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Computers & Geosciences 35 (2009) 19–32

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Sheet 280—Fosombrone 3D: A study project for a newgeological map of Italy in three dimensions

Mauro De Donatis�, Francesco Borraccini, Sara Susini

L.In.E.E.—Laboratory of Information-tech for Earth and Environmental Sciences, University of Urbino,

Campus Scientifico, 61029 Urbino (PU), Italy

Received 26 September 2007

Abstract

The goal of this project is to define and test a method for building a three-dimensional (3D) geological model of Italy

based on maps at a 1:50,000 scale, using the new national geological mapping program (CARG project). A structural

model of Sheet 280—Fossombrone (Northern Apennines, central Italy) was produced using recently developed 3D

visualization techniques. This area is characterized by faulted anticlines and broad synclines, involving a

Triassic–Palaeogene succession detached from its underlying basement. Exhaustive knowledge of the regional and local

geology, combined with available subsurface (well and seismic) data, makes this area a good test site for developing a 3D

geological modeling method.

The model of Sheet 280—Fossombrone was built in two steps. In the first step, we built a 2.5D geological model using

the digital elevation model combined with the new 1:50,000 scale geological map of the area. This 2.5D model shows

relationships between topographic elements, geology and major structures much better than traditional 2D geological

maps. In the second step, we constructed an in-depth model integrating a large amount of subsurface data with field data

from the recent mapping project.

The geological model of Sheet 280—Fossombrone clarifies structural geometries and kinematics of this external part of

the Northern Apennines. Structural and geomorphic analyses were performed on the 3D model to evaluate how additional

information can be obtained from 3D cartography in order to improve knowledge of the study area. We present results of

these analyses as examples.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Structural geology; Northern Apennines; 3D geological mapping; CARG project; Thrust fault

1. Introduction

Understanding the geometry of structures andrelationships between stratigraphic and tectonicunits at depth is one of the main challenges facedby geologists. This goal is traditionally pursued by

e front matter r 2007 Elsevier Ltd. All rights reserved

geo.2007.09.004

ing author. Tel./fax: +39 722 304295.

ess: mauro.dedonatis@uniurb.it (M. De Donatis).

interpreting geological and geophysical data in oneor two dimensions (logs of deep wells, stratigraphiccolumns, cross-sections, structural maps) and per-forming structural analysis (cut-off line maps,branch line maps, restoration and balancing ofcross-sections).

The recent development of software devoted togeological modeling in three dimensions representsa significant improvement for geologists who have

.

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to understand and visualize geological bodies inthree dimensions at depth (Schetselaar, 1995; Slattet al., 1996; de Kemp, 2000; Lees, 2000; De Donatis,2001; Jessell, 2001; Sirakov and Muge, 2001; DeDonatis et al., 2002; Sirakov et al., 2002; Galeraet al., 2003; Tanner et al., 2003; Wu and Xu, 2003;Guillaume et al., 2004; Witten, 2004; Arens et al.,2005). Geological models in three dimensionsintegrate different kinds of data (cross-sections,seismic profiles, logs of deep wells) much moreeasily than traditional techniques and allow thethree-dimensional (3D) structure to be representedmore coherently and exhaustively as a result(Breunig, 1999; Lemon and Jones, 2003; Wuet al., 2005). Furthermore, adding new data andderived interpretations to the model enables thegeologist to verify the quality of previous inter-pretations and to reach better results throughiterative corrections. Finally, an integrated ap-proach with 3D tools makes geologic informationmore accessible to a wider audience of non-geologicspecialists and decision-makers; as a result, 3Dgeological models are useful in diffusing geologicalknowledge.

Fig. 1. Location map of She

The 3D geological model of Sheet 280—Fossombrone (Fig. 1) was constructed in order toclarify deep structures in the study area and todefine and test a method suitable for differentgeological settings in Italy (De Donatis et al., 2002).We used a multidisciplinary approach, involvinggeological mapping, seismic data interpretation andcomputer science. We preformed geomorphic andstructural analyses on the model (presented here asexamples), increasing understanding of severalgeomorphic and structural aspects of the study area.

2. Study area

2.1. Geological setting

The Northern Apennines are a NE-verging arc-shaped mountain belt, created since the Oligoceneby the convergence and collision between theCorsican and Sardinian continental blocks and theAdriatic continental margin. Gravitational subsi-dence of the Adriatic and Ionic lithosphere andassociated slab roll-back controlled the superposi-tion of the tectonic units over the Adriatic

et 280—Fossombrone.

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continental margin and back-arc stretching of theTyrrenian sea area during the Miocene to lowerPleistocene (Malinverno and Ryan, 1986). In thenorthern and central parts of the Apennine belt,oceanic-provenance units (Liguride Complex) tec-tonically overly foredeep and passive marginsequences (Tuscan and Umbro-Romagna Units).

The Umbria-Marche Apennines are characterizedby thrust faults and associated anticlines involvinga Mesozoic–Tertiary passive margin succession(Deiana and Pialli, 1994) and underlying Triassicbasement (Barchi et al., 1998; Coward et al., 1999).In the Marche-Romagna area, the Mesozoic–Palaeogene succession of the Umbria-Marche

Fig. 2. Stratigraphic column of Umbria-Marche succession in

domain is buried under Upper Miocene–Plioceneforedeep deposits; the Pliocene–Quaternary fore-deep lies over the coastline, in the Adriatic Sea. Inthe above-mentioned NW–SE-oriented basins, de-formation and depocentres, mostly involving Oligo-cene to Quaternary terrigenous deposits, pro-gressively migrated to the NE. Low angle NE-verging thrusts controlled the deformation style anddepositional conditions.

Since Miocene to Pliocene times, normal andstrike-slip faults dissected the Apennine mountainbelt; these faults controlled basin development inthe internal areas, while thrust faults were still activefurther out. The mountain chain can be defined as a

study area, with scheme of related tectonic evolution.

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paired tectonic belt with extension in its inner partthat balanced orogenic shortening in the outer part(Lavecchia, 1988). Fluvial and slopes depositsthat look terraced and/or carved record recentuplift and tectonic activity. Structural evidence alsoshows that some areas are still affected by extension(Borraccini et al., 2002; Savelli et al., 2002; Di Bucciet al., 2003).

2.2. Stratigraphic evolution

The oldest stratigraphic unit that crops out in thestudy area is the Calcare Massiccio Formation(Upper Triassic—Lower Liassic), which is detachedfrom the underlying Triassic basement (Fig. 2). Thepresence of normal faults in the Calcare MassiccioFormation indicates that rifting tectonics wereactive during Permo-Triassic times. The subsequentevolution of the passive margin is recorded by theMesozoic–Eocene succession, which consists ofUpper Triassic anhydrites, massive shelf carbonates,limestone with flinty nodules and middle Liassic–Middle Eocene marls. The upper part of the

Fig. 3. Geological sketch of Sheet 280—Fossombrone

succession (Upper Cretaceous–Oligocene) containsterrigenous sediments that record the earliest phasesof shortening and the development of the incipientNeogene Apennine foredeep. A complex system ofmigrating foredeep and associated thrust-top basinswere controlled by the migration of the thrust-faultsystem from west to east. The stratigraphic succes-sion, with highly variable facies and diachronicityfrom inner to outer zones as well as along thedepocentral axes of the basins, testifies to simulta-neous thrusting and sedimentation.

The upper part of the succession is composed ofPlio-Pleistocene marine deposits followed by Qua-ternary continental deposits (slope and fluvialsediments) (Fig. 3).

2.3. Structural setting

The current structural setting of the study areais the result of a complex evolution history dueto convergence and collision of the Sardinianand Adriatic lithospheric blocks occurring sinceMiocene times.

showing location of interpreted seismic profiles.

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The area is characterized by NE-verging folds andthrust faults caused by a compressive stress field-oriented NW–SE from the Miocene to the MiddlePleistocene. Syncline–anticline couples in the hang-ing-wall cover comprise the major regional struc-tures; these are detached from the basement in thefootwall. In map view, major regional structures areeastwardly convex due to the rotation of stress axesthrough time (Mazzoli et al., 2001).

Fold geometries seem to be controlled by thestructure of the Calcare Massiccio Formation, thethickest and most competent unit of the Umbria-Marche succession. Thrust faults are associatedwith regional folds, and show geometries andkinematics described by Jamison (1987) as fault-propagation folding whereas McNaught and Mitra(1993) and De Donatis and Mazzoli (1994) inter-preted the same structures related to detachmentfolding. The location and development of folds andthrust faults appear to be controlled by the positionsof basement discontinuities that developed duringthe Liassic phase of extension and were subse-quently re-activated as thrust faults (De Donatis,2001).

The outer sector of the study area shows ashallow structural style, characterized by the pre-sence of thrust and back-thrust faults (with asso-ciated gentle to recumbent folds). These structuresare propagated from shallow detachment levelspassing through the Marne a Fucoidi Formation,the Scaglia Cinerea Formation or the SchlierFormation (De Donatis et al., 1995). This type ofdeformation is concentrated on the hinge zones ofthe major anticlines and is interpreted as out-of-syncline differential shortening (De Donatis et al.,1995; Coward et al., 1999). Shortening structuresare dissected by normal faults caused by theextensional tectonic regime active from the Pleisto-cene onward, which migrated from west to east.Normal faults trend oblique to the pre-existingshortening structures and are mostly oriented N–S(N 1701). Recent studies prove that these normalfaults orientations match the focal mechanisms ofmicro-seismic events (Di Bucci et al., 2003).

3. Data set

Field and subsurface data recently collected in theNational Geological Database (created within theCARG—National Mapping Program) were inte-grated in a 3D geological model of the Fossom-brone area in order to test its suitability for 3D

structural visualization and analysis. In particular,we integrated the recently compiled 1:50,000 geolo-gical map with logs of deep wells and seismicprofiles provided by ENI, an Italian oil company.

The database contains two categories of data(AA.VV., 1997): (1) data with geometric propertiesas well-descriptive properties (e.g. geological ob-servation points where measurements and descrip-tions were performed) and (2) data with descriptiveproperties only (e.g. glossary of stratigraphic unitsor lithological descriptions).

All the features are organized into ‘‘informationlayers’’ that link features to attributes and aremanaged as relational tables. In this kind ofphysical model, geometric properties are repre-sented by geometric primitives as points, lines andpolygons. Additional information (e.g. geologicalschemes, diagrams, cross-sections and legends) isincluded in the database as first type features (e.g.survey areas, cross-section traces), ASCII files (e.g.lithological descriptions) or the results of carto-graphic elaboration of other data (e.g. tectonicmodels). Data contained in informative layersST018 (mapped geological units), ST019 (geologicalobservation points), ST027 (geological cross-sec-tions and seismic profiles) and ST013 (resources andinvestigations) were used for the 3D modeling of theFossombrone area.

3.1. Subsurface data

It is essential to have access to subsurface data inorder to understand the geological structure of anarea and to model it in 3D. For this project, ENIprovided a large number of seismic profiles collectedfor hydrocarbon exploration in the NorthernApennines. Interpretations of the seismic profileswere calibrated using logs of the ‘‘Senigallia 1’’ and‘‘Fossombrone 2’’ wells. Logs of deep wells werealso used to construct the 3D model more precisely.Interpreted seismic profiles cross the entire studyarea, particularly in the north and east. Seismicprofiles are generally perpendicular to the axes ofthe major structures, and have a cumulative lengthof about 300 km within the Sheet 280 and adjoiningareas.

The seismic profiles clearly show major reflectorsthat indicate boundaries between geological bodieswith considerable lithological differences. Logsof deep wells made it possible to correlatebetween seismic reflectors and litho-stratigraphicboundaries.

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Fig. 4. Structures and stratigraphic horizons interpreted from available seismic profiles (location of seismic profiles in Fig. 3; vertical scale

in two-way travel time; explanation in text).

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Recognized stratigraphic horizons are (Fig. 4)(1) the base of Plio-Pleistocene siliciclastic depositscharacterized by an obvious erosive unconformitywith the lower stand Miocene foredeep deposits; (2)the Gessoso-solfifera Formation highlighted by a setof parallel and laterally continuous reflectors;(3) the top of the Scaglie Group; (4) the top of theMarne a Fucoidi Formation that can be recognizedby a strong acoustic impedance contrast withsurroundings units; and (5) the top of the CalcareMassiccio Formation, characterized by a deforma-tional style different from the surrounding strati-graphic units.

