Define attitude of a rock

The attitude of a rock (geological structure) is its three-dimensional orientation in space, that is, the direction in which a plane or line is inclined with respect to the horizontal and to north. The attitude of a bedding plane is expressed by its strike and dip.

Components of attitude

1. Strike
   • The direction of the horizontal line drawn on an inclined plane (the line of intersection of the plane with a horizontal plane).
   • It is measured as a bearing from north, for example N45°E.
2. Dip
   • The maximum inclination of the plane with the horizontal, measured perpendicular to the strike.
   • It has two components: dip direction (the direction in which the plane goes down, at 90° to the strike) and dip amount (angle of dip) (the angle between the plane and the horizontal).
3. For a line (such as fold axis or lineation) the attitude is given by trend (compass bearing of the line projected on the horizontal) and plunge (angle of the line below the horizontal).

             N
             |   strike
             |  /
        _____|_/______
       /    /|/      /|
      /    / /      / |
     /____/_/______/  |  dip angle (a)
     |   /-> dip direction (90 deg to strike)
     |__/___________|/

Expressing orientation

• Quadrant method: strike N30°E, dip 40° towards SE (written N30°E/40°SE).
• Azimuth (dip direction/dip) method: 120°/40°.
• Measured in the field with a Brunton or Clar geological compass, which gives strike with the compass and dip with a clinometer.
• Strike is always at right angles to the dip direction, so if the dip direction is known, the strike is dip direction plus or minus 90°.