Introduction to Faults

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Introduction to Faults (p. 269-279 286-296)

• 1) Hanging wall vs. footwall
• 2) Fault names based on geometry kinematics
• 3) Characteristics and terminology
• Strike-slip faults
• Normal faults
• Thrust faults

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Fault Fractures along which there is visible
offset by shear displacement generally planar or
curviplanar
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Strike-slip faults Accommodate horizontal slip
between adjacent blocks
left lateral (sinistral)
right lateral (dextral)
left lateral vs. right lateral sense-of-slip
relative to a chosen block
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What is it? left lateral vs. right lateral
Las Vegas shear zone
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What is it?
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What is it? (interpretation) left-lateral
strike-slip fault
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Hanging wall The block toward which the fault
dips. Footwall The block on the underside of
the fault.
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Normal fault hanging wall moves down with
respect to footwall
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Normal faults generally place younger and/or
lower-grade rocks (in HW) on top of older and/or
higher-grade rocks (in FW)
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Normal faults generally place younger and/or
lower-grade rocks (in HW) on top of older and/or
higher-grade rocks (in FW)
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Thrust fault (reverse fault) hanging wall moves
upward relative to footwall
HW
FW
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
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• Normal faults accommodate lengthening

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• Thrust faults accommodate shortening

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http//earth.leeds.ac.uk/learnstructure/index.htm
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Slip vs. Separation Slip actual relative
displacement Separation apparent relative
displacement
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A real example of apparent separation vs. true
slip!
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• The key to describing slip along a fault lies in
  measuring
• (1) Direction of displacement
• (2) Sense of displacement
• (3) Magnitude of displacement

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Listric curved faults that flatten with depth
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Fault scarp results when a fault displaces the
ground surface
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• Map Symbols a start
• Strike-slip fault
• Normal fault
• Thrust fault
• Fault dip and slip vector

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Next lecture Intro to folds Read pp. 372-413
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• Important terminology/concepts
• Faults- how are they defined?
• Hanging wall
• Footwall
• Strike-slip fault left-lateral (sinistral) vs.
  right-lateral (dextral)
• Normal faults younger/lower grade on
  older/higher grade
• Lengthening
• Thrust faults older/higher grade on
  younger/lower grade
• Shortening
• Slip vs. Separation?
• Drag fold
• Listric
• Fault scarp