Faulting and folding

Question 1

What are the four main types of fault?

Answer 1

Normal
Reverse
Strike-slip
Thrust

Question 2

Movement of hanging wall and footwall on normal faults?

Answer 2

Hanging wall down
Footwall up

Question 3

Where are the rocks on the normal fault in relation to the fault plane?

Answer 3

Footwall= rocks underneath fault plane
Hanging wall= rocks above the fault plane

Question 4

Is a normal fault dip-slip?

Answer 4

Yes

Question 5

Normal fault, force?

Answer 5

Tensional (crust extended)

Question 6

Normal fault degree/angle of dip?

Answer 6

Steep, 60-65 degrees

Question 7

Movement of hanging wall and footwall on reverse faults?

Answer 7

Hanging wall up
Footwall down

Question 8

Where are the rocks on the normal fault in relation to the fault plane?

Answer 8

Footwall= rocks above fault plane
Hanging wall= rocks underneath the fault plane

Question 9

Is a reverse fault dip-slip?

Answer 9

Yes

Question 10

Can reverse faults be normal faults reactivated?

Answer 10

Yes

Question 11

In a reverse fault, how can the beds of rock be repeated?

Answer 11

In a borehole

Question 12

Reverse fault, forces?

Answer 12

Compressional (push rocks together)

Question 13

Angle of dip/degree of reverse faults?

Answer 13

Steep 60-65 degrees

Question 14

Thrust fault, which is the upthrown side and which is the downthrown side?

Answer 14

Upthrown side= hanging wall
Downthrown side= footwall

Question 15

Thrust fault forces?

Answer 15

Formed via compression

Question 16

What is the angle of dip/degree of a thrust fault?

Answer 16

<45 degrees

Question 17

Thrust fault, dip-slip (direction of movement is same as the fault)?

Answer 17

Yes

Question 18

Thrust fault, which side is above the fault and which side is below the fault?

Answer 18

Side above fault= hanging wall
Side below fault= footwall

Question 19

Is a strike-slip fault compressional?

Answer 19

No, it is neither compressional or tensional, it is shear

Question 20

Degree/ angle of dip of strike-slip fault?

Answer 20

Vertical

Question 21

What does strike-slip mean?

Answer 21

Same movement as surface direction of the fault

Question 22

Strike-slip fault, hanging and footwall directions?

Answer 22

There is not a hanging wall or a footwall in relation to strike-slip faults

Question 23

Immediately after faulting, what are the relative positions of the upthrown and downthrown blocks?

Answer 23

Upward block will be above the downthrown block

Question 24

What happens to the upthrown block and what does this indicate?

Answer 24

The upthrown block is eroded to the level of the downward block and this indicates that the rocks exposed at the surface on the downthrown block will be younger than those on the surface of the upthrown block

Question 25

What are marker beds used for?

Answer 25

To establish the relative displacement of rocks across a fault

Question 26

What is fault throw?

Answer 26

The amount of vertical displacement of beds due to fault movement

Question 27

What is a right lateral/dextral strike-slip fault?

Answer 27

Where relative movement is to the right due to shear forces

Question 28

What is a left lateral/sinistral strike-slip fault?

Answer 28

Where relative movement is to the left due to shear forces

Question 29

What are the two main types of fold?

Answer 29

Antiforms and synforms

Question 30

What is folding caused by?

Answer 30

Compressional forces

Question 31

What is an antiform?

Answer 31

Arch shaped rock structures , which close upwards. There is no indication of the relative age of the beds involved

Question 32

What is an anticline?

Answer 32

Arch shaped folds, where the oldest bed is in the centre (core)

Question 33

What is a synform?

Answer 33

Trough shaped rock structures, which close downwards. There is no indication of the relative age of the beds involved

Question 34

What is a syncline?

Answer 34

Trough shaped folds, where the youngest bed is in the centre (core)

Question 35

What is important to remember about anitclines?

Answer 35

All anticlines are antiforms but not all antiforms are anticlines. The antiform could be an upside-down or overturned syncline

Question 36

What is important to remember about synclines?

Answer 36

All synclines are synforms but not all synforms are synclines. The synform could be an upside-down or overturned anticline

Question 37

What position are the axial planes if the limbs dip away from the fold axis at the same angle?

Answer 37

Vertical

Question 38

What are some key characteristics of anticlines with limbs of unequal dip?

Answer 38

-Gentle angle of dip=wider outcrop -Axial planes are inclined if the limbs dip away from the fold axis at different angles -Steeper dip=narrower outcrop -Core is the oldest -Axial plane dips towards more gently dipping side -Beds get younger away from core in both directions

Question 39

What are symmetrical folds?

Answer 39

Folds with limbs of equal length

Question 40

What are asymmetrical folds?

Answer 40

Folds with limbs of differing lengths

Question 41

What is the fold crest?

Answer 41

The top of the fold

Question 42

What is the fold trough?

Answer 42

The bottom of the fold

Question 43

What is wavelength?

Answer 43

The horizontal distance between adjacent fold troughs or fold crests

Question 44

What is amplitude?

Answer 44

The vertical difference between the fold crest and the fold trough in a fold divided by 2

Question 45

What are the interlimb angles of gentle folds?

Answer 45

120°-180°

Question 46

What are the interlimb angles of open folds?

Answer 46

70°-120°

Question 47

What are the interlimb angles of closed folds?

Answer 47

30°-70°

Question 48

What are the interlimb angles of tight folds?

Answer 48

<30°

Question 49

What is special about the limbs in isoclinal folds?

Answer 49

The limbs are parallel to each other

Question 50

What is a monocline?

Answer 50

A fold with only one limb

Question 51

What are characteristics of overturned folds/overfolds?

Answer 51

-Upside down sedimentary structures -Youngest bed at top and oldest bed at bottom -Axial planes dips at 45° and in the same direction as the limbs -Overturned strata present here

Question 52

What are some characteristics of recumbent folds?

Answer 52

-Youngest bed at top and oldest bed at bottom -Sedimentary structures upside down or inverted -Axial plane is between horizontal and 10°

Question 53

What is the axial plane?

Answer 53

The plane/surface that divides the fold as symmetrically as possible

Question 54

What is the axial plane trace?

Answer 54

Outcrop of the axial plane at the Earths surface

Question 55

What is the hinge?

Answer 55

Line or point where the curve of the fold is greatest

Question 56

What is the fold limb?

Answer 56

Sides of the fold structure

Question 57

What is the fold axis?

Answer 57

The imaginary line that runs along the crest (anticline) or trough (syncline)

Question 58

What is plunge?

Answer 58

The vertical angle between the horizontal plane and the axis or line of maximum elongation of a feature.