8/3/2019 3D Reconstruction of Complex Geological Bodies
1/21
Computers & Geosciences 35 (2009) 4969
3D reconstruction of complex geological bodies:
Examples from the Alps
Andrea Zanchia,b,, Salvi Francescac, Zanchetta Stefanoa,Sterlacchini Simoneb, Guerra Grazianod
aDipartimento di Scienze Geologiche e Geotecnologie, Universita degli studi di MilanoBicocca, P.za della Scienza 4, 20126 Milan, ItalybCNR-IDPA, Sezione di Milano, P.za della Scienza 1, 20126 Milan, Italy
cDipartimento di Scienze dellAmbiente e del Territoria, P.za della Scienza 1, 20126 Milan, ItalydDipartimento di Matematica e Applicazioni, Universita degli studi di MilanoBicocca, Via Bicocca degli Arcimboldi, 8, 20126 Milan, Italy
Received 26 September 2007
Abstract
Cartographic geological and structural data collected in the field and managed by Geographic Information Systems
(GIS) technology can be used for 3D reconstruction of complex geological bodies. Using a link between GIS tools and
gOcad, stratigraphic and tectonic surfaces can be reconstructed taking into account any geometrical constraint derived
from field observations. Complex surfaces can be reconstructed using large data sets analysed by suitable geometrical
techniques.
Three main typologies of geometric features and related attributes are exported from a GIS-geodatabase:(1) topographic data as points from a digital elevation model; (2) stratigraphic and tectonic boundaries, and linear
features as 2D polylines; (3) structural data as points. After having imported the available information into gOcad, the
following steps should be performed: (1) construction of the topographic surface by interpolation of points; (2) 3D
mapping of the linear geological boundaries and linear features by vertical projection on the reconstructed topographic
surface; (3) definition of geometrical constraints from planar and linear outcrop data; (4) construction of a network of
cross-sections based on field observations and geometrical constraints; (5) creation of 3D surfaces, closed volumes and
grids from the constructed objects.
Three examples of the reconstruction of complex geological bodies from the Italian Alps are presented here. The
methodology demonstrates that although only outcrop data were available, 3D modelling has allows the checking of the
geometrical consistency of the interpretative 2D sections and of the field geology, through a 3D visualisation of geometrical
models. Application of a 3D geometrical model to the case studies can be very useful in geomechanical modelling for slope-
stability or resource evaluation.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: 3D modelling; Field mapping; Structural geology; gOcad; Alps
1. Introduction
A geological map is one of the most effective tools
to show the geometrical relationships among rock
ARTICLE IN PRESS
www.elsevier.com/locate/cageo
0098-3004/$- see front matterr 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cageo.2007.09.003
Corresponding author. Dipartimento di Scienze Geologiche e
Geotecnologie, Universita` degli studi di MilanoBicocca, P.za
della Scienza 4, 20126 Milan, Italy.
E-mail address: [email protected] (A. Zanchi).
http://www.elsevier.com/locate/cageohttp://dx.doi.org/10.1016/j.cageo.2007.09.003mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.cageo.2007.09.003http://www.elsevier.com/locate/cageo8/3/2019 3D Reconstruction of Complex Geological Bodies
2/21
bodies. However, their geometry may be better
appreciated in three dimensions by applying geome-
trical techniques (e.g. Ramsay and Huber, 1987;
Powell, 1992; Groshong, 1999; Moore and Johnson,
2001). This is especially true in high mountain
ranges with a strong topographic relief, where 3Dgeological structures can be directly observed.
The recent development of software for 3D
reconstruction (Lynx, 3D GeoModeller, gOcad,
Earth Vision, 3D-Move, etc.) has opened a new
frontier in the Earth Sciences leading to n-dimension
analyses of the spatial extension of any kind of
geological structure and to 3D virtual models.
Several examples of integration among different
typologies of data have been published on subsur-
face structures at a regional scale (Ledru, 2001 and
references therein; Courrioux et al., 2001; Galera
et al., 2003; Wu et al., 2005). Nevertheless, fewapplications concern hard rock 3D analyses based
on outcrop geological and structural data (de
Kemp, 1999, 2000; Husson & Mugnier, 2003;
Maxelon & Mancktelow, 2005; de Kemp et al.,
2006).
The systematic use of tools provided in Geo-
graphic Information Systems (GIS) in field mapping
makes easy the management of the information
commonly contained in a geological map (Breunig,
1999). Exposed stratigraphic and structural bound-
aries, as well as structural information (attitude ofplanar and linear elements: bedding, faults, folia-
tions, fold axes, lineations), are a potential source of
information to be used in 3D reconstruction (Jessel,
2001; Chile` s et al., 2004). These data represent
spatially continuous information on the geological
framework of a region, and have been traditionally
used by generations of geologists to make previsions
about the extension of geological structures at
depth.
The aim of this work is to show how geological
cartographic data managed by GIS technology can
be used for 3D modelling of complex geological
bodies. 3D reconstruction has been performed by
gOcad, a software based on the discrete smooth
interpolation (DSI) algorithm (Mallet, 1997). Using
this algorithm, 3D surfaces, volumes and grids can
be obtained interpolating simple features with a
discrete atomic structure, such as points and lines.
Two software have been developed for the
management and construction of geometrical con-
straints in gOcad (Appendices A and B). The
proposed procedures can take into account any
other typology of data such as boreholes and
seismic information, which can be integrated in
order to complete and check the model.
Three examples, based on detailed geological and
structural field data (1:5000) surveyed in the Italian
Alps (Fig. 1), have been studied by these techniques.
The first and second case studies concern thesedimentary cover of the central Southern Alps;
the third one deals with superposed folds developed
in the Austroalpine metamorphic basement of the
Eastern Alps.
