Regione SicilianaAssessorato Beni Culturali ed Ambientali e della Pubblièa IstruzioneDipartimento Beni Culturali ed Amblentali ed Educazion4e Permane~teCentro Regionale per la Progettazione e il Restauro

Centro Regionale per la Progettazione ed il Restauroe per le Scienze Naturali ed Applicate ai Beni Culturali

Scienza e Patrimonio Culturale nel Mediterraneo

DIAGNOSTICA E CONSERVAZIONE

ESPERIENZE E PROPOSTE PER UNA CARTA DEL RISCHIO

Atti del m convegno internazionale di studiLa materia e i segni della storia

Palermo 18-21 ottobre 2007

REGIONE SICILIANA

Assessorato dei Beni Culturali ed Ambientali e della Pubblica Istruzione

Dipartimento Beni Culturali ed Ambientali ed Educazione Permanente

Palermo

INDAGINI E DIAGNOSTICA - terza parte

256 Radiologia versus diagnostica per immagini nell'arteG. Salerno

266 La riflenografia infrarossa ad alta risoluzione: un unico processo dalla ripresa alla stampa dei riflettogrammi.C. Perez Garda, P. lneba T'amari/,]. Perez Miralles, L. Pini, G. Valagussa

269 Physical identification of precious artefacts: their sonic imprintP. L. Cosentino, P. Capizzi, G. Fiandaca, R. Martorana, P. Messina, I. Razo Amoroz

277 Integratecl archaeological and geophysical survey for searching the Roman of Augustus tempIe in Tarragona,Spain

A. Casas, P.L. Cosentino, Y Diaz, E. Garcia, M. Himi, M. Lafuente, R. Mar/orana, J.M. Macias, J. Menchòn, A.Murnoz, R. Sala, 1, Teixell

284 Indagini archeopalinologiche in Sicily at Taormina, Piazza Armerina and MoziaF Terranova, C. A. Accorsi, M. Bandini Mazzanti, A. M. Mercuri, P. T0171,E. Manicardi, /VI. C. Montecchi, L.Olmi, R. Rinaldi, A. Valenti, F Benassi, P. pensabene, S. Tusa

295 Materia e segni della storia sostanzialmente e formalmente uniti: alcuni casi di studioS. Lorusso, C. Malteucci, A. Na/ali, S. Tumidei

304 Caratterizzazione spettrale e visiva dei materiali antichi per l'ottimizzazione della progettazione iIIuminotecnicaF Gugliermelti, F Bisegna, L. Monti

INDAGINI E DIAGNOSTICA - quarta parte

314 PRErAZIONI di Claudia Sorlini

316 On the efficiency of biocides and cleaning treatments in restoration works of subterranean monumentsE. Aka/ova, M. Roldan, M. Hernandez-Marine, ].M. Gonzalez, C. Saiz-}imenez.

323 A non-invasive approach to the polyphasic study of biodeteriogenic biofilms at St Agatha crypt and catacombsat Rabat, Malta.G. Zammit, F De Leo, C. Urz~ P. Albe1tano

328 Studio della colonizzazione microbica di tessere mosaicali mediante tecniche fisiche e molecolariF. Palla, S. Drago, M. R. Di Pierro, A. Lanza, G. Morici

333 Express-method of estimation of biocide properties of different materials and substances and application ofnanotechnology in biocide treatmentM. Dmitrieva, N. Reb11kova

337 Colonization by actinobacteria in the cave of Dona Trinidad (Malaga, Spain)F Stomeo,J.M. Gonzalez, C. Saiz-jimenez

INTEGRATED ARCHAEOLOGICAL AND GEO­PHYSICAL SURVEY FOR SEARCHING THEROMAN TEMPLE OF AUGUSTUS IN TERRAGO­NA, SPAINA.Casas, PL.Cosenlino, Y Dfaz, G. Fiandaca, E. Garcfa, M. J-limi, M.

ù(jilenle, R. Mm1orcma,j.M lvlacfas,j. Menehon, A. i\;/1I/10Z, R. Sala,

l. 'f'eLx°ell

INTRODUCTION

Tarragona's cathedral is located on the highest topo­

graphic pIace of the city. Romans occupied this space

since the III century B.e. and converted it on a military

camp since the wars against the Carthaginian, com­

manded by Hannibal, took pIace in the Iberian

Peninsula. Subsequently, Tarraco was the pIace where

the Roman soldiers arrived to conquer Hispania.

