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