Geology Reference
In-Depth Information
Fig. 7.18.
Vertical and stratigraphic fault
separation.
a
Reverse fault.
b
Normal fault: the marker
horizon must be projected
across the fault in order to
measure the vertical separation
Vertical separation is the distance, measured vertically, between the two parts of
a displaced surface (Fig. 7.18; Dennis 1967). In the case of a normal-separation fault,
one of the surfaces must be projected across the fault to make the measurement. The
vertical separation of an offset marker horizon is shown in a vertical cross section in
the direction of dip of the bedding across the fault from the fault cut (Fig. 7.19). The
separation is measured from the marker horizon at the point of the fault cut to the
position of the same marker horizon across the fault (reverse separation; Fig. 7.19a)
or from the marker horizon at the fault cut to the
projection
of the marker horizon
from its location across the fault (normal separation, Fig. 7.19b). The amount of the
vertical separation is
v
=
t
/cos
δ
,
(7.3)
where
v
= vertical separation,
t
= stratigraphic separation = amount of the fault cut,
and
= cross-fault bedding dip. The cross-fault bedding dip is the dip of bedding across
the fault from the marker horizon at the fault cut. The vertical separation of a vertical
bed is undefined.
δ
