Structures with Hammy

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Steno’s Laws

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law of superposition, law of original horizontality, law of cross-cutting relationships, and law of lateral continuity. Also important: Fossil Succession

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Folds

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a stack of originally planar surfaces that are bent or curved during permanent deformation

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92 Terms

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Steno’s Laws

law of superposition, law of original horizontality, law of cross-cutting relationships, and law of lateral continuity. Also important: Fossil Succession

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Folds

a stack of originally planar surfaces that are bent or curved during permanent deformation

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Fault

a planar fracture or discontinuity in a volume of rock across which there has been significant displacement

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Fracture

any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces

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Primary Structure

Structures that go back to the formation of the rock

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Secondary Structure

Structures that were created after the formation of the rock

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Fracture Set

A group of fractures

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Fracture Modes

Opening, Sliding, Tearing, Hybrid

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Plumose Structures

aggregates of gentle curvilinear undulations that radiate from the point where the joint originated and fan outward from a generally straight axial line, then resembling the shape and imprint of a feather

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Elastic Deformation

a temporary deformation of a material's shape that is self-reversing after removing the force or load

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Plastic Deformation

the permanent distortion that occurs when a material is subjected to stresses that exceed its yield strength

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Poisson Effect

 In an elastic body, volume change is resisted and therefore there will be longitudinal strain as well. E.g. things thin as stretched or widen as compressed

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Poisson’s Ratio

v = -((dy/y)/(dx/x)) = -(eyy/exx)

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Sections of the Failure Envelope

Tensile Failure, Frictional Sliding, Von Mises

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Conjugate Sets

Faults organized into two intersecting sets with opposite shear sense formed simultaneously

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Dihedral Angle

Acute angle between fracture sets

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Mode I Fractures

Opening. Displacement is perpendicular to the fracture face. Tension

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Mode II Fractures

Sliding. Displacement is parallel to the fracture face. Shear

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Mode III Fractures

Tearing. Displacement is parallel to the fracture face. Shear

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Hybrid

Mode I + Mode II or III

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Joints

Mode I fractures that are barely opened with no displacement along fracture plane

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Fissure

Mode I fractures more open than joints

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Regional Geometries

Longitudinal, Transverse, Oblique

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Longitudinal Regional Geometry

Parallel to tectonic trend

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Transverse Regional Geometry

Cuts tectonic trend at a high angle

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Oblique Regional Geometry

Cuts tectonic trend at a low angle

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Fracture Geometries

Radial, Ring, En Echelon, Pinnate, Columnar, Exfoliation

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Radial Fracture Geometry

Form from point stesses, something rising up or falling down

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Ring Fracture Geometry

Form from point stresses

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En Echelon Fracture Geometry

Laterally offset, stepwise geometry, may indicate shear

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Pinnate Fracture Geometry

Form in association with faults. Motion of the fracture is in direction of acute to obtuse angle

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Columnar Fracture Geometry

Usually hexagonal in cross-section, cooling of igneous rock

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Exfoliation Fracture Geometry

Expansion of rock due to decompression and/or weathering

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Joint Intersection Geometries

Y, T, X

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Hackles

Radiate outward from origin point and converse along line of propogation

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Ribs

Concentric around origin point and indicate location where fracture propagation slowed or halted

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Fringe

Outer margin of joint face where energy was low

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Fracture Kinks

Result of mixed-mode loading

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Hybrid Fracture Tip Types

Abrupt, wing-tip, hook, en echelon segments

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Stress

Force over an area

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Normal Stress

Stress perpendicular to faces

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Shear Stress

Stress along faces

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Shear Tensor

the state of stress for a unit volume consisting of stresses on all surfaces

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Normal Fault Stress

Vertical stress is the largest

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Thrust Fault Stress

Vertical stress is the smallest

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Strike-Slip Fault

Max and min stresses are both horizontal

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Strain

the relative displacement or deformation of a material due to an applied stress

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Brittle

Material that breaks under 5% strain

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Mohr Circle Diameter

sigma1 - sigma3

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Mohr Circle Center

Average of max and min stress

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Differential Stress

Max stress (sigma1) - min stress (sigma3)

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Frictional Sliding Equation

t = Co + sig_ntan(phi)

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Frictional Coefficient Equation

tan(phi) = mu

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Listric Fault

a fault with a curved fault plane, flattens at depth

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Yield Stress

the point at which a material begins to deform plastically

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Ultimate Stress

The highest possible stress after strain hardening

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Strain Hardening

irreversible deformation where yield strength increases with strain

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Strain Softening

irreversible deformation where yield strength decreases with strain

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Hooke’s Law

sig = kE

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Young’s Modulus

linear proportion of stress along one axis to strain in the same direction

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Shear Modulus

linear proportion of shear stress to strain in the same direction

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Bulk Modulus

Linear proportion of hydrostatic stress to volume change

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Hysteresis

Strain is fully recovered when stress is released, but not perfectly reversible

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Types of Elasticity

Linear, perfect, hysteresis

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Anelastic

The time delay between an applied stress and the resulting strain

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Effect of pore pressure

Weakens the material

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Von Mises

The highest yield strength where a material cannot support shear

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Viscous Behavior

the yield stress depends on the strain rate

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Strain Rate

the amount of time over which strain occurs

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Primary Creep

Plastic behavior takes over from elastic; strain hardening and strain softening

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Secondary Creep

Strain rate approaches a steady state

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Tertiary Creep

Microfractures grow or crystallographic changes allow strain rate to increase, followed by fracture

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Anisotropy

Difference in properties as a function of direction/orientation

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Griffith Theory of Fracture

Stress is concentrated at the tips of a void

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Borehole Breakouts

Shear fractures occur on the sides of a circular void where there is the min stress

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Fluid Pressure Impact on Mohr Circle

Shifts the circle to the left relative to fluid pressure. The circle will be outside the envelope

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Induced Extension Fractures

Extensional fractures that open in the direction of maximum compression

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Deformation Bands

small faults with very small displacements

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Point Defects

Vacancies, impurities, substitutions, interstitial ions. Move by solid-state diffusion processes

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Line Defects

Line, Edge, Screw. Move by slip or creep and my result in twinning

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Cataclasis

the crushing or fracturing of rocks and minerals due to stress

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Microcrack Types

Intragranular, intergranular, transgranular

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Intragranular

Cracks inside a grain

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Intergranular

Cracks between grains

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Transgranular

Cracks across multiple grains

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Dilatancy

an increase in volume, can be the result of cataclasis

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Kink Banding

Lattice bent along a discrete plane through the crystal

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Volume Diffusion

Vacancy diffusion through crystals, aka Nabarro-Herring Creep, temperature dependent. Lower crust and mantle

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Grain Boundary Diffusion

Preferential diffusion of vacancies along crystal boundaries, aka Coble Creep. Middle and upper crust

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Syntaxial Vein

Crystals grow from the middle

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Antitaxial Vein

Crystal grow from the vein wall(s)

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Crack-and-Seal Texture

The result of a repeating pattern of fracture and fill