Chapter 8

Question 1

is a tabular volume of rock consisting of a central slip surface or core, formed by intense shearing, and a surrounding volume of rock that has been affected by more gentle brittle deformation spatially and genetically related to the fault.

Answer 1

fault

Question 2

The opposite case, where the hanging wall is upthrown relative to the footwall

Answer 2

reverse fault

Question 3

Where the hanging wall is lowered or downthrown relative to the footwall, the fault is

Answer 3

normal fault

Question 4

If the movement is lateral, i.e. in the horizontal plane, then the fault is a

Answer 4

strike slip fault

Question 5

traditionally means a series of subparallel faults or slip surfaces close enough to each other to define a zone.

Answer 5

fault zone

Question 6

Two separate normal faults dipping toward each other create a downthrown block known as a

Answer 6

graben

Question 7

Normal faults dipping away from each other create an upthrown block called

Answer 7

horst

Question 8

The largest faults in a faulted area

Answer 8

master faults

Question 9

dips toward the master fault

Answer 9

antithetic fault

Question 10

dips in the same direction as the master fault.

Answer 10

synthetic fault

Question 11

Many faults show some deviation from true dip-slip and strike-slip displacement in the sense that the net slip vector is oblique

Answer 11

oblique-slip faults.

Question 12

A series of displacement vectors over the slip surface gives us

Answer 12

displacement field

Question 13

The vector connecting two points that were connected prior to faulting indicates

Answer 13

net slip direction

Question 14

The degree of obliquity is given by the
which is the angle between the strike of the slip surface and the slip vector (striation).

Answer 14

pitch

Question 15

is the separation of layers observed on a horizontal exposure or map

Answer 15

Horizontal seperation

Question 16

is that observed in a vertical section

Answer 16

dip separation

Question 17

In a vertical section the dip separation can be decomposed into the horizontal and vertical separation. These two separations recorded in a vertical section are more commonly referred to as

Answer 17

heave (horizontal component) and throw (vertical component).

Question 18

The general term for the stratigraphic section missing or repeated in wells drilled through a fault

Answer 18

stratigraphic separation

Question 19

Brittlely deformed wallrock known as the

Answer 19

fault damage zone

Question 20

In crystalline rocks, the fault core can consist of practically non-cohesive

Answer 20

fault gouge

Question 21

In extreme cases, friction causes crystalline rocks to melt locally and temporarily, creating a glassy fault rock known as

Answer 21

pseudotachylyte.

Question 22

constitute the fault core, particularly for faults formed in the lower part of the brittle upper crust.

Answer 22

catclasite

Question 23

If the matrix fragment ratio is higher, the rock is called a

Answer 23

fault gouge.

Question 24

are characterized by their large fragments. They all have less than 10% matrix and are cohesive and hard rocks.

Answer 24

Crush breccias

Question 25

are distinguished from crush breccias by their lower fragment–matrix ratio.

Answer 25

Cataclasites

Question 26

which are not really fault rocks although loosely referred to as such by Sibson, are subdivided based on the amount of large, original grains and recrystallized matrix

Answer 26

Mylonite

Question 27

Layers are commonly deflected (folded) around faults, particularly in faulted sedimentary rocks. The classic term for this behavior is

Answer 27

drag

Question 28

Faults that fall below seismic resolution are generally referred to as

Answer 28

subseismic faults

Question 29

Another characteristic feature is the presence of local intervals with rapid but progressive changes in dip and/or dip azimuth

Answer 29

cusps.

Question 30

Some cored fault rocks may be so non-cohesive that they fall apart to form what is known

Answer 30

rubble zones.

Question 31

The zone of microfractures (and mesofractures) ahead of the fracture tip zone is called the

Answer 31

process zone.

Question 32

is the shear zone-like geometry where layers flex toward parallelism with the fault.

Answer 32

Normal drag

Question 33

is used for the usually larger-scale rollover structures that occur on the hanging-wall side of listric normal faults.

Answer 33

Reverse drag

Question 34

models the ductile deformation in a triangular fault propagation fold area in front of a propagating fault tip.

Answer 34

trishear method

Question 35

Fold structures are commonly referred to

Answer 35

Force folds

Question 36

Folds that form ahead of a propagating fault tip are called

Answer 36

fault propagation folds.

Question 37

The latter mechanism can take drag to the point where the rotated layer, which typically consists of clay or shale, forms a

Answer 37

smear

Question 38

where slip accumulates at very sudden seismic slip events, separated by periods of no slip.

Answer 38

stick-slip

Question 39

Some laboratory experiments show that a gradually increasing force is needed for slip to continue

Answer 39

slip hardening

Question 40

Below this depth one would expect abundant seismic or stickslip activity until the brittle–plastic transition is reached. This is exactly what earthquake data indicate, and the zone is called the

Answer 40

seismogenic zone.

Question 41

predicts that both the amount of slip and the rupture length vary from event to event,

Answer 41

variable slip model

Question 42

considers the slip at a given point to be the same in each slip event.

Answer 42

uniform slip model

Question 43

Faults tend to nucleate at many different places as a region is critically stressed, for instance during rifting, and we refer to such groups of faults as

Answer 43

fault populations.

Question 44

Before the tips have reached each other (but after their strain fields have started to interfere) the faults are said to

Answer 44

underlap

Question 45

Under- and overlapping faults are said to be

Answer 45

soft linked

Question 46

If the fault interference occurs perpendicular to the slip direction, which for normal and reverse faults means in the horizontal direction, and if the layering is subhorizontal, then the folding is well expressed in the form of a ramp-like fold. The fold itself is called a

Answer 46

relay ramp and the entire structure is known as a relay structure.

Question 47

Eventually the ramp will break to form

Answer 47

breached relay ramp.

Question 48

The fracture (or deformation band) has not yet (or just barely) reached the upper and lower boundaries of the layer. Once the fracture touches the layer boundaries it is called

Answer 48

vertically constrained fracture

Question 49

The ability of faults to affect fluid flow is commonly referred to

Answer 49

transmissivity.

Question 50

Where sand is completely juxtaposed against shale, the fault is sealing regardless of the properties of the fault itself. This type of seal is called

Answer 50

juxtaposition seal.

Question 51

in the fault core reduces grain size and therefore reduces porosity and permeability.

Answer 51

Cataclasis

Question 52

The process where clay or shale is smeared out into a more or less continuous membrane is simply

Answer 52

smearing

Question 53

If such a membrane represents a physical barrier to fluid flow it is called a

Answer 53

seal, and the fault is a sealing fault.

Question 54

where clay is tectonically eroded from clay-rich layers along the fault and incorporated into the fault core, is a third mechanism that contributes to clay smearing.

Answer 54

Clay abrasion

Question 55

(SSF) gives the ratio between fault throw T and the thickness of the shale or clay layer.

Answer 55

shale smear factor

Question 56

relates to how far a clay or shale layer can be smeared before it breaks and becomes discontinuous.

Answer 56

clay smear potential