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Deformation of Rocks. How Rocks Deform Brittle-Ductile Behavior Faulting and Folding. Stress and Strain. The keys to understanding any deformation are stress (the cause) and strain (the effect). Compression. Rocks are squeezed or compressed by forces directed toward one another.

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deformation of rocks
Deformation of Rocks

How Rocks Deform

Brittle-Ductile Behavior

Faulting and Folding

stress and strain
Stress and Strain
  • The keys to understanding any deformation are stress (the cause) and strain (the effect)
compression
Compression
  • Rocks are squeezed or compressed by forces directed toward one another.
  • Rocks are shortened by folding or faulting
tension
Tension
  • Rocks are lengthened or pulled apart by forces acting in opposite directions
  • Rocks are stretched and thinned
shear
Shear
  • Forces act parallel to one another but in opposite directions
  • Results in displacement of adjacent layers along closely spaced planes
relationship between stress and strain
Rock

Stress

Rubber band

Strain 

Relationship between stress and strain

Elastic behavior

Fracture, breaks

X

Ductile behavior

Permanent strain

relationship between stress and strain1
Stress

Strain 

Relationship between stress and strain

Brittle behavior:

Very little ductile deformation before fracturing

X

X

Fracture

Ductile behavior:

Extensive ductile deformation before fracturing

slide11
Ductile

Brittle

slide12
Ductile Behavior

Folding of Rocks

Brittle Behavior

Faulting of Rocks

what controls brittle vs ductile
What controls brittle vs. ductile?
    • Rate of deformation (fast = brittle)
    • Rock strength (strong = brittle)
    • Temperature (cold = brittle)
    • Confining pressure (shallow = brittle)
  • Just remember deeper = ductile
    • Near surface= rocks are brittle
    • At depth= rocks are ductile
what controls brittle vs ductile1
What controls brittle vs. ductile?

Rate of deformation (strain rate)

Low strain rates Ductile (Mantle Convection)

High strain rates  Brittle (Earthquake waves)

slide15
Yield stress

Elastic limit

Effects of Temperature and Strain Rate

brittle ductile transition
Brittle-DuctileTransition

Limits the depths of

earthquakes

surface

Brittle

Low Temperature

Low Pressure

15-20 km

Higher Temperature

Higher Pressure

Ductile

Crust

Mantle

slide17
T=1300 C

Yield

strength=0

Stress

Strain

Lithosphere-Asthenosphere

schematic

strength

profile through

continental

lithosphere

slide21
LA

SA

uplift

subsidence

Gradual Movement: Perspective view of the Los Angeles region with superimposed InSAR( Interferometric Synthetic Aperture Radar) measurements of ground motions between May and September 1999. Large regions of metropolitan Los Angeles are rising and falling by up to 11 cm annually, and a large portion of the city of Santa Ana is sinking at a rate of 12 mm per year.

past deformation folding
Past Deformation: Folding

Large scale and small scale folds

past deformation faulting
Past Deformation: Faulting

Large scale and small scale

faults
Faults
  • Fractures along which there is relative motion parallel to the fracture
  • The fracture is called the fault plane
    • Vertical motion (dip-slip)
    • horizontal (strike-slip).
    • Most faults have a combination of both types of motion (oblique).
slide28
Types of Faults

Classified according to:

Dip of fault

Direction of relative movement

normal faulting
Normal Faulting

Foot wall

Hanging wall

basin and range
Basin and Range

Death Valley, CA

Normal Faulting

Horst-Graben Structures

slide37
Thrust Fault

Older rocks

Younger rocks

san andreas fault
San Andreas Fault
  • Transform plate boundary (Pac / N.A.)
  • System of right lateral faults
slide42
Offset Streams (San Andreas Fault)

A pair of streams that has been offset by right-lateral slip on the San Andreas fault (lineament extending from left to right edge of photograph). View northeastward across fault toward the Temblor Range. Photograph by Sandra Schultz Burford, U.S. Geological Survey.

strike slip fault1
Strike-slip fault

Off-set stream

Right-lateral

Strike-slip

Stress: shear

types of folds
anticline

syncline

Typesof Folds

During mountain building or compressional stress, rocks undergo ductile deformation to produce folds

slide46
Anticline: Warped upwards. Limbs dip outward. When eroded, oldest rocks crop out in the center (assuming everything is right-side-up).
slide47
Syncline: Warped downwards. Limbs dip inward. When eroded, youngest rocks crop out in the center (assuming everything is right-side-up).
slide50
Basins and Domes resemble anticlines & synclines

 vertical motions instead of lateral motions

stress strain plate tectonics
Stress, Strain & Plate Tectonics
  • Plate collisions (convergent margins)
    • Compressive strsses
    • Folds & reverse faults
stress strain plate tectonics1
Stress, Strain & Plate Tectonics
  • Divergent plate boundaries
    • Tensional stresses
    • Normal faults
stress strain plate tectonics2
Stress, Strain & Plate Tectonics
  • Transform plate boundaries
    • Shear stress
    • Transform faults
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