Faults

Faults

Faults defined as :  ruptures along which the opposite walls have moved past each other , the essential feature is differential movement parallel to the surface of the fracture.

Another definition :  it is a secondary planer or curve planar structure element ,formed due to tectonic processes  , it is a fracture which its displacement can be detected "measurable".

# Understanding faults is useful in design for long-term stability of dams, bridges, buildings and power plants. The study of fault helps understand mountain building.

 Faults may be hundred of meters or a few centimeters in length.# 

                                                              

Parts of the Fault                                                

1) Horizontal and vertical displacement.

2)  Fault plane: it's the plane where the opposite walls move about it.

3) Strike: it's the trend of horizontal line on the fault plane.

4)  Dip: it's the angle between a horizontal surface and the fault plane .

5)  Hade : it's the complement angle of the dip .

6)  Hanging wall : it's the block above the plane.

7)  Foot wall : it's the block blow the fault plane .

8)  Up thrown – down thrown side. 

     

 10) slip : Describes the movement parallel to the fault plane.

11) Dip slip: Describes the up and down movement parallel to the dip direction of the fault.

12) Strike slip: Applies where movement is parallel to strike of the fault plane

Oblique slip: Is a combination of strike slip and dip slip . 13)

14) Net slip (true displacement): Is the total amount of motion measured parallel to 

the direction of motion .

 

Natural of movement along the fault

1)  Translation and rotational movements:-

_ In the translational movement , no rotation of the blocks relative to each other , all straight lines on the opposite sides of the fault which were parallel before the displacements, are parallel afterwards.

_ in the rotational movements,  are those in which some straight lines on the opposite sides of the fault which were parallel before displacement are not parallel 

afterwards

Geometric classification :-

According to rake of net slip :   A_

1) strike slip fault : net slip =strike slip and dip slip equal to zero.

2) dip slip fault: net slip = dip slip and strike slip equal to zero.

3) Oblique slip fault: net slip =component of strike and dip slip.

B_ According to attitude of fault relative to adjacent beds:

1) Strike fault: which its strikes are essentially parallel to the strikes of the adjacent rocks.

2)bedding fault: which its strikes are parallel to the bedding planes.

3) Dip fault: which its strikes are essentially parallel to the directios of dip the adjacent rocks.

4) Oblique fault: is that one where its strikes obliquely to the strike of the adjacent 

rocks.

C_ According to fault pattern :

Such classification is based on the pattern on a map or cross section.

1)  Parallel faults: the have essentially the same dip and strike

2) en-echelon faults : are relatively short fault that overlap each other.

3) Peripheral faults : are circular faults that bound a circular area or part of a circular area.

4) radial faults : belong to a system of faults that radiate out from a point .

D_classification based on value of dip fault :

1) Low angle faults : dip less than45 o

2) high angle faults : dip is greater than 45 o and less than 90 o

3) Vertical faults: dip is equal to 90 o

E_ classification according to the apparent movement:

1) Normal fault : when the hanging wall has apparently gone down relative to the foot wall .

2) Reverse fault : is one in which the hanging wall has apparently gone up relative to 

the foot wall .