Geology Reference
In-Depth Information
and
= angle of shear. Replacing D s in Eq. 11.34 by 11.35 and substituting into Eq. 11.33
ψ
gives
h 2
Ä
tan
ψ
+ h D - S = 0 .
(11.36)
This is a quadratic equation in h of a curve through the origin.The curvature of the
area-depth line is a constant that depends on the shear angle. If the shear angle is low,
the value of tan
ψ
is small, the curvature is not very great, and therefore could easily
go undetected.
11.4.5
Applications
The first application is to the full graben model in Fig. 11.18. The reference level is at
the regional elevation of horizon 1. The points representing the pre-growth interval
fall on a straight line because they all have the same displacement. The inverse slope
of the best-fitting straight line (-4.5 units) is the total displacement on the lower de-
tachment used to generate the model. The point at which the lost area goes to zero is
the location of the lower detachment (-9.62 units below the reference level) which is
the position of the lower detachment in the model. The growth beds (horizons 1-5)
have lost areas that decrease upward. The lost area of the youngest growth bed is not
zero because an increment of extension has occurred after the deposition of this unit.
Layer-parallel strain is found with Eq. 11.27 and thickness changes by substituting the
layer-parallel strains into Eq. 11.16. The pre-growth sequence is significantly stretched
horizontally and thinned vertically by the deformation (Table 11.1), as is obvious on
the cross section. The total displacements of the growth beds have been determined
from Eq. 11.18 (Table 11.1), given the position of the lower detachment, and match the
Table 11.1.
Structural data calculated
from the full graben model
in Fig. 11.18a (Groshong et al.
2003)
 
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