Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Earth structure and tectonics - 33740 > Lecture 2- Joints, Cleavage, Veins, Faults, Earthquakes > Flashcards

Lecture 2- Joints, Cleavage, Veins, Faults, Earthquakes Flashcards

1
Q

What are joints?

A

fractures with minimum opening (mm to cm) with no displacement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What do joints form in response to?

A

extensions and perpendicular to stretching direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do joints form from lavas?

A

By contraction vertically due to thermal gradient cool at tip and base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are plumouse structures?

A

feather like on top of joints and develop when the crack is propagating laterally

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What can plumouse structures allow you to distinguish?

A

Joints from bedding planes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why are joints imporant?

A

Paleostress analysis
Oil exploration
Volcanic hazards
Seismic hazard
Landslide Hazard

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How are joints arranged in simple shear?

A

‘En echelon’ in shear zone (will step down) and dip in shear direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are joints like for pure shear?

A

Parallel and overlap

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are veins?

A

joints filled with minerals that precipitate from fluids circulating through fractures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do veins form from pure shear?

A

straight veins (lens shape)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How will simple shear veins form?

A

Sigmoidal veins (S shape) as rotation occurs the core and growth rotates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What can veins form?

A

large ore deposits (gold, copper, lead, zinc, silver)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is a fault?

A

planar surface or zone which one side is displaced relative to the other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the range for displacement?

A

mm to Km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the 2 main forms of deformation?

A

Brittle
Ductile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is brittle deformation?

A

rock break into rigid blocks each portion separated by discontinuities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is ductile deformation?

A

apply stress, no discontinuity but will deform as single piece

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the conditions of brittle deformation?

A

<350*c
or
High strain rates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the conditions of ductile deformation?

A

> 350*c
or
Low strain rates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What deformation leads to faults?

A

brittle deformation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the typical conditions for fault formation if by brittle deformation?

A

Shallow depth (less than approx ~15km)
where temp is below 350*c

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How do faults form?

A

when the internal friction of rocks is overcome due to stress

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What happens when stress approaches internal friction?

A

micro-cracks form a fault form when these microcracks merge together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What plays a key role in fault formation?

A

pre-existing weaknesses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the 2 blocks in a fault called?

A

Hanging wall (above the fault plane)
Footwall (below the fault plane)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is a normal fault?

A

the hanging wall moves down relative to the footwall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is a reverse (thrust) fault?

A

the hanging wall moves up relative to the footwall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are strike slip faults?

A

the two blocks are displaced laterally (i.e.
in the horizontal plane). There is no hanging wall or footwall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is Dextral and Sinistral with strike-slip faults?

A

Dextral- right lateral
Sinistral- Left lateral

30
Q

What are thrust faults?

A

low angle <30* reverse faults

31
Q

What are detachment faults?

A

low angle ~30* normal faults (normal fault typically 60*)

32
Q

What does thrust play a key role in?

A

Orogenesis (mountain building)

33
Q

What does detachment fault allow?

A

deep rocks to be exhumed at the surface

34
Q

What is heave?

A

horizontal displacement between 2 points which were adjacent

35
Q

What is throw?

A

vertical displacements between 2 points that were once adjacent

36
Q

What is total slip?

A

displacement along the fault plane between two points that were once adjacent

37
Q

How do faults terminte?

A

Faults may terminate laterally by decreasing progressively their displacement.

38
Q

What is displacement at tip points?

A

zero

39
Q

What is a transfer fault?

A

when faults terminate against another fault

40
Q

What are relay ramps?

A

when a fault terminates by overlapping eachother

41
Q

How do normal faults affect stratigraphy?

A

OMIT and thin the crust (erase)

42
Q

How do reverse faults affect stratigraphy?

A

Repeat stratigraphy so thicken crust

43
Q

What are the 2 divisions of fault rock?

A

Incoesive
Coesive

44
Q

Where do incoesive rocks faults form?

A

shallow part of crust

45
Q

Where do coesive fault rocks form?

A

deep part of crust

46
Q

What are the 2 types of incoesive rock?

A

Fault breccia (>30% visible grains)
Fault gouge (<30% visible grains)

47
Q

What is the reason for the difference between fault breccia and fault gouge?

A

Fault gouge has experienced more deformation and friction

48
Q

What are the coesive fault rocks?

A

Crush breccia - Matrix <10%
Cataclasite - matrix predominate

49
Q

What are mylonites?

A

Fine grained rocks formed by dynamic recrystallization of new minerals during strain at high temperature

50
Q

What depth do mylonites form at?

A

> 15km
shear zones where deformation is ductile

51
Q

What is the stick phase of the stick-slip mechanism?

A

stress increases and elastic strain builds up over years

52
Q

What is the slip phase?

A

when the elastic limit of rocks is reached and a fault forms

53
Q

What is the speed of elastic recovery?

A

recovered in seconds

54
Q

What is generated when elastic strain is recovered?

A

seismic waves

55
Q

What are the types of seismic waves?

A

Compressional P waves
Shear S waves

56
Q

What are the characteristics of compressional P waves?

A

Faster, arrive first to seismograms (aka “primary”)
Travel as a caterpillar
Travel in both solids and liquids

57
Q

What are the characteristics of Shear S waves?

A

Slower, arrive after P waves (aka “secondary”)
Travel as a snake
Can only travel in solids

58
Q

What is the seismic cycle?

A

Interseismic (strain build up) and Coseismic (strain recovered)

59
Q

What is the primary cause of earth quakes?

A

Faults

60
Q

How do faults grow?

A

repeated slip; so, large-offset faults are the products of hundreds/thousands of earthquakes

61
Q

Why is repeated slip likely to occur on faults?

A

more likely to be reactivated due to the presence of the weakness

62
Q

What increases at a fault with continued slip?

A

displacement and length

63
Q

What is the ratio of length to displacement?

A

Length 10,000 times displacement (10km length = 1m displacement)

64
Q

What is aseismic slip?

A

If the frictional resistance on the fault is low elastic energy cannot be stored, and displacement is accumulated at a constant rate without causing any earthquake

65
Q

Where does aseismic slip commonly occur?

A

uppermost part of the crust (3-4km) where normal stress is lower (not enough friction)

66
Q

What is the depth range for stick-slip?

A

~4 to ~15 km

67
Q

Why does aseismic slip occur after 15km?

A

as rocks become ductile due to high temperature (>350*c)

68
Q

How can earthquakes occur below 15km?

A

at subduction zones in the subducting plate as the temperature at the plate interface is <350*c

69
Q

What is the thermal gradient at a subduction margin compared to normal thermal gradient?

A

subduction - 10c per km
Normal - 30c per km

70
Q

What are the depth of shallow, intermediate and deep earthquakes?

A

Shallow <99km
Intermediate 100-300km
Deep 300~700 km

71
Q
A

Earth structure and tectonics - 33740 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions