Compagnoni M.

Di Capua G.

Famiani D.

Franceschini A.

Pergalani F.

Viganò A.

PERGALANI, FLORIANA

COMPAGNONI, MASSIMO

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206Seismic Microzonation in a Small Municipality:The Canazei Case Study (Trentino, N Italy)Floriana Pergalani, Massimo Compagnoni, Giuseppe Di Capua,Daniela Famiani, Andrea Franceschini, and Alfio ViganòAbstractThe results of a detailed seismic microzonation study performed at Canazei (Trentino—Northern Italy) are here presented. We investigated the local seismic response of this smallvillage using a Level 3 seismic microzonation, the most accurate according to the Italian Codeof Seismic Microzonation. This method consists of gradual steps of knowledge to considerdifferent aspects of the ampliﬁcation phenomena. A multidisciplinary approach has beenperformed, including a local geological study, geophysical investigations, geotechnicalcharacterization of lithologies and numerical analyses. The obtained elastic response spectrawere compared to the spectra prescribed by the Italian Building Code. Our results show thegeologic and geophysical subsoil heterogeneities, responsible for different local seismicresponses in terms of acceleration spectra and ampliﬁcation factors.KeywordsSeismic microzonation  Response spectra  Ampliﬁcation factor206.1 IntroductionIn the activities ﬁnalized to the knowledge of the localseismic hazard and the seismic risk, geological and geo-physical studies are essential to perform prevention andreconstruction activities, especially where seismic hazard isrelated to high building vulnerability and the artistic andhistoric importance of urban centers.Seismic microzonation evaluates the expected localseismic hazard that originates from the peculiar geologicaland geomorphological characters of the site, by a multidis-ciplinary approach and speciﬁc levels of in-depth analyses.The Italian Guidelines for the Seismic Microzonation(ICMS) (GdL MS 2008) prescribe 3 levels of knowledge:the Level 1 (qualitative approach) is dedicated to the indi-viduation of the areas where ampliﬁcation and/or instabilityphenomena can occur. The Level 2 (semi-quantitativeapproach) deﬁnes the expected ampliﬁcation factors usingabacuses, starting from deposit thicknesses (z) and theequivalent average shear-wave velocity within the H depthinterval (VsH). The Level 3 (quantitative approach) quanti-tatively evaluates ampliﬁcation and instability by applyingexperimental and numerical analyses.The Provincia Autonoma di Trento promoted a multi-disciplinary study in the small municipality of Canazei withthe aim of seismic risk reduction, applying a Level 3 ICMSapproach. Principal phases performed by the multidisci-plinary working group were:F. Pergalani (&)  M. CompagnoniDICA, Politecnico di Milano, Piazzale Leonardo da Vinci, 20133,Milan, Italye-mail: ﬂoriana.pergalani@polimi.itG. Di Capua  D. FamianiIstituto Nazionale di Geoﬁsica e Vulcanologia, Via Vigna Murata,Rome, ItalyA. FranceschiniProvincia Autonoma di Trento, Trento, ItalyA. ViganòINOGS, CRS, Via Treviso 55, Udine, ItalyG. Lollino et al. (eds.), Engineering Geology for Society and Territory – Volume 5,DOI: 10.1007/978-3-319-09048-1_206, © Springer International Publishing Switzerland 20151085• geological and geomorphological survey (scale 1:5,000);• geophysical characterization of lithologic units and con-struction of the subsoil physical model, by using Hori-zontal-to-Vertical Spectral Ratio (HVSR) and othergeophysical techniques (MASW, Multi-Channel Analy-sis of Surface Waves; ERT, Electrical ResistivityTomography);• determination of the site-speciﬁc seismic motion (i.e.,input accelerograms);• numerical analysis (two-dimensional models) to calculateexpected ampliﬁcation in terms of elastic accelerationresponse spectra and ampliﬁcation factors.206.2 Deep Structure and MaterialPropertiesCanazei is located in a typical alpine valley (NE Alps) atabout 1,500 m asl. On the basis of the available geologicaland Level 1 seismic microzonation maps, local depositsalluvial, landslide debris and colluvial deposits formingalluvial and debris fans. Igneous and sedimentary (mainlycarbonate) rocks constitute the local geological bedrock. Thegeophysical model has been obtained by geophysical sitecharacterization (MASW, HVSR and ERT analyses;Fig. 206.1) along six cross-sections across the valley(Fig. 206.2). Geotechnical and geophysical parameters foreach geophysical unit are listed in Table 206.1.206.3 Reference Seismic MotionThe numerical analyses of Level 3 (ICMS) requires realisticaccelerograms and acceleration response spectra as seismicinput. The maximum acceleration (amax) and the spectralordinates of the acceleration response spectra (for conven-tional return periods of 475 years) were calculated accordingto the Italian seismic hazard map (GdL MPS 2004). Thereference amax value, obtained by inverse-distance interpo-lation on four grid points of the study area (cf. GdL MPS2004), is 0.066 g.Instrumentally-recorded accelerograms were extractedfrom the ITACA Database (Working Group ITACA 2010),according to rules prescribed by the National Code (IBC2008). The ﬁve selected accelerograms were scaled in orderto have the acceleration peaks close to the reference amaxvalue (Fig. 206.3).206.4 Numerical Modeling and ResultsDue to the observed geological and geophysical complexity,analyses