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Geosciences LibreTexts

Part I: Brittle Deformation and Mechanics

  • Page ID
    394
  • Chapters 1-9 in the textbook, covering faulting of various styles, and an introduction to the continuum mechanics of fault frictional strength and stability. The midterm (scheduled for February 11) will cover these chapters, and materials presented in Appendix 1.

    • 1B: Faults
      Faults are shear fractures or tabular zones with measurable displacement. As this displacement accumulates, faults tend to form a zone of fractured rock around them, called a damage zone, and form a zone of fault gouge along the slip surface. Thus, faults with significant offset appear very different from joints.
    • 1B: Fractures
      A fracture is any break where cohesion, the binding between particles, has been overcome. When no displacement has occurred after the fracture has formed, this fracture is called a joint; if displacement by sliding has occurred, it is a fault; and if opening has happened, it is called a fissure.
    • 2A: Normal Faults
      On normal faults, the hanging wall has moved down relative to the foot wall. These faults are generally steeply dipping, with a dip angle of 60° or greater. Low-angle normal faults have a dip of below 45°, accomplishing more extension per unit slip. How these faults are able to form and slip at such a low angle is a mechanical mystery.
    • 2B Reverse Faults
      A reverse fault is a dip-slip fault where the hanging wall moves up relative to the foot wall. Reverse faults are generally recognized by the emplacement of older rocks above younger ones, though in areas of complex deformation this is not always the case. These faults often dip at low angles, generally lower than 30º, and so are called thrust faults. All thrust faults are also reverse faults.
    • 3A Strike-Slip Faults
      Strike-slip faults accomplish lateral relative motion, which may be dextral (right lateral) or sinistral (left-lateral). Terminology for strike-slip faults has evolved based on the spatial scale and context of faulting.

    Thumbnail: Normal Fault.

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