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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How Rocks Deform
Faulting and Folding
Plate Boundary: Convergence Zones
Plate Boundary: Divergence Zones
Plate Boundary: Transform Faults
Very little ductile deformation before fracturing
Extensive ductile deformation before fracturing
Folding of Rocks
Faulting of Rocks
Rate of deformation (strain rate)
Low strain rates Ductile (Mantle Convection)
High strain rates Brittle (Earthquake waves)
Effects of Temperature and Strain Rate
Limits the depths of
Abrupt Movement along Faults
Uplifted sea floor at Cape Cleare, Montague Island, Prince William Sound. Uplift about 33 ft
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.
Large scale and small scale folds
Large scale and small scale
Strike and Dip
Measuring Deformation in the Rocks Strike & Dip
Types of Faults
Classified according to:
Dip of fault
Direction of relative movement
Normal Fault (dip-slip)
Tetons – fault range scale
Death Valley, CA
Reverse Fault (dip slip)
> 45° dip
Thrust Fault (dip-slip)
< 45° dip
Thrust Faults. Snake Range, Wy
Strike-Slip Fault (horizontal motion, no vertical motion)
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.
During mountain building or compressional stress, rocks undergo ductile deformation to produce folds
Anticline: Warped upwards. Limbs dip outward. When eroded, oldest rocks crop out in the center (assuming everything is right-side-up).
Syncline: Warped downwards. Limbs dip inward. When eroded, youngest rocks crop out in the center (assuming everything is right-side-up).
Basins and Domes resemble anticlines & synclines
vertical motions instead of lateral motions