Quick questions on Dip, strike and true thickness: measuring orientation and calculating bed thickness with trigonometry - Eduqas A-Level Geology

A structure contour is a line joining points of equal height (elevation) on a particular geological surface (such as the top of a bed), exactly as a topographic contour joins points of equal ground height. Evenly spaced, parallel structure contours show a planar bed dipping uniformly; the spacing gives the dip (closely spaced means a steep dip), and the contours run parallel to the strike, with dip down the steepest direction across them. Structure contours let you predict the depth of a bed at any point and where it will outcrop.

The true thickness of a bed is measured perpendicular to the bedding, not across the ground, so a dipping bed's true thickness is less than its horizontal outcrop width. For a bed measured horizontally across its outcrop at right angles to the strike on flat ground:

Define the strike of a bed and state its angular relationship to the dip. [2 marks]

A bed dips at $40^{\circ}$ and its horizontal outcrop width (at right angles to strike, flat ground) is $30\ \mathrm{m}$. Calculate the true thickness. [2 marks]

Using the rule of Vs, state the dip direction of a bed whose outcrop Vs upstream (up-valley) where it crosses a valley. [1 mark]