Dip direction from strike N55°E, dip 30°

The dip direction is at 90° to the strike, so it is found by adding or subtracting 90° from the strike.

Given: strike = N55°E (azimuth 55°), dip amount = 30°.

$$\begin{aligned} 55° + 90° &= 145° \ (\text{S}35°\text{E}) \\ 55° - 90° &= -35° = 325° \ (\text{N}35°\text{W}) \end{aligned}$$

The strike alone does not say which side of it is lower, so the dip direction is either S35°E or N35°W; both are at 90° to the strike. In the field, the side is decided by seeing which way the bed slopes down (or from the geological map). If the bed dips towards the south-east side, the dip direction is S35°E. (By the right-hand-rule convention, where the dip is to the right of the quoted strike direction, N55°E gives S35°E.)

                    N
      or N35W \     |     / N55E
                \   |   /
                  \ | /
  W ----------------+--------------------- E
                  / | \
                /   |   \
         S55W /     |     \ dip S35E
                    S
   ( / = strike line N55E-S55W,  \ = dip direction S35E, or N35W )

Answer: Dip direction = S35°E (if dipping to the south-east) or N35°W (if dipping to the north-west); dip amount 30°.