This graph shows the response to increasing stress as applied to two different rock types: BRITTLE vs. DUCTILE/PLASTIC
Definitions:
- STRESS: The force applied to a plane divided by the area of the plane.
- COMPRESSIVE STRESS: The stress generated by forces directed toward one another on opposite sides of a real or imaginary plane.
- TENSILE STRESS: The stress generated by forces directed away from one another on opposite sides of a real or imaginary plane.
- SHEAR STRESS: Stress (force per unit area) that acts parallel to a (fault) plane and tends to cause the rocks on either side of the plane to slide by one another.
- STRAIN: The result of stress applied to a body, causing the deformation of its shape and/or a change of volume.
- ELASTIC RESPONSE: The deformation of a body in proportion to the applied stress and its recovery once the stress is removed.
- ELASTIC LIMIT: The maximum amount of stress a material can withstand before it deforms permanently.
- DUCTILE RESPONSE: The permanent deformation, without fracture in the shape of a solid.
- BRITTLE RESPONSE: The fracturing of a rock in response to stress with little or no permanent deformation prior to its rupture.
- FOLD: Permanent wavelike deformation in layered rock or sediment.
- FAULT: A fracture in bedrock along which rocks on one side have moved relative to the other side.
- JOINT: A fracture on a rock without noticeable movement.
This Diagram depicts the types of stresses available.
Modified from: Page 374
George H. Davis: Structural Geology of Rocks and Regions Copyright C 1984, by John Wiley & Sons, Inc.
This diagram depicts some common fold types.
Acetate 54 (Figure 14-13)
Syncline and Anticline
C 1992 West Publishing Company
This diagram depicts an adjacent ANTICLINE and SYNCLINE with their representative FOLD AXIS and AXIAL PLANES.
Figure 1.4
Press and Siever: Understanding Earth Copyright C 1994 W. H. Freeman and Company
This Diagram depicts some of the differences between Asymmetrical, Symmetrical, and OVERTURNED folds.
More Fold types
Figures 11.17 and 11.18 from
George H. Davis: Structural Geology of Rocks and Regions Copyright C 1984, by John Wiley & Sons, Inc.
These diagrams show the affect of plunge on the fold axis.
More Fold Types
59 Strike and Dip Diagram
Plummer, Charles C., and David McGeary, Physical Geology, 6/e. Copyright C 1993 Wm. C Brown Publishers, Dubuque, Iowa. All Rights Reserved.
DIP: The angle formed by the intersection of a bedding or fault plane and the horizontal plane; measured in a vertical plane perpendicular to the strike.
This diagram uses Strike and Dip of repeating rock units to produce a geologic map and to infer the underlying fold.
Notice the differential weathering of different rock layers, especially on the right side of the image. This differential weathering allows the tilted/dipping limbs to be more noticeable. Notice the V-shape of the outcrop pattern. This ANTICLINE is plunging toward the top of the picture, therefore, it is a PLUNGING ANTICLINE!
Folding produced by fault action typically produces angular and/or box-folds
Notice the affect of differential weathering on the joints in the background on the left side of the image.
Fault Nomenclature
Fault Types
A and B are REVERSE faults and C is a low-angle reverse fault, typically called a THRUST fault.
A, B, and C depict Normal Faulting. In D, normal faulting has produced HORSTS and GRABENS. Horsts are the up-thrown blocks and the Grabens are the down-thrown blocks. In other words, the Horsts are the ridges and the Grabens are the valleys.
Strike-Slip Faults typically have near-vertical fault surfaces. They also come in two varieties: Left-Lateral Strike-Slip and Right-Lateral Strike-Slip Faults. Notice the pond in C. This is a SAG POND, which is usually due to INTERSEISMIC SUBSIDENCE. Following the release in stress as the result of an Earthquake, the rocks/ground relaxes and subsides, thus forming sag ponds in some situations.
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