Integration of HVSR Measures and Stratigraphic Constraints for Seismic Microzonation Studies: the Case Of(ME) Oliveri P

Open Access Discussions Sciences spectra in the frequency Natural Hazards Hazards Natural and Earth System System and Earth H/V ects and define a preliminary ff 2598 2597 ering relevant site e [email protected]) ff ff subsurface model for the first level of microzonation, we performed 23 HVSR mea- The reconstructed trend of the top of the seismic bedrock highlight its deepening be- A very minor heterogeneity of the same parameters, in large part explained by dif- This discussion paper is/has beenSystem under Sciences review (NHESS). for Please the refer journal to Natural the Hazards corresponding and final Earth paper in NHESS if available. s ferences between the ray paths from the source to the observation points and by the low the mouth of the Eliconapaleo-valley. Torrent, thus suggesting the possible presence of a buried 1 Introduction The dynamic characteristics ofby a an seismic earthquake phase and ofvariations, body incident frequency or dependent, on sometimes surface a having waves, portion extremely generated local of character. the ground surface, often show sharp graphic data of athe borehole. complete To set map of the model trenderates parameters of peaks only the the fitting depth roof those ofhas of belonging the been the to seismic extracted. seismic interface two that bedrock, clusters gen- from characterized by lower frequency V surements. A clustering technique ofcalculation continuous signals of has the been HVSR used curves.range to 42 optimize 0.6–10 reliable the Hz peaks have ofplied the been to identified. the set A ofamplitude second 42 of clustering vectors, each containing peak technique Cartesian totial has coordinates, identify phenomena. central been subsets The frequency which algorithm ap- and can hasparts identified be of the three attributed territory main to of clusters continuous Oliveri. that The spa- HVSR cover data significant inversion has been constrained by strati- Because of its highlevel seismic seismic hazard microzonation. The the town urban developsfluvial/marine on area sediments, a of overlapping large a Oliveri coastal complexly has plain deformedtify substrate. made been In points of subject order mixed on to of the iden- first area probably su Abstract Nat. Hazards Earth Syst. Sci.www.nat-hazards-earth-syst-sci-discuss.net/2/2597/2014/ Discuss., 2, 2597–2637, 2014 doi:10.5194/nhessd-2-2597-2014 © Author(s) 2014. CC Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Integration of HVSR measures and stratigraphic constraints for seismic microzonation studies: the case of(ME) Oliveri P. Di Stefano, D. Luzio, P.N. Renda, Messina, R. G. Martorana, Napoli, P. S. Capizzi, Todaro, A. and D’Alessandro, G.Dipartimento Zarcone di Scienze della Terra e del MareReceived: – 6 DiSTeM, University March of 2014 Palermo, – Italy Accepted: 1Correspondence April to: 2014 R. – Martorana Published: (ra 10 April 2014 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects ff waves, generated S ects or even determine ect the characteristics of ff ff ected by characteristics of ective resonance period of ff ff ects on incident waves trains. However, ap- ff 2600 2599 ects) (Ben-Menahem and Singh, 1981; Yuncha and Luzon, ff . A layer with these characteristics, generally not outcropping, is called ects (site e 1 ects. In general all this phenomena are controlled by anomalies in the ff ects and those due to wave propagation. − ff ff culty and costliness of the reconstruction of a suitable model of subsurface ffi ects (fractures, landslides, liquefaction, . . . ) for buildings and infrastructure, are ff Assuming a simple composition of the noise in terms of body and surface waves, The seismic microzonation of a territory aims to recognize the small scale geologi- The main sources of seismic noise are: atmospheric and hydrodynamic phenomena, Nakamura (1989) proposed a technique based on the calculation of the ratio of the The di Everywhere on the Earth’s surface a seismic station may record ground vibrations Significant increases in amplitude of the phases for which occur peak values of the If we knew a very detailed mechanical model of the cover layer, consisting of soft There can be many causes for the sharp spatial variation of the transfer function earthquake. and having an adequate informationof on the constraints subsoil, for which can athe be one-dimensional unknown expressed by model parameters means of of the the model subsoil, by inversion it of is thecal curves possible and HVSR. geomorphological to conditions determine thatthe may seismic significantly motion, generating a high stressand on critical structures e that could produce2000). permanent The first phaseritory of in the homogeneous seismic areas micro-zoning with is respect the to detailed the partition expected of ground the shaking ter- during an and fluid circulation and micro-fracturingareas, processes anthropogenic in sources the produce subsoil. seismicerage Close noise, frequency, compared to mainly to residential with the a natural relatively noise high (typically av- higher than 10 Hz). a sequence of layers,noise the presents Horizontal peaks well to correlated Vertical withby the Spectral earthquakes, amplification Ratio factor between of (HVSR) the of bottomhowever, an the and HVSR seismic the peak roof must be ofture, attributed the it to stratification. resonance might Not frequencies also necessarily, of dependwill a buried on not struc- characteristics be of correlatedpropriate the with techniques sources amplification of of e data noise analysisby and may source help in e to such discriminate, case between peaks caused power spectra of the horizontala and vertical single components three of components thevertical seismic seismic components noise of station. recorded the The seismicthe noise power sources, are spectra everywhere as of a wellsoil. the as Nakamura horizontal (1989) by showed and that the in distribution correspondence to of the the resonance frequencies mechanical of parameters in the sub- distributed in the subsoil and known as seismic noise or microtremors. univocally its transfer function by means of numerical calculation. using geophysical techniquesas: and deamplification the of strong necessity motionsoil of and deposits not increase as of neglecting the theresearchers level nonlinear e to of develop e excitation and increasesproximated adopt empirical more (Dimitriu transfer direct et functions. techniques al., that 2000) allow has to led determineproduced many ap- by interference of body and surface waves, generated by sources randomly iments, or bytopographic the surface. shape of surfaces of discontinuitysediment, close assuming to that or thein coincident layer an behaves with with approximately the respect linear to way, the we propagation could of predict waves the site e between the roof of themultiple bedrock reflection, constructive and interference the and surface focusingburied of geometry interface for the topographic irregularities. soil and as e.g.: resonance in soils, kinematic parameters of groundmic shaking, e which may becalled the site cause of e relevantmechanical coseis- properties of the shallowest layers of subsoil, when it consists of soft sed- acterized by high bodycommonly wave approximated velocity by the and requirement highthan that 800 the layer ms velocity thickness. of These shearseismic conditions waves bedrock. is are greater source model, has often been observed in extensive sub-planar outcrops of rocks char- 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent ff ect on the site response. ff erent tectonic units. ff , established by the Prime Minister’s Order ected the area since the Upper Miocene re- 2602 2601 ff erent deformation steps that are related to the Alpine ff ected by a strike-slip tectonic phase that generated two di ff Studies of Seismic Micro-zoning Aspromonte Unit, consisting ofwith paragneiss a and medium-high micaschists, gneiss, degree metagranits, amphibolites, metamorphic and basement, marbles. Mela Unit, characterized by aneiss polimetamorphic and basement, micaschists, represented with by intercalations parag- of metabasites and marbles; Longi-Taormina Unit, made of anCenozoic epimetamorphic sedimentary basement sequence; covered by a Meso- Fondachelli Unit, consisting ofmeta-limestones; phyllites and rare metarenites,Mandanici metabasites Unit, and consisting of phyllites,firoids; quartzites, metabasites, marbles and por- – – – – – The deformations are still actives and result in thrusts, within the chain, and crustal In the Peloritani Mountains di Reverse fault systems (breaching) a Upward follow, through a tectonic contact, the Antisicilide Units (Ogniben, 1970), According to Giunta et al. (1998), the tectonic pile of the Peloritani Mountains is This paper focus on a recent micro-zoning study ofThis the area Oliveri is urban among area, those a with village highest seismic hazard, selected for theTaking first into account year that of a geological feature of this area is a thick blanket of coastal 1996). systems: the first one synthetic withsecond right one cinematic and antithetical, oriented mainly NW–SEVezzani, and sinistral 1977, E–W; 1984; and the Ghisetti, oriented 1979; N–SMalinverno Boccaletti et and and al., NE–SW Ryan, 1986; (Ghisetti 1986; Finetti1995; and and Giunta, Abate Del et 1991; Ben, al., Mauz 1986; 1998; and Nigro, 1998; Renda, Nigro 1995; and Renda,thinning Nigro 1999, in and 2000, the Sulli, 2002, Tyrrhenian 2005). areaThe (Finetti, geometry 1982; of Finetti thrusts et areor al., ramp-flat-ramp in like 1996; some (Nigro, Giunta cases 1994; et are Giunta al., the and 2000). result Nigro, 1998) of duplex structures (Nigro,1994; Giunta and Somma, sulting in moderate shorteningthe Tyrrhenian (Giunta rifting and produced Nigro, aa series 1998). thinning of At of extensional the the low chain.tani end angle During Mountains faults of Plio-Pleistocene was that a the times resulted the Miocene in area occupied by the Pelori- which are represented by theby Argille the Variegate, Miocene that Floresta are Calcarenites in (Ogniben,Plio-Pleistocene turn 1960, calcarenites unconformably 1969; and overlain Guerrera clays e are Wezel, preserved 1974). in tectonic depression. orogeny, are superimposed to thecontraction Hercynian ductile has deformations. been The characterized Oligo-Miocene formation of by folds several associated phasesthe with crystalline in rocks thrust which and systems their there sedimentary that has covers have in been fragmented di the and stacked These units are overlappedStilo-Capo by d’Orlando Formation. Oligo-Miocene siliciclastic turbidites pertaining to the The area of Oliverichain is that is part mainly of constitutedmorphic the by a rocks Peloritani pile and Mountains, of their tectonic a Meso-Cenozoic units segment sedimentary consisting covers. of of Hercynian the meta- Maghrebian formed by the following units: deposits that cover the substratestruction seismic, of in the this thickness paper ofThe we the experimental focused sedimentary data only that cover on and havean the been its inventory collected recon- of e are existing wells derived andHVSR. from: a a geophysical geological survey, carried survey, out using the technique 2 Seismotectonic setting settled on a coastal plain in Northeastern Sicily. the project no. 3907. 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent source mechanisms have been ff erent geodynamic domains: compressive ff 2604 2603 6.6), related to movements along these faults (Neri = W M ) has been estimated on the base of paleontological data (Di 1 − Neri et al. (2003) have determined the focal mechanisms of earthquakes with depths The earthquake of 1978 ( The earthquakes of Novara di Sicilia, with lower magnitude and shallower hypocen- The high rate of seismicity in the Gulf of Patti and in the area between Alicudi and Vul- The lithostratigraphic framework of the substrate of the urban area (Fig. 1) is made up The Oliveri territory is located in the area 932 of the ZS9 seismogenic zonation of The morphological features of Oliveri town are represented mainly by an alluvial Around the Oliveri‘s plain there is evidence of active tectonics due to a right-lateral sponsible for the liftingTyrrhenian sea, of those oriented the aroundwestern chain. EO, sector Among would of be the the responsibleone structures for Aeolian in the Islands, present 1823. events and in of may the the have generated southern earthquakesless like than the 50 km, occurredcate in a high Calabria heterogeneity and of Sicily thestyle deformation between ranges field from 1978 in extensional and with the southwest area 2001.exposure, exposure 932. to These proceeding Here compressional from indi- the with deformation SE northeast to NW. in the Oliveri areaand was significant VII soil fractures MCS, (Barbano where et it al., 1979). caused seriousters, damage seem in to be some linkedThe buildings to earthquakes structures of other Naso than might the fault instead system be Patti–Volcano–Salina. associated with NE–SW normal faults re- phus, respectively oriented NW–SE andearthquakes WNW–ESE. The have most occurred energetic in instrumental magnitude this of area 5.5 and 15 5.7 April respectively. 1978 and 28et May al., 1996), 1980 caused with considerableand a damage was local in many felt countries upTrapani of to to the the west Messina the and province Cosenza toimum the province macroseismic Ionian in intensity coast of has the Calabria been north, to VIII-IX the to MCS. east. Dubrovnik The Its estimated mean in max- macroseismic the intensity south, to proposed, some of which are,systems probably, or associated blind with faults the (Ghisetti, activationtorici, 1992; of 1995). Valensise complex and fault Pantosti, 1992; Monaco and Tor- cano is associated to the two right-slip fault systems, Patti–Volcano–Salina and Sisy- occurred the earthquake of 1908, for which di 932 is one of the areas with the highest seismic potential of the whole Sicily. In it by the metamorphic basementby of the the arenaceus Aspromonte member Unit ofiments that the is are Capo covered tectonically D’Orlando unconformably overlain Flysch.Unit. The by Upwards previous the the deposits flyschoid Argille are sed- age. capped Scagliose The by most belonging sands recent to and sediments calcarenites consist the of of Antisicilide alluvial Plio-Pleistocene andItaly beach deposits. (Meletti and Valensise,through 2004). geophysical It exploration. includes TheCalabrian faults seismogenic Arc in structures and this largely some area known are partly synthetic allow faults the that retreat segment of the the Gulf of Patti. The area plain, where lies theand town western itself, part and of byCastello a the plain. hilly and Both landscape Torrente the that Eliconapebbly hills surrounds sediments. rivers and the valleys, the southern plain that are are crossed partly by the filled Torrente by silty-sandy and and structural and morphological surveys showas evidence recent of tectonic as activity the in1979; this middle-upper De area Pleistocene Guidi et (Catalano al., andacterized 2013). some Di Recent geothermal studies, Stefano, not springs 1997; far andthe Ghisetti, from gas generation the vents Oliveri‘s of and plain, discussed earthquakes havelift their char- (Giammanco possible (up et role to in al., 5.5 mmStefano 2008) year et and al., a 2012). very high rate of up- shear zone named Aeolian–Tindari–Letojannizani, fault 1979). This (Ghisetti, fault 1979; isto Ghisetti generated west, by and two related Vez- di to asional roughly to N–S east, trusting controlled produced by byet NW–SE continental al., expansion collision, 2013). of and The the exten- analysis Calabro-Peloritan of Arc seismic (De and Guidi geodetic data, acquired in the last 15 years, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | wave trans- S 0.2 while for superficial , transfer functions de- ± H/V ects expressed in terms of ff peak frequency and amplitude may curves is mainly controlled by the polar- H/V ect in the Oliveri area, reported in the cat- 0.13 which is comparable with the value ob- ff ± culties in the assessing of these techniques, 2606 2605 H/V ffi peak amplitude and the site amplification can be H/V 6.15, epicenter at Oliveri and MCS intensity equal to IX in = W M and are distributed rather uniformly with respect to depths up to 400 km. ◦ Because of the above conceptual di Some open questions and doubts remain, however, on the reliability of HVSR tech- In fact, if the shape of the HVSR curves is mainly controlled by the The geometric characteristics of the clusters related to the shallower seismicity iden- The seismicity of the last 20 years has also been analyzed in the magnitude domain. An analysis of completeness of theseThe data shallow sets seismic has activity indicated has a a local marked magnitude tendency to occur through sequences The first earthquake whit a destructive e The seismic activity recorded in the last 20 years the area surrounding the urban increases of macroseismic intensity or peak values of the usual ground motion pa- ization of the fundamental1994; mode Kudo, of 1995; the Bard, Rayleigh 1999;indirect waves correlation Konno (ellipticity) between and (Lachet the Ohmachi, andexpected. 1998; Bard, Fäh et al., 2001), only an many experimental works have playedalyzed an correlations important between: role. In peaksrived these of by were crosswise the the an- spectral method ratio SSR (Borcherdt, 1970) and site e fer function within theet shallowest sedimentary al., layers 2000; (Nakamura, Mucciarellibe, 1989, respectively, et 2000; related Parolai al., to 2003),On subsoil both the resonance other frequency hand, and if site the amplification shape factor. of the 3 HVSR measurements and processing The HVSR technique, is todaymicrozonation one studies of of the urban most commonly areas. applied methods of expedite nique, mainly related tomicrotremor sources, the composition numerous of assumptions theLove about: seismic waves and noise spatial characterization in distribution of terms the of of propagation body, the medium, Rayleigh often and hard to verify. associated with the Ionian slab,events the has been value estimated of the b valuetained is 1.15 for equal the to independent 0.6 componentarea of (see Adelfio the et seismicity al., of 2006). the whole south-Tyrrhenian Mulargia (1987) not distorted by the data grouping. In particular, for deeper events, Gutenberg–Richter and the 95 % confidence interval, using the estimator of Tinti and constituted by events not followed bythat aftershocks and for the the main shock totaltime of set the correlation sequences of dimension relating events to (Adelfiofor independent uniform et events distributions, al., are as close opposed 2006). to to The those those estimates for expected the of totaltify the set orientations space that are and that much arearea. smaller. consistent with those of the mainFor tectonic the events structures of of the the area of Fig. 2 have been estimated the value of b of the law of threshold equal to about 2.6. of aftershocks sometimesa preceded quantitative by way foreshocks. by comparing Thismains the of tendency estimates the was of epicenter assessed the coordinates and correlation in time, dimension both in for the the do- component of the seismicity center of Oliveri represented inmagnitude Fig. greater 2 than is 2. characterized Ofaround by these an about average about 3500 depth 89 of events % about withhypocenters have 10 local km. hypocenters are The tightly thickened remaining concentrated around 11 % aof consists of plane about events that 60 whose dips towardThe the sources northwest of at these anunder events the angle are Calabrian Arc located (Giunta inside et the al., 2004). Ionian lithospheric slab that dips alogs of historical Italianwas characterized seismicity, by occurred inthe 10 urban area. March This 1786.northern earthquake This severely Sicily damaged and seismic all almost event destroyed the the cities town of of the Oliveri Gulf (Guidoboni of et al., Patti 2007). in 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent survey techniques and between these ff 2608 2607 waves velocity models. ects and areas in which the spectral ratios are charac- ff S ects in sedimentary basins, near faults or cavities or to estimate the res- ff ects. ff The lack of objective selection criteria leads to several drawbacks. In particular, in- Another problematic aspect must be addressed when the HVSR method is applied The windows selection can be made scanning in time domain the three components In both cases, while there are in the literature numerous suggestions and prescrip- One of the most controversial aspects in the application of the HVSR technique The foregoing highlights the importance of improving the processing techniques of For this reason an issue to be addressed is related to the processing procedure for In most of the studies reported in the literature this technique has been used to The results of these analyzes indicate that there is a high spatial correlation between creasing of the processing durationon of the the; skill producing results of whosethe