2. GIS techniques for data management and 3D
modelling with gOcad
The first step of the proposed methodology
concerns the creation of a geological database,
which includes all the information needed for 3Dmodelling (Fig. 2). This step has been realized in a
GIS environment, exploiting the available tools and
techniques to store and manage the following layers:
topographic data, including detailed 2D eleva-tion contour lines (10 m contour interval) and
single points with elevation values. Vector to
raster conversions and linear interpolations are
needed to obtain Digital Elevation Models
(DEM), in raster format. The contour interpola-
tion method is based on the Borgefors distance
method and the pixel size has been chosen
according to the complexity of the topographic
surface;
ARTICLE IN PRESS
Fig. 1. Location of case studies in the Italian Alps. (1) Corno
Zuccone deep-seated gravitational deformation; (2) Mt.Misma
fault and thrust structure, (3) Texel massif superposed folds. Bg:
Bergamo; Mi: Milan; TB: deformed Tertiary basins, Ad:
Adamello alpine pluton.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496950
8/3/2019 3D Reconstruction of Complex Geological Bodies
3/21
2D linear features representing stratigraphicboundaries, faults, fold axial traces, foliations,
morphostructural elements, etc. These polylines
have been obtained by generalising the surveyed
geological maps;
2D polygonal features and related attributesrepresenting the spatial distribution of outcrop-
ping units;
mesoscopic field structural measurements (bed-ding, faults, fold axes, lineations, etc.) represented
ARTICLE IN PRESS
Fig. 2. Schematic flow-chart for 3D modelling through data integration between GIS and gOcad.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 51
8/3/2019 3D Reconstruction of Complex Geological Bodies
4/21
as points with properties (strike, dip-direction,
dip, trend, plunge, etc.).
Three basic gOcad objects have been created with
the data exported: a 3D point set (vset) with elevation
values, a line set (plines) including all the geological
linear features and related attributes with no elevationvalue, surfaces (tsurf) interpolated from the curves
representing the boundaries of the outcropping units,
and point sets-related mesoscopic structural observa-
tions. The geological model has been constructed in
gOcad using this georeferenced data set, adding
further information from cross-sections.
In the beginning, the topographic surface has
been reconstructed interpolating the point set
extracted from the DEM. This simple procedure
has allowed an effective data transfer with an
optimum definition of the topography in compar-
ison with other methods. After having obtained thetopographic surface, properties such as the eleva-
tion value have been successively attributed to the
geological boundaries and surfaces by projection on
the 3D topographic surface. After transferring the
original attributes to the constructed surfaces, a 3D
geological map is obtained (Fig. 2).
Structural measurements have been transformed
into down-dip plunging lines to be used in the
construction of cross-sections (Scheetselaar, 1995) as
linear constraints. Further information concerning
concealed linear features (traces of stratigraphic andstructural surfaces) has been added from 3D
geological cross-sections. Cross-sections automati-
cally constructed in gOcad contain the topographic
profile, its intersection with geological boundaries
and structural measurement corrected with the
apparent dip. These cross-sections have been com-
pleted manually in a CAD software taking into
account geometrical constraints and using 2D
balancing techniques in a few cases. A tool has been
developed in order to georeference the cross-sections
in gOcad (Appendix B). Surfaces can be constructed
using the 3D linear features and can be combined in
order to define volumes and grids, according to the
cross-cutting relationships recognised in the field.
3. Case-study I: the Corno Zuccone klippe and
related deep-seated slope gravitational deformation
(DSSGD)
3.1. Geological setting
The first study area (Fig. 3) is located NW of
Bergamo within the south-vergent thrust stack
forming the upper portion of the Southern Alps, con-
sisting of Mesozoic carbonate successions (Forcella
and Jadoul, 2000). Three main tectonic units occur in
the area. The lowermost tectonic unit (Taleggio
Imagna Unit: TIU) includes three formations: the
Riva di Solto Shale (RSS) at the base, includingshales, marlstones and marly limestones (200 m), the
Zu Limestone with massive to well-bedded bioclastic
limestones and marlstones (550 m), and the Dolomia
a Conchodon at the top with massive oolitic lime-
stones (100 m). The TIU shows important tectonic
repetitions in the western part of the area around
Avolasio. The Zuccone-Maesimo (ZMU) and the
Corno del Bruco (BU) Units form isolated klippen
covering the TIU. They both comprise strongly
fractured carbonate successions gently dipping
southward (Fig. 3A). The ZMU includes a few
isolated outcrops of Dolomia Principale, which arethe remnants of a continuous thrust sheet dismem-
bered by NS left-lateral strikeslip faults (e.g. Valle
del Chignolo fault system); the largest klippe forms
the Corno Zuccone peak. The BU mainly consists of
the Esino Limestone.
3D modelling has been focused on the reconstruc-
tion of a large landslide, which affects the southern
slope of the Corno Zuccone massif. The slide is
considered a deep-seated slope gravitational defor-
mation (DSSGD, Varnes et al., 1989), described in
detail in other works (Zanchi et al., 2002, 2003). Thewhole slope of the Corno Zuccone shows several
large morphostructures as down- and up-hill facing
scarps and trenches (Fig. 3B), affecting both the rigid
dolostones of the Zuccone Klippe (Dolomia Princi-
pale) belonging to the ZMU and the underlying TIU,
which here consists of the Riva di Solto Shale (RSS).
These features represent the superficial expression of
south-dipping sliding planes associated with minor
antithetic fractures rooting into the RSS, which
form the tectonic substratum of the klippe (Fig. 4).
A vertical down-throw of at least 100 m of the
southern portion of the klippe has been observed
along the main scarp. Rotational landslides occur
along the lower part of the slope, which entirely
consists of the RRS. Continuous movements in
recent times are suggested by strong damages to the
infrastructures and by the sharp southward diversion
of Enna River along the toe of the slide.
3.2. The 3D model of the Corno Zuccone DSSGD
The 3D topographic surface of the area has been
obtained by a detailed DEM (pixel size 2.5 m),
ARTICLE IN PRESS
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496952
8/3/2019 3D Reconstruction of Complex Geological Bodies
5/21
ARTICLE IN PRESS
Fig. 3. Geological data for the reconstruction of the Corno Zuccone Deep Seated Slope Gravitational Deformation (DSSGD) (modifiedfrom Zanchi et al., 2002). (A) Simplified geological map obtained from detailed field survey (tics show the Gauss-Boaga national grid);
(B) geomorphologic features from photo-interpretation with extension of the Corno Zuccone slide.
