Geology Reference
In-Depth Information
Fig. 6.7.
Relationship between true dip and vertically exaggerated dip (Eq. 6.3) for various amounts of
vertical exaggeration. (After Langstaff and Morrill 1981)
The effect of exaggeration on the thickness of a unit is given by (derived as Eqs. 6.26
and 6.28)
t
h
/
t
=cos
δ
h
/cos
,
(6.6)
δ
t
v
/
t
=
V
e
(cos
δ
v
/cos
δ
) .
(6.7)
The symbols are the same as in Eqs. 6.1-6.4. Horizontal exaggeration has no effect
on the thickness of a horizontal bed, whereas vertical exaggeration changes the thick-
ness of a horizontal bed by an amount equal to the exaggeration. Horizontal exaggera-
tion changes the thickness of a vertical bed by the full amount of the exaggeration,
whereas vertical exaggeration has no effect on the thickness of a vertical bed. For beds
dipping between 0 and 90°, both horizontal and vertical exaggeration cause the appar-
ent thickness to increase.
Exaggeration creates several problems in the interpretation of a cross section. The
first is that a large vertical exaggeration or horizontal squeeze may so distort the struc-
ture that the structural style becomes unrecognizable. This will lead to difficulties in
interpretation or to misinterpretations. For example, the exaggerated cross section
in Fig. 6.5a looks more like a wrench-fault style than the correct thin-skinned con-
traction style. Cross-section construction and validation techniques and models for
the dip angles and angle relationships do not apply to the exaggerated geometry. Ex-
aggeration also causes thicknesses to be a function of dip (Fig. 6.8). Care must be
taken not to interpret exaggerated thicknesses as being caused by tectonic thinning
