fault - Parts & Types - Field Evidences

Fault is a fracture discontinuity along which the rocks on either side have moved past each other . It describes about the parts and types of fault an also the various field evidences for the occurrence of a fault .

1. FAULTS ANANDU.S.V University college, Trivandrum

2. FAULT What is a Fault ? A fault is a fracture discontinuity along which the rocks on either side have moved past each other .

3. Fault

4. PARTS OF FAULT

5. THE PARTS OF A FAULT 1. Fault plane. 2. Hanging wall and Footwall. 3. Hade. 4. Throw. 5. Heave.

6. 1. Fault plane : A plane along which the rupture has actually taken place or where one block is moved with respect to other is known as ‘Fault Plane’. It may be noted that such a plane is generally formed along the line of least resistance.

7. 2. Hanging wall and Footwall: The upper block or, in other words, the block above the fault plane is called ‘Hanging wall’. The block below the fault plane or, in other words, beneath the fault plane is called the Footwall.

8. 3. Hade: It is the inclination of the fault plane that is vertical. 4. Throw: It is the vertical displacement between the Hanging wall and Footwall. 5 . Heave: It is the horizontal displacement between the Hanging wall and Footwall.

9. TYPES OF FAULTS NORMAL FAULT REVERSE FAULT THRUST FAULT VERTICAL FAULT HORST FAULT TRENCH FAULT DIP SLIP FAULT STRIKE SLIP FAULT OBLIQUE FAULT STEP FAULT

10. 1. Normal Fault : A fault in which Hanging wall (HW) has apparently come down with respect to the Footwall (FW) is termed as ‘Normal Fault’.

11. 2. Reverse Fault: A fault in which hanging wall has apparently gone up with respect to the Footwall is termed as ‘Reverse Fault’.

12. What is the difference between a normal fault and a reverse fault ? The only difference between the Normal Fault and Reverse Fault is that, in Normal Fault the Hanging wall is downward with respect to the Footwall whereas in a Reverse Fault the apparent movement of the Hanging wall is upwards with respect to the Footwall.

13. 3. Thrust Fault: A fault which is a very small angle of hade (i.e. the inclination of fault plane with the vertical plane is very small) and the Hanging wall that apparently goes up with respect to the Footwall is called ‘Thrust Fault’.

14. 4. Vertical Fault: A fault in which the fault plane is vertical (having an angle of hade up to 5 degrees) and either of the walls has moved upwards or downwards.

15. 5. Horst Fault: Horst (German, Horst = upthrow) Fault is one in which wedge shaped block has gone up with respect to the side blocks.

16. HORST & GRABEN

17. 6. Graben Fault or Rift Fault or Trench fault: 6. Graben Fault or Rift Fault or Trench fault: Graben (German, Graben= Trench)Fault is one in which wedge shaped block has down with respect to side block.

18. 7. Dip Slip Fault Dip - slip faults  are inclined fractures where the blocks have mostly shifted vertically.

19. 8.Strike Slip Fault A  fault  is a fracture in the earth. These cracks will run through rock and soil and anything else that gets in the way. When the earth moves parallel to the fracture, we call it a  strike-slip fault . Another way to think of this is as a side-to-side motion.

20. Difference between a Strike-Slip F ault and a Dip-Slip Fault ? Based on direction of slip and movement along the fault  plane .    Dip slip   - fractures where the blocks have mostly moved vertically Strike slip – vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally.

21. 9.Oblique Slip Fault A  fault  which has a component of dip-slip and a component of strike-slip is termed an  oblique -slip fault . Nearly all  faults  will have some component of both dip-slip and strike-slip, so defining a  fault   as oblique  requires both dip and strike components to be measurable and significant.

22. 10. Step Fault: The term ‘Step Fault’ is applied to that parallel fault where downthrown of all is in the same direction and it gives a step-like arrangement . What is parallel fault ?

23. Parallel Fault A series of faults running more or less parallel to one another and all handing in the same direction is called ‘Parallel Fault’.

24. Field Evidence of Faulting : 1. Lithological Evidence 2. Physiographic Evidence

25. 1. Lithological Evidence i. Slickensides, ii. Fault Breccia and Gouge, iii. Drag, iv. Dislocations, v. Repetition and Omission of Beds, vi. Abrupt Termination of Structures, and vii. Silicification and Mineralization.

26. Slickensides : The movements of one wall against another along fault results in polishing and grooving of one or both surfaces . Fault Breccia and Gouge : Along some faults the rocks are found highly fractured or even crushed to angular fragments.  Drag : Drag is the minor folding of strata along the walls of a fault. It is caused by fault displacement. Dislocations: The displacement of beds, igneous dykes; veins, etc. along a fault may be seen in either plan or section. Repetition or Omission of Beds : The repetition and omission of beds often establish the fault.

27. Abrupt Termination of Structures : An abrupt termination of structures such as folds, beds or dykes along a common line or zone suggests faulting. Silicification and Mineralization : Action water while percolation through a fault zone may deposit fine­-grained Quartz causing Silicification. Many mineral deposits have also been localized along faults.

28. Physiographic Evidence: Fault Scrap : An actual surface of fault displacement may stand up unmodified by erosion as in escarpment or cliff. It is called a ‘Fault Scrap’. In this case the escarpment faces towards the down throw side . Fait Line Scrap : Fault frequently brings together resistant and non-resistant rocks. The resistant rock will stand out prominently as ridge along a fault zone. Such ridges that will generally face the upthrow side of the faults are called ‘Fault Scrap Side’.

29. Fault Control or Streams : Streams may be guided in the direction and course of their flow by faulting such stream, which may follow a straight line or make approximately right angle turns.

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