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)