Geological Faults and its Types

Definition

Fault is a fracture / crack / joint along which there has been relative displacement of beds.

Classification of faults

Faults can be classified on the following different basis: (Click to Read)

1. Classification of faults on the basis of net slip
2. Classification of faults on the basis of apparent movement of blocks
3. Classification of faults on the basis of dip angle
4. Classification of faults on the basis of fault pattern
5. Classification of faults on the basis of altitude of fault relative to the altitude of the adjacent rocks/formation

Also Read: GeoTextiles | GeoTechnical Engineering | Geodetic Survey Method

1) Classification of faults on the basis of net slip

On the basis of net slip faults have the following three types

1. Dip slip fault
2. Strike slip fault
3. Oblique slip fault

a) Dip slip fault:

The faults in which the slip takes place along the direction of the slip is called dip slip fault .in the dip slip fault net slip is parallel to the dip of fault

b) Strike slip fault

The faults in which the slip takes place along the direction of the strike is called dip slip fault .in the dip slip fault net slip is parallel to the strike fault 

c) Oblique strike fault

When the net slip is neither parallel to strike nor parallel to the dip of fault is called Oblique strike fault.

OR

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 

2) Classification of faults on the basis of apparent movement of blocks:

On the basis of the apparent movement of blocks fault have the following types

1. Normal fault
2. Reverse fault

a) Normal fault

 Normal fault is one in which the hanging wall falls down relative to the foot wall due to tensional stress it is also called gravity fault/apparent normal fault. Normal faults with very shallow dipping fault planes (<10 degrees) are called "detachment" faults or "decollemonts".

b) Reverse fault 

Reverse fault is one in which the hanging wall moves up relative to the foot wall due to compression. If the hanging wall is pushed up and then over the foot wall at a low angle it is called a thrust fault. Reverse faults with very shallow dipping fault planes (<10 degrees) are called "thrust" faults;

3) Classification of faults on the basis of dip angle

On the basis of the dip angle fault has the following types

1. High angle fault
2. Low angle fault

a) High angle fault

A high angle fault is one that dips at angle greater than 45°

b) Low angle fault

A low angle fault is one that dips at angle smaller than 45°

4) Classification of faults on the basis of fault pattern

On the basis of pattern faults are classified into the following types

1. Parallel faults
2. Step faults
3. Grabe or rift fault
4. Horst
5. Radial fault
6. Peripheral faults
7. Enechelon faults

a) Parallel fault

A series of faults running more or less parallel to one another and all handing in the same direction, are called “parallel faults”

b) Step fault

 It is consists of those parallel faults where down throw of all are in the same direction and it gives a step like arrangement

c) Graben or Rift fault

When two normal faults fade towards each other and the beds between them are thrown down in the from of a wedge, the structure is called graben or rift fault

d) Horst

A horst consists of a central block on the both sides of which adjacent beds appear to have been faulted down

e) Radial faults

A number of faults exhibiting a radial pattern are descried as radial faults

f) Peripheral faults

Curved faults of more or less circular, or are like outcrops on level surface are called peripheral faults

g) Enechelon Faults

Enechelon fault are comparatively short faults which overlap each other

5) Classification of faults on the basis of altitude of fault relative to the altitude of the adjacent rocks/formation

It can be classified as

1. Dip fault
2. Strike fault
3. Bedding fault
4. Oblique fault
5. Tear fault or Transcurrent fault

a) Dip fault

A dip fault is one shore strike is parallel to the dip of sstrata and also called transverse faults when it runs across the general structure o the region

b) Strike Fault

A strike fault is one shore strike is parallel to the strike of strata and also called longnitudal faults when it runs across the general structure o the region

c) Bedding fault

When strike of the fault plane is oblique to the strike of  dip of strata, it is called an oblique fault

e) Oblique fault

When the strike of the fault plane is oblique to he strike and dip of strata, it is called an oblique Fault.

f) Tear fault or yTranscurrent fault

It generally strikes transverse to the strike of country rocks .the fault plane is more or les vertical and often extend fro along distances its is also called a wrench fault