Fig. 4. A balanced cross-section of the Corno Zuccone DSSGD; trace of section in Figs. 3A and B.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 53
8/3/2019 3D Reconstruction of Complex Geological Bodies
6/21
resampled to a 10 m pixel size, on which generalised
geological and geomorphologic linear features have
been projected (Fig. 5AE). A 3D regular grid
(voxet object in gOcad) is constructed where several
geological cross-sections have been traced (Fig. 5F).
Some of the cross-sections have been balanced(Fig. 4), based on dip-slip motion along gravitational
features, and limited block rotation along listric
faults (51101). Buried surfaces including sliding
planes due to gravitational motion and tectonic
surfaces (thrust and strikeslip faults) are built. In
order to reconstruct the fault systems affecting the
klippe, cross-cutting relationships among the differ-
ent tectonic structures must be established on thebasis of field observations. Gravitational surfaces are
the most recent ones and include two different sets:
ARTICLE IN PRESS
Fig. 5. A 3D point set is extracted from the DEM and imported in gOcad (A); interpolation of point set and construction of a triangulated
topographic surface in gOcad (B). Geological boundaries are imported in gOcad with a fictitious elevation (C), and are projected on
topographic surface (D). A 3D view of geological linear and polygonal features (E). Topography, 3D geological boundaries and cross-
sections (F) are the main constraints for the construction of geological models.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496954
8/3/2019 3D Reconstruction of Complex Geological Bodies
7/21
ENEWSW fractures related to the DSSGD and
recent scarps relative to superficial slides. The Valle
del Chignolo and Valle dellAcqua strikeslip faults
clearly post-date the emplacement of the ZMU and
BU thrust sheets, which are the earliest tectonic
structures. In addition, gravitational structuressharply end against the two strikeslip faults. We
began the reconstruction of the fracture systems
from the gravitational structures, successively con-
structing thrusts and strikeslip faults. Each single
surface has been obtained through interpolation of
the surface trace of the structures, down-dip projec-
tions of the attitude of the structure and linear
elements derived from the cross-sections
(Fig. 6). Due to their surface trace, gravitational
structures have been supposed to be listric, progres-
sively flattening within the shale beds of the RRS
occurring below the klippe. The reconstructed planeshave been supposed to join a basal sliding surface,
which is bounded to the west by the Valle del
Chignolo fault (Fig. 7A). During this stage, this fault
has been partially reactivated with a dextral-normal
slip (Zanchi et al., 2002).
Finally, the floor thrust of the Corno Zuccone
klippe, which crops out only along its eastern
margin and is displaced by faults and gravitational
structures, has been reconstructed through the trace
of geological boundaries and cross-sections based
on the observed superficial displacements (Fig. 7B).
Using these surfaces, closed volumes have been
obtained and the volume of the slide mass
(0.627 km3) has been measured.
The 3D geological model has also provided the
definition of a 3D grid with deformable cells
(S-Grid), which has been fitted to the structuraland stratigraphic surfaces. An S-Grid with four
layers, each of those corresponding to rocks with
different mechanical properties, has been created for
the Corno Zuccone DSSGD (Fig. 8). The 3D
geological model has been thus transformed into a
geomechanical model, to visualise and explore in 3D
the mechanical properties of the rock bodies. The
fence diagram of Fig. 8B suggests that the
maximum deformation at surface, enhanced by
the occurrence of morphostructures in the upper
middle part of the DSSGD, corresponds to the
maximum thickness of rocks with low geomechani-cal parameters at depth. Similar models can be
eventually used for slope stability analyses.
4. Case-study II: the fold and thrust structure of Mt.
Misma
4.1. Geological setting
Mt. Misma is located NE of Bergamo (Fig. 1) and
shows a complex overturned faulted anticline
ARTICLE IN PRESS
Fig. 6. Progressive reconstruction from serial cross-sections of the floor thrust of the Corno Zuccone klippe and of fracture systems related
to Corno Zuccone DSSGD. (A) Construction of boundaries of the floor thrust by connecting linear features obtained from serial cross-
sections. (B) Construction of triangulated surface from linear features obtained in (A).
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 55
8/3/2019 3D Reconstruction of Complex Geological Bodies
8/21
related to south-vergent thrust propagation along
the frontal part of the Southern Alps (Forcella and
Jadoul, 2000). This structure develops in the foot
wall of the Dolomia Principale thrust sheet, an EW
regional overthrust occurring north of the study
area. The Mt. Misma Triassic to Lower Cretaceous
folded succession is in turn stacked along a high-
angle reverse fault on the Upper Cretaceous
turbidites, which form the southern foothills of the
Alps (Bersezio et al., 1990).
The deformed succession of Mt. Misma includes
the Upper Triassic to Lower Jurassic Zu Limestone
followed by the Dolomia a Conchodon Fm., and by
the cherty limestones of the Sedrina and Moltrasio
Limestone (200 m), at the core of the Mt. Misma
anticline. The Sedrina an Moltrasio Limestones
are unconformably covered by the red nodurlar
limestones condensed facies of the Stalla Cura
unit, which suggests the occurrence of an Early
Jurassic structural high possibly related to NS
extensional faults active in the Lombardian basin at
this time. This unit is followed upward by a well-
bedded Liassic to Early Cretaceous basin succession
with cherty limestones (Concesio Fm., 200300 m),
radiolarian cherts (Radiolariti, 60 m), red marly
limestones (Rosso ad Aptici, 40 m), cherty lime-
stones (Maiolica, 100 m), marls and marly lime-
stones of the Sass de la Luna and finally by the
ARTICLE IN PRESS
Fig. 7. Complex surfaces in the Corno Zuccone area: (A) main sliding surfaces of the Corno Zuccone DSSGD, including the basal failure
surface; (B) displaced floor thrust of the Corno Zuccone klippe with the Valle dellAcqua and Valle del Chignolo strikeslip faults.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496956
8/3/2019 3D Reconstruction of Complex Geological Bodies
9/21
Bruntino Marlstone. This hemipelagic succession is
unconformably covered by thick Upper Cretaceous
turbidites cropping out along the southern slope of
Mt. Misma. The Mt. Misma anticline (Fig. 10)
grows above a complex high-angle thrust fault
(Salvi et al., 2002) well exposed east of the fold.The fold is markedly non-cylindrical, dying out
westward, with an upper limb dipping WSSW-ward
and a lower overturned limb that dips northward.
