Chapter 7

Question 1

Grain boundary sliding is influenced by friction, and the mechanism is therefore called

Answer 1

frictional sliding

Question 2

The grains translate and rotate to accommodate frictional grain boundary slip, and the whole process is called

Answer 2

granular flow

Question 3

are fractures restricted to single grains.

Answer 3

Intragranular fractures

Question 4

are fractures that extend across a few grains.

Answer 4

Intergranular fractures

Question 5

The fracture and crushing of grains, coupled with frictional sliding along grain contacts and grain rotation

Answer 5

cataclasis

Question 6

More moderate cataclastic deformation can occur in somewhat wider brittle or cataclastic shear zones. In this case the fragments resulting from grain crushing flow during shearing

Answer 6

cataclastic flow.

Question 7

Strong grain crushing without evidence of shear offset has also been observed and is called

Answer 7

pulverization

Question 8

any planar or subplanar discontinuity that is very narrow in one dimension compared to the other two and forms as a result of external (e.g. tectonic) or internal (thermal or residual) stress.

Answer 8

fracture

Question 9

Fractures can be separated into:

Answer 9

• shear fractures (slip surfaces)
• opening or extension fractures (joints, fissures and veins)

Question 10

are very narrow zones, often thought of as surfaces, associated with discontinuities in displacement and mechanical properties (strength or stiffness).

Answer 10

Fractures

Question 11

is a fracture along which the relative movement is parallel to the fracture

is used for fractures with small (mm- to dm-scale) displacements

Answer 11

shear fracture

Question 12

is more commonly restricted to discontinuities with larger offset.

Answer 12

fault

Question 13

used for fractures with fracture-parallel movements regardless of the amount of displacement and is consistent with the traditional use of the term fault.

Answer 13

slip surface

Question 14

are fractures that show extension perpendicular to the walls.

Answer 14

Extension Fractures

Question 15

have little or no macroscopically detectable displacement, but close examination reveals that most joints have a minute extensional displacement across the joint surfaces, and therefore they are classified as true extension fractures.

Answer 15

Joints

Question 16

When filled with air or fluid we use the term

Answer 16

fissure

Question 17

Mineral-filled extension fractures are called

Answer 17

veins

Question 18

while magma-filled fractures are classified

Answer 18

dikes

Question 19

have contractional displacements across them and are filled with immobile residue from the host rock.

Answer 19

Contractional planar features

Question 20

are compactional structures characterized by very irregular, rather than planar, surfaces.

Answer 20

Stylolites

Question 21

as they nicely define one of three endmembers in a complete kinematic fracture framework together with shear and extension fractures.

Answer 21

Contraction fractures

Question 22

can be used to test the uniaxial compressive or tensile strength of rocks.

Answer 22

Uniaxial rigs

Question 23

is used to explore the effect of large shear strain under vertical compression of up to about 25 MPa.

Answer 23

ringshear apparatus

Question 24

where rock cylinders are loaded in the axial direction while the sample is confined in fluid that can be pumped up to a certain confining pressure.

Answer 24

Triaxial tests

Question 25

where the resistance against shear is explored. The higher the normal stress, the higher the shear stress necessary to activate the fracture.

Answer 25

Shearbox experiment

Question 26

ideally develop perpendicular to σ3 and thus contain the intermediate and maximum principal stresses. In terms of strain, they develop perpendicular to the stretching direction under tensile conditions, and parallel to the compression axis during compression tests.

Answer 26

Extension Fractures

Question 27

If extension fractures form under conditions where at least one of the stress axes is tensile, then such fractures are

Answer 27

tensile fracture

Question 28

The line that tangent the Mohr circles represents the Coulomb fracture criterion

Answer 28

Coulomb failure envelope

Question 29

is the envelope or curve in the Mohr diagram that describes the critical states of stress over a range of differential stress, regardless of whether it obeys the Coulomb criterion or not.

Answer 29

Mohr failure envelope

Question 30

In this zone microdefects expand and connect so that the macrofracture can grow

Answer 30

Process zone

Question 31

far-field stress, we mean the stress that exists away from the local anomaly, or the state of stress if the anomaly was not there.

Answer 31

Remote stress

Question 32

Long, narrow planes slightly oblique to the main fracture surface named

Answer 32

Hackles

Question 33

This would typically be a bedding interface or some other boundary between two rock types of different mechanical properties, in which case a series of twisted joints or twist hackles form

Answer 33

fringe zone

Question 34

are thus locations of minimum propagation velocity and form parabolic (elliptic in massive rocks) irregularities sometimes referred to as arrest lines.

Answer 34

Ribs

Question 35

which are tensile fractures at the end of shear fracture

Answer 35

Wing Cracks

Question 36

In other cases, a whole population of minor, typically tensile fractures occur in the tip zone. These are asymmetrically arranged with respect to the main fracture and referred to

Answer 36

horsetail fractures.

Question 37

If the secondary fractures in the tip zone represent a fan shaped splaying of the main fracture, then the commonly used term is

Answer 37

splay faults.

Question 38

While splay faults are synthetic with respect to the main fault___________ may also occur in the tip zone of fractures

Answer 38

, antithetic fractures

Question 39

describes the vertical increase in critical shear stress (stress required for faulting) through the frictional upper crust

Answer 39

Byerlee’s law

Question 40

is the difference between the applied or remote stress and the fluid pressure.

Answer 40

Effective stress

Question 41

In highly porous rocks and sediments, brittle deformation is expressed by related, although different, deformation structures referred to as

are restricted to highly porous granular media, notably porous sandstones.

Answer 41

deformation bands.

Question 42

develop by shear-related disaggregation of grains by means of grain rolling, grain boundary sliding and breaking of grain bonding cements; the process that we called particulate or granular flow.

Answer 42

Disaggregation bands

Question 43

(also called framework phyllosilicate bands) form in sand(stone) where the content of platy minerals exceeds about 10–15%.

Answer 43

Phyllosilicate bands

Question 44

typically show striations and classify as slip surfaces rather than deformation bands.

Answer 44

Clay smears

Question 45

form where mechanical grain breaking is significant (Figure 7.39). These are the classic deformation bands first described by Atilla Aydin from the Colorado Plateau in the western USA

Answer 45

Clastic bands