the reliability estimates operator. depends The of permanence thecan of expected lead abnormal value to windows and overestimates can of the the cause dispersion true bias of uncertainty of of thefor the set the spectral of seismic ratios. microzonation selected of curves uniform an with area, respect that to is, their forwith response its to which subdivision a into we seismic areas input. arerelated relatively The experimental facing to information this a problem fairly very dense often distribution consists of of measurement a points, set and of sometimes HVSR a curves little dows, as function of time. tions about this stagewindows of to the be processing used (SESAME in the Project calculation 2004), of the the selection HVSR of curve the is highly subjective. recorded noise for the computationthe of low-amplitude part the of average signal. HVSR Someobserved curve, authors by thus instead correlation considering (Mucciarelli studies, and only that Gallipoli,improves the 2004) the non-stationary, high-amplitude capability noise of windows therecordings HVSR of vibrations curve induced to by mimic weakshould the earthquakes not and, HVESR be therefore, curves, suggest removed. obtained that they with noise signal, or observing the whole set of HVSR curves, related to single time win- concerns the criteriaappropriate for for the the calculation of selection, theand HVSR in transients, curves. common Several the authors in assume all microtremor thatsource the spikes signals, records, and bring of cannot information highly time beet dependent used windows al., from to the 2001). estimate For this the reason resonance many frequency authors of exclude the the site non-stationary (Horike portion of the the recorded signals to bewith able to site link, e more reliably, the results of HVSR investigations the determination of thecurves, spectral several ratio. criteria In mustselection particular, be in of order respected the to for: timeamplitude obtain spectrum acquisition windows for reliable each to of time HVSR window, be 3-components compositionto of the used signals, the amplitude horizontal in spectra components, relative thecomputation computation of SR of the the calculation, average HVSR HVSR computation (SESAME for of Project each 2004). the window and, finally, authors (Fäh et al.,et 2003; al., Scherbaum 2005, et 2006; Picozzi al., etHVSR 2003; al., curves 2005) Arai with perform and joint information Tokimatsu, and/orgeophysical relating 2004; constrained survey, to inversion to Parolai of obtain neighboring the perforations and other types of the subsurface structures. Aamplitudes very of minor the correlation peaks is relatingand observed, to the instead, the local between di amplification the ofparameters. the macroseismic intensity or peak values of the shaking study site e onance frequency of building (e.g.1994; Field Mucciarelli, and 1998; Jacob, 1993; Bard, Lermo 1999; and Fäh Chávez-García, et al., 2001). In some recent studies some Panou et al., 2005; De Rubeis et al., 2011). areas in which there areterized site by e peaks ofof significant the amplitude, frequencies also of highlight the the peaks correlation of between the some HVSR curves and the main eigenfrequencies of rameters (Dimitriu et al., 2000; Rodriguez et al., 2000; Mucciarelli and Gallipoli, 2004; 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ® ect due to ects and to ects, which ff ff ff erent causes ) and the av- ff xy 20 Hz. Their attribution − erent from the measuring ff ects and to identify all the signif- ff ect and characterize it in frequency ff ects. ff 2610 2609 ects allowed us to determine for each cluster an av- ff erent hierarchical and non-hierarchical clustering algo- ff spectra in the frequency range 0.6 H/V erent sites, so as to identify areas characterized by site e ff erent characteristics of the subsurface. This raises the problem of defining ff ects from other perhaps related to source e The HVSR data (Fig. 4) have revealed the likely presence of amplification of ground The separation of the two e In each HVSR curve all the significant peaks were identified and characterized by To determine the HVSR curves of each measurement point, we implemented a pro- This procedure allowed us to split, almost automatically, peaks probably linked to site For each measurement point the recording length was 46 min and the sampling fre- In this paper, both the aforementioned problems, have beenTo try addressed to by identify areas clus- of the town of Oliveri probably interested in site e For the measurements has been used the 3C seismic digital station TROMINO Each HVSR curve may contain more significant peaks attributable to di ff related to di because of the similarity in frequency and amplitude of the corresponding HVSR peaks motion in the frequencythickness of range the 0.7–2.6 soft Hz, coverageposition over in allow few a us places to large where hypothesize part itsame that coverage. is the of known cause the and of its amplification urban lithological is area. com- the The resonance of the 4 Frequency maps A clustering procedure may be also used to group peaks of HVSR average curves mean curve of a clusterazimuthally stable. have been attributed to characteristics of the subsoiltheir only center it frequency is and amplitude. These parameters are reported in Table 1. e erage HVSR curve bettericant related peaks to the of local the to site resonance e phenomena ofSESAME buried criteria, structures by has analyzing beenthe the validated, independence standard in from deviation agreement the of with approximately azimuth the one-dimensional ground of spectral around the amplitudes each mean and measurement point, spectral a ratio peak of (Fig. the 3). Assuming an cedure based on anbeen Agglomerative Hierarchical selected Clustering by (AHC) algorithm.rithms. testing This We di has used aserage linkage proximity (AL) measure criteria the (D’Alessandro Standard et al., Correlation 2014a). (SC to obtain a smoothing of 10 %. lowed us to have athe analysis, minimum with numerosity the of clustering technique, thethe not sets less SESAME than of criteria, 150 sampling the (Sesame, signal 2004). windowscorrected, Following relative selected tapered to for each and time band window passthe was filtered de-trended, FFT between baseline of 0.1 each and signaland 25 Hz. components Ohmachi Than and we (1998). determined performed thewhich The HVSR is analysis the curve frequency following were range Konno gineering. limited of The interest data to in for the seismic the frequency microzonation domain frequency and have been earthquake range filtered en- with 0.1–20 a Hz, triangular window quite uniformly distributed with a mean spacing of about 250(Micromed), m. equipped with three velocity transducers. quency 256 Hz. Each record was divided into 247 windows 10 s long. This choice al- points, it will beand reasonable amplitude to with a assumemeasurement technique a points. of site 2-D e interpolation of parameters determinedter at analysis the techniques(D’Alessandro described et al., and 2013). assessed through