The growth of the whole structure has been possibly
driven by the peculiar paleogeographic setting of the
area, where a thin condensed succession has
favoured the development of the thrust-related fold.
A small high-angle reverse fault splays off the main
thrust along the overturned limb of the anticline.
A NS trending strikeslip fault interrupts the main
thrust, which stacks the Zu Limestone on the
Concesio Fm. eastward of the Mt. Misma summit.
To the west of this fault, the thrust surface is
displaced southward, propagating between the
Rosso ad Aptici and the Radiolariti, as suggested
by their tectonic reduction. The upper normal limb
of the Mt. Misma anticline evolves northward into a
regional overturned syncline with a steep N-dipping
axial surface related to footwall folding along the
inferred continuation of the Dolomia Principale
thrust.
The whole structure is thrusted southward along
an EW trending, bedding parallel, north-dipping
reverse fault, which stacks the overturned Jurassic
units over the Cretaceous turbidites.
4.2. 3D model of the Mt. Misma structure
Particular attention has been given to themeasurement of mesoscopic features (bedding and
cleavage) in order to provide an accurate geome-
trical description of this complex structure, to better
evaluate its geometry (conical/cylindrical fold,
Fig. 9). The distribution of poles to bedding shows
that the Mt. Misma anticline is a sub-conical fold
with a moderately dipping plunging axis and a N- to
NE-dipping axial surface. The upper syncline
developed in the upper limb of the anticline is a
tight to isoclinal cylindroidal fold with a low-angle
NW-dipping axis. The plunge of the fold axes has
been calculated using the cylindrical and conical
best fits obtained through statistical analysis
(Woodcock and Naylor, 1983). The obtained fold
axis of the anticline dips steeply in its eastern and
western terminations (320/30 and 314/35), whereas
in its central part it dips more gently (300/27). The
anticline shows an overturned forelimb and a gentle
westward dipping (301) back-limb; the back-limb of
the syncline is very steep (60701) and its axis is
more regular (Figs. 9 and 10).
The analysed folds have been divided into
different domains with an approximately cylindrical
ARTICLE IN PRESS
Fig. 8. (A) Fence diagram of the S-Grid of Zuccone DSSGD including four layers with different cohesion values; volume of slided mass is
0.627 km3
. Very low values (0.10.2MPa) have been assigned to RRS close to basal sliding surface and to thrust plane (layers 24), andhigher values to the core of slide (0.30.4 MPa) (layer 3). The klippe has been considered as a homogeneous mass with a high cohesion
(layer 1). (B) Zoom of S-Grid.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 57
8/3/2019 3D Reconstruction of Complex Geological Bodies
10/21
geometry (Fig. 11A). A representative cross-section
has been traced along the central part of each
domain. Point set regions, which contain structural
data sets (bedding, cleavage, faults, etc.), have been
extracted from each domain and projected along
plunge lines (Groshong, 1999) on each cross-section
using an original script in gOcad (Fig. 11A). The
apparent dip has been then calculated in gOcad
according to the strike of the section. Finally, the
dip-direction lines for each projected structural
observation have been traced for a length of 50 m,
due to the complexity of the structural setting
(Appendix A).
After having evaluated the thickness of each
stratigraphic unit, its style of folding and its relation-
ships with thrust geometry, cross-sections have been
traced using the obtained constraints (Fig. 11B).
Folded surfaces have been finally constructed in
gOcad using cross-sections, fold axes and surface
stratigraphic boundaries as constraints (Fig. 11C).
ARTICLE IN PRESS
Fig. 9. Simplified geological map of the Mt. Misma area (original survey 1:5000), with stereographic projections of main structural
features; Schmidts lower hemisphere. (A) Bedding measurements in the whole studied area; (B) bedding of main anticline of Mt. Misma:
conical best fit is reported as a dashed line and calculated fold axis as a triangle; (C) bedding of main syncline; (D) bedding in footwall of
main thrust; (E) fracture cleavage in Bruntino Marlstone and Concesio Fm.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496958
8/3/2019 3D Reconstruction of Complex Geological Bodies
11/21
The 3D reconstruction of the folded and faulted
stratigraphic horizons of the Mt. Misma structure
and of their relationships with the thrust faults has
greatly improved the understanding of this complex
structure. 3D modelling takes into consideration the
strong lateral variations of the tectonic structures
and of the thickness of each unit, the latter due to
onlaps and tectonic reductions.
The main tectonic surfaces of Mt. Misma are
represented in Fig. 12A. Eastward, the Th1 thrust is
interrupted by the NS trending fault (Te1), here
interpreted as a high-angle left-lateral tear fault.
This fault may represent the reactivation of a
Liassic-inherited normal fault bounding the Mt.
Misma block. According to our reconstruction, to
the west of Te1, the thrust Th2 is represented by a
surface with a complex geometry. The thrust dips
steeply in its southernmost and northern parts as in
the case of Th1, but it seems to gently dip in its
central portion, driving the growth of the Mt.
Misma S-verging anticline. The Th2 system is
considered to die out westward, being partitioned
into soft-linked en-e chelon bedding-parallel blind
thrusts, as suggested by the occurrence of local tight
folds within the Radiolariti and Concesio Fm.
The geometry of the anticline-syncline km-scale
system and the lateral variations of the fold axes
is well shown in the 3D reconstruction (Fig. 12B
and C).
