FAULTS

&

CRITERIA FOR FAULTING

GROUP MEMBERS

•ALI IMTIAZ

•MUNEEB-UR-REHMAN

•UMER ABDUR REHMAN

WHAT IS A FAULT?

A fault is a fracture, along which a rock on one side move relative to the rock on other side.

The real question is,

What is a fracture?

FAULT TERMINOLOGIES• Fault planePlaner surface along which rocks on opposite side move.

• The walls:1) Hanging wall

2) Foot wall

• Slips 1) strike slip

2) dip slip

3) oblique slip

NET SLIP

• Net slip is measured by the vector that traces the displacement between originally adjacent points.

• 3 components: 1-net slip

2- dip slip

3- strike slip

TYPES OF SLIPS

THROW & HEAVE

Throw:

Horizontal component of seperation.

Heave:

Vertical component of seperation.

GENETIC CLASSIFICATION OF FAULTS

1) Normal Faults2) Thrust Faults3) strike slip Faults4) Net slip Faults

NORMAL FAULTS

• Hanging wall moves downward w.r.t. foot wall.

• Extensional environment

NORMAL FAULTS

• Also known as gravity faults by some geologist • A detechmant fault is a special category of

low angle normal faults due to downhill sliding of rocks from an uplifted region.

EXAMPLE

• Amorgos fault:Location: greece

Length: >100km

Type: normal fault

Status: active

THRUST FAULT• Thrust fault is a fault along which the hanging wall moves up relative to foot wall

• Further classified into 3 types:• Reverse fault: is thrust that dips > 45’• Thrust: that dips <45’• Overthrust: that dips < 10’ and has large net-slip,

For example,

Longmen shan fault

Location: china

Status: active

REVERSE FAULT

• Hanging wall moves upward at >45 degree angle.

• Compressional environment.

STRIKE SLIP FAULTS

• Also called as wrench faults.• walls slide pass each other or displacement parallel to the strike.

• Further classify into 2 types:• 1-Sinistral:Left lateral strike-slip fault (sinistral): Where

the side opposite the observer moves to the left. • 2-dextral: Right lateral strike-slip fault (dextral): Where

the side opposite the observer moves to the right Example is: an Andreas Fault..

TEAR FAULTS• Tear faults can be be defined as relatively small-

scale, local strike-slip faults that are associated with other structures such as folds, thrust faults and normal faults (Twiss and Moore 1992). The tear faults may be a result of drastic lateral changes when the thrust front advances or by differential shortening of the thrustal sheet. For example as one part of the thrust sheet is shortened by faulting and the other is shortened by folding, the displacement is taken up by the tear fault. The Jacksboro fault in the Appalachians is a good example of a tear fault that segments the Pine Mountain Thrust Belt (Twiss and Moores 1992).

TEAR FAULTS

STRIKE SLIP FAULTS

• It is also classified into transform faults and transcurrent faults. Transform faults end at the junction of another plate boundary or fault type, while transcurrent faults die out without a junction. In addition, transform faults have equal deformation across the entire fault line, while transcurrent faults have greater displacement in the middle of the fault zone and less on the margins. Finally, transform faults can form a tectonic plate boundary, while transcurrent faults cannot.

TRANSFORM & TRANSCURRENT FAULTS

GEOMETRICAL CLASSIFICATION

i- rake of net slip

ii- attitude of fault w.r.t adjacent beds.

iii- fault pattern

iv- apparent movement

v- dip of the fault

BASED ON RAKE OF NET SLIP

BASED ON RAKE OF NET SLIP

• Strike-slip Fault: in which netslip is parallel to strike of fault. i.e strike=netslip and there is no dip slip.• Dip-slip fault: in which netslip is up or down the dip

of the fault i.e dipslip=netslip and there is no strikeslip component, rake of netslip=90’• Diagonal-slip Fault: in which netslip is diagonally up

or down the fault plane. There is bothe strike slip and dipslip component, rake of netslip>0’ but <90’

BASED ON ATTITUDE OF FAULT REALATIVE TO ATTITUDE OF ADJACENT BEDS• Strike fault: that essentially parallel to the

strike of the adjacent rocks.