somedefine experimental a preliminary tests subsurface model 23 HVSR measurements have been performed, from some drilling. namely di the areas in whicha it particular is cause. acceptable In to each assume interior the presence point of to the that site area, e di information about the subsurface from past geophysical and geological surveys and 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | G 0. ∪ B = ≡ lith and their w 0 F ect of a cov- ff 0.4, vs. = dist H/V w erent mechanical pa- ff 0.2, = ampl w ects of the sedimentary cover down ff 0.4, erence between pairs of parameters is ff = vs. frequency for di per w 2612 2611 H/V erence in the sample. To disadvantage the inclusion in ff G, show the resonance e ∪ erent maps can be reconstructed, each of them grouping and sep- ff G and is characterized by higher frequencies respect to the corresponding ∪ An area south of the town, interesting for the spatial planning, seems to be charac- Therefore, two di For the processing of the maps, the kriging algorithm has been applied to interpolate Figure 6 shows the characteristics of the clusters in the diagram As the two clusters B and G are very near in the scatter plot and their areas have an The procedure of clustering made it possible to split the total set of peaks in four To this end we implemented a clustering procedure to be applied to the parameter simplifying assumptions about thebody and composition surface of waves. For the example microseismic that field the microseismic in field terms is of totally constituted terized by higher amplification at frequencies greater than 1.2 Hz (Fig. 7, right). 5 Seismic bedrock mapping by HVSRFor inversion media consistingpossible of to homogeneous express elastic therameters, or behaviour in viscoelastic particular of shear horizontal wave layers, velocity, and it thicknesses is of the layers, if you make in the maps, being not reliably mappable with smoothed trendsthe over experimental large peak areas. frequencies atto the 10 nodes m. of The a frequency(Fig. regular 7). maps lattice are with spacing plotted equal using a contour equidistance equal to 0.05 ering layer delimited at itsConversely it base is by assumed the that same thethat cluster discontinuity of R, surface whose B with extent represent variableones a depth. of significant part the of peaks ofto B a shallower interface. arately representing the continuousand trend R. The of amplification the estimated frequency at the for measurement the points clusters is reported A numerically spatial distribution. empty intersection, it was consideredfects, reasonable continuously to variable assume on that the they unionIn represent of their the particular areas, ef- of it a is single source assumed phenomenon. that B and G are related to the resonance e et al., 2014b). For this application we set clusters referred to as: B (Blue),of R 21, (Red), 12, G 7, (Green), and Vin 2 (Violet), the respectively, peaks. consisting overall The description clusterby of made the up the parameters of area listed only dueprocess. in two From to this peaks Table it 1. poor has is Figure reliability been clear that,one neglected 5 of adopting adopted shows a both cut by the peaks, threshold the dendrogram slightly highlighted lowerin calculation of than a code, the the single optimal the clustering cluster. three remaining clusters would be gathered normalized by the maximum di the same cluster ofdistance more of peaks coincident relative points to wastype placed the of equal same to parameter measurement 1. must point,parameters The be the intrinsic weight the to to relative be the result attributed clustering of to process an any and optimization geological constraint that (D’Alessandro takes into account both vectors that characterize the individual peaks.plane Each Cartesian vector coordinate contains: and period, a amplitude, parameternumber indicative of of vectors the outcropping is lithology. equal The dure is to based the on number an ofaverage Agglomerative peaks linkage Hierarchical considered (AL) Clustering significant. (AHC) criteria. Theerages algorithm, The proce- of using elements the Euclidean of relativeof distances the peaks, between similarity while the matrix for quantitativecoincident the are parameters lithologies lithological weighted and of parameter av- 1 a the otherwise. distance pair Each has di been set equal to 0 for the same buried structure.spatial Considering the trends parameters that of arepossible such continuous to peaks estimate on as the sampling thearea expected of area by peak two-dimensional containing amplitude interpolation the and techniques. frequency measuring at points, each it point is of the and the not excessive distance between the measuring points, are probably caused by 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − curves have been wave velocity were S H/V ). 1 − erent structures or vice versa. ff ) curves requires the solution of a nonlinear 2614 2613 f ( H/V erent random seeds, an integer value that initializes the pseudo-random ff erent geological structures, it was decided to group and correlate frequen- ff In almost all the HVSR measurements carried out on the alluvial material a maximum Analyzing the 1-D inverse models (Fig. 9) derived by inverting HVSR measurements, Unfortunately, it has been possible to constrain the model using the data of a sin- The depth of transition of the shear wave velocity from less to greater than 800 ms The a priori density of probability is set as uniform over the whole parameter space, The inversion has been carried out using the Dinver inversion code developed in the It should be, also, pointed out that, due to lateral variations of geologic parameters Taking into account the available geological information, the Even with these simplistic assumptions, the determination of the parameters that estimates of the depth of the seismic bedrock have been obtained. These, together with suming minimal lateral variations.due To avoid to interpolation di between depthscies of related to interfaces the samebelonging cluster. to However the it same is cluster not are possible due to to exclude di thatpeak frequencies is evident inrelated the to range a variation 0.7–1.4 of Hz.values the This, attributable shear-wave by velocities to that, a the under seismic inversions a bedrock results, depth (about of seems 800 40–60 ms to m reach be is considered the depthestimate of of the this seismic depth, bedrock. weenced When must by consider evaluating the that the interpolation the reliabilityvalues trends process of obtained represented between the from are the every heavily HVSR measuring influ- measuring points points. are The in depth fact only possible estimates, as- times with di generator. gle borehole, located atconstraints the on the eastern thicknesses boundary ofto of the the layers the nearest in municipality recording the inversion point. (Fig.obtained, of From which 8), the this were to HVSR model subsequently curve impose estimates usedof related of to the the define other HVSR the curves. starting model for the inversion the