5. Case-study III: superposed folds in the Texel
Group (Merano, NE Italy)
5.1. Geological setting
The third case study concerns the Texel Massif, a
high mountain relief reaching 3500m, in the
ARTICLE IN PRESS
Fig. 10. 3D geological map ofFig. 8; numbers identify the position of geological cross-sections used in the reconstruction. MiU Misma
Unit; SL Sass de la Luna; BM Bruntino Marlstone; Ma Maiolica; Ap Rosso ad Aptici; Rd Radiolariti; Cs Concesio Fm.;Do Domaro Limestone; StU Stalla Cura unit; Mo Moltrasio Limestone; Se Sedrina Limestone; DC Dolomia a Conchodon;
Zu Zu Limestone; Th1, Th2, Th3 thrusts and Te1 tear fault. Fault symbols as in Fig. 9.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 59
8/3/2019 3D Reconstruction of Complex Geological Bodies
12/21
Austroalpine Texel Unit probably part of the
Oetztal Nappe (Hoinkes et al., 1987; Handy and
Oberhaensli, 2004), NNE of Merano (Fig. 13). The
mapped area comprises the transition between the
Schneeberg Complex and the surrounding Texel
basement, which contains a rock association with
micaschists, garnet- and amphibole-schists, marbles,
calcschists and amphibolites. This area has been
chosen for its high morphological relief, excellent
outcrop conditions and the occurrence of well-
defined lithological boundaries.
Four distinctive deformational phases have been
recognised (Fig. 14), in agreement with previous
works (van Gool et al., 1987; Spalla, 1990). The D1
ARTICLE IN PRESS
Fig. 11. Construction of cross-sections through projection of bedding attitude along plunge lines. (A) Subdivision of a non-cylindrical fold
in domains with cylindrical geometries and projection of attitude along plunging lines in case of plunging folds; (B) projection of attitude
data on cross-section plane and tracing of stratigraphic and structural features. Anticline (left) and syncline (right) fold axes (triangle in theplots) were calculated for each domain with cylindrical/conical best-fit (see text); (C) portion of folded top of Sedrina Limestone
reconstructed using cross-sections and fold axes as constraints. See text and Appendix A.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496960
8/3/2019 3D Reconstruction of Complex Geological Bodies
13/21
structures are almost completely transposed and
occur as small decimetric isoclinal folds or as relict
foliations in D2 fold hinge zones. The D2 deforma-
tional phase is characterized by the development of
NESW trending tight to isoclinal synforms
(SchneebergMulde of Sander, 1921). A S2 folia-
tion, developed under amphibolite-facies conditions,
is the most pervasive fabric. The S2 mainly dips to
WNW with values ranging from 301 to 801 and is
often associated with a poorly defined L2 lineation.
D2 fold axes trend between NW and NNE, showing
highly variable plunging. The scatter of D2 structural
elements is mainly due to the successive D3deformational phase, which deeply influences the
regional pattern. This phase is associated with the
formation of S- to SE-vergent pervasive asymmetric
folds with a closely spaced crenulation and a
poorly defined foliation developed in the green-
schits/epidote amphibolite facies. These structures
have a 100 m wavelength and become very steep
moving westward from the Hoch Wilde to the lower
Pfossen valley, culminating in a zone where vertical
fold axes and axial planes form the so-called
Schlingen folds (Schmidegg, 1933). Gentle, km-
scale, D4 folds have only minor influence on the
structural pattern.
5.2. The 3D model of the superposed folds of the
Lodner Peak
The 3D model of the Lo dner Peak folds has been
obtained based on detailed mapping and structural
ARTICLE IN PRESS
Fig. 12. 3D visualisation of the Mt. Misma structure. (A) Main tectonic surfaces of the area; to be noted tear the fault responsible for
lateral shift of the upper thrust. (B) NS 3D-section across folds and thrusts; acronyms refers to thrust planes (th2, th3) and to
stratigraphic units present in the area (Fig. 9). (C) The main tectonic and stratigraphic surfaces seen from east; the conical fold system
developed along the upper thrusts is evident.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 61
8/3/2019 3D Reconstruction of Complex Geological Bodies
14/21
analysis. Structural elements such as fold axes, axial
planes and foliations have been traced in the map in
order to obtain a complete 2D representation of the
fold style of the area (Fig. 14). Field studies have
taken to the interpretation of the marble layers of
the Lo dner and Kleine WeiXe peaks as a single D2isoclinal synform fold, successively refolded during
the D3 deformation phase. This structure has
been chosen for 3D modelling due to its exposure
and its significance in the deformation pattern of the
area.
The 3D topographic surface has been obtained as in
the previously described case studies. Draping of an
ortho-photo on this surface and projection of the linear
features effectively visualise the complex fold pattern
(Fig. 15). Linear elements (marbles/gneisses lithological
boundaries, foliations and axial planes traces) have
been traced along 24 cross-sections after projecting the
mesoscopic data sets into the chosen profiles. The D2axial plane has been built projecting its trace on the
topographic surface; the hinge line has been obtained
joining the hinge points defined in the cross-sections.
The D2 axial surface has been used as a further
constraint for the 3D model. Due to the complexity
of the interference pattern between the D2 and D3folds, four different domains have been defined and
3D surfaces have been built separately for each of
them.
ARTICLE IN PRESS
Fig. 13. Geological outline of Texel Massif (Merano) with the main structural units of the Eastern Alps in up-right scheme. VSZ:
Vinschgau Shear Zone.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496962
8/3/2019 3D Reconstruction of Complex Geological Bodies
15/21
According to our reconstruction, the Loedner
Kleine Weibe marbles represent a huge D2 isoclinal
synform. The 3D visualisation of the final model
clearly shows the influence of the D3 folding event
on the D2 isoclinal synform. The superposed fold
pattern (between type 2 and 3 of Ramsay and
Huber, 1987) is evident along the eastern closure of
the D2 fold, where both axial planes and axes cross
each other at high angles (Fig. 16).
The change in attitude of the marbles/gneisses
boundary and the D2 axial plane is also well
recorded west of the Lodner peak to the Kleine
Weibe, where both lithological boundaries and axial
surfaces change their dip-direction from NE to
WSW, becoming progressively steeper due to the D3
event. The inflection zone, clearly visible in the
3D model, is located approximately 300 m SW of
the Kleine Weibe peak. The 3D visualisation of the
LodnerKleine Weibe fold and its exploration
through gOcad represents a useful tool in testing
the reliability of the structural interpretation of the
studied area. Once the consistency of the structural
interpretation has been confirmed by the 3D model,
it can be extended to adjacent areas that show the
same deformational pattern.
