Apparent dip refers to the dip of a rock layer or geological feature as measured in a direction that is not perpendicular to the strike of that feature. It is the inclination angle observed along any section or exposure that does not cut the feature at a right angle to its strike. Because it is measured at an angle to the true dip direction, apparent dip is always shallower (lesser in angle) than the true dip, which is the steepest angle of descent measured perpendicular to the strike. In simpler terms, if the true dip is the actual steepness of a rock layer going straight downhill, the apparent dip is a less steep slope that you might measure if you're looking at it from a different angle, not directly downhill. This concept is important in geology for understanding the orientation of rock layers from observations taken at various angles. The relationship between apparent dip, true dip, and the angle between the strike and the direction of measurement can be calculated using trigonometry:
α=arctan(sinβ×tanδ)\alpha =\arctan(\sin \beta \times \tan \delta)α=arctan(sinβ×tanδ)
where
- α\alpha α is the apparent dip,
- δ\delta δ is the true dip,
- β\beta β is the angle between the strike direction and the direction in which the apparent dip is measured.
Therefore, the apparent dip provides a way to understand the dip observed when the geologic feature is not being viewed from the ideal perpendicular direction to the strike.
