Strike and Dip Calculator

Because true dip is defined as the MAXIMUM dip angle the layer shows in any direction -- it's measured perpendicular to strike, which is the one direction that captures the full tilt. Any other cross-section direction cuts across the layer at a shallower effective angle, the same way a road climbing straight up a hillside is steeper than the same road traversing diagonally across it. Apparent dip only equals true dip when the section happens to run exactly perpendicular to strike.

Because that angle controls how much of the true dip's steepness the cross-section actually captures, via sin(angle). At 90 degrees (section perpendicular to strike), sin(90) = 1, so the section captures the full true dip. As the angle shrinks toward 0 degrees (section running parallel to strike), sin approaches 0, so apparent dip approaches 0 regardless of how steep the true dip actually is -- a section parallel to strike shows a flat-lying layer even if it's actually dipping steeply.

Thickness measured vertically through an outcrop or straight down a borehole is NOT the same as the layer's true perpendicular thickness unless the layer happens to be horizontal -- a tilted layer intersected vertically reads thicker than its real, bed-perpendicular thickness. Multiplying the vertically-measured thickness by cos(true dip) removes that foreshortening effect, which matters for accurately comparing stratigraphic thicknesses between different locations or wells.

No -- the true/apparent thickness ratio depends only on true dip (it's simply cos of the true dip angle), because it's converting a vertically-measured thickness to a bed-perpendicular one, a relationship that's fixed by how steeply the layer itself is tilted. The direction of the cross-section used to view or measure the layer doesn't change how tilted the layer actually is, so it has no effect on this particular ratio.