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Brittle Deformation and Fault Mechanics
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Brittle Deformation and Fault Mechanics
Brittle Deformation and Fault Mechanics
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1
Question
What is Brittle Deformation?
Answer
Permanent change to a solid material due to growth of fractures and/or due to sliding on fractures. Occurs only when stresses exceed a critical value.
2
Question
What is a Fracture in geology?
Answer
Any surface discontinuity in rock; a general term for a surface in a material across which there has been loss of continuity and strength.
3
Question
What characterizes a Joint in geology?
Answer
A fracture with NO DISCERNABLE AMOUNT of displacement, planar-tensile opening-mode fracture with little or no displacement parallel to the fracture plane.
4
Question
What are Joint sets?
Answer
Families of parallel, evenly spaced joints that can be identified through mapping and analysis of orientations, spacing, and physical properties of the joints within a given system.
5
Question
Differentiate between Systematic and Nonsystematic joints.
Answer
Systematic joints are planar, parallel, traceable, and evenly spaced, while nonsystematic joints are irregular in form, spacing, and orientation.
6
Question
What do shear joints and tension joints refer to?
Answer
Shear joints are where shear planes/lines intersect. Tension joints are where tension planes/lines are parallel.
7
Question
What are STYLOLITES?
Answer
Nonplanar, crooked planes resulting from the dissolution of materials in rocks as a reaction to compression due to high pressure, also called antijoints.
8
Question
What is Stable Crack Propagation?
Answer
The process of tensile mode (Mode I) and shear mode cracks (Mode II) forming without breaking.
9
Question
What is Unstable Crack Propagation?
Answer
The development of broken cracks, forming stretched and unstretched bonds.
10
Question
What are Fringe Joints?
Answer
Joints that occupy the fringe of a joint surface beyond the joint face, produced by mixed-mode loading.
11
Question
Describe the concept of Joint Propagation.
Answer
Joints start at a single point and propagate outward in all 2D directions, forming two types of marks.
12
Question
What is the Origin Initiation Point?
Answer
The point where joints start, which might be surrounded by a mirror-smooth circular or elliptical area due to slow, accelerating rupture.
13
Question
What are Ribs in geology?
Answer
Ribs are undulations that are parabolically curved, spaced markings that tend to be concentric about the origin of a joint.
14
Question
How does Joint Spacing change with bed thickness?
Answer
Thicker beds generally have larger joint spacing, while thinner beds have closer joint spacing.
15
Question
What is a Fault?
Answer
Any surface or zone in the Earth across which shear displacement develops.
16
Question
What is a Fault Zone?
Answer
For brittle structures in which loss of cohesion and slip occurs on several faults within a band of definable width.
17
Question
What is a Microfault?
Answer
A fault that has microscopic offsets.
18
Question
Explain the difference between a Fault and a Fissure.
Answer
A fault is a surface or zone of shear displacement, while a fissure forms at the surface of the Earth with active tectonic processes.
19
Question
What are the types of Faults?
Answer
Normal Fault, Reverse Fault, Strike-slip Fault.
20
Question
Define a Normal Fault.
Answer
A high angle or low angle fault where the hanging wall moves down.
21
Question
What is a Reverse Fault?
Answer
A fault where the hanging wall moves up.
22
Question
What is a Strike-slip Fault?
Answer
Lateral faults where movement is purely lateral.
23
Question
Differentiate between Sinistral and Dextral Strike-slip faults.
Answer
Sinistral (left-lateral) and Dextral (right-lateral) describe the direction of lateral movement.
24
Question
What is a Graben?
Answer
A narrow, symmetric trough or basin, bounded on both sides by normal faults.
25
Question
What is a Horst?
Answer
An elongate, symmetric crustal block bordered on both sides by normal faults that dip away from the center.
26
Question
Define Thrust Faults.
Answer
Thrust faults are reverse faults with a gentle dip angle.
27
Question
What are Imbricate Fans?
Answer
Thrusts that either intersect the ground surface or die out up dip.
28
Question
What is a Duplex in geology?
Answer
Thrusts that span the interval of rock between a roof thrust and a floor thrust.
29
Question
What does Allochthon refer to?
Answer
A hanging thrust sheet above a detachment composed of rock that has moved substantially from its place of origin.
30
Question
What does Autochthon refer to?
Answer
A footwall thrust sheet below the detachment composed of rock still in its original position.