limits of whichthe are data defined misfit by function the isway a of determined, interpolating priori the an neighbourhood ranges irregular algorithmto of distribution find provides all of and a points, chosen investigate simple making the parameters. use mostbustness Once promising of of parts the Voronoi geometry final of results the is parameter generally space. checked Hence, by the running ro- the same inversion several fit inside a multidimensional parameter space. the computation of thelayers dispersion is determined curve (Haskell, forered 1953). a as Only stack the the of experimentalvertical Rayleigh horizontal dispersion components phase and curve of velocities noise. is homogeneous As aredirections, generally ambient consid- as obtained vibrations body may from contain waves processing waves andthe travelling the Rayleigh in uncertain and all composition Love of waves,the a seismic limit unknown noise of parameters and thisterson, in those method 1993). the lies relating For impossibility in to the toused. inversion the include the This model among is neighbourhood of a algorithm stochastic (Sambridge, the direct-search 1999) microseismic method was field for finding (Pe- models of acceptable data the seismic bedrock. inverted to estimate the depth of the seismic bedrock, alsoframe reported of in the Table project 1. Geopsy (Wathelet et al., 2004; Wathelet, 2008). In this technique will certainly be unreliableof if the you real are geological notological stratification, using observations because an or it initial is results modelsurveys. well already of constrained representative other by geophysical drilling surveys data, mostly, ge- in-hole seismic as: porosity, water content, fracturinglayer degree, will etc. not the be mechanicalcuracy uniformly parameters of distributed of the each with estimate obvious of negative the depth consequences of on geological the interfaces ac- and in particular the roof of Reyleigh waves. characterize the subsoil frominverse problem, the poorly constrained by theunivocal experimental and data unstable, and therefore especially highly in non- complex cases as velocity inversions. The results by body waves emerging almost vertically or totally by the fundamental mode of the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | for alluvium and 1 − 2616 2615 in correspondence of silty sands. 1 − The lack of good data of wells has hampered the definition of the lithological distribu- In the section A, oriented from west to east, it possible to observe, in the westernmost For the above mentioned reasons the inversion of HVSR curves and evaluation of the However the seismic velocity values used results close to thoseOn characteristic of the the basis of the 3-D trend of seismic bedrock and of geological information The map of the bedrock depth contours was obtained by extracting from the Digital Considering the geological configuration of the subsoil and the values of shear-wave in the first 1.6 m,morphic followed by origin, 3.4 m 5.5 m of of well graded silty sands sands, with with gravel elements rare of rounded meta- gravel elements, and 5.4 m of side, while the southernlogue side the is floodplain bounded is by crossedHowever, buried by in faults. a the According NNW–SSE normal studied toexistence fault ITHACA area, of named cata- this there Tindari–Letojanni. fault are (Ghisetti, 1979). not morphological evidencestion, that in testify particular under the the town.the It first is is been located possible close tohill. to use The Torrente only Elicona, the analysis the data of second from the is two core located wells; close of to the the first Castello well shows the presence of anthropic deposits able percentage of silt and clayposition and frequent of alternations these of sediments silty-sandy is gravels.and The “Torrente related de- Castello”, to which cross the the presenceplain, floodplain. of is The a two only hill, outcrop, rivers, named inner “Torrente “Il to Elicona” hill Castello”, the characterized is by flood- the Gneiss of result the of Aspromonte the Unit. This morphological evolution of the Torrente Castello, in the northern catalogs (e.g. ITHACA) andpresence structural of studies an active (Ghisetti fault and that Vezzani,1977) in testify geological sections the is approximately shown. 6 Geological-technical model The Oliveri’s territory consists oftains are a constituted floodplain by surrounded a byand metamorphic calcarenites mountains. basement (Aspromonte sediments. These Unit) The moun- covered dominant by lithology flysch of this floodplain is sand with vari- part, the stratigraphic overlay of thestrate, Flysch which of is Capo D’Orlando lowered eastward on by theare normal metamorphic onlapping sub- faults. The on alluvial the deposits of substratetions coastal whose B plain lithology and is C) not duethe known to only in the information most lack is of of related the information to area deriving geophysical (sec- from analysis. deep Along boreholes. the Therefore Oliveri’s plain some thickness of the coverand did instead, not the take mean values into ofwere account shear-wave considered. velocity the of In available the particular, seismic cover, we availableabout down-hole in considered 350 literature, data about to 200 400 ms to 250 ms rock in the area. from field surveys and fromdrawn published (Fig. geological 11). maps, three geological sections were is not less than 300 m. velocity (deduced from direct bore-hole measurements)made a of preliminary the identification was geological structures that can cause seismic resonance. nodes equal to 10 m. Elevation Model of thesponding area lattice a of grid thein of depth order points of to equidistant the obtain 50detail bedrock a m. but were trend which, From subtracted. however, of did these This not the thetopographic present isobaths choice surface. unrealistic corre- that was It areas with should was made higher however notnot elevations emphasize of excessively be that the tied higher the to than real topographic the detail of sampling the density maps of can the HVSR measurements, which generally the map of thealtitude thickness of the of top the of seismicthe sedimentary bedrock bedrock a.s.l. were cover (Fig. interpolated (Fig. 10, by imposing right). 