IMEKO International Conference on Metrology for Archaeology and Cultural Heritage Torino, Italy, October 19-21, 2 16 Multi-disciplinary approaches using non-invasive portable instruments to investigate cultural heritage sites and their surrounding area Sebastiano D(Amico 1, Raffaele Persico 2 1 Department of Geosciences, University of Malta, [email protected] 2 Raffaele Persico, I AM-CNR, [email protected] Abstract The paper describes integrated geophysical and 6a 7erla Cross09 a 1atchto1er built by the Knights of investigations for investigating cultural heritage sites. St. :ohn in the XVII century and in the hold cemetery of In particular, we focus on data collected at several Santa Maria Church /8ir3ir3ara0, and the St. :ohn Co- locations in the Maltese Archipelago (central Cathedral /this results 1ill be not sho1ed in the present Mediterranean). The analysis consists in collecting paper0. The data 1ere mainly gathered during a short data with non-invasive portable instru ents. we were term scientific mission performed under the COST able to locate and deter ine fracture on cliff area as Action T-12 8 >Civil Engineering Applications of well as to locate graves and buried structures at the 2round Penetrating Radar?. The purpose of the measures investigate sites. In this paper, so e effects of has been t1ofold, namely to test the performances of an electro agnetic interferences on GPR data have been innovative 2PR system /Persico and Prisco, 2 80, studied. recently upgraded, and to perform 2PR and passive seismic analyses in several sites of interest in Malta, in I. I,TROD-CTIO, order to get an insight about the geological conditions in The opportunities offered by modern technology for the some sites of interest and about the internal status of safeguarding and fruition of cultural heritage are virtually some historical monuments. boundless, yet their successful implementation re.uires that all players involved /scientific community, public institutions, private sector, sector operators0 adopt ne1 attitudes. 2round Penetrating Radar /2PR0 is the main tool that allo1s the best available resolution 1ithin the non-invasive subsurface geophysical techni.ues. Ho1ever, integrations 1ith other geophysical techni.ues can provide information of geological, and structural behavior of cultural heritage sites. On the other hand, several sources of uncertainty can affect the data, among 1hich clutter, several 3inds of noises, model errors and interferences from other electromagnetic devices. This papers aims to serve a proof-of-concept to act as an e4ample for future coordination among conservators, researchers, and developers 1ho share the goals of revealing, researching, preserving, and presenting cultural heritage. In addition, 1e propose also some results regarding the reconfiguration of the integration time of the harmonic tones radiated and received by a stepped fre.uency ground penetrating radar /2PR0 system in a Fig. 1. Location of investigated sites 1ay programmable vs. the fre.uency. The e4ploited 2PR system 1as a prototypal stepped II. DATA AC5-ISITIO, PROCESSI,2 A,D fre.uency reconfigurable 2PR, implemented by I8AM- RES-6TS C,R together 1ith the -niversity of 7lorence and the IDS Corporation 1ithin the research project AITECH In this paper 1e close describe results obtained at /httpA//111.aitechnet.com/ibam.html0. This system several sites /7igure 10 located on the Maltese contains three e.uivalent couples of antennas 1ith the archipelago. In particular, on t1o cliff areas /2olden 8ay same gap, achieved from t1o series of s1itches along the 115 arms. The on and off state of the s1itches ma3e study using numerical modelling. Moving from the inland e.uivalently longer or shorter the antennas, so to achieve area to1ards the cliff edge and roc3 sliding area, the efficient transmission on three bands that cover the nature of the H/V response changes stri3ingly. On the comprehensive fre.uency range from C MHD to 1 2HD. plateau a1ay from the cliff edge, the site response sho1s Some passive seismic techni.ues 1here used in order to only the simple and consistent pea3 at around 1.C HD as gather useful data to be compared and integrated 1ith described above, 1hile the rest of the H/V amplitudes those obtained 1ith the 2PR. Ambient noise 1as remain at a level 1ell belo1 2. Moreover, it is observed recorded using a three-component Tromino E that at higher fre.uency of the spectrum there are seismometer in order to obtain H/V curves 1hich can fre.uencies pea3s not observed on the plateau area that give information about the geological site condition and may be tentatively associated 1ith mechanical vibration the passive seismic array measurements 1ere conducted modes of the 1hole bloc3s. using Micromed SoilSpy RosinaTM seismic digital ac.uisition system e.uipped 1ith 4.C HD vertical geophones. A total of 42 geophones 1ere used, and placed in an 6- or C-shaped configuration 1ith a regular interstation distance of C m. Data 1ere processed using standard techni.ues G1H. Ie have performed a first set of measurements in the >2olden 8ay? area in the vicinity of >2Jajn TuffieJa To1er?. The to1er is part of the fortification structures built by the 3nights of St. :ohn. In particular it belongs to the >6ascari to1ers? bet1een 1637 and 16C2 and commissioned by the Italian 3night 2iovanni Paolo 6ascaris 1ho 1as 2rand Master of the Order. The area is affected by the presence of later spreading and the retreating of the cliff edge due to the fracturing of the -pper Coralline overlaying the 8lue Clay typical formations of the Maltese islands G2H. The geology of the Fig. 2. The golden bay. The prospected area is Maltese islands is 1ell 3no1n G3,4 and references approximately indicated by the rectangle. The arrows thereinH and consists of four main sedimentary layers, but indicate two point where the soil is collapsed. The stars the relief, 1hich is largely controlled by the neotectonic indicate the locations where ambient vibration pattern, is rather comple4. The Maltese islands are made measurements have been ta,en up of a sedimentary se.uence deposited during the Oligocene and Miocene epochs. There are four main In the area 1e also performed some 2PR strata, reflecting abrupt changes in the depositional measurements 1hich 1ere able to identify a fracture in environment during this periodA 6o1er Coralline, the pro4imity of the to1er. This area 1as chosen because 2lobigerina, 8lue Clay and -pper Coralline G3,4H. the presence of large fractures in the nearby region and The passive seismic techni.ues sho1 of a ubi.uitous being the main one not yet mapped and imaged. The area resonance pea3 at bet1een 1. and 2. HD at several investigated using the 2PR can be appro4imated to a locations far a1ay from the cliff. Moving from the inland rectangle of siDe about C.246.C s.uare meters /7ig. 20, and area to1ards the cliff edge and roc3 sliding area, the has been prospected 1ith 8scans parallel to each other, nature of the pea3 and it is observed that at higher directed to1ard the sea and spaced 4 cm from each fre.uency of the spectrum there are pea3s not observed other. The scan end in pro4imity of the cliff, about 3 on the plateau area that may be tentatively associated meters high, sharply overhanging the sea. On the top of 1ith mechanical vibration modes of the bloc3s present in the cliff, some naturally opened holes 1itness the the unstable cliff area. This is not surprising because possibility of the presence of deep fractures in the cliff, previous ambient noise studies have repeatedly confirmed 1hich might one day lead to some collapse. T1o of these that all areas of the Maltese islands 1here -C6 outcrops subsidence points are indicated 1ith the arro1s in 7ig. 2. and is underlain by a layer of 8lue Clay e4hibits a pea3 in As can be seen they are .uite aligned to each other. To the H/V of this consistent fre.uency GC,6,7H. Several investigate and locate the fracture the lo1 fre.uency authors interpret the dip in the H/V ratio in terms of a e.uivalent antennas have been e4ploited, because the shallo1 shear-1ave velocity inversion, 1hich in this case anomalies of interest are .uite e4tended and it 1as of corresponds to the interface bet1een the -C6 and 8C. interest to increase the penetration depth of the signal. The interpretation of other features of this pea3 in terms The processing has been minimal, including Dero timing, of Rayleigh 1ave ellipticity and/or trapping of SH 1aves gain vs. the depth, bac3ground removal, and slicing. ,o in the lo1-velocity layer is the subject of an ongoing migration has been performed, being the anomalies .uite 116 large. The processing has been performed 1ith the The church of 6a 7erla is an abandoned church on the reflexw commercial code. At this site combination of top of a small hill, near to a cross visible at distance. In 2PR and passive seismic measurements 1ere used to 7ig. 4, 6a 7erla church is the building on the central lo1 reconstruct the geometry of the fracture. part of the image. Indeed, there is a geological sliding, The Madliena to1er /7ig. 30 is a mighty structure, mainly due to the local geological condition in the area, e4ploited in the past as 1atchto1ers bet1een 16C8 and that has strongly damaged the church. Ho1ever, since the 16C9 1ith very thic3 1alls since it 1as a military importance of the old church there are proposals of defensive to1er. the inner of the to1er at the ground floor moving it a1ay from its current position. So, it 1as of in just a rectangle of 2.943.9 s.uare meters, plus a small interest to perform a preventive investigation in order to corridor to1ard the door.