Fault and its classification

FAULTS

1. FAULT AND ITS CLASSIFICATION GUIDED BY- Dr. POONAM BHATNAGAR PRESENTED BY- SHIVANI THAKUR CLASS- M.Sc.I-SEM GOVT. HOLKAR SCIENCE COLLEGE , INDORE (M.P.)

2. CONTENT- INTRODUCTION ELEMENTS OF FAULTS/GEOMETRY OF FAULTS CLASSIFICATION OF FAULTS GEOMETRIC CLASSIFICATION GENETIC CLASSIFICATION DISTRIBUTION OF FAULTS MAJOR FAULTS IN INDIA CONCLUSION REFERENCES San Andreas Fault in the Carrizo Plane, western California.

3. INTRODUCTION Fault is a rupture, fracture or crack in a rock along which a significant differential displacement of rock body has taken place due to some compressional and tensional stresses within the rock. When the rock on one side has moved along the fracture relative to the other side, the fracture is termed a 'fault'. It is a planar structure always develops along a particular plane. Figure showing a faulted rock in which displacement of rock blocks along a fracture surface is seen.

4. GEOMETRY OF FAULTS 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’. A fault plane can be classified in 3 types: Vertical fault plane- Forming vertical fault . Inclined fault plane- forming normal and reverse fault. Horizontal fault plane- Horzontal fault . For faults having inclined fault plane (not for vertical) the following terminology is used:- 1.Dip and Strike : The inclination of a fault plane may be given as a dip (angle between horizontal surface and fault plane) and the strike is the trend of a horizontal line in the fault plane . 2. Hanging wall and Footwall : The block above the fault plane is called ‘Hanging wall’. And The block below the fault plane is called the Footwall. 3. Hade : It is the inclination of the fault plane that is vertical. .

5. 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 6. Rake : the angle between a line (or a feature) and the strike line of the fault plane. A planar fault is defined by the strike and dip of the fault surface and the direction of the slip vector. {λ-Rake, φ-plunge}

6. CLASSIFICATION OF FAULTS- FAULTS CAN BE CLASSIFIED IN TWO TYPES- GEOMETRIC CLASSIFICATION GENETIC CASSIFICATION GEOMETRIC CLASSIFICATION- Faults can be classified on the basis of their geometry or their genesis. Geologists consider geometric classification at first as they are less hazardous than genetic because no interpretation is involved in them. The basis of 5 different geometric classification are- The rake of the net slip The attitude of the fault relative to the attitude of relative rock The pattern of the faults The angle at which the fault dip The apparent movement on the fault

7. On the basis of rake of net slip- Strike-slip fault- Fault in which the net slip is parallel to the strike and dip slip component is absent , That is the rake of net slip is zero is known as strike-slip fault. Dip-slip fault- Fault in which dip slip is equal to the net slip and there is no strike slip component ,That is the rake of net slip is 90 degree is known as dip-slip fault. Diagonal-slip fault- fault in which both strike-slip and dip-slip components are present and rake of the net slip is <0 and >90 are termed as Diagonal-slip fault.

8. Classification of faults based on the dip of the fault plane and the pitch, the strike. Based on Angelier (1994).

9. ON THE BASIS OF ATTITUDE OF FAULT- Strike fault- Fault that strikes essentially parallel to the strike of adjacent rock is termed as strike fault. Bedding fault- it is a strike fault that is parallel to the bedding. Dip fault- it strikes essentially parallel to the dip of the adjacent beds. Oblique or Diagonal fault- it strikes obliquely of diagonally to the strike of the adjacent rocks. Longitudinal fault- it strikes parallel to the strike of the regional structure like fold etc. Transverse fault –it strikes perpendicularly or diagonally to the strike of the regional structure.

10. Fig. Showing Longitudinal And Transverse Faults FIg Showing Bedding and Dip Faults

11. ON THE BASIS OF FAULT PATTERN - Parallel faults- The faults have essentially same dip and strike , there fault planes are parallel to each other are termed as parallel fault. En echelon faults- these are closely spaced, parallel or sub parallel, step like short faults that overlap each other. Peripheral faults- these are circular or arcuate faults that bound a circular area or a part of it. Radial faults- these faults belong to a system of fault that radiate out of a point.

12. A) Parallel Fault B) En-Echelon Fault C) Concentric Fault D) Radial Fault

13. On The Basis Of Amount Of Dip Of Fault - Low angle faults- faults that dip less than 45 degree are termed as low angle faults. High angle fault- are those that dip more than 45 degee.

14. ON THE BASIS OF APPARENT MOVEMENT - Three fundamental types of faults are commonly distinguished on the basis of apparent Movement: 1. Apparent Normal fault- Such a fault in which hanging wall has apparently moved down with respect to foot wall is classified as a apparent Normal Fault. 2. Apparent Reverse Faults : fault in which the hanging wall appears to have relatively moved up with respect to the foot wall is termed as apparent reverse fault and some times termed as apparent thrust fault. 3. Strike-slip fault- in which the movement along the fault is parallel to the strike of the fault.

15. Piqiang Fault, Northwest trending left lateral strike-slip fault, in Taklamakan Desert, China.

16. GENETIC CLASSIFICATION- The most satisfactory genetic classification is based on the relative movement along the fault. Normal fault/gravity fault- Such a fault in which hanging wall has a moved relatively down with respect to foot wall is known as Normal Fault and also as gravity fault. Detachment fault -it is a special category of low –angle normal faults formed due to gravitational instability of uplifted region. Graben - A graben is an elongated wedge shaped central block, which has moved downward with respect to the side blocks along two downward converging normal faults. The bordering faults are almost parallel in strike and high angled in character. Major graben which extend for long distance are termed as RIFTS. Horst - When two normal faults appear on either side of a central wedge shaped elongated block, which appears raised high up with respect to the sides, the outstanding structure is called a Horst.

