Faults: Basics

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Faults Basics
Goal To understand and use the basic terminology
for describing faults.
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• Dip-slip faults Slip up or down the dip.
• Normal fault Hanging wall down indicates
  extension
• Reverse fault Hanging wall up indicates
  shortening

Reverse
Normal
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Strike-slip faults

• Slip parallel with earths surface
• Typically have subvertical dip

• Sense of motion
• Dextral right-lateral right-handed
• Sinistral left-lateral left-handed

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Oblique-slip faults

• Strike-slip and dip-slip components
• Most faults are oblique-slip, but are often
  dominantly strike-slip or dip-slip

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Slip vs. Separation

• Slip Total movement along fault surface.
• Vector lying in fault surface
• Direction of vector (slip-line) expressed as
  trend and plunge or rake in fault plane
• Separation Total apparent offset along fault
  when viewed in 2-D (either map or cross section).

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Same separation, different slip

• Dip-slip fault

• Strike-slip fault

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• To determine slip, you need a piercing point
• Piercing point Line that intersects fault
  surface and is off-set by fault
• Match hanging-wall cutoff with footwall cutoff

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Fault Rocks

• Frictional/brittle fault rocks Mechanical
  disaggregation and grinding
• Plastic fault rocks Plastic flow of minerals at
  atomic scale
• grain-size reduction due to deformation-driven
  dynamic recrystallization

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Breccia/gouge zone
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Brittle-plastic transition