Fig. 2 - Front of the Gothic Cathedral of Tarragona.

INDAGINI E DIAGNOSTICA •

Fig. 1 - !dealized illustration of

the Au-gustus tempie in a coinof Tiberian's emperor age.

The evidence of this activity is the Roman wall that has

been preserved and stili surrounding the historic center

of Tarragona CAqllilllé, 2000),

After getting the rank of provincial capital, Tarraco start­

ed a set of urban transformations presided over the hill

by a great sacred enclosllre that surrollnded the tempIe

devoted to the emperor Augllst. It is worth noticing that

Fig. 3 - Plant of the Gothic Cathedral overdrawn are assllmed the exter­nal structllre of sacred area (dots).

Il S C I E N Z A E P A T R I M O N I O C U L T U I{ A L E [) E L M E [) I T E R R A N E O

the Roman cult was carried out outsicle of the templesancl not insicle.

Since the encl of the IV centll1Y A.C. (the Christian religion

was then the official one of the Roman Empire), the

emperors ordered a graduai legislative process that

favored the replacement of the pagan cults with the

Christian ones. At this time, the site undelwent manychanges in urban planning and ideological reassessments.

During the V ancl VI centuries, the urban characteristics

of this zone changecl radically with residential spaces ­

inciuding open-air waste clumps-ancl spaces for offidalrepresentations both civil and religious.In this framework also the Meclieval Catheclral was erect­

ecl with the Bishopy ancl burial grouncl spaces.

At the beginning of the VIII centll1Y the Islamic invasion hada period of decline far more than four centuries unti! the

clefinitive restoration of the metropolitan bishop and the

starting of the new meclieval cathedral in the micldle of the

XII centll1y. Since this time, the Catheclral has dominated the

skyline of Tarragona and probably concealing in the subsoil

some of the answers we need to recognize ancl unclerstancl

the historical evolution of the city (Munoz, 2001).The usefulness of geophysical techniques (e.g., dc cur­rent, electromagnetic, ancl magnetic methocls) for archae­

ological investigation is well known :mcl has been repolt­

ecl in many papers, for instance Casas et al. (1995), Dabas

et al. (1993), Pérez-Garcfa (2000), Carrara et al. (2001),

Negri ancl Leucci (2006). Therefore, as the latest archaeo­

logical researches from Macfas et al. (2007) assumed that

there are remains of older builclings uncler the Meclieval

See, related to the Roman emperor, a geophysical survey

was consiclerecl - also taking into account the potential

interest of the remains. The objective was to obtain a first

picture of the archaeological remains existing in the sub­soil without disturbing both the religious cult ancl the cul­

turaI visits to the tempie.

On the other hancl, the obtained results will be consicl­

erecl of interest to clefine some strategies in the futurefourth phase of Director Pian for the Cathedral of

Tarragona (Figuerola et aL, 2002). The aim of the geo­

physical survey is to get as much information as possible

on the structure and composition of the materials existing

in the subsoil and, particularly to cletect remains of foun­

dations of previous builclings. For this reason, a cletailecl

geophysical mapping has been concluctecl.

METHODOLOGIES

The geophysical methocls used in this stucly area arebased on the cletection of variations in the electric ancl

electromagnetic propelties of the subsoil and the use of

these data for identifying altifacts ancl clistinguishing themfrom the natural variations of the subsoil. EI{T,FDEM ancl

GPR were appliecl.

Geophysical investigations play an important role in

defining shallow subsurface structures. In particular,their application is a non-clestructive and cost effective

way to locate buried archaeological structures in the sur­

veyecl areas. Taking into account prececling experiences

in other similar surveys three complementary geophysi­cal methods were plannecl:

-Electrical resistivity tomography (EI{T)-Frequency domain electromagnetics (FDEM)

-Grouncl probing raclar (G PR)

The first method (ERT) aimecl to recognize the geometri­cal characteristics of the structures of the subsoil as a

function of the electrical resistivity of the materials that

constituted the subsoi!, which in tum depends on theporosity, ciay content ancl water content.

