Skip to main content

Dip amount, strike; fold identification criteria

Short answer

Dip amount is the maximum inclination of a plane to the horizontal, measured perpendicular to strike. Strike is the compass bearing of the horizontal line on the plane; it is 90° from the dip direction. A fold is identified by repetition of beds in reverse order, opposite dips across an axis, curved outcrop patterns, older beds in core of an anticline, younger in core of a syncline, drag folds, fan cleavage, and plunging noses on topography.

Define dip amount and strike of a geological plane. Write down the field identification criteria of fold in the field.

Dip amount

The dip amount (angle of dip) is the maximum angle that an inclined geological plane makes with the horizontal plane. It is measured in a vertical plane at right angles to the strike, with a clinometer. It ranges from 0° (horizontal) to 90° (vertical). The direction towards which the plane goes down is the dip direction.

Strike

The strike is the direction (compass bearing) of the horizontal line drawn on an inclined plane, i.e. the line of intersection of that plane with a horizontal plane. It is always perpendicular to the dip direction, for example N30°E.

Field identification of fold

  • Repetition of beds in reverse order on both sides of an axis (A B C D C B A).
  • Opposite dips on two sides of a line (axis), either converging (syncline) or diverging (anticline).
  • Outcrop pattern on a map: a series of curved or zig-zag outcrops (V-shaped patterns) with plunge.
  • Age relation: in an anticline older beds are in the core; in a syncline younger beds are in the core.
  • Drag folds and minor folds in the small scale, and variation of strike or dip along a traverse.
  • Topography: ridges and valleys following the folded beds, and plunging noses on hill slopes.
  • Cleavage or joints (fan or radiating pattern) related to the axial plane.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Engineering Geology I chapter 5 questions →