UNIT 4FAULT AND JOINTS

INTRODUCTION TO FAULTFAULT-DEFINITIONFault is always a crack or surface of rupture or a simple fracture surface or a zone having numerous closely spaced fractures that has to be present in rocks; it may be pre existing or may develop instantaneously just before the movement of the blocks..

a) Three layer of rock under stressb) Produce fracture and divide into a1 and a2c) Relative displacement of two block a1 and a2 is a FAULT

FAULT TERMINOLOGY• Fault Plane: It is the planar surface of fracture • Dip and Hade: Dip is the inclination with the horizontal & Hade is the

angle made with the vertical• The Walls (Hanging walls and footwalls): Hanging wall is one above

and foot wall is the wall below• Fault Zone: Region with definite thickness and distinct compostion

having numerous closely placed parallel fractures• Shear Zone: Same as fault zone• Slip and separation: PTO

FAULT PLANE

FAULT ZONE

SLIP AND SEPARATION

The slip is defined as a relative displacement of any two points that were formerly contiguous to each other, as measured along the fault plane

On the basis of direction it is classified as DIP SLIP, STRIKE SLIP & OBLIQUE

SLIP AND SEPARATION

Separation is the distance between two parts of the faulted bed or layer of rock which were formerly in contact with each other as measured in any given direction

Offset: Normal horizontal displacementThrow: Vertical componentHeave: Horizontal component

CLASSIFICATION OF FAULTSa) The apparent movement of the disrupted blocks along the fault planeb) The direction of slipc) The relation of fault attitude with the attitude of the displacement bedd) The amount of dip of the faulte) Mode of Occurance

a) APPARENT MOVEMENT AS BASIS1. Normal Faults 2. Reverse Faults3. Strike-Slip Faults4. Hinge Faults

1.NORMAL FAULT

Such a fault in which hanging wall has apparently moved down with respect to footwall is classified as Normal Fault.

1.NORMAL FAULT (HORST & GRABEN)

When two normal fault appears on either side of a central wedge shaped elongated block in such a way that the central wedge raised high up with respect to the sides, the outstanding structure is called Horst

1.NORMAL FAULT(VERTICAL FAULT)

Fault in which fault plane is vertical

2.REVERSE FAULT

It is such a type of fault in which the hanging wall appears to have moved up with respect to the footwall. (fault plane inclined at 45deg)

Thrust: Process of adjustment of rocks to the imposed stress

Nappes: Is the translated distance-ranging to several hundred kilometer, along the thrust plane

2.REVERSE FAULT (THRUST AND NAPPE)

3.STRIKE-SLIP FAULT

Faulted block have been moved against each other in an essentially horizontal direction.eg: San Andres Fault of california

4.HINGE FAULTS

These are also called pivoted fault or rotational faults. A hinge fault is characterized by a movement of the disrupted block and a medial point called hinge point.

b) ATTITUDE OF FAULT AS BASIS1. Strike Faults (Parallel to the strike of the strata)2. Dip Faults (Perpendicular to the strike of the strataP)3. Oblique Faults (Fault strike makes an oblique angle with the strike of

the rock)

a) STRIKE FAULT b) DIP FAULT c) OBLIQUE FAULT

c) SLIP AS BASIS1. Strike-Slip Faults

i. Wrench Faults (continent & oceanic)ii. Transform Faults (oceanic ridge)iii. Tear Faults (continents)

2. Dip-Slip Faults3. Oblique-Slip Faults

1.STRIKE SLIP FAULT

2.DIP SLIP 3.OBLIQUE SLIP

d) MODE OF OCCURANCE AS BASIS1. Parallel Faults(group of fault parallel and equal dip)2. Enechelon Faults(group of small sized fault that overlap each other)3. Peripheral Faults(faults along the peripheral)4. Radial Faults(group of faults that appear emerging outward from a central region)

1.PARALLEL 2.ENECHELON 3.PERIPHERAL 4.RADIAL