were carried out applying two-dimensionalnumerical models. The applied numerical code derives fromthe ﬁnite-element Quad4 m code (Hudson et al. 1993) andpermits both to model any section characterized by speciﬁcmaterials and to analyze the non-linear soil response byequivalent-linear analyses.The results are reported as average of the ﬁve outputs atspeciﬁc points of the studied cross-sections, in terms ofelastic acceleration response spectra (5 % critical damping,Fig. 206.4) and ampliﬁcation factors (Fa, Fig. 206.5). Fa iscalculated as the ratio between the output and input integralson the elastic velocity response spectra in the period ranges0.1–0.5 s (Fa0.1 − 0.5) and 0.5–1.5 s (Fa0.5 − 1.5) (Pergalaniet al. 1999).The obtained average acceleration response spectra arecompared with the response spectra prescribed by the ItalianBuilding Code (IBC 2008) assuming the correspondentsubsoil category for each point (using the Vs30 value)(Fig. 206.4).To perform this comparison, the calculated spectra weremodiﬁed using the procedure by GdL MS (2008), producingspectra characterized by three segments with constantFig. 206.1 Location of the HVSR, MASW and ERT investigation in the Canazei study area and related key map1086 F. Pergalani et al.spectral acceleration, spectral velocity and spectral dis-placement, respectively.In general, the IBC (2008) spectra are lower than thecalculated spectra, particularly for low periods and for Bcategory subsoils (Fig. 206.4).Figure 206.5 maps the result in terms of average ampli-ﬁcation factors, where each singular value at a speciﬁc pointhas been laterally extrapolated considering geologichomogeneity.Fa0.1 − 0.5 values locally reach values higher than 2.8,showing signiﬁcant ampliﬁcation. Fa0.5 − 1.5 values rangebetween 1.0 and 1.8, corresponding to a medium-highampliﬁcation.Table 206.1 Geotechnical and geophysical parameters used for the numerical analysesGeophysical unit γ (kN/m3) ν (−) D0 (%) Vs (m/s)Section 1 Section 2 Section 3 Section 4 Section 5 Section 6U1a 18.5 0.40 0.010 200U1b 19.0 0.40 0.010 270 260 290 310 250 300U2 20.0 0.45 0.010 470 410 490 510 440 520U3 22.0 0.40 0.007 780 670 720 740 680 –Bedrock 24.0 0.37 0.005 1,000 930 1,200 1,000 940 800γ unit weight, ν Poisson coefﬁcient, D0 initial damping ratio, Vs shear-wave velocityFig. 2 Geophysical sections referred to the six areas highlighted in Fig. 206.10.000.050.100.150.200.250.300.350.400.0 0.5 1.0 1.5 2.0 2.5PSA (g)Periodo (s)SRC0_WE - SF 0.5SRC0_NS - SF 0.8GRR_NS - SF 3.5GRR_WE - SF 3.5SLP_WE - SF 1.0AverageNTCFig. 206.3 Elastic acceleration response spectra, with average, of theselected input motions (SF, scaling factor),with response spectrumaccording to IBC (2008)206 Seismic Microzonation in a Small Municipality 1087Fig. 206.4 Elastic acceleration response spectra of selected points along each section (cf. Fig. 206.2) from 1 (ﬁrst row) to 6 (last row), withreference response spectra according to IBC (2008)1088 F. Pergalani et al.206.5 ConclusionsThe Canazei study permitted to highlight geologic andgeophysical local heterogeneities of the subsoil, able toproduce different local seismic responses. The Level 3seismic microzonation carefully deﬁnes the effective seismichazard at this site, necessary to evaluate risk for seismic andcivil protection.The results, expressed in terms of elastic accelerationresponse spectra and ampliﬁcation factors for speciﬁc periodintervals, show signiﬁcant differences with respect to theresponse spectra of the Italian Building Code (IBC 2008).The use of these new calculated spectra is proposed forbuilding design projects.We conﬁrm that, in urban contexts, seismic microzona-tion analyses offer a necessary and valid method to improveknowledge and quantitatively evaluate seismic responseuseful for risk reduction and building safety improvements.ReferencesGdL MPS (2004) Redazione della mappa di pericolosità sismicaprevista dall’Ordinanza PCM 3274 del 20 marzo 2003. Rapp.conclusivo per il DPC, INGV, Milano-Roma, pp 65 + 5 appendiciGdL MS (2008) Indirizzi e criteri per la microzonazione sismica.Conferenza delle Regioni e delle Province autonome—Dipartimen-to della Protezione Civile, Roma, Italy, vol 3 DvdHudson MB, Idriss IM, Beikae M (1993) QUAD4 M, A computerprogram for evaluating the seismic response of soil structure byvariable damping ﬁnite element procedures. Report of Departmentof Civil and Environment. Engineering University of California,DavisIBC (2008) Norme Tecniche per le Costruzioni, DM 14 gennaio 2008,Gazzetta Ufﬁciale n. 29 del 4 febbraio 2008, Supplemento Ordinarion. 30. Istituto Poligraﬁco e Zecca dello Stato, Roma (www.cslp.it)Pergalani F, Romeo R, Luzi L, Petrini V, Pugliese A, Sanò T (1999)Seismic microzoning of the area struck by Umbria-Marche (centralItaly) Ms 5.9 earthquake of the 26 September 1997, Soil Dyn.Earthq Eng vol 18, 4, pp 279–296Working Group ITACA (2010) Data base of the italian strong motionrecords. http://itaca.mi.ingv.itFig. 206.5 Ampliﬁcation factor(Fa) maps for periods 0.1–0.5 and0.5–1.5 s206 Seismic Microzonation in a Small Municipality 1089

Seismic microzonation in a small municipality: the Canazei case study (Trentino, N Italy)

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Seismic microzonation in a small municipality: the Canazei case study (Trentino, N Italy)

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