These three cross-sections of Alpine geology show different interpretations of the subsurface structures. The main differences are: (1) The number and geometry of faults, ranging from two straight faults to complex fault patterns with varying dips. (2) The amount and style of folding, with one section having additional synclines/anticlines. (3) The depth reached by one brown rock layer. Overall, the interpretations partition the deformation between faulting and folding in different proportions, leading to variation in their predicted shortening amounts.

1. Alps Cross-SectionsAberdeen University 2016/17 MGeol
Google maps, 2016
Bornes Section
These three interpretations differ most dramatically in there interpretation of the subsurface strata.
One model (middle) contains two major faults with two sub-faults on the north most of the major
ones. The other two interpretations have three (upper) and two (lower) faults. The bottom
interpretation just uses straight faults while the upper interpretation includes bends in the faults and
the central image includes complex fault shapes.
Another difference is to be seen within the north-westerly folded section where the upper interpretation
has an added syncline/anticline in place of a larger anticline seen in the other two interpretations.
Section runs WNW to ESE and contains two sections of uplifted folded beds separated by a large syncline in
each of the models.
The central interpretation also differs from the other two at the most south-easterly section with a brown
layer (Terres noires) reaching the surface in the other interpretations.
Bauges Section
Chartreuse Section
These three sections run from WNW to ESE and have a great variation in the interpretations. The top
and base interpretations show the horizons below the topography for the whole section while the
central model has an anticline above the surface.
Amy - 6.1%
Ben – 7.2%
Laura – 6.8%
Predicted shortening
The bottom model includes overturned beds in two places while in the other two models the beds
remain upright.
The faults used to create the models differ as well. In the bottom model only two faults are used, one
of which only cuts the bottom few horizons. In the top model three faults are used, the east-most of
which is normal and in the central model four faults are used. All are listric in nature.
Folding also differs between these interpretations. In the bottom cross-section the folding is most
concentric-like while the central interpretation shows the least folding.
Callum – 8.2%
Catriona– 14.2%
Zuzanna– 11.6%
Cameron – 8.25%
Florin – 13%
Symone – 22.9%
These sections run from WNW to ESE, are the south most section and include great difference in
interpretations.
Predicted shortening
Predicted shortening
The upper most section contains six faults, two of which cut to basement depths while
the others are only present in the upper horizons. The two basement cutting faults create a horst
that raises up the section between. The central model contains nine faults
all cutting to basement level. Two of these faults combine at depth. All are listric apart
from the most west fault. The bottom interpretation contains only one fault, listric in nature.
The folds that the sections include also differ greatly. For the bottom interpretation the
horizons are continuous and the difference in exposed horizon on the surface has been explained
using folding alone. The central model uses folding to explain the section also but very much a
sublunary method compared to the fault used. The upper section includes minimal folding.
From the results of our deformation modelling we can see that strain is differential laterally along strike in the sub alpine chain. The furthest north and south sections
receive twice the percentage shortening (10% compared to 5%) than the Born section which lies central. Averaging of the percentage shortening within each group has
reduced some of the uncertainty related to these interpretations however user interpretation could still play a role.
All three interpretations include large amounts of deformation however they all partition this
deformation differently. The top model dominantly explains it through the use of faulting and
the bottom majority folding whilst the middle interpretation is a hybrid.
To summarise these three interpretations they are all very similar however differ most in the deep faults
which creates the greatest difference in line length balance and therefore effect the predicted shortening
of the sections.
These three sections differ in shortening mainly due to the combination of fault use and folding.
The more folding and the larger offset on the faults results in the greatest shortening.