17. Showing a Normal fault or a Gravity Fault or Detachment Fault. Normal Fault in LA Herradura Formation, Morro Solar, Peru.

18. Normal Fault In Spain, Forming Graben structure. Both Emages Showing Horst and Graben Near Zarjan, Iran.

19. Strike-slip fault/ wrench fault- are those along which displacement has been essentially parallel to the strike of the fault ,that is dip-slip component is very small or absent. Strike-slip faults also known as lateral faults, transverse faults, wrench faults, transcurrent fault, tear fault and transform faults. Left lateral fault/Sinistral fault/Left slip fault- when in strike-slip or lateral fault displacement of block is in left side to the observer then it is termed as left lateral fault or Sinistral fault or left-slip fault. Right lateral fault/Dextral fault/Right slip fault- when in strike-slip or lateral fault displacement of block is in right side to the observer then it is termed as right lateral fault or Dextral fault or right-slip fault Dip slip fault- faults in which displacement has been essentially parallel to the dip of the fault plane.

20. Reverse fault- faults in which the hanging wall appears to have moved up with respect to the foot wall is termed as reverse faults, in which the fault plane dips more than 45 degrees. Thrust fault- It is a low angle reverse fault in which fault plane dips less than 45 degree. Under thrust fault- it is a thrust fault in which the foot wall moved and the hanging wall did not. Over thrust fault- it is a thrust fault that dips less than 10 degree and has a large net slip. In such faults the hanging wall has been the active element not the foot wall. Up thrust fault- it is a high angle thrust fault in which hanging wall is an active element.

21. Reverse Fault Over Thrust Fault

22. Reverse Fault Zone, Ketobe Knob, Utah (Jurassic Stratigraphy of Colarado Plateau US.)

23. Nappe- A nappe or thrust-sheet is a large sheet like body of rock that has been moved more than 2 km or 5 km often ranging to several hundred kilometers, along a thrust plane from its original position. Listric fault- A listric fault is a curved normal fault which achieves a rotation in the hanging wall as a geometric consequence of the displacement, (the fault plane is concave upward its dip decreases with depth) . Hinge fault- These are also called pivotal faults or rotational faults. A hinge fault is characterised by a movement of the disrupted blocks along a medial point called the hinge point. The movement is, therefore, rotational rather than translational . In such faults, the amount of displacement increases away from the hinge point.

24. Ring fault - Ring faults, also known as caldera faults, are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater. Ring faults are result of a series of overlapping normal faults, forming a circular outline. Synthetic and Antithetic Fault- Synthetic and antithetic faults are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction.

25. DISTRIBUTION OF FAULTS- A map of global tectonic and volcanic activity over the last one million years, showing: active ridges, continental extensions, transform faults, ridge spreading rates and directions, continental rifts, subduction and overthrust zones, and generalized volcanic activity. Illustration prepared by Paul D. Lowman Jr., NASA Goddard Space Flight Center.

26. MAJOR FAULTS IN INDIA- Integration of geological/geomorphic and seismological data has led to the identification of 67 active faults of regional scale, 15 in the Himalaya, 17 in the adjoining foredeep with as many as 30 neotectonic faults in the stable Peninsular India. Major faults of India are Main Central Thrust, Main Boundary Thrust and Himalayan Frontal Thrust in the Himalayan collision zone; Mishmi thrust, Lohit thrust, Kopili fault in the North-East (NE) Indian region; Narmada-Son-Tapti and Godavari rift zones in the peninsular India; Allah Bund fault, Kuchch Mainland fault, Katrol Hill fault and Bhuj fault in the western Indian region; and N–S trending faults in the Andaman Sumatra subduction zone. Map of Peninsular India displaying the eleven seismic source zones. The background illustrates the faults digitized from the seismotectonic atlas (GSI 2000).

27. Illustration of Faults in Great Himalaya And Tibetan Zone:

28. Illustration of Major faults of Peninsular India:

29. CONCLUSION- Faulting is a major tectonic process of great geological importance. The geological history of the Earth bears innumerable events recorded major faulting processes. The mechanism of faulting is based on the plate tectonic theory as all plate boundaries are the zone of faulting such like transform plate boundaries. Study of faults is also useful Economic geology as hydrothermal ore deposits originate associated with regional fault places The study of faults is essentially important for civil engineering works . The study of faults and their accurate recognition is of great importance for the disaster Management. Many destructions can be precured and mitigated by preducting them.

30. REFERENCES- Billings ,M.P. Structural Geology Published in NY: By Prentice-Hall (1946). Page no.(175 to 190) Haakon Fossen, Structural Geology, NY:Published by Cambridge University Press (2010). Page No. (151-181) Park, R.G. Foundation Of Structural Geology, 3rd edition published by Chapman Hall. Page No.(9 to10) Twiss, R.J. & Moores, E.M. Structural Geology, 2nd ed. Published by Susan Finnemore Brennan. Page No. (61-149) https://en.m.wikipedia.org (Accesed on 3 October 2019) http://www.geographynotes.com (Accesed on 3 October 2019)

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