The seismic dataset also highlights many of themajor structural features reconstructed in thismodel, such as the Monti della Cesana anticlinethat appears to be dissected by a complex system offaults (Fig. 4). Two high-angle splays of a deeperlow-angle thrust fault constitute the Fonte Cornialepositive structure, located in the external part of thestudy area. Two back-thrust faults forming a fewpop-up structures surrounding a complex negativestructure are associated with those faults. Theseismic data also show the angular unconformitythat separates Pliocene marine sediments fromlower stand Miocene foredeep deposits. Locally,the unconformity cuts down into the top of theGessoso-Solfifera Formation (middle Messinian)

due to syntectonic erosion occurring since UpperMessinian to Lower Pliocene times.

4. Model building

The following sections describe in detail howavailable data were used to build the new 3Dgeological map, as summarized by the flow chart inFig. 5. A 2.5D geological model was first built byusing digital topographic maps (generating a DEM)together with lithostratigraphic boundaries (layerST018 of the geological database) and beddingmeasurements (ST019). Geologic data (lithostrati-graphic boundaries, ST018; bedding measurement,ST019) together with seismic profiles (ST027) andborehole stratigraphy (ST013) were used to build anin-depth 3D model of Sheet 280—Fossombrone.

4.1. Hardware and software

We used several software packages for advancedgraphics in UNIX and Windows environments tointerpret and manage the collected data and to buildthe 3D model. CAD and GIS software (MicroSta-tion V8TM and MicroStation GeographicTM; Arc-GisTM and AutoCadTM) were used to digitizegeological maps and to collect geological andtopographic data.

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Fig. 5. Flow chart showing use of available data (white boxes) and three-dimensional modeling workflow followed. Dark gray boxes

represent main processes, while light gray boxes represent main documents. Dotted lines indicate reiterated processes.

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We used 2DMoveTM to digitize, elaborate andanalyze geological cross-sections and seismic pro-files. This software is dedicated to managinggeological data in two dimensions (maps andcross-sections). The 3D model was built andanalyzed with 3DMoveTM (Midland Valley Ex-ploration Ltd.), which enables the user to recon-struct geological features in three dimensions andincludes algorithms dedicated to modeling geologi-cal structures.

4.2. Digital elevation model (DEM) and 2.5D

geological map of the Fossombrone area

DEM can be combined with geological maps toclarify relationships between complex geologicalstructures and topographic relief, as well as to maketectonic, climatic and anthropic landforms morerecognizable.

The quality of the DEM strictly depends on howdata were collected (field measurement, photogram-metric methods), their type (lines, points) and

interpolation algorithms. The DEM of Sheet-280Fossombrone was built using topographic mapswith a 10m contour interval.

Digitized topographic maps were imported into3DMove and the contours were interpolated using atessellation algorithm to create a triangulatedirregular network (Fig. 5). The new geologicalmap was digitized and imported into 3DMove.Geological boundaries (vector lines) were used tosubdivide the DEM into several smaller coloredareas representing different outcrops of strati-graphic units.

In this preliminary model, strata orientations(Informative layer ST019 of the CARG database)were inserted to better constrain the 3D reconstruc-tion of geologic structures and stratigraphic units(Fig. 5).

The model (Fig. 6), integrating the DEM with thegeological map, clearly shows the relationshipbetween the geology, the topographic relief andthe major structures. This model is called ‘‘2.5Dmodel’’ because, although it contains elevation

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Fig. 6. View from SW of 2.5-dimensional geological model of Sheet 280—Fossombrone.

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information, it is a surface (does not includevolumes).

4.3. 3D geological model

Cross-sections, derived from seismic profilesinterpretation (vertical scale in milliseconds), wereimported into 2DMove (Fig. 5).

We created a database containing properties ofrecognized horizons (porosity, depth coefficient,seismic velocity, k value and age) for each cross-section. These properties are essential for depthconversion (seismic velocity and k value), decom-paction (porosity and depth coefficient) and burialhistory determination (age of horizons).

The cross-sections were automatically depthconverted using an algorithm included in 2DMo-veTM, based on the following equation:

Z ¼ V�0ðekt � 1Þ=k,

where Z is the thickness of the layer (m), V0 is theseismic velocity at the top of the layer (m/s), k is therate of change of velocity with increasing depth andt is the one-way travel time for layer thickness (s).The function assumes a linear relationship betweenvelocity and depth and is based on the work ofMarsden (1992). To depth-converted interpretedreflectors, we used an average V0 for each formationand 0.5 as the rate of change of velocity withincreasing depth.

Several shallow cross-sections based on the recentgeologic survey at 1:25,000 scale with tracescoincident with seismic profiles were drawn andintegrated into the depth-converted seismic profiles.