6. Conclusions
These methodologies give the opportunity toconstruct and visualise preliminary geometrical
ARTICLE IN PRESS
Fig. 14. Simplified geological and structural data for the reconstruction of LoednerKleine Weibe synform obtained from interpretation
of a detailed field map. Plots refer to representative mesoscopic features measured during field work. Schmidts lower hemisphere; Sn:
poles to foliations, PAn: poles to axial planes, An: fold axes.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 63
8/3/2019 3D Reconstruction of Complex Geological Bodies
16/21
models starting from surface geological data,
once the general structural setting of an area has
been established by field mapping and strati-graphic/structural analyses. The integration of
field data in a 3D model reduces the gap existing
between field geology and interpretations at
depth, which derive from different sources of
information.
Although general geometrical models can be usedfor the description of cylindrical geological
structures honouring a pure or simple shear
behaviour (Galera et al., 2003), in many real
situations, deformation can be hardly modelled
a priori. Field mapping is still one of the best
tools to describe the geometrical features of
geological objects resulting from natural defor-
mation processes.
A 3D visualisation of geometrical solutionshelps one to understand the extension at
depth of geological objects and avoid unrealistic
interpretations. For example, in the Corno
Zuccone case study, 3D modelling led us to
reconstruct the position of the buried floor
thrust of the klippe and to locate the basal
sliding surface. Also in the second case study the
complex relationships between oblique ramps
and plunging fault-related folds have been
established through the comparison of serial 2D
cross-sections, leading to a consistent geometricalinterpretation. This is particularly true when
structures are not cylindrical, as in the analysed
situations. In all the three case studies, a 2D
representation is to be considered incomplete and
may lead to misleading interpretations. The
construction of 3D models is an iterative
procedure: from a test of the geometrical
consistency between field data and interpretative
models it provides the progressive corrections
of imprecision and eventually field mapping
mistakes.
The definition of the volume of the reconstructedbodies provides a more complete and quantita-
tive evaluation of the geological setting
of an area. In landslide-prone areas, as for
the Corno Zuccone case study, it provides
important constraints in establishing stability
conditions for hazard assessment. In the
second and third case study, related to shallow
and deep tectonic structures, volume evalua-
tions give further insights on the amount of
distorsion and on deformation mechanisms,
respectively.
ARTICLE IN PRESS
Fig. 15. 3D visualisation of LodnerKleine Weibe structures. The topographic surface has been draped with an orthophoto, on which the
main lithological boundaries have been projected. Marble/gneiss boundaries used for 3D reconstruction are represented in yellow; green
line represents the trace of D2 LodnerKleine Weibe synform; mb: marble layers.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496964
8/3/2019 3D Reconstruction of Complex Geological Bodies
17/21
3D grids with geomechanical properties havebeen obtained for the Corno Zuccone landslide,
starting from the geometrical definition of the
model. This can be considered as a new kind of
approach for future 3D geomechanical numerical
modelling, which is often based on over-simpli-
fied geometrical constraints. The same holds true
also for the characterization of the 3D strain
patterns of deformed bodies, when detailed
structural data are available.
Finally, the geometric features of the recon-structed geological bodies can be used to eva-
luate primary resources, or consciously plan
subsurface investigations through seismic surveys
and drilling, as well as to design prelimi-
nary monitoring plans in the case of landslide
analysis.
Acknowledgements
This work was developed within the gOcad
Consortium; ASGA is also warmly thanked. The
paper strongly benefited of the revisions by Andreas
Pletsch and Patrick Ledru.
ARTICLE IN PRESS
Fig. 16. (A) 3D surface of the LodnerKleine Weibe synform is represented together with the traces of D2D3 axial planes (left) and the
D2 (right) axial plane surface. (B) D2D3 superposed fold in NE termination of Lodner marble layers. Linear elements used as constraints
and D2 and D3 axial planes on left; final 3D surface is on right.
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 65
8/3/2019 3D Reconstruction of Complex Geological Bodies
18/21
ARTICLE IN PRESS
Appendix A. Convnew.exe
This program creates a set of points along the dip-direction of a geological surface, starting from its attitude
(dip-direction and dip). Down-dip plunging lines of a desired length can then be created in gOcad as control
features from the obtained point set. Input data are given by the location of the field observation (x, y and z)
its two angles of dip-direction direz (azimuth between the north and the dip-direction/plunge measuredclock-wise from the north: east-dip is 901, west-dip is 2701) and dip incl (angle of dip measured from the
horizontal), and its length L. The program can be used as well as with any kind of lineations, in this case
direz will correspond to the plunge of the line.
First of all the director cosines are evaluated, corresponding to the reference axes x, y and z
(the y-axis in parallel to the north) in the following way:
a cosincl sindirez,
b cosincl cosdirez;
g sinincl:
Ifx0, y0 and z0 are the three coordinates of the starting point P0, then the coordinates of the nth point Pn on
the down-dip line are given byxn x0 a n p;
yn y0 b n p;
zn z0 g n p;
where p is the distance between two neighbouring points. The number of points is given by the integer part of
L/p.
In the following, the input file is denoted by fp, while the gocad output file is denoted by fv.
The first loop while reads the first line of the input file that does not contain data (comments). The second
while reads all the subsequent lines and for each one of them writes, in the output file, the gOcad object
corresponding to a set of points aligned along the down-dip plunging line. The distance between two
neighbouring points is given in the command line: step_length. The coordinates, x, y and z, of the startingpoint, the two angles: dip-direction, dip, and the length: length, of the plunging line are read from the input file.
