Outcrop on Mars

Strike

• Strike line = a line in a horizontal plane

• Strike = angle between true north and the strike line

• Azimuth = Bearing = angle clockwise from north

Line Orientation

Plunge = angle line makes with horizontal (angle measured in vertical plane)

Bearing = The azimuth of the projection of the line onto the horizontal plane

Special Lines in Dipping Plane

• Strike of plane=bearing of plane’s strike line

• Dip of plane = steepest plunging line in plane

• Ambiguity of dip direction.

• Necessary to define direction, e.g., 45° NE

Strike and Dip Symbols

Rake or Pitch

• Rake or Pitch = angle line makes with the strike line as measured on the plane

True North and Magnetic North

• True North = direction to North Pole

• Magnetic North = direction to Magnetic Pole

• Declination = angular difference between North Pole and magnetic North

True Dip and Apparent Dip

• Dip is always between 0 and 90°

• True dip is measured in vertical plane that is perpendicular to strike line

• Apparent dip is measured in vertical plane that is at arbitrary angle to strike line

• Apparent dip is always less than True Dip

Relationship between True Dip and Apparent Dip

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δa = arctan tan δ t( )cos θ( )[ ]

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δa = arctan tan δ t( )sin α( )( )or

Where

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δa = apparent dip

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δt = true dip

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α = angle between line of section and strike line