BASED ON ATTITUDE OF FAULT REALATIVE TO ATTITUDE OF ADJACENT BEDS• Bedding Fault: is variety of strike fault that is

parallel to the bedding

BASED ON ATTITUDE OF FAULT REALATIVE TO ATTITUDE OF ADJACENT BEDS

• Dip Fault: strikes essentialy parallel to the direction of dip of the adjacent beds.

BASED ON ATTITUDE OF FAULT REALATIVE TO ATTITUDE OF ADJACENT BEDS• Oblique/diagonal Fault: that strikes obliquely

or diagonally to the strike of the adjacent rocks.

OBLIQUE SLIP FAULT

TRANSTENSION FAULT

TRANSPRESSION FAULT

BASED ON ATTITUDE OF FAULT REALATIVE TO ATTITUDE OF ADJACENT BEDS• Longitudinal Fault: is parallel to the strikes of

the regional structure. • Transverse Fault: strikes perpendicularly or

diagonally to the strike of the regional structure.

LONGITUDANAL & TRANSVERSE FAULTS

BASED ON FAULT PATTERN

• Parallel Faults: set of faults having same strike and dip. (dip may be change). • En echelon fault: are relatively short faults

that overlap each other.

BASED ON FAULT PATTERN

• Peripheral Faults: are circular or arcuate faults that bounds a circular area.• Radial Faults: belongs to a system of faults

that radiates out from a point.

BASED ON VALUE OF DIP OF FAULT

This is based on the angle of the dip of the fault.

a- high angle faults: that dips greater than 45’

b- low angle faults: that dips less than 45’

BASED UPON APPARENT MOVEMENT • Apparent Normal Fault: in which hanging wall

appears to have gone downward relative to footwall.• Apparent Thrust Fault: in which hanging wall

appears to have gone upward relative to footwall.

SYNTHETIC AND ANTITHETIC FAULTS• 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. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style).

LISTRIC FAULTS• listric faults can be defined as curved normal

faults in which the fault surface in concave upwards; its dip decreases with depth. These faults also occur in extension zones where there is a main detachment fracture following a curved path rather than a planar path.

DETACHMENT FAULTS

• Detachment faulting is associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km)

COMPLETE PICTURE OF FAULTS

CRITERIA FOR FAULTING

• Several criteria are there, some of them are discussed here:

1- discontinuity of structure

2- repetition or omission of strata

3- feature/characteristics of fault plane

4- silicification and mineralization

5- sudden change in sedimentary facies

6- physiographic data

DISCONTINUITY OF STRATA

REPETITION OR OMISSION OF STRATA

FEATURE OF FAULT PLANE

• Following features can be seen in a fault:

1- Slickensides

2- Gouge

3- Breccia

4- Mylonite

SLICKENSIDES

GOUGE, BRECCIA & MYLONITE

• These are identified on the basis of size and percentage of matrix given by:

Gouge : <0.1mm (30% matrix)

Breccia : >0.5 to <1mm (30% matrix)

Megabreccia: >0.5 mm (30% matrix)

Microbreccia <1mm (30% matrix)

Mylonite: <50 micrometer (50% matrix)

SILICIFICATION AND MINERALIZATION

• Silicification is the process in which a rock’s part is replaced due to solution passage from the fractures.

• Due to different type of solution precipetation, mineralization may also found in faults.

SUDDEN CHANGE IN SEDIMENTARY FACIES

• By horizontal displacement, different sedimentary facies of the same age come in contact with each other.

PHYSIOGRAPHIC DATA

• Scarp: features that show a sudden increase in slope and indicate the presence of faults.

IMPORTANCE OF FAULTS

• This trap is formed by the movement of permeable and impermeable layers of rock along a fault line. The permeable reservoir rock faults such that it is now adjacent to an impermeable rock, preventing hydrocarbons from further migration.

MAJOR FAULTS OF PAKISTAN

• 1. Main Karakoram Thrust • 2. Raikot Fault • 3. Panjal-Khairabad Thrust• 4. Riasi Thrust • 5. Salt Range Thrust • 6. Bannu Fault • 7. Chaman Transform Fault • 8. Quetta-Chiltan Fault • 9. Pab Fault

THANK YOUPRESENTED BY: MUNEEB UR REHMAN QAU ISLAMABADMUNEEBURREHMAN424@YAHOO.COM