Seismic profile interpretation was therefore con-strained by surface geology. Integrating shallowcross-sections with depth-converted seismic profilesallowed us to draw 9 major geologic transects thatcross the whole study area perpendicular to the axesof the major structures. These geologic transectswere imported into 3DMoveTM and placed in a 3Dvirtual space together with logs of the deep wells‘‘Senigallia 1’’ and ‘‘Fossombrone 2.’’

Surfaces representing faults and horizons at depthwere drawn using 3DMoveTM, respecting all geolo-gical constraints from cross-sections, seismic pro-files, logs of deep wells and bedding orientationdata. Geometric modeling in 3DMove involvescreating surfaces by connecting interpolated pointsinto triangular nets. Each line representing ahorizon or fault in one cross-section was connectedwith lines to the same horizon or fault in anothersection in order to obtain surfaces in three dimen-sions. This work provided a preliminary reconstruc-tion of the structure.

In building a 3D model of a large area, as in thecase of Sheet 280—Fossombrone, we must face thedifficulty of non-continuity of structures betweencross-sections. Integrating auxiliary cross-sections istherefore essential to reconstructing fault tips. Thedepths and horizontal locations of inserted fault tipswere chosen based on aspect ratios of the faults anddisplacement distribution along fault strike.

Restoration and structural analyses do notrequire a graphically correct model with a tidysurface, but are useful for visualization and forcalculating volumes and fault displacements. Wetherefore performed a tidy reconstruction of fault

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cut-offs using several interpolation and projectiontools.

5. Analysis of the 3D model

5.1. 3D model description

The new 3D model of the study area integrates allthe available data; it makes it easier to visualizestructures at depth than do the 2D representa-tions (cross-sections, maps). The quality of a 3D model(created as described above) strictly depends on thequality and quantity of available data. We had a largeamount of subsurface data, which allowed us to createa well-constrained model. Although seismic data in theinner zones were of lower quality, this was compen-sated by the high quality of field mapping due toextensive outcrops of lithological contacts and struc-tures. In the outer parts of the study area, however, thehigh quality of the seismic profiles allowed an easyreconstruction despite the scarcity of outcrops.

Viewed from the SE, the model clearly showsfolds and thrust-fault structures involving theMesozoic–Eocene carbonatic multilayer and theMiocene siliciclastic foredeep deposits (Fig. 7).The Monti della Cesana and Monte Paganuccio—Monte Pietralata anticlines are dissected by thrustand back-thrust faults probably associated with a

Fig. 7. View from south of digital geolo

major detachment passing through the Triassicanhydrites (Fig. 8B).

Very complex NW–SE-oriented thrust structures arerecognizable in the northeastern sector of the 3Dmodel(Fig. 8C). These structures consist of two parallel thrustfaults associated with two shallower back-thrust faults,forming a few contiguous pop-up structures.

The carbonate succession and the foredeepdeposits deepen toward the east where theyare buried under Pliocene marine sediments.Thrust faults, associated with the Apennine build-ing, seem to be locally sutured by Pliocene marinedeposits.

The outer part of Sheet 280—Fossombrone ischaracterized by an obvious erosive unconformitybetween Miocene foredeep units and Pliocenedeposits. This unconformity locally involves Messi-nian evaporites.

Although most of these features can be visualizedwith 2D cross-sections, the 3D visualization isuseful because it better shows along-strike char-acteristics of the structures (e.g., segmentationpattern, linkage, overlap zones). Like a geologicalmap, a 3D model is the synthesis of severalinterpretations made by a geologist. One of themajor benefits of 3D modeling derives from the factthat interpretations (and therefore, reconstruction)of horizons and faults must satisfy 3D constraintsand geometric rules.

gical model without topography.

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Fig. 8. (A) View from south of whole 3D geological model; (B) view from south of 3D model in depth; (C) detailed view of Fontecorniale

thrust structures in NE sector; and (D) view from east of model.

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5.2. Examples of 3D model-based structural and

geomorphic analyses

3D modeling also has an advantage over 2Dvisualization techniques because it allows analysesthat can help to improve the model itself and, as aresult, geologic knowledge of a study area. 3DMoveactually includes several tools for geometric ana-lyses (qualitative and quantitative) as well asrestoration and balancing algorithms in 3D, basedon the most common deformational models (e.g.flexural slip unfolding, fault parallel flow andinclined shear).