This methocl was carried out using two clifferent multi­

channel resistivity meters. An Iris Syscal Plus with 48

channels for recording 2]) sections ancl a MRS256 Systemfrom G F Instruments with 350 channels for 3D moclels. In

both cases, the proceclure for clata acquisition was to

apply a DC electrical current by means of two electroclesand to measure the potential generatecl over two other

electrocles placed along profiles (2D-ERT) or regular gricls

(3D-ERT) spacecl one meter apan over the pavement. In

order to cany out the bi-dimensional profiles, stainlesssteel flat-base electrocles were used, similar to those usecl

by Athanasiou et al. (2004), while to clecrease the contact

resistances a concluctive gel was placed between the

metallic electrocles ancl the soil pavement; with this strat­egy the contact resistances were set below 10 kohms.

--....-.-/

Fig. 4 - Pictllre showing a portion of a 2D alTay lIsing the f1at-ba­se stainless-stecl clectrodes.

Fig. 5 - Pictllre showing aspect of a 3D array covering a signify­cant arca of the cathedral.

INDAGINI E DIAGNOSTICA Il

Fig. 6 - Distriblltion of the ali the electrodes lIsed for recording the dif­ferent 3D arrays.

Twenty two protìles were record ed both in transversal anel

longituelinal orientation using a mixed Wenner-Schlumberger

an-ay, giving up to six thousand apparent resistivity values.

AIso, for 3D acquisition the main technical problem

affecting the measurements was causecl by the contact

resistances at the potential electrodes. In fact, we neecl-y small-sizeel electrodes with limited but similar contact

Il SCIENZA E PATRIMONIO CULTURALE DEL MEDITERRANEO

resistances. A good choice was the use 01' disposable Foam

AgiAgCl ECG electrocles (Cosentino et aL, 1999), The large

amount 01' data, produced by multielectrode systems,

requires automated data handling and processing.l'o ohtain a more accurate picture 01' the suhsurt~lCe it is

necessmy to invel1 the apparent resistivity data. The inver­sion method was based on the smoothness-constrained

least square method. In this method, the subsurface is divid­ed into cells 01' fixed dimensions l'or which the resistivities

are adjusted iteratively until an acceptable agreement

between the input data and the mode! responses is

achieved. It is based on a non-linea l' optimization technique

by least-squares fitting (Loke and Barker, 1996). During the

inversion process the root mean square value 01' the ditTer­ence between experimental data and updated mode l

response is used as a criterion to assess the convergence.

The second method, EM conductivity mapping, is based on

the application 01' a variable primalY field by means 01' a

loop measuring the resulting fielel in another loop. In spite01' the instrument used, an EM138 l'rom GF Instruments,

gave reliable results in the sectors 01' the cathedral elose tothe main door.

ll1is effect has been justified as a result 01' the high electri­

cal resistivity 01' the subsoil in most sectors 01' the cathedralwhich inhibit the electromagnetic induction phenomena.

For this reason this technique was discarded to concentrate

the effot1s on the other methods which provided more sig­nificant result<;.

For the Ground Probing Radar survey (GPR) a Subsurt~lCeIntert~lCe Radar System (SIR 3000) manufactured by

Geophysical SU1veySystems, GSSI was used. Two antenna e

with centre frequencies 01' 270 and 100 MHz were used.Most 01' the work used the 270 MHz antenna, because theresolution obtained with the 100 MHz antenna was too low

to be effective.

Appropriate data processing stacking, filtering, migration

and advanced visualization techniques were applied to help

in understanding and interpreting GPR data.In addition, to obtain a significant "picture" 01' the under­

ground electromagnetic discontinuities, both 3D data col­

lection - along closely-spaced parallel survey lines with suf­

ficient spatial sampling - and time-consuming 3D data pro-

Fig. 7 - l'icture showing the record 01' a GI'R profile along the centraInave 01' the cathedral.

cessing were required. This in order to reduce aliasing

problems.

The surface 01' the tempie sU1veyed by a grid 01' profiles

spaced 0.4 m apal1 and a horizontal resolution 01' 0.02 m (50

scans per meter). Due to the ne ed 01' having a greatest res­olution on the centrai nave, a perpendicular grid was tracedin order to obtain records in both directions.

The acquisition along the elose parallel profiles allowed the

assembly 01' GPR time slices making easy the corre!ation 01'

anomalies recorded at the sa me time. This proved to be one

01' the most useful data presentations l'or understanding the

nature 01' subsurface structures over large areas at different

depths (Goodman et aL, 1995), Oepths were estimated l'roman approximate velocity analysis based on the geometlY 01'

hyperboles.

