Geology Reference
In-Depth Information
Fig. 7.19.
Vertical separation calculated in a vertical cross section in the direction of the cross-fault
bedding dip.
a
Reverse separation fault.
b
Normal separation fault
7.4.3
Heave and Throw from Stratigraphic Separation
Heave and throw have a special significance because they are the separation compo-
nents visible on the structure contour map of a faulted horizon. Throw is the vertical
component of the dip separation and heave is the horizontal component of the dip
separation, both being measured in a vertical cross section in the dip direction of the
fault (Dennis 1967; Billings 1972). Throw and heave can be found directly from the
stratigraphic separation. The following discussion refers to the geometry shown in
Fig. 7.20. Let point P
1
be the location of the fault cut in a well or exposed in outcrop.
The marker horizon is shaded. P
2
is the location of the marker horizon in a vertical
plane oriented in the direction of fault dip. The calculation of throw and heave is a
projection across the fault from the control location (P
1
) to a predicted location (P
2
).
The stratigraphic separation at the point of the fault cut is the thickness of the missing
or repeated section,
t
. The dip separation,
S
d
, is equal to the apparent thickness of the
missing or repeated section in the direction of the fault dip (dip vector) between
points P
1
and P
2
. The dip separation can be found from Eq. 4.1 as
S
d
=
t
/cos
ρ
,
(7.4)
where
t
= the stratigraphic separation and
= the angle between the pole to the cross-
fault bedding attitude and the dip vector of the fault. The dip of bedding used is always
that belonging the side of the fault to which the projection is being made (P
2
), that is,
across the fault from the fault cut on the marker horizon. The value of
ρ
can be found
with a stereogram (Sect. 4.1.1.1) or from any of the analytical methods in Sect. 4.1.1.2.
The heave and throw are determined by taking the horizontal (
H
) and vertical (
T
)
components (Fig. 7.20) of
S
d
from Eq. 7.4:
ρ
H
=
t
cos
φ
/cos
ρ
,
(7.5)
T
=
t
sin
φ
/cos
ρ
,
(7.6)
