Structure contours / orthographic projection

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Structure contours / orthographic projection

• Lab 5 - Feb 26

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Calculating strike, dip, thickness

1. Visualize structure - is it planar? - detm dip
   direction
2. Determine strike by connecting two points of
   equal elevation on surface
3. Draw mini cross section perp to strike
4. Measure or calculate dip (tan (dip) elevation
   difference/map distance)
5. Measure thickness on cross section or calculate
   if applicable (sin (dip) thickness/map d from
   bottom to top of bed)

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Example

1. Visualize structure - is it planar? - detm dip
   direction

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• 2) Determine strike by connecting two points of
  equal elevation on surface

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Example

• 2) Draw mini cross section perp to strike

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Example

• 3) Measure or calculate dip using upper OR lower
  contact at 2 different elevations (tan (dip)
  elevation difference/map distance)

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• 4) Measure thickness on cross section or
  calculate (sin (dip) thickness/map d from
  bottom to top of bed)

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Structure contours/3 point probs

• If you dont have 2 points of equal elevation,
  need 3 points
• Visualize
• Connect points
• Calculate ds from points to contours
• Detm strike
• Draw upper and lower contacts
• Detm dip
• Draw cross section - detm thickness

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example

1. Visualize

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example

• 2) Connect points

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1. Calculate ds from points to contours

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• 4) Detm strike, draw contours

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• 5) Draw upper and lower contacts

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1. Draw cross section - detm dip
2. detm thickness

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Orthographic projection

• 2D drawings that help detm angular and spatial
  relationships in 3D
• Slip - actual relative displacement (piercing
  points)
• Slip vector - direction and magnitude of slip
  accommodated along a fault
• Separation - distance between map traces of
  planar marker feature across fault

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Orthographic projection

• Method
• Detm appropriate rakes with stereonet
• Draw a scaled map in the plane of the fault, with
  the rakes of lines plotted for both sides of the
  fault
• Locate piercing points
• Measure displacement with ruler and scale
• To detm fault type, measure rake of displacement
  vector and plot as right triangle

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Example (same as lab notes)

1. Detm appropriate rakes with stereonet

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Example (same as lab notes)

• 2) Draw a scaled map in the plane of the fault,
  with the rakes of lines plotted for both sides of
  the fault

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Example (same as lab notes)

• 3) Locate piercing points

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Example (same as lab notes)

• 4) Measure displacement with ruler and scale

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• 5) To detm fault type, measure rake of
  displacement vector and plot as right triangle