STRUCTURAL GEOLOGY HATCHER 10

Question 1

Rupture does not occur on the planes of maximum shear that bisect the angles between he greatest and least principal stresses.

Answer 1

Theory of Shear Fracture

Question 2

Maximum stress bisecting the acute angle between two conjugate shear planes of stress of the stress elipsoid

Answer 2

Hartmans Rule

Question 3

Max and Inter principal stresses are oriented horizontally and the minimum oriented vertically and is on a “State of Compression” shear planes are lying 45 deg or less

Answer 3

Thrust Fault

Question 4

How can thrust faulting be achieved in two ways?

Answer 4

1) Increase the radius of the circles until failure envlope is reached
2) decresae Vertical Min Stress by erosion

Question 5

Shear planes corresponds to

Answer 5

Fault planes

Question 6

Max and Min Principal stress are horizontal while intermediate is vertical lying 45 deg or less

Answer 6

Strike Slip

Question 7

Involves extension on one horizontal axis (X or Y) with the maimum principal stress vertical

Answer 7

Normal Fault

Question 8

angle between shear planes at a normal fault

Answer 8

45 deg or less than the axes of Max and Min

Question 9

Effective Normal Stress (S) is equal to

Answer 9

Normal Stress - Fluid Pressure

Question 10

States that the Tangential force parallel (Shear Force) to a farcture surface necessary to initiate slip is directly proportional to the force normal to the fracture surface

Answer 10

Amonton’s First Law

Question 11

The frictional resistance of motion is Independent of the contact area

Answer 11

Amonton’s Second Law

Question 12

whats the effect of Fluid Pressure to Shear Stress

Answer 12

Decreases thus initiating slip

Question 13

involves Sudden movement on the fault after long term accumulation of stress and is accompanied by elastic rebound which causes the earthquake

Answer 13

Stick-Slip (Unstable Frictional Sliding)

Question 14

Involves uninterrupted motion along a fault so that stress is relieved continuously and does not accumulate

Answer 14

Stable Sliding (Continuous Creep)

Question 15

Microscopic and Megascopic irregularities and imperfections on fault surfaces

Answer 15

Asperities

Question 16

When will shear heating be significant?

Answer 16

When motion >1cm/ yr
shear >50MPa

Question 17

Evidence of Shear Heating

Answer 17

1) Pseudotachylite - dark vein fillings of glass like material frome by brittlle failure and sudden release of elastic energy and friction generated heat
2) Metamorphic Aureoles in subduction zones

Question 18

Depth of Brittle Ductile Transition

Answer 18

10-15km

Question 19

What types of faults have both Birttle and Ductile Zones?

Answer 19

Very large faults that penetrate the entire crust

Question 20

Zones of weakness and represent localized strain softening which can be caracterized by Zone of closely spaced interleaving anastamosing brittle faults and crushed rocks (Cataclasites) near the surface or zone of ductile faults and associated mylonitic rocks at hreat dept

Answer 20

Shear Zones

Question 21

Strain softening in Ductile zones are characterized by the formation of

Answer 21

Mylonites

Question 22

Shear Sense Indicators are used to determine shear sense in

Answer 22

Zones of Ductile Shearing

Question 23

Large grains that have grown in the rock mass during deformation and metamorphism

Answer 23

Porphyroblast

Question 24

Relict of earlier larhe grains that have survived shearig

Answer 24

Pophyroclast

Question 25

Wedge shaped winged/tailed inclusion that DO NOT CROSS THE REFERENCE PLANE tracing tail away from grains

Answer 25

Sigma type (Nangiiwan)

Question 26

Winged or Tailed inclusion where in tails wrap around tha grain so they CROSS THE REFERENCE PLANE

Answer 26

Delta Type (Yumayakap)

Question 27

If the rotation is clockwise the shear sense is

Answer 27

Dextral

Question 28

Inclusions without tails

Answer 28

Theta Type

Question 29

SAUSAGE SHAPED features formed by EXTENSION of A STRONG LAYER in a more DUCTILE GROUND MASS

Answer 29

Boudins

Question 30

Mineral lineations or foliation composed of quartz muscovite chlorite magnetite or other mineral that forms in extensional strain field on either side of a large crystals and are commonly oriented parallel to the prominent foliation

Answer 30

Pressure shadows

Question 31

large, lenticular eye-shaped mineral grains or mineral aggregates visible in some foliated metamorphic rocks

Answer 31

Augen

Question 32

Parallel alignment of plat minerals or bands in a metamorphic rock of sevaral types develop in shear zones as products of proregssive simple shear

Answer 32

S-C Surface

Question 33

A progresive shearing-induced foliation which forms at an angle of 18-25 deg to the dominant foliation surface (eto ung horizontal lines)

Answer 33

C-Surface

Question 34

C means

Answer 34

Cissaillement meaning shear

Question 35

Exitsing Dominant Foliation parallel to the walls so vertical ito na nadform of the shear zone (Eto ung diagonal)

Answer 35

S-Surface

Question 36

Mica fish is what type of S-C fabric?

Answer 36

Type II S-C (C-Mica, S-Qtz)

Question 37

S-C surfaces which originate by aparrent extension and rotation as the shear zone moves and are structures resembling INTRAFOLIAL Folds appera between cveniently oriented active S-Surfaces inclines opposite to the shear direction and C-Surface Orientation

Answer 37

Extensional Crenulation Cleavage

Question 38

Form early in the movement history of a brittle shear zone and then are either destroyed or ceased movements
En enchelon shear farctures formed at 10-15 deg to the principal shear and have the same displacement sense as the primary shear fractures

Answer 38

Riedel Shear

Question 39

Forms at high angle with opposite movement

Answer 39

Antiriedel shear