# Find the Apparent Dip of a Plane

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Sometimes we see sections of planes oblique to their strike. In cases like these, the slope of the plane is not its true dip but shallower. In the case of a section parallel to the strike, the plane can appear horizontal. The dip of a plane as seen in an oblique section is called its apparent dip. We might want to know the apparent dip a bed would have in order to draw a cross-section, calculate where it would outcrop in a trench or highway cut, or for a variety of other reasons.

This problem is actually an intersecting-plane problem where one of the planes is vertical. We already know the trend of the intersection -- it's simply the strike of the section plane. All we need to do, then, is find the plunge, which is the apparent dip as seen in the section plane.

## Trigonometric Solution

Tan (Apparent Dip) = Tan (True Dip) Sin (Angle between strike and cross-section).

In the example above, the true dip = 36 degrees and the angle between the strike and cross-section equals 53 degrees, so we have Tan (Apparent Dip) = Tan (36) Sin (53) = 0.58, and Apparent dip = 30 degrees.

Created 5 January 1999, Last Update 30 January 2012
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