RESUI:rS

Preliminary results obtained in this sU1vey give us an idea

01' the archaeological potentiality 01' the anomalies after pro­

cessing geophysical data. One 01' the main results is that the

erection 01' the building 01' the Medieval Cathedral was car­

ried out without completely removing the existing elementsresting on the bedrock.

The anomaly, with high resistivity values up to 2000 Q.m,

which appears in the centraI pal1 01' most 01' the 20 ERT

profiles is interpreted as remains 01' the Augustus tempIebasement (Figure 8).

INDAGINI E DIAGNOSTICA.

Dopth Ihrlltion 5 Abs. orror : 2.9 t9.9 8.0

9.1259.676

l. 3'1

2.152.623.13

3.69

1f.31

16.0 32.0 '10.9

,..

Unit electrode spllcing 0.500 •.

Unit eIectrode spaeing 9.589 •.

..119.932.9

Inverse "odel Resistivi ty Section____.D.~.CO _59.9 811.5 1113 21f1 1f08 689 1165 1969

Resistivity in oh•.•

2.152.623.13

3.69

If .31

Invor •• Hodei Reoiotivity Soction_____ D_C __ o _59.9 8'1.5 1'13 2'11 '108 689 1165 1969

Rooiotivity in oh•.•

Depth Iteretion 5 RHS error : 2.1f 7-0.0 8.9 16.0 21f.0

0.125

0.676

1. 31f

Dopth Iteretion 5 RHS error : 1,16 7-0.0 8.9

0.125

0.676

1. 31f

2.152.623.13

3.69

1f.31

16.0 21f.0 32.9 119.8 ..

Inverse "odel Resistivity Seetion_____ DC~.CD ._59.9 811.5 11f3 21f1 IIG8 689 1165 1969

Resistivity in oh•.• Unit eleetrode spacing 9.599 •.

'"Invorse Hodol Rosiotivi ty SocHon_____ D_~ __ D _

5e.a 811.5 1113 21f1 1198 689 11651969Rooistivity in oh•.•

Dopth Itoretion 'I Abo. orror : 9.811 t9.9 8.9

9.125

9.676

l. 311

2.152.623.13

3.69

'1.31

16.9 21f.9 32.e 110.0

Unit oloctrodo opaeing e. 5ee •.

Fig. 8- Inverted 2D sections of the electrical resistivity tomographies record ed along the cathedral showing the almost rectan-gular resistive body

• SCIENZA E PATl{IMONIO CULTURALE DEL MEDITERRANEO

Using a GPR analysis, the exisrence 01' an archaeologi­

cal stratigraphy is asslImed and the analysis 01' the data

suggested clepth alterations or differences between the

centraI ancl the lateral naves, as well as between thecentraI nave ancl the main entrance to the medieval tem­

pie.

A generai characteristic al' the surveyecl area is the good

penetration 01' the electromagnetic energy, 100 ns corre­

sponcling to a depth 01' about 4.0 m when a mean veloc­

ity vaille of 0.08 m/ns is lIsed. This is essentially due to

the physical characteristics 01' the materials lIsed far the

construction 01' the tempie (limestone), which have high

resistivity values and therefore dissipate the EM energy

only slightly.

In spite of the clarity 01' some of the described struc­

tures, it musr be pointecl out that their vertical projec­

tions are irregular. This wOlllcl indicate a reuse 01' preex­

isting elements for the erection of the bllilcling' ancl anirregular conclition 01' preservation.

CONCLUSIONS

The effectiveness or the different geophysical methocls

in mapping the archaeological features in Tarragona'sCatheclral has been confirmecl. The 20 ancl 30 moclels

obtainecl uncler the Catheclral 01' Tarragona will play an

important role in archaeological investigations since

they furnish a synthetic view 01' the location ancl sizes 01'

the most important structures in the area.The results indicate that the lise 01' flat-base electrocles ­

insteacl of standard pointecl electrocles - is a velY gooclalternative in sites where the latter can not be nailed. It

provicles the aclvantage al' fully nonclestructive applica­

tion and the expansion 01' using geoelectrical methocls inenvironments that otherwise we woulcl never consicler.