Then the gOcad header is written, the director cosines are computed and eventually the loop for writes all the
coordinates of the points corresponding to the plunging line.
void plungelines(step_length,fp,fv)
double step_length;
FILE *fp, *fv;
{
int i, s, points, h;
double sin(), cos(), n2;
double x, y, z, dip_direction, dip, length, p;
double a, b, c;Int *r;
s 0;
while((h getc(fp)) ! \n)
;
while ( fscanf(fp,%s %lf %lf %lf %lf %lf %lf, \
&r,&x,&y,&z,&dip_direction,&dip,&length) 7) {
fprintf (fv,GOCAD VSet\nHEADER{\nName:Without Property\n\n);
points length/step_length;
a cos(dip/57.2958) * sin(dip_direction/57.2958);
b cos(dip/57.2958) * cos(dip_direction/57.2958);
c sin(dip/57.2958);
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496966
8/3/2019 3D Reconstruction of Complex Geological Bodies
19/21
ARTICLE IN PRESS
for (i 0; io points; ++i) {
fprintf(fv,VRTX %d ,i+1);
p i * step_length;
fprintf(fv,%f %f %f\n, x+p * a, y+p * b, zp * c);
}
fprintf(fv,END\n);
}
}
Program functionality convnew [-h][-f n1] file1 file2
convnew h: shows help
convnew f n1 (step) file1 (input), file2(output): gives point sets along dip-
direction of planar elements or along the plunge direction of linear features from
attitude data (record number, x, y, z, dip-direction, dip, length)
file 1 espl.txt (Input ascii file)
convert line2_2110 (comment)
1 8428 4809.120 13998 65 75 5002 80992 4809.714 12894 65 70 500
file 2 espl.vs (Output ascii gOcad file)
GOCAD Vset
HEADER{
Name:Without Property
}
VRTX 1 8428.000 4809.120 13998.000
VRTX 2 8474.914 4830.996 13804.814
VRTX 3 8521.828 4852.872 13611.629
END
GOCAD Vset
HEADER{
Name:Without Property
}
VRTX 1 80992.000 4809.714 12894.000
VRTX 2 81053.995 4838.622 12706.061
VRTX 3 81115.99033 4867.531 12518.123
END
Appendix B. gOcad scripts vertex.psc and georef.psc
These two scripts allow 3D georeferencing of 2D geological cross-sections. They can be used when we have
to modify cross-sections using friendly-use cad systems with no 3D georeference. In order to georeference an
ungeoreferenced 2D cross-section, we have to draw a horizontal line below the section with only two vertices,
which must have the same coordinate of the starting and ending point of the section; the y coordinate must
be the same for the two vertices and must have the minimum y value in the file. We also have to know the x, y
and z coordinates of the two extremities of the reference line in the real world.
The first script finds the x and y coordinates of the two extremities in gOcad and writes them in the file
coordinates.txt; the second script gives the correct 3D georeference system to the cross-section, using the 2D
gOcad coordinates written in coordinates.txt and the x and y coordinates of the two extremities of the
reference line. The z value must be already known.
gOcad script vertex.psc
BEGIN{ counter 0; }
{
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 67
8/3/2019 3D Reconstruction of Complex Geological Bodies
20/21
ARTICLE IN PRESS
if ( counter 0) {
first_min_X X;
second_min_X X;
first_min_Y Y;
second_min_Y Y;
}
else {
If (Yo first_min_Y) {
second_min_X first_min_X;
second_min_Y first_min_Y;
first_min_X X;
first_min_Y Y;
}
}
counter counter+1;
}
END{ print 4 coordinates.txt first_min_X, first_min_Y, second_min_X, second_min_Y; }
gOcad script georef.pscBEGIN {
# old coordinates of the reference line obtained from vertex.psc
X_min_old 4.58028;
X_max_old 5.66;
Y_old 0.167232;
z_old 0;
# new coordinates of the reference line, according to the real world georeference system
X_min_new 750,000;
X_max_new 763,000;
Y_min_new 4,500,000;
Y_max_new 4,500,000;Z_new 2000;
# rotated old coordinates
X_min_rot x_min_old;
X_max_rot x_max_old;
Y_rot z_old;
z_rot y_old;
# computation of the transformation coefficients
L_old fabs(x_min_rot-x_max_rot);
L_new sqrt(pow(x_min_new-x_max_new,2)+pow(y_min_new-y_max_new,2));
A (x_max_new-x_min_new)/L_new;
B sqrt(1-pow(A,2))*(y_max_new-y_min_new)/fabs(y_max_new-y_min_new);
D L_new/L_old;E x_min_new-D*A*x_min_rot+D*B*y_rot;
F y_min_new-D*B*x_min_rotD*A*y_rot;
}
{
# transformation
Xtmp X;
Ytmp Y;
Ztmp Z;
X D*(A*Xtmp+B*Ztmp)+E;
Y D*(B*Xtmp-A*Ztmp)+F;
Z (Ytmp-z_rot)*D+z_new;}
A. Zanchi et al. / Computers & Geosciences 35 (2009) 496968
8/3/2019 3D Reconstruction of Complex Geological Bodies
21/21
References
Bersezio, R., Fornaciari, M., Gelati R., 1990. Geological map of
the Southalpine foothills between Brianza and Lake Iseo.
Dipartimento di Scienze della Terra Universita` degli studi di
Milano. Nuova Serie Pubblicazione no. 597, LAC, Firenze.
Breunig, M., 1999. An approach to the integration of spatial dataand systems for a 3D geo-information system. Computers &
Geosciences 25 (1), 3948.
Chile` s, J.P., Aug, C., Guillen, A., Lees, T., 2004. Modelling the
geometry of geological units and its uncertainty in 3D from
structural data: the potential-field method. In: Proceedings
Orebody Modelling and Strategic Mine Planning, Perth, WA,
2224 November 2004, pp. 313320.
Courrioux, G., Nullans, S., Guillen, A., Boissonnat, J.D., 2001.