10,where a The left) constraint estimates geological of of and a the strata depth the depth equalkriging with of map to interpolation zero elastic of in algorithm areas the characteristics was used, of obtaining seismic a lattice bedrock with outcrop. equidistance between The other reliable data like drilling and other geophysical surveys, were used to construct 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ered ff ects, often has ff ects between waves trains of ff ects of the subsurface structures are ff 2618 2617 ects of the same buried structures. ff ects at frequencies of engineering interest. The most innovative aspects of the ff erent nature. ff ects of layers with varying thickness, it was possible to reconstruct the possible trend The good quality of the estimates of frequency and amplitude of the peaks, allowed Assuming that the three identified clusters contain peaks produced by resonance The application of a clustering procedure to the set of signals related to the elemen- The average spectral ratio of the cluster dominated by structural e The core relative to the second well shows evidence of a tectonic dislocation that ff the 3-D model obtained is limited by the lack of geophysical and drilling data, which to use, with good results,of a which second could be clustering considered procedurepeaks reasonable to to attributable identify to interpolate areas the the in values e of the the inside parameters of e of the roof ofall the the geological seismic and bedrocklateral lithological variability by available of inversion information the physical and of and by the geometrical a parameters. HVSR criterion Although curves the of reliability constrained minimum of by tics of the noisea sources di or to accidental interference e been characterized by smallernificant variance peaks, of compared the to frequencies those and of the amplitudes peaks of determined the with sig- standard methods. results that go farsite beyond e the simple identification,processing in of some the recording recorded points, signals,result, of underlying are likely based the on significant the improvement use in of the clustering final techniquestary in two recording phases intervals, of allowed a theter study. more of objective the identification noise and windowsdominant, grouping in compared in to which a those clus- the dominated spectral by e trends attributable to spectral characteris- The main purpose of thisfirst work level microzonation is study not, carried ofhazard, out course, in but to an to present urban the show centerthanks complete of how results to an a of area some survey the of significant performed high seismic by improvements the in seismic the noise processing HVSR procedure, technique, can produce 7 Conclusions a depth of 40 m whileof the the floor town of there basinsThis show is a could another depth be basin of related in 60–70 to m.the which another In hydrogeological minor the map the river the southern bedrock joined presence part reaches with ofat a the groundwater a level deepness Torrente depth in Elicona. less of the Based than 40 floodplain on risk. 15 m. is m. attested This condition renders the floodplain exposed to liquefaction thickness in these twoseismic areas bedrock is chart about in 45a which m. migration is Using possible toward a to the DEMlittle observe present support bit as day shifted was the position. while produced river the Intoday. the beds According other particular have to one, su the the the bedrock Torrente Torrente Castello, map Elicona was the was much relief moved a that north separates than the two depressions has work is alsoreconstruct supported the by thickness geophysical ofthe data. the flyschoid From coverage coverage. HVSR has Inthickness results a the of thickness it northern clay of and was side about calcarenitescoverages possible 20 of coverages is m exceeds to related Torrente while, 45 to Castello, m in the (Fig.tuations. sedimentary the 1). Thanks contribution, southern The of to part, nature the the of rivers the struct interpretation and the the of of variation sea geophysical of level the data fluc- suggest cover it thickness the has in the been presence studied possible of area. recon- The two reconstructed model buried river beds separated by a relief. The sediment tion by HVSR data, seemsof to core samples be has made permitted bylevel is to incoherent placed recognize sand at a and a bivalve grey mollusk depth silt. fauna. of The The 7.5 analysis m. groundwater put in contact the “Argille Scagliose” unit with the metamorphic basement. This frame- poorly graded sand. 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B.: Ambient Nigro, F.: Neotectonic events and kinematic of rhegmatic-like basins in Sicily and adjacent ar- Ogniben, L.: Schemi paleotettonici anzichè paleogeografici in regioni di corrugamento: Nigro, F.: L’Unità Longi-Taormina. Stratigrafia e Tettonica Delle Coperture Mesozoico-Terziarie Neri, G., Barberi, G., Orecchio, B., and Mostaccio, A.: Seismic strain and seismogenic stress Neri, G., Caccamo, D., Cocina, O., and Montalto, A.: Geodynamic implications of earthquake Nakamura, Y.: Clear Identification of Fundamental Idea of Nakamura’s Technique and its Appli- Nakamura, Y.: A Method for Dynamic Characteristics Estimation of Subsurface using Mi- Mucciarelli, M., Gallipoli, M. R., and Arcieri, M.: The stability of the horizontal-to-vertical spectral 5 5 30 25 20 30 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | H/V , 2008. 2626 2625 10.1029/2008GL033256 ID Longitude1 Latitude2 15.0668713 15.063414 38.125908 Frequency3 (Hz) 0.73 15.059912 38.1268924 Amplitude 1.23 38.127903 15.0599125 Cluster 0.76 15.057073 38.1279036 1.13 15.055261 38.1298337 0.77 15.055074 38.1322418 0.82 15.056796 38.127563 4.498 1.03 38.126292 15.059567 7.649 1.00 15.059567 38.124235 3.809 1.00 15.062717 38.124235 4.23 1 10 1.78 15.062717 38.125018 8.12 1 10 15.065124 0.84 38.125018 5.96 1 15.06512411 38.124719 1.10 6.17 1 0.7711 38.124719 15.065406 5.35 1 1.1012 15.065406 38.121772 5.10 1 0.8313 15.062658 38.121772 3.19 1 1.4314 15.064252 38.122990 6.08 1 0.9314 15.060934 38.119654 7.09 1 1.53 15.06093414 38.121026 6.48 2 1.1015 38.121026 15.060934 4.30 1 1.3716 15.057181 38.121026 4.21 1 1.7316 15.054749 38.121650 4.51 1 1.8316 15.054749 38.118991 4.68 1 0.9017 15.054749 38.118991 6.00 1 1.53 15.05174017 38.118991 3.56 1 10.1417 38.122412 15.051740 2.55 1 0.9018 15.051740 38.122412 2.71 1 1.7018 15.049392 38.122412 3.22 1 2.6719 15.049392 38.119468 4.28 1 0.87 15.04696219 38.119468 4.35 2 3.10 1.5019 38.114408 15.046962 2 0.8720 15.046962 38.114408 2.57 3 2.2020 15.051695 38.114408 3.24 2 4 6.0821 15.051695 38.116305 4.94 0.9721 15.054697 38.116305 2.60 3 1.43 15.05469721 38.114280 2.67 2 0.8722 38.114280 15.054697 3.12 2 1.3722 15.050217 38.114280 4.23 3 1.7323 15.050217 38.111984 2.80 2 0.8723 15.058505 38.111984 4.00 3 1.23 15.058505 38.118050 4.54 2 0.77 38.118050 3.31 4 1.30 4.41 3 4.31 2 4.10 3 5.39 2 3.83 2 3.63 3 2 1 1 Measurement points, UTM coordinates, frequencies of the significant peaks, the Messina Straits472–483, (southern 1992. Italy) and the 1908 earthquakeGeophys. (Ms Res. Lett., 7 35, L09301, 1/2), doi: Terra Nova, 4, algorithm and its application211–221, 2004. to ambient vibration measurements, Near Surf.B. Geophys., Seismol. Soc. 2, Am., 90, 1101–1106, 2000. Soc. Am., 77, 2125–2134, 1987. Table 1. ratios. Wathelet, M.: An improved neighborhood algorithm: parameter conditions and dynamic scaling, Yuncha, Z. A. and Luzon, F.: On the horizontal-to-vertical spectral ratio in sedimentary basins, Valensise, G. and Pantosti, D.: A 125 kyr-long geological record of seismic source repeatability: Tinti, S. and Mulargia, F.: Confidence intervals of bvalues for grouped magnitudes, B. Seismol. Wathelet, M., Jongmans, D., and Ohrnberger, M.: Surface wave inversion using a direct search 5 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) active

