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)
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Thickness & Depth Problems Lab Lecture