Geology Reference
In-Depth Information
Fig. 6.51.
Projection along plunge. a Per-
spective diagram. b Ve r t i c a l
plane through plunge line PP' .
c Vertical plane normal to the
cross section through line OP' .
d Plan view. Projection of the
cross section is shaded . Point Q
is vertically above A at A - Q and
point P' is vertically above O
at O - P'
the position of point P ( x , y , z ) is P' ( x ', z '). The apparent dip of the intersection line, q ,
of the vertical plane through PP' with the cross section is
δ
'. The relationship between
the apparent dip and the true dip,
δ
, of the z ' line, is given by Eq. 2.18 as
tan
δ
'=tan
δ
cos
α
.
(6.29)
Begin by finding z '. In the plane normal to the cross section (Fig. 6.51a,c),
z '=OP'/sin
δ
.
(6.30)
In the plane of the plunge (Fig. 6.51b), using triangles AQP' and PQR,
OP' = q sin
δ
' ,
(6.31)
z = L tan
φ
,
(6.32)
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