We assessed several geomorphic and structuralfeatures of the study area, applying dedicated toolsto the 3D model. The most important analyses aredescribed below.

5.2.1. Along-strike fault-displacement variations

The method of Allan’s lines was used tocharacterize the thrust fault that dissects the north-eastern limb of the Monte Paganuccio–MontePietralata anticline (Fig. 9A). This thrust structurelies in the southwestern part of the area and plunges

SW (dip ¼ 451). We plotted cut-off lines of the topof Calcare Massiccio Formation on the fault surfaceusing the Allan Mapper tool included in 3DMove.Graphs of the separation between hanging-wall andfootwall cut-off lines (similar to displacemen-t–length profiles) were drawn, and heave, throwand displacement were measured at several pointsalong fault strike.

The separation profile shows moderate displace-ment gradients. The average values of throw, heaveand slip are 75, 100 and 125m, respectively.Separation graphs and displacement values areuseful for cinematic restoration of the 3D modelas well as for obtaining insights about the linkage offault segments.

5.2.2. Cylindrical analysis of folded surfaces

We performed a cylindrical analysis on thesouthwestern part of the 3D model; this allowedus to calculate the average Cylindrical Vector of thefolded surface and to recognize the general trend ofthe major structures. The average cylindrical vectorcorresponds to the mean axis of a fold; it is the poleof the best-fit plane of the poles of the triangles that

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Fig. 9. Examples of 3D model-based structural and geomorphic analyses. (A) Allan analysis of thrust fault dissecting northeastern limb of

Monte Paganuccio–Monte Pietralata anticline. Main window shows 3D model of anticline (top of Calcare Massiccio Formation shown in

dark blue) and thrust faults. Window on left shows trend of cut-off lines. Diagram of separation between hanging-wall cut-off and

footwall cut-off is shown on window on right. (B) Results of cylindrical analysis of surface representing top of Calcare Massiccio

Formation. Dark blue arrow represents average cylindrical vector (dip ¼ 01, 33; azimuth ¼ 3051N) of Monte Paganuccio–Monte

Pietralata and Monti della Cesana anticlines. Gaussian curvature (C) and simple curvature (D) analyses of surface representing top of

Calcare Massiccio Formation in western sector of study area (high curvature in red, low curvature in blue).

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constitute the surface. Cylindrical analysis comparesthe orientation of the poles of the folded surfacewith the orientation of the average cylindricalvector. A surface’s normal that forms an angle of901 with the average cylindrical vector has a zerodeviation; irregular and non-cylindrical surfacesgenerate normal vectors that do not coincide withthe best-fit plane. The angular deviation between thenormal and best-fit planes is assessed by thedeviated attribute value; this can be visualized onthe folded surface using color ranges.

The used algorithm calculates a weighted averagethat considers the area of the triangles. The average

angular difference between surfaces and averagecylindrical vector is the angular deviation, whichprovides information on the shape of the foldedsurface.

The above-mentioned analysis (Fig. 9B), per-formed on the southwestern anticlines, points out aNW–SE-oriented subhorizontal average cylindricalvector (dip ¼ 01, 33; azimuth ¼ 3051N). The centralparts of the Monte Paganuccio–Monte Pietralataand Monti della Cesana anticlines are quitecylindrical, as shown by the low value of angulardeviation between the surfaces and the averagecylindrical vector.

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5.2.3. Curvature analysis

In order to locate the most strained and fracturedparts of the study area, we analyzed the curvature offolded surfaces (Lisle, 1994). The localization of themost deformed and fractured areas could proveuseful for the characterization and exploitation ofgroundwater and hydrocarbon reservoirs. 3DMove’salgorithms made it possible to measure both simpleand Gaussian curvature.

Simple curvature measures the rate of variation ofdip along a surface. It is assessed for each vertex ofthe TIN by calculating the average normal of thetriangles that surround the study point. Curvaturevalue is a function of the angular difference betweenthe average normal and the normal to each triangle.

Gaussian curvature is a measurement of the 3Dshape of a folded surface. The straining of a foldedsurface depends on the 3D shape of the fold and, inparticular, on the Gaussian curvature calculated foreach vertex of the surface. Maps of Gaussiancurvature are useful in predicting subseismic struc-ture density due to strain and small-scale fracturing.