3D volumetric modeling of Cadomian terranes (Northern
Brittany, France): an automatic method using Voronoi
diagrams. Tectonophysics 331, 181196.
de Kemp, E.A., 1999. Visualization of complex geological
structures using 3-D Bezier construction tools. Computer &
Geosciences 25 (5), 581597.de Kemp, E.A., 2000. 3D visualization of structural field data:
examples from the Archean Caopatina Formation, Abitibi
greenstone belt, Quebec, Canada. Computer & Geosciences
26 (5), 509530.
de Kemp, E.A., Schetselaar, E.M., Sprague, K., 2006. 3-D
symbolization of LS fabrics as an aid to the analysis
of geological structures. Computers & Geosciences 32 (1),
5263.
Forcella, F., Jadoul, F., 2000. Carta Geologica Della Provincia
Di Bergamo a Scala 1:50.000 (Geological Map of the
Bergamo Province, scale 1:50.000). Grafica Monti, Bergamo.
Galera, C., Tennis, C., Moretti, I., Mallet, J-L., 2003. Construc-
tion of coherent 3D geological blocks. Computers &
Geosciences 29 (8), 971984.
Groshong, J.R.H., 1999. 3D Structural Geology: A Practical
Guide to Surface and Subsurface Map Interpretation. Springer,
Berlin, 400pp.
Handy, M.R., Oberhaensli, R., 2004. Explanatory notes of the
tectonic and metamorphic map of the Alps. Mitteillungen der
Osterreichischen Mineralogischen Gesellschaft 149, 201225.
Hoinkes, G., Frank, W., Mauracher, J., Peschel, R., Purtscheller,
F., Tessadri, R., 1987. Petrography of the Schneeberg
Complex. In: Flu gel, H.W., Faupl, P. (Eds.), Geodynamics
of the Eastern Alps. Deuticke, Vienna, pp. 190199.
Husson, L., Mugnier, J.L., 2003. Three-dimensional horizon
reconstruction from outcrop structural data, restoration, and
strain filed of the Baisahi anticline, Western Nepal. Journal ofStructural Geology 25 (1), 7990.
Jessel, M., 2001. Three-dimensional geological modeling of
potential-field data. Computers & Geoscience 27 (4), 455465.
Ledru, P., 2001. The Cadomian crust of Britanny (France): 3D
imagery from multisource data (Ge ofrance 3D). Tectonophy-
sics 331, ixxi.
Mallet, J.L., 1997. Discrete modeling for natural objects.
Mathematical Geology 29 (2), 199219.
Maxelon, M., Mancktelow, N.S., 2005. Three-dimensional
geometry and tectonostratigraphy of the Pennine zone,
Central Alps, Switzerland and Northern Italy. Earth-Science
Reviews 71, 171227.
Moore, R.R., Johnson, S.E., 2001. Three-dimensional recon-
struction and modeling of complexly folded surfaces using
Mathematica. Computers & Geoscience 27 (4), 401418.
Powell, D., 1992. Interpretation of Geological Structures
Through Maps. Longman Scientific and Technical, UK,
176pp.
Ramsay, J.G., Huber, M.I., 1987. The Techniques of ModernStructural Geology. Folds and Fractures, vol. 2. Academic
Press, London, 391pp.
Salvi, F., Sterlacchini, S., Zanchi, A., 2002. 3D Modeling with
Gocad of complex geological structures in the frontal part of
the Southern Alps. In: Proceedings of the IAMG Annual
Conference of the International Association for Mathematical
Geology, vol. 4(2). Terra Nostra, Berlin, Germany,
pp. 127132.
Sander, B., 1921. Tektonik des Schneeberger gesteinszuges
zwischen Sterzing und Meran (Tectonics of the Scheneeberg
Complex between Sterzing and Meran). Jahrbuch Geolo-
gischen Bundesanstalt Abhandlungen 70, 325334.
Schmidegg, O., 1933. Neue Ergebnisse in den su dlichen O tztaler-
Alpen (New data on the southern Oetzal Alps). Verhandlun-gen der Geologischen Bundesanstalt Abhandlungen 56,
8395 Wien.
Scheetselaar, E.M., 1995. Computerized field-data capture
and GIS analysis for generation of cross sections in
3-D perspective views. Computers & Geosciences 21 (5),
687701.
Spalla, M.I., 1990. Polyphased deformation during uplifting of
metamorphic rocks: the example of the deformational history
of the Texel Gruppe (Central-Western Austroalpine domain
of the Italian Eastern Alps). Memorie della Societa` Geologica
Italiana 45, 125134.
van Gool, J.A.M., Kemme, M.M.J., Schreurs, G.M.M.F., 1987.
Structural investigations along an EW cross section in the
Southern O tztaler Alps. In: Flu gel, H.W., Faupl, P. (Eds.),
Geodynamics of the Eastern Alps. Deuticke, Vienna,
pp. 214225.
Varnes, D.J., Radbruch-Hall, D., Savage, W.Z., 1989. Topo-
graphic and structural conditions in area of gravitational
spreading of ridges in the western United States. US
Geological Survev Professional Paper 1496, Washington,
DC, 32pp.
Woodcock, N.H., Naylor, M.A., 1983. Randomness testing in
three-dimensional orientation data. Journal of Structural
Geology 5 (5), 539548.
Wu, Q., Xu, H., Zou, X., 2005. An effective method for 3D
geological modeling with multi-source data integration.
Computers & Geosciences 31 (1), 3543.Zanchi, A., Crosta, G., Stelluti, G., Sterlacchini, S., 2002. 3D
geological modeling for slope stability problems. The case
study of the Corno Zuccone sackung, Val Taleggio (Italy).
Memorie della Societa` Geologica Italiana 57, 585594.
Zanchi, A., Crosta, G., Stelluti, G., Sterlacchini, S., 2003. Using
GIS and gOcad for the 3D reconstruction of the Corno
Zuccone sackung, Val Taleggio (Italy). In: Rosenbaum, M.,
Turner K. (Eds.), New Paradigms in Subsurface Prediction.
Characterization of the Shallow Subsurface Implications for
Urban Infrastructure and Environmental Assessment. Lec-
ture Notes in Earth Sciences, vol. 99, Springer, Heidelberg,
Germany, pp. 141150.
ARTICLE IN PRESS
A. Zanchi et al. / Computers & Geosciences 35 (2009) 4969 69
Top Related