) inactive allu- n

- - - n1 g ) Paragneiss, micas- Paleo c

– −

b − ) alluvial and b a b ) paragneiss and Paleozoic). b

- a – “Foglio Geologico 600

- PMA tta Fm., Upper Pliocene ) terraced marine deposits; ROE ) (Apromonte unit a 5 ) Capo d’Orlando Flysch: areana- c ) active strandlines (beaches); 2 −− PMP − g 1 b n ) active alluvial deposits; a ) Capo d’Orlando Flysch: areanaceous facies b c - b lower Burdigalian);

) eluvium and colluvium; b – 2 COD pegmatitic dykes ( -

16 ) slope debris; a 17 2628 2627 ISPRA): ) inactive alluvial terraced deposits; - n b

Biodetrital calcarenites, clays and sandy clays (Rome

marly marly levels (Upper Oligocene - ) Paragneiss, micaschists, marbles, eclogites, quartzites (Mela unit c - b - a ROE ) Argille Scagliose (Upper Cretaceous); MLE ASI

map of Oliveri town (from SERVIZIO GEOLOGICO D’ITALIA (2011)

) eluvium and colluvium; 2 b Permian); Permian);

– ) active strandlines (beaches); g epicenters instrumentalof earthquakes located the INGV by between 1981 and 2011. Geological 2

- ssic micaschists, silicate marbles, quartzites and aplo

) terraced marine deposits;

Fig. Fig. 1 Barcellona Pozzo di Gotto” 1:50.000 CARG litoral deposits; 5 Middle Pleistocene); (arkose) with alternation of clay gnei Proterozoic ) alluvial and litoral deposits; b b Distribution of ) (Apromonte unit–Paleo-Proterozoic–Permian); MLE

- a ) paragneiss and gneissic micaschists, silicate marbles, quartzites and aplo-pegmatitic Fig. 2Fig. Distribution of epicenters of instrumental earthquakes located by the INGV between Geological map of Oliveri town (from SERVIZIO GEOLOGICO D’ITALIA (2011) – “Foglio b

− a

Biodetrital calcarenites, clays andtocene); ASI) sandy Argille clays Scagliose (Upper (Rometta Cretaceous); Fm., COD Upper Pliocene–Middle Pleis- 1981 and 2011. Fig. 2. ceous facies (arkose) with alternation ofPMA clay-marly levels (Upper Oligocene–lower Burdigalian); dykes (PMP alluvial deposits; b vial terraced deposits; g chists, marbles, eclogites, quartzites (Mela unit–Paleozoic). Fig. 1. Geologico 600 Barcellona Pozzo di Gotto” 1 : 50000 CARG-ISPRA): a) slope debris; b Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

of 23

considered to be dominant the structural effects

19 18 2630 2629 have been in which HVSR analysisHVSR of the microtremor record nr. 2.

–

Fig. 3Fig.

R R average curves of the clusters in the inarea the Oliveri.of

HVS ects of 23 measures in the area of Oliveri.

– ﬀ

HVSR analysis of the microtremor record nr. 2. HVSR average curves of the clusters in which have been considered to be dominant the

. distributions

and their spatial

clusters

HVSR

the fourthe

20 21 for 2632 2631 Dendrogram theof clustering process.

– Fig. 5Fig.

amplitude versus peak frequency of of catter plot S

–

Dendrogram of the clustering process. Scatter plot of amplitude vs. peak frequency for the four HVSR clusters and their spatial

Fig. Fig.

(right).

. cluster R cluster (left) and

 G (left) and cluster R (right). ∪

cluster B

22 23 of: 2634 2633 Stratigraphic Stratigraphic column borehole the of

–

8 HVSR peakHVSR frequency maps

– Fig. Fig.

Fig. Fig.

Stratigraphic column of the borehole. HVSR peak frequency maps of: cluster B

Fig. 8. Fig. 7.

Map altitude the of theof seismic bedrock Right) Right)

25 24 2636 2635 ellipticity curve theof measurement point n.2 HVSR

the

Inversion of

–

9 Map thickness the of of the sedimentary cover. Fig. Fig. Left) Left)

. Oliveri. Oliveri.

–

Oliveri. (Left) Map of the thickness of the sedimentary cover. (Right) Map of the altitude Inversion of the HVSR ellipticity curve of the measurement point n.2.

Fig. Fig. above sea level

Fig. 10. of the seismic bedrock a.s.l. Fig. 9. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

. and the andsoft the cover

the seismic bedrock 26 2637 Sections representing Oliveri. Oliveri.

–

1 Fig. 1 Fig. Oliveri. Sections representing the seismic bedrock and the soft cover.

Fig. 11.