3D Reconstruction of Complex Geological Bodies

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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

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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/cageo


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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;

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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


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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

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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


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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),

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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.



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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:

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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.



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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


Mt. Misma is located NE of Bergamo (Fig. 1) and

shows a complex overturned faulted anticline

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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).



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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

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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.



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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

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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.



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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).

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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.



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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)


The third case study concerns the Texel Massif, a

high mountain relief reaching 3500m, in the

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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.



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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

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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.



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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

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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.



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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.



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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.



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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.



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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.



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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);



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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; }

{



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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;}



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