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GY403 Structural Geology Lab Thickness and Depth Problems Special Case: horizontal attitude Note: geological contacts will parallel topographic contour lines on map. 93 ft. 87 ft. T=93-87 = 6 ft. Thickness (t) = Elev. Upper contact – Elev. Lower contact Special Case: vertical attitude Note: cross-section is perpendicular to strike of unit. Thickness = outcrop width in this case. w General Rule: If the dip (δ) of the unit is perpendicular to the ground surface then w = t. δ t NOTE: cross section is perpendicular to strike of strata w= true outcrop width δ t= true thickness Cos β = (w) / (w’) w = Cos β * (w’) w’ = apparent outcrop width N β 40 w = true outcrop width 40 West East Scenario: slope and dip are inclined in opposite directions West-facing slope δ w σ t δ = true dip angle σ = slope angle Sin(δ+σ) = t/w t = Sin(δ+σ) * w Note: cross-section must be perpendicular to strike of bedding West East East-facing slope Scenario: slope and dip are inclined in same direction δ-σ w δ = true dip angle σ = slope angle t σ δ Sin(δ-σ) = t/w t = Sin(δ-σ ) * w Note: cross-section must be perpendicular to strike of bedding, and slope angle (σ ) must be measured perpendicular to strike. NOTE: cross section is perpendicular to strike of strata w= true outcrop width δ δ t d= depth in vertical drill hole Cos (δ) = t / d d = t / Cos( δ)