The Gaussian curvature of a point is the productof the two main curvatures (max and min), whichare orthogonal (Lisle, 1994). The Gaussian curva-ture of a cylindrical fold (e.g. a fold developed in athin-skinned tectonic setting with planar faultsurfaces) is 0; the highest values are reached forstrongly non-cylindrical folds (e.g. folds related tosalt domes).

Curvature analysis of the surface representing thetop of the Calcare Massiccio Formation indicatesthat most strained areas are located close to thehinge zones of major anticlines (Figs. 9C and D).

5.2.4. Fluid and sediment migration analyses

Fluid and sediment migration analyses wereperformed on the DTM of Monti della Cesana inorder to characterize its hydrological and deposi-tional systems.

This analysis was performed using dedicatedalgorithms included in the 3DMove softwarepackage (Fig. 10). Fluid and sediment migrationanalysis is based exclusively on geometric aspects oftopographic relief; it ignores the effects of perme-ability and pressure. The potential pathway consistsof streamlines generated by a point or area sourcethat follow lines of maximum dip. Drainage basinsare bounded by watersheds and depocenters areidentified as lower points inside each drainage area.

Fluid and sediments analysis can provide statis-tical information about the hydrological system,

like the area, the maximum volume of sediments,the depocenter and nick point locations. Theseresults are very useful in assessing hydrogeologicrisks and environmental planning.

6. Concluding remarks

We created a 3D geological model of Sheet 280—Fossombrone as a prototype to test a workflowsuitable for geologically mapping all of Italy in threedimensions.

This project allowed us to draw several conclu-sions about constructing 3D models out of all the1:50,000 geological maps of Italy.

The chosen software packages (2DMoveTM and3DMoveTM by Midland Valley Exploration Ltd.)allowed us to construct the 3D geological model andto integrate different kinds of data quite easily.Graphical editing of the model was more difficult,mostly due to the vocation for structural analysisrather than problems with visualization in thesoftware. It must be emphasized that restorationand structural analysis tools (included in 3DMove)provided useful additional constraints in recon-structing 3D structures at depth, as well as forpredicting fault linkages, especially in areas lackingsufficient subsurface data.

We obtained new structural and geomorphicinformation about this part of the northernAppenines using algorithms dedicated to the analy-sis of the 3D model. The possibility of easilyderiving additional information about an area isone of the main values of 3D modeling. Forinstance, the Allan Mapper tool was very usefulfor measuring displacement along faults and forproviding constraints regarding 3D structural re-constructions throughout the analysis of displace-ment–distance profiles. Cylindrical analysisprovided information about the general trends ofthe major structures and allowed to identify themean axis of the folds (average cylindrical vector).Curvature analysis allowed the most fracturedgeological bodies to be located, providing usefulinformation regarding the exploitation of under-ground resources like water and hydrocarbons.Finally, fluid and sediment migration analysis,performed on the digital elevation model of thestudy area, allowed potential hydrographic patternsand basins to be characterized and zones withhigher hydrogeological risks to be identified.

The CARG geological database is suitable for 3Dreconstruction purpose. In fact, it could contain all

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Fig. 10. Fluids and sediment migration analysis performed on DEM of Monti della Cesana area. (A) Map view and view from NW (B) of

DEM with ‘‘flow pathway’’ system (white lines). (C) Map view and view from NW (D) of drainage system with catchment areas.

M. De Donatis et al. / Computers & Geosciences 35 (2009) 19–32 31

the needed data, although some informative layers(e.g. ST027—cross-sections and seismic profiles) canonly be used after the data are integrated andelaborated. We are convinced that building 3Dmodels of all the geological map sheets of Italywould be useful; however, we are aware that severalproblems must still be faced. One of these problemsconcerns the limited availability of subsurface datain some parts of Italy, which could reduce thequality of some models.

Acknowledgments

The project was funded by the APAT—NationalAgency for the Environment. We are grateful toC. D’Ambrogi and M. Pantaloni for providing datafrom the CARG database and for fruitful discussions.

We also thank S. Merlini and M. Bello (ENI-AGIP)who allowed us the consultation of commercial seismicprofiles. We thank H.J.T. Weerts and E.M. Schetselaarfor their helpful reviews of the manuscript. We aregrateful to the Midland Valley Exploration forproviding the software used in this work.

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