The structure of the tempIe basement seems to be

revealecl both using 20 ancl 3D electrical imaging tech­

niques. Furthermore, the anomalous areas cletectecl by

the clifferent geophysical techniques are velY consistent.

ti

resistivity (ohm.m)-y-.,~o 100 200 300 400 500 600 700 800 900 1000

Fig. 9- 3D image of the high resistive anomaly detected under the centrai paI1 of the Cathedral.

ACK1\OWLEl)GEME1\TS

The allthors are indebted to jallme Plljol (Archbishop ofTarragona's Cathedral), josep Martl (Diocesan Delegate forHeritage), Francesc Gallart (Dea n of the Bishop's Chapter) andIsabel Rodà (Oirector of the Catalan Institllte for ClassicalArchaeology).

REfEI{ENCES

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ANO G. VARGEMEZIS (2004) Nondestrllctive DC ResistivitySllrveying Using Flat Base Electrodes. Proeeedings 77th NearSlIIfaee Geophysies iHeeting, Palermo (Italy).CARRARA, E., CARROZZO, M. T, FEDI, M., FLORIO, G.,NEGRI, S., PAOLETTI, v., PAOLILLO, G., QUARTA, T, RAPOL­LA, A. ANO ROBERTI, N. (200]) Resistivity and Radar sllrveysat the Archaeological site of Ercolano. lournal oIEnuironmenlal and Engineering Geophysies, 6 (3): 123-132.CASAS, A., PINTO, v., RIVERO, L., CAMERLINK, c., DABAS,M. (995) Urban Geophysics: The case of Cathedrals and otherreligiolls monllments. Proeeedings oI the XX EuropeanGeophysieal Soeie(y GeneraI Meeting, Hambllrg (Germany).COSENTINO P., MARTORANA R. ANO TERRANOVA L.M.

(999) The resistivity grid to optimize tomographic 3D imaging.Proeeedings oI the 5th Meeting oi EAEG, European Seetion,1311dapest, Hungary, Em12.DABAS, M., STEGEMAN, c., HESSE, A., jOLIVET, A., MOUNIR,A. ANO CASAS, A. (993) Prospection de la Cathédrale deChartres. BuI. Soc. Areh. d'Ellre el Loir, 36, 5-24.

FIGUEROLA, j., GAVALOA, j., MENCHON, j., TEIXELL, I.,MUNOZ, A. ANO MACIAS, jM" (2002) La catedral de Tarragona:obres de restauraci6 i treball arqueològic", Vllè CoUoquiConservar i reslaurm:' arqueologia i arquiteetum. Amies delRomànie. Lambard. Estudis d'art medieval XIV, Barcelona, 75-107.GOODMAN, D., NISHIMURA, Y. ANO ROGERS, j.O. (995)

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GPR time-slices in archaeological prospection. ArehaeologiealPro~jJeetion, 2: 85-89.

LOKE JVI.H. AND BARKER R.O. (996) Rapid least-sqllaresinversion of apparent resistivity pseudosections by a quasi­Newton method. Geophysieal Pro.\jJeeting, 44: 131- 152.MACIAS, j.Ma, MENCHON, j.j., MUNOZ, A., TEIXELL, I. (2007)Excavaciones en la Catedral de Tarragona y su entorno:avances y retrocesos en la investigaci6n sobre el culto Imperial,In: Nogales, T, Gonzalez, j. (eds.), Culto Imperial: polftiw ypoder, Proeeedings oI the fnternational Meeting (Mérida 2006),L'Enna di Bretschneider, Roma, 765-787.

MUNOZ, A. (200]) El Cristianisme a l'Antiga 'l'arragona. Delsorfgens a la ineursi6 islàmiea. Institut superior de ciències reli­gioses Sant Fructu6s., Tarragona.

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CASELLES, O., GARCfA, F. ANO OSO RIO, R. (2000) GPR sllrveyto confirm the location of ancient structures llnder the

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A. CASAS, Y. OfAZ, M. HIMI, Department of Geochemistry,Petrology and Applied Geology - University of Barcelona ­SPAIN

P.L. COSENTINO, G. FIANOACA, R. MARTORANA,Department of Chemistry and Physics of the Earth andApplications - University of Palermo - ITALYE. GAR.cfA, M. LAFUENTE, R. SALA, SOT - Prospecci6Arqueològica. Sant Cugat del Vallès. Barcelona - SPAIN

j.M" MACfAS, Catalan Institute for Classica I Archaeology.Tarragona - SPAIN

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