Engineering Geology for Society and Territory – Volume 8 Preservation of Cultural Heritage

Giorgio LollinoDaniele GiordanCristian MarunteanuBasiles ChristarasIwasaki YoshinoriClaudio Margottini Editors

69Ambient Noise Recordings in the CircoMassimo and Vallis Murciae Areas: MainResults Compared with the Dynamic Responseof the XII Cen. A.D. Torre Della Moletta

Emiliano Di Luzio, Francesco Fazio, Sebastiano Imposa,and Giuseppe Rannisi

AbstractIn this work we present the results of ambient noise recordings carried out in the CircoMassimo area, within the central archaeological district of Rome. The study area was part of aQuaternary alluvial valley, the Vallis Murciae, a secondary feeder of the Tiber River. Ninety-two recordings of ambient noise were performed in 2013 on a 20 meters regularly-spaced grid.By applying the Horizontal-to-Vertical Spectral Ratio (HVSR) technique, the first-moderesonance frequency (f0) of the Holocene-Upper Pleistocene alluvial infilling was determined,ranging between 1.2 and 1.8 Hz. The f0 local spatial variation was analyzed and a trend of f0increase moving south-eastwards was confirmed by a noise recording taken at the easterntermination of the Vallis Murciae (Terme di Caracalla site). To characterize also the dynamicresponse of local monumental buildings, vibration recordings were done at the Torre dellaMoletta, a stony-tower built at the south-eastern limit of the Circo Massimo area during theMiddle Age (XII cen. A.D.). The vibration pattern features a Hi/Ho peak at a frequency ofabout 3 Hz, that is close to the ground resonant frequency. This evidence reveals potentiallydestructive site effects for the Torre della Moletta building during seismic events and set thebasis for further studies on seismic hazard assessment in the Rome downtown area.

KeywordsAmbient noise � Building vibration � Seismic hazard � Rome � Italy

69.1 Introduction

Macroseismic studies (e.g. Sbarra et al. 2012) and numericalmodelling of ground motion (e.g. Rovelli et al. 1995) evi-denced that severe damages and site effects in the Romehistorical centre have to be expected within the Tiber Valleyand its tributaries (Fig. 69.1). However, despite the incom-parable cultural heritage potentially threatened by seismichazard, a relative lack of data persists on the dynamiccharacterization of the subsoil (e.g. Bozzano et al. 2008;Moscatelli et al. 2012).

In this study we present the results of several (92)recordings of ambient noise carried out in 2013 within theCirco Massimo area, that belongs to the ancient course of theVallis Murciae, a former tributary of the Tiber River on itseastern bank (Fig. 69.1). Main aims of this work are: (i) afurther contribute to the dynamic characterization of the

E. Di Luzio (&)Institute for Technologies Applied to Cultural Heritage. ResearchArea RM1, CNR-ITABC, Via Salaria Km. 29.300, 00171Monterotondo, Rome, Italye-mail: ediluzio@libero.it

F. Fazio � G. RannisiGeodixi s.r.l, Via Alfonsetti, 46, 95100 Catania, Italy

S. ImposaDepartment of Biological, Geological and Environmental ScienceSection—Earth Science Section, University of Catania, CorsoItalia, 57, 95129 Catania, Italy

G. Lollino et al. (eds.), Engineering Geology for Society and Territory – Volume 8,DOI: 10.1007/978-3-319-09408-3_69, © Springer International Publishing Switzerland 2015

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geological substratum in Rome in terms of first mode reso-nant frequency (f0) of the Quaternary alluvial terrains; (ii)the analysis of the f0 spatial variation over short distanceswithin an alluvial valley in the downtown area.

Moreover, the dynamic response of the XII cen. A.D.Torre della Moletta—located at the south-eastern limit of theCirco Massimo area—was analyzed and compared to theground resonant frequencies revealing potential destructivesite effects for the medieval building and, perhaps, for othermonumental structures.

69.2 Ambient Noise Recordings

69.2.1 Field Survey, Parameters Settingand Results

Recordings of ambient noise (Fig. 69.2) were taken at dif-ferent dates by using a Tromino Engy® tromograph placedon a rectangular grid (490 × 40 m) with a regular 20 m step(see Fig. 69.2). Each of the 92 recording was carried outwith a sampling frequency of 128 Hz and lasted 14 min.Traces were elaborated by applying the HVSR (Horizontalto Vertical Spectral Ratio) technique and removing tran-sients incoherent noise. Figure 69.2 shows the 18 H/V

average curves preserving more than 50 % of the processedsignal after removal and fully respecting the Sesame criteria(Sesame 2004). A clear, stable H/V peak lies between 1.2and 1.8 Hz and should be related to the bottom of the alluvialinfilling (plus backfill deposits) found at 40 meters of depthin the CM1 well (Fig. 69.3); a greater variability exists athigher frequencies (15–40 Hz), while in the low frequenciesfield a less pronounced, wider peak can be observed within0.3 and 0.4 Hz.

69.2.2 H/V Spatial Variation

Values of f0 for the main peak between 1.2 and 1.8 Hz werecountered over the whole study area (Fig. 69.3). Highervalues (1.5–1.8 Hz) were observed in the central part of theCirco Massimo at its south-eastern termination. Over a dis-tance of about 500 m along the NW–SE longitudinal axis ofthe Circo Massimo valley, a Δf0 of about 0.6 Hz is realised.A trend of f0 increase moving south-eastwards is confirmedby a measurement taken at the eastern termination of theVallis Murciae, at the Terme di Caracalla site. (Figure 69.2,see Fig. 69.1 for location), where the main H/V peak relatedto the bottom of the alluvial cover is both less pronouncedand shifted towards f0 between 3 and 4 Hz.

Fig. 69.1 The Circo Massimoarea and the Vallis Murciae in thecentral archaeological area ofRome. Location of the Terme diCaracalla site is indicated

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69.3 Vibration Recordings at the Torre DellaMoletta Building (XII Cen. A.D.)

Vibration recordings were taken into the Torre della Molettamedieval building (Fig. 69.4a), at the south-eastern limit ofthe Circo Massimo area. The tower was built in the XII cen.A.D. using stony materials and is about 10 meters high fromthe present basal ground level (0 level). Backfill depositsaround the tower mask the lowermost two levels (−1 and −2levels). Hi/H0 values were determined by setting the

Tromino Engy ® on a vertical alignment into the tower andassuming the −2 level as the reference (Ho). A Hi/Ho peakcan be observed at a vibration frequency of 3 Hz, clearlyvisible on the North-South component, and partially on theEast-West component (Fig. 69.4b, c, respectively).

This values is coherent with the vibration frequencies ofsmall-to-medium sized monuments in Rome such as free-standing columns, walls, arches (e.g. Marzi et al. 1990) andis close to f0 values for the alluvial cover in the south-easternzone of the Circo Massimo area (1.5–1.8 Hz). Therefore, a

Fig. 69.2 Results of ambientnoise recordings in the CircoMassimo area (selected 18 traces)and at the Terme di Caracallla site

Fig. 69.3 H/V spatial variationover the Circo Massimo area andlocation of the Torre dellaMoletta building

69 Ambient Noise Recordings in the Circo Massimo and Vallis Murciae Areas: Main Results Compared 401

potential destructive double resonance effect during seismicevents can be inferred for the medieval building; possiblesite effects on monumental buildings in the area are alsosuggested by ruins of two Imperial Age marble pillars whichlie close to the Torre della Moletta, both fallen along theNorth-South direction (Fig. 69.4a).

69.4 Concluding Remarks

Processing and elaboration of 92 ambient noise recordingsperformed in the Circo Massimo area revealed a stable H/Vpeak in a f0 range between 1.2 and 1.8 Hz for the anthropicbackfill and the alluvial cover filling the former alluvialvalley. Spatial variation of f0 values over the area account fora trend of f0 increase moving south-eastwards along thelongitudinal valley axis, whereas shorter wavelength

variations are likely due to an irregular morphology of thevalley bottom.

The analysis of the dynamic response of the Torre dellaMoletta building (XII cen. A.D.), once compared to the localf0 values, suggests potential double resonance effects for themedieval tower; site effects in the Circo Massimo area canalso be inferred by other archaeo-seismological evidence.

References

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Marzi C, Bongiovanni G, Clemente P (1990) Seismic preservation ofhistorical monuments in Roma, preliminary results from ambientvibration tests. In: Marinos P, Koukis G (eds). Engineering

Fig. 69.4 a The Torre dellaMoletta medieval building(XII cen. A.D.) at the south-eastern limit of the CircoMassimo area; b North-Southcomponent of the